JP2018066793A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the thickness of a particle layer formed of particle images to laminate the particle images.SOLUTION: High dielectric constant particles and low dielectric constant particles are transferred by an electric field generated by a secondary transfer voltage in a state where the high dielectric constant particles and low dielectric constant particles are alternately transferred at a secondary transfer nip formed by a backup roll (42) of a secondary transfer device, from a state where both particles are alternately transferred to a surface of an intermediate transfer belt (32), and thereby secondarily transferred to a recording medium (MD). When both particles are secondarily transferred from the intermediate transfer belt (32) to the recording medium (MD), the high dielectric constant particles are brought into contact with a surface of a metal plate to neutralize electric charges of the high dielectric constant particles, but the state of the electric charges is maintained by the low dielectric constant particles. The high dielectric constant particles have a small dielectric thickness, and loss of the electric charges of the high dielectric constant particles prevents an increase in voltage of particle layers, and thereby allowing a margin for the upper limit of transfer latitude due to discharge.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an image forming apparatus.

  An image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic system has a developing device filled with a developer (for example, a so-called two-component developer composed of toner and a carrier). The toner is electrostatically attached to the surface of an image holding member such as a photoconductor mounted and opposed to the developing device, the electrostatic latent image is visualized with toner, and the toner image is transferred to a recording medium. Thus, an image forming apparatus that forms an image is known.

In such an image forming apparatus, a technique is known that suppresses deterioration of image quality even when environmental conditions such as temperature and humidity change using conductive toner and insulating toner (see Patent Document 1 and the like). ). An image forming apparatus that uses conductive toner to suppress image density or image quality deterioration is also known (see Patent Documents 2 to 3, etc.).
Japanese Patent Laid-Open No. 6-138383 JP-A 61-77868 JP 2000-181129 A

By the way, when a plurality of toner images formed by electrostatically adhering toner on the image carrier are stacked and transferred in multiple layers, the transfer efficiency of the stacked toner images is determined by the number of toner layers, that is, the number of colors. As the number of toner images increases, the thickness of the toner layer formed by each toner image may be difficult to ensure.
The present invention provides an image forming apparatus capable of laminating particle images while ensuring the thickness of the particle layer formed by the particle image as compared with the case of laminating particle images regardless of the dielectric constant of the particles. For the purpose.

  In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention includes a first developing unit that develops an electrostatic latent image formed on an image carrier with first powder particles, A second developing unit that develops an electrostatic latent image formed on the image carrier with second powder particles having a dielectric constant higher than that of the first powder particles, and a first developed by the first developing unit. The first powder particle image and the second powder are formed such that a stacked portion is formed by stacking the second powder particle image developed by the second developing unit on the powder particle image of A first transfer unit that transfers the body particle image to a transfer medium; and a second transfer unit that transfers the image transferred to the transfer medium to a recording medium.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a plurality of the first developing units and the second developing units are provided, and the first transfer unit is configured by the first powder. A plurality of the stacked portions are stacked so that the body particle image and the second powder particle image are alternated.

  A third aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein the first powder particle image and the second powder particle image are a common predetermined image. Formed in the formation region.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the first powder particle image and the second powder particle image are recorded on the recording medium. It was formed in a predetermined image forming area of the medium.

  The invention according to claim 5 is the image forming apparatus according to any one of claims 1 to 4, wherein the powder particles of the first development unit and the powder particles of the second development unit are: Each is a powder particle of a different color.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the recording medium is a metal.

  According to the first aspect of the present invention, the particle image can be laminated while ensuring the thickness of the particle layer formed by the particle image, as compared with the case where the particle image is laminated regardless of the dielectric constant of the particle. It has the effect.

  According to the invention of claim 2, it is possible to easily ensure the thickness of the laminated portion as compared with the case of forming a laminated portion in which a plurality of particle images are laminated regardless of the dielectric constant of the particles. Have.

  According to the third and fourth aspects of the present invention, it is possible to form a region in which the thickness of the particle layer is ensured with a predetermined size as compared with the case where the particle image is formed regardless of the size of the particle image. Has the effect.

  According to the fifth aspect of the present invention, the color reproducibility of the formed image can be improved as compared with the case where the image is formed regardless of the color relationship of the plurality of powder particles.

  According to the invention of claim 6, it is possible to stack the particle image while ensuring the thickness of the particle layer formed by the particle image, as compared with the case where the image is formed regardless of the conductivity of the recording material. It has the effect.

1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram illustrating a developing unit according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional side view showing a main configuration of a two-component developing type developing device according to an embodiment of the present invention. FIG. 2 is a schematic sectional side view showing a main part configuration of a developing device of a non-magnetic one-component developing system according to an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a relationship between powder particle layers of each color in an intermediate transfer belt and a recording medium according to an embodiment of the present invention. It is a characteristic view showing the relationship between the weight of the powder particles and the transfer voltage according to the embodiment of the present invention. It is a schematic sectional drawing which shows the structure of the image development roll in the image development apparatus which concerns on embodiment of this invention. It is a characteristic view showing the relationship between the weight of the powder particles and the transfer voltage according to the embodiment of the present invention. It is a schematic diagram showing a transfer state of the powder particles transferred to the surface of the intermediate transfer belt according to the embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of an image formation control unit according to an embodiment of the present invention. It is a flowchart which shows the flow of a process of the image formation control program which concerns on embodiment of this invention. 6 is a test result regarding a layer formed by the image forming apparatus according to the embodiment of the invention.

  Hereinafter, an example of an image forming apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is provided to the component and process which an effect | action and a function bear the same function through all drawings, and the overlapping description may be abbreviate | omitted suitably.

FIG. 1 shows an example of a schematic side view showing a main configuration of an image forming apparatus using an electrophotographic system according to this embodiment.
The image forming apparatus 10 is equipped with a multilayer formation function that receives various data via the communication unit 64 (see FIG. 10) and performs multilayer formation processing on the recording medium MD based on the received data.

  Note that the image forming apparatus 10 according to the present embodiment has a multicolor of four colors in which white (white) is added to three colors of yellow, magenta, and cyan for each layer formed by stacking multiple layers on the recording medium MD. Although the case of performing color image formation processing using colors will be described, the colors used for color image formation processing are not limited to four colors. For example, a black color may be added, or a plurality of colors obtained by adding one or more different colors to three colors of yellow, magenta, and cyan may be used. Furthermore, two or more of the four colors of yellow, magenta, cyan, and white may be the same color with one of yellow, magenta, cyan, and white, or another color. That is, the same color may be stacked a plurality of times.

  Further, regarding colors, each of yellow, magenta, cyan, and white will be described using Y, M, C, and W alphabets (color codes). In addition, when distinguishing each color of yellow, magenta, cyan, and white in the components of the image forming apparatus 10, description will be made by adding Y, M, C, and W alphabets (color codes) after the numbers. If there is no need to distinguish between the colors, the letters Y, M, C, and W (color codes) after the numbers are omitted.

  The image forming apparatus 10 includes an image forming unit 12 that develops and transfers a particle image onto a recording medium MD, and a heat fixing unit 14 that heats and fixes the particle image transferred onto the recording medium MD. The image forming apparatus 10 also includes a carry-in unit 16 that carries the recording medium MD into the image forming unit 12 and a carry-out unit 18 that carries out the recording medium MD on which the image is heated and fixed by the heat fixing unit 14. The carry-in unit 16 includes a carry-in roller 16A and a carry-in belt 16B wound around the carry-in roller 16A, and the recording medium is transferred to the image forming unit 12 by moving the carry-in belt 16B by rotational driving of the carry-in roller 16A. Bring in the MD. The carry-out unit 18 includes a carry-out roller 18A and a carry-out belt 18B wound around the carry-out roller 18A, and the recording medium MD heated and fixed by moving the carry-out belt 18B by the rotation of the carry-out roller 18A. Is taken out of the device.

  In the present embodiment, a case where a metal plate is used as an example of the recording medium MD and a particle image of powder particles is formed in a predetermined image formable area (for example, the entire surface) on the metal plate will be described.

  The image forming unit 12 includes a developing unit 20 for each of Y, M, C, and W colors. The image forming unit 12 includes a primary transfer device 30 corresponding to the developing unit 20 for each of Y, M, C, and W colors.

FIG. 2 shows an example of a schematic side cross-sectional view showing the main configuration of the developing unit 20.
The developing unit 20 includes a photoconductor 21 as an image carrier that rotates in the direction of arrow A, a charger 22, an exposure unit 23, and a developing unit 24. In addition, the photosensitive member 21 of the developing unit 20 is disposed to face the primary transfer unit 30, and an intermediate transfer belt 32 is positioned between the photosensitive member 21 and the primary transfer unit 30.

  The charger 22 charges the surface of each photoconductor 21 by applying a charging bias. The exposure unit 23 exposes the surface of the charged photoconductor 21 with exposure light modulated based on the image information of each color, and forms an electrostatic latent image on the photoconductor 21. The developing device 24 includes a developing roll 240 that holds the developer (powder particles) of each color. The developing device 24 develops the electrostatic latent image on the photosensitive member 21 with powder particles of each color by applying a developing bias to the developing roll 240 by a developing bias power source (not shown), and powder on the photosensitive member 21. A particle image is formed.

