JPH05229116A - Ink jet head - Google Patents

Abstract

PURPOSE:To solve the ink delivery drop problem caused by a fluid resistance in a groove by a method wherein in a shearing mode-ink jet head, a nozzle hole is provided on approximately the center of the groove, and ink reservoirs are provided on both end parts of the grooves. CONSTITUTION:Partition walls 5 are integrally formed on a substrate 1 made of a piezoelectric material polarized as a whole. In this invention, grooves 2 serving as ink chambers doubling ink flow paths are obtained by cutting. On each side of the grooves 2, shallow grooves 12 are provided by forming a step on parts of the grooves 2. Electrodes formed in the shallow grooves 12 are electrically connected to electrodes on side faces of the partition walls 5. The shallow grooves 12 serve as a connection part to an external electrode. A sealing plate 10 is mounted on the stepped groove parts to prevent ink from flowing out. The grooves 2 are connected to each other by a common ink reservoir 7 on each end parts thereof. Furthermore, a top plate 8 with nozzle holes 3 is mounted over the grooves 2 and the ink reservoirs 7 so that the nozzle hole 3 is disposed on approximately the center of the groove 2 serving as an ink chamber doubling an ink flow path. Ink is supplied to the grooves 2 from ink supply ports 6 through the common ink reservoirs 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drop-on-demand (DOD) type ink jet head.

[0002]

2. Description of the Related Art Among the non-impact printers that are expanding their market today, the principle is the simplest,
Inkjet printers are also suitable for color printing, and among them, the so-called DOD type, which ejects ink droplets only during dot formation, can be said to be the mainstream.
Typical examples of the DOD type are the Kaiser type disclosed in Japanese Patent Publication No. 53-12138 and the thermal jet type disclosed in Japanese Patent Publication No. 61-59914. Of these, the former is difficult to miniaturize, and the latter says that the ink sticks because it adds high heat to the ink.
Each has very difficult problems.

As a new method for simultaneously solving the above-mentioned defects, Japanese Patent Laid-Open No. 63-252750 has been proposed.
The shear mode type disclosed in. The structure and operating principle are shown in FIG. FIG. 9A is a cross-sectional structure diagram when not driven, in which partition walls 95ab, 95bc, 95cd, etc. are adhered in parallel at equal intervals on an insulating substrate 91 such as glass or ceramics to form an elongated ink chamber / ink channel. Groove 92
Many a, 92b, and 92c are formed. And the groove 92
Ink is supplied from a common ink reservoir to one end of a, 92b and 92c, and a nozzle plate having small nozzle holes 93a, 93b and 93c is adhered to the other end. Further, the partition wall is flexibly adhered to the lid 98 made of glass or ceramics by the elastic member 21. Here, as the partition wall, a piezoelectric material such as PZT (lead zirconate titanate) is used and is polarized in one direction as shown by an arrow 22 (or in the opposite direction). In addition, the electrodes 94a2, 94b1,
94b2, 94c1 and the like are formed. Next, FIG.
If a sufficiently large positive potential is applied to the electrode 94a2 of (a) with respect to the electrode 94b1, the partition wall 95ab causes shear mode deformation as shown in FIG. 9 (b). The same applies to the partition 9
For 5 bc (usually, 94b1 and 94b2 have the same potential), the cross-sectional area of the groove 92b of the ink chamber / ink flow path decreases from the initial state shown in FIG. 9A to FIG. 9B. That is, if the groove is filled with ink, the pressure of the ink instantaneously rises due to the volume decrease of the groove,
Ink droplets jump out from the nozzle hole 93b.

FIG. 8 is a perspective view of an ink jet head constructed as described above, which is similar to that disclosed in Japanese Patent Laid-Open No. 63-252750. This head includes a partition wall 85 made of a piezoelectric material adhered to an insulating substrate 81, an elongated groove 82 serving as an ink chamber and an ink flow path, a nozzle plate 80 adhered so as to close the end of the groove, and the entire groove portion. It is composed of a lid 88 for covering. And, the nozzle plate has nozzle holes 8
3 and the ink droplet 84 is ejected as described in FIG. Ink is introduced from the ink supply port 86 and is supplied to each of the grooves through a common ink reservoir 87.

