JP2012101365A - Inkjet head, inkjet recording apparatus, and method for cleaning nozzle plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet head that can continuously and stably discharge ink.SOLUTION: The inkjet head includes: a nozzle plate having a nozzle hole for discharging liquid; and a pressure generating element provided with a pressure chamber connected to the nozzle hole via a flow channel, and a drive element for applying pressure to the liquid in the pressure chamber. The nozzle plate has a discharge surface from which liquid is discharged. The discharge surface has a concavo-convex structure 30. The concavo-convex structure 30 includes: a convex portion 31 whose tip end has water repellency; and a concave portion 32 whose side and bottom are hydrophilic, wherein the length of the concave portion in the wiping direction is 100 μm or less.

Description

  The present invention relates to an ink jet head, an ink jet recording apparatus, and a nozzle plate cleaning method, and more particularly to an ink jet head, an ink jet recording apparatus, and a nozzle plate cleaning method that impart water repellency to an ink ejection surface.

  In an ink jet head used in an ink jet recording apparatus, if ink adheres to the surface of a nozzle plate, ink ejected from the nozzle may be affected, resulting in variations in the ink ejection direction. For this reason, it becomes difficult to land the ink at a predetermined position on the recording medium, which causes deterioration in image quality. Therefore, various methods for imparting water repellency to the nozzle plate surface have been proposed in order to prevent ink from adhering to the nozzle plate surface.

  For example, in Patent Document 1 below, a central water-repellent region surrounding a region having a plurality of discharge ports, and a groove-shaped hydrophilic region provided along the arrangement direction of the plurality of discharge ports, a predetermined distance away from the discharge ports An ink jet head comprising: Japanese Patent Application Laid-Open No. 2004-228561 describes a liquid ejecting head in which a high water repellent area is provided around a nozzle opening and a low water repellent area is provided around the high water repellent area.

JP-A-6-210859 JP 2007-245549 A

  However, since the ink jet head described in Patent Document 1 has a groove-like hydrophilic region having a width of 100 μm or more, ink collected and solidified in the groove is pulled out from the groove when wiping is performed, and the water-repellent surface is scratched. There was a problem that it was easy to stick. Further, if wiping is strengthened in order to completely remove the ink accumulated in the hydrophilic area, the water repellency in the water-repellent area surrounding the ejection port is impaired, which causes wetness around the ejection port. Also in Patent Document 2, when the ink adhering to the low water-repellent area is left to solidify, the high water-repellent area is easily damaged when wiping is performed, and ejection failure is likely to occur. It was.

  SUMMARY An advantage of some aspects of the invention is that it prevents the water-repellent film from being deteriorated by the solidified ink and improves the ejection stability.

  According to a first aspect of the present invention, in order to achieve the above object, a nozzle plate having a nozzle hole for discharging a liquid, a pressure chamber connected to the nozzle hole via a flow path, and a pressure applied to the liquid in the pressure chamber. A pressure generating element to be applied, and a discharge surface side of the nozzle plate for discharging the liquid has a concavo-convex structure, and a front end side of the convex portion of the concavo-convex structure has water repellency. The side surface and the bottom surface of the recess have hydrophilicity, and the length of the recess in the wiping direction is 100 μm or less.

  According to the first aspect, an uneven structure is provided on the discharge surface side of the nozzle plate, the protrusions of the uneven structure are water repellent and the recesses are hydrophilic. Therefore, the ink adhering to the surface of the nozzle plate is drawn into the concave portion, which is a hydrophilic region, and dried, so that the solidified ink does not adhere to the convex portion (surface of the nozzle plate). Therefore, even if wiping is performed, the solidified ink is not dragged, so that the periphery of the nozzle hole is not damaged. In addition, since the size of the concave portion is as fine as 100 μm or less in the wiping direction, the ink solidified material formed in the concave portion is not swept out, so that the periphery of the nozzle hole can be prevented from being damaged and discharged. Stability can be maintained.

  A second aspect is characterized in that, in the first aspect, a water-repellent film is formed on a tip end side of the convex portion.

  According to the second aspect, the water repellency can be imparted to the front end side of the convex portion by forming the water repellent film on the front end side of the convex portion.

  A third aspect of the present invention is characterized in that in the first or second aspect, the length of the convex portion in the wiping direction is 1/2 or more of the depth of the concave portion.

  According to the third aspect, since the length of the convex portion in the wiping direction is set to ½ or more of the depth of the concave portion, it is possible to prevent the convex portion from being destroyed by wiping.

