Image formation method

Abstract

The image formation method includes a step of ejecting a solvent-based ink containing an alcohol having 2-4 carbon atoms from a nozzle of an inkjet head. The image formation method includes a step of vibrating the solvent-based ink in the nozzle without ejecting the solvent-based ink. Whether to perform the vibrating step is changed according to the length of a non-ejection time during which the solvent-based ink is not ejected from the nozzle.

Description

Image forming method

[0001] The present invention relates to an image forming method.

[0002] The inkjet method is used in a wide range of applications because it can form images on various base materials including paper, films and the like. On the other hand, when forming an image on a non-absorbent base material such as a film, if the applied ink is not sufficiently dried, the image may be blurred or transferred due to contact with another base material, resulting in degraded image quality. Accordingly, quick-drying ink is in demand.

[0003] Highly volatile ketones and alcohols are used as solvents in quick-drying inks. For example, Patent Document 1 describes an inkjet ink containing an alcohol having 2 to 4 carbon atoms.

[0004] JP 2017-061637 A

[0005] The ink with improved quick-drying property by containing a lower alcohol having 2 to 4 carbon atoms as described in Patent Document 1 not only tends to dry easily on the base material after ejection, but also tends to dry near the nozzle opening before ejection. Depending on the content of print data, there may be a long non-ejection time after the ejection of ink from a certain nozzle is finished until the next start of ink ejection from the same nozzle. When the non-ejection time becomes long, the drying of ink progresses from the nozzle opening, which locally changes liquid physical properties such as surface tension and viscosity, making the liquid physical properties non-uniform within the ink droplets, leading to the problem that ejection stability is deteriorated.

[0006] The present invention has been made in view of the above problem. An object of the present invention is to provide an image forming method capable of improving ejection stability when using highly quick-drying ink.

[0007] One aspect of the present invention for solving the above problems relates to the image forming methods of [1] to

[11] below.

[0008] [1] An image forming method comprising the steps of ejecting a solvent-based ink containing an alcohol having 2 to 4 carbon atoms from a nozzle of an inkjet head, and shaking the nozzle without ejecting the solvent-based ink, wherein the shaking step is changed depending on the length of the non-ejection time during which the solvent-based ink is not ejected from the nozzle.

[0009] [2] The image forming method according to [1], wherein the shaking step is performed when the non-ejection time is shorter than a first predetermined time depending on the composition or characteristics of the solvent-based ink, environmental conditions, or the configuration of the inkjet head.

[0010] [3] The image forming method according to [1], wherein the shaking step is performed when the non-ejection time is longer than a second predetermined time depending on the composition or characteristics of the solvent-based ink, environmental conditions, or the configuration of the inkjet head.

[0011] [4] The image forming method according to [1], wherein the non-ejection time is shorter than a first predetermined time according to the composition or characteristics of the solvent-based ink, environmental conditions, or the configuration of the inkjet head, and longer than a second predetermined time according to the composition or characteristics of the solvent-based ink, environmental conditions, or the configuration of the inkjet head.

[0012] [5] The image forming method according to any one of [2] to [4], wherein the composition of the solvent-based ink is the ratio of the content of the carbon 2 to carbon 4 alcohol to the total mass of the solvent-based ink.

[0013] [6] The image forming method according to any one of [2] to [5], wherein the characteristic of the solvent-based ink is the boiling point of the solvent-based ink.

[0014] [7] The image forming method according to any one of [1] to [6], wherein the boiling point of the solvent-based ink is 140°C or lower.

[0015] [8] The image forming method according to any one of [1] to [7], wherein the inkjet head has piezoelectric elements corresponding to each of the nozzles, the shaking step is performed by applying shaking pulses to the piezoelectric elements, and when AL is 1 / 2 of the acoustic resonance period of the pressure wave in the pressure chamber corresponding to the piezoelectric element, the pulse width of the shaking pulse is 0.75 AL or less.

[0016] [9] The image forming method according to any one of [1] to [8], wherein the inkjet head has piezoelectric elements corresponding to each of the nozzles, the ejection step is performed by applying an ejection pulse to the piezoelectric element, the shaking step is performed by applying a shaking pulse to the piezoelectric element, and the standby voltage before applying the ejection pulse and the standby voltage before applying the shaking pulse are the same voltage.

[0017]

[10] The image forming method according to any one of [1] to [9], wherein the initial ejection speed of the solvent-based ink is 7 m / s or more.

[0018]

[11] The image forming method according to any one of [1] to

[10] , wherein in the ejection step, two or more ink droplets are combined and deposited onto a recording medium.

[0019] Figure 1 is a diagram showing the schematic configuration of an inkjet printer equipped with an inkjet head according to an embodiment. Figure 2 is a block diagram showing the main parts of the control system of the inkjet printer. Figure 3A is a schematic diagram showing the main components of a cross-section of the head chip in the inkjet head along the short direction. Figure 3B is a schematic diagram showing the main components of a cross-section of the head chip in the inkjet head along the longitudinal direction. Figure 4 is a schematic diagram showing the cross-sectional configuration of the pressure chamber forming plate in the inkjet head. Figure 5 is a schematic diagram showing the arrangement configuration of the inkjet heads in the head unit of the inkjet printer. Figure 6 is a schematic diagram showing an example of a drive pulse applied when printing based on a single print data. Figure 7 is an enlarged view of an example of a drive pulse applied when printing based on a single print data.

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0021] 1. Image Forming Method The image forming method according to this embodiment comprises the steps of ejecting a solvent-based ink containing an alcohol with 2 to 4 carbon atoms from a nozzle of an inkjet head, and shaking the nozzle without ejecting the solvent-based ink, wherein the shaking step is changed depending on the length of the non-ejection time during which the solvent-based ink is not ejected from the nozzle.

[0022] In the image forming method according to this embodiment, when a solvent-based ink containing an alcohol with 2 to 4 carbon atoms is used, the shaking process is changed depending on the length of the non-ejection time during which the solvent-based ink is not ejected from the nozzle. The reason why this can improve injection stability is not entirely clear, but it is thought to be as follows.

[0023] For example, when printing on multiple recording media using a single print data, a certain amount of time may be required for the ejection and supply of recording media between printing on one recording media and printing on the next. Also, when printing on a roll-shaped recording media M, the printing time may vary depending on the size of the recording media. In such cases, the non-ejection time between the end of ink ejection from a nozzle and the start of ink ejection from the same nozzle is not constant, and the non-ejection time may be longer or shorter depending on the print data. For example, nozzles located at the edges of the recording media tend to have longer ejection intervals.

