JP2011173332A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and an image forming method, capable of suppressing the occurrence of blotting and surface staining, even when a processing liquid is not applied. <P>SOLUTION: The image forming apparatus 100 includes: recording heads (21Y, 21M, 21C and 21BK) having a nozzle for discharging a conductive ink where a pigment is dispersed in a solvent containing water; an intermediate transfer drum 10 having a conductive surface capable of forming an ink image; a power supply 30 applying a voltage to between the conductive surface of the intermediate transfer drum 10 and the conductive ink; a transfer roller 40 transferring the ink image formed on the conductive surface of the intermediate transfer drum 10 to a recording paper S; and a cleaning roller 52 cleaning the intermediate transfer drum 10 after the ink image is transferred to the recording paper S. <P>COPYRIGHT: (C)2011,JPO&INPIT

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 the treatment liquid to form the ink image, it is difficult to remove the ink image remaining on the intermediate transfer body on which the ink image has been transferred to the recording medium, and the background is not stained. There is a problem that occurs.

  The present invention provides an image forming apparatus and an image forming method capable of suppressing the occurrence of blurring and the occurrence of background contamination without applying a treatment liquid in view of the problems of the above-described conventional technology. For the purpose.

  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 member having a conductive surface capable of forming an ink image by temporarily forming a bridge of the liquid column, and between the conductive surface of the intermediate transfer member and the conductive ink. And a voltage applying means for applying a voltage capable of electrolyzing water contained in the bridge of the liquid column in the vicinity of the conductive surface, and a conductive surface of the intermediate transfer member. Transfer means for transferring an ink image to a recording medium; and a first cleaning roller for cleaning a conductive surface of the intermediate transfer body on which the ink image has been transferred to the recording medium. The surface that cleans the conductive surface of the intermediate transfer member of the cleaning roller has a smaller receding contact angle with respect to water than the conductive surface of the intermediate transfer member, and the conductivity of the intermediate transfer member of the first cleaning roller is smaller. The surface that cleans the surface of the adhesive has a tack value larger than that of the conductive surface of the intermediate transfer member.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the receding contact angle with respect to water of the surface for cleaning the conductive surface of the intermediate transfer member of the first cleaning roller is 1 ° or more. It is characterized by being less than 60 °.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the tack value of the surface for cleaning the conductive surface of the intermediate transfer member of the first cleaning roller is 50 gf / cm ^2. It is characterized by being 150 gf / cm ² or more.

  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 conductive surface of the intermediate transfer member on which the ink image is transferred to the recording medium is cleaned. The surface of the second cleaning roller for cleaning the conductive surface of the intermediate transfer member has a receding contact angle with respect to water rather than the conductive surface of the intermediate transfer member. The surface of the second cleaning roller that cleans the conductive surface of the intermediate transfer member has a smaller tack value than the surface of the first cleaning roller that cleans the conductive surface of the intermediate transfer member. The conductive surface of the intermediate transfer member on which the ink image has been transferred to the recording medium is cleaned using the second cleaning roller. After, wherein the cleaning using the first cleaning roller.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the receding contact angle with respect to water of the surface for cleaning the conductive surface of the intermediate transfer member of the second cleaning roller is 1 ° or more. It is characterized by being less than 60 °.

  According to a sixth aspect of the invention, there is provided a process of forming an ink image on an intermediate transfer member having a conductive surface by discharging conductive ink in which a pigment is dispersed in a solvent containing water from a nozzle of a recording head. A step of transferring an ink image formed on the conductive surface of the intermediate transfer member to a recording medium, and a conductive surface of the intermediate transfer member having the ink image transferred to the recording medium, using a cleaning roller. An image forming method including a step of cleaning the conductive ink between the nozzle and the intermediate transfer body in a state where a voltage is applied between the conductive ink and the conductive surface. A bridge of the liquid column is temporarily formed, and water in the bridge of the liquid column is electrolyzed and aggregated in the vicinity of the conductive surface to aggregate the pigment. Guidance The surface that forms an ink image on the conductive surface and cleans the conductive surface of the intermediate transfer member of the cleaning roller has a receding contact angle with respect to water smaller than the conductive surface of the intermediate transfer member. The surface for cleaning the conductive surface of the intermediate transfer member of the cleaning roller has a tack value larger than that of the conductive surface of the intermediate transfer member.

