JP2021122983A - Image forming device - Google Patents

Abstract

To remove liquid from an ink image without disturbing the image.SOLUTION: An image forming device 1 comprises: an image formation unit 30 which supplies ink to an image formation body to form an ink image on the image formation body; and a liquid removal device 40 which removes the liquid from the ink image. The liquid removal device 40 comprises: a liquid absorption member 41 which absorbs the liquid included in the ink image by being in contact with the ink image; and a moistening liquid imparting unit 50 which imparts moistening liquid 52 for moistening the liquid absorption member 41 to the liquid absorption member 41. A control device 100 controls the moistening liquid imparting unit 50 in such a manner that the total liquid amount of the liquid amount in the ink image on the image formation body and the liquid amount of the moistening liquid 52 on the liquid absorption member 41 in a nip portion formed by the image formation body and the liquid absorption member 41 falls within a prescribed range.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an image forming apparatus.

In an inkjet image forming apparatus, an image is formed on a recording medium by directly supplying ink containing a coloring material to the recording medium or indirectly supplying the ink to the recording medium via an intermediate transfer body. NS. In order to suppress deformation of the recording medium after printing, the image forming apparatus may be provided with a liquid removing apparatus for removing excess liquid in the ink image formed on the recording medium or the intermediate transfer body.

Japanese Unexamined Patent Publication No. 2018-161868 (Patent Document 1) describes that the amount of moisturizing liquid applied to the liquid absorbing member is controlled based on the amount of water on the surface of the liquid absorbing member that absorbs the liquid component. Has been done.

Japanese Unexamined Patent Publication No. 2018-161868

The present inventors have confirmed a phenomenon in which the ink image is distorted when the liquid absorbing member is brought into contact with the ink image to absorb and remove the liquid from the ink image.

Therefore, the present disclosure proposes an image forming apparatus capable of removing a liquid from an ink image without disturbing the image.

As a result of diligent studies, the present inventors have an appropriate range in the amount of liquid in the nip portion formed by the image forming body on which the ink image is formed and the liquid absorbing member, and if the amount of liquid is too large, it is small. It has been found that if the amount is too large, the ink image may be distorted when the liquid is absorbed and removed from the ink image. Based on this finding, the present inventors can remove the liquid from the ink image without disturbing the image by keeping the amount of liquid in the nip portion between the image forming body and the liquid absorbing member within an appropriate range. We found that it would be, and devised the following configuration.

That is, the image forming apparatus according to the present disclosure includes an image forming unit that supplies ink to the image forming body to form an ink image on the image forming body, and a liquid removing device that removes liquid from the ink image. There is. The liquid removing device has a liquid absorbing member that absorbs the liquid contained in the ink image by coming into contact with the ink image, and a dampening liquid applying portion that applies a dampening liquid that moistens the liquid absorbing member to the liquid absorbing member. ing. The image forming apparatus further includes a control device for controlling the image forming apparatus. The control device is a total liquid of the liquid amount in the ink image on the image forming body and the liquid amount of the wetting liquid on the liquid absorbing member in the nip portion formed by the image forming body and the liquid absorbing member. The dampening liquid application unit is controlled so that the amount falls within a predetermined range.

In the above image forming apparatus, when a multicolor image is formed on the image forming body, the control device sets the amount of the wetting liquid applied to the liquid absorbing member by the wetting liquid applying portion on the image forming body. It may be less than when a monochromatic image having the same area as the multicolor image is formed.

In the above image forming apparatus, when a halftone dot image is formed on the image forming body, the control device sets the amount of the wetting liquid applied to the liquid absorbing member by the wetting liquid applying portion on the image forming body. It may be larger than when a solid image having the same area as the halftone dot image is formed.

In the above image forming apparatus, the control device controls the amount of the wetting liquid applied to the liquid absorbing member by the wetting liquid applying portion according to the size of the ink image formed on the image forming body. You may.

In the above image forming apparatus, the control device forms on the image forming body the amount of the dampening liquid applied to the liquid absorbing member by the dampening liquid applying portion in the orthogonal direction orthogonal to the moving direction of the liquid absorbing member. It may be changed according to the ink image to be obtained.

In the above-mentioned image forming apparatus, the dampening liquid applying portions are arranged side by side in the above-mentioned orthogonal directions and each has a plurality of dispensers for discharging the dampening liquid, and the control device is a dampening liquid discharged from each dispenser. The amount of liquid in the above may be controlled.

In the above image forming apparatus, the dampening liquid applying portion has a dispenser having a plurality of discharge ports arranged side by side in the orthogonal direction, and the control device is a liquid of the dampening liquid discharged from each discharge port. The amount may be controlled.

In the above image forming apparatus, when the ink image is not formed on the image forming body, the control device inks the amount of the wetting liquid applied to the liquid absorbing member by the wetting liquid applying portion on the image forming body. It may be more than when the image is formed.

In the above image forming apparatus, the control device does not have to apply the wetting liquid to the liquid absorbing member when the ink image is not formed on the image forming body.

The above image forming apparatus further includes an input unit that accepts a user's operation, and the control device absorbs the liquid by the wetting liquid applying unit when an ink image is not formed on the image forming body according to the operation of the input unit by the user. The first mode in which the amount of the dampening liquid applied to the member is larger than that when the ink image is formed on the image forming body, and when the ink image is not formed on the image forming body, the liquid absorbing member The image forming apparatus may be controlled in any one of the second mode in which the dampening liquid is not applied to the image.

According to the image forming apparatus according to the present disclosure, the liquid can be removed from the ink image without disturbing the image.

