JP2005037643A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reliably extract only a low charged toner and/or a reverse polarity charged toner in a high humidity environment where the low charged toner and/or the reverse polarity charged toner may be generated, and to collect the low charged toner and/or the reverse polarity charged toner without installing a cleaning member physically touching at least the surface of an image carrying body. <P>SOLUTION: The potential difference from the low charged toner to transfer the toner from a developing roll 21 to a photoreceptor drum 14 is ensured by changing the duty in the AC component of the developing bias for the low charged toner due to a high temperature and high humidity environment by disposing a cleaning blade or the like directly in contact with the peripheral face of the photoreceptor drum 14 without scraping the toner. Thereby, the low charged toner can be successively transferred to a final transfer roll 28 without employing a cleaning method such as by actively scraping. Although the final transfer roll 28 is provided with a cleaning blade 50A, the cleaning process in this portion does not directly influence the picture quality, which results that degradation in the picture quality such as fog can be prevented and the life of the photoreceptor drum can be extended. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a charger for uniformly charging an image carrier, an exposure unit for forming a latent image of an image on the surface of the image carrier, and an AC bias to an electrostatic latent image formed by the exposure unit. And a developing means for supplying toner through a developing member with a developing bias on which a DC bias is superimposed to visualize the toner image as a toner image. The toner image formed by the developing means is passed through an intermediate transfer member by a potential difference. The present invention relates to an image forming apparatus that forms an image by transferring it to a recording medium.

  Conventionally, in an image forming apparatus, for example, when a developing bias is −370 V, the surface of a photoconductor as an image carrier is uniformly charged at −450 V, and light is irradiated by an optical scanning device as an exposure unit. By scanning the beam, an electrostatic latent image is formed in which the light receiving portion has a higher potential (−100 V) than the developing bias.

  To the electrostatic latent image on the photosensitive member, toner charged with a developing bias supplied from a developing unit adheres and is visualized.

  Thereafter, the toner image on the photosensitive member is transferred to a storage medium via an intermediate transfer member, whereby an image is formed on the recording medium. The recording medium after the image formation is fixed with toner by a fixing device and discharged.

  In the image forming process as described above, the toner supplied from the developing device is transferred to a recording medium via a photosensitive member, an intermediate transfer member, etc. At this time, a part of the toner is transferred to the photosensitive member or the intermediate transfer member. This is a cause of image quality degradation (image defects) such as fogging and ghosting during the next image formation.

  For this reason, a cleaning member is generally provided on the peripheral surface of the photoreceptor. The cleaning member includes a cleaning blade, and one end (one side) of the cleaning member is in contact with the peripheral surface of the photoconductor in a state along the axial direction of the photoconductor. The cleaning blade scrapes and collects the toner by rotating the photosensitive member in a state where the cleaning blade is in contact.

  However, such a cleaning blade or other mechanical scraping structure may cause a considerable damage to the surface of the photoreceptor, and may cause fatal damage over time.

  Therefore, a so-called cleaner-less method has been proposed in which a developing device is also used for cleaning for collecting transfer residual toner on the photoconductor in order to cope with ecology and extend the life of the photoconductor.

  In addition, the cleaning blade that contacts the photoconductor is abolished. Instead, the transfer residual toner is temporarily held using a brush or roll, and biased to the transfer body equipped with a cleaner that can be collected in a specific area of the non-image area. It has been proposed to clean by phase shifting by force.

  As a technique related to such cleaning, Japanese Patent Application Laid-Open No. H10-228667 discloses that residual toner is adsorbed and removed by applying a voltage having a polarity opposite to that of the toner to a brush in contact with the photoreceptor.

  Japanese Patent Application Laid-Open No. H10-228561 discloses a brush configuration for suction removal cleaning, but discloses that a positive electrode bias is applied.

  Further, various proposals such as the following (1) to (3) have been made as a structure for collecting residual toner and the like.

  (1) The toner is removed before toner development, that is, in (or in the vicinity of) the developing device (see Patent Documents 3 and 4).

  In both Patent Document 3 and Patent Document 4, a toner electric adsorption removing member is disposed upstream of the developing nip of the developing roll.

  (2) In cooperation with the toner density detection sensor, the toner is discharged by a bias (see Patent Document 5).

  In this Patent Document 4, there is no description that suggests the idea of the environment or the removal of the low-charged toner limitation.

  (3) Corresponding development conditions are changed according to the values of environmental sensors (temperature, humidity) (see Patent Document 6).

  This is to change the development conditions by an environmental sensor, and there is no concept of eliminating low-charge toner and reverse-polarity toner.

  By the way, considering the environment in which residual toner is generated, insufficient charging of toner under high humidity is a major cause.

In particular, styrene acrylic resins and polyester resins are often used as toner binder resins in recent years because of the widespread use of color images, because of the advantage that they do not impair the resistance to PVC mats and the original color of the coloring material. Color toners are generally susceptible to temperature and humidity. For this reason, in image formation under high humidity using color toners, image quality degradation (image defects) such as fogging and retransfer due to insufficient charging is likely to occur.
JP 2000-276020 A Japanese Patent Laid-Open No. 5-289402 JP 2001-125371 A JP 2000-267442 A JP 2000-31954 A JP 2001-249504 A

  However, the concept of actively collecting low-charged toner and reverse-polarity charged toner that can be generated due to high humidity and in a cleaner-less structure, which is generated due to the high humidity, is disclosed in Patent Documents 1 to There is no patent document 6 and it has not yet been possible to exclude low-charged toner and reverse-polarized toner that can reliably remain.

