JP2018132607A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent image defects from occurring due to an aggregation of toner.SOLUTION: A CPU can operate in a first mode and a second mode. In the first mode, it performs image formation operation regarding a development condition for developing an electrostatic latent image on a photosensitive drum 1 with a first developing sleeve 42 and a second developing sleeve 43 as a first condition. In the second mode, it changes the development condition to a second condition different from the first condition so that toner having particle diameters smaller than an average particle diameter attaches to the photosensitive drum 1 more than toner having particles diameters equal to or more than the average particle diameter of toner in a toner container 41.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having a plurality of these functions.

  The image forming apparatus develops an electrostatic latent image on a photosensitive drum as an image carrier with toner by a developing device. As such a developing device, a configuration including a plurality of developing sleeves (toner carriers) has been proposed (for example, Patent Documents 1 and 2). In the configurations described in Patent Documents 1 and 2, two developing sleeves are brought close to each other through a gap, and the layer thickness of the toner carried on the developing sleeve on the downstream side in the rotation direction of the photosensitive drum is regulated by the gap. .

JP 2004-29569 A JP 2011-257533 A

  However, in the configuration in which the layer thickness of the toner carried on the downstream development sleeve is regulated by the gap between the development sleeves as described above, for example, the regulation is compared with the configuration in which the layer thickness is regulated by a regulating member such as a blade. The power is weak. This is because the collection of the toner carried on the upstream developing sleeve by the downstream developing sleeve and the above-described regulation are simultaneously performed in this gap, and thus the regulating force in this gap cannot be increased.

  For this reason, when agglomerates due to toner having a high charge amount are generated in the developing device, the agglomerates cannot be regulated by the gaps described above and may appear on the downstream developing sleeve and cause image defects. is there. Here, since the toner tends to have a higher charge amount as the particle size is smaller, if the amount of toner having a smaller particle size is larger in the developing device, the above-described aggregate tends to be generated.

  An object of the present invention is to suppress the occurrence of image defects due to toner agglomerates.

  According to the present invention, a rotating image carrier, a toner container containing toner, a toner in the toner container is carried and rotated, and an electrostatic latent image formed on the image carrier is developed with toner. A toner carrier, and a first toner carrier that is disposed downstream of the image carrier in a rotation direction with a gap between the first toner carrier and the toner in the toner container. And a second toner carrier that develops the electrostatic latent image formed on the image carrier with toner, the layer thickness of the toner being regulated by the gap, the first toner carrier, A first mode in which an image forming operation is performed with a development condition for developing an electrostatic latent image on the image carrier by the second toner carrier as a first condition; Toner with a small particle size exceeds the average particle size Execution means capable of executing a second mode in which development is performed by changing the development condition to a second condition different from the first condition so that more toner adheres to the image carrier. An image forming apparatus characterized by the above.

  According to the present application, it is possible to suppress the occurrence of image defects due to toner agglomerates.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. FIG. 3 is a schematic diagram of a toner charge amount measuring device. FIG. 2 is a schematic diagram illustrating a part of the developing device according to the first embodiment. 6 is a graph showing a developing bias according to the first embodiment. FIG. 6 is a diagram illustrating a particle size distribution of toner in a toner container in an initial state. FIG. 6 is a schematic diagram showing the charge amount on the surface of the toner depending on the particle diameter. The schematic diagram for demonstrating the generation | occurrence | production mechanism of the aggregate by the toner of high charge amount. FIG. 5 is a schematic diagram for explaining a mechanism of occurrence of defective coating due to toner agglomerates. The graph which shows the relationship between a fine powder rate and a toner charge amount. FIG. 6 is a schematic diagram for explaining that toner having a small particle diameter is discharged preferentially. (A) A schematic view showing a discharge state of a toner having a small particle diameter when Vpp is low, and (b) a discharge state of a toner having a small particle diameter when Vpp is high. 6 is a graph showing a particle size distribution of toner developed on a photosensitive drum from a first developing sleeve and a second developing sleeve by discharge control. The block diagram which concerns on the discharge control of 1st Embodiment. The flowchart of the discharge control of 1st Embodiment. The figure which shows the electrostatic latent image used for the discharge control of 1st Embodiment. The flowchart of the discharge control of 2nd Embodiment. The flowchart of the discharge control of 3rd Embodiment. The flowchart of the discharge control of 4th Embodiment. The flowchart of the discharge control of 5th Embodiment.

<First Embodiment>
A first embodiment will be described with reference to FIGS. First, a schematic configuration of the image forming apparatus of the present embodiment will be described with reference to FIG.

[Image forming apparatus]
The image forming apparatus 100 is an electrophotographic monochrome copying machine. The image forming apparatus 100 receives an image signal from an external terminal 400 (see FIG. 13) such as a scanner (original reading apparatus) connected to the image forming apparatus body or a personal computer connected to the image forming apparatus body so as to be communicable. Accordingly, a toner image is formed on the recording material S. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

  In the image forming apparatus 100, a cylindrical photosensitive member, that is, a photosensitive drum 1 is provided as an image carrier. The photosensitive drum 1 is rotationally driven in the arrow direction in the figure. Around the photosensitive drum 1, a corona charger 2, a laser scanner 3, a developing device 4, a post charger 5, a transfer roller 6, a cleaning device 7, and a pre-exposure device 8 are arranged. A recording material conveyance belt 10 and a fixing device 9 are disposed downstream of the transfer portion formed by the photosensitive drum 1 and the transfer roller 6 in the conveyance direction of the recording material S.

  An electrostatic latent image is formed on the photosensitive drum 1 by irradiating the photosensitive drum 1 whose surface is charged by a corona charger 2 as a charging means with light from a laser scanner 3 as an exposure means, and discharging the charge on the photosensitive drum 1. Form. In the developing device 4, the electrostatic latent image on the photosensitive drum 1 is developed as a toner image using an electric field with charged toner. Thereafter, the toner image further charged by the post charger 5 is transferred to the recording material S conveyed to a transfer portion formed by the transfer roller 6 and the photosensitive drum 1. The recording material to which the toner image has been transferred is conveyed by the recording material conveying belt 10 and is fixed to the recording material by heating and pressing the toner image by the fixing device 9.

  On the other hand, the toner that remains on the photosensitive drum 1 without being completely transferred at the transfer portion is scraped off by a blade provided in the cleaning device 7. Thereafter, the surface of the photosensitive drum 1 is exposed by the pre-exposure device 8, whereby the charge on the surface of the photosensitive drum 1 is uniformly attenuated in the direction of the rotation axis of the photosensitive drum 1. Thereafter, the photosensitive drum 1 is charged again by the corona charger 2, and the above-described process is repeated. The transfer roller 6 can be brought into contact with and separated from the photosensitive drum 1.

  The image forming apparatus 100 of the present invention can form an image on 75 sheets (75 ppm) of recording material per minute. For the photosensitive drum 1, an organic photosensitive member, an amorphous silicon photosensitive member, or the like is used, and the drum has a diameter of 90 mm.

  In the present embodiment, BAE (background exposure method) is adopted. That is, a non-image portion where a toner image is not formed on the surface of the charged photosensitive drum 1 is exposed by the laser scanner 3, and an unexposed portion on the surface becomes an electrostatic latent image and is developed with toner. Is done. For example, the surface of the photosensitive drum 1 is charged to Vd = 550 V by the corona charger 2, and the non-image portion is exposed by the laser scanner 3, and the potential of the non-image portion is lowered to Vl = 150.

  Specifically, a developing bias in which an alternating voltage (alternating current component) is superimposed on a direct current voltage (DC component) is applied to a first developing sleeve 42 and a second developing sleeve 43 (see FIG. 3) of the developing device 4 described later. Thus, the electrostatic latent image is developed with toner. For example, Vdc = 250 V is applied as the DC component to the first developing sleeve 42 and the second developing sleeve 43, and the negatively charged toner is the portion of the potential Vd of the non-exposed portion (that is, the electrostatic latent image). The electrostatic latent image is developed with toner.

