JP2005125773A - Liquid drop ejection head and ink jet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid drop ejection head suitable for fabrication in which high density nozzle arrangement and high viscosity ejection are realized by enhancing pressurization power of a piezoelectric while preventing crosstalk between nozzles, and to provide an ink jet recorder comprising it. <P>SOLUTION: A multilayer piezoelectric 58 is bonded to the pressurizing part on a diaphragm 57 corresponding to each pressure chamber 52, and ink is ejected from a nozzle 51 by pressurizing the pressure chamber 52 through expansion/contraction of the multilayer piezoelectric 58. The multilayer piezoelectric 58 has a free end or is added with a weight member on the side opposite to the diaphragm bonding face, and individual electrodes are wired to the outside collectively through a flexible board 59. With regard to the planar shape of the pressure chamber 52 when viewed from the diaphragm 57 side, aspect ratio of the pressure chamber defined by the minimum value/maximum value of inter-wall distance (line-of-sight distance) in the pressure chamber 52 satisfies a relation 0.45≤ aspect ratio ≤0.89. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a droplet discharge head and an ink jet recording apparatus, and more particularly, to a structure of a piezoelectric drive type droplet discharge head that discharges droplets from a nozzle by pressurizing a pressure chamber using a multilayer piezoelectric body and uses the same. The present invention relates to an inkjet recording apparatus.

  An ink jet head that ejects ink using a multilayer piezoelectric element is disclosed in Patent Document 1. Typical indexes representing the drive characteristics of this type of piezo drive type ink jet head are the pressure volume excluded by the piezoelectric body and the generated pressure. The higher the generated pressure, the higher the controllability and the higher viscosity liquid can be discharged, or the head can be miniaturized.

  In other words, by utilizing the aspect in which the source for improving the excluded volume is directed to the discharge of the high-viscosity liquid, and the area required for obtaining the excluded volume is reduced, the source is directed to downsizing the head. A mode of realizing a small-sized head with a density is possible.

  When aiming to achieve both high speed and high image quality using a full line type head having a nozzle row with a length corresponding to the paper width of the recording medium, in order to reduce visual unevenness and prevent droplet ejection interference such as bleeding, It must be possible to spread fine droplets of high viscosity on paper, for example, at about 2400 dpi.

  If this is to be realized with a conventional piezo drive type ink jet head, a length in the transport direction of about 25 mm per color is required, and it is calculated as 150 mm for 6 colors.

  However, in the inkjet system, considering the necessity of installing a maintenance system such as capping and wiping, functioning stably, paper conveyance accuracy, etc., the length of the head in the conveyance direction is about 1 inch wide as before. Is required to be paid.

  In order to prevent bleeding using functional ink, for example, when a high-viscosity liquid 10 times that of general ink is ejected without changing the flow path configuration of the head, the flow path resistance is approximately 10%. Therefore, it is necessary to realize an area density of the number of colors × 10 times by simple calculation, but this cannot be achieved within the design range of the conventional piezo drive type inkjet head.

The conventional piezo drive type inkjet head technology can be classified into the following three types. The first is a unimorph actuator distributed by printing technology (Patent Document 2). Second, a laminated piezoelectric body is provided on a support, and a pressure chamber is pressurized using the free end side (Patent Document 1). The third is a method (electrode separation method) in which driving is separated by electrode pattern wiring corresponding to the pressure chamber without mechanically separating the laminated piezoelectric material (Patent Documents 3 and 4).
Japanese Patent No. 3182931 Japanese Patent No. 3302515 JP 2002-166543 A JP 2001-246744 A

  Although the technique according to the first classification can realize a head at low cost by using a printing technique, it is difficult to realize a thin piezoelectric body with high accuracy and to increase the area, and is practically limited to about 2 cm or less. The Therefore, in order to create a full-line type head, it is necessary to connect a plurality of short head units, and it is difficult to realize a single line head by a method other than this connection method.

  In the technique according to the second classification, the density in the nozzle row direction is the rate-limiting of the cutting blade because of the manufacturing method in which one side of the relatively large laminated piezoelectric material is used as a common fixed end and the other end is cut. Therefore, when the nozzles are arranged at high density, it is necessary to make each piezoelectric body a rectangular shape that is long in the depth direction perpendicular to the dividing direction, thereby increasing the volume excluded by the piezoelectric body. In this method, the practical density limit is about 200 dpi, and the aspect ratio of the rectangular shape is about 1:10.

