JP5146246B2 - Inkjet recording device - Google Patents

Description

  The present invention relates to an ink jet recording apparatus.

  In a multi-drop driving ink jet recording apparatus, the density of ink dots constituting one pixel can be adjusted by changing the number of ejected ink droplets in one printing cycle, thereby enabling multi-tone printing. Yes.

However, sufficient examination has not been made from the viewpoint of ejection stability, and as a multi-drop drive inkjet recording apparatus, a plurality of drive pulses are usually applied at equal intervals (time intervals) during one printing cycle. However, in a method in which a plurality of drive pulses are simply applied at short time intervals, ejection stability becomes a problem. Therefore, it has been proposed to add a stabilization waveform in order to improve ejection stability (see, for example, Patent Documents 1 and 2).
JP 2007-144659 A JP 2006-256094 A

  The techniques of Patent Documents 1 and 2 both have a problem that the drive circuit becomes complicated because a stabilization waveform is added.

  In addition, it is possible to stably discharge by providing a long pause time during which no drive pulse is applied until the next drive pulse is applied after one droplet is ejected. As a result, a plurality of nozzles discharged from the same nozzle during one printing cycle Ink droplets are likely to land at positions shifted from each other on the recording paper. For this reason, the print quality was liable to deteriorate.

  Therefore, by increasing the voltage value of the drive pulse sequentially so that the ejection speed of the ink droplets ejected later is higher than the ejection speed of the ink droplets ejected first, the two inks ejected from the same nozzle There has been proposed a method in which droplets are combined before landing or after landing to form a single ink droplet before landing.

  However, this method requires a voltage circuit that changes in an analog manner, and the drive circuit becomes complicated and expensive, and the control of the drive pulse is also complicated.

  In particular, from the viewpoint of multi-tone recording, when the number of ink droplets increases, the ejection speed of the ink droplets ejected toward the end must be considerably increased, and in order to generate such a drive signal, For example, it is necessary to make the specifications of the driver IC compatible with a high voltage, which increases the load on the drive circuit.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide an ink jet recording apparatus capable of stably ejecting multidrops of three or more drops while suppressing landing position deviation without complicating a drive circuit.

  The object of the present invention is achieved by the invention described below.

1. One printing of a nozzle for ejecting ink droplets, a pressure chamber communicating with the nozzle, a recording head having pressure generating means for changing the volume of the pressure chamber, and at least three drive pulses for ejecting ink droplets, respectively An ink-jet printing apparatus comprising: a driving signal generating unit configured to generate a driving signal that is continuously applied within a cycle; and the application of the driving signal causes the pressure generating unit to operate to eject ink droplets from the nozzle. In the recording device,
Each drive pulse in one printing cycle includes an expansion pulse for expanding the volume of the pressure chamber, a contraction pulse for contracting the volume of the pressure chamber following the expansion pulse, and a waiting time following the contraction pulse. Have
Among these drive pulses, the waiting time of the first pulse to be applied first is longer than 2 times and shorter than 4 times AL (AL is 1/2 of the acoustic resonance period of the pressure chamber), and finally applied. The waiting time of the final pulse is an even multiple of the AL, and the waiting time of each intermediate pulse applied between the first pulse and the final pulse is longer than the AL and shorter than twice the AL. ,
An ink jet recording apparatus, wherein voltages of expansion pulses in each drive pulse are substantially equal to each other, and voltages of contraction pulses are substantially equal to each other.

  2. 2. The ink jet recording apparatus according to 1 above, wherein a waiting time of the first pulse is three times the AL.

  3. 3. The inkjet recording apparatus according to 1 or 2, wherein a waiting time of the final pulse is twice or four times the AL.

  4). 4. The ink jet recording apparatus according to any one of 1 to 3, wherein a waiting time of the intermediate pulse is 1.5 times the AL.

  5). 5. The ink jet recording apparatus according to any one of 1 to 4, wherein a surface tension of the ink is 31 mN / m or less.

  6). 6. The ink jet recording apparatus according to any one of 1 to 5, wherein the ink is a non-aqueous ink and contains a resin.

  7). 6. The ink jet recording apparatus according to any one of 1 to 5, wherein the ink is a photocurable ink.

  8). 8. The ink jet recording apparatus according to any one of 1 to 7, wherein the driving pulse is a pulse composed of a rectangular wave.

  9. 9. The ink jet recording apparatus according to any one of 1 to 8, wherein the pressure generating unit is an electric / mechanical converting unit.

  10. The electro-mechanical conversion means is formed of a piezoelectric material that forms at least a part of a partition wall between adjacent pressure chambers and is deformed in a shear mode by applying a driving pulse. The ink jet recording apparatus described.

  11. 11. The ink jet recording apparatus according to any one of 1 to 10, wherein a pulse width of the expansion pulse is an odd multiple of the AL and a pulse width of the contraction pulse is an even multiple of the AL.

  12 12. The inkjet recording apparatus according to any one of 1 to 11, wherein a period of the driving pulse is longer than four times the AL.

  13. The drive pulse expands the volume of the pressure chamber from a predetermined reference state, then returns to the reference state, and contracts the volume of the pressure chamber following the expansion pulse, and then the reference state. 13. The ink jet recording apparatus according to any one of 1 to 12, further comprising: a contraction pulse to be returned to (1), and a standby time for maintaining the reference state following the contraction pulse.

  According to the present invention, it is possible to provide an ink jet recording apparatus capable of stably ejecting multidrops of three or more drops while suppressing landing position deviation without complicating the drive circuit.

  Although the example of embodiment regarding this invention is shown below, the aspect of this invention is not limited to these.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, the electrical / mechanical conversion means uses a shear mode type recording head that forms a partition wall between adjacent pressure chambers, and ejects ink in the pressure chamber by driving the partition wall, and is composed of a rectangular wave. An example in which a drive pulse is applied will be described.

  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 flexible 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 drive signal generation means 100 (see FIG. 3) provided with a circuit for generating a drive signal.

  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, and the recording head 2 is provided at a standby position such as a home position during non-recording. When the recording head 2 is in this standby position, a small amount of ink droplets are discarded 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.

  2A and 2B are diagrams showing a schematic configuration of a shear mode type recording head which is an embodiment of the recording head, in which FIG. 2A is a perspective view partially showing a cross section, and FIG. 2B is a state in which an ink supply unit is provided. It is sectional drawing. 3A to 3C are diagrams showing the operation.

  2 and 3, 100 is a drive signal generating means, 2 is a recording head, 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 substrate. The partition, L is the length of the pressure chamber, D is the depth of the pressure chamber, and W is the width of the pressure chamber. A pressure chamber 28 is formed by the partition wall 27, the cover plate 24, and the substrate 26.

  FIG. 1B shows a cross-sectional view of the pressure chamber 28 having one nozzle 23. In the recording head 2 operating in the actual shear mode, as shown in FIG. A large number of pressure chambers 28A, 28B, 28C,... Separated by partition walls 27A, 27B, 27C, 27D,.

  One end of the pressure chamber 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 also referred to as a manifold end) is connected to the manifold 77 and ink. The ink tube 21 is connected to an ink tank (not shown) through the supply port 25.

  Further, the pressure chamber 28 is a shallow groove that gradually becomes shallower from the deep groove portion 28a toward the inlet side (right side in FIG. 2) of the deep groove portion 28a on the outlet side (left side in FIG. 2) of the pressure chamber 28. And a groove portion 28b.

  Each of the partition walls 27A, 27B, 27C, 27D... Is composed of partition walls 27a and 27b made of two piezoelectric materials having different polarization directions as indicated by arrows in FIG. Electrodes 29A, 29B, and 29C connected from above the partition wall 27 to the bottom surface of the substrate 26 are formed in close contact with each other, and each electrode 29A, 29B, and 29C generates a drive signal via the anisotropic conductive film 78 and the flexible cable 6. Connected to means 100.

  Each partition 27 is composed of two partition walls 27a and 27b having different polarization directions as indicated by arrows in FIG. 3, but the piezoelectric material may be, for example, only the portion 27a. Of at least some of them.

  The drive signal generation means 100 generates a series of drive signals for continuously applying at least three drive pulses every pixel period (every print period), and the drive signal for each pressure chamber. A drive pulse selection circuit that selects a drive pulse from the drive signal supplied from the generation circuit according to the image data of each pixel and supplies it to each pressure chamber. The electrical / mechanical machine according to the image data of each pixel A drive pulse for driving the partition wall 27 as the conversion means is supplied. Each drive pulse has an expansion pulse that expands the volume of the pressure chamber, a contraction pulse that contracts the volume of the pressure chamber following the expansion pulse, and a waiting time that follows the contraction pulse. In the standby time, neither the expansion pulse nor the contraction pulse is applied, and a predetermined reference state is maintained.

  When the image data is received, a control unit (not shown) controls the motor of the conveyance roller and the carriage motor, and causes the drive signal generation circuit to generate a drive signal having at least three drive pulses. Further, the control unit outputs information on the drive pulse to be selected to the drive pulse selection circuit based on the image data. The drive pulse selection circuit selects one or more predetermined drive pulses from at least three drive pulses based on the above information and supplies the selected one to the partition wall 27. Thereby, one or more ink droplets can be ejected from the nozzles 23 of the recording head 2 within one pixel period.

  In such a recording head 2, when a drive pulse 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 generating means 100, the operation in the pressure chamber 28 is performed by the operation exemplified below. Ink is ejected from the nozzle 23 as ink droplets. In FIG. 3, the nozzle is omitted.

  When no drive pulse is applied to any of the electrodes 29A, 29B, and 29C, none of the partition walls 27A, 27B, and 27C is deformed, but in the state shown in FIG. 3A, the electrodes 29A and 29C are grounded and the electrodes When a drive pulse is applied to 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 shown in FIG. 3B, the partition walls 27B and 27C are deformed toward each other, expand the volume of the pressure chamber 28B, generate a negative pressure in the pressure chamber 28B, and ink flows.

  Further, after maintaining this state for a predetermined time, when the potential is returned to 0, the partition walls 27B and 27C return from the expanded position shown in FIG. 3B to the neutral position shown in FIG. High pressure is applied to the ink. Next, as shown in FIG. 3C, when the drive pulse is applied so as to deform the partition walls 27B and 27C in the opposite directions to contract the volume of the pressure chamber 28B, a positive pressure is generated in the pressure chamber 28B. Occurs. As a result, the ink meniscus in the nozzle due to a part of the ink filling the pressure chamber 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. After holding this state for a predetermined time, when the potential is returned to 0 and the partition walls 27B and 27C are returned from the contracted position to the neutral position, a part of the remaining pressure wave is canceled. Each of the other pressure chambers operates in the same manner as described above by applying a drive pulse.

  As described above, ink droplets fly to form an image. In order to form a gradation image or a high-density image in detail, the pressure generating means according to the image data within the same pixel period as described above. A series of drive pulses are applied several times in succession to cause a plurality of ink droplets to fly, and before the plurality of ink droplets land on the recording paper, that is, coalesce during flight, or after landing ( By combining them as dots), one pixel (dot) can be formed at the time of landing. As a result, it is possible to form a high-quality image by enlarging the dots filling the pixels or by forming a plurality of ink droplets on one pixel to form gradation and high density pixels.