[0024] When using fast-drying solvent-based inks containing alcohols with 2 to 4 carbon atoms, depending on the length of the non-discharge time, localized drying of the ink may occur from the nozzle opening. Generally, liquid properties such as surface tension and viscosity change depending on the solid content concentration and temperature of the ink, so the above-mentioned drying causes localized changes in the liquid properties of the ink at the nozzle. This can lead to uneven liquid properties of the solvent-based ink at the nozzle, making injection defects such as bending during ejection more likely and potentially worsening injection stability. Therefore, it is thought that by performing a process of shaking the nozzle without discharging the solvent-based ink (hereinafter simply referred to as the "shaking process"), the solvent-based ink can be appropriately agitated, making it easier to uniformize the liquid properties of the ink and improving injection stability.

[0025] However, depending on the length of the non-ejection time, performing a shaking process without ejecting solvent-based ink sometimes resulted in a deterioration of ejection stability compared to not performing the shaking process. This is thought to be partly due to the heat generated by the power source, such as a piezoelectric element, during the shaking process, causing localized heating of the ink before ejection. In other words, when the non-ejection time is short, drying from the opening is insufficient, and there is almost no non-uniformity of liquid properties due to drying. However, localized heating from the power source can cause non-uniformity of the liquid properties of the ink at the nozzle, potentially worsening the ink ejection stability. Conversely, when the non-ejection time is long, drying from the nozzle opening progresses sufficiently. As a result, while the solid content concentration of the ink at the nozzle becomes relatively uniform, localized heating from the power source can cause non-uniformity of the liquid properties of the ink at the nozzle, potentially worsening the ink ejection stability. Therefore, it is thought that stable ejection of solvent-based ink can be achieved by changing whether or not to apply shaking pulses depending on the length of the non-ejection time.

[0026] The following are examples of methods for changing whether or not to perform the shaking process depending on the length of the non-discharge time during which the solvent-based ink is not discharged from the nozzle: a) Performing the shaking process when the non-discharge time is shorter than a first predetermined time. b) Performing the shaking process when the non-discharge time is longer than a second predetermined time. c) Performing the shaking process when the non-discharge time is shorter than a first predetermined time and longer than a second predetermined time.

[0027] Any of the methods a) to c) described above may be used, but method a) or method b) is preferred, and method c) is more preferred.

[0028] Furthermore, in a) above, it is preferable not to perform the shaking process if the time exceeds the first predetermined time, and in b) above, it is preferable not to perform the shaking process if the time is less than or equal to the second predetermined time. Similarly, in c) above, it is preferable not to perform the shaking process if the time exceeds the first predetermined time and if the time is less than or equal to the second predetermined time.

[0029] In the methods a) to c) above, the first predetermined time and the second predetermined time (hereinafter collectively referred to simply as "predetermined time") are set, for example, by the following method: i) Setting method 1 In setting method 1, parameters that affect the drying of ink from the opening and the amount of heat supplied to the ink from the surrounding members of the pressure chamber are first input to the control unit of the inkjet printer from the operation display unit, etc. This input method may be performed by the operator before each print job, or, for example, if the ink used and the environmental conditions do not change significantly, the input may be performed once before multiple print jobs. Also, for example, if the ink used and the environmental conditions are roughly determined, the input may be performed by the manufacturer before shipment. Furthermore, the inkjet printer may be equipped with a measurement unit for the above parameters, and the results obtained from measurements taken by the measurement unit may be input.

[0030] Examples of the above parameters include the composition of the solvent-based ink (content of pigment, resin, surfactant, C2-C4 alcohol, water, etc., and the model number of the solvent-based ink), the characteristics of the solvent-based ink (viscosity, surface tension, boiling point, etc.), the environmental conditions of the inkjet printer during ejection (temperature, humidity, atmospheric pressure, etc.), and the head configuration (nozzle opening diameter, flow path length, head temperature during ejection, degree of deterioration over time, etc.). Among these, it is preferable to input the composition of the solvent-based ink or the environmental conditions of the inkjet printer during ejection, from the viewpoint of the degree of influence on the drying speed of the solvent-based ink. Furthermore, from the same viewpoint, it is more preferable to input both the composition of the solvent-based ink and the environmental conditions of the inkjet printer during ejection. The input composition of the solvent-based ink is preferably the content ratio of C2-C4 alcohol to the total mass of the solvent-based ink or the boiling point of the solvent-based ink, and more preferably the content ratio of C2-C4 alcohol to the total mass of the ink. Furthermore, the input environmental conditions are preferably the ambient temperature or ambient humidity, and more preferably both ambient temperature and ambient humidity.

[0031] Then, a predetermined time is set based on the above parameters. As a method for setting the predetermined time based on the parameters, the control unit may be pre-stored setting data for the predetermined time corresponding to each parameter, and the predetermined time corresponding to the input parameter may be set based on that setting data. Alternatively, the control unit may be connected to a communication device, and the predetermined time corresponding to the input parameter may be read via the internet or the like to set the predetermined time.

[0032] Furthermore, the environmental conditions of the inkjet printer during ejection may be input as values ​​measured by the operator, or the inkjet printer may be equipped with an environmental condition measurement unit, and the environmental conditions measured by the environmental condition measurement unit may be input.

[0033] For example, when the content of C2-C4 alcohol is 10% to 35% by mass relative to the total mass of the ink, and the temperature is 15°C to 40°C, it is preferable to set the first predetermined time to 10.0 seconds and form the image using the method described in a) above, from the viewpoint of improving injection stability. Furthermore, it is even more preferable to set the first predetermined time to 10.0 seconds and the second predetermined time to 0.5 seconds and form the image using the method described in c) above, from the viewpoint of improving injection stability.

[0034] ii) Setting Method 2 In Setting Method 2, the injection stability is checked in advance by varying the length of the non-ejection time with the solvent-based ink to be used in the printing environment, and an appropriate predetermined time is obtained experimentally. The predetermined time obtained experimentally is then input, and the predetermined time is set. The input method is the same as the input method described in i) Setting Method 1.

[0035] The above examples illustrate i) setting method 1 and ii) setting method 2, but the method for setting the predetermined time is not limited to these.

[0036] First, the inkjet printer used in the image forming method according to this embodiment will be described, and then the method for driving the inkjet head will be described. The inkjet printer described below is an example of an inkjet printer having a piezoelectric element that is driven by the application of a drive pulse, but is not limited to the configuration described below.

