Image forming apparatus

Abstract

To provide an image forming apparatus that prevents deterioration of thin line reproducibility.SOLUTION: An image forming apparatus comprises: an electrophotographic photoreceptor; a charging device; an electrostatic charge image forming device; a developing device having a first developing member that is arranged opposite to the electrophotographic photoreceptor and holds a developer to convey it to a developing area, a second developing member that is arranged opposite to the electrophotographic photoreceptor on the downstream side of the first developing member in a direction of rotation of the electrophotographic photoreceptor and holds the developer to convey it to the developing area, a first power supply that applies, to the first developing member, developing voltage in which AC voltage is superimposed on DC voltage, and a second power supply that applies, to the second developing member, developing voltage in which AC voltage is superimposed on DC voltage; a transfer device; a fixing device; and a control unit that acquires image information of a toner image, controls at least one of the first power supply and the second power supply according to the image information, and reduces a frequency of the AC voltage in the developing voltage applied to the second developing member compared to a frequency of the AC voltage in the developing voltage applied to the first developing member.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Formation of an image by electrophotography is carried out, for example, by charging the surface of a photoreceptor, forming an electrostatic image on the surface of the photoreceptor in accordance with image information, developing the electrostatic image with a developer containing toner to form a toner image, and transferring and fixing the toner image to the surface of a recording medium.

[0003] Here, Patent Document 1 discloses "a color image forming apparatus in which a latent image carrier that carries a latent image is used to form a plurality of color toner images on the latent image carrier by a plurality of developing means having a latent image carrier and a plurality of developer carriers that carry and transport developer, and then the toner images are transferred collectively to a transfer material, the plurality of developing means having bias application means for applying a DC bias superimposed on an AC bias to each of the developer carriers, the AC bias having a constant frequency, and the peak value of the developer carrier arranged upstream with respect to the rotation direction of the latent image carrier being set higher than that of the developer carrier arranged downstream."

[0004] Patent Document 2 discloses a developing device comprising "a plurality of toner carriers, each of which carries toner on its outer circumferential surface and is disposed in a non-contact manner with respect to the image carrier along the direction of rotation of the image carrier, and a developer carrier, each of which carries a developer consisting of toner and a carrier and supplies toner to the plurality of toner carriers, wherein the toner is attached to the electrostatic latent image by an electric field formed between the voltage of the electrostatic latent image formed on the image carrier and an AC bias voltage applied to the toner carrier, characterized in that a development duty ratio of an AC bias voltage applied to a first toner carrier disposed upstream of the image carrier in the direction of rotation is greater than a development duty ratio of an AC bias voltage applied to a second toner carrier disposed downstream of the image carrier in the direction of rotation." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-172043 A [Patent Document 2] JP 2011-257534 A Summary of the Invention [Problem to be solved by the invention]

[0006] The electrophotographic image forming apparatus includes "an electrophotographic photoreceptor, a charging device which charges the surface of the electrophotographic photoreceptor, an electrostatic image forming device which forms an electrostatic image on the surface of the charged electrophotographic photoreceptor, and a developing device which contains a developer containing toner, supplies the developer, and develops the electrostatic image formed on the surface of the electrophotographic photoreceptor as a toner image, a first developing member which is disposed opposite the electrophotographic photoreceptor and holds the developer and transports it to a development area, a second developing member which is disposed opposite the electrophotographic photoreceptor downstream of the first developing member in the direction of rotation of the electrophotographic photoreceptor, There is known an image forming apparatus (hereinafter also referred to as a "specific image forming apparatus") that includes a developing device having a second developing member that holds a developer and transports it to a development area, a first power source that applies a developing voltage in the form of a DC voltage superimposed on an AC voltage to the first developing member, and a second power source that applies a developing voltage in the form of a DC voltage superimposed on an AC voltage to the second developing member, a transfer device that transfers a toner image formed on the surface of an electrophotographic photosensitive member to the surface of a recording medium, and a fixing device that fixes the toner image to the surface of the recording medium (for example, Patent Documents 1-2, etc.). However, when the image density of the toner image is low, for example, 40% or less, the reproducibility of thin lines may deteriorate.

[0007] Therefore, the object of the present invention is to provide an image forming apparatus in which, in a specific image forming apparatus, when the image density of a toner image is low, deterioration of fine line reproducibility is suppressed compared to a case in which the frequency of the AC voltage of the developing voltage applied to the first developing member is the same as the frequency of the AC voltage of the developing voltage applied to the second developing member. [Means for solving the problem]

[0008] Means for solving the above problems include the following aspects. <1> An electrophotographic photoreceptor; a charging device for charging a surface of the electrophotographic photoreceptor; an electrostatic image forming device for forming an electrostatic image on the charged surface of the electrophotographic photoreceptor; a developing device that contains a developer containing a toner, supplies the developer, and develops the electrostatic charge image formed on the surface of the electrophotographic photosensitive member into a toner image, the developing device having a first developing member that is disposed opposite the electrophotographic photosensitive member and holds and transports the developer to a development area, a second developing member that is disposed opposite the electrophotographic photosensitive member on the downstream side of the first developing member in a rotation direction of the electrophotographic photosensitive member and holds and transports the developer to the development area, a first power source that applies a developing voltage in which an AC voltage is superimposed on a DC voltage to the first developing member, and a second power source that applies a developing voltage in which an AC voltage is superimposed on a DC voltage to the second developing member; a transfer device for transferring the toner image formed on the surface of the electrophotographic photoreceptor to a surface of a recording medium; a fixing device for fixing the toner image onto a surface of a recording medium; a control device that acquires image information of the toner image, and controls at least one of the first power source and the second power source in accordance with the image information to make the frequency of the AC voltage of the developing voltage applied to the second developing member lower than the frequency of the AC voltage of the developing voltage applied to the first developing member; An image forming apparatus comprising: <2> The control device controls a second power source to lower a frequency of the AC voltage of the developing voltage applied to the second developing member so that the frequency of the AC voltage of the developing voltage applied to the second developing member is lower than the frequency of the AC voltage of the developing voltage applied to the first developing member. <1> 2. The image forming apparatus according to claim 1 . <3> The control device controls at least one of the first power source and the second power source, and sets a ratio (Fd / Fu) between a frequency Fd of the AC voltage of the developing voltage applied to the first developing member and a frequency Fu of the AC voltage of the developing voltage applied to the second developing member to be 2.0 or more and 9.0 or less. <1> or <2> 2. The image forming apparatus according to claim 1 . <4> The control device obtains an image density of the toner image and controls at least one of the first power source and the second power source. <1> ~ <3> 13. The image forming apparatus according to claim 12 . <5> The toner has an adhesive strength of 5 MPa or more and 15 MPa or less. <1> ~ <4> 13. The image forming apparatus according to claim 12 . <6> The toner has toner particles containing a binder resin and resin particles. <5> 2. The image forming apparatus according to claim 1 . <7> The content of the resin particles is 3% by mass or more and 25% by mass or less with respect to the toner particles. <6> 2. The image forming apparatus according to claim 1 . <8> The resin particles are made of a styrene (meth)acrylic resin. <6> or <7> 2. The image forming apparatus according to claim 1 . <9> The average primary particle diameter of the resin particles is 20 nm or more and 300 nm or less. <6> ~ <8> 13. The image forming apparatus according to claim 12 . Effect of the Invention

[0009] <1> According to the invention, in a specific image forming apparatus, when the image density of a toner image is low, for example, an image forming apparatus is provided in which deterioration of fine line reproducibility is suppressed compared to a case in which the frequency of the AC voltage of the developing voltage applied to the first developing member is the same as the frequency of the AC voltage of the developing voltage applied to the second developing member.

[0010] <2> According to the invention, an image forming apparatus is provided in which a control device controls a first power source to increase the frequency of the AC voltage of the developing voltage applied to the first developing member, thereby suppressing deterioration of fine line reproducibility compared to a case in which the frequency of the AC voltage of the developing voltage applied to the second developing member is made lower than the frequency of the AC voltage of the developing voltage applied to the first developing member. <3> According to the invention, an image forming apparatus is provided in which the ratio (Fd / Fu) is less than 1.7 or exceeds 10.0, and deterioration of thin-line reproducibility is suppressed. <4> According to the invention, in a specific image forming apparatus, when the image density of a toner image is low, an image forming apparatus is provided in which deterioration of fine line reproducibility is suppressed compared to a case in which the frequency of the AC voltage of the developing voltage applied to the first developing member is the same as the frequency of the AC voltage of the developing voltage applied to the second developing member. <5> , <6> , <7> , <8> or <9> According to the invention, in a specific image forming apparatus, when the image density of a toner image is 40% or less, even if the toner adhesion force is 5 MPa or more and 15 MPa or less, deterioration of thin line reproducibility is suppressed compared to when the frequency of the AC voltage of the developing voltage applied to the first developing member is the same as the frequency of the AC voltage of the developing voltage applied to the second developing member, an image forming apparatus is provided in which deterioration of thin line reproducibility is suppressed. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic configuration diagram illustrating an example of a control system of the image forming apparatus according to the present embodiment. [Diagram 3] FIG. 2 is a schematic configuration diagram illustrating an example of a developing device of the image forming apparatus according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described in detail.

[0013] <Image forming device> The image forming apparatus according to the present embodiment includes: An electrophotographic photoreceptor; a charging device for charging a surface of an electrophotographic photoreceptor; an electrostatic image forming device for forming an electrostatic image on a surface of a charged electrophotographic photosensitive member; a developing device that contains a developer containing a toner, supplies the developer, and develops an electrostatic charge image formed on the surface of an electrophotographic photosensitive member into a toner image, the developing device having a first developing member that is disposed opposite the electrophotographic photosensitive member and holds and transports the developer to a development area, a second developing member that is disposed opposite the electrophotographic photosensitive member on the downstream side of the first developing member in a rotation direction of the electrophotographic photosensitive member and holds and transports the developer to the development area, a first power source that applies a developing voltage in which an AC voltage is superimposed on a DC voltage to the first developing member, and a second power source that applies a developing voltage in which an AC voltage is superimposed on a DC voltage to the second developing member; a transfer device that transfers a toner image formed on the surface of the electrophotographic photoreceptor onto a surface of a recording medium; a fixing device for fixing the toner image onto the surface of the recording medium; a control device that acquires image information of a toner image, and controls at least one of the first power source and the second power source in accordance with the image information to make the frequency of the AC voltage of the developing voltage applied to the second developing member lower than the frequency of the AC voltage of the developing voltage applied to the first developing member; Equipped with.

[0014] The image forming apparatus of this embodiment has the above-described configuration, and thus the deterioration of thin line reproducibility is suppressed. The reason for this is presumed to be as follows.

