JPH0911460A - Ink-jet head - Google Patents

Abstract

PURPOSE: To provide an ink-jet head in which the time for filling ink into a pressure chamber is short and frequency responsivity is high. CONSTITUTION: In an ink-jet head, printing is performed by generating bubbles in ink 28 in a pressure chamber 27 and discharging ink 28 from a discharge port 26 provided in the pressure chamber 27. Bubbles are generated in ink 28 in the pressure chamber 27 in such a degree as ink 28 is not discharged from the discharged port 26 in the interval from the first discharge of ink 28 to the next discharge.

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 of an ink jet printer for printing by applying ink ejected from nozzles to a recording paper.

[0002]

2. Description of the Related Art In recent years, ink jet printers have come to be widely used as output printers for home and office computers because of their advantages of quietness during recording, high speed recording, and easy colorization. Such an ink jet printer is for making ink into small droplets, flying them, and adhering them to a recording paper for recording, and is roughly classified into a continuous system and an on-demand system according to a method of generating small droplets and a flying direction control method. .

The continuous system is disclosed in, for example, US Pat.
The method disclosed in the specification of 3,060,429,
The ink droplets are electrostatically attracted, the generated droplets are controlled by an electric field according to the recording signal, and the droplets are selectively adhered to the recording paper for recording. It is not suitable for high-speed recording because it requires a high voltage and it is difficult to form multiple nozzles.

The on-demand system is disclosed in, for example, US Pat.
According to the method disclosed in Japanese Patent No. 3,474,120, a piezoelectric vibrator is attached to a recording head having nozzle holes for ejecting small droplets, and an applied electric recording signal is mechanically vibrated by the piezoelectric vibrator. In accordance with this mechanical vibration, small droplets of ink are ejected from the nozzle holes to adhere to the recording paper for recording, and ink is ejected from the nozzle holes in response to a recording request. Since it is not necessary to collect the droplets that were not required for image recording from among the droplets ejected and ejected as in the method,
Although a simple configuration is possible, it is difficult to make a multi-nozzle because it is difficult to process the recording head and it is extremely difficult to miniaturize the piezo-vibrator, and the mechanical energy of mechanical vibration of the piezo-vibrator causes droplets to fly. It also has the drawback of not being suitable for high-speed recording. In addition, Japanese Examined Sho 61-5
No. 9911, Japanese Patent Publication No. 61-59914, and Japanese Patent Publication No. 62-11035 disclose that a heating resistor causes boiling of ink.
A bubble jet recording method for flying droplets has been published.

As another example of the on-demand system, the system disclosed in US Pat. No. 3,179,042 describes that thermal energy is used instead of mechanical energy of a piezoelectric oscillator or the like. However, this has the advantage that the energy conversion efficiency is higher than that of the method using mechanical energy and that multi-nozzle can be easily realized.

An example of a conventional ink jet head of the bubble jet system will be described below with reference to FIGS. 10 and 11. FIG. 10 is a partial sectional side view of one ink ejecting portion of a conventional bubble jet type inkjet head, and FIG. 11 is a sectional view taken along the line AA of FIG. Figure
In FIG. 10 and FIG. 11, 1 is the substrate of the inkjet head,
Reference numeral 2 is a heating resistor forming a pattern-formed electric-heat converter on the substrate 1, and reference numeral 3 is a protective film for insulating and protecting the heating resistor 2. Reference numeral 4 is a flow path wall formed on the substrate 1 that partitions the plurality of heat generating resistors 2, and 5 is an orifice member formed on the flow path wall 4 so as to correspond to the heat generating resistors 2. A discharge port 6 serving as an injection port is provided. The substrate 1, the flow path wall 4 and the orifice member 5 form a pressure chamber 7. Reference numeral 8 is an ink flow path for supplying the ink 9 to the pressure chamber 7, 10 is an ink droplet ejected from the orifice member 5, and 11 is a recording paper to which the ink droplet 10 is attached.

It should be noted that the filling state of the ink 9 in the pressure chamber 7 shown in FIG. 10 and the shape of the ink droplet 10 are shown in principle and are different from the actual ones.

Next, the operation will be described. First, a pulse voltage is applied to the heating resistor 2 by a signal generator (not shown).
In addition to this, by the applied pulse voltage, the heating resistor 2
Generate heat and heat the ink 9 filled in the pressure chamber 7. Due to the rapid temperature rise of the heating resistor 2, the ink 9 in the vicinity thereof starts to boil, and a thin bubble film is generated on the heating resistor 2. The bubble film absorbs heat from the heat-generating resistor 2 and the ink 9 around the bubble film to rapidly expand its volume.
The pressure of the ink 9 in the pressure chamber 7 rapidly increases, and the discharge port 6
Ink droplets 10 jump out of the recording medium and adhere to the recording paper 11 to form dots. Ink consumed by this dot formation 9
Is supplied from an ink tank (not shown) through the ink flow path 8, and thereafter, any continuous dot formation can be performed.

