JP2959056B2 - Inkjet print head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a technique in which, when print data is received, liquid ink is caused to fly as droplets or mist, and the ink droplet or mist is used to print dots on recording paper. The present invention relates to an on-demand type ink jet print head for forming a print head. This type of head is widely used for an output terminal of a computer and a color printer.

[Conventional technology]

On-demand type ink jet print heads are roughly classified into three types. The first type is a so-called bubble jet type in which a heater for instantaneously evaporating ink is provided at the tip of a nozzle, and ink droplets are generated by the expansion pressure at the time of vaporization and fly. In the second type, a piezoelectric element that is deformed by a signal is provided in a container that forms an ink reservoir, and ink is caused to fly as droplets by pressure generated during the deformation. In the third type, a piezoelectric element is provided in the ink reservoir so as to face the nozzle, and a dynamic pressure is generated in the nozzle region by the expansion and contraction of the piezoelectric element to cause the ink droplet to fly.

The on-demand type ink jet print head of the third type has a plurality of nozzle openings formed on a wall surface of a container constituting an ink tank, as shown in Japanese Patent Publication No. 60-8933. The piezoelectric element is arranged so that the expansion and contraction directions are matched so as to face each nozzle opening.

In this print head, a print signal is applied to a piezoelectric element to expand the piezoelectric element, and ink droplets are ejected from nozzles by a dynamic pressure of ink generated at this time to form dots on printing paper.

[Problems to be solved by the invention]

In a print head of this type, it is desirable that the droplet formation efficiency and the flying force be large. However,
Since the length of the piezoelectric element and the expansion / contraction ratio per unit voltage are extremely small, it is necessary to apply a high voltage to obtain the flying force required for printing, which complicates the drive circuit and measures for electrical insulation. There is a problem.

To solve such a problem, Japanese Patent Publication No.
As disclosed in JP-A-63-295269, there has been proposed a piezoelectric element for an ink jet print head in which electrodes and piezoelectric materials are alternately laminated in a sandwich form. According to this piezoelectric element, the distance between the electrodes can be made as small as possible, so that the voltage of the drive signal can be reduced.

However, since it is difficult to form such a piezoelectric element into a small size, there is a problem that its use is limited.

A first object of the present invention is to provide a novel on-demand type ink jet head capable of generating ink droplets having a sufficient flying force at a voltage as low as possible.

A second object of the present invention is to provide a small, high-density, practical ink jet print head.

A third object of the present invention is to provide an ink jet print head which is inexpensive and excellent in mass productivity.

[Means for solving the problem]

The ink jet print head of the present invention has a plurality of piezoelectric elements vibrating in the axial direction in which a plurality of piezoelectric materials and conductive materials are alternately laminated in the same direction as the vibration direction, and one end of the plurality of piezoelectric elements is a free end. A substrate having a Young's modulus equivalent to that of the piezoelectric element having the other end fixed thereto, a partition block disposed opposite to the free end via a space serving as a cavity, and the piezoelectric element of the piezoelectric element communicating with the cavity. A nozzle opening disposed in a direction perpendicular to the vibration direction, a partition member provided between the piezoelectric elements, a slit communicating with the cavity formed in the substrate, and a conductive electrode formed in the substrate. Wherein the piezoelectric element, the nozzle opening, and the partition member are similarly formed with the partition block interposed therebetween.

〔Example〕

1A and 1B show an on-demand type ink jet print head according to the present invention. FIG. 1A is a sectional view, and FIG. 1B is a view seen from above with a nozzle plate 7 removed. is there. The piezoelectric element 4 is fixed to the substrate 1 and the housing 2 by a strong adhesive or brazing material 8. The piezoelectric element vibrates longitudinally in the d33 direction so that the internal electrodes 4
0 and 42 are alternately formed in a direction facing the cavity 11. The external electrodes 47 and 48 (see FIG. 4 (II)) of the piezoelectric element are formed over the entire upper and lower surfaces, and the lead electrodes 14 formed on the substrate 1 via an adhesive or brazing material 8 or a conductive material. Are electrically connected to the common electrode 13. Further, the piezoelectric element row is filled with a partition member (adhesive or filler) 5 whose Young's modulus is 1/5 or less of the Young's modulus of the piezoelectric element. Further, the cavity portion is partitioned by a material equivalent to the material 5 filling the gaps of the piezoelectric element row, and an independent cavity 11 is formed for each element. The side surface of the cavity 11 facing the piezoelectric element 4 is formed of a partition block 3 made of ceramic, plastic, metal, or the like. The partition block 3 is fixed to the substrate 1. The on-demand type ink jet print head having the above configuration will be described in detail while following the manufacturing process.

