Image forming apparatus

Abstract

To provide an image forming apparatus capable of forming an excellent image even when the amount of an external additive carried on the surface of toner is fluctuated by a lot at the time of manufacturing the toner.SOLUTION: The image forming apparatus includes a developing unit configured to develop an electrostatic image formed on an image bearing member with toner, the developing unit including an image bearing member, a developer accommodating portion configured to accommodate a developer including toner and a carrier, and a developer carrying member configured to carry and convey the developer, a detecting unit configured to detect a toner concentration of the developer accommodated in the developing unit, a control unit configured to control the toner concentration of the developer in the developing unit based on a result detected by the detecting unit, the image forming apparatus includes a developer supply container that stores a developer containing a toner having fine particles attached to a surface thereof and supplies the developer to a developing unit, and a storage unit that is provided in the developer supply container and stores information specific to the toner stored in the developer supply container.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine that uses an electrophotographic system. [Background technology]

[0002] In an electrophotographic image forming apparatus, when a latent image formed on a photosensitive drum is developed with toner in a developing unit, some of the inorganic fine particles (hereinafter referred to as external additives) added to the toner are also developed. The external additives developed on the photosensitive drum have a smaller particle size than the toner, so they are difficult to remove even when passed through a cleaning unit and may remain on the photosensitive drum.

[0003] In this case, when the area where the external additives remain on the photosensitive drum reaches the developing unit again, the toner is more likely to be developed by the electric field formed by the fine particles. Therefore, when a uniform image such as a halftone image is formed, the difference in the amount of external additives remaining on the photosensitive drum may cause density differences, which may be visually recognized as ghost images.

[0004] Therefore, a technology has been proposed in which the photosensitive drum is rotated while the development bias applied to the developer holder is higher than that during image formation, and external additives in the developer unit are discharged onto the photosensitive drum when no image is being formed (Patent Document 1).

[0005] In recent years, when toner used in electrophotographic image forming apparatuses is required to have low-temperature fixability, which allows it to be fixed to recording media at low temperatures, there is a trade-off between durability and stability against wear of the toner surface, etc. For this reason, a technology has been proposed in which a large amount of external additives is carried on the toner surface (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-66547 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-139063 Summary of the Invention [Problem to be solved by the invention]

[0007] However, if the manufacturing conditions vary depending on the toner production lot, the amount of external additive carried on the toner surface may vary. For example, if the amount of external additive carried on the toner surface increases, the amount of external additive remaining on the photosensitive drum without being cleaned also increases, which deteriorates the visibility of ghost images caused by differences in the amount of external additive remaining on the photosensitive drum. On the other hand, if the amount of external additive carried on the toner surface decreases, the toner concentration will be too low, which will deteriorate the developability of the toner on the photosensitive drum.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that can form good images even if the amount of external additive carried on the toner surface varies depending on the lot during toner production. [Means for solving the problem]

[0009] A typical configuration of the present invention includes a developing means including an image carrier, a developer storage section that stores developer containing toner and a carrier, and a developer carrier that carries and transports the developer, and that develops an electrostatic image formed on the image carrier with toner, a detection means that detects the toner concentration of the developer stored in the developing means, a control means that controls the toner concentration of the developer in the developing means based on the results detected by the detection means, a developer supply container that is detachably attached to the image forming apparatus, stores developer containing toner having fine particles adhered to its surface, and supplies the developer to the developing means, and a memory means that is provided in the developer supply container and stores information specific to the toner stored in the developer supply container, and the control means sets the toner concentration of the developer in the developing means based on the information stored in the memory means. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an image forming apparatus that can form a good image even if the amount of external additive carried on the toner surface varies depending on the lot during toner production. [Brief explanation of the drawings]

[0011] [Figure 1] Image forming device schematic diagram [Figure 2] Cross-sectional view of the image forming unit [Figure 3] (a) Cross-sectional view of the developing device, (b) Top view of the developing device [Figure 4] Cross-sectional view showing the transfer of external additives between toner and carrier [Figure 5] A perspective view of a developer supply container [Figure 6] (a)(b) Ghost image [Figure 7] FIG. 10 is a diagram showing the relationship between the external additive coverage of the toner itself and the external additive coverage of the developer in the developing device. [Figure 8] FIG. 10 is a table showing the relationship between the external additive coverage rate of the toner itself and the external additive coverage rate of the toner in the developer in the developing device for each toner concentration. [Figure 9] Flowchart showing a toner concentration calculation method DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments described below are preferred embodiments of the present invention, and therefore have technically preferable limitations, but the scope of the present invention is not limited to these aspects unless otherwise specified in the following description to the effect that the present invention is limited.

[0013] Example 1 <Image forming device> First, the overall configuration and operation of an image forming apparatus according to the present invention will be described. Figure 1 shows a schematic cross-sectional configuration of an image forming apparatus 100 according to this embodiment. The image forming apparatus 100 according to this embodiment is a full-color electrophotographic image forming apparatus having four photosensitive drums and employing an intermediate transfer system. In this embodiment, the process speed, which corresponds to the surface movement speed of the photosensitive drums 1 and intermediate transfer belt 51, is 150 mm / sec.

[0014] The image forming apparatus 100 has a plurality of image forming units, namely, first, second, third, and fourth image forming units (process units) Sa, Sb, Sc, and Sd. Each image forming unit Sa, Sb, Sc, and Sd is for forming a corresponding color: yellow (Y), magenta (M), cyan (C), and black (Bk). In this embodiment, the configurations of the image forming units Sa to Sd are essentially the same except for the different colors of toner used. Therefore, hereinafter, unless otherwise required, the subscripts a, b, c, and d, which are added to the reference numerals in the drawings to indicate that the element is provided for a particular color, will be omitted and the description will be generalized.