[0015] Conventionally, image forming apparatuses equipped with a developing device having a plurality of developing members are known (Patent Documents 1-2, etc.). This image forming apparatus can ensure developability in high-speed printing. However, when forming an image with a low image density of 40% or less, thin lines may be missing, and thin line reproducibility may deteriorate. This is because, when the frequency of AC voltages applied to the first developing member and the second developing member arranged facing the photoconductor downstream of the first developing member in the rotation direction of the photoconductor, is the same, the toner developed by the first developing member returns to the second developing member due to the cohesive force of the toner. In particular, when the toner returns to the second developing member and toner missing occurs, the toner missing is visually recognized because the amount of toner in the thin lines is small, and thin line reproducibility deteriorates.

[0016] Therefore, in the image forming apparatus according to this embodiment, the control device acquires image information of the toner image, and controls at least one of the first power source and the second power source according to the image information, so as to make the frequency of the AC voltage of the developing voltage applied to the second developing member lower than the frequency of the AC voltage of the developing voltage applied to the first developing member. Thereby, the developability of the first developing member is ensured, and the developability of the second developing member is reduced, thereby suppressing the toner from returning to the second developing member. Therefore, in the case of thin lines, toner loss is suppressed, and deterioration of thin line reproducibility is suppressed.

[0017] From the above, it is presumed that the image forming apparatus of the embodiment has the above-mentioned configuration, which suppresses deterioration of thin line reproducibility.

[0018] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus in which a toner image formed on the surface of a photoconductor is directly transferred to a recording medium; an intermediate transfer type apparatus in which a toner image formed on the surface of a photoconductor is primarily transferred to the surface of an intermediate transfer body, and the toner image transferred to the surface of the intermediate transfer body is then secondarily transferred to the surface of a recording medium; and an apparatus equipped with a static elimination device that irradiates the surface of a photoconductor with static elimination light to eliminate static electricity before charging after the toner image is transferred. In the case of an intermediate transfer type device, the transfer device is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer device which primarily transfers the toner image formed on the surface of a photosensitive body onto the surface of the intermediate transfer body, and a secondary transfer device which secondarily transfers the toner image transferred onto the surface of the intermediate transfer body onto the surface of a recording medium.

[0019] In the image forming apparatus according to this embodiment, a portion including at least the photoconductor constitutes a unit for the image forming apparatus, and may have a cartridge structure (that is, a process cartridge) that is detachably attached to the image forming apparatus. For example, the image forming apparatus unit may be a unit including a photoconductor and a developing device.

[0020] Next, an example of the configuration of the image forming apparatus according to the present embodiment will be described in detail.

[0021] An example of an image forming apparatus according to the present embodiment will be described below, but the present invention is not limited to this. Note that only the main parts shown in the drawings will be described, and descriptions of the rest will be omitted.

[0022] FIG. 1 is a schematic diagram showing an example of an image forming apparatus according to the present embodiment. As shown in Fig. 1, an image forming apparatus 10 according to this embodiment is provided with, for example, a photoconductor 12. The photoconductor 12 is cylindrical and connected to a driving unit 27 such as a motor via a driving force transmitting member (not shown) such as a gear, and is driven to rotate around a rotation axis indicated by a black dot by the driving unit 27. In the example shown in Fig. 1, the photoconductor 12 is driven to rotate in the direction of arrow A.

[0023] Around the photoconductor 12, for example, a charging device 15 (an example of a charging device), an electrostatic image forming device 16 (an example of an electrostatic image forming device), a developing device 18 (an example of a developing device), a transfer device 31 (an example of a transfer device), a cleaning device 22 (an example of a cleaning device), and a charge removing device 24 are arranged in this order along the rotation direction of the photoconductor 12. The image forming apparatus 10 is also provided with a fixing device 26 having a fixing member 26A and a pressure member 26B arranged in contact with the fixing member 26A. The image forming apparatus 10 also has a control device 36 that controls the operation of each device (each part). The unit including the photoconductor 12, the charging device 15, the electrostatic image forming device 16, the developing device 18, the transfer device 31, and the cleaning device 22 corresponds to an image forming unit.

[0024] In the image forming apparatus 10, at least the photoconductor 12 may be provided as a process cartridge integrated with another device.

[0025] Hereinafter, each device (each section) of the image forming apparatus 10 will be described in detail.

[0026] [Electrophotographic photoreceptor] The photoreceptor 12 has, for example, a conductive substrate, an undercoat layer formed on the conductive substrate, and a photosensitive layer formed on the undercoat layer. The photosensitive layer may have a two-layer structure of a charge generating layer and a charge transport layer. The photosensitive layer may be an organic photosensitive layer or an inorganic photosensitive layer. The photoreceptor 12 may have a configuration in which a protective layer is provided on the photosensitive layer.

[0027] [Charging device] The charging device 15 charges the surface of the photoreceptor 12. The charging device 15 includes, for example, a charging member 14 that is provided in contact with or not in contact with the surface of the photoreceptor 12 and charges the surface of the photoreceptor 12, and a power source 28 (an example of a voltage application unit for a charging member) that applies a charging voltage to the charging member 14. The power source 28 is electrically connected to the charging member 14.

[0028] The charging member 14 of the charging device 15 may be, for example, a contact type charger using a conductive charging roll, a charging brush, a charging film, a charging rubber blade, a charging tube, etc. In addition, the charging member 14 may be, for example, a non-contact type roller charger, a scorotron charger or a corotron charger that utilizes corona discharge, or other chargers known per se. In particular, when a charging member that charges the photoconductor without contacting the photoconductor is provided as the charging device, the lubricant is preferably used because the surface of the charging member is not contaminated by the lubricant.

[0029] [Electrostatic image forming device] The electrostatic image forming device 16 forms an electrostatic image on the charged surface of the photoreceptor 12. Specifically, for example, the electrostatic image forming device 16 irradiates the surface of the photoreceptor 12 charged by the charging member 14 with light L modulated based on image information of an image to be formed, and forms an electrostatic image on the photoreceptor 12 according to the image of the image information.

[0030] The electrostatic image forming device 16 may be, for example, a semiconductor laser, an LED, or a liquid crystal shutter. and optical system devices having a light source that imagewise exposes light such as the above.

[0031] [Developing device] The developing device 18 is provided, for example, downstream in the rotation direction of the photoconductor 12 from the irradiation position of light L by the electrostatic image forming device 16. A container for containing a developer is provided inside the developing device 18. The container contains an electrostatic image developer having toner. The toner is contained, for example, in a charged state inside the developing device 18.

[0032] The developing device 18 has, for example, a first developing member 18A that is arranged opposite the photoconductor 12 and holds the developer and transports it to the developing area, and a second developing member 18B that is arranged opposite the photoconductor 12 downstream in the rotation direction of the photoconductor 12 from the first developing member 18A and holds the developer and transports it to the developing area (see Figure 3). The developing device 18 has a first power source 32A that applies a developing voltage, which is a DC voltage superimposed on an AC voltage, to the first developing member 18A, and a second power source 32B that applies a developing voltage, which is a DC voltage superimposed on an AC voltage, to the second developing member 18B (see Figure 3). The developing device 18 is arranged so that a developer supply screw roller 19A is located to the right of the first developing member 18A in the figure, and developer supply screw rollers 19B and 19C are located to the right of the second developing member 18B in the figure, with their respective axes positioned at the vertices of a triangle (see Figure 3). Each screw roller is disposed in a supply / transport path for developer, which is partitioned by a partition member.

[0033] First and second development members 18A and 18B are connected to a first and second power source 32A and 32B, respectively. The first developing member 18A and the second developing member 18B may be, for example, a developing roll having a developing sleeve with a built-in magnet.

[0034] The developing device 18 (including the first power source 32A and the second power source 32B) is electrically connected to, for example, a control device 36 provided in the image forming apparatus 10, and the control device 36 drives and controls the first power source 32A and the second power source 32B to apply a developing voltage to the first developing member 18A and the second developing member 18B. The first developing member 18A and the second developing member 18B to which the developing voltage is applied are charged to a developing potential corresponding to the developing voltage. Then, the first developing member 18A and the second developing member 18B charged to the developing potential hold, for example, the developer contained in the developing device 18 on their surfaces, and supply the toner contained in the developer from inside the developing device 18 to the surface of the photoconductor 12. On the surface of the photoconductor 12 to which the toner is supplied, the electrostatic charge image formed is developed into a toner image.

[0035] In the developing device 18, the DC voltage applied to the first developing member 18A and the second developing member 18B is preferably in the range of 10V to 800V, and more preferably in the range of 20V to 650V. The AC voltage superimposed on the DC voltage is preferably in the range of 200V to 2000V, more preferably 300V to 1500V, in peak-to-peak voltage. The frequency of the AC voltage superimposed on the DC voltage is preferably in the range of 2 kHz to 20 kHz, and more preferably in the range of 3 kHz to 18 kHz.

[0036] [Transfer device] The transfer device 31 is provided, for example, downstream of the position where the developing device 18 is disposed in the rotation direction of the photoreceptor 12. The transfer device 31 includes, for example, a transfer member 20 that transfers a toner image formed on the surface of the photoreceptor 12 to a recording medium 30A, and a power source 30 that applies a transfer voltage to the transfer member 20. The transfer member 20 is, for example, cylindrical, and conveys the recording medium 30A while sandwiching it between the transfer member 20 and the photoreceptor 12. The transfer member 20 is, for example, electrically connected to the power source 30.

[0037] Examples of the transfer member 20 include contact type transfer chargers using a belt, roller, film, rubber cleaning blade, etc., and non-contact type transfer chargers known per se, such as a scorotron transfer charger or corotron transfer charger that utilizes corona discharge.

[0038] The transfer device 31 (including the power source 30) is electrically connected to, for example, a control device 36 provided in the image forming apparatus 10, and is driven and controlled by the control device 36 to apply a transfer voltage to the transfer member 20. The transfer member 20 to which the transfer voltage has been applied is charged to a transfer potential corresponding to the transfer voltage.

[0039] When a transfer voltage of a polarity opposite to that of the toner constituting the toner image formed on the photoconductor 12 is applied to the transfer member 20 from the power source 30 of the transfer member 20, for example, in the area where the photoconductor 12 and the transfer member 20 face each other (see transfer area 31A in FIG. 1), an electric field strength is generated that moves each toner constituting the toner image on the photoconductor 12 from the photoconductor 12 to the transfer member 20 side by electrostatic force. A transfer electric field of a certain degree is formed.

[0040] The recording medium 30A is, for example, stored in a storage unit (not shown), and is transported from this storage unit along a transport path 34 by a plurality of transport members (not shown) to a transfer area 31A, which is an area where the photoconductor 12 and the transfer member 20 face each other. In the example shown in FIG. 1, the recording medium 30A is transported in the direction of arrow B. When the recording medium 30A reaches the transfer area 31A, the toner image on the photoconductor 12 is transferred to the recording medium 30A by a transfer electric field formed in the area by applying a transfer voltage to the transfer member 20. That is, for example, the toner image is transferred onto the recording medium 30A by the movement of the toner from the surface of the photoconductor 12 to the recording medium 30A. Then, the toner image on the photoconductor 12 is transferred onto the recording medium 30A by the transfer electric field.

