JP7504695B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus that uses an electrophotographic process, etc.

Image forming devices that form images using electrophotographic processes, such as copying machines and laser printers, are known.

In the transfer process, this image forming device applies a voltage from a voltage power source to a transfer member arranged opposite the photosensitive drum as an image carrier, thereby electrostatically transferring the toner image formed on the surface of the photosensitive drum onto an intermediate transfer body or recording material. When forming a toner image of multiple colors, this transfer process is repeatedly performed for the toner images of multiple colors, thereby forming a toner image of multiple colors on the surface of the intermediate transfer body or recording material. The developer (toner) that is not transferred from the photosensitive drum to the intermediate transfer body or recording material is removed from the photosensitive drum by a cleaning member and stored as waste toner in a waste toner storage section in the cleaning unit.

However, in recent years, cleanerless systems have been proposed that omit the cleaning system for the photosensitive drum surface in order to reduce the size of the device. To achieve a cleanerless system, it is preferable to improve the transfer efficiency of the toner image from the photosensitive drum to the intermediate transfer body and reduce the amount of residual toner remaining on the photosensitive drum surface after the toner image is transferred by the transfer member.

In order to achieve a cleanerless system, Patent Document 1 proposes a configuration in which fine particles are attached to the surface of the photosensitive drum in advance, and the fine particles are placed between the photosensitive drum and the toner image, reducing the adhesive force between the photosensitive drum and the toner, thereby improving transfer efficiency.

Furthermore, Patent Document 1 proposes a configuration in which toner with externally added fine particles is used as a means for adhering fine particles to the surface of the photosensitive drum, and the fine particles are supplied from the developing device onto the photosensitive drum.

JP 10-63027 A

However, as in Patent Document 1, when the photosensitive drum rotates with fine particles adhering to its surface, the fine particles adhering to the photosensitive drum surface may migrate to the surface of the member in contact with the photosensitive drum. In particular, when the toner image formed on the surface of the photosensitive drum is transferred, the fine particles migrate together with the toner image to the surface of the intermediate transfer belt in contact with the photosensitive drum, making it difficult to retain the fine particles on the surface of the photosensitive drum.

The present invention aims to prevent the fine particles attached to the surface of the photosensitive drum from being transferred from the surface of the photosensitive drum to the intermediate transfer body, thereby improving transfer efficiency.

Therefore, the image forming apparatus according to the present invention has a rotatable image carrier, a developer container that contains a developer composed of toner particles and carrier particles adhering to the surfaces of the toner particles, a developer carrier that carries the developer and contacts the image carrier to form a development section and supplies the developer to the surface of the image carrier in the development section, and an intermediate transfer body that contacts the image carrier to form a transfer section and to which a toner image formed by the developer supplied to the surface of the image carrier is transferred in the transfer section, and the image forming apparatus is capable of supplying the carrier particles carried on the surface of the developer carrier and contained in the developer container to the surface of the image carrier in the development section while the image carrier is rotating, and pressing the image carrier against the intermediate transfer body. When a pressing force is F1 and a total number of the carrier particles interposed between the image carrier and the intermediate transfer body at the transfer portion is N1, an adhesive force Fi formed between the carrier particles and the intermediate transfer body, which is measured when the carrier particles are pressed against the intermediate transfer body with a pressing force per unit carrier particle, F1/N1, and an adhesive force Fdr1 formed between the carrier particles and the image carrier, which is measured when the carrier particles are pressed against the image carrier with F1/N1, satisfy a relationship of Fi<Fdr1, and the developer has convex portions formed on the surfaces of the toner particles, the carrier particles are arranged on the convex portions, and when a closest distance between adjacent convex portions is defined as a convex spacing G, an average of the convex spacing G is equal to or less than an average particle size of the carrier particles .

As described above, the present invention can prevent fine particles attached to the surface of the photosensitive drum from being transferred from the surface of the photosensitive drum to the intermediate transfer body, thereby improving transfer efficiency.

1 is an outline of an image forming apparatus according to a first embodiment. FIG. 2 is a control block diagram according to the first embodiment. FIG. 2 is a schematic diagram of a toner surface in Example 1. 3 is a schematic diagram of a convex shape of a toner surface in Example 1. FIG. 3 is a schematic diagram of a convex shape of a toner surface in Example 1. FIG. 3 is a schematic diagram of a convex shape of a toner surface in Example 1. FIG. FIG. 2 is a schematic diagram of a toner and a transfer carrier in the first embodiment. FIG. 4 is a schematic diagram illustrating a transfer carrier supply time in the first embodiment. FIG. 4 is a schematic diagram showing primary transfer in the first embodiment. 4 is a timing chart of an image forming operation in the first embodiment. 5A and 5B are diagrams illustrating a contact state of toner in the developing unit in the first embodiment. FIG. 4 is a diagram showing the state of toner and transfer carrier particles in a developing section in Example 1. 5A and 5B are diagrams illustrating the state of transfer carrier particles in the developing section in the first embodiment. 5 is a schematic diagram showing the relationship of adhesive forces of transfer carrier particles in Example 1. FIG. 5A and 5B are diagrams illustrating a state of transfer carrier particles in a transfer section in the first embodiment. This shows the relationship between the materials of the photosensitive drum and intermediate transfer belt and their adhesive strength in the first embodiment and the like. This shows the relationship between the material of the intermediate transfer belt and the adhesive force in the first embodiment and the like. FIG. 11 is an enlarged view of a primary transfer portion in a second embodiment.

The following describes in detail preferred embodiments of the present invention by way of example, with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiments should be modified as appropriate depending on the configuration and various conditions of the device to which the present invention is applied. Therefore, unless otherwise specified, it is not intended to limit the scope of the present invention to these alone.

1. Image Forming Apparatus The present invention particularly relates to an image forming apparatus using a so-called drum cleanerless system that does not have a cleaning means for an image carrier.

Figure 1 is a schematic diagram showing an example of a color image forming apparatus, and the configuration and operation of the image forming apparatus of this embodiment will be described using Figure 1. The image forming apparatus 100 of this embodiment is a so-called tandem type printer equipped with image forming stations a to d. The first image forming station a forms images of yellow (Y), the second image forming station b forms images of magenta (M), the third image forming station c forms images of cyan (C), and the fourth image forming station d forms images of black (Bk). The configuration of each image forming station is the same except for the color of toner they contain, and the following description will be given using the first image forming station a. Furthermore, hereinafter, unless a distinction is particularly required, a to d in Y, M, C, and K will be omitted and a general description will be given.

The first image forming station a includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as the photosensitive drum) 1a, a charging roller 2a as a charging means, an exposure unit 3a, and a developing unit 4a.

The photosensitive drum 1a is an image carrier that is rotated by the photosensitive drum drive unit 110 in the direction of the arrow at a peripheral speed (process speed) of 150 mm/sec and carries a toner image. The photosensitive drum 1a is an aluminum tube with a diameter of φ20 mm on which a photosensitive layer and a surface layer are provided. The surface layer is a thin film layer with a thickness of 20 μm formed from polyarylate.

When the control unit 200, such as a controller, receives an image signal, the image forming operation is started, and the photosensitive drum 1a is rotated. During the rotation process, the photosensitive drum 1a is uniformly charged to a predetermined potential with a predetermined polarity (in this embodiment, the normal polarity is negative) by the charging roller 2a, and is exposed to light according to the image signal by the exposure unit 3a. This forms an electrostatic latent image corresponding to the yellow color component image of the target color image. Next, the electrostatic latent image is developed by the developer (yellow developer) 4a at the development position and visualized as a yellow toner image.

The charging roller 2a as a charging member is in contact with the surface of the photosensitive drum 1a at a charging portion with a predetermined pressure contact force, and rotates relative to the photosensitive drum 1a due to friction with the surface of the photosensitive drum 1a. A predetermined DC voltage is applied to the rotating shaft of the charging roller 2a from a charging voltage power source 120 in accordance with the image forming operation. In this embodiment, the charging roller 2a is a metal shaft with a diameter of φ5.5 mm, on which an elastic layer made of a conductive elastic body with a thickness of 1.5 mm and a volume resistivity of about 1×10 ⁶ Ωcm is provided. In accordance with the image forming operation, the control unit 200 applies a DC voltage of −1050 V as a charging voltage to the rotating shaft of the charging roller 2a to charge the surface of the photosensitive drum 1a to a predetermined potential of −500 V. The surface potential of the photosensitive drum 1a was measured using a surface potential meter Model 344 manufactured by Trek. The surface potential of the photosensitive drum 1a at this time, −500 V, is the surface potential of the photosensitive drum 1 when no image is formed, and is a dark potential (Vd) where no toner image is developed. In addition, a large number of convex portions are provided on the surface layer of the charging roller 2a, and the average height of the convex portions is about 10 μm. The convex portions provided on the surface layer of the charging roller 2a play a role as spacers between the charging roller 2a and the photosensitive drum 1a in the charging section. When the transfer residual toner, which is the toner that remains on the photosensitive drum 1a without being transferred in the primary transfer section described later, enters the charging section, the role of the convex portions is to prevent the charging roller 2a from being soiled with the transfer residual toner by contacting the parts other than the convex portions.

The exposure unit 3a includes a laser driver, a laser diode, a polygon mirror, an optical lens system, etc. As shown in FIG. 2, the exposure unit 3 receives a time-series electric digital pixel signal of image information that has been image-processed and input from the controller 202 to the control unit 200 via the interface 201. In this embodiment, the exposure amount is adjusted so that the image formation potential Vl of the photosensitive drum 1 in the electrostatic latent image area after exposure by the exposure unit 3a is -100V. The image formation potential is also called the bright area potential.

The developing unit 4a is provided with a developing roller 41a as a developing member (developer carrier) and a non-magnetic one-component developer composed of toner and transfer carrier particles described later. The developing unit 4a is a developing means that performs a developing action on the photosensitive drum 1 in order to develop the electrostatic latent image into a toner image, and is a developer storage section that stores the developer. The developing unit 4a and the image forming apparatus main body 100 are provided with a contact/separation mechanism 40 that controls the contact/separation (development/separation) state of the developing roller 41a and the photosensitive drum 1a as shown in FIG. 2. The control section 200 causes the developing roller 41a and the photosensitive drum 1a to contact and separate in accordance with the image forming operation, etc. When the developing roller 41a and the photosensitive drum 1a are in contact with each other, the developing roller 41a is in contact with the photosensitive drum 1a with a pressing force of 200 gf. The width of the development nip portion, which is the contact portion between the development roller 41a and the photosensitive drum 1a, is 2 mm in the rotation direction of the photosensitive drum 1 and 220 mm in the longitudinal direction of the photosensitive drum. The development roller 41a is driven to rotate by the development roller drive unit 130 in the forward direction of the surface movement of the photosensitive drum 1a so that the surface movement speed (hereinafter, the circumferential speed) in the development nip portion is equal to the circumferential speed of the photosensitive drum 1a.

The pre-exposure unit 5a, which serves as a static elimination means, eliminates static electricity by exposing the surface of the photosensitive drum 1a to light before the surface of the photosensitive drum 1a is charged by the charging roller 2a. By eliminating static electricity from the surface of the photosensitive drum 1a, it has the role of leveling out the surface potential formed on the photosensitive drum 1 and the role of controlling the amount of discharge caused by the discharge generated in the charging section.

The control unit 200 also controls the development voltage power supply 140 to apply a DC voltage of -300V as the development voltage Vdc to the core of the development roller 41a when the development roller 41a and the photosensitive drum 1a are in contact during image formation. During image formation, the toner carried on the development roller 41a is developed on the image formation potential Vl of the photosensitive drum 1a by the electrostatic force generated by the potential difference between the development voltage Vdc = -300V and the image formation potential Vl = -100V of the photosensitive drum 1a.

In the following explanation, a high potential and applied voltage refers to an absolute value that is larger on the negative polarity side (e.g., -1000V compared to -500V), and a low potential refers to an absolute value that is smaller on the negative polarity side (e.g., -300V compared to -500V). This is because the negatively charged toner in this embodiment is considered as the standard.

In addition, the voltage in this embodiment is expressed as a potential difference with respect to the earth potential (0 V). Therefore, the development voltage Vdc = -300 V is interpreted as having a potential difference of -300 V with respect to the earth potential due to the development voltage applied to the core metal of the development roller 41a. This is also true for the charging voltage, transfer voltage, etc.

Next, the control unit 200 will be described. FIG. 2 is a control block diagram showing the outline of the control mode of the main parts of the image forming apparatus 100 in this embodiment. The controller 202 exchanges various electrical information with the host device, and controls the image forming operation of the image forming apparatus 100 in a comprehensive manner via the interface 201 by the control unit 202 according to a predetermined control program and a reference table. The control unit 202 is configured with a CPU 155, which is a central element that performs various arithmetic processing, and a memory 154 such as a ROM and a RAM, which are storage elements. The RAM stores the detection results of the sensor, the count results of the counter, and the calculation results, and the ROM stores the control program, a data table obtained in advance by experiments, etc. The control unit 200 is connected to each control object, sensor, counter, etc. in the image forming apparatus 100. The control unit 200 controls the exchange of various electrical information signals and the timing of driving each part, and controls a predetermined image formation sequence. For example, the controller 200 controls the voltages and exposure amounts applied by the charging voltage power supply 120, the developing voltage power supply 140, the exposure unit 3, the primary transfer voltage power supply 160, and the secondary transfer voltage power supply 150. In addition, the controller 200 also controls the photosensitive drum drive unit 110, the developing roller drive unit 130, and the developing contact/separation mechanism 40. The image forming apparatus 100 forms an image on the recording material P based on an electrical image signal input from a host device to the controller 202. Examples of the host device include an image reader, a personal computer, a facsimile, and a smartphone.

