JP2006235035A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device forming a high quality image. <P>SOLUTION: A droplet image W corresponding to an image signal is formed on a latent image carrier 61 with droplets. A latent image S corresponding to the image signal is formed on the latent image carrier 61 by the injection charging to the portion of the droplet image W on the latent image carrier 61 by a charge applier 63. That is, only at the position where the droplet image W intervenes at a nip NP, the injection charging to the latent image carrier 61 by the charge applier 63 is carried out, and the latent image S are formed on the latent image carrier 61. Thus, the latent image S which is of the same shape as the shape of the droplet image W corresponding to the image signal is formed on the latent image carrier 61, thereby stably carrying out formation of the electrostatic latent image on the latent image carrier 61. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms a latent image by injecting charges into a latent image carrier.

  Conventionally, in an image forming apparatus such as a laser beam printer, a copying machine, or a facsimile machine, a photosensitive member having a photoconductive layer is charged, and then a light beam corresponding to an image signal is irradiated to the photosensitive member to form a latent image. This is visualized with a developer. In order to improve image quality, for example, as described in Patent Document 1, a resin carrier prepared by a polymerization method is used as a development carrier for a small particle size toner, and an amorphous silicon drum is used as a photoreceptor. It has been proposed to use.

JP 2003-345054 A ([0002], [0008])

  However, in an image forming apparatus that forms a latent image using a light beam, the potential distribution of the latent image is a Gaussian distribution, and the spot diameter is generally about 60 to 80 μm. Therefore, even if the toner particle size is reduced, the latent image itself is large and broad (Gaussian distribution), so that there is a certain limit to improving the image quality.

  The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus capable of forming a high-quality image.

  The present invention is an image forming apparatus for forming a toner image corresponding to an image signal, and has a surface layer formed of a water-repellent resin and rotates around a predetermined rotation axis in order to achieve the above object. The latent image carrier and droplets are ejected in accordance with the image signal toward the surface of the latent image carrier, which is higher than the virtual horizontal plane including the rotation axis of the latent image carrier, and attached to the latent image carrier to cause the image signal A droplet ejecting head for forming a droplet image corresponding to the liquid crystal, and a nip by contacting the surface of the latent image carrier on which the droplet image is formed on the downstream side of the droplet image forming position in the rotation direction of the latent image carrier. A charge imparting member that forms a latent image, a charge imparting control unit that applies a charging bias to the charge imparting member and injects and charges the latent image carrier at the nip portion to form a latent image corresponding to the droplet image, and a latent image And developing means for developing the toner.

  In the invention configured as described above, droplets are jetted and attached to the latent image carrier in accordance with the image signal to form a droplet image corresponding to the image signal. In the nip portion, injection charging is executed by the charge applying member via the droplets on the latent image carrier, and a latent image corresponding to the image signal is formed on the latent image carrier. Thus, the present invention forms a latent image by a completely different method. That is, since a latent image is formed using droplets, a sharp latent image can be obtained unlike a latent image formation using a light beam. Moreover, since the surface layer of the latent image carrier is formed of a water-repellent resin, it is possible to prevent the droplets from spreading on the surface layer of the latent image carrier when the droplets adhere to the latent image carrier. And a sharp latent image can be reliably formed, and the image quality can be improved.

  Note that the latent image carrier rotates around a predetermined rotation axis, and droplets are ejected and adhered to the surface of the rotating latent image carrier, so that the droplet ejecting head causes the droplets to become latent images. Although the liquid is ejected toward the latent image carrier surface position higher than the virtual horizontal plane including the rotation axis of the carrier, in order to further improve the adhesion performance, the position of the liquid droplet ejection head and the direction of liquid droplet ejection It is desirable to devise. For example, the liquid droplet ejecting head may be arranged on a virtual vertical line passing through the rotation axis of the latent image carrier, and the liquid droplets may be ejected along the virtual vertical line.

