Image forming apparatus

Abstract

Image defects occur due to lot-to-lot variations in the amount of toner additive in the developer replenishment container. [Solution] Information regarding the amount of toner additive in the developer replenishment container is stored in the toner memory, and the transfer bias is controlled based on the information from the toner memory read by the image forming apparatus.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] In an electrophotographic image forming apparatus, when a toner image is formed in a developing portion on a photosensitive drum, a part of inorganic fine particles (external additives) added to the toner is also developed together with the toner. At this time, since the amount of toner developed varies according to the image ratio of the image portion, the amount of external additives developed and transferred to the photosensitive drum also varies according to the image ratio. Although the external additives transferred onto the photosensitive drum together with the toner reach the cleaning portion together with the residual transferred toner via the primary transfer portion, due to their small particle size, they have a large adhesion force to the photosensitive drum and are difficult to remove even with a cleaning member.

[0003] Therefore, the external additives transferred onto the photosensitive drum remain on the photosensitive drum without being cleaned and reach the developing portion again via the charging portion. At this time, in a region where a large amount of external additives remains on the photosensitive drum, the toner is more likely to be developed due to 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 residual external additives on the photosensitive drum, and it may be visually recognized as a ghost image.

[0004] This phenomenon is likely to become apparent when the conditions are such that the toner is easily developed, when the charge amount of the external additives is large, or when images of the same or similar patterns are repeatedly formed.

[0005] In recent years, toners used in electrophotographic image forming apparatuses are required to further reduce energy consumption, and the development of low-temperature fixing toners that can be fixed at low temperatures to an output medium has been promoted. In order to satisfy the low-temperature fixing property of the toner, there is a trade-off relationship with the stress resistance against wear of the toner matrix. For this reason, as in Patent Document Ⅰ, a technique has been proposed to protect the toner matrix by supporting more external additives on the surface of the toner matrix. [Prior art documents] [Patent Documents]

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

[0007] When a large amount of external additives are loaded onto the toner matrix surface, the amount of external additives transferred to the photosensitive drum increases, and the amount of external additives remaining on the photosensitive drum without being cleaned also increases. As a result, the visibility of ghost images caused by differences in the amount of external additives remaining on the photosensitive drum deteriorates.

[0008] On the other hand, because toner manufacturing conditions vary depending on the lot, the amount of external additives supported on the toner matrix fluctuates from lot to lot. Therefore, in lots with a large amount of external additives, the amount of external additives on the toner surface increases, making ghost images more apparent. [Means for solving the problem]

[0009] This invention has been made in view of the above circumstances, and aims to provide an image forming apparatus that can form good images even if the amount of external additive supported on the toner matrix varies from lot to lot during toner manufacturing.

[0010] To achieve the above objective, the present invention provides an image forming apparatus comprising: an image carrier that carries an electrostatic image; a developing device that develops the electrostatic image formed on the image carrier into a toner image using a developer containing an external additive; a supply container detachably provided on the main body of the image forming apparatus for supplying the developer to the developing device; a memory attached to the supply container and storing information regarding the amount of external additive in the developer contained in the supply container; a transfer member that transfers the toner image formed on the image carrier to a transfer material; a power supply that applies a voltage to the transfer member; a detection unit that detects the current flowing through the transfer member; and a control unit that, when not transferring, executes a mode that determines a target voltage to be applied to the transfer member during transfer based on the current flowing through the transfer member when a test voltage is applied to the transfer member and a predetermined target current, wherein the control unit is configured to control the power supply so as to maintain a constant voltage with the target voltage determined in the mode during transfer, and the control unit is configured to change the target current based on information regarding the amount of the external additive stored in the memory. [Effects of the Invention]

[0011] With the above 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 toner matrix varies from lot to lot during toner manufacturing. [Brief explanation of the drawing]

[0012] [Figure 1] Schematic diagram of an image forming apparatus [Figure 2] Cross-sectional view of the image forming unit [Figure 3a] Cross-sectional view of a developing apparatus [Figure 3b] Diagram showing the circulation pathway of the developer. [Figure 4] Cross-sectional view showing the transfer of external additives between toner and carrier. [Figure 5] Cross-sectional perspective view of a developer supply container. [Figure 6] Figure showing a ghost image related to this embodiment. [Figure 7]Figure showing the relationship between the external additive coating rate of toner alone and the external additive coating rate of the developer in the developing device [Figure 8] Table showing the relationship between the external additive coating rate of toner alone for each toner concentration and the external additive coating rate of the developer in the developing device [Figure 9] Figure showing the relationship between the amount of external additive on the photosensitive drum and the primary transfer current [Figure 10] Flowchart showing the procedure for determining the adjustment values in Example 1 [Figure 11] Figure showing the difference in the amount of fine particle adhesion on the photosensitive drum in this example

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below are preferred embodiments of the present invention, and thus are technically preferably limited. However, the scope of the present invention is not limited to these aspects unless there is a description specifically limiting the present invention in the following description.

Example

[0014] <Image forming apparatus> First, the overall configuration and operation of the image forming apparatus according to the present invention will be described. FIG. 1 shows a schematic cross-sectional configuration of the image forming apparatus 100 of this example. The image forming apparatus 100 of this example has four photosensitive drums and is a full-color electrophotographic image forming apparatus using an intermediate transfer method. In this example, the process speed corresponding to the surface movement speed of the photosensitive drum 1 and the intermediate transfer belt 51 is 150 mm / sec.

