JP4449914B2 - Droplet discharge device - Google Patents

Description

  The present invention relates to a droplet discharge head that discharges droplets, a conveyance member that holds a recording medium and conveys the recording medium to face the droplet discharge head, and conveys the recording medium by charging at least one of the conveyance member and the recording medium. The present invention relates to a droplet discharge device including a charging unit that electrostatically attracts a member.

  In an ink jet printer as a droplet discharge device, the sheet P is pressed against a conveying member such as a conveying belt or a conveying drum by a charging means such as a charging roll and charged, or an alternating electric field is formed on the conveying member. Then, an electrostatic attraction force is generated between the paper and the transport member, and the paper is attracted to the transport member. In this state, the paper is conveyed in the ink droplet ejection area of the recording head, and an image is recorded on the paper (see, for example, Patent Documents 1 and 2). This increases the uniformity of the distance between the paper and the nozzle surface of the recording head (hereinafter referred to as TD: Throw Distance), improves the accuracy of the ink droplet landing position on the paper, and improves the image quality.

  In recent years, the distance between the paper and the nozzle surface of the recording head has been reduced to 1 to 2 mm for the purpose of further improving the accuracy of the ink droplet landing position on the paper, that is, further improving the image quality. Has been done. On the other hand, in order to improve the uniformity of TD, it is required to increase the electrostatic adsorption force between the paper and the conveying member. Also, the uniformity of TD depends on the environmental change such as temperature and humidity and the difference in the type of paper. In order to prevent the decrease in the electrostatic force, it is required to further increase the electrostatic attraction between the paper and the conveying member.

  For this reason, the separation failure of the paper from the conveyance member occurs, or the electrostatic adsorption force generated between the recording head 32 and the conveyance belt 28 increases as shown in FIG. 13, and the conveyance belt 28 is lifted. In some cases, troubles that contact the recording head 32 may occur. When the conveyance belt 28 comes into contact with the recording head 32, the conveyance belt 28 is stained with ink, ink is transferred from one recording head 32 to another recording head 32 via the conveyance belt 28, color mixing occurs, or the conveyance belt 28. There arises a problem that foreign matter adhered to the recording head 32 is mixed into the recording head 32 from the nozzles. In particular, a system that uses a transparent ink (reaction liquid) that mixes with yellow (Y), magenta (M), cyan (C), and black (K) inks to cause an agglomeration reaction, mainly for the purpose of improving image quality. In a so-called two-liquid system or a system in which different color inks such as K and Y are mixed and reacted (a so-called inter-ink reaction system), ink aggregation or discoloration occurs in the recording head 32, and recovery is not possible. It becomes possible.

  Here, as shown in FIG. 14, in the normal state, the contact portion between the charging roll 36 and the conveyance belt 28 has a high resistance, so that the movement of electric charge between the charging roll 36 and the conveyance belt 28 is caused by the charging roll. This is due to the discharge in the region of the minute gap between the belt 36 and the conveyor belt 28. However, when water droplets, ink droplets, or the like adhere to the contact portion between the charging roll 36 and the conveyor belt 28, the resistance is low, and the charge is moved in this portion. For this reason, as shown in the graph of FIG. 15, the surface potential on the conveyor belt 28 in the abnormal state increases as compared with the normal state.

  A configuration has been devised that suppresses vibration of the conveyor belt by sucking the conveyor belt to the side opposite to the recording head (see, for example, Patent Document 3). In the configuration described in Patent Document 3, a voltage is applied to the comb-like electrodes built in the conveyor belt, and electrostatic attraction is generated on both the front and back surfaces of the conveyor belt, whereby a recording medium is placed on the surface of the conveyor belt. At the same time, the back surface of the conveyance belt is sucked by a member disposed on the opposite side of the recording belt side of the conveyance belt as a belt suction member.

Here, in order to continuously apply a high voltage to the electrodes built in the rotating conveyor belt, the electrodes are exposed along the belt rotating direction, and a conductive brush is slid onto the exposed portion of the electrodes. Although it is rubbed, high-voltage power feeding is performed at the rubbing part between the conductive brush and the electrode, so that electric discharge is likely to occur, and electromagnetic waves generated with the electric discharge become a noise source, and cause of malfunction It becomes. In addition, the occurrence of sparks at the rubbing portion between the conductive brush and the electrode damages the electrode and the conductive brush, and their life is significantly shortened.
JP-A-10-193585 JP 2003-103857 A JP 2002-145474 A

  The present invention has been made in consideration of the above-described facts, and an object thereof is to suppress excessive charging of the conveying member by the charging means.

  The liquid droplet ejection apparatus according to claim 1, a liquid droplet ejection head that ejects liquid droplets, a conveyance member that holds a recording medium and conveys the recording medium to face the liquid droplet ejection head, the conveyance member, A droplet discharge device comprising: a charging unit that charges at least one of the recording medium on the conveying member and electrostatically attracts the recording medium to the conveying member; A high-resistance liquid having a volume resistivity higher than that of the liquid discharged from the droplet discharge head is interposed.