[0015] 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 arranged in this order along the rotation direction of the photosensitive drum 1. In addition, adjacent to the photosensitive drums 1a to 1d of each of the image forming units Sa to Sd, a rotatable belt member as an intermediate transfer member, i.e., an intermediate transfer belt 51, is arranged.

[0016] The intermediate transfer belt 51 is stretched over a plurality of support members, including a drive roller 52, a steering roller 55, a secondary transfer inner roller 56, and an upstream regulating roller 58. The steering roller 55 also functions to apply a tensioning force for tensioning the intermediate transfer belt 51. Specifically, both ends of the steering roller 55 are biased substantially leftward in FIG. 1 (in a direction away from the drive roller 52) by spring biasing means (not shown). The drive force is transmitted to the intermediate transfer belt 51 by the drive roller 52, which serves as a belt driving means, and the intermediate transfer belt 51 moves in a direction indicated by an arrow R3 in the drawing.

[0017] Primary transfer rollers 53a to 53d as primary transfer members are arranged at positions facing the photosensitive drums 1a to 1d on the inner circumferential surface side of the intermediate transfer belt 51. The primary transfer rollers 53a to 53d are urged toward the photosensitive drums 1a to 1d via the intermediate transfer belt 51, and primary transfer portions (primary transfer nips) N1a to N1d are formed where the photosensitive drums 1a to 1d come into contact with the intermediate transfer belt 51.

[0018] Furthermore, a secondary transfer outer roller 57 as a secondary transfer member is disposed at a position facing the secondary transfer inner roller 56 on the outer peripheral surface side of the intermediate transfer belt 51. The secondary transfer outer roller 57 comes into contact with the outer peripheral surface of the intermediate transfer belt 51, forming a secondary transfer portion (secondary transfer nip) N2.

[0019] The images formed on the photosensitive drums 1a to 1d at the image forming stations Sa to Sd are sequentially transferred in multiple layers onto an intermediate transfer belt 51 that moves adjacent to the photosensitive drums 1a to 1d. After that, the images transferred onto the intermediate transfer belt 51 are further transferred onto a transfer material P such as paper at a secondary transfer station N2.

[0020] The transfer material P such as paper is fed one sheet at a time from the feed cassette 81 by the feed roller 82 and conveyed to the registration roller pair 83. The registration roller pair 83 stops the leading edge of the transfer material P to correct skew, and resumes conveyance of the transfer material P in accordance with the progress of the image formation operation, which is the toner image formation process by the image forming unit.

[0021] The fixing device 7 has a rotatably disposed fixing roller 71 and a pressure roller 72 that rotates while being in pressure contact with the fixing roller 71. A heater 73 such as a halogen lamp is disposed inside the fixing roller 71. The temperature of the surface of the fixing roller 71 is adjusted by controlling the voltage supplied to the heater 73. When the transfer material P is conveyed 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 the front and back sides with a substantially constant pressure and temperature. As a result, the unfixed toner image on the surface of the transfer material P is melted and 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, FIG. 2 shows the image forming unit S in detail. Further explaining with reference to FIG. 2, the photosensitive drum 1 is rotatably supported by the image forming apparatus main body. The photosensitive drum 1 is a cylindrical electrophotographic photosensitive member basically composed of a conductive substrate 11 made of aluminum or the like and a photoconductive layer 12 formed on the outer periphery of the substrate. The photosensitive drum 1 has a support shaft 13 at its center. The photosensitive drum 1 is driven to rotate around the support shaft 13 in the direction of arrow R1 in the figure by a driving means (not shown). In this embodiment, a φ30 organic photosensitive semiconductor photosensitive drum is used, but an amorphous silicon-based photosensitive drum may also be used.

[0023] A charging roller 2 serving as a primary charging means is disposed above the photosensitive drum 1 in the figure. 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 21 disposed at the center, a low-resistance conductive layer 22 formed on its outer periphery, and a medium-resistance conductive layer 23, forming an overall roller-like configuration. The charging roller 2 is rotatably supported at both ends of the core 21 by bearing members (not shown) and is disposed parallel to the photosensitive drum 1. These bearing members at both ends are biased toward the photosensitive drum 1 by pressing means (not shown). This causes the charging roller 2 to be pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. The charging roller 2 is rotated in the direction of arrow R2 in accordance with the rotation of the photosensitive drum 1 in the direction of arrow R1 in the figure. A charging bias voltage is applied to the charging roller 2 by a charging bias power supply 24 serving as 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 disposed downstream of the charging roller 2 in the rotation direction of the photosensitive drum 1. The laser scanner 3 scans while turning a laser beam on and off based on image information, exposing the surface of 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 λ of the laser scanner used in this embodiment is 780 nm, and the resolution is 600 dpi.

[0025] A developing device 4 is disposed downstream of the laser scanner 3 in the rotation 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 toner supply device 9, which supplies toner to the developing device 4, will be described later.

