LIQUID EJECTION HEAD AND LIQUID EJECTION APPARATUS

A liquid ejection head including an ejection port forming part, a flow path forming part including a liquid chamber, and an individual supply flow path configured to supply liquid to the liquid chamber, and a substrate including a supply flow path configured to supply liquid to the individual supply flow path and an outflow flow path configured to cause liquid to flow out of the liquid chamber, wherein a height of the individual supply flow path is larger than a height from a surface of the liquid chamber facing the ejection port to the ejection port forming member, and when viewed from the direction perpendicular to the surface of the substrate, a sidewall surface of the liquid chamber on a side with the supply flow path (1) coincides with an end surface of the ejection port, or (2) is disposed within the ejection port.

BACKGROUND

Field of the Disclosure

The present disclosure relates to a liquid ejection head and a liquid ejection apparatus.

Description of the Related Art

In recent years, printing using a liquid ejection head has been utilized extensively, and with increase of use of printing, it has been expected that printing is able to be performed on various types of media. Optimum amounts of liquid droplets vary among target media. In printing on corrugated cardboards, for example, a liquid ejection head having the ejection amount per liquid droplet of 20 to 30 picoliters (pL) is used in some cases. Thus, the demand for stable and reliable ejection of a large liquid-droplet amount has been raised.

A liquid ejection head included in a liquid ejection apparatus that ejects liquid, such as ink, has an issue that a volatile component in the liquid evaporates from an ejection port from which the liquid is ejected, and thus a liquid viscosity in the vicinity of the ejection port may increase. This leads to a change in the ejection speed of an ejected liquid droplet and affects landing accuracy. In particular, in a case where a halt time after ejection is long, increase in liquid viscosity is significant, and the fluid resistance of liquid increases because of a solid component adhering to an area in the vicinity of the ejection port, which may results in an ejection defect.

Examples of measures against the above described issue include a method of causing liquid to flow into an ejection port part (inside a nozzle) of a liquid ejection head to prevent increase in liquid viscosity. Because the liquid flows not only in a flow path but also in the ejection port part, the liquid in the ejection port part is constantly replaced, whereby increase in viscosity of the liquid due to evaporation from the ejection port is reduced. Japanese Patent Application Laid-Open No. 2017-124610 discusses a liquid ejection head that causes liquid in a flow path of the liquid ejection head to efficiently flow into an ejection port part, by specifying a relationship among the height of the flow path, the thickness of a member forming an ejection port (the length of the ejection port part), and the length of the ejection port in a liquid flow direction in the flow path.

In order to increase the ejection amount per liquid droplet in the liquid ejection head having the configuration in which liquid is caused to efficiently flow into the ejection port part as discussed in Japanese Patent Application Laid-Open No. 2017-124610, the height of the flow path for supplying liquid to the ejection port may be increased, and the thickness of the member forming the ejection port may be increased. In this case, however, the liquid may not flow into the entire ejection port part, and an increase in liquid viscosity may occur.

SUMMARY

Aspects of the present disclosure generally provide a liquid ejection head capable of preventing an increase in liquid viscosity, and capable of ejecting a liquid droplet that is large in volume.

According to an aspect of the present disclosure, a liquid ejection head including an ejection port forming part having an ejection port from which liquid is ejected, a flow path forming part including a liquid chamber facing the ejection port in a direction of liquid ejection from the ejection port and configured to supply liquid to the ejection port, and an individual supply flow path configured to supply liquid to the liquid chamber, and a substrate including a supply flow path configured to cause liquid to flow into the individual supply flow path and an outflow flow path configured to cause liquid to flow out of the liquid chamber, wherein the following inequality is satisfied:

where, in a direction perpendicular to a surface of the substrate, a height of the individual supply flow path is Hs μm, and a height from a surface of the liquid chamber facing the ejection port to the ejection port forming member is Hj μm, and wherein on a straight line passing through a center of the ejection port in a liquid flow direction when viewed from the direction perpendicular to the surface of the substrate, (1) a sidewall surface of the liquid chamber on a side with the supply flow path coincides with an end surface of the ejection port, or (2) the sidewall surface is disposed within the ejection port.

DESCRIPTION OF THE EMBODIMENTS

A liquid ejection head according to each of embodiments of the present disclosure will be described below with reference to the drawings. Each of the following embodiments is directed to an inkjet printing head from which ink as liquid is ejected and an inkjet printing apparatus, but the present disclosure is not limited thereto. The liquid to be ejected is not limited to ink. In each of the embodiments, a thermal-type element that generates a bubble by heat to eject liquid is used as an energy generating element, but the present disclosure is also applicable to a configuration using a piezoelectric-type element and elements of other various liquid ejection types.

Examples of the liquid ejection head of each of the embodiments include a line-type long head having a length corresponding to the width of a printed medium and a serial-type liquid ejection head that performs printing while scanning in a direction perpendicular to a direction of conveyance of a printed medium. Some of the serial-type liquid ejection heads have a plurality of printing element substrates, which is a case that separate printing element substrates for black ink and color ink are mounted, for example. In such a case, the plurality of printing element substrates can be disposed such that the ejection ports of adjacent printing element substrates overlap each other in an ejection port array direction.