  A fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the length of the concave portion in the wiping direction is ½ or more of the depth of the concave portion.

  According to the fourth aspect of the present invention, the length of the concave portion in the wiping direction is ½ or more of the depth of the concave portion, so that the ink after being dissolved with the cleaning liquid can be removed during wiping.

  A fifth aspect is characterized in that, in the first or second aspect, the concavo-convex structure is arranged in a staggered manner.

  According to claim 5, since the concavo-convex structure is arranged in a staggered manner, the water-repellent part and the hydrophilic part of the concavo-convex structure are alternately arranged, and the ink adhering to the surface of the nozzle plate is efficiently removed from the hydrophilic part. Can be drawn into the recess.

  A sixth aspect of the present invention is characterized in that, in the fifth aspect, one side of the concave portion of the concavo-convex structure arranged in a staggered pattern is 100 μm or less.

  According to the sixth aspect, since the length of one side of the recess is made as fine as 100 μm or less, the solidified ink formed in the recess is not swept out, so that the periphery of the nozzle hole can be prevented from being damaged. , Discharge stability can be maintained.

  According to a seventh aspect of the present invention, in any one of the second to sixth aspects, the substrate on which the nozzle plate is formed is made of a silicon-based material, and the water-repellent film is made of fluoroalkylsilane.

  According to the seventh aspect, by using a silicon-based material for the substrate on which the nozzle plate is formed and using fluoroalkylsilane for the water repellent film, a water repellent film strongly bonded to the base material can be formed.

  An eighth aspect of the present invention is the method according to any one of the first to seventh aspects, wherein a flat water-repellent region is provided around the discharge surface side of the nozzle hole, and the uneven structure is provided around the flat water-repellent region. It is characterized by.

  According to the eighth aspect, the flat water-repellent region is a region having higher water repellency than the region having the concavo-convex structure because the entire surface has water repellency than the water-repellent region having the concavo-convex structure. Therefore, it is possible to make ink adhere to the water-repellent region having the uneven structure around the nozzle hole on the surface of the nozzle plate. Therefore, ink can be prevented from adhering to the periphery of the nozzle, and nozzle clogging can be prevented.

  According to a ninth aspect of the present invention, there is provided an ink jet recording apparatus comprising the ink jet head according to any one of the first to eighth aspects, in order to achieve the object.

  The ink jet head of the present invention can be suitably used for an ink jet recording apparatus.

  According to a tenth aspect of the present invention, in order to achieve the above object, a cleaning liquid for dissolving the ink is applied to the nozzle plate surface of the ink jet head according to any one of the first to eighth aspects and adhered thereto. Provided is a method for cleaning a nozzle plate, characterized in that wiping is performed after dissolving a solidified product.

  According to the tenth aspect, the ink jet head according to any one of the first to eighth aspects cannot sweep the ink solidified material formed in the concave portion of the concavo-convex structure, but the cleaning liquid is applied to the ink solidified material. By dissolving, the solidified ink formed in the concave portion can be removed.

  According to the inkjet head, the inkjet recording apparatus, and the nozzle plate cleaning method of the present invention, the surface of the nozzle plate has a fine concavo-convex structure, and the ink is drawn into the concave portion, so that the water-repellent region is formed by the solidified ink. Can be prevented from being damaged. Accordingly, it is possible to maintain ink ejection stability.

1 is an overall configuration diagram showing an outline of an inkjet recording apparatus. It is a plane perspective view which shows the structural example of an inkjet head. It is sectional drawing which follows the IV-IV line in FIG. It is a figure explaining the manufacturing method of an inkjet head. It is a figure explaining the manufacturing method of an inkjet head. It is a figure explaining an uneven structure. It is a figure explaining other embodiment of the nozzle plate surface.

  Hereinafter, preferred embodiments of an inkjet, an inkjet recording apparatus, and a nozzle plate cleaning method according to the present invention will be described with reference to the accompanying drawings.

<Overall configuration of inkjet recording apparatus>
FIG. 1 is a configuration diagram of an inkjet recording apparatus including an inkjet head. In the inkjet recording apparatus 100, a recording medium 124 (sometimes referred to as “paper” for convenience) held on the impression cylinder (drawing drum 170) of the drawing unit 116 is provided with a plurality of colors from the inkjet heads 172M, 172K, 172C, 172Y. Is an impression cylinder direct drawing type ink jet recording apparatus that forms a desired color image by applying ink droplets of the ink. A treatment liquid (in this case, an aggregating treatment liquid) is applied onto the recording medium 124 before ink ejection. This is an on-demand type image forming apparatus to which a two-liquid reaction (aggregation) method for forming an image on a recording medium 124 by reacting a processing liquid and an ink liquid is applied.

