Liquid ejecting head and liquid ejecting apparatus

In a circulating system which circulates liquid within a liquid ejecting head, thickening of liquid in the vicinity of an ejection port section can be more securely suppressed. The ejection port section includes a first ejection port disposed at an upstream side with respect to an ejecting direction of ink and a second ejection port disposed at a downstream side with respect to the ejecting direction. The second ejection port includes an enlarged diameter portion whose diameter is enlarged in a radially outward manner from at least a part of an opening edge portion of the first ejection port.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a liquid ejecting head which can eject liquid such as ink and a liquid ejecting apparatus.

Description of the Related Art

In a print head (liquid ejecting head) included in an inkjet printing apparatus as a liquid ejecting apparatus, ink in the vicinity of an ejection port thickens as a result of evaporation of a volatile component included in ink from the ejection port in which liquid ink is to be ejected. In a case where such thickening of ink occurs, an ink ejection speed and an ink ejecting direction from the ejection port are changed and the landing accuracy of ink droplets may be possibly affected. Particularly, in a case where pause time of not ejecting ink is long, the increase of the viscosity of ink is remarkable and the solid component of ink adheres to the vicinity of the ejection port, thereby increasing fluid resistance of ink and possibly inducing failure of ink ejection.

Japanese Patent Laid-Open No. 2002-355973 discloses a configuration of circulating ink within a print head for suppressing thickening of ink along with evaporation of a volatile component of ink from an ejection port.

However, the present inventors have found out, as a result of the study, that the mere configuration of circulating ink as disclosed in Japanese Patent Laid-Open No. 2002-355973 may have a possibility of causing color unevenness on a printed image due to a change in concentration of a coloring material in ink. Particularly, in a case where at least one of the following conditions is satisfied, that is, a case where the volume of an ink droplet to be ejected is small, a case where the print head has a high temperature, and a case where a solid component of ink is high, the concentration of the coloring material in ink has been changed, and thus the color unevenness on a printed image has likely occurred.

SUMMARY OF THE INVENTION

The present invention provides a liquid ejecting head and a liquid ejecting apparatus which can suitably suppress thickening of liquid in the vicinity of an ejection port in a circulating system which circulates liquid within the liquid ejecting head.

In the first aspect of the present invention, there is provided a liquid ejecting head comprising:a pressure chamber to which liquid flows in through an inflow path and from which the liquid flows out through an outflow path;an ejection port which is communicated with the pressure chamber; andan ejection energy generating element for causing the liquid in the pressure chamber to be ejected from the ejection port, whereinthe ejection port includes a first ejection port disposed in an upstream side in an ejecting direction of liquid and a second ejection port disposed in a downstream side in the ejecting direction, andthe second ejection port includes an enlarged diameter portion whose diameter is enlarged in a radially outward manner from at least a part of an opening edge portion of the first ejection port.

In the second aspect of the present invention, there is provided a liquid ejecting head comprising:an ejection port through which liquid is ejected;a pressure chamber which is communicated with the ejection port and which includes an ejection energy generating element inside the pressure chamber for generating energy to be used for ejecting liquid;a first flow path which is communicated with the pressure chamber and through which liquid is supplied to the pressure chamber;a second flow path which is communicated with the pressure chamber and through which liquid is collected from the pressure chamber, whereinthe ejection port includes a first ejection port which is disposed in an upstream side in an ejecting direction of liquid and in which liquid meniscus is formed and a second ejection port disposed in a downstream side of the ejecting direction, andan opening diameter of the second ejection port is larger than an opening diameter of the first ejection port.

In the third aspect of the present invention, there is provided a liquid ejecting apparatus comprising:a liquid ejecting head of the first aspect of the present invention;a liquid supplying flow path for supplying liquid to the liquid ejecting head;a liquid collecting flow path for collecting liquid from the liquid ejecting head; anda control unit for controlling the ejection energy generating element of the liquid ejecting head.

According to the present invention, by specifying a configuration of the ejection port in the circulating system which circulates liquid within the liquid ejecting head, the thickening of liquid in the vicinity of the ejection port can be suitably suppressed. In a case where the liquid ejecting head is a print head that ejects liquid ink, the thickening of ink in the vicinity of the ejection port can be suppressed to print an image of a high quality.