  When the plurality of ink droplets are combined to form one pixel, the plurality of individual ink droplets are referred to as sub-drop SD, and the combination is referred to as super drop.

In order to form a super drop by combining a plurality of sub-drops SD during flight or at a landing position (which may be combined as dots), basically, the first sub-drop SD ₁ has a speed higher than that of the first sub-drop SD ₁ . it is difficult to 2 sub-drop SD ₂ is united with the people of the speed is not fast to flying. Therefore, it is necessary to sequentially fast with the third sub-drop _SD 3 · · · SD _N.

  However, when driven by a drive pulse whose basic unit is an expansion pulse, a contraction pulse, and a predetermined waiting time (for example, length 1AL), each subdrop tends to fly separately, and the subdrop during flight There is a problem that it is difficult to unite and it becomes unstable to form a super drop. In addition, there is a problem that a plurality of ink droplets forming one pixel lands separately from each other and the pixel is disturbed.

Therefore, compared with a negative voltage value -V1 of the positive voltage values + V1 and decreasing pulse expansion pulses of the driving pulse P ₁ for jetting the first sub-drop SD _1, the drive for jetting the second sub Drop SD ₂ the voltage + V2 of the expansion pulse of the pulse _{P 2,} the values of the voltage -V2 contraction pulse, respectively + V2> + V1, driven by a large voltage value of the absolute value such that -V2 <-V1. Then, the second sub-drop SD ₂ flies at a higher speed than the first sub-drop SD ₁ and merges during the flight. Similarly, a method of forming super-drops by combining the sub-drops during flight by sequentially driving the third sub-drops SD ₃ ... SD _{N with} a voltage having a large absolute value is also conceivable.

  However, this method requires a voltage circuit that changes in an analog manner, and the drive circuit becomes complicated and expensive, and the control of the drive pulse is also complicated.

  In multidrop driving, it is necessary to cancel the residual pressure wave for each SD discharge as appropriate. If the residual pressure wave is too large, the speed varies among SDs, and a plurality of SD (ink droplets) forming one pixel lands away from each other, and the pixels are distorted or cannot be stably ejected due to fluctuations in the meniscus position. Occur.

  Note that AL (Acoustic Length) is ½ of the acoustic resonance period of the pressure chamber. The pulse width is defined as the time between 10% from the start of voltage rise and 10% from the start of voltage fall. 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. Further, the rectangular wave is a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within ½, preferably within ¼ of AL.

  The driving signal in the present invention is a driving signal for continuously applying at least three driving pulses for ejecting ink droplets within one printing cycle, and each driving pulse within one printing cycle is the pressure chamber. An expansion pulse that expands the volume of the pressure chamber, a contraction pulse that contracts the volume of the pressure chamber following the expansion pulse, and a waiting time that follows the contraction pulse. The waiting time of the first pulse to be applied is longer than 2 times and shorter than 4 times AL (AL is 1/2 of the acoustic resonance period of the pressure chamber), and the waiting time of the last pulse applied last is the AL The standby time of each intermediate pulse applied between the first pulse and the last pulse is longer than the AL and shorter than twice the AL, and the voltage of the expansion pulse in each drive pulse is Mutual Substantially equal to, and the voltage of the contraction pulse is characterized by substantially equal to each other.

  Here, “substantially equal” means that the voltage of the expansion pulse (contraction pulse) in each drive pulse is in the range of ± 0.5V. The voltage indicates the maximum voltage of the pulse.

  FIG. 4 shows a drive signal applied from the drive signal generating means 100 to the partition wall 27 in order to eject ink droplets in this embodiment. FIG. 4 is a diagram showing the waveform of the drive pulse for forming and flying the super drop in the present embodiment in contrast to the basic waveform of the drive pulse for forming and flying the super drop UD. Time is taken and the vertical axis represents the voltage of the drive pulse.

If in this embodiment, to form the N (N is an integer of 3 or more) sub-drop _SD 1 _of, SD 2, 1 or super drop UD by · · · _{SD N-1,} SD _N, FIG. as shown in 4, sub-drop _{SD 1, SD 2 ··· SD N} -1, SD N drive for ejecting the pulse _{P 1, P 2, ··· P} N-1, P N of the voltage ( Although the expansion pulse voltage + Von and the contraction pulse voltage -Voff are equal to each other, as will be apparent from the following description, the super drop UD can be formed stably.

4, B ₁ , B ₂ ,... B _N−1 , B _N are pulse widths of the respective expansion pulses, and S ₁ , S ₂ ,... S _N−1 , S _N are pulses of the respective contraction pulses. Width, Y ₁ , Y ₂ ,... Y _N−1 , Y _N are standby times following each contraction pulse, t ₁ , t ₂ ,... T _N−1 , t _N are periods of each drive pulse Respectively.

As already described, the basic waveform of the drive pulse is that when the half of the acoustic resonance period of the pressure chamber is AL (time), the expansion pulse of width AL, the contraction pulse of width 2AL following it, and the subsequent voltage zero a drive signal of length 4AL consisting waiting period (length AL), to form a sub-drop _{SD 1, SD} 2 ··· _{SD N} is applied to the pressure chamber the drive signal N times in a row.

In the driving of the pressure chamber with the driving pulse having such a basic waveform, it is difficult to surely combine the second sub-drop SD ₂ with the first sub-drop SD ₁ , and the inventor of the present invention stably stabilizes the super-drop. The sub-drop ejection stability was evaluated by searching for an ink jet recording apparatus that can be formed and driving the pressure chamber by changing the waiting time of the sub-drop driving pulse in various ways with AL as a basic unit.

  The positive pressure wave generated by the contraction in the drive pulse is not sufficiently canceled even when the application of the contraction pulse is released, and residual vibration exists in the pressure chamber. Depending on the setting of the waiting time following each drive pulse, the next drive pulse can be applied in accordance with the residual vibration in the pressure chamber caused by the previous drive pulse, and the speed of the ink droplets to be ejected later can be set appropriately. I found that it can be enhanced.

There is residual vibration in the pressure chamber after the first first pulse P ₁ that discharges the SD ₁ sub-drop is applied. If the wait time Y ₁ of the first of the first pulse P ₁ is set to be shorter than four times the longer AL than twice the AL, super drop and discharge stability of the stable form and ink droplets A balance can be achieved.

The reason is that the residual vibration of the pressure wave at the time of contraction of the first first pulse P ₁ and the phase of the pressure wave at the start of application of the expansion pulse in the intermediate pulse P ₂ for discharging the _second SD ₂ are the same phase. This is probably because a moderately large pressure is generated by the superposition of the pressure waves, so that the discharge speed of SD ₂ can be made larger than that of SD ₁ . Further, it is preferable that the waiting time Y ₁ of the first drive pulse P ₁ is set to three times the AL for the same reason.

The twice or four times the waiting time Y ₁ is AL, the pressure at the start application of the expansion pulse at the intermediate pulse P ₂ for ejecting the SD ₂ pressure wave and 2 shots th at the first of the first pulse P ₁ contraction The wave phase is reversed, the superposition of the pressure waves is suppressed, and the discharge speed of SD ₂ cannot be made higher than SD _1, so that the request for stable formation of the super drop cannot be satisfied.

If the wait time Y ₁ is greater than four times the AL, under the influence of the attenuation of the pressure wave at the time of shrinkage initial first pulse P _1, is suppressed superposition between pressure waves, from SD ₁ the discharge speed of the SD ₂ Therefore, the demand for stable formation of the super drop cannot be satisfied.

If it is less than twice AL, the ink drop speed of the _second SD ₂ will be too high, and it will be difficult to make the ink drop speed of the third and subsequent inks relatively larger, so that the super drop can be stably formed. The request cannot be satisfied. In particular, discharge is likely to become unstable due to the influence of residual vibration below 1 AL.

The waiting time Y ₁ by reducing the rate rise from the first ink droplet by shortening than 4AL longer than 2AL, thereby suppressing ink droplet speed of the second drop.

Intermediate pulse P ₂ for discharging a sub-drop SD _2, by setting the waiting time Y ₂ to be shorter than twice the longer AL than 1AL, the second drop of ink droplets 3 drop at the ink It is possible to achieve both a higher speed than the droplet speed and the ejection stability of the ink droplets.

The reason is that the pressure wave at the time of contraction of the _second pulse SD ₂ of the second SD ₂ and the phase of the pressure wave at the start of application of the expansion pulse in the drive pulse P ₃ for discharging the _third SD ₃ are in phase. In addition, since the attenuation of the pressure wave is small, a larger pressure is generated by the superposition of the pressure waves, and thus it is considered that the discharge speed of SD ₃ can be made larger than that of SD ₂ . Further, it is preferable that the waiting time Y ₂ is set to 1.5 times the AL for the same reason.

In double waiting time Y ₂ is AL, at the start of the application of the expansion pulse at the intermediate pulse P ₃ for ejecting 2 shot eyes intermediate pulse P ₂ of systolic pressure wave and SD ₃ of 3 shot eyes of SD ₂ of The phase of the pressure wave becomes an opposite phase, the superposition of the pressure waves is suppressed, and the discharge speed of SD ₃ cannot be made larger than that of SD _2, so that the request for stable formation of the super drop cannot be satisfied. Below 1 AL, ejection tends to become unstable due to the effects of residual vibration.

SD ₃ ~SD _N-1 other intermediate pulse for ejecting sub-drop _(P 3 _{~P N-1)} is 2 times the SD _2, including in the waiting time _Y 2 _{to Y N-1} and longer than AL AL May be set within a shorter range.

After final pulse P _N that eject sub drop SD _N is applied, the residual vibration is present in the pressure chamber. If the next pixel is driven while the residual vibration remains, the first ink ejection speed of the next pixel increases, and the second and subsequent ink droplet velocities are further increased relative to each other. Since it becomes difficult to increase the size, it cannot satisfy the demand for stable formation of the super drop. To suppress this residual vibration, the waiting time Y _N of the last pulse P _N is an even multiple of AL.

The waiting time Y _N of the last driving pulse P _N by being set to an even multiple of AL, an initial first pulse P ₁ of the expansion pulse pressure wave and the next pixel period when shrinkage in the final pulse P _N The phase of the pressure wave at the start of application becomes an opposite phase, the superposition of the pressure waves is suppressed, and the next SD ₁ sub-drop can be discharged at a normal speed.

  Furthermore, in order to drive at high speed, 2 times or 4 times AL is preferable.

  Since the pulse width of the expansion pulse of each drive pulse is set to an odd multiple of the AL, the phase of the pressure wave at the start of application of the expansion pulse and the pressure wave at the time of application release (at the start of application of the contraction pulse) Are in phase, and a large positive pressure is generated by the superposition of pressure waves, which is preferable because it can be discharged at a lower voltage. For the same reason, the pulse width of the expansion pulse is more preferably 1AL.

