JP2007114510A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of avoiding a low electrification phenomenon on the first round of a photoreceptor by making electrifying ability largely differ between electrifiers and giving different roles to them respectively, and capable of temporarily keeping out abnormality by a main electrifier alone even when a sub electrifier becomes abnormal, thereby continuing image formation without stopping the apparatus. <P>SOLUTION: The image forming apparatus has an organic photoreceptor which rotates endlessly, and at least a destaticizing stage, an electrifying stage and an exposure stage which are arranged around the organic photoreceptor in this order. In the apparatus, the sub electrifier 9 is arranged on a side near to the destaticizing stage and the main electrifier 2 is arranged on a side near to the exposure stage in the electrifying stage. The power sources of both electrifiers have the same polarity but are provided separately. The main electrifier is constituted to electrify the surface of the organic photoreceptor to desired electrification potential by itself, but the sub electrifier is constituted to electrify it to potential equal to or under the desired electrification potential. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system.

In recent years, higher durability than ever has been required in organic photoreceptor (also referred to as organic optical semiconductor) OPC.
In order to increase the durability of the organic photoreceptor, it is necessary to improve the wear resistance. As the wear resistance improving technology, (1) a method using a curable binder in a crosslinkable charge transport layer (for example, refer to Patent Document 1), and (2) a method using a polymer type charge transport material (for example, (See Patent Document 2), (3) An inorganic filler dispersed in a crosslinkable charge transport layer (for example, see Patent Document 3), and the like.
Due to the improved wear resistance, it has become possible to use it for a longer period of time, and accordingly, a phenomenon that has not been seen before has occurred.
As one of them, a phenomenon of a decrease in the charging potential in the first round of OPC has appeared.
FIG. 5 is a diagram showing the measurement result of the surface potential after the start of charging of the photoconductor that has changed with time.
In the figure, the vertical axis represents charging potential and the horizontal axis represents time.
This figure shows the case where the desired charging potential on the surface of the photoreceptor is −800 V for normal image formation. It can be seen that only the first rotation of the photoconductor is charged up to -600V. After the second round, the battery is charged to a desired potential. In this way, since charging is performed with a negative polarity, in order to avoid confusion, the absolute value is used when referring to the magnitude of the potential.
This phenomenon in which the charge is reduced only in the first round of OPC is similar to the conventional delay in charging rise (so-called Qi).
The generation of Qi in the electrostatic fatigue of the photoreceptor is caused by the fact that the amount of charge corresponding to the rising delay of charging (reverse charging polarity) is trapped in the photosensitive layer bulk. As a result, trap charges (holes) generated by repeated use of the photoreceptor are formed in the bulk of the photosensitive layer, and are released in the first charging cycle, thereby canceling the surface charges. The phenomenon appears only in the first charging cycle because it takes time to recover (re-trap) the holes emitted from the trap.

When the potential of the first round at the time of starting the OPC is extremely low, various problems as described below occur.
-Since the potential on the first round of the photoreceptor is low, no image can be formed on the first round. → Delay of first copy.
-Even if the first copy is delayed, if the potential of the first round is too low and the photoconductor surface is developed by the developing unit, a photoconductor cleaning defect will occur, and the image will be poorly cleaned. End up.
In the above case, when the contact type transfer device is used, the transfer device is soiled and the back surface is soiled.
Further, as a means for achieving high durability, there is a method of using a photosensitive member having a thinner film thickness than conventional ones.
In general, since the surface potential of OPC is kept constant, the electric field strength increases as the photoconductor is scraped, and electric charges leak locally, causing soiling, resulting in a lifetime. Therefore, the service life is extended by increasing the withstand voltage by increasing the thickness of the undercoat layer or by using a two-layer structure so that even thinner film thicknesses can be used. In this case as well, there is a problem that the charging potential at the first round with time is low as in the case where a long life is achieved by improving the wear resistance. In this case, since the change in film thickness increases when the wear resistance is equivalent to the conventional one, the phenomenon that the charge potential at the first round is lower than the conventional phenomenon is combined with the increase in the capacitance change. Cheap.
In order to solve these problems, means for increasing the charging capability by providing two chargers on the machine side has been proposed (for example, see Patent Document 4).

JP 56-48637 A JP-A 64-1728 JP-A-4-281461 JP-A-2-193163

However, even if two chargers are provided as described above, there is a problem that if one of them stops, the charging capability will be insufficient, and the machine must also be stopped.
The present invention is intended to solve these problems.

