JP2013109153A - Wet-type image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a high quality image by suppressing the occurence of particle unevenness.SOLUTION: A wet-type image forming apparatus 100 comprises: image forming means for forming a toner image on an image carrier 30; carrier liquid quantity adjusting means 33; density detecting means 43; and control means 40. The image forming means forms a patch image on the image carrier 30, the patch image formed on the image carrier 30 is transferred onto a recording medium 50 by changing the quantity of the carrier liquid by the carrier liquid quantity adjusting means 33, and the control means 40 calculates the quantity of the carrier liquid when the image density of the patch image transferred onto the recording medium 50 is a predetermined value or more, based on a value of the image density of the patch image detected by the density detecting means 43.

Description

  The present invention relates to a wet image forming apparatus that forms an image on a recording medium using a developer in which toner is dispersed in a carrier liquid.

  Conventionally, an image forming apparatus employing an electrophotographic system has been put into practical use. In an image forming apparatus employing an electrophotographic system, the surface of a photoreceptor is charged and the surface is exposed by an exposure unit. An electrostatic latent image based on a predetermined image signal is formed on the photoreceptor. Toner is supplied to the electrostatic latent image by developing means. The toner adheres to the electrostatic latent image to form a toner image on the photoreceptor. The toner image is transferred from the photoreceptor to the recording medium, and then fixed by a fixing unit. In an image forming apparatus employing an electrophotographic system, an image is formed on a recording medium through the above image forming process.

  In recent years, as disclosed in Japanese Patent Laid-Open No. 2002-091174 (Patent Document 1), a wet image forming apparatus that forms an image on a recording medium using a developer in which toner is dispersed in a carrier liquid is known. ing. In the wet image forming apparatus, toner particles having a smaller particle diameter than that in the dry image forming apparatus are used. With toner particles having a smaller particle size (for example, the average particle size is 0.1 μm to 2 μm), a high-resolution image expressed to a fine portion of the image is formed on the recording medium.

The ratio of the amount of toner particles contained in the developer (or toner image) (toner amount ratio) is referred to as toner concentration (TC: Toner Concentration). The toner density is expressed by the following formula.
Toner density = (toner amount) / (developer amount) ≈ (toner amount) / (toner amount + carrier liquid amount)
As represented by this equation, there is a correlation between the amount of carrier liquid (carrier liquid amount) and the toner concentration. On the other hand, the amount of the carrier liquid is easily changed through an image forming process in the wet image forming apparatus. The amount of the carrier liquid during the image forming process is likely to change depending on the use environment of the wet image forming apparatus or the use state of the wet image forming apparatus. When the amount of the carrier liquid varies from a predetermined value, the toner concentration also varies accordingly. If the amount of the carrier liquid fluctuates excessively from a predetermined value, when transferring the toner image, the toner particles tend to aggregate in a part of the region, and image unevenness called granular unevenness occurs.

JP 2002-091174 A

  An object of the present invention is to provide a wet image forming apparatus capable of forming a high quality image by suppressing the occurrence of granular unevenness.

  A wet-type image forming apparatus according to an aspect of the present invention is a wet-type image forming apparatus that forms an image on a recording medium using a developer in which a toner is dispersed in a carrier liquid. Image forming means for forming a toner image containing the liquid and the toner on the image carrier, carrier liquid amount adjusting means for adjusting the amount of the carrier liquid contained in the toner image on the image carrier, Transfer means for transferring the toner image on the image carrier onto the recording medium by applying a transfer bias between the image carrier and the recording medium, and a patch transferred onto the recording medium A density detecting unit that detects an image density of the toner image as an image; and a control unit that controls the carrier liquid amount adjusting unit. The image forming unit forms the patch image on the image carrier. And The patch image formed on the image bearing member is transferred onto the recording medium by changing the amount of the carrier liquid by the carrier liquid amount adjusting means, and the density detecting means is transferred onto the recording medium. And the control means detects the image density of the patch image transferred onto the recording medium based on the image density value of the patch image detected by the density detection means. The amount of the carrier liquid when the value is equal to or greater than a predetermined value is calculated, and when normal image formation for forming the image on the recording medium is performed, the control unit calculates the amount according to the result calculated by the control unit. By controlling the carrier liquid amount adjusting means, the amount of the carrier liquid contained in the toner image on the image carrier is set so that the image density of the toner image transferred onto the recording medium is desired. It is set to be higher.

  A wet-type image forming apparatus according to another aspect of the present invention is a wet-type image forming apparatus that forms an image on a recording medium using a developer in which toner is dispersed in a carrier liquid. Image forming means for forming a toner image including a carrier liquid and the toner on the image carrier, and a carrier liquid amount adjusting means for adjusting the amount of the carrier liquid contained in the toner image on the image carrier. Then, by applying a transfer bias between the image carrier and the recording medium, the toner image on the image carrier is transferred onto the recording medium, and transferred onto the recording medium. First density detecting means for detecting the image density of the toner image as the previous patch image, and second density detecting means for detecting the image density of the toner image as the patch image transferred onto the recording medium ,the above Control means for controlling the carrier liquid amount adjusting means, wherein the image forming means forms the patch image on the image carrier, and the patch image formed on the image carrier is the carrier. The amount of the carrier liquid is changed by the liquid amount adjusting means and transferred onto the recording medium, and the first density detecting means detects the image density of the patch image before being transferred onto the recording medium, The second density detecting unit detects an image density of the patch image transferred onto the recording medium, and the control unit detects an image density value of the patch image detected by the first density detecting unit and the above-described image density. Based on the image density value of the patch image on the recording medium detected by the second density detection means, the amount of the carrier liquid when the difference between these values becomes a predetermined value or less is calculated, The above image is displayed on the recording medium. When the normal image formation is performed, the carrier liquid amount adjusting unit is controlled according to the result calculated by the control unit, so that the toner image included in the toner image on the image carrier is The amount of the carrier liquid is set so that the image density of the toner image transferred onto the recording medium is not less than a desired value.

  Preferably, when normal image formation for forming the image on the recording medium is performed, the control means further controls the carrier liquid amount adjusting means according to the type of the recording medium, and The amount of the carrier liquid contained in the toner image on the carrier is set so that the image density of the toner image transferred onto the recording medium is not less than the desired value. Preferably, the transfer unit is configured to be capable of adjusting a bias value of the transfer bias and is configured to be controllable by the control unit, and the patch image formed on the image carrier is the transfer unit. When the normal image formation for forming the image on the recording medium is performed, the bias value of the transfer bias is changed by the above, and according to the result calculated by the control means. By controlling the carrier liquid amount adjusting means and the transfer means, the amount of the carrier liquid contained in the toner image on the image carrier is the image density of the toner image transferred onto the recording medium. Is set to be equal to or greater than the desired value.

  ADVANTAGE OF THE INVENTION According to this invention, the wet image forming apparatus which can form a high quality image by suppressing generation | occurrence | production of a granular nonuniformity can be obtained.

