JP2005212413A - Inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable high-speed and stable ejection even in the use of ink including an organic solvent with high volatility. <P>SOLUTION: An ejection pulse and a microvibration pulse for microvibrating a meniscus in a nozzle to such an extent as not to eject a droplet from the nozzle are included as driving pulses. The ejection pulse comprises a driving pulse which includes a first pulse composed of rectangular wave for expanding the capacity of a channel and restoring it to the original capacity after 1 AL (AL represents half the acoustic resonant period of the channel) and a second pulse composed of a rectangular wave for reducing the capacity of the channel and restoring it to the original capacity after a lapse of a predetermined time, and wherein a voltage Von of the first pulse is larger than a voltage Voff of the second pulse. The microvibration pulse includes the rectangular wave with a pulse width of 2AL, which restores the capacity of the channel to the original one after reducing it, and has the same voltage as the voltage Voff of the second pulse of the ejection pulse. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet recording apparatus, and more specifically, ink jet recording capable of stably ejecting ink containing a highly volatile organic solvent by causing a meniscus in a nozzle to vibrate so as not to eject liquid droplets from the nozzle. Relates to the device.

  In an ink jet recording apparatus that records an image on a recording medium by ejecting ink in the form of fine droplets from a nozzle of a head, an improvement in print productivity is demanded along with an increase in image quality.

  In order to increase print productivity, efforts have been made to increase the printing speed. However, in order to increase the printing speed, it is necessary to increase the drying speed of the printed image. In many cases, an ink using a highly volatile and dry solvent is used. For example, many images posted outdoors with a display sign such as an outdoor advertisement are printed on a PVC sheet, and the ink used for this is PVC-soluble so as to improve its fixability on the PVC sheet. A certain solvent is used, and in general, a highly volatile organic solvent is often used.

  In an ink jet recording apparatus that uses ink containing an organic solvent having high volatility and drying properties, the ink is rapidly dried at the meniscus of the nozzle, and the meniscus ink is thickened by drying while scanning the head. As a result, the ejection speed of the droplets decreases and the emission becomes unstable.

  Further, a polymer component is often added to the ink in order to increase the abrasion resistance and weather resistance of the printed material, or to impart gloss to the printed material or prevent adhesion of dirt such as fingerprints. In such an ink, the ink viscosity rapidly rises due to the volatilization of the ink solvent, so that the ink is dried at the meniscus of the nozzle, and the ejection speed of the droplet is lowered and destabilized in a short time.

  On the other hand, an ink in which pigment particles are dispersed using an organic solvent as a dispersion medium is different from a homogeneous soluble dye ink in that the physical properties at the time of ink ejection and the static physical properties of the ink are often greatly different. Although the dynamic viscosity is low, the static viscosity becomes high while the printing is paused, so that the emission is likely to become unstable when the ejection is resumed from the ejection pause.

In order to suppress the thickening of the ink meniscus, a method of stirring the meniscus finely with the ink in the channel is conventionally known. It is described that the ink at the nozzle tip is agitated and the ink viscosity is lowered by applying a slight vibration to the nozzle tip in a state where printing is paused.
JP-A-11-268264 JP 2000-94669 A Japanese Patent Laid-Open No. 9-29996

  When ink having high volatility and dryness is used, even if the ejection is interrupted for a very short time, the ejection is not normally ejected from the first drop when the ejection is resumed, and the image quality is remarkably deteriorated. In particular, an ink having high volatility and drying property has a very rapid increase in viscosity due to drying of the ink. Therefore, the ink must be ejected immediately after giving a slight vibration to the meniscus. For this reason, when ink having high volatility and dryness is used, it is effective to slightly vibrate the meniscus for each pixel position during the print scanning of the head.

  However, if the meniscus is vibrated finely by applying a fine vibration pulse before and after the pixel for discharging the droplet, there is a problem that the reverberation of the fine vibration affects the discharge and makes it difficult to discharge stably. In other words, in order to perform stable ejection, it is necessary to eject the meniscus with a slight vibration and a constant position, otherwise the size of the ejected ink droplet The sheath flight speed fluctuates, causing landing errors. Furthermore, in order to efficiently stir and mix the ink, it is necessary to vibrate the meniscus greatly. However, when performing high-speed driving, it is necessary to attenuate the meniscus vibration early. In particular, in inks in which pigment particles are dispersed in an organic solvent, it is difficult to achieve both such fine vibration and stable emission.

