JP2005212412A - Inkjet recording apparatus and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording apparatus, which is made excellent in intermittent ejectability by restraining the viscosity of ultraviolet curing ink from being increased by light leakage and which can decrease an ejection voltage by restraining the viscosity of the ink containing dispersed pigment particulates from being increased by thixotropy, and an inkjet recording method. <P>SOLUTION: This inkjet recording apparatus is equipped with: a recording head which ejects the ultraviolet curing ink in a channel to a recording medium from a nozzle while moving relatively to the recording medium, by imparting an ejection signal to a pressure generating means of the channel; a light source for curing the ink by irradiating the ink immediately after ejection with ultraviolet rays; and a microvibration signal generating means which imparts a microvibration signal, for preventing the viscosity of the ink from being increased by microvibrating a meniscus in the nozzle so as to bring the ink in the nozzle into contact with air outside the nozzle and for suppressing an increase in the viscosity of the ink due to thixotropy by using an agitating effect, to a pressure generating means of a nonejection channel of the recording head. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, immediately after the ultraviolet curable ink is ejected from the nozzle onto the medium, the ink is cured by irradiating the ultraviolet light from a light source provided in the vicinity of the head, and an image is recorded on the recording medium. The present invention relates to an ink jet recording apparatus and an ink jet recording method.

  In recent years, a recording method in which ink jet recording is performed on a recording medium using an ink curable with ultraviolet rays (ultraviolet curable ink) and cured by irradiating with ultraviolet rays has been developed and is being put to practical use.

  Inkjet recording has the feature that printing is easy because it does not require plate making, but with conventional recording methods using water-based inks or solvent-based inks, the fastness to friction, water resistance, and solvent resistance of the recorded material In addition, the light resistance and the like are not sufficient, and depending on the recording medium, a subbing treatment or the like is required, so that it is not suitable for industrial printing applications. However, by using UV curable ink, the components in the ink start to polymerize upon irradiation with UV light, and form a polymer, which increases the wear resistance, water resistance, solvent resistance, and light resistance of the recorded matter. In addition, an image having good adhesion can be formed without performing a subbing process or the like on the support constituting the recording medium. Furthermore, since ink is cured instantaneously by simply irradiating ultraviolet rays after ink ejection, there is no need for a drying device, there is no need to treat the discharged solvent, and it is extremely suitable for industrial printing applications that need to be recorded on various supports. In the industrial printing field, the market for inkjet recording devices using ultraviolet curable ink is expanding.

  In general, an ultraviolet curable ink comprises a photocurable prepolymer, a photocurable monomer, a photopolymerization initiator, and additives such as a pigment and an activator. Since the ink does not contain volatile components such as water and solvent, the water and solvent will not volatilize from the meniscus formed in the nozzles of the recording head, and the ink viscosity on the meniscus surface will not increase. Since it hardens instantaneously only by irradiating the film, there is an advantage that it is not necessary to dry the recording medium or to treat the discharged solvent. On the other hand, since the ultraviolet curable ink does not contain water or a solvent, the ink has a high viscosity and cannot be discharged from the recording head as it is. In order to stably discharge this hard-to-discharge ultraviolet curable ink from the recording head, it is necessary to heat the ink and reduce the viscosity at the time of discharge to 10 cp or less. As described above, since the ultraviolet curable ink has a higher viscosity than the water-based ink or the like, there is a drawback that the dischargeability is deteriorated if the viscosity is increased even a little.

  The technology for ejecting UV curable ink from the recording head has just begun to be put into practical use and is not yet reliable enough.In particular, the intermittent ejection property is poor, and when the ejection is temporarily stopped and restarted, a certain volume is required. There is a problem that ink droplets cannot be ejected stably from the beginning and the image deteriorates. When the ejection is paused and restarted, if the ejection cannot be normally performed from the beginning, image degradation occurs. That is, during ink jet recording, a nozzle that ejects ink and a nozzle that does not eject ink are formed depending on the recording pattern.

  The cause of the poor intermittent discharge property of UV curable ink is that the viscosity of the ink is high, so even if it thickens even a little, it causes discharge failure, but the main cause is the meniscus of the nozzle that stopped discharging ink, When the ultraviolet rays irradiated to the ink ejected to the recording medium leak and hit, the ink in the nozzle hardens, the viscosity of the ink in this area rises, and when the ejection is restarted, a predetermined amount of ink droplets from the beginning This is because a phenomenon such as inability to discharge in a predetermined direction at a predetermined speed, or in an extreme case, does not discharge at first and then gradually recovers. Such a discharge failure is particularly undesirable because it causes image quality deterioration in the image edge portion. The increase in ink viscosity at the resting meniscus is mainly due to the volatilization of water and solvent from the nozzle meniscus in general water-based inks and solvent-based inks, but UV curable inks contain volatile components such as water and solvents. Since it is not included, it is not affected by volatilization, and the leakage light of ultraviolet light irradiated to cure the ejected ink is irradiated into the nozzle, and the polymerization of the ink in the nozzle proceeds. Conceivable.

  In addition, as the ultraviolet curable ink, a pigment ink in which pigment particles are dispersed is often used. However, in general, a system in which pigment particles are dispersed reduces the surface free energy of dispersed pigment fine particles when left after being dispersed. The dispersed pigment particles gather together and loosely bond to each other to form a structure, increasing the apparent viscosity. However, when an external force is applied during the viscosity measurement, the structure is broken and the viscosity is lowered according to the strength. This phenomenon is called thixotropy. UV curable ink containing pigment is an unstable system in which minute pigment particles are dispersed. Therefore, the viscosity characteristics are non-Newtonian and the thixotropy appears. This is a major cause of the viscosity increase.

  During continuous ejection, new ink is supplied to the nozzles more and more, so even if light leaks into the nozzles, there is little effect. In addition, during continuous ejection, the ink flows at high speed in the nozzle at a high shift speed, so that there is no increase in ink viscosity based on thixotropy. However, if light leaks into the ink on the meniscus surface in the nozzle while ejection is interrupted, ink polymerization starts and the ink viscosity increases. Further, while the ejection is interrupted, the ink flow rate in the nozzle becomes 0, so the shear rate becomes 0, thixotropy appears, and the ink viscosity increases. Due to both of these effects, the ink viscosity in the nozzle becomes high, and it becomes difficult to eject normal ink from the beginning when resuming ejection. If this thickened ink is purged (discharged), the ejection returns to normal, but cannot be purged during image recording, resulting in image degradation.

  In this way, the cause of the increase in ink viscosity in the idle nozzle is thought to be caused by leaked ultraviolet light and thixotropy, but during printing, the discharge pause period is extremely short, so the influence of leaked light is large, and thixotropy. The effect of is considered to be slight. However, when the recording head has stopped discharging for a long time outside the printing area, it is hardly affected by ultraviolet rays, but rather greatly influenced by thixotropy. Ink thickened by stopping recording for a long period of time needs to be purged, but since the viscosity has increased, it is necessary to apply a higher voltage than normal ejection, so there is no need to prepare a separate power supply for purging. must not. In addition, the voltage setting must be changed according to the degree of thickening, and the viscosity is lowered when the thickened ink is ejected. Therefore, the voltage setting must be changed accordingly.

  Conventionally, in an inkjet recording apparatus that uses ultraviolet curable ink, the amount of ultraviolet light that strikes the nozzle surface is regulated so that it does not exceed a certain amount to prevent an increase in ink viscosity, and the interval between the recording head and the light source is increased to prevent leakage. There are methods such as preventing the light or the light irregularly reflected by the recording medium and the nozzle surface from entering the nozzle, and devising the arrangement of the recording head and the light source so that the ink viscosity does not increase. However, since UV curable ink needs to be cured before the ink spreads on the recording medium, soaks into the recording medium, or mixes with the ink discharged next to the ink, Since it is necessary to irradiate, the distance between the nozzle and the light source cannot be so great. For this reason, in the conventional method, it is impossible to completely prevent leakage light or the like that has been reflected multiple times from the recording medium or the nozzle surface from entering the idle nozzle.

Further, in order to avoid the influence of thixotropy, at 25 ° C., the shear rate is changed from 10 ¹ to 10 ³ (1 / sec), the ink viscosity is measured, and the fluctuation range of the viscosity is 5 mPa * sec or less. There is a method of selecting an ultraviolet curable ink with little thixotropy and avoiding unstable ejection due to thixotropy.

  During printing pause, the ink thickened in the nozzle may be purged by moving the carriage to the home position, but if it is purged every time the ink in the nozzle thickens, it will be purged frequently, Expensive UV-curable ink is wasted. In addition, the line head is extremely troublesome because it is necessary to lift a large head and apply an ink receiver below the large head for purging.

  In this way, there has been no method to prevent the viscosity of thixotropic UV-curable ink from rising inside the recording head, especially inside the nozzles, during ejection pause, so select and use ink with low thixotropy. I had to. However, thixotropy is a phenomenon that always appears in a system in which pigment particles are dispersed, and thixotropy changes greatly depending on the dispersion state of the pigment particles, so that the dispersibility and dispersion stability are good, and a stable structure between the pigment particles is obtained. It is necessary to select ink that is difficult to make. For this reason, the ink that can be used is limited, and the usable period of the ink is also limited.

  Patent Document 1 discloses a technique in which a water-repellent film provided on the nozzle surface is inserted into the nozzle and the meniscus formation position is moved back deep into the nozzle. Although this is less susceptible to light leakage, since the meniscus is deep in the nozzle, it is not preferable because the drive voltage for ink ejection is increased and the ejection performance is lowered. Furthermore, thickening due to thixotropy cannot be prevented.

  All of the methods described above are symptomatic treatments, and can fundamentally solve the problems of ink thickening due to ultraviolet light leaking into a pause nozzle that does not eject ink droplets and ink thickening due to thixotropy. It is not a thing and needs to be changed whenever conditions change.

