JP2009145753A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method and an image forming apparatus for obtaining good transfer efficiency while preventing the charge amount of toner from being excessive. <P>SOLUTION: In the image forming method, a toner charger for charging a liquid developer on a developer carrying member, and a bias applying means for applying a bias to a liquid developer image on the image carrying member, are used, wherein the bias set value of the bias applying means is adjusted in accordance with the charge amount of the toner charger. The image forming apparatus includes: the toner charger for charging the liquid developer on the developer carrying member; a charge adjusting means adjusting the charge amount from the toner charger; the bias applying means for applying the bias to the liquid developer image on the image carrying member; and a bias value adjusting means adjusting the bias value of the bias applying means in accordance with the charge amount adjusted by the charge adjusting means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention applies a developing bias to a developing roller using a liquid developer in which toner is dispersed in a non-volatile carrier liquid to develop a latent image on a latent image carrier to form a liquid developer image. The present invention relates to an image forming method and an image forming apparatus for transferring a liquid developer image on an image carrier onto the image carrier and transferring the liquid developer image transferred onto the image carrier onto a transfer material such as paper. .

Conventionally, an image forming apparatus using a liquid developer forms a liquid developer image by developing a latent image on a latent image carrier using a liquid developer in which toner is dispersed in a non-volatile carrier liquid. It has been practiced to form a full-color image by repeatedly transferring a liquid developer image on an image carrier a plurality of times and transferring the image onto a transfer material such as paper. In such an image forming apparatus, when the superimposed images on the image carrier are collectively transferred to the transfer material, there is a problem that the transfer efficiency is lowered due to the increase in the solid content concentration of the superimposed image. Japanese Patent Application Laid-Open No. 2000-122427 discloses a toner solid content of a liquid developer used for developing the second and subsequent colors when a plurality of colors are superimposed on an image carrier in order to suppress the occurrence of such problems. An image forming method has been proposed in which the rate is lower than the toner solid content of the liquid developer used for the development of the first color, and the superimposed image formed on the image carrier is easily transferred by electrophoresis. .
JP 2000-122427 A.

  In an image forming method using a liquid developer in which toner is dispersed in a non-volatile carrier liquid, in a method in which liquid developer images of a plurality of colors are superimposed on an image carrier, the toner layer transferred onto the image carrier is Every time color superposition is performed, an electric field that is pressed against the image carrier is received. In particular, the effect of the first color toner is significant. For example, in the case of a system having four color developing units, the first color is subjected to three electric fields after being transferred to the image carrier. Each time an electric field is applied, the toner particles are pressed against the image carrier, increasing the adhesion and making it difficult to peel off the image carrier.

  Further, when the image carrier has a squeeze mechanism for collecting the carrier liquid, an electric field that is pressed against the image carrier by passing through the squeeze nip is received, thereby increasing the charge amount of the toner particles to the image carrier. This increases the adhesion force of the toner, making it difficult to peel off from the image carrier and causing a problem that the transfer efficiency is lowered. As described above, in the image forming method using the liquid developer in which the toner is dispersed in the nonvolatile carrier liquid, the method of superimposing the liquid developer images of a plurality of colors on the image carrier, the toner particles and the image carrier are overlapped. There is a problem that the adhesive force tends to be high and a strong electric field is required to peel it off. Further, when the toner particle charge amount was investigated, it was found that if the toner particle charge amount becomes too high, transfer defects are likely to occur. This is because, as described above, a strong electric field is required to peel off the toner particles from the image carrier, that is, a large voltage difference is required between the transfer nips. As a result, the current flowing increases, and as a result, the voltage drop in the nip forming member (intermediate transfer member, transfer roller, etc.) and the paper increases, the voltage difference formed between the nips decreases, and a sufficient electric field is generated. The main reason is that it does not take.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image forming method and an image forming apparatus that prevent toner charge amount from becoming excessive and improve transfer efficiency. is there.

