Image forming apparatus

Abstract

To provide an image forming apparatus capable of forming good images even when the amount of external additives supported on the surface of the toner varies depending on the lot during toner manufacturing. [Solution] The image forming apparatus 100 includes a developing bias power supply 81 that applies a developing bias to the developing sleeve 41, a developer supply container 91 that is detachably attached to the image forming apparatus 100 and contains toner, and supplies the contained toner to the developing apparatus 4A, a developer supply container memory 90 provided in the developer supply container 91 that stores information regarding the coating rate of the external additive carried on the surface of the toner contained in the developer supply container 91, and a control unit 11 that corrects the developing bias based on the information stored in the developer supply container memory 90.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine using an electrophotographic method.

Background Art

[0002] In an electrophotographic image forming apparatus, when a latent image formed on a photosensitive drum is developed by toner using a developing device, a part of an external additive which is inorganic fine particles added to the toner is also developed together. Since the particle size of the external additive developed on the photosensitive drum is smaller than that of the toner, it is difficult to remove even through a cleaning device and may remain on the photosensitive drum.

[0003] In this case, when the area where a large amount of the external additive remains on the photosensitive drum reaches the developing device again, the toner is more likely to be developed by the electric field formed by the fine particles. Therefore, when forming a uniform image such as a halftone image, a density difference may occur due to the difference in the amount of the external additive remaining on the photosensitive drum, and there is a possibility that it may be visually recognized as a ghost image. Such a phenomenon is likely to become apparent when the toner is easily developed, when the charge amount of the external additive is large, or when images of the same or similar patterns are repeatedly formed.

[0004] In such a situation, Patent Document 1 discloses an image forming apparatus that rotates a photosensitive drum with a developing bias applied to a developer carrier higher than that during image formation to discharge the external additive in the developing device to the photosensitive drum during non-image formation.

[0005] In recent years, when a toner used in an electrophotographic image forming apparatus tries to satisfy low-temperature fixing property that enables fixing at a low temperature with respect to a recording medium, the durability stability against wear on the surface of the toner has a trade-off relationship. In contrast, Patent Document 2 discloses a technique for supporting a large amount of an external additive on the surface of the toner. Thereby, it is possible to provide a toner having both durability stability and low-temperature fixing property.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-66547 [Patent Document 2] Japanese Patent Publication No. 2016-139063 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in conventional image forming apparatuses, variations in toner manufacturing conditions due to differences in toner production lots can cause fluctuations in the amount of external additives supported on the toner surface. For example, if the amount of external additives supported on the toner surface increases, the amount of external additives remaining on the photosensitive drum without being cleaned also increases, leading to the appearance of ghost images due to differences in the amount of external additives remaining on the photosensitive drum. On the other hand, if the amount of external additives supported on the toner surface decreases, the toner density will be lowered too much, worsening the toner's developability on the photosensitive drum.

[0008] The objective of the present invention is to provide an image forming apparatus that can form good images even if the amount of external additive supported on the surface of the toner varies depending on the lot during toner manufacturing. [Means for solving the problem]

[0009] An image forming apparatus according to one aspect of the present invention is an image forming apparatus comprising: an image carrier on which an electrostatic image is formed; a developer storage unit for storing a developer containing toner and a carrier; a developer carrier for carrying and transporting the developer stored in the developer storage unit and developing the electrostatic image formed on the image carrier with the toner; a developing bias power supply for applying a developing bias to the developer carrier when the developing apparatus develops the electrostatic image; a control unit for controlling the developing bias applied to the developer carrier from the developing bias power supply; a toner supply container detachably attached to the image forming apparatus for storing the toner and supplying the stored toner to the developing apparatus; and a storage unit provided in the toner supply container for storing information relating to the coating rate of an external additive carried on the surface of the toner stored in the toner supply container, wherein the control unit corrects the developing bias based on the information stored in the storage unit.

[0010] Furthermore, an image forming apparatus according to another aspect of the present invention is an image forming apparatus comprising: an image carrier on which an electrostatic image is formed; a developer storage unit for storing a developer containing toner and a carrier; a developer carrier for carrying and transporting the developer stored in the developer storage unit and developing the electrostatic image formed on the image carrier with the toner; a developing bias power supply for applying a developing bias to the developer carrier when the developing apparatus develops the electrostatic image; a control unit for controlling the developing bias applied to the developer carrier from the developing bias power supply; and a storage unit provided in the developing apparatus for storing information regarding the coverage rate of an external additive carried on the surface of the toner stored in the developer storage unit, wherein the control unit corrects the developing bias based on the information stored in the storage unit. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an image forming apparatus that can form good images even if the amount of external additive supported on the surface of the toner varies depending on the lot during toner manufacturing. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 2] This is a schematic cross-sectional view of the developing sleeve of the developing apparatus of the image forming apparatus according to Embodiment 1 of the present invention, cut by a plane perpendicular to the axial direction. [Figure 3] This is a schematic cross-sectional view of the developing sleeve of the developing apparatus of the image forming apparatus according to Embodiment 1 of the present invention, cut by a plane parallel to the axial direction. [Figure 4] This is a block diagram showing the configuration of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 5] This figure shows the waveform of the development bias applied to the developing device from the developing power supply of the image forming apparatus according to Embodiment 1 of the present invention. [Figure 6] A flowchart illustrating the development bias correction process performed by the image forming apparatus according to Embodiment 1 of the present invention. [Figure 7] This figure shows an example of an image formed on a sheet for detecting toner density using a reflective density sensor in an image forming apparatus according to Embodiment 1 of the present invention. [Figure 8] This figure shows the density difference between the ghosted area and the non-ghosted area of ​​the image forming apparatus according to Embodiment 1 of the present invention, in comparison with the conventional method. [Figure 9] This is a schematic diagram of a developer used in a developing apparatus of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 10] This is a perspective view of a developer supply container for an image forming apparatus according to Embodiment 1 of the present invention. [Figure 11] This figure shows the relationship between the coating rate of the toner unit with external additives in the image forming apparatus according to Embodiment 1 of the present invention and the coating rate of the toner unit with external additives in the developing apparatus. [Figure 12]It is a schematic diagram showing the configuration of a reflection type density sensor of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 13] It is a diagram showing the relationship between the externally added agent coating rate of toner alone and the developing bias correction value of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 14] It is a block diagram showing the configuration of an image forming apparatus according to Embodiment 2 of the present invention.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments will be described in detail with reference to the drawings.

[0014] (Embodiment 1) <Configuration of Image Forming Apparatus> The configuration of an image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail while referring to FIGS. 1, 4, 10, and 12.

[0015] The image forming apparatus 100 exemplifies a so-called tandem type image forming apparatus in which a drum cartridge for forming toner images of four colors, yellow, magenta, cyan, and black, is provided here.

[0016] The image forming apparatus 100 includes photosensitive drums 1A, 1B, 1C, 1D, charging rollers 2A, 2B, 2C, 2D, exposure devices 3A, 3B, 3C, 3D, developing devices 4A, 4B, 4C, 4D, and a fixing device 7. Further, the image forming apparatus 100 includes cleaners 8A, 8B, 8C, 8D, supply devices 9A, 9B, 9C, 9D, a control unit 11, an operation unit 12, and primary transfer rollers 61A, 61B, 61C, 61D.