  Although the technology relating to the third classification increases the suitability for manufacturing the laminated piezoelectric material, the adjacent actuators are mechanically connected to each other, so that there is a lot of crosstalk (mutual interference between adjacent nozzles) and there is a restriction. In order to obtain a strong and large displacement, the number of stacked layers must be increased, leading to an increase in head size.

  The present invention has been made in view of such circumstances, while preventing crosstalk between nozzles, improving the pressurization capacity of the piezoelectric body, enabling high density nozzle discharge and high viscosity discharge, An object of the present invention is to provide a droplet discharge head suitable for manufacturing and an ink jet recording apparatus using the same.

  In order to achieve the above object, a liquid droplet ejection head according to the first aspect of the present invention includes a plurality of nozzles for ejecting liquid droplets, and a liquid ejected from each nozzle provided corresponding to the plurality of nozzles. A plurality of pressure chambers to be filled; a diaphragm that constitutes one wall surface of the pressure chamber; and a plurality of pressure chambers that are independently bonded and fixed to positions corresponding to the plurality of pressure chambers on the diaphragm. A non-constrained end that is displaceable in the pressurizing direction of the multi-layer piezoelectric body on the diaphragm by the multi-layer piezoelectric body. In this state, the liquid in the pressure chamber is pressurized through the diaphragm by the expansion and contraction of the multilayer piezoelectric body, and the liquid droplets are ejected from the nozzle.

  Multilayer piezoelectric bodies that are joined in a laminated structure can obtain a larger excluded volume than single-layer piezoelectric bodies. In addition, the configuration in which the nozzles are individually arranged can increase the density of the nozzles and discharge the high-viscosity liquid. Further, in the present invention, the stacked piezoelectric bodies are individually arranged for each pressure chamber, and the stacked piezoelectric bodies in the adjacent pressure chambers are separated from each other (independent), so that at the time of ejection driving Crosstalk is prevented.

  Furthermore, according to the present invention, since the one end opposite to the diaphragm side of the multilayer piezoelectric body bonded and fixed to the diaphragm is an unconstrained end (free end), The degree of freedom of installation increases. This eliminates the need for advanced tension adjustment, facilitates production, and realizes cost reduction.

A droplet discharge head according to a second aspect of the invention includes a plurality of nozzles that discharge droplets, and a plurality of pressure chambers that are provided corresponding to the plurality of nozzles and are filled with liquid discharged from each nozzle. A diaphragm that constitutes one wall surface of the pressure chamber, and a plurality of stacked piezoelectric bodies that are independently bonded and fixed to positions corresponding to the plurality of pressure chambers on the diaphragm. A weight member that inhibits displacement of the end portion in the pressurizing direction to the diaphragm is provided at an end portion of the multilayer piezoelectric body opposite to the joint surface with the diaphragm; It is characterized in that the liquid in the pressure chamber is pressurized via the vibration plate by expansion and contraction and the liquid droplets are ejected from the nozzle.

  According to the invention described in claim 2, as in the invention described in claim 1, it is possible to realize high-density nozzles, high-viscosity liquid discharge, prevention of crosstalk, improvement in manufacturing suitability, etc. A load is applied by the weight member provided at the end of the piezoelectric element, and a large amount of expansion / contraction displacement of the multilayer piezoelectric element can be directed to the bonding surface side, so that a larger excluded volume can be obtained. As a result, it is possible to further increase the density of the nozzle and to discharge a highly viscous liquid.

  A third aspect of the present invention relates to the droplet discharge head according to the first or second aspect, wherein the planar shape of the pressure chamber viewed from the diaphragm side is defined by the minimum value / maximum value of the distance between the walls in the pressure chamber. When the ratio value is the aspect ratio of the pressure chamber, the pressure chamber satisfies the following formula: 0.45 ≦ aspect ratio ≦ 0.89.

  When the pressure chamber aspect ratio defined by the ratio (minimum value / maximum value) of the minimum value and the maximum value of the distance between walls (line-of-sight distance) in the pressure chamber satisfies the condition of 0.45 ≦ aspect ratio ≦ 0.89 Thus, the ease of displacement of the diaphragm due to the shape is combined with the large displacement amount of the multilayer piezoelectric body, and the displacement amount of the diaphragm with respect to the applied pressure can be made relatively large. That is, the volume change amount (excluded volume) of the pressure chamber per unit occupation area can be increased. Therefore, according to the present invention, unprecedented high-viscosity liquid discharge capability or downsizing of the head can be realized.