  The powder particle image formed on the photoreceptor 21 is transferred to the intermediate transfer belt 32 by the primary transfer device 30.

  The developing unit 20 includes a cleaning device 25 including a cleaner that cleans the surface of the photoconductor 21 and a static eliminator that removes residual charges on the surface of the photoconductor 21.

The developing device 24 of the developing unit 20 in the image forming apparatus 10 according to the present embodiment will be described. In the present embodiment, the developing unit 20 is arranged such that powder particle images of each color of Y, M, C, and W are stacked on the intermediate transfer belt 32 in the order of Y, M, C, and W. In addition, although details will be described later, in this embodiment, the developing device 24 (24Y, 24C) for each color of Y and C is used for developing with low dielectric constant powder particles (hereinafter referred to as low dielectric constant particles). A non-magnetic one-component development type or two-component development type developer is used. In addition, development with high-dielectric-constant powder particles (hereinafter referred to as high-dielectric constant particles) having a dielectric constant higher than that of the low-dielectric constant particles is performed on the developer 24 (24M, 24W) of each color of M and white (W). For this purpose, a non-magnetic one-component developing type developing device is used.
Therefore, in this embodiment, powder image of each color by Y-color low dielectric constant particles, M-color high dielectric constant particles, C-color low dielectric constant particles, and W-color high dielectric constant particles is intermediate transfer belt 32. The layers are stacked in the order of Y, M, C, and W.

  In the present embodiment, the high dielectric constant particles include particles having resistance and simultaneously polarized by a transfer electric field to conductive particles, and these are collectively referred to as high dielectric constant particles.

  FIG. 3 shows an example of a schematic side cross-sectional view showing a main configuration of the developing device 24Y of the two-component developing system for Y color. In the present embodiment, the developing devices 24Y and 24C for the respective colors Y and C are configured in the same manner. Therefore, the Y developing device 24Y will be described here, and the description of the developing device 24C will be omitted.

  As shown in FIG. 3, the Y-color developing device 24Y includes a developing roll 240Y, a first stirring member 241Y, a second stirring member 242Y, and a particle layer regulating member 243Y. The Y-color developing device 24Y has the non-magnetic one-component particles (non-magnetic one-component developer) on the surface of the developing roll 240Y by the first stirring member 241Y and the second stirring member 242Y. Then, a powder particle layer is formed by the particle layer regulating member 243Y, and the powder particles are charged. Then, the powder particles are attached to the electrostatic latent image on the surface of the photoreceptor 21Y for development. That is, the developer mixed with the powder particles by the second stirring member 242Y moves toward the first stirring member 241Y, and the powder particles are applied to the surface of the developing roll 240Y while being stirred by the first stirring member 241Y. It is attached by. Then, the developer is conveyed to the photosensitive member 21Y side by the developing roller 240Y from the direction opposite to the rotation direction of the photosensitive member 21Y, and the electrostatic latent image on the photosensitive member 21Y is developed. A well-known apparatus (for example, refer to Japanese Patent Application Laid-Open No. 2006-91183) may be adopted as the developing unit of the non-magnetic one-component developing system.

  FIG. 4 shows an example of a schematic side view showing the main configuration of a non-magnetic one-component developing type developing device for W color. In the present embodiment, the developing devices 24M and 24W for the respective colors of M and W are configured in the same manner, and therefore, the developing device 24W for W color will be described here, and the description of the developing device 24M will be omitted.

  As shown in FIG. 4, in the image forming apparatus 10 according to the present embodiment, a developing device of a developing unit 20 </ b> W that develops white (W) powder particles is a non-magnetic one-component developing type developing device. The The non-magnetic one-component developing type developing device 24W is configured to, for example, develop non-magnetic one-component particles (non-magnetic one-component developer) by using a particle supply roller 244W and a stirring member 245W adjacent to the developing roller 240W, After supplying the surface of 240 W and forming a W-color powder particle layer by the particle layer regulating member 243 W and charging the W-color powder particles, the powder particles are applied to the electrostatic image on the surface of the photoreceptor 21 W. This is a developing unit of the type that attaches and develops. A well-known apparatus (for example, refer to Japanese Patent Application Laid-Open No. 2003-76120) may be adopted as the developing unit of the non-magnetic one-component developing system.

  As shown in FIG. 1, the image forming apparatus 10 includes a secondary transfer device 40 that transfers a powder particle image on the intermediate transfer belt 32 to a recording medium MD. The secondary transfer device 40 is provided at a position facing the backup roll 42 with the intermediate transfer belt 32 sandwiched between the backup roll 42 that conveys the intermediate transfer belt 32 while stretching the intermediate transfer belt 32 together with rollers 34 and 35 by a motor (not shown). A secondary transfer roll 44. That is, the intermediate transfer belt 32 is conveyed to a gap between the backup roll 42 and the secondary transfer roll 44 (hereinafter referred to as a roll pair) of the secondary transfer device 40.

  A voltage (or current) is applied from the secondary transfer power supply 46 to the roll pair of the secondary transfer device 40, and the applied voltage can be adjusted by a transfer control unit (not shown). The negative electrode of the secondary transfer power supply 46 is connected to the ground potential (for example, 0 V), and the positive electrode is connected to the metal shaft of the backup roll 42. Further, the metal shaft of the backup roll 42 is also connected to the ground potential (for example, 0 V).

  The backup roll 42 is, for example, a rotatable roller having a diameter of 18 mm in which a solid rubber is formed around a metal shaft having a diameter of 14 mm. Solid rubber is a conductive material that is adjusted to a resistance of 1 × 106Ω or more and 1 × 107Ω or less by mixing an ionic conductive agent with acrylonitrile butadiene rubber (NBR), which has excellent oil resistance, wear resistance, and aging resistance. Used. As an example of the solid rubber, a conductive material obtained by blending NBR and epichlorohydrin rubber (ECO) can be used. As another example, a conductive material made of urethane rubber in which an ionic conductive agent is mixed in rubber obtained by reacting polyether polyol and isocyanate can be used. Further, as another example, a conductive material made of ethylene propylene diene rubber (EPDM) can be used. The metal shaft is connected to a ground potential (for example, 0V).

  The secondary transfer roll 44 is, for example, a rotatable roller having a diameter of 18 mm in which a foam rubber is formed around a metal shaft having a diameter of 12 mm. The foam rubber has an ion conductive agent applied to urethane having excellent buffer properties. The resistance value of the foamed rubber 7E is adjusted to 1 × 10 7 Ω or more and 1 × 10 8 Ω or less by mixing. The metal shaft is connected to the positive electrode side of the secondary transfer power supply 46.

  A transfer control unit (not shown) of the secondary transfer device 40 applies a negative voltage from the secondary transfer power supply 46 to the roll pair at the timing when the recording medium MD is conveyed to the gap formed by the roll pair.

  The image forming apparatus 10 includes a belt cleaner 52 that cleans powder particles remaining on the surface of the intermediate transfer belt 32 after the powder particle image is transferred to the recording medium MD. The image forming apparatus 10 also includes an image formation control unit 50 that performs control related to image formation. The image forming apparatus 10 further includes a heat fixing unit 14 that heat-fixes the powder particle image transferred to the recording medium MD.

  Next, an outline of an image forming operation in the image forming apparatus 10 shown in FIG. 1 will be described.

  First, original image information to be imaged is output from a terminal device such as a personal computer (not shown) to the image forming apparatus 10 via a communication line (not shown). When the original image information is input to the image forming apparatus 10, the image forming apparatus 10 applies a charging bias to the charger 22 and charges the surface of the photoreceptor 21 to the negative electrode.

  On the other hand, the original image information is input to the image formation control unit 50. The image formation control unit 50 decomposes the original image information into image data of each color of YMCK, and then outputs a modulation signal based on the image data of each color to the exposure unit 23 of the corresponding color. The exposure unit 23 outputs a laser beam modulated according to the input modulation signal.

  In this embodiment, when a metal plate is used as the recording medium MD, a particle image is formed by powder particles in a predetermined image formable area (for example, the entire surface) on the metal plate. The modulation signal based on the image data of each color after being separated into the image data of each color is a signal for exposing an image formable area (for example, the entire surface) on the metal plate.

  The modulated laser light is applied to the surface of the photoreceptor 21. The surface of the photoconductor 21 is in a state of being charged to the negative electrode by the charger 22. When the surface of the photoconductor 21 is irradiated with laser light, the charge of the portion irradiated with the laser light disappears and the surface of the photoconductor 21 is removed. An electrostatic latent image corresponding to the image data (YMCK colors) included in the original image information is formed.

  Each color developing device 24 includes powder particles colored in the corresponding colors and charged on the negative electrode, and a developing roll 240 that adheres the powder particles to the surface of the photoreceptor 21.