  According to a first aspect of the present invention, in the image forming method, the image forming method includes a toner charger that charges the liquid developer on the developer carrier, and a bias application unit that applies a bias to the liquid developer image on the image carrier. The bias setting value of the bias applying means is adjusted according to the charge amount of the toner charger. After the toner charge amount is appropriately adjusted by the toner charger disposed on the developer carrying member, the bias value from the bias applying unit is appropriately adjusted to suppress the charge injection to the toner, so that the toner charge amount is excessive. Can be prevented, and poor transfer to paper can be prevented.

  According to a second aspect of the present invention, in the image forming method according to the first aspect of the invention, the bias applying unit is at least one of a primary transfer bias applying unit, an on-photosensitive squeeze bias applying unit, and an intermediate transfer member squeeze bias applying unit. It is characterized by being. By adjusting at least one set value of the primary transfer bias, the squeeze on the photosensitive member, and the squeeze on the intermediate transfer member, the charge injection to the toner at the corresponding bias application unit is suppressed and the charge amount of the toner is increased. Can be prevented.

  The third invention is characterized in that, in the image forming method of the first or second invention, the charge amount of the toner charger is adjusted by patch density information of a patch density detecting means. By controlling the charge amount of the toner charger based on the patch density, it is possible to set an appropriate charge amount according to a change in toner characteristics, and to appropriately adjust the set value of the bias applying unit based on the charge amount.

  According to a fourth aspect of the invention, in the image forming method according to any one of the first to third aspects of the invention, the toner charger is a corona charger.

  According to a fifth aspect of the present invention, in the image forming apparatus, a toner charger for charging the liquid developer on the developer carrying member, a charge adjusting unit for adjusting a charge amount from the toner charger, and a liquid developer image on the image carrying member. And a bias value adjusting means for adjusting a bias value of the bias applying means in accordance with a charge amount adjusted by the charge adjusting means. After the toner charge amount is appropriately adjusted by the toner charger disposed on the developer carrying member, the bias value from the bias applying unit is appropriately adjusted to suppress the charge injection to the toner, so that the toner charge amount is excessive. Can be prevented, and poor transfer to paper can be prevented.

  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 a first embodiment 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, on-photosensitive squeeze devices 6Y, 6M, 6C, 6K, primary transfer devices 7Y, 7M, 7C, 7K, and static eliminating devices 8Y, 8M, 8C, 8K are arranged. Photoreceptor cleaning devices 9Y, 9M, 9C, and 9K are disposed between the charge removal devices 8Y, 8M, 8C, and 8K and the charging members 3Y, 3M, 3C, and 3K, respectively.

  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 around a belt driving roller 11 and a driven roller 13 to which a driving force of a motor (not shown) is transmitted, and is provided to be able to rotate counterclockwise in FIG.

  For example, as shown in FIG. 6, the intermediate transfer belt 10 uses a multilayer structure in which an elastic layer 10b is laminated on a base material layer 10a, and a coat layer 10c is formed on the surface of the elastic layer 10b. Also good. By adopting a multi-layer structure including the elastic layer 10b, the intermediate transfer belt 10 has an appropriate elasticity in the thickness direction so that the liquid developer images from the photoreceptors 2Y, 2M, 2C, and 2K can be transferred to the transfer material. The transferability is improved, and in particular, the transferability with large unevenness is excellent, and a clean image can be transferred to the recesses. The material constituting the base material layer 10a is a polyimide resin or polyamideimide resin, the material constituting the elastic layer 10b is polyurethane rubber or the like, and the material constituting the coat layer 10c is a fluororesin or the like. The intermediate transfer belt 10 may have a single layer structure. The intermediate transfer member may be an intermediate transfer roller.

  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 these colors Y, M, C, and K can be arbitrarily set.

