JP2008119871A - Liquid delivering head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose an inkjet head capable of generating a sufficient ink delivery pressure by using a polymer piezoelectric element and delivering a necessary amount of ink droplets by an enough delivery speed. <P>SOLUTION: In the inkjet head 1, an outer peripheral wall part of an ink flow path 5 is formed of a piezoelectric body frame 2 with a constitution winding a polymer piezoelectric film into a multi-layers, and when a high electric voltage is loaded on the piezoelectric body frame 2 by a high electric voltage loading means 8, first and second rigid plates 3 and 4 on both ends are displaced in the approaching and separating directions to change the volume of the ink flow path 5. Even though the displacement force per unit volume for the polymer piezoelectric element material is extremely small in comparison with a piezo-element, as the whole of the outer peripheral wall part of the ink flow path 5 is made to the piezoelectric body frame 2 consisting of the polymer piezoelectric element material, it is possible to generate a pressure change necessary for delivering ink droplets from the ink nozzle 61 communicating with the ink flow path 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid discharge head such as an ink jet head capable of discharging droplets such as ink using a polymer piezoelectric element material at a sufficient discharge pressure and discharge speed.

  As an inkjet head of an inkjet printer, a piezoelectric inkjet head configured to eject ink droplets using a piezoelectric element is known. Patent Documents 1 and 2 disclose an inkjet head that ejects ink droplets using a PZT element (lead zirconate titanate). In recent years, in the fields of medicine and biotechnology, attempts have been made to use a liquid discharge head having a structure similar to that of an ink jet head for supplying and dispensing chemical solutions and test solutions.

  Here, the PZT element has the largest piezoelectric constant and Young's modulus that determine the ink discharge pressure, among many other ferroelectrics (piezoelectric bodies), and serves as a pressure generating actuator for discharging ink droplets. Is the optimal material. As an actuator for an inkjet head using a PZT element, an actuator having a unimorph structure that converts the displacement of the PZT element into a flexure, and an ink discharge pressure is generated by directly pressurizing the ink flow path (ink pressure chamber) with the PZT element. A structure having a structure in which a side wall of an ink flow path formed by a piezoelectric element is bent in an out-of-plane direction to pressurize the ink flow path has been proposed.

  However, since the PZT element contains lead although it is an oxide, processing steps from manufacture to disposal in consideration of safety and environmental pollution are required. Further, since the PZT element is made of ceramics, there is a problem that a high temperature firing process exceeding 1000 ° C. is required and the environmental load is large.

In order to solve such a problem of the piezo element, it is conceivable to construct an actuator using a polymer piezoelectric element material such as a polyvinylidene fluoride copolymer. For example, when a copolymer of vinylidene fluoride and ethylene trifluoride is stretched and then crystallized in a paraelectric phase above the Curie temperature, a ferroelectric polymer is obtained, and a high electric field is applied to the polymer. It is known that when polarized, a piezoelectric / pyroelectric polymer is obtained. Patent Document 3 discloses a printer head using such a polymer piezoelectric element material.
JP 2006-35791 A JP 2005-104163 A JP 2004-281711 A, Example 10, FIG.

  However, the polymer piezoelectric element material has a problem that the piezoelectric constant and Young's modulus are remarkably low as compared with a ferroelectric such as a PZT element. Therefore, an inkjet head capable of ejecting a sufficient amount of ink droplets at a sufficient ejection pressure and ejection speed even when an actuator for generating ink droplet ejection pressure using a polymer piezoelectric element material is obtained. Is difficult.

  For example, in the printer head disclosed in Patent Document 3, a pair of electrodes is formed at a site apart from the outer peripheral surface of a tube made of P (VDF-TrFE), and an ink droplet is ejected by applying an electric field. Yes. In other words, the actuator disclosed here is called a squeeze type, and the tube is provided with two contracting portions, and a pulse-like pressure is generated in the tube using the time difference of contraction to eject ink droplets. Yes. However, the actuator having this structure cannot obtain a sufficient ink discharge pressure and cannot discharge a desired amount of ink droplets at a sufficient discharge speed.

