JPH08309985A - Inkjet head - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object of the present invention to provide an inkjet head capable of forming a high-quality image by controlling the dot diameter of a printed dot, by suppressing the oxidation of an electrode and the adhered matter, by having a stable electrode life. To do. [Structure] In order to remove oxides and deposits on the electrode 4,
An alternating voltage pulse is applied between the electrode 4 and the counter electrode 5. Further, in order to control the print dot diameter, the application time of the AC voltage pulse and the number of preliminary ejection pulses after application of the AC voltage pulse are controlled. [Effect] Stable electrode performance can be obtained without forming oxides or deposits on the electrode, and long life can be obtained. Further, it is possible to form a high quality image by area gradation printing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head for ejecting ink droplets to print or print on a printing paper.

[0002]

2. Description of the Related Art In recent years, inkjet printers have come to be widely used as output printers for home and office computers because of their quietness during recording, high-speed recording capability, and easy colorization. This inkjet printer drops the ink into small droplets and makes them fly.
The recording is performed by adhering it to a recording paper, and is roughly classified into a continuous method and an on-demand method according to a method of generating a droplet and a method of controlling a flight direction.

The continuous system is a system disclosed, for example, in US Pat. No. 3,604,029, in which ink droplets are electrostatically attracted and the generated droplets are responded to a recording signal. Electrolysis control is performed to selectively deposit small droplets on the recording paper for recording.High voltage is required to generate small droplets, and multi-nozzle is difficult to achieve, so it is not suitable for high-speed recording. .

The on-demand system is, for example, US Pat.
In the system disclosed in the specification of Japanese Patent No. 4747120,
An electric recording signal is added to the piezoelectric vibrating element attached to the recording head having a nozzle hole for ejecting a small droplet,
This electric recording signal is converted into mechanical vibration of the piezoelectric vibration element, and recording is performed by ejecting a small droplet from the nozzle hole according to the mechanical vibration and attaching it to the recording paper.
Since ink is ejected from the nozzle holes on-demand for recording, it is not necessary to collect the droplets that were not required for image recording among the ejected droplets as in the continuous method. Configurable. On the other hand, it is difficult to process the recording head and it is very difficult to miniaturize the piezo vibrating element to make it into a multi-nozzle type. It has drawbacks.

Further, Japanese Patent Publication No. 61-59911, Japanese Patent Publication No. 62-11035, and Japanese Patent Publication No. 61-59914 disclose recording methods of a system in which a heating resistor causes boiling to cause droplets to fly. ing.

As another example of the on-demand system, the system disclosed in US Pat. No. 3,179,042 (Sperry's patent) uses a thermal vibration energy instead of using mechanical vibration energy by means such as a piezoelectric vibration element. It describes the use of energy. Compared with the method that uses mechanical vibration energy, it has the features of high energy conversion efficiency and easy multi-nozzle formation.

Next, the ejection principle will be described. FIG.
3 is a sectional view of a conventional ink ejection device. In FIG. 13, 42 is a conductive ink, 43 is an ink chamber filled with the conductive ink 42, 21 is an ink tank containing the conductive ink 42, 4 is a pair of electrodes arranged below the liquid level of the conductive ink, 44 is a power supply, 45 is a switch of the power supply 44,
Reference numeral 7 is a nozzle for ejecting the conductive ink 42, 10 is a recording medium, and 9 is an ink droplet ejected from the nozzle 7.

When a voltage is applied to the pair of electrodes 4, a current flows through the conductive ink 42, and the Joule heat causes a portion of the conductive ink 42 between the tips of the electrodes 4 to vaporize. Further, the vaporized vapor of the conductive ink 42 expands until a sufficient pressure is generated to eject the ink droplet 9 from the nozzle 7 to the recording medium 10. By applying a voltage with the switch 45, it is possible to select a nozzle hole for ejecting the conductive ink 42 and form a desired character on the recording medium 10.

FIG. 14 is a sectional view of a main part of a conventional ink jet head, and FIG. 15 is a sectional view taken along line AA of FIG. In FIG. 14, 8 is a pressure chamber, 7 is a nozzle formed on the upper surface of the pressure chamber 8, 1 is a substrate that forms the bottom surface of the pressure chamber 8, 2 is a partition plate that forms the side surface of the pressure chamber 8, and 3 is a nozzle. The nozzle plate 7 is formed to form the upper surface of the pressure chamber 8, 14 is a discharge signal generator that generates a signal to be sent to the electrode 4, 9 is an ink droplet discharged from the nozzle 7, and 10 is a front surface of the nozzle 7. A recording medium, 4 is a pair of electrodes arranged on the bottom surface of the pressure chamber 8, and 39 is the substrate 1 for generating heat of ink.
A heat insulating layer laminated on the upper surface of the substrate 1 so as not to escape to
Reference numeral 41 is an ink flow path connected to the pressure chamber 8, arrow a shown in FIG. 15 is a line of electric force passing between the electrodes 4, and arrow B is a current passage portion passing through the ink.

A method of manufacturing the ink jet head having the above structure will be described below.

A heat insulating layer 39 made of SiO ₂ is sputtered on a non-conductive substrate 1 made of glass or ceramics such as silicon, and the Ar pressure is set to 10 mTorr.
Then, sputtering is performed at an output of 300 W for 30 minutes, and a SiO ₂ layer having a thickness of 1 μm is formed to be laminated. Then T
Conductive electrode 4 made of i, Au, Pt, Ni or the like is attached to heat insulating layer 3
9 is laminated on the substrate 9 by a physical film forming method such as a vapor deposition method or a sputtering method or a plating method. A pattern of the electrodes 4 is formed on the substrate 1 on which the electrodes 4 are laminated by a photolithography method, and a portion other than the electrodes 4 is removed by ion milling or chemical etching. Then, a durable film 40 such as an organic polymer or ceramics is formed by coating or sputtering on the portion of the electrode 4 other than the portion exposed to the pressure chamber 8 and the substrate 1. A nozzle plate 3 having a partition plate 2 made of a polymer resin and a nozzle 7 formed by an excimer laser processing machine on a substrate 1 on which the durable film 40 and the electrode 4 are laminated, and the nozzle 7 being the center of two electrodes 4. Glue so that it is located in the area.

