JP3021820B2 - Droplet ejector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid droplet ejecting apparatus,
In particular, the present invention relates to an improvement in a printer head (droplet ejecting device) using a piezoelectric element that is deformed by a piezoelectric thickness-shear effect as a piezoelectric transducer.

[0002]

2. Description of the Related Art In recent years, a printer head using a piezoelectric ink jet has been proposed. This type of printer head changes the volume of the ink flow path based on the dimensional displacement of the piezoelectric actuator, so that the ink in the ink flow path is ejected from the orifice when the volume decreases, and conversely, from the other valve when the volume increases. The ink is introduced into the ink flow path, and is called a drop-on-demand method. A large number of such ejecting devices are arranged close to each other, and ink is ejected from an ejecting device at a predetermined position to form a desired character or image.

[0003] Japanese Patent Application No. 3-54669 (Japanese Unexamined Patent Application Publication No. Hei.
No. 90750) . FIG. 6 is a cross-sectional view of an example of the array of the droplet ejecting apparatus. As shown in FIG. 6, one ink flow path 4 is surrounded by six deformable side walls 5, which are polarized in the direction of the ink flow path 4 (perpendicular to the plane of the drawing) and A driving electric field is applied through the electrode 6 in the thickness direction. Since the direction of polarization and the direction of the driving electric field are orthogonal,
The six side walls 5 are deformed to the inside of the ink flow path 4 by the deformation in the piezoelectric thickness-shear mode, and increase the ink pressure in the ink flow path 4 to eject droplets from an orifice (not shown).

In this liquid drop ejecting apparatus, as described above, a plurality of through holes are provided in a piezoelectric element, polarization is performed in a penetrating direction, and driving electrodes are provided on the surface of the through holes to provide a multi-head, high resolution head, and the like. The miniaturization and the simple structure are achieved, and the manufacturing cost is reduced.

[0005]

However, the above-described conventional liquid droplet ejecting apparatus (Japanese Patent Application No. 3-54669 (Japanese Unexamined Patent Application Publication No.
No. -290750 ) has a problem that the required driving voltage greatly changes depending on the shape of the side wall of the ink flow path made of piezoelectric ceramics. For example, in the case of the conventional example shown in FIG. 6, when the six side walls 5 are deformed to the inside of the common ink flow path 4 at the time of driving, the contacts of the adjacent side walls 5 (a regular hexagonal cross section of the ink flow path 4) are formed. (A vertex portion) hardly deforms to the inside of the ink flow path 4 and becomes a fixed end, so that a high driving voltage is required to deform the side wall 5 by the thickness shear deformation.

As a means for solving such a problem, it is effective to increase the distance between the fixed ends, that is, to increase the side wall in the direction perpendicular to the flow path direction. However, there arises a problem that the printing resolution is reduced, the strength of the side wall is reduced, and the reliability of the apparatus is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a high-resolution, low-cost, low-cost manufacturing apparatus capable of driving at a low voltage with high strength and reliability. The purpose is to:

[0008]

According to the present invention, in order to achieve the above object, a plurality of ink flow paths are arranged in parallel with the polarization direction of a piezoelectric transducer, and the ink flow paths are driven perpendicular to the polarization directions in the individual ink flow paths. A droplet ejecting apparatus which deforms the piezoelectric transducer by applying an electric field to change the volume of an ink flow path, thereby jetting ink retained in the ink flow path, wherein the ink ejected from the adjacent ink Of the side walls formed by the piezoelectric transducer between the flow paths,
Distribution of the plurality of ink flow paths as opposed side walls in the direction of arrangement of said plurality of ink flow paths intersect at an acute angle to one another
Configured so as to be inclined with respect to the column direction.

