JP2018140521A - Liquid discharge head and liquid discharge method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make air bubbles more securely communicate with the atmosphere, and suppress occurrence of cavitation.SOLUTION: A liquid discharge head includes: a foaming chamber 9 in which a depth wall 16 is provided on the downstream side in a liquid supply direction X and a liquid introduction port 15 is provided on the upstream side in the direction; a discharge flow passage 11 which communicates with the foaming chamber 9 and includes a discharge port discharging a liquid; and a heating resistor element 14 which faces the discharge flow passage 11 across the foaming chamber 9 and gives energy for discharging the liquid. The air bubbles generated in the foaming chamber 9 by the energy of the heating resistor element 14 first communicate with air flowing from the discharge flow passage 11 in a volume reduction process after the air bubbles is grown to the maximum volume. A flow passage cross-sectional area of a first region 18A on the upstream side of a middle point LC of the whole length L in the liquid supply direction X of the discharge flow channel 11 is smaller than a flow passage cross-sectional area of a second region 18B on the downstream side.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a liquid ejection head and a liquid ejection method for ejecting liquid, and more particularly to a liquid ejection head that ejects liquid by the energy of a heating resistance element.

  In an ink jet recording apparatus, a method of discharging a liquid such as ink using a heating resistor element is widely adopted. In this type of liquid ejection device, liquid is ejected from the liquid ejection head by generating bubbles on the heating resistor element. When recording is performed with this type of liquid ejection device, bubbles generated on the heating resistor element may disappear at that location and cavitation may occur. Cavitation may affect the life of the heating resistor element.

  Patent Document 1 discloses a liquid discharge head in which the center of the discharge port is offset from the center of the heat generation resistance element to the downstream side in the ink supply direction in order to suppress the influence of cavitation on the heat generation resistance element. Since the atmosphere communicates with the atmosphere at the downstream side of the bubbles with respect to the ink supply direction, the bubbles are not easily separated during the bubble defoaming process. Therefore, cavitation due to the divided bubbles is less likely to occur on the heating resistance element, and the influence on the life of the heating resistance element is suppressed.

JP 2008-238401 A

  In the liquid discharge head described in Patent Document 1, whether or not the air is communicated is unstablely changed due to a slight change in the offset amount with respect to the discharge port of the heating resistor element. When the air does not communicate with each other, cavitation is likely to occur because the bubbles are divided. Although it is conceivable to control the bubbles so as to communicate with the atmosphere more reliably by increasing the positional accuracy of the discharge port and the heating resistor element, it may be difficult in the manufacturing method. In the case of a circular discharge port, it is conceivable to reduce the meniscus by increasing the diameter of the discharge port, thereby promoting air communication, but the influence on the discharge amount is great.

  An object of the present invention is to provide a liquid discharge head that more reliably causes bubbles to communicate with the atmosphere and is less likely to cause cavitation.

  The liquid discharge head of the present invention includes a foaming chamber having a back wall on the downstream side in the liquid supply direction and a liquid introduction port on the upstream side, and a discharge flow having a discharge port that communicates with the foaming chamber and discharges liquid. And a heating resistance element that opposes the discharge flow path across the foaming chamber and imparts energy for discharge to the liquid. Bubbles generated in the foaming chamber due to the energy of the heating resistance element communicate with the air flowing in from the discharge passage in the volume reduction process after growing to the maximum volume. The channel cross-sectional area of the first region upstream of the midpoint of the total length of the discharge channel in the liquid supply direction is smaller than the channel cross-sectional area of the second region downstream.

  Bubbles are formed on the heating resistor element, but since there is a back wall on the downstream side of the foaming chamber, the bubbles are displaced to the upstream side, and the heating resistor element is formed so as to be thicker on the upstream side. . In the present invention, the channel cross-sectional area of the first region upstream of the midpoint of the total length in the liquid supply direction of the discharge channel is smaller than the channel cross-sectional area of the second region downstream. For this reason, the part where the distance from the heating resistance element of the meniscus of the liquid entering the foaming chamber from the discharge flow path becomes the minimum is formed on the upstream side of the discharge flow path. Therefore, the meniscus reaches the bubbles earlier, and air communication occurs early. Therefore, according to the present invention, it is possible to provide a liquid discharge head in which air communication is likely to occur before the bubbles that cause cavitation are generated, and cavitation is less likely to occur.

