JP2935886B2 - Inkjet head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a drop-on-demand (DOD) type ink jet head.

[Conventional technology]

Among the non-impact printers whose market is greatly expanding today, an ink jet printer is the simplest in principle and suitable for color printing. Historically, the continuous ejection type first appeared, and the so-called DO that ejects ink droplets only when dots are to be formed soon
The D type is the main focus, and it is up to the present.

As the DOD type, a Kaiser type disclosed in Japanese Patent Publication No. 53-12138 and a thermal jet type disclosed in Japanese Patent Publication No. 61-59914 are typical examples. Among them, the former is said to be difficult to miniaturize, and the latter says that the ink burns to apply high heat to the ink,
Each has very difficult problems.

A shear mode type disclosed in Japanese Patent Application Laid-Open No. 63-252750 has been proposed as a new method for simultaneously solving the above-mentioned defects. The structure and operation principle are shown in FIG. FIG. 9 (a) is a cross-sectional structural view in a non-driving state, in which a partition wall 95a is formed on an insulating substrate 1 such as glass or ceramics.
b, 95bc, 95cd, etc. are adhered at equal intervals and in parallel by the adhesive layer 8, and the elongated grooves 92a, 92b,
Many 92c are formed. One end of each of the grooves 92a, 92b and 92c is adapted to supply ink from a common ink reservoir, and a nozzle plate having small nozzle holes 93a, 93b and 93c is bonded to the other end. Further, the partition is flexibly bonded to the lid 6 made of glass or ceramics by the elastic member 9. Here, a piezoelectric material such as PZT (lead zirconate titanate) is used for the partition,
As shown by (or in the opposite direction), polarization is performed in one direction. The electrodes 94a2, 94b
1, 94b2, 94c1, 94c2 are formed.

Here, if a sufficiently large positive potential is applied to the electrode 94a2 in FIG. 9A with respect to the electrode 94b1, the partition 95ab deforms in a shear mode as shown in FIG. 9B. here,
Usually, the flexibility of the elastic member 9 is higher than that of the adhesive layer 8, so that the deformation of the partition 95 ab mainly appears as a displacement with respect to the lid 6. If the same is performed for the partition wall 95bc (usually, the same potential is set for 94b1 and 94b2), the cross-sectional area of the groove 92b of the ink chamber and the ink flow path is changed from the initial state in FIG. 9 (a) to FIG. 9 (b). ) To decrease. That is, if the groove is filled with ink, the pressure of the ink instantaneously rises due to the decrease in the volume of the groove, and the ink droplet jumps out of the nozzle hole 93b.

FIG. 7 is a shear mode type head in which six nozzles are integrated based on the principle of FIG. 9, and includes an insulating substrate 1, grooves 2a to 2f, nozzle holes 3a to 3f, partition walls 5ab to 5ef of piezoelectric material, and electrodes 4a2. ~Four
f1 and lid 6. Reference numeral 8 denotes an adhesive layer, 9 denotes an elastic member, and 7 denotes a polarization direction of the partition. If the spacing between the grooves is made sufficiently small, it is easy to reduce the size as in the thermal jet type, and there is no problem due to high heat as in the Kaiser type. FIG. 10 is a perspective view of an ink jet head constructed in this manner, which is disclosed in Japanese Patent Application Laid-Open No. 63-252750. Here, 101 is an insulating substrate, 1
02 is an elongated groove of the ink chamber and ink channel, 105 is a partition wall made of a piezoelectric material, 100 is a nozzle plate, 103 is a nozzle hole, and 104 is an ink droplet.

[Problems to be solved by the invention]

Consider the driving of the head shown in FIG. The four grooves 2b to 2e can discharge ink droplets by the mechanism shown in FIG. 9, but the ink discharge at the two ends at both ends of the grooves 2a and 2f is as follows.
Each is driven by only one partition 5ab or 5ef. For this reason, the drive of the partition 5ab or 5ef is changed to another partition 5bc.
If the same is used, the effective driving force in the grooves at both ends is reduced, and the ink droplet volume and the ejection speed are reduced. In an extreme case, the ink ejection itself cannot be performed. This leads to irregular dot sizes and missing dots, resulting in a significant reduction in print quality.

