JP2019211730A - Image forming apparatus - Google Patents

Abstract

To reduce execution time of an aging operation in a low-temperature and low-humidity environment, while preventing an increase in manufacturing cost of an image forming apparatus.SOLUTION: An image forming apparatus 1 according to the present invention comprises: photoreceptors; charging members 25 that charges the surfaces of the photoreceptor; application units 43 that apply a charging bias to the charging members 25; and exposure devices that expose the surfaces of the photoreceptor to form electrostatic latent images. The exposure devices each include a light source that emits a light beam, a polygon mirror that deflects the light beam emitted from the light source, and a polygon motor 37 that rotates the polygon mirror. When the temperature inside or outside the apparatus is equal to or less than a reference temperature and the humidity inside or outside the apparatus is equal to or less than a reference humidity, before the start of execution of a printing operation, an aging operation is executed where the polygon motors 37 rotate and the application units 43 apply the charging bias to the charging members 25.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an electrophotographic image forming apparatus.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus includes a photoconductor, a charging member that charges the surface of the photoconductor, and an exposure device that exposes the surface of the photoconductor to form an electrostatic latent image. In such an image forming apparatus, when the power is turned on or when returning from the sleep state, the aging operation is executed until the potential of the surface of the photosensitive member is stabilized before the execution of the printing operation. In this aging operation, the surface of the photoconductor is charged by the charging member while rotating the photoconductor, thereby urging the temperature of the photoconductor and the charging member to increase.

  In particular, in a low-temperature and low-humidity environment, the amount of discharge from the charging member to the photosensitive member decreases due to a decrease in the charging ability of the photosensitive member and an increase in the resistance of the charging member. The execution time of the operation becomes longer. When the execution time of the aging operation becomes longer as described above, the consumption speed of the photoconductor is increased and the life of the photoconductor is shortened. In addition, when the execution time of the aging operation becomes longer, the waiting time of the user becomes longer, and the usability of the image forming apparatus is lowered.

  Therefore, Patent Document 1 discloses an image forming apparatus including a dedicated heating mechanism (see “Heater 7” in Patent Document 1) for heating a charging member (see “Charging Roller 2” in Patent Document 1). Has been.

JP-A-3-288174

  However, providing a dedicated heating mechanism for heating the charging member as described above complicates the configuration of the image forming apparatus and increases the manufacturing cost of the image forming apparatus.

  SUMMARY An advantage of some aspects of the invention is to shorten the execution time of an aging operation in a low-temperature and low-humidity environment while suppressing an increase in manufacturing cost of the image forming apparatus.

  The image forming apparatus forms an electrostatic latent image by exposing the surface of the photoconductor, a charging member that charges the surface of the photoconductor, an application unit that applies a charging bias to the charging member, and the surface of the photoconductor. An exposure apparatus, the exposure apparatus comprising: a light source that emits a light beam; a polygon mirror that deflects the light beam emitted from the light source; and a polygon motor that rotates the polygon mirror. When the temperature outside the machine is equal to or lower than the reference temperature and the humidity inside or outside the machine is equal to or lower than the reference humidity, the polygon motor is rotated and the application unit is the charging member before the start of the printing operation. An aging operation for applying a charging bias is performed.

  A charging bias until the charging member charges the surface of the photoconductor one turn at the time of the aging operation is set as a first charging bias, and the charging member moves the surface of the photoconductor at the time of the aging operation. When the charging bias after charging for one round is the second charging bias and the charging bias at the time of execution of the printing operation is the basic charging bias, the application unit is a predetermined unit at least from the start of use of the photoreceptor. Until the condition is satisfied, the first charging bias may be larger than the basic charging bias, and the second charging bias may be set to the same value as the basic charging bias.

  The applying unit may reduce the first charging bias when a traveling distance of the photoconductor reaches a reference distance.

  The applying unit may reduce the first charging bias when a current flowing through the photoconductor reaches a reference value.

  The application unit may gradually decrease the first charging bias until the first charging bias has the same value as the basic charging bias.