1 is a diagram schematically showing an overall configuration of a wet image forming apparatus in Embodiment 1. FIG. FIG. 4 is a diagram for explaining the relationship between the amount of carrier liquid contained in a toner image on an image carrier (intermediate transfer member) and aggregation of toner particles (the amount of carrier liquid contained in a toner image is a predetermined value or more). If it is). FIG. 4 is a diagram for explaining the relationship between the amount of carrier liquid contained in a toner image on an image carrier (intermediate transfer member) and aggregation of toner particles (the amount of carrier liquid contained in a toner image is less than a predetermined value); If there are few). FIG. 6 is a diagram showing a relationship between the amount of carrier liquid (horizontal axis) contained in a toner image formed on an intermediate transfer member and the image density (vertical axis) of a patch image transferred onto a recording sheet. 6 is a diagram illustrating a carrier liquid amount setting process executed by the wet image forming apparatus in Embodiment 1. FIG. FIG. 4 is a diagram schematically showing an overall configuration of a wet image forming apparatus in a second embodiment. 6 is a diagram schematically showing an overall configuration of a wet-type image forming apparatus in Embodiment 3. FIG. FIG. 10 is a diagram schematically showing an overall configuration of a wet image forming apparatus in a modification of the third embodiment. FIG. 10 is a diagram illustrating a carrier liquid amount setting process executed by a wet image forming apparatus in a fourth embodiment. FIG. 4 is a diagram illustrating a relationship between a carrier liquid amount in a toner image on an intermediate transfer member adjusted by a carrier liquid amount adjusting unit and a secondary transfer bias applied to a transfer roller by a transfer bias applying device. FIG. 10 is a diagram illustrating a carrier liquid amount setting process executed by a wet image forming apparatus in a fifth embodiment.

  Embodiments based on the present invention will be described below with reference to the drawings. In the description of each embodiment, when referring to the number, amount, or the like, the scope of the present invention is not necessarily limited to the number, amount, or the like unless otherwise specified. In the description of each embodiment, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated. Unless there is a restriction | limiting in particular, it is planned from the beginning to use suitably combining the structure shown in each embodiment.

[Embodiment 1]
A wet image forming apparatus 100 in the present embodiment will be described with reference to FIG. FIG. 1 is a diagram schematically illustrating the overall configuration of the wet image forming apparatus 100. The wet image forming apparatus 100 forms an image on a recording paper 50 (recording medium). Although details will be described later, the recording paper 50 in the present embodiment is transported between the intermediate transfer body 30 and the transfer roller 35 along a predetermined transport direction AR50.

  The wet image forming apparatus 100 includes a developing unit 10, a photoreceptor unit 20, an intermediate transfer body 30, a carrier liquid amount adjusting unit 33, a control device 40 (control unit), a density sensor 43 (density detection unit), and a fixing unit 53. Is provided.

(Developing unit 10)
The developing unit 10 includes a developing tank 11, a developer 12, a supply roller 13, a delivery roller 14, a developing roller 15, a charger 16, a static eliminator 17, and a developing bias applying device 18. The developer 12 is stored in the developer tank 11. The developer 12 includes an insulating liquid that is a carrier liquid, a toner that develops an electrostatic latent image, and a dispersant that disperses the toner in the carrier liquid. The developer 12 is appropriately supplied into the developing tank 11 by a supply device (not shown) connected to the developing tank 11.

  The developer 12 is produced, for example, as follows. First, 100 parts of a polyester resin and 15 parts of copper phthalocyanine are sufficiently mixed using a Henschel mixer (registered trademark). The obtained mixture is melted and kneaded using a co-rotating twin-screw extruder in which the heating temperature of the roll is set to 100 ° C.

  The melted and kneaded mixture is cooled and pulverized to obtain a pulverized toner. Thereafter, 75 parts of IP2028 (manufactured by Idemitsu Kosan Co., Ltd.), 25 parts of pulverized toner, and 0.8 part of V216 (manufactured by ISP) as a dispersant are mixed. The developer 12 is obtained by mixing these for 1 hour using a sand mill. In this case, the particle size of the developer 12 is 2.0 μm. The value of the particle size is a value measured by a laser diffraction particle size distribution analyzer SALD-2200 (manufactured by Shimadzu Corporation).

  A supply roller 13 is provided so as to come into contact with the developer 12 in the developing tank 11. As the supply roller 13 rotates, the developer 12 is pumped up on the surface of the supply roller 13. The developer 12 is carried on the surface of the supply roller 13 and is conveyed toward a portion where the supply roller 13 and the delivery roller 14 are opposed to each other by the rotation of the supply roller 13.

  The developer 12 on the supply roller 13 is transferred from the supply roller 13 to the transfer roller 14 in a state where an excessive amount is scraped off by the doctor blade 13T. The developer 12 is carried on the surface of the delivery roller 14. Thereafter, the developer 12 is conveyed toward a portion where the delivery roller 14 and the development roller 15 face each other as the delivery roller 14 rotates.

  The developer 12 on the surface of the delivery roller 14 is delivered from the delivery roller 14 to the development roller 15. By passing through the supply roller 13 and the delivery roller 14, the developer 12 adjusted so that the film thickness is uniform in the longitudinal direction of the developing roller 15 is formed on the surface of the developing roller 15. The developer 12 is conveyed toward the developing position 24 by the rotation of the developing roller 15. The development position 24 is a portion where the development roller 15 and a photoreceptor 21 described later are in contact with each other.

  When the developing solution 12 is transported toward the developing position 24, the toner particles in the developing solution 12 having formed a thin layer are charged to an appropriate charge amount (for example, voltage +3 kV to +5 kV) by the charger 16. The developer 12 containing charged toner particles is further conveyed toward the developing position 24 by the rotation of the developing roller 15.

  The developing roller 15 is disposed with a certain amount of pressing with respect to the photoreceptor 21 of the photoreceptor unit 20 described below. A predetermined developing bias is applied to the developing roller 15 by a developing bias applying device 18. Although details will be described below, the developer 12 of the developing roller 15 visualizes the electrostatic latent image formed on the photosensitive member 21 by applying a developing bias.

(Photoreceptor unit 20)
The photoconductor unit 20 includes a photoconductor 21, a charger 22, an exposure device 23, a pre-transfer charger 25, a static eliminator 27, and a cleaning blade 28. As described above, the drum-shaped photoconductor 21 is provided so as to be in contact with the developing roller 15. As the photoconductor 21, for example, a photoconductor made of amorphous silicon is used. The photoconductor 21 rotates in the direction of the arrow AR21. The rotational speed of the photoconductor 21 is, for example, 400 mm / s.

  Around the periphery of the photoconductor 21, along the rotation direction of the photoconductor 21 (the direction of the arrow AR21), the charger 22, the exposure device 23, the developing roller 15 (development position 24), the pre-transfer charger 25, and the intermediate transfer body 30 ( The transfer unit 26), the static eliminator 27, and the cleaning blade 28 are arranged in this order.

  The surface of the photoreceptor 21 is uniformly charged to a predetermined surface potential (for example, −700 V) by the charger 22. The surface of the photoreceptor 21 is irradiated with laser from the exposure device 23. The laser from the exposure device 23 is modulated in accordance with an image signal from a digital image processing unit (not shown) built in the wet image forming apparatus 100. The surface of the photoreceptor 21 is exposed by a laser. An electrostatic latent image corresponding to the image signal is formed on the surface of the photoreceptor 21.