  As shown in the figure, the ink jet recording apparatus 100 mainly includes a paper feeding unit 112, a treatment liquid application unit 114, a drawing unit 116, a drying unit 118, a fixing unit 120, and a discharge unit 122.

(Paper Feeder)
The paper feeding unit 112 is a mechanism that supplies the recording medium 124 to the processing liquid application unit 114, and the recording medium 124 that is a sheet is stacked on the paper feeding unit 112. The paper feed unit 112 is provided with a paper feed tray 150, and the recording medium 124 is fed from the paper feed tray 150 to the processing liquid application unit 114 one by one.

(Processing liquid application part)
The processing liquid application unit 114 is a mechanism that applies the processing liquid to the recording surface of the recording medium 124. The treatment liquid contains a color material aggregating agent that agglomerates the color material (pigment in this example) in the ink applied by the drawing unit 116, and the ink comes into contact with the treatment liquid and the ink. And the solvent are promoted.

  As shown in FIG. 1, the treatment liquid application unit 114 includes a paper feed drum 152, a treatment liquid drum 154, and a treatment liquid application device 156. The treatment liquid drum 154 is a drum that holds and rotates the recording medium 124. The processing liquid drum 154 includes a claw-shaped holding means (gripper) 155 on the outer peripheral surface thereof, and the recording medium 124 is sandwiched between the claw of the holding means 155 and the peripheral surface of the processing liquid drum 154. The tip can be held.

  A processing liquid coating device 156 is provided outside the processing liquid drum 154 so as to face the peripheral surface thereof. The processing liquid coating device 156 includes a processing liquid container in which the processing liquid is stored, an anix roller partially immersed in the processing liquid in the processing liquid container, and the recording medium 124 on the anix roller and the processing liquid drum 154. And a rubber roller that transfers the measured processing liquid to the recording medium 124. According to the processing liquid coating apparatus 156, the processing liquid can be applied to the recording medium 124 while being measured.

  The recording medium 124 to which the processing liquid is applied by the processing liquid applying unit 114 is transferred from the processing liquid drum 154 to the drawing drum 170 of the drawing unit 116 via the intermediate transport unit 126.

(Drawing part)
The drawing unit 116 includes a drawing drum (second transport body) 170, a sheet pressing roller 174, and ink jet heads 172M, 172K, 172C, and 172Y. Similar to the treatment liquid drum 154, the drawing drum 170 includes a claw-shaped holding means (gripper) 171 on the outer peripheral surface thereof. The recording medium 124 fixed to the drawing drum 170 is conveyed with the recording surface facing outward, and ink is applied to the recording surface from the inkjet heads 172M, 172K, 172C, 172Y.

  The inkjet heads 172M, 172K, 172C, and 172Y are preferably full-line inkjet recording heads (inkjet heads) each having a length corresponding to the maximum width of the image forming area on the recording medium 124. On the ink ejection surface, a nozzle row in which a plurality of nozzles for ink ejection are arranged over the entire width of the image forming area is formed. Each inkjet head 172M, 172K, 172C, 172Y is installed so as to extend in a direction orthogonal to the conveyance direction of the recording medium 124 (the rotation direction of the drawing drum 170).

  The droplets of the corresponding color ink are ejected from the inkjet heads 172M, 172K, 172C, and 172Y toward the recording surface of the recording medium 124 held in close contact with the drawing drum 170, whereby the processing liquid application unit 114 performs the processing. The ink comes into contact with the treatment liquid previously applied to the recording surface, and the color material (pigment) dispersed in the ink is aggregated to form a color material aggregate. Thereby, the color material flow on the recording medium 124 is prevented, and an image is formed on the recording surface of the recording medium 124.

  The recording medium 124 on which an image is formed by the drawing unit 116 is transferred from the drawing drum 170 to the drying drum 176 of the drying unit 118 via the intermediate conveyance unit 128.

(Drying part)
The drying unit 118 is a mechanism for drying moisture contained in the solvent separated by the color material aggregating action, and includes a drying drum 176 and a solvent drying device 178, as shown in FIG.

  Similar to the processing liquid drum 154, the drying drum 176 includes a claw-shaped holding unit (gripper) 177 on the outer peripheral surface thereof, and the holding unit 177 can hold the leading end of the recording medium 124.