The toner in this embodiment is a negatively charged non-magnetic toner produced by suspension polymerization, has a volume average particle size of 7.0 μm, and is negatively charged when carried on the developing roller 41a. The volume average particle size of the toner was measured using a laser diffraction particle size distribution analyzer LS-230 manufactured by Beckman Coulter, Inc. Details of the toner will be described later.

The intermediate transfer belt 10 as an intermediate transfer body is stretched by a plurality of tension members 11, 12, and 13, and is rotated at the same peripheral speed as the photosensitive drum 1a in a direction moving in the circumferential direction at the opposing portion where it abuts against the photosensitive drum 1a. A DC voltage of 200 V is applied from the primary transfer voltage power source 160 to the primary transfer roller 14a as a primary transfer member during the primary transfer during the image forming operation. The yellow toner image formed on the photosensitive drum 1a is electrostatically transferred onto the intermediate transfer belt 10 in the process of passing through the primary transfer portion, which is the abutment portion of the primary transfer roller 14a via the photosensitive drum 1a and the intermediate transfer belt 10. The intermediate transfer belt 10 in Example 1 has a maximum roughness Rz of 0.12 μm or less. In addition, an acrylic coating is applied to the surface layer, and the film thickness of the surface layer is 2.3 μm.

The primary transfer roller 14a is an elastic roller with a diameter of 14 mm, and the core metal material is SUS, and the material of the elastic layer is urethane foam. The primary transfer roller 14a is disposed directly below the center position of the photosensitive drum 1a in the direction of movement of the intermediate transfer belt 10, and presses the intermediate transfer belt 10 with a force of about 220 gf. The primary transfer roller 14a rotates in response to the rotation of the intermediate transfer belt 10. The primary transfer roller 14b disposed in the second image forming station b, the primary transfer roller 14c disposed in the third image forming station c, and the primary transfer roller 14d disposed in the fourth image forming station d are also configured in the same manner as the primary transfer roller 14a. In the same manner, a magenta toner image of the second color, a cyan toner image of the third color, and a black toner image of the fourth color are formed by the second, third, and fourth image forming stations b, c, and d, and are transferred onto the intermediate transfer belt 10 in a superimposed manner in sequence. Then, a composite color image corresponding to the desired color image is obtained.

The four color toner images on the intermediate transfer belt 10 are transferred en bloc onto the surface of the recording material P fed by the paper feed means 50 during the secondary transfer process, which passes through a secondary transfer nip formed by the intermediate transfer belt 10 and the secondary transfer roller 15 as a secondary transfer member. The secondary transfer roller 15 contacts the intermediate transfer belt 10 with a pressure of 50 N to form the secondary transfer nip. The secondary transfer roller 15 rotates in response to the rotation of the intermediate transfer belt 10, and a voltage of 1500 V is applied from the secondary transfer voltage power supply 150 when the toner on the intermediate transfer belt 10 is secondarily transferred to the recording material P such as paper.

Then, the recording material P carrying the four-color toner image is introduced into the fixing device 30. The fixing device 30 applies heat and pressure to the four color toners, which melt, mix, and are fixed to the recording material P. Any toner remaining on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by the cleaning device 17.

The cleaning device 17 has a cleaning blade that contacts the outer peripheral surface of the intermediate transfer belt 10 to scrape off the toner remaining on the intermediate transfer belt 10 and collect it in the intermediate transfer belt cleaning device 17. The intermediate transfer belt cleaning device 17 is positioned downstream of the secondary transfer section of the intermediate transfer belt 10 in the rotation direction of the intermediate transfer belt 10 so as to collect the toner adhering to the intermediate transfer belt 10.

Through the above operations, a full-color print image is formed.
2. Developer, Toner, and Transfer Carrier Particles Next, the developer, toner, and transfer carrier particles used in this embodiment will be described in detail.

In this embodiment, a mixture of toner and external additive A, which is transfer carrier particles, is used as the developer. Here, the transfer carrier particles refer to particles that are present between the toner image developed on the photosensitive drum 1 and the photosensitive drum 1, thereby reducing the adhesive force between the toner image and the photosensitive drum 1 and improving the primary transfer efficiency of the toner image. The toner is toner particles that contain a release agent and an organosilicon polymer on the surface of the toner particle.

The organosilicon polymer has a T3 unit structure represented by R-Si(O _1/2 ) ₃ , where R represents an alkyl group or a phenyl group having 1 to 6 carbon atoms, and the organosilicon polymer forms convex portions on the surfaces of the toner base particles.

The protrusions are characterized by being in surface contact with the surface of the toner base particle, and this surface contact is expected to have a significant effect in inhibiting the movement, detachment, and embedding of the protrusions.

The degree of surface contact is explained using the schematic diagrams of the protrusions shown in Figures 3, 4, 5, and 6.

In FIG. 3, 61 is a cross-sectional image of a toner particle in which about 1/4 of the toner particle can be seen, 62 is a toner particle, 63 is the surface of the toner base particle, and 64 is a protrusion. The cross section of a toner particle can be observed using a scanning transmission electron microscope (hereinafter also referred to as STEM) described later.

Observe the cross-sectional image of the toner and draw a line along the periphery of the toner base particle surface. Convert the image into a horizontal image based on the line along the periphery. In the horizontal image, the length of the line along the periphery in the part where the convex portion and the toner base particle form a continuous interface is defined as the convex width w.

The maximum length of the convex portion in the normal direction of the convex width w is the convex diameter D, and the length from the apex of the convex portion to a line along the circumference on the line segment that forms the convex diameter D is the convex height H.

In Figures 4 and 6, the convex diameter D and the convex height H are the same, and in Figure 5, the convex diameter D is greater than the convex height H.

Figure 6 shows a schematic representation of the adhesion state of particles similar to bowl-shaped particles, which are hemispherical particles with a concave center, obtained by crushing or breaking hollow particles.

In Figure 6, the convex width W is the total length of the organosilicon polymer in contact with the toner base particle surface. In other words, the convex width W in Figure 6 is the sum of W1 and W2.

The number average value of the convex height H is 30 nm or more and 300 nm or less, and preferably 30 nm or more and 200 nm or less. When the number average value of the convex height H is 30 nm or more, a spacer effect occurs between the surface of the toner base particle and the transfer member, and the transferability is significantly improved. On the other hand, when the number average value of the convex height H is 300 nm or less, the effect of suppressing movement, detachment, and embedding is significant, and high transferability is maintained even during long-term use. A cumulative distribution of the convex height H is taken for the convex portion having a convex height H of 30 nm or more and 300 nm or less. When the convex height H that corresponds to 80% by number of the smallest convex heights H is H80, H80 is preferably 65 nm or more and 120 nm or less, and more preferably 75 nm or more and 100 nm or less. By setting H80 in the above range, the transferability can be further improved.

The number-average particle size R of the primary particles of the external additive A is preferably 30 nm or more and 1200 nm or less. When R is 30 nm or more, a spacer effect is exerted between the transfer member and the external additive A, and high transferability is exhibited. In addition, the larger R is, the more the transferability tends to improve. On the other hand, when R is more than 1200 nm, the fluidity of the toner decreases, and image unevenness is easily generated.

It is preferable that the ratio of the number average particle diameter R of the primary particles of the external additive A to the number average value of the convex height H is 1.00 or more and 4.00 or less. When the ratio [(number average particle diameter R of the primary particles of the external additive A)/(number average value of the convex height H)] is in the above range, it is possible to achieve both excellent transferability and low-temperature fixability that can withstand a long life.

When the number average value of the convex height H is 30 nm, which is the minimum value, if R is 30 nm or more, a spacer effect can be exerted between the transfer member and the convexity, improving transferability. This is thought to be because the external additive A is substituted in places where there are no convexities due to the effects of detachment, etc., exerting the spacer effect. In other words, if R is less than 30 nm, the spacer effect is difficult to exert.

The adhesion rate of external additive A to the toner particle surface is preferably 0% or more and 20% or less, and more preferably 0% or more and 10% or less. When the adhesion rate is in the above range, external additive A can move easily on the surface of the toner particles, and the transferability can be further improved by the protrusion substitution effect. In the fixing process in which the toner is fixed to the fixing member, an appropriate amount of release agent seeps out from the toner base particles, improving the separation performance between the fixing member and the paper.

By observing the surface of the toner with a scanning electron microscope, a reflected electron image of 1.5 μm square of the toner surface is obtained. When an image is obtained by binarizing the reflected electron image so that the organosilicon polymer portion becomes a bright portion, the area ratio of the bright portion area of the image to the total area of the image (hereinafter also simply referred to as the area ratio of the bright portion area) is 30.0% or more and 75.0% or less. In addition, it is preferable that the area ratio of the bright portion area of the image is 35.0% or more and 70.0% or less. The higher the area ratio of the bright portion area, the higher the presence ratio of the organosilicon polymer on the toner mother particle surface. When the area ratio of the bright portion area is higher than 75.0%, the presence ratio of the components derived from the toner mother particle on the toner mother particle surface is low, the exudation of the release agent from the toner mother particle is difficult to occur, and the thin paper is likely to wrap around the fixing device during low-temperature fixing. On the other hand, when the area ratio of the bright portion area of the image is less than 30.0%, the presence ratio of the components derived from the toner mother particle on the toner mother particle surface is high. In other words, the exposed area of the components derived from the toner base particles on the surface of the toner base particles is large, and the transferability is reduced in the initial stage of use. The area ratio of the bright area of the image is hereafter also referred to as the coverage rate of the organosilicon polymer on the surface of the toner base particles.

External additive A is not particularly limited as long as the number average particle diameter R of the primary particles is 30 nm or more and 1000 nm or less, and various organic or inorganic fine particles can be used. From the viewpoint of easily imparting fluidity and being easily negatively charged like the toner mother particles, external additive A preferably contains silica fine particles. The content of silica fine particles in external additive A is preferably 50 mass% or more, and external additive A is more preferably silica fine particles. The content of external additive A in the toner is preferably 0.02 mass% or more and 5.00 mass% or less, and more preferably 0.05 mass% or more and 3.00 mass% or less.

Examples of organic or inorganic fine particles other than silica fine particles include the following.
(1) Fluidity imparting agents: alumina fine particles, titanium oxide fine particles, carbon black and carbon fluoride.
(2) Abrasives: fine particles of metal oxides (fine particles of strontium titanate, cerium oxide, alumina, magnesium oxide, chromium oxide, etc.), fine particles of nitrides (fine particles of silicon nitride, etc.), fine particles of carbides (fine particles of silicon carbide, etc.), fine particles of metal salts (fine particles of calcium sulfate, barium sulfate, calcium carbonate, etc.).
(3) Lubricants: fine particles of fluororesin (fine particles of vinylidene fluoride, polytetrafluoroethylene, etc.), fine particles of fatty acid metal salts (fine particles of zinc stearate, calcium stearate, etc.).
(4) Charge-controlling fine particles: fine particles of metal oxides (fine particles of tin oxide, titanium oxide, zinc oxide, alumina, etc.), carbon black.

The silica fine particles and the organic or inorganic fine particles may be subjected to a hydrophobic treatment to improve the flowability of the toner and to uniformly charge the toner particles.

Examples of treatment agents for the hydrophobic treatment include unmodified silicone varnish, various modified silicone varnishes, unmodified silicone oil, various modified silicone oils, silane compounds, silane coupling agents, other organosilicon compounds, and organotitanium compounds. These treatment agents may be used alone or in combination.

The silica fine particles can be any known silica fine particles, and may be either dry silica fine particles or wet silica fine particles. Preferably, the silica fine particles are wet silica fine particles obtained by the sol-gel method (hereinafter, also referred to as sol-gel silica).

Figure 7 is an enlarged view of the developer used in this embodiment. As shown in Figure 7, the developer in this embodiment has external additive A, which is a transfer carrier particle, placed on a toner surface on which numerous protrusions of an organosilicon polymer are formed.

The convex spacing G and convex height H on the toner surface shown in Figure 7 can be measured using a scanning transmission electron microscope (hereinafter referred to as STEM), which will be described later. The convex spacing G and convex height H can also be measured with a scanning probe microscope (hereinafter referred to as SPM). A scanning probe microscope (hereinafter referred to as SPM) is equipped with a probe, a cantilever that supports the probe, and a displacement measurement system that detects the bending of the cantilever, and detects the atomic force (attractive or repulsive force) between the probe and the sample to observe the shape of the sample surface.

If the convex spacing G is larger than the transfer carrier, the transfer carrier particles will come into contact with the toner matrix when placed between the convex portions, and the adhesive force Ft between the transfer carrier particles and the toner will increase, making it difficult for the transfer carrier particles to transfer from the toner to the photosensitive drum 1. Therefore, it is preferable that the number-average convex spacing G is smaller than the number-average particle size of the transfer carrier particles.

