JP2007293177A - Image forming apparatus and liquid developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and a liquid developing device that can suppress toner image disorder during developing nip passage and obtain excellent image with respect to fogging and image unevenness even when employing a liquid development system which develops a latent image on an image carrier by rotating a developer carrier carrying and conveying a thin film of a liquid developer of high concentration so that the image carrier and the surface move in the same direction. <P>SOLUTION: A carrier liquid amount control member is disposed downstream from a developing nip part in a developer conveying direction, and a stagnation part of the liquid developer of low toner concentration is formed before the liquid developer carried out of the developing nip part is parted to the surface of the image carrier and the surface of the developer carrier to put the parting surface for the liquid developer away from a toner image on the image carrier, thereby suppressing toner image disorder during developing nip passage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and a liquid developing apparatus that form a thin layer of a developer using a liquid developer and develop a latent image on an image carrier.

  An electrophotographic image forming apparatus that forms an electrostatic latent image on a photoconductor (photosensitive drum), attaches toner to the photoconductor, and transfers and fixes the image onto paper or the like is a copying machine, an MFP (multifunctional printer), Widely used in FAX, printers, etc. The developing system generally used in these image forming apparatuses is dry development using powder toner.

  However, the powder toner has a problem that the toner is scattered, and also has a problem in image quality that the resolution is poor because the toner particles are as large as 7 to 10 μm.

  Therefore, in image forming apparatuses that require higher image quality and higher resolution, such as office printers for mass printing and on-demand printing apparatuses, liquid toners in which toner is dispersed in a nonpolar organic solvent such as liquid paraffin A wet development system that uses the above has been used. This is because the liquid toner has toner particles as small as about 1 μm and a large charge amount, so that the toner image is hardly disturbed and high resolution can be realized.

  In a conventional wet image forming apparatus, a low-viscosity liquid developer obtained by mixing toner in an organic solvent at a ratio of 1 to 2% is used as a wet developer (hereinafter also referred to as a liquid developer or simply a developer). It was. However, since such a developer has a low toner concentration, it needs to be deposited in large amounts on paper and dried at the time of fixing, and has a large environmental problem in that a large amount of steam is generated. Further, only a low boiling point carrier liquid can be used for volatilization, and there is a big problem in safety such as a low flash point.

  Against this backdrop, high viscosity and high concentration, which is constituted by dispersing toner as solid content consisting of resin and pigment in high concentration in insulating liquid “carrier liquid” such as silicone oil. An image forming apparatus using a liquid developer has been proposed. When this liquid developer is used, there are advantages that the above-described problems do not occur and the toner concentration is high, so that it is not necessary to use a large amount of developer.

  When developing with this liquid developer, the charged toner moves in the insulating liquid by the electrostatic force to develop the electrostatic latent image. Accordingly, the development efficiency is improved as the moving distance is shorter. For this purpose, it is desirable to form a thin layer of a micron unit of developer on a developer carrying member such as a developing roller, and to develop the thinned developer in contact with the photoreceptor. This is particularly remarkable when a high viscosity liquid developer of 100 mPa · s or more is used.

  Thus, when developing with a thin layer of liquid developer, the image density after development is determined by the amount of toner in the thin layer in the development area, so that a constant density is required to stabilize the image density. Forming a uniform thin layer with a developer is an important issue.

  However, when a thin layer of liquid developer is formed and developed, the liquid developer itself has a high concentration, and thus has a high viscosity, and toner movement in the liquid developer thin layer is slow.

  If the thickness of the thin layer is made thinner in order to increase the development efficiency, it is necessary to increase the density for securing the image density. As a result, the interaction between the toners also increases, which eventually leads to a decrease in toner moving speed.

  Further, when the moving speed of the toner is reduced, there is a problem that the toner adheres to the non-image portion, or the toner is not able to move in the image portion and image unevenness occurs.

  In order to solve these problems, a technique of using the effect of an electric field or performing two-stage development has been proposed (see Patent Documents 1, 2, and 3).

  In Patent Document 1, a blank pulse in which an AC voltage waveform and a DC voltage waveform are superimposed is applied during development, and the developer is minutely vibrated with a high-frequency AC electric field to develop a DC electric field from a state in which electric field reactivity is enhanced. Technology has been proposed. This is to compensate for a decrease in toner moving speed.

  In Japanese Patent Application Laid-Open No. 2004-260688, most of the toner is moved onto the image carrier by the first developer carrier, and then the toner adhering to the background on the image carrier, that is, the fog toner is collected by the second developer carrier. It proposes technology for step development. As a result, development without fogging is performed while increasing development efficiency.

In Patent Document 3, a technique similar to that described in Patent Document 2 is applied, but a strong electric field is applied to further ensure toner movement during the first development.
JP 2005-91718 A JP 2001-305866 A JP 2001-356606 A

  Although the techniques described in Patent Documents 1, 2, and 3 all have a certain effect on the occurrence of fog and density unevenness related to the difficulty in moving the toner in the thin layer of the high-concentration liquid developer, It does not wipe out all the adverse effects on the image generated in the development by the density developer thin layer.

  For example, in the development method in which the developer carrying body and the image carrying body are rotated and developed so that the surfaces move in the same direction, the developer thin layer is formed on the exit side where the developer thin layer is carried out from the development nip. When dividing into the carrier side and the developer carrier side, the toner image on the image carrier developed at the development nip may be disturbed. At this time, there is a problem that the higher the developer concentration is, the closer the divided surface is to the surface of the toner layer on the image carrier, and the greater the disturbance of the toner image.