  When the electrostatic latent image formed on the photoreceptor 21 reaches the developing unit 24, a developing bias is applied to the developing roll 240 in the developing unit 24 by a developing bias power source (not shown). As a result, the powder particles of each color held on the peripheral surface of the developing roll 240 adhere to the electrostatic latent image of the photoconductor 21, and the powder particles corresponding to the image data of each color of the original image information on the photoconductor 21. An image is formed.

  Further, the intermediate transfer belt 32 is conveyed to the gap formed by the primary transfer device 30 and the photoconductor 21 of each color, so that the intermediate transfer belt 32 is pressed against the photoconductor 21 of each color. At this time, when a primary transfer bias is applied by the primary transfer device 30 of each color, the powder particle image of the image data of each color formed on the photoreceptor 21 is transferred to the intermediate transfer belt 32. Therefore, by controlling the movement of the intermediate transfer belt 32 so that the transfer start positions of the powder particle images of the respective colors to the intermediate transfer belt 32 are matched, the powder particle images of the respective colors are superimposed and correspond to the original image information. The powder particle image thus formed is formed on the intermediate transfer belt 32.

  The photosensitive member 21 that has transferred the powder particle image to the intermediate transfer belt 32 is removed by the cleaning device 25 to remove the adhered matter such as residual toner adhered to the surface, and the residual charge is removed.

  On the other hand, the secondary transfer device 40 includes a backup roll 42 and a secondary transfer roll 44 that stretch the intermediate transfer belt 32, and the secondary transfer roll 44 comes into contact with the intermediate transfer belt 32 and the intermediate transfer belt 32. It rotates following the conveyance of 32.

  A voltage (or current) is applied from the secondary transfer power supply 46 to the roll pair of the secondary transfer device 40, and the applied voltage can be adjusted by a transfer control unit (not shown). A transfer control unit (not shown) of the secondary transfer device 40 applies a negative voltage from the secondary transfer power supply 46 to the roll pair at the timing when the recording medium MD is conveyed to the gap formed by the roll pair.

  The charged powder particle image is peeled off from the intermediate transfer belt 32 by an electric field generated in the gap between the roll pair in addition to the pressing force pressing the recording medium MD and the intermediate transfer belt 32 while the roll pair rotates. A force is generated, and the powder particle image formed on the intermediate transfer belt 32 is transferred to the recording medium MD.

  In addition, the recording medium MD is carried into the image forming unit 12 when the carry-in belt 16B moves in the carry-in unit 16 by the rotational drive of the carry-in roller 16A. The recording medium MD carried into the image forming apparatus 10 is rotated between the backup roll 42 and the secondary transfer roll 44 (hereinafter referred to as a roll pair) of the secondary transfer apparatus 40 by the rotation of the carry-in conveyance roller 54 by a motor (not shown). It is conveyed to the gap.

  When the recording medium MD is pressed against the intermediate transfer belt 32 by the roll pair while facing the surface of the intermediate transfer belt 32 on which the powder particle image is formed, a secondary transfer bias is applied to the roll pair, A powder particle image corresponding to the original image information formed on the intermediate transfer belt 32 is transferred to the recording medium MD. The recording medium MD on which the powder particle image is transferred is discharged toward the heat fixing unit 14 by the rotation of the carry-out side conveyance roller 56 by a motor (not shown). The powder particle image transferred onto the recording medium MD is heated and melted by the heat fixing unit 14 and fixed on the recording medium MD.

  In addition, the intermediate transfer belt 32 that has transferred the powder particle image to the recording medium MD is removed by the belt cleaner 52 to remove deposits such as residual toner.

  As described above, an image corresponding to the original image information is formed on the recording medium MD, and the image forming operation is completed. In the present embodiment, layers of the respective powder particle images are formed with a sufficient thickness so as to be uniform and uniform on the image forming surface side of the recording medium MD.

  Next, the image forming operation in the image forming apparatus 10 according to the present embodiment will be further described. Here, a case will be described in which the layer based on each powder particle image is formed while ensuring the thickness of the layer based on the powder particle image.

  FIG. 5 shows an example of the relationship between the powder particle layers of each color in the intermediate transfer belt 32 and the recording medium MD. In FIG. 5, in the image forming apparatus 10, the electrostatic latent image of each color is developed to form a uniform layer of powder particle images of each color on the intermediate transfer belt 32 and then transferred to the recording medium MD. A state in which a color image (multicolor image) is formed on the entire surface of the image forming area of the recording material MD is shown.

  As shown in FIG. 5, in the image forming apparatus 10, when a color image (multicolor image) is formed and transferred, a powder particle image of each color obtained by developing each color latent image on the intermediate transfer belt 32, that is, Layers (powder particle layers) of powder particles of Y, M, C, and W are sequentially stacked. The powder particle image formed by the plurality of powder particle layers laminated on the intermediate transfer belt 32 is fixed after being transferred to the recording medium MD. As described above, when transferring a powder particle image of a plurality of powder particle layers to the recording medium MD, the recording medium MD is maintained while the powder particle layers of different colors are stacked on the intermediate transfer belt 32. Transcript to.

  By the way, powder particle layers of each color of Y, M, C, and W are sequentially laminated on the intermediate transfer belt 32. Here, considering each layer laminated on the intermediate transfer belt 32 from the viewpoint of dielectric constant, the layer transferred onto the intermediate transfer belt 32 by each of the Y-color and M-color low dielectric constant particles is a low dielectric constant layer. It is. The layer transferred onto the intermediate transfer belt 32 by each of the M and W high dielectric constant particles is a high dielectric constant layer. That is, the image is transferred onto the intermediate transfer belt 32 in a state where low dielectric constant layers and high dielectric constant layers are alternately laminated. Further, each layer laminated on the intermediate transfer belt 32 is transferred onto the recording material MD, that is, powder particle layers of each color of W, C, M, and Y are sequentially laminated. Here, when each layer laminated on the recording material MD is considered from the viewpoint of dielectric constant, the low dielectric constant layer and the high dielectric constant layer are alternately transferred on the recording material MD.

  However, when the powder particles of each color are insulating particles, transfer becomes difficult as the plurality of laminated powder particle layers become thicker.

FIG. 6 shows an example of the relationship between the weight of the powder particles and the transfer voltage.
FIG. 6 shows the weight-voltage characteristics at the time of transfer with a curve Lc, with the transfer particle weight per unit area as the weight of the powder particles on the vertical axis, the transfer applied voltage applied at the time of transfer as the transfer voltage, and the horizontal axis. It was.

  As shown in FIG. 6, the transfer application voltage increases as the weight of the powder particles increases. However, when the transfer application voltage exceeds the limit voltage, the weight of the powder particles gradually decreases due to Paschen discharge. For this reason, for example, the average weight of the transfer particles per unit area is set as the weight Wth, and the transfer voltage lower limit value V1 to the transfer voltage upper limit value V2 are set as the transfer latitude which is the allowable range of the transfer voltage. In addition, when the transfer voltage is applied exceeding the upper limit value V2, the weight of the powder particles to be transferred by the discharge is reduced, and image unevenness is also caused by the weight reduction of the powder particles to be transferred. Therefore, it is preferable to control the transfer voltage within the transfer latitude.

  Therefore, in the present embodiment, a means for developing and transferring the powder particles is constructed in a state where there is a margin in the upper limit value V2 of the transfer latitude. That is, by forming layers having different dielectric constants alternately, it is possible to develop and transfer an image with powder particles in a state where there is a margin in the upper limit value V2 of the transfer latitude.

  Specifically, in this embodiment, when a plurality of layers having a certain thickness for applying a color material are formed on the recording medium MD, layers having different dielectric constants are alternately stacked a plurality of times. The image is transferred onto the recording medium MD, and then each layer is fixed on the recording medium MD by heat treatment. That is, in the present embodiment, a laminated portion in which a high dielectric layer made of high dielectric particles and a low dielectric layer made of low dielectric particles are alternately laminated a plurality of times using an electric field is transferred onto the recording medium MD, and thereafter The laminated portion transferred to is fixed on the recording medium MD by heat treatment.

  More specifically, in the present embodiment, the powder particles of the first color layer having a high reflectance are formed on the recording medium MD to form a layer having a uniform thickness on the formed layer. An image is formed by thermally curing the first layer and the second layer after depositing light-transparent color powder particles as the second layer. In this case, the powder particle layer which is the first color layer is a high dielectric constant particle layer, and the powder particle layer which is the second color layer is a low dielectric constant particle layer. The laminated portion in which the low dielectric constant particle layer and the high dielectric constant particle layer are alternately laminated a plurality of times using an electric field is transferred onto the recording medium MD, and the transferred laminated portion is fixed by heat treatment.

  Here, when transferring powder particles using an electric field, it is difficult to apply a thick particle layer (for example, a thickness exceeding 20 μm) due to a discharge limit. However, in the present embodiment, the stacked portion can be formed thick by forming a stacked portion in which the high dielectric constant particle layer and the low dielectric particle layer are alternately stacked a plurality of times. This is because the electric discharge is dependent on the potential difference and the distance (the thickness of the laminated portion), and the electric field from the upper layer of the laminated portion toward the intermediate transfer belt 32 or the recording medium MD is divided into the high dielectric constant particle layer. This is probably because the distance is not reached.

