JP2002001965A - Ink jet head and ink jet recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize jet volume of ink as consistently as possible even though a taper angle θ of a taper portion 14a varies to some extent when a nozzle 14 to jet ink in a pressure chamber 4 toward a recording paper 41 is to be formed of the taper portion 14a and a straight portion 14b. SOLUTION: The nozzle 14 is designed to have the taper portion 14a with a taper angle θ of 50 deg. to 110 deg. (preferably 60 deg. to 90 deg.).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the technical field of an ink jet head for discharging ink in a pressure chamber from a nozzle and an ink jet recording apparatus provided with the ink jet head.

[0002]

2. Description of the Related Art Conventionally, an ink jet head in which ink in a pressure chamber is ejected from a nozzle is well known. The ink jet head includes a pressure chamber filled with ink, and a nozzle communicating with the pressure chamber. And a pressure applying means such as a piezoelectric actuator for applying pressure to the pressure chamber and ejecting the ink in the pressure chamber from the nozzle.

In the above-described ink jet head,
Since the shape of the nozzle greatly affects the ink ejection performance, for example, as shown in JP-A-6-246918, by setting the nozzle to a tapered shape and setting the taper angle within a predetermined range, It has been proposed to stably improve the ink ejection speed (flying speed).

Further, in the above proposed example, since the nozzle has only a tapered portion, it is difficult to improve the dimensional accuracy of the nozzle diameter (minimum diameter of the tapered portion) at the nozzle tip in processing the tapered portion. If the dimensional accuracy is poor, the ink ejection amount will vary.
As disclosed in Japanese Patent Publication No. 2358, it is known to provide a straight portion that can be easily machined with high precision at the nozzle tip side of the tapered portion.

[0005]

However, in the nozzle including the tapered portion and the straight portion as described above,
Although the diameter of the nozzle at the tip of the nozzle can be stabilized by the straight portion, the ink ejection amount fluctuates due to variations in the taper angle of the tapered portion, and there is room for improvement in stabilizing the ink ejection amount. In particular, when a large number of nozzles are provided while reducing the size of the ink jet head, and the discharge amount is considerably reduced to increase the resolution, it is necessary to stabilize the discharge amount of the ink discharged from each nozzle as much as possible. However, it is difficult to keep the variation of the tapered portions of many nozzles small, and if the tapered portions are to be finished with high accuracy, the productivity will be reduced.

[0006] The present invention has been made in view of the above point, and an object thereof is to provide a nozzle having a tapered portion and a straight portion as described above, in which the taper angle of the tapered portion is reduced. An object of the present invention is to stabilize the ink discharge amount as much as possible even if there is some variation.

[0007]

In order to achieve the above object, according to the present invention, the taper angle of the tapered portion of the nozzle is set to 50 ° to 110 °.

Specifically, according to the first aspect of the present invention, a pressure chamber filled with ink, a nozzle communicating with the pressure chamber,
The present invention is directed to an inkjet head including pressure application means for applying pressure to the pressure chamber and discharging ink in the pressure chamber from the nozzle.

The nozzle comprises a tapered portion in which the nozzle diameter decreases toward the nozzle tip and a straight portion provided on the nozzle tip of the tapered portion. , 50 ° ~ 110 °
It is assumed that is set to

That is, if the taper angle of the tapered portion of the nozzle is smaller than 50 ° or larger than 110 °, the discharge amount of the ink discharged from the nozzle fluctuates considerably due to a manufacturing error of the taper angle. , 50
° to 110 °. Therefore, even if the taper angle of the tapered portion slightly varies, the ink discharge amount can be stabilized, and when a large number of nozzles are provided, the resolution can be improved while improving the productivity of the inkjet head.

According to a second aspect of the present invention, in the first aspect, the taper angle of the tapered portion of the nozzle is 60 ° to 90 °.
°.

[0012] This makes it possible to further stabilize the ink discharge amount, stabilize the ink discharge direction, and improve the accuracy of the landing position of the ink on the recording paper. Therefore, the resolution can be further increased, and the stability of the image quality can be improved.