[0015] The image forming apparatus 100 includes, as a plurality of image forming units, first, second, third, and fourth image forming units (process units) Sa, Sb, Sc, and Sd. Each of the image forming units Sa, Sb, Sc, and Sd is for forming each color of yellow (Y), magenta (M), cyan (C), and black (Bk). In this embodiment, the configurations of the image forming units Sa to Sd are substantially the same except that the colors of the toners used are different. Therefore, hereinafter, when there is no particular need for distinction, the subscripts a, b, c, and d given to the reference numerals in the drawings to represent elements provided for any one of the colors are omitted and described generically.

[0016] The image forming unit S has a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, a charging roller 2 as a primary charging means, a laser scanner 3 as an exposure means, a developing device 4 as a developing means, a drum cleaner 6 as a drum cleaning means, etc. are sequentially arranged along the rotation direction of the photosensitive drum 1. Further, adjacent to the photosensitive drums 1a to 1d of each of the image forming units Sa to Sd, a belt body that can circulate and move, that is, an intermediate transfer belt 51, is arranged as an intermediate transfer member.

[0017] The intermediate transfer belt 51 is stretched over a driving roller 52, a steering roller 55, a secondary transfer inner roller 56, and an upstream regulating roller 58 as a plurality of support members. The steering roller 55 also has a function of applying a stretching force for stretching the intermediate transfer belt 51, and both ends of the steering roller 55 are biased in the substantially left direction of FIG. 1 by a spring biasing means (not shown). The driving force is transmitted to the intermediate transfer belt 51 by the driving roller 52 which is a belt driving means, and the intermediate transfer belt 51 moves in a circulating manner in the direction of the illustrated arrow R3.

[0018] At positions facing the photosensitive drums 1a to 1d on the inner peripheral surface side of the intermediate transfer belt 51, primary transfer rollers 53a to 53d as primary transfer members are arranged. Each of the primary transfer rollers 53a to 53d is biased toward each of the photosensitive drums 1a to 1d via the intermediate transfer belt 51, and primary transfer portions (primary transfer nips) Nia to Nid where each of the photosensitive drums 1a to 1d and the intermediate transfer belt 51 are in contact are formed.

[0019] Furthermore, a secondary transfer outer roller 57, which serves as a secondary transfer member, is positioned on the outer circumferential surface of the intermediate transfer belt 51, facing the secondary transfer inner roller 56. The secondary transfer outer roller 57 contacts the outer circumferential surface of the intermediate transfer belt 51, forming a secondary transfer portion (secondary transfer nip) N2. The secondary transfer high-voltage power supply 571 is configured to apply a secondary transfer voltage to the secondary transfer outer roller 57.

[0020] The images formed on the photosensitive drums 1a to 1d in each image forming section Sa to Sd are sequentially transferred in multiple layers onto an intermediate transfer belt 51 that moves adjacent to each photosensitive drum 1a to 1d. Subsequently, the images transferred onto the intermediate transfer belt 51 are further transferred to a transfer material P such as paper in a secondary transfer section N2.

[0021] The fixing device 7 includes a fixing roller 71 that is rotatably positioned and a pressure roller 72 that rotates while pressing against the fixing roller 71. A heater 73, such as a halogen lamp, is installed inside the fixing roller 71. The surface temperature of the fixing roller 71 is controlled by controlling the voltage supplied to this heater 73. When the transfer material P is transported to the fixing device 7, as the transfer material P passes between the fixing roller 71 and the pressure roller 72, which rotate at a constant speed, the transfer material P is pressurized and heated from both its front and back surfaces at a nearly constant pressure and temperature. As a result, the unfixed toner image on the surface of the transfer material P melts and is fixed to the transfer material P. In this way, a full-color image is formed on the transfer material P.

[0022] <Image Forming Section> Next, Figure 2 shows the details of the image forming unit S. Referring further to Figure 2, the photosensitive drum 1 is rotatably supported by the main body of the image forming apparatus. The photosensitive drum 1 is a cylindrical electrophotographic photoreceptor whose basic structure consists of a conductive substrate 11 such as aluminum and a photoconductive layer 12 formed on its outer circumference. The photosensitive drum 1 has a pivot shaft 13 at its center. The photosensitive drum 1 is rotated by a driving means (not shown) in the direction of the arrow R1 shown in the figure, around the pivot shaft 13. In this embodiment, a φ30 organic photosemiconductor photosensitive drum was used, but an amorphous silicon-based photosensitive drum may also be used.

[0023] A charging roller 2, serving as a primary charging means, is positioned above the photosensitive drum 1 in the diagram. The charging roller 2 contacts the surface of the photosensitive drum 1 and uniformly charges the surface of the photosensitive drum 1 to a predetermined polarity and potential. The charging roller 2 has a conductive core metal 21 positioned in the center, a low-resistance conductive layer 22 formed on its outer circumference, and a medium-resistance conductive layer 23, and is configured as a roller overall. The charging roller 2 is rotatably supported at both ends of the core metal 21 by bearing members (not shown) and is positioned parallel to the photosensitive drum 1. These bearing members at both ends are biased toward the photosensitive drum 1 by pressing means (not shown). As a result, the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. The charging roller 2 rotates in the direction of arrow R2 in the diagram as the photosensitive drum 1 rotates in the direction of arrow R1. A charging bias voltage is applied to the charging roller 2 by a charging bias power supply 24, which serves as a charging bias output means. As a result, in this embodiment, the surface of the photosensitive drum 1 is uniformly charged to -600V.