  Although details will be described later, the exposure apparatus 23 in the present embodiment forms a patch image in addition to controlling the exposure amount, exposure range, exposure timing, and the like based on normal image information. It is also controlled by various values such as the exposure amount, exposure range, and exposure timing required for the above. By controlling the exposure device 23 in this way, an electrostatic latent image corresponding to a patch image (details will be described later) is formed on the surface of the photoreceptor 21.

  As described above, a predetermined developing bias (for example, −450 V) is applied to the developing roller 15 by the developing bias applying device 18. An electric field is formed between the developing roller 15 and the photoconductor 21 due to the development potential difference formed between the developing roller 15 and the photoconductor 21.

  When the electrostatic latent image is transported to the developing position 24 on the photosensitive member 21, the toner particles in the developer 12 carried on the developing roller 15 are caused by the action of an electric field formed by the developing bias applying device 18. Electrostatically moves from the surface of the developing roller 15 to the surface of the photoreceptor 21. At this time, not only the toner particles but also the carrier liquid adheres to the surface of the photoreceptor 21. The electrostatic latent image formed on the surface of the photoreceptor 21 is visualized (visualized) as a toner image (or a patch image described later).

  The developer 12 remaining on the developing roller 15 without being transferred from the developing roller 15 to the photosensitive member 21 is neutralized by the static eliminator 17 (for example, a voltage of −3 kV to −5 kV), and then the developing blade 15 is cleaned by the cleaning blade 15T. It is collected after being scraped off the surface. The collected developer is conveyed to the toner concentration adjusting means and then conveyed into the developing tank 11 with the toner concentration adjusted appropriately.

  The photosensitive member 21 moves the toner image toward the transfer unit 26 while carrying the toner image formed on the surface. The transfer portion 26 is a portion where the photosensitive member 21 and an intermediate transfer member 30 described below are in contact with each other. The toner image on the photoreceptor 21 conveyed toward the transfer unit 26 is charged to a predetermined charge amount (for example, voltage +3 kV to +5 kV) by the pre-transfer charger 25. After the surface potential is adjusted, the toner image is further conveyed toward the transfer unit 26 by the rotation of the photosensitive member 21.

(Intermediate transfer member 30)
The intermediate transfer member 30 is disposed so as to face the photoconductor 21. The intermediate transfer member 30 rotates in the direction of arrow AR30. Around the intermediate transfer member 30, along the rotation direction of the intermediate transfer member 30 (the direction of the arrow AR30), there are a photosensitive member 21, a carrier liquid amount adjusting unit 33, a transfer roller 35 (transfer unit 36), and a cleaning blade 38. Arranged in order.

  A transfer portion 26 (primary transfer portion) is formed between the photosensitive member 21 and the intermediate transfer member 30. A predetermined transfer bias (for example, +600 V) is applied to the intermediate transfer member 30 by the transfer bias applying device 34. An electric field is formed between the photosensitive member 21 and the intermediate transfer member 30 due to the potential difference formed between the photosensitive member 21 and the intermediate transfer member 30.

  The toner image conveyed to the transfer unit 26 by the rotation of the photosensitive member 21 is primarily transferred from the surface of the photosensitive member 21 to the surface of the intermediate transfer member 30 by the action of the electric field formed by the transfer bias applying device 34. The toner remaining on the surface of the photoconductor 21 without being primarily transferred is discharged by the charge eliminator 27 and then scraped off from the surface of the photoconductor 21 by the cleaning blade 28 along with dirt on the surface of the photoconductor 21. To be recovered.

  The intermediate transfer member 30 moves the toner image toward the transfer unit 36 (secondary transfer unit) while carrying a toner image (or a patch image described later) transferred (formed) on the surface. The transfer unit 36 is a part where the intermediate transfer member 30 and a transfer roller 35 described later are in contact with each other.

  Although details will be described later, the patch image formed on the photosensitive member 21 is also transferred from the surface of the photosensitive member 21 to the intermediate transfer member by the action of the electric field formed by the transfer bias applying device 34 as in the case of a normal toner image. 30 is transferred to the surface. By the transfer, a patch image is formed on the surface of the intermediate transfer body 30. The image forming unit in the present embodiment forms a toner image (and a patch image) on the intermediate transfer member 30 (image carrier), and includes a developing unit 10, a photosensitive unit 20, and a transfer bias applying device 34. Contains.

(Carrier liquid amount adjusting means 33)
The carrier liquid amount adjusting means 33 is disposed so as to face the toner image (and patch image) formed on the intermediate transfer body 30. The carrier liquid amount adjusting means 33 is located downstream of the transfer unit 26 and upstream of the transfer unit 36 in the rotation direction of the intermediate transfer body 30 (in the direction of the arrow AR30). The carrier liquid amount adjusting means 33 in the present embodiment includes a pre-wet device 31 and a squeeze device 32.

  The pre-wet device 31 has a roller 31 </ b> R disposed to face the intermediate transfer body 30. The pre-wet device 31 supplies a carrier liquid 31P (pre-wet liquid) to a toner image (patch image) on the intermediate transfer body 30 by being controlled by a control device 40 described later. When the carrier liquid contained in the toner image on the intermediate transfer member 30 is insufficient, the pre-wet device 31 is driven by the control device 40.

  By supplying the carrier liquid 31P to the toner image on the intermediate transfer body 30 through the roller 31R, the amount of carrier liquid contained in the toner image on the intermediate transfer body 30 can be increased. By increasing the rotation speed of the roller 31R, the amount of the carrier liquid 31P supplied to the toner image on the intermediate transfer body 30 can be increased. By reducing the rotation speed of the roller 31R, the amount of the carrier liquid 31P supplied to the toner image on the intermediate transfer member 30 can be reduced.

  The squeeze device 32 has a roller 32 </ b> R disposed to face the intermediate transfer member 30. The squeeze device 32 is controlled by a control device 40 described later, and collects the carrier liquid absorbed from the toner image (patch image) on the intermediate transfer member 30 by the blade 32Q. When there is too much carrier liquid contained in the toner image on the intermediate transfer member 30, the squeeze device 32 is driven by the control device 40.

  By recovering the carrier liquid from the toner image on the intermediate transfer body 30 through the roller 32R, the amount of the carrier liquid contained in the toner image on the intermediate transfer body 30 can be reduced. By increasing the rotation speed of the roller 32R, the amount of carrier liquid recovered from the toner image on the intermediate transfer member 30 can be increased. By reducing the rotation speed of the roller 32R, the amount of carrier liquid recovered from the toner image on the intermediate transfer member 30 can be reduced.

  After the toner image is primarily transferred from the surface of the photosensitive member 21 to the surface of the intermediate transfer member 30 in the transfer unit 26, the intermediate transfer member 30 carries the toner image transferred to the surface and transfers the toner image to the carrier. It moves toward the position facing the liquid amount adjusting means 33. Although details will be described later, the amount of carrier liquid of this toner image is set to an optimum value by the carrier liquid amount adjusting means 33 controlled by the control device 40. The toner image is further conveyed toward the transfer unit 36 by the rotation of the intermediate transfer body 30 after the amount of the carrier liquid is set to an optimum value.

  The recording sheet 50 passes through the transfer unit 36 along the transport direction AR50 by the intermediate transfer member 30 that rotates in the direction of the arrow AR30 and the transfer roller 35 that rotates in the direction of the arrow AR35. A predetermined transfer bias (for example, +1200 V) is applied to the transfer roller 35 by a transfer bias applying device 37 (transfer means). An electric field is formed between the intermediate transfer member 30 and the recording paper 50 due to the potential difference formed between the intermediate transfer member 30 and the transfer roller 35.