Examples of the liquid ejection head of each of the embodiments include a head in which ink is supplied individually from ink tanks of cyan, magenta, yellow, and black (CMYK) to four ejection port arrays corresponding to the respective colors such that full color printing is able to be performed. The ejection port arrays for ejecting the respective inks of CMYK can be formed on the same printing element substrate. Alternatively, the ejection port arrays can be formed on separate printing element substrates.

The embodiments to be described below are preferred specific examples of the present disclosure, and provided with technically desirable various limitations. However, the present disclosure is not limited to the embodiments to be described below, as long as the idea of the present disclosure is satisfied.

FIG.1is a perspective schematic view of a printing element substrate100of a liquid ejection head according to a first embodiment of the present disclosure, andFIGS.2A to2Dare enlarged views of a part in the vicinity of an ejection port7of the liquid ejection head.FIG.2Ais an enlarged plan view of the part in the vicinity of the ejection port7of the liquid ejection head,FIG.2Bis a cross-sectional view taken along a line lib-III) ofFIG.2A,FIG.2Cis a cross-sectional view taken along a line IIc-IIc ofFIG.2A, andFIG.2Dis a cross-sectional view taken along a line IId-IId ofFIG.2A.

As illustrated inFIG.2B, the liquid ejection head of the present embodiment includes a substrate1, a first flow path forming member3(flow path forming part) forming an individual flow path8for liquid on the front surface of the substrate1, and an ejection port forming member4connected to an upper part of the first flow path forming member3. The ejection port forming member4(ejection port forming part) has the ejection port7for ejecting liquid, and an ejection port part7b(nozzle) communicating with the ejection port7and the individual flow path8. The ejection port forming member4can have a layered structure including a plurality of layers. The substrate1includes an energy generating element2that generates energy for ejecting ink from the ejection port7, a liquid supply path9afor supplying ink into the individual flow path8, and a liquid collection path9b(outflow flow path) for draining ink out from the individual flow path8.

In the ejection port forming member4, the ejection port7is formed such that the ejection port7substantially faces the energy generating element2, and thus the ejection port7and the energy generating element2form one ink ejection unit. As illustrated inFIG.1, a plurality of ink ejection units arranged in a row on the printing element substrate100forms an ejection port array110. While, in the present embodiment, the ejection ports7are arranged at an in-array density of 300 dots per inch (dpi) and the ejection port arrays110are formed in two rows in the printing element substrate100, the number of the ejection port arrays110is not limited to the above described configuration.

FIG.2Bis a cross-sectional view in a direction parallel to the flow direction of ink10in the flow path. A liquid chamber6including the energy generating element2and a second flow path forming member5are disposed in the individual flow path8formed with the first flow path forming member3. The individual flow path8formed between the second flow path forming member5and the ejection port forming member4includes an individual supply flow path8a, which is on a side with the liquid supply path9aand supplies liquid to the liquid chamber6and the ejection port7, and an individual collection flow path8b(individual outflow flow path), which is on a side with liquid collection path9band drains liquid out from the liquid chamber6and the ejection port7. As long as the second flow path forming member5is disposed on a side with the individual supply flow path8a, the position of the second flow path forming member5is not limited to a position to interpose the energy generating element2. The second flow path forming member5can be formed integrally with the first flow path forming member3.

The individual supply flow path8aand the individual collection flow path8bare connected to the liquid supply path9a(supply flow path) and the liquid collection path9b(outflow flow path), respectively, which are disposed on the substrate1. With this configuration, the ink10supplied from the liquid supply path9aflows a flow path that reaches the liquid collection path9bvia the individual supply flow path8a, a part in the vicinity of the ejection port7, the liquid chamber6, and the individual collection flow path8b. The flow path connected to the liquid chamber6and communicating with the liquid supply path9aand the liquid collection path9b, as a whole, can be referred to as the individual flow path8. In the present embodiment, the individual supply flow path8ais formed on the side with the liquid supply path9aand the individual collection flow path8bis formed on the side with the liquid collection path9b, with respect to one liquid chamber, i.e., the liquid chamber6.