  According to the present invention, it is possible to provide an image forming apparatus and an image forming method capable of suppressing the occurrence of bleeding and the occurrence of background contamination 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 sectional drawing which shows the cleaning roller of FIG. 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. It is a figure which shows the state which the pigment disperse | distributed with the anionic dispersing agent aggregated through the proton and the metal cation. FIG. 8 is a partial enlarged view of a modification of the image forming apparatus in FIG. 1. 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 is formed on the surface of the intermediate transfer drum 10 around the intermediate transfer drum 10 by discharging conductive ink and forming an ink image on the surface of the intermediate transfer drum 10. A transfer roller 40 that transfers the ink image to the recording paper S, a cleaning member 50 that cleans the surface of the intermediate transfer drum 10 on which the ink image is transferred to the recording paper S, a transport unit 60 that transports the recording paper S, a CPU, a memory, and the like A control unit (not shown). At this time, the cleaning member 50 cleans the surfaces of the intermediate transfer drum 10 on which the ink image is transferred to the recording paper S, and cleaning blades 53 and 54 that clean the surfaces of the cleaning rollers 51 and 52, respectively. Have

  As shown in FIG. 2, the intermediate transfer drum 10 has a conductive layer 12 formed on a conductive substrate 11, and is driven to rotate in the 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, and stainless steel, are mentioned.

  The receding contact angle of the conductive layer 12 with respect to water is usually 60 to 120 °, and preferably 75 to 100 °. If the receding contact angle of the conductive layer 12 with respect to the conductive ink is less than 60 °, the ink image remaining on the surface of the conductive layer 12 may not be sufficiently removed, and if it exceeds 120 °, the surface of the conductive layer 12 The conductive ink may move and coalesce.

  The receding contact angle of the conductive layer 12 with respect to the conductive ink is usually 20 to 120 °, and preferably 25 to 100 °. If the receding contact angle of the conductive layer 12 with respect to the conductive ink is less than 20 °, the ink image remaining on the surface of the conductive layer 12 may not be sufficiently removed, and if it exceeds 120 °, the surface of the conductive layer 12 The conductive ink may move and coalesce.

The tack value of the conductive layer 12 is usually 10 to 70 gf / cm ² , and preferably ²⁰ to 50 gf / cm ² . If the tack value of the elastic layer 12 is less than 10 gf / cm ² , the recording paper S may be easily displaced and the ink image may be disturbed. If it exceeds 70 gf / cm ² , the high-viscosity component contained in the ink image is sufficient. May not be removed.

  The conductive layer 12 has a conductive agent dispersed in an elastic body. Although it does not specifically limit as a electrically conductive agent, Carbon, platinum, gold | metal | money etc. are mentioned. The elastic body is not particularly limited, and examples thereof include silicone rubber, urethane rubber, fluorine rubber, and nitrile butadiene rubber.

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

The volume resistivity of the conductive layer 12 is smaller than the volume resistivity of the conductive ink, but is preferably less than 1 × 10 ³ Ω · cm.

  Instead of the intermediate transfer drum 10, a conductive substrate 11 on which the conductive layer 12 is not formed and an insulating substrate on which the conductive layer 12 is formed may be used as the intermediate transfer drum. Further, instead of the intermediate transfer drum 10, an endless belt or sheet having a conductive surface 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 21, 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 is 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 ink discharge means may be a shape deformation element method such as a piezo method, or may be another method such as a heater method such as a thermal method.

