JP2017095814A - Liquid injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of mist in injection of printing ink effectively.SOLUTION: A liquid injection system possesses: a liquid injection head injecting printing ink containing at least penetration solvent which water/octanol distribution coefficient logP is in -0.5 to 0.5, coloring agent and water from a nozzle; and an actuator driving the liquid injection head so that a first ink drop injected from the nozzle and a second ink drop injected from the nozzle after the injection of the first ink drop unite before impact to a medium. The diameter of the nozzle is 20-30 μm.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a technique for ejecting a liquid such as ink.

  Conventionally, a liquid ejecting apparatus that ejects a liquid such as ink from a nozzle by supplying a drive signal has been proposed. For example, Patent Document 1 discloses that a plurality of ink droplets (hereinafter referred to as “ink droplets”) ejected from nozzles one after the other are combined before landing on a medium such as printing paper, so that A configuration is disclosed in which the generation of mist-like fine droplets (hereinafter referred to as “mist”) caused by ink tailing is suppressed.

JP 2013-184459 A

  By the way, an ink used for printing a fibrous medium such as a fabric contains a penetrating solvent for allowing the ink to penetrate into the fiber. Ink containing a penetrating solvent tends to cause tailing at the time of ejection as compared with general ink used for printing on printing paper. Therefore, there is a possibility that mist cannot be sufficiently suppressed only by combining a plurality of ink droplets before and after landing. In view of the above circumstances, it is an object of the present invention to effectively suppress the generation of mist when jetting printing ink.

  In order to solve the above problems, the liquid jet apparatus of the present invention is a textile printing containing at least a penetrating solvent having a water / octanol partition coefficient logP of −0.5 or more and 0.5 or less, a colorant and water. The liquid ejecting head that ejects ink from the nozzle, the first ink droplet ejected from the nozzle, and the second ink droplet ejected from the nozzle after ejecting the first ink droplet are combined before landing on the medium. And a drive unit for driving the liquid jet head, and the nozzle has a diameter of 20 μm or more and 30 μm or less. In the above configuration, since the diameter of the nozzle for ejecting the printing ink containing the penetrating solvent is set to 20 μm or more and 30 μm or less, it is possible to effectively suppress the generation of mist and ensure the landing accuracy.

  In a preferred embodiment of the present invention, the nozzle diameter is 24 μm or more and 28 μm or less. According to the above aspect, it is possible to achieve both a reduction in mist and securing of landing accuracy at a high level.

  In a preferred aspect of the present invention, the interval between the ejection surface on which the nozzle in the liquid ejection head is installed and the surface of the medium is 2 mm or more and 5 mm or less (more preferably 2 mm or more and 4 mm or less). In the above aspect, by securing an interval of 2 mm or more between the ejection surface and the surface of the medium, for example, while reducing the possibility of contact between the fuzz generated on the surface of the fibrous medium and the ejection surface, By suppressing the interval to 5 mm or less, it is possible to achieve both reduction of mist and securing of landing accuracy.

  In a preferred embodiment of the present invention, the content of the penetrating solvent in the printing ink is 1% by weight or more and 10% by weight or less. There is a tendency that the amount of mist generated increases as the content of the permeation solvent in the textile printing ink increases. According to the configuration in which the content of the osmotic solvent is 1% by weight or more and 10% by weight or less, the generation of mist can be effectively suppressed by the configuration of the present invention in which the nozzle diameter is 20 μm or more and 30 μm or less. is there.

It is a block diagram of the liquid ejecting apparatus which concerns on the suitable aspect of this invention. It is explanatory drawing of the osmosis | permeation solvent contained in textile printing ink. It is a block diagram of the function of a liquid ejecting apparatus. It is a wave form diagram of a drive signal. It is a top view of an ejection surface. FIG. 3 is a cross-sectional view of a liquid ejecting head. It is explanatory drawing of ejection and uniting of an ink drop. It is a graph of the relationship between the nozzle diameter and the speed of the ink droplet after coalescence. It is a chart of the result of having observed mist generation amount and landing accuracy. It is a chart of the observation result of the amount of mist generation and impact accuracy in contrast.