  Since the pulse width of the contraction pulse of each drive pulse is set to an even multiple of the AL, the phase of the pressure wave at the start of application of the contraction pulse (when application of the expansion pulse is released) and the pressure wave when application is released Is preferable because the phase is reversed, the superposition of pressure waves is suppressed, and discharge can be performed more stably. For the same reason, the pulse width of the contraction pulse is more preferably 2AL.

  In the drive pulse of FIG. 4, it is preferable that the ratio of the expansion pulse voltage Von (V) and the contraction pulse voltage Voff (V) is | Von |> | Voff |. Thus, the relationship | Von |> | Voff | has an effect of promoting the supply of ink into the pressure chamber, and is particularly preferable when high-frequency driving is performed with high-viscosity ink. For the same reason, it is more preferable to set | Von | / | Voff | = 2.

  Note that the reference voltage of the voltage Von and the voltage Voff is not always zero. The voltage Von and the voltage Voff are respectively differential voltages from the reference voltage. In the present embodiment, since the reference voltage is set at the GND level, the voltage can be lowered, and the reduction of the driving voltage can suppress the deterioration of the piezoelectric material (PZT) and the driving voltage is low. It is possible to give a large pressure fluctuation in the pressure chamber.

  Further, when the state held at the reference voltage is set as the reference state, each drive pulse includes an expansion pulse that expands the volume of the pressure chamber from a predetermined reference state and then returns to the reference state, and the expansion pulse. Subsequently, it is preferable that the pressure chamber is contracted and then contracted to return to the reference state, and the reference state is maintained during the standby time of each drive pulse. Since the voltage (reference voltage) at the start point and end point of each drive pulse can be made equal, it is not necessary to add an unnecessary signal for returning the voltage when the drive pulse is continuously generated.

  The pressure chamber in the reference state is preferably in a reference volume state that is neither in an expanded state nor a contracted state.

  Each drive pulse is preferably composed of drive pulses having the same waveform. The configuration of the drive signal generation means can be simplified. In the present embodiment, a rectangular wave pulse having a rise time and a fall time which are both nearly zero is used. By using a pulse composed of a rectangular wave, the driving efficiency is improved and the setting of the pulse width is facilitated.

  In the shear mode type recording head 2, when the side walls 27 </ b> B and 27 </ b> C of the pressure chamber 28 </ b> B that ejects ink droplets are deformed as described above, the adjacent pressure chambers 28 </ b> A and 28 </ b> C are affected. Ink droplets cannot be ejected simultaneously from 28A and 28C. For this reason, normally, among the plurality of pressure chambers 28, the pressure chambers 28 that are separated from each other by sandwiching one or more pressure chambers 28 are combined into one set and divided into two or more sets. The drive control is performed so that the ink discharge operation is sequentially performed in a time division manner for each set. For example, a so-called three-cycle discharge method is performed in which every two pressure chambers 28 are selected and discharged in three phases. When an ink droplet is ejected from one pressure chamber, the vibration of the ejected pressure chamber is also transmitted to the adjacent pressure chamber, so that the next ejection can be performed after these vibrations have settled to some extent. As another channel configuration, a pressure chamber and an air chamber (dummy channel) that does not contain ink, that is, does not emit ink, are provided alternately at least on both sides of the pressure chamber to discharge ink droplets. There is a way to prevent the influence from being transmitted to the adjacent pressure chamber. In this case, each pressure chamber can eject ink droplets at the same timing. The present invention can be applied to any of the above-described methods, but the latter case is particularly preferable because multidrop ink droplets can be ejected more stably.

  Such a 3-cycle discharge operation will be further described with reference to FIG. In the example shown in FIG. 5, it is assumed that the recording head has nine pressure chambers 28 of A1, B1, C1, A2, B2, C2, A3, B3, and C3. Basically, an example in which three (N = 3) ink droplets are ejected in one pixel cycle will be described. Further, FIG. 6 shows a timing chart of drive signals applied to the electrodes of the pressure chambers 28 in each set of A, B, and C at this time.

In order to discharge the first sub-drop SD ₁ , an expansion pulse with a pulse width of B ₁ followed by a contraction pulse with a pulse width of S ₁ followed by a length Y ₁ (more than 2 times AL but less than 4 times) applying a first pulse P ₁ consisting of waiting time.

Next, in order to discharge the sub-drop SD ₂ , an expansion pulse having a pulse width of B ₂ , a subsequent contraction pulse having a pulse width of S ₂ , and a subsequent length Y ₂ (longer than AL and shorter than twice AL) applying the intermediate pulse P ₂ consisting of waiting time.

In order to discharge the last sub-drop SD ₃ , a final consisting of an expansion pulse with a pulse width of B ₃ , a subsequent contraction pulse with a pulse width of S ₃ , followed by a waiting time of length Y ₃ (an even multiple of AL) applying a pulse _{P 3.} A period for forming a super drop by three drops of SD _{1 to} SD ₃ is defined as a pixel period.

When a super drop is formed by a drive pulse shown in FIG. 6 and then caused to fly, the sub-drops SD _{1 to} SD ₃ can be stably combined during the flight or on the recording medium.

At the time of ink ejection, first, a series of driving pulses for ejecting SD ₁ to SD ₃ are applied to the electrodes of the pressure chambers 28 of the A group (A1, A2, A3), and the electrodes of the pressure chambers adjacent to both are grounded. , to eject ink droplets of _SD 1 to SD ₃ from group a nozzle.

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

The above is a case of a solid image (full drive), but actually, the number of ink droplets to be ejected among SD ₁ to SD ₃ is changed according to the image data of each pixel.

When N = 3, 0 drop (0 gradation), 1 drop (1 gradation) of sub-drop SD ₁ ejected by the first first pulse within one pixel period, SD ₁ and one pixel period 2 drops of SD ₂ ejected by the second intermediate pulse (2 gradations), 3 drops of SD ₃ ejected by SD ₁ and SD ₂ and the third (last) last pulse in one pixel period Each of (3 gradations) can be printed from 0 gradation to 3 gradations.

  In the above example, N = 3, but N may be an integer of 4 or more. N is preferably 10 or less, and more preferably 5 or less. If the length is too long, the driving cycle becomes longer, which is not preferable.

  In such a shear mode type ink jet recording head, the deformation of the partition wall 27 occurs due to 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 pressure chamber for discharging ink, FIG. As described above, the same operation can be performed by grounding the electrode of the pressure chamber for discharging ink and applying a positive voltage to the electrodes of the pressure chambers on both sides. According to this latter method, the same effect as that obtained when the drive signal shown in FIG. 6 is applied can be obtained, and a circuit configuration can be made only with a positive voltage, which is advantageous in terms of circuit design.

  As described above, according to the present embodiment, the waiting time of the first first pulse among at least three drive pulses in one printing cycle is longer than twice AL and shorter than four times, and the intermediate pulse Since the standby time is set to be longer than 1 time and shorter than 2 times AL, the discharge speed of a plurality of ink droplets can be gradually increased. Further, it is possible to discharge a small and stable ink droplet such as a landing curve, and it is possible to obtain a high-quality print.

  Therefore, when a high density image is formed by forming a super drop by continuously applying at least three drive pulses to the pressure generating means and ejecting each sub drop from the nozzle in succession. Super drop formation by combining sub-drops in the inside is performed stably, and it becomes possible to form a high-quality image. Further, even when one pixel is formed on the recording material by each sub-drop, it is possible to form a high-quality image by performing controlled pixel formation.

  Further, since the voltages of the drive pulses are substantially equal, it is possible to provide an ink jet recording apparatus capable of stably discharging multidrops without complicating the drive circuit.

Further, since the waiting time of the last final pulse in one printing period it was from even multiple of AL, the residual vibration of the pressure chamber after discharging the last sub-drop SD _N, the first sub next printing cycle This is sufficiently reduced until the drop SD ₁ is discharged. Therefore, when the discharge of the first sub-drop SD _1, the ink in the pressure chamber and the nozzle is sufficiently settled down. Therefore, the first sub-drop SD ₁ can be stably discharged at a normal speed.

  In the above embodiment, the pressure generating means (partition wall) is constituted by a piezoelectric element. The ink jet recording apparatus of the present invention is preferable because the control of expanding the volume of the pressure chamber can be easily performed when the pressure generating means is constituted by a piezoelectric element.

  In the above embodiment, a rectangular-wave drive pulse having a sufficiently short rise time and fall time as compared with AL is applied to the piezoelectric element. By using the rectangular wave, it is possible to perform driving using the acoustic resonance of the pressure wave more effectively. Compared with a method using a trapezoidal wave, the ink droplets are ejected more efficiently, and can be driven at a low voltage. In addition, the driving circuit can be designed with a simple digital circuit. In addition, the pulse width can be easily set.

  In the above embodiment, a shear mode type piezoelectric element that deforms in a shear mode by applying an electric field as a pressure generating means is used. The shear mode type piezoelectric element is preferable because the rectangular-wave drive pulse can be used more effectively, the voltage is lowered, and more efficient drive is possible. However, the present invention is not necessarily limited to ejecting ink droplets from the nozzles by driving the partition wall composed of the electro-mechanical conversion means for the volume of the pressure chamber of the recording head. For example, a recording head of a type that ejects ink droplets from nozzles by changing the volume in the pressure chamber by an electromechanical conversion means made of a piezoelectric material provided outside the pressure chamber, and a heater in the pressure chamber are arranged. An ink jet recording apparatus using a recording head of a type in which ink in a pressure chamber is heated using a heater as a heat source and ink droplets are ejected using energy of bubbles generated during heating may be used.

"ink"
Next, the ink according to the present invention will be described.

  Further, the ink jet recording apparatus of the present invention exhibits a remarkable effect when the surface tension of the ink at 25 ° C. is 31 mN / m or less. This is because such a low surface tension ink has a slow return speed of the meniscus to the steady state after the ink droplets are ejected, and therefore the ejection tends to become unstable when continuously driven by multidrop.

  When such an ink having a low surface tension is used for image recording, it can be quickly absorbed by the recording medium after image recording, so that the fixability of the image can be improved.

  If the surface tension of the ink is too low, the wettability with respect to the nozzle forming member 22 increases, so that the ink tends to adhere to the vicinity of the nozzle 23 on the ejection side surface, and the ink ejection is easily affected. For this reason, the surface tension of the ink is preferably 10 mN / m or more.

  The surface tension can be measured using a surface tension meter CBVP type A-3 (Kyowa Kagaku Co., Ltd.).

  As the ink used in the inkjet recording apparatus, water-based ink mainly containing water, non-volatile solvent that does not volatilize at room temperature, oil-based ink that does not substantially contain water, mainly solvent that volatilizes at room temperature, There are multiple inks such as non-water-based ink that does not substantially contain water, hot-melt ink that heats and melts solid ink at room temperature, and photo-curing ink that polymerizes and cures with light after printing. It is used properly according to.

