JPH08118619A - Inkjet recording head - Google Patents

Abstract

(57) [Summary] [Object] To provide an inexpensive and easily manufactured inkjet recording head having uniform ink droplet ejection characteristics even when ink flow paths have different flow path resistances. [Structure] A substrate 9 having a plurality of ink channels 1 each consisting of a series of ink pressurizing chambers 4, nozzle channels 3, and nozzles 2.
A vibrating plate 10 covering the ink flow path, and a rectangular parallelepiped piezoelectric element 12 adhered to the surface of the vibrating plate facing the ink pressurizing chamber via a common electrode 11, respectively. In the case of ejecting ink from a nozzle using electric field induced strain in a direction parallel to the surface as a drive source, for example, the size of the piezoelectric element is set so that the electric field induced strain amount of the piezoelectric element is proportional to the flow path resistance of the ink flow path. A piezoelectric element 12A having a large adhesive area is provided for the piezoelectric element of the ink flow path having a high path resistance, and a piezoelectric element 12B having a small adhesive area is provided for the piezoelectric element of the ink flow path having a low flow resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer for a desktop printer, a fax machine, etc., an ink jet recording head used as a main part of a printer, and in particular, it has uniform discharge characteristics of ink droplets discharged from a plurality of nozzles. An inkjet recording head.

[0002]

2. Description of the Related Art Conventionally, a method of ejecting ink droplets from fine nozzles and spotting them on a recording medium such as paper for recording has been known as an ink jet recording method. Demand type ink jet recording heads are known. FIG. 2 is a plan view schematically showing an example of an ink flow path of an ink jet recording head, and FIG. 3 is a sectional view schematically showing an example of an ink flow path of an ink jet recording head in a direction along the ink flow path. In the figure, a substrate 9 made of a glass plate, a Si wafer, a metal plate, or a plastic molded product is provided with a nozzle 2, a nozzle channel 3, an ink pressurizing chamber 4, and an ink supply channel 5 which are formed as concave grooves communicating with each other. A plurality of ink flow paths 1 and an ink reservoir 7 communicating with the back flow prevention filter flow path 6 and a seal plate 8 having a flat plate-like vibrating plate made of the same material as the substrate 9. By airtightly bonding or adhering 10, the plurality of ink flow paths 1 defined by the seal surface 8 and in which the ink flow direction is regulated by the filter flow paths 6 are formed. A common electrode 11 is formed on the surface of the vibrating plate 10 facing the ink pressurizing chamber 4 of the ink flow path 1 as a metal vapor deposition film or a printed film of a conductive coating material across the plurality of ink pressurizing chambers 4. In addition, in the portion of the common electrode 11 corresponding to each ink pressurizing chamber 4, one electrode 13 of the rectangular parallelepiped piezoelectric element 12 as an electromechanical conversion element is extremely thin so as to make conductive contact with the common electrode 11. The inkjet recording head is formed by being fixed by the adhesive layer 14.

The ink jet recording head having the above-mentioned structure includes the other electrode 13 of the piezoelectric element 12 and the common electrode 1.
When a driving voltage of, for example, a square wave is applied between the piezoelectric element 12 and 1, the piezoelectric element 12 expands and contracts (electric field induced strain) in the plane direction parallel to the bonding surface. At this time, since the piezoelectric element 12 is in a state of being restrained by the vibration plate 10 via the adhesive layer 14 and the common electrode 11, the expansion and contraction of the piezoelectric element in the surface direction causes the vibration plate 1 to contract.
It is converted into a displacement in the direction perpendicular to 0, and the vibration plate is pushed and bent toward the ink pressurizing chamber side, and the volume of the ink pressurizing chamber is instantaneously reduced. Ink is ejected from the nozzle 2 through the nozzle flow path 3 and becomes an ink droplet, which is spotted on the opposite recording paper.
Printing is performed with an ink density of an amount proportional to the magnitude of the drive voltage applied to 2.

