JPH06234211A - Ink injection device - Google Patents

Abstract

PURPOSE:To form an adhesive agent thin to improve adhering rigidity end secure a pressure in an ink chamber by setting the surface roughness of the adhering surface of a cover plate so as to be a specified value (mum) or less, in a device which injects ink by deforming the side wall of the ink chamber. CONSTITUTION:An ink injection device 1 is provided with a piezo-electric ceramics plate 2 and a cover plate 10. A plurality of grooves 3 and side walls 6, defining the grooves, are formed on the piezoelectric ceramics plate 2. An ink introducing port and a manifold are formed on the cover plate 10. The piezoelectric ceramics plate 2 is adhered to the cover plate 10 through an adhesive agent to form an ink channel or an ink chamber 4. In this case, a surface roughness in the adhering surface of the cover plate 10 is set at least 5mum or less. According to this method, the adhesive agent 20 is formed so as to be thin to improve the adhering rigidity whereby the pressure in the ink chamber 4 can be maintained and printing quality can be retained excellent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet device.

[0002]

2. Description of the Related Art Among the non-impact type printers, which have been expanding the market to replace the impact type printers used up to now, the principle is the simplest, and multi-gradation and colorization are possible. Inkjet type printers are mentioned as being easy to use. Above all, a drop that ejects only the ink drops used for printing
The on-demand type is rapidly spreading due to its good injection efficiency and low running cost.

The Kaiser type disclosed in Japanese Patent Publication No. 53-12138 as a drop-on-demand type,
Alternatively, a thermal jet type disclosed in Japanese Patent Publication No. 61-59914 is a typical method.
Of these, the former is difficult to miniaturize, and the latter requires a high heat resistance of the ink in order to apply high heat to the ink, and each has a very difficult problem.

A method proposed to solve the above-mentioned defects at the same time is Japanese Patent Laid-Open No. 252750/1988.
It is the shear mode type disclosed in the publication.

As shown in FIG. 16, the shear mode type ink jet device 1 is composed of a piezoelectric ceramic plate 2, a cover plate 10, a nozzle plate 14 and a substrate 41.

The piezoelectric ceramic plate 2 is cut with a diamond blade or the like to form a plurality of grooves 3.
Are formed. In addition, a side wall 6 that is a side surface of the groove 3
Is polarized in the direction of arrow 5. The grooves 3 are of the same depth and are parallel. The depths of the grooves 3 gradually become shallower as they approach the one end face 15 of the piezoelectric ceramic plate 2, and a shallow groove 7 is formed near the one end face 15. Then, on the inner surface of the groove 3, metal electrodes 8 are formed by sputtering or the like on the upper halves of both side surfaces thereof. Further, on the inner surface of the shallow groove 7, a metal electrode 9 is formed on the side surface and the bottom surface by sputtering or the like. Thereby, the metal electrodes 8 formed on both sides of the groove 3
Are connected by a metal electrode 9 formed in the shallow groove 7.

Next, the cover plate 10 is made of a ceramic material, a resin material, or the like. And
An ink inlet 16 and a manifold 18 are formed in the cover plate 10 by grinding or cutting. Then, the surface of the piezoelectric ceramic plate 2 on the side where the groove 3 is processed and the surface of the cover plate 10 on the side where the manifold 18 is processed are adhered by an epoxy adhesive 20 (see FIG. 18). Therefore, the ink ejecting apparatus 1 is provided with the ink chambers 4 (see FIG. 18) that are the plurality of ink flow paths that are covered with the upper surfaces of the grooves 3 and have the same intervals in the lateral direction. As shown in FIG. 18, the ink chamber 4 has an elongated shape with a rectangular cross section, and ink is filled in all the ink chambers 4.

As shown in FIG. 16, a nozzle plate 14 having nozzles 12 provided at positions corresponding to the positions of the ink chambers 4 is adhered to the end faces of the piezoelectric ceramic plate 2 and the cover plate 10. The nozzle plate 14 is made of polyalkylene (for example, ethylene), terephthalate, polyimide, polyetherimide, polyetherketone, polyethersulfone, polycarbonate,
It is made of plastic such as cellulose acetate.

A substrate 41 is adhered to the surface of the piezoelectric ceramic plate 2 opposite to the processed side of the groove 3 with an epoxy adhesive or the like. Its substrate 41
A conductive layer pattern 42 is formed at a position corresponding to the position of each ink chamber 4. The conductive layer pattern 42
And the metal electrode 9 on the bottom surface of the shallow groove 7 are connected by a conductive wire 43 by wire bonding.

Next, the configuration of the control unit will be described with reference to FIG. 17 showing a block diagram of the control unit. The conductive layer patterns 42 formed on the substrate 41 are individually formed on the LSI chip 51.
It is connected to the. The clock line 52, the data line 53, the voltage line 54, and the ground line 55 are also L
It is connected to the SI chip 51. LSI chip 51
Determines which nozzle 12 should eject an ink drop, according to the data appearing on the data line 53, based on the continuous clock pulses supplied from the clock line 52. Then, 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 8 in the driven ink chamber 4. In addition, the ink chamber 4 to be driven
A voltage of 0 V on the ground line 55 is applied to the pattern 42 of the conductive layer which is electrically connected to the metal electrodes 8 other than the above.