  Examples of the ink having a surface tension of 31 mN / m or less as described above include oil-based ink, non-aqueous ink, and photo-curable ink. The oil-based ink refers to an ink containing 80% by mass or more of a saturated hydrocarbon having 15 to 18 carbon atoms, a monohydric alcohol having 15 to 18 carbon atoms, or a derivative thereof as a solvent. The oil-based ink has an advantage that an image having good water resistance can be obtained.

<Photocurable ink>
The photocurable ink according to the present invention will be described.

  The photocurable ink according to the present invention is mainly composed of a photopolymerizable compound (hereinafter also simply referred to as a polymerizable compound), a constituent compound of a photopolymerization initiator group, and a color material. The constitution of the photopolymerization initiator group referred to in the present invention is a single photopolymerization initiator, a plurality of photopolymerization initiators, a combination of a photopolymerization initiator and a sensitizer, and a photopolymerization initiator and a sensitizer. And a starting aid.

[Photopolymerizable compound]
Examples of the photopolymerizable compound applicable to the photocurable ink according to the present invention include a radical polymerizable compound and a cationic polymerizable compound.

(Radically polymerizable compound)
The radically polymerizable compound applicable to the present invention is a compound having an ethylenically unsaturated bond capable of radical polymerization, and any compound having at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. In other words, those having chemical forms such as monomers, oligomers and polymers are included. Only one kind of radically polymerizable compound may be used, or two or more kinds thereof may be used in combination at an arbitrary ratio in order to improve desired properties. A polyfunctional compound having two or more functional groups is more preferable than a monofunctional compound. More preferably, two or more polyfunctional compounds are used in combination for controlling performance such as reactivity and physical properties.

  Examples of compounds having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and their salts, esters, urethanes, amides. And radically polymerizable compounds such as unsaturated monomers, acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Specifically, acryloylmorpholine, phenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate Bis (4-acryloxypolyethoxyphenyl) propane, EO-modified bisphenol A diacrylate, polyethylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, glycerin epoxy acrylate, neopentyl glycol diacrylate, 1,6-hexane Diol diacrylate, ethylene glycol dia Relate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol tetraacrylate, trimethylolpropane triacrylate, Acrylic acid derivatives such as tetramethylol methane tetraacrylate, oligoester acrylate, N-methylol acrylamide, diacetone acrylamide, epoxy acrylate, methyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, allyl methacrylate, glycine Methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, trimethylolethane trimethacrylate, trimethylolpropane Examples include methacrylic derivatives such as trimethacrylate, 2,2-bis (4-methacryloxypolyethoxyphenyl) propane, and other derivatives of allyl compounds such as allyl glycidyl ether, diallyl phthalate, and triallyl trimellitate. , Yamashita Shinzo, “Crosslinker Handbook” (1981, Taiseisha); Kato Kiyomi, “UV / EB Curing Han” Dobook (Raw Materials) "(1985, Polymer Press Society); Radtech Research Group," Application and Market of UV / EB Curing Technology ", p. 79, (1989, CMC); Eiichiro Takiyama," Polyester Commercially available products described in “Resin Handbook”, (1988, Nikkan Kogyo Shimbun), or radically polymerizable or crosslinkable monomers, oligomers and polymers known in the industry can be used. The amount of the radical polymerizable compound added is preferably 1 to 97% by mass, more preferably 30 to 95% by mass.

(Cationically polymerizable compound)
Examples of the cationic polymerizable compound applicable to the present invention include an epoxy compound, an oxetane compound, and a vinyl ether compound that can be polymerized by cationic polymerization.

  Examples of the epoxy compound that can be used in the present invention include JP-A No. 2001-220526, JP-A No. 2002-188025, JP-A No. 2002-317139, JP-A No. 2003-55449, and JP-A No. 2003-73481. Any known epoxy compound described in 1. can be used by epoxidizing a compound having at least one cycloalkane ring such as cyclohexene or cyclopentene ring with a suitable oxidizing agent such as hydrogen peroxide or peracid. The resulting cyclohexene oxide or cyclopentene oxide-containing compound is preferred.

  As the oxetane compound that can be used in the present invention, for example, any known oxetane compound as disclosed in JP-A Nos. 2001-220526 and 2001-310937 can be used.

  Examples of the vinyl ether compound that can be used in the present invention include ethylene glycol divinyl ether, ethylene glycol monovinyl ether, diethylene glycol divinyl ether, triethylene glycol monovinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, and dipropylene glycol divinyl ether. , Butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, hydroxyethyl monovinyl ether, hydroxynonyl monovinyl ether, trimethylolpropane trivinyl ether, and other di- or trivinyl ether compounds, ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether Monomers such as octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, octadecyl vinyl ether Examples include vinyl ether compounds.

  One of the polymerizable compounds may be used alone, but two or more may be used in appropriate combination.

  In addition, as a means for preventing a decrease in sensitivity due to the light-shielding effect due to the ink color material, it is possible to combine a cationically polymerizable monomer having a long initiator lifetime with an initiator to obtain a radical-cation hybrid curable ink.

[Configuration of photopolymerization initiator group]
Examples of the additive constituting the photopolymerization initiator group according to the present invention include radical polymerization initiators, cationic polymerization initiators, initiation assistants, and sensitizers. The added amount of these photopolymerization initiator groups in the ink is required to be 1 to 10 parts by mass of the whole ink.

  Various known compounds can be used for the photopolymerization initiator group according to the present invention, and the photopolymerization initiator group is selected from those soluble in the polymerizable compound.

(Photopolymerization initiator)
<Radical polymerization initiator>
Examples of the radical polymerization initiator include triazine derivatives described in JP-B-59-1281, JP-A-69-1621, and JP-A-60-60104, JP-A-59-1504 and JP-A-61-2243807. And other publications such as JP-B Nos. 43-23684, 44-6413, 44-6413, and 47-1604, and US Pat. No. 3,567,453. Diazonium compounds described in the specification, organic azide compounds described in U.S. Pat. Nos. 2,848,328, 2,852,379 and 2,940,853, Japanese Patent Publication No. 36-22062, Ortho-quinonediazides described in JP-A-37-13109, JP-A-38-18015, JP-A-45-9610, JP-B-55-39162, JP-A-59-1 No. 023 etc. and various onium compounds described in “Macromolecules, Vol. 10, Volume 1307 (1977)”, azo compounds described in JP-A-59-142205, 1-54440, European Patent Nos. 109,851 and 126,712, “Journal of Imaging Science” (J. Imag. Sci.), Vol. 30, No. 174 Page (1986), metal allene complexes described in JP-A-4-213861 and JP-A-4-255347, organoboron complexes described in JP-A-4-151197, and titanocene described in JP-A-61-151197. "Coordination Chemist Review" y Review), 84, 85-277 (1988) and JP-A-2-182701, transition metal complexes containing a transition metal such as ruthenium, JP-A-3-209477 Examples include 2,4,5-triarylimidazole dimer, carbon tetrabromide, and organic halogen compounds described in JP-A-59-107344. These polymerization initiators are preferably contained in the range of 0.01 to 10 parts by mass with respect to 100 parts by mass of the compound having an ethylenically unsaturated bond capable of radical polymerization.

<Cationic polymerization initiator>
The photocurable ink according to the present invention preferably contains a cationic polymerization initiator as a photopolymerization initiator together with the cationic polymerizable compound.

  Specific examples of the cationic polymerization initiator include a photoacid generator and the like. For example, a chemical amplification type photoresist or a compound used for photocationic polymerization is used (edited by Organic Electronics Materials Research Group, “ Organic materials for imaging ", Bunshin Publishing (1993), see pages 187-192). Examples of compounds suitable for the present invention are listed below.

First, diazonium, ammonium, iodonium, sulfonium, aromatic onium compounds of phosphonium such as ^{_{B (C 6 F 5) 4}} -, PF 6 -, AsF 6 -, SbF 6 -, CF 3 SO 3 - and salts be able to.

  Specific examples of onium compounds that can be used in the present invention are shown below.

  Secondly, sulfonated compounds that generate sulfonic acid can be mentioned, and specific compounds thereof are exemplified below.

  Thirdly, halides that generate hydrogen halide can also be used, and specific compounds thereof are exemplified below.

  Fourthly, an iron allene complex can be mentioned.

(Sensitizer)
In the photocurable ink according to the present invention, it is preferable to use a sensitizer having ultraviolet spectrum absorption at a wavelength longer than 300 nm. For example, a hydroxyl group, an optionally substituted aralkyloxy group or an alkoxy group is used as a substituent. And polycyclic aromatic compounds having at least one, carbazole derivatives, thioxanthone derivatives, and the like.

  As the polycyclic aromatic compound that can be used in the present invention, naphthalene derivatives, anthracene derivatives, chrysene derivatives, and phenanthrene derivatives are preferable. As an alkoxy group which is a substituent, a C1-C18 thing is preferable and a C1-C8 thing is especially preferable. As the aralkyloxy group, those having 7 to 10 carbon atoms are preferable, and benzyloxy groups and phenethyloxy groups having 7 to 8 carbon atoms are particularly preferable.

  Examples of these sensitizers that can be used in the present invention include carbazole derivatives such as carbazole, N-ethylcarbazole, N-vinylcarbazole, N-phenylcarbazole, 1-naphthol, 2-naphthol, 1-methoxynaphthalene, 1-stearyloxynaphthalene, 2-methoxynaphthalene, 2-dodecyloxynaphthalene, 4-methoxy-1-naphthol, glycidyl-1-naphthyl ether, 2- (2-naphthoxy) ethyl vinyl ether, 1,4-dihydroxynaphthalene, 1, , 5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 2,7-dimethoxynaphthalene, 1,1′-thiobis (2-naphthol), 1,1′-bi-2-naphthol, 1,5-naphthyl diglycid Ether, 2,7-di (2-vinyloxyethyl) naphthyl ether, 4-methoxy-1-naphthol, ESN-175 (epoxy resin manufactured by Nippon Steel Chemical Co., Ltd.) or its series, condensate of naphthol derivative and formalin, etc. Naphthalene derivatives, 9,10-dimethoxyanthracene, 2-ethyl-9,10-dimethoxyanthracene, 2-tbutyl-9,10-dimethoxyanthracene, 2,3-dimethyl-9,10-dimethoxyanthracene, 9-methoxy -10-methylanthracene, 9,10-diethoxyanthracene, 2-ethyl-9,10-diethoxyanthracene, 2-tbutyl-9,10-diethoxyanthracene, 2,3-dimethyl-9,10-di Ethoxyanthracene, 9-ethoxy-10-methylanthracene, 9, 0-dipropoxyanthracene, 2-ethyl-9,10-dipropoxyanthracene, 2-tbutyl-9,10-dipropoxyanthracene, 2,3-dimethyl-9,10-dipropoxyanthracene, 9-isopropoxy- 10-methylanthracene, 9,10-dibenzyloxyanthracene, 2-ethyl-9,10-dibenzyloxyanthracene, 2-tbutyl-9,10-dibenzyloxyanthracene, 2,3-dimethyl-9,10 -Dibenzyloxyanthracene, 9-benzyloxy-10-methylanthracene, 9,10-di-α-methylbenzyloxyanthracene, 2-ethyl-9,10-di-α-methylbenzyloxyanthracene, 2-tbutyl -9,10-di-α-methylbenzyloxyanthracene, 2,3- Dimethyl-9,10-di-α-methylbenzyloxyanthracene, 9- (α-methylbenzyloxy) -10-methylanthracene, 9,10-di (2-hydroxyethoxy) anthracene, 2-ethyl-9,10 -Anthracene derivatives such as di (2-carboxyethoxy) anthracene, 1,4-dimethoxychrysene, 1,4-diethoxychrysene, 1,4-dipropoxychrysene, 1,4-dibenzyloxychrysene, 1,4- Examples include chrysene derivatives such as di-α-methylbenzyloxychrysene, phenanthrene derivatives such as 9-hydroxyphenanthrene, 9,10-dimethoxyphenanthrene, and 9,10-diethoxyphenanthrene. Among these derivatives, 9,10-dialkoxyanthracene derivatives which may have an alkyl group having 1 to 4 carbon atoms as a substituent are particularly preferable, and the methoxy group and ethoxy group are preferable as the alkoxy group.