  Japanese Patent Application Laid-Open No. H10-228688 discloses a technique for causing a meniscus in a nozzle to vibrate by giving a fine vibration signal to a recording head using ultraviolet curable ink. However, this technology uses ultraviolet curable ink to which a solvent is added for the purpose of reducing the ink viscosity, ejects the ink onto the recording medium, evaporates the solvent in the ink, and then sets the ultraviolet ray provided outside the recording apparatus. In this method, the ink is cured by irradiation from an irradiation lamp. In this method, irradiation of ultraviolet light is performed at a location away from the recording apparatus after the recording medium is ejected from the recording apparatus, so that thickening of ink in the nozzles due to ultraviolet light leakage is a problem. There is no. Therefore, the micro-vibration of the meniscus in this patent does not prevent thickening due to ultraviolet light leakage, but the thickening caused by evaporation of the solvent from the dormant nozzle is compared with the low-viscosity ink in the channel. This is prevented by stirring, and is only a conventional method.

Patent Document 3 discloses a technique for applying a discharge preliminary waveform of a sawtooth wave after discharge is stopped and before discharge is restarted in order to suppress the thixotropy of water-based ink. However, UV curable ink has much higher viscosity than water-based ink, and its thixotropy is much higher than water-based ink, so it uses a sawtooth wave to apply a slight vibration that is effective for gradually increasing the voltage. I can't. Further, there is no description about the ultraviolet curable ink.
Japanese Patent Laid-Open No. 11-10874 JP 2003-159790 A JP 2000-203020 A

  The present invention discharges an ultraviolet curable ink containing a pigment and immediately irradiates and cures the ultraviolet light to cure the above-mentioned problem in an ink jet recording apparatus that performs image recording, that is, discharge is stopped during printing. Then, ultraviolet leaking light enters the nozzle during the pause, the ink viscosity increases, the image quality deteriorates when resuming ejection, and the ink viscosity increases due to thixotropy of the pigment ink when printing is paused for a long time. The result of diligent investigation on the problem of high purge voltage is that the start of radical polymerization type UV curable ink is inhibited by oxygen in the air by slightly vibrating the meniscus of the idle nozzle, In addition, by utilizing the fact that the initiation of polymerization of cationic polymerization type UV curable ink is hindered by the humidity in the air, an increase in viscosity due to leakage light is suppressed. In addition, it is superior in intermittent ejection properties, and furthermore, by stirring the ink by slightly vibrating the meniscus, it suppresses the thickening due to thixotropy of ink containing dispersed pigment fine particles, lowers the ejection voltage, and reduces the normal viscosity of the ink It is an object of the present invention to provide an ink jet recording apparatus and an ink jet recording method in which a dedicated power source for purging is not required by enabling discharge at a voltage for discharging ink.

  According to the present invention, three types of micro vibrations having different vibration intensities are prepared, and the image quality is always improved by changing the intensity of the micro vibrations in the ink, the environmental conditions, the print area and the print area, respectively. Can be obtained.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

  According to the first aspect of the present invention, the UV curable ink in the channel is ejected from the nozzle toward the recording medium while moving relative to the recording medium by giving an ejection signal to the pressure generating means of the channel. By slightly vibrating the meniscus in the nozzle against the recording head, the light source for curing the ink by irradiating the ink just after ejection with ultraviolet light, and the pressure generating means of the non-ejection channel in the recording head A fine vibration signal generating means for bringing the ink in the nozzle into contact with air outside the nozzle to prevent an increase in the ink viscosity due to ultraviolet light leakage and for providing a fine vibration signal for suppressing an increase in the ink viscosity due to thixotropy. An ink jet recording apparatus comprising the ink jet recording apparatus.

  According to a second aspect of the present invention, when the recording head is in the printing region, the micro-vibration signal generating means sets AL to 1/2 the acoustic resonance period of the channel with respect to the pressure generating means of the non-ejection channel. 2. The meniscus in the nozzle is finely vibrated by applying a single pulse composed of a 2AL width rectangular wave for reducing and enlarging the channel volume when (Acoustic Length) is set. Inkjet recording apparatus.

  According to a third aspect of the present invention, when the recording head is in the printing area, the micro-vibration signal generating means AL reduces half of the acoustic resonance period of the channel to the pressure generating means of the non-ejection channel. (Acoustic Length), a meniscus in the nozzle is applied by applying a double pulse in which a 1AL width rectangular wave and a 2AL width rectangular wave are arranged at 1AL intervals to reduce and expand the channel volume. The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is slightly vibrated.

  According to a fourth aspect of the present invention, when the recording head is outside the printing area, the micro-vibration signal generating means AL sets 1/2 of the acoustic resonance period of the channel to the pressure generating means of all channels. (Acoustic Length), (N1) AL width rectangular wave for reducing and expanding the channel volume, (N2) AL width first pause period, and for expanding and reducing the channel volume. Of (N3) AL width rectangular wave and (N4) AL width second continuous period (N1, N2, N3, N4 are integers of 2 or more). 4. The ink jet recording apparatus according to claim 1, wherein the meniscus is vibrated slightly.

The invention of claim 5, wherein is an ink jet recording apparatus according to claim 1, wherein the ultraviolet light quantity by said light source is a ^{1mJ / cm 2 ~3000mJ / cm 2} .

  A sixth aspect of the present invention is the ink jet recording apparatus according to any one of the first to fifth aspects, wherein the ultraviolet curable ink absorbs ultraviolet rays and starts radical polymerization.

  A seventh aspect of the invention is the ink jet recording apparatus according to any one of the first to fifth aspects, wherein the ultraviolet curable ink absorbs ultraviolet rays and starts cationic polymerization.

  The invention according to claim 8 is the ink jet recording apparatus according to any one of claims 1 to 7, wherein a relative speed at the time of recording between the recording head and the recording medium is 40 cm / sec or more. is there.

  A ninth aspect of the present invention is the ink jet recording apparatus according to any one of the first to eighth aspects, wherein a nozzle diameter of the recording head is 30 μm or less.

  A tenth aspect of the present invention is the ink jet recording apparatus according to any one of the first to ninth aspects, wherein the ink droplets ejected from the recording head are 10 pl or less.

  An eleventh aspect of the present invention is the ink jet recording apparatus according to any one of the first to tenth aspects, wherein a distance between a nozzle surface of the recording head and the recording medium is 1 mm to 3 mm.

  A twelfth aspect of the invention is the ink jet recording apparatus according to any one of the first to eleventh aspects, wherein the recording medium is non-ink-absorbing.

  A thirteenth aspect of the invention is the ink jet recording apparatus according to any one of the first to eleventh aspects, wherein the recording medium is paper.

  According to a fourteenth aspect of the present invention, the recording head is a line-shaped recording head having a length in the width direction of the recording medium, and the light source has a line having a length in the width direction of the recording medium. The inkjet recording apparatus according to claim 1, wherein the inkjet recording apparatus is a shaped light source.

  According to the fifteenth aspect of the present invention, an ultraviolet ray curable ink in the channel is directed from the nozzle to the recording medium while moving relative to the recording medium by giving an ejection signal to the pressure generating means of the channel of the recording head. An ink jet recording method in which ink is cured by irradiating ultraviolet light from a light source provided in the vicinity of the head with respect to the ink immediately after the ejection, and a nozzle for pressure generating means of a non-ejection channel in the recording head Gives a fine vibration signal to finely vibrate the meniscus in the nozzle, contacts the ink inside the nozzle with the air outside the nozzle to prevent the start of polymerization, prevents the ink viscosity from rising, and stirs the meniscus to thixotropy An ink jet recording method characterized by suppressing an increase in ink viscosity due to the ink.

  According to a sixteenth aspect of the present invention, when the recording head is in the printing area, the fine vibration signal is obtained by setting AL (Acoustic) to ½ of the acoustic resonance period of the channel with respect to the pressure generating means of the non-ejection channel. 16. The inkjet according to claim 15, wherein the meniscus in the nozzle is finely vibrated by applying a single pulse composed of a 2AL-width rectangular wave for reducing and enlarging the channel volume. It is a recording method.

  According to a seventeenth aspect of the present invention, when the recording head is in the printing area, the micro-vibration signal is obtained by setting AL (Acoustic) to ½ of the acoustic resonance period of the channel with respect to the pressure generating means of the non-ejection channel. Length), a double pulse consisting of a 1AL width rectangular wave and a 2AL width rectangular wave arranged at 1AL intervals for reducing and expanding the channel volume is applied to finely reduce the meniscus in the nozzle. 16. The ink jet recording method according to claim 15, wherein the ink jet recording method is vibrated.

  According to an eighteenth aspect of the present invention, when the recording head is out of the printing area, 1/2 of the acoustic resonance period of the channel is set to AL (Acoustic) for the pressure generating means of all the channels when the recording head is outside the printing region. (N1) AL width rectangular wave for reducing and enlarging the channel volume, (N2) first pause period for AL width, and for expanding and reducing the channel volume ( N3) By applying a continuous wave (N1, N2, N3, N4 is an integer of 2 or more) consisting of a rectangular wave of AL width and a second pause period of (N4) AL width, the meniscus in all nozzles is reduced. 18. The ink jet recording method according to claim 15, 16 or 17, wherein the ink jet recording method is slightly vibrated.

The invention of claim 19 wherein is an ink jet recording method according to any one of claims 15-18, wherein the ultraviolet light intensity is 1mJ / cm ² ~3000mJ / cm ² by the light source.

  The invention according to claim 20 is the ink jet recording method according to any one of claims 15 to 19, wherein the ultraviolet curable ink absorbs ultraviolet rays and starts radical polymerization.

  A twenty-first aspect of the invention is the ink jet recording method according to any one of the fifteenth to nineteenth aspects, wherein the ultraviolet curable ink absorbs ultraviolet rays and starts cationic polymerization.

  The invention according to claim 22 is the ink jet recording method according to any one of claims 15 to 21, wherein a relative velocity during recording between the recording head and the recording medium is 40 cm / sec or more. is there.