DESCRIPTION OF THE EMBODIMENTS

A liquid ejecting head and a liquid ejecting apparatus in the following embodiments are application examples as an inkjet print head which can eject liquid ink and an inkjet printing apparatus.

(Configuration of Printing Apparatus)

FIG. 1Ais a schematic perspective view of major parts for illustrating a basic configuration of an inkjet printing apparatus (liquid ejecting apparatus)100applicable to the present invention. The printing apparatus100of this example is a printing apparatus of a so-called full line system, which includes a conveying unit101which conveys a print medium W in a conveying direction of an arrow A and an inkjet print head (liquid ejecting head)10capable of ejecting ink (liquid). The conveying unit101of this example conveys the print medium W by using a conveying belt101A. The print head10is a print head of a line type (page-wide type) extending in a direction crossing (orthogonal in the case of this example) the conveying direction of the print medium W, and has a plurality of ejection ports capable of ejecting ink arranged along the width direction of the print medium W. As for the print head10, ink is supplied from a non-illustrated ink tank through an ink supply unit composed of ink flow paths. By ejecting ink from the ejection ports of the print head10based on print data (ejection data) while continuously conveying the print medium W, an image is printed on the print medium W. The print medium W is not limited to a cut sheet, and may be an elongate roll sheet.

FIG. 1Bis a block diagram for illustrating a configuration example of a control system of the printing apparatus100. A CPU (control unit)102executes control processing on operation of the printing apparatus100, data processing, and the like. In a ROM103, a program including procedures for such processing is stored. A RAM104is used as a work area for executing such processing. The print head10includes the plurality of ejection ports, the plurality of ink flow paths that are communicated with the respective ejection ports, and a plurality of ejection energy generating elements arranged for the respective ink flow paths. The ejection ports, the ink flow paths, and the ejection energy generating elements form a plurality of nozzles capable of ejecting ink. These nozzles function as printing elements. As for the ejection energy generating elements, an electrothermal transducing element (heater) and a piezoelectric element, for example, may be used. In the case of using the electrothermal transducing element, ink in the ink flow paths is bubbled by the heating of the electrothermal transducing element, and the resultant bubble energy is used to eject ink from the ejection port. The ejection of ink from the print head10is made such that the CPU102drives the ejection energy generating elements via a head driver10A based on image data to be inputted from a host apparatus105or the like. The CPU102drives a conveyance motor101C in the conveying unit101via a motor driver101B.

(Configuration of Ink Supply System)

FIG. 2is a schematic diagram of the ink supply system for supplying ink to the print head10in the present embodiment. Ink in an ink tank201is supplied to the print head10through an ink supplying flow path (liquid supplying flow path)202. A part of ink supplied to the print head10is ejected from an ejection port11and other ink is collected by the ink tank201through an ink collecting flow path (liquid collecting flow path)204. By using a negative pressure adjustment device203included in the ink supplying flow path202and a fixed flow rate pump205included in the ink collecting flow path204, ink pressure in the ejection port11is adjusted while inducing circulation flow of ink between the ink tank201and the print head10. The fixed flow rate pump205and the negative pressure adjustment device203which generate ink circulation flow can be integrally provided with the print head10, or can be attached to the outside of the print head10so as to be connected with the print head10via a supply tube or the like. Alternatively, the fixed flow rate pump205and the negative pressure adjustment device203can be incorporated into a printing element substrate as a MEMS element such as a micropump. As will be described later, the present invention can be suitably applied to the liquid ejecting head and the liquid ejecting apparatus having a form of supplying liquid to a pressure chamber R which provides the energy generating elements therein and causing the ink not ejected from the ejection ports to flow outside the pressure chamber R from the inside. The configuration ofFIG. 2is one example of generating ink flow, but other configurations can be applied as well. For instance, the present invention can also be applied to a case of forming the above ink flow by providing a microactuator within the print head10in place of the fixed flow rate pump205ofFIG. 2.

