JP2010091803A - Development method and device for image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a development method and device for an image forming apparatus that prevent the occurrence of image failure due to increase or decrease in the density of a magnetic brush on a magnetic roller with the toner charge amount changing with the environmental condition, or the like, in a touchdown development method, reduction in toner thin-layer forming capability to a development roller, excessive friction to the development roller by the magnetic brush caused by the increase in the toner conveyance amount, or the like. <P>SOLUTION: The relationship between the toner charge amount, varied by varying the environmental temperature and humidity and the magnetic brush density, is previously stored in a table form as the relationship between the environmental temperature and humidity and the frequency of alternating-current toner thin layer formation bias for making the toner charge amount to the development roller by the magnetic brush. The frequency of the table corresponding to the temperature and humidity is read when forming an image; the frequency of the alternating-current toner thin layer formation bias is set to the read frequency; a toner layer on the development roller is formed; and the electrostatic latent image is developed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing method and an apparatus in an image forming apparatus such as a copying machine, a printer, a facsimile, and a composite machine using an electrophotographic method, and more particularly, a two component for charging a nonmagnetic toner using a magnetic carrier. A developer is used to form a thin layer of only the charged toner uniformly on the developing roller, and the electrostatic latent image formed on the photosensitive drum is developed by flying the toner from the developing roller to form an image. The present invention relates to a developing method and apparatus in an image forming apparatus.

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

  Of these, the two-component development system is suitable for extending the life because a stable charge amount can be obtained over a long period of time by friction between the toner and the carrier. However, in the two-component development method, since the magnetic brush formed by the carrier and the toner is brought into contact with an electrostatic latent image carrier (hereinafter referred to as a photosensitive drum) for development, the electrostatic latent image is faithfully developed. However, there is a problem of print smearing (fogging) on the non-latent image area and a carrier adhesion problem where the carrier is used for development together with the toner or developed to the non-latent image area. In addition, the toner image formed on the photosensitive member is disturbed.

  On the other hand, the one-component development method that does not contact the photoconductor provides a sharp image with an edge effect without disturbing the formed toner image, and is a method advantageous for fogging and is suitable for high image quality. Yes. However, in this method, the toner is charged by the charge roller, and the layer thickness on the developing roller is regulated by the elastic regulating blade, so that it is difficult to stably maintain the charge amount of the toner. May adhere to the charge roller and reduce the charging ability, or toner may adhere to the regulating blade, resulting in non-uniform layer formation and image defects. Since it is required, it must be a non-magnetic toner.

  Therefore, in a full-color image forming apparatus, a non-magnetic toner is used to develop a one-component development method with the aim of improving the image quality of the development region, and a two-component development method is adopted for the charging region in consideration of extending the service life. A development method called a touch-down development method or a hybrid development method that takes advantage of the respective advantages of these two development methods 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.

  This touch-down development method uses a two-component developer containing toner and carrier to secure a stable charge amount and forms a magnetic brush on the surface of the developer carrying member (hereinafter referred to as a magnetic roller). After only a toner is transferred from a magnetic brush to the surface of a toner carrier (hereinafter referred to as a developing roller) to form a thin layer of toner, the toner is allowed to fly to the surface of the photoreceptor on which the electrostatic latent image is formed. This is a method of developing as a toner image.

  In this touch-down development method, in order to maintain stable image quality over a long period of time, the optimization / stabilization of the toner conveyance amount from the magnetic brush formed on the magnetic roller to the development roller is the image quality improvement. This is very important for improvement / stability. When the developer amount of the magnetic brush decreases, the image density decreases due to a decrease in toner thin layer forming ability on the developing roller, and an afterimage after the toner jumps from the developing roller to the photosensitive drum appears on the second developing roller. It causes deterioration of development ghost (history phenomenon).

  If the developer amount of the magnetic brush is too large, toner thin layer unevenness due to excessive rubbing on the developing roller by the magnetic brush, image unevenness, and further, between the magnetic roller and the developing roller gap due to excessive developer transport amount. In this case, the developer overflows. In order to prevent these problems from occurring, the blade gap is set to be as narrow as 0.27 to 0.33 mm with the aim of achieving proper stabilization and uniformization of the developer conveyance amount.

  However, changes in the charge amount of toner due to environmental changes, particularly an increase in developer fluidity due to a decrease in charge amount in a high-temperature / high-humidity (H / H) environment, lead to an increase in developer transport amount, and the amount of magnetic brush The toner thin layer formed on the developing roller causes unevenness in sweeping with the magnetic brush, and the image also causes unevenness in sweeping of the magnetic brush, resulting in an image defect. Further, the developer between the magnetic roller and the developing roller gap Cause overflow.

  Conversely, when the toner charge amount increases in a low temperature / low humidity (L / L) environment, the developer fluidity decreases, the developer transport amount decreases, the magnetic brush amount decreases, and the developing roller is moved to the developing roller. As a result, the toner thin layer forming ability is reduced, resulting in a reduction in image density and a development ghost.

  As a technique for the problem of the touch-down development method, for example, in Patent Document 1, an aluminum oxide film having a thickness of 5 μm or more is formed on the surface as a developing roll in order to suppress leakage of an applied potential between the developing roll and the photosensitive drum. When the aluminum roll is used and the distance between the developing roll and the photosensitive drum base tube is set to 150 to 300 μm, an alternating current is applied to the developing roll in order to cause the toner to fly from the developing roller to the photosensitive body. In addition, there is shown an image forming method in which the frequency of alternating current during non-image formation is controlled to be higher than during image formation.