  The toner image conveyed to the transfer unit 36 by the rotation of the intermediate transfer member 30 is secondarily transferred from the surface of the intermediate transfer member 30 to the surface of the recording paper 50 by the action of the electric field formed by the transfer bias applying device 37. . By the transfer, an image corresponding to the toner image is formed on the surface of the recording paper 50. The toner remaining on the surface of the intermediate transfer member 30 without being subjected to the secondary transfer is scraped off and collected together with dirt on the surface of the intermediate transfer member 30 by the cleaning blade 38. The recording paper 50 on which the toner image is secondarily transferred is sent to the fixing unit 53.

  Although details will be described later, the patch image formed on the intermediate transfer member 30 is also recorded from the surface of the intermediate transfer member 30 by the action of the electric field formed by the transfer bias applying device 37, as in the case of a normal toner image. It is transferred to the surface of the paper 50. By the transfer, an image corresponding to the patch image is formed on the surface of the recording paper 50.

(Fixing unit 53)
The fixing unit 53 includes fixing rollers 51 and 52. The toner particles in the toner image transferred to the recording paper 50 are heated and pressurized by the fixing rollers 51 and 52. The toner image (patch image) transferred to the recording paper 50 is fixed on the surface of the recording paper 50 by these heating and pressing. Thereafter, the recording paper 50 is discharged to the outside through a paper discharge device (not shown).

(Control device 40 / concentration sensor 43)
In the wet image forming apparatus 100 according to the present embodiment, the density sensor 43 connected to the control device 40 is disposed so as to face the recording surface of the recording paper 50. The density sensor 43 is located downstream of the transfer unit 36 and upstream of the fixing unit 53 in the conveyance direction (arrow AR direction) of the recording paper 50. The concentration sensor 43 in the present embodiment includes a light emitting unit 41 and a light receiving unit 42. The density sensor 43 detects the image density of the toner image as a patch image transferred onto the recording surface of the recording paper 50.

  Predetermined detection light is emitted from the light emitting unit 41 toward the toner image as a patch image transferred onto the recording surface of the recording paper 50. The reflected light of the detection light reflected on the toner image is received by the light receiving unit 42. Depending on the intensity of the reflected light received by the light receiving unit 42, the density sensor 43 sends a detection signal based on the toner density of the toner image as a patch image transferred onto the recording surface of the recording paper 50 to the control device 40. Send it out.

  As the concentration sensor 43, for example, SpectroEye (registered trademark) manufactured by X-rite may be used. In this case, as a detection condition, a polarizing filter is used, a standard light source is set to D50, paper viewing is set to D50, an observation visual field is set to 2 °, and a density reference is set to DIN.

  As the density sensor 43, a sensor using a scattered light detection method for detecting scattered light may be used in addition to the reflected light detection method as described above, and light transmitted through the intermediate transfer body 30 may be used. A device that adopts a transmitted light detection method for detecting the light may be used.

  As will be described in detail later, based on the value of the detection signal output from the density sensor 43 (the toner density of the toner image as a patch image transferred onto the recording surface of the recording paper 50), the control device 40 uses the carrier The liquid amount adjusting means 33 is controlled. When normal image formation for forming an image according to the image signal from the digital image processing unit is performed by the control, the amount of the carrier liquid contained in the toner image on the intermediate transfer body 30 is the recording paper 50. It is possible to set an optimum value so that the image density of the toner image transferred above becomes a desired value or more.

(Causes of grainy unevenness)
Here, the relationship between the amount of the carrier liquid 11C contained in the toner image on the intermediate transfer body 30 and the aggregation of the toner particles 11T will be described with reference to FIGS. As shown in FIG. 2, the toner image on the intermediate transfer body 30 is conveyed to the transfer section 36 (transfer nip section) by the rotation of the intermediate transfer body 30.

  When the amount of the carrier liquid 11C included in the toner image is equal to or larger than a predetermined value, the carrier liquid 11C is interposed between the intermediate transfer body 30 and the recording paper 50 (not shown) on the upstream side of the transfer nip portion. A good liquid bridge 11E is formed.

  The toner particles 11T included in the toner image on the intermediate transfer body 30 start moving toward the recording paper 50 after a good liquid bridge 11E is formed by the carrier liquid 11C in the toner image. In other words, after the liquid bridge 11E is formed at the position P1 in FIG. 2, the toner particles 11T start moving by the action of the electric field at the position P2 in FIG. Therefore, when the amount of the carrier liquid 11C included in the toner image is equal to or greater than a predetermined value, the toner particles are not aggregated in a part of the region, and the granular unevenness hardly occurs.

  Referring to FIG. 3, on the other hand, when the amount of carrier liquid 11C included in the toner image is smaller than a predetermined value, sufficient liquid bridge 11E is not formed. The toner particles 11T included in the toner image on the intermediate transfer body 30 start to move toward the recording paper 50 before an appropriate liquid bridge 11E is formed by the carrier liquid 11C in the toner image.

  Specifically, before the liquid bridge 11E is formed at the position P3 in FIG. 3, the toner particles 11T start to move by the action of the electric field at the position P2 in FIG. Therefore, when the amount of the carrier liquid 11C included in the toner image is smaller than a predetermined value, the toner particles are aggregated in a part of the region, and granular unevenness occurs. The uniformity of the solid portion in the image formed on the recording paper 50 is impaired, and it becomes difficult to form a high-quality image.

FIG. 4 shows the relationship between the amount of carrier liquid contained in the toner image formed on the intermediate transfer member 30 (horizontal axis) and the image density (vertical axis) of the patch image transferred onto the recording paper 50. FIG. In the case shown in FIG. 4, the toner amount is set to 1.8 g / m ^2, and the bias value of the transfer bias applied to the transfer roller 35 by the transfer bias applying device 37 is set to 400V. Under these conditions, the change in image density of the patch image transferred onto the recording paper 50 when the amount of carrier liquid contained in the toner image formed on the intermediate transfer member 30 is sequentially changed is shown in FIG. Is shown in

  As shown in FIG. 4, when the amount of carrier liquid contained in the toner image on the intermediate transfer member 30 is smaller than a certain value (C1 to C3), the image density of the patch image transferred onto the recording paper 50 is , Lower than a predetermined value T. On the other hand, when the amount of the carrier liquid contained in the toner image on the intermediate transfer body 30 is equal to or greater than a certain value (C4 to C6), the image density of the patch image transferred onto the recording paper 50 is a predetermined value T. That's it.

  That is, by adjusting the amount of the carrier liquid contained in the toner image conveyed to the transfer unit 36 (transfer nip unit) to an appropriate amount, a decrease in image density due to the occurrence of toner aggregation (granular unevenness) is suppressed. It is understood that is possible.

