JP2008018675A - Inkjet recording head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording head having a high drive frequency and high printing quality. <P>SOLUTION: A liquid flow channel is constituted in a structure including a plurality of grooves 5 which are formed by engraving, from the vicinity of both sides of ejection pressure generating elements 2, the substrate having the ejection pressure generating elements arranged toward supply ports. A shielding object blocking the flow of liquid is arranged in a part of the flow channel formed in a region other than the plurality of grooves. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet recording head that performs recording by ejecting liquid such as ink as droplets and attaching it to a recording material such as paper.

  An ink jet recording head applied to an ink jet recording method (liquid jet recording method) is generally a fine discharge port (orifice), a liquid flow path leading to it, and a discharge pressure generation provided in a part of the liquid flow path. A plurality of discharge pressure generation units including elements are provided. For example, an electrothermal conversion element is used as the discharge pressure generating element. In this ink jet recording head, a drive signal is applied to the electrothermal conversion element, whereby the electrothermal conversion element causes a rapid temperature rise exceeding the nucleate boiling of the ink, thereby generating bubbles in the ink. The ink droplets are ejected by the pressure generated at this time. A drive signal is applied to each electrothermal conversion element in accordance with recording information, whereby ink is selectively ejected from each ejection port.

  In such an ink jet recording head, it is desired to obtain a high-definition and high-quality image. For this purpose, it is desirable that small droplets can be discharged from the discharge ports, and that the droplets can always be discharged from each discharge port at the same volume and discharge speed.

  As a method for achieving this, Patent Documents 1 to 3 disclose a method in which bubbles generated by an electrothermal conversion element are communicated with outside air to discharge droplets. According to this method, the size of the ejected droplet is determined by the size of the ejection port and the distance between the electrothermal transducer and the orifice surface (hereinafter referred to as “OH distance”), and is almost constant. Droplets having a small size can be ejected.

  In an ink jet recording head that ejects droplets by such a method, it is preferable to shorten the OH distance in order to eject smaller droplets and form a higher-definition image.

  In an ink jet recording head, the discharged liquid is usually divided into a plurality of droplets, which are divided into droplets having the largest volume (hereinafter referred to as main droplets) and other droplets (hereinafter referred to as satellites). In general, satellites cause a reduction in image quality, so it is desirable to suppress the generation of satellites. In order to suppress the generation of this satellite, it is effective to shorten the OH distance.

  In order to obtain a desired droplet size, it is necessary to set the OH distance accurately and with good reproducibility.

  As a method for manufacturing an ink jet recording head that can set the OH distance to a predetermined distance accurately and with good reproducibility, there is a method disclosed in Patent Document 4. In this manufacturing method, the liquid flow path mold is formed of a soluble resin on the substrate on which the discharge pressure generating element is formed. Thereafter, a coating resin containing an epoxy resin that is solid at room temperature is dissolved in a solvent, and this is solvent-coated on a resin layer that can be dissolved to form a coating that forms a channel wall that partitions each liquid channel A resin layer is formed. Thereafter, a discharge port is opened in the coating resin layer. Finally, the soluble resin layer is eluted and removed.

  FIG. 13 is a schematic diagram of the ink jet recording head thus manufactured. FIG. 13A is a perspective view showing the ink jet recording head with the orifice plate 23 formed by the coating resin layer removed, and FIG. 13B shows the AA ′ line in FIG. It is the expanded sectional view cut | disconnected along.

  This ink jet recording head has a substrate 21 on which a plurality of ejection pressure generating elements 22 are formed on the front side surface. The substrate 21 is provided with a supply port 26 formed as a through hole penetrating the substrate 21 by etching using the back mask layer 25 as a mask. The discharge pressure generating elements 22 are formed in a line at a predetermined pitch on both sides of the supply port 26 on the front side surface of the substrate 21 along the longitudinal direction of the opening. This ink jet recording head is a so-called side shooter type recording head, and the orifice plate 23 formed on the substrate 21 has a discharge port 24 opened at a position facing the surface of each discharge pressure generating element 22. .