  In the droplet discharge device according to the first aspect, the recording medium is held by the transport member and transported while facing the droplet discharge head, and the droplet discharge head discharges the droplet. Thereby, an image or the like is recorded on the recording medium. At this time, at least one of the transport member and the recording medium on the transport member is charged by the charging unit, and the recording medium is electrostatically attracted to the transport member. Therefore, the uniformity of the distance between the droplet discharge head and the recording medium is improved. This increases the accuracy of the landing position of the droplet on the recording medium.

  Here, a high-resistance liquid having a volume resistivity higher than that of the liquid ejected from the droplet ejection head is interposed between the charging unit and the transport member. For this reason, when a liquid, a water droplet, or the like discharged from the droplet discharge head is interposed between the charging unit and the transport member, a decrease in electrical resistance between the charging unit and the transport member is suppressed. Therefore, excessive charging of the conveying member by the charging unit can be suppressed.

  Further, when the conveying member is an endless belt, a force for urging the belt to the side opposite to the droplet discharge head side becomes unnecessary, and the configuration described in Patent Document 3 described above becomes unnecessary. The occurrence of discharge in the surroundings can be suppressed and electromagnetic interference can be suppressed. In addition, since the occurrence of sparks around the belt can be prevented, damage to the belt can be suppressed, and shortening of the belt can be suppressed.

  Since the present invention is configured as described above, it is possible to suppress excessive charging of the conveying member by the charging means.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows an ink jet recording apparatus 12 of the present embodiment. A paper feed tray 16 is provided in the lower part of the casing 14 of the ink jet recording apparatus 12, and the sheets P stacked in the paper feed tray 16 can be taken out one by one by a pickup roll 18. The taken paper P is transported by a plurality of transport roller pairs 20 constituting a predetermined transport path 22.

  Above the paper feed tray 16, an endless transport belt 28 is stretched around a drive roll 24 and driven rolls 26 and 27. The driving roll 24 and the driven roll 26 are disposed substantially horizontally, and a driven roll 27 is disposed below the driving roll 24 and the driven roll 26.

  A recording head array 30 is disposed above the conveyor belt 28 and faces a flat portion 28 </ b> F of the conveyor belt 28 between the drive roll 24 and the driven roll 26. This opposed area is an ejection area SE where ink droplets are ejected from the recording head array 30. The sheet P transported along the transport path 22 is held by the transport belt 28 and reaches the discharge area SE, and ink droplets corresponding to image information are attached from the recording head array 30 in a state of facing the recording head array 30. The

  In this embodiment, the recording head array 30 has a long shape in which the effective recording area is equal to or larger than the width of the paper P (the length in the direction orthogonal to the transport direction), and is yellow (Y) and magenta (M). , Four ink jet recording heads (hereinafter referred to as recording heads) 32 corresponding to the four colors of Sian (C) and Black (K) are arranged along the transport direction, and a full color image can be recorded. ing.

  Each recording head 32 is driven by a head drive circuit (not shown). The head drive circuit has a configuration in which, for example, the ejection timing of ink droplets and the ink ejection port (nozzle) to be used are determined according to image information and a drive signal is sent to the recording head 32.

  The recording head array 30 may be stationary in a direction orthogonal to the transport direction. However, if the recording head array 30 is configured to move as necessary, an image with higher resolution can be obtained by multi-pass image recording. Or the failure of the recording head 32 is not reflected in the recording result.

  Four maintenance units 34 corresponding to the respective recording heads 32 are arranged on both sides of the recording head array 30. As shown in FIG. 2, when performing maintenance on the recording head 32, the recording head array 30 is moved upward, and the maintenance unit 34 moves into the gap formed between the conveyance belt 28 and enters. . Then, a predetermined maintenance operation (suction, wiping, capping, etc.) is performed while facing the nozzle surface.

  Further, an ink tank 35 for storing ink of each color is disposed above the recording head array 30. Each recording head 32 is connected to each ink tank 35.

  As shown in FIG. 3, a charging roll 36 to which a power source 38 is connected is disposed on the upstream side of the recording head array 30. The charging roll 36 is driven while sandwiching the conveyance belt 28 and the paper P with the driven roll 26, and presses the paper P against the conveyance belt 28. At this time, since a predetermined potential difference is generated between the grounded follower roll 26, the sheet P can be electrostatically adsorbed to the transport belt 28 by applying an electric charge to the sheet P.

  A separation plate 40 is disposed on the downstream side of the recording head array 30 and separates the paper P from the conveyance belt 28. As shown in FIG. 1, the peeled paper P is conveyed by a plurality of discharge roller pairs 42 that constitute a discharge path 44 on the downstream side of the peeling plate 40, and is a paper discharge tray 46 provided at the top of the housing 14. To be discharged.

  Further, as shown in FIG. 3, a belt cleaning unit 48 is disposed below the peeling plate 40. The belt cleaning unit 48 is in contact with a portion of the transport belt 28 wound around the drive roll 24 and scrapes off the ink and the like adhering to the transport belt 28, and is scraped off from the transport belt 28 by the blade 49. And a collection box 51 for collecting ink and the like.