  The photoreceptor includes a single-layer type organic photosensitive layer, the charging member is a rubber charging roller in contact with the surface of the photoreceptor, and the application unit applies a charging bias composed only of a direct current component. You may apply to a charging member.

  According to the present invention, it is possible to shorten the execution time of the aging operation in a low temperature and low humidity environment while suppressing an increase in the manufacturing cost of the image forming apparatus.

1 is a schematic diagram illustrating an outline of an image forming apparatus according to an embodiment of the present disclosure. 1 is a cross-sectional view illustrating an intermediate transfer belt and an image forming unit according to an embodiment of the present invention. 1 is a perspective view showing a photosensitive drum and an exposure apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a control system of an image forming apparatus according to an embodiment of the present invention. 6 is a timing chart showing a charging bias application state and a polygon motor rotation state in Experiment 1. FIG. 6 is a graph showing the results of Experiment 1. 10 is a graph showing the results of Experiment 2. 10 is a graph showing the results of Experiment 3. 10 is a table showing the results of Experiment 3.

  Hereinafter, an image forming apparatus 1 according to an embodiment of the present disclosure will be described with reference to the drawings. Arrows Fr, Rr, L, R, U, and Lo appropriately attached to the drawings respectively indicate the front side, the rear side, the left side, the right side, the upper side, and the lower side of the image forming apparatus 1.

  First, the overall configuration of the image forming apparatus 1 will be described. The image forming apparatus 1 is, for example, a complex machine that is provided with a print function, a copy function, a fax function, and the like.

  Referring to FIG. 1, the image forming apparatus 1 includes a box-shaped apparatus main body 2. A paper discharge tray 4 is provided on the upper part of the apparatus main body 2.

  An intermediate transfer belt 6 is accommodated in a substantially central portion of the apparatus main body 2. Four image forming portions 7 are accommodated below the intermediate transfer belt 6 in a substantially central portion of the apparatus main body 2. The four image forming units 7 correspond to yellow, magenta, cyan, and black toners, respectively. Each image forming unit 7 includes a photosensitive drum 8 (an example of a photosensitive member), a charging device 9, a developing device 10, a primary transfer roller 11 (an example of a transfer member), a cleaning device 12, and a charge eliminating device 13. It is equipped with.

  In the lower part of the apparatus main body 2, four exposure apparatuses 14 are accommodated below the four image forming units 7. At the lower end of the apparatus body 2, a paper feed cassette 15 is accommodated below the four exposure apparatuses 14. A sheet S is stored in the sheet feeding cassette 15.

  A conveyance path P for the sheet S is provided on the right side of the apparatus main body 2. A paper feed unit 16 is provided upstream of the transport path P. A secondary transfer roller 17 is provided in the middle portion of the conveyance path P. A fixing device 18 is provided in the downstream portion of the transport path P. The fixing device 18 includes a fixing member 19 and a pressure member 20 that are in contact with each other.

  Next, the operation of the image forming apparatus 1 having such a configuration will be described.

  First, an image forming operation is executed in each image forming unit 7. That is, the charging device 9 charges the surface of the photosensitive drum 8. Next, each exposure device 14 exposes the surface of the photosensitive drum 8 to form an electrostatic latent image on the surface of the photosensitive drum 8 (see the dotted arrow in FIG. 1). Next, the developing device 10 develops the electrostatic latent image on the surface of the photosensitive drum 8 into a toner image. Next, the primary transfer roller 11 primarily transfers the toner image on the surface of the photosensitive drum 8 onto the surface of the intermediate transfer belt 6.

  By performing the image forming operation as described above in each image forming unit 7, a full-color toner image is formed on the surface of the intermediate transfer belt 6. The toner remaining on the surface of the photosensitive drum 8 is removed by the cleaning device 12, and the charge remaining on the surface of the photosensitive drum 8 is removed by the static eliminator 13.