Next, the operation of the ink ejecting apparatus 1 will be described with reference to FIGS. The LSI chip 51 determines to eject the ink from the ink chamber 4b of the ink ejecting apparatus 1 according to the required data. Then, the positive drive voltage V is applied to the metal electrodes 8e and 8f, and the metal electrode 8e
d and 8g are grounded. As shown in FIG. 19, the side wall 6
A driving electric field in the direction of the arrow 13b is generated on the side b of the side wall 6c.
A driving electric field in the direction of the arrow 13c is generated at. Then,
Since the driving electric field directions 13b and 13c are orthogonal to the polarization direction 5, the side walls 6b and 6c are rapidly deformed inward in the ink chamber 4b due to the piezoelectric thickness sliding effect. Due to this deformation, the volume of the ink chamber 4b is reduced, the ink pressure is rapidly increased, a pressure wave is generated, and an ink droplet is ejected from the nozzle 12 (FIG. 16) communicating with the ink chamber 4b.

When the application of the driving voltage V is stopped,
Since the side walls 6b and 6c gradually return to the positions before deformation (see FIG. 18), the ink pressure in the ink chamber 4b gradually decreases. Then, ink is supplied from the ink tank (not shown) into the ink chamber 4b through the ink supply port 16 (FIG. 16) and the manifold 18 (FIG. 16).

[0013]

In the ink ejecting apparatus 1 having the above-mentioned structure, the side wall 6 is integrated with the piezoelectric ceramic plate 2 as shown in FIG.
The cover plate 10 is adhered with an adhesive 20. When the surface of the cover plate 10 is smooth, the adhesive 20 is formed very thin, and the rigidity of the adhesive portion is high. If the surface of the cover plate 10 is rough, as shown in FIG. 10B, the amount of the adhesive 20 becomes large and the rigidity of the adhesive portion becomes low, so that the inside of the ink chamber 4 is ejected at the time of ink ejection. The pressure cannot be increased sufficiently and a predetermined ink droplet volume cannot be obtained. Therefore, there is a problem that the print quality is deteriorated.

The present invention has been made in order to solve the above-mentioned problems, and makes it possible to form a thin adhesive and to increase the adhesive rigidity between the side wall and the cover plate. Accordingly, it is an object of the present invention to provide an ink ejecting apparatus that keeps a pressure increase in the ink chamber 4 and has good print quality.

[0015]

In order to achieve this object, according to the present invention, a piezoelectric ceramic plate having a plurality of grooves formed therein and a cover adhered to the upper ends of the side walls of the grooves to form an ink chamber. In the ink ejecting apparatus that ejects ink in the ink chamber by deforming the plate and the side wall of each ink chamber, the surface roughness of the adhesive surface of the cover plate is at least 5 μm or less.

[0016]

In the ink ejecting apparatus of the present invention having the above structure, the surface roughness of the adhesive surface of the cover plate is sufficiently small,
Therefore, a sufficiently thin adhesive layer can be formed, and the rigidity of the adhesive portion is high.

[0017]

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.

FIG. 1 is an enlarged view of the ink inlet 16 and the manifold 18 of this embodiment. FIG. 1A is a cross section of the ink ejecting apparatus as seen from the side surface.
1B is a cross section taken along the line AA of FIG.

As shown in FIG. 1B, the ink ejecting apparatus 1 includes a piezoelectric ceramic plate 2 and a cover plate 1.
It has 0 and. The piezoelectric ceramic plate 2 has a plurality of grooves 3 and side walls 6 separating the grooves 3. Further, the cover plate 10 is provided with an ink inlet 16 and a manifold 18. Then, the piezoelectric ceramic plate 2 and the cover plate 10
And are bonded by the adhesive 20 to form the ink chamber 4 which is an ink flow path.

As shown in FIG. 1 (a), ink is indicated by an arrow 3.
As shown in 0, the ink flows from the ink tank through the ink supply tube (both not shown) into the ink introduction port 16 having the diameter d, and is supplied to each ink chamber 4 by the manifold 18. As shown in the figure, since the manifold 18 has a larger cross-sectional area than the ink introduction port 16, the ink ejected from the ink introduction port 16 to the manifold 18 is in a jet state. Therefore, a spreading loss occurs in the ink due to the rapid expansion of the flow path.
On the other hand, the total flow loss that occurs in the ink that flows into the manifold 18 from the ink introduction port 16 changes depending on the state of the jet flow. If the jet flow is laminar, the total flow loss is equal to the above-mentioned spreading loss. If the jet flow is in a turbulent state, the total flow loss is the above-mentioned spreading loss plus turbulent flow loss.

In order to reduce the total flow loss and to obtain a stable ink flow that does not include minute fluctuations, the jet state must be kept laminar. For that purpose, the Reynolds number Re, which is an important parameter that determines the state of the fluid flow, must be kept below about 30 as is well known (Author: Takefumi Ikui, Masahiro Inoue, Publisher: Science & Engineering, "Viscosity" Fluid dynamics ”, p. 206). And
The Reynolds number Re is given by the equation Re = ud / ν. In the above equation, u is the velocity of the ink ejected from the ink inlet 16, d is the diameter of the illustrated ink inlet 16, and ν is the kinematic viscosity of the ink. On the other hand, if the consumption amount of ink per unit time is determined, the flow velocity u is set to the ink inlet 1
Since it is inversely proportional to the square of the diameter d of 6, the Reynolds number Re is inversely proportional to the diameter d of the ink inlet 16 as shown in FIG.

In the present embodiment, the maximum ink consumption amount per unit time is calculated assuming that ink droplets having a volume of 40 pl are ejected simultaneously from 25 nozzles at a frequency of 5 kHz. As the kinematic viscosity coefficient ν of the ink, a value of 10 cps at room temperature of a pigment ink based on tripropylene glycol monomethyl ether (TPM) was used. And
When the Reynolds number Re was obtained by changing the value of the diameter d of the ink introduction port 16, the relationship of the solid line 32 shown in FIG. 2 was obtained.

