JP2005271298A - Liquid droplet ejector and liquid droplet ejecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid droplet ejector which enables a change in dot diameter per unit volume and time for permeation into a ejection target medium by bringing about a desired impact liquid droplet state by a plurality of ejected liquid droplets, and a liquid droplet ejecting method. <P>SOLUTION: A first liquid droplet (91') and a second liquid droplet (92) are ejected from the same nozzle; the second liquid droplet (92) is made to collide with the top of an impact liquid droplet which is brought about by the first liquid droplet (91') having arrived on the ejection target medium (16), in first, so that the area of the contact of the impact liquid droplet with the ejection target medium can be increased by the kinetic energy of the second liquid droplet (92); and one dot is formed by using the impact liquid droplets (93) which are united together by the collision. This brings about a dot with a dot diameter (Dms) larger than a dot diameter (Dm), which can be obtained by ejecting the single liquid droplet (91) with the same volume. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a droplet discharge apparatus and method, and more particularly to a droplet discharge apparatus and method suitable for use in an image forming apparatus such as an inkjet recording apparatus that discharges droplets from a discharge head to form an image on a recording medium. .

  An ink jet recording apparatus ejects ink droplets on a recording medium by ejecting ink from the recording head in accordance with a print signal while relatively moving the recording head having the ink ejection nozzle and the recording medium. A desired image is recorded by forming.

  The ink coming out of the nozzle may separate into a plurality of droplets during the flight. At this time, the ink droplets that land on the recording medium first are called “main ink droplets (main droplets)”, and the ink droplets that land afterwards are called “sub-ink droplets (satellite droplets)”. A technique has been proposed in which this satellite droplet is landed on a recording medium at a position different from that of the main droplet to improve the resolution and improve the graininess (Patent Document 1).

  On the other hand, there is also known a technique for preventing image quality deterioration due to satellite dots by landing satellite droplets at the same position as the main droplet (Patent Document 2). In addition, in the case of a shuttle scan type recording apparatus that reciprocates the recording head, the relative landing position of satellite droplets with respect to the main droplets differs between the forward path and the return path. There has been proposed a technique for switching the direction printing to prevent image quality deterioration due to satellite droplets (Patent Document 3). In addition, a technique has been proposed in which the printing energy is switched between the forward path and the backward path during shuttle scan reciprocating operation to prevent density changes caused by satellite droplets (Patent Document 4).

  Furthermore, the method (Patent Document 5) that realizes high gradation gradation image expression by changing the overlap (area) of main droplets and satellite droplets on the recording medium, and the number of satellite droplets to be discharged is controlled. Then, a method for realizing gradation recording by changing the landing area has been proposed (Patent Document 6).

A technique is also known in which a plurality of droplets ejected from different nozzles are attached to the same point regardless of whether they are satellite droplets or main droplets (Patent Documents 7 and 8). In Patent Document 7, gradation expression is performed by driving a plurality of drops into the same pixel from a plurality of ejection openings. In Patent Document 8, gradation expression is performed by driving dark ink and light ink of similar colors into the same pixel.
JP 7-285222 A JP 2000-203012 A JP 2002-254616 A JP-A-10-119291 JP 10-193649 A JP-A-11-10878 JP-A-6-255132 JP 11-91088 A

  However, in any of the above-described Patent Documents 1 to 8, a method for obtaining a state of an intended landing droplet by hitting substantially the same point as the first droplet with the same nozzle for the second droplet and its discharge control are described. It has not been.

  In recent ink jet recording apparatuses, a multi-tone is expressed in units of one dot by controlling the ink discharge amount and the number of discharges according to the contents to be printed. For example, when changing the size of the ink droplets to be ejected, small dots are formed on the recording medium if small ink droplets are ejected, and large dots are formed on the recording medium if large ink droplets are ejected.

  Since the discharge amount (liquid amount) affects the dot density, changing the liquid volume and changing the dot diameter also changes the density of one dot. Further, when a large droplet is landed on a permeable medium, it takes time for the ink to penetrate and fix. From such a viewpoint, it is required to form dots appropriately according to the combination of the type of recording medium (discharged medium), the nature of the ink to be used, and the drawing content.

  The present invention has been made in view of such circumstances, and creates a desired landing droplet state by using a plurality of droplets, and changes the dot diameter per unit volume and the permeation time to the discharge medium. It is an object of the present invention to provide a droplet discharge apparatus and method capable of performing the above.

  In order to achieve the above object, a droplet discharge device according to claim 1 is a nozzle for discharging a droplet, a pressure generating means for generating a pressure for discharging a droplet from the nozzle, and The first droplet and the second droplet are ejected from the same nozzle by controlling the pressure generating means, and the second droplet is placed on the landing droplet by the first droplet that has landed first on the medium to be ejected. The contact area of the landing droplet with the medium to be ejected is expanded by the kinetic energy of the second liquid droplet by causing the liquid droplet to collide with the liquid droplet, and the contact area of the droplet combined with the medium with the medium to be ejected is increased. Discharge control means for performing discharge control for making the landing droplets formed by single droplet discharge of the same droplet amount larger than the contact area with the target medium.