  On the other hand, the paper S taken out from the paper feed cassette 15 by the paper feed unit 16 is transported downstream in the transport path P and enters a nip portion between the intermediate transfer belt 6 and the secondary transfer roller 17. The secondary transfer roller 17 secondarily transfers the full color toner image on the surface of the intermediate transfer belt 6 onto the paper S. The sheet S on which the toner image is secondarily transferred is further conveyed downstream along the conveyance path P and enters the fixing device 18. When the sheet S enters the fixing device 18, the fixing member 19 and the pressure member 20 fix the toner image on the sheet S. The paper S on which the toner image is fixed is discharged onto the paper discharge tray 4.

  Next, each image forming unit 7 will be further described.

  Referring to FIG. 2, each image forming unit 7 includes a photosensitive drum 8, a charging device 9, a developing device 10, a primary transfer roller 11, a cleaning device 12, a static elimination device 13, as described above. It has.

  The photosensitive drum 8 of each image forming unit 7 includes a cylindrical base material layer 21 and a photosensitive layer 22 that covers the surface of the base material layer 21. The base material layer 21 is made of a metal such as aluminum or stainless steel, for example. The photosensitive layer 22 is, for example, a positively charged single layer type organic photosensitive layer, and includes a charge generator, a charge transport agent, a binder resin, and a filler in a single layer. Hereinafter, the surface of the photosensitive layer 22 is referred to as “the surface of the photosensitive drum 8”.

  The charging device 9 of each image forming unit 7 includes a holder 24, a charging roller 25 (an example of a charging member) held on the top of the holder 24, and a cleaning roller 26 held on the bottom of the holder 24. Yes. The charging roller 25 is in contact with the surface of the photosensitive drum 8. The cleaning roller 26 is in contact with the charging roller 25.

  The developing device 10 of each image forming unit 7 includes a housing 28, a pair of left and right stirring members 29 housed in the lower portion of the housing 28, and a developing roller 30 housed in the upper portion of the housing 28. Yes. The housing 28 contains a developer.

  The primary transfer roller 11 of each image forming unit 7 is in contact with the intermediate transfer belt 6. The primary transfer roller 11 sandwiches the intermediate transfer belt 6 together with the photosensitive drum 8.

  The cleaning device 12 of each image forming unit 7 includes a case 31, a blade 32 held in the case 31, and a recovery screw 33 accommodated in the case 31. The blade 32 is made of polyurethane rubber, for example, and is in contact with the surface of the photosensitive drum 8.

  The neutralization device 13 of each image forming unit 7 is disposed between the intermediate transfer belt 6 and the cleaning device 12. The static eliminator 13 includes a plurality of light emitting elements.

  Next, each exposure apparatus 14 will be further described.

  Referring to FIG. 3, each exposure apparatus 14 includes a light source 35, a polygon mirror 36, a polygon motor 37, and an optical lens 38.

  The light source 35 of each exposure apparatus 14 is constituted by, for example, a laser diode, and is provided so as to be able to emit a light beam (see a dotted arrow in FIG. 3).

  The polygon mirror 36 of each exposure device 14 has a regular hexagonal shape. Six reflecting surfaces 36 </ b> A are provided on the outer peripheral surface of the polygon mirror 36. The polygon mirror 36 is rotatably provided.

  The polygon motor 37 of each exposure apparatus 14 is connected to a polygon mirror 36. The polygon motor 37 rotates the polygon mirror 36 by rotating at a predetermined rotation speed.

  The optical lens 38 of each exposure apparatus 14 is, for example, an fθ lens. The optical lens 38 is provided between the polygon mirror 36 and the photosensitive drum 8. Each exposure device 14 includes a plurality of optical lenses (not shown) in addition to the optical lens 38.

  Next, a control system of the image forming apparatus 1 will be described.

  With reference to FIG. 4, the image forming apparatus 1 includes a control unit 41. The control unit 41 is configured by, for example, a CPU (Central Processing Unit). The control unit 41 is connected to each unit (for example, the image forming unit 7) of the image forming apparatus 1 and controls each unit of the image forming apparatus 1.