  Although not shown, the image forming apparatus 1 of this example transfers, for example, paper or the like to the upstream side in the transfer material conveyance direction from the secondary transfer apparatus 16 in the same manner as a conventional general image forming apparatus that performs secondary transfer. A transfer material storage device that stores the material, and a registration roller pair 55 that conveys and supplies the transfer material from the transfer material storage device to the secondary transfer device 16 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 conveyance direction from the secondary transfer device 16.

  Each of the charging members 3Y, 3M, 3C, 3K is composed of, for example, a corona charger. 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 developer supplying units 18Y, 18M, 18C, and 18K, developing rollers 19Y, 19M, 19C, and 19K, toner chargers 20Y, 20M, 20C, and 20K, and developing rollers, respectively. Cleaners 21Y, 21M, 21C, and 21K are provided.

  The developer supply units 18Y, 18M, 18C, and 18K respectively include developer containers 24Y, 24M, 24C, and 24K that store liquid developers 23Y, 23M, 23C, and 23K including toner particles and a nonvolatile liquid carrier. Developer pumping rollers 25Y, 25M, 25C, and 25K, anilox rollers 26Y, 26M, 26C, and 26K, and developer regulating blades 27Y, 27M, 27C, and 27K are provided.

  In the liquid developers 23Y, 23M, 23C, and 23K accommodated in the developer containers 24Y, 24M, 24C, and 24K, as the toner, a known pigment or the like is similarly added into 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. On the other hand, as the liquid carrier, in the case of a low-viscosity low-concentration liquid developer, for example, an insulating liquid carrier of Isopar (trademark: Exxon) can be used. In the case of a liquid developer having a high viscosity and high concentration as a liquid carrier, for example, an organic solvent, a silicone oil having a flash point of 210 ° C. or higher, mineral oil, boiling point, such as phenylmethylsiloxane, dimethylpolysiloxane and polydimethylcyclosiloxane Use an insulating liquid carrier such as aliphatic saturated hydrocarbons such as liquid paraffin with a relatively low viscosity having a viscosity of 3 mPa · s at 170 ° C. or higher and normal viscosity, vegetable oil, edible oil, higher fatty acid ester, etc. Can do. The liquid developers 23Y, 23M, 23C, and 23K are obtained by adding toner particles to a liquid carrier together with a dispersant to a toner solid content concentration of about 20%. Further, the liquid developer can be charged by the action of a charge control agent or the like.

  The developer pumping rollers 25Y, 25M, 25C, and 25K pump up the liquid developers 23Y, 23M, 23C, and 23K in the developer containers 24Y, 24M, 24C, and 24K, respectively, and the anilox rollers 26Y, 26M, and 26K, respectively. It is a roller which supplies to 26C and 26K. Each of the developer pumping rollers 25Y, 25M, 25C, and 25K is configured to rotate clockwise as indicated by an arrow in FIG. Each of the anilox rollers 26Y, 26M, 26C, and 26K is a roller in which a spiral groove is finely and uniformly formed on the surface by a cylindrical member. For example, the groove pitch is set to about 170 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 26Y, 26M, 26C, and 26K is configured to rotate counterclockwise as indicated by an arrow in FIG. 1 in the same direction as each of the developing rollers 19Y, 19M, 19C, and 19K. The anilox rollers 26Y, 26M, 26C, and 26K can be rotated together with the developing rollers 19Y, 19M, 19C, and 19K. That is, the rotation direction of the anilox rollers 26Y, 26M, 26C, and 26K is not limited and is arbitrary.

  The developer regulating blades 27Y, 27M, 27C, and 27K are provided in contact with the surfaces of the anilox rollers 26Y, 26M, 26C, and 26K, respectively. These developer regulating blades 27Y, 27M, 27C, and 27K are respectively rubber parts made of urethane rubber and the like that contact the surfaces of the anilox rollers 26Y, 26M, 26C, and 26K, and a metal that supports the rubber parts. Etc., and the like. Each of the developer regulating blades 27Y, 27M, 27C, and 27K scrapes and removes the liquid developer that adheres to the surfaces other than the groove portions of the respective anilox rollers 26Y, 26M, 26C, and 26K with a rubber portion. Therefore, each anilox roller 26Y, 26M, 26C, 26K supplies only the liquid developer adhering in the groove to each developing roller 19Y, 19M, 19C, 19K.

