JPH06226969A - Ink jetting device - Google Patents

Abstract

PURPOSE:To eject an ink drop having a speed and a volume which are sufficient for forming a character or an image with a low driving voltage. CONSTITUTION:In an ink jetting device wherein a driving voltage is impressed to an electrode 13 formed to a part of an inside of a groove provided to a piezoelectric ceramics plate 1, and ink filling the inside of the groove is jetted by varying a volume of the inside of the groove by means of a piezoelectric thickness sliding effect of the piezoelectric ceramics plate 1, an angle made between a height direction A of side walls 11 with the groove 15 between them and a polarizing direction 4 is desirably within a range of 18 degree or under and more desirably within a range of 14 degree or under.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink ejecting apparatus, and more particularly to an ink ejecting apparatus utilizing deformation of piezoelectric ceramics.

[0002]

2. Description of the Related Art Conventionally, as a printer head, a drop-on-demand type ink jet printer head applying piezoelectric ceramics has been proposed. This is because by changing the volume of the ink liquid chamber by the deformation of the piezoelectric ceramics, the ink in the ink liquid chamber is ejected as droplets from the nozzle when the volume is decreased, and when the volume is increased, the ink is injected from the other ink introduction path into the ink liquid chamber. The ink is introduced. Then, a large number of such ink liquid chambers are arranged close to each other, and ink droplets are ejected from nozzles at required positions according to required print data, so that desired characters or characters are printed on a paper surface facing the nozzles. It forms an image.

Examples of this type of ink ejecting device include, for example, Japanese Patent Laid-Open Nos. 63-247051 and 63-252.
750 and JP-A-2-150355. FIG. 15, FIG. 16, FIG. 17 and FIG. 18 show schematic diagrams of these conventional examples. The configuration of the conventional example will be specifically described below with reference to FIG. 15 showing a cross-sectional view of the ink ejecting apparatus. A plurality of grooves 15 and side walls 1 separating the grooves
1 and a piezoelectric ceramic plate 1 which is polarized in the direction of arrow 4 and a cover plate 2 made of a ceramic material or a resin material are joined together via a joining layer 3 made of an epoxy adhesive or the like. By doing so, groove 15
Are a plurality of ink liquid chambers 12 which are laterally spaced from each other. The ink liquid chamber 12 has an elongated shape with a rectangular cross section, and the side wall 11 extends over the entire length of the ink liquid chamber 12. Metal electrodes 13 for applying a driving electric field are formed on both surfaces of the side wall 11 near the adhesive layer 3 from the upper side wall to the central part of the side wall. Ink is filled in all the ink liquid chambers 12.

Next, FIG. 1 showing a sectional view of the ink ejecting apparatus.
6, the operation of the conventional example will be described. In the ink ejecting apparatus, for example, when the ink liquid chamber 12b is selected according to the required print data, a positive drive voltage is rapidly applied to the metal electrodes 13e and 13f, and the metal electrodes 13d and 13g.
Is grounded. As a result, the driving electric field in the direction of arrow 14b acts on the side wall 11b, and the driving electric field in the direction of arrow 14c acts on the side wall 11c. At this time, since the driving electric field directions 14b and 14c are orthogonal to the polarization direction 4, the side wall 11b
And 11c are rapidly deformed toward the inside of the ink liquid chamber 12b due to the piezoelectric thickness sliding effect. Due to this deformation, the volume of the ink liquid chamber 12b decreases, the ink pressure in the ink liquid chamber 12b rapidly increases, a pressure wave is generated, and ink droplets are ejected from the nozzle 32 (FIG. 17) communicating with the ink liquid chamber 12b. Is jetted. Further, when the application of the drive voltage is gradually stopped, the side walls 11b and 11c return to the positions before the deformation, so that the ink pressure in the ink liquid chamber 12b gradually decreases, and the manifold 22 (from the ink supply port 21 (FIG. 17)). Figure 1
Ink is supplied into the ink liquid chamber 12b through 7).

However, the above operation is only the basic operation of the conventional example, and when it is embodied as a product, first, the drive voltage is applied in the direction of increasing the volume, and first, the ink liquid chamber 12b.
The above operation may be performed after the ink is supplied to the.

Next, FIG. 1 showing a perspective view of the ink ejecting apparatus.
7, the configuration and manufacturing method of the conventional example will be described. The parallel grooves 1 that form the ink liquid chamber 12 having the above-described shape are formed on the piezoelectric ceramic plate 1 that has been subjected to the polarization treatment by grinding using a thin disk-shaped diamond blade or the like.
5 is produced. The groove 15 is a parallel groove having the same depth over almost the entire area of the piezoelectric ceramic plate 1, but the groove 15 is gradually shallowed toward the end face 17, and is formed so as to be a shallow parallel groove 18 near the end face 17. The metal electrodes 13 are formed on the inner surfaces of the grooves 15 and the shallow parallel grooves 18 by sputtering or the like. Metal electrodes are formed on the inner surface of the groove 15 only on the upper half of the side surface thereof, while metal electrodes are formed on the entire side surface and bottom surface of the inner surface of the shallow and parallel groove 18. In addition, the ink inlet 21 and the manifold 22 are formed in the cover plate 2 made of a ceramic material or a resin material by grinding or cutting.