  The control unit 41 is connected to the storage unit 42. The storage unit 42 stores a control program and data. The storage unit 42 includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The storage unit 42 stores a first reference temperature and a second reference temperature (second reference temperature <first reference temperature). The first reference temperature is, for example, 50 ° C., and the second reference temperature is, for example, 18 ° C. The storage unit 42 stores reference humidity. The reference humidity is 40%, for example. The storage unit 42 stores a first reference distance and a second reference distance (second reference distance> first reference distance).

  The control unit 41 is connected to a charging bias application unit 43 (an example of an application unit). The charging bias application unit 43 is connected to the charging roller 25 and applies a charging bias to the charging roller 25 based on a signal from the control unit 41. The charging bias is, for example, a bias composed only of a direct current component. The polarity of the charging bias is the same as the charging polarity of the toner contained in the developer.

  The control unit 41 is connected to the development bias application unit 44. The development bias application unit 44 is connected to the development roller 30 and applies a development bias to the development roller 30. The development bias is, for example, a bias in which an AC component is superimposed on a DC component. The polarity of the developing bias is the same as the charging polarity of the toner contained in the developer.

  The control unit 41 is connected to the transfer bias application unit 45. The transfer bias application unit 45 is connected to the primary transfer roller 11 and applies a transfer bias to the primary transfer roller 11. The transfer bias is, for example, a bias composed of only a DC component or a bias in which an AC component is superimposed on a DC component. The polarity of the transfer bias is the same as or opposite to the charging polarity of the toner contained in the developer.

  The control unit 41 is connected to the drum motor 46. The drum motor 46 is connected to the photosensitive drum 8 and rotates at a predetermined rotation speed based on a signal from the control unit 41 to rotate the photosensitive drum 8.

  The control unit 41 is connected to the polygon motor 37. The polygon motor 37 is connected to the polygon mirror 36 and rotates at a predetermined rotation speed based on a signal from the control unit 41 to rotate the polygon mirror 36.

  The control unit 41 is connected to the first temperature sensor 51. The first temperature sensor 51 detects the temperature of the fixing member 19 and outputs it to the control unit 41.

  The control unit 41 is connected to the second temperature sensor 52. The second temperature sensor 52 detects the temperature outside the machine and outputs it to the control unit 41.

  The control unit 41 is connected to the humidity sensor 53. The humidity sensor 53 detects the relative humidity outside the machine (hereinafter simply referred to as “humidity outside the machine”) and outputs it to the control unit 41.

  The control unit 41 is connected to the current sensor 54. The current sensor 54 detects a current flowing from the charging roller 25 to the photosensitive drum 8 and outputs the detected current to the control unit 41.

  Next, the printing operation will be described.

  When the printing operation is performed, the charging bias application unit 43 applies a charging bias to the charging roller 25 to charge the charging roller 25. When the printing operation is executed, the drum motor 46 rotates the photosensitive drum 8, and the charging roller 25 that contacts the surface of the photosensitive drum 8 rotates following the photosensitive drum 8. As a result, the charging roller 25 uniformly charges the surface of the photosensitive drum 8.

  Further, when the printing operation is executed, the polygon mirror 36 is rotated by the polygon motor 37 rotating at a predetermined rotation speed. Further, when the printing operation is executed, a light beam is emitted from the light source 35 (see the dotted line arrow in FIG. 3). The light beam emitted from the light source 35 is deflected by each reflecting surface 36 </ b> A of the polygon mirror 36, passes through the optical lens 38, and reaches the surface of the photosensitive drum 8. As a result, the surface of the photosensitive drum 8 is exposed and an electrostatic latent image is formed on the surface of the photosensitive drum 8.

  Further, when the printing operation is executed, the developer in the housing 28 is stirred and charged by rotating each stirring member 29. In addition, when the printing operation is performed, the developing roller 30 is rotated so that the charged developer is conveyed by the developing roller 30. Further, the developing bias application unit 44 applies a developing bias to the developing roller 30 when the printing operation is executed. As a result, the toner in the developer is supplied from the developing roller 30 to the surface of the photosensitive drum 8, and the electrostatic latent image on the surface of the photosensitive drum 8 is developed into a toner image.