[0017] In addition, the image forming apparatus 100 includes an intermediate transfer belt 62, a secondary transfer unit 65, a developing bias power source 81, and a charging bias power source 82. Furthermore, the image forming apparatus 100 includes a primary transfer bias power source 83, a secondary transfer bias power source 84, a developer supply container memory 90, and a reflection type density sensor 140.

[0018] Note that in Figure 4, the photosensitive drums 1B, 1C, 1D and the charging rollers 2B, 2C, 2D are not shown, but the photosensitive drums 1B, 1C, 1D and the charging rollers 2B, 2C, 2D have the same configuration as the photosensitive drum 1A and the charging roller 2A. The same applies to the exposure units 3B, 3C, 3D, the developing units 4B, 4C, 4D, the cleaners 8B, 8C, 8D, the replenishment units 9B, 9C, 9D, and the primary transfer rollers 61B, 61C, 61D.

[0019] The photosensitive drums 1A, 1B, 1C, and 1D, which serve as image carriers, are charged by the charging rollers 2A, 2B, 2C, and 2D. An electrostatic image is formed on the photosensitive drums 1A, 1B, 1C, and 1D when they are irradiated with laser light by the exposure devices 3A, 3B, 3C, and 3D, and a toner image is formed when they are developed by the developing devices 4A, 4B, 4C, and 4D.

[0020] The charging rollers 2A, 2B, 2C, and 2D are in contact with the surfaces of the photosensitive drums 1A, 1B, 1C, and 1D. The charging rollers 2A, 2B, 2C, and 2D are uniformly charged on the surfaces of the photosensitive drums 1A, 1B, 1C, and 1D by applying a DC voltage as a charging bias from the charging bias power supply 82. The charging rollers 2A, 2B, 2C, and 2D are rubber rollers that rotate in accordance with the rotation of the photosensitive drums 1A, 1B, 1C, and 1D.

[0021] The exposure devices 3A, 3B, 3C, and 3D are laser scanners that irradiate the surfaces of the photosensitive drums 1A, 1B, 1C, and 1D with laser light according to the image information of the separated colors input from the control unit 11.

[0022] The developing units 4A, 4B, 4C, and 4D receive a developing bias from the developing bias power supply 81, which then develops the electrostatic image formed on the photosensitive drums 1A, 1B, 1C, and 1D with toner, forming a toner image on the drums 1A, 1B, 1C, and 1D. Details of the configuration of the developing units 4A, 4B, 4C, and 4D will be described later.

[0023] The fixing device 7 fixes the toner image onto the sheet S, which is a recording material that has been transported after the toner image has been secondarily transferred by the secondary transfer unit 65, by heating and pressurizing the sheet S. The fixing device 7 discharges the sheet S with the fixed toner image to the outside of the image forming apparatus 100.

[0024] Cleaners 8A, 8B, 8C, and 8D remove any remaining toner on the photosensitive drums 1A, 1B, 1C, and 1D after the initial transfer.

[0025] The replenishment devices 9A, 9B, 9C, and 9D contain developer and replenish the developer to the developing devices 4A, 4B, 4C, and 4D. The replenishment devices 9A, 9B, 9C, and 9D are equipped with a developer replenishment container 91.

[0026] The developer supply container 91, which serves as a toner supply container, contains a developer that includes at least toner. The developer supply container 91 is detachably attached to the image forming apparatus 100. When the developer supply container 91 is attached to the image forming apparatus 100, it discharges the contained developer through an discharge hole (not shown) and supplies it to the developing devices 4A, 4B, 4C, and 4D. The developer supply container 91 is provided with a developer supply container memory 90.

[0027] The control unit 11, acting as a control means, controls the overall operation of the image forming apparatus 100. The control unit 11 performs patch detection density control processing to faithfully reproduce the input image as an output image, and appropriately changes the image forming conditions when forming an image on the sheet S.

[0028] Specifically, the control unit 11 calculates the difference in light intensity between the amount of light reflected from the surface of the intermediate transfer belt 62 and the amount of light reflected from the toner patch T provided on the outer surface of the intermediate transfer belt 62, based on the electrical signal input from the reflective density sensor 140. Based on the calculated difference in light intensity, the control unit 11 detects the amount of toner adhering to the toner patch T, and based on the detection result of the amount of toner adhering to the toner patch T, it determines the amount of laser light irradiated from the exposure devices 3A, 3B, 3C, and 3D during the image formation process. Details of the patch detection density control process will be described later.

[0029] The control unit 11 corrects the development bias applied to the development sleeve 41 from the development bias power supply 81 during image formation by performing the development bias correction process described later. The control unit 11 also performs the patch detection density control process described above during the development bias correction process.

[0030] The control unit 11 includes a CPU 400 that performs calculations by reading and executing a control program stored in a memory (not shown).

[0031] The CPU 400 includes an external additive information determination unit 410 and an image formation condition calculation unit 420, which are configured as functional blocks during the execution of the control program.

[0032] The external additive information determination unit 410 acquires the unique toner information stored in the developer replenishment container memory 90 of the developer replenishment container 91 by reading it via an information reading unit (not shown) of the image forming apparatus 100.

[0033] The image formation condition calculation unit 420 corrects the development bias applied to the development sleeve 41 from the development bias power supply 81 during image formation, based on the information obtained by the external additive information determination unit 410. After correcting the development bias, the image formation condition calculation unit 420 performs patch detection density control processing.

[0034] The operation unit 12 is an input / output device such as a touch panel that operates under the control of the control unit 11, accepts user operations, and outputs electrical signals to the control unit 11 corresponding to the accepted operations.

[0035] The primary transfer rollers 61A, 61B, 61C, and 61D are positioned opposite the photosensitive drums 1A, 1B, 1C, and 1D via the intermediate transfer belt 62 and are in contact with the intermediate transfer belt 62. The primary transfer rollers 61A, 61B, 61C, and 61D are subjected to a primary transfer bias from the primary transfer bias power supply 83, thereby transferring the toner image formed on the photosensitive drums 1A, 1B, 1C, and 1D to the intermediate transfer belt 62.

[0036] The intermediate transfer belt 62 is in contact with the photosensitive drums 1A, 1B, 1C, and 1D, forming a primary transfer section between it and the photosensitive drums 1A, 1B, 1C, and 1D. The toner images formed on the photosensitive drums 1A, 1B, 1C, and 1D are first transferred to the intermediate transfer belt 62 by the primary transfer rollers 61A, 61B, 61C, and 61D in the primary transfer section. Specifically, a positive primary transfer bias is applied to the intermediate transfer belt 62 by the primary transfer rollers 61A, 61B, 61C, and 61D, causing the toner images with negative polarity on the photosensitive drums 1A, 1B, 1C, and 1D to be sequentially and multiple times transferred. Toner patches T are formed on the outer circumferential surface of the intermediate transfer belt 62.

[0037] The secondary transfer unit 65 transfers the toner image, which has been primary transferred to the intermediate transfer belt 62, to a sheet S fed by a feeding unit (not shown), and also transports the sheet S with the toner image transferred to it to the fixing unit 7. It is equipped with a secondary transfer inner roller 63 and a secondary transfer outer roller 64.