  In view of this point, an object of the present invention is to generate a sufficient droplet discharge pressure using a polymer piezoelectric element material and to discharge a necessary amount of droplets at a sufficient discharge speed. It is to propose a liquid discharge head.

In order to solve the above problems, the liquid ejection head of the present invention is
A cylindrical piezoelectric frame formed from a polymeric piezoelectric element material;
A first rigid plate sealing one open end of the piezoelectric body frame;
A second rigid plate sealing the other open end of the piezoelectric frame;
A liquid flow path formed inside the piezoelectric body frame sealed by the first and second rigid plates;
A liquid supply hole formed in the first rigid plate for supplying liquid to the liquid flow path;
A liquid droplet discharge head formed on the second rigid plate for discharging the liquid supplied to the liquid flow path as liquid droplets;
The piezoelectric frame is characterized by being displaced in an in-plane direction along the inner and outer peripheral surfaces thereof.

  In the liquid discharge head of the present invention, the outer peripheral wall portion of the ink flow path is formed of a piezoelectric frame made of a polymer piezoelectric element material, and this piezoelectric frame approaches the first and second rigid plates at both ends. It is configured to be displaced in the direction of separation. The displacement force per unit volume is extremely small, about 1/300, for a polymer piezoelectric element material compared to a piezoelectric element. However, in the present invention, since the entire outer peripheral wall portion of the ink flow path is a piezoelectric body made of a polymer piezoelectric element material, the volume of the piezoelectric body is 300 times that of a conventional actuator such as a unimorph structure using a piezoelectric element. This can be done.

  Further, since the piezoelectric frame expands and contracts in the in-plane direction, the first and second rigid plates at both ends are displaced in a direction approaching and separating from the piezoelectric frame, and the piezoelectric frame itself contracts due to contraction. Therefore, the volume of the liquid channel surrounded by the piezoelectric body frame and the first and second rigid plates can be sufficiently increased and decreased to generate sufficient pressure fluctuations necessary for droplet discharge. .

  In addition to this, in the case of an actuator using a conventional piezo element, in order to transmit a small displacement of the piezo element so as to cause a volume change of the ink flow path without loss, the piezo element is supported, Although a support structure for receiving the reaction force accompanying the displacement is necessary, according to the present invention, such a support structure is unnecessary.

  Here, the piezoelectric frame can be formed by winding a polymer piezoelectric film made of a polymer piezoelectric element material in a frame shape. In this case, what laminated | stacked the electrode thin film on both surfaces of the polymer piezoelectric film should just be wound in multiple so that an insulating thin film may be pinched | interposed and it may become a cylindrical frame.

  The present invention is characterized by having high voltage applying means for applying a high voltage of 100 to 800 V to the piezoelectric frame in order to displace the cylindrical frame. By applying a high voltage, a sufficient displacement can be generated, and thereby a sufficient droplet discharge pressure can be secured.

  That is, the mine electric field of the polymer piezoelectric element material, for example, P (VDF / TrFE) is 400 to 450 KV / cm. When the thickness of the polymer piezoelectric film is 5 μm, the applied voltage needs to be 200 V or less. When the thickness of the polymer piezoelectric film is 20 μm, it is necessary to drive with an applied voltage of 800 V or less so as not to exceed the well electric field. Here, in order to generate a driving force for ejecting a sufficient amount of droplets, it is desirable that the thickness of the piezoelectric body frame be 1 mm or more. Therefore, when a polymer piezoelectric film having a thickness of 20 μm is wound 50 times to form a piezoelectric frame having a thickness of 1 mm, the piezoelectric film is driven at 800 V or less, and a polymer piezoelectric film having a thickness of 5 μm is wound 200 times to obtain a thickness. When a 1 mm-thick piezoelectric body frame is formed, it may be driven at 200 V or less. In order to obtain a large driving force, the piezoelectric frame may be driven with as high an electric field as possible within a range not exceeding 400 to 450 KV / cm.

