JP2007206118A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of surely preventing the contamination of a photoreceptor surface due to an ion product. <P>SOLUTION: A printer 1 includes a corona charger 102, a cleaning blade 108, and a temperature and humidity sensor 501 detecting an atmosphere temperature and humidity. In a series of operations from the end of printing before the stop of the machine at the time of performing print processing using a toner including titanium oxide, the printer performs toner development on a photoreceptor drum 103 when the atmosphere temperature and humidity, etc., detected by the temperature and humidity sensor 501 is in a prescribed range, so that after the toner layer is made to pass the cleaning blade 108, the rotation of the photoreceptor drum 103 is stopped by allowing the photoreceptor drum 103 to align to the position opposite to the corona charger 102. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer.

  Conventionally, in an electrophotographic image forming apparatus, a corona charger has been used as a charging means for charging an electrophotographic photosensitive member as a member to be charged to a predetermined polarity and potential. In this method, a corona charger is arranged in a non-contact state on the photosensitive member, and the surface of the photosensitive member is exposed to the corona discharged from the corona charger, so that the photosensitive member is charged to a predetermined polarity and potential. In recent years, it has advantages such as low ozone generation compared to this corona charger, so that the surface of the photoreceptor is charged to a predetermined polarity and potential by contacting a charging member to which a charging bias is applied to the photoreceptor as the object to be charged. A contact charging method is proposed and put into practical use. However, from the viewpoint of charge uniformity and cost, the contact charging method still has many problems to be solved, and there are many examples in which the corona charging method is adopted (for example, see Patent Document 1).

  The surface of the photosensitive member is uniformly charged to a predetermined polarity by the above means, and then an electrostatic charge image is formed by performing image exposure by light irradiation based on predetermined document information. An image is formed.

  Subsequently, the toner image is transferred to a recording material such as paper. From the advantage of paper transportability, a roller such as an elastic body, rubber, foam, or the like that rotates in contact with the photoreceptor is used. In general, the toner image is transferred to a recording material such as paper by applying a predetermined voltage to the recording medium. Finally, image formation is performed by fixing the toner image on the recording material by overheating and pressurization with a fixing roller in the fixing step.

Further, after the toner image transfer, the surface of the photoconductor is cleaned by a cleaning blade to remove the remaining toner, and further, if necessary, neutralization by light irradiation or the like is performed,
The next image forming process is performed.
JP 2002-31998 A

  By the way, as corona chargers used in the image forming apparatus as described above, corotron and scorotron chargers are widely used. When charging is performed by the corona charger, ozone is generated by discharge of the charger. . The components in the air are decomposed by the generated ozone, and ion products such as NOx and SOx are generated. The ion products contaminate the surface of the photoconductor, causing the following problems.

  In other words, since the ion product is water-soluble, it adheres to the photoconductor and further absorbs moisture in the air, so that the surface resistance of the photoconductor is reduced and electrostatic latent ions formed on the surface of the photoconductor are reduced. A lateral flow of potential occurs at the edge of the image, resulting in an image flow. Also in the corona charger, ion products generated by discharge accumulate on the shield. In addition, since the corona charger is disposed in the vicinity of the photosensitive member, the ion product deposited on the shield is detached from the shield in a high-humidity environment and moves to the surface of the photosensitive member. The image flow of the portion stopped in the vicinity becomes remarkable.

  As a conventional technique, by putting a heater inside the photoconductor, it gives energy to release the moisture that has taken in the ion product from the surface of the photoconductor, and suppresses the decrease in resistance of the surface of the photoconductor in a high humidity environment. Yes. However, in recent years, energy saving is also desired in OA equipment due to environmental problems and energy problems, and a method of constantly heating the heater inside the photoconductor to remove moisture from the surface of the photoconductor is not preferable from the viewpoint of power consumption.

  The method of detecting that the humidity sensor is in a high humidity environment and controlling the heater to be turned on only in the high humidity environment has a large temperature dependency of sensitivity in the amorphous silicon photoconductor. Not applicable.

  In addition, a system in which the elastic roller is pressed against the photoconductor using a toner mixed with an abrasive to polish the photoconductor surface, or other polishing system is used to polish the ion product adhering to the photoconductor surface, There is also a technique for suppressing a decrease in resistance on the surface of the photoreceptor. However, since the ion product enters a roughness of 0.1 μm, the conventional polishing system cannot sufficiently remove the ion product.

  In Patent Document 1, in a system that collects untransferred toner and the like downstream of the electrophotographic process and does not have a cleaning mechanism, a toner layer is formed immediately below the charger to prevent problems such as image flow. Although proposed, it is difficult to employ because the toner lacks thermal stability, and in the above polishing system, a toner layer cannot be formed.