In order to print with the same density, it is required that the ejection characteristics such as the initial ejection velocity of the ink droplets ejected from a plurality of nozzles and the ink droplet amount are uniform with respect to a constant drive voltage. Conventionally, the following proposals have been made in order to achieve such an object. An ink jet recording head (US Pat. No. 3,988,745) in which the head has a fan shape and the nozzle flow paths from the nozzle to the ink pressurizing chamber have the same length.

An ink jet recording head in which the ejection characteristics of ink droplets are made uniform by compensating on the drive circuit side of the piezoelectric element (JP-A-51-55239). An ink jet recording head (JP-B-59-3150) in which the ejection characteristics of ink droplets are made uniform by changing the cross-sectional area of the nozzle flow path from the ink pressure chamber to the nozzle in proportion to the flow path resistance.

[0006]

In the above-mentioned conventional technique, the method of forming the head shape into a fan shape has a problem that the size of the ink jet recording head cannot be avoided, and therefore, the desktop printer is required to be small and lightweight. There will be restrictions on applicability to e-mails, faxes, etc. Further, in the method of compensating on the drive circuit side, there is a problem that the control circuit is complicated because the drive conditions such as the drive voltage and the drive time supplied to a large number of piezoelectric elements are individually controlled, which causes an economic disadvantage. . Further, in the method of changing the cross-sectional area of the nozzle flow path, it is necessary to finely adjust the diameter of the nozzle flow path, and there is a problem that the processing cost rises in order to maintain high processing accuracy.

An object of the present invention is to provide an inexpensive and easy-to-manufacture ink jet recording head having uniform ink droplet ejection characteristics even when the ink flow paths have different flow path resistances.

[0008]

In order to solve the above-mentioned problems, an ink jet recording head according to the present invention comprises a series of ink pressurizing chambers, nozzle flow paths, and nozzles branched from an ink reservoir through a filter flow path. A substrate having a plurality of ink flow paths, a vibrating plate covering the ink flow paths, and a rectangular parallelepiped piezoelectric element bonded to a surface of the vibrating plate facing the ink pressurizing chamber via a common electrode. Equipped with
In the one that ejects ink from the nozzle by using the electric field induced strain in the direction parallel to the bonding surface of the piezoelectric element as a drive source,
The dimensions of the rectangular parallelepiped piezoelectric element are changed stepwise according to the flow path resistance so that the electric field induced strain amount of the piezoelectric element is proportional to the flow path resistance of the ink flow path from the ink pressurizing chamber to the nozzle. It will be.

Here, the size of the piezoelectric element is wide for the piezoelectric element of the ink flow path having a high flow path resistance, and for the piezoelectric element of the ink flow path having a low flow path resistance. Changes narrowly and gradually. Also, regarding the size of the piezoelectric element, the thickness in the direction perpendicular to the bonding surface of the rectangular parallelepiped piezoelectric element is thin for the piezoelectric element of the ink flow path with high flow resistance, and the thickness of the piezoelectric element for the ink flow path with low flow resistance is Is thick and changes gradually.

[0010]

In the ink jet recording head of the present invention, the source of the force for pushing the ink from the ink pressurizing chamber to the nozzle is the expansion and contraction (electric field induced strain) of the piezoelectric element as the electromechanical conversion element in the plane direction. The strain is converted into a displacement in the direction perpendicular to the vibration plate by the piezoelectric element being constrained by the vibration plate, and the volume of the ink pressurizing chamber is contracted, and an amount of ink droplets corresponding to the contraction amount is ejected from the nozzle. Make it jet. Therefore, the dimensions of the rectangular parallelepiped piezoelectric element are changed stepwise according to the flow path resistance so that the amount of electric field induced strain of the piezoelectric element is proportional to the flow path resistance of the ink flow path from the ink pressurizing chamber to the nozzle. Then, the variation in the ink ejection characteristics caused by the difference in the flow path resistance of the plurality of ink flow paths is compensated by the difference in the amount of electric field induced strain corresponding to this, and an inkjet recording head with uniform ink ejection characteristics can be obtained.

