JPH05318726A - Liquid drop discharger - Google Patents

Abstract

PURPOSE:To improve durability of a liquid drop discharger in a simple construction by a method wherein miniaturization and high efficiency of a multi-nozzle type liquid drop discharger capable of printing in high density are achieved. CONSTITUTION:A plurality of partition walls 1a-1d are provided normally to a passage substrate 3, and a cover plate 6 consisting of a piezoelectric element board is fixed to its upper end surface. The cover plate 6 is polarized in a thickness direction. When, for example, voltage is impressed to electrodes 4b, 5, the cover plate 6 is shrunk, and the partition walls 1b, 1c are bent to be deformed. A cubic volume of a passage 2b is decreased, and liquid in the passage 2b is discharged from the nozzle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a droplet discharge device, and more particularly, it is used in an on-demand type multi-nozzle ink jet recording apparatus having a plurality of nozzles and ejecting ink droplets from each nozzle as needed. Droplet discharge device.

[0002]

2. Description of the Related Art Presently, on-demand type multi-nozzle ink jet recording apparatuses include a method in which an electric signal is converted into a mechanical displacement by using a piezoelectric element and pressure is applied to ink in a flow path to eject ink droplets. There is a so-called bubble jet method in which ink droplets are ejected by the pressure of vapor generated by applying heat to the ink in the path.

As a piezoelectric element, a cylindrical structure for covering a flow path is disclosed in US Pat. No. 3,683,212, and a diaphragm structure is disclosed in US Pat. No. 3,946,398. Has been done. Further, JP-A-55-
No. 65559 discloses a structure in which a bimorph element, which is generally called a Kaiser type, in which a piezoelectric element and a vibration plate are combined is attached to the upper portion of each flow path. In the conventional inkjet head using these piezoelectric elements,
It is difficult to realize a high-density multi-nozzle head for realizing high print quality because one piezoelectric element must be associated with one nozzle and the piezoelectric element is large. FIG. 7 shows a typical conventional example of a Kaiser type head. As described above, in the Kaiser type head, the vibration plate 22 also serving as a cover is bonded to the substrate 21 in which the flow path 20 is formed, and the piezoelectric element 23 is bonded to each flow path portion on the vibration plate. As is clear from FIG. 7A, the nozzle 24
Since the piezoelectric element 23 is larger than the pitch, the flow path becomes fan-shaped and it is difficult to increase the nozzle density. Also the flow path 2
The shapes of 0 are different from each other, and the characteristics of the ink droplets ejected from the respective flow paths are not constant. Further, it is necessary to attach a large number of piezoelectric elements to respective fixed positions, which causes a problem that the manufacturing process becomes complicated.

Japanese Patent Publication No. 61-59911 discloses the so-called bubble jet principle. In this method, since the heating element for heating the ink can be made small, the above-mentioned problems caused by the high density and the large number of nozzles, which are found in the ink jet head using the conventional piezoelectric element, are small. However, the bubble jet method is much less efficient than the piezoelectric element method, and it is necessary to give 10 times or more energy to eject one ink droplet. Further, since it is necessary to boil the ink, it is necessary to use an ink that has a relatively low boiling point and does not cause deterioration due to heat or form an adhered substance on the heating element. Further, there is a problem in durability such that the heating element is damaged by cavitation generated when the vapor bubbles are generated and extinguished.

In order to overcome these problems, Japanese Patent Laid-Open No. 63-63
No. 247051 discloses a method using a shear mode of a piezoelectric element. A typical configuration is shown in FIG. 8. In this method, a flow path partition is constituted by a piezoelectric element 28 that is polarized in the height direction of the head 27 and is perpendicular to the substrates 25 and 26, and electrodes formed on both sides of the partition are used. An electric field perpendicular to the polarization direction 29 is applied, the flow path partition of the piezoelectric element is deformed by the shear mode, pressure is applied to the ink in the flow path, and an ink droplet is ejected from the nozzle 30. In this method, by optimizing the two dimensions of the flow path partition vertical to the nozzle array direction and the flow path length, it is possible to secure the displacement amount of the flow path partition necessary for ink droplet ejection. The flow paths can be arranged at the same pitch as the nozzles, and an inkjet head having a high density and a large number of nozzles can be constructed.
Further, similar to the conventional inkjet head using a piezoelectric element, any ink having high energy efficiency can be used.