  Further, the recording head 21 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 salts, alkyl sulfate esters, alkyl benzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl phosphate esters, naphthalene sulfonate formalin condensates, 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 source 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 conductive 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 conductive layer 12, water contained in the bridge of the liquid column can be electrolyzed. As a result, an ink image can be formed on the surface of the conductive layer 12 of 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 conductive 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.

  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 rollers 51 and 52 are in contact with the surface of the conductive layer 12 of the intermediate transfer drum 10, respectively, and are driven to rotate in the directions of A3 and A4.

  As shown in FIG. 4, the cleaning roller 51 (52) has an elastic layer 51b (52b) formed on a base 51a (52a).

  At this time, the surface of the elastic layer 51 b and the surface of the elastic layer 51 b have smaller receding contact angles with respect to water than the surface of the conductive layer 12 of the intermediate transfer drum 10. Further, the surface of the elastic layer 51 b and the surface of the elastic layer 51 b preferably have a receding contact angle with respect to the conductive ink I smaller than the surface of the conductive layer 12 of the intermediate transfer drum 10. On the other hand, the elastic layer 51b has a smaller tack value than the elastic layer 52b, and the elastic layer 52b has a larger tack value than the conductive layer 12 of the intermediate transfer drum 10. The elastic layer 51b preferably has a hardness higher than that of the elastic layer 52b, and the elastic layer 52b preferably has a hardness lower than that of the conductive layer 12 of the intermediate transfer drum 10. For this reason, the cleaning roller 51 can remove low-viscosity components contained in the ink image remaining on the surface of the conductive layer 12 of the intermediate transfer drum 10. On the other hand, the cleaning roller 52 can remove the high viscosity component contained in the ink image remaining on the surface of the conductive layer 12 of the intermediate transfer drum 10. As a result, the occurrence of soiling can be suppressed.

  Although it does not specifically limit as a material which comprises the base | substrate 51a, Metals, such as aluminum, an aluminum alloy, copper, and stainless steel, are mentioned.

  The receding contact angle of the elastic layer 51b with respect to water is usually 1 ° to 60 °, and preferably 5 ° to 50 °. If the receding contact angle of the elastic layer 51b with respect to water is less than 1 °, the low-viscosity component wets and spreads on the surface of the elastic layer 51b, making it difficult to remove the low-viscosity component from the surface of the elastic layer 51b. If it is more than 0 °, the low viscosity component contained in the ink image may not be sufficiently removed.

  The difference in receding contact angle with respect to water between the elastic layer 51b and the conductive layer 12 of the intermediate transfer drum 10 is usually 20 ° or more. If the difference in receding contact angle with respect to water is less than 20 °, the low viscosity component contained in the ink image may not be sufficiently removed.

  The receding contact angle of the elastic layer 51b with respect to the conductive ink I is usually 1 ° to 10 °, and preferably 1 ° to 5 °. When the receding contact angle of the elastic layer 51b with respect to the conductive ink I is less than 1 °, the low viscosity component wets and spreads on the surface of the elastic layer 51b, and it becomes difficult to remove the low viscosity component from the surface of the elastic layer 51b. Yes, if it exceeds 10 °, the low viscosity component contained in the ink image may not be sufficiently removed.

  The difference in receding contact angle with respect to the conductive ink I between the elastic layer 51b and the conductive layer 12 of the intermediate transfer drum 10 is usually 5 ° or more. If the difference in receding contact angle with respect to the conductive ink I is less than 5 °, the low viscosity component contained in the ink image may not be sufficiently removed.

  The material constituting the elastic layer 51b is not particularly limited, and examples thereof include nitrile rubber and urethane rubber that have been subjected to a hydrophilic treatment as needed.

  Instead of the cleaning roller 51, a cleaning roller made of a metal such as aluminum or stainless steel; a material such as Teflon (registered trademark) subjected to hydrophilic treatment may be used.

