JPH07117228A - Ink jet recording head and driving thereof - Google Patents

Abstract

PURPOSE:To enable the driving of the element in an ink liquid by arranging the element, of which the electrode part or whole is coated with an insulating film, generating a-volumetric change accompanied by ferroelectric phase-inverse ferroelectric phase transfer in the ink liquid and pressurizing the ink liquid by the driving of the element to inject an ink droplet. CONSTITUTION:An ink pressurizing means is formed within an ink cavity from an element constituted of an inverse ferroelectric phaseferroelectric phase transfer material 8 and the ink in the cavity is emitted as an ink droplet by utilizing the volumetric change of the element. The electrode 2 or internal and external electrodes 21, 22 is coated with an insulating material 7 to enable the driving of the element in the ink. When the electrode 2 or the internal and external electrodes 21, 22 are coated, the short-circuit between electrodes is prevented even when the distance between the electrodes is shortened and, by reducing the thickness of the element, the phase transfer start voltage of the phase transfer material 8 can be dropped. When the thickness of the element is reduced and the cross-sectional area thereof is made constant, change volume quantity is reduced but, by forming the element by alternately laminating the phase transfer materials 8 and electrode layers, the volumetric change necessary for emission is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording head and its driving method.

[0002]

2. Description of the Related Art Various printers have been proposed as a method of recording images and characters, and some have been commercialized. Examples of the recording method include various ones such as wire dots, thermal recording and laser printers. The wire dot method has a low printing speed, causes noise during printing, and has a low resolution, but has a relatively low cost. Since the thermal recording method requires a special recording paper or recording medium, it can be said that it is inferior to other methods in this respect. Further, the laser printer method is the most excellent of the existing recording methods, but it is expensive and has a complicated recording mechanism, so that there are restrictions in making the apparatus short, small and light. For this reason, the same printing quality as that of the laser printer can be obtained, the cost is almost intermediate between the laser printer and the wire dot printer, there is no noise, and printing on plain paper is possible. Inkjet recording methods are drawing attention.

As the ink jet recording method (generally, "on-demand type" is generally used), two kinds of methods, that is, an electrostatic suction type and a pressure conversion type, are usually adopted. The former electrostatic attraction type requires an ink charging mechanism, a bias power source of up to several kilovolts for attracting ink, and the printer device is complicated. On the other hand, the pressure generation mechanism in the latter pressure conversion system uses a thermal IJ (inkjet) recording system that uses energy when a phase of ink changes from a liquid to a gas, and an ink volume change caused by an inverse piezoelectric effect of a piezoelectric body. The thermal type ink jet recording method can be roughly classified into a DOD type ink jet recording method used for blowing. The thermal type ink jet recording method has a simple head configuration and can be miniaturized easily because a semiconductor manufacturing process can be used, but the life of the head is semi-permanent. Not the target
It is necessary to replace the heads with different inks, which raises the running cost and other restrictions. Further, this thermal IJ recording method is very effective for high-speed printing and colorization, and it is difficult to realize a head using solid ink at an early stage. Therefore, of the inkjet recording methods, the DOD type inkjet recording method is currently the most excellent.

By the way, the DOD type ink jet recording system applies a pressure to the ink in the ink chamber and ejects the ink in the form of a droplet from the ink nozzle by this pressure (FIG. 7). The ejected ink droplet has a high speed of 10 m / sec, and the pressure for ejecting the ink is a volume change due to the inverse piezoelectric effect of the piezoelectric material in order to efficiently convert an electric signal into a pressure wave. The features of the DOD type inkjet recording system are that the head has a long life and can be used semipermanently, and the running cost can be reduced as compared with the thermal type in which the head needs to be replaced together with the ink. Although a method of pressurizing the ink liquid chamber with a piezoelectric material through a vibrating plate is shown, it is possible to effectively apply pressure to the ink by installing the piezoelectric material in the ink liquid chamber. Japanese Patent Publication No. Sho 60-8953 proposes a method in which a piezoelectric element having a cantilever structure immersed in an ink liquid is vibrated to pressurize the ink droplets. Further, in Japanese Patent Publication No. 3-216344, at least one of the electrodes is covered with an insulating film to enable use in a conductive ink.

When an electric field is applied, the piezoelectric material expands in the direction parallel to the electric field and contracts in the direction perpendicular to the electric field. The volume change at this time is used as a pressure for ejecting ink. However, PZT (lead zirconate titanate ceramic) is generally used as the piezoelectric material, and in this case, since the volume change rate is as small as 0.03%, miniaturization is difficult, and the density of the ink ejection nozzle is increased. Is limited. Especially when installed in the ink liquid chamber, the size of the PZT is a constraint on the design of the ink liquid chamber.