  FIG. 1 is a partial configuration diagram of a liquid ejecting apparatus 100 according to a preferred embodiment of the present invention. The liquid ejecting apparatus 100 according to the present embodiment is an ink jet printing apparatus that ejects ink suitable for printing a fibrous medium 22 such as a fabric (hereinafter referred to as “printing ink”). A liquid container 24 for storing printing ink is fixed to the liquid ejecting apparatus 100. For example, a cartridge that can be attached to and detached from the liquid ejecting apparatus 100, a bag-like ink pack formed of a flexible film, or an ink tank that can be replenished with printing ink can be used as the liquid container 24. A plurality of types of printing inks having different colors are stored in the liquid container 24.

  The textile printing ink contains a colorant, a penetrating solvent, and water. The colorant (coloring material) is a dye or pigment having a specific color. The penetrating solvent is a water-soluble solvent for promoting the penetration of the printing ink into the fibers of the medium 22. FIG. 2 is a chart illustrating penetrating solvents that can be used in textile inks. In FIG. 2, the water / octanol partition coefficient logP is shown for each type of osmotic solvent. The water / octanol partition coefficient logP is the common logarithm of the ratio Co / Cw of the substance concentration Co in 1-octanol to the substance concentration Cw in moisture and is used as an indicator of the hydrophilicity or hydrophobicity of the substance.

  The textile printing ink of this embodiment contains a penetrating solvent having a water / octanol distribution coefficient log P of −0.5 or more and 0.5 or less (−0.5 ≦ log P ≦ 0.5). Specifically, as indicated by symbol α in FIG. 2, 1,2-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,2-pentanediol, triethylene glycol One or more substances selected from monobutyl ether and 1,2-hexanediol are contained in the textile printing ink as a penetrating solvent. The content of the penetrating solvent in the printing ink (the total content when the printing ink contains plural kinds of penetrating solvents) is, for example, 1% by weight or more and 10% by weight or less. It is also possible to use textile printing inks containing components other than the components exemplified above (colorant, penetrating solvent, water). For example, a printing ink using a pigment as a colorant contains a bonding agent for fixing the pigment.

  As illustrated in FIG. 1, the liquid ejecting apparatus 100 includes a control unit 10, a transport mechanism 32, a moving mechanism 34, and a liquid ejecting unit 40. The control unit 10 includes, for example, a control device such as a CPU (Central Processing Unit) or FPGA (Field Programmable Gate Array) and a recording device such as a semiconductor memory (not shown), and stores a program stored in the storage device. When executed by the control device, each element of the liquid ejecting apparatus 100 is comprehensively controlled.

  The transport mechanism 32 transports the medium 22 in the Y direction under the control of the control unit 10. The transport mechanism 32 of this embodiment includes a supply roller 322 and a discharge roller 324. The supply roller 322 is installed on the upstream side (negative side in the Y direction) of the discharge roller 324 and conveys the medium 22 to the discharge roller 324 side. The discharge roller 324 downstream of the medium 22 supplied from the supply roller 322 Transport to (positive side in Y direction). In addition, the structure of the conveyance mechanism 32 is not limited to the above illustration.

  The moving mechanism 34 is a mechanism that reciprocates the liquid ejecting unit 40 in the X direction under the control of the control unit 10. The X direction in which the liquid ejecting unit 40 reciprocates is a direction that intersects (typically orthogonal) the Y direction in which the medium 22 is conveyed. The moving mechanism 34 of this embodiment includes a carriage 342 and a conveyor belt 344. The carriage 342 is a substantially box-shaped structure that supports the liquid ejecting unit 40, and is fixed to the transport belt 344. The conveyor belt 344 is an endless belt that is extended in the X direction. The liquid ejecting unit 40 reciprocates in the X direction together with the carriage 342 by rotating the transport belt 344 under the control of the control unit 10. In addition, the structure of the moving mechanism 34 is not limited to the above illustration. In addition, the liquid container 24 can be mounted on the carriage 342 together with the liquid ejecting unit 40.