Next, the grooves 15 on the surface of the piezoelectric ceramic plate 1 on the groove processing side and the surface of the cover plate 2 on the manifold processing side are formed with epoxy adhesive or the like so that each groove 15 forms the ink liquid chamber 12 having the above-described shape. Glue to form.
Next, a nozzle plate 31 having nozzles 32 provided at positions corresponding to the positions of the ink liquid chambers 12 is bonded to the end faces 16 of the piezoelectric ceramic plate 1 and the cover plate 2. On the surface of the piezoelectric ceramic plate 1 opposite to the grooved side, a substrate 41 having a pattern 42 of a conductive layer provided at a position corresponding to the position of each ink liquid chamber 12 is bonded by an epoxy adhesive or the like. And shallow parallel grooves 1
The metal electrode on the bottom surface of 8 and the pattern 42 of the conductive layer are connected by a conductive wire 43 by wire bonding.

Next, the configuration of the conventional control unit will be described with reference to FIG. 18 showing a block diagram of the control unit. The conductive layer patterns 42 provided on the substrate 41 are individually connected to the LSI chip 51, and the clock line 52, the data line 53, the voltage line 54, and the ground line 55 are also LSI.
It is connected to the chip 51. The LSI chip 51 determines which nozzle should eject an ink droplet from the data appearing on the data line 53 based on the continuous clock pulses supplied from the clock line 52, and drives the ink liquid chamber. The voltage V of the voltage line 54 is applied to the pattern 42 of the conductive layer which is electrically connected to the metal electrode. Further, the voltage 0 of the earth line 55 is applied to the pattern 42 of the conductive layer which is electrically connected to the metal electrode other than the ink liquid chamber.

[0009]

However, in the conventional ink ejecting apparatus as described above, the deformation amount of the side wall of the piezoelectric ceramic is small as compared with the electric energy applied to the metal voltage, and the volume of the ink liquid chamber is reduced. Because the amount is small,
There is a problem that the ink pressure generated in the ink liquid chamber is small. Therefore, there is a problem in that the speed and volume of the ejected ink droplets are insufficient for forming characters and images on the paper surface facing the ejecting device. In order to eject ink droplets of a speed and volume sufficient for forming characters and images with such a device, a high driving voltage is required, which complicates and increases the size of the driving circuit and reduces the cost of the device. There was a limit to miniaturization.

The present invention has been made to solve the above-mentioned problems, and it is possible to eject ink droplets at a speed and volume sufficient to form characters and images with a low driving voltage. It is an object to provide an ink ejecting device.

[0011]

In order to achieve this object, the ink ejecting apparatus of the present invention applies a driving voltage to an electrode formed in a part of a groove provided in a piezoelectric ceramic, thereby applying the piezoelectric voltage. In the ink ejecting device that ejects the ink filled in the groove by changing the volume inside the groove by using the piezoelectric thickness sliding effect of ceramics, the height direction and the polarization direction of the side wall separating the groove. The angle formed by and is less than or equal to 18 degrees.

[0012]

According to the ink ejecting apparatus of the present invention having the above-described structure, by setting the angle between the height direction of the side wall separating the groove and the polarization direction to be 18 degrees or less, other values can be obtained. In comparison, the ink pressure generated inside the groove is much higher.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The same members as those of the conventional technique are designated by the same reference numerals, and the description thereof will be omitted.

1. Description of the relationship between the height / width ratio H / B of the side wall and the pressure P in the ink liquid chamber First, referring to FIG. 1 showing a partial cross-sectional view of the ink ejecting apparatus, parameters representing the shapes of the side wall 11 and the metal electrode 13 are shown. Will be explained. The height of the side wall 11 provided on the piezoelectric ceramic plate 1 is H, the width is B, the pitch is Z, the curvature of the bottom is R, and the length from the upper end to the lower end of the metal electrode 13 formed on the surface of the side wall 11 is defined as: Let be D.

Next, the configuration of the embodiment of the present invention will be described with reference to FIG. 2 which illustrates the relationship between the height / width ratio H / B of the side wall and the pressure P in the ink liquid chamber. Ink ejection devices having various height / width ratios H / B of side walls were manufactured to produce metal electrodes 13.
The same drive voltage was applied to the ink and the pressure generated in the ink liquid chamber 12 was measured. The side wall 11 of the manufactured ink ejecting apparatus has a width B of 40 μm to 120 μm and a height of 100 μm to 600 μm, and the length D of the metal electrode 13 is about ½ of the height H of the side wall 11. The material of the piezoelectric ceramics 1 is barium titanate-based piezoelectric ceramics,
The metal electrode 13 has a thickness of 1 μm formed by vacuum deposition.
An aluminum layer, a material of the cover plate 2 is borosilicate glass, and an adhesive 3 is an epoxy adhesive. The ink is a pigment ink based on tripropylene glycol monomethyl ether (TPM), and the driving voltage applied to the metal electrode 13 is 40 volts.