[0026] A primary transfer roller 53 is disposed below the photosensitive drum 1, downstream of the developing device 4 in the direction of rotation of the photosensitive drum 1. The primary transfer roller 53 is composed of a core metal 531 and a cylindrical conductive layer 532 formed on the outer circumferential surface of the core metal 531. 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 serving as a primary transfer bias output means is connected to the core metal 531. A primary transfer portion 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 portion N1. The primary transfer roller 53 contacts the inner circumferential surface of the intermediate transfer belt 51 and rotates in accordance with the movement of the intermediate transfer belt 51. During image formation, a primary transfer bias voltage of a polarity (second polarity: positive polarity in this embodiment) opposite to the normal charging polarity of the toner (first polarity: negative polarity in this embodiment) is applied to the primary transfer roller 53 by a primary transfer bias power supply 54. An electric field is then formed between the primary transfer roller 53 and the photosensitive drum 1 in a direction that moves the toner of 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) onto the surface of the intermediate transfer belt 51.

[0027] Adherents such as toner remaining on the surface of the photosensitive drum 1 after the primary transfer process (primary transfer residual toner) are cleaned by a drum cleaner 6. The drum cleaner 6 has a cleaning blade 61 as a drum cleaning member, a conveying 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 pressure means (not shown). As a result, the toner remaining on the surface of the photosensitive drum 1 is scraped off and removed from the photosensitive drum 1 by the cleaning blade 61, and is collected in the drum cleaner housing 63. The collected toner is transported by the conveying screw 62 and discharged into a waste toner storage unit (not shown).

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

[0029] The developing device 4 has a developer container 40 as a developer container that contains a two-component developer containing non-magnetic toner and magnetic carrier. Here, the mixture ratio of the two-component developer contained in the developer container 40 is approximately 1:9 by weight. In other words, the weight ratio of non-magnetic toner to the two-component developer contained in the developer container 40, i.e., the toner concentration, is approximately 10 wt%. This ratio should be appropriately adjusted depending on the charge amount of the toner, the particle size of the carrier, or the configuration and usage conditions of the image forming apparatus, and does not necessarily have to follow this numerical value.

[0030] As the magnetic carrier, for example, surface-oxidized or unoxidized metals such as iron, nickel, cobalt, manganese, chromium, rare earth metals, and their alloys or oxide ferrites can be suitably used, and the manufacturing method of these magnetic particles is not particularly limited. In this embodiment, ferrite particles coated with silicone resin are used as the magnetic carrier. This magnetic carrier has a saturation magnetization of 294 am when a magnetic field of 240 kA / m is applied. 2 / kg, and the specific resistance at an electric field strength of 3000V / cm is 1×10 7~8 In addition, the magnetic carrier may be a resin magnetic carrier produced by polymerization using a binder resin, a magnetic metal oxide, and a non-magnetic metal oxide as starting materials.

[0031] The volume average particle size of the magnetic carrier is measured using a laser diffraction particle size distribution analyzer HEROS (manufactured by JEOL Ltd.) by dividing the particle size range of 0.5 to 350 μm by volume into 32 logarithmic divisions, and the number of particles in each channel is measured.The median diameter at 50% volume from the measurement results is then taken as the volume average particle size of the magnetic carrier.The volume average particle size of the magnetic carrier in this example is 50 μm.

[0032] The non-magnetic toner is composed 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 styrene-based, polyester-based, or polyethylene-based resins can also be used. Phthalocyanine blue is used as the colorant in this embodiment. However, various pigments and dyes, such as carbon black, chrome yellow, Hansa yellow, benzidine yellow, threne yellow, quinoline yellow, Permanent Orange GTR, pyrazolone orange, Vulcan orange, Watch Young Red, Permanent Red, Brillian Carmine 3B, Brillian Carmine 6B, Daypon Oil Red, pyrazolone red, lithol red, rhodamine B lake, lake red C, rose bengal, aniline blue, ultramarine blue, chalcoeol blue, methylene blue chloride, phthalocyanine green, and malachite green oxalate, may be used alone or in combination.

[0033] The charge control agent may contain a reinforcing charge control agent as needed. Any known reinforcing charge control agent can be used. Examples include nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxyamines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts), alkylamides, phosphorus simple substance or compounds, tungsten simple substance or compounds, fluorine-based surfactants, metal salicylate salts, and metal salts of salicylic acid derivatives.

[0034] The non-magnetic toner may also contain wax or an external additive. Wax is contained to improve the fixability and release properties from the fixing member during fixing. Examples of wax that can be used include paraffin wax, carnauba wax, and polyolefin, which are kneaded and dispersed in a binder resin. In this embodiment, a resin in which a binder, a colorant, a charge control agent, and wax are kneaded and dispersed is used, which is pulverized using a mechanical pulverizer.

[0035] Examples of the external additive particles include those obtained by subjecting amorphous silica to a hydrophobic treatment, or inorganic oxide fine particles such as titanium oxide and titanium compounds. By externally adding these fine particles to the toner base, it is suitable to control the powder fluidity and charge amount of the toner. The particle size of the external additive particles is preferably about 1 nm to 100 nm. In this example, titanium oxide with an average particle size of 50 nm was externally added at 0.5 wt% by weight ratio, and amorphous silica with average particle sizes of 2 nm and 100 nm was externally added at 0.5 wt% and 1.0 wt% respectively.

[0036] When the particle size of the toner having the above configuration was measured with a powder particle size image analyzer FPIA - 3000 manufactured by Sysmex Corporation, the volume average particle size was 6.0 μm. Also, when the degree of aggregation of the toner was measured with a powder tester manufactured by Hosokawa Micron Corporation, it was 30. Further, when the coating rate of the external additive in the toner was measured using ESCA, it was 60%.

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

[0038] The ESCA apparatus and measurement conditions are as follows.