Further, the liquid droplet ejecting head may be configured to adhere the liquid droplets to the surface position of the latent image carrier while satisfying the first and second arrangement conditions. Here, the “first arrangement condition” When the tangent vector at the surface position of the latent image carrier is parallel to the tangent at the surface position of the latent image carrier and is forward in the rotational movement direction, the tangent vector at the surface position of the latent image carrier is used as a base point. The arrangement condition is that the angle α formed around the rotational movement direction is 0 ° ≦ α <90 °, and the “second arrangement condition” is that the ejection direction of the droplets from the droplet ejection head is the latent image carrier. The arrangement condition is almost perpendicular to the tangent of the surface position.

Further, the liquid droplet ejecting head may be configured to cause the liquid droplets to adhere to the surface position of the latent image carrier while satisfying the third and fourth arrangement conditions. Here, the “third arrangement condition” When the tangent vector at the surface position of the latent image carrier is parallel to the tangent at the surface position of the latent image carrier and is forward in the rotational movement direction, the tangent vector at the surface position of the latent image carrier is used as a base point. The angle α formed around the rotational movement direction is 90 ° <α ≦ 180 °, and the “fourth arrangement condition” is the tangent vector with the tangent vector at the latent image carrier surface position as a base point. Is an arrangement condition in which the angle β formed between the ejection vector parallel to the ejection direction of the droplet from the droplet ejection head and the rotational movement direction is 0 ° <β <90 °.

<Effects of droplets at the nip>
One of the main constituent elements of the present invention is that a droplet image is formed by using a droplet, and a latent image carrier is injected and charged through the droplet image to form a latent image corresponding to the droplet image. Is a point. The technical significance of using droplets in this way will be described in detail based on the verification results, and then embodiments according to the present invention will be described.

  A technique for forming a latent image on a latent image carrier by injecting charges into the latent image carrier is well known in the art. The contact resistance varies depending on the contact state between the latent image carrier and the charging member or the writing member in the technology), which may greatly affect the formation accuracy of the latent image on the latent image carrier. In order to improve the charging efficiency of the latent image carrier when the latent image carrier is injected and charged at the nip portion between the latent image carrier and the charge applying member, the latent image carrier and the charge at the nip portion are improved. It shows that the contact state with the applying member is very important. Therefore, the inventor of this application intervened various substances in the nip portion, and verified whether or not improvement of the contact state between the latent image carrier and the charge imparting member was recognized by the interposition, such as ethanol. It has been found that the charging efficiency of the latent image carrier can be increased by performing injection charging with the droplet image interposed in the nip portion.

  In order to perform the above verification, when a charging roller (corresponding to the “charge imparting member” of the present invention) is brought into contact with the latent image carrier and the surface of the latent image carrier is injected and charged by the charging roller at the contact portion, the latent image is obtained. Various materials were interposed in the nip portion between the carrier and the charging roller, and the charging efficiency of the surface of the latent image carrier in each case was compared. At this time, injection charging is performed in a state where a substance is interposed in one part of the nip portion and no substance is interposed in the other part, and the charging efficiency of each part is compared.

  FIG. 1 is a graph showing the charging efficiency of the latent image carrier obtained by the above method. This figure shows the surface potential on the surface of the latent image carrier, with the horizontal axis representing time (S) and the vertical axis representing surface potential (V). As a substance interposed in the nip portion between the latent image carrier and the charging roller, ethanol which is a lower alcohol is used. The solid line in the figure shows the surface potential of one part where ethanol is interposed in the nip, and the broken line shows the surface potential of another part where ethanol is not interposed. At time 0, a charging bias set in advance so that the surface potential of the latent image carrier becomes a predetermined surface potential V0 by the charging roller is applied to the charging roller.

  As is apparent from FIG. 1, when a charging bias is applied to the charging roller, the surface position of the latent image carrier on which the droplet image is interposed is instantaneously injected and charged to a substantially set potential V0. However, the surface position of the latent image carrier in which the droplet image is not interposed has a lower charging efficiency than the surface position of the latent image carrier in which the droplet image is interposed, and is not charged by injection. Thus, from this verification result, by partially interposing a droplet of ethanol or the like in the nip portion, injection charging is performed at an arbitrary position on the surface of the latent image carrier, and an arbitrary surface is formed on the surface of the latent image carrier. The knowledge that a latent image having a shape can be formed was obtained.