  By the way, in order to form a powder particle having a thickness exceeding 20 μm, for example, it is conceivable to form it by electric field transfer after coating with a coating gun and heat treatment. However, when the electric field transfer is separately processed after the coating with the coating gun and the heat treatment, the processing time becomes long, so that the processing efficiency is deteriorated. Further, when these processes can be performed by one apparatus, the image forming apparatus becomes large.

  In order to form a plurality of layers having a certain thickness, it is also conceivable to form a first particle layer with an electric field and then remove the charge, and then form a next particle layer on the first particle layer after the charge removal. However, when the next particle layer is formed on the first particle layer after static elimination, the charge of the first formed particle layer is lost, and the holding force to the intermediate transfer belt 32 or the recording medium MD is reduced. It may collapse. In addition, when the next layer is formed after the first formed particle layer is heat-treated, the processing time becomes long, so that the processing efficiency deteriorates. Further, when these processes can be performed by one apparatus, the image forming apparatus becomes large.

  On the other hand, as in the present embodiment, a laminated portion in which a high dielectric constant layer and a low dielectric constant layer are alternately laminated a plurality of times using an electric field is transferred onto the recording medium MD, and the transferred laminated portion is then recorded by heat treatment. If the fixing is performed on the medium MD, the electric field to the outside is neutralized while maintaining the charge from the recording medium MD to the high dielectric constant layer when the high dielectric constant layer is formed. The voltage does not increase, and it is possible to stack like overcoat.

  FIG. 7 shows an example of the state of components related to the development of white high dielectric constant particles. FIG. 7A shows an example of the state of white high dielectric constant particles in the development process, and FIG. 7B shows an example of the potential in the development process.

  As shown in FIG. 7A, white high dielectric constant particles are adhered to the surface of the developing roll 240W by magnetic force, and the white high dielectric constant particles are developed by the developing roll 240W from the direction opposite to the rotation direction of the photoreceptor 21W. Is conveyed to the photoconductor 21W side, and the electrostatic latent image on the photoconductor 21W is developed. Specifically, white high dielectric constant particles are attached to the developing roll 240W by frictional charging, magnetic force, or the like, and the layer thickness of the white high dielectric constant particles is regulated by the particle layer regulating member 243W. Then, in the region (development nip) where the developing roll 240W of the developing unit 24W is in contact with the photoreceptor 21W, electric charges are injected into the white high dielectric constant particles in the portion corresponding to the electrostatic latent image (that is, the direction of the electric field is neutralized). The white high dielectric constant particles adhere to the surface of the photoreceptor 21W by electrostatic force. That is, in the state where the laser beam is not irradiated from the exposure unit 23W, the surface of the photoconductor 21W is insulative, so that the charge of the attached white high dielectric constant particles is retained. For this reason, white high dielectric constant particles adhere to the surface of the photoconductor 21W due to electrostatic attraction with the reverse charge induced in the photoconductor 21W. Note that, when the high dielectric constant particles pass through the development nip, the polarization in the high dielectric constant particles gradually weakens, but since there is no strong electric field, the polarization in the high dielectric constant particles is temporarily retained. Therefore, the charge of the high dielectric constant particles is retained by the initial charged charge and polarization, and the high dielectric constant particles adhere to the surface of the photoreceptor. The white high dielectric constant particles attached to the photosensitive member 21W are moved toward a region (primary transfer nip) where the primary transfer unit 30W is in pressure contact with the intermediate transfer belt 32.

  As shown in FIG. 7B, the potential Vdp1 at the portion of the photoreceptor 21W where the electrostatic latent image is formed may be set to a potential higher than the surface potential Vdp2 of the developing roll 240W (Vdp1> Vdp2). Further, the surface potential Vdp2 of the developing roll 240W may be set to a potential higher than the potential Vdp3 at the portion where the electrostatic latent image of the photoconductor 21W is not formed (Vdp2> Vdp3). Each potential of the surface potential Vdp2 of the developing roll 240W and the potential Vdp3 in the portion where the electrostatic latent image of the photoconductor 21W is not formed has a reverse charge while passing through the developing nip due to the resistance of white high dielectric constant particles. What is necessary is just to derive | lead-out and determine the electric potential of the grade which is not inject | poured by simulation or experiment.

  Next, the white high dielectric constant particles attached to the photoconductor 21W are primarily transferred to the intermediate transfer belt 32 in the primary transfer nip.

  FIG. 8 shows an example of a state in which white high dielectric constant particles are transferred to the intermediate transfer belt 32. FIG. 8A shows an example of a state of white high dielectric constant particles in the primary transfer process to the intermediate transfer belt 32, and FIG. 8B shows an example of a potential in the primary transfer process. In the example of FIG. 8, the case where the high-permittivity particles of each color are transferred after the Y-color low-permittivity particles are transferred to the intermediate transfer belt 32 is shown.

  As shown in FIG. 8A, the white high dielectric constant particles are primarily transferred to the intermediate transfer belt 32 from the state of being attached to the surface of the photoreceptor 21W. Specifically, in the region where the primary transfer device 30W is in pressure contact with the intermediate transfer belt 32 (primary transfer nip), the white high dielectric constant particles are moved by the electric field generated by the transfer voltage, thereby causing the intermediate transfer belt 32 to move. Transcribed to the side. Then, the white high dielectric constant particles primarily transferred to the intermediate transfer belt 32 are in a region where the intermediate transfer belt 32 is pressed into contact with the gap between the backup roll 42 and the secondary transfer roll 44 of the secondary transfer device 40 (secondary transfer). Moved toward the transfer nip).

  Here, the intermediate transfer belt 32 is conductive because it is a resistor. However, between the white high-permittivity particles and the intermediate transfer belt 32, there are Y-color low-permittivity particles that act as insulating particles. Intervene. For this reason, the electric charge of white high dielectric constant particles is retained. In addition, since the white high dielectric constant particles have a small dielectric thickness, the increase in the total particle layer voltage in the stacked state is suppressed, and the insulating powder particles or the low dielectric constant particles are replaced with the white high dielectric constant. The transfer electric field generated can be reduced as compared with the case where the same amount as that of the rate particles is stacked. As a result, there is a margin with respect to the upper limit value of the transfer latitude due to Paschen discharge, and the transfer amount can be stabilized.

  As shown in FIG. 8B, the surface potential Vtr1 of the intermediate transfer belt 32 may be set to a potential higher than the potential Vdp1 at the portion of the photoreceptor 21W where the electrostatic latent image is formed (Vtr1> Vdp1).

  Next, the white high dielectric constant particles and insulating color particles transferred to the surface of the intermediate transfer belt 32 are secondarily transferred to the recording medium MD in the secondary transfer nip.

  FIG. 9 shows an example of a state in which the high-permittivity particles and the low-permittivity particles are alternately transferred onto the surface of the intermediate transfer belt 32 and then secondarily transferred to the recording medium MD. FIG. 9A shows an example of the state of the high dielectric constant particles and insulating color particles of Y, M, C, and W in the secondary transfer process to the recording medium MD, and FIG. Shows an example of the potential in the secondary transfer process. Note that in FIG. 9A, the low dielectric constant particles retain the charge of the same polarity as the high dielectric constant particles, but the illustration is omitted in order to avoid complicated explanation.

  As shown in FIG. 9A, the high dielectric constant particles and the low dielectric constant particles are secondarily transferred to the recording medium MD from the state where they are alternately transferred onto the surface of the intermediate transfer belt 32. Specifically, in the region (secondary transfer nip) where the intermediate transfer belt 32 is pressed in the gap between the backup roll 42 and the secondary transfer roll 44 of the secondary transfer device 40, the high dielectric constant particles and the low dielectric constant particles. Are transferred to the recording medium MD side by being moved by the electric field generated by the secondary transfer voltage. Then, the high dielectric constant particles and the low dielectric constant particles secondarily transferred to the recording medium MD are moved toward the heat fixing unit 14.

  In the present embodiment, a metal plate is used as an example of the recording medium MD. For this reason, when secondary transfer is performed from the intermediate transfer belt 32 to the recording medium MD (metal plate), the high dielectric constant particles come into contact with the surface of the metal plate to neutralize the charge of the high dielectric constant particles. The low dielectric constant particles stacked on the dielectric constant particles maintain the state of charge in the transferred state. Further, in addition to the small dielectric thickness of the high dielectric constant particles, the increase in the total particle layer voltage in the stacked state is suppressed by the disappearance of the charge of the high dielectric constant particles, so that the insulating powder The transfer electric field generated can be reduced as compared with the case where body particles or low dielectric constant particles are stacked in the same amount as high dielectric constant particles. As a result, there is a margin with respect to the upper limit value of the transfer latitude due to Paschen discharge, and the transfer amount can be stabilized.