  Further, Patent Document 2 discloses that a toner image having a small particle diameter is prevented from accumulating in the developing device and that a good image without deterioration in image quality is obtained between a developing roll and a magnetic roll on a regular basis. A first step of applying an AC bias voltage with a potential difference of, and rotating for a predetermined time to form a toner layer with a lot of fine powder, and the rotation of the developing roll on which the fine powder toner layer is formed are completely stopped to carry a latent image An image forming apparatus is provided that adjusts the particle size distribution of toner by providing a second step of causing toner on a developing roll at a position facing the body to fly onto the latent image carrier and completely peeling it off. .

  In Patent Document 3, the toner layer thickness on the developing roller is always stabilized over a long period of time without complicating the developing device and without causing a decrease in printing speed, and a stable image without density change is maintained. Therefore, at the non-development interval between any latent images corresponding to the recording paper, the potential difference between the supply roller and the development roller is rotated differently from that during development, and the thin toner layer on the development roller is peeled off. After that, a re-formation cycle for re-forming a new thin toner layer on the developing roller is set, and this toner layer peeling and re-formation cycle is equal to or larger than the developing roller circumference (d1 + d2) + first roller circumferential surface distance d1 In addition, there is shown a developing method and apparatus in which a developing bias return timing is set so that the developing cycle is returned to the developing cycle at a cycle end timing of less than two laps.

  Further, Patent Document 4 discloses a divided area on the surface of the photoreceptor in order to prevent the occurrence of density unevenness in the image according to changes in development conditions and environmental conditions while avoiding an increase in size and cost of the apparatus. For each change in development conditions and environmental conditions from among a plurality of conversion information (individual conversion information) candidates used for converting the pixel gradation determined by the image processing means into an exposure amount (individual exposure amount conversion) Appropriate individual conversion information is selected according to, and pixel gradation to exposure amount conversion (individual exposure amount conversion) is individually performed for each divided region based on the selected individual conversion information. Of the exposure characteristics representing the correspondence between the exposure amount in each divided area and the potential after exposure, the individual linear exposure characteristic excluding the convergence area to the residual potential or the exposure characteristic obtained by extending the characteristic by extrapolation By exposure conversion The potential after exposure when applying the exposure amount obtained by converting one reference pixel gradation, the image forming apparatus is shown in which the information to match to a reference potential.

JP 2004-318092 A JP 2005-10290 A JP 2005-55837 A JP 2006-181783 A

  However, these methods disclosed in Patent Documents 1 to 4 are technologies that suppress leakage of applied potential between the developing roll and the photosensitive drum (Patent Document 1), and prevent toner having a small particle diameter from accumulating in the developing device. Technology (Patent Document 2), a refresh technology (Patent Document 3) that re-forms a new toner thin layer on the developing roller after peeling off the toner thin layer on the developing roller, and according to changes in development conditions and environmental conditions In the technique (Patent Document 4) using information for matching the potential after exposure to one reference potential, the toner conveyance amount from the magnetic brush formed on the magnetic roller to the developing roller is optimized / stable. It is not meant to be used.

  Therefore, in the present invention, even if the toner charge amount changes due to environmental conditions or the like in the touch-down development method, the image density decreases due to the decrease in the ability to form a toner thin layer on the developing roller due to the decrease in the density of the magnetic brush on the magnetic roller. The toner thinning due to the deterioration of the development ghost (history phenomenon) in which the afterimage after the toner flies from the developing roller to the photosensitive drum appears on the second circumference of the developing roller, and excessive rubbing on the developing roller due to the increase in the magnetic brush density. Development method and apparatus in an image forming apparatus in which problems such as non-uniformity of layers and image unevenness, and overflow of developer between the magnetic roller and the developing roller gap due to excessive developer transport amount do not occur It is a problem to provide.

In order to solve the above problems, the developing method in the image forming apparatus 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 containing a magnet and applied with a bias for forming a toner thin layer in which alternating current is superimposed on direct current. From the magnetic brush, alternating current is applied to direct current. Development in an image forming apparatus in which a toner thin layer is formed on a developing roller to which a developing bias with superimposed toner is applied and then toner is ejected onto an electrostatic latent image formed on a photoreceptor by electrophotography. In the method
The relationship between the toner charge amount changed by changing the environmental temperature and humidity and the magnetic brush density in advance is the same as the AC toner thinning that makes the environmental temperature and humidity and the toner conveyance amount to the developing roller by the magnetic brush constant. The table is stored as a relationship of the layer forming bias frequency, the frequency of the table corresponding to the temperature and humidity is read at the time of image formation, and the frequency of the AC toner thin layer forming bias is set to the read frequency. An upper toner layer is formed to develop the electrostatic latent image.

And the developing device for carrying out this developing method is:
A magnetic roller that forms a magnetic brush of a two-component developer composed of toner and a carrier by applying a bias for applying a toner thin layer containing a magnet and superposing an alternating current on a direct current, and forming a toner thin layer on which an alternating current is superimposed on a direct current An image having a developing roller for applying a bias to form a toner thin layer with the magnetic brush and developing the electrostatic latent image formed on the photoreceptor by electrophotography with the toner flying from the toner thin layer. In the developing device in the forming device,
The relationship between the temperature and humidity sensor that detects the environmental temperature and humidity, the toner charge amount that varies with the environmental temperature and humidity, and the magnetic brush density, the amount of toner transported to the developing roller by the environmental temperature and humidity, and the magnetic brush A storage device that stores data tabulated as a frequency relationship of the AC toner thin layer formation bias, and a temperature and humidity signal detected by the temperature and humidity sensor, and a corresponding stored in the storage device. A development control device that reads the frequency of the table, sets the frequency of the alternating toner thin layer forming bias to the read frequency, forms a toner layer on a developing roller, and develops the electrostatic latent image; It is characterized by comprising.