  Therefore, the present embodiment forms a latent image on the latent image carrier using droplets based on these findings. Hereinafter, each embodiment will be described in detail with reference to the drawings.

<First Embodiment>
FIG. 2 is a diagram showing a first embodiment of an image forming apparatus according to the present invention. FIG. 3 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. The apparatus 1 includes a color printing process for forming a full-color image by superposing four color toners (developers) of black (K), cyan (C), magenta (M), and yellow (Y), and black (K ) To selectively execute a monochrome printing process for forming a monochrome image using only toner. In this image forming apparatus 1, when an image forming command (printing command) is given to the main controller 3 from an external device such as a host computer, the engine controller 4 causes the engine unit EG to operate in response to a command from the CPU 31 of the main controller 3. Are controlled to execute a predetermined image forming operation, and an image corresponding to the image forming command is formed on a sheet (recording material) SH such as plain paper, thick paper, and an OHP transparent sheet.

  In the image forming apparatus 1 of the present embodiment, as shown in FIG. 2, an electrical component box (illustrated) in which a power source circuit board, a main controller 3 (FIG. 3), and an engine controller 4 (FIG. 3) are built in a housing body 2. (Omitted) is provided. An image forming unit 6, a transfer fixing unit 7, and a paper feeding unit 8 are also disposed in the housing body 2.

  Among these constituent units, the transfer fixing unit 7 is stretched between two rollers 71 and 72 arranged substantially horizontally, and between the two rollers 71 and 72, and can be circulated and moved in the direction indicated by an arrow D73. The intermediate transfer belt 73 is provided. Then, one of the rollers 71 and 72 is rotationally driven as a driving roller by a driving force from a driving motor (not shown), whereby the intermediate transfer belt 73 is rotationally driven in the direction D73. Further, a heating element 74 such as a halogen heater is built in the roller 71. Then, the transfer / fixing control unit 42 is operated in accordance with a command from the CPU 41 of the engine controller 4, and the heating element 74 is controlled to be controlled to an optimum fixing temperature. Thus, the roller 71 functions as a heating roller. On the other hand, a pressure roller 75 is disposed opposite to the heating roller 71 to press and urge the heating roller 71. As described above, in this embodiment, an image formed as described later by the two rollers 71 and 75 is transferred and fixed to the sheet SH conveyed by the paper feeding unit 8.

  The transfer fixing unit 7 includes a primary transfer roller 76 disposed to face the latent image carrier 61 of the image forming stations Y, M, and C of yellow (Y), magenta (M), and cyan (C). Approaches the drum-like latent image carrier 61 and moves away from the latent image carrier 61. Therefore, when the primary transfer rollers 21 for yellow, magenta, and cyan move close to the latent image carrier 61, they come into contact with the latent image carrier 61 with the intermediate transfer belt 73 interposed therebetween (solid line in FIG. 2). ). This contact position is the primary transfer position, and the toner image is transferred to the intermediate transfer belt 73 at the primary transfer position. Conversely, when color printing is not performed, the primary transfer rollers 76 for yellow, magenta, and cyan move away from the latent image carrier 61 (broken line in FIG. 2). On the other hand, the primary transfer roller 76 disposed facing the latent image carrier 61 of the black (K) image forming station K is in contact with the latent image carrier 61 with the intermediate transfer belt 73 interposed therebetween. It is configured to rotate as it is. Therefore, as shown by the solid line in FIG. 2, the color printing process can be executed by positioning all the primary transfer rollers 76 on the latent image carrier 61 side. On the other hand, as shown by the broken line in the figure, intermediate transfer is performed while only the monochrome printing process is performed by leaving the primary transfer roller 76 for black and separating the other primary transfer roller 76 from the latent image carrier 61. The belt 73 is separated from the image forming stations Y, M, and C, and the yellow, magenta, and cyan colors can be in a non-printing state. The black primary transfer roller 76 may also be configured to move away from the latent image carrier 61 as necessary.