  The object of the present invention is to solve the above-mentioned problems and rotate the developer carrying member carrying and transporting a thin layer of a high-concentration liquid developer so that the image carrier and the surface move in the same direction. Also in the liquid development method for developing the latent image on the carrier, an image forming apparatus capable of suppressing the occurrence of toner image disturbance when passing through the development nip and obtaining a good image with respect to fog and image unevenness A liquid developing device is provided.

  In order to solve the above problems, the present invention has the following features.

  1. An image carrier that forms a latent image on the surface; and a developer carrier that is opposed to the image carrier and carries a thin layer of a liquid developer containing toner and carrier liquid on the surface. The image carrier that moves in the same direction as the transport direction of the liquid developer by using the liquid developer carried and transported by the developer carrier in a development nip portion where the carrier and the developer carrier face each other In the image forming apparatus that develops the latent image on the surface of the toner and forms a toner image, the liquid developer that is disposed downstream of the developing nip portion in the developer conveying direction and is carried out of the developing nip portion An image forming apparatus comprising: a carrier liquid amount control member for forming a stay portion of the liquid developer before being separated from the surface of the image carrier and the surface of the developer carrier.

  2. 2. The image forming apparatus according to 1, wherein the carrier liquid amount control member is a blade facing the image carrier and the developer carrier.

  3. The carrier liquid amount control member is a roller facing the image carrier and the developer carrier, and the moving direction of the surface is the same as the moving direction of the surface of the opposing developer carrier. 2. The image forming apparatus as described in 1 above.

  4). The developer carrying member and the carrier liquid amount control member are disposed on the downstream side in the developer transport direction at a nip portion where the developer carrier and the carrier liquid amount control member are opposed to each other, and form a second stay portion of the liquid developer carried out from the nip portion. 4. The image forming apparatus according to claim 3, further comprising a carrier liquid amount control member.

  5. 5. The image forming apparatus according to claim 4, wherein the second carrier liquid amount control member is a blade disposed in contact with the carrier liquid amount control member.

  6). A second low-concentration developer for supplying a liquid developer having a concentration lower than that of the liquid developer on the downstream side in the developer transport direction of the nip portion where the developer carrier and the carrier liquid amount control member face each other. 4. The image forming apparatus according to item 3, further comprising a supply unit.

  7). An image carrier that forms a latent image on the surface; and a developer carrier that is opposed to the image carrier and carries a thin layer of a liquid developer containing toner and carrier liquid on the surface. The image carrier that moves in the same direction as the transport direction of the liquid developer by using the liquid developer carried and transported by the developer carrier in a development nip portion where the carrier and the developer carrier face each other In the image forming apparatus that develops a latent image on the surface of the toner and forms a toner image, the liquid developer carried out from the developing nip portion is downstream of the developing nip portion in the developer conveying direction. An image forming apparatus comprising: a low concentration developer supplying means for supplying a liquid developer having a lower concentration than the liquid developer before being separated from the surface of the developer carrying member and the surface of the developer carrying member. .

  8). The image forming apparatus according to any one of claims 1 to 6, wherein the carrier liquid amount control member is given a potential having the same polarity as a charging potential of toner in the liquid developer.

  9. A developer carrying member for carrying and transporting a thin layer of a liquid developer containing toner and carrier liquid on the surface thereof, facing the developer carrying member, and the direction of movement of the surface at the opposed position is the developer carrying member. In a liquid developing apparatus for developing a latent image on an image carrier that is in the same direction as the surface movement direction of the image with a liquid developer carried and transported by the developer carrier, and forming a toner image, the image carrier and The liquid developer disposed on the downstream side in the developer conveying direction at the developing nip portion facing the developer carrying member, and the liquid developer carried out from the developing nip portion is disposed on the surface of the image carrier and the developer carrying member. A liquid developing apparatus comprising a carrier liquid amount control member for forming a liquid developer retention portion before being separated from the surface of the liquid developer.

  10. A developer carrying member for carrying and transporting a thin layer of a liquid developer containing toner and carrier liquid on the surface thereof, facing the developer carrying member, and the direction of movement of the surface at the opposed position is the developer carrying member. In a liquid developing apparatus for developing a latent image on an image carrier that is in the same direction as the surface movement direction of the image with a liquid developer carried and transported by the developer carrier, and forming a toner image, the image carrier and On the downstream side in the developer conveying direction of the developing nip portion facing the developer carrying member, the liquid developer carried out from the developing nip portion is formed on the surface of the image carrier and the surface of the developer carrying member. A liquid developing apparatus comprising a low concentration developer supplying means for supplying a liquid developer having a concentration lower than that of the liquid developer before the separation.

  According to the image forming apparatus and the liquid developing device of the present invention, the developer carrying member carrying and transporting the thin layer of the high concentration liquid developer is rotated so that the surface moves in the same direction as the image carrying member. In the liquid developing method for developing the latent image on the image carrier, a carrier liquid amount control member is disposed on the downstream side in the developer transport direction of the development nip where the image carrier and the developer carrier face each other. The liquid developer staying portion is formed before the liquid developer carried out from the developing nip portion is separated from the surface of the image carrier and the surface of the developer carrier.