[0039] Apparatus used: PHI5000VersaProbeII manufactured by ULVAC - PHI, Inc. Analysis method: Narrow analysis Measurement conditions: X-ray source: Al-Kα X-ray conditions: 100μ25W15kV Photoelectron capture angle: 45 Pass Energy: 58.70 eV Measurement range: 300 μm x 200 μm

[0040] Measurements were performed under the above conditions. The analysis method involves first correcting the peak derived from the C-C bond of the carbon 1s orbital to 285 eV. Then, the amount of Si derived from silica relative to the total amount of constituent elements is calculated from the peak area derived from the silicon 2p orbital, whose peak top is detected between 100 eV and 105 eV, using a relative sensitivity factor provided by ULVAC-PHI. Next, the silica alone applied to the toner is measured in the same manner as above, and the amount of Si derived from silica relative to the total amount of constituent elements is calculated. The ratio of the amount of Si when measuring the toner relative to the amount of Si when measuring the external additive alone is defined as the silica coverage in this invention.

[0041] In this example, 200 g of developer D, which is a mixture of the above toner and carrier at a mixture ratio (toner concentration) of 10 wt %, is placed in the developing device.

[0042] The developing device 4 has an opening in the development area facing the photosensitive drum 1, and a developing sleeve 41, which is a developer carrier, is rotatably disposed so as to be partially exposed in this opening. The developing sleeve 41 contains a fixed magnet roll 42, which is a magnetic field generating means. During development, the developing sleeve 41 rotates in the direction of the arrow in FIG. 3(a), holds the developer in the developing container 40 in a layer, carries and transports the developer to the development 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 transported as the developing sleeve 41 rotates and is collected into the developing container 40.

[0043] The developing container 40 is partitioned by a partition wall 40C into a developing chamber 40A and an agitating chamber 40B, which form a circulation path for the developer. In the developing container 40, the side closer to the developing sleeve 41 is the developing chamber 40A, and the side farther away is the agitating chamber 40B. The developing sleeve 41 carries and transports the developer in the developing chamber 40A. A screw 43 (hereinafter referred to as the "developing screw") is disposed in the developing chamber 40A of the developing container 40 as a first transport member. A screw 44 (hereinafter referred to as the "agitating screw") is disposed in the agitating chamber 40B of the developing container 40 as a second transport member. The developer in the developing container 40 is circulated and transported within the developing container 40 while being mixed and agitated by the developing screw 43 and the agitating screw 44. The developer circulates from the front side to the back side in FIG. 3(a) on the developing screw 43 side, and from the back side to the front side on the agitating screw 44 side. The developing screw 43 and the stirring screw 44 both have a central shaft diameter of 7 mm and an outer diameter of 14 mm, and the rotation speed is 300 rpm. The distance between the developing container and each screw was set to 1 mm.

[0044] In this embodiment, the developing sleeve 41 is disposed opposite the photosensitive drum 1 with a gap of 300 μm, and is arranged to rotate in the same direction as the rotation direction of the photosensitive drum 1 (the direction of the arrow in the figure) and at 180% of the peripheral speed of the photosensitive drum 1. The developing sleeve 41 is formed into a cylindrical shape from a metal such as aluminum or SUS, and its surface is subjected to a blasting treatment, plating treatment, or coating treatment to adjust the developer transportability and frictional charging ability. In this embodiment, a metal sleeve with an aluminum surface subjected to a blasting treatment was used.

[0045] A magnet roll 42 having multiple magnetic poles is fixedly disposed within the developing sleeve 41 as a magnetic field generating means. In this embodiment, a magnet roll 42 with five magnetized poles is used. The S1 pole is a developer amount regulating pole that regulates the amount of developer transported to the development area. The N1 pole is a development pole that contributes to development. The S2 pole is a transport pole that transports the developer. The N2 pole is a repulsion pole that peels off the developer carried on the developing sleeve. The N3 is an intake pole that causes the developer sent from the developing screw 43 to be carried on the developing sleeve 41.

[0046] In this embodiment, the developer amount regulating member is a flat non-magnetic blade 45 having a thickness of 1 mm, which is disposed facing the developing sleeve 41 with a constant gap uniformly spaced along the longitudinal direction. The shape of the non-magnetic blade 45 is not limited to a flat plate, and the tip may be sharpened to a thickness of about 0.3 mm. Depending on the shape of this non-magnetic blade 45, the gap between the developing sleeve 41 and the non-magnetic blade 45, and the size and angle of the developer amount regulating magnetic pole S1, the developer carried on the developing sleeve 41 is uniformly coated and transported to the development zone. In this embodiment, the gap between the developing sleeve 41 and the non-magnetic blade 45 is set to 300 μm, and the amount of developer transported to the development zone is set to a mass per unit area (M / S) of 30 mg / cm. 2 It is regulated to.

[0047] With the above configuration, the developer in the developing device 4 is carried by the developing sleeve 41 containing the magnet roll and transported to a position facing the photosensitive drum 1, while a magnetic brush is formed at the position facing the photosensitive drum 1. Then, an appropriate developing bias is applied to the developing sleeve 41 to develop the electrostatic latent image on the photosensitive drum 1. In this embodiment, a voltage obtained by superimposing 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 is applied from the high-voltage power supply 401, but the values ​​are not limited to these.