[0009]

According to the present invention, for example, as shown in FIG. 2B, when the cross section of the ink flow path is formed as an isosceles triangle,
Extensions of opposing side walls intersect. In this way, L
Since / W can be 3 or more, the driving voltage can be suppressed low. Further, since the angle of the side wall with respect to the ink flow path array 15 is set to, for example, 72 degrees, the width W of the side wall required to be deformed into a “C” is secured, and the ink flow path arrangement is performed.
Dimensions of the column direction (direction of electric field application) 15 can be kept low.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments. Note that the same portions and equivalent portions as those described in FIG. 6 are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1A is a cross-sectional view of an array 1 used in a piezoelectric droplet ejecting apparatus, and FIG. 1B is a vertical cross-sectional view of the array 1 (XX vertical cross-sectional view in FIG. 1A). ). As shown in FIGS. 1A and 1B, the array 1 is formed by joining an upper piezoelectric ceramic plate 2 and a lower piezoelectric ceramic plate 3 together.

The upper piezoelectric ceramics plate 2 is subjected to polarization processing in the direction of arrow 26 (polarization direction) and has a height of 0.75.
11 mm thick, 0.5 mm bottom isosceles triangular cross-section through holes with a center-to-center distance of 0.5 mm. 1.
It is a 5 mm plate.

The lower piezoelectric ceramic plate 3 is polarized in the direction of arrow 28 and has a through hole having a height of 0.75 mm and a base of 0.5 mm having an isosceles triangular cross section, similarly to the upper piezoelectric ceramic plate 2. This is a 1.5 mm-thick plate in which 11 pieces are arranged in the horizontal direction 15 with the distance between them being 0.5 mm and every other piece is turned upside down and arranged in two rows in the vertical direction.

The ink flow path 4 formed by the through holes has a flow path length of 3.0 mm, and the flow path is arranged in an ink flow path arrangement.
The side walls 5 and 7 of the two piezoelectric ceramic plates 2 and 3 divided in the direction (the horizontal direction) 15 have an angle of about 72 degrees with respect to the ink flow path arrangement direction 15 and have a width of about 0.24 mm and a length of about 0.24 mm. Is about 0.8 mm, and the side walls 9 and 11 extending in the direction parallel to the ink flow path arrangement direction 15 have a width of 0.25 mm and a length of 0.5 mm.

Electrodes 6 are provided on the inner wall surfaces of all ink flow paths 4.
Is formed, and the surface of the electrode 6 is subjected to insulation treatment for insulation from ink. An orifice plate 8 having an orifice 10 corresponding to each ink flow path 4 is provided on an upper surface of the upper piezoelectric ceramic plate 2, and an ink (not shown) corresponding to each ink flow path 4 is provided on a lower surface of the lower piezoelectric ceramic plate 3. A bottom plate 12 having an ink supply path 13 connected to the supply device is joined.

The ejecting device 34 includes an orifice 10 for ejecting liquid droplets, an ink flow path 4, an ink supply path 13, and piezoelectric ceramic plates 2, 3 for changing the internal volume of the flow path and applying pressure to the ink. The array 1 constitutes a piezoelectric droplet ejector having 22 ejectors 34.

Next, a method of manufacturing the array 1 will be described with reference to FIGS. As shown in FIGS. 2A and 2B, first, a piezoelectric ceramic plate 2 having a through hole for forming the ink flow path 4 is made of a ferroelectric lead zirconate titanate (PZT) -based ceramic material. , 3
Is formed by injection molding. After the injection molding,
Performs degreasing process, sintering process, polarization process in the thickness direction of the plate, electrode formation by electroless copper (or nickel) plating process, and electrode insulation process. Next, the piezoelectric ceramic plates 2 and 3 are obtained through a cutting process along the dotted line P and upper and lower end surface processing for removing excess electrodes attached to the upper and lower surfaces of the piezoelectric ceramic plate and improving the flatness. In such a case, as a forming method, an extruding method may be used, or a hole may be formed by machining a piezoelectric ceramics plate which has been sintered in advance.
The same piezoelectric ceramic plate 2 can be formed by using a copper or nickel sputtering method (in order to form an electrode on the inner surface of the hole, tilt the axis of the hole and a parallel beam of metal atoms) as the electrode forming method. And 3 are obtained.