[0024] A laser scanner 3 is positioned downstream of the charging roller 2 in the rotational direction of the photosensitive drum 1. The laser scanner 3 scans the photosensitive drum 1 by turning the laser light OFF / ON based on image information, thereby exposing it to the photosensitive drum 1. As a result, an electrostatic image (latent image) corresponding to the image information is formed on the photosensitive drum 1. The wavelength of the laser scanner used in this embodiment is λ=780nm, and the resolution is 600dpi.

[0025] A developing device 4 is located downstream of the laser scanner 3 in the rotational direction of the photosensitive drum 1. Details of the developing device 4, which visualizes the electrostatic image formed on the photosensitive drum 1, and the replenishment device 9, which supplies toner to the developing device 4, will be described later.

[0026] A primary transfer roller 53 is positioned below the photosensitive drum 1 in the diagram, downstream of the developing device 4, in the rotational direction of the photosensitive drum 1. The primary transfer roller 53 consists of a core metal 531 and a conductive layer 532 formed in a cylindrical shape on its outer circumferential surface. Both ends of the primary transfer roller 53 are biased toward the photosensitive drum 1 by pressing members (not shown), such as springs. As a result, the conductive layer 532 of the primary transfer roller 53 is pressed against the surface of the photosensitive drum 1 via the intermediate transfer belt 51 with a predetermined pressing force. A primary transfer bias power supply 54, which serves as a primary transfer bias output means, is connected to the core metal 531. A primary transfer section N1 is formed between the photosensitive drum 1 and the primary transfer roller 53. The intermediate transfer belt 51 is sandwiched in the primary transfer section N1. The primary transfer roller 53 contacts the inner circumferential surface of the intermediate transfer belt 51 and rotates as the intermediate transfer belt 51 moves. During image formation, a primary transfer bias voltage is applied to the primary transfer roller 53 by the primary transfer bias power supply 54, which is the opposite polarity (second polarity: positive polarity in this embodiment) to the normal charging polarity (first polarity: negative polarity in this embodiment) of the toner. An electric field is then formed between the primary transfer roller 53 and the photosensitive drum 1 in a direction that moves the toner with the first polarity from the photosensitive drum 1 toward the intermediate transfer belt 51. As a result, the toner image on the photosensitive drum 1 is transferred (primary transfer) to the surface of the intermediate transfer belt 51.

[0027] Toner and other deposits remaining on the surface of the photosensitive drum 1 after the primary transfer process (primary transfer residue toner) are cleaned by the drum cleaner 6. The drum cleaner 6 comprises a cleaning blade 61 as a drum cleaning member, a transport screw 62, and a drum cleaner housing 63. The cleaning blade 61 is brought into contact with the photosensitive drum 1 at a predetermined angle and pressure by a pressurizing means (not shown). As a result, toner and other deposits remaining on the surface of the photosensitive drum 1 are scraped off and removed from the photosensitive drum 1 by the cleaning blade 62 and collected in the drum cleaner housing 63. The collected toner and other deposits are transported by the transport screw 62 and discharged into a waste toner storage section (not shown).

[0028] <Developing equipment> Next, with reference to Figure 3, the developing apparatus 4 will be described in detail. Figures 3a and 3b are a cross-sectional view and a top view of the developing apparatus 4, respectively.

[0029] The developing container 40 of the developing device 4 contains a two-component developer consisting of non-magnetic toner and magnetic carriers, and the weight ratio of non-magnetic toner to the two-component developer, i.e., the toner concentration, is approximately 10 wt%. This ratio should be appropriately adjusted depending on the charge amount of the toner, the carrier particle size, or the configuration and usage conditions of the image forming apparatus, and it is not necessary to adhere to this value.

[0030] Suitable magnetic carriers include, for example, surface-oxidized or unoxidized iron, nickel, cobalt, manganese, chromium, rare earth elements, and other metals, as well as their alloys, or oxide ferrites. The manufacturing method of these magnetic particles is not particularly limited. In this embodiment, ferrite particles coated with silicone resin are used as magnetic carriers. These magnetic carriers have a saturation magnetization of 294 am for an applied magnetic field of 240 kA / m. 2 The resistivity at an electric field strength of 3000 V / cm is 1 × 10¹⁶ / kg. 7~8The coefficient is Ω·cm. In addition, as a magnetic carrier, a resin magnetic carrier manufactured by polymerization using a binder resin, magnetic metal oxide, and non-magnetic metal oxide as starting materials may also be used.

[0031] The volume-average particle size of the magnetic carriers is measured using a laser diffraction particle size distribution analyzer, HEROS (manufactured by JEOL). The measurement conditions involve dividing the particle size range of 0.5 to 350 μm into 32 logarithmic sections and measuring the number of particles in each channel. The median diameter at 50% of the volume is then used as the volume-average particle size. In this example, the volume-average particle size of the magnetic carriers is 50 μm.

[0032] The non-magnetic toner consists of at least a binder, a colorant, and a charge control agent. In this embodiment, a styrene-acrylic resin is used as the binder resin, but resins such as styrene, polyester, and polyethylene can also be used. In this embodiment, phthalocyanine blue is used as the colorant, but carbon black, chrome yellow, Hansa yellow, benzidine yellow, surene yellow, quinoline yellow, permanent orange GTR, pyrazolone orange, and balkan orange may also be used. Alternatively, watch young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, deipon oil red, pyrazolone red, lysol red, rhodamine B lake, lake red C, rose bengal, and aniline blue may also be used. Furthermore, ultramarine blue, chalcoid blue, methylene blue chloride, phthalocyanine green, and malachite green oxalerate may also be used. The colorant may be a single colorant or a combination of various pigments and dyes.

