JPH0445943A - On-demand type ink jet print head - Google Patents

Abstract

PURPOSE:To generate ink drips having sufficient flying force with the lowest voltage possible by coating surfaces of piezoelectric devices with insulating resin material. CONSTITUTION:An insulating thin film 5 is applied to the whole surface of a piezoelectric device 4. As an applying material, there are plastic materials such as groups of polyimide resin, polyester resin, fluorine resin, silicone resin, epoxy resin, and their mixtures and rubber material group. Those resins and rubbers are diluted with solvents appropriate to each of them so that solutions are made. The piezoelectric device 4 is dipped in the solution with a face of the substrate 1 directing upward, dried, stuck fast so as to make the insulating film 5. Although the thinner the film thickness is, the better it is, about 3-15mum is preferable.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention causes liquid ink to fly as droplets or mist when print data is input, and the ink droplets or mist to create dots on recording paper. The present invention relates to an on-demand inkjet printhead that forms an inkjet printhead. Widely used as computer output terminals and color printers.

[Conventional technology]

On-demand inkjet print heads can be broadly divided into three types.The first type is equipped with a heater that instantaneously vaporizes ink at the tip of the nozzle, and generates ink droplets by the expansion pressure during vaporization. The second type is a so-called bubble jet type in which the ink is ejected, and the second type is a type in which a piezoelectric element that deforms in response to a signal is provided in a container forming an ink reservoir, and the pressure generated during deformation causes ink to be ejected as droplets. In this method, a piezoelectric element is disposed in an ink reservoir so as to face a nozzle, and the expansion and contraction of this piezoelectric element generates dynamic pressure in the nozzle area, causing ink droplets to fly.

The third type of on-demand inkjet printhead has a plurality of nozzle openings formed on the wall of a container constituting an ink tank, as shown in Japanese Patent Publication No. 8953/1989. A piezoelectric element is arranged so as to face each nozzle opening and extend and contract in the same direction.

This print head applies a print signal to a piezoelectric element to cause the piezoelectric element to expand, and the dynamic pressure of the ink generated at this time causes ink droplets to fly out from a nozzle to form dots on printing paper.

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

In order to solve such problems, Japanese Patent Publication No. 6
As shown in Japanese Patent No. 3-295269, a piezoelectric element for an inkjet print head has been proposed in which electrodes and piezoelectric materials are alternately laminated in a sandwich manner. According to this piezoelectric element, since the distance between the electrodes can be made as small as possible, there is an effect that the voltage of the drive signal can be lowered.

Since then, many patents have been issued that take advantage of these characteristics, and one way to use them is to drive a piezoelectric element in ink to further enhance the effect.

[Problem to be solved by the invention]

However, this method has a problem in that it cannot be used if the ink itself has conductivity.

The purpose of the present invention is to solve the problems described in (-) above, and it is possible to generate ink droplets with sufficient flying force at the lowest possible voltage, to enable miniaturization and high density, to be inexpensive, and to be electrically conductive. sex/
An object of the present invention is to provide an on-demand inkjet head that is compatible with both insulating and insulating inks.

[Means to solve the problem]

The on-demand inkjet print head of the present invention is characterized in that the surface of each piezoelectric element is coated with an insulating resin material. Further, it is characterized in that a first partition member is provided between each row of piezoelectric elements. Furthermore, it is characterized in that the first partition member extends to the second partition member facing each piezoelectric element. Furthermore, what about the insulating resin material? It is characterized in that it is formed by dipping an on-demand inkjet print head into a 8-molten or molten diaphragm, pulling it up, and drying it.

〔Example〕

FIG. 1 shows an example of an on-demand type print head according to the present invention, in which FIG. 1(a) is a sectional view, and FIG. 1(b) is a nozzle plate. 7 is a view seen from above with part 7 removed.

The piezoelectric element 4 is fixed to the substrate 1 and the housing 2 by strong adhesive or brazing 15.