  The invention according to claim 23 is the ink jet recording method according to any one of claims 15 to 22, wherein the nozzle diameter of the recording head is 30 μm or less.

  A twenty-fourth aspect of the invention is the ink jet recording method according to any one of the fifteenth to twenty-third aspects, wherein the ink droplets ejected from the recording head are 10 pl or less.

  A twenty-fifth aspect of the invention is the ink jet recording method according to any one of the fifteenth to twenty-fourth aspects, wherein the distance between the nozzle surface of the recording head and the recording medium is 1 mm to 3 mm.

  A twenty-sixth aspect of the invention is the ink jet recording method according to any one of the fifteenth to twenty-fifth aspects, wherein the recording medium is non-ink-absorbing.

  The invention according to claim 27 is the ink jet recording method according to any one of claims 15 to 25, wherein the recording medium is paper.

  According to a twenty-eighth aspect of the invention, the recording head is a line-shaped recording head having a length in the width direction of the recording medium, and the light source has a line having a length in the width direction of the recording medium. The inkjet recording method according to claim 15, wherein the inkjet recording method is a shaped light source.

  According to the present invention, the meniscus in the idle nozzle is finely vibrated, so that the meniscus in the idle nozzle is always brought into contact with new oxygen or moisture in the air, thereby stopping the meniscus of the idle nozzle. Even if ultraviolet light leaks into the ink, the polymerization of the photopolymerizable material in the UV curable ink can be prevented and the increase in viscosity can be prevented, providing superior intermittent ejection, preventing image deterioration, and printing. Reliability can be increased. In addition, the ink is stirred when the meniscus that has stopped discharging is slightly vibrated, so that the structure formed by the pigment dispersed particles in the ink is destroyed during a long-term stop to prevent the ink from thickening due to thixotropy. The power supply for the operation can be made unnecessary. Furthermore, micro vibration waveforms having different intensities can be prepared, and optimal micro vibration can be applied according to ink, environment, printing area, and printing area.

  Hereinafter, embodiments of the present invention will be described in detail.

  The basic components of UV curable ink are typically UV curable resin, a photopolymerizable prepolymer with a slightly higher molecular weight to determine the structure and physical properties of the image, and the viscosity of the ink by diluting this prepolymer. And a photopolymerizable monomer that also participates in polymerization and acts as a crosslinking agent when irradiated with ultraviolet rays, a photopolymerization initiator that absorbs ultraviolet rays and initiates a photopolymerization reaction, a pigment, Consists of additives such as activators and defoamers, and does not contain volatile components such as water and solvents. Therefore, since most of the components can be polymerized, the recording apparatus requires an ultraviolet light source for curing, but does not require a drying apparatus for removing volatile components after recording, and is a harmful organic solvent during printing. Is not released into the atmosphere, so that no solvent recovery device is required.

  As described above, since the ultraviolet curable ink does not contain a volatile component, the volatile component does not volatilize from the nozzle surface during the ejection stop and the ink viscosity of the meniscus in the nozzle does not increase.

  There are two types of ultraviolet curable ink, radical polymerization type and cationic polymerization type, and any of them can be preferably used in the present invention.

  Radical polymerization type ultraviolet curable ink has a property that the initiation of radical polymerization is inhibited by oxygen. That is, when ultraviolet light is irradiated to the ultraviolet curable ink, the photopolymerization initiator generates radicals and initiates a crosslinking reaction between the photopolymerizable prepolymer and the photopolymerizable monomer. If oxygen is present in the reaction atmosphere, The radicals generated by the absorption of ultraviolet rays by the photopolymerization initiator are preferentially reacted with oxygen and consumed, and when the oxygen is completely consumed, the polymer formation reaction is started for the first time. Since the reaction between radicals and oxygen is said to be about 100 times faster than the reaction between radicals and photopolymerizable monomers or polymers, oxygen in the air is a powerful factor that inhibits the initiation of polymerization.

  An acrylic compound is used as the radical polymerization material. For example, urethane acrylate, epoxy acrylate, amino resin acrylate, acrylic resin acrylate, and the like can be given.

  In addition, the cationic polymerization type UV curable ink using a cationic polymerizable material does not inhibit the polymerization by oxygen, but the cationic polymerization reaction is sensitive to moisture (humidity) in the air, so the polymerization starts when the humidity is high. Disappear. For example, when the humidity increases from 45% to 85%, the reaction rate decreases to 1/60.

  Examples of the cationic polymerization material include epoxy resins, vinyl ether compounds, cyclic ether compounds, spiro compounds, and okitacene resins.

  The photopolymerization initiator includes a radical reaction type and an ion reaction type. The radical reaction type includes one that absorbs ultraviolet energy and cleaves itself to generate a radical, and the other that extracts hydrogen from a nearby hydrogen-containing compound to generate a radical.

  The ion-reactive type is a compound that releases a catalyst component that initiates cationic polymerization upon irradiation with ultraviolet light, and examples thereof include aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, and metallocene compounds. Should be used appropriately.

  In the present invention, by utilizing the property that the polymerization initiation of radical polymerization type ultraviolet curable ink is inhibited by oxygen and the polymerization initiation of cationic polymerization type ultraviolet curable ink is inhibited by humidity, ink droplets are formed. Even if ultraviolet light leaks into the meniscus in the nozzle of the non-ejection channel that does not eject, the meniscus is vibrated slightly to bring the ultraviolet curable ink in the nozzle into contact with oxygen or moisture in the air outside the nozzle. This is a new method for preventing an increase in ink viscosity. For example, when using a radical polymerization type ultraviolet curable ink, even if the ultraviolet light leaks into the nozzle by mistake and radicals are generated from the photopolymerization initiator in the ink, the meniscus is vibrated slightly, If the ink in the nozzle is always brought into contact with oxygen or moisture in the external new air in contact with the meniscus, the generated radicals react preferentially with oxygen and moisture, preventing the polymerization of the photopolymerizable material from starting. Therefore, an increase in viscosity can be prevented.

  Unless the meniscus is vibrated slightly, radical polymerization starts when oxygen in the air in contact with the ink meniscus in the nozzle is consumed. Since new oxygen is supplied immediately, no polymer is produced, but the viscosity of the ink at that location increases. For example, even if a viscosity increase of 1 cp occurs, the discharge amount is reduced by several percent, leading to image deterioration, which is not preferable. When the meniscus is vibrated slightly, new oxygen is always supplied to the ink in the nozzle forming the meniscus, and as long as these are supplied, the polymerization cannot be started, so that an increase in viscosity can be prevented.

  Similarly, in the cationic polymerization type ultraviolet curable ink, unless the meniscus is vibrated, if the moisture contacting the meniscus is consumed, the ultraviolet curable ink in the nozzle starts cationic polymerization. When the meniscus is finely vibrated, new moisture is always supplied to the meniscus, so that no polymerization occurs even when light leaks onto the photopolymerization initiator in the ink in the meniscus, and an increase in viscosity can be suppressed.

  Further, according to the present invention, the ink is stirred by finely vibrating the meniscus to prevent the pigment-dispersed particles in the ink from forming during the long-term stop, and the formed structure is destroyed. Thus, an increase in the viscosity of the ink due to thixotropy can also be prevented.

  By finely vibrating the meniscus in this way, the effect of improving the contact between the ink on the meniscus and the air and the effect of stirring the ink thickened by the meniscus overlap, which is extremely effective and increases the viscosity of UV curable ink with high viscosity. Can prevent viscosity.

  That is, according to the present invention, a fine vibration signal is given to the pressure generating means of the non-ejection channel to cause the meniscus in the nozzle to vibrate, and the fine vibration causes the ink in the nozzle to contact the air outside the nozzle. The photopolymerization of the ink is prevented, and the thixotropic property is suppressed by destroying the structure formed by the pigment dispersed particles in the ink by stirring by slight vibration, thereby suppressing the viscosity increase of the ink.

  The viscosity of ultraviolet curable ink is much higher than that of water-based ink, and the actual situation is that a low-viscosity monomer is added, the ink is heated to lower the viscosity, and finally discharged from the recording head. For this reason, if the viscosity is increased even a little, ejection failure tends to occur. Depending on the type of ink, it is not sufficient to apply a slight vibration to the idle nozzle, and it may be preferable for the drive nozzle to also apply a slight vibration immediately before ejection. That is, a method may be employed in which all the nozzles are always subjected to slight vibration, and when an ejection signal is received, an ejection pulse is sandwiched.

The viscosity (η) of a Newtonian fluid is proportional to the ratio of shear stress (τ) / slip rate (D). The viscosity of the Newtonian fluid is represented by η = τ / D, and is constant regardless of the shear rate. The viscosity of the low-viscosity water-based dye ink takes the behavior of a Newtonian fluid, but the ultraviolet curable ink has high viscosity and contains solid pigment-dispersed particles, so that thixotropy tends to appear in the viscosity behavior. Since the viscosity of a thixotropic fluid is not proportional to the ratio of shear stress (τ) / slip velocity (D), the shear rate must be defined when defining the viscosity of a thixotropic fluid. Ordinary thixotropic fluids exhibit shear fluidization characteristics in which the viscosity decreases as the shear rate increases. When ink flows inside the recording head, the displacement speed in the channel is about 10 ⁰ to 10 ² (1 / sec), but the displacement speed in the nozzle is because the ink passes through the narrow nozzle at high speed. It becomes a high value of 10 ³ to 10 ⁴ (1 / sec). Therefore, even if the viscosity is high in the channel where the shear rate is low, the flow rate is high in the narrow nozzle when ejecting, so that the viscosity decreases due to the high shear rate, and stable ejection can be achieved. However, since the DOD recording head repeatedly discharges and pauses, the slippage speed fluctuates rapidly in the range of 0 to 10 ⁴ (1 / sec). Therefore, if the thixotropy is large, the viscosity fluctuation increases and the discharge is performed. Ink droplet sizes and speeds vary, making it impossible to discharge stably.