[0033] As a charge control agent, a reinforcing charge control agent may be included as needed. Any known reinforcing charge control agent can be used. For example, nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxyamines, and quaternary ammonium salts (including fluorine-modified quaternary ammonium salts). Also, for example, alkylamides, elemental or compound phosphorus, elemental or compound tungsten, fluorine-based surfactants, metal salicylic acid salts, and metal salts of salicylic acid derivatives.

[0034] Furthermore, the non-magnetic toner may contain wax or external additives. The wax is included to improve release and adhesion from the fixing material during fixing. Examples of waxes that can be used include paraffin wax, carnauba wax, and polyolefin, which are mixed and dispersed in the binder resin before use. In this embodiment, a resin in which the binder, colorant, charge control agent, and wax were mixed and dispersed was pulverized using a mechanical pulverizer.

[0035] Examples of external additive particles include amorphous silica that has undergone hydrophobic treatment, or inorganic oxide fine particles such as titanium dioxide or titanium compounds. It is preferable to control the powder flowability and charge amount of the toner by externally adding these fine particles to the toner matrix. The particle size of the external additive particles 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.

[0036] 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 coating rate of the external additive in the toner, a characteristic feature of the present invention, was measured using ESCA and was found to be 60%.

[0037] <Method for Measuring Coating Rate by ESCA> The external additive coating rate in the present invention is calculated from the atomic weight of silicon derived from silica present on the surface of toner particles, which is measured by ESCA (X-ray photoelectron spectroscopy). ESCA is an analytical method for detecting atoms in a region of several nanometers or less in the depth direction of the sample surface. Therefore, it is possible to detect the atoms on the surface of the toner. As the sample holder, a 75 mm square platen attached to the apparatus (equipped with a screw hole with a diameter of about 1 mm for fixing the sample) was used. Since the screw hole of the platen penetrates, the hole is filled with resin or the like to create a recess for powder measurement with a depth of about 0.5 mm. The measurement sample was packed into the recess with a spatula or the like and smoothed to prepare a sample.

[0038] The ESCA apparatus and measurement conditions are as follows. Apparatus used: PHI5000VersaProbeII manufactured by ULVAC-PHI, Inc. Analysis method: Narrow analysis Measurement conditions: X-ray source: Al-Kα X-ray conditions: 100 μ25W15kV Photoelectron capture angle: 45 PassEnergy: 58.70 eV Measurement range: 300 μm × 200 μm

[0039] Measurement was performed under the above conditions. The analysis method is as follows: First, the peak derived from the C-C bond of the carbon 1s orbital is corrected to 285 eV. Then, from the peak area derived from the silicon 2p orbital where the peak top is detected between 100 eV and 105 eV, the Si amount derived from silica with respect to the total amount of constituent elements is calculated by using the relative sensitivity factor provided by ULVAC-PHI, Inc. Next, the silica alone applied to the toner is measured in the same manner as above, the Si amount derived from silica with respect to the total amount of constituent elements is calculated, and the ratio of the Si amount when the toner is measured to the Si amount when the external additive alone is measured is defined as the silica coating rate in the present invention.

[0040] In this embodiment, 200g of developer D, which was prepared by mixing the above-mentioned toner and carrier at a mixing ratio (toner concentration) of 10 wt%, was put into the developing device.

[0041] The developing device 4 has an opening in the developing area facing the photosensitive drum 1, and a developing sleeve 41 is rotatably positioned so as to be partially exposed to this opening. The developing sleeve 41, which contains a fixed magnet 42 that is a means of generating a magnetic field, rotates in the direction of the arrow in the figure during the developing operation, holding the developer in the developing container in layers and carrying it to the developing area. The developing sleeve 41 then supplies the developer to the developing area facing the photosensitive drum 1 and develops the electrostatic latent image formed on the photosensitive drum 1 with toner. After developing the electrostatic latent image, the developer is carried in accordance with the rotation of the developing sleeve 41 and collected in the developing container. The developing chamber A of the developing container is equipped with a screw 43 (hereinafter referred to as the "developing screw") as a first developer stirring and transporting member. The stirring chamber B is equipped with a screw 44 (hereinafter referred to as the "stirring screw") as a second developer stirring and transporting member. After developing the electrostatic latent image, the developer is circulated within the developing container by screws 43 and 44 and mixed and stirred again. The direction of developer circulation is from the front to the back on the developing screw 43 side (as shown in Figure 3a), and from the back to the front on the agitating screw 44 side. Both the developing screw 43 and the agitating screw 44 have a central shaft diameter of 7 mm and an outer diameter of 14 mm, and rotate at a speed of 300 rpm. The distance between the developing container and each screw is set to 1 mm.

[0042] In this embodiment, the developing sleeve 41 is positioned opposite the photosensitive drum 1 with a gap of 300 μm between them, and is rotatable in the direction of rotation of the photosensitive drum 1 (indicated by the arrow in the figure) and at 180% of the peripheral speed of the photosensitive drum 1. The developing sleeve 41 is formed from a metal such as aluminum or stainless steel into a cylindrical shape, and its surface is subjected to blast treatment, plating, or coating to adjust the developer transportability and triboelectric charging properties. In this embodiment, a metal sleeve with a blast-treated aluminum surface was used.

