JP2009031454A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method and image forming apparatus, whereby development ghost is prevented in the image forming apparatus that has a developing means of a touch down development system, and images with secured image density can be obtained for a long term. <P>SOLUTION: The image forming apparatus having the developing means of the touch down development system is provided with a surface potential sensor 48 for detecting the surface potential of a developing roller 28. The surface potentials of the developing roller 28 during the first and second rotations made to form a thin toner layer on the roller 28 are measured. Based on the difference between the surface potentials, the formation of the toner layer during the first rotation of the developing roller is adjusted so that the amount of toner on the developing roller becomes a saturated amount of toner. Thereafter, image formation is carried out. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming method and an image forming apparatus such as a copying machine, a printer, a facsimile, and a composite machine using an electrophotographic method, and more particularly, two-component development for charging nonmagnetic toner using a magnetic carrier. After forming a uniform thin layer of only the charged toner on the developing roller using the agent, the toner is ejected from the developing roller to the electrostatic latent image formed on the photosensitive member for development to form an image. The present invention relates to an image forming method and an image forming apparatus.

  Development methods using dry toner in image forming apparatuses such as copiers, printers, facsimiles, and composite machines using electrophotography include a one-component development method using only toner, and a toner and a carrier. A two-component development method using a two-component developer is known.

  Since the one-component development method does not use a carrier, the electrostatic latent image on the electrostatic latent image carrier (hereinafter also referred to as a photosensitive member) is not disturbed by a magnetic brush formed from the carrier and the toner. Suitable for image quality. However, in the one-component development method, it is difficult to stably maintain the charge amount of the toner. In the case of a color toner, since transparency is required, it must be a non-magnetic toner. For this reason, full-color image forming apparatuses often employ a two-component development system that uses a carrier as a medium for charging and transporting toner.

  The two-component development method is suitable for extending the life because a stable charge amount can be obtained over a long period of time. However, the two-component development method is disadvantageous in terms of image quality because of the influence of the magnetic brush described above. Therefore, in order to take advantage of each of these two development methods, the charging area adopts a two-component development system in consideration of extending the life, and the development area uses a one-component development system to improve image quality. A development system called a down development system or a hybrid development system has attracted attention. In particular, in a full-color image forming apparatus in which high image quality and long life are important, the characteristics of this development method are sufficiently exhibited.

  In this touch-down development method, a magnetic brush is formed on the surface of a developer carrier (hereinafter also referred to as a magnetic roller) with a two-component developer containing toner and carrier, and only the toner is transferred from the magnetic brush to a toner carrier (hereinafter referred to as a magnetic carrier). The toner is transferred to the surface of a developing roller to form a thin layer of toner, and then the toner is ejected onto the surface of the photoreceptor on which the electrostatic latent image is formed to develop it as a toner image.

  However, in the touch-down development method, it is necessary to remove the residual toner that has not been used for development on the developing roller with the magnetic brush of the magnetic roller and simultaneously supply the toner from the magnetic brush to the developing roller. Insufficient removal or insufficient supply of toner to the developing roller causes a so-called development ghost (history phenomenon) in which the afterimage after the toner flies from the developing roller to the photoreceptor appears on the second round. There is a problem that it is easy to do.

  As shown in FIG. 5, the development ghost is obtained by developing the electrostatic latent image of the solid image 50 having the maximum density on the first round of the development roller, and, for example, on the development roller (second round), for example, a half density image. When the electrostatic latent image 52 is developed, the image density of the development area 54 of the half-density image 52 is different from the area used to form the solid image 50 on the first round of the toner thin layer on the developing roller. This is a phenomenon that becomes lower than the area and appears as an afterimage. This becomes more prominent when the background 52 of the second round has a half density.

  In order to solve such a problem, it is only necessary to develop the electrostatic latent image formed on the photoconductor with a stable density. For this reason, for example, Patent Document 1 discloses an image using a one-component developer. Although related to the forming apparatus, the photosensitive member surface potential sensor 91 for detecting the bright portion potential of the surface portion of the photosensitive member 2 and the electrostatic latent image formed on the surface of the photosensitive member 2 are developed with toner. From the developing device 1, a bias power source 12 for applying a bias voltage to the developing device 1, a developing roller surface potential sensor 92 for detecting the surface potential of the developing roller 11, and the photoreceptor surface potential sensor 91. In response to the detection output and the detection output from the developing roller surface potential sensor 92, an image provided with bias voltage control means 20 for controlling the bias power source 12 so that the difference between the two potentials becomes constant. Forming apparatus is shown.

  In order to cope with this development ghost by the touch-down development method, for example, in Patent Document 2, the magnetic roll is made conductive, and the carrier constituting the developer has a saturation magnetization value of 45 emu / g or less in a 5 K Oersted applied magnetic field. In addition, while forming with a high resistance insulating carrier having an average particle size of 45 μm or less, the gap between the magnetic roll and the developing roll is set to 500 μm or less, and the bias and the magnetizing force are effected by using the transport bias applied to the magnetic roll side as a DC power source. A compact hybrid type developer that prevents development ghosts and carrier scattering without complicating the development device, and ensures stable image quality over a long period of time by ensuring image quality stability during continuous development. An image forming apparatus having the apparatus is shown.