[0037] 2. Inkjet Printer Figure 1 is a schematic diagram showing the configuration of an inkjet printer used to form an image in this embodiment, and Figure 2 is a block diagram showing the main part of the control system of the inkjet printer.

[0038] As shown in Figures 1 and 2, the inkjet printer 1 includes a transport unit 10, a supply unit 20, an ejection unit 30, an ink supply unit 40, a drawing unit 50, a drying unit 95, a reading unit 60, an operation display unit 70, an input / output interface 80, and a control unit 90, etc.

[0039] The transport unit 10 has multiple transport components, including a transport belt 11, a drive roller 12, and a driven roller 13. The transport unit 10 transports the recording medium M by the transport operation of the transport belt 11 and other components. Specifically, in the transport unit 10, the transport belt 11 is stretched over the drive roller 12 and the driven roller 13, and is driven by rotating the drive roller 12. As a result, the recording medium M supplied from the supply unit 20 is transported to the drawing unit 50 while placed on the transport surface 11a of the transport belt 11, and after being drawn (also called image formation or printing) in the drawing unit 50, it is transported to the discharge unit 30.

[0040] The recording medium M can be any medium capable of fixing the ink ejected from the inkjet head 55. For example, the recording medium M may be a sheet of paper, cloth, or resin. However, the recording medium M is not limited to a sheet of paper, cloth, or resin; it may also be a roll of paper, cloth, or resin. An example of a resin-based recording medium M is PET film used for food packaging. Other examples of recording medium M that can be used as drawing surfaces include the metal bodies of automobiles, building materials (exterior walls, roofing materials, tiles, etc.), and metal cans (metal cans for storing food and beverages, etc.).

[0041] Figure 1 illustrates a transport unit 10 that transports a recording medium M using a transport belt 11 as an example of an image forming apparatus. However, the transport unit 10 is not limited to a transport belt 11; it may also be configured to transport the recording medium M using drums or rollers.

[0042] The supply unit 20 includes a supply stacking unit 21 for stacking and storing multiple recording media M, a supply transport unit 22 for transporting and supplying the recording media M from the supply stacking unit 21 to the transport unit 10, and the like. The supply stacking unit 21 is configured to be able to move up and down, and when the topmost recording media M is transported to the transport unit 10 by the supply transport unit 22, the supply stacking unit 21 rises so that the recording media M that becomes the topmost after the transport can be transported to the supply transport unit 22.

[0043] The discharge unit 30 includes a discharge stacking unit 31 that stacks and stores a plurality of recording media M, a discharge conveyance unit 32 that conveys the recording media M discharged from the conveyance unit 10 to the discharge stacking unit 31, and the like. The discharge stacking unit 31 is configured to be movable up and down, and when a recording medium M is conveyed from the discharge conveyance unit 32 to the discharge stacking unit 31, the discharge stacking unit 31 descends.

[0044] The supply conveyance unit 22 and the discharge conveyance unit 32 each have, for example, a plurality of rollers, and convey the recording medium M by rotating the rollers. The supply conveyance unit 22 and the discharge conveyance unit 32 are not limited to rollers, and may be configured with belts, or may be configured with a combination of rollers and belts.

[0045] When a roll-shaped medium is used as the recording medium M, instead of the supply stacking unit 21 and the discharge stacking unit 31, an unwinding roller that stores the roll-shaped medium in a wound state or a take-up roller that winds the roll-shaped medium is used. The roll-shaped medium is conveyed to the conveyance unit 10 by rotating the unwinding roller, and is wound onto the take-up roller by rotating the take-up roller.

[0046] Further, a post-processing device that performs post-processing on the recording medium M on which an image has been formed by the image forming unit 50 may be provided between the conveyance unit 10 and the discharge unit 30. One of the post-processing devices is a fixing device that fixes ink to the recording medium M. For example, a fixing device that fixes ink to the recording medium M by a method such as drying is used. Further, as the post-processing device, a device other than the fixing device, for example, a cutting device that cuts the recording medium M into a desired length, or the like may be used.

[0047] Note that the configurations of the conveyance unit 10, the supply unit 20, and the discharge unit 30 can be variously modified and implemented according to the type of the recording medium M that is the drawing target.

[0048] The ink supply unit 40 is a device that supplies ink to a first sub-tank 52a of a drawing unit 50 described later. The ink supply unit 40 includes a main tank 41 and members related to ink supply not shown in the drawings (for example, a pump, a valve, etc.). The main tank 41 stores ink to be supplied to the first sub-tank 52a at room temperature. The ink supply unit 40 supplies ink from the main tank 41 to the first sub-tank 52a via the flow path 42 using a pump or the like (not shown).

[0049] The drawing unit 50 includes a carriage 51, a first sub-tank 52a, a second sub-tank 52b, flow paths 53a, 53b, 53c, a head driving unit 54, an inkjet head 55, and the like (see FIG. 1 and FIG. 2). In the present embodiment, the drawing unit 50 forms an image by applying a solvent-based ink containing an alcohol having 2 to 4 carbon atoms to a recording medium M.

[0050] The solvent-based ink according to the present embodiment is not particularly limited as long as it contains water and an alcohol having 2 to 4 carbon atoms. From the viewpoint of easily enhancing quick-drying properties, the content of the alcohol having 2 to 4 carbon atoms is preferably 10% by mass to 50% by mass, and more preferably 10% by mass to 35% by mass, relative to the total mass of the solvent-based ink. In addition, the boiling point of the solvent-based ink is preferably 140°C or lower.

[0051] Examples of the alcohol having 2 to 4 carbon atoms contained in the solvent-based ink include ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, and the like. Among these, only one type may be used, or two or more types may be used.

[0052] Note that, in FIG. 1, for the sake of simplifying the drawing, the ink supply unit 40 and the drawing unit 50 for one color are illustrated, but the ink supply unit 40 and the drawing unit 50 are arranged according to the number of colors to be used. For example, when four colors of yellow (Y), magenta (M), cyan (C), and black (K) are used, the ink supply unit 40 and the drawing unit 50 for four colors are arranged, and the drawing units 50 are arranged so as to be lined up at predetermined intervals along the transport direction T.

[0053] Furthermore, multiple second sub-tanks 52b and inkjet heads 55 are connected to the downstream side of the first sub-tank 52a, but in Figure 1, for the sake of simplicity, only one of each is shown.

