3. The diaphragm 4 is a member that is capable of vibrating elastically, and applies pressure to the ink that is present inside the pressure compartment CB1, CB2. The diaphragm 4 is disposed substantially in parallel with an X-Y plane. On the −Z-side surface of the diaphragm 4, M-number of piezoelectric elements PZ1 corresponding respectively to the M-number of pressure compartments CB1, and M-number of piezoelectric elements PZ2 corresponding respectively to the M-number of pressure compartments CB2, are provided. The piezoelectric element PZ1, PZ2 is an energy conversion element that converts the electric energy of a drive signal transmitted from the control unit 90 into motion energy. In the present embodiment, the piezoelectric element PZ1, PZ2 is a passive element that deforms in accordance with a change in potential of the drive signal.

The wiring substrate 8 is mounted on the −Z-side surface of the diaphragm 4. The wiring substrate 8 is a component that provides electric connection between the control unit 90 and the liquid ejecting head 1. A flexible wiring board such as, for example, FPC or FFC is used as the wiring substrate 8. A drive circuit 81 is mounted on the wiring substrate 8. Based on a control signal, the drive circuit 81 switches whether or not to supply a drive signal to the piezoelectric element PZ1, PZ2.

The piezoelectric element PZ1, PZ2 deforms in accordance with a change in potential of the drive signal. The diaphragm 4 vibrates by being driven by the deformation of the piezoelectric element PZ1, PZ2. The vibration of the diaphragm 4 causes a change in the internal pressure of the pressure compartment CB1, CB2. Due to the change in the internal pressure of the pressure compartment CB1, CB2, ink with which the inside of the pressure compartment CB1, CB2 is filled is ejected from the nozzle N after flowing through the supply flow passage RR1/the discharge flow passage RR2 and the nozzle flow passage RN. Specifically, when the piezoelectric element PZ1 is driven by means of a drive signal, a part of the ink with which the inside of the pressure compartment CB1 is filled flows through the supply flow passage RR1 and then through the nozzle flow passage RN to be ejected from the nozzle N. When the piezoelectric element PZ2 is driven by means of a drive signal, a part of the ink with which the inside of the pressure compartment CB2 is filled flows through the discharge flow passage RR2 and then through the nozzle flow passage RN to be ejected from the nozzle N.

The liquid ejecting apparatus 100 according to the present embodiment circulates the ink from the common supply flow passage RA1 to the common discharge flow passage RA2 through the circulation flow passages RJ. For this reason, even if there is a period during which no ink that is present inside the pressure compartment CB1, CB2 is ejected from the nozzle N, it is possible to reduce or prevent the stagnation of the ink inside the pressure compartment CB1, CB2, the nozzle flow passage RN, and the like. Therefore, the liquid ejecting apparatus 100 according to the present embodiment makes it possible to reduce or prevent an increase in the viscosity of the ink inside the pressure compartment CB1, CB2, the nozzle flow passage RN, and the like and thus suppress the occurrence of ejection abnormality that disables the ejection of the ink from the nozzle N.

The liquid ejecting apparatus 100 according to the present embodiment ejects, from the nozzle N, the ink with which the inside of the pressure compartment CB1 is filled and the ink with which the inside of the pressure compartment CB2 is filled. Therefore, for example, as compared with a structure in which the ink of one pressure compartment CB1, CB2 only is ejected from the nozzle N, the liquid ejecting apparatus 100 according to the present embodiment makes it possible to make an amount of the ink ejected from the nozzle N larger.

A3. Detailed Structure of Nozzle N

FIGS. 5 to 7 are diagrams for explaining the nozzle N according to the present embodiment. FIG. 5 is a Z-directional view of the nozzle N. FIG. 6 illustrates a cross section taken along the line VI-VI of FIG. 5. FIG. 7 illustrates a cross section taken along the line VII-VII of FIG. 5. Note that, in FIGS. 5 to 7, the structure of the nozzle substrate 60 and the nozzle N only in the nozzle flow passage RN is illustrated, and the illustration of the structure of others is omitted.