  The method of effectively finely vibrating the ink meniscus and effectively canceling the residual vibration can be explained from acoustic theory as follows.

  By expanding (or contracting) the channel, the pressure wave generated in the channel is gradually attenuated while repeating the reversal of pressure every 1 AL. When the deformation of the channel is restored at the timing when the pressure is reversed 1 AL after the deformation of the channel, the original pressure and the newly generated pressure strengthen each other and greatly vibrate the ink meniscus. Note that AL (Acoustic Length) is ½ of the acoustic resonance period of the channel. Therefore, if the time from the deformation of the channel to the return to the original time is set to an odd multiple of AL, the meniscus can be vibrated greatly. However, since the residual pressure is not canceled and the meniscus is vibrated, it cannot be discharged immediately.

  On the other hand, if the channel is deformed and the deformation of the channel is restored at the timing when the pressure after 2AL is inverted → re-inverted, the original pressure and the newly generated pressure cancel each other, so the meniscus does not vibrate greatly. Therefore, if the time from when the channel is deformed to when the deformation is restored is set to an even multiple of AL, the residual pressure is canceled, so that the meniscus can be finely vibrated quickly and can be discharged immediately.

  As can be understood from the above, in order to discharge the thickened ink at high speed and stably, the meniscus is vibrated greatly and the ink on the nozzle surface is stirred efficiently, and the residual generated by the fine vibration is generated. We must solve the conflicting problem of canceling vibrations efficiently.

  In each of the techniques of Patent Documents 1 and 2 described above, a fine vibration pulse is applied to a nozzle that does not eject ink to cause the meniscus to vibrate slightly. There is a time until ejection, and in particular, when ink with high volatility and drying properties is used, the ink viscosity rises again during that time, and there is a problem that normal ejection becomes difficult. Although a trapezoidal wave is used as the fine vibration pulse, the trapezoidal wave complicates the circuit configuration and lowers the voltage sensitivity, so that the necessary drive voltage increases and power consumption increases. Furthermore, unless the number of times of applying the fine vibration pulse is increased, a sufficient effect cannot be obtained, resulting in a decrease in printing speed and the like, and improvement in print productivity cannot be expected.

  Further, the technique of Patent Document 3 described above can be used even when ink having a remarkable increase in viscosity due to volatilization is given by giving a slight vibration to the meniscus until the next ejection signal or refresh signal is input during non-ejection after ink ejection. Although stable ejection is possible, after applying a slight vibration to the meniscus, the problem caused by the residual vibration caused by this slight vibration cannot be solved at all, making high-speed driving difficult and also improving print productivity. Can't hope.

  Therefore, the problem of the present invention is that even if an ink containing a highly volatile organic solvent is used, the effect of improving the decap characteristics is high by efficiently stirring the liquid in the nozzle, and also immediately after the slight vibration of the meniscus. However, it is an object of the present invention to provide an ink jet recording apparatus that enables high-speed and stable discharge of droplets and can improve print productivity.

  Here, the decap characteristic indicates the amount of decrease in the initial speed due to the so-called decap phenomenon, in which the liquid thickens by meniscus drying when the nozzle surface is open.

  The above problems are solved by the following inventions.

  According to the first aspect of the present invention, drive signal generation means for generating a drive signal including a plurality of drive pulses, drive pulse selection means for selecting a drive pulse in accordance with data of each pixel, and selected drive pulse And a head that discharges liquid in the channel as droplets from a nozzle provided corresponding to the channel by changing the volume of the channel based on the liquid crystal, and the liquid is volatile Ink containing a high organic solvent, and the drive signal as a drive pulse is a discharge pulse for discharging the droplet, and a fine vibration pulse for causing the meniscus in the nozzle to vibrate so as not to discharge the droplet from the nozzle. The ejection pulse expands the volume of the channel and after 1 AL (AL is 1/2 of the acoustic resonance period of the channel) A first pulse composed of a rectangular wave to be returned and a second pulse composed of a rectangular wave that contracts the volume of the channel and returns to the original volume after a predetermined time, and the voltage Von of the first pulse is The micro-vibration pulse includes a rectangular wave having a pulse width of 2AL for returning to the original volume after contracting the volume of the channel, and the voltage Voff of the second pulse of the ejection pulse. The ink jet recording apparatus is characterized by having the same voltage as that of the ink jet recording apparatus.

  A second aspect of the present invention is the ink jet recording apparatus according to the first aspect, wherein the micro-vibration pulse is applied to all pixels regardless of whether or not the ejection pulse is applied.