[0054] The carriage 51 is a housing that internally holds the first sub-tank 52a, the second sub-tank 52b, the flow channels 53a, 53b, 53c, the head drive unit 54, the inkjet head 55, and other equipment and components necessary for image formation. The carriage 51 may also have an ink heating unit, although it is not shown in the figures, which heats and maintains the ink inside the carriage 51.

[0055] The first sub-tank 52a is connected to the downstream side of the main tank 41. The first sub-tank 52a stores the ink supplied from the main tank 41 within the carriage 51. The ink in the sub-tank 52 is supplied to the second sub-tank 52b via the flow path 53a using a pump or the like (not shown) within the carriage 51.

[0056] Multiple second sub-tanks 52b are connected downstream of the first sub-tank 52a. The second sub-tanks 52b store the ink supplied from the first sub-tank 52a within the carriage 51. The ink in the second sub-tanks 52b is supplied to the manifold 56 of the inkjet head 55 (described later) via the flow path 53b using a pump or the like (not shown) within the carriage 51. In addition, a portion of the ink supplied to the manifold 56 is recirculated (recovered) to the second sub-tank 52b via the flow path 53c, making it possible to resupply it to the manifold 56. In other words, the ink circulates between the second sub-tank 52b and the manifold 56 via the flow paths 53b and 53c.

[0057] The head drive unit 54 is controlled by the control unit 90 (described later) and outputs drive pulses based on print data to the piezoelectric element 58 of the inkjet head 55 (described later). The piezoelectric element 58 is driven by the drive pulses from the head drive unit 54. The drive pulses include ejection pulses that eject an amount of ink corresponding to the image data from the nozzle 59 of the inkjet head 55 (described later), and oscillating pulses that cause the solvent-based ink to flow slightly without ejection. The oscillating pulses contract or expand the volume of the pressure chamber 57 within a range where only pressure waves are generated without ejection. By oscillating the ink interface near the nozzle 59 with the oscillating pulses, changes in surface tension and viscosity due to temperature changes or changes in solid content concentration due to drying of the ink can be suppressed, and even if a temperature change occurs in part of the ink or part of it dries, the liquid properties can be suppressed from changing unevenly by causing the ink to flow.

[0058] Multiple inkjet heads 55 are connected to the downstream side of each of the multiple second sub-tanks 52b. In other words, multiple second sub-tanks 52b and inkjet heads 55 are connected to the downstream side of the first sub-tank 52a. The inkjet head 55 includes a head chip 110 inside a housing (not shown).

[0059] As shown in Figures 3A and 3B, the head chip 110 is constructed by stacking and bonding multiple substrates (a nozzle plate 111, a pressure chamber forming plate 112 (pressure chamber forming substrate), a drive plate 113, and a housing portion 114, stacked in that order). The head chip 110 has a manifold 56, a pressure chamber 57, a piezoelectric element 58, nozzles 59, and a common supply channel 112a, an individual supply channel 112b, a vertical supply channel 112c, a common discharge channel 112d, an individual discharge channel 112e, and a vertical discharge channel 112f (see Figures 3A, 3B, and 4). The inkjet head 55 has multiple nozzles 59, and the number of pressure chambers 57 and piezoelectric elements 58 is provided according to the number of nozzles 59.

[0060] The nozzle plate 111 is provided with a plurality of nozzles 59 (discharge holes), each of which is a hole that penetrates in the thickness direction (corresponding to the ink discharge direction, which is typically along the vertical direction), arranged in a row along its longitudinal direction.

[0061] A liquid-repellent film 111a is formed on the ink-discharging surface of the nozzle plate 111. The material contained in the liquid-repellent film 111a is not particularly limited, but for example, it is a fluororesin. The thickness of the liquid-repellent film 111a is not particularly limited, but for example, it is 1 nm or more and less than 100 nm.

[0062] The pressure chamber forming plate 112 is provided with a plurality of pressure chambers 57 arranged in a row along its longitudinal direction, each of which is a hole that penetrates in the thickness direction and communicates with a corresponding nozzle 59 (see Figure 5). Furthermore, the pressure chamber forming plate 112 is provided with a common supply channel 112a and an individual supply channel 112b, both located along the row of pressure chambers 57. The pressure chamber forming plate 112 is also provided with a common discharge channel 112d and an individual discharge channel 112e, both located along the row of pressure chambers 57. A vertical supply channel 112c communicating with the manifold 56 is provided at the end of the common supply channel 112a. A vertical discharge channel 112f is provided at the end of the common discharge channel 112d.

[0063] The drive plate 113 has a diaphragm 57c provided on its lower surface (the surface on the pressure chamber forming plate 112 side) and a space 113a positioned opposite the pressure chamber 57 with the diaphragm 57c in between. A piezoelectric element 58 is housed in the space 113a. The piezoelectric elements 58 are positioned opposite the pressure chamber 57 with the diaphragm 57c in between, one for each pressure chamber 57 (one for each nozzle 59).

[0064] The manifold 56 communicates with a plurality of pressure chambers 57 via each supply channel, and the ink supplied to the manifold 56 is supplied to the pressure chambers 57. The pressure chamber 57 is a chamber that has an internal space in which ink ejected from the nozzle 59 can be temporarily stored, either partially or entirely. A piezoelectric element 58 is located at the top of the pressure chamber 57. The nozzle 59 has one end communicating with the pressure chamber 57 and the other end is an open end.

[0065] Each of the multiple pressure chambers 57 is separated by a partition wall 57a. Furthermore, the pressure chambers are separated from the common supply channel 112a and the common discharge channel 112d by a partition wall 57b. Both partition walls 57a and 57b are formed entirely of an electroplatable metal such as nickel (Ni). This increases the rigidity of partition wall 57a, making the inkjet head 55 less susceptible to damage from vibration and providing a more stable structure.

[0066] The piezoelectric element 58 is electrically connected to the head drive unit 54 by electrodes and wiring (not shown). The piezoelectric element 58 is driven in response to drive pulses applied from the head drive unit 54 via the electrodes and wiring, thereby repeatedly generating push-mode type displacements in the diaphragm 57c and pressure chamber 57, and causing fluctuations in the ink pressure. In response to these pressure fluctuations, the ink flows, and when the pressure fluctuations become large, the ink is ejected from the nozzle 59. In other words, the inkjet head 55 according to this embodiment is an inkjet head that performs push-mode type ink ejection. Note that this embodiment is not limited to a push-mode inkjet head. As long as it has a resin part containing the material described later, it may be another type of piezo-type inkjet head such as bend-mode or shear-mode, or a thermal-type inkjet head.

