Inkjet printer head

Abstract

In accordance with one embodiment, an inkjet head comprises a plurality of groove-shaped pressure chambers formed on piezoelectric members of which the polarization directions are opposite, and a nozzle plate arranged at the lateral side of the pressure chambers across a lid section with high rigidity. A plurality of through holes connected to a plurality of nozzles formed on the nozzle plate is formed in the lid section. The inkjet head is set in a range of 10˜25% before and after a center, that is, a length ratio where the relation between ejection voltage of ink ejected from the nozzles and a length ratio between the length of the through hole of the lid section in the longitudinal direction of the pressure chamber and the length of the pressure chamber in the longitudinal direction of the pressure chamber is minimized.

Description

FIELD

Embodiments described herein relate generally to an inkjet printer head.

BACKGROUND

As an inkjet printer head, for example, there is known a side shooter type device serving as a share mode share wall type inkjet printer head equipped with nozzles at the lateral side of a pressure chamber. Such an inkjet head includes a substrate, a frame member adhered to the substrate, a nozzle plate adhered to the frame member, a piezoelectric member adhered to the substrate at a position inside the frame member and a head drive IC for driving the piezoelectric member. In the printing process, the piezoelectric member is driven, and pillars serving as driving elements arranged at both sides of each pressure chamber in the piezoelectric member are curved by performing shear mode deformation, and in this way, the ink in the pressure chamber is pressurized, and ink drops are ejected from the nozzles.

In a case of a conventional inkjet printer head in which a soft nozzle plate made of resin is fixed on the piezoelectric member, the nozzle plate may also be deformed when each pressure chamber in the piezoelectric member is deformed. As a result, there is a possibility that part of the driving force of the piezoelectric member is used for the deformation of the nozzle plate.

Further, there is also an inkjet printer head in which, for example, a metal lid member with high rigidity is arranged between the piezoelectric member and the nozzle plate. In this case, the fixing part of the lid member and the pressure chamber is firmly connected, in this way, it is possible to prevent that part of the driving force of the piezoelectric member is used for the deformation of the nozzle plate and that the ink ejection efficiency is decreased.

However, the conventional inkjet printer head does not pay much attention to the relation between the nozzle diameter of the nozzle plate serving as a resin member with nozzles and the diameter of through holes of the metal lid section laminated on the nozzle plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an inkjet head according to a first embodiment in which one part of the inkjet head is broken;

FIG. 2 is a cross-sectional view obtained by cutting at a position of a line F2-F2 shown in FIG. 1;

FIG. 3 is a diagram illustrating the operation of the inkjet head according to the first embodiment, (A) is a longitudinal section view illustrating the main portions of the components around a pressure chamber, (B) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber is depressurized, and (C) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber is pressurized to eject ink;

FIG. 4 is a characteristic diagram illustrating results of a test for evaluating ejection voltage and pressure transmission time in a case in which a pressure chamber density is 150 dpi in a case in which the inkjet head according to the first embodiment is prototyped by reference to a table 1;

FIG. 5 is a characteristic diagram illustrating results of a test for evaluating ejection voltage and pressure transmission time in a case in which a pressure chamber density is 300 dpi in a case in which the inkjet head according to the first embodiment is prototyped by reference to a table 1;

FIG. 6 is a perspective view of an inkjet head according to a second embodiment in which one part of the inkjet head is broken;

FIG. 7 is a cross-sectional view obtained by cutting at a position of a line F2-F2 shown in FIG. 6;

FIG. 8 is a diagram illustrating the operation of the inkjet head according to the second embodiment, (A) is a longitudinal section view illustrating the main portions of the components around a pressure chamber, (B) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber is depressurized, and (C) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber is pressurized to eject ink;

FIG. 9 is a characteristic diagram illustrating results of a test for evaluating ejection voltage and pressure transmission time in a case in which a pressure chamber density is 150 dpi in a case in which the inkjet head according to the second embodiment is prototyped by reference to a table 3;

FIG. 10 is a characteristic diagram illustrating results of a test for evaluating ejection voltage and pressure transmission time in a case in which a pressure chamber density is 300 dpi in a case in which the inkjet head according to the second embodiment is prototyped by reference to a table 3;

FIG. 11 is a perspective view of an inkjet head according to a third embodiment in which one part of the inkjet head is broken;

FIG. 12 is a cross-sectional view obtained by cutting at a position of a line F2-F2 shown in FIG. 11;

FIG. 13 is a diagram illustrating the operation of the inkjet head according to the third embodiment, (A) is a longitudinal section view illustrating the main portions of the components around a pressure chamber, (B) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber is depressurized, and (C) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber is pressurized to eject ink;

FIG. 14 is a characteristic diagram illustrating results of a test for evaluating ejection voltage and pressure transmission time in a case in which a pressure chamber density is 150 dpi in a case in which the inkjet head according to the third embodiment is prototyped by reference to a table 5; and

FIG. 15 is a characteristic diagram illustrating results of a test for evaluating ejection voltage and pressure transmission time in a case in which a pressure chamber density is 300 dpi in a case in which the inkjet head according to the third embodiment is prototyped by reference to a table 5.

DETAILED DESCRIPTION

In accordance with one embodiment, an inkjet head comprises a plurality of groove-shaped pressure chambers formed on piezoelectric members of which the polarization directions are opposite, and a nozzle plate arranged at the lateral side of the pressure chambers across a lid section with high rigidity. A plurality of through holes connected to a plurality of nozzles formed on the nozzle plate is formed in the lid section. The inkjet head is set in a range of 10˜25% before and after a center, that is, a length ratio where the relation between ejection voltage of ink ejected from the nozzles and a length ratio between the length of the through hole of the lid section in the longitudinal direction of the pressure chamber and the length of the pressure chamber in the longitudinal direction of the pressure chamber is minimized.

A First Embodiment

Constitution

The first embodiment of the present invention is described with reference to FIG. 1-FIG. 5. An inkjet head 11 according to the present embodiment is an ink circulation type inkjet head of a so called share mode share wall type, and has a structure called as a side shooter type. As shown in FIG. 1 and FIG. 2, the inkjet head 11 includes a substrate 12, a frame member 13 adhered to the substrate 12, a nozzle plate 14 adhered to the frame member 13, a piezoelectric member 15 adhered to the substrate 12 at a position inside the frame member 13 and a head drive IC 16 for driving the piezoelectric member 15.

The nozzle plate 14 formed by a square-shaped polyimide film includes a pair of nozzle arrays 21. Each nozzle array 21 includes a plurality of nozzles 22.

The piezoelectric member 15 is formed by binding two piezoelectric plates 23 which are made of, for example, PZT (lead zirconate titanate) in such a manner that the polarization directions thereof are opposite. The piezoelectric member 15, which is trapezoidal, is formed into a rod-shape. The piezoelectric member 15 includes a plurality of pressure chambers 24 formed by grooves cut in the surface, pillar sections 25 serving as driving elements arranged at two sides of each pressure chamber 24 and electrodes 26 formed at the lateral sides of each pillar section 25 and the bottom of the pressure chamber 24.

The nozzle plate 14 is adhered to the pillar sections 25 of the piezoelectric member 15 across a lid section 27 including a strong, rigid material such as metal, ceramics and the like. The piezoelectric member 15 is adhered to the substrate 12 in such a manner that it corresponds to the nozzle arrays 21 on the nozzle plate 14. The pressure chambers 24 and the pillar sections 25 are formed corresponding to the nozzles 22.

Further, through holes 28 connected to each pressure chamber 24 are formed in the lid section 27. The nozzles 22 of the nozzle plate 14 are opened in a state of being connected to each through hole 28. A plurality of electrical wiring 29 is arranged on the substrate 12. One end of each electrical wiring 29 is connected with the electrode 26 and the other end is connected with the head drive IC 16.