1 is a perspective view of an ink jet recording apparatus according to an embodiment of the present invention. FIG. 2 is a partially broken perspective view of a liquid discharge head used in the recording apparatus of FIG. 1. It is sectional drawing along the AA line of FIG. FIG. 3 is a plan view of the vicinity of the discharge port of the liquid discharge head according to the first embodiment. 6 is a cross-sectional view showing changes in bubbles and meniscuses in Example 1. FIG. 6 is a plan view of the vicinity of an ejection opening of a liquid ejection head of Comparative Example 1. FIG. 6 is a cross-sectional view showing changes in bubbles and meniscus in Comparative Example 1. FIG. FIG. 6 is a plan view of the vicinity of a discharge port according to a modified example of the first embodiment. FIG. 6 is a plan view of the vicinity of an ejection opening of a liquid ejection head according to a second embodiment. 6 is a cross-sectional view showing changes in bubbles and meniscuses in Example 2. FIG. 10 is a plan view of the vicinity of an ejection opening of a liquid ejection head of Comparative Example 2. FIG. 10 is a cross-sectional view showing changes in bubbles and meniscus in Comparative Example 2. FIG. FIG. 10 is a plan view of the vicinity of a discharge port according to a modification of the second embodiment.

  Hereinafter, a liquid discharge head and a recording apparatus according to an embodiment of the invention will be described with reference to the accompanying drawings. Although the embodiments described below relate to an ink jet recording head that performs recording by discharging ink, the present invention can be widely applied to a liquid discharging head that discharges a liquid such as ink using the thermal energy of a heating resistor. The liquid discharge head according to the present invention is the first to communicate with the air flowing from the discharge flow path in the volume reduction process after the bubbles generated in the foaming chamber by the energy of the heating resistance element grow to the maximum volume. In the following description, the direction parallel to the liquid supply direction of the foaming chamber is the X direction, the direction parallel to the central axis of the discharge channel is the Z direction, and the width direction of the foaming chamber, that is, the direction perpendicular to the X direction and the Z direction is the Y direction. That's it.

  FIG. 1 is a schematic perspective view of an ink jet recording apparatus (hereinafter referred to as a recording apparatus 1) according to an embodiment of the present invention. The recording apparatus 1 has a carriage 2 that is slidably guided and supported in the A direction. The carriage 2 is equipped with a liquid ejection head 3 that performs recording by ejecting ink to the recording medium P from a plurality of ejection ports 12 by applying energy to the ink in accordance with a recording signal. In addition, four ink cartridges 4 containing four colors of ink supplied to the liquid discharge head 3 are detachably mounted on the carriage 2. The carriage 2 on which the liquid ejection head 3 is mounted is reciprocated in the main scanning direction A perpendicular to the conveyance direction B of the recording medium P by a driving force of a carriage motor (not shown). Recording is performed over the entire width of the recording medium P by discharging ink from the liquid discharge head 3 while the liquid discharge head 3 scans in the main scanning direction A.

  2 is a partially broken perspective view of the liquid discharge head 3 shown in FIG. 1, and FIG. 3 is a cross-sectional view of the liquid discharge head 3 taken along line AA in FIG. The liquid discharge head 3 includes a substrate 5 made of silicon and a discharge port forming member 6 provided on the substrate 5. An ink supply path 7 that penetrates the substrate 5 is formed in the substrate 5, and an opening on the surface of the ink supply path 7 that faces the discharge port forming member 6 is an elongated rectangular ink supply port 8 that extends in the Y direction. It has become. A plurality of foaming chambers 9 and a common liquid chamber 10 provided in common for the plurality of foaming chambers 9 are formed between the substrate 5 and the discharge port forming member 6. The common liquid chamber 10 communicates with the ink supply port 8 and the plurality of foaming chambers 9. The discharge port forming member 6 is provided with a discharge flow path 11 which is a through hole for discharging the ink stored in the foaming chamber 9. The discharge channel 11 has a constant channel cross section in the Z direction. The discharge channel 11 communicates with the foaming chamber 9. The end of the discharge channel 11 opposite to the foaming chamber 9 is a discharge port 12 through which ink is discharged. The height h1 of the foaming chamber 9 is 16 μm, and the thickness h2 of the discharge port forming member 6 in the foaming chamber 9 is 12 μm.