[0043] A magnet roll 42 with multiple magnetic poles is fixedly installed inside the developing sleeve 41 as a means of generating a magnetic field. In this embodiment, a magnet roll 42 with five magnetic poles is used. The S1 pole is a developer quantity regulating pole that regulates the amount of developer transported to the developing area, the N1 pole is a developing pole that contributes to development, the S2 pole is a transport pole that transports the developer, and the N2 pole is a repulsion pole that peels off the developer supported on the developing sleeve. In addition, N3 is an intake pole that allows the developer sent from the developing screw 43 to be supported on the developing sleeve 41.

[0044] In this embodiment, the developer quantity regulating member is a 1 mm thick flat non-magnetic blade 45, which is arranged opposite the developing sleeve 41 with a uniform gap along its longitudinal direction. The shape of the non-magnetic blade 45 is not limited to a flat shape; the tip may be sharpened to a thickness of approximately 0.3 mm. The shape of this non-magnetic blade, the distance between the developing sleeve 41 and the non-magnetic blade 45, and the size and angle of the developer quantity regulating magnetic pole S1 ensure that the developer carried on the developing sleeve 41 is uniformly coated and transported to the developing area. In this embodiment, the distance between the developing sleeve 41 and the non-magnetic blade 45 is set to 300 μm, and the amount of developer transported to the developing area is regulated to a mass per unit area (M / S) of 30 mg / cm2.

[0045] With the above configuration, the developing sleeve 41 containing a magnet carries the developer in the developing device 4 and transports it to a position opposite the photosensitive drum 1, where a magnetic brush is formed. Then, by applying a suitable developing bias to the developing sleeve 41, the electrostatic latent image on the photosensitive drum 1 is developed. In this embodiment, a voltage consisting of an AC component with a frequency of 10 kHz and a peak-to-peak voltage Vpp of 1.6 kV and a DC component (Vdc) of -450 V was applied from the high-voltage power supply 401, but the values ​​are not limited to these.

[0046] In this embodiment, a permeability sensor 49 is used as a toner concentration detection unit (toner concentration sensor) to detect the mixing ratio of toner and magnetic carriers in the developer in the developing device. The permeability sensor determines the toner concentration by detecting the apparent change in the permeability of the developer, which decreases as the toner concentration of the developer increases (inductance detection). In this embodiment, as shown in Figure 3b, the toner concentration sensor is located downstream of the stirring chamber B, on the side of the developing device. It is preferable that the toner concentration sensor is positioned so that there is always enough developer to detect the permeability. Furthermore, the position is determined so that the developer in the area detected by the permeability sensor is always subjected to the stirring action of the stirring screw 44. The detected value of the toner concentration sensor is output to a replenishment control unit controlled by the CPU 400.

[0047] To calculate the toner concentration, the output values ​​of the magnetic permeability sensor are sampled at multiple points, averaged, and the vibration component caused by the rotation period of the stirring screw 44 is canceled out to extract the DC component of the magnetic permeability sensor's output value. Then, the relationship between this value and the toner concentration is investigated in advance, and the toner concentration is calculated by referring to a prepared table.

[0048] Furthermore, a video count type counter (not shown), which is a means for calculating the amount of toner consumed for each image, is also provided. The level of the output signal of the image signal processing circuit (not shown) is counted for each pixel. The video count is accumulated by the counter for each pixel to calculate the video count for each image. The video count corresponds to the amount of toner consumed from the developer 4 to form one toner image for each image.

[0049] Based on the output of the toner density sensor 49 and the video count, the CPU 400 determines the amount of toner to be supplied using the toner supply control method described later, and supplies a predetermined amount of toner to the developer 4 using the toner supply means described later. In other words, in this embodiment, the supply control is performed so that the output of the toner density sensor 49 reaches a predetermined target toner density (target value of the density sensor). In addition, in this embodiment, a patch image is formed on the drum every predetermined number of sheets, and the target toner density (target value of the density sensor) during toner supply control is changed so that the density of this patch image approaches a predetermined image density.

[0050] <Toner replenishment device> Next, the toner replenishment means (replenishment device 9) in this embodiment will be described. The developer replenishment container 91 (toner bottle) in Figure 5 can be easily attached to and detached from the mounting section 910 of the image forming apparatus. When the developer replenishment container 91 is mounted, it communicates with the discharge port (discharge hole) (not shown) of the developer replenishment container 91, and the developer discharged from the developer replenishment container 91 is supplied to the developer unit 4 through the developer receiving port 47. The developer sealed in the developer replenishment container 91 is a two-component developer in which a negatively charged non-magnetic toner and a magnetic carrier are mixed. Furthermore, the developer sealed in the developer replenishment container 91 uses the same toner and carrier as the developer sealed in the developer unit 4. The developer in the developer unit 4 is manufactured by mixing toner and carrier at a toner concentration of 10 wt%. In contrast, the developer sealed in the developer replenishment container 91 is manufactured by mixing toner and carrier at a carrier concentration of 9 wt% (toner concentration of approximately 90 wt%).

[0051] The developer supply container 91 according to this embodiment is equipped with a storage means (non-volatile memory) for each color. The storage means can be an IC chip, a barcode, or the like, and is preferably one that can be automatically read by the information reading means on the main unit. In this embodiment, the toner memory 90, which is the storage means, is installed on the front of the developer supply container 91, and data can be read and written from the CPU 400 of the image forming apparatus. The image forming apparatus is provided with an information reading means (not shown) for reading information from the memory, and is configured to communicate with the memory tag when the developer supply container is attached to the image forming apparatus.

[0052] The toner memory 90 stores information specific to each developer replenishment container. Examples of this specific information include the toner's manufacturing date, manufacturing lot, and the characteristics of the external additives. In Example 1, this includes at least the external additive coating rate at the time of toner manufacturing.

