JP2017072770A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can suppress a transfer residual toner and a re-transfer residual toner to improve transfer efficiency.SOLUTION: An image forming apparatus 100 comprises: photoreceptors 2; image forming means 3 and 7 that form electrostatic images on the photoreceptors 2; developing means 4 that supply a toner to the electrostatic images formed on the photoreceptors 2; and a transfer body 8 to which the toner images are electrostatically transferred from the photoreceptors 2. When the relative dielectric constant of the photoreceptors 2 is εdr, the relative dielectric constant of the transfer body 8 is εit, and the relative dielectric constant of the toner is ε, the relationships εdr<ε and εdr<εit are satisfied.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine using an electrophotographic system.

  Conventionally, an electrophotographic image forming apparatus uniformly charges a photosensitive member (electrophotographic photosensitive member) and then exposes it to form an electrostatic latent image, and develops the electrostatic latent image with toner. A toner image is formed, and this toner image is finally transferred to a transfer material such as paper to form an image. As such an image forming apparatus, there is an intermediate transfer type image forming apparatus in which a toner image formed on a photosensitive member is temporarily transferred to an intermediate transfer member and then secondarily transferred to a transfer material. In addition, the color image forming apparatus has an image forming unit that forms toner images of different colors independently, and transfers the toner image formed by each image forming unit so as to be superimposed on the intermediate transfer member. There is a type. As the intermediate transfer member, an intermediate transfer belt composed of an endless belt is widely used.

  In an image forming apparatus using an electrophotographic system, it is important to suppress transfer residue and retransfer residue. Here, “transfer residue” is a phenomenon in which the toner of the toner image formed on the photoconductor cannot be completely transferred onto the intermediate transfer belt. The main cause of this phenomenon is that there are many toners whose charge polarity is reversed and the non-electrostatic adhesion of the toner is large. It can also occur when the charge of the toner is attenuated at the primary transfer portion. The toner remaining on the photoreceptor due to the transfer residue is referred to as “transfer residual toner”. “Retransfer remaining” means that the toner of the toner image primarily transferred onto the intermediate transfer belt in the primary transfer portion in the previous process adheres to the photoconductor in the primary transfer portion in the subsequent process (retransfer, reverse transfer). This is a phenomenon. This phenomenon also occurs for the same reason as the occurrence of transfer residue. The toner remaining on the photoreceptor due to the retransfer residue is referred to as “retransfer residual toner”.

  In addition, there is a cleanerless system in which a cleaning unit that removes and collects transfer residual toner and retransfer residual toner from a photoconductor is not provided for downsizing and cost reduction. In this method, it is particularly important to improve the transfer efficiency by reducing the residual transfer toner and the residual retransfer toner from the viewpoint of suppressing the adhesion of the toner to the charging member for charging the photosensitive member. This is because toner adhering to the charging member may cause fluctuations in the charging potential of the photosensitive member and image disturbance (image ghost).

  In response to the above problems, attempts have been made to reduce the adhesion of toner by using spherical toner by suspension polymerization or the like instead of pulverized toner having a large amount of different formation. In addition, attempts have been made to improve the chargeability of toner by using various substances as toner particles (toner base) and external additives.

  Japanese Patent Application Laid-Open No. H10-228561 proposes reducing the retransfer residual toner by reducing the non-electrostatic adhesion force of the toner (defined by the surface contact angle). In Patent Document 2, it is proposed to improve transfer efficiency (transferability) by using an intermediate transfer belt. Patent Document 3 proposes to improve transfer efficiency as follows. That is, the dielectric constant εdr of the surface layer of the image carrier in the primary transfer portion, the dielectric constant εit of the surface layer of the intermediate transfer member, and the dielectric constant εtr of the surface layer of the contact transfer means in the secondary transfer portion are εdr ≦ εit ≦ εtr. It is assumed that the relational expression is satisfied.

JP-A-9-146334 JP 2001-92275 A JP-A-9-127801

  However, it has been difficult to sufficiently improve the transfer efficiency by the conventional method.

  According to the study of the present inventors, the magnitude of the non-electrostatic adhesion force is about 10 nN in the case of the spherical toner, and it is not so large that the toner behavior can be influenced by itself. Therefore, there is a limit to the improvement of transfer efficiency by the method described in Patent Document 1.

  Further, in a system using an intermediate transfer belt, it is considered that it is less affected by electric discharge than a method of transferring directly to paper, and good transfer efficiency can be obtained. Here, the intermediate transfer belt generally contains a resistance adjusting agent such as carbon black in order to prevent the belt from being charged. For this reason, for example, in a system using an intermediate transfer belt having a relatively low electric resistance value, the charge of the toner tends to be attenuated at the primary transfer portion. For this reason, there is a limit to the improvement in transfer efficiency by the method described in Patent Document 2.

  The method described in Patent Document 3 is considered to be effective to some extent for the transfer of a single-layer toner, but its effect is limited in the transfer of a multilayer toner.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing transfer residue and retransfer residue and improving transfer efficiency.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a photosensitive member, an image forming unit that forms an electrostatic image on the photosensitive member, a developing unit that supplies toner to the electrostatic image formed on the photosensitive member, and the photosensitive member. A transfer body on which a toner image is electrostatically transferred from the body, and the relative permittivity of the photoconductor is εdr, the relative permittivity of the transfer body is εit, and the relative permittivity of the toner is ε. In this case, the image forming apparatus satisfies the relations of εdr <ε and εdr <εit.

  According to the present invention, transfer efficiency can be improved by suppressing transfer residue and retransfer residue.

1 is a schematic sectional view of an image forming apparatus. It is a schematic diagram which shows the layer structure of a photosensitive drum. 6 is a graph showing the dielectric constant of toners of Example 1 and Comparative Example 1. FIG. 6 is a graph showing the charge amount of toners of Example 1 and Comparative Example 1. FIG. 6 is a graph showing transfer efficiency of Example 1 and Comparative Example 1. FIG. FIG. 6 is a schematic diagram for explaining a force acting on toner. FIG. 6 is a schematic diagram for explaining a force acting on toner. FIG. 6 is a schematic diagram for explaining a force acting on toner. FIG. 6 is a schematic diagram for explaining a force acting on toner. FIG. 6 is a schematic diagram and a graph showing the simulation conditions and results of the force received by the toner. FIG. 6 is a graph showing the relationship between the dielectric constant of toner and the force received by toner. FIG. 6 is a schematic diagram for explaining a force acting on toner. FIG. 6 is a schematic diagram for explaining a force acting on toner. FIG. 3 is a schematic diagram illustrating a configuration of a touch-down developing device. FIG. 6 is a graph showing the relationship between toner charge amount and transfer efficiency in Example 1 and Comparative Example 1 when a touch-down developing device is used. FIG. 6 is a graph showing the charge amounts of toners of Examples 2-1 and 2-2. It is a graph showing the dielectric constant of the toner of Examples 2-1 and 2-2. It is a graph which shows the transfer efficiency of Examples 2-1 and 2-2. It is a schematic diagram of the primary transfer part in 3rd Embodiment. It is a schematic diagram for demonstrating the force which the point charge on the dielectric material of several layers receives. It is a graph which shows the relationship between the thickness of the surface layer of a dielectric material of multiple layers, and the force which a point charge receives. It is a schematic diagram of the primary transfer part in 4th Embodiment. FIG. 3 is a schematic diagram illustrating a dispersion state of high dielectric particles in toner.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

[First Embodiment]
1. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus according to the present embodiment is a tandem type (in-line type) laser beam printer that employs an intermediate transfer method and is capable of forming a full-color image using an electrophotographic method.

  The image forming apparatus 100 forms first, second, and second images that form yellow (Y), magenta (M), cyan (C), and black (K) images as a plurality of image forming units (image forming units), respectively. 3, 4th image formation part 1Y, 1M, 1C, and 1K are included. These four image forming units 1Y, 1M, 1C, and 1K are arranged in a line at regular intervals. In the present embodiment, the configurations and operations of the image forming units 1Y, 1M, 1C, and 1K are substantially the same except that the color of the toner used in the development process described later is different. Therefore, unless distinction is particularly required, the Y, M, C, and K at the end of the reference numeral indicating any color element will be omitted, and the element will be described generally.

  The image forming unit 1 includes a photosensitive drum 2 which is a rotatable drum type electrophotographic photosensitive member (photosensitive member) as an image carrier. The photosensitive drum 2 is rotationally driven at a predetermined process speed (circumferential speed) in the direction of arrow R1 in the figure by a drum driving motor (not shown) as a photosensitive member driving means. In this embodiment, the photosensitive drum 2 is a negatively charged organic photoreceptor (OPC), and is configured to have a photosensitive layer on a conductive substrate (in this embodiment, an aluminum drum) (in detail). Will be described later). In the image forming unit 1, the following devices are arranged around the photosensitive drum 2. First, a charging roller 3 which is a roller-type charging member as a charging unit is disposed. Next, an exposure device (laser scanner) 7 as an exposure unit is arranged. Next, a developing device 4 as a developing unit is arranged. Each of the developing devices 4Y, 4M, 4C, and 4K stores toner of each color of yellow, cyan, magenta, and black. Next, a primary transfer roller 5 that is a roller-type primary transfer member as a primary transfer means is disposed.

  The surface of the rotating photosensitive drum 2 is uniformly charged by the charging roller 3 to a predetermined potential having a predetermined polarity (negative polarity in this embodiment). The surface of the charged photosensitive drum 2 is scanned and exposed with laser light in accordance with image information by the exposure device 7, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 2. The electrostatic latent image formed on the photosensitive drum 2 is developed (visualized) with toner as a developer by the developing device 4, and a toner image is formed on the photosensitive drum 2.

In this embodiment, the charging potential (image portion potential) after being charged by the charging roller 3 of the photosensitive drum 2 is −500 V, and the potential (non-image portion potential) after being exposed by the exposure device 7 is −100 V. Thus, the charge amount and the exposure amount are adjusted. In this embodiment, the process speed is 250 mm / sec. In the present embodiment, the developing device 4 as a developing unit that supplies toner to the electrostatic image formed on the photoreceptor is a non-magnetic one-component system that uses a non-magnetic one-component developer (toner) as the developer. Development apparatus. The developing device 4 includes a developing roller as a developer carrying member that carries toner and conveys the toner to a portion (developing portion) facing the photosensitive drum 2. During development, a developing bias (developing bias) that is a DC voltage having the same polarity as the charging polarity of the photosensitive drum 2 (negative polarity in this embodiment) is applied to the developing roller. In the present embodiment, the developing bias is −300V. In this embodiment, the length (image forming width) of the image in the main scanning direction (substantially perpendicular to the rotation direction of the photosensitive drum 2) is 215 mm, and the solid image portion (maximum density level portion) is on the photosensitive drum 2. The toner amount is set to 0.45 mg / cm ² .

