Image forming device and process cartridge

Abstract

To provide an image forming device that suppresses occurrence of a color stripe that occurs when an image of low image density is formed under a hot and humid environment after repeatedly forming images of high image density.SOLUTION: Provided is an image forming device in which a collected toner having been collected by a cleaning blade contains a toner particle and a titanate metal particle, and the grain size distribution curve of the titanate metal particle satisfies a formula (1). Formula (1): 1.4≤(2b) / (a+b)≤1.95. (In formula (1), a represents a width on a smaller diameter side than a perpendicular at a 50% height of maximum peak height when the perpendicular is lowered from the maximum peak of the grain size distribution curve, and b represents width on a larger diameter side than the perpendicular at a 50% height of maximum peak height when the perpendicular is lowered from the maximum peak of the grain size distribution curve.)SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and a process cartridge. [Background technology]

[0002] Patent Document 1 describes a toner containing toner particles containing a binder resin and inorganic fine particles, wherein the inorganic fine particles contain aggregated particles, and the aggregated particles contain primary particles of at least one metal salt selected from the group consisting of metal titanates and metal zirconates, the primary particles of the metal salt having a number average particle diameter of 15 nm to 55 nm, an aggregate diameter of the aggregated particles being 80 nm to 300 nm, and a volume resistivity of the aggregated particles being 2×10 9 Ω·cm~2×10 13 The toner is characterized in that the surface area of ​​the aggregated particles is 0.3 area % to 10.0 area %.

[0003] Patent Document 2 proposes "a toner for developing electrostatic images, comprising toner particles and an external additive including particles A containing a perovskite compound and having an equivalent circle diameter of 15 nm to 90 nm and particles B containing a perovskite compound and having an equivalent circle diameter of 1.0 μm to 3.0 μm, wherein the particles B account for 0.3% to 3.5% by number of all the toner particles." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-34651 [Patent Document 2] Japanese Patent Application Publication No. 2023-47228 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention addresses the problem of providing an image forming apparatus that includes an image carrier, a charging device that charges the surface of the image carrier, an electrostatic image forming apparatus that contains a developer including toner and forms an electrostatic image on the surface of the charged image carrier using the developer, a developing device that contains a developer including toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier as a toner image, a transfer device that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium, a cleaning device that has a cleaning blade that cleans the surface of the image carrier, and a fixing device that fixes the toner image to the surface of the recording medium, wherein the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, and the image forming apparatus suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming high-density images, compared to an image forming apparatus in which the particle size distribution curve of the metal titanate particles does not satisfy the following formula (1): [Means for solving the problem]

[0006] The above problems are solved by the following means: <1> an image carrier; a charging device that charges the surface of the image carrier; an electrostatic image forming device that contains a developer containing a toner and forms an electrostatic image on the charged surface of the image carrier by the developer; a developing device that contains a developer having a toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier into a toner image; a transfer device that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium; a cleaning device having a cleaning blade for cleaning the surface of the image carrier; a fixing device for fixing the toner image to a surface of a recording medium; Equipped with the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, An image forming apparatus in which the particle size distribution curve of the metal titanate particles satisfies the following formula (1): Formula (1) 1.4≦2b / (a+b)≦1.95 (In formula (1), a represents the width on the smaller diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve, and b represents the width on the larger diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve.) <2> 2. The image forming apparatus according to claim 1, wherein the particle size distribution curve of the metal titanate particles satisfies the following formula (2): Formula (2) 1.6≦2b / (a+b)≦1.9 (In formula (2), a represents the width on the smaller diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve, and b represents the width on the larger diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve.) <3> the width b of the particle size distribution curve of the metal titanate particles is 0.5 μm or more and 2.0 μm or less; 3. The image forming apparatus according to claim 1, wherein the maximum peak height of the particle size distribution curve of the metal titanate particles is 5% or more and 40% or less. <4> the width b of the particle size distribution curve of the metal titanate particles is 0.75 μm or more and 1.5 μm or less; 4. The image forming apparatus according to claim 3, wherein the maximum peak height in the particle size distribution curve of the metal titanate particles is 10% or more and 25% or less. <5> 5. The image forming apparatus according to claim 1, wherein the particle diameter of the metal titanate particles at the maximum peak in the particle size distribution curve is 0.5 μm or more and 3.0 μm or less. <6> 6. The image forming apparatus according to claim 5, wherein the particle diameter of the metal titanate particles at the maximum peak in the particle size distribution curve is 0.75 μm or more and 2.0 μm or less. <7> 7. The image forming apparatus according to claim 1, wherein the metal titanate particles have an average circularity of 0.75 or more and 1.0 or less. <8> 8. The image forming apparatus according to claim 1, wherein the ratio of the number of the metal titanate particles to the number of the toner particles in the recovered toner is 0.3% by number or more and 3.5% by number or less. <9> 9. The image forming apparatus according to claim 1, wherein the metal titanate particles are strontium titanate particles. <10> 10. The image forming apparatus according to claim 9, wherein the strontium titanate particles contain a dopant. <11> 11. The image forming apparatus according to claim 10, wherein the dopant is silica or lanthanum. <12> an image carrier; a charging device that charges the surface of the image carrier; an electrostatic image forming device that contains a developer containing a toner and forms an electrostatic image on the charged surface of the image carrier by the developer; a developing device that contains a developer having a toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier into a toner image; a cleaning device having a cleaning blade for cleaning the surface of the image carrier; Equipped with the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, The particle size distribution curve of the metal titanate particles satisfies the following formula (1): A process cartridge that is detachably attached to an image forming apparatus. Formula (1) 1.4≦(2b) / (a+b)≦1.95 (In formula (1), a represents the width on the smaller diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve, and b represents the width on the larger diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve. [Effects of the Invention]

[0007] <1> According to the invention, there is provided an image forming apparatus comprising: an image carrier; a charging device for charging the surface of the image carrier; an electrostatic image forming apparatus that contains a developer including toner and forms an electrostatic image on the surface of the charged image carrier using the developer; a developing device that contains a developer including toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier as a toner image; a transfer device that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium; a cleaning device that has a cleaning blade that cleans the surface of the image carrier; and a fixing device that fixes the toner image to the surface of the recording medium, wherein the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, and the image forming apparatus suppresses the occurrence of color streaks that occur when a low image density image is formed in a high temperature and high humidity environment after repeatedly forming high image density images, compared to an image forming apparatus in which the particle size distribution curve of the metal titanate particles does not satisfy the following formula (1):

[0008] <2> According to the invention, an image forming apparatus is provided that suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming a high-density image, compared to when formula (2) is not satisfied. <3> According to the invention, an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming high-density images, compared to when the width b in the particle size distribution curve of the metal titanate particles is less than 0.5 or exceeds 2.0, or when the maximum peak height in the particle size distribution curve of the metal titanate particles is less than 5% or exceeds 40%. <4> According to the invention, an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming high-density images, compared to when the width b in the particle size distribution curve of the metal titanate particles is less than 0.75 μm or exceeds 1.5 μm, or when the maximum peak height in the particle size distribution curve of the metal titanate particles is less than 10% or exceeds 25%. <5> According to the invention, an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming high-density images, compared to when the particle size of the maximum peak in the particle size distribution curve of the metal titanate particles is less than 0.5 μm or greater than 3.0 μm. <6> According to the invention, an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming high-density images, compared to when the particle size of the maximum peak in the particle size distribution curve of the metal titanate particles is less than 0.75 μm or more than 2.0 μm. <7> According to the invention, an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming a high-density image, compared to when the average circularity of the metal titanate particles is less than 0.75 or more than 1.0. <8> According to the invention, an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a high-density image is repeatedly formed and then a low-density image is formed in a high-temperature, high-humidity environment, compared to when the ratio of metal titanate particles to toner particles in the recovered toner is less than 0.3% by number or more than 3.5% by number. <9> According to the invention, an image forming apparatus is provided which, compared to when the metal titanate particles are calcium titanate particles, suppresses the occurrence of color streaks that occur when a high-density image is repeatedly formed and then a low-density image is formed in a high-temperature, high-humidity environment. <10> According to the invention, an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming a high-density image, compared to when the strontium titanate particles do not contain a dopant. <11> According to the invention, an image forming apparatus is provided which, compared to when the dopant is niobium, suppresses the occurrence of color streaks that occur when a low image density image is formed in a high-temperature, high-humidity environment after repeatedly forming a high image density image. <12> According to the invention described in the above, there is provided a process cartridge comprising: an image carrier; a charging device for charging the surface of the image carrier; an electrostatic image forming device that contains a developer including toner and forms an electrostatic image on the surface of the charged image carrier using the developer; a developing device that contains a developer including toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier as a toner image; and a cleaning device that has a cleaning blade that cleans the surface of the image carrier, wherein the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, and the process cartridge suppresses the occurrence of color streaks that occur when a low image density image is formed in a high temperature and high humidity environment after repeatedly forming high image density images, compared to a process cartridge in which the particle size distribution curve of the metal titanate particles does not satisfy the following formula (1): [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 2 is an enlarged view showing the position where the cleaning blade contacts the photosensitive member in the image forming apparatus of FIG. 1. FIG. [Figure 3] FIG. 3 is a schematic diagram for explaining a particle size distribution curve of collected toner in the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0011] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

[0012] <Image forming device> The image forming apparatus according to this embodiment includes: an image carrier; a charging device for charging the surface of the image carrier; an electrostatic image forming device that contains a developer containing toner and forms an electrostatic image on the surface of a charged carrier by the developer; a developing device that contains a developer having toner and supplies the developer to develop the electrostatic image formed on the surface of the support into a toner image; a transfer device that transfers the toner image formed on the surface of the support to the surface of a recording medium; a cleaning device having a cleaning blade for cleaning the surface of the holder; a fixing device for fixing the toner image to the surface of the recording medium; Equipped with The toner collected by the cleaning blade contains toner particles and metal titanate particles. In addition, the particle size distribution curve of the metal titanate particles satisfies the formula (1) described below.

[0013] The image forming apparatus according to the present embodiment, with the above-described configuration, suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming a high-density image. The reason for this is presumed to be as follows.

[0014] Conventionally, an abrasive is used as an external additive in a toner to remove discharge products and the like that adhere to an image carrier during charging. Metal titanate particles are suitable as the abrasive because they are cubic, rectangular, or other shaped particles with high crystallinity and high resistance.