The operation of the ink jet head manufactured as described above will be described below. The pressure chamber 8 and the ink flow path 41 are filled with ink, and a signal generated by the ejection signal generator 14 applies a voltage between the electrodes 4. Next, lines of electric force a are generated in the ink filled between the pair of electrodes 4. Since the ink has a predetermined volume resistivity, a current flows through the current passing portion b in the ink.
As a result, Joule heat is generated in the ink, so that the temperature of the ink rises and bubbles (not shown) are generated on the electrode 4 and the common electrode in the pressure chamber 8. When the bubble becomes large, the pressure in the pressure chamber 8 rises rapidly, and the ink in the pressure chamber 8 is ejected from the nozzle 7 toward the recording medium 10. At this time, due to the volume decrease in the pressure chamber 8, ink is supplied from the ink flow path 41 to complete one cycle of ink ejection. By repeating this cycle according to the signal from the ejection signal generator 14, an arbitrary dot is formed on the recording medium 10.

[0013]

However, in the conventional ink jet ink described above, it is necessary to reduce the specific resistance in order to reduce the voltage applied to the electrodes. Therefore, a large amount of an inorganic salt such as LiCl must be contained, but when a large amount of an inorganic salt is contained, the dissolution stability of the color forming agent, especially the dye, is lowered and the solidification is apt to occur, and the nozzle hole is clogged. It had a problem that it would end up.

Furthermore, when printing on printer paper,
In order to enhance the contrast of printing, it is preferable to contain a large amount of a color former, but if a large amount of the color former is contained, the color former is easily solidified, and if the inkjet ink is stored for a long period of time, a solid content is generated. However, there is a problem that solid content adheres to the nozzle holes, which adversely affects the uniformity of the ink droplets or the stability of the ink droplets in the flight direction, and deteriorates ejection stability, ejection response, and continuous recording performance. Was there.

Furthermore, the inclusion of a halogen compound adversely affects the stability / adhesion of the material forming the head, for example, the adhesion stability of the polyimide material to the adhesion, and the ejection stability, ejection response, and continuous recording property. Had a problem that Further, when the AC frequency of the voltage applied to the electrodes is lower than 5 MHz, it is not a bubble that contracts like a boiling bubble, but a chemical reaction such as electrolysis of the ink jet ink causes the electrolysis that does not shrink and extinguish hydrogen and oxygen. Bubbles are generated, the bubbles stay between the electrodes and in the nozzle holes, and the current does not flow to the inkjet ink, so that boiling cannot be continued, or even if the current flows to the inkjet ink and boil. Bubbles due to electrolysis stay in the nozzle holes and discharge is not performed normally. Further, at the same time, a dissolution reaction of the electrodes occurs, so that it becomes difficult for an electric current to flow in the inkjet ink and it becomes impossible to boil it. This problem is solved by increasing the AC frequency of the voltage applied to the electrode to 5 MHz or more, but the AC frequency applied to the electrode is 5 MHz.
If it is set higher than the above, unnecessary radiation noise generated from the drive circuit increases, and the price of the drive driver becomes very high.

In the conventional ink jet head described above, when it is used for a long time, the electrode is oxidized or dissolved due to an electrochemical reaction that takes place at the interface between the ink and the electrode, and a composition such as a dye in the ink causes a deposit on the electrode. Due to such a phenomenon, the ejection life of the head is significantly deteriorated. Further, since the electrode life is deteriorated by the oxidation and dissolution of the electrode and the adhered substances, it is impossible to control the size of the boiling bubble to control the ink amount at the time of ejection,
Area gradation printing was impossible.

The present invention solves the above-mentioned conventional problems, and provides a durable ink jet head capable of preventing the corrosion reaction and dissolution at the interface between the electrode and the ink and having no influence of the deposit on the electrode. The purpose is to provide and achieve area gradation printing.

[0018]

In order to achieve this object, an ink jet head according to claim 1 of the present invention comprises:
A pressure chamber, a nozzle hole formed in the pressure chamber wall surface, and a wall surface of the pressure chamber facing the nozzle hole.
Formed at a pair of electrodes, one counter electrode disposed separately from the electrodes, an ink flow path connected to the pressure chamber, and an end of the ink flow path opposite to the pressure chamber. An ink jet head having a formed ink supply port, characterized in that it has means for applying a voltage between the pair of electrodes and the counter electrode.

In the ink jet head according to a second aspect of the invention, the counter electrode is arranged in a part of the cartridge, and a voltage is applied between the pair of electrodes and the counter electrode.

The inkjet head according to claim 3 is
When a voltage is applied between the pair of electrodes and the counter electrode, the pair of electrodes has a low potential with respect to the counter electrode.

In the ink jet head according to a fourth aspect, when a voltage is applied between the counter electrode and the pair of electrodes, the pair of electrodes are anode-dissolving electrodes, the pair of electrodes are A high electric potential is applied to the counter electrode.

In the ink jet head according to a fifth aspect of the present invention, an alternating voltage is applied when a voltage is applied between the counter electrode and the pair of electrodes.

In the ink jet head according to the sixth aspect, the voltage is applied between the counter electrode and the pair of electrodes at an alternating frequency of 100 kHz or more.

In the ink jet head according to the seventh aspect, when a voltage is applied between the counter electrode and the pair of electrodes, the applied voltage is 50 V or less.

In the ink jet head according to the present invention, when the voltage pulse is applied between the counter electrode and the pair of electrodes, the voltage pulse is applied when the ink ejection pulse is not applied. We are in control.

In the ink jet head according to the ninth aspect, when the voltage pulse is applied between the counter electrode and the pair of electrodes, the application time of the voltage pulse is when the head block is at the home position of the carriage. ,
It is set to 10 μsec or more.

In the ink jet head according to the tenth aspect, when the voltage pulse is applied between the counter electrode and the pair of electrodes, the voltage pulse is applied for a time when the head block is not printing at the home position. At this time, it is set to 100 msec or less.