It is a schematic diagram which shows the schematic structure of the image forming apparatus according to an embodiment. It is a graph which shows the wettable liquid amount for each type of ink image formed on an image form | body. It is a graph which shows the relationship between the area of the ink image formed on an image forming body, and the amount of a wetting liquid. It is a schematic diagram which shows the schematic structure of the image forming apparatus provided with the wetting liquid application part of another embodiment. It is a figure which shows about the application of the wetting liquid to the liquid absorption member using a plurality of dispensers. It is a figure which shows about the application of the wetting liquid to the liquid absorption member using a multi-dispenser. It is the first chart which shows the relationship between the timing of forming an ink image on an image forming body, and the amount of a wetting liquid. 2 is a second chart showing the relationship between the timing of forming an ink image on an image forming body and the amount of dampening liquid. It is a schematic diagram which shows an example of the structure of an input part. It is a table which shows the result of the experiment A which concerns on Example 1. It is a table which shows the result of the experiment B which concerns on Example 2. It is a table which shows the result of the experiment C which concerns on Example 3. It is a table which shows the result of the experiment D which concerns on Example 4.

Hereinafter, embodiments of the image forming apparatus according to the present disclosure will be described with reference to the drawings. In the following description, the same parts and components are designated by the same reference numerals. Their names and functions are the same. Therefore, the detailed description of these will not be repeated.

[Structure of image forming apparatus 1]
FIG. 1 is a schematic view showing a schematic configuration of an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 is, for example, an inkjet recording apparatus that forms an ink image on a recording medium as an image forming body.

As shown in FIG. 1, the image forming apparatus 1 mainly includes a conveying unit 10, a reaction liquid applying unit 20, an image forming unit 30, a liquid removing device 40, and an ink drying unit 60.

The transport unit 10 transports the recording medium. The transport unit 10 includes a feeding roller 11, winding rollers 12 and 13, and a transport belt 14. The feeding roller 11 is a roller for feeding a recording medium. The take-up rollers 12 and 13 are rollers that take up the recording medium. The transport belt 14 is bridged between the feeding roller 11 and the take-up rollers 12 and 13, and transports the recording medium. The recording medium is conveyed from the feeding roller 11 toward the winding rollers 12 and 13 on the conveying belt 14 along the conveying direction indicated by the arrow in FIG.

As the recording medium, a resin film (for example, PET film, PP film, PE film), plain paper, or the like can be used.

The reaction liquid coating unit 20 coats the reaction liquid on the recording medium transported on the transport belt 14. The reaction solution is contained in the reaction solution accommodating unit 21. The carrier roller 22 is arranged at a position in contact with the reaction solution contained in the reaction solution accommodating portion 21. The reaction solution is pumped up from the reaction solution accommodating portion 21 by the carrier roller 22, and is transferred to the supply roller 25 via the intermediate rollers 23 and 24 in order. The supply roller 25 applies the received reaction solution to the recording medium. As a result, a layer of the reaction solution is formed on the recording medium. The reaction solution drying unit 28 dries the reaction solution applied to the recording medium.

As a method of applying the reaction solution to the recording medium, a known coating method such as inkjet coating, curtain coating, or spray coating may be used in addition to the roller coating described above. The above roller coating is preferable in terms of a coating method with a small amount of liquid. When the place to be applied or the amount of the reaction solution to be applied is limited as necessary according to the printing rate of the image or the paper type, the application of the reaction solution by the inkjet method is preferably used.

The image forming unit 30 ejects ink to a portion of the recording medium after coating the reaction liquid, which is conveyed on the transport belt 14, in which the reaction liquid exists. The image forming unit 30 is a water-based inkjet type. The image forming unit 30 has a plurality of inkjet heads 31. Each inkjet head 31 supplies inks of each color, for example, Y (yellow), M (magenta), C (cyan), and K (black) inks to the recording medium. The ink ejected from the inkjet head 31 is applied to the recording medium and mixed with the reaction liquid on the recording medium to form an ink image on the recording medium.

The liquid removing device 40 removes excess liquid in the ink image from the ink image formed on the storage medium. The liquid removing device 40 has a belt-shaped liquid absorbing member 41. The liquid absorbing member 41 has a porous body layer. The porous medium forming the porous body layer is preferably made of a hydrophilic material. For example, hydrophilically treated PTFE (polytetrafluoroethylene) and PE (polyethylene) can be used. The pore size of the porous medium may be 0.1 μm or more and 100 μm or less. The thickness of the porous body layer may be about 10 μm or more and 5 mm or less.

The liquid absorbing member 41 may have a laminated structure in which a base layer for ensuring strength is provided on the inner peripheral side of the porous body layer. The base layer is formed of a solid body having excellent durability and high rigidity, and is made of, for example, rubber or a metal typified by aluminum or nickel.

The liquid removing device 40 has a pressing roller 42 that presses the liquid absorbing member 41 against the recording medium to bring it into contact with the ink image on the recording medium. The pressing roller 42 has a cylindrical shape. By pressing the pressing roller 42, the liquid absorbing member 41 comes into contact with the ink image formed on the recording medium and absorbs the liquid contained in the ink image into the porous body layer.

The liquid removing device 40 further includes a plurality of tension rollers 43, 44, 45. The liquid absorbing member 41 is hung around the pressing roller 42 and the tension rollers 43, 44, 45. The number of tension rollers is not limited to the three shown in FIG. 1, and a required number of tension rollers may be provided according to the configuration and size of the device.