The upper piezoelectric ceramic plate 2 and the lower piezoelectric ceramic plate 3 thus obtained, and the orifice plate 8 having the orifices 10 corresponding to each ink flow path.
And a bottom plate 12 that forms an ink supply path 13 corresponding to each ink flow path 4 and has a lower surface provided with wiring for electrically connecting electrodes in the flow path and the driving LSI chip 16. The bonding is performed at a temperature sufficiently lower than the Curie temperature of the piezoelectric ceramics plates 2 and 3 so that the polarization of the piezoelectric ceramics plates 2 and 3 does not decrease. After this joining, the driving LS
The array 1 is obtained by mounting the I chip 16.

An electric circuit as shown in FIG. 3B is provided on the array 1 obtained as described above. In this electric circuit, the surface electrode 6e obtained by the cutting step
(FIG. 3A) is all grounded. Electrodes 6a to 6d
Are connected to the driving LSI chip 16 separately,
Clock line 18, data line 20, voltage line 2
2 and the ground line 24 are also connected to the driving LSI chip 16.

The ink flow path 4 is divided into groups A and B which are not adjacent to each other as shown in FIG. 1A, and a continuous clock pulse supplied from the clock line 18 is applied to the groups A and B. Are sequentially driven. The data in the multi-bit word format appearing on the data line 20 determines which ink flow path 4 to operate in each group, and determines the ink flow path 4 of the group selected by the circuit of the driving LSI chip 16. The voltage V of the voltage line 22 is applied to the electrode 6. At this time, the electrodes 6 of the ink channels 4 of the same group that are not operated and the electrodes 6 of all the ink channels 4 belonging to other groups are grounded. As a result, an electric field is applied between the electrodes in the ink flow path 4 adjacent to the selected ink flow path 4 between the electrodes in a direction perpendicular to the polarization directions of the two piezoelectric ceramic plates 2, 3. The flow path walls of the plates 2 and 3 are deformed based on the piezoelectric thickness-shear effect, and change the volume of the selected ink flow path 4. Accordingly, all the ink flow paths 4 can be operated in each group.

Next, the operation of the ejection device when the ejection device 34b is selected based on predetermined print data will be described with reference to FIGS. 3A and 3B. FIG. 3A is a cross-sectional view of the array 1 and shows a cross-section of the ink flow path 4, and FIG.
It is a longitudinal sectional view taken along the X ₁ -X ₁ line in (A).

As shown in FIGS. 3A and 3B, the voltage V of the voltage line 22 is applied to the electrode 6b in the ink flow path 4b, and the ink flow path 4b including the other electrodes 6a and 6c is started.
All the electrodes 6 of the ink flow path 4 adjacent to the side wall 5 are grounded.
A driving electric field is applied in the direction of arrow 32 to the side walls 5, 7, 9, 11 surrounding the ink flow path 4b including b, 7b, 5c, 7c. Since the driving electric field and the polarization direction are orthogonal to each other, the side walls 5, 7, 9, 11 surrounding the ink flow paths 4b including the side walls 5b, 7b, 5c, 7c due to deformation of the piezoelectric thickness effect.
Is deformed in a “U” shape toward the inside of the ink flow path 4b. Due to this deformation, the volume of the ink flow path 4b is reduced, and the ink 30 is ejected from the orifice 10b. When the application of the voltage is cut off and the side walls 5, 7, 9, 11 surrounding the ink flow paths 4b including the side walls 5b, 7b, 5c, 7c are returned to the original positions, the ink flow path 4b at that time is returned. As the volume increases, ink is supplied from an ink supply device (not shown) via the ink supply path 13b. For example, when another injection device 34c is selected, the side walls 5c, 7c, 5c
d, a side wall 5 surrounding the ink flow path 4c including 7d,
7, 9, and 11 are deformed in a “C” shape toward the inside of the ink flow path 4c, and the ink in the ink flow path 4c is ejected.