  As a result, the toner concentration in the developer retaining portion can be reduced, and the divided section of the liquid developer can be moved away from the toner image on the image carrier, and as a result, the occurrence of toner image disturbance when passing through the development nip can be suppressed. And good images can be obtained with respect to fog and image unevenness.

  Embodiments according to the present invention will be described with reference to the drawings.

  Development devices that develop using a thin developer layer are used in image forming apparatuses such as copiers, simple printers, and printers. In particular, a wet type image forming apparatus is generally developed using a thin layer of a liquid developer, and a liquid developing apparatus including means for forming and developing a thin developer layer is used. In general, an electrophotographic image forming process is commonly used for these. The electrophotographic wet-type image forming unit will be described as an example, and the configuration and functional operation of the liquid developing device used there will be described.

(Configuration of image forming unit and functional operation)
A configuration example of an image forming unit in the image forming apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view illustrating a schematic configuration example of an image forming unit in a wet image forming apparatus.

  In FIG. 1, reference numeral 1 denotes a photosensitive drum, which functions as an image carrier. The image forming unit 10 irradiates a laser beam onto the charged photosensitive drum 1, the charging device 2 disposed uniformly around the photosensitive drum 1 and charging the surface of the photosensitive drum 1 uniformly. An exposure device 3 for forming an electrostatic latent image, a liquid developing device 4 for developing the electrostatic latent image using a liquid developer, a transfer device 5 for transferring the developed toner image to a transfer material 7, and a transfer A cleaning device 6 for removing the liquid developer remaining on the surface of the subsequent photosensitive drum is provided.

  In some cases, before and after the liquid developing device 4, a device for applying or collecting a part of the liquid developer in advance is provided. The transfer material 7 may be a recording material such as recording paper as it is, or may be configured such that the transfer material 7 is transferred again to the recording material using an intermediate transfer belt or the like.

  The photosensitive drum 1 rotates in the direction of arrow A shown in FIG. 1, and the charging device 2 charges the surface of the rotating photosensitive drum 1 to about several hundred volts by corona discharge or the like. On the downstream side of the charging device 2 in the rotation direction of the photosensitive drum, an electrostatic latent image whose surface potential is lowered to about 100 V or less is formed by the laser beam emitted from the exposure device 3.

  A liquid developing device 4 is disposed further downstream of the exposure device 3, and the electrostatic latent image formed on the photosensitive drum 1 is developed using the liquid developer 8.

  In the liquid developing device 4, a liquid developer 8 in which toner is dispersed in an insulating solvent (hereinafter also referred to as a carrier liquid) is accommodated in a developing tank 44, and is supplied to the surface of the conveying roller 42 by a supply roller 43. Liquid developer 8 is supplied. The conveying roller 42 conveys a thin layer of the liquid developer 8 and transfers it to the developing roller 41. A thin layer of the liquid developer 8 is carried and conveyed on the developing roller 41. Therefore, the developing roller 41 functions as a developer carrier.

  Further, due to the potential difference between the developing roller 41 and the electrostatic latent image on the photosensitive drum 1, the toner particles in the thin layer of the liquid developer 8 carried on the developing roller 41 become an electrostatic latent image on the photosensitive drum 1. Moving, the electrostatic latent image is developed. Further, a carrier liquid amount control member 91 is provided downstream of the nip after development, and the amount of carrier liquid at the nip portion outlet is controlled to form a staying portion, thereby suppressing the disturbance of the toner image. The function of the carrier liquid amount control member 91 after development will be described in detail later.

  In the transfer device 5, the developed toner image on the photosensitive drum 1 is transferred to the transfer material 7 by charging the transfer material 7 conveyed at the same speed as the peripheral speed of the photosensitive drum 1 or applying a voltage. Transcribed above.

  A cleaning device 6 for removing the liquid developer 8 remaining on the surface of the photosensitive drum 1 is disposed on the downstream side of the transfer device 5. The cleaning device 6 removes the liquid developer 8 remaining on the photosensitive drum 1.

  If the transfer material 7 onto which the toner image has been transferred by the transfer device 5 is a recording material, it is conveyed to a fixing device (not shown), and is discharged after heating and fixing. If the transfer material 7 is an intermediate transfer member such as an intermediate transfer belt, then the toner image is re-transferred to the recording material, and the recording material onto which the toner image has been transferred is also conveyed to the fixing device, where it is heated and fixed. Discharged.

(Developer composition)
The liquid developer 8 used for development will be described. In the liquid developer 8, colored toner particles are dispersed at a high concentration in a carrier liquid as a solvent. In addition, additives such as a dispersant and a charge control agent may be appropriately selected and added to the liquid developer 8.

  As the carrier liquid, an insulating, non-volatile solvent at room temperature is used. The toner particles are mainly composed of a resin and a pigment or dye for coloring. The resin has a function of uniformly dispersing pigments and dyes in the resin and a function as a binder when being fixed to the recording material.

  The volume average particle diameter of the toner is suitably in the range of 0.1 μm or more and 5 μm or less. When the average particle diameter of the toner is less than 0.1 μm, the developability is greatly lowered. On the other hand, when the average particle diameter exceeds 5 μm, the quality of the image is deteriorated.