  A heating resistance element 14 is disposed at a position facing the foaming chamber 9 of the substrate 5 so as to face the ejection flow path 11 with the foaming chamber 9 interposed therebetween and to impart thermal energy for ejection to the ink. The heating resistance elements 14 are provided corresponding to the respective foaming chambers 9 and arranged at a pitch of 600 dpi, one row on each side in the longitudinal direction (Y direction) of the ink supply port 8. The ink supplied from the ink supply path 7 of the substrate 5 is supplied to the foaming chamber 9 via the common liquid chamber 10. The heating resistance element 14 is driven, the ink in the foaming chamber 9 is heated, and bubbles are formed in the liquid (in the ink) above the heating resistance element 14. The bubbles give kinetic energy to the ink in the discharge flow path 11 and the ink is discharged from the discharge port 12.

  Next, some examples and comparative examples in which the configuration of the discharge flow path 11 is different in the above-described embodiment will be described. In the following description, “upstream side” and “downstream side” are defined with reference to the liquid supply direction (X direction). 4, 6, 8, 9, 11, and 13, the upstream side is the lower side of the drawing, the downstream side is the upper side of the drawing, and in FIGS. 5, 7, 10, and 12, the upstream side is the right side of the drawing. Means.

Example 1
FIG. 4 is a plan view of the vicinity of the discharge port of the liquid discharge head 3 according to the first embodiment. The foaming chamber 9 has a substantially rectangular planar shape, the short side on the upstream side in the liquid supply direction is a liquid inlet 15 into which ink flows, and the short side on the downstream side in the liquid supply direction is the back wall 16. It has become. That is, the foaming chamber 9 has a dead end shape. The center of gravity 14G of the heating resistor element 14 is located upstream from the midpoint LC of the full length L in the liquid supply direction (X direction) of the discharge flow path 11. In this embodiment, the offset amount a with respect to the midpoint LC of the center of gravity 14G of the heating resistor element 14 is 2 μm. The ejection amount of ink droplets ejected from the ejection port 12 is 6 ng. The heating resistor element 14 has a rectangular shape whose Y direction length is smaller than the X direction length.

  The discharge channel 11 has a substantially circular channel cross section, and is asymmetric with respect to the X direction axis. Specifically, the discharge flow path 11 has a first protrusion 17 extending from the side wall 13 of the discharge flow path 11 in the direction intersecting with the liquid supply direction X, in this embodiment, the Y direction. Here, the region upstream of the midpoint LC of the full length L in the liquid supply direction X of the discharge channel 11 is referred to as a first region 18A, and the region downstream of the midpoint LC is referred to as a second region 18B. That is, the region upstream of the straight line 19 passing through the midpoint LC of the entire length L in the X direction of the discharge flow path 11 and drawn in the Y direction is the first region 18A, and the region downstream of the straight line 19 is the second region. Region 18B. In this embodiment, the Y-direction center line 17C of the first protrusion 17 is in the first region 18A. In the present embodiment, all of the first protrusions 17 are in the first region 18A, but some may be in the second region 18B. That is, at least a part of the first protrusion 17 is in the first region 18A. The first protrusions 17 are parallel to the Y-direction center line 17C and positioned on the upstream side of the Y-direction center line 17C, and are parallel to the Y-direction center line and positioned on the downstream side of the Y-direction center line 17C. And a second side surface 17B. The Y direction length of the first side surface 17A is shorter than the Y direction length of the second side surface 17B. As a result, the channel cross-sectional area of the first region 18A of the discharge channel 11 is smaller than the channel cross-sectional area of the second region 18B. Further, the Y direction average width of the first region 18A is smaller than the Y direction average width of the second region 18B.

  In the discharge flow path 11 having such a configuration, cavitation on the upper surface of the heating resistor element 14 and the influence on the heating resistor element 14 associated therewith are suppressed. The principle will be described with reference to FIG. FIG. 5 is a schematic cross-sectional view of the XZ plane passing through the central axis in the X direction of the heating resistor element 14 and shows the bubble defoaming process after ink ejection in this embodiment in time series.