  According to the present invention, the first liquid droplet and the second liquid droplet discharged from the same nozzle are substantially in the same position on the medium to be discharged (the landing liquid droplets can be combined to form one liquid droplet state. 1 dot is formed upon landing within a range close to the degree. At this time, the second droplet collides with the landing droplet by the first droplet previously attached to the medium to be discharged, so that the first droplet (landing droplet) is crushed, The contact area with the ejection medium is increased. At the same time, the first droplet and the second droplet are combined by collision to form one droplet state corresponding to the total droplet amount. The landing droplet thus obtained has a larger contact area with the medium to be discharged as compared to a landing droplet obtained by discharging a single droplet of the same droplet amount (same volume) at a time. The difference in contact area appears as a difference in dot size (dot diameter) and affects the penetration time.

  According to the present invention, by forming one dot by two droplets that land with a time difference, the dot diameter and the penetration time are compared with the case of forming one dot by discharging one droplet having the same total droplet amount. Can create different states. In addition, by landing in two drops, the dot diameter per unit volume is increased, and the ink consumption can be reduced. Further, the contact area with the recording medium is large, and the permeation time is shortened.

  A second aspect of the invention relates to a form of the droplet discharge device according to the first aspect of the invention, and is a full line type having a nozzle row in which a plurality of the nozzles are arranged over a length corresponding to the full width of the discharge target medium. And at least one of the ejection head and the medium to be ejected is conveyed in a direction substantially perpendicular to the longitudinal direction of the ejection head, and the ejection head and the medium to be ejected are relatively moved in a certain direction. And a group of dots formed on the medium to be ejected by ejecting liquid from the nozzle row of the ejection head along with the relative movement in the fixed direction.

  Droplet ejection according to the present invention is a single-pass configuration in which a full-line ejection head can be used to form dot groups corresponding to the entire ejection width by only relative movement in one direction (by only one scan). An apparatus can be used suitably.

  A third aspect of the present invention relates to an aspect of the droplet discharge device according to the first or second aspect, wherein the discharge control unit is configured to discharge the first droplet after the first droplet has landed. The second droplet is landed before 30% of the penetration into the medium is completed.

  In order to increase the contact area of the landing droplet, the second droplet is landed (collised) when the landing droplet due to the first droplet landed first is in a sufficiently large liquid state on the medium to be ejected. Preferably, as shown in claim 3, it is preferable that the second droplet is landed before the penetration of the first droplet according to the first landing is completed by 30%. More preferably, the second droplet is landed before the penetration of the first droplet is completed by 10%.

  The invention according to claim 4 relates to an aspect of the droplet discharge device according to claim 1, 2, or 3, wherein the flight kinetic energy of the first droplet is E1, and the flight kinetic energy of the second droplet. When E2 is E2, the relationship of E1 <E2 is satisfied.

  By relatively increasing the kinetic energy of the second droplet, the amount of crushing (crushing amount) of the first droplet (landing droplet) increases, and the contact area with the medium to be discharged increases. .

  The invention according to claim 5 relates to an aspect of the droplet discharge device according to any one of claims 1 to 4, wherein the first droplet and the second droplet have substantially the same droplet amount. It is characterized by being.

  According to this aspect, since the amount of the first droplet that lands first is substantially equal to the amount (volume) of the second droplet that collides with the first droplet, the contact area of the landing droplet is effective. Therefore, it is easy to control the ejection drive.

  The invention according to claim 6 relates to an aspect of the droplet discharge apparatus according to any one of claims 1 to 5, wherein the first droplet is a main droplet and the second droplet is a satellite liquid. It includes discharge drive signal generation means for generating a drive waveform that realizes discharge as droplets.

  As an example of a method for generating the first and second droplets, there is an aspect in which main droplets and satellite droplets are obtained by separating the liquid during flight by one ejection drive.

  The invention according to claim 7 relates to an aspect of the droplet discharge device according to any one of claims 1 to 5, wherein both the first droplet and the second droplet are main droplets. In order to discharge these droplets, the discharge driving is performed twice.

  As another example of the method for generating the first and second droplets, there is an aspect in which the first droplet ejection drive and the second droplet ejection drive are performed. At this time, the overlap of the first and second droplets is set to 50% or less as a guideline for the condition for landing the two droplets obtained by each ejection drive at substantially the same position on the ejection medium. Here, the overlap within 50% means that the distance between the landing centers of the first and second drops is within 50% of the landing diameter of the first drop.

The invention according to claim 8 describes the landing conditions of the first and second drops. That is, the invention according to claim 8, claim 6 or 7 relates to an embodiment of the liquid droplet ejection apparatus according, the landing diameter of the first droplet D _1, the said first droplet second When the distance between the landing centers of the droplets is δL, δL / D ₁ ≦ 0.5 is satisfied. More preferably, δL / D ₁ ≦ 0.25.

The ejection frequency f for realizing the conditions described in claim 8 is f ≧ 1 / {(D _1/2) , where the landing diameter D _{1 of the first} droplet and the relative transport speed V of the medium to be ejected. ) / V}. More preferably, to satisfy _{f ≧ 1 / {(D 1} /4) / V}.

  A ninth aspect of the invention provides an image forming apparatus comprising the liquid droplet ejection device according to any one of the first to eighth aspects, wherein an image is formed by the liquid ejected from the nozzle. .