  The ratio of the toner particle mass to the liquid developer mass is suitably about 10 to 40%. If it is less than 10%, toner particles are liable to settle, and there is a problem with the stability over time during long-term storage. Further, in order to obtain a required image density, it is necessary to supply a large amount of developer, the carrier liquid adhering to the paper increases, and it must be dried at the time of fixing, and steam is generated, resulting in environmental problems. If it exceeds 40%, the viscosity of the liquid developer becomes too high, making it difficult to manufacture and handle.

(Configuration and operation of liquid developing device 4c: conventional example)
For the sake of comparison, FIG. 2 shows a schematic configuration of a conventional developing device 4c in which a mechanism for forming a staying portion downstream of the developing nip portion from the liquid developing device 4 in FIG. 1 is omitted. The configuration and operation of a conventional liquid developing device 4c will be described with reference to FIG.

  The developer tank 44 contains the liquid developer 8 described above.

  The supply roller 43 is disposed so as to be immersed in the liquid developer 8 in the developer tank 44, rotates in the direction of arrow D, and draws the liquid developer 8 from the developer tank 44. The high-viscosity liquid developer 8 is conveyed while adhering to the surface of the supply roller 43 due to its adhesive force.

  The supply roller 43 may be a smooth roller or an anilox roller. An anilox roller is a roller having a concave fine groove structure on the surface thereof, and the amount of liquid developer conveyed is adjusted by providing a regulating member 45 or the like.

  When the supply roller 43 is the above-mentioned anilox roller, a hard elastic blade made of metal or the like is generally used as the regulating member 45, and when the supply roller 43 is a smooth roller, an elastic blade made of metal or rubber or the like. Is often used.

  As shown in the figure, the regulating member 45 is disposed so as to face the supply roller 43 and abut against the rotation in the counter direction, and regulates the amount of developer that adheres to the surface of the supply roller 43 and is conveyed. Is. As a result, an excessive amount of developer is peeled off, and a thin developer layer is formed on the surface of the supply roller 43 and is conveyed toward the next conveying roller 42.

  As the conveying roller 42, a rubber roller is generally used. The conveying roller 42 is disposed to face the supply roller 43 and rotates in the direction of arrow C while contacting. At this nip portion, the developer thin layer formed on the surface of the supply roller 43 is copied onto the surface of the conveying roller 42 and conveyed toward the developing roller 41.

  As the developing roller 41, a low hardness rubber roller is used. The developing roller 41 is disposed to face the conveying roller 42 and rotates in the direction of arrow B while contacting. The developer thin layer transported to the surface of the transport roller 42 at this nip is scraped off by the developing roller 41, and the developer thin layer is carried and transported to the surface of the developing roller 41.

  The developing roller 41 also rotates in contact with the photosensitive drum 1 that is an image carrier, and the developer thin layer conveyed to the nip portion with the photosensitive drum 1, that is, the developing region, is on the photosensitive drum 1. The latent image will be developed. The pre-developing charger 47 assists the electrical movement of the charged toner to the latent image by applying a charge to the developing roller 41.

  However, a thin layer of developer remains on the surface of the developing roller 41 even after the latent image on the photosensitive drum 1 is developed. If the remaining developer is transported to the development area again as it is, it adversely affects the next development. The removing member 46 is a blade for cleaning, and removes the remaining developer.

  In the above description, as the configuration of the liquid developing device 4c, the conveying roller 42 may be omitted, and the developing roller 41 may have the function. That is, it is possible to adopt a method of transferring the developer directly from the supply roller 43 to the developing roller 41.

(Regarding the occurrence of toner image disturbance in the development nip)
With reference to FIGS. 3 and 4, the toner image disturbance that occurs in the developing nip portion when the above-described conventional liquid developing device 4c is used will be described. FIG. 3 is a graph showing the relationship between the layer thickness of the developer tank at the development nip, that is, the gap size and the wraparound of the electric field. FIG. 4 is a diagram showing the relationship between separation of the developer thin layer and toner image disturbance when exiting the development nip.

  FIG. 3A shows an electric field wraparound 11 when the thickness t of the developer layer is equal to or smaller than the diameter φ of the dot portion 12 constituting the latent image on the image carrier 1 (t ≦ φ). Indicates. The direction of the electric field is reversed between the dot portion 12 and the outside thereof, but the electric field wraparound 11 at the boundary portion is relatively small.

  FIG. 3B shows the electric field wrap 11 when the thickness t of the developer layer is larger than the diameter φ of the dot portion 12 constituting the latent image on the image carrier 1 (t> φ). A considerably large electric field wraparound 11 occurs at the boundary between the dot portion 12 and the outside thereof.

  These indicate the following. The thinner the liquid developer layer, the closer the electric field due to the latent image potential is to a parallel electric field that is less affected by the wraparound electric field at the edge, so that the toner is more easily developed faithfully to the latent image. For example, in the case of a latent image having a line width φ, if the layer thickness t of the developer is smaller than the line width φ (t ≦ φ), it is less likely to be affected by a reverse electric field around.

  Strictly speaking, FIG. 3B shows the electric field when the line extends infinitely in the vertical direction on the paper surface. In the case of dots, the vertical electric field side of the drawing is also affected by the reverse electric field. By setting the developer layer thickness t ≦ φ / 2, it is possible to make it less susceptible to the influence of the surrounding reverse electric field.

  However, if the layer thickness of the developer layer is reduced, the image density is lowered, and it is necessary to set the toner density of the developer high in order to ensure the image density.