  Each of the developing rollers 19Y, 19M, 19C, and 19K is a cylindrical member having a width of, for example, about 320 mm. For example, an elastic body such as conductive urethane rubber and a resin layer or rubber are provided on the outer periphery of a metal shaft such as iron. With a layer. The toner chargers 20Y, 20M, 20C, and 20K are disposed on the upstream side of the developing nip, and a current is supplied to the toner charger toner chargers 20Y, 20M, 20C, and 20K to charge the toner on the developing rollers 19Y, 19M, 19C, and 19K. The toner chargers 20Y, 20M, 20C, and 20K will be described later. These developing rollers 19Y, 19M, 19C, and 19K are in contact with the photosensitive members 2Y, 2M, 2C, and 2K, respectively, and are rotated counterclockwise as indicated by arrows in FIG. The toner is transferred from the developing rollers 19Y, 19M, 19C, and 19K to the photoreceptors 2Y, 2M, 2C, and the developing bias by the developing bias applied to the developing rollers 19Y, 19M, 19C, and 19K from a developing bias applying unit (not shown) at the developing position. Moving to 2K, the electrostatic latent image is visualized.

  Further, each of the developing roller cleaners 21Y, 21M, 21C, and 21K is configured by, for example, rubber or the like that contacts the surface of the corresponding developing roller 19Y, 19M, 19C, or 19K, and is connected to the developing rollers 19Y, 19M, 19C, and 19K. The residual developer is scraped off and removed. The developer scraped off from the developing rollers 19Y, 19M, 19C, and 19K by the developing roller cleaners 21Y, 21M, 21C, and 21K falls into the developer containers 24Y, 24M, 24C, and 24K.

  Further, the image forming apparatus 1 of this example includes developer supply devices 30Y, 30M, 30C, and 30K that supply the liquid developers 23Y, 23M, 23C, and 23K to the developer containers 24Y, 24M, 24C, and 24K, respectively. Yes. These developer replenishing devices 30Y, 30M, 30C, and 30K include toner tanks 31Y, 31M, 31C, and 31K, and carrier tanks 32Y, 32M, 32C, and 32K, respectively.

  The toner tanks 31Y, 31M, 31C, and 31K store the high-concentration liquid toners 34Y, 34M, 34C, and 34K, respectively. The carrier tanks 32Y, 32M, 32C, and 32K store liquid carriers (carrier oils) 35Y, 35M, 35C, and 35K, respectively. A predetermined amount of each high-concentration liquid toner 34Y, 34M, 34C, 34K from each toner tank 31Y, 31M, 31C, 31K and a predetermined amount of each liquid carrier 35Y, 35M, from each carrier tank 32Y, 32M, 32C, 32K 35C and 35K are supplied to the developer containers 24Y, 24M, 24C and 24K. The developer supply devices 30Y, 30M, 30C, and 30K are provided with a recovery carrier tank 70 that stores the recovered carriers and a new carrier tank 80 that stores new carriers, and the carrier tanks 32Y, 32M, 32C, Supply new carrier or collection carrier to 32K.

  In an image forming apparatus using a non-volatile carrier, if a large amount of carrier liquid is present in the step of melting and fixing a toner image transferred to a transfer material by heat, fixing failure occurs. For this reason, it is necessary to reduce the amount of the carrier liquid to a level at which it can be fixed by squeeze.