  Although it does not specifically limit as a material which comprises the base | substrate 51b, Metals, such as aluminum, an aluminum alloy, copper, and stainless steel, are mentioned.

  The receding contact angle of the elastic layer 52b with respect to water is usually 1 ° to 60 °, and preferably 5 ° to 50 °. When the receding contact angle of the elastic layer 52b with respect to water is less than 1 °, the high-viscosity component wets and spreads on the surface of the elastic layer 52b, making it difficult to remove the high-viscosity component from the surface of the elastic layer 52b. If it is more than 0 °, the high viscosity component contained in the ink image may not be sufficiently removed.

  The difference in receding contact angle with respect to water between the elastic layer 52b and the conductive layer 12 of the intermediate transfer drum 10 is usually 20 ° or more. If the difference in receding contact angle with respect to water is less than 20 °, the high viscosity component contained in the ink image may not be sufficiently removed.

  The receding contact angle of the elastic layer 52b with respect to the conductive ink I is usually 1 ° to 10 °, and preferably 1 ° to 5 °. When the receding contact angle of the elastic layer 52b with respect to the conductive ink I is less than 1 °, the high viscosity component wets and spreads on the surface of the elastic layer 52b, and it becomes difficult to remove the high viscosity component from the surface of the elastic layer 52b. Yes, if it exceeds 10 °, the high viscosity component contained in the ink image may not be sufficiently removed.

  The difference in receding contact angle for the conductive ink I between the elastic layer 52b and the conductive layer 12 of the intermediate transfer drum 10 is usually 10 ° or more. If the difference in the receding contact angle with respect to the conductive ink I is less than 10 °, the high viscosity component contained in the ink image may not be sufficiently removed.

The tack value of the elastic layer 52b is usually 50 to 150 gf / cm ² and preferably 80 to 150 gf / cm ² . When the tack value of the elastic layer 52b is less than 50 gf / cm ^2, may not be able to sufficiently remove the high viscosity components in the ink image, it exceeds 150 gf / cm ^2, a high viscosity from the surface of the elastic layer 52b It may be difficult to remove components.

The difference in tack value between the elastic layer 52b and the conductive layer 12 of the intermediate transfer drum 10 is usually 20 gf / cm ² or more. If the difference in tack value is less than 20 gf / cm ² , the high viscosity component contained in the ink image may not be sufficiently removed.

  The material constituting the elastic layer 52b is not particularly limited, and examples thereof include nitrile rubber and urethane rubber that have been subjected to a hydrophilic treatment as necessary.

  When the viscosity of the ink image remaining on the surface of the conductive layer 12 of the intermediate transfer drum 10 is high, the cleaning roller 51 can be omitted.

  The cleaning blades 53 and 54 are in contact with the surfaces of the cleaning rollers 51 and 52 in a counter manner, respectively. Thereby, the low-viscosity component and the high-viscosity component which have been transferred to the surfaces of the cleaning rollers 51 and 52 can be removed, and the occurrence of background contamination can be suppressed.

  The material constituting the cleaning blades 53 and 54 is not particularly limited, and examples thereof include elastic bodies such as silicone rubber, urethane rubber, fluorine rubber, and nitrile butadiene rubber.

  Instead of the cleaning blades 53 and 54, members for sucking the low viscosity component and the high viscosity component transferred to the surfaces of the cleaning rollers 51 and 52, respectively, may be provided.

  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 A5 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.

FIG. 5 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. 5A). 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 conductive layer 12. It is formed (see FIG. 5B). At this time, the nozzle plate 21b and the conductive 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 conductive 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 surface of the conductive layer 12 of the intermediate transfer drum 10 (see FIG. 5C).

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 conductive 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. Therefore, in order to form the ink image I ′ on the surface of the conductive layer 12 of the intermediate transfer drum 10, the voltage of the power supply 30 is 1.23 V, which is the theoretical decomposition voltage of water, or the general electrolysis of water. The condition of several V to several tens V is insufficient, and several tens V to several hundred V is preferable.