FIG. 12 is a vertical cross-sectional view of the nozzle portion showing a state immediately after the ink droplet 10 has ejected from the ejection port 6. In the figure, 12 is generated by the heating resistor 2 acting on the ink 9. Bubbles and arrows indicate the flow of the ink 9. In this way, the ink 9 expands into the ink droplet 10 from the ejection port 6 by the expansion of the bubble 12 and flows out from the ink flow path 8 toward the ink tank, and after a certain time, as shown in FIG. Ink 9 flows out from the ejection port 6 and the ink flow path 8, and the amount of ink 9 in the pressure chamber 7 is significantly reduced. After that, the capillary force acting on the meniscus surface of the ink 9 causes the ink 9 to flow from the ink tank through the ink flow path 8 to raise the meniscus surface of the ink 9 until the pressure chamber 7 is filled with the ink 9 again. It is ready for ejection. The capillary force F acting on the surface of the ink 9 is, as shown in FIG. 13, the surface tension of the ink 9 is T, the wetting angle of the ink 9 with respect to the orifice member 5 is θ, and the meniscus surface of the ink 9 is the orifice member 5. When the radius of the touched portion is r, it is expressed as in (Equation 1), which is a value substantially determined by the physical properties of the ink 9.

[0010]

## EQU00001 ## F = 2.pi.T cos.theta./r Further, the volume of the ink droplet 10 is a value determined in order to make the dot area after adhering to the recording paper 11 a desired value,
The shortage of the ink 9 for filling the pressure chamber 7 with the ink 9 after printing is constant, and this constant shortage is the ink flow path 8.
Will be supplied from. Therefore, after printing,
The time required for the next printing is almost the same value when trying to obtain the same printing result. Further, in order to improve (increase) the capillary force F, changing the surface tension T of the ink 9 is particularly effective when the recording paper 11 is plain paper.
It is not very practical because the image quality of the printed matter attached to 11 deteriorates significantly.

[0011]

As described above, in the ink jet head as described above, the time from the ejection of the ink 9 to the time when the next printing is possible is determined by the printing result (printing content, etc.). Therefore, there is a limit in terms of ink supply in order to improve the frequency response (printing speed etc.) of the printer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an ink jet head having high frequency response and high image quality.

[0013]

In order to solve the above-mentioned problems, the ink jet head of the present invention generates bubbles in the ink in the pressure chamber so that the ink is ejected from the ejection port provided in the pressure chamber. The secondary bubbles are generated in the ink in the pressure chamber to the extent that the ink is not ejected from the ejection port until the ink is ejected again.

[0014]

According to the present invention, a secondary bubble that does not eject ink from the ejection port is generated in the ink in the pressure chamber between the ejection of the ink from the ejection port and the ejection of the ink again. As a result, it is possible to shorten the filling time of the pressure chamber with ink after the ink is ejected.

[0015]

EXAMPLES Regarding the recording principle of an ink jet head, the following method has been proposed.

(1) The ink is heated by a heat generating source such as a resistance heater and boiled, and the expansion force of the boiling bubble causes
A method of printing on recording paper by ejecting ink from a direction control mechanism such as a nozzle.

(2) A method in which a high voltage is applied to ink and the ink is ejected from a direction control mechanism such as a nozzle by an electrostatic field to print on recording paper.

(3) A method in which pressure is applied to ink by mechanical movement of a piezoelectric element, and the ink is ejected from a direction control mechanism such as a nozzle to print on recording paper.

(4) A method in which a magnetic material is added to ink, kinetic energy is applied to this ink by an external magnetic field, and this is ejected from a direction control mechanism such as a nozzle to print on recording paper.

(5) A conductive material is added to the ink, electric energy is externally applied to the ink, and the expansion force of a boiling bubble generated by the self-heating of the ink causes the ink to be ejected from a direction control mechanism such as a nozzle to cause recording paper to be ejected. How to print on.