  Therefore, in the image forming apparatus 1 of this embodiment, the on-photosensitive squeeze devices 6Y, 6M, 6C, and 6K are arranged. Each of the on-photosensitive squeeze devices 6Y, 6M, 6C, and 6K includes the on-photosensitive squeeze rollers 36Y, 36M, 36C, and 36K, the on-photosensitive squeeze roller cleaners 37Y, 37M, 37C, and 37K, and the on-photosensitive squeeze roller. Roller cleaner recovery liquid storage containers 38Y, 38M, 38C, 38K are provided. The squeeze rollers 36Y, 36M, 36C, and 36K on the photosensitive members are respectively exposed to contact portions (nip portions) between the photosensitive members 2Y, 2M, 2C, and 2K and the developing rollers 19Y, 19M, 19C, and 19K. The body 2Y, 2M, 2C, 2K is installed downstream in the rotational direction. These on-photosensitive squeeze rollers 36Y, 36M, 36C, and 36K are rotated in the opposite direction (counterclockwise in FIG. 1) to the respective photosensitive elements 2Y, 2M, 2C, and 2K, and the same as the toner charging. By applying a voltage of polarity, the toner particles are pressed against the photoreceptors 2Y, 2M, 2C, and 2K, and only the supernatant carrier liquid is removed.

  As each of the on-photosensitive squeeze rollers 36Y, 36M, 36C, 36K, 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 on-photosensitive squeeze roller cleaners 37Y, 37M, 37C, and 37K is made of an elastic body such as rubber and is in contact with the surface of the corresponding squeeze roller 36Y, 36M, 36C, or 36K. The liquid carrier remaining on the body squeeze rollers 36Y, 36M, 36C, 36K is scraped off and removed. Further, the squeeze roller cleaner recovery liquid storage containers 38Y, 38M, 38C, and 38K are containers such as tanks that store the developer scraped off by the corresponding squeeze roller cleaners 37Y, 37M, 37C, and 37K. The collection carriers in each squeeze roller cleaner collection liquid storage container 38Y, 38M, 38C, 38K are transported to the collection carrier tank 70 and reused.

  Each of the primary transfer devices 7Y, 7M, 7C, and 7K includes backup rollers 39Y, 39M, 39C, and 39K for primary transfer that bring the intermediate transfer belt 10 into contact with the photoreceptors 2Y, 2M, 2C, and 2K, respectively. Yes. Each backup roller 39Y, 39M, 39C, 39K is applied with a voltage having a polarity opposite to the charged polarity of the toner particles, and each color toner image (liquid developer image) on each photoconductor 2Y, 2M, 2C, 2K is applied. Primary transfer is performed on the intermediate transfer belt 10. The photoreceptor cleaning devices 9Y, 9M, 9C, and 9K come into contact with the photoreceptors 2Y, 2M, 2C, and 2K after the primary transfer to scrape off and remove the remaining developer, and transport it to the collection carrier tank 70 for reuse. . 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.

  The secondary transfer device 16 includes a secondary transfer roller 43 that can be brought into contact with the belt driving roller 11 via the intermediate transfer belt 10. Further, the secondary transfer device 16 includes a secondary transfer roller cleaner 45 and a secondary transfer roller cleaner recovery liquid storage container 47 for the secondary transfer roller 43. The secondary transfer roller cleaner 45 is in contact with the secondary transfer roller 43 and scrapes off and removes foreign matters such as liquid developer remaining on the surface of the secondary transfer roller 43 after the secondary transfer. The secondary transfer roller cleaner recovered liquid storage container 47 recovers and stores the developer scraped off from the secondary transfer roller 43 by the secondary transfer roller cleaner 45, and is transported to the recovery carrier tank 70 for reuse. The Accordingly, it is possible to prevent the next transfer material from being affected by foreign matters such as liquid developer adhering to the secondary transfer roller 43. A squeeze roller 90 for collecting the carrier is provided on the driven roller 13 side of the intermediate transfer belt 10 after the secondary transfer, and an intermediate transfer belt cleaning device 17 is provided downstream thereof. The intermediate transfer belt cleaning device 17 includes an intermediate transfer belt cleaning blade 49 and an intermediate transfer belt cleaning recovery liquid storage container 60.