  Further, at the time of executing the printing operation, the transfer bias applying unit 45 applies a transfer bias having a polarity opposite to the toner charging polarity to the primary transfer roller 11. As a result, the toner image on the surface of the photosensitive drum 8 is primarily transferred onto the surface of the intermediate transfer belt 6. The toner image primarily transferred onto the surface of the intermediate transfer belt 6 is secondarily transferred onto the paper S by the secondary transfer roller 17.

  Next, the aging operation will be described.

  When the power is turned on or when returning from the sleep state, the first temperature sensor 51 detects the temperature of the fixing member 19 and outputs it to the control unit 41. Further, the second temperature sensor 52 detects the temperature outside the apparatus and outputs it to the control unit 41. Further, the humidity sensor 53 detects the humidity outside the apparatus and outputs it to the control unit 41.

  When the temperature of the fixing member 19 is equal to or lower than the first reference temperature, the temperature outside the apparatus is equal to or lower than the second reference temperature, and the humidity outside the apparatus is equal to or lower than the reference humidity, Before starting the printing operation, the following aging operation is executed. On the other hand, the controller 41 determines that the temperature of the fixing member 19 exceeds the first reference temperature, the temperature outside the machine exceeds the second reference temperature, and the humidity outside the machine exceeds the reference humidity. In this case, the execution of the printing operation is started without performing the following aging operation.

  When performing the aging operation, the charging bias applying unit 43 applies a charging bias to the charging roller 25 to charge the charging roller 25. In addition, when the aging operation is performed, the drum motor 46 rotates the photosensitive drum 8, and the charging roller 25 that contacts the photosensitive drum 8 rotates following the photosensitive drum 8. As a result, the charging roller 25 uniformly charges the surface of the photosensitive drum 8.

  Further, when the aging operation is performed, the polygon mirror 36 is rotated by rotating the polygon motor 37 at a predetermined rotation speed. When the aging operation is executed, no light beam is emitted from the light source 35 and no electrostatic latent image is formed on the surface of the photosensitive drum 8.

  Further, when the aging operation is performed, the transfer bias applying unit 45 applies a transfer bias having the same polarity as the charging polarity of the toner (a transfer bias having a polarity opposite to that when the printing operation is performed) to the primary transfer roller 11.

  When the aging operation is performed, each stirring member 29 and the developing roller 30 do not rotate, and the developing bias application unit 44 does not apply the developing bias to the developing roller 30. Therefore, the toner in the developer is not supplied from the developing roller 30 to the surface of the photosensitive drum 8.

  Next, a method for determining the charging bias when performing the aging operation will be described. Hereinafter, a charging bias until the charging roller 25 charges the surface of the photosensitive drum 8 for one round when the aging operation is performed is referred to as a “first charging bias”, and the charging roller 25 performs the photosensitive member when the aging operation is performed. A charging bias after charging the surface of the drum 8 for one round is referred to as a “second charging bias”, and a charging bias when the printing operation is performed is referred to as a “basic charging bias”.

  The charging bias application unit 43 increases the first charging bias by X (%) from the basic charging bias from the start of use of the photosensitive drum 8 until the travel distance of the photosensitive drum 8 reaches the first reference distance. The second charging bias is set to the same value as the basic charging bias.

  On the other hand, the charging bias application unit 43 applies the first charging bias from the time when the traveling distance of the photosensitive drum 8 reaches the first reference distance to the time when the traveling distance of the photosensitive drum 8 reaches the second reference distance. The second charging bias is set to the same value as the basic charging bias by making X / 2 (%) larger than the basic charging bias. That is, the charging bias application unit 43 reduces the first charging bias when the traveling distance of the photosensitive drum 8 reaches the first reference distance.