As illustrated in FIGS. 5 to 7, the nozzle N includes a first portion P1 and a second portion P2. The second portion P2 is located closer to the nozzle flow passage RN in the Z direction than the first portion P1 is. That is, the nozzle N is configured as a two-tiered nozzle. The first portion P1 and the second portion P2 are formed by processing the nozzle substrate 60 by using an etching technology or the like. The first portion P1 is connected from the +Z-directional side to approximately the center in the X direction and the Y direction of the second portion P2. The first portion P1 ejects ink supplied from the second portion P2 toward the outside. As illustrated in FIG. 5, the length L1 of the first portion P1 in the X direction is substantially equal to the width W1 of the first portion P1 in the Y direction, and the first portion P1 has a shape that looks like a circle when viewed in the Z direction.

As illustrated in FIGS. 5 to 7, the length L2, the width W2, and the depth D2 of the second portion P2 are greater than the length L1, the width W1, and the depth D1 of the first portion P1 respectively. The width W2 of the second portion P2 is less than the width W10 of the nozzle flow passage RN. The capacity of the second portion P2 is larger than the capacity of the first portion P1. As illustrated in FIG. 5, the length L2 of the second portion P2 in the X direction is substantially equal to the width W2 of the second portion P2 in the Y direction, and the second portion P2 has a shape that looks like a circle. Therefore, it can also be said that the first portion P1 and the second portion P2 are concentric circles. A part of ink that flows through the nozzle flow passage RN in the X direction flows into the second portion P2. At least a part of the ink having flowed into the second portion P2 is supplied to the first portion P1.

In the present embodiment, a ratio between inertance M1 of the first portion P1 and inertance M2 of the second portion P2 (hereinafter will be referred to as “inertance ratio”) satisfies a relation of M2/M1<0.26. Let S be the cross-sectional area of the flow passage. Let 1 be the length of the flow passage. Let p be the density of the liquid. Given these definitions, inertance M of a flow passage through which liquid flows can be calculated using the following formula (1):

M=ρl/S (1)

Since the first portion P1 and the second portion P2 can be regarded each as a flow passage through which ink flows in the Z direction, the inertance M1 of the first portion P1 can be expressed as M1=ρd1/S1, where S1 denotes the cross-sectional area of the first portion P1 in a section on an X-Y plane, d1 denotes the length of the flow passage, that is, the length in the Z direction, and p denotes the density of the ink. Similarly, the inertance M2 of the second portion P2 can be expressed as M2=ρd2/S2, where S2 denotes the cross-sectional area of the second portion P2 in a section on an X-Y plane, d2 denotes the length of the flow passage, that is, the length in the Z direction, and ρ denotes the density of the ink. In the present embodiment, it is preferable if the inertance M1 is greater than 0.10, and it is preferable if the inertance M2 is greater than 0.001.

The inventors of the present application discovered that, by setting the inertance ratio in such a way as to satisfy the above-described relation of M2/M1<0.26, it is possible to suppress an increase in viscosity of ink inside the nozzle N. In related art, it was believed to be preferable to set a relatively high inertance ratio (for example, M2/M1>0.30) in a two-tiered nozzle. This is because a stable ejected droplet is achieved by making a difference between the inertance M2 and the inertance M1 small and reducing an inertance change between the second portion P2 and the first portion P1. When a two-tiered nozzle structure is applied to a nozzle that ejects a micro droplet, since its droplet ejection amount is smaller than that of an ordinary nozzle, liquid replacement occurs less frequently between the nozzle and the nozzle flow passage. Moreover, because of a smaller ejected droplet, an amount of meniscus oscillations is smaller, and it is thus difficult to agitate the ink (ink circulation) inside the nozzle by means of the meniscus oscillations. For this reason, the liquid whose viscosity has increased due to exposure to the air at a boundary interface between the nozzle and the air might stagnate inside the nozzle and, therefore, the liquid might not be ejected properly.