The liquid supply path9aand the liquid collection path9bare disposed at positions between which the ejection port array110is disposed, in a direction parallel to the ejection port array110. The liquid supply path9aand the liquid collection path9bare connected to a common supply path (not illustrated) and a common collection path (not illustrated), respectively, which are connected to an ink supply tank (not illustrated). In the present embodiment, the ink10circulates the inside of the individual flow path8up to the liquid ejection head and the ink supply tank disposed outside the individual flow path8, by the pressure difference between the liquid supply path9aand the liquid collection path9b. The energy generating element2is driven to apply energy to the ink10supplied from the liquid supply path9ato the liquid chamber6through the individual supply flow path8a, and the ink is ejected from the ejection port7, so that a liquid droplet is formed. The ink10not ejected from the ejection port7is guided from the liquid chamber6to the liquid collection path9bthrough the individual collection flow path8b. The energy generating element2of the present disclosure is not particularly limited in terms of configuration as long as the energy generating element2is an ejection element capable of controlling the ejection of the ink10from the ejection port7. While, in the present embodiment, a resistance-type heater is used as an example of the energy generating element2, other types of heater, such as a piezoelectric actuator and an open-close valve, can also be used. In addition, in the present disclosure, the means for supplying the ink10to the above-described circulation path is not limited to the differential pressure between the liquid supply path9aand the liquid collection path9b. Alternatively, a liquid flow generation source can be disposed in the individual flow path8, in the liquid supply path9aand the liquid collection path9b, or in the common path. Examples of the liquid flow generation source include a resistance-type heater, a piezoelectric actuator, and an electroosmotic flow.

FIG.2Cis a cross-sectional view in the vicinity of the individual flow path8(individual supply flow path8a) taken in a direction perpendicular to an ink flow direction in the flow path. The individual flow path8is formed by the ejection port forming member4and the second flow path forming member5, and has a height Hs(μm) in an ink ejection direction (direction of liquid ejection).

FIG.2Dis a cross-sectional view in the vicinity of the center of the liquid chamber6taken in the direction perpendicular to the ink flow direction in the flow path. The liquid chamber6is formed with the substrate1, the ejection port forming member4, and the first flow path forming member3. In the ejection port forming member4, the ejection port7is formed at a position corresponding to the energy generating element2. A height from a surface where the energy generating element2is disposed in the liquid chamber6to a surface of the ejection port forming member4(ejection port part7b) on the side with the individual flow path8in the ink ejection direction will be hereinafter expressed as height Hj(μm). Similarly, a height from the surface where the energy generating element2is disposed in the liquid chamber6to the individual supply flow path8aon a side with the liquid chamber6(the substrate side) will be expressed as height Hw(μm). Here, desirably, the height Hjis 40 μm or more, to obtain a large liquid-droplet volume intended in the present disclosure. Further, a diameter D (μm) of the ejection port7is, desirably, 20 μm or more. Satisfying the above-described conditions realizes a configuration advantageous to obtain an ink ejection amount (the volume of one ink droplet) of 20 picoliters (pL) or more.

As described above, in the present disclosure, the liquid chamber6satisfying Hj>Hsis formed. In other words, a liquid chamber being recessed more than the individual supply flow path in a direction opposite to the direction of liquid ejection is disposed, whereby a large liquid-droplet volume intended in the present disclosure is realized. Thus, as compared with a case where the diameter D of the ejection port is increased as a means of increasing the liquid droplet volume, a distance between the adjacent ejection ports can be set short, which is advantageous in that resolution of the ejection port can be increased.

In the liquid ejection head of the present disclosure, desirably, the length of the opening of the liquid chamber6is less than the length (diameter D) of the ejection port7on a straight line passing through the center of the ejection port7in the ink flow direction.FIGS.3and4are diagrams each illustrating a flow distribution of ink in a state in which the circulation of ink flowing through the liquid ejection head is in a steady state. Arrows in each ofFIGS.3and4indicate the speed of the flow of the ink, from the individual supply flow path8ato the liquid chamber6, the ejection port7, and the individual collection flow path8b, and the magnitude of the flow velocity of the ink is expressed by the length of each of the arrows. In the configuration illustrated inFIG.3, the length of the opening of the liquid chamber6is less than the diameter D of the ejection port7on the straight line passing through the center of the ejection port7in the ink flow direction. In this case, the ink flows into the ejection port part7b, reaches the vicinity of the liquid surface (meniscus position) of the ejection port7, and then flows again through the ejection port part7btoward the individual collection flow path8b. In such an ink flow, the concentrated ink is constantly replaced by the ink supplied from the liquid supply path9anot only in the ejection port part7bthat is easily affected by evaporation but also the vicinity of the liquid surface of the ejection port7where evaporation particularly occur.

Meanwhile, in the configuration illustrated inFIG.4, the length of the opening of the liquid chamber6is greater than the diameter D of the ejection port7on the straight line passing through the center of the ejection port in the ink flow direction. In this case, the ink flow toward the ejection port part7bis small, and concentrated ink in the ejection port part7bis not sufficiently replaced.