  The present invention has been made in view of such a situation, and provides an image forming apparatus that can reliably prevent contamination of the surface of a photoconductor by an ion product while having a low-cost and compact configuration. It is an object.

  The present invention relates to a photosensitive member that can rotate within the apparatus main body, a charging unit that charges the photosensitive member, and an exposure unit that exposes the charged photosensitive member to form an electrostatic latent image based on predetermined image data. Developing means for developing the electrostatic latent image with a developer containing a metal oxide as an external additive; transfer means for transferring the developed image onto a recording paper; and the photoreceptor after transfer An image forming apparatus comprising a cleaning means for removing developer remaining on the surface and a control means, wherein the charging means can generate an ion product by a corona discharge phenomenon, and the control means The developer forcibly ejects the developer onto the photoreceptor during non-image formation to form a developer layer at a predetermined position on the photoreceptor, and the developer layer is cleaned by the rotation of the photoreceptor. After passing the means, the feeling When the body reaches a position facing the charging means, the anti-contamination mode for preventing contamination of the surface of the photoreceptor by ion products from the charging means is executed by stopping the rotation of the photoreceptor. It is characterized by being.

  By the way, the ion product is more easily transferred to the photoreceptor as the ambient temperature and humidity are larger. Therefore, as in the second aspect of the present invention, the apparatus includes temperature / humidity detection means for detecting the atmospheric temperature / humidity in the apparatus main body, and the control means has a predetermined temperature / humidity detected by the temperature / humidity detection means. In the range, it is preferable to execute the contamination prevention mode.

  In addition, when developing the photoreceptor using a developer containing a metal oxide as an external additive in order to prevent migration of the ion product to the photoreceptor, the developer in the predetermined image processing The image density changes depending on the state of the metal oxide on the surface of the photoreceptor, which changes according to the consumption. Accordingly, as in the third aspect of the invention, the printing apparatus includes a printing rate calculation unit that calculates an average printing rate per print job from the image data, and the control unit calculates the average printing rate calculated by the printing rate calculation unit. It is preferable that the anti-contamination mode is executed when is in a predetermined range.

  According to a fourth aspect of the present invention, the charging means is preferably a corona charger.

  According to a fifth aspect of the present invention, it is preferable that the cleaning means is composed of an elastic blade.

  According to a sixth aspect of the present invention, in the contamination prevention mode, the control unit applies a transfer bias to the transfer unit for the developer layer formed on the photoconductor, thereby the developer layer. After the metal oxide contained in is separated and transferred to the transfer means while remaining on the photoconductor, a non-transfer bias having a polarity opposite to the transfer bias is applied to the transfer means, It is preferable to perform control such that the developer transferred to the transfer means is moved onto the photoconductor to form a developer layer on which the metal oxide is separated on the photoconductor.

  Preferably, the photoconductor is an amorphous silicon drum.

  According to the present invention, the charging unit can generate an ion product due to a corona discharge phenomenon, and the control unit forcibly discharges the developer onto the photoreceptor by the developing unit during non-image formation. When a developer layer is formed at a predetermined position on the photoconductor, and the developer layer reaches the position facing the charging unit after passing through the cleaning unit by rotation of the photoconductor Since the anti-contamination mode for preventing contamination of the surface of the photoconductor by the ion product from the charging unit is executed by stopping the rotation of the photoconductor, the developer layer is cleaned by the execution of the anti-contamination mode. The developer particle body is removed from the surface of the photoconductor when passing through the surface, but metal oxide particles having an outer diameter of about one-tenth or less of the developer particle size remain on the photoconductor. And There. Accordingly, the developer layer remaining on the photosensitive member is aligned with the opposing position of the charging unit and the photosensitive member to stop the rotation of the photosensitive member, whereby the metal oxide can be interposed at the opposing position. . As a result, contamination of the surface of the photoreceptor with ion products can be reliably prevented, and subsequent image forming processing can be performed satisfactorily. In addition, as a metal oxide, because it is physically and chemically very stable, does not change in quality and is stable in conductivity, there is no adhesion to the photoreceptor, no influence on the image, etc. Titanium oxide is preferably used.

  According to the second aspect of the present invention, the temperature / humidity detection means for detecting the atmosphere temperature / humidity in the apparatus main body is provided, and the control means has an atmospheric temperature / humidity detected by the temperature / humidity detection means within a predetermined range. In this case, the contamination prevention mode is executed. Therefore, the activation of the contamination prevention mode is performed by detecting the atmospheric temperature / humidity in the apparatus main body by a temperature / humidity sensor as a temperature / humidity detection means. Even when the temperature and humidity fluctuate, it is possible to prevent the ion product from being transferred to the surface of the photoreceptor and to perform subsequent image forming processing satisfactorily.