[0053] <Explanation of the ghost image> The developer used in this invention is a dry two-component developer containing toner and a carrier to which negative polarity fine particles (external additive) with the same polarity as the charge polarity of the toner are added. As described above, the external additive in this embodiment contains at least titanium dioxide and amorphous silica (silica) in order to suitably control the powder flow characteristics and charge characteristics of the toner.

[0054] In the development process, in which this developer is developed according to the electrostatic latent image formed on the photosensitive drum 1, the toner is mainly developed in the image area (the bright potential area of ​​the electrostatic latent image) of the developer carried on the developing sleeve 41 in the developing device 4.

[0055] At this time, external additives with the same charge polarity as the toner, which are negatively polarized, are also developed simultaneously. In addition, some external additives added to the toner lose their adhesion to the toner due to agitation in the developing device, and some external additives separate from the toner. These external additives, like the toner, are negatively polarized and are easily developed in the image area, so the amount of external additive developed in the image area of ​​the photosensitive drum is greater than in the non-image area. The toner and external additives developed on the photosensitive drum are first transferred onto the intermediate transfer belt in the transfer process, but some of the toner and external additives with small particle sizes and high non-electrostatic adhesion remain on the photosensitive drum without being transferred.

[0056] Next, the remaining toner and external additives that reach the cleaning process are cleaned by the cleaning component, but the external additives remain on the photosensitive drum 1 because they have small particle sizes and strong adhesion to the photosensitive drum 1, and are not completely cleaned.

[0057] When the external additive reaches the charging process, the negative charge received by the particles themselves and the charging voltage applied by the charging roller creates an electric field between the external additive particles attached to the photosensitive drum 1 that draws in toner. The electric field formed between the external additive particles in a direction that draws in toner becomes stronger when there is a large amount of external additive attached to the photosensitive drum 1.

[0058] Figure 6 illustrates the difference in the amount of external additives adhering to the photosensitive drum. The image shown in Figure 6-A consists of a vertical band with a main scanning width of 30 mm and a sub-scanning width of 200 mm, with an image ratio of 100%, and a horizontal band downstream of the vertical band with a main scanning width of 210 mm and a sub-scanning width of 50 mm, with an image ratio of 30%. In the printing area, a large amount of external additives are supplied to the photosensitive drum along with the toner, resulting in a large amount of external additives remaining on the drum. In contrast, in the non-printing area, no toner image is formed, so toner is not supplied, and the amount of external additives adhering is small.

[0059] When the difference in the amount of external additive adhering to the printed and unprinted areas on the photosensitive drum becomes large, a difference also occurs in the force that draws in the toner in the areas with external additives. As a result, the electric field formed by the external additive is stronger in the printed area during the next image formation, making it easier for the toner to be drawn in. When the same or similar image patterns are formed continuously, these processes continue indefinitely. Consequently, the amount of external additive accumulated in the printed area on the photosensitive drum 1 increases, resulting in a greater amount of toner being developed. As a result, when forming a uniform image such as a halftone image, a density difference occurs between the printed and unprinted areas, which is visible as a ghost as shown in Figure 6-B.

[0060] As described 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 drum 1. Frequent replenishment of developer with a high proportion of external additives into the developing device causes the concentration of external additives in the developer in the developing unit 4 to rise excessively, resulting in a large amount of external additives being developed along with the toner, increasing the risk of the ghosting images described above. In other words, the higher the amount of external additives in the toner, the higher the risk of ghosting images. As mentioned above, the amount of external additives in the toner is defined by the coverage rate of the external additive silica in the toner, as measured by ESCA, and in this embodiment, the silica coverage rate at the center of the mass production variation of the toner alone is 60%.

[0061] As shown in Figure 4, in a two-component developer consisting of toner and carrier, contact between the toner and carrier causes the external additive supported on the toner surface to migrate to the carrier, and the toner and carrier as a whole share the total amount of external additive. Therefore, when the toner concentration is low relative to a certain amount of carrier, that is, when the number of toner particles is small, the amount of carrier increases relative to the toner, so the amount of external additive that migrates to the carrier increases, and the amount of external additive supported per toner particle decreases.

[0062] As mentioned above, in a two-component developer consisting of toner and carrier, contact between the toner and carrier causes the external additive supported on the toner surface to migrate to the carrier, resulting in a shared total amount of external additive between the toner and carrier, creating a certain equilibrium relationship. For example, if the external additive coverage rate of the toner alone is 60%, and the toner concentration of the developer consisting of toner and carrier is 10%, then the external additive coverage rate of the toner in the developer unit 4 will be 58%. This indicates that 2% of the 60% external additive coverage rate of the toner alone has migrated to the carrier surface.

[0063] In this embodiment, when the toner's external additive coating rate in the developer within the developer unit 4 reaches 61%, the amount of external additive adhering to the photosensitive drum 1 becomes excessive, and ghost images become apparent. In other words, at the center of mass production variation, the toner's external additive coating rate in the developer within the developer unit 4 is 58%, so ghost images do not occur.

[0064] However, in the toner manufacturing process, variations in manufacturing conditions can cause fluctuations in the external additive coating rate of the toner itself. Specifically, the external additive coating rate of the toner itself can vary from 56% to 64%. Figure 7 shows the relationship between the external additive coating rate of the toner itself and the external additive coating rate of the developer in the developer unit at a toner concentration of 10%, and Figure 8 is a table showing the relationship between the "external additive coating rate of the toner itself" and the "external additive coating rate of the developer in the developer unit" for each toner concentration. The numbers in the table in Figure 8 represent the "external additive coating rate of the toner in the developer in the developer unit."