  It is desirable to increase the concentration of the liquid developer and reduce the layer thickness of the developer layer. However, using a high concentration developer layer increases the viscosity and increases the interaction between the toners. The toner moving speed decreases and the developing speed decreases. In addition, there is a case where the toner adheres to the non-image area due to the influence of the deterioration of the toner mobility, or the image unevenness occurs because the toner cannot move completely in the image area.

  In particular, when developing a latent image on the surface of the image carrier 1 that moves in the same direction as the surface of the developer carrier 41, the developer used is developed at the development nip portion as the concentration of the developer is higher and the layer thickness is thinner. The toner image is likely to be disturbed, and fog and unevenness are likely to occur. The situation will be described with reference to FIG.

  FIG. 4A is a diagram illustrating a state when the developer nip portion N has passed when the developer layer is thin (t ≦ φ), that is, corresponding to the case of FIG. The direction of movement (left to right) is indicated by arrows in the figure. A thin developer layer on the surface of the developer carrier 41 is sandwiched between the image carriers 1, and the toner 81 is separated from the non-image portion by the electric field generated therebetween, and moves in the carrier liquid 82 toward the image portion. Developed.

  When passing through the nip portion N, the developer layer is separated from the image carrier 1 side and the developer carrier 41 side. At that time, the toner 81 in the developer is developed on the image carrier 1 side to form a toner image M or adheres to the developer carrier 41 side, and the carrier liquid 82 is mainly separated. However, if the divided section F of the liquid developer at that time is too close to the toner image M on the image carrier 1, the developed toner image will be disturbed. As a result, density unevenness and fogging occur.

  On the other hand, FIG. 4B is a diagram showing a state when the developer nip N has passed when the developer layer is thick (t> φ), that is, in the case corresponding to the case of FIG. is there. The moving direction is the same as in FIG. A thin developer layer on the surface of the developer carrier 41 is sandwiched between the image carriers 1, and the toner 81 is separated from the non-image portion by the electric field generated therebetween, and moves in the carrier liquid 82 toward the image portion. Developed.

  When passing through the nip portion N, the developer layer is separated from the image carrier 1 side and the developer carrier 41 side. At that time, the toner 81 in the developer is also developed on the image carrier 1 side to form a toner image M or adheres to the developer carrier 41 side, and the carrier liquid 82 is mainly separated. However, since the dividing section F of the liquid developer at that time is relatively far from the toner image M on the image carrier 1, the developed toner image is not disturbed. Neither density unevenness nor fog occurs.

  Thus, when a high-concentration developer thin layer is used, the occurrence of toner image disturbance when the developer thin layer is carried out of the development nip N has been a major problem.

(Configuration and operation of the liquid developing device 4a)
FIG. 5 shows a configuration example of a liquid developing device 4a as a developing device according to this embodiment. The configuration and operation of the liquid developing device 4a will be described with reference to FIG. However, the components other than the carrier liquid amount control member 91 shown in the drawing are the same as those of the conventional liquid developing device 4c shown in FIG.

  FIG. 5 is an enlarged cross-sectional view of the development nip N between the image carrier 1 and the developer carrier 41. The surface moving directions of the image carrier 1 and the developer carrier 41 are indicated by arrows A and B, respectively. The thin layer of developer contains toner 81 and carrier liquid 82, and is transported on the surface of the developer carrier 41 from the left to the right in the figure. In the developing nip portion N, the toner 81 in the developer thin layer is developed under the action of a developing electric field.

  That is, the toner 81 in the developer moves in the carrier liquid 82 so that the latent image on the image carrier 1 approaches the image portion and moves away from the non-image portion. Therefore, after passing through the development nip N, the toner 81 in the developer is separated into the toner image on the image carrier 1 and the residual toner on the developer carrier 41, and the carrier liquid 82 is mainly used in the meantime. It becomes a state to do.

  Here, in the case of the conventional liquid developing device 4c (conventional case where the carrier liquid amount control member 91 shown in the figure is not provided), the carrier liquid 82 is divided into the image carrier 1 and the developer carrier 41. As a result, the toner image on the image carrier 1 is disturbed.

  However, in the liquid developing device 4a, the carrier liquid amount control member 91 is provided before the carrier liquid 82 is divided as shown in the drawing. The carrier liquid amount control member 91 was a urethane rubber blade having a thickness of about 10 μm. The material of the blade may be silicone rubber, NBR rubber, or metal such as stainless steel. Moreover, it does not need to be a blade shape, and may be a shape such as a roller.

  The purpose of disposing the carrier liquid amount control member 91 is to prevent the developer from being transported before the liquid developer is divided, thereby generating a liquid developer retention portion T, The developer is smoothly divided after the carrier liquid is rich and has a low concentration state. Thereby, the influence on the toner image on the image carrier 1 can be suppressed.

  In order to make the staying portion T of the liquid developer more positively rich in the carrier liquid, a carrier liquid pool is formed in the staying portion T by intentionally developing solid white before image output. Alternatively, it is more effective to replenish the carrier liquid amount control member 91 with a developer having a low toner concentration or a carrier liquid rich (or the carrier liquid itself) using a nozzle or the like (not shown). In this case, the nozzle or the like functions as a low-concentration developer supply unit.

  Further, by applying a potential for repelling the toner particles to the carrier liquid amount control member 91, the developed toner is not disturbed by the carrier liquid amount control member 91 and is retained in the retention portion T. An abrupt increase in the toner concentration in the developing agent can also be suppressed.

