JPH08230183A - Ink jet record head and recording device equipped with head - Google Patents

Abstract

PURPOSE: To lessen misregistration of dot and difference in density so as to improve printing function by aligning directions of dielectric polarizations of a plurality of piezoelectric elements consisting of piezoelectric ceramics based on the electric field cooling method in a state that the piezoelectric elements are fixed to an ink jet record head. CONSTITUTION: Temperature of the whole of a drop-on-demand type ink jet record head 21 is heated to a Curie point or higher of piezoelectric ceramic. In this state, an electric field having a given strength is applied in between a pair of electrodes 27 of a piezoelectric element 24. In a process to gradually cool the temperature of the record head to room temperature in the state that the electric field is held, polarization treatment is performed based on the electric field cooling method which aligns directions of polarizations with the direction of the electric field. As a result, increase of electrostatic volume of the piezoelectric element, improving effects of ink discharge speed and ink discharge quantity are verified. By improving the polarization treatment method of the piezoelectric element, a drop-on-demand type ink jet record head having an ink discharge force higher than that of a conventional one can be obtained, and misregistration of dot in printing line is reduced and Macbeth density is also improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording head generally called a drop-on-demand type, and an ink jet recording apparatus equipped with this ink jet recording head.

[0002]

2. Description of the Related Art A recording apparatus using an ink jet recording head has an advantage that it has a simple structure, and is widely used in fields such as desktop printers and fax machines, which are required to be compact and lightweight. Several methods have been proposed for the mechanism of the inkjet recording head. Among them, the drop-on-demand type ink jet recording head is configured such that a piezoelectric element is bonded to a vibrating plate, and the vibrating plate is curved by utilizing a secondary piezoelectric effect generated in the piezoelectric element when an electric field is applied to the piezoelectric element. Ink is ejected from a nozzle by using a pressure generated in a flow path as a driving source, and it has a feature of a semi-permanent head life and a low running cost, and is being widely used.

FIG. 3 is a simplified perspective view showing an example of the internal structure of the ink jet recording apparatus. In the ink jet recording apparatus 1, the carriage 2 is provided with two guide rails 4 in parallel with the bottom plate of the U-shaped frame 9. The carriage 2 is guided so that it can travel straight ahead, and the carriage 2 is driven to travel by a belt drive unit 5 controlled by a control unit (not shown). Further, a paper feeding mechanism portion 6 including a paper feeding roller that feeds the recording paper 7 in a direction orthogonal to the traveling direction of the carriage 2 is provided, and the recording paper 7 is fed onto a plate-shaped platen 8. Inkjet recording head 3
Is mounted on the lower surface of the carriage 2 such that a plurality of nozzles face the recording paper surface on the platen 8 and a plurality of nozzles are aligned in a direction orthogonal to the straight traveling direction of the carriage 2 (recording paper feeding direction). Further, ink is supplied from the ink tank 10 to the ink flow path of the inkjet recording head 3 via the carriage 2.

FIG. 4 is a diagram showing the change over time of the voltage applied to the piezoelectric element in the drop-on-demand type ink jet recording head, and FIG. 5 shows the operating states of the drop-on-demand type ink jet recording head (a), (b),
FIG. 6 is an operation principle diagram disassembled and shown in four diagrams of (c) and (d), and the operating states of each diagram correspond to A time, B time, C time, and D time of the applied voltage in FIG. There is. In the figure, (a) shows a state in which the ink ejection operation is completed, and the drop-on-demand type inkjet recording head 11 has a pressurizing chamber portion along the vibrating plate inside the laminated body of the substrate 12 and the vibrating plate 13. An ink flow path 15 including 16 is formed, and a nozzle 17 is opened on the end face of the stack,
A plurality of piezoelectric elements 14 made of piezoelectric ceramics are fixed to the surface of the diaphragm facing the pressure chamber 16. When a voltage is applied between a pair of electrodes (not shown) of the piezoelectric element 14 (at time A of the applied voltage), the piezoelectric element bends convexly toward the diaphragm due to the secondary piezoelectric effect, and the piezoelectric element 14 is pressed as shown in (a). The chamber 16 is compressed. When the applied voltage decreases at time B, the bent piezoelectric element returns to a flat state as shown in (b),
At this time, the pressurizing chamber portion expands and sucks the ink 19. When the applied voltage further rises at time C, the piezoelectric element 14 again bends to the diaphragm side as shown in FIG.
Instantaneously contract and the ink 19 is ejected from the nozzle 17 in the form of a thin column, and the contraction of the pressure chamber 16 ends.
At this point in time, as shown in (d), the columnar ink runs out and changes into an ink droplet 19d, which adheres to the surface of the recording paper (not shown) at a constant speed and records information as, for example, a print dot.
Further, the head that has completed the ink droplet ejection operation returns to the state of (a) and enters the standby state of the ink suction operation (b).