  In addition, such an ink jet recording head is required to have a high-definition and high-quality image, and at the same time, a high speed is also desired. For this purpose, in order to increase the ejection frequency (driving frequency), it is necessary to refill the ink in the flow path after droplet ejection, that is, to refill the ink quickly. In order to speed up the refill, it is desired to reduce the flow resistance of the ink supply path between the supply port and the discharge port.

  As described above, Patent Document 5 and Patent Document 6 are characterized in that the flow path height near the supply port is higher than the flow path height near the discharge pressure generating element as a configuration for reducing the flow resistance of the ink supply path. Inkjet recording heads and methods for manufacturing the same have been proposed. In the manufacturing methods described in these publications, the height of the flow path in the vicinity of the supply port is increased by digging a corresponding portion of the substrate between the vicinity of the supply port and the vicinity of the discharge pressure generating element. This increases the cross-sectional area of the ink supply path, thus reducing its flow resistance. As described above, the configurations described in these publications are effective techniques for realizing high speed.

  As a method of manufacturing a recording head having such a configuration, there is a method in which a supply port which is a digging or a through hole is formed on a substrate before forming an orifice plate constituting a flow path and a discharge port on the substrate.

  In addition, there is a method of digging after forming the discharge port and forming a supply port which is a through hole in the substrate. In this case, a hole is formed in the substrate from the back surface to the front surface, and then the digging portion is formed.

  Further, the digging portion may be formed by dry etching or the like, and the liquid flow path may be subsequently formed by the method disclosed in Patent Document 4 described above.

  Incidentally, the recording heads described in Patent Document 5 and Patent Document 6 have the following problems. This will be described in detail with reference to FIG.

  FIG. 11 is a view showing a structure in the vicinity of a discharge pressure generating element of a conventional inkjet head. In FIG. 11, 1 is a substrate on which discharge pressure generating elements are formed, 2 is a discharge pressure generating element, 3 is an orifice plate on which discharge ports and flow path walls are formed. Reference numeral 5 denotes a flow path, 6 denotes a dug portion in which the substrate 1 is dug, 7 denotes a supply port, and 8 denotes a discharge port.

  As described above, in the structure shown in FIG. 11, the distance OH between the discharge pressure generating element 2 and the orifice surface is short, the portion constituting the flow path of the substrate 1 is dug, and the dug portion 6 is formed. Therefore, the flow path 5 has a high height and a low flow resistance. Therefore, an ink jet head having excellent printing characteristics and a high refill frequency is possible.

  However, since the flow resistance of the flow path 5 is low in the structure shown in FIG. 11, when the discharge pressure generating element is driven and ink is discharged, bubbles 9 are formed on the flow path side and the opposite side of the flow path as shown in FIG. There was a problem of growing asymmetrically. At this time, the pressure applied to the discharged liquid becomes asymmetrical, and the liquid does not fly in the ideal discharge direction (usually perpendicular to the orifice surface), but with a certain inclination from the ideal discharge direction. The problem of end up occurs. In this case, since the liquid droplets are displaced from the desired position and land on the recording material, the print quality is lowered.

  As described above, in the ink jet recording head, the ejected liquid is usually divided into a plurality of parts and divided into main droplets and satellites.

  When the pressure applied to the liquid becomes asymmetric, not only the ejection direction of the main droplet is deviated from the ideal direction, but also a problem that the ejection directions of the main droplet and the satellite are deviated occurs.

In this case, since the main droplet and the satellite are separated and land on the recording material, the shape of the droplet landed on the recording material is deviated from an ideal perfect circular shape, and the print quality is lowered.
Japanese Patent Laid-Open No. 4-10940 JP-A-4-10941 JP-A-4-10942 Japanese Patent Registration No. 3143307 JP-A-10-095119 Japanese Patent Laid-Open No. 10-034928

  The present invention solves the above-mentioned problems, and the OH distance is short, the flow resistance of the flow path is small, the droplets fly in the direction perpendicular to the orifice surface, that is, the drive frequency is high and the print quality is high. An inkjet head is provided.