  The droplet discharge device described in claims 1 to 8 can be suitably used for an image forming apparatus represented by an ink jet recording apparatus.

  As a form of the ejection head, a nozzle array in which a plurality of nozzles for ejecting ink are arranged over a length corresponding to the entire width of the recording medium in a direction substantially orthogonal to the relative feeding direction of the recording medium (ejection medium). It can be a full line type recording head.

  The “full-line type recording head” is usually arranged along a direction perpendicular to the relative feeding direction of the recording medium, but has a predetermined angle with respect to the direction perpendicular to the feeding direction. There may be a mode in which the recording head is arranged along an oblique direction. Furthermore, by combining a plurality of short recording head units having nozzle rows that are less than the length corresponding to the entire width of the recording medium, a nozzle row corresponding to the entire width of the recording medium may be configured as a whole of these units. .

  The “recording medium” is a medium (which can be called a print medium, an image forming medium, a recording medium, an image receiving medium, or the like) that receives an image by the action of a recording head, and is a continuous sheet, a cut sheet, a seal sheet, Various media are included regardless of the material and shape, such as a resin sheet such as an OHP sheet, a film, a cloth, a printed board on which a wiring pattern is formed by an inkjet recording apparatus, an intermediate transfer medium, and the like. In this specification, the term “printing” represents the concept of forming an image in a broad sense including characters.

  The conveying means for relatively moving the recording medium and the recording head is a mode for conveying the recording medium to the stopped (fixed) ejection head, a mode for moving the ejection head with respect to the stopped recording medium, or Any of the modes in which both the ejection head and the recording medium are moved is included.

  The invention according to claim 10 provides a method invention for achieving the object. That is, in the droplet discharge method according to the tenth aspect, the first droplet and the second droplet are discharged from the same nozzle, and the landing droplet by the first droplet that has landed on the discharge medium first. The second droplet collides with the second droplet, and the contact area of the landing droplet with the medium to be ejected is expanded by the kinetic energy of the second droplet, and the medium to be ejected of the droplet combined by the collision And the contact area of the landing droplet formed by single droplet discharge of the same droplet amount with the medium to be discharged.

  According to the present invention, the first and second droplets ejected from the same nozzle are landed on the medium to be ejected with a slight time difference, and the second droplet collides with the first landed first droplet. In this way, one dot is formed by the combined droplets while expanding the contact area of the landing droplets with the medium to be discharged, so that one dot is formed by discharging one droplet having the same total droplet amount. Compared to the case, it is possible to create a state in which the dot diameter and permeation time are different while maintaining the density.

  Accordingly, it is possible to perform appropriate dot formation according to the type of the medium to be ejected, the nature of the liquid to be used, the arrangement pattern of the dot group to be formed (drawing content), and the like.

  In addition, according to the present invention, since the dot diameter per unit volume is increased by landing in two drops, a larger dot diameter can be obtained with a smaller amount of ink than before, and ink consumption can be reduced. Can be achieved. Furthermore, according to the present invention, since the contact area of the landing droplet with the recording medium is increased, the permeation time is shortened, and the print productivity can be improved.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[Overall configuration of inkjet recording apparatus]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus using a droplet discharge device according to an embodiment of the present invention. As shown in the figure, the ink jet recording apparatus 10 includes a plurality of ink jet heads (hereinafter referred to as “ink jet heads”) corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. A printing unit 12 having 12K, 12C, 12M, and 12Y, an ink storage / loading unit 14 that stores ink to be supplied to each of the heads 12K, 12C, 12M, and 12Y, and a recording sheet as a recording medium 16 is disposed opposite to the decurling unit 20 for removing the curl of the recording paper 16 and the nozzle surface (ink ejection surface) of the printing unit 12 to improve the flatness of the recording paper 16. A suction belt conveyance unit 22 that conveys the recording paper 16 while holding it, a print detection unit 24 that reads a printing result by the printing unit 12, and a discharge that discharges the printed recording paper (printed matter) to the outside. And parts 26, and a.

  The ink storage / loading unit 14 has an ink tank that stores ink of a color corresponding to each of the heads 12K, 12C, 12M, and 12Y, and each tank has a head 12K, 12C, 12M, and 12Y through a required pipe line. Communicated with. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When multiple types of recording paper are used, an information recording body such as a barcode or wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Thus, it is preferable to automatically determine the type of recording medium (media type) to be used and perform ink ejection control so as to realize appropriate ink ejection according to the media type.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration that uses roll paper, a cutter (first cutter) 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least portions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 are horizontal ( Flat surface).

  The belt 33 has a width that is wider than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. The recording paper 16 is sucked and held on the belt 33 by sucking the suction chamber 34 with a fan 35 to a negative pressure.