The pressure inside the ink liquid chamber 12 was measured by the following method. A parallel laser beam is applied to the inside of the ink liquid chamber 12 from above the transparent cover plate 2 through the objective lens of the metallographic microscope, and the laser beam is emitted.
In the state where the light is condensed at the bottom of the ink liquid chamber 12, the phase difference between the laser beam reflected by the bottom of the ink liquid chamber 12 and passing through the objective lens again and the irradiated laser beam is detected. TPM in the ink liquid chamber 12
When the refractive index changes due to the change in pressure, the time during which the laser beam passes through the ink liquid chamber 12 changes, and the pressure inside the ink liquid chamber 12 can be measured by detecting the change in the phase difference. . As shown in FIG. 2, the measurement result shows that the pressure in the ink liquid chamber 12 becomes almost maximum when the height / width ratio H / B of the side wall 11 is 2.5 or more and 8 or less.

On the other hand, models of the piezoelectric ceramic plate 1, the side wall 11, the adhesive layer 3 and the cover plate 2 having various ratios H / B of the height and width of the side wall in the range of 1 to 10 were prepared, and the finite element was prepared. A numerical analysis was performed by the method to investigate the relationship between the height / width ratio H / B of the side wall and the pressure P in the ink liquid chamber. The pressure P in the ink liquid chamber 12 is the static deformation amount of the side wall 11 when the drive voltage is applied to the metal electrode 13 when the ink is not introduced into the ink liquid chamber 12, that is, the volume decrease in the ink liquid chamber 12. Amount ΔV, pressure P on the surface of the side wall 11
Of static deformation of the side wall 11 when the side wall is applied, that is, the side wall 1
1 can be estimated by P = K · ΔV / C, where C is the compliance of 1 and K is a constant determined by the piezoelectric and mechanical properties of the piezoelectric ceramic plate 1 and the compression property of ink. As a result of the analysis, as shown in FIG.
The pressure in the ink liquid chamber 12 takes a value of about 85% or more of the maximum value in the range of height / width ratio H / B of 2.5 or more and 8 or less, and in the range of 2 or more and 9 or less. It shows that the pressure in the chamber 12 takes a value of about 70% or more of the maximum value. This is in agreement with the above measurement result.

From the above results, in the ink jet apparatus of this embodiment, the ratio H / B of the height H of the side wall separating the groove and the width B of the side wall is H / B.
However, the range is preferably 2 or more and 9 or less, and more preferably 2.5 or more and 8 or less. Here, supposing that a value outside the above range is taken into consideration, the ratio of the ink pressure generated in the ink liquid chamber 12 to the drive voltage applied to the metal voltage 13 is small, and the speed of the ejected ink droplets and The volume is insufficient for forming characters and images on a paper surface facing the ejection device. Therefore, in order to obtain a high drive voltage, the drive circuit becomes complicated and large. On the other hand, according to this embodiment, the pressure generated in the ink liquid chamber 12 can be efficiently increased. That is, a high pressure can be generated in the ink liquid chamber 12 with a low driving voltage, and ink droplets can be ejected at a speed and volume sufficient to form a character or an image. According to this ink ejecting apparatus, at a driving voltage as low as about 20 to 50 V, the speed of the ink droplet is 3 to 8.
m / sec, the volume can be about 30 to 90 pl,
The drive circuit can be simplified and downsized, and the cost and size of the entire ink ejecting apparatus can be reduced.

2. Description of Relationship between Sidewall Width / Pitch Ratio B / Z and Ink Liquid Chamber Pressure P FIG. 3 shows the relationship between the sidewall width / pitch ratio B / Z and the ink liquid chamber pressure P in this embodiment. It will be specifically described by.
Ink jetting devices having various side wall width / pitch ratios B / Z were manufactured, and the same drive voltage was applied to the metal electrode 13 to measure the pressure generated in the ink liquid chamber 12. The dimensional conditions, materials, manufacturing method, and pressure measuring method of the manufactured ink ejecting apparatus are the same as those in Item 1 above.

As shown in FIG. 3, the measurement result shows that the side wall 11
It is shown that the pressure in the ink liquid chamber 12 becomes maximum when the width / pitch ratio B / Z is 0.3 or more and 0.8 or less.

On the other hand, the piezoelectric ceramic plate 1, the side wall 11 having various width / pitch ratio B / Z of the side wall in the range of 0.1 to 0.9, the adhesive layer 3, and the cover plate 2.
Was prepared and numerical analysis was performed by the finite element method to investigate the relationship between the side wall width / pitch ratio B / Z and the pressure P in the ink liquid chamber. The method for estimating the pressure P in the ink liquid chamber is also the same as in item 1 above. As a result of the analysis, as shown in FIG. 3, the width / pitch ratio B / Z of the side wall 11 is 0.3 or more.
In the range of 8 or less, the pressure in the ink liquid chamber 12 is 85, which is the maximum value.
It shows that the pressure in the ink liquid chamber 12 takes a value of about 70% or more of the maximum value in the range of 0.2 or more and 0.9 or less. This is in agreement with the above measurement result.

From the above results, in the ink ejecting apparatus of the present embodiment, the ratio B / the width B of the side walls separating the grooves and the pitch Z of the side walls B /
Z is preferably in the range of 0.2 or more and 0.9 or less, more preferably 0.3 or more and 0.8 or less. Here, supposing that a value outside the above range is taken into consideration, the ratio of the ink pressure generated in the ink liquid chamber 12 to the drive voltage applied to the metal voltage 13 is small, and the speed of the ejected ink droplets and The volume is insufficient for forming characters and images on a paper surface facing the ejection device.
Therefore, in order to obtain a high drive voltage, the drive circuit becomes complicated and large. On the other hand, according to this embodiment, the pressure generated in the ink liquid chamber 12 can be efficiently increased. That is, a high pressure can be generated in the ink liquid chamber 12 with a low driving voltage, and ink droplets can be ejected at a speed and volume sufficient to form a character or an image. According to this ink ejecting apparatus, 20
At a driving voltage as low as about 50 V, the speed of ink droplets can be about 3 to 8 m / sec, the volume can be about 30 to 90 pl, the driving circuit can be simplified and downsized, and the entire ink ejecting apparatus can be made low. Cost and size can be reduced.

