JP2008137341A - Liquid droplet ejection head and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize the high-frequency ejection of a high-viscosity microdroplet by suppressing the excessive elongation of a liquid column. <P>SOLUTION: This liquid droplet ejection head ejects a liquid droplet from a nozzle communicating with a liquid channel. The nozzle is composed of a plurality of hole portions which are almost uniformly arranged around a nozzle shaft. In the hole portion, an opening ridge line, which is directed toward the nozzle shaft or its vicinity from the side of the ejection-side opening edge of the nozzle, is provided on the side of liquid droplet ejection. In the opening ridge line, a nozzle shaft-side end is shifted to the side of the liquid channel, and obliquely inclined with respect to the nozzle shaft. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a droplet discharge head and an image forming apparatus, and more particularly to a droplet discharge head and an image forming apparatus that discharge droplets from nozzles communicating with a liquid flow path.

  Inkjet recording apparatuses are widely used because they have low noise during recording operations, low running costs, and can record high-quality images on a wide variety of recording media. This recording apparatus performs recording by discharging ink from a recording head toward a recording medium. A plurality of nozzles are formed in the recording head. For example, by applying a pressure change to the ink in the pressure chamber using the displacement of a piezoelectric element as an ejection element, ink droplets are ejected from the nozzle communicating with the pressure chamber. The

  In an ink jet recording apparatus, when an ink droplet is ejected from a nozzle, a phenomenon (tailing phenomenon) occurs in which the ink droplet elongates in the ejection direction and forms a columnar shape (tailing phenomenon), which accompanies the main ink droplet. The generated fine ink droplets (satellite) may be generated, leading to a decrease in image quality. Particularly in the case of high-viscosity ink (for example, about 10 to 15 cp), the liquid column tends to extend excessively, satellites frequently occur, leading to deterioration in image quality and a decrease in ejection frequency. Therefore, various devices have been devised in the nozzle shape in order to suppress excessive elongation of the liquid column.

For example, in Patent Document 1, a cylindrical portion that faces the center of the tip of the ink flow path, a slit-shaped hole that is located around the cylindrical part and communicates with the ink flow path, and an outer wall of the circular column and the slit-shaped hole There has been proposed a nozzle shape that includes a connecting portion that connects the nozzles and is formed so that the cross-sectional shape of the nozzle is substantially annular. According to such a nozzle shape, ink is ejected in a cylindrical shape from the slit-shaped hole, and eventually, the ink is collected into a spherical shape to form a flying droplet and land on the recording medium.
JP-A-8-1930

  However, in the conventional nozzle shape described in Patent Document 1, since the surface tension pressure of the ink can be increased by the slit-shaped hole portion, the excessive extension of the liquid column can be suppressed. Since the ink is ejected as a cylindrical ink (cylindrical liquid film), a large droplet is formed as a droplet. This is thought to be due to the fact that bubbles are inevitably involved in the liquid column and the droplet, and the substantial size of the droplet increases accordingly. Further, if it is attempted to reduce the width of the slit-shaped hole portion in order to reduce the droplet size, the flow path resistance at the slit-shaped hole portion increases, and a large discharge force is required, leading to deterioration in discharge efficiency. On the other hand, if the width of the slit-shaped hole is too narrow, clogging is likely to occur due to ink thickening.

  In addition, the conventional nozzle shape requires a certain distance from the nozzle shaft to the slit-shaped hole, and therefore the discharge speed at the slit-shaped hole is very small due to the processing accuracy of the slit-shaped hole. The error becomes a factor causing a deviation in the flying direction of the droplet.

  Thus, with the conventional nozzle shape, it is difficult to realize high-frequency ejection of high-viscosity fine droplets while suppressing excessive elongation of the liquid column.

  The present invention has been made in view of such circumstances, and provides a droplet discharge head and an image forming apparatus that suppress excessive extension of a liquid column and enable high-frequency discharge of high-viscosity fine droplets. With the goal.