The substrate 12 is formed by, for example, ceramic such as alumina and the like into a square-shaped plate. The substrate 12 includes supply ports 31 and discharge ports 32 which are formed by holes. The supply port 31 is connected with an ink tank of a printer (not shown), and the discharge port 32 is connected with an ink tank (not shown). During the operation of the inkjet head 11, the ink supply is carried out through the supply port 31, and the ink flowing out from the ink tank is filled into the pressure chamber 24 via the supply port 31. The ink that is not used in the pressure chamber 24 is collected to the ink tank through the discharge port 32. The inkjet head 11 according to the present embodiment is a circulation type head which can circulate the ink in the pressure chamber 24 and remove the entrained air bubbles automatically.

The operation of the inkjet head 11 is described with reference to FIG. 3 (A)˜(C). FIG. 3 (A) is a longitudinal section view illustrating the main portions of the components around the pressure chamber 24, FIG. 3 (B) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber 24 is depressurized (a state in which the pressure chamber 24 is enlarged), and FIG. 3 (C) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber 24 is pressurized to eject ink (a state in which the pressure chamber 24 is contracted). When a user instructs the printer to carry out printing, the control section of the printer outputs a print signal to the head drive IC 16 of the inkjet head 11. After the print signal is received, the head drive IC 16 applies a driving pulse voltage to the pillar section 25 through the electrical wiring 29. In this way, the pair of pillar sections 25 at two sides is deformed (curved) into a “<” shape in opposite directions by performing shear mode deformation. At this time, as shown in FIG. 3 (B), the pressure chamber 24 is depressurized (enlarged). Then, as shown in FIG. 3 (C), these are returned to an initial position and the pressure in the pressure chamber 24 is increased (pressure chamber 24 is contracted). In this way, the ink in the pressure chamber 24 is supplied to the nozzle 22 of the nozzle plate 14 via the through hole 28 of the lid section 27, and the ink drops are ejected from the nozzle 22 vigorously.

In such an inkjet head 11, the lid section 27 constitutes one wall surface of the pressure chamber 24, which brings influences on the rigidity of the pressure chamber 24. The higher the rigidity of the lid section 27 is (that is, the more rigid/thick the lid section 27 is), the higher the rigidity of the pressure chamber 24 is; thus, the pressure generated in the piezoelectric member 15 is used efficiently in the ink ejection, and the pressure transmission speed in the ink is increased, and the high-speed driving can be carried out. Herein, it is necessary to arrange openings of through holes 28 connected to the nozzles 22 in the lid section 27, thus, if the thickness of the lid section 27 is too thick, the fluid resistance until the nozzles 22 is increased, which decreases the ejection efficiency. On the contrary, if the openings of the through holes 28 of the lid section 27 are enlarged to avoid the decrease in the ejection efficiency, the rigidity of the pressure chamber 24 is decreased, and the pressure chamber 24 is also increased, which leads to a decrease in the pressure transmission speed. Thus, it is considered that there is an optimum value for the thickness of the lid section 27 and the size of the through hole 28.

The inkjet head 11 according to the present embodiment has a length ratio (referred to as a minimum value X1 shown in FIG. 4 (A2) and a minimum value Y1 shown in FIG. 5 (B2)) in a range of 10-25%, such that the relation between the ejection voltage of the ink ejected from the nozzles 22 and a length ratio between the length (refer to L6 shown in FIG. 2) of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length (refer to L3 shown in FIG. 2) of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24 is minimized.

(Prototype of Inkjet Head 11)

The inkjet head 11 is prototyped by reference to the following table 1.

TABLE 1
	LID SECTION
	PRESSURE CHAMBER	YOUNG'S		OPENING
	PITCH	WIDTH	LENGTH	DEPTH	MODULUS	THICKNESS	LENGTH
NO.	μm	μm	μm	μm	Gpa	μm	μm
1	155	80	2000	300	50	30	100
2							200
3							300
4							400
5							500
6						70	100
7							200
8							300
9							400
10							500
11						110	100
12							200
13							300
14							400
15							500
16						150	100
17							200
18							300
19							400
20							500
21					150	30	100
22							200
23							300
24							400
25							500
26						70	100
27							200
28							300
29							400
30							500
31						110	100
32							200
33							300
34							400
35							500
36						150	100
37							200
38							300
39							400
40							500
41					250	30	100
42							200
43							300
44							400
45							500
46						70	100
47							200
48							300
49							400
50							500
51						110	100
52							200
53							300
54							400
55							500
56						150	100
57							200
58							300
59							400
60							500
61	64.5	40	1500	150	50	30	100
62							200
63							300
64							400
65							500
66						70	100
67							200
68							300
69							400
70							500
71						110	100
72							200
73							300
74							400
75							500
76						150	100
77							200
78							300
79							400
80							500
81					150	30	100
82							200
83							300
84							400
85							500
86						70	100
87							200
88							300
89							400
90							500
91						110	100
92							200
93							300
94							400
95							500
96						150	100
97							200
98							300
99							400
100							500
101					250	30	100
102							200
103							300
104							400
105							500
106						70	100
107							200
108							300
109							400
110							500
111						110	100
112							200
113							300
114							400
115							500
116						150	100
117							200
118							300
119							400
120							500

The head 11 is broadly classified into two categories, and two representative categories of heads, that is, one with a pressure chamber density of 150 dpi and one with a pressure chamber density of 300 dpi, are prototyped. In the table 1, as to the pressure chambers 24 in samples No. 1˜60, the pitch (L1) is 169 μm, the width (L2) is 80 μm, the length (L3) is 2000 μm, and the depth (L4) is 300 μm. As to the pressure chambers 24 in samples No. 61˜120, the pitch (L1) is 84.5 μm, the width (L2) is 40 μm, the length (L3) is 1500 μm, and the depth (L4) is 150 μm. Further, the Young's modulus (Gpa), the thickness (L5) and the opening length (L6) of the through hole 28 of the lid section 27 are set as shown in the table 1. The material of the lid section 27 may be PZT of which the Young's modulus is about 50 GPa, Ni—Fe alloy (42Alloy) of which the Young's modulus is about 150 GPa and 92alumina of which the Young's modulus is about 250 GPa; and the width of the through hole 28 of the lid section 27 is approximately equal to the width (L2) of the pressure chamber 24.

(Test)

The ejection voltage (the voltage required to eject a certain amount of ink drops at a predetermined driving speed) and the pressure transmission time (the time the pressure transmits in the pressure chamber; in inverse proportion to the pressure transmission speed) are evaluated for each inkjet head 11 shown in the samples No. 1˜120. The test results are as shown in the following table 2.