  The liquid ejecting unit 40 ejects the printing ink supplied from the liquid container 24 onto the medium 22 under the control of the control unit 10. In parallel with the transport of the medium 22 by the transport mechanism 32 and the reciprocating reciprocation of the carriage 342, the liquid ejecting unit 40 ejects the printing ink onto the medium 22, whereby a desired image is formed on the medium 22.

  FIG. 3 is a functional configuration diagram of the liquid ejecting apparatus 100. The illustration of the transport mechanism 32, the moving mechanism 34, etc. is omitted for convenience. As illustrated in FIG. 3, the control unit 10 of the present embodiment functions as a drive signal generation unit 12 that generates the drive signal COM. The drive signal COM is a signal for causing the liquid ejecting unit 40 to eject the printing ink. As illustrated in FIG. 4, the drive signal COM of the present embodiment is a voltage signal that includes a drive pulse W1 and a drive pulse W2 that follow each other on the time axis at predetermined intervals. Each of the drive pulse W1 and the drive pulse W2 is a pulse signal for ejecting printing ink.

  In FIG. 4, the voltage when the minimum value (E1_L, E2_L) of the drive signal COM is 0% and the maximum value (E2_H) is 100% is shown on the vertical axis. The voltage E0 (60%) in FIG. 4 is a predetermined voltage (hereinafter referred to as “reference voltage”) that serves as a reference for the voltage of the drive signal COM. As illustrated in FIG. 4, the voltage of the drive pulse W1 decreases from the reference voltage E0 to the lower voltage E1_L (E1_L <E0), and after holding for a predetermined time, the voltage E1_L is higher than the reference voltage E0. It rises to E1_H (E1_H> E0), and drops from the voltage E1_H to the reference voltage E0 after holding for a predetermined time. The drive pulse W2 is a pulse immediately after the drive pulse W1. Specifically, the drive pulse W2 starts when a predetermined time (for example, about 10 μs) δ elapses from the end point of the drive pulse W1. The voltage of the driving pulse W2 decreases from the reference voltage E0 to the lower voltage E2_L (E2_L <E0), and after holding for a predetermined time, increases from the voltage E2_L to the higher voltage E2_H (E2_H> E0) for a predetermined time. The voltage E2_H drops to the reference voltage E0 after the voltage is held. In the present embodiment, the voltage E1_L of the drive pulse W1 and the voltage E2_L of the drive pulse W2 are the same voltage, and the voltage E2_H of the drive pulse W2 exceeds the voltage E1_H of the drive pulse W1. Therefore, the amplitude A2 of the drive pulse W2 exceeds the amplitude A1 of the drive pulse W1 (A2> A1). For example, the voltage E1_H is set to 75% of the voltage E2_H (100%). The waveforms of the drive pulse W1 and the drive pulse W2 can be changed as appropriate.

  As illustrated in FIG. 3, the liquid ejecting unit 40 of this embodiment includes a drive unit 42 and a liquid ejecting head 44. The drive unit 42 drives the liquid jet head 44 under the control of the control unit 10. A drive signal COM generated by the drive signal generation unit 12 and a print signal SI instructing, for each nozzle, whether or not the printing ink is ejected (ejection / non-ejection) according to the content of the print image are output from the control unit 10 to the drive unit. 42.

  The liquid ejecting head 44 ejects the printing ink supplied from the liquid container 24 onto the medium 22 from a plurality of nozzles. FIG. 5 is a plan view of a surface F (hereinafter referred to as “ejection surface”) F of the liquid ejection head 44 that faces the medium 22. As illustrated in FIG. 5, a plurality of nozzles N are formed on the ejection surface F. Specifically, a plurality of nozzle rows corresponding to textile printing inks of different colors are installed at intervals in the X direction, and each of the plurality of nozzle rows is composed of a plurality of nozzles N arranged in the Y direction. The Any one nozzle row may be a plurality of nozzles N (for example, a staggered arrangement or a staggered arrangement).