  In order to achieve the above object, the invention according to claim 1 is a liquid droplet ejection head that ejects liquid droplets from a nozzle communicating with a liquid flow path, and the nozzles are substantially evenly arranged around a nozzle axis. The hole includes an opening ridge line on the liquid droplet discharge side from the discharge side opening edge side of the nozzle toward the nozzle axis or the vicinity thereof, and the opening ridge line is a nozzle. Provided is a droplet discharge head characterized in that an axial end is shifted to the liquid flow path side and is inclined obliquely with respect to the nozzle axis.

  According to the present invention, the central portion of the nozzle on the droplet discharge side is recessed on the side opposite to the droplet discharge side (the liquid flow channel side) by the opening ridge line on the droplet discharge side of each hole substantially on the nozzle axis. Therefore, the average curvature of the meniscus of each hole in a steady state can be kept high. As a result, the surface tension pressure of the meniscus can be maintained at a high level, and excessive extension of the liquid column is suppressed and the generation of satellites is prevented, so that the image quality is improved, and the discharge frequency and refill properties are also improved. Can also be improved. As a result, high-frequency discharge of high-viscosity fine droplets can be realized.

  A second aspect of the present invention is the liquid droplet ejection head according to the first aspect, wherein a columnar portion having the nozzle axis as a substantially central axis is provided in the nozzle, and the droplets of the columnar portion are provided. The opening ridge line extends from the discharge side surface.

  According to the aspect of the second aspect, the nozzle shaft side end of the meniscus formed in the hole can be reliably pinched, and excessive extension of the liquid column can be effectively prevented.

  According to a third aspect of the present invention, in the liquid droplet ejection head according to the first aspect, a columnar cavity that connects the plurality of holes to each other is provided so that the nozzle axis is a substantially central axis. It is characterized by.

  According to the aspect of claim 3, since the flow path resistance of the columnar cavity portion is extremely high, an effect substantially equivalent to the case where the portion corresponding to the cavity portion is a non-hole portion can be obtained. .

  In order to achieve the above object, an invention according to claim 4 provides an image forming apparatus comprising the droplet discharge head according to any one of claims 1 to 3. To do.

  According to the present invention, the central portion of the nozzle on the droplet discharge side is recessed on the side opposite to the droplet discharge side (the liquid flow channel side) by the opening ridge line on the droplet discharge side of each hole substantially on the nozzle axis. Therefore, the average curvature of the meniscus of each hole in a steady state can be kept high. As a result, the surface tension pressure of the meniscus can be maintained at a high level, and excessive extension of the liquid column is suppressed and the generation of satellites is prevented, so that the image quality is improved, and the discharge frequency and refill properties are also improved. Can also be improved. As a result, high-frequency discharge of high-viscosity fine droplets can be realized.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is an overall configuration diagram showing an outline of an ink jet recording apparatus which is an embodiment of an image forming apparatus according to the present invention. As shown in FIG. 1, the inkjet recording apparatus 10 includes a printing unit 12 having a plurality of recording heads 12K, 12C, 12M, and 12Y provided for each ink color, and each recording head 12K, 12C, 12M, and 12Y. An ink storage / loading unit 14 for storing ink to be supplied to the paper, a paper feeding unit 18 for supplying the recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle surface of the printing unit 12 An adsorption belt conveyance unit 22 that is arranged opposite to the (ink ejection surface) and conveys the recording paper 16 while maintaining the flatness of the recording paper 16, a print detection unit 24 that reads a printing result by the printing unit 12, and a print And a paper discharge unit 26 for discharging the printed 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.

  In the case of an apparatus configuration using roll paper, a 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 arranged on the print surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  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.

  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 a portion facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 is flat. It is configured to make.

  The belt 33 has a width that is greater 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, an adsorption 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.

  The power of a motor (not shown) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that the belt 33 is driven in the clockwise direction in FIG. The 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 blowing method of spraying 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 transport mechanism instead of the suction belt transport unit 22 is also conceivable, when the print area is transported by a roller / nip, the roller comes into contact with the print surface of the paper immediately after printing, so that the image blurs. There is a problem that it is easy. Therefore, as in this example, suction belt conveyance that does not contact the image surface in the printing 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 (main scanning direction) orthogonal to the paper transport direction (sub-scanning direction). In the recording heads 12K, 12C, 12M, and 12Y constituting the printing unit 12, ink discharge ports (nozzles) are arranged over a length exceeding at least one side of the maximum size recording paper 16 targeted by the inkjet recording apparatus 10. Line type head.