[0038] The secondary transfer inner roller 63, together with the secondary transfer outer roller 64, grips and conveys the sheet S fed by the feeding unit.

[0039] The secondary transfer outer roller 64 receives a secondary transfer bias from a positive polarity secondary transfer bias power supply 84, thereby secondary transferring the full-color toner image formed on the intermediate transfer belt 62 to the sheet S fed by the feeding unit.

[0040] The developing bias power supply 81 applies a developing bias to the developing sleeves 41 of the developing devices 4A, 4B, 4C, and 4D under the control of the control unit 11.

[0041] The charging bias power supply 82, under the control of the control unit 11, applies a DC voltage as a charging bias to the charging rollers 2A, 2B, 2C, and 2D, thereby charging the photosensitive drums 1A, 1B, 1C, and 1D via the charging rollers 2A, 2B, 2C, and 2D.

[0042] The primary transfer bias power supply 83 applies a primary transfer bias to the primary transfer rollers 61A, 61B, 61C, and 61D under the control of the control unit 11.

[0043] The secondary transfer bias power supply 84 applies a secondary transfer bias to the secondary transfer outer roller 64 under the control of the control unit 11.

[0044] The developer replenishment container memory 90, which serves as a memory unit, is provided in each developer replenishment container 91 for each color of toner contained in the replenishment devices 9A, 9B, 9C, and 9D. Here, the mounting position of the developer replenishment container memory 90 on the developer replenishment container 91 is exemplified by the front of the developer replenishment container 91. The developer replenishment container memory 90 is an IC chip or a barcode, etc.

[0045] The developer replenishment container memory 90 is able to communicate with an information reading unit (not shown) of the image forming apparatus 100 when the developer replenishment container 91 is mounted on the main body of the image forming apparatus 100. Data is read from and written to the developer replenishment container memory 90 via the information reading unit by the CPU 400 of the control unit 11. The developer replenishment container memory 90 stores unique information about the toner contained in each developer replenishment container 91.

[0046] The toner-specific information described above is read by the external additive information determination unit 410 of the CPU 400 via the information reading unit. Here, the toner-specific information includes information such as the toner's manufacturing date, the lot number at the time of toner's manufacture, the characteristics of the external additive, and the coverage rate of the external additive supported on the surface of the toner (hereinafter referred to as "toner external additive coverage rate"). In this embodiment, the toner-specific information includes at least the information on the toner's external additive coverage rate.

[0047] The information on the coating rate of the external additive is the information on the coating rate of the external additive for each toner cartridge from each manufacturing lot, which was measured in advance during the manufacturing stage of the toner contained in the developer supply container 91. The developer supply container memory 90, which is installed in the developer supply container 91 into which the toner of the same lot is filled, stores the information on the external additive coating rate of the same toner cartridge.

[0048] Furthermore, the developer replenishment container memory 90 is not limited to IC chips and barcodes; it may also be a non-volatile memory other than IC chips and barcodes that can be automatically read by the information reading unit of the image forming apparatus 100.

[0049] The reflective density sensor 140 is used to control the amount of toner deposited in order to faithfully reproduce the input image as an output image. The reflective density sensor 140 is positioned in the center of the intermediate transfer belt 62 in the main scanning direction. The reflective density sensor 140 receives reflected light when light is irradiated onto the outer surface of the intermediate transfer belt 62 and the toner patch T formed on the outer surface of the intermediate transfer belt 62, and outputs an electrical signal with a voltage value corresponding to the amount of reflected light received to the control unit 11.

[0050] As shown in Figure 12, the reflective density sensor 140 includes a light-emitting unit 141, a light-receiving unit 142a, a light-receiving unit 142b, and an IC 143.

[0051] The light-emitting unit 141 is an LED or the like. The light-emitting unit 141 is positioned at a 45-degree angle to the normal of the intermediate transfer belt 62 and irradiates the outer surface of the intermediate transfer belt 62 and the toner patch T with light at a light intensity level controlled by IC 143.

[0052] The light-receiving unit 142a is positioned symmetrically to the light-emitting unit 141 with respect to the normal of the intermediate transfer belt 62. The light-receiving unit 142a is a photodiode or the like that receives specularly reflected light when light is irradiated from the light-emitting unit 141 onto the outer surface of the intermediate transfer belt 62 and the toner patch T, and outputs an electrical signal with a voltage value corresponding to the amount of light of the received specularly reflected light to the control unit 11. The amount of reflected light received by the light-receiving unit 142a increases as the amount of light emitted by the light-emitting unit 141 increases.

[0053] The light-receiving unit 142b is positioned on the light-emitting unit 141 side with respect to the normal of the intermediate transfer belt 62, and is positioned at a 60-degree angle to the normal. The light-receiving unit 142b is a photodiode or the like that receives diffusely reflected light when light is irradiated from the light-emitting unit 141 onto the outer surface of the intermediate transfer belt 62 and the toner patch T, and outputs an electrical signal with a voltage value corresponding to the amount of diffusely reflected light received to the control unit 11. The amount of reflected light received by the light-receiving unit 142b increases as the amount of light emitted by the light-emitting unit 141 increases.

[0054] IC143 controls the amount of light emitted from the light-emitting unit 141 by adjusting the voltage applied to the light-emitting unit 141 under the control of the control unit 11, thereby setting the light intensity level to be suitable for detecting the toner density of the toner patch T.

[0055] In the image forming apparatus 100 having the above configuration, the developer sealed in the developer replenishment container 91 contains the same toner and carrier as the developers sealed in the developing devices 4A, 4B, 4C, and 4D. The developer sealed in the developer replenishment container 91 is manufactured by mixing toner and carrier to achieve a carrier concentration of 9 wt%. On the other hand, the developers sealed in the developing devices 4A, 4B, 4C, and 4D are manufactured by mixing toner and carrier to achieve a toner concentration of 10 wt%.

[0056] <Configuration of the developing device> The configurations of the developing devices 4A, 4B, 4C, and 4D of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 2 and 3. The arrows in Figure 3 indicate the direction of movement of the developer as it circulates through the developing devices 4A, 4B, 4C, and 4D.

[0057] The developing devices 4A, 4B, 4C, and 4D each include a developing sleeve 41, a magnetic field generating unit 42, a regulating member 43, and a developer storage unit 44. Furthermore, the developing devices 4A, 4B, 4C, and 4D each include a first screw 45a, a second screw 45b, a first connecting unit 46a, a second connecting unit 46b, and a developer receiving port 47.

[0058] The developing sleeve 41, which serves as a developer carrier, is made of a non-magnetic material and rotates at a predetermined process speed (peripheral speed) during the developing operation. The developing sleeve 41 carries and transports the developer in the developing chamber 44a with the magnetic field generated by the magnetic field generating unit 42, and when a developing bias is applied from the developing bias power supply 81, it supplies the carried developer to the surfaces of the photosensitive drums 1A, 1B, 1C, and 1D.

[0059] The magnetic field generating unit 42 is located inside the developing sleeve 41 and generates a magnetic field to support the developer on the surface of the developing sleeve 41.

[0060] The regulating member 43 regulates the height of the magnetic spike formed on the developing sleeve 41.

[0061] The developer storage section 44 contains the developer. The developer storage section 44 is divided into a developing chamber 44a and an agitation chamber 44b by a partition wall 44c that extends vertically.