[0048] In this embodiment, a magnetic permeability sensor is used as the toner concentration sensor (detection means) 49, which detects the mixing ratio of toner and magnetic carrier in the developer in the developing device. The magnetic permeability sensor measures the toner concentration by detecting (by inductance detection) the change in the apparent magnetic permeability of the developer, which decreases as the toner concentration in the developer increases. In this embodiment, as shown in FIG. 3(a), the toner concentration sensor 49 is disposed downstream of the stirring chamber 40B, on the side of the developing device 4. The toner concentration sensor 49 is preferably disposed so that there is always enough developer present to detect the magnetic permeability. The toner concentration sensor 49 is positioned so that the developer present in the area detected by the magnetic permeability sensor is always subjected to the stirring action of the stirring screw 44. The detection value of the toner concentration sensor 49 is output to the CPU 400, which serves as the control means.

[0049] To calculate the toner concentration, the output value of the magnetic permeability sensor is sampled at multiple points and then averaged, and the DC component of the output value of the magnetic permeability sensor is extracted by canceling the vibration component due to the rotation period of the stirring screw 44. The toner concentration is then calculated by looking up the relationship between this value and the toner concentration and referring to a table prepared in advance.

[0050] A video counting counter (not shown) is also provided as a means for calculating the amount of toner consumed for each image, and the level of the output signal from an image signal processing circuit (not shown) is counted for each pixel. The counter adds up the counts for each pixel to calculate the video count for each image. The video count corresponds to the amount of toner consumed from the developing device 4 to form one toner image for each image.

[0051] Based on the output of the toner density sensor 49 and the video count, the CPU 400 determines the amount of toner to be replenished by a toner replenishment control method to be described later, and causes the toner replenishment device 9 to be described later to replenish the developing device 4 with a predetermined amount of toner.

[0052] <Toner supply device> Next, the toner supply device 9 as the toner supply means in this embodiment will be described with reference to Figures 2, 3 and 5. Figure 5 is a perspective view of the developer supply container 91.

[0053] 5 can be easily attached to and detached from the mounting portion 910 of the image forming apparatus. When the developer supply container 91 is attached to the mounting portion 910, a discharge port (not shown) of the developer supply container 91 communicates with the developer receiving port 47, and the developer discharged from the developer supply container 91 is supplied to the developing device 4 through the developer receiving port 47. The developer enclosed in the developer supply container 91 is a two-component developer in which a negatively charged non-magnetic toner and a magnetic carrier are mixed, and the developer uses the same toner and carrier as the developer enclosed in the developing device 4. Here, the developer enclosed in the developing device 4 is manufactured by mixing the toner and carrier at a toner concentration of 10 wt%, whereas the developer enclosed in the developer supply container 91 is manufactured by mixing the toner and carrier at a carrier concentration of 9 wt%.

[0054] The developer supply container 91 according to this embodiment is equipped with 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 information reading means on the main body side. In this embodiment, the toner memory 90, which is the storage means, is installed in 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 information reading means (not shown) that reads information from the toner memory 90, and is configured to be able to communicate with the toner memory 90 when the developer supply container 91 is attached to the image forming apparatus.

[0055] The toner memory 90 stores information specific to the toner contained in each developer supply container 91. Examples of the specific information include the toner manufacturing date, manufacturing lot, characteristics of external additives, etc. In this embodiment, the specific information includes at least the external additive coverage rate at the time of toner manufacturing.

[0056] <Ghost image explanation> The developer used in this example is a dry two-component developer containing a carrier and toner to which negatively charged particles (external additives) that are the same polarity as the toner are added. As mentioned above, the external additives in this example contain at least titanium oxide and amorphous silica (silica) to suitably control the powder fluidity and charge amount of the toner.

[0057] In the development process in which this developer is developed in accordance with the electrostatic latent image formed on the photosensitive drum 1, the toner of the developer carried on the development sleeve 41 in the development device 4 is mainly developed in the image area (the bright potential area of ​​the electrostatic latent image).

[0058] At this time, negative external additives, which have the same polarity as the toner's charge polarity, are also simultaneously developed. In addition, some external additives added to the toner lose their adhesive force to the toner when stirred in the developing device, causing some external additives to separate from the toner.

[0059] These external additives, like the toner, have a negative polarity and are easily developed in the image area, so a larger amount of external additive is developed in the image area than in the non-image area on the photosensitive drum 1. The toner and external additives developed on the photosensitive drum 1 are primarily transferred onto the intermediate transfer belt 51 in the transfer process. However, some of the toner and external additives that have smaller particle diameters than the toner and have a stronger non-electrostatic adhesive force remain on the photosensitive drum 1 without being transferred to the intermediate transfer belt 51 in the transfer process.

[0060] After the transfer process, the residual toner and external additives remaining on the photosensitive drum 1 reach the cleaning process (drum cleaner 6). The residual toner remaining on the photosensitive drum 1 is cleaned by the cleaning blade 61, but the external additives cannot be completely cleaned away because they have a smaller particle size than the toner and have a strong adhesive force to the photosensitive drum 1, and so remain on the photosensitive drum 1.

[0061] After the cleaning process, the external additives remaining on the photosensitive drum 1 reach the charging process (charging roller 2). The external additives remaining on the photosensitive drum 1 form an electric field in a direction that attracts toner between the external additives attached to the photosensitive drum 1 due to the negative charge polarity of the particles themselves and the negative charge received by the charging voltage applied by the charging roller 2. The electric field formed in a direction that attracts toner between the external additives becomes stronger as the amount of external additives attached to the photosensitive drum 1 increases.