Process 1 FIG. 2 is a plan view of a substrate. In the illustrated example, a large number of substrates 1 can be taken at the same time. By cutting along a broken line a in the figure, a large number of substrates 1 for one unit, that is, one head can be taken. The number of sheets to be taken is determined by the number of nozzles of each head and the capacity of the manufacturing apparatus. This substrate is made of an insulating material, and a ceramic such as alumina or a glass substrate is used. In the figure, reference numeral 21 denotes a through hole for introducing ink, which penetrates to the back surface by laser or molding. Reference numeral 22 denotes a conductive paste for a through electrode made by firing, which is generally Ag / Pd-based, Au / Pd-based,
A Pt / Pd system is used. Of course, other conductive pastes can also be used, and the thickness is preferably from 3 μm to 20 μm.

Process 2 The partition block 3 and the piezoelectric element block 34 are bonded on the substrate 1 of the unit obtained by cutting such a substrate. The adhesive is a resin-based adhesive such as an epoxy-based or silicone-based adhesive,
Alternatively, Ag wax or the like is used.

FIG. 3 is a view showing a state in which the block 3 and the piezoelectric element block 34 are adhered on the substrate 1 of one unit. At this point, the piezoelectric element block 34 is not divided into the respective piezoelectric element rows and is in a block state. The piezoelectric element block 34 has external electrodes 47 and 48 (see FIG. 4 (II)) covering the entire upper and lower surfaces, respectively. In the figure, reference numeral 31 denotes a space for forming the cavity 11 in the future. A film that can be removed later, such as a resist film, is attached to the gap 31. Alternatively, a photolithographic resist may be poured and solidified.

When the piezoelectric element block 34 is fixed to the substrate 1, the end opposite to the cavity side is fixed by a member having high strength (the same Young's modulus as the piezoelectric element). Thereby, the amount of expansion and contraction of the piezoelectric element effectively acts on the free end side on the cavity side. In this embodiment, the housing 2 (see FIG. 1) is disposed as a high Young's modulus material such as ceramic so as to be in close contact with the fixed end of the piezoelectric element. A high Young's modulus adhesive was used as the brazing material 8 (see FIG. 1). For example, using glass frit material, ceramic paste material, etc.
It was fixed by firing. Here, the piezoelectric element will be described in detail. FIG. 4 (b) shows a piezoelectric element block, and reference numerals 40, 40, 40 ... in the figure denote conductive layers constituting one internal electrode, respectively. Are conductive layers constituting the other internal electrode. The conductive layers 40 and 42 are alternately arranged in parallel with each other so as to be parallel to each other in the piezoelectric materials 44, 44,. One end of the conductive layer 40 serving as an internal electrode is exposed on the back surface of the block, and the other end of the conductive layer 42 serving as the other internal electrode is exposed on the surface of the block. On the exposed surfaces of these internal electrodes, conductive layers constituting external electrodes 47 and 48 are formed, and conductive layers 40...
Are conductively connected in parallel. The piezoelectric element row is formed by separating such a piezoelectric element block by slits 46, 46, 46 as described later.

The layer structure of the piezoelectric element block as described above can be obtained as follows. First, a suitable paste-like piezoelectric element material, for example, a lead titanate / zirconate-based composite perovskite ceramic material is formed into a green sheet,
An internal electrode material is printed on this surface by a printing method. Next, the required number of sheets are alternately stacked and laminated.
Thereafter, preliminary drying and sintering are performed to obtain a sintered body. This state is shown in FIG. Conductive materials 47 and 48 are applied to the surfaces of the rectangular parallelepiped, on which the internal electrodes 42 and 40 are exposed, and dried or fired, respectively, to obtain a state shown in FIG. 4 (b). This is a piezoelectric element block, which is finally divided into each piezoelectric element row with slits 46 and used.

One internal electrode 40 of each piezoelectric element row thus configured
As shown in FIG. 6, an independent lead electrode 14 is connected to the external electrode 48 connecting the electrodes, and a common electrode 13 is connected to the external electrode 47 connecting the other internal electrode 42. . Accordingly, when an electric signal is applied between the independent lead electrode 14 and the common electrode 13, the piezoelectric element to which the signal is selectively applied by the independent lead electrode 14 is applied to the external electrodes 47 and 48.
, The same voltage is simultaneously applied between the internal electrodes 40 and 42, so that the piezoelectric material between the internal electrodes expands at the same time, the displacement of each layer is added, and the free end side is displaced in the axial direction. Of course, since the piezoelectric material between the internal electrodes is formed to be extremely thin, the voltage for performing the maximum elongation requires an extremely small value.