To achieve the above objective,
The ink jet recording head of the present invention includes a supply port through which liquid is supplied from the outside, a discharge port through which the liquid is discharged, and the discharge port that communicates with the liquid supplied from the supply port to the discharge port. A liquid flow path for guiding, and a discharge pressure generating section for generating a pressure for discharging the liquid provided in a part of the liquid flow path, and the supply port constitutes the discharge pressure generating section An inkjet recording head formed as a through-hole in a substrate on which a discharge pressure generating element is formed,
The liquid flow path has a structure including a plurality of grooves formed by digging the substrate from the vicinity of both sides of the discharge pressure generating element toward the supply port.

  The height LH1 of the flow path formed on the plurality of grooves and the height LH2 of the flow path formed in a region other than the plurality of grooves satisfy LH1> LH2.

  When the plurality of grooves are two and the width of the flow path formed on the grooves is W1, and the width W2 of the flow path formed in a region other than the plurality of grooves, LH1 × W1 × 2> LH2 × W2.

  A part of the flow path formed in a region other than the plurality of grooves may have a shield that prevents the liquid flow.

  In the ink jet recording head of this embodiment, the OH distance and the flow resistance of the ink flow path can be freely adjusted, and pressure is uniformly applied to the ejected ink.

  Therefore, even if the OH distance is shortened so that a smaller droplet can be ejected and a higher-definition image can be formed, the flow resistance of the ink supply path can be reduced. It is possible to increase the recording speed.

  In addition, the ejected droplets fly in an almost ideal ejection direction (usually perpendicular to the orifice surface), and the dot shape of the droplets that land on the paper surface is an ideal object that is close to a perfect circle. The quality can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
An ink jet recording head according to a first embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a case where an electrothermal conversion element (heater) is used as the discharge pressure generating element and ink is used as the liquid will be described.

  FIG. 1 is a plan view of the ink jet recording head of the present invention, and FIG. 2 is a cross-sectional view taken along the line A-A 'of FIG. 3 is a cross-sectional view taken along the line B-B 'of FIG. 4 is a cross-sectional view taken along the line C-C 'of FIG.

  1 to 4, 1 is a substrate made of silicon or the like, 2 is a heater, 3 is an orifice plate in which ink flow path walls and discharge ports are formed.

  4 is an ink flow path having a low flow path composed of a substrate surface on which a heater is disposed and a region sandwiched between orifice plates, and 5 is a flow channel composed of a region where the substrate is dug and a region sandwiched between orifice plates. This is a high ink flow path.

  6 is a digging portion (groove) in which the substrate 1 is dug, 7 is a supply port, and 8 is a discharge port.

  Usually, the substrate 1 is formed with a semiconductor circuit including a transistor for driving the heater 2 and an electrode pad for electrically connecting the recording head to the recording apparatus main body side. For ease of illustration, illustration is omitted in each figure. Further, FIG. 1 shows only the side wall of the flow path formed of a part of the orifice plate 3, and the surface of the orifice plate 3 on which the discharge port 8 and the discharge port are arranged is not shown.

  As shown in FIG. 1, in the ink jet recording head of this embodiment, a plurality of heaters 2 that generate pressure for ejecting ink are arranged on a substrate at desired intervals.

  The heaters 2 are arranged in a line on both sides along the longitudinal direction of the supply port 7 and arranged at a predetermined pitch, and the arrangement of the discharge pressure generating elements 2 in both the lines is shifted by a half pitch. As shown in FIGS. 2 and 4, a discharge port 8 is disposed at a position facing the surface of each heater 2.

  As shown in FIGS. 1, 3, and 4, a part of the front surface of the substrate 1 on which the heater 2 is formed has a desired width from the vicinity of both ends of the heater 2 to the supply port 7 in FIG. 3. The digging portion 6 is formed by digging at a depth indicated by X.

  An ink flow path 5 having a high flow path height is formed from a region between the digging portion 6 and the orifice plate 3. The flow path height of the ink flow path 5 having a high flow path height is indicated by LH1 in FIG.