  The invention according to claim 3 is characterized in that the ratio Von / Voff between the voltage Von of the first pulse and the voltage Voff of the second pulse of the ejection pulse is 1.5 or more. It is an inkjet recording device of description.

  According to a fourth aspect of the invention, in the ink jet recording apparatus according to the first, second or third aspect, the fine vibration pulse is applied prior to the ejection pulse.

  A fifth aspect of the present invention is the ink jet recording apparatus according to any one of the first to fourth aspects, wherein the ink is a pigment dispersion ink.

  The invention according to claim 6 is the ink jet recording apparatus according to any one of claims 1 to 5, wherein the ink contains a polymer component.

  A seventh aspect of the present invention is the inkjet according to any one of the first to sixth aspects, wherein a rectangular wave having a pulse width of 2AL in the fine vibration pulse is applied at least at the end of the fine vibration pulse. It is a recording device.

  The invention according to claim 8 is the ink jet recording apparatus according to claim 7, wherein the ejection pulse is applied after 1 AL of the 2 AL square wave applied last.

  The invention according to claim 9 is characterized in that the head has electro-mechanical conversion means for changing the volume of the channel by applying the ejection pulse or the micro-vibration pulse. The inkjet recording apparatus according to the above.

  The invention according to claim 10 is characterized in that the electromechanical conversion means is formed of a piezoelectric material which forms a partition between adjacent channels and is deformed in a shear mode by applying a voltage. Item 10. The ink jet recording apparatus according to Item 9.

  According to the present invention, it is possible to solve the conflicting problems of efficiently stirring the liquid on the nozzle surface by greatly vibrating the meniscus and efficiently canceling the residual vibration generated by the vibration. The ability to stir the liquid efficiently ensures that the decap characteristics are improved even when ink containing highly volatile organic solvents is used, and that droplets can be stably ejected even immediately after slight vibration of the meniscus. Therefore, it is possible to provide an ink jet recording apparatus capable of improving print productivity by enabling high-speed and stable discharge.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an ink jet recording apparatus according to the present invention. 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. The flexure cable 6 is mounted on a carriage 5 provided so as to be capable of reciprocating along the XX ′ direction (main scanning direction) so that the nozzle surface side faces the recording surface PS of the recording medium P. Is electrically connected to a drive signal generator 100 (see FIG. 3) provided with a circuit for generating ejection pulses and micro-vibration pulses, which will be described later.

  The recording head 2 records a desired inkjet image by moving the recording surface PS of the recording medium P in the direction XX ′ in the drawing as the carriage 5 moves, and ejecting ink droplets in this moving process. It has become.

  In the figure, reference numeral 7 denotes an ink receiver, which is provided in a standby position such as a home position when the recording head 2 is not recording, or a carriage scanning path outside the recording area. When the recording head 2 is in this standby position, the ink thickened at the nozzle openings is slightly vibrated to reduce the viscosity, and then a small amount of ink droplets are scraped off toward the ink receiver 7. When the recording head 2 has stopped operating for a long time at this standby position, although not shown, the nozzle surface of the recording head 2 is covered by a cap. Reference numeral 8 denotes an ink receiver provided at a position opposite to the ink receiver 7 with the recording medium P in between. When recording in both reciprocating directions, the same operation is performed when switching from forward to backward movement. Accept discarded ink drops.

  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 is formed by the partition wall 27, the cover plate 24 and the substrate 26.

  Here, as shown in FIG. 3, 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 means. A shear mode (share mode) type recording head in which a number of channels 28 are arranged in parallel is shown. In FIG. 3, three (28A, 28B, 28C) which are a part of many channels 28 are shown. 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 fine vibration pulse and an ejection pulse. Here, the drive signal generation circuit corresponds to the drive signal generation means in the claims, and the drive pulse selection circuit corresponds to the drive pulse selection means in the claims.

  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 ejection pulses are applied to the electrodes 29A, 29B, and 29C formed in close contact with the surfaces of the partition walls 27 by the control of the drive signal generator 100, the ink illustrated in the channel 28 is used as ink droplets from the nozzles 23 by the operation exemplified below. Discharge. In FIG. 3, the nozzle is omitted.