Furthermore, if the convex height H is greater than the particle size of the transfer carrier particles, the convex portion will come into contact with the photosensitive drum 1 before the transfer carrier particles, making it difficult for the transfer carrier particles to come into contact with the photosensitive drum 1, and making it difficult for the transfer carrier particles to transfer from the toner to the photosensitive drum 1. Therefore, it is preferable that the number-average value of the convex height H is smaller than the number-average particle size of the transfer carrier particles.

However, as mentioned above, it is preferable that the adhesive force Ft between the transfer carrier particles and the toner is smaller than the adhesive force Fdr between the transfer carrier particles and the photosensitive drum 1. Therefore, it is preferable to select a material for the transfer carrier particles that reduces the adhesive force Ft of the transfer carrier particles to the toner. For example, as in this embodiment, when the convex portions on the toner surface are formed of a silica-based material such as an organic silica polymer, it is preferable to select a silica-based material with a material composition similar to that of the convex portions as the material for the transfer carrier particles, in order to reduce the adhesive force between the convex portions and the transfer carrier particles.

A larger number of transfer carrier particles covering the toner is preferable from the viewpoint of supplying the transfer carrier particles from the developing roller 41 to the photosensitive drum 1. However, adding too many transfer carrier particles increases the risk of contaminating components inside the image forming device 100, so it is preferable to adjust the amount according to the desired primary transferability.

The primary transferability improves with an increase in the coverage of the transfer carrier particles on the photosensitive drum 1, and in order to obtain sufficient primary transferability, it is preferable that the coverage of the transfer carrier particles on the photosensitive drum 1 is 10% or more. However, as the coverage of the transfer carrier particles on the photosensitive drum 1 increases, the degree of improvement in the primary transferability slows down, and the risk of contamination of various members within the image forming apparatus by the transfer carrier particles increases. Therefore, it is preferable to keep the coverage of the transfer carrier particles on the photosensitive drum 1 within 50%.
3. Methods for Measuring Developer Properties Various measuring methods will be described below.

<Method of observing a cross section of a toner using a scanning transmission electron microscope (STEM)>
A cross section of a toner to be observed with a scanning transmission electron microscope (STEM) is prepared as follows.

The procedure for preparing a cross section of a toner is explained below. If organic or inorganic fine particles are added to the toner, the toner from which the organic or inorganic fine particles have been removed using the method described below or similar is used as the sample.

160 g of sucrose (Kishida Chemical) is added to 100 mL of ion-exchanged water, and dissolved in a hot water bath to prepare a concentrated sucrose solution. 31 g of the concentrated sucrose solution and 6 mL of Contaminon N (a 10% aqueous solution of a neutral detergent for cleaning precision measuring instruments, pH 7, consisting of a nonionic surfactant, anionic surfactant, and organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) are placed in a centrifuge tube (50 mL capacity). 1.0 g of toner is added to this, and the toner clumps are loosened with a spatula or the like. The centrifuge tube is shaken at 300 spm (strokes per minute) for 20 minutes in a shaker (AS-1N, sold by AS ONE Corporation). After shaking, the solution is transferred to a glass tube for a swing rotor (50 mL) and separated at 3500 rpm for 30 minutes in a centrifuge (H-9R, manufactured by Kokusan Co., Ltd.). This operation separates the toner particles from the external additives. Visually check that the toner particles and the aqueous solution are sufficiently separated, and collect the toner particles that have separated into the top layer with a spatula or similar. The collected toner particles are filtered through a vacuum filter, and then dried in a dryer for at least one hour to obtain a sample for measurement. This operation is carried out multiple times to ensure the required amount.

In addition, whether or not the convex portion contains an organosilicon polymer will be confirmed by combining elemental analysis using energy dispersive X-ray analysis (EDS).

Toner is spread onto a cover glass (Matsunami Glass Co., Ltd., square cover glass; square No. 1) in a single layer, and an osmium (Os) plasma coater (Filgen, OPC80T) is used to apply an Os film (5 nm) and a naphthalene film (20 nm) to the toner as a protective film. Next, a PTFE tube (outer diameter 3 mm (inner diameter 1.5 mm) x 3 mm) is filled with photocurable resin D800 (JEOL Ltd.), and the cover glass is gently placed on top of the tube so that the toner is in contact with the photocurable resin D800. In this state, light is irradiated to harden the resin, and then the cover glass and tube are removed to form a cylindrical resin with the toner embedded in the outermost surface. Using an ultrasonic ultramicrotome (Leica, UC7), a cutting speed of 0.6 mm/s is used to cut from the outermost surface of the cylindrical resin to the length of the toner radius (for example, 4.0 μm when the weight average particle size (D4) is 8.0 μm) to expose the cross section of the center of the toner.

Next, the toner is cut to a thickness of 100 nm to produce a thin sample of the toner cross section. By cutting in this manner, a cross section of the center of the toner can be obtained.

A JEM-2800 manufactured by JEOL was used as the scanning transmission electron microscope (STEM). The probe size of the STEM was 1 nm, and images were acquired with an image size of 1024 x 1024 pixels. In addition, the contrast of the Detector Control panel for the bright field image was adjusted to 1425, the brightness to 3750, and the contrast of the Image Control panel to 0.0, the brightness to 0.5, and the gamma to 1.00, to acquire the image. The image magnification was 100,000 times, and the image was acquired so that it covered about one-quarter to one-half of the circumference of the cross section of one toner particle, as shown in Figure 3. The obtained STEM image is subjected to image analysis using image processing software (ImageJ (available from https://imagej.nih.gov/ij/)) and the convex portions containing the organosilicon polymer are measured. The measurement is performed on 30 convex portions arbitrarily selected from the STEM image. Whether or not the convex portions contain the organosilicon polymer is confirmed by a combination of elemental analysis using a scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDS). First, a line is drawn along the periphery of the toner base particle using a line drawing tool (select Segmented line in the Strong tab). Parts where the organosilicon polymer convex portions are buried in the toner base particle are connected smoothly with a line, assuming that they are not buried. The image is converted to a horizontal image based on that line (select Selection on the Edit tab, change line width to 500 pixels in properties, then select Selection on the Edit tab and perform Strengthener). In the horizontal image, the following measurements are performed on one of the convex parts containing the organosilicon polymer. The length of the line along the circumference in the part where the convex part and the toner base particle form a continuous interface is defined as the convex width w. The maximum length of the convex part in the normal direction of the convex width w is defined as the convex diameter D, and the length from the apex of the convex part to the line along the circumference in the line segment that forms the convex diameter D is defined as the convex height H. The measurements are performed on 30 arbitrarily selected convex parts, and the arithmetic average of each measurement value is defined as the number average of the convex height H.

<Calculation method of H80>
In the STEM image of the cross section of the toner obtained by the above-mentioned scanning transmission electron microscope (STEM), a cumulative distribution of the convex height H is taken for convex portions having a convex height H of 30 nm or more and 300 nm or less. The convex height H that is integrated from the smallest convex height H and accounts for 80% by number is defined as H80 (unit: nm).

<Method of calculating the area ratio of bright areas in a 1.5 μm square reflected electron image of a toner surface>
The bright area ratio is determined by observing the toner surface using a scanning electron microscope. A backscattered electron image of a 1.5 μm square area of the toner surface is obtained. An image is then obtained that is binarized so that the organosilicon polymer portion in the backscattered electron image becomes the bright area, and the ratio of the bright area of the image to the total area of the image is determined. When organic or inorganic fine particles are externally added to the toner, the organic or inorganic fine particles are removed by the following method or the like, and the sample is used.

160 g of sucrose (Kishida Chemical) is added to 100 mL of ion-exchanged water, and dissolved in a hot water bath to prepare a concentrated sucrose solution. 31 g of the concentrated sucrose solution and 6 mL of Contaminon N (a 10% aqueous solution of a neutral detergent for cleaning precision measuring instruments, pH 7, consisting of a nonionic surfactant, anionic surfactant, and organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) are placed in a centrifuge tube (50 mL capacity). 1.0 g of toner is added to this, and the toner clumps are loosened with a spatula or the like. The centrifuge tube is shaken at 300 spm (strokes per minute) for 20 minutes in a shaker (AS-1N, sold by AS ONE Corporation). After shaking, the solution is transferred to a glass tube for a swing rotor (50 mL) and separated at 3500 rpm for 30 minutes in a centrifuge (H-9R, manufactured by Kokusan Co., Ltd.). This operation separates the toner particles from the external additives. Visually check that the toner particles and the aqueous solution are sufficiently separated, and collect the toner particles that have separated into the top layer with a spatula or similar. The collected toner particles are filtered through a vacuum filter, and then dried in a dryer for at least one hour to obtain a sample for measurement. This operation is carried out multiple times to ensure the required amount.

Whether or not the convex portions contain an organosilicon polymer will be confirmed by combining this with elemental analysis using energy dispersive X-ray analysis (EDS), which will be described later.

The SEM equipment and observation conditions are as follows.
Equipment used: ULTRA PLUS manufactured by Carl Zeiss Microscopy Co., Ltd.
Acceleration voltage: 1.0 kV
WD: 2.0 mm
Aperture Size: 30.0 μm
Detection signal: EsB (energy selective backscattered electrons)
EsB Grid: 800V
Observation magnification: 50,000 times Contrast: 63.0±5.0% (reference value)
Brightness: 38.0±5.0% (reference value)
Resolution: 1024 x 768
Pretreatment: Toner particles are scattered onto carbon tape (no deposition is performed)
The accelerating voltage and EsB Grid are set to achieve the following: obtaining structural information on the outermost surface of the toner particles, preventing charging up of undeposited samples, and selectively detecting high-energy reflected electrons. The observation field is selected to be near the apex where the curvature of the toner particles is smallest. It was confirmed that the bright areas of the reflected electron image were derived from the organosilicon polymer by superimposing the reflected electron image on an element mapping image obtained by energy dispersive X-ray analysis (EDS) that can be obtained by a scanning electron microscope (SEM).

The SEM/EDS equipment and observation conditions are as follows.
Equipment used (SEM): ULTRA PLUS manufactured by Carl Zeiss Microscopy Co., Ltd.
Equipment used (EDS): NORAN System 7, Ultra Dry EDS Detector, manufactured by Thermo Fisher Scientific Co., Ltd.
Acceleration voltage: 5.0 kV
WD: 7.0 mm
Aperture Size: 30.0 μm
Detection signal: SE2 (secondary electrons)
Observation magnification: 50,000x Mode: Spectral Imaging
Pretreatment: Toner particles are scattered on carbon tape and platinum sputtered. The mapping image of silicon element obtained by this method is superimposed on the above-mentioned reflected electron image, and it is confirmed that the silicon atom parts of the mapping image match the bright parts of the reflected electron image.

The ratio of the bright area to the total area of the reflected electron image was calculated by analyzing the reflected electron image of the toner particle surface obtained by the above method using image processing software ImageJ (developed by Wayne Rashand). The procedure is as follows:

First, convert the backscattered electron image to 8-bit from Type in the Image menu. Next, set the Median diameter to 2.0 pixels from Filters in the Process menu to reduce image noise. Estimate the image center after excluding the observation condition display section displayed at the bottom of the backscattered electron image, and select a 1.5 μm square range from the center of the backscattered electron image using the Rectangle Tool on the toolbar. Next, select Threshold from Adjust in the Image menu. Select Default, click Auto, and then click Apply to obtain a binarized image. This operation displays the bright areas of the backscattered electron image in white. Again, estimate the image center after excluding the observation condition display section displayed at the bottom of the backscattered electron image, and select a 1.5 μm square range from the center of the backscattered electron image using the Rectangle Tool on the toolbar. Next, select Histogram from the Analyze menu. Read the Count value from the newly opened Histogram window (corresponding to the total area of the reflected electron image). Also, click List and read the Count value when the brightness is 0 (corresponding to the bright area of the reflected electron image). From this value, calculate the area ratio of the bright area to the total area of the reflected electron image. The above procedure is carried out for 10 fields of view for the toner particles to be evaluated, and the number average value is calculated to obtain the area ratio (%) of the bright area of the image to the total area of the image that has been binarized so that the organosilicon polymer portion in the reflected electron image becomes the bright area.

<Method of Identifying Organosilicon Polymer>
The organosilicon polymer is identified by a combination of observation with a scanning electron microscope (SEM) and elemental analysis by energy dispersive X-ray analysis (EDS).

Using a scanning electron microscope "Hitachi Ultra High Resolution Field Emission Scanning Electron Microscope S-4800" (Hitachi High-Technologies Corporation), the toner is observed in a field of view magnified up to 50,000 times. The surface is observed by focusing on the surface of the toner particles. EDS analysis is performed on the particles present on the surface, and the presence or absence of an Si element peak is used to determine whether the particles analyzed are organosilicon polymers. If the toner particle surface contains both organosilicon polymers and silica fine particles, the organosilicon polymer is identified by comparing the ratio of the elemental contents (atomic %) of Si and O (Si/O ratio) with a standard. EDS analysis is performed under the same conditions on standard samples of the organosilicon polymer and silica fine particles to obtain the elemental contents (atomic %) of Si and O. The Si/O ratio of the organosilicon polymer is designated as A, and the Si/O ratio of the silica fine particles is designated as B. Measurement conditions are selected under which A is significantly greater than B. Specifically, a standard sample is measured 10 times under the same conditions, and the arithmetic mean values for A and B are obtained. Measurement conditions are selected such that the obtained mean value is A/B>1.1. If the Si/O ratio of the particle to be identified is on the A side of [(A+B)/2], the particle is determined to be an organosilicon polymer.