[0067] The positions of the diaphragm 57c and the piezoelectric element 58 are not limited to those shown in Figures 3A and 3B. For example, the diaphragm 57c may be positioned on the nozzle 59 side of the pressure chamber 57, and the piezoelectric element 58 may be positioned on the nozzle 59 side of the diaphragm 57c. Alternatively, the diaphragm 57c may be positioned along the ink flow direction on the side wall of the pressure chamber 57, and the piezoelectric element 58 may be positioned inside the partition wall 57a. The diaphragm 57c and the piezoelectric element 58 may be positioned in any location as long as the pressure chamber can be contracted or expanded.

[0068] The materials of the nozzle plate 111, the pressure chamber forming plate 112, and the drive plate 113 are not particularly limited, and known materials such as silicon (Si), nickel (Ni), stainless steel, and polyimide can be used.

[0069] The housing portion 114 is provided with a manifold 56 that extends along the longitudinal direction of the inkjet head 55, and through which all of the multiple pressure chambers 57 communicate at the upstream end. The housing portion 114 may be made of a resin substrate such as polyimide, or a metal substrate such as SUS.

[0070] In the carriage 51, the inkjet head 55 may be configured to operate in a single-pass (one-pass) manner, where an image is formed in a single scan, or in a multi-pass (scan) manner, where an image is formed in multiple scans. In the single-pass manner, the carriage 51 has an equal number of inkjet heads 55 corresponding to the image formation width in the width direction of the recording medium M (in the direction perpendicular to the transport direction T of the recording medium M) (see Figure 5). As shown in Figure 5, the multiple inkjet heads 55 are arranged in one or more rows with their longitudinal direction aligned along the width direction of the recording medium M, and in each inkjet head 55, the multiple nozzles 59 are arranged linearly or in a grid along the longitudinal direction of the inkjet head 55.

[0071] The drying unit 95 is located downstream of the drawing unit 50 in the transport direction T of the recording medium M, and heats and dries the ink applied to the recording medium M. The drying unit 95 is connected to the control unit 90 (see Figure 2) and controlled by the control unit 90.

[0072] For example, the drying unit 95 has an infrared heater or the like, and power is supplied to the infrared heater based on a control signal supplied from the control unit 90, causing the infrared heater to heat up and dry the ink. The heating conditions of the drying unit 95 can be any conditions that allow the solvent-based ink of this embodiment to dry. Also, if the ink dries sufficiently, the inkjet printer 1 does not need to have a drying unit 95.

[0073] The reading unit 60 is positioned downstream of the drawing unit 50 and the drying unit 95 in the transport direction T of the recording medium M, and reads the image (for example, a predetermined pattern image) formed on the recording medium M that is transported by the transport belt 11. The reading unit 60 outputs the reading result of the predetermined pattern image to the control unit 90. Based on the reading result, the control unit 90 changes the image formation conditions, for example, the image formation position and the driving conditions of the inkjet head 55.

[0074] Although not shown in the diagram, the inkjet printer 1 is also equipped with a maintenance unit for performing maintenance such as cleaning the inkjet head 55.

[0075] The operation display unit 70 is, for example, a flat panel display such as a liquid crystal or organic EL (Electro Luminescence) with a touch panel. The operation display unit 70 displays operation menus for the user, information related to print data, various statuses of the inkjet printer 1, etc. The operation display unit 70 also has multiple keys and can accept parameters as exemplified in i) setting method 1 above, predetermined time periods as shown in ii) setting method 2 above, or various user input operations.

[0076] The environmental status of the inkjet printer may be input to the control unit 90 without going through the operation display unit 70 by providing an environmental status measurement unit (not shown) in the inkjet printer 1.

[0077] The input / output interface 80 mediates the transmission and reception of data between the external device 99 and the control unit 90. The input / output interface 80 is composed of, for example, various serial interfaces, various parallel interfaces, or a combination thereof.

[0078] The external device 99 is, for example, a personal computer or a facsimile machine, and supplies print jobs, image data, etc., to the control unit 90 via the input / output interface 80.

[0079] The control unit 90 includes a CPU (Central Processing Unit) 91, RAM (Random Access Memory) 92, ROM (Read Only Memory) 93, a storage unit 94, etc. The control unit 90 may also have a communication device (not shown) and may be connected to the Internet or the like. When parameters as exemplified in i) setting method 1 are input from the operation display unit 70 etc., and a predetermined time is set, the predetermined time corresponding to the input parameters may be read via the Internet or the like and the predetermined time may be set.

[0080] The CPU 91 reads various control programs and setting data stored in the ROM 93, stores them in the RAM 92, and executes the programs to perform various calculations. For example, the control unit 90 generates a drive signal for the image to be formed based on the image data received from the input / output interface 80 and outputs it to the inkjet head 55.

[0081] RAM 92 provides the CPU 91 with a working memory space and stores temporary data. RAM 92 may also include non-volatile memory.

[0082] ROM 93 stores various control programs and setting data executed by the CPU 91. This setting data may include setting data for predetermined times corresponding to each parameter exemplified in setting method 1. Alternatively, a rewritable non-volatile memory such as EEPROM (Electrically Erasable Programmable Read Only Memory) or flash memory may be used instead of ROM 93.

[0083] The storage unit 94 stores print jobs and image data related to print jobs that are input from an external device 99 via the input / output interface 80. For the storage unit 94, for example, a non-volatile semiconductor memory (so-called flash memory) or an HDD (Hard Disk Drive) may be used, and DRAM (Dynamic Random Access Memory) may also be used in combination.

[0084] The control unit 90 is connected to the transport unit 10, supply unit 20, discharge unit 30, ink supply unit 40, drawing unit 50, reading unit 60, operation display unit 70, input / output interface 80, drying unit 95, etc. The control unit 90 provides overall control over the operation of the inkjet printer 1. The transport unit 10, supply unit 20, discharge unit 30, ink supply unit 40, drawing unit 50, reading unit 60, operation display unit 70, input / output interface 80, drying unit 95, etc. are controlled by the control unit 90 to perform predetermined processes.

[0085] The inkjet printer 1 having the above configuration supplies the recording medium M from the supply unit 20 to the transport unit 10 under the control of the control unit 90, draws on the recording medium M transported to the transport unit 10 with the drawing unit 50, and transports the image-formed recording medium M to the discharge unit 30.

[0086] 3. Method for Driving the Inkjet Head The method for driving the inkjet head 55 according to the image forming method according to this embodiment will be explained with reference to Figures 6 and 7.