At least one of the pressing roller 42 and the tension roller 43, 44, 45 is a drive roller that is rotationally driven. Due to the rotational drive of the drive roller, the pressing roller 42 and the tension rollers 43, 44, 45 rotate in the direction of the arrow shown in FIG. As the pressing roller 42 and the tension rollers 43, 44, 45 rotate, the liquid absorbing member 41 rotates in the direction of the arrow shown in FIG.

The liquid removing device 40 further includes a wetting liquid applying unit 50 that applies a wetting liquid 52 that moistens the liquid absorbing member 41 to the liquid absorbing member 41. The dampening liquid 52 is housed in the container 51. The pumping roller 53 is arranged at a position in contact with the wetting liquid 52 contained in the container 51. The dampening liquid 52 is pumped up from the container 51 by the pumping roller 53 and transferred to the coating roller 55 via the intermediate roller 54. The coating roller 55 applies the received wetting liquid 52 to the liquid absorbing member 41. As a result, the wetting liquid 52 is applied to the liquid absorbing member 41.

By applying the wetting liquid 52 to the porous medium of the liquid absorbing member 41 to moisten it, the liquid component in the ink image and the porous medium quickly become familiar with each other, and the liquid component in the ink image becomes the porous medium. It is taken in smoothly. Water can be used as the wetting liquid 52. The wetting liquid 52 may contain an organic solvent, a surfactant, or the like.

The wetting liquid applying portion 50 shown in FIG. 1 is arranged such that the liquid absorbing member 41 is sandwiched between the coating roller 55 and the tension roller 45. The arrangement is not limited to this, and the dampening liquid applying portion 50 may be arranged in any arrangement as long as the coating roller 55 is in contact with the liquid absorbing member 41.

The liquid removing device 40 is not limited to a configuration having a belt-shaped liquid absorbing member 41. In the liquid removing device 40, a liquid absorbing member 41 including a porous body layer is provided on the outer peripheral surface of a rotary-driven hollow cylindrical roller, and the roller is urged in a direction toward the transport belt 14 to urge the liquid absorbing member. The configuration may be such that the 41 is pressed against the recording medium.

The ink drying unit 60 heats the recording medium after passing through the liquid removing device 40 to evaporate the residual liquid on the recording medium, dry the ink image, and fix it on the recording medium. The ink drying unit 60 may heat the recording medium from the front surface on which the ink image is formed, or may heat the recording medium from the back surface on which the ink image is not formed. The ink drying unit 60 may be provided by selecting a necessary heater from known heaters such as an infrared heater, a heating wire, an ultraviolet lamp, a gas, and a hot air dryer. From the viewpoint of safety and energy efficiency, heating with a heating wire or an infrared heater is preferable.

FIG. 1 shows a control device 100 that controls the image forming device 1. The control device 100 transmits a control signal to each of the transport unit 10, the reaction liquid coating unit 20, the image forming unit 30, the liquid removing device 40, the dampening liquid applying unit 50, and the ink drying unit 60, and attaches these devices to each of them. Control. The input unit 101 is electrically connected to the control device 100. The input unit 101 accepts an operation of a user who uses the image forming apparatus 1. The user inputs various information and commands to the image forming apparatus 1 by operating the input unit 101.

<Reaction solution>
The reaction liquid in the embodiment refers to a liquid having a component that acts on the solid content in the ink to insolubilize it and aggregate or thicken the ink component.

For example, when a liquid containing a polyvalent metal salt or the like is brought into contact with the ink, the anionic groups in the pigment or resin are blocked and coagulation sedimentation occurs. Although it depends on the selection of the pigment and the resin in the ink, examples of the reaction solution having such an aggregation mechanism include an acidic liquid and a cationic resin solution in addition to the above polyvalent metal salt solution.

As the polyvalent metal salt, a metal salt having a valence of divalent or higher can be used. As the type of salt, known salts such as carbonate, sulfate, nitric acid, hydrochloric acid, organic acid, boric acid and phosphoric acid can be used. It is also preferable to adjust the pH for dissolution of the polyvalent metal salt, if necessary.

When an acidic liquid is used as the reaction solution, the acid of the pH adjuster that makes the reaction solution acidic is not particularly limited, but considering that it causes a reaction with a carboxylic acid group in the ink, pKa Is preferably an acid with a value of less than 4.5. Considering the quality of the final printed matter (yellowing of the printed matter, image preservation, etc.), an organic acid is preferable to an inorganic acid.

The cationic resin is not particularly limited, but a resin having a quaternary amine is preferable because a high effect can be obtained with a small amount of addition. As the group that imparts cation to the resin, it is preferable that the resin has a nitrogenous cation or a metallic cation.

As the agent to be contained in these reaction liquids, it is preferable to dissolve a polyvalent metal salt, an organic acid having a pKa of less than 4.5, a quaternary amine resin, or the like. These exhibit high cohesiveness with a small amount of addition. It is preferable that the components causing these agglutinations are contained in the reaction solution by adjusting an appropriate amount with respect to the setting of the amount of the ink or the reaction solution.

In addition to the component that aggregates or thickens the solid content in the ink, the reaction solution preferably contains a compound that adjusts the physical characteristics of the liquid, such as a solvent or an activator, if necessary.

It is preferable to use one or a mixture of a plurality of types of the reaction solution in order to obtain a liquid property that is convenient for the coating method. In particular, it is preferable to include water as a part of the solvent from the viewpoints of coatability, drying property, image quality, safety and the like.

If necessary, the reaction solution preferably contains an activator. As the surfactant used, any of cationic, anionic, amphoteric and nonionic surfactants can be used. For example, the activator exemplified as the activator that can be used in the ink of the present invention can be similarly used in the reaction solution.