  As illustrated in FIG. 3, the liquid ejecting head 44 includes a plurality of ejecting units 46 corresponding to different nozzles N. Each ejection unit 46 ejects printing ink in accordance with a signal supplied from the drive unit 42. The drive unit 42 of the present embodiment supplies the drive signal COM including the drive pulse W1 and the drive pulse W2 to each of the ejection units 46 that the print signal SI instructs ejection of the plurality of ejection units 46, and the print signal A reference voltage E0 is supplied to each injection unit 46 in which SI instructs non-injection. The ejection unit 46 ejects printing ink from the nozzles N by supplying the drive signal COM. Note that it is also possible to selectively supply a plurality of drive signals COM having different waveforms to the ejection unit 46.

  FIG. 6 is a cross-sectional view focusing on an arbitrary one of the liquid ejecting heads 44. As illustrated in FIG. 6, in the liquid jet head 44, the pressure chamber substrate 72, the vibration plate 73, and the piezoelectric element 74 support body 75 are disposed on one side of the flow path substrate 71, and the nozzle plate 76 is disposed on the other side. Arranged structure. The flow path substrate 71, the pressure chamber substrate 72, and the nozzle plate 76 are formed of, for example, a silicon flat plate material, and the support body 75 is formed of, for example, an injection molding of a resin material.

  A plurality of nozzles N are formed on the nozzle plate 76. The surface of the nozzle plate 76 opposite to the flow path substrate 71 corresponds to the ejection surface F. The ejection surface F and the surface of the medium 22 face each other with an interval G (hereinafter referred to as “working interval”) G therebetween. In a situation where fluff is formed on the surface of the medium 22, the distance between the surface of the medium 22 excluding the fluff and the ejection surface F corresponds to the working interval (working gap) G. As shown in an enlarged view in FIG. 6, one nozzle N is a circular through hole having a diameter φ in a plan view (that is, viewed from a direction perpendicular to the XY plane). In addition, although the straight tubular nozzle N is illustrated in FIG. 6, the diameter of the nozzle N can be changed along the thickness direction of the nozzle plate 76. The diameter φ is the diameter of the nozzle N in the same plane as the ejection surface F (that is, the diameter of the portion of the nozzle N that is closest to the medium 22 in the axial direction).

  In the flow path substrate 71, an opening 712, a branch flow path (restricted flow path) 714, and a communication flow path 716 are formed. The branch flow path 714 and the communication flow path 716 are through holes formed for each nozzle N, and the opening 712 is an opening continuous over a plurality of nozzles N. A space in which the accommodating portion (concave portion) 752 formed in the support body 752 and the opening 712 of the flow path substrate 71 communicate with each other is supplied from the liquid container 24 through the introduction flow path 754 of the support body 75. It functions as a common liquid chamber (reservoir) SR for storing the printing ink.

  An opening 722 is formed for each nozzle N in the pressure chamber substrate 72. The vibration plate 73 is an elastically deformable flat plate that is installed on the surface of the pressure chamber substrate 72 opposite to the flow path substrate 71. A space sandwiched between the diaphragm 73 and the flow path substrate 71 inside each opening 722 of the pressure chamber substrate 72 is filled with the printing ink supplied from the common liquid chamber SR via the branch flow path 714. It functions as a chamber (cavity) SC. Each pressure chamber SC communicates with the nozzle N via the communication channel 716 of the channel substrate 71.