In order to stably discharge UV-curing ink, the speed of the viscosity is measured in the range of 10 ¹ to 10 ³ (1 / sec) at 25 ° C. by changing the speed of the rotor of the viscometer. It is preferably 5 mPa * sec or less. As described above, thixotropy shows a low value immediately after dispersion when the dispersion state is good, but as time passes, the pigment dispersed particles become agglomerated, and as the structure is formed, the thixotropy gradually increases and the viscosity increases. As a result, the usable time is limited.

  In the present invention, an ink having a good pigment dispersion such that the viscosity difference measured by changing the shear rate does not exceed 5 cp is preferable, but this is not a limitation. The reason for this is that even if the dispersion deteriorates with time and the thixotropy increases and the viscosity difference exceeds 5 cp, the viscosity decreases when an acoustic wave is applied to the ink. After purging, stable discharge is possible thereafter.

  However, if the ejection is interrupted, especially if it is interrupted for a long time outside the printing area, the viscosity increases greatly. When purging this thickened ink, it cannot be purged with a normal ejection voltage, but a dedicated power supply is required. In the present invention, since the viscosity is lowered by applying a slight vibration, a dedicated power source for purging is not required.

  Next, an example of an ink jet recording apparatus for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of an ink jet recording apparatus. In the inkjet recording apparatus 1, the recording medium P is sandwiched between the conveyance roller pair 32 of the conveyance mechanism 3 and further conveyed in the Y direction in the figure by a conveyance roller 31 that is rotationally driven by a conveyance motor 33.

  The recording head 2 is provided between the conveying roller 31 and the conveying roller pair 32 so as to face the recording surface PS of the recording medium P. The recording head 2 is shown substantially orthogonal to the conveyance direction (sub-scanning direction) of the recording medium P by a driving means (not shown) along the guide rail 4 spanning the width direction of the recording medium P. A carriage 5 provided so as to be capable of reciprocating along the XX ′ direction (main scanning direction) is mounted so that the nozzle surface of the recording head 2 faces the recording surface PS of the recording medium P. The drive signal generator 100 (see FIG. 3) provided with a circuit for generating a discharge signal and a micro-vibration signal, which will be described later, is electrically connected via the flex cable 6.

  Further, on the carriage 5 on which the recording head 2 is mounted, ultraviolet light sources 7 and 7 are provided alongside both sides of the recording head 2 so as to sandwich the recording head 2 in the main scanning direction. Therefore, a predetermined amount of ultraviolet light is emitted toward the recording surface PS of the recording medium P by lighting.

In the present invention, the amount of ultraviolet light emitted from the ultraviolet light sources 7 and 7 is preferably ¹ mj / cm ² to 3000 mj / cm ² . If the amount of ultraviolet light exceeds this range, the recording medium P is overheated, or light that is irregularly reflected by the recording medium P becomes strong, which is not preferable. On the other hand, if the amount is less than this, the curing speed becomes slow, and the image quality and image physical properties deteriorate.

  In the present invention, when the amount of ultraviolet light is in the above range, an increase in the viscosity of the ultraviolet curable ink in the rest nozzle is prevented, and the effect of being excellent in intermittent discharge performance is remarkably exhibited. Alternatively, when ink that tends to thicken is ejected, it is preferable to apply a slight vibration immediately before ejection. This fine vibration immediately before the discharge has an effect of uniforming the meniscus position in addition to the effect of reducing the viscosity, and has an extremely large effect of keeping the discharge amount constant. This is an effective technique for uniforming the size of the ejected droplets in multi-drop ejection.

If the ink of a radical polymerization type, the ultraviolet light intensity, it is preferable that a ^{50mJ / cm 2 ~100mJ / cm 2} , the ink case of the cationic polymerization type, it is preferable that the 1mJ / cm ² ~200mJ / cm ² . There is a relationship of (mW / cm ² ) (sec) = mJ / cm ² between the illuminance of ultraviolet rays (mW / cm ² ) and the amount of light (mJ / cm ² ), which can be converted into each other.

  The recording head 2 moves the recording surface PS of the recording medium P in the direction XX ′ in the drawing as the carriage 5 moves. The ink is cured by irradiating ultraviolet light from the light sources 7, 7, and a desired inkjet image is recorded on the recording surface PS of the recording medium P.

  In the present invention, the nozzle diameter of the nozzle 23 is preferably 30 μm or less. The reason is that it is possible to eject a minute droplet of 10 pl or less and it is difficult to pick up leaked light.

  In the present invention, the relative speed during recording between the recording head 2 and the recording medium P due to the movement of the carriage 5 is preferably 40 cm / second or more. When the relative speed is increased in order to increase the recording speed, the irradiation amount of the ultraviolet light of the ink on the recording medium P decreases, so that the amount of ultraviolet light must be increased or the ultraviolet sensitivity of the ink must be increased. Then, since an increase in viscosity is likely to occur, the effect of the present invention can be exhibited more remarkably.

  Further, the distance between the nozzle surface of the recording head 2 and the recording medium P is preferably 1 mm to 3 mm. The reason is that the narrower the interval, the more difficult it is to pick up leaked light. However, if the distance is smaller than 1 mm, the recording head 2 and the recording medium P are likely to come into contact with each other. However, by applying a slight vibration to the meniscus in the nozzle, it is possible to suppress an increase in the viscosity of the ink due to leakage light, so that the distance between the two can be widened and troubles such as contact accidents are reduced.

  Furthermore, if the recording medium P is non-ink-absorbing, it is essential to cure the ink by irradiating it with ultraviolet light before the ink wets and spreads on the surface of the recording medium P. Further, when the recording medium P is paper, the ultraviolet light does not reach when the ink soaks into the paper fiber. Therefore, it is essential that the ink is cured by irradiating the ultraviolet light before the ink soaks. For this reason, it is necessary to provide the ultraviolet light source 7 immediately beside the recording head 2, and the interval is preferably 1 cm to 5 cm. When the interval is narrowed in this way, an increase in the ink viscosity of the pause nozzle due to the leaked light is inevitable, but according to the present invention, the increase in the ink viscosity due to the leak light is caused by slightly vibrating the meniscus in the pause nozzle. Since this does not occur, this interval can be narrowed as described above.

  In the figure, reference numeral 8 denotes an ink receiver, which is arranged on both sides of the recording medium P. When the recording head 2 is positioned on the ink receivers 8 and 8 (regardless of stopping or moving), a small amount of ink droplets are purged toward the ink receiver 8. Further, when the recording head 2 has stopped operating for a long time at the home position, although not shown in FIG. 1, the nozzle 9 of the recording head 2 is protected by covering with a cap 9 (see FIG. 8). It is like that.

  2 and 3 are diagrams showing an example of the recording head 2. FIG. 2A is a schematic perspective view, FIG. 2B is a cross-sectional view, and FIG. 3 is a diagram showing an operation during ink ejection.

  In the figure, 21 is an ink tube, 22 is a nozzle forming member, 23 is a nozzle, 24 is a cover plate, 25 is an ink supply port, 26 is a substrate, and 27 is a partition wall. A channel 28 serving as an ink chamber is formed by the partition wall 27, the cover plate 24, and the substrate 26.

  Here, as shown in FIG. 2, the recording head 2 is separated between the cover plate 24 and the substrate 26 by a plurality of partition walls 27A, 27B, and 27C made of a piezoelectric material such as PZT that is an electromechanical conversion element. A shear mode (share mode) type recording head in which a number of channels 28 are arranged in parallel is shown. In such a recording head 2, the partition wall 27 is deformed to generate a pressure change in the channel 28. Therefore, the partition wall 27 made of the piezoelectric material constitutes a pressure generating unit.

  Although three chambers (28A, 28B, 28C) which are a part of many channels 28 are shown in FIG. 3, the number of channels 28 is not limited. One end of the channel 28 (hereinafter sometimes referred to as a nozzle end) is connected to the nozzle 23 formed on the nozzle forming member 22, and the other end (hereinafter sometimes referred to as a manifold end) is connected to the ink supply port 25. Then, the ink tube 21 is connected to an ink tank (not shown). Electrodes 29A, 29B, and 29C connected from above the partition walls 27 to the bottom surface of the substrate 26 are formed in close contact with the surfaces of the partition walls 27 in the channels 28. The electrodes 29A, 29B, and 29C are connected to the drive signal generator 100. Connected to.

  The drive signal generator 100 generates a drive signal generation circuit that generates a series of drive signals including a plurality of drive pulses for each pixel period, and a drive signal supplied from the drive signal generation circuit for each channel. A drive pulse selection circuit that selects a drive pulse according to the data of each pixel and supplies the channel to each channel. A drive pulse for driving the partition wall 27 as an electro-mechanical conversion means according to the data of each pixel. Supply. This drive pulse includes a micro vibration pulse based on the micro vibration signal and an ejection pulse based on the ink ejection signal.

  Here, each partition wall 27 is constituted by two piezoelectric materials 27a and 27b having different polarization directions as indicated by arrows in FIG. 3, but the piezoelectric material may be only a portion 27a, for example. 27 may be present in at least a part of 27.

  When an ejection signal is applied to the electrodes 29A, 29B, and 29C formed in close contact with the surfaces of the partition walls 27 under the control of the drive signal generator 100, ink droplets are ejected from the nozzles 23 by the operation exemplified below. In FIG. 3, the nozzle is omitted.

  First, when no discharge signal is applied to any of the electrodes 29A, 29B, and 29C, none of the partition walls 27A, 27B, and 27C is deformed, but the electrodes 29A and 29C are grounded in the state shown in FIG. At the same time, when an ejection signal is applied to the electrode 29B from the drive signal generator 100, an electric field in a direction perpendicular to the polarization direction of the piezoelectric material constituting the partition walls 27B and 27C is generated, and both the partition walls 27B and 27C As shown in FIG. 3B, the partition walls 27B and 27C are deformed toward each other, expanding the volume of the channel 28B and generating a negative pressure in the channel 28B. Draw. When the potential is returned to 0 from this state, the partition walls 27B and 27C return from the expanded position shown in FIG. 3B to the neutral position shown in FIG. 3A, and high pressure is applied to the ink in the channel 28B ( Release). Next, as shown in FIG. 3C, when a discharge signal is applied to deform the partition walls 27B and 27C in the opposite directions to reduce the volume of the channel 28B, a positive pressure is generated in the channel 28B ( Reinforce).