  According to a third aspect of the present invention, there is provided a printing rate calculation means for calculating an average printing rate per print job from the image data, and the control means has an average printing rate calculated by the printing rate calculation means. Since the contamination prevention mode is executed when it is within the predetermined range, the contamination prevention mode is activated by a dot counter or the like as a printing rate calculation means in order to prevent contamination of the photoreceptor surface by ion products. Even when a photoconductor is developed using a developer containing a metal oxide as an external additive, an image is formed depending on the state of the metal oxide in the developer formed at a predetermined position on the photoconductor. It is possible to prevent the density from changing and to perform the subsequent image forming treatment satisfactorily.

  According to the fourth aspect of the present invention, since the charging means is a corona charger, development is performed at a position on the photosensitive member facing the corona charger, and a metal oxide can be disposed at the same time.

  According to the invention described in claim 5, since the cleaning means is constituted by an elastic blade, while collecting the developer, only the metal oxide is allowed to pass through on the photosensitive member and is placed at a position facing the charging means. Can be placed.

  According to a sixth aspect of the present invention, in the contamination prevention mode, the control unit applies a transfer bias to the developer layer formed on the photoconductor, so that the developer layer is applied. After the metal oxide contained in is separated and transferred to the transfer means while remaining on the photoconductor, a non-transfer bias having a polarity opposite to the transfer bias is applied to the transfer means, The developer transferred to the transfer means is moved onto the photoreceptor, and control is performed so as to form a developer layer on which the metal oxide is separated on the photoreceptor. When the toner passes through the transfer means, the metal oxide particles having an outer diameter of about one-tenth or less of the developer particle diameter are released from the developer particle main body and become a single substance on the photoreceptor. Adhering, and the developer particle body adheres on it That. Therefore, only the developer particle body can be easily removed by the cleaning means.

  According to the seventh aspect of the present invention, even if the photoconductor is an amorphous silicon drum that is liable to deteriorate in performance due to adhesion of ion products, the deterioration in performance can be reliably prevented.

  FIG. 1 is a cross-sectional view showing the overall configuration of a printer 1 according to an embodiment of the present invention. As shown in the figure, this printer (an example of an image forming apparatus) 1 supplies electric charges in a non-contact state from a corona charger (charging means) 102 in a box-shaped printer main body (apparatus main body) 101. , The peripheral surface of the photosensitive drum (photosensitive member) 103 rotating in the direction A in the figure is uniformly charged, and the laser beam B based on the print data (image data) input from the outside is exposed to an exposure device (such as LSU) ( An exposure unit) 104 irradiates the circumferential surface of the photosensitive drum 103 to form an electrostatic latent image, and the electrostatic latent image formed on the circumferential surface of the photosensitive drum 103 is transferred from the developing device (developing unit) 105 to, for example, By supplying toner as a one-component developer, a toner image is formed on the peripheral surface of the photosensitive drum 103.

  On the other hand, the paper P is conveyed from the paper feeding device 200 toward the photosensitive drum 103 through the conveyance path 300, and the toner image on the surface of the photosensitive drum 103 is transferred to the surface of the paper P by the contact of the transfer roller (transfer means) 106. It has become so. The toner remaining on the photoconductive drum 103 after the transfer is removed by a cleaning roller 107 and a cleaning blade (cleaning means, elastic blade) 108 and conveyed to a waste toner bottle (not shown), while the photoconductive drum 103 remains. The electric charge is removed by a static eliminator 109 composed of a halogen lamp or the like.

  Here, the corona charger 102 employs a charging method using corona discharge, and two types of coronatron and scorotron are generally used. Corona discharge refers to continuous discharge caused by local breakdown of air performed in a non-uniform electric field. In general, a minute diameter wire (corona wire) is stretched in a shield case made of aluminum, and an opening surface is provided in a part of the shield case. Corona ions are released from the opening surface. As the voltage applied to the corona wire is increased, a strong local electric field is formed around the corona wire, causing partial breakdown of air and sustaining the discharge.

  The corotron has a structure in which corona wires having a diameter of 50 to 100 μm are shielded with aluminum at a distance of about 1 cm. With the opening surface facing the surface of the photosensitive drum 103, a high voltage of 5 to 10 kV is applied to the corona wire, and positive or negative ions generated thereby are moved to the surface of the photosensitive drum 103 for charging. To do. Since the corotron generates a certain amount of charge, it is difficult to charge the surface of the photosensitive drum 103 to a constant potential, and uneven charging tends to occur.