  When the frequency component of the AC toner thin layer forming bias applied to the magnetic roller is increased, the magnetic brush on the surface of the magnetic roller is more erected, and when the frequency component is decreased, the magnetic brush is less lowered. Therefore, in this way, the relationship between the toner charge amount that changes depending on the environmental temperature and humidity and the magnetic brush density on the magnetic roller is constant, and the environmental temperature, humidity, and toner conveyance amount to the developing roller by the magnetic brush are made constant. The frequency relationship of the AC toner thin layer formation bias is tabulated so that, for example, when the ambient temperature and humidity are detected and the developer charge amount is reduced and the magnetic brush density is increased, the frequency is changed. Decrease the magnetic brush standing by lowering it, and when it is determined that the developer charge amount has increased and the magnetic brush density has decreased, the magnetic brush is raised by increasing the frequency to lower the magnetic brush standing. When it is suppressed, image defects due to uneven sweeping with the magnetic brush can be prevented, and when the magnetic brush is erected, the image density is prevented from decreasing due to a decrease in the ability to form a toner thin layer on the developing roller. It can be.

  Therefore, when the image is formed, the frequency corresponding to the environmental temperature and humidity is read from the table, and the frequency of the AC toner thin layer forming bias is set to the read frequency, so that the toner conveyance amount to the developing roller by the magnetic brush is always constant. Thus, the density of the magnetic brush on the magnetic roller is lowered, the image density is lowered due to the reduction in the ability to form a toner thin layer on the developing roller, and the afterimage after the toner has jumped from the developing roller to the photosensitive drum Deterioration of developing ghost (history phenomenon) appearing, unevenness of toner thin layer due to excessive rubbing on developing roller due to increase in magnetic brush density, occurrence of image unevenness, and magnetic roller and development due to excessive amount of developer transport The present invention provides an image forming apparatus that can always form high-quality images by preventing problems such as developer overflow between roller gaps. The method and it is possible to provide a device.

  Furthermore, the frequency reading from the table and the setting of the AC toner thin layer formation bias are performed when the image forming apparatus is turned on and after a predetermined time has elapsed since the previous image formation. A timer for measuring time, and the development control device reads out the frequency from the table and sets the AC toner thin layer forming bias when the image forming apparatus is turned on and the timer measures a predetermined time. Since the toner charge amount naturally decreases if the toner is left as it is after being charged, it is not only a change in environmental temperature and humidity. Is measured by a timer, and after a predetermined time, the toner charge amount is set by setting the frequency of the AC toner thin layer formation bias in this way. It can be a developing method was also addressed to the natural decline.

  Further, the setting of the AC toner thin layer formation bias frequency to be performed after the elapse of a predetermined time from the previous image formation is performed using the minimum frequency stored as the table. By setting the AC toner thin layer forming bias frequency to be performed after the lapse of a predetermined time using the minimum frequency stored as the table, as described above, the charge amount of the toner is increased after the lapse of the predetermined time. Therefore, by reducing the frequency and suppressing the magnetic brush, it is possible to prevent image defects due to unevenness in sweeping with the magnetic brush.

  When the predetermined number of image formations are continuously performed after setting the AC toner thin layer formation bias frequency after the predetermined time has elapsed since the previous image formation, the frequency corresponding to the environmental temperature and humidity is set. The frequency of the AC toner thin layer formation bias read from the table is set as the frequency, so that the development control device forms a predetermined number of images after setting the AC toner thin layer formation bias frequency after a predetermined time has elapsed since the previous image formation. Is continuously performed, the frequency corresponding to the environmental temperature and humidity is read from the table, and the frequency is set as the frequency of the AC toner thin layer forming bias. After image formation, the toner charge amount corresponds to the environmental temperature and humidity, so a predetermined number of image formations are continuously performed. In this case, by reading out the frequency from the table and setting it as the frequency of the AC toner thin layer formation bias as described above, the toner conveyance amount to the developing roller by the magnetic brush is always constant as described above, and the quality is always high. It is possible to provide a developing method and apparatus in an image forming apparatus capable of forming a clear image.

  As described above, the developing method and apparatus in the image forming apparatus according to the present invention can develop with the magnetic brush even if the toner charge amount changes due to the environmental change such as temperature and humidity or the image formation is not performed for a predetermined time. After the toner transport amount to the roller is always constant, the density of the magnetic brush on the magnetic roller decreases, the image density decreases due to the decrease in the ability to form a toner thin layer on the developing roller, and the toner flies from the developing roller to the photosensitive drum The afterimage of the toner appears on the second round of the developing roller, the development ghost (history phenomenon) deteriorates, the toner thin layer unevenness due to excessive rubbing on the developing roller due to the increase in magnetic brush density, the occurrence of image unevenness, and further development An image forming device that can always form high-quality images by preventing problems such as overflow of developer between the magnetic roller and developer roller gap due to excessive amount of agent transport Kicking it is possible to provide a developing method and apparatus.

  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 component parts described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Absent.