  The solvent drying device 178 is disposed at a position facing the outer peripheral surface of the drying drum 176, and includes a plurality of halogen heaters 180 and hot air ejection nozzles 182 disposed between the halogen heaters 180.

  The recording medium 124 that has been dried by the drying unit 118 is transferred from the drying drum 176 to the fixing drum 184 of the fixing unit 120 via the intermediate conveyance unit 130.

(Fixing part)
The fixing unit 120 includes a fixing drum 184, a halogen heater 186, a fixing roller 188, and an inline sensor 190. Like the processing liquid drum 154, the fixing drum 184 includes a claw-shaped holding unit (gripper) 185 on the outer peripheral surface, and the leading end of the recording medium 124 can be held by the holding unit 185.

  With the rotation of the fixing drum 184, the recording medium 124 is conveyed with the recording surface facing outward. The recording surface is preheated by the halogen heater 186, fixing processing by the fixing roller 188, and by the inline sensor 190. Inspection is performed.

  According to the fixing unit 120, the thermoplastic resin fine particles in the thin image layer formed by the drying unit 118 are heated and pressurized by the fixing roller 188 and are melted, and can be fixed and fixed to the recording medium 124. . Further, by setting the surface temperature of the fixing drum 184 to 50 ° C. or higher, drying is promoted by heating the recording medium 124 held on the outer peripheral surface of the fixing drum 184 from the back surface, thereby preventing image destruction during fixing. In addition, the image intensity can be increased by the effect of increasing the image temperature.

  In addition, when a UV curable monomer is contained in the ink, after the water is sufficiently volatilized in the drying unit, the image is irradiated with UV at the fixing unit equipped with a UV irradiation lamp. The monomer can be cured and polymerized to improve the image strength.

(Discharge part)
As shown in FIG. 1, a discharge unit 122 is provided following the fixing unit 120. The discharge unit 122 includes a discharge tray 192, and a transfer drum 194, a conveyance belt 196, and a stretching roller 198 are provided between the discharge tray 192 and the fixing drum 184 of the fixing unit 120 so as to be in contact therewith. It has been. The recording medium 124 is sent to the conveyor belt 196 by the transfer drum 194 and discharged to the discharge tray 192.

  Although not shown in the drawing, the ink jet recording apparatus 100 of the present example has an ink storage / loading unit for supplying ink to each of the ink jet heads 172M, 172K, 172C, and 172Y in addition to the above-described configuration, and application of processing liquid. A means for supplying a processing liquid to the unit 114, and a head maintenance unit for cleaning each ink jet head 172M, 172K, 172C, 172Y (wiping, purging, nozzle suction, etc. of the nozzle surface), A position detection sensor for detecting the position of the recording medium 124, a temperature sensor for detecting the temperature of each part of the apparatus, and the like are provided.

  Although the drum conveyance type inkjet recording apparatus has been described with reference to FIG. 1, the present invention is not limited to this, and the invention can also be used in a belt conveyance type inkjet recording apparatus.

[Inkjet head structure]
Next, the structure of the inkjet heads 172M, 172K, 172C, 172Y will be described. In addition, since the structure of each inkjet head 172M, 172K, 172C, 172Y is common, hereinafter, the head is represented by reference numeral 250 as a representative of these.

  FIG. 2A is a plan perspective view showing a structural example of the inkjet head 250, and FIG. 2B is a plan perspective view showing another structural example of the inkjet head 250. FIG. 3 is a cross-sectional view (a cross-sectional view taken along line IV-IV in FIG. 2A) showing a three-dimensional configuration of the ink chamber unit.

  In order to increase the dot pitch formed on the recording paper surface, it is necessary to increase the nozzle pitch in the inkjet head 250. As shown in FIG. 2A, the ink jet head 250 of this example includes a plurality of ink chamber units 253 including nozzles 251 that are ink droplet ejection holes and pressure chambers 252 corresponding to the nozzles 251. It has a structure that is arranged in a matrix (two-dimensionally), and as a result, a substantial nozzle interval (projection) projected so as to be aligned along the head longitudinal direction (main scanning direction orthogonal to the paper transport direction). Nozzle pitch) is increased.

  The configuration in which one or more nozzle rows are configured over a length corresponding to the entire width of the recording medium 124 in a direction substantially orthogonal to the paper conveyance direction is not limited to this example. For example, instead of the configuration of FIG. 2A, as shown in FIG. 2B, short head blocks (head chips) 250 ′ in which a plurality of nozzles 251 are two-dimensionally arranged are arranged in a staggered manner. By connecting them together, a line head having a nozzle row having a length corresponding to the entire width of the recording medium 124 may be configured. Although not shown, a line head may be configured by arranging short heads in a line.