  The scorotron was devised to reduce uneven charging on the surface of the photosensitive drum 103, and several wires or meshes were arranged as grid electrodes on the opening surface of the corotron so as to be insulated from the shield electrode. It is a configuration. A bias voltage is applied to the grid electrode in a state where the photosensitive drum 103 faces the opening surface of the scorotron. As a result, even if the charging time becomes long, the charging potential is regulated and the surface potential is saturated. This saturation value is controlled by the grid voltage. The scorotron has a more complicated structure and lower charging efficiency than the corotron, but has excellent uniformity of the charging potential.

  FIG. 2 is an explanatory diagram schematically showing the structure of the photosensitive drum 103.

  As shown in FIG. 2, the photosensitive drum 103 is made of an amorphous silicon-based material, and has a carrier injection blocking layer 103b, a carrier generation layer 103c1, and a carrier transport layer 103c2 on a conductive substrate 103a made of an aluminum base tube. A plurality of layers composed of a photosensitive layer 103c consisting of the above and a surface protective layer 103d formed thereon are used. The conductive substrate 103a can be driven by a motor (not shown) so that the photosensitive drum 103 rotates.

  The constituent material of the photosensitive layer 103c is not particularly limited as long as it is an amorphous silicon-based material. Amorphous silicon (a-Si), amorphous silicon carbide (a-SiC), amorphous silicon oxide (a-SiO), An inorganic material such as amorphous silicon nitride (a-SiN) is exemplified. Since a-SiC in these materials has a particularly high resistance, and more excellent charging ability, wear resistance, and environmental resistance can be obtained, it is suitable as a photosensitive layer material in the present embodiment.

Moreover, it is preferable to use a specific ratio of a-SiC between silicon (Si) and carbon (C). Such _{a-SiC, a-Si 1} -x C x ( the value of x is less than 0.3) are more _preferable, the value of _{a-Si 1-x C x} (x 0.5~ 0.95 or less) is more preferable. Such a-SiC has a particularly high resistance of 10 ¹² to 10 ¹³ Ωcm, the flow of the latent image on the surface of the photosensitive drum 103 is small, and the electrostatic latent image maintaining ability and moisture resistance are also low. This is because it is excellent.

  The developing device 105 uses a so-called magnetic one-component jumping phenomenon as its developing method, and is made of resin, and is provided with titanium oxide (metal oxide) as an external additive and charged controllable toner. use. At this time, the toner is charged on the developing roller (magnet roller) 105a and is developed between the developing roller 105a having a certain gap from the photosensitive drum 103. The potential on the developing roller 105a is preferably a form in which alternating current is superimposed on direct current.

  The transfer roller 106 includes a metal shaft, a semiconductive elastic rubber layer formed so as to cover the periphery of the shaft, and a semiconductive material formed so as to cover the outer peripheral surface of the elastic rubber layer. It consists of a coating film. The transfer roller 106 is elastically pressed against the surface of the photosensitive drum 103 by a spring (not shown) or the like, and rotates around the photosensitive drum 103. The voltage applied to the transfer roller 106 is preferably in a form in which alternating current is superimposed on direct current.

  As with the transfer roller 106, the cleaning roller 107 covers a metal shaft, a semiconductive elastic rubber layer formed so as to cover the periphery of the shaft, and an outer peripheral surface of the elastic rubber layer. It consists of a formed semiconductive coating film. The cleaning roller 107 is elastically pressed against the surface of the photosensitive drum 103 by a spring (not shown) or the like, and rotates around the photosensitive drum 103. The cleaning roller 107 is configured to hold a certain amount of transfer residual toner by applying a voltage, and to always polish the surface of the photosensitive drum 103 efficiently and uniformly.

  The cleaning blade 108 is made of a urethane rubber blade that is an elastic body and has wear resistance, and the tip portion thereof is in sliding contact with the surface of the photosensitive drum 103 by the elastic force. The cleaning blade 108 scrapes off the toner remaining on the surface of the photosensitive drum 103 after passing through the cleaning roller 107, conveys it to the waste toner bottle with a screw feeder (not shown), and collects it in the bottle. It has become.

  Then, the sheet P on which the unfixed toner image from the photosensitive drum 103 is transferred by the transfer roller 106 is conveyed to the fixing roller unit 110, and the sheet P on which the toner image is fixed is left as it is (or not shown). After being reversed at the switchback portion and printed on both sides), the paper is discharged to the paper discharge tray 113 via the conveyance roller pair 111 and the discharge roller pair 112 in this order. The corona charger 102, the photosensitive drum 103, the exposure device 104, the developing device 105, the transfer roller 106, the cleaning roller 107, the cleaning blade 108, the charge removal device 109, and the like onto the paper P using a normal electrophotographic technique. The image forming unit 100 that performs the printing process is configured.