(Configuration of Print Head)

FIGS. 3A, 3B, and 3Care diagrams illustrating parts in the vicinity of the ejection port11in the print head10.FIG. 3Ais a plan view of the major parts of the print head10viewed from the ejection port11,FIG. 3Bis a cross-sectional view taken from line IIIB-IIIB ofFIG. 3A, andFIG. 3Cis a perspective view of a cross section of the major parts of the print head10.

In the print head10of this example, the ejection port11, a flow path13, and an electrothermal transducing element (heater)14as an ejection energy generating element are formed. In the flow path13, ink is supplied from its one end to the other end. In an area between one end and the other end of the flow path13, the pressure chamber R and the ejection port11which is communicated with the pressure chamber R are formed. The flow path13includes a first flow path provided in an upstream side of the pressure chamber R and a second flow path provided in a downstream side thereof. Ink supplied to the pressure chamber R through the first flow path is collected to the outside of the pressure chamber R through the second flow path. In the ejection port11, an interface12is formed between ink and atmosphere as a result of meniscus of ink. Ink can be ejected from the ejection port11by making ink in the pressure chamber R bubbled by the heating of the heater14and by using the resultant bubble energy. The ejection energy generating element is not limited only to the heater14, but various energy generating elements such as the piezoelectric element, for example, may be used.

In an element substrate18of the print head10, an inflow path15and an outflow path16which extend in directions that intersect the flow path13are formed as through holes. The inflow path15is communicated with the ink supplying flow path202ofFIG. 2and the outflow path16is communicated with the ink collecting flow path204ofFIG. 2. Accordingly, in the print head10, as shown with arrows inFIG. 3B, ink is circulated through the ink supplying flow path202, the inflow path15, one end side of the flow path13, the ejection port11, the other end side of the flow path13, the outflow path16, and the ink collecting flow path (liquid collecting flow path)204. In the case of this example, in a state in which ink flows within the flow path13, ink can be ejected from the ejection port11by driving the heater14. The flow rate of ink circulation flow within the flow path13is, for example, about 0.1 mm/s to 100 mm/s. Even if ink ejection operation is performed in the state in which ink flows within the flow path13, its effect on the landing accuracy of ink droplets, for example, is low. The pressure chamber R allows the ink flow of such a flow rate, thereby forming meniscus of the ink in the ejection port11.

The heater14is formed in the element substrate18made of silicon (Si). The ejection port11and an ejection port part17communicating between the ejection port11and the flow path13are formed in an orifice plate19. The ejection port11is an opening formed on the surface of the orifice plate19(ejection port forming face), and the ejection port part17is a cylindrical communication part connecting between the ejection port11and the flow path13.

(Relation of Dimensions (P, W, and H) in Print Head)

As shown inFIG. 3B, a height of the flow path13in the upstream side (the left side inFIG. 3B) in an ink flowing direction with respect to the communication part between the flow path13and the ejection port part17is denoted as H, and a length of the ejection port part17in an ink ejecting direction is denoted as P. Further, a width of the ejection port part17in the ink flowing direction in the flow path13is denoted as W. In this example, a height H is 3 to 30 μm, a length P is 3 to 30 μm, and a width W is 6 to 30 μm. Ink to be used is adjusted such that the concentration of a non-volatile solvent is 30%, the concentration of the coloring material is 3%, and viscosity is 0.002 to 0.003 Pa·s.

FIG. 4Ais a diagram illustrating ink flow in the ejection port11, the ejection port part17, and the flow path13in the case where ink circulation flow within the print head10is in a stationary state. The lengths of vectors shown inFIG. 4Ado not represent the amount of speed and are unrelated to all speed values. InFIG. 4A, with respect to the print head10having a height H of 14 μm, a length P of 5 μm, and a width W of 12.4 μm, the flow of ink flowing into the flow path13from the inflow path15at a speed of 1.26×10-4 ml/min is shown with arrows.