  When the power of the motor (reference numeral 88 in FIG. 7) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, the belt 33 is driven in the clockwise direction in FIG. The held recording paper 16 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although a mode using a roller / nip conveyance mechanism instead of the suction belt conveyance unit 22 is also conceivable, if the roller / nip conveyance is performed in the print area, the image easily spreads because the roller contacts the printing surface of the sheet immediately after printing. There is a problem. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print region is preferable.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  Each of the heads 12K, 12C, 12M, and 12Y of the printing unit 12 has a length corresponding to the maximum paper width of the recording paper 16 targeted by the inkjet recording apparatus 10, and the nozzle surface has a recording medium of the maximum size. This is a full-line type head in which a plurality of nozzles for ink discharge are arranged over a length exceeding at least one side (full width of the drawable range) (see FIG. 2).

  The heads 12K, 12C, 12M, and 12Y are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side in the recording paper 16 feed direction. 12K, 12C, 12M, and 12Y are fixedly installed so as to extend along a direction substantially orthogonal to the conveyance direction of the recording paper 16.

  A color image can be formed on the recording paper 16 by discharging different color inks from the heads 12K, 12C, 12M, and 12Y while transporting the recording paper 16 by the suction belt transporting section 22.

  As described above, according to the configuration in which the full-line heads 12K, 12C, 12M, and 12Y having nozzle rows that cover the entire width of the paper are provided for each color, the recording paper 16 and the printing unit in the paper feeding direction (sub-scanning direction). The image can be recorded on the entire surface of the recording paper 16 by performing the operation of moving the 12 relatively once (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the recording head reciprocates in a direction orthogonal to the paper transport direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink may be added as necessary. Good. For example, it is possible to add an ink jet head that discharges light ink such as light cyan and light magenta.

  The print detection unit 24 shown in FIG. 1 includes an image sensor for imaging the droplet ejection result of the printing unit 12, and means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor. Function as.

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than at least the ink ejection width (image recording width) by the heads 12K, 12C, 12M, and 12Y. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor is composed of a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  A test pattern or practical image printed by the heads 12K, 12C, 12M, and 12Y of each color is read by the print detection unit 24, and ejection determination of each head is performed. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  A post-drying unit 42 is provided following the print detection unit 24. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other substances that cause dye molecules to break by pressurizing the paper holes with pressure. There is an effect to.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined surface uneven shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) that switches the paper discharge path so as to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

[Head structure]
Next, the structure of the head will be described. Since the structures of the respective heads 12K, 12C, 12M, and 12Y for each color are common, the heads are represented by the reference numeral 50 in the following.

  FIG. 3A is a plan perspective view showing an example of the structure of the head 50, and FIG. 3B is an enlarged view of a part thereof. 3C is a plan perspective view showing another structure example of the head 50, and FIG. 4 is a cross-sectional view showing a three-dimensional configuration of one droplet discharge element (an ink chamber unit corresponding to one nozzle 51). FIG. 4 is a sectional view taken along line 4-4 in FIG.

  In order to increase the dot pitch printed on the recording paper 16, it is necessary to increase the nozzle pitch in the head 50. As shown in FIGS. 3A and 3B, the head 50 of this example includes a plurality of ink chamber units including nozzles 51 serving as ink droplet ejection openings, pressure chambers 52 corresponding to the nozzles 51, and the like. It has a structure in which (droplet discharge elements) 53 are arranged in a zigzag matrix (two-dimensionally), and is thereby projected so as to be arranged along the head longitudinal direction (direction perpendicular to the paper feed direction). High density of substantial nozzle interval (projection nozzle pitch) is achieved.

  The configuration in which one or more nozzle rows are configured over a length corresponding to the entire width of the recording paper 16 in a direction substantially orthogonal to the feeding direction of the recording paper 16 is not limited to this example. For example, instead of the configuration of FIG. 3 (a), short head units 50 ′ in which a plurality of nozzles 51 are two-dimensionally arranged are arranged in a staggered manner and connected as shown in FIG. 3 (c). A line head having a nozzle row having a length corresponding to the entire width of the recording paper 16 may be configured.

  The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape (see FIGS. 3 (a) and 3 (b)), and is connected to the nozzle 51 at both corners on a diagonal line. An outlet and an inlet (supply port) 54 for supply ink are provided.

  As shown in FIG. 4, each pressure chamber 52 communicates with a common flow channel 55 through a supply port 54. The common channel 55 communicates with an ink tank (not shown in FIG. 4, not shown in FIG. 6 and indicated by reference numeral 60) serving as an ink supply source, and the ink supplied from the ink tank 60 passes through the common channel 55 in FIG. Then, it is distributed and supplied to each pressure chamber 52.

  An actuator 58 having an individual electrode 57 is joined to a pressure plate (vibration plate) 56 constituting the top surface of the pressure chamber 52. By applying a driving voltage to the individual electrode 57, the actuator 58 is deformed to change the volume of the pressure chamber 52, and ink is ejected from the nozzle 51 due to the pressure change accompanying this. For the actuator 58, a piezoelectric body such as a piezoelectric element is preferably used. After ink discharge, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54.

  As shown in FIG. 5, a large number of ink chamber units 53 having such a structure are arranged in a row direction along the main scanning direction and an oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. The structure is arranged in a lattice pattern. With a structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along a certain angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos θ. .

  That is, in the main scanning direction, each nozzle 51 can be handled equivalently as a linear arrangement with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  When the nozzles are driven by a full line head having a nozzle row having a length corresponding to the entire printable width, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially moved from one side to the other. (3) The nozzles are divided into blocks, and each block is sequentially driven from one side to the other, etc., and one line or one in the sheet width direction (direction perpendicular to the sheet conveyance direction) Nozzle driving for printing individual strips is defined as main scanning.