  As shown in FIG. 9B, the surface potential Vtr2 of the recording medium MD (metal plate) may be set higher than the surface potential Vtr1 of the intermediate transfer belt 32 (Vtr2> Vtr1).

<Powder particles>
Next, powder particles used for a thermosetting powder coating suitable for high dielectric constant particles and low dielectric constant particles used in the image forming apparatus 10 according to the present embodiment will be described.

As a specific method for adjusting the dielectric constant, there is a method of lowering the dielectric constant by adding a conductive colorant, resin, or other additive, preferably a material having high conductivity such as carbon black. Is added to such an extent that color turbidity cannot be recognized, and the dielectric constant is adjusted.
Here, as a method for measuring the relative dielectric constant, first, the powder particles are pressure molded at 98067 KPa (1000 Kgf / cm ² ) for 1 minute so as to form a disk shape having a diameter of 50 mm and a thickness of 3 mm. After being left in an atmosphere of 30 ° C. and 90% relative humidity for 24 hours, the relative dielectric constant is measured. For measurement, the electrode diameter is set to 38 mm for a solid electrode (manufactured by Ando Electric Co., SE-71), and a dielectric measurement system (Solartron Co., 126096W type) is used. Measure under conditions.
In addition, when the additive has adhered to the powder particle surface, for example, the powder particle is dispersed in ion-exchanged water to which a dispersant such as a surfactant is added, and an ultrasonic homogenizer (US-300T: (stock) ) Nippon Seiki Seisakusho, etc.) to separate the additive and powder particles by applying ultrasonic waves. Thereafter, only the toner particles are taken out by filtration and washing, and the powder particles are used.
Needless to say, the magnitude relation of the dielectric constant is the same as the magnitude relation of the relative dielectric constant described above.

  The powder particles according to the present embodiment include a thermosetting resin and a thermosetting agent. As the powder particles, particles having a so-called core / shell structure may be used.

  The powder particles according to the present embodiment may be either a transparent powder paint (clear paint) in which the powder particles do not contain a colorant, or a colored powder paint in which the powder particles contain a colorant. . In order to reduce the diameter of the powder particles, those having a volume particle size distribution index GSDv of the powder particles of 1.50 or less and an average circularity of the powder particles of 0.96 or more can be used. .

(Thermosetting resin)
The thermosetting resin is a resin having a thermosetting reactive group. As the thermosetting resin, various types of resins conventionally used for powder particles can be mentioned.
The thermosetting resin is preferably a water-insoluble (hydrophobic) resin. When a water-insoluble (hydrophobic) resin is applied as the thermosetting resin, the environmental dependency of the charging characteristics of the powder particles is reduced. Further, when the powder particles are produced by an aggregation and coalescence method, the thermosetting resin is preferably a water-insoluble (hydrophobic) resin from the viewpoint of realizing emulsification and dispersion in an aqueous medium. In addition, water-insoluble (hydrophobic) means that the amount of the target substance dissolved in 100 parts by mass of water at 25 ° C. is less than 5 parts by mass.

  Among thermosetting resins, at least one selected from the group consisting of thermosetting (meth) acrylic resins and thermosetting polyester resins is preferable.

(Thermosetting agent)
The thermosetting agent is selected according to the type of the curing reactive group of the thermosetting resin.
Specifically, when the curing reactive group of the thermosetting resin is an epoxy group, examples of the thermosetting agent include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dodecane. Diacid, eicosane diacid, maleic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, trimellitic acid, pyromellitic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexene-1,2-dicarboxylic acid, trimellitic Examples thereof include acids, acids such as pyromellitic acid, anhydrides of these acids, and urethane-modified products of these acids. Among these, as the thermosetting agent, an aliphatic dibasic acid is preferable from the viewpoint of coating film physical properties and storage stability, and dodecanedioic acid is particularly preferable from the viewpoint of coating film physical properties.

  When the curing reactive group of the thermosetting resin is a carboxyl group, examples of the thermosetting agent include various epoxy resins (for example, polyglycidyl ether of bisphenol A), epoxy group-containing acrylic resins (for example, glycidyl group-containing acrylic resins). Etc.), polyglycidyl ethers of various polyhydric alcohols (eg 1,6-hexanediol, trimethylolpropane, trimethylolethane etc.), polyglycidyl esters of various polycarboxylic acids (eg phthalic acid, terephthalic acid, isophthalic acid) Acid, hexahydrophthalic acid, methylhexahydrophthalic acid, trimellitic acid, pyromellitic acid, etc.), various alicyclic epoxy group-containing compounds (eg bis (3,4-epoxycyclohexyl) methyl adipate), hydroxyamide (For example, triglycidyl isocyania Rate, beta-hydroxyalkyl amide) and the like.

  When the curing reactive group of the thermosetting resin is a hydroxyl group, examples of the thermosetting agent include polyblock isocyanate and aminoplast. Examples of the polyblock polyisocyanate include various aliphatic diisocyanates (such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate), various cyclic aliphatic diisocyanates (such as xylylene diisocyanate and isophorone diisocyanate), and various aromatic diisocyanates (for example). For example, organic diisocyanates such as tolylene diisocyanate and 4,4'-diphenylmethane diisocyanate); adducts of these organic diisocyanates with polyhydric alcohols, low molecular weight polyester resins (for example, polyester polyols) or water; Polymers (polymers including isocyanurate type polyisocyanate compounds); various polyisotopes such as isocyanate and biuret bodies The Aneto Compound those that have been blocked with blocking agents known customary; and self-blocked polyisocyanate compound containing uretdione bond as a structural unit thereof.

  A thermosetting agent may be used individually or in combination of 2 or more types.

1 mass% or more and 30 mass% or less are preferable with respect to thermosetting resin, and, as for content of a thermosetting agent, 3 mass% or more and 20 mass% or less are preferable.
In addition, when applying a thermosetting resin as resin of a resin coating part, content of a thermosetting agent means content with respect to all the thermosetting resins of a core part and a resin coating part.

-Colorant-
The powder particles may contain a colorant.
Examples of the colorant include pigments. The colorant may use a dye together with the pigment.
Examples of the pigment include inorganic pigments such as iron oxide (eg, Bengala), titanium oxide, titanium yellow, zinc white, lead white, zinc sulfide, lithopone, antimony oxide, cobalt blue, and carbon black; quinacridone red, phthalocyanine blue, Organic pigments such as phthalocyanine green, permanent red, Hansa yellow, indanthrene blue, brilliant first scarlet, and benzimidazolone yellow are listed.
Other examples of pigments include glitter pigments. Examples of glitter pigments include metal powders such as pearl pigments, aluminum powder, and stainless steel powder; metal flakes; glass beads; glass flakes; mica; flake iron oxide (MIO).

  The colorants may be used alone or in combination of two or more.

  The content of the colorant is selected according to the type of pigment and the color, brightness, depth, etc. required for the coating film. For example, the content of the colorant is preferably 1% by mass or more and 70% by mass or less, and more preferably 2% by mass or more and 60% by mass or less with respect to the total resin of the core part and the resin coating part.

-Other additives-
The powder particles may contain other additives.
Other additives include various additives used for powder coatings. Specifically, other additives include, for example, a surface conditioner (silicone oil, acrylic oligomer, etc.), a foaming prevention agent (eg, benzoin, benzoin derivative, etc.), and a curing accelerator (amine compound, imidazole compound). , Cationic polymerization catalyst, etc.), plasticizers, charge control agents, antioxidants, pigment dispersants, flame retardants, flow imparting agents and the like.

(Production method of powder particles)
Next, the manufacturing method of the powder particle which concerns on this embodiment is demonstrated.
The powder particles according to this embodiment may be externally added with an external additive.

  The powder particles may be produced by any of a dry production method (for example, a kneading pulverization method) and a wet production method (for example, an aggregation coalescence method, a suspension polymerization method, a dissolution suspension method, etc.). The production method of the powder particles is not particularly limited, and a known production method is adopted.

For example, in the dry production method, 1) kneading, pulverizing, and classifying the thermosetting resin and other raw materials, and the shape of the particles obtained by kneading and pulverizing is changed by mechanical impact force or thermal energy. There are dry manufacturing methods.
On the other hand, in the wet manufacturing method, for example, 1) an agglomeration and coalescence method in which a dispersion obtained by emulsifying a thermosetting resin and a dispersion of another raw material are mixed and agglomerated and heat-fused to obtain powder particles. 2) Suspension polymerization method in which a polymerizable monomer for obtaining a thermosetting resin and a solution of another raw material are suspended in an aqueous solvent for polymerization, and 3) a thermosetting resin and another raw material. There is a solution suspension method in which the solution is suspended in an aqueous solvent and granulated. The wet manufacturing method can be preferably used because it has a smaller thermal effect.
Alternatively, powder particles obtained by the above production method may be used as cores (cores), and resin particles may be further adhered and heat-fused to obtain powder particles that are core-shell type particles.

  Among these, it is preferable to obtain powder particles by the aggregation coalescence method from the viewpoint that the volume particle size distribution index GSDv, the volume average particle diameter D50v, and the average circularity can be easily controlled within the above preferable ranges.