  FIG. 2 is a diagram schematically and partially showing a second embodiment of the image forming apparatus of the present invention. In addition, the same code | symbol is attached | subjected to the same component as the above-mentioned embodiment, and the detailed description is abbreviate | omitted. In the image forming apparatus 1 of the embodiment shown in FIG. 1 described above, the squeeze devices 6Y, 6M, 6C, and 6K on the photoconductor are arranged, whereas the image forming apparatus 1 of the second embodiment is an intermediate device. Intermediate transfer member squeeze devices 15Y, 15M, 15C, and 15K are arranged on the transfer belt 10. The intermediate transfer member squeeze devices 15Y, 15M, 15C, and 15K respectively include intermediate transfer member squeeze rollers 40Y, 40M, 40C, and 40K, and intermediate transfer member squeeze roller contact members 50Y, 50M, 50C, and 50K. Intermediate transfer body squeeze roller cleaners 41Y, 41M, 41C, and 41K and intermediate transfer body squeeze roller cleaner recovery liquid storage containers 42Y, 42C, 42K, and 42K are provided.

  The squeeze rollers 40Y, 40M, 40C, and 40K on the intermediate transfer body collect liquid carriers of corresponding colors on the intermediate transfer belt 10, respectively. By applying a voltage having the same polarity as the toner charge to the squeeze rollers 40Y, 40M, 40C, and 40K on each intermediate transfer member, the toner particles are pressed against the intermediate transfer belt 10 to remove only the supernatant carrier liquid.

  Each of the intermediate transfer member squeeze roller cleaners 41Y, 41M, 41C, and 41K scrapes the collected liquid carrier on the intermediate transfer member squeeze rollers 40Y, 40M, 40C, and 40K. These squeeze roller cleaners 41Y, 41M, 41C, and 41K on the intermediate transfer member are made of an elastic body such as rubber. Further, the squeeze roller cleaner recovery liquid storage containers 42M, 42C, 42K, and 42K on the intermediate transfer members recover and store the liquid carriers scraped by the squeeze roller cleaners 41Y, 41M, 41C, and 41K on the intermediate transfer members, respectively. It is transported to the collection carrier tank 70 and reused.

  FIG. 3 is a diagram schematically and partially showing the image forming apparatus 1 according to the third embodiment of the present invention. FIG. 5 is a partially enlarged view of the yellow image forming unit in FIG. In addition, the same code | symbol is attached | subjected to the same component as the above-mentioned embodiment, and the detailed description is abbreviate | omitted. In the image forming apparatus 1 of this embodiment, both the on-photosensitive squeeze devices 6Y, 6M, 6C, and 6K and the on-transfer intermediate squeeze devices 15Y, 15M, 15C, and 15K are arranged.

  FIG. 4 is a diagram schematically and partially showing an image forming apparatus 1 according to the fourth embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same component as the above-mentioned embodiment, and the detailed description is abbreviate | omitted. In the image forming apparatus 1 of this embodiment, both the on-photosensitive squeeze devices 6Y, 6M, 6C, and 6K and the intermediate transfer member squeezing devices 15Y, 15M, 15C, and 15K are arranged, and the on-photosensitive squeeze devices 6Y and 6M are arranged. , 6C, and 6K are provided with two stages of squeeze rollers 36Y, 36M, 36C, and 36K on the photoreceptor. Although not shown, the intermediate transfer member squeeze devices 15Y, 15M, 15C, and 15K may be arranged in a plurality of stages.

  The image forming apparatus 1 of the first to fourth embodiments shown in FIGS. 1 to 4 of the present invention includes on-photosensitive squeeze devices 6Y, 6M, 6C, 6K, primary transfer units 7Y, 7M, 7C, 7K, intermediate. Since a plurality of biases are applied to the liquid developer image by the on-transfer squeeze devices 15Y, 15M, 15C, and 15K, the charge amount of the toner particles may become too high, and as a result, transfer defects tend to occur. I understood that. This is because the toner charge amount increases and the current that flows as the toner moves in the paper transfer nip increases. As a result, the voltage drop on the members (intermediate transfer member, transfer roller, etc.) forming the nip and the paper is reduced. The main reason is considered to be that the toner layer becomes large and no sufficient electric field is applied to the toner layer.