  When the difference between these Vd and Vl and the DC component Vdc of the developing bias is Vcont and Vback, respectively, in this embodiment, Vcont = 300V and Vback = 100V. That is, the potential difference (Vd−Vdc = 550V−250V = 300V) between the DC voltage Vdc of the developing bias and the potential Vd of the non-exposed portion is Vcont. Also, the potential difference (Vdc−Vl = 250 V−150 V = 100 V) between the DC voltage Vdc of the developing bias and the potential Vl of the non-image portion where the toner image is not formed on the surface of the charged photosensitive drum 1 is Vback. .

  By increasing Vcont, the density of the toner image can be increased, and by adjusting this value, the density of the toner image can be made appropriate. Further, by adjusting Vback, it is possible to suppress fogging that toner (for example, toner having a high charge amount) adheres to the non-image portion.

[toner]
The toner used in the image forming apparatus 100 of the present embodiment is a magnetic one-component, pulverized toner, and is classified to a size of 3 to 10 μm as a distribution. Further, the number ratio (hereinafter referred to as the fine powder ratio) of toners having a volume average particle diameter of 7.0 μm and 4 μm or less is 23%. Further, silica, titanium oxide, and strontium titanate fine particles of 0.1 μm or less are externally added as charge control agents. The toner may be formed by a polymerization method.

  For the toner used in the present embodiment, the volume average particle diameter and the fine powder ratio were measured by the following apparatus and method. As a measuring device, a Coulter counter TA-II type (manufactured by Coulter), an interface for outputting number average distribution and volume average distribution (manufactured by Nikka) and a CX-I personal computer (manufactured by Canon) were used. A 1% NaCl aqueous solution prepared using primary sodium chloride was used as the electric field aqueous solution.

  The measuring method is as follows. That is, 0.1 ml of a surfactant, preferably alkyl benzene sulfonate, is added as a dispersant to 100 to 150 ml of the electric field aqueous solution, and 0.5 to 50 mg of a measurement sample is added. The aqueous solution of the electric field in which the sample is suspended is dispersed for about 1 to 3 minutes with an ultrasonic disperser, and the particle size distribution of 2 to 40 μm particles is measured using the above Coulter counter TA-II using a 100 μm aperture as the aperture. To obtain the distribution. From the distribution thus obtained, a volume average distribution is calculated to obtain a volume average particle diameter. Similarly, the number average distribution is calculated, and the ratio of the toner of 4 μm or less to the whole is calculated as the fine powder ratio.

  Further, as shown in FIG. 2, the charge amount (Q / M) of the toner was calculated using the measuring device 20. The measuring device 20 is configured by combining a suction type Faraday cage 21, a cylindrical filter paper 22, a suction device 23, and an electrometer 24. The toner charge amount was calculated as follows. First, the thin layer toner 25 was sucked by the suction device 23 and collected in the suction type Faraday cage, and the charge Q (μC) was measured by the electrometer 24. Further, the mass M (mg) of the collected toner was measured with a balance. Then, the charge amount of the toner was calculated from the measured charge Q and mass M.

  The balance used was AB204S manufactured by METTTLER TOLEDO, the electrometer 24 used 6517A manufactured by KEITHLEY, the suction machine 23 used CV-TN96 manufactured by Hitachi, and the cylindrical filter paper manufactured by ADVANTEST. I made my Faraday cage.

[Developer]
Next, the developing device 4 will be described in detail with reference to FIGS. As shown in FIG. 3, the developing device 4 includes a toner container 41, a first developing sleeve 42 as a first toner carrier, a second developing sleeve 43 as a second toner carrier, a regulating blade 44, and the like. Such a developing device 4 can be attached to and detached from the main body of the image forming apparatus 100. The toner container 41 contains the one-component toner described above. A toner replenishing device (not shown) is connected to the toner container 41, and the toner replenished into the toner container 41 from the toner replenishing device is supplied to the first developing sleeve 42 and the second developing member by a conveying member (not shown). It is conveyed toward the sleeve 43.

  The first developing sleeve 42 carries toner in the toner container 41 (in the toner container), rotates in the direction of the arrow in the figure, and develops the electrostatic latent image formed on the photosensitive drum 1 with the toner. The layer thickness of the toner carried on the first developing sleeve 42 is regulated by the regulating blade 44. The second developing sleeve 43 is disposed downstream of the first developing sleeve 42 in the rotation direction of the photosensitive drum 1 with a gap G between the first developing sleeve 42 and the first developing sleeve 42. The second developing sleeve 43 carries the toner in the toner container 41 and the toner collected from the first developing sleeve 42, rotates in the direction of the arrow in the figure, and the electrostatic latent image formed on the photosensitive drum 1 is transferred by the toner. develop. The layer thickness of the toner carried on the second developing sleeve 43 is regulated by the gap G with the first developing sleeve 42.

  The first developing sleeve 42 and the second developing sleeve 43 are cylindrical bodies that can be transported by attaching toner to the surface and rotating, and a portion close to the photosensitive drum 1 is a developing region. The photosensitive drum 1 is opposed to the first developing sleeve 42 and the second developing sleeve 43 with a gap of about 100 to 400 μm. This gap is preferably about 150 to 300 μm.

  The first developing sleeve 42 and the second developing sleeve 43 will be described more specifically. Both the first developing sleeve 42 and the second developing sleeve 43 are made of aluminum or stainless steel having a diameter of about 10 to 40 mm. In this embodiment, the photosensitive drum 1 has a diameter of 90 mm, the first developing sleeve 42 has a diameter of 20 mm, and the second developing sleeve 43 has a diameter of 18 mm. The first developing sleeve 42 and the second developing sleeve 43 are formed as follows. First, after cutting a round bar or pipe made of aluminum or stainless steel, a semiconductive layer such as phenol resin is provided on the circumferential surface, mechanical polishing is performed, and arithmetic average roughness Ra = 0.1 to 1.0 μm. The surface roughness. The surface roughness is preferably 0.6 to 0.9 μm.

  Since the first developing sleeve 42 and the second developing sleeve 43 convey the toner due to the unevenness of the surface, it becomes difficult to convey the toner when Ra becomes 0.1 μm or less. Therefore, in this embodiment, Ra is 0.1 μm or more. Note that Ra is preferably 0.6 μm or more in order to more reliably maintain the toner transportability for achieving the maximum density.

  On the other hand, when Ra exceeds 1.0 μm, the force for conveying the toner becomes too strong and the toner deteriorates. Therefore, in this embodiment, Ra is 1.0 μm or less. In order to further suppress the deterioration of the toner, Ra is preferably 0.9 μm or less.

Since the first developing sleeve 42 and the second developing sleeve 43 have semiconductive layers on their peripheral surfaces, the volume resistance in the thickness direction of the surface layer of the sleeve is about 10 ⁵ to 10 ¹² Ω · cm. When the volume resistance is less than 10 ⁵ Ω, the conductivity is too high, and the mirroring power of the toner with respect to the developing sleeve becomes too large, and the developability deteriorates. On the other hand, when the volume resistance exceeds 10 ¹² Ω, the ability to impart charge to the toner is reduced, so the developability of the toner is reduced. Therefore, in this embodiment, the volume resistance is set to 10 ⁵ or more and 10 ¹² or less.

  Further, fixed magnets are disposed inside the first developing sleeve 42 and the second developing sleeve 43, respectively. The magnet has a plurality of magnetic poles as indicated by the radial lines in the first developing sleeve 42 and the second developing sleeve 43 in FIG. The position indicated by the radial line indicates the peak of the magnetic force of each magnetic pole. By arranging such magnets inside the first developing sleeve 42 and the second developing sleeve 43, magnetic toner can be carried on each sleeve by magnetic force.