  FIG. 1 is a schematic configuration diagram of a touch-down developing device for carrying out a developing method in an image forming apparatus according to the present invention, and FIG. 2 is a schematic view of an embodiment of an image forming apparatus for performing a developing method according to the present invention. .

  In the image forming apparatus 30 shown in FIG. 2, an endless belt 31 is arranged so that the recording paper from the paper feed cassette 32 can be conveyed toward the fixing device 33, and the endless belt 31 that conveys the recording paper is arranged. On the upper side of the figure, a black developing device 34K, a yellow developing device 34Y, a cyan developing device 34C, and a magenta developing device 34M are arranged. These developing devices 34 (K, Y, C, M) are developed in close proximity to the magnetic roller 15 (K, Y, C, M) and the magnetic roller 15 (K, Y, C, M), respectively. A roller 11 (K, Y, C, M) is disposed, and the photosensitive drum 10 (K, Y, C, M) faces the developing roller 11, and further around the photosensitive drum 10, A charger 35 (K, Y, C, M) and an exposure device 36 (K, Y, C, M) are arranged.

  FIG. 1 is a schematic configuration diagram of a touch-down developing device for carrying out the developing method in the image forming apparatus according to the present invention. The photosensitive drum 10 (K, Y, C, M) and the developing roller 11 shown in FIG. (K, Y, C, M), magnetic roller 15 (K, Y, C, M), bias power source indicated by 13, 14, 19, 20 and control circuits 22, 23, etc. It is. In the figure, reference numeral 10 denotes a photosensitive drum, and an amorphous silicon (a-Si) photosensitive member, an organic photosensitive member (OPC), or the like is used as a material. An electrostatic latent image 11 is formed on the photosensitive drum 10 by an electrophotographic method with a developing bias applied from a DC developing bias power supply (DC1) 13 and an AC developing bias power supply (AC1) 14. A developing roller 15 for developing the toner 16 by flying the toner 16 is formed in a cylindrical shape with a nonmagnetic metal material, and has a rotatable sleeve in which a plurality of fixed magnets are disposed. A toner thin layer forming bias applied from a DC toner thin layer forming bias power source (DC2) 19 and an AC toner thin layer forming bias power source (AC2) 20 is formed by forming a magnetic brush 18 of a two-component developer comprising a carrier 17. Thus, a magnetic roller for forming the toner layer 12 on the developing roller 11, and 21 is a cutting blade for keeping the height of the magnetic brush 18 on the magnetic roller 15 constant. It is over de.

  Reference numeral 22 denotes a developing roller bias power source controller for controlling the voltages of the DC developing bias power source (DC1) 13 and the AC developing bias power source (AC1) 14 of the developing roller 11, and 23 denotes a DC toner thin layer forming bias power source for the magnetic roller 15. (DC2) 19, a magnetic roller bias power supply controller for controlling AC toner thin layer forming bias power supply (AC2) 20, and 24 for giving a voltage instruction to the developing roller bias power supply controller 22 and magnetic roller bias power supply controller 23. A development control device that controls the development device, 25 is a storage device that stores the temperature detected by the temperature / humidity sensor 26, the frequency of the AC toner thin layer forming bias to the magnetic roller 15 corresponding to the humidity, and 27 is the previous image formation. It is a timer that measures the elapsed time from.

  The storage device 25 stores the amount of toner transported to the developing roller 11 by the magnetic brush 18 when the charge amount of the toner 16 changes due to changes in temperature and humidity in the image forming apparatus 20 and the density of the magnetic brush 18 changes. In order to make it constant, data as shown in FIG. 3 is stored in which the relationship between the environmental temperature and humidity and the frequency of the AC toner thin layer forming bias that makes the toner transport amount to the developing roller 11 constant is tabulated.

  The table shown in FIG. 3 shows in advance the relationship between the toner charge amount that changes depending on the environmental temperature and humidity, and the frequency at which the toner conveyance amount to the developing roller 11 by the magnetic brush 18 is constant. The table shows the relationship with the frequency corresponding to the humidity. As an example, the temperature range of 2 ° C to 4 ° C is taken in the horizontal direction and the humidity range of 10% in the vertical direction. The frequency corresponding to the toner charge amount is arranged. Therefore, the frequency is 4.2 kHz in the low temperature / low humidity (L / L) environment region such as a temperature of 15 degrees or less and the humidity is 35% or less, and 3. in the region corresponding to the normal temperature / normal humidity (N / N) environment. In the region corresponding to the high-temperature / high-humidity (H / H) environment at 8 kHz, the frequency is lowered to 3.8 kHz and the higher the high-temperature / high-humidity side.

  That is, as described above, the charge amount of the toner decreases under a high temperature and high humidity (H / H) environment, and the developer fluidity increases, leading to an increase in the developer transport amount. Then, the amount of the magnetic brush is increased, and the toner thin layer formed on the developing roller is caused to be uneven by the magnetic brush, and the image is also caused to be uneven by the magnetic brush. Further, the magnetic roller and the developing roller The developer overflows between the gaps. Conversely, when the charge amount of the toner increases in a low temperature / low humidity (L / L) environment, the developer fluidity decreases, the developer transport amount decreases, and the magnetic brush amount decreases. As a result, the toner thin layer forming ability is reduced, resulting in a decrease in image density, deterioration in development ghosting property, and the like.