Here, the deformation in the thickness-shear mode will be described with reference to FIGS. 4 (A) and 4 (B). FIG.
3A is a perspective view of a wall 40 fixed to a base 41, wherein the dimension of the wall 40 in the polarization direction 28 is height H, the dimension in the direction of the driving electric field applied by the pair of electrodes 42 is the thickness W, When the length in the direction perpendicular to both the direction 28 and the driving electric field direction is length L, the wall 40 is sheared leftward in the drawing as indicated by the dotted line T when the driving electric field direction is rightward in the drawing. I do. When the volume of the ink flow path 4 is changed by the shearing deformation as described above, the amount of change in the volume is proportional to the length L when the thickness W and the driving voltage are fixed,
Since it is proportional to the square of the height H, it is advantageous to make the height H higher in order to increase the volume change amount.

FIG. 4B is a plan view of the case where the wall 40 is fixed to the horizontal base 43 at both ends 44 in the length L direction, and is actually applied to the array 1 of the droplet ejecting apparatus. Has the configuration shown in FIG. The deformation in this case is indicated by the dotted line T1
As shown by, the wall 40 has a shape that is warped in the deformation direction with both ends 44 being fixed ends, and the wall 40 has a smaller shape than the case where both ends in the length L direction shown in FIG. 4A are free. Extra energy (drive voltage) is required for the applied stress. The extra necessary driving voltage decreases as the L / W ratio increases. According to the calculation, in order to obtain a certain volume change when both ends 44 in the length direction are fixed, when L / W = 1, it becomes several hundred times larger than when both ends are free, and L
It was confirmed that when L / W was 3 or more, it was several times to 10 times, although it was several tens times when / W = 2.

Therefore, the L / W ratio must be at least 3 or more. However, in order to simply increase the L / W ratio, the piezoelectric ceramics 2 and 3 are provided with very thin side walls 5, 7, 9 and 11 in the L direction (see FIG. 3), and the side walls are also formed in the H direction. prolong the, during molding by the injection molding method, during drilling by machining, or the strength and reliability significantly or drop during driving, the pitch of the orifices 10 and in
The outer dimensions of the array 1 in the direction perpendicular to the flow channel arrangement direction 15 increase. Therefore, as shown in FIG. 1 (A), b
The above-mentioned problem can be avoided by providing a structure in which the side wall perpendicular to the link channel arrangement direction 15 is not provided.

That is, as shown in FIG.
7 extend perpendicularly to the polarization directions 26 and 28 and extend in a direction of about 72 degrees in the ink flow path arrangement direction 15, and the side walls 9 and 11 are configured to extend in the polarization directions 26 and 2.
8 and an ink flow path perpendicular to the polarization directions 26 and 28 and
It was configured to extend in the arrangement direction 15. With this configuration, a strong structure is obtained.
Strength during drilling and driving during machining,
A decrease in reliability can be suppressed, and therefore, the side walls 5, 7
Can be obtained sufficiently, so that the side walls 5, 7, 9,
The drive voltage can be reduced without increasing the length L of the drive 11. Further, the side walls 5 and 7 are aligned with the ink flow path arrangement direction 15.
Since extending in the direction of about 72 degrees, Lee sidewalls same dimensions
Compared with the case where extended perpendicularly to the ink flow path arrangement direction, in
Pitch of the orifices 10 of the click channel arrangement direction 15, in
The outer dimensions of the array 1 perpendicular to the flow channel arrangement direction 15 can be suppressed to about 94%.

As described above, in the piezoelectric droplet ejecting apparatus of the present embodiment, the piezoelectric transducer for driving the 22 ejecting apparatuses 34 is composed of the two piezoelectric ceramic plates 2 and 3, and the array 1 Is simplified, the number of manufacturing steps of the piezoelectric droplet ejecting apparatus is reduced by assembling the array 1 and a large number of the arrays 1, and the manufacturing cost is also reduced. Also, piezoelectric ceramics 2, 3
In addition, the number of ejecting devices 34 is increased, the size of the array 1 is reduced, and printing is performed by densely arranging a large number of ink flow paths 4 formed of through holes whose side walls 5 and 7 are not orthogonal to the ink flow path array 15. The resolution can be improved and the driving voltage can be reduced.

