JPH0939251A - Inkjet printer - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object to provide an inkjet printer capable of gradation printing and environmental correction with a simple configuration. [Structure] Ink tank 1 containing conductive ink 11
2, the nozzle 13, and the conductive ink 11 to the nozzle 13
Electrode 1 which is an energy generating means for further discharging
4 and 15 and pulse voltage applying means 18, and a control block 19 for changing the energy generated per unit time by the energy generating means in accordance with the gradation information of the image data and the surrounding environment. As a result, the dot size can be changed, multi-tone printing and environmental correction can be easily realized, and an inkjet printer with high printing quality can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printer used for output printing of office computers, personal computers and the like.

[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. Inkjet printers like this drop the ink into small droplets and make them fly.
Recording is performed by attaching the recording medium to recording paper, and is broadly classified into a continuous system and an on-demand system depending on a method of generating small droplets and a method of controlling a flying direction.

The continuous system is a system disclosed in, for example, US Pat. No. 3,060,429, in which ink droplets are reduced by electrostatic attraction, and the generated droplets are subjected to electric field control in accordance with a recording signal. In addition, recording is performed by selectively attaching small droplets on recording paper, and a high voltage is required for the generation of small droplets, and it is difficult to form a multi-nozzle.

[0004] The on-demand system is described in, for example, US Pat.
No. 4,747,120, an electric recording signal is added to a piezoelectric vibration element attached to a recording head having a nozzle hole for ejecting a small droplet, and this electric recording signal is mechanically applied to the piezoelectric vibration element. Recording is performed by changing to vibration and ejecting small droplets from the nozzle holes according to mechanical vibration to adhere to the recording paper. Since ink is ejected from the nozzle holes on demand, continuous recording is performed. It is not necessary to collect the droplets that were not required to record an image among the droplets ejected and ejected as in the method, so that a simple configuration is possible. However, it is difficult to process the recording head, and it is extremely difficult to miniaturize the piezo vibrating element, and it is difficult to make multiple nozzles. Has the drawback of.

Japanese Patent Publication No. 61-59911, Japanese Patent Publication No. 62
-11035, Japanese Examined Patent Publication No. 61-59914 discloses a recording method of a system in which boiling is caused by a heating resistor to cause droplets to fly.

As another example of the on-demand system, the system disclosed in US Pat. No. 3,179,042 uses thermal energy instead of mechanical vibration energy by means such as a piezoelectric vibrating element. Compared with the method that uses mechanical vibration energy, this method has the features of high energy conversion efficiency and easy multi-nozzle formation.

Next, the principle of the ejection will be described. Figure 7
FIG. 6 is a sectional view of a conventional ink ejection device. In FIG. 7, 1 is a conductive ink, 2 is an ink chamber filled with the conductive ink 1, 3 is an ink tank containing the conductive ink 1, and 4 and 5 are arranged below the conductive ink liquid surface. A pair of electrodes, 6 is a power source, 7 is a switch for the power source 6, 8 is a nozzle for ejecting the conductive ink 1, 9 is a recording paper, and 10 is a nozzle 8.
Are ink droplets ejected from the

When a voltage is applied to the pair of electrodes 4 and 5, a current flows through the conductive ink 1, and the Joule heat causes a portion of the conductive ink 1 between the tips of the electrodes 4 and 5 to vaporize.
Further, the vaporized conductive ink 1 vapor is discharged from the nozzle 8
To expand until a sufficient pressure is generated to eject the ink droplet 10 onto the recording paper 9. By applying a voltage with the switch 7, a nozzle hole for ejecting the conductive ink 1 is selected and desired characters can be formed on the recording paper 9.

[0009]

In the above energized ink jet system, the resistance value, viscosity, temperature distribution, etc. of the ink changes depending on, for example, the ambient environment temperature, so that the size of the bubble generated by boiling changes and the ink is ejected. There is a problem that the size of the ink droplet changes. However, taking advantage of the feature of high energy conversion efficiency, the amount of energy is positively controlled to change the size of the bubble, and the size of the ink dot landed on the recording material is arbitrarily changed to adjust the environment and It is also possible to perform high quality gradation printing.