  An oil application unit 62 is disposed below the driven roll 26. The oil application unit 62 includes an oil application roll 64 that is rotatably supported by a frame (not shown). The oil application roll 64 is in contact with a portion of the conveyor belt 28 that is wound around the driven roll 26 and rotates following the conveyor belt 28. The oil application roll 64 is a roll capable of absorbing a liquid formed of a porous material such as polyethylene or urethane, impregnated with silicone oil, and applies the silicone oil to the conveyor belt 28.

  Here, the silicone oil is insoluble in an aqueous liquid, has a surface tension of, for example, 20.8 [mN / m], a surface tension of the aqueous ink (for example, 30 [mN / m]), water It is lower than the surface tension (for example, 70 [mN / m]).

  For this reason, as shown in FIGS. 4A and 4B, mist-like ink generated when the recording head 32 ejects ink droplets or water-based liquid W such as water due to condensation is formed on the conveying belt 28. In the case where it adheres, the silicone oil wets and spreads on the aqueous liquid W. That is, a silicone oil layer (hereinafter referred to as a coating layer) O covering the aqueous liquid W is formed on the transport belt 28.

Since silicone oil has a volume resistivity of, for example, 10 ¹⁴ Ω · cm or more and a high resistance and high insulation property, the coating layer O functions as an insulating layer. For this reason, even if the aqueous liquid W is interposed between the charging roll 36 and the conveyance belt 28, the contact portion between the charging roll 36 and the conveyance belt 28 always has a high resistance. The movement of the electric charge between the charging roller 36 and the conveying belt 28 is caused by the discharge in the area of the minute gap between the charging roller 36 and the conveying belt 28.

  As a result, the surface potential on the conveyor belt 28 can be prevented from rising abnormally, thereby preventing the contact between the conveyor belt 28 and the recording head 32, while increasing the charge amount of the conveyor belt 28, TD can be made narrower. Accordingly, the ink droplet landing accuracy on the paper P can be further improved, and thus the image quality can be further improved.

  By the way, as shown in FIGS. 5A and 5B, when the paper P is interposed between the charging roll 36 and the transport belt 28, a minute gap region is formed between the charging roll 36 and the paper P. The electric charge is moved by the electric discharge in the paper, and the electric charge is moved between the paper P and the transport belt 28 at the contact portion between the paper P and the transport belt 28, but the contact portion between the paper P and the transport belt 28. There is a proportional relationship between the amount of charge movement in the sheet and the amount of charge discharged between the charging roll 36 and the paper P.

  For this reason, as shown in FIG. 5A, the lower the resistance of the contact portion between the paper P and the conveyor belt 28, the greater the amount of discharge charge between the charging roll 36 and the paper P, causing abnormal charging. It becomes easy to do. However, as shown in FIG. 5B, in this embodiment, since the coating layer O having high resistance and high insulation is formed between the paper P and the transport belt 28, the charging roll 36 and the paper An increase in discharge charge amount with P can be suppressed, and abnormal charging can be prevented.

  In addition, an electrostatic attraction force between the paper P and the transport belt 28 is generated due to a potential difference between the paper P and the transport belt 28, but the movement of electric charge from the paper P to the transport belt 28 is suppressed, so that the paper P And the transport belt 28 can be maintained for a longer time, and the electrostatic adsorption force between the paper P and the transport belt 28 can be maintained for a longer time.

  In addition, since the application unit 62 is disposed on the upstream side in the rotation direction of the conveyance belt 28 from the charging roll 36 and on the downstream side in the rotation direction of the conveyance belt 28 from the belt cleaning unit 48, adhesion of ink to the oil application roll 64 can be suppressed. . Further, since the coating layer O on the conveyor belt 28 is removed by the belt cleaning unit 48 while the conveyor belt 28 makes one round, the coating layer O is newly formed on the conveyor belt 28 by the oil application unit 62. Management of the thickness of the coating layer O is easy.

  The oil application roll 64 may be a drive roll. In this case, the oil application roll 64 can be prevented from slipping with respect to the transport belt 28. Further, the means for applying a liquid having a high volume resistivity such as silicone oil (hereinafter referred to as “high resistance liquid”) is not limited to the roll as in the present embodiment, and may be changed to another one such as a web. good.

The conveyor belt 28 is formed of a resin such as PET, PI, PA, or PC, or a rubber material such as CR, NBR, HNBR, or urethane rubber, and has a surface resistance value of 10 ⁸ to 10 ¹³ Ω · cm, volume resistance. The one with a rate of 10 ⁹ to 10 ¹⁴ Ω · cm is used.

The charging roll 36 has an elastic layer in which a conductivity imparting material is dispersed on the outer peripheral surface of a rod-like or pipe-like shaft made of aluminum, stainless steel or the like, and has a volume resistivity of 10 ⁴ to 10 ^8. A roll having a diameter of 10 to 25 mm adjusted to about Ω · cm can be used.

  The material of the elastic layer may be a resin material such as urethane resin, thermoplastic elastomer, epichlorohydrin rubber, ethylene-propylene-diene copolymer rubber, acrylonitrile-butadiene copolymer rubber, polynorbornene rubber or the like alone or in combination of two or more. Usable as a mixture, urethane foam resin is desirable.

  In addition, the surface of the elastic layer may be covered with a water-repellent skin layer having a thickness of 5 to 100 μm. In this case, the characteristic change (volume resistance) due to interaction with a high-resistance liquid, adhesion of ink mist, etc. Rate change).