The ink jet head of the present invention has the above structure.
This is a type in which ink is ejected from a direction control mechanism such as a nozzle to print on recording paper by the expansion force of a boiling bubble in the item (1), and one embodiment thereof will be described below with reference to the drawings. 1 is a partial cross-sectional side view of an ink ejecting portion of an ink jet head in one embodiment of the ink jet head of the present invention, and FIG. 2 is a cross sectional view taken along line BB of FIG. In FIGS. 1 and 2, 20 is an inkjet head, 21 is a substrate of the inkjet head 20, 22a and 22b are counter electrodes having the same shape and patterned on the upper surface of the substrate 21, and 23 is a counter electrode 22a and 22b. It is a protective film for insulation and protection. Reference numeral 24 is a flow path wall formed on the upper surface of the substrate 21 that divides the counter electrodes 22a and 22b, and 25 is a flow path wall.
A discharge port 26 is provided at the end of the orifice member formed on the 24. The substrate 21, the flow path wall 24 and the orifice member 25 form a pressure chamber 27. 29 is a pressure chamber 27
An ink flow path for replenishing the ink 28 with the ink, 30 is the counter electrodes 22a,
It is a signal generator that applies a voltage to 2b. 40 is an ink droplet ejected from the orifice member 25, 41 is the ink droplet 40
Is a recording paper on which is attached (printing is performed).

It should be noted that the filling state of the ink 28 in the pressure chamber 27 shown in FIG. 1 and the shape of the ink droplet 40 are shown in principle, and are different from the actual ones.

FIG. 3 is a partially cutaway perspective view of the ink jet head viewed from a wider field of view than FIG. 1, FIG. 4 is a perspective view of an ink cartridge in which the ink jet head is further incorporated, and FIG. 5 is the ink cartridge. It is the perspective view which notched a part of. In FIGS. 3 to 5, 31 is a common ink chamber for supplying the ink 28 to the pressure chamber 27,
It is composed of the substrate 21, the flow path wall 24, and the orifice member 25. 32 is an ink cartridge to which the inkjet head 20 is attached, 33 is an ink tank provided inside the ink cartridge 32, 34 is an ink filter for removing dust contained in the ink 28, and 35 is the same ink 28 from the ink tank 33. An ink introduction groove leading to the ink chamber 31.

FIG. 6 is a partially cutaway perspective view of a serial type ink jet printer in which the ink cartridge 32 is mounted. In the figure, 36 is a cartridge insertion port for inserting the ink cartridge 32 into the printer, and 37 is an ink jet head. A carriage for fixing the ink cartridge 32 provided with 20, a guide shaft 38 for guiding the carriage 37 in the horizontal direction, a platen roller 39 for conveying the recording paper 41, and an ink cartridge fixed on the carriage 39. 32 is a guide shaft 38 in response to a signal sent from a terminal device such as a computer device.
The inkjet head 20 mounted on the lower surface of the ink cartridge 32 is reciprocated continuously along with the carriage by the platen roller 39 while being controlled at the timing of voltage application to the counter electrodes 22a and 22b. Printing is performed on the recording paper 41 that has been printed. In addition,
As the printer, a line type printer or a plotter type printer can be used.

The details of the operation will be described below. First, the operation of ejecting ink droplets will be described. In FIG. 1 and FIG. 2, inside the pressure chamber 27 filled with the ink 28, a pair of counter electrodes 22a and 22b, which are means for generating energy for the ink 28 provided on the substrate 21, are connected to the energy generating means. When a voltage (10 to 30 V in this embodiment) is applied by the signal generator 30 serving as an energy supply means, the counter electrode 22a, through the ink 28 having a certain resistivity (20 to 50 Ω · cm in this embodiment), A line of electric force P _L is generated between 22b, and a current flows along the line of electric force P _L , and due to the Joule loss of the current represented by I ² × R (I: current value, R: resistance value of ink 28), this electric field is generated. The ink 28 in the current concentrating portion P _C of the force line P _L self-heats, and after 10 to 20 μs, boiling starts and bubbles (not shown) are generated. The pressure of the ink 28 in the pressure chamber 27 rapidly increases due to the expansion of the generated bubble, and the ink 28 is ejected as the ink droplet 40 from the ejection port 26 to the recording paper 41 by the force to release this pressure. Adhere to form dots. On the other hand, the signal generation device 30 causes the counter electrode 22 to start when the boiling of the ink 28 is started.
The voltage application to a and 22b is stopped, and the ink 28
The ink 28 consumed by the ejection of the
Before the next voltage application, the pressure chamber 27 is replenished by the capillary force of the ink 28 from the ink flow path 29, and the state returns to the initial state. Note that these more detailed operations will be described later (explanation of FIG. 9).