  Further, in the conventional residual toner collecting structure, there is a high possibility that normally charged toner is also collected, and toner loss is large.

  Furthermore, in the case of color toners, it is conceivable to change to a toner binder having physical properties that do not cause insufficient charging under high humidity. However, it takes a lot of labor and time to replace all of the toner binders in circulation.

  In consideration of the above facts, the present invention reliably extracts only the low-charged toner and / or reverse-polarized toner in a high-humidity environment where low-charged toner and / or reverse-polarized charged toner can be generated. An object of the present invention is to obtain an image forming apparatus that can collect the low-charge toner and / or the reverse-polarity charge toner without providing a cleaning member that physically contacts the surface of the image carrier.

  According to a first aspect of the present invention, there is provided a charger for uniformly charging an image carrier, an exposure unit for forming a latent image of an image on the surface of the image carrier, and an electrostatic latent image formed by the exposure unit. A developing means for supplying toner through a developing member by a developing bias in which an AC bias and a DC bias are superimposed to visualize the toner image as a toner image. The toner image formed by the developing means is subjected to an intermediate transfer member by a potential difference. An image forming apparatus that forms an image by transferring the image to a recording medium via a detection unit that detects at least humidity in a use environment, and when the humidity higher than a predetermined level is detected by the detection unit, the image The AC component waveform adjusting means that adjusts the waveform of the AC component of the developing bias to reduce the holding force of the toner on the developing member side as compared with the case of forming the AC, and the AC component waveform adjusting means A non-sheet-passing operation executing means for executing a non-sheet-passing operation for a predetermined time in a holding force reduction state, and a toner collecting means for recovering toner supplied during the execution of the non-sheet-passing operation executing means. Yes.

  According to the first aspect of the present invention, it is determined that the charge amount of the toner is decreased when the detection unit detects a predetermined humidity or higher. Note that the temperature may be added to this determination. In other words, it may be determined that the charge amount of the toner is decreasing at high temperature and high humidity.

  If it is determined that the toner charge amount is decreasing, the AC component of the developing bias is adjusted by the AC component waveform adjusting means. The adjustment of the AC component of the developing bias reduces the retention force of the toner on the developing member. In this state, the non-sheet passing operation is executed by the non-sheet passing operation executing means. As a result, the deteriorated toner whose charge amount in the toner carried on the developing member has been reduced can be selectively developed to the image carrier side, and the toner collecting means can transfer the image carrier to the intermediate transfer from the developing member. The toner transferred through the body can be collected, and image defects such as fog and transfer ghost can be avoided.

  As a result, for example, cleaning can be performed without providing a blade or the like that directly contacts the image carrier, and image quality deterioration due to wear over time due to contact between the image carrier and the blade can be prevented. .

  In the first aspect of the invention, the alternating current component waveform adjusting means may increase the peak to peak voltage of the alternating current component of the developing bias applied to the developing member or the alternating current of the developing bias applied to the developing member. The holding power of the toner is reduced by executing at least one of the duty increase on the image carrier surface potential side that is uniformly charged by the charger with the DC line segment of the developing bias in the component as a boundary. It is characterized by.

  As an embodiment of the AC component waveform adjusting means, (1) expansion of the peak-to-peak voltage of the AC component of the developing bias can be considered. In other words, by increasing the amplitude of the alternating current component, the momentum at which the toner is developed from the developing member to the image carrier increases, and the fogging phenomenon of the toner can be promoted.

  (2) The duty on the image carrier surface potential side (unexposed state potential side) due to charging of the charger may be increased with the direct current component in the alternating current component of the developing bias applied to the developing member as a boundary. Conceivable.

  By increasing the timing of biasing to the image carrier surface potential side from those that are substantially equally amplituded by the AC component, the result is equivalent to moving the level of the DC component to the image carrier surface potential side. The effect is obtained and the low charge of the toner can be offset.

  In the above embodiments (1) and (2), either one may be executed, or there is no problem even if they are used in combination.

  According to a second aspect of the present invention, there is provided a charger for uniformly charging the image carrier, an exposure unit for forming a latent image of the image on the surface of the image carrier, and an electrostatic latent image formed by the exposure unit. A developing means for supplying toner through a developing member by a developing bias in which an AC bias and a DC bias are superimposed to visualize the toner image as a toner image. The toner image formed by the developing means is subjected to an intermediate transfer member by a potential difference. An image forming apparatus that forms an image by transferring the image to a recording medium via a detection unit that detects at least humidity in a use environment, and when the humidity higher than a predetermined level is detected by the detection unit, the image By adjusting the potential difference between the DC component of the developing bias and the surface potential of the image carrier uniformly charged by the charger as compared with the case of forming the image, the low charge state and the reverse polarity charge state are reduced. DC component potential difference adjusting means for accelerating the transfer of the toner, non-sheet passing operation executing means for executing a non-sheet passing operation for a predetermined time in a potential difference adjustment state by the DC component potential difference adjusting means, and the non-sheet passing operation execution Toner collecting means for collecting low-charged or reverse-polarized charged toner supplied during execution of the means.