  A droplet discharge head according to a fourth aspect of the invention includes a plurality of nozzles that discharge droplets, and a plurality of pressure chambers that are provided corresponding to the plurality of nozzles and are filled with liquid discharged from each nozzle. A diaphragm that constitutes one wall surface of the pressure chamber, and a plurality of stacked piezoelectric bodies that are independently bonded and fixed to positions corresponding to the plurality of pressure chambers on the diaphragm. The aspect ratio of the pressure chamber defined by the minimum value / maximum value of the distance between the walls in the pressure chamber with respect to the planar shape of the pressure chamber viewed from the diaphragm side is expressed by the following equation: 0.45 ≦ aspect ratio ≦ 0. No. 89 is satisfied, and the liquid in the pressure chamber is pressurized via the diaphragm by the expansion and contraction of the multilayer piezoelectric body, and the liquid droplets are ejected from the nozzle.

  According to the fourth aspect of the present invention, the ability to deform the pressure chamber with the multilayer piezoelectric body is improved while preventing the crosstalk between the nozzles by the separated arrangement structure of the multilayer piezoelectric body. And high-viscosity liquid can be discharged.

  According to a fifth aspect of the present invention, the liquid droplet ejection head according to any one of the first to fourth aspects is used as an ink jet recording head, and an ink is ejected from the nozzle while moving a recording medium relative to the ink jet recording head. An inkjet recording apparatus is provided that records an image on the recording medium by ejecting droplets.

  In the implementation of the present invention, the form of the recording head is not particularly limited, and may be a shuttle type recording head that performs printing while the recording head reciprocates in a direction substantially orthogonal to the feeding direction of the recording medium. A full-line type recording head having a nozzle row in which a plurality of nozzles for ejecting ink are arranged in a direction substantially orthogonal to the feeding direction of the recording medium over a length corresponding to the entire width of the recording medium may be used.

  The “full-line type recording head (droplet discharge head)” is usually arranged along a direction perpendicular to the relative feeding direction of the recording medium, but is in a predetermined direction with respect to the direction perpendicular to the feeding direction. There may also be a mode in which the recording head is arranged along an oblique direction having the angle. Further, the arrangement form of the nozzles in the recording head is not limited to a single line arrangement, and may be a matrix arrangement composed of a plurality of columns. 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, It includes various media 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 or the like is formed by an inkjet recording apparatus. In this specification, the term “printing” represents the concept of forming an image in a broad sense including characters.

  The moving means (conveying means) for moving the recording medium and the recording head relatively moves the recording medium relative to the stopped (fixed) recording head, and moves the recording head relative to the stopped recording medium. Either the aspect or the aspect in which both the recording head and the recording medium are moved is included.

  According to the present invention, the laminated piezoelectric body is individually arranged on the diaphragm for each pressure chamber communicating with the nozzle, and one end on the opposite side to the joint surface of the diaphragm is added with an unconstrained end or a weight member. Since the end structure is used, crosstalk between nozzles can be prevented, the nozzle density can be increased, high-viscosity liquid can be discharged, and manufacturing can be facilitated.

  Also, according to another aspect of the present invention, the pressure chambers communicating with the nozzles are shaped so that the aspect ratio of the planar shape satisfies the condition of 0.45 or more and 0.89 or less, and each pressure chamber is individually provided. Since the multilayer piezoelectric body is provided, it is possible to realize unprecedented high-viscosity liquid discharge capacity or downsizing of the head by the synergistic effect of the large driving force of the multilayer piezoelectric body and the ease of displacement of the diaphragm due to the shape .

  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 according to an embodiment of the present invention. As shown in the figure, the inkjet recording apparatus 10 includes a print unit 12 having a plurality of print heads 12K, 12C, 12M, and 12Y provided for each ink color, and each print head 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feeding unit 18 for supplying recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle of the printing unit 12 A suction belt transport unit 22 that is disposed to face a surface (ink ejection surface) and transports the recording paper 16 while maintaining the flatness of the recording paper 16, and a print detection unit 24 that reads a printing result by the printing unit 12, A paper discharge unit 26 that discharges recorded recording paper (printed matter) to the outside.