As described above, it is desirable that the length of the opening of the liquid chamber6is less than the diameter D of the ejection port7on the straight line passing through the center of the ejection port7in the ink flow direction. In this case, in a plan view from the ink ejection direction, a sidewall surface of the second flow path forming member5(sidewall surface of the liquid chamber6) on the side with the ejection port7in the ink flow direction is disposed within the ejection port7. In this case, in an area where the second flow path forming member5and the ejection port7overlap each other with an overlap amount L, a flow field toward the inside of the ejection port part7bis formed. Here, the overlap amount L indicates the length of the second flow path forming member5disposed within the ejection port7on the straight line passing through the center of the ejection port7in the ink flow direction, when viewed from the ink ejection direction (seeFIG.2B). With increase in the overlap amount L, efficiency of the ink entering the ejection port part7bis increased, so that a strong ink flow toward the vicinity of the liquid surface of the ejection port7is formed. Even in a configuration in which the sidewall surface of the second flow path forming member5on the side with the ejection port7and an end surface of the ejection port7substantially coincide with each other (the overlap amount L=0), when viewed from the ink ejection direction, an ink flow formation effect similar to the effect inFIG.3can be obtained. Based on the foregoing, a configuration in which the overlap amount L is 0 or more is desirable. In the liquid ejection head of the present disclosure, an effect of the present disclosure can be obtained even in a case in which the length of the opening of the liquid chamber6is greater than the diameter D of the ejection port7, as long as the overlap amount L on the side with the individual supply flow path8ais 0 or more.

More desirably, the relationship between the height Hsof the individual flow path8and the height Hwof the liquid chamber6is Hw≥Hs. With this configuration, the liquid droplet volume to be ejected is increased, and increase in liquid viscosity due to evaporation of liquid from the ejection port7is decreased. Specifically, a sufficient volume of the liquid chamber6is secured because the height Hwis large, and moreover, the flow velocity of the ink increases because the height Hsis small, whereby the ink easily flows into the ejection port part7b.

In addition, it is more desirable that the relationship between a height (thickness) Hn(μm) of the ejection port forming member4in the ink ejection direction and the height Hwis Hw≥Hn. With this configuration, the liquid droplet volume to be ejected is increased, and increase in liquid viscosity due to evaporation of liquid from the ejection port7is decreased. Specifically, a sufficient volume of the liquid chamber6is secured because the height Hwis large, and moreover, the ink flowing into the ejection port part7beasily flows the vicinity of the liquid surface of the ejection port7because the height Hnis small.

Next, a condition for efficiently replacing the ink in the ejection port7will be described.FIG.3is a diagram illustrating a flow distribution of the ink10in the ejection port7, the ejection port part7b, the liquid chamber6, and the individual flow path8in a state in which the ink flow (seeFIG.2B) of the ink10flowing through the individual flow path8, the ejection port part7b, and the liquid chamber6of the liquid ejection head is in a steady state. The arrows inFIG.3indicate the speed of the flow of the ink, and the magnitude of the flow velocity of the ink is expressed by the length of each of the arrows.

In the liquid ejection head of the present embodiment, an effect of causing the ink to flow efficiently into the ejection port part7bcan be obtained when the height Hsof the individual supply flow path8a, the height Hnof the ejection port forming member4, and the diameter D of the ejection port7in the ink flow direction have a relationship represented by the following inequality (1).

In the following description, the left-side value of the above-described inequality (1) will be referred to as circulation efficiency J. The ink flowing through the individual supply flow path8aflows into the ejection port part7band returns to the individual flow path8(individual collection flow path8b) as illustrated inFIG.3, when the above-described inequality (1) is satisfied. This flow can reduce increase in viscosity of the ink in the ejection port part7b. With increase in the value of the circulation efficiency, the effect of reducing increase in viscosity of the ink is obtained at a higher level.

The relationship between dimensions and circulation efficiency in the vicinity of the ejection port7in liquid ejection heads of various shapes including the liquid ejection head of the present disclosure will be described.FIG.5illustrates the relationship between structure dimensions and circulation efficiency J in the vicinity of the ejection port part. Four curves inFIG.5are contour lines each indicating the relationship among values that can be taken by Hn, Hs, and D, in a case where the circulation efficiency J is at 1.0, 1.7, 2.5, and 4.0, in the liquid ejection heads satisfying the above-described inequality (1). It is desirable that the liquid ejection head of the present disclosure have a configuration in which Hs, Hn, and D satisfy the above-described inequality (1) and which is in an area higher than a curve of J=1.7 inFIG.5. In particular, a liquid ejection head in which Hnis 15 μm or less, Hsis 20 μm or less, and D is 30 μm or more in the ink ejection direction perform higher definition printing, and is therefore desirable.

An ink replacement amount in the ejection port part7bis determined by a circulation flow velocity. In the present embodiment, the ink flow velocity at a part (individual supply flow path8a) corresponding to the smallest height of a connection part between the individual flow path serving as the supply flow path and the liquid chamber is, for example, about 0.1 to 100 mm/sec. In this case, even in a case where ejection operation is performed in a state where ink flows while an ink flow is formed in the ejection port part7b, an influence on landing accuracy and the like is relatively small.