  In the second invention, the DC component potential difference adjusting means relatively approaches at least one of the DC component of the developing bias applied to the developing member or the surface potential of the image carrier due to charging of the charger. Thus, the developing member holding power of the low-charge toner due to the humidity is reduced.

  Further, in the second invention, the DC component potential difference adjusting means relatively separates at least one of the DC component of the developing bias applied to the developing member or the image carrier surface potential due to charging of the charger. By doing so, the reverse polarity charged toner caused by the humidity is discharged from the developing device.

  According to the second aspect of the invention, it is determined that the charge amount of the toner is reduced when the detection unit detects a humidity higher than a predetermined level. Note that the temperature may be added to this determination. In other words, it may be determined that the charge amount of the toner is decreasing at high temperature and high humidity.

  When it is determined that the charge amount of the toner is reduced, the potential difference between the DC component of the developing bias and the surface potential of the image carrier is adjusted by the DC component potential difference adjusting means as compared to when forming an image, The holding power of the low-charged toner on the developing member side is reduced, and the reverse-polarized charged toner is discharged from the developing device.

  For example, when adjusting the potential difference by displacing the DC component of the developing bias, there are a case where the charge amount of the toner itself is reduced and a case where the charge of the toner itself reaches a reverse polarity.

  Therefore, these are extracted for each case. That is, when the charge amount of the toner itself appears, the holding force of the developing member is reduced by bringing the DC component of the developing bias closer to the surface potential side of the image carrier.

  On the other hand, when the charge of the toner itself has a reverse polarity, it is easy to transfer the reverse polarity toner to the image carrier by moving the DC component of the developing bias away from the image carrier surface potential side. Since the ratio of the toner having the opposite polarity is extremely small (about several percent of the total), the main adjustment is to bring the DC component of the developing bias closer to the surface potential side of the image carrier.

  In this state, the non-sheet passing operation execution means executes the non-sheet passing operation. As a result, it is possible to selectively develop the toner (reverse polarity charged toner) whose charge amount in the toner carried on the developing member is reduced to the image carrier side, and the toner collecting means can carry the image from the developing member. The toner transferred through the body and the intermediate transfer body can be collected, and image defects such as fogging and transfer ghost can be avoided.

  As a result, for example, cleaning can be performed without providing a blade or the like that directly contacts the image carrier, and image quality deterioration due to wear over time due to contact between the image carrier and the blade can be prevented. .

  In the first or second aspect of the invention, the toner collecting unit may receive the toner image from the image carrier in the toner transfer direction or a predetermined position downstream of the intermediate transfer. It is characterized by being provided.

  As the toner collecting means, the intermediate transfer member that receives the toner image from the image carrier or the downstream side of the intermediate transfer may affect the image carrier even if a cleaning blade that is in direct contact is disposed. Absent.

  Further, in the first invention or the second invention, the detection by the detection means is performed during setup when the main power supply is turned on.

  When the toner charge amount is reduced or the toner charge becomes high humidity with the opposite polarity, the main power is turned off for a relatively long time (for example, the operation of the previous day ended) This can happen when it has elapsed from the start of operation to the next day. Therefore, by performing detection by the detection means during setup when the main power source is turned on, it is possible to avoid causes that affect the image quality such as fogging, transfer efficiency reduction, retransfer, and transfer ghost from the start of operation.

  In the first or second invention, the toner is a polymerized toner having a shape factor SF-1 with a true sphere of 100 and having a value of 120 or less.

  It is known that the closer the toner is to a true sphere, the better the image quality. However, it is also known that scraping with a cleaning blade or the like is more difficult as it is closer to a true sphere. In the present invention, a polymerized toner having a shape factor SF-1 of 120 or less is applied to a commonly applied toner having a shape factor SF-1 of 150. The collection efficiency due to toner scraping has deteriorated. Therefore, by removing the toner using charging (electrostatic adsorption force), the toner is reliably transferred to the developing member, the image carrier, and the intermediate transfer without contact, and then collected by the toner collecting means. In other words, the contradictory purpose of improving image quality and improving toner recovery efficiency can be achieved.

  Further, in the first invention or the second invention, the toner is a tandem structure having a plurality of image carriers, and the toner is collected for a developing device provided corresponding to a predetermined image carrier. It is characterized by that.

  For example, when a full color image is formed by arranging a plurality of image carriers and superimposing toners for each color of CMYK, the degree of influence of environmental humidity differs depending on the physical properties of the toner (or carrier) of each color. For this reason, toner recovery can be avoided by using a developing device provided corresponding to a predetermined image carrier as a target.

  As described above, in the present invention, in a high humidity environment where low-charged toner and / or reverse-polarity charged toner can be generated, only this low-charged toner and / or reverse-polarity-charged toner is reliably extracted, and at least There is an excellent effect that the low charge toner and / or the reverse polarity charge toner can be collected without providing a cleaning member that physically contacts the surface of the image carrier.

(First embodiment)
As shown in FIG. 1, the image forming unit 80 according to the first embodiment includes an image forming unit 12, a laser optical unit 60, and a fixing unit 34.

