JPH106495A - Ink jet recording head and piezoelectric member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise an ink discharging efficiency from a nozzle by obliquely deforming an ink channel opposed part of a piezoelectric member, and urging ink in an ink channel in a nozzle direction based on this deformation, thus forming an ink flow. SOLUTION: In this ink jet recording head, a piezoelectric member 15 is formed of a plurality of laminated piezoelectric element layers 21, each layer 21 has electrode layers 31, 32 on an ink channel opposed surface and its opposite surface, respectively, a part of the layer 21 sandwiched between the layers 31 and 32 becomes a polarized active part B, and lengths of the parts B of the layers 21 with respect to a direction directed from one end toward a nozzle 14 are stepwisely differentiated. Therefore, a deforming amount of the member 15 at the time of applying a voltage is increased as it separates from the nozzle 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drop-on-demand (DOD) for recording an image by causing an ink drop to fly in response to an image signal and attaching the ink drop to a recording medium such as recording paper.
The present invention relates to an inkjet recording head of the type. The present invention also relates to a piezoelectric member used for the above-mentioned ink jet recording head.

[0002]

2. Description of the Related Art Conventionally, there has been known an ink jet recording head which ejects ink by deformation of a piezoelectric member. FIG. 6 shows an example of an ink jet recording head using such a piezoelectric member. As shown in FIG.
The ink jet recording head 51 has a channel plate 52 made of resin, metal, or the like. A plurality of recesses are formed in the channel plate 52 by a method such as molding or etching, and a partition wall 53 made of a thin film of resin, metal, or the like is adhered so as to cover the recess formation surface. In each of the concave portions covered with the partition walls 53, an ink channel 55, an ink supply chamber 58,
An inlet 57 that connects each ink channel 55 and the ink supply chamber 58 is formed. Further, a plurality of nozzles 6 each communicating with an end of the ink channel 55 are provided.
0 is formed on the channel plate 52. The ink channels 55, the inlets 57, and the nozzles 60 are formed at equal pitches in the depth direction (a direction perpendicular to the drawing) of FIG.

A spacer member 6 is provided below the partition wall 53.
The substrate 54 is fixed via the first and the second 62. A plurality of piezoelectric members 63 are fixed between the partition wall 53 and the substrate 54 below the ink channel 55 so as to face each ink channel 55 via the partition wall 53.
Electrode layers 64 and 65 are formed on the upper and lower surfaces of the piezoelectric member 63, respectively, and a voltage is applied to the piezoelectric member 63 via the electrode layers 64 and 65.

When a voltage is applied to the piezoelectric member 63 in the ink jet recording head 51 having the above configuration, the piezoelectric member 63 is suddenly moved in the thickness direction, that is, in the direction in which the partition wall 53 and the substrate 54 face each other, as shown by the broken line in FIG. Then, the partition wall 53 is pushed up to the ink channel 55 side.
As a result, the ink in the ink channel 55 is momentarily pressurized, and the ink drop flies from the nozzle 60.

[0005]

The piezoelectric member 63 is
It expands and deforms almost uniformly in the longitudinal direction (the left-right direction in FIG. 6), and this deformation causes ink to flow through the ink channel 55.
Will be pushed up evenly toward the upper wall surface 56. On the other hand, since the nozzle 14 is formed at the end of the ink channel 55, the ink flows in the ink channel 55 toward the nozzle 60 and is ejected from the nozzle 60. For this reason, the ink jet recording head 51
In this case, the direction in which the ink flows in the ink channel 55 is orthogonal to the direction in which the ink moves due to the deformation of the piezoelectric member 63, and the ink ejection efficiency is not necessarily high.

[0006]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made for the purpose of increasing the ink ejection efficiency. In the ink jet recording head of the first invention, the ink jet recording head based on the deformation of the piezoelectric member when voltage is applied. In an ink jet recording head that pressurizes ink contained in an ink channel and causes an ink drop to fly from a nozzle, the amount of deformation of a portion of the piezoelectric member away from the nozzle when voltage is applied is:
The amount of deformation of the piezoelectric member near the nozzle when the voltage is applied is larger than that of the piezoelectric member.

A piezoelectric member according to a second aspect of the present invention is a piezoelectric member in which a plurality of electrode layers and piezoelectric layers are alternately laminated, and a voltage is applied to each piezoelectric layer between upper and lower electrodes. An active portion that deforms in the case is provided from one end to the other end of the piezoelectric member, and the length of the active portion is shorter in the upper layer than in the lower layer.