(Carrier liquid amount setting process ST100)
Referring to FIGS. 1 and 5, in wet image forming apparatus 100 in the present embodiment, when a normal image is formed on recording paper 50, granular unevenness occurs or the image density due to this occurs. Carrier liquid amount setting processing ST100 (see FIG. 5) is executed to suppress the occurrence of a decrease in the amount of liquid. When the control device 40 controls the carrier liquid amount adjusting means 33, in the carrier liquid amount setting process ST100, the amount of the carrier liquid contained in the toner image conveyed to the transfer unit 36 (transfer nip portion) is an appropriate amount. Adjusted to

  The carrier liquid amount setting process ST100 is performed, for example, immediately after the wet image forming apparatus 100 is turned on, after a predetermined number of images are formed by the wet image forming apparatus 100, and / or by the wet image forming apparatus 100. This is carried out after a predetermined time has elapsed since the formation of.

  The timing at which the carrier liquid amount setting process ST100 is performed is stored in a memory (not shown) connected to, for example, a main controller (not shown) in the wet image forming apparatus 100. The main control unit determines that the predetermined condition is satisfied, and the main control unit sends a signal for executing the carrier liquid amount setting process ST100 to each device constituting the wet image forming apparatus 100.

  Referring to FIGS. 1 and 5, when the carrier liquid amount setting process ST <b> 100 is performed, first, a control unit (not shown) connected to the exposure device 23 displays a plurality of patch images on the photoconductor 21. Information relating to the exposure amount, exposure range, exposure timing, and the like necessary for formation is read from a memory (not shown) connected to this control. The exposure device 23 controlled by the control unit based on the information sequentially forms a plurality of electrostatic latent images corresponding to the plurality of patch images on the photoreceptor 21.

  The plurality of electrostatic latent images are conveyed to the development position 24. The plurality of electrostatic latent images are visualized at the developing position 24 by the action of the electric field formed by the developing bias applying device 18. A plurality of patch images are formed on the surface of the photoconductor 21 at a portion downstream of the developing position 24 and upstream of the transfer portion 26 (primary transfer portion). The plurality of patch images formed on the photoconductor 21 sequentially move toward the transfer unit 26 as the photoconductor 21 rotates.

  The plurality of patch images on the photosensitive member 21 are sequentially transferred onto the intermediate transfer member 30 by the action of the electric field formed by the transfer bias applying device 34. A plurality of patch images are formed on the surface of the intermediate transfer body 30 at a portion downstream of the transfer portion 26 (primary transfer portion) and upstream of the transfer portion 36 (secondary transfer portion). (Sequence ST1).

  The plurality of patch images formed (transferred) on the intermediate transfer body 30 move toward the portion where the carrier liquid amount adjusting means 33 and the intermediate transfer body 30 face each other by the rotation of the intermediate transfer body 30. . When a plurality of patch images sequentially pass through a portion facing the carrier liquid amount adjusting unit 33, the carrier liquid amount adjusting unit 33 is configured to perform predetermined conditions (for example, the usage environment of the wet image forming apparatus or the wet image forming apparatus). The carrier liquid amount (initial value) in the plurality of patch images is set based on the usage state (sequence ST2).

  After the first patch image of the plurality passes through the portion facing the carrier liquid amount adjusting means 33, the carrier liquid amount adjusting means 33 thereafter passes through the portion facing the carrier liquid amount adjusting means 33. The amount of the carrier liquid may be adjusted continuously or discretely so that the amount of the carrier liquid in the medium sequentially increases.

  Each of the plurality of patch images formed on the intermediate transfer body 30 is sequentially transferred onto the recording paper 50 by the action of the electric field formed by the transfer bias applying device 37. Each of the plurality of patch images formed on the intermediate transfer body 30 is sequentially transferred each time the amount of the carrier liquid is changed by the carrier liquid amount adjusting means 33.

  The density sensor 43 detects the density of a toner image as a patch image on the recording paper 50 that passes through the detection range of the density sensor 43. The density sensor 43 sends a detection signal based on the toner density of the toner image as a patch image transferred onto the recording surface of the recording paper 50 to the control device 40 (sequence ST3).

  The control device 40 determines the value of the detection signal output from the density sensor 43 (the toner density of the toner image as a patch image transferred onto the recording surface of the recording paper 50) equal to or greater than a predetermined value that has been obtained and stored in advance. Is determined (sequence ST4). If the toner concentration is equal to or higher than the predetermined value, the carrier liquid amount setting process ST100 is terminated (sequence ST5).

  On the other hand, when the toner concentration is less than the predetermined value, control device 40 controls carrier liquid amount adjusting means 33 (sequence ST6). Specifically, when a plurality of patch images sequentially pass through a portion facing the carrier liquid amount adjusting unit 33, the carrier liquid amount adjusting unit 33 detects the value of the detection signal output from the concentration sensor 43 (on the recording paper 50. The amount of carrier liquid in the plurality of patch images is changed based on the toner density of the toner image as the patch image transferred onto the recording surface.

  When the pre-wetting device 31 is driven by the control device 40, the carrier liquid 31P is supplied to the toner image on the intermediate transfer body 30, and the amount of the carrier liquid in the toner image (patch image) increases. When the squeeze device 32 is driven by the control device 40, the carrier liquid is recovered from the toner image (patch image) on the intermediate transfer member 30, and the amount of the carrier liquid in the toner image decreases. As described above, the amount of carrier liquid contained in the toner image (patch image) on the intermediate transfer member 30 is changed by the operation control of the pre-wet device 31 and the squeeze device 32.

  Each of the plurality of patch images formed on the intermediate transfer body 30 is sequentially transferred onto the recording paper 50 by the action of the electric field formed by the transfer bias applying device 37. Each of the plurality of patch images formed on the intermediate transfer body 30 is sequentially transferred each time the amount of the carrier liquid is changed by the carrier liquid amount adjusting means 33.

  The density sensor 43 detects the density of a toner image as a patch image on the recording paper 50 that passes through the detection range of the density sensor 43. The density sensor 43 sends a detection signal based on the toner density of the toner image as a patch image transferred onto the recording surface of the recording paper 50 to the control device 40 (sequence ST7).

  The control device 40 determines the value of the detection signal output from the density sensor 43 (the toner density of the toner image as a patch image transferred onto the recording surface of the recording paper 50) equal to or greater than a predetermined value that has been obtained and stored in advance. Is determined (sequence ST8). When the toner concentration is equal to or higher than a predetermined value, the detected value is calculated as the amount of carrier liquid when the image density of the patch image transferred onto the recording paper 50 is equal to or higher than the predetermined value, and the carrier liquid amount setting process ST100 ends (sequence ST9). This value detected by the density sensor 43 is set as the amount of carrier liquid in the toner image on the intermediate transfer member 30 to be used during normal image formation.

  When the toner density is less than the predetermined value, the sequences ST6 to ST8 are repeated until the toner density becomes equal to or higher than the predetermined value.

(Action / Effect)
In wet image forming apparatus 100 in the present embodiment, control device 40 controls carrier liquid amount adjusting means 33 by executing carrier liquid amount setting processing ST100. Before the toner particles move due to the electric field in the transfer portion 36 (transfer nip entry portion), the carrier liquid in the toner image to be used in normal image formation is formed so that the liquid bridge of the developer 12 is satisfactorily formed. The amount is set to an optimal value.

  The wet image forming apparatus 100 can not only suppress the occurrence of granular unevenness in the toner image transferred onto the recording paper 50 during normal image formation, but also increase the image density of the toner image to a desired value or more. It can be. Therefore, according to the wet image forming apparatus 100, a high-quality image can be formed on the recording paper 50.