  On the other hand, the charging bias application unit 43 uses the first charging bias and the second charging bias as the basic charging bias from the time when the traveling distance of the photosensitive drum 8 reaches the second reference distance to the end of use of the photosensitive drum 8. Same value as. That is, the charging bias application unit 43 decreases the first charging bias when the traveling distance of the photosensitive drum 8 reaches the second reference distance.

  As described above, in the present embodiment, the polygon motor 37 is rotated when the aging operation is performed. By adopting such a configuration, the temperatures of the photosensitive drum 8 and the charging roller 25 can be quickly raised by the heat generated by the polygon motor 37, so that the execution time of the aging operation in a low temperature and low humidity environment can be shortened. it can. Further, since the temperatures of the photosensitive drum 8 and the charging roller 25 are increased by using the heat generated by the polygon motor 37, it is not necessary to provide a dedicated heating mechanism for heating the photosensitive drum 8 and the charging roller 25. . Therefore, an increase in manufacturing cost of the image forming apparatus 1 can be suppressed.

  Further, the charging bias applying unit 43 makes the first charging bias larger than the basic charging bias from the start of use of the photosensitive drum 8 until the travel distance of the photosensitive drum 8 reaches the second reference distance. . By adopting such a configuration, the temperatures of the photosensitive drum 8 and the charging roller 25 can be increased more quickly, so that the execution time of the aging operation in a low temperature and low humidity environment can be further shortened. Further, the charging bias application unit 43 sets the second charging bias to the same value as the basic charging bias from the start of use of the photoconductor drum 8 to the end of use of the photoconductor drum 8. By adopting such a configuration, it is possible to suppress an excessive increase in the potential of the photosensitive drum 8.

  By the way, in the present embodiment, as described above, the photosensitive layer 22 of the photosensitive drum 8 is an organic photosensitive layer, and as the use of the photosensitive drum 8 progresses, the thickness of the photosensitive layer 22 of the photosensitive drum 8 increases. Become thin. When a large current flows from the charging roller 25 to the photosensitive drum 8 in a state where the photosensitive layer 22 of the photosensitive drum 8 is thin, the photosensitive layer 22 of the photosensitive drum 8 is locally lost. As a result, a black spot image may be generated.

  Therefore, the charging bias application unit 43 reduces the first charging bias when the traveling distance of the photosensitive drum 8 reaches the first and second reference distances. By adopting such a configuration, it is possible to suppress a large current from flowing from the charging roller 25 to the photosensitive drum 8 in a state where the film thickness of the photosensitive layer 22 of the photosensitive drum 8 is reduced. It is possible to suppress the occurrence of secondary harmful effects such as images.

  Further, the charging bias application unit 43 applies the first charging bias in the order of a value X (%) larger than the basic charging bias → a value X / 2 (%) larger than the basic charging bias → the same value as the basic charging bias. It is small. That is, the charging bias application unit 43 gradually decreases the first charging bias until the first charging bias becomes the same value as the basic charging bias. By adopting such a configuration, an optimal value of the first charging bias can be applied to the charging roller 25 in accordance with the usage state of the photosensitive drum 8.

  In the present embodiment, the photosensitive layer 22 of the photosensitive drum 8 is a single-layer type organic photosensitive layer. In such a case, in the low temperature and low humidity environment, the charging ability of the photosensitive drum 8 is particularly likely to be lowered, and the execution time of the aging operation is likely to be long. Therefore, there is a great merit of shortening the execution time of the aging operation using the above configuration.

  In this embodiment, a rubber charging roller 25 that contacts the surface of the photosensitive drum 8 is used as a charging member. In such a case, the resistance value of the charging roller 25 changes greatly according to the change in the ambient temperature, and the potential of the surface of the photosensitive drum 8 also changes greatly. Therefore, there is a great merit of quickly stabilizing the surface potential of the photosensitive drum 8 by using the above configuration.