There are various conduction methods for conducting the piezoelectric element block 34 to the electrodes on the substrate 1 with a conductive agent, but generally, an Ag brazing material or a conductive paste is used. In some cases, a metal bowl is used by being crushed between a substrate and a piezoelectric element. The conductive space does not need to be the entire surface of the electrode, and it is sufficient if a certain portion is properly conducted. However, since the piezoelectric element block 34 is used by cutting as described above, it is necessary to take care that each piezoelectric element row is electrically connected.

Process 3 A slit obtained by the process 2 shown in FIG. 3 is cut in the direction of the dashed line AA 'in FIG. 5 using a dicing saw or a wire saw. At this time, the surface electrode 22 of the substrate 1 is divided by 10 to 50 μm from the substrate surface so that the surface electrode 22 is also divided.
Perform cutting to a depth of m. The pitch may be a desired value. For example, if you want to make a 300DPI head, one side
At 150 DPI, the pitch becomes 169.3 μm. The housing 2 shown in FIG. 1 is installed so as to surround the piezoelectric element block 34 thus cut. Housing 2 is board 1
And, it is firmly fixed to the end face opposite to the cavity side of each piezoelectric element row. It is desirable that the adhesive used here has as large a Young's modulus as possible.

Process 4 A resin material is filled into a slit space formed by cutting with a wire saw or the like and cured. The resin-based material is suitably epoxy-based, silicon-based, or the like. However, if the cured film has appropriate hardness, adhesion, and strength, there is no need to stick to this.

Process 5 The electrodes formed on the upper surface of each piezoelectric element row are made conductive to take out the common electrode. The electrodes on the substrate side and the lower surface of each piezoelectric element row have already been formed as individual lead electrodes by cutting in process 3. The upper surface is electrically connected to the substrate-side common electrode 13 by using, for example, an outer wall of the housing. FIG. 6 shows an example of this, in which a conductive path 61 is formed on the surface of the housing 2 with a conductive paste. The conductive path 61 is electrically connected to the upper electrode 47 of the piezoelectric element row by the conductive paste 62. The conductive path 61 is also electrically connected to the common electrode 13 on the substrate by the conductive paste 63. There are various types of this electrical bonding method, and for example, a flexible cable can be used or wire bonding can be performed.

Process 6 The soluble resin in the space (the void 31 in FIG. 3) filled to form the cavity is removed. In the case of a positive photoresist, it is preferable to remove it with acetone or ammonia water. In the case of a negative photoresist film, a strong acid aqueous solution is heated and sprayed to remove. Thus, the cavity 11 as shown in FIG. 7 can be formed. The drawing shows a case where the partition block 3 is also cut at the same time as the piezoelectric element, and the resin material 5 is caused to flow into the space to form the cavity 11.

Process 7 The surface of the head unit thus formed may be covered with the resin material 5 up to the upper surface of the piezoelectric element. But,
In this state, the surface is uneven, and the nozzle plate cannot be firmly fixed on the upper surface. Therefore, the upper surface of the resin including the housing 2 is ground to be smooth.
Grinding is performed using a surface grinder, a lapping device, or a dicing saw. Thereafter, the nozzle plate 7 is fixed to the entire upper surface of the resin material 5 and the surface of the partition block 3 with an adhesive or a melt adhesive. The upper hole of the cavity 11 and the nozzle 9 of the nozzle plate 7 (see FIG. 1A) correspond one to one.

In this embodiment, the cavity is sandwiched between the partition blocks 3.
Although the method in which 11 are opposed to each other has been described, it is easy to form four rows.

In the print head (FIG. 1) configured as described above, when an electric signal is applied to the piezoelectric element 4 via the cable 12, the piezoelectric element 4 extends in the direction in which the electrodes are stacked. The ink in the cavity 11 is extruded toward the partition block 3. As a result, the ink enters the nozzle 9 under the dynamic pressure, flies as ink droplets in the external space, and forms dots on the printing paper.

When the application of the electric signal is stopped, the piezoelectric element is reduced to the original state, and the cavity 11 between the partition block 3 and the piezoelectric element is reduced.
Ink flows through the through hole 21 to prepare for the next ink droplet generation.