The table in FIG. 5 and the graph in FIG. 6 are examined. First, in the table of FIG. 5, the left column labeled “Condition” represents the DC toner thin layer formation bias Mag, the DC development bias SLV, and the potential difference ΔV. The next column “Vmag” is the DC toner thin layer forming bias voltage, the next “environment” column is temperature / humidity, and 32.5 ° C./80% is high temperature / high humidity. (N / N) environment, 23.5 ° C./50% represents a normal temperature / normal humidity (N / N) environment, and 10 ° C./15% represents a low temperature / low humidity (L / L) environment. The column next to “on the mag roller” is the toner density (unit:%) and the toner charge amount (unit: μC / g) on the magnetic roller, and the next column “on the developing roller” is The amount of toner on the developing roller (unit: mg / cm ² ), the toner charge amount (unit: μC / g), and the next column “on the drum” are the amounts of toner on the photosensitive drum (unit: mg / cm ² ). cm ² ) and toner charge amount (unit: μC / g).

  As can be seen from the table of FIG. 5, the DC toner thin layer forming bias Mag and the DC developing bias SLV are changed while keeping the potential difference ΔV between the DC toner thin layer forming bias Mag and the DC developing bias SLV constant. Looking at the toner amount and the toner charge amount in each environment, the toner concentration on the magnetic roller does not change much in each environment, but the charge amount is large in the low temperature / low humidity (L / L) environment, and the high temperature / high humidity. Low in (N / N) environment. It is almost the same on the “developing roller”, and the toner amount is 0.54 to 0.67, which is not significantly changed in each environment, but the charge amount is 18.1 to 21 in a low temperature / low humidity (L / L) environment. In contrast, the temperature is 8.2 to 9.3 in a high temperature and high humidity (N / N) environment.

  However, in the case of “on the photosensitive drum”, the toner density is greatly different from 0.33 to 0.60 in a low temperature / low humidity (L / L) environment, and from 0.44 in a high temperature / high humidity (N / N) environment. It can be seen that the development characteristics are changed by 0.76. However, the tendency of the charge amount is almost the same as “on the developing roller”, which is 14.01 to 17.71 in the low temperature / low humidity (L / L) environment, and 6.37 in the high temperature / high humidity (N / N) environment. It is as low as 7.99.

The developer flow rate varies greatly depending on the environment as seen in the graph of FIG. In the graph of FIG. 6, the horizontal axis is the blade gap (unit: mm) between the ear cutting blade 21 and the magnetic roller 15, and the vertical axis is the developer flow rate (unit: mg / cm ² ). 6 is a graph plotting how the developer flow rate changes when the gap is changed. Each line is plotted in a low temperature / low humidity (L / L) environment with a temperature of 10 ° C. and a humidity of 15%, and a line plotted with ■ is a room temperature / normal humidity with a temperature of 23.5 ° C. and a humidity of 50%. In the case of the (N / N) environment, the line in which the triangle is plotted is the case of the high temperature / high humidity (N / N) environment where the temperature is 32.5 ° C. and the humidity is 80%. As can be seen from the graph of FIG. 6, in the high temperature / high humidity (N / N) environment, the developer flow rate greatly increases as the blade gap increases, and conversely, in the low temperature / low humidity (L / L) environment, the raid gap increases. Even if it becomes larger, the developer flow rate does not increase so much.

  That is, these facts indicate that the toner has a low charge amount in a high temperature and high humidity (H / H) environment, and the developer fluidity is increased, leading to an increase in the developer transport amount. When the amount of magnetic brush increases, the toner thin layer formed on the developing roller causes unevenness of the magnetic brush, and the magnetic brush also causes unevenness of the magnetic brush. It shows that the developer overflows between the two. Conversely, in a low-temperature / low-humidity (L / L) environment, the charge amount of the toner increases, the developer fluidity decreases, the developer transport amount decreases, and the magnetic brush amount decreases. As a result, the ability to form a toner thin layer is reduced, resulting in a decrease in image density and a deterioration in development ghost.

  The table in FIG. 5 and the graph in FIG. 6 were examined using an image forming apparatus equipped with a touch-down developing device manufactured by Kyocera Mita. The photosensitive drum 10 used had an outer diameter of 30 mm and a linear velocity of 169. Development roller 1 has an outer diameter of 16 mm and a peripheral speed of 270.4 mm / sec, and magnetic roller 15 has an outer diameter of 16 mm and a peripheral speed of 421.8 mm / sec. Further, the blade gap between the magnetic roller 15 and the ear cutting blade 21 is 0.27 to 0.32 mm, the M / S gap between the magnetic roller 15 and the developing roller 11 is 0.29 mm, and the developing roller 11 and the photosensitive drum 10 are The D / S gap is 0.15 mm, the ratio (S / D) of the peripheral speed of the developing roller 11 to the peripheral speed of the photosensitive drum 10 is about 1.6, the peripheral speed of the magnetic roller 15 and the developing roller 11 The ratio (M / S) to the peripheral speed was about 1.56, and the developer used was a two-component developer composed of black (K) toner having a reduced average particle diameter of 6.8 μm and a carrier.

  Returning to FIG. 3 again, in the present invention, as described above, when the frequency component of the AC toner thin layer forming bias applied to the magnetic roller 15 is increased, the magnetic brush 18 on the surface of the magnetic roller 15 is made to stand more. As shown in FIG. 3, the relationship between the toner charge amount that changes depending on the environmental temperature and humidity and the density of the magnetic brush 18 on the magnetic roller 15 is used. The relationship between the environmental temperature and humidity and the frequency of the AC toner thin layer forming bias that makes the amount of toner transported to the developing roller 11 by the magnetic brush 18 constant is tabulated.