  Examples of the thioxanthone derivative include thioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone 2-chlorothioxanthone, and the like.

(Starting aid)
An initiator is a substance that acts as a sensitizing dye that improves the radical or acid generation efficiency of an initiator by donating energy to the initiator by light irradiation, electron donation, electron attraction, heat generation, etc. Yes, applied in combination with initiator.

  Examples of the initiation assistant include xanthene, thioxanthone dye, ketocoumarin, thioxanthene dye, cyanine, phthalocyanine, merocyanine, porphyrin, spiro compound, ferrocene, fluorene, fulgide, imidazole, perylene, phenazine, phenothiazine, polyene, azo compound, diphenylmethane , Triphenylmethane, polymethine acridine, coumarin, ketocoumarin, quinacridone, indigo, styryl, pyrylium compound, pyromethene compound, pyrazolotriazole compound, benzothiazole compound, barbituric acid derivative, thiobarbituric acid derivative and the like can be applied.

  In addition to the above-mentioned compounds, it is well known that the initiator acts as a sensitizing dye in documents such as “Development technology of polymer additives” (CMC Publishing Co., Ltd., supervised by Junichi Daikatsu). The substance may be applied. The initiation assistant can also be regarded as a component that forms part of the photopolymerization initiator.

  In addition to these photoinitiators, an accelerator aid may be added to accelerate the photopolymerization (curing) reaction. Examples of these include ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, ethanolamine, diethanolamine, triethanolamine and the like.

  Examples of a combination of a radical polymerization initiator and an initiator that are applied to the radical polymerizable composition include a peracid ester as a radical polymerization initiator and xanthene, a thioxanthone dye, a ketocoumarin, a thiopyrylium salt as an initiator. And a combination of an onium salt such as diphenyliodonium salt which is a radical polymerization initiator and a thioxanthene dye which is an initiation assistant are well known.

  Further, when applying titanocenes as radical polymerization initiators, as initiators for sensitizing the titanocenes from visible light to near infrared light corresponding to lasers or LEDs, for example, cyanine, phthalocyanine, merocyanine, porphyrin, Spiro compound, ferrocene, fluorene, fulgide, imidazole, perylene, phenazine, phenothiazine, polyene, azo compound, diphenylmethane, triphenylmethane, polymethine acridine, coumarin, ketocoumarin, quinacridone, indigo, styryl, pyrylium compound, pyromethene compound, pyrazolotriazole A compound, a benzothiazole compound, a barbituric acid derivative, a thiobarbituric acid derivative, or the like can be applied.

  As the starting aid used in combination with titanocene, further, European Patent No. 568,993, US Patent Nos. 4,508,811, 5,227,227, JP 2001-125255 A, JP 11-271969 A, etc. The compounds described in (1) are also applicable. Specific examples of combinations of such titanocene radical polymerization initiators and initiation assistants include combinations described in JP-A Nos. 2001-125255 and 11-271969.

[Color material]
A pigment or dye can be used as the color material used in the photocurable ink according to the present invention. From the viewpoint of the weather resistance of the image, it is preferable to use a pigment.

  The pigments that can be preferably used in the present invention are listed below.

C. I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 81, 83, 87, 93, 95, 97, 98, 109, 114, 120, 128, 129, 138, 150, 151, 154, 180, 185,
C. I. Pigment Red 5, 7, 12, 22, 38, 48: 1, 48: 2, 48: 4, 49: 1, 53: 1, 57: 1, 63: 1, 101, 112, 122, 123, 144, 146, 168, 184, 185, 202,
C. I. Pigment Violet 19, 23,
C. I. Pigment Blue 1, 2, 3, 15: 1, 15: 2, 15: 3, 15: 4, 18, 22, 27, 29, 60,
C. I. Pigment Green 7, 36,
C. I. Pigment White 6, 18, 21,
C. I. Pigment Black 7.

  For the dispersion of the pigment, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like can be used. Further, a dispersing agent can be added when dispersing the pigment. As the dispersant, a polymer dispersant is preferably used, and examples of the polymer dispersant include Avecia's Solsperse series and Ajinomoto Fine-Techno's PB series. Moreover, it is also possible to use a synergist according to various pigments as a dispersion aid. These dispersants and dispersion aids are preferably added in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the pigment. The dispersion medium is used using a solvent or a polymerizable compound. However, the photocurable ink used in the present invention is preferably solvent-free because it is reacted and cured immediately after ink landing. If the solvent remains in the cured image, the solvent resistance deteriorates and the VOC of the remaining solvent arises. Therefore, it is preferable in view of dispersibility that the dispersion medium is not a solvent but a polymerizable compound, and among them, a monomer having the lowest viscosity is selected.

  The pigment is preferably dispersed so that the average particle diameter of the pigment particles is 0.08 to 0.2 μm, and the maximum particle diameter is 0.3 to 10 μm, preferably 0.3 to 3 μm. The selection of the dispersion medium, the dispersion conditions, and the filtration conditions are appropriately set. By controlling the particle size, clogging of the head nozzle can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained.

  In the ink according to the present invention, the color material concentration is preferably 1% by mass to 30% by mass of the entire ink. For inks other than white, the content is more preferably 1% by mass to 10% by mass.

[Other additives]
A polymerization inhibitor can be added to the ink according to the present invention in an amount of 200 to 20000 ppm from the viewpoint of improving the storage stability. Since the ink according to the present invention is preferably ejected by heating and lowering the viscosity in the range of 40 to 80 ° C., it is preferable to add a polymerization inhibitor in order to prevent head clogging due to thermal polymerization.

  In addition to this, surfactants, leveling additives, matting agents, polyester resins, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes are added to adjust film properties as necessary. can do.

  The viscosity at 25 ° C. is preferably 25 mPa · s or more and 500 mPa · s or less from the viewpoint of ease of fixing of the droplet after landing, and the viscosity at the time of discharge is 8 mPa · s or more and 20 mPa · s or more from the driving voltage and stability at the time of discharge. S or less is preferable. The surface tension of the ink is preferably 31 mN / m or less with little receding after landing and good line outline drawing performance.

  As described above, the contact angle with the recording medium is preferably 10 to 30 ° from the viewpoint that the receding after landing due to the liquid is small and the drawing of the outline of the line is good and fixing on the recording medium is easy.

  As light, image recording is performed mainly with ink that is cured using ultraviolet rays, but the ink is not necessarily limited to this. For example, by irradiating light other than ultraviolet rays, such as electromagnetic waves such as visible rays and infrared rays. It may be a curable ink. In this case, a polymerizable compound that is polymerized and cured with light other than ultraviolet light and a photoinitiator that initiates a polymerization reaction between the polymerizable compounds with light other than ultraviolet light are applied to the ink. When using a photocurable ink that is cured by light other than ultraviolet light, a light source that emits the light is applied instead of the ultraviolet light source.

  When photo-curable ink is used for image recording, the photo-curable ink is polymerized and cured if light is irradiated after image recording, so that the image can be maintained without disappearing for a long period of time. Can improve the quality. Furthermore, if a photocurable ink is used for image recording, even if the recording medium is not a recording medium with good ink absorption (for example, paper), the recording medium with no ink absorption or the recording medium with low ink absorption may be used. Even if it exists, image recording can be performed.

《Non-aqueous ink》
For outdoor postings that require long-term weather resistance and printed matters that require adhesion to curved objects, plastic recording media such as polyvinyl chloride and polyethylene are used as the recording media, especially for a wide range of applications. In addition, a recording medium made of soft polyvinyl chloride is used. There are many methods for printing on soft polyvinyl chloride, but there is an inkjet recording method as a method suitable for the production of a small variety of products because there is no need to prepare a plate and the time to finish is short.

  When ink-jet recording is performed on soft polyvinyl chloride, the ink used is a non-aqueous ink containing cyclohexanone, N-methylpyrrolidone, etc. having solubility in soft polyvinyl chloride and containing glycol acetates as the main solvent Is used. In these inks, solvents such as cyclohexanone and N-methylpyrrolidone have high solubility in soft polyvinyl chloride, and the pigment in the ink gets into soft polyvinyl chloride, so that good scratch resistance and gloss can be obtained. It is done.

  The non-aqueous ink according to the present invention (hereinafter also simply referred to as ink) can contain a non-aqueous solvent, but one or more compounds selected from the compound groups represented by the general formulas (1) and (2) It is preferable to contain the solvent (A) which consists of.

In the general formula (1), R ¹ and R ² each represent a methyl group or an ethyl group, and OX ¹ represents an oxyethylene group or an oxypropylene group.

In the general formula (2), R ³ and R ⁴ each represent a methyl group or an ethyl group, and OX ² represents an oxyethylene group or an oxypropylene group.

  Specific compounds represented by the general formulas (1) and (2) according to the present invention include, for example, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, ethylene glycol diacetate, propylene Examples thereof include glycol diacetate.

  Among these, the component of the solvent (A) is preferably at least one selected from diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, ethylene glycol diacetate and propylene glycol diacetate. The quick drying property of the ink when printed on vinyl and the long-term storage stability of the ink can be further improved. Among them, a particularly preferable solvent (A) is one containing diethylene glycol diethyl ether and ethylene glycol diacetate in a ratio of at least 1: 1 to 10: 1.

  The content of the solvent (A) in the ink is preferably 50% by mass or more and 90% by mass or less. By using such a solvent configuration, quick drying property and emission stability at the time of polyvinyl chloride printing can be obtained. In addition to being good, the odor of the ink is reduced and it contributes to long-term storage stability of the ink.

[Other solvents]
The non-aqueous ink according to the present invention may contain a conventionally known solvent in addition to the solvent (A) according to the present invention as long as the object and effects of the present invention are not impaired. For example, alkylene glycol monoalkyl ethers such as diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and alkylene glycol dialkyl ethers such as ethylene glycol dibutyl ether and tetraethylene glycol dimethyl ether Is mentioned.