Tospearl 120A (Momentive Performance Materials Japan, LLC) is used as a sample of organosilicon polymer particles, and HDK V15 (Asahi Kasei) is used as a sample of silica microparticles.

<Method of measuring number average particle size R of primary particles of external additive>
This is performed in combination with a scanning electron microscope "Hitachi Ultra-High Resolution Field Emission Scanning Electron Microscope S-4800" (Hitachi High-Technologies Corporation) and elemental analysis using energy dispersive X-ray analysis (EDS).

In a field of view magnified up to 50,000 times, the external additive particles are randomly photographed using the EDS elemental analysis method described above. From the photographed image, 100 external additive particles are randomly selected, the major axis of the primary particles of the target external additive particles is measured, and the arithmetic average value is taken as the number-average particle size R. The observation magnification is adjusted appropriately depending on the size of the external additive particles.

<Method for identifying the composition and ratio of constituent compounds of organosilicon polymer>
The composition and ratio of the constituent compounds of the organosilicon polymer contained in the toner are identified using NMR. When the toner contains an external additive such as silica fine particles in addition to the organosilicon polymer, the following procedure is carried out.

1 g of the toner is placed in a vial, dissolved in 31 g of chloroform, and dispersed in the vial by treating with an ultrasonic homogenizer for 30 minutes to prepare a dispersion liquid.
Ultrasonic treatment device: Ultrasonic homogenizer VP-050 (manufactured by Taitec Co., Ltd.)
Microchip: Step type microchip, tip diameter φ2mm
Tip position of the microchip: Center of the glass vial, and 5 mm above the bottom of the vial. Ultrasonic conditions: Intensity 30%, 30 minutes. At this time, ultrasonic waves are applied while cooling the vial with ice water so that the temperature of the dispersion does not rise. The dispersion is transferred to a glass tube for a swing rotor (50 mL) and centrifuged in a centrifuge (H-9R; manufactured by Kokusan Co., Ltd.) at 58.33 S ^-1 for 30 minutes. After centrifugation, the lower layer of the glass tube contains particles with a high specific gravity, such as silica fine particles. The chloroform solution containing the organosilicon polymer in the upper layer is collected, and the chloroform is removed by vacuum drying (40°C/24 hours) to prepare a sample. Using the above sample or the organosilicon polymer, the abundance ratio of the constituent compounds of the organosilicon polymer and the proportion of the T3 unit structure represented by R-Si(O _1/2 ) ₃ in the organosilicon polymer are measured and calculated by solid-state ²⁹ Si-NMR.

First, the hydrocarbon group represented by R is confirmed by ¹³ C-NMR.
< ^13C -NMR (solid) measurement conditions>
Equipment: JEOL RESONANCE JNM-ECX500II
Sample tube: 3.2 mm diameter
Sample: Sample or organosilicon polymer Measurement temperature: Room temperature Pulse mode: CP/MAS
Measurement nuclear frequency: 123.25MHz ( ^13C )
Reference substance: Adamantane (external standard: 29.5 ppm)
Sample rotation speed: 20 kHz
Contact time: 2 ms
Delay time: 2s
Number of integrations: 1024 times. Using this method, the presence or absence of signals due to methyl groups (Si-CH ₃ ), ethyl groups (Si-C ₂ H ₅ ), propyl groups (Si-C ₃ H ₇ ), butyl groups (Si-C ₄ H ₉ ), pentyl groups (Si-C ₅ H ₁₁ ), hexyl groups (Si-C ₆ H ₁₃ ), or phenyl groups (Si-C ₆ H ₅ -) bonded to silicon atoms is used to confirm the presence or absence of the hydrocarbon group represented by R. On the other hand, in solid-state ²⁹ Si-NMR, peaks are detected in different shift regions depending on the structure of the functional groups bonded to Si in the constituent compounds of the organosilicon polymer. The structure bonded to Si can be identified by identifying the position of each peak using a standard sample. Furthermore, the abundance ratio of each constituent compound can be calculated from the obtained peak area. The ratio of the peak area of the T3 unit structure to the total peak area can be calculated.

The specific measurement conditions for solid-state ^29Si -NMR are as follows.
Apparatus: JNM-ECX5002 (JEOL RESONANCE)
Temperature: Room temperature Measurement method: DDMAS method ²⁹ Si 45°
Sample tube: Zirconia 3.2 mm diameter
Sample: Powdered sample filled in test tube Sample rotation speed: 10 kHz
Relaxation delay: 180s
Scan: 2000
After the measurement, the peaks of a plurality of silane components having different substituents and bonding groups of the sample or organosilicon polymer are separated into the following X1, X2, X3, and X4 structures by curve fitting, and the peak areas of each are calculated.

The following X3 structure is a T3 unit structure.
X1 structure: (Ri) (Rj) (Rk) SiO _1/2 (A1)
X2 structure: (Rg)(Rh)Si(O1 _/2 ) ₂ (A2)
X3 structure: RmSi(O1 _/2 ) ₃ (A3)
X4 structure: Si(O1 _/2 ) ₄ (A4)

In the formulae (A1), (A2) and (A3), Ri, Rj, Rk, Rg, Rh and Rm each represent an organic group such as a hydrocarbon group having 1 to 6 carbon atoms, a halogen atom, a hydroxyl group, an acetoxy group or an alkoxy group, which is bonded to a silicon atom. When it is necessary to confirm the structure in more detail, it may be identified by the results of ¹ H-NMR measurement together with the results of ¹³ C-NMR and ²⁹ Si-NMR measurement.

<Method for quantifying organosilicon polymer or silica fine particles contained in toner>
The toner is dispersed in chloroform as described above, and then centrifugal separation is used to separate the external additives such as the organosilicon polymer and silica fine particles based on the difference in specific gravity to obtain samples, and the content of the external additives such as the organosilicon polymer or silica fine particles is determined.

The following is an example of an external additive that is silica microparticles. Other microparticles can also be quantified using the same method.

First, the pressed toner is measured by fluorescent X-rays, and the silicon content in the toner is determined by performing analytical processing such as the calibration curve method or FP method. Next, the structures of the constituent compounds forming the organosilicon polymer and the silica fine particles are identified using solid-state ^29Si -NMR and pyrolysis GC/MS, and the silicon content in the organosilicon polymer and the silica fine particles is determined. The content of the organosilicon polymer and the silica fine particles in the toner is calculated from the relationship between the silicon content in the toner determined by fluorescent X-rays and the silicon content in the organosilicon polymer and the silica fine particles determined by solid-state ^29Si -NMR and pyrolysis GC/MS.

<Method of measuring the adhesion rate of external additives such as organosilicon polymers or silica fine particles to toner base particles or toner particles by water washing method>
(Water washing process)
20 g of a 30% by weight aqueous solution of "Contaminon N" (a neutral detergent for cleaning precision measuring instruments, consisting of a nonionic surfactant, an anionic surfactant, and an organic builder, with a pH of 7) is weighed out and placed in a 50 mL vial, and mixed with 1 g of toner. The vial is then set in a "KM Shaker" (model: V.SX) manufactured by Iwaki Sangyo Co., Ltd., and shaken for 120 seconds at a speed of 50. Depending on the adhesion state of the organosilicon polymer or silica fine particles, the external additives such as the organosilicon polymer or silica fine particles will migrate from the toner base particles or toner particle surfaces to the dispersion liquid. Thereafter, the toner and the external additives such as the organosilicon polymer or silica fine particles that have migrated to the supernatant liquid are separated using a centrifuge (H-9R; manufactured by Kokusan Co., Ltd.) (16.67 S-1 for 5 minutes). The precipitated toner is dried by vacuum drying (40°C/24 hours) and is used as a toner after washing with water.

Next, a Hitachi ultra-high resolution field emission scanning electron microscope S-4800 (Hitachi High-Technologies Corporation) was used to photograph the toner that was not subjected to the above-mentioned washing process (toner before washing) and the toner obtained through the above-mentioned washing process (toner after washing).

The measurement target is identified by elemental analysis using energy dispersive X-ray analysis (EDS).

The captured toner surface image is then analyzed using image analysis software Image-Pro Plus ver. 5.0 (Nippon Roper Co., Ltd.) to calculate the coverage rate.

The image capture conditions for the S-4800 are as follows:

(1) Sample preparation: Apply a thin layer of conductive paste to a sample stage (aluminum sample stage 15 mm x 6 mm), then spray toner onto the paste. Then, use air to remove excess toner from the sample stage and allow it to dry thoroughly. Set the sample stage in the sample holder, and adjust the sample stage height to 36 mm using the sample height gauge.

(2) Setting the S-4800 observation conditions When measuring the coverage, perform elemental analysis by the energy dispersive X-ray analysis (EDS) described above in advance to distinguish between external additives such as organosilicon polymers or silica fine particles on the toner surface before carrying out the measurement. Pour liquid nitrogen into the anti-contamination trap attached to the S-4800 housing until it overflows, and leave it for 30 minutes. Start the S-4800's "PC-SEM" and perform flushing (cleaning the FE chip, which is the electron source). Click on the accelerating voltage display area on the control panel on the screen, press the [Flushing] button, and open the flushing execution dialog. Check that the flushing intensity is 2 and execute it. Check that the emission current due to flushing is 20 to 40 μA. Insert the sample holder into the sample chamber of the S-4800 housing. Press [Origin] on the control panel to move the sample holder to the observation position.

Click the acceleration voltage display to open the HV setting dialog, and set the acceleration voltage to [1.1 kV] and the emission current to [20 μA]. In the [Basic] tab of the operation panel, set the signal selection to [SE], select the SE detector to [Upper (U)] and [+BSE], and select [L.A. 100] in the selection box to the right of [+BSE] to set the mode to observation with backscattered electron images. In the same [Basic] tab of the operation panel, set the probe current in the electron optical system condition block to [Normal], the focus mode to [UHR], and the WD to [4.5 mm]. Press the [ON] button on the acceleration voltage display of the control panel to apply the acceleration voltage.

(3) Calculation of toner number average particle diameter (D1) Drag within the magnification display area of the control panel to set the magnification to 5000 (5k). Rotate the focus knob [COARSE] on the operation panel to adjust the aperture alignment when the image is in focus to a certain extent. Click [Align] on the control panel to display the alignment dialog and select [Beam]. Rotate the STIGMA/ALIGNMENT knobs (X, Y) on the operation panel to move the displayed beam to the center of the concentric circle. Next, select [Aperture] and rotate the STIGMA/ALIGNMENT knobs (X, Y) one by one to stop the image movement or adjust it so that the movement is minimized. Close the aperture dialog and adjust the focus with autofocus. Repeat this operation two more times to adjust the focus.

Then, the particle size of 300 toner particles is measured to determine the number average particle size (D1). The particle size of each particle is the maximum diameter observed when the toner particles are observed.

(4) Focus Adjustment For the particles obtained in (3) with a number average particle diameter (D1) of ±0.1 μm, align the midpoint of the maximum diameter with the center of the measurement screen, and drag within the magnification display section of the control panel to set the magnification to 10,000 (10k) times.

Rotate the focus knob [COARSE] on the operation panel, and adjust the aperture alignment when the image is in focus to a certain extent. Click [Align] on the control panel to display the alignment dialog and select [Beam]. Rotate the STIGMA/ALIGNMENT knobs (X, Y) on the operation panel to move the displayed beam to the center of the concentric circles. Next, select [Aperture] and rotate the STIGMA/ALIGNMENT knobs (X, Y) one by one to stop the image movement or to minimize its movement. Close the aperture dialog and use autofocus to adjust the focus. Then, set the magnification to 50,000 (50k) times, adjust the focus using the focus knob and STIGMA/ALIGNMENT knob as above, and use autofocus to adjust the focus again. Repeat this operation to adjust the focus. Here, if the inclination angle of the observation surface is large, the accuracy of the coverage measurement tends to be low, so when adjusting the focus, select an object that can simultaneously bring the entire observation surface into focus, and select an object with as little surface inclination as possible for analysis.

(5) Image storage Adjust the brightness in ABC mode, take a photograph with a size of 640 x 480 pixels, and save it. Use this image file to perform the following analysis. Take one photograph for each toner particle to obtain an image of the toner particles.

(6) Image Analysis The image obtained by the above-mentioned method is binarized using the following analysis software to calculate the coverage. At this time, the above screen is divided into 12 squares and each is analyzed. The analysis conditions for the image analysis software Image-Pro Plus ver. 5.0 are as follows. However, if an external additive such as an organosilicon polymer with a particle size of less than 30 nm and more than 300 nm, or silica fine particles with a particle size of less than 30 nm and more than 1200 nm is included in a divided section, the coverage is not calculated for that section.

In the image analysis software Image-Pro Plus 5.0, select "Count/Size" from "Measurement" on the toolbar, then "Options" to set the binarization conditions. Select 8 connectivity in the object extraction options and set smoothing to 0. Other options include not selecting in advance, not filling holes, and not including lines, and setting "Exclude boundaries" to "None." Select "Measurement item" from "Measurement" on the toolbar and enter 2 to ¹⁰⁷ as the selection range for area.

The coverage rate is calculated by enclosing a square region. In this case, the area of the region (C) should be between 24,000 and 26,000 pixels. Automatic binarization is performed using "Processing" - Binarization, and the total area (D) of regions free of external additives such as organosilicon polymers or silica microparticles is calculated. The coverage rate can be calculated using the following formula from the area C of the square region and the total area D of regions free of external additives such as organosilicon polymers or silica microparticles.