[0041] [Cleaning device] The cleaning device 22 is provided downstream of the transfer area 31A in the rotation direction of the photoreceptor 12. After the toner image is transferred to the recording medium 30A, the cleaning device 22 cleans the residual toner adhering to the photoreceptor 12. In addition to the residual toner, the cleaning device 22 also cleans adhering matters such as paper powder.

[0042] The cleaning device 22 has a cleaning blade 22A, and removes deposits on the surface of the photoreceptor 12 by contacting the photoreceptor 12 with the tip of the cleaning blade 22A in a direction opposite to the direction of rotation of the photoreceptor 12.

[0043] [Static eliminator] The static eliminator 24 is provided, for example, downstream of the cleaning device 22 in the rotation direction of the photoreceptor 12. After the toner image is transferred, the static eliminator 24 exposes the surface of the photoreceptor 12 to eliminate static electricity. Specifically, for example, the static eliminator 24 is electrically connected to a control device 36 provided in the image forming apparatus 10, and is driven and controlled by the control device 36 to expose the entire surface of the photoreceptor 12 (specifically, for example, the entire surface of the image forming area) to eliminate static electricity.

[0044] The static eliminator 24 may be, for example, a device having a light source such as a tungsten lamp that irradiates white light, or a light emitting diode (LED) that irradiates red light.

[0045] [Fixing device] The fixing device 26 is provided, for example, downstream of the transfer area 31A in the conveying direction of the conveying path 34 of the recording medium 30A. The fixing device 26 has a fixing member 26A and a pressure member 26B arranged in contact with the fixing member 26A, and fixes the toner image transferred onto the recording medium 30A at the contact portion between the fixing member 26A and the pressure member 26B. Specifically, for example, the fixing device 26 is electrically connected to a control device 36 provided in the image forming apparatus 10, and is driven and controlled by the control device 36 to fix the toner image transferred onto the recording medium 30A to the recording medium 30A by heat and pressure.

[0046] The fixing device 26 may be a known fixing device, such as a heat roller fixing device or an oven fixing device. Examples include vessels. Specifically, for example, the fixing device 26 is a known fixing device including a fixing roll or a fixing belt as the fixing member 26A, and a pressure roll or a pressure belt as the pressure member 26B.

[0047] Here, the recording medium 30A, onto which the toner image has been transferred by being transported along the transport path 34 and passing through the area (transfer area 31A) where the photoconductor 12 and the transfer member 20 face each other, is further transported along the transport path 34 by, for example, a transport member not shown in the figure, to the installation position of the fixing device 26, where the toner image on the recording medium 30A is fixed.

[0048] The recording medium 30A on which the toner image has been fixed is discharged by a plurality of conveying members (not shown) to the outside of the image forming apparatus 10. After the photoconductor 12 is neutralized by the neutralizing device 24, the photoconductor 12 is charged again to a charging potential by the charging device 15.

[0049] [Control device] Next, an example of the configuration of a control system of the image forming apparatus 10 will be described with reference to FIG. The image forming apparatus 10 has a control device 36 that controls the operation of each device (each section). The control device 36 is configured as a computer that controls the entire device and performs various calculations. Specifically, as shown in Fig. 2, the control device 36 includes a CPU (Central Processing Unit) 400A, a ROM (Read Only Memory) 400B that stores various programs, a RAM (Random Access Memory) 400C that is used as a work area when the programs are executed, a non-volatile memory 400D that stores various information, and an input / output interface (I / O) 400E. The CPU 400A, the ROM 400B, the RAM 400C, the non-volatile memory 400D, and the I / O 400E are each connected via a bus 400F.

[0050] Further, the image forming apparatus 10 includes an operation display unit 402, an image processing unit 404, an image memory 406, an image forming unit 408, a storage unit 410, and a communication unit 412 in addition to the control device 36. The operation display unit 402, the image processing unit 404, the image memory 406, the image forming unit 408, the storage unit 410, and the communication unit 412 are each connected to an I / O 400E of the control device 36. The control device 36 transmits and receives information to and from each of the operation display unit 402, the image processing unit 404, the image memory 406, the image forming unit 408, the storage unit 410, and the communication unit 412 to control each unit.

[0051] The operation display unit 402 includes various buttons such as a start button, a numeric keypad, a touch panel for displaying various screens such as a warning screen, a setting screen, etc. With the above configuration, the operation display unit 402 accepts operations from a user and displays various information to the user.

[0052] The image processing unit 404 performs predetermined image processing on image information acquired from an external device 414 via the communication unit 412, and generates image information to be output to the image forming unit 408. For example, it performs expansion processing on PDL data described in a page description language, converts it into raster data (RGB data) expanded into each of RGB colors, and performs color conversion processing on the RGB data to generate YMCK data or the like expressed in colors reproduced by the image forming device. It may also perform screen processing, gamma correction processing, and the like.

[0053] Image memory 406 stores various types of image information acquired by image forming apparatus 10, such as image information acquired from external device 414 and image information generated by image processing unit 404. Image memory 406 stores, for example, at least image information after image processing by image processing unit 404, i.e., image information to be output to image forming unit 408.

[0054] The image forming unit 408 has been described as a main component of the image forming apparatus 10. The image forming unit 408 includes, for example, the photoconductor 12 (and its drive unit (not shown)), the charging device 15, the electrostatic image forming device 16, the developing device 18, the transfer device 31, the static eliminator 24, the fixing device 26, and the like. Each of these units is connected to the control device 36. The control device 36 controls each unit by sending and receiving information between each of these units.

[0055] The storage unit 410 includes a storage device such as a hard disk, etc. The storage unit 410 stores various data such as log data, various programs, etc. The communication unit 412 is an interface for communicating with an external device 414 via a wired or wireless communication line. For example, the communication unit 412 acquires image formation information together with an image formation instruction or image information of an electronic document from the external device 414. The image formation information includes parameters that indicate attributes such as the type (size, etc.) of the recording paper P, the paper feed direction of the recording paper P, the number of copies, and the color mode.

[0056] Various drives may be connected to the control device 36. The various drives are devices that read data from and write data to computer-readable portable recording media such as flexible disks, optical magnetic disks, CD-ROMs, DVD-ROMs, and USB memories. When the various drives are provided, the control program may be recorded on the portable recording media and read and executed by the corresponding drives.

[0057] [Operation of image forming device] An example of the operation of the image forming apparatus 10 according to the present embodiment will be described below. Note that the various operations of the image forming apparatus 10 are performed by a control program executed by the control device 36.

[0058] Here, in the image forming apparatus 10, for example, control programs for "image formation processing" and "development condition change processing" are pre-stored in the ROM 400B. The pre-stored control programs are read by the CPU 400A and executed using the RAM 400C as a work area. In addition, in the image forming apparatus 10, for example, various data such as "image formation conditions (various process control values)" are pre-stored in the non-volatile memory 400D. These control programs and various data may be stored in other storage devices such as the ROM 400B, the non-volatile memory 400D, or the storage unit 410, or may be acquired from the outside via the communication unit 412.

[0059] The image forming operation of the image forming apparatus 10 will be described. First, the surface of the photoreceptor 12 is charged by the charging device 15. The electrostatic image forming device 16 exposes the charged surface of the photoreceptor 12 based on image information. As a result, an electrostatic image corresponding to the image information is formed on the photoreceptor 12. In the developing device 18, the electrostatic image formed on the surface of the photoreceptor 12 is developed by a developer containing toner. As a result, a toner image is formed on the surface of the photoreceptor 12. In the transfer device 31, the toner image formed on the surface of the photoreceptor 12 is transferred to the recording medium 30A. The toner image transferred to the recording medium 30A is fixed by the fixing device . On the other hand, the surface of the photoconductor 12 after the toner image is transferred is cleaned by a cleaning blade 22A of the cleaning device 22, and then the static electricity is removed by a static eliminator .

[0060] On the other hand, in the image forming apparatus 10, when an image forming operation is being performed, if the control device 36 determines that the toner image is an image that will deteriorate the image reproducibility, the control device 36 executes control to change the developing conditions for the developing device 18.

[0061] The operation of changing the development conditions by the developing device 18 will be described. The operation of changing the development conditions by the developing device 18 is performed by a control program of "development condition change processing" executed in the control device 36. The control program of the "development condition change processing" is started, for example, when an image formation instruction or the like is received from the operation display unit 402 or from the external device 414 via the communication unit 412.

[0062] First, in the developing condition changing process, image information of a toner image is obtained. The method of acquiring the image information is not particularly limited, and may be, for example, a method of reading the toner image formed on the recording paper P with a reading device (not shown), or a method of acquiring image information of the image to be formed.

[0063] As image information for determining whether an image has poor image reproducibility of a toner image, information on image density is preferable. Note that image density is the area ratio of the image to be formed to the area of ​​the surface (image forming surface) of recording paper P (an example of a recording medium).

[0064] Next, in the developing condition change process, it is determined from the acquired toner image information whether or not the image is one in which image reproducibility will be deteriorated. For example, in the case where the image reproducibility of thin lines deteriorates in an image having an image density of 40% or less, in the development condition change process, if it is determined that the image density of the acquired toner image is 40% or less, at least one of the first power source 32A and the second power source 32B is controlled from a state in which the frequencies of the AC voltages applied to the first developing member 18A and the second developing member 18B are the same, so that the frequency of the AC voltage of the developing voltage applied to the second developing member is made lower than the frequency of the AC voltage of the developing voltage applied to the first developing member. A specific mode of frequency change by the control device 36 is as follows. Mode 1: The second power source 32B is controlled to lower the frequency of the AC voltage of the developing voltage applied to the second developing member 18B, so that the frequency of the AC voltage of the developing voltage applied to the second developing member 18B is made lower than the frequency of the AC voltage of the developing voltage applied to the first developing member 18A. Mode 2: The second power source 32B is controlled to increase the frequency of the AC developing voltage applied to the first developing member 18A, and to make the frequency of the AC developing voltage applied to the second developing member 18B lower than the frequency of the AC developing voltage applied to the first developing member 18A. Aspect 3: A combination of Aspect 1 and Aspect 2.

[0065] However, from the viewpoint of preventing deterioration of thin-line reproducibility while maintaining developability, embodiment 1 is preferred.

[0066] Here, the ratio (Fd / Fu) of the frequency Fd of the AC voltage of the developing voltage applied to the first developing member 18A to the frequency Fu of the AC voltage of the developing voltage applied to the second developing member 18B is set to, for example, 1.7 or more and 10.0 or less (preferably 2.0 or more and 9.0 or less, and more preferably 3.0 or more and 6 or less). By setting the ratio (Fd / Fu) within the above range, deterioration of thin line reproducibility can be easily prevented while maintaining developability.

[0067] In addition, in the development condition change process, if it is determined that the acquired toner image is not an image that will result in poor image reproducibility, the development conditions are returned to the initial settings (i.e., when the frequency of the AC voltage of the development voltage applied to the first developing member is the same as the frequency of the AC voltage of the development voltage applied to the second developing member).