[0015] Here, when high-density images are repeatedly formed, the amount of toner that reaches the contact point between the image carrier and the cleaning blade (hereinafter also referred to as the "blade contact point") increases. As a result, the amount of discharge products that adhere to the image carrier also increases, but the amount of abrasive that reaches the blade contact point also increases, resulting in a sufficient amount of abrasive remaining at the blade contact point and improved cleaning performance. However, when a low-density image is formed after repeatedly forming a high-density image, the amount of toner that reaches the blade contact area decreases, even though the amount of discharge products adhering to the image carrier increases. As a result, the amount of abrasive that reaches the blade contact area decreases, the abrasive action of the abrasive decreases, and cleaning performance deteriorates. As a result, color streaks become more likely to occur.

[0016] Therefore, the image forming apparatus according to this embodiment employs metal titanate particles whose particle size distribution curve satisfies formula (1). By employing metal titanate particles having such a particle size distribution, small, medium, and large diameter metal titanate particles tend to be regularly retained and arranged at the blade contact portion from the downstream side in the image carrier rotation direction. By regularly accumulating and arranging the metal titanate particles at the blade contact area, the particle filling amount in the accumulation area (i.e., the polishing layer made of metal titanate particles) increases, making the accumulation area less likely to collapse and more stable. As a result, even if the accumulation amount decreases, the polishing action of the metal titanate particles is more likely to be exerted. This improves cleaning performance and reduces the occurrence of color streaks. Furthermore, some of the toner metal titanate particles in the developer stored in the developing device are developed into a toner image, which may result in a particle size distribution that differs from that of the metal titanate particles in the toner recovered by the blade. The metal titanate particles used as an abrasive have multiple particle size ranges. As a result, metal titanate particles below a certain particle size strongly adhere to the toner, and only metal titanate particles above a certain particle size are selectively supplied into the recovered toner, resulting in a particle size distribution in the recovered toner that cannot be achieved with metal titanate particles of a single particle size. Therefore, when the particle size distribution curve of the metal titanate particles in the toner collected by the blade satisfies the formula (1), color streaks are less likely to occur.

[0017] From the above, it is presumed that the image forming apparatus according to this embodiment suppresses the occurrence of color streaks that occur when a high-density image is repeatedly formed and then a low-density image is formed in a high-temperature, high-humidity environment.

[0018] In addition, the reason why the particle size distribution curve of the metal titanate particles in the recovered toner is adopted in the image forming apparatus according to this embodiment is that the amount of metal titanate particles in the recovered toner is large compared to the small amount of metal titanate particles in the developer toner contained in the developing device, and this increases the measurement accuracy of the particle size distribution of the metal titanate particles.

[0019] Here, the image forming apparatus according to this embodiment may be a well-known image forming apparatus such as a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an intermediate transfer type apparatus that primarily transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer medium, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer medium to the surface of a recording medium; an apparatus equipped with a static elimination device that irradiates the surface of the image carrier with static elimination light to eliminate static electricity after the toner image is transferred and before charging; or an apparatus equipped with an image carrier heating member that increases the temperature of the image carrier and reduces the relative temperature.

[0020] 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 that performs primary transfer of the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer device that performs secondary transfer of the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0021] The image forming apparatus according to this embodiment may be either a dry development type image forming apparatus or a wet development type image forming apparatus (a development type using a liquid developer).

[0022] In the image forming apparatus according to the present embodiment, for example, the portion including the electrophotographic photosensitive member may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. Examples of the process cartridge include a device including an image carrier, a charging device, an electrostatic latent image forming device, and a developing device.

[0023] 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 other parts will be omitted.

[0024] FIG. 1 is a schematic diagram showing an example of the configuration of an image forming apparatus according to the present embodiment. 1, an image forming apparatus 10 according to this embodiment is provided with, for example, a photoconductor 12. The photoconductor 12 (an example of an image carrier) is cylindrical and connected to a drive unit 27 such as a motor via a driving force transmission member (not shown) such as a gear, and is driven to rotate around a rotation axis indicated by a black dot by the drive unit 27. In the example shown in FIG. 1, the photoconductor 12 is driven to rotate in the direction of arrow A.

[0025] Around the photoreceptor 12, for example, a charging device 15, an electrostatic image forming device 16, a developing device 18, a transfer device 31, a cleaning device 22, and a static eliminator 24 are arranged in this order along the rotation direction of the photoreceptor 12. The image forming apparatus 10 also includes 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 includes a control device 36 that controls the operation of each device (each section). The unit including the photoreceptor 12, charging device 15, electrostatic image forming device 16, developing device 18, transfer device 31, and cleaning device 22 corresponds to an image forming unit.

[0026] In the image forming apparatus 10, at least the photosensitive member 12, the developing device 18, and the cleaning device 22 may be provided as a process cartridge integrated with other devices.

[0027] Hereinafter, each device (each section) of the image forming apparatus 10 will be described in detail.

[0028] [Photoreceptor] The photoreceptor 12 has a photosensitive layer. The photosensitive layer may be a single-layer photosensitive layer in which a charge generating material and a charge transport material are contained in the same photosensitive layer to integrate their functions, or a laminated photosensitive layer having a charge generating layer and a charge transport layer with separate functions. When the photosensitive layer is a laminated photosensitive layer, the order of the charge generating layer and the charge transport layer is not particularly limited, but the photoreceptor preferably has a structure in which the charge generating layer, the charge transport layer, and the surface protective layer are arranged in this order on a conductive substrate. The photoreceptor may also include layers other than these layers.

[0029] [Charging device] The charging device 15 charges the surface of the photoreceptor 12. The charging device 15 is provided, for example, in contact with or without contact with the surface of the photoreceptor 12 and includes a charging member 14 that 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.

[0030] The charging member 14 of the charging device 15 may be, for example, a contact-type charger using a conductive charging roller, a charging brush, a charging film, a charging rubber blade, a charging tube, etc. The charging member 14 may also be, for example, a non-contact-type roller charger, or a charger known per se, such as a scorotron charger or corotron charger that utilizes corona discharge.

[0031] [Electrostatic image forming device] The electrostatic image forming device 16 forms an electrostatic image on the surface of the charged photoreceptor 12. Specifically, for example, the electrostatic image forming device 16 irradiates the surface of the photoreceptor 12, which has been charged by the charging member 14, with light L modulated based on image information of the image to be formed, and forms an electrostatic image on the photoreceptor 12 according to the image of the image information.

[0032] The electrostatic image forming device 16 may be, for example, an optical system having a light source that exposes light such as semiconductor laser light, LED light, or liquid crystal shutter light in an imagewise manner.

[0033] [Developing device] The developing device 18 is provided, for example, downstream in the rotation direction of the photoconductor 12 from the position where light L is irradiated by the electrostatic image forming device 16. A container for containing a developer is provided within the developing device 18. The container contains a developer including toner. The toner is contained within the developing device 18 in a charged state, for example.

[0034] The developing device 18 includes a developing member 18A that develops the electrostatic image formed on the surface of the photoreceptor 12 with a developer containing, for example, toner, and a power source 32 that applies a developing voltage to the developing member 18A. The developing member 18A is electrically connected to the power source 32, for example.

[0035] The developing member 18A of the developing device 18 is selected depending on the type of developer, and may be, for example, a developing roll having a developing sleeve with a built-in magnet.

[0036] The developing device 18 (including the power supply 32) 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 developing voltage to the developing member 18A. The developing member 18A to which the developing voltage is applied is charged to a developing potential corresponding to the developing voltage. The developing member 18A charged to the developing potential then holds, for example, the developer contained in the developing device 18 on its surface and supplies 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.

[0037] [Transfer device] The transfer device 31 is provided, for example, downstream of the position where the developing member 18A 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 the 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 itself and the photoreceptor 12. The transfer member 20 is, for example, electrically connected to the power source 30.

[0038] 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.

[0039] The transfer device 31 (including the power supply 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 is applied is charged to a transfer potential corresponding to the transfer voltage.

[0040] When a transfer voltage of the opposite polarity to the toner constituting the toner image formed on the photosensitive member 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 photosensitive member 12 and the transfer member 20 face each other (see transfer area 32A in Figure 1), a transfer electric field of an electric field strength is formed that moves each toner constituting the image on the photosensitive member 12 from the photosensitive member 12 to the transfer member 20 side by electrostatic force.

[0041] The recording medium 30A is housed, for example, in a storage unit (not shown), and is transported from this storage unit along a transport path 34 by multiple transport members (not shown) to a transfer area 32A, which is an area where the photoreceptor 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 32A, the toner image on the photoreceptor 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 moves from the surface of the photoreceptor 12 to the recording medium 30A, and the toner image is transferred onto the recording medium 30A. The toner image on the photoreceptor 12 is then transferred onto the recording medium 30A by the transfer electric field.

[0042] [Cleaning device]

[0043] The cleaning device 22 has a cleaning blade 220 that cleans the surface of the photoreceptor 12. The tip of the cleaning blade 220 is brought into contact with the photoreceptor 12 in a direction opposite to the rotation direction of the photoreceptor 12 to remove any deposits on the surface of the photoreceptor 12.

[0044] The cleaning device 22 is provided downstream of the transfer device 31 in the rotation direction of the photoreceptor 12. The cleaning device 22 transfers the toner image onto the recording medium 30A and cleans the photoreceptor 12 of residual toner and the like. Specifically, the cleaning device 22 cleans not only the residual toner but also other deposits such as discharge products generated by the charging means and paper dust.

[0045] Now, with reference to FIG. 2, the cleaning device 22 will be described. FIG. 2 is a schematic diagram showing the arrangement of the cleaning blade 220 in the cleaning device 22 shown in FIG. As shown in FIG. 2, the tip of the cleaning blade 220 faces in a direction opposite to the rotation direction (direction of the arrow) of the photoreceptor 12, and in this state is in contact with the surface of the photoreceptor 12.

[0046] The angle θ between the cleaning blade 220 and the photoreceptor 12 is preferably set to be equal to or greater than 5° and equal to or less than 35°, and more preferably set to be equal to or greater than 10° and equal to or less than 25°. The pressure N of the cleaning blade 220 against the photosensitive member 12 is 0.6 gf / mm 2 Over 6.0gf / mm 2 It is preferable to set it as follows: Here, the angle θ specifically refers to the angle formed by the tangent line (the dashed line in FIG. 2) at the contact point between the tip of the cleaning blade 220 and the photosensitive member 12 and the non-deformed portion of the cleaning blade 220, as shown in FIG. 2. The pressing pressure N is the pressure (gf / mm ) that the cleaning blade 220 presses toward the center of the photosensitive member 12 at the position where it contacts the photosensitive member 12, as shown in FIG. 2 )

[0047] The cleaning blade 220 in this embodiment is an elastic plate-like member.