Therefore, an object of the present invention is to provide an ink jet printer capable of gradation printing and environmental correction with a simple structure.

[0011]

To this end, the present invention provides an ink jet printer having an ink containing portion for containing ink, a nozzle, and energy generating means for ejecting the ink from the nozzle. The energy generating means is provided with control means for changing the energy generated per unit time according to the gradation information of the data and the surrounding environment.

As the energy generating means, an electrode pair in contact with the ink is provided, an AC voltage is applied to the electrode pair to apply an AC current to the ink, and the ink is generated by the pressure of bubbles generated when heating and boiling the ink. It was made to discharge from a nozzle. Further, the control means is adapted to change the frequency of the AC voltage applied to the electrode pair.

[0013]

With the above structure, the size of the ink dot landed on the recording material can be arbitrarily changed, and environmental correction and high-quality gradation printing can be performed.

[0014]

Embodiments of the present invention will be described below. First, a preferred embodiment that can be carried out in the present invention will be described in detail.

(Principle of Recording) In an ink jet recording head, a recording liquid is heated by a heat generating source such as a resistance heater and boiled, and the recording liquid is ejected from a direction control mechanism such as a nozzle by the expansive force of the boiling bubbles. A method of printing, a method of applying a high voltage to the recording liquid and discharging the recording liquid from a direction control mechanism such as a nozzle by an electrostatic field to print on the paper surface, a pressure is applied to the recording liquid by the mechanical movement of the piezoelectric element, and the recording liquid Is printed on the paper surface by ejecting the liquid from a direction control mechanism such as a nozzle, and a magnetic material is added to the recording liquid to give kinetic energy to the recording liquid by an external magnetic field, and the recording liquid is ejected from the direction control mechanism such as a nozzle onto the paper surface. Method of printing, electric energy is applied to the recording liquid with conductive material added, and the recording liquid is controlled by the expansion force of boiling bubbles generated by self-heating of the recording liquid. Numerous operating principles method or the like to be printed on paper by ejecting from have been proposed and put into practical use. Various methods, structures, and construction methods have been proposed for the structure of the active element device for realizing these operating principles. Since higher resolution printing patterns are required with the improvement of printing quality, most active element devices are formed by thin film technology.

(Head Constituent Material) As the constituent material of the active element device, various materials are used in consideration of characteristics, life, reliability, manufacturing cost and the like.

(Substrate) As a substrate material, an insulating material such as glass or ceramic, a semiconductor, a metal whose surface is coated with a high resistance material, a metal alloy, an insulator or a semiconductor can be used.
As the glass substrate, potassium lime glass, soda lime glass, borosilicate glass, crown glass, zinc crown glass, soda potassium glass, barium borosilicate glass, 96%
Silicate glass, 99.5% silicate glass, phosphate glass, low-melting glass, lithium silicate glass, zinc aluminum silicate glass, zirconium silicate glass, and the like can be used. As the ceramic substrate, aluminum oxide (alumina), titanium oxide (titania), MgO.SiO ₂ (steatite) 2MgO.SiO ₂ (holsterite), BeO
(Beryllia), MgO.Al ₂ O ₃ (spinel) or the like can be used. As the semiconductor substrate, silicon, silicon carbide, diamond, germanium, or the like can be used.

(Electrode) The electrode material is a Ti group metal (Ti, Zr, Hf), a platinum group metal (Pt, Ru, R).
h, Pd, Os, Ir), refractory metal (W, Ta, M)
o), other V, Cr, Fe, Co, Ni, Nb, A
u, Ag, Al and other single metals or their alloys (Ni-F
e, NiCr, TiCr, etc.) can be used. In addition, these oxides (titanium oxide, hafnium oxide, tin oxide, indium oxide, and the like), nitrides (titanium nitride, chromium nitride, and the like), carbides (titanium carbide, tungsten carbide, and the like), and borides can also be used.