  The image forming unit 6 includes image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality (four in this embodiment) of different color images. I have. These image forming stations Y, M, C, and K are arranged in this order along the rotational movement direction D73 of the intermediate transfer belt 73, as shown in FIG. Further, in each of the image forming stations Y, M, C, and K, as shown in FIGS. 4 and 5, a latent image carrier 61 is provided so as to be rotatable around the rotation axis AX in the rotation direction D61. In this embodiment, the surface layer 611 is formed of a water-repellent resin so that the surface of the latent image carrier 61 has water repellency. Here, the water-repellent resin is preferably a fluororesin, for example, tetrafluoroethylene resin (polytetrafluoroethylene), polytrifluorochloroethylene, etc., in addition, vinyl fluoride, ethylene trifluoride, vinylidene fluoride. -Polymers and copolymers such as propylene hexafluoride and dichlorodifluoroethylene can be used.

  Further, around each latent image carrier 61, a droplet jet head 62, a charge applying unit 63, a developing unit 64, a charge eliminating unit 65, and a cleaner unit 66 are disposed. Then, a droplet image forming operation, a charge applying operation (latent image forming operation), a developing operation, a charge eliminating operation, and a cleaning operation are executed by these functional units. The order of arrangement of the image forming stations Y, M, C, and K is arbitrary.

  The latent image carriers 61 of the image forming stations Y, M, C, and K are disposed so as to contact the upward belt surface of the intermediate transfer belt 73 at the primary transfer position TR1. Each of these latent image carriers 61 is connected to a dedicated drive motor, and is driven to rotate at a predetermined peripheral speed in the conveyance direction of the intermediate transfer belt 73 as shown by an arrow D61 in the drawing.

  The liquid droplet ejecting head 62 is disposed above the latent image carrier 61 and on a virtual vertical line VL passing through the rotation axis AX with the front end directed to the latent image carrier 61. Further, the length of the droplet ejecting head 62 in the major axis direction (direction parallel to the rotation axis AX) is substantially the same as the length of the latent image carrier 61 in the axial direction, The distal end portion is provided with a plurality of ejection ports 621 for ejecting predetermined droplets, and these ejection ports 621 are arranged in a state of being arranged in the direction of the rotation axis AX of the latent image carrier 61. Further, as shown in FIG. 2, the droplet ejecting head 62 is connected to a liquid storage tank 672 for storing a liquid such as pure water or ethanol constituting the droplet by a pipe 671. For this reason, the head controller 43 operates in response to the image signal included in the image formation command in response to the command from the CPU 41, thereby causing the latent image along the virtual vertical line VL from the tip ejection port 621 of the droplet ejection head 62. A droplet WL is ejected toward the surface of the image carrier 61 to form a droplet image W corresponding to the image signal. For example, when droplets are ejected from all the ejection ports 621, one line-shaped droplet image is formed on the surface of the latent image carrier 61 at the droplet image forming position 622. As the droplet WL discharged from the droplet ejection head 62 to the latent image carrier 61, pure water can be used. For example, volatile lower alcohol such as ethanol, methanol, isopropyl alcohol or the like is used. May be. In the present embodiment, the droplet image W is formed using ethanol as a droplet based on the above experimental results.

  In the rotation direction D61 of the latent image carrier 61, a charge imparting portion 63 constituted by a charging roller or the like downstream of the droplet image forming position 622 rotates in a direction D63 that follows the rotation direction D61 of the latent image carrier 61. Arranged freely. The charge imparting portion 63 is in contact with the latent image carrier 61 to form a nip portion NP. In addition, a charge application control unit 44 is electrically connected to the charge application unit 63, and when a predetermined bias is applied to the charge application unit 63, the latent image carrier 61 is charged in the nip part NP. A droplet position is selectively charged by injection charging by the applying unit 63, and a latent image S (FIG. 4) corresponding to the image signal is formed on the surface layer 611 of the latent image carrier 61.