[0048] A support member (not shown in FIG. 2) is joined to the surface of the cleaning blade 220 opposite to the surface that comes into contact with the photoreceptor 12, and the cleaning blade 220 is supported by this support member. This support member presses the cleaning blade 220 against the photoreceptor 12 with the above-mentioned pressing pressure. Examples of the support member include metal materials such as aluminum and stainless steel. An adhesive layer made of an adhesive or the like may be provided between the support member and the cleaning blade 220 to bond them together. The cleaning device may include known members other than the cleaning blade 220 and the support member that supports it.

[0049] At least the contact portion of the cleaning blade 220 that comes into contact with the photoreceptor 12 is made of, for example, polyurethane rubber. The polyurethane rubber is a polyurethane rubber obtained by polymerizing at least a polyol component and a polyisocyanate component. If necessary, the polyurethane rubber may be a polyurethane rubber obtained by polymerizing a resin having a functional group capable of reacting with an isocyanate group of the polyisocyanate in addition to the polyol component.

[0050] The polyurethane rubber preferably has hard segments and soft segments. The terms "hard segment" and "soft segment" refer to segments in which the former is made of a material that is relatively harder than the material that makes up the latter, and the latter is made of a material that is relatively softer than the material that makes up the former, in a polyurethane rubber material. Examples of materials constituting the hard segments (hard segment materials) include low-molecular-weight polyol components among polyol components, resins having functional groups capable of reacting with the isocyanate groups of polyisocyanates, etc. On the other hand, examples of materials constituting the soft segments (soft segment materials) include high-molecular-weight polyol components among polyol components.

[0051] There are no particular limitations on the composition of the polyurethane rubber, and any well-known polyurethane rubber that is used for the cleaning blade 220 may be used.

[0052] [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 light to eliminate static. 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 image forming area) to eliminate static.

[0053] The static eliminator 24 may be, for example, a device having a light source such as a tungsten lamp that emits white light or a light emitting diode (LED) that emits red light.

[0054] [Fusing device] The fixing device 26 is provided, for example, downstream of the transfer area 32A in the conveyance direction of the conveyance 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.

[0055] The fixing device 26 may be a known fixing device, such as a heat roller fixing device or an oven fixing device. Specifically, for example, the fixing device 26 is a well-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.

[0056] 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 32A) where the photosensitive element 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, to the installation position of the fixing device 26, where the toner image on the recording medium 30A is fixed.

[0057] 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 photoreceptor 12 is neutralized by the neutralization device 24, it is again charged to a charging potential by the charging device 15.

[0058] [Operation of image forming device] An example of the operation of the image forming apparatus 10 according to this embodiment will be described. Note that the various operations of the image forming apparatus 10 are performed by a control program executed by the control device 36.

[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 with 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 photoreceptor 12 after the toner image has been transferred is cleaned by a cleaning blade 220 in a cleaning device 22, and then neutralized by a neutralization device .

[0060] [Recovered toner] The following describes the toner collected by the cleaning blade 220 in the image forming apparatus 10. Note that the following description will omit reference numerals.

[0061] The recovered toner contains toner particles and metal titanate particles. The recovered toner may contain an external additive other than the metal titanate particles. Details of the components of the recovered toner are the same as those of the toner contained in the developer stored in the developing device, so they will be described in detail with respect to the developer.

[0062] (particle size distribution curve) The particle size distribution curve of the metal titanate particles in the recovered toner satisfies the following formula (1), preferably the following formula (2), and more preferably the following formula (3). Formula (1) 1.4≦2b / (a+b)≦1.95 Formula (2) 1.6≦2b / (a+b)≦1.9 Formula (3) 1.6≦2b / (a+b)≦1.85 In formulas (1) to (3), a represents the width (unit: μm) on the smaller diameter side of the perpendicular line at a height of 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve, and b represents the width (unit: μm) on the larger diameter side of the perpendicular line at a height of 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve (see FIG. 3).

[0063] If the "2b / (a+b)" value exceeds 1.95, the metal titanate particles will have a large diameter, which increases the load on the cleaning blade, causing the metal titanate particles to slip through the cleaning blade and making color streaks more likely to occur. If the "2b / (a+b)" value is less than 1.4, the particle size distribution of the metal titanate particles becomes narrow, and it becomes difficult for small, medium, and large diameter metal titanate particles to be regularly accumulated and arranged in the blade contact area from the downstream side in the image carrier rotation direction. This makes it difficult for the metal titanate particles to be regularly accumulated and arranged in the blade contact area. As a result, the particle packing density in the accumulation area decreases, and the polishing effect of the metal titanate particles becomes difficult to exert. As a result, cleaning performance deteriorates and color streaks become more likely to occur.

[0064] The width b of the particle size distribution curve of the metal titanate particles is preferably 0.5 μm or more and 2.0 μm or less, more preferably 0.75 μm or more and 1.5 μm or less, and even more preferably 0.9 μm or more and 1.3 μm or less. When the width b is 0.5 μm or more, the metal titanate particles do not contain excessively large particles, which reduces the load on the cleaning blade, making it difficult for the metal titanate particles to slip through the cleaning blade, and as a result, color streaks are less likely to occur. When the width b is 2.0 μm or less, the particle size distribution of the metal titanate particles is appropriately broadened, and small, medium, and large diameter metal titanate particles tend to be regularly accumulated and arranged at the blade contact portion from the downstream side in the image carrier rotation direction. This facilitates regular accumulation and arrangement of the metal titanate particles at the blade contact portion. This increases the particle packing density at the accumulation portion, making it easier for the metal titanate particles to exert their abrasive action. As a result, cleaning performance is improved and color streaks are less likely to occur.

[0065] The maximum peak height of the particle size distribution curve of the metal titanate particles, expressed as the frequency of each particle size relative to the total number of particles (see H in Figure 3), is preferably 5% or more and 40% or less, more preferably 10% or more and 25% or less, and even more preferably 15% or more and 20% or less. When the maximum peak height of the frequency of the metal titanate particles relative to the total particle number is 5% or more and 40% or less, the particle packing density in the stagnant area (i.e., the polishing layer of the metal titanate particles) at the blade contact area increases, improving cleaning performance and reducing the occurrence of color streaks.

[0066] The particle size of the maximum peak in the particle size distribution curve of the metal titanate particles is preferably 0.5 μm or more and 3.0 μm or less, more preferably 0.75 μm or more and 2.0 μm or less, and even more preferably 1.0 μm or more and 1.5 μm or less. When the maximum peak particle size is 0.5 μm or more, the amount of metal titanate particles remaining at the blade contact area increases, and the abrasive action of the metal titanate particles is more easily exerted, resulting in improved cleaning performance and less color streaks. When the maximum peak particle size is 3.0 μm or less, the load on the cleaning blade caused by large diameter metal titanate particles is reduced, which makes it difficult for the metal titanate particles to slip through the cleaning blade, thereby making it difficult for color streaks to occur.

[0067] (average circularity) The average circularity of the metal titanate particles is preferably 0.75 or more and 1.0 or less, more preferably 0.8 or more and 1.0 or less, and even more preferably 0.85 or more and 1.0 or less. When the average circularity is 0.75 or more and 1.0 or less, the particle packing density of the retained portion (i.e., the polishing layer of the metal titanate particles) at the blade contact portion tends to increase. As a result, even if the retained amount decreases, the polishing action of the metal titanate particles tends to be exerted. As a result, cleaning performance is improved and color streaks are less likely to occur.

[0068] (Number ratio) In the recovered toner, the number ratio of metal titanate particles to toner particles is preferably 0.3 to 3.5% by number, more preferably 0.7 to 3.1% by number, and even more preferably 0.9 to 2.9% by number. When the number ratio is 0.3% by number or more, the amount of metal titanate particles remaining at the blade contact area increases, and the abrasive action of the metal titanate particles is more easily exerted, resulting in improved cleaning performance and less color streaks. When the number ratio is 3.5% by number or less, the amount of metal titanate particles remaining at the blade contact portion is prevented from increasing excessively, which makes it difficult for the metal titanate particles to slip through the cleaning blade and reduces the occurrence of color streaks.

[0069] (Method for measuring each characteristic of metal titanate particles) The particle size distribution curve, average circularity and number ratio of the metal titanate particles in the recovered toner are measured as follows.

[0070] First, an unused image forming apparatus is prepared in which unused developer to be measured is accommodated in the developing device. Next, in a high temperature and humidity environment (28°C, 90% RH), an unused image forming device is used to print an image (halftone image with an image density of 1%) using the developer to be measured on the entire surface of 10,000 A4 sheets of paper. Next, the recovered toner collected by the cleaning blade is collected from the image forming apparatus after image formation. Specifically, the recovered toner is collected from the discharge pipe to which the recovered toner cleaned by the cleaning blade is transported.

[0071] Next, an energy dispersive X-ray analyzer (EDX) (Horiba, EMAX Evolution X-Max 80mm 2 The collected recovered toner is observed at a magnification of 1500 times using a scanning electron microscope (SEM) (Hitachi High-Technologies Corporation, S-4800) equipped with a ion beam splitter. Based on elemental analysis using an EDX device, 200 particles of metal titanate are identified. If there are not 200 particles in one field of view, they may be identified from multiple fields of view. Images of the 200 metal titanate particles are analyzed using image processing and analysis software WinRoof (Mitani Shoji Co., Ltd.). The circle-equivalent diameter, area, and perimeter of the primary particle images of the metal titanate particles are then determined. From the circle-equivalent diameters of the obtained primary particle image, a cumulative distribution is drawn from the small diameter side on a number basis to obtain a particle size distribution curve of the metal titanate particles. Based on the area and perimeter of the obtained primary particle image, the circularity was calculated using the formula: circularity=4π×(area of ​​particle image)÷(perimeter of particle image). 2 The circularity of the metal titanate particles is then determined by arithmetically averaging the obtained circularities to obtain the average circularity.

[0072] On the other hand, the collected recovered toner is observed to determine the number ratio of metal titanate particles to toner particles, where the number ratio of metal titanate particles is the calculated average number ratio in 200 fields of view of the recovered toner.