[0006]

From this point of view, the energy conversion is not preferable due to the principle limitation that the strain has anisotropy due to the inverse piezoelectric effect of the piezoelectric material, and other energy conversion is desirable. The inventors of the present invention focused on the phenomenon that a huge strain, that is, a volume change, is caused by forcibly changing the phase from the antiferroelectric phase to the ferroelectric phase by an electric field, and attempted to solve the above problem by that. is there. Therefore, as compared with the piezoelectric material, a material having a large volume change rate by applying an electric field includes a ferroelectric phase-antiferroelectric phase transition material.

[0007]

A first aspect of the present invention is an ink jet recording head, in which an electrode portion or the entire element is covered with an insulating film to cause a volume change accompanying a ferroelectric phase-antiferroelectric layer transition. Is disposed inside the ink liquid chamber, and the element is driven to pressurize the ink to eject ink droplets. When the ink is in a liquid state, the means for ejecting the ink can be driven at a constant temperature with little temperature change. In addition to the phase transition caused by the electric field, there are phase transition materials caused by pressure, temperature, or light that cause the phase transition. In the present invention, any of these materials can be used. A phase change material by an electric field is desirable because high speed is required.

A second aspect of the present invention is a method for driving an ink jet recording head, which uses the head of the first aspect of the present invention to apply an offset voltage to a common electrode and a driving voltage to an individual electrode on the counter electrode side. It is characterized in that the recording is performed. When a solid ink is used as the ink, the above element can be heated by a heater for heating and driven at high temperature and constant temperature.

The present invention will be described in more detail below. FIG. 1 is a diagram for explaining the electric field induced strain of the antiferroelectric phase-ferroelectric phase transition material used in the present invention. From FIG. 1 showing the relationship between the PE hysteresis characteristic and the electric field induced strain,
The digital change of P (polarizability) with respect to the electric field corresponds to the digital change of the electric field induced strain. The electric field that increases the electric field from zero electric field and causes the phase transition is transferred to E _AF (at this time, the sample is in the state in which the antiferroelectric phase is changed to the ferroelectric phase), and is also transferred from the ferroelectric phase to the antiferroelectric phase. The electric field at is defined as E _FA in this specification. The inverse piezoelectric effect of the conventional piezoelectric material (PZT) has a displacement X _{3 in the} direction parallel to the electric field direction of about 0.09%, and a displacement X _{1 in the} direction perpendicular to the electric field direction is about −0.03. It is about%. Therefore, the volume change rate ΔV / V of this piezoelectric material is 0.03% from the following relational expression. ΔV / V = X ₃ + 2X ₁ (1) On the other hand, these values due to the antiferroelectric-ferroelectric phase transition of the present invention are about 0.3% to 0.4% for X _{3 and} about 0 for X _1. 0.07%
Is 0.08%, and the volume change rate ΔV is calculated from the equation (1).
A / V of 0.44% is obtained. This is because the PZT is anisotropically displaced, whereas the phase transition isotropically displaced. Further, as a result of examination of various compositions, some compositions show a larger volume change, for example, the volume change rate ΔV / V reaches 1.10%. Thus, the volume change rate ΔV accompanying the antiferroelectric phase-ferroelectric phase transition
/ V compared to that of conventional piezoelectric materials and 1-2
An order-of-magnitude change in volume can be obtained, which is larger than the order of magnitude.

The present invention utilizes the above-mentioned characteristics of the antiferroelectric phase-ferroelectric phase transition material to form an ink pressurizing means in the ink cavity by the material, and the ink in the cavity is Ink droplets are ejected from the nozzle by utilizing the volume change of the material. The "ink cavity" is an ink liquid chamber, and the "nozzle" is an ink ejection port.

As the antiferroelectric phase-ferroelectric phase transition material,
It is composed of a lead-based composite oxide containing at least one of lead zirconate and lead stannate, and specifically includes the following A, B, and C. A: Pb _1-0.5Z Nb _Z [(Zr _1-X Sn _X ) _1-Y Ti _Y ] _1-Z
O ₃ (0 ≦ X ≦ 0.5, 0 ≦ Y ≦ 0.1, 0 ≦ Z ≦ 0.0
2) B: Pb _{1-3 / 2Z} La _Z [(Zr _1-X Sn _X ) _1-Y Ti _Y ] O ₃ (0 ≦ X ≦ 0.5, 0 ≦ Y ≦ 0.2, 0 ≦ Z ≦ 0.0
2) C: Pb _1-X La _X (Zr _1-Y Ti _Y ) _{1-X / 4} O ₃ (0.08 ≦ X ≦ 0.24, 0 ≦ Y ≦ 0.8) Preferred composition among them Is shown in Table 1. In addition, Table 1 also shows the relationship between the composition and each value of strain when a phase transition occurs due to an electric field.