  The latent image S formed in this way is visualized by the toner supplied from the developing roller 641 of the developing unit 64 (developing process). That is, the toner is attached from the developing roller 641 to the latent image position by the developing bias applied from the developing control unit 45 to the developing roller 641 to form a toner image. In this embodiment, as shown in FIG. 2, the developing unit 64 includes an internal tank 642 and a supply roller 643 for temporarily storing toner in addition to the developing roller 641. In addition, a toner storage tank 68 for storing toner is connected to the internal tank 642 so that the toner can be replenished to the internal tank 642 at an appropriate timing.

  The toner image thus formed is transferred onto the surface of the intermediate transfer belt 73 at the primary transfer position TR1. Further, in this embodiment, a neutralization unit 65 for neutralizing the surface of the latent image carrier 61 is provided on the downstream side of the primary transfer position in the rotation direction D61 of the latent image carrier 61. The surface of the latent image carrier 61 is neutralized by driving control. In addition, a cleaner unit 66 is provided so as to contact the latent image carrier 61 on the downstream side of the static eliminating unit 65. The cleaner 66 abuts on the surface of the latent image carrier 61 to remove the toner remaining on the surface of the latent image carrier 61 after the primary transfer.

  The sheet feeding unit 8 includes a sheet feeding unit including a sheet feeding cassette 81 in which sheets SH are stacked and held, and a pickup roller 82 that feeds the sheet SH from the sheet feeding cassette 81 one by one. Then, the sheet SH taken out from the paper feed cassette 81 by the pickup roller 82 is sent to the secondary transfer position TR2 through a pair of registration rollers (not shown), and the image formed on the intermediate transfer belt 73 is transferred and fixed. The Further, the sheet SH thus subjected to the transfer and fixing process is conveyed to a paper discharge tray 9 provided on the upper surface portion of the housing body 2 via a paper discharge roller pair 83.

  In FIG. 3, reference numeral 33 denotes an image memory provided in the main controller 3 for storing an image given from an external device such as a host computer via the interface 32. Reference numeral 48 denotes a memory for storing a calculation program executed by the CPU 41, control data for controlling the engine unit EG, and the like, and temporarily storing calculation results in the CPU 41 and other data.

  Next, the process of forming the toner image T on the latent image carrier 11 will be described in detail with reference to FIG. FIG. 6 is a schematic diagram showing steps until the toner image T is formed on the latent image carrier 61 in the present embodiment.

(1) Droplet image forming step (FIG. 6A)
A droplet is ejected toward the surface of the latent image carrier 61 from the ejection port 621 selected from the plurality of ejection ports 621 according to the control signal from the head control unit 43. Then, a droplet image W corresponding to the image signal is formed on the latent image carrier 61 at the droplet image forming position 622. The droplet ejection head 62 is fixed vertically above the latent image carrier 61 at the droplet image forming position 622, but the latent image carrier 61 rotates in the arrow direction D61. Therefore, by controlling the droplet ejection timing of the plurality of ejection ports 621 according to the image signal, a droplet image W corresponding to the image signal can be formed on the latent image carrier 61 (FIG. 6 ( a) See plan view).

(2) Latent image forming step (FIG. 6B)
The droplet image W formed in the droplet image forming step is conveyed to the nip portion NP formed by the latent image carrier 61 and the charge applying unit 63 as the latent image carrier 61 rotates. Then, by applying a predetermined bias from the charge application control unit 44 to the charge application unit 63, injection charging is selectively performed at the position of the droplet image W on the latent image carrier 61 at the nip NP. The By performing injection charging in this way, a latent image S corresponding to the image signal is formed on the surface of the latent image carrier 61 (see a plan view in FIG. 6B). In addition, the effect of the droplet WL intervening in the nip portion NP is based on the above experimental result.

  Further, volatile ethanol is used as a droplet for forming the droplet image W. Therefore, after the injection charging is performed to the position of the droplet image W on the surface of the latent image carrier 61 at the nip portion NP to form the latent image S, the formed latent image S is rotated by the latent image carrier 61. Accordingly, the droplet image W is volatilized in the process of being conveyed to the next development process position.