TABLE 2
	PRESSURE	6 pl		PRESSURE	4 pl
	TRANS-	EJECTION		TRANS-	EJECTION
	MISSION	VOLTAGE		MISSION	VOLTAGE
NO.	TIME (μsec)	(V)	NO.	TIME (μsec)	(V)
1	2.180	23.3	61	1.546	28.9
2	2.209	23.2	62	1.613	28.0
3	2.251	22.9	63	1.722	27.4
4	2.286	23.0	64	1.799	28.3
5	2.356	24.2	65	2.179	33.5
6	2.159	25.2	66	1.585	30.8
7	2.199	23.4	67	1.715	27.7
8	2.270	23.2	68	1.930	29.9
9	2.359	23.4	69	2.222	32.2
10	2.449	24.6	70	2.602	37.4
11	2.155	26.2	71	1.563	33.0
12	2.202	23.9	72	1.785	28.4
13	2.297	23.0	73	2.232	31.8
14	2.428	23.6	74	2.578	35.0
15	2.519	24.8	75	2.258	40.2
16	2.158	27.7	76	1.434	34.4
17	2.208	24.4	77	1.506	26.6
18	2.319	23.1	78	2.430	32.2
19	2.480	23.7	79	2.827	35.5
20	2.570	24.9	80	3.207	41.7
21	2.106	24.2	81	1.485	29.8
22	2.132	22.7	82	1.547	27.6
23	2.172	22.8	83	1.659	27.2
24	2.221	22.8	84	1.729	27.8
25	2.311	24.0	85	2.109	33.0
26	2.077	24.5	86	1.490	31.8
27	2.105	23.8	87	1.581	28.5
28	2.163	22.9	88	1.791	28.8
29	2.245	22.9	89	2.077	30.9
30	2.335	24.1	90	2.457	36.1
31	2.070	26.8	91	1.500	32.6
32	2.101	24.4	92	1.629	28.2
33	2.171	23.2	93	1.977	29.4
34	2.277	23.3	94	2.406	32.6
35	2.357	24.5	95	2.785	37.8
36	2.073	27.6	96	1.508	33.8
37	2.105	23.8	97	1.680	28.5
38	2.152	23.0	98	2.061	30.1
39	2.303	22.7	99	2.575	34.5
40	2.393	23.9	100	2.965	39.7
41	2.052	23.4	101	1.470	28.5
42	2.103	22.8	102	1.524	27.5
43	2.141	22.5	103	1.612	26.8
44	2.190	22.5	104	1.721	27.7
45	2.250	23.7	105	2.101	32.8
46	2.050	24.4	106	1.480	30.4
47	2.073	23.1	107	1.538	28.1
48	2.124	22.7	108	1.725	28.0
49	2.198	22.8	109	2.060	30.3
50	2.288	24.0	110	2.440	35.5
51	2.045	26.6	111	1.490	33.8
52	2.070	23.2	112	1.578	29.0
53	2.128	23.2	113	1.508	29.1
54	2.219	23.2	114	2.231	32.7
55	2.309	24.4	115	2.611	37.9
56	2.049	27.5	116	1.498	33.8
57	2.075	23.6	117	1.606	29.6
58	2.138	23.4	118	1.592	29.1
59	2.238	22.6	119	2.426	33.4
60	2.329	23.5	120	2.506	35.6

Further, the result totalized for each parameter of the lid section 27 is as shown in the following FIG. 4 and FIG. 5. FIG. 4 is a characteristic diagram illustrating the result of the test for evaluating the ejection voltage V1 (V) and the pressure transmission time T1 (μsec) in a case in which the pressure chamber density is 150 dpi. FIG. 4 (A1) is a characteristic diagram illustrating the relation between T1 and the length ratio X (%) between the length L6 of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length L3 of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24. FIG. 4 (A2) is a characteristic diagram illustrating the relation between the ejection voltage V1 and X. FIG. 4 (A3) is a characteristic diagram illustrating the relation between T1 and the thickness L5 of the lid section 27. FIG. 4 (A4) is a characteristic diagram illustrating the relation between the ejection voltage V1 and L5. FIG. 4 (A5) is a characteristic diagram illustrating the relation between T1 and the Young's modulus of the lid section 27. FIG. 4 (A6) is a characteristic diagram illustrating the relation between the ejection voltage V1 and the Young's modulus of the lid section 27.

FIG. 5 is a characteristic diagram illustrating the result of the test for evaluating the ejection voltage V2 (V) and the pressure transmission time T2 (μsec) in a case in which the pressure chamber density is 300 dpi. FIG. 5 (B1) is a characteristic diagram illustrating the relation between T2 and the length ratio Y (%) between the length L6 of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length L3 of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24. FIG. 5 (B2) is a characteristic diagram illustrating the relation between the ejection voltage V2 and Y. FIG. 5 (B3) is a characteristic diagram illustrating the relation between T2 and the thickness L5 of the lid section 27. FIG. 5 (B4) is a characteristic diagram illustrating the relation between the ejection voltage V2 and L5. FIG. 5 (B5) is a characteristic diagram illustrating the relation between T2 and the Young's modulus of the lid section 27. FIG. 5 (B6) is a characteristic diagram illustrating the relation between the ejection voltage V2 and the Young's modulus of the lid section 27.

(Effect)

It can be known from each characteristic diagram shown in FIG. 4 and FIG. 5 that the parameter which has the most influences on the characteristic is the length L6 of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24, and that both of the two categories of inkjet heads 11 are used suitably in the range in which the length ratios X and Y of the pressure chamber 24 are 10˜25%.

The thinner the thickness (L5) of the lid section 27 is, the better; however, the thickness (L5) of the lid section 27 has less influence on the characteristic compared with the length (L6) of the through hole 28, thus, the lid section 27 may be appropriately manufactured with the handling property, the manufacturability or the cost and the like taken into consideration. The higher the Young's modulus of the lid section 27 is (that is, the firmer the lid section 27 is), the better; however, viewing from the perspective of manufacturability, the manufacturing process becomes more difficult if the lid section 27 is too firm, thus, the Young's modulus of the lid section 27 is preferred to be about 150 GPa.

Moreover, since various kinds of ink are used in the inkjet head 11, thus, the lid section 27 is adhered by thermosetting adhesive in consideration of ink resistance. Thus, the warping of the head 11 is reduced if the coefficient of thermal expansion of the lid section 27 is approximate to that of the piezoelectric member 15. Even if the lid section 27 can be adhered by room temperature curing adhesive, the ink with low viscosity is ejected because of the high temperature when the head 11 is being used. Thus, it is preferred that the coefficient of thermal expansion of the lid section 27 is approximate to that of the piezoelectric member 15, thus, 42Alloy, invar, kovar and the like are preferred.

In addition, in a case in which the lid section 27 is made of these conductive materials, as the lid section 27 is contacted with the electrode 26 of the pressure chamber 24 across the adhesive, thus, an insulating thin film such as SiO₂ and the like is formed at the contacting surface.

Thus, the inkjet head 11 with the constitution described above has the following effects. That is, in the inkjet head 11, within each parameter of the thickness (L5), the Young's modulus and the opening length (L6) of the through hole 28 of the lid section 27, the parameter of the opening length (L6) of the through hole 28 has the most influences on the characteristic of the inkjet head 11. The inkjet head 11 according to the present embodiment is set in a range of 10˜25% before and after the center, that is, the length ratio (refer to X1 shown in FIG. 4 (A2) and Y1 shown in FIG. 5 (B2)) where the relation between the ejection voltage of the ink ejected from the nozzles 22 and the length ratio between the length (refer to L6 shown in FIG. 2) of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length (refer to L3 shown in FIG. 2) of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24 is minimized. In this way, the opening length (L6) of the through hole 28 is optimized to improve the ink ejection efficiency, reduce the drive voltage, and to increase the drive frequency.

In accordance with the embodiment described above, there can be provided an inkjet printer head capable of optimizing the ejection efficiency.

Further, it is also applicable to arrange the electrode 26 up to half without laminating the piezoelectric member 15.

A Second Embodiment

Constitution

The second embodiment of the present invention is described with reference to FIG. 6-FIG. 10. The same components as those described in the first embodiment are indicated by the same reference numerals in the drawings. The inkjet head 11 according to the present embodiment is an ink circulation type inkjet head of a so called share mode share wall type, and has a structure called as a side shooter type. As shown in FIG. 6 and FIG. 7, the inkjet head 11 includes a substrate 12, a frame member 13 adhered to the substrate 12, a nozzle plate 14 adhered to the frame member 13, a piezoelectric member 15 adhered to the substrate 12 at a position inside the frame member 13 and a head drive IC 16 for driving the piezoelectric member 15.

The nozzle plate 14, which is a resin material having a thickness of 25˜75 μm, is formed by, for example, a square-shaped polyimide film. The nozzle plate 14 includes a pair of nozzle arrays 21. Each nozzle array 21 includes a plurality of nozzles 22.