While repeating the above operation, the ink cartridge 32 inserted from the cartridge insertion port 36 and mounted on the carriage 37 reciprocates along the guide shaft 38 in response to a print signal sent from a computer or the like. The signal generator 30 applies a drive voltage between predetermined counter electrodes 22a and 22b of the inkjet head 20 attached to the ink cartridge 32 in accordance with the position of the carriage 37, and ink droplets 40 are continuously generated to cause a platen. roller
The dots can be printed on the recording paper 41 sent by 39. As a replenishment operation of the consumed ink 28, dust is removed when the ink 28 passes through the ink filter 34 from the ink tank 33, passes through the ink introduction groove 35, enters the common ink chamber 31, and is discharged from the common ink chamber 31 as described above. As described above, the ink is supplied into the pressure chamber 27 through the ink flow path 29 to be replenished, and continuous printing is possible.

The ink cartridge 32 has been described as the one in which the portion of the ejection port 26 for ejecting the ink 28 (recording head portion) and the ink tank 33 are integrated, but a separate type in which these are separated may be used. , Also ink filter
34 is a three-dimensionally braided metal such as stainless steel having a filtration particle size of about 10 microns, which is advantageous in terms of reliability. Furthermore, as conditions for improving print quality,
It is desirable to apply a static negative pressure to the ejection port 26, and this negative pressure causes the liquid surface of this ejection port 26 part to become a negative meniscus (like a concave lens), pulling the ink inside,
The landing accuracy is improved, and extra droplets (extra dots) can be reduced. To generate this negative pressure,
It is preferable to provide a negative pressure generating means such as filling the ink tank 33 with a sponge made of polyurethane foam or providing a spring member inside and outside the ink tank 33.

Next, the secondary boiling which is the essence of the present invention will be described. This secondary boiling is performed within a predetermined time from the stop of voltage application after ink ejection to the start of the next ink ejection operation, and the signal generator 30
The drive voltage applied between the opposite electrodes 22a and 22b is set higher than that during ink droplet ejection. In this way, bubbles are generated as in the case of ejecting the ink droplets, but as described above, since the drive voltage applied between the counter electrodes 22a and 22b is high, the current density between these electrodes becomes high, and The temperature of the concentrated portion P _C rises rapidly and starts boiling in a short time (10 μs or less).

At this time, ink around the counter electrodes 22a and 22b
Since the heat is not sufficiently transferred to 28, the volume of this bubble is very small, and the ink 28 is
It is never discharged from. That is, as shown in FIG.
The relationship between the voltage applied to the counter electrodes 22a and 22b, the volume of the bubble generated at that time, and the diameter of the print dot when the ejected ink droplet 40 adheres to the recording paper 41 is as follows.
When the voltage exceeds V, the ink droplet 40 is not ejected and the area of the print dot becomes 0. Therefore, in this secondary boiling, the ink 28 is ejected if a voltage of 30 V or more is applied to the counter electrodes 22a and 22b. It is not discharged from the outlet 26. In addition, the signal generator 30 has a counter electrode when the secondary boiling is started.
The voltage application to 22a and 22b is stopped.

Such control by the signal generator 30 is performed at the timing shown in FIG. 8, and FIG.
0 indicates the waveform of the voltage applied to the counter electrodes 22a and 22b, time T ₁ is the voltage application time for ink ejection, and time T ₂ is the voltage application time for secondary boiling. As described above, in the secondary boiling, a voltage higher than that at the time of ink ejection is applied for a short time in order to increase the current density between the counter electrodes 22a and 22b and cause a small boiling. In addition, as in this embodiment, the counter electrode 22
In an energization type inkjet head that generates a bubble by applying a voltage between a and 22b, when the bubble grows, the counter electrode 22
Bubbles cover a and 22b and shut off the current between the electrodes.
Since the ink 28 is not heated during this time, by utilizing this characteristic, when voltage is applied while continuously increasing the voltage as shown in FIG. 8B, the time T ₃ (time T ₁ and time T ₁ because during the T time between ₂₎ that blocks the bubble current, is substantially applied voltage waveform since the ink 28 is not heated 8
As shown in FIG. 8C, the applied voltage waveform becomes substantially the same as that of FIG. 8A, and the object can be achieved despite the simple control.