  By disposing the carrier liquid amount control member 91 in this way, the developer staying portion T is generated, so that the developer is smoothly divided after the carrier liquid is rich and the low concentration state is formed. By doing so, the influence on the toner image on the image carrier 1 can be suppressed.

(Configuration and operation of the liquid developing device 4b)
FIG. 6 shows a configuration example of a liquid developing device 4b as a developing device according to this embodiment. The configuration and operation of the liquid developing device 4b will be described with reference to FIG. However, except for the carrier liquid amount control member 91 and the second carrier liquid amount control member 92 shown in the drawing, it is the same as the conventional liquid developing device 4c shown in FIG.

  FIG. 6 shows the development nip N between the image carrier 1 and the developer carrier 41 through the developer nip N until the residual developer on the developer carrier 41 is removed by the developer carrier cleaner 46. It is sectional drawing of the part. The surface moving directions of the image carrier 1 and the developer carrier 41 are indicated by arrows A and B, respectively. The thin layer of developer contains toner 81 and carrier liquid 82, and is transported on the surface of the developer carrier 41 from the left to the right in the figure. In the developing nip portion N, the toner 81 in the developer thin layer is developed under the action of a developing electric field.

  Thereafter, the developer mainly composed of the carrier liquid 82 is divided into the image carrier 1 and the developer carrier 41. In the liquid developing device 4b, however, before the carrier liquid 82 is divided as shown in the figure. A carrier liquid amount control member 91 is provided. As the carrier liquid amount control member 91, a stainless roller having a diameter of about 20 mm was used. The material of the roller may be rubber. The direction of rotation of the carrier liquid amount control member 91 is such that the moving direction of the surface of the opposite developer carrying member 41 is the same as indicated by an arrow E in the figure.

  The carrier liquid amount control member 91 is arranged in such a manner as to prevent the developer from being conveyed before the developer is divided. That is, by disposing the image carrier 1 and the developer carrier 41 so as to face both, the developer retention portion T is generated at the center of the three, and the carrier liquid is rich and in a low concentration state. So that the developer is smoothly divided. As a result, the influence on the toner image on the image carrier 1 can also be suppressed.

  The carrier liquid retention portion T by the carrier liquid amount control member 91 changes depending on the roller diameter to be used, but occupies a considerably large volume. In order to efficiently maintain the carrier liquid in the staying portion T, the second carrier liquid amount control member 92 is disposed downstream of the developer carrying direction in the nip portion between the developer carrier 41 and the carrier liquid amount control member 91. Set up.

  The second carrier liquid amount control member 92 is configured to block the carrier liquid mainly from the carrier liquid 82 carried out from the nip portion between the developer carrier 41 and the carrier liquid amount control member 91. This is a blade provided in contact with a roller which is a quantity control member 91.

  The second carrier liquid amount control member 92 scrapes the carrier liquid 82 from the surface of the roller 91 which is a carrier liquid amount control member. As a result, the carrier liquid outflow from the staying portion T is suppressed and contributes to maintaining the carrier liquid in the staying portion T, and the surface of the developer carrying body 41 is transported and collected by the developer carrying body cleaner 46. The amount of carrier liquid can also be reduced.

  Further, not only the carrier liquid outflow from the staying part T but also the toner density is low in the staying part T by using a nozzle, a coating roller or the like (not shown). It is also more effective to replenish a different developer. In this case, a nozzle, a coating roller, or the like may be provided as a low-concentration developer supply unit other than the second carrier liquid amount control member, or may be in contact with the first carrier liquid amount control member to It may function as a low-concentration developer supply unit.

  By disposing the carrier liquid amount control member 91 and the second carrier liquid amount control member 92 in this manner, the developer retention portion T is more effectively generated, and the carrier liquid is rich and in a low concentration state. By making the developer smoothly divided after the formation, the influence on the toner image on the image carrier 1 can be suppressed.

  An example of an experiment using the liquid developing apparatus of this embodiment will be described.

  The image forming apparatus used has the configuration shown in FIG. The image forming process conditions were a system speed of 400 mm / s. The photosensitive drum was negatively charged OPC, and the charging potential was −700 v. An LED was used as the exposure light source. The development voltage is -450v and the transfer voltage is + 600v. The corona charge before development was adjusted as appropriate with a needle application voltage of -3 to 5 kv.

  Table 1 shows the liquid developing apparatus used, the conditions of the developer thin layer, and the evaluation results.

  As a comparative example, the liquid developing device includes a liquid developing device 4c having no conventional carrier liquid amount control member, and as an example, a liquid developing device 4a (see FIG. 5) having a carrier liquid amount control member, and a carrier liquid. A liquid developing device 4b (see FIG. 6) having an amount control member and a second carrier liquid amount control member was used.

  In the liquid developing device 4a, a urethane rubber blade having a thickness of 10 mm is used as a carrier liquid amount control member. Further, white solid development is performed before image formation, and a carrier liquid pool is formed in the staying portion.

  In the liquid developing device 4b, a stainless steel roller having a diameter of 20 mm is used as a carrier liquid amount control member. The rotation direction is the same as described with reference to FIG. A rubber blade was used as the second carrier liquid amount control member. The second carrier liquid amount control member is brought into contact with the carrier liquid amount control member and scrapes off the carrier liquid on the surface thereof. In addition, a carrier liquid supply nozzle and an excess carrier liquid outlet are provided at both ends in the longitudinal direction of the roller so that the carrier liquid retention amount can be kept constant.