Further, as described above, silicone oil is used as the high resistance liquid, and water-based ink is used as the ink. Here, the high resistance liquid is preferably a liquid having a volume resistivity of 10 ¹² Ω · cm or more, more preferably a liquid having a volume resistivity of 10 ¹⁴ Ω · cm or more, but at least a liquid having a higher volume resistivity than ink. Furthermore, a liquid having a volume resistivity equal to or higher than that of the conveyor belt 28 is desirable. By making the volume resistivity of the high resistance liquid higher than that of the ink, when an aqueous liquid such as water or ink is interposed between the charging roll 36 and the conveying belt 28, the charging roll 36 and the conveying belt 28 It is possible to suppress a decrease in electrical resistance at the contact portion, the contact portion between the paper P and the conveyance belt 28. As a result, the movement of electric charges at the contact portion between the charging roll 36 and the conveying belt 28 can be suppressed, so that an abnormal increase in the charging potential of the conveying belt 28 can be suppressed. Further, since the movement of electric charges at the contact portion between the paper P and the conveying belt 28 can be suppressed, the movement of electric charges due to the discharge from the charging roll 36 to the paper P can be suppressed, and an abnormal increase in the charging potential of the paper P can be suppressed. .

  Further, by making the volume resistivity of the high resistance liquid equal to or higher than the volume resistivity of the transport belt 28, the electrical resistance at the contact portion between the charging roll 36 and the transport belt 28 is always an aqueous liquid such as water or ink. Therefore, the abnormal increase in the charging potential of the transport belt 28 and the paper P can be further suppressed.

  High-resistance liquids are suitable for repelling ink. For water-based inks, in addition to silicone oil, higher fatty acids such as oleic acid and linoleic acid, dibutyl phthalate, diisodecyl phthalate, and dibutyl maleate Water-repellent liquids such as water-insoluble alcohols such as n-decanol and dimethylbutanol, fluorine oil, mineral oil, and vegetable oil can be used. These may be used singly or as long as they can be mixed uniformly, a plurality of types may be mixed and used. For oil-based ink, a liquid having high oil repellency such as water can be used.

In order to stabilize the application of the high resistance liquid to the transport belt 28, the kinematic viscosity of the high resistance liquid is desirably in the range of 10 to 10 ⁵ mm ² / s, and is preferably 50 to 10 ² mm ² / s. It is more desirable to be in the range.

  In addition, if the coating thickness of the high-resistance liquid is too thick, oil may permeate the paper P and the paper P will repel ink, causing image quality degradation when printing on the back side, etc. On the contrary, if the coating thickness of the high resistance liquid is too thin, the coating layer O cannot be stably formed. Therefore, it is necessary to set the coating thickness of the high resistance liquid within an appropriate range. An appropriate range of the coating thickness of the high resistance liquid is 1 nm to 20 μm, but 10 nm or more is desirable for stably forming the coating layer, and the adhesion of the high resistance liquid to the paper P is reduced. For this purpose, 2 μm or less is desirable.

  Further, the color of the high resistance liquid is preferably colorless and transparent in order to reduce the influence on the image quality when adhering to the paper P.

  The high resistance liquid needs to be non-volatile at room temperature. Specifically, the vapor pressure is 13.33 Pa or less at 25 ° C. Further, the high resistance liquid needs to have a property that is not compatible with an aqueous liquid such as ink. Specifically, the solubility in an aqueous liquid such as ink is 0.1 wt% or less at normal temperature (25 ° C.).

Further, the surface tension of the high resistance liquid is preferably 30 mN / m or less, and more preferably 25 mN / m or less. However, since the high resistance liquid needs to spread on the conveyor belt 28, the relationship of the following formula (1) is satisfied. is necessary. However, the surface tension of the coating layer O is γ ₀ , and the critical surface tension γ _b of the conveyor belt 28 is set. The critical surface tension is the relationship between the surface tension of various liquids and the contact angle θ of the solid surface, when cos θ is corrected to 1 (that is, when the contact angle of the liquid with respect to the solid surface becomes 0 °). Refers to the surface tension. In general, a solid surface wets well with a liquid having a surface tension smaller than the critical surface tension of the surface.

γ ₀ <γ _b (1)
Further, in order to give the high resistance liquid water repellency, the relationship of the following formula (2) is required. However, the surface tension of the ink I is γ _i .

γ ₀ <γ _i (2)
As a result, the high resistance liquid wets and spreads from the ink onto the transport belt 28. In this embodiment, the transport belt 28 has a critical surface tension γ _b of 43 [mN / m], a width × perimeter × thickness of 365 mm × 762 mm × 75 μm, a volume resistivity of 5 × 10 ¹³ Ω · cm, carbon Belt made of polyimide in which is dispersed, silicone oil having a volume resistivity of 10 ¹⁴ Ω · cm, a surface tension γ ₀ of 20.8 [mN / m], a kinematic viscosity of 100 mm ² / s, and a coating layer O Is a water-based pigment ink having a thickness of 0.05 μm, an ink volume resistivity of 10 ² Ω · cm, and a surface tension γ _i of about 30 [mN / m], a voltage applied to the charging roll 36 is DC + 1500 [V], and conveyed The distance (TD) d between the belt 28 and the nozzle surface 32N of the recording head 32 is 1.5 [mm], and the area S of the conveying belt 28 facing the nozzle surface 32N of the recording head 32 is 0.1 [m ² ]. did. Further, the distance between sheets during continuous printing is 44 mm, the printing speed is 90 sheets / minute for A4 size, the process speed is 15 inches / second, and all the nozzles of the recording head 32 of each color are 200 shots per minute. The jet was made between paper sheets. When printing was performed continuously for 30 minutes in this state, no jamming occurred.

