JP3024291B2 - 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. 5 shows a cross-sectional view of an example of the array of the droplet ejecting apparatus. As shown in FIG. 5, 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). As described above, this droplet ejecting apparatus provides a plurality of through holes in a piezoelectric element, polarizes them in a penetrating direction, and provides driving electrodes on the surface of the through holes to provide a multi-head, high resolution, small size, A simple structure has been achieved to reduce manufacturing costs.

[0004]

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. 5, 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 (the regular hexagonal cross section of the ink flow path 4) (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 length of 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-mentioned problems, and provides a high-resolution, low-cost, low-cost manufacturing apparatus which can be driven at a low voltage with high strength and reliability. The purpose is to:

[0007]

According to the present invention, in order to achieve the above object, a plurality of ink flow paths are formed in parallel with the polarization direction of a piezoelectric transducer, and a driving electric field is formed perpendicularly to the polarization direction in each ink flow path. A droplet ejecting device that deforms the piezoelectric transducer by applying a pressure to change the volume of the ink flow path so as to eject the ink retained in the ink flow path. The driving electric field direction length W in the width direction in the cross-sectional shape of the side wall formed by the piezoelectric transducer between the paths, the length L in the longitudinal direction of the side wall, the entire piezoelectric transducer
When the length in the polarization direction forming the depth of the side wall of the body is H, the side wall is configured to satisfy H ≧ L and L / W ≧ 3.

[0008]

According to the present invention, for example, FIG. 1 (B) and FIG.
As shown in (B), the ink flow path is formed in a rectangular parallelepiped shape in parallel to the polarization direction, and the length of each side of the side wall formed by the entire piezoelectric transducer between the adjacent rectangular parallelepipeds is determined by the polarization direction (depth) H,
It is assumed that the driving electric field direction (width) W and the direction perpendicular to both the polarization direction and the driving electric field direction (longitudinal width) L. And the depth H
Since the width L in the longitudinal direction is set to be equal, the ejection direction of the ink is constant, and the width W is reduced so that the resolution is not reduced. As a result, the "C" shape deformation of the side wall can be made relatively large, and a relatively large volume change of the ink flow path can be obtained. For example, when L / W = 4, the driving voltage for ejecting a droplet of about 90 pl is 43 V, and a large droplet ejection amount can be obtained with a low practical voltage.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments. Note that the same parts and equivalent parts as those described in FIG. 5 are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1A is a sectional view of an array 1 used in a piezoelectric droplet ejecting apparatus, and FIG. 1B is a longitudinal sectional view taken along line XX in FIG. 1A. FIG. 1 (A),
As shown in (B), the array 1 is polarized in the direction of the arrow 26, and is provided with a through hole having a rectangular cross section of 1.0 mm in length and 0.25 mm in width at a center-to-center distance of 0.5 mm (array Direction) and four rows in the vertical direction, thickness 1.5
The upper piezoelectric ceramic plate 2 having a rectangular cross section of 1.0 mm in length and 0.25 mm in width, similarly to the upper piezoelectric ceramic plate 2, is subjected to a polarization treatment in the direction of arrow 28. The lower piezoelectric ceramic plate 3 having a thickness of 1.5 mm, which is arranged in four rows in the horizontal direction (array direction) of 5 mm and two rows in the vertical direction, is joined. Here, the flow path length of the ink flow path 4 formed by the through hole is 3.0.
The width (array direction) of the side walls 5, 7 of the two piezoelectric ceramic plates 2, 3 for dividing the flow path is 0.25 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. Injection device 34
Is an orifice 10 for ejecting droplets and an ink flow path 4
And an ink supply path 13, and piezoelectric ceramic plates 2 and 3 for changing the volume in the flow path and applying pressure to the ink, and the array 1 constitutes a piezoelectric droplet ejecting apparatus having eight ejecting apparatuses 34. are doing.

