JP2008197330A - Developing device and image forming apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain proper image quality by making the film thickness of liquid developer on a developing roller after non-contact compaction more uniform. <P>SOLUTION: Respective compaction rollers 18Y, 18M, 18C and 18K are arranged to leave a predetermined gap G(μm) in between with the outer peripheral surfaces of respective developing rollers 17Y, 17M, 17C and 17K, to which their outer peripheral surfaces correspond. In such a case, each gap G(μm) is set to be larger than the film thickness t(μm) of a developer layer 21a formed of the liquid developer 21Y, 21M, 21C or 21K supplied from each anilox roller 24Y, 24M, 24C or 24K on the outer peripheral surface of each developing roller. Then, the width W<SB>CPR</SB>of the compaction roller is set to be smaller than the width W<SB>DR</SB>of the corresponding developing roller. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developing device for developing an electrostatic latent image formed on a latent image carrier such as a photoconductor with a liquid developer composed of toner and a liquid carrier, and a latent image carrier developed using the same. The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer that obtains an image by transferring the liquid developer image of the above to a transfer material such as paper.

  Conventionally, in an image forming apparatus using a liquid developer, a liquid developer regulated to a predetermined amount by an anilox roller is supplied to the developing roller. Next, toner in the liquid developer on the developing roller is pressed against the developing roller and compacted by compaction means that applies a voltage to the developing roller (compaction). Then, the electrostatic latent image on the photosensitive member is developed by the compacted toner on the developing roller.

By the way, conventionally, a developing device using a corona charger as a compaction means has been proposed (for example, see Patent Document 1). Further, a developing device using a compaction roller that comes into contact with the developing roller as a compaction means has been proposed (see, for example, Patent Document 2).
Japanese Patent Application Laid-Open No. 2005-62466. Japanese Patent Application Laid-Open No. 2006-242352.

In the developing device described in Patent Document 1, the corona charger is disposed below the developing roller and the photosensitive member in view of the layout. However, foreign matter such as liquid developer dripping from the developing roller causes the corona charger wire to become dirty or the house to become dirty. For this reason, there is a problem that regular maintenance of the corona charger is frequently required.
On the other hand, in the developing device described in Patent Document 2, the foreign matter adhering to the compaction roller that contacts the developing roller is removed by the cleaning blade. Thereby, the frequency | count of the regular maintenance of a compaction roller is suppressed.
However, the compaction roller that contacts the developing roller has the following problems.
(1) A liquid developer pool (nip pool) is generated upstream of the nip portion (contact portion) between the development roller and the compaction roller in the rotation direction of the development roller. Due to this nip accumulation, the film thickness of the liquid developer on the developing roller after compaction becomes non-uniform.
(2) Contact between the developing roller and the compaction roller causes liquid disturbance such as a rib (rivulet) where the carry liquid adheres to the compaction roller after compaction.
(3) The image quality is disturbed by the above (1) and (2).
(4) Since a relatively large amount of liquid carrier adheres to the compaction roller, the liquid carrier is reduced.

  The present invention has been made in view of such circumstances, and an object of the present invention is to make the film thickness of the liquid developer on the developing roller after non-contact compaction more uniform and obtain good image quality. A developing device and an image forming apparatus provided with the developing device are provided.

  In order to solve the above problems, in the developing device and the image forming apparatus according to the present invention, a gap larger than the film thickness of the liquid developer on the developing roller is provided between the developing roller and the compaction roller. Accordingly, the compaction roller compacts the liquid developer in a non-contact manner without contacting the liquid developer on the developing roller.

  Therefore, it is possible to suppress the nip accumulation of the liquid developer between the developing roller and the compaction roller. Further, since the developing roller and the compaction roller do not come into contact with each other, it is possible to suppress the liquid disturbance such as the above-described rib. As described above, since nip accumulation and liquid disturbance of the liquid developer can be suppressed, good image quality can be obtained for a long time and effectively.

  In addition, since the width of the developing roller is set to be larger than the width of the compaction roller, the occurrence of nip accumulation of the liquid developer between the developing roller and the compaction roller at the left and right ends of the compaction roller is further effectively suppressed. can do. Thereby, the film thickness of the liquid developer on the developing roller after compaction can be made even more uniform. Accordingly, it is possible to prevent image disturbance due to non-uniform film thickness of the liquid developer, and to obtain good image quality stably over the long term.

  Further, since the width of the developing roller cleaner is set to be larger than the width of the compaction roller, the liquid developer moving outward from the left and right ends of the compaction roller is removed by the developing roller cleaner at the left and right ends of the developing roller. . Thereby, it is possible to more effectively suppress the nip accumulation of the liquid developer between the developing roller and the compaction roller. Therefore, the film thickness of the liquid developer on the developing roller after compaction can be made more uniform.

  Furthermore, the liquid developer can be uniformly compacted even when non-contact compaction is performed by setting the applied voltage of the compaction roller to a superimposed voltage of a DC voltage and an AC voltage. Thereby, much better image quality can be obtained.