  The image forming unit 12 includes yellow (Y), magenta (M), cyan (C), and black (K) photosensitive drums 14Y, 14M, 14C, and 14K (hereinafter collectively referred to as photosensitive drums 14). A charging device 16Y, 16M, 16C, 16K for primary charging (hereinafter collectively referred to as a charging device 16) that contacts each of the photosensitive drums 14, and a developer containing toner of each color component. The developing devices 20Y, 20M, 20C, and 20K (hereinafter collectively referred to as the developing device 20) are housed.

  Note that the toner applied in the first embodiment has a shape factor SF-1 of 120 or less. This shape factor indicates the true sphere degree of the toner. 100 is represented as a true sphere, and the larger the value, the more elliptical or elongated circle the toner is. The shape factor SF-1 is 120 or less. Compared to conventional toner (shape factor SF-1 is 150), it is very close to a true sphere, leading to improved image quality.

  Further, the image forming unit 12 contacts the primary intermediate transfer drum 22 that contacts the photosensitive drums 14Y and 14M, the primary intermediate transfer drum 24 that contacts the photosensitive drums 14C and 14K, and the primary intermediate transfer drums 22 and 24. A secondary intermediate transfer drum 26 and a final transfer roll 28 in contact with the secondary intermediate transfer drum 26 are configured.

  The respective photoconductive drums 14 are arranged at regular intervals in the vertical direction of FIG. Further, the primary intermediate transfer drums 22 and 24 and the secondary intermediate transfer drum 26 are arranged such that their respective rotation axes are parallel to the rotation axis of the photosensitive drum 14.

  In the image forming unit 12 according to the first embodiment, the photosensitive drum 14, the charging device 16, the developing device 20, the primary intermediate transfer drums 22 and 24, and the secondary intermediate transfer drum 26 are integrally mounted. It is configured as a process cartridge (CRU: Customer Replaceable Unit).

  On the other hand, the laser optical unit 60 outputs light sources 62Y, 62M, 62C, and 62K (Y, M, C, and K) that output laser beams 18Y, 18M, 18C, and 18K (hereinafter collectively referred to as laser beams 18). Hereinafter, the light source 62 is referred to generically), the modulation processing unit 66 that modulates and scans the laser light 18, the fθ lens that corrects the scanning speed on the exposure surface, and the surface tilt that has the lens power in the scanning direction. The optical system 68 includes a correction cylindrical lens or the like, and a mirror group 70 including a plurality of mirrors.

  Further, the modulation processing unit 66 includes a polygon mirror 64 for scanning the laser light 18 on each photosensitive drum 14, and a polygon motor 65 for rotating the polygon mirror 64 at a predetermined rotational speed. .

  In the laser optical unit 60, the laser light 18 of each color emitted from the light source 62 enters the modulation processing unit 66, is modulated according to the image information for each color, and is rotated by the polygon motor 65. Is scanned (main scan). The laser beams 18 of the respective colors scanned by the polygon mirror 64 are corrected by the optical system 68, and then reflected by the mirror group 70 in the arrangement direction of the photosensitive drums 14 corresponding to the respective colors, so as to be reflected on the respective photosensitive drums 14. Imaged.

  On the other hand, the fixing unit 34 includes a heating roller 38A as a heating member having a heating source 36 therein, and a pressure roller 38B that forms a nip portion in contact with the heating roller 38A. The pressure roller 38B presses the heating roller 38A at the nip portion. The pressure roller 38B is conveyed by the driving of the paper conveyance roll 32, conveyed in the image forming unit 80, and reaches the nip portion. Then, it is nipped and conveyed while being thermocompression bonded.

  The heating source 36 is operated so as to maintain the temperature of the surface of the heating roller 38A at the fixing temperature corresponding to the type of the paper 30 used as a recording medium when the image forming process is executed, and after the completion of the image forming process, the heating source 36 is heated. The roller 38A is operated so as to keep the surface temperature at a predetermined standby temperature lower than the fixing temperature.

  The charging device 16 includes a charging roll 40 that charges the photosensitive drum 14. The final transfer roll 28 has a blade 50A.

  In the blade 50A, the low-charged toner in the developing device 20 generated at high temperature and high humidity is operated in a non-sheet-passing state, so that the developing rolls 21Y, 21M, 21C and 21K (hereinafter collectively referred to as the developing roll 21), the photosensitive drum 14, the primary intermediate transfer drums 22 and 24, and the secondary intermediate transfer drum 26 are sequentially transferred, and the low-charged toner collected on the final transfer roll 28 is collected. It is configured to be scraped off and collected by the cleaning device 50.

  FIG. 2 shows the distribution of the toner amount (toner number) in the developing device 20 according to the environmental humidity.

  At normal environmental humidity, the charge amount is distributed in a state close to a so-called Gaussian distribution centering on the normal (minus) polarity, whereas at low humidity, the peak charge amount shifts to the negative side. Although the balance between the left and right centered at the center is lost, the shift on the negative side tends to promote transfer, so there is no particular problem.

  On the other hand, the distribution of the toner amount at high humidity shifts the peak charge amount to the plus side with respect to the toner distribution of the normal environmental humidity, and the distribution on the left and right with the peak charge amount as the center is expanded. The amount of variation becomes significant. In addition, the polarity of the charge amount is reversed in the vicinity of the skirt on the plus side. As a result, it can be seen that there are low-charge toner and reverse-polar charge toner that can cause transfer failure. The reverse polarity charged toner is only a few percent of the whole and has a little influence, but the low charge toner is a factor that greatly affects the image quality.