  On the other hand, when printing was performed under the same conditions as in this embodiment without applying silicone oil to the conveyor belt 28, the charged potential of the conveyor belt 28 was twice that in this embodiment. It was.

  From the above, in the present embodiment, it is possible to increase the charge amount of the conveyor belt 28 and further reduce the TD while preventing the contact between the conveyor belt 28 and the nozzle surface 32N of the recording head 32. The landing accuracy of ink droplets on P can be further improved, and thus the image quality can be further improved.

  Further, since the force for urging the conveying belt 28 to the opposite side of the recording head 32 is not required, and the configuration described in Patent Document 3 is not required, the occurrence of discharge around the conveying belt 28 can be suppressed. , Electromagnetic interference can be suppressed. Further, since the occurrence of sparks around the conveyor belt 28 can be prevented, damage to the conveyor belt 28 can be suppressed, and shortening of the conveyor belt 28 can be suppressed.

  Next, a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the structure similar to 1st Embodiment, and description is abbreviate | omitted.

  As shown in FIG. 6, a charging roll 66 connected to a power source 38 is disposed on the upstream side of the recording head array 30. The charging roll 66 is driven while sandwiching the conveyance belt 28 and the paper P with the driven roll 26 and presses the paper P against the conveyance belt 28. At this time, since a predetermined potential difference is generated between the grounded follower roll 26, the sheet P can be electrostatically adsorbed to the transport belt 28 by applying an electric charge to the sheet P.

As shown in FIG. 7, in the charging roll 66, an elastic layer 66B in which a conductivity-imparting material is dispersed is formed on the outer peripheral surface of a rod-like or pipe-like shaft 66A made of aluminum, stainless steel or the like. A roll having a diameter of 10 to 25 mm whose rate is adjusted to about 10 ³ to 10 ¹⁰ Ω · cm can be used.

  The material of the elastic layer 66B is, for example, a resin such as polyester, polyamide, PE, PC, polyolefin, polyurethane, polyvinylidene fluoride, PI, PEN, PEK, PES, PPS, PFA, PVdF, ETFE, CTFE, or silicone rubber. Synthetic rubber such as ethylene propylene rubber (EPDM), ethylene propylene rubber, butyl rubber, acrylic rubber, urethane rubber, nitrile rubber (NBR), conductive powder such as carbon black, metal powder, metal oxide and quaternary ammonium salt What mixed ionic conductive materials, such as, can be used.

  Further, when the elastic layer 66B is formed, the elastic layer 66B is made porous in a sponge shape by a known technique such as a gas mixing method, a foaming agent decomposition method, a solvent diffusion method, a chemical reaction method, etc. Gives elasticity and moderate liquid absorption.

Further, if the volume resistivity is 10 ² Ω · cm or less, spark discharge is likely to occur, and if it is 10 ¹¹ Ω · cm or more, dot-like charging defects are likely to occur, so that 10 ³ to 10 ¹⁰ Ω · cm. Adjust to the range.

In consideration of suppression of the voltage applied from the power supply 38 to the charging roll 66 and suppression of potential fluctuation in an apparatus that performs high-speed printing with a process speed of 150 mm / s or more, the volume resistivity is 10 ⁴ to 10 ⁸ Ω · It is desirable to adjust to the range of cm.

  Here, the elastic layer 66B is impregnated with silicone oil. For this reason, when a mist-like ink generated when the recording head 32 ejects ink droplets or an aqueous liquid such as water due to condensation is interposed between the transport belt 28 and the charging roll 66, the transport belt 28. A layer of silicone oil is interposed between the upper aqueous liquid and the elastic layer 66B.

Silicone oil has a volume resistivity of, for example, 10 ¹⁶ Ω · cm or more and is a liquid having high resistance and high insulation, so the silicone oil layer functions as an insulating layer. For this reason, as in the first embodiment, even if an aqueous liquid is interposed between the charging roll 66 and the conveyance belt 28, the contact portion between the charging roll 66 and the conveyance belt 28 always has a high resistance. The movement of electric charge between the roll 66 and the conveyance belt 28 is caused by discharge in the region of a minute gap between the charging roll 66 and the conveyance belt 28.

  As a result, the surface potential on the conveyor belt 28 can be prevented from rising abnormally, thereby preventing the contact between the conveyor belt 28 and the recording head 32, while increasing the charge amount of the conveyor belt 28, TD can be made narrower. Accordingly, the ink droplet landing accuracy on the paper P can be further improved, and thus the image quality can be further improved.