Such voltage control causes changes in the pressure chamber 27 as shown in FIGS. 9 (a), 9 (b) and 9 (c). That is, FIG. 9A shows the time T ₁ of FIG. 8A between the counter electrodes 22a and 22b.
9 shows the state immediately after the voltage is applied only and as a result, the ink 28 is ejected from the ejection port 26, and the bubble 42 still remains, but when a certain time elapses from this state, FIG.
As shown in (b), the bubble 42 rapidly contracts and disappears, and the ink 28 in the pressure chamber 27 flows out from the ejection port 26 and the ink flow path 29, and is extremely small. FIG. 9 (c) shows a change based on the voltage application for the secondary boiling shown in FIG. 8 (a) performed immediately after the state of FIG. 9 (b), and during this application time T ₂ . Although a small bubble 43 is generated, this bubble 43 is discharged from the ink outlet 28 through the ink 28 as described above.
There is no force to eject the ink, and it works to push up the meniscus surface of the ink 28 toward the ejection port 26. In addition to the force for pushing the meniscus surface upward, a force for causing the ink 28 to flow out from the ink flow path 29 is also generated, but this force is much smaller than the force in the direction of the ejection port 26, and the meniscus surface The rise is effective. By performing the secondary boiling immediately after the bubble 43 rapidly contracts and disappears in this way, the meniscus surface of the ink 28 rapidly rises, and the replenishment time of the ink 28 is considerably shortened. .

That is, the time from the start of ink ejection until the ink 28 is completely filled in the pressure chamber 27 is about 50% as compared with the case where the secondary boiling is not performed. The ejection can be repeated, and the frequency response of the inkjet head is significantly improved. It should be noted that there is no need to change any part relating to the image quality after printing, such as the physical properties of the ink.

Inkjet head 20 in this embodiment
The mechanism and its surroundings and the operation thereof are as described above. Next, a preferable mode of each component that can effectively implement the present invention will be described.

1. Substrate material (corresponding to the substrate 21 in the embodiment) Insulating materials such as glass and ceramics, semiconductors, metals whose surface is coated with a high resistance material, metal alloys, insulators and semiconductors can be used. There is something.

(1) Glass substrate Potassium lime glass, soda lime glass, borosilicate glass, crown glass, zinc crown glass, soda potash glass, barium borosilicate glass, 96% silicate glass, 99.5% silicate glass, phosphate glass, low melting point Glass, lithium silicate glass, zinc aluminum silicate glass, zirconium silicate glass, etc.

(2) Ceramic substrate Aluminum oxide (alumina), titanium oxide (titania),
MgO · SiO ₂ (steatite), 2MgO · SiO ₂ (holsterite), BeO (beryllia), MgO · Al ₂ O ₃ (spinel), etc.

(3) Semiconductor substrate Silicon, silicon carbide, diamond, germanium, etc.

2. Electrode material (counter electrodes 22a and 22b of the embodiment)
Ti group metal (Ti, Zr, Hf), platinum group metal (Pt, Ru, R)
h, Pd, Os, Ir), refractory metal (W, Ta, Mo), other single metals such as V, Cr, Fe, Co, Ni, Nb, Au, Ag, Al, etc., or alloys thereof (Ni) -Fe, NiCr, TiCr
Etc.) can be used. In addition, these oxides (titanium oxide,
Hafnium oxide, tin oxide, indium oxide, etc.), nitride
(Titanium nitride, chromium nitride, etc.), carbides (titanium carbide, tungsten carbide, etc.), and borides can also be used.

3. Insulating layer material (corresponding to the protective film 23 in the embodiment) As the insulating layer, an insulating organic material (a photoresist such as heat-resistant polyimide resin or acrylic resin) or an insulating inorganic material can be used.

4. Material of flow path and nozzle (corresponding to the ink flow path 29 and discharge port 26 forming portion of the embodiment) polyimide, acrylic, polymer such as polyethylene terephthalate sheet, insulating material such as glass and ceramic,
A semiconductor, a metal, a metal alloy, an insulator, or a semiconductor whose surface is coated with a high resistance material can be used.

5. Inkjet head (corresponding to the inkjet head 20 of the embodiment) (1) Manufacturing method An example of a method of manufacturing an inkjet head using the above materials will be described. First, on a non-conductive substrate made of glass or ceramics such as silicon, Ti,
A conductive metal film such as Au or Pt is laminated by a physical film forming method such as a vapor deposition method or a sputtering method or a plating method. An electrode pattern is formed on the substrate on which this metal film is laminated by a photolithography method, and a portion other than the electrode is removed by ion milling or chemical etching. An insulating film such as an organic polymer or ceramics is formed on the electrode and the substrate which are not exposed in the pressure chamber by coating, vapor deposition or sputtering. A resin sheet having a nozzle hole (corresponding to the discharge port) formed by an excimer laser processing machine on a substrate on which the insulating film and the electrode are laminated, and the center of the nozzle hole are aligned with the centers of the two electrodes. Glue with glue. Examples of the organic polymer used for the insulating film include polyimide, polyamideimide, urea resin, phenol resin, epoxy resin, fluororesin, acrylic resin, and silicone resin, and heat resistant polymers such as polyimide are particularly preferable. Moreover, you may use the metal alkoxide used for a sol-gel method. Furthermore, SiO ₂ , Al ₂ O ₃ , and TiO ₂
It is also conceivable to form a metal oxide such as by a vapor deposition method or a sputtering method.