  Furthermore, since the compaction roller does not contact the liquid carrier, the liquid carrier is less likely to adhere to the compaction roller after compaction. Thereby, it can suppress that a liquid carrier reduces.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically and partially showing an example of an embodiment of an image forming apparatus according to the present invention.
As shown in FIG. 1, the image forming apparatus 1 of this example includes a photoreceptor 2Y that is a latent image carrier of yellow (Y), magenta (M), cyan (C), and black (K) arranged in tandem. , 2M, 2C, 2K. Here, in each of the photoreceptors 2Y, 2M, 2C, and 2K, 2Y represents a yellow photoreceptor, 2M represents a magenta photoreceptor, 2C represents a cyan photoreceptor, and 2K represents a black photoreceptor. Similarly, the members of the respective colors are represented by adding Y, M, C, and K of the respective colors to the reference numerals of the members.
Each of the photoreceptors 2Y, 2M, 2C, and 2K is composed of a photoreceptor drum in the example shown in FIG. Each of the photoconductors 2Y, 2M, 2C, and 2K can also be configured as an endless belt.

  These photoreceptors 2Y, 2M, 2C, and 2K are configured to rotate clockwise as indicated by arrows in FIG. 1 during operation. Around the photoreceptors 2Y, 2M, 2C, 2K, charging members 3Y, 3M, 3C, 3K, exposure devices 4Y, 4M, 4C, 4K, developing devices 5Y, 5M, 5C, 5K, photoconductor squeeze devices 6Y, 6M, 6C, 6K, primary transfer devices 7Y, 7M, 7C, 7K, static eliminators 8Y, 8M, 8C, 8K, and photoconductor cleaning devices 9Y, 9M, 9C, 9K is provided.

  Further, the image forming apparatus 1 includes an endless intermediate transfer belt 10 that is an intermediate transfer medium. The intermediate transfer belt 10 is stretched between a pair of driving rollers 11 and a driven roller 12 that are spaced apart from each other, and is provided to be able to rotate counterclockwise in FIG. The intermediate transfer belt 10 is preferably an elastic intermediate transfer belt in order to improve at least the transfer efficiency of secondary transfer onto a transfer material such as paper.

  Further, in the image forming apparatus 1 of this example, the photoreceptors 2Y, 2M, 2C, and 2K and the developing devices 5Y, 5M, 5C, and 5K have colors Y, M, C, and C from the upstream side in the rotation direction of the intermediate transfer belt 10, respectively. Although arranged in the order of K, the arrangement order of the colors Y, M, C, and K can be arbitrarily set. The intermediate transfer medium can also be constituted by an intermediate transfer drum.

  In the vicinity of the primary transfer devices 7Y, 7M, 7C, and 7K on the downstream side in the rotation direction of the intermediate transfer belt 10 from the primary transfer devices 7Y, 7M, 7C, and 7K, intermediate transfer belt squeeze devices 13Y, 13M, and 13C, respectively. , 13K are arranged. Further, a secondary transfer device 14 is provided on the drive roller 11 side of the intermediate transfer belt 10, and an intermediate transfer belt cleaning device 15 is provided on the driven roller 12 side of the intermediate transfer belt 10.

  Although not shown, the image forming apparatus 1 in this example transfers, for example, paper or the like to the upstream side in the transfer material conveyance direction from the secondary transfer apparatus 14 in the same manner as a conventional general image forming apparatus that performs secondary transfer. A transfer material storage device for storing the material, and a pair of registration rollers for supplying the transfer material from the transfer material storage device to the secondary transfer device 14 are provided. Similarly, the image forming apparatus 1 includes a fixing device and a paper discharge tray on the downstream side in the transfer material transport direction from the secondary transfer device 14.

Each charging member 3Y, 3M, 3C, 3K is composed of, for example, a charging roller. A bias having the same polarity as the charging polarity of the liquid developer is applied to each charging member 3Y, 3M, 3C, 3K from a power supply device (not shown). The charging members 3Y, 3M, 3C, and 3K charge the corresponding photoreceptors 2Y, 2M, 2C, and 2K, respectively.
In addition, each of the exposure devices 4Y, 4M, 4C, and 4K irradiates the electrostatic latent image by irradiating the corresponding charged photoreceptors 2Y, 2M, 2C, and 2K with laser light from, for example, a laser scanning optical system. An image is formed.

  Each of the developing devices 5Y, 5M, 5C, and 5K includes a developer supply unit 16Y, 16M, 16C, and 16K, a developing roller 17Y, 17M, 17C, and 17K, a compaction roller 18Y, 18M, 18C, and 18K, and a developing unit. The roller cleaners 19Y, 19M, 19C, and 19K and the developing roller cleaner recovery liquid storage units 20Y, 20M, 20C, and 20K are configured.

  The developer supply units 16Y, 16M, 16C, and 16K respectively include developer containers 22Y, 22M, 22C, and 22K that store liquid developers 21Y, 21M, 21C, and 21K including toner particles and a nonvolatile liquid carrier. It comprises developer pumping rollers 23Y, 23M, 23C, and 23K, anilox rollers 24Y, 24M, 24C, and 24K, and developer regulating blades 25Y, 25M, 25C, and 25K.

  In the liquid developers 21Y, 21M, 21C, and 21K accommodated in the developer containers 22Y, 22M, 22C, and 22K, the toner may be a known pigment or the like in a known thermoplastic resin used for the toner. For example, particles having an average particle diameter of 1 μm in which a colorant is dispersed can be used. In the case of a low-viscosity low-concentration liquid developer, for example, an organic solvent, phenylmethylsiloxane, dimethylpolysiloxane can be used. Insulating liquid carriers such as silicone oil and mineral oil having a flash point of 210 ° C. or higher such as polydimethylcyclosiloxane can be used. The liquid developers 21Y, 21M, 21C, and 21K are obtained by adding toner particles together with a dispersant to a liquid carrier so that the toner solid content concentration is about 20%.