  On the other hand, the flow path 4 having a low flow path height is formed from a region between the surface of the substrate 1 on which the heater 2 is disposed and the orifice plate 3 as shown in FIGS. 1, 2, and 4. The flow path height of the ink flow path 4 having a low flow path height is indicated by LH2 in FIG.

  Further, the width of the ink flow path 5 having a high flow path height is indicated by W1 in FIG. 4, and the width of the ink flow path 4 having a low flow path height is indicated by W2 in FIG.

  As described above, the ink jet recording head according to the present embodiment has a structure including a plurality of dug portions 6 formed by dug the substrate 1 from both sides of the heater 2 toward the supply port 7.

  The flow resistance of the ink flow path can be changed by adjusting the depth and width of the digging portion 6.

  Therefore, by adopting this configuration, it is possible to freely set the flow resistance of the ink flow path that affects the drive frequency while freely setting the OH distance that affects image formation.

  Ink is supplied from the supply port 7 to the heater 2 via the ink flow path 4 having a low flow path height and the ink flow path 5 having a high flow path height.

  When the dimensions of the ink flow path 4 having a low flow path height and the ink flow path 5 having a high flow path height satisfy the following relationship (Equation 1), the ink flow path 5 having a high flow path height: Therefore, the ink flows mainly from the supply port 7 to the vicinity of the heater 2 via the ink flow path 5 having a high flow path height. Supplied.

LH1 × W1 × 2> LH2 × W2 (Formula 1)
This is shown in FIG.

  In the case of such a configuration, FIGS. 6 to 8 show states when the heater is driven and ink is ejected. 6 to 8, reference numeral 9 denotes bubbles and 10 denotes the ejected ink.

  6 is a plan view of the ink jet recording head of the present invention, and FIG. 7 is a cross-sectional view taken along the line A-A 'of FIG. FIG. 8 is a cross-sectional view taken along the line B-B ′ of FIG. 6.

  Bubbles grow mainly in the direction of low flow resistance, that is, toward the ink flow path 5 having a high flow path height as shown in FIGS. 6 to 8, and the region of the ink flow path 4 having a low flow path height. Then it doesn't grow very much.

  Since the ink flow path 5 having a high flow path height is arranged on both sides of the heater 2, the bubbles are almost parallel to the longitudinal direction of the supply port 7 and also in the direction perpendicular to the longitudinal direction of the supply port 7. Grows symmetrically.

  At this time, since the pressure applied to the ejected ink is also applied substantially uniformly, the ejected ink 10 flies almost in the ideal ejection direction (usually perpendicular to the orifice surface).

  In such a discharge state, the discharge directions of the main droplet and the satellite are substantially the same, and the dot shape of the droplet that has landed on the paper surface is an ideal thing close to a perfect circle.

  As described above, in the ink jet recording head of this embodiment, the OH distance and the flow resistance of the ink flow path can be freely adjusted, and pressure is uniformly applied to the ejected ink.

  Therefore, even if the OH distance is shortened so that a smaller droplet can be ejected and a higher-definition image can be formed, the flow resistance of the ink supply path can be reduced. It is possible to increase the recording speed.

  In addition, the ejected liquid droplets fly substantially perpendicular to the ideal ejection direction, and the dot shape of the liquid droplets that have landed on the paper surface becomes an ideal thing close to a perfect circle, and the image quality can be improved.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS.

  In the second embodiment, in addition to the structure shown in the first embodiment, the ink flow path 4 having a low flow path height has a shield 11 that blocks the flow of liquid. The presence of the shield 11 prevents the ink flow from the heater 2 toward the supply port 7 in the ink flow path 4 having a low flow path height. Therefore, the growth of bubbles from the heater to the supply port during ink discharge is suppressed, and the bubbles during ink discharge are both parallel to the longitudinal direction of the supply port 7 and in the direction perpendicular to the longitudinal direction of the supply port 7. Grows more symmetrically. Further, the uniformity of the pressure applied to the ejected ink is improved, and as a result, the image quality can be further improved.