  First, when no ejection pulse 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. In addition, when an ejection pulse is applied to the electrode 29B, 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 are deformed in the joint surfaces of the partition walls 27a and 27b. As a result, as shown in FIG. 3B, the partition walls 27B and 27C are deformed outward from each other, the volume of the channel 28B is enlarged, a negative pressure is generated in the channel 28B, and ink flows (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 the ejection pulse 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 ink meniscus in the nozzle due to a part of the ink filling the channel 28B changes in the direction pushed out from the nozzle. When the positive pressure becomes so large that the ink droplet is ejected from the nozzle, the ink droplet is ejected from the nozzle. The other channels operate in the same manner as described above by applying the ejection pulse. Such an ejection method is called a DRR driving method, which is a typical driving method for a share mode type recording head.

  When the recording head 2 having the plurality of channels 28 separated by the partition walls 27 at least partially made of the piezoelectric material is driven as described above, when the partition wall of one channel performs the ejection operation, the adjacent channel is affected. In general, among the plurality of channels 28, the channels 28 that are separated from each other by sandwiching one or more channels 28 are collectively divided into two or more sets so as to form one set. Drive control is performed so that the ink ejection operation is sequentially performed in a time-sharing manner for each set. For example, when all the channels 28 are driven and a solid image is output, a so-called three-cycle discharge method is performed in which the channels 28 are selected every two channels and discharged in three phases.

  Such a 3-cycle discharge operation will be further described with reference to FIG. In the example shown in FIG. 4, the recording head is described as having nine channels 28 of A1, B1, C1, A2, B2, C2, A3, B3, and C3. Further, FIG. 5 shows a timing chart of pulse waveforms applied to the respective channels 28 of A, B, and C at this time.

  When ink is ejected, first, a voltage is applied to the electrodes of each channel of the A group (A1, A2, A3), and the electrodes of the adjacent channels are grounded. For example, when a discharge pulse having a positive voltage of 1 AL width is applied to the A group of channels, the partition walls of the A group of channels to be discharged are deformed outward, and negative pressure is generated in the channel 28. By this negative pressure, ink flows from the ink tank into the A set of channels 28 (Draw).

  If this state is maintained for 1 AL, the pressure is reversed to a positive pressure. Therefore, when the electrode is grounded at this timing, the deformation of the partition wall is restored, and a high pressure is applied to the ink in the A set of channels 28 (Release). Further, when a negative voltage is applied to the electrodes of each channel of the A group at the same timing, the partition wall is deformed inward, and a higher pressure is applied to the ink (Reinforce), and the ink column is pushed out from the nozzle. After 1AL, the pressure reverses and the inside of the channel 28 becomes negative pressure. When 1AL further elapses, the pressure in the channel 28 reverses and becomes positive pressure. If the electrode is grounded at this timing, the deformation of the partition wall is restored. The remaining pressure wave can be canceled.

  Subsequently, the operation is performed in the same manner as described above for each channel 28 of the group B (B1, B2, B3), and further to each channel 28 of the group C (C1, C2, C3).

  In addition, AL (Acoustic Length) is 1/2 of the acoustic resonance period of the channel as described above. This AL measures the speed of ink droplets ejected by applying a rectangular wave voltage pulse to the partition wall 27 which is an electrical / mechanical conversion means, and changes the pulse width of the rectangular wave while keeping the rectangular wave voltage value constant. The pulse width at which the flying speed of the ink droplet is maximized. A pulse is a rectangular wave having a constant voltage peak value. When 0V is 0% and a peak voltage is 100%, the pulse width is 10% of the voltage from 0V and the peak voltage. It is defined as the time between 10% of the falling edge. Furthermore, the rectangular wave here refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within 1/2, preferably within 1/4 of AL.

  In such a shear mode type ink jet recording head, the deformation of the partition wall is caused by a voltage difference applied to the electrodes provided on both sides of the wall. Therefore, instead of applying a negative voltage to the electrode of the channel for discharging ink, as shown in FIG. The same operation can be performed by grounding the electrode of the channel for discharging ink and applying a positive voltage to the electrodes of the adjacent channels. This latter method is preferable because it can be driven only by a positive voltage.

  These discharge pulses shown in FIG. 5 and FIG. 6 used in the present invention are, as shown in the figure, a first pulse P1 composed of a rectangular wave that expands the volume of the channel 28 and returns it to the original volume after 1AL, and And a second pulse P2 composed of a rectangular wave that contracts the volume of the channel 28 and returns to the original volume after a certain time, and the voltage Von of the first pulse P1 is larger than the voltage Voff of the second pulse P2. It consists of drive pulses. Setting the voltage Von to be larger than the voltage Voff in this manner also has an effect of promoting the supply of ink into the channel 28 particularly when the viscosity of the ejected ink is high.