  Further, in Patent Document 3, a thin toner layer is carried on a developing roller by rubbing with a magnetic brush formed of a two-component developer, and an alternating electric field consisting of a rectangular wave by a first power source is placed between the developing roller and the photoreceptor. And developing the latent image on the photosensitive member by causing the toner to fly from the developing roller at the same frequency as the alternating electric field formed by the first power source between the magnetic roller and the developing roller. A second power source for applying an alternating electric field by a rectangular wave having a reverse phase and a reverse duty ratio is provided, thereby forming a thin toner layer on the developing roller to prevent ghosting and to the developing roller. 1 shows a developing device in an image forming apparatus that prevents toner adhesion and a decrease in image density due to the toner adhesion.

JP-A-6-0955481 JP 2003-295613 A JP-A-2005-242281

  However, in the image forming apparatus disclosed in Patent Document 1, the developing bias is set so that the difference between the developing roller surface potential and the post-exposure potential of the photosensitive member is always constant. However, it is thought that it is difficult to prevent the development ghost and other problems from occurring, especially in the case of solid images, etc. It is done.

  Further, the image forming apparatus disclosed in Patent Document 2 eliminates development ghosts over a long period of time because if the density and uniformity of the magnetic brush is impaired due to carrier deterioration, the stripping performance deteriorates and development ghosts are generated. Since the developing device shown in Patent Document 3 also requires complicated control to cope with changes in the level of occurrence of development ghosts and development leaks due to the deterioration of the developer, It is not easy to prevent completely.

  Therefore, in the present invention, in an image forming apparatus having a touch-down developing type developing unit, an image forming method and an image forming apparatus capable of obtaining a high-quality image over a long period of time with a simple configuration and suppressing development ghosts. It is a problem to provide.

  As a result of intensive studies to solve the above problems, the present inventors have made the toner amount of the toner thin layer the saturated toner amount around the toner carrier when forming the toner thin layer on the toner carrier. The inventors have found that the problems such as the development ghost can be solved and have completed the present invention.

  That is, the cause of development ghost is that the toner thin layer on the developing roller is missing due to the development of the electrostatic latent image, and then the toner brush is sufficiently invisible so that the missing portion of the toner thin layer cannot be recognized by the magnetic brush carried by the magnetic roller. The toner is supplied so that the portion where the toner thin layer is missing in the development is fully filled and the missing portion and the amount of toner around it are almost the same. Failure to do so is raised as a second development ghost occurrence factor.

  In particular, this second development ghost generation factor is important. From the magnetic roller to the development roller, the part on the development roller where the toner has not been used in the previous development is filled in one round, and the missing part and its surroundings The fact that the toner cannot be supplied so that the toner amount of the toner is almost the same as the amount of toner in the toner cartridge is that when the toner is supplied to the developing roller, the toner is also added to the missing portion and the surrounding area. It is thought that occurred. This is because the amount of toner that can be supplied to the developing roller is not limited unless the toner is supplied to the developing roller over a plurality of turns, that is, the amount of toner that can be supplied to the developing roller in one round of the developing roller is limited. This means that there is a margin (that is, the amount of saturated toner is large).

  That is, when the saturated toner amount is large and the toner must be supplied over a plurality of circumferences of the developing roller in order to supply the saturated toner amount on the developing roller, as shown in FIG. When the electrostatic latent image is developed on the first round of the developing roller and the electrostatic latent image of the half density image 52 is developed on the second round, the remaining solid image 50 portion that is not used in the development on the first round If the toner other than the toner is not sufficiently collected due to the first development ghost occurrence factor, when the toner is supplied to the next developing roller, the toner is supplied onto the remaining toner without being collected except for the solid image 50 portion. In the solid image 50 portion, toner is supplied with almost no toner. Therefore, even if the toner is supplied in the same manner, a difference in toner amount occurs between the solid image 50 portion and other areas, which is a development ghost. Cause It is considered to be a factor.

  On the other hand, if the amount of saturated toner is equal to the amount of toner on the developing roller that is optimal for development and the toner of this saturated toner amount is supplied to the developing roller during one round of the developing roller, for example, 1 Even if toner other than the remaining solid image 50 portion that is not used in the peripheral development is not sufficiently collected, when the toner is supplied to the next developing roller, the solid image 50 portion and the other areas are also saturated. If an amount of toner is supplied, it is considered that there is no difference between the two, and therefore no development ghost is generated.

  Furthermore, when the amount of saturated toner is large, the toner is supplied while the developing roller makes one round to form an image by forming a thin toner layer, and the toner is supplied over two or more rounds of the developing roller to form the thin toner layer. In the case of forming an image, there is a problem that the image density becomes higher when the toner is supplied over two or more rounds to form a thin toner layer, and over two or more rounds of the developing roller. Supplying the toner also causes a problem that development takes time.

  Therefore, when the toner thin layer is formed on the developing roller, the present inventors supply the toner to the developing roller and the difference ΔV between the DC voltage supplied from the direct current (DC) bias power source to the magnetic roller and the developing roller, respectively. It was examined how the surface potential on the developing roller changes according to the number of rotations of the developing roller during the operation, and whether there is a relationship between the change in the surface potential and the development ghost.

  As a result, the difference in DC voltage supplied from the direct current (DC) bias power source to the magnetic roller and the developing roller, that is, the DC potential difference ΔV, causes a large difference in the surface potential after the first and second rounds of the developing roller. There is a case where the development ghost does not occur and the surface potential is different between the first and second rounds of the developing roller, the surface potential rises stepwise depending on the number of rotations, and the development ghost may occur. I understood.