Since the amount of electric field induced strain of the piezoelectric element is proportional to the area of the piezoelectric element, especially the area of adhesion to the vibration plate, the size of the piezoelectric element is the area of the adhesion portion of the rectangular parallelepiped piezoelectric element. The ink element of the ink jet recording head is compensated for by compensating for variations in ink ejection characteristics by changing the piezoelectric element in the ink flow path having a high path resistance wide and the piezoelectric element in the ink flow path having a low path resistance narrowly in a stepwise manner. Ejection characteristics can be made uniform.

Further, since the amount of electric field induced strain of the piezoelectric element is proportional to the electrostatic capacity of the piezoelectric element, the dimension of the piezoelectric element is such that the flow path resistance is high in the thickness in the direction perpendicular to the bonding surface of the rectangular parallelepiped piezoelectric element. The thickness should be changed stepwise so that the piezoelectric element in the ink flow path is made thin to increase the capacitance, and the piezoelectric element in the ink flow path having a low flow resistance is made thick to suppress the capacitance. This makes it possible to compensate for variations in ink ejection characteristics and make the ink ejection characteristics of the inkjet recording head uniform.

[0013]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 is a plan view schematically showing an ink jet recording head according to an embodiment of the present invention. Since members to which the same reference numerals as those of the conventional example are attached have the same functions as those of the conventional example,
The description is omitted. In the figure, the ink jet recording head is the widest ink pressurizing chamber 4 in the ink flow path 1.
In order to save the space of the part and downsize the substrate 9,
The plurality of ink flow paths 1 are staggered with respect to one end surface of the substrate 9 where the nozzles 2 are opened so that the line connecting the center points of the ink pressurization chambers 4 adjacent to each other has a triangular waveform. Therefore, the ink flow paths 1 are arranged so that the lengths of the nozzle flow paths 3 from the ink pressurizing chambers 4 to the openings of the nozzles 2 are arranged alternately in length and short.

The manufacturing procedure of the ink jet recording head is as follows.
First, the substrate 9 and the vibrating plate 10 are bonded to each other, the film thickness is 9 to 11 μm, and the average roughness on the center line is 0.8 to 1.
The common electrode 11 of 0 μm is formed by a screen printing method of silver powder paste. The printed silver powder paste layer is dried and cured at a predetermined temperature for a predetermined time. In the figure, the common electrode branched into two columns is formed in a shape and size corresponding to the bonding surface of the piezoelectric element bonded to the upper portion of the ink pressurizing chamber 4. Next, an epoxy resin adhesive is applied to a predetermined position on the common electrode by screen printing. The amount of adhesive to be applied is proportional to the adhesive area of the piezoelectric element, and the adhesive reservoir 15 is provided on the side surface of the piezoelectric element.
(See FIG. 3). A rectangular parallelepiped piezoelectric element bonded at a predetermined position on the common electrode has a relative dielectric constant ε = 50.
Nozzle N0 2A, 2 with high flow resistance
The size of the ink flow path to which C and 2E belong is 3.3 ×.
A large element 12A of 3.1 × 0.15 mm is used, and a small element 12B of 3.0 × 1.5 × 0.15 mm is used for the ink channels of the nozzles N0 2B, 2D and 2F having low channel resistance. These two types of piezoelectric elements are placed on the common electrode of the ink pressurizing chamber 4 of each ink flow path and a load is applied to the one electrode 13
Is conductively contacted with the common electrode 11, and a fillet-shaped resin reservoir 15 (see FIG. 3) is formed on the side surface of the piezoelectric element. The piezoelectric element was prepositioned such that its long side direction (direction in which electric field-induced distortion occurs) was parallel to the ink flow direction.