  The developer pumping rollers 23Y, 23M, 23C, and 23K pump the liquid developers 21Y, 21M, 21C, and 21K in the developer containers 22Y, 22M, 22C, and 22K, respectively, and the anilox rollers 24Y, 24M, and 24K, respectively. It is a roller for supplying to 24C and 24K. Each of the developer pumping rollers 23Y, 23M, 23C, and 23K is configured to rotate clockwise as indicated by an arrow in FIG. Each of the anilox rollers 24Y, 24M, 24C, and 24K is a roller that is a cylindrical member and has a fine and uniform spiral groove formed on the surface thereof. For example, the groove pitch is set to about 130 μm and the groove depth is set to about 30 μm. Of course, the dimension of the groove is not limited to these values. Each of the anilox rollers 24Y, 24M, 24C, and 24K is configured to rotate counterclockwise as indicated by an arrow in FIG. 1 in the same direction as each of the developing rollers 17Y, 17M, 17C, and 17K. The anilox rollers 24Y, 24M, 24C, and 24K can be rotated together with the developing rollers 17Y, 17M, 17C, and 17K. That is, the rotation direction of the anilox rollers 24Y, 24M, 24C, and 24K is not limited and is arbitrary.

  The developer regulating blades 25Y, 25M, 25C, and 25K are provided in contact with the surfaces of the anilox rollers 24Y, 24M, 24C, and 24K, respectively. These developer regulating blades 25Y, 25M, 25C, and 25K are respectively made of a rubber portion made of urethane rubber or the like that contacts the surfaces of the anilox rollers 24Y, 24M, 24C, and 24K, and a metal that supports the rubber portion. Etc., and the like. Each of the developer regulating blades 25Y, 25M, 25C, and 25K scrapes and removes the liquid developer that adheres to the surfaces other than the groove portions of the anilox rollers 24Y, 24M, 24C, and 24K with a rubber portion. Therefore, each anilox roller 24Y, 24M, 24C, 24K supplies only the liquid developer adhering in the groove portion to each developing roller 17Y, 17M, 17C, 17K.

  Each of the developing rollers 17Y, 17M, 17C, and 17K is a cylindrical member having a predetermined width. For example, an elastic body such as conductive urethane rubber, a resin layer, or a rubber layer is provided on the outer periphery of a metal shaft such as iron. It is provided. These developing rollers 17Y, 17M, 17C, and 17K are in contact with the photosensitive members 2Y, 2M, 2C, and 2K, respectively, and are rotated counterclockwise as indicated by arrows in FIG.

  Each of the developing rollers 17Y, 17M, 17C, and 17K is, for example, a cylindrical conductive material having a predetermined width formed of a conductive resin layer such as conductive urethane rubber or a conductive rubber layer on the outer peripheral portion of a metal shaft such as iron. An elastic body is provided. These developing rollers 17Y, 17M, 17C, and 17K are in contact with the photosensitive members 2Y, 2M, 2C, and 2K, respectively, and are rotated counterclockwise as indicated by arrows in FIG.

  Each of the compaction rollers 18Y, 18M, 18C, and 18K is rotated clockwise as indicated by an arrow in FIG. Each of the compaction rollers 18Y, 18M, 18C, and 18K is applied with a voltage to charge the corresponding developing rollers 17Y, 17M, 17C, and 17K. In that case, the voltage applied to each compaction roller 18Y, 18M, 18C, 18K is set to a direct current voltage (DC). Further, as shown in FIG. 2, the voltage applied to each of the compaction rollers 18Y, 18M, 18C, and 18K can be set to a voltage in which an AC voltage (AC) is superimposed on a DC voltage (DC). The compaction rollers 18Y, 18M may be applied to the compaction rollers 18Y, 18M, 18C, 18K, regardless of whether they are a direct current voltage or a superimposed voltage of a direct current voltage (DC) and an alternating current voltage (AC). , 18C, 18K and the developing rollers 17Y, 17M, 17C, 17K are set to be larger than the discharge start voltage for starting discharge according to Paschen's law.

  When the developing rollers 17Y, 17M, 17C, and 17K are charged by the compaction rollers 18Y, 18M, 18C, and 18K, the liquid developers 21Y, 21M, 21C, and 21K on the developing rollers 17Y, 17M, 17C, and 17K, respectively. Is pressed against the developing rollers 17Y, 17M, 17C, and 17K. By the way, the resistance of each compaction roller 18Y, 18M, 18C, 18K is relatively important. That is, when the resistance of each of the compaction rollers 18Y, 18M, 18C, and 18K is low, spark discharge occurs, and each of the developing rollers 17Y, 17M, 17C, and 17K, each of the compaction rollers 18Y, 18M, 18C, and 18K, and the liquid development. The agent will be damaged. Therefore, it is preferable that the compaction rollers 18Y, 18M, 18C, and 18K have an actual resistance value of Log 7Ω or more in order to uniformly perform good compaction of the liquid developer without causing such damage.

The measurement of the resistance of each compaction roller 18Y, 18M, 18C, 18K will be described.
As shown in FIG. 3, a compaction roller β, which is an object to be measured, is brought into contact with a metal roller α such as an aluminum tube. In a contact state between the metal roller α and the compaction roller β, the metal roller α and the compaction roller β are electrically connected by a constant voltage power source γ (for example, R8340A manufactured by Advantest). Then, a predetermined load F (for example, 250 g) is applied to the metal shafts at both ends of the compaction roller β so that the compaction roller β is in pressure contact with the metal roller α. Further, the metal roller α is rotated at a predetermined rotation speed (for example, 5 rpm). In this state, a predetermined voltage (for example, 100 V to 500 V) is applied from the constant voltage power source γ, and the current value flowing through the ammeter γ1 of the constant voltage power source γ is read. Finally, based on the read current value and voltage, the resistance value R is calculated from the equation V = IR (V: voltage, I: current, R: resistance).