  As a result, the meniscus in the nozzle 23 due to a part of the ink filling the channel 28 </ b> B changes in the direction in which it is pushed out of the nozzle 23. When the positive pressure becomes so large that the ink droplet is ejected from the nozzle 23, the ink droplet is ejected from the nozzle 23. The other channels operate in the same manner as described above by applying the ejection signal. Such an ejection method is called a DRR driving method, and is a typical driving method for a share mode type recording head. However, the method for ejecting ink droplets is not particularly limited in the present invention.

  In such a shear mode type recording head 2, the deformation of the partition wall 27 occurs due to a voltage difference applied to the electrodes 29 provided on both sides of the partition wall 27. Therefore, instead of applying a negative voltage to the electrode 29 of the channel 28 for ink ejection, The same operation can be performed by grounding the electrode 29 of the channel 28 for discharging and applying a positive voltage to the electrode 29 of the adjacent channel 28. According to this latter method, it can be driven only by a positive voltage.

  Further, since the shear mode type recording head 2 shares the partition wall 27 of the channel 28 with the adjacent channel 28, it cannot simultaneously discharge from the adjacent channel 28 on both sides. For this reason, it is preferable to perform three-cycle driving in which every two channels 28 are divided into three sets of channel groups for driving. Alternatively, each channel may be driven independently by alternately providing channels and air chambers not containing ink.

  Next, in the ink jet recording apparatus 1, a configuration for finely vibrating the meniscus will be described.

  In the case where an image is recorded by moving the recording head 2 along the main scanning direction as in the ink jet recording apparatus 1 shown in the present embodiment, the operation position of the recording head 2 is as shown in FIG. Along the direction, there are a home position, a first standby position, an acceleration (deceleration) area, a printing area, a reduction (acceleration) acceleration area, and a second standby position. Performs image recording in a printing area where image recording is performed on the recording medium P, and the recording head 2 is in one of the home position, the first standby position, each acceleration (deceleration) speed area, and the second standby position. There is no printing area outside.

  In the present invention, the nozzle from the drive signal generator 100 (microvibration signal generator) to the pressure generator of the non-ejection channel 28 in the recording head 2 both inside and outside the print area. It is preferable to give a fine vibration signal for finely vibrating the meniscus in 23. The purpose of finely vibrating the meniscus of the non-ejection nozzle in the printing area is to prevent ink thickening due to leaked ultraviolet light, and to improve intermittent ejection and prevent image deterioration. On the other hand, the purpose of finely vibrating the meniscus of the non-ejection nozzle outside the printing region is to stir the ink in the meniscus to prevent thickening due to thixotropy of the ink due to long-term stop, and to lower the purge voltage.

  In particular, in the case of ink that tends to thicken, it is preferable to apply a slight vibration immediately before ejection. This not only has the effect of lowering the viscosity, but also has the effect of making the meniscus position constant, so that the proper discharge amount can be kept constant.

  It is preferable to use a rectangular wave for this fine vibration signal. Here, the rectangular wave refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within ½, preferably ¼ of AL. Note that AL (Acoustic Length) is ½ of the acoustic resonance period of the channel. This AL measures the speed of ink droplets ejected by applying a rectangular wave voltage pulse to the partition wall 27 made of a piezoelectric material which is an electrical / mechanical conversion means, and keeps the rectangular wave voltage value constant. When the pulse width is changed, it is obtained as the pulse width that maximizes the flying speed of the ink droplet. The pulse width is defined as the time between the point where the voltage rises and reaches 50% of the maximum voltage and the point where the voltage falls and reaches 50% of the maximum voltage.

  The micro-vibration signal composed of a rectangular wave appears to cause a greater variation in the pressure of the ink than the trapezoidal wave in which the rise and fall of the voltage are inclined. The recording head 2 shown is a shear mode head in which the partition wall 27 constituting the channel 28 is made of a piezoelectric material, and the partition wall 27 is shear-deformed to eject ink droplets from the nozzle 23. Less deformation. Since such a recording head discharges using the resonance of the generated pressure wave, the displacement amount of the partition wall 27 that undergoes shear deformation is on the order of nanometers, and uses a laminated piezoelectric element and a diaphragm that operate in an expansion / contraction mode. Compared to the type of recording head, the deformation of the channel 28 is as small as 1/10 to 1/100. For this reason, even if the partition wall 27 is suddenly displaced using a rectangular wave, the meniscus does not vibrate as much as the above-described laminated type, and it takes time to suck in air or stabilize the meniscus vibration. No problem.

  Further, according to the shear mode type recording head 2, the rectangular wave has a faster meniscus response than the trapezoidal wave and can be finely vibrated efficiently, so that the driving voltage of the fine vibration signal can be kept low. is there. Regardless of ejection or non-ejection, a voltage is always applied to the shear mode type recording head, so that a low driving voltage is important for suppressing heat generation of the recording head and ejecting ink droplets stably. In addition, since the drive waveform of the micro-vibration signal is shorter than half of the square wave compared to the trapezoidal wave, the printing speed is greatly reduced whether the micro-vibration signal is incorporated in the non-ejection period or just before ejection. There is nothing to do.

  Furthermore, since the rectangular wave can be easily generated by using a simple digital circuit, there is an advantage that the circuit configuration can be simplified as compared with the trapezoidal wave.

  When the meniscus is finely vibrated, the next discharge cannot be performed unless the fine vibration is subtracted. Therefore, the fine vibration signal applied to the pressure generating means of the non-ejection channel that stops the ejection of ink droplets in the printing region is In order to prepare for the discharge, it is necessary to stop the fine vibration before canceling the discharge, cancel the residual pressure due to the residual vibration, and return the meniscus to the standard position. For this reason, the length of the pulse used for the fine vibration signal is important, and it is desired that the fine vibration is started at the rising edge of the pulse, and the fine vibration is stopped at the falling edge of the pulse, and at the same time the residual vibration can be canceled. For this reason, it is preferable that the fine vibration signal composed of a rectangular wave for finely vibrating the meniscus includes at least a signal whose pulse width is an even multiple of AL both inside and outside the print area. According to this, it is possible to start the fine vibration at the rising edge of the pulse waveform, stop the fine vibration at the falling edge of the waveform, and simultaneously cancel the residual pressure.

  That is, when the pulse waveform of the micro vibration signal rises and the channel 28 expands, a negative pressure wave is generated in the channel 28. The generated negative pressure wave attenuates while repeating pressure inversion every AL time according to acoustic theory. For example, 2 AL after the voltage rises, when the ink pressure in the channel 28 is reversed from negative → positive → negative, the voltage is lowered and the expansion of the channel 28 is restored to return the positive pressure. , The negative pressure remaining in the channel can be canceled. Thereby, an ink droplet can be immediately ejected immediately after that.

  As described above, it is preferable to set the pulse width of the fine vibration signal to an even multiple of AL because the fine vibration is applied at the rising edge of the pulse, the fine vibration is stopped at the falling edge, and the residual pressure can be canceled at the same time. Applying such a slight vibration has the effect of keeping the meniscus position constant as well as the effect of preventing thickening.

  Since the shear mode type recording head 2 shares one partition wall 27 with both adjacent channels 28, when ink droplets are ejected from the nozzles 23 of one channel 28, A small vibration is automatically applied. Therefore, it is not always necessary to apply a fine vibration signal from the drive signal generator 100 to all the non-ejection channels. In order to efficiently suppress the ink thickening and suppress the heat generation of the recording head 2, for example, the three adjacent channels 28A, 28B and 28C shown in FIG. 3A are all non-ejection channels and contribute to image recording. If not, it may be applied only to the electrodes 29A and 29C of the partition walls 27B and 27C of the center channel 28B.

  Therefore, first, a description will be given of a micro-vibration signal that is applied when the recording head 2 is in a printing area where image recording is performed on the recording medium P.

  When the recording head 2 is within the printing area for the recording medium P, the recording head 2 is recording an image. Therefore, a non-ejection nozzle that does not eject ink droplets is detected from the image signal, and the fine vibration of the meniscus is selectively performed. Need to do. In this case, an ink droplet is not ejected from the nozzle 23 to the electrode 29 of the partition wall 27 of the channel 28 that does not contribute to image recording, and the meniscus in the nozzle 23 of the channel 28 is finely vibrated. A fine vibration signal is applied to slightly vibrate the meniscus so that the ink in the nozzle 23 comes into contact with the air outside the nozzle 23. In particular, when ejecting highly viscous ink that tends to thicken, it is preferable to slightly vibrate not only the idle nozzle but also the ejection nozzle immediately before ejection. This fine vibration has a great effect of stabilizing the meniscus position in addition to the effect of preventing thickening, so that the size of the ink droplet can be kept constant during continuous ejection.

  When the recording head 2 moves into the print area, since one line (one swath) of image data has already been sent to the data buffer, the ink is used while the recording head 2 performs one main scan from this image data. It is possible to detect the nozzle 23 of the channel 28 that does not eject droplets. Therefore, even when the recording head 2 is in the printing region, even if ejection is interrupted for a very short time during printing, a slight vibration is applied to the meniscus in the nozzle 23 of the channel 28 that does not contribute to the image recording. It is possible to suppress the viscosity increase of the ultraviolet curable ink.

  In this printing area, since the ejection pause period is relatively short and, depending on the image data, ejection must be performed immediately after the slight vibration, so that a strong slight vibration is applied so as not to adversely affect the ejection. Preferably not.