[0008]

According to the ink jet recording head of the first invention, when a voltage is applied to the piezoelectric member,
The piezoelectric member is deformed so as to increase the amount of deformation of the piezoelectric member in a portion away from the nozzle. This deformation acts to push the ink in the ink channel toward the nozzle.
Based on this action, the ink flows in the ink channel in the direction of the nozzle, is ejected from the nozzle, and flies as an ink drop. As described above, the ink ejection efficiency can be increased by deforming the piezoelectric member so as to form the flow of the ink in the ink channel in the nozzle direction.

Further, according to the piezoelectric member of the second invention,
When a voltage is applied to this piezoelectric member via each electrode layer, the active portion of each piezoelectric layer expands and deforms. The active portion of the upper layer of the piezoelectric layer has a length from one end of the piezoelectric member shorter than that of the lower portion. Therefore, in the piezoelectric member, the lower the number of layers, the larger the number of stacked active portions, and accordingly, the greater the deformation of the piezoelectric member, which is the cumulative amount of deformation of each active portion. As a result, the piezoelectric member deforms such that the amount of deformation increases from one end to the other. For this reason, when the piezoelectric member is used as ink pressurizing means of an ink jet recording head, by arranging the piezoelectric member so that a portion having a large deformation amount is separated from the nozzle,
A flow toward the nozzle direction can be formed in the ink in the ink channel based on the deformation of the piezoelectric member, and the ink ejection efficiency can be increased.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 show an ink jet recording head 1 using a piezoelectric member according to the present invention. This ink jet recording head 1 has a first
It has a head section 10 and a second head section 20. The first and second head portions 10 and 20 are integrally formed by the channel plate 2, the partition 3, and the substrate 4,
Since the head 1 is configured symmetrically with respect to the central cross section X, the first head section 10 will be mainly described below.

The channel plate 2 is made of a flat plate made of resin, metal, or the like.
A plurality of recesses are formed by fine processing such as photolithography and electroforming. The partition 3 is made of a thin film of metal, resin, or the like, and is adhered so as to cover the concave surface of the channel plate 2. The inside of each concave portion of the channel plate 2 covered by the partition 3 serves as an ink channel 11, an inlet 12, and an ink supply chamber 13, respectively.

The plurality of ink channels 11 are arranged at equal pitches in parallel. Each ink channel 11 receives ink from an ink supply chamber 13 via a corresponding inlet 12. In addition, the channel plate 2 includes each ink channel 1.
The plurality of nozzles 14 communicating with each other in the vicinity of one end
Are formed on two straight lines. The nozzle 14 has a tapered circular cross section having a large diameter on the ink channel 11 side and a small diameter on the discharge side facing the outside.

The channel plate 2 and the partition 3 are
It is fixed to a substrate 4 made of a highly rigid material such as ceramic via spacer members 6, 7, 8. A plurality of piezoelectric members 15 are fixed on the substrate 4 so as to face the ink channels 11 with the partition walls 3 interposed therebetween. The piezoelectric member 15 is a pressurizing unit that pressurizes the ink in the ink channel 11 via the partition 3 based on the deformation at the time of applying a voltage, and causes the ink drop to fly from the nozzle 14.

The piezoelectric member 15 is, as shown in FIG.
For example, a rectangular parallelepiped formed by laminating a plurality of piezoelectric layers 21 made of a piezoelectric material such as lead zirconate or lead titanate in the direction facing the ink channel 11 (the direction of arrow A) and having a slightly smaller length and width than the ink channel 11 Is formed.

Each of the piezoelectric layers 21 includes the ink channel 11.
A first electrode layer 31 and a second electrode layer 32 are respectively provided on the surface facing and the surface opposite thereto. The second electrode layer 32 extends from the second common electrode 27 provided on the side surface 26 of the piezoelectric member 15 on the side of the nozzle 14, and its tip end is located near the side surface 22 of the piezoelectric member 15 distant from the nozzle. They are formed to have the same length so as to be located, and are connected to the ground via the second common electrode 27. On the other hand, each first electrode layer 31 extends from a first common electrode 24 provided on the side surface 22 of the piezoelectric member 15, and is connected to the driver 23 via the first common electrode 24. The portion of each piezoelectric layer 21 sandwiched between the first and second electrode layers 31 and 32 is an active portion that has been subjected to a polarization process as described later.