Coverage rate (%) = 100 - (D / C x 100)
The arithmetic mean value of all the data obtained is taken as the coverage rate.

Then, the coverage of the toner before and after washing is calculated,
[Toner coverage after washing]/[Toner coverage before washing]×100 is defined as the “adhesion rate” in the present invention.
4. Methods for Producing Toner Particles, External Additives, and Developer Next, examples of producing the toner particles, external additive A, and developer of this embodiment will be described.

<Production Example of Toner Particles>
(Preparation of aqueous medium 1)
In a reaction vessel equipped with a stirrer, a thermometer, and a reflux tube, 650.0 parts of ion-exchanged water and 14.0 parts of sodium phosphate (12-hydrate, manufactured by Rasa Kogyo Co., Ltd.) were charged, and the mixture was kept warm at 65 ° C. for 1.0 hours while purging with nitrogen. A calcium chloride aqueous solution in which 9.2 parts of calcium chloride (dihydrate) was dissolved in 10.0 parts of ion-exchanged water was charged all at once using a T.K. homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) while stirring at 15,000 rpm, to prepare an aqueous medium containing a dispersion stabilizer. Furthermore, 10% by mass of hydrochloric acid was charged into the aqueous medium, and the pH was adjusted to 5.0, to obtain aqueous medium 1.

(Preparation of Polymerizable Monomer Composition)
The above materials were put into an attritor (manufactured by Mitsui Miike Chemical Engineering Co., Ltd.), and further dispersed at 220 rpm for 5.0 hours using zirconia particles having a diameter of 1.7 mm, and then the zirconia particles were removed to prepare a colorant dispersion.
Styrene: 20.0 parts n-Butyl acrylate: 20.0 parts Crosslinking agent (divinylbenzene): 0.3 parts Saturated polyester resin: 5.0 parts (polycondensate of propylene oxide modified bisphenol A (2 mole adduct) and terephthalic acid (molar ratio 10:12), glass transition temperature (Tg) 68°C, weight average molecular weight (Mw) 10,000, molecular weight distribution (Mw/Mn) 5.12)
Fischer-Tropsch wax (melting point 78° C.): 7.0 parts This material was added to the colorant dispersion and heated to 65° C., and then dissolved and dispersed uniformly at 500 rpm using a T.K. homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to prepare a polymerizable monomer composition.

(Granulation process)
The temperature of the aqueous medium 1 was adjusted to 70° C., and the polymerizable monomer composition was charged into the aqueous medium 1 while maintaining the rotation speed of the T.K. homomixer at 15,000 rpm, and 10.0 parts of t-butyl peroxypivalate as a polymerization initiator was added. Granulation was continued for 10 minutes while maintaining the rotation speed at 15,000 rpm with the stirring device.

(Polymerization process and distillation process)
After the granulation step, the agitator was replaced with a propeller agitator blade, and polymerization was carried out for 5.0 hours while stirring at 150 rpm and maintaining the temperature at 70° C., and then the temperature was raised to 85° C. and maintained at that temperature for 2.0 hours. Thereafter, the reflux tube of the reaction vessel was replaced with a cooling tube, and the obtained slurry was heated to 100° C. to carry out distillation for 6 hours, thereby distilling off the unreacted polymerizable monomer, and a resin particle dispersion was obtained.

(Organosilicon Polymer Formation Step)
In a reaction vessel equipped with a stirrer and a thermometer, 60.0 parts of ion-exchanged water was weighed, and the pH was adjusted to 4.0 using 10% by mass hydrochloric acid. This was heated while stirring, and the temperature was set to 40°C. Then, 40.0 parts of methyltriethoxysilane, an organosilicon compound, was added, and the mixture was stirred for 2 hours or more to carry out hydrolysis. The end point of hydrolysis was confirmed by visual observation that the oil and water were not separated and became one layer, and the mixture was cooled to obtain a hydrolyzed liquid of an organosilicon compound.

After adjusting the temperature of the resin particle dispersion obtained above to 55°C, 25.0 parts of the hydrolyzed liquid of the organosilicon compound (addition amount of organosilicon compound was 10.0 parts) was added to initiate polymerization of the organosilicon compound. After holding for 0.25 hours, the pH was adjusted to 5.5 with a 3.0% aqueous sodium bicarbonate solution. With continued stirring at 55°C, the mixture was held for 1.0 hour (condensation reaction 1), after which the pH was adjusted to 9.5 with a 3.0% aqueous sodium bicarbonate solution and held for a further 4.0 hours (condensation reaction 2) to obtain a toner particle dispersion.

(Washing process and drying process)
After the organosilicon polymer formation process was completed, the toner particle dispersion was cooled, and hydrochloric acid was added to the toner particle dispersion to adjust the pH to 1.5 or less, and the mixture was left for 1.0 hour while stirring. Thereafter, the mixture was subjected to solid-liquid separation using a pressure filter to obtain a toner cake. The obtained toner cake was reslurried with ion-exchanged water to form a dispersion again, and then subjected to solid-liquid separation using the aforementioned filter to obtain a toner cake. The obtained toner cake was transferred to a thermostatic chamber at 40°C, and dried and classified for 72 hours to obtain toner particles.

<Production Example of External Additive A>
The external additive A was produced as follows. 150 parts of 5% aqueous ammonia was added to a 1.5 L glass reaction vessel equipped with a stirrer, a dropping nozzle, and a thermometer to prepare an alkaline catalyst solution. After adjusting the alkaline catalyst solution to 50°C, 100 parts of tetraethoxysilane and 50 parts of 5% aqueous ammonia were dropped simultaneously while stirring, and reacted for 8 hours to obtain a silica microparticle dispersion. The obtained silica microparticle dispersion was then dried by spray drying and crushed with a pin mill to obtain silica microparticles with a number average particle size of 100 nm as the external additive A.

<Production Example of Developer>
100.00 parts of toner particles 1 and 1.00 parts of external additive A were charged into a Henschel mixer (FM10C type manufactured by Nippon Coke & Engineering Co., Ltd.) with water at 7°C passing through the jacket. Next, after the water temperature in the jacket stabilized at 7°C ± 1°C, the mixture was mixed for 10 minutes with the peripheral speed of the rotating blade set to 38 m/sec. During the mixing, the amount of water passing through the jacket was appropriately adjusted so that the temperature inside the tank of the Henschel mixer did not exceed 25°C. The obtained mixture was sieved through a mesh with an opening of 75 μm to obtain a developer.

The physical properties of the developer are shown in Table 1.

In the table, "X" represents the ratio of the number average particle diameter R of the primary particles of external additive A to the number average value of the convex height H. When the produced developer was observed using an SEM, it was confirmed that external additive A was disposed as transfer carrier particles on the convex portions of the organosilicon polymer of the toner particles, and the average number of external additive A coated per toner particle was about 500 particles.
5. Supply of Transfer Carrier Next, a description will be given of a means for supplying transfer carrier particles onto the photosensitive drum 1, which is a feature of this embodiment. As described above, the transfer carrier particles refer to particles that are present between the toner image developed on the photosensitive drum 1 and the photosensitive drum 1, thereby reducing the adhesive force between the toner image and the photosensitive drum 1 and improving the primary transfer efficiency of the toner image.

In this embodiment, before the toner image is developed, transfer carrier particles are supplied to the surface of the photosensitive drum 1 in advance using the toner carried by the developing roller 41. By coating the photosensitive drum 1 with transfer carrier particles in advance, the transfer carrier particles are interposed between the toner image and the photosensitive drum 1.

Figure 8(a) is a schematic diagram of the development nip when the development roller 41 and the photosensitive drum 1 are in contact with each other. As shown in Figure 8(a), in the development nip, the toner carried on the development roller 41 and the photosensitive drum 1 are in contact with each other via the transfer carrier particles. Figure 8(b) is a schematic diagram showing the state after the toner carried on the development roller 41 and the photosensitive drum 1 shown in Figure 8(a) have passed through the development nip. As shown in Figure 8(b), the transfer carrier particles that were interposed between the toner and the photosensitive drum 1 in the development nip are transferred from the surface of the toner carried on the development roller 41 to the surface of the photosensitive drum 1 after passing through the development nip, and are supplied.

As shown in FIG. 8(a), if the adhesive force Ft between the transfer carrier particles and the toner present between the toner and the photosensitive drum 1 in the development nip portion is greater than the adhesive force Fdr between the transfer carrier particles and the photosensitive drum 1, the transfer carrier particles are less likely to transfer onto the photosensitive drum 1. Therefore, it is preferable that Ft is smaller than Fdr.

Figure 9(a) is a schematic diagram of the primary transfer section when a toner image is carried on the surface of the photosensitive drum 1. Figure 9(b) is a schematic diagram of the state in which the photosensitive drum 1 and intermediate transfer belt 10 are separated after the primary transfer of the toner image shown in Figure 9(a) is completed. When Ft is smaller than Fdr, when the toner image is primarily transferred from the photosensitive drum 1 onto the surface of the intermediate transfer belt 10, only the toner image is primarily transferred onto the intermediate transfer belt 10, and the transfer carrier particles interposed between the toner image and the photosensitive drum 1 remain on the photosensitive drum 1.

Let us consider a case where the transfer carrier particles interposed between the toner image and the photosensitive drum 1 are transferred to the intermediate transfer belt 10 together with the toner image, and the transfer carrier particles are lost from the surface of the photosensitive drum 1. In that case, the transfer carrier particles are not interposed between the toner image developed next on the surface of the photosensitive drum 1 and the photosensitive drum 1, and the adhesive force between the toner image and the photosensitive drum 1 is large, so the primary transferability is reduced.

Therefore, it is preferable that Ft is smaller than Fdr, not only because this makes it easier to supply transfer carrier particles from the toner carried on the developing roller 41 to the photosensitive drum 1, but also from the viewpoint of maintaining the transfer carrier particles coated on the photosensitive drum 1.

Figure 10 is a timing chart of the print operation of the image forming apparatus 100 used in this embodiment. As shown in Figure 10, during image formation operation, the image forming apparatus 100 of this embodiment rotates while the developing roller 41 and the photosensitive drum 1 are in contact with each other before starting to develop toner from the developing roller 41 to the photosensitive drum 1. This provides a timing for supplying transfer carrier particles from the developing roller 41 to the photosensitive drum 1 (transfer carrier supply mode).

In order to improve the primary transfer efficiency of the toner image over the entire surface of the photosensitive drum 1, the entire surface of the photosensitive drum 1 is coated with transfer carrier particles before the development of the toner image begins. For this reason, it is preferable to set the time for supplying the transfer carrier particles to the time it takes for the photosensitive drum 1 to rotate one or more revolutions. Therefore, in this embodiment, the length of the transfer carrier particle supply timing shown in FIG. 10 is set to 500 msec, which is approximately the same as the time it takes for the photosensitive drum 1 to rotate one revolution, so that the entire surface of the photosensitive drum 1 can be coated with the transfer carrier particles.

In addition, in this embodiment, at the timing of supplying transfer carrier particles shown in FIG. 10, the surface potential of the photosensitive drum 1 is set to a non-image forming potential Vd = -500 V at which toner charged to the normal polarity is not developed. Therefore, at the timing of supplying transfer carrier particles in this embodiment, toner whose normal polarity is negative is not developed on the surface of the photosensitive drum 1 from the developing roller 41, and only the transfer carrier particles are supplied from the developing roller 41 onto the photosensitive drum 1.

When transfer carrier particles are supplied from the toner on the developing roller 41 to the photosensitive drum 1 in a state where there is a potential difference between the developing roller 41 and the photosensitive drum 1 as in this embodiment, the following problem occurs. If the particle size of the transfer carrier particles is too large, the transfer carrier particles are easily affected by the electrostatic force generated by the potential difference between the developing roller 41 and the photosensitive drum 1. Therefore, it becomes difficult to control the supply of transfer carrier particles from the toner on the developing roller 41 to the photosensitive drum 1. For example, in a configuration in which transfer carrier particles are supplied at a non-image forming potential as in this embodiment, if the transfer carrier particles are negatively charged, the transfer carrier particles are attracted to the developing roller 41 side by electrostatic force. Therefore, it becomes difficult to supply the transfer carrier particles from the toner on the developing roller 41 to the photosensitive drum 1. Here, it is preferable that the particle size of the transfer carrier particles is set to 1000 nm or less, which is less susceptible to electrostatic forces. In this embodiment, particles with a particle diameter of 100 nm are used as the transfer carrier particles in order to stably supply transfer carrier particles from the toner on the development roller 41 to the surface of the photosensitive drum 1 regardless of the potential difference between the development roller 41 and the photosensitive drum 1.

The developer used in this embodiment is a mixture of the toner and transfer carrier particles described above. Figure 7 is an enlarged view of the developer used in this embodiment. As shown in Figure 7, the developer in this embodiment is a toner surface on which a large number of protrusions of an organosilicon polymer are formed, with transfer carrier particles arranged on the toner surface. The protrusion interval G and protrusion height H on the toner surface shown in Figure 7 can be measured by a scanning probe microscope (hereinafter SPM). A scanning probe microscope (hereinafter SPM) is equipped with a probe, a cantilever that supports the probe, and a displacement measurement system that detects the bending of the cantilever, and detects the atomic force (attractive or repulsive force) between the probe and the sample to observe the shape of the sample surface.