The piezoelectric member 15 is formed by binding two piezoelectric plates 23 which are made of, for example, PZT (lead zirconate titanate) in such a manner that the polarization directions thereof are opposite. The piezoelectric member 15, which is trapezoidal, is formed into a rod-shape. The piezoelectric member 15 includes a plurality of pressure chambers 24 formed by grooves cut in the surface, pillar sections 25 serving as driving elements arranged at two sides of each pressure chamber 24 and electrodes 26 formed at the lateral sides of each pillar section 25 and the bottom of the pressure chamber 24.

The nozzle plate 14 is adhered to the pillar sections 25 of the piezoelectric member 15 across a lid section 27 including a strong, rigid material such as metal, ceramics and the like. The piezoelectric member 15 is adhered to the substrate 12 in such a manner that it corresponds to the nozzle arrays 21 on the nozzle plate 14. The pressure chambers 24 and the pillar sections 25 are formed corresponding to the nozzles 22.

Further, through holes 28 connected to each pressure chamber 24 are formed in the lid section 27. In the present embodiment, the Young's modulus of the lid section 27 is set to 100˜200 Gpa. Further, the lid section 27 according to the present embodiment includes a first part 27a which covers the pressure chamber 24 and a second part 27b which covers a common liquid chamber 41 between the pressure chambers 24. The thickness of the first part 27a is set to 30˜60 μm, and the second part 27b includes a thin part 27b2 of which the thickness is thinner than that of the first part 27a. In the present embodiment, the thin part 27b2 of the second part 27b is set to be half as thick as the first part 27a.

The nozzles 22 of the nozzle plate 14 are opened in a state of being connected to each through hole 28. A plurality of electrical wiring 29 is arranged on the substrate 12. One end of each electrical wiring 29 is connected with the electrode 26 and the other end is connected with the head drive IC 16.

The substrate 12 is formed by, for example, ceramic such as alumina and the like into a square-shaped plate. The substrate 12 includes supply ports 31 and discharge ports 32 which are formed by holes. The supply port 31 is connected with an ink tank of a printer (not shown), and the discharge port 32 is connected with an ink tank (not shown). During the operation of the inkjet head 11, the ink supply is carried out through the supply port 31, and the ink flowing out from the ink tank is filled into the pressure chamber 24 via the supply port 31. The ink that is not used in the pressure chamber 24 is collected to the ink tank through the discharge port 32. The inkjet head 11 according to the present embodiment is a circulation type head which can circulate the ink in the pressure chamber 24 and remove the entrained air bubbles automatically.

The operation of the inkjet head 11 is described with reference to FIG. 8 (A)˜(C). FIG. 8 (A) is a longitudinal section view illustrating the main portions of the components around the pressure chamber 24, FIG. 8 (B) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber 24 is depressurized (a state in which the pressure chamber 24 is enlarged), and FIG. 8 (C) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber 24 is pressurized to eject ink (a state in which the pressure chamber 24 is contracted). When a user instructs the printer to carry out printing, the control section of the printer outputs a print signal to the head drive IC 16 of the inkjet head 11. After the print signal is received, the head drive IC 16 applies a driving pulse voltage to the pillar section 25 through the electrical wiring 29. In this way, the pair of pillar sections 25 at two sides is deformed (curved) into a “<” shape in opposite directions by performing shear mode deformation. At this time, as shown in FIG. 8 (B), the pressure chamber 24 is depressurized (enlarged). Then, as shown in FIG. 8 (C), these are returned to an initial position and the pressure in the pressure chamber 24 is increased (pressure chamber 24 is contracted). In this way, the ink in the pressure chamber 24 is supplied to the nozzle 22 of the nozzle plate 14 via the through hole 28 of the lid section 27, and the ink drops are ejected from the nozzle 22 vigorously.

In such an inkjet head 11, the lid section 27 constitutes one wall surface of the pressure chamber 24, which brings influences on the rigidity of the pressure chamber 24. The higher the rigidity of the lid section 27 is (that is, the more rigid/thick the lid section 27 is), the higher the rigidity of the pressure chamber 24 is; thus, the pressure generated in the piezoelectric member 15 is used efficiently in the ink ejection, and the pressure transmission speed in the ink is increased, and the high-speed driving can be carried out. Herein, it is necessary to arrange openings of through holes 28 connected to the nozzles 22 in the lid section 27, thus, if the thickness of the lid section 27 is too thick, the fluid resistance until the nozzles 22 is increased, which decreases the ejection efficiency. On the contrary, if the openings of the through holes 28 of the lid section 27 are enlarged to avoid the decrease in the ejection efficiency, the rigidity of the pressure chamber 24 is decreased, and the pressure chamber 24 is also increased, which leads to a decrease in the pressure transmission speed. Thus, it is considered that there is an optimum value for the thickness of the lid section 27 and the size of the through hole 28.

The inkjet head 11 according to the present embodiment is set in a range of 10˜25% before and after a center, that is, a length ratio (refer to a minimum value X1 shown in FIG. 9 (A2) and a minimum value Y1 shown in FIG. 10 (B2)) where the relation between the ejection voltage of the ink ejected from the nozzles 22 and a length ratio between the length (refer to L6 shown in FIG. 7) of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length (refer to L3 shown in FIG. 7) of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24 is minimized.

(Prototype of Inkjet Head 11)

The inkjet head 11 is prototyped by reference to the following table 3.

TABLE 3
	LID SECTION
	PRESSURE CHAMBER	YOUNG'S		OPENING
	PITCH	WIDTH	LENGTH	DEPTH	MODULUS	THICKNESS	LENGTH
NO.	μm	μm	μm	μm	Gpa	μm	μm
1	169	80	2000	300	50	30	100
2							200
3							300
4							400
5							500
6						70	100
7							200
8							300
9							400
10							500
11						110	100
12							200
13							300
14							400
15							500
16						150	100
17							200
18							300
19							400
20							500
21					150	30	100
22							200
23							300
24							400
25							500
26						70	100
27							200
28							300
29							400
30							500
31						110	100
32							200
33							300
34							400
35							500
36						150	100
37							200
38							300
39							400
40							500
41					250	30	100
42							200
43							300
44							400
45							500
46						70	100
47							200
48							300
49							400
50							500
51						110	100
52							200
53							300
54							400
55							500
56						150	100
57							200
58							300
59							400
60							500
61	94.5	40	1500	150	50	30	100
62							200
63							300
64							400
65							500
66						70	100
67							200
68							300
69							400
70							500
71						110	100
72							200
73							300
74							400
75							500
76						150	100
77							200
78							300
79							400
80							500
81					150	30	100
82							200
83							300
84							400
85							500
86						70	100
87							200
88							300
89							400
90							500
91						110	100
92							200
93							300
94							400
95							500
96						150	100
97							200
98							300
99							400
100							500
101					250	30	100
102							200
103							300
104							400
105							500
106						70	100
107							200
108							300
109							400
110							500
111						110	100
112							200
113							300
114							400
115							500
116						150	100
117							200
118							300
119							400
120							500

The head 11 is broadly classified into two categories, and two representative categories of heads, that is, one with a pressure chamber density of 150 dpi and one with a pressure chamber density of 300 dpi, are prototyped. In the table 3, as to the pressure chambers 24 in samples No. 1˜60, the pitch (L1) is 169 μm, the width (L2) is 80 μm, the length (L3) is 2000 μm, and the depth (L4) is 300 μm. As to the pressure chambers 24 in samples No. 61˜120, the pitch (L1) is 84.5 μm, the width (L2) is 40 μm, the length (L3) is 1500 μm, and the depth (L4) is 150 μm. Further, the Young's modulus (Gpa), the thickness (L5) and the opening length (L6) of the through hole 28 of the lid section 27 are set as shown in the table 3. The material of the lid section 27 may be PZT of which the Young's modulus is about 50 GPa, Ni—Fe alloy (42Alloy) of which the Young's modulus is about 150 GPa and 92alumina of which the Young's modulus is about 250 GPa; and the width of the through hole 28 of the lid section 27 is approximately equal to the width (L2) of the pressure chamber 24.