In addition, when using the electroconductive base | substrate 11 in which the conductive layer 12 is not formed as an intermediate transfer drum instead of the intermediate transfer drum 10, a metal is oxidized with water on the surface of the electroconductive base | substrate 11 which functions as an anode. be able to. As a result, a metal cation excellent in the effect of aggregating the pigment is produced together with the proton, so that the pigment dispersed by the anionic dispersant D via the proton and the metal cation (M ^{n +} ) as shown in FIG. P can be aggregated.

  In this case, as shown in FIG. 8, a cleaning member similar to the intermediate transfer drum 10 ′ in which the elastic layer 12 ′ is formed on the base 11 ′ and the cleaning member 50 between the conductive base 11 and the transfer roller 40. 50 'is preferably further provided. Thus, the ink image formed on the surface of the conductive substrate 11 is transferred to the surface of the elastic layer 12 ′ of the intermediate transfer drum 10 ′, and then transferred to the surface of the elastic layer 12 ′ of the intermediate transfer drum 10 ′. Since the image can be transferred to the recording paper S, the transferability can be improved.

  At this time, the intermediate transfer drum 10 ′ is in contact with the surface of the conductive substrate 11 and is rotated following the direction of A1 ′. The transfer roller 40 is in contact with the surface of the elastic layer 12 ′ of the intermediate transfer drum 10 ′. It rotates following the direction of A2 ′.

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

  The material constituting the elastic layer 12 ′ is not particularly limited, and examples thereof include elastic bodies such as silicone rubber, urethane rubber, fluorine rubber, and nitrile butadiene rubber.

  Further, instead of aggregating the pigment dispersed by the anionic dispersant via the protons generated on the surface of the conductive 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 conductive layer.

  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 black conductive ink]
35.0% by mass of sulfonic acid group-bonded carbon black pigment dispersion CAB-O-JET-200 (Cabot Specialty Chemicals Inc.) having a solid content of 20% by mass, 10.0% by mass of 2-pyrrolidone, A mixed liquid consisting of 14.0% by mass of glycerin, 0.9% by mass of propylene glycol monobutyl ether, 0.1% by mass of sodium dehydroacetate and distilled water (residue) was obtained. Next, after adjusting the pH of the mixed solution to 9.1 using a 5% by mass aqueous solution of lithium hydroxide, it was filtered under pressure using a membrane filter having an average pore size of 0.8 μm, and a black conductive ink was obtained. Got.

[Preparation of yellow conductive ink]
Sulfonic acid group-bonded yellow pigment dispersion CAB-O-JET-270Y (manufactured by Cabot Specialty Chemicals Inc.) having a solid content of 10% by mass 40.0% by mass, triethylene glycol 15.0% by mass, glycerin A mixed liquid consisting of 25.0% by mass, propylene glycol monobutyl ether 6.0% by mass, sodium dehydroacetate 0.1% by mass and distilled water (residue) was obtained. Next, after adjusting the pH of the mixed solution to 9.1 using a 5% by mass aqueous solution of lithium hydroxide, pressure filtration is performed using a membrane filter having an average pore size of 0.8 μm, and a yellow conductive ink is obtained. Got.

