JP5343890B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method.

  2. Description of the Related Art There is known an ink jet recording type image forming apparatus that includes a recording head that ejects ink from nozzles by a movable actuator method typified by a piezo method, a heated film boiling method typified by a thermal method, or the like.

  In such an image forming apparatus, ink is directly ejected from the recording head to the recording paper. Since the recording head and the recording paper are close to each other, paper dust, dust and the like are likely to adhere to the nozzle. As a result, the flying direction of the droplets ejected from the nozzle is disturbed or the nozzle is blocked, resulting in a reduction in image quality and reliability. In general, ink having a low viscosity is used with priority given to ejectability from the nozzles, but ink bleeding tends to occur when landing on recording paper.

  Therefore, Patent Document 1 discloses an intermediate transfer body that carries an ink image, a treatment liquid application section that applies a treatment liquid onto the intermediate transfer body, an ink discharge section that discharges ink onto the treatment liquid, and an intermediate transfer body. An image forming apparatus including a solvent removing unit that removes the solvent of the ink image formed above and a transfer unit that transfers the ink image from which the solvent has been removed to a recording medium is disclosed. At this time, the ink contains a resin emulsion having a color material and an ionic group, and the treatment liquid causes a pH change by contact with the ink and causes a cohesive action on the resin emulsion having the color material and the ionic group. At the same time, the pH difference between the ink and the treatment liquid is 3 or more.

  However, in addition to having to apply a treatment liquid to form an ink image, there is a problem that transferability is low.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide an image forming apparatus and an image forming method that are excellent in transferability and can suppress the occurrence of bleeding without applying a treatment liquid. To do.

  According to a first aspect of the present invention, in the image forming apparatus, the conductive ink is provided between the recording head having a nozzle for discharging the conductive ink in which the pigment is dispersed in a solvent containing water, and the nozzle. An intermediate transfer body having an elastic layer containing carbon nanotubes formed on the surface thereof, capable of forming an ink image by temporarily forming a bridge of the liquid column, and the elastic layer and the conductive ink. A voltage applying unit that applies a voltage capable of electrolyzing water contained in the bridge of the liquid column, and a transfer unit that transfers the ink image formed on the intermediate transfer member to a recording medium. It is characterized by that.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the carbon nanotube content in the elastic layer is 0.1% by mass or more and 1.0% by mass or less. To do.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the elastic layer has a volume resistivity of less than 1 × 10 ³ Ω · cm.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the elastic layer has a receding contact angle with respect to water of greater than 60 °.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the pigment is dispersed by an anionic dispersant, and the voltage application unit is the elastic layer. A voltage is applied so that the elastic layer functions as an anode.

  According to a sixth aspect of the invention, there is provided a step of ejecting a conductive ink in which a pigment is dispersed in a solvent containing water from a nozzle of a recording head to form an ink image on the intermediate transfer member, and the intermediate transfer member. An image forming method including a step of transferring an ink image formed on a recording medium, wherein the intermediate transfer body has an elastic layer containing carbon nanotubes formed on a surface thereof, and the conductive ink and the elastic layer In the state where a voltage is applied between the nozzle and the intermediate transfer member, a bridge of a liquid column made of the conductive ink is temporarily formed, and water contained in the bridge of the liquid column is formed. The ink is electrolyzed to form an ink image on the intermediate transfer member.

  According to the present invention, it is possible to provide an image forming apparatus and an image forming method which are excellent in transferability and can suppress the occurrence of bleeding without applying a treatment liquid.

It is a figure which shows an example of the image forming apparatus used by this invention. FIG. 2 is a partially enlarged view of the image forming apparatus in FIG. 1. It is a figure which shows the state which the pigment disperse | distributed with the anionic dispersing agent aggregated through the proton. It is a figure which shows the mechanism in which an ink image is formed. It is a schematic diagram which shows the bridge | bridging of the liquid column formed between a cathode and an anode. FIG. 3 is a diagram illustrating a halftone image formed on an intermediate transfer drum of an example.

  Next, the form for implementing this invention is demonstrated with drawing.

  FIG. 1 shows an example of an image forming apparatus used in the present invention. The image forming apparatus 100 is an ink jet printer, and forms a full-color image on one side of the recording paper S based on an image signal corresponding to image information received from the outside.