In view of these considerations, the inventors of the present application discovered that, by setting a smaller value for the inertance ratio in such a way as to satisfy the above-described relation of M2/M1<0.26, it is possible to circulate the ink inside the nozzle more and thus suppress an increase in the viscosity of the ink. FIG. 8 is an explanation diagram schematically illustrating an example of a state of a meniscus. The left part of FIG. 8 illustrates a meniscus Mn1 in a case where the inertance ratio is relatively low (for example, M2/M1<0.26), that is, a case where an inertance change between the second portion P2 and the first portion P1 is large. The right part of FIG. 8 illustrates a meniscus Mn2 in a case where the inertance ratio is relatively high (for example, M2/M1>0.30), that is, a case where an inertance change between a fourth portion P200 and a third portion P100 is small. The fourth portion P200 and the third portion P100 constitute a nozzle, and the capacity of the fourth portion P200 is larger than the capacity of the third portion P100. The thick arrow in FIG. 8 indicates the direction in which ink is ejected. As illustrated at the left part of FIG. 8, when the inertance change is large, the interface of the meniscus Mn1 inside the second portion P2 extends in a tapering manner in the −Z direction. This seems to be because the change in inertance is large when moving from the second portion P2, at which the inertance is relatively large (that is, it is easier for the ink to move), to the first portion P1, at which the inertance is relatively small (that is, it is harder for the ink to move). Since the meniscus Mn1 described above is formed, relatively great meniscus oscillations occur. For this reason, vortices indicated by arrows near the meniscus Mn1 are generated when the ink is ejected. The vortices agitate the ink inside the nozzle N greatly. On the other hand, as illustrated at the right part of FIG. 8, when the inertance change is small, the interface of the meniscus Mn2 inside the second portion P300 is relatively flat when compared with the meniscus Mn1. For this reason, vortices generated near the meniscus Mn2 when the ink is ejected are smaller than those generated near the meniscus Mn1. Since the vortices that are generated are smaller, the ink is harder to be agitated. Therefore, it is considered that, by setting the inertance ratio in such a way as to satisfy the relation of M2/M1<0.26, it is possible to suppress an increase in viscosity of ink inside the nozzle N and thus eject the ink properly.

In the liquid ejecting head 1 described above, the capacity of the first portion P1 is smaller than the capacity of the second portion P2, and the relation of M2/M1<0.26 is satisfied where M1 denotes the inertance of the first portion P1, and M2 denotes the inertance of the second portion P2; therefore, relatively great oscillations of the meniscus Mn1 occur when the liquid is ejected, and it is possible to greatly agitate the liquid inside the second portion. By this means, it is possible to suppress an increase in the viscosity of the liquid inside the nozzle.

B. Examples

An ejection test was conducted using a nozzle having various sizes. The ejection test was conducted by ejecting ink by using an ink-jet printer. The results are shown in Tables 1 and 2 below. In Examples, the test was conducted using the nozzle N the inertance ratio M2/M1 of which was set to be less than 0.26. In Comparative Examples, the test was conducted using the nozzle N the inertance ratio M2/M1 of which was set to be not less than 0.26. The density p of the liquid when calculating the inertance M1, M2 is 1. In Tables 1 and 2, all of the lengths L1 and L2, the widths W1 and W2, and the depths D1 and D2 are shown in micrometers. Both in Examples and Comparative Examples, the capacity of the first portion P1 is smaller than the capacity of the second portion P2. Since each of the first portion P1 and the second portion P2 is formed by etching a single nozzle substrate 60, the sum of the depth D1 and the depth D2 is equal to the thickness of the nozzle substrate 60.