  First, the heating resistor element 14 is driven through a wiring and an electrode (not shown) to generate heat. Due to the heat generated by the heat generating resistor element 14, the ink inside the foaming chamber 9 is heated, and bubbles B are generated in the ink due to film boiling. Since the back wall 16 is provided on the downstream side of the foaming chamber 9, the bubbles B grow by being shifted to the upstream side of the center of gravity 14 </ b> G of the heating resistor element 14. The bubble B is formed on the heating resistor element 14 so as to be thicker toward the upstream side. The bubbles B are heated and further grow, and a part of the ink stored in the foaming chamber 9 is ejected from the ejection port 12 by the foaming pressure. After the volume of the bubble B increases once and reaches the maximum volume, the bubble B shrinks. As shown in FIG. 5A, ink meniscus M is generated in the discharge flow path 11 almost simultaneously with the decrease in the volume of the bubble B, and proceeds in the direction away from the discharge port 12 in the foaming chamber 9. . This is because the amount of ink inside the foaming chamber 9 decreases due to the ejection of ink, and a reverse flow of ink from the ejection flow path 11 toward the foaming chamber 9 occurs. Since the ink backflow hardly occurs immediately below the first protrusion 17, the ink meniscus M in the ejection flow path 11 is formed so that the outer peripheral portion is concave. In the present embodiment, as described above, the channel cross-sectional area of the first region 18A is smaller than the channel cross-sectional area of the second region 18B. This affects the formation of the meniscus M on the liquid surface, and the drop of the meniscus M on the side of the first region 18A having a small cross-sectional area becomes larger than the drop of the meniscus M on the side of the second region 18B having a large cross-sectional area.

  When the time further elapses, the meniscus M enters the inside of the foaming chamber 9 as shown in FIG. Although the bubble B contracts, the meniscus M approaches the bubble B. The bubble B is pushed by the backflowing ink and is partially recessed, but as a whole, a thicker shape is maintained on the upstream side. At this time, the meniscus M is formed with a first sagging portion M1 on the upstream side and a second sagging portion M2 on the downstream side. The first sagging portion M1 is a portion where the distance from the heating resistor element 14 is minimized, and the second sagging portion M2 on the downstream side is a portion where the distance from the heating resistor element 14 is minimized. Since the second sagging portion M2 is farther from the heating resistor element 14 than the first sagging portion M1, and the bubble B is entirely displaced upstream, the distance from the bubble B is also the first distance. It is larger than the depression M1.

  Then, the first sagging portion M1 of the meniscus M reaches the bubble B, and the air that has entered the foaming chamber 9 from the discharge channel 11 comes into contact with the bubble B and is integrated. Thereby, as shown in FIG. 5C, the atmosphere outside the discharge flow channel 11 communicates with the bubbles B. The bubble B communicates with the atmosphere upstream of the center of gravity 14G of the heating resistor element 14.

  As time further elapses, the air bubbles B integrated with the atmosphere spread almost entirely over the heating resistor element 14, and the state shown in FIG. 5D is obtained. Since the bubble B communicates with the atmosphere, the pressure thereof is about the same as that of the atmosphere. Thereafter, the ink is refilled into the foaming chamber 9 while the bubbles B are in communication with the atmosphere, the air forming the bubbles B communicating with the atmosphere is discharged to the outside from the discharge flow path 11, and the bubbles B in the foaming chamber 9 are Defoam.

  As described above, in this embodiment, the meniscus M on the first region 18A side with the small cross-sectional area reaches the bubbles earlier than the meniscus M on the second region 18B side with the large cross-sectional area, and the bubbles B communicate with the atmosphere. To do. Atmospheric communication occurs upstream of the center of gravity 14G of the heating resistor element 14. Since the bubble B is formed thicker toward the upstream side, the meniscus M reaches the bubble B earlier, and the air communication occurs earlier. For this reason, it becomes difficult for the bubble B to be divided between the upstream side and the downstream side. Thereby, generation | occurrence | production of the cavitation by the division | segmentation of the bubble B which has arisen conventionally can be suppressed, and durability of the liquid discharge head 3 can be improved.

  The drop speed of the first drop portion M1 also varies depending on the ratio of the flow area (the cross-sectional area of the cross section cut along the XY plane) between the first region 18A and the second region 18B. In the present embodiment, the ratio of the channel area of the second region 18B to the channel area of the first region 18A is about 1.5 times, but if it exceeds 1.5, the first sagging portion M1 falls. Is more effective because it is promoted.

(Comparative Example 1)
FIG. 6 is a plan view of the vicinity of the discharge port of the liquid discharge head 3 of Comparative Example 1. In the liquid discharge head 3 of Comparative Example 1, the discharge channel 11 has a circular cross section, and the first protrusion 17 is not provided. The channel cross-sectional area of the discharge channel 11 is the same as that of the first embodiment. The other configuration is the same as that of the first embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, description thereof is omitted, and only different portions will be described.