  In the present embodiment, a plurality of patch images are formed by the image forming unit, and the image density of each of the plurality of patch images transferred onto the recording surface of the recording paper 50 through the carrier liquid amount adjusting unit 33 is a density sensor. The control device 40 determines whether each detected value is equal to or greater than a predetermined value stored in advance.

  On the other hand, as the patch image formed by the image forming unit, one continuous patch image may be formed. When the patch image is formed as a series of long images, the patch image passes through the carrier liquid amount adjusting means 33, and thus includes a different carrier liquid amount for each partial portion (each region) in the longitudinal direction. The patch images that contain different carrier liquid amounts for each part in the longitudinal direction are transferred onto the recording surface of the recording paper 50, and the image density for each part is detected by the density sensor 43. The controller 40 determines whether or not the detected value is equal to or greater than a predetermined value stored in advance. The amount of the carrier liquid when the image density of the patch image is equal to or higher than a predetermined value is calculated, and this calculated value is the value of the carrier liquid in the toner image on the intermediate transfer body 30 to be used in normal image formation. Set as a quantity. Even with this configuration, the toner image to be used in normal image formation is formed so that the liquid bridge of the developer 12 is well formed before the toner particles move due to the electric field in the transfer portion 36 (transfer nip entry portion). The amount of the carrier liquid in the medium can be set to an optimum value, and a high-quality image can be formed on the recording paper 50.

[Embodiment 2]
With reference to FIG. 6, a wet image forming apparatus 101 in the present embodiment will be described. In the wet image forming apparatus 100 according to Embodiment 1 described above, the intermediate transfer member 30 is used. The intermediate transfer member 30 may be provided as necessary.

  When the intermediate transfer member 30 is not used as in the wet image forming apparatus 101 illustrated in FIG. 6, the charger 22, around the photosensitive member 21, along the rotation direction of the photosensitive member 21 (the direction of the arrow AR 21). Exposure device 23, developing roller 15 (developing position 24), carrier liquid amount adjusting means 33 (pre-wetting device 31 and squeeze device 32), pre-transfer charger 25, transfer roller 35 (transfer portion 36), static eliminator 27, and cleaning Blades 28 are arranged in order.

  In the wet image forming apparatus 101, toner particles are supplied from the developing unit 10 (developing roller 15) to the electrostatic latent image corresponding to the patch image formed on the photoreceptor 21. The electrostatic latent image corresponding to the patch image formed on the photoreceptor 21 is visualized as a patch image, and a plurality of patch images are formed on the surface of the developing unit 10.

  The image forming means in the present embodiment includes a developing unit 10 that forms a toner image (and a patch image) on the photoreceptor 21 (image carrier). A transfer bias is applied between the photoconductor 21 and the recording paper 50 by the transfer bias applying device 37 (transfer means), and the toner image on the photoconductor 21 is transferred onto the recording paper 50.

  Also in the wet image forming apparatus 101, the density sensor 43 connected to the control device 40 is disposed so as to face the recording surface of the recording paper 50. The density sensor 43 is disposed downstream of the transfer unit 36 and upstream of the fixing unit 53 in the conveyance direction (arrow AR direction) of the recording paper 50, and is a patch image transferred onto the recording surface of the recording paper 50. The image density of the toner image is detected.

  Based on the value of the detection signal output from the density sensor 43 (the toner density of the toner image as a patch image transferred onto the recording surface of the recording paper 50), the control device 40 controls the carrier liquid amount adjusting means 33. To do. When normal image formation for forming an image according to the image signal from the digital image processing unit is performed by the control, the amount of the carrier liquid contained in the toner image on the photosensitive member 21 is set on the recording paper 50. Is set to an optimum value so that the image density of the toner image transferred onto the toner image becomes a desired value or more.

(Action / Effect)
Also in the wet image forming apparatus 101 according to the present embodiment, as in the first embodiment described above, the control device 40 causes the carrier liquid amount adjusting unit to execute the carrier liquid amount setting process ST100 (see FIG. 5). 33 is controlled. Before the toner particles move due to the electric field in the transfer portion 36 (transfer nip entry portion), the carrier liquid in the toner image to be used in normal image formation is formed so that the liquid bridge of the developer 12 is satisfactorily formed. The amount is set to an optimal value.

  The wet image forming apparatus 101 not only can suppress the occurrence of granular unevenness in the toner image transferred onto the recording paper 50 during normal image formation, but also makes the image density of the toner image equal to or higher than a desired value. It can be. Therefore, the wet image forming apparatus 101 can also form a high-quality image on the recording paper 50.

  Also in the present embodiment, one continuous patch image may be formed as the patch image formed by the image forming unit. Even with this configuration, the toner image to be used in normal image formation is formed so that the liquid bridge of the developer 12 is well formed before the toner particles move due to the electric field in the transfer portion 36 (transfer nip entry portion). The amount of the carrier liquid in the medium can be set to an optimum value, and a high-quality image can be formed on the recording paper 50.

[Embodiment 3]
With reference to FIG. 7, a wet image forming apparatus 102 in the present embodiment will be described. The wet image forming apparatus 102 further includes a density sensor 46 in addition to the configuration of the wet image forming apparatus 100 in the first embodiment. The density sensor 46 corresponds to the first density detection means in the present invention, and the density sensor 43 corresponds to the second density detection means in the present invention.

  As shown in FIG. 7, the density sensor 46 is also connected to the control device 40. The density sensor 46 is disposed so as to face the surface of the intermediate transfer member 30, and in the rotation direction of the intermediate transfer member 30 (in the direction of the arrow AR 30), is downstream of the carrier liquid amount adjusting unit 33 and the transfer unit 36. It arrange | positions in the upstream position rather than. The density sensor 46 in the present embodiment includes a light emitting unit 44 and a light receiving unit 45. The density sensor 46 detects the image density of a toner image that is formed on the intermediate transfer body 30 and is a patch image before being transferred to the recording paper 50.

  Predetermined detection light is emitted from the light emitting unit 44 toward the toner image as a patch image formed on the intermediate transfer member 30. The reflected light of the detection light reflected on the toner image is received by the light receiving unit 45. Depending on the intensity of the reflected light received by the light receiving unit 45, the density sensor 46 sends a detection signal based on the toner density of the toner image as a patch image formed on the intermediate transfer body 30 to the control device 40. .

  As the concentration sensor 46, for example, SpectroEye (registered trademark) manufactured by X-rite may be used as in the case of the concentration sensor 43. In this case, as a detection condition, a polarizing filter is used, a standard light source is set to D50, paper viewing is set to D50, an observation visual field is set to 2 °, and a density reference is set to DIN.

  As the density sensor 46, in addition to the sensor that uses the reflected light detection method as described above, a sensor that uses a scattered light detection method that detects scattered light may be used, and light that has passed through the intermediate transfer body 30 may be used. A device that adopts a transmitted light detection method for detecting the light may be used.

  Based on the value of the detection signal output from the density sensor 46 (image density of the toner image as a patch image before being transferred to the recording paper 50), the control device 40 controls the carrier liquid amount adjusting means 33. The control device 40 in the present embodiment corresponds to the image density value of the patch image detected by the density sensor 46 and the patch image on the recording paper 50 detected by the density sensor 43 (the patch image detected by the density sensor 46). Based on the image density value of the patch image), the amount of the carrier liquid when the difference between these values is equal to or less than a predetermined value is calculated.

