JPS6010264A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To use a photosensitive layer consisting of an org. photoconductor and to maintain stably the surface potential of the 1st and succeeding cycles by performing main electrostatic charging and destaticization in specific flow-in current regions. CONSTITUTION:Destaticization by an AC corona discharge and main electrostatic charging by DC corona discharge are performed by using a photosensitive layer consisting of a perylene pigment charge generating layer/polyvinyl carbazole charge transfer layer, etc. The main electrostatic charging is performed in a flow-in current region to be satd. at 500-700V (embodiment -695V) and the destaticization in 40-90% (embodiment 52.6%) of the flow-in current of the main electrostatic charging. Then the decrease in the absolute value of the surface potential at the 1st cycle as in the example for comparison (-717V, 96.4%) is obviated and the specified stable potential is obtainable in each cycle.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic method using an organic photoconductor photosensitive layer, and more specifically, the present invention relates to an electrophotographic method using an organic photoconductor photosensitive layer. Concerning photographic methods.

Commercial electrophotographic copying machines employ a system in which the photosensitive layer is first neutralized and cleaned before copying is started, and then main charging, exposure, toner development, transfer, and static elimination cleaning are repeated as many times as necessary. There is.

In this type of electrophotographic copying machine, the static elimination cleaning operation is performed at the start of copying and at the end of copying to prevent the influence of stains on the photosensitive layer when the copying machine is stopped. It has been found that the use of organic photoconductor photosensitive layers as photoreceptors causes certain drawbacks. That is, the image density of the copy in the first copying cycle is 2.
There is a tendency for the image density to be lower than the image density of copies after the cycle. The exact reason for this is unclear, but in the case of an organic photoconductor photosensitive layer, carriers with a relatively longer life are formed compared to the case of an inorganic photoconductor photosensitive layer, and at the end of copying, carriers are formed. This is thought to be because the charge for static elimination is further performed on the photosensitive layer that has already been neutralized, so that the influence of this charge for static elimination is significant.

According to the present invention, there is provided an electrophotographic method using an organic leading conductor photosensitive layer which eliminates the above-mentioned drawbacks, and according to this method, a stable surface potential is always maintained in the first cycle and after the second cycle. As a result, stable image formation is possible.

That is, in the present invention, the photosensitive layer of an organic photoconductor is subjected to charge removal by alternating current corona discharge and main charge by direct current corona discharge, and then subjected to image exposure, toner development, and toner transfer, and these steps are repeated. In the electrophotographic method in which images are formed using
An electrophotographic method characterized in that static electricity is removed in an inflow current range that saturates at 0.00 volts (absolute value), and that static electricity is removed at an inflow current value that is lower than the saturated inflow current range and is 40 to 90% of the main band current inflow current value. is provided.

The present invention will be described in detail below based on specific examples shown in the accompanying drawings.

In FIG. 1 for explaining the electrophotographic process, an organic photoconductor photosensitive layer 6 is provided on the surface of a conductive substrate 2 of a driving rotary drum 1. As shown in FIG.

Along the drum surface, there are a main charging DC corona charger 4, an image exposure optical system 5, a developing mechanism 7 for holding toner 6, a transfer corona charger 8, a static elimination AC corona charger 9, a static elimination light source 10, and The toner cleaning mechanisms 11 are provided in this order.

At the start of copying, the static elimination charger 9, the static elimination light source 10, and the toner cleaning mechanism 11 are operated to remove dust, dirt, etc. attached to the surface of the photosensitive layer 60.

Next, the photosensitive layer 3 is charged to a constant polarity by the main charging corona charger 4, and imagewise exposed through the optical system 5 to form an electrostatic image corresponding to the original image. Using toner 6 charged to the opposite polarity to this electrostatic image, a toner image corresponding to the electrostatic image is formed on the photosensitive layer 3 by a developing mechanism 7.

A copy paper 12 is supplied to the surface of the photosensitive layer 6 having this toner image, and from the back side of the copy paper 12, a charge of the same polarity as the electrostatic image is charged by a transfer corona charger 8, and the toner image is transferred to the copy paper. 120 surface. The copy paper on which the toner image has been transferred is peeled off from the photosensitive layer 6 and sent to a fixing mechanism (not shown) to form a copy with the toner image fixed thereon.

After the toner image has been transferred, toner remains in the photosensitive layer in an amount that corresponds to the transfer efficiency. The toner particles are still electrically charged, corresponding to their tendency to triboelectrically charge. Corona charging is performed from an AC corona charger 9 in order to remove this electrical charge, and furthermore, the entire surface is exposed to light from a light source 10 for removing charges in order to remove charges remaining in the photosensitive layer. In this way, the toner is cleaned by the cleaning mechanism 11 while the Coulomb force between the toner and the photosensitive layer is weakened. After that, the main charging and cleaning operations are repeated for the number of copies, and then the -th copy is made. Process terminates. In the second and subsequent copying cycles, following this cleaning, the operations after main charging are repeated.