  The liquid developer used was Moresco White P-120 or P-40 (manufactured by Matsumura Oil Research Co., Ltd.) as the carrier liquid and carbon dispersed in a polyester resin as the toner. The toner concentration is basically 25% by mass with respect to the liquid developer, and the concentration is adjusted by experiment. The toner concentration was controlled by adding a carrier liquid or removing the carrier liquid on the developer carrying member with a squeeze roller.

  A small amount of a dispersant was added to the liquid developer. In the toner production method, the particle size was adjusted by wet grinding in a sand mill and changing the grinding time. The volume average particle diameter is 2 μm.

  The developer concentration setting is a setting for changing the layer thickness of the developer layer. Considering the image density, the density is set low when the layer thickness is large, and the density is set high when the layer thickness is small (see Table 1).

  In the evaluation method, an ordinary printout was performed on the original image as shown below, and the output sample was observed using a 150 × microscope, and visually evaluated for toner image distortion.

  FIG. 7 shows an original image for evaluation. FIG. 7A shows a black solid image. The output image is evaluated as ◯ if the black solid is uniform, Δ if there is a partial shading, and × if a streaky pattern called a rib pattern appears. did.

  FIG. 7B is an image of a thin line, and four types of images having a line width of 40 μm, 20 μm, 10 μm, and 5 μm were used. In both cases, the line widths of the black part and the white part are equal. The evaluation of the output image is indicated by the limit line width that satisfies the conditions that the line is not cut, the line width is constant, and the line width is not too thin (80% or more with respect to the white portion).

  FIG. 7C shows a dot image, which has one square dot in 2 × 2 squares. Four types of dot images having a size of one square of 40 μm, 20 μm, 10 μm, and 5 μm were used. The evaluation of the output image is shown by the limit dot diameter that satisfies the conditions that the dots are not missing, the dot diameter is constant, and the diameter is not too thin (50% or more for one square).

In addition, as a comprehensive evaluation, the following ◎, ○, △, × evaluation was performed,
◎ Uniform solid density, 5μm fine lines and 10μm dots can be reproduced (equivalent to 2400 dpi)
○ Uniform solid density, 10μm fine lines and 20μm dots can be reproduced (equivalent to 1200 dpi)
Δ Solid density is not uniform, 10 μm fine line or 20 μm dot cannot be reproduced. X Solid density is not uniform, or 20 μm thin line is not reproducible.

  Table 1 shows the liquid developing apparatus used, the conditions of the developer thin layer, and the evaluation results.

  In each of Example 1 and Example 2 using the liquid developing device 4a having the carrier liquid amount control member, the overall evaluation is “good”, indicating good results. In Example 2, the developer layer is thinner than Example 1, and the dot reproduction is particularly good.

  In Example 3 and Example 4 using the liquid developing device 4b having the carrier liquid amount control member and the second carrier liquid amount control member, the overall evaluation is “good” and “good”, indicating good results. In Example 4, the layer thickness of the developer layer was halved compared to Example 3, and the developer concentration was doubled accordingly. However, the overall evaluation was あ り, and the toner image was not disturbed. The dot reproduction is particularly good.

  In Comparative Example 1 and Comparative Example 2 using the conventional liquid developing device 4c that does not have a carrier liquid amount control member, the overall evaluation is Δ and ×, indicating unacceptable results. In particular, as in Comparative Example 2, when the developer layer is made thinner, the dot reproduction, which was not good in Comparative Example 1, is improved. However, since the toner is likely to be disturbed at the time of division, a rib pattern is formed even in a solid image. To occur.

  As described above, in the embodiment, the developer layer was thinned to improve the reproducibility of fine lines and dots, and the toner image disturbance at the time of carrying out the development nip could be suppressed.

  As shown in the above examples, according to this embodiment, the developer carrying member carrying and transporting a thin layer of high-concentration liquid developer is rotated so that the surface of the developer carrying member moves in the same direction. Then, in the liquid developing system for developing the latent image on the image carrier, a carrier liquid amount control member is disposed on the downstream side in the developer transport direction of the development nip portion where the image carrier and the developer carrier face each other. Thus, the liquid developer staying portion is formed before the liquid developer carried out from the developing nip portion is separated from the surface of the image carrier and the surface of the developer carrier.

  As a result, the toner concentration in the developer retaining portion can be reduced, and the divided section of the liquid developer can be moved away from the toner image on the image carrier, and as a result, the occurrence of toner image disturbance when passing through the development nip can be suppressed. Therefore, it is possible to provide an image forming apparatus and a liquid developing apparatus that can obtain a good image with respect to fog and image unevenness.

  In the present embodiment, the configuration in which the liquid developing device includes the carrier liquid amount control member has been described. Of course, the image forming apparatus main body, not the liquid developing device, includes the carrier liquid amount control member. It doesn't matter.

  Further, the scope of the present invention is not limited to the above embodiment. Unless it deviates from the meaning of this invention, those changed forms are also included in the range.