3. Description of Relationship between Curvature R at Side Wall Bottom and Principal Stress σ at Side Wall Bottom Various types of ink ejecting apparatuses having side wall bottom curvature R are manufactured, and a driving voltage is applied to the metal electrode 13 to eject ink droplets. I went about a billion times. The dimensional conditions and materials of the manufactured ink ejecting apparatus are the same as in Item 1 above. However, the groove 15 was manufactured by grinding using a disc-shaped diamond blade having a width slightly smaller than the width of the groove 15, but the outer peripheral edge of the diamond blade was ground in advance to various curvatures. The curvature R of the bottom of the side wall
The side wall 11 having a thickness of 3 μm to 40 μm was manufactured.

As a result of ejecting the ink droplets about 1 billion times with the above-mentioned ink ejecting apparatus, it was found that a minute crack was generated at the bottom of a part of the side wall, leading to destruction. Even if a drive voltage is applied to the metal electrode 13 on such a side wall, the side wall is not deformed normally, and the ejection of ink droplets is stopped. The destroyed side walls are concentrated on the side wall having a small curvature R at the bottom, and the side wall having a curvature R of 3 μm reaches 8% of the side wall tested, 1% of the side wall of 4 μm and 0.2% of the side wall of 5 μm. %, 6% of the side wall was destroyed by 0.02%. There was no case of fracture on the side wall having a curvature R of 7 μm or more.

On the other hand, a model of the piezoelectric ceramic plate 1, the side wall 11, the adhesive layer 3 and the cover plate 2 having various values of the curvature R of the bottom of the side wall in the range of 3 μm to 40 μm was prepared, and numerical analysis by the finite element method was performed. Then, the relationship between the curvature R at the bottom of the side wall and the principal stress σ at the bottom of the side wall was investigated. The analysis results show that, as shown in FIG. 4, when the curvature R of the bottom of the side wall becomes small, the main stress σ at the bottom of the side wall rapidly increases. The above test results and analysis results show that when the curvature R of the bottom of the side wall becomes small, the principal stress σ at the bottom of the side wall rapidly increases, and when the principal stress σ at the bottom of the side wall exceeds the fracture strength of the piezoelectric ceramic plate 1, it is partially. It is shown that a microcrack is generated at the bottom of the side wall of the and leads to fracture.

From the above results, the ink ejecting apparatus of this embodiment is constructed so that the curvature of the bottom of the side wall separating the grooves is preferably 5 μm or more, more preferably 7 μm or more. According to the ink ejecting apparatus of the present embodiment, even if the ink droplets are ejected about 1 billion times, no microcracks are generated at the bottom of the side wall and no destruction occurs. Therefore, it is possible to provide a reliable ink ejecting apparatus in which the ejection of the ink droplets does not stop even if the ejection of the ink droplets is performed many times.

4. Description of Relation between Sidewall Taper T and Pressure P in Ink Liquid Chamber First, the configuration of the present embodiment will be described with reference to FIG. 5 which is a partial cross-sectional view of the ink ejecting apparatus. A piezoelectric ceramic plate 1 having a plurality of grooves 15 and side walls 11 separating the grooves and polarized in the direction of arrow 4, and a cover plate 2 made of a ceramic material or a resin material,
By joining via the joining layer 3 made of an epoxy adhesive or the like, the grooves 15 become a plurality of ink liquid chambers 12 which are laterally spaced from each other. The side wall 11 has an elongated shape of a trapezoidal cross section having a narrow width in the upper part and a wide width in the lower part, which is in contact with the cover plate 2, and extends over the entire length of the ink liquid chamber 12. Metal electrodes 13 for applying a driving electric field are formed on both surfaces of the side wall 11 near the adhesive layer 3 from the upper side wall to the central part of the side wall. Ink is filled in all the ink liquid chambers 12. Next, parameters showing the shapes of the side wall 11 and the metal electrode 13 will be described. The height of the side wall 11 is H, the width of the upper part is Bu, the width of the lower part is Bl, the pitch is Z, the curvature of the bottom is R, and the length of the metal electrode 13 formed on the surface of the side wall 11 from the upper end to the lower end. Let be D. The side wall taper T is the formula T
= (B1-Bu) / H

Next, the ratio of the length of the electrode to the height of the side wall D / H
And the pressure P in the ink liquid chamber, and FIG. 7 illustrating the relation between the side wall taper T and the pressure P in the ink liquid chamber, the configuration of the present embodiment will be described. An ink ejecting apparatus is manufactured in which the taper T of the side wall is various values from 0 to 0.2 and the ratio D / H of the length of the electrode to the height of the side wall is various value from 0.2 to 0.8, The same drive voltage was applied to the metal electrode 13 and the pressure generated in the ink liquid chamber 12 was measured. The dimensional conditions other than the electrode length of the manufactured ink ejecting apparatus, materials, manufacturing method, and pressure measuring method are described in the above item 1.
Is the same as.