If the convex spacing G is larger than the transfer carrier, when the transfer carrier particles are placed between the convex portions, they will come into contact with the toner matrix, and the adhesive force Ft between the transfer carrier particles and the toner will increase, making it difficult for the transfer carrier particles to transfer from the toner to the photosensitive drum 1. For this reason, it is preferable that the convex spacing G is narrower than the particle size of the transfer carrier particles. Therefore, when the closest distance between adjacent convex portions is defined as the convex spacing G, it is preferable that the average convex spacing G is equal to or smaller than the average particle size of the transfer carrier particles.

Furthermore, if the convex height H is higher than the particle size of the transfer carrier particles, the convex portion will come into contact with the photosensitive drum 1 before the transfer carrier particles, making it difficult for the transfer carrier particles to come into contact with the photosensitive drum 1. Therefore, since it becomes difficult for the transfer carrier particles to be transferred from the toner to the photosensitive drum 1, it is preferable that the convex height H is lower than the particle size of the transfer carrier particles. Therefore, when the height of the convex portion from the surface of the toner particle is defined as the convex height H, it is preferable that the average convex height H is equal to or less than the average particle size of the transfer carrier particles.

When the convex portions on the toner surface of this embodiment were measured, the average convex spacing G on the toner surface was approximately 30 nm, and the average convex height H was 50 nm, and both the convex spacing G and the convex height H were smaller than the particle diameter of the transfer carrier, which was 100 nm.

The transfer carrier particles used in this embodiment are silica particles with a particle size of 100 nm manufactured by the sol-gel method. In this embodiment, silica is used as the transfer carrier particles, but the material of the transfer carrier particles is not limited to silica and may be various organic or inorganic fine powders. However, as described above, it is preferable that the adhesion force Ft between the transfer carrier particles and the toner is smaller than the adhesion force Fdr between the transfer carrier particles and the photosensitive drum 1. Therefore, it is preferable to select a material for the transfer carrier particles that reduces the adhesion force Ft of the transfer carrier particles to the toner. For example, as in this embodiment, when the convex parts on the toner surface are formed of a silica-based material such as an organic silica polymer, it is preferable to select a silica-based material with a material composition similar to that of the convex parts as the material for the transfer carrier particles. It is preferable to select a silica-based material with a material composition similar to that of the convex parts from the viewpoint of reducing the adhesion force between the convex parts and the transfer carrier particles.

In addition, in this embodiment, the amount of transfer carrier particles added was adjusted so that the number of transfer carrier particles coated per toner particle was about 500. The more transfer carrier particles that coat the toner, the more transfer carrier particles can be transferred from the developing roller 41 to the surface of the photosensitive drum 1. However, if too many transfer carrier particles are added, the risk of contamination of components within the image forming apparatus 100 increases, so it is preferable to adjust the amount according to the desired primary transfer properties.

Furthermore, the primary transferability improves to a certain extent with an increase in the coverage of the transfer carrier particles occupying the surface of the photosensitive drum 1. However, as the coverage of the transfer carrier particles occupying the surface of the photosensitive drum 1 increases, the degree of improvement in the primary transferability slows down, and the risk of contamination of various members within the image forming apparatus by the transfer carrier particles increases. Therefore, it is preferable to keep the coverage of the transfer carrier particles occupying the surface of the photosensitive drum 1 within 80%.
6. Effect of Transfer Carrier Particles Next, an effect confirmation experiment conducted to confirm the effect of the means for supplying transfer carrier particles to the photosensitive drum 1 in this embodiment will be described.

First, a yellow patch image with a density of 100% is formed using the image forming apparatus 100 equipped with a brand new photosensitive drum 1 that is not coated with transfer carrier particles. Then, immediately after the primary transfer of the formed yellow patch image is completed, the image forming apparatus 100 is stopped. At that time, the residual toner density of the patch image portion remaining on the surface of the photosensitive drum 1a of the yellow station was confirmed.

The measurement of the residual toner density was performed by the following method. First, a transparent tape (polyester tape 5511, Nichiban) was applied to the residual toner portion of the yellow patch image on the surface of the photosensitive drum 1a, and the residual toner was collected on the transparent tape. Then, the transparent tape that had collected the residual toner peeled off from the surface of the photosensitive drum 1a and a new transparent tape were each applied to a high-whiteness paper (GFC081, Canon). Then, the density D1 of the transparent tape at the residual toner collection portion and the density D0 of the new transparent tape portion were each measured using a reflection densitometer (Reflectometer Model TC-6DS, Tokyo Denshoku Co., Ltd.). The difference "D0-D1" obtained by the measurement was taken as the residual toner density. The smaller the value of the residual toner density, the less the residual toner is. If the value is 1.0 or less, it can be determined that there is almost no residual toner, and no image problems caused by adhesion to the charging roller 2a will occur.

The surface of the photosensitive drum 1a where the residual toner concentration was measured was observed under a microscope, and the coverage rate of the surface of the photosensitive drum 1a occupied by the transfer carrier particles was calculated. Specifically, the coverage rate was calculated using the following procedure for an observation image of the surface of the photosensitive drum 1a at a magnification of 3000 times taken with a laser microscope (VK-X200, Keyence). The area of the transfer carrier particles and the other areas were subjected to binarization processing, and the total area rate of the transfer carrier particles occupied on the surface of the photosensitive drum 1 was calculated as the coverage rate of the transfer carrier particles on the surface of the photosensitive drum 1.

The adhesive force between the transfer carrier particles and toner used in this example was measured using an SPM. Specifically, a cantilever was created with a transfer carrier particle fixed to the tip of the lever, and the cantilever was pressed against the toner with a specified pressure. After that, the force required to detach the cantilever from the toner was measured as the adhesive force Ft between the transfer carrier particles and toner.

The specified pressure with which the cantilever is pressed against the toner during adhesion measurement is preferably set to the force with which the transfer carrier particles interposed between the toner and the photosensitive drum 1 in the development nip are pressed against the toner. The pressing force was calculated using the calculation method described below. Here, "transfer carrier interposed between the toner and the photosensitive drum 1 in the development nip" refers to a state in which the transfer carrier particles are in contact with both the toner and the photosensitive drum 1 at the same time.

First, the conditions assumed for the calculation will be explained with reference to Figs. 11 and 12. Fig. 11(a) is a schematic diagram of the development nip portion, and it is assumed that the development roller 41 and the photosensitive drum 1 are in contact with each other through the toner in the development nip portion. Fig. 11(b) shows a cross section parallel to the surface of the photosensitive drum 1 at the dotted line AB in Fig. 11(a), and it is assumed that the toner in contact with the photosensitive drum 1 is packed closely as shown in the hatched area. Fig. 12 is a schematic diagram showing an enlarged contact area between the toner and the photosensitive drum 1 surrounded by the dotted line in Fig. 11. As shown in Fig. 12, it is assumed that the toner and the photosensitive drum 1 are in contact with each other through the transfer carrier particles. It is also assumed that the transfer carrier particles have not yet been supplied to the surface of the photosensitive drum 1, and that there are no transfer carrier particles on the surface of the photosensitive drum 1 in advance.

Based on the above assumptions, the total number N of transfer carrier particles present between the toner and the photosensitive drum 1 in the development nip was calculated as follows: From the calculated N and the contact force F between the development roller 41 and the photosensitive drum 1, F/N, which is the pressing force on the toner per transfer carrier particle in the development section, was calculated, and the calculated F/N was used as the specified pressing force of the cantilever on the toner when measuring the adhesion force.

First, we will explain how to calculate the total number N of transfer carrier particles present between the toner and the photosensitive drum 1 in the development nip.

Figure 13(a) is a schematic diagram showing the contact state of the toner, transfer carrier particles, and photosensitive drum 1 in the development section in two dimensions. As shown in Figure 13(b), if the particle size of the transfer carrier particles is r, when the distance between the photosensitive drum 1 and the toner surface exceeds r, the transfer carrier particles on the toner will almost never come into contact with the photosensitive drum 1. Therefore, the toner circumferential portion where the transfer carrier particles arranged on the toner circumference can come into contact with the photosensitive drum 1 is on an arc connecting A to B. In reality, it is necessary to consider the toner as a sphere as shown in Figure 13(b), and it is necessary to find the ratio of the surface area (shaded area in Figure 13(b)) obtained by integrating the arc AB in the circumferential direction to the toner surface area. The surface area of the shaded area can generally be found as the surface area of a spherical crown, as shown in formula (2). Therefore, the ratio of the toner surface area is as shown in formula (3). The actual value can be calculated from the average particle size R of the toner and the particle size r of the transfer carrier particles.

From the above calculations, the ratio of the arc AB in the configuration of this embodiment to the toner circumference is calculated to be approximately 1.43%.

Therefore, it can be considered that the area of the transfer carrier particles between the toner and the photosensitive drum 1 in the development nip portion is approximately 1.43% of the entire toner surface. Since the number of transfer carrier particles covering one toner particle is 500, the number M of transfer carrier particles between the toner and the photosensitive drum 1 per toner particle is calculated as "500 particles x 1.43%", which is approximately 7.2 particles.

Then, multiply the number of transfer carrier particles between the toner and the photosensitive drum 1 per toner particle (7.2) by the total number of toner particles in contact with the photosensitive drum 1 in the development section. Then, the total number N of transfer carrier particles between the toner and the photosensitive drum 1 in the development nip can be calculated.

The total amount of toner L in contact with the photosensitive drum 1 in the development nip can be calculated by (area of the development nip x toner filling rate) / maximum cross-sectional area of the toner.

(Total number of toner particles in contact with the photosensitive drum 1 at the development nip)
= (220 [mm] × 2.0 [mm] × π / √12) / (π × (7.0 / 2) ² )
= approx. 10.37 x ¹⁰⁶ (The closest packing rate of a two-dimensional circle, π/√12 ≒ 0.9069, was used.)
Therefore, the "total number N of transfer carrier particles present between the toner and the photosensitive drum 1 in the development nip" is calculated as follows: It is calculated by multiplying the "total number of toner particles in contact with the photosensitive drum 1 in the development nip" by the "number of transfer carrier particles present between the toner and the photosensitive drum 1 per toner particle", and the total number N is approximately 7.47× ¹⁰⁷ .

In this embodiment, the pressing force of the developing roller 41 against the photosensitive drum 1 is F=200 gf, so F/N, which is the "pressing force against the toner per transfer carrier particle in the developing section," is calculated to be 26.3 nN. The value of F/N calculated above was used as the predetermined pressing force for pressing the cantilever against the toner when measuring the adhesion force by SPM. In addition, a similar adhesion force measurement was also performed on the photosensitive drum 1, and the adhesion force Fdr between the transfer carrier particle fixed to the tip of the cantilever and the photosensitive drum 1 was measured.
7. Relationship between Adhesion Force of Transfer Carrier Particles to the Photosensitive Drum and to the Intermediate Transfer Belt Next, the relationship between the adhesion force of the transfer carrier particles to the photosensitive drum 1 and the adhesion force to the intermediate transfer belt 10, which is a feature of this embodiment, will be described. In this embodiment, the transfer efficiency is improved by performing an image forming operation in a state in which the transfer carrier particles are attached to the surface of the photosensitive drum 1. For this purpose, it is necessary to configure the transfer carrier particles so that they do not move from the photosensitive drum 1 to the surface of the intermediate transfer belt 10 with which they come into contact at the transfer portion as much as possible. Therefore, in the configuration of the first embodiment, the relationship between the adhesion force Fdr between the transfer carrier particles and the photosensitive drum 1 and the adhesion force Fi between the transfer carrier particles and the intermediate transfer belt 10 is set to Fdr>Fi.

Next, we will explain how to calculate the adhesion force Fdr between the transfer carrier particles and the photosensitive drum 1 and the adhesion force Fi of the transfer carrier particles to the intermediate transfer belt 10. The adhesion force Fdr between the transfer carrier particles and the photosensitive drum 1 and the adhesion force Fi between the transfer carrier particles and the intermediate transfer belt 10 are calculated using formula (4).

Here, A1 (hamaker constant): 6.58E-20 (J), Z0 (separation distance): 4.00E-10 (m), R (composite diameter): 5.00E-8 (m). α is the particle deformation amount. The particle deformation amount α can be calculated using formula (5).

f represents the pressure (N) applied to one transfer carrier particle. E* is calculated from the relationship (6) between E (Young's modulus (Pa)) and ν (Poisson's ratio).

Therefore, from equations (5) and (6), it can be seen that the adhesion force Fdr between the transfer carrier particles and the photosensitive drum 1 and the adhesion force Fi between the transfer carrier particles and the intermediate transfer belt 10 depend on the pressing force, Young's modulus, and Poisson's ratio of the material for one transfer carrier particle.

Therefore, from equations (4), (5), and (6), it can be seen that if the Young's modulus and Poisson's ratio of the material of the surface of the photosensitive drum 1 are small, the adhesive force when the photosensitive drum 1 and the intermediate transfer belt 10 are pressed together will be large. Therefore, in order to make Fdr>Fi, it is preferable that the Young's modulus and Poisson's ratio of the material used for the photosensitive drum 1 are smaller than the Young's modulus and Poisson's ratio of the material used for the intermediate transfer belt 10.