  From this result, the difference between the voltages supplied from the direct current (DC) bias power source to the magnetic roller and the developing roller, that is, the difference between the surface potentials of the first and second rounds of the developing roller caused by the DC potential difference ΔV, that is, the surface potential difference. Is considered to be related to the saturated toner amount of the toner thin layer formed on the developing roller, and development is performed when the saturated toner amount is larger than the toner amount that can be supplied from the magnetic roller to the developing roller around the circumference of the developing roller. If a ghost is generated and the amount of toner supplied during one rotation of the developing roller is equal to or less than the amount of toner, it is assumed that the developing ghost does not occur. Therefore, if this saturated toner amount is the toner amount on the developing roller that is optimal for development, it is possible to provide an image forming method and an image forming apparatus in which development ghost does not occur and the image density is also optimal.

  Therefore, for example, a toner thin layer is formed on the developing roller over two rounds before image formation, and the surface potential on the first round and the surface potential on the second round are measured and developed based on the difference between the two surface potentials. The adjustment of the direction in which the toner amount on the developing roller is set to the saturated toner amount by forming the toner layer around the roller, that is, the difference between the DC bias voltages supplied to the magnetic roller and the developing roller so as to reduce the difference between the surface potentials. By adjusting ΔV, it is considered that the development ghost does not occur and the image formation with the optimum image density can be performed.

  The adjustment of the difference ΔV in the DC bias voltage supplied to the magnetic roller and the developing roller, respectively, changes the development conditions when the bias applied to the developing roller is changed. Therefore, the bias applied to the developing roller is fixed. It is preferable to perform this by changing the DC bias applied to the magnetic roller. In addition, an AC bias is applied to the developing roller during image formation. However, if an AC bias is present when measuring the surface potential, accurate measurement cannot be performed. Therefore, the AC roller has an AC phase opposite to the AC bias applied to the developing roller. It is preferable to apply a bias.

  Also, there is a correlation between the relationship between the surface potential of the first round of the developing roller, the difference between the surface potential of the second round and the toner amount on the developing roller, and the density in the formed image, and development ghost is recognized. It was also found that development ghosts can be prevented by adjusting the ratio between the surface potential of the first round of the developing roller and the surface potential of the second round to be 0.9 or more in order to achieve a low image density.

From the above results, the image forming method according to the present invention is as follows.
A magnetic brush of a two-component developer composed of toner and carrier is formed on a magnetic roller having a plurality of magnetic poles and applied with a DC bias, and a bias in which AC is superimposed on the DC is applied by the magnetic brush. In the image forming method of forming an image by forming a toner thin layer on the developed developing roller and then developing the electrostatic latent image formed on the photoreceptor with the toner of the toner thin layer.
Before forming the image, the toner thin layer is formed on the developing roller over two rounds, and the surface potential on the first round and the surface potential on the second round are measured, and the development is performed based on the difference between the two surface potentials. The bias voltage applied to the magnetic roller and the developing roller is adjusted in the direction in which the toner amount on the developing roller is set to the saturated toner amount by forming a toner layer around one roller.

Similarly,
A magnetic brush of a two-component developer composed of toner and carrier is formed on a magnetic roller having a plurality of magnetic poles and applied with a DC bias, and a bias in which AC is superimposed on the DC is applied by the magnetic brush. In the image forming method of forming an image by forming a toner thin layer on the developed developing roller and then developing the electrostatic latent image formed on the photoreceptor with the toner of the toner thin layer.
Before forming the image, a toner thin layer is formed on the developing roller over two rounds, and the surface potential on the first round and the surface potential on the second round are measured, and the difference is determined based on the difference between the two surface potentials. The bias voltage to be applied to the magnetic roller and the developing roller is adjusted in the direction of decreasing the magnetic field.

An image forming apparatus that implements this image forming method is:
A magnetic roller having a magnetic brush of a two-component developer having a plurality of magnetic poles therein and composed of toner and carrier; a developing roller having a thin toner layer formed by the magnetic brush on the magnetic roller; A photosensitive member on which an electrostatic latent image is formed by a photographic method and the electrostatic latent image is developed into a toner image by toner flying from the developing roller, and the developing roller and the magnetic roller are provided correspondingly, respectively. In an image forming apparatus having a bias power supply for applying a bias voltage,
Based on the measurement results of the surface potential measuring means for measuring the surface potential on the developing roller and the surface potential measuring means on the first and second rounds of toner thin layer formation on the developing roller, A toner layer formed on one circumference of the developing roller, comprising a magnetic roller and a control means for adjusting a bias voltage applied to the developing roller in a direction in which the toner amount on the developing roller is set to a saturated toner amount in forming the toner layer. The amount is a saturated toner amount, and development ghost is prevented.

  By forming an image in this way, as described above, it is possible to provide an image forming method and an image forming apparatus capable of suppressing development ghosts with a simple configuration and obtaining a high-quality image over a long period of time. it can.

  The adjustment based on the difference between the surface potentials can be easily performed without causing any trouble in development by fixing the bias applied to the developing roller and changing the DC bias applied to the magnetic roller. it can.

  Further, the adjustment based on the difference between the surface potentials is performed by applying an AC bias having a phase opposite to that of the AC bias applied to the developing roller to the magnetic roller. Therefore, the surface potential on the developing roller by the surface potential measuring unit is adjusted. In the measurement state, the surface potential of the developing roller can be accurately measured by providing the magnetic roller with a power source that applies a bias that cancels the AC bias applied to the developing roller.