  In addition, the thing similar to 1st Embodiment can be used for the conveyance belt 28. FIG. Further, as described above, silicone oil is used as the liquid impregnated in the elastic layer 66B (hereinafter referred to as high resistance liquid), and the aqueous pigment ink is used as the ink.

Here, the high resistance liquid, the ink, and the conveyance belt 28 may be the same as those in the first embodiment. In this embodiment, the transport belt 28 has a critical surface tension γ _b of 43 [mN / m], a width × perimeter × thickness of 365 mm × 762 mm × 75 μm, a volume resistivity of 5 × 10 ¹³ Ω · cm, carbon Made of PI, in which a high resistance liquid is coated with a silicone oil having a volume resistivity of 10 ¹³ Ω · cm, a surface tension γ ₀ of 20.8 [mN / m], a kinematic viscosity of 100 mm ² / s, and a coating layer O Is a water pigment ink having a thickness of 0.05 μm, an ink volume resistivity of 10 ³ Ω · cm, and a surface tension γ _i of about 30 [mN / m], a voltage applied to the charging roll 36 is DC + 1500 [V], and conveyed The distance (TD) d between the belt 28 and the nozzle surface 32N of the recording head 32 is 1.5 [mm], and the area S of the conveying belt 28 facing the nozzle surface 32N of the recording head 32 is 0.1 [m ² ]. did. Further, the distance between sheets during continuous printing is 44 mm, the printing speed is 90 sheets / minute for A4 size, the process speed is 15 inches / second, and all the nozzles of the recording head 32 of each color are 200 shots per minute. The jet was made between paper sheets. When printing was continuously performed for 30 minutes in this state, no jamming occurred.

  On the other hand, when a charging roll not impregnated with silicone oil was used and printing was performed under the same conditions as in the present embodiment, the charging potential of the conveyor belt 28 was double that of the present embodiment.

  From the above, it is possible to increase the charge amount of the conveyance belt 28 and narrow the TD while preventing contact between the conveyance belt 28 and the nozzle surface 32N of the recording head 32. The landing accuracy can be further improved, so that the image quality can be further improved.

  Next, a third embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the structure similar to 1st, 2nd embodiment, and description is abbreviate | omitted.

  As shown in FIG. 8, a charging roll 68 to which a power source 38 is connected is disposed on the upstream side of the recording head array 30. The charging roll 68 is driven while sandwiching the conveyance belt 28 and the paper P between the charging roll 68 and presses the paper P against the conveyance belt 28. At this time, since a predetermined potential difference is generated between the grounded follower roll 26, the sheet P can be electrostatically adsorbed to the transport belt 28 by applying an electric charge to the sheet P.

As shown in FIG. 9A, in the charging roll 68, an elastic layer 68B in which a conductivity imparting material is dispersed is formed on the outer peripheral surface of a rod-like or pipe-like shaft 68A made of aluminum, stainless steel or the like. A roll having a diameter of 10 to 25 mm and a volume resistivity adjusted to about 10 ³ to 10 ¹⁰ Ω · cm can be used.

  Here, the elastic layer 68B is not made porous, and the elastic layer 68C is solid and difficult to impregnate with liquid. For this reason, as shown in FIG. 8, an insulating layer is interposed between the charging roll 68 and the conveyor belt 28 by supplying silicone oil to the surface of the charging roll 68 by the oil supply unit 70.

  The oil supply unit 70 includes a case 72 that contains silicone oil, a first roll 74 and a second roll 76 that are rotatably supported by the case 72, a suction member 78 that is supported by the case 72, and a regulating blade 80. And. The first roll 74 and the second roll 76 are arranged in parallel with the charging roll 68, the second roll 76 is in contact with the surface of the charging roll 68, and the first roll 74 and the second roll 76 are in contact with each other.

  Further, the suction member 78 is a highly absorbent member such as a felt material extending from the bottom of the case 72 to above the first roll 76, and the lower end is immersed in the silicone oil in the case 72, The upper end is refracted in a bowl shape and is directed to the upper surface of the first roll 74. Further, the suction member 78 extends from one axial end side of the first roll 74 to the other end side. For this reason, the silicone oil in the case 72 is sucked up by the sucking member 78 and dropped over the entire area in the axial direction on the upper surface of the first roll 74.

  The regulating blade 80 is a plate material that extends along the axial direction of the first roll 74, and is in contact with the entire area of the first roll 74 in the axial direction. Here, the regulating blade 80 is downstream in the rotational direction of the first roll 74 relative to the position where the silicone oil drips from the suction member 78 and upstream in the rotational direction of the first roll 74 relative to the contact portion with the second roll 76. It is arranged on the side. For this reason, the silicone oil dripped onto the first roll 74 from the suction member 78 is stretched by the regulating blade 80, and the silicone oil on the first roll 74 has a predetermined thickness.

  Then, the silicone oil having a predetermined thickness is transferred from the first roll 74 to the second roll 76 and transferred from the second roll 76 to the charging roll 68, whereby a predetermined thickness of silicone is transferred onto the charging roll 68. An oil layer is formed.