  Whether the micro-vibration intensity is strong or weak can be determined from the amount of meniscus extrusion by observing the nozzle surface from the outside when a micro-vibration signal is applied. When the meniscus is pushed out with a length longer than the nozzle radius, the radius of curvature of the ink meniscus formed decreases, so the pressure difference between the inside and outside of the meniscus increases, and a strong force is required to retract the meniscus against this differential pressure. Since the meniscus does not return unless it is pulled back, strong micro-vibration is applied and the ink inside the nozzle can be brought into efficient contact with the air outside the nozzle, but it takes time to settle the meniscus. On the other hand, if the meniscus is extruded with a length less than the nozzle radius, the radius of curvature formed by the extruded meniscus is large, so the differential pressure is small, and in order to retract the meniscus against this differential pressure, do not pull back with a strong force However, since the meniscus returns, weak micro-vibration is applied and the ink in the nozzle can be brought into contact with the air outside the nozzle, but it does not take time for the meniscus to settle.

  The opening shape of the nozzle is not limited to a perfect circle and may be various such as an ellipse. The nozzle radius is ½ of the longest diameter on the nozzle tip (surface of the nozzle forming member 22) side.

  The meniscus push-out amount can be measured by strobe synchronization using, for example, a digital microscope “VH-6300” manufactured by KEYENCE. As shown in FIG. 11, the extrusion amount is a value obtained by measuring the amount of protrusion of the meniscus M from the nozzle tip at the center of the approximately nozzle 23 in a direction substantially perpendicular to the nozzle forming member 22.

  For the fine vibration signal applied in the printing region, a mode in which one single pulse consisting of a 2AL-width rectangular wave is applied from the drive signal generating unit 100 to give a fine vibration, and a 1AL-width rectangular wave and a 2AL-width are applied. A mode in which a fine pulse is applied by applying a double pulse in which rectangular waves are arranged at intervals of 1 AL can be preferably used.

  An example of the former single-pulse fine vibration signal is shown in FIG. This is an example in which one pixel is printed in order from adjacent A, B, and C3 channels and one pixel is printed, and the next one pixel stops ejection, and a slight vibration is applied to the A, B, and C3 channels in order. is there. This is an example in which a fine vibration is applied to the meniscus by applying a single pulse composed of a 2AL width rectangular wave to the electrode of the channel where the ejection is suspended. The recording head in the shear mode shares the partition wall of the channel with the adjacent channel, and the partition wall is deformed according to the voltage difference applied to the electrodes provided on both sides of the partition wall. If a voltage is applied to the two channels on both sides of the three channels and the middle channel is grounded, a voltage difference is generated in the partition wall, resulting in deformation. Further, since the partition walls are shared, they cannot be discharged simultaneously from the A, B, and C3 channels, and are discharged in order.

  The ON waveform and the OFF waveform in FIG. 5 indicate two types of drive signals generated by the drive signal generation unit 100. This drive signal is composed of two types of drive pulses: a fine vibration pulse (OFF waveform) and a discharge pulse (ON waveform) to be combined with this fine vibration pulse to form a discharge pulse. The ON waveform and the OFF waveform are respectively supplied to the drive pulse selection circuit of each channel, and are selectively supplied to the electrodes of each channel by controlling the pulse selection gate signal corresponding to the print data of each channel. The drive pulse selection circuit supplies an ON waveform to the electrode when the pulse selection gate signal is High, and supplies an OFF waveform to the electrode when the pulse selection gate signal is Low. The period for applying the micro-vibration pulse and the period for applying the ejection pulse are controlled by the pulse division signal. In order to apply a slight vibration to the meniscus of the non-ejection nozzle, an ON waveform may be sent to the electrode of the channel and an OFF waveform may be sent to the remaining two channels.

  In this way, since the ON waveform and the OFF waveform are switched to perform discharge and fine vibration, by appropriately switching timing, it is possible to apply the fine vibration not only to the rest nozzle but also immediately before discharge.

  Such a single-pulse microvibration signal is effective in preventing the viscosity of an ultraviolet curable ink having a low viscosity or a low thixotropic property. Since the pulse of the fine vibration signal is 2AL width, the meniscus can be slightly vibrated at the rising edge of the waveform, the residual pressure can be canceled at the falling edge, the meniscus can be settled, and then the ink droplet is immediately ejected. Even in this case, there is no influence from the residual pressure. In addition, by setting the width to 2AL, it is possible to drive without significantly reducing the printing speed while canceling the residual pressure.

  An example of the fine vibration signal of the double pulse is shown in FIG. Here, only the shape of the pulse of the OFF waveform is different, and the others are the same as in FIG. 5, so only the result is shown.

  A double pulse micro-vibration signal that imparts a micro-vibration to the meniscus by applying a signal with a pulse width of 1 AL and a signal with a width of 2 AL in between is highly viscous or thixotropic. Is effective in preventing thickening of UV curable inks that are strong. When the first pulse of 1AL width is applied, the channel 28 expands at the rising edge of the pulse, a negative pressure is generated in the channel 28, and after 1AL, the pulse falls at the timing when the ink pressure is reversed to the positive pressure, Since the expansion of the channel 28 is removed, more positive pressure is applied to the ink, and the meniscus in the nozzle vibrates greatly. Since a 2AL width pulse is subsequently applied, the meniscus vibrates again, but this time it is 2AL width, so the residual pressure can be canceled at the falling edge. Since the second pulse has a width of 2AL, it can be driven at a high speed while canceling the residual pressure. Thus, it can be seen that applying a slight vibration with an even AL width has a thickening prevention effect and a meniscus position stabilization effect.

  Next, the case where the recording head 2 is in any one of the home position, the first standby position, the acceleration / deceleration area, and the second standby position and outside the printing area where image recording is not performed will be described. Outside the printing region, the stop period is long, thixotropy appears, the viscosity becomes high, and this ink cannot be purged with a normal discharge voltage, so a strong micro vibration is continuously applied.

  FIG. 7 shows an example of a micro-vibration signal composed of continuous pulses applied when the recording head 2 is outside the printing region where image recording is not performed. Again, three adjacent channels are shown as A, B, and C.

  This micro-vibration signal includes (N1) AL width pulses that reduce and expand the channel volume, (N2) a first pause period of AL width, and (N3) AL width that increases and decreases the channel volume. And a second pause period of (N4) AL width. Here, N1, N2, N3, and N4 are integers of 2 or more. In FIG. 7, N1 = N2 = N3 = N4 = 4 is illustrated. Outside the printing area, such a fine vibration signal is repeatedly and continuously applied.

  Since this fine vibration outside the printing area repeatedly applies a pulse voltage so that a positive and negative differential voltage is generated, a fine vibration having a larger amplitude than that of the fine vibration signal for applying a positive differential voltage pulse is applied within the printing area. In addition, since the stirring effect is great, an increase in the viscosity of the ink due to thixotropy can be suppressed even when left for a long period of time.

  When the carriage 5 starts decelerating after the printing is finished, the fine vibration signal in the print area is switched to the fine vibration signal outside the print area, and the print area is stopped while the recording head 2 is stopped at each standby position. If an external micro-vibration signal is applied from the drive signal generating unit 100 to the pressure generating means of all the channels 28, an increase in ink viscosity due to thixotropy can be prevented, so that the ink has the same magnitude as that during ejection. Can be purged toward the ink receivers 8 and 8, and it is not necessary to prepare a separate power source for purging.

  Here, the meaning of applying the discharge and the micro-vibration signal with the same magnitude voltage means that the discharge signal continuously applies a positive difference voltage and a negative difference voltage, and therefore, through the electrodes 29 on both sides of the partition wall 27, Double the voltage is applied to the partition wall 27. The fine vibration signal outside the printing area applies a positive difference voltage and a negative difference voltage at intervals, so that the meniscus vibrates strongly without applying double voltage, but ink droplets do not discharge. . Since the fine vibration signal in the printing area is only applied with a positive differential voltage, the meniscus only vibrates weakly.

  The fine vibration of the meniscus in the printing area and outside the printing area described above causes the ink droplets to be recorded for image recording so that the ink drops can be stably ejected by the subsequent application of the ejection pulse. It is preferable to stop the discharge at least 1 AL time before starting the discharge.

  In addition, the behavior of the meniscus due to the application of a minute vibration signal is greatly affected by the viscosity, surface tension, recording head temperature, and environmental humidity of the ink. It is preferable to finely adjust the pulse voltage and the pulse length by oscillating and observing the ink column pushed out from the nozzle 23 with respect to the magnitude of the fine vibration.

  When recording is stopped for a long period of time, the recording head 2 is moved to the home position, and the recording head 2 is covered with a cap 9 for the purpose of protecting the nozzle surface and the like, as shown in FIG. UV curable inks that do not contain volatile components such as water and solvents do not increase in viscosity due to volatilization of these volatile components, but when recording is stopped for a long period of time, the ink contains pigment dispersed particles, so thixotropy There is an increase in viscosity. The cap 90 shown in the present embodiment is connected to the decompression pump 91 via the suction pipe 92. When the thickening due to thixotropy is severe for a long period of time, the decompression pump 91 is driven to force ink from the nozzles 23. By sucking into the nozzle 23, the nozzle 23 can be cleaned. Reference numeral 93 denotes a waste ink tank that stores the sucked waste ink. The cap that simply seals the nozzle surface of the recording head 2 and the cap 90 for forcibly sucking ink as described above may be physically separated and arranged independently. Good.

  Next, a specific operation flow of the ink jet recording apparatus will be described with reference to a flowchart shown in FIG.

  First, after stopping for a long period of time, when the power is turned on for image recording, ink is sucked from the nozzle 23 at the home position to clean the nozzle 23 (S1). Next, the ultraviolet light sources 7 and 7 on both sides of the recording head 2 placed on the carriage 5 are turned on (S2). At this time, since the leakage light from the ultraviolet light sources 7 and 7 enters the nozzle 23 of the recording head 2, when the recording head 2 moves from the home position to the first standby position (S3), all nozzles are shown in FIG. A fine vibration signal outside the printing area shown is applied (S4). The application of the fine vibration signal outside the printing area continues until image data is sent.