(Insulating Layer) As the insulating layer, an insulating organic material (a photoresist such as heat-resistant polyimide resin or acrylic resin) or an inorganic material of the insulating layer can be used.

(Flow channel / nozzle) The flow channel and the nozzle material are polyimide, acrylic, a polymer such as polyethylene terephthalate sheet, an insulating material such as glass or ceramic, a semiconductor, or a metal or metal whose surface is coated with a high resistance material. Alloys, insulators and semiconductors can be used.

(Structure such as photolithography) An example of a method of forming a head using the above materials will be described. T on a non-conductive substrate made of glass or ceramics such as silicon
Conductive metal films of i, Au, Pt, etc. are 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 not exposed in the ink chamber and the substrate by coating or vapor deposition or sputtering. A resin sheet having nozzle holes formed by an excimer laser processing machine on a substrate on which this insulating film and electrodes are laminated and the center of the nozzle holes are 2
Adhere with the adhesive so that it is aligned with the centers of the two electrodes. 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.

In addition and / or SiO ₂ , Al ₂ O ₃ ,
A metal oxide such as TiO _{2 is} formed by a vapor deposition method or a sputtering method. As the resin sheet, polyimide, polyamideimide, polyether sulfone, polyphenylene sulfide,
Although heat-resistant engineering plastics such as polyether ether ketone can be used, polyimide and polyether sulfone are preferable in consideration of ink resistance and laser processability. 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. It is also possible to add a thermoplastic resin such as nitrile rubber, silicone rubber, nylon or polyester resin in order to impart flexibility. In addition, SiO ₂ , Al ₂ O ₃ ,
Fine powder of a metal oxide such as TiO ₂ may be added as a filler, and an appropriate amount of a coupling agent may be added to improve adhesiveness. Epoxy resin and / or polyimide resin are preferable in consideration of ink resistance and heat resistance.
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.

Injecting an excimer laser from the adhesive surface side,
Nozzle holes are formed in the resin sheet. When a heat-resistant plastic film such as polyimide is attached as a protective sheet to the surface of the adhesive during excimer laser processing and processed, high-temperature processing waste does not come into direct contact with the adhesive, so the adhesiveness does not decrease. The resin sheet having the nozzle holes and the substrate are bonded by a rubber pressing method or the like. The bonding temperature is appropriately set according to the curing temperature of the adhesive. Apply pressure with an optimum load that does not cause the adhesive to float or bleed.

(Ink) The recording liquid usable in the present invention may be either water-soluble or oil-soluble. Considering odor and safety, water-soluble is preferred. It is bleed to add dyes, water-soluble organic solvents such as alcohols and glycols as wetting agents, surfactants, or a mixture thereof to the ink, drying speed, adjustment of boiling state, electrode life, nozzle It is preferable for clogging. In addition, preservatives are used. Specifically, the one described in “Inkjet recording technology” by Trikeps Co., p.177, Tokuya Ohta, Nikkei Electronics, No. 303, 1982.11.8,
The same, Journal of Electrophotographic Society, vol 24, 354 (198
5), Akio Owatari, "Proceedings of the 4th Symposium on Non-Impact Printing Technology", IEICE, 93 (1)
987), Shinichi Hirasawa, "Todo" 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. Coloring materials (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, berylen pigments, berynone pigments, atraquinone pigments, quinacridone Pigments, dioxazine pigments, thioindico pigments, isoindolinone pigments, quinophthalone pigments, basic dye lakes, acid dye lakes, nitro pigments, aniline black, fluorescent pigments, titanium oxide, iron oxide, etc.), solvents (water, etc.), Solvent (ethyl alcohol, methyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec
-Butyl alcohol, tert-butyl alcohol, isobutyl alcohol, lower dialkyl ethers of polyhydric alcohols such as n-pentanol, diethylene glycol, etc.), anti-drying agents (glycerin, urea, sorbitan,
Sorbitol, inositol, chelating agents, etc., viscosity adjusting agents (glycerin, etc.), surface tension adjusting agents (diethanolamine, triethanolamine, anionic surfactants, nonionic surfactants), pH adjusting agents (potassium hydroxide (KOH) ), Sodium hydroxide (NaOH), diethanolamine, etc.), dispersant (proteins, natural rubber,
Cellulose derivatives, natural polymers, nonionic polymers, anionic surfactants, nonionic surfactants, etc.), foaming agents (isopropyl alcohol, polyhydric alcohols), antioxidants (vitamin C, sodium sulfite, hydroquinone, Pyrazolidone, hydrazine, etc.) and preservatives (alcohol, formalin, omasine sodium, etc.).