Internal electrodes are alternately formed in opposite directions to the cavity 11 so that the piezoelectric element vibrates longitudinally in the d33 direction. The external electrodes of the piezoelectric element are formed entirely on the upper and lower surfaces, and
The adhesive or braze is electrically connected to the lead electrode 14 formed on the substrate through the material or conductor. Furthermore, the gaps between the rows of piezoelectric elements are filled with an adhesive or filler whose Young's modulus is 115 or less than the Young's modulus of the piezoelectric elements. Further, the cavity portion is partitioned with a material similar to the material used to fill the gaps between the piezoelectric element rows, and each element has an independent cavity. The side surface of the cavity facing the piezoelectric element is formed of a partition block 3 made of ceramic, plastic, metal, etc., and is fixed to the substrate 1. The on-demand inkjet print head having the above-mentioned configuration will be described in detail following the manufacturing process.

FIG. 2 shows the substrate 1. FIG. Each broken line a in the figure indicates one unit of the head so that a large number of pieces can be taken out at the same time. The number of sheets to be produced is determined by the number of nozzles in each head and the capacity of the manufacturing equipment. This substrate is made of an insulating material, such as a ceramic such as alumina, a glass substrate, or the like. In the figure, reference numeral 21 denotes a through hole for ink introduction, which is penetrated through the back surface by laser or molding. 22 is a conductive paste for conductive electrodes made by firing, and is generally Ag/Pd type, A u / P d type, P t / P
d system is used. Of course, other conductive pastes can also be used, and the thickness is preferably from 3 μm to 20 μm. On top of this, (-1: tJ rib block 3 and a piezoelectric element block are glued. As the adhesive, a resin adhesive such as epoxy or silicone adhesive, or Ag wax or the like is used.

FIG. 3 shows a block 3 and a piezoelectric element block 34 bonded to a unit substrate. At this point, piezoelectric element 3
4 is not divided into each array and is in a block state. This piezoelectric element block has external electrodes covering the entire surface of the upper and lower surfaces, respectively.

Further, numeral 31 in the figure is a void that will form a cavity in the future. This void is filled with a resist film, etc. that can be removed later (I
The F membrane is stretched = J is being kicked. Alternatively, 1/cyst for photolithography may be poured and solidified to fill the space. When fixing the piezoelectric element block to the substrate, the free end on the side opposite to the cavity side needs to be fixed with a member having high strength and a Young's modulus equivalent to that of the piezoelectric element. Thereby, the amount of expansion and contraction of the piezoelectric element can effectively act on the self-mounted end side on the cavity side. Therefore, in this embodiment, a housing (FIG. 1, 2), which will be described later, is made of a high Young's modulus material such as ceramic and is arranged so as to be in close contact with the fixed end of the piezoelectric element.
The first electrode between the piezoelectric element of the substrate 1 and the piezoelectric element of the housing 2
An adhesive with a high Young's modulus was used for the part 8 in the figure. For example, glass frit materials, ceramic base shrines, etc.
It is solidified by firing.

Here, the piezoelectric element will be explained in detail. FIG. 3 (II) shows a piezoelectric element block, with reference numerals 40 and 4 in the figure.
0. 40. . . . are conductive layers constituting one electrode, and 42. 42. 42゜... is a conductive layer constituting the other electrode, and each conductive layer is made of piezoelectric material 44゜44 alternately so as to be parallel to each other.
, . . . in a sandwich manner, and one electrode 30. 30. 30. . . . The conductive layer is exposed on one side, and the other electrode 42
, 42° 42, . . . are configured to be exposed on the other side. A conductive layer is formed on the exposed surface of these electrodes, and the multi-pole conductive layers are electrically conductively connected in parallel, and each piezoelectric element has a slit 4.
Separate according to 6.46.46.

Such a layer) I♂ structure is made by forming an appropriate piezoelectric element material, such as a composite perovskite ceramic material based on titanate/lead zirconate, into a green sheet, and printing an inner 71i polar layer on the surface of this green sheet using a printing method. Laminate the required number of sheets alternately.

In this way, a predetermined number of sheets are formed, and pre-drying and sintering are performed to obtain a sintered body. This state is shown in FIG. 4(a). Conductive materials 47 and 48 are respectively applied to the exposed surfaces of the rectangular parallelepiped and where the internal electrodes 42 and 40 are exposed, and then dried or fired to form the structure shown in FIG. 4(b). This is a piezoelectric element block, which is ultimately divided into arrays by making slits 46 for use.