Next, a method of manufacturing the array 1 will be described with reference to FIGS. As shown in FIG. 2A, first, lead zirconate titanate (PZ) having ferroelectricity is used.
A molded body of the piezoelectric ceramic plates 2 and 3 having through holes for forming the ink flow paths 4 is formed by injection molding using a T) -based ceramic material. After the injection molding, a degreasing process, a sintering process, a polarization process in the thickness direction of the plate, an electrode formation by an electroless copper (or nickel) plating process, and an electrode insulation process are performed. Next, a cutting step along the dotted line W;
Piezoelectric ceramics 2 and 3 are obtained through upper and lower end surface processing to remove excess electrodes attached to the upper and lower surfaces of the piezoelectric ceramic plate and to improve 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. Also,
Similar piezoelectric ceramic plates 2 and 3 can be formed by using a copper or nickel sputtering method (in order to form an electrode on the inner surface of a hole, the axis of the hole and a parallel beam of metal atoms are inclined) as an electrode forming method. Is obtained.

The upper piezoelectric ceramic plate 2 and the lower piezoelectric ceramic plate 3 thus obtained, and an orifice plate 8 having 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. At this time,
Upper piezoelectric ceramics plate 2 with side wall depth H 'and side wall depth
H ′ and the lower piezoelectric ceramic plate 3
A polarization method that forms the depth of the side wall of the entire electric transducer
The direction length is H as shown in FIG.

An electric circuit as shown in FIG. 3B is provided on the array 1 obtained as described above. In this electric circuit, the electrodes 6e on the surface obtained by the cutting step are all grounded. The electrodes 6a to 6d are separately connected to the driving LSI chip 16, respectively.
8, the data line 20, the voltage line 22, 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 drive electric field is applied in the direction of arrow 32 to the side walls 5, 7 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 and 7 surrounding the ink flow paths 4b including the side walls 5b, 7b, 5c and 7c are formed in a “U” shape by the deformation of the piezoelectric thickness effect. 4b. Due to this deformation, the volume of the ink flow path 4b is reduced, and
b. Further, the application of the voltage is cut off,
When the side walls 5, 7 surrounding the ink flow path 4b, including b, 7b, 5c, 7c, are returned to their original positions, the volume of the ink flow path 4b at that time is increased and the ink supply path 13b is not shown. The ink is supplied from the ink supply device. For example, when another ejection device 34c is selected, the ink flow path 4c including the side walls 5c, 7c, 5d, and 7d is used.
Are deformed in a “U” shape toward the inside of the ink flow path 4c, and the ink in the ink flow path 4c is ejected.

Here, deformation in the thickness-shear mode will be described with reference to FIGS. 4 (A) and 4 (B). FIG.
(A) is a perspective view of a wall 40 fixed to a base 41, wherein the dimension in the polarization direction 28 of the wall 40 is a height H ′ , the dimension in the driving electric field direction applied by the pair of electrodes 42 is a thickness W, Assuming that the length in the direction perpendicular to both the polarization direction 28 and the driving electric field direction is length L, when the driving electric field direction is rightward in the drawing, the wall 40 is sheared leftward in the drawing as indicated by the dotted line T. Deform. Therefore, as described above, this height
The wall 40 in the polarization direction 28 at H ′ and the polarization direction 2 at the height H ′
6 and the ink flow path 4 having a height H by overlapping the wall 40 with two layers.
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 constant, and the height H is 2 Since it is proportional to the power, it is advantageous to increase the height H to increase the volume change.

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, if the L / W ratio is too large, it is necessary to provide the piezoelectric ceramics 2 and 3 with very thin side walls 5 and 7 (see FIG. 3) in the L direction. Since the strength and reliability at the time of processing or driving are significantly reduced, preferably L / W ≦
It is good to set to 10. That is, in order to more efficiently deform the wall 40 in the thickness-shear mode, when the dimension H in the polarization direction, the thickness dimension W, and the dimension L in the direction perpendicular to both the polarization direction and the thickness direction, the height H , And L
The / H ratio may be 3 or more.