[0087] In the driving method of the inkjet head 55 according to this embodiment, a voltage signal (driving pulse) of a composite driving waveform, which is a combination of multiple unit driving waveforms, is used. By applying this driving pulse to the piezoelectric element 58, displacement is repeatedly generated in the diaphragm 57c and the pressure chamber 57, thereby fluctuating the ink pressure.

[0088] In the image forming method according to this embodiment, the step of ejecting a solvent-based ink containing an alcohol having 2 to 4 carbon atoms from the nozzle of an inkjet head is performed by applying an ejection pulse to a piezoelectric element. Furthermore, the step of agitating the solvent-based ink in the nozzle is performed by applying an agitation pulse to the piezoelectric element. In this application, the "drive pulse" includes an "ejection pulse" that ejects the ink and an "agitation pulse" that causes the solvent-based ink in the nozzle to flow slightly without ejecting it, thereby agitating the solvent-based ink.

[0089] Figure 6 shows an example of a drive pulse applied when printing based on certain print data, as a potential ratio with a reference potential of 0 and the lowest negative potential of -1. In this example, the time it takes to print one piece of print data includes an ejection time when the ejection pulse WF is applied and non-ejection times 1 to 3 when the ejection pulse WF is not applied. Figure 6 shows an example of "c) a method of performing a shaking process when the non-ejection time is shorter than the first predetermined time and longer than the second predetermined time." In this example, non-ejection time 1 is less than or equal to the second predetermined time, non-ejection time 2 is greater than or equal to the first predetermined time, and non-ejection time 3 is shorter than the first predetermined time and longer than the second predetermined time. The shaking pulse WF is applied only during non-ejection period 3. The reference potential represents the potential during standby immediately before applying the ejection pulse.

[0090] The ejection pulse WF in Figure 6 includes two first unit drive waveforms W1 that eject individual ink droplets, and two second unit drive waveforms W2 that are applied after these first unit drive waveforms W1 and eject individual ink droplets (hereinafter, when referring to either the first unit drive waveform W1 or the second unit drive waveform W2, it will be written as "unit drive waveform Wn"). Therefore, the ejection pulse WF in Figure 6 includes four unit drive waveforms Wn, and by applying this ejection pulse WF to the piezoelectric element 58, the four ink droplets ejected from the nozzle 59 can be combined and landed on the recording medium M.

[0091] Furthermore, the ejection pulse WF may be applied in such a way that it omits the first two first unit drive waveforms W1 and includes the remaining two second unit drive waveforms W2, thereby merging two droplets and landing them on the recording medium M. Alternatively, the ejection pulse may be applied as a composite drive waveform WF that includes only the last second unit drive waveform W2, thereby landing one droplet on the recording medium M. Of these, it is preferable to merge two or more droplets and land them on the recording medium M. When two or more droplets are merged, even if the liquid properties inside the first droplet are non-uniform, the second droplet will be an ink droplet with uniform liquid properties that has not yet dried. Therefore, even if an ejection failure occurs in the first droplet, it is thought that the ejection failure in the first droplet can be corrected by the stable ejection of the second and subsequent droplets.

[0092] In Figure 6, the first two first unit drive waveforms W1 of the discharge pulse WF constitute the repeating waveform WA. Furthermore, the last two second unit drive waveforms W2 of the discharge pulse WF constitute the termination waveform WB. Therefore, the final unit drive waveform in the composite drive waveform WF is the second unit drive waveform W2.

[0093] With the ejection pulse WF of this embodiment, each droplet of ink ejected from the nozzle 59 can be made to be unified at the time of ejection. That is, four droplets are ejected from the nozzle 59 in a columnar arrangement and land on the recording medium M without separating during flight.

[0094] In the following sections, the configuration and operation of the oscillation pulse WS, the repeating waveform WA, and the termination waveform WB will be explained using Figure 7.

[0095] 3-1. Oscillating Pulse WS Figure 7 is an enlarged view of a portion of the oscillating pulse WS. The oscillating pulse WS contains multiple unit oscillating pulses P0, and Figure 7 shows the last two unit oscillating pulses P0 during the non-discharge time of 3.

[0096] A unit oscillation pulse P0 includes an expansion portion S1 in which the potential decreases, and a contraction portion S2 in which the potential increases after the expansion portion S1. In the expansion portion S1 of the unit oscillation pulse P0, the piezoelectric element 58 fluctuates so that the pressure chamber 57 expands, and in the subsequent contraction portion S2, the piezoelectric element 58 fluctuates so that the pressure chamber 57 contracts in a direction that returns it to its original shape.

[0097] By performing the expansion and contraction of the pressure chamber 57 at a timing that makes it difficult for resonance of the pressure wave within the pressure chamber 57 to occur, pressure is less likely to be applied to the ink within the pressure chamber 57, and ink is less likely to be ejected from the nozzle 59. Specifically, when AL (Acoustic Length) is set to 1 / 2 of the acoustic resonance period of the pressure wave within the pressure chamber 57, the pulse width pw0 of the unit oscillation pulse P0 is preferably 0.75AL or less, and more preferably 0.50AL to 0.75AL. Note that AL is a value determined by the structure of the inkjet head and is usually about a few microseconds. Furthermore, the length from the start timing of the expansion portion S1 to the start timing of the contraction portion S2 in the unit oscillation pulse P0 is defined as the pulse width pw0 of the unit oscillation pulse P0.

[0098] The interval wt0 between unit oscillation pulses P0 is preferably 0.20 AL to 0.50 AL, from the viewpoint of easily improving injection stability.

[0099] Furthermore, the voltage amplitude ΔV0 of the unit oscillation pulse P0 is preferably 0.05 to 0.35 as a voltage ratio. If it is 0.05 or higher, the solvent-based ink is appropriately stirred in the nozzle, which tends to improve injection stability. If it is 0.35 or lower, it tends to suppress accidental ink ejection.

[0100] Furthermore, from the viewpoint of reducing power consumption, it is preferable to make the standby voltage before applying the oscillation pulse the same as the standby voltage before applying the discharge pulse described later.

[0101] When applying a vibration pulse, it is preferable to apply a unit vibration pulse P0 periodically at regular intervals to facilitate improved injection stability.

[0102] 3-2. Repeating waveform WA Figure 7 is a magnified view of the repeating waveform WA.