[Example 1]
Ink images were formed by using the recording heads 21Y and 21BK of the image forming apparatus 100 having the ejection device of the inkjet printer IPSiO GX5000 (manufactured by Ricoh) as the ejection device 20. The intermediate transfer drum 10 has a silicone rubber layer (conductive layer 12) having a volume resistivity of 5 Ω · cm and a thickness of 0.2 mm, in which carbon is dispersed, on the outer periphery of an aluminum base tube (conductive base 11). The outer peripheral linear velocity is 100 mm / second and is driven to rotate in the direction of A1 in the drawing by a motor (not shown). At this time, the silicone rubber layer has a receding contact angle with respect to water of 75 °, a tack value of 53 gf / cm ² , and a hardness of 50 °. The recording heads 21Y and 21BK have metal nozzle plates 21b, and the ink chambers 21c are filled with yellow and black conductive inks, respectively. At this time, a 120 V power source 30 is connected between the nozzle plate 21 b and the conductive substrate 11. Further, the gap between the conductive layer 12 of the intermediate transfer drum 10 and the nozzle plate 21b of the recording head 21 was set to 100 μm. Furthermore, the transfer roller 40 has a rubber layer having a thickness of 5 mm formed on a metal core. In the cleaning roller 51, a nitrile rubber layer (elastic layer 51b) having a thickness of 5 mm is formed on a metal core (base 51a). At this time, the nitrile rubber layer has a receding contact angle with water of 15 °, a tack value of 25 gf / cm ² , and a hardness of 90 °. Further, in the cleaning roller 52, a urethane rubber layer (elastic layer 52b) having a thickness of 5 mm is formed on a metal core (base 52a). At this time, the urethane rubber layer has a receding contact angle with respect to water of 40 to 50 °, a tack value of 128 gf / cm ² , and a hardness of 30 °. The cleaning blades 53 and 54 are blades made of fluorine rubber. Further, high-quality paper TYPE 6200 (manufactured by Ricoh) was used as the recording paper S.

  The receding contact angle was measured at 23 ° C. using an automatic contact angle meter DM500 (manufactured by Kyowa Interface Science) and analysis software FAMAS (manufactured by Kyowa Interface Science). The tack value is a stress applied when pulling out a cylinder-shaped stainless steel probe having a diameter of 5 mm with a compressive load of 200 gf for 1 second and then pulling out at 120 mm / min. . Furthermore, the hardness is a value measured using a JIS-A hardness meter.

  Using the image forming apparatus 100 as described above, 100 mm square yellow halftone dot images PA and black 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. 9). Further, a mixed solid image of 100 mm square yellow and black consisting of isolated dots having a dot diameter of 50 μm was formed.

[Example 2]
A halftone image and a mixed solid image were formed in the same manner as in Example 1 except that a SUS cored bar was used as the cleaning roller 51. At this time, the SUS core has a receding contact angle with respect to water of 20 ° and a tack value of 3 gf / cm ² .

[Example 3]
A halftone image and a mixed solid image were formed in the same manner as in Example 1 except that a hydrophilic fluororubber layer and a hydrophilic urethane rubber layer were used as the elastic layers 51b and 52b, respectively. At this time, the hydrophilized fluororubber layer has a receding contact angle with respect to water of 30 °, a tack value of 20 gf / cm ² , and a hardness of 90 °. The hydrophilized urethane rubber layer has a receding contact angle with water of 40 °, a tack value of 105 gf / cm ² , and a hardness of 30 °.

[Example 4]
A halftone image and a mixed solid image were formed in the same manner as in Example 3 except that the cleaning roller 51 was not used.

[Comparative Example 1]
A halftone image and a mixed solid image were formed in the same manner as in Example 2 except that the cleaning roller 52 was not used.

[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.

[Soil dirt]
After affixing a print tape (manufactured by Print Technica) on the surface of the conductive layer 12 of the intermediate transfer drum 10 cleaned using the cleaning member 50, the peeled tape is affixed to paper and visually (enlarged). Evaluation). At this time, the case where the image does not remain is ◯, the case where the image is slightly left but the level where the background is not generated is Δ, and the case where the image remains is the level where the background is generated. Judged as x.

  The evaluation results are shown in Table 1.

実施例１〜４では、インク画像の滲みの発生が抑制され、地汚れの発生が抑制されることが確認された。

In Examples 1 to 4, it was confirmed that the occurrence of bleeding of the ink image was suppressed and the occurrence of background stains was suppressed.