By the way, piezoelectric ceramics often used as the piezoelectric element 14 in the drop-on-demand type ink jet recording head, such as lead zirconate titanate (abbreviated as PZT) and barium titanate, are polycrystalline sintered bodies. Since the directions of the dielectric polarization of the fluid are different, the bending due to the large secondary piezoelectric effect does not occur even if a voltage is applied as it is. Therefore, a pretreatment called poling is performed in which a high electric field significantly higher than the electric field used is applied between the electrodes of the piezoelectric element made of piezoelectric ceramics for a certain period of time to align the direction of dielectric polarization with the electric field direction.

FIG. 6 is an enlarged view schematically showing the direction of the dielectric polarization of the lead zirconate titanate crystal before and after poling at room temperature. (A) shows the state before poling, (b) Indicates the status after polling is completed. In the figure, it can be seen that the directions of the dielectric polarization, which were different before the poling, are aligned to the direction of the applied electric field to some extent by the poling.

FIG. 7 is a plan view schematically showing an example of the flow channel structure of the drop-on-demand type ink jet recording apparatus head. The ink flow channel 15 formed with a plurality of grooves (for example, 48 grooves) as concave grooves on the substrate 12 is shown in FIG. In order to form a linear print line 20 having a constant dot density (for example, 200 dots / inch) on the surface of the recording paper 7, the ejection direction of the ink droplet 19d ejected from the nozzle 17 is from the pressure chamber 16 to the nozzle 17. Is controlled by the direction of the nozzle flow path leading to.

[0008]

FIG. 8 is an enlarged view schematically showing a printing line obtained by a conventional ink jet recording apparatus. After the piezoelectric element 14 is fixed to the vibration plate of the recording head, a pair of electrodes is formed. High voltage between (3000V / cm)
A drop-on-demand type inkjet recording head was used which was subjected to poling at room temperature. In the figure, a print line 20 on which a dot row is to be formed in a straight line on the surface of the recording paper 7 with a constant dot density (in this case, a dot density of 200 dots / inch, 0.127 mm / dot)
Was found to show a dot misalignment δ of 2/3 of 1 dot (0.127 mm). It was also found that the difference in print density between the dots was noticeable. When the dot positional deviation δ exceeds 1/4 dot (about 30 μm), the disturbance of the print line 20 is noticeable even with the naked eye, and the density of the density is added to this, so that the quality of the print line is significantly deteriorated. Therefore, in order to improve the quality of the print line, it is important to reduce the dot positional deviation δ and the density difference.

An object of the present invention is to provide a drop-on-demand type ink jet recording head which has a small amount of dot positional deviation and a density difference in a printing line and is excellent in printing performance.
Another object of the present invention is to provide an inkjet recording apparatus including the same.

[0010]

In order to solve the above-mentioned problems, an ink jet recording head according to the present invention is provided with a plurality of nozzles that are opened at the end faces of the substrate and the vibrating plate, and the above-mentioned lamination so as to communicate with each nozzle. A plurality of ink flow paths formed along the vibration plate inside the body, and a plurality of piezoelectric elements made of piezoelectric ceramics fixed to the surface of the vibration plate facing the pressure chamber portion of each ink flow path. In an ink jet recording head that ejects ink from nozzles by using the bending of the vibration plate due to the secondary piezoelectric effect of the piezoelectric element as a drive source, the piezoelectric element is fixed to the ink jet recording head by the electric field cooling method. The directions of the dielectric polarization of a plurality of piezoelectric elements made of a conductive ceramic are aligned.

Here, the dielectric polarization based on the electric field cooling method is
The temperature of the entire inkjet recording head is heated to the Curie point of the piezoelectric ceramics or above, an electric field of constant strength is applied between the pair of electrodes of the piezoelectric element in this state, and the inkjet recording head The direction of polarization may be aligned with the direction of the electric field during the process of gradually cooling the temperature to room temperature.