It is particularly preferable to use a conductive ink in the present invention. US 4,53 for conductive ink
6, 776 (JP-A-59-129274) "In an ink for an selective ink-jet printer consisting of an aqueous mixture of dyes, this mixture is 1
An ink characterized in that it comprises an amount of hydrolyzed salt which gives the ink a resistivity of 5 to 50 ohms ". JP-A-5-179182 (DIC) states that "aqueous ink composition for ink jet recording containing water and a colorant contains a salt comprising an alkanolamine or an ethylene oxide adduct and / or a propylene oxide adduct and a hydrogen halide. An ink characterized by the following "is disclosed. Japanese Patent Publication No. 2-5785 specifically describes inorganic salts. The conductivity-imparting agent used in the present invention may be any of alkali metal compound salts such as lithium (Li), inorganic salts such as ammonium sulfate, lithium chloride, sodium chloride and potassium chloride, and organic salts, but quaternary organic ammonium. A derivative of a salt 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, tripropylamine sulfate, phenylamine sulfate, diphenylamine sulfate, dimethyleneamine sulfate, trimethyleneamine sulfate, diethyleneamine sulfate, triethyleneamine sulfate, dipropyleneamine sulfate, tripropyleneamine Sulfate, pyridine sulfate,
Pyrrole sulfate and the like can be mentioned.

The wetting agent has a boiling point higher than that of water,
Used to prevent drying of the nozzle tip. 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 polyhydric alcohol becomes less than 0.5% by weight, the nozzle tip tends to be clogged due to the drying of the ink, and as the polyhydric alcohol exceeds 3.0% by weight, the ink specific resistance tends to increase. And it was found that each was not preferable.

Examples of the solvent include water and an organic solvent 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. Ethers, ether alcohols such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether, and water-soluble polymer compounds. Water used as a solvent is 30 to 80% by weight, preferably 5 to 80% by weight.
It is contained in an amount of 0 to 70% by weight. As the amount of water becomes less than 50% by weight, the permeability to paper tends to be improved. As the amount of water exceeds 70% by weight, the permeability to paper tends to decrease. all right.

A surfactant, a pH adjuster, a viscosity adjustor, etc. 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. As the adjusting agent, a water-soluble organic solvent or a surfactant is preferably used. The water-soluble organic solvent may be selected from the above solvents. The surfactant may be, for example, a fatty acid salt, a higher alcohol sulfate ester salt, a liquid fatty oil sulfate ester salt, a fatty alcohol phosphate ester salt, a dibasic fatty acid ester sulfone salt, or a fatty acid amide sulfonate. , Alkyl allyl sulfonates, 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. Specific examples include lower alkanolamines and alkali metal hydroxides. 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 film when it adheres to printing paper, alkyd resin, acrylic resin, acrylamide resin, polyvinyl alcohol,
A resin polymer such as polyvinylpyrrolidone may be added. Addition of an antifungal agent is advantageous from the viewpoint of ensuring reliability during long-term storage.