  FIG. 7 is a view similar to FIG. 5 showing the defoaming process of the bubbles B after ink ejection in time series.

  First, as in the first embodiment, the heating resistor element 14 is driven to discharge ink. As in the first embodiment, the ink meniscus M generated in the discharge flow path 11 proceeds in the direction away from the discharge port 12 in the foaming chamber 9. However, in this comparative example, since the flow passage section of the discharge flow passage 11 is circular, the manner in which the meniscus M descends is different from that in the first embodiment. That is, as shown in FIG. 7A, the meniscus M is deformed into two substantially symmetric concave shapes at the same time as the bubble B starts to decrease in volume.

  When the time further elapses, the meniscus M enters the foaming chamber 9 as shown in FIG. Unlike the first embodiment, the meniscus M in the foaming chamber 9 has almost no difference in shape between the upstream side and the downstream side, and is slightly symmetric although it is slightly displaced upstream. Therefore, the depression of the meniscus M approaches the position where the bubble B slightly downstream of the center of gravity of the heating resistor element 14 of the bubble B is thin, and the timing when the bubble B approaches the heating resistor element 14 is compared with the first embodiment. And slow down. Thereby, the part near the center part of the bubble B is deformed into an annular shape and recessed, and the possibility that the bubble B is divided as shown in FIG. 7C increases (the divided bubble is shown as B1). As shown in FIG. 7 (d), when the bubble B1 that has been divided when the bubbles are removed collapses, the heating resistance element 14 may be impacted and damaged. In the liquid discharge head 3 according to the comparative example 1, the meniscus M is not biased between the upstream side and the downstream side as compared with the first example, so that the bubbles B are easily separated before communicating with the atmosphere. As described above, in Comparative Example 1, the timing of communicating with the atmosphere is slower than that in Example 1, and thus cavitation is likely to occur, leading to a decrease in durability of the liquid discharge head 3.

(Modification of Example 1)
Although the liquid discharge head 3 of the first embodiment has one protrusion, it may have two protrusions as shown in FIG. The second protrusion 20 is provided in the discharge flow path 11 symmetrically with the first protrusion 17 with respect to the X axis, and is in a mirror image relationship with the first protrusion 17. The Y-direction center line 20C of the second protrusion 20 coincides with the Y-direction center line 17C of the first protrusion 17, but may be displaced in the X direction with respect to the Y-direction center line 17C. The second protrusion 20 is parallel to the Y-direction center line 20C and positioned on the upstream side of the Y-direction center line 20C, and is parallel to the Y-direction center line and positioned on the downstream side of the Y-direction center line 20C. And a second side surface 20B.

  The discharge flow path 11 of the modified example of FIG. 8A has a shape in which a semicircle having a large diameter and a semicircle having a small diameter are connected by a rectangle having a dimension in the Y direction smaller than the diameter of these semicircles. The length of the first side surface 17A is shorter than the length of the second side surface 17B, and similarly, the length of the first side surface 20A is shorter than the length of the second side surface 20B. The discharge flow path 11 of the modified example of FIG. 8B includes a semicircle, a rectangle having the same Y-direction width as the diameter of the semicircle, a rectangle having a smaller Y-direction width than the rectangle, and the semicircle. It is a shape in which semicircles of the same diameter are connected in sequence. The lengths of the first side surface 17A and the second side surface 17B are the same, and the lengths of the first side surface 20A and the second side surface 20B are also the same.

  In any of the modified examples, the flow passage cross-sectional area of the first region 18A is smaller than the flow passage cross-sectional area of the second region 18B, so that the drop of the meniscus on the upstream side is larger than the drop of the meniscus on the downstream side. It is more preferable to provide two protrusions because the depression of the meniscus on the upstream side is promoted. By providing the two protrusions, the tailing length of the discharged droplet can be stably shortened as compared with the second embodiment described below. As a result, satellites can be reduced and print quality can be improved. In any modification, as in the first embodiment, the ratio of the flow area of the second region 18B to the flow area of the first region 18A is preferably 1.5 times or more.