Further, the piezoelectric element is made of lead zirconate titanate, and the measured value of the electrostatic capacity of this piezoelectric element is divided by this and the geometrical capacity of the vacuum gap having the same electrode area and electrode spacing. The apparent relative dielectric constant is preferably 5000 or more. On the other hand, inkjet recording provided with a carriage supported by a guide rail so as to be capable of traveling straight, an inkjet recording head supported by the carriage, and a paper feeding mechanism unit for driving a recording paper in a direction orthogonal to the straight traveling direction. In the apparatus, a plurality of nozzles that are opened on the end face of the stack of the substrate and the vibration plate, a plurality of ink flow paths formed along the vibration plate in the stack so as to communicate with each nozzle, and a plurality of ink flow paths A plurality of piezoelectric elements made of piezoelectric ceramics fixed to the surface of the vibrating plate facing the pressurizing chamber, the piezoelectric ceramics being fixed to an ink jet recording head by the electric field cooling method. An ink jet recording head in which the directions of the dielectric polarization of a plurality of piezoelectric elements are aligned is In a direction perpendicular to the traveling direction, and is fixed to the carriage so as to face the recording paper.

[0013]

The drop-on-demand type ink jet recording head of the present invention heats the piezoelectric element made of piezoelectric ceramics to the Curie point or higher, and in this state, applies an electric field of a constant strength between the pair of electrodes of the piezoelectric element. By gradually cooling the temperature of the inkjet recording head to room temperature while maintaining the electric field, by performing poling based on the so-called electric field cooling method, the direction of dielectric polarization of the polycrystalline particles can be better aligned with the direction of application of the electric field. By performing poling based on the electric field cooling method with the piezoelectric element fixed to the vibration plate of the recording head, the dielectric polarization of the plurality of piezoelectric elements can be equalized. Since the displacement amount of the piezoelectric element is increased by aligning the directions of the dielectric polarization of the polycrystalline particles, the ink ejection force of the recording head, in other words, the ejection speed and ejection amount of ink droplets ejected from a plurality of nozzles are stabilized at a high level. Can be converted.

Here, by performing poling based on the electric field cooling method using lead zirconate titanate for the piezoelectric element, the apparent relative permittivity is higher than the relative permittivity obtained by conventional poling by about 20%, or more than 5000. Can be Therefore, it is possible to evaluate how to align the directions of the dielectric polarization of the polycrystalline particles based on this apparent relative permittivity.

Further, if an ink jet recording apparatus is constructed using the drop-on-demand type ink jet recording head of the present invention, the ejection speed and ejection amount of ink droplets ejected simultaneously from a plurality of nozzles can be stabilized at a high level. A plurality of ink droplets are spotted on the paper surface at the same time to form a print line composed of a dot row. Therefore, even if the carriage that supports the head moves in the direction orthogonal to the print line, a plurality of ink droplets having no speed difference arrive at the recording paper surface at the same time, so that the influence of the movement of the carriage is eliminated. It is possible to reduce the positional deviation of dots in the print line and form a print line without density unevenness.

[0016]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 is a cross-sectional view of a drop-on-demand type ink jet recording head according to an embodiment of the present invention, taken along the ink flow path, and FIG. 2 is a schematic view showing the direction of dielectric polarization of lead zirconate titanate crystals after polarization treatment. Since the members having the same reference numerals as those of the conventional example have the same functions as those of the conventional example, the description thereof will be omitted. In the figure, a drop-on-demand type ink jet recording head 21 has a plurality of nozzles 17 that are opened at the end face of the stack formed by adhering a substrate 12 made of, for example, a polyetherimide resin and a diaphragm 13 with a sealing surface 18.
A plurality of ink flow paths 15 formed along the vibration plate in the laminated body so as to communicate therewith, and a common electrode 25 and an adhesive agent on the surface of the vibration plate 13 facing the pressure chamber portion 16 of each ink flow path. A piezoelectric element 24 made of piezoelectric ceramics and bonded via a layer 26.