  An intermediate transfer belt 8 composed of a rotatable endless belt serving as an intermediate transfer member is disposed opposite to the photosensitive drums 2Y, 2M, 2C, and 2K of the image forming units 1Y, 1M, 1C, and 1K. ing. The intermediate transfer belt 8 is an example of a transfer body on which a toner image is electrostatically transferred from a photoreceptor. The intermediate transfer belt 8 is stretched around a driving roller 81, a secondary transfer counter roller 82, and a tension roller 83 as a plurality of support rollers (stretching rollers) and stretched with a predetermined tension. The intermediate transfer belt 8 rotates (circulates) in the direction of the arrow R2 in the drawing when the drive roller 81 is driven to rotate by a belt drive motor (not shown) as an intermediate transfer body drive unit. On the inner peripheral surface side of the intermediate transfer belt 8, the above-described primary transfer rollers 5Y, 5M, 5C, and 5K are arranged corresponding to the photosensitive drums 2Y, 2M, 2C, and 2K. The primary transfer roller 5 is urged toward the photosensitive drum 2 via the intermediate transfer belt 8 to form a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 2 and the intermediate transfer belt 8 are in contact with each other. Further, on the outer peripheral surface side of the intermediate transfer belt 8, a secondary transfer roller 15, which is a roller-type secondary transfer member as a secondary transfer unit, is disposed so as to face the secondary transfer counter roller 82. The secondary transfer roller 15 is urged toward the secondary transfer counter roller 82 via the intermediate transfer belt 8, and a secondary transfer portion (secondary transfer nip) where the intermediate transfer belt 8 and the secondary transfer roller 15 come into contact with each other. ) N2 is formed. Further, on the outer peripheral surface side of the intermediate transfer belt 8, a belt as an intermediate transfer member cleaning unit is provided at a position facing the secondary transfer counter roller 82 on the downstream side of the secondary transfer portion N 2 in the rotation direction of the intermediate transfer belt 8. A cleaning device 84 is arranged.

  The toner image formed on the photosensitive drum 2 as described above is electrostatically transferred (primary transfer) onto the intermediate transfer belt 8 at the primary transfer portion N1. At this time, the primary transfer roller 5 is supplied with a DC voltage having a polarity (negative polarity in this embodiment) opposite to the charging polarity (normal charging polarity) of the toner at the time of development by a primary transfer power supply (high voltage power supply circuit) 51. A certain primary transfer bias (primary transfer voltage) is applied. For example, when forming a full-color image, four color toner images formed on the photosensitive drums 2Y, 2M, 2C, and 2K are superimposed on the intermediate transfer belt 8 at the primary transfer portions N1Y, N1M, N1C, and N1K. Are sequentially transferred. In this embodiment, a cleanerless system is adopted in which the toner remaining on the surface of the photosensitive drum 2 after the primary transfer process (primary transfer residual toner) is collected by the developing device 4 instead of the blade that contacts the photosensitive drum 2. That is, the primary transfer residual toner on the photosensitive drum 2 is transferred from the photosensitive drum 2 to the developing roller due to a potential difference between the developing roller of the developing device 4 and the photosensitive drum 2, and is collected by the developing device 4.

  The toner image formed on the intermediate transfer belt 8 is electrostatically transferred (secondary transfer) onto a transfer material (recording material, recording medium) P such as paper in the secondary transfer portion N2. At this time, a secondary transfer bias (secondary transfer voltage), which is a DC voltage having a polarity opposite to the normal charging polarity of the toner, is applied to the secondary transfer roller 15 by a secondary transfer power supply (high voltage power supply circuit) 52. Is done. The transfer material P is fed from a cassette (not shown) as a transfer material container, and is aligned with the toner image on the intermediate transfer belt 8 by a registration roller (not shown) as a conveying means. It is conveyed to the secondary transfer portion N2. Further, deposits such as toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 8 after the secondary transfer process are removed from the surface of the intermediate transfer belt 8 by the belt cleaning device 84 and collected.

  The transfer material P onto which the toner image has been transferred is conveyed to a fixing device 17 as a fixing unit, and is nipped and conveyed by a fixing roller 17a and a pressure roller 17b, whereby the toner image is melted and fixed (fixed). The image forming apparatus 100 is discharged (output) outside the apparatus main body.

  In this embodiment, the charging roller 3 and the exposure device 7 of each image forming unit 1 constitute an image forming unit that forms an electrostatic image on the photosensitive member.

  Here, in the present embodiment, as the intermediate transfer belt 8, a belt having a thickness of 100 μm, in which carbon black is dispersed as a conductive powder (conductive filler) in polyimide (PI) resin to adjust electric resistance, is used. The resin used as the material of the intermediate transfer belt 8 may be polyphenylene sulfide (PPS), polyimide (PI), PVdF, nylon, PET, PBT, polycarbonate, PEEK, PEN, or the like. In the present embodiment, carbon black is used as an additive (resistance adjusting agent) to be mixed in order to adjust the electric resistance of the intermediate transfer belt 8, but the resistance adjusting agent is not particularly limited. Examples of the conductive filler include carbon black and various conductive metal oxides. Non-filler resistance adjusters include low molecular weight ionic conductive materials such as various metal salts and glycols, antistatic resins containing ether bonds and hydroxyl groups in the molecule, or organic polymer compounds exhibiting electronic conductivity. and so on. When the amount of carbon black added to the resin material of the intermediate transfer belt 8 is increased, the electrical resistance of the intermediate transfer belt 8 is lowered. However, if the amount of addition is excessively increased, the strength of the intermediate transfer belt 8 itself is insufficient and is easily broken. Become. In this embodiment, the electrical resistance of the intermediate transfer belt 8 is lowered so that the strength of the intermediate transfer belt 8 is within a range that can be used in the image forming apparatus 100. The Young's modulus of the intermediate transfer belt 8 of this embodiment is about 3000 MPa. Here, the Young's modulus E was measured according to the tensile modulus measurement method of JIS-K7127, and the thickness of the measurement sample was 100 μm.

In this embodiment, the driving roller 81 is provided with a high-friction rubber layer on the surface layer for driving the intermediate transfer belt 8, and this rubber layer has a conductivity of a volume resistivity of 10 ⁵ Ωcm or less. . In this embodiment, the secondary transfer counter roller 82 is provided with a rubber layer on the surface layer, and this rubber layer has a conductivity of a volume resistivity of 10 ⁵ Ωcm or less. In the present embodiment, the tension roller 13 is composed of a metal roller, and applies a tension of a total pressure of about 60 N to the intermediate transfer belt 8. The secondary transfer counter roller 82 and the tension roller 83 are driven to rotate as the intermediate transfer belt 8 rotates. The drive roller 81, the secondary transfer counter roller 82, and the tension roller 83 are electrically grounded (connected to the ground) via resistance members having the same electrical resistance value. In the present embodiment, as the resistance member, one of three types having a resistance value of 1 GΩ, 100 MΩ, and 10 MΩ is used. Since the resistance of each rubber layer of the driving roller 81 and the secondary transfer counter roller 82 is sufficiently smaller than the above 1 GΩ, 100 MΩ, and 10 MΩ, the electrical influence can be ignored. In this embodiment, an elastic roller having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm and a rubber hardness of 30 ° (Asker C hardness meter) is used as the secondary transfer roller 15. The secondary transfer roller 15 is pressed against the secondary transfer counter roller 82 via the intermediate transfer belt 8 with a total pressure of about 39.2N. The secondary transfer roller 15 is driven to rotate as the intermediate transfer belt 8 rotates. A voltage of −7.0 to 7.0 kV can be applied to the secondary transfer roller 15 from the secondary transfer power supply 52.

  In the present embodiment, toner charged to positive polarity adheres to a charged potential region (non-exposed portion) on the negatively chargeable photosensitive drum 2 to form a toner image. However, the present invention is not limited to this. For example, in the case of using negatively charged toner, the polarity of the primary transfer bias and the secondary transfer bias is set to positive polarity, and the exposed portion on the photosensitive drum 2 is an image portion. It should just become.

2. Next, the photosensitive drum 2 will be described. In the present embodiment, the photosensitive layer of the photosensitive drum 2 is a laminated type in which a function is separated into a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material. The photosensitive drum 2 may have a protective layer formed as a surface layer (surface layer) on the laminated photosensitive layer.

  FIG. 2 is a schematic cross-sectional view showing the layer structure of the photosensitive drum 2. The photosensitive drum 2 has a base 20a composed of an aluminum drum as a conductive support (conductive base). An undercoat layer 20b having a barrier function and an adhesive function is provided on the base body 20a. On this undercoat layer 20b, a medium-resistance positive charge injection prevention layer 20c that serves to prevent the positive charge injected from the substrate 20a from canceling the negative charge charged on the surface of the charge transport layer 20e. Is provided. A charge generation layer 20d containing a charge generation material is provided on the positive charge injection prevention layer 20c. The charge generation layer 1d can be formed by applying a charge generation layer coating solution obtained by dispersing a charge generation material together with a binder resin and a solvent and drying the coating solution. A charge transport layer 20e containing a charge transport material is provided on the charge generation layer 20d. This charge transport layer can be formed by applying a charge transport layer coating solution obtained by dissolving a charge transport material and a binder resin in a solvent, and drying it. Here, the entire layer formed on the base layer 20a is referred to as a photosensitive layer.

  In this embodiment, the charge transport layer 20e has a thickness of about 20 μm, and the other layers all have a thickness of 1 μm or less. Therefore, in this embodiment, the dielectric constant of the photosensitive layer of the photosensitive drum 2 is dominated by the dielectric constant of the charge transport layer. That is, in terms of the dielectric constant, the photosensitive drum 2 in the present embodiment can be considered as a photosensitive drum having a single charge transport layer. In this embodiment, the surface layer of the photosensitive drum 2 is this charge transport layer.

3. Toner In the image forming apparatus 100 having the configuration of the present embodiment, the transfer efficiency described below was evaluated for Example 1 and Comparative Example 1 using different toners.