As shown in FIG. 3, each nozzle 251 is formed on a nozzle plate 260 that constitutes the ink ejection surface 250 a of the inkjet head 250. The nozzle plate 260 is made of, for example, a silicon-based material such as Si, SiO ₂ , SiN, or quartz glass, a metal-based material such as Al, Fe, Ni, Cu, or an alloy containing these, or an oxide such as alumina or iron oxide. It is composed of physical materials, carbon black, carbon-based materials such as graphite, and resin-based materials such as polyimide.

  A water repellent film 262 having liquid repellency with respect to ink is formed on the surface of the nozzle plate 260 (the surface on the ink discharge side) to prevent ink adhesion.

  The pressure chamber 252 provided corresponding to each nozzle 251 has a substantially square planar shape, and the nozzle 251 and the supply port 254 are provided at both corners on the diagonal line. Each pressure chamber 252 is in communication with a common channel 255 through a supply port 254. The common channel 255 communicates with an ink supply tank (not shown) as an ink supply source, and the ink supplied from the ink supply tank is distributed and supplied to each pressure chamber 252 through the common channel 255.

  A piezoelectric element 258 having an individual electrode 257 is joined to a diaphragm 256 that constitutes the top surface of the pressure chamber 252 and also serves as a common electrode. By applying a driving voltage to the individual electrode 257, the piezoelectric element 258 is formed. Deformation causes ink to be ejected from the nozzle 251. When ink is ejected, new ink is supplied from the common flow channel 255 to the pressure chamber 252 through the supply port 254.

  The nozzle arrangement structure is not limited to the illustrated example, and various nozzle arrangement structures such as an arrangement structure having one nozzle row in the sub-scanning direction can be applied.

  Further, the printing method is not limited to a line type head, and printing in the width direction is performed by scanning a short head less than the length of the recording medium 124 in the width direction (main scanning direction) in the width direction of the recording medium 124. When the printing in the width direction is completed once, the recording medium 124 is moved by a predetermined amount in the direction orthogonal to the width direction (sub-scanning direction), and printing in the width direction of the recording medium 124 in the next printing area is performed. A serial method in which printing is performed over the entire printing area of the recording medium 124 by repeating this operation may be applied.

<Manufacturing method of nozzle plate>
4 and 5 are views for explaining a method of manufacturing an ink jet head according to the present invention.

  The structuring of the base material (nozzle plate substrate) 10 will be described with reference to FIG. First, as shown in FIG. 4A, a mask material 20 is formed by photolithography on a portion that becomes a convex portion of the concavo-convex structure on the substrate 10. As the mask material, Al, resist or the like can be used.

  Next, as shown in FIG. 4B, an uneven structure 30 is formed on the substrate 10 by etching. The uneven structure 30 is formed by, for example, using a dry etching apparatus to form a highly vertical uneven structure 30 by alternately performing a plasma synthesis film formation on the side surface and a plasma etching process, which is called a so-called Bosch process. Obtainable. The etching conditions can be appropriately set depending on the size of the uneven structure to be formed. Further, the etching method is not limited to this method, and other methods can be used. However, in the case of isotropic etching with low verticality, the ink solidified material in the recesses is easily swept out by wiping. Therefore, it is preferable to form the concavo-convex structure 30 so that the verticality is high.

  Thereafter, as shown in FIG. 4C, the base material 10 is formed with the concavo-convex structure 30 by removing the mask material 20 with an etching solution.

  Next, a method of forming a water repellent film on the upper surface of the convex portion 31 of the concavo-convex structure 30 will be described with reference to FIG. As shown in FIG. 5D, a resist material 40 is applied on the entire surface by spin coating so that the concave portion 32 of the substrate 10 is filled, and baking is performed. Thereafter, as shown in FIG. 5E, ashing is performed on the entire surface by reactive ion etching (RIE) while controlling so that the resist material 40 formed on the upper surface of the convex portion 31 is just removed. It may be slightly over-etched so that the residue of the resist material 40 does not remain on the convex portion 31.

  Next, an ink jet head is manufactured by bonding the flow path structure manufactured in another process to the side of the substrate 10 where the uneven structure 30 is not formed. In the figure, the flow path structure will be omitted.

