Inkjet printer, method for adjusting same, and program

Abstract

The present invention provides: an inkjet printer which secures ejection performance of an inkjet head that has a non-fluorine-based liquid repellent film; a method for adjusting the same; and a program. An inkjet printer according to the present disclosure comprises an inkjet head in which a nozzle for ejecting an ink is disposed on a nozzle surface. The inkjet head has one of a fluorine-based liquid repellent film and a non-fluorine-based liquid repellent film on the nozzle surface. The pressure of the ink in the nozzle of the inkjet head when printing an image is set to a first pressure in cases where the nozzle surface has a fluorine-based liquid repellent film, while the pressure of the ink is set to a second pressure that is lower than the first pressure in cases where the nozzle surface has a non-fluorine-based liquid repellent film.

Description

Inkjet printing apparatus, adjustment method thereof, and program

[0001] The present invention relates to an inkjet printing apparatus, an adjustment method thereof, and a program, and particularly relates to a technique using an inkjet head having a non-fluorine-based liquid repellent film.

[0002] An inkjet head that discharges ink from nozzles onto a substrate is known. In order to maintain the discharge performance of the ink, a liquid repellent film is provided on the nozzle surface where the nozzles are arranged on the inkjet head.

[0003] For example, in Patent Document 1, as a specific example of the liquid repellent treatment of the ink discharge surface of a nozzle plate on which nozzles are formed, a liquid repellent film is formed by performing a vapor deposition treatment using a fluorine-containing organic liquid repellent material as a vapor deposition raw material on the ink discharge surface.

[0004] Japanese Patent Application Laid-Open No. 2013-199021

[0005] The "fluorine-based liquid repellent film" used as the liquid repellent film of the inkjet head is becoming unavailable due to PFAS (Per- and PolyFluoroAlkyl Substances) regulations. As a result, replacement with an inkjet head provided with a "non-fluorine-based liquid repellent film" is being promoted.

[0006] . However, the non-fluorine-based liquid repellent film is inferior in liquid repellency to the fluorine-based liquid repellent film. As a result, in an inkjet head having a non-fluorine-based liquid repellent film, the return of the ink overflowing from the nozzles into the nozzles during ink discharge is relatively poor, and the discharge tends to become unstable when continuously discharging ink.

[0007] The present invention has been made in view of such circumstances, and an object thereof is to provide an inkjet printing apparatus, an adjustment method thereof, and a program that ensure the discharge performance of an inkjet head having a non-fluorine-based liquid repellent film.

[0008] To achieve the above objective, an inkjet printing apparatus according to a first aspect of the present disclosure is an inkjet printing apparatus that prints an image by ejecting ink onto a substrate, comprising an inkjet head on which nozzles for ejecting ink are arranged on the nozzle surface, the inkjet head having one of a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film on the nozzle surface, and the ink pressure of the nozzles of the inkjet head when printing an image is set to a first pressure when the nozzle surface has a fluorine-based liquid-repellent film, and to a second pressure that is smaller than the first pressure when the nozzle surface has a non-fluorine-based liquid-repellent film.

[0009] According to this embodiment, the ejection performance of an inkjet head having a non-fluorine-based liquid-repellent film can be ensured.

[0010] In the inkjet printing apparatus according to the second aspect of this disclosure, it is preferable that the non-fluorine-based liquid-repellent film comprises at least one of silicone, hydrocarbon, metal oxide, and hydrophobic metal, in the inkjet printing apparatus according to the first aspect.

[0011] In the inkjet printing apparatus according to the third aspect of this disclosure, in the inkjet printing apparatus according to the first or second aspect, it is preferable that the difference between the first pressure and the second pressure exceeds 500 [Pa]. It is preferable that the difference between the first pressure and the second pressure is 2500 [Pa] or less.

[0012] In the inkjet printing apparatus according to the fourth aspect of this disclosure, it is preferable that the static contact angle of the fluorine-based liquid-repellent film with respect to the ink is greater than the static contact angle of the non-fluorine-based liquid-repellent film with respect to the ink, in the inkjet printing apparatus according to any of the first to third aspects.

[0013] In the inkjet printing apparatus according to the fifth aspect of this disclosure, it is preferable that the dynamic contact angle of the fluorine-based liquid-repellent film with respect to the ink is greater than the dynamic contact angle of the non-fluorine-based liquid-repellent film with respect to the ink, in the inkjet printing apparatus according to any of the first to fourth aspects.

[0014] In the inkjet printing apparatus according to the sixth aspect of this disclosure, in the inkjet printing apparatus according to any of the first to fifth aspects, it is preferable that the static surface tension of the ink is 38.0 [mN / m] or less. The static surface tension of the ink is preferably 21.0 [mN / m] to 38.0 [mN / m], more preferably 23.0 [mN / m] to 33.0 [mN / m], and even more preferably 24.0 [mN / m] to 30.0 m [mN / m]. The static surface tension is the value measured using an automatic surface tension meter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

[0015] In the seventh aspect of this disclosure, the inkjet printing apparatus is preferably an active energy ray curable ink, in which the ink is an active energy ray curable ink that hardens upon irradiation with active energy rays, in any of the first to sixth aspects of this disclosure.

[0016] In the eighth aspect of this disclosure, the inkjet printing apparatus is preferably an aqueous ink in any of the first to sixth aspects.

[0017] In the inkjet printing apparatus according to the ninth aspect of this disclosure, in the inkjet printing apparatus according to any of the first to eighth aspects, the ink ejection frequency of the inkjet head is preferably 50 kHz or higher. More preferably, the ink ejection frequency of the inkjet head is 75 kHz or higher, and even more preferably 100 kHz or higher. It is preferable that the ink ejection frequency of the inkjet head is 150 kHz or lower.