  The paper feeding device 200 includes paper feeding cassettes 210 and 220 that are detachably accommodated in two upper and lower cassette housing portions formed in the lower part of the printer main body 101. The paper feed cassettes 210 and 220 can store paper P in a state in which a plurality of papers P are stacked on the lift plates 211 and 221 as storage cassettes for the paper P, respectively. Pickup rollers 212 and 222 for taking out, and paper feed roller pairs 213 and 223 for sending out the paper P picked up by the pickup rollers 212 and 222 one by one to the conveying path 300 are provided.

  The conveyance path 300 includes a first conveyance path 301, a second conveyance path 302, a third conveyance path 303, and a fourth conveyance path 304, and the first conveyance path 301 supplies paper when performing printing processing on the paper P. The paper P taken out from the cassette 210 by the pickup roller 212 is sent out to the photosensitive drum 103 via the paper feed roller pair 213, the transport roller pair 214 and the registration roller pair 215. The second transport path 302 sends out the paper P taken out from the paper feed cassette 220 by the pickup roller 222 to the first transport path 301 via the paper feed roller pair 223 and the transport roller pair 224. The third transport path 303 is for sending the paper P sent out from the first transport path 301 from the photosensitive drum 103 toward the fixing roller unit 110. The fourth transport path 304 feeds the sheet P sent out from the third transport path 303 from the fixing roller unit 110 to the discharge roller pair 112 through the transport roller pair 111.

  A controller (control means) 500 including a microcomputer is provided on the upper portion of the printer main body 101, and FIG. 3 is a functional block diagram of the controller 500. As shown in FIG. 3, the controller 500 has a basic configuration including a CPU 510, and a ROM 504 and a RAM 503 attached to the CPU 510, and the CPU 510 is further arranged at an appropriate position in the printer main body 101. The temperature / humidity sensor (temperature / humidity detection means) 501 and the dot counter 502 are electrically connected to each other. The ROM 504 stores a program for executing this control, and the program is read into the CPU 510 every time the printer 1 is turned on. The RAM 503 is used for reading and writing temporary data necessary for control. The CPU 510 reads an average printing rate calculation unit (printing rate calculation unit) 511, a toner discharge ON / OFF determination unit 512, a temperature / humidity determination unit 513, a discharge mode execution unit 514, and a pollution prevention mode by reading a program. An execution unit 515 is constructed.

  By the way, since the printer 1 uses the above-described developing method, the image density changes depending on the external additive state of the toner surface. Therefore, a so-called discharge mode in which a certain amount of toner is forcibly developed depending on the printing rate, etc. At the time of printing, a toner layer is formed at a predetermined position on the photosensitive drum 103 with the toner that is forcibly discharged, and the toner layer passes through the cleaning blade 108 by the rotation of the photosensitive drum 103, and then the photosensitive drum 103 When the opposite position between the photosensitive drum 103 and the corona charger 102 is reached, the rotation of the photosensitive drum 103 is stopped to prevent contamination of the surface of the photosensitive drum 103 by the ion product from the corona charger 02. There is a pollution prevention mode. Here, toner corresponding to a printing rate of 1 to 4% is discharged. For this purpose, the average printing rate calculation unit 511 averages the printing rate based on the number of dots of the printing data counted using the dot counter 502 for each predetermined number of prints (usually 7 to 14). Calculate the average print rate (average print rate per print job).

  The toner discharge ON / OFF determination unit 512 determines whether or not the average printing rate calculated by the average printing rate calculation unit 511 is 1% or less, and when the average printing rate is less than 1% (predetermined range). If the average printing rate is 1% or more, it is determined that the discharge mode is not set (toner discharge OFF).

  When the temperature of the atmosphere detected by the temperature / humidity sensor 501 is 30 ° C. or higher and the humidity is 60% or higher, the temperature / humidity determination unit 513 determines that the mode is the pollution prevention mode, and the temperature / humidity sensor 501. If the temperature of the atmosphere detected in step 3 is 30 ° C. or higher and the humidity is not 60% or higher, it is determined that the mode is not the pollution prevention mode.

  The discharge mode execution unit 514 executes a discharge mode in which the developing device 105 forcibly discharges toner for one rotation of the developing roller 105a when the toner discharge ON / OFF determination unit 512 determines that the toner discharge is ON. To do. The consumption amount T per unit length in the axial direction can be expressed by the following equation (1) using the diameter φM of the developing roller 105 a and the linear speed ratio S between the developing roller 105 a and the photosensitive drum 103.

T = M × 3.14 × 1 / S (1)
A belt having a circumferential length (width) corresponding to the consumption amount T is drawn on the photosensitive drum 103.