  Recording corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side (left side in FIG. 1) along the conveyance direction (paper conveyance direction) of the recording paper 16. Heads 12K, 12C, 12M, and 12Y are arranged. A color image can be formed on the recording paper 16 by discharging the color inks from the recording heads 12K, 12C, 12M, and 12Y while conveying the recording paper 16.

  Thus, according to the printing unit 12 in which the full line head that covers the entire width of the paper is provided for each ink color, the recording paper 16 and the printing unit 12 are relatively moved in the paper transport direction (sub-scanning direction). It is possible to record an image on the entire surface of the recording paper 16 by performing this operation only once (that is, by one sub-scan). Thereby, high-speed printing is possible and productivity can be improved as compared with the shuttle type head in which the recording head reciprocates in the direction (main scanning direction) orthogonal to the paper transport direction.

  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 are added as necessary. May be. For example, it is possible to add a recording head that discharges light ink such as light cyan and light magenta.

  As shown in FIG. 1, the ink storage / loading unit 14 has tanks that store inks of colors corresponding to the recording heads 12K, 12C, 12M, and 12Y, and each tank has a pipeline that is not shown. Via the recording heads 12K, 12C, 12M, and 12Y. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means, etc.) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. is doing.

  The print detection unit 24 includes an image sensor (line sensor or the like) for imaging the droplet ejection result of the print 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 recording 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 includes 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.

  The print detection unit 24 reads the test pattern printed by the recording heads 12K, 12C, 12M, and 12Y for each color, and detects the ejection of each recording head. 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 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 uneven surface 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 sorting means (not shown) for switching the paper discharge path in order 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. ing. 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, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

  Since the recording heads 12K, 12C, 12M, and 12Y provided for each ink color have the same configuration, the recording head is represented by the reference numeral 50 in the following.

  Next, the configuration of the recording head 50 will be described. FIG. 2 is a partial cross-sectional view showing the main configuration of the recording head 50. As shown in FIG. 2, the recording head 50 is provided with a pressure chamber 52 filled with ink for each nozzle (ejection port) 51. The pressure chamber 52 and the nozzle 51 communicate with each other through a nozzle channel 62. Although not shown, there is a mode in which the pressure chamber 52 and the nozzle 51 communicate directly with each other without using the nozzle flow path 62. A plurality of nozzles 51 are arranged in a two-dimensional shape (matrix shape) at high density on the nozzle plate 60 that forms the nozzle surface of the recording head 50. The structure of the nozzle 51 which is a characteristic part of the present invention will be described in detail later.

  A supply port 54 is formed at one end of the pressure chamber 52, and the pressure chamber 52 communicates with the common liquid chamber 55 through the supply port 54. A plurality of pressure chambers 52 communicate with the common liquid chamber 55. The common liquid chamber 55 is a storage section in which ink supplied from the ink storage / loading section 14 of FIG. 1 is stored, and the ink in the common liquid chamber 55 is distributed and supplied to each pressure chamber 52.

  One wall surface (the upper surface in FIG. 2) of the pressure chamber 52 is constituted by the diaphragm 56, and a position corresponding to the pressure chamber 52 on the diaphragm 56 (that is, a position facing the pressure chamber 52 with the diaphragm 56 interposed therebetween). ) Is provided with a piezoelectric element 58 provided with individual electrodes 57. The diaphragm 56 also serves as a common electrode for the piezoelectric element 58. For the piezoelectric element 58, a piezoelectric body such as a piezo is preferably used.

  With this configuration, when a predetermined drive voltage is applied to the piezoelectric element 58, the ink in the pressure chamber 52 is pressurized by the deformation of the diaphragm 56 due to the expansion and contraction of the piezoelectric element 58 and communicates with the pressure chamber 52. Ink droplets are ejected from the nozzle 51 that performs the operation.

  In the present embodiment, the piezoelectric recording head 50 that discharges ink using the piezoelectric element 58 has been described. However, the present invention is not limited to this. For example, the present invention can also be applied to a thermal method in which ink is ejected using a heating element such as a heater or other various types of recording heads.