However, in the second copying cycle, AC corona charging is performed on the photosensitive layer, which has already been subjected to static elimination and cleaning, prior to main charging. As already pointed out, in the photosensitive layer of an organic photoconductor, carriers with a significantly longer 2-year time than in an inorganic photoconductor are likely to be generated due to charging and exposure. The influence of the pre-charging in the first cycle is exerted on the next main charging, and the surface potential of the photosensitive layer during the main charging tends to be lower than that during the main charging from the second cycle onward.

As an example, in the case of a composite photosensitive layer consisting of a perylene pigment charge generation layer/polyvinyl carbazole charge transport layer, the surface potential after the second cycle is approximately 600 volts, while the surface potential during the first cycle is approximately 500 volts. It is observed that the voltage decreases to volts.

In the present invention, main charging and static elimination are carried out in independent specific current flow ranges, which will be explained in detail below, to improve the surface potential in the first cycle to the surface potential in the second and subsequent cycles. The surface potential is kept constant throughout the cycle, so that stable images can always be obtained.

According to the present invention, first, the main charging is carried out when the surface potential of the photosensitive layer is 500.
This is carried out in the inflow current range that saturates between 700 volts (absolute value). Generally, when charging a photosensitive layer of an organic photoconductor, it is recognized that as the thickness of the photosensitive layer increases, the charging potential tends to increase proportionally. Furthermore, as shown in FIG. 2, when the current flowing in from the charger is increased, the surface potential (absolute value) of the photosensitive layer initially increases almost proportionally as the current value increases;
From this position, the surface potential becomes saturated to a constant value regardless of an increase in the current value. This saturated surface potential is related to the thickness of the same type of photosensitive layer, and tends to decrease as the thickness decreases and increases as the thickness increases.

In the present invention, this saturation surface potential is set at 500 to 70
It is set to 0 volts (absolute value), and main charging is performed with a flowing current value corresponding to this saturated surface potential. The reason why this saturated surface potential is set in the above range is that if it is too low than this range, an image with a sufficiently high density cannot be obtained, whereas if it is higher than this range, the toner will In addition, carrier particles may also adhere to the electrostatic image, and even with a one-component developer, image quality such as trailing may be formed. In addition, the inflow current value corresponding to the saturated surface potential, that is, the saturated inflow current region (I8
) By performing the format charging, it is possible to always stably maintain the surface potential of the photosensitive layer within a certain range in which proper development is performed, and also to suppress the decrease in surface potential due to static elimination in the first cycle or pre-charging. It is possible.

In the present invention, static elimination or pre-charging is lower than the above-mentioned saturation inflow current range (I8), and the inflow current value of 40 to 90% of the main band current inflow current value is less than 1. ) is also extremely important.

That is, the inflow current (Ip) during static elimination or pre-charging with
When is in the saturated inflow current region (I8), the surface potential of the photosensitive layer due to main charging tends to drop significantly due to the influence of this static elimination or pre-charging. This tendency shows that the inflow current for static elimination or pre-charging is 90% of the main charge current inflow current.
The same is allowed even if the amount exceeds. The inflow current value for static elimination or pre-charging is for the purpose of toner charge removal, so it may be considerably smaller than the main charge current inflow current value, but it is less than 40% of the main charge current inflow current value. Sometimes this is detrimental to the purpose of toner charge removal.

In the present invention, the reason why the surface potential in the first cycle can be improved to almost the same level as the surface potential in the second and subsequent cycles by performing the main charging, static neutralization, and pre-charging within the above range is as follows. It is unclear, but it can be thought of as follows. In other words, in the above range, the generation of carriers with relatively long lifetimes is suppressed to a low ratio by static elimination, and even these carriers with long lifetimes are mainly charged by the saturation current, so that the surface potential is substantially reduced. This seems to be because it is neutralized without any deterioration.

In the present invention, it is difficult to directly measure the value of current flowing into the photosensitive layer during main charging, neutralization, or pre-charging.

However, to determine whether the inflow current during main charging is the saturated inflow current, for example, by changing the applied voltage to the charger to change the current, and examining the relationship between this change and the surface potential of the photosensitive layer. However, since the surface potential remains almost constant, it can be confirmed that the main charging is performed by a saturated inflow current. In the same way, it can be confirmed that the inflow current value for static elimination or pre-charging is smaller than the saturation inflow current.

In addition, the ratio of the inflow current value for main charging and the inflow current value for static elimination or pre-charging is determined by positioning the metal surface instead of the photosensitive layer surface, and comparing the inflow current from the main charger with the inflow from static elimination or pre-charging. This can be easily determined by actually measuring the current and calculating the ratio between the two.

The sink current of each charger can be set to the desired level by means known per se. For example, since this current is approximately proportional to the applied voltage of the charger, it can be set to the desired level by adjusting the applied voltage. In addition, this current becomes smaller when the distance between the corona wire and the g-light 71N is increased (if the distance is increased), and vice versa, so that it can reach zero cycles. If you bring them closer together, they will become smaller, and if you move them in the opposite direction, you will get the opposite effect, so you can adjust this as well.