(3) Development process (FIG. 6C)
The latent image S formed in the latent image forming step is conveyed to a developing position (position where the latent image carrier 61 and the developing roller 641 face each other) as the latent image carrier 61 rotates. At this time, as described above, the droplet image W is volatilized and removed from the surface of the latent image carrier 61 in the process of transporting the latent image S to the development position. Then, at the development position, toner is applied from the developing roller 641 to the latent image carrier 61 to develop the latent image S, and a toner image T corresponding to the image signal is formed on the surface of the latent image carrier 61. (See the plan view of FIG. 6C).

  As described above, according to the present embodiment, the droplet image W corresponding to the image signal is formed on the latent image carrier 61 by the droplet. The latent image S corresponding to the image signal is formed on the latent image carrier 61 by injecting and charging the droplet image W on the latent image carrier 61 by the charge applying unit 63. That is, in the nip portion NP, injection charging from the charge applying unit 63 to the latent image carrier 61 is performed only at a position where the droplet image W is interposed, and a latent image S is formed on the latent image carrier 61. Therefore, a latent image S having the same shape as the droplet image W corresponding to the image signal is formed on the latent image carrier 61. Therefore, it is possible to stably form the electrostatic latent image on the latent image carrier 61. As described above, when the charging is performed by the charge applying unit 63 via the droplet image W on the latent image carrier 61, the injection charging efficiency is significantly improved and stable compared to the case where the latent image carrier 61 is not via the droplet image W. The injection charging is performed as described above in the section “Effects of Droplet Intervention at the Nip Portion”. Further, since the latent image S thus formed is developed to obtain the toner image T, a good toner image T can be obtained.

  Further, since the latent image S is formed using the droplets WL, a sharp latent image can be obtained unlike the latent image formation using the light beam. For example, when an ink jet head is employed as the droplet ejecting head 62, the droplet volume can be set to about 2 picoliters. In this case, the droplet diameter is about 15 μm, and a high-definition latent image can be formed as compared with the light beam exposure method in which the spot diameter is about 60 to 80 μm. In addition, in this embodiment, since the surface layer 611 of the latent image carrier 61 is formed of a water-repellent resin, when the droplets adhere to the latent image carrier 61, the droplets become the surface of the latent image carrier 61. Spreading in the layer 611 can be prevented, a sharp latent image can be reliably formed, and image quality can be improved.

  In this embodiment, the droplet image W is formed using volatile ethanol as the droplet WL. Therefore, after the droplet image W is present in the nip NP, the latent image S is formed on the latent image carrier 61 by the charge applying unit 63 in the nip NP, and then the latent image S is the latent image carrier. The droplet image W, which is ethanol, volatilizes from the surface of the latent image carrier 61 in the process of moving away from the nip portion NP with the rotation of 61. Therefore, it is not necessary to take any means for removing the droplet image W from the surface of the latent image carrier 61. Further, since the droplet image W is formed of ethanol, which is a lower alcohol, the surface of the latent image carrier 61 can be kept more clean by the cleaning effect.

Second Embodiment
FIG. 7 is a view showing a second embodiment of the image forming apparatus according to the present invention. The second embodiment is greatly different from the first embodiment in the arrangement position of the droplet ejecting head 62. Here, in order to clarify the disposition position of the droplet ejecting head 62 with respect to the latent image carrier 61, a virtual horizontal line passing through the rotation axis AX of the latent image carrier 61 is shown in FIG. HL and virtual vertical line VL are described, and four quadrants [I] to [IV] are provided. In the second embodiment, the droplet ejecting head 62 is located in the first quadrant [I] with respect to the latent image carrier 61.