  The regulating blade 44 as a layer thickness regulating member that regulates the toner layer thickness of the first developing sleeve 42 is constituted by, for example, a blade body made of a ferromagnetic material having a thickness of about 3 mm, and a nonmagnetic member such as SUS. It is comprised by the supported sheet metal. The regulating blade 44 is cut into a knife edge shape with a width of about 5 mm from the first developing sleeve 42 side on the front end side, and the thickness of the front end portion is about 0.3 mm.

The regulating blade 44 is disposed so that the tip thereof is opposed to the peak of one magnetic pole disposed in the first developing sleeve 42. With this arrangement, the magnetic toner is uniformly coated on the first developing sleeve 42 with a thickness of about 0.7 to 1.2 g / cm ² by the magnetic field between the tip of the regulating blade 44 and the magnetic pole. Is done. Further, the toner carried on the first developing sleeve 42 passes through the gap with the regulating blade 44 so that the charge amount (Q / M) is about 4 to 7 μC / g. Note that the variation in the charge amount is an effect of temperature and humidity. In this embodiment, the charge amount in a high temperature and high humidity environment is 4 μC / g, and the charge amount in a low humidity environment is 7 μC / g.

  The first developing sleeve 42 and the second developing sleeve 43 are rotationally driven by a driving device 210 (see FIG. 13) as driving means. The driving device 210 includes a motor and a power transmission unit such as a gear train that transmits power from the motor to the first developing sleeve 42 and the second developing sleeve 43. The photosensitive drum 1 is rotationally driven by driving a motor (not shown).

  In this embodiment, the circumferential speed vd of the photosensitive drum 1 is 450 mm / sec, the circumferential speed va of the first developing sleeve 42 is 460 mm / sec, and the circumferential speed vb of the second developing sleeve 43 is 440 mm / sec. The first developing sleeve 42 is arranged in parallel to the photosensitive drum 1 with a gap of 250 μm from the photosensitive drum 1 and 240 μm from the regulating blade 44. On the other hand, the second developing sleeve 43 is arranged in parallel to the photosensitive drum 1 with a gap of 300 μm from the photosensitive drum 1. The first developing sleeve 42 and the second developing sleeve 43 are arranged in parallel with a gap G of 400 μm.

  Further, a development high-voltage substrate 200 as a development bias applying unit is connected to the first development sleeve 42 and the second development sleeve 43. As shown in FIG. 13, the development high-voltage substrate 200 includes an AC high-voltage circuit 201 and a DC high-voltage circuit 202, and a development bias in which an AC voltage is superimposed on a DC voltage can be applied to the first development sleeve 42 and the second development sleeve 43. It is configured. The first developing sleeve 42 and the second developing sleeve 43 develop the electrostatic latent image formed on the photosensitive drum 1 with toner by applying a developing bias.

  In the present embodiment, as such a development bias, as shown in FIG. 4, a slope bias in which an AC component is intermittently superimposed on a DC component is used. Vdc in FIG. 4 is a DC component. By applying the AC component with the DC component as a center, the development bias has a waveform as shown in FIG. By adding the AC component (AC development bias voltage) to the DC component (DC development bias voltage) in this way, it becomes possible to suppress image roughness and to obtain a sufficient image density. .

  A value that is twice the amplitude of the AC component of the developing bias voltage (AC developing bias voltage) is Vp-p. The slope bias has such a relationship that the toner develops the latent image toward the photosensitive drum at TDEV in FIG. 4 and that excess toner is returned from the photosensitive drum to the sleeve at TDEF. 4 is an engine that gradually returns the bias from TDEV to TDEF in order not to peel off toner on the latent image due to sudden bias fluctuation. In this embodiment, the ratio is TDEV: TSLP: TDEF = 4: 5: 4. In addition, these three regions are combined into one cycle, and the sum T of these three times is 1 / f (f is a frequency).

  Thus, in this embodiment, the developing device 4 is configured to use two developing sleeves. For this reason, it is possible to achieve both high speed and high image quality of the image forming apparatus. That is, by providing a plurality of developing sleeves in this manner, toner can be supplied to the latent image on the photosensitive drum many times, so that even when the image forming speed is increased, the toner image Concentration can be maintained properly. Further, since the developing sleeve arranged on the downstream side of the developing sleeve arranged on the photosensitive drum is once peeled off by the developing sleeve on the upstream side in the rotation direction of the photosensitive drum and rearranged, an image faithful to the latent image can be obtained. it can.

  However, in the case of the configuration in which the toner layer thickness of the second developing sleeve 43 on the downstream side is regulated by the gap with the first developing sleeve 42 on the upstream side in the rotation direction of the photosensitive drum 1 as in the present embodiment, toner aggregation When a lump is formed, it is difficult to sufficiently regulate the agglomerate. If the agglomerates cannot be sufficiently regulated by the gaps, a coating defect in which the agglomerates appear on the surface of the second developing sleeve 43 occurs, and accordingly, a defective image tends to occur in the toner image on the photosensitive drum 1. Therefore, in this embodiment, as will be described later, a sequence for discharging the toner in the toner container 41 is executed.

[Mechanism of agglomeration]
First, the generation mechanism of agglomerates that cause a coating failure will be described with reference to FIGS. FIG. 5 shows the particle size distribution of the toner that normally enters the toner container 41 when the toner container 41 is replenished with toner when the image forming apparatus 100 is installed. That is, when the image forming apparatus 100 shipped from the factory is installed, the toner container 41 is empty, and toner is supplied into the toner container 41 during the installation work. The toner in the toner container 41 in this state, that is, the toner that has never been discharged from the toner container 41 by development is referred to as initial toner. In the initial toner, it is known that there is a certain proportion of coarse powder having a large particle diameter and fine powder having a small particle diameter in addition to a toner having a target particle diameter in the production method. It has a particle size distribution as shown.

  When toners having different sizes are frictionally charged in this way, the charge amount (Q / M) of the toner having a smaller particle diameter increases. That is, as shown in FIG. 6, since the charge is distributed on the surface of the toner, the charge amount is proportional to the surface area of the toner, and the charge amount increases with the square of the particle diameter. On the other hand, since the volume increases with the cube of the particle diameter, the amount of charge per unit volume is higher for fine powder. Therefore, since the toner density is substantially constant, the toner charge amount is higher for fine powder. As a result, a toner having a small particle size usually has a high charge amount, and a toner having a large particle size has a low charge amount. It is also known that the charge polarity of the toner is reversed by charge exchange due to friction between the toners.

  Therefore, when the developing device 4 is driven for a long time during the installation operation or the like and the average charge amount of the toner exceeds a certain level, the charge amount of the toner having a small particle diameter becomes very large as shown in FIG. The reversely charged toners are gathered together and electrostatically aggregated to form aggregates. In the configuration of the present embodiment, the threshold value of the average charge amount of the toner in which the aggregates are generated is Q / M = 8. When the developing device 4 is driven in such a state where there are many agglomerates, the agglomerates enter between the first developing sleeve 42 and the second developing sleeve 43 as shown in FIG. Appears as bad.

  From the above, if the amount of fine powder toner from the developing device 4 can be reduced, it is possible to reduce coating defects by reducing the amount of agglomerates and the toner charge amount. FIG. 9 shows the relationship between the fine powder ratio and the charge amount. From FIG. 9, when the fine powder ratio was 20% or less, the charge amount of the toner did not exceed 8. Therefore, in this embodiment, the following toner discharge control is executed so that the fine powder ratio is 20% or less.