Table 1 shows resin particles for toner A and toner B, which are toner particles (toner base material) used in Example 1 and Comparative Example 1, respectively. The soliostar used in Example 1 is a spherical resin particle composed mainly of a silica / acrylic composite compound manufactured by Nippon Shokubai. Further, SX-500 used in Comparative Example 1 is a spherical resin particle mainly composed of a styrene polymer manufactured by Soken Chemical. These spherical resin particles obtained by adding a colorant and wax described later in advance were used as toner particles. Further, TGC-110 manufactured by Cabot Specialty Chemicals, Inc., which is an example of an inorganic fine powder as an external additive, was externally added to the toner particles. This TGC-110 is a spherical fumed silica having a particle diameter (number average particle diameter) of 110 nm as an example of a silica fine powder. This TGC-110 has a size larger than that of a commonly used external additive for electrophotography, and is a direct combination of toner particles and the surface layer of the photosensitive drum 2, the intermediate transfer belt 8, and other toner particles. To prevent unwanted contact. As a result, the influence of non-electrostatic adhesion can be suppressed, and the transfer efficiency (transferability) can be evaluated by two factors, ie, the toner charge amount and the toner dielectric constant. As a prescription of the external additive, for both toner A and toner B, 2 g of external additive was added to 80 g of toner particles (2.5 parts by mass of external additive with respect to 100 parts by mass of toner particles). In both toner A and toner B, the electrical resistance of the toner particles is 10 ¹¹ [Ω · cm] in terms of resistivity. In all of the following examples and comparative examples, the electrical resistance of the toner particles is 10 ¹¹ [Ω · cm] in resistivity, and the toner particles are higher than the electrical resistance of the photosensitive drum 2 and the intermediate transfer belt 8. Shows insulation. Both the toner A and the toner B have a particle size (number average particle size) of 5 μm.

4). Dielectric Constant of Toner, Intermediate Transfer Belt, and Photosensitive Drum The relative dielectric constant of toner (herein, the relative dielectric constant is also simply referred to as “dielectric constant”) was measured as follows. The toner particles are put in a toner folder SH1-8 (manufactured by Toyo Technica Co., Ltd.), pressed into a cylindrical shape (height 1.5 mm × bottom diameter 26 mm) from above and below. Then, a voltage was applied between the metal electrodes having a radius of 10 mm above and below the folder to measure a current value, and a dielectric constant was calculated. Application of voltage and measurement of data were performed with Solatron 1255B and Solatron 1296 manufactured by Toyo Technica.

  The dielectric constant of the intermediate transfer belt 8 was measured as follows. After the intermediate transfer belt 2 was cut out on a sheet of 2 cm square, platinum electrodes were vapor-deposited on the upper and lower surfaces, and the ends of the platinum electrodes on the upper and lower surfaces were shielded with an insulator. Measurements were taken with a Solatron 1296. The dielectric constant of the surface layer of the photosensitive drum 2 was also measured by the same method.

The measurement results of the dielectric constant of toner A and toner B are shown in FIG. The value of the dielectric constant is determined as an average value of values between frequencies 10 ⁻² (Hz) and 10 ⁺⁶ (Hz). Table 2 shows the measurement results of the dielectric constant of toner A, toner B, the surface layer of the photosensitive drum 2, and the intermediate transfer belt (ITB) 8. Here, the dielectric constants of the toner, the surface layer of the photosensitive drum 2, and the intermediate transfer belt 8 are ε, εdr, and εit, respectively.

  As shown in Table 2, both Example 1 and Comparative Example 1 satisfy εdr <εit. On the other hand, the toner A of Example 1 satisfies εdr <ε, and the toner B of Comparative Example 1 satisfies εdr> ε. Both toner A and toner B satisfy ε <εit.

FIG. 5 shows the results of evaluating transfer efficiency in Example 1 and Comparative Example 1 using the applied primary transfer bias as a parameter. The transfer efficiency was evaluated as follows. The solid black image was collected primary transfer residual toner on the photosensitive drum 2 after printing by Nichiban Co. Sellotape T18, adhered the tape onto a PET sheet, the number of toner per 100 [mu] m ² under an optical microscope It was evaluated by counting.

In the present embodiment, the amount of toner on the photosensitive drum 2 immediately before the primary transfer portion N1 is 0.45 mg / cm ² in the case of toner A and toner B. However, in the following examples and comparative examples, when the specific gravity of the toner is extremely light or heavy, the toner load is set so that the value of “toner load amount / toner specific gravity” is substantially the same as that of toner A and toner B. The amount was adjusted. As a result, the number of toners per unit area becomes substantially equal, so that the transfer efficiency can be compared under substantially the same conditions.

  FIG. 4 shows the charge amount of the toner on the photosensitive drum 2 between the developing unit and the primary transfer unit N1. The amount of charge of the toner was measured with an Espart Analyzer EST-II manufactured by Hosokawa Micron. The value of the charge amount was evaluated by a value Q / D obtained by dividing the charge amount Q per toner by the diameter D of the toner.

From FIG. 4, it can be seen that there is almost no difference in the amount of toner charge between toner A and toner B, and in particular, the proportion of the toner whose polarity of charge, which is the main cause of the increase in the primary transfer residual toner, is almost equal. . On the other hand, it can be seen from FIG. 5 that Example 1 using toner A can significantly reduce the primary transfer residual toner compared to Comparative Example 1 using toner B. Although the evaluation result regarding the transfer residual toner is shown here, the retransfer residual toner also increases or decreases due to the same factors as the transfer residual toner as described above. Therefore, it can be seen that Example 1 using toner A can remarkably reduce the retransfer residual toner as compared with Comparative Example 1 using toner B. That is, it can be seen that Example 1 using toner A satisfying εdr <ε can significantly improve transfer efficiency compared to Comparative Example 1 using toner B satisfying εdr> ε. As described above, since there is almost no difference in toner charge amount between toner A and toner B, it can be seen that this difference in transfer efficiency is due to the dielectric constant of the toner particles. Further, in the setting of the toner loading amount in this embodiment (here, 0.45 mg / cm ² ), it is generally considered that the toner is laminated in two or more layers. Therefore, it can be seen that transfer efficiency can be improved in Example 1 as compared with Comparative Example 1 in the transfer of the multilayer toner.

Thus, the relative dielectric constant εit of the intermediate transfer belt 8, the relative dielectric constant εdr of the surface layer of the photosensitive drum 2, and the relative dielectric constant ε of the toner particles are
εdr <ε and εdr <εit
By satisfying this relationship, it is possible to improve transfer efficiency.

  Here, the transfer efficiency is evaluated by taking black toner as an example. However, if the above relationship is satisfied, the transfer efficiency can be similarly improved for other color toners. The same applies when toners of different colors are laminated in two or more layers.

5. Inorganic Fine Powder In this embodiment, as described above, TGC-110, which is an inorganic fine powder (inorganic fine particle), is externally added to toner particles (toner base material) for the purpose of improving fluidity. The inorganic fine powder externally added to the toner particles is not limited to this, but preferably contains at least silica fine powder. The number average primary particle size of the inorganic fine powder is preferably 4 nm or more and 150 nm or less. When the number average primary particle size of the inorganic fine powder is in the above range, the fluidity of the toner is improved and the storage stability of the toner is also improved. The number average primary particle size of the inorganic fine powder can be determined by observing with a scanning electron microscope, measuring the particle size of 100 inorganic fine powders in the field of view, and calculating the average particle size. Further, as the inorganic fine powder, silica fine powder and fine powder of titanium oxide, alumina or their double oxide can be used in combination. As the inorganic fine powder used in combination, titanium oxide is preferable.

Silica fine powder includes both dry silica produced by vapor phase oxidation of silicon halides, called dry silica or fumed silica, and wet silica produced from water glass. As the silica, dry silica having less silanol groups on the surface and inside of silica and less production residue of Na ₂ O and SO ₃ ²⁻ is preferable. In addition, dry silica can be used in the production process to obtain a composite fine powder of silica and other metal oxides by using other metal halogen compounds such as aluminum chloride and titanium chloride together with silicon halogen compounds. . Silica also includes them.

  The inorganic fine powder is added to improve the fluidity of the toner particles and to make the toner particles triboelectrically charged. By hydrophobizing inorganic fine powder, functions such as adjusting the triboelectric charge amount of toner particles, improving environmental stability, and improving characteristics under high-humidity environments can be added. It is preferable to use inorganic fine powder. When the inorganic fine powder externally added to the toner particles absorbs moisture, the triboelectric charge amount of the toner particles is lowered, and the developability and transferability are easily lowered. Examples of the treatment agent for the hydrophobic treatment of the inorganic fine powder include the following. 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. Among these, inorganic fine powder treated with silicone oil is preferable. More preferably, the inorganic fine powder is treated with a silicone oil simultaneously with the hydrophobic treatment with the coupling agent or after the hydrophobic treatment with the coupling agent. Hydrophobized inorganic fine powder maintains a high triboelectric charge amount of toner particles even in a high humidity environment, and develops selectively (a part of the toner is selectively developed depending on the charge of the toner). Can be reduced.

6). Charge Control Agent In order to exhibit sufficient charging characteristics, the surface of toner particles can be coated with a charge control agent.

  Negatively chargeable charge control agents include polymer compounds having sulfonic acid groups, sulfonic acid groups or sulfonic acid ester groups, salicylic acid derivatives and their metal complexes, monoazo metal compounds, acetylacetone metal compounds, aromatic oxycarboxylic acids, aromatic Group mono- and polycarboxylic acids, their metal salts, anhydrides, esters, phenol derivatives such as bisphenol, urea derivatives, boron compounds, calixarene, and the like.

  Examples of positively chargeable charge control agents include nigrosine and fatty acid metal salts modified nigrosine, guanidine compounds, imidazole compounds, tributylbenzylammonium-1-hydroxy-4-naphthosulfonate, tetrabutylammonium tetrafluoroborate. Quaternary ammonium salts such as, and onium salts such as phosphonium salts thereof and their lake pigments, triphenylmethane dyes and these lake pigments (as rake agents include phosphotungstic acid, phosphomolybdic acid, Phosphotungstic molybdic acid, tannic acid, lauric acid, gallic acid, ferricyanide, ferrocyanide, etc.), higher fatty acid metal salts, dibutyltin oxide, dioctyltin oxide, dicyclohexyltin oxide, etc. Organotin oxide, dibutyl tin borate, dioctyl tin borate, and the like diorgano tin borate such as dicyclohexyl tin borate.

7). Colorant and wax Toner particles may be added with a colorant and a wax as necessary. As the colorant, known colorants such as various conventionally known dyes and pigments can be used.

  Examples of the magenta colorant include C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 41, 48, 49, 50, 51, 52, 53, 54, 55, 57, 58, 60, 63, 64, 68, 81, 83, 87, 88, 89, 90, 112, 114, 122, 123, 163, 202, 206, 207, 209; I. Pigment Violet 19; C.I. I. VatRed 1, 2, 10, 13, 15, 23, 29, 35 etc. are mentioned.

  Examples of cyan colorants include C.I. I. Pigment Blue 2, 3, 15: 1, 15: 3, 16, 17, 25, 26; I. Vat Blue 6; C.I. I. Acid Blue 45; or a copper phthalocyanine pigment in which 1 to 5 phthalimidomethyl groups are substituted on the phthalocyanine skeleton.

  Examples of the colorant for yellow include C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 23, 65, 73, 74, 83, 93, 155, 180; I. Solvent Yellow 9, 17, 24, 31, 35, 58, 93, 100, 102, 103, 105, 112, 162, 163; C.I. I. Vat Yellow 1, 3, 20, etc. are mentioned.