TABLE 1

First Nozzle (N1)

First Portion (P1)
Second Portion (P2)
Inertance

Length
Width
Depth
Length
Width
Depth

M2/

L1
W1
D1
L2
W2
D2
M1
M2
M1
Evaluation

Example 1
10
10
16
37
37
49
0.2
0.04
0.22
A

Example 2
9
9
16
37
37
49
0.22
0.04
0.18
A

Example 3
8
8
16
37
37
49
0.29
0.04
0.14
A

Example 4
10
10
20
37
37
49
0.25
0.04
0.16
A

Example 5
10
10
25
37
37
49
0.34
0.04
0.11
A

Example 6
10
10
16
44
44
49
0.2
0.03
0.16
A

Example 7
10
10
16
52
52
49
0.2
0.02
0.11
A

Example 8
10
10
16
841
45
49
0.2
0.002
0.008
A

Example 9
10
10
16
841
45
40
0.32
0.002
0.005
A

Example 10
10
10
16
50
45
49
0.2
0.007
0.034
A

Example 11
10
10
16
70
45
49
0.2
0.005
0.025
A

Example 12
10
10
16
90
45
49
0.2
0.004
0.019
A

Example 13
10
10
16
120
45
49
0.2
0.003
0.014
A

Example 14
10
10
25
50
45
40
0.2
0.006
0.018
A

Example 15
10
10
25
70
45
40
0.2
0.004
0.013
A

Example 16
10
10
25
90
45
40
0.2
0.003
0.01
A

Example 17
10
10
25
120
45
40
0.2
0.002
0.007
A

TABLE 2

First Nozzle (N1)

First Portion (P1)
Second Portion (P2)
Inertance

Length
Width
Depth
Length
Width
Depth

M2/

L1
W1
D1
L2
W2
D2
M1
M2
M1
Evaluation

Comparative
11
11
16
37
37
49
0.17
0.04
0.26
B

Example 1

Comparative
20
20
30
37
37
35
0.1
0.03
0.33
C

Example 2

Comparative
22
22
30
37
37
35
0.08
0.03
0.4
C

Example 3

Comparative
23
23
25
37
37
40
0.06
0.04
0.61
C

Example 4

Comparative
21
21
35
37
37
40
0.1
0.04
0.61
C

Example 5

Comparative
26
26
35
37
37
30
0.07
0.03
0.4
C

Example 6

Comparative
29
29
25
37
37
40
0.04
0.04
0.93
C

Example 7

Comparative
26
26
20
37
37
45
0.04
0.04
1.09
C

Example 8

“Evaluation” shown at the right end of Tables 1 and 2 indicates the evaluation of ejection performance in the ejection test. Specifically, “A” means that an increase in viscosity of ink was suppressed due to sufficient agitation of the ink inside the nozzle N and that the ink was ejected properly. “B” means that, though the ink was ejected properly, there is a possibility that the agitation of the ink inside the nozzle N might be insufficient, and the viscosity of the ink might increase during use over a relatively long time. “C” means that the ink was not ejected properly with an increase in viscosity because of insufficient agitation of the ink inside the nozzle N.

In Examples 1 to 5, the test was conducted while changing the size of the first portion P1 only, without changing the size of the second portion P2. In Examples 6 to 13, the test was conducted while changing the size of the second portion P2 only, with the size of the first portion P1 set to be the same as the size in Example 1. Examples 14 to 17 correspond to Examples 10 to 13 respectively. Specifically, in each of Examples 14 to 17, the test was conducted while changing the depth D1 of the first portion P1 and the depth D2 of the second portion P2 only from their values of the corresponding one of Examples 10 to 13. As shown in Table 1, the evaluation result was “A” for all of Examples 1 to 17. This is presumably because, since the inertance ratio M2/M1 was set to be less than 0.26, the ink was agitated sufficiently inside the nozzle N, and an increase in viscosity of the ink was therefore suppressed. Note that, among them, the inertance ratio in Example 17 is 0.007, which is relatively low, and an amount of change between the inertance M1 and the inertance M2 is relatively large. For this reason, the agitation of ink can be performed sufficiently, and an increase in viscosity inside the nozzle N can be suppressed well; however, there is a possibility that the ejection of the ink might be unstable with an excessive extending of a meniscus in the direction of ejection. The inertance ratio in Example 9 is 0.005, which is relatively low. For the same reason as that of Example 17, the ejection of the ink might be unstable in Example 9, too.