[0068] In each of the above embodiments, the processes executed by the CPU after reading the software (i.e., the program) may be executed by various processors other than the CPU. In this case, examples of the processor include a PLD (Programmable Logic Device) such as an FPGA (Field-Programmable Gate Array) whose circuit configuration can be changed after manufacture, and a dedicated electric circuit such as an ASIC (Application Specific Integrated Circuit) which is a processor having a circuit configuration designed exclusively for executing a specific process. Each process may be executed by one of these various processors, or may be executed by a combination of two or more processors of the same or different types (e.g., a plurality of FPGAs, and a combination of a CPU and an FPGA). More specifically, the hardware structure of these various processors is an electric circuit that combines circuit elements such as semiconductor elements.

[0069] Although the above description has been given of a mode in which each program is prestored (i.e., installed) in a ROM or non-volatile memory, the present invention is not limited to this. The programs may be provided in a form recorded on a recording medium such as a CD-ROM (Compact Disk Read Only Memory), a DVD-ROM (Digital Versatile Disk Read Only Memory), or a USB (Universal Serial Bus) memory. The programs may also be provided in a form in which they are downloaded from an external device via a network.

[0070] In the above-described developing condition change process, the image density is acquired as the image information, but the developing condition change process may be performed in a manner in which the thickness of a thin-line image is acquired as the image information. That is, the developing condition change process may be executed in accordance with the thickness of the thin line image (for example, when image information is acquired in which the thickness of the thin line image is 1 dot or more and 2 dots or less).

[0071] [Electrostatic image developer] Next, the electrostatic image developer contained in the developing device in the image forming apparatus according to this embodiment (hereinafter also referred to as "electrostatic image developer according to this embodiment") will be described.

[0072] The electrostatic image developer according to this embodiment contains at least a toner. The electrostatic image developer according to the present embodiment may be a one-component developer containing only toner, or may be a two-component developer containing toner and a carrier.

[0073] The toner includes toner particles, and preferably includes toner particles and an external additive. The toner adhesion may be greater than or equal to 5 MPa and less than or equal to 15 MPa. If the toner adhesion is higher than the above range, it becomes difficult to separate from the carrier or photoconductor, and the developability is likely to decrease. Therefore, when forming a toner image with an image density of 40% or less, the reproducibility of fine lines is likely to deteriorate. In particular, since the cohesive force between toner particles becomes high, in an image forming apparatus equipped with a developing device having multiple developing members, the phenomenon of toner returning to the second developing member is likely to occur, which is likely to cause the reproducibility of fine lines to deteriorate. However, in the image forming apparatus according to this embodiment, even if the toner having the above-mentioned high adhesive strength is used, the deterioration of thin line reproducibility is suppressed.

[0074] The toner adhesion is measured as follows. Using a copy machine, Docu Centre Color 450 (manufactured by Fujifilm Business Innovation Co., Ltd.), a chart image with a horizontal band of 5% image density was printed on 500 sheets of A4 paper, and then a developing toner amount of 4.0 g / m was applied to the photoconductor. 2 A patch image of 10 mm x 100 mm is applied and developed so that the image is formed in an environment of 25°C temperature and 50% humidity. Next, an air nozzle with an opening diameter of 0.5 mm was placed 10 mm away from the photoconductor, and the air was sprayed perpendicularly to the patch image while increasing the air pressure at a speed of 0.1 Pa / s. The air pressure at the moment when the image peeled off and the surface of the photoconductor became visible was taken as the adhesion force. The wind pressure was measured by installing an AP-V80 (Keyence) in the flow path 10 cm upstream from the tip of the injection nozzle. If the toner has a high adhesive strength, it is difficult to remove, and therefore the toner will not be removed unless a strong wind pressure is applied. However, if the toner has a low adhesive strength, the toner will be removed even with a weak wind pressure.

[0075] The toner adhesion can be increased to the above range in the following manner. Aspect 1: Toner has toner particles containing a binder resin and resin particles Aspect 2: Aspect in which the content of resin particles is 3% by mass or more and 25% by mass or less with respect to the toner particles Aspect 3: The resin particles are styrene (meth)acrylic resin Aspect 4: An aspect in which the average primary particle diameter of the resin particles is 20 nm or more and 300 nm or less

[0076] The toner will be described in detail below.

[0077] (Toner particles) The toner particles contain, for example, a binder resin. The toner particles may also contain a colorant, a release agent, resin particles, and other additives.

[0078] -Binding resin- Examples of the binder resin include vinyl resins made of homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), or copolymers of two or more of these monomers. Examples of the binder resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosin, mixtures of these with the vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the coexistence of these. These binder resins may be used alone or in combination of two or more kinds.

[0079] The binder resin is preferably a polyester resin. The polyester resin may be, for example, a known amorphous polyester resin. The polyester resin may be used in combination with a crystalline polyester resin together with the amorphous polyester resin. However, the content of the crystalline polyester resin is preferably in the range of 2% by mass to 40% by mass (preferably 2% by mass to 20% by mass) based on the total binder resin.

[0080] The "crystalline" nature of a resin refers to the presence of a clear endothermic peak rather than a stepwise change in the amount of endothermic heat in differential scanning calorimetry (DSC); specifically, the half-width of the endothermic peak is within 10°C when measured at a heating rate of 10 (°C / min). On the other hand, the term "amorphous" for a resin refers to a half-width exceeding 10° C., a stepwise change in endothermic heat quantity, or no clear endothermic peak being observed.

[0081] Amorphous polyester resin The amorphous polyester resin may be, for example, a condensation polymer of a polyvalent carboxylic acid and a polyhydric alcohol. The amorphous polyester resin may be a commercially available product or a synthesized product.

[0082] Examples of polyvalent carboxylic acids include aliphatic dicarboxylic acids (e.g., oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenylsuccinic acid, adipic acid, sebacic acid, etc.), alicyclic dicarboxylic acids (e.g., cyclohexanedicarboxylic acid, etc.), aromatic dicarboxylic acids (e.g., terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, etc.), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). Among these, aromatic dicarboxylic acids are preferable as polyvalent carboxylic acids. The polyvalent carboxylic acid may be a trivalent or higher carboxylic acid having a crosslinked or branched structure in combination with a dicarboxylic acid. Examples of the trivalent or higher carboxylic acid include trimellitic acid, pyromellitic acid, anhydrides thereof, and lower (e.g., carbon number 1 to 5) alkyl esters thereof. The polyvalent carboxylic acids may be used alone or in combination of two or more kinds.

[0083] Examples of polyhydric alcohols include aliphatic diols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, etc.), alicyclic diols (e.g., cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, etc.), and aromatic diols (e.g., ethylene oxide adducts of bisphenol A, propylene oxide adducts of bisphenol A, etc.). Among these, examples of polyhydric alcohols include aromatic diols and alicyclic diols, and more preferably aromatic diols. As the polyhydric alcohol, a polyhydric alcohol having a crosslinked or branched structure of three or more may be used in combination with the diol. Examples of the polyhydric alcohol having a trihydric or higher valence include glycerin, trimethylolpropane, and pentaerythritol. The polyhydric alcohols may be used alone or in combination of two or more kinds.

[0084] The glass transition temperature (Tg) of the amorphous polyester resin is preferably 50°C or higher and 80°C or lower, and more preferably 50°C or higher and 65°C or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), more specifically, from the "extrapolated glass transition onset temperature" described in the method for determining glass transition temperature in JIS K 7121-1987 "Method for measuring transition temperature of plastics."

[0085] The weight average molecular weight (Mw) of the amorphous polyester resin is preferably 5,000 or more and 1,000,000 or less, and more preferably 7,000 or more and 500,000 or less. The number average molecular weight (Mn) of the amorphous polyester resin is preferably 2,000 or more and 100,000 or less. The molecular weight distribution Mw / Mn of the amorphous polyester resin is preferably 1.5 or more and 100 or less, and more preferably 2 or more and 60 or less. The weight average molecular weight and number average molecular weight are measured by gel permeation chromatography (GPC). The molecular weight measurement by GPC is performed using a Tosoh GPC HLC-8120GPC as the measuring device, a Tosoh TSKgel SuperHM-M (15 cm) column, and THF solvent. The weight average molecular weight and number average molecular weight are calculated from the measurement results using a molecular weight calibration curve created with a monodisperse polystyrene standard sample.

[0086] The amorphous polyester resin can be obtained by a known manufacturing method, for example, by carrying out the reaction while removing water and alcohol generated during condensation by setting the polymerization temperature to 180° C. or higher and 230° C. or lower, and reducing the pressure in the reaction system as necessary. If the raw material monomer is not soluble or compatible at the reaction temperature, a high boiling point solvent may be added as a solubilizing agent to dissolve it. In this case, the polycondensation reaction is carried out while distilling off the solubilizing agent. If a monomer with poor compatibility is present, it is recommended that the monomer with poor compatibility is condensed in advance with the acid or alcohol to be polycondensed, and then polycondensed with the main component.

[0087] Crystalline polyester resin The crystalline polyester resin may be, for example, a polycondensate of a polyvalent carboxylic acid and a polyhydric alcohol. The crystalline polyester resin may be a commercially available product or a synthesized product. Here, the crystalline polyester resin is preferably a polycondensate using a polymerizable monomer having a linear aliphatic group rather than a polymerizable monomer having an aromatic group, since the crystalline polyester resin can easily form a crystalline structure.

[0088] Examples of polyvalent carboxylic acids include aliphatic dicarboxylic acids (e.g., oxalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, etc.), aromatic dicarboxylic acids (e.g., dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalene-2,6-dicarboxylic acid, etc.), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). The polyvalent carboxylic acid may be a trivalent or higher carboxylic acid having a crosslinked or branched structure in combination with a dicarboxylic acid. Examples of the trivalent carboxylic acid include aromatic carboxylic acids (e.g., 1,2,3-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, etc.), their anhydrides, and their lower alkyl esters (e.g., carbon number 1 to 5). As the polyvalent carboxylic acid, a dicarboxylic acid having a sulfonic acid group and a dicarboxylic acid having an ethylenic double bond may be used in combination with these dicarboxylic acids. The polyvalent carboxylic acids may be used alone or in combination of two or more kinds.

[0089] Examples of polyhydric alcohols include aliphatic diols (for example, straight-chain aliphatic diols having 7 to 20 carbon atoms in the main chain). Examples of aliphatic diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, and 1,14-eicosanedecanediol. Among these, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol are preferred as aliphatic diols. The polyhydric alcohol may be a trihydric or higher alcohol having a crosslinked or branched structure in combination with the diol. Examples of the trihydric or higher alcohol include glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol. The polyhydric alcohols may be used alone or in combination of two or more kinds.

[0090] Here, the polyhydric alcohol has an aliphatic diol content of 80 mol % or more, preferably 90 mol % or more.