  Here, the stress acting on the droplet WL ejected from the droplet ejecting head 62 and attached to the latent image carrier 61 will be examined. A stress Fg that tries to slide down the surface of the latent image carrier 61 by gravity acts on the droplet WL. On the other hand, when the droplet ejecting head 62 is arranged as described above, it is parallel to the tangent line TG at the surface position of the latent image carrier 61 and is forward in the rotational movement direction D61 of the latent image carrier 61. When the object is a tangent vector Vt, an angle α formed by the tangent vector Vt around the gravity vector Vg and the rotational movement direction D61 with respect to the tangent vector Vt at the latent image carrier surface position is an acute angle. When the droplet ejection direction D62 from the droplet ejection head 62 is substantially perpendicular to the tangent line TG of the latent image carrier surface position, the droplet WL thus adhered to the surface of the latent image carrier 61 Stress Ft acts in the direction opposite to the rotational movement direction D61 of the latent image carrier 61. Accordingly, the forward stress Fg and the reverse stress Ft in the rotational movement direction D61 act against each other in the rotational movement direction D61, and the movement of the droplet WL on the surface of the latent image carrier is suppressed. can do.

As described above, in the second embodiment, the droplet ejecting head 62 is disposed on the latent image carrier 61 so that the following two disposition conditions (1) and (2) are satisfied. ing:
Arrangement condition (1): “first arrangement condition” of the present invention
The droplet ejecting head 62 is positioned in the first quadrant [I] with respect to the latent image carrier 61. In other words, the tangent vector Vt based on the tangent vector Vt at the surface position of the latent image carrier is the gravity vector Vg. The angle α formed around the rotational movement direction D61 is 0 ° ≦ α <90 °;
Arrangement condition (2): “second arrangement condition” of the present invention
The droplet ejection direction D62 from the droplet ejection head 62 is substantially orthogonal to the tangent to the latent image carrier surface position.
For this reason, the two stresses Fg and Ft acting on the droplet WL cancel each other, and the movement of the droplet WL attached to the surface of the latent image carrier 61 is suppressed, and the droplet image W is accurately formed. As a result, an image corresponding to the image signal can be formed accurately and with high accuracy. In particular, when the surface layer 611 of the latent image carrier 61 is formed of a water-repellent resin, if the stress balance with respect to the droplet WL on the surface layer 611 is lost, the droplet WL easily deviates from the attachment position, and the droplet WL It is very important to control the stress acting on the surface.

<Third Embodiment>
In the second embodiment, the droplet ejecting head 62 is disposed in the first quadrant [I] with respect to the latent image carrier 61. However, as shown in FIG. ], That is,
Arrangement condition (3): “third arrangement condition” of the present invention
The angle α formed by the tangent vector Vt around the gravitational vector Vg and the rotational movement direction D61 with respect to the tangent vector Vt at the surface position of the latent image carrier is set to satisfy 90 ° <α ≦ 180 °. May be. However, in this case, two stresses Ft and Fg act on the droplet WL attached to the surface of the latent image carrier 61 in the direction opposite to the rotational movement direction D61 of the latent image carrier 61. . Therefore, in the third embodiment, in order to eliminate or alleviate the influence due to the stress (Ft, Fg) in the direction opposite to the rotational movement direction D61,
Arrangement condition (4): “fourth arrangement condition” of the present invention
Using the tangent vector Vt at the latent image carrier surface position as a base point, the angle β formed by the tangent vector Vt around the ejection vector Vi parallel to the ejection direction D62 of the droplet from the droplet ejection head 62 and the rotational movement direction D61 is 0. It is constructed so as to satisfy that ≦ <β <90 °.

  In the image forming apparatus configured in this way, as shown in FIG. 5B, the ejection direction D62 is ejected with the perpendicular to the surface of the latent image carrier inclined in the direction opposite to the rotational movement direction D61. The rotational movement direction D61 and the forward stress Fi are acting on the droplet WL. The stress Fi reduces the stress (Ft, Fg) in the direction opposite to the rotational movement direction D61, and the same effect as in the second embodiment, that is, the movement of the droplet WL attached to the surface of the latent image carrier 61. Therefore, the droplet image W can be accurately formed, and as a result, an image corresponding to the image signal can be formed accurately and with high accuracy.

<Others>
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the surface layer 611 of the latent image carrier 61 is formed of a water repellent resin, but the surface layer of the charge imparting portion 63 may also be formed of a water repellent resin. With this configuration, it is possible to prevent droplets from adhering to the charge applying unit 63 and to stably perform charge application.