  In making this table, as described above, the temperature range is 2 ° C. to 4 ° C., the humidity is changed by about 10%, and each temperature is changed with reference to the values in the table of FIG. 5 and the graph of FIG. The frequency of the AC toner thin layer forming bias was changed for each humidity, and it was investigated which frequency would not cause unevenness in sweeping with a magnetic brush, and the maximum frequency without sweeping unevenness was adopted. The result is the table of FIG. In this way, for example, when the ambient temperature and humidity are detected and the developer charge amount is reduced, and it is determined that the density of the magnetic brush 18 is increased, a low frequency is adopted to stand the magnetic brush 18. When the developer charge amount is increased and the density of the magnetic brush 18 is determined to be decreased, a high frequency is adopted, and the magnetic brush 18 is raised to keep the magnetic brush 18 standing low. When the magnetic brush 18 is erected, it is possible to prevent a decrease in image density due to a decrease in the ability to form a toner thin layer on the developing roller 11.

  The data stored in the storage device 25 has been described above. Returning to FIG. 1 again, the elements constituting the developing device will be described. The outermost surface of the developing roller 11 has uniform conductive aluminum, SUS, conductive resin coating, and the like. In order to prevent leakage, it is preferable to increase the resistance value by applying an alumite treatment of about 20 μm and a resin coat, for example. A DC developing bias power supply (DC1) 13 and an AC developing bias power supply (AC1) 14 are connected to the shaft portion, and the direct current and alternating current are connected between the rotating developing roller 11, the photosensitive drum 10, and the magnetic roller 15. The developing bias voltage superimposed with the above is applied. The AC component supplied by the AC developing bias power source (AC1) 14 is constituted by, for example, a rectangular wave having a duty ratio of 73% or less.

For the toner 16, for example, a toner having a small particle diameter on the order of 6 μm of about 6.8 μm with 10 ¹³ to 10 ¹⁴ Ω is used to increase the definition of the formed image. In order to avoid selective developability, it is important to define the particle size distribution. Generally, the spread of the particle size distribution of the toner is measured by a Coulter counter, and the spread of the particle size distribution is determined by the volume distribution average particle size and number. Expressed as a ratio of the distribution average particle size. When the distribution is wide, toner having a relatively small particle size is accumulated on the developing roller 11 during continuous printing, and developability is deteriorated.

As the carrier 17, a magnetite carrier, Mn-based ferrite, Mn—Mg-based ferrite, or the like can be used, and it can also be used after being surface-treated within a range that does not increase an appropriate resistance value. In the present invention, as an example, a ferrite carrier having a volume resistivity of 10 ⁸ Ωcm ³ and a saturation magnetization of 40 emu / g and an average particle size of 35 μm was used. When the average particle size exceeds 50 μm, the carrier stress increases and the toner density cannot be increased, and the amount of toner supplied to the developing roller 11 decreases.

  The mixing ratio of the toner 16 and the carrier 17 is 5 to 20% by weight, preferably 5 to 15% by weight, based on the total amount of the carrier 17 and the toner 16. If the mixing ratio of the toner 16 is less than 5% by weight, the charge amount of the toner 16 becomes high and a sufficient image density cannot be obtained, and if it exceeds 20% by weight, a sufficient charge amount cannot be obtained this time. The toner 16 scatters from the developing device and contaminates the inside of the image forming apparatus, or toner fog occurs on the image.

  Returning to FIG. 2 again, in the tandem type image forming apparatus having the hybrid type developing apparatus configured as described above, the two-component composed of the toner 16 and the carrier 17 corresponding to the respective colors such as yellow, cyan, magenta, and black. The developer is supplied from the developer container to each developing device 34, and the magnetic brush 10 is formed on the magnetic roller 15 shown in FIG. 1, and the toner 16 is charged by stirring. Then, the magnetic brush 10 on the magnetic roller 15 is layer-regulated by the regulating blade 9, and between the DC toner thin layer forming bias (Vmag) 19 applied to the magnetic roller 15 and the DC developing bias (Vslv) 13 applied to the developing roller 11. The toner layer 12 including only the toner 16 is formed on the developing roller 11 by the potential difference ΔV and the AC biases 14 and 20.

  When a print start signal is received from a control circuit (not shown), first, the photosensitive drum 10 composed of a positively charged organic photosensitive member (positive OPC) is charged to, for example, 420 V by the charger 35 shown in FIG. For example, by exposure by the exposure device 36 using an LED having a wavelength of 770 nm, the post-exposure potential of the photosensitive drum 10 becomes about 100 V and a latent image is formed. The latent image is developed with the toner 16 that has jumped from the toner layer 12 on the developing roller 11 to the photosensitive drum 10 by the DC developing bias 13 and the AC bias 14 applied to the developing roller 11 to form a toner image. The Then, when the recording paper is fed from the paper feed cassette 32 and sent by the belt 54 and reaches the photosensitive drum 10, a transfer bias is applied by the transfer device 37 (K, Y, C, M) to record the recording paper. The toner image is transferred to the toner image, fixed by the fixing device 33, and discharged. The toner 16 that has not been used for the development on the developing roller 11 is peeled off by the magnetic brush 18 formed on the magnetic roller 15 and the above-described bias voltage, and a new toner layer 12 is formed and the next toner layer 12 is formed. Prepared for development.