[0091] The melting temperature of the crystalline polyester resin is preferably 50°C or higher and 100°C or lower, more preferably 55°C or higher and 90°C or lower, and even more preferably 60°C or higher and 85°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) based on the "melting peak temperature" described in the method for determining melting temperature in JIS K7121-1987 "Method for measuring transition temperature of plastics."

[0092] The weight average molecular weight (Mw) of the crystalline polyester resin is preferably 6,000 or more and 35,000 or less.

[0093] The crystalline polyester resin can be obtained by a known manufacturing method, for example, in the same manner as the amorphous polyester.

[0094] The content of the binder resin is, for example, preferably from 40% by mass to 95% by mass, more preferably from 50% by mass to 90% by mass, and even more preferably from 60% by mass to 85% by mass, based on the total amount of the toner particles.

[0095] -Coloring agent- Examples of colorants include carbon black, chrome yellow, Hansa Yellow, benzidine yellow, threne yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Balkan orange, watch young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, ultramarine blue, and tetrahydrofuran. Examples of the pigments include phosphorus blue, chalcoil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate, as well as various dyes such as acridine-based, xanthene-based, azo-based, benzoquinone-based, azine-based, anthraquinone-based, thioindigo-based, dioxazine-based, thiazine-based, azomethine-based, indigo-based, phthalocyanine-based, aniline black-based, polymethine-based, triphenylmethane-based, diphenylmethane-based, and thiazole-based dyes. The colorant may be used alone or in combination of two or more kinds.

[0096] The colorant may be surface-treated as necessary, or may be used in combination with a dispersant. In addition, a plurality of types of colorants may be used in combination.

[0097] The content of the colorant is, for example, preferably from 1% by mass to 30% by mass, and more preferably from 3% by mass to 15% by mass, based on the total mass of the toner particles.

[0098] -Release agent- Examples of the release agent include hydrocarbon waxes, natural waxes such as carnauba wax, rice wax, and candelilla wax, synthetic or mineral / petroleum waxes such as montan wax, and ester waxes such as fatty acid esters and montan acid esters. The release agent is not limited to these.

[0099] The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, and more preferably 60°C or higher and 100°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) based on the "melting peak temperature" as described in the method for determining melting temperature in JIS K 7121-1987 "Method for measuring transition temperature of plastics."

[0100] The content of the release agent is, for example, preferably from 1% by mass to 20% by mass, and more preferably from 5% by mass to 15% by mass, based on the total amount of the toner particles.

[0101] -Resin particles- Examples of the resin particles include polyolefin resins (polyethylene, polypropylene, etc.), styrene resins (polystyrene, α-polymethylstyrene, etc.), (meth)acrylic resins (polymethyl methacrylate, polyacrylonitrile, etc.), epoxy resins, polyurethane resins, polyurea resins, polyamide resins, polycarbonate resins, polyether resins, polyester resins, and copolymer resins thereof. As the resin particles, styrene-(meth)acrylic copolymer resin particles are preferred.

[0102] The styrene-(meth)acrylic copolymer resin particles include, for example, resin particles obtained by radical polymerization of a styrene monomer and a (meth)acrylic acid monomer.

[0103] Examples of styrene-based monomers include styrene, α-methylstyrene, vinylnaphthalene, alkyl-substituted styrenes having alkyl chains such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene, halogen-substituted styrenes such as 2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene, and fluorine-substituted styrenes such as 4-fluorostyrene and 2,5-difluorostyrene, etc. Among these, styrene and α-methylstyrene are preferred as styrene-based monomers.

[0104] Examples of (meth)acrylic acid monomers include (meth)acrylic acid, n-methyl (meth)acrylate, n-ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, n-lauryl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate, n-octadecyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, amyl (meth)acrylate, Examples of the (meth)acrylate include neopentyl acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, phenyl (meth)acrylate, biphenyl (meth)acrylate, diphenylethyl (meth)acrylate, t-butylphenyl (meth)acrylate, terphenyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, β-carboxyethyl (meth)acrylate, (meth)acrylonitrile, and (meth)acrylamide. Among these, the (meth)acrylic acid monomer is preferably n-butyl (meth)acrylate or β-carboxyethyl (meth)acrylate.

[0105] The resin particles are preferably crosslinked resin particles. In the crosslinked resin particles, examples of the crosslinking agent for crosslinking the resin include aromatic polyvinyl compounds such as divinylbenzene and divinylnaphthalene; polyvinyl esters of aromatic polyvalent carboxylic acids such as divinyl phthalate, divinyl isophthalate, divinyl terephthalate, divinyl homophthalate, divinyl trimesate, trivinyl trimesate, divinyl naphthalenedicarboxylate, and divinyl biphenylcarboxylate; divinyl esters of nitrogen-containing aromatic compounds such as divinyl pyridinedicarboxylate; vinyl esters of unsaturated heterocyclic carboxylic acids such as vinyl pyrromucate, vinyl furancarboxylate, vinyl pyrrole-2-carboxylate, and vinyl thiophenecarboxylate; linear polyhydric alcohols such as butanediol methacrylate, hexanediol acrylate, octanediol methacrylate, decanediol acrylate, and dodecanediol methacrylate; (meth)acrylic acid esters; (meth)acrylic acid esters of branched, substituted polyhydric alcohols such as neopentyl glycol dimethacrylate and 2-hydroxy, 1,3-diacryloxypropane; polyvinyl esters of polyvalent carboxylic acids such as polyethylene glycol di(meth)acrylate, polypropylene polyethylene glycol di(meth)acrylate, divinyl succinate, divinyl fumarate, vinyl maleate, divinyl maleate, divinyl diglycolate, vinyl itaconate, divinyl itaconate, divinyl acetone dicarboxylate, divinyl glutarate, divinyl 3,3'-thiodipropionate, divinyl trans-aconitate, trivinyl trans-aconitate, divinyl adipate, divinyl pimelate, divinyl suberate, divinyl azelaate, divinyl sebacate, divinyl dodecanedioate, and divinyl brassylate, etc. The crosslinking agent may be used alone or in combination of two or more.

[0106] Here, examples of resin particles that tend to increase the adhesive strength of toner include (meth)acrylic acid-based resin particles. Examples of the (meth)acrylic acid-based resin particles include homopolymer resin particles containing only a (meth)acrylic acid-based monomer, and copolymer resin particles of a styrene-based monomer and a (meth)acrylic acid-based monomer. Examples of homopolymer resin particles containing only a (meth)acrylic acid monomer include homopolymer particles of a monomer such as polymethyl methacrylate, polyethyl acrylate, and the like. The copolymer resin particles of a styrene-based monomer and a (meth)acrylic acid-based monomer are, for example, copolymer resin particles in which the styrene-based monomer is styrene, the (meth)acrylic acid-based monomer is n-butyl acrylate, and the mass ratio of the styrene-based monomer to the (meth)acrylic acid-based monomer (styrene-based monomer to (meth)acrylic acid-based monomer) is 70 / 30 or more and 10 / 90 or less (preferably 65 / 35 or more and 20 / 80 or less). Furthermore, when the (meth)acrylic acid-based resin particles are crosslinked resin particles using a crosslinking agent, the crosslinking agent is preferably a bifunctional alkyl acrylate having an alkylene chain having 6 to 12 carbon atoms, and the content of the crosslinking agent is, for example, preferably 0.3 to 5.0 parts by mass, more preferably 0.5 to 2.5 parts by mass, and even more preferably 1.0 to 2.0 parts by mass, relative to 100 parts by mass in total of the styrene-based monomer, the (meth)acrylic acid-based monomer, and the crosslinking agent.

[0107] Even when a toner containing such resin particles and having high adhesive strength is used, the image forming apparatus according to this embodiment suppresses deterioration in thin line reproducibility.

[0108] The average primary particle size of the resin particles is preferably 50 nm or more and 500 nm or less, more preferably 20 nm or more and 300 nm or less, and even more preferably 30 nm or more and 250 nm or less. The average primary particle size of the resin particles is a value measured using a transmission electron microscope (TEM). As a transmission electron microscope, for example, JEM-2100plus manufactured by JEOL Ltd. can be used. Specifically, the method for measuring the average primary particle size of the resin particles is as follows. The toner particles are cut into pieces with a thickness of about 0.1 μm using a microtome. The cross sections of the toner particles are photographed at 10,000 times magnification using a transmission electron microscope, and the circular equivalent diameters of 100 resin particles dispersed in the toner particles are calculated from the individual cross-sectional areas, and the arithmetic mean of these is taken as the average primary particle diameter.

[0109] The content of the resin particles is preferably from 1% by mass to 30% by mass, more preferably from 3% by mass to 25% by mass, and even more preferably from 5% by mass to 20% by mass, based on the toner particles.

[0110] -Other additives- Examples of other additives include well-known additives such as magnetic materials, charge control agents, inorganic powders, etc. These additives are contained in the toner particles as internal additives.

[0111] -Characteristics of toner particles, etc.- The toner particles may be toner particles having a single layer structure, or may be toner particles having a so-called core-shell structure composed of a core portion (core particle) and a coating layer (shell layer) that coats the core portion. Here, the toner particles having a core-shell structure may be composed of, for example, a core containing a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer containing the binder resin.

[0112] The volume average particle size (D50v) of the toner particles is preferably from 2 μm to 10 μm, and more preferably from 4 μm to 8 μm.

[0113] The various average particle sizes and particle size distribution indexes of the toner particles are measured using a Coulter Multisizer II (manufactured by Beckman Coulter, Inc.), and the electrolyte is measured using an ISOTON-II (manufactured by Beckman Coulter, Inc.). For the measurement, 0.5 mg to 50 mg of the measurement sample is added to 2 ml of a 5% aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant, and this is then added to 100 ml to 150 ml of the electrolyte. The electrolyte with the sample suspended in it is dispersed for 1 minute using an ultrasonic disperser, and the particle size distribution of particles with diameters in the range of 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. The number of particles sampled is 50,000. Based on the measured particle size distribution, cumulative distributions of volume and number are drawn for each divided particle size range (channel) from the smallest diameter side, and the particle size at 16% of the cumulative size is defined as the volume particle size D16v, the number particle size D16p, the particle size at 50% of the cumulative size as the volume average particle size D50v, the cumulative number average particle size D50p, and the particle size at 84% of the cumulative size as the volume particle size D84v and number particle size D84p. Using these, the volumetric particle size distribution index (GSDv) is (D84v / D16v) 1 / 2 The number size distribution index (GSDp) is (D84p / D16p) 1 / 2 It is calculated as:

[0114] The average circularity of the toner particles is preferably 0.90 or more and 1.00 or less, and more preferably 0.92 or more and 0.98 or less.