Here, the Reynolds number Re is influenced by the consumption amount of ink per unit time and the kinematic viscosity coefficient ν of ink, in addition to the diameter d of the ink inlet port 16. However, the former cannot be made small in order to maintain the printing speed and the sharpness, and the latter cannot be greatly increased from the viewpoint of stable ejection of ink droplets, especially prevention of generation of unnecessary ink droplets, so-called satellites. Therefore, even if the relationship between the Reynolds number Re and the ink introduction port diameter d shifts to the upper right as shown by the broken line 34 in FIG. The solid line 32 calculated using the velocity and the viscosity of the ink does not shift further to the lower left.

When the lower limit of the diameter d of the ink inlet 16 is obtained using the relationship of the solid line 32 shown in FIG. 2, in order to prevent the jet flow from becoming turbulent, that is, the Reynolds number Re is 30. In order to make it below, it is better that the diameter d of the ink inlet 16 is larger, but at least 0.2 mm.
You have to do more than that.

As described above, if the diameter d of the ink introducing port 16 is formed to be 0.2 mm or more, the ink introducing port 1
The flow of ink from 6 to the manifold 18 is in a laminar flow state. Therefore, the total flow loss that occurs in the ink that flows into the manifold 18 from the ink introduction port 16 is equal to the above-mentioned spreading loss, so that the total flow loss can be minimized.
Disturbance does not occur in the ink flow in the manifold. Therefore, since the pressure of the ink in the manifold is constant,
The pressure of the ink in the ink chamber 4 is constant, and the volume and flight speed of the ejected ink droplet are constant. Therefore, the print quality is good. Further, since the amount of ink to be supplied is supplied to the ink chamber 4, the volume of the ejected ink droplet becomes a predetermined volume, and the printing quality is good.

In this embodiment, since the shape of the ink introducing port 16 was circular, the size of the ink introducing port 16 was determined with the Reynolds number Re of 30 or less. In the case of a shape such as a circle or an ellipse, the Reynolds number Re at which the ink does not become a turbulent flow may be obtained by an experiment to obtain the size of the ink inlet 16.

In the ink ejecting apparatus 1 of the present embodiment, the ratio of the pressure generated in the ink chamber 4 to the drive voltage applied to the electrode 8 is large, and the ink flowing into the ink chamber 4 is stable and received. The resistance is also small. Therefore, high pressure can be generated in the ink chamber 4 with a low driving voltage,
It is possible to eject ink droplets at a velocity and volume sufficient to form characters and images. According to an experiment using this ink ejecting apparatus 1, at a low driving voltage of about 20 to 50 volts, ink droplets can be ejected stably at a speed of 3 to 8 m / sec and a volume of about 30 to 90 pl. The cost and size can be reduced, and the cost and size of the ink ejecting apparatus 1 as a whole can be reduced.

Next, the depth of the manifold 18 will be described.

As shown in FIG. 3 (a), the ink is indicated by the arrow 3
As shown in 0, the ink flows from the ink tank through the ink supply tube (both not shown) into the ink introduction port 16 and is supplied to the ink chamber 4 by the manifold 18. At this time, in the manifold 18, each arrow 3 shown in FIG.
Ink flows as shown by 1 and is supplied to each ink chamber 4.
Since the ink chambers 4a and 4b directly face the ink introduction port 16, the pressure of the ink in the ink chambers 4a and 4b changes due to the jet flow of the ink flowing from the ink introduction port 16.

FIG. 4 shows an ink chamber 4 in which the ink jet flows out from the ink inlet 16 and directly faces the ink inlet 16.
The change of the center velocity when flowing into a and 4b is shown. In FIG. 4, the horizontal axis represents the depth h of the manifold 18, and the vertical axis represents the central velocity of the jet flow. In the experiment of this embodiment, three values of the diameter d of the ink inlet 16 are used, and the maximum ink consumption amount per unit time is 40 pl from 20 nozzles.
Of the ink droplets were simultaneously ejected at a frequency of 5 kHz. Solid lines 35, 36, and 37 in FIG. 4 are experimental results when the diameter d of the ink introduction port 16 is 0.7, 1.0, and 1.4 mm, respectively.

As is apparent from FIG. 4, the manifold 1
When the depth h of 8 is 0, the central velocity u of the jet flow when the ink is ejected from the ink inlet 16 is the largest. At this time, the central velocity u of the jet flow is, as is well known, the diameter d of the ink introduction port 16.
It is a value inversely proportional to the square of. Then, when h increases, u decreases relatively quickly, but when h is about 0.2 mm or more, and particularly when h is 0.3 mm or more, u is sufficiently decreased for any d, and further decrease is almost zero. Absent. If the diameter d of the ink inlet 16 is 0.2 mm or more, the same tendency as in FIG. 4 is obtained.

Here, since the flow velocity of the jet flow is proportional to the ink consumption amount per unit time and the ink consumption amount changes depending on the printing pattern, the effect of the jet flow of the ink flowing from the ink introduction port 16 can be sufficiently attenuated. Unless the depth h of the manifold 18 is set, the ink pressure in the ink chambers 4a and 4b directly facing the ink inlet 16 changes depending on the print pattern, and stable ink droplet ejection cannot be performed.

From the results described above, in the ink ejecting apparatus 1 of this embodiment, the depth of the manifold 18 for distributing the ink flowing from the ink introducing port 16 to each of the ink chambers 4 is 0.3 mm or more, and at least 0. It is at least 2 mm.