  In particular, when driving the nozzles 51 arranged in a matrix as shown in FIG. 5, the main scanning as described in (3) above is preferable. That is, nozzles 51-11, 51-12, 51-13, 51-14, 51-15, 51-16 are made into one block (other nozzles 51-21,..., 51-26 are made into one block, Nozzles 51-31,..., 51-36 as one block,...), And the nozzles 51-11, 51-12,. One line is printed in 16 width directions.

  On the other hand, repetitively moving the above-described full line head and the paper to repeatedly perform one line or one band-like printing formed by the above-described main scanning is defined as sub-scanning.

  In implementing the present invention, the nozzle arrangement structure is not limited to the illustrated example. In the present embodiment, a method of ejecting ink droplets by deformation of an actuator 58 typified by a piezo element (piezoelectric element) is adopted. However, in the practice of the present invention, the method of ejecting ink is not particularly limited. Instead of the piezo jet method, various methods such as a thermal jet method in which ink is heated by a heating element such as a heater to generate bubbles and ink droplets are ejected by the pressure can be applied.

[Configuration of ink supply system]
FIG. 6 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10. The ink tank 60 is a base tank that supplies ink to the head 50 and is installed in the ink storage / loading unit 14 described with reference to FIG. In the form of the ink tank 60, there are a system that replenishes ink from a replenishing port (not shown) and a cartridge system that replaces the entire tank when the remaining amount of ink is low. A cartridge system is suitable for changing the ink type according to the intended use. In this case, it is preferable that the ink type information is identified by a barcode or the like, and ejection control is performed according to the ink type. The ink tank 60 in FIG. 6 is equivalent to the ink storage / loading unit 14 in FIG. 1 described above.

  As shown in FIG. 6, a filter 62 is provided between the ink tank 60 and the head 50 in order to remove foreign matters and bubbles. The filter mesh size is preferably equal to or smaller than the nozzle diameter (generally about 20 μm). Although not shown in FIG. 6, a configuration in which a sub tank is provided in the vicinity of the head 50 or integrally with the head 50 is also preferable. The sub-tank has a function of improving a damper effect and refill that prevents fluctuations in the internal pressure of the head.

  Further, the inkjet recording apparatus 10 is provided with a cap 64 as a means for preventing the nozzle 51 from drying or preventing an increase in ink viscosity near the nozzle, and a cleaning blade 66 as a means for cleaning the nozzle surface 50A. . The maintenance unit including the cap 64 and the cleaning blade 66 can be moved relative to the head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the head 50 as necessary.

  The cap 64 is displaced up and down relatively with respect to the head 50 by an elevator mechanism (not shown). The cap 64 is lifted to a predetermined raised position when the power is turned off or during printing standby and is brought into close contact with the head 50, thereby covering the nozzle surface 50 </ b> A with the cap 64.

  The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the ink discharge surface (nozzle plate surface) of the head 50 by a blade moving mechanism (not shown). When ink droplets or foreign substances adhere to the nozzle plate, the nozzle plate surface is wiped by sliding the cleaning blade 66 on the nozzle plate to clean the nozzle plate surface.

  During printing or standby, when a specific nozzle is used less frequently and the ink viscosity in the vicinity of the nozzle increases, preliminary discharge is performed toward the cap 64 to discharge the deteriorated ink.

  Further, when bubbles are mixed in the ink (pressure chamber) in the head 50, the cap 64 is applied to the head 50, and the ink (ink in which the bubbles are mixed) is removed by suction with the suction pump 67, and is removed by suction. Ink is fed to the collection tank 68. In this suction operation, the deteriorated ink that has increased in viscosity (solidified) is sucked out when the ink is initially loaded into the head 50 or when the ink is used after being stopped for a long time.

  If the head 50 is not ejected for a certain period of time, the ink solvent near the nozzles evaporates and the viscosity of the ink near the nozzles increases. Will not discharge. Therefore, before this state is reached (within the viscosity range in which ink can be discharged by the operation of the actuator 58), the actuator 58 is operated toward the ink receiver to discharge ink in the vicinity of the nozzle whose viscosity has increased. “Preliminary discharge” is performed. In addition, after the dirt on the surface of the nozzle plate is cleaned by a wiper such as a cleaning blade 66 provided as a cleaning means for the nozzle surface 50A, the foreign matter is prevented from entering the nozzle 51 by the wiper rubbing operation. Also, preliminary discharge is performed. Note that the preliminary discharge may be referred to as “empty discharge”, “purge”, “spitting”, or the like.

  In addition, if bubbles are mixed into the nozzle 51 or the pressure chamber 52 or if the viscosity increase of the ink in the nozzle 51 exceeds a certain level, ink cannot be ejected by the preliminary ejection, and the suction operation described below is performed.

  That is, when bubbles are mixed in the ink in the nozzle 51 or the pressure chamber 52, or when the ink viscosity in the nozzle 51 rises to a certain level or more, the ink can be ejected from the nozzle 51 even if the actuator 58 is operated. Disappear. In such a case, a suction means for sucking ink in the pressure chamber 52 with a pump or the like is brought into contact with the nozzle surface of the head 50 to suck ink mixed with bubbles or thickened ink.