[0062] The first screw 45a is located in the developing chamber 44a. The first screw 45a agitates and transports the developer in the developing chamber 44a.

[0063] The second screw 45b is located in the stirring chamber 44b. The second screw 45b stirs and transports the toner supplied from a toner supply member (not shown) and the developer in the stirring chamber 44b, thereby making the toner concentration in the stirring chamber 44b uniform.

[0064] The first connecting section 46a is formed in the partition wall 44c and connects the developing chamber 44a and the agitation chamber 44b at one end in the width direction perpendicular to the conveying direction of the sheet S. The first connecting section 46a transfers the developer from the developing chamber 44a to the agitation chamber 44b.

[0065] The second connecting section 46b is formed in the partition wall 44c and connects the developing chamber 44a and the agitation chamber 44b at its other end in the width direction. The second connecting section 46b transfers the developer from the agitation chamber 44b to the developing chamber 44a.

[0066] The developer receiving port 47 connects the stirring chamber 44b to the outside. The developer receiving port 47 allows the developer sealed in the developer supply containers 91 of the supply devices 9A, 9B, 9C, and 9D, and discharged from an outlet (not shown) of the developer supply containers 91, to be supplied to the stirring chamber 44b.

[0067] In the developing apparatuses 4A, 4B, 4C, and 4D having the above configuration, the first screw 45a and the second screw 45b transport the developer in opposite directions along the rotation axis direction of the developing sleeve 41. The first connecting section 46a transfers the developer from the developing chamber 44a to the agitation chamber 44b, and the second connecting section 46b transfers the developer from the agitation chamber 44b to the developing chamber 44a. As a result, the developer circulates through the developer storage section 44 in the order of agitation chamber 44b, second connecting section 46b, developing chamber 44a, and first connecting section 46a.

[0068] Furthermore, the transport force of the first screw 45a and the second screw 45b causes the developer in the developing chamber 44a, whose toner concentration has decreased due to toner consumption during the developing process, to move into the stirring chamber 44b via the first connecting section 46a.

[0069] <Composition of Developer> The configuration of the developer used in the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail.

[0070] The developer contained in the developing units 4A, 4B, 4C, and 4D is a two-component developer consisting of a mixture of negatively charged non-magnetic toner and a magnetic carrier.

[0071] The magnetic carrier is formed by coating the surface of a core made of resin particles mixed with ferrite particles and magnetic powder with resin. Suitable magnetic carriers include, for example, surface-oxidized or surface-unoxidized iron, nickel, cobalt, manganese, chromium, rare earth elements, or alloys of these metals, or oxide ferrite. The manufacturing method of these magnetic particles is not particularly limited. Here, a magnetic carrier in which ferrite particles are coated with silicone resin is given as an example.

[0072] The above-mentioned magnetic carrier has a saturation magnetization of 294 am² / kg for an applied magnetic field of 240 kA / m, and a resistivity of 1 × 10⁷ to 8 Ω·cm at an electric field strength of 3000 V / cm. Note that the magnetic carrier is not limited to the above; a resin magnetic carrier manufactured by polymerization using a binder resin, magnetic metal oxide, and non-magnetic metal oxide as starting materials is also acceptable.

[0073] For magnetic carriers, a HEROS laser diffraction particle size distribution analyzer (manufactured by JEOL) is used to measure the particle size in the range of 0.5 to 350 μm based on volume, dividing the region into 32 logarithmic sections. The number of particles in each channel is then measured. The median diameter at 50% of the volume is then used as the volume-average particle size of the magnetic carriers. Here, a volume-average particle size of 50 μm is used as an example.

[0074] Non-magnetic toner is made by encapsulating colorants and wax components in a resin such as polyester or styrene, and then crushing or polymerizing it to form a powder.

[0075] The non-magnetic toner consists of at least a binder resin, a colorant, and a charge control agent. While styrene-acrylic resin is used as an example of the binder resin here, it is not limited to styrene-acrylic resin; styrene-based, polyester-based, or polyethylene resins can also be used.

[0076] As a coloring agent, phthalocyanine blue is used as an example here, but other colors such as carbon black, chrome yellow, Hansa yellow, benzidine yellow, suren yellow, and quinoline yellow can be used. Additionally, permanent orange GTR, pyrazolone orange, balkan orange, Watch Young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, Deipon oil red, and pyrazolone red can be used.

[0077] Additionally, Risol Red, Rhodamine B Lake, Lake Red C, Rose Bengal, Aniline Blue, and Ultramarine Blue can be used. Furthermore, chalcioyl blue, methylene blue chloride, phthalocyanine green, or malachite green oxalerate can be used.

[0078] As described above, various pigments or dyes can be used as colorants. Furthermore, one type of colorant may be used alone, or multiple types may be used in combination.

[0079] The charge control agent may contain a charge control agent for reinforcement as needed. Any known charge control agent can be used for reinforcement, such as nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, or alkoxyamines. Alternatively, these may be quaternary ammonium salts (including fluorine-modified quaternary ammonium salts), alkylamides, elemental or compound phosphorus, or elemental or compound tungsten. Alternatively, these may be fluorine-based surfactants, metal salicylate salts, or metal salts of salicylic acid derivatives.

[0080] Furthermore, non-magnetic toner may contain wax or an external additive. Wax is included to improve release and adhesion from the fixing material during the fixing process.

[0081] As the wax, paraffin wax, carnauba wax, or polyolefin can be used. The wax is mixed and dispersed in the binder resin. In this example, the non-magnetic toner is obtained by grinding the resin, which is a mixture of the binder, colorant, charge control agent, and wax, using a mechanical grinder.

[0082] Examples of external additives include fine particles formed by hydrophobic treatment of amorphous silica, or inorganic oxide fine particles such as titanium dioxide or titanium compounds. The external additive is added to the toner base to control the powder fluidity and charge level of the toner. The particle size of the external additive is preferably between 1 nm and 100 nm. In this example, a mixture was used in which titanium dioxide with an average particle size of 50 nm was added at a weight ratio of 0.5 wt%, and amorphous silica with average particle sizes of 2 nm and 100 nm were added at a weight ratio of 0.5 wt% and 1.0 wt%, respectively.

[0083] The particle size of the toner with the above configuration was measured using a Sysmex FPIA-3000 powder particle size image analyzer, and the volume-average particle size was found to be 6.0 μm. The degree of toner aggregation was measured using a Hosokawa Micron powder tester and was found to be 30. Furthermore, the toner's external additive coating rate was measured using ESCA and was found to be 60%. The toner's external additive coating rate can be calculated using the following equation (1).

[0084] Toner coating rate (%) = (SG / ST) × 100 (1) Here, SG is the area of ​​the external additive portion added to the toner particles. ST refers to the surface area of ​​the toner particles, including the area of ​​the external additive portion (SG).

[0085] The coating rate of the toner's external additives was measured by ESCA (X-ray photoelectron spectroscopy) and calculated from the atomic weight of silica-derived silicon (hereinafter referred to as "Si") present on the surface of the toner particles. ESCA is an analytical method that detects atoms in the region of a few nanometers or less in the depth direction of the sample surface. Therefore, it is possible to detect atoms on the surface of the toner. A 75 mm square platen (equipped with a screw hole of approximately 1 mm in diameter for fixing the sample) attached to the instrument was used as the sample holder. Since the screw hole of the platen was through, it was sealed with resin or the like to create a recess for powder measurement with a depth of about 0.5 mm. The sample to be measured was packed into this recess with a spatula or the like and leveled off to prepare the sample.