  As shown in FIGS. 4 and 5, each compaction roller 18Y, 18M, 18C, 18K has a predetermined gap with respect to the outer peripheral surface of each developing roller 17Y, 17M, 17C, 17K to which the outer peripheral surface corresponds. G (μm) is placed. In this case, the gaps G (μm) of these developing rollers 17Y, 17M, 17C, and 17K are formed by the liquid developers 21Y, 21M, 21C, and 21K supplied from the anilox rollers 24Y, 24M, 24C, and 24K. It is set to be larger than the film thickness t (μm) of the developer layer 21a formed on the outer peripheral surface. Accordingly, the compaction rollers 18Y, 18M, 18C, and 18K perform non-contact compaction on the liquid developers 21Y, 21M, 21C, and 21K on the development rollers 17Y, 17M, 17C, and 17K.

  As described above, when non-contact compaction is performed on the liquid developers 21Y, 21M, 21C, and 21K, the above-described ribs in which the liquid carrier partially adheres to the compaction rollers 18Y, 18M, 18C, and 18K after the compaction occurs. The minimum bias (DC voltage) VCR (V) applied to each of the compaction rollers 18Y, 18M, 18C, and 18K that can be developed with high efficiency without change varies according to the gap G. For example, as shown in FIG. 6, when a bias (DC voltage) VDR applied to each developing roller 17Y, 17M, 17C, 17K is 400 (V), it is applied to each compaction roller 18Y, 18M, 18C, 18K. The relationship between the minimum bias VCR (V) and the gap G (μm) is such that the minimum bias VCR (V) increases as the gap G (μm) increases. Therefore, the gap G can be determined based on the relationship between the voltage applied to each of the compaction rollers 18Y, 18M, 18C, and 18K shown in FIG.

Further, in each of the developing devices 5Y, 5M, 5C, and 5K in this example, the width of each developing roller 17Y, 17M, 17C, and 17K (the length in the axial direction) and the width of each compaction roller 18Y, 18M, 18C, and 18K, respectively. (Axial length), the width (axial length) of each anilox roller 24Y, 24M, 24C, 24K and each developing roller (DR) cleaner 19Y, 19M, 19C, 19K is set as follows: Has been. That is, as shown in FIG. 5, in any of the developing devices 5Y, 5M, 5C, and 5K, the width W _CPR (mm) of each of the compaction rollers 18Y, 18M, 18C, and 18K is set to be the smallest. Further, the width W _DR (mm) of each of the developing rollers 17Y, 17M, 17C, and 17K is set larger than the width W _CPR (mm) of each of the compaction rollers 18Y, 18M, 18C, and 18K. Further, the width W _AR (mm) of each anilox roller 24Y, 24M, 24C, 24K is set larger than the width W _DR (mm) of each developing roller 17Y, 17M, 17C, 17K. Further, the width W _DRC (mm) of each developing roller (DR) cleaner 19Y, 19M, 19C, 19K is set to be greater than the width W _AR (mm) of each anilox roller 24Y, 24M, 24C, 24K. That is, W _CPR <W _DR <W _AR ≦ W _DRC . Further, the width W _CPR (mm) of each of the compaction rollers 18Y, 18M, 18C, and 18K is based on the effective width W _DRI (mm) that is the conveyance area of the image forming developer of each of the developing rollers 17Y, 17M, 17C, and 17K. It is set large. That is, W _CPR > W _DRI .

  Each of the compaction rollers 18Y, 18M, 18C, and 18K is provided with compaction roller cleaner blades 26Y, 26M, 26C, and 26K, and compaction roller cleaner recovery liquid storage units 27Y, 27M, 27C, and 27K, respectively. These compaction roller cleaner blades 26Y, 26M, 26C, and 26K are made of, for example, rubber that abuts against the surfaces of the corresponding compaction rollers 18Y, 18M, 18C, and 18K, and remain on the compaction rollers 18Y, 18M, 18C, and 18K. The developer to be removed is scraped off and removed. Further, each of the compaction roller cleaner recovered liquid reservoirs 27Y, 27M, 27C, and 27K is respectively scraped off from the compaction rollers 18Y, 18M, 18C, and 18K by the compaction roller cleaner blades 26Y, 26M, 26C, and 26K. It is comprised from containers, such as a tank which stores.

  Further, each of the developing roller cleaners 19Y, 19M, 19C, 19K is formed in a blade shape, and is composed of, for example, rubber or the like that abuts against the surface of the corresponding developing roller 17Y, 17M, 17C, 17K. The developing rollers 17Y, 17M , 17C, 17K for scraping off and removing the developer. Further, the developing roller cleaner collection liquid storage units 20Y, 20M, 20C, and 20K respectively remove the developer scraped off from the developing rollers 17Y, 17M, 17C, and 17K by the developing roller cleaners 19Y, 19M, 19C, and 19K. It is comprised from containers, such as a tank to store.

  Further, the image forming apparatus 1 of this example includes developer replenishing devices 28Y, 28M, 28C, and 28K that replenish liquid developers 21Y, 21M, 21C, and 21K to the developer containers 22Y, 22M, 22C, and 22K, respectively. Yes. These developer replenishing devices 28Y, 28M, 28C, and 28K are respectively composed of toner tanks 29Y, 29M, 29C, and 29K, carrier tanks 30Y, 30M, 30C, and 30K, and stirring devices 31Y, 31M, 31C, and 31K. It has become.