  However, since the above suction operation is performed on the entire ink in the pressure chamber 52, the amount of ink consumption is large. Therefore, when the increase in viscosity is small, it is preferable to perform preliminary discharge as much as possible.

[Explanation of control system]
Next, the control system of the inkjet recording apparatus 10 will be described. FIG. 7 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, an image memory 74, a media detection unit 75, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as USB, IEEE 1394, Ethernet, and wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted. Image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the image memory 74. The image memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The image memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 is a control unit that controls each unit such as the communication interface 70, the image memory 74, the motor driver 76, and the heater driver 78. The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 86, read / write control of the image memory 74, and the like, as well as a transport system motor 88 and heater 89. A control signal for controlling is generated.

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heaters 89 of the post-drying unit 42 and other units in accordance with instructions from the system controller 72.

  The media detection unit 75 is means for detecting the paper type and size (paper width) of the recording paper 16. For example, means for reading information such as a bar code attached to a magazine of a paper feed unit, a sensor (paper width detection sensor, sensor for detecting the thickness of paper, reflection of paper) disposed at an appropriate place in the paper conveyance path A sensor for detecting the rate) is used, and an appropriate combination thereof is also possible. Further, instead of or in combination with these automatic detection means, it is possible to specify information such as paper type and size by inputting from a predetermined user interface.

  Information acquired by the media detection unit 75 is notified to the system controller 72 and used for ink ejection control and the like.

  The print control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from the image data in the image memory 74 according to the control of the system controller 72, and the generated print A control unit that supplies a control signal (dot data) to the head driver 84. Necessary signal processing is performed in the print control unit 80, and the ejection amount and ejection timing of the ink droplets of the head 50 are controlled via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 7, the image buffer memory 82 is shown in a mode associated with the print control unit 80, but it can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with one processor.

  The head driver 84 drives the ejection driving actuator 524 of the head 50 of each color based on the print data given from the print controller 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  Image data to be printed is input from the outside via the communication interface 70 and stored in the image memory 74. At this stage, for example, RGB image data is stored in the image memory 74. The image data stored in the image memory 74 is sent to the print control unit 80 via the system controller 72, and the print control unit 80 converts it into dot data for each ink color by a known method such as dithering or error diffusion. Converted.

  In this way, the head 50 is driven and controlled based on the dot data generated by the print controller 80, and ink is ejected from the head 50. An image is formed on the recording paper 16 by controlling the ink ejection from the head 50 in synchronization with the conveyance speed of the recording paper 16.

  As described with reference to FIG. 1, the print detection unit 24 is a block including a line sensor, reads an image printed on the recording paper 16, performs necessary signal processing, and the like to perform a print status (whether ejection is performed, droplet ejection And the detection result is provided to the print control unit 80. The reading start timing of the line sensor is determined from the distance between the sensor and the nozzle and the conveyance speed of the recording paper 16.

  The print controller 80 performs various corrections on the head 50 based on information obtained from the print detector 24 as necessary. Further, the print control unit 80 determines whether or not the nozzle 51 is ejected based on the detection information obtained through the print detection unit 24, and performs a predetermined recovery operation when a non-ejection nozzle is detected. I do.

  Next, an ink ejection operation in the inkjet recording apparatus 10 configured as described above will be described.

  In the ink jet recording apparatus 10 of the present example, when ejecting ink droplets from the nozzle 51, there are driving for ejecting only main droplets by one ejection driving and driving for ejecting satellite droplets together with the main droplets. These driving methods can be selectively switched as necessary. That is, by changing the waveform of the drive voltage applied to the actuator 58 described with reference to FIG. 4, it is possible to discharge only the main droplets or to discharge satellite droplets together with the main droplets. Further, by controlling the drive waveform of the actuator 58, it is possible to control the droplet amount, the flying speed, or the landing time difference between the main droplet and the satellite droplet.

  FIG. 8A is a schematic diagram when only the main droplet (one droplet) is discharged, and FIG. 8B is a schematic diagram when the discharge including the main droplet and the satellite droplet is performed. As shown in FIG. 5A, only the main droplet 91 is ejected, and when this main droplet 91 lands on the recording paper 16, it becomes a landing droplet 91A having a landing dot diameter Dm and a dot height hm. The landing dot diameter Dm and the dot height hm at this time are values reflecting the discharge amount (droplet amount) Vm of the main droplet 91. The landing droplet 91A penetrates and is fixed on the recording paper 16 as time passes.

  On the other hand, as shown in FIG. 5B, when the main droplet 91 ′ and the satellite droplet 92 are ejected and land at substantially the same position on the recording paper 16 with a time difference, the recording paper Two droplets merge on 16 to form one droplet, and a landing droplet 93 having a landing dot diameter Dms and a dot height hms is obtained.