According to the first aspect of the present invention, in the image forming apparatus having an organic photoreceptor rotating endlessly, at least a static elimination stage, a charging stage, and an exposure stage in this order around the organic photoreceptor, the charging stage Includes a sub-charger on the side close to the charge removal stage and a main charger on the side close to the exposure stage, and the power sources of both chargers have the same polarity but are provided separately. Is characterized in that the surface of the organic photoreceptor can be charged to a desired charging potential by itself, and the sub-charger can be charged to a potential equal to or lower than the desired charging potential.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the sub-charger is operated only for the first rotation of the organic photoreceptor during image formation.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, when the sub charger becomes unable to operate normally, the power of the sub charger is stopped. The image forming is continued without stopping the operation of the apparatus.
According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, when the power supply of the sub-charger is stopped, it is supplied to the main charger only during the first rotation of the organic photoreceptor. The absolute values of the voltage and the total current are made larger than those supplied before the power supply of the sub-charger is stopped.
According to a fifth aspect of the present invention, in the image forming apparatus according to the third or fourth aspect, when the power supply of the sub-charger is stopped, a display or warning sound for notifying the user of the apparatus is given. It is characterized by.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, at least one of the main charger and the sub charger is a scorotron charger.
According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, when the main charger is a scorotron charger, the charger is provided with an automatic cleaning device, and the sub-charger Is a scorotron charger, the charger is not provided with an automatic cleaning device.

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, at least one of the main charger and the sub charger is a contact charger.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, at least one of the main charger and the sub charger is a proximity charger.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, the organic photoreceptor and at least the main charger and the sub charger are integrated as a process cartridge. It is characterized by.

According to the present invention, in an image forming apparatus using an organic photoreceptor,
Since the main and sub chargers are provided and the respective power supplies are made independent, the low charging phenomenon on the first round of the photoconductor can be avoided by making the charging capacities different and having different roles.
Even if an abnormality occurs in the sub-charger, the image formation can be continued without stopping the apparatus because only the main charger can be used for temporary suspension. Since the user of the apparatus is informed of this, there is no possibility that the temporary delay due to the abnormal state will continue for a long time.
Since the scorotron charger, contact charger, and proximity charger can be arbitrarily selected for each of the main and sub chargers, the design range is greatly expanded. In particular, when a scorotron charger is used as a sub-charger, a low-life sub-charger that can be used until the end of the machine life without the need for automatic cleaning or maintenance can be obtained.
By using a process cartridge in which the organic photoreceptor and at least the main / sub charger are integrated, the configuration of the image forming apparatus can be simplified.

FIG. 1 is a schematic view showing the periphery of a photosensitive member according to the first embodiment of the present invention.
FIG. 2 is a schematic diagram of the prior art shown for comparison.
In both figures, reference numeral 1 is an organic photoconductor, 2 is a main charger, 3 is a potential sensor, 4 is a developing device, 5 is a transfer belt, 6 is a fur brush, 7 is a cleaning blade, 8 is a static elimination lamp, and 9 is a secondary charge. Scorotron, L, indicates the exposure light beam.
Around the organic photoreceptor 1, stages necessary for electrophotographic image formation are arranged in a predetermined order. In FIG. 1, the organic photoreceptor 1 rotating in the direction of arrow A is irradiated with light by a charge removal lamp 8 at a charge removal stage to erase charges existing on the surface of the photoreceptor. Next, on the charging stage, the surface of the photoreceptor is charged to a predetermined potential by the sub charger 9 and the main charger 2. The role of the sub charger will be described later. Next, on the exposure stage, the exposure light beam L from a writing device (not shown) lowers the potential at the position where the light hits to form an electrostatic latent image on the surface of the photosensitive member. Next, in the developing stage, the electrostatic latent image is visualized by attaching toner to the portion where the potential is lowered by the developing device 4. Next, in the transfer stage, the visualized toner image is transferred onto transfer paper (not shown) conveyed by the transfer belt 5, and the transfer paper is peeled off from the organic photoreceptor 1 and discharged from the transfer stage by the transfer belt 5. Is done. The photoconductor surface that has passed through the transfer stage is freed of the so-called residual toner that remains without being transferred by the action of the fur brush 6 and the cleaning blade 7 in the cleaning stage, and prepares for the next image formation.
In the present embodiment, the drum-shaped organic photoreceptor is used for explanation, but it may be a belt shape as long as it is endless.