Thus, the manifold 18 of this embodiment is
Since the depth is 0.2 mm or more, preferably 0.3 mm or more, the ink flowing into each ink chamber 4 is stable and uniform. Therefore, when a drive voltage is applied to the electrode 8, the pressure generated in each ink chamber 4 is uniform, and it is possible to eject ink droplets of sufficient speed and uniform volume to form characters and images. Then, according to an experiment using the ink ejecting apparatus 1, the speed of the ink droplet is 3 to 8 at a driving voltage of about 20 to 50 volts.
A stable and uniform injection can be performed at m / sec and a volume of about 30 to 90 pl. In addition, the ink flowing into each ink chamber 4 is stable and uniform, and the drive circuit does not need to have a function for performing a particular correction, so that the drive circuit can be simplified and downsized, and It can be stabilized, reduced in cost, and downsized.

Next, the relationship between the sectional area of the manifold 18 and the total sectional area of the ink chamber 4 will be described.

As shown in FIG. 5 (a), the ink is indicated by arrow 3.
As shown in 0, the ink flows from the ink tank through the ink supply tube (both not shown) into the ink introduction port 16 and is supplied to the ink chamber 4 by the manifold 18. At this time, in the manifold 18, the arrows 3 shown in FIG.
Ink flows as shown by 1 and is supplied to each ink chamber 4.

Here, the manifold 18 is a rectangular channel having a cross-sectional area S1 = w × h as shown. The ink chamber 4 is a rectangular channel having a cross-sectional area S2 = b × H. When the ink flows in these flow paths, it receives flow resistance. This flow resistance generally increases in proportion to the length of the flow channel, and sharply increases as the cross-sectional area of the flow channel decreases. Manifold 18 and ink chamber 4
When the cross-sectional size changes and the aspect ratio is kept substantially constant, the flow resistance received by the unit length of the flow path of the ink is almost the same when the cross-section size changes. It is inversely proportional to the square of the cross-sectional area, and is as shown in FIG. 6, for example. However, when the vertical and horizontal lengths of the rectangle are extremely different from each other, the result is not as shown in FIG. Assuming that the vertical and horizontal lengths of the cross section of the manifold 18 and the ink chamber 4 do not differ significantly, the relationship between the cross-sectional areas of both and the flow resistance shows almost the same tendency as in FIG.

On the other hand, the ink flowing from the ink supply port 16 receives the flow resistance of both the manifold 18 and the ink chamber 4 until it reaches the nozzle (not shown). That is, the total resistance received by the ink is the sum of the resistance due to the manifold 18 and the resistance due to the ink chamber 4. As shown in FIG. 5B, for example, the ink flowing into the ink chamber 4c is
Since the flow distance in the manifold 18 is long, the ink flowing into the ink chamber 4c receives a larger flow resistance than the ink flowing into the ink chamber 4a. Furthermore, the ink inlet 16
The ink flowing to the ink chamber 4 at a position away from is subjected to a larger flow resistance.

Therefore, in order to make the ink flowing into each ink chamber 4 uniform, a manifold having the same flow resistance irrespective of the position of the ink chamber 4 is provided, or the flow resistance in the manifold 18 is changed to the ink chamber. It is possible to provide the manifold 18 having a cross-sectional area which can be ignored as compared with the flow resistance inside the nozzle 4. However, the former is generally impractical because it complicates the shape and processing of the manifold 18, so the latter will be described here.

FIG. 7 shows the change in the total flow resistance of the ink in this embodiment, where the horizontal axis represents the manifold 18.
And the cross-sectional area ratio S1 / SA of the total ink chamber 4 was taken. The sectional area SA of all the ink chambers 4 is the sectional area S2 of each ink chamber 4.
Is multiplied by the number of ink chambers 4. In the experiment of this example, the maximum ink consumption amount per unit time was calculated assuming that ink droplets having a volume of 40 pl are ejected simultaneously from 50 nozzles at a frequency of 2.5 kHz. As the kinematic viscosity coefficient ν of the ink, a value of 10 cps at room temperature of a pigment ink based on tripropylene glycol monomethyl ether (TPM) was used. The height of the ink chamber 4 is H = 4
The width was 00 μm, the width b was 80 μm, and the length was 12 mm.

A solid line 38 in FIG. 7 is a curve showing the total flow resistance of ink, and a horizontal dotted line 39 is a line showing only the resistance of the ink chamber 4 without the resistance of the manifold 18. The total flow resistance sharply increases as the cross-sectional area ratio S1 / SA is about 1 on the left side of the figure, that is, as the cross-sectional area ratio decreases. Further, when the right side in the drawing, that is, the cross-sectional area ratio increases, the total flow resistance suddenly approaches the resistance value of only the ink chamber 4 shown by the dotted line 39. That is, when the cross-sectional area ratio S1 / SA becomes 1 or less, the flow resistance in the manifold 18 sharply increases, and when the cross-sectional area ratio S1 / SA becomes 1 or more, the ratio of the flow resistance in the manifold 18 sharply decreases.

Therefore, in order to reduce the flow resistance of the manifold 18, it is necessary to set the sectional area ratio S1 / SA to 1 or more. Further, in the ink ejecting apparatus having the structure as in the present embodiment, since the ink is not ejected from the adjacent ink chambers 4 at the same time, the apparent sectional area of the ink chambers 4 becomes half. Even taking this into account, the cross-sectional area ratio S1 / S
A needs to be 0.5 or more.