(Test)

The ejection voltage (the voltage required to eject a certain amount of ink drops at a predetermined driving speed) and the pressure transmission time (the time the pressure transmits in the pressure chamber; in inverse proportion to the pressure transmission speed) are evaluated for each inkjet head 11 shown in the samples No. 1˜120. The test results are as shown in the following table 4.

TABLE 4
	PRESSURE	6 pl		PRESSURE	4 pl
	TRANS-	EJECTION		TRANS-	EJECTION
	MISSION	VOLTAGE		MISSION	VOLTAGE
NO.	TIME (μsec)	(V)	NO.	TIME (μsec)	(V)
1	2.180	23.3	61	1.546	28.9
2	2.209	23.2	62	1.613	28.0
3	2.251	22.9	63	1.722	27.4
4	2.256	23.0	64	1.799	28.3
5	2.386	24.2	65	2.179	33.5
6	2.159	25.2	66	1.565	30.8
7	2.199	23.4	67	1.715	27.7
8	2.270	23.2	68	1.980	29.9
9	2.359	23.4	69	2.222	32.2
10	2.449	24.6	70	2.602	37.4
11	2.155	26.2	71	1.563	33.0
12	2.202	23.9	72	1.785	28.4
13	2.297	23.0	73	2.232	31.8
14	2.429	23.6	74	2.578	35.0
15	2.519	24.8	75	2.958	40.2
16	2.158	27.7	76	1.584	34.4
17	2.208	24.4	77	1.506	26.6
18	2.319	23.1	78	2.430	32.2
19	2.480	23.7	79	2.827	36.5
20	2.570	24.9	80	3.207	41.7
21	2.106	24.2	81	1.485	29.8
22	2.132	22.7	82	1.547	27.6
23	2.172	22.8	83	1.659	27.2
24	2.221	22.8	84	1.729	27.8
25	2.311	24.0	85	2.109	33.0
26	2.077	24.5	86	1.490	31.8
27	2.105	23.8	87	1.581	28.5
28	2.163	22.9	88	1.791	28.8
29	2.245	22.9	89	2.077	30.9
30	2.335	24.1	90	2.457	36.1
31	2.070	26.8	91	1.500	32.6
32	2.101	24.4	92	1.629	28.2
33	2.171	23.2	93	1.977	29.4
34	2.277	23.3	94	2.406	32.6
35	2.387	24.5	95	2.786	37.8
36	2.073	27.6	96	1.508	33.8
37	2.105	23.8	97	1.660	28.5
38	2.182	23.0	98	2.081	30.1
39	2.303	22.7	99	2.575	34.5
40	2.393	23.9	100	2.955	39.7
41	2.052	23.4	101	1.470	28.5
42	2.103	22.8	102	1.524	27.5
43	2.141	22.5	103	1.612	26.5
44	2.190	22.5	104	1.721	27.7
45	2.280	23.7	105	2.101	32.8
46	2.080	24.4	106	1.480	30.4
47	2.073	23.1	107	1.538	28.1
48	2.124	22.7	108	1.725	28.0
49	2.198	22.8	109	2.060	30.3
50	2.288	24.0	110	2.440	35.5
51	2.045	26.6	111	1.490	33.8
52	2.070	23.2	112	1.578	29.0
53	2.128	23.2	113	1.808	29.1
54	2.219	23.2	114	2.231	32.7
55	2.309	24.4	115	2.611	37.9
56	2.049	27.5	116	1.498	33.8
57	2.075	23.6	117	1.606	29.6
58	2.138	23.4	118	1.892	29.1
59	2.239	22.6	119	2.426	33.4
60	2.329	23.8	120	2.806	38.6

Further, the result totalized for each parameter of the lid section 27 is as shown in the following FIG. 9 and FIG. 10. FIG. 9 is a characteristic diagram illustrating the result of the test for evaluating the ejection voltage V1 (V) and the pressure transmission time T1 (μsec) in a case in which the pressure chamber density is 150 dpi. FIG. 9 (A1) is a characteristic diagram illustrating the relation between T1 and the length ratio X (%) between the length L6 of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length L3 of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24. FIG. 9 (A2) is a characteristic diagram illustrating the relation between the ejection voltage V1 and X. FIG. 9 (A3) is a characteristic diagram illustrating the relation between T1 and the thickness L5 of the lid section 27. FIG. 9 (A4) is a characteristic diagram illustrating the relation between the ejection voltage V1 and L5. FIG. 9 (A5) is a characteristic diagram illustrating the relation between T1 and the Young's modulus of the lid section 27. FIG. 9 (A6) is a characteristic diagram illustrating the relation between the ejection voltage V1 and the Young's modulus of the lid section 27.

FIG. 10 is a characteristic diagram illustrating the result of the test for evaluating the ejection voltage V2 (V) and the pressure transmission time T2 (μsec) in a case in which the pressure chamber density is 300 dpi. FIG. 10 (B1) is a characteristic diagram illustrating the relation between T2 and the length ratio Y (%) between the length L6 of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length L3 of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24. FIG. 10 (B2) is a characteristic diagram illustrating the relation between the ejection voltage V2 and Y. FIG. 10 (B3) is a characteristic diagram illustrating the relation between T2 and the thickness L5 of the lid section 27. FIG. 10 (B4) is a characteristic diagram illustrating the relation between the ejection voltage V2 and L5. FIG. 10 (B5) is a characteristic diagram illustrating the relation between T2 and the Young's modulus of the lid section 27. FIG. 10 (B6) is a characteristic diagram illustrating the relation between the ejection voltage V2 and the Young's modulus of the lid section 27.

(Effect)

It can be known from each characteristic diagram shown in FIG. 9 and FIG. 10 that the parameter which has the most influences on the characteristic is the length L6 of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24, and that both of the two categories of inkjet heads 11 are used suitably in the range in which the length ratios X and Y of the pressure chamber 24 are 10˜25%.

The thinner the thickness (L5) of the lid section 27 is, the better; however, the thickness (L5) of the lid section 27 has less influence on the characteristic compared with the length (L6) of the through hole 28, thus, the lid section 27 may be appropriately manufactured with the handling property, the manufacturability or the cost and the like taken into consideration. The higher the Young's modulus of the lid section 27 is (that is, the firmer the lid section 27 is), the better; however, viewing from the perspective of manufacturability, the manufacturing process becomes more difficult if the lid section 27 is too firm, thus, the Young's modulus of the lid section 27 is preferred to be about 150 GPa.

Moreover, since various kinds of ink are used in the inkjet head 11, thus, the lid section 27 is adhered by thermosetting adhesive in consideration of ink resistance. Thus, the warping of the head 11 is reduced if the coefficient of thermal expansion of the lid section 27 is approximate to that of the piezoelectric member 15. Even if the lid section 27 can be adhered by room temperature curing adhesive, the ink with low viscosity is ejected because of the high temperature when the head 11 is being used. Thus, it is preferred that the coefficient of thermal expansion of the lid section 27 is approximate to that of the piezoelectric member 15, thus, 42Alloy, invar, kovar and the like are preferred.

In addition, in a case in which the lid section 27 is made of these conductive materials, as the lid section 27 is contacted with the electrode 26 of the pressure chamber 24 across the adhesive, thus, an insulating thin film such as SiO₂ and the like is formed at the contacting surface.

Thus, the inkjet head 11 with the constitution described above has the following effects. That is, in the inkjet head 11 according to the present embodiment, within each parameter of the thickness (L5), the Young's modulus and the opening length (L6) of the through hole 28 of the lid section 27, the parameter of the opening length (L6) of the through hole 28 has the most influences on the characteristic of the inkjet head 11. The inkjet head 11 according to the present embodiment is set in a range of 10˜25% before and after the center, that is, the length ratio (refer to X1 shown in FIG. 9 (A2) and Y1 shown in FIG. 10 (B2)) where the relation between the ejection voltage of the ink ejected from the nozzles 22 and the length ratio between the length (refer to L6 shown in FIG. 7) of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length (refer to L3 shown in FIG. 7) of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24 is minimized. In this way, the opening length (L6) of the through hole 28 is optimized to improve the ink ejection efficiency, reduce the drive voltage, and to increase the drive frequency.