  Instead of forming a full color image on one side of the recording paper S, a configuration may be adopted in which full color images are formed on both sides of the recording paper S.

  The recording paper S is not particularly limited as long as it is in the form of a sheet. Examples of the recording paper S include ordinary paper generally used for copying and the like; thick paper such as cards and postcards;

  Instead of the recording paper S, an OHP sheet or the like may be used.

  The image forming apparatus 100 records an ink image formed on the intermediate transfer drum 10, a discharge device 20 that discharges conductive ink to form an ink image on the intermediate transfer drum 10, a power source 30, and the intermediate transfer drum 10. A transfer roller 40 that transfers to the paper S, a cleaning blade 50 that cleans the intermediate transfer drum 10 to which the ink image has been transferred, a transport unit 60 that transports the recording paper S, a control unit (not shown) having a CPU, memory, and the like. .

  As shown in FIG. 2, the intermediate transfer drum 10 has an elastic layer 12 formed on a conductive substrate 11, and is driven to rotate in a direction A1 in the drawing by a driving means (not shown) such as a motor. .

  Although it does not specifically limit as a material which comprises the electroconductive base | substrate 11, Metals, such as aluminum, an aluminum alloy, copper, stainless steel, are mentioned.

  Instead of the conductive substrate 11, an insulating substrate may be used.

  The elastic layer 12 has carbon nanotubes dispersed in an elastic body. Thereby, since the elastic layer 12 is excellent in electroconductivity, the water contained in the bridge | bridging of the liquid column mentioned later can be electrolyzed in the vicinity of the elastic layer 12. Further, the elastic layer 12 is excellent in transferability because it has excellent releasability with respect to an ink image.

  The elastic body is not particularly limited, and examples thereof include silicone rubber, urethane rubber, fluorine rubber, and nitrile butadiene rubber.

  The rubber hardness of the elastic body is usually 60 ° or less. If the rubber hardness of the elastic body exceeds 60 °, the transferability may be lowered.

  The carbon nanotube may be either a single-wall nanotube or a multi-wall nanotube.

  The content of carbon nanotubes in the elastic layer 12 is usually 0.1 to 1.0% by mass, preferably 0.1 to 0.5% by mass. When the content of the carbon nanotubes in the elastic layer 12 is less than 0.1% by mass, the distribution of the carbon nanotubes in the elastic layer 12 becomes non-uniform, and a liquid column bridge to be described later in the vicinity of the elastic layer 12. A region where water contained in water cannot be electrolyzed may be formed. If the amount exceeds 1.0% by mass, physical properties such as the hardness of the elastic layer 12, the receding contact angle with respect to water, and the arithmetic average roughness Ra are not uniform. As a result, transferability may be reduced.

The volume resistivity of the elastic layer 12 is smaller than the volume resistivity of the conductive ink, but is preferably less than 1 × 10 ³ Ω · cm. If the volume resistivity of the elastic layer 12 is 1 × 10 ³ Ω · cm or more, it may be difficult to electrolyze water contained in the bridge of the liquid column described later in the vicinity of the elastic layer 12.

  The receding contact angle of the elastic layer 12 with respect to water is usually larger than 60 ° and preferably larger than 80 °. If the receding contact angle of the elastic layer 12 with respect to water is 60 ° or less, the transferability may be lowered.

  The arithmetic average roughness Ra of the elastic layer 12 is usually 1 or less. When the arithmetic average roughness Ra of the elastic layer 12 exceeds 1, the transferability may be deteriorated.

  The thickness of the elastic layer 12 is usually 0.1 to 1 mm, preferably 0.2 to 0.6 mm.

  The elastic layer 12 can be formed by applying a dispersion liquid containing carbon nanotubes, an ionic liquid, and an elastic body to the conductive substrate 11 (see JP 2009-5536 A).

The carbon nanotubes used for producing the dispersion liquid preferably have an aspect ratio of 1 × 10 ⁴ or more. When the aspect ratio of the carbon nanotube is less than 1 × 10 ⁴ , the carbon nanotubes are difficult to contact each other, and it may be difficult to achieve both the conductivity and the release property of the elastic layer 12.

  The aspect ratio is the ratio of the average length to the average diameter.