On the other hand, it is good for the cross-sectional area ratio S1 / SA to be large in order to reduce the flow resistance. However, when the cross-sectional area ratio S1 / SA is about 5 or more, the flow resistance due to the manifold 18 causes the flow resistance in the ink chamber. However, it is almost 1% or less, so it can be almost ignored. Therefore, even if the cross-sectional area ratio is about 5 or more, only the ink ejecting apparatus 1 becomes large, and the effect of reducing the flow resistance can hardly be expected. From the viewpoints of downsizing of the ink ejecting apparatus 1 and cost, it is appropriate that the ratio of the cross-sectional area S1 / SA is up to 5.

In the experiment of this embodiment, the ink chamber 4
The height is H = 400 μm, width b = 80 μm, length =
Although it is set to 12 mm, even when the size of the ink chamber 4 is changed, the curve 38 showing the pressure loss in FIG.
The preferred cross-sectional area ratio S1 / SA does not change only by expanding and contracting in the vertical direction as indicated by broken lines 38a and 38b in the figure.

From the above results, in the ink ejecting apparatus 1 of the present embodiment, the sectional area of the manifold 18 for distributing the ink flowing from the ink inlet 16 to each of the ink chambers 4 is the total sectional area of the ink chamber 4. It is about 0.5 to 5 times.

As described above, since the cross-sectional area of the manifold 18 is formed to be about 0.5 to 5 times the total cross-sectional area of the ink chamber 4, the ink supplied is supplied to the manifold 1.
8 distributes each ink chamber 4 substantially evenly, and the resistance received is small. Therefore, it is possible to smoothly introduce the ink, generate a high pressure in the ink chamber 4 with a low driving voltage, and eject an ink droplet having a sufficient speed and a uniform volume to form a character or an image. You can According to an experiment using this ink ejecting apparatus, an ink droplet has a velocity of 3 at a low driving voltage of about 20 to 50 volts.
-8 m / sec., The volume can be stably ejected at about 30-90 pl, the drive circuit can be simplified and downsized, and the ink ejecting apparatus as a whole can be reduced in cost and downsized.

Next, the depth of the groove 3 and the thickness of the cover plate 10 forming the ink chamber 4 of this embodiment will be described.

FIG. 8 is a sectional view of a part of the ink ejecting apparatus 1, showing the groove 3, the side wall 6, the metal electrode 8 and the cover plate 1.
It represents the shape of 0. The width of the groove 3 formed in the piezoelectric ceramic plate 2 is b, and the depth of the groove 3 is H. In this case, since the metal electrode 8 is formed on the upper half of the side wall 6 as described above, the length from the upper end to the lower end of the metal electrode 8 is half the depth of the groove 8 H / 2. The thickness of the cover plate 10 made of the same material as the piezoelectric ceramic plate 2 is k.

The relationship between the depth H of the groove 3 which is the ink chamber 4 and the thickness k of the cover plate 10 in order to obtain the velocity of the ink droplet required for stable printing was examined.

The piezoelectric ceramic plate 2 used in the experiment has a side wall 6 having a width of 80 μm, a groove 3 having a width b of 80 μm and a depth H of 0.2 mm, and the groove 3 has a depth H of 0.4 μm.
There were three types, one with 0.6 mm. The materials of the piezoelectric ceramic plate 2 and the cover plate 10 are lead zirconate titanate (PZT) -based piezoelectric ceramics, the metal electrode 8 is an aluminum film having a thickness of about 1 μm formed by vacuum deposition, and the adhesive 20 is an epoxy-based adhesive. The agent was used. Further, the cover plate 10 has 0.25, 0.
Four types of thicknesses of 5, 1 and 2 mm are prepared and combined with the substrate having the depth H of the three types of grooves 3 to make a total of 12
A variety of ink ejection devices 1 were assembled. The ink is a pigment ink based on tripropylene glycol monomethyl ether (TPM), and the driving voltage applied to the metal electrode 8 is 40 volts. The ink ejection speed is calculated from the moving distance of the ink droplet still image when the light emitting diode is caused to emit light in synchronization with the drive voltage pulse to form a still image of the ink droplet and the light emission timing with respect to the drive voltage pulse is shifted. did.

Next, the flight speed of ink droplets was measured using the various ink jetting apparatuses 1 described above. The measurement results are shown in FIG. 9, in which the horizontal axis is the product H × k of the depth H of the groove 3 and the thickness k of the cover plate, and the vertical axis is the ink droplet flight velocity.
Solid lines 40, 42 and 44 in the figure correspond to the ink jetting apparatus 1 having groove depths H of 0.2, 0.4 and 0.6 mm, respectively.

As can be seen from FIG. 9, the flight speed of the ink drops increases as the depth H of the groove 3 increases, but in any case, the flight speed suddenly decreases when H × k becomes about 0.2 or less. turn into. The reason is that, in FIG. 8, when the side wall 6 is deformed as shown by the broken line when ink is ejected, the cover plate 10 is slightly deformed as shown by the broken line in the drawing. The larger the deformation of the cover plate 10 relative to the volume of the ink chamber 4, the more the ink chamber 4
The increase in the internal pressure is reduced, and the flight speed of the ink droplet is reduced. In order to reduce the deformation of the cover plate 10 with respect to the volume of the ink chamber 4, the depth H of the groove 3 is increased or the thickness k of the cover plate 19 is increased. That is, it is sufficient to increase H × k. As can be seen from FIG. 9, it is preferable to set H × k to 0.2 or more in order not to extremely reduce the flight speed of the ink droplet.

In the experiment of this embodiment, the width of the side wall 6 is set to 80 μm. However, even when the width of the side wall 6 is changed, the same tendency as in FIG. 9 is obtained.

Further, in the experiment of this embodiment, the width b of the groove 3 is set to 80 μm, but if the width b of the groove 3 is about 80 μm, the same tendency as in FIG. 9 is obtained.