[0012]

[Table 1] Note X _3: displacement in a direction parallel to the electric field direction X _1: the direction parallel displacement relative to the electric field direction △ V / V: volume change rate A: (X = 0.3, Y = 0.045, Z = 0.02) B: (X = 0.26, Y = 0.11, Z = 0.02) C: (X = 0.08, Y = 0.3)

By using such a phase change material, the volume change rate can be 1.10% by examining various compositions, which is 0.03% in the conventional piezoelectric material.
It has extremely excellent characteristics compared to. Since the phase change material has a larger volume change rate than the piezoelectric material, the size of the element can be small, and the head can be downsized and the density can be increased. Further, as described above, the phase change material isotropically changes in the vertical and horizontal directions by the electric field induction. Therefore, the effect of isotropic distortion due to the phase transition is more prominent when the phase transition actuator is provided in the ink liquid chamber than when the displacement in a single direction is used as the pressure for ejecting ink through the vibration plate. Is fully available. Since the force generated by strain is directly used as the pressure for ejecting ink by not passing through the vibration plate, and the energy conversion efficiency of volume change-pressure is also improved, the element can be made smaller, and the element can be installed in the ink liquid chamber. However, there are few restrictions on the ink liquid chamber.

In the ink jet recording head of the present invention, at least the electrode portion or the entire element is covered with an insulating material (FIGS. 2 (a) (b)). By covering the electrode 2, or the internal electrode 21 and the external electrode 22 with the insulating materials 7 and 7 ', the deposition of dye or the like of the ink is prevented, and thereby the element can be driven even in the ink liquid. Examples of the insulating film material include SiO ₂ glass, diallyl phthalate resin, epoxy resin, methacrylic resin, polycarbonate, acrylic resin, polyamide resin, polyethylene, vinyl chloride and other insulating resins. Note that these materials may be used as a single layer,
Further, several kinds of films may be combined and used as a multilayer film. For example, a SiO ₂ film can be obtained by a vapor phase growth method, and an organic material can be formed by a spin coating method.

The electric field induced strain characteristics at 25 ° C. of the composition A sample in Table 1 are shown in FIG. The pressurization of the ink by the material is performed by the element made of the material provided in the ink cavity. Further, in the present invention, it is desirable to provide a mechanism for holding the inside of the ink cavity at a temperature higher than room temperature (in the temperature range of 25 to 135 ° C.) by a well-known technique. When no voltage is applied, the phase is an antiferroelectric phase, but when the electric field is raised (or lowered), a phase transition occurs in the electric field E _AF to become a ferroelectric phase, and when the electric field is subsequently lowered (or raised), the ferroelectric phase is generated in the electric field E _AF . Return to phase. For example, in the formula A, X = 0.3, Y =
When 0.045 and Z = 0.02, E _AF = 40 kV /
cm. If the element has a thickness of 200 μm, the phase transition start voltage is 800V. However, if the thickness is 20 μm, the phase transition start voltage may be 80V. If the distance between the electrodes is shorter with the electrodes exposed, a short circuit between the electrodes is more likely to occur, but by covering the electrode part or the entire element, the short circuit between the electrodes can be prevented even if the distance between the electrodes is short. By reducing the film thickness of the device, the phase transition starting voltage of the phase transition material can be lowered. In addition, if the cross-sectional area is kept constant by reducing the thickness of the element, the volume of change will also decrease. However, the volume change required for ejection can be obtained by alternately stacking the phase-change material and the electrode layer on the element. You can

In the present invention, it is desirable to use an element that exhibits a sequential transition by taking a ferroelectric phase at a low temperature, an antiferroelectric phase at a room temperature, and a paraelectric phase at a Curie temperature or higher. Therefore, the temperature in the environment where the printer device is placed is desirable. Within the range, it is desirable to drive at a constant temperature in order to keep the characteristics constant. However, E _AF due to the temperature change of the antiferroelectric phase,
The change of E _FA is that E _AF is constant, but in E _FA , it shifts to the higher electric field side as the temperature increases. Further, the electric field-induced strain up to 135 ° C. is a value comparable to room temperature. Therefore, as an element of an inkjet recording head that ejects solid ink, it is desirable to heat it by a heater for heating and to drive it under a high temperature of about 135 ° C. and in a constant temperature state without being affected by the ambient temperature. .