  The voltage ratio Von / Voff between the voltage Von of the first pulse P1 and the voltage Voff of the second pulse P2 is preferably 1.5 or more. In the present invention, the voltage of the micro-vibration pulse is set to the same voltage as the voltage Voff of the second pulse P2 of the ejection pulse, but the voltage ratio Von / Voff at this time is set to 1.5 or more. In addition, the vibration of the meniscus of the nozzle due to the fine vibration pulse can be set to an appropriate amount, and even when the fine vibration pulse is applied immediately before and after the discharge pulse, the reverberation of the pressure wave due to the discharge pulse and the pressure wave due to the fine vibration pulse Stable discharge can be realized by canceling the reverberation moderately. In particular, inks containing an organic solvent as a main solvent, and pigment dispersed inks and inks added with a polymer often have a lower dynamic viscosity at the time of ink ejection than a static viscosity. It is preferable to set / Voff to a large value of 1.5 or more because fine vibration can be stably added.

  When the voltage ratio Von / Voff is reduced to 1 or less, the meniscus vibration due to the micro-vibration pulse increases, and the reverberation of the pressure wave after the micro-vibration pulse is applied greatly affects the driving by the ejection pulse, and the droplet Discharge becomes unstable. On the other hand, if the voltage ratio Von / Voff is increased to 5 or more, the meniscus vibration due to the fine vibration pulse is small, and it is difficult to obtain the effect of improving the decap characteristics, which is not preferable.

  In the present invention, an ink containing a highly volatile organic solvent is used as the ink in the channel 28 ejected as ink droplets from the nozzle 23. Here, the high volatility means that having an evaporation rate equal to or higher than that of water.

  Such organic solvents include methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, hexanetriol, hexylene glycol, glycerin, thioglycol, ethylene Glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate, ethylene glycol mono Chill ether acetate, butyl lactate, .gamma.-butyrolactone, trimethylol ethane, 2-pyrrolidone, N- methyl-2-pyrrolidone. The organic solvent is not limited to one type, and two or more types may be used.

  In particular, in the present invention, a pigment-dispersed ink in which pigment particles are dispersed using such a highly volatile organic solvent as a dispersion medium is preferable, and a particularly remarkable effect is exhibited when such an ink is used. .

  In particular, in the present invention, a remarkable effect is exhibited when the ink contains a polymer component. As the polymer component, a resin having solubility in a solvent having a molecular weight of about 1000 to 100,000 is used. When the ink contains a highly volatile organic solvent and a polymer component is added, the ink viscosity increases rapidly due to the volatile drying of the ink solvent. Ink thickening at the meniscus of the nozzle can be effectively suppressed.

  Next, with reference to FIGS. 7 and 8, the operation of giving a slight vibration to the meniscus in the share mode type recording head 2 using the ink containing the highly volatile organic solvent will be described. Here, a description will be given of the case where the three-cycle discharge operation is performed as described above. Further, here, it is assumed that only the positive voltage is used as the drive waveform voltage as in FIG. 6 and the discharge is performed in the order of A set → B set → C set. In addition, here, a description will be given by taking as an example a drive signal composed of one type of drive pulse for each of the fine vibration pulse and the ejection pulse.

  In the present invention, the micro-vibration pulse that causes micro-vibration to such an extent that ink droplets are not ejected from the nozzles is generated in the drive signal generator 100 shown in FIG. The micro-vibration pulse in the present invention includes only a rectangular wave that is restored after being contracted in the volume of the channel, and includes a rectangular wave having a pulse width of 2AL. By using a square wave for the micro-vibration pulse, the efficiency of micro-vibration of the meniscus can be improved compared to the method using a trapezoidal wave, and the drive circuit can be designed with a simple digital circuit. There is an effect that can be done. Further, since the volume of the channel is contracted and then returned to the original, it is possible to effectively give a fine vibration without ejecting ink droplets from the nozzle.

  For example, in the example shown in FIG. 7, in the image recording area, first, the electrodes of the A group of channels are grounded, and the B and C group channel electrodes are fine vibration pulses composed of a 2AL width positive voltage rectangular wave. Is applied. As a result, the channel of the A group returns to its original state after the volume contracts, and the meniscus in the nozzle is given a slight vibration so as not to eject ink droplets from the nozzle. In each channel, only the partition on one side is displaced, and a slight vibration with half the strength of the A-set channels is given.