  When the image data for one swath (the length from the first nozzle to the last nozzle of the nozzle row composed of a large number of nozzles 23 of the recording head 2 = the recording width) is sent (S5), this print area The application of the external fine vibration signal is stopped, and the fine vibration of the meniscus is stopped (S6). Next, the carriage 5 starts traveling and enters the acceleration region (S7). While accelerating the recording head 2, ejection signals are applied to all channels 28 from the drive signal generator 100, and the ink thickened by thixotropy in each nozzle 23 is supplied to the ink receiver 8 with a predetermined number of drops. Purge (S8).

  Subsequently, when the recording head 2 enters the printing area, the recording head 2 reaches a constant speed and performs image recording by ejecting ink droplets toward the recording medium P in accordance with the image data. At this time, by analyzing the image data, the fine vibration signal in the printing region shown in FIG. 5 or FIG. 6 is applied to the meniscus of the nozzles 23 that are not ejecting ink droplets (S9).

  When recording for one swath is completed, the carriage 5 enters the deceleration region (S10), and the recording head 2 is stopped at the second standby position provided on the opposite side (S11). Here, since ink droplets are not ejected from all the nozzles 23, the fine vibration signal outside the printing region shown in FIG. 7 is applied to all the nozzles (S12). Thus, the one-pass image recording is completed.

  The above is the case where image recording is performed in one pass. However, in the case of performing n-pass multi-pass recording, after the recording medium P is sent by 1 / n of the swath length, the image data for the next one swath is stored. When sent, it stops the slight vibration of the meniscus. Then, while the carriage 5 starts running and the recording head 2 is accelerating, a small amount of ink is purged to the ink receiver 8. Next, when the carriage 5 enters the printing area and becomes a constant speed, the next swath recording is started. Repeat this operation.

  FIG. 10 shows another embodiment of the ink jet recording apparatus.

  In the ink jet recording apparatus 10, the recording head 101 is constituted by a long line-shaped recording head having a length in the width direction of the recording medium P. In such a linear recording head 101, a number of nozzles are arranged along the length direction on the nozzle surface facing the recording surface PS of the recording medium P. Accordingly, the recording head 101 does not record an image while moving in the main scanning direction, and the relative movement with respect to the recording medium P generally fixes the recording head 101 and moves the recording medium P in the secondary direction shown in the Y direction in the figure. The image is recorded by continuously moving at a predetermined speed along the scanning direction and ejecting ink droplets in the process. The structure for ejecting ink in the recording head 101 is the same as that of the recording head 2 described above. In the figure, reference numerals 103 and 104 denote conveyance roller pairs for conveying the recording medium P.

  In such an ink jet recording apparatus 10, the ultraviolet light source 102 for irradiating ultraviolet light is a linear light source having a length in the width direction of the recording medium P as with the recording head 101. In the vicinity, the recording medium P is juxtaposed downstream in the transport direction. Thereby, the ink is cured by irradiating the entire ink in the width direction of the recording medium P from the linear ultraviolet light source 102 to the ink immediately after being ejected from the recording head 101. Yes.

  In this way, the recording head 101 is a line-shaped recording head, and the ultraviolet light source 102 is also a line-shaped light source having a length in the width direction of the recording medium P. There is a high probability that nozzles that do not eject ink frequently occur, and an increase in viscosity is likely to occur when ultraviolet light is irradiated to ink in nozzles that do not eject ink. Further, since the ultraviolet light source 102 is also in a line shape, the amount of ultraviolet light as a whole increases, and the amount of ultraviolet light due to leakage light to the ink in the nozzle also increases, so that an increase in viscosity is likely to occur. Furthermore, unlike a serial printer, the recording head 101 cannot be purged by ejecting the recording head 101 out of the recording medium P. In general, purging in the case of a line-shaped recording head is performed by lifting the recording head and inserting an ink receiver and purging here, but this operation is very troublesome and cannot be performed frequently. .

  Accordingly, in the ink jet recording apparatus 10 having such a line-shaped recording head 101, a fine vibration signal is given to the pressure generating means of the non-ejection channel to finely vibrate the meniscus in the nozzle, thereby When the ink is brought into contact with the air outside the nozzle and thixotropy is suppressed, the effect of preventing the ink from thickening is more remarkably exhibited.

  In such a line-shaped recording head 101, there is no distinction between the inside of the printing area and the outside of the printing area. However, when the image recording operation is started, the above-described pressure generating means for the non-ejection channel is described. The same minute vibration signal (FIG. 5 or FIG. 6) as that in the print area is applied, and the same minute vibration signal (outside the print area as described above) at the time of recording pause or temporary recording interruption between images. FIG. 7) may be applied.

(Example 1)
This is an example in which a recording head including a cationically polymerizable ultraviolet curable ink is subjected to a slight vibration consisting of a single pulse in a printing region.

<Preparation of inkjet ink>
About the composition of the following colors, after using a zirconia bead for dispersion for 4 hours with a sand grinder, additional dispersion was performed for 10 minutes with an ultrasonic disperser to obtain a pigment dispersion.

Yellow PY180 (Clariant Yellow HG AF LP901) 2.5 parts by weight Aron Oxetane OXT221 (Toagosei) 70 parts by weight Celoxide 2021P (Daicel) 30 parts by weight Dispersant (Avecia, Solsperse 24000) 0.5 parts by weight

  Next, 5 parts by mass of a photopolymerization initiator (Asahi Denka Co., Ltd., SP152) is mixed with 100 parts by mass of this pigment dispersion, filtered through a 0.8 μm membrane filter, and heated to 50 ° C. under reduced pressure. The ink was dehydrated to obtain an ultraviolet curable ink for inkjet.

The viscosity of this ink at 25 ° C. was 32.1 cp at a shear rate of 10 ¹ (1 / sec) and 28.7 cp at a shear rate of 10 ³ (1 / sec). The fluctuation range of the viscosity was 3.4 cp. The surface tension at 25 ° C. was 34.7 mN / m ² .

<Fine vibration test>
Using this ultraviolet curable ink, the decap effect by applying a slight vibration in the printing area was tested. Decap refers to the shortest stop time from when ejection is stopped and left without capping, and then ejection is restarted until the initial speed starts to decrease. The initial speed due to ink thickening on the nozzle surface This represents the ease of lowering.

The ultraviolet light was irradiated from an integration high-pressure mercury lamp installed next to the recording head toward the recording medium at an illuminance of 80 W / cm ² .

  As the micro-vibration signal, a single pulse composed of a rectangular wave having a pulse width of 2AL shown in FIG. 5 was used.

  The recording head used has an AL of 2 μsec, a nozzle diameter of 23 μm, a carriage speed of 50 cm / sec, an ink droplet of 5 pl, and a distance between the nozzle and the recording medium of 1.5 mm.

  While controlling the ejection voltage and keeping the ink droplet speed at 6 m / sec, the recording stop time was changed, and the ink droplet velocity at the time of resuming recording was measured.

  The fine vibration signal voltage was 10 V, and the amount of meniscus extrusion from the nozzle was 18 μm.

  As a result, a speed of 6 m / sec was obtained at a discharge voltage of 20V. Although the stop time was extended by 100 seconds or more, the speed of the first droplet was not reduced even when the discharge was resumed. This is because ink thickening did not occur due to slight vibration even when leakage light of ultraviolet light was picked up during the stop period.

(Comparative Example 1)
Under the same conditions as in Example 1, when the fine vibration was not applied, the viscosity of the initial droplet decreased to 3 m / sec or less because of thickening even when the stop time was 1 second.

(Example 2)
This is an example in which a slight vibration of a continuous pulse is applied when the discharge of a recording head containing a cationic polymerizable ultraviolet curable ink is stopped outside the printing region.

   Using the same UV curable ink as in Example 1, the decap effect of slight vibration outside the printing area was tested.

  The micro-vibration signal was continuously applied for 1 hour with a voltage of 11 V and a pulse width of 4 μsec with an interval of 4 μsec as a rectangular pulse shown in FIG.

  The amount of extrusion from the meniscus nozzle and the drive voltage required for purging were measured.

  The amount of extrusion from the meniscus nozzle was 26 μm.

  The drive voltage for purging was 10 V, which was the same as the ink discharge voltage. This is because the increase in viscosity due to thixotropy can be prevented by slight vibration.

(Comparative Example 2)
Example 2 was the same as Example 2 except that no fine vibration signal was applied.

  The viscosity increased to 30 mPa * sec due to thixotropy, and a dedicated power source was required for purging.

(Example 3)
This is an example in which a single-pulse fine vibration is applied to a radical polymerizable ultraviolet curable ink.

<Adjustment of inkjet ink>
About the composition of the following colors, after using a zirconia bead for dispersion for 4 hours with a sand grinder, additional dispersion was performed for 10 minutes with an ultrasonic disperser to obtain a pigment dispersion.

Cyan ink
mass%
Pigment CI. Pigment blue 15: 3 2.5
Photopolymerizable compound Lauryl acrylate (monofunctional) 20
Tetraethylene glycol diacrylate (bifunctional)
20
Trimethylolpropane triacrylate (trifunctional)
30
Photoradical initiator Irgacure 1850 (manufactured by Ciba Specialty Chemicals) 5
Irgacure 951 (Ciba Specialty Chemicals) 2
Diethylthioxanthone 0.5

  The mixture was filtered through a 0.8 μm membrane filter and dehydrated under reduced pressure while being heated to 50 ° C. to obtain an ultraviolet curable cyan ink for inkjet. The viscosity at 25 ° C. of this ink was 28 cp at a shear rate of 10 (1 / sec) and 25 cp at a shear rate of 1000 (1 / sec).

<Fine vibration test>
Using this ink, the decap effect was tested by applying a slight vibration within the printing area. Ultraviolet rays were irradiated at an illuminance of 70 W / cm ² .

  A single pulse shown in FIG. 5 was used as the minute vibration signal.