  The average length of the carbon nanotubes used for producing the dispersion is usually 1 μm or more, preferably 50 μm or more, and more preferably 500 μm or more.

The cation constituting the ionic liquid is not particularly limited, 1-ethyl-3-methylimidazolium, chemical formula _{(CH 3) 2 (CH 3} CH 2) (CH 2 CH 2 OCH 2 CH 2 OCH 3) N +
And a quaternary ammonium salt represented by The anion constituting the ionic liquid is not particularly limited, and examples thereof include tetrafluoroborate ions and bis (trifluoromethanesulfonyl) imidate ions. At this time, two or more kinds of cations and / or anions may be used in combination.

  Instead of the intermediate transfer drum 10, an endless belt or sheet on which an elastic layer 12 is formed may be used.

  The ejection device 20 has a fixed type in which a plurality of recording heads 21Y, 21M, 21C, and 21BK that eject conductive inks of each color of yellow, magenta, cyan, and black are arranged in parallel in a direction perpendicular to the paper surface in the drawing. The full line type. The recording heads 21 </ b> Y, 21 </ b> M, 21 </ b> C, and 21 </ b> BK are sequentially provided from the upstream side in the direction of A <b> 1 at positions facing the outer peripheral surface of the intermediate transfer drum 10. At this time, the control unit shifts the timing of each color from the upstream side toward the downstream side in the direction of A1 so that the image areas of each color of yellow, magenta, cyan, and black overlap on the intermediate transfer drum 10. The recording heads 21Y, 21M, 21C, and 21BK are controlled so as to eject conductive ink.

  The ejection device 20 was accommodated in ink cartridges 22Y, 22M, 22C, and 22BK that store conductive inks of the respective colors supplied to the recording heads 21Y, 21M, 21C, and 21BK, and ink cartridges 22Y, 22M, 22C, and 22BK. A pump (not shown) for transferring the conductive ink of each color and a supply tank (not shown) for distributing and supplying the conductive ink of each color transferred by the pump to the recording heads 21Y, 21M, 21C and 21BK are provided. The ink cartridges 22Y, 22M, 22C and 22BK and the supply tank are connected by a pipe (not shown) via a pump, and between the supply tank and the recording heads 21Y, 21M, 21C and 21BK. Are connected by a pipe (not shown). The ink cartridges 22Y, 22M, 22C, and 22BK are detachable so that they can be replaced when the conductive ink is low or no more, and the maintenance is facilitated.

  The ejection device 20 further includes a sensor (not shown) that detects the amount of conductive ink in the supply tank. When the sensor detects that the amount of the conductive ink in the supply tank is less than the predetermined amount, the control unit drives the pump until the amount of the conductive ink in the supply tank exceeds the predetermined amount, and the ink cartridge 22Y. , 22M, 22C and 22BK are transferred to the supply tank.

  The ejection device 20 includes a carriage 23 that integrally supports the recording heads 21Y, 21M, 21C, and 21BK, and is detachable. At this time, the recording heads 21Y, 21M, 21C and 21BK are detachable independently. Thereby, the recording heads 21Y, 21M, 21C and 21BK can be exchanged.

  As shown in FIG. 2, the recording head 21 includes a conductive nozzle plate 21b on which nozzles 21a are formed, an ink chamber 21c corresponding to each nozzle 21a, and ink ejection means (not shown). At this time, the nozzle plate 21b has a plurality of nozzles 21a, and each recording head 21 has a single nozzle 21a. That is, the plurality of recording heads 21 share the nozzle plate 21b. The ink chamber 21c is filled with conductive ink I supplied using a supply tank (not shown). The ink discharge means includes a piezoelectric element, and the conductive ink I is discharged from the nozzle 21a in accordance with a voltage pulse applied to the piezoelectric element.

  The nozzle plate 21b functions as a cathode. Although it does not specifically limit as a material which comprises the nozzle plate 21b, A metal, carbon, etc. are mentioned.

  The gap between the intermediate transfer drum 10 and the nozzle plate 21b is preferably 50 to 200 μm. If the gap is less than 50 μm, it may be difficult to maintain the gap between the rotating intermediate transfer drum 10 and the nozzle plate 21 b, and if it exceeds 200 μm, the liquid is between the nozzle 21 a and the intermediate transfer drum 10. It may be difficult to form pillar bridges.