The array 1 of the liquid droplet ejecting apparatus of this embodiment has a total of four side walls 5 and 7 surrounding one ink flow path 4, and each side wall 5 and 7 has H ' = 1.5 mm (H = 3.0m
m) , L = 1.0 mm, W = 0.25 mm, H is maximum and L / W = 4, which satisfies the above condition. At this time, the driving voltage for ejecting a droplet of about 90 pl was 43 V. As a comparative example, H and W, and the pitch of the orifice 10 in the array direction were kept constant and L was changed
When the / W ratio is changed from 2.6 to 3.6, the driving voltage is 3
73V (L / W = 2.6), 257V (L / W = 2.
8), 182 V (L / W = 3), 132 V (L / W =
3.2), 97V (L / W = 3.4), 73V (L / W)
= 3.6), and when the L / W ratio is smaller than 3, the driving voltage exceeds 200 V, which is not practical.

Further, at this time, the fact that the pitch of the orifices 10 in the array direction is constant in any case means that, in other words, according to the present invention, low voltage driving can be realized without lowering the printing resolution. Furthermore, the length L of the side walls 5, 7 in the direction perpendicular to the array direction can be minimized by increasing the height H in the polarization direction.

As described above, in the piezoelectric droplet ejecting apparatus of the present embodiment, the piezoelectric transducer for driving the eight 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. Further, by densely arranging a large number of ink flow paths 4 having through holes in the piezoelectric ceramics 2 and 3, the number of ejecting devices 34 can be increased, the size of the array 1 can be reduced, the resolution of printing can be improved, and the driving voltage can be reduced. Can be.

For example, when the ink channels 4 having the same dimensions as those of this embodiment are arranged at 64 (2 × 32) at the same center distance, the outer dimensions of the array 1 are 2.2 mm × 16.2 m.
It may be mx5 mm or less. In the case of this embodiment, when the dimension in the polarization direction of the side wall is H, the thickness dimension is W, and the dimension in the direction perpendicular to both the polarization direction and the thickness direction is L, H
Since the shape of the side wall is optimally selected such that ≧ L and L / W ≧ 3, about 90 pl of ink droplets are ejected at a low driving voltage of 43 V without lowering the strength and reliability of the side wall and the resolution of printing. Can be conventionally about 120-170
What required a driving voltage of V can be drastically reduced in voltage.

In this embodiment, the sectional shape of the ink flow path is rectangular, but may be an oval shape with rounded short sides. 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.

[0026]

As described above, according to the present invention, the dimension in the polarization direction of the side wall of the entire piezoelectric transducer formed between the ink flow paths is H, the thickness dimension is W, and the polarization direction is W. When the dimension in the direction perpendicular to both of the thickness directions is L, the ink flow path is configured as H ≧ L and L / W ≧ 3, so that the printing resolution is kept good and the ink flow path is A droplet ejecting apparatus that can be easily formed and has a low driving voltage can be provided.

[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.

FIG. 5 is a cross-sectional view of an array constituting a conventional droplet ejecting apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 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 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: forming the longitudinal direction in the cross-sectional shape of the ink flow path length

Claims (1)

(57) [Claims] A plurality of ink flow paths are formed in parallel with the 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 and thereby form the ink flow. What is claimed is: 1. A liquid droplet ejecting apparatus that ejects ink retained in an ink flow path by changing a volume of a passage, wherein a width direction in a cross-sectional shape of a side wall formed by a piezoelectric transducer between adjacent ink flow paths , The length L of the side wall in the longitudinal direction, and the length of the piezoelectric transformer.
Assuming that the length H in the polarization direction is the depth of the side wall of the entire inducer , the side wall is H ≧ L and L / W ≧
3. A droplet ejecting apparatus characterized in that the droplet ejecting apparatus is configured so as to be 3.