The recording head 21 thus constructed heats the entire temperature above the Curie point of the piezoelectric ceramic, and in this state an electric field of constant strength is applied between the pair of electrodes 27 of the piezoelectric element 24. In the process of gradually cooling the temperature of the inkjet recording head to room temperature while maintaining this electric field, a polarization process based on an electric field cooling method is performed in which the direction of polarization is aligned with the direction of the electric field as shown in FIG.

The features of the drop-on-demand type ink jet recording head of the present invention and the ink jet recording apparatus using the same will be described below based on two embodiments. (Example 1) Electrode area of the piezoelectric element 24 is 4.5 m
After using a piezoelectric element made of lead zirconate titanate having a distance of m ² and a distance between electrodes of 0 and 15 mm, the whole temperature of the recording head 21 was Curie point (150 ° C.) after being bonded to the vibration plate 13.
To a temperature slightly above, and in this state, an electric field of 3000 V / cm is applied between the pair of electrodes 27 of the piezoelectric element 24,
With the electric field held, the temperature of the recording head 21 is set to 30
The polarization treatment was performed based on the electric field cooling method in which the temperature was lowered to room temperature over a period of time, and then the electric field was released. Table 1 is a table showing the measurement results of the capacitance of the piezoelectric element, the apparent dielectric constant, the ink droplet ejection speed, and the ink droplet ejection amount of the obtained drop-on-demand type inkjet recording head 21. The measurement results of the conventional drop-on-demand type inkjet recording head 11 having the same configuration as that of the example except that the poling treatment was performed at room temperature are also shown as a comparative example.

[0019]

[Table 1]

From the results shown in Table 1, in the example subjected to the polarization treatment by the electric field cooling method, the electrostatic capacity of the piezoelectric element increased by about 23% to 1600 pF, which is larger than the 1300 pF of the comparative example, and the ink was accompanied by this. Discharge speed is 7m / s
ec to 10 m / sec, and it was confirmed that the ejection amount of the ink droplets also increased from 0.3 μcc to 0.4 μcc, and the electrostatic capacity of the piezoelectric element increased due to the polarization treatment by the electric field cooling method. Along with this, it was demonstrated that the ink ejection force of the drop-on-demand type inkjet recording head was improved.

Also, the apparent relative permittivity obtained by dividing the measured value of the electrostatic capacity of the piezoelectric element by the measured electrostatic capacity of the piezoelectric element and the geometrical capacity of the vacuum gap having the same electrode area and electrode spacing is from 4900 of the comparative example. It has risen to 6000 in the example.
In this case, the measured value of capacitance includes stray capacitance, whereas geometric capacitance does not include stray capacitance, so the obtained permittivity is an apparent permittivity slightly larger than the true permittivity. However, by using this apparent dielectric constant, the poling effect between piezoelectric elements having different electrode areas and electrode intervals can be easily compared with each other.

(Embodiment 2) A carriage 2 of an ink jet recording apparatus 1 in which a drop-on-demand type ink jet recording head according to Embodiment 1 and a comparative example is shown in FIG.
Then, the nozzle array is fixed in a direction orthogonal to the straight traveling direction of the carriage and opposite to the surface of the recording paper 7, and a voltage is applied to 48 piezoelectric elements at the same time to obtain a dot density of 200.
A printing line of dots / in (0.127 mm / dot) is recorded, and the positional deviation δ of the dots of the obtained printing line,
And Macbeth concentrations were compared. The results are shown in Table 2.

[0023]

[Table 2]

From the results shown in Table 2, the dot misregistration in the example is reduced from ± 30 μm in the comparative example to ± 15 μm, the disturbance of the print line becomes inconspicuous, and Macbeth is used as a general criterion for the print density. It was demonstrated that the density also increased and the print quality was greatly improved by improving the polarization treatment method of the piezoelectric element.

[0025]

As described above, the drop-on-demand type ink jet recording head of the present invention is constructed so that the assembled ink jet recording head is subjected to polarization treatment based on the electric field cooling method. As a result, the increase in the capacitance of the piezoelectric element and the effect of improving the ink ejection speed and the ink ejection amount have been demonstrated. Can be provided.

Further, the ink jet recording apparatus using the drop-on-demand type ink jet recording head according to the present invention reduces the positional deviation of the dots on the print line by half due to the effect of improving the ink ejection speed and the ink ejection amount, and It is possible to improve the Macbeth concentration,
Therefore, it is possible to provide an inkjet recording apparatus with high print quality.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a drop-on-demand type ink jet recording head according to an embodiment of the present invention in a direction along an ink flow path.