[0073] The particle size distribution curve, average circularity and number ratio of the metal titanate particles are shown in EMAX Evolution X-Max 80mm. 2 The images observed by an SEM equipped with a microscope (manufactured by Horiba Ltd.) were analyzed using the image processing and analysis software WinRoof (Mitani Corporation).

[0074] The particle size distribution of the metal titanate particles can be controlled, for example, by various conditions when producing the metal titanate particles by a wet process, and the average circularity of the metal titanate particles can be controlled, for example, by the type and amount of dopant doped into the metal titanate particles. The ratio of the number of metal titanate particles to the number of toner particles can be controlled by the amount of metal titanate particles in the toner in the developer contained in the developing device.

[0075] [Developer] The following describes the developer contained in the developing device 18 in the image forming apparatus 10. Note that the reference numerals will be omitted in the following description.

[0076] The developer may be a one-component developer containing only toner, or a two-component developer containing toner and a carrier.

[0077] <Toner> The toner contains toner particles and external additives, and the external additives include metal titanate particles.

[0078] (toner particles) The toner particles contain, for example, a binder resin, and may also contain a colorant, a release agent, internally added resin particles, other additives, and the like.

[0079] -Binder resin- Examples of binder resins include 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.), and vinyl resins made of 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 presence of these. These binder resins may be used alone or in combination of two or more.

[0080] As the binder resin, a polyester resin is preferable. Examples of polyester resins include known amorphous polyester resins. The polyester resin may be used in combination with a crystalline 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) relative to the total binder resin.

[0081] The "crystalline" nature of a resin refers to the presence of a clear endothermic peak rather than a stepwise change in endothermic heat in differential scanning calorimetry (DSC). Specifically, this refers to the half-width of the endothermic peak being within 10°C when measured at a heating rate of 10°C / min. On the other hand, the term "amorphous" for a resin means that the half-width exceeds 10°C, that the endothermic amount exhibits a stepwise change, or that no clear endothermic peak is observed.

[0082] As the binder resin, a polyester resin is preferable. Examples of polyester resins include known polyester resins.

[0083] The polyester resin may be, for example, a condensation polymer of a polycarboxylic acid and a polyhydric alcohol. The polyester resin may be a commercially available product or a synthesized product.

[0084] Examples of polycarboxylic acids include aliphatic dicarboxylic acids (such as oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenylsuccinic acid, adipic acid, and sebacic acid), alicyclic dicarboxylic acids (such as cyclohexanedicarboxylic acid), aromatic dicarboxylic acids (such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). Among these, aromatic dicarboxylic acids are preferred as polycarboxylic acids. The polycarboxylic 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 alkyl esters thereof (e.g., having 1 to 5 carbon atoms). The polycarboxylic acids may be used alone or in combination of two or more.

[0085] 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, preferred polyhydric alcohols are aromatic diols and alicyclic diols, and more preferred are aromatic diols. As the polyhydric alcohol, a trihydric or higher polyhydric alcohol having a crosslinked or branched structure may be used in combination with the diol. Examples of trihydric or higher polyhydric alcohols include glycerin, trimethylolpropane, and pentaerythritol. The polyhydric alcohols may be used alone or in combination of two or more.

[0086] The glass transition temperature (Tg) of the 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 JIS K 7121-1987 "Method for measuring transition temperatures of plastics."

[0087] The weight average molecular weight (Mw) of the 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 polyester resin is preferably 2,000 or more and 100,000 or less. The molecular weight distribution Mw / Mn of the 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). Molecular weight measurements by GPC are performed using a Tosoh GPC HLC-8120GPC measuring device and a Tosoh TSKgel SuperHM-M (15 cm) column in THF solvent. The weight-average molecular weight and number-average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples.

[0088] The polyester resin can be obtained by a known manufacturing method, for example, by carrying out the reaction at a polymerization temperature of 180°C or higher and 230°C or lower, reducing the pressure in the reaction system as necessary, and removing water and alcohol generated during the condensation. If the raw material monomer is not soluble or compatible at the reaction temperature, a high-boiling solvent may be added as a solubilizer to dissolve it. In this case, the polycondensation reaction is carried out while distilling off the solubilizer. If a monomer with poor compatibility is present, it is advisable to first condense the poorly compatible monomer with the acid or alcohol to be polycondensed, and then polycondense the monomer with the main component.

[0089] The polyester resin may be a hybrid resin having a polyester resin segment and a styrene-acrylic copolymer segment.

[0090] The content of the binder resin is, for example, preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and even more preferably 60% by mass to 85% by mass, based on the total mass of the toner particles.

[0091] -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 the like. Examples of the dyes include various pigments such as phosphorus blue, chalco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate, and 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.

[0092] The colorant may be surface-treated as needed, or may be used in combination with a dispersant. Furthermore, a plurality of colorants may be used in combination.

[0093] The content of the colorant is, for example, preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 15% by mass or less, based on the total mass of the toner particles.

[0094] -Mold release agent- Examples of release agents 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 montanic acid esters, but are not limited thereto.

[0095] 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) by using the "melting peak temperature" as described in the method for determining the melting temperature in JIS K 7121-1987 "Method for measuring transition temperatures of plastics."

[0096] The content of the release agent is, for example, preferably 1% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less, based on the total mass of the toner particles.

[0097] -Internal resin particles- Examples of the internally added 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. The internally added resin particles are preferably styrene-(meth)acrylic copolymer resin particles, and may be crosslinked resin particles.

[0098] The content of the internal 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.

[0099] -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.

[0100] -Characteristics of toner particles, etc.- The toner particles may be toner particles of a single layer structure, or may be toner particles of a so-called core-shell structure composed of a core part (core particle) and a coating layer (shell layer) that coats the core part. 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.

[0101] The volume average particle size (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less.

[0102] The various average particle sizes and particle size distribution indices of the toner particles are measured using a Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolyte is measured using an ISOTON-II (manufactured by Beckman Coulter). For the measurement, 0.5 mg to 50 mg of the sample to be measured 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 solution containing the suspended sample is dispersed for 1 minute using an ultrasonic disperser, and the particle size distribution of particles with a particle size 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 particle size distribution measured, 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 total is defined as the volume particle size D16v, the number particle size D16p, the particle size at 50% of the cumulative total as the volume average particle size D50v, the cumulative number average particle size D50p, and the particle size at 84% of the cumulative total as the volume particle size D84v and the number particle size D84p. Using these, the volumetric particle size distribution index (GSDv) is (D84v / D16v) 1 / 2 , the number particle size distribution index (GSDp) is (D84p / D16p) 1 / 2 It is calculated as:

[0103] 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.

[0104] 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, this value is measured by the following method. First, the toner particles to be measured are sucked and collected, forming a flat flow, and a still image of the particles is captured by instantaneously activating a strobe light, and the particle image is analyzed using a flow-type particle image analyzer (FPIA-3000 manufactured by Sysmex Corporation).The number of samples to be sampled when calculating the average circularity is 3,500. When the toner contains external additives, 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 additives have been removed.

[0105] (external additives) As the external additive, metal titanate particles are used. Examples of the metal titanate particles include calcium titanate particles, strontium titanate particles, and barium titanate particles. Among these, strontium titanate particles are preferred from the viewpoint of good cleaning properties and suppression of color streaks.

[0106] The metal titanate particles (specifically, strontium titanate particles) are preferably doped with a metal element (ie, a dopant) other than elements forming the main structure, such as titanium and metal elements in the metal salt structure. When metal titanate particles (specifically, strontium titanate particles) contain a dopant, the crystallinity of the perovskite structure decreases, resulting in a rounded shape, which controls the average circularity, improves cleaning properties, and reduces the occurrence of color streaks.

[0107] The dopant of the metal titanate particles (specifically, strontium titanate particles) is preferably a metal element that, when ionized, has an ionic radius that can be incorporated into the crystal structure that constitutes the metal titanate particles. From this perspective, the dopant of the metal titanate particles is preferably a metal element that, when ionized, has an ionic radius of 35 pm to 200 pm, more preferably 40 pm to 150 pm.

[0108] Specific examples of dopants for metal titanate particles (specifically, strontium titanate particles) include lanthanoids, silica (silicon), aluminum, magnesium, calcium, barium, phosphorus, sulfur, calcium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, yttrium, zinc, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, antimony, barium, tantalum, tungsten, rhenium, osmium, iridium, platinum, bismuth, etc. As the lanthanoid, lanthanum or cerium is preferred. Among these, from the viewpoint of good cleaning properties and suppression of color streaks, the metal titanate particles (specifically, strontium titanate particles) are preferably silica or lanthanum.

[0109] From the viewpoint of achieving a rounded shape while maintaining a perovskite-type crystal structure, the amount of dopant in the metal titanate salt particles is preferably in the range of 0.1 mol % to 20 mol % of the metal element in the metal salt structure, more preferably in the range of 0.1 mol % to 15 mol %, and even more preferably in the range of 0.1 mol % to 10 mol %.

[0110] The metal titanate particles may be particles whose surfaces have been subjected to a hydrophobic treatment. The surface treatment of the metal titanate particles is carried out, for example, by preparing a treatment liquid by mixing a silicon-containing organic compound, which is a hydrophobic treatment agent, with a solvent, and mixing the metal titanate particles with the treatment liquid under stirring, and then continuing to stir. After the surface treatment, a drying treatment is carried out to remove the solvent from the treatment liquid.

[0111] Examples of the silicon-containing organic compound used for the surface treatment of the metal titanate particles include alkoxysilane compounds, silazane compounds, silicone oils, etc. Among these, the silicon-containing organic compound is preferably an alkoxysilane compound.

[0112] Examples of the alkoxysilane compound include tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, n-butyltrimethoxysilane, i-butyltrimethoxysilane, hexyltrimethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, and hexyltriethoxysilane. Examples of suitable silanes include dimethylsilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, trimethylmethoxysilane, and trimethylethoxysilane.

[0113] Examples of the silazane compound include dimethyldisilazane, trimethyldisilazane, tetramethyldisilazane, pentamethyldisilazane, and hexamethyldisilazane.

[0114] Examples of silicone oils include silicone oils such as dimethylpolysiloxane, diphenylpolysiloxane, and phenylmethylpolysiloxane; and reactive silicone oils such as amino-modified polysiloxane, epoxy-modified polysiloxane, carboxyl-modified polysiloxane, carbinol-modified polysiloxane, fluorine-modified polysiloxane, methacryl-modified polysiloxane, mercapto-modified polysiloxane, and phenol-modified polysiloxane.