Further, the reaction solution may contain additives for various purposes. For example, a polysaccharide, a viscosity modifier, a resistivity adjuster, a film forming agent, an ultraviolet absorber, an antioxidant, a fading inhibitor, an antibacterial agent, an anticorrosive agent and the like can be appropriately selected and used.

<Ink>
(Color material)
As the coloring material, pigments and dyes can be used.

Conventionally known pigments can be used without particular limitation, and any of water-dispersible pigments, solvent-dispersible pigments and the like can be used. For example, organic pigments such as insoluble pigments and lake pigments, carbon black and the like can be used. Inorganic pigments can be preferably used.

The average particle size of the pigment dispersion is preferably 10 nm or more and 200 nm or less, more preferably 10 nm or more and 100 nm or less, and further preferably 10 nm or more and 50 nm or less. If the average particle size of the pigment dispersion exceeds 100 nm, the dispersion becomes unstable. Further, even if the average particle size of the pigment dispersion is less than 10 nm, the stability of the pigment dispersion tends to deteriorate, and the storage stability of the ink tends to deteriorate.

The particle size of the pigment dispersion can be measured by a commercially available particle size measuring device using a light scattering method, an electrophoresis method, a laser Doppler method or the like. It is also possible to obtain a particle image by taking a particle image with a transmission electron microscope for at least 100 particles or more, and performing statistical processing on this image using image analysis software such as Image-Pro (manufactured by Media Cybernetics). It is possible.

As the dye, it is preferable to use a dye having an anionic group. Specific examples of the dye include dyes such as azo, triphenylmethane, (aza) phthalocyanine, xanthene, and anthrapyridone.

Among them, the coloring material is preferably a pigment, and more preferably a resin-dispersed pigment.

(resin)
Examples of the resin contained in the ink include acrylic type, styrene acrylic type, acrylonitrile-acrylic type, vinyl acetate acrylic type, polyurethane type, polyester type and the like.

Such a resin may be obtained by polymerizing a monomer having an acid group. Examples of such a monomer include those obtained by radical copolymerizing an acid derivative of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and styrene. Further, if necessary, it may be copolymerized with another monomer.

The molecular weight of the resin is 3,000 or more, preferably 30,000 or less, and more preferably 10,000 or more and 20,000 or less, from the viewpoint of injection property and viscosity. Further, the acid value is preferably 60 or more and less than 300.

The amount of the ink-soluble resin varies depending on the degree of polymerization of the resin, but is preferably 2 to 10%, more preferably 3 to 6% of the total ink mass. If the amount of the resin is small, the effect of the present invention cannot be obtained, and conversely, if the amount of the resin is large, the ejection property and storage stability of the inkjet will be abnormal.

Further, a plurality of resins may be contained or a copolymer may be contained, and the resins may be dispersed in an emulsion state. When dispersed in an emulsion state, the particle size is preferably 300 nm or less from the viewpoint of not impairing the ejection property of inkjet. In the case of a soluble polymer, the composition and the molecular weight are not particularly limited, but the higher the degree of polymerization, the worse the injection property tends to be. Therefore, the molecular weight is preferably 50,000 or less, although it depends on the composition of the polymer.

The solvent of the ink that dissolves and disperses the solute preferably contains a solvent component that dissolves in water in addition to water for the purpose of improving ejection properties and adjusting the physical characteristics of the ink. The type of solvent is not particularly limited as long as the effect of the present invention is not impaired.

(Aqueous medium)
The ink may be water or an aqueous ink containing an aqueous medium which is a mixed solvent of water and a water-soluble organic solvent. As the water, it is preferable to use deionized water or ion-exchanged water. The water content (mass%) in the ink is preferably 20% by mass or more and 95% by mass or less based on the total mass of the ink. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3% by mass or more and 50% by mass or less based on the total mass of the ink.

(Surfactant)
As the surfactant used, any of cationic, anionic, amphoteric and nonionic surfactants can be used. The surfactant and the solvent may be used alone or in combination of two or more.

(Other additives)
Various known additives such as polysaccharides, viscosity modifiers, and specific resistance modifiers, depending on the purpose of emission stability, printhead and ink cartridge compatibility, storage stability, image storage, and other performance improvements. , A film-forming agent, an ultraviolet absorber, an antioxidant, a fading inhibitor, an antibacterial agent, an anticorrosive agent and the like can be appropriately selected and used.

[Setting the amount of dampening liquid]
In the image forming apparatus 1 of the embodiment, the control device 100 controls the amount of the wetting liquid 52 applied to the liquid absorbing member 41 by the wetting liquid applying unit 50. The control device 100 is on the liquid absorbing member 41 when collecting the liquid from the ink image according to the amount of the liquid contained in the ink image formed by the image forming unit 30 on the recording medium conveyed by the conveying unit 10. The amount of the wetting liquid 52 is controlled. Specifically, the amount of liquid in the ink image on the recording medium at the nip portion where the liquid absorbing member 41 contacts the recording medium, and the wetting liquid on the liquid absorbing member 41 given by the wetting liquid applying portion 50. The control device 100 controls the dampening liquid application unit 50 so that the liquid amount of 52 and the total liquid amount of 52 are within a predetermined range.

FIG. 2 is a graph showing the amount of dampening liquid for each type of ink image formed on the image forming body. FIG. 2 schematically shows a comparison of the amount of dampening liquid applied to the liquid absorbing member 41 when forming a monochromatic solid image, a multicolor solid image, and a monochromatic halftone dot image of the same area. .. Here, the solid image means an image that is continuous without gaps over the entire formed ink image.