In the ink jet head according to the eleventh aspect, when the voltage pulse is applied between the counter electrode and the pair of electrodes, the application time of the voltage pulse is 10 msec when the recording paper is exchanged. The above is applied.

In the ink jet head according to the twelfth aspect of the invention, when the voltage pulse is applied between the counter electrode and the pair of electrodes, the application time of the voltage pulse is changed when the recording paper is changed by other than automatic paper feeding. When I am there, I try to keep it for one hour or less.

In the ink jet head according to the thirteenth aspect, when a voltage pulse is applied between the counter electrode and the pair of electrodes, the print dot diameter is controlled by controlling the application time of the voltage pulse. There is.

In the ink jet head according to claim 14, the voltage pulse is applied between the counter electrode and the pair of electrodes when a voltage pulse whose application time is controlled is applied to control the print dot diameter. After that, the preliminary ejection pulse is applied.

In the ink jet head according to the fifteenth aspect of the present invention, the voltage pulse is applied between the counter electrode and the pair of electrodes when a voltage pulse having a controlled application time is applied to control the print dot diameter. After that, the preliminary ejection pulse is applied 1,000,000 times or less.

The preferred embodiments of the present invention will be described in detail below. The recording liquid that can be used in the present invention is
It may be either water-soluble or oil-soluble. In view of odor and safety, water-soluble is preferable. To the ink, a dye, alcohol as a wetting agent, a water-soluble organic solvent such as glycols, a surfactant, or a mixture thereof is added, which causes bleeding, drying rate, adjustment of boiling state, electrode life,
It is preferable for nozzle clogging. In addition, preservatives are also used. Specifically, those described in “Inkjet Recording Technology” p177 of Trikeps Co., Ltd., Tokuya Ota, Nikkei Electronics, No. 303, 1982, 11.8,
The same, Journal of Electrophotography, vo124, 354 (198).
5)), Akio Owatari, "Proceedings of the 4th Symposium on Non-Impact Printing Technology", IEICE, 93 (1)
987), Shinichi Hirasawa, "Do" 89 (1987), Kenji Sawaki, Textile and Industry, vol. 47, 212, (199
The materials described in 1) and JP-A-63-1579 can be used.

Next, specific examples of the constitution of the recording liquid usable in the present invention will be described. Colorants (dyes; azo dyes, acid dyes, basic dyes, direct dyes, pigments; carbon black, azo lake pigments, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, berylene pigments, berinone pigments, atlaquinone pigments, quinacridone Pigment, dioxazine pigment, thioindico pigment, isoindolinone pigment, quinophthalone pigment, basic dye type lake, acidic dye type lake, nitro pigment, aniline black, fluorescent pigment, titanium oxide, iron oxide, etc.), solvent (water etc.), Solvent (ethyl alcohol, methyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec
-Butyl alcohol, tert-butyl alcohol, isobutyl alcohol, n-pentanol, lower dialkyl ethers of polyhydric alcohols such as diethylene glycol), anti-drying agents (glycerin, urea, sorbitan,
Sorbitol, inositol, chelating agents, etc., viscosity adjusting agents (glycerin, etc.), surface tension adjusting agents (diaeranolamine, triethanolamine, anionic surfactants, nonionic surfactants), pH adjusting agents (potassium hydroxide) (KOH), sodium hydroxide (NaOH), dieranolamine, etc.), dispersant (proteins, natural rubber,
Cellulose derivative, natural polymer, nonionic polymer, anionic surfactant, nonionic surfactant, etc.), foaming agent (isopropyl alcohol, polyhydric alcohol), antioxidant (vitamin C, sodium sulfite, hydroquinone, Pyrazolidone, hydrazine, etc.), preservatives (alcohol, formalin, omasin sodium, etc.) and the like.

It is particularly preferable to use a conductive ink in the present invention. US 4,5 for conductive ink
36,776 (JP 59-129274 A) (Olivetti patent), "In an ink for an selective ink jet printing press comprising an aqueous mixture of dyes, the mixture having a resistivity of 15 to 50 ohms / cm. An ink characterized in that it comprises a hydrolyzed salt in such an amount as to give the ink. Japanese Patent Laid-Open No. 5-179
No. 182, “Aqueous ink composition for ink jet recording containing water and a colorant, containing an alkanolamine or ethylene oxide adduct and / or propylene oxide adduct, and a salt consisting of hydrogen halide. Is disclosed. In addition, Japanese Patent Publication No. 2785/1990 describes concretely the inorganic salts. The conductivity-imparting agent used in the present invention may be an alkali metal compound salt such as lithium (Li), an inorganic salt such as ammonium sulfate, lithium chloride, sodium chloride or potassium chloride, or an organic salt, but a quaternary organic compound. Derivatives of ammonium salts can be preferably used. Specific examples of the compound, monoethanolamine sulfate, diethanolamine sulfate, triethanolamine sulfate, monoethanolamine nitrate, diethanolamine nitrate, triethanolamine nitrate, monoethanolamine phosphate, diethanolamine phosphate, Triethanolamine phosphate, dimethanolamine sulfate, trimethanolamine sulfate, diethylamine sulfate, triethylamine sulfate, dimethylamine sulfate, trimethylamine sulfate, monopropylamine sulfate, dipropylamine sulfate, tripropyl Amine sulfate, phenylamine sulfate, diphenylamine sulfate, dimethyleneamine sulfate, trimethyleneamine sulfate, diethyleneamine sulfate, triethyleneamine sulfate, dipropyleneamine Salt, tripropylene amine sulfate, pyridine sulfate, can be mentioned pyrrole sulfate or the like.