Further, in the present embodiment, the Young's modulus of the lid section 27 is set to 100˜200 Gpa. The lid section 27 according to the present embodiment includes the first part 27a which covers the pressure chamber 24 and the second part 27b which covers the common liquid chamber 41 between the pressure chambers 24. The thickness of the first part 27a is set to 30˜60 μm, and the second part 27b includes the thin part 27b2 of which the thickness is thinner than that of the first part 27a. Herein, the lid section 27 arranges, for example, groove-shaped cutout portions 27b1 at the part of the surface side corresponding to the second part 27b to form the thin part 27b2. In this way, in the lid section 27, the rigidity of the second part 27b is lower than that of the first part 27a. In this case, it is possible to suppress the residual vibration caused by the pressure fluctuation of the ink in the chamber 24 used in the first ink ejecting operation, and obtain a damper effect in the common liquid chamber 41 between the pressure chambers 24. Thus, it is possible to prevent that the vibration of the pressure fluctuation of the ink in the chamber 24 used in the first ink ejecting operation is transmitted to the lid section 27, and as a result, other pressure chambers 24 which are not used in the ink ejection vibrate. Thus, it is possible to prevent that other pressure chambers 24 which are not used in the ink ejection are used in the next ink ejecting operation in a vibration state, which can prevent crosstalk in the next ink ejecting operation and improve the printing stability.

In the present embodiment, the lid section 27 is formed by one plate, thus, the manufacture of the lid section 27 can be carried out easily, and the assembly workability of the lid section 27 with other components can be carried out easily when assembling the inkjet head 11.

Further, it is applicable to construct an ink flow path by forming the nozzle plate 14 after the lid section 27 of the pressure chamber 24 is adhered.

In accordance with the embodiment described above, there can be provided an inkjet printer head capable of ejecting ink efficiently at a high speed.

Further, it is also applicable to arrange the electrode 26 up to half without laminating the piezoelectric member 15.

A Third Embodiment

Constitution

The third embodiment of the present invention is described with reference to FIG. 11-FIG. 15. The same components as those described in the first embodiment and the second embodiment are indicated by the same reference numerals in the drawings. The inkjet head 11 according to the present embodiment is an ink circulation type inkjet head of a so called share mode share wall type, and has a structure called as a side shooter type. As shown in FIG. 11 and FIG. 12, the inkjet head 11 includes a substrate 12, a frame member 13 adhered to the substrate 12, a nozzle plate 14 adhered to the frame member 13, a piezoelectric member 15 adhered to the substrate 12 at a position inside the frame member 13 and a head drive IC 16 for driving the piezoelectric member 15.

The nozzle plate 14, which is a resin material having a thickness of 25˜75 μm, is formed by, for example, a square-shaped polyimide film. The nozzle plate 14 includes a pair of nozzle arrays 21. Each nozzle array 21 includes a plurality of nozzles 22.

The piezoelectric member 15 is formed by binding two piezoelectric plates 23 which are made of, for example, PZT (lead zirconate titanate) in such a manner that the polarization directions thereof are opposite. The piezoelectric member 15, which is trapezoidal, is formed into a rod-shape. The piezoelectric member 15 includes a plurality of pressure chambers 24 formed by grooves cut in the surface, pillar sections 25 serving as driving elements arranged at two sides of each pressure chamber 24 and electrodes 26 formed at the lateral sides of each pillar section 25 and the bottom of the pressure chamber 24.

The nozzle plate 14 is adhered to the pillar sections 25 of the piezoelectric member 15 across a lid section 27 including a strong, rigid material such as metal, ceramics and the like. The piezoelectric member 15 is adhered to the substrate 12 in such a manner that it corresponds to the nozzle arrays 21 on the nozzle plate 14. The pressure chambers 24 and the pillar sections 25 are formed corresponding to the nozzles 22.

Further, through holes 28 connected to each pressure chamber 24 are formed in the lid section 27. In the present embodiment, the lid section 27 is formed by elongated rectangular flat plates corresponding to the outer edge shape of the surface of the piezoelectric member 15. The lid section 27 is only formed at the parts that cover the pressure chamber 24. The thickness of the lid section 27 is set to 30˜60 μm, and the Young's modulus of the lid section 27 is set to 100˜200 Gpa. The nozzles 22 of the nozzle plate 14 are opened in a state of being connected to each through hole 28. A plurality of electrical wiring 29 is arranged on the substrate 12. One end of each electrical wiring 29 is connected with the electrode 26 and the other end is connected with the head drive IC 16.

The substrate 12 is formed by, for example, ceramic such as alumina and the like into a square-shaped plate. The substrate 12 includes supply ports 31 and discharge ports 32 which are formed by holes. The supply port 31 is connected with an ink tank of a printer (not shown), and the discharge port 32 is connected with an ink tank (not shown). During the operation of the inkjet head 11, the ink supply is carried out through the supply port 31, and the ink flowing out from the ink tank is filled into the pressure chamber 24 via the supply port 31. The ink that is not used in the pressure chamber 24 is collected to the ink tank through the discharge port 32. The inkjet head 11 according to the present embodiment is a circulation type head which can circulate the ink in the pressure chamber 24 and remove the entrained air bubbles automatically.

The operation of the inkjet head 11 is described with reference to FIG. 13 (A)˜(C). FIG. 13 (A) is a longitudinal section view illustrating the main portions of the components around the pressure chamber 24, FIG. 13 (B) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber 24 is depressurized (a state in which the pressure chamber 24 is enlarged), and FIG. 13 (C) is a longitudinal section view illustrating the main portions in a state in which the pressure chamber 24 is pressurized to eject ink (a state in which the pressure chamber 24 is contracted). When a user instructs the printer to carry out printing, the control section of the printer outputs a print signal to the head drive IC 16 of the inkjet head 11. After the print signal is received, the head drive IC 16 applies a driving pulse voltage to the pillar section 25 through the electrical wiring 29. In this way, the pair of pillar sections 25 at two sides is deformed (curved) into a “<” shape in opposite directions by performing shear mode deformation. At this time, as shown in FIG. 13 (B), the pressure chamber 24 is depressurized (enlarged). Then, as shown in FIG. 13 (C), these are returned to an initial position and the pressure in the pressure chamber 24 is increased (pressure chamber 24 is contracted). In this way, the ink in the pressure chamber 24 is supplied to the nozzle 22 of the nozzle plate 14 via the through hole 28 of the lid section 27, and the ink drops are ejected from the nozzle 22 vigorously.

In such an inkjet head 11, the lid section 27 constitutes one wall surface of the pressure chamber 24, which brings influences on the rigidity of the pressure chamber 24. The higher the rigidity of the lid section 27 is (that is, the more rigid/thick the lid section 27 is), the higher the rigidity of the pressure chamber 24 is; thus, the pressure generated in the piezoelectric member 15 is used efficiently in the ink ejection, and the pressure transmission speed in the ink is increased, and the high-speed driving can be carried out. Herein, it is necessary to arrange openings of through holes 28 connected to the nozzles 22 in the lid section 27, thus, if the thickness of the lid section 27 is too thick, the fluid resistance until the nozzles 22 is increased, which decreases the ejection efficiency. On the contrary, if the openings of the through holes 28 of the lid section 27 are enlarged to avoid the decrease in the ejection efficiency, the rigidity of the pressure chamber 24 is decreased, and the pressure chamber 24 is also increased, which leads to a decrease in the pressure transmission speed. Thus, it is considered that there is an optimum value for the thickness of the lid section 27 and the size of the through hole 28.