[0005]

In the case of the head structure of FIG. 8, the ink droplets are ejected from the nozzle holes 83 by the pressure generated in the elongated groove 82 of the ink chamber / ink channel. Because of the extremely elongated structure, the fluid resistance here is not negligible. Then, most of the pressure generated in the groove is lost (finally becomes thermal energy) due to the fluid resistance, which causes a problem that the ejection speed of the ink droplet is reduced. This decrease in the ejection speed not only induces instability in the ejection direction of ink droplets and causes positional deviation of printed dots, but also makes it impossible to eject highly viscous ink near the nozzle holes, which is referred to as print dot omission. It also leads to a fatal defect.
This problem is particularly important because when the pitch of the nozzle is made fine, the fluid resistance increases substantially in inverse proportion to the fourth power of the pitch (the groove cross-sectional shape assumes a similar shape). That is, in a head compatible with high-density printing, the degree of decrease in ejection speed becomes remarkable. On the other hand, high-density printing is indispensable in order to obtain high-quality printing, which is a natural requirement. SUMMARY OF THE INVENTION The present invention eliminates the problem of a decrease in ink droplet ejection speed due to the conventional head structure, and provides an inkjet head that can obtain highly reliable and high quality printing.

[0006]

[Means for Solving the Problems] To achieve the above object,
Conventionally, as shown in FIG. 8, the nozzle hole is arranged on the end side of the elongated groove of the ink chamber / ink flow path in the present invention. However, in the present invention, the nozzle hole is located substantially at the center of the groove, and A common ink reservoir is provided on both sides of the groove.

[0007]

By providing the nozzle hole at the center of the groove and supplying ink from both sides of the groove, the effect of the fluid resistance in the groove can be greatly reduced. This is equivalent to reducing the length to 1/2 and the effective number of grooves to the nozzle to 1/2 to reduce it to 1/4 in total. As a result, the reduction in ink droplet ejection force due to the fluid resistance up to the nozzle holes is significantly reduced, and an inkjet head with good ink ejection performance can be obtained.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the configuration of an inkjet head according to the present invention corresponding to FIG. 8 of a conventional example. Here, the insulating substrate 81 and the partition wall 85 of the piezoelectric material are integrally formed, and the substrate 1 of the piezoelectric material is used, but this change does not particularly affect the content of the present invention. Since the partition wall 5 needs to be polarized in one direction as in FIG. 8, the entire substrate 1 is actually polarized. When such integral formation is performed, the groove 2 of the ink chamber / ink flow path is usually obtained by cutting with a dicing saw. On both sides of the groove, part of the groove is processed to form a shallow groove 12.
Is formed, and the electrode formed in the shallow groove and the electrode on the side surface of the partition wall 5 are formed so as to be electrically connected to each other, so that the shallow groove serves as a connection portion with the external electrode. Then, the sealing plate 10 is attached to the stepped end portion to prevent the outflow of ink. The grooves 2 are communicated with each other by a common ink reservoir 7 at both ends. Further, as a structure according to the present invention, the nozzles 3 are arranged so that they are substantially in the center of the grooves 2 of the ink chamber / ink passage. An upper plate 8 having a hole is attached so as to cover the groove and the ink reservoir. In this upper plate, a portion having a nozzle hole and a portion functioning as a lid on the ink reservoir side may be separately formed, and each of them may be separately attached, and as a result, the groove and the ink reservoir may be covered.
Ink is introduced from the ink supply port 6 and supplied to each groove 2 through a common ink reservoir 7.

2 and 3 are respectively AA 'of FIG.
It is sectional drawing in BB '. The substrate 1 made of a piezoelectric material is polarized in at least the partition wall 5 in one direction as shown by an arrow 22, and is bonded to the upper plate 8 by an elastic member 21. However, without using the elastic member, the upper surface of the partition wall,
It is also possible to adopt a structure in which the lower surface of the upper plate is in close contact.
As shown in FIG. 3, the nozzle hole 3 is arranged substantially at the center of the elongated groove 2 of the ink chamber / ink flow path. Further, an obstacle 31 for generating a fluid resistance is provided at the connection portion between the common ink reservoir 30 and the groove 2, but the purpose is to effectively use the pressure generated in the groove during the ink discharging operation. To do so. Therefore, the magnitude of the fluid resistance due to the obstacle 31 is set so as not to interfere with the steady ink supply from the common ink reservoir. An electrode similar to that shown in FIG. 9 is required, but it is omitted here. Ink drops 20
By driving the partition wall 5 in the same manner as described in FIG. 9, the ink is discharged in the direction perpendicular to the upper plate surface.