  Instead of forming the piezoelectric frame from a polymer piezoelectric film, the piezoelectric frame can be an injection-molded frame made of a polymer piezoelectric element material. In this case, electrodes may be formed respectively on the inner peripheral surface and the outer peripheral surface of the injection molding frame. In this case, it is desirable to cover the outer peripheral surface and inner peripheral surface of the piezoelectric body frame with an insulating thin film.

  Here, when the thickness of the piezoelectric body frame is at least 1 mm, it has high voltage applying means for applying a high voltage of 10,000 to 40,000 V to the piezoelectric body frame in order to displace the piezoelectric body frame. Is desirable. By applying a high voltage, a sufficient displacement can be generated, and thereby a sufficient droplet discharge pressure can be secured.

On the other hand, the polymeric piezoelectric element material used in the present invention may contain a polyvinylidene fluoride copolymer. Any of the following can be used as the polyvinylidene fluoride copolymer.
Polyvinylidene fluoride ethylene trifluoride (P (VDF-TrFE))
Polyvinylidene fluoride tetrafluoride ethylene (P (VDF-TFE))
Polyvinylidene fluoride trifluoride ethylene
(Hexafluoropropylene P (VDETFE-HFE)
Polyvinylidene fluoride (hexafluoropropylene P (VDF-HFE))

  In particular, polyvinylidene fluoride trifluoride ethylene (P (VDF-TrFE)) has an advantage of being easy to manufacture because it exhibits a piezoelectric effect without performing a stretching treatment.

  In the liquid discharge head of the present invention, the entire outer peripheral wall portion of the ink flow path is formed by a piezoelectric frame that extends and contracts in the in-plane direction made of a polymer piezoelectric element material, and ink supply holes are formed at both ends of the piezoelectric frame. And a second rigid body on which a droplet discharge nozzle is formed are pasted. Therefore, the volume of the piezoelectric element can be remarkably increased as compared with the actuator for generating the droplet discharge force using the conventional piezoelectric element. Therefore, it is possible to generate a sufficient droplet discharge pressure using a piezoelectric element made of a polymer piezoelectric material having an extremely small piezoelectric constant and Young's modulus, so that a desired amount of droplets can be discharged at a sufficient droplet discharge speed. A possible liquid discharge head can be realized.

  Embodiments of a liquid discharge head to which the present invention is applied will be described below with reference to the drawings.

  FIG. 1 is a perspective view showing an ink jet head according to the present embodiment, FIG. 2 is a longitudinal sectional view showing a portion cut along the line AA, and FIG. 3 is an exploded perspective view thereof. The ink jet head 1 according to the present embodiment includes an elongated rectangular cylindrical piezoelectric body frame 2 formed from a polymer piezoelectric element material and a first rectangular body sealing one open end 2a of the piezoelectric body frame 2. The rigid plate 3 and a rectangular second rigid plate 4 that seals the opening end 2b on the opposite side of the piezoelectric body frame 2 are provided. A liquid-tight ink flow path 5 is defined in the piezoelectric body frame 2 and the first and second rigid plates 3 and 4.

  The first rigid plate 3 is thick at one end in the long side direction, and a circular hole 32 extending vertically from the inner surface 31 in the thickness direction is formed in this portion. Yes. The hole 32 communicates with an ink introduction tube 34 protruding from the end surface 33 of the first rigid plate 3. In this example, the hole 32 is press-fitted with an insertion tube 36 in which an orifice 35 for supplying ink is formed, and ink from an external ink supply source (not shown) is supplied to the ink introduction tube 34 and the orifice. The ink flow path 5 is supplied to the ink flow path 5.