  As the black colorant, for example, carbon black, aniline black, acetylene black, and those that are toned in black using the yellow / magenta / cyan colorant shown above can be used.

  The amount of these colorants to be added varies depending on the kind of the colorant, but is preferably 0.1 to 60 parts by mass, and preferably 0.5 to 50 parts by mass with respect to 100 parts by mass of the binder resin. More preferably.

  Specific examples of the wax component include petroleum waxes and derivatives thereof such as paraffin wax, microcrystalline wax and petrolatum, montan wax and derivatives thereof, hydrocarbon waxes and derivatives thereof by Fischer-Tropsch method, and polyethylene. Examples thereof include polyolefin waxes and derivatives thereof, natural waxes such as carnauba wax and candelilla wax, and derivatives thereof. The derivatives include oxides, block copolymers with vinyl monomers, and graft modified products. Further, alcohols such as higher aliphatic alcohols, fatty acids such as stearic acid and palmitic acid, or acid amides and esters of these compounds, hydrogenated castor oil and derivatives thereof, plant waxes, animal waxes and the like can be mentioned. These can be used alone or in combination.

  The added amount of the wax component is preferably 2.5 to 15.0 parts by mass, more preferably 3.0 to 10.0 parts by mass with respect to 100 parts by mass of the binder resin. If the added amount of the wax component is less than 2.5 parts by mass, oilless fixing becomes difficult. On the other hand, if the added amount of the wax component exceeds 15.0 parts by mass, the amount of the wax component in the toner is too large, so that a large amount of excess wax component is present on the surface of the toner particles, and desired charging characteristics are obtained. May be inhibited.

8). Toner Particle Size and Manufacturing Method The number average particle size (D1) of the toner particles is preferably 3.0 μm or more and 15.0 μm or less from the viewpoint of obtaining stable charging and high-quality images. More preferably, it is not less than 0.0 μm and not more than 12.0 μm. The number average particle diameter of the toner particles can be measured and calculated in the same manner as in the case of the inorganic fine powder. The toner particles can be manufactured by various manufacturing methods. For example, there is a kneading and pulverizing method in which a binder resin, a pigment, and a release agent are mixed and toner particles are obtained through a kneading, pulverizing, and classification process. There is also a suspension polymerization method in which a polymerizable monomer, a pigment, and a release agent are mixed, dispersed or dissolved, granulated in an aqueous medium, and toner particles are obtained by a polymerization reaction. Further, there is a dissolution suspension method in which a binder resin, a pigment, and a release agent are dissolved or dispersed in an organic solvent, granulated in an aqueous medium, and then removed to remove the solvent to obtain toner particles. Further, there is an emulsion aggregation method in which fine particles of a binder resin, a pigment, and a release agent are finely dispersed in an aqueous medium, and agglomerated them into a toner particle size to obtain toner particles. Any of these methods may be used.

9. Mechanism Next, a mechanism for improving the transfer efficiency as described above will be described.

9-1. Outline In this embodiment, the amount of toner developed on the photosensitive drum 2 is 0.45 g / cm ² for a solid black image, and it is considered that two or more layers of toner are usually laminated. Here, the force received by the toner stacked in two layers in the primary transfer portion N1 will be described. Here, the primary transfer of the toner charged to the positive polarity will be described, but the same mechanism is applied to the toner charged to the negative polarity. FIG. 6 (FIGS. 6A to 6H) is a schematic diagram for explaining the force applied to the two toner layers of the toner 10a and the toner 10b in the primary transfer portion N1.

Generally, the force received by the toner present in the electric field is divided into the following five.
(1) The force that polarizes the toner and acts between the polarized charges (FIG. 6B)
(2) The force that the true charge of the toner itself receives from the external field and the force that acts between the true charges (FIG. 6C)
(3) Non-electrostatic adhesion force such as liquid cross-linking force and van der Waals force (Fig. 6 (d))
(4) Image force acting on the polarization charge of the toner (FIGS. 6E and 6G)
(5) Image force acting on the true charge of the toner (FIG. 6 (f), FIG. 6 (h))

9-2. FIG. 6B shows the surface force of the photosensitive drum 2 in the primary transfer portion N1, the intermediate transfer belt 8 and the polarization state of the toner therebetween, and the polarization charge in the external field (externally applied voltage, external force). Indicates the force received from the applied electric field. When a voltage is applied to the primary transfer power supply 51, the toner 10a (intermediate transfer belt 8 side), the toner 10b (photosensitive drum 2 side), the intermediate transfer belt 8, and the surface layer of the photosensitive drum 2 are sized according to their dielectric constants. Polarize with. If the applied voltage of the primary transfer power source 51 is negative, negative polarization charges 9a, 9c, 9e and positive polarization charges 9b, 9d, 9f are induced as shown in the figure. Coulomb attractive force acts between polarized charges with different polarities. Here, with respect to the toner 10b, a Coulomb attractive force Fb_a between the polarization charges 9c and 9d acts on the toner 10a, and a Coulomb attractive force Fb_dr between the polarization charges 9e and 9f acts on the surface layer of the photosensitive drum 2. Both Fb_a and Fb_dr depend on the dielectric constant ε of the toner and the dielectric constant εdr of the surface layer of the photosensitive drum 2.

  FIG. 6C shows the force that the true charge receives from the externally applied voltage and the force that acts between the true charges. A coulomb force (≈qb · E) generated by the externally applied voltage E acting on the true charge qb of the toner 10b and a force Fqb_qa generated by the interaction with the true charge qa of the toner 10a simultaneously act on the toner 10b. .

  FIG. 6D shows non-electrostatic adhesion. A non-electrostatic adhesion force Ab_a between the toner 10a and a non-electrostatic adhesion force Ab_dr between the photosensitive drum 2 and the toner 10b acts.

  FIG. 6E shows the interaction with the mirror image formed by the polarization charge on the surrounding dielectric. The toner 10b has a mirror image force Mb_a between the toner 10a and the toner drum 10b, and a mirror image force Mb_dr between the toner 10b and the photosensitive drum 2.

  FIG. 6F shows the interaction with the mirror image created by the true charge. The toner 10b has a mirror image force Mqb_qa between the toner 10a and a mirror image force Mqb_dr with the photosensitive drum 2.

After all, the force Fb acting on the toner 10b is a function of the dielectric constant ε of the toner, the dielectric constant εdr of the surface layer of the photosensitive drum 2, the externally applied voltage E, and the charge amounts qa and qb of the toner. It is represented by
Fb = Fb (ε, εdr, E, qa, qb)
= Fb_a + Fb_dr + Fqb_qa + E.qb + Mb_dr + Mb_a + Mqb_qa + Mqb_dr + Ab_dr + Ab_a (1)

  If this Fb is directed toward the intermediate transfer belt 8, the toner 10b receives a force in the transfer direction. Each section will be further described.

In general, the magnitude of polarization charge | P | of a dielectric existing in the externally applied voltage E is expressed by the following equation, where the dielectric constant is ε.
| P | = (ε−1) · E · ε ₀ / ε

Therefore, the polarization charge excited in the photosensitive drum 2 is expressed by the following formula.
(Εdr-1) · E · ε ₀ / εdr

Further, the polarization charge excited on the toner surface is expressed by the following formula.
(Ε-1) · E · ε ₀ / ε

Therefore, the Fb_a shown in FIG. 6B, which is the force in the direction of the intermediate transfer belt 8, is proportional to the product of the polarized charges of the toner, and is expressed by the following equation. C1 in the following formula is a positive constant.
Fb_a = c 1 · E ² · (ε−1) ² / ε ²

Further, Fb_dr shown in FIG. 6B, which is a force in the direction of the photosensitive drum 2, is proportional to the product of the polarization charge of the toner and the polarization charge of the photosensitive drum 2, and is expressed by the following equation. C2 in the following formula is a negative constant.
Fb_dr = c2 · E ² · (εdr-1) · (ε-1) / εdr / ε

  Here, assuming that the distances between the toners, between the toner and the photosensitive drum 2, and between the toner and the intermediate transfer belt 8 are all equal to the particle diameter of the external additive, c1 = −c2 = C. I can.

Further, the above Fqb_qa shown in FIG. 6C is proportional to the product qa · qb of the charge amount of the toner, and therefore is expressed by the following equation with c3 as a constant.
Fqb_qa = c3 · qa · qb

In addition, as shown in FIG. 6A, generally, the image force F generated between the point charge having the charge amount q and the dielectric separated by the distance d is expressed by the following equation.
F = q ² · (ε−1) / (ε + 1) / 16 / π / ε ₀ / d ²

  Note that 0 <(ε−1) / (ε + 1) <1 is a monotonically increasing function of ε.

Therefore, assuming that d is equal to the distance between the toner and the photosensitive drum 2 and the distance between the toner and the intermediate transfer belt 8, the Mb_dr and Mb_a shown in FIG. .
Mb_dr =-(ε-1) ² · ε ₀ ² · E ² / ε ² · (εdr-1) / (εdr + 1) / 16 / π / ε ₀ / d ²
Mb_a = (ε-1) ² · ε ₀ ² · E ² / ε ² · (ε-1) / (ε + 1) / 16 / π / ε ₀ / d ²

Assuming that r is the radius of the toner and the true charge of the toner is at the center of the toner, the above Mqb_dr and Mqb_qa shown in FIG.
Mqb_dr = −qb ² · (εdr−1) / (εdr + 1) / 16 / π / ε ₀ / r ²
Mqb_qa = qb ² · (ε−1) / (ε + 1) / 16 / π / ε ₀ / r ²

As an example, qb = several fC, d = 100 nm, r = 3 μm, E = 5 · 10 ⁶ [V / m]. The sum of the image forces shown in FIG. 6E and FIG. 6F is expressed by the following formula as Mb (εdr, | qb |, | E |).
Mb (εdr, | qb |, | E |)
= Mb_dr + Mb_a + Mqb_qa + Mqb_dr

  From the above formulas of mirror image forces, the sum of the mirror image forces is a monotonically increasing function of ε and | E | when ε> εdr, and a monotonically increasing function of ε when ε <εdr, and a monotone decreasing function of | E |. is there. Each increases and decreases with the square of E. Further, Mb (εdr, | qb |, | E |) = 0 is satisfied.

After all, the above-described equation (1) is expressed by the following equation as a function of E, ε, and εdr.
Fb = Fb_a + Fb_dr + Fqb_qa + E · qb + Mb (ε, | qb |, | E |) + Ab_a + Ab_dr
= C · E ² · (ε-1) ² ε ₀ ² / ε ² -C · E ² · (εdr-1) · (ε-1) ε ₀ ² / ε / εdr + c3 · qa · qb + Mb (ε, | qb |, | E |) + E · qb + Ab_a + Ab_dr (2)

As can be seen from the above equation (2), if ε> εdr,
Fb_a + Fb_dr> 0
This value is proportional to the square of the externally applied voltage E. Therefore, as E is increased, the sum of the first term, the second term, and the fourth term on the right side of the equation (2) is increased by the square of E. And
Fb> 0
Thus, the toner 10b receives a large force in the direction of the intermediate transfer belt 8 (transfer direction) regardless of the polarity of the charge qb of the toner 10b itself.