  In the flow path structure, flow paths (including a pressure chamber, a nozzle communication path, a common flow path, and the like) connected to the nozzle holes are formed. Further, the diaphragm and the piezoelectric film are joined, and an electrode layer corresponding to a common electrode is formed on the boundary surface between the diaphragm and the piezoelectric film, and each nozzle is formed on the upper surface of the piezoelectric film layer. Individual electrodes corresponding to the upper electrodes of the corresponding piezoelectric elements are patterned.

  Next, as shown in FIG. 5F, a water repellent film 50 is formed on the convex portion 31 and the resist material 40. The material of the water repellent film 50 is preferably selected from materials that are easily bonded to the substrate 10. For example, when silicon is used for the substrate, fluoroalkylsilane that can bond to a natural oxide film on the silicon surface is used. It is preferable.

  As a method of forming a water repellent film, a method of depositing fluoroalkylsilane by a vacuum deposition method, a method of plasma-polymerizing a low-molecular siloxane to form a fluorine-containing plasma polymerized film, a silicon-based plasma polymerized liquid repellent film, A method of applying a silane coupling agent having a fluorocarbon chain can be used.

The silane coupling agent is a silicon compound represented by Y _n SiX _4-n (n = 1, 2, 3). Y includes a relatively inactive group such as an alkyl group or a reactive group such as a vinyl group, an amino group, or an epoxy group. X is a group that can be bonded by condensation with a hydroxyl group on the substrate surface such as halogen, methoxy group, ethoxy group, or acetoxy group, or adsorbed water. Silane coupling agents are widely used as mediators of these bonds in the production of organic and inorganic composite materials such as glass fiber reinforced plastics, and Y is an inert group such as an alkyl group. In some cases, properties such as adhesion and friction prevention, gloss retention, water repellency, and lubrication are imparted on the modified surface. Moreover, when a reactive group is included, it is mainly used for the improvement of adhesiveness. Furthermore, the surface modified by using a fluorine-based silane coupling agent in which a linear fluorocarbon chain is introduced into Y has a low surface free energy like a PTFE (polytetrafluoroethylene) surface, and is water repellent. In addition, properties such as lubrication and mold release are improved, and oil repellency is also exhibited.

  As a method of forming a water-repellent film using a fluorine-based silane coupling agent (chlorine type, methoxy type, ethoxy type, isocyanato type, etc.), for example, physical vapor deposition (evaporation method, sputtering method, etc.) Further, it can be formed by a dry process method such as chemical vapor deposition (CVD method, ALD method or the like), a wet process method such as sol-gel method or coating method.

  Thereafter, as shown in FIG. 5G, the resist material 40 is removed with an organic solvent such as acetone, so that the water-repellent film 50 can be left only on the top of the convex portion 31.

  FIG. 6 shows the surface of the nozzle plate having the concavo-convex structure thus formed. FIG. 6A is a plan view showing an example of the surface of the nozzle plate, and FIG. 6B is a cross-sectional view taken along the line A-A ′ of FIG.

  As shown to Fig.6 (a), it is preferable that the pattern of the uneven structure 30 formed in the nozzle plate surface is formed in zigzag form. Since the water-repellent film is formed on the convex portion 31 of the concavo-convex structure 30 and the concave portion 32 remains the base material 10, it is hydrophilic. Therefore, the ink adhering to the nozzle plate surface enters the concave portion of the concave-convex structure. Therefore, even if the ink is dried and solidified, it is solidified in the concave portion 32, and no solidified ink is formed on the convex portion 31, so that it is possible to prevent the nozzle surface from being damaged by wiping. Further, by forming the pattern of the concavo-convex structure 30 in a staggered pattern, the hydrophilic portions and the water repellent portions can be alternately arranged, and the ink adhering efficiently can be drawn into the concave portions 32 that are hydrophilic portions. .

The size of the uneven structure 30 (in FIG. 6 (a), the indicated by the arrow X1) the wiping direction of the recess 32 the length _{L 1} with respect to 100μm or less. The L ₁ With 100μm or less, it is possible to prevent the ink solidified material formed in the recess are swept out by the wiping member. When L ₁ is more than 100 [mu] m, because it may damage the surface of the nozzle plate ink solidified is swept out by the wiping by the wiping member during maintenance undesirable. The length _{L 1} is preferably at most 50μm or less, more preferably 20μm or less. As the wiping member, a belt-like web, a brush, a blade, or the like can be used. When using a blade as the wiping member, as the blade does not enter all the way into the recess 32, it is preferable to reduce the L ₁ from the blade R.