FIG. 6 shows the ratio of the electrode length to the height of the side wall D / in the ink ejecting apparatus having the side wall taper T of 0.05.
The relationship between H and the pressure P in the ink liquid chamber is shown. The measurement result shows that in this case, the pressure in the ink liquid chamber 12 becomes maximum when the ratio D / H of the length of the electrode and the height of the side wall is about 0.5.

On the other hand, the piezoelectric ceramic plate 1 has various side wall taper T values of 0 to 0.2 and various electrode length / side wall height ratios D / H of 0.2 to 0.8. A model of the side wall 11, the adhesive layer 3, and the cover plate 2 that are values is created, and numerical analysis is performed by the finite element method to measure the taper T of the side wall and the ratio D / H between the length of the electrode and the side wall height and the ink liquid chamber. Was investigated with respect to the pressure P. The method for estimating the pressure P in the ink liquid chamber is also the same as in item 1 above.

FIG. 6 shows the ratio of the electrode length to the height of the side wall D / in the ink ejecting apparatus having the side wall taper T of 0.05.
The relationship between H and the pressure P in the ink liquid chamber is shown. The analysis result shows that in this case, the pressure in the ink liquid chamber 12 becomes maximum when the ratio D / H of the length of the electrode and the height of the side wall is about 0.5. This is in agreement with the above measurement result.

From the above results, the side wall taper T is 0.0
In the ink jet device of No. 5, it is shown that the pressure in the ink liquid chamber 12 becomes maximum when the ratio D / H of the length of the electrode and the height of the side wall is about 0.5.

The above-described measurement and analysis were carried out by an ink jet apparatus having a side wall taper T of various values from 0 to 0.2, and the ratio of the length of the electrode to the height of the side wall of the side wall of each shape. The maximum value of the pressure P in the ink liquid chamber when D / H was changed was examined. As shown in FIG. 7, when the side wall taper T is 0, the pressure P in the ink liquid chamber is maximum, and when the side wall taper T is 0.1, the pressure P in the ink liquid chamber is 1.
Although the decrease is only about 5%, when the taper T of the side wall becomes 0.16 or more, the pressure P in the ink liquid chamber decreases by 30% or more, which is lower than the electric energy applied to the metal voltage 13. There is a problem that the ink pressure generated in 12 is small and the speed and volume of the ejected ink droplets are insufficient to form characters and images on the paper surface facing the ejecting device. In order to eject ink droplets of a speed and volume sufficient for forming characters and images with such a device, a high driving voltage is required, which complicates and increases the size of the driving circuit and reduces the cost of the device. There is a limit to miniaturization.

Further, when the taper T of the side wall is negative, that is, in the reverse taper, the same measurement and analysis as described above were performed. As a result, it was found that the same tendency as described above was obtained when the absolute value of the taper T was considered.

From the above results, in the ink jet apparatus of this embodiment, the absolute value of the taper T of the side wall separating the groove is
The range is preferably 0.16 or less, more preferably 0.1.
It is configured to have the following range. As a result, in the ink ejecting apparatus of this embodiment, the pressure generated in the ink liquid chamber 12 can be efficiently increased. That is, a high pressure can be generated in the ink liquid chamber 12 with a low driving voltage, and ink droplets can be ejected at a speed and volume sufficient to form a character or an image. According to this ink ejecting apparatus, at a low driving voltage of about 20 to 50 V, the speed of ink droplets is 3 to 8 m / sec and the volume is 30 to 9 m.
It can be about 0 pl, the drive circuit can be simplified and downsized, and the cost and size of the entire ink ejecting apparatus can be reduced.

5. Description of Relationship between Angle θ Formed by Sidewall Height Direction and Polarization Direction and Pressure P in Ink Liquid Chamber First, the shapes of the side wall 11 and the metal electrode 13 will be described with reference to FIG. 8 which is a partial sectional view of the ink ejecting apparatus. The parameter to represent is demonstrated. The height of the side wall 11 provided on the piezoelectric ceramic plate 1 is H, the width is B, the pitch is Z, the curvature of the bottom is R, and the length from the upper end to the lower end of the metal electrode 13 formed on the surface of the side wall 11 is defined as: Let D be the angle between the height direction of the side wall 11 and the polarization direction 4.

Next, the relationship between the angle P formed by the direction of arrow A and the direction of polarization and the pressure P in the ink liquid chamber will be described with reference to FIG.
The configuration of this embodiment will be described below. An ink ejecting apparatus was manufactured in which the angle θ formed by the direction of arrow A, which is the height direction of the side wall 11, and the polarization direction has various values, and the metal electrode 13
The same drive voltage was applied to the ink and the pressure generated in the ink liquid chamber 12 was measured. The dimensional conditions, manufacturing method, and pressure measuring method of the manufactured ink ejecting apparatus are the same as those in the above item 1. However, the material of the piezoelectric ceramics 1 was manufactured by cutting a wafer having a plane direction of 90-θ degrees with respect to the polarization direction of the block from a block of polarized barium titanate-based piezoelectric ceramics with a slicer.
The metal electrode 13 has a thickness of 1 μm formed by vacuum deposition.
An aluminum layer, a material of the cover plate 2 is borosilicate glass, and an adhesive 3 is an epoxy adhesive. θ is in the range of 0 to 20 degrees.