(Physical properties of ink) The specific resistance of the ink jet ink used in the present invention is 8 at 25 ° C.
˜50 Ω · cm, preferably 15 to 25 Ω · cm. As the specific resistance becomes less than 8 Ω · cm, the content of the conductivity-imparting agent in the inkjet ink increases, so that the dissolution stability of the dye decreases and the nozzle clogging tends to deteriorate. As the content of conductive compound decreases as it exceeds 50 Ω · cm, lowering the AC frequency of the voltage applied to the electrodes makes it impossible to prevent chemical reactions on the substrate, and the electrodes are dissolved or discharge is stable. There was a tendency that the sex deteriorated, and it was found that each was not preferable. The viscosity is 10 cp or less, preferably 5 cp or less. As the viscosity exceeded 5 cp, it was observed that ink droplets tended to be inconveniently ejected from the nozzle holes, which was not preferable. Surface tension is 28 to 55 dyne / cm, preferably 30 to 45
dyne / cm. Surface tension is 30 dyne / cm
It is recognized that the fine line bleeding of the print becomes worse and the print density tends to decrease as the number becomes less than the range.
It has been found that the color bleeding property of the color overprinting tends to decrease as the density exceeds 45 dyne / cm, which is not preferable. The pH is 6-10, preferably 7-9. It was observed that the solubility stability of the dye tends to decrease as the pH becomes less than 6, and that the fading of the dye tends to occur as the pH exceeds 10, which is not preferable. all right.

(Clogging Prevention Mechanism) Since the ink in the ink jet recording apparatus is generally composed of highly volatile water or alcohol as a component, the ink is accumulated in the ejection port (nozzle) of the recording head. If the ejection port is exposed to the atmosphere as it is, water or the like may evaporate from the ejection port, the ink may be dried, and the ink may be fixed, resulting in ejection failure. Even when the ink can be ejected, the ink whose viscosity is increased due to the evaporation of the water or the like adheres to the vicinity of the ejection port, which may disturb the ejection direction of the ink and deteriorate the print quality.

As a countermeasure, the recording head is moved to a fixed position such as a home position during non-printing,
Capping means for blocking the ejection port from the atmosphere by an elastic member such as rubber, preliminary ejection for driving an ink ejection element to eject ink not directly related to recording to a predetermined ink receptor, contact with the ink ejection port surface An elastic member such as rubber is provided, and the two members are moved relative to each other to wipe ink and dust or other foreign matter adhering to the vicinity of the ink ejection port, and the ink supply system is pressurized or sucked from the ink ejection port. It is desirable to provide a purging means for forcibly discharging the ink by applying a predetermined pressure to the ink by the method.

(Cartridge) The ink cartridge used in the present invention may be an integral type in which a recording head for ejecting ink and an ink tank for storing ink to be supplied to the recording head are integrally formed, A separate type in which the ink tank is detachably configured may be used. It is desirable to provide a filter between the ink flow path from the ink tank to the recording head in order to trap foreign matters and bubbles in the ink that adversely affect the ejection.

It is advantageous in terms of reliability that the filter is formed by three-dimensionally knitting a metal such as stainless so as to have a filtering particle size of about 10 microns.

As a condition for improving the print quality,
It has been known for some time that it is important to apply a static negative pressure to the ink ejection port. By applying a negative pressure, the liquid surface of the ink ejection port becomes a negative meniscus, and it is possible to prevent the ink from being drawn in, improving the landing accuracy, and reducing the extra droplets (extra dots). In order to generate a negative pressure at the ink ejection port, it is desirable to provide a negative pressure generating means such as filling the ink tank with a sponge made of polyurethane foam or providing a spring member inside and outside the ink tank.

(Apparatus) The recording apparatus in which the present invention is used is
One or more recording heads are mounted on a carriage, ink is ejected from the recording heads while reciprocating in the main scanning direction on the front surface of the recording material, and the recording material is fed by a predetermined amount in the sub-scanning direction. Even in a so-called serial type recording apparatus that performs recording in a so-called line type in which a recording head is provided over the entire width of the recording material in the main scanning direction and the recording material is fed by a predetermined amount in the sub-scanning direction. Either a recording device may be used.