  Further, the adjustment based on the difference between the surface potentials is adjusted to the toner amount on the developing roller by adjusting the ratio of the surface potential of the first round to the surface potential of the second round to be 0.9 or more. It is possible to optimize the density in the obtained image.

  According to the present invention, the surface potentials of the first and second circumferences of the developing roller when the toner thin layer is formed on the developing roller are measured, and the magnetic roller and the developing roller are measured in a direction to reduce the difference between the surface potentials. By adjusting the bias voltage to be applied and making the amount of toner in the toner thin layer the saturated toner amount around the circumference of the toner carrier, the development ghost is expected to occur in the touch-down development method. Thus, it is possible to provide an image forming method and an image forming apparatus capable of avoiding a development ghost with high accuracy and obtaining a high-quality image over a long period of time.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  First, an image forming apparatus that performs the image forming method according to the present invention will be described with reference to FIG. An image forming apparatus 10 that performs the image forming method of the present invention includes, for example, a drum-shaped electrostatic latent image carrier (photoconductor) 12 and a surface of the photoconductor 12 provided around the drum-like electrostatic latent image carrier (photoconductor) 12 as shown in FIG. A charging means 14 for charging the toner, an exposure means 16 for exposing the surface of the photoconductor 12 to form an electrostatic latent image, and a toner image attached to the electrostatic latent image formed on the photoconductor 12 for development. Developing means 18, transfer means 22 for transferring the toner image from the photosensitive member 12 to a transfer target (not shown) such as paper conveyed by the endless belt 20, cleaning means 24 for cleaning the surface of the photosensitive member, Etc.

  Among these, as the photoreceptor 12, an organic photoreceptor having an inorganic photoreceptor such as selenium or amorphous silicon, or a single or laminated photosensitive layer containing a charge generating agent, a charge transporting agent, a binder resin, etc. formed on a conductive substrate. A photoreceptor or the like is used. Examples of the charging unit 14 include a scorotron system, a charging roller system, and a charging brush system. As the exposure unit 16, the transfer unit 22, and the cleaning unit 24, conventionally known ones are used.

  The developing means 18 includes a developer carrier (magnetic roller) 26 comprising a plurality of fixed magnets disposed inside and a sleeve that can rotate around the fixed magnet, and a magnetic brush (not shown) formed on the magnetic roller 26. ), A toner carrier (developing roller) 28 on which a toner thin layer (not shown) is formed, a surface potential sensor 48 serving as a surface potential measuring means for detecting the surface potential of the toner carrier 28, and a direct current to the magnetic roller 26. A power source 30 for applying a (DC) bias, a power source 32 for applying a direct current (DC) bias to the developing roller 28, a power source 34 for applying an alternating current (AC) bias to the developing roller 28, and an alternating current (AC) bias for the magnetic roller 26 A power supply 60 to be applied, a regulating blade 36 for keeping the height of the magnetic brush formed on the magnetic roller 26 constant, and a toner container 38 containing toner. A stirring mixer 40 that stirs and charges the toner supplied from the toner container 38 together with the carrier, and a paddle mixer that supplies the magnetic roller 26 while stirring the two-component developer supplied from the stirring mixer 40 through the partition plate 42. 44, a magnetic roller 26 having a plurality of magnetic poles therein and forming a magnetic brush of a two-component developer composed of toner and carrier, and a developing roller 28 having a thin toner layer formed by the magnetic brush on the magnetic roller 26 The magnet 46 controls the direct current (DC) bias power supply 30 and the alternating current (AC) bias power supply 60 for the magnetic roller 26 in response to the measurement results of the frame 46 in which the stirring mixer 40 and the paddle mixer 44 are housed, and the surface potential sensor 48. Roller bias power supply controller 62, direct current (DC) bias power supply 32 for developing roller 28 and alternating current (AC) Developing roller bias power source control apparatus for controlling the bias power source 34 64, these magnetic roller bias power source control unit 62, and the like developing roller bias power supply control device 64 control device 58 sends a control instruction to.

  In a normal image forming method in the image forming apparatus 10 configured as described above, first, the surface of the photoconductor 12 is charged by the charging unit 14 (charging process), and then the surface of the photoconductor 12 is exposed by the exposure unit 16. Thus, an electrostatic latent image is formed (exposure process). On the other hand, in the developing means 18, a two-component developer is carried on the surface of the magnetic roller 26 to form a magnetic brush, and only the toner is transferred from the magnetic brush to the surface of the developing roller 28, and the surface of the developing roller 28 is transferred. A thin toner layer is formed. Then, the toner is allowed to fly from the toner thin layer of the developing roller 28 to the photosensitive member 12, and the toner is attached to the electrostatic latent image formed on the photosensitive member 12 to develop it as a toner image (developing step).

  This toner image is transferred from the photoconductor 12 to the transfer medium such as paper conveyed by the endless belt 20 by the transfer unit 22 (transfer process), and the remaining toner remaining on the surface of the photoconductor 12 is cleaned by the cleaning unit. 24 is used to prepare for the next image formation. It is obvious that the image forming apparatus 10 is not limited to the configuration described above, but may be any type of image forming apparatus as long as the developing apparatus uses the touch-down developing method. It is.