The method of the present invention is equally applicable to all organic photoconductor photosensitive layers, but when applied to a functionally separated organic photosensitive layer in which a charge-generating layer and a charge transport layer are provided on a conductive substrate, the rp Excellent effects are expressed in potatoes. As the charge generation layer, perylene pigments, quinacridone pigments, pyranthrone pigments, phthalocyanine pigments, disazo pigments,
A photoconductive organic pigment such as a trisazo pigment applied in the form of a vapor deposited film or as a resin dispersion is used, while a charge transporting layer such as a charge transporting resin such as polyvinylcarbazole, a hydrazone derivative, A resin in which a low-molecular charge transporting substance such as a pyrazoline type derivative is dispersed is used.

The developer consists of a visible toner and a magnetic carrier.

Although magnetic brush development is performed using a two-component developer made of magnetic toner or a one-component developer made of magnetic toner, it is of course possible to use other developing means.

Toner cleaning can be performed using electromagnetic cleaning using a magnetic brush in addition to mechanical cleaning using a Fabrush 'P blade. In the latter case, a developing magnetic brush can also be used for cleaning, and 2. It is also possible to make one copy cycle per rotation.

The invention is illustrated by the following example.

Example (1) Production of photoreceptor (α) Preparation of charge generation layer Chlordiane blue 10 parts by weight Methanol 80 parts by weight Butanol 20 parts by weight The above weighed chemicals were placed in a stainless steel ball mill and heated at 6 min.
A coating liquid was prepared by dispersing and pulverizing the pigment at a rotation speed of 0.00 rpm for 12 hours. Next, an aluminum foil with a thickness of 60 μm was prepared, and the coating solution was applied using a blade coater.
After heat treatment at 00℃ for 1 hour, the thickness after drying is 2μ.
A charge generation layer was prepared.

(6) Preparation of Charge Transport N Coating Solution Tetrahydrofuran 80 parts by weight The above weighed chemicals were placed in a reagent bottle and dissolved at a speed of 600 revolutions per minute for 6 hours.

(6) Preparation of photoreceptor The above charge transport layer coating solution was applied using a blade coater onto the charge generation layer prepared in step (α) above, heat treated at 100°C for 1 hour, and the thickness after drying was determined. A charge transport layer with a thickness of 8μ was prepared, and a laminated photoreceptor with a total thickness of the charge generation layer and charge transport layer of 10μ was prepared.

Oi) Photoconductor test The photoconductor produced in the above was sent to Sanda Kogyo, K, MPP.
It was installed in the C-121 copying machine and tested under the following usage conditions.

D? )/Is') X 100='52.6%However,
The developing section of the copying machine was removed, and the surface potential of the photoreceptor was measured by setting the probe of a surface electrometer at the position where the developer contacted the photoreceptor drum. As shown in the table and FIG. 6, a stable surface potential was obtained from the first cycle. Since this photoreceptor is for negative charging, the surface potential is represented by a minus sign.

Also, when I installed the developer and did a copying test, I found 1.
Copies of satisfactory image quality without image disturbance were obtained from the 1st cycle, and almost no difference was observed even after the 10th cycle.

Comparative Example A photoreceptor was prepared in exactly the same manner as in the example except that the structure of the photoreceptor after heat treatment was such that the charge generation layer had a thickness of 2 .mu.m and the charge transport layer had a thickness of 16 .mu.m. Note that the structure of the photoreceptor differs from the example in that the surface potential (50
0 volts to 700 ports) in the inflow current range of the comparative example.Next, the comparative example photoreceptor configured as above was installed in a copying machine in the same manner as in the example, and tested under the following conditions. I did it.

(Ip/Is)
The surface potential in the 2nd cycle was 70 V lower than that in the 2nd cycle, and after that it rose, and finally a stable surface potential was obtained from the 3rd cycle.

When a copying test was conducted in the same manner as in the example, only copies with lower image density were obtained in the first and second cycles than in the third and subsequent cycles.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram explaining the electrophotographic process, Figure 2 is a diagram showing the relationship between the current flowing into the drum and the surface potential of the photoreceptor, and Figure 3 is a diagram showing changes in surface potential due to copy cycles. . 6... Photosensitive layer 4... Main charging charger 7...
Developing mechanism 9... Charger for static elimination % Applicant Sanda Kogyo Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] (1) After performing charge removal by AC corona discharge and main charging by DC corona discharge on the organic photoconductor photosensitive layer, image exposure, toner development, and toner transfer are performed, and these steps are repeated to form an image. In an electrophotographic method, main charging is carried out in an inflow current range where the surface potential of the photosensitive layer is saturated at 500 to 700 volts (absolute value), and charge removal is carried out in a flow current range lower than the saturation current range and 40 volts of the main band current inflow current value. An electrophotographic method characterized in that it is carried out with an inflow current value of 90 to 90 inches.