The inkjet head 11 according to the present embodiment is set in a range of 10˜25% before and after a center, that is, a length ratio (refer to a minimum value X1 shown in FIG. 14 (A2) and a minimum value Y1 shown in FIG. 15 (B2)) where the relation between the ejection voltage of the ink ejected from the nozzles 22 and a length ratio between the length (refer to L6 shown in FIG. 12) of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length (refer to L3 shown in FIG. 12) of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24 is minimized.

(Prototype of Inkjet Head 11)

The inkjet head 11 is prototyped by reference to the following table 5.

TABLE 5
	LID SECTION
	PRESSURE CHAMBER	YOUNG'S		OPENING
	PITCH	WIDTH	LENGTH	DEPTH	MODULUS	THICKNESS	LENGTH
NO.	μm	μm	μm	μm	Gpa	μm	μm
1	169	80	2000	300	50	30	100
2							200
3							300
4							400
5							500
6						70	100
7							200
8							300
9							400
10							500
11						110	100
12							200
13							300
14							400
15							500
16						150	100
17							200
18							300
19							400
20							500
21					150	30	100
22							200
23							300
24							400
25							500
26						70	100
27							200
28							300
29							400
30							500
31						110	100
32							200
33							300
34							400
35							500
36						150	100
37							200
38							300
39							400
40							500
41					250	30	100
42							200
43							300
44							400
45							500
46						70	100
47							200
48							300
49							400
50							500
51						110	100
52							200
53							300
54							400
55							500
56						150	100
57							200
58							300
59							400
60							500
61	84.5	40	1500	150	50	30	100
62							200
63							300
64							400
65							500
66						70	100
67							200
68							300
69							400
70							500
71						110	100
72							200
73							300
74							400
75							500
76						150	100
77							200
78							300
79							400
80							500
81					150	30	100
82							200
83							300
84							400
85							500
86						70	100
87							200
88							300
89							400
90							500
91						110	100
92							200
93							300
94							400
95							500
96						150	100
97							200
98							300
99							400
100							500
101					250	30	100
102							200
103							300
104							400
105							500
106						70	100
107							200
108							300
109							400
110							500
111						110	100
112							200
113							300
114							400
115							500
116						150	100
117							200
118							300
119							400
120							500

The head 11 is broadly classified into two categories, and two representative categories of heads, that is, one with a pressure chamber density of 150 dpi and one with a pressure chamber density of 300 dpi, are prototyped. In the table 5, as to the pressure chambers 24 in samples No. 1˜60, the pitch (L1) is 169 μm, the width (L2) is 80 μm, the length (L3) is 2000 μm, and the depth (L4) is 300 μm. As to the pressure chambers 24 in samples No. 61˜120, the pitch (L1) is 84.5 μm, the width (L2) is 40 μm, the length (L3) is 1500 μm, and the depth (L4) is 150 μm. Further, the Young's modulus (Gpa), the thickness (L5) and the opening length (L6) of the through hole 28 of the lid section 27 are set as shown in the table 5. The material of the lid section 27 may be PZT of which the Young's modulus is about 50 GPa, Ni—Fe alloy (42Alloy) of which the Young's modulus is about 150 GPa and 92alumina of which the Young's modulus is about 250 GPa; and the width of the through hole 28 of the lid section 27 is approximately equal to the width (L2) of the pressure chamber 24.

(Test)

The ejection voltage (the voltage required to eject a certain amount of ink drops at a predetermined driving speed) and the pressure transmission time (the time the pressure transmits in the pressure chamber; in inverse proportion to the pressure transmission speed) are evaluated for each inkjet head 11 shown in the samples No. 1˜120. The test results are as shown in the following table 6.

	TABLE 6
		PRESSURE	6 pl	4 pl
		TRANSMISSION	EJECTION	EJECTION
	NO.	TIME (μsec)	VOLTAGE (V)	VOLTAGE (V)
	1	2.180	23.3
	2	2.209	23.2
	3	2.251	22.9
	4	2.286	23.0
	5	2.386	24.2
	6	2.159	25.2
	7	2.199	23.4
	8	2.270	23.2
	9	2.359	23.4
	10	2.449	24.6
	11	2.155	26.2
	12	2.202	23.9
	13	2.297	23.0
	14	2.429	23.6
	15	2.519	24.8
	16	2.158	27.7
	17	2.208	24.4
	18	2.319	23.1
	19	2.480	23.7
	20	2.570	24.9
	21	2.105	24.2
	22	2.132	22.7
	23	2.172	22.8
	24	2.221	22.8
	25	2.311	24.0
	26	2.077	24.5
	27	2.105	23.8
	23	2.163	22.9
	22	2.245	22.9
	20	2.335	24.1
	31	2.070	26.8
	32	2.101	24.4
	33	2.171	23.2
	34	2.277	23.3
	35	2.367	24.5
	38	2.073	27.6
	37	2.105	23.8
	36	2.182	23.0
	39	2.303	22.7
	40	2.393	23.9
	41	2.052	23.4
	42	2.103	22.8
	43	2.141	22.5
	44	2.190	22.5
	45	2.250	23.7
	46	2.050	24.4
	47	2.073	23.1
	48	2.124	22.7
	49	2.195	22.8
	50	2.288	24.0
	51	2.045	26.6
	52	2.070	23.2
	53	2.128	23.2
	54	2.219	23.2
	55	2.309	24.4
	58	2.049	27.5
	57	2.075	23.6
	58	2.138	23.4
	59	2.239	22.6
	60	2.329	23.8
	61	1.546		28.9
	62	1.613		28.0
	63	1.722		27.4
	64	1.799		28.3
	65	2.179		33.5
	66	1.565		30.8
	67	1.715		27.7
	68	1.980		29.9
	69	2.222		32.2
	70	2.602		37.4
	71	1.563		33.0
	72	1.785		28.4
	73	2.232		31.8
	74	2.578		35.0
	75	2.958		40.2
	76	1.584		34.4
	77	1.506		26.6
	78	2.430		32.2
	79	2.827		36.5
	80	3.207		41.7
	81	1.485		29.8
	82	1.547		27.6
	83	1.659		27.2
	84	1.729		27.8
	85	2.109		33.0
	86	1.490		31.8
	87	1.581		28.5
	88	1.791		28.8
	89	2.077		30.9
	90	2.457		36.1
	91	1.500		32.6
	92	1.629		28.2
	93	1.977		29.4
	94	2.406		32.6
	95	2.786		37.8
	96	1.508		33.8
	97	1.660		28.5
	98	2.081		30.1
	99	2.575		34.5
	100	2.955		39.7
	101	1.470		28.5
	102	1.524		27.5
	103	1.612		26.8
	104	1.721		27.7
	105	2.101		32.8
	106	1.480		30.4
	107	1.538		28.1
	108	1.725		28.0
	109	2.060		30.3
	110	2.440		35.5
	111	1.490		33.8
	112	1.578		29.0
	113	1.808		29.1
	114	2.231		32.7
	115	2.611		37.9
	118	1.498		33.5
	117	1.606		29.6
	118	1.892		29.1
	119	2.426		33.4
	120	2.806		35.6

Further, the result totalized for each parameter of the lid section 27 is as shown in the following FIG. 14 and FIG. 15. FIG. 14 is a characteristic diagram illustrating the result of the test for evaluating the ejection voltage V1 (V) and the pressure transmission time T1 (μsec) in a case in which the pressure chamber density is 150 dpi. FIG. 14 (A1) is a characteristic diagram illustrating the relation between T1 and the length ratio X (%) between the length L6 of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length L3 of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24. FIG. 14 (A2) is a characteristic diagram illustrating the relation between the ejection voltage V1 and X. FIG. 14 (A3) is a characteristic diagram illustrating the relation between T1 and the thickness L5 of the lid section 27. FIG. 14 (A4) is a characteristic diagram illustrating the relation between the ejection voltage V1 and L5. FIG. 14 (A5) is a characteristic diagram illustrating the relation between T1 and the Young's modulus of the lid section 27. FIG. 14 (A6) is a characteristic diagram illustrating the relation between the ejection voltage V1 and the Young's modulus of the lid section 27.