Hereinafter, an example of an aggregation and coalescence method for producing powder particles that are core-shell type particles will be described.
In particular,
In the dispersion liquid in which the first resin particles containing the thermosetting resin and the thermosetting agent are dispersed, the first resin particles and the thermosetting agent are aggregated, or the thermosetting resin and the thermosetting are combined. A step of aggregating the composite particles in a dispersion in which composite particles containing an agent are dispersed to form first aggregated particles (first aggregated particle forming step);
The first aggregated particle dispersion in which the first aggregated particles are dispersed and the second resin particle dispersion in which the second resin particles containing a resin are dispersed are mixed, and the second aggregated particles are formed on the surface of the first aggregated particles. A step of aggregating resin particles to form second agglomerated particles in which the second resin particles adhere to the surface of the first agglomerated particles (second agglomerated particle forming step);
Heating the second aggregated particle dispersion in which the second aggregated particles are dispersed, and fusing and coalescing the second aggregated particles (fusion coalescence process);
Through this process, it is preferable to produce powder particles.
In the powder particles produced by this aggregation and coalescence method, the portion where the first aggregated particles are fused and united becomes the core, and the portion where the second resin particles attached to the surface of the first aggregated particles are fused and united Is the resin coating.
Therefore, if the first aggregated particles formed in the first aggregated particle formation step are not subjected to the second aggregated particle formation step, they are subjected to the fusion coalescence step, and instead of the second aggregated particles, fusion and coalescence are performed. Powder particles having a single layer structure are obtained.

Details of each step will be described below.
In addition, although the following description demonstrates the manufacturing method of the powder particle containing a coloring agent, a coloring agent is contained as needed.

<Each dispersion preparation step>
First, each dispersion used in the aggregation coalescence method is prepared.
Specifically, the first resin particle dispersion in which the first resin particles containing the thermosetting resin in the core are dispersed, the thermosetting agent dispersion in which the thermosetting agent is dispersed, and the colorant in which the colorant is dispersed. A second resin particle dispersion in which the second resin particles including the dispersion and the resin of the resin coating portion are dispersed is prepared.
Moreover, it replaces with a 1st resin particle dispersion and a thermosetting agent dispersion, and prepares the composite particle dispersion in which the composite particle containing the thermosetting resin for core parts and the thermosetting agent was disperse | distributed.
In each step of the powder coating production method, the first resin particles, the second resin particles, and the composite particles are generally referred to as “resin particles”, and a dispersion of these resin particles is referred to as a “resin particle dispersion”. Will be described.

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

Examples of the dispersion medium used for the resin particle dispersion include an aqueous medium.
Examples of the aqueous medium include water such as distilled water and ion exchange water; alcohols and the like. These may be used individually by 1 type and may use 2 or more types together.

Examples of the surfactant include anionic surfactants such as sulfate ester, sulfonate, phosphate, and soap; cationic surfactants such as amine salt type and quaternary ammonium salt type; Nonionic surfactants such as polyethylene glycol, alkylphenol ethylene oxide adducts, and polyhydric alcohols can be used. Among these, anionic surfactants and cationic surfactants are particularly mentioned. The nonionic surfactant may be used in combination with an anionic surfactant or a cationic surfactant.
Surfactant may be used individually by 1 type and may use 2 or more types together.

Examples of the method for dispersing the resin particles in the dispersion medium in the resin particle dispersion include a general dispersion method such as a rotary shear homogenizer, a ball mill having media, a sand mill, and a dyno mill. Depending on the type of resin particles, the resin particles may be dispersed in the resin particle dispersion using, for example, a phase inversion emulsification method.
The phase inversion emulsification method is a method in which a resin to be dispersed is dissolved in a hydrophobic organic solvent in which the resin is soluble, a base is added to the organic continuous phase (O phase), and the aqueous medium is neutralized. By introducing (W phase), conversion of the resin from W / O to O / W (so-called phase inversion) is performed to form a discontinuous phase, and the resin is dispersed in an aqueous medium in the form of particles. is there.

Specific methods for preparing the resin particle dispersion include the following methods.
For example, when the resin particle dispersion is a polyester resin particle dispersion in which polyester resin particles are dispersed, the polyester resin particle dispersion is obtained by heat-melting the raw material monomer and polycondensing under reduced pressure, and The condensate is dissolved by adding a solvent (for example, ethyl acetate or the like), and further, stirring and phase-inversion emulsification while adding a weak alkaline aqueous solution to the resulting solution.

  When the resin particle dispersion is a composite particle dispersion, the composite particle dispersion is obtained by mixing a thermosetting resin and a thermosetting agent and dispersing the mixture in a dispersion medium (for example, emulsification such as phase inversion emulsification). Get liquid

  Here, in order to prepare the resin particle dispersion, a known emulsification method can be used, but the obtained particle size distribution is narrow and the volume average particle size is 1 μm or less (particularly 0.08 μm or more and 0.40 μm or less). The phase inversion emulsification method which is easy to be in the range of) is effective.

  In the phase inversion emulsification method, the resin is dissolved in an organic solvent that dissolves the resin, an amphiphilic organic solvent alone, or a mixed solvent to obtain an oil phase. A small amount of a basic compound is dropped while stirring the oil phase, and water is dropped little by little while stirring, and water droplets are taken into the oil phase. Next, when the dripping amount of water exceeds a certain amount, the oil phase and the water phase are reversed and the oil phase becomes oil droplets. Thereafter, an aqueous dispersion is obtained through a desolvation step of depressurization.

<First Aggregated Particle Formation Step>
Next, the first resin particle dispersion, the thermosetting agent dispersion, and the colorant dispersion are mixed.
Then, the first resin particles, the thermosetting agent, and the colorant having a diameter close to the diameter of the target powder particles are obtained by heteroaggregating the first resin particles, the thermosetting agent, and the colorant in the mixed dispersion. First agglomerated particles are formed.

  Specifically, for example, the flocculant is added to the mixed dispersion, and the pH of the mixed dispersion is adjusted to acidic (for example, the pH is 2 or more and 5 or less), and a dispersion stabilizer is added as necessary. Particles heated to the glass transition temperature of the first resin particles (specifically, for example, the glass transition temperature of the first resin particles −30 ° C. or more and the glass transition temperature −10 ° C. or less) and dispersed in the mixed dispersion liquid Are aggregated to form first aggregated particles.

  In the first aggregated particle forming step, a composite particle dispersion containing a thermosetting resin and a thermosetting agent and a colorant dispersion are mixed, and the composite particles and the colorant are mixed in the mixed dispersion. May be heteroaggregated to form the first aggregated particles.

  In the first aggregated particle forming step, for example, the above-mentioned flocculant is added at room temperature (for example, 25 ° C.) while stirring the mixed dispersion with a rotary shearing homogenizer, and the pH of the mixed dispersion is acidic (for example, pH is 2 or more). 5 or less) and, if necessary, after adding a dispersion stabilizer, the heating may be performed.

Examples of the flocculant include surfactants having a polarity opposite to that of the surfactant used as the dispersant added to the mixed dispersion, metal salts, metal salt polymers, and metal complexes. When a metal complex is used as the aggregating agent, the amount of the surfactant used is reduced and the charging characteristics are improved.
In addition, after completion | finish of aggregation, you may use the additive which forms a complex or a similar bond with the metal ion of an aggregating agent as needed. As this additive, a chelating agent is preferably used. By adding this chelating agent, when the flocculant is added excessively, the adjustment of the metal ion content of the powder particles is realized.

<Second Aggregated Particle Formation Step>
Next, the first aggregated particle dispersion in which the obtained first aggregated particles are dispersed is mixed with the second resin particle dispersion.
The second resin particles may be the same type as the first resin particles or different types.

  Then, in the mixed dispersion liquid in which the first aggregated particles and the second resin particles are dispersed, the aggregates so that the second resin particles adhere to the surface of the first aggregated particles, 2nd aggregated particles to which 2 resin particles are attached are formed.

Specifically, for example, in the first aggregated particle forming step, when the first aggregated particle reaches a target particle size, the second aggregated particle dispersion is mixed with the second resin particle dispersion, The mixed dispersion is heated below the glass transition temperature of the second resin particles.
Thereby, the second aggregated particles aggregated so that the second resin particles adhere to the surface of the first aggregated particles are obtained.

<Fusion coalescence process>
Next, with respect to the second agglomerated particle dispersion in which the second agglomerated particles are dispersed, for example, the glass transition temperature of the first and second resin particles is higher than the glass transition temperature (for example, 10 from the glass transition temperature of the first and second resin particles). To 30 ° C. or higher temperature), the second aggregated particles are fused and united to form powder particles.
Through the above steps, powder particles are obtained.

Here, after the fusion and coalescence process is completed, the powder particles formed in the dispersion are obtained through a known washing process, solid-liquid separation process, and drying process to obtain powder particles.
In the washing step, it is preferable to sufficiently carry out substitution washing with ion-exchanged water from the viewpoint of chargeability. The solid-liquid separation step is not particularly limited, but suction filtration, pressure filtration, and the like are preferably performed from the viewpoint of productivity. In addition, the drying process is not particularly limited, but from the viewpoint of productivity, freeze drying, airflow drying, fluidized drying, vibration fluidized drying, or the like is preferably performed.