  In the above embodiment, the present invention is applied to a color image forming apparatus. However, the application target of the present invention is not limited to this, and the present invention is applied to an image forming apparatus that performs monochromatic image formation. Can also be applied.

The schematic diagram which shows the charging efficiency of a latent image carrier. 1 is a diagram illustrating a first embodiment of an image forming apparatus according to the present invention. FIG. 3 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 2. FIG. 3 is an enlarged view of a main part of the image forming apparatus in FIG. 2. FIG. 3 is an enlarged view of a main part of the image forming apparatus in FIG. 2. FIG. 5 is a schematic diagram showing a process until a toner image is formed on a latent image carrier. The principal part enlarged view of 2nd Embodiment of the image forming apparatus concerning this invention. The principal part enlarged view of 3rd Embodiment of the image forming apparatus concerning this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 44 ... Charge application control part, 61 ... Latent image carrier, 62 ... Droplet ejecting head, 63 ... Charge application part, 64 ... Developing part (developing means), 611 ... (Latent image carrier of ) Surface layer, 622 ... Droplet image forming position, AX ... Rotating axis of (latent image carrier), D61 ... (Rotating direction of latent image carrier), D62 ... Ejecting direction, HL ... Virtual horizon, NP ... Nip Part, S ... latent image, T ... toner image, TG ... tangent, Vg ... gravity vector, Vi ... jet vector, Vt ... tangential vector, VL ... virtual vertical line, W ... droplet image, WL ... droplet

Claims (4)

In an image forming apparatus that forms a toner image corresponding to an image signal,
A latent image carrier having a surface layer formed of a water repellent resin and rotating about a predetermined rotation axis;
A droplet is ejected according to the image signal toward the surface position of the latent image carrier that is higher than the virtual horizontal plane including the rotation axis of the latent image carrier, and is attached to the latent image carrier to form the image signal. A droplet ejection head for forming a corresponding droplet image;
A charge imparting member which forms a nip portion in contact with the surface of the latent image carrier on which the droplet image is formed, on the downstream side of a droplet image formation position in the rotation direction of the latent image carrier;
Charge applying control means for applying a charging bias to the charge applying member to inject and charge the latent image carrier in the nip portion to form a latent image corresponding to the droplet image;
An image forming apparatus comprising: developing means for developing the latent image.   The image forming apparatus according to claim 1, wherein the liquid droplet ejecting head is disposed on a virtual vertical line passing through a rotation axis of the latent image carrier, and ejects liquid droplets along the virtual vertical line. The image forming apparatus according to claim 1, wherein the liquid droplet ejecting head adheres liquid droplets to a surface position of the latent image carrier while satisfying the following first and second arrangement conditions.
The first arrangement condition is that a tangent vector at the surface position of the latent image carrier is defined as a base point when a tangential vector that is parallel to the tangent line at the surface position of the latent image carrier and is forward in the rotational movement direction is a tangent vector. As a result, the angle α between the tangent vector and the gravity vector around the rotational movement direction is 0 ° ≦ α <90 °.
In the second arrangement condition, the ejection direction of the droplets from the droplet ejection head is substantially orthogonal to the tangent to the surface position of the latent image carrier. The image forming apparatus according to claim 1, wherein the liquid droplet ejecting head adheres liquid droplets to a surface position of the latent image carrier while satisfying the following third and fourth arrangement conditions.
The third arrangement condition is that the tangent vector at the surface position of the latent image carrier is a base point when the tangent vector is parallel to the tangent at the surface position of the latent image carrier and is forward in the rotational movement direction. The angle α formed by the tangent vector and the gravity vector around the rotational movement direction is 90 ° <α ≦ 180 °.
The fourth arrangement condition is that an angle formed by the tangent vector at the surface of the latent image carrier surface as a base point and the rotation vector in the direction of rotation and the ejection vector parallel to the direction of ejection of the droplet from the droplet ejection head β becomes 0 ° <β <90 °.

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