Next, the influence of the dimensions, the circulation efficiency J, and the overlap amount L in the vicinity of the ejection port7in the liquid ejection head of the present disclosure on ejection stability will be described.FIG.6is a diagram illustrating the circulation efficiency J and the ejection stability in liquid ejection heads of various shapes.FIG.6illustrates stability of ink ejection performance in dimension configuration examples in the vicinity of the ejection port part, in a case where reference ink is used. Here, the reference ink is liquid that represents ink properties for the present liquid ejection head, and the viscosity and surface tension of the reference ink have been adjusted. For example, liquid in a range of ink viscosity of 1.5 to 10 centipoise (cP) and surface tension of 20 to 50 mN/m is used. As illustrated inFIG.6, in Configuration Example 1 in which the above-described inequality (1) is satisfied and the circulation efficiency J is 4.4 that is sufficiently large, the ejection stability is satisfactory in both cases of L=0 and L=5. In Comparative Examples 1 to 3 in which the inequality (1) is not satisfied, satisfactory ejection stability is not obtained even in a case of L=5. In Configuration Examples 2 to 4 in which the circulation efficiency J is smaller than in Configuration Example 1, although the inequality (1) is satisfied, satisfactory ejection stability is obtained in the case of L=5. From the above-described results, it is apparent that, in addition to the size of the circulation efficiency J, the presence of the overlap amount L is important, to perform stable ejection while suppressing concentration of the liquid in the ejection port part in the liquid ejection head of the present disclosure.

Desirably, the overlap amount L has a sufficient length of Hnor more. In this case, a sufficient inflow of ink into the ejection port part7bcan be obtained when the circulation efficiency J is about 1.7 μm or more satisfying the above-described inequality (1). On the other hand, in a case where the overlap amount L is small, a configuration for higher circulation efficiency J is used to cause the ink to sufficiently flow into the ejection port part7b. As for the value of each of the circulation efficiency J and the overlap amount L, a value of each dimension in the liquid ejection head is determined such that an intended liquid droplet volume can be obtained.

As illustrated inFIG.2A, in the present embodiment, a width W of the liquid chamber6in a direction orthogonal to the ink flow direction when viewed from the ink ejection direction is less than the width of the individual flow path8. With this configuration, the flow velocity of the ink in the vicinity of the ejection port7is increased. In this configuration, however, an ink refill speed after ink ejection decreases. Thus, the structure can be selected based on the purpose to obtain an optimum outcome.

In addition, in the present embodiment, the ink flow direction is the same between ink ejection units adjacent in the ejection port array. Thus, reduction of ink concentration in the ejection port part7bwith respect to the plurality of ink ejection units can be realized by a differential pressure between the common supply path communicating with the plurality of liquid supply paths9aand the common collection path communicating with the plurality of liquid collection paths9b.

With the above-described configuration, even in a case where the concentrated ink stays in the ejection port part7b, the ink supplied from the liquid supply path9aflows into the ejection port part7bby the ink flow, whereby the concentrated ink is pushed out to the outside of the ejection port part7b. This reduces increase in viscosity in the ejection port7and reduces color unevenness of an image printed by ink ejection.

While, in the present embodiment, the inkjet printing apparatus (printing apparatus) having the configuration that circulates the liquid, such as ink, between the tank and the liquid ejection head is described, other configurations can be adopted.

Examples of configurations other than circulation of ink includes a configuration in which two tanks disposed at upstream and downstream sides of the liquid ejection head supply ink from one tank of the two tanks to the other tank, whereby ink in an individual flow path flows.

An example of a specific configuration in the present embodiment is as follows. The energy generating element2is a rectangle of 42 μm×30 μm, the height Hjof the first flow path forming member3is 40 μm, and the height Hnof the ejection port forming member4is 10 μm. The ejection port7is an ellipse with semicircular end parts and a long diameter in the ink flow direction, and has a long diameter (diameter D) of 45 μm, and a short diameter of 20 μm. The height Hwof the second flow path forming member5is 30 μm, and the length in the ink flow direction is 30 μm. When viewed from the ink ejection direction, the width in the direction orthogonal to the ink flow direction is 60 μm in the vicinity of the liquid chamber6(W), and 70 μm in an area other than the vicinity of the liquid chamber6. The overlap amount L is 7.5 μm, the height Hsof the individual supply flow path8aformed between the second flow path forming member5and the ejection port forming member4is 10 μm, and the length of the liquid chamber6in the flow direction is 35 μm. In this case, the circulation efficiency defined by the above-described inequality (1) is 4.5 μm. The ink viscosity is 4 cP, and the ink ejection amount (the volume of one ink droplet) in this case is about 25 pL.

When the differential pressure between the liquid supply path9aand the liquid collection path9bis 200 mmH2O, the flow velocity of the ink inflow into the ejection port part7bis 10 mm/sec at a maximum. Consequently, a sufficient ink flow toward the ejection port7can be obtained, and thus an effect of reducing the ink concentration in the ejection port7is obtained.

A liquid ejection head according to a second embodiment of the present disclosure will be described with reference toFIGS.7A to7D. The difference from the first embodiment will be mainly described below, and the redundant specific description of a configuration similar to the configuration of the first embodiment is omitted.

FIG.7Ais an enlarged plan view of a part of the liquid ejection head according to the second embodiment of the present disclosure.FIG.7Bis a cross-sectional view taken along a line VIIb-VIIb ofFIG.7A,FIG.7Cis a cross-sectional view taken along a line VIIc-VIIc ofFIG.7A, andFIG.7Dis a cross-sectional view taken along a line VIId-VIId ofFIG.7A.