  In the present embodiment, when the travel distance of the photosensitive drum 8 reaches the first and second reference distances, the charging bias application unit 43 decreases the first charging bias. On the other hand, in another different embodiment, when the current flowing from the charging roller 25 to the photosensitive drum 8 reaches the reference value, the charging bias application unit 43 may decrease the first charging bias. By adopting such a configuration, it is possible to accurately grasp the change in the film thickness of the photosensitive layer 22 of the photosensitive drum 8 based on the current flowing through the photosensitive drum 8. Even when the first charging bias is changed in accordance with the current flowing through the photosensitive drum 8 in this way, the charging bias application unit 43 does not charge the first charging until the first charging bias becomes the same value as the basic charging bias. The bias may be reduced stepwise.

  In the present embodiment, the photosensitive layer 22 of the photosensitive drum 8 is a single layer type organic photosensitive layer. On the other hand, in another different embodiment, the photosensitive layer 22 of the photosensitive drum 8 may be a stacked organic photosensitive layer or a photosensitive layer other than the organic photosensitive layer.

  In the present embodiment, the transfer bias application unit 45 applies a transfer bias having the same polarity as the charging polarity of the toner to the primary transfer roller 11 when performing the aging operation. On the other hand, in another different embodiment, the transfer bias application unit 45 may not apply the transfer bias to the primary transfer roller 11 when the aging operation is performed.

  In the present embodiment, the image forming apparatus 1 is a multifunction machine. On the other hand, in other different embodiments, the image forming apparatus 1 may be a printer, a copier, a facsimile, or the like.

<Experiment>
An experiment for demonstrating the above effects was performed as follows.

<Experimental conditions>
The main experimental conditions are as follows.
Image forming apparatus: FS-1320D manufactured by Kyocera Document Solutions Remodeling machine Photosensitive layer of photosensitive drum: Positively charged single-layer type organic photosensitive layer charging member: Charging roller (remodeled scorotron)
Charging bias: Bias consisting only of DC component Transfer bias: Bias of the same polarity as charging bias

<Experiment 1>
In Experiment 1, with respect to the image forming apparatuses according to Examples 1 and 2 and the image forming apparatus according to the comparative example, an aging operation was performed in a low-temperature and low-humidity environment (external temperature of 18 ° C., external humidity of 10%). The transition of the surface potential of the body drum was measured. The definitions of the first and second charging biases and the basic charging bias are the same as in the above embodiment.

  Referring to FIG. 5, in Example 1, when the aging operation was performed, the first charging bias was set to 100 V larger than the basic charging bias, and the second charging bias was set to the same value as the basic charging bias. In Example 1, the polygon motor was rotated when the aging operation was performed. In Example 2, when the aging operation was performed, the first charging bias and the second charging bias were set to the same value as the basic charging bias. In Example 2, the polygon motor was rotated when the aging operation was performed. In the comparative example, when the aging operation is performed, the first charging bias and the second charging bias are set to the same value as the basic charging bias. In the comparative example, the polygon motor was not rotated when the aging operation was performed.

  Referring to FIG. 6, in Examples 1 and 2 in which the polygon motor is rotated when the aging operation is performed, the surface potential of the photosensitive drum is faster than the comparative example in which the polygon motor is not rotated when the aging operation is performed. Standing up to. From this, it was proved that the execution time of the aging operation in the low temperature and low humidity environment can be shortened by rotating the polygon motor during the aging operation.

  Further, in Example 1 in which the first charging bias is 100 V larger than the basic charging bias, the surface potential of the photosensitive drum is faster than in Example 2 and Comparative Example in which the first charging bias is set to the same value as the basic charging bias. Standing up to. From this, it was demonstrated that the execution time of the aging operation in the low temperature and low humidity environment can be further shortened by making the first charging bias larger than the basic charging bias.

<Experiment 2>
In Experiment 2, for each of 20 intermittent printing (printing which alternately repeats 20 continuous printings and printing stop) and 1 intermittent printing (printing which alternately repeats 1 printing and printing stop), the photosensitive drum is used. While rotating, the current flowing from the charging roller to the photosensitive drum was measured.