In this example, a case where the concentration of the coloring material in ink has been changed as a result of evaporation of the ink volatile component from the ejection port11is considered so as to suppress such ink from being retained in the ejection port11and the ejection port part17. In order to achieve this, as shown inFIG. 4A, part of the ink circulation flow within the flow path13is caused to enter the inside of the ejection port part17. Then, after the ink inside the ejection port part17reaches the vicinity of the interface12, the ink is returned from the ejection port part17to the flow path13. The ink returned to the flow path13passes through the outflow path16and then through the ink collecting flow path204shown inFIG. 2for circulation. As such, the part of the ink circulation flow enters the inside of the ejection port part17and reaches a position in the vicinity of ink meniscus (interface12) formed on the ejection port11, and then returns to the flow path13. Due to this movement, not only ink inside the ejection port part17which is likely to be influenced by evaporation of the ink volatile component, but also ink in the vicinity of the interface12which is significantly influenced in particular by such evaporation can be prevented from being retained inside the ejection port part17and can flow out to the flow path13.

Ink flow in at least a center part in the vicinity of the interface12(the center part of the ejection port11) has a velocity component (hereinafter referred to as a “positive velocity component”) in the ink flowing direction inside the flow path13(from the left side to the right side inFIG. 4A) as shown inFIG. 4A. In the following descriptions, as shown inFIG. 4A, a mode of ink flow having the positive velocity component at the center part in the vicinity of the interface12is represented as a “flow mode A”. Further, as in comparison examples shown inFIG. 5BandFIG. 5Dto be described later, a mode of ink flow having a “negative velocity component” which is the opposite of the positive velocity component at the center part in the vicinity of the interface12is represented as a “flow mode B”.

As a result of the study by the inventors, the print head of the flow mode A is found to satisfy the following relational expression (1). As described above, the print head of the flow mode A can prevent the ink in which the concentration of the coloring material has been changed as a result of evaporation of the ink volatile component from being retained inside the ejection port11and can cause such ink to flow out to the flow path13. Specifically, the print head of the flow mode A satisfies the following relational expression (1) for a height H (μm), a length P (μm), and a width W (μm) shown inFIG. 3B:
H−0.34×P−0.66×W>1.7  (1)

The left side of the relational expression (1) is represented as a determination value J. It is found that the print head of the flow mode A as inFIG. 4Asatisfies the relational expression (1), whereas the print head of the flow mode B does not satisfy the relational expression (1).

FIG. 4Bis a graph illustrating the relation between the print head of the flow mode A and the print head of the flow mode B. A horizontal axis inFIG. 4Bindicates the ratio of a length P to a height H (P/H) and a vertical axis therein indicates the ratio of a width W to a length P (W/P). A line L indicated inFIG. 4Brepresents a threshold line that satisfies the following relational expression (2).

It is found that a print head having the relation of H, P, and W which falls within a range of an upper part of the threshold line L (a diagonally shaded area inFIG. 4B) is in the flow mode A, whereas a print head having the relation of H, P, and W which falls within a range of a lower part of the threshold line L is in the flow mode B. To be more specific, a print head that satisfies the following relational expression (3) will be in the flow mode A.

Sorting the relational expression (3) leads to the relational expression (1), and therefore, a print head (the one having the determination value J of 1.7 or more) having the relation of H, P, and W which satisfies the relational expression (1) will be in the flow mode A.

FIG. 5A,FIG. 5B,FIG. 5C, andFIG. 5Dare diagrams illustrating ink circulation flow in the vicinity of various types of ejection ports11in different print heads.FIG. 4Cis a graph illustrating determination results of the flow modes for the plurality of print heads including those shown inFIG. 5A,FIG. 5B,FIG. 5C, andFIG. 5D. A dot mark (•) in the diagram indicates a print head that has been determined to be in the flow mode A, whereas an x mark (x) therein indicates a print head that has been determined to be in the flow mode B.