  The toner tanks 29Y, 29M, 29C, and 29K store the high-concentration liquid toners 32Y, 32M, 32C, and 32K, respectively. The carrier tanks 30Y, 30M, 30C, and 30K contain liquid carriers (carrier oils) 33Y, 33M, 33C, and 33K, respectively. Further, the stirrers 31Y, 31M, 31C, and 31K include a predetermined amount of the high-concentration liquid toners 32Y, 32M, 32C, and 32K from the toner tanks 29Y, 29M, 29C, and 29K and the carrier tanks 30Y, 30M, and 30K, respectively. A predetermined amount of each liquid carrier 33Y, 33M, 33C, 33K from 30C, 30K is supplied.

  The stirrers 31Y, 31M, 31C, and 31K respectively mix and stir the supplied high-concentration liquid toners 32Y, 32M, 32C, and 32K and the liquid carriers 33Y, 33M, 33C, and 33K, respectively, and develop each of them. Liquid developers 21Y, 21M, 21C, and 21K used in the apparatuses 5Y, 5M, 5C, and 5K are prepared. In that case, the viscosity of each liquid developer 21Y, 21M, 21C, 21K is preferably 100 mPas to 1000 mPas, and the viscosity of the liquid carrier (carrier oil) alone is preferably 10 mPas to 200 mPas. The measuring method of a viscosity is measured, for example using viscoelasticity measuring apparatus ARES (made by TA instrument Japan). The liquid developers 21Y, 21M, 21C, and 21K produced by the stirrers 31Y, 31M, 31C, and 31K are supplied to the developer containers 22Y, 22M, 22C, and 22K, respectively.

  Each photoconductor squeeze device 6Y, 6M, 6C, 6K includes a squeeze roller 34Y, 34M, 34C, 34K, a squeeze roller cleaner 35Y, 35M, 35C, 35K, and a squeeze roller cleaner recovery liquid storage container 36Y, 36M, 36C, 36K. The squeeze rollers 34Y, 34M, 34C, and 34K are respectively connected to the photosensitive members 2Y, 2Y, and the contact portions (nip portions) between the photosensitive members 2Y, 2M, 2C, and 2K and the developing rollers 17Y, 17M, 17C, and 17K. It is installed on the downstream side in the rotational direction of 2M, 2C, 2K. These squeeze rollers 34Y, 34M, 34C, and 34K are rotated in the opposite direction (counterclockwise in FIG. 1) to the respective photoreceptors 2Y, 2M, 2C, and 2K, and thus the respective photoreceptors 2Y, 2M, and The liquid carrier on 2C, 2K is removed.

  As each of the squeeze rollers 34Y, 34M, 34C, 34K, an elastic roller in which an elastic member such as conductive urethane rubber and a fluororesin surface layer are arranged on the surface of a metal core is suitable. Each of the squeeze roller cleaners 35Y, 35M, 35C, and 35K is made of an elastic body such as rubber and is in contact with the surface of the corresponding squeeze roller 34Y, 34M, 34C, 34K. The liquid carrier remaining on 34M, 34C, and 34K is scraped off and removed. Furthermore, each squeeze roller cleaner recovery liquid storage container 36Y, 36M, 36C, 36K is a container such as a tank for storing developer scraped off by the corresponding squeeze roller cleaner 35Y, 35M, 35C, 35K.

  Each of the primary transfer devices 7Y, 7M, 7C, and 7K includes primary transfer backup rollers 37Y, 37M, 37C, and 37K that bring the intermediate transfer belt 10 into contact with the photoreceptors 2Y, 2M, 2C, and 2K, respectively. Yes. Each of the backup rollers 37Y, 37M, 37C, and 37K is applied with, for example, about -200 V having a polarity opposite to the charged polarity of the toner particles, and the developer images on the photoreceptors 2Y, 2M, 2C, and 2K are transferred to the intermediate transfer belt 10. Primary transfer. Further, the static eliminators 8Y, 8M, 8C, and 8K remove charges remaining on the photoreceptors 2Y, 2M, 2C, and 2K after the primary transfer, respectively.

  Each of the photoconductor cleaning devices 9Y, 9M, 9C, and 9K includes photoconductor cleaners 38Y, 38M, 38C, and 38K and photoconductor cleaner collection liquid storage containers 39Y, 39M, 39C, and 39K. Each of the photoconductor cleaners 38Y, 38M, 38C, and 38K is made of an elastic material such as rubber, and is in contact with the surface of the corresponding photoconductor 2Y, 2M, 2C, 2K, respectively, so that the photoconductors 2Y, 2M, 2C, The developer remaining at 2K is scraped off and removed. The photoreceptor cleaner collection liquid storage containers 39Y, 39M, 39C, and 39K collect the developer scraped off from the photoreceptors 2Y, 2M, 2C, and 2K by the photoreceptor cleaners 38Y, 38M, 38C, and 38K, respectively. It is to be stored.