[0103] Each of the two first unit drive waveforms W1 included in the repeating waveform WA includes a main pulse P1 (first pulse waveform) that ejects an ink droplet from the nozzle 59, and a pull-back pulse P2 (second pulse waveform) that pulls back the ink droplet ejected by the main pulse P1 in the opposite direction to the ejection direction. The combination of the main pulse P1 and the pull-back pulse P2 ejects one ink droplet from the nozzle 59.

[0104] The main pulse P1 includes an expansion portion S1 in which the potential decreases, and a contraction portion S2 in which the potential increases after the expansion portion S1. In the expansion portion S1 of the main pulse P1, the piezoelectric element 58 fluctuates so that the pressure chamber 57 expands, and in the subsequent contraction portion S2, the piezoelectric element 58 fluctuates so that the pressure chamber 57 contracts in the direction of returning to its original shape. By performing this expansion and contraction of the pressure chamber 57 at the timing when resonance occurs in the pressure wave within the pressure chamber 57, pressure is applied to the ink in the pressure chamber 57 and the ink is ejected from the nozzle 59.

[0105] The length from the start timing of the expansion portion S1 to the start timing of the contraction portion S2 in the main pulse P1 is defined as the pulse width of the main pulse P1. The pulse width of the main pulse P1 is preferably 0.7 AL to 1.0 AL, and more preferably 0.7 AL to 0.9 AL.

[0106] On the other hand, the pull-back pulse P2 also includes an expansion portion S1 and a contraction portion S2, similar to the main pulse P1. The length from the start timing of the expansion portion S1 to the start timing of the contraction portion S2 in the pull-back pulse P2 is defined as the pulse width (pw21, pw22) of the pull-back pulse P2. The pulse width of the pull-back pulse P2 is preferably 0.3AL to 0.6AL. It is also preferable that it be set within a range shorter than the pulse width of the pulse waveform of the main pulse P1.

[0107] Furthermore, the waiting time wt1 between pulse width pw11 and pulse width pw21 is, for example, 0.2 AL, the waiting time wt2 between pulse width pw21 and pulse width pw12 is, for example, 0.3 AL, and the waiting time wt3 between pulse width pw12 and pulse width pw22 is, for example, 0.4 AL.

[0108] By applying the expansion portion S1 of the pull-back pulse P2 at the timing to suppress the reverberation vibration caused by the main pulse P1, the pressure chamber 57 is expanded, thereby applying a force to the ink droplet in the direction of pulling it back. This allows the ink droplet ejected by the main pulse P1 to be decelerated.

[0109] Furthermore, as the ink droplet is pulled back by the pull-back pulse P2, the meniscus, which had retracted to the back side of the nozzle 59 (opposite side from the ejection direction) due to the influence of the main pulse P1, can be advanced toward the opening of the nozzle 59. By advancing the meniscus in this way, the amount of ink droplet ejected by the next unit drive waveform Wn can be increased, and the velocity of the droplet can be suppressed in accordance with the increase in droplet volume. In addition, because the advancement of the meniscus brings the position of the meniscus closer to the steady position, it is possible to stably eject droplets of the desired amount and velocity even when ejecting ink at high frequencies.

[0110] Furthermore, the first unit drive waveform W1 is a waveform in which the potential changes within a range below the reference potential. Specifically, in the expansion portion S1 of the first main pulse P1 of the repeating waveform WA, the voltage ratio is reduced to -1.0, and then the potential is gradually increased upwards over the two first unit drive waveforms W1, returning to the reference potential at the end of the repeating waveform WA. Focusing on the maximum potential of each contraction portion S2, the maximum potential of the contraction portion S2 in the first main pulse P1 of the repeating waveform WA is the lowest, and the maximum potential of the contraction portion S2 in the subsequent pull-back pulse P2, main pulse P1, and pull-back pulse P2 increases in order, with the contraction portion S2 in the final pull-back pulse P2 ending at the reference potential.

[0111] Due to the potential transition within this repeating waveform WA, the voltage amplitude ΔV1 of the contracted portion S2 of the pull-back pulse P2 is kept small in the first unit drive waveform W1. This suppresses the acceleration of the ink due to the contraction of the pressure chamber 57 corresponding to the contracted portion S2 of the pull-back pulse P2. As a result, it is possible to make the velocity of the ink droplets ejected by the combination of the main pulse P1 and the pull-back pulse P2 in the first unit drive waveform W1 extremely low. The velocity of the ink droplets ejected by the first unit drive waveform W1 is, for example, about 1 m / sec.

[0112] The potential at the end of each repeating waveform WA is always at the reference potential. By returning to the reference potential in this way, it is easy to apply the same repeating waveform WA two or more times.

[0113] Furthermore, it is preferable that the repeating waveform WA be adjusted so that its overall length is within the range of 3.5 AL to less than 4.5 AL, and more preferably so that its waveform is within the range of 3.7 AL to 4.3 AL. This allows the pressure wave in the nozzle 59 at the end of the preceding repeating waveform WA to accelerate the ink ejected by the subsequent waveform, thereby making it easier to suppress the occurrence of problems where the droplet velocity of the subsequently ejected ink is too low and the droplets cannot coalesce. Note that as long as the length of the repeating waveform WA satisfies the above conditions, the lengths of each first unit drive waveform W1 included in the repeating waveform WA do not have to be equal.

[0114] 3-3. Termination Waveform WB Figure 7 is an enlarged view of the termination waveform WB.

[0115] The two second unit drive waveforms W2 included in the termination waveform WB each include a main pulse P1 and a pull-back pulse P2, similar to the first unit drive waveform W1. The main pulse P1 and pull-back pulse P2 of the second unit drive waveform W2 also include an expansion portion S1 and a contraction portion S2, respectively. In the second unit drive waveform W2 as well, a single ink droplet is ejected from the nozzle 59 by the combination of the main pulse P1 and the pull-back pulse P2.

[0116] The pulse width of the main pulse P1 in the second unit drive waveform W2 is preferably 0.7AL to 1.0AL, and more preferably 0.7AL to 0.9AL, similar to the first unit drive waveform W1. Furthermore, the pulse width of the main pulse P1 in the second unit drive waveform W2 is set to be greater than or equal to the pulse width of the main pulse P1 in the first unit drive waveform W1.

[0117] Furthermore, the pulse width of the main pulse P1 in each second unit drive waveform W2 may be greater than any of the pulse widths of the main pulse P1 in the first unit drive waveform W1.