Further, so-called plotter type recording in which one or a plurality of recording heads are mounted on a carriage and ink is ejected from the recording heads while moving the front surface of a recording material in the main scanning direction and the sub scanning direction. It may be a device.

Next, a circuit for driving the head in the present invention will be described. FIG. 1 is a head drive circuit diagram of an inkjet printer according to an embodiment of the present invention. In FIG. 1, 11 is a conductive ink, 12 is an ink tank, 1
3 is a nozzle, 14 and 15 are electrodes, 16 is a passing current, 17
Is the power supply. Reference numeral 18 denotes a pulse voltage applying means, which is composed of transistors Q1, Q2, Q3 and Q4. 1
9 is a control block, 20 is a discharge control circuit, 21
Is an AC pulse generator, and 22 and 23 are AND circuits.

Now, the pulse signal i input to the bases of the transistors Q1 and Q2 is at high level, and the transistor Q3 and
When the pulse signal j input to the base of Q4 is low level, Q1 is OFF, Q2 is ON, Q3 is ON, Q4
Becomes an OFF state, the voltage of the power supply 17 is applied to the electrode 15, and the electrode 14 becomes the ground level, so that the energizing current 16 flows in the direction of the arrow. Similarly, when the pulse signal i is low level and the pulse signal j is high level, Q1 is O
N, Q2 are OFF, Q3 is OFF, Q4 is ON, the voltage of the power supply 17 is applied to the electrode 14, and the electrode 15
Becomes the ground level, so that the energizing current 16 flows in the direction opposite to the arrow. In this way, when ejecting ink, the logics of the pulse signals i and j are alternately repeated for a certain period, and an alternating current is applied between the electrodes 14 and 15 to boil the conductive ink 11 and change its pressure. The ink 11 is ejected from the nozzle 13 by. The greatest merit of passing an alternating current is that the deterioration of the electrode due to electrolysis can be prevented and the life of the electrode can be maintained.

The outputs c and d of the AC pulse generator 21 are out of phase with each other by 180 ° at a high frequency of several 100 kHz to several MHz and a duty of 50% or less. These signals c and d are basic pulses for switching the transistors Q1 to Q4. The output e of the ejection control circuit 20 is an on-time setting signal during printing. The frequency of the output e is several kHz corresponding to the print dot frequency and is a signal that enables the basic pulses c and d. The control block 19 corrects image data containing gradation information by a temperature sensor signal and outputs a binary print data signal f and a control signal g for controlling the frequencies of outputs c and d of the AC pulse generator. The logic of the print data signal f is high for printing and low for non-printing.

FIG. 2 is a graph showing dot diameter gradation control according to an embodiment of the present invention. In FIG. 2A, the horizontal axis represents the heating time, and the vertical axis represents the applied power and the bubble volume that determines the dot diameter. When 0.4W electric power is applied to the head, the heating time until the start of boiling becomes 7 μs and E1 = 0.4 ×
Energy of 7 = 2.8 μJ is given. The bubbles at that time grow like B1 and the maximum bubble volume becomes 200 pl. Similarly, when 0.23 W of electric power is applied to the head, the heating time until the start of boiling becomes 22 μs and E2 = 0.23 × 2.
Energy of 2 = 5.06 μJ is given, and the bubble at that time grows like B2 and the maximum bubble volume becomes 400 pl. In this way, the time until the start of boiling is determined by the applied power, and the heated volume of the ink changes accordingly. The larger the heated volume, the larger the maximum growth bubble volume. That is, if heated slowly, larger bubbles can be formed. In this way, it is possible to change the bubble volume and control the gradation of the dot diameter.