As the resin sheet, heat-resistant engineering plastics such as polyimide, polyamide-imide, polyether sulfone, polyphenylene sulfide, and polyether ether ketone can be used.
Considering laser processability, polyimide and polyether sulfone are preferable. A thermosetting resin such as an epoxy resin, a polyimide resin, a triazine resin, an acrylic resin, a polyurethane resin, a silicone resin, or a urea resin can be used as the adhesive. Nitrile rubber to give flexibility,
It is also possible to add a thermoplastic resin such as silicone rubber, nylon or polyester resin. In addition, SiO ₂ , Al ₂ O
A fine powder of a metal oxide such as ₃ , TiO ₂ may be added as a filler, and an appropriate amount of a coupling agent may be added to improve adhesiveness. In consideration of ink resistance and heat resistance, epoxy resin is used. And / or a polyimide resin is preferred.
The adhesive is diluted with an organic solvent to a concentration to obtain a predetermined film thickness, applied on the resin sheet in advance, and then the solvent is volatilized by heating to form an adhesive layer.

Next, an excimer laser is incident from the surface side of the adhesive to form nozzle holes (ejection ports) in the resin sheet. When a heat-resistant plastic film such as polyimide is applied as a protective sheet on the surface of the adhesive during excimer laser processing and then processed, high-temperature processing waste does not directly contact the adhesive, so the adhesiveness does not decrease. The resin sheet having the nozzle holes is bonded to the substrate by a rubber pressure method or the like, the bonding temperature is set according to the curing temperature of the adhesive, and the pressing force is an optimum load that does not cause the adhesive to float or bleed.

(2) Peripheral Mechanism In order to prevent the ink 28 in the ejection port 26 from being dried or thickened to cause a problem in the ejection of the ink 28, the ink cartridge 32 is moved to a certain place during non-printing, and An elastic member such as rubber that covers the portion of the ejection port 26 is provided at a location, and a capping unit that shuts off the ejection port 26 from the atmosphere by this, or an ink receptor is provided at a certain location, and printing is performed from the ejection port 26. A means for preliminarily ejecting ink before entering, an elastic member such as rubber that comes into contact with the surface of the ejection port 26 is provided at a certain place, and the ink cartridge 32 is moved relative to this, and the ejection port Wiping means for wiping off foreign matter such as ink and dust adhering to the vicinity of 26, pressurizing the ink supply system, or sucking from the ejection port 26 to exert a predetermined pressure on the ink 28 to force the ink. Purge to discharge It is desirable to provide stage and the like.

6 Ink (1) Outline The ink 28 in this embodiment may be either water-soluble or oil-soluble, but the water-soluble ink is preferable in consideration of odor and safety. The ink includes dyes, water-soluble organic solvents such as alcohols and glycols as lubricants, surfactants,
Alternatively, it is preferable to add these mixtures for bleeding, drying rate, adjustment of boiling state, electrode life, nozzle clogging, etc., and a preservative is also used. Specifically, the materials described in the following documents can be used.

(A) "Inkjet recording technology" P-177 by Trikeps, Tokuya Ota (b) Nikkei Electronics No.303, No. 1982.11.8, Tokuya Ota (c) Journal of the Electrophotographic Society Vol 24, 354 (1985), Akio Ohwatari (d) "The 4th Non-Impact Printing Technology Symposium Proceedings" The Institute of Electrophotography, 93 (1987), Shinichi Hirasawa, 89 (1987), Kenji Sawaki (e) Textile & Industry Vol 47, 212 (1991) ( f) Japanese Patent Laid-Open No. 63-1579 (2) Specific examples of ink composition (a) Dye serving as colorant Azo dye, acid dye, basic dye, direct dye, etc.

(B) Pigment Carbon black, azo lake pigment, insoluble azo pigment,
Condensed azo pigment, phthalocyanine pigment, berylene pigment, berynone pigment, atraquinone pigment, quinagridone 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.

(C) Solvent Water and the like.

(D) Solvents Alkyl alcohols such as ethyl alcohol, methyl alcohol, n-propyl alcohol and isopropyl alcohol, ketones or keto alcohols such as acetone and diacetone alcohol, amides such as dimethylformamide and dimethylacetamide, tetrahydrofuran and dioxane. Ethers such as ethylene glycol monomethyl ether, ether alcohols such as ethylene glycol monoethyl ether, n-butyl alcohol, sec-
Lower dialkyl ethers of polyhydric alcohols such as butyl alcohol, tert-butyl alcohol, isobutyl alcohol, n-pentanol and diethylene glycol, water-soluble polymer compounds and the like are used, and water used as a solvent is 30 to 80% by weight, It is preferably contained in an amount of 50 to 70% by weight. It can be seen that as the water content falls below 50% by weight, the ink penetration into the paper tends to improve, and as the water content exceeds 70% by weight, the ink penetration into the paper tends to decrease. It is supported by that.