From the above results, in the ink ejecting apparatus 1 of this embodiment, the product of the depth of the groove 3 and the thickness of the cover plate 10 is 0.2 (mm × mm) or more.

Since the product of the depth of the groove 3 and the thickness of the cover plate 10 is 0.2 (mm × mm) or more, the cover plate 10 can be deformed by the deformation of the side wall 6 as much as possible. To be prevented. Therefore, the ratio of the pressure generated in the ink chamber 4 to the drive voltage applied to the metal electrode 8 is large. Therefore, a high pressure can be generated in the ink chamber 4 with a low drive voltage, and an ink droplet having a speed and volume sufficient to form a character or an image can be ejected. According to this ink ejecting apparatus 1, the speed of the ink droplet is 3 to 8 at a driving voltage as low as 20 to 50 volts.
m / sec, the volume can be about 30 to 90 pl,
The cost and size of the drive circuit can be reduced, and the cost and size of the ink ejecting apparatus 1 as a whole can be reduced.

Next, the influence of the surface roughness of the cover plate 10 on the ink ejection characteristics will be described.

As shown in FIG. 10A, the side wall 6 is integrated with the piezoelectric ceramic plate 2, but is adhered to the cover plate 10 with an adhesive agent 20. When the surface of the cover plate 10 is smooth, the adhesive 20 is formed very thin, and the rigidity of the adhesive portion is high. If the surface of the cover plate 10 is rough, the amount of the adhesive 20 becomes large as shown in FIG.
Since the rigidity of the adhesive portion becomes low, the pressure in the ink chamber 4 cannot be sufficiently increased at the time of ink ejection, and a predetermined ink droplet volume cannot be obtained.

Here, the volume of the ejected ink droplet was measured using the cover plate 10 having various surface roughnesses.

In the ink jet device 1 used in this experiment,
The width W of the side wall 6 was 80 μm, the depth H of the groove 4 which is the height of the side wall 6 was 400 μm, and the width b of the groove 3 was 80 μm. The material of the piezoelectric ceramic plate 2 and the cover plate 10 is lead zirconate titanate (PZT) -based piezoelectric ceramics, and the metal electrode 8 has a thickness of 1 formed by vacuum deposition.
An epoxy adhesive was used for the aluminum film having a thickness of about μm and the adhesive 20. The cover plate 10 having a thickness k of 1 mm was used, and the surface roughness of the surface bonded to the side wall 6 was changed from 1 to 8 μm. Further, in order to eliminate influences other than surface roughness, the adhesive 20 was devised so as to be applied uniformly and thinly. The volume of the ink droplet was calculated by measuring the weight of a predetermined number of ink droplets using a high precision analytical balance and using the density of the ink.

As is clear from FIG. 11, when the surface roughness of the cover plate 10 is 3 μm or less, the volume of the ink droplet is the maximum and is almost constant. On the other hand, when the surface roughness is about 4 μm, the volume of the ink droplet is reduced by about 10%, and when the surface roughness is 5 μm or more, the volume of the ink droplet is reduced by 20% or more, forming the ink droplet. The efficiency is significantly reduced.

A jetting experiment using the ink jetting apparatus 1 having a size other than the above was also conducted. As a result, the absolute amount of the ink droplet volume changes, but the aspect of the change due to the surface roughness of the cover plate 10 is almost the same as that shown in FIG.

Also, even if a phenol-based adhesive other than the epoxy-based adhesive is used as the adhesive 20, the same tendency as in FIG. 11 is obtained.

From the above results, in the ink ejecting apparatus 1 of this embodiment, the surface roughness of the cover plate 10 is preferably 3 μm or less, and at least 5 μm or less.

Since the surface roughness of the cover plate 10 is 5 μm or less, preferably 3 μm or less, the ratio of the pressure generated in the ink chamber 4 to the drive voltage applied to the metal electrode 8 is large. Therefore, a high pressure can be generated in the ink chamber 4 with a low drive voltage, and an ink droplet having a speed and volume sufficient to form a character or an image can be ejected. According to this ink ejecting apparatus 1,
At a driving voltage as low as about 20 to 50 V, the speed of the ink droplet is 3 to 8 m / sec, and the volume can be set to about 30 to 90 pl, depending on the length of the ink chamber 4, thus reducing the cost of the driving circuit. The size and size of the ink ejecting apparatus 1 can be reduced, and the cost and size of the entire ink ejecting apparatus 1 can be reduced.

Next, the influence of the difference in material between the piezoelectric ceramic plate 2 and the cover plate 10 will be described.

As shown in FIG. 12A, the piezoelectric ceramic plate 2 of the ink ejecting apparatus 1 has a plurality of grooves 3 forming the ink chamber 4, and a side wall 6 separating the grooves 3 from each other. ing. The groove 3 has a width b of 80 μ
m, depth H is 400 μm, and side wall 6 has a width W of 80 μm.
m. Then, the upper surface of the side wall 6 and the cover plate 10
And are bonded by the adhesive 20. The adhesive 2
A heat-curable adhesive, for example, an epoxy adhesive is used for No. 0. The adhesive 20 is heated to about 160 ° C. and hardened. The cover plate has a thickness of 1 mm.

Since the piezoelectric ceramic plate 2 and the cover plate 10 of the ink ejecting apparatus 1 are not necessarily made of the same material, the adhesive 20 is cured and the temperature is kept at room temperature when the materials have different linear expansion coefficients. When returned to, the deformation of both becomes non-uniform. Therefore, even if the side walls 6 are bonded so as to be parallel to each other at about 160 ° C. as shown in FIG. 12A, the side walls 6 are deformed as shown in FIG. Residual stress is generated inside the agent 20, and particularly the strength of the adhesive portion is reduced.