[0062] The difference in the amount of external additives attached to the photosensitive drum will be explained using Figures 6(a) and 6(b). The image areas Pa and Pb shown in Figure 6(a) are a vertical band image area Pa with a main scanning width of 30 mm, a sub-scanning width of 200 mm, and an image ratio of 100%, and a horizontal band image area Pb downstream of the vertical band with a main scanning width of 210 mm, a sub-scanning width of 50 mm, and an image ratio of 30%. In this image area, a large amount of external additives is supplied onto the photosensitive drum along with toner, resulting in a large amount of external additives remaining on the photosensitive drum. In contrast, in the non-image area Pd, no toner image is formed, so no toner is supplied and the amount of external additives attached is small.

[0063] As a result, when the difference in the amount of external additives between the image and non-image areas on the photosensitive drum increases, the toner-attracting force also differs between the image and non-image areas on the photosensitive drum. Therefore, the electric field formed by the external additives is stronger in the image area on the photosensitive drum during the next image formation compared to the non-image area, making it easier for toner to be attracted. Furthermore, when identical or similar image patterns are continuously formed, these processes are continued continuously, resulting in an increase in the amount of external additives accumulated in the image area on the photosensitive drum 1. In this case, the area on the photosensitive drum with an increased amount of external additives has an even stronger ability to attract toner, resulting in a greater amount of toner being developed. Therefore, when a uniform image such as a halftone image is formed, a density difference occurs between the image and non-image areas, which is perceived as a ghost image.

[0064] For example, if a vertical image area Pa shown in Figure 6(a) is continuously formed with a horizontal image area Pb downstream of the vertical image area Pa that is lower in tone than the image area Pa, the amount of external additives accumulated will be greater in the area Pc on the photosensitive drum where the image areas Pb and Pa overlap compared to other areas. As a result, the overlapping area Pc on the photosensitive drum has a stronger force attracting toner than other areas, resulting in a larger amount of toner being developed, which is visible as a ghost image (overlapping area Pc) as shown in Figure 6(b).

[0065] As described above, the occurrence of ghost images is caused by a large amount of toner developed due to differences in the amount of external additives remaining on the photosensitive drum. Therefore, frequent replenishment of developer with a high ratio of external additives into the developing device causes the concentration of external additives in the developer in the developing device to rise excessively, resulting in a large amount of external additives being developed along with the toner, increasing the risk of the occurrence of the aforementioned ghost images. In other words, the greater the amount of external additives in the toner, the greater the risk of ghost images occurring. As described above, the amount of external additives in the toner is defined by the coverage rate of the external additive silica in the toner measured by ESCA, and the silica coverage rate at the center of mass production variation of the toner alone in this embodiment is 60%.

[0066] As shown in Figure 4, in a two-component developer consisting of toner and carrier, when the toner and carrier come into contact, the external additives carried on the toner surface migrate to the carrier, and the total amount of external additives is shared between the toner and carrier, resulting in a certain equilibrium. For example, if the external additive coverage of the toner alone is 60%, and the toner concentration of the developer consisting of toner and carrier is 10%, the external additive coverage of the toner in the developing device will be 58%. In other words, this means that 2% of the 60% external additive coverage of the toner alone has migrated to the carrier surface.

[0067] In this embodiment, when the coverage rate of the external additives on the toner in the developer in the developing device reaches 61%, the amount of external additives adhering to the photosensitive drum becomes excessive, and ghost images become apparent. In other words, at the center of mass production variation (when the coverage rate of the external additives does not exceed the threshold), the coverage rate of the external additives on the toner in the developer in the developing device is 58%, so ghost images do not occur.

[0068] However, during the toner manufacturing process, variations in manufacturing conditions can cause the additive coverage of the toner itself to fluctuate. Specifically, the additive coverage of the toner itself can vary from 56 to 64%. As a result, as shown in Figure 7, for a developer with a toner concentration of 10%, the additive coverage of the toner in the developer in the developing device can vary from 54 to 62%. If the additive coverage of the toner in the developer in the developing device exceeds 61%, which is the threshold for the additive coverage at which ghost images occur, this can become apparent as an abnormal image.

[0069] <Toner concentration control> The toner concentration control in this embodiment will be described with reference to Figures 2, 8, and 9. Figure 2 is a block diagram showing the control system of the image forming apparatus 100 and the developing device 4. Figure 8 is a table showing the relationship between the external additive coverage rate of the toner alone for each toner concentration and the external additive coverage rate of the toner in the developer in the developing device. Figure 9 is a flowchart showing the toner concentration calculation method in this embodiment.

[0070] 2, CPU 400 includes a toner concentration control unit 410 and a toner concentration calculation unit 420. CPU 400 is connected to a toner concentration sensor 49, which is a detection means provided in developing device 4, and a toner memory 90, which is a storage means provided in developer supply container 91.

[0071] The output relating to the toner concentration obtained by the toner concentration sensor 49 of the developing device 4 is calculated by the toner concentration calculation unit 420. Furthermore, the toner concentration control unit 410 calculates (sets) the target toner concentration during operation of the image forming apparatus from the information relating to the external additives of the toner alone stored in the toner memory 90 of the developer supply container 91.

[0072] In this embodiment, the coverage rate of external additives on the toner alone is measured in advance for each lot at the toner manufacturing stage, and data on the coverage rate of external additives on the toner contained when the toner is filled into the developer supply container 91 is stored in the toner memory 90. In this way, the coverage rate of external additives on the toner is measured for each toner manufacturing lot, and the same coverage rate is stored in the toner memory 90 of the developer supply container 91 filled with toner from the same manufacturing lot.