Independent lead members are connected to the conductive layer 47 connecting one electrode of each element configured in this way,
Further, a common lead member is connected to the conductive layer 48 connecting the other electrode. As a result, when an electric signal is applied between the independent lead members and the common lead member, the piezoelectric element to which the signal is selectively applied by the independent lead member will receive the same voltage between the electrodes via the conductive layer. are applied at the same time, the piezoelectric material between the electrodes simultaneously expands, the displacements of each layer are added up, and the free end side is displaced in the axial direction. Of course, since each conductive layer is formed extremely thin, an extremely small voltage is required to achieve maximum elongation.

This piezoelectric element block is electrically connected to the electrode on the substrate 1 through a conductive agent. There are various conduction methods, but generally Ag
Use wax or conductive paste. Also, a metal bowl may be pressed between the substrate and the piezoelectric element. The conductive space does not need to be the entire electrode surface, it is sufficient that a certain portion is properly conductive. However, as mentioned above, since the piezoelectric element block is used by cutting, it is necessary to take care to ensure continuity for each array.

Next, the thing in this state is
Cut a slit in the direction of ' using a dicing saw or wire saw. At this time, cutting is performed to a depth of 10 to 50 μm from the substrate surface so that the substrate surface electrode 22 is also divided. Of course, the pitch may be any desired value. For example, if you are making a 300DP head, one side will be 150D.
PI has a pitch of 169.3 μm. At this time, since the actual cutting is performed in units of large substrates, several dozen head units can be cut at once.

Furthermore, it is only necessary that the cutting pitch be accurate, which is a major point in making this method inexpensive.

FIG. 5(b) is a top view of the cutting process, and AA' is the cutting line.

D in the figure is the outermost dummy that is not used as a piezoelectric element. Due to this D, the accuracy of bonding the piezoelectric element block and the partition block to the substrate is not so important. At this point, the sides of the cut piezoelectric element are
Internal electrodes are exposed. If the piezoelectric element is immersed in ink in this state, if the ink is conductive, not only will it not be possible to drive the piezoelectric element, but there will also be a risk of electrical leakage or destruction. To prevent this, an insulating thin film is applied to the entire piezoelectric element. The materials to be applied include plastic materials such as polyimide persimmon resin, polyester resin, fluororesin, silicone resin, and epoxy resin, mixtures thereof, and rubber materials. The piezoelectric element portion is immersed with the substrate side facing up in a hot solution prepared by diluting these resins or rubbers with a suitable solvent, and then dried and brought into close contact to form an insulating film. The film thickness is preferably as large as M, but in order to ensure reliability, it is preferably about 3 to 15 μm.

Furthermore, as will be described later, since it is necessary to take out the common electrode from the top surface of the piezoelectric element, this part must be protected with tape or a resist film, and after the insulating film is formed, it must be peeled off to ensure conductivity. The portion d in FIG. 6 corresponds to that portion on the piezoelectric element electrode.

Next, a resin material is filled into the slit space created by cutting with a wire saw or the like and hardened. Suitable resin materials include epoxy, silicone, etc., but there is no need to be particular about these as long as the cured film has appropriate hardness, adhesion, and strength.

Next, the electrodes formed on the top surface of each piezoelectric element array are made conductive and one common pole is taken out. The electrodes on the substrate side and the lower surface of each piezoelectric element array are already configured as individual lead electrodes, and the upper surface is electrically connected to the common electrode terminal on the substrate side by using, for example, the outer wall of the housing. FIG. 6 shows one example, in which a conductive path is formed on the surface of the housing using conductive paste. In the figure, 61 is a housing surface conductive path,
It is electrically connected to the two-sided electrode of the piezoelectric element array through a 34-electrode paste 62. Further, the conductive path 61 is also electrically connected to the common electrode 13 on the substrate through a conductive paste 63. There are various methods of electrical connection, such as using a flexible cable or wire bonding.