As shown in FIG. 9, when the angle θ formed by the direction of arrow A and the polarization direction is 0 °, the pressure P in the ink liquid chamber is P.
Is the maximum, and in comparison with this, when θ is 14 degrees, the pressure P in the ink liquid chamber is only reduced by about 15%.
Is 18 degrees or more, the pressure P in the ink liquid chamber decreases by 30% or more, the ink pressure generated in the ink liquid chamber 12 is smaller than the electric energy applied to the metal voltage 13, and the ejected ink droplets However, there is a problem in that the speed and volume are insufficient to form characters and images on the paper surface facing the ejection device. In order to eject ink droplets of a speed and volume sufficient for forming characters and images with such a device, a high driving voltage is required, which complicates and increases the size of the driving circuit and reduces the cost of the device. There is a limit to miniaturization.

From the above results, in the ink ejecting apparatus of this embodiment, the angle formed by the height direction of the side wall separating the groove and the polarization direction is preferably 18 degrees or less, more preferably 14 degrees or less. Configured to be. Thereby, in the ink ejecting apparatus of this embodiment, the pressure generated in the ink liquid chamber 12 can be efficiently increased. That is, a high pressure can be generated in the ink liquid chamber 12 with a low driving voltage, and ink droplets can be ejected at a speed and volume sufficient to form a character or an image. According to this ink ejecting apparatus, at a driving voltage as low as about 20 to 50 volts, the speed of ink droplets is 3 to 8 m / sec and the volume is 3
The drive circuit can be simplified and downsized, and the cost and size of the entire ink ejecting apparatus can be reduced.

6. Description of Relationship Between Curvature r and Droplet Ejection Velocity First, the configuration of this embodiment and parameters representing the shape of the groove 15 will be described with reference to FIG. 10 which is a partial cross-sectional view of the ink ejecting apparatus. The groove 15 forming the ink liquid chamber 12 has a point 51 inside the piezoelectric ceramic plate 1 from the end face 16.
Up to parallel grooves of the same depth, but from point 51 to end face 1
The groove 18 gradually becomes shallower with a curvature R in the direction 7 and becomes a shallow parallel groove 18 near the end face 17. The position of the point 51 in the ink liquid chamber longitudinal direction is such that the length of the drive portion of the side wall 11 is made as long as possible, the volume of the manifold 22 is made as large as possible, and the cover plate 2 is made as small as possible. End 2 on the 31 side
It agrees with 3. The metal electrode 13 is formed on the inner surfaces of the groove 15 and the shallow parallel groove 18 by sputtering or the like. Metal electrodes are formed on the inner surface of the groove 15 only on the upper half of the side surface thereof, while metal electrodes are formed on the entire side surface and bottom surface of the inner surface of the shallow and parallel groove 18.

Next, the configuration of this embodiment will be described with reference to FIG. 11 which illustrates the relationship between the curvature r and the droplet ejection velocity v. Ink jetting devices having various curvatures r were manufactured, the same driving voltage was applied to the metal electrode 13, and the jetting speed v of the liquid droplets from the nozzle 32 was measured. The dimensional conditions, materials, and manufacturing method of the manufactured ink ejecting apparatus are the same as in Item 1 above.

As shown in FIG. 11, when the curvature r is 15 mm or more, the droplet ejection velocity v is almost constant and reaches the maximum, and in comparison, when the curvature r is 7 mm, the droplet ejection velocity v is 10%. The curvature r is only 5 mm, but the curvature r is 5 mm.
When it becomes below, the ejection speed v of the droplet is reduced by 15% or more, the ejection speed of the droplet is smaller than the electric energy applied to the metal voltage 13, and the ejection speed of the droplet is on the paper surface facing the ejecting device. However, there is a problem that it is insufficient to form characters and images. A high drive voltage is required to eject ink droplets at a speed sufficient for forming characters and images with such a device, which complicates and increases the size of the drive circuit and reduces the cost and size of the device. Is limited.

The reason for this is that when the curvature r becomes small, when ink is supplied from the ink supply port 21 into the ink liquid chamber 12 through the manifold 22, the ink liquid flows from the manifold 22 through the portion where the bottom of the groove 15 has the curvature r. When the ink flows into the chamber 12, the flow resistance of the ink increases. Then, as a result of the supply amount of ink catching up with the amount of ink ejected as droplets, a negative pressure is generated in the ink liquid chamber 12, and when a drive voltage is applied to the metal electrode 13, the ink liquid chamber 12 is supplied with a negative pressure. This is because the generated pressure decreases. Then, the smaller the pressure inside the ink liquid chamber 12, the smaller the ejection speed of the liquid droplets.

From the above results, in the ink ejecting apparatus of the present embodiment, the curvature of the groove which is continuous with the groove of the ink liquid chamber having a substantially constant depth is preferably 5 mm or more, more preferably 7 mm or more. Configured to be in range. As a result, in the ink ejecting apparatus of this embodiment, it is possible to efficiently increase the ejection speed of droplets. That is, it is possible to eject ink droplets at a speed and volume sufficient to form characters and images with a low driving voltage. According to this ink ejecting apparatus, at a low driving voltage of about 20 to 50 V, the speed of ink droplets is 3 to 8 m / sec and the volume is 30 to 9 m.
It can be about 0 pl, the drive circuit can be simplified and downsized, and the cost and size of the entire ink ejecting apparatus can be reduced.