Compared with PZT piezoelectric materials, the materials for manufacturing these elements have a relative dielectric constant value that is lower by about one digit, and therefore reduce the load on the driver transistor in pulse driving. Since the E _FA value shifts to the high electric field side at high temperatures, a more realistic driving method is to apply an offset voltage to the vicinity of this E _FA value and separately provide only the signal corresponding to the print data. Driving with a pulsed electric field enables low voltage driving. In other words, when driving the element, an electric field such that the electric field applied to the element is equal to or less than E _FA is applied as an offset voltage to the common electrode side, and the ejection signal is used as a driving voltage on the counter electrode side. By applying the pulse voltage, the driving voltage can be lowered and the driving circuit can be simplified. FIG. 5 shows the relationship between the drive voltage waveform and the distortion of the element when (a) the offset voltage is applied and (b) when the offset voltage is not applied. By using the offset voltage, the same amount of change can be obtained even if the drive voltage is lowered.

As a printing method, the ink is ejected (pushing) by increasing the volume of this material from before the ink is ejected, or the ink is ejected by contracting and increasing after the ink is ejected. (Striking)
Ink ejection methods are possible, and in order to realize them, an offset electric field below and / or above the phase transition electric field is applied, and the element is driven by applying a positive and / or negative driving pulse electric field corresponding to the ink ejection signal. You can do it. The phase change material may be arranged in a laminated structure or a bisilk type or multimorph type actuator structure.

[0019]

EXAMPLES Next, the present invention will be described more specifically with reference to examples.

[0020] Example 1 ferroelectric phase -... As an anti-ferroelectric phase transition _{material, Pb 0 997 La 0 02 [} (.. Zr 0 725 Sn 0 275) 0 91 T
i _{0 .09} ] O ₃ was used. The element was formed into a green sheet with a thickness of about 20 μm, and an electrode was formed by using Pt paste by a thick film printing method repeatedly on a phase change material to form an eight-layer laminate, which was about 60 μm wide. After cutting out with a glass, a glass film having a thickness of about 10 μm was formed as an insulating film on the electrode portion.
An element shown in (a) was obtained. The element thus prepared was placed in an ink liquid chamber as shown in FIG. 4A to prepare a recording head. The common electrode was connected to a 60V offset power supply and the individual electrodes were connected to a driving power supply. FIG. 6 shows a drive circuit. When the recording head produced in this manner was used for driving, ink ejection was observed.

Example 2 A phase change material having the same composition as in Example 1 was applied to a 3
After cutting the laminated body having a layered structure to a thickness of about 160 μm, the entire element was covered with polycarbonate and installed as shown in FIG. 4 (b), and when driving was attempted, ink ejection was confirmed.

Example 3 As an antiferroelectric phase-ferroelectric phase transition material, Pb was used._0.985Nb_0.3[(Zr_0.998Sn_0.02)_0.955Ti
_0.045] O₃  It was used. Electric field induced strain characteristics with respect to temperature of this material
Is E at 135 ° C_AF= 40 kV / cm, E_FA= 2
6 kV / cm, and the electric field induced strain at this time is X₃=
0.34%, X₁= 0.085%, volume change rate Δ
V / V = 0.51. This element is the same as in Example 1.
The recording head was made by using
Ink containing natural wax and having a melting point of 100 ° C.
When printing using, it can be seen that good ink ejection
It was

Example 4 C: Pb _0.92 La _0.08 (Zr _0.7 Ti _0.3 ) _0.992 O ₃ was used as the antiferroelectric phase-ferroelectric phase transition material. E _{AF at} 30 ° C. = 35 kV / cm,
E _FA = 18 kV / cm, the electric field induced strain at this time was X ₃ = 0.21%, X ₁ = 0.07%, and the volume change rate ΔV / V = 0.35. A laminate was prepared in the same manner as in Example 2 and printing was performed, and similar results were obtained.

[0030]

According to the present invention, the following effects are brought about. (1) In the ink recording head in which the phase change material is installed in the ink liquid chamber, the element can be driven in the ink liquid by covering the electrode portion with the insulating material. (2) By covering the electrode part or the entire element, short circuit between electrodes can be prevented even if the distance between electrodes is shortened, and the phase transition starting voltage of the phase change material can be reduced by reducing the film thickness of the element. Became possible. (3) By alternately stacking the phase change material and the electrode layer, the volume change required for ejection can be obtained even when the element using the phase change material is thinned. (4) As a method of constructing the head, bimorph and multimorph type actuators can be arranged. (5) Applying an electric field such that the electric field applied to the element is equal to or less than E _AF as an offset voltage to the common electrode side, and applying a pulse voltage corresponding to the ejection signal as a driving voltage to the individual electrode on the counter electrode side As a result, the driving voltage can be lowered and the driving circuit can be simplified.