  An ink jet recording head having the structure shown in the first embodiment was prototyped, and the dot shape was observed. The digging was performed by dry etching, and LH1 was 15 μm, LH2 was 6 μm, W1 was 9 μm, and W2 was 20 μm.

  The ink jet recording head thus obtained satisfies LH1 × W1 × 2> LH2 × W2, and even if printing is performed at a driving frequency of 20 kHz, a printed matter with a dot diameter close to a perfect circle and high image quality can be obtained. Obtained.

Schematic diagram (plan view) of the ink jet recording head of the first embodiment of the present invention FIG. 2 is a schematic diagram of the ink jet recording head according to the first embodiment of the present invention, and is a cross-sectional view cut along the line A-A ′ of FIG. 1. FIG. 2 is a schematic view of the ink jet recording head according to the first embodiment of the present invention, and is a cross-sectional view taken along line B-B ′ of FIG. 1. FIG. 2 is a schematic diagram of the ink jet recording head according to the first embodiment of the present invention, and is a cross-sectional view taken along the line C-C ′ of FIG. 1. Schematic diagram (plan view) for explaining the effect of the ink jet recording head according to the first embodiment of the present invention. Schematic diagram (plan view) for explaining the effect of the ink jet recording head according to the first embodiment of the present invention. FIG. 7 is a schematic diagram for explaining the effect of the ink jet recording head according to the first embodiment of the present invention, and is a cross-sectional view taken along the line A-A ′ of FIG. 6. FIG. 7 is a schematic diagram for explaining the effect of the ink jet recording head according to the first embodiment of the present invention, and is a cross-sectional view taken along the line B-B ′ of FIG. 6. Schematic diagram (plan view) of an ink jet recording head according to a second embodiment of the present invention. FIG. 10 is a schematic diagram of an ink jet recording head according to a second embodiment of the present invention, and is a cross-sectional view taken along line A-A ′ of FIG. 9. Schematic diagram (cross-sectional view) of a conventional inkjet recording head Schematic diagram (cross-sectional view) for explaining problems of a conventional ink jet recording head FIG. 13A is a schematic view of a conventional ink jet recording head, FIG. 13A is a perspective view showing a state where an orifice plate is removed, and FIG. 13B is a cross-sectional view taken along the line AA ′ in FIG. FIG.

Explanation of symbols

1 Substrate 2 Heater (Discharge pressure generating element)
3 Orifice plate 4 Ink flow path with low flow path height 5 Ink flow path with high flow path height 6 Digging part (groove)
7 Supply Port 8 Discharge Port 9 Bubble 10 Discharged Ink 11 Shielding Object 21 Substrate 22 Discharge Pressure Generating Element 23 Orifice Plate 24 Discharge Port 25 Back Mask Layer 26 Supply Port

Claims (4)

A supply port through which liquid is supplied from the outside, a discharge port through which the liquid is discharged, a liquid flow path that communicates with the discharge port and guides the liquid supplied from the supply port to the discharge port, and the liquid A discharge pressure generating unit that is provided in a part of the flow path and generates a pressure for discharging the liquid, and the supply port forms a discharge pressure generating element that constitutes the discharge pressure generating unit. An ink jet recording head formed as a through hole in the substrate,
The ink jet recording head according to claim 1, wherein the liquid flow path includes a plurality of grooves formed by digging the substrate from the vicinity of both sides of the discharge pressure generating element toward the supply port.   The height LH1 of the flow path formed on the plurality of grooves and the height LH2 of the flow path formed in a region other than the plurality of grooves satisfy LH1> LH2. The inkjet recording head described.   When the plurality of grooves are two and the width of the flow path formed on the grooves is W1, and the width W2 of the flow path formed in a region other than the plurality of grooves, LH1 × W1 × 2> LH2 The inkjet recording head according to claim 2, wherein the inkjet recording head is × W2.   4. The ink jet recording head according to claim 1, wherein a part of the flow path formed in a region other than the plurality of grooves has a shielding member for blocking a liquid flow. 5.

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