  Referring to FIG. 7, the current flowing through the photoconductive drum increases in proportion to the increase in the travel distance of the photoconductive drum, and secondary adverse effects such as black spot images are likely to occur. For this reason, it is effective to reduce the occurrence of secondary adverse effects such as a black spot image by reducing the first charging bias as the travel distance of the photosensitive drum increases.

  In addition, the current flowing through the photosensitive drum varies depending on the print duty (20-sheet intermittent print or 1-sheet intermittent print) even at the same travel distance. Therefore, it is more effective to reduce the occurrence of secondary adverse effects such as a black spot image by reducing the first charging bias as the current flowing through the photosensitive drum increases.

<Experiment 3>
In Experiment 3, an aging operation and continuous printing of 250 sheets were performed once a day in a low temperature environment, and the amount of film abrasion of the photosensitive layer of the photosensitive drum was measured. In Experiment 3, the allowable limit value of the film scraping amount of the photosensitive layer of the photosensitive drum was set to 20 μm.

  As shown in FIG. 8, when compared with the same number of printed sheets, the aging operation execution time (hereinafter referred to as “aging operation time”) is shortened, thereby reducing the amount of film removal of the photosensitive layer of the photosensitive drum. Become. From this, it was demonstrated that the life of the photosensitive drum is prolonged by shortening the aging operation time.

  In addition, as shown in FIG. 9, by reducing the aging operation time by 30% from the standard value, the number of printed sheets until the film scraping amount of the photosensitive layer of the photosensitive drum reaches the allowable limit value is 18.2%. Can be up. Further, by reducing the aging operation time by 60% from the standard value, it is possible to increase the number of printed sheets by 42% until the film scraping amount of the photosensitive layer of the photosensitive drum reaches the allowable limit value. From this, it was demonstrated that the life of the photosensitive drum is prolonged by shortening the aging operation time.

1 Image forming apparatus 8 Photosensitive drum (an example of a photosensitive member)
14 Exposure device 25 Charging roller (an example of a charging member)
35 Light source 36 Polygon mirror 37 Polygon motor 43 Charging bias application unit (an example of application unit)

Claims (6)

A photoreceptor,
A charging member for charging the surface of the photoreceptor;
An application unit for applying a charging bias to the charging member;
An exposure device that exposes the surface of the photoreceptor to form an electrostatic latent image, and
The exposure apparatus includes:
A light source that emits a light beam;
A polygon mirror for deflecting a light beam emitted from the light source;
A polygon motor for rotating the polygon mirror,
When at least one of the temperature inside or outside the machine is equal to or lower than the reference temperature, and the humidity of at least one inside or outside the machine is equal to or lower than the reference humidity, the polygon motor rotates before starting the printing operation. And an aging operation in which the applying unit applies a charging bias to the charging member. A charging bias until the charging member charges the surface of the photoconductor one turn at the time of the aging operation is set as a first charging bias, and the charging member moves the surface of the photoconductor at the time of the aging operation. When the charging bias after charging for one round is the second charging bias and the charging bias at the time of executing the printing operation is the basic charging bias,
The application unit sets the first charging bias to be larger than the basic charging bias and the second charging bias to be the same as the basic charging bias at least from the start of use of the photoconductor to when a predetermined condition is satisfied. The image forming apparatus according to claim 1, wherein the image forming apparatus is a value.   The image forming apparatus according to claim 2, wherein the application unit reduces the first charging bias when a traveling distance of the photosensitive member reaches a reference distance.   The image forming apparatus according to claim 2, wherein the application unit reduces the first charging bias when a current flowing through the photoconductor reaches a reference value.   5. The image formation according to claim 3, wherein the application unit gradually decreases the first charging bias until the first charging bias has the same value as the basic charging bias. 6. apparatus. The photoreceptor includes a single-layer type organic photosensitive layer,
The charging member is a rubber charging roller in contact with the surface of the photoreceptor,
The image forming apparatus according to claim 1, wherein the applying unit applies a charging bias including only a direct current component to the charging member.

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