(Example 2)
In the liquid discharge head 3 of the second embodiment shown in FIG. 9, the width in the Y direction of the discharge flow path 11 continuously decreases from the downstream side toward the upstream side, and the other configuration is the same as that of the first embodiment. It is. The same components as those in the first embodiment are denoted by the same reference numerals, description thereof is omitted, and only different portions will be described. Specifically, the cross section of the discharge flow channel 11 has a regular triangular shape. The length of one side of the channel cross section is 18.6 μm. The center of gravity of the discharge channel 11 is shifted by 4 μm downstream from the center of gravity 14G of the heating resistor element 14. The heating resistor element 14 has a square shape of 24 μm in both the X-direction dimension and the Y-direction dimension. The amount of ink droplets discharged from the discharge port 12 is about 4.5 ng.

  FIG. 10 is a view similar to FIG. 5 showing the defoaming process of the bubbles B after ink ejection in time series. First, as in the first embodiment, the heating resistor element 14 is driven to discharge ink. Similar to the first embodiment, the ink meniscus M generated in the discharge flow path 11 proceeds in the direction away from the discharge port 12 in the foaming chamber 9. As shown in FIG. 10A, the meniscus M is formed on the liquid surface in this embodiment as in the first embodiment. That is, the drop of the meniscus M on the first region 18A side having a small cross-sectional area on the upstream side is larger than the drop of the meniscus M on the second region 18B side having a large cross-sectional area on the downstream side. In the present embodiment, the cross-sectional shape of the discharge flow path 11 is formed in a triangular shape in which the width in the Y direction decreases as it goes upstream, so the cross-sectional area of the discharge flow path 11 per unit length in the X direction is also The upstream side is smaller. For this reason, the drop of the meniscus M on the upstream side of the heating resistor element 14 is larger than the drop of the meniscus M on the downstream side, and the shape of the meniscus M is similar to that of the first embodiment.

  When the time further elapses, the meniscus M enters the inside of the foaming chamber 9 as shown in FIG. In the same manner as in the first embodiment, the shrinkage of the bubble B proceeds and the meniscus M approaches the bubble B. Then, as shown in FIG. 10C, the meniscus M reaches the bubble B, and the air that has entered the foaming chamber 9 from the discharge channel 11 comes into contact with the bubble B and is integrated. Thereby, the external atmosphere communicates with the bubbles B. When the time further elapses, the bubbles B integrated with the atmosphere spread almost entirely over the heating resistor element 14, and the state shown in FIG.

  Also in the present embodiment, the first sagging portion M1 of the meniscus M on the first region 18A side having a small cross-sectional area becomes the bubble B earlier than the second sagging portion M2 on the second region 18B side having a large cross-sectional area. Reach and communicate with bubble B. For this reason, it is possible to suppress the occurrence of cavitation due to the division of the bubbles B that has occurred in the past, and the durability of the liquid ejection head 3 can be improved.

(Comparative Example 2)
In the liquid discharge head 3 of Comparative Example 2 shown in FIG. 11, the Y direction width of the discharge flow path 11 continuously decreases from the upstream side toward the downstream side. That is, the discharge channel 11 of Comparative Example 2 has a shape obtained by inverting the discharge channel 11 of Example 2 with respect to the Y-direction axis. The other configuration is the same as that of the second embodiment. The same components as those in the second embodiment are denoted by the same reference numerals, description thereof is omitted, and only different portions will be described.

  FIG. 12 is a view similar to FIG. 5 showing the defoaming process of the bubbles B after ink ejection in time series. Also in Comparative Example 2, as shown in FIG. 12A, the ink liquid surface in the discharge flow path 11 is deformed into a concave shape almost simultaneously with the bubble B turning into a volume reduction, and the formation of the meniscus M starts. The depressed portion of the meniscus M has a shape opposite to that of the second embodiment. That is, the drop of the meniscus M on the downstream side is larger than the drop of the meniscus M on the upstream side. When the time further elapses, the meniscus M enters the inside of the foaming chamber 9 as shown in FIG. 12B, but the meniscus M maintains the shape shown in FIG. Is closer to the bubble B than in the second embodiment. Thereby, the part close | similar to the center part of the bubble B deform | transforms into a ring shape, and becomes dented, and the possibility that the bubble B will be divided becomes high. As a result, the possibility of cavitation increases. In Comparative Example 2, as shown in FIG. 12C, the bubble B1 separated from the bubble B remains in the foaming chamber 9. When the time further elapses, the bubble B integrated with the atmosphere spreads almost over the entire heating resistor element 14, and the state shown in FIG.