A three-dimensional electric field simulation was performed on the system of Example 1. FIG. 7A schematically shows the outline of the system in which this simulation was performed, the size and shape of each part, and the like. In this simulation, the dielectric constant of the toner epsilon = 2.8, the photosensitive drum 2 surface layer of the dielectric constant Ipushirondr = 2, the dielectric constant of vacuum was set to epsilon _0. Further, the intermediate transfer belt 8 is assumed to be a complete conductor, and its potential is set to Vtr so that a variable potential can be applied. Further, the potential of the intermediate transfer belt 8 is set to Vtr, the lower surface (opposite side of the intermediate transfer belt 8) of the photosensitive drum 2 is set to 0 [V], and the primary transfer nip is set on the upper surface (intermediate transfer belt 8 side). The charge density σ was set such that the upper surface potential in N1 was Vl = −100 [V]. Specifically, σ was obtained by the following equation, where d1 was the distance between the intermediate transfer belt 8 and the photosensitive drum 2, and d2 was the film thickness (surface layer thickness) of the photosensitive drum 2. Thereby, the surface potential of the photosensitive drum 2 can be set to Vl = −100 [V].
σ = − (Vtr−Vl) ÷ d1 × ε ₀ + Vl ÷ d2 × εdr

  FIG. 7B is a graph in which the force Fb received by the toner 10b is plotted as a function of the charge amount (tribo) qb of the toner 10b. The parameter is the potential Vtr of the surface of the intermediate transfer belt 8. When the force Fb received by the toner 10b is a positive value, it is the direction of the intermediate transfer belt 8, and the larger the value, the more advantageous the transfer. Here, it is assumed that the charge amount of the toner 10a is +5 fC / piece. As can be seen from FIG. 7B, the gradient of the force Fb with respect to the charge amount increases as a stronger electric field is applied, and the toner having a positive charge amount receives a stronger force in the transfer direction. On the other hand, it can be seen that the toner having the negative charge amount reversed from the normal charging polarity receives a force in the opposite direction to the transfer when the applied voltage is as low as -100V. However, it can be seen that as the applied voltage is increased to -300V and -500V, the toner having a negative charge which is not so large receives a force in the transfer direction. That is, it is indicated that even a toner having a reversed charging polarity can be transferred.

  Next, the relationship between the force Fb received by the toner 10b and the dielectric constant ε of the toner will be described. In the above formula (2), when ε is increased (ε >> εdr), the first term on the right side becomes dominant. Therefore, as in the case where the externally applied voltage E is increased, the toner 10b receives a large force in the direction of the intermediate transfer belt 8 (transfer direction) regardless of the polarity of the charge qb of the toner 10b itself. .

  FIG. 8 is a graph in which the force Fb received by the toner 10b with respect to the charge amount qb of the toner when the externally applied voltage E = −400 V is plotted using the dielectric constant ε of the toner as a parameter by the same three-dimensional electric field simulation as described above. . FIG. 8 shows that as the dielectric constant ε of the toner is increased, the toner receives a stronger force in the transfer direction regardless of the charge amount of the toner.

  In summary, it can be seen that the toner 10b receives a force in the transfer direction as the externally applied voltage E is increased and the dielectric constant ε of the toner is increased (εdr <ε). On the other hand, when εdr> ε, the toner 10b receives a force in the direction of the photosensitive drum 2 as the externally applied voltage E is increased. Then, separation between the toner 10a and the toner 10b occurs, and the toner 10b remains on the photosensitive drum 2 as the primary transfer residual toner.

9-3.2 Force Received by Toner of Layer Next, a discussion similar to the force received by the toner 10b (photosensitive drum 2 side) will be made. This applies to the entire two toner layers.

As shown in FIGS. 6A to 6H, the force received by the toner 10a is expressed by the following formula (3) in the same manner as in the case of the force received by the toner 10b.
Fa = Fa_b + Fa_it + Fqa_qb + Ma_it + Ma_b + Mqa_qb + Mqa_it + E · qa + Aa_b + Aa_it (3)

  Here, Aa_b shown in FIG. 6D is a non-electrostatic adhesion force between the toner 10a and the toner 10b, and Aa_it shown in FIG. 6D is a non-static state between the toner 10a and the intermediate transfer belt 8. Electric adhesion.

Further, the coulomb attractive force Fa_it between the polarization charge 9b of the toner 10a and the polarization charge 9a of the intermediate transfer belt 8 shown in FIG. Is represented by the following formula.
Fa_it = C · (εit-1) · (ε-1) · E ² / εit / ε

  Further, the Coulomb attractive force Fa_b between the polarization charge 9c of the toner 10a and the polarization charge 9d of the toner 10b shown in FIG. 6B satisfies Fa_b + Fb_a = 0 by the law of action and reaction. Therefore, when the toner 10a and the toner 10b are considered together, Fa_b and Fb_a are canceled out.

  Similarly, the force Fqa_qb that the true charge of the toner 10a shown in FIG. 6C receives from the true charge of the toner 10b satisfies Fqa_qb + Fqb_qa = 0. Further, the non-electrostatic adhesive force Aa_b between the toner 10a and the toner 10b shown in FIG. 6D satisfies Aa_b + Ab_a = 0. In this way, the drag force exerted by the toners is canceled out.

Further, Ma_it, Ma_b, Mqa_qb, and Mqa_it shown in FIGS. 6G and 6H are mirror image forces acting on the polarization charge and the true charge of the toner 10a. In the same manner as in the case of the force received by the toner 10b, these are respectively expressed by the following equations.
Ma_it = (ε-1) ² · ε ₀ ² · E ² / ε ² · (εit-1) / (εit + 1) / 16 / π / ε ₀ / d ²
Ma_b =-(ε-1) ² · ε ₀ ² · E ² / ε ² · (ε-1) / (ε + 1) / 16 / π / ε ₀ / d ²
Mqa_it = qa ² · (εdr−1) / (εdr + 1) / 16 / π / ε ₀ / r ²
Mqa_qb = −qa ² · (ε−1) / (ε + 1) / 16 / π / ε ₀ / r ²

  According to the law of action and reaction, the above Ma_b and Mqa_qb act on the toner 10b side with forces of equal magnitude and opposite directions. For the same reason, the above-described Mb_a and Mqb_qa also apply forces having the same magnitude and opposite directions to the toner 10a side. Further, it is considered that Ma_b = Mb_a.

As a result, the force M (ε, E) obtained by adding the mirror image force Ma acting on the toner 10a and the mirror image force Mb acting on the toner 10b is expressed by the following equation (4).
Ma = Ma_it + Ma_b + Mqa_qb + Mqa_it
Mb = Mb_dr + Mb_a + Mqb_qa + Mqb_dr
M (ε, E) = Ma + Mb
= Ma_it + Mqa_it + Mb_dr + Mqb_dr
= (Ε-1) ² · ε ₀ ² · E ² / ε ² · (εit-1) / (εit + 1) / 16 / π / ε ₀ / d ² + qa ² · (εdr-1) / (εdr + 1) / 16 / π / ε ₀ / r ^2- (ε-1) ² · ε ₀ ² · E ² / ε ² · (εdr-1) / (εdr + 1) / 16 / π / ε ₀ / d ² -qb ² · (Εdr−1) / (εdr + 1) / 16 / π / ε ₀ / r ² (4)

  As is clear from the above equation (4), the image force M (ε, E) is a monotonically increasing function of ε and E when εit> εdr, and monotonically decreasing of ε and E when εit <εdr. It is a function.

From the above, the force F (= Fa + Fb) acting on the entire two toner layers of the toner 10a and the toner 10b is expressed by the following equation (5) with reference to the above equation (2).
F = Fa + Fb
= Fa_it + Fb_dr + E. (Qa + qb) + M (ε, E) + Aa_it + Ab_dr
≈ C · (εit-1) · (ε-1) / ε / εit · E ² −C · (εdr-1) · (ε-1) / ε / εdr · E ² + E · (qa + qb) + M (ε , E) + Aa_it + Ab_dr
(5)

  From the above equation (5), when εit> εdr, the sum of the first term, the second term, and the fourth term on the right side increases as the dielectric constant ε of the toner increases and the external applied voltage E increases. To do. Therefore, it can be seen that the entire toner layer receives a large force in the direction of the intermediate transfer belt 8 (transfer direction).

  Therefore, by satisfying εit> εdr and ε> εdr, the transfer efficiency of the entire toner layer can be improved as the externally applied voltage is increased regardless of the charge amount of the toner 10a and the toner 10b. Toner and retransfer residual toner can be reduced. Even when the toner is laminated in three or more layers, the transfer residual toner and the retransfer residual toner can be reduced by the same mechanism by satisfying εit> εdr and ε> εdr.

9-4. Finally, the case where the toner on the photosensitive drum 2 is a single layer will be described. FIG. 9 (FIGS. 9A to 9D) is a schematic diagram for explaining the force applied to the single-layer toner 10a at the primary transfer portion N1.

  As shown in FIG. 9A, in the case of a single-layer toner, the toner 10a is polarized by the voltage applied to the primary transfer portion N1, and as shown in the figure, positive polarity charges 9b and 9d and negative polarity Polarization charges 9a and 9c are generated. These polarization charges are attracted by the forces Fa_dr and Fa_it.

FIG. 9D shows non-electrostatic adhesion forces Aa_it and Aa_dr between the toner and the intermediate transfer belt 8 and between the toner and the photosensitive drum 2. FIG. 9B shows the image forces Ma_it and Ma_dr created by the polarization charge. FIG. 9C shows the image forces Mqa_it and Mqa_dr created by the true charge and the force qa · E that the true charge receives from the electric field. The Ma_it, Ma_dr, Mqa_it, and Mqa_dr are each expressed by the following formula.
Ma_it = (ε-1) ² · ε ₀ ² · E ² / ε ² · (εit-1) / (εit + 1) / 16 / π / ε ₀ / d ²
Ma_dr =-(ε-1) ² · ε ₀ ² · E ² / ε ² · (εdr-1) / (εdr + 1) / 16 / π / ε ₀ / d ²
Mqa_it = qa ² · (εit−1) / (εit + 1) / 16 / π / ε ₀ / r ²
Mqa_dr = −qa ² · (εdr−1) / (εdr + 1) / 16 / π / ε ₀ / r ²

From the above formulas of mirror image forces, when εit> εdr, the mirror force M acting on the toner 10a is:
Ma = Ma_it + Ma_b + Mqa_qb + Mqa_it> 0
It becomes. Therefore, the mirror image force Ma acting on the toner 10a is a monotonically increasing function for both ε and E. In consideration of the true charge qa of the toner, the force Fa applied to the toner 10a is expressed by the following formula (6), as in the case where the toner layer has two layers.
Fa = Fa_dr + Fa_it + E · qa + Ma + Aa_it + Aa_dr
= C · (εit-1) · (ε-1) · E 2 -C · (εdr-1) · (ε-1) · E 2 + E · qa + Ma + Aa_it + Aa_dr ····· (6)

  From the above equation (6), as in the case of two toner layers, when εit> εdr, the magnitude of the force in the direction of the intermediate transfer belt 8 (transfer direction) acting on the toner 10a is the magnitude of the externally applied voltage E. Increases in proportion to the square of. Therefore, the toner 10a receives a force in the transfer direction regardless of the charge of the toner 10a.