The wetting agent has a boiling point higher than that of water,
It is used to prevent the nozzle tip from drying. Specific examples of the wetting agent include alkylene glycols having an alkylene group of 2 to 6 carbon atoms, such as polyethylene glycol, polypropylene glycol, butylene glycol, and hexylene glycol, such as ethylene glycol ethyl ether, diethylene glycol methyl ether, and diethylene glycol. Examples include lower alkyl ethers of diethylene glycol such as ethyl ether, glycerin and the like. The polyhydric alcohol is contained in an amount of 0.1 to 10% by weight, preferably 0.5 to 3.0% by weight. As the amount of polyhydric alcohol was less than 0.5% by weight, the nozzle tip tended to become clogged due to ink drying, and as the amount of polyhydric alcohol exceeded 3.0% by weight, the ink specific resistance tended to increase. Was found, and it was found that each was not preferable.

Examples of the solvent include water and organic solvents which can be mixed with water. Examples of the organic solvent include alkyl alcohol such as methyl alcohol, ethyl alcohol, n-propyl alcohol and isopropyl alcohol, ketone or keto alcohol such as acetone and diacetone alcohol, amides such as dimethylformamide and dimethylacetamide, tetrahydrofuran, dioxane and the like. And ether alcohols such as ethylene glycol monomethyl ether and ethylene bricol monoethyl ether, and water-soluble polymer compounds. Water used as a solvent is 30 to 80% by weight, preferably 5
It is contained in an amount of 0 to 70% by weight. As the water content is less than 50% by weight, the penetrability into paper tends to improve, and as the water content exceeds 70% by weight, the penetrability into paper tends to decrease. all right.

A surfactant, a pH adjuster, a viscosity adjustor and the like may be added to the ink jet ink in order to adjust the physical properties of the liquid.

The surface tension adjusting agent is added to improve the quick-drying property of the inkjet ink and at the same time prevents evaporation of the inkjet ink, and it is preferable to use a water-soluble organic solvent or a surfactant as the adjusting agent. The water-soluble organic solvent may be selected from the above solvents. Specific examples of the surfactant include fatty acid salts, higher alcohol sulfate ester salts, liquid fatty acid sulfate ester salts, fatty alcohol phosphate ester salts, dibasic fatty acid ester sulfone salts, fatty acid amide sulfonates, and alkylallyl sulfones. Acid salts, formalin-condensed naphthalene sulfonates, alkylpyridium salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters Can be mentioned.

Any pH adjusting agent may be used as long as it can adjust the pH value to a desired value without adversely affecting the ink-jet ink to be prepared. Specifically, lower alkanolamines and alkali metal hydroxides can be used. Examples of the monovalent hydroxide, ammonium hydroxide and the like.

The viscosity modifier adjusts the viscosity of the ink jet ink, and specifically, polyvinyl alcohol, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, water-soluble acrylic resin, polyvinyl pyrrolidone, gum arabic. Starch etc. are mentioned.

Further, in order to reinforce the strength of the ink coating when it adheres to printing paper, alkyd resin, acrylic resin, acrylamide resin, polyvinyl alcohol,
A resin polymer such as polyvinylpyrrolidone may be added. In addition, it is advantageous to add a fungicide in terms of ensuring reliability during long-term storage.

[0043]

With this configuration and control, a reducing current is efficiently applied to the electrodes of the pair of electrodes by high-frequency alternating current to reduce the oxides of the electrodes and remove the deposits on the electrodes, and to prevent corrosion of the electrodes. Dissolution can be prevented.

Further, when the reduction current is applied when the printer is driven, it is efficiently performed during printing and during printing pauses, so that the reduction of the electrode and the adhered substances can be efficiently performed without affecting the printing speed of the printer. Since it can be removed, the inkjet head has excellent durability and can prevent corrosion and dissolution of the electrode.

Further, the boiling bubble volume can be controlled and the ink ejection amount can be controlled by the application time of the reducing current or the preliminary ejection after the application of the reducing current, so that the area gradation printing can be performed. It is possible to provide an inkjet printer having high image forming ability.

[0046]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is an exploded perspective view of an essential part of an ink jet head in one embodiment of the present invention, and FIG.
FIG. 9 is a sectional view taken along line AA ′ of FIG. 1 and 2, 1 is a substrate, 2 is a partition plate, 3 is a nozzle plate, 4 is an electrode, 6
Is an insulating film, 7 is a nozzle, 8 is a pressure chamber, 9 is an ink drop,
Reference numeral 10 is a recording medium, and these are the same as those in the conventional example. In the present invention, 5 is a counter electrode for applying a reduction pulse to the electrode 4. Further, 11 is an ink supply hole, 12 is a common ink chamber, 13 is an inter-electrode electric field concentration portion, and 31 is an insulating film opening portion.

FIG. 3 is a conceptual diagram regarding the driving system of the ink jet head in the embodiment of the present invention. FIG.
In FIG. 14, 14 is an ejection signal generator for boiling and ejecting ink, 15 is a reduction signal generator for applying a reduction pulse, and 16 is a changeover switch for switching between the ejection signal and the reduction signal.

Further, FIG. 9 is a conceptual diagram of a pulse application waveform relating to the drive of the ejection pulse and the reduction pulse in the present invention. 9A is a diagram showing the voltage waveform of the ejection pulse of the first embodiment, FIG. 9B is a diagram showing the voltage waveform when the ejection pulse of the first embodiment is continuously applied, and FIG. 9C is the first diagram. The figure which shows the voltage waveform of the reduction pulse of the Example is shown, and the horizontal axis shows time and the vertical axis shows voltage. (D) is a diagram showing a current waveform for the ejection pulse (a) of the first embodiment.
In each waveform, 32 is an ejection pulse application time, 33 is an ejection pulse rest time, 34 is an ejection driving cycle, 35 is an ejection pulse application voltage, 36 is a continuous ejection time, 37 is a reduction pulse application time, and 38 is a reduction. It is a pulse applied voltage. In the current waveform, 46 indicates the boiling start time and 47 indicates the bubble growth time. The horizontal axis represents time and the vertical axis represents current value.
The horizontal axis of each of the voltage and current waveforms (a) to (d) shown in FIG. 9 is the same time axis and indicates the timing of application or response of each pulse.