According to a third aspect of the present invention, there is provided an ink jet recording apparatus. In the present invention, the ink jet head according to the first or second aspect and a relative moving means for relatively moving the ink jet head and a recording medium are provided. Prepared,
When the ink jet head is relatively moving with respect to the recording medium by the relative moving means, the ink is ejected from the nozzles of the head body of the ink jet head onto the recording medium to perform recording. .
According to this invention, the same function and effect as those of the first or second invention can be obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 schematically illustrates an ink jet recording apparatus according to an embodiment of the present invention. The ink jet recording apparatus includes an ink jet head 1 that discharges ink onto a recording paper 41 as a recording medium as described later. . This ink jet head 1 has a carriage 3
The carriage 31 is provided with a carriage motor (not shown). The carriage motor extends the inkjet head 1 and the carriage 31 in the main scanning direction (X direction shown in FIGS. 1 and 2). It is guided by the carriage shaft 32 and reciprocates in that direction. The carriage 31, the carriage shaft 32, and the carriage motor constitute a relative moving unit that relatively moves the inkjet head 1 and the recording paper 41.

The recording paper 41 is sandwiched between two transport rollers 42 that are driven to rotate by a transport motor (not shown). The sheet is transported in a sub-scanning direction (Y direction shown in FIGS. 1 and 2) perpendicular to the main scanning direction.

As shown in FIGS. 2 to 4, the ink jet head 1 has a plurality of pressure chamber recesses 3 having a supply port 3a for supplying ink and a discharge port 3b for discharging ink. Head body 2.
The recesses 3 of the head main body 2 are opened on the upper surface of the head main body 2 so as to extend in the main scanning direction, and are arranged side by side at substantially equal intervals in the sub scanning direction. The entire length of the opening of each recess 3 is set to about 1500 μm, and the width is set to about 150 μm. Note that both ends of the opening of each of the recesses 3 have a substantially semicircular shape.

The side wall of each recess 3 of the head body 2 is
The first substrate 6 is made of a photosensitive glass having a thickness of about 200 μm, and the bottom wall of each recess 3 is made of a second substrate 7 bonded and fixed to the lower surface of the first substrate 6. The second substrate 7 is made of stainless steel having a thickness of about 30 μm, and the supply port 3a and the discharge port 3b are formed in the second substrate 7.

On the lower surface of the second substrate 7, about 300 μm
A third substrate 8 made of thick stainless steel is adhered and fixed, and the third substrate 8 has one supply ink flow path 1 connected to the supply port 3a of each of the recesses 3 and extending in the sub-scanning direction.
1 and a plurality of ejection ink flow paths 12 respectively connected to the ejection ports 3b. The supply ink flow path 11 is connected to an ink tank (not shown), and ink is supplied from the ink tank into the supply ink flow path 11. In addition, the supply port 3 of each of the concave portions 3
a, the ejection port 3b, and the ejection ink flow path 12 are formed in a circular cross section, the diameter of the supply port 3a is set to about 30 μm, and the diameter of both the ejection port 3b and the ejection ink flow path 12 is set to about 180 μm. Have been.

On the lower surface of the third substrate 8, a fourth substrate 9 constituting the lower surface of the ink jet head 1 is adhered and fixed. The fourth substrate 9 is made of stainless steel having a thickness of about 70 μm, and has a plurality of nozzles 14 for discharging ink droplets toward the recording paper 41. The nozzles 14 are respectively connected to the ejection ink flow paths 12, and communicate with the ejection ports 3 b of the recesses 3 via the ejection ink flow paths 12, respectively. Are provided in a row in the sub-scanning direction.

As shown in FIG. 5, each of the nozzles 14
A taper portion 14a in which the nozzle diameter decreases toward the nozzle tip side (increases toward the pressure chamber 4 described later);
And a straight portion 14b provided continuously on the nozzle tip side of the tapered portion 14a. Nozzle diameter of this straight part 14b (minimum nozzle diameter of the tapered part 14a)
Is about 20 μm, and its length L may be set to about 1 to 10 μm.

The taper angle θ of the tapered portion 14a is 5
It is set to 0 ° to 110 °. This means that if less than 50 ° or greater than 110 °, the taper angle θ
This is because the slightest manufacturing error causes the amount of ink ejected from the nozzles 14 to fluctuate considerably (see the later-described embodiment). A more desirable range of the taper angle θ of the tapered portion 14a is 60 ° to 90 °.

Above each recess 3 of the head body 2,
Each of the piezoelectric actuators 21 is provided. Each of the piezoelectric actuators 21 is an approximately 4 μm-thick Cr diaphragm 22 that covers the recesses 3 of the head body 2 and forms a pressure chamber 4 together with the recesses 3 in a state of being adhered and fixed to the upper surface of the head body 2. have. The vibrating plate 22 is made of one common to all the piezoelectric actuators 21 and also serves as a common electrode common to all the piezoelectric elements 23 described later.