  The second rigid plate 4 attached to the opening end 2b on the opposite side of the piezoelectric body frame 2 is formed with an ink flow channel groove 41 having a constant depth on the inner surface thereof. The ink channel groove 41 has a deep bottom at the end opposite to the ink supply orifice 35, and an ink supply hole 42 is formed at the bottom of the portion. A nozzle plate 6 is affixed to the protruding end face 43 of the second rigid plate 4 where the outer opening of the ink supply hole 42 is located, and the rear of the ink nozzle 61 formed so as to penetrate the nozzle plate 6. The end opening communicates coaxially with the ink supply hole 42.

  As the first and second rigid plates 3 and 4, plastic injection molded products can be used. For example, materials such as PSF, PES, POM, ABS, and PC can be used. The nozzle plate 6 can be a semiconductor substrate such as silicon, a plastic plate, or the like. The ink nozzle 61 may be formed on the semiconductor substrate by etching. In the case of a plastic plate, the ink nozzle 61 may be formed by laser processing.

  The piezoelectric frame 2 is formed by winding a polymer piezoelectric film in multiple layers as described below, and an outer peripheral end portion is drawn outward to form an electrode terminal portion 7. A high voltage of 800 to 1000 V is applied to the electrode terminal portion 7 by a high voltage applying means 8 comprising a high voltage generating circuit or the like.

  4A and 4B are a perspective view and a partial cross-sectional view showing the piezoelectric body frame 2 formed of a polymer piezoelectric element material. The piezoelectric body frame 2 of this example is a laminated body having a structure in which an inner electrode thin film 22 and an outer electrode thin film 23 are laminated on an inner surface and an outer surface of a polymer piezoelectric film 21 made of a P (VDF-TrFE) copolymer. The insulating thin film 24 is sandwiched and wrapped in a rectangular frame shape. For example, the inner electrode thin film 22 and the outer electrode thin film 23 are formed on both surfaces of the polymer piezoelectric film 21, and the laminated body 20 having a structure in which the insulating thin film 24 is laminated on the surface of the outer electrode thin film 23 is wound and bonded. It is obtained by doing.

  In this way, the rectangular cylindrical frame made of the laminate 20 is heated and recrystallized, and then a high voltage direct current is applied between the electrodes to perform polarization treatment, thereby obtaining the piezoelectric frame 2. It is done. In this example, the inner peripheral surface of the piezoelectric frame 2 is covered with an insulating thin film 25.

  As the electrode thin film material, a metal material such as Au, Al, or Cr can be used, and the metal material can be laminated on the surface of the polymer piezoelectric film 21 by sputtering, vapor deposition, CVD, or the like. As the insulating thin film, a metal oxide film such as SiO 2 or a thin film made of an organic material can be used.

  The end portion of the laminated body 20 wound around the outermost peripheral side of the piezoelectric body frame 2 configured in this manner is drawn outward as described above to form the electrode terminal portion 7. In the electrode terminal portion 7, the electrode thin films 22 and 23 on both sides of the polymer piezoelectric film 21 are exposed, and a high voltage is applied to the exposed portion by the high voltage applying means 8. The polymer piezoelectric film 21 contracts in a direction perpendicular to the electric field application direction. That is, since an electric field is applied in a direction perpendicular to the surface of the polymer piezoelectric film 21, the polymer piezoelectric film 21 contracts in the in-plane direction, and the piezoelectric body frame 2 is shown by arrows a to in FIG. As shown by h, it shrinks in the in-plane direction along the inner and outer peripheral surfaces.

  The inventors of the present invention form an inner electrode thin film 22 and an outer electrode thin film 23 made of Au on both surfaces of a polymer piezoelectric film 21 made of a P (VDF-TrFE) copolymer having a thickness of 5 μm, and the outer electrode A piezoelectric body having a thickness T of approximately 0.612 mm is obtained by winding a laminate 20 (thickness approximately 5.1 μm) having a structure in which the thin film 23 is covered with an insulating thin film 24 made of SiO 2 in a rectangular frame shape 120 times. Frame 2 was produced. Further, as shown in FIG. 4A, the height H of the piezoelectric body frame 2 is 5 to 8 mm, the length L of the ink flow path 5 inside thereof is 8 mm, and the width W is 1.5 mm.