7. Taper t at groove bottom and droplet ejection velocity v
First, referring to FIG. 12 showing a cross-sectional view of the ink ejecting apparatus,
The parameters of the structure of this embodiment and the shape of the groove 15 will be described. The groove 15 forming the ink liquid chamber 12 has an end face 16
To a point 51 inside the piezoelectric ceramics plate 1 are parallel grooves of the same depth or grooves whose depth gradually changes linearly with respect to the longitudinal direction of the grooves, and the depth at the portion contacting the nozzle plate 31. Is Hn, and the depth in the portion close to the manifold 22 is Hm. The taper t at the bottom of the groove 15 is point 51 from the portion of the groove 15 that abuts the nozzle plate 31.
When the length up to is L, it is expressed by the equation t = (Hn-Hm) / L. The groove 15 has a curvature R from the point 51 toward the end surface 17.
Gradually becomes shallower at
Is. On the inner surfaces of the groove 15 and the shallow parallel groove 18,
The metal electrode 13 is formed by sputtering or the like. Metal electrodes are formed on the inner surface of the groove 15 only on the upper half of the side surface thereof, while metal electrodes are formed on the entire side surface and bottom surface of the inner surface of the shallow and parallel groove 18.

Next, the structure of this embodiment will be described with reference to FIG. 13 for explaining the relationship between the taper t at the bottom of the groove 15 and the jetting speed v of the droplet. Ink jetting devices having various t's were manufactured, and the same driving voltage was applied to the metal electrode 13 so that the nozzle 32
The jetting speed v of the droplet from was measured. The width B of the side wall 11 of the manufactured ink ejecting apparatus is 40 μm to 120 μm, and the height is in the range of 200 μm to 1000 μm at the highest part of the portion where the height gradually changes in a straight line, and in the range of 100 μm to 400 μm at the lowest part. Further, the length D of the metal electrode 13 is approximately 1/2 of the height H of the side wall 11 where the metal electrode 13 is formed, and in the portion where the height of the side wall 11 gradually changes linearly. The length D of the metal electrode 13 gradually changes linearly. The piezoelectric ceramics 1 is made of barium titanate-based piezoelectric ceramics, the metal electrode 13 is an aluminum layer having a thickness of about 1 μm formed by vacuum deposition, the cover plate 2 is made of borosilicate glass, and the adhesive 3 is made of epoxy-based material. An adhesive was used. The ink is a pigment ink based on tripropylene glycol monomethyl ether (TPM), and the metal electrode 13
The drive voltage applied to is 40 volts.

As shown in FIG. 13, when the taper t at the bottom of the groove 15 is 0, the droplet ejection speed v is maximum, and in comparison with this, when t is 0.012, the droplet ejection speed v is 10. %
However, when t becomes 0.02 or more, the ejection velocity v of the liquid droplet decreases by 15% or more, and the metal voltage 1
There is a problem that the ejection speed of the liquid droplets is smaller than the electric energy applied to No. 3, and the ejection speed of the liquid droplets is insufficient to form characters and images on the paper surface facing the ejection device. . A high drive voltage is required to eject ink droplets at a speed sufficient for forming characters and images with such a device, which complicates and increases the size of the drive circuit and reduces the cost and size of the device. Is limited.

The following can be considered as the cause of this. When the taper t at the bottom of the groove 15 increases, the metal electrode 1
When a drive voltage is applied to the groove 3, a difference occurs between the pressure of the ink generated in the portion of the groove 15 that abuts the nozzle plate 31 and the pressure of the ink generated in the portion that is close to the manifold 22. As the pressure wave generated in 1 reaches the nozzle, the ink pressure at the nozzle fluctuates. Therefore, the flow velocity of the ink flowing in the nozzle changes due to the influence of the change of the ink pressure immediately after the application of the driving voltage, and the flow velocity of the ink is changed by the fluid resistance of the ink such as inertial resistance as compared with the case where the ink flow velocity is constant. The energy loss increases, and the droplet ejection speed v decreases.

Further, it is known that when the taper t is negative, that is, when the taper t is an inverse taper, the same tendency as described above is obtained when the absolute value of t is taken.

From the above results, in the ink ejecting apparatus of this embodiment, among the grooves forming the ink liquid chamber, the bottom of the groove whose depth gradually changes linearly with the surface direction of the piezoelectric ceramic plate. The absolute value of the taper formed is preferably 0.02 or less, more preferably 0.012 or less. As a result, in the ink ejecting apparatus of this embodiment, it is possible to efficiently increase the ejection speed of droplets. That is, it is possible to eject ink droplets at a speed and volume sufficient to form characters and images with a low driving voltage. According to this ink ejecting apparatus, at a driving voltage as low as about 20 to 50 V, the speed of the ink droplet is 3 to 8.
m / sec, the volume can be about 30 to 90 pl,
The drive circuit can be simplified and downsized, and the cost and size of the entire ink ejecting apparatus can be reduced.