  Subsequently, when a discharge pulse having a positive voltage of 1 AL width is applied to the A group of channels, and a discharge pulse of a positive voltage of 2 AL width is subsequently applied to the B and C channels, respectively, the A set of channels is obtained by the DRR driving method described above. Ink is ejected from the channel and the pixels are recorded. When performing multi-drop ejection, these two types of pulses are repeated for the number of droplets to be ejected.

  Similarly, when the discharge from the A set channel is completed and then the discharge from the B set channel is performed, similarly, the electrodes of the B set channel are grounded, and then the electrodes of the A set and C set channels are each 2AL wide. A fine vibration pulse of a positive voltage is applied to slightly vibrate the meniscus. Thereafter, a discharge pulse having a positive voltage of 1AL width is applied to the electrodes of the B group channels, and then a discharge pulse having a positive voltage of 2AL width is applied to the electrodes of the A group and C group channels to discharge from the B group channels. And a pixel is recorded. The application and ejection of the micro-vibration pulse of the C sets of channels are performed in the same manner.

  Next, the case where all of the channels of the A group, the B group, and the C group do not discharge and gives a slight vibration to the meniscus in the order of A group → B group → C group will be described with reference to FIG.

  As in FIG. 7, first, the electrodes of the A group channels are grounded, and the volume of the A group channels contracts by applying a positive vibration pulse of 2AL width to the B group and C group channel electrodes. Then, returning to the original state gives a slight vibration to the meniscus in the nozzle. Subsequently, when a pulse of 2AL width positive voltage is applied to any of the channels of the A group, the B group, and the C group, the partition wall is not displaced, so that ink ejection is not performed.

  Such a fine vibration pulse in the present invention is set to the same voltage as the voltage Voff of the second pulse P2 constituting the ejection pulse. Thus, by setting the voltage of the fine vibration pulse to the Voff voltage having a low voltage, the fine vibration is not excessively applied and the fine vibration to the extent that the ink droplet is not ejected from the nozzle can be efficiently applied. In addition, there is an effect that the circuit cost can be reduced by reducing the number of power supply voltages in the drive signal generator 100 for generating the ejection pulse and the fine vibration pulse.

  Next, a driving pulse selection method in each pixel will be described with reference to FIG. The ON waveform and the OFF waveform in FIG. 9 indicate two types of drive signals generated by the drive signal generation circuit. This drive signal is composed of three types of drive pulses: micro-vibration pulse (1) and discharge pulses (2) and (3). is there. Here, since the voltage of the micro-vibration pulse is set to the same voltage as the voltage Voff of the second pulse that constitutes the ejection pulse, the ON waveform and the OFF waveform are obtained by digitalizing a single power supply voltage, Von and Voff, respectively. Waveforms can be generated simply by switching.

  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 electrode of each channel by controlling the pulse selection gate signal according 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. FIG. 9 shows one cycle of each channel drive of the A group, the B group, and the C group. Hereinafter, the timing of the A group channel drive will be described as an example.

  The pulse division signal is applied to the period before the application of the micro-vibration pulse, the period from the application of the micro-oscillation pulse to the period before the application of the ejection pulse, and the period after the application of the ejection pulse. When the pixel print data is given, the pulse selection gate signal synchronized with the pulse division signal is turned ON accordingly. During the period in which the pulse selection gate signal corresponding to the A group channel is ON ((1) to (2) in FIG. 9), the ON waveform of the drive waveform is applied to the electrode of the A group channel. Since the pulse selection gate signals corresponding to the channel C and the channel C are OFF, the OFF waveform is applied to the electrodes of the channels B and C, and the partition walls on both sides of the channel A are displaced. Further, during the period of (3) in FIG. 9, since the pulse selection gate signals of the A group, the B group, and the C group are all OFF, the OFF waveform is applied to the electrodes of the channels of the A group, the B group, and the C group. When applied, neither partition is displaced.

  The timings for driving the B set and C set channels are also the same.

  In the present invention, a fine vibration pulse is always applied to both the printing pixel (in the case of FIG. 7) and the non-printing pixel (in the case of FIG. 8), thereby including a highly volatile organic solvent. Even if ink is used, thickening of the ink near the nozzle opening can be effectively suppressed.