[0115] The amount of the silicon-containing organic compound used for the surface treatment is preferably 1 part by mass or more and 50 parts by mass or less, more preferably 5 parts by mass or more and 40 parts by mass or less, and even more preferably 5 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of the metal titanate particles.

[0116] The amount of the metal titanate particles added externally is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less, based on the toner particles.

[0117] Here, the method for producing the metal titanate particles can be a known method, and as an example, a method for producing strontium titanate particles will be described.

[0118] The strontium titanate particles are produced, for example, by reacting a titanium oxide source and a strontium source with an aqueous alkaline solution, followed by an acid treatment, and then, if necessary, a hydrophobic treatment of the strontium titanate particles. In this production method, the particle size of the titanium compound is controlled by the mixing ratio of the titanium oxide source and the strontium source, the concentration of the titanium oxide source at the beginning of the reaction, the temperature and rate at which the alkaline aqueous solution is added, and the like.

[0119] ≪Pelletization process≫ In the method for producing strontium titanate particles, the mixing ratio of the titanium oxide source and the strontium source is preferably an SrO / TiO molar ratio of 0.9 to 1.4, more preferably 1.05 to 1.20. The concentration of the titanium oxide source at the start of the reaction is preferably 0.05 to 1.3 mol / L, more preferably 0.5 to 1.0 mol / L, in terms of TiO.

[0120] When a dopant source is added to the mixture of the titanium oxide source and the strontium source, a metal oxide is used as the dopant source. The metal oxide as the dopant source is added to the mixture as a solution in, for example, nitric acid, hydrochloric acid, sulfuric acid, etc. The amount of the dopant source added is preferably an amount such that the amount of the metal dopant is 0.1 mol or more and 10 mol or less, and more preferably an amount such that the amount of the metal dopant is 0.5 mol or more and 10 mol or less, per 100 mol of strontium. The dopant source may be added when the alkaline aqueous solution is added to the mixed solution of the titanium oxide source and the strontium source. In this case, the metal oxide of the dopant source may be added as a solution dissolved in nitric acid, hydrochloric acid, or sulfuric acid.

[0121] The alkaline aqueous solution is preferably a sodium hydroxide aqueous solution. The higher the temperature at which the alkaline aqueous solution is added, the more likely it is that strontium titanate particles with good crystallinity will be obtained. In this embodiment, the temperature is preferably in the range of 60°C or higher and 100°C or lower. The slower the addition rate of the alkaline aqueous solution, the larger the particle size of the resulting strontium titanate particles, and the faster the addition rate, the smaller the particle size of the resulting strontium titanate particles. The addition rate of the alkaline aqueous solution is, for example, from 0.001 equivalents / h to 1.2 equivalents / h, and preferably from 0.002 equivalents / h to 1.1 equivalents / h, relative to the amount of the raw material.

[0122] <Acid treatment process> After the addition of the alkaline aqueous solution, an acid treatment is carried out to remove unreacted strontium source, for example, by adjusting the pH of the reaction solution to 2.5 to 7.0, more preferably 4.5 to 6.0, using hydrochloric acid. After the acid treatment, the reaction liquid is subjected to solid-liquid separation, and the solid content is dried to obtain strontium titanate particles.

[0123] <Hydrophobic treatment> The hydrophobic treatment of the surfaces of strontium titanate particles is carried out, for example, by preparing a treatment liquid by mixing a hydrophobic treatment agent with a solvent, mixing the strontium titanate particles with the treatment liquid under stirring, and continuing to stir. After the surface treatment, a drying treatment is carried out in order to remove the solvent from the treatment solution. Examples of the hydrophobic treatment agent include those already mentioned above. The solvent used to prepare the treatment liquid is preferably an alcohol (for example, methanol, ethanol, propanol, or butanol), or a hydrocarbon (for example, benzene, toluene, normal hexane, or normal heptane). In the treatment liquid, the concentration of the hydrophobic treatment agent is preferably 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, and even more preferably 10% by mass or more and 30% by mass or less. Here, when producing strontium titanate particles in which the particle size distribution in the recovered toner satisfies formula (1), for example, after producing strontium titanate, moisture is removed by a filter press or suction filtration, and then hot air drying is performed at a temperature of 80°C for 2 hours.

[0124] Examples of external additives other than the metal titanate particles include inorganic particles such as SiO2, TiO2, Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, KO, Na2O, ZrO2, CaO·SiO2, KO·(TiO2)n, Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, and MgSO4.

[0125] The surfaces of the inorganic particles as other external additives are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, 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 hydrophobic treatment 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.

[0126] Other 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 particles of fluorine-based polymers).

[0127] The amount of other external additives added is, for example, preferably 0.01% by mass or more and 10% by mass or less, and more preferably 0.01% by mass or more and 6.0% by mass or less, based on the toner particles.

[0128] (Toner manufacturing method) Next, a method for producing the toner according to this embodiment will be described. The toner according to this exemplary embodiment is obtained by producing toner particles and then externally adding an external additive to the toner particles.

[0129] The toner particles may be produced by any of a dry production method (for example, a kneading and pulverization method) and a wet production method (for example, an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method). The method for producing the toner particles is not particularly limited, and any well-known production method may be used. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0130] Specifically, for example, when toner particles are produced by an 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 particles of a release agent (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); 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 release agent are components that are contained in the toner particles as needed.

[0131] Each step will be described in detail below.

[0132] -Each dispersion preparation process- First, the various dispersions to be used in the aggregation-coalescence method are prepared: a first resin particle dispersion in which first resin particles that will become the binder resin are dispersed, a colorant dispersion in which a colorant is dispersed, a second resin particle dispersion in which second resin particles that will become the binder resin are dispersed, and a release agent particle dispersion in which release agent particles are dispersed. In each dispersion preparation step, the first resin particles and the second resin particles will be referred to as "resin particles."

[0133] Here, the resin particle dispersion liquid is prepared, for example, by dispersing resin particles in a dispersion medium using a surfactant.

[0134] Examples of the dispersion medium used in the resin particle dispersion include aqueous media. Examples of aqueous media include water such as distilled water and ion-exchanged water, alcohols, etc. These may be used alone or in combination of two or more.

[0135] Examples of surfactants include anionic surfactants such as sulfate ester salts, sulfonate salts, phosphate esters, 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. Nonionic surfactants may be used in combination with anionic surfactants or cationic surfactants. The surfactants may be used alone or in combination of two or more.

[0136] In the resin particle dispersion, resin particles can be dispersed in a dispersion medium by a general dispersion method such as a rotary shear homogenizer, a ball mill having a medium, 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 by, for example, a phase inversion emulsification method. The phase inversion emulsification method involves dissolving the resin to be dispersed in a hydrophobic organic solvent in which the resin is soluble, adding a base to the organic continuous phase (O phase) to neutralize it, and then adding an aqueous medium (W phase), thereby converting the resin from W / O to O / W (so-called phase inversion) and forming a discontinuous phase, and dispersing the resin in particulate form in the aqueous medium.

[0137] The volume average particle size of the resin particles dispersed in the resin particle dispersion is, for example, preferably 0.01 μm or more and 1 μm or less, more preferably 0.08 μm or more and 0.8 μm or less, and even more preferably 0.1 μm or more and 0.6 μm or less. The volume average particle size of the resin particles is measured using a particle size distribution obtained by measurement with a laser diffraction particle size distribution analyzer (e.g., LA-700 manufactured by Horiba, Ltd.), and the cumulative distribution for the volume of the divided particle size range (channel) is subtracted from the small particle size side, and the particle size at which the cumulative 50% of all particles is measured is defined as the volume average particle size D50v. The volume average particle sizes of particles in other dispersions are also measured in the same way.

[0138] The content of resin particles contained 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.

[0139] Note that, 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 particle content of the 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.

[0140] -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.

[0141] Specifically, for example, an aggregating agent 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), and a dispersion stabilizer is added as necessary.After that, 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 aggregated to form first aggregated particles. In the first aggregate particle formation step, for example, the mixed dispersion may be stirred with a rotary shear homogenizer, the aggregating agent may be added at room temperature (e.g., 25°C), the pH of the mixed dispersion may be adjusted to an acidic value (e.g., a pH of 2 or more and 5 or less), a dispersion stabilizer may be added as needed, and then the heating may be carried out.

[0142] 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 can be reduced and the charging characteristics can be 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.

[0143] 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, such as hydroxycarboxylic acid (e.g., 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.

[0144] -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.

[0145] 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 the mixture is heated 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 by aggregating the first aggregated particles so that the second resin particles adhere to the surfaces of the first aggregated particles.

[0146] -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 temperature of the first and second resin particles) to fuse and coalesce the second aggregate particles and form toner particles.

[0147] Through the above steps, toner particles are obtained. In the above-described aggregation and coalescence method, the first aggregated particles may be fused and coalesced to form toner particles without performing the second aggregated particle forming step. Also, the second aggregated particle forming step may be repeatedly performed multiple times.

[0148] 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 dry toner particles. In the washing step, it is preferable to carry out sufficient replacement washing with ion-exchanged water from the viewpoint of electrostatic chargeability. Furthermore, the solid-liquid separation step is not particularly limited, but from the viewpoint of productivity, it is preferable to carry out suction filtration, pressure filtration, etc. Furthermore, in the drying step, there is no particular limitation on the method, but from the viewpoint of productivity, it is preferable to carry out freeze drying, flash drying, fluidized drying, vibration-type fluidized drying, etc.

[0149] The toner according to this embodiment is produced by, for example, adding an external additive to the obtained dry toner particles and mixing them. The mixing can be carried out using, for example, a V blender, a Henschel mixer, a Loedige mixer, or the like. Furthermore, if necessary, coarse particles may be removed from the toner using a vibrating sieve, an air sieve, or the like.

[0150] <Career> The carrier is not particularly limited, and examples thereof include known carriers, such as coated carriers in which the surface of a core material made of magnetic powder is coated with a coating resin, magnetic powder dispersion carriers in which magnetic powder is dispersed and blended in a matrix resin, and resin-impregnated carriers 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.

[0151] Examples of magnetic powder include magnetic metals such as iron, nickel, and cobalt, and magnetic oxides such as ferrite and magnetite.