FIG. 5 is a block diagram of an ink jet printer incorporating the ink jet head having the electrode structure of the present invention shown in FIGS. In FIG. 5, 10 is a recording medium, 18 is an ink cartridge incorporating an ink jet head, 25 is a guide shift on which the ink cartridge 18 is placed, 22 is a carriage, 23 is a platen roller that conveys the recording medium 10, and home position 2 is shown.
Reference numeral 4 denotes a place where ink is purged while the ink cartridge 18 is moving on the carriage 22. No ejection pulse is applied, and the ink cartridge 18 returns to this place during printing standby.

The operation of the ink jet head configured as described above will be described with reference to FIGS. 1, 2, 3 and 9. First, the discharge signal generator 14 generates a discharge pulse of 3 MHz by setting the discharge pulse application voltage 35 to 25 V and the discharge pulse application time 32 to 50 μs to generate the electrode 4
Apply to. As a result, a current flows through the ink between the electrodes 4 facing each other, and Joule heat is generated in the ink itself due to the electric resistance of the ink, and the ink is heated. When the ink reaches the boiling point, bubbles (not shown) are generated in the ink. When the bubble expands, no current flows in the bubble, so that the current concentrates on the bubble surface, the bubble surface is further heated, and the bubble grows. As a result, the pressure of the ink in the pressure chamber 8 rapidly increases, and the ink droplet 9 is ejected from the nozzle 7. The ink droplet 9 is the recording medium 1.
At 0, dots are formed. When the bubble becomes large enough to eject the ink droplet 9, the ink between the electrodes 4 becomes small, and the current does not flow between the electrodes 4. When the electric current stops flowing, Joule heat is less generated, the ink is cooled, and the bubbles disappear. Ink is supplied from the ink supply hole 11 to the pressure chamber 8, and the inside of the pressure chamber 8 returns to the initial state. Since it takes several microseconds or more for heating the ink to start boiling again, during this period, the ejection signal generator 14 provides the ejection pulse pause time 33 to pause the application of the voltage to the electrode 4, It is possible to prevent unnecessary ejection of the ink droplet 9 due to double boiling of the ink. By repeating the above operation at intervals of the ejection drive cycle 34, dots are formed at arbitrary positions on the recording medium 10.

After repeating the above-mentioned discharge operation for the continuous discharge time 36, the signal path is switched to the reducing pulse by the changeover switch 16, and the reducing signal generator 15 changes the AC frequency to 100 kHz or more and the reducing pulse applying voltage 38. A reduction pulse of 50 V or less is applied between the electrode 4 and the counter electrode 5 for the reduction pulse application time 37 to reduce the oxide of the electrode 4 and remove the deposit on the electrode 4. After that, the changeover switch 16 is switched to the ejection signal path again, and the ejection pulse changes to the ejection signal generator 1.
4 is applied.

When the electrode 4 is made of a material containing Ti, Ti is subjected to a reduction action by applying a cathode current, but an anode pass current is formed by oxide on the surface of the electrode 4. Then, the oxidation of the electrode 4 proceeds. Therefore, in order to reduce the electrode 4,
It is necessary to apply a reduction pulse to the counter electrode 5 on the lower potential side. Further, in the case where the electrode 4 is other than Ti, for example, Cu, Pt, Au, Ni, Fe, etc. which dissolves the anode, a reduction pulse is applied between the electrode 4 and the counter electrode 5 contrary to the case of Ti. At this time, the reduction pulse is applied to the counter electrode 5 with the electrode 4 on the high potential side.

In the present embodiment, since Ti is used for the electrode 4, the reduction pulse sets the electrode 4 to the ground level, and the counter electrode 5 is supplied with an AC voltage of 50 V or less, preferably 2 to 10 V, at an AC frequency of 100 kHz, preferably 0. ．
The voltage was applied at 5 MHz or higher. As described above, Ti has an oxide passivation film on the surface, and is itself an insulator. However, when an AC voltage is applied, it is possible to energize the capacitor by charging and discharging due to the electrostatic capacity of the Ti oxide. Since the DC impedance of the Ti electrode 4 in this embodiment is several MΩ, no current flows,
The AC impedance becomes 100 kΩ or less after exceeding 100 kHz, and 10 kΩ at 0.5 MHz or more.
Since it becomes below, current flows. For these reasons,
In order to apply the reduction pulse efficiently, the AC frequency is
100 kHz or more is required, and in this embodiment, the AC frequency of the reduction pulse was 3 MHz.

When the reduction pulse application voltage 38 is low in consideration of the electrode life, the electrochemical reaction is less likely to occur, but it is several M.
When an AC frequency of about Hz is applied, considering the mobility of ions such as anions and cations in the ink, it is considered that the electrochemical reaction does not proceed as much as that under DC. Therefore, even if a reduction pulse application voltage of several tens V is applied, the electrode 4 does not significantly dissolve, and the oxide on the electrode 4 can be reduced and the deposit can be removed. In this embodiment, 5V was applied as the reduction pulse application voltage.

FIG. 10 shows the relationship between the reduction pulse application time 37 and the boiling start time 46 when the reduction pulse is applied between the electrode 4 and the counter electrode 5 of the present invention.
As shown in FIG. 9D, the boiling start time 46 depends on the current value flowing in the ink due to the temperature rise of the ink when Joule heat is generated in the ink by the ejection pulse applied to the ink between the pair of electrodes 4. The current value increases because the specific resistance of the ink decreases. At some point when the ink temperature rises, boiling bubbles grow rapidly and cover the electrodes 4, so that the current value flowing between the electrodes 4 decreases. This phenomenon continues for the bubble growth time 47. The boiling start time 46 becomes gradually longer due to the fact that the electrode 4 is gradually oxidized by the energization of the electrode 4 with the application of the ejection pulse, or the deposits are deposited on the electrode 4. In FIG. 10, the boiling start time 46
The Y side of the is the boiling start time 46 after the ejection pulse is already applied tens of millions of times, and is a state in which oxides and deposits are formed on the electrode 4. The boiling start time 46 decreases with the reduction pulse application time 37 because the reduction of the electrode oxide by the reduction current and the reduction and removal of the deposits occur. As shown in FIG. 10, boiling start time 4
When the reduction pulse application time 37 is 100 ms or less, 6 decreases as the reduction pulse application time 37 increases, but when the reduction pulse application time 37 is 100 ms or more, the decrease in the boiling start time 46 reaches the saturation point, It is no longer decreasing. This indicates that when the reducing pulse in this example was 3 MHz and 5 V, the oxide and the deposit on the electrode 4 were completely removed by applying the reducing pulse for 100 ms.