  Therefore, in the first embodiment, in order to collect such low-charged toner, the AC component of the developing bias is adjusted to promote the transfer of the low-charged toner.

  As shown in FIG. 3, the developing bias at the time of image formation is −370 V (direct current), which is between the surface potential (−450 V) of the photosensitive drum 14 and the potential at the time of writing with the laser beam 18 (−100 V). Component).

  Here, an alternating current component is superimposed on the developing bias, and as shown by a thin line A in FIG. 4, the amplitude is on the basis of −370 V at a constant period.

  Since this amplitude is almost a sine wave, the integral value on the plus side of −370 V and the integral value on the minus side are substantially the same, that is, the duty is 50%.

  By biasing this duty to the minus side (duty 60% in the first embodiment), the potential of the DC component of the developing bias is substantially shifted to the minus side so as to approach the surface potential of the photosensitive drum. I have to. By this development bias shift (increase in duty), the potential difference between the voltage of the development bias and the voltage of the low-charged toner is expanded, and the force that the toner holds on the development roll 21 can be reduced.

  For this reason, the low-charged toner adhered to the developing device 20 or the developing roll 21 at the discharge port of the developing device 20 is transferred to the cleaning device 50 and collected by the cleaning device 50.

  FIG. 5 shows a functional block diagram for low-charged toner collection control.

  A temperature sensor 102 and a humidity sensor 104 are connected to the environmental temperature / humidity determination unit 100, and the temperature measured by the temperature sensor 102 and the humidity measured by the humidity sensor 104 are input. If the temperature sensor 102 and the humidity sensor 104 are arranged in the vicinity of the apparatus, there is no need to pinpoint the position, but it is preferable that the temperature sensor 102 and the humidity sensor 104 be in the vicinity of the developing device 20.

  The environmental temperature / humidity determination unit 100 is connected to a toner recovery operation execution determination table memory 106. The toner recovery operation execution determination table memory 106 stores a table (see Table 1) for determining whether the toner recovery operation is performed or not according to temperature and humidity.

  Based on Table 1 above, the environmental temperature / humidity determination unit 100 determines whether or not to perform the toner recovery operation at the current temperature / humidity.

  In addition, a power supply state determination unit 108 is connected to the environmental temperature / humidity determination unit 100. The power supply state determination unit 108 receives a signal from the main power supply line 110, and monitors the power on / off state. An execution signal is sent to the humidity determination unit 100. Note that long-time power off assumes from the end of operation on the previous day to the start of operation on the next day.

  When the environmental temperature / humidity determination unit 100 determines that the operation is performed according to the table stored in the toner recovery operation execution determination table memory 106 and an execution signal is input from the power supply state determination unit 108, the toner recovery operation is performed. It is determined that it is time to perform, and a start signal is sent to the toner collection operation instruction unit 112.

  The toner recovery operation instruction unit 112 sends an activation signal to the development bias AC component adjustment amount reading unit 114 and the non-sheet passing operation execution instruction unit 116 based on the start signal.

  A toner collection duty memory 118 is connected to the developing bias AC star cluster adjustment amount reading unit 114, and the duty stored in the toner collection duty memory 118 is read out. In the first embodiment, a duty of 60% is stored, but this numerical value is not particularly limited and may be larger than a normal duty (50%).

  The read duty is sent to the development bias controller 120, whereby the development bias controller 120 changes the waveform of the AC component of the development bias to the instructed duty (from the thin line A to the thick line B in FIG. 4). Change). By changing the duty, the DC component of the developing bias is substantially shifted to the surface potential side of the photosensitive drum, the potential difference from the charged toner is enlarged, and the holding power of the low-charged toner to the developing roll 21 is reduced. It will be.

  On the other hand, the non-sheet passing operation execution instruction unit 116 instructs the image forming operation execution control unit 122 to perform the image forming operation in a non-sheet passing state.

  As a result, the image forming operation is performed in a state where the duty of the AC component of the developing bias is 60% and in the non-sheet passing state, and the low-charged toner in the developing device 20 and on the developing roll 21 is transferred to the photosensitive drum. 14, the images are successively transferred to the final transfer roll 28 via the primary intermediate transfer drums 22 and 24 and the secondary intermediate transfer drum 26.

  The operation of the first embodiment will be described below.

  Around each photosensitive drum 14 of the image forming unit 80, an image forming (printing) process for each color by a known electrophotographic method is performed as follows.

  First, each photosensitive drum 14 is rotationally driven at a predetermined rotational speed (for example, 95 mm / sec).

  As shown in FIG. 1, the surface of the photosensitive drum 14 is uniformly charged to a predetermined level by applying a developing bias voltage of a predetermined charging level (for example, about −450 V) to the charging device 16. The In the first embodiment, the developing bias is configured to superimpose not only a DC voltage but also an AC component on the DC component.

  Next, the laser optical unit 60 irradiates the surface of each photosensitive drum 14 having a uniform surface potential with the laser light 18 corresponding to each color, thereby forming an electrostatic latent image corresponding to the image information for each color. Is done. Thereby, the surface potential of the exposed portion of the photosensitive drum 14 by the laser light is neutralized to a predetermined level (for example, about −100).