  In particular, as shown in FIG. 7, a fine vibration pulse is applied to all the printing pixels in the image recording area prior to the ejection pulse, so that the meniscus is always in front of each pixel to be printed. Because fine vibrations are applied, high-quality recording can be performed with stable ink ejection at all times, and during continuous ejection, residual pressure waves that are ejected first can be canceled by applying micro-vibration pulses. Therefore, higher quality image recording is possible.

  The term “prior to the ejection pulse” refers to a time within a range in which the effect of improving the decap characteristics can be seen in the ejection of the ink droplet after the slight vibration.

  In the present invention, it is sufficient that at least one rectangular wave having a pulse width of 2AL is included in the micro-vibration pulse. However, if the rectangular wave having a pulse width of 2AL is included at least at the end of the series of micro-vibration pulses, Since there is an effect of canceling the residual pressure wave due to the vibration pulse, it is preferable when high-frequency driving is performed such that ejection is performed immediately after the meniscus is slightly vibrated.

  When a rectangular wave having a pulse width of 2AL is applied at the end of the fine vibration pulse, it is preferable to apply the ejection pulse after 1AL as shown in FIG. The reason for this is that cancellation of the residual pressure wave by the micro-vibration pulse is not necessarily complete. Therefore, if the discharge pulse is applied after 1 AL of the micro-vibration pulse, the residual pressure wave and the pressure wave by the discharge pulse are in opposite phases, and the residual pressure wave This is because the influence of the wave on the ejection pulse can be minimized.

  7 to 9, it is assumed that the micro-vibration pulse includes only a rectangular wave having a pulse width of 2AL. In this case, since the meniscus can be micro-vibrated efficiently in a short time, a system with particularly severe decap phenomenon is used. Therefore, this is a preferable mode because the meniscus can be finely oscillated in all the pixels without significantly reducing the image recording speed at the time of high frequency driving in which ink is ejected immediately after the meniscus is slightly oscillated.

  When the fine vibration pulse has two or more fine vibration pulses including at least one rectangular wave having a pulse width of 2AL, the interval between the previous rectangular wave and the subsequent rectangular wave is an integer of AL. Double is preferable because the meniscus can be vibrated efficiently.

  As described above, the electro-mechanical conversion means in the present invention is not limited to a recording medium formed of a piezoelectric material that forms a partition between adjacent channels and deforms in a shear mode by applying an electric field. Any structure may be used as long as it gives the head a function of changing the volume of the channel. However, as shown in the present embodiment, when the head is made of a piezoelectric material that is deformed in a shear mode, The rectangular wave described above can be used more effectively, so that the drive voltage is lowered and more efficient driving is possible, which is preferable.

(Evaluation of output stability)
Each channel of the share mode type recording head (nozzle number: 256, nozzle diameter 27 μm) shown in FIG. 2 is divided into three groups as shown in FIG. 4, and a rectangular wave having a pulse width as shown in Table 1 is finely divided. Using one vibration pulse and a discharge pulse having a voltage ratio Von / Voff as shown in Table 1, three-cycle driving was performed under the following conditions. Table 1 shows the results of measuring the emission stability and the decap characteristic improvement effect at this time by the following method.

  As shown in FIG. 7, the discharge pulse includes a first pulse composed of a rectangular wave that expands the volume of the channel and returns it to the original volume after 1 AL, and a rectangle that contracts the volume of the channel and returns it to the original volume after 2 AL. The fine vibration pulse has the same voltage as the second pulse Voff of the ejection pulse.

Condition head: AL = 4.7 μs
Ink: Pigment dispersion solvent ink
Solvent: 2-butoxyethyl acetate + γ-butyrolactone
(Viscosity: 10 mPa · s, surface tension: 28 mN / m, at 25 ° C.)
Discharge pulse: DRR waveform

Measuring method of emission stability Under the conditions of applying the micro-vibration pulse and the ejection pulse for each, the flying speed of the ink droplet was increased by increasing the driving voltage, and the flying state was observed. The upper limit of the flying speed at which no bending in the discharge direction or satellite scattering occurs was defined as the upper limit of the stable emission speed.

Evaluation standard of output stability : ○: 8 m / s ≦ Stable output speed upper limit Δ: 6 m / s ≦ Stable output speed upper limit <8 m / s
X: Stable emission speed upper limit <6 m / s

Measurement method of decap characteristics When the ink is ejected while fixing the driving voltage to a voltage at which the flying speed of the ink droplet during steady driving is 6 m / s under the conditions of applying the micro-vibration pulse and the ejection pulse, respectively. The change in the initial rate was measured. The smaller the speed change at that time, the greater the improvement effect.