  In addition, the structure which supplies high resistance liquid, such as a silicone oil, to the charging roll 68 is not limited to a structure like this embodiment, As shown to FIG. 10 (A), the roll 82 which impregnates high resistance liquid. 10 may be in contact with the charging roll 68, or as shown in FIG. 10B, a structure in which a web 84 impregnated with a high resistance liquid is in contact with the charging roll may be used.

  In this embodiment, the elastic layer 68B of the charging roll 68 is solid, but as shown in FIG. 9B, the elastic layer 68B having the skin layer 68C on the surface is also solid solid layer 68B. Since the liquid cannot be impregnated and exuded from the surface, the configuration of this embodiment in which the high resistance liquid is applied to the surface of the elastic layer 68B is suitable.

  The layer thickness of the silicone oil transferred from the charging roll 68 to the conveying belt 28 is adjusted by changing the material, contact pressure, etc. of the charging roll 68, the first roll 74, the second roll 76, and the regulating blade 80. 1 nm to 20 μm is desirable, and 10 nm to 2 μm is more desirable. If the silicone oil layer on the transport belt 28 becomes too thick, the amount of adhesion to the paper P increases, and the fixing of ink droplets to the paper P is poor, and sticky notes cannot be attached to the paper P after printing. Various problems occur. On the other hand, if the silicone oil layer on the conveyor belt 28 becomes too thin, the effect of preventing abnormal charging cannot be exhibited.

  Here, in the present embodiment, charging is performed with the paper P sandwiched between the charging roll 68 and the conveyance belt 28, and therefore, silicone oil is applied from the charging roll 68 to the paper P. Although depending on the type of paper P, generally, the amount of silicone oil applied from the charging roll 68 to the paper P is greater than the amount of silicone oil applied from the charging roll 68 to the conveyor belt 28. It is desirable to adjust the upper limit of the layer thickness of the silicone oil transferred from the charging roll 68 to the conveyance belt 28 to 1/2 of the above 20 μm and 2 μm.

  Next, a fourth embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the structure similar to 1st thru | or 3rd embodiment, and description is abbreviate | omitted.

  As shown in FIG. 11, the charging roll 66 to which the AC power supply 86 is connected is in contact with the portion of the conveyance belt 28 wound around the driven roll 26 below the conveyance path of the paper P. A sine wave having an AC of ± 2000 V and a frequency of 50 Hz is applied to the charging roll 66 from a power source 86, and an electric field alternating between positive and negative with a period of 7.62 mm is formed on the conveyor belt. The paper P is transported onto the transport belt 28 on which the alternating electric field is formed, and the paper P is electrostatically attracted to the transport belt 28 by the alternating electric field.

  When printing was performed continuously for 30 minutes under the same conditions as in the second embodiment, such as the high resistance liquid, the ink, the function of the apparatus, and the conveyance belt 28, no jamming occurred. On the other hand, when a charging roll not impregnated with silicone oil was used and printing was performed in the same manner as in this embodiment, the positive and negative peak values of the charging potential of the conveying belt 28 were twice that in this embodiment. It became.

  From the above, it is possible to increase the charge amount of the conveyance belt 28 and narrow the TD while preventing contact between the conveyance belt 28 and the nozzle surface 32N of the recording head 32. The landing accuracy can be further improved, so that the image quality can be further improved.

  Next, a fifth embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the structure similar to 1st thru | or 4th embodiment, and description is abbreviate | omitted.

  As shown in FIG. 12, the charging roll 66 to which the power supply 38 is connected is in contact with the portion wound around the driven roll 26 of the transport belt 28 on the lower side of the transport path of the paper P. A voltage of DC + 1500 V is applied to the charging roll 66 from a power source 86.

  A grounded pressing roll 88 is disposed on the upstream side of the recording head array 30. The pressing roll 88 is driven while sandwiching the conveyance belt 28 and the paper P between the driven roll 26 and presses the paper P against the conveyance belt 28. At this time, the sheet P is electrostatically attracted to the conveyance belt 28 by applying a charge having a polarity opposite to the charge on the surface of the conveyance belt 28 to the surface of the sheet P.

  When printing was performed continuously for 30 minutes under the same conditions as in the second embodiment, such as the high resistance liquid, the ink, the function of the apparatus, and the conveyance belt 28, no jamming occurred. On the other hand, when a charging roll not impregnated with silicone oil was used and printing was performed under the same conditions as in the present embodiment, the charging potential of the conveyor belt 28 was double that of the present embodiment.

  From the above, it is possible to increase the charge amount of the conveyance belt 28 and narrow the TD while preventing contact between the conveyance belt 28 and the nozzle surface 32N of the recording head 32. The landing accuracy can be further improved, so that the image quality can be further improved.

  In the first to fifth embodiments, the present invention has been described by taking the inkjet recording apparatus as an example. However, the present invention is not limited to the inkjet recording apparatus, and the display is performed by discharging colored ink onto a polymer film. The present invention can be applied to a general liquid droplet ejection apparatus for various industrial uses such as production of a color filter for liquid crystal and formation of an EL display panel by discharging an organic EL solution onto a substrate.

  In addition, the “recording medium” that is a target of image recording in the droplet discharge device of the present invention includes a wide range of objects as long as the droplet discharge head discharges droplets. Accordingly, the recording medium includes recording paper, an OHP sheet, and the like, but also includes, for example, a polymer film.