[0086] The ESCA equipment and measurement conditions are as follows: • Equipment used: ULVAC-PHI PHI5000VersaProbeII • Analysis method: Narrow analysis ·X-ray source: Al-Kα ·X-ray conditions: 100μ25W15kV • Photoelectron acquisition angle: 45 • PassEnergy: 58.70eV Measurement range: 300 μm × 200 μm

[0087] The analysis method first corrects the peak originating from the CC bond of the carbon 1s orbital to 285 eV. Then, using the peak area originating from the Si2p orbital, where the peak top is detected between 100 eV and 105 eV, the amount of Si originating from silica relative to the total amount of constituent elements is calculated using a relative sensitivity factor provided by ULVAC-PHIE. Next, the silica element applied to the toner is measured using the same method as above, and the amount of Si originating from silica relative to the total amount of constituent elements is calculated. The silica coverage rate, which is the ratio of the Si amount measured in the toner to the Si amount measured in the external additive element, is defined as the external additive coverage rate of the toner.

[0088] In this embodiment, 200g of developer, prepared by mixing the above-mentioned toner and carrier at a mixing ratio (toner concentration) of 10 wt%, was added to developing devices 4A, 4B, 4C, and 4D. In this embodiment, the silica coating rate at the center of the mass production variation of the toner alone was set to 60%.

[0089] <About ghost images> The ghost images generated during image formation in the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 9 and 11.

[0090] The developer used in the image forming apparatus 100 is a dry two-component developer containing toner to which an external additive, which is a negative polarity fine particle with the same polarity as the charge polarity of the toner, has been added, and a carrier. In the development process in which such a developer is developed according to the electrostatic image formed on the photosensitive drums 1A, 1B, 1C, and 1D, the toner from the developer supported on the developing sleeve 41 in the developing apparatus 4A, 4B, 4C, and 4D is mainly developed in the image area (the bright potential area of ​​the electrostatic image). At this time, the external additive added to the toner is also developed simultaneously.

[0091] Furthermore, some of the external additives added to the toner are agitated in the developing units 4A, 4B, 4C, and 4D, which reduces their adhesion to the toner and causes them to separate. In a two-component developer consisting of toner and a carrier, as shown in Figure 9, contact between the toner and the carrier causes the external additives supported on the surface of the toner to separate from the toner and migrate to the carrier. In a two-component developer, the toner and the carrier then share the total amount of external additives, achieving a certain equilibrium.

[0092] For example, as shown in Figure 11, when the toner's external additive coating rate is 60%, and the toner concentration of the developer (consisting of toner and carrier) is 10%, the toner's external additive coating rate in the developer units 4A, 4B, 4C, and 4D becomes 58%. This indicates that 2% of the 60% external additive coating rate of the toner has migrated to the surface of the carrier.

[0093] The external additives added to the toner are negatively polarized, just like the toner, making them easily developed in the image area. Therefore, the image area on photosensitive drums 1A, 1B, 1C, and 1D receives a greater amount of development of the external additives compared to the non-image area on the same drums.

[0094] The toner and external additives developed on the photosensitive drums 1A, 1B, 1C, and 1D are first transferred onto the intermediate transfer belt 62 during the transfer process. On the other hand, some of the toner and external additives with small particle sizes and high non-electrostatic adhesion remain on the photosensitive drums 1A, 1B, 1C, and 1D without being transferred onto the intermediate transfer belt 62.

[0095] Next, the remaining toner on the photosensitive drums 1A, 1B, 1C, and 1D that have reached the cleaning process is cleaned by the cleaning component. On the other hand, the external additives remaining on the photosensitive drums 1A, 1B, 1C, and 1D that have reached the cleaning process have small particle sizes and strong adhesion to the photosensitive drums 1A, 1B, 1C, and 1D, so they cannot be completely cleaned and remain on the photosensitive drums 1A, 1B, 1C, and 1D.

[0096] Next, the external additives remaining on the photosensitive drums 1A, 1B, 1C, and 1D and reaching the charging process form an electric field between the external additives that draws toner in due to the negative polarity of the external additives themselves and the negative charge received from the charging voltage applied by the charging rollers 2A, 2B, 2C, and 2D. The parts of the photosensitive drums 1A, 1B, 1C, and 1D to which the external additives are attached have increased adhesion to the toner due to the electric field described above, making the toner more easily developed during the next image formation.

[0097] When identical or similar image patterns are continuously formed on the image areas of the photosensitive drums 1A, 1B, 1C, and 1D, the above process continues continuously, leading to an increase in the accumulation of external additives and a corresponding increase in the amount of toner developed. As a result, when forming a uniform image such as a halftone image, density differences occur in the image area, which are visible as so-called ghosts on the image.

[0098] As mentioned above, the likelihood of ghosting is due to the ease with which toner is developed, which is caused by the difference in the amount of external additives remaining on the photosensitive drums 1A, 1B, 1C, and 1D. Therefore, frequent replenishment of developers with a high proportion of external additives into the developing units 4A, 4B, 4C, and 4D leads to an excessive increase in the concentration of external additives in the developer within the developing units 4A, 4B, 4C, and 4D. As a result, a large amount of external additives is developed along with the toner, increasing the risk of the aforementioned ghosting images. In other words, the higher the amount of external additives contained in the toner, the higher the risk of ghosting images.

[0099] In this embodiment, when the toner's external additive coating rate in the developer within the developing units 4A, 4B, 4C, and 4D exceeds 61%, the amount of external additive adhering to the photosensitive drums 1A, 1B, 1C, and 1D becomes excessive, and ghost images become apparent. On the other hand, when the toner's external additive coating rate in the developer within the developing units 4A, 4B, 4C, and 4D is 58% at the center of the mass production variation, ghost images do not occur.

[0100] However, in the toner manufacturing process, variations in manufacturing conditions can cause fluctuations in the toner's external additive coating rate. Specifically, in a developer with a toner concentration of 10%, the toner's external additive coating rate fluctuates between 56% and 64%, as shown in Figure 13, exceeding the 61% threshold at which ghost images occur. When the toner's external additive coating rate exceeds 61%, it may manifest as an abnormal image.

[0101] In the image forming apparatus 100 according to this embodiment, ghosting caused by density differences resulting from the accumulation of external additives remaining on the photosensitive drums 1A, 1B, 1C, and 1D can be reduced.

[0102] <About development bias> The development bias applied to the development devices 4A, 4B, 4C, and 4D from the development bias power supply 81 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figure 5.

[0103] Figure 5 shows the waveform of the development bias output from the development bias power supply 81 during image formation, when toner is launched to the photosensitive drums 1A, 1B, 1C, and 1D.

[0104] The developing bias power supply 81 applies a developing bias to the developing sleeve 41, which is a superposition of an AC component (AC voltage) and a DC component (DC voltage). The AC component of the developing bias is a 11kHz square wave. The developing bias also has a blank section where the AC component is intermittently thinned out, leaving only the DC component. The square wave pulses that would have been present in the blank section if the AC component had not been thinned out, in other words, the pulses that became blank due to the thinning out of the AC component (pulses that no longer exist), are called "blank pulses."