Each of the piezoelectric actuators 21 includes:
On the side surface (upper surface) of the vibration plate 22 opposite to the pressure chamber 4, a portion corresponding to the pressure chamber 4 (a portion facing the opening of the concave portion 3) is joined and lead zirconate titanate (P
ZT) and a piezoelectric element 23 (piezoelectric constant 8
( ^{Approximately} × 10 ⁻¹¹ m / V), and the piezoelectric element 23 is bonded to the side (upper surface) of the piezoelectric element 23 opposite to the vibration plate 22, and a voltage (drive voltage) is applied to the piezoelectric element 23 together with the vibration plate 22. And a Pt individual electrode 24 having a thickness of about 0.1 μm. The piezoelectric elements 23 and the individual electrodes 24 are provided so as to extend in the same direction (main scanning direction) as the opening of the recess 3 at a substantially central portion in the width direction of the opening of the recess 3 of the head body 2 in a state where they overlap each other. And
Its length is set to about 1440 μm, and its width is set to about 90 μm, and both ends are substantially semicircular like the opening of the recess 3. The vibration plate 22, the piezoelectric element 23, and the individual electrodes 24 are formed of a thin film by a sputtering method, as shown in a manufacturing method described later.

Each of the piezoelectric actuators 21 applies a drive voltage to each of the piezoelectric elements 23 via the vibration plate 22 and each of the individual electrodes 24 to thereby control the pressure chamber 4 of the vibration plate 22.
Is deformed so that the ink in the pressure chamber 4 is discharged from the ejection port 3b or the nozzle 1
4 is ejected. That is, when a pulse-like voltage is applied between the vibration plate 22 and the individual electrode 24, the rising of the pulse voltage causes the piezoelectric element 23 to contract in the width direction perpendicular to the thickness direction due to the piezoelectric effect. Since the plate 22 and the individual electrodes 24 do not shrink, the portion of the vibration plate 22 corresponding to the pressure chamber 4 is bent and deformed toward the pressure chamber 4 due to the so-called bimetal effect. Due to this bending deformation, a pressure is generated in the pressure chamber 4, and the ink in the pressure chamber 4 is ejected as ink droplets from the nozzle 14 to the recording paper 41 via the ejection port 3 b and the ejection ink flow path 12 by this pressure. Is attached to the recording paper 41 in the form of dots. Thus, each piezoelectric actuator 21 constitutes a pressure application unit that applies pressure to the pressure chamber 4 and discharges the ink in the pressure chamber 4 from the nozzle 14. When the pulse voltage falls, the piezoelectric element 23 expands, and the portion of the vibration plate 22 corresponding to the pressure chamber 4 returns to the original state.
The inside is filled with ink from the ink tank via the supply ink flow path 11 and the supply port 3a. The pulse voltage applied to each piezoelectric element 23 is not limited to the push-pull type as described above, but may be the first voltage to the first voltage.
May be a push-pull type in which the voltage falls to a second voltage lower than the first voltage and then rises to the first voltage.

The driving voltage is applied to each of the piezoelectric elements 23 for a predetermined time (for example, when the ink jet head 1 and the carriage 31 are moved at a substantially constant speed from one end to the other end of the recording paper 41 in the main scanning direction. It is performed every 50 μs (drive frequency: 20 kHz) (however, no voltage is applied when the ink jet head 1 reaches a position on the recording paper 41 where ink droplets do not land),
As a result, ink droplets land on predetermined positions of the recording paper 41. When printing for one scan is completed, the recording paper 41 is conveyed by a predetermined amount in the sub-scanning direction by the conveying motor and the respective conveying rollers 42, and the ink droplets are again moved while the inkjet head 1 and the carriage 31 are moved in the main scanning direction. Is ejected to perform printing for one new scan. By repeating this operation, a desired image is formed on the entire recording paper 41.

Next, a schematic procedure of the method of manufacturing the ink jet head 1 will be described with reference to FIG.
In FIG. 6, the vertical relationship between the ink jet head 1 and FIGS. 3 and 4 is reversed.

First, Pt is formed on the entire surface of the MgO film forming substrate 51.
A film 52 is formed by a sputtering method (see FIG. 6A),
Thereafter, a PZT film 53 is formed on the entire Pt film 52 by a sputtering method (see FIG. 6B). Then, a Cr film 54 is formed on the entire PZT film 53 by a sputtering method (see FIG. 6C).