(E) Anti-drying agent Glycerin, urea, sorbitan, sorbitol, inositol, chelating agent, etc.

(F) Surface tension adjusting agent (improvement of quick drying property of ink and prevention of evaporation) A water-soluble organic solvent and a surfactant are used, and as the surfactant, fatty acid salts, higher alcohol sulfate ester, liquid fatty oil are used. Sulfate salts, sulfonates of fatty alcohol phosphates, fatty acid amide sulfonates, alkylallyl sulfonates, formalin condensation naphthalene sulfonates, alkylpyridinium salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl Esters, sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters, other dieranolamines, triethanolamine, anionic surfactants, nonionic surfactants and the like are used.
The surface tension is 28-55 dyne / cm, preferably 30-45 dy
ne / cm. This is because as the surface tension falls below 30 dyne / cm, fine lines in the print are blurred and the surface tension is 45 dyne / cm.
This is supported by the tendency that the color fringing property of the color overprinting tends to decrease as the value exceeds / cm.

(G) pH adjuster (adjustment of liquid physical properties) Lower alkanolamines, monovalent hydroxides of alkali metal hydroxides, specifically potassium hydroxide, sodium hydroxide, diaanolamine, etc. Used. The pH is 6-10, preferably 7-9. This has a pH of 6
This is supported by the fact that the solubility stability of the dye tends to decrease as the pH falls below the range, and that the fading of the dye tends to occur as the pH exceeds 10.

(H) Viscosity modifier (adjustment of liquid physical properties) Polyvinyl alcohol, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, water-soluble acrylic resin, polyvinylpyrrolidone, gum arabic starch, glycerin, etc. are used and the viscosity is Is 10 cp or less, preferably 5 cp or less.

(I) Dispersant Proteins, natural rubbers, cellulose dielectrics, natural polymers, nonionic polymers, anionic surfactants, nonionic surfactants, etc.

(J) Foaming agent Isopropyl alcohol, polyhydric alcohol, etc.

(K) Antioxidant Vitamin C, sodium sulfite, hydroquinone, pyrazolidone, hydrazine and the like.

(L) Preservatives Alcohol, formalin, omasin sodium, etc.

(M) Wetting agent (prevention of nozzle tip drying) A material having a boiling point higher than that of water is suitable, and specific examples thereof include alkylene groups such as polyethylene glycol, polypropylene glycol, butylene glycol, and hexylene glycol. Alkylene glycols containing 6 to 6 carbon atoms, for example, lower alkyl ethers of diethylene glycol such as ethylene glycol ethyl ether, diethylene glycol methyl ether and diethylene glycol ethyl ether, and glycerin. These wetting agents contain 0.1 to 10% by weight of polyhydric alcohol, preferably 0.5.
~ 3.0 wt% is contained. This is because as the content of polyhydric alcohol falls below 0.5% by weight, the tip of the nozzle tends to become clogged due to ink drying.
This is supported by the tendency of the specific resistance of the ink to increase as the weight percentage exceeds.

(N) Others In order to reinforce the strength of the ink film adhered to the printing paper, a resin polymer such as an alkyd resin, an acrylic resin, an acrylamide resin, an alcohol, or polyvinylpyrrolidrin may be added. It is advantageous to add a fungicide in terms of ensuring reliability during long-term storage.

(3) Physical Properties of Ink The ink 28 needs to have conductivity as its physical property, and is described in US Pat. No. 4,536,776 (corresponding Japanese application: JP-A-59-129274). "In an ink for an selective ink jet printing press comprising an aqueous mixture of dyes, an ink comprising an amount of a hydrolyzed salt such that the mixture provides the ink with a resistivity of 15 to 50 ohms per cm." Further, JP-A-5-179182 discloses that in an aqueous ink composition for ink jet recording containing water and a colorant, an alkanolamine or an ethylene oxide adduct and / or a propylene oxide adduct and a hydrogen halide are used. And an ink containing a salt, which is disclosed in Japanese Patent Publication No. 2-5785. As for the conductivity imparting to the ink, various developments have been made.