  Each of the intermediate transfer belt squeeze devices 13Y, 13M, 13C, and 13K includes an intermediate transfer belt squeeze roller 40Y, 40M, 40C, and 40K, an intermediate transfer belt squeeze roller cleaner 41Y, 41M, 41C, and 41K, and an intermediate transfer belt squeeze, respectively. It consists of roller cleaner collection liquid storage containers 42Y, 42C, 42K, and 42K. Each of the intermediate transfer belt squeeze rollers 40Y, 40M, 40C, and 40K collects the liquid carrier of the corresponding color on the intermediate transfer belt 10, respectively. The intermediate transfer belt squeeze roller cleaners 41Y, 41M, 41C, and 41K scrape the collected liquid carriers on the intermediate transfer belt squeeze rollers 40Y, 40M, 40C, and 40K, respectively. These intermediate transfer belt squeeze roller cleaners 41Y, 41M, 41C, and 41K are each made of an elastic material such as rubber, like the squeeze roller cleaners 35Y, 35M, 35C, and 35K. Further, each intermediate transfer belt squeeze roller cleaner recovery liquid storage container 42M, 42C, 42K, 42K collects and stores the liquid carrier scraped by each intermediate transfer belt squeeze roller cleaner 41Y, 41M, 41C, 41K. .

  The secondary transfer device 14 includes a secondary transfer roller 43. The secondary transfer roller 43 brings a transfer material such as paper into contact with the intermediate transfer belt 10 hung on the driving roller 11 to produce a color toner image obtained by combining the toner images of the respective colors on the intermediate transfer belt 10. It is transferred to a transfer material. In that case, the drive roller 11 also functions as a backup roller during secondary transfer.

  Although not shown, the secondary transfer device 14 includes a secondary transfer roller cleaner and a secondary transfer roller cleaner recovery liquid storage container. The secondary transfer roller cleaner is made of an elastic body such as rubber similarly to the squeeze roller cleaners 35Y, 35M, 35C, and 35K. The secondary transfer roller cleaner is in contact with the secondary transfer roller 43 and scrapes off and removes the developer remaining on the surface of the secondary transfer roller 43 after the secondary transfer. The secondary transfer roller cleaner collection liquid storage container collects and stores the developer scraped off from the secondary transfer roller 43 by the secondary transfer roller cleaner.

  The intermediate transfer belt cleaning device 15 includes an intermediate transfer belt cleaner 44 and an intermediate transfer belt cleaner recovery liquid storage container 45. The intermediate transfer belt cleaner 44 is in contact with the intermediate transfer belt 10 and scrapes off and removes the developer remaining on the surface of the intermediate transfer belt 10 after the secondary transfer. In that case, the driven roller 12 also functions as a backup roller at the time of cleaning the intermediate transfer belt. The intermediate transfer belt cleaner 44 is made of an elastic body such as rubber. The intermediate transfer belt cleaner collection liquid storage container 45 collects and stores the developer scraped off from the intermediate transfer belt 10 by the intermediate transfer belt cleaner 44.

  In the image forming apparatus 1 of this example configured as described above, when the image forming operation is started, the photoconductors 2Y, 2M, 2C, and 2K are uniformly formed by the charging members 3Y, 3M, 3C, and 3K, respectively. Charged. Next, an electrostatic latent image of each color is formed on each photoreceptor 2Y, 2M, 2C, 2K by each exposure device 4Y, 4M, 4C, 4K.

  In the yellow Y developing device 5Y, the yellow Y liquid developer 21Y is pumped up to the anilox roller 24Y by the developer pumping roller 23Y. An appropriate amount of the liquid developer 21Y attached to the anilox roller 24Y is attached to the groove of the anilox roller 24Y by the developer regulating blade 25Y. The liquid developer 21Y in the groove of the anilox roller 24Y is supplied to the developing roller 17Y.

At this time, a part of the liquid developer 21Y supplied to the developing roller 17Y moves toward the left and right ends of the developing roller 17Y. However, since the width W _AR of the anilox roller 24Y is larger than the width W _DR of the developing roller 17Y, the liquid developer 21Y reaches the left and right ends of the developing roller 17Y includes a developing roller 17Y further outside of the anilox roller from both ends of 24Y Move towards the left and right ends of. This suppresses occurrence of a nip accumulation of the liquid developer 21Y immediately before the nip portion between the developing roller 17Y and the anilox roller 24Y at both left and right ends of the developing roller 17Y. Therefore, the film thickness of the liquid developer 21Y on the developing roller 17Y is substantially uniform.

  Further, the yellow (Y) toner particles of the liquid developer 21 on the developing roller 17Y are pressed against the developing roller 17Y by non-contact compaction by the compaction roller 18Y. In this state, the liquid developer 21Y on the developing roller 17Y is conveyed toward the photoreceptor 2Y by the rotation of the developing roller 17Y.

  The carrier remaining on the compaction roller 18Y after the non-contact compaction by the developing roller 17Y is removed from the compaction roller 18Y by the compaction roller cleaner blade 26Y.

The electrostatic latent image formed on the yellow Y photoreceptor 2Y is developed with the yellow Y liquid developer 21Y in the developing device 5Y, and a yellow Y liquid developer image is formed on the photoreceptor 2Y. The developer remaining on the developing roller 17Y after development is removed from the developing roller 17Y by the developing roller cleaner 19Y. At this time, since the width W _DRC (mm) of the developing roller cleaner 19Y is set larger than the width W _CPR (mm) of the compaction roller 18Y (W _DRC > W _CPR ), the compaction is performed at both left and right ends of the developing roller 17Y. The liquid developer moving outward from the left and right ends of the roller 18Y is removed by the developing roller cleaner 19Y. As a result, the occurrence of nip accumulation of the liquid developer between the developing roller 17Y and the compaction roller 18Y is further effectively suppressed.