The print head ofFIG. 5Ahas the height H of 3 μm, the length P of 9 μm, and the width W of 12 μm, and the determination value J on the left side of the relational expression (1) is 1.93, which is larger than 1.7. As a result of confirming an actual flow of the circulation flow in this print head, the flow mode A as shown inFIG. 5Ahas been found. The determination result of this print head corresponds to a point PA inFIG. 4C. A print head ofFIG. 5Bhas the height H of 8 μm, the length P of 9 μm, and the width W of 12 μm, and the determination value J is 1.39, which is smaller than 1.7. As a result of confirming an actual flow of the circulation flow in this print head, the flow mode B as shown inFIG. 5Bhas been found. The determination result of this print head corresponds to a point PB inFIG. 4C. A print head ofFIG. 5Chas the height H of 6 μm, the length P of 6 μm, and the width W of 12 μm, and the determination value J is 2.0, which is larger than 1.7. As a result of confirming an actual flow of the circulation flow in this print head, the flow mode A as shown inFIG. 5Chas been found. The determination result of this print head corresponds to a point PC inFIG. 4C. A print head ofFIG. 5Dhas the height H of 6 μm, the length P of 6 μm, and the width W of 6 μm, and the determination value J is 1.0, which is smaller than 1.7. As a result of confirming an actual flow of the circulation flow in this print head, the flow mode B as shown inFIG. 5Dhas been found. The determination result of this print head corresponds to a point PD inFIG. 4C.

As such, the print head of the flow mode A and the print head of the flow mode B can be classified based on a boundary of the threshold line L indicated inFIG. 4B. Specifically, a print head having the determination value J larger than 1.7 in the relational expression (1) belongs to the flow mode A, and such a print head has the positive velocity component for the ink flow in at least the center part of the interface12.

The ink flow of the ejection port part belonging to either the flow mode A or the flow mode B is predominantly affected by the above relation of P, W, and H. An influence caused by other conditions besides the condition associated with the relation of P, W, and H, such as a flow rate of the ink circulation flow, a viscosity of ink, a flow direction of the circulation flow, and a width of the ejection port11in a direction orthogonal to the width W, is extremely smaller than the influence caused by the relation of P, W, and H. Accordingly, the flow rate of the ink circulation flow and the viscosity of ink may be appropriately set in accordance with the specifications of a required print head and printing apparatus and their use environment conditions. For instance, the flow rate of the ink circulation flow in the flow path13can be set to be 0.1 to 100 mm/s, and the viscosity of ink can be set to be 10 cP or less. Further, in a case where the evaporation rate of the ink volatile component from the ejection port is increased due to a change in the use environment or the like, a flow amount of the ink circulation flow can be appropriately increased to make the ink flow belong to the flow mode A. With respect to the print head of the flow mode B, even if the flow amount of ink circulation flow is increased as much as possible, a mode is not changed to the flow mode A. In other words, whether a print head belongs to the flow mode A or the flow mode B is not determined by conditions such as the flow rate of ink and the viscosity of ink, but is predominantly determined by the condition associated with the relation of H, P, and W. In addition, among print heads of the flow mode A, a print head having the height H of 20 μm or less, the length P of 20 μm or less, and the width W of 30 μm or less, in particular, is preferable because such a print head is capable of printing finer images.

(Relation Between Ink Evaporation Speed and Circulation Flow)

FIG. 6Ais a diagram illustrating the state of concentrated ink in the print head of the flow mode B (J=1.3) andFIG. 6Bis a diagram illustrating the state of concentrated ink in the print head of the flow mode A (J=2.3). In the print head of the flow mode B, as shown inFIG. 6A, the ink circulation flow is unlikely to enter the ejection port part17and a concentrated area S in which ink is concentrated is large. Meanwhile, in the print head of the flow mode A, as shown inFIG. 6B, the ink circulation flow is likely to enter the ejection port part17. However, as inFIG. 6B, in the vicinity of an opening edge portion of the ejection port11, that is, in particular, at a position of the downstream side in an ink flow direction inside the ejection port part17, there is a possibility of occurrence of the concentrated area S in which ink is likely to be retained. In a case where such concentrated area S has occurred, the ink in the vicinity of the opening edge portion of the ejection port11is thickened, and in a case where the solid content of ink is high (for example, in the case of 8 wt % or more), in particular, there may be a concern that the ink is unlikely to be normally ejected.