  Instead of using the conductive nozzle plate 21b, an insulating nozzle plate in which only the inner surface in contact with the conductive ink I is subjected to conductive treatment may be used, or only the inner surface in contact with the conductive ink I may be used. A conductive nozzle plate that is insulated may be used, or a nozzle plate in which an insulating layer and a conductive layer are laminated may be used. At this time, by making the surface in contact with the conductive ink I insulative, the generation of bubbles due to electrolysis described later can be suppressed.

  The recording head 21 may be a shape deforming element method such as a piezo method, or may be another method such as a heater method such as a thermal method.

  Further, the ejection device 20 may be a shuttle type in which the recording head moves in a direction (main scanning direction) perpendicular to the direction in which the surface of the intermediate transfer drum 10 moves. At this time, the number of recording heads may be plural.

  Further, four intermediate transfer drums 10 and four transfer rollers 40 corresponding to the respective recording heads 21Y, 21M, 21C and 21BK may be provided.

  In the conductive ink I, a pigment is dispersed in a solvent containing water by an anionic dispersant.

  Although it does not specifically limit as a pigment, C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 151, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 180, C.I. I. Pigments for orange or yellow such as CI Pigment Yellow 185; I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. Pigment Red 222 and other red or magenta pigments; C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. Pigment Green 7 or other green or cyan pigments; C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. And black pigments such as CI Pigment Black 7.

  The content of the pigment in the conductive ink I is usually 0.1 to 40% by mass, preferably 1 to 30% by mass, and more preferably 2 to 20% by mass.

  Examples of the anionic dispersant include, but are not limited to, fatty acid salt, alkyl sulfate ester salt, alkyl benzene sulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate, alkyl phosphate ester salt, naphthalene sulfonate formalin condensate, poly Examples thereof include oxyethylene alkyl sulfate esters, and two or more of them may be used in combination.

  From the viewpoint of transferability, the conductive ink I is obtained by neutralizing a resin having an acidic group such as a carboxyl group, a sulfonic acid group, or a phosphonic acid group with a base such as sodium hydroxide or potassium hydroxide. It is preferable to further contain a resin having an anionic group. Although it does not specifically limit as resin which has an acidic group, Polyacrylic acid, polyamide, polyvinyl alcohol, etc. are mentioned, You may use 2 or more types together.

  The content of the resin having an anionic group in the conductive ink I is usually 0.5 to 10% by mass, and preferably 0.5 to 5% by mass.

  The conductive ink I may further contain a solvent soluble in water. Solvents that are soluble in water are not particularly limited, but are polyvalent such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, and glycerin. Alcohols: ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, ethylene oxide adduct of diglycerin Polyhydric alcohol derivatives such as pyrrolidone, N-methyl-2-pyrrolidone, Nitrogen-containing solvents such as hexylpyrrolidone and triethanolamine; alcohols such as ethanol, isopropyl alcohol, butyl alcohol, and benzyl alcohol; sulfur-containing solvents such as thiodiethanol, thiodiglycerol, sulfolane, and dimethyl sulfoxide; propylene carbonate, ethylene carbonate, and the like These may be used in combination of two or more.

  The conductive ink I is preferably alkaline from the viewpoint of storage stability.

As shown in FIG. 2, the power supply 30 is connected between the nozzle plate 21 b and the conductive substrate 11, and the control unit has a predetermined voltage between the conductive ink I and the elastic layer 12 at a predetermined timing. The power supply 30 is controlled so that is applied. For this reason, by temporarily forming a bridge of the liquid column made of the conductive ink I between the nozzle 21a and the elastic layer 12, the water contained in the bridge of the liquid column can be electrolyzed. As a result, an ink image can be formed on the intermediate transfer drum 10. At this time, since water contained in the bridge of the liquid column is oxidized on the surface of the elastic layer 12 functioning as the anode to generate protons (H ⁺ ), it is dispersed by the anionic dispersant D as shown in FIG. The pigment P which has been prepared can be aggregated via protons. Thereby, it is possible to suppress the occurrence of bleeding between adjacent dots, and a high-definition image can be formed. Moreover, clogging of the nozzle 21a can be suppressed.