FIG. 3 is an output waveform diagram of an ink jet printer according to an embodiment of the present invention, which shows transistors Q1 to Q.
4 output is shown. The phase is 18 when the duty is 50%.
0 °, which has a rise time Tr and a fall time Tf depending on the characteristics of the transistors Q1 to Q4.
It becomes a trapezoidal wave of V to Vo. Here, Tr is the time varying from 0 V to Vo, Tf is the time varying from Vo to 0 V, and the frequency of the voltage and current applied to the ink is f (where Tr + Tf ≦ 1 / f). The potential difference of each output, that is, the potential difference applied to the ink becomes a trapezoidal wave of amplitude Vo, and when the ink is a pure resistance R, an alternating current of trapezoidal wave of amplitude Vo / R flows through the ink. Therefore, the energy supplied to the ink per unit time t is expressed by the integrated value of current × voltage (trapezoidal area), so E = Vo ² / R × {1
-(Tr + Tf) × f / 2} × t. That is, by changing the energization frequency, the energy supplied to the ink per unit time can be changed.

FIG. 4 is a relationship diagram of energy per unit time and dot size according to one embodiment of the present invention, showing a relationship between energization frequency, power supplied to ink within a unit time, and dot size. There is. The gradient of the graph of the energization frequency and the supplied power is determined by Vo, R, Tr, and Tf. For example, at energizing frequency of 1MHz, 0.4W, 4MH
Since the energy per unit time decreases as the energization frequency increases, such as 0.2 W for z, the time until the start of boiling increases and the dot size increases. Further, when the environmental temperature is high, the volume of the high temperature portion of the ink becomes larger and the bubbles also become larger. Therefore, to obtain the same 400 pl bubbles, 3.7 MHz at 30 ° C and 4 MH at 20 ° C.
It is necessary to correct the bubble size by varying the supplied energy, that is, the energization frequency at 4.3 MHz at 10 ° C.

An example will be described below in which original image data of 16 gradations of 4 dots per line is converted into 4 gradations, and 1 gradation is performed by one print scan, and 1 nozzle is printed by 4 scans in total.

FIG. 5 is a control block diagram of the ink jet printer of one embodiment of the present invention, and FIG. 6 is a timing chart thereof. In FIG. 5, reference numeral 24 is a 2-bit gradation counter unit that counts the scanning clock clk1 generated for each scanning and outputs the gradation counter value q indicating the current number of gradations and the energization frequency data fdat, and 25 is the 16th floor. A memory unit for storing a threshold value thrdat for converting the original image data of tones into 4 gradations and outputting it according to the gradation counter value q;
Is the original image data da transferred by the transfer clock clk2
A comparator 27 which compares ta with a threshold value thrdat and outputs a binarized output permission signal enb, 27 is energization frequency data f
AC signals fdrv and fdrv that count clk3 using a value obtained by correcting dat with temperature data temp as a preset value and have a phase difference of 180 ° with a duty of 50%
An energization frequency counter section 28 outputs an energization driver section that outputs a drive signal Vo obtained by amplifying fdrv and fdrv, which is a period preset by the energization start signal trg when the output permission signal enb is at a high level, to 29 a head. Reference numeral 30 is a paper feed motor control unit that is triggered when four scans are completed, and reference numeral 31 is a paper feed motor.

A detailed description will be given below with reference to the timing chart of FIG. 2-bit gradation counter value q obtained by counting the scanning clock clk1 by the gradation counter unit 24
Represents the current gradation, 0, 1, 2, 3, 0, ...
.. changes.

Original image data d with 4 dots per line and 16 gradations
It is assumed that ata is 3, 5, 1, 9 and that the smaller the numerical value, the higher the gradation of the density. The original image data data is transferred four times and processed four times like 3, 5, 1, 9, 3, 5, 1, .... Paper feed motor 31
Is driven when each processing of gradations 0 to 3 is completed.