Such a decrease in the driving force can be prevented by making the driving voltage applied to the partition different between the central part and the partition as shown in FIG. That is, in FIG.
The voltage waveforms applied to b, 5bc, and 5cd are linear 8
7, 88, and 89 are represented by voltage 0V level, the vertical axis is voltage, and the horizontal axis is time, such as 81 and 84. In this case, the ninth
As shown in the figure, signals of opposite phases are applied to adjacent partitions. In addition, since it is necessary to move the partition wall abruptly when ejecting ink and to move it gently when returning it, the waveform is asymmetric. Now, the important thing is the partition
This means that a voltage waveform 82 having an absolute value twice as large as that of the other 81, 83, 84, 85, 86, etc. must be applied only to 5ab. By taking such a waveform, it is possible to prevent the above-mentioned decrease in the ejection force in the grooves at both ends, but on the other hand, the following new problem occurs.

(1) Since the displacement amount of the partition wall 5ab due to the voltage waveform 82 is large, the pressure of the adjacent groove 2b is significantly reduced when the pressure of the groove 2a is increased.
There is a tendency for troubles to occur such that bubbles are generated in the ink in 2b and the ink cannot be ejected properly.

(2) Since the displacement amount of the partition wall 5ab due to the voltage waveform 82 is large, the displacement amount of the partition wall to the groove 2b side due to the reaction of the partition wall after application of the voltage is also increased, and erroneous ejection from the nozzle 3b is likely to occur.

(3) Since the voltage waveforms 81 and 82 are asymmetric and the absolute value of the voltage at 82 is large, new polarization in the direction from the electrodes 4a2 to 4b1 is easily generated in the partition wall 5ab. This lowers the driving force of the partition 5ab.

The present invention solves the non-uniformity of the ink ejection characteristics of the head having the conventional structure and the instability of the ejection characteristics newly generated when the head is removed, thereby achieving high print quality. It is intended to provide an inkjet head.

[Means for solving the problem]

In order to achieve the above object, in the present invention, in addition to the same number of ink chamber / ink flow path grooves as the number of nozzles involved in printing in the conventional example of FIG. This is for forming a dummy groove. As a result, almost the same driving force can be applied to all the grooves of the ink chamber and the ink flow path by applying the same absolute voltage to each partition, and the speed of the ejected ink droplet and the speed of the ejected ink droplet can be increased. The size is uniform and the print quality is improved. Moreover, since all the grooves of the ink chamber and the ink flow path operate substantially equally, the driving of the entire head becomes extremely stable.

Embodiment An embodiment according to the present invention will be described below with reference to the drawings.
FIG. 1 is an example of the configuration of an ink jet head according to the present invention, and corresponds to FIG. That is, FIG. 1 shows a shear mode type head in which six nozzles having nozzle holes 3a to 3f are integrated. Partition walls 5ab, 5bc, 5cd, etc. are arranged on an insulating substrate 1 made of glass or ceramics at equal intervals and parallel by an adhesive layer 8. To form the elongated grooves 2a to 2f of the ink chamber and the ink flow path. These grooves are connected by a common ink reservoir. Further, the partition is flexibly bonded to the lid 6 made of glass or ceramics by the elastic member 9. Also, electrodes are placed on the entire wall surface of the partition.
4a2, 4b1, 4b2, 4c1, etc. are formed. Up to here is the seventh
It can be said that it is essentially the same as the figure. On the other hand, what is newly added to FIG. 7 in FIG. 1 is the dummy grooves 12a and 12b according to the present invention. In this example, apparently only the partition wall 5a
The configuration is such that dummy partitions 15aa and 15fb, which are the same partitions as b to 5ef, are increased one by one on both sides at the same pitch. Therefore, the dummy electrode is added to the entire dummy wall.
4a1, 14a2, 4f2, 14b1 are formed, and the dummy groove 12 is formed.
a, one end of 12b leads to the common reservoir,
The ink can be supplied from there. Although the other end is closed, a small hole for facilitating the introduction of the ink into the dummy groove may be provided in the same manner as the nozzle hole 3a in some cases. In this case, the shape and size of the small holes may be freely selected as long as ink leakage does not occur. Further, the arrangement of the nozzle holes 3a to 3f is restricted, for example, as disclosed in JP-A-63-252750, whereas the arrangement of the small holes is the dummy grooves 12a, 12,
There is no problem as long as it is located at the end of b. In this case, the substrate 1 is made of alumina, the five partition walls and the two dummy partition walls are all PZT polarized as shown by the arrow 7, the adhesive layer 8 between alumina and PZT is epoxy resin, and the grooves are all of width 1.
The electrode and the dummy electrode are 00 μm in depth and 150 μm in depth, and all of the electrodes and the dummy electrodes are laminated films of chromium and gold by evaporation, and the total film thickness is 0.8 μm. The lid 6 is an alumina plate, which is adhered to the partition by an elastic member 9 made of silicon resin, and the nozzle hole is a 35 μm diameter round hole obtained by etching a stainless steel nozzle plate.