The magnitude of the internal residual stress depends not only on the difference in linear expansion coefficient but also on the elastic modulus (Young's modulus) of the material. Since the cover plate 10 is sufficiently thicker than the side wall 6, the influence of the change in the Young's modulus due to the difference in the material of the cover plate 10 can be almost ignored.

Here, the influence of the above phenomenon on the life of the ink ejecting apparatus 1 will be examined. The linear expansion coefficient is 1, respectively
Three types of lead zirconate titanate (P, 2,4 ppm / ° C)
ZT) -based materials were used to form three types of piezoelectric ceramic plates 2 having different linear expansion coefficients. A cover plate 10 made of the same material as the piezoelectric ceramic plate 2 was formed. Furthermore, magnesia (Mg
O), zirconia (ZrO ₂ ) and alumina (AL ₂ O ₃ ) were used to form the cover plate 10. Therefore, six types of cover plates 10 having different linear expansion coefficients were formed.

Various piezoelectric ceramic plates 2 described above
Various ink ejecting apparatuses 1 are configured by using the cover plate 10 and the cover plate 10. Then, a drive pulse having a voltage level of 40 V was continuously applied to the ink ejecting apparatuses 1 at a frequency of 8 kHz. At this time, the number of drive pulses applied was measured until the ejection function of the ink ejection device 1 deteriorated and ink droplets could not be formed.

As shown in FIG. 13, the measurement result shows that when the difference in linear expansion coefficient between the piezoelectric ceramic plate 2 and the cover plate 10 is 6.0 ppm / ° C. or less, the ink ejecting apparatus 1
Has a life of 3 billion times or more, whereas when the difference in the coefficient of linear expansion reaches 8.5 ppm / ° C., the life decreases to 2 billion times. Then, it can be seen that the life is more remarkably reduced when the difference between the linear expansion coefficients is further increased.

Although an epoxy type was used for the adhesive 20,
If it is a heat-curable adhesive, even if it is a phenol-based adhesive, the same tendency as in FIG. 13 is obtained.

From the above results, in the ink ejecting apparatus 1 of this embodiment, the difference in the coefficient of linear expansion between the piezoelectric ceramic plate 2 and the cover plate 19 is 8.5 ppm / ° C. or less, preferably 6.0 ppm / ° C. or less. is there.

Thus, the piezoelectric ceramic plate 2
Of the linear expansion coefficient between the cover plate 19 and the cover plate 19 is 8.5 pp
In the ink jetting apparatus 1 having m / ° C. or less, preferably 6.0 ppm / ° C. or less, the jetting life is 3 billion times, which is sufficiently large for practical use, and at least about 2 billion times. It can also be applied to the printing of graphics, which requires a large number of jets. Therefore, the number of times the ink ejecting apparatus 1 is replaced is reduced, and the reliability of the printing apparatus is high.

Next, the relative position between the ink chamber 4 and the manifold 18 will be described.

FIG. 14 is a cross section as viewed from the side of the ink ejecting apparatus. Ink flows from an ink tank through an ink supply tube (both not shown) as shown by an arrow 30 into an ink inlet 16 and is distributed to each ink chamber 4 by a manifold 18. In the ink ejecting apparatus 1 used in the experiment, the materials of the piezoelectric ceramic plate 2 and the cover plate 10 are both lead zirconate titanate (P
ZT) -based piezoelectric ceramics were used. The total length L of the ink chamber 4 is 17 mm, and in order to investigate the volume change of the ink droplet due to the change in the relative position between the manifold 18 and the ink chamber 4, the front side face of the manifold 18 and the rear end face of the ink chamber 4 in the figure are examined. Those having different values of the relative position x were prepared. The depth h of the manifold 18 was 0.5 mm, and the width w thereof was 5 mm. The volume of the ink droplet was calculated by using the density of the ink by jetting a predetermined number of ink droplets using a high precision analytical balance and measuring the weight.

Next, the manifold 18 and the ink chamber 4
The volume of ink droplets ejected by the ink ejecting apparatus 1 was measured using a plurality of ink ejecting apparatuses 1 having different relative positions from. The measurement results are shown in FIG. 15. The horizontal axis represents the relative position x between the manifold 18 and the ink chamber 4, and the vertical axis represents the volume of the ink droplet. As can be seen from FIG. 15, x is 1
The maximum ink droplet volume is 60 pl between mm and 6 mm
Reached almost constant.

When x becomes 1 mm or less, the volume of the ink drop suddenly decreases, and when x is about 0.2 mm, the ink cannot be ejected. This is because there is only 1 mm where the manifold 18 and the ink chamber 4 overlap when x = 1, and if x is made smaller, it becomes difficult for the ink to suddenly flow into the ink chamber 4.

On the other hand, when x is 6 mm or more, the volume of the ink droplet decreases, although not so suddenly. This is because when x increases, the manifold 18 approaches the nozzle plate 14, and the distance y between the front surface of the manifold 18 and the nozzle plate 14 decreases. That is, when the pressure in the ink chamber 4 is increased to eject an ink droplet, the ink is pushed out from the nozzle 12 and at the same time the manifold 18 is ejected.
Also, the ink flows back to the ink introduction port 16, the pressure in the vicinity of the manifold 18 decreases sharply, and a negative pressure wave is generated. When this negative pressure wave reaches the nozzle 12, the outflow of ink from the nozzle 12 is stopped, but the shorter the y, the shorter the time for the negative pressure wave to reach the nozzle 12. For this reason, the outflow of ink is stopped quickly, and as a result, the volume of the ink droplet is reduced.