  On the other hand, in Comparative Example 1, it was confirmed that the smearing of the ink image is suppressed, but the background is stained. From this, it was found that the SUS cored bar has a tack value smaller than that of the conductive layer 12 of the intermediate transfer drum 10 and therefore cannot sufficiently remove the high viscosity component of the ink image remaining on the surface of the conductive layer 12. .

10, 10 'Intermediate transfer drum 11 Conductive substrate 11' Substrate 12 Conductive layer 12 'Elastic layer 21 Recording head 21a Nozzle 21b Nozzle plate 21c Ink chamber 30 Power supply 40 Transfer roller 50, 50' Cleaning member 51, 52, 51 ', 52 'cleaning roller 51a, 52a substrate 51b, 52b elastic layer 53, 54, 53', 54 '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 a conductive surface 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;
A voltage for applying a voltage capable of electrolyzing water contained in the bridge of the liquid column in the vicinity of the conductive surface between the conductive surface of the intermediate transfer member and the conductive ink. Applying means;
Transfer means for transferring an ink image formed on the conductive surface of the intermediate transfer member to a recording medium;
A first cleaning roller that cleans a conductive surface of the intermediate transfer body onto which the ink image has been transferred to the recording medium;
The surface for cleaning the conductive surface of the intermediate transfer member of the first cleaning roller has a receding contact angle with respect to water smaller than the conductive surface of the intermediate transfer member,
An image forming apparatus, wherein a surface of the first cleaning roller for cleaning the conductive surface of the intermediate transfer member has a tack value larger than that of the conductive surface of the intermediate transfer member.   2. The image forming apparatus according to claim 1, wherein a receding contact angle with respect to water of a surface for cleaning the conductive surface of the intermediate transfer member of the first cleaning roller is 1 ° or more and less than 60 °. 3. The image according to claim 1, wherein a tack value of a surface for cleaning the conductive surface of the intermediate transfer member of the first cleaning roller is 50 gf / cm ² or more and 150 gf / cm ² or less. Forming equipment. A second cleaning roller for cleaning the conductive surface of the intermediate transfer body on which the ink image has been transferred to the recording medium;
The surface for cleaning the conductive surface of the intermediate transfer member of the second cleaning roller has a receding contact angle with respect to water smaller than the conductive surface of the intermediate transfer member,
The surface for cleaning the conductive surface of the intermediate transfer member of the second cleaning roller has a tack value smaller than the surface for cleaning the conductive surface of the intermediate transfer member of the first cleaning roller,
The conductive surface of the intermediate transfer body on which the ink image has been transferred to the recording medium is cleaned using the second cleaning roller, and then cleaned using the first cleaning roller. The image forming apparatus according to any one of claims 1 to 3.   5. The image forming apparatus according to claim 4, wherein a receding contact angle with respect to water of a surface for cleaning the conductive surface of the intermediate transfer member of the second cleaning roller is 1 ° or more and less than 60 °. 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 an intermediate transfer member having a conductive surface; and the conductivity of the intermediate transfer member An image forming method comprising: a step of transferring an ink image formed on the surface of the recording medium to a recording medium; and a step of cleaning the conductive surface of the intermediate transfer member on which the ink image is transferred to the recording medium, using a cleaning roller. Because
While a voltage is applied between the conductive ink and the conductive surface, a bridge of a liquid column made of the conductive ink is temporarily formed between the nozzle and the intermediate transfer member. Forming an ink image on the conductive surface of the intermediate transfer member by electrolyzing water contained in the bridge of the liquid column and aggregating the pigment in the vicinity of the conductive surface;
The surface for cleaning the conductive surface of the intermediate transfer member of the cleaning roller has a receding contact angle with respect to water smaller than the conductive surface of the intermediate transfer member,
An image forming method, wherein a surface of the cleaning roller that cleans the conductive surface of the intermediate transfer member has a tack value larger than that of the conductive surface of the intermediate transfer member.

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