As described above, in the print head of the flow mode A, the ink circulation flow reaches the vicinity of the interface12to have the positive velocity component. Accordingly, the ink inside the ejection port part17, or the ink in the vicinity of the interface12, in particular, can be easily replaced with ink in the flow path13, and can reduce the retention of the ink inside the ejection port part17. Therefore, the influence of the evaporation of the ink volatile component from the ejection port11, that is, the increase of the concentration of the coloring material in the ink inside the ejection port part17can be alleviated. However, as shown inFIG. 6B, even if the ink circulation flow exists inside the ejection port part17, there is a possibility of occurrence of the ink retention in the vicinity of the opening edge portion of the ejection port11. Reasons for this are that, due to the viscosity of ink, the ink circulation flow is unlikely to occur in the vicinity of the opening edge portion of the ejection port11, and that the evaporation rate of the ink volatile component at the opening edge portion of the ejection port11is too high so that the ink is apt to thicken in the vicinity of the opening edge portion of the ejection port11. InFIG. 6C, a horizontal axis indicates positions of the ejection port11in its width direction by assuming a central position of the ejection port11as a fiducial point, whereas a vertical axis indicates evaporation speeds of the ink volatile component at corresponding positions. As shown inFIG. 6C, the evaporation speed for the opening edge portion of the ejection port11is high. This is because that, as will be described later, ink from the opening edge portion of the ejection port11is apt to be diffused compared to the ink at the central part of the ejection port11. As such, the evaporation rate of the ink volatile component at the opening edge portion of the ejection port11is high and the ink circulation flow is unlikely to occur, and therefore, the ink in the vicinity of the opening edge portion of the ejection port11is apt to be concentrated.

In the present embodiment, for suppressing such evaporation rate of the ink volatile component at the opening edge portion of the ejection port11, besides the ejection port11and the ejection port part17, an ejection port and an ejection port part in which an ink meniscus interface is not formed in a stationary state are newly provided. Hereinafter, the former ejection port11and ejection port part17are referred to as a first ejection port and a first ejection port part, whereas the latter ejection port and ejection port part are referred to as a second ejection port and a second ejection port part.

In this example, with respect to the print head in which the first ejection port11and the first ejection port part17are formed as shown inFIGS. 7A and 7B, second ejection ports21,23and second ejection port parts22,24as shown inFIGS. 8A and 8BandFIGS. 9A and 9Bare respectively provided. It should be noted that columns20constituting filters are formed between the element substrate18and the orifice plate19. An opening diameter of the second ejection port21inFIGS. 8A and 8Bis larger than that of the first ejection port11, and the second ejection port part22communicating between the second ejection port21and the first ejection port11extends in a straight manner in an ink ejecting direction. The second ejection port23shown inFIGS. 9A and 9Bhas a larger diameter than that of the first ejection port11, and the second ejection port part24communicating between the second ejection port23and the first ejection port11includes an inclined face which is inclined radially outward along a direction from the first ejection port11to the second ejection port23. The inclined face in the second ejection port part24of this example is a concave face along a curve line (for example, a catenary curve). These second ejection ports21,23and ejection port parts22,24are formed on a second orifice plate25which is located above the orifice plate19. Hereinafter, the forms of ejection ports shown inFIGS. 7A and 7B,FIGS. 8A and 8B, andFIGS. 9A and 9Bare referred to as a form A, a form B, and a form C, respectively.

The second ejection ports21,23in this example have cross-sectional circular shapes which are identical to that of the first ejection port11, and their central axes are identical to that of the first ejection port11. Therefore, those second ejection ports21,23include enlarged diameter portions in which diameters are enlarged in a radially outward manner from the opening edge portion of the first ejection port11. The enlarged diameter portion is located at the entire perimeter of the opening edge portion of the first ejection port11. Such an enlarged diameter portion may not necessarily be located at the entire perimeter of the opening edge portion of the first ejection port11, but may be enlarged radially outward from at least a part of the opening edge portion of the ejection port11. As described above, since ink is apt to be retained in the downstream side in the ink flow direction inside the ejection port part17, it is preferable that the enlarged diameter portion be located at least in the downstream side of the flow direction. Further, the shapes of the first ejection port and the second ejection port are not limited to a circular shape as shown inFIG. 9A, but may be, for example, an oval shape. In addition, as will be described later with reference toFIGS. 15A and 15B, their shapes may be an ejection port shape including a plurality of protrusions extending from the outer edge of the ejection port toward a center thereof.