  Even with this control, when normal image formation for forming an image according to the image signal from the digital image processing unit is performed, the amount of the carrier liquid contained in the toner image on the intermediate transfer body 30 is the recording paper. The toner image transferred onto the toner image 50 can be set to an optimum value so that the image density becomes a desired value or more. The same applies to the case where the intermediate transfer member 30 is not used as in the second embodiment. The same applies to the case where the patch images formed by the image forming unit are one continuous image.

[Modification of Embodiment 3]
Like the wet image forming apparatus 103 shown in FIG. 8, the density sensor 46 is disposed so as to face the surface of the photoconductor 21, and from the developing position 24 in the rotation direction of the photoconductor 21 (in the direction of the arrow AR <b> 21). Also, it may be arranged at a position downstream of the transfer section 26. The density sensor 46 detects the image density of the toner image formed on the photoconductor 21 and as a patch image before being transferred to the intermediate transfer body 30.

  The density sensor 46 sends a detection signal based on the toner density of the toner image as a patch image formed on the photoconductor 21 to the control device 40. Based on the value of the detection signal output from the density sensor 46 (image density of the toner image as a patch image before being transferred to the intermediate transfer body 30), the control device 40 controls the carrier liquid amount adjusting means 33. .

  The control device 40 detects the image density value of the patch image detected by the density sensor 46 and the image of the patch image on the recording paper 50 detected by the density sensor 43 (a patch image corresponding to the patch image detected by the density sensor 46). Based on the concentration value, the amount of the carrier liquid when the difference between these values is equal to or less than a predetermined value is calculated.

  Even with this control, when normal image formation for forming an image according to the image signal from the digital image processing unit is performed, the amount of the carrier liquid contained in the toner image on the intermediate transfer body 30 is the recording paper. The toner image transferred onto the toner image 50 can be set to an optimum value so that the image density becomes a desired value or more.

[Embodiment 4]
Like the carrier liquid amount setting process ST200 shown in FIG. 9, after forming a patch image (after the sequence ST1) in the same manner as the carrier liquid amount setting process ST100 (see FIG. 5), the recording paper 50 (recording medium) The carrier liquid amount adjusting means 33 may be further controlled according to the type (sequence ST2A).

  If an excessive amount of carrier liquid remains in the toner image formed by secondary transfer on the recording paper 50, problems such as poor fixability may occur. For example, in the case of paper with a smooth surface such as coated paper, the amount of toner required to cover the surface may be small. On the other hand, in the case of paper having a rough surface such as high-quality paper, more toner is required to cover the surface.

  If printing is performed on high quality paper with a set toner amount of coated paper, the toner cannot cover the entire surface of the paper, and the surface of the paper is partially exposed, resulting in a non-uniform image. On the other hand, when printing on coated paper with a set amount of high-quality paper, there is too much toner, causing problems such as high density and thick characters and lines.

Therefore, in the carrier liquid amount setting process ST200, the carrier liquid amount in the toner image during the secondary transfer is adjusted in consideration of the type (paper type) of the recording paper 50. The amount of the developing solution 12 is preferably about 5 g / m ^{2 in} the case of coated paper, and about 7 g / m ^{2 in} the case of fine paper. As the amount of the developer 12 conveyed to the transfer nip portion increases, the liquid bridge is formed on the upstream side. Therefore, when the amount of the developer 12 is large, the amount of the carrier liquid in the toner image is smaller. However, toner aggregation can be suppressed.

  As in the carrier liquid amount setting process ST200, the carrier liquid amount adjusting means 33 is further controlled in accordance with the type of the recording paper 50 (recording medium), thereby ensuring stable fixing properties and suppressing the decrease in density due to toner aggregation. It becomes possible to achieve both. Although the case where the carrier liquid amount is automatically controlled according to the paper type has been described, adjustment by the user may be added thereto. The same applies to the case where the patch images formed by the image forming unit are one continuous image.

[Embodiment 5]
When normal image formation for forming an image on the recording paper 50 is performed, the carrier liquid amount adjusting means 33 and the transfer bias applying device 37 for applying the secondary transfer bias according to the result calculated by the control device 40. Both (transfer means) may be controlled. In this case, the transfer bias applying device 37 is configured to be able to adjust the bias value of the secondary transfer bias and to be controllable by the control device 40.

  FIG. 10 shows the amount of carrier liquid in the toner image on the intermediate transfer body 30 adjusted by the carrier liquid amount adjusting means 33 and the secondary applied to the transfer roller 35 by the transfer bias applying device 37 (see FIG. 1 and the like). It is a figure which shows the relationship with a transfer bias. In FIG. 10, when the density of the toner image transferred onto the recording paper 50 is detected, and the difference between the density of the toner image and the target desired density is 0.2 or less, “◯ (round shape) )] Is plotted, and when the difference between the density of the toner image and the target desired density is larger than 0.2, “Δ (triangle shape)” is plotted.

  As shown in FIG. 10, even when the amount of carrier liquid in the toner image before transfer is constant, image uniformity is improved by lowering the secondary transfer bias, and image density due to toner aggregation is reduced. It turns out that a fall can be suppressed. Further, it can be seen that even when the secondary transfer bias is constant, the uniformity of the image is improved by increasing the amount of carrier liquid in the toner image before transfer. From these results, by controlling both the carrier liquid amount adjusting means 33 and the transfer bias applying device 37 (transfer means) for applying the secondary transfer bias, a more uniform image in which toner aggregation is suppressed is obtained. It turns out that it becomes possible.

  Specifically, as in the carrier liquid amount setting process ST300 shown in FIG. 11, a plurality of patch images are formed (sequence ST1). Thereafter, the carrier liquid amount (initial value) in the plurality of patch images is set based on a predetermined condition (for example, the use environment of the wet image forming apparatus or the use state of the wet image forming apparatus) (sequence ST2). ). Thereafter, a secondary transfer bias (initial value) is set based on a predetermined condition (for example, a use environment of the wet image forming apparatus or a use state of the wet image forming apparatus) (sequence ST2B).

  Each of the plurality of patch images formed on the intermediate transfer body 30 is sequentially transferred onto the recording paper 50 by the action of the electric field formed by the transfer bias applying device 37. In each of the plurality of patch images formed on the intermediate transfer body 30, the amount of the carrier liquid is changed by the carrier liquid amount adjusting unit 33 and the bias value of the secondary transfer bias is changed by the transfer bias applying device 37. Each time it is transferred, it is transferred sequentially.

  The density sensor 43 detects the density of a toner image as a patch image on the recording paper 50 that passes through the detection range of the density sensor 43. The density sensor 43 sends a detection signal based on the toner density of the toner image as a patch image transferred onto the recording surface of the recording paper 50 to the control device 40 (sequence ST3).

  The control device 40 determines the value of the detection signal output from the density sensor 43 (the toner density of the toner image as a patch image transferred onto the recording surface of the recording paper 50) equal to or more than a predetermined value that has been previously obtained and stored. Is determined (sequence ST4). When the toner density is less than the predetermined value, the control device 40 controls the carrier liquid amount adjusting means 33 (sequence ST6) and also controls the transfer bias applying device 37 (sequence ST6A).