In addition, when L ₁ is shorter than the depth L ₃ of the recess, foreign matter (ink solidified product) inside the recess 32 may not be removed by wiping after applying a cleaning liquid described later. Therefore, L ₁ is preferably ½ or more of L ₃ . Specifically, the thickness is preferably 5 μm or more.

Further, the wiping direction of the length _{L 2} of the convex portion 31 is preferably set to 1/2 or more the depth _{L 3.} If relative depth L ₃ L ₂ is too short, there is a case where the convex portion 31 is broken by wiping undesirable. Specifically, the thickness is preferably 5 μm or more and 100 μm or less.

In FIG. 6A, the wiping direction X1 and one side of the recess 32 are formed in parallel. However, wiping may be performed at a predetermined angle with respect to one side of the recess 32 (the wiping direction is indicated by an arrow). X2). In this case, the length of the recess 32 in the wiping direction is in a range indicated by L _X2 in the figure. When the wiping direction has a predetermined angle with one side of the recess 32, the length L _X2 of the recess 32 in the wiping direction is set to 100 μm or less.

  In addition, in FIG. 6A, although the description has been given using the pattern in which the concavo-convex structure is formed in a staggered pattern, the present invention is not limited to this, for example, a pattern in which the concave portion and the convex portion are formed in stripes. It can be. Also in this case, the pattern is formed so that the length of the concave portion in the wiping direction is 100 μm or less.

  FIG. 7 is a view showing another embodiment of the nozzle plate surface of the inkjet head. As shown in FIG. 7, the periphery of the nozzle 251 is a first water-repellent region 310 in which a water-repellent film is formed on a flat substrate that does not have a concavo-convex structure, and further around the first water-repellent region 310. The second water-repellent region 320 having the concavo-convex structure described above is provided.

  The entire surface of the first water-repellent region 310 is water-repellent, and the second water-repellent region 320 is water-repellent in the convex portion and hydrophilic in the concave portion. The water repellency is higher than that of the second water repellent region 320. Since the ink is more likely to adhere to the second water-repellent area 320 than the first water-repellent area 310, the ink adheres to the first water-repellent area 310 and the first water-repellent area 320 causes the first water-repellent area 320 to adhere. Ink movement to the water region 310 can be prevented. Therefore, the ink solidified material does not adhere to the first water repellent region that is the peripheral portion of the nozzle 251, so that nozzle clogging can be prevented.

  In such a method of forming the nozzle plate surface, when the base material is structured in the nozzle plate manufacturing method, a region that becomes the first water-repellent region 310 is covered with a mask agent. Thereby, since the uneven structure is not formed in the region to be the first water-repellent region 310, the water-repellent region of the entire water-repellent film can be formed.

  The first water repellent area 310 is preferably an area of 100 μm from the nozzle 251. By setting the first water repellent area 310 within this range, nozzle clogging can be prevented. For example, when the space between the nozzles 251 is 300 μm, the range of 100 μm in the vicinity of the nozzles is the first water-repellent region 310, and therefore the range of 100 μm therebetween is the second water-repellent region 320.

<Cleaning method of nozzle plate>
Next, a method for cleaning the nozzle plate of the inkjet head of the present invention will be described. As described above, the ink jet head of the present invention can form an ink solidified product in the concave portion on the surface of the nozzle plate. Therefore, when the ink solidified product is removed, the cleaning liquid is applied to dissolve the adhered ink solidified product. Thereafter, the dissolved ink solidified product can be removed by wiping the nozzle plate surface with a wiping member.

  As the cleaning liquid, DEGmBE (diethylene glycol monobutyl ether) having a viscosity of 20 cP, water, ink used for drawing itself, and the like can be used.

[Example]
(Test 1)
An ink jet head having an uneven structure on the entire discharge surface side of the nozzle plate was manufactured by the method of the above embodiment. The depth of the concavo-convex structure was fixed at 10 μm, and the concave and convex portions were arranged in a staggered manner with a vertical to horizontal ratio of 1: 1. Moreover, the length of the recessed part and the convex part was changed and performed in each Example.

  In the test, after 700000 ink droplets were continuously ejected from the ink jet head, hot air of 40 ° C. was blown on the surface of the nozzle plate for 1 minute to solidify the ink and perform one wiping. This was set as one set, and the number of nozzles with deteriorated water repellency after discharging and wiping a predetermined number of times was measured with a microscope. Moreover, the deviation of the discharge curve of all 2048 nozzles, which is the total number of nozzles used in the test, was measured. The wiping was performed by applying a nozzle cleaning liquid, using a web as a wiping member, and wiping from one end of the nozzle plate to the other end with the web. Every time wiping was performed 100 times, an ink cleaning liquid was applied to the nozzle surface, and wiping was performed after the ink was sufficiently dissolved.