  Next, a mechanism for generating a development ghost as described in FIG. 5 will be described. The developing ghost is formed by using a toner thin layer on the developing roller 28 in the shape of the image when forming the image, and then the toner is sufficiently invisible so that the image shape cannot be recognized by the magnetic brush formed on the magnetic roller 26. The first generation factor is that it cannot be peeled off. In addition, if the amount of toner supplied to the portion where the toner has been used due to the development and the amount of toner around the image finally becomes the same, such a problem does not occur. As a cause of the development ghost, the amount of toner supplied to the portion where the toner has not been used in the previous development is not equal to the amount of toner around the image.

  In particular, this second development ghost occurrence factor is important. The portion on the developing roller 28 where the toner has not been used in the previous development is filled from the magnetic roller 26 to the developing roller 28 in one round. The toner cannot be supplied so that the amount of toner around and the surrounding toner amount is substantially the same. When toner is supplied to the developing roller 28, the toner is also added to the missing portion and the surrounding area. It is considered that a difference has occurred in the toner amount. This is because the toner amount is not saturated unless the toner is supplied to the developing roller 28 over a plurality of circumferences, that is, the amount of toner that can be supplied to the developing roller 28 in one round of the developing roller 28 is limited. This means that there is a margin in the amount of toner that can be supplied to (that is, the saturated toner amount is large).

  That is, when the saturated toner amount is large and the toner must be supplied over a plurality of circumferences of the developing roller in order to supply the saturated toner amount on the developing roller, as shown in FIG. When the electrostatic latent image is developed on the first round of the developing roller and the electrostatic latent image of the half density image 52 is developed on the second round, the remaining solid image 50 portion that is not used in the development on the first round If the toner other than the toner is not sufficiently collected due to the first development ghost occurrence factor, when the toner is supplied to the next developing roller, the toner is supplied onto the remaining toner without being collected except for the solid image 50 portion. Since the toner is supplied with almost no toner in the solid image 50 portion, even if the toner is supplied in exactly the same manner, a difference in toner amount occurs between the solid image 50 portion and other regions, which is developed. ghost It is considered to be a cause for.

  On the other hand, if the saturated toner amount is equal to, for example, the toner amount on the developing roller 28 that is optimal for development, and the toner of this saturated toner amount is supplied to the developing roller 28 during one round of the developing roller 28. Even if the toner other than the solid image 50 portion remaining not used in the development of the first round is not sufficiently collected, when the toner is supplied to the next developing roller 28, the solid image 50 portion is also in the other region. It is considered that the toner of the saturated toner amount is supplied to the surface, so that there is no difference between the two, and therefore no development ghost is generated.

  In particular, when the amount of saturated toner is large, the toner is supplied while the developing roller 28 makes one turn to form an image by forming a thin toner layer, and the toner is supplied over two or more turns of the developing roller 28 to thin the toner. In the case of forming an image by forming a layer, there is a problem that the image density becomes higher when the toner is supplied over two or more rounds to form a thin toner layer, and the developing roller 28 Supplying toner over two or more rounds also causes a problem that it takes time for development.

  Therefore, the present inventors have examined how the surface potential of the developing roller 28 changes depending on the number of rotations of the developing roller 28 when a thin toner layer is formed on the developing roller 28. A graph showing the results is shown in FIG. In FIG. 4, the horizontal axis indicates the number of rotations of the developing roller 28, the vertical axis indicates the toner layer potential (V) on the developing roller 28, and the solid line and the broken line indicate direct current (DC) to the magnetic roller 26 and the developing roller 28, respectively. The difference ΔV between the voltages supplied from the bias power supply is shown. The solid line indicates 200 V, and the broken line indicates 300 V.

  Note that the image forming apparatus used in this experiment is a printer FS-C5016N using a touch-down developing method manufactured by Kyocera Mita, Inc., in the vicinity of the developing roller 28 of the developing apparatus in this image forming apparatus. A surface potential sensor of MODEL 344 manufactured by TREK Co., Ltd. was installed so that the surface potential on the developing roller 28 could be detected.

  From the graph of FIG. 4, when the potential difference ΔV of the DC bias voltage between the magnetic roller 26 and the developing roller 28 is 300 V, the toner thin layer formed becomes thicker as the number of rotations of the developing roller 28 increases, and the surface of the developing roller 28 It can be seen that the potential rises stepwise. That is, when two or more rounds are required to form a thin toner layer uniformly on the developing roller 28, that is, when the amount of saturated toner in the developing roller 28 is large as described above, the number of times of toner supply to the developing roller 28 is As the number increases, the surface potential of the developing roller 28 rises stepwise.

  On the other hand, when ΔV is 200 V, the amount of saturated toner in the toner thin layer on the developing roller 28 is small, and the toner thin layer can be formed in one turn of the developing roller 28. Therefore, when ΔV is 300 V in the second turn. After a potential increase of less than half, the surface potential is almost constant and the surface potential is not stepped. In other words, this indicates that it is only necessary to supply the toner while the developing roller 28 makes one turn to form a uniform toner thin layer over the entire circumference of the developing roller 28, even if 50 in FIG. This means that even if the electrostatic latent image of the solid image as shown is developed, a thin toner layer that does not leave the influence and does not generate the development ghost 54 can be formed.

  Accordingly, the difference ΔV in the DC bias voltage is set to 200 V in this case, for example, so that the potential difference between the surface potentials in the first and second rounds of the developing roller 28 is reduced, that is, the saturated toner amount in the first round of the developing roller 28. It is shown that a thin layer with a saturated toner amount is formed on the developing roller 28 in one circumference of the developing roller 28 by adjusting so as to reach the value of the developing roller 28, and the development can be performed without generating a developing ghost.