  The control unit controls the time for forming the bridge of the liquid column by changing the peak voltage and the pulse width of the voltage pulse applied to the piezoelectric element.

FIG. 4 shows a mechanism for forming an ink image. First, the meniscus of the conductive ink I filled in the ink chamber 21c is formed in the nozzle 21a, and a predetermined voltage is applied to the power supply 30 (see FIG. 4A). Next, when a voltage pulse is applied to the piezoelectric element, the conductive ink I is ejected from the nozzle 21a, and a bridge of the liquid column made of the conductive ink I is temporarily interposed between the nozzle 21a and the elastic layer 12. It is formed (see FIG. 4B). At this time, the nozzle plate 21b and the elastic layer 12 function as a cathode and an anode, respectively, and the reaction formulas 4H ₂ O + 4e ⁻ → 2H ₂ + 4OH ^{− on} the surfaces of the nozzle plate 21b and the elastic layer 12, respectively.
Electrode reaction and reaction formula 2H ₂ O → 4H ⁺ + O ₂ + 4e ⁻
The electrode reaction indicated by the following occurs, and water contained in the bridge of the liquid column is electrolyzed. Further, the bridge of the liquid column is divided to form an ink image I ′ on the intermediate transfer drum 10 (see FIG. 4C).

Here, the bridge of the liquid column formed between the cathode and the anode will be described with reference to FIG. Inside the bridge B of the liquid column, cations and anions move in the vicinity of the cathode C and the anode A, respectively. As a result, electric double layers E _C and E _A are formed on the surfaces of the cathode C and the anode A, respectively. The charging rate of the electric double layers E _C and E _A depends on the resistance R _B of the bridge B of the liquid column, It is almost determined by the concentration of ions contained in the conductive ink I. At this time, when the voltage of the electric double layer E _A reaches several V, Faraday current flows water is electrolyzed. As a result, on the surface of the anode A, water is oxidized to generate protons, and the pigment dispersed by the anionic dispersant is aggregated. On the other hand, the capacitance C _EC of the electric double layer E _C, since sufficiently larger than the capacitance C _EA of the electric double layer E _A, the surface of the cathode C, water is unlikely to reduction. This is because the area of the nozzle plate 21b that contacts the conductive ink I as the cathode C is sufficiently larger than the area of the elastic layer 12 that contacts the liquid column as the anode A.

  The control unit can control the degree of aggregation of the pigment by changing the amount of proton generation, that is, the time for forming the bridge of the liquid column and the voltage applied to the power supply 30.

  Further, when water is oxidized and protons are generated, oxygen is also generated. However, since it is considered to be dissolved in water in addition to a very small amount, formation of the ink image I ′ is not inhibited.

  The time from the formation of the liquid column bridge B to the separation is usually several microseconds to several tens of microseconds, and the conductivity of the conductive ink I is usually several tens of mS / m to several hundreds. mS / m. For this reason, in order to form the ink image I ′ on the intermediate transfer drum 10, the voltage of the power supply 30 is 1.23 V, which is a theoretical decomposition voltage of water, or several V, which is a general condition for electrolysis of water. Tens of volts is insufficient, and it is preferably several tens to several hundreds of volts.

  Instead of aggregating the pigment dispersed by the anionic dispersant via the protons generated on the surface of the elastic layer 12 functioning as the anode, the pigment dispersed by the cationic dispersant is used as the cathode. Aggregation may be performed via hydroxide ions generated on the surface of the functional elastic layer.

  The transfer roller 40 is driven to rotate in the direction of A <b> 2 and transfers the ink image to the recording paper S conveyed between the intermediate transfer drum 10.

  The transfer roller 40 may incorporate a heater. In order to fix the ink image transferred to the recording paper S, a fixing roller may be further provided.

  The cleaning blade 50 cleans the intermediate transfer drum 10 after transferring the ink image to the recording paper S, and contacts the intermediate transfer drum 10 in a counter manner. As a result, even when the ink image is repeatedly formed, the background stain due to the offset can be suppressed, and the ink image can be favorably formed.

  The material constituting the cleaning blade 50 is not particularly limited, and examples thereof include elastic bodies such as silicone rubber, urethane rubber, fluorine rubber, and nitrile butadiene rubber.