  Next, the structure of the nozzle 51 which is a characteristic part of the present invention will be described in detail. FIG. 3 is a plan view of the nozzle 51 as viewed from the nozzle surface 50a side. 4 is a cross-sectional view taken along line 4-4 in FIG. 3, and corresponds to an enlarged cross-sectional view of the peripheral portion of the nozzle in FIG. FIG. 5 is a perspective view showing the internal structure of the nozzle 51. In FIGS. 4 and 5, the ink discharge direction is displayed so as to face the upper side in the vertical direction.

  As shown in these drawings, the nozzle 51 according to the present embodiment is composed of two holes 70 and 70 that are evenly arranged around the nozzle axis P. Each hole 70 communicates with the same nozzle flow path 62.

  Specifically, a columnar portion 72 having the nozzle axis P as a central axis and two connecting portions 74 and 74 arranged evenly around the columnar portion 72 are provided inside the cylindrical region 60 a of the nozzle plate 60. Thus, two holes 70, 70 are defined by these. That is, two connecting parts 74 and two hole parts 70 are alternately arranged around the columnar part 72. The columnar portion 72 and the connecting portion 74 may be configured integrally with the nozzle plate 60 or may be configured as separate bodies.

  The columnar portion 72 is disposed at a position facing the center of the tip of the nozzle channel 62. Further, the flat surface 72a on the ink discharge side of the columnar portion 72 is disposed at a position shifted from the nozzle surface 50a toward the nozzle flow path 62, and the flat surface 72a and the nozzle surface 50a are formed on the ink discharge side of the connecting portion 74. Are connected via an inclined surface 74a.

  The hole 70 has an opening ridge line (a boundary line with the inclined surface 74 a) 76 from the ink discharge side opening edge 51 a of the nozzle 51 toward the nozzle axis P (that is, in the radial direction). The end of the opening ridge 76 on the nozzle axis P side is connected to the flat surface 72 a of the columnar portion 72. In other words, the opening ridge line 76 extends from the flat surface 72 a of the columnar portion 72. Further, the opening ridge line 76 is not perpendicular to the nozzle axis P, but the end portion on the nozzle axis P side is shifted to the nozzle flow path 62 side and is inclined obliquely with respect to the nozzle axis P. By such an opening ridge line 76 of each hole 70, the central portion of the ink ejection side of the nozzle 51 is recessed on the side opposite to the ink ejection side (nozzle flow path 62 side), and is substantially restricted to one point on the nozzle axis P. It has become a shape.

  FIG. 6 is a diagram illustrating a state where ink droplets are ejected from the nozzle 51.

  As described above, the nozzle 51 of the present embodiment has a central portion on the ink ejection side of the nozzle 51 that is recessed on the side opposite to the ink ejection side (nozzle channel 62 side), and is substantially restricted to one point on the nozzle axis P. Therefore, in the steady state before the ink discharge operation is started, the end of the meniscus in each hole 70 on the nozzle axis P side is the nozzle channel, as shown in FIG. Since pinching (holding and clipping) is performed at a deep position on the 62 side, the average curvature of the meniscus can be kept high.

  In particular, the meniscus is pinched (held, clipped) more easily by the ridgelines of the flat surface 72a on the ink ejection side of the columnar portion 72 disposed at the center of the nozzle 51.

  When the piezoelectric element 58 is driven, the meniscus in each hole 70 is drawn into the nozzle channel 62 side, and then the ink in the pressure chamber 52 is pressurized, as shown in FIG. A liquid column 80 extending from each hole 70 in a direction facing each other oblique to the ink ejection direction parallel to the nozzle axis P is formed. Thereafter, each liquid column 80 gradually grows and collides, but the momentum in the horizontal direction (direction perpendicular to the ink ejection direction) of each liquid column 80 cancels each other, so that only the momentum in the ink ejection direction remains. Accordingly, as shown in FIG. 6C, a liquid column 82 extending in the ink discharge direction is formed. At this time, since the columnar portion 72 facing the center of the tip of the nozzle flow path 62 inhibits the ink flow in the ink ejection direction, ink supply to the liquid column 82 is also inhibited. Accordingly, excessive extension of the liquid column 82 is suppressed, and as shown in FIG. 6D, a droplet 84 having a volume corresponding to the liquid column 82 flies from the nozzle 51 toward the ink ejection direction. Thereafter, as shown in FIG. 6E, the meniscus of each hole 70 returns to the steady state.