On the ink channel side surface of each piezoelectric layer 21 and on an extension of the first electrode layer 31, a dummy electrode layer 35 is sandwiched by a divided region 34 where no electrode layer is formed.
(Indicated by a dashed line in FIG. 3). The length of each first electrode layer 31 is formed so as to gradually decrease from the lower part to the upper part of the piezoelectric member 15 by changing the position of the dividing region 34. By forming the length of the first electrode layer 31 in this manner, as shown by the hatched area B in FIG. The length of the active portion of each piezoelectric layer 21 with respect to the direction is different so that it gradually decreases in the direction toward the ink channel 11.

The piezoelectric member 15 having the above configuration is formed, for example, as follows. First, a first piezoelectric layer 21 is formed on a substrate 4 by a green sheet method, and a metal thin film is attached to the surface of the first piezoelectric layer 21 by a sputtering method, a plating method, or the like to form a second electrode layer 32. Next, a second piezoelectric layer 21 is laminated on the upper surface by the same method, and the first electrode layer 31 is formed on the surface of the second layer by the above method. By keeping the mask, a divided region 34 to which the metal thin film does not adhere and a dummy electrode layer 35 that does not conduct to the first electrode layer 31 due to the presence of this region are formed simultaneously with the first electrode layer 31. By repeating these steps sequentially, the piezoelectric member 15
Is formed, but by slightly shifting the mask position when forming the first electrode layer 31 in a direction away from the nozzle 14, the length of each first electrode layer 31 is gradually reduced. It is formed.

After the piezoelectric layer 21 is laminated and fired, the first and second common electrodes 2 are formed on both sides 22, 26 of the piezoelectric member 15 by a conductive adhesive layer or a metal thin film.
4 and 27 are provided respectively. When a high voltage is applied to each of the electrode layers 31 and 32 at a high temperature via the first and second common electrodes 24 and 27, each of the electrode layers 31 and 32 of each piezoelectric layer 21 is applied.
Only the portion sandwiched between the portions 32 is polarized, and active portions having different lengths are formed as described above. The first
The active portions of the two piezoelectric layers 21 sandwiching the electrode layer 31 are polarized in directions opposite to each other, but when a voltage is applied to the first electrode layer 31 by the driver 23, the active portions are opposite to each other. Since an electric field is generated in each direction, any of the active portions expands and deforms in the vertical direction. As a result, each active portion expands and deforms in the direction toward the ink channel 11.

The first head section 10 has the above configuration. On the other hand, the ink channel 1 of the second head unit 20
1, the inlet 12 and the piezoelectric member 15 are also formed in the same size as those of the first head unit 10, respectively.
The nozzle 14 is also formed with the same diameter. Ink channel 11, inlet 12, piezoelectric member 15, nozzle 1
The size such as 4 may be made different for each head portion, and ink drops having different diameters may be ejected from each head portion.

Next, a method of driving the piezoelectric member 15 of the ink jet recording head 1 having the above configuration and an ink discharging operation will be described. Each of the ink channels 11 stores ink supplied from the ink supply chamber 13 through the inlet 12. Driver 2 in this state
3, when a voltage is applied to the first common electrode 24,
An electric field is formed between the first and second electrodes 31, 32, and the active portion of each piezoelectric layer 21 is instantaneously expanded and deformed in the direction of arrow A based on the electric field.

The number of layers of each active portion deformed in this way is
The piezoelectric member 15 is configured such that it is small in a region near the nozzle 14 and is large in a region farther from the nozzle 14. Since the deformation of the piezoelectric member 15 appears as an accumulation of the deformation of each piezoelectric layer 21, the amount of deformation continuously increases as the distance from the nozzle 14 increases, as indicated by a dotted line in FIG. This shows a deformation that is inclined upward in a direction away from the nozzle 14.

The partition wall 3 is momentarily pushed into the ink channel 11 by this inclined deformation. As a result, the ink in the ink channel 11 is pushed out in the direction of arrow C, flows toward the nozzle 14, is ejected from the nozzle 14, and flies as an ink drop.

As described above, according to the piezoelectric member 15,
The ink ejection efficiency can be increased by making the direction in which the ink is pushed out and the direction in which the ink flows in the ink channel 11 substantially match based on the inclination deformation.