  A piezoelectric element 74 is formed for each nozzle N on the surface of the diaphragm 73 opposite to the pressure chamber substrate 72. Each piezoelectric element 74 is a driving element in which a piezoelectric body 744 is interposed between the first electrode 742 and the second electrode 746. One injection unit 46 illustrated in FIG. 3 is a part including the piezoelectric element 74, the diaphragm 73, the pressure chamber SC, and the nozzle N. The output signal (drive signal COM or reference voltage E0) of the drive unit 42 is supplied to one of the first electrode 742 and the second electrode 746 of the piezoelectric element 74, and the reference voltage E0 is supplied to the other. When the diaphragm 73 is vibrated by the deformation of the piezoelectric element 74 by the supply of the drive signal COM, the pressure in the pressure chamber SC varies and the printing ink in the pressure chamber SC is ejected from the nozzle N. Specifically, the volume of the pressure chamber SC increases (pressure reduction) when a voltage lower than the reference voltage E0 is supplied, and the volume of the pressure chamber SC decreases (pressurization) when a voltage higher than the reference voltage E0 is supplied. The piezoelectric element 74 of this embodiment operates.

  FIG. 7 is an explanatory diagram showing how ink is ejected from an arbitrary nozzle N. FIG. As illustrated in FIG. 7, by supplying a drive pulse W1 of the drive signal COM to the piezoelectric element 74, an ink droplet (first ink droplet) D1 is ejected from the nozzle N, and immediately after that, the drive pulse W2 is applied to the piezoelectric element 74. Ink droplets (second ink droplets) D2 are ejected from the nozzle N. That is, ink droplets D1 and D2 that are separate from each other are ejected from one nozzle N one after another.

  As described above with reference to FIG. 4, since the amplitude A2 of the drive pulse W2 exceeds the amplitude A1 of the drive pulse W1 (A2> A1), the velocity V2 of the ink droplet D2 ejected from the nozzle N is the velocity of the ink droplet D1. It exceeds V1 (V2> V1). Therefore, as illustrated in FIG. 7, before the ink droplet D1 and the ink droplet D2 land on the surface of the medium 22, the ink droplet D2 follows the ink droplet D1, and the space between the ejection surface F and the medium 22. As a result, the ink droplet D1 and the ink droplet D2 are combined (that is, in the air). Specifically, the ink droplet D1 and the ink droplet D2 coalesce within a section QA of about 0.5 mm from the ejection surface F. The combined ink droplets Dm travel at a speed Vm corresponding to the speed V1 and the speed V2 and land on the surface of the medium 22, and penetrate and fix (dry) inside the fiber. Note that the weight of the ink droplet D2 exceeds the weight of the ink droplet D1.

  In the above description, the case where the drive pulse W2 is set to have a larger amplitude A2 compared to the drive pulse W1 has been illustrated, but the configuration for causing the ink droplet D2 to proceed at a velocity V2 exceeding the ink droplet D1 is illustrated above. It is not limited. For example, the ink droplet D2 can be advanced at a speed V2 faster than the ink droplet D1 by making the voltage change rates (gradients) of the driving pulse W1 and the driving pulse W2 different. Further, since the velocity V2 of the ink droplet D2 also depends on the interval δ between the driving pulse W1 and the driving pulse W2, the interval δ may be adjusted so that the velocity V2 of the ink droplet D2 exceeds the velocity V1 of the ink droplet D1. Is possible. As understood from the above description, the drive unit 42 according to the present embodiment is configured so that the ink droplet D1 ejected from the nozzle N and the ink droplet D2 ejected from the nozzle N after the ejection of the ink droplet D1 are applied to the medium 22. It functions as an element that drives the liquid ejecting head 44 so as to be united before landing.

  As described above, in a configuration in which a plurality of ink droplets (ink droplet D1 and ink droplet D2) ejected one after the other are combined before each landing, for example, mist due to tailing of the ink droplet D1 is generated. The ink droplet D1 is combined with the subsequent ink droplet D2. Therefore, generation of mist can be suppressed as compared with a configuration in which a single ink droplet is landed on the medium 22.