According to this structure, it is possible to solve the problem that the ink ejection force is conventionally reduced due to the fluid resistance of the elongated groove 2 of the ink chamber / ink flow path. FIG. 4 shows the change in ink ejection force as the ink ejection speed when the ratio of the width and depth of the groove and the length thereof are made constant and the pitch of the grooves formed at equal intervals is changed. (Pitch indicates the number of lines per inch in dpi). in this case,
Since the magnitude of the fluid resistance in the groove increases substantially in inverse proportion to the fourth power of the pitch, it is judged that the remarkable decrease in the ink ejection speed when the pitch is made fine is mainly due to the effect of the fluid resistance. It Actually, in the head of 180 dpi according to the present invention shown below (the ratio of the width to the depth of the groove and the length thereof are the same as those of the head in FIG. 4).
A discharge speed of 7 m / s was obtained. This is because the groove length from the common ink chamber to the nozzle holes is effectively halved and the fluid resistance is also halved when compared with the conventional structure, and the effective number of grooves to the nozzle holes. There are two and the fluid resistance is one more
It is considered that when the ratio becomes / 2, the fluid resistance is reduced to 1/4 as a whole.

The created head is as follows. First, as shown in FIG. 2, a PZT substrate 1 having a thickness of 1 mm, which is entirely polarized as indicated by an arrow 22, is cut by a dicing saw to form partition walls 5 having a width of 70 μm and a height of 150 μm at a pitch of 141 μm. .. The length of the groove is 20 mm. Electrodes were formed on the side surfaces of the partition walls by vapor deposition with a laminated film of chromium and gold having a total thickness of 0.8 μm. Then, a plastic upper plate 8 having a nozzle hole 3 having a diameter of 35 μm was bonded to the partition wall by an elastic member 21 made of silicon resin.

FIG. 5 shows another embodiment of the present invention.
3-252750 Based on the driving principle already disclosed in FIG. FIG. 6 is a sectional view taken along the line CC ′ of FIG.
This structure substantially corresponds to FIG. 1, but the piezoelectric material substrate 1 used in FIG. 1 is bonded to two types of piezoelectric material substrates 51 and 52 with polarization directions reversed such as 63 and 64. It is replaced with an integrated substrate 61 formed by. In this case, the partition wall 65 is deformed in a V shape as shown in FIGS.
Although different from the above case, the effect of the nozzle hole arrangement of the present invention is the same as that already described.

FIG. 7 shows another embodiment according to the present invention, in which the arrangement of the nozzle holes 3 which is aligned in the configuration of FIG. 1 or 5 is changed. In FIG. 1, the dot pitch for printing is determined by the nozzle hole pitches 11a to 11d arranged at equal intervals, but in the case of FIG. 7 which is the present invention, the pitches 71a to 7d.
The difference is that 1e corresponds to this. Note that 71a to 71
e has the same value. In this case, compared to the length of the groove 71a
Since the sum total of ~ 71e can be small, each nozzle hole 3 can be arranged substantially at the center of the groove 2 of the ink chamber / ink flow path. An important effect of the present invention is that by adopting such a nozzle arrangement, the relationship between the groove pitch and the dot pitch for printing can be independently determined. As a result, the degree of freedom in designing the groove pitch is increased, which is extremely useful for head production.

[0014]

As described above, according to the structure of the present invention, there is a problem that the ink ejection force is lowered due to the fluid resistance in the groove of the ink chamber / ink channel, which is one of the serious problems in the shear mode type ink jet head. Can be greatly improved, and as a result, a head having stable print quality can be obtained. The ink jet head disclosed in JP-A-63-252749 has structural similarities to the present invention, but it is clear from the contents that they are different in the purpose, effect, and structure. ..

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of an inkjet head according to the present invention and is a perspective view.

FIG. 2 is an explanatory view of a first embodiment of the ink jet head according to the present invention and is a sectional view.

FIG. 3 is an explanatory view of the first embodiment of the ink jet head according to the present invention and is a sectional view.

FIG. 4 is a diagram for explaining the effect of the inkjet head according to the present invention.

FIG. 5 is an explanatory diagram of a second embodiment of the inkjet head according to the present invention, and is a perspective view.

FIG. 6 is an explanatory view of a second embodiment of the inkjet head according to the present invention and is a sectional view.

FIG. 7 is an explanatory view of a third embodiment of the inkjet head according to the present invention and is a plan view.

FIG. 8 is an explanatory diagram of a conventional technique and is a perspective view.

FIG. 9 is an explanatory diagram of a conventional technique and is a cross-sectional view.

[Explanation of symbols]

 1 substrate of piezoelectric material 2 groove 3 nozzle hole 5 partition wall 8 upper plate 20, 84 ink droplet 30 common ink reservoir

Claims (1)

[Claims] 1. A piezoelectric material having a groove separated by a partition, an ink reservoir for supplying ink to the groove, and a nozzle hole, the partition being applied to an electrode formed on a wall surface of the partition. In a shear mode inkjet head that causes the ink in the groove to be ejected from the nozzle hole by causing displacement of the shear mode by a voltage, the nozzle hole is arranged at approximately the center of the groove, and the ink reservoir is An inkjet head provided at both ends of the groove.