  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. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

  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. Then, the suction chamber 34 is sucked by the fan 35 to be a negative pressure, whereby the recording paper 16 on the belt 33 is sucked and held.

  When the power of a motor (not shown in FIG. 1, described as 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 rotates in the clockwise direction in FIG. , And the recording paper 16 held on the belt 33 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.

  The printing unit 12 is a so-called full line type head in which line type heads having a length corresponding to the maximum paper width are arranged in a direction orthogonal to the paper feed direction (see FIG. 2). Although a detailed structural example will be described later (FIGS. 3 to 5), each of the print heads 12K, 12C, 12M, and 12Y is a recording paper of the maximum size targeted by the inkjet recording apparatus 10 as shown in FIG. The line head includes a plurality of ink discharge ports (nozzles) arranged over a length exceeding at least one side of 16.

  A print head 12K corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 16 (hereinafter referred to as the paper transport direction). , 12C, 12M, and 12Y are arranged, and color images can be formed on the recording paper 16 by ejecting the color inks from the print heads 12K, 12C, 12M, and 12Y while conveying the recording paper 16, respectively.

  As described above, according to the printing unit 12 in which the full line head that covers the entire paper width is provided for each ink color, the operation of relatively moving the recording paper 16 and the printing unit 12 in the sub-scanning direction is performed. The image can be recorded on the entire surface of the recording paper 16 only by performing it 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 print head reciprocates in the main scanning 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 a print head that discharges light ink such as light cyan and light magenta.

  As shown in FIG. 1, the ink storage / loading unit 14 includes tanks (ink tanks) that store inks of colors corresponding to the print heads 12K, 12C, 12M, and 12Y, and each ink tank is not shown. The print heads 12K, 12C, 12M, and 12Y communicate with each other through the pipe line. 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.

  The print detection unit 24 includes an image sensor for imaging the droplet ejection result of the print unit 12, and functions as a means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor. The print detection unit 24 is configured by a line sensor or an area sensor having a light receiving element array that is wider than at least the ink ejection width (image recording width) by the print heads 12K, 12C, 12M, and 12Y.

  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 things that cause dye molecules to break by blocking the paper holes by pressurization. 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.

  Next, the structure of the print head will be described. Since the structures of the print heads 12K, 12C, 12M, and 12Y provided for the respective ink colors are common, the print heads are represented by reference numeral 50 in the following.

  FIG. 3 (a) is a plan perspective view showing an example of the structure of the print head 50, and FIG. 3 (b) is an enlarged view of a part thereof. 3C is a perspective plan view showing another example of the structure of the print head 50, and FIG. 4 is a cross-sectional view showing the three-dimensional configuration of the ink chamber unit (along line 4-4 in FIG. 3A). FIG.

  In order to increase the dot pitch printed on the recording paper surface, it is necessary to increase the nozzle pitch in the print head 50. As shown in FIGS. 3A to 3C and FIG. 4, the print head 50 of this example includes a plurality of inks including nozzles 51 from which ink droplets are ejected and pressure chambers 52 corresponding to the nozzles 51. The chamber units 53 have a structure in which the chamber units 53 are arranged in a staggered matrix (two-dimensional), thereby achieving an increase in the apparent nozzle pitch density.

  That is, in the print head 50 according to the present embodiment, as shown in FIGS. 3A and 3B, the plurality of nozzles 51 that eject ink correspond to the entire width of the print medium in a direction substantially orthogonal to the print medium feed direction. This is a full line head having one or more nozzle rows arranged over a length of the same.

  However, the arrangement structure of the nozzles is not limited to the illustrated example in carrying out the present invention. Further, as shown in FIG. 3C, a length corresponding to the full width of the recording paper 16 is obtained by arranging short head units 50 'in which a plurality of nozzles 51 are arranged two-dimensionally in a staggered manner. You may comprise the full line head which has the nozzle row of.

  As shown in FIGS. 3 (a) to 3 (c), the pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape, and nozzles are formed at both corners on the diagonal line. 51 and a supply port 54 are provided.