  The electrostatic latent image formed on the surface of each photoconductive drum 14 is developed by the corresponding developing device 20 and visualized on each photoconductive drum 14 as a toner image of each color.

  Next, the toner images of the respective colors formed on the respective photoconductive drums 14 are electrostatically primarily transferred onto the corresponding primary intermediate transfer drums 22 and 24. Here, the Y and M toner images formed on the photosensitive drums 14Y and 14M are on the primary intermediate transfer drum 22, and the C and K toner images formed on the photosensitive drums 14C and 14K are the primary intermediate. Each image is transferred onto the transfer drum 24.

  Thereafter, the toner images formed on the primary intermediate transfer drums 22 and 24 are electrostatically secondary-transferred onto the secondary intermediate transfer drum 26. As a result, on the secondary intermediate transfer drum 26, a toner image from a single color image to a quadruple color image of each color of Y, M, C, and K is formed.

  Finally, the toner image formed on the secondary intermediate transfer drum 26 is tertiary-transferred onto the paper passing through the paper conveyance path 30 by the final transfer roll 28. The paper passes through a paper transporting roll 32 through a paper feeding process (not shown), and is fed into the nip portion between the secondary intermediate transfer drum 26 and the final transfer roll 28. After the tertiary transfer, the toner image formed on the paper is heated and fixed by the fixing unit 34, and the image forming process is completed.

  Here, conventionally, particularly in a high temperature and high humidity environment, a low-charged toner is generated, which may cause a transfer defect, resulting in image defects such as fogging, retransfer, and transfer ghost. . In order to solve this problem, a cleaning blade is brought into direct contact with the peripheral surface of the photosensitive drum 14 to scrape off the toner. However, there is a problem that the wear of the photosensitive drum 14 is accelerated over time.

  Therefore, in the first embodiment, when the power is high and the humidity is high when the power is turned on, the AC component of the developing bias is set to recover the low-charged toner adhering to the developing device 20 and the developing roll 21. The low-charge toner is reliably transferred from the developing roll 21 to the final transfer roll 28 one after another through the photosensitive drum 14, the primary transfer drums 22, 24 and the secondary transfer drum 26, and scraped off by the cleaning blade 50A. Then, it is collected into the cleaning device 50.

  That is, there is no member in direct contact with the peripheral surface of the photosensitive drum 14, and wear of the peripheral surface of the photosensitive drum 14 due to cleaning can be avoided.

  Hereinafter, the procedure of toner collection control will be described with reference to the flowchart of FIG.

  In step 150, it is determined whether the power source has been switched from off to on. This basically detects when the operation is stopped on the previous day and the operation is started the next day.

  If an affirmative determination is made in step 150, the process proceeds to step 152 where the environmental temperature is detected by the temperature sensor 102, and then the environmental humidity is detected by the humidity sensor 104 in step 154.

  The temperature sensor 102 and the humidity sensor 104 are not particularly limited in the installation location, but are preferably around the developing device 20 in the apparatus.

  In the next step 156, the toner collection operation execution / non-execution determination table is read, and in step 158, it is determined whether or not the toner collection operation is necessary at the current temperature and humidity (see Table 1).

  If a negative determination is made in step 158, it is determined that the amount of low-charged toner is small at the current temperature and humidity and there is no need for toner collection, and this routine ends.

  If an affirmative determination is made in step 158, it is determined that the amount of low-charged toner has increased at the development temperature and humidity, and that toner collection is necessary, and the routine proceeds to step 160.

  At step 160, the duty for toner collection is read, and then the routine proceeds to step 162, where the AC component of the developing bias is set from the normal duty (50%) to the duty for toner collection (60%).

  In the next step 164, execution of the non-sheet passing operation is started. As a result, the low-charged toner adhering to the developing device 20 and the developing roll 21 is reliably transferred to the photosensitive drum 14, and then reliably transferred to the primary intermediate transfer drums 22, 24 and the secondary intermediate transfer drum 26. Transcript to.

  The low-charged toner thus transferred is finally transferred to a final transfer roll 28 facing the secondary intermediate transfer drum 26, usually via a sheet.

  In the next step 166, the low-charged toner that has reached the final transfer roll 28 is scraped off by the cleaning blade 50 </ b> A and collected in the cleaning device 50.

  In the next step 168, it is determined whether or not a predetermined time has elapsed. If an affirmative determination is made, the process proceeds to step 170, the non-sheet passing operation is terminated, and the process proceeds to step 172.

  In step 172, the duty of the AC component of the developing bias is returned to the normal duty (50%), and this routine ends.

  As described above, in the first embodiment, a cleaning blade or the like is disposed in direct contact with the peripheral surface of the photosensitive drum 14 to reduce the charge in a high temperature and high humidity environment without scraping off the toner. By changing the duty of the AC component of the developing bias with respect to the applied toner, a potential difference from the low-charged toner for ensuring transfer from the developing roll 21 to the photosensitive drum 14 was ensured. Thereby, the low-charged toner can be successively transferred to the final transfer roll 28 without adopting a cleaning method that actively scrapes off. Although the final transfer roll 28 is provided with a cleaning blade 50A, the cleaning at this portion does not directly affect the image quality, thus preventing deterioration of image quality such as fogging and extending the life of the photosensitive drum. Can be stretched.