  The piezoelectric frame 2 having this dimension was recrystallized by heating at about 140 ° C. Next, a polarization treatment was performed by applying a DC high voltage of about 4000 V to the inner electrode 22 and the outer electrode 23. Thereafter, an insulating thin film 25 was formed on the inner peripheral surface of the piezoelectric body frame 2. Finally, the first rigid plate 3 and the second rigid plate 4 to which the nozzle plate 6 is attached are attached to the piezoelectric body frame 2 to obtain the ink jet head 1.

  A high voltage of 100 to 200 V was applied to the piezoelectric body frame 2 of the inkjet head 1 by the high voltage applying means 8. As a result, the first and second rigid plates 3, 4 are displaced in a direction approaching each other due to the contraction of the piezoelectric body frame 2, the volume of the ink flow path 5 is decreased, the internal pressure is increased, and the ink nozzle 61 It was confirmed that about 1000 picoliters of ink droplets can be ejected. Further, it was confirmed that a sufficient ink droplet discharge amount can be secured by setting the thickness T of the piezoelectric body frame 2 to 1 mm or more.

(Another example of a piezoelectric frame)
FIGS. 5A and 5B are a perspective view and a partial cross-sectional view showing another example of the piezoelectric body frame 2. The piezoelectric body frame 2A of this example is an injection molded product using a polymer piezoelectric element material made of a P (VDF-TrFE) copolymer. In this case, after the frame body 20A of the piezoelectric body frame 2A is manufactured by injection molding, the inner electrode thin film 22A and the outer electrode thin film 23A are formed so as to cover the inner and outer peripheral surfaces thereof. Thereafter, after recrystallization by heating at a high temperature, a direct current high voltage is applied between the electrodes to perform polarization treatment. Next, the inner insulating thin film 25A and the outer insulating thin film 24A are formed so as to cover the inner electrode 22A and the outer electrode 23A. Finally, the ink jet head is obtained by attaching the first and second rigid plates 3 and 4 to both ends of the piezoelectric body frame 2A.

  Here, when a piezoelectric frame 2A having a thickness of 1 mm is manufactured and a high voltage of 10,000 to 40,000 V is applied to the piezoelectric frame 2 in order to displace the piezoelectric frame 2A, sufficient displacement is generated. It was confirmed that a sufficient droplet discharge pressure can be secured.

  The electrode material and the insulating material can be the same materials as in the piezoelectric body frame 2, and the film formation method can be the same as that in the piezoelectric body frame 2.

  Further, one or both of the first and second rigid plates 3 and 4 can be integrally formed with the frame body 20 of the piezoelectric body frame 2A by injection molding. In this case, the same material as that of the frame body 20 can be used for injection molding. Alternatively, these parts can be integrally molded by two-color molding using different materials.

(Other embodiments)
In each of the above examples, the inner and outer peripheral surfaces of the piezoelectric body frames 2 and 2A are covered with an insulating thin film. For example, in the case of a disposable type, the inner insulating thin film can be omitted.

In addition to the P (VDF-TrFE) copolymer, the following polyvinylidene fluoride copolymer can be used as the polymer piezoelectric element material.
Polyvinylidene fluoride tetrafluoride ethylene (P (VDF-TFE))
Polyvinylidene fluoride trifluoride ethylene
(Hexafluoropropylene P (VDETFE-HFE)
Polyvinylidene fluoride (hexafluoropropylene P (VDF-HFE))

  Furthermore, although the above example is one in which the present invention is applied to an ink jet head, the present invention can be similarly applied to a liquid discharge head for supplying a liquid other than ink such as a chemical liquid or a test liquid.