FIG. 15 is a characteristic diagram illustrating the result of the test for evaluating the ejection voltage V2 (V) and the pressure transmission time T2 (μsec) in a case in which the pressure chamber density is 300 dpi. FIG. 15 (B1) is a characteristic diagram illustrating the relation between T2 and the length ratio Y (%) between the length L6 of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length L3 of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24. FIG. 15 (B2) is a characteristic diagram illustrating the relation between the ejection voltage V2 and Y. FIG. 15 (B3) is a characteristic diagram illustrating the relation between T2 and the thickness L5 of the lid section 27. FIG. 15 (B4) is a characteristic diagram illustrating the relation between the ejection voltage V2 and L5. FIG. 15 (B5) is a characteristic diagram illustrating the relation between T2 and the Young's modulus of the lid section 27. FIG. 15 (B6) is a characteristic diagram illustrating the relation between the ejection voltage V2 and the Young's modulus of the lid section 27.

(Effect)

It can be known from each characteristic diagram shown in FIG. 14 and FIG. 15 that the parameter which has the most influences on the characteristic is the length L6 of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24, and that both of the two categories of inkjet heads 11 are used suitably in the range in which the length ratios X and Y of the pressure chamber 24 are 10˜25%.

The thinner the thickness (L5) of the lid section 27 is, the better; however, the thickness (L5) of the lid section 27 has less influence on the characteristic compared with the length (L6) of the through hole 28, thus, the lid section 27 may be appropriately manufactured with the handling property, the manufacturability or the cost and the like taken into consideration. The higher the Young's modulus of the lid section 27 is (that is, the firmer the lid section 27 is), the better; however, viewing from the perspective of manufacturability, the manufacturing process becomes more difficult if the lid section 27 is too firm, thus, the Young's modulus of the lid section 27 is preferred to be about 150 GPa.

Moreover, since various kinds of ink are used in the inkjet head 11, thus, the lid section 27 is adhered by thermosetting adhesive in consideration of ink resistance. Thus, the warping of the head 11 is reduced if the coefficient of thermal expansion of the lid section 27 is approximate to that of the piezoelectric member 15. Even if the lid section 27 can be adhered by room temperature curing adhesive, the ink with low viscosity is ejected because of the high temperature when the head 11 is being used. Thus, it is preferred that the coefficient of thermal expansion of the lid section 27 is approximate to that of the piezoelectric member 15, thus, 42Alloy, invar, kovar and the like are preferred.

In addition, in a case in which the lid section 27 is made of these conductive materials, as the lid section 27 is contacted with the electrode 26 of the pressure chamber 24 across the adhesive, thus, an insulating thin film such as SiO₂ and the like is formed at the contacting surface.

Thus, the inkjet head 11 with the constitution described above has the following effects. That is, in the inkjet head 11 according to the present embodiment, within each parameter of the thickness (L5), the Young's modulus and the opening length (L6) of the through hole 28 of the lid section 27, the parameter of the opening length (L6) of the through hole 28 has the most influences on the characteristic of the inkjet head 11. The inkjet head 11 according to the present embodiment is set in a range of 10˜25% before and after the center, that is, the length ratio (refer to X1 shown in FIG. 14 (A2) and Y1 shown in FIG. 15 (B2)) where the relation between the ejection voltage of the ink ejected from the nozzles 22 and the length ratio between the length (refer to L6 shown in FIG. 12) of the through hole 28 of the lid section 27 in the longitudinal direction of the pressure chamber 24 and the length (refer to L3 shown in FIG. 12) of the pressure chamber 24 in the longitudinal direction of the pressure chamber 24 is minimized. In this way, the opening length (L6) of the through hole 28 is optimized to improve the ink ejection efficiency, reduce the drive voltage, and to increase the drive frequency.

Further, in the present embodiment, the lid section 27 is only formed at the parts that cover the pressure chamber 24; and the thickness of the lid section 27 at the parts that cover the pressure chamber 24 is set to 30˜60 μm, and the Young's modulus of the lid section 27 is set to 100˜200 Gpa. In this way, it is possible to obtain a damper effect in the common liquid chamber 41 between the pressure chambers 24, thus, it is possible to reduce the residual vibration caused by the pressure fluctuation of the ink in the chamber 24 used in the first ink ejecting operation. Thus, it is possible to prevent that the pressure fluctuation of the ink in the chamber 24 used in the first ink ejecting operation is transmitted to the lid section 27, and as a result, other pressure chambers 24 which are not used in the ink ejection vibrate. Thus, it is possible to prevent that other pressure chambers 24 which are not used in the ink ejection are used in the next ink ejecting operation in a vibration state, which can prevent crosstalk in the next ink ejecting operation and improve the printing stability.

In the present embodiment, the lid section 27 is formed by elongated rectangular flat plates corresponding to the outer edge shape of the surface of the piezoelectric member 15, thus, the used material can be reduced, which can contribute to the decrease in the material cost.

Further, it is applicable to construct an ink flow path by forming the nozzle plate 14 after the lid section 27 of the pressure chamber 24 is adhered.

In accordance with the embodiment described above, there can be provided an inkjet printer head capable of ejecting ink efficiently at a high speed.

Further, it is also applicable to arrange the electrode 26 up to half without laminating the piezoelectric member 15.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.

Claims

1. An inkjet head comprising: a plurality of groove-shaped pressure chambers configured to be formed on piezoelectric members of which the polarization directions are opposite;a nozzle plate arranged at the lateral side of the pressure chambers across a lid section with high rigidity; anda lid section in which a plurality of through holes connected to a plurality of nozzles formed on the nozzle plate is formed; whereinthe Young's modulus of the lid section is set to 100˜200 Gpa, the thickness of a first part of the lid section that covers the pressure chamber is set to 30˜60 μm, and a thin part of which the thickness is thinner than that of the first part is arranged at a second part that covers a common liquid chamber between the pressure chambers; andthe nozzle plate is formed by a resin material having a thickness of 25˜75 μm.

2. The inkjet printer head according to claim 1, wherein the thin part of the second part of the lid section is set to be half as thick as the first part.

3. The inkjet printer head according to claim 2, wherein the lid section is metal with low coefficient of thermal expansion.

4. The inkjet printer head according to claim 3, wherein the inkjet printer head is a side shooter type device serving as a share mode share wall type inkjet printer head.

5. The inkjet printer head according to claim 4, wherein the piezoelectric member includes two PZT laminating plates of which the polarization directions are opposite.

6. An inkjet head comprising: a plurality of groove-shaped pressure chambers configured to be formed on piezoelectric members of which the polarization directions are opposite;a nozzle plate arranged at the lateral side of the pressure chambers across a lid section with high rigidity; anda lid section in which a plurality of through holes connected to a plurality of nozzles formed on the nozzle plate is formed; whereinthe lid section sets the thickness of the part which covers the pressure chamber to 30˜60 μm, and sets the Young's modulus to 100˜200 Gpa; andthe nozzle plate is formed by a resin material having a thickness of 25˜75 μm.

7. The inkjet printer head according to claim 6, wherein the lid section is formed by a flat plate of a size covering the pressure chambers.

8. The inkjet printer head according to claim 7, wherein the lid section is metal with low coefficient of thermal expansion.

9. The inkjet printer head according to claim 8, wherein the inkjet printer head is a side shooter type device serving as a share mode share wall type inkjet printer head.

10. The inkjet printer head according to claim 9, wherein the piezoelectric member includes two PZT laminating plates of which the polarization directions are opposite.