[0115] The average circularity of toner particles is calculated by (circular equivalent perimeter) / (perimeter) [(perimeter of a circle having the same projected area as the particle image) / (perimeter of the particle projected image)]. Specifically, it is a value measured by the following method. First, the toner particles to be measured are sucked and collected, flattened, and a still image of the particles is captured by instantaneous strobe light emission, and the particle image is analyzed by a flow-type particle image analyzer (FPIA-3000 manufactured by Sysmex Corporation). The number of samples to be taken in order to calculate the average circularity is 3,500. When the toner contains an external additive, the toner (developer) to be measured is dispersed in water containing a surfactant, and then ultrasonic treatment is performed to obtain toner particles from which the external additive has been removed.

[0116] (External additives) The external additive may be, for example, inorganic particles. Examples of the inorganic particles include SiO 2 , TiO 2, Al 2 O 3 , SrTiO 3 , CuO, ZnO, SnO 2 , CEO 2 , Fe 2 O 3 , MgO, BaO, CaO, K 2 O, Na 2 O, ZrO 2 , CaO SiO 2 , K 2 O (TiO 2 )n, Al 2 O 3 2SiO 2 , CaCO 3 , MgCO 3 , BaSO 4 , MgSO 4 etc.

[0117] The surface of the inorganic particles as an external additive may be subjected to a hydrophobic treatment. The hydrophobic treatment may be performed, for example, by immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobizing agent is usually, for example, 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the inorganic particles.

[0118] Examples of external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate (PMMA), and melamine resin), cleaning agents (for example, metal salts of higher fatty acids such as zinc stearate, and fluorine-based polymer particles).

[0119] The amount of the external additive added is, for example, preferably from 0.01% by mass to 10% by mass, and more preferably from 0.01% by mass to 6.0% by mass, based on the toner particles.

[0120] (Toner manufacturing method) Next, a method for producing the toner according to the present embodiment will be described. The toner according to the exemplary embodiment is obtained by producing toner particles and then externally adding an external additive to the toner particles.

[0121] The toner particles may be produced by any of a dry production method (e.g., a kneading and pulverizing method, etc.) and a wet production method (e.g., an aggregation-coalescence method, a suspension polymerization method, a dissolution suspension method, etc.). The method for producing the toner particles is not particularly limited, and a well-known production method is adopted. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0122] Specifically, for example, when the toner particles are produced by the aggregation and coalescence method, for example, a step of mixing a first resin particle dispersion liquid in which first resin particles serving as a binder resin are dispersed, a colorant dispersion liquid in which a colorant is dispersed, and a release agent particle dispersion liquid in which release agent particles (hereinafter also referred to as "release agent particles") are dispersed, and aggregating the particles and the colorant in the obtained dispersion liquid to form first aggregated particles (first aggregated particle forming step); a step of adding second resin particles serving as a binder resin to the first aggregated particle dispersion liquid after obtaining the first aggregated particle dispersion liquid in which the first aggregated particles are dispersed, and aggregating the second resin particles onto the surfaces of the first aggregated particles to form second aggregated particles (second aggregated particle forming step); a step of heating the second aggregate particle dispersion liquid in which the second aggregate particles are dispersed to fuse and coalesce the second aggregate particles to form toner particles (fusion and coalescence step); The toner particles are produced through the above steps. The aggregation-coalescence method will be described as a method for producing toner particles containing a binder resin, a colorant, and a release agent, but the colorant and the release agent are components that are contained in the toner particles as necessary.

[0123] Each step will be described in detail below.

[0124] -Each dispersion preparation process- First, the various dispersions to be used in the aggregation-coalescence method are prepared. Specifically, a first resin particle dispersion in which the first resin particles to be the binder resin are dispersed, a colorant dispersion in which the colorant is dispersed, a second resin particle dispersion in which the second resin particles to be the binder resin are dispersed, and a release agent particle dispersion in which the release agent particles are dispersed are prepared. In each dispersion preparation step, the first resin particles and the second resin particles will be referred to as "resin particles" in the following description.

[0125] Here, the resin particle dispersion liquid is prepared, for example, by dispersing resin particles in a dispersion medium with the aid of a surfactant.

[0126] The dispersion medium used in the resin particle dispersion liquid is, for example, an aqueous medium. Examples of the aqueous medium include water such as distilled water and ion-exchanged water, alcohols, etc. These may be used alone or in combination of two or more kinds.

[0127] Examples of the surfactant include anionic surfactants such as sulfate salts, sulfonates, phosphates, and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; and nonionic surfactants such as polyethylene glycols, alkylphenol ethylene oxide adducts, and polyhydric alcohols. Among these, anionic surfactants and cationic surfactants are particularly preferred. The nonionic surfactants may be used in combination with anionic surfactants or cationic surfactants. The surfactant may be used alone or in combination of two or more kinds.

[0128] In the resin particle dispersion, examples of the method for dispersing the resin particles in the dispersion medium include general dispersion methods using, for example, a rotary shear type homogenizer, a ball mill having a media, a sand mill, a dyno mill, etc. Depending on the type of resin particles, the resin particles may be dispersed in the resin particle dispersion using, for example, a phase inversion emulsification method. The phase inversion emulsification method is a method in which the resin to be dispersed is dissolved in a hydrophobic organic solvent in which the resin is soluble, a base is added to the organic continuous phase (O phase) to neutralize it, and then an aqueous medium (W phase) is added to effect conversion of the resin from W / O to O / W (so-called phase inversion), resulting in a discontinuous phase, and the resin is dispersed in particulate form in the aqueous medium.

[0129] The volume average particle size of the resin particles dispersed in the resin particle dispersion is, for example, preferably from 0.01 μm to 1 μm, more preferably from 0.08 μm to 0.8 μm, and even more preferably from 0.1 μm to 0.6 μm. The volume average particle size of the resin particles is measured by using a particle size distribution obtained by measurement using a laser diffraction particle size distribution measuring device (e.g., LA-700 manufactured by Horiba, Ltd.), subtracting the cumulative distribution from the small particle size side for the volume of the divided particle size range (channel), and measuring the particle size at which the cumulative distribution is 50% of all particles as the volume average particle size D50v. The volume average particle sizes of particles in other dispersions are also measured in the same manner.

[0130] The content of the resin particles in the resin particle dispersion is, for example, preferably from 5% by mass to 50% by mass, and more preferably from 10% by mass to 40% by mass.

[0131] In addition, for example, a colorant dispersion and a release agent particle dispersion are also prepared in the same manner as the resin particle dispersion. That is, the volume average particle size, dispersion medium, dispersion method, and content of particles in the resin particle dispersion are the same for the colorant dispersed in the colorant dispersion and the release agent particles dispersed in the release agent particle dispersion.

[0132] -First agglomerated particle formation process- Next, the first resin particle dispersion liquid, the colorant dispersion liquid, and the release agent particle dispersion liquid are mixed together. Then, in this mixed dispersion, the first resin particles, the colorant, and the release agent particles are hetero-aggregated to form first aggregated particles containing the first resin particles, the colorant, and the release agent particles.

[0133] Specifically, for example, a coagulant is added to a dispersion liquid obtained by mixing a first resin particle dispersion liquid, a colorant dispersion liquid, and a release agent particle dispersion liquid, and the pH of the mixed dispersion liquid is adjusted to be acidic (for example, a pH of 2 or more and 5 or less), a dispersion stabilizer is added as necessary, and then the temperature is set to a range of 20°C or more and 50°C or less, and the particles dispersed in the mixed dispersion liquid are coagulated to form first coagulated particles. In the first aggregate particle formation step, for example, the above-mentioned aggregating agent may be added to the mixed dispersion at room temperature (e.g., 25°C) while stirring the mixed dispersion with a rotary shear homogenizer, the pH of the mixed dispersion may be adjusted to an acidic state (e.g., a pH of 2 or more and 5 or less), and a dispersion stabilizer may be added as necessary, followed by the above-mentioned heating.

[0134] Examples of the flocculant include a surfactant having a polarity opposite to that of the surfactant used as the dispersant added to the mixed dispersion, an inorganic metal salt, and a divalent or higher metal complex. In particular, when a metal complex is used as the flocculant, the amount of surfactant used is reduced and the charging characteristics are improved. If necessary, an additive that forms a complex or a similar bond with the metal ions of the flocculant may be used, and a chelating agent is preferably used as this additive.

[0135] Examples of inorganic metal salts include metal salts such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, and aluminum sulfate, as well as inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, and calcium polysulfide. The chelating agent may be a water-soluble chelating agent, for example, oxycarboxylic acid such as tartaric acid, citric acid, gluconic acid, iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), etc. The amount of the chelating agent added is, for example, preferably 0.01 parts by mass or more and 5.0 parts by mass or less, and more preferably 0.1 parts by mass or more and less than 3.0 parts by mass, relative to 100 parts by mass of the first resin particles.

[0136] -Second agglomerated particle formation process- Next, after obtaining the first aggregated particle dispersion liquid in which the first aggregated particles are dispersed, the second resin particle dispersion liquid in which the second resin particles are dispersed is added to the first aggregated particle dispersion liquid. The second resin particles may be of the same type as the first resin particles, or may be of a different type.

[0137] Then, in the dispersion of the first aggregated particles and the second resin particles, the second resin particles are aggregated on the surfaces of the first aggregated particles. At this time, a release agent particle dispersion may also be added to aggregate the second resin particles and the release agent particles on the surfaces of the first aggregated particles. Specifically, for example, in the first aggregated particle forming step, when the first aggregated particles reach a target particle size, the second resin particle dispersion is added to the first aggregated particle dispersion, and heating is performed at a temperature equal to or lower than the glass transition temperature of the second resin particles. Then, the pH of the dispersion is adjusted to, for example, a range of about 6.5 to 8.5, thereby stopping the progress of aggregation. In this manner, the second aggregated particles are obtained, which are aggregated such that the second resin particles adhere to the surfaces of the first aggregated particles.

[0138] -Fusion / coalescence process- Next, the second aggregate particle dispersion liquid in which the second aggregate particles are dispersed is heated, for example, to a temperature equal to or higher than the glass transition temperature of the first and second resin particles (for example, a temperature 10 to 30° C. higher than the glass transition temperatures of the first and second resin particles) to fuse and coalesce the second aggregate particles, thereby forming toner particles.

[0139] Through the above steps, toner particles are obtained. In the above-described aggregation-coalescence method, the first aggregated particles may be fused and coalesced to form toner particles without carrying out the second aggregated particle forming step. Also, the second aggregated particle forming step may be repeated multiple times.

[0140] After the fusion and coalescence process, the toner particles formed in the solution are subjected to a known washing process, solid-liquid separation process, and drying process to obtain toner particles in a dried state. In the washing step, it is preferable to carry out sufficient replacement washing with ion-exchanged water from the viewpoint of electrostatic charge. In addition, the solid-liquid separation step is not particularly limited, but it is preferable to carry out suction filtration, pressure filtration, etc. from the viewpoint of productivity. In addition, in the drying step, there is no particular limit to the method, but it is preferable to carry out freeze drying, air flow drying, fluidized drying, vibration type fluidized drying, etc. from the viewpoint of productivity.