As illustrated inFIGS.7A and7B, in the present embodiment, the center of the ejection port7is shifted to the side with the individual supply flow path8a, with respect to the center of the liquid chamber6on a straight line passing through the center of the ejection port7in the ink flow direction, when viewed from the ink ejection direction. In other words, when viewed from the ink ejection direction, the ejection port7is disposed at a position where the ejection port7overlaps a second flow path forming member5on the side with the individual supply flow path8a, that is, there is the overlap amount L, whereby ink easily flows into an ejection port part7b. Further, as illustrated inFIG.7C, in the individual supply flow path8a, the width in a direction orthogonal to a liquid flow direction is less than the width of the liquid chamber6. Thus, the flow velocity of ink flowing into the ejection port part7bis increased.

As illustrated inFIG.7D, in an individual flow path8on the side with the liquid collection path9bin the present embodiment, the second flow path forming member5the width of which in the direction orthogonal to the liquid flow direction is less than the width of the individual flow path8is disposed. In this case, the individual flow path8on the side with the liquid collection path9bincludes, in addition to an individual collection flow path8b, a bypass flow path between a first flow path forming member3and the second flow path forming member5. Thus, flow resistance in the individual collection flow path8bis reduced, whereby refilling the liquid chamber6and the ejection port7with ink after ink ejection proceeds faster. However, the flow velocity of ink flowing into the ejection port part7bis reduced. Thus, the structure is determined to obtain an optimum outcome in consideration of circulation efficiency in the ejection port part7band an ink refill speed.

In addition, in the present embodiment, since the ejection port7is formed in a circle, ink ejection stability is increased. Alternatively, in a case where the ejection port7is formed in an ellipse having a length in the ink flow direction, ink easily flows into the ejection port part7b. As for the shape of the ejection port7in the present disclosure, a known shape, such as a circle or an oval, can be used.

With the above-described embodiment, it is possible to reduce increase in viscosity of ink in the vicinity of the ejection port and to increase the volume of one ink droplet.

An example of a specific configuration in the present embodiment is as follows. The shift amount of the ejection port7with respect to the liquid chamber6is 7.5 μm, the diameter of the ejection port7is 30 μm, and the overlap amount L is 5 μm. The height Hjof the first flow path forming member3is 60 μm, the height Hnof an ejection port forming member4is 7.5 μm, and the height Hwof the second flow path forming member5is 45 μm. The height Hsof the individual supply flow path8aformed between the second flow path forming member5and the ejection port forming member4is 15 μm, and in this case, the circulation efficiency J defined by the above-described inequality (1) is 3.2 μm. The width W of the liquid chamber6is 70 μm that is the same as the width of the individual flow path8. The second flow path forming member5on the side with the liquid collection path9bhas a width of 30 μm, and is disposed at the center of the individual flow path8, when viewed from the ink flow direction. Thus, the individual flow path8on the side with the liquid collection path9bincludes the bypass flow path having a width of 20 μm on each of both sides with respect to the second flow path forming member5, when viewed from the ink flow direction. The ink viscosity is 3 cP, and the ink ejection amount (the volume of one ink droplet) in this case is about 35 pL.

An ink ejection head according to a third embodiment of the present disclosure will be described with reference toFIGS.8A and8B. The difference from the first embodiment will be mainly described below, and the redundant specific description of the configuration similar to the configuration of the first embodiment is omitted.

FIG.8Ais an enlarged plan view of a part of the liquid ejection head according to the third embodiment of the present disclosure, andFIG.8Bis a cross-sectional view taken along a line VIIIb-VIIIb ofFIG.8A.

As illustrated inFIG.8A, in the present embodiment, the individual flow path8is divided by a partition having a length in the liquid flow direction, and thus the resolution of the ejection port is increased.

In addition, it is possible to reduce the number of ejection ports to the half even with which printing resolution equivalent to that in a case where the partition is not present is obtainable.

An example of specific dimensions of each part in the present embodiment is as follows. The individual flow path8communicates with the liquid supply path9ashared between adjacent two ink ejection units, and the resolution of the ejection port7is 600 dpi. The ejection port7is an ellipse form with semicircular end parts having a long diameter in the ink flow direction, and has a long diameter (diameter D) of 40 μm and a short diameter of 20 μm. The ejection port7is disposed at a position shifted by 10 μm to the side with the individual supply flow path8awith respect to the liquid chamber6, and the overlap amount L is 10 μm. The height Hjof the first flow path forming member3is 44 μm, and the height Hnof the ejection port forming member4is 10 μm. The height Hwof the second flow path forming member5is 24 μm, the height Hsof the individual supply flow path8aformed between the second flow path forming member5and the ejection port forming member4is 15 μm, and the circulation efficiency J in an ejection port part7bis 3.2 μm. The width W of the liquid chamber6is 36 μm that is the same as the width of the individual flow path8, the length of the second flow path forming member5in the flow direction is 15 μm, and the energy generating element2is a rectangle of 35 μm×38 μm. The ink viscosity is 3 cP, and the ink ejection amount (the volume of one ink droplet) in this case is about 20 pL.