  A cleaning roller may be provided instead of the cleaning blade 50 or together with the cleaning blade 50.

  The transport unit 60 includes a paper feed tray 61 on which a large number of recording sheets S can be stacked, and only the uppermost recording sheet S among the stacked recording sheets S is transferred to the intermediate transfer drum 10 and the transfer roller 40. A paper feed roller 62 that feeds the paper, a housing 63 that supports the paper feed tray 61 and the paper feed roller 62, a guide plate 64 that guides the recording paper S fed by the paper feed roller 62, and a guide A paper discharge tray 65 for discharging the recording paper S guided by the plate 64 is provided. The paper feed roller 62 is rotationally driven in the direction of A3 by a driving means (not shown) such as a motor. At this time, the control unit controls the rotation drive of the driving unit so that the ink image is transferred to the recording paper S.

  Ink images formed on the recording paper S using the image forming apparatus 100 are aggregated with pigments dispersed by an anionic dispersant, so that even if the recording paper S is plain paper, feathering or A high-quality ink image can be formed at high speed with high image density while suppressing bleeding.

  The image forming apparatus of the present invention is a copying machine, a single facsimile, a complex machine of these, a multifunction machine such as a monochrome machine related thereto, an image forming apparatus used for forming an electric circuit, or an image forming apparatus used in the biotechnology field. There may be.

[Preparation of conductive ink]
Ketjen Black EC-600JD (manufactured by Ketjen Black International Co., Ltd.) 4% by mass, sodium polyoxyethylene alkyl ether sulfonate 2% by mass, urea 15% by mass, glycerin 5% by mass, 2-pyrrolidone 0.5% by mass, A mixed solution consisting of 0.5% by mass of 1,2-octanediol, 15% by mass of tetramethylammonium nitrate, 0.1% by mass of 2-amino-2-ethyl-1,3-propanediol and distilled water (residue) After the adjustment, pressure filtration was performed using a membrane filter having an average pore diameter of 0.8 μm to obtain a black conductive ink.

  Instead of Ketjen Black EC-600JD (manufactured by Ketjen Black International), Pigment Yellow 152 was used to obtain a yellow conductive ink.

  A cyan conductive ink was obtained using Pigment Blue 15 instead of Ketjen Black EC-600JD (Ketjen Black International).

  Magenta conductive ink was obtained using Pigment Red 83 instead of Ketjen Black EC-600JD (Ketjen Black International).

[Example 1]
An ink image was formed by using the image forming apparatus 100 having an ink jet printer IPSiO GX5000 (manufactured by Ricoh) as the ejection device 20. The intermediate transfer drum 10 is formed with a silicone rubber layer (elastic layer 12) having a volume resistivity of 1 Ω · cm, a receding contact angle with respect to water of 75 °, and a thickness of 0.2 mm, and a motor (not shown). As a result, the outer peripheral linear velocity is 100 mm / sec and is driven to rotate in the direction of A1 in the figure. At this time, carbon nanotubes LS-CNT (made by the National Institute of Advanced Industrial Science and Technology Nanocarbon Research Center) having an aspect ratio of 1 × 10 ⁴ and an average length of 1 mm are dispersed in the silicone rubber layer. The recording heads 21Y, 21M, 21C, and 21BK have a metal nozzle plate 21b, and the ink chambers 21c are filled with conductive inks of yellow, magenta, cyan, and black, respectively. At this time, a 120 V power source 30 is connected between the nozzle plate 21 b and the conductive substrate 11. The gap between the elastic layer 12 of the intermediate transfer drum 10 and the nozzle plates 21b of the recording heads 21Y, 21M, 21C, and 21BK was set to 100 μm. Furthermore, the transfer roller 40 has a rubber layer having a thickness of 1 mm formed on a metal core. The cleaning blade 50 is a blade made of fluorine rubber. Further, high-quality paper TYPE 6200 (manufactured by Ricoh) was used as the recording paper S.

  Using the image forming apparatus 100 as described above, 100 mm square yellow halftone dot images PA and magenta halftone dot images PB made of isolated dots having a dot diameter of 50 μm were formed on the intermediate transfer drum 10 at intervals of 35 mm (see FIG. (See FIG. 6). Further, a 100 mm square black solid image consisting of isolated dots having a dot diameter of 50 μm was formed.