[Toner discharge control]
First, in the case of the present embodiment, the CPU 301 (see FIG. 13) as the execution unit or the control unit has different development conditions for developing the electrostatic latent image on the photosensitive drum 1 by the first development sleeve 42 and the second development sleeve 43. The first mode and the second mode can be executed. The first mode is a mode in which an image forming operation is performed with a development condition as a first condition during normal image formation, that is, during an image forming operation of an image forming job.

  Here, the image formation job is a period from the start of image formation to the completion of image formation based on a print signal (image formation signal) for forming an image on a recording material. That is, the image forming job performs a series of operations including a pre-operation (pre-rotation) performed before the image forming operation, an image-forming operation, and a post-operation (post-rotation) performed after the image forming operation in response to the input of the image forming signal. It is a period.

  More specifically, the image forming job refers to the period from the pre-rotation to the post-rotation after receiving the print signal (input of the image forming job). Time). The pre-rotation is a period in which rotation of the photosensitive drum is started as a preparatory operation before the image forming operation, and various voltages are sequentially raised and various voltages are adjusted. The image forming operation is a period during which an image to be formed on the recording material is actually formed. The post-rotation is a period in which various voltages are sequentially lowered while the rotation of the photosensitive drum is continued as an operation after the image forming operation, and finally the rotation of the photosensitive drum is stopped. The interval between the sheets is a period corresponding to the interval between the recording material that continuously passes through the transfer portion.

  On the other hand, in the second mode, the first development condition is set so that the toner in the toner container 41 has more toner having a particle diameter smaller than the average particle diameter adhered to the photosensitive drum 1 more than the toner having the average particle diameter or more. In this mode, development is performed by changing to a second condition different from the condition. That is, this is a mode (discharge control) in which a large amount of toner smaller than the average particle diameter is discharged onto the photosensitive drum 1 by changing the development conditions. In the second mode, a predetermined electrostatic latent image is formed on the photosensitive drum 1, and the predetermined electrostatic latent image is developed under the development condition as a second condition, thereby discharging a large amount of toner having a small particle diameter. I am doing so.

  In this embodiment, in order to discharge toner having such a small particle size, the amplitude of the alternating voltage of the developing bias, specifically, Vpp is set to be larger in the second condition than in the first condition as the developing condition. Has been changed. It is known that toner having a small particle diameter has a high charge amount and is easily influenced by a developing bias and is preferentially developed. Therefore, by applying a strong biasing force to the developing unit (between the first developing sleeve 42 and the second developing sleeve 43 and the photosensitive drum 1), toner having a small diameter is discharged from the toner container 41 as shown in FIG. The amount of agglomerates can be reduced by discharging. In FIG. 10 and FIGS. 11A and 11B to be described next, the front (left) is before the development bias is applied, and the rear (right) is after the development bias is applied. For this reason, in the present embodiment, Vpp, which is an AC component of the developing bias, is increased as a means for increasing the developing bias.

  FIG. 11A shows the toner discharge state at the developing unit when Vpp is low (low Vpp), and FIG. 11B shows the case where Vpp is high (high Vpp). By increasing Vpp, as shown in FIG. 11B, fine powder having a large charge amount (Q / M) can be greatly moved in the developing portion, and the first developing sleeve 42 (second developing sleeve 43) can be moved. Certain fine powders that are difficult to develop are also easily developed. For this reason, it is possible to selectively develop only the fine powder as compared with the normal development bias (Vpp of the first condition).

  Here, if normal Vpp is set to 2.0 kV or more, image quality deterioration such as fogging occurs. Therefore, in this embodiment, image formation is performed with normal Vpp, that is, Vpp under the first condition set to 2.0 kV. However, in the discharge control for discharging fine powder, the developability of fine powder is more important than the image quality, so Vpp is raised to the leak limit of 2.5 kV. That is, the second condition Vpp of this embodiment is 2.5 kV.

  FIG. 12 shows the particle size distribution of the toner developed on the photosensitive drum 1 from the first developing sleeve 42 and the second developing sleeve 43 (that is, discharged) by the discharge control described above. As described above, in the present embodiment, the volume average particle diameter of the toner is 7.0 μm. From FIG. 12, it can be seen that the toner having a smaller particle diameter than the volume average particle diameter of 7.0 μm is discharged more than the toner having the average particle diameter or more.

  After the ratio of fine powder in the toner container 41 is once lowered by the discharge control described above, the high charge amount toner is easily developed even during normal image formation. For this reason, the proportion of fine powder does not increase as much as when the image forming apparatus is installed, as long as the developing device is not replaced no matter what image is formed thereafter. Therefore, the discharge control may be performed when the image forming apparatus is installed and when the developing device is replaced. In other words, the discharge control is performed when the image forming apparatus is installed for the first time (when the power is turned on), before the execution of the first image forming job, and after the development apparatus containing the initial toner is mounted. This may be performed at the time of the first activation and before the execution of the first image forming job. It should be noted that the discharge control may be performed only at either one or both.

  Next, the operation of each part of the discharge control will be described with reference to FIGS. 13 and 14. FIG. 13 is a block diagram illustrating configurations of the development high-voltage substrate 200 and the control substrate 300 of the image forming apparatus 100 according to the present embodiment. An AC high voltage circuit 201 and a DC high voltage circuit 202 are mounted on the development high voltage substrate 200. A CPU 301 (execution means, control means) is mounted on the control board 300. In the developing high-voltage substrate 200, the AC high-voltage circuit 201 generates an AC voltage for developing bias and supplies it to the first developing sleeve 42, the second developing sleeve 43, and the regulating blade 44. The DC high voltage circuit 202 generates a DC voltage of the developing bias and supplies it to the first developing sleeve 42, the second developing sleeve 43, and the regulating blade 44.

  The CPU 301 of the control board 300 controls each unit, and executes operations such as image formation, driving, and processing based on a program stored in the memory 302. That is, the memory 302 includes a RAM and a ROM, and a program corresponding to a control procedure is stored in the ROM. The CPU 301 controls each unit while reading the program. The RAM stores work data and input data. The CPU 301 performs control by referring to data stored in the RAM based on the above-described program and the like. Further, the CPU 301 drives the driving device 210 through the driving circuit 303.

  FIG. 14 shows an example of the above-described discharge control flow. First, when the power of the image forming apparatus 100 is first turned on after the installation of the image forming apparatus or after replacement of the developing device, the image forming apparatus 100 starts operating (S11). Then, the transfer roller 6 is separated from the photosensitive drum 1, and the setting of the development bias Vpp is changed. That is, the value of Vpp is changed from 2 kV to 2.5 kV (S12).

  Next, the discharge operation is started. That is, the predetermined electrostatic latent image shown in FIG. 15 is formed on the photosensitive drum 1, and the predetermined electrostatic latent image is developed under the development condition of Vpp of 2.5 kV (S13). The toner developed on the photosensitive drum 1 rotates with the photosensitive drum 1 and is scraped off by the cleaning device 7. The image in FIG. 15 has a pattern in which a line image, a non-image portion, and a halftone image are appropriately arranged, and it has been found that the effect of developing small particle size toner is high. A hatched line at the center of the image in FIG. 15 indicates a halftone image. In this embodiment, this discharge operation was performed for 20 minutes. When the discharge operation is completed (S14), the transfer roller 6 returns to the original position and comes into contact with the photosensitive drum 1, and the development bias setting is also returned to the original value (S15).

  In the present embodiment, the toner discharge operation is performed by changing the development conditions as described above, thereby changing the particle size portion of the toner in the toner container 41 and reducing the fine powder rate. As a result, an increase in the toner charge amount can be suppressed with an easy configuration, and the occurrence of defective coating can be suppressed by reducing the formation of aggregates.