However, in the method using the above shearing mode,
Since the flow path partition is composed of a piezoelectric element, it is 50 to 500 [μ
[m]], it is necessary to combine a large number of very thin piezoelectric element plates, or to form a large number of flow path partition walls having a height of several hundred μm or more on a rectangular parallelepiped piezoelectric element substrate by some method. As the piezoelectric material, PZT, quartz, niobate rezyme, etc. are known, but all of them are hard and brittle.
It is not suitable for forming a large number of flow path partition walls by machining. Further, it is possible to form the flow path partition wall by a chemical method such as etching, but these materials cannot be said to have good workability, and it is very difficult to process them to a depth of several hundred μm. Therefore, in the configuration using the shearing mode, the manufacturing cost becomes enormous and mass production is difficult.

[0007]

As described above, the ink jet recording apparatus using the conventional piezoelectric element has the advantages of high energy efficiency and the ability to use any ink, but high density printing for high quality printing. However, it is not suitable for a large number of nozzles.

Further, the bubble jet method has problems such as poor energy efficiency, large restrictions on ink, and poor durability.

In order to solve these problems, an ink jet recording apparatus using a shearing mode of a piezoelectric element is also disclosed, but it is necessary to perform fine processing on a fragile piezoelectric material, which is difficult to manufacture and mass production is difficult. Not suitable.

Therefore, an object of the present invention is to provide a droplet discharge device having a large number of nozzles arranged at high density, energy efficiency and durability with a novel principle and structure, which can be mass-produced and inexpensively provided. is there.

[0011]

In order to achieve the above object, the present invention provides a flow having a plurality of partition walls provided in a direction substantially perpendicular to the plane direction and a flow path defined by the partition walls. It is characterized in that it includes a path substrate and a cover plate made of a piezoelectric element plate polarized in the thickness direction and fixed to the end face of the partition wall.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the preferred embodiments shown in the accompanying drawings. FIG. 1 is a flow path cross-sectional view showing the basic configuration of a droplet discharge device according to the present invention. In the droplet discharge device according to the present invention, a plurality of partition walls 1a, 1b, 1c, 1d are formed substantially at right angles to the surface direction.
Ink flow paths 2a, 2b, 2 by a, 1b, 1c, 1d
The flow path substrate 3 in which c is partitioned and the drive electrodes 4 are formed on both surfaces.
a, 4b, 4c and a ground electrode 5 are formed respectively, and a cover plate 6 made of a piezoelectric element plate polarized in the thickness direction (direction of arrow P) and, although not shown in FIG. And a nozzle plate provided.
Considering both the ease of deformation of the partition walls and the processability of the flow paths and the partition walls, the flow paths 2a, 2b, 2c and the partition walls 1a, 1 are considered.
The cross section of b, 1c and 1d is preferably rectangular.

FIG. 2 is a principle diagram for explaining the droplet discharge operation of the above apparatus. Here, the operation of ejecting a droplet from the flow path 2b will be described. Of the three drive electrodes 4a to 4c shown, the drive electrode 4b corresponding to the flow path 2b.
Only, the voltage is applied in the direction in which the piezoelectric element (cover plate 6) contracts in the plane. Channel 2 of cover plate 6
Since only the upper part of b shrinks, the partition walls 1 on both sides of the flow path 2b
b and 1c are attracted, and the volume of the flow path 2b is reduced. For this reason, pressure is applied to the liquid in the flow path 2b, and droplets are ejected from the nozzle. Further, when the non-selected channel 2a is described, the piezoelectric element plate above the adjacent channel 2b contracts,
The piezoelectric element portion above the flow path 2a, and further the partition wall 1a is also the flow path 2b.
It is drawn in the direction and deforms. However, in this case, since the partition wall 1a is deformed in the same direction as the partition wall 1b, the volume of the flow channel 2a does not change, and no pressure is applied to the ink in the flow channel 2a. The same applies to the flow path 2c. As described above, according to the present invention, it is possible to eject droplets by selecting only a specific channel using the cover plate 6 that is a structurally integrated piezoelectric element plate.

Next, FIG. 3 is a perspective view of a multi-nozzle ink jet head using the present invention, and FIG. 4 is a sectional view thereof. A large number of flow paths 8 and partition walls 9 are formed on the flow path substrate 7. The cross section of each flow path 8 and the partition wall 9 is substantially rectangular. Each flow path 8 is independent on the nozzle plate 10 side and communicates with a common ink chamber 11 for supplying ink on the opposite side. Each flow path 8 and the partition wall 9 extend in parallel from the nozzle portion to the common ink chamber portion and correspond to the pitch of the nozzles 10a. For this reason, it is not necessary to take a fan-shaped flow path arrangement as seen in an ink jet head using a conventional piezoelectric element, and it is possible to create a multi-nozzle ink jet head having an arbitrary number of nozzles. It can be applied to both serial printers and line printers.