  However, an ink containing a penetrating solvent, such as a textile printing ink used in the present embodiment, tends to generate mist more easily than a general ink used for printing on printing paper. Therefore, particularly when the velocity Vm of the combined ink droplet Dm is excessively high, mist may be generated even in the configuration in which the ink droplet D1 and the ink droplet D2 are combined. When mist adheres to the periphery of the nozzle N and ink is deposited (for example, ink attached to the periphery of the nozzle N partially blocks the nozzle N), there is an error in the ejection characteristics such as the ink droplet traveling direction and ejection amount. May occur. In addition, the nozzle N may be partially or wholly blocked by the accumulated mist, and as a result, ink droplets may not be ejected. In other words, the mist can cause an injection failure such as an error in injection characteristics or inability to inject.

  On the other hand, when the speed Vm is decreased (that is, when the kinetic energy of the ink droplet Dm is small), the generation of mist is suppressed, but the thickening of the printing ink and the influence of the airflow are relatively increased. Therefore, there is a problem in that the accuracy of the position where the ink droplet Dm lands on the surface of the medium 22 (hereinafter referred to as “landing accuracy”) decreases. Against the background described above, the inventor of the present application examined the velocity Vm of the ink droplet Dm that can achieve both a reduction in mist and securing of landing accuracy at a high level even in an environment in which a printing ink containing a penetrating solvent is used.

  FIG. 8 is a graph showing the relationship between the diameter (hereinafter referred to as “nozzle diameter”) φ of the nozzle N of the liquid ejecting head 44 and the velocity Vm of the combined ink droplet Dm. Under an environment in which conditions other than the nozzle diameter φ are made common, as understood from FIG. 8, a substantially linear correlation is observed in which the velocity Vm of the ink droplet Dm decreases as the nozzle diameter φ increases. In consideration of the above tendency, in the present embodiment, the nozzle diameter of the liquid ejecting head 44 is set such that the combined ink droplet Dm flies at a speed Vm that can achieve both the above-described reduction of mist and ensuring of landing accuracy. Select φ.

  FIG. 9 shows the velocity Vm of the combined ink droplet Dm, the degree of mist generation (hereinafter referred to as “mist generation amount”) and the landing accuracy, the nozzle diameter φ and the work interval G (the ejection surface F and the surface of the medium 22). Is a result of observation for each of a plurality of cases with different distances. In FIG. 9, it is assumed that acidic yellow printing ink is jetted at 16 kHz over 120 minutes so that the weight of the combined ink droplet Dm is 18 ng.

  The velocity Vm is an average velocity (m / s) of the ink droplet Dm in the section QB in FIG. 7 from 0.5 mm to 1 mm with respect to the ejection surface F. As described above, since the ink droplet D1 and the ink droplet D2 are merged in the interval QA between the interval QB and the ejection surface F, the combined ink droplet Dm advances toward the medium 22 in the interval QB.

  The observation results of the mist generation amount and the landing accuracy are expressed in three stages (good / normal / bad). Regarding the amount of mist generated, the symbol “◯” means a “good” state in which there is little mist adhering to the ejection surface F and no ejection failure due to mist has occurred. The symbol “Δ” means a “normal” state in which a corresponding mist adheres to the injection surface F, although it does not occur until the injection failure. The symbol “x” indicates a “bad” state in which a large amount of mist adheres to the ejection surface F and ejection failure (here, a state in which printing ink cannot be ejected) also occurs.

  On the other hand, the symbol “◯” relating to the landing accuracy means a “good” state in which the ink droplet has landed with high accuracy to such an extent that an error in the landing position can hardly be visually confirmed. The symbol “Δ” indicates that the landing position error can hardly be confirmed by visual inspection if it is limited to printing an image of a natural object such as a landscape, but the landing position error can be confirmed when a regular image such as a ruled line is printed. It means “normal” state. The symbol “x” means a “bad” state in which the landing accuracy is low enough that the deterioration of the image quality can be confirmed visually.