Table 1 is a data table showing the ink ejection characteristic test results of the ink jet recording head according to the embodiment of the present invention in comparison with that of the prior art. In the embodiment, three piezoelectric elements 12A and 12B are provided respectively. This is data obtained by commonly applying a rectangular wave voltage having a voltage value of 100 V and a pulse width of 80 μm as a driving voltage. In the case of the comparative example, the data obtained from the ink jet recording head in which the small piezoelectric elements 12B of 3.0 × 1.5 × 0.15 mm are bonded to the plurality of ink pressurizing chambers arranged in a staggered pattern shown in FIG. is there.

[0016]

[Table 1]

As is clear from the table, the average value of the example data exceeds the average value of the comparative example data by about 10% in both the ink droplet ejection initial velocity (m / s) and the ink droplet amount (μcc). In addition, the standard deviation indicating the variation of the data is also reduced to ½ or less of the comparative example at the ink droplet ejection initial speed and ¼ or less of the comparative example in terms of the ink droplet amount. The length of the bonding surface of the rectangular parallelepiped piezoelectric elements 12A and 12B is approximately proportional to the flow path resistance of the ink flow path 3 from the ink pressurizing chamber 4 to the nozzle 2 (in this case, the length of the ink flow path 3). By changing the length of the long side of the piezoelectric element in two steps, the electric field induced strain amount of the piezoelectric element compensates for the difference in flow path resistance, and the ink ejection characteristics in the six ink flow paths are better than those of the conventional one. Completed inkjet recording head It has been demonstrated to be. Also,
The problem that the recording head becomes large in the conventional method of making the head shape fan-shaped can be replaced by the effect that the recording head can be made smaller by arranging the ink pressurizing chambers in a zigzag manner in the embodiment. Further, in the conventional method of compensating on the drive circuit side, the problem that the control circuit becomes complicated is
In the embodiment, this can be avoided by changing the bonding area of the piezoelectric element to stepwise drops. Further, the problem of fine processing accuracy of the nozzle flow path diameter, which has been a problem in the method of changing the cross-sectional area of the nozzle flow path, is not necessary in the embodiment, and the increase in processing cost can be eliminated.

Table 2 is a data table showing the ink ejection characteristic test results of the ink jet recording head according to the different embodiments of the present invention. In the different embodiments, the large piezoelectric element 1 is used.
The piezoelectric element of 3.0 × 1.5 × 0.14 mm is used instead of 2A, and the small piezoelectric element 12B is left as it is, which is different from the above-mentioned embodiment, and the driving voltage is 1
Ink ejection characteristics were measured by applying a rectangular wave voltage of 00 V and a pulse width of 80 μm.

Comparing the data in Table 2 with the data in Table 1, the average values of the example data of Table 2 are the same as those of the comparative example data in terms of both the ink droplet ejection initial velocity (m / s) and the ink droplet amount (μcc). The standard deviation, which is higher than the value and which shows the variation in data, is also reduced to 1/3 or less of the comparative example at the initial velocity of ink droplet ejection and 1/2 or less of the comparative example in terms of the ink droplet amount. In the recording head, the capacitance of the rectangular parallelepiped piezoelectric element 12A is approximately proportional to the flow resistance of the ink flow path 3 from the ink pressurizing chamber 4 to the nozzle 2 (in this case, the length of the ink flow path 3). By changing the thickness of the piezoelectric element in two steps, the electric field induced strain amount of the piezoelectric element compensates for the difference in the flow path resistance, and the ink jet characteristics of the six ink flow paths are more uniform than those of the conventional ink jet recording. The head can be obtained It was testified.

[0020]

[Table 2]

In the two embodiments, the case where the dimension of the piezoelectric element is changed in two steps has been described as an example. However, the step of changing the dimension can be changed into three steps and four steps corresponding to the flow path resistance. By doing so, it is clear that an ink jet recording head with more uniform ink ejection characteristics can be obtained. The inkjet recording head can be provided economically and advantageously.