8. Explanation of Relationship between Sidewall Surface Roughness Rz and Droplet Ejection Velocity The relationship between the sidewall surface roughness Rz and the droplet ejection velocity v of this embodiment will be specifically described with reference to FIG. Ink jetting devices having various surface roughness Rz of the side wall were manufactured, and the same drive voltage was applied to the metal electrode 13 to measure the pressure generated in the ink liquid chamber 12. Sidewalls having various surface roughnesses Rz in the range of 2 μm to 8 μm were manufactured by changing the grain size of the diamond abrasive grains of the thin disk-shaped diamond blade for processing the groove 15. The dimensional conditions, materials, manufacturing method, and pressure measuring method of the manufactured ink ejecting apparatus are the same as those in Item 1 above.

As shown in FIG. 14, the measurement result shows that when the surface roughness Rz of the side wall is 3 μm or less, the ejection velocity v of the droplet becomes almost constant at the maximum, and in comparison with this, when Rz is 5 μm, the droplet ejection velocity v is constant. The ejection speed v of the droplets is only about 10% lower, but when Rz is 6.5 μm or more, the droplet ejection speed v
Is 15% or more, the ejection speed of the liquid droplets is lower than the electric energy applied to the metal voltage 13, and the ejection speed of the liquid droplets is not suitable for forming characters or images on the paper surface facing the ejection device. There is a problem that it is insufficient. A high drive voltage is required to eject ink droplets at a speed sufficient for forming characters and images with such a device, which complicates and increases the size of the drive circuit and reduces the cost and size of the device. Is limited. This is because when the surface roughness Rz of the side wall increases, the fluid resistance of the ink flowing from the manifold 22 to the nozzle 32 in the ink liquid chamber 12 increases, and the metal electrode 13
That is, the loss of electric energy applied to is increased.

From the above results, the ink jet apparatus of this embodiment is constructed so that the surface roughness Rz of the side wall separating the grooves is preferably 6.5 μm or less, more preferably 5 μm or less. As a result, in the ink ejecting apparatus of this embodiment, the pressure generated in the ink liquid chamber 12 can be efficiently increased. That is, it is possible to eject ink droplets at a speed and volume sufficient to form characters and images with a low driving voltage. According to this ink ejecting apparatus, at a driving voltage as low as about 20 to 50 volts, the speed of ink droplets is 3 to 8 m / sec and the volume is 30 to 90 pl.
The drive circuit can be simplified and miniaturized, and the cost and size of the entire ink ejecting apparatus can be reduced.

[0054]

As is apparent from the above description, according to the ink ejecting apparatus of the present invention, the angle formed by the height direction of the side wall separating the groove and the polarization direction is 18 degrees or less, so that the angle is low. A high voltage can be generated in the ink liquid chamber by the driving voltage, and ink droplets can be ejected at a speed and volume sufficient to form a character or an image. Therefore, the drive circuit can be simplified and downsized, and the device can be reduced in cost and downsized.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an ink ejecting apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a height-width ratio H / B of a side wall and a pressure P in an ink liquid chamber.

FIG. 3 is a diagram illustrating a relationship between a side wall width / pitch ratio B / Z and a pressure P in the ink liquid chamber.

FIG. 4 is a diagram illustrating a relationship between a curvature R of a sidewall bottom and a principal stress σ at the sidewall bottom.

FIG. 5 is a partial cross-sectional view of the ink ejecting apparatus according to the embodiment of the present invention.

FIG. 6 is a diagram illustrating the relationship between the ratio D / H of the electrode length and the height of the side wall and the pressure P in the ink liquid chamber.

FIG. 7 is a diagram illustrating a relationship between a side wall taper T and a pressure P in an ink liquid chamber.

FIG. 8 is a partial cross-sectional view of the ink ejecting apparatus according to the embodiment of the present invention.

FIG. 9 is a diagram illustrating a relationship between an angle θ formed by a longitudinal direction of a side wall and a polarization direction and a pressure P in an ink liquid chamber.

FIG. 10 is a partial cross-sectional view of the ink ejecting apparatus according to the embodiment of the present invention.

FIG. 11 is a diagram illustrating a relationship between a curvature r and a droplet ejection velocity v.

FIG. 12 is a partial cross-sectional view of the ink ejecting apparatus according to the embodiment of the present invention.

FIG. 13 is a diagram for explaining the relationship between the taper t of the groove bottom and the droplet ejection velocity v.

FIG. 14 is a diagram illustrating a relationship between a surface roughness Rz of a side wall and a droplet ejection velocity v.

FIG. 15 is a sectional view of a conventional ink ejecting apparatus.

FIG. 16 is a sectional view of a conventional ink ejecting apparatus.

FIG. 17 is a perspective view of a conventional ink ejecting apparatus.

FIG. 18 is a block diagram of a control unit of a conventional example.

[Explanation of symbols]

 1 Piezoelectric Ceramics Plate 11 Side Wall 12 Ink Liquid Chamber 13 Metal Electrode 15 Groove

Claims (1)

[Claims] 1. A drive voltage is applied to an electrode formed in a part of the inside of a groove provided in the piezoelectric ceramic, and the volume inside the groove is changed by using the piezoelectric thickness sliding effect of the piezoelectric ceramic. In the ink ejecting apparatus for ejecting the ink filled in the groove, the angle formed by the height direction of the side wall separating the groove and the polarization direction is 18 degrees or less. .