  The above is the operation during normal image formation. In the present invention, when the power of the image forming apparatus is turned on, the development control device 24 starts from the temperature / humidity sensor 26 according to the flowchart shown in FIG. In response to the environmental temperature / humidity detection result signal, the AC toner thin layer forming bias frequency optimum for the current temperature / humidity is set from the table shown in FIG. That is, when the process starts in step S10, a batch for frequency calibration is printed in step S11. For example, as shown in step S11, pattern 1 has DC toner thin layer forming bias Vmag19 set to 450V, DC developing bias Vslv13 set to 200V, pattern 2 has DC toner thin layer forming bias Vmag19 set to 400V, and DC developed. Drawing is performed with the bias Vslv13 set to 150V, the DC toner thin layer forming bias Vmag19 set to 350V, and the DC developing bias Vslv13 set to 100V.

  When it is drawn, the development control device 24 checks the signal from the temperature / humidity sensor 26 in step S12 to detect the environmental temperature and humidity, and based on the detection result, the development control device 24 shows in FIG. 3 in step S13. The frequency of the AC toner thin layer forming bias corresponding to the current temperature and humidity is read from the storage device 25 in which the table is stored. In step S14, it is sent to the magnetic roller bias power source controller 23. The magnetic roller bias power source controller 23 sets the frequency of the AC toner thin layer forming bias power source (AC2) 20 to the transmitted frequency. As a result, the toner 16 moves from the magnetic brush 18 on the magnetic roller 15 to the developing roller 11, and the process ends in step S15.

  By doing so, the frequency of the AC toner thin layer forming bias is such that, even if the charge amount of the toner changes due to the environmental temperature and humidity, the developer charge amount decreases as described above, and the magnetic brush 18 When it is determined that the density of the magnetic brush 18 has increased, the frequency is lowered to suppress the standing of the magnetic brush 18, and when it is determined that the developer charge amount has increased and the density of the magnetic brush 18 has decreased, the frequency is decreased. Since the magnetic brush 18 is raised at a high level, the frequency is set according to the amount of change in the toner charge amount, and the image density is caused by unevenness of sweeping by the magnetic brush 18 and the ability to form a toner thin layer on the developing roller 11 is decreased. Therefore, it is possible to prevent a decrease in the level.

  In addition, in the present invention, in view of the fact that the toner charge escapes when image formation is not performed for a long time, it is determined in advance how much the toner charge amount decreases in the elapsed time after image formation. A check is made corresponding to the humidity, and this is stored in the storage device 25. The development control device 24 constantly monitors the elapsed time of the timer 27 that measures the elapsed time from the previous image formation together with the environmental temperature and humidity, and the elapsed time corresponds to the environmental temperature and humidity to determine the toner charge amount. When the predetermined time determined to have decreased is reached, the minimum frequency corresponding to the high-temperature / high-humidity (H / H) environment from the storage device 25 storing the table shown in FIG. In this case, 3.4 kHz) is read out and sent to the magnetic roller bias power source controller 23.

  Therefore, the magnetic roller bias power source controller 23 sets the frequency of the AC toner thin layer forming bias power source (AC2) 20 to the frequency that has been sent, that is, 3.4 kHz in this example, and thereby the magnetic roller bias power source controller 23 on the magnetic roller 15 The toner 16 is moved from the magnetic brush 18 to the developing roller 11. This is because if the elapsed time from the previous image formation has passed as described above, the charge amount of the toner is considered to have decreased. In addition, it is possible to provide a developing method and apparatus in an image forming apparatus that can cope with a case where the toner charge amount is reduced in the elapsed time from image formation.

  In this case, when the predetermined number of image formations are continuously performed after setting the AC toner thin layer formation bias frequency to the lowest frequency, the toner charge amount is an amount corresponding to the environmental temperature and humidity. Therefore, as in the case when the power is turned on, the development control device 24 uses the ambient temperature / humidity detection result signal from the temperature / humidity sensor 26 to generate an alternating current corresponding to the current temperature / humidity from the table shown in FIG. The frequency of the toner thin layer formation bias is read, and the frequency of the AC toner thin layer formation bias power supply (AC2) 20 is set to this frequency. Accordingly, the toner conveying amount to the developing roller 11 by the magnetic brush 18 is always constant, and a developing method and apparatus in an image forming apparatus that can always form a high quality image can be obtained.

  Note that the temperature / humidity table shown in FIG. 3 is an example, and it is obvious that the temperature interval, humidity interval, and frequency values shown here are not limited to these values. Although the case where the timer 27 is provided to measure the decrease in the charge amount has been described as an example, for example, a control is provided to lower the heater temperature of the fixing device when a thermal fixing device is provided and image formation is not performed for a certain period of time. If the temperature is measured, the temperature may be measured by a temperature sensor such as a thermistor, and it may be determined that a predetermined time has elapsed.

  According to the present invention, the toner thin layer is caused by excessive rubbing on the developing roller by the magnetic brush due to a decrease in image density, deterioration in development ghost (history phenomenon), and increase in the toner conveyance amount at any environmental temperature and humidity. In an image forming apparatus capable of always forming a high quality image by preventing the occurrence of unevenness of image, unevenness of image, and overflow of developer between the magnetic roller and the developing roller gap due to excessive developer transport amount. A development method and apparatus can be provided.