Next, it was filled to form a cavity (second
Space in Figure 31) Remove the soluble resin in the space.

If it is a positive type photoresist, it is suitable to remove it with acetone or aqueous ammonia, and if it is a negative type photoresist film, it can be removed by spraying a heated strong acid type aqueous solution.

As a result, a cavity as shown in FIG. 7 can be formed. The figure shows a case where a spacer is also cut at the same time as the piezoelectric element, and a cavity 71 is formed by pouring the resin material 5 into the space.

The surface of the head unit thus formed may be covered with the resin material 5 up to the top surface of the piezoelectric element. However, in this state, the surface is uneven and the nozzle plate cannot be firmly fixed to the upper surface. Therefore, the upper surface of the resin including the housing is ground to make it smooth. Grinding is performed using a surface grinder, lapping machine, or dicing saw. Thereafter, the nozzle plate is fixed to the entire resin material surface and the surface of the spacer portion 6 using adhesive or melt bonding. Of course, the upper hole of the cavity forming part and the nozzle 1
No ↑・ nozzles have a one-to-one correspondence.

Although this embodiment has described a method in which the cavities face each other with the partition block 3 in between, it goes without saying that the number of nozzle openings L1 may be in one row, or it is easy to have four rows.

The print head (FIG. 1) configured in this manner is configured such that when an electrical signal is applied to the piezoelectric element 4 via the cable 12, the piezoelectric element 4. 4. 4. . . extends in the stacking direction of the electrodes, so the free end of the piezoelectric element pushes out the ink on the front surface toward the spacer 6.

As a result, the ink rushes into the nozzle opening 9 under dynamic pressure, becomes an ink droplet, flies in the external space, and forms a driver I on the printing paper.

When the electric signal is no longer applied, the piezoelectric element contracts to its original state, and ink flows into the gap between the spacer 6 and the piezoelectric element 4 in preparation for the generation of the next ink droplet.

〔Effect of the invention〕

As described above, with the configuration of the present invention, d3
A head that uses vibration in three directions has sufficient flying power, and can be supplied at a low cost with a small size and high performance.
It can be used regardless of whether the ink is conductive or insulative. In this way, it is an extremely effective invention.

[Brief explanation of drawings]

FIG. 1(a) and FIG. 1 (one) are cross-sectional views showing the configuration of an on-demand inkjet print head according to a first embodiment of the present invention, respectively. FIG. 2 is a diagram showing an embodiment of a substrate used in the apparatus of FIG. 1. FIG. 3 is a perspective view showing the manufacturing process of the device shown in FIG. 1. FIGS. 4(a) and 4(b) are explanatory diagrams showing a method for manufacturing and using a piezoelectric element used in the apparatus shown in FIG. 1. FIG. 5 (aL (b) is an explanatory diagram showing a method of cutting a row of piezoelectric elements. FIG. 6 is an explanatory diagram of an embodiment showing a method of electrically connecting to a piezoelectric element, and FIG. 7 is an explanatory diagram showing a method of cutting a row of piezoelectric elements. 4. Piezoelectric element 5. Resin material Applicant: Seiko Epson Corporation

Claims (4)

[Claims] (1) An ink reservoir is formed by fixing a piezoelectric material sheet, or a row of piezoelectric elements made by laminating paste materials and conductive materials alternately in layers and firing them, to a base and leaving the other end free. In an inkjet head, in which a space is provided and partition members are arranged to face each other, and a nozzle part is provided to face the space, each piezoelectric element has a surface covered with an insulating resin material. An on-demand inkjet print head that is characterized by (2) The on-demand inkjet print head according to claim 1, wherein a first partition member is disposed between each row of piezoelectric elements. (3) The first partition member between each piezoelectric element row is connected to the opposing second partition member so that the ink reservoir space also corresponds to each piezoelectric element row.
2. The on-demand ink jet print head according to claim 1, wherein the print head extends to a partition member. (4) The insulating resin material is formed by immersing an on-demand inkjet print head in a solvent in which the insulating resin is dissolved or melted, and then being pulled up and dried. Demand type inkjet print head.