  Furthermore, in the ink of the present invention, an organic solvent for imparting vinyl chloride solubility may be added for the purpose of improving the adhesion with the vinyl chloride recording medium, but in order to achieve better long-term storage stability, It is preferable to contain a compound as shown in FIG.

  Examples of the solvent include a solvent (B) composed of one or more compounds selected from the group of compounds represented by the following general formula (3) or (4).

In the general formula (3), R ⁵ and R ⁶ each represent a substituent having 1 to 6 carbon atoms, for example, a linear or branched alkyl group such as a methyl group, an ethyl group, an n-propyl group, or an isopropyl group. And alkyl groups substituted with heteroatoms such as hydroxyethyl group, acetyl group, and acetonyl group, cyclic groups such as cyclohexyl group and phenyl group, or aromatic substituents, and R ⁵ and R ⁶ are the same. Or R ⁵ and R ⁶ may be bonded to each other to form a ring.

In the general formula (4), R ⁷ and R ⁸ each represent a substituent having 1 to 6 carbon atoms, for example, a linear or branched alkyl group such as a methyl group, an ethyl group, an n-propyl group, or an isopropyl group. And a cyclic or aromatic substituent such as an alkyl group substituted with a hetero atom such as a hydroxyethyl group, an acetyl group or an acetonyl group, a cyclohexyl group or a phenyl group, and R ⁷ and R ⁸ are the same. Or R ⁷ and R ⁸ may be bonded to each other to form a ring.

  Examples of the compounds represented by the general formulas (3) and (4) according to the present invention include dimethyl sulfoxide, diethyl sulfoxide, methyl ethyl sulfoxide, diphenyl sulfoxide, tetraethylene sulfoxide, dimethyl sulfone, methyl ethyl sulfone, and methyl-isopropyl. Examples include sulfone, methyl-hydroxyethyl sulfone, and sulfolane.

  The content of the solvent (B) in the ink is preferably 1.5% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and particularly preferably 5% by mass. As mentioned above, it is 15 mass% or less. When the content of the solvent (B) is 1.5% by mass or more, the solubility of the ink in polyvinyl chloride is sufficient, and scratch resistance and alcohol wiping resistance against polyvinyl chloride can be obtained. Moreover, if it is 3 mass% or more, the abrasion resistance with respect to polyvinyl chloride and alcohol wiping resistance are favorable, and if it is 30 mass% or less, stable emission without causing abnormalities of the inkjet head due to long-term use. It can be performed.

  In addition, examples of the solvent include compounds represented by the following general formula (5) or (6).

[Wherein, R ₁ represents an alkylene group having 3 to 11 carbon atoms, and R ₂ represents a hydrogen atom or a methyl group. ]
General formula (6)
R ₃ CON (R ₄ ) _2
Wherein, R 3, _{R 4} each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. ]
Specific examples of the solvent represented by the general formula (5) include β-lactam, 2-pyrrolidone, δ-lactam, ε-caprolactam, laurolactam, N-methyl-2-pyrrolidone and the like.

  Specific examples of the solvent represented by the general formula (6) include N-methylformamide, N, N-dimethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-dimethylacetamide, N, N-diethylacetamide and the like can be mentioned.

  In addition, examples of the soluble solvent for the polyvinyl chloride resin include 1,2-dichloroethane, nitroethane, acetone, methyl ethyl ketone, butyl acetate, dioxane, cyclohexane, cyclohexanone, pyridine, morpholine, diethylene glycol dimethyl ether, and the like.

  Moreover, a lactone type | system | group solvent can be mentioned as another solvent which can be used together.

  The lactone solvent is a compound having a cyclic structure by an ester bond, and includes a 5-membered ring structure γ-lactone, a 6-membered ring structure δ-lactone, a 7-membered ring structure ε-lactone, and the like. Butyrolactone, γ-valerolactone, γ-hexalactone, γ-heptalactone, γ-octalactone, γ-nonalactone, γ-decalactone, γ-undecalactone, δ-valerolactone, δ-hexalactone, δ-heptalactone , Δ-octalactone, δ-nonalactone, δ-decalactone, δ-undecalactone, and ε-caprolactam. The lactone solvent is a γ-lactone having a 5-membered ring structure in a preferred embodiment, and in a more preferred embodiment, γ-butyrolactone and γ-valerolactone.

  Furthermore, the solvent shown below can be mentioned as another solvent which can be used together.

  Next, other components of the ink according to the present invention will be described.

[Pigment]
In the non-aqueous ink according to the present invention, a pigment is used as a coloring material. By using a pigment as the color material, the weather resistance of the recorded matter recorded on a plastic recording medium such as polyvinyl chloride can be improved.

  As the pigment that can be used in the present invention, conventionally known pigments can be used without particular limitation, and examples thereof include the same types of pigments that can be applied to the aforementioned photocurable ink.

(Pigment dispersant)
In the ink according to the present invention, a surfactant, a polymer dispersant, or the like can be used as the pigment dispersant. Polymer dispersing agents include (meth) acrylic resins, styrene- (meth) acrylic resins, hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, long Salts of chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, condensates or salt formations of polyesters having polyallylamine and free carboxylic acids, modified polyurethanes, modified polyacrylates, polyether ester type anionic activators , Naphthalenesulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene nonylphenyl ether, stearylamine acetate, pigment derivatives and the like.

  Specifically, Jonkrill (manufactured by Johnson Polymer), Anti-Terra-U (manufactured by BYK Chemie), Disperbyk (manufactured by BYK Chemie), Efka (manufactured by Efka CHEMICALS), Floren (manufactured by Kyoeisha Chemical), Disparon (manufactured by Enomoto Kasei Co., Ltd.), Demole (manufactured by Kao Corporation), homogenol, Emulgen (manufactured by Kao Corporation), Solspers (manufactured by Avisia), Nikkor (manufactured by Nikko Chemical Co., Ltd.), Ajispur (Ajinomoto Finetech), etc. It is done.

  The content of the dispersant in the ink of the present invention is preferably added in the range of 10% by mass to 200% by mass with respect to the pigment. By setting the content to 10% by mass or more, the pigment dispersion stability is enhanced, and by setting the content to 200% by mass or less, the ink ejection from the inkjet head is easily stabilized.

〔resin〕
In the non-aqueous ink according to the present invention, various resins (hereinafter also simply referred to as “resins”) are added in order to improve fixability when recording on a plastic recording medium such as polyvinyl chloride.

  When performing multi-drop high-speed driving, it is necessary to attenuate meniscus vibrations early. In particular, in a non-aqueous ink containing a resin, it is difficult to attenuate such meniscus vibrations early and stable emission is difficult. According to the ink jet recording apparatus of the present invention, the waiting period of each drive pulse can be optimized and the residual vibration of the meniscus can be set to an appropriate amount, thereby increasing the speed of the subsequent ink droplet using the residual vibration of the previous ejection. And an ink jet recording apparatus that can solve the conflicting problem of unstable ejection due to residual vibration and can stably form a super drop even when a non-aqueous ink containing a resin is used. Can be provided.

  Examples of the resin to be added include acrylic resins, polyester resins, polyurethane resins, vinyl chloride resins, vinyl chloride-vinyl acetate copolymer resins, and the like.

  Specifically, acrylic resins such as John Crill (manufactured by Johnson Polymer Co., Ltd.), ESREC P (manufactured by Sekisui Chemical Co., Ltd.), polyester resins such as Elitel (manufactured by Unitika Ltd.) and Byron (manufactured by Toyobo Co., Ltd.), Byron UR ( Toyobo Co., Ltd.), NT-Hilamic (Daiichi Seika Co., Ltd.), Crisbon (Dainippon Ink Chemical Co., Ltd.), Nipporan (Nippon Polyurethane Co., Ltd.) and other polyurethane resins, SOLBIN (Nisshin Chemical Co., Ltd.), Vinyl Blanc (Nissin Chemical Industry Co., Ltd.), Saran Latex (Asahi Kasei Chemicals Co., Ltd.), Sumielite (Sumitomo Chemical Co., Ltd.), Sekisui PVC (Sekisui Chemical Co., Ltd.), UCAR (Dow Chemical Co., Ltd.) Can be mentioned.

  The resin acts as a binder that adheres a color material such as a pigment to the recording medium after printing. However, the resin has higher adhesion and durability as the molecular weight increases. In addition, the smaller the molecular weight, the lower the viscosity of the ink. However, the lower the viscosity, the lower the energy required for ejecting the ink during printing, so that the inkjet head is not burdened and it is easier to eject stably. Therefore, if the number average molecular weight is 10,000 or more, the fixability after printing is sufficiently exhibited, and if it is 30000 or less, it does not impose a load on the ejection of the ink, which is preferable.

  Particularly preferred resins have a number average molecular weight in the range of 10,000 to 30,000, and the composition includes vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, vinyl chloride-vinyl acetate-vinyl. And at least one resin selected from an alcohol copolymer and a vinyl chloride-vinyl acetate-hydroxyalkyl acrylate copolymer, and a vinyl chloride-vinyl acetate copolymer and a vinyl chloride-vinyl acetate-maleic anhydride copolymer. They may be used as a mixture. Furthermore, these vinyl chloride-vinyl acetate copolymers and vinyl chloride-vinyl acetate-maleic anhydride copolymers may be mixed with acrylic resins, polyester resins, polyurethane resins, etc. May be used.

  By adding these resins to the ink according to the present invention, the emission stability, scratch resistance and alcohol wiping resistance can be improved in a balanced manner.

  The alcohol wiping resistance referred to in the present invention is resistance to disturbance such as image peeling when wiping the surface of the image with ethanol or a mixed solvent of ethanol and water. Wipe off dirt on the image surface with alcohol for posters for outdoor use. It is a user need for that.

  As a method for synthesizing the resin according to the present invention, a suspension polymerization method, an emulsion polymerization method, a solution polymerization method, and the like can be applied without particular limitation. Among them, the solution polymerization method is preferable.

  The solution polymerization method is one of the methods used for radical polymerization of a monomer having a vinyl group. The monomer and initiator are dissolved in a solvent in which the polymer to be generated is soluble, and the polymerization is performed by heating. Is the method.

  Resins synthesized by the solution polymerization method have high solubility even at a relatively high molecular weight, and more resin can be contained in the ink, so that the scratch resistance can be improved.

  The resin content in the ink according to the present invention is preferably 1 to 10% by mass. When the content is 1% by mass or more, the image weather resistance when recorded on polyvinyl chloride is enhanced, and when the content is 10% by mass or less, the ink ejection from the inkjet head is easily stabilized, and more preferable. The range of content is 3-7 mass%.

[Other additives]
In the non-aqueous ink according to the present invention, in addition to the above description, depending on the purpose of improving the emission stability, the compatibility with the print head and the ink cartridge, the storage stability, the image storage stability, and other various performances as necessary. Various known additives, for example, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, antifouling agents, rust inhibitors, etc., can be appropriately selected and used. it can.

  In the ink jet recording method using the non-aqueous ink according to the present invention, for example, an ink jet recorded image is obtained by ejecting ink from an ink jet head based on a digital signal and attaching the ink to a recording medium by a printer loaded with ink. It is done. In order to quickly and surely dry the ink adhered to the recording medium, a method of forming an image by increasing the surface temperature of the recording medium is preferable.