  In the present embodiment, as a configuration for using the two chargers most efficiently, a conventional two-wire scorotron is used as the main charger 2 and a single-wire scorotron is used as the sub-charger 9 in total. It is installed. The main charger 2 and the sub charger 9 have a very large difference in charging capability, and the sub charger 9 has an auxiliary role (applying a charge, it is enough to lift the surface of the photosensitive member which has been positive until then). In other words, the main charger 2 plays a role of raising to a predetermined charging potential and making it uniform. For this purpose, the main charger 2 requires periodic parts replacement and cleaning (or automatic cleaning) as usual, but the performance required for the sub-charger 9 is low (low charging capability, even unevenness is acceptable). Thus, there is no maintenance, that is, it is possible to use the machine until the end of the machine life without arranging an automatic cleaning device.

An example in the present embodiment will be described below.
In this way, a high voltage power supply is provided for each charger having completely different charging capabilities, and the total wire current and grid voltage can be set to arbitrary values. For example, in the above configuration, the total current of the main charger 2 is set to −1800 μA, and the total current of the sub charger 9 is set to −700 μA. The grid voltage is adjusted using the built-in potential sensor 3 so that the desired charging voltage is −800 V and the charging potential is −800 V every morning. For example, the grid voltage V1 of the main charger 2 is −900 V, The grid voltage V2 of the charger 9 is set to −400V. In this example, V2 is adopted as an absolute value 500 V smaller than V1, but in principle it is important that it is lower than the desired charging potential of the photoreceptor surface, and the value itself should be changed depending on the characteristics of the photoreceptor. .
On the other hand, since the sub charger 9 tries to be used until the lifetime of the machine without maintenance, there is a risk of leakage due to wire deterioration or the like. If the machine is stopped when a leak occurs at this time, downtime will occur until the service person visits. In the present invention, in order to avoid this, even if a leak occurs in the sub charger 9, the output of the sub charger 9 is stopped, but the machine is not stopped.
In this embodiment, as a photoreceptor having improved wear resistance, a photosensitive layer comprising at least a charge generation layer, a charge transport layer, and a crosslinked charge transport layer is provided on a support, and the crosslinked charge transport layer is at least A trifunctional or higher-functional radical polymerizable monomer having no charge transporting structure and a radical polymerizable compound having a monofunctional charge transporting structure were used.
The OPC was a φ100 drum type OPC, and the evaluation was performed at an OPC linear speed of 500 mm / sec. Evaluation was performed using a machine modified from RICOH imagioNeo1050Pro.

FIG. 3 is a diagram showing the transition of the first-cycle charging potential over time.
In the drawing, G0 is a curve showing a change in charging potential when the sub charger 9 and the main charger 2 are operated together, and G1 is a curve showing a change in charging potential when only the main charger 2 is operated.
By operating the sub charger 9 and the main charger 2 together, as shown by a curve G0 in the same figure, a potential drop hardly occurs even after passing 2000K (2 million) sheets. The sub-charger 9 may have no effect on the result even if charging is continued from the second round onward. However, from the viewpoint of energy saving and the life of the charger itself, the secondary charger 9 operates from the second round onward. It is better to stop.
On the other hand, in the curve G1 in the example of only the main charger 2, the charging potential of the first round is lowered to −600 V after passing about 2000K sheets. However, although not shown in the figure, the second and subsequent turns are charged to a desired charging potential.

In the machine of this embodiment, the developing bias is −550V. From the time when the charging potential decreased from −680 V (in absolute value), a phenomenon occurred in which toner adhered to the potential decreased portion in the first round (including toner contamination and increased toner adhesion).
However, by increasing the grid voltage of the main charger 2 from -900 V to -1200 V and the total current from -1800 μA to -2200 μA, the charging potential is restored to -720 V (white circle in the figure), and the photosensitive member is developed. The phenomenon was avoided. Note that the original potential and the original total current value are restored after the second round of the photoreceptor.
Here, consider a case where the normal operation of the sub-charger becomes impossible. If the power supply fails and no voltage can be generated, there is no risk of damaging the photoconductor, but if an abnormal discharge occurs between the sub-charger and the photoconductor, the photoconductor cannot be used as it is. The power supply must be shut down immediately because there is a risk. However, if there is no abnormality in the main charger, as described above, it is possible to compensate to some extent for a decrease in the charging potential at the first rotation of the photosensitive member by temporarily changing the grid voltage of the main charger. As a result, it is possible to continue image formation.
As described above, by increasing the grid voltage and the total current as a temporary stop, it is possible to prevent the potential drop in the first round only by the main charger 2 without the sub charger 9, but the lifetime of the main charger 2 is increased. Therefore, it is used as a temporary provisional measure only when an abnormality occurs in the sub charger 9.
Therefore, if the sub-charger 9 has an abnormality such as leakage, the machine is not stopped even if the power of the sub-charger 9 is stopped. Alternatively, it is necessary to issue a warning sound so that appropriate measures can be taken early.