[0105] Therefore, the development bias output by the development bias power supply 81 has a waveform that consists of an AC bias section in which a DC component Vdc is superimposed on the AC component, and a blank section consisting only of the DC component Vdc following the AC bias section, with each period being one cycle. In the blank section, the development performance is reduced compared to the AC bias section. As shown in Figure 5, the development bias power supply 81 outputs a double blank pulse waveform ("WBP") as the development bias, in which a blank section is provided after the AC bias section of a two-pulse rectangular wave.

[0106] In the AC bias section, the number of pulses of the square wave is counted as one pulse for half a period of the square wave. The blank time t1 is defined as the time of the blank section in one period of the development bias. The development time t2 is defined as the total time during which the electric field (pulse) is generated on the development side (developer application side) of the AC bias section in one period of the development bias. The recovery time t3 is defined as the total time during which the electric field is generated on the developer recovery side (developer return side) in one period of the development bias. The peak voltage Vpp is defined as the sum of the voltage on the development side and the voltage on the developer recovery side in the AC bias section. Here, the peak voltage Vpp is exemplified as 1.40kV. Here, one period of the development bias is exemplified as 1 sec.

[0107] Here, the electric field on the developing side is the electric field in which toner is propelled from the developing sleeve 41 side to the photosensitive drums 1A, 1B, 1C, and 1D side by the AC bias section during one cycle of the developing bias. The electric field on the developer recovery side is the electric field in which toner is pulled back from the photosensitive drums 1A, 1B, 1C, and 1D side to the developing sleeve 41 side by the AC bias section during one cycle of the developing bias. In this embodiment, the duty cycle, which is the ratio of the electric field on the developing side to the electric field on the developer recovery side, is set to 60%.

[0108] <Development bias correction process> The development bias correction process performed by the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 5 and 6.

[0109] The CPU 400 controls the development bias applied during image formation based on the unique information of the toner stored in the developer supply container memory 90. Specifically, the CPU 400 can determine the external additive coating rate of the toner supplied to the development devices 4A, 4B, 4C, and 4D from the information on the external additive coating rate of the toner stored in the developer supply container memory 90. This allows the CPU 400 to determine whether or not ghost images will occur due to variations between toner manufacturing lots.

[0110] The CPU400 then determines that ghost images occur due to lot-to-lot variations in toner production, and corrects the amount of toner flying onto the photosensitive drums 1A, 1B, 1C, and 1D. Specifically, the CPU400 corrects the peak voltage Vpp of the development bias, the blank time t1, and the frequency or duty cycle of the AC bias section to reduce the amount of toner flying onto the photosensitive drums 1A, 1B, 1C, and 1D. Here, the frequency of the AC bias section is the number of times one waveform occurs in one cycle of the development bias. This reduces the amount of external additives at the same potential as the toner flying onto the photosensitive drums 1A, 1B, 1C, and 1D, thereby suppressing the occurrence of ghost images.

[0111] Specifically, the CPU400 performs corrections such as reducing the peak voltage Vpp, reducing the frequency of the AC bias section, reducing the electric field ratio on the developing side of the duty cycle (for example, from 60% to 50%), or increasing the blank time t1 in one cycle.

[0112] Here, by applying a correction that increases the blank time t1 in one cycle, the time of the AC bias section in one cycle of the developing bias can be reduced. This reduces the amount of external additives that fly from the developing units 4A, 4B, 4C, and 4D to the photosensitive drums 1A, 1B, 1C, and 1D along with the toner.

[0113] Furthermore, by applying a correction to lengthen the blank time t1 during which a development bias is applied to recover toner from the photosensitive drums 1A, 1B, 1C, and 1D to the developing units 4A, 4B, 4C, and 4D, the toner that has flown to the photosensitive drums 1A, 1B, 1C, and 1D can be recovered. As a result, external additives can be recovered along with the toner from the photosensitive drums 1A, 1B, 1C, and 1D, thus reducing the amount of external additives in the photosensitive drums 1A, 1B, 1C, and 1D.

[0114] Furthermore, by correcting the frequency of the AC bias section, the number of times toner is launched from the developing units 4A, 4B, 4C, and 4D to the photosensitive drums 1A, 1B, 1C, and 1D can be reduced. This reduces the amount of external additives launched along with the toner from the developing units 4A, 4B, 4C, and 4D to the photosensitive drums 1A, 1B, 1C, and 1D.

[0115] On the other hand, if the amount of toner flying to the photosensitive drums 1A, 1B, 1C, and 1D is corrected to reduce the amount of toner flying to them, that is, if the AC component of the development bias is changed to reduce the developability, there is a risk that the amount of toner developed will be insufficient and the image density will decrease. However, if there is a large amount of external additive in the toner supplied to the developing units 4A, 4B, 4C, and 4D, the amount of external additive adhering to the carrier surface in the developer will increase, which will reduce the carrier's ability to impart charge to the toner, and thus the amount of charge in the toner will decrease.

[0116] When the charge amount of the toner decreases, the electrostatic adhesion between the carrier and the toner decreases, and the amount of toner developed increases at the same development bias compared to when less toner additive is supplied to the developer units 4A, 4B, 4C, and 4D. Therefore, when the coating rate of toner additive supplied to the developer units 4A, 4B, 4C, and 4D is high, a decrease in image density is unlikely to occur even if the development bias is corrected to reduce the amount of toner developed.

[0117] Next, we will explain the development bias correction process in more detail, referring to Figure 6.

[0118] The development bias correction process shown in Figure 6 is initiated when the image forming apparatus 100 detects that the developer supply container 91 has been installed.

[0119] First, the external additive information determination unit 410 of the CPU 400 reads and acquires the unique toner information stored in the developer replenishment container memory 90 (S101).

[0120] Next, the external additive information determination unit 410 of the CPU 400 acquires information on the external additive coating rate of the toner, which is included in the toner's unique information (S102).

[0121] Next, the image formation condition calculation unit 420 of the CPU 400 determines the amount of correction for the development bias based on the information on the toner's external additive coating rate obtained by the external additive information determination unit 410 (S103).

[0122] For example, as shown in Figure 13, the image formation condition calculation unit 420 performs a correction to reduce the peak voltage Vpp when the toner's external additive coating rate is 61% compared to when the toner's external additive coating rate is 60%. Alternatively, the image formation condition calculation unit 420 performs a correction to reduce the frequency of the AC bias section when the toner's external additive coating rate is 61% compared to when the toner's external additive coating rate is 60%.

[0123] Alternatively, the image formation condition calculation unit 420 performs a correction to reduce the electric field ratio on the developing side of the duty cycle when the toner's external additive coating rate is 61% compared to when the toner's external additive coating rate is 60%. Alternatively, the image formation condition calculation unit 420 performs a correction to lengthen the blank time t1 in one cycle when the toner's external additive coating rate is 61% compared to when the toner's external additive coating rate is 60%.