As shown in FIG. 2, when a multicolor image is formed on the image forming body, the control device 100 forms an image of the amount of the wetting liquid applied to the liquid absorbing member 41 by the wetting liquid applying unit 50. It is less than when a monochromatic image having the same area as the multicolor image is formed on the body. A multicolor image contains a larger amount of liquid than a monochromatic image. By making the amount of wettable liquid when forming a multicolor image smaller than that when forming a monochromatic image, the ink image in the nip portion is formed between when the multicolor image is formed and when the monochromatic image is formed. The uniformity of the total liquid amount of the liquid amount and the liquid amount of the dampening liquid can be improved.

Further, when the halftone dot image is formed on the image forming body, the control device 100 applies the amount of the wetting liquid applied to the liquid absorbing member 41 by the wetting liquid applying unit 50 to the halftone dot image on the image forming body. More than when a solid image of the same area as is formed. The halftone dot image contains less liquid than the solid image. By increasing the amount of dampening liquid when forming the halftone dot image more than when forming the solid image, the ink image in the nip portion is formed between when the halftone dot image is formed and when the solid image is formed. The uniformity of the total liquid amount of the liquid amount and the liquid amount of the dampening liquid can be improved.

By controlling the amount of the dampening liquid according to the type of the ink image formed on the image forming body, the total amount of the liquid amount in the ink image and the amount of the dampening liquid in the nip portion can be made uniform. By controlling the amount of dampening liquid so that the total amount of liquid in the ink image and the amount of dampening liquid falls within the range of the predetermined amount of liquid, image distortion when removing liquid from the ink image can be prevented. It can be suppressed.

FIG. 3 is a graph showing the relationship between the area of the ink image formed on the image forming body and the amount of the dampening liquid. The horizontal axis of the graph shown in FIG. 3 indicates the area of the ink image formed on the image forming body. The vertical axis of the graph shown in FIG. 3 indicates the amount of the dampening liquid applied to the liquid absorbing member 41 by the dampening liquid applying portion 50.

As shown in FIG. 3, the control device 100 determines the amount of dampening liquid applied to the liquid absorbing member 41 by the dampening liquid applying unit 50 according to the size of the ink image formed on the image forming body. Control. Specifically, as the area of the ink image increases, the amount of dampening liquid is reduced. As the area of the ink image increases, the amount of liquid contained in the image increases. By increasing or decreasing the amount of dampening liquid according to the size of the ink image, the amount of liquid and the dampening liquid in the ink image at the nip part are used when forming a large-area image and when forming a small-area image. The uniformity of the total liquid amount with the liquid amount can be improved.

By controlling the amount of dampening liquid according to the size of the ink image formed on the image forming body, the total amount of liquid in the ink image at the nip portion and the amount of dampening liquid can be made uniform. .. By setting the total liquid amount of the liquid amount and the wetting liquid amount in the ink image to be within a predetermined liquid amount range, image distortion when removing the liquid from the ink image can be suppressed.

The area of the ink image formed on the image forming body and the amount of the dampening liquid 52 applied to the liquid absorbing member 41 by the dampening liquid applying portion 50 have a linear correlation shown in FIG. You do not have to have it. The dampening liquid application unit 50 may be controlled by the control device 100 so that the amount of the dampening liquid 52 gradually decreases as the area of the ink image increases.

[Adjustment of amount of wettable powder in the axial direction]
FIG. 4 is a schematic view showing a schematic configuration of an image forming apparatus 1 including a dampening liquid applying portion 50 of another embodiment. The wetting liquid applying unit 50 is not limited to the configuration described with reference to FIG. 1 in which the wetting liquid 52 is applied to the liquid absorbing member 41 by roller coating. The dampening liquid applying portion 50 of another embodiment shown in FIG. 4 includes a dispenser 57. When the dispenser 57 discharges the dampening liquid, the dampening liquid is applied to the liquid absorbing member 41.

FIG. 5 is a diagram showing the application of the wetting liquid to the liquid absorbing member 41 using the plurality of dispensers 57. As shown in FIG. 5, the wetting liquid applying unit 50 includes a plurality of dispensers 57. Each of the plurality of dispensers 57 discharges the wetting liquid and applies the wetting liquid to the liquid absorbing member 41. In FIG. 5, the moving direction of the liquid absorbing member 41 that is rotationally moved by the rotational driving of the driving roller is indicated by an arrow. The plurality of dispensers 57 are arranged side by side in a direction orthogonal to the moving direction of the liquid absorbing member 41 (hereinafter, referred to as an orthogonal direction; in FIG. 1, the direction perpendicular to the paper surface).

Further, in FIG. 5, the dampening liquid discharged from each dispenser 57 and applied to the liquid absorbing member 41 is indicated by an arrow extending from the lower end of each dispenser 57 toward the liquid absorbing member 41. The length of the arrow indicates the amount of the dampening liquid to be discharged. The amount of the dampening liquid discharged from each dispenser 57 is controlled by the control device 100. The control device 100 changes the amount of the dampening liquid discharged from each dispenser 57 for each dispenser 57. As a result, the amount of the dampening liquid applied to the liquid absorbing member 41 by the dampening liquid applying unit 50 is not the same amount in the orthogonal direction, and the amount of the dampening liquid is changed in the orthogonal direction.