[0141] The toner according to the present embodiment is produced, for example, by adding an external additive to the obtained toner particles in a dry state and mixing them. The mixing may be performed, for example, by using a V blender, a Henschel mixer, a Loedige mixer, etc. Furthermore, if necessary, coarse particles of the toner may be removed using a vibration sieve, an air sieve, etc.

[0142] <Electrostatic image developer> The electrostatic image developer according to this embodiment contains at least the toner according to this embodiment. The electrostatic image developer according to the present embodiment may be a one-component developer containing only the toner according to the present embodiment, or may be a two-component developer in which the toner is mixed with a carrier.

[0143] The carrier is not particularly limited, and may be any known carrier, such as a coated carrier in which the surface of a core material made of magnetic powder is coated with a coating resin, a magnetic powder dispersion type carrier in which magnetic powder is dispersed and mixed in a matrix resin, or a resin impregnated type carrier in which porous magnetic powder is impregnated with a resin. The magnetic powder dispersion type carrier and the resin impregnated type carrier may be a carrier in which the constituent particles of the carrier are used as a core material and are coated with a coating resin.

[0144] Examples of the magnetic powder include magnetic metals such as iron, nickel, and cobalt, and magnetic oxides such as ferrite and magnetite.

[0145] Examples of the coating resin and matrix resin include styrene-(meth)acrylic acid resin; polyolefin resins such as polyethylene resin and polypropylene resin; polyvinyl or polyvinylidene resins such as polystyrene, (meth)acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymer; straight silicone resin or modified product thereof consisting of organosiloxane bonds; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyester; polyurethane; polycarbonate; amino resins such as urea-formaldehyde resin; and epoxy resins. The coating resin and the matrix resin preferably contain a (meth)acrylic resin, more preferably contain 50 mass% or more of the (meth)acrylic resin based on the total mass of the resin, and further preferably contain 80 mass% or more of the (meth)acrylic resin based on the total mass of the resin. In particular, the coating resin and the matrix resin preferably contain an alicyclic (meth)acrylic resin as the (meth)acrylic resin. The coating resin and the matrix resin may contain other additives such as conductive particles. Examples of the conductive particles include particles of metals such as gold, silver, and copper, carbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate, and potassium titanate.

[0146] Here, the method of coating the surface of the core material with the coating resin includes a method of coating with a solution for forming a coating layer in which the coating resin and, if necessary, various additives are dissolved in an appropriate solvent, etc. The solvent is not particularly limited and may be selected taking into consideration the coating resin to be used, the suitability for application, etc. Specific resin coating methods include an immersion method in which the core material is immersed in a solution for forming a coating layer, a spray method in which the solution for forming a coating layer is sprayed onto the surface of the core material, a fluidized bed method in which the solution for forming a coating layer is sprayed onto the core material while it is suspended in flowing air, and a kneader coater method in which the core material of a carrier and the solution for forming a coating layer are mixed in a kneader coater and the solvent is removed.

[0147] In the two-component developer, the mixture ratio (mass ratio) of the toner and the carrier is preferably toner:carrier=1:100 to 30:100, and more preferably 3:100 to 20:100. EXAMPLES

[0148] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0149] <Preparation of amorphous resin particle dispersion 1> Terephthalic acid: 98 parts by mole Trimellitic anhydride: 2 mol parts Bisphenol A ethylene oxide 2 mole adduct: 20 mole parts Bisphenol A propylene oxide 2 mole adduct: 80 mole parts The above materials were charged into a reaction vessel equipped with a stirrer, a nitrogen inlet tube, a temperature sensor, and a distillation column, the temperature was raised to 190°C over 1 hour, and 1.2 parts of dibutyltin oxide was added per 100 parts of the above materials. The temperature was raised to 240°C over 6 hours while distilling off the generated water, and the dehydration condensation reaction was continued for 3 hours while maintaining the temperature at 240°C, after which the reaction product was cooled.

[0150] The reaction product was transferred to a Cavitron CD1010 (manufactured by Eurotech) at a rate of 100 g per minute while remaining in a molten state. At the same time, ammonia water with a concentration of 0.37% by mass, which was prepared separately, was heated to 120°C by a heat exchanger and transferred to the Cavitron CD1010 at a rate of 0.1 liters per minute. The Cavitron CD1010 was operated under conditions of a rotor rotation speed of 60 Hz and a pressure of 5 kg / cm2 to obtain a resin particle dispersion in which resin particles with a volume average particle size of 160 nm were dispersed. Ion-exchanged water was added to the resin particle dispersion to adjust the solid content to 20% by mass, thereby obtaining amorphous resin particle dispersion 1.

[0151] <Preparation of Crystalline Resin Particle Dispersion> Sebacic acid: 202 parts by weight Ethylene glycol: 62 parts by weight The above materials were charged into a reaction vessel equipped with a stirrer, a nitrogen inlet tube, a temperature sensor, and a distillation column, and the temperature was raised to 160°C over 1 hour, and 0.8 parts by mass of dibutyltin oxide was added. The temperature was raised to 180°C over 6 hours while distilling off the generated water, and the dehydration condensation reaction was continued for 5 hours while maintaining the temperature at 180°C. Thereafter, the temperature was gradually raised to 230°C under reduced pressure, and stirring was performed for 2 hours while maintaining the temperature at 230°C. The reactant was then cooled. After cooling, solid-liquid separation was performed, and the solid was dried to obtain a crystalline polyester resin.

[0152] Crystalline polyester resin: 100 parts Methyl ethyl ketone: 40 parts Isopropyl alcohol: 30 parts 10% ammonia solution: 6 parts The above materials were added to a 3-liter jacketed reaction tank (manufactured by Tokyo Rikakikai Co., Ltd.: BJ-30N) equipped with a condenser, a thermometer, a water dropping device, and an anchor blade, and the resin was dissolved while stirring and mixing at 100 rpm while maintaining the temperature at 80°C in a water circulation type thermostatic bath. Thereafter, the water circulation type thermostatic bath was set to 50°C, and a total of 400 parts of ion-exchanged water kept at 50°C was dropped at a rate of 7 parts by mass / min to cause phase inversion, thereby obtaining an emulsion. 576 parts by mass of the obtained emulsion and 500 parts by mass of ion-exchanged water were placed in a 2-liter eggplant flask, and set in an evaporator (manufactured by Tokyo Rikakikai Co., Ltd.) equipped with a vacuum control unit via a trap ball. The eggplant flask was rotated and heated in a hot water bath at 60°C, and the pressure was reduced to 7 kPa while paying attention to bumping, and the solvent was removed. Then, ion-exchanged water was added to obtain a crystalline resin particle dispersion liquid with a solid content concentration of 20% by mass.

[0153] <Preparation of styrene (meth)acrylic resin particle dispersion 1> (Preparation of Emulsion A) Styrene: 45 parts -n-Butyl acrylate: 53 parts Divinylbenzene: 2 parts The above materials were charged into a mixing vessel equipped with a stirrer and stirred. A mixed solution of 1.5 parts of anionic surfactant (SS-H manufactured by Kao Corporation) and 98.5 parts of ion-exchanged water was added to the mixing vessel and stirred to prepare emulsion A.

[0154] (Preparation of Emulsion B) Styrene: 45 parts n-Butyl acrylate: 54 parts Divinylbenzene: 1 part The above materials were charged into a mixing vessel equipped with a stirrer and stirred. A mixed solution of 1.5 parts of anionic surfactant (SS-H manufactured by Kao Corporation) and 98.5 parts of ion-exchanged water was added to the mixing vessel and stirred to prepare emulsion B.

[0155] (Preparation of Styrene (Meth) Acrylic Resin Particle Dispersion 1) In a reaction vessel equipped with a stirring device and a nitrogen inlet tube, 2.0 parts of an anionic surfactant (SS-H manufactured by Kao Corporation) and 300 parts of ion-exchanged water were added and stirred. 50 parts of emulsion A were added. The atmosphere in the reaction vessel was replaced with nitrogen, and the reaction solution was heated in an oil bath while stirring until the temperature of the reaction solution reached 75°C. 10 parts of ammonium persulfate with a concentration of 10% by mass was further added and maintained for 30 minutes. Thereafter, while maintaining the temperature of the reaction solution at 75°C, 150 parts of emulsion A was gradually dripped into the reaction vessel over 60 minutes ("Dropping Time A" described below) using a pump. After completion of the dripping, the temperature of the reaction solution was changed to 70°C and maintained for 15 minutes, after which, while maintaining the temperature of the reaction solution ("Polymerization Temperature B" described below) at 70°C, 200 parts of emulsion B was dripped into the reaction vessel over 120 minutes ("Dropping Time B" described below) using a pump. After completion of the dripping, 10 mass % of emulsion B was added dropwise to the reaction vessel over 60 minutes ("Dropping Time B" described below). % ammonium persulfate was added, and the mixture was held for 2 hours, then cooled to room temperature. Ion-exchanged water was added to give a solids concentration of 20%, to give styrene (meth)acrylic resin particle dispersion 1.

[0156] <Preparation of Colorant Dispersion> Carbon black (Cabot, Regal 330): 50 parts Anionic surfactant Neogen RK (Dai-ichi Kogyo Seiyaku): 5 parts Ion-exchanged water: 192.9 parts The above components were mixed and treated for 10 minutes at 240 MPa using an Ultimizer (manufactured by Sugino Machine Co., Ltd.) to prepare a colorant dispersion (solid content: 20%).

[0157] <Preparation of release agent dispersion 1> Fischer-Tropsch wax (FNP0090 manufactured by Nippon Seiro Co., Ltd., melting temperature Tw: 90°C): 50 parts Anionic surfactant (Neogen RK, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 1 part Ion-exchanged water: 200 parts The above materials were mixed and heated to 130°C, dispersed using a homogenizer (IKA Ultra Turrax T50), and then dispersed using a Manton-Gaulin high pressure homogenizer (Gaulin) to obtain a release agent dispersion (solid content 20% by mass) in which release agent particles were dispersed. The volume average particle size of the release agent particles was 180 nm.

[0158] <Preparation of developers 1 to 3> ·Amorphous resin particle dispersion 1: 225 parts ·Crystalline resin particle dispersion: 25 parts Styrene (meth)acrylic resin particle dispersion 1:60 parts Colorant dispersion: 30 parts Release agent dispersion 1: 30 parts Ion-exchanged water: 100 parts The above materials were placed in a reaction vessel equipped with a thermometer, a pH meter, and a stirrer, and heated to a temperature of 30°C from the outside using a mantle heater, and held for 30 minutes while stirring at a rotation speed of 150 rpm. Next, a 0.3N nitric acid aqueous solution was added to adjust the pH to 3.0, and then a 3% by mass polyaluminum chloride aqueous solution was added while dispersing with a homogenizer (Ultra Turrax T50 manufactured by IKA). Next, the temperature was raised to 50°C while stirring, and held for 30 minutes. Next, 130 parts of amorphous resin particle dispersion 1 was added and held for 1 hour, and a 0.1N sodium hydroxide aqueous solution was added to adjust the pH to 8.5, and then the mixture was heated to 85°C while continuing to stir, and held for 5 hours. Next, cooling, solid-liquid separation, washing and drying of the solids were sequentially performed, and toner particles 1 having a volume average particle size of 4.8 μm and a shape factor of 0.969 were obtained. Similarly, the mixture was heated to 85° C. and held for 4 hours to obtain toner particles 2 having a volume average particle size of 4.5 μm and a shape factor of 0.958. Similarly, the mixture was heated to 85° C. and held for 6.5 hours to obtain toner particles 3 having a volume average particle size of 5.0 μm and a shape factor of 0.975.