  Further, as shown in FIG. 4, each pressure chamber 52 communicates with a common channel 55 through a supply port 54. The common channel 55 communicates with an ink tank (not shown in FIG. 4, described as reference numeral 60 in FIG. 6) serving as an ink supply source, and the ink supplied from the ink tank 60 passes through each common pressure 55 via each pressure. It is distributed and supplied to the chamber 52. In addition to the ink tank 60, a sub tank (not shown) or the like may be provided near the print head 50 or integrally with the print head 50. The sub-tank has a function of improving a damper effect and refill that prevents fluctuations in the internal pressure of the head.

  As shown in FIG. 4, the nozzle 51 communicates with the pressure chamber 52 via the nozzle flow path 56. On the vibration plate 57 constituting the top surface of the pressure chamber 52, the laminated piezoelectric body 58 is joined at a position corresponding to each pressure chamber 52 as an independent structure. The laminated piezoelectric body 58 has a structure in which thin piezoelectric plates and internal electrodes are alternately stacked. The diaphragm 57 of this example also serves as a common electrode for the laminated piezoelectric body 58.

  Further, a flexible substrate 59 is connected to the end (the upper end in FIG. 4) on the free end side of the laminated piezoelectric body 58. A wiring pattern corresponding to the individual electrodes of the multilayer piezoelectric body 58 is formed on the flexible substrate 59, and a driving voltage is applied to each multilayer piezoelectric body 58 via the flexible substrate 59. When the driving voltage is applied to the multilayer piezoelectric body 58, the multilayer piezoelectric body 58 expands and contracts in the stacking direction, and the ink in the pressure chamber 52 is pressurized along with the displacement, and the ink is ejected from the nozzle 51. Is done. When ink is ejected, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54.

  Note that the flexible substrate 59 is made of a flexible resin material and is connected across a plurality of laminated piezoelectric bodies 58, but does not constrain the upper ends of the individual laminated piezoelectric bodies 58. Therefore, the upper end portion (the end portion on the opposite side of the bonding surface of the vibration plate 57) of each laminated piezoelectric body 58 is in a free end state that can be displaced in the pressurizing direction of the vibration plate 57.

  As shown in FIG. 5, a large number of ink chamber units 53 having the above-described structure are fixed along the row direction along the main scanning direction and the oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. The print head 50 of this example is realized by a structure arranged in a grid pattern with an arrangement pattern.

  As shown in FIG. 5, the pitch of the nozzles projected so as to be aligned in the main scanning direction by a structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along the direction of an angle θ with respect to the main scanning direction. P 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 corresponding to the entire width of the paper (recording paper 16), (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially driven from one side to the other. (3) The nozzles are divided into blocks and sequentially driven from one side to the other for each block, etc., and one line (one row) in the width direction of the paper (direction perpendicular to the paper conveyance direction). Driving a nozzle that prints a dot line or a line composed of a plurality of rows of dots) 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, by relatively moving the above-mentioned full line head and the paper, printing of one line (a line formed by one line of dots or a line composed of a plurality of lines) formed by the above-described main scanning is repeatedly performed. This is defined as sub-scanning.

  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 for supplying ink, 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 in the middle of the conduit connecting the ink tank 60 and the print head 50 in order to remove foreign matter 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 print head 50 or integrally with the print 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 nozzle surface cleaning means.

  The maintenance unit including the cap 64 and the cleaning blade 66 can be moved relative to the print head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the print head 50 as necessary. The

  The cap 64 is displaced up and down relatively with respect to the print head 50 by an elevator mechanism (not shown). The cap 64 is raised to a predetermined raised position when the power is turned off or during printing standby, and is brought into close contact with the print head 50, thereby covering the nozzle surface 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 (surface of the nozzle plate) of the print 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 air bubbles are mixed into the ink (pressure chamber) in the print head 50, the cap 64 is applied to the print head 50, and the ink in the pressure chamber (ink mixed with air bubbles) is removed by suction with the suction pump 67, and suction is performed. The removed ink is sent to the collection tank 68. In this suction operation, the deteriorated ink with increased viscosity (solidified) is sucked out when the ink is initially loaded into the head or when the ink is used after being stopped for a long time.

  That is, if the print 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, and the ejection drive actuator (laminated piezoelectric body 58) Ink does not discharge from the nozzle 51 even when the operation is performed. Therefore, before this state is reached (within the range of viscosity that allows ink to be ejected by the operation of the actuator), the actuator is operated toward the ink receiver to eject ink in the vicinity of the nozzle whose viscosity has increased. Discharge "is performed. In order to prevent foreign matter from entering the nozzle 51 by the wiper rubbing operation after the dirt on the nozzle plate surface is cleaned by a wiper such as a cleaning blade 66 provided as a nozzle surface cleaning means. 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, ink cannot be ejected from the nozzle 51 even if the actuator is operated. . In such a case, a suction means for sucking the ink in the pressure chamber 52 with a pump or the like is brought into contact with the nozzle surface of the print head 50, and an operation of sucking ink mixed with bubbles or thickened ink is performed.