Along the axial direction of the feeding roller 11 and the winding rollers 12 and 13 (in FIG. 1, the direction perpendicular to the paper surface, which is the same as the above-mentioned orthogonal direction) constituting the conveying portion 10 that conveys the image forming body (recording medium). Ink images having different image densities may be formed on the image forming body. In this case, it is effective to change the amount of the dampening liquid applied to the liquid absorbing member 41 along the axial direction according to the image density in the axial direction. By changing the amount of the dampening liquid according to the ink image formed on the image forming body, it becomes possible to more precisely control the amount of the dampening liquid according to the image concentration in the axial direction, and the image. Disturbance is less likely to occur.

As shown in FIG. 5, a plurality of dispensers 57 are arranged side by side in the orthogonal direction, and the amount of the dampening liquid discharged from each dispenser 57 is adjusted to prepare the dampening liquid according to the image density in the axial direction. The amount of liquid can be adjusted.

FIG. 6 is a diagram showing the application of the wetting liquid to the liquid absorbing member 41 using the multi-dispenser 59. The dampening liquid applying unit 50 shown in FIG. 6 includes one multi-dispenser 59 instead of the plurality of dispensers 57 shown in FIG. The multi-dispenser 59 has a plurality of discharge ports. The plurality of discharge ports are arranged side by side in the above-mentioned orthogonal directions. The multi-dispenser 59 may be realized by an inkjet head.

The dampening liquid discharged from each discharge port of the multi-dispenser 59 and applied to the liquid absorbing member 41 is indicated by an arrow extending from the lower end of the multi-dispenser 59 toward the liquid absorbing member 41 in FIG. The length of the arrow indicates the amount of the dampening liquid to be discharged. The amount of the dampening liquid discharged from each discharge port of the multi-dispenser 59 is controlled by the control device 100. The control device 100 changes the amount of the dampening liquid discharged from each discharge port of the multi-dispenser 59 for each discharge port. As a result, the amount of the dampening liquid applied to the liquid absorbing member 41 by the dampening liquid applying unit 50 is not the same amount in the orthogonal direction, and the amount of the dampening liquid is changed in the orthogonal direction.

In this way, by arranging the plurality of discharge ports of the multi-dispenser 59 side by side in the orthogonal direction and adjusting the discharge amount of the dampening liquid from each discharge port, the dampening liquid according to the image density in the axial direction can be obtained. The amount of liquid can be adjusted.

[Adhesive strength priority mode, productivity priority mode]
FIG. 7 is a first chart showing the relationship between the timing of forming an ink image on the image forming body and the amount of dampening liquid. In the example shown in FIG. 7 and FIG. 8 described later, the ink image includes an object that is the main object to be printed and a background portion that forms the background of the object. 7 and 8 show the timing of forming the objects and the background portion constituting the ink image on the image forming body. There is a period in which neither the object nor the background portion is formed on the image forming body, and the period is referred to as an image interval in the following description. Further, FIGS. 7 and 8 show the amount of the wetting liquid applied to the liquid absorbing member 41 when the ink image is formed on the image forming body.

As shown in FIG. 7, the amount of the dampening liquid applied to the liquid absorbing member 41 by the dampening liquid applying portion 50 is relatively small when the object is formed on the image forming body, and is on the image forming body. It is relatively large when the background is formed in and between the images. The control device 100 determines the amount of the dampening liquid applied to the liquid absorbing member 41 when the background portion is formed on the image forming body, and the amount of the dampening liquid when the object is formed on the image forming body. The dampening liquid application unit 50 is controlled so as to have a larger amount than the liquid amount. The control device 100 determines the amount of the wetting liquid applied to the liquid absorbing member 41 between the images in which the ink image is not formed on the image forming body, and determines the amount of the wetting liquid when the object is formed on the image forming body. The dampening liquid application unit 50 is controlled so as to have a larger amount than the liquid amount.

If the flocculant contained in the reaction solution remains on the recording medium, the adhesive strength decreases during use, which may cause problems such as unintentional peeling of the recording medium. When printing the background portion and controlling so as to apply a large amount of wetting liquid between the images, the coagulant in the reaction liquid is easily collected by the liquid absorbing member 41. In this case, it is possible to improve the adhesive strength when the recording medium is attached to another member. In this way, the image forming apparatus 1 is controlled to operate in the adhesive strength priority mode in which the adhesive strength of the recording medium is prioritized.

FIG. 8 is a second chart showing the relationship between the timing of forming the ink image on the image forming body and the amount of the wetting liquid. In FIG. 8, when an object is formed on the image forming body, the wetting liquid applying portion 50 applies the wetting liquid to the liquid absorbing member 41, and when the background portion is formed on the image forming body and between the images. Then, the dampening liquid is not applied to the liquid absorbing member 41. The control device 100 controls the wetting liquid applying unit 50 so as not to apply the liquid to the liquid absorbing member 41 between the images in which the ink image is not formed on the image forming body.

When the flocculant contained in the reaction solution is recovered by the liquid absorbing member 41, the viscosity of the liquid in the liquid absorbing member 41 increases, and the liquid absorbing capacity of the liquid absorbing member 41 decreases. When this effect exceeds a certain level, it becomes necessary to replace the liquid absorbing member 41 with a new one. When the background portion is printed and when the dampening liquid is controlled so as not to be applied between the images, it becomes difficult for the liquid absorbing member 41 to collect the coagulant in the reaction liquid, and it is possible to suppress a decrease in the absorbing capacity of the liquid absorbing member 41. , It is possible to avoid a decrease in productivity due to replacement of the liquid absorbing member 41 with a new one. In this way, the image forming apparatus 1 is controlled to operate in the productivity priority mode in which productivity is prioritized.