  The surface temperature is adjusted according to the durability of the recording medium and the drying property of the ink used, but is preferably 40 to 100 ° C. In particular, when polyvinyl chloride is used as the recording medium, increasing the surface temperature improves the wettability of the ink with respect to the surface of the recording medium. Therefore, it is more preferable to record at a higher surface temperature.

  Depending on the brand of the recording medium made of polyvinyl chloride, there may be a difference in wettability and ink drying, so the surface temperature may be adjusted according to the characteristics of each medium.

  When recording is performed by increasing the surface temperature of the recording medium, it is preferable to mount a heater on the ink jet recording apparatus, and by heating the recording medium before or during transport of the recording medium, the surface temperature of the recording medium alone by the ink jet recording apparatus Can be adjusted.

〔recoding media〕
In the ink jet recording apparatus of the present invention, various recording media such as paper, resin, metal, and glass can be applied.

  When an image is recorded on a recording medium using the non-aqueous ink according to the present invention, the recording medium includes polyvinyl chloride, a resin base material that does not contain a plasticizer, and a non-absorbing inorganic base material as constituent elements. It is preferable to use at least one recording medium selected from the media.

  Specific examples of polyvinyl chloride, which is one of the recording media used in the ink jet recording method of the present invention, include SOL-371G, SOL-373M, SOL-4701 (manufactured by Big Technos Co., Ltd.), glossy PVC (Co., Ltd.). Systemgraph Co., Ltd.), KSM-VS, KSM-VST, KSM-VT (above, manufactured by Kimoto Co., Ltd.), J-CAL-HGX, J-CAL-YHG, J-CAL-WWWG (above, Showa Co., Ltd.) (Made in Osaka), BUS MARK V400 F vinyl, litecal V-600F vinyl (above, made by Flexcon), FR2 (made by Hanwha) LLBAU13713 (above, made by Sakurai Co., Ltd.), P-370B, P-400M (above , Manufactured by Kambo Plus Co., Ltd.), S02P, S12P S13P, S14P, S22P, S24P, S34P, S27P (above, manufactured by Grafityp), P-223RW, P-224RW, P-249ZW, P-284ZC (above, manufactured by Lintec Corporation), LKG-19, LPA-70 , LPE-248, LPM-45, LTG-11, LTG-21 (above, manufactured by Shinsei Co., Ltd.), MPI 3023 (manufactured by Toyo Corporation), Napoleon Gloss gloss PVC (manufactured by Futaki Electronics Co., Ltd.), JV-610, Y-114 (above, manufactured by ICC Corporation), NIJ-CAPVC, NIJ-SPVCGT (above, manufactured by Nichie Corporation), 3101 / H12 / P4, 3104 / H12 / P4, 3104 / H12 / P4S 9800 / H12 / P4, 3100 / H12 / R2, 3 101 / H12 / R2, 3104 / H12 / R2, 1445 / H14 / P3, 1438 / One Way Vision (manufactured by Inetrcoat), JT5129PM, JT5728P, JT5822P, JT5829P, JT5829R, JT5829PM, JT5829PM, JM59t MPI1005, MPI1900, MPI2000, MPI2001, MPI2002, MPI3000, MPI3021, MPI3500, MPI3501 (above, manufactured by Avery), AM-101G, AM-501G (above, manufactured by Ginichi Co., Ltd.), FR2 (Hanfa Japan Co., Ltd.), AY-15P, AY-60P, AY-80P, DBSP137GGH, DBSP137GGL (above, Inc.) Insight Co., Ltd.), SJT-V200F, SJT-V400F-1 (above, manufactured by Hiraoka Orizome Co., Ltd.), SPS-98, SPSM-98, SPSH-98, SVGL-137, SVGS-137, MD3-200, MD3-301M, MD5-100, MD5-101M, MD5-105 (manufactured by Metamark), 640M, 641G, 641M, 3105M, 3105SG, 3162G, 3164G, 3164M, 3164XG, 3164XM, 3165G, 3165SG, 3165M, 3169M , 3451SG, 3551G, 3551M, 3631, 3641M, 3651G, 3651M, 3651SG, 3951G, 3641M (above, manufactured by Orafol), SVTL-HQ130 (manufactured by Lamy Corporation), SP 00 GWF, SPCLEARAD vinyl (above, manufactured by Catalina), RM-SJR (produced by Ryoyo Corporation), Hi Lucky, New Lucky PVC (above, made by LG), SIY-110, SIY-310, SIY-320 ( As described above, Sekisui Chemical Co., Ltd., PRINT MI Frontlit, PRINT XL Light weight banner (hereinafter, manufactured by Endutex), RIJET 100, RIJET 145, RIJET 165 (above, manufactured by Ritrama), NM-SG, NM-SM NEIEI KAKO Co., Ltd.), LTO3GS (Lukio Co., Ltd.), Easy Print 80, Performance Print 80 (above, Jetgraph Co., Ltd.), DSE 550, DSB 550, DSE 800 G, DSE 802/137, V250WG, V300WG, V350WG (above, manufactured by Hexis), Digital White 6005PE, 6010PE (above, made by Multifix), and the like.

  Moreover, as a recording medium having a resin base material containing no plasticizer or a non-absorbing inorganic base material as a constituent element, the following various base materials are used as constituent elements, and one kind of base material is used alone, or a plurality of kinds are used. These substrates can be used in combination. Examples of the resin base material containing no plasticizer used in the present invention include ABS resin, polycarbonate (PC) resin, polyacetal (POM) resin, polyamide (PA) resin, polyethylene terephthalate (PET) resin, and polyimide (PI). Examples thereof include a resin, an acrylic resin, a polyethylene (PE) resin, a polypropylene (PP) resin, and a hard polyvinyl chloride (PVC) resin that does not contain a plasticizer.

  These resins are characterized by not containing a plasticizer, but there are no particular restrictions on other properties such as thickness, shape, color, softening temperature, and hardness.

  The recording medium used in the present invention is preferably ABS resin, PET resin, PC resin, POM resin, PA resin, PI resin, hard PVC resin containing no plasticizer, acrylic resin, PE resin, or PP resin. More preferred are ABS resin, PET resin, PC resin, PA resin, hard PVC resin not containing plasticizer, and acrylic resin.

  Moreover, as a non-absorbing inorganic base material used for this invention, a metal plate, such as a glass plate, iron, and aluminum, a ceramic plate etc. are mentioned, for example. These inorganic substrates are characterized by not having an ink-absorbing layer on the surface. These non-absorbing inorganic base materials are not particularly limited with respect to other properties such as thickness, shape, color, softening temperature, and hardness.

Hereinafter, although the effect of the present invention is illustrated based on an example, the present invention is not limited to these.
Example 1
<Ink>
In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.
<Preparation of photocurable ink 1>
[Preparation of Dispersion 1]
Each of the following compounds was placed in a stainless beaker and dissolved by stirring and heating for 1 hour while heating on a hot plate at 65 ° C.

PB822 (dispersant manufactured by Ajinomoto Fine Techno Co., Ltd.) 8 parts Tetraethylene glycol diacrylate (TEGDA, bifunctional) 72 parts After cooling to room temperature, 20 parts Pigment Blue 15: 4 (Cyanine Blue 4044 made by Sanyo Dye) In addition, 200 g of zirconia beads having a diameter of 0.3 mm were placed in a glass bottle and sealed, and after a dispersion treatment for 4 hours with a paint shaker, the zirconia beads were removed to prepare dispersion 1.

[Preparation of Ink 1]
14 parts of the dispersion 1 prepared as described above, 24.9 parts of RA as a polymerizable compound (radical polymerizability), 29.0 parts of TEGDA, 25.0 parts of A-400, and SDX-1843 as a modified silicone oil As a photopolymerization initiator group, 0.1 part, 5.0 parts of photopolymerization initiator I-907 and 2.0 parts of sensitizer IPTX were mixed, and then filtered through a 0.8 μm filter. Filtration was performed to obtain ink 1 of a photocurable ink.
<Preparation of photocurable ink 2>
[Preparation of Dispersion 2]
Each of the following compounds was placed in a stainless beaker and dissolved by stirring and heating for 1 hour while heating on a hot plate at 65 ° C.

PB821 (Ajinomoto Fine Techno Co., Ltd. dispersant) 9 parts OXT221 (Tojo Gosei Co., Ltd. oxetane compound) 71 parts Then, 200 g of zirconia beads having a diameter of 0.3 mm were put in a glass bottle and sealed, and after a dispersion treatment for 4 hours with a paint shaker, the zirconia beads were removed to prepare dispersion 2.

[Preparation of ink 2]
14 parts of the dispersion 2 prepared above, 20.0 parts of 2021P, 43.9 parts of OXT221 and 15.0 parts of OXT212 as a polymerizable compound (cationic polymerizable), and SDX-1843 as 0. As a photopolymerization initiator group, 1 part of UVI6992 which is a photopolymerization initiator and 5.0 parts of CPTX which is a sensitizer are mixed, and then filtered through a 0.8 μm filter, Ink 2 of a photocurable ink was obtained.

  Details of the compounds described by abbreviations are as follows.

<Radically polymerizable compound>
RA: Lauryl acrylate TEGDA: Tetraethylene glycol diacrylate A-400: NK ester Shin-Nakamura Chemical Co., Ltd. <Cationically polymerizable compound>
2021P: Celloxide 2021P (alicyclic epoxy compound, bifunctional, manufactured by Daicel Chemical Industries)
OXT212: Monofunctional oxetane compound, manufactured by Toagosei Co., Ltd. OXT221: Bifunctional oxetane compound, manufactured by Toagosei Co., Ltd. <Modified silicone oil>
SDX-1843: Modified silicone oil SDX-1843, manufactured by Asahi Denka Kogyo Co., Ltd. <Photopolymerization initiator>
I-907: Irgacure 907 Ciba Japan UVI6992: Triarylsulfonium salt, UVI6992, Dow Chemical Co., Ltd. <sensitizer>
IPTX: isopropylthioxanthone CPTX: 1-chloro-4-propoxythioxanthone AHC: 3-acetyl-7-hydroxycoumarin <Preparation of non-aqueous ink 3>
The pigment dispersants and resins described below were used after diluting with an organic solvent used for dispersion so that the low boiling point solvent was distilled off under reduced pressure and the solid content was 20% by mass. Hereinafter, the amounts used of the pigment dispersant and the resin represent solid content converted values.

[Preparation of Pigment Dispersion 3]
C. I. 10 parts of Pigment Blue 15: 3 (hereinafter abbreviated as PB15: 3), 5 parts of Solspers 24000 (manufactured by Lubrizol) as a pigment dispersant, and 10 parts of sulfolane (S-10) as a solvent (B) As a solvent (A), 60 parts of diethylene glycol diethyl ether and 15 parts of ethylene glycol diacetate were mixed, and a horizontal bead mill (system zeta mini manufactured by Ashizawa Co., Ltd.) filled with 60% by volume of 0.5 mm diameter zirconia beads was used. Then, the zirconia beads were removed to obtain a pigment dispersion 3.