[0065] Figure 7 shows that with a toner concentration of 10%, the toner coating rate in the developer within the developer unit 4 varies from 54% to 62%. Depending on variations in manufacturing conditions during the toner manufacturing process, the coating rate may exceed the threshold of 61% at which ghost images occur, resulting in abnormal images.

[0066] <Toner density control> Figure 2 is a block diagram showing the control system of the image forming apparatus 100 and the developing apparatus 4.

[0067] The CPU 400 is connected to a toner density control unit 410, a toner density calculation unit 420, and a developer supply container memory 90.

[0068] The toner concentration output obtained by the toner concentration sensor 49 of the developer unit 4 is calculated by the toner concentration calculation unit 420. Furthermore, the toner concentration control unit 410 can determine the target toner concentration during image forming apparatus operation from the information on the toner itself stored in the developer supply container memory 90. In this embodiment, the toner concentration in the developer unit is controlled so as not to exceed 61%, which is the threshold for the coverage rate of the external additive that causes ghost images. In this embodiment, the upper and lower limits of the toner concentration are controlled so as not to exceed the toner concentration in the shaded area in Figure 8. That is, the CPU 400 limits changes to the target toner concentration so that the toner concentration falls between the upper and lower limits based on the detection result of the toner concentration sensor 49. For example, when using a developer supply container 91 containing developer from a manufacturing lot with a coverage rate of 62% for the external additive of the toner itself, the upper limit of the toner concentration in the developer unit is set to 11%. Also, in this embodiment, the lower limit of the toner concentration in the developer unit is set so as not to fall below a predetermined lower limit for the coverage rate of the external additive.

[0069] Specifically, during the toner manufacturing process, the coating rate of the external additive to each individual toner is measured in advance, and the data of the coating rate of the external additive to the toner contained in the developer replenishment container 91 is stored in the memory tag when the toner is filled. As a result, the coating rate of the external additive to the toner is measured for each toner manufacturing lot, and the same coating rate is stored in the memory tag of the developer replenishment container 91 filled with toner from the same manufacturing lot.

[0070] Based on the information regarding the external additive coating rate of the toner stored in the developer supply container memory 90, it is possible to estimate the external additive coating rate of the toner supplied to the developer unit 4 and determine whether or not ghost images will occur due to variations in the toner lot.

[0071] Figure 9 is a graph showing the primary transfer current and the difference in the amount of fine particles adhering to the printed and unprinted areas on the photosensitive drum after primary transfer NIP. The solid line represents the case when the external additive coating rate is 62%, and the dashed line represents the case when the external additive coating rate is 54%. As shown in Figure 6, when the external additive coating rate is high, the difference in the amount of external additive adhering to the printed and unprinted areas on the drum becomes large. Also, increasing the primary transfer current reduces both the difference in the amount of external additive adhering to the drum.

[0072] As described above, an increase in the coating rate of toner with external additives in the developer leads to a larger difference in the amount of external additives adhering to the printed and non-printed areas on the photosensitive drum, which is the main cause of ghost images. Therefore, by reducing the difference in the amount of external additives adhering to the photosensitive drum through one-turn bias control according to the coating rate of toner with external additives in the developer, the occurrence of ghost images can be reduced.

[0073] Next, the operation of the adjustment mode in this embodiment will be described. Figure 10 is a flowchart illustrating the general procedure of the adjustment mode in this embodiment.

[0074] First, the CPU 400 obtains job information from an operation unit (not shown) and starts the job operation (S101). Next, the CPU 400 reads the developer replenishment container memory 90 (S102) and obtains toner lot information to get information on the coating rate of the toner cartridge (S103).

[0075] Next, CPU400 calculates the primary transfer target current from the following formula (1) based on the acquired developer information (S104). Reference primary transcription target current x read external additive coverage rate / reference external additive coverage rate…(1)

[0076] Here, the "read external additive coating rate" in the calculation formula (1) is determined from the table in FIG. 8. That is, the CPU 400 obtains the toner concentration in the current developing device by the toner concentration sensor 49. Then, based on this toner concentration and the information on the external additive coating rate of the toner alone obtained in S103, the "external additive coating rate of the developer in the developing device" is obtained from the table in FIG. 8. This is the "read external additive coating rate" in the calculation formula (1).

[0077] For example, when the reference primary transfer target current is 20 μA, the reference external additive coating rate is 50%, and the read external additive coating rate is 65%, the primary transfer target current becomes 26 μA.

[0078] Next, information regarding the electrical resistance of the primary transfer unit is obtained by performing ATVC (Active Transfer Voltage Control) control with the calculated primary target current value. Then, the primary transfer voltage applied during image formation is determined (S105, S106). Details of the ATVC control will be described later.

[0079] Thereafter, the CPU 400 repeats the operation of S107 until all the images of the job are output.

[0080] FIG. 11 is a table showing the amount of fine particles attached to the drum and the ghost image determination. It can be seen that the generation of ghost images can be suppressed by the difference in the amount of fine particles attached to the photosensitive drum in this embodiment.

[0081] <ATVC Control> In this embodiment, the primary transfer voltage applied during image formation is configured to perform constant voltage control so as to become a predetermined target voltage. The target voltage of the primary transfer voltage applied at this time is determined by ATVC control. That is, the CPU 400 is configured to execute a mode (ATVC control) for determining the target voltage applied during transfer.