During printing on an actual printer,
The time for applying the reduction pulse is 10 μs or more when the ink cartridge 18 is at the home position 24, and preferably 10 ms to 100 ms. This is because the reduction effect is not exhibited unless the reduction pulse application time 37 is 10 μs or more as shown in FIG.
When ms to 100 ms, the reduction effect is remarkable, and the electrode 4 can be reduced and the adhering substances can be removed within the time during which the ink cartridge 18 reciprocates at the home position 24 even during the continuous printing operation. The electrode can be effectively reduced without affecting the temperature. Further, when the reduction pulse is applied when the ink cartridge 18 is not in the home position 24 but during the printing operation, the reduction pulse application time 37 for performing effective electrode reduction without affecting the printing speed is 100 ms. The following is preferably 10 μs to 1
It is 0 ms.

When the recording medium 10 (recording paper) is replaced by automatic paper feeding, the reduction pulse application time 37 is set to 1
By setting the time to 0 sec or less, preferably 3 sec or less, the printing speed is not affected and effective reduction can be performed.
When the recording medium 10 (recording paper) is replaced by manual feeding other than automatic paper feeding, the reduction pulse application time 3
Keep 7 for less than an hour. This includes the print standby state,
When the printer is powered on and printing is not in progress, a reduction pulse can be applied to reduce the electrode 4, but by setting the reduction time to 1 hour or less, excessive reduction of the electrode 4 can be avoided. This is for preventing the electrode 4 from being melted by the application of the reduction pulse.

In this embodiment, 50 ms is returned each time the ink cartridge 18 returns to the home position 24.
The reduction pulse of ec was applied. That is, FIG.
In FIG. 9B, continuous ejection time 36 is about 0.5 sec for solid printing at 5 kHz, reduction pulse application time 37 in FIG. 9C is set to 50 ms, and printing is performed 300 million times. Formation was confirmed.

Next, the control of the print dot diameter using the electrode reduction effect of the reduction pulse will be described. FIG.
1 shows the relationship between the number of boiling times and the boiling start time 46 immediately after the application of the reduction pulse of 100 ms or more, but immediately after the application of the reduction pulse, as shown in FIG. 10, the boiling start time 46 is as small as 20 μs or less. However, it can be seen that the number of boiling times is increased up to 100,000 times. As the boiling start time 46 increases, the bubble volume shown in FIG. 12 gradually increases. Therefore, in order to control the size of the boiling bubble with the change of the boiling start time 46 and control the print dot diameter, the reduction pulse application time 37 is applied between 10 μs and 100 μs as shown in FIG. Method and after applying the reduction pulse, as shown in FIG. 12, the cartridge is set to the home position 2 before printing.
In the case of No. 4, there is a method of controlling the print dots by performing preliminary ejection 1 to 1,000,000 times. In the former control of print dots by controlling the reduction pulse application time 37, the reduction pulse application time 37 is set to 0.2 ms and 50 m in this embodiment.
By setting s, the print dot diameter could be controlled to 50 and 75 μm. In the latter case, in the control of the print dots by the preliminary ejection of the ejection pulse after the application of the reduction pulse, in the present embodiment, the number of the preliminary ejection pulses is set to 10, 1000 and 10000 times so that the print dot diameters are 25, 50 and 75 μm. I was able to control it.

Next, a method of forming the electrodes 4 and the counter electrodes 5 of the ink jet head of this embodiment will be described with reference to FIGS.
This will be described using 8. 6A is an electrode layer forming process diagram of the first embodiment, FIG. 6B is a resist film forming process diagram of the first embodiment, and FIG. 6C is an electrode forming resist pattern forming process diagram of the first embodiment. 7D is an electrode pattern forming process diagram of the first embodiment, FIG. 7A is an electrode forming process diagram of the first embodiment,
(B) is a process chart of forming a resist film for forming a counter electrode of the first embodiment, (c) is a process diagram of forming a resist pattern for forming a counter electrode of the first embodiment, and (d) is a counter electrode layer of the first embodiment. FIG. 8A is a process chart of forming a counter electrode of the first embodiment, FIG. 8B is a process diagram of forming an insulating film of the first embodiment, and FIG. 8C is a process of forming an insulating film opening of the first embodiment. It is a process drawing.

As shown in FIG. 6 (a), a borosilicate glass substrate 1 was formed by sputtering using Ti as a target.
A Ti thin film having a thickness of 2 μm was formed on a glass substrate by applying high frequency power of 200 W for 30 minutes at an r pressure of 50 mTorr and a substrate temperature of 400 ° C. As shown in FIG. 6B, a photosensitive resist material containing a phenol resin as a main component is applied onto the substrate 1 on which the electrode layer 26 is formed by a spin coater and then baked at 90 ° C. for 30 minutes to have a thickness of 7 μm. The resist film 27 of No. 1 was formed. As shown in FIG. 6C, a photomask having the pattern of the electrodes 4 was superposed on the resist film 27, exposed by a UV irradiator for 7 seconds, and then developed to form an electrode forming resist pattern 28. Next, as shown in FIG. 6D, the argon pressure is 2 × 10 ^−4.
Torr, beam power 300W, stage tilt angle 45
The milling process was performed with an argon beam under a molding condition of 70 minutes for milling time to form an electrode pattern. The resist film 27 on the electrode pattern was dissolved by the solvent to form the electrode 4 as shown in FIG. Next, FIG.
As shown in (b), a photosensitive resist material containing a phenol resin as a main component is applied on the substrate 1 on which the electrodes 4 are formed by a spin coater, and then baked at 90 ° C. for 30 minutes to form a resist film having a thickness of 7 μm. 27 was formed to be a resist film for forming a counter electrode. As shown in FIG. 7C, a photomask having a pattern of counter electrodes was overlaid on the resist film 27, exposed by a UV irradiator for 7 seconds, and then developed to form a resist pattern for forming a counter electrode. As shown in FIG. 7D, a Pt thin film is formed by applying a high frequency power of 200 W for 10 minutes at an Ar pressure of 20 mTorr and a substrate temperature of 200 ° C. using Pt as a target on the counter electrode forming resist pattern. 1 μm was formed on the resist pattern for forming the counter electrode to form a counter electrode layer 29. As shown in FIG. 8A, the resist film 27 was dissolved and peeled off with a solvent to form the counter electrode 5. FIG.
As shown in (b), the photosensitive polyimide is added to 3000 rp.
m and the coating time is 30 seconds, the substrate 1 is spin-coated and then baked at 80 ° C. for 30 minutes to form the insulating film layer 30.
Was formed. Next, a photomask having a pattern of openings of the insulating film is overlaid on the insulating film layer 30, exposed by a UV irradiator for 7 seconds, developed, and then baked at 400 ° C. for 1 hour. The insulating film opening 31 shown in (c) was formed.