As shown in Table 2, the evaluation result was “B” for Comparative Example 1. This is because, though the ink was ejected properly by setting the inertance ratio to be 0.26, there is a possibility that the agitation of the ink inside the nozzle N might be insufficient, and the viscosity of the ink might increase during use over a relatively long time. The evaluation result was “C” for all of Comparative Examples 2 to 8. This is because the agitation inside the nozzle N was insufficient due to their relatively high inertance ratio.

As is clear from the results of the ejection test described above, by setting the ratio between the inertance M1 of the first portion P1 and the inertance M2 of the second portion P2 of the nozzle N in such a way as to satisfy the relation of M2/M1<0.26, it is possible to greatly agitate the ink inside the nozzle N and thus suppress an increase in the viscosity of the ink.

C. Other Embodiments

(C1) As disclosed in the above embodiment and Examples 1 to 17 described above, the length L2 of the second portion P2 in the X direction may be greater than the length L1 of the first portion P1 in the X direction. With this structure, as compared with a structure in which the length L2 is less than the length L1, it is possible to make the region of contact of the second portion P2 and the nozzle flow passage RN in the liquid flow direction (X direction) larger, and it is therefore possible to improve the efficiency of ink supply and ink discharge between the second portion P2 and the nozzle flow passage RN. By this means, it is possible to suppress an increase in the viscosity of the ink inside the nozzle N.

(C2) As disclosed in the above embodiment and Examples 1 to 17 described above, the depth D1 of the first portion P1 in the Z direction may be less than the depth D2 of the second portion P2 in the Z direction. With this structure, as compared with a structure in which the depth D1 is greater than the depth D2, it is possible to suppress pressure loss of liquid inside the first portion P1 and thus improve the performance of ejecting the liquid. Moreover, since it is possible to make the inertance M1 of the first portion P1 smaller, the liquid inside the first portion P1 is easier to move, which makes the ejection of the liquid easier.

(C3) In the above embodiment, the inertance M1 is greater than 0.10, and the inertance M2 is greater than 0.001. However, the scope of the present disclosure is not limited to this example. As long as the condition that the capacity of the first portion P1 is smaller than the capacity of the second portion P2 is met, the inertance M1 may be 0.10 or less, and the inertance M2 may be 0.001 or less.

(C4) In the above embodiment, the width W1 of the first portion P1 in the Y direction and the width W2 of the second portion P2 in the Y direction may be equal to each other.

(C5) In the above embodiment, liquid is supplied to each of the plurality of nozzle flow passages RN via the common supply flow passage RA1, and the liquid is discharged from each of the plurality of nozzle flow passages RN via the common discharge flow passage RA2. However, the scope of the present disclosure is not limited to this example. A plurality of supply flow passages via which liquid is supplied to the plurality of nozzle flow passages RN respectively, and a plurality of discharge flow passages via which the liquid is discharged from the plurality of nozzle flow passages RN respectively, may be provided. In other words, individual supply flow passages connected directly or indirectly to, and individual discharge flow passages connected directly or indirectly from, the plurality of nozzle flow passages RN respectively may be provided.

(C6) In the above embodiment, the second portion P2 may be chamfered or rounded at its end portion located at the side closer to the first portion P1. FIGS. 9 and 10 are diagrams for explaining a nozzle N2 according to another embodiment. FIG. 9 illustrates a cross section parallel to an X-Z plane of the nozzle N2. FIG. 10 illustrates a cross section taken along the line X-X of FIG. 9. As illustrated in FIGS. 9 and 10, chamfering the end portion, of a second portion P22, located at the side closer to the first portion P1 makes it possible to suppress pressure loss of liquid flowing in the +Z direction from the nozzle flow passage RN into the second portion P22, as compared with a non-chamfered structure. The processing is not limited to chamfering but may be rounding. The length L2 of the second portion P22 in this structure means the length in the X direction of its end portion located at the side closer to the nozzle flow passage RN.