  The recording head used has an AL of 2 μsec, a nozzle diameter of 23 μm, a carriage speed of 50 cm / sec, an ink droplet of 5 pl, and a distance between the nozzle and the recording medium of 1.5 mm.

  The ink droplet speed was measured when the recording was resumed by changing the recording stop time while maintaining the ink droplet speed at 6 m / sec. The micro-vibration voltage was 7 V, and the amount of extrusion from the meniscus nozzle was 20 μm.

  Although the discharge stop time was extended by 150 seconds or more, when the discharge was resumed, the discharge was started at 6 m / sec from the first droplet. On the other hand, when fine vibration was not applied, the discharge speed of several drops from the first shot was 6 m / sec or less just by stopping the discharge for 1 second, and the landing position shifted and the image edge deteriorated. This is because of thickening due to leakage of ultraviolet light.

Example 4
This is an example in which a double-pulsed slight vibration is applied to a radically polymerizable ultraviolet curable ink that tends to thicken.

  This is a combination of the cyan ink of Example 3 and the following yellow ink. The composition is the same except for the pigment, but this pigment has poor dispersibility, tends to thicken, and is less effective with a single pulse.

yellow
mass%
Pigment CI. Pigment Yellow 13 2.5
Photopolymerizable compound Lauryl acrylate (monofunctional) 20
Tetraethylene glycol diacrylate (bifunctional)
20
Trimethylolpropane triacrylate (trifunctional)
30
Photoradical initiator Irgacure 1850 (manufactured by Ciba Specialty Chemicals) 5
Irgacure 951 (Ciba Specialty Chemicals) 2
Diethylthioxanthone 0.5

  The viscosity at 25 ° C. of this ink was 35 cp at a shear rate of 10 (1 / sec) and 25 cp at a shear rate of 1000 (1 / sec).

  The same conditions as in Example 3 were used, and a double pulse slight vibration shown in FIG. 6 was applied. Even after stopping for 300 seconds, when the discharge was resumed, the discharge was performed at 6 m / sec from the first droplet. On the other hand, when the single pulse shown in FIG. 5 was applied, the speed of the first droplet was reduced to 5 m / sec, and returned to 6 m / sec after discharging 5 droplets.

The figure which shows schematic structure of an inkjet recording device (A) is a schematic perspective view of the recording head, (b) is a sectional view. Diagram showing operation during ink ejection Explanatory drawing of the operating position of the recording head in the ink jet recording apparatus Waveform diagram showing the fine vibration signal in the print area Waveform diagram showing another example of micro vibration signal in print area Waveform diagram showing the fine vibration signal outside the printing area The figure which shows the state where the cap was stuck to the recording head Flow chart showing specific operation of inkjet recording apparatus The figure which shows schematic structure of the inkjet recording device which concerns on other embodiment. Diagram explaining the amount of meniscus extrusion from the nozzle tip

Explanation of symbols

1: Inkjet recording apparatus 2: Recording head 21: Ink tube 22: Nozzle forming member 23: Nozzle 24: Cover plate 25: Ink supply port 26: Substrate 27: Partition wall 28: Channel 3: Transport mechanism 31: Transport roller 32: Transport Roller pair 33: Conveyance motor 4: Guide rail 5: Carriage 6: Flexi cable 7: Ultraviolet light source 8: Ink receiver 100: Drive signal generator P: Recording medium PS: Recording surface

Claims (28)

  A recording head that discharges ultraviolet curable ink in the channel from the nozzle toward the recording medium while moving relative to the recording medium by applying an ejection signal to the pressure generating means of the channel, and ink immediately after ejection The ink in the nozzle is finely vibrated with respect to the light source for curing the ink by irradiating the ultraviolet ray to the pressure and the pressure generating means of the non-ejection channel in the recording head. Ink jet recording, comprising: a fine vibration signal generating means for preventing a rise in ink viscosity by being brought into contact with outside air and providing a fine vibration signal for suppressing an increase in ink viscosity due to thixotropy by a stirring effect apparatus.   When the recording head is in the printing region, the micro-vibration signal generating means is set to AL (Acoustic Length) when 1/2 of the acoustic resonance cycle of the channel is set to the pressure generating means of the non-ejection channel, 2. The ink jet recording apparatus according to claim 1, wherein the meniscus in the nozzle is finely vibrated by applying a single pulse composed of a 2AL width rectangular wave for reducing and enlarging the volume of the channel.   When the recording head is in the print region, the fine vibration signal generating means is set to AL (Acoustic Length) when 1/2 of the acoustic resonance period of the channel is set to the pressure generating means of the non-ejection channel, A meniscus in the nozzle is finely vibrated by applying a double pulse in which a 1AL width rectangular wave and a 2AL width rectangular wave are arranged at 1AL intervals to reduce and expand the channel volume. The inkjet recording apparatus according to claim 1.   When the recording head is outside the printing area, the micro-vibration signal generating means is set to AL (Acoustic Length) when 1/2 of the acoustic resonance period of the channel is set to the pressure generating means of all channels. (N1) AL-width rectangular wave for reducing and enlarging the channel volume, (N2) AL-width first rest period, and (N3) AL-width rectangle for enlarging and reducing the channel volume By applying a wave and a continuous pulse (N1, N2, N3, N4 are integers of 2 or more) consisting of a second pause period of (N4) AL width, the meniscus in all the nozzles is finely vibrated. An ink jet recording apparatus according to claim 1, 2, or 3. An ink jet recording apparatus according to claim 1, wherein the ultraviolet light quantity by said light source is a ^{1mJ / cm 2 ~3000mJ / cm 2} .   The inkjet recording apparatus according to claim 1, wherein the ultraviolet curable ink absorbs ultraviolet rays and starts radical polymerization.   The inkjet recording apparatus according to claim 1, wherein the ultraviolet curable ink absorbs ultraviolet rays and starts cationic polymerization.   The ink jet recording apparatus according to claim 1, wherein a relative speed at the time of recording between the recording head and the recording medium is 40 cm / sec or more.   The ink jet recording apparatus according to claim 1, wherein a nozzle diameter of the recording head is 30 μm or less.   The ink jet recording apparatus according to claim 1, wherein the ink droplets ejected from the recording head are 10 pl or less.   The inkjet recording apparatus according to any one of claims 1 to 10, wherein a distance between a nozzle surface of the recording head and the recording medium is 1 mm to 3 mm.   The inkjet recording apparatus according to claim 1, wherein the recording medium is non-ink-absorbing.   The inkjet recording apparatus according to claim 1, wherein the recording medium is paper.   The recording head is a linear recording head having a length in the width direction of the recording medium, and the light source is a linear light source having a length in the width direction of the recording medium. An ink jet recording apparatus according to claim 1.   By applying an ejection signal to the pressure generation means of the channel of the recording head, the ultraviolet curable ink in the channel is ejected from the nozzle toward the recording medium while moving relative to the recording medium, and the ink immediately after ejection An ink jet recording method in which ink is cured by irradiating ultraviolet rays from a light source provided in the vicinity of the head, in order to slightly vibrate the meniscus in the nozzle against the pressure generating means of the non-ejection channel in the recording head An ink jet recording method characterized in that the ink in the nozzle is brought into contact with the air outside the nozzle to prevent the ink viscosity from increasing and the ink viscosity increase due to thixotropy is suppressed by the stirring effect.   When the recording head is in the printing area, the micro-vibration signal is obtained when the channel's acoustic resonance period is set to AL (Acoustic Length) with respect to the pressure generating means of the non-ejection channel. 16. The ink jet recording method according to claim 15, wherein the meniscus in the nozzle is finely vibrated by applying a single pulse consisting of a 2AL width rectangular wave in order to reduce the volume.   When the recording head is in the printing area, the micro-vibration signal is obtained when the channel's acoustic resonance period is set to AL (Acoustic Length) with respect to the pressure generating means of the non-ejection channel. The meniscus in the nozzle is finely vibrated by applying a double pulse in which a 1AL width rectangular wave and a 2AL width rectangular wave are disposed at 1AL intervals for shrinking and expanding the volume. Item 15. The inkjet recording method according to Item 15.   As the fine vibration signal, when the recording head is outside the printing area, when the half of the acoustic resonance period of the channel is AL (Acoustic Length) with respect to the pressure generating means of all the channels, (N1) AL width rectangular wave for reducing and expanding volume, (N2) AL width first rest period, and (N3) AL width rectangular wave for increasing and reducing channel volume , (N4) By applying a continuous pulse (N1, N2, N3, N4 is an integer of 2 or more) consisting of a second pause period of AL width, the meniscus in all the nozzles is slightly vibrated. The ink jet recording method according to claim 15, 16 or 17. The ink jet recording method according to claim 15, wherein the ultraviolet light quantity by said light source is a ^{1mJ / cm 2 ~3000mJ / cm 2} .   The inkjet recording method according to claim 15, wherein the ultraviolet curable ink absorbs ultraviolet rays and starts radical polymerization.   The inkjet recording method according to claim 15, wherein the ultraviolet curable ink absorbs ultraviolet rays and starts cationic polymerization.   The inkjet recording method according to any one of claims 15 to 21, wherein a relative speed during recording between the recording head and the recording medium is 40 cm / sec or more.   The inkjet recording method according to any one of claims 15 to 22, wherein a nozzle diameter of the recording head is 30 m or less.   24. The ink jet recording method according to claim 15, wherein the ink droplets ejected from the recording head are 10 pl or less.   The inkjet recording method according to any one of claims 15 to 24, wherein a distance between a nozzle surface of the recording head and the recording medium is 1 mm to 3 mm.   The ink jet recording method according to any one of claims 15 to 25, wherein the recording medium is non-ink-absorbing.   26. The ink jet recording method according to claim 15, wherein the recording medium is paper.   The recording head is a linear recording head having a length in the width direction of the recording medium, and the light source is a linear light source having a length in the width direction of the recording medium. An ink jet recording method according to any one of claims 15 to 27.

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