  As shown in Table 1, even in the case of a fine vibration pulse composed of a rectangular wave with a pulse width of 2AL, when the discharge pulse voltage ratio Von / Voff is less than 1.5, the discharge pulse voltage ratio Von / Voff is 1. Even if the pulse width of the fine vibration pulse is not 2AL even if it is 5 or more, the emission stability is not sufficient, but the fine vibration pulse including a rectangular wave with a pulse width of 2AL and the discharge having a voltage ratio Von / Voff of 1.5 or more. It can be seen that when the pulse is applied, the emission stability is excellent.

  Moreover, the result of having measured about the decap characteristic at the time of not applying a fine vibration pulse on the same conditions as Example 2 shown in Table 1 is shown in FIG.

  As shown in the figure, it can be seen that when no micro-vibration pulse is applied, the droplet velocity decreases as the emission interval increases.

The figure which shows schematic structure of an inkjet recording device (A) is a general perspective view showing an example of a recording head, (b) is a sectional view. (A)-(c) is a figure which shows the action | operation at the time of the ink discharge of a recording head. (A)-(c) is explanatory drawing of the time division operation | movement of a recording head. Timing chart of pulse waveforms applied to each set of channels A, B, and C Timing chart of pulse waveform when only positive voltage is used Timing chart of pulse waveform applied to each set of channels A, B, and C at the time of slight meniscus vibration for all print pixels Timing chart of pulse waveform applied to each channel of A, B, C when meniscus is finely vibrated for non-printing pixel Timing chart showing an example in which the fine vibration pulse and the ejection pulse are selectively applied to the channels of the A group, the B group, and the C group Graph showing decap characteristics measurement results

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, 8: Ink receiver 100: Drive signal generation circuit P: Recording medium PS: Recording surface

Claims (10)

Drive signal generating means for generating a drive signal including a plurality of drive pulses;
Drive pulse selection means for selecting a drive pulse according to the data of each pixel;
A head that discharges liquid in the channel as droplets from a nozzle provided corresponding to the channel by changing a volume of the channel based on a selected drive pulse,
The liquid is an ink containing a highly volatile organic solvent,
The drive signal includes, as drive pulses, a discharge pulse for discharging the droplet, and a fine vibration pulse for causing the meniscus in the nozzle to vibrate so as not to discharge the droplet from the nozzle.
The ejection pulse is a first pulse composed of a rectangular wave that expands the volume of the channel and returns to the original volume after 1AL (AL is 1/2 of the acoustic resonance period of the channel), and contracts the volume of the channel to be constant. A second pulse composed of a rectangular wave that returns to its original volume after time, and comprises a drive pulse in which the voltage Von of the first pulse is greater than the voltage Voff of the second pulse,
The micro-vibration pulse includes a rectangular wave having a pulse width of 2AL that is returned to the original volume after contracting the volume of the channel, and has the same voltage as the voltage Voff of the second pulse of the ejection pulse. Inkjet recording device.   The inkjet recording apparatus according to claim 1, wherein the minute vibration pulse is applied to all pixels regardless of whether the ejection pulse is applied.   3. The ink jet recording apparatus according to claim 1, wherein a ratio Von / Voff between the voltage Von of the first pulse and the voltage Voff of the second pulse of the ejection pulse is 1.5 or more.   4. The ink jet recording apparatus according to claim 1, wherein the fine vibration pulse is applied prior to the ejection pulse.   The ink jet recording apparatus according to claim 1, wherein the ink is a pigment dispersion ink.   The ink jet recording apparatus according to claim 1, wherein the ink contains a polymer component.   The inkjet recording apparatus according to claim 1, wherein a rectangular wave having a pulse width of 2 AL in the fine vibration pulse is applied at least at the end of the fine vibration pulse.   8. The ink jet recording apparatus according to claim 7, wherein an ejection pulse is applied after 1AL of the last applied 2AL rectangular wave.   The inkjet recording apparatus according to claim 1, wherein the head includes an electromechanical conversion unit that changes a volume of the channel by applying the ejection pulse or the micro-vibration pulse.   10. The ink jet recording apparatus according to claim 9, wherein the electro-mechanical conversion means is made of a piezoelectric material that forms a partition between adjacent channels and is deformed in a shear mode by applying a voltage.

Images