[0152] Examples of coating resins and matrix resins include styrene-(meth)acrylic acid resins; polyolefin resins such as polyethylene resins and polypropylene resins; polyvinyl or polyvinylidene resins such as polystyrene, (meth)acrylic resins, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymers; straight silicone resins or modified silicone resins consisting of organosiloxane bonds; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyesters; polyurethanes; polycarbonates; amino resins such as urea-formaldehyde resins; and epoxy resins. The coating resin and the matrix resin preferably contain a (meth)acrylic resin, more preferably contain 50% by mass or more of the (meth)acrylic resin relative to the total mass of the resin, and even more preferably contain 80% by mass or more of the (meth)acrylic resin relative to 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 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.

[0153] Here, the method of coating the surface of the core material with a 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. The solvent is not particularly limited and may be selected taking into consideration the coating resin to be used, its applicability, 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 the carrier and the solution for forming a coating layer are mixed in a kneader coater and the solvent is removed.

[0154] In the two-component developer, the mixing ratio (mass ratio) of toner to carrier is preferably toner:carrier=1:100 to 30:100, and more preferably 3:100 to 20:100. [Example]

[0155] Examples of the present invention will be described below, but the present invention is not limited to the following examples. In the following description, unless otherwise specified, all "parts" and "%" are based on mass.

[0156] <Carrier manufacturing> Cyclohexyl methacrylate resin (weight average molecular weight 50,000): 54 parts Carbon black (Cabot VXC72): 6 parts Toluene: 250 parts Isopropyl alcohol: 50 parts The above materials and glass beads (1 mm diameter, same amount as toluene) were placed in a sand mill and stirred at a rotation speed of 190 rpm for 30 minutes to obtain a coating agent.

[0157] 1000 parts of ferrite particles (volume average particle size 35 μm) and 150 parts of a coating agent were placed in a kneader and mixed at room temperature (25°C) for 20 minutes. The mixture was then heated to 70°C and dried under reduced pressure. The dried product was cooled to room temperature (25°C), removed from the kneader, and sieved through a 75 μm mesh to remove coarse powder, yielding a carrier.

[0158] <Preparation of particle dispersion> [Preparation of Amorphous Resin Particle Dispersion (1-1)] Terephthalic acid: 28 parts Fumaric acid: 164 parts Adipic acid: 10 parts Bisphenol A ethylene oxide 2 mole adduct: 26 parts Bisphenol A propylene oxide 2 mole adduct: 542 parts The above materials were charged into a reaction vessel equipped with a stirrer, a nitrogen inlet tube, a temperature sensor, and a rectification 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 produced 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.

[0159] 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, a 0.37% concentration of ammonia water was transferred to the heat exchanger. The mixture was heated to 120°C in a vessel and transferred to a Cavitron CD1010 at a rate of 0.1 liters per minute. The rotor rotation speed was 60 Hz and the pressure was 5 kg / cm. 2 The Cavitron CD1010 was operated under the conditions shown above to obtain a resin particle dispersion containing amorphous polyester resin particles with a volume average particle size of 169 nm. Ion-exchanged water was added to this resin particle dispersion to adjust the solid content to 20%, resulting in amorphous resin particle dispersion (1-1). The SP value (R) of the amorphous polyester resin was 9.41.

[0160] [Preparation of Crystalline Resin Particle Dispersion (1-2)] 1,10-dodecanedioic acid: 225 parts 1,6-Hexanediol: 143 parts The above materials were charged into a reaction vessel equipped with a stirrer, a nitrogen inlet tube, a temperature sensor, and a rectification column, and the temperature was raised to 160°C over 1 hour, followed by the addition of 0.8 parts of dibutyltin oxide. The temperature was raised to 180°C over 6 hours while distilling off the water produced, and the dehydration condensation reaction was continued for 5 hours while maintaining the temperature at 180°C. The temperature was then gradually raised to 230°C under reduced pressure, and stirring was continued for 2 hours while maintaining the temperature at 230°C. The reaction product was then cooled and subjected to solid-liquid separation, and the solid The product was dried to obtain a crystalline polyester resin.

[0161] Crystalline polyester resin: 100 parts Methyl ethyl ketone: 40 parts Isopropyl alcohol: 30 parts 10% aqueous ammonia solution: 6 parts The above materials were charged into a jacketed reaction vessel equipped with a condenser, thermometer, water dripper, and anchor blade. The resin was dissolved by stirring at 100 rpm while maintaining the liquid temperature at 80°C in a water-circulating thermostatic bath. The water-circulating thermostatic bath was then set to 50°C, and a total of 400 parts of ion-exchanged water maintained at 50°C was added dropwise at a rate of 7 parts / min to obtain an emulsion. 576 parts of the emulsion and 500 parts of ion-exchanged water were placed in an eggplant-shaped flask and placed in an evaporator equipped with a vacuum control unit via a trap bulb. While rotating the eggplant-shaped flask, the pressure was reduced to 7 kPa, taking care to avoid bumping, to remove the solvent. The volume average particle size of the resin particles in this dispersion was 185 nm. Ion-exchanged water was added to obtain a crystalline resin particle dispersion (1-2) with a solids content of 22.1%.

[0162] [Preparation of Resin Particle Dispersion (2)] Styrene: 47.9 parts n-Butyl acrylate: 51.8 parts 2-carboxyethyl acrylate: 0.3 parts 1,10-decanediol diacrylate: 1.65 parts Anionic surfactant (Dowfax2A1, manufactured by The Dow Chemical Company): 0.8 parts The above materials were placed in a flask, mixed, and dissolved. 60 parts of ion-exchanged water was then added and dispersed to produce an emulsion. 1.3 parts of an anionic surfactant (Dowfax 2A1, manufactured by The Dow Chemical Company) was dissolved in 90 parts of ion-exchanged water, and 1 part of the emulsion was added. A solution of 5.4 parts of ammonium persulfate in 10 parts of ion-exchanged water was then added. The remaining emulsion was then added over 180 minutes. The atmosphere in the flask was then purged with nitrogen, and the solution in the flask was heated to 65°C in an oil bath while stirring. Stirring was continued for 500 minutes while maintaining the temperature at 65°C, allowing for emulsion polymerization. The solids content was then adjusted to 24.5% with ion-exchanged water to obtain resin particle dispersion (2).

[0163] [Preparation of Colorant Particle Dispersion (1)] Cyan pigment (Pigment Blue 15:3, manufactured by Dainichi Seika Color & Chemicals Mfg. Co., Ltd.): 98 parts Anionic surfactant (Tayca Power, manufactured by Tayca Corporation): 2 parts Ion-exchanged water: 420 parts The above materials were mixed and dispersed for 10 minutes using a homogenizer (IKA Ultra Turrax) to obtain a colorant particle dispersion (1) having a volume average particle size of 164 nm and a solid content of 21.1%.

[0164] [Preparation of Release Agent Particle Dispersion (1)] Synthetic wax (FNP92, manufactured by Nippon Seiro Co., Ltd.): 50 parts Anionic surfactant (TaycaPower, manufactured by Tayca Corporation): 1 part Ion-exchanged water: 200 parts The above materials were mixed and heated to 130°C, and dispersed using a homogenizer (Ultra Turrax T50, manufactured by IKA), and then dispersed using a pressure discharge homogenizer. When the volume average particle size reached 200 nm, the mixture was collected to obtain a release agent particle dispersion (1) with a solid content of 20%.

[0165] <Production of toner particles> [Production of toner particles (1)] ·Amorphous resin particle dispersion (1-1): 169 parts ·Crystalline resin particle dispersion (1-2): 53 parts ·Resin particle dispersion (2): 33 parts Colorant dispersion (1): 33 parts Release agent dispersion (1): 25 parts Anionic surfactant (Dowfax2A1, manufactured by The Dow Chemical Company): 4.8 parts The above materials, adjusted to a liquid temperature of 10°C, were placed in a cylindrical stainless steel container and dispersed and mixed for 2 minutes using a homogenizer (IKA Ultra Turrax T50) at 4000 rpm while applying shear force. Next, 1.75 parts of a 10% aqueous solution of aluminum sulfate in nitric acid was gradually added dropwise as a flocculant, and the homogenizer rotation speed was increased to 10,000 rpm, followed by dispersion for 10 minutes to obtain a raw material dispersion.

[0166] The raw material dispersion was transferred to a reaction vessel equipped with a stirrer with two paddle blades and a thermometer. While stirring at 550 rpm, heating was initiated with a mantle heater, raising the liquid temperature to 40°C. The pH of the raw material dispersion was controlled between 2.2 and 3.5 using 0.3 M nitric acid and 1 M sodium hydroxide aqueous solution, and the temperature and pH were maintained for approximately 2 hours to allow the growth of aggregated particles. Next, a dispersion mixture of 21 parts of amorphous resin particle dispersion (1-1) and 8 parts of resin particle dispersion (2) was added and maintained for 60 minutes, allowing the amorphous resin particles and crosslinked resin particles to adhere to the surfaces of the aggregated particles. The liquid temperature was then raised to 53°C, and 21 parts of amorphous resin particle dispersion (1-1) was added and maintained for 60 minutes, allowing the amorphous resin particles to further adhere to the surfaces of the aggregated particles.

[0167] The aggregated particles were adjusted while checking the particle size and shape using an optical microscope and a particle size measuring device. The pH was then adjusted to 7.8 using a 5% aqueous sodium hydroxide solution and maintained for 15 minutes. The pH was then increased to 8.0 using a 5% aqueous sodium hydroxide solution, and the liquid temperature was then raised to 85°C. After confirming that the aggregated particles had fused using an optical microscope, heating was stopped after 2 hours and the mixture was cooled at a rate of 1.0°C / min. The solid-liquid separation was carried out using a 20 μm mesh, and the mixture was repeatedly washed with water, followed by drying in a vacuum dryer to obtain toner particles (1). The volume average particle size of the toner particles (1) was 5.3 μm.

[0168] <Preparation of metal titanate particles> (Metal titanate particles (T1)) 0.7 moles of desulfurized and peptized metatitanic acid, the titanium source, was collected and placed in a reaction vessel. Next, 0.77 moles of strontium chloride aqueous solution was added to the reaction vessel to achieve a SrO / TiO molar ratio of 1.1. Next, a solution of silicon dioxide dissolved in nitric acid was added to the reaction vessel in an amount equivalent to 1.0 mole of silicon per 100 moles of strontium. The initial TiO concentration in the mixture of the three materials was adjusted to 0.75 moles / L. The mixture was then stirred and heated to 90°C. While maintaining the temperature at 90°C and stirring, 153 mL of 10 N (mol / L) aqueous sodium hydroxide solution was added over 2 hours. Stirring was then continued for another hour while maintaining the temperature at 90°C. The reaction solution was then cooled to 40°C, and hydrochloric acid was added until the pH reached 5.5, followed by stirring for 1 hour. The precipitate was then washed by repeated decantation and redispersion in water. Hydrochloric acid was added to the slurry containing the washed precipitate to adjust the pH to 6.5, and the solids were filtered off and dried. An ethanol solution of i-butyltrimethoxysilane (i-BTMS) was added to the dried solids in an amount of 20 parts i-BTMS per 100 parts solids, and the mixture was stirred for 1 hour. The solids were filtered off and dried with hot air at 80°C for 2 hours to obtain metal titanate particles (T1).