  In addition, a surface potential sensor is used to determine whether or not development ghost is generated, and the surface potential on the first round and the surface potential on the second round when the toner thin layer is formed on the developing roller 28 are detected. It is also shown that it can be determined by examining whether or not it is rising. Accordingly, the difference between the DC bias voltages supplied to the magnetic roller 26 and the developing roller 28, that is, the bias potential difference ΔV is determined so as to reduce the difference between the surface potential of the first round of the developing roller 28 and the surface potential of the second round. Thus, the development ghost can be suppressed.

  In FIG. 3, in order to verify the relationship between the surface potential on the developing roller 28 and the developing ghost described above, direct current (DC) bias power supplies 30 and 32 are supplied to the magnetic roller 26 and the developing roller 28, respectively. Depending on the DC bias voltage and its potential difference ΔV, the surface potential and the difference between the first and second rounds of the developing roller 28 change, and thereby whether the development ghost appears and how the image density changes. It is the table | surface which showed the result of having experimented. The image forming apparatus and the surface potential sensor used in this experiment are the same as the image forming apparatus and the surface potential sensor used in the experiment of FIG.

  First, a bias is applied to the magnetic roller 26 and the developing roller 28 from an external power source so that an AC component is not applied to the developing roller 28, and a thin toner layer is formed on the developing roller 28 to form the first and second rounds. The surface potential of was measured. At that time, the DC bias applied to the developing roller 28 is fixed to 100 V as shown in “DC bias B applied to the developing roller” so as not to change the developing condition, and the DC bias applied to the magnetic roller 26 is “ The potential difference ΔV between the two was changed from 300V to 150V by changing as shown in “DC bias A applied to magnetic roller”.

Also, as shown in FIG. 5, at each development bias setting value, a solid image 50 is printed at the head, and a sample image (development ghost pattern) having a half portion 52 is printed, and the development ghost 52 appears. Whether or not it was visually confirmed and evaluated, the image density was measured. Evaluation criteria for development ghost are as follows. Further, the image density needs to be 1.00 or more, and preferably 1.20 or more. The “judgment” column in the table of FIG. 3 indicates that “NG” cannot be used because the image quality is impaired by the development ghost, and “OK” is maintained without deteriorating the image quality. Is shown.
○: No afterimage in the half part. (Judgment: Pass)
Δ: There is an afterimage in the half, but it is slight. (Judgment: Pass)
X: There is an afterimage in the half portion. (Judgment: Fail)

From the evaluation results shown in FIG. 3, the potential difference ΔV of the DC bias whose evaluation result of the development ghost pattern is “OK” is 200 V and 150 V. In this case, the surface potential of the first round of the development roller 28 is The ratio of the surface potential on the second round of the developing roller 28 is 0.90 for 200 V and 1.00 for 150 V, both being 0.9 or more. Therefore, as shown in the following formula (1), it is considered that development ghost can be prevented when (surface potential of the first rotation of the developing roller / surface potential of the second rotation of the developing roller) is 0.9 or more. .
(Surface potential at the first round of the developing roller / Surface potential at the second round of the developing roller) ≧ 0.9 (1)

  However, when ΔV = 250V, the development ghost is very slight and it is possible to make a pass judgment. However, in view of fluctuations in various conditions, in order to completely eliminate the development ghost, ΔV = 200V The following is desirable. Further, when ΔV is 150 V, the amount of toner in the toner thin layer on the developing roller 28 has decreased, so the image density is slightly insufficient at 1.08, and in order to ensure sufficient image density. ΔV = 200V is more preferable.

  Thus, from this experimental result, the development ghost is the difference between the direct current (DC) biases of the magnetic roller 26 and the development roller 28, that is, the voltage supplied from the direct current (DC) bias power source 30 and the direct current (DC) bias power source 32. It can be understood that a so-called potential difference (hereinafter referred to as ΔV) is involved.

  That is, even if the electrostatic latent image of the solid image as indicated by 50 in FIG. 5 is developed, the solid image 50 is supplied by supplying toner from the magnetic roller 26 to the developing roller 28 for one rotation of the developing roller. If the toner is supplied so that the toner amount in the area used for the development and the surrounding area is the same, the development ghost does not occur. Thus, the potential difference ΔV between the voltages supplied from the direct current (DC) bias power supply 30 and the direct current (DC) bias power supply 32 is determined, and the toner amount on the developing roller 28 is made the saturated toner amount with a small toner amount transition. In this way, it is possible to easily suppress the development ghost.

  Further, when the potential difference ΔV of the direct current (DC) bias applied to the magnetic roller 26 and the developing roller 28 is reduced, the development ghost is not generated. Conversely, if the potential difference ΔV is reduced, the saturated toner amount is reduced. However, if the amount of toner on the developing roller 28 is too small, the image density becomes insufficient. Therefore, the amount of toner in the thin toner layer formed on the developing roller 28 is increased to such an extent that the image density is not impaired. It is necessary to keep. Therefore, in order to maintain the image density while avoiding the development ghost, the potential difference ΔV of the direct current (DC) bias between the magnetic roller and the development roller is the optimum potential difference that satisfies the image density while preventing the development ghost. It is preferable to set so that.