  Thus, in the liquid discharge head 3 of Comparative Example 2, the shape of the meniscus M is reversed on the left and right (on the upstream side and the downstream side) as compared with Example 2, so that the air B is separated from the atmosphere before the bubble B is divided. There is no communication. For this reason, cavitation occurs due to the late timing of communication with the atmosphere as compared with the second embodiment, and the durability of the liquid discharge head 3 is reduced.

(Modification of Example 2)
Although the cross-sectional shape of the discharge flow path 11 of Example 2 is a triangle, it is not limited to a triangle as long as the width of the discharge flow path 11 in the Y direction decreases from the downstream side toward the upstream side. The cross-sectional shape of the discharge channel 11 may be a trapezoidal shape as shown in FIG. 13A, or may be a curved shape as a whole as shown in FIG. Although not shown, the linear shape and the curved shape may be mixed, or the Y-direction width of the discharge flow path 11 may be decreased stepwise from the downstream side toward the upstream side.

DESCRIPTION OF SYMBOLS 3 Liquid discharge head 9 Foaming chamber 11 Discharge flow path 12 Discharge port 14 Heating resistance element 15 Liquid inlet 16 Back wall 18A 1st area | region 18B 2nd area | region

Claims (11)

A foaming chamber provided with a back wall on the downstream side in the liquid supply direction and a liquid introduction port on the upstream side; a discharge channel that communicates with the foaming chamber and has a discharge port for discharging the liquid; and the foaming chamber A heating resistance element that opposes the ejection flow path across the surface and imparts energy for ejection to the liquid, and the bubbles generated in the foaming chamber by the energy of the heating resistance element reach a maximum volume. A liquid discharge head in communication with air flowing in from the discharge flow path in a volume reduction process after growth;
The liquid discharge head, wherein the flow passage cross-sectional area of the first region upstream of the midpoint of the total length of the discharge flow channel in the liquid supply direction is smaller than the flow passage cross-sectional area of the second region downstream. .   2. The liquid ejection head according to claim 1, wherein an average width of the first region in a direction orthogonal to the liquid supply direction is smaller than an average width of the second region in a direction orthogonal to the liquid supply direction.   3. The liquid ejection head according to claim 1, wherein a flow path cross-sectional area of the second area is 1.5 times or more a flow path cross-sectional area of the first area.   The discharge flow path has a first protrusion extending from a side wall of the discharge flow path in a direction intersecting the liquid supply direction, and at least a part of the first protrusion is in the first region. Item 4. The liquid discharge head according to any one of Items 1 to 3.   The discharge channel includes a first protrusion extending from a side wall of the discharge channel in a direction crossing the liquid supply direction, and a center line of the first protrusion is in the first region. 4. The liquid discharge head according to any one of 1 to 3.   The first protrusion includes a first side surface that is parallel to the center line and located on the upstream side, and a second side surface that is parallel to the center line and located on the downstream side. The liquid discharge head according to claim 5, wherein a length of the side surface is shorter than a length of the second side surface.   The discharge channel has a second protrusion extending from the side wall in a direction intersecting the liquid supply direction, and at least a part of the second protrusion is in the first region. The liquid discharge head according to any one of the above.   4. The liquid discharge head according to claim 1, wherein a width of the discharge flow channel in a direction orthogonal to the liquid supply direction decreases from the downstream side toward the upstream side. 5.   9. The liquid ejection head according to claim 1, wherein a center of gravity of the heating resistor element is located on the upstream side of the midpoint of the ejection flow path. A foaming chamber provided with a back wall on the downstream side in the liquid supply direction and a liquid introduction port on the upstream side; a discharge channel that communicates with the foaming chamber and has a discharge port for discharging the liquid; and the foaming chamber A heating resistance element that opposes the ejection flow path across the surface and imparts energy for ejection to the liquid, and the bubbles generated in the foaming chamber by the energy of the heating resistance element reach a maximum volume. A liquid discharge method using a liquid discharge head communicating with the atmosphere flowing in from the discharge flow path in a volume reduction process after growth,
The heating resistor element is driven to generate bubbles in the liquid, and the liquid is discharged from the discharge port. After the liquid is discharged from the discharge port, the discharge flow path to the foaming chamber Generating a meniscus of the liquid to enter,
The liquid discharge method, wherein the meniscus has a portion where the distance from the heating resistor element is minimum on the upstream side and a portion where the distance from the heating resistor element is minimal on the downstream side.   The liquid discharge method according to claim 10, wherein the bubble communicates with air that has entered the foaming chamber from the discharge flow path, on the upstream side of the center of gravity of the heating resistor element.

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