  The yellow Y liquid developer image on the photoreceptor 2Y is made into a yellow Y toner image by collecting the liquid carrier on the photoreceptor 2Y by the squeeze roller 34Y. Further, the yellow Y toner image is transferred to the intermediate transfer belt 10 by the primary transfer device 7Y. The yellow Y toner image on the intermediate transfer belt 10 is conveyed toward the primary transfer device 7M of magenta M while the liquid carrier on the intermediate transfer belt 10 is collected by the intermediate transfer belt squeeze roller 40Y.

Next, the electrostatic latent image formed on the photoconductor 2M of magenta M is developed in the developing device 5M with the magenta M liquid developer conveyed in the same manner as in the case of yellow Y, and the magenta M is developed on the photoconductor 2M. The liquid developer image is formed.
At this time, the carrier remaining on the compaction roller 18M after the non-contact compaction by the compaction roller 18M is removed from the compaction roller 18M by the compaction roller cleaner blade 26M. The developer remaining on the developing roller 17M after development is removed from the developing roller 17M by the developing roller cleaner 19M.

  The magenta M liquid developer image on the photoconductor 2M is recovered as a magenta M toner image by collecting the liquid carrier on the photoconductor 2M by the squeeze roller 34M, and this magenta M toner image is intermediated by the primary transfer device 7M. The yellow Y toner image is superimposed on the transfer belt 10 and transferred. Similarly, the color-superposed yellow Y and magenta M toner images are conveyed toward the cyan C primary transfer device 7C while the liquid carrier on the intermediate transfer belt 10 is collected by the intermediate transfer belt squeeze roller 40Y. . In the same manner, a cyan toner image and a black toner image are sequentially superimposed and transferred onto the intermediate transfer belt 10 to form a full-color toner image on the intermediate transfer belt 10.

  Next, the secondary transfer device 14 secondarily transfers the color toner image on the intermediate transfer belt 10 onto the transfer surface of a transfer material such as paper. The color toner image transferred onto the transfer material is fixed by a fixing device (not shown) as in the prior art, and the transfer material on which the full-color fixed image is formed is conveyed to a paper discharge tray, and the color image forming operation is completed. To do.

  According to the image forming apparatus 1 of this example, between the developing rollers 17Y, 17M, 17C, and 17K and the compaction rollers 18Y, 18M, 18C, and 18K, on the developing rollers 17Y, 17M, 17C, and 17K, respectively. A gap G larger than the film thickness t of each of the liquid developers 21Y, 21M, 21C, and 21K is provided. Accordingly, the compaction rollers 18Y, 18M, 18C, and 18K are not in contact with the liquid developers 21Y, 21M, 21C, and 21K on the development rollers 17Y, 17M, 17C, and 17K, respectively. Compact without contact.

  Therefore, it is possible to suppress the nip accumulation of the liquid developer between the developing rollers 17Y, 17M, 17C, and 17K and the compaction rollers 18Y, 18M, 18C, and 18K. Further, since each of the developing rollers 17Y, 17M, 17C, and 17K and each of the compaction rollers 18Y, 18M, 18C, and 18K are not in contact with each other, it is possible to suppress the liquid disturbance of the aforementioned ribs and the like. Thus, since the nip accumulation and liquid disturbance of each liquid developer 21Y, 21M, 21C, 21K can be suppressed, good image quality can be obtained for a long time and effectively.

Further, since the width _WDR of each developing roller is set to be larger than the width W _{CPR of} each corresponding compaction roller, there is a liquid between each developing roller and each compaction roller at the left and right ends of each compaction roller. Occurrence of developer nip accumulation can be more effectively suppressed. Thereby, the film thickness of the liquid developer on the developing rollers 17Y, 17M, 17C, and 17K after compaction can be made even more uniform. Accordingly, it is possible to prevent image disturbance due to non-uniform film thickness of the liquid developer, and to obtain good image quality stably over the long term.

In particular, in each of the developing devices 5Y, 5M, 5C, and 5K in this example, the width W _DRC of each of the developing roller cleaners 19Y, 19M, 19C, and 19K is set to the width W _DR of each of the corresponding compaction rollers 18Y, 18M, 18C, and 18K. Since it is set to be larger than _CPR, the liquid developer that moves outward from the left and right ends of the respective compaction rollers 18Y, 18M, 18C, and 18K at the left and right ends of each of the developing rollers 17Y, 17M, 17C, and 17K. It is removed by developing roller cleaners 19Y, 19M, 19C, and 19K. Accordingly, it is possible to more effectively suppress the nip accumulation of the liquid developer between the developing rollers 17Y, 17M, 17C, and 17K and the compaction rollers 18Y, 18M, 18C, and 18K. Therefore, the film thickness of the liquid developer on the developing rollers 17Y, 17M, 17C, and 17K after compaction can be made more uniform.

  Furthermore, the applied voltage of each of the compaction rollers 18Y, 18M, 18C, and 18K is a superimposed voltage of a direct current voltage (DC) and an alternating current voltage (AC), so that the liquid developer can be made uniform even when non-contact compaction is performed. Compaction is possible. Thereby, much better image quality can be obtained.

  Furthermore, since each compaction roller 18Y, 18M, 18C, 18K does not contact the liquid carrier, each liquid carrier is difficult to adhere to each compaction roller 18Y, 18M, 18C, 18K after compaction. Thereby, it can suppress that each liquid carrier reduces, respectively.

  Next, specific examples 1 relating to the developing roller (DR), the compaction roller (CPR), the anilox rollers 24Y, 24M, 24C, and 24K and the developing roller cleaners 19Y, 19M, 19C, and 19K in the developing device of the present invention. And 2 will be described. These Examples 1 and 2 are shown in Table 1. The electrical resistance of each roller shown in Table 1 is measured by the measurement method shown in FIG.