  As described above, according to the present embodiment, the central portion of the ink ejection side of the nozzle 51 is recessed toward the nozzle flow path 62 by the opening ridge line 76 on the ink ejection side of each hole 70, and is substantially one point on the nozzle axis P. Therefore, the end of the meniscus in each hole 70 on the nozzle shaft P side can be pinched at a deep position on the nozzle flow path 62 side, and the average curvature of the meniscus in a steady state can be increased. Can be held. The surface tension pressure is the product of the surface tension coefficient and the surface average curvature (that is, surface tension pressure = surface tension coefficient × surface average curvature). The higher the meniscus surface tension pressure, the more the formation and development of the initial constriction of the liquid column. The liquid runs out quickly and quickly. In addition, the higher the surface tension pressure of the meniscus, the shorter the time required for refilling, so that the responsiveness increases and high-frequency ejection becomes possible. In other words, by maintaining the average meniscus curvature in a steady state at a high level, it becomes possible to maintain the surface tension pressure of the meniscus at a high level, suppressing excessive expansion of the liquid column and preventing the occurrence of satellites. As a result, the image quality can be improved, and the ejection frequency and refill properties can be improved. As a result, high-frequency discharge of high-viscosity fine droplets can be realized.

  In particular, in this embodiment, the ink formed after the liquid column 80 extending obliquely with respect to the ink ejection direction from each hole 70 collides with the columnar portion 72 provided at the center of the tip of the nozzle channel 62. Since the ink supply to the liquid column 82 in the ejection direction is hindered, excessive extension of the liquid column 82 can be effectively suppressed.

  Further, according to the present embodiment, with respect to the cross-sectional area of the nozzle 51 perpendicular to the nozzle axis P, the non-hole region (the columnar portion 72 and the connecting portions 74 and 74) is the same as the hole region (hole portions 70 and 70). The non-hole region is formed so wide that the cylindrical liquid film is not formed inside the nozzle 51. That is, the cross section of the nozzle 51 perpendicular to the nozzle axis P has a shape in which the solid region (non-hole region) is constricted at the center, and the solid region area and the liquid region (non-hole region) area are approximately the same. It is arranged with good balance. For this reason, the size (volume) of the droplets discharged from the nozzle 51 can be reduced, and fine droplets can be discharged. In addition, a wide cross-sectional area of each hole 70, 70 can be ensured, and the discharge efficiency is improved by reducing the flow resistance, and nozzle clogging due to ink thickening can be prevented.

  In addition, according to the present embodiment, the distance from the nozzle axis P to the hole 70 is the same as that of the liquid column 82 (see FIG. 6C) formed after the liquid column 80 extending from each hole 70 collides. It can be configured as short as the radius of the cross section perpendicular to the ink ejection direction (several μm to several tens μm), and the influence on the deviation in the flight direction due to processing accuracy can be suppressed.

  In the present embodiment, it is preferable that the liquid repellent treatment is performed on the flat surface 72 a of the columnar portion 72 and the inclined surface 74 a of the connecting portion 74 and the lyophilic treatment is performed on the inner wall surface of the hole portion 70. The shape of the meniscus formed in the hole 70 can be stabilized.

  7-12 is explanatory drawing which showed each modification (1st-6th modification) of this embodiment. These drawings (excluding FIG. 11B) are plan views when viewed from the nozzle surface 50a side, and FIG. 11B is a cross-sectional view taken along the line 11b-11b in FIG. 11A. . 7 to 12, the same reference numerals are given to the portions common to FIGS. 3 and 4.

  In the nozzle 51 </ b> A as the first modification shown in FIG. 7, three hole portions 70 are arranged around the hexagonal columnar portion 72. Thus, the number of the hole portions 70 arranged around the columnar portion 72 is not limited to two, and may be three or more. Further, the shape of the columnar portion 72 is not limited to a square columnar shape as in the present embodiment, and may be a hexagonal columnar shape, other polygonal columnar shapes, a cylindrical shape, an elliptical columnar shape, or the like as in the present modification.