1 is a schematic configuration diagram of a touch-down developing device for performing a developing method in an image forming apparatus according to the present invention. 1 is a schematic diagram of an embodiment of an image forming apparatus that performs a developing method according to the present invention. An AC toner thin layer that makes the relationship between the toner charge amount that changes depending on the temperature and humidity of the environment and the magnetic brush density on the magnetic roller 15 constant, and the amount of toner transported to the developing roller by the environment temperature and humidity and the magnetic brush is constant. It is an example of the data tabulated as a relationship of the frequency of formation bias. In the developing method according to the present invention, it is a flowchart for setting the frequency of the AC toner thin layer forming bias corresponding to the toner charge amount. Toner density on the magnetic roller, on the developing roller, and on the photosensitive drum in high temperature / high humidity (H / H) environment, normal temperature / normal humidity (N / N) environment, and low temperature / low humidity (L / L) environment And a table in which the toner charge amount was examined. How is the developer flow rate when changing the blade gap in high temperature / high humidity (H / H) environment, normal temperature / normal humidity (N / N) environment, low temperature / low humidity (L / L) environment? It is the graph which plotted whether it changes.

Explanation of symbols

10 Photosensitive drum 11 Developing roller 12 Toner layer 13 DC developing bias power supply (DC1)
14 AC development bias power supply (AC1)
15 Magnetic roller 16 Non-magnetic toner 17 Carrier 18 Magnetic brush 19 DC toner thin layer forming bias power source (DC2)
20 AC toner thin layer forming bias power supply (AC2)
21 Bone Cutting Blade 22 Developing Roller Bias Power Supply Control Device 23 Magnetic Roller Bias Power Supply Control Device 24 Development Control Device 25 Storage Device 26 Temperature / Humidity Sensor 27 Timer

Claims (8)

A magnetic brush of a two-component developer composed of toner and carrier is formed on a magnetic roller to which a bias for toner thin layer formation in which alternating current is superimposed on direct current and magnet is contained, and the alternating current from the magnetic brush to direct current is formed. Development in an image forming apparatus in which a toner thin layer is formed on a developing roller to which a developing bias with superimposed toner is applied and then toner is ejected onto an electrostatic latent image formed on a photoreceptor by electrophotography. In the method
The relationship between the toner charge amount changed by changing the environmental temperature and humidity and the magnetic brush density in advance is the same as the AC toner thinning that makes the environmental temperature and humidity and the toner conveyance amount to the developing roller by the magnetic brush constant. The table is stored as a relationship of the layer forming bias frequency, the frequency of the table corresponding to the temperature and humidity is read at the time of image formation, and the frequency of the AC toner thin layer forming bias is set to the read frequency. A developing method in an image forming apparatus, comprising: forming an upper toner layer; and developing the electrostatic latent image.   2. The image according to claim 1, wherein the reading of the frequency from the table and the setting of the AC toner thin layer formation bias are performed when the image forming apparatus is turned on and after a predetermined time has elapsed since the previous image formation. Development method in forming apparatus.   3. The image forming apparatus according to claim 2, wherein the setting of the AC toner thin layer forming bias frequency to be performed after a predetermined time has elapsed since the previous image formation is performed using the minimum frequency stored as the table. Development method.   When a predetermined number of image formations are continuously performed after setting the AC toner thin layer formation bias frequency performed after a predetermined time has elapsed since the previous image formation, the frequency corresponding to the environmental temperature and humidity is set in the table. 4. The developing method in an image forming apparatus according to claim 2, wherein the frequency of the AC toner thin layer forming bias is read out from the AC toner thin layer forming bias. A magnetic roller that forms a magnetic brush of a two-component developer composed of toner and a carrier by applying a bias for applying a toner thin layer containing a magnet and superposing an alternating current on a direct current, and forming a toner thin layer on which an alternating current is superimposed on a direct current An image having a developing roller for applying a bias to form a toner thin layer with the magnetic brush and developing the electrostatic latent image formed on the photoreceptor by electrophotography with the toner flying from the toner thin layer. In the developing device in the forming device,
A temperature and humidity sensor that detects environmental temperature and humidity;
The relationship between the toner charge amount that changes depending on the environmental temperature and humidity and the magnetic brush density, and the frequency of the AC toner thin layer forming bias that makes the amount of toner transported to the developing roller by the environmental temperature and humidity constant and the magnetic brush constant. A storage device that stores data tabulated as a relationship between
The temperature and humidity signals detected by the temperature and humidity sensor are received, the frequency of the corresponding table stored in the storage device is read, and the AC toner thin layer forming bias frequency is set to the read frequency and developed. A developing device in an image forming apparatus, comprising: a developing control device that forms a toner layer on a roller and develops the electrostatic latent image.   A timer for measuring an elapsed time since the previous image formation, and the development control device reads the frequency from the table and sets the AC toner thin layer formation bias when the image forming apparatus is turned on and the timer 6. The developing device in an image forming apparatus according to claim 5, wherein the developing device is configured to perform the measurement in a state where a predetermined time is measured.   The development control device is configured to perform setting of an AC toner thin layer formation bias frequency to be performed after a predetermined time has elapsed since the previous image formation, using the minimum frequency stored as the table. A developing device in the image forming apparatus according to 6.   The development control device responds to the environmental temperature and humidity in a state where a predetermined number of images are continuously formed after setting a bias frequency for forming an AC toner thin layer after a predetermined time has elapsed since the previous image formation. 8. The developing device in an image forming apparatus according to claim 6, wherein the frequency is read from the table and the frequency is set as the frequency of the AC toner thin layer forming bias.

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