And the powder coating material which concerns on this embodiment is manufactured by adding an inorganic particle to the obtained powder particle of the dried state, and mixing.
In addition, it is good to perform said mixing with a V blender, a Henschel mixer, a Ladige mixer, etc., for example.
Furthermore, if necessary, coarse particles of the powder particles may be removed using a vibration sieving machine, a wind sieving machine, or the like.

FIG. 10 shows an example of the configuration of the image forming control unit 50 that performs the image forming operation in the image forming apparatus 10.
FIG. 10 shows an example of a computer 50X in which the image formation control unit 50 is configured by a computer. The computer 50X has a configuration in which a CPU (Central Processing Unit) 50A, a ROM (Read Only Memory) 50B, a RAM (Random Access Memory) 50C, and an input / output interface (I / O) 50E are connected via a bus 50F. Yes, a non-volatile memory 50D is also connected to the I / O 50E. An image forming unit 60, an operation display unit 62, and a communication unit 64 are connected to the I / O 50E.

  The ROM 50B stores an image formation control program 50P that is executed by the computer 50X. The CPU 50A reads the image formation control program 50P from the ROM 50B, expands it in the RAM 50C, and executes processing by the image formation control program 50P. The computer 50 </ b> X operates as the image formation control unit 50 by the CPU 50 </ b> A executing the processing by the image formation control program 50 </ b> P. The image formation control program 50P may be provided by a recording medium such as a CD-ROM.

  Further, the nonvolatile memory 50D obtains information indicating a potential necessary for the image forming apparatus 10 to execute an image forming operation, for example, a potential Vdp1 at a portion where the electrostatic latent image of the photoreceptor 21 is formed. Information indicating various voltages is stored.

  The image forming unit 60 is a device necessary for the image forming apparatus 10 to perform an image forming operation, such as the photosensitive member 21, the charger 22, the exposure unit 23, the developing unit 24, the intermediate transfer belt 32, and the secondary transfer. Each of the devices 40 is configured to include a drive unit. Note that the image forming unit 60 may include the driving units of the carry-in unit 16, the carry-out unit 18, and the heat fixing unit 14.

  The operation display unit 62 includes a display button that realizes reception of an operation instruction, a touch panel type display (not shown) on which various types of information are displayed, a hardware key (not shown) such as a numeric keypad and a start button, and the like. .

  The communication unit 62 is an interface for performing data communication with a terminal device such as a personal computer (not shown).

  Next, an image forming process executed by the computer 50X that operates as the image forming control unit 50 will be described.

  FIG. 11 shows a flow of processing of the image formation control program 50P executed by the CPU 50A of the computer 50X.

  The image formation control program 50P is executed by the CPU 50A when the image forming apparatus 10 is turned on and receives an image formation start instruction from the CPU 50A.

  First, in step S100, original image information indicating a color image to be formed on the recording medium MD is acquired from a terminal device (not shown) via the communication unit 64. Next, in step S102, an electrostatic latent image is formed using the original image information acquired in step S100. That is, a charging bias is applied to the charger 22, the surface of the photoreceptor 21 is charged to the negative electrode, YMCK color modulation signals based on the original image information are output, and the exposure unit 23 of the corresponding developing unit 20 outputs the modulated signal. A laser beam corresponding to the modulation signal is output. The laser beam is irradiated onto the surface of the photosensitive member 21, the charge on the irradiated portion of the laser beam disappears, and an electrostatic latent image is formed.

  In the next step S104, the electrostatic latent image formed in step S102 is developed. That is, in each color developing device 24, the powder particles colored in the corresponding colors and charged on the negative electrode are attached to the surface of the photoreceptor 21 where the electrostatic latent image is formed. Specifically, a developing bias is applied to the developing roll 240 in the developing unit 24, and the powder particles of each color held on the peripheral surface of the developing roll 240 are attached to the electrostatic latent image on the photoreceptor 21. Therefore, when the electrostatic latent image formed on the photoreceptor 21 reaches the developing device 24, a powder particle image corresponding to the electrostatic latent image is formed.

  In the next step S106, the powder particle image developed in step S104 is transferred. That is, first, a primary transfer bias is applied to the primary transfer device 30 of each color, and the powder particle image of each color formed on the photoreceptor 21 is transferred to the intermediate transfer belt 32. Next, a secondary transfer voltage (or current) is applied to the secondary transfer device 40 to transfer the powder particle image formed on the intermediate transfer belt 32 to the recording medium MD.

  In the next step S108, the powder particle image transferred onto the recording medium MD is heated and melted by the heat fixing unit 14 and fixed on the recording medium MD, and the image forming process is completed.

  As described above, according to the present embodiment, the layers of powder particles are stacked by alternately transferring the high dielectric constant particles and the low dielectric constant particles to the recording medium MD. In this way, by transferring the high dielectric constant particles and low dielectric constant particles alternately and laminating layers of each powder particle, the dielectric thickness in the case of laminating multiple powder particle layers is reduced, and multiple transfer is performed. It is possible to reduce the burden of transfer voltage control when performing. In other words, since the dielectric thickness of high dielectric constant particles is small, the increase in the overall particle layer voltage in the stacked state is suppressed, and the amount of insulating powder particles is the same as that of conductive powder particles. The transfer electric field generated can be reduced as compared with the case of overlapping. As a result, there is a margin with respect to the upper limit value of the transfer latitude due to Paschen discharge, and the transfer amount can be stabilized.

  In the present embodiment, by alternately transferring high dielectric constant particles and low dielectric constant particles and laminating layers of each powder particle, compared with the case of forming a layer in which powder particles having insulating properties are laminated. Thus, the thickness of the stacked layers can be increased. In addition, by making the colors of the high dielectric constant particles and the low dielectric constant particles different from each other, it is possible to obtain a colorful color image.

[Test example]
<Preparation of Colorant Dispersion (C1)>
Cyan pigment (Daiichi Seika Co., Ltd., CI Pigment Blue 15: 3, (copper phthalocyanine)): 100 parts by mass Anionic surfactant (Daiichi Kogyo Seiyaku Co., Ltd .: Neogen RK): 15 parts by mass Part ・ Ion-exchanged water: 450 parts by mass The above is mixed, dissolved, and dispersed for 1 hour using a high-pressure impact disperser Ultimateizer (manufactured by Sugino Machine Co., Ltd., HJP30006) to disperse the colorant (cyan pigment). A colorant dispersion (C1) was prepared.

<Preparation of Colorant Dispersion (M1)>
Instead of cyan pigment, C.I. I. 99.5 parts by mass of Pigment Red 122, carbon black (Ketjen Black ECP manufactured by Lion Specialty Chemicals): Dispersing the colorant in the same manner as in the preparation of the colorant dispersion (C1) except that 0.5 part by mass was used. A liquid (M1) was obtained.

<Preparation of colorant dispersion (Y1)>
Instead of cyan pigment, C.I. I. A colorant dispersion (Y1) was obtained in the same manner as in the preparation of the colorant dispersion (C1) except that Pigment Yellow 17 was used.

<Preparation of white pigment dispersion (W1)>
-Titanium oxide (A-220 manufactured by Ishihara Sangyo): 99.5 parts by mass-Carbon black (Ketjen Black ECP manufactured by Lion Specialty Chemicals): 0.5 parts by mass-Anionic surfactant (Daiichi Kogyo Seiyaku Co., Ltd .: Neogen RK): 15 parts by mass Ion exchange water: 400 parts by mass 0.3 mol / l nitric acid: 4 parts by mass The above is mixed and dissolved, and a high-pressure impact disperser Ultimateizer (manufactured by Sugino Machine Co., Ltd.) HJP30006) was used for 3 hours to prepare a white pigment dispersion (W1) in which titanium oxide was dispersed.

<Preparation of white pigment dispersion (W2)>
A white pigment dispersion (W2) was obtained in the same manner as the preparation of the white pigment dispersion (W1) except that carbon black was not added and the titanium oxide was changed to 100 parts by mass.