  7 and 8 are partially enlarged views for explaining the state of transfer at the primary transfer portion.

  7 and FIG. 8 (1), when the developer layer on the photosensitive member enters the temporary transfer nip, the toner particles start moving toward the intermediate transfer member due to the electric field.

  7 and 8 (2), some toner particles eventually reach the intermediate transfer member.

  In the stage of (3) in FIG. 7 and FIG. 8, all the toner particles thereafter reach the intermediate transfer member side. At this time, between the toner particles, there is an electric repulsive force due to charging of each particle and a repulsive force due to the dispersing agent adhering around the particles, so that the particles try to maintain a certain distance. On the other hand, since all the particles are pressed toward the intermediate transfer body by the electric field in the nip, the particles are brought closer to each other, so that the distance between the particles is reduced (compressed state) compared to the state where there is no electric field. Become.

  As a result of the investigation, it was found that in the stage of (3), the electric field is continuously applied in a state where the particles are compressed, so that charge injection into the toner is likely to occur. When the toner charge mechanism gives a stronger charge than usual, it is considered that the movement of the particles in the nip is accelerated, so that the state (3) is reached at an early stage as shown in FIG. It is considered that the charge injection is larger than usual. In this case, excessive charge injection can be prevented by setting the bias applied to the nip lower than usual so as to slow the movement of the particles so that the state of (3) does not continue in the nip for a long time. .

  FIG. 9 and FIG. 10 are diagrams for explaining the state of toner particles in the case of squeeze, taking squeeze on the intermediate transfer member as an example.

  9 and 10A, the toner in the toner layer on the intermediate transfer member is in a relatively dispersed state, but when entering the nip, the toner particles move to the intermediate transfer member side by an electric field. To start.

  In the stage of FIG. 9 and FIG. 10 (B), the particles are pressed toward the intermediate transfer member by the electric field in the nip, so that the particles are brought closer to each other. (Compressed state). In this state, when an electric field is continuously applied, charge injection into the toner is likely to occur.

  In other words, even in the case of squeeze, if the toner charge mechanism gives strong charge and the speed of movement of the particles is high, the state becomes (B) at an early stage as shown in FIG. It is thought that it receives a larger charge injection. In this case as well, by setting the bias applied to the nip lower than usual, the movement of particles is slowed so that the state (B) does not last for a long time in the nip, thereby preventing excessive charge injection. it can.

Example 1
The first embodiment for adjusting the charge amount by the toner charger uses a corotron type toner charging corona charger 90 shown in FIG. 11 as the toner chargers 20Y, 20M, 20C, and 20K. The toner charging corona charger 90 includes a corona house 92 having openings formed toward the developing rollers 19Y, 19M, 10C, and 19K, and a corona wire 91 stretched in the corona house 92. By supplying a current to the corona wire 91, a corona ion flow is generated from the opening of the corona house 92 toward the developing rollers 19Y, 19M, 10C, and 19K to charge the toner. Corona wire current measuring means 93 is disposed in the current supply means of the corona wire 91, and corona house current measuring means 94 for measuring the current flowing into the corona house 92 is disposed in the corona house 92.

  In the patch sequence, first, a solid patch as shown in FIG. 12 is formed while the current value applied to the toner on the developing rollers 19Y, 19M, 10C, and 19K is increased from 0 μA to 2.5 μA by the toner charging corona charger 90. In each case, the patch density is referred to by using a density sensor provided facing the intermediate transfer member. When the specified density is reached, the patch sequence is terminated and the current value at that time is adopted. At this time, the toner charge current applied to the developing rollers 19Y, 19M, 10C, and 19K does not directly measure itself, but the current value Iw obtained by measuring the current flowing through the corona wire 91 by the corona wire current measuring means 93. A value obtained by subtracting the absolute value of the current value Ih measured by the corona house current measuring means 94 from the absolute value of? Iw? -? Ih? Is used.