(Print Head of Flow Mode B)

FIG. 10Ais a graph illustrating the temporal change in average evaporation speeds of the volatile component of ink from the ejection port in the print head of the flow mode B (J=1.3), and the comparison results of a case where the forms of ejection ports in the print head are set to be forms A, B, and C shown inFIGS. 7A and 7B,FIGS. 8A and 8B, andFIGS. 9A and 9B, respectively. The evaporation rates of the ink volatile component for the forms A, B, and C in an initial stage become lower in the named order. Such a result is caused by the degree of ink diffusivity at the opening edge portion of the ejection port.FIG. 11AandFIG. 11Bare diagrams illustrating the degree of ink diffusivity in the ejection ports of the forms A and C as shown inFIGS. 7A and 7BandFIGS. 9A and 9B, respectively. As for those ejection ports of the forms A and C, their degrees of diffusivity of ink located at respective portions other than the opening edge portions of the ejection ports are identical. Meanwhile, as for each of those ejection ports of the forms A and C, an atmosphere area in which ink located at the opening edge portion of the ejection port is apt to be diffused is larger than an atmosphere area in which ink located at a portion other than the opening edge portion of the ejection port is apt to be diffused. For this reason, in each of the ejection ports of the forms A and C, ink located at the opening edge portion of the ejection port is more likely to be diffused than ink located at a portion other than the opening edge portion of the ejection port.

In a case of comparing the ejection ports of the forms A and C, the form C has the second ejection port23and the second ejection port part24, and thus, the atmosphere area in which ink located at the opening edge portion of the ejection port of the form C is apt to be diffused is decreased, and diffusion of such ink is suppressed.FIG. 11Cis a diagram illustrating the distribution of evaporation speeds of the volatile component of ink from the ejection ports of the forms A and C. In the form C, the evaporation rate of the volatile component of ink located at the opening edge portion of the ejection port is suppressed. As such, due to the existence of the second ejection port23and the second ejection port part24, the evaporation rate of the ink volatile component at the opening edge portion of the ejection port is suppressed.

Incidentally, along with the lapse of time, a difference among the evaporation rates of the volatile components of ink from the ejection ports of the forms A, B, and C becomes small. A reason for this is that, as the print head is in the flow mode B, ink inside the ejection port part17, in particular, the ink in the vicinity of the interface12is unlikely to be replaced by the ink circulation flow.FIG. 12AandFIG. 12Bare diagrams illustrating the states of concentrated ink in the print heads of the flow mode B in the ejection ports of the forms A and C. In each of the forms A and C, the concentrating of ink in the vicinity of the interface of the ejection port is not resolved, and thus, it is assumed that a difference in the evaporation rates of the volatile component of ink at the opening edge portions of the ejection ports is unlikely to occur as shown inFIG. 11C.

(Print Head of Flow Mode A)

FIG. 10Bis a graph illustrating the temporal change in average evaporation speeds of ink from ejection ports in the print head of the flow mode A (J=2.3), and the comparison results of a case where the forms of ejection ports in the print head are set to be forms A, B, and C shown inFIGS. 7A and 7B,FIGS. 8A and 8B, andFIGS. 9A and 9B, respectively. Although a difference in the evaporation rates of the ink volatile component for the forms A, B, and C in an initial stage is similar to the above-described case ofFIG. 10A, the difference remains to be large irrespective of the lapse of time. A reason for this is that, as the print head is in the flow mode A, ink in the ejection port part17, in particular, the ink in the vicinity of the interface12is apt to be replaced by the ink circulation flow, and thus, the difference in the evaporation rates of the volatile component of ink at the opening edge portions in the ejection ports of the forms A, B, and C is apt to be apparent.FIG. 12CandFIG. 12Dare diagrams illustrating the states of concentrated ink in the print head of the flow mode A in the ejection ports of the forms A and C. Regardless of the print head having the flow mode A, in the case of the form A, the concentrating of ink occurs at the opening edge portion of the ejection port as shown inFIG. 12C. Meanwhile, in the case of the form C, the concentrating of ink is suppressed at the opening edge portion of the ejection port as shown inFIG. 12D. Therefore, normal ejection can be achieved even in a case where the thickening caused by the concentrating of ink at the opening edge portion of the ejection port is less affected, in particular, in a case where the solid content of ink is high (for example, 8% or more).