  The nozzle 51B as the second modification shown in FIG. 8 is not a circular planar shape as in the present embodiment, but a rectangular planar shape. Moreover, it is not limited to these, and other polygonal shapes and elliptical planar shapes may be used.

  The nozzle 51C as the third modified example shown in FIG. 9 is not provided with the columnar portion 72 as in the present embodiment, and the opening ridge line 76 of each hole 70 is the nozzle center portion (that is, the nozzle axis P). Cross over) Although not shown, there is also an aspect in which the tip part of the ink discharge side of the columnar part 72 is degenerated into a needle shape so that the area of the flat surface 72a becomes zero. In either case, an effect equivalent to that of the present embodiment can be obtained.

  A nozzle 51D as a fourth modification shown in FIG. 10 is provided with a columnar cavity 90 at a position corresponding to the columnar section 72 of the present embodiment, and two holes 70 and 70 are formed in the cavity 90. It communicates through. The flow path resistance in such a cavity 90 is extremely high, and the central portion of the ink ejection side of the nozzle 51 is recessed toward the nozzle flow path 62 by the opening ridge line 76 of each hole 70 so that it is substantially at one point on the nozzle axis P. The same shape as in the present embodiment can be obtained without changing the narrowed shape.

  In the nozzle 51E as the fifth modified example shown in FIG. 11, the opening ridgeline 78 on the ink ejection side of each hole 70 is configured as a curved closed curve. The opening ridge line 78 is a ridge line from the discharge side opening edge 51a side of the nozzle 51E toward the nozzle axis P (that is, in the radial direction), and the ink discharge side central portion of the nozzle 51 is formed by the opening ridge line 78 of each hole 70. However, it is a shape that is recessed toward the nozzle flow path 62 and substantially narrowed to one point on the nozzle axis P, and the same effect as in the present embodiment can be obtained.

  The nozzle 51F as the sixth modification shown in FIG. 12 corresponds to a mode in which the third modification and the fifth modification are combined, and the opening ridge line 78 of each hole 70 is the nozzle center (on the nozzle axis P). It is possible to obtain the same effect as the present embodiment.

  Although the liquid droplet ejection head and the image forming apparatus of the present invention have been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications are made without departing from the gist of the present invention. Of course.

Overall configuration diagram showing outline of inkjet recording apparatus Partial cross-sectional view showing the main configuration of the recording head 50 Top view when the nozzle is viewed from the nozzle side Sectional view along line 4-4 in FIG. Perspective view showing the internal structure of the nozzle Diagram showing how ink droplets are ejected from nozzles Explanatory drawing which showed the 1st modification Explanatory drawing which showed the 2nd modification Explanatory drawing showing a third modification Explanatory drawing showing a fourth modification Explanatory drawing showing a fifth modification Explanatory drawing showing a sixth modification

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 50 ... Recording head, 51 ... Nozzle, 52 ... Pressure chamber, 54 ... Supply port, 55 ... Common flow path, 56 ... Vibrating plate, 57 ... Individual electrode, 58 ... Piezoelectric element, 60 ... Nozzle plate 62 ... Nozzle flow path, 70 ... Hole, 72 ... Columnar part, 74 ... Connection part, 76 ... Opening edge line

Claims (4)

A droplet discharge head for discharging droplets from a nozzle communicating with a liquid flow path,
The nozzle is composed of a plurality of holes arranged substantially evenly around the nozzle shaft,
The hole has an opening ridge line on the droplet discharge side from the discharge side opening edge side of the nozzle toward the nozzle axis or the vicinity thereof,
The liquid droplet ejection head is characterized in that the opening ridge line has an end portion on the nozzle axis side shifted to the liquid flow path side and is inclined obliquely with respect to the nozzle axis. A columnar part having the nozzle axis as a substantially central axis is provided inside the nozzle,
The droplet discharge head according to claim 1, wherein the opening ridge line extends from a surface of the columnar portion on the droplet discharge side.   2. The liquid droplet ejection head according to claim 1, wherein a columnar cavity that communicates the plurality of holes with each other is provided with the nozzle axis as a substantially central axis.   An image forming apparatus comprising the droplet discharge head according to any one of claims 1 to 3.

Images