[0159] The obtained toner particles 1 to 3 were each used, and 100 parts of the toner particles and 0.7 parts of dimethyl silicone oil-treated silica particles (RY200 manufactured by Nippon Aerosil Co., Ltd.) were mixed in a Henschel mixer to obtain a toner. Then, 8 parts of the obtained toner and 100 parts of the following carrier were mixed to obtain developer 1.

[0160] -Creating the carrier- Ferrite particles (average particle size 35 μm) 100 parts Toluene 14 parts Styrene / methyl methacrylate copolymer (copolymer ratio 15 / 85) 3 parts Carbon black 0.2 parts The above components except for the ferrite particles were dispersed in a sand mill to prepare a dispersion liquid, and this dispersion liquid was placed in a vacuum degassing kneader together with the ferrite particles, and the mixture was dried under reduced pressure while stirring to obtain a carrier.

[0161] <Examples 1 to 7, Comparative Example 1> The developer shown in Table 1 was placed in the developing device of a modified image forming apparatus "Color1000iPress (manufactured by Fujifilm Business Innovation Co., Ltd.)." The developing device had a configuration equivalent to that shown in FIG. 3, and was modified so that the frequencies of the AC voltages applied to the two developing members (i.e., developing sleeves) could be controlled independently. In this image forming apparatus, the development conditions (DC voltage, and AC voltage superimposed on the DC voltage and its frequency) when the image density of the toner image was 40% or less were set as shown in Table 1, and the image forming apparatus of each example was produced. Except for Comparative Example 1, the development conditions when the image density of the toner image is 40% or less are as follows: when the image density of the toner image is more than 40%, the development conditions for the first and second developing rolls are the same, but the frequency of the AC voltage of the developing voltage applied to the second developing roll is lowered so that the frequency of the AC voltage of the developing voltage applied to the second developing roll is lower than the frequency of the AC voltage of the developing voltage applied to the first developing roll.

[0162] <Evaluation> (Fine line reproducibility) Using the image forming apparatus of each example with the development conditions set as shown in Table 1, 1000 sheets of a chart with an image density of 1% were printed in an environment of 30°C temperature and 88% relative humidity, and then a 1on1off image (an image with 1-dot lines arranged in parallel at 1-dot intervals, with an image density of 5%) with a resolution of 2,400 dpi (dots per inch: number of dots per 2.54 cm) was output as a 5 cm x 5 cm chart. Evaluation was then performed according to the following criteria. A: There are no missing or blurred lines. B: Line omissions and blurring are observed, but they are minor and do not affect usability. C: Lines are missing or blurred, making the image unsuitable for practical use.

[0163] [Table 1]

[0164] From the above results, it is understood that the deterioration of thin line reproducibility is suppressed in this embodiment compared to the comparative example.

[0165] The present embodiment includes the following aspects. (((1))) An electrophotographic photoreceptor; a charging device for charging a surface of the electrophotographic photoreceptor; an electrostatic image forming device for forming an electrostatic image on the charged surface of the electrophotographic photoreceptor; a developing device that contains a developer containing a toner, supplies the developer, and develops the electrostatic charge image formed on the surface of the electrophotographic photosensitive member into a toner image, the developing device having a first developing member that is disposed opposite the electrophotographic photosensitive member and holds and transports the developer to a development area, a second developing member that is disposed opposite the electrophotographic photosensitive member on the downstream side of the first developing member in a rotation direction of the electrophotographic photosensitive member and holds and transports the developer to the development area, a first power source that applies a developing voltage in which an AC voltage is superimposed on a DC voltage to the first developing member, and a second power source that applies a developing voltage in which an AC voltage is superimposed on a DC voltage to the second developing member; a transfer device for transferring the toner image formed on the surface of the electrophotographic photoreceptor to a surface of a recording medium; a fixing device for fixing the toner image onto a surface of a recording medium; a control device that acquires image information of the toner image, and controls at least one of the first power source and the second power source in accordance with the image information to make the frequency of the AC voltage of the developing voltage applied to the second developing member lower than the frequency of the AC voltage of the developing voltage applied to the first developing member; An image forming apparatus comprising: (((2))) The control device controls a second power source to lower the frequency of the AC voltage of the developing voltage applied to the second developing member, thereby making the frequency of the AC voltage of the developing voltage applied to the second developing member lower than the frequency of the AC voltage of the developing voltage applied to the first developing member. (((3))) The image forming apparatus described in (((1))) or (((2))), wherein the control device controls at least one of the first power source and the second power source, and sets a ratio (Fd / Fu) of a frequency Fd of the AC voltage of the developing voltage applied to the first developing member to a frequency Fu of the AC voltage of the developing voltage applied to the second developing member to be 2.0 or more and 9.0 or less. (((4))) The image forming apparatus according to any one of ((1))) to (((3))), wherein the control device acquires an image density of the toner image and controls at least one of the first power source and the second power source. (((5))) The image forming apparatus according to any one of ((1))) to (((4))), wherein the toner has an adhesive force of 5 MPa or more and 15 MPa or less. (((6))) The image forming apparatus according to (((5))), wherein the toner has toner particles containing a binder resin and resin particles. (((7))) The image forming apparatus according to (((6))), wherein the content of the resin particles is 3% by mass or more and 25% by mass or less with respect to the toner particles. (((8))) The image forming apparatus according to (((6))) or (((7))), wherein the resin particles are a styrene (meth)acrylic resin. (((9))) The image forming apparatus according to any one of (((6))) to (((8))), wherein the average primary particle diameter of the resin particles is 20 nm or more and 300 nm or less.

[0166] The advantages of the above aspect are as follows. According to the invention relating to (((1))), in a specific image forming apparatus, when the image density of a toner image is low, for example, an image forming apparatus is provided in which deterioration of fine line reproducibility is suppressed compared to a case in which the frequency of the AC voltage of the developing voltage applied to the first developing member and the frequency of the AC voltage of the developing voltage applied to the second developing member are the same.

[0167] According to the invention relating to (((2))), an image forming apparatus is provided in which a control device controls a first power source to increase the frequency of the AC voltage of the developing voltage applied to the first developing member, thereby suppressing deterioration of fine line reproducibility compared to a case in which the frequency of the AC voltage of the developing voltage applied to the second developing member is made lower than the frequency of the AC voltage of the developing voltage applied to the first developing member. According to the invention related to (((3))), an image forming apparatus is provided in which deterioration of thin-line reproducibility is suppressed compared to when the ratio (Fd / Fu) is less than 1.7 or exceeds 10.0. According to the invention relating to (((4))), in a specific image forming apparatus, when the image density of a toner image is low, an image forming apparatus is provided in which deterioration of fine line reproducibility is suppressed compared to a case in which the frequency of the AC voltage of the developing voltage applied to the first developing member is the same as the frequency of the AC voltage of the developing voltage applied to the second developing member. According to the invention pertaining to (((5))), (((6))), (((7))), (((8))) or (((9))), in a specific image forming apparatus, when the image density of a toner image is 40% or less, even if the adhesion force of the toner is 5 MPa or more and 15 MPa or less, compared to when the frequency of the AC voltage of the developing voltage applied to the first developing member and the frequency of the AC voltage of the developing voltage applied to the second developing member are the same, an image forming apparatus is provided in which deterioration of thin line reproducibility is suppressed. [Explanation of symbols]

[0168] 10 Image forming device 12 Photoreceptor 14 Electrostatic materials 15 Charging device 16 Electrostatic image forming device 18 Developing device 20 Transfer material 22 Cleaning device 22A Cleaning Blade 24 Static eliminator 26 Fixing device 30A Recording medium 31 Transcription device 36 Control device

Claims

1. An electrophotographic photoreceptor; a charging device for charging a surface of the electrophotographic photoreceptor; an electrostatic image forming device for forming an electrostatic image on the charged surface of the electrophotographic photoreceptor; a developing device that contains a developer containing a toner, supplies the developer, and develops the electrostatic charge image formed on the surface of the electrophotographic photosensitive member into a toner image, the developing device having a first developing member that is disposed opposite the electrophotographic photosensitive member and holds and transports the developer to a development area, a second developing member that is disposed opposite the electrophotographic photosensitive member on the downstream side of the first developing member in a rotation direction of the electrophotographic photosensitive member and holds and transports the developer to the development area, a first power source that applies a developing voltage in which an AC voltage is superimposed on a DC voltage to the first developing member, and a second power source that applies a developing voltage in which an AC voltage is superimposed on a DC voltage to the second developing member; a transfer device for transferring the toner image formed on the surface of the electrophotographic photoreceptor to a surface of a recording medium; a fixing device for fixing the toner image onto a surface of a recording medium; a control device that acquires image information of the toner image, and controls at least one of the first power source and the second power source in accordance with the image information to make the frequency of the AC voltage of the developing voltage applied to the second developing member lower than the frequency of the AC voltage of the developing voltage applied to the first developing member; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the control device controls a second power source to lower a frequency of the AC voltage of the developing voltage applied to the second developing member, so as to make the frequency of the AC voltage of the developing voltage applied to the second developing member lower than the frequency of the AC voltage of the developing voltage applied to the first developing member.

3. 2. The image forming apparatus according to claim 1, wherein the control device controls at least one of the first power source and the second power source to set a ratio (Fd / Fu) of a frequency Fd of the AC voltage of the developing voltage applied to the first developing member to a frequency Fu of the AC voltage of the developing voltage applied to the second developing member to be 2.0 or more and 9.0 or less.

4. The image forming apparatus according to claim 1 , wherein the control device acquires an image density of the toner image and controls at least one of the first power source and the second power source.

5. 2. The image forming apparatus according to claim 1, wherein the toner has an adhesive force of 5 MPa or more and 15 MPa or less.

6. 6. The image forming apparatus according to claim 5, wherein the toner has toner particles containing a binder resin and resin particles.

7. 7. The image forming apparatus according to claim 6, wherein the content of the resin particles is 3% by mass or more and 25% by mass or less based on the toner particles.

8. 7. The image forming apparatus according to claim 6, wherein the resin particles are made of a styrene (meth)acrylic resin.

9. 7. The image forming apparatus according to claim 6, wherein the average primary particle diameter of the resin particles is 20 nm or more and 300 nm or less.

Images