[0124] Furthermore, for example, as shown in Figure 13, the image formation condition calculation unit 420 performs a correction to increase the peak voltage Vpp when the toner's external additive coating rate is 59% compared to when the toner's external additive coating rate is 60%. Alternatively, the image formation condition calculation unit 420 performs a correction to increase the frequency of the AC bias section when the toner's external additive coating rate is 59% compared to when the toner's external additive coating rate is 60%.

[0125] Alternatively, the image formation condition calculation unit 420 performs a correction to increase the electric field ratio on the developing side of the duty cycle when the toner's external additive coating rate is 59% compared to when the toner's external additive coating rate is 60%. Alternatively, the image formation condition calculation unit 420 performs a correction to shorten the blank time t1 in one cycle when the toner's external additive coating rate is 59% compared to when the toner's external additive coating rate is 60%.

[0126] Next, the image formation condition calculation unit 420 of the CPU 400 applies the corrected development bias by the determined correction amount to the development devices 4A, 4B, 4C, and 4D, and performs patch detection density control processing (S104), after which the development bias correction process is terminated. In this way, by performing patch detection density control processing after determining the amount of correction for the development bias, it is possible to suppress abrupt fluctuations in image density before and after correcting the development bias.

[0127] Here, the above-described development bias correction process may not be necessary depending on the environment in which the image forming apparatus 100 is used. For example, if the environment in which the image forming apparatus 100 is used is humid, triboelectric charging between the toner and the carrier becomes less likely, and the amount of charge on the toner and the external additive decreases. As a result, the electric field that draws in the toner, generated by the external additive remaining on the photosensitive drums 1A, 1B, 1C, and 1D, decreases, making it less likely for ghost images to occur.

[0128] Based on the above facts, the image forming apparatus 100 may switch between performing development bias correction processing by the control unit 11 and not performing development bias correction processing via user operation via the operation unit 12. In this case, the CPU 400 executes the development bias correction processing when the operation unit 12 switches to the operation of performing development bias correction processing. Also, the CPU 400 does not execute the development bias correction processing when the operation unit 12 switches to the operation of not performing development bias correction processing.

[0129] <Patch detection concentration control process> The patch detection concentration control process performed by the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail below.

[0130] The CPU 400 performs patch detection density control processing to set the laser light intensity of exposure devices 3A, 3B, 3C, and 3D so that the image density is appropriate based on the correction amount of the development bias determined by the processing in step S103 of the development bias correction process described above.

[0131] In this process, the reflective density sensor 140 detects the density of the patch image formed by varying the amount of laser light emitted from the exposure devices 3A, 3B, 3C, and 3D in five steps. The CPU 400 then calculates a linear function by linearly interpolating the amount of laser light emitted from the exposure devices 3A, 3B, 3C, and 3D on the X axis and the density of the patch image detected by the reflective density sensor 140 on the Y axis. Based on the calculated linear function, the CPU 400 determines the amount of laser light that will result in a predetermined target patch image density, and controls the exposure devices 3A, 3B, 3C, and 3D to emit laser light of the determined amount during the image formation process.

[0132] Here, we will explain why the reflective density sensor 140 detects both specular reflection and diffuse reflection.

[0133] In high-density toner patches T with a large amount of toner, the specular reflected P-wave tends to decrease and saturate. In this case, the light intensity of the diffusely reflected S-wave tends to maintain linearity. On the other hand, in low-density toner patches T with a small amount of toner, the diffusely reflected S-wave tends to decrease and saturate. In this case, the light intensity of the specular reflected P-wave tends to maintain linearity. Therefore, in order to accurately detect both low-density and high-density toner patches T, it is desirable to calculate using both specular reflected P-wave and diffusely reflected S-wave in combination.

[0134] Furthermore, the optimal light intensity for detecting the amount of toner deposited on the toner patch T is one that provides good sensitivity to both low concentrations (small amount of toner deposited) and high concentrations (large amount of toner deposited). The absolute value of the reflected light from a toner patch T with a low concentration of toner deposited decreases as the amount of light irradiated onto the toner patch T decreases, and it tends to become difficult to distinguish from gloss unevenness on the surface of the intermediate transfer belt 62. On the other hand, the absolute value of the reflected light from a toner patch T with a high concentration of toner deposited tends to become less sensitive to changes in the concentration of toner deposited on the toner patch T as the amount of light irradiated onto the toner patch T increases.

[0135] Therefore, the appropriate light intensity for detecting the amount of toner deposited on the toner patch T is preferably such that the amount of reflected light from a toner patch T with a low concentration of toner can be distinguished from the gloss unevenness on the surface of the intermediate transfer belt 62. Furthermore, the appropriate light intensity for detecting the amount of toner deposited on the toner patch T is preferably such that the amount of reflected light from a toner patch T with a high concentration of toner has good sensitivity to changes in the concentration of toner deposited on the toner patch T.

[0136] In this way, the CPU 400 adjusts the amount of reflected light from the surface of the intermediate transfer belt 62 where no toner image has been formed so that it reaches the appropriate target light intensity level. For example, the CPU 400 adjusts the light intensity level so that the average amount of reflected light over one rotation of the surface of the intermediate transfer belt 62 is 3.5 ± 0.05 [V]. By adjusting the average amount of reflected light, it becomes possible to properly control the system even if the glossiness of the surface of the intermediate transfer belt 62 changes over time.

[0137] <Effect of preventing the occurrence of ghost images> The effect of preventing the occurrence of ghost images in the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 7 and 8.

[0138] In the image forming apparatus 100, images with an image ratio of 30% were formed on A4-sized sheets S and 200 copies were printed, while replenishing the developer with a toner external additive coating rate of 64% in advance. Subsequently, as shown in Figure 7(a), vertical bands with a main scanning width of 30 mm and a sub-scanning width of 410 mm and an image ratio of 100% were formed on A3-sized sheets S and 5 copies were printed.

[0139] Subsequently, one sheet S with the image shown in Figure 7(b) was printed. Then, the reflectance density of the overlapping area G, enclosed by the dotted line immediately after the solid vertical band image in the 30HT halftone image, and the non-overlapping area where no solid image was formed immediately before the 30HT halftone image was measured using a reflective density sensor 140. Furthermore, the difference in reflectance density between the overlapping area G and the non-overlapping area was calculated, and this difference in reflectance density was used as the halftone reflectance density step (=ghosting severity).

[0140] The reflection density step was compared between two cases: one where the peak voltage Vpp of the development bias was corrected by -0.2kV to 1.2kV during image formation, and another where it was left uncorrected at 1.4kV. As shown in Figure 8, the reflection density step when corrected, as shown in this embodiment, was smaller than the reflection density step when uncorrected, as shown in the conventional method, for each image aspect ratio. This indicates that ghosting was improved when corrected compared to when uncorrected.

[0141] In this embodiment, the developer supply container 91 has a developer supply container memory 90 that stores information regarding the coating rate of the external additive supported on the surface of the toner contained in the developer supply container 91. Furthermore, this embodiment has a control unit 11 that corrects the development bias based on the information stored in the developer supply container memory 90. As a result, it is possible to provide an image forming apparatus 100 that can form good images even if the amount of external additive supported on the surface of the toner varies depending on the lot in which the toner is manufactured.

[0142] (Embodiment 2) The configuration of the image forming apparatus 1000 according to Embodiment 2 of the present invention will be described in detail with reference to Figure 14.