InFIGS.8A and8B, the overlap amount L on the side with the liquid supply path9ais approximately equivalent to the height Haof the ejection port forming member4. With this configuration, an effect of causing ink to flow into the ejection port part more efficiently can be obtained. In addition, the length of the second flow path forming member5in the ink flow direction is shorter than the length of a second flow path forming member5in the first and second embodiments. A volume in a part connecting the liquid supply path9aand the liquid collection path9bwith the individual flow path8is thus increased, whereby refilling the liquid chamber6and the ejection port7with ink after ink ejection proceeds faster.

With the above-described embodiment, it is possible to reduce increase in viscosity of ink in the vicinity of the ejection port and to increase the volume of one ink droplet.

An ink ejection head according to a fourth embodiment of the present disclosure will be described with reference toFIG.9. The difference from the first embodiment will be mainly described below, and the redundant specific description of a configuration similar to the configuration of the first embodiment is omitted.

FIG.9is an enlarged cross-sectional view of a part of the liquid ejection head according to the fourth embodiment of the present disclosure.

In the present embodiment, the individual flow path8includes, in addition to the individual collection flow path8b, a bypass flow path8ccommunicating with the liquid chamber6and the liquid collection path9bbelow the individual collection flow path8b, when viewed from an ink ejection direction. In a configuration illustrated inFIG.9, two flow paths that are the individual collection flow path8band the bypass flow path8care disposed at the respective positions at different levels in a substrate vertical direction on the side with the liquid collection path9b. Thus, even in a case where the bubble accidentally stays in the liquid chamber6, it is possible to obtain an effect of stabilizing ink ejection from the ejection port7by discharging a bubble. Further, in this configuration, since one flow path, which is the individual supply flow path8a, is disposed on the side with liquid supply path9a, ink efficiently flows into the ejection port part7b.

InFIG.9, while the three flow paths including the individual supply flow path8a, the individual collection flow path8b, and the bypass flow path8c, are connected to the liquid chamber6, the number of the bypass flow paths8ccan be two or more and can be disposed on the side with the individual supply flow path8a. However, in a case of the configuration including the bypass flow path8c, an ink circulatory flow flowing through the individual supply flow path8aand the individual collection flow path8bdecrease, and an ink flow flowing into the ejection port part7balso decrease. Thus, the arrangement of the bypass flow path8cis determined based on the purpose.

The arrangement of the bypass flow path8cconnecting to the liquid chamber is not limited to the above described configuration as long as the arrangement achieves implementation of ink circulation efficiency of the ejection port part and bubble discharge from the liquid chamber, and ink replacement of a fixed amount of ink in the liquid chamber.

According to the above-described embodiment, it is possible to reduce increase in viscosity of ink in the vicinity of the ejection port and to increase the volume of one ink droplet.

An ink ejection head according to a fifth embodiment of the present disclosure will be described with reference toFIG.10. The difference from the first embodiment will be mainly described below, and the redundant specific description of the configuration similar to the configuration of the first embodiment is omitted.

FIG.10is an enlarged cross-sectional view of a part of the liquid ejection head according to the fifth embodiment of the present disclosure. In the present embodiment, the second flow path forming member5is disposed at an individual supply flow path8aon the side with the liquid supply path9aand is not disposed at the individual collection flow path8bon the side with liquid collection path9b. In other words, a liquid chamber6and the individual collection flow path8bare integrated with each other. In this case, the height of the individual flow path8on the side with the liquid collection path9bis greater than the height of the individual flow path8on the side with the liquid supply path9a(the individual supply flow path8a). Thus, even in a case where the bubble stays in the liquid chamber6, it is possible to discharge a bubble effectively from the liquid chamber6, which leads to an effect of stabilizing ink ejection from an ejection port7. Meanwhile, since the individual supply flow path8ato which liquid is supplied is disposed in the vicinity of the ejection port7, ink efficiently flows into the ejection port part7b.

According to the above-described embodiment, it is possible to reduce increase in viscosity of ink in the vicinity of the ejection port and to increase the volume of one ink droplet.

A configuration of a printing element substrate of an ink ejection head according to a sixth embodiment of the present disclosure will be described with reference toFIGS.11A to11C. The difference from the first embodiment will be mainly described below, and the redundant specific description of a part having a configuration similar to the configuration of the first embodiment is omitted.

FIG.11Ais an enlarged plan view of a part of the liquid ejection head according to the sixth embodiment of the present disclosure.FIG.11Bis a cross-sectional view taken along a line XIb-XIb ofFIG.11A.