10. Next, a case where a touch-down developing device 4 is used in place of the non-magnetic one-component developing device 4 will be described. FIG. 10 is a schematic diagram of the touch-down developing device (herein simply referred to as “developing device”) 4 (the photosensitive drum 2 and the intermediate transfer belt 8 are also shown).

  The developing device 4 has a developing container 41 as a developer container (developing device main body), and in the developing container 41 is a mixture of a toner (nonmagnetic toner) 10 and a carrier (magnetic carrier) 18 as a developer. A two-component developer is accommodated.

  The developing device 4 has a stirring roller 42 as a stirring member. The agitation roller 42 agitates the two-component developer accommodated in the developing container 41. In the stirred two-component developer, static electricity is generated by friction, the carrier 18 is negatively charged, and the toner 10 is positively charged. Further, the toner 10 adheres to the carrier 18 by this electrostatic force.

  The developing device 4 includes a first developing roller 43 as a first developer carrier. The first developing roller 43 includes a first developing sleeve 43a formed of a cylindrical nonmagnetic member, and a first magnetic field generating unit arranged fixedly in a hollow portion of the first developing sleeve 43a. Magnetic pole member 43b. The first developing sleeve 43a is rotationally driven in the direction of arrow R3 in the drawing. The first magnetic pole member 43b has a plurality of magnetic poles in the circumferential direction of the first developing sleeve 43a. The two-component developer in the developing container 41 is carried on the surface of the first developing sleeve 43a by the force of the magnetic field generated by the first magnetic pole member 43b.

  The developing device 4 has a regulating blade 45 as a developer regulating member. The regulating blade 45 is configured by a plate-like member, and is disposed so as to face the first developing roller 43 so that the tip end side is close to the surface of the first developing roller 43. A predetermined gap (gap) is formed between the tip of the regulating blade 45 and the surface of the first developing roller 43. The regulating blade 45 regulates the layer thickness of the two-component developer carried on the surface of the first developing roller 43 as the first developing roller 43 rotates.

  Further, the developing device 4 includes a second developing roller 44 as a second developer carrier. The second developing roller 44 includes a second developing sleeve 44a formed of a cylindrical non-magnetic member, and a second magnetic field generating unit that is fixedly disposed in the hollow portion of the second developing sleeve 44a. Magnetic pole member 44b. The second developing sleeve 44a is arranged to face the first developing sleeve 43a. The second developing sleeve 44a is rotationally driven in the direction of arrow R4 in the drawing. That is, the first developing sleeve 43a and the second developing sleeve 44a rotate in directions in which their respective surfaces move in opposite directions at the opposing portions. The second magnetic pole member 44b is disposed to face the first magnetic pole member 43b at a position corresponding to the closest portion between the first developing sleeve 43a and the second developing sleeve 44a. The polarity of the magnetic pole of the second magnetic pole member 44b is different from the polarity of the magnetic pole of the first magnetic pole member 43b facing the second magnetic pole member 44b. Therefore, a magnetic field is formed between the first magnetic pole member 43b and the second magnetic pole member 44b at the closest portion. The developer layer on the surface of the first developing sleeve 43a rises under the influence of this magnetic field, forms a magnetic brush, and comes into contact with the surface of the second developing sleeve 44a.

  A predetermined bias is applied to each of the first developing sleeve 43a and the second developing sleeve 44a, and positively charged toner is applied from the first sleeve 43a to the second developing portion at the closest portion. An electric field is formed in a direction toward the sleeve 44a. As a result, the toner 10 moves from the magnetic brush to the surface of the second developing sleeve 44 a, and a toner layer is formed on the surface of the second developing sleeve 44 a by the moved toner 10.

  Thus, the toner 10 carried on the second developing sleeve 44a is conveyed to a portion (developing portion) facing the photosensitive drum 2 as the second developing sleeve 44a rotates, and the above-described non-magnetic one-component system. It is used for development in the same manner as in.

  When the above-described touch-down developing device 4 was used as the developing device 4, the transfer efficiencies of the toner A and the toner B were compared. As in the case of Example 1 and Comparative Example 1 described above, an external additive is externally added to toner A and toner B. Here, when the charge amount Q / M [μC / g] per toner unit weight (an index obtained by dividing the toner charge amount by the toner weight) is changed to 30, 20, 10, 0 [μC / g]. The amount of primary transfer residual toner was measured in the same manner as described above.

  Generally, when the mixing ratio of toner to the carrier is increased, the charge amount of the toner is decreased, and when the mixing ratio is decreased, the charge amount of the toner is increased. Therefore, it is possible to adjust the charge amount of the toner by adjusting the mixing ratio of the toner to the carrier.

  FIG. 11 shows the relationship between the toner charge amount Q / M and the minimum transfer residual value when toner A and toner B are used. Here, the minimum transfer residual value means the minimum value of the amount of primary transfer residual toner when the amount of primary transfer residual toner is measured using the primary transfer bias applied as a parameter in the same manner as described above. From FIG. 11, it can be seen that when toner A is used, the amount of residual primary transfer toner is smaller (the transfer efficiency is better) for the same toner charge amount than when toner B is used. . It can also be seen that when toner A is used, good transfer efficiency can be obtained regardless of the charge amount of the toner.

  As described above, according to the present embodiment, transfer efficiency can be improved by suppressing transfer residue and retransfer residue. For example, it is very effective for improving transfer efficiency in a cleaner-less system in which a transfer efficiency of 99% or more may be required.

[Second Embodiment]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions and configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, toner particles containing high dielectric particles that are particles of a high dielectric (high dielectric constant material) are used as toner particles. In this embodiment, the high dielectric particles are kneaded with the resin constituting the toner particles and dispersed substantially uniformly in the toner particles.

1. Toner In the image forming apparatus 100 having the configuration of the present embodiment, the transfer efficiency described later was evaluated for Examples 2-1 and 2-2 using different toners.

  Table 3 shows toner C and toner D, which are toner particles (toner base materials) used in Example 2-1 and Example 2-2, respectively. As the resin for toner C and toner D, a resin mainly composed of polyester resin particles HP325 manufactured by Nippon Synthetic Chemical Industry was used. The toner C (Example 2-1) is obtained by adding 15 parts by mass of barium titanate particles BTHP9DX manufactured by Kyoritsu Chemical Co., Ltd. to 100 parts by mass of the resin, and the toner D (Example) is not added at all. 2-2). Barium titanate is an example of a dielectric ceramic that is a typical high dielectric (high dielectric constant material) having a dielectric constant of 1000 or more at room temperature. The kneading of the resin and barium titanate was performed with a biaxial kneader in which the temperature inside the machine was set to be equal to or higher than the glass transition temperature of the polyester resin. The kneaded resin was pulverized with a counter jet mill 100AFG manufactured by Hosokawa Micron, and then classified with a classifier 50ATP manufactured by the same company to obtain toner C and toner D. The number average particle diameter (center diameter) of the classified toner is 7 μm for both toner C and toner D. For both toner C and toner D, the same TGC-110 as in the first embodiment was externally added as an external additive. In the present embodiment, the same colorant and charge control agent as those described in the first embodiment can be used. As for the formulation of the external additive, for toner D, 2 g of external additive was added to 80 g of toner particles (2.5 parts by mass of external additive with respect to 100 parts by mass of toner particles). Regarding toner C, since the specific gravity is heavy, 2 g of external additive was added to 90 g of toner particles (2.2 parts by mass of external additive with respect to 100 parts by mass of toner particles). As a result, the number distribution density of the external additive on the surface of the toner is the same between the toner C and the toner D.

2. Component of toner As the resin of the toner particle for kneading the high dielectric particles, in addition to the above-mentioned polyester, a known toner binder resin can be used.

  For example, a vinyl resin such as styrene-acrylic resin, a polyester resin, or a hybrid resin obtained by bonding them can be used. In a method for directly obtaining toner particles by a polymerization method, a monomer for forming them is used. Specifically, styrene monomers such as styrene, o- (m-, p-) methylstyrene, o- (m-, p-) ethylstyrene; methyl acrylate, ethyl acrylate, propyl acrylate, Acrylate monomers such as butyl acrylate, octyl acrylate, dodecyl acrylate, stearyl acrylate, behenyl acrylate, 2-ethylhexyl acrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, acrylonitrile, acrylamide; Methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, octyl methacrylate, dodecyl methacrylate, stearyl methacrylate, behenyl methacrylate, 2-ethylhexyl methacrylate, dimethylaminoethyl methacrylate, meta Diethylaminoethyl acrylic acid, methacrylonitrile, methacrylate based monomers, such as methacrylic acid amide; butadiene, isoprene, olefinic monomers such as cyclohexene is preferably used. These can be used alone or in general in J. Org. Brandrup, E.I. H. Immergut, “Polymer Handbook”, (USA), 3rd edition, John Wiley & Sons, 1989, p. The theoretical glass transition temperature (Tg) described in 209-277 is used by appropriately mixing monomers so that the glass transition temperature (Tg) is 40 to 75 ° C. When the theoretical glass transition temperature is less than 40 ° C., problems are likely to occur in terms of storage stability and durability stability of the toner. On the other hand, when it exceeds 75 ° C., the transparency of the image in the case of forming a full-color image of the toner. Decreases.

  Furthermore, in order to increase the mechanical strength of the toner particles and to control the molecular weight of the binder resin, a crosslinking agent can be used during the synthesis of the binder resin. As the crosslinking agent, difunctional linking agents such as divinylbenzene, 2,2-bis (4-acryloxyethoxyphenyl) propane, 2,2-bis (4-methacryloxyphenyl) propane, diallyl phthalate, ethylene glycol di Acrylate, 1,3-butylene glycol diacrylate, 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol diacrylate, triethylene Glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol # 200, # 400, # 600 diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate Acrylate include those obtained by changing the polyester type diacrylate, and the above diacrylate dimethacrylate. Polyfunctional crosslinkers include pentaerythritol triacrylate, trimethylol ethane triacrylate, trimethylol propane triacrylate, tetramethylol methane tetraacrylate, oligoester acrylate and its methacrylate, triallyl cyanurate, triallyl isocyanurate and triallyl Trimellitate is mentioned. These cross-linking agents are preferably used in an amount of 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the monomer, from the viewpoint of toner fixability and offset resistance. be able to.