As a result, the amount of carrier liquid contained in the toner image (patch image) on the intermediate transfer body 30 is changed to an optimum value, and the bias value of the secondary transfer bias is also changed to an optimum value. When the toner density is equal to or higher than a predetermined value, the amount of the carrier liquid and the bias value of the secondary transfer bias when the detected value is equal to or higher than the predetermined value of the patch image transferred onto the recording paper 50 Thus, the carrier liquid amount setting process ST300 ends (sequence ST9). These values detected by the density sensor 43 are set as the amount of carrier liquid in the toner image on the intermediate transfer body 30 to be used during normal image formation and the bias value of the secondary transfer bias. When the toner density is less than the predetermined value, the sequences ST6 to ST8 are repeated until the toner density becomes equal to or higher than the predetermined value.
(Action / Effect)
By executing the carrier liquid amount setting process ST300, the control device 40 controls both the carrier liquid amount adjusting means 33 and the transfer bias applying device 37. Before the toner particles move due to the electric field in the transfer portion 36 (transfer nip entry portion), the carrier liquid in the toner image to be used in normal image formation is formed so that the liquid bridge of the developer 12 is satisfactorily formed. The amount and the bias value of the secondary transfer bias are set to optimum values.

  During normal image formation, it is possible not only to suppress the occurrence of granular unevenness in the toner image transferred onto the recording paper 50, but also to increase the image density of the toner image to a desired value or more. Therefore, according to the wet image forming apparatus in the present embodiment, a higher quality image can be formed on the recording paper 50.

  In the carrier liquid amount setting process ST300, the optimum carrier liquid amount and the secondary transfer bias are determined while changing both the carrier liquid amount and the secondary transfer bias. The image density is detected with the bias value of the transfer bias fixed at a temporary value, and when the image density is equal to or lower than the predetermined value, the carrier liquid amount adjustment condition is changed to obtain the predetermined image density. It is possible to change and determine the carrier liquid amount adjustment condition until it is adjusted, and then perform fine adjustment by changing the bias condition. Alternatively, the carrier liquid amount is fixed at a tentative value, and the image density is detected. If the value is equal to or less than the predetermined value, the bias value of the secondary transfer bias is changed, and the bias value of the secondary transfer bias is changed and determined until a predetermined image density is obtained. Or a method that al the finely adjusted by changing the carrier liquid adjustment condition. The same applies to the case where the patch images formed by the image forming unit are one continuous image.

  As mentioned above, although each embodiment based on this invention was described, each embodiment disclosed this time is an illustration and restrictive at no points. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 10 Developing unit, 11 Developing tank, 11C, 31P Carrier liquid, 11E Liquid bridge, 11T Toner particle, 12 Developer, 13 Supply roller, 13T Doctor blade, 14 Delivery roller, 15 Developing roller, 15T, 28, 38 Cleaning blade, 16, 22 Charger, 17, 27 Static eliminator, 18 Development bias applying device, 20 Photoreceptor unit, 21 Photoreceptor, 23 Exposure device, 24 Development position, 25 Charger before transfer, 26, 36 Transfer part, 30 Intermediate transfer member , 31 Pre-wet device, 31R, 32R roller, 32 squeeze device, 32Q blade, 33 carrier liquid amount adjusting means, 34, 37 transfer bias applying device, 35 transfer roller, 40 control device, 41, 44 light emitting unit, 42, 45 Light receiving part, 43, 46 dark Degree sensor, 50 recording paper, 51, 52 fixing roller, 53 fixing unit, 100, 101, 102, 103 wet image forming apparatus, AR50 transport direction.

Claims (4)

A wet image forming apparatus for forming an image on a recording medium using a developer in which toner is dispersed in a carrier liquid,
An image carrier;
Image forming means for forming a toner image including the carrier liquid and the toner on the image carrier;
A carrier liquid amount adjusting means for adjusting the amount of the carrier liquid contained in the toner image on the image carrier;
Transfer means for transferring the toner image on the image carrier onto the recording medium by applying a transfer bias between the image carrier and the recording medium;
Density detecting means for detecting an image density of the toner image as a patch image transferred onto the recording medium;
Control means for controlling the carrier liquid amount adjusting means,
The image forming means forms the patch image on the image carrier,
The patch image formed on the image carrier is transferred onto the recording medium by changing the amount of the carrier liquid by the carrier liquid amount adjusting means,
The density detecting means detects an image density of the patch image transferred onto the recording medium;
The control unit is configured to generate the carrier liquid when the image density of the patch image transferred onto the recording medium is equal to or higher than a predetermined value based on the image density value of the patch image detected by the density detection unit. Calculate the amount of
When normal image formation for forming the image on the recording medium is performed, the carrier liquid amount adjusting unit is controlled in accordance with the result calculated by the control unit, so that the image on the image carrier is The amount of the carrier liquid contained in the toner image is set so that the image density of the toner image transferred onto the recording medium is not less than a desired value.
Wet image forming apparatus. A wet image forming apparatus for forming an image on a recording medium using a developer in which toner is dispersed in a carrier liquid,
An image carrier;
Image forming means for forming a toner image including the carrier liquid and the toner on the image carrier;
A carrier liquid amount adjusting means for adjusting the amount of the carrier liquid contained in the toner image on the image carrier;
Transfer means for transferring the toner image on the image carrier onto the recording medium by applying a transfer bias between the image carrier and the recording medium;
First density detecting means for detecting an image density of the toner image as a patch image before being transferred onto the recording medium;
Second density detecting means for detecting an image density of the toner image as the patch image transferred onto the recording medium;
Control means for controlling the carrier liquid amount adjusting means,
The image forming means forms the patch image on the image carrier,
The patch image formed on the image carrier is transferred onto the recording medium by changing the amount of the carrier liquid by the carrier liquid amount adjusting means,
The first density detecting means detects an image density of the patch image before being transferred onto the recording medium;
The second density detecting means detects an image density of the patch image transferred onto the recording medium;
The control means is based on the image density value of the patch image detected by the first density detection means and the image density value of the patch image on the recording medium detected by the second density detection means, Calculate the amount of the carrier liquid when the difference between these values is a predetermined value or less,
When normal image formation for forming the image on the recording medium is performed, the carrier liquid amount adjusting unit is controlled in accordance with the result calculated by the control unit, so that the image on the image carrier is The amount of the carrier liquid contained in the toner image is set so that the image density of the toner image transferred onto the recording medium is not less than a desired value.
Wet image forming apparatus. When normal image formation for forming the image on the recording medium is performed, the control means further controls the carrier liquid amount adjusting means according to the type of the recording medium, and the image on the image carrier. The amount of the carrier liquid contained in the toner image is set so that the image density of the toner image transferred onto the recording medium is not less than the desired value.
The wet image forming apparatus according to claim 1. The transfer unit is configured to be capable of adjusting a bias value of the transfer bias, and is configured to be controllable by the control unit,
The patch image formed on the image carrier is transferred onto the recording medium by changing the bias value of the transfer bias by the transfer means,
When normal image formation for forming the image on the recording medium is performed, the carrier liquid amount adjusting unit and the transfer unit are controlled according to the result calculated by the control unit, whereby the image The amount of the carrier liquid contained in the toner image on the carrier is set so that the image density of the toner image transferred onto the recording medium is not less than the desired value.
The wet image forming apparatus according to claim 1.

Images