In the present embodiment, the center of a liquid chamber6and the center of an ejection port7are aligned on a straight line passing through the center of the ejection port7in the ink flow direction, and the length of the liquid chamber6in the ink flow direction is greater than the diameter D of the ejection port7. Thus, the configuration of the present embodiment has no overlap amount L between a second flow path forming member5and the ejection port7. Meanwhile, when viewed from the ink ejection direction, protrusions51protruding toward the center of the liquid chamber6to overlap the ejection port7is disposed on a side wall of the second flow path forming member5on the side with the ejection port7. The protrusions51are disposed on the straight line passing through the center of the ejection port7in the ink flow direction, when viewed from the ink ejection direction, and are disposed substantially symmetrical about the center of the ejection port7, in the configuration illustrated inFIGS.11A to11C. Because of the protrusions51, an effect of causing ink to flow easily into an ejection port part7bis obtained. Further, the protrusions51in the configurations illustrated inFIGS.11A to11Care disposed to be substantially symmetrical about the center of the liquid chamber6on the straight line passing through the center of the ejection port7in the ink flow direction. Thus, the configurations lead to an effect of preventing twisting of ejected ink with respect to an ejection pressure by an energy generating element, whereby tailing of the ejected ink is stabilized. The protrusions51are not necessarily formed continuously from the second flow path forming member5. As long as the protrusions51are disposed in the liquid chamber6, the protrusions51can be formed such that the protrusions51are supported by the first flow path forming member3, the ejection port forming member4or the substrate1, or can be disposed more than one.

In addition, as illustrated inFIG.11C, protrusions52similar to the protrusions51of the second flow path forming member5can be disposed in the ejection port7as well, to stabilize ink ejection. In this case, although a circulatory flow of ink to the vicinity of the liquid surface of the ejection port7may reduce, the protrusions52disposed with the protrusions51in an overlapping manner when viewed from the ink ejection direction lead to an effect of causing ink to flow into the ejection port part7b. InFIG.11C, the protrusions52are on the straight line passing through the center of the ejection port7in the ink flow direction when viewed from the ink ejection direction. In addition, the protrusions52are disposed substantially symmetrical about the center of the ejection port7. Because of the protrusions52, an effect of reducing tailing of an ejected liquid droplet is obtained. More specifically, the meniscus of ink formed between the protrusions52is easily maintained as compared with the meniscus formed by other parts. Thus, tailing of a liquid droplet extending from the ejection port7can be cut at earlier timing, whereby generation of mist formed of minuscule droplets generated accompanying a main droplet can be reduced.

If the distance between the protrusions52is long, tailing of the ejected liquid droplet increases, which results in generation of small satellite droplets. Thus, desirably, the distance between the protrusions52on the straight line passing through the center of the ejection port7in the ink flow direction when viewed from the ink ejection direction is 5.0 μm or less. On the other hand, if the distance between the protrusions52is too short, forming of the protrusions is difficult and an ejected liquid droplet may be separated into two. Thus, desirably, the distance between the protrusions52is 2.0 μm or more. In other words, the distance between the protrusions52is, desirably, 2.0 μm or more and 5.0 μm or less.

According to the above-described embodiment, it is possible to reduce increase in viscosity of ink in the vicinity of the ejection port and to increase the volume of one ink droplet.

A configuration of a printing element substrate of an ink ejection head according to a seventh embodiment of the present disclosure will be described with reference toFIGS.12A and12B. The difference from the first embodiment will be mainly described below, and the redundant specific description of a configuration similar to the configuration of the first embodiment is omitted.

FIG.12Ais an enlarged plan view of a part of the liquid ejection head according to the seventh embodiment of the present disclosure.FIG.12Bis a cross-sectional view taken along a line XIIb-XIIb ofFIG.12A.

In the present embodiment, the second flow path forming member5is disposed within an ejection port7when viewed from the ink ejection direction, and the height of a first flow path forming member3and the height of the second flow path forming member5are the same in the ink ejection direction. The second flow path forming member5is disposed such that the second flow path forming member5blocks a part of the individual flow path8on the side with the liquid supply path9a. Because the width of the individual flow path8communicating with the ejection port part7bfrom the side with the liquid supply path9ais narrow, ink flows into the ejection port part7band pushes ink in the ejection port part7b, and the pushed ink is discharged to a liquid collection path9b. The arrangement and shape of each of the first flow path forming member3and the second flow path forming member5that determine the shape of the individual flow path8on the side with the liquid supply path9aof the present embodiment are not limited to the structure illustrated inFIGS.12A and12B. These can be freely designed as long as ink efficiently flows into the ejection port part7bunder conditions in consideration of stability of ejected ink and an ink refill speed. Moreover, the stability of ink ejection can be enhanced by the ejection port7having a circular shape.

According to the above-described embodiment, it is possible to reduce increase in viscosity of ink in the vicinity of the ejection port and to increase the volume of one ink droplet.

According to the present disclosure, it is possible to provide a liquid ejection head capable of reducing increase in viscosity of liquid in a vicinity of an ejection port and also capable of ejecting a liquid droplet that is large in volume.

This application claims the benefit of Japanese Patent Applications No. 2022-108581, filed Jul. 5, 2022, and No. 2023-074226, filed Apr. 28, 2023, which are hereby incorporated by reference herein in their entirety.