  At this time, the developing bias value is set to a specified value (+400 V). Further, the primary transfer bias employs an upper limit value within a set range to prevent the patch image from being disturbed by the primary transfer. Similarly, in the case of having a squeeze mechanism, the bias applied to each squeeze mechanism adopts an upper limit value within a set range to prevent the patch image from being disturbed by squeeze.

  The patch density, that is, the signal intensity of the patch sensor with respect to the toner charge current value of the toner charging corona charger 90 is as shown in FIG. That is, if the toner charge current value is too low, the toner is not sufficiently transferred from the developing roller to the photosensitive member. In this case, the amount of toner in the image area on the photosensitive member is insufficient, or toner particles are present at the interface where the liquid crys off at the developing nip exit, resulting in disturbance due to the ribs. Due to these problems, the patch density is lower than specified. In the case of FIG. 13, the toner charge current value reaches a specified density at 7.5 μA, so the new toner charge current value is set to 7.5 μA.

  The set value of the bias applying unit is adjusted according to the determined toner charge current value. The bias applying means for adjusting can be appropriately selected according to the apparatus configuration and toner characteristics. The apparatus has a map as shown in the following Tables 1 to 8 according to the type of bias applying means to be adjusted.

  The set value of the bias applying means is determined with reference to this map to a value corresponding to the set toner charge current value. For example, Table 1 above is a case where only the primary transfer bias is adjusted. When the toner charge current value is set to 7.5 μA as described above, the primary transfer bias value is adjusted to −375V.

  In addition to this, when adjusting the bias on the photoconductor squeeze in addition to the primary transfer bias, as shown in Table 2, the primary transfer bias is adjusted to -375V, and the photoconductor squeeze bias value is adjusted to 340V. Also, as shown in Table 8, when there are two stages of squeeze on the photoreceptor, they may be controlled independently.

  The timing of performing the patch sequence is when the apparatus is activated, when a certain number of sheets are printed (for example, every 41,000 MA sheets), after a certain period of time (for example, every 30 minutes), or the like.

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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 ... Each color photoconductor squeeze device, 7Y, 7M, 7C, 7K ... primary transfer device for each color, 10 ... intermediate transfer belt, 11 ... belt drive roller, 13 ... driven roller, 15Y, 15M, 15C, 15K ... squeeze device on intermediate transfer member, 16 ... secondary transfer device , 18Y, 18M, 18C, 18K ... Developers for each color, 20Y, 20M, 20C, 20K ... Toner charger for each color, 23Y, 23M, 23C, 23K ... Liquid developer for each color, 43 ... Secondary transfer roller, 45 ... Secondary transfer roller cleaner, 47 ... Secondary transfer roller cleaner recovered liquid storage container

Claims (5)

A toner charger for charging the liquid developer on the developer carrying member; and bias applying means for applying a bias to the liquid developer image on the image carrying member. The bias application according to the charge amount of the toner charger. An image forming method comprising adjusting a bias setting value of the means. 2. The image forming method according to claim 1, wherein the bias applying unit is at least one of a primary transfer bias applying unit, an on-photosensitive squeeze bias applying unit, and an intermediate transfer member squeeze bias applying unit. 3. The image forming method according to claim 1, wherein the charge amount of the toner charger is adjusted by patch density information of a patch density detecting unit. The image forming method according to claim 1, wherein the toner charger is a corona charger. A toner charger for charging a liquid developer on the developer carrying member; a charge adjusting unit for adjusting a charge amount from the toner charger; a bias applying unit for applying a bias to the liquid developer image on the image carrying member; An image forming apparatus comprising: a bias value adjusting unit that adjusts a bias value of the bias applying unit according to a charge amount adjusted by the charge adjusting unit.

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