[Example 1]
The results of experiments conducted to confirm the effects of this embodiment will be described. In the experiment, the image forming apparatus was installed in the conventional example in which the above-described discharge operation was not performed and in the first example in which the above-described discharge operation was performed. The development sleeve 43 was examined for coating defects. In addition, the average toner charge amount (Q / M) on the first developing sleeve 42 immediately after the installation work and the fine powder ratio in the toner container 41 were examined. The experiment was conducted in a low humidity environment. Further, in the case of the first embodiment, the installation work includes discharge control performed at the time of installation.

The results are shown in Table 1.

  As can be seen from Table 1, in Example 1, the Q / M decreased due to the decrease in fine powder, and the occurrence of defective coating that occurred when the conventional image forming apparatus was installed could be suppressed. In addition, the installation time of Example 1 is 30 minutes because the discharging operation is performed for 20 minutes in addition to the installation time of 10 minutes as in the conventional example.

<Second Embodiment>
A second embodiment will be described using FIG. 16 with reference to FIGS. In the above-described first embodiment, the example in which Vpp is changed by the discharge control and the electric field strength is increased to preferentially fly fine powder has been described. In contrast, in the present embodiment, in the discharge control, the frequency f of the AC voltage of the developing bias is changed in addition to Vpp as the developing condition. Since other configurations and operations are the same as those of the first embodiment, overlapping descriptions and illustrations are omitted or simplified, and the following description will focus on portions that are different from the first embodiment.

  In the case of the above-described first embodiment, in the experiment of Example 1, in addition to the usual (conventional example) 10 minutes, the discharge operation took 20 minutes and substantially 30 minutes in the installation time of the image forming apparatus. However, in the market, such a time may not be available at the time of installation, and the service efficiency also decreases. For this reason, in this embodiment, the frequency is further changed and the installation time is shortened by skipping a lot of fine powder.

  That is, in the present embodiment, in the second mode (discharge control), Vpp is changed so that the second condition is larger than the first condition, and the frequency f of the alternating voltage is set to be higher than the first condition. Change the condition to be lower. By reducing the frequency f, the time of one cycle is extended, and the time during which the development bias influences the development side (the period in which the toner flies from the developing sleeve to the photosensitive drum, TDEV in FIG. 4) can be lengthened. Due to the influence, it becomes possible to develop fine powder toner which has not normally reached on the photosensitive drum 1. Further, by reducing the frequency, the amplitude of the velocity of the toner in the direction toward the photosensitive drum 1 can be increased, and the amount of toner (fine powder) discharged can be increased.

  Here, if the normal (first condition) frequency is lowered to 2.5 kHz or less, image quality degradation such as fogging occurs. For this reason, the normal frequency is preferably 2.5 kHz or higher, and in this embodiment, image formation is performed with the frequency f of the first condition being 3 kHz. However, in the discharge control for discharging fine powder, since the developability of fine powder is more important than image quality, the frequency f is lowered to 2.0 kHz which is the limit of the electric circuit. That is, the second condition frequency f of the present embodiment is 2.0 kHz.

  Next, the operation of each part of the discharge control will be described with reference to FIG. FIG. 16 is an example of a flow of discharge control according to the present embodiment. First, when the image forming apparatus 100 is first turned on after the image forming apparatus is installed or the developing apparatus is replaced, the image forming apparatus 100 starts operating (S21). Then, the transfer roller 6 is separated from the photosensitive drum 1, and the setting of the development bias Vpp and the frequency f is changed. That is, the value of Vpp is 2 kV to 2.5 kV, and the frequency f is 3 kHz to 2 kHz (S22).

  Next, the discharge operation is started. That is, the predetermined electrostatic latent image shown in FIG. 15 is formed on the photosensitive drum 1, and the predetermined electrostatic latent image is developed under the development conditions where Vpp is 2.5 kV and frequency f is 2 kHz (S23). ). The toner developed on the photosensitive drum 1 rotates with the photosensitive drum 1 and is scraped off by the cleaning device 7. In this embodiment, this discharge operation was performed for 15 minutes. When the discharge operation is completed (S24), the transfer roller 6 returns to the original position and comes into contact with the photosensitive drum 1, and the development bias setting is also returned to the original value (S25).

  In this embodiment, since the frequency f is also changed in addition to Vpp, fine powder can be discharged more efficiently, and the fine powder rate can be reduced and coating defects can be suppressed in a shorter time than in the first embodiment. As a result, it is possible to shorten the discharge control time executed at the time of installation, and to shorten the time required at the time of installation.

[Example 2]
The results of experiments conducted to confirm the effects of this embodiment will be described. In the experiment, the image forming apparatus was installed in the conventional example in which the above-described discharge operation was not performed and in the second example in which the above-described discharge operation was performed. The development sleeve 43 was examined for coating defects. In addition, the average toner charge amount (Q / M) on the first developing sleeve 42 immediately after the installation work and the fine powder ratio in the toner container 41 were examined. The experiment was conducted in a low humidity environment. Moreover, in the case of Example 2, the installation work includes discharge control performed at the time of installation.

The results are shown in Table 2. Table 2 also shows Example 1 described above.

  As is clear from Table 2, in Example 2, the installation time is shorter than that in Example 1, and as in Example 1, the Q / M decreases due to the decrease in fine powder, which occurs when the conventional image forming apparatus is installed. The occurrence of defective coating could be suppressed. In addition, the installation time of Example 2 is 25 minutes because the discharging operation is performed for 15 minutes in addition to the installation time of 10 minutes as in the conventional example.

<Third Embodiment>
A third embodiment will be described using FIG. 17 with reference to FIGS. In the above-described second embodiment, the example in which Vpp and the frequency f are changed by the discharge control to preferentially fly fine powder has been described. In contrast, in the present embodiment, Vback is changed in addition to Vpp and frequency f as development conditions in the discharge control. As described above, Vback is a potential difference between the DC voltage Vdc of the developing bias and the potential Vl of the non-image portion where the toner image is not formed on the surface of the charged photosensitive drum 1. Since other configurations and operations are the same as those of the first and second embodiments, the overlapping description and illustration are omitted or simplified, and the following description will be focused on portions that are different from the first and second embodiments. .

  In the present embodiment, in the second mode, in addition to the development conditions of the second embodiment described above, Vback is further changed so that much fine powder is blown. That is, in the present embodiment, in the second mode (discharge control), the frequency f of the AC voltage is set to be higher in the second condition than in the first condition so that Vpp is larger in the second condition than in the first condition. Change to be lower. At the same time, Vback is changed so that the second condition is smaller than the first condition.

  In general, it has been found that a toner having a high charge amount (Q / M) can be developed in a non-image portion by making Vback applied to prevent toner scattering to the non-image portion smaller than usual. That is, by lowering Vback during the toner discharging operation in the toner container 41, fine powder can be further scattered to the non-image portion. Therefore, in this embodiment, the Vback is further changed by the discharge control, and the installation time is further shortened by flying a lot of fine powder.

  Here, if the normal (first condition) Vback is lowered to 100 V or less, image quality degradation such as fogging occurs. For this reason, in this embodiment, image formation is performed with the first condition of Vback being 100V. However, in the discharge control for discharging fine powder, developability of fine powder is more important than image quality, so Vback is lowered to the limit. However, since toner other than fine powder is developed when Vback becomes negative, Vback is set to +10 V leaving a margin of 10 V, which is a potential variation on the photosensitive drum 1. That is, the second condition Vback in this embodiment is 10V.

  Note that Vback is changed by changing either or both of the DC voltage Vdc of the developing bias and the potential Vl of the non-image portion. In this embodiment, when Vback is lowered, the DC voltage Vdc is lowered, or the potential Vl of the non-image portion is raised, and both of these are performed.