3. Toner Particle Size and Manufacturing Method The preferred particle size of the toner particles and the usable manufacturing method are the same as those described in the first embodiment.

  In the present embodiment, the toner particles used a kneading and pulverizing method in which a binder resin, a pigment, and a release agent are mixed and kneaded, pulverized, and classified to obtain toner particles.

4). Dielectric Constants of Toner, Intermediate Transfer Belt, and Photosensitive Drum FIG. 13 shows the measurement results of the dielectric constants of toner C and toner D. Table 4 shows the measurement results of the dielectric constants of toner C, toner D, the surface layer of the photosensitive drum 2, the intermediate transfer belt 8, and barium titanate. Here, the dielectric constant of barium titanate is εa.

  As shown in Table 4, the relative dielectric constant εa of barium titanate and the relative dielectric constant εdr of the surface layer of the photosensitive drum 2 are εa >> εdr. Therefore, both the toner C of Example 2-1 and the toner D of Example 2-2 satisfy εdr <ε, but the dielectric constant of the toner C is larger than the dielectric constant of the toner D. In addition, in both Example 2-1 and Example 2-2, εdr <εit. The dielectric constant εa of barium titanate satisfies εa >> εit, and the dielectric constants ε of toner C and toner D both satisfy ε <εit.

  FIG. 14 shows the results of evaluating transfer efficiency in Example 2-1 and Example 2-2 using the applied primary transfer bias as a parameter. FIG. 12 shows the charge amount of toner on the photosensitive drum 2 between the developing unit and the primary transfer unit N1.

  From FIG. 12, there is almost no difference in the toner charge amount between toner C and toner D, and the ratio of the toner whose charge polarity is reversed, which is the main cause of lower transfer efficiency (increase in primary transfer residual toner). Are almost equal. On the other hand, it can be seen from FIG. 14 that Example 2-1 using toner C can reduce the primary transfer residual toner more than Example 2-2 using toner D. Although the evaluation result regarding the transfer residual toner is shown here, the retransfer residual toner also increases or decreases due to the same factors as the transfer residual toner as described above. Therefore, it can be seen that Example 2-1 using toner C can reduce the retransfer residual toner more than Example 2-2 using toner D. That is, Example 2-1 using toner C containing high dielectric particles satisfying εa> εdr can improve transfer efficiency compared to Example 2-2 using toner D containing no high dielectric particles. I understand. As described above, since there is almost no difference in toner charge amount between toner C and toner D, it can be seen that this difference in transfer efficiency is due to the dielectric constant of the toner particles.

5. Mechanism Next, a mechanism for improving the transfer efficiency as described above will be described. In the primary transfer portion N1, the polyester and barium titanate constituting the toner particles are polarized under an externally applied voltage. Since barium titanate has a much higher dielectric constant than polyester, it induces a large polarization charge in the toner particles under an externally applied voltage. Considering in the same manner as described in the first embodiment, the higher the dielectric constant εa of the high dielectric particles added to the toner particles, the larger the polarization charge becomes. In particular, the transfer efficiency when εa> εdr is satisfied. Will improve. Further, the attractive force due to the polarization charge between the barium titanates in the toner particles does not affect the motion of the toner particles due to the law of action and reaction, as described in the first embodiment.

  As described above, according to this embodiment, it is possible to further suppress the transfer residue and the re-transfer residue and further improve the transfer efficiency. The toner particles of the present embodiment can also be used in the embodiments described later.

[Third Embodiment]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions and configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, an intermediate transfer belt 8 having a plurality of layers is used as the intermediate transfer belt 8. In this embodiment, in this case, the dielectric constant of at least one of the plurality of layers of the intermediate transfer belt 8 is set higher than the dielectric constant of the surface layer of the photosensitive drum 2. In the present embodiment, the toner particles, the external additive, the formulation of the external additive, and the like are the same as those in Example 1, except that the intermediate transfer belt 8 is different.

  FIG. 15 is a schematic sectional view of the intermediate transfer belt 8 having a multilayer structure in the present embodiment (the photosensitive drum 2 and the primary transfer roller 5 are also shown). In the present embodiment, the intermediate transfer belt 8 includes a base layer 8b and a surface layer (surface coat layer) 8a provided on the outer surface of the base layer 8b. In the present embodiment, the surface layer 8a has a thickness of 0.5 to 3 μm and is formed of an acrylic resin. The surface layer 8a is a high resistance layer having a sufficiently high electric resistance, and reduces a current difference between a region where the transfer material P passes and a region where the transfer material P does not pass in the longitudinal direction of the secondary transfer portion N2. It is provided to improve the transfer efficiency at the time of secondary transfer of the toner image onto the transfer material P having the size.

  Here, a method for manufacturing the intermediate transfer belt 8 of the present embodiment will be described. In this embodiment, the intermediate transfer belt 8 is manufactured using an extrusion method. A blended component of PPS as a base material and carbon black as a conductor powder is melt-kneaded by a biaxial kneader. The obtained kneaded product is extruded by an annular die to produce an endless belt constituting the base layer 8b. The surface layer 8a is formed by spray-coating an ultraviolet curable resin on the surface of the molded endless belt, drying, and curing by ultraviolet irradiation. If the surface layer 8a is too thick, the surface layer 8a is easily cracked.

  In the image forming apparatus 100 of the present embodiment, Examples 3-1, 3-2, 3-3, and Comparative Example 2 in which the dielectric constants of the surface layer 8a and the base layer 8b of the intermediate transfer belt 8 are changed will be described. The transfer efficiency was evaluated in the same manner as described in the first embodiment. Here, the dielectric constant of the surface layer 8a of the intermediate transfer belt 8 is εits, and the dielectric constant of the base layer 8b is εitb.

  Relationship between the dielectric constants of the surface layer 8a and the base layer 8b of the intermediate transfer belt 8 and the dielectric constant of the surface layer of the photosensitive drum 2 used in Example 3-1, Example 3-2, Example 3-3, and Comparative Example 2, respectively. Is shown in Table 5. In Example 3-1, the dielectric constant of both the surface layer 8 a and the base layer 8 b is larger than the dielectric constant of the surface layer of the photosensitive drum 2. In Example 3-2, only the dielectric constant of the surface layer 8 a out of the surface layer 8 a and the base layer 8 b is larger than the dielectric constant of the surface layer of the photosensitive drum 2. In Example 3-3, only the dielectric constant of the base layer 8 b out of the surface layer 8 a and the base layer 8 b is larger than the dielectric constant of the surface layer of the photosensitive drum 2. On the other hand, in Comparative Example 2, the dielectric constant of both the surface layer 8 a and the base layer 8 b is smaller than the dielectric constant of the surface layer of the photosensitive drum 2. In each example, among the plurality of layers of the intermediate transfer belt 8, the layer having a dielectric constant larger than that of the surface layer of the photosensitive drum 2 has a dielectric constant larger than that of the toner particles. In any of the examples, the dielectric constant of the surface layer of the photosensitive drum 2 is smaller than the dielectric constant of the toner particles.

  When the transfer efficiency was compared, it was in the order of Example 3-1> Example 3-2> Example 3-3 >> Comparative Example 2.

  As shown in FIG. 16, it is known that charges in the vicinity of the dielectric cause a mirror image charge in the dielectric and receive a force in the direction of the dielectric with a force F. Here, as shown in FIG. 16, the dielectric (in this embodiment, the intermediate transfer belt 8) is composed of a plurality of layers having different dielectric constants, and the point charge q is located at a position away from the intermediate transfer belt 8 by a distance d. Consider the case where is located. This charge generates mirror image charges in the outermost layer (surface layer 8a in the present embodiment) of the intermediate transfer belt 8 and in the dielectric layers below the outermost layer (base layer 8b in the present example). Since the mirror image force is inversely proportional to the square of the distance, the charge is strongly influenced by the mirror image charge generated on the outermost layer.

  FIG. 17 shows a plot of the relationship between the thickness of the surface layer 8a of the two-layer dielectric as shown in FIG. 16 and the force received by the point charge q on the two-layer dielectric by three-dimensional electric field simulation. It is a thing. Here, the distance d of the point charge q from the two-layer dielectric is constant. From FIG. 17, it can be seen that the thicker the surface layer 8a, the greater the influence of the dielectric constant of the surface layer 8a, and the thinner the surface layer 8b, the greater the influence of the dielectric constant of the base layer 8b. It can also be seen that when the thickness of the surface layer 8a is made thinner than the distance between the charge and the surface layer 9a, the influence of the base layer 8b becomes significant. That is, the thinner the surface layer 8a, the closer the image force received by the charges on the two dielectric layers approaches the image force received when the dielectric constants of the surface layer 8a and the base layer 8b are both equal to the dielectric constant of the base layer 8b. . On the contrary, when the surface layer 8a is thick, the mirror image force received by the charges on the two dielectric layers is assumed to be a mirror image when assuming that the dielectric constants of the surface layer 8a and the base layer 8b are both equal to the dielectric constant of the surface layer 8a. Approaching power.

  In other words, when the intermediate transfer belt 8 has a two-layer configuration, even if the dielectric constant of the surface layer 8a is low, if the dielectric constant of the base layer 8b is sufficiently high, the polarization charge and true charge of the toner particles and the mirror image generated on the base layer 8b. The transfer efficiency can be improved by the interaction between the charge and the polarization charge. This is particularly noticeable when the thickness of the surface layer 8a is thin, typically when it is equal to or smaller than the particle size (average particle size) of the toner particles. Thus, when the transfer body has a surface layer constituting the surface on the photoreceptor side and a base layer provided on the side opposite to the photoreceptor on the surface layer, at least the dielectric constant of the base layer is higher than the dielectric constant of the photoreceptor. It is preferable that the thickness of the surface layer is not more than the average particle diameter of the toner.

[Fourth Embodiment]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions and configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, a photosensitive drum 2 having a plurality of dielectric layers is used as the photosensitive drum 2. That is, in the present embodiment, the photosensitive drum 2 has a plurality of dielectric layers that cannot be ignored in terms of dielectric constant on the substrate 20a. In this embodiment, in this case, the dielectric constant of at least one of the plurality of dielectric layers of the photosensitive drum 2 is set lower than the dielectric constant of the toner particles. In the present embodiment, the intermediate transfer belt 8, the toner particles, the external additive, the prescription of the external additive, and the like are the same as those in Example 1, except that the photosensitive drum 2 is different.