In addition, the adhesion force when the photosensitive drum 1 and intermediate transfer belt 10 are pressed against each other increases depending on the pressing force. In order to make Fdr > Fi, it is preferable to increase the force pressing the transfer carrier particles against the photosensitive drum 1 and decrease the force pressing the transfer carrier particles against the intermediate transfer belt 10.

In this embodiment, the Young's modulus of the polycarbonate surface layer of the photosensitive drum 1 is 2.20 (GPa) and the Poisson's ratio is 0.37, while the Young's modulus of the acrylic surface layer of the intermediate transfer belt 10 is 3.00 (GPa) and the Poisson's ratio is 0.38. Therefore, the Young's modulus and Poisson's ratio of the material used for the photosensitive drum 1 are smaller than those of the material used for the intermediate transfer belt 10.

The pressing force of the intermediate transfer belt 10 against the photosensitive drum 1 in the transfer section is 220 gf. FIG. 14(a) is a schematic diagram of the transfer nip section when the photosensitive drum 1 and the intermediate transfer belt 10 are in contact with each other. As shown in FIG. 14(a), in the transfer nip section, the transfer carrier particles receive an adhesion force Fdr from the photosensitive drum 1 and an adhesion force Fi from the intermediate transfer belt 10. FIG. 14(b) is a schematic diagram showing the state after the toner carried on the photosensitive drum 1 and the intermediate transfer belt 10 shown in FIG. 14(a) have passed through the transfer section. As shown in FIG. 14(b), the transfer carrier particles interposed between the photosensitive drum 1 and the intermediate transfer belt 10 in the transfer section are configured to satisfy the relationship Fdr>Fi, thereby suppressing the movement of the transfer carrier particles from the photosensitive drum 1 to the intermediate transfer belt 10.

A pressing member that comes into contact with the photosensitive drum 1 and presses the transfer carrier particles on the surface of the photosensitive drum 1 may also be installed separately. The pressing force on the photosensitive drum 1 can be added by the pressing member, so that the relationship Fdr>Fi can be more effectively maintained. Here, the relationship between the adhesion force of the pressing member and the photosensitive drum 1 to the transfer carrier particles is the same as the relationship between the adhesion force of the photosensitive drum 1 and the intermediate transfer belt 10. This makes it possible to preferably obtain the effect of adhering the transfer carrier particles to the photosensitive drum 1.

In this embodiment, the developing roller 41 not only supplies transfer carrier particles to the photosensitive drum 1, but also presses it. The developing roller 41 presses the transfer carrier particles on the surface of the photosensitive drum 1, increasing the pressing force of the photosensitive drum 1, which is preferable in order to maintain Fdr>Fi. This developing roller 41 may be used as a pressing member. The developing roller 41 may also be used as a transfer carrier particle supplying member.

In addition, in this embodiment, the transfer carrier particles are supplied from the developing roller 41 to the photosensitive drum 1, but a transfer carrier particle supply member in contact with the photosensitive drum 1 may be provided separately. When this transfer carrier particle supply member presses the transfer carrier particles on the surface of the photosensitive drum 1, the adhesion force to the photosensitive drum 1 increases, so that Fdr>Fi can be maintained. This transfer carrier particle supply member may also be used as the above-mentioned pressing member. Furthermore, in order to maintain Fdr>Fi, it is preferable that the pressing force of the transfer carrier particle member on the photosensitive drum 1 at the transfer carrier particle supply unit or the pressing member is greater than the pressing force of the photosensitive drum 1 at the transfer unit. In this embodiment, the photosensitive drum 1 is pressed with 200 gf in the development unit, and the development nip width is 2 mm. On the other hand, the photosensitive drum 1 is pressed with 220 gf in the transfer unit, and the nip width at the primary transfer unit is 3 mm. Therefore, the pressing force exerted on the transfer carrier particles per unit area is 100 gf/mm in the development section and 73.3 gf/mm in the primary transfer section. Therefore, in this embodiment, the pressing force of the transfer carrier particles in the development section is greater than the pressing force of the transfer carrier particles in the transfer section.

In addition, the primary transferability improves to a certain extent with an increase in the coverage of the transfer carrier particles on the photosensitive drum 1. In order to obtain sufficient primary transferability, it is preferable that the coverage of the transfer carrier particles on the photosensitive drum 1 is 10% or more, assuming that the entire photosensitive drum surface is 100%. However, as the coverage of the transfer carrier particles on the photosensitive drum 1 increases, the following problems may occur. If there are too many transfer carrier particles on the surface of the photosensitive drum 1, the risk of contamination by the transfer carrier particles increases for the member that contacts the surface of the photosensitive drum 1. Therefore, it is preferable to keep the coverage of the transfer carrier particles on the photosensitive drum 1 within 50%. From the observation of the surface of the photosensitive drum 1, it was confirmed that the coverage of the transfer carrier particles present on the surface of the photosensitive drum 1 is 10% or more in this embodiment.
8. Effect of Setting Adhesion Force Fi to Intermediate Transfer Belt Next, in this embodiment, an effect of suppressing the movement of transfer carrier particles from the photosensitive drum 1 to the intermediate transfer belt 10 was confirmed. The experimental method is explained below. First, a method of confirming the movement of transfer carrier particles from the photosensitive drum 1 to the intermediate transfer belt 10 is explained.

The image forming apparatus of Example 1 was prepared with the photosensitive drum 1 with the transfer carrier particles attached thereto, and the photosensitive drum 1 and the intermediate transfer belt 10 were pressed together with a primary transfer pressure of 220 gf. The surface of the photosensitive drum 1 after pressing was observed under a microscope, and the coverage rate of the transfer carrier particles on the surface of the photosensitive drum 1 was calculated. Specifically, an observation image was first obtained by observing the surface of the photosensitive drum 1 at a magnification of 3000 times using a laser microscope (VK-X200, Keyence). After that, the surface of the photosensitive drum 1 in the observation image was binarized in the areas covered with the transfer carrier particles and the areas not covered with the transfer carrier particles, and the area rate of the transfer carrier particles on the surface of the photosensitive drum 1 was calculated.

To obtain an observation image, the image forming apparatus is stopped with transfer carrier particles being supplied to the surface of the photosensitive drum 1. Observations are performed on the photosensitive drum 1 both upstream and downstream of the transfer nip position where the photosensitive drum 1 and intermediate transfer belt 10 are in contact. Accordingly, the area ratios are calculated on both the upstream and downstream sides of the transfer nip. The figure with the upstream area ratio as the denominator and the amount of change in the area ratio obtained by subtracting the downstream area ratio from the upstream area ratio as the numerator is defined as the "change rate of the coverage rate of the transfer carrier particles on the photosensitive drum 1."

If there is no new supply of transfer carrier particles, and the rate of change in the coverage of the transfer carrier particles on the photosensitive drum 1 is 50% or more, the transfer carrier particles will be almost completely removed from the surface of the photosensitive drum 1 after about 10 rotations. It is preferable that the rate of change in the coverage of the transfer carrier particles on the photosensitive drum 1 is less than 20%.

Next, the calculation method of Fdr and Fi will be described. The adhesive force was calculated using the above-mentioned formulas (4), (5), and (6). In this embodiment, focusing on the elasticity of the material, the adhesive force of each material was calculated from formulas (4), (5), and (6), and the materials were screened. Therefore, constants unrelated to the elasticity are not dependent on the material, and the actual measurement results of the adhesive force, which will be described later, performed in several combinations from the results obtained by screening by calculation are regarded as accurate adhesive forces. In this embodiment, the adhesive force was calculated using the Young's modulus and Poisson's ratio of each material shown in FIG. 16. Furthermore, the adhesive force between the transfer carrier particles and the toner used in this embodiment was measured using an SPM. Specifically, after pressing the cantilever against the toner with a predetermined pressing force, the force required to detach the cantilever from the toner was measured as Fdr and Fi, which are the adhesive forces between the transfer carrier particles, the photosensitive drum 1, and the intermediate transfer belt 10. The cantilever used was made of silicon, the surface of which was covered with a silicon oxide film, and had a round tip with a tip diameter of 100 nm. By using SiO2 as the surface material of the cantilever, which is the same as the transfer carrier particles, and setting the tip diameter to 100 nm, which is equal to the number-average particle diameter of the transfer carrier particles, it is possible to accurately reproduce the adhesive force with the transfer carrier particles. When measuring the adhesive force, it is preferable to set the predetermined pressing force applied to the photosensitive drum 1 and the intermediate transfer belt 10 to the force that presses the transfer carrier particles interposed between the photosensitive drum 1 and the intermediate transfer belt 10 in the transfer section. The pressing force was calculated using the calculation method described below. Here, in the transfer section, "transfer carrier particles are interposed between the photosensitive drum 1 and the intermediate transfer belt 10" means that the transfer carrier particles are in contact with both the photosensitive drum 1 and the intermediate transfer belt 10 at the same time.

First, the conditions assumed in the calculation will be explained using FIG. 15. FIG. 15(a) is a schematic diagram of the development nip, and it is assumed that the photosensitive drum 1 and intermediate transfer belt 10 are in contact with each other via transfer carrier particles at the transfer section. FIG. 15(b) shows a cross section parallel to the surface of the photosensitive drum 1 at dotted line AB in FIG. 15(a), and it is assumed that the toner in contact with the intermediate transfer belt 10 is closest packed as shown in the shaded area. The total number N of transfer carrier particles interposed between the intermediate transfer belt 10 and the photosensitive drum 1 can be calculated from the area of the nip between the intermediate transfer belt 10 and the photosensitive drum 1 at the transfer section and the maximum cross-sectional area of the transfer carrier particles.

The total number Nt of transfer carrier particles in contact with the photosensitive drum 1 at the transfer section can be calculated by "area of transfer section x coverage rate of transfer carrier particles / maximum cross-sectional area of transfer carrier particles", which is approximately 6.6 x 10E9 (pieces). From the above calculation results and the fact that the pressing force F between the primary transfer roller 14 and the photosensitive drum 1 in this embodiment is 220 gf, the "pressure on the toner per transfer carrier particle at the transfer section" = F/Nt is approximately 0.33 (nN). This 0.33 (nN) was adopted as the predetermined pressing force of the cantilever on the toner at the transfer section when measuring adhesion force using the SPM.

Next, we will explain the results of the effectiveness verification of this embodiment. First, we will explain the materials of the photosensitive drum 1 and intermediate transfer belt 10 for which the effectiveness was verified.

In Example 1, the surface layer of the photosensitive drum 1 was a thin film layer made of polycarbonate with a thickness of 20 μm. The Young's modulus was 2.20 (GPa) and the Poisson's ratio was 0.37. The intermediate transfer belt 10 had a maximum roughness Rz of 0.12 μm or less. The surface layer was coated with acrylic and had a thickness of 2.3 μm. The Young's modulus was 3.00 (GPa) and the Poisson's ratio was 0.38. Modifications 1 to 5 and Comparative Examples 1 to 4 will be described below. Note that a description of the same configuration as in Example 1 will be omitted.

[Modification 1]
A thin film layer made of polyarylate and having a thickness of 23 μm was used as the surface layer of the photosensitive drum 1. The Young's modulus was 2.15 (GPa), the Poisson's ratio was 0.37, and the Rz was 0.1 μm.

[Modification 2]
A single-layer belt made of polyimide and having a thickness of 65 μm was used as the intermediate transfer belt 10. The Young's modulus was 2.65 (GPa) and the Poisson's ratio was 0.30.

[Modification 3]
A thin film layer having a thickness of 23 μm and made of polyarylate was used as the surface layer of the photosensitive drum 1. A single layer belt having a thickness of 65 μm and made of polyimide was used as the intermediate transfer belt 10. The Young's modulus was 2.65 (GPa) and the Poisson's ratio was 0.30.

[Modification 4]
A single-layer belt made of polyether ether ketone (PEEK) and having a thickness of 55 μm was used as the intermediate transfer belt 10. The Young's modulus was 3.70 (GPa) and the Poisson's ratio was 0.40.

[Modification 5]
A thin film layer having a thickness of 23 μm and made of polyarylate was used as the surface layer of the photosensitive drum 1. A single-layer belt having a thickness of 55 μm and made of polyether ether ketone (PEEK) was used as the intermediate transfer belt 10. The Young's modulus was 3.70 (GPa) and the Poisson's ratio was 0.40.

Comparative Example 1
The intermediate transfer belt 10 had a surface layer of about 2 μm made of urethane. The Young's modulus was 1.50 (GPa) and the Poisson's ratio was 0.48. The elastic layer was made of silicone rubber with a thickness of about 350 μm, and the base layer was made of polyimide with a thickness of about 60 μm.

Comparative Example 2
A surface layer made of Si and having a thickness of 1.2 μm was formed on the surface of the photosensitive drum 1. The Young's modulus was 185 (GPa) and the Poisson's ratio was 0.28.

Comparative Example 3
A single-layer belt of about 80 μm made of polybutylene terephthalate (PBN) was used as the intermediate transfer belt 10. The Young's modulus was 2.20 (GPa) and the Poisson's ratio was 0.38.

Comparative Example 4
A thin film layer having a thickness of 23 μm and made of polyarylate was used as the surface layer of the photosensitive drum 1. A single layer belt having a thickness of about 80 μm and made of polybutylene terephthalate (PBN) was used as the intermediate transfer belt 10. The Young's modulus was 2.20 (GPa) and the Poisson's ratio was 0.38.