  Next, the operation of each part of the discharge control will be described with reference to FIG. FIG. 17 is an example of a discharge control flow according to the present embodiment. First, when the image forming apparatus 100 is first turned on after the image forming apparatus is installed or the developing apparatus is replaced, the image forming apparatus 100 starts operating (S31). Then, the transfer roller 6 is separated from the photosensitive drum 1, and the settings of the development bias Vpp, frequency f, and Vback are changed. That is, the value of Vpp is 2 kV to 2.5 kV, the frequency f is 3 kHz to 2 kHz, and the value of Vback is 100 V to 10 V (S32).

  Next, the discharge operation is started. That is, the predetermined electrostatic latent image shown in FIG. 15 is formed on the photosensitive drum 1, and this predetermined electrostatic latent image is developed under the development conditions of Vpp of 2.5 kV, frequency f of 2 kHz, and Vback of 10 V. Develop (S33). The toner developed on the photosensitive drum 1 rotates with the photosensitive drum 1 and is scraped off by the cleaning device 7. In this embodiment, this discharge operation was performed for 10 minutes. When the discharging operation is completed (S34), the transfer roller 6 returns to the original position and comes into contact with the photosensitive drum 1, and the development bias and Vback settings are also returned to the original values (S35).

  In this embodiment, Vback is also changed in addition to Vpp and frequency f, so that fine powder can be discharged more efficiently, and the fine powder rate can be reduced in a shorter time than in the second embodiment, thereby suppressing poor coating. it can. As a result, it is possible to shorten the discharge control time executed at the time of installation, and to shorten the time required at the time of installation.

[Example 3]
The results of experiments conducted to confirm the effects of this embodiment will be described. In the experiment, the image forming apparatus was installed in the conventional example in which the above-described discharge operation was not performed and in Example 3 in which the above-described discharge operation was performed. The development sleeve 43 was examined for coating defects. In addition, the average toner charge amount (Q / M) on the first developing sleeve 42 immediately after the installation work and the fine powder ratio in the toner container 41 were examined. The experiment was conducted in a low humidity environment. In the case of the third embodiment, the installation work includes discharge control performed at the time of installation.

The results are shown in Table 3. Table 3 also shows Examples 1 and 2 described above.

  As apparent from Table 3, in Example 3, the installation time is shorter than in Examples 1 and 2, and Q / M decreases due to the reduction of fine powder, as in Examples 1 and 2, and the conventional image forming apparatus It was possible to suppress the occurrence of coating defects that had occurred during installation. In addition, the installation time of Example 3 is 20 minutes because the discharging operation is performed for 10 minutes in addition to the installation time of 10 minutes as in the conventional example.

<Fourth Embodiment>
A fourth embodiment will be described using FIG. 18 with reference to FIGS. In the above-described third embodiment, an example in which Vpp, frequency f, and Vback are changed by discharging control to preferentially fly fine powder has been described. On the other hand, in the present embodiment, in the discharge control, the peripheral speeds va and vb of the first developing sleeve 42 and the second developing sleeve 43 are changed in addition to Vpp, frequency f, and Vback as developing conditions. Since other configurations and operations are the same as those in the first to third embodiments, overlapping explanations and illustrations are omitted or simplified, and the following description will focus on portions that are different from the first to third embodiments. .

  In the present embodiment, in the second mode (discharge control), in addition to the development conditions of the third embodiment described above, the peripheral speeds va and vb of the first developing sleeve 42 and the second developing sleeve 43 are further changed, I try to fly a lot of fine powder. That is, in this embodiment, in the second mode, the frequency f of the AC voltage is set to be lower in the second condition than in the first condition so that Vpp is higher in the second condition than in the first condition. In addition, Vback is changed so that the second condition is smaller than the first condition. At the same time, the peripheral speeds va and vb of the first developing sleeve 42 and the second developing sleeve 43 are changed so that the second condition is slower than the first condition.

  When the peripheral speeds va and vb of the first developing sleeve 42 and the second developing sleeve 43 are low, the toner can be reciprocated many times at the same location on the photosensitive drum 1, so that fine powder having a high charge amount (Q / M) is generated. Efficient ejection can be performed toward the latent image. Therefore, in the present embodiment, the installation time is further shortened by changing the peripheral speeds va and vb (development speeds) of the first developing sleeve 42 and the second developing sleeve 43 by discharging control so as to fly a lot of fine powder. I have to.

  Here, in the present embodiment, the peripheral speed va of the first developing sleeve 42 under normal conditions (first condition) is 460 mm / sec, and the peripheral speed vb of the second developing sleeve 43 is 440 mm / sec. Further, the peripheral speed vd of the photosensitive drum 1 is set to 450 mm / sec. Therefore, the peripheral speed ratio of the first developing sleeve 42 to the photosensitive drum 1 is 1.02, and the peripheral speed ratio of the second developing sleeve 43 to the photosensitive drum 1 is 0.98. When the value is smaller than this value, that is, when the peripheral speeds of the first developing sleeve 42 and the second developing sleeve 43 are decreased, the developability cannot be ensured at the maximum image density. Therefore, image formation is usually performed with the above-described peripheral speed ratios set to 1.02 and 0.98, respectively.

  However, in the fine powder discharge control, the maximum density image is not used, and only a half-density toner band (a belt-like toner image) is formed. Therefore, the peripheral speed ratios are 0.51 and 0.49, which are half of them, respectively. did. That is, in the discharge control, the peripheral speed of the first developing sleeve 42 is changed from 460 mm / sec to 230 mm / sec, and the peripheral speed of the second developing sleeve 43 is changed from 440 mm / sec to 220 mm / sec.

  Next, the operation of each part of the discharge control will be described with reference to FIG. FIG. 18 is an example of a discharge control flow according to the present embodiment. First, when the image forming apparatus 100 is first turned on after the installation of the image forming apparatus or after the replacement of the developing device, the image forming apparatus 100 starts operating (S41). Then, the transfer roller 6 is separated from the photosensitive drum 1, and the settings of the development bias Vpp, the frequency f, Vback, and the peripheral speeds (development speeds) va, vb of the first development sleeve 42 and the second development sleeve 43 are changed. . That is, the Vpp value is 2 kV to 2.5 kV, the frequency f is 3 kHz to 2 kHz, the Vback value is 100 V to 10 V, the development speed va is 460 mm / sec to 230 mm / sec, and the vb is 440 mm / sec to 220 mm / sec. (S42).

  Next, the discharge operation is started. That is, the predetermined electrostatic latent image shown in FIG. 15 is formed on the photosensitive drum 1, and Vpp is 2.5 kV, frequency f is 2 kHz, Vback is 10 V, va is 230 mm / sec, and vb is 220 mm / sec. The predetermined electrostatic latent image is developed under development conditions (S43). The toner developed on the photosensitive drum 1 rotates with the photosensitive drum 1 and is scraped off by the cleaning device 7. In this embodiment, this discharge operation was performed for 5 minutes. When the discharging operation is completed (S44), the transfer roller 6 returns to the original position and comes into contact with the photosensitive drum 1, and the development bias, Vback, and development speed settings are also restored to the original values (S45).

  In this embodiment, since development speeds va and vb are also changed in addition to Vpp, frequency f and Vback, fine powder can be discharged more efficiently, and the fine powder ratio can be reduced in a shorter time than in the third embodiment. Lowering of the coating can be suppressed. As a result, it is possible to shorten the discharge control time executed at the time of installation, and to shorten the time required at the time of installation.

[Example 4]
The results of experiments conducted to confirm the effects of this embodiment will be described. In the experiment, the image forming apparatus was installed in the conventional example in which the above-described discharge operation was not performed and in the fourth embodiment in which the above-described discharge operation was performed. The development sleeve 43 was examined for coating defects. In addition, the average toner charge amount (Q / M) on the first developing sleeve 42 immediately after the installation work and the fine powder ratio in the toner container 41 were examined. The experiment was conducted in a low humidity environment. In the case of the fourth embodiment, the installation work includes discharge control performed at the time of installation.