[0118] Furthermore, the pulse width pw23 of the pull-back pulse P2 in the first second unit drive waveform W2 can be, for example, 0.5AL, and the pulse width pw24 of the pull-back pulse P2 in the second second unit drive waveform W2 can be, for example, 0.4AL.

[0119] Furthermore, the waiting time wt4 between pulse widths pw13 and pw23 can be, for example, 0.5AL, and the waiting time wt5 between pulse widths pw23 and pw14 can be, for example, 0.6AL. The waiting time wt6 between pulse widths pw14 and pw24 can be, for example, 0.5AL. Each waiting time wt4 to wt6 in the termination waveform WB can be longer than any of the waiting times wt1 to wt3 in the repeating waveform WA.

[0120] Furthermore, the voltage amplitude ΔV2 of the contracted portion S2 of the pull-back pulse P2 in the second unit drive waveform W2 is greater than the voltage amplitude ΔV1 of the contracted portion S2 of the pull-back pulse P2 in the first unit drive waveform W1. For example, ΔV2 can be set to 1.1.

[0121] Furthermore, in order to ensure such a voltage amplitude ΔV2, in the second unit drive waveform W2, a portion of the pull-back pulse P2 is higher than the reference potential. That is, the contraction portion S2 of the pull-back pulse P2 is displaced to a potential exceeding the reference potential.

[0122] By increasing the voltage amplitude ΔV2 in this way, the ink ejected by the main pulse P1 is greatly accelerated by the contraction of the pressure chamber 57 corresponding to the contraction portion S2 of the pull-back pulse P2. This increases the velocity of the ink droplets ejected by the second unit drive waveform W2, making it easier for them to catch up with the ink droplets ejected earlier by the first unit drive waveform W1. The initial ejection speed of the ink ejected by the second unit drive waveform W2 is preferably 7 m / sec or more, and more preferably 7 m / sec to 20 m / sec.

[0123] As described above, the embodiment described provides an image forming method that can improve injection stability when using a fast-drying ink.

[0124] The embodiments described above are merely examples of how the present invention may be implemented, and the technical scope of the invention should not be interpreted as being limited by them. In other words, the present invention can be implemented in various forms without departing from its gist or its main features.

[0125] This application claims priority under Japanese Patent Application No. 2025-068690, filed on 18 April 2025. All provisions of the said application are incorporated herein by reference.

[0126] The present invention provides an image forming method that can improve injection stability when using a fast-drying ink.

[0127] 1 Inkjet printer 10 Transport unit 11 Transport belt 11a Transport surface 12 Drive roller 13 Driven roller 20 Supply unit 21 Storage unit 22 Unwinding roller 30 Discharge unit 31 Storage unit 32 Take-up roller 40 Ink supply unit 41 Main tank 42 Flow path 50 Drawing unit 51 Carriage 52a First sub-tank 52b Second sub-tank 53a, 53b, 53c Flow path 54 Head drive unit 55 Inkjet head 56 Manifold (common supply flow path) 57 Pressure chamber 57a, 57b Partition wall 57c Diaphragm 58 Piezoelectric element 59 Nozzle 60 Reading unit 70 Operation display unit 80 Input / output interface 90 Control unit 91 CPU 92 RAM 93 ROM 94 Storage unit 95 Drying section 99 External device 110 Head tip 111 Nozzle plate 111a Liquid-repellent film 112 Pressure chamber forming plate 112a Common supply channel 112b Individual supply channel 112c Vertical supply channel 112d Common discharge channel 112e Individual discharge channel 112f Vertical discharge channel 113 Drive plate 113a Space 113c Vertical supply channel 113f Vertical discharge channel 114 Housing section M Recording medium P0 Unit oscillation pulse P1 Main pulse (first pulse waveform) P2 Pullback pulse (second pulse waveform) S1 Expansion section S2 Contraction section W0 Oscillation waveform W1 First unit drive waveform W2 Second unit drive waveform WA Repeat waveform WB Termination waveform WF Discharge pulse WS Oscillation pulse

Claims

1. An image forming method comprising the steps of: ejecting a solvent-based ink containing an alcohol with 2 to 4 carbon atoms from a nozzle of an inkjet head; and shaking the nozzle without ejecting the solvent-based ink, wherein the shaking step is changed depending on the length of the non-ejection time during which the solvent-based ink is not ejected from the nozzle.

2. The image forming method according to claim 1, wherein the shaking step is performed when the non-ejection time is shorter than a first predetermined time depending on the composition or characteristics of the solvent-based ink, environmental conditions, or the configuration of the inkjet head.

3. The image forming method according to claim 1, wherein the shaking step is performed when the non-ejection time is longer than a second predetermined time depending on the composition or characteristics of the solvent-based ink, environmental conditions, or the configuration of the inkjet head.

4. The image forming method according to claim 1, wherein the shaking step is performed when the non-ejection time is shorter than a first predetermined time depending on the composition or characteristics of the solvent-based ink, environmental conditions, or the configuration of the inkjet head, and longer than a second predetermined time depending on the composition or characteristics of the solvent-based ink, environmental conditions, or the configuration of the inkjet head.

5. The image forming method according to any one of claims 2 to 4, wherein the composition of the solvent-based ink is the ratio of the content of the carbon-2 to carbon-4 alcohol to the total mass of the solvent-based ink.

6. The image forming method according to any one of claims 2 to 4, wherein the characteristic of the solvent-based ink is the boiling point of the solvent-based ink.

7. The image forming method according to any one of claims 2 to 4, wherein the boiling point of the solvent-based ink is 140°C or lower.

8. The image forming method according to any one of claims 1 to 4, wherein the inkjet head has piezoelectric elements corresponding to each of the nozzles, the shaking step is performed by applying shaking pulses to the piezoelectric elements, and when AL is half the acoustic resonance period of the pressure wave in the pressure chamber corresponding to the piezoelectric element, the pulse width of the shaking pulse is 0.75 AL or less.

9. The image forming method according to any one of claims 1 to 4, wherein the inkjet head has piezoelectric elements corresponding to each of the nozzles, the ejection step is performed by applying ejection pulses to the piezoelectric elements, the shaking step is performed by applying shaking pulses to the piezoelectric elements, and the standby voltage before applying the ejection pulses and the standby voltage before applying the shaking pulses are the same voltage.

10. The image forming method according to any one of claims 1 to 4, wherein the initial ejection speed of the solvent-based ink is 7 m / s or more.

11. The image forming method according to any one of claims 1 to 4, wherein in the ejection step, two or more ink droplets are combined and deposited onto a recording medium.

Images