[0022]

As described above, according to the present invention, in the ink jet recording head of the present invention, the initial velocity of ink droplet ejection and the driving force of the ink droplet amount are the expansion and contraction amount (electric field induced strain amount) of the piezoelectric element in the surface direction. Utilizing the proportionality, the size of the piezoelectric element is changed stepwise according to the flow path resistance so that the electric field induced strain amount of the piezoelectric element is proportional to the flow path resistance. As a result, the variation in the ink ejection characteristics that has conventionally occurred due to the difference in the flow path resistance between the plurality of inkjet recording heads is compensated by the change in the amount of electric field induced strain corresponding to this, and the ink pressurizing chambers are arranged in a staggered manner. The inkjet recording head can be miniaturized, and it is possible to provide a small inkjet recording head with uniform ink ejection characteristics. Further, the complicated control circuit and the precision processing technology of the nozzle flow path diameter, which have been problems in the conventional technology, become unnecessary, and an advantage that an inkjet recording head with uniform ink ejection characteristics can be provided easily and economically is advantageous. can get.

Here, the size of the piezoelectric element can be determined by changing the area of the bonded portion of the piezoelectric element in a stepwise manner in proportion to the flow path resistance, or by changing the thickness in the direction perpendicular to the bonding surface of the piezoelectric element to the flow path. Even if the capacitance is adjusted by changing stepwise in inverse proportion to the resistance, the initial speed of ink droplet ejection and the amount of ink droplets are higher than before, and their standard deviation is reduced to a fraction of the conventional one. It has been confirmed that this is possible, and even when the flow resistances of a plurality of ink flow paths are different from each other, it is possible to easily and economically provide an ink jet recording head having uniform ink ejection characteristics without increasing the processing cost.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing an inkjet recording head according to an embodiment of the present invention.

FIG. 2 is a plan view schematically showing an example of an ink flow path of an inkjet recording head.

FIG. 3 is a sectional view schematically showing an example of an inkjet recording head in a direction along an ink flow path.

[Explanation of symbols]

 1 Ink Flow Path 2 Nozzle 3 Nozzle Flow Path 4 Ink Pressurizing Chamber 5 Ink Supply Path 6 Filter Flow Path 7 Ink Pool 8 Sealing Surface 9 Substrate 10 Vibration Plate 11 Common Electrode 12 Piezoelectric Element 12A Piezoelectric Element (Large) 12B Piezoelectric Element ( Small size 13 Electrode 14 Adhesive layer 15 Adhesive reservoir (fillet)

Claims (3)

[Claims] 1. A substrate having a plurality of ink flow paths consisting of a series of ink pressurizing chambers, nozzle flow paths, and nozzles branched from an ink reservoir via a filter flow path, and a vibration plate covering the ink flow path. , A rectangular parallelepiped piezoelectric element bonded to each surface of the vibrating plate facing the ink pressurizing chamber via a common electrode, and the electric field-induced strain in a direction parallel to the bonding surface of the piezoelectric element is used as a driving source. In the case of ejecting ink from a nozzle, the dimension of a rectangular parallelepiped piezoelectric element is used as the flow path resistance so that the electric field induced strain amount of the piezoelectric element is proportional to the flow path resistance of the ink flow path from the ink pressure chamber to the nozzle. An ink jet recording head characterized by being changed stepwise correspondingly. 2. An area of an adhesive portion of a rectangular parallelepiped piezoelectric element is changed in a stepwise manner for a piezoelectric element of an ink flow channel having a high flow channel resistance and narrowly in a stepwise manner for a piezoelectric element of an ink flow channel having a low flow channel resistance. The ink jet recording head according to claim 1, wherein 3. A thickness of a rectangular parallelepiped piezoelectric element in a direction perpendicular to an adhesive surface is thin for an ink flow path piezoelectric element having a high flow path resistance and thick for an ink flow path piezoelectric element having a low flow path resistance. The ink jet recording head according to claim 1, wherein the ink jet recording head is formed by changing the shape.