[0082] ATVC control is a mode performed when no transfer is occurring (when no image is being formed), and it performs the following operations. Specifically, when no transfer is occurring, a test voltage is applied to the primary transfer roller 53 with no paper in the primary transfer section, and the current flowing through the primary transfer roller 53 at this time is detected by a current detection means 54b provided on the high-voltage substrate of the primary transfer bias power supply 54. The detection result of the current detection means 54b determines a voltage value (roller-assigned voltage) Vb that becomes a predetermined target current. The CPU 400 then sets Vb + Vp, which is Vb + Vp plus a predetermined paper-assigned voltage Vp set for each paper type, as the target voltage for transfer.

[0083] Based on the above, information regarding the lot variation in the toner's external additive coating rate during the toner manufacturing process is stored in the developer replenishment container memory 90. Then, based on the stored information, if the toner's external additive coating rate is high (a large amount of external additive), the target current can be increased to prevent ghost images.

[0084] In this embodiment, an example was described in which information regarding the coating rate of the external additive is stored in the developer replenishment container memory 90, but the invention is not limited to this. For example, only information regarding the manufacturing lot may be stored in the developer replenishment container memory 90. The relationship between the manufacturing lot and the coating rate of the external additive may be stored in a memory provided on the main unit, and the transfer current may be determined by referring to this information.

[0085] Furthermore, in this embodiment, the primary target current was determined by calculating the assumed "external additive coating rate of the toner in the developer" based on the "toner concentration in the developer" and the "external additive coating rate of the toner alone" from Figure 8, but this is not the only way. To simplify control, the "external additive coating rate of the toner in the developer" may be considered constant as equal to the "external additive coating rate of the toner alone". In this case, the calculation can be done using the formula: standard primary transfer target current x external additive coating rate of the toner alone / standard external additive coating rate. [Explanation of Symbols]

[0086] 1 Photosensitive drum 2 Charging rollers 3. Laser Scanner 4. Developing device 41 Developing Sleeves 42 Magnetic Rolls 43 Developer Screw 44 Stirring screw 45 Non-magnetic blades 49 Toner concentration sensor 51 Intermediate transfer belt 52 Drive rollers 53 Primary transfer roller 54 Primary Transfer Bias Power Supply 55 Steering Roller 56 Secondary transfer inner roller 57 Secondary transfer outer roller 6 Drum Cleaner 61 Cleaning Blade 71 Fixing roller 72 Pressure rollers 73 Heater 9 Supply device 90 Toner Memory 91 Developer refill container 400 CPU

Claims

1. An image carrier that holds an electrostatic image, A developing apparatus for developing an electrostatic image formed on the image carrier into a toner image using a developer containing an external additive, A supply container for supplying developer to the developing apparatus is detachably attached to the main body of the image forming apparatus, A memory attached to the supply container, which stores information regarding the amount of external additives for the developer contained in the supply container, A transfer member for transferring a toner image formed on the image carrier to a transfer material, A power supply for applying voltage to the transfer member, A detection unit for detecting the current flowing through the transfer member, The system includes a control unit that, when not transferring, executes a mode that determines a target voltage to be applied to the transfer member during transfer, based on the current flowing through the transfer member when a test voltage is applied to the transfer member and a predetermined target current. In an image forming apparatus, the control unit is configured to control the power supply so as to maintain a constant voltage at a target voltage determined by the mode during transfer, The image forming apparatus is characterized in that the control unit is configured to change the target current based on information regarding the amount of the external additive stored in the memory.

2. The image forming apparatus according to claim 1, characterized in that the control unit, based on information regarding the amount of the external additive stored in the memory, sets the target current to a first current when the amount of the external additive relative to the toner contained in the supply container is a first predetermined amount, and changes the target current to a second current that is greater than the first current when the amount of the external additive relative to the toner contained in the supply container is a second predetermined amount greater than the first predetermined amount.

3. The image forming apparatus according to claim 1 or 2, further comprising a density detection unit for detecting information regarding the toner concentration in the developing apparatus, wherein the control unit changes the target current based on the detection result of the density detection unit and information regarding the amount of the external additive stored in the memory.

4. The image forming apparatus according to any one of claims 1 to 3, characterized in that the information is information relating to the manufacturing lot of the toner.

5. The image forming apparatus according to any one of claims 1 to 3, characterized in that the information is information relating to the coating rate of the fine particles on the toner.

6. The image forming apparatus according to any one of claims 3 to 5, characterized in that the control unit is configured to control the amount of developer supplied from the supply container based on the detection result of the density detection unit, and to control the amount of developer supplied from the supply container based on information regarding the amount of the external additive stored in the memory so that the toner concentration in the developing apparatus does not exceed a predetermined upper limit.

7. The image forming apparatus according to claim 6, characterized in that the control unit controls the upper limit of the toner concentration in the developing apparatus to a first upper limit when the amount of the external additive relative to the toner contained in the replenishment container is a first predetermined amount, based on information regarding the amount of the external additive stored in the memory, and controls the upper limit of the toner concentration in the developing apparatus to a second upper limit lower than the first upper limit when the amount of the external additive relative to the toner contained in the replenishment container is a second predetermined amount greater than the first predetermined amount.

8. The image forming apparatus according to any one of claims 3 to 5, characterized in that the control unit is configured to control the amount of developer supplied from the supply container based on the detection result of the density detection unit, and to control the amount of developer supplied from the supply container based on information regarding the amount of the external additive stored in the memory so that the toner concentration in the developing apparatus does not fall below a predetermined lower limit.

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