  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.

  The cap 64 described with reference to FIG. 6 functions as a suction unit and can also function as a preliminary discharge ink receiver.

[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 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 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 (print data) to the head driver 84. Necessary signal processing is performed in the print controller 80, and the ejection amount and ejection timing of the ink droplets of the print 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 a single processor.

  The head driver 84 drives the stacked piezoelectric bodies 58 of the print heads 12K, 12C, 12M, and 12Y for each color based on the print data given from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  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 print control unit 80 performs various corrections on the print head 50 based on information obtained from the print detection unit 24 as necessary.

[Head manufacturing method]
Here, a method for manufacturing the print head 50 will be described.

  In recent years, surface mounting technology is a technology in which sub-millimeter-sized elements are arranged on a circuit board with a high accuracy of about 10 μm and adhered. By using this type of mounting apparatus, it is possible to accurately arrange sub-millimeter-square stacked piezoelectric elements at the positions of the individual pressure chambers of the inkjet head.

  In the production of the print head 50 of this example, the laminated piezoelectric body 58 or a further one having a weight member (denoted by reference numeral 92 in FIG. 8) attached to one end thereof (the end opposite to the diaphragm bonding surface) is used as described above. The mounting device is used to position the pressure plate of the vibration plate 57, temporarily fix each of them, and then UV bond or heat bond all at once.

  As shown in FIG. 8, by providing a weight member 92 on the non-restraining end side opposite to the joint surface of the multilayer piezoelectric body 58 with the vibration plate 57, the expansion and contraction displacement of the multilayer piezoelectric body 58 is reduced to the pressure chamber 52 side ( Efficiently transmitted to the lower part of FIG. In FIG. 8, reference numeral 94 denotes a pressure chamber plate that forms the side wall surface of the pressure chamber 52, and reference numeral 95 denotes a flow path plate that forms the lower surface of the pressure chamber 52 and forms the nozzle flow path 56.

  Further, as shown in FIGS. 8 and 9, a protrusion 97 is provided on the piezoelectric material bonding surface side of the vibration plate 57, and the laminated piezoelectric material 58 is formed using the uneven shape of the vibration plate 57 by the protrusion 97. Even if it arranges roughly, the aspect in which the pressurization state of the pressure chamber 52 aligns substantially constant irrespective of the dispersion | variation in the arrangement | positioning is also preferable.

  As described with reference to FIG. 4, how to take out the electrodes from the multilayer piezoelectric body 58 is drawn out to the free end side of the multilayer piezoelectric body 58 and individually wired to the outside via the flexible substrate 59 and the like.

  Further, the common electrode (common electrode) is electrically connected to the metal diaphragm 57 through an adhesive. In addition, conduction | electrical_connection by an adhesive agent may be conducted by the effect of surface roughness, and a conductive adhesive agent may be used.

  In the print head 50 of this example, since the stacked piezoelectric body 58 having about 10 layers is used, the piezoelectric body is operated in an expansion / contraction mode (a mode using displacement in the d33 direction). As shown in FIG. 9, the piezoelectric material may be stacked in a structure in which piezoelectric materials are stacked in the vertical direction (normal direction) with respect to the joint surface of the diaphragm 57. A laminated piezoelectric body 58 ′ shown in FIG. 5 may have a structure in which piezoelectric bodies are stacked in a lateral direction (a direction perpendicular to the normal line) with respect to the joint surface of the diaphragm 57. In this case, the piezoelectric body is used in a mode that utilizes displacement in the d31 direction.

[Synergy of the shape of the pressure chamber and the laminated piezoelectric material]
As described with reference to FIGS. 3A to 3C, the pressure chamber 52 of the print head 50 according to the present embodiment has a substantially square planar shape when viewed from the actuator side (see through).