FIG. 9 is a schematic view showing an example of the configuration of the input unit 101. The input unit 101 shown in FIG. 9 has mode selection units 111 and 112. The mode selection unit 111 is operated by the user in order to select the adhesive strength priority mode described with reference to FIG. 7. The mode selection unit 112 is operated by the user in order to select the productivity priority mode described with reference to FIG. The mode selection units 111 and 112 may be physical buttons, switches, or the like. Alternatively, the input unit 101 may be a touch panel, and the mode selection units 111 and 112 may be icons displayed on the screen.

Whether to prioritize adhesive strength or productivity depends on the user's circumstances, and therefore it is preferable that either mode can be selected. The input unit 101 has the mode selection units 111 and 112, and the user can instruct whether to select the adhesive strength priority mode or the productivity priority mode by operating the input unit 101 according to the purpose. It may be configured. Depending on the mode selected, the control device 100 may be programmed to control the amount of wettling applied when printing the background and between the images.

The image forming apparatus 1 shown in FIG. 1 has a configuration in which a recording medium is used as an image forming body and an ink image is directly formed on the recording medium. The image forming apparatus 1 is not limited to such a configuration, and ink may be supplied from the image forming unit to the intermediate transfer body to form an ink image on the intermediate transfer body as the image forming body. In this case, after the liquid in the ink image on the intermediate transfer body is absorbed and removed by the liquid removing device 40, the image can be transferred from the intermediate transfer body to the recording medium.

Hereinafter, examples will be described. With the apparatus shown in FIG. 1, various images were formed on the recording medium by the inkjet head 31, and the images output through the liquid removing apparatus 40 and the ink drying unit 60 were observed. A PET film having a thickness of 20 μm was used as the recording medium. As the liquid absorbing member 41, a porous sheet made of hydrophilically treated PTFE was used. The porous pore diameter was 0.5 μm, and the thickness of the porous sheet was 40 μm.

Water was used as the dampening liquid. The dampening liquid was applied to the liquid absorbing member 41 using the coating roller 55. By changing the rotation speed of the pumping roller 53 for supplying the liquid to the coating roller 55, the amount of liquid on the coating roller 55, that is, the amount of the wetting liquid applied to the liquid absorbing member 41 can be changed. It was possible.

In Example 1, the dependence of image distortion on the image pattern was investigated. FIG. 10 is a table showing the results of Experiment A according to Example 1. There are three types of image patterns: a two-color solid image, a one-color solid image, and a one-color halftone dot image. In Example 1, it was assumed that a solid image having a size over the entire surface of the image-formable range on the recording medium was formed.

In two-color solid images, ink amount is 30 g / ^{m 2,} the amount of liquid ink was 27.3 g / ^{m 2.} In one color solid image, the ink amount is 15 g / ^{m 2,} the ink in the liquid amount was 13.7 g / ^{m 2.} In one color halftone image, the ink amount is 3.2 g / ^{m 2,} the amount of liquid ink was 2.9 g / ^{m 2.}

In Experiment A-1, when each image pattern was formed, the amount of the wetting liquid contained in the liquid absorbing member 41 was adjusted to be ^{30 g / m 2.} Image distortion was evaluated for each image pattern. In the image distortion results, "good" was evaluated as good without image distortion, "possible" was evaluated as a usable range with some image distortion, and "impossible" was evaluated as unusable due to large image distortion. The one-color solid image was "good", the one-color halftone dot image was "possible", but the two-color solid image was "impossible". In the two-color solid image, the total amount of liquid in the nip portion is too large, so that the liquid cannot smoothly pass through the nip portion and a liquid pool is generated on the upstream side of the nip portion, and the ink image passes through this liquid pool. It is probable that the image was distorted at that time.

Therefore, the amount of the dampening liquid was reduced to 25 g / m ^{2 in Experiment A-2} and 20 g / m 2 in Experiment A-3. The image distortion result of the two-color solid image was improved as "OK" in Experiment A-2 and "Good" in Experiment A-3. On the other hand, in Experiments A-2 and A-3, the image distortion result of the one-color halftone dot image deteriorated to "impossible". In the one-color halftone dot image, since the total amount of liquid in the nip portion is small, it is considered that the liquid component is excessively absorbed by the liquid absorbing member 41, and the pigment enters the liquid absorbing member 41 to cause image distortion. Be done.

As described above, it was found that the occurrence of image distortion is strongly influenced by the image pattern, and it is difficult to set the amount of the dampening liquid to be constant so as to obtain good results for all the image patterns.

In Example 2, in order to investigate the appropriate range of the total liquid amount in the nip, the image pattern was fixed with a one-color solid image, the amount of the dampening liquid was changed, and the relationship with the image distortion was investigated. FIG. 11 is a table showing the results of Experiment B according to Example 2.

As shown in Experiment B, ^{it was found that if the total liquid volume in the nip is set to be within the range of 34 g / m 2} or more and 54 g / m ² or less, the image distortion result of "possible" or more can be secured.

In Example 3, the amount of the dampening liquid was adjusted according to the image pattern to evaluate the image distortion. FIG. 12 is a table showing the results of Experiment C according to Example 3.

As shown in FIG. 12, in the case of a two-color solid image having a large amount of liquid in the ink, the amount of the wetting liquid is relatively small, and in the case of a one-color halftone dot image having a small amount of liquid in the ink, wetting. By increasing the amount of liquid relatively large, the total amount of liquid in the nip was set to be within the range of ^{34 g / m 2} or more and 54 g / m ^{2 or less.} As a result, a good image without image distortion was obtained for any of the image patterns.