  When the water repellency around the nozzle hole is broken when observed with a microscope and the wetting occurs, the nozzle having deteriorated water repellency is indicated as NG in the table. Moreover, the initial value of the discharge curve is 3 mrad, and is shown in the table as a deviation. The results are shown in Table 1. Further, as a reference example 1, a test was performed on a nozzle plate not provided with an uneven structure.

  Comparative Example 1 is a case where one side of the concavo-convex structure is 200 μm, and when wiping is repeated in a state where the ink on the nozzle surface is dry, the ink solidified product is dragged out from the hydrophilic region of the concave portion. The water repellent film was damaged. As the water-repellent film deteriorated, the discharge performance gradually deteriorated.

  On the other hand, in Example 1, since one side of the concavo-convex structure was set to 100 μm, the solidified ink was not dragged out of the concave portion even if the wiping operation was repeated, so that a good state was obtained even after wiping 5000 times. I was able to keep it.

  Example 2 is a case where one side of the concavo-convex structure is 5 μm, the convex part is not destroyed by wiping, the water-repellent film is not deteriorated even after 5000 times, and the ejection performance is also good. It was.

  Comparative Example 2 is a result when wiping is performed without applying the ink solution every 100 times of wiping, with one side of the concavo-convex structure being 100 μm. In comparative example 2. Since most of the solidified ink remains without being removed in the recesses, the water repellency and discharge performance were relatively good up to 1,000 times of wiping. It was deteriorated.

  DESCRIPTION OF SYMBOLS 10 ... Base material, 20 ... Mask material, 30 ... Uneven structure, 31 ... Convex part, 32 ... Concave part, 40 ... Resist material, 50, 262 ... Water-repellent film, 100 ... Inkjet recording apparatus, 112 ... Paper feed part, 114 ... Processing liquid application unit 116 ... Drawing unit 118 ... Drying unit 120 ... Fixing unit 122 ... Discharging unit 124 ... Recording medium 154 ... Processing liquid drum 156 ... Processing liquid coating device 170 ... Drawing drum 172M 172K, 172C, 172Y ... inkjet head, 176 ... drying drum, 180 ... hot air ejection nozzle, 182 ... IR heater, 184 ... fixing drum, 186 ... halogen heater, 188 ... fixing roller, 192 ... discharge tray, 196 ... Conveying belt, 251 ... nozzle, 260 ... nozzle plate, 310 ... first water repellent area, 320 ... second water repellent area

Claims (10)

A nozzle plate having nozzle holes for discharging liquid;
A pressure chamber connected to the nozzle hole via a flow path, and a pressure generating element that applies pressure to the liquid in the pressure chamber, and a flow path structure,
The discharge surface side for discharging the liquid of the nozzle plate has an uneven structure,
The convex portion tip side of the concave-convex structure has water repellency, and the side surface and bottom surface of the concave portion have hydrophilicity,
An inkjet head characterized in that the length of the concave portion in the wiping direction is 100 μm or less.   The inkjet head according to claim 1, wherein a water-repellent film is formed on a tip end side of the convex portion.   The inkjet head according to claim 1 or 2, wherein the length of the convex portion in the wiping direction is 1/2 or more of the depth of the concave portion.   The inkjet head according to any one of claims 1 to 3, wherein a length of the concave portion in the wiping direction is 1/2 or more of a depth of the concave portion.   The inkjet head according to claim 1, wherein the concavo-convex structure is arranged in a staggered manner.   6. The inkjet head according to claim 5, wherein one side of the concave portions of the concave-convex structure arranged in a staggered pattern is 100 μm or less.   The inkjet head according to any one of claims 2 to 6, wherein a substrate forming the nozzle plate is made of a silicon-based material, and the water-repellent film is made of fluoroalkylsilane.   The flat water-repellent region is provided around the discharge surface side of the nozzle hole, and the uneven structure is provided around the flat water-repellent region. Inkjet head.   An ink jet recording apparatus comprising the ink jet head according to claim 1.   A cleaning liquid for dissolving the ink is applied to the nozzle plate surface of the ink jet head according to any one of claims 1 to 8, and after the adhered ink solidified material is dissolved, wiping is performed. Nozzle plate cleaning method.

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