A ground electrode 12 is provided on the lower surface of the flow path substrate 7,
A cover plate 14 made of a piezoelectric element plate having a drive electrode 13 corresponding to each flow path formed on the upper surface is mounted. This piezoelectric element plate serves as an actuator that deforms the flow path partition wall 9 and also has a function as a flow path cover. Each drive electrode 13 has an electrode terminal 13a for supplying a signal from a flexible cable or the like. A nozzle plate 10 having nozzles 10a corresponding to the respective flow paths is mounted on the front surface of the head.

In this structure, the flow path substrate 7 is a passive component in which the partition wall 9 formed in a part of the flow path substrate 7 is deformed by the cover plate 14 made of a piezoelectric element plate. Therefore, the flow path partition wall itself is a piezoelectric element. The selection range of the material and forming method of the flow path substrate 7 is very wide as compared with the configured conventional inkjet recording apparatus. For example, a plastic member formed by injection molding suitable for mass production can be used. Further, particularly when durability of the head is required, it is possible to use a photosensitive glass whose physical properties are changed by exposure to ultraviolet rays and which can be selectively etched by further heat treatment. In the case of this configuration, since it is necessary to form a relatively deep channel, XeF and XeC, which are ultraviolet light sources excellent in linearity, are used as the exposure light source.
It is desirable to use an excimer laser using a gas such as 1, KrF, KrCl, or ArF.

Next, the dimensions for actually designing the multi-nozzle ink jet head will be described. X [dp
i] (dots per inch) printing density is realized with n flow passage rows, the adjacent flow passage pitch DN is: DN = 0.0254 × n / X [m] (1) Become. Further, the dot diameter DD required at this time is DD = √2 × 0.0254 / X [m] (2) It is empirically known that flying ink droplets become dots having a diameter of about twice when they adhere to paper, so the required ink droplet amount Qi is as follows. ^{Qi = π × DD 3/48} [m 3] ··· (3) By the way, the ink in the pressurized flow path in addition emitted as an ink droplet from a nozzle, also flowing back into the common ink chamber side. For this reason, the partition wall must provide the flow path with a volume reduction of about twice or more the required ink droplet amount. Therefore, the required channel volume change amount Qc is: Qc ≧ 2 × Qi (4)

Next, the contraction amount ω of the piezoelectric element plate is obtained. The thickness of the piezoelectric element plate is T, and the width of the drive electrode is 0.8 of the flow path pitch.
When the applied voltage is V and the lateral piezoelectric constant is d, the contraction amount ω is as follows. ω = d × V × 0.8 × DN / T (5) Since the partition wall is deformed substantially as shown in FIG. 2, the partition wall height is H and the flow path length is L. The flow path volume change amount dQ at this time is as follows: dQ = ω × H × L / 2 (6) At this time, it is assumed that the lateral rigidity of the partition wall is sufficiently smaller than that of the piezoelectric element plate.

Since the flow path volume change amounts Qc and dQ must be equal, from Equations 4 and 6, 2 × Qi ≦ ω × H0 × L0 / 2 (7) Here, by rewriting Qi using the equations (1) to (3) and substituting the equation (5) for ω, the following equation is obtained. 1.9 × 10 ⁻⁴ × π / X ² ≦ d × V × H × L × n / T (8) Deformation gives H × L ≧ 1.9 × 10 ⁻⁴ × π × T / (X ² × d × V × n) (9) With this formula, it is possible to roughly estimate the relationship between the dimensions of each part, the physical properties of the material, and the driving conditions, which are necessary to obtain an arbitrary nozzle density.

Here, the lateral piezoelectric strain constant d is 198 × 10 ⁻¹²
[M / V], driving voltage V of 200 [V], and thickness T of the piezoelectric element plate of 10 ⁻⁴ [m], a flow path length L required for heads having various nozzle densities is obtained. The relationship between the heights H of the partition walls is shown in FIG. FIG. 5 (a) shows a case where the flow path is configured by one row (n = 1), and FIG. 5 (b) shows a case where the head is configured by two flow path rows that are shifted by a half pitch (n = 2). is there.
In FIG. 5, the relationship between the partition wall height and the flow path length must be at the upper right of the curve in order to create a head of each print density. Explaining in more detail with reference to FIG. 5A, it is at the upper right of the curve of 400 [dpi] under the condition of the flow path length of 30 [mm] and the partition wall height of 0.4 [mm].
Although it can be applied to a 00 [dpi] head,
Since it is located on the lower left of the curve of 0 [dpi], it is not possible to obtain a sufficient amount of ink droplets for printing, and it cannot be applied to the 300 [dpi] head.