FIG. 2 shows this driving waveform, and the dummy partition 15aa, the partition
The voltage waveforms applied to 5ab and 5bc are straight lines 29, 27,
28 is the voltage 0V level, the vertical axis is the voltage, and the horizontal axis is the time
Indicated as 20, 21, 24, etc. In this case, the remarkable difference from the conventional example of FIG. 8 is the waveform for the partition wall 5ab, and in FIG. 2 of the present invention, the voltage of a large absolute value like 82 in FIG. Need not be applied, it is sufficient to apply 22 having the same size as 24. Dummy bulkhead 15
It is self-evident that applying the voltage waveform 20 to aa causes the same volume change in the groove 2a as in the central groove 2b and the like. Further, it is obvious that there is no need to apply a voltage waveform of the opposite phase to the dummy partition, and that the discussion of the dummy partition 15ab is applied to the dummy partition 15fb as it is.

As described above, the effective driving force in the grooves 2a and 2f at both ends related to printing is almost the same as that in the central portion. Moreover, since the driving voltage can be made substantially the same for all the partition walls, the driving stability of the entire head is not impaired for the reason described in the conventional example. Therefore, good and stable printing characteristics can be obtained.

FIG. 3 shows a different embodiment of the present invention. Here, a piezoelectric material substrate 31 in which the insulating substrate 1 and the partition walls 5ab and the like in FIG. 1 are integrally formed is used. The partition walls 5ab to 5ef and the dummy partition walls 15aa and 15fb are polarized in one direction as shown by an arrow 7, as in FIG. The grooves of the ink chamber and ink flow path are 2a to 2f, the dummy grooves are 12a and 12b, and the lid is 6. The electrodes on the wall surfaces of the partition walls are the electrodes 4a to 4f in the groove, and the electrodes on the wall surfaces of the dummy partition walls are the grooves. These are the dummy electrodes 14a and 14b. Here, in FIG. 1, the electrodes in the grooves were separated like 4a1 and 4a2, for example.
In the present invention, 4a is used for driving the electrodes 4a1 and 4a2.
Is generally used as the same potential, but they may be separated as shown in FIG. Now, the meaning of the integration of the insulating substrate 1 and the partition walls 5ab and the like in FIG. 1 according to the present invention is to increase the rigidity of the adhesive layer 8 equivalently in FIG. . The necessity of increasing the rigidity is that the stress generated in the adhesive layer 8 due to the deformation in the shear mode at the time of driving shown in FIG. 9B becomes difficult to ignore in the head for high resolution. The reason is as follows.

For example, 300dpi (dots per inc
h) Assume a head of resolution. Partition wall pitch is about 80
μm, the partition wall width is about 40 μm, and inevitably the elastic member 9
The maximum thickness is about 10 μm. On the other hand, the adhesive layer is required to have an insulating property first, and to maintain the polarization of the partition walls at a temperature higher than the Curie temperature of the piezoelectric material (usually 150 ° C.).
Below). For this reason, the adhesive layer must be limited to a polymer based on epoxy or the like, but the thickness becomes several μm. As a result, the following major problems occur.

(1) As described above, if the thickness of the adhesive layer 8 with respect to the elastic member 9 is not so small as to be negligible, the adhesive layer undergoes a non-negligible level of deformation with respect to the elastic member due to the stress caused by the shear mode deformation of the partition walls. Become. In this case, the deformation of the adhesive layer acts to suppress a decrease in the cross-sectional area of the groove 92b of the ink chamber and the ink flow path, as can be seen from FIG. 9B. As a result, the driving force of ink ejection is reduced by the amount of deformation of the adhesive layer 8.

(2) When trying to repeat the ink discharge operation at high speed, the stiffness of the partition wall as a vibration system is required, but the contribution of the elastic member 9 to this is small and the adhesive layer 8
Is governed by the hardness of However, a polymer adhesive does not provide sufficient stiffness.

As described above, a decrease in the ink ejection force and the ejection frequency is expected, which causes a decrease in printing stability and speed as a printer.

FIG. 4 shows still another embodiment of the present invention.
It is based on the driving principle already disclosed in FIG. Although this structure mainly corresponds to FIG. 3, a completely similar discussion is possible with the structure corresponding to FIG. Here, instead of the lid 6 used in FIG. 3, a piezoelectric material substrate 41 in which a groove is formed in the same manner as the substrate 31 is used.
By stacking such two piezoelectric materials, grooves 2a to 2f corresponding to the grooves in the previous embodiment, and 12a, 12b
Is formed. The reason for using two piezoelectric materials in this way is to increase the driving force of ink ejection as compared with FIG. The point to be noted here is that the polarization directions of the piezoelectric materials should be opposite to each other like the polarization directions 7 and 27 of the partition walls 5ab and 52ab in the figure. The positions must match as shown in FIG.