By the way, the ink for an ink jet printer may be insulative or conductive. Particularly when using conductive ink, the electrodes of the piezoelectric element 4 must be completely sealed from the ink. In order to clear these points, the piezoelectric element 4 as shown in the layer b of FIG.
It is desirable to form a layer that does not participate in the piezoelectric action with a piezoelectric material at both ends. Further, it is also a good method that the entire piezoelectric element array is dipped in an insulating resin liquid, for example, a polyimide solution before the resin material 5 is poured into the slit, and a thin insulating film is coated on the surface of the piezoelectric element.

FIG. 9 is a partial perspective view showing the second embodiment. In this embodiment, the resin material 5 as a partition member of each cavity does not extend to the partition block 3. Since the first embodiment is a high-density head, there is a problem of crosstalk. This embodiment is relatively effective when the density of adjacent nozzle openings is not high, and is sufficiently practical. In the figure, the nozzle plate 7 is seen through, and the space between the piezoelectric elements is filled with a resin material 5. In the case of this embodiment, the third
It is not necessary to provide the void 31 shown in the figure, and the partition block 3 and the piezoelectric element block 34 are adhered and adhered, and after filling the resin,
A portion corresponding to the gap 31 can be cut with a dicing saw or the like to form a slit-shaped cavity 91. or,
The partition block 3 can be used as the partition block 3 by extending a layer that does not contribute to the piezoelectric action of the piezoelectric element block, and then cutting that layer later.

If the width of each cavity 11 in FIG. 7, that is, w is sufficiently small, the nozzle plate 7 is not required,
The upper opening of 11 can also serve as a nozzle as it is, which was confirmed as the third example of the embodiment.

The ink jet head using the d33 direction vibration as described above can generate ink droplets having a sufficient flying force at a voltage of 30 V or less. This depends on the number of laminated internal electrodes of the piezoelectric element, but as the number of laminated layers increases, the voltage can be reduced.

Furthermore, the above-described manufacturing method enables simultaneous multi-cavity production, so that a very inexpensive inkjet head can be manufactured. In addition, with a method that is also excellent in high density, miniaturization and cost reduction can be realized at the same time.

〔The invention's effect〕

According to the present invention, a plurality of piezoelectric elements vibrating in the axial direction in which a plurality of piezoelectric materials and conductive materials are alternately stacked in layers in the same direction as the vibration direction, and one end in the axial direction of the plurality of piezoelectric elements is a free end. A substrate having a Young's modulus equivalent to that of the piezoelectric element having the other end fixed thereto, a partition block facing the free end via a space serving as a cavity, and the piezoelectric element communicating with the cavity. A nozzle opening disposed in a direction perpendicular to the vibration direction of the piezoelectric element, a partition member provided between the piezoelectric elements, a slit communicating with the cavity formed in the substrate, and a conductive electrode formed in the substrate. With this arrangement, it is possible to provide a print head that can fly ink droplets with high flying power and small size, high density. Further, since the piezoelectric element, the nozzle opening, and the partition member are similarly formed with the partition block interposed therebetween, two rows of nozzles can be manufactured efficiently.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) show a first embodiment of the present invention, respectively.
2A and 2B are a cross-sectional view and a partially omitted plan view showing a configuration of an on-demand type ink jet print head according to an embodiment of the present invention. FIG. 2 is a partial plan view of the substrate in a manufacturing process. FIG. 3 is a perspective view showing a manufacturing process. 4 (a) and 4 (b) are explanatory views showing a method for manufacturing a piezoelectric element. FIG. 5 is an explanatory view showing a method of cutting a piezoelectric element row. FIG. 6 is an explanatory view of an embodiment showing a method of electrically connecting to a piezoelectric element, and FIG. 7 is a perspective view near a cavity. FIG. 8 is an explanatory view showing another embodiment of the piezoelectric element. FIG. 9 is a perspective view of the vicinity of a cavity in another embodiment.

Claims (1)

(57) [Claims] 1. A plurality of piezoelectric elements vibrating in the axial direction in which a plurality of piezoelectric materials and conductive materials are alternately stacked in layers in the same direction as the vibration direction, and the other end such that one end of the plurality of piezoelectric elements is a free end. A substrate having a Young's modulus equivalent to that of the piezoelectric element, a partition block facing the free end and a space serving as a cavity, and a direction perpendicular to the vibration direction of the piezoelectric element so as to communicate with the cavity. Nozzle openings disposed in different directions, a partition member provided between the piezoelectric elements, a slit communicating with the cavity formed in the substrate, and a conductive electrode formed in the substrate, An ink jet print head, wherein a piezoelectric element, a nozzle opening, and a partition member are similarly formed with the partition block interposed therebetween.