It is a perspective view which shows the inkjet head to which this invention is applied. It is a longitudinal cross-sectional view which shows the part cut | disconnected by the AA line of FIG. It is a disassembled perspective view of an inkjet head. (A), (b) is the perspective view and fragmentary sectional view of a piezoelectric material frame. (A) And (b) is the perspective view and partial sectional view which show another example of a piezoelectric material frame.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet head, 2 Piezoelectric frame, 2a, 2b Open end, 1st rigid board, 4th rigid board, 5 Ink flow path, 6 Nozzle plate, 7 Electrode terminal part, 8 High voltage application means, 20 Frame body, 20A Frame body, 21 Polymer piezoelectric film, 22, 22A Inner electrode thin film, 23, 23A Outer electrode thin film, 24, 24A, 25, 25A Insulating thin film, 31 Inner surface, 32 holes, 33 End face, 34 Ink introduction Pipe, 35 Orifice, 36 Insertion pipe, 41 Ink channel groove, 42 Ink supply hole, 43 Projecting end face, 61 Ink nozzle

Claims (9)

A cylindrical piezoelectric frame formed from a polymeric piezoelectric element material;
A first rigid plate sealing one open end of the piezoelectric body frame;
A second rigid plate sealing the other open end of the piezoelectric frame;
A liquid flow path formed inside the piezoelectric body frame sealed by the first and second rigid plates;
A liquid supply hole formed in the first rigid plate for supplying liquid to the liquid flow path;
A liquid droplet discharge head formed on the second rigid plate for discharging the liquid supplied to the liquid flow path as liquid droplets;
The liquid discharge head using a polymer piezoelectric element material, wherein the piezoelectric body frame is displaced in an in-plane direction along an inner and outer peripheral surface thereof. In claim 1,
The piezoelectric body frame is
Formed by winding a polymer piezoelectric film composed of the polymer piezoelectric element material and a laminate composed of electrode thin films formed on both sides of the polymer piezoelectric film in multiple layers so as to form a cylindrical frame with an insulating thin film interposed therebetween A liquid discharge head characterized by being made. In claim 2,
The polymer piezoelectric film has a thickness of 5 to 20 μm,
A liquid discharge head comprising high voltage applying means for applying a high voltage of 100 to 800 V to the piezoelectric frame in order to displace the piezoelectric frame. In claim 1,
The piezoelectric frame is an injection-molded frame formed using the polymer piezoelectric element material,
A liquid discharge head, wherein electrodes are respectively formed on an inner peripheral surface and an outer peripheral surface of the injection molding frame. In claim 4,
The liquid discharge head according to claim 1, wherein an outer peripheral surface and an inner peripheral surface of the piezoelectric frame are covered with an insulating thin film. In claim 4 or 5,
The piezoelectric frame has a thickness of at least 1 mm;
A liquid discharge head comprising high voltage applying means for applying a high voltage of 10,000 to 40,000 V to the piezoelectric frame in order to displace the piezoelectric frame. In any one of claims 1 to 6,
The liquid piezoelectric head is characterized in that the polymer piezoelectric element material contains a polyvinylidene fluoride copolymer. In claim 7,
The polyvinylidene fluoride copolymer is
Polyvinylidene fluoride ethylene trifluoride (P (VDF-TrFE))
Polyvinylidene fluoride tetrafluoride ethylene (P (VDF-TFE))
Polyvinylidene fluoride trifluoride (hexafluoropropylene P (VDETFE-HFE), and
Polyvinylidene fluoride (hexafluoropropylene P (VDF-HFE))
Any one of the above-mentioned liquid discharge heads. In claim 7,
The liquid discharge head, wherein the polyvinylidene fluoride copolymer is polyvinylidene fluoride trifluoride ethylene (P (VDF-TrFE)).

Images