(Second Embodiment)
The second embodiment of the present invention (first invention) will be described below. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description of the configuration is omitted.

  As shown in FIG. 7, the feature of the second embodiment is that the first embodiment adjusts the duty of the AC component of the developing bias, whereas the peak-to-peak of the AC component is adjusted. There is.

  FIG. 7 is a functional block diagram for adjusting the peak toe peak according to the second embodiment. The difference from FIG. 5 is that the developing bias alternating current component adjustment amount reading unit 114 has a toner recovery peak toe. The peak data memory 124 is connected.

  That is, when execution of the toner recovery operation is determined, the development bias AC component adjustment amount reading unit 114 reads a preset peak toe peak from the toner recovery peak toe peak data memory 124 and sends it to the development bias controller 120. Send it out.

  As a result, the development bias controller 120 adjusts the peak-to-peak of the AC component of the development bias.

  In the second embodiment, at the time of toner recovery, the peak toe peak is larger than the peak toe peak of the AC component of the normal developing bias.

  That is, in the second embodiment, as shown in FIG. 8, the peak toe peak is larger than the peak toe peak (see thin line C in FIG. 8) of the AC component of the normal developing bias during toner recovery. (Refer to the thick line D in FIG. 8), the increase in the peak-to-peak (amplitude) increases the momentum for transferring the low-charged toner from the developing roll 21 to the photosensitive drum 14.

  The greatest feature of the second embodiment is that the DC component of the development bias is not displaced and is maintained at −370 V. By maintaining the DC component of the development bias, There is no influence (for example, a difference from the surface potential of the photosensitive drum 14). In addition, since the frequency of the AC component of the developing bias can be maintained, no change occurs in the generation of noise.

  FIG. 9 is a flowchart showing the procedure of toner collection control according to the second embodiment.

  9 is different from the flowchart of FIG. 9 in that, in step 158, when the determination of whether or not to perform toner recovery is affirmed, the toner recovery peak toe peak is read in step 260, and in the next step 262, The developing bias AC component is set to the read toner recovery peak-to-peak, and after completion of the non-sheet passing operation in step 170, the recovery bias AC component is changed to the normal peak-to-peak in step 272 after completion of the recovery. To set. Since other controls are the same as in FIG. 6, the same step numbers are assigned and description thereof is omitted.

(Third embodiment)
The third embodiment of the present invention (second invention) will be described below. In the third embodiment, the same components as those in the first and second embodiments are denoted by the same reference numerals, and the description of the configuration is omitted.

  The feature of the third embodiment is that the DC component of the developing bias is increased / decreased, and the collection of the reversely charged toner as well as the lowly charged toner that was the collection target of the first and second embodiments. It is also possible.

  As described above, the voltage DB of the DC component of the developing bias is −370 V as shown in FIG.

  With reference to this, as shown in FIG. 10, when the difference from the surface potential VH of the photosensitive drum 14 is applied as the cleaning bias Vcln (| VH−DB |), the potential difference (80 V) of the developing bias during image formation is a boundary. As the potential difference decreases, the potential difference with the lower charged toner increases, the holding force on the developing roll 21 decreases, and the transfer to the photosensitive drum 14 becomes easy.

  On the other hand, if the potential difference increases with the potential difference (80 V) of the developing bias during image formation as the boundary, the potential difference with the reverse polarity charged toner increases, and transfer from the developing roll 21 to the photosensitive drum 14 becomes possible.

  Therefore, by performing the shift of the DC line segment of the developing bias twice in the opposite direction to the surface potential side of the photoreceptor, it is possible to collect the low charge toner and the reverse polarity charge toner. Become.

  In the first to third embodiments, the image forming unit 80 forms an electrostatic latent image using CMYK toners of the respective colors using the separate photoconductors 14Y, 14M, 14C, and 14K. The tandem type is used to form a full-color image by transferring the image onto the paper 30 through the primary intermediate transfer drums 22 and 24 and the secondary intermediate transfer drum 26. However, the image forming apparatus has a single photosensitive drum configuration. It is also applicable to. Moreover, the apparatus which can perform color printing of two or more colors may be sufficient.

  In the case of the image forming apparatus of two or more colors, it is not necessary to perform the toner collection described in the first to third embodiments for all the toners, and the high temperature and high humidity are not affected. What is necessary is just to perform with respect to the toner in which low electrification is promoted.

  In the first to third embodiments, the toner having a shape factor SF-1 value of 120 or less is applied. However, the closer to such a true sphere, the more remarkable the effect. It does not exclude toner having a shape factor SF-1 exceeding 120.

FIG. 2 is a schematic diagram illustrating a configuration of an image forming unit in the image forming apparatus according to the first embodiment. FIG. 7 is a number distribution characteristic diagram of toner charge amount depending on humidity. FIG. 6 is a development bias characteristic diagram. FIG. 6 is a characteristic diagram showing a duty adjustment state of an AC component of a developing bias according to the first embodiment. FIG. 6 is a functional block diagram for low-charged toner collection control according to the first embodiment. 4 is a flowchart illustrating a procedure of low-charged toner collection control according to the first embodiment. FIG. 10 is a functional block diagram for low-charge toner collection control according to a second embodiment. It is a characteristic view which shows the adjustment state of the peak toe peak of the alternating current component of the developing bias which concerns on 2nd Embodiment. 12 is a flowchart illustrating a procedure of low-charged toner collection control according to the second embodiment. FIG. 9 is a cleaning bias-toner discharge amount characteristic diagram according to a third embodiment.