  As represented by a square, the pressure chamber 52 having an aspect ratio of about 1 is combined with the ease of displacement of the diaphragm 57 by the large driving force of the laminated piezoelectric body 58, and the generated pressure is further increased. Improvement is realized. As a result, unprecedented high-viscosity liquid can be discharged, or the head can be miniaturized.

  Here, the relationship between the ease of displacement of the diaphragm 57 and the shape of the pressure chamber 52 will be described.

  In order to apply not only to the square but also to various pressure chambers, the aspect ratio is defined as follows for the planar shape of the pressure chamber.

  That is, the aspect ratio of the pressure chamber is defined by the ratio of the minimum value / maximum value of the in-plane distance between walls (line-of-sight distance).

  As shown in FIG. 11 (a), when the planar shape of the pressure chamber 100 is a square, the minimum value of the inter-wall distance matches the diameter of the inscribed circle 102, and the maximum value of the inter-wall distance is the circumscribed circle 104. It matches the diameter. Therefore, the aspect ratio of the pressure chamber 100 is 1 / √2≈0.707.

Further, as shown in FIG. 11B, when the planar shape of the pressure chamber 110 is a rectangle, and the vertical and horizontal sides are a: b (a ≧ b), the aspect ratio is b / √ (a ² + b ² )

  When a pressure chamber of equal area with restrained four sides (a × b = constant) and a ratio a: b = 1: k, assuming that isobaric load is applied to the diaphragm of the pressure chamber, the maximum displacement of the diaphragm The amount (relative value) is as shown in the table of FIG. Even when vibration is applied using a piezoelectric body, it can be considered that the characteristics are almost the same as those in the table of FIG.

FIG. 13A to FIG. 13C are graphs showing the displacement characteristics of the diaphragm when a uniform pressure is applied to the diaphragm having the same area. FIG. 13A shows the relationship between the vertical dimension a of the pressure chamber and the displacement, the horizontal axis indicates the vertical dimension a, and the vertical axis indicates the standardized displacement. FIG. 13B shows the relationship between the ratio k and displacement, where the horizontal axis is the ratio k (= b / a). FIG. 13C shows the aspect ratio b / √ (a ² + b ² ) on the horizontal axis, and shows the relationship between the aspect ratio and displacement.

  FIG. 14 is a data table showing the correspondence between the ratio k and the aspect ratio.

  As shown in FIG. 13B, the displacement becomes maximum when k = 1. With respect to this maximum displacement, 0.5 ≦ k ≦ 2, more preferably, the amplitude of the graph of FIG. 13 (b) falls within a 40% reduction range (within −40% of the maximum value), more preferably 2/3 ≦ k ≦ 1.5, which is a 20% reduction range (within −20% of the maximum value), is an efficient pressure chamber shape.

  Since the shape of the pressure chamber is not limited to a rectangle, it can be applied to any shape including a rhombus, a hexagon, and other polygons. Ratio ≦ 0.89, more preferably 0.55 ≦ aspect ratio ≦ 0.83 (see FIG. 13C and FIG. 14).

  In the above embodiment, an inkjet recording apparatus using a page-wide full-line head having a nozzle row having a length corresponding to the entire width of the recording medium has been described. However, the scope of application of the present invention is not limited to this, and the short length The present invention can also be applied to an ink jet recording apparatus using a shuttle head that records an image while reciprocating the recording head.

  In the above description, an ink jet recording apparatus is 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 present invention can be applied to a photographic image forming apparatus that applies a developing solution to a photographic paper in a non-contact manner. That is, the present invention can be widely applied not only to ink but also to other image forming apparatuses including a droplet discharge process in which a processing liquid, a functional liquid, or other liquid is applied to a medium. Other than the inkjet method, the present invention is applied to various types of image forming apparatuses such as an optical photographic print production apparatus, a thermal transfer recording apparatus having a line head, an LED electrophotographic printer, and a silver salt photographic printer having an LED line exposure head. It is possible.

  The scope of application of the present invention is not limited to the image forming apparatus, and can be applied to various liquid ejection apparatuses such as a coating apparatus that applies a treatment liquid and other liquids to a medium using a droplet ejection head.