  As described above, the higher the velocity Vm (the smaller the nozzle diameter φ), the easier the mist is generated, and the lower the velocity Vm (the larger the nozzle diameter φ), the lower the landing accuracy. As understood from FIG. 9, in an environment where the work interval G is 4 mm, when the nozzle diameter φ is less than 20 μm (φ <20 μm), the amount of mist generated becomes “defective” and the nozzle diameter φ exceeds 30 μm ( When φ <30 μm), the landing accuracy is “normal” or “bad”. In consideration of the above results, in this embodiment, the nozzle diameter φ is set to a size within the range of 20 μm to 30 μm (20 μm ≦ φ ≦ 30 μm). In the configuration where the nozzle diameter φ is less than 20 μm, the velocity Vm exceeds 10 m / s, and in the configuration where the nozzle diameter φ exceeds 30 μm, the velocity Vm is less than 5 m / s. Accordingly, it can be said that the nozzle diameter φ is set so that the velocity Vm is 5 m / s or more and 10 m / s or less (5 m / s ≦ Vm ≦ 10 m / s).

  Also, in an environment where the work interval G is 4 mm, both the mist generation amount and the landing accuracy are “good” when the nozzle diameter φ is set to 24 μm or 28 μm. Furthermore, in an environment where the working interval G is 5 mm, when the nozzle diameter φ is set to 24 μm, the amount of mist generated is “normal” but the landing accuracy is “good”, and the nozzle diameter φ is set to 28 μm. The mist generation amount and the landing accuracy are both “good”. Considering the above results, a configuration in which the nozzle diameter φ is 24 μm or more and 28 μm or less (24 μm ≦ φ ≦ 28 μm) is suitable, and the nozzle diameter φ is 26 μm or more and 27 μm or less (26 μm ≦ φ ≦ 27 μm). The above configuration is more preferable. For example, in the configuration in which the nozzle diameter φ is set to 27 μm, the speed Vm is 6.5 m / s.

  As can be understood from the comparison between the case where the work interval G is set to 4 mm and the case where the work interval G is set to 5 mm, when the work interval G is reduced, the occurrence of mist and the reduction in landing accuracy are suppressed. On the other hand, when the fibrous medium 22 is to be ejected, it is desirable to ensure a work interval G of 2 mm or more so that the fluff on the surface of the medium 22 does not contact the ejection surface F. In consideration of the above circumstances, a configuration in which the work interval G is set in the range of 2 mm or more and 5 mm or less is desirable (2 mm ≦ G ≦ 5 mm), and work in the range of 2 mm or more and 4 mm or less (2 mm ≦ G ≦ 4 mm) The interval G is more preferable. According to the above configuration, there is an advantage that it is possible to reduce both mist and ensure landing accuracy while reducing the possibility of contact between the medium 22 and the ejection surface F.

  FIG. 10 shows observation results in a configuration in which the liquid ejecting head 44 ejects and lands a single ink droplet (weight: 18 ng) (hereinafter referred to as “proportional”). In other words, a plurality of ink droplets are not merged in contrast. The velocity Vm in FIG. 10 is the velocity of a single ink drop. It can be confirmed from FIG. 10 that the nozzle diameter φ and the velocity Vm at which both the mist generation amount and the landing accuracy are “good” cannot be found in proportion.

  As described above, in this embodiment, since the diameter φ of the nozzle N that ejects the printing ink containing the penetrating solvent is set to 20 μm or more and 30 μm or less, the mist can be reduced as understood from FIG. And ensuring landing accuracy can be achieved at a high level. Particularly in the present embodiment, since the nozzle diameter φ is set to 24 μm or more and 28 μm or less, the effect of being able to achieve both reduction of mist and securing of landing accuracy is particularly remarkable. By reducing the mist, it is possible to suppress injection failures such as errors in injection characteristics and inability to inject. When the speed Vm is excessively slow, the influence of the thickening of the printing ink inside the nozzle N becomes significant, and it is difficult to ensure intermittent capability (ability to maintain proper ejection characteristics even after being left for a long time). There is also the problem of becoming. In the present embodiment, since the nozzle diameter φ is selected so that the speed Vm is a numerical value within an appropriate range, there is an advantage that the intermittent capability can be effectively secured.