  In addition, when the temperature of the atmosphere detected by the temperature / humidity sensor 501 is 30 ° C. or higher and the humidity is 60% or higher (in a predetermined range), the temperature / humidity determination unit 513 performs the contamination prevention mode. Therefore, the pollution prevention mode execution unit 515 executes the pollution prevention mode. That is, the developing device 105 forcibly discharges the toner from the developing roller 105a to form a band (titanium oxide band) on the photosensitive drum 103, and the band beyond the cleaning blade 108 is exposed to such high temperature and high humidity. At the end of the job, the rotation of the photosensitive drum 103 is controlled to stop at the position facing the corona charger 102 on the surface of the photosensitive drum 103.

  FIG. 5 shows the positional relationship between the corona charger 102 and the photosensitive drum 103.

  The opening width a of the corona charger 102 and points on the photosensitive drum 103 immediately below both ends of the opening width are A, B, and C, respectively, and positions where toner development is performed on the photosensitive drum 103 by the developing roller 105a (developing position) ) Is D, and the angle b (rad) from the development position D to the point B just below the corona charger 102 and the angular velocity ω of the photosensitive drum 103, the time for the development position D to reach the point C is ∠AOB = ∠BOC = a / 2r (rad), (b + a / 2r) / ω, and the time for the development position D to reach point A is (b−a / 2r) / ω.

Therefore, at the position directly below the corona charger 102, the time t passing C → A is
(B + a / 2r) / ω <t <(b−a / 2r) / ω (2)
At this time t, the titanium oxide band is present immediately below the corona charger 102, so that defects such as image flow due to transfer of ion products generated in the corona charger 102 to the surface of the photosensitive drum 103 can be prevented. Can be prevented. The opening width a of the corona charger 102 is generally a ≧ 10 mm.

  FIG. 4 is a flowchart showing the operation of the printer 1. Hereinafter, the operation of the printer 1 will be described with reference to FIG. As shown in FIG. 4, after the printer 1 is turned on, the dot counter 502 counts the number of dots of the print data, and the average print rate calculation unit 511 calculates the print rate based on this count value to a predetermined number of prints. An average printing rate is calculated by averaging every time (step S1).

  Now, it is assumed that the toner discharge ON / OFF determination unit 512 determines that the average printing rate <1% and toner discharge is ON (YES in step S2). Then, the temperature / humidity determination unit 513 determines whether the ambient temperature is 30 ° C. or higher and the humidity is 60% or higher based on the detection signal of the temperature / humidity sensor 501 (step S3).

  If the temperature / humidity determination unit 513 determines that the ambient temperature is 30 ° C. or higher and the humidity is not 60% or higher (NO in step S3), the discharge mode execution unit 514 operates to execute the discharge mode. (Step S4). Here, as described above, a band having the length of consumption T is drawn on the photosensitive drum 103. Then, the job is finished.

  On the other hand, if the temperature / humidity determination unit 513 determines that the ambient temperature is 30 ° C. or higher and the humidity is 60% or higher in step S3 (YES in step S3), the pollution prevention mode execution unit 515 is activated. Then, the contamination prevention mode is executed (step S5). That is, toner development is performed at the development position by the developing device 105 from the end of printing to the end of rotation of the photosensitive drum 103, and the developed toner layer on the photosensitive drum 103 is temporarily After passing the transfer roller 106, the cleaning roller 107, and the cleaning blade 108 in this order, the toner layer is aligned with the position of the corona charger 102 facing the photosensitive drum 103, and the rotation of the photosensitive drum 103 is stopped. The time t for that is as shown in the above equation (2).

  FIG. 6 is a timing chart when the contamination prevention mode is executed in the printer 1. As shown in FIG. 6, at the time of execution of the contamination prevention mode, the photosensitive drum 103 is driven and the corona charger 102 which is a charging unit of the photosensitive drum 103 is turned off at a predetermined timing. The normal development bias is turned on. At this time, if the circumferential length of the photosensitive drum 103 is L, the distance from the developing roller 105a of the developing device 105 to the transfer roller 106 is La, and the distance from the charging roller 102 to the developing roller 105a is Lb, the predetermined timing is , (La + Lb) / V. The time for which the developing bias is ON is a time corresponding to the opening width a or more of the corona charger 102, during which toner is forcibly developed on the photosensitive drum 103.

  Subsequently, the developed toner layer on the photosensitive drum 103 reaches the transfer roller 106. Then, a normal transfer bias is applied to the transfer roller 106 and the toner is transferred to the transfer roller 106 with a delay of La / V after the development bias is turned on. At that time, titanium oxide is released from the toner particles and remains on the photosensitive drum 103. Further, a non-transfer bias having a polarity opposite to the transfer bias is applied to the toner transferred to the transfer roller 106, and the toner is moved to the photosensitive drum 103.