The results are shown in Table 4. Table 4 also shows Examples 1 to 3 described above.

  As is apparent from Table 4, in Example 4, the installation time is shorter than in Examples 1 to 3, and the Q / M decreases due to the decrease in fine powder, as in Examples 1 to 3, and the image forming apparatus of the conventional example It was possible to suppress the occurrence of coating defects that had occurred during installation. In addition, the installation time of Example 4 is 15 minutes because the discharging operation is performed for 5 minutes in addition to the installation time of 10 minutes as in the conventional example.

<Fifth Embodiment>
A fifth embodiment will be described with reference to FIG. 19 with reference to FIGS. In the above-described fourth embodiment, the discharge control is performed before the first image forming job is executed and at the first start-up after the development device containing the initial toner is mounted, and the first image forming job. The example performed at the time of initial installation before the execution of was explained. On the other hand, in the present embodiment, the discharge control is performed separately at the time of initial installation and at the time of post-rotation of the image forming job. Since other configurations and operations are the same as those of the fourth embodiment, overlapping descriptions and illustrations are omitted or simplified, and the following description will be focused on parts that are different from the fourth embodiment.

  In the present embodiment, the second mode (discharge control) is performed for a short time (for example, 1 minute) at the time of initial installation, and then divided into a plurality of times and also for a short time (for example, for 1 minute) at the time of post-rotation. went. As described in the fourth embodiment, when Vpp, the frequency f, Vback, and the peripheral speeds va and vb of the first developing sleeve 42 and the second developing sleeve 43 are changed as the developing conditions for the discharge control, in 5 minutes, Coat defects can be suppressed as in the first to third embodiments. Therefore, in the present embodiment, the discharge control is performed five times in total for 1 minute each at the time of initial installation and after the rotation.

  As described above, in this embodiment, the discharge control is performed for a predetermined time at the time of post-rotation for each image forming job (one minute), and is not performed for the image forming job after the predetermined number of times (after five times) from the initial installation. That is, after the discharge control is performed a number of times that the fine powder in the toner container 41 is discharged and the fine powder ratio is lower than a predetermined value, the discharge control is not performed. In this embodiment, the CPU 301 counts the number of discharge control operations, and stores the count value (counter C) in the memory 302.

  By performing the discharge control in this way, it is possible to suppress coating defects without changing the installation time so much compared to the conventional example. Further, if discharge control is performed during the post-rotation of the image forming job, the downtime from the start of the image forming job to the completion of the image forming operation immediately before the post-rotation can be reduced.

  However, the discharge control performed in this way is performed after a predetermined number of times of image forming operation (for example, image formation on a predetermined number of recording materials) at the time of pre-rotation (during pre-operation), other than during post-rotation. May be performed when the image forming job is interrupted. In other words, the discharge control may be executed at least at the time of pre-rotation, post-rotation, or interruption.

  As described above, even when the discharge control is performed in a divided manner, the fine powder is frequently blown before the fine powder in the toner container 41 is aggregated.

  Next, the operation of each part of the discharge control will be described with reference to FIG. FIG. 19 is an example of a flow of discharge control according to the present embodiment. Moreover, FIG. 19 demonstrates the case where discharge control is performed at the time of back rotation. The discharge control at the time of initial installation is the same as that in FIG. 18 described in the fourth embodiment except that the discharge operation time is 1 minute.

  First, when the last image formation of the image forming job is completed, the CPU 301 confirms the counter C in the memory 302 (S51). If the counter C is 5 or more (YES in S51), the discharge control is performed. Instead, the normal post-rotation is performed to complete the image forming job.

  On the other hand, when the counter C is less than 5 in S51 (NO in S51), the transfer roller 6 is separated from the photosensitive drum 1, and the settings of the development bias Vpp, frequency f, Vback, development speed va, vb are changed. That is, the Vpp value is 2 kV to 2.5 kV, the frequency f is 3 kHz to 2 kHz, the Vback value is 100 V to 10 V, the development speed va is 460 mm / sec to 230 mm / sec, and the vb is 440 mm / sec to 220 mm / sec. (S52).

  Next, the discharge operation is started. That is, the predetermined electrostatic latent image shown in FIG. 15 is formed on the photosensitive drum 1, and Vpp is 2.5 kV, frequency f is 2 kHz, Vback is 10 V, va is 230 mm / sec, and vb is 220 mm / sec. The predetermined electrostatic latent image is developed under development conditions (S53). The toner developed on the photosensitive drum 1 rotates with the photosensitive drum 1 and is scraped off by the cleaning device 7. In this embodiment, this discharge operation was performed for 1 minute. When the discharge operation is completed (S54), the transfer roller 6 returns to the original position and comes into contact with the photosensitive drum 1, and the development bias, Vback, and development speed settings are also restored to the original values (S55). Then, the counter C is incremented once (S56).

  In the present embodiment, since the discharge control is divided into a plurality of times, it is possible to suppress coating defects while significantly shortening the installation time such as when the image forming apparatus is installed as compared with the fourth embodiment.

[Example 5]
The results of experiments conducted to confirm the effects of this embodiment will be described. In the experiment, the image forming apparatus was installed in the conventional example in which the above-described discharge operation was not performed and in Example 5 in which the above-described discharge operation was performed. The development sleeve 43 was examined for coating defects. In Example 5, the presence / absence of a coating defect on the second developing sleeve 43 after all discharge control was completed was examined. In addition, immediately after the installation work (conventional example), after the completion of all the discharge control (example 5), the average toner charge amount (Q / M) on the first developing sleeve 42 and the fine powder ratio in the toner container 41 are examined. It was. The experiment was conducted in a low humidity environment. In the case of the fifth embodiment, the installation work includes discharge control performed at the time of installation.

The results are shown in Table 5. Table 5 also shows Examples 1 to 4 described above.

  As is apparent from Table 5, in Example 5, the installation time is shorter than in Examples 1 to 4, and similarly to Examples 1 to 4, the Q / M decreases due to the reduction of fine powder, and the conventional image forming apparatus It was possible to suppress the occurrence of coating defects that had occurred during installation. In addition, the installation time of Example 5 is 11 minutes because the discharging operation is performed for 1 minute in addition to the installation time of 10 minutes as in the conventional example.

<Other embodiments>
In each of the above-described embodiments, the development bias Vpp, the frequency f, Vback, and the peripheral speeds (development speeds) va, vb of the first development sleeve 42 and the second development sleeve 43 are set as examples of development conditions to be changed by discharge control. Listed. However, the development conditions to be changed are other conditions as long as the toner in the toner container 41 has a smaller particle diameter than the average particle diameter and adheres to the photosensitive drum 1 more than the toner having the average particle diameter or more. Condition may be sufficient.

  In the discharge control, at least one of the conditions of the development bias Vpp, the frequency f, the Vback, and the peripheral speeds (development speeds) va, vb of the first developing sleeve 42 and the second developing sleeve 43 is changed. Anyway. Moreover, the combination of these conditions and the number of combinations can be set suitably. For example, only the frequency f and Vback may be changed, only Vpp and the development speed may be changed, or only the frequency f, Vback, and the development speed may be changed.

  In the fifth embodiment, discharge control is performed at the time of post-rotation in addition to at the time of initial installation. However, it is not performed at the time of initial installation, but only at any one of post-rotation, pre-rotation, and interruption of an image forming job. You can go. Further, the discharge control may be performed at the time of any two or all of a single image forming job at the time of pre-rotation, post-rotation, and interruption.