  Consider when and how much to increase the grid voltage and total current of the main charger. For example, referring to FIG. 3, with reference to −700 V so that toner adhesion does not occur, as long as the cumulative number of image formations does not exceed 1500K, the operating conditions of the main charger even if the secondary charger fails The operation is continued with the current status maintained, and if it exceeds that, the value is changed to an appropriate value. In the case of the grid voltage, a voltage at least equal to or lower than the decrease in charging potential is increased. The specific value is determined by referring to the relationship between the decrease in the charged potential estimated from the cumulative number of image formations and the increase in the voltage necessary to exceed the −700 V line in advance. The same applies to the total current value. These relationships may be stored in a memory and read as necessary. However, the numerical value given here is an example based on FIG. 3, and the transition of the charging potential at the first round over OPC as shown in FIG. 3 is examined according to the characteristics of the organic photoreceptor actually used. It is better to obtain the necessary values from

FIG. 4 is a view for explaining another embodiment of the present invention. FIG. 4A is a diagram showing a contact charger, and FIG. 4B is a diagram showing a proximity charger.
In the figure, reference numeral 10 is a charging roller for contact charging, 11 is a charging roller for proximity charging, 12 is a flange for making a predetermined gap between the charging roller and the photosensitive member, and G is a gap.
Although the embodiment of the present invention has been described above, the charger can be a contact charger or a proximity charger in addition to the scorotron. Further, it is not necessary that both the main and the sub are the same type of charger.
FIG. 2A shows a charging roller 10 of a contact charger that performs charging by directly contacting the organic photoreceptor 1. The charging roller 10 is made of a conductive member, and is supplied with a potential necessary for charging from a power source.
FIG. 2B shows a charging roller 11 provided with a flange 12 for forming a minute step (corresponding to G) at both ends with a gap G of several μm to several tens of μm from the organic photoreceptor 1. By applying a potential in which direct current and alternating current are superimposed on the charging roller 11, a discharge is generated from the charging roller 11, and the photosensitive member 1 is charged to a desired charging potential.
In addition, the charger can be a single member of the image forming apparatus, or can be a process cartridge in combination with a photoconductor, a cleaning device (not shown), and a developing device.

FIG. 3 is a schematic view showing the periphery of the photoconductor of the first exemplary embodiment of the present invention. It is a schematic diagram of the prior art shown for comparison. It is a figure which shows transition of the 1st round charging potential of OPC time passage. It is a figure for demonstrating the other Example of this invention. It is a figure which shows the measurement result of the surface potential after charge start. .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Main charger 4 Developing device 8 Static elimination lamp 9 Subcharger 10 Contact charging roller 11 Proximity charging roller L Exposure light beam

Claims (10)

  In an image forming apparatus having an organic photoreceptor rotating endlessly, at least a static elimination stage, a charging stage, and an exposure stage around the organic photoreceptor in this order, the charging stage is closer to the side of the static elimination stage. The main charger is arranged on the side close to the sub-charger and the exposure stage, and the power sources of both chargers are the same in polarity, but are individually provided. An image forming apparatus, wherein the sub charger is configured to be able to be charged to a potential equal to or lower than the desired charging potential.   2. The image forming apparatus according to claim 1, wherein the sub-charger is operated only for the first rotation of the organic photoconductor during image formation.   3. The image forming apparatus according to claim 1, wherein when the sub charger becomes unable to operate normally, the power of the sub charger is stopped, but the operation of the main charger is not stopped, and An image forming apparatus characterized by continuing the formation.   4. The image forming apparatus according to claim 3, wherein when the power supply of the sub-charger is stopped, the voltage and the total current supplied to the main charger are limited to the first charge of the organic photoconductor. An image forming apparatus characterized in that the absolute value is made larger than those supplied before the power of the apparatus is stopped.   5. The image forming apparatus according to claim 3, wherein when the power supply of the sub-charger is stopped, a display informing the user of the apparatus or a warning sound is transmitted.   6. The image forming apparatus according to claim 1, wherein at least one of the main charger and the sub charger is a scorotron charger.   The image forming apparatus according to claim 6, wherein when the main charger is a scorotron charger, an automatic cleaning device is disposed in the charger, and when the sub charger is a scorotron charger, An image forming apparatus characterized in that an automatic cleaning device is not disposed in the charger.   6. The image forming apparatus according to claim 1, wherein at least one of the main charger and the sub charger is a contact charger.   6. The image forming apparatus according to claim 1, wherein at least one of the main charger and the sub charger is a proximity charger.   The image forming apparatus according to claim 1, wherein the organic photosensitive member and at least the main charger and the sub charger are integrated as a process cartridge. apparatus.

Images