  However, regarding the toner supply performance from the magnetic roller 26 to the developing roller 28 and the ability to peel off the toner on the developing roller 28, the distance between the developing roller 28 and the magnetic roller 26, the layout of the magnetic poles, the height of the head of the magnetic brush (Gap between the regulating blade 36 and the magnetic roller 26), the particle size of the carrier, the saturation magnetization, and the like. In addition, the optimum amount of toner layer supplied to the developing roller 28 is very likely to fluctuate through the process of forming a large number of images, depending on the toner concentration in the two-component developer and the change in toner charge amount due to carrier deterioration. . Therefore, it is appropriate to consider that the potential difference that satisfies the image density while preventing the development ghost as described above fluctuates each time.

  Therefore, in the present invention, before the image formation, the developing roller 28 is rotated twice to form a thin toner layer, the surface potentials of the first and second rounds are measured, and according to the measurement results, 58 is shown in FIG. The control device instructs the magnetic roller bias power source control device 62 and the developing roller bias power source control device 64 to apply the voltages of the DC bias power sources 30 and 32 applied to the magnetic roller 26 and the developing roller 28 over one cycle of the developing roller 28. In order to prevent the development ghost, the image is formed after adjusting the toner amount of the toner thin layer to the saturated toner amount, that is, adjusting the potential difference between the first and second surface potentials to be small. is there.

  In the conventional development ghost detection, a patch or the like that is likely to cause a ghost is formed on the photoconductor 12 and is determined by detecting the density mainly using a density sensor or the like. Since toner is consumed for printing and the development ghost cannot be determined unless the patch is formed, it takes time.

  On the other hand, in the method of the present invention described above, the surface potential sensor 48 is installed in the vicinity of the developing roller 28, and when the toner thin layer is formed on the developing roller 28, the surface potential of the developing roller 28 is measured. Whether or not a development ghost is generated can be determined in advance, thereby preventing the development ghost and controlling the image density to cope with these problems.

  The surface potential sensor 48 is preferably disposed so as to face the developing roller 28 shown in FIG. 1 and at an interval of about 1 mm. When the toner is supplied from the magnetic roller 26 to the developing roller 28, the surface potential sensor 48 is provided. The sensor 48 can detect the surface potential of the developing roller 28.

  Further, the adjustment of the difference ΔV between the DC bias voltages supplied to the magnetic roller and the developing roller, respectively, changes the developing conditions when the bias applied to the developing roller is changed. Therefore, the controller 58 controls the magnetic roller bias power supply. It is preferable to instruct the device 62 and the developing roller bias power source control device 64 to fix the bias applied to the developing roller and change the DC bias applied to the magnetic roller.

  Furthermore, if an AC component is superimposed on the developing bias applied to the developing roller 28 from the alternating current (AC) bias power supply 34, a normal potential cannot be detected depending on the sensitivity of the surface potential sensor 48. It is necessary to supply toner to 28 while applying only a DC component. Therefore, when an AC component is applied to the developing roller 28 during normal printing, the controller 58 instructs the magnetic roller bias power source controller 62 when detecting the surface potential, and the AC (AC) bias power source 60 A thin toner layer is formed by applying an AC component applied to 28 and an AC component having an opposite phase to the magnetic roller 26.

  Next, the image forming method according to the present invention described above will be described with reference to the flowchart shown in FIG. When the process starts, first, an instruction is sent from the controller 58 to the magnetic roller bias power source controller 62 in step S2, and a direct current (DC) bias power source 30 that supplies a DC bias to the magnetic roller 26 is set to a predetermined bias. Set to output voltage. In step S3, the toner that has not been used for development on the developing roller (toner carrier) 28 is peeled off by the magnetic brush using the two-component developer formed on the magnetic roller (developer carrier) 26. In step S4, toner is similarly supplied from the magnetic brush to the developing roller 28 to form a thin toner layer.

  The toner thin layer is formed by the controller 58 by the controller 58 so that the surface potential can be accurately measured when the AC component is applied to the developing roller 28 as a bias at the time of image formation. An instruction is sent, and the alternating current component having the opposite phase to the alternating current is applied from the alternating current (AC) bias power source 60 to the magnetic roller 26 to eliminate the alternating current component. In the next step S5, the surface potential of the first round of the developing roller is detected and stored. Then, in the next step S6, it is determined whether or not the surface potential has been detected for two rotations of the developing roller 28. Since only one rotation has been detected at present, the process returns to step S3 and the same thing is repeated. .

  When the surface potential of the second turn of the developing roller 28 is detected in step S5, the process proceeds from step S6 to step S7, and the control device 58 makes one turn of the developing roller 28 based on the equation (1). Divide the surface potential of the eye by the surface potential of the second round to determine whether the quotient is greater than 0.9.

  If the quotient is less than 0.9, the process proceeds to step S8, the controller 58 sends an instruction to the magnetic roller bias power source controller 62, and the direct current (DC) bias power source previously set in step S2 The DC bias voltage supplied from 30 to the magnetic roller 26 is changed, and the difference between the two bias voltages, that is, the potential difference ΔV is adjusted to be smaller than the initially set value.

  The processing described above is continued until the expression (1) in step S7 is satisfied. When the developing bias potential difference ΔV that satisfies the above expression is obtained, the processing proceeds to step S9, where the potential difference ΔV, that is, direct current (DC) ) The DC bias voltage supplied from the bias power source 30 to the magnetic roller 26 and the developing roller 28 is determined, and the processing is completed in step S20 to perform image formation.