The conductivity-imparting agent used in this embodiment may be an alkali metal compound salt of lithium (Li) or the like, an inorganic salt such as ammonium sulfate, lithium chloride, sodium chloride, potassium chloride or an organic salt. Derivatives of quaternary organic ammonium salts can be preferably used, and specific examples of the compounds include 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, tripropylamine sulfate, phenylamine sulfate, diphenylamine sulfate,
Dimethylene amine sulfate, trimethylene amine sulfate,
Diethyleneamine sulfate, triethyleneamine sulfate,
Examples thereof include dipropylene amine sulfate, pyridine sulfate, and pyrrole sulfate.

The resistivity of the ink jet ink used in this example is 8 to 50 Ω · cm, preferably 15 to 25 Ω · cm at 25 ° C. This has a resistivity of 8 Ω · cm
As the content of the conductivity-imparting agent in the inkjet ink increases, the solubility stability of the dye decreases,
The nozzle clogging tended to deteriorate, and the resistivity
As it exceeds 50 Ω ・ cm, the content of the conductivity-imparting agent will decrease, and if the AC frequency of the voltage applied to the electrode is lowered, it will not be possible to prevent chemical reactions on the substrate, the electrode will melt, and ejection will be stable. This is supported by the fact that the tendency to deteriorate in sex is recognized.

Although many examples of material relations have been described above, it is needless to say that the present invention is not limited to these and appropriate changes can be made.

[0064]

As described above, according to the present invention, it is possible to shorten the filling time of ink into the pressure chamber by causing secondary boiling which again generates small bubbles after the ink is ejected. Without deterioration of print quality,
An inkjet head with high frequency response can be provided.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional side view showing an embodiment of an inkjet head of the present invention.

FIG. 2 is a sectional view taken along line BB of FIG.

FIG. 3 is a partially cutaway perspective view showing an embodiment of the inkjet head of the present invention.

FIG. 4 is a perspective view of an ink cartridge in which the inkjet head shown in FIG. 3 is incorporated.

5 is a partially cutaway perspective view of the ink cartridge shown in FIG.

FIG. 6 is an external perspective view of an inkjet printer equipped with the inkjet head of the present invention.

FIG. 7 is a curve diagram for explaining secondary boiling in an embodiment of the inkjet head of the present invention.

FIG. 8 is a voltage waveform diagram showing a time change timing of voltage application in an embodiment of the inkjet head of the present invention.

FIG. 9 is an operation explanatory view in one embodiment of the inkjet head of the present invention.

FIG. 10 is a partial cross-sectional side view showing an example of a conventional inkjet head.

11 is a sectional view taken along the line AA of FIG.

FIG. 12 is an explanatory diagram when ejecting ink in an example of a conventional inkjet head.

FIG. 13 is an explanatory diagram after ink ejection in an example of a conventional inkjet head.

[Explanation of symbols]

20 ... Inkjet head, 21 ... Substrate, ink, 22
a, 22b ... Counter electrode, 23 ... Protective film, 24 ... Flow path wall, 25 ...
Orifice member, 26 ... Discharge port, 27 ... Pressure chamber, 28 ...
Ink, 29 ... Ink flow path, 30 ... Signal generator, 31
… Common ink chamber, 32… Ink cartridge, 33… Ink tank, 34… Ink filter, 35… Ink introduction groove, 36… Cartridge insertion port, 37… Carriage,
38 ... Guide shaft, 39 ... Platen roller, 40 ... Ink drop, 41 ... Recording paper, 42, 43 ... Bubble.

Claims (4)

[Claims] 1. A pressure chamber filled with ink, an ink flow path for supplying ink to the pressure chamber, an ejection port provided in the pressure chamber as an ink ejection port, and an ink inside the pressure chamber. An ink jet head comprising an energy generating unit for generating a bubble and an energy supplying unit for controlling the operation of the energy generating unit, which is configured to generate a bubble in the ink and eject the ink from the ejection port. An inkjet head characterized in that, between the ejection and the ejection of ink again, at least a bubble that does not eject ink from the ejection port is generated in the ink in the pressure chamber by the energy generating means. 2. A first energy supply mode used by the energy supply means when a bubble is generated to eject ink from the ejection port, and a second energy supply mode used when a bubble is generated to the extent that ink is not ejected from the ejection port. 2. The inkjet head according to claim 1, wherein the energy generating means is alternately controlled in the first energy supply mode and the second energy supply mode. 3. The energy generating means from the time when the ink is ejected from the ejection port until the time when the ink is ejected again is controlled by the energy supply means so as to continuously increase as the energy per unit time. The ink jet head according to claim 1, which is characterized in that. 4. The ink jet head according to claim 1, wherein the energy generating means is electrodes facing each other.