(Preparation of resin solution)
Vinyl chloride-vinyl acetate copolymer synthesized by solution polymerization using 10 parts of dimethyl sulfoxide as solvent (B), 65 parts of diethylene glycol diethyl ether and 15 parts of ethylene glycol diacetate as solvent (A), and resin 10 parts (trade name VYHD, number average molecular weight 22000, manufactured by Dow Chemicals) were mixed and dissolved to prepare a resin solution.

[Preparation of ink 3]
While stirring 50 parts of the resin solution, 50 parts of the pigment dispersion 3 was mixed and then filtered through a 0.8 μm filter to obtain a non-aqueous ink 3.
<Preparation of photocurable ink 4>
In the preparation of the ink 2, a photocurable ink 4 was prepared in the same manner except that 0.1 part of the modified silicone oil (SDX-1843) was added and 44.0 parts of OXT221 was used.

  The surface tension of each ink can be measured using a surface tension meter CBVP type A-3 (Kyowa Science Co., Ltd.).

<< Image formation and evaluation >>
(Image numbers 1-32)
Two shear mode type recording heads (nozzle pitch: 180 dpi, number of nozzles: 256, nozzle diameter: 23 μm, AL: 2.4 μs, ink droplet amount: 4 pl) shown in FIG. 2 are prepared. They were attached so that they were shifted by 1/2 pitch from each other and arranged in a staggered manner. Accordingly, since each of the heads is a 180 dpi head, the nozzle pitch can be shifted by ½, so that it can be used as a 360 dpi recording head, the number of nozzles can be increased, and a high density recording head can be used. It can be.

  Each ink prepared above is loaded into the ink jet recording apparatus having the configuration shown in FIG. 1 equipped with the two-row head (nozzle pitch: 360 dpi, number of nozzles: 512), and various recording media shown in Table 1 are loaded. The discharge was performed under the following conditions.

Three drive pulses P _{1 to} P ₃ for ejecting sub-drops SD ₁ to SD ₃ shown in FIG. 6 from the pressure chambers of each row of the two-row head (nozzle pitch: 360 dpi, number of nozzles: 512) are 1 Based on the drive signal applied continuously within the pixel period, it was divided into 3 groups and 3 cycle drive was performed.

  For each drive pulse, the voltage Von of each expansion pulse was 16 V, the voltage Voff of each contraction pulse was 8 V, and the ratio of Von to Voff (| Von | / | Voff |) was 2/1.

In addition, the pulse width (B ₁ , B ₂ , B ₃ ) of each expansion pulse was 1 AL, and the pulse width (S ₁ , S ₂ , S ₃ ) of each contraction pulse was ₂ AL.

The standby time (Y ₁ , Y ₂ , Y ₃ ) of each drive pulse was changed as shown in Table 1.

When discharging the photocurable ink, the ink tank was insulated from the head portion and heated at 50 ° C. Further, LEDs (illuminance (light quantity): 100 mW / cm ² (manufactured by Nichia Corporation (special order), peak wavelength: 365 nm)), which are light irradiation means, are installed on both sides (on the carriage) of the recording head 2, and ink is used. The ink was cured by irradiation with ultraviolet rays 0.1 seconds after landing.

  As a recording medium, JT5929PM (manufactured by Mactac), which is a recording medium made of high-quality paper and PVC (polyvinyl chloride), was used. During printing, the recording medium was heated from the back side, and the heater temperature was set so that the surface temperature of the recording medium during image recording was 45 ° C. The surface temperature of the recording medium was measured using a non-contact thermometer (IT-530N type, manufactured by Horiba, Ltd.).

[Evaluation of image]
According to the above method, each image created was evaluated according to the following method. In all cases, the performance of Δ or higher was regarded as an acceptable level.

(Evaluation of pixel shape)
With respect to the formed image, the shape of one dot formed by three ink droplets driven into one pixel was enlarged and observed with a loupe, and the dot shape was evaluated according to the following evaluation criteria.

○: Three SD (ink droplets) forming one pixel land at almost the same position, and there is almost no disorder of the dot shape. Δ: Three SD (ink droplets) forming one pixel land slightly apart from each other. Although the dot shape is slightly disturbed, it is within the allowable range. X: Three SD (ink droplets) forming a pixel land away from each other, the pixel is disturbed, the dot shape is poor, and this is a practical problem. level.

(Evaluation of output stability)
In a 20 ° C., 30% RH environment, the state after the discharge was continued for 1 hour without cleaning was visually observed, and the discharge stability was evaluated according to the criteria shown below.

○: Normal emission from all nozzles △: Clogging or discharge bend is observed in 1 to 3 nozzles, but recovered by suction cleaning from the nozzle surface, and is in a practically acceptable range ×: Clogged to 4 nozzles or more Or discharge bend occurs, and one nozzle generates clogging or discharge bend that cannot be recovered by suction cleaning.

(Evaluation of fixability)
The recorded image surface was rubbed 50 times with dry cotton, and the difference in image density before and after rubbing was determined. Based on this result, the fixability was evaluated according to the following criteria.

○: Image density difference before and after rubbing does not change Δ: Image density difference before and after rubbing is within −10% ×: Image density difference before and after rubbing exceeds −10% The obtained results are shown in Table 1.

From Table 1, the ink jet recording apparatus of the present invention is superior in the 1-dot pixel shape formed by the respective ink droplets of SD ₁ to SD ₃ and has good emission stability as compared with the ink jet recording apparatus of the comparative example. Was confirmed.

It can also be seen that the fixability is improved when the surface tension of the ink is 31 mN / m or less.
(Example 2)
(Image numbers 33-52)
According to the method of Example 1, in place of the drive signal for continuously applying a SD ₁ to SD ₃ sub drop three for ejecting respective driving pulses P ₁ to P ₃ in 1 pixel cycle, in the same manner, Image formation and evaluation were performed using drive signals for continuously applying _four drive pulses P _{1 to} P ₄ for ejecting sub-drops SD _{1 to} SD ₄ within one pixel period.

  For each drive pulse, the voltage Von of each expansion pulse was 16 V, the voltage Voff of each contraction pulse was 8 V, and the ratio of Von to Voff (| Von | / | Voff |) was 2/1.

In addition, the pulse width (B ₁ , B ₂ , B ₃ , B ₄ ) of each expansion pulse was 1AL, and the pulse width (S ₁ , S ₂ , S ₃ , S ₄ ) of each contraction pulse was 2AL.

The standby time (Y ₁ , Y ₂ , Y ₃ , Y ₄ ) of each drive pulse was changed as shown in Table 2.

  Table 2 shows the results obtained as described above.

From Table 2, the ink jet recording apparatus of the present invention, it compared to the ink jet recording apparatus of the comparative example, good shape of pixels of one dot formed by each ink droplet SD ₁ to SD _4, it is also good ejection stability Was confirmed.

  It can also be seen that the fixability is improved when the surface tension of the ink is 31 mN / m or less.

It is a figure which shows schematic structure of an inkjet recording device. It is a figure which shows schematic structure of the shear mode (shear mode) type inkjet recording head which is one aspect | mode of a droplet discharge head, (a) is a perspective view which shows a partial cross section, (b) is provided with the ink supply part. FIG. (A)-(c) is a figure which shows operation | movement of a recording head. It is a figure which shows the drive signal for implement | achieving the inkjet recording device of embodiment which concerns on this invention. (A)-(c) is explanatory drawing of the time division operation | movement of a recording head. It is a timing chart of the drive signal applied to the electrode of the pressure chamber of each set of A, B, and C. It is a timing chart of a drive signal at the time of using only a positive voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet recording apparatus 2 Recording head 21 Ink tube 22 Nozzle formation member 23 Nozzle 24 Cover plate 25 Ink supply port 26 Substrate 27 Partition 28 Pressure chamber 3 Conveyance mechanism 31 Conveyance roller 32 Conveyance roller pair 33 Conveyance motor 4 Guide rail 5 Carriage 6 Flexible Cable 7, 8 Ink receiver 100 Drive signal generating means P Recording medium PS Recording surface

Claims (13)

One printing of a nozzle for ejecting ink droplets, a pressure chamber communicating with the nozzle, a recording head having pressure generating means for changing the volume of the pressure chamber, and at least three drive pulses for ejecting ink droplets, respectively An ink-jet printing apparatus comprising: a driving signal generating unit configured to generate a driving signal that is continuously applied within a cycle; and the application of the driving signal causes the pressure generating unit to operate to eject ink droplets from the nozzle. In the recording device,
Each drive pulse in one printing cycle includes an expansion pulse for expanding the volume of the pressure chamber, a contraction pulse for contracting the volume of the pressure chamber following the expansion pulse, and a waiting time following the contraction pulse. Have
Among these drive pulses, the waiting time of the first pulse to be applied first is longer than 2 times and shorter than 4 times AL (AL is 1/2 of the acoustic resonance period of the pressure chamber), and finally applied. The waiting time of the final pulse is an even multiple of the AL, and the waiting time of each intermediate pulse applied between the first pulse and the final pulse is longer than the AL and shorter than twice the AL. ,
An ink jet recording apparatus, wherein voltages of expansion pulses in each drive pulse are substantially equal to each other, and voltages of contraction pulses are substantially equal to each other. 2. The ink jet recording apparatus according to claim 1, wherein a waiting time of the first pulse is three times the AL. 3. The ink jet recording apparatus according to claim 1, wherein a waiting time of the final pulse is twice or four times the AL. 4. The ink jet recording apparatus according to claim 1, wherein a waiting time of the intermediate pulse is 1.5 times the AL. The ink jet recording apparatus according to claim 1, wherein the ink has a surface tension of 31 mN / m or less. The ink jet recording apparatus according to claim 1, wherein the ink is a non-aqueous ink and contains a resin. The ink jet recording apparatus according to claim 1, wherein the ink is a photocurable ink. 8. The ink jet recording apparatus according to claim 1, wherein the driving pulse is a pulse composed of a rectangular wave. 9. The ink jet recording apparatus according to claim 1, wherein the pressure generating unit is an electric / mechanical converting unit. 10. The electromechanical conversion means is formed of a piezoelectric material that forms at least a part of a partition wall between adjacent pressure chambers and deforms in a shear mode by applying a driving pulse. 2. An ink jet recording apparatus according to 1. 11. The inkjet recording apparatus according to claim 1, wherein a pulse width of the expansion pulse is an odd multiple of the AL, and a pulse width of the contraction pulse is an even multiple of the AL. The inkjet recording apparatus according to claim 1, wherein a period of the driving pulse is longer than four times the AL. The drive pulse expands the volume of the pressure chamber from a predetermined reference state, then returns to the reference state, and contracts the volume of the pressure chamber following the expansion pulse, and then the reference state. 13. The inkjet recording apparatus according to claim 1, further comprising: a contraction pulse to be returned to the initial position and a standby time for maintaining the reference state following the contraction pulse.

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