[Brief description of drawings]

FIG. 1 is a diagram for explaining electric field induced strain of an antiferroelectric phase-ferroelectric phase transition material.

2 (a) and 2 (b) are views of two examples of a device that causes a phase transition change used in the present invention.

3A and 3B are diagrams showing electric field distortion characteristics of a phase change material.

FIG. 4A is an example of a recording head incorporating an element using a laminated phase transition material, and FIG. 4B is an example of a recording head incorporating a phase transition material as a multimorph type actuator.

FIG. 5 shows the relationship between the drive voltage waveform and the distortion of the element. (A) is an example when an offset voltage is used,
(B) is an example when the offset voltage is not used.

FIG. 6 is a diagram showing a drive circuit.

FIG. 7 is a diagram showing a structure of a conventional inkjet recording head.

[Explanation of symbols]

 1 Support Substrate 2 Electrodes (21 Internal Electrodes, 22 External Electrodes) 3 Ink Liquid Chamber 4 Ink Liquid Flow Path 5 Ink Nozzle Hole 6 Protective Layer 7 Insulating Material 8 Phase Change Material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiji Murakami 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (14)

[Claims] 1. An element, in which an electrode portion or the entire element is covered with an insulating film, which causes a volume change associated with a ferroelectric phase-antiferroelectric phase transition, is arranged inside an ink liquid chamber, and ink is applied by driving the element. An ink jet recording head characterized in that pressure is applied to eject ink droplets. 2. The ink jet recording head according to claim 1, wherein a distance between electrodes for driving the element is 100 μm or less. 3. The ink jet recording head according to claim 1, wherein the element has a laminated structure having electrodes made of the same material. 4. The ink jet recording head according to claim 1, 2 or 3, wherein the element has a bimorph or multimorph structure. 5. The inkjet according to claim 1, wherein the substance having a ferroelectric phase-antiferroelectric phase transition is a lead-based composite oxide containing at least one of lead zirconate and lead stannate. Recording head. 6. The lead-based composite oxide has the following general formula (I) Pb 1 _-0.5Z Nb _Z [(Zr _1-X Sn _X ) _1-Y Ti _Y ] O ₃ (I) (0 ≦ X ≦ 0.5, 0 ≦ Y ≦ 0.1, 0 ≦ Z ≦ 0.
The ink jet recording head according to claim 5, which is represented by 02). 7. The lead-based composite oxide is represented by the following general formula (I
I) Pb _{1-3 / 2Z} La _Z [(Zr _1-X Sn _X ) _1-Y Ti _Y ] O ₃ (II) (0 ≦ X ≦ 0.5, 0 ≦ Y ≦ 0.2, 0 ≦ Z ≦ 0.
The ink jet recording head according to claim 5, which is represented by 02). 8. The lead-based composite oxide is represented by the following general formula (II
I) Pb _1-X La _X (Zr _1-Y Ti _Y ) _{1-X / 4} O ₃ (III) (0.08 ≦ X ≦ 0.24, 0 ≦ Y ≦ 0.85) The inkjet recording head according to claim 5, wherein 9. The ink jet recording head according to claim 1, further comprising a device for driving the element at a constant temperature. 10. A multi-inkjet recording head in which a plurality of heads according to any one of claims 1 to 4 and 9 are mounted and each bit is independently driven. 11. An ink jet recording head according to any one of claims 1 to 4 and 9, wherein an offset voltage is applied to a common electrode and a drive voltage is applied to an individual electrode on the counter electrode side for recording. An inkjet recording method characterized by the above. 12. The method for driving an inkjet recording head according to claim 11, wherein when the solid ink is used, the element is heated by a heater for heating and is driven at a high temperature and a constant temperature. 13. The head according to any one of claims 1 to 4 and 9, wherein the volume of the element is made larger than that before ink ejection, or the volume of the element is once contracted from before ink ejection. 13. The method for driving an inkjet recording head according to claim 11, wherein the ink is ejected by increasing the amount afterward. 14. The head according to claim 1, wherein an offset electric field equal to or less than a phase transition electric field of a substance having a ferroelectric phase-antiferroelectric phase transition is applied to the common electrode. 14. The method for driving an inkjet recording head according to claim 11, 12 or 13, wherein positive and / or negative driving pulse electric fields corresponding to ink ejection signals are applied to individual electrodes to drive the elements.