Next, the first substrate 6 of the head main body 2 (having holes for forming the recesses 3 in advance) is bonded and fixed to the upper surface of the Cr film 54 (see FIG. 6D). Thereafter, the film-forming substrate 51 is melted and removed with hot phosphoric acid, KOH, or the like, and the second to fourth substrates 7 formed in a predetermined shape in advance on the first substrate 6 and integrated with each other by bonding.
9 are adhered and fixed (see FIG. 6E).

Subsequently, the Pt film 52 and the PZT film 53
Is divided for each pressure chamber 4 by a dry etching method such as an ion milling method or a reactive ion etching method, so that the individual electrode 24 and the piezoelectric element 23 having a predetermined shape can be obtained, and unnecessary portions of the Cr film 54 can be removed. By removing by a dry etching method, a diaphragm 22 having a predetermined shape is obtained (see FIG. 6F).

Next, although not shown, each individual electrode 2
4 and other necessary processing, the ink jet head 1 is completed.

Therefore, in the above embodiment, the nozzle 1
4 has a taper angle θ of 50 ° to 110 °.
, The ink ejection amount can be stabilized even if the taper angle θ slightly varies due to manufacturing errors. As a result, a large number of nozzles 14 having the tapered portion 14a can be easily processed. Therefore, the resolution can be increased while increasing the productivity of the inkjet head 1. Further, a low driving voltage is required to obtain the same ejection amount, and the driving voltage of the piezoelectric actuator 21 can be reduced.

If the taper angle θ is set at 60 ° to 90 °, the ink discharge amount can be further satisfactorily stabilized, and the ink discharge direction can be stabilized. Landing position accuracy can be improved. Therefore, the resolution can be further increased, and the stability of the image quality can be improved.

In the above embodiment, the vibration plate 22, the piezoelectric element 23 and the individual electrode 24 of each piezoelectric actuator 21 are used.
Was formed in a thin film by a sputtering method, but may be formed in a thin film by another method such as a CVD method or a sol-gel method,
Instead of a thin film, the vibration plate 22 or the piezoelectric element 23 formed in a predetermined shape in advance may be bonded by bonding. However, when the piezoelectric actuator 21 is formed of a thin film as in the above embodiment, a large number of piezoelectric actuators 21 can be easily and accurately formed by sputtering and etching, and the productivity of the inkjet head 1 can be further improved. .

In the above embodiment, the diaphragm 22 is
Although one common element is used for all the piezoelectric actuators 21, the vibration plate 22 may be provided individually for each piezoelectric actuator 21 like the piezoelectric element 23 or the individual electrode 24. The diaphragm 22 may not be used also as an electrode, and an electrode may be separately provided between the piezoelectric element 23 and the diaphragm 22.

Further, in the above embodiment, the plurality of nozzles 14 are provided in the ink jet head 1 and the plurality of pressure chambers 4 and the piezoelectric actuators 21 are provided correspondingly. The present invention can be applied to a single actuator 21 or the like.

In the above-described embodiment, the piezoelectric actuator 21 is used as the pressure applying means for applying pressure to the pressure chamber 4 and discharging the ink in the pressure chamber 4 from the nozzle 14. However, the present invention is not limited to this. Any of the above may be used.

In addition, other various modifications are possible. For example, the vibration plate 22, the piezoelectric element 23, and the individual electrode 24 of the piezoelectric actuator 21 may be made of a material and a thickness different from those of the above embodiment. Alternatively, the first to fourth substrates 6 to 9 of the head main body 2 may be made of a material and a thickness different from those of the above embodiment.

The straight portion 14b of each nozzle 14
The present invention is not limited to a completely straight shape, and the present invention can be applied even if the taper angle is formed to be 10 ° or less due to a manufacturing error or the like. In this case, as long as the taper angle is 10 ° or less, the straight portion 14b may be expanded toward the nozzle tip side, or may be expanded toward the pressure chamber 4 side.

[0039]

Next, a specific embodiment will be described. First, an ink jet head having the same configuration as the above-described embodiment (the dimensions such as the thickness and size of each component are the same as the numerical values shown in the above-described embodiment) and having different taper angles θ of the nozzle taper portion. Were produced (θ = 3
0 °, 44 °, 60 °, 76 °, 90 °, 100 °, 1
10 °). In addition, the straight part of the nozzle was formed in a substantially perfect straight, and the length L was 5 μm.