From FIG. 15, x is about 11 mm (y = L−x =
6mm), the volume of the ink drop is about half, 30pl,
Further, if x = 14 mm or more (y = 3 mm or less),
Ink droplets cannot be ejected. Therefore, the relative position between the manifold 18 and the ink chamber 4 is such that x is 0.2 mm or more and y is 3 mm, considering that the volume of the ink droplet can be adjusted to some extent by adjusting the applied drive pulse.
As described above, y is preferably 6 mm or more.

The depth h of the manifold 18 is 0.5 m.
Although the m and the width w were 5 mm, the same tendency as in FIG. 15 is exhibited even if the dimensions of the manifold 18 are changed.

Even if the total length L of the ink chamber 4 is other than 17 mm, the same tendency as in FIG. 15 is exhibited.

From the above results, in the ink ejecting apparatus 1 of the present embodiment, at the position of the manifold 18 formed on the cover plate 10, the distance between the front side surface and the rear end surface of the ink chamber 4 is 0.2 mm. Above, and nozzle plate 1
The distance from 4 is 6 mm or more, and at least 3 mm or more.

As described above, the distance between the front side surface of the manifold 18 and the rear end surface of the ink chamber 4 is 0.2 mm or more, and the distance between the front side surface of the manifold 18 and the nozzle plate 14 is 6 mm or more, and at least 3 mm or more. Therefore, the ink droplets can be efficiently ejected, the ink can be replenished smoothly, and the ink droplets can be ejected at a speed and volume sufficient to form a character or an image. According to this ink ejecting apparatus 1, at a low driving voltage of about 20 to 50 V, the speed of the ink droplet is 3 to 8 m / sec,
The volume can be set to about 30 to 90 pl, the cost and size of the drive circuit can be reduced by low voltage driving, and the cost and size of the ink ejecting apparatus 1 as a whole can be reduced.

The present invention is not limited to the embodiments described in detail above, and modifications can be made without departing from the spirit of the invention.

In the present embodiment, the ink in the ink chamber 4 is ejected by the deformation of the side wall 6 which is a piezoelectric ceramic in the shear mode, but the ejection method such as the above-mentioned Kaiser type or thermal jet type may be used. Good.

[0088]

According to the ink ejecting apparatus of the present invention, since the surface roughness of the adhesive surface of the cover plate is 5 μm or less, the thickness of the adhesive layer for adhering the side wall and the cover plate can be made sufficiently thin, and the adhesive portion Has high rigidity. Therefore, when the side wall is deformed, a sufficient pressure can be generated in the ink chamber. Therefore, the volume of the ink droplet and the flying speed required for printing can be obtained, and the printing quality is good.

[Brief description of drawings]

FIG. 1A is a sectional view showing an ink ejecting apparatus according to an embodiment of the present invention. (B) is an AA sectional view of (a).

FIG. 2 is a relationship diagram of a diameter of an ink inlet and a Reynolds number in the embodiment.

FIG. 3A is a cross-sectional view showing the ink ejecting apparatus of the above embodiment. (B) is an AA sectional view of (a).

FIG. 4 is a relationship diagram of a manifold and a jet flow center flow velocity in the embodiment.

FIG. 5A is a sectional view showing the ink ejecting apparatus of the embodiment. (B) is an AA sectional view of (a).

FIG. 6 is a relationship diagram of a flow passage cross-sectional area and pressure loss.

FIG. 7 is a relationship diagram of the pressure loss and the ratio of the cross-sectional area of the manifold and the ink chamber of the embodiment.

FIG. 8 is a cross-sectional view showing the ink ejecting apparatus of the above embodiment.

FIG. 9 is a relationship diagram of a product of an ink chamber and a thickness of a cover plate and a droplet velocity in the embodiment.

FIG. 10A is a cross-sectional view showing an ink ejecting apparatus in which the cover plate of the embodiment has a smooth surface. (B)
FIG. 4 is a cross-sectional view showing an ink ejecting apparatus having a cover plate with a rough surface in the above-mentioned embodiment.

FIG. 11 is a relationship diagram of the surface roughness and the ink droplet volume of the cover plate of the above embodiment.

FIG. 12A is a cross-sectional view showing an ink ejecting apparatus when the adhesive of the embodiment is heated and cured.
FIG. 6B is a sectional view showing the ink ejecting apparatus at room temperature according to the embodiment.

FIG. 13 is an explanatory diagram showing a result of a durability test of the ink ejecting apparatus according to the embodiment.

FIG. 14 is a cross-sectional view showing the ink ejecting apparatus of the embodiment.

FIG. 15 is a relational diagram of the position of the manifold and the ink droplet volume in the above embodiment.

FIG. 16 is a perspective view showing a conventional shear mode type ink jet device.

FIG. 17 is an explanatory diagram showing a conventional control unit.

FIG. 18 is a cross-sectional view showing a conventional shear mode type ink jet device.

FIG. 19 is an explanatory diagram showing an operation of the conventional shear mode type ink jet device.

[Explanation of symbols]

 2 piezoelectric ceramics plate 4 ink chamber 6 side wall 10 cover plate 16 ink inlet port 18 manifold

Claims (1)

[Claims] 1. A piezoelectric ceramic plate having a plurality of grooves formed therein, a cover plate adhered to an upper end of a side wall of the groove to form an ink chamber, and a side wall of each of the ink chambers being deformed. In the ink ejecting apparatus for ejecting ink in the ink chamber, the surface roughness of the adhesive surface of the cover plate is at least 5
An ink ejecting apparatus having a thickness of not more than μm.