In the ink-jet head 17 having the electrode 4 and the counter electrode 5 formed as described above, monoethanolamine sulfate is used as an ink conductive material in water as a solvent so that the specific resistance of the ink becomes 20 Ωcm. Add 3% each of polyethylene glycol and glycerin as a wetting agent, add 1% of polyoxyethylene alkylphenyl ether as a surfactant to adjust the physical properties of ink, and KOH to adjust the pH.
Using a conductive ink in which H is 7.2, 3
When repetitive driving was performed by applying a reducing pulse for 50 ms every 5000 times of a discharge pulse of 25 MHz at 25 MHz, stable printing was formed up to 300 million times and there was no change in the electrode size.

(Second Embodiment) The second embodiment of the present invention has the same structure and driving method as those of the first embodiment except the structure of the counter electrode 5 in the first embodiment.

FIG. 4 shows the structure of the ink cartridge of this embodiment. 4A is an exploded perspective view of the ink jet head and the ink cartridge of the second embodiment, FIG.
FIG. 7B is an exploded perspective view of the ink cartridge of the second embodiment. In FIG. 4, 18 is an ink cartridge incorporating an ink jet cartridge, 17 is an ink jet head, 7 is a nozzle formed on the ink jet head 17, 12 is a common ink chamber for supplying ink to the electrodes 4 of the ink jet head 17, and 21 is An ink tank in the ink cartridge 18. Further, 19 is an ink filter for preventing dust and the like from entering the ink when the ink in the ink cartridge 18 is introduced into the inkjet head 17, 5 is a counter electrode for applying a reduction pulse to the electrode 4, 20 Is an ink introduction hole for introducing ink from the ink cartridge 18 into the common ink chamber 12 of the inkjet head 17.

In this embodiment, the counter electrode 5 is provided at the ink contact portion of the ink cartridge 18. The counter electrode 5 is a plate-shaped or linear electrode made of Pt, Au, Cr, Ni, Cu, C or the like.
Fig. 4 (b) with a size of mm and a plate thickness of 0.05 mm
As shown in FIG.

Ink was filled in the ink cartridge constructed as described above, and discharge was performed by applying an alternating frequency of 500 kHz and 20 V to the electrodes and the ink. Further, as shown in Example 1, by repeatedly applying the discharge pulse 5000 times and the reduction pulse of 50 ms, stable print formation could be performed up to 300 million times and the electrode size did not change.

[0068]

As described above, according to the present invention, since printing is performed while reducing the electrodes, oxides and deposits on the electrodes are eliminated, and as a result, the boiling time is increased by the oxides and deposits on the electrodes. It is possible to realize an ink jet head which can be suppressed and has a very long life without a loss of electrodes while maintaining a stable print dot diameter. Further, according to the present invention, by reducing the electrode, even if the AC frequency applied to the electrode is reduced, the reduction of the electrode life due to the oxidation of the electrode can be suppressed. It is possible to realize an inkjet head device that exhibits a good life even in ejection and can significantly reduce unnecessary radiation noise generated from the drive circuit.

Since a water-soluble organic solvent such as alcohols or glycols is added to the ink as a wetting agent, nozzle clogging does not occur and ink droplet flight stability can be obtained. Further, since the halogen compound is not used for the ink conductive material, the stability of the adhesive force of the head constituent material can be obtained. Further, since the physical properties of the ink are controlled by a surfactant, a pH adjusting agent, a viscosity adjusting agent, etc., it is possible to realize an inkjet head and an inkjet ink having good ejection response and excellent continuous recording properties.

Further, according to the present invention, since the print dot diameter can be arbitrarily controlled by controlling the application time of the reduction pulse and the number of preliminary ejections after the application of the reduction pulse, the area gradation printing is performed.
It is possible to realize an inkjet head that can form a high-resolution image with high quality.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of essential parts of an inkjet head according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line A-A ′ in FIG.

FIG. 3 is a conceptual diagram regarding a drive system of an inkjet head in an embodiment of the present invention.

4A is an exploded perspective view of an ink jet head and an ink cartridge of a second embodiment. FIG. 4B is an exploded perspective view of an ink cartridge of a second embodiment.

FIG. 5 is a configuration diagram of an inkjet printer incorporating an inkjet head having an electrode configuration of the present invention.

6A is a process diagram of an electrode layer forming process of the first embodiment; FIG. 6B is a process diagram of forming a resist film of the first embodiment process; and FIG. 6C is a process diagram of forming a resist pattern for electrode formation of the first embodiment process. Electrode pattern forming process drawing of one embodiment

FIG. 7A is an electrode formation process diagram of the first embodiment. FIG. 7B is a counter electrode formation resist film formation process diagram of the first embodiment. FIG. 7C is a counter electrode formation resist pattern formation process diagram of the first embodiment. (D) Counter electrode layer forming process chart of the first embodiment

FIG. 8A is a process diagram of forming a counter electrode in the first embodiment; FIG. 8B is a process diagram of forming an insulating film in the first embodiment; and FIG. 8C is a process diagram of forming an insulating film in the first embodiment.