  Here, the total discharge amount Vm ′s at the time of discharge including the main droplet 91 ′ and the satellite droplet 92 is substantially the same as the discharge amount Vm when only the main droplet 91 in FIG. Further, it is assumed that the discharge amount Vm ′ of the main droplet 91 ′ and the discharge amount Vs of the satellite droplet 92 are substantially equal. That is, Vm′s≈Vm ′ + Vs, Vm≈Vm ′s, and Vm′≈Vs.

  Under such conditions, the landing dot diameter Dms formed by ejection including the satellite droplet 92 is larger than the landing dot diameter Dm in the case of only the main droplet 91 (Dm <Dms), and the dot height hms. Is smaller than the dot height hm obtained with only the main droplet 91 (hm> hms).

  FIG. 8B illustrates the landing of two droplets, but the same applies to the case where three or more droplets land. When there are a plurality of satellite droplets, the “satellite droplet discharge amount Vs” in the above discussion is the total droplet amount of all satellite droplets. That is, if the sum of the discharge amounts Vsi (i = 1, 2,...) Of each satellite droplet is Vs (Vs = Vs1 + Vs2 +...), It can be handled in the same manner as described above.

  The phenomenon shown in FIG. 8B will be further described with reference to FIG. When the main droplet 91 ′ and the satellite droplet 92 are ejected from the nozzle 51 (FIG. 9A), first, the main droplet 91 ′ is landed on the recording paper 16 (FIG. 9B), and the landed The satellite droplet 92 is landed on the droplet 91′A (FIG. 9C). At this time, the landing droplet 91 ′ A by the main droplet 91 ′ that has landed first is pressed onto the recording paper 16 by the kinetic energy of the satellite droplet 92 and deformed, and the contact area with the recording paper 16 Spread. Along with the movement of the liquid in the direction of expanding the contact area, the landing droplet 91′A by the main droplet 91 ′ and the satellite droplet 92 are combined to form one droplet by collision due to landing, thereby forming a dot diameter. Dms landing droplets 93 are formed.

  In this way, even if the total droplet amount is the same, it is more difficult to form one dot at a time (by ejecting only one droplet) as shown in FIG. As shown in FIG. 9, the dot diameter is broadened by dividing one or more droplets into two or more to form one dot. In other words, the dot height changes and so does the penetration time.

  As a result, in the case of only the main droplet 91, the landing dot diameter Dm is small, but the dot height hm is high and the permeation time is long. On the other hand, when the satellite droplet 92 is included, the landing dot diameter Dms is large, but the dot height hms is low and the permeation time is short. However, since the total droplet amount is the same, the concentration is substantially constant.

  Utilizing this fact, when printing a pattern such as a fine line that requires high-resolution image reproduction, only the main droplet 91 is ejected. Further, when it is desired to shorten the penetration time (for example, when printing a pattern that requires droplets of a plurality of colors), droplet ejection including satellite droplets 92 is performed.

  In this way, it is possible to create a state in which the dot diameter of one dot and the permeation time are different while maintaining the density, and to perform ejection suitable for the print pattern.

  In order to obtain an effect of expanding the contact area by causing the satellite droplet 92 with the landing timing delayed to collide with the first landing droplet 91′A, the landing droplet 91′A by the main droplet 91 ′ that has landed first is obtained. It is desirable that the satellite droplet 92 is landed when the liquid is in a liquid state with a corresponding volume on the recording paper 16. Specifically, before the main droplet 91 ′ permeating through the first landing reaches 30%, that is, in a droplet state in which 70% or more of the discharge amount of the main droplet 91 remains on the recording paper 16. Sometimes it is preferable to land the satellite droplet 92. More preferably, the satellite droplet 92 is landed before the penetration of the main droplet 91 'is completed by 10%.

  In the above description, the satellite droplet 92 has substantially the same droplet amount as the main droplet 91 ′. However, even if the satellite droplet 92 has a smaller droplet amount than the main droplet 91 ′, the flight speed May be set so that the kinetic energy is substantially the same.

  In the above description, the second droplet is described as a “satellite droplet”. However, the second droplet is not limited to the satellite droplet when the present invention is implemented, and the actuator 58 is operated at a high frequency. A mode is also possible in which two droplets are landed at substantially the same position by driving and ejecting two droplets within a short time.

As shown in FIG. 10, when the landing dot diameter D ₁ by the first droplet 101 and the conveyance speed of the recording paper 16 are V, the first droplet when the second droplet 102 is landed. It is desirable that the distance δL between the landing centers of the first and second droplets 102 is within ½ of the landing dot diameter D ₁ of the first droplet.

That is, the following formula
[Equation 1] δL / D ₁ ≦ 0.5
It is preferable to discharge the droplets 101 and 102 so as to satisfy the above. The discharge frequency f (unit: Hz) for satisfying this [Equation 1] is set so as to satisfy the following equation.

[Number 2] f ≧ 1 / {D 1/2) / V} (Hz)
For example, when D ₁ = 30 μm and V = 400 mm / s, f = 27 kHz or more.

  In the above description, the ejection frequency f is set by the sheet conveyance speed V, but it may be defined by the penetration speed and drying speed of the first drop. As a guide, when T is the time from the first drop landing until the completion of penetration, the discharge frequency f is f ≧ 10 / T (Hz).