1 is an overall configuration diagram of an ink jet recording apparatus 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 structural example of print head Enlarged view of the main part of Fig. 3 (a) Plane perspective view showing another structural example of the print head Sectional view along line 4-4 in Fig. 3 (a) Enlarged view showing the nozzle arrangement of the print head shown in FIG. Schematic diagram showing the configuration of an ink supply system in the inkjet recording apparatus according to the present embodiment Main block diagram showing the system configuration of the inkjet recording apparatus 10 of this example Sectional drawing which shows the example which provided the weight member in the one side edge part of a laminated piezoelectric material Sectional drawing which shows the example which provided the protrusion in the piezoelectric material joining surface of a diaphragm Sectional view showing an example of the stacking direction of a stacked piezoelectric body Diagram used to explain the aspect ratio of the pressure chamber Chart showing the relationship between the shape of the pressure chamber and the displacement of the diaphragm A graph showing the relationship between the pressure chamber shape (vertical dimension a) and the displacement of the diaphragm A graph showing the relationship between the pressure chamber shape (aspect ratio k) and the displacement of the diaphragm Graph showing the relationship between pressure chamber shape (aspect ratio) and diaphragm displacement Chart showing correspondence between shape of pressure chamber (aspect ratio k) and aspect ratio

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device 12 ... Printing part, 12K, 12C, 12M, 12Y ... Print head, 14 ... Ink storage / loading part, 16 ... Recording paper, 50 ... Print head, 51 ... Nozzle, 52 ... Pressure chamber, 54 DESCRIPTION OF SYMBOLS Supply port 56 ... Nozzle flow path 57 ... Diaphragm 58 ... Multilayer piezoelectric body 59 ... Flexible substrate 92 ... Weight member 97 ... Protrusion

Claims (5)

A plurality of nozzles for discharging droplets;
A plurality of pressure chambers provided corresponding to the plurality of nozzles and filled with liquid discharged from each nozzle;
A diaphragm constituting one wall surface of the pressure chamber;
A plurality of stacked piezoelectric bodies that are independently bonded and fixed at respective positions corresponding to the plurality of pressure chambers on the diaphragm;
An end of the laminated piezoelectric body opposite to the joint surface with the diaphragm is in a non-constrained end state that is displaceable in the pressurizing direction to the diaphragm by the laminated piezoelectric body, and the laminated piezoelectric body A liquid droplet ejection head configured to pressurize the liquid in the pressure chamber through the vibration plate by the expansion and contraction displacement of the liquid and discharge the liquid droplets from the nozzle. A plurality of nozzles for discharging droplets;
A plurality of pressure chambers provided corresponding to the plurality of nozzles and filled with liquid discharged from each nozzle;
A diaphragm constituting one wall surface of the pressure chamber;
A plurality of stacked piezoelectric bodies that are independently bonded and fixed at respective positions corresponding to the plurality of pressure chambers on the diaphragm;
A weight member that inhibits displacement of the end portion in the pressurizing direction to the diaphragm is provided at an end of the multilayer piezoelectric body opposite to the joint surface with the diaphragm, and the expansion and contraction of the multilayer piezoelectric body is provided. A droplet discharge head configured to pressurize a liquid in the pressure chamber through the vibration plate by displacement and discharge a droplet from the nozzle. When the aspect ratio of the pressure chamber is a ratio value defined by the minimum value / maximum value of the distance between the walls in the pressure chamber with respect to the planar shape of the pressure chamber viewed from the diaphragm side, the pressure chamber is expressed by the following equation: ,
0.45 ≦ aspect ratio ≦ 0.89
The droplet discharge head according to claim 1, wherein: A plurality of nozzles for discharging droplets;
A plurality of pressure chambers provided corresponding to the plurality of nozzles and filled with liquid discharged from each nozzle;
A diaphragm constituting one wall surface of the pressure chamber;
A plurality of stacked piezoelectric bodies that are independently bonded and fixed at respective positions corresponding to the plurality of pressure chambers on the diaphragm;
The aspect ratio of the pressure chamber defined by the minimum / maximum value of the distance between the walls in the pressure chamber with respect to the planar shape of the pressure chamber viewed from the diaphragm side is expressed by the following equation:
0.45 ≦ aspect ratio ≦ 0.89
And a liquid droplet ejection head configured to eject liquid droplets from the nozzles by pressurizing the liquid in the pressure chamber through the diaphragm by expansion and contraction displacement of the multilayer piezoelectric body. 5. The recording is performed by using the droplet discharge head according to claim 1 as an ink jet recording head and discharging ink droplets from the nozzle while moving a recording medium relative to the ink jet recording head. An ink jet recording apparatus for recording an image on a medium.

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