[0073] Then, from the information on the external additive coverage rate of the toner stored in the toner memory 90 of the developer supply container 91, it is possible to estimate what the external additive coverage rate of the toner in the developer to be supplied to the developing device 4 will be. Therefore, it is possible to determine whether or not ghost images will occur due to variations in each toner production lot, and by performing toner concentration control that sets the toner concentration of the developer in the developing device 4 based on the information stored in the toner memory 90, it is possible to prevent the occurrence of ghost images.

[0074] Here, CPU 400 has a table showing the relationship between the external additive coverage rate of toner alone for each toner concentration and the external additive coverage rate of toner in the developer in the developing device, as shown in Fig. 8. Then, CPU 400 sets the toner concentration of the developer in developing device 4 from the table based on the information stored in toner memory 90, using the toner concentration control described below.

[0075] We will now explain toner concentration control as a countermeasure against ghost images. In a two-component developer consisting of toner and carrier, when the toner concentration is low for a given amount of carrier, that is, when the number of toner particles is small, the amount of carrier increases relative to the toner. Therefore, when the toner and carrier share the external additives and reach an equilibrium state, the amount of external additives carried by the carrier increases, and conversely, the amount of external additives carried by the toner decreases.

[0076] 8, for example, when the coverage rate of the external additives in the toner alone is 64%, in other words, when the coverage rate of the external additives stored in the toner memory 90 of the developer supply container 91 is 64%. When the coverage rate of the external additives in the toner alone is 64%, if the toner concentration of the developer in the developing device 4 is 10%, the coverage rate of the external additives in the toner in the developer in the developing device 4 is 62%, which exceeds the threshold of 61% at which ghost images occur. However, even when the coverage rate of the external additives in the toner alone is 64%, if the toner concentration of the developer in the developing device 4 is reduced to 7%, the coverage rate of the external additives in the toner in the developer in the developing device 4 becomes 60.5%, making it possible to suppress the occurrence of ghost images.

[0077] The flow of toner concentration control according to this embodiment will be described with reference to FIG. 9. The CPU 400 reads information stored in the toner memory 90 of the developer supply container 91 using an information reading unit (not shown) on the image forming apparatus side (step S1) and acquires toner lot information, which is information specific to the toner (step S2). This acquires information about the external additive coverage of the toner alone contained in the developer supply container 91. The CPU 400 sets the toner concentration of the developer in the developing device 4 to a target toner concentration based on the information about the external additive coverage of the toner alone contained in the developer supply container 91 (step S3). That is, based on the information stored in the toner memory 90, the CPU 400 sets the toner concentration of the developer in the developing device 4 to a toner concentration at which the external additive coverage of the toner in the developer in the developing device 4 is below a first threshold. Here, the first threshold for the external additive coverage of the toner in the developer in the developing device 4 is a threshold at which ghost images occur (61% in FIG. 8).

[0078] As described above, information on lot variations in the additive coverage rate of toner during the toner manufacturing process is stored in the toner memory 90 of the developer supply container 91, and when the stored information is read and the additive coverage rate of the toner is found to be high, the target toner concentration is lowered, thereby preventing the occurrence of ghost images.

[0079] Example 2 Next, an image forming apparatus according to this embodiment will be described. The general configuration of the image forming apparatus according to this embodiment is the same as that of the previously described embodiment, so a description thereof will be omitted here.

[0080] In the above-described embodiment, in order to suppress the occurrence of ghost images, the toner concentration of the developer in the developing device 4 is set to a toner concentration at which the external additive coverage rate of the toner in the developer in the developing device 4 is below the first threshold value, based on the external additive coverage rate of the toner stored in the toner memory 90.

[0081] As a result, even if the external additive coverage rate of the toner becomes low due to variations in the external additive coverage rate for each toner production lot, suitable image formation is possible by feeding back the information stored in the toner memory 90 of the developer supply container 91 to the toner concentration control.

[0082] On the other hand, in this embodiment, based on the external additive coverage rate of the toner stored in the toner memory 90, the toner concentration of the developer in the developing device 4 is set to a toner concentration at which the external additive coverage rate of the toner in the developer in the developing device 4 exceeds a second threshold value that is smaller than the first threshold value. This will be explained below.

[0083] First, by carrying small particle size external additives on the toner surface, the contact area between the toner and carrier can be reduced, and the adhesive force between the toner and carrier can be reduced, thereby improving the flying ability of the toner in the developer on the developing sleeve 41 to fly to the photosensitive drum 1.

[0084] However, when the coverage of the external additive on the toner is low, the amount of external additive carried on the toner surface is small, which increases the contact area between the toner and the carrier, and increases the adhesive force between the toner and the carrier. As a result, the toner in the developer on the developing sleeve 41 cannot be sufficiently propelled to the photosensitive drum 1, resulting in a low density output image (low density).

[0085] When this low density occurs, the coverage rate of the external additives on the toner in the developer in the developing device 4 is a second threshold value (55% in FIG. 8) that is smaller than the first threshold value described above.

[0086] During the toner manufacturing process, variations in manufacturing conditions can cause fluctuations in the external additive coverage of the toner itself. Specifically, the external additive coverage of the toner itself varies from 56 to 64%. As a result, as shown in Figure 7, for a developer with a toner concentration of 10%, the external additive coverage of the toner in the developer in the developing device 4 varies from 54 to 62%. If the external additive coverage of the toner in the developer in the developing device falls below 55%, which is the threshold (second threshold) for the external additive coverage at which low density occurs, this may become apparent as an abnormal image.