The threshold value for converting the original image data data of 16 gradations into 4 gradations is thrdat, which is loaded according to the gradation counter value q. Density 0 to 3 of the original image data data is gradation 0, density 4 to 7 is gradation 1, density 8 to 11
Is gradation 2, and densities 12 to 15 are gradation 3. When the result of binarizing the original image data data and the threshold value thrdat in the comparator 26 and binarizing the result is an enb signal, the original image data data is 3, 5, 1, 9; , 0, 1, 0, 0 for gradation 1, 0, 1, 0, 0,
0, 0, 0, 1 for gradation 2 and 0, 0, 0, 0 for gradation 3
Becomes

The energization frequency counter unit 27 is a counter having a preset value which is a value obtained by correcting the energization frequency data fdat input according to the gradation based on the temperature information detected by the temperature sensor, and the signals fdrv and fdr having a duty of 50%.
Output v. If the temperature is high, the temperature of the ink as a whole is also high, so the bubbles become large. Therefore, when the air temperature is high, the energization frequency is set to be low to reduce the applied energy, and when the air temperature is low, the energization frequency is set to be high to increase the applied energy, thereby performing the temperature correction. For example, when the temperature is 20 ° C., gradation 0 is 4 MHz, gradation 1 is 3 MHz, gradation 2 is 2 MHz, gradation 3 is 1 MHz, and when temperature is 10 ° C., gradation 0 is 4.3 MHz and gradation 1 is 3. 3MHz, gradation 2 is 2.3MHz, gradation 3 is 1.3
When the frequency is 30 MHz and the temperature is 30 ° C., a signal whose frequency is variable is output such that the gradation 0 is 3.7 MHz, the gradation 1 is 2.7 MHz, the gradation 2 is 1.7 MHz, and the gradation 3 is 0.7 MHz.

When the enb signal is 1, the energization driver unit 28 amplifies the preset periods fdrv and fdrv by the energization start signal trg and outputs the amplified periods to the head unit 29. In this way, the frequency of the alternating current supplied to the ink can be varied depending on the gradation, and the energy supplied to the ink can be varied, so that the dot size can be varied. It is also possible to correct the effect of ambient temperature,
It is possible to realize an inkjet printer that can exhibit stable printing performance in a wide range of surrounding environments.

[0056]

As described above, according to the present invention, the dot size can be varied, multi-tone printing and environmental correction can be easily realized, and an ink jet printer with high printing quality can be realized.

[Brief description of drawings]

FIG. 1 is a head drive circuit diagram of an inkjet printer according to an embodiment of the present invention.

FIG. 2 is a graph showing dot diameter gradation control according to an embodiment of the present invention.

FIG. 3 is an output waveform diagram of an inkjet printer according to an embodiment of the present invention.

FIG. 4 is a relationship diagram of energy per unit time and dot size according to an embodiment of the present invention.

FIG. 5 is a control block diagram of an inkjet printer according to an embodiment of the present invention.

FIG. 6 is a timing chart of an inkjet printer according to an embodiment of the present invention.

FIG. 7 is a sectional view of a conventional ink ejection device.

[Explanation of symbols]

 11 Conductive Ink 12 Ink Tank 13 Nozzle 14, 15 Electrode 18 Pulse Voltage Applying Device 19 Control Block 20 Ejection Control Circuit 21 AC Pulse Generator 24 Gradation Counter 25 Memory Unit 26 Comparator 27 Conduction Frequency Counter 28 Part 29 head part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takuma Takasu, 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. An ink jet printer comprising an ink containing portion for containing ink, a nozzle, and an energy generating means for ejecting the ink from the nozzle, the ink jet printer according to gradation information of image data and surrounding environment. An ink jet printer comprising a control means for changing the energy generated by the energy generating means per unit time. 2. As the energy generating means, an electrode pair in contact with the ink is provided, and an AC voltage is applied to the electrode pair to apply an AC current to the ink, and the ink is generated by the pressure of bubbles generated when the ink is heated and boiled. The inkjet printer according to claim 1, wherein the ink is ejected from the nozzle. 3. The ink jet printer according to claim 1, wherein the control means varies the frequency of the AC voltage applied to the electrode pair.