  It should be noted that the adjustment of the development conditions according to the flowchart shown in FIG. 2 is performed before the image is formed (printed) on the transfer medium, and it is necessary to prevent the development ghost from occurring in the actual printed matter. is there. Of course, it is ideal to carry out before all image formation, but it causes a decrease in printing efficiency. For example, every 500 image formation, every fixed drive time in which the developer state may change. It is preferable to carry out. Also, when the printing environment has changed significantly, or when it has been left without image formation for a long time, the image quality of the image to be formed is likely to change. .

  According to the present invention, there is provided an image forming apparatus capable of preventing a development ghost, which has been a problem in the conventional touchdown development method, with a simple configuration and obtaining a stable high-quality image over a long period of time. be able to.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of a touch-down development system that performs an image forming method according to the present invention. 3 is a flowchart of an image forming method according to the present invention. The first and second rounds of the developing roller 28 are generated by a direct current bias voltage supplied from the direct current (DC) bias power source 30 and the direct current (DC) bias power source 32 to the magnetic roller 26 and the developing roller 28 and the potential difference ΔV. It is a table | surface which showed the result of having experimented how the surface potential of each eye and its difference change, and by which development ghost appears, how image density changes. 6 is a graph showing a result of measuring a transition of a surface potential when a toner thin layer is formed on the developing roller with a surface potential sensor 48; It is a figure for demonstrating the generation | occurrence | production mechanism of a development ghost.

Explanation of symbols

10 Image forming apparatus 12 Electrostatic latent image carrier (photosensitive member)
14 Charging means 16 Exposure means 18 Developing means 20 Endless belt 22 Transfer means 24 Cleaning means 26 Developer carrier (magnetic roller)
28 Toner carrier (developing roller)
30 DC (DC) Bias Power Supply 32 DC (DC) Bias Power Supply 34 AC (AC) Bias Power Supply 36 Regulating Blade 38 Toner Container 40 Stir Mixer 42 Partition Plate 44 Paddle Mixer 46 Frame 48 Surface Potential Sensor 50 Solid Image 52 Half Image 54 Area 58 used for solid image development 58 Control device 60 AC (AC) bias power supply 62 Magnetic roller bias power supply control device 64 Development roller bias power supply control device

Claims (7)

A magnetic brush of a two-component developer composed of toner and carrier is formed on a magnetic roller having a plurality of magnetic poles and applied with a DC bias, and a bias in which AC is superimposed on the DC is applied by the magnetic brush. In the image forming method of forming an image by forming a toner thin layer on the developed developing roller and then developing the electrostatic latent image formed on the photoreceptor with the toner of the toner thin layer.
Before forming the image, the toner thin layer is formed on the developing roller over two rounds, and the surface potential on the first round and the surface potential on the second round are measured, and the development is performed based on the difference between the two surface potentials. An image forming method comprising: adjusting a bias voltage applied to the magnetic roller and the developing roller in a direction in which a toner amount on the developing roller is set to a saturated toner amount by forming a toner layer around one roller. A magnetic brush of a two-component developer composed of toner and carrier is formed on a magnetic roller having a plurality of magnetic poles and applied with a DC bias, and a bias in which AC is superimposed on the DC is applied by the magnetic brush. In the image forming method of forming an image by forming a toner thin layer on the developed developing roller and then developing the electrostatic latent image formed on the photoreceptor with the toner of the toner thin layer.
Before forming the image, a toner thin layer is formed on the developing roller over two rounds, and the surface potential on the first round and the surface potential on the second round are measured, and the difference is determined based on the difference between the two surface potentials. An image forming method comprising adjusting a bias voltage applied to the magnetic roller and the developing roller in a direction of decreasing the size of the magnetic roller.   3. The image formation according to claim 1, wherein the adjustment based on the difference between the surface potentials is performed by fixing a bias applied to the developing roller and changing a DC bias applied to the magnetic roller. Method.   4. The image according to claim 1, wherein the adjustment based on the difference between the surface potentials is performed by applying an AC bias having a phase opposite to that of the AC bias applied to the developing roller to the magnetic roller. Forming method.   5. The adjustment based on the difference between the surface potentials is adjusted such that the ratio of the surface potential of the first round to the surface potential of the second round is 0.9 or more. The described image forming method. A magnetic roller having a magnetic brush of a two-component developer having a plurality of magnetic poles therein and composed of toner and carrier; a developing roller having a thin toner layer formed by the magnetic brush on the magnetic roller; A photosensitive member on which an electrostatic latent image is formed by a photographic method and the electrostatic latent image is developed into a toner image by toner flying from the developing roller, and the developing roller and the magnetic roller are provided correspondingly, respectively. In an image forming apparatus having a bias power supply for applying a bias voltage,
Based on the measurement results of the surface potential measuring means for measuring the surface potential on the developing roller and the surface potential measuring means on the first and second rounds of toner thin layer formation on the developing roller, A toner layer formed on one circumference of the developing roller, comprising a magnetic roller and a control means for adjusting a bias voltage applied to the developing roller in a direction in which the toner amount on the developing roller is set to a saturated toner amount in forming the toner layer. An image forming apparatus, wherein the amount is a saturated toner amount to prevent development ghost.   7. The power supply for applying a bias that cancels an AC bias applied to the developing roller to the magnetic roller in a state in which the surface potential is measured on the developing roller by the surface potential sensor. The described image forming apparatus.

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