  The image forming apparatus of the present invention can be applied to a printer, a facsimile machine, a multifunction machine having a plurality of these functions, in addition to a copying machine.

  DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum (image carrier) / 2 ... Corona charger (charging means) / 3 ... Laser scanner (exposure means) / 4 ... Developing device / 41 ... Toner container / 42 ... First developing sleeve (first toner carrier) / 43 ... Second developing sleeve (second toner carrier) / 44 ... Regulator blade / 200 ... Developing high voltage substrate (developing bias applying means) ) / 210 ... Drive device (drive means) / 301 ... CPU (execution means, control means)

Claims (14)

A rotating image carrier;
A toner container that contains toner, a first toner carrier that carries and rotates the toner in the toner container, and that develops the electrostatic latent image formed on the image carrier with toner; and the first toner carrier The first toner carrier is disposed downstream of the image carrier in the rotation direction of the image carrier through a gap, and the toner in the toner container is carried and rotated, and the layer thickness of the carried toner is regulated by the gap. A developing device having a second toner carrier for developing the electrostatic latent image formed on the image carrier with toner,
A first mode in which an image forming operation is performed under a development condition in which an electrostatic latent image on the image carrier is developed by the first toner carrier and the second toner carrier, and the toner in the toner container Among these, the development condition is changed to a second condition different from the first condition so that more toner having a smaller particle diameter than the average particle diameter adheres to the image carrier more than the average particle diameter. Execution means capable of executing a second mode for performing
An image forming apparatus. By applying a developing bias in which an AC voltage is superimposed on a DC voltage to the first toner carrier and the second toner carrier, the image carrier is statically moved by the first toner carrier and the second toner carrier. A developing bias applying means for developing the electrostatic latent image;
The execution means changes the amplitude of the AC voltage so that the second condition is larger than the first condition.
The image forming apparatus according to claim 1, wherein: By applying a developing bias in which an AC voltage is superimposed on a DC voltage to the first toner carrier and the second toner carrier, the image carrier is statically moved by the first toner carrier and the second toner carrier. A developing bias applying means for developing the electrostatic latent image;
The execution means changes the frequency of the AC voltage so that the second condition is lower than the first condition.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Charging means for charging the surface of the image carrier;
Exposure means for exposing the surface of the charged image carrier to form an electrostatic latent image;
By applying a developing bias in which an AC voltage is superimposed on a DC voltage to the first toner carrier and the second toner carrier, the image carrier is statically moved by the first toner carrier and the second toner carrier. A developing bias applying means for developing the electrostatic latent image,
The execution means determines a potential difference between the DC voltage and a potential of a non-image portion where a toner image is not formed on the surface of the charged image carrier under the second condition rather than the first condition. Change it to be smaller,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Drive means for driving the first toner carrier and the second toner carrier;
The execution means changes the peripheral speeds of the first toner carrier and the second toner carrier so that the second condition is slower than the first condition.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The second mode is executed at the first startup of the image forming apparatus and before execution of the first image forming job.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The developing device is detachable from a main body of the image forming apparatus,
The second mode is executed at the first startup after the developing device containing the initial toner is mounted and before the execution of the first image forming job.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The execution means can execute an image forming job that performs a series of operations including a pre-operation performed before the image forming operation, the image forming operation, and a post-operation performed after the image forming operation by inputting an image forming signal. ,
The second mode is executed at least at the time of the pre-operation, the post-operation, or an interruption in which the image forming job is interrupted after the image forming operation is performed a predetermined number of times.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The second mode is performed for a predetermined time at any of the pre-operation, the post-operation, and the interruption for each image forming job, and the second mode is a predetermined number of times after the initial activation of the image forming apparatus. Not performed in the image forming job,
The image forming apparatus according to claim 8, wherein: The developing device is detachable from a main body of the image forming apparatus,
The second mode is at the first start-up of the image forming apparatus, before the execution of the first image forming job, and at the first start-up after mounting the developing device containing the initial toner. And executed only before execution of the first image forming job.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A rotating image carrier;
A toner container that contains toner, a first toner carrier that carries and rotates the toner in the toner container, and that develops the electrostatic latent image formed on the image carrier with toner; and the first toner carrier The first toner carrier is disposed downstream of the image carrier in the rotation direction of the image carrier through a gap, and the toner in the toner container is carried and rotated, and the layer thickness of the carried toner is regulated by the gap. A developing device having a second toner carrier for developing the electrostatic latent image formed on the image carrier with toner,
By applying a developing bias in which an AC voltage is superimposed on a DC voltage to the first toner carrier and the second toner carrier, the image carrier is statically moved by the first toner carrier and the second toner carrier. A developing bias applying means for developing the electrostatic latent image;
The AC voltage amplitude is developed under the first condition during the image forming operation of the image forming job, and the amplitude is set to the first condition at the first start-up of the image forming apparatus and before the first image forming job is executed. Control means for performing development under a second condition larger than
An image forming apparatus. A rotating image carrier;
A toner container that contains toner, a first toner carrier that carries and rotates the toner in the toner container, and that develops the electrostatic latent image formed on the image carrier with toner; and the first toner carrier The first toner carrier is disposed downstream of the image carrier in the rotation direction of the image carrier through a gap, and the toner in the toner container is carried and rotated, and the layer thickness of the carried toner is regulated by the gap. A developing device having a second toner carrier for developing the electrostatic latent image formed on the image carrier with toner,
By applying a developing bias in which an AC voltage is superimposed on a DC voltage to the first toner carrier and the second toner carrier, the image carrier is statically moved by the first toner carrier and the second toner carrier. A developing bias applying means for developing the electrostatic latent image;
The AC voltage frequency is developed under the first condition during the image forming operation of the image forming job, and the frequency is set to the first condition when the image forming apparatus is first activated and before the first image forming job is executed. Control means for performing development under a second condition lower than,
An image forming apparatus. A rotating image carrier;
Charging means for charging the surface of the image carrier;
Exposure means for exposing the surface of the charged image carrier to form an electrostatic latent image;
A toner container that contains toner, a first toner carrier that carries and rotates the toner in the toner container, and that develops the electrostatic latent image formed on the image carrier with toner; and the first toner carrier The first toner carrier is disposed downstream of the image carrier in the rotation direction of the image carrier through a gap, and the toner in the toner container is carried and rotated, and the layer thickness of the carried toner is regulated by the gap. A developing device having a second toner carrier for developing the electrostatic latent image formed on the image carrier with toner,
By applying a developing bias in which an AC voltage is superimposed on a DC voltage to the first toner carrier and the second toner carrier, the image carrier is statically moved by the first toner carrier and the second toner carrier. A developing bias applying means for developing the electrostatic latent image;
At the time of image forming operation of the image forming job, the potential difference between the DC voltage and the potential of the non-image portion where the toner image is not formed on the surface of the charged image carrier is developed under the first condition to form an image. Control means for performing development under a second condition in which the potential difference is smaller than the first condition at the first start-up of the apparatus and before execution of the first image forming job;
An image forming apparatus. A rotating image carrier;
A toner container that contains toner, a first toner carrier that carries and rotates the toner in the toner container, and that develops the electrostatic latent image formed on the image carrier with toner; and the first toner carrier The first toner carrier is disposed downstream of the image carrier in the rotation direction of the image carrier through a gap, and the toner in the toner container is carried and rotated, and the layer thickness of the carried toner is regulated by the gap. A developing device having a second toner carrier for developing the electrostatic latent image formed on the image carrier with toner,
Drive means for driving the first toner carrier and the second toner carrier;
When the image forming operation of the image forming job, the first toner carrier and the second toner carrier perform development under the first condition, and the image forming apparatus is started for the first time and the first image forming job. Control means for performing development under a second condition where the peripheral speed is slower than the first condition before execution of
An image forming apparatus.

Images