  FIG. 18 is a schematic cross-sectional view of the photosensitive drum 2 in the present embodiment (the intermediate transfer belt 8 and the primary transfer roller 5 are also shown). In the present embodiment, the photosensitive drum 2 includes a charge transport layer that includes a first layer (surface layer) 2a and a second layer (base layer) 2b. The layer configuration of the photosensitive layer of the photosensitive drum 2 other than the charge transport layer is the same as that of the first embodiment, but is not shown in FIG. In the present embodiment, the thickness of the first layer (surface layer) is smaller than the particle size (average particle size) of the toner.

  In the image forming apparatus 100 of the present embodiment, Example 4-1, Example 4-2, and Example 4-3 in which the dielectric constants of the first layer 2a and the second layer 2b of the charge transport layer of the photosensitive drum 2 are changed. In Comparative Example 3, the transfer efficiency was evaluated in the same manner as described in the first embodiment. Here, the dielectric constant of the first layer 2a of the charge transport layer of the photosensitive drum 2 is εdrs, and the dielectric constant of the second layer 2b is εdrb.

  The dielectric constant of the first layer 2a and the second layer 2b of the charge transport layer of the photosensitive drum 2 and the dielectric of the toner particles used in Example 4-1, Example 4-2, Example 4-3, and Comparative Example 3, respectively. Table 6 shows the relationship with the rate. In Example 4-1, the dielectric constant of both the first layer 2a and the second layer 2b is smaller than the dielectric constant of the toner particles. In Example 4-2, only the dielectric constant of the first layer 2a out of the first layer 2a and the second layer 2b is smaller than the dielectric constant of the toner particles. In Example 4-3, only the dielectric constant of the second layer 2b out of the first layer 2a and the second layer 2b is smaller than the dielectric constant of the toner particles. On the other hand, in Comparative Example 3, the dielectric constants of both the first layer 2a and the second layer 2b are larger than the dielectric constant of the toner particles. In each example, among the plurality of charge transport layers of the photosensitive drum 2, the dielectric constant of a layer having a dielectric constant smaller than that of the toner particles is smaller than that of the intermediate transfer belt 8. In any of the examples, the dielectric constant of the toner particles is smaller than the dielectric constant of the intermediate transfer belt 8.

  When the transfer efficiency was compared, it was in the order of Example 4-1> Example 4-2> Example 4-3 >> Comparative Example 3.

  As described in the third embodiment, polarization charges and true charges of the toner particles are generated in the dielectric bodies of a plurality of dielectric layers (two charge transport layers in this embodiment) of the photosensitive drum 2. The force received from the polarization charge is also felt. As a result, when the charge transport layer has two layers, even if the dielectric constant of the first layer 2a is high, if the dielectric constant of the second layer 2b is sufficiently low, the polarization charge and true charge of the toner particles and the second layer The transfer efficiency can be improved by the interaction between the mirror image charge and the polarization charge generated in 2b. This is particularly noticeable when the thickness of the first layer 2a is thin, typically when it is equal to or smaller than the particle size (average particle size) of the toner particles. As described above, when the photosensitive member includes the first layer constituting the surface on the transfer member side and the second layer provided on the side opposite to the transfer member of the first layer, at least the dielectric constant of the second layer. Is lower than the dielectric constant of the toner, and the thickness of the first layer is preferably not more than the average particle diameter of the toner.

  In addition, you may implement combining 3rd Embodiment and 4th Embodiment. That is, the dielectric constant of at least one of the plurality of dielectric layers of the photosensitive drum 2 is set lower than the dielectric constant of the toner particles, and the dielectric constant of that layer is at least one of the plurality of layers of the intermediate transfer belt 8. Increase the dielectric constant.

[Fifth Embodiment]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions and configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, as in the second embodiment, toner particles containing high dielectric particles, which are particles of a high dielectric material (high dielectric constant material), are used as toner particles. In this embodiment, the high dielectric particles are dispersed in the resin constituting the toner particles so as to be present more in the outer edge portion of the toner particles.

  In this embodiment, the resin for toner particles is mainly composed of the same polyester resin (polyester resin particles HP325 manufactured by Nippon Synthetic Chemical Industry) as in the second embodiment (Examples 2-1 and 2-2). Resin used was used. The resin particles are produced by a kneading pulverization method. In the present embodiment, the same barium titanate (barium titanate particles BTHP9DX manufactured by Kyoritsu Chemical Co., Ltd.) as in the second embodiment (Example 2-1) was used as the high dielectric particles. In this embodiment, 15 parts by mass of barium titanate particles were added to 100 parts by mass of the resin particles, and stirred with an external addition miller to embed the barium titanate particles on the surface of the resin particles. As a result, as shown in FIG. 19B, toner particles in which high dielectric particles are dispersed at a higher concentration in the outer edge portion of the toner particles can be created. That is, in the present embodiment, the distribution concentration of the high dielectric particles in the toner particles increases from the center side to the surface side of the toner particles. Also in this embodiment, the number average particle diameter (center diameter) of the toner particles is 7 μm. Also in this embodiment, the same TGC-110 as that of the second embodiment was externally added to the toner particles as an external additive. The formulation of the external additive was the same as in Example 2-1 (Toner B), in which 2 g of external additive was added to 90 g of toner particles (external additive 2. 2 parts by mass).

  In the second embodiment (Example 2-1), the toner particles are prepared so that barium titanate is dispersed substantially uniformly in the resin by a biaxial kneader. Therefore, as shown in FIG. 19A, barium titanate is dispersed substantially uniformly in the toner particles. That is, in the second embodiment (Example 2-1), the distribution density of the high dielectric particles in the toner particles is substantially constant from the center to the surface.

  As shown in FIG. 19B, the high dielectric particles are distributed at a higher concentration in the outer edge of the toner particles, and as shown in FIG. 19A, the high dielectric particles are substantially uniformly in the toner particles. The transfer efficiency similar to that described in the first embodiment was evaluated in the case of distribution. As a result, it was found that better transfer efficiency can be obtained when the distribution is as shown in FIG. 19B than when the distribution is as shown in FIG.

  This is considered due to the following reasons. As described in the first embodiment, the polarization charge generated in the toner particles by the externally applied voltage E interacts with the polarization charge generated in the dielectric such as the surrounding intermediate transfer belt 8 and the photosensitive drum 2. The magnitude of this interaction depends on the magnitude of the polarization charge itself, but is inversely proportional to the square of the distance between the polarization charges. In this respect, when the high dielectric particles are distributed on the outer edge portion of the toner particles as in the present embodiment, the distance between the polarization charge generated by the polarization and the polarization charge generated in the surrounding dielectric material becomes close. Therefore, in this case, Fb in the above equation (2) and F in the above equation (5) are larger than in the case where the high dielectric particles are uniformly distributed throughout the toner particles. It is considered that the transfer efficiency is improved.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  In the above-described embodiments, the intermediate transfer type image forming apparatus has been described as an example. However, the present invention can also be applied to a direct transfer type image forming apparatus. As is well known to those skilled in the art, a direct transfer type image forming apparatus has a transfer material carrier, such as an endless belt, instead of the intermediate transfer belt in the image forming apparatus of FIG. The toner image formed on the photosensitive drum in each image forming unit is directly transferred to the transfer material carried and conveyed on the transfer material carrier in each transfer unit. Alternatively, there is an image forming apparatus that directly transfers a toner image formed on a photosensitive drum to a transfer material that passes through contact between the photosensitive drum and a transfer member such as a transfer roller. In the case of the direct transfer method, a transfer material such as paper or a plastic sheet constitutes a transfer body on which a toner image is electrostatically transferred from a photoreceptor. Even in such a direct transfer type image forming apparatus, the transfer efficiency can be improved by setting the relationship among the dielectric constants of the photosensitive drum, toner, and transfer body in the same manner as in the above-described embodiment.

  In the above-described embodiments, the cleanerless system is employed. However, a cleaning device including a cleaning member such as a cleaning blade that contacts the photoconductor may be provided as the photoconductor cleaning means.

DESCRIPTION OF SYMBOLS 1 Image formation part 2 Photosensitive drum 5 Primary transfer roller 8 Intermediate transfer belt 10 Toner particle P Transfer material

Claims (14)

A photosensitive member; an image forming unit that forms an electrostatic image on the photosensitive member; a developing unit that supplies toner to the electrostatic image formed on the photosensitive member; A transfer body to be transferred to
When the relative permittivity of the photoconductor is εdr, the relative permittivity of the transfer member is εit, and the relative permittivity of the toner is ε,
εdr <ε and εdr <εit
An image forming apparatus satisfying the relationship: The toner is configured to contain particles having a relative dielectric constant εa in a resin,
εa> εdr
The image forming apparatus according to claim 1, wherein the relationship is satisfied.   The image forming apparatus according to claim 2, wherein the concentration of the particles in the toner increases from the central side toward the surface side of the toner.   The image forming apparatus according to claim 2, wherein the εa is 1000 or more.   The image forming apparatus according to claim 4, wherein the particles are barium titanate particles.   The transfer body has a plurality of layers, and the εit, which is a relative dielectric constant of at least one of the plurality of layers, is higher than a relative dielectric constant εdr of the photoconductor. The image forming apparatus according to claim 5.   The transfer body has a surface layer constituting the surface on the photoreceptor side, and a base layer provided on the surface layer opposite to the photoreceptor, and at least the εit which is a relative dielectric constant of the base layer, The image forming apparatus according to claim 6, wherein a relative dielectric constant εdr of the photoconductor is higher and a thickness of the surface layer is equal to or less than an average particle diameter of toner.   8. The photoreceptor according to claim 1, wherein the photoreceptor has a plurality of layers, and the εdr, which is a relative dielectric constant of at least one of the plurality of layers, is lower than a relative dielectric constant ε of the toner. The image forming apparatus according to claim 1.   The photoreceptor includes a first layer constituting a surface on the transfer body side and a second layer provided on the opposite side of the first layer to the transfer body, and at least a ratio of the second layer. 9. The image forming apparatus according to claim 8, wherein the dielectric constant εdr is lower than the relative dielectric constant ε of the toner, and the thickness of the first layer is equal to or less than the average particle diameter of the toner. A photosensitive member; an image forming unit that forms an electrostatic image on the photosensitive member; a developing unit that supplies toner to the electrostatic image formed on the photosensitive member; A transfer body to be transferred to
The toner comprises particles having a relative dielectric constant εa in a resin, where the relative dielectric constant of the photoconductor is εdr and the relative dielectric constant of the transfer body is εit.
εdr <εa and εdr <εit
An image forming apparatus satisfying the relationship:   The image forming apparatus according to claim 10, wherein the concentration of the particles in the toner increases from the central side toward the surface side of the toner.   The image forming apparatus according to claim 10, wherein the εa is 1000 or more.   The image forming apparatus according to claim 12, wherein the particles are barium titanate particles.   The image forming apparatus according to claim 1, wherein the transfer body is an endless belt.

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