FIG. 2 is an enlarged view schematically showing the direction of dielectric polarization of lead zirconate titanate crystals after polarization treatment in Examples.

FIG. 3 is a perspective view showing a simplified example of the internal structure of an inkjet recording apparatus.

FIG. 4 is a diagram showing changes over time in applied voltage to a piezoelectric element in a drop-on-demand type inkjet recording head.

FIG. 5 shows the operating states of a drop-on-demand type ink jet recording head in (a), (b), (c), (d),
Figure of operation principle disassembled and shown in 4 figures

6A and 6B are enlarged views schematically showing the directions of the dielectric polarization of lead zirconate titanate crystals before and after poling at room temperature, where FIG. 6A is a state before poling and FIG. After state

FIG. 7 is a plan view schematically showing an example of a flow path structure of a drop-on-demand type inkjet recording device head.

FIG. 8 is an enlarged view schematically showing a print line obtained by a conventional inkjet recording device.

[Explanation of symbols]

1 Inkjet recording device 2 Carriage 3 Inkjet recording head 4 Guide rail 5 Belt drive unit 6 Paper feed mechanism unit 7 Recording paper 8 Platen 9 Frame 10 Ink tank 11 Drop-on-demand type inkjet recording device head 12 Substrate 13 Vibrating plate 14 Piezoelectric element 15 Ink Flow path 16 Pressurizing chamber 17 Nozzle 18 Sealing surface 19 Ink 19d Ink droplet 20 Printing line (dot row) 21 Drop-on-demand type inkjet recording device head 24 Piezoelectric element (polarized by electric field cooling method) 25 Common electrode 26 Adhesive Layer 27 Electrode δ Dot displacement amount

Claims (4)

[Claims] 1. A plurality of nozzles opened on the end face of the substrate and the vibrating plate laminated together, a plurality of ink flow paths formed along the vibrating plate in the laminated body so as to communicate with each nozzle, and each ink flow. A plurality of piezoelectric elements made of piezoelectric ceramics fixed to the surface of the vibrating plate facing the pressure chamber of the passage, and the deflection of the vibrating plate due to the secondary piezoelectric effect of the piezoelectric element is used as a drive source from the nozzle. In an ink jet recording head for ejecting ink, in a state where the piezoelectric element is fixed to the ink jet recording head, the directions of dielectric polarization of the plurality of piezoelectric elements made of the piezoelectric ceramic are aligned based on the electric field cooling method. Inkjet recording head. 2. A dielectric polarization based on an electric field cooling method heats the temperature of the entire ink jet recording head to a temperature not lower than the Curie point of the piezoelectric ceramic, and in this state, an electric field of constant strength is generated between a pair of electrodes of the piezoelectric element. 2. The ink jet recording head according to claim 1, wherein the direction of polarization is aligned with the direction of the electric field during the process of gradually cooling the temperature of the ink jet recording head to room temperature while applying the electric field. 3. The piezoelectric element is made of lead zirconate titanate and is obtained by dividing the actual measured value of the electrostatic capacity of the piezoelectric element by the geometrical capacity of a vacuum gap having the same electrode area and electrode spacing. The inkjet recording head according to claim 1, wherein the apparent relative dielectric constant is 5000 or more. 4. A carriage supported by a guide rail so as to be able to travel straight, an ink jet recording head supported by the carriage, and a paper feed mechanism portion for driving a recording paper in a direction orthogonal to the direction of straight travel. In the ink jet recording apparatus described above, a plurality of nozzles opened on the end face of the laminated substrate and the diaphragm, a plurality of ink flow paths formed along the diaphragm in the laminate so as to communicate with each nozzle, and each ink A plurality of piezoelectric elements made of piezoelectric ceramics fixed to the surface of the vibrating plate facing the pressure chamber portion of the flow path, and the piezoelectric elements being fixed to an ink jet recording head based on an electric field cooling method. In an ink jet recording head in which the directions of the dielectric polarization of a plurality of piezoelectric elements made of piezoelectric ceramics are aligned, the direction of the plurality of nozzle rows is a carriage. In the direction of the straight running direction of the perpendicular,
An ink jet recording apparatus characterized by being fixed to a carriage so as to face a recording paper surface.