Next, a drive voltage (push-pull type) was applied to the piezoelectric actuators of the above seven types of ink jet heads, and ink was ejected from the nozzles. At this time, the drive voltage applied to the piezoelectric actuator was changed to change the ink discharge amount, and the ink discharge amount and the ink discharge speed (flying speed) were measured. Also, each taper angle θ
With respect to the above, the required applied voltage (maximum pulse voltage) when the ink ejection amount was set to 15 pl was measured.

FIG. 7 shows the relationship between the ink ejection amount and the ink ejection speed, and FIG. 8 shows the relationship between the taper angle θ and the required applied voltage.

As a result, the ink ejection amount and the ink ejection speed are in a substantially proportional relationship irrespective of the taper angle θ, and the taper angle θ can be set in any manner based on this relationship.
However, as can be seen from the relationship between the taper angle θ and the required applied voltage, the taper angle θ is smaller than 50 ° or 11
When the angle is larger than 0 °, the required applied voltage is larger than when the taper angle θ is 50 ° to 110 ° and the taper angle θ
When the taper angle θ is in the range of 50 ° to 110 °, the required applied voltage is small and hardly changes with respect to the change of the taper angle θ.
In the range of ９０90 °, the required applied voltage is smaller and stable. That is, in an actual use state in which the drive voltage is constant, the taper angle θ is set to 50 ° to 110 ° (particularly, 60 ° to 110 °).
90 °), the ink discharge amount hardly changes even if the set value fluctuates due to a manufacturing error, and the target discharge amount can be stabilized. In addition, a low drive voltage is required to obtain the same ejection amount.

When observing the flight trajectory of the ink ejected from the nozzle, the taper angles θ are 100 ° and 110 °.
In the case of °, a phenomenon was observed in which the ink did not fly straight in the nozzle axis direction but was slightly bent. Therefore, if the taper angle θ is set in the range of 60 ° to 90 °, in addition to the effect of stabilizing the ink ejection amount and lowering the driving voltage of the piezoelectric actuator, the ink ejection direction is set in the nozzle axis direction. This can stabilize the ink and improve the accuracy of the impact position of the ink on the recording paper.

[0044]

As described above, according to the ink jet head and the ink jet recording apparatus of the present invention,
By setting the taper angle of the tapered portion of the nozzle to 50 ° to 110 °, the ink ejection amount can be stabilized regardless of the variation of the taper angle of the tapered portion. The resolution can be improved while increasing the productivity of the head.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an ink jet recording apparatus according to an embodiment of the present invention.

FIG. 2 is a partial bottom view of the inkjet head.

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a sectional view taken along line IV-IV of FIG. 2;

FIG. 5 is an enlarged sectional view showing details of a nozzle.

FIG. 6 is a schematic explanatory view showing a method for manufacturing an ink jet head.

FIG. 7 is a graph showing a relationship between an ink ejection amount and an ink ejection speed.

FIG. 8 is a graph showing a relationship between a taper angle of a tapered portion of a nozzle and a required applied voltage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink-jet head 4 Pressure chamber 14 Nozzle 14a Taper part 14b Straight part 21 Piezoelectric actuator (pressure applying means) 31 Carriage (relative moving means) 32 Carriage shaft (relative moving means) 41 Recording paper (recording medium)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koji Matsuo 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F-term (reference) 2C057 AF23 AF93 AG02 AG12 AN01 AP71 AQ06 BA04 BA14

Claims (3)

[Claims] A pressure chamber filled with ink; a nozzle communicating with the pressure chamber; and a pressure applying means for applying pressure to the pressure chamber to discharge ink in the pressure chamber from the nozzle. In the ink jet head, the nozzle includes a tapered portion in which a nozzle diameter decreases toward a nozzle tip side, and a straight portion provided on the nozzle tip side of the tapered portion, and a taper angle of the tapered portion of the nozzle. But 50 ° ~ 110
An inkjet head characterized by being set to °. 2. The ink jet head according to claim 1, wherein the taper angle of the tapered portion of the nozzle is set to 60 ° to 90 °. 3. An ink jet head according to claim 1, further comprising: a relative moving means for relatively moving the ink jet head and the recording medium, wherein the relative moving means moves the ink jet head relative to the recording medium. An ink jet recording apparatus configured to eject ink from a nozzle of a head body of the ink jet head onto a recording medium to perform recording.