  Furthermore, in the first to fifth embodiments, the present invention has been described by taking as an example a configuration in which a plurality of inkjet recording heads shorter than the width of the paper P are arranged in the width direction of the paper P as a unit. For example, the present invention can be applied to a configuration in which an inkjet recording head having a length shorter than the width of the paper P is moved in the width direction of the paper P.

1 is a side view illustrating an outline of an ink jet recording apparatus according to a first embodiment of the present invention. 1 is a side view illustrating an outline of an ink jet recording apparatus according to a first embodiment of the present invention. It is a side view which shows the outline of the printing part of the inkjet recording device of 1st Embodiment of this invention. FIGS. 2A and 2B are cross-sectional views illustrating an enlargement of a charging roll and a conveyance belt provided in the ink jet recording apparatus according to the first embodiment of the present invention. FIG. 3 is a perspective view illustrating a first example of a charging roll unit provided in the ink jet recording apparatus according to the first embodiment of the present invention. It is a side view which shows the outline of the printing part of the inkjet recording device of 2nd Embodiment of this invention. It is sectional drawing which expands and shows the charging roll and conveyance belt with which the inkjet recording device of 2nd Embodiment of this invention was equipped. It is a side view which shows the outline of the printing part of the inkjet recording device of 3rd Embodiment of this invention. (A) and (B) are enlarged sectional views showing a charging roll and a conveying belt provided in the ink jet recording apparatus according to the second embodiment of the present invention. (A), (B) is sectional drawing which shows the modification of the oil application unit with which the inkjet recording device of 2nd Embodiment of this invention was equipped. It is a side view which shows the outline of the printing part of the inkjet recording device of 4th Embodiment of this invention. It is a side view which shows the outline of the printing part of the inkjet recording device of 5th Embodiment of this invention. It is a side view which shows typically the recording head and the conveyance belt in the conventional inkjet recording device. It is a side view which shows typically the mode of the discharge between the charging roll and conveyance belt in the conventional inkjet recording device. It is a graph which shows the relationship between the voltage applied to the charging roll in the conventional inkjet recording device, and the surface potential on a conveyance belt.

Explanation of symbols

12 Inkjet recording device (droplet ejection device)
28 Conveying belt (conveying member)
32 Inkjet recording head (droplet ejection head)
36 Charging roll (charging means)
48 Belt cleaning unit (cleaning means)
64 Oil application roll (application means)
66 Charging roll (charging means)
68 Charging roll (charging means)
70 Oil supply unit (supply means)
82 rolls (supply means)
84 Web (supply means)
P paper (recording medium)

Claims (13)

A droplet discharge head for discharging droplets;
A conveying member that holds the recording medium and conveys the recording medium to face the droplet discharge head;
A droplet discharge device comprising: a charging unit that charges at least one of the transport member and a recording medium on the transport member to electrostatically attract the recording medium to the transport member;
A droplet discharge apparatus characterized in that a high-resistance liquid having a volume resistivity higher than that of the liquid discharged from the droplet discharge head is interposed between the charging unit and the transport member.   The liquid droplet ejection apparatus according to claim 1, further comprising an application unit that applies the high-resistance liquid to the transport member.   The droplet discharge device according to claim 2, further comprising a cleaning unit that cleans the transport member. The conveying member is a rotating body that holds and rotates a recording medium;
4. The droplet discharge device according to claim 3, wherein the application unit is disposed upstream of the charging unit in the rotation direction of the transport member and downstream of the cleaning unit in the rotation direction of the transport member. .   2. The droplet discharge device according to claim 1, wherein the charging unit is a charging roll that contacts the transport member to charge the recording medium and applies the high-resistance liquid to the transport member.   The droplet discharge device according to claim 5, wherein the charging roll is formed of a member capable of absorbing a liquid and impregnated with the high resistance liquid.   The liquid droplet ejection apparatus according to claim 5, further comprising a supply unit configured to supply the high resistance liquid to a surface of the charging roll.   8. The liquid droplet ejection apparatus according to claim 1, wherein a volume resistivity of the high-resistance liquid is equal to or greater than a volume resistivity of the transport member.   The liquid droplet ejection apparatus according to claim 1, wherein the high resistance liquid is insoluble in a liquid ejected from the liquid droplet ejection head.   10. The liquid droplet ejection apparatus according to claim 1, wherein the high resistance liquid has a property of repelling the liquid ejected from the liquid droplet ejection head. The surface tension γ ₀ of the high resistance liquid, the critical surface tension γ _{b of} the conveying member, and the surface tension γ _{i of the} liquid discharged from the droplet discharge head satisfy the following expressions (1) and (2). The liquid droplet ejection apparatus according to claim 1, wherein the liquid droplet ejection apparatus is a liquid crystal display apparatus.
γ ₀ <γ _b (1)
γ ₀ <γ _i (2)   12. The liquid droplet according to claim 1, wherein the liquid ejected from the liquid droplet ejection head is a water-based ink, and the high resistance liquid is a liquid having a property of repelling the water-based ink. Discharge device.   The liquid droplet ejection apparatus according to claim 1, wherein the transport member is an endless belt.

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