(C7) In the above embodiment, the second portion P2 may be tapered toward the side opposite to the nozzle flow passage RN in the Z direction. FIGS. 11 and 12 are diagrams for explaining a nozzle N3 according to another embodiment. FIG. 11 illustrates a cross section parallel to an X-Z plane of the nozzle N3. FIG. 12 illustrates a cross section taken along the line XII-XII of FIG. 11. As illustrated in FIGS. 11 and 12, tapering a second portion P23 toward the side opposite to the nozzle flow passage RN in the Z direction makes it possible to suppress pressure loss of liquid flowing in the +Z direction from the nozzle flow passage RN into the second portion P23, as compared with a non-tapered structure. The length L2 of the second portion P23 in this structure means the length in the X direction of its end portion located at the side closer to the nozzle flow passage RN.

(C8) In the above embodiment, the second portion P2 may have a shape that looks like a rectangle when viewed in the Z direction. FIG. 13 is a diagram for explaining a nozzle N4 according to another embodiment. FIG. 13 is a Z-directional view of the nozzle N4. It is possible to make the capacity of the second portion P24 relatively large by configuring the second portion P24 in such a way as to have a shape that looks like a rectangle when viewed in the z direction as illustrated in FIG. 13.

(C9) In the above embodiment, the first portion P1 has a shape that looks like a circle when viewed in the Z direction. However, the scope of the present disclosure is not limited to this example. The first portion P1 may have any shape when viewed in the Z direction.

D. Other Modes

The scope of the present disclosure is not limited to the foregoing embodiments. The present disclosure may be modified in various ways within a range of not departing from its spirit. For example, technical features in the foregoing embodiments corresponding to technical features in each mode described in SUMMARY section of this specification may be replaced or combined in order to solve a part or a whole of problems described above or produce a part or a whole of effects described above. Some technical features may be deleted where unnecessary unless they are explained explicitly as indispensable in this specification.

(1) In a certain mode of the present disclosure, a liquid ejecting head is provided. The liquid ejecting head includes: a plurality of nozzles arranged in a Y direction and ejecting liquid in a Z direction intersecting with the Y direction; and a plurality of nozzle flow passages each being continuous to corresponding one of the plurality of nozzles and extending in an X direction intersecting with the Y direction and with the Z direction, wherein each of the plurality of nozzles includes a first portion and a second portion, the second portion being located closer to the nozzle flow passage in the Z direction than the first portion is, capacity of the first portion is smaller than capacity of the second portion, and M2/M1<0.26, where M1 is inertance of the first portion, and M2 is inertance of the second portion.

With the liquid ejecting head according to this mode, since the relation of M2/M1<0.26 is satisfied, relatively great oscillations of a meniscus occur when the liquid is ejected, and it is possible to greatly agitate the liquid inside the nozzle. By this means, it is possible to suppress an increase in the viscosity of the liquid inside the nozzle.

(2) In the liquid ejecting head according to the above mode, the following relation may be satisfied: M2/M1<0.22.

With the liquid ejecting head according to this mode, since the relation of M2/M1<0.22 is satisfied, as compared with a structure in which M2/M1≥0.22 holds, a greater agitation of the liquid inside the second portion occurs when the liquid is ejected, and it is therefore possible to achieve a greater suppression of an increase in the viscosity of the liquid inside the nozzle.

(3) In the liquid ejecting head according to the above mode, the following relation may be satisfied: M2/M1<0.16.

With the liquid ejecting head according to this mode, since the relation of M2/M1<0.16 is satisfied, as compared with a structure in which M2/M1>0.16 holds, a greater agitation of the liquid inside the second portion occurs when the liquid is ejected, and it is therefore possible to achieve a greater suppression of an increase in the viscosity of the liquid inside the nozzle.