[0169] (Metal titanate particles (T2)) Metal titanate particles (T2) were obtained in the same manner as for the metal titanate particles (T1), except that the solution in which silicon dioxide was dissolved in nitric acid was changed to a solution in which lanthanum oxide was dissolved in nitric acid.

[0170] (Metal titanate particles (T3)) Metal titanate particles (T3) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature during the addition of the aqueous sodium hydroxide solution was changed to 96°C.

[0171] (Metal titanate particles (T4)) Metal titanate particles (T4) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature during the addition of the sodium hydroxide aqueous solution was changed to 94°C.

[0172] (Metal titanate particles (T5)) Metal titanate particles (T5) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature during the addition of the aqueous sodium hydroxide solution was changed to 88°C.

[0173] (Metal titanate particles (T6)) Metal titanate particles (T6) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature during the addition of the aqueous sodium hydroxide solution was changed to 86°C.

[0174] (Metal titanate particles (T7)) Metal titanate particles (T7) were obtained in the same manner as for the metal titanate particles (T1), except that the hot air drying temperature was changed to 60° C. and the drying time was changed to 3 hours.

[0175] (Metal titanate particles (T8)) Metal titanate particles (T2) were obtained in the same manner as for the metal titanate particles (T1), except that the hot air drying temperature was changed to 60°C.

[0176] (Metal titanate particles (T9)) Metal titanate particles (T9) were obtained in the same manner as for the metal titanate particles (T1), except that the hot air drying temperature was changed to 70°C.

[0177] (Metal titanate particles (T10)) Metal titanate particles (T10) were obtained in the same manner as for the metal titanate particles (T1), except that the hot air drying temperature was changed to 100°C.

[0178] (Metal titanate particles (T11)) Metal titanate particles (T11) were obtained in the same manner as for the metal titanate particles (T1), except that the hot air drying temperature was changed to 120°C.

[0179] (Metal titanate particles (T12)) Metal titanate particles (T12) were obtained in the same manner as for the metal titanate particles (T1), except that the hot air drying temperature was changed to 120° C. and the drying time was changed to 1 hour.

[0180] (Metal titanate particles (T13)) Metal titanate particles (T13) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature was changed to 84°C during and after the addition of sodium hydroxide.

[0181] (Metal titanate particles (T14)) Metal titanate particles (T14) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature was changed to 84°C during the addition of sodium hydroxide and to 88°C after the addition.

[0182] (Metal titanate particles (T15)) Metal titanate particles (T15) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature was changed to 88°C during and after the addition of sodium hydroxide.

[0183] (Metal titanate particles (T16)) Metal titanate particles (T16) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature was changed to 92°C during and after the addition of sodium hydroxide.

[0184] (Metal titanate particles (T17)) Metal titanate particles (T17) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature was changed to 96°C during and after the addition of sodium hydroxide.

[0185] (Metal titanate particles (T18)) Metal titanate particles (T18) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature was changed to 96°C during the addition of sodium hydroxide and to 98°C after the addition.

[0186] (Metal titanate particles (T19)) Metal titanate particles (T19) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature after the addition of sodium hydroxide was changed to 86° C. and the stirring time was changed to 50 minutes.

[0187] (Metal titanate particles (T20)) Metal titanate particles (T20) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature after the addition of sodium hydroxide was changed to 86°C.

[0188] (Metal titanate particles (T21)) Metal titanate particles (T21) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature after the addition of sodium hydroxide was changed to 88°C.

[0189] (Metal titanate particles (T22)) Metal titanate particles (T22) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature after the addition of sodium hydroxide was changed to 93°C.

[0190] (Metal titanate particles (T23)) Metal titanate particles (T23) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature after the addition of sodium hydroxide was changed to 95°C.

[0191] (Metal titanate particles (T24)) Metal titanate particles (T24) were obtained in the same manner as for the metal titanate particles (T1), except that the liquid temperature after the addition of sodium hydroxide was changed to 95° C. and the stirring time was changed to 70 minutes.

[0192] (Metal titanate particles (T25)) Metal titanate particles (T25) were obtained in the same manner as for the metal titanate particles (T1), except that the amount of aqueous sodium hydroxide solution was 143 mL and the addition time of the aqueous sodium hydroxide solution was changed to 5 hours.

[0193] (Metal titanate particles (T26)) Metal titanate particles (T26) were obtained in the same manner as for the metal titanate particles (T1), except that the addition time of the aqueous sodium hydroxide solution was changed to 4 hours.

[0194] (Metal titanate particles (T27)) Metal titanate particles (T27) were obtained in the same manner as for the metal titanate particles (T1), except that the amount of sodium hydroxide aqueous solution was 163 mL and the liquid temperature after the addition of sodium hydroxide was changed to 92°C.

[0195] (Metal titanate particles (T28)) Metal titanate particles (T28) were obtained in the same manner as for the metal titanate particles (T1), except that the aqueous strontium chloride solution was changed to an aqueous calcium chloride solution.

[0196] (Metal titanate particles (T29)) Metal titanate particles (T29) were obtained in the same manner as for the metal titanate particles (T1), except that the solution of silicon oxide dissolved in nitric acid was not added.

[0197] (Metal titanate particles (T30)) Metal titanate particles (T30) were obtained in the same manner as metal titanate particles (T1), except that the solution in which silicon oxide was dissolved in nitric acid was changed to a solution in which niobium oxide was dissolved in nitric acid.

[0198] (Metal titanate particles (T31)) Metal titanate particles (T31) were obtained in the same manner as metal titanate particles (T1), except that the liquid temperature during addition of the sodium hydroxide aqueous solution was changed to 96°C and the addition time of the sodium hydroxide aqueous solution was changed to 5 hours.

[0199] (Metal titanate particles (T32)) Titanate metal salt particles (T32) were obtained in the same manner as titanate metal salt particles (T1), except that the drying method was changed from hot air drying to static drying at a drying temperature of 100°C and for a drying time of 2 hours.

[0200] <Production of Developer (1)> [Developer (1)] Toner particles (1): 100 parts Strontium titanate particles (1): 0.80 parts The above materials were mixed in a Henschel mixer and sieved through a vibrating sieve with 45 μm openings to obtain a toner. 8 parts of the toner and 100 parts of the carrier were placed in a V-blender, stirred, and sieved through a sieve with 212 μm openings to obtain developer (1).

[0201] [Developers (2) to (35) and Developers (C1) to (C2)] Developers (2) to (35) and developers (C1) and (C2) were obtained in the same manner as for developer 1. However, the type of strontium titanate particles and the amount of external addition were changed as shown in Table 1.

[0202] <Examples 1 to 35 and Comparative Examples 1 and 2> An image forming device "ApeosPort C7070 manufactured by Fujifilm Business Innovation Co., Ltd." was prepared. Then, the developing device of the image forming apparatus was filled with each of the prepared developers to prepare the image forming apparatus of each example.

[0203] <Characteristics> In the image forming apparatus of each example, the following properties of the metal titanate particles of the recovered toner were measured according to the methods described below. In addition, the following properties of the toner metal titanate particles in the developer contained in the developing device of the image forming apparatus were measured according to the described methods, except that the following properties of the toner metal titanate particles before external addition (i.e., the following properties of the toner metal titanate particles in the developer) were also measured. The width a (unit: μm) of the smaller diameter side of the perpendicular line at 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve of the metal titanate particles in the recovered toner The width b (unit: μm) of the larger diameter side of the perpendicular line at 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve of the metal titanate particles in the recovered toner The maximum peak height H (unit: %) of the particle size distribution curve of the metal titanate particles in the recovered toner, expressed as the frequency of each particle size relative to the total number of particles. The particle size D (unit: μm) of the maximum peak in the particle size distribution curve of metal titanate particles in recovered toner Average circularity AC of metal titanate particles in recovered toner and developer toner The ratio of the number of titanium oxide particles in the recovered toner to the number of toner particles (unit: %) For the developer toner, the maximum peak particle size in the particle size distribution curve of the metal titanate particles indicates the maximum peak particle size D1 (unit: μm) on the larger diameter side and the maximum peak particle size D2 (unit: μm) on the smaller diameter side.

[0204] <Color streak evaluation> Using the image forming apparatus of each example, the following color streak evaluation was carried out. A halftone image with an image density of 30% was copied onto 30,000 sheets of A4 paper in a low-temperature, low-humidity environment (temperature 10°C and relative humidity 15%). This operation was repeated twice, and then a halftone image with an image density of 5% was copied onto 10,000 sheets of A4 paper in a high-temperature, high-humidity environment (temperature 28°C and relative humidity 85%). After copying onto 10,000 sheets, the surface of the photoreceptor was inspected visually and with a microscope, and the image quality of the last 10 sheets was inspected visually. The contamination of the photoreceptor was classified as follows. The evaluation criteria are as follows: A+: No deposits are observed on the surface of the photoconductor either visually or under a microscope. No color streaks or the like are observed on the paper surface. A: No deposits are visible on the surface of the photoconductor. Fine deposits are visible under a microscope. No color streaks are visible on the paper surface. A-: No deposits are observed visually on the surface of the photoconductor. Fine streaks of deposits are observed on the surface of the photoconductor under a microscope. No color streaks are observed on the paper surface. B: Deposits are visually observed on the surface of the photoconductor. Deposits are observed under a microscope. No color streaks or the like are observed on the paper surface. C: Streaky deposits are visually observed on the surface of the photosensitive member. Deposits are observed on the surface of the photosensitive member under a microscope. No color streaks or the like are observed on the paper surface. D: Streaky deposits are visually observed on the surface of the photosensitive member. Deposits are observed under a microscope on the surface of the photosensitive member. Colored streaks are observed on the paper surface.