  For reference, FIG. 11 shows the experimental results that clarified the difference between the penetration time and the dot diameter when one drop was ejected with the same total liquid amount and when two drops were landed in a short time. Shown in

  FIG. 11 shows a case where a total droplet volume of 10 picoliters (pl) is discharged as a single drop and a case where two droplets are discharged separately (when a discharge volume of 5 picoliters is discharged twice) The measurement results are shown.

  In the above description, an inkjet recording apparatus has been illustrated as an example of an image forming apparatus, but the scope of application of the present invention is not limited to this. For example, the droplet discharge device of the present invention can also be applied to a photographic image forming apparatus that applies a developing solution to a photographic paper in a non-contact manner. In addition, the application range of the droplet discharge device according to the present invention is not limited to the image forming apparatus, and various devices (coating device, coating device) that eject processing liquid and other various liquids toward the discharge medium using the discharge head. The present invention can be applied to devices and the like.

1 is an overall configuration diagram of an ink jet recording apparatus using a droplet discharge device according to an embodiment of the present invention. FIG. 1 is a plan view of a main part around a printing unit of the ink jet recording apparatus shown in FIG. Plane perspective view showing the configuration of the head Enlarged view of the main part of Fig. 3 (a) Plane perspective view showing another configuration example of a full-line head Sectional view along line 4-4 in Fig. 3 (a) Enlarged view showing the nozzle arrangement of the head shown in FIG. Schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus of this example Main block diagram showing the system configuration of the inkjet recording apparatus of this example FIG. 8A is a schematic diagram when only the main droplet (one droplet) is discharged, and FIG. 8B is a schematic diagram when the discharge including the main droplet and the satellite droplet is performed. Schematic diagram showing how a single dot is formed by landing two droplets The figure used in order to explain the conditions of the discharge frequency when forming one dot by discharging two drops in a short time Chart showing measurement results of penetration time and dot diameter when the total droplet volume is the same and landed by ejecting one drop and landing in two drops

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 12K, 12C, 12M, 12Y ... Head, 14 ... Ink storage / loading part, 16 ... Recording paper, 18 ... Supply part, 22 ... Adsorption belt conveyance part, 50 ... Head, 51 ... Nozzle, 58 ... Actuator, 72 ... System controller, 80 ... Print controller, 84 ... Head driver, 91, 91 '... Main droplet, 91A, 91'A ... Landing droplet, 92 ... Satellite droplet, 93 ... landing droplets

Claims (10)

A nozzle for discharging droplets;
Pressure generating means for generating pressure for discharging droplets from the nozzle;
The first and second droplets are ejected from the same nozzle by controlling the pressure generating means, and the first droplet is landed on the ejected medium and the first droplet is landed on the first droplet. The contact area of the landing droplet with respect to the medium to be ejected is expanded by colliding two liquid droplets by the kinetic energy of the second liquid droplet, and the contact area of the droplet combined by the collision with the medium to be ejected Discharge control means for performing discharge control to make the landing droplet formed by single droplet discharge of the same droplet amount larger than the contact area with the target medium;
A droplet discharge apparatus comprising: A full-line type ejection head having a nozzle row in which a plurality of the nozzles are arranged over a length corresponding to the entire width of the ejection medium;
Transporting means for transporting at least one of the ejection head and the medium to be ejected in a direction substantially orthogonal to a longitudinal direction of the ejection head and relatively moving the ejection head and the medium to be ejected in a certain direction; ,
The liquid droplet ejection apparatus according to claim 1, wherein a dot group is formed on the medium to be ejected by performing liquid ejection from a nozzle row of the ejection head along with the relative movement in the certain direction.   The ejection control means causes the second droplet to land after the first droplet has landed and before the penetration of the first droplet into the medium to be ejected is completed by 30%. The droplet discharge device according to claim 1 or 2.   4. The relation of E1 <E2 is satisfied, where E1 is the flying kinetic energy of the first droplet and E2 is the flying kinetic energy of the second droplet. The liquid droplet ejection apparatus described.   5. The droplet discharge device according to claim 1, wherein the first droplet and the second droplet have substantially the same droplet amount.   6. The discharge drive signal generating means for generating a drive waveform for realizing discharge in which the first droplet is a main droplet and the second droplet is a satellite droplet. The droplet discharge device according to any one of the preceding claims.   6. The first droplet and the second droplet are both main droplets, and the ejection drive is performed twice in order to eject these droplets. 2. A droplet discharge device according to item 1. When the landing diameter of the first droplet is D ₁ and the distance between the landing centers of the first droplet and the second droplet is δL, δL / D ₁ ≦ 0.5 is satisfied. The droplet discharge device according to claim 6 or 7.   An image forming apparatus comprising the droplet discharge device according to claim 1, wherein an image is formed by the liquid discharged from the nozzle. The first droplet and the second droplet are ejected from the same nozzle, and the second droplet is caused to collide with the landing droplet by the first droplet that has landed first on the medium to be ejected. Due to the kinetic energy of the second droplet, the contact area of the landing droplet with respect to the medium to be ejected is expanded, and the contact area of the droplet combined by the collision with the medium to be ejected is a single liquid having the same droplet amount. A droplet discharge method, wherein a landing area of a landing droplet formed by droplet discharge is larger than a contact area with the medium to be discharged.

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