  First, Example 1 will be described. As shown in Table 1, in Example 1, the developing roller (DR) is made of urethane rubber, and the outer diameter is set to 24 mm. The developing roller (DR) (urethane rubber) has a hardness of JIS-A 30 °. Further, the electric resistance of the developing roller (DR) (urethane rubber) is Log 4Ω as an actual resistance.

For the compaction roller (CPR), a steel metal shaft having a diameter of 20 mm is used as a core material. A compaction portion is formed on the outer peripheral surface of the metal shaft. A PFA 100 μm tube is used for this compaction section. The electric resistance of the compaction roller is an actual resistance of Log 7Ω.
Further, the gap G between the developing roller (DR) and the compaction roller (CPR) is set to 150 μm.

Further, the width W _DR (mm) of the developing roller (DR) is set to 307 mm, the width W _AR (mm) of the anilox roller is set to 320 (mm), and the width W _CPR of the compaction roller (CPR). (Mm) is set to 300 mm, and the width W _DRC (mm) of the developing roller cleaner (DR cleaner) is set to 320 mm. At this time, the effective width W _DRI (mm) that is the conveyance area (image effective range) of the image forming developer of the developing roller (DR) is set to 291 mm.

The applied voltage (bias) of the developing roller (DR) is a DC voltage V _DR (V), and this DC voltage V _DR (V) is set to 300 (V). The applied voltage (bias) of the compaction roller (CPR) is also a DC voltage V _CPR (V), and this DC voltage V _CPR (V) is set to 1800 (V). That is, in Example 1, the applied voltage of the compaction roller (CPR) is only the direct-current voltage (DC) V _CPR (V). At this time, the voltage difference ΔV of the voltage between V _CPR (V) applied for the applied voltage V _DR (V) and compaction roller (CPR) of the developing roller (DR) is 1500 (V).

Next, Example 2 will be described. As shown in Table 1, in Example 2, the shape and material of the developing roller (DR), the shape and material of the compaction roller (CPR), the shape of the anilox roller (AR), and the gap G Is the same as that of the first embodiment. Also, the applied voltage (bias) of the developing roller (DR) is only the same DC voltage V _DR 300 (V) as in the first embodiment. Further, the applied voltage of the compaction roller (CPR) is a superimposed voltage of a direct current voltage (DC) and an alternating voltage (AC). In that case, the direct-current voltage (DC) V _CPR (V) is 1800 (V) which is the same as that in the first embodiment. The alternating voltage (AC) is a sine wave having an amplitude of 600 (V) and a frequency of 1500 Hz.

1 is a diagram schematically and partially showing an example of an embodiment of an image forming apparatus according to the present invention. It is a figure explaining the superimposed voltage of direct-current voltage and alternating current voltage. It is a figure explaining the measurement of the electrical resistance of each roller. It is a figure explaining the gap of a developing roller and a compaction roller. 2 is a diagram illustrating a positional relationship of each roller of the developing device. It is a figure explaining the relationship between the gap and applied voltage in non-contact compaction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2Y, 2M, 2C, 2K ... Each color photoconductor, 5Y, 5M, 5C, 5K ... Each color developing device, 6Y, 6M, 6C, 6K ... Photoconductor squeeze device, 7Y, 7M, 7C , 7K ... primary transfer device for each color, 10 ... intermediate transfer belt, 17Y, 17M, 17C, 17K ... developing roller, 18Y, 18M, 18C, 18K ... compaction roller, 19Y, 19M, 19C, 19K ... developing roller cleaner (DR Cleaner), 21Y, 21M, 21C, 21K ... Liquid developer, 21a ... Developer layer on developing roller, 24Y, 24M, 24C, 24K ... Anilox roller, 25Y, 25M, 25C, 25K ... Developer regulating blade, 26Y, 26M, 26C, 26K ... compaction roller cleaner blade, G ... gap, t ... thickness of the liquid developer on the developing roller, W _DR ... width of the developing roller, W _DRI ... developing low Image forming effective width, W _DRC ... width of the developing roller cleaner, W _CPR ... compaction roller width, W _AR ... anilox roller width

Claims (4)

A rotatable developing roller for transporting a liquid developer composed of toner and a liquid carrier for developing an electrostatic latent image on the latent image carrier, and a predetermined amount of liquid developer is supplied to the developing roller. At least a rotatable anilox roller, and a rotatable compaction roller that presses the toner of the liquid developer on the developing roller supplied by the anilox roller against the developing roller with an applied voltage;
The compaction roller is disposed with a gap larger than the film thickness of the liquid developer on the developing roller supplied by the anilox roller with respect to the developing roller,
The developing device, wherein a width of the developing roller is set larger than a width of the compaction roller. A developing roller cleaner for removing the liquid developer remaining on the developing roller after development;
The developing device according to claim 1, wherein a width of the developing roller cleaner is set larger than a width of the compaction roller. 3. The developing device according to claim 1, wherein the applied voltage of the compaction roller is only a DC voltage or a superimposed voltage of a DC voltage and an AC voltage. A latent image carrier that is provided rotatably and on which an electrostatic latent image is formed, and the electrostatic latent image is developed with a liquid developer composed of toner and a liquid carrier to form a developer image on the latent image carrier. At least a developing device to be formed, and a transfer device for transferring the developer image on the latent image carrier to a transferred transfer material,
The image forming apparatus according to claim 1, wherein the developing device is a developing device according to claim 1.

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