As described above, by using the equation (9), it is possible to know the lower limits of the flow path length and the head partition height for designing a head having desired specifications. On the other hand, the flow path length and the partition wall height have upper limits in order to satisfy requirements such as reduction of material cost, realization of a small and light printing device, and reduction of partition wall height to improve workability. The upper limits of these practical dimensions are: flow path length L ≦ 100 [mm] ... (10) Partition wall height H ≦ 2 [mm] ... (11). Therefore, in order to realize the recording apparatus based on the present invention, the flow path length and the partition wall height are expressed by equations (9), (10), (1)
It must be within the range that satisfies the expression (1).

Another embodiment using the present invention is shown in FIG. In order to realize a printing device having a high printing density, it is necessary to perform fine processing to form the flow path and the partition. Therefore, by forming the channels 16 and the partition walls 17 on both surfaces of the channel substrate 15 as shown in FIG. 6, the distance between the channels and the partition walls on each of these surfaces can be doubled, and the workability is improved. Further, as is apparent from the expression (9), the flow passage length L and the flow passage partition wall height H can be reduced by using two rows, and the workability can be improved and the printing apparatus can be downsized. it can.

In the droplet discharge device of the present invention, since the partition wall is deformed and pressure is applied to the liquid in the flow path so that the droplets are ejected from the nozzle, the physical properties of the liquid are not limited at all. It can also be used with ink. Therefore, the present invention is not limited to the recording device as a computer terminal, but can be applied to a wide range of applications such as ejecting any liquid, for example, industrial printing devices, small amount ejection of reagents, and facsimiles.

[0024]

As described above, according to the present invention, it is possible to inexpensively provide a droplet discharge device having a large number of nozzles arranged at high density, having high energy efficiency and excellent durability. is there.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing the operation of the first embodiment.

FIG. 3 is a perspective view of a second embodiment.

FIG. 4 is a sectional view of the second embodiment.

FIG. 5 is a relationship diagram showing a relationship between flow path length and partition wall height.

FIG. 6 is a sectional view of the third embodiment.

FIG. 7 is a plan view and a sectional view showing a first conventional example.

FIG. 8 is a plan sectional view and a front view showing a second conventional example.

[Explanation of symbols]

1a, 1b, 1c, 1d, 9, 17 Partition walls 2a, 2b, 2c, 8, 16 Channels 3, 7, 15 Channel substrates 4a, 4b, 4c, 13 Drive electrodes 5, 12 Ground electrodes 6, 14 Cover plate (Piezoelectric element plate) 10 Nozzle plate 10a Nozzle 11 Common ink chamber

Claims (9)

[Claims] 1. A flow path substrate having a plurality of partition walls provided in a direction substantially perpendicular to a plane direction, and a flow path partitioned by the partition walls, and a piezoelectric element plate polarized in a thickness direction. And a cover plate fixed on the end face of the partition wall. 2. The droplet according to claim 1, wherein a nozzle communicating with the flow path is provided, and the nozzle plate is fixed to end surfaces of the flow path substrate and the cover plate. Discharge device. 3. The nozzle according to claim 2, wherein the plurality of channels are connected at one end to form a common ink chamber and the other end communicates with the nozzle. The droplet discharge device is characterized in that it has a constant cross-sectional area between and. 4. The flow channel substrate according to claim 1, wherein the flow channel and the partition wall are formed on both sides of the flow channel substrate, and the pair of the flow channel substrates are mounted on both sides of the flow channel substrate. A droplet discharge device comprising a cover plate and the nozzle plate having a plurality of nozzle rows. 5. The cover plate according to claim 1, wherein a thickness of the cover plate is T, a lateral piezoelectric constant is d, an applied voltage is V, and a printing density is X [dpi], and the number of flow channels is n. In the case of forming a head, the flow path length L of the flow path and the height H of the flow path partition are configured so as to satisfy the following three formulas. H × L ≧ 1.9 × 10 ⁻⁴ × π × T / (X ² × d × V ×
n) L ≦ 100 [mm] H ≦ 2 [mm] 6. The droplet discharge device according to claim 1, wherein the flow path substrate is a plastic member formed by injection molding. 7. The flow channel substrate according to claim 1, wherein the flow channel substrate is a member formed by exposing a photosensitive glass substrate in a flow channel shape and performing anisotropic anisotropic etching. Droplet discharge device. 8. The droplet discharge device according to claim 7, wherein an excimer laser is used as the light source for exposure. 9. The cover plate according to claim 1, wherein the cover plate is made of a piezoelectric element having electrodes formed on both surfaces thereof, and at least one of the electrodes is patterned according to the shape of the flow path. A droplet discharge device, wherein an electric field parallel to a polarization axis can be applied only to a portion of the cover plate corresponding to an arbitrary selected flow path.