[0087] 8, for example, when the coverage rate of the external additives in the toner alone is 56%, in other words, when the coverage rate of the external additives stored in the toner memory 90 of the developer supply container 91 is 56%. When the coverage rate of the external additives in the toner alone is 56%, if the toner concentration of the developer in the developing device 4 is 10%, the coverage rate of the external additives in the toner in the developer in the developing device 4 will be 54%, which is below the second threshold of 55% at which low concentration occurs. However, even when the coverage rate of the external additives in the toner alone is 56%, if the toner concentration of the developer in the developing device 4 is increased to 13%, the coverage rate of the external additives in the developer in the developing device 4 will be 55.5%, making it possible to prevent low concentration from occurring.

[0088] As described above, information on lot variations in the additive coverage rate of toner during the toner manufacturing process is stored in the toner memory 90 of the developer supply container 91, and when the stored information is read and the additive coverage rate of the toner is found to be low, the target toner density is increased, thereby preventing low density from occurring.

[0089] Other Examples In the above-described embodiment, information on lot variations in the external additive coverage rate of toner during the toner manufacturing process is stored in the toner memory 90 of the developer supply container 91, and the stored information is read and fed back to toner concentration control. However, the external additive information stored in the toner memory 90 of the developer supply container 91 is not limited to the external additive coverage rate. For example, it may be information on the adhesion state of the external additive (fine particles) to the toner, such as characteristic values ​​indicating the adhesion of the external additive to the toner surface, such as the strength with which the external additive adheres to the toner surface or the ease with which the external additive carried on the toner surface migrates to the carrier.

[0090] In the above-described embodiment, four image forming units are used, but the number of units used is not limited to this and may be set appropriately as required.

[0091] In the above-described embodiment, a laser scanner was used as the exposure means, but this is not limited to this. For example, an optical print head (exposure head) having a substrate on which multiple light-emitting elements are mounted or a lens array may also be used.

[0092] Furthermore, in the above-described embodiment, a printer is used as an example of an image forming apparatus, but the present invention is not limited to this. For example, other image forming apparatuses such as a copier or facsimile machine, or other image forming apparatuses such as a multifunction peripheral that combines the functions of these, may also be used. An image forming apparatus that uses an intermediate transfer member, sequentially transfers toner images of each color onto the intermediate transfer member in a superimposed manner, and then transfers the toner images carried on the intermediate transfer member to a transfer material all at once, is exemplified, but the present invention is not limited to this. For example, an image forming apparatus that uses a transfer material carrier, sequentially transfers toner images of each color onto a transfer material carried on the transfer material carrier in a superimposed manner, may also be used. Similar effects can be obtained by applying the present invention to these image forming apparatuses. [Explanation of symbols]

[0093] Pa, Pb ... Image area Pd: Overlapping area Pd: Non-image area S...Image forming section 1...Photosensitive drum (image carrier) 4...Developing device (developing means) 9...Toner supply device 40...developer container (developer storage section) 41...Developing sleeve (developer carrier) 49...Toner concentration sensor (detection means) 90...Toner memory (storage means) 91 ... Developer supply container 100...Image forming device 400...CPU (control means) 910 ... Mounting part

Claims

1. an image carrier; a developing means including a developer storage section that stores a developer containing a toner and a carrier, and a developer carrier that carries and transports the developer, and that develops an electrostatic image formed on the image carrier with the toner; a detecting means for detecting a toner concentration of the developer contained in the developing means; a control means for controlling the toner concentration of the developer in the developing means based on the result detected by the detection means; a developer supply container that is detachably mounted on the image forming apparatus, contains a developer containing toner having fine particles attached to its surface, and supplies the developer to the developing means; a storage means provided in the developer supply container, for storing information specific to the toner contained in the developer supply container; The image forming apparatus is characterized in that the control means sets the toner concentration of the developer of the developing means based on the information stored in the storage means.

2. 2. The image forming apparatus according to claim 1, wherein the information stored in the storage means is information relating to the adhesion state of fine particles to the toner.

3. 2. The image forming apparatus according to claim 1, wherein the information stored in the storage means is information relating to a coverage rate of fine particles relative to toner.

4. The image forming apparatus according to claim 1, characterized in that the control means obtains the coverage rate of fine particles with respect to the toner contained in the developer supply container from the information stored in the memory means, and sets the toner concentration of the developer of the developing means based on the coverage rate of fine particles with respect to the toner.

5. The image forming apparatus according to claim 1, characterized in that the control means obtains the coverage rate of fine particles on the toner contained in the developer supply container from the information stored in the memory means, and based on the obtained coverage rate of fine particles on the toner, sets the toner concentration of the developer of the developing means to a toner concentration at which the coverage rate of fine particles on the developer of the developing means is below a first threshold value.

6. The image forming apparatus of claim 5, wherein the control means obtains the coverage rate of fine particles for the toner contained in the developer supply container from the information stored in the memory means, and based on the obtained coverage rate of fine particles for the toner, sets the toner concentration of the developer of the developing means to a toner concentration at which the coverage rate of fine particles for the developer of the developing means exceeds a second threshold value that is smaller than the first threshold value.

7. 2. The image forming apparatus according to claim 1, wherein the control means has a table showing the relationship between the coverage rate of external additives on toner for each toner concentration and the coverage rate of external additives on toner in the developer of the developing means, and sets the toner concentration of the developer of the developing means from the table based on the information stored in the memory means.

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