  As a result, when the toner layer resulting from the execution of the contamination prevention mode passes through the transfer roller 106, titanium oxide particles having an outer diameter of about one-tenth or less of the toner particle diameter are released from the toner particle body. As a result, the toner particles adhere to the surface of the photosensitive drum 103 as a single unit, and the toner particle body adheres to the surface.

  Subsequently, the surface of the photosensitive drum 103 reaches the cleaning roller 107 to which a voltage is applied while the toner is adhered on the titanium oxide. Here, the toner is held at a constant amount, and the toner of the photosensitive drum 103 is always kept. Polish the surface efficiently and uniformly.

  The toner that has passed through the cleaning roller 107 reaches the cleaning blade 108 together with the underlying titanium oxide. Here, the toner is scraped off by the cleaning blade 108 and collected in the waste toner bottle, but when the titanium oxide passes through the cleaning blade 108 and reaches the corona charger 102, the driving of the photosensitive drum 103 is stopped. Is done. This timing is represented by (L + La) / V in FIG. As a result, titanium oxide is interposed at a position where the corona charger 102 and the photosensitive drum 103 are opposed to each other.

  In this embodiment, the toner is developed on the photosensitive drum 103 in this operation by developing the toner by applying a developing bias with the surface potential of the photosensitive drum 103 set to 0V. As in the normal print processing operation, the electrostatic latent image may be formed by the exposure system and the toner may be developed.

  Although not shown in the figure, the operation after the job is completed is reset. The dot counter 502 is reset, and only the photosensitive drum 103 is idly rotated without performing the printing process. After the titanium oxide on the drum 103 is scraped off, the next job is executed.

  In the next job, the dot counter 502 again counts the number of dots in the print data, and the average print rate calculation unit 511 calculates the average print rate based on this count value (step S1).

  At this time, assuming that the average printing rate is not <1%, the toner discharge ON / OFF determination unit 512 determines that the toner discharge is OFF (NO in step S2). Then, the temperature / humidity determination unit 513 determines whether the ambient temperature is 30 ° C. or higher and the humidity is 60% or higher based on the detection signal of the temperature / humidity sensor 501 (step S6).

  If the temperature / humidity determining unit 513 determines that the ambient temperature is 30 ° C. or higher and the humidity is not 60% or higher (NO in step S6), the job is terminated with no toner consumption.

  On the other hand, if the temperature / humidity determination unit 513 determines that the ambient temperature is 30 ° C. or higher and the humidity is 60% or higher in step S6 (YES in step S6), the pollution prevention mode execution unit 515 is activated. Then, the contamination prevention mode is executed (step S8). Here, after the job is finished, the rotation of the photosensitive drum 103 is stopped after the toner layer on the photosensitive drum 103 is positioned at a position facing the corona charger 102. The operation after the job is not shown, but in this case as well, the dot counter 502 is reset, the photosensitive drum 103 is idled, and the cleaning roller 107 oxidizes the photosensitive drum 103. Scrap titanium and execute the next job if any.

  Hereinafter, a comparative example of the control (the present invention control having the discharge mode and the pollution prevention mode) in the printer 1 and the normal control having only the discharge mode will be described. That is, in the 8-hour standing test after printing 10,000 pages, the image flow prevention performance was compared. Here, the control of the present invention is applied only to the corona charger 102. Condition 1 is normal control, and condition 2 is control of the present invention. The test environment has a temperature of 32.5 ° C. and a humidity of 80%. The test machine is our monochrome laser printer (24 ppm).

  The test results were as follows. That is, when an image was output under condition 1, an image flow occurred, whereas with the control performed under condition 2, no image flow occurred.

  As described above, according to the present embodiment, when the ambient temperature and humidity detected by the temperature and humidity sensor 501 are within a predetermined range in a series of operations from the end of printing to the stop of the machine, the photosensitive drum Since the toner is developed on the surface 103 and the toner layer is once passed through the cleaning blade 108, the rotation of the photosensitive drum 103 is stopped in accordance with the position where the photosensitive drum 103 faces the corona charger 102. When using a toner containing titanium oxide as an external additive, when the toner passes through the transfer step, titanium oxide particles having an outer diameter of about 1/10 or less of the toner particle diameter are removed from the toner particle main body. It is released as a single unit and adheres to the surface of the photosensitive drum 103. When the titanium oxide particles pass through the cleaning blade 108, the titanium oxide portion on the surface of the photosensitive drum 103 is stopped at a position where the corona charger 102 and the photosensitive drum 103 are opposed to each other, and the photosensitive drum 103 is stopped. The titanium oxide is present at a position opposite to the corona charger 102. As a result, it is possible to reliably prevent the phenomenon of image flow due to adhesion of ion products to the surface of the photoreceptor when the machine is stopped, and to perform subsequent printing processing satisfactorily.