There are solid patterns of various sizes in the image to be printed. In Example 4, the relationship between the size of the two-color solid image and the image distortion was investigated. FIG. 13 is a table showing the results of Experiment D according to Example 4.

As shown in Experiment A-1, when forming a two-color solid image of the entire surface size, the image distortion evaluation was "impossible" when the ^{amount of the dampening liquid was 30 g / m 2.} On the other hand, when the size of the two-color solid image in the transport direction of the recording medium was 2 cm, the image distortion evaluation was “good” when the ^{amount of the dampening liquid was 30 g / m 2.} When the size of the two-color solid image is as small as 2 cm, the liquid in the ink image can pass through the nip and move to the downstream side in the transport direction, so that the amount of the dampening liquid is relatively large. It is considered that the image was not disturbed at most.

When the size of the two-color solid image was increased, the image distortion evaluation became "OK" when the size of the image was 7 cm. In a large image pattern, it is considered that the liquid in the ink is difficult to move to the surroundings due to the large total amount of liquid in the nip portion, and the image distortion occurs due to the formation of a liquid pool.

When the size of the image was 7 cm, the image distortion evaluation was “good” by reducing the amount of the dampening liquid to 20 g / m ^2. That is, it was found that when the ink image contains a solid image having a size of 7 cm or more, the image distortion can be more reliably prevented by controlling the amount of the dampening liquid to be smaller than usual. On the other hand, when the ink image does not include a solid image having a size of 7 cm or more, it is not necessary to change the amount of the dampening liquid to be smaller than usual, so that simpler control is required.

The embodiments and examples disclosed this time should be considered as exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims, not the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 Image forming device, 10 Transporting unit, 11 Feeding roller, 12, 13 Winding roller, 14 Conveying belt, 20 Reaction liquid coating part, 21 Reaction liquid storage part, 22 Supporting roller, 23, 24, 54 Intermediate roller, 25 Supply Roller, 28 Reaction liquid drying part, 30 Image forming part, 31 Ink head, 40 Liquid removing device, 41 Liquid absorbing member, 42 Pressing roller, 43, 44, 45 Stretching roller, 50 Wetting liquid applying part, 51 Container, 52 Wetting liquid, 53 Pumping roller, 55 Coating roller, 57 Dispenser, 59 Multi-dispenser, 60 Ink drying unit, 100 Control device, 101 Input unit, 111, 112 Mode selection unit.

Claims (10)

An image forming unit that supplies ink to an image forming body to form an ink image on the image forming body,
An image forming apparatus including a liquid removing device for removing a liquid from the ink image.
The liquid removing device is
A liquid absorbing member that absorbs the liquid contained in the ink image by coming into contact with the ink image,
It has a wetting liquid applying portion that applies a wetting liquid that moistens the liquid absorbing member to the liquid absorbing member.
A control device for controlling the image forming device is further provided.
The control device includes the amount of liquid in the ink image on the image forming body and the liquid of the dampening liquid on the liquid absorbing member in the nip portion formed by the image forming body and the liquid absorbing member. An image forming apparatus that controls the dampening liquid application unit so that the total amount of the liquid amount and the liquid amount falls within a predetermined range. When a multicolor image is formed on the image forming body, the control device applies the amount of the wetting liquid applied to the liquid absorbing member by the dampening liquid applying portion onto the image forming body. The image forming apparatus according to claim 1, wherein the number is less than when a monochromatic image having the same area as the multicolor image is formed. When a halftone dot image is formed on the image forming body, the control device applies a liquid amount of the dampening liquid applied to the liquid absorbing member by the dampening liquid applying portion onto the image forming body. The image forming apparatus according to claim 1, wherein the number of solid images having the same area as that of the halftone dot image is increased more than when a solid image is formed. The control device controls the amount of the dampening liquid applied to the liquid absorbing member by the dampening liquid applying portion according to the size of the ink image formed on the image forming body. The image forming apparatus according to claim 1. In the control device, the amount of the dampening liquid applied to the liquid absorbing member by the dampening liquid applying portion in an orthogonal direction orthogonal to the moving direction of the liquid absorbing member is formed on the image forming body. The image forming apparatus according to claim 1, which is changed according to the ink image. The dampening liquid applying portions are arranged side by side in the orthogonal direction, and each has a plurality of dispensers for discharging the dampening liquid.
The image forming apparatus according to claim 5, wherein the control device controls the amount of the dampening liquid discharged from each of the dispensers. The dampening liquid application portion has a dispenser having a plurality of discharge ports arranged side by side in the orthogonal direction.
The image forming apparatus according to claim 5, wherein the control device controls the amount of the dampening liquid discharged from each of the discharge ports. When the ink image is not formed on the image forming body, the control device applies the amount of the dampening liquid applied to the liquid absorbing member by the dampening liquid applying portion on the image forming body. The image forming apparatus according to claim 1, wherein the number of ink images is increased more than when an ink image is formed. The image forming apparatus according to claim 1, wherein the control device does not apply the wetting liquid to the liquid absorbing member when the ink image is not formed on the image forming body. It also has an input section that accepts user operations.
In the control device, when the ink image is not formed on the image forming body according to the operation of the input unit by the user, the liquid amount of the dampening liquid applied to the liquid absorbing member by the dampening liquid applying unit. In the first mode in which the amount of the ink image is increased more than when the ink image is formed on the image forming body, and when the ink image is not formed on the image forming body, the dampening liquid is applied to the liquid absorbing member. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled in any of the second mode in which the image forming apparatus is not applied.

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