  Further, as a result of the combination of the ink droplet D1 and the ink droplet D2, the inertial force is increased as compared with the case where each of the droplets individually fly. Therefore, it is possible to stabilize the flight of the ink droplet Dm. For example, the possibility that the direction of the ink droplet fluctuates due to the influence of the airflow generated in the space between the ejection surface F and the medium 22 or the thickening (or drying) of the printing ink in the vicinity of the nozzle N is reduced. Therefore, for example, it is possible to improve the landing accuracy as compared with the above-described comparison in which a single ink droplet is landed on the medium 22.

<Modification>
The form illustrated above can be variously modified. Specific modifications are exemplified below. Two or more aspects arbitrarily selected from the following examples can be appropriately combined as long as they do not contradict each other.

(1) In the above-described embodiment, two ink droplets D1 and D2 are combined, but three or more ink droplets are combined in the space (working interval G) between the ejection surface F and the medium 22. It is also possible. A configuration in which the nozzle diameter φ is set so that the velocity Vm of the combined ink droplets is 5 m / s or more and 10 m / s or less is suitable regardless of the number of ink droplets to be combined.

(2) In the above-described embodiment, the serial head in which the carriage 342 on which the liquid ejecting unit 40 is mounted moves in the X direction is illustrated, but the present invention is also applied to a line head in which a plurality of liquid ejecting units 40 are arranged in the X direction. Is possible.

(3) The element (driving element) that applies pressure to the inside of the pressure chamber SC is not limited to the piezoelectric element 74 exemplified in the above-described embodiments. For example, a heating element that generates bubbles in the pressure chamber SC by heating to change the pressure can be used as the driving element. As understood from the above examples, the drive element is comprehensively expressed as an element for ejecting liquid (typically, an element that applies pressure to the inside of the pressure chamber SC), and an operation method (piezoelectric method / The heat system) and the specific configuration are not questioned.

DESCRIPTION OF SYMBOLS 100 ... Liquid ejecting apparatus, 10 ... Control unit, 12 ... Drive signal production | generation part, 22 ... Medium, 24 ... Liquid container, 32 ... Conveyance mechanism, 322 ... Supply roller, 324 ... Discharge roller, 34 ... Moving mechanism, 342 ... Carriage 344, conveying belt, 40, liquid ejecting unit, 42, driving unit, 44, liquid ejecting head, 46, ejecting unit, F, ejecting surface, N, nozzle, 71, flow path substrate, 72, pressure chamber substrate, 73 ... vibration plate, 74 ... piezoelectric element, 75 ... support, 76 ... nozzle plate.

Claims (4)

A liquid ejecting head for ejecting a printing ink containing at least a penetrating solvent having a water / octanol distribution coefficient log P of −0.5 or more and 0.5 or less, a colorant and water from a nozzle;
Drive that drives the liquid ejecting head so that the first ink droplet ejected from the nozzle and the second ink droplet ejected from the nozzle after ejection of the first ink droplet are combined before landing on the medium. And comprising
The nozzle has a diameter of 20 μm or more and 30 μm or less. The liquid ejecting apparatus according to claim 1, wherein the nozzle has a diameter of 24 μm or more and 28 μm or less. 3. The liquid ejecting apparatus according to claim 1, wherein a distance between an ejection surface on which the nozzle is installed in the liquid ejecting head and a surface of the medium is 2 mm or more and 5 mm or less. 4. The liquid ejecting apparatus according to claim 1, wherein a content of the penetrating solvent in the textile printing ink is 1% by weight or more and 10% by weight or less.

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