The point of the present invention shown in FIG.
With the provision of 12a and 12b, this groove is formed by two piezoelectric substrates 3
The grooves provided in 1, 41 are integrally formed. This integration is usually achieved by bonding two sheets. If the dummy partition walls 15aa, 25aa, 15fb, 25fb are driven using the electrodes 14a, 24a, 14b, 24b formed on the inner walls of the dummy grooves, the same effects as described in FIG. 3 can be obtained. Is clear.

FIG. 5 shows another embodiment according to the present invention, in which a second dummy groove is newly provided outside the dummy groove in the configuration of FIG.
12c and 12d are provided. The meaning of the present invention is that the dummy groove 12 in the configuration of FIGS. 1, 3 and 4 is used.
The outer wall of a, 12b (the opposite side of the partition 15aa or 15fb) is a fixed wall, and the compliance of the dummy groove when filled with ink is smaller than that of the other grooves 2a, 2b, etc. It is to improve the problem that the partition walls 15aa and 15fb are stiffer than the other partition walls 5a and 5b and the like, and as a result, non-uniformity remains in the ink discharge performance. Therefore, since the second dummy groove need only function as a mechanical buffer, there is no need to form an electrode on the inner wall of the groove as shown in FIG.
bd need not be polarized. However, there is no problem even if the electrode remains or is polarized due to a manufacturing process. Whether or not to provide small holes in the nozzle plates at the ends of these dummy grooves is determined by the first method.
The description in the figure can be applied as it is. Further, it is clear from the above discussion that it is effective to provide three or more dummy grooves at one end.

FIG. 6 shows still another embodiment of the present invention having the same effect as that of FIG. 5 except that a second dummy groove is formed instead of a second dummy groove.
Dummy grooves 42a and 42b having a larger sectional area than 2a and 2b
By forming via the aa and the 45fb, the reduction of the compliance of the dummy groove caused in the embodiment shown in FIG. 1 or FIG. 3 is corrected. Enlarging the cross-sectional area is easily achieved by increasing the groove width or increasing the groove depth.

In FIG. 6, 44a and 44b are dummy electrodes in the groove.

〔The invention's effect〕

As described above, according to the structure of the present invention, the problem of non-uniformity of the ink droplet ejection characteristics at both ends and the nozzle hole at the center, which was one of the serious problems in the shear mode type ink jet head, was solved. This significantly improves the printing characteristics.

[Brief description of the drawings]

1 is a sectional view of a shear mode ink jet head of the present invention, FIG. 2 is a driving waveform thereof, FIGS. 3 to 6 are sectional views of a head showing another structure of the present invention, and FIG. FIG. 8 is a cross-sectional view of a shear mode ink jet head, FIG. 8 is a drive waveform thereof, FIG. 9 is a view showing a shear mode drive principle, and FIG. 10 is a perspective view of the shear mode ink jet head. 1 ... insulating substrate, 31, 41 ... piezoelectric material substrate, 2a-2f ... groove, 3a-3f ... nozzle hole, 4a-4f ... electrode, 12a-12d, 42a, 42b ... dummy groove, 5ab-5ef, 15aa, 15fb ... Partition walls.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshihiko Yanagawa, 840 Takeno, Shimotomi, Tokorozawa, Saitama Prefecture Within the Research Institute of Citizen Watch Co., Ltd. Examiner in the Research Institute of Citizen Watch Co., Ltd. Teruki Yumoto (56) References JP-A-3-175046 (JP, A) JP-A-3-175045 (JP, A) JP-A-2-165962 (JP, A JP-A-63-247051 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/045 B41J 2/055

Claims (3)

(57) [Claims] 1. A method according to claim 1, wherein said partition has N grooves related to printing separated by a partition wall made of piezoelectric material, each groove communicating with a common ink reservoir at one end, and having a nozzle hole at the other end. Causes a shear mode displacement by a voltage applied to an electrode formed on the wall surface of the partition wall, thereby discharging ink in the groove from the nozzle hole. An ink jet head having dummy grooves provided on both outer sides thereof via a partition made of a piezoelectric material and not accompanied by ink ejection. 2. The ink jet head according to claim 1, wherein two or more dummy grooves are provided on each side. 3. The ink jet head according to claim 1, wherein a sectional area of the dummy groove is larger than a sectional area of each of the N grooves.