<Preparation of polyester resin / curing agent composite dispersion (E1)>
While maintaining a jacketed 3 liter reaction tank (manufactured by Tokyo Rika Kikai Co., Ltd .: BJ-30N) equipped with a condenser, a thermometer, a water dropping device, and an anchor wing at 40 ° C. in a water circulation thermostat, the reaction tank Into this, a mixed solvent of 180 parts by mass of ethyl acetate and 80 parts by mass of isopropyl alcohol was added, and the following composition was added thereto.
Polyester resin (PES1) [terephthalic acid / ethylene glycol / neopentyl glycol / trimethylolpropane polycondensate (molar ratio = 100/60/38/2 (mol%), glass transition temperature = 62 ° C., acid value ( Av) = 12 mgKOH / g, hydroxyl value (OHv) = 55 mgKOH / g, weight average molecular weight (Mw) = 12,000, number average molecular weight (Mn) = 4,000]: 240 parts by mass Blocked isocyanate curing agent VESTAGONB 1530 ( EVONIK Co.): 60 parts by mass Benzoin: 1.5 parts by mass Acrylic oligomer (Acronal 4F BASF): 3 parts by mass

After the addition, the mixture was stirred at 150 rpm using a three-one motor and dissolved to obtain an oil phase. A mixture of 1 part by mass of a 10% by mass aqueous ammonia solution and 47 parts by mass of a 5% by mass aqueous sodium hydroxide solution was added dropwise to the stirred oil phase in 5 minutes, followed by mixing for 10 minutes, and further ion exchange. 900 parts by mass of water was added dropwise at a rate of 5 parts by mass to invert the phase to obtain an emulsion.
Immediately, 800 parts by mass of the obtained emulsion and 700 parts by mass of ion-exchanged water were placed in a 2-liter eggplant flask, and placed in an evaporator (manufactured by Tokyo Rika Kikai Co., Ltd.) equipped with a vacuum control unit via a trap ball. I set it. While rotating the eggplant flask, the mixture was heated in a hot water bath at 60 ° C., and the solvent was removed by reducing the pressure to 7 kPa while paying attention to bumping. When the solvent recovery amount reached 1100 parts by mass, the pressure was returned to normal pressure, and the eggplant flask was cooled with water to obtain a dispersion. There was no solvent odor in the obtained dispersion. The volume average particle diameter of the resin particles in this dispersion was 145 nm. Then, 2% by mass of an anionic surfactant (Dow Chemical, Dowfax 2A1, effective component amount 45% by mass) is added and mixed as an active component with respect to the resin component in the dispersion. The concentration was adjusted to 25% by mass. This was designated as a polyester resin / curing agent composite dispersion (E1).

<Preparation of blue powder particles (C)>
-Aggregation process-
Polyester resin / curing agent composite dispersion (E1): 180 parts by mass (solid content 45 parts by mass)
White pigment dispersion (W2): 160 parts by mass (solid content 40 parts by mass)
Colorant dispersion (C1): 8 parts by mass (solid content 2 parts by mass)
-Ion-exchanged water: 200 parts by mass The above was mixed and dispersed in a round stainless steel flask using a homogenizer (manufactured by IKA, Ultra Turrax T50). Subsequently, pH was adjusted to 3.5 using 1.0 mass% nitric acid aqueous solution. To this, 0.50 part by mass of a 10% by mass aqueous polyaluminum chloride solution was added, and the dispersion operation was continued with an ultra turrax.
A stirrer and a mantle heater were installed, and the temperature was raised to 50 ° C. while adjusting the number of revolutions of the agitation so that the slurry was sufficiently stirred. After holding at 50 ° C. for 15 minutes, the Coulter Counter [TA-II] type (Aperture diameter: 50 μm, manufactured by Beckman-Coulter) The particle size of the aggregated particles was measured, and when the volume average particle size became 5.5 μm, the polyester resin / curing agent composite dispersion (E1) 60 was used as the shell. The mass part was slowly charged. (Shell input).

-Fusion integration process-
After holding for 30 minutes, the pH was adjusted to 7.0 using a 5% aqueous sodium hydroxide solution. Then, it heated up to 85 degreeC and hold | maintained for 2 hours.

-Filtration, washing, drying process-
After completion of the reaction, the solution in the flask was cooled and filtered to obtain a solid content. Next, this solid content was washed with ion-exchanged water and then solid-liquid separated by Nutsche suction filtration to obtain a solid content again.
Next, this solid content was redispersed in 3 liters of ion-exchanged water at 40 ° C., and stirred and washed at 300 rpm for 15 minutes. This washing operation was repeated 5 times, and the solid content obtained by solid-liquid separation by Nutsche suction filtration was vacuum dried for 12 hours to obtain blue powder particles (C).
The relative dielectric constant of the blue powder particles (C) was measured to be 3.3.

<Preparation of red powder particles (M)>
The colorant dispersion liquid (M1) was used instead of the colorant dispersion liquid (C1), the white pigment dispersion liquid (W1) was 140 parts by mass, and the polyester resin / curing agent composite dispersion liquid (E1) was 200 parts by mass. Produced red powder particles (M) in the same manner as the production of blue powder particles (C).
The relative dielectric constant of the red powder particles (M) was measured and found to be 10.1.

<Preparation of yellow powder particles (Y)>
A colorant dispersion (M1) was used in place of the colorant dispersion (C1), the white pigment dispersion (W2) was 120 parts by mass, and the polyester resin / curing agent composite dispersion (E1) was 220 parts by mass. Produced yellow powder particles (Y) in the same manner as the production of blue powder particles (C).
It was 2.5 when the dielectric constant of this yellow powder particle (Y) was measured.

<Preparation of white powder particles (W1)>
A white powder was produced in the same manner as the production of the blue powder particles (C), except that the white pigment dispersion (W1) was used instead of the white pigment dispersion (W2) without adding the colorant dispersion (C1). Particles (W1) were obtained.
The relative dielectric constant of the white powder particles (W1) was measured and found to be 11.8.

  Using the image forming apparatus 10 according to the present embodiment, a test was performed on a layer formed of powder particles on the recording medium MD.

FIG. 12 shows the test results regarding the layers formed on the recording medium MD using the image forming apparatus 10.
The test method is to measure the particle weight before and after the secondary transfer in the case where the particle layer that has been multiple-transferred six times on the intermediate transfer belt 32 is secondarily transferred onto the metal plate twice, and obtain the result. In this case, the amount of developed particles per one time is in the range of 1 to 6 g / m 2 for low dielectric constant particles, and is changed in the range of 1 to 4 g / m 2 for high dielectric constant particles or conductive particles, and is shown in FIG. An experiment was performed in which the voltage indicated by the weight-voltage characteristics during transfer according to the curve Lc was varied. FIG. 12 is a plot of points where the transfer weight obtained as a result of the experiment has a peak.

  In FIG. 12, the weight at the time of secondary transfer is shown with the particle weight per unit area after the secondary transfer as the weight after transfer on the vertical axis and the particle weight per unit area before the secondary transfer as the weight before transfer on the horizontal axis. The characteristics are shown. In FIG. 12, the characteristics when the particle layer composed of only the low dielectric constant particles is transferred to form on the recording medium MD are indicated by a one-dot chain line. Further, in FIG. 12, the characteristics when the particle layers of the high dielectric constant particles and the low dielectric constant particles are transferred so as to be alternately formed on the recording medium MD are indicated by dotted lines. Further, in FIG. 12, the solid line shows the characteristics when transferring to form each particle layer of conductive particles and low dielectric constant particles alternately on the recording medium MD as an example of the high dielectric constant particles.

  From FIG. 12, it can be seen that a thicker layer can be formed without discharging by alternately stacking particles of high dielectric constant and low dielectric constant.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various modifications or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such modifications or improvements are added are also included in the technical scope of the present invention.

  Although the image forming apparatus 10 according to the present embodiment performs color image formation, it is needless to say that the image forming apparatus 10 may perform monochrome image formation. Further, the secondary transfer roll 44 of the transfer device 7 according to the present embodiment is not limited to a single roller. For example, the secondary transfer roll 44, other rollers (not shown), and the secondary transfer roll It may be configured by a plurality of rollers and belts including the belt 44 and a belt stretched around the other rollers (not shown).

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image forming part 14 Heat fixing part 16 Carry-in part 18 Carry-out part 20 Developing unit 21 Photoconductor 22 Charger 23 Exposure part 24 Developer 30 Primary transfer device 32 Intermediate transfer belt 40 Secondary transfer device 42 Backup roll 44 Secondary transfer roll 50 Image formation controller 50X Computer MD Recording medium

Claims (6)

A first developing unit that develops the electrostatic latent image formed on the image carrier by the first powder particles;
A second developing unit for developing an electrostatic latent image formed on the image carrier with second powder particles having a dielectric constant higher than that of the first powder particles;
The first powder particle image developed by the first development unit is formed on the first powder particle image so as to form a laminated portion in which the second powder particle image developed by the second development unit is laminated. A first transfer unit that transfers the powder particle image and the second powder particle image to a transfer medium;
A second transfer portion that transfers the image transferred to the transfer medium to a recording medium;
An image forming apparatus. A plurality of the first developing units and the second developing units are provided, and the first transfer unit is configured such that the first powder particle images and the second powder particle images are alternately arranged. The image forming apparatus according to claim 1, wherein a plurality of the stacked portions are stacked. The image forming apparatus according to claim 1, wherein the first powder particle image and the second powder particle image are formed in a common predetermined image forming region. The image forming apparatus according to any one of claims 1 to 3, wherein the first powder particle image and the second powder particle image are formed in a predetermined image forming area of the recording medium. . The image forming apparatus according to claim 1, wherein the powder particles of the first developing unit and the powder particles of the second developing unit are powder particles of different colors. The image forming apparatus according to claim 1, wherein the recording medium is a metal.