[0205] [Table 1-1]

[0206] [Table 1-2]

[0207] From the above results, it can be seen that the image forming apparatus of this embodiment is able to suppress the occurrence of color streaks that occur when a high-density image is repeatedly formed and then a low-density image is formed in a high-temperature, high-humidity environment, compared to the image forming apparatus of the comparative example.

[0208] The present embodiment includes the following aspects. (((1))) an image carrier; a charging device that charges the surface of the image carrier; an electrostatic image forming device that contains a developer containing a toner and forms an electrostatic image on the charged surface of the image carrier by the developer; a developing device that contains a developer having a toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier into a toner image; a transfer device that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium; a cleaning device having a cleaning blade for cleaning the surface of the image carrier; a fixing device for fixing the toner image to a surface of a recording medium; Equipped with the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, An image forming apparatus in which the particle size distribution curve of the metal titanate particles satisfies the following formula (1): Formula (1) 1.4≦2b / (a+b)≦1.95 (In formula (1), a represents the width on the smaller diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve, and b represents the width on the larger diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve.) (((2))) 2. The image forming apparatus according to claim 1, wherein the particle size distribution curve of the metal titanate particles satisfies the following formula (2): Formula (2) 1.6≦2b / (a+b)≦1.9 (In formula (2), a represents the width on the smaller diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve, and b represents the width on the larger diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve.) (((3))) the width b of the particle size distribution curve of the metal titanate particles is 0.5 μm or more and 2.0 μm or less; 3. The image forming apparatus according to claim 1, wherein the maximum peak height of the particle size distribution curve of the metal titanate particles is 5% or more and 40% or less. (((4))) the width b of the particle size distribution curve of the metal titanate particles is 0.75 μm or more and 1.5 μm or less; 4. The image forming apparatus according to claim 3, wherein the maximum peak height in the particle size distribution curve of the metal titanate particles is 10% or more and 25% or less. (((5))) 5. The image forming apparatus according to claim 1, wherein the particle diameter of the metal titanate particles at the maximum peak in the particle size distribution curve is 0.5 μm or more and 3.0 μm or less. (((6))) 6. The image forming apparatus according to claim 5, wherein the particle diameter of the metal titanate particles at the maximum peak in the particle size distribution curve is 0.75 μm or more and 2.0 μm or less. (((7))) 7. The image forming apparatus according to claim 1, wherein the metal titanate particles have an average circularity of 0.75 or more and 1.0 or less. (((8))) 8. The image forming apparatus according to claim 1, wherein the ratio of the number of the metal titanate particles to the number of the toner particles in the recovered toner is 0.3% by number or more and 3.5% by number or less. (((9))) 9. The image forming apparatus according to claim 1, wherein the metal titanate particles are strontium titanate particles. (((10))) 10. The image forming apparatus according to claim 9, wherein the strontium titanate particles contain a dopant. (((11))) 11. The image forming apparatus according to claim 10, wherein the dopant is silica or lanthanum. (((12))) an image carrier; a charging device that charges the surface of the image carrier; an electrostatic image forming device that contains a developer containing a toner and forms an electrostatic image on the charged surface of the image carrier by the developer; a developing device that contains a developer having a toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier into a toner image; a cleaning device having a cleaning blade for cleaning the surface of the image carrier; Equipped with the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, The particle size distribution curve of the metal titanate particles satisfies the following formula (1): A process cartridge that is detachably attached to an image forming apparatus. Formula (1) 1.4≦(2b) / (a+b)≦1.95 (In formula (1), a represents the width on the smaller diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve, and b represents the width on the larger diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve.

[0209] The effects of the above embodiment are as follows. According to the invention of (((1))), there is provided an image forming apparatus comprising: an image carrier; a charging device for charging the surface of the image carrier; an electrostatic image forming apparatus that contains a developer including toner and forms an electrostatic image on the surface of the charged image carrier using the developer; a developing device that contains a developer including toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier as a toner image; a transfer device that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium; a cleaning device having a cleaning blade that cleans the surface of the image carrier; and a fixing device that fixes the toner image to the surface of the recording medium, wherein the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, and which suppresses the occurrence of color streaks that occur when a low image density image is formed in a high temperature and high humidity environment after repeatedly forming high image density images, compared to an image forming apparatus in which the particle size distribution curve of the metal titanate particles does not satisfy the following formula (1):

[0210] According to the invention relating to (((2))), an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming a high-density image, compared to when formula (2) is not satisfied. According to the invention related to (((3))), an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming high-density images, compared to when the width b in the particle size distribution curve of the metal titanate particles is less than 0.5 or exceeds 2.0, or when the maximum peak height in the particle size distribution curve of the metal titanate particles is less than 5% or exceeds 40%. According to the invention related to (((4))), an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming high-density images, compared to when the width b in the particle size distribution curve of the metal titanate particles is less than 0.75 or exceeds 1.5, or when the maximum peak height in the particle size distribution curve of the metal titanate particles is less than 10% or exceeds 25%. According to the invention (((5))), an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming high-density images, compared to when the particle size of the maximum peak in the particle size distribution curve of the metal titanate particles is less than 0.5 μm or greater than 3.0 μm. According to the invention related to (((6))), an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming high-density images, compared to when the particle size of the maximum peak in the particle size distribution curve of the metal titanate particles is less than 0.75 μm or more than 2.0 μm. According to the invention (((7))), an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming a high-density image, compared to when the average circularity of metal titanate particles is less than 0.75 or more than 1.0. According to the invention related to (((8))), an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a high-density image is repeatedly formed and then a low-density image is formed in a high-temperature, high-humidity environment, compared to when the ratio of metal titanate particles to toner particles in recovered toner is less than 0.3% by number or more than 3.5% by number. According to the invention (((9))), an image forming apparatus is provided which, compared to when the metal titanate particles are calcium titanate particles, suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming a high-density image. According to the invention (((10))), an image forming apparatus is provided which suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming a high-density image, compared to when the strontium titanate particles do not contain a dopant. According to the invention (((11))), an image forming apparatus is provided which, compared to when the dopant is niobium, suppresses the occurrence of color streaks that occur when a low-density image is formed in a high-temperature, high-humidity environment after repeatedly forming a high-density image. According to the invention described in (((12))), there is provided a process cartridge comprising: an image carrier; a charging device for charging the surface of the image carrier; an electrostatic image forming device that contains a developer including toner and forms an electrostatic image on the surface of the charged image carrier using the developer; a developing device that contains a developer including toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier as a toner image; and a cleaning device that has a cleaning blade that cleans the surface of the image carrier, wherein the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, and the process cartridge suppresses the occurrence of color streaks that occur when a low image density image is formed in a high temperature and high humidity environment after repeatedly forming high image density images, compared to a process cartridge in which the particle size distribution curve of the metal titanate particles does not satisfy the following formula (1): [Explanation of symbols]

[0211] 10 Image forming device 12 Photoconductor (an example of an image carrier) 14 Charging member 15 Charging device 16 Electrostatic image forming device 18 Developing device 20 Transfer member 22 Cleaning device 24 Static eliminator 26 Fixing device 30A Recording Media 31 Transcription device 36 Control device

Claims

1. an image carrier; a charging device that charges the surface of the image carrier; an electrostatic image forming device that contains a developer containing a toner and forms an electrostatic image on the charged surface of the image carrier by the developer; a developing device that contains a developer having a toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier into a toner image; a transfer device that transfers the toner image formed on the surface of the image carrier to a surface of a recording medium; a cleaning device having a cleaning blade for cleaning the surface of the image carrier; a fixing device for fixing the toner image to a surface of a recording medium; Equipped with the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, The particle size distribution curve of the metal titanate particles satisfies the following formula (1): Formula (1) 1.4≦2b / (a+b)≦1.95 (In formula (1), a represents the width on the smaller diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve, and b represents the width on the larger diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve.)

2. 2. The image forming apparatus according to claim 1, wherein the particle size distribution curve of the metal titanate particles satisfies the following formula (2): Formula (2) 1.6≦2b / (a+b)≦1.9 (In formula (2), a represents the width on the smaller diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve, and b represents the width on the larger diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve.)

3. the width b of the particle size distribution curve of the metal titanate particles is 0.5 μm or more and 2.0 μm or less; 2. The image forming apparatus according to claim 1, wherein the maximum peak height of the particle size distribution curve of the metal titanate particles is 5% or more and 40% or less.

4. the width b of the particle size distribution curve of the metal titanate particles is 0.75 μm or more and 1.5 μm or less; 4. The image forming apparatus according to claim 3, wherein the maximum peak height in the particle size distribution curve of the metal titanate particles is 10% or more and 25% or less.

5. 2. The image forming apparatus according to claim 1, wherein the particle diameter of the metal titanate particles at the maximum peak in the particle size distribution curve is 0.5 [mu]m or more and 3.0 [mu]m or less.

6. 6. The image forming apparatus according to claim 5, wherein the particle diameter of the metal titanate particles at the maximum peak in the particle size distribution curve is 0.75 [mu]m or more and 2.0 [mu]m or less.

7. 2. The image forming apparatus according to claim 1, wherein the metal titanate particles have an average circularity of 0.75 or more and 1.0 or less.

8. 2. The image forming apparatus according to claim 1, wherein the ratio of the number of the metal titanate particles to the number of the toner particles in the recovered toner is 0.3% by number or more and 3.5% by number or less.

9. 2. The image forming apparatus according to claim 1, wherein the metal titanate particles are strontium titanate particles.

10. 10. The image forming apparatus according to claim 9, wherein the strontium titanate particles contain a dopant.

11. 11. The image forming apparatus according to claim 10, wherein the dopant is silica or lanthanum.

12. an image carrier; a charging device that charges the surface of the image carrier; an electrostatic image forming device that contains a developer containing a toner and forms an electrostatic image on the charged surface of the image carrier by the developer; a developing device that contains a developer having a toner and supplies the developer to develop the electrostatic image formed on the surface of the image carrier into a toner image; a cleaning device having a cleaning blade for cleaning the surface of the image carrier; Equipped with the recovered toner collected by the cleaning blade contains toner particles and metal titanate particles, The particle size distribution curve of the metal titanate particles satisfies the following formula (1): A process cartridge that is detachably attached to an image forming apparatus. Formula (1) 1.4≦(2b) / (a+b)≦1.95 (In formula (1), a represents the width on the smaller diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve, and b represents the width on the larger diameter side of the perpendicular line at a height that is 50% of the maximum peak height when a perpendicular line is dropped from the maximum peak of the particle size distribution curve.

Images