[Comparative Example 1]
As the elastic layer 12, except that a silicone rubber layer having a volume resistivity of 5 Ω · cm, a receding contact angle with respect to water of 45 °, and a thickness of 0.2 mm in which 10% by mass of carbon powder is dispersed is used. A dot image and a solid image were formed in the same manner as in Example 1.

[Comparative Example 2]
As the elastic layer 12, a silicone rubber layer in which 5% by mass of carbon powder having a volume resistivity of 1 × 10 ³ Ω · cm, a receding contact angle with respect to water of 60 °, and a thickness of 0.2 mm is dispersed is used. A halftone image and a solid image were formed in the same manner as in Example 1 except that.

[Bleeding]
Using a microscope, the dot shape of the halftone dot image transferred to the recording paper S was observed and evaluated. At this time, the case where the dots were independent was determined as ◯, the case where the dots were slightly blurred, and the case where the dots were blurred as x.

[Transferability]
Using X-rite, the density of the solid image transferred to the recording paper S was measured and evaluated. At this time, the case where the density of the solid image was 1.35 or more was judged as ◯, the case where it was 1.25 or more and less than 1.35 was judged as Δ, and the case where it was less than 1.25 was judged as x.

  The evaluation results are shown in Table 1.

実施例１では、網点画像のドットが独立しており、ベタ画像の濃度が高いことが確認された。このことから、インク画像の滲みの発生が抑制され、転写性が優れることがわかった。

In Example 1, it was confirmed that the dots of the halftone dot image were independent and the density of the solid image was high. From this, it was found that the bleeding of the ink image was suppressed and the transferability was excellent.

  On the other hand, in Comparative Example 1, it was confirmed that the dots of the halftone dot image are independent, but the density of the solid image is low. From this, it was found that transferability was inferior to that of Example 1.

  In Comparative Example 2, it was confirmed that the dots of the halftone dot image were slightly blurred and the density of the solid image was slightly low. From this, it was found that the bleeding and transferability were inferior to those of Example 1.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer drum 11 Conductive substrate 12 Elastic layer 21 Recording head 21a Nozzle 21b Nozzle plate 21c Ink chamber 30 Power supply 40 Transfer roller 50 Cleaning blade 100 Image forming apparatus I Conductive ink I ′ Ink image S Recording paper

JP 2008-19286 A

Claims (6)

A recording head having a nozzle for discharging a conductive ink in which a pigment is dispersed in a solvent containing water;
An intermediate transfer member having an elastic layer containing carbon nanotubes formed on the surface thereof, capable of forming an ink image by temporarily forming a bridge of a liquid column made of the conductive ink between the nozzle and the nozzle When,
Voltage applying means for applying a voltage capable of electrolyzing water contained in the bridge of the liquid column between the elastic layer and the conductive ink;
An image forming apparatus comprising transfer means for transferring an ink image formed on the intermediate transfer member to a recording medium.   The image forming apparatus according to claim 1, wherein a content of the carbon nanotube in the elastic layer is 0.1% by mass or more and 1.0% by mass or less. The image forming apparatus according to claim 1, wherein the elastic layer has a volume resistivity of less than 1 × 10 ³ Ω · cm.   The image forming apparatus according to claim 1, wherein the elastic layer has a receding contact angle with respect to water of greater than 60 °. The pigment is dispersed by an anionic dispersant,
The image forming apparatus according to claim 1, wherein the voltage applying unit applies a voltage so that the elastic layer functions as an anode. A step of ejecting a conductive ink in which a pigment is dispersed in a solvent containing water from a nozzle of a recording head to form an ink image on the intermediate transfer member, and an ink image formed on the intermediate transfer member as a recording medium An image forming method having a step of transferring to
The intermediate transfer body has an elastic layer containing carbon nanotubes formed on the surface,
While a voltage is applied between the conductive ink and the elastic layer, a bridge of a liquid column made of the conductive ink is temporarily formed between the nozzle and the intermediate transfer member, and the An image forming method comprising forming an ink image on the intermediate transfer member by electrolyzing water contained in a bridge of a liquid column.

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