9A is a diagram showing a voltage waveform of an ejection pulse of the first embodiment. FIG. 9B is a diagram showing a voltage waveform of the ejection pulse of the first embodiment during continuous application. FIG. 9C is a reduction of the first embodiment. FIG. 3 is a diagram showing a voltage waveform of a pulse. (D) A diagram showing a current waveform with respect to the ejection pulse of the first embodiment.

FIG. 10 is a diagram showing a relationship between a reduction pulse application time and a boiling start time in the first embodiment of the present invention.

FIG. 11 is a diagram showing the relationship between the number of boiling times and the boiling start time after the application of the reduction pulse in the first embodiment of the present invention.

FIG. 12 is a graph showing the relationship between the number of boiling times and the bubble volume after applying a reducing pulse in the first embodiment of the present invention.

FIG. 13 is a sectional view of a conventional ink ejection device.

FIG. 14 is a sectional view of a main part of a conventional inkjet head.

15 is a cross-sectional view taken along the line AA of FIG.

[Explanation of symbols]

 1 Substrate 2 Partition Plate 3 Nozzle Plate 4 Electrode 5 Counter Electrode 6 Insulating Film 7 Nozzle 8 Pressure Chamber 9 Ink Drop 10 Recording Medium 11 Ink Supply Hole 12 Common Ink Chamber 13 Electrode Electric Field Concentration Section 14 Ejection Signal Generator 15 Reduction Signal Generation Device 16 Changeover switch 17 Inkjet head 18 Ink cartridge 19 Ink filter 20 Ink introduction hole 21 Ink tank 22 Carriage 23 Platen roller 24 Home position 25 Guide shift 26 Electrode layer 27 Resist film 28 Electrode forming resist pattern 29 Counter electrode layer 30 Insulating film Layer 31 Insulating film opening 32 Discharge pulse application time 33 Discharge pulse rest time 34 Discharge drive cycle 35 Discharge pulse applied voltage 36 Continuous discharge time 37 Reducing pulse applying time 38 Reduction Pulse applied voltage 39 insulation layer 40 endurance film 41 ink channel 42 conductive ink 43 ink chamber 44 power source 45 switch 46 boiling start time 47 bubble growth time

Claims (15)

[Claims] 1. A pressure chamber, a nozzle hole formed in a wall surface of the pressure chamber, a pair of electrodes arranged on a wall surface of the pressure chamber facing the nozzle hole, and a separate electrode. An ink jet head having a single counter electrode formed therein, an ink channel connected to the pressure chamber, and an ink supply port formed at an end of the ink channel opposite to the pressure chamber. And an ink jet head having means for applying a voltage between the pair of electrodes and the counter electrode. 2. A counter electrode attached to an ink contact portion of an ink cartridge, a pressure chamber, a nozzle hole formed in the wall surface of the pressure chamber, and a wall surface of the pressure chamber facing the nozzle hole. Attached to an end portion of the ink cartridge, which has a pair of electrodes, an ink channel connected to the pressure chamber, and an ink supply port formed at an end portion of the ink channel opposite to the pressure chamber. An ink jet head having a head part provided with a means for applying a voltage between a counter electrode attached to an ink contact part of the ink cartridge and a pair of electrodes arranged in the head part. An inkjet head characterized in that. 3. When applying a voltage between the counter electrode and the pair of electrodes, when the pair of electrodes are electrodes containing Ti, the pair of electrodes are relative to the counter electrode. The inkjet head according to any one of claims 1 and 2, which has a low electric potential. 4. When a voltage is applied between the counter electrode and the pair of electrodes, the pair of electrodes are higher than the counter electrode when the pair of electrodes are electrodes that dissolve an anode. 3. The inkjet head according to claim 1, wherein the inkjet head has a potential. 5. The inkjet head according to claim 1, wherein an alternating voltage is applied when a voltage is applied between the counter electrode and the pair of electrodes. 6. The ink jet head according to claim 5, wherein an AC frequency of a voltage when a voltage is applied between the counter electrode and the pair of electrodes is 100 kHz or more. 7. The ink jet head according to claim 1, wherein when a voltage is applied between the counter electrode and the pair of electrodes, the applied voltage is 50 V or less. 8. The voltage pulse is applied between the counter electrode and the pair of electrodes when the voltage discharge pulse is not applied, and the voltage pulse is applied. The inkjet head according to any one of claims 1. 9. When applying a voltage pulse between the counter electrode and the pair of electrodes, the application time of the voltage pulse is 10 μsec or more when the ink cartridge is at the home position. Claim 7
The inkjet head described in 1. 10. When a voltage pulse is applied between the counter electrode and the pair of electrodes, the application time of the voltage pulse is 100 msec or less when the ink cartridge is printing other than the home position of the carriage. The inkjet head according to claim 7, wherein the inkjet head is provided. 11. The application time of the voltage pulse when applying the voltage pulse between the counter electrode and the pair of electrodes is 10 msec or more when the recording paper is exchanged. The inkjet head according to claim 7. 12. When a voltage pulse is applied between the counter electrode and the pair of electrodes, the voltage pulse application time is 1 hour or less when the recording paper is replaced by other than automatic paper feeding. The inkjet head according to claim 10, wherein the inkjet head is provided. 13. A means for controlling a print dot diameter by controlling an application time of the voltage pulse when a voltage pulse is applied between the counter electrode and the pair of electrodes. 2. The inkjet head according to any one of 2 above. 14. When controlling a print dot diameter by applying a voltage pulse whose application time is controlled between the counter electrode and the pair of electrodes, a preliminary ejection pulse is applied after applying the voltage pulse. The ink jet head according to claim 13, wherein the print dot control is performed by means of the following. 15. When controlling a print dot diameter by applying a voltage pulse whose application time is controlled between the counter electrode and the pair of electrodes, 1 is applied after the voltage pulse is applied.
The inkjet head according to claim 14, wherein the preliminary ejection pulse is applied up to, 000,000 times.