For example, the array 1 of the present embodiment constitutes a multi-head having 22 ejection devices 34,
m, a vertical size of 2.75 mm, and a thickness of about 3 mm were realized. Further, the array 1 of the present embodiment has one ink flow path 4.
There are a total of six side walls 5, 7, 9, 11 surrounding H. The dimensions of each side wall 5, 7 are 1.5 mm for H and 0.24 m for W
m, L is about 0.8 mm, the ink flow path arrangement direction 15
For the side walls 9 and 11 extending in parallel with, the condition that H is maximum and L / W ≧ 3 is selected so that H is 1.5 mm, W is 0.25 mm, and L is 0.5 mm, About 90pl
The driving voltage for ejecting the ink droplets is 35 V, and a drastically lower driving voltage, which has conventionally required a driving voltage of about 120 to 170 V, has been realized.

In this embodiment, the sectional shape of the ink flow path is an isosceles triangle, but it may be trapezoidal. FIG.
As shown in (A), the corners may be rounded,
This facilitates the formation of the flow path by injection molding and machining, and reduces the concentration of stress during driving, contributing to an improvement in reliability.

Further, it is not necessary to make the inner diameter of the through hole forming the ink flow path constant. That is, X in FIG.
As shown in FIG. 5 showing a sectional view taken along ₂ -X _2-wire (B), the narrow portion of the inner diameter of the through-hole and the orifice 10 and the ink supply path 13, if the thick portion and the ink flow path, easier Configuration.

[0031]

As described above, according to the present invention, since the extension lines of the opposed side walls of the ink flow path intersect with each other, the width of the side wall required for the "C" shape deformation can be secured. , L / W of 3 or more, the driving voltage can be reduced.

[Brief description of the drawings]

1A is a cross-sectional view of an array used in an embodiment of the present invention, and FIG. 1B is a cross-sectional view of the array taken along line XX.

FIG. 2A is a front view of a piezoelectric ceramic plate used for the array, and FIG. 2B is an exploded perspective view of the array.

FIG. 3A is a cross-sectional view of a driving state of the array,
(B) is a diagram showing a driving state of a cross section along line X ₁ -X ₁ in (A).

4A is a perspective view showing deformation of a wall in a piezoelectric thickness-slip mode, and FIG. 4B is a plan view showing deformation of a wall fixed at both ends in a piezoelectric thickness-slip mode.

5A is a cross-sectional view of an array according to a modification, and FIG. 5B is a cross-sectional view of the array along the line X ₂ -X ₂ .

FIG. 6 is a sectional view of an array constituting a conventional droplet ejecting apparatus.

[Description of Signs] 1 Array 2 Upper piezoelectric ceramics (piezoelectric transducer) 3 Lower piezoelectric ceramics (piezoelectric transducer) 4 Ink flow path 5, 7 Side wall 6 Electrode 10 Orifice 13 Ink supply path 15 Ink Flow path arrangement directions 26, 28 ... Polarization direction 34 ... Injection device H ... Length in the polarization direction forming the depth of the ink flow path W ... Length in the driving electric field direction forming the width direction in the cross-sectional shape of the ink flow path L ... Length in the longitudinal direction in the cross-sectional shape of the ink flow path

Claims (1)

(57) [Claims] A plurality of ink flow paths arranged in parallel with a polarization direction of a piezoelectric transducer, and a driving electric field is applied perpendicularly to the polarization direction in each ink flow path to deform the piezoelectric transducer to form an ink. A droplet ejecting apparatus that changes a volume of a flow path to jet ink retained in the ink flow path, wherein the plurality of the plurality of side walls formed by piezoelectric transducers between adjacent ink flow paths are provided. The plurality of inks are arranged such that side walls facing each other in the arrangement direction of the ink flow paths intersect at an acute angle.
A droplet ejecting apparatus characterized in that it is configured to be inclined with respect to the direction in which the flow paths are arranged .