It is sectional drawing which shows the schematic structural example of the image formation part in a wet image forming apparatus. It is sectional drawing which shows the schematic structural example of the conventional liquid developing device 4c. It is a figure which shows the relationship between the layer thickness of the developer layer in a development nip part, and the wraparound of an electric field. FIG. 6 is a diagram illustrating a relationship between separation of a developer thin layer and toner image disturbance when passing through a development nip portion. FIG. 5 is a diagram illustrating a configuration example of a liquid developing device 4a having a carrier liquid amount control member, and is an enlarged cross-sectional view of a developing nip portion between an image carrier and a developer carrier. FIG. 6 is a diagram illustrating a configuration example of a liquid developing device 4b having a carrier liquid amount control member and a second carrier liquid amount control member, and passes through a developing nip portion between an image carrier and a developer carrier, FIG. 5 is a cross-sectional view of a portion until a residual developer on a developer carrier is removed by a developer carrier cleaner. It is a figure which shows the original image for evaluation in an Example.

Explanation of symbols

1 Image carrier (photosensitive drum)
DESCRIPTION OF SYMBOLS 2 Charging device 3 Exposure device 4 Liquid developing device 5 Transfer device 6 Cleaning device 7 Transfer material 8 Liquid developer 10 Image forming portion 11 Electric field wrapping region 12 Latent image portion (dot portion)
41 Developer carrier (developing roller)
42 Conveying roller 43 Supply roller 44 Developer tank 45 Regulating member 46 Developer carrier cleaner 47 Pre-development charger 81 Toner 82 Carrier liquid 91 Carrier liquid amount control member 92 Second carrier liquid amount control member

Claims (10)

An image carrier that forms a latent image on the surface;
A developer carrying body facing the image carrying body and carrying and transporting a thin layer of a liquid developer containing toner and carrier liquid on the surface;
The image moving in the same direction as the transport direction of the liquid developer using the liquid developer carried and transported by the developer carrier in a development nip where the image carrier and the developer carrier face each other In the image forming apparatus for developing the latent image on the surface of the carrier and forming a toner image,
Before the liquid developer, which is disposed downstream of the developing nip portion in the developing nip portion and is carried out from the developing nip portion, separates between the surface of the image carrier and the surface of the developer carrier. And a carrier liquid amount control member for forming the liquid developer retention portion,
An image forming apparatus. The carrier liquid amount control member is
A blade facing the image carrier and the developer carrier;
The image forming apparatus according to claim 1. The carrier liquid amount control member is
A roller facing the image carrier and the developer carrier;
The surface moving direction is the same direction as the surface moving direction of the developer carrier facing the surface.
The image forming apparatus according to claim 1. The developer carrying member and the carrier liquid amount control member are disposed on the downstream side in the developer transport direction at a nip portion where the developer carrier and the carrier liquid amount control member are opposed to each other, and form a second stay portion of the liquid developer carried out from the nip portion. Having a carrier liquid amount control member of
The image forming apparatus according to claim 3. The second carrier liquid amount control member is
A blade disposed in contact with the carrier liquid amount control member;
The image forming apparatus according to claim 4. A second low-concentration developer for supplying a liquid developer having a concentration lower than that of the liquid developer on the downstream side in the developer transport direction of the nip portion where the developer carrier and the carrier liquid amount control member face each other. Having supply means,
The image forming apparatus according to claim 3. An image carrier that forms a latent image on the surface;
A developer carrying body facing the image carrying body and carrying and transporting a thin layer of a liquid developer containing toner and carrier liquid on the surface;
The image moving in the same direction as the transport direction of the liquid developer using the liquid developer carried and transported by the developer carrier in a development nip where the image carrier and the developer carrier face each other In the image forming apparatus for developing the latent image on the surface of the carrier and forming a toner image,
Before the liquid developer carried out from the development nip portion is separated from the surface of the image carrier and the surface of the developer carrier on the downstream side in the developer conveyance direction of the development nip portion, the liquid Having a low-concentration developer supply means for supplying a liquid developer having a lower concentration than the developer;
An image forming apparatus. The carrier liquid amount control member is
A potential having the same polarity as the charging potential of the toner in the liquid developer is applied,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A developer carrying member for carrying and transporting a thin layer of liquid developer containing toner and carrier liquid on the surface;
A latent image on the image carrier that faces the developer carrier and whose surface movement direction at the opposite position is the same as the surface movement direction of the developer carrier is carried and conveyed by the developer carrier. In a liquid developing apparatus that develops with a liquid developer and forms a toner image,
The image carrier and the developer carrier are disposed on the downstream side in the developer transport direction at a developing nip portion where the developer carrier is opposed, and the liquid developer carried out from the developing nip portion is in contact with the surface of the image carrier. A carrier liquid amount control member for forming a retention portion of the liquid developer before being separated from the surface of the developer carrier;
A liquid developing apparatus. A developer carrying member for carrying and transporting a thin layer of liquid developer containing toner and carrier liquid on the surface;
A latent image on the image carrier that faces the developer carrier and whose surface movement direction at the opposite position is the same as the surface movement direction of the developer carrier is carried and conveyed by the developer carrier. In a liquid developing apparatus that develops with a liquid developer and forms a toner image,
On the downstream side in the developer transport direction of the development nip portion where the image carrier and the developer carrier face each other, the liquid developer carried out from the development nip portion and the surface of the image carrier and the developer A low concentration developer supplying means for supplying a liquid developer having a lower concentration than the liquid developer before being separated from the surface of the carrier;
A liquid developing apparatus.

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