Forms of the second ejection port are not limited only to the forms B and C as shown inFIGS. 8A and 8BandFIGS. 9A and 9B, respectively, but the same effect can be obtained even in the forms shown in, for example,FIGS. 13A and 13B,FIGS. 14A and 14B, andFIGS. 15A and 15B. A second ejection port26shown inFIGS. 13A and 13Bhas a larger diameter than that of the first ejection port11, and a second ejection port part27has a shape in which the inner diameter becomes smaller as it approaches the first ejection port11with the inner face of the second ejection port part27running along a straight line. A second ejection port28shown inFIGS. 14A and 14Bhas a larger diameter than that of the first ejection port11, and a second ejection port part29has a shape in which the inner diameter becomes smaller as it approaches the first ejection port11with the inner face of the second ejection port part29depicting a convex curve. Particularly, the second ejection port28and the second ejection port part29inFIGS. 14A and 14Bare effective in suppressing the evaporation of the volatile component of ink from the ejection port. A second ejection port30shown inFIGS. 15A and 15Bhas a larger diameter than that of the first ejection port11, and a second ejection port part31has a shape in which the inner diameter becomes smaller as it approaches the first ejection port11with the inner face of the second ejection port part31running along a concave curve. As for an opening diameter in the case of an ejection port of a variant shape in place of the circular shape as shown inFIG. 15A, a largest opening diameter of the variant shape is to be considered. Specifically, in the case of the first ejection port11inFIGS. 15A and 15B, the relation between an opening diameter of a portion other than two protrusions and an opening diameter of the second ejection port30therein are to be considered. The first ejection port11inFIGS. 15A and 15Bis provided with protrusions11A facing each other, and the same effect can be obtained by such a structure.

As described in each of the above embodiments, it is preferable that the liquid ejecting head include the first ejection port disposed in an upstream side in an ejecting direction of liquid to be ejected from the ejection port and the second ejection port disposed in a downstream side, and that an opening diameter of the second ejection port be larger than a diameter of the first ejection port. Further, in the ejection port part (second ejection port part) communicating between the first ejection port and the second ejection port, an opening diameter on a second ejection port side should preferably be larger than an opening diameter on a first ejection port side.

OTHER EMBODIMENTS

The present invention may have a configuration such that a liquid ejecting head in which liquid is circulated includes first and second ejection ports disposed in an upstream side and downstream side in a liquid ejecting direction, wherein the second ejection port includes an enlarged diameter portion whose diameter is enlarged in a radially outward manner from at least a part of an opening edge portion of the first ejection port. A second ejection port part communicating between the first ejection port and the second ejection port may include a gap portion as inFIGS. 8A and 8B, and the degree of a gap for the gap portion should desirably be small. The first ejection port may be located at a position where ink meniscus is formed. Further, three or more ejection ports may be configured to be located at positions deviated in the liquid ejecting direction. Such a configuration of the first and second ejection ports allows suppressing thickening of liquid in the vicinity of the ejection port. Furthermore, the relation between a height H, a length P, and a width W may be specified to set a liquid flow mode to be A and thus more securely suppress the liquid thickening in the vicinity of the ejection port.

The present invention can be widely applied to a liquid ejecting head and a liquid ejecting apparatus which eject various kinds of liquid. For instance, a printer, a copying machine, a facsimile machine including a communication system, an apparatus such as a word processor including a printing unit, and further, an industrial printing apparatus combined with various processing apparatuses for multifunctional use such as a 3D printer are applicable. In addition, the present invention can be used for the purpose of biochip fabrication and electronic circuit printing.

This application claims the benefit of Japanese Patent Application No. 2017-123087 filed Jun. 23, 2017, which is hereby incorporated by reference herein in its entirety.