The amount of deformation of the piezoelectric member 15 away from the nozzle 14 is reduced by the amount of deformation of the piezoelectric member 15 near the nozzle 14.
By increasing the amount of deformation, the pressure wave generated at a portion distant from the nozzle 14 and the pressure wave generated at a portion close to the nozzle 14 can be increased. Thereby, the peak of the pressure wave can be concentrated at the time of ejection of the ink drop, and the ejection efficiency of the ink drop is improved. Further, the piezoelectric member 1 near the nozzle 14
Since the deformation amount of No. 5 is relatively small, the transmission of the vibration of the piezoelectric portion 15 directly to the nozzle 14 is suppressed, which is advantageous in improving the accuracy of the ink ejection direction. Furthermore, since the piezoelectric member 15 is made to gradually increase in the longitudinal direction, that is, to be inclinedly deformed, it is advantageous to secure a stable ink discharging operation.

As shown in FIG. 4, the nozzle center axis Y
If the nozzle 14 is arranged such that the nozzles 14 are parallel to the upper part of the piezoelectric member 15, the direction of ink flow in the ink channel 11 caused by the inclined deformation of the piezoelectric member 15 and the direction of ink drop ejection more accurately match. Therefore, the ink ejection efficiency can be further improved.

Further, in the piezoelectric member 15, the length of each electrode 31 is set such that the tip of each first electrode layer 31 is substantially one straight line. The upper part of 15 is also inclined and deformed almost flatly,
As shown by a two-dot chain line in FIG.
According to the piezoelectric member 40 in which the length of each electrode layer 31 is set such that the line Z connecting the tips of the electrodes becomes a curve, each common electrode 2
When a voltage is applied between the electrodes 4 and 27, the upper part of the piezoelectric member 40 is inclined in the direction of the nozzle 14 and can be deformed into a curved surface convexly curved toward the ink channel 11 side.

The piezoelectric members 15 and 40 may be arranged upside down. Alternatively, the first common electrode 24 may be connected to ground and a voltage may be applied to the second common electrode 27. Is also good. In any of these cases, the same inclination deformation as described above can be obtained. In each of the piezoelectric members 15 and 40, the same effect can be achieved without providing the dummy electrode layer 35. However, without the dummy electrode layer 35, the thickness of the piezoelectric members 15 and 40 is reduced accordingly. In order to avoid this, it is preferable to form the dummy electrode layer 35.

In the ink jet recording head 1, the piezoelectric member 15 is separated from the ink channel 11 by the partition 3.
However, a moisture-proof coating may be applied to the surface of the piezoelectric member 15 or the like so that the surface directly faces the ink channel 11.

[Brief description of the drawings]

FIG. 1 is a plan view of an ink jet recording head using a piezoelectric member according to the present invention.

FIG. 2 is a cross-sectional view of the head shown in FIG. 1, taken along the line II-II.

FIG. 3 is a side view of the piezoelectric member according to the embodiment.

FIG. 4 is a diagram illustrating a modified example of a nozzle position.

FIG. 5 is a side view showing a modification of the piezoelectric member.

FIG. 6 is a cross-sectional view showing an example of a conventional ink jet recording head using a piezoelectric member.

[Description of Signs] 1 ... Inkjet recording head, 2 ... Channel plate, 3 ... Partition wall, 4 ... Substrate, 11 ... Ink channel, 1
4 ... nozzle, 15, 40 ... piezoelectric member, 21 ... piezoelectric layer,
31: first electrode layer, 32: second electrode layer, B: active portion of each piezoelectric layer.

Claims (2)

[Claims] 1. An ink jet recording head that presses ink contained in an ink channel based on a deformation of a piezoelectric member when a voltage is applied, thereby causing an ink drop to fly from a nozzle. An ink jet recording head in which a deformation amount at the time is larger than a deformation amount at the time of applying a voltage to a portion of the piezoelectric member close to the nozzle. 2. A piezoelectric member comprising a plurality of electrode layers and piezoelectric layers alternately laminated, wherein each of the piezoelectric layers has an active portion which deforms when a voltage is applied between upper and lower electrodes. A piezoelectric member provided from one end to the other end of the member, wherein the length of the active portion is shorter in an upper layer than in a lower layer.