Figure 16 shows the adhesion force Fdr between the transfer carrier particles and the photosensitive drum, and the adhesion force Fi between the transfer carrier particles and the intermediate transfer belt 10 at a pressing force of 220 gf and a pressure of 0.33 nN applied to one transfer carrier particle, along with the configurations of Example 1, Modifications 1-5, and Comparative Examples 1-4. By applying a pressure of 220 gf to the photosensitive drum to which the transfer carrier particles are attached, it was confirmed whether the transfer carrier particles would move to the intermediate transfer belt 10. Figure 16 also shows the "rate of change in the coverage of the transfer carrier particles on the photosensitive drum 1." In addition, the calculation results of the adhesion forces Fdr and Fi of each material and the SPM measurement results of the adhesion forces Fdr and Fi are shown.

As shown in the "change rate of the coverage of the transfer carrier particles on the photosensitive drum 1" in FIG. 16, in the combination of the material of the photosensitive drum 1 and the material of the intermediate transfer belt 10 in Example 1 and Modifications 1 to 5, the "change rate of the coverage of the transfer carrier particles on the photosensitive drum 1" is less than 20%. On the other hand, in Comparative Examples 1, 3, and 4, the "change rate of the coverage of the transfer carrier particles on the photosensitive drum 1" is 20% or more and less than 50%. In Comparative Example 2, the "change rate of the coverage of the transfer carrier particles on the photosensitive drum 1" is 50% or more. Comparing the adhesion force calculation results in FIG. 16, in Example 1 and Modifications 1 to 5, where the adhesion force relationship between the photosensitive drum 1 and the intermediate transfer belt 10 is Fdr>Fi, the movement of the transfer carrier particles can be suppressed and the transfer efficiency is maintained. In addition, in Comparative Examples 1 to 4, where the adhesion force relationship between the photosensitive drum 1 and the intermediate transfer belt 10 is Fdr<Fi, the transfer carrier particles move, resulting in a decrease in the transfer efficiency.

Figure 17 shows the relationship between pressure and adhesion measured using an SPM. As shown in Figure 17, for any material, adhesion depends on the pressure of the transfer carrier particles. Therefore, in order to reduce Fi, it is preferable to make the pressure as small as possible.

From the above results, the configuration of Example 1 has the following features:

Let us consider the case where the pressing force pressing the photosensitive drum 1 against the intermediate transfer belt 10 is F1, and the total number of transfer carrier particles interposed between the photosensitive drum 1 and the intermediate transfer belt 10 at the transfer section is N1. Let Fi be the adhesion force formed between the transfer carrier particle and the intermediate transfer belt 10 measured when the transfer carrier particle is pressed against the intermediate transfer belt 10 with F1/N1, which is the pressing force per unit transfer carrier particle. Let Fdr1 be the adhesion force formed between the transfer carrier particle and the photosensitive drum 1 measured when the transfer carrier particle is pressed against the photosensitive drum 1 with F1/N1. The relationship between Fi and Fdr1 satisfies Fi<Fdr1.

The developing unit 4 contains a developer, and the developing roller 41 carries the developer composed of toner particles and transfer carrier particles adhering to the surface of the toner particles. The developing roller 41 contacts the photosensitive drum 1 to form a developing section, and supplies the developer in the developing section. Consider the case where the pressing force pressing the developing roller 41 against the photosensitive drum 1 is F2, and the total number of transfer carrier particles interposed between the toner particles and the photosensitive drum 1 in the developing section is N2. The adhesion force formed between the transfer carrier particles and the toner particles measured when the transfer carrier particles are pressed against the toner particles with F2/N2, which is the pressing force per unit transfer carrier particle, is Ft. The adhesion force formed between the transfer carrier particles and the photosensitive drum 1 measured when the transfer carrier particles are pressed against the photosensitive drum 1 with F/N is Fdr2. The relationship between Ft and Fdr2 satisfies Ft≦Fdr2.

A pressing member may also be provided to press the transfer carrier particles adhering to the surface of the photosensitive drum 1. Here, consider the case where the pressing force of the pressing member against the photosensitive drum 1 is F3, and the total number of transfer carrier particles interposed between the photosensitive drum 1 and the pressing member at the pressing portion is N3. The adhesion force formed between the transfer carrier particles and the pressing member measured when the transfer carrier particles are pressed against the photosensitive drum 1 with F3/N3, which is the pressing force per unit transfer carrier particle, is Fp. The adhesion force formed between the transfer carrier particles and the photosensitive drum 1 measured when the transfer carrier particles are pressed against the photosensitive drum 1 with F3/N3 is Fdr3. The relationship between Fp and Fdr3 satisfies Fp<Fdr3.

A transfer carrier supply member may also be provided to supply transfer carrier particles to the surface of the photosensitive drum 1. Consider the case where the pressing force pressing the transfer carrier supply member against the photosensitive drum 1 is F4, and the total number of transfer carrier particles interposed between the photosensitive drum 1 and the supply member in the supply section is N4. Let Fs be the adhesive force formed between the transfer carrier particles and the supply member measured when the transfer carrier particles are pressed against the photosensitive drum 1 with F4/N4, which is the pressing force per unit transfer carrier particle. Let Fdr4 be the adhesive force formed between the transfer carrier particles and the photosensitive drum 1 measured when the transfer carrier particles are supplied to the photosensitive drum 1 with F4/N4. The relationship between Fs and Fdr4 satisfies Fs<Fdr4.

As described above, the configuration of this embodiment makes it possible to supply a sufficient amount of transfer carrier particles onto the photosensitive drum 1 to improve transfer efficiency while maintaining the transfer carrier particles on the surface of the photosensitive drum 1.

In addition, a roller may be inserted at the end of the primary transfer roller 14 as a rigid body with a diameter larger than that of the primary transfer roller 14. By inserting a roller at the end of the primary transfer roller 14, the primary transfer roller 14 does not directly press against the photosensitive drum 1, so the pressing force at the transfer section can be reduced.

In addition, in this embodiment, a primary transfer roller 14 is used as the primary transfer member, but a sheet-shaped or brush-shaped primary transfer member may also be used.

In the configuration of the image forming device applied in this embodiment, the same members as those in the first embodiment described above are given the same reference numerals and the description thereof is omitted.

In Example 2, unlike Example 1, a metal roller is used for the primary transfer roller 51, which stabilizes the contact pressure between the intermediate transfer belt 10 and the photosensitive drum 1, and further maintains the adhesive force relationship over a long period of time.

The configuration of this embodiment will be described. FIG. 18 shows a schematic diagram of the image forming apparatus used in this embodiment, with the parts changed from those in the first embodiment enlarged. The primary transfer roller 51a is a cylindrical metal roller with a diameter of 6 mm, and is made of nickel-plated SUS. The primary transfer roller 51a is disposed at a position offset by 7 mm downstream of the center position of the photosensitive drum 1a in the surface movement direction of the intermediate transfer belt 10. The intermediate transfer belt 10 is configured to wrap around the photosensitive drum 1a. The primary transfer member 51a is disposed at a position raised by 0.3 mm from the horizontal plane formed by the photosensitive drum 1a and the intermediate transfer belt 10 so that the amount of winding of the intermediate transfer belt 10 around the photosensitive drum 1a can be secured. At that time, the intermediate transfer belt 10 is pressed with a force of about 200 gf. The primary transfer roller 51a rotates following the rotation of the intermediate transfer belt 10. Additionally, the primary transfer roller 51b arranged in the second image forming station b, the primary transfer roller 51c arranged in the third image forming station c, and the primary transfer roller 51d arranged in the fourth image forming station d are configured in the same manner as the primary transfer member roller 51a.

The operation of this embodiment is explained below.

As shown in FIG. 17, the adhesion force Fi between the intermediate transfer belt 10 and the transfer carrier particles varies depending on the pressing force of the intermediate transfer belt 10 at the transfer section. Therefore, in order to maintain Fdr>Fi and suppress the movement of the transfer carrier particles from the photosensitive drum 1 to the intermediate transfer belt 10, a configuration that reduces the pressing force of the intermediate transfer belt 10 at the transfer section is preferable. In the second embodiment, the photosensitive drum 1 is not directly pressed by the primary transfer roller 51. Therefore, compared to the first embodiment, the pressing force of the intermediate transfer belt 10 at the transfer section can be reduced. This makes it possible to maintain the adhesion force relationship of Fdr>Fi over a long period of time.

REFERENCE SIGNS LIST 1 Photosensitive drum 2 Charging roller 3 Exposure unit 4 Development unit 14 Transfer roller 41 Development roller 62 Toner particles

Claims (14)

A rotatable image carrier ;
a developer storage section that stores a developer composed of toner particles and carrier particles adhered to the surfaces of the toner particles;
a developer carrier that carries the developer , that comes into contact with the image carrier to form a development section, and that supplies the developer to a surface of the image carrier in the development section ;
an intermediate transfer body that contacts the image carrier to form a transfer section, and a toner image formed by the developer supplied to the surface of the image carrier is transferred to the intermediate transfer body in the transfer section;
an image forming apparatus capable of supplying the carrier particles carried on the surface of the developer carrier and accommodated in the developer accommodating section to the surface of the image carrier in a state in which the image carrier is rotated, in the developing section;
When the pressing force with which the image carrier is pressed against the intermediate transfer body is F1 and the total number of the carrier particles present between the image carrier and the intermediate transfer body in the transfer portion is N1,
an adhesive force Fi formed between the carrier particles and the intermediate transfer body, the adhesive force being measured when the carrier particles are pressed against the intermediate transfer body with a pressing force per unit carrier particle, F1/N1;
and an adhesive force Fdr1 formed between the carrier particles and the image carrier, the adhesive force Fdr1 being measured when the carrier particles are pressed against the image carrier at F1/N1,
Fi < Fdr1
The filling,
The developer has convex portions formed on the surfaces of the toner particles, the carrier particles are arranged on the convex portions, and when the closest distance between adjacent convex portions is defined as a convex spacing G, the average of the convex spacing G is equal to or less than the average particle size of the carrier particles . When the pressing force with which the developer carrier is pressed against the image carrier is F2 and the total number of the carrier particles present between the toner particles and the image carrier in the developing section is N2,
an adhesive force Ft formed between the carrier particles and the toner particles, the adhesive force Ft being measured when the carrier particles are pressed against the toner particles with a pressing force F2/N2 per unit carrier particle;
and an adhesive force Fdr2 formed between the carrier particles and the image carrier, the adhesive force Fdr2 being measured when the carrier particles are pressed against the image carrier at F2/N2,
Ft≦Fdr2
2. The image forming apparatus according to claim 1, wherein the above-mentioned condition is satisfied. 3. The image forming apparatus according to claim 2, wherein said convex portions are formed from fine particles containing an organosilicon polymer having a structure represented by the following formula (1):
R-Si(O1/2)3 (1)
(The above R represents a hydrocarbon group having 1 to 6 carbon atoms.) The image forming apparatus according to claim 2 or 3, characterized in that the developer remaining on the image carrier without being transferred to the intermediate transfer body is collected by the developer carrier. The image forming apparatus according to claim 4, characterized in that the developer is a one-component developer. The image forming apparatus according to claim 3, characterized in that, when the height of the convex portion from the surface of the toner particle is defined as a convex height H, the average of the convex height H is equal to or less than the average particle size of the carrier particles. 7. The image forming apparatus according to claim 1, wherein the carrier particles are silica. 8. The image forming apparatus according to claim 1, wherein the carrier particles are made of an organic silica polymer. 9. The image forming apparatus according to claim 1, wherein the average particle size of the carrier particles is 30 nm or more and 1000 nm or less. a transfer member for transferring the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer member;
10. The image forming apparatus according to claim 1, wherein the transfer member is disposed downstream of the transfer portion in a moving direction of the surface of the intermediate transfer body. a pressing member that contacts the image carrier to form a pressing portion,
11. The image forming apparatus according to claim 1, wherein the pressing member is configured to press the carrier particles on the surface of the image carrier at the pressing portion. When the pressing force of the pressing member against the image carrier is F3 and the total number of the carrier particles present between the image carrier and the pressing member in the pressing portion is N3,
an adhesive force Fp formed between the carrier particles and the pressing member, the adhesive force Fp being measured when the carrier particles are pressed against the image carrier with a pressing force F3/N3 per unit carrier particle;
and an adhesive force Fdr3 formed between the carrier particles and the image carrier, the adhesive force Fdr3 being measured when the carrier particles are pressed against the image carrier at F3/N3,
Fp<Fdr3
13. The image forming apparatus according to claim 12 , wherein the above formula is satisfied. 13. The image forming apparatus according to claim 1, further comprising a supply member that contacts the image carrier to form a supply section and supplies the carrier particles in the supply section. When a pressing force with which the supply member is pressed against the image carrier is F4, and a total number of the carrier particles present between the image carrier and the supply member in the supply section is N4,
an adhesive force Fs formed between the carrier particles and the supply member, the adhesive force Fs being measured when the carrier particles are pressed against the image carrier with a pressing force F4/N4 per unit carrier particle;
and an adhesive force Fdr4 formed between the carrier particles and the image carrier, which is measured when the carrier particles are supplied to the image carrier at F4/N4,
Fs < Fdr4
13. The image forming apparatus according to claim 12 , wherein the above expression is satisfied.

Images