  In the above embodiment, the case where a one-component developer composed of toner containing titanium oxide is used has been described. However, in the case where a two-component developer composed of toner containing titanium oxide and a carrier is used. There may be. Further, the metal oxide contained as an external additive in the developer may be other than titanium oxide.

  In the above embodiment, the case where both the ambient temperature and humidity and the average printing rate are used in the determination of whether or not to execute the pollution prevention mode is illustrated, but only one of them is used. Also good. Further, instead of using the average printing rate, a function of storing and accumulating a count of factors that can be converted into the toner development amount per print job, for example, a developing frequency or the like may be provided.

  In the above embodiment, the monochrome printer 1 has been described as an example. However, the present invention can also be applied to color printing, and can also be applied to other image forming apparatuses such as a copying machine, a facsimile machine, and a multifunction machine. Can do.

1 is a cross-sectional view illustrating an overall configuration of a printer according to an embodiment of the present invention. FIG. 2 is an explanatory diagram schematically showing a structure of a photosensitive drum of the printer. 2 is a functional block diagram of a controller of the printer. FIG. 3 is a flowchart illustrating an operation of the printer. It is explanatory drawing which shows typically the positional relationship of a corona charger and a photoreceptor drum. 6 is a timing chart when executing a pollution prevention mode in the printer.

Explanation of symbols

1 Printer (image forming device)
100 Image forming unit 101 Printer main body (device main body)
102 Corona charger (charging means)
103 photoconductor drum (photoconductor)
104 Exposure apparatus (exposure means)
105 Developing device (developing means)
105a Developing roller 106 Transfer roller (transfer means)
107 Cleaning roller 108 Cleaning blade (cleaning means, elastic blade)
109 Static eliminator 500 Controller (control means)
501 Temperature / humidity sensor (temperature / humidity detection means)
502 dot counter 503 RAM
504 ROM
510 CPU
511 Average printing rate calculation unit (printing rate calculation means)
512 toner discharge ON / OFF determination unit 513 temperature / humidity determination unit 514 discharge mode execution unit 515 anti-contamination mode execution unit P paper (recording paper)

Claims (7)

A photosensitive member that can rotate within the apparatus main body, a charging unit that charges the photosensitive member, an exposure unit that exposes the charged photosensitive member to form an electrostatic latent image based on predetermined image data, and the static A developing means for developing the electrostatic latent image with a developer containing a metal oxide as an external additive, a transfer means for transferring the developed image onto a recording paper, and the photoconductor after transfer. An image forming apparatus comprising a cleaning means for removing developer and a control means,
The charging means can generate an ion product by a corona discharge phenomenon,
The control means forcibly ejects the developer onto the photoreceptor by the developing means during non-image formation, forms a developer layer at a predetermined position on the photoreceptor, and the developer layer is rotated by the rotation of the photoreceptor. However, when the photosensitive member reaches a position facing the charging unit after passing through the cleaning unit, the photosensitive member surface is contaminated by the ion product from the charging unit by stopping the rotation of the photosensitive member. An image forming apparatus that executes a pollution prevention mode for preventing the occurrence of contamination.   A temperature / humidity detection means for detecting the atmospheric temperature / humidity in the apparatus main body is provided, and the control means executes the contamination prevention mode when the atmospheric temperature / humidity detected by the temperature / humidity detection means is within a predetermined range. The image forming apparatus according to claim 1, wherein:   A printing rate calculation unit that calculates an average printing rate per print job from the image data, and the control unit prevents the contamination when the average printing rate calculated by the printing rate calculation unit is within a predetermined range. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus executes a mode.   The image forming apparatus according to claim 1, wherein the charging unit is a corona charger.   The image forming apparatus according to claim 1, wherein the cleaning unit includes an elastic blade.   In the contamination prevention mode, the control means separates the metal oxide contained in the developer layer by applying a transfer bias to the developer layer formed on the photoreceptor. Then, after being transferred to the transfer means while remaining on the photoreceptor, the developer transferred to the transfer means is applied to the transfer means by applying a non-transfer bias having a polarity opposite to the transfer bias. 6. The image forming apparatus according to claim 5, wherein the image forming apparatus is controlled so as to be moved onto the photoreceptor and to form a developer layer on which the metal oxide is separated on the photoreceptor.   The image forming apparatus according to claim 1, wherein the photosensitive member is an amorphous silicon drum.

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