[0143] In Figure 14, parts that have the same configuration as those in Figure 4 are denoted by the same reference numerals, and their descriptions are omitted.

[0144] The image forming apparatus 1000 includes photosensitive drums 1A, 1B, 1C, 1D, charging rollers 2A, 2B, 2C, 2D, exposure devices 3A, 3B, 3C, 3D, developing devices 4A, 4B, 4C, 4D, and fixing device 7. The image forming apparatus 1000 also includes cleaners 8A, 8B, 8C, 8D, replenishment devices 9A, 9B, 9C, 9D, control unit 11, operation unit 12, developing device memory 48, and primary transfer rollers 61A, 61B, 61C, 61D. Furthermore, the image forming apparatus 1000 includes an intermediate transfer belt 62, a secondary transfer unit 65, a developing bias power supply 81, a charging bias power supply 82, a primary transfer bias power supply 83, a secondary transfer bias power supply 84, and a reflective density sensor 140.

[0145] Although Figure 14 omits the description of the photosensitive drums 1B, 1C, 1D and the charging rollers 2B, 2C, 2D, the photosensitive drums 1B, 1C, 1D and the charging rollers 2B, 2C, 2D have the same configuration as the photosensitive drum 1A and the charging roller 2A. The same applies to the exposure units 3B, 3C, 3D, the developing units 4B, 4C, 4D, the cleaners 8B, 8C, 8D, the replenishment units 9B, 9C, 9D, and the primary transfer rollers 61B, 61C, 61D.

[0146] The developing device memory 48, which serves as a storage unit, is provided for each color of toner stored in the developing devices 4A, 4B, 4C, and 4D. The developing device memory 48 is an IC chip or a barcode, etc.

[0147] The developing device memory 48 is capable of communicating with an information reading unit (not shown) of the image forming apparatus 1000. Data is read from and written to the developing device memory 48 via the information reading unit by the CPU 400 of the control unit 11. The developing device memory 48 stores unique information about the toner stored in the developer storage unit 44 of the developing devices 4A, 4B, 4C, and 4D.

[0148] The external additive information determination unit 410 of the CPU 400 of the control unit 11 acquires toner-specific information from the developing device memory 48 by reading it via an information reading unit (not shown) of the image forming apparatus 1000.

[0149] The development bias correction process performed by the image forming apparatus 1000 according to this second embodiment is the same as that shown in Figure 6, so its explanation will be omitted.

[0150] In this embodiment, the developing apparatus 4A, 4B, 4C, and 4D are provided with a developing apparatus memory 48 that stores unique information about the toner stored in the developer storage section 44, and a control unit 11 that corrects the development bias based on the information stored in the developing apparatus memory 48. This makes it possible to provide an image forming apparatus 1000 that can form good images even if the amount of external additives supported on the surface of the toner varies depending on the lot in which the toner is manufactured.

[0151] In this embodiment, the developer replenishment container memory 90 is not provided, but the embodiment is not limited to this configuration, and the developer replenishment container memory 90 may be provided. In this case, the CPU 400 performs the same processing and operation as in Embodiment 1 based on the unique toner information stored in the developer replenishment container memory 90.

[0152] The present invention is not limited to the embodiments described above, and it goes without saying that various modifications are possible without departing from the spirit of the invention.

[0153] In Embodiments 1 and 2 described above, the peak voltage Vpp of the development bias, the blank time t1, and the frequency or duty cycle of the AC bias section were corrected to reduce the amount of toner flying onto the photosensitive drums 1A, 1B, 1C, and 1D. However, the invention is not limited to this, and any two or more of the peak voltage Vpp of the development bias, the blank time t1, the frequency of the AC bias section, and the duty cycle may be corrected to reduce the amount of toner flying onto the photosensitive drums 1A, 1B, 1C, and 1D. [Explanation of Symbols]

[0154] 1A Photosensitive drum 4A Developer 11 Control Unit 41 Developing Sleeves 44 Developer storage section 48 Developer Memory 81 Developer bias power supply 90 Developer Refill Container Measuring Mark 91 Developer refill container 100 Image forming apparatus 1000 Image forming apparatus

Claims

1. An image forming apparatus, An image carrier on which an electrostatic image is formed, A developing apparatus comprising: a developer container for containing a developer including toner and a carrier; and a developer carrier for carrying and transporting the developer contained in the developer container and developing the electrostatic image formed on the image carrier by the toner; A developing bias power supply for applying a developing bias to the developer carrier when developing the electrostatic image using the developing apparatus, A control unit that controls the development bias applied to the developer carrier from the development bias power supply, A toner supply container is detachably attached to the image forming apparatus, contains the toner, and supplies the contained toner to the developing apparatus. A storage unit provided in the toner supply container stores information regarding the coating rate of an external additive supported on the surface of the toner contained in the toner supply container, Equipped with, The control unit, Based on the information stored in the memory unit, the development bias is corrected. An image forming apparatus characterized by the following:

2. The aforementioned developer bias power supply is The developing bias, having a waveform with a period consisting of an AC bias section in which an AC voltage and a DC voltage are superimposed, and a blank section consisting only of a DC voltage following the AC bias section, is applied to the developer carrier. The control unit, Based on the information stored in the memory unit, at least one of the following is corrected: the peak voltage in the AC bias section, the duty cycle in the AC bias section which is the ratio of the electric field that causes the developer to fly from the developer carrier to the image carrier to the electric field that returns the developer from the image carrier to the developer carrier, the frequency of the AC bias section, and the time of the blank section. The image forming apparatus according to feature 1.

3. The control unit further includes an operation unit for switching between correcting the development bias and not correcting it. The control unit, When the operation unit switches to the operation of correcting the development bias, the development bias is corrected based on the information stored in the memory unit. The image forming apparatus according to feature 1.

4. An image forming apparatus, An image carrier on which an electrostatic image is formed, A developing apparatus comprising: a developer container for containing a developer including toner and a carrier; and a developer carrier for carrying and transporting the developer contained in the developer container and developing the electrostatic image formed on the image carrier by the toner; A developing bias power supply for applying a developing bias to the developer carrier when developing the electrostatic image using the developing apparatus, A control unit that controls the development bias applied to the developer carrier from the development bias power supply, A storage unit provided in the developing apparatus stores information regarding the coating rate of an external additive supported on the surface of the toner contained in the developer storage unit, Equipped with, The control unit, Based on the information stored in the memory unit, the development bias is corrected. An image forming apparatus characterized by the following:

5. The aforementioned developer bias power supply is The developing bias, having a waveform with a period consisting of an AC bias section in which an AC voltage and a DC voltage are superimposed, and a blank section consisting only of a DC voltage following the AC bias section, is applied to the developer carrier. The control unit, Based on the information stored in the memory unit, at least one of the following is corrected: the peak voltage in the AC bias section, the duty cycle in the AC bias section which is the ratio of the electric field that causes the developer to fly from the developer carrier to the image carrier to the electric field that returns the developer from the image carrier to the developer carrier, the frequency of the AC bias section, and the time of the blank section. The image forming apparatus according to feature 4.

6. The control unit further includes an operation unit for switching between correcting the development bias and not correcting it. The control unit, When the operation unit switches to the operation of correcting the development bias, the development bias is corrected based on the information stored in the memory unit. The image forming apparatus according to feature 4.

Images