Explanation of symbols

12 Image forming unit (image forming apparatus)
18Y, 18M, 18C, 18K Laser light 20 Developer (Developer)
22, 24 Primary intermediate transfer drum (intermediate transfer member)
26 Secondary intermediate transfer drum (intermediate transfer member)
30 Paper 34 Fixing unit 36 Heating source 38A Heating roller 38B Pressure roller 50 Cleaning device (collecting means)
50A Cleaning blade (collection means)
60 Laser optical unit (exposure means)
80 Image forming unit (image forming apparatus)
100 Environmental Temperature / Humidity Discriminator 102 Temperature Sensor 104 Humidity Sensor (Detection Means)
106 Toner recovery operation execution determination table memory 108 Power supply state determination unit 110 Main power supply line 112 Toner recovery operation instruction unit (holding force reduction means)
114 Development bias AC component adjustment amount reading unit (holding force reducing means)
116 Non-sheet-passing operation execution instructing section (non-sheet-passing operation executing means)
118 Toner recovery duty memory 120 Development bias controller 122 Image forming operation execution control unit (non-sheet passing operation executing means)

Claims (9)

A charger for uniformly charging the image carrier, an exposure unit for forming a latent image of the image on the surface of the image carrier, and an AC bias and a DC bias are applied to the electrostatic latent image formed by the exposure unit. And a developing unit that supplies toner through a developing member with an overlaid developing bias and visualizes the toner image as a toner image, and transfers the toner image formed by the developing unit to a recording medium through an intermediate transfer member by a potential difference. An image forming apparatus that forms an image by
Detection means for detecting at least the humidity of the use environment;
When the detection unit detects a humidity higher than a predetermined level, the waveform of the AC component of the developing bias is adjusted compared to when the image is formed, and the holding force of the toner on the developing member side is reduced. AC component waveform adjusting means;
A non-sheet passing operation executing means for executing a non-sheet passing operation for a predetermined time in a holding force reduced state by the AC component waveform adjusting means;
Toner collecting means for collecting toner supplied during the execution of the non-sheet passing operation executing means;
An image forming apparatus.   The AC component waveform adjusting means expands the peak-to-peak voltage of the AC component of the developing bias applied to the developing member or the DC line of the developing bias in the AC component of the developing bias applied to the developing member. 2. The toner holding force is reduced by executing at least one of an increase in duty on the surface potential side of the image carrier that is uniformly charged by the charger with a minute as a boundary. Image forming apparatus. A charger for uniformly charging the image carrier, an exposure unit for forming a latent image of the image on the surface of the image carrier, and an AC bias and a DC bias are applied to the electrostatic latent image formed by the exposure unit. And a developing unit that supplies toner through a developing member with an overlaid developing bias and visualizes the toner image as a toner image, and transfers the toner image formed by the developing unit to a recording medium through an intermediate transfer member by a potential difference. An image forming apparatus that forms an image by
Detection means for detecting at least the humidity of the use environment;
When a humidity higher than a predetermined level is detected by the detection means, the potential difference between the DC component of the developing bias and the surface potential of the image carrier uniformly charged by the charger is compared to when the image is formed. DC component potential difference adjusting means for adjusting and facilitating transfer of the toner in at least one of a low charge state and a reverse polarity charge state;
A non-sheet passing operation executing means for executing a non-sheet passing operation for a predetermined time in a potential difference adjustment state by the DC component potential difference adjusting means;
Toner collecting means for collecting toner in a low-charge state or a reverse-polarity charge state supplied during execution of the non-sheet-passing operation executing means;
An image forming apparatus.   The direct current component potential difference adjusting means relatively brings at least one of the direct current component of the developing bias applied to the developing member or the surface potential of the image carrier due to charging of the charger, thereby causing the humidity. 4. The image forming apparatus according to claim 3, wherein a holding force of the developing member for the low-charged toner is reduced.   The direct current component potential difference adjusting means relatively separates at least one of the direct current component of the developing bias applied to the developing member or the surface potential of the image carrier due to charging of the charger, thereby causing the humidity. The image forming apparatus according to claim 3, wherein the reverse polarity charged toner is discharged from the developing device.   2. The toner collecting unit is provided in the intermediate transfer member that receives a toner image from the image carrier in the toner transfer direction or in a predetermined position downstream of the intermediate transfer member. The image forming apparatus according to claim 5.   The image forming apparatus according to claim 1, wherein the detection by the detection unit is executed during setup when the main power source is turned on. 8. The image forming apparatus according to claim 1, wherein a polymerized toner having a shape factor SF- 1 having a true sphere of 100 and a shape factor SF- 1 of 120 or less is applied as the toner. 9.   9. The image forming apparatus according to claim 1, wherein the image forming apparatus has a tandem structure including a plurality of image carriers, and the toner is collected corresponding to a predetermined image carrier. An image forming apparatus that targets a developed developing device.

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