[0018] In the inkjet printing apparatus according to the tenth aspect of this disclosure, in the inkjet printing apparatus according to any of the first to ninth aspects, it is preferable that the inkjet head is equipped with a memory for storing information on the liquid-repellent film. The inkjet printing apparatus may read the information on the liquid-repellent film from the memory and determine whether the nozzle surface of the inkjet head has a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film.

[0019] An inkjet printing apparatus according to the eleventh aspect of this disclosure is an inkjet printing apparatus according to any of the first to tenth aspects, wherein the processor preferably sets the ink pressure of the nozzles of the inkjet head when printing an image to a first pressure if the nozzle surface has a fluorine-based liquid-repellent film, and to a second pressure if the nozzle surface has a non-fluorine-based liquid-repellent film. The processor may also determine whether the nozzle surface of the inkjet head has a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film.

[0020] In the twelfth aspect of this disclosure, the inkjet printing apparatus preferably comprises a plurality of inkjet heads, wherein the plurality of inkjet heads constitute a print bar that ejects one color of ink, in addition to the inkjet printing apparatus according to any of the first to eleventh aspects.

[0021] An inkjet printing apparatus according to a thirteenth aspect of the present disclosure is an inkjet printing apparatus according to a twelfth aspect, further comprising a plurality of supply channels for supplying ink to a plurality of inkjet heads, wherein the flow resistance of the supply channels when printing an image is preferably such that the flow resistance of the supply channels is a first flow resistance for supplying ink to an inkjet head whose nozzle surface has a fluorine-based liquid-repellent film, and the flow resistance of the supply channels for supplying ink to an inkjet head whose nozzle surface has a non-fluorine-based liquid-repellent film is a second flow resistance that is greater than the first flow resistance.

[0022] In the inkjet printing apparatus according to the 14th aspect of this disclosure, it is preferable that the inkjet printing apparatus according to the 12th or 13th aspect comprises a plurality of print bars each ejecting ink of a different color, and prints an image in a single-pass manner by moving the plurality of print bars and the substrate in the relative movement direction.

[0023] To achieve the above objective, the method for adjusting an inkjet printing apparatus according to the 15th aspect of this disclosure is a method for adjusting an inkjet printing apparatus that prints an image by ejecting ink onto a substrate, wherein the inkjet printing apparatus comprises an inkjet head on which nozzles for ejecting ink are arranged on the nozzle surface, the inkjet head has one of a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film on the nozzle surface, and the method for adjusting an inkjet printing apparatus is to set the pressure of the ink in the nozzles of the inkjet head when printing an image to a first pressure when the nozzle surface has a fluorine-based liquid-repellent film, and to set the pressure of the ink in the nozzles of the inkjet head to a second pressure which is less than the first pressure when the nozzle surface has a non-fluorine-based liquid-repellent film.

[0024] To achieve the above objective, the program according to the 16th aspect of this disclosure is a program that causes a computer to execute the adjustment method for an inkjet printing apparatus according to the 15th aspect. A non-temporary and computer-readable storage medium on which the program according to the 16th aspect is stored is also included in this disclosure.

[0025] The adjustment method for an inkjet printing apparatus according to the 15th embodiment and the program according to the 16th embodiment can be configured to include specific embodiments similar to those of the inkjet printing apparatus described above.

[0026] According to the present invention, the ejection performance of an inkjet head having a non-fluorine-based liquid-repellent film can be ensured.

[0027] Figure 1 is a schematic diagram showing an example of the state transition when two ink droplets are ejected consecutively from a nozzle. Figure 2 is a diagram illustrating static contact angle measurement. Figure 3 is a diagram illustrating dynamic contact angle measurement. Figure 4 is a diagram illustrating slide angle measurement. Figure 5 is a diagram illustrating an example of controlling the ink pressure of the nozzles of an inkjet head. Figure 6 is a diagram illustrating an example of controlling the ink pressure of the nozzles of an inkjet head. Figure 7 is a diagram illustrating an example of controlling the ink pressure of the nozzles of an inkjet head. Figure 8 is a diagram illustrating an example of controlling the ink pressure of the nozzles of an inkjet head. Figure 9 is a diagram illustrating the configuration of an inkjet printing apparatus. Figure 10 is a perspective view showing the configuration of the tip portion of the print bar. Figure 11 is an enlarged view of a part of the nozzle surface. Figure 12 is a plan view of the nozzle arrangement section. Figure 13 is a cross-sectional view showing an example of the structure of a print bar. Figure 14 is a block diagram showing the electrical configuration of an inkjet printing apparatus. Figure 15 is a flowchart showing a method for adjusting an inkjet printing apparatus.

[0028] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0029] <Challenges of Inkjet Heads> Inkjet heads installed in inkjet printing devices have a liquid-repellent film on the nozzle surface. This liquid-repellent film makes it easier for ink that has overflowed from the nozzle to return to the nozzle, resulting in excellent stability during continuous ejection. In addition, since less ink remains on the nozzle surface during cleaning of the inkjet head, failure modes such as dried ink on the nozzle surface being pushed into the nozzle are less likely to occur.

[0030] Traditionally, fluorine-based liquid-repellent films have been used as liquid-repellent coatings. Fluorine-based coatings include fluorine-based silane coupling agents and fluorine-based resins. To comply with PFAS regulations, fluorine-based liquid-repellent films are being replaced with fluorine-free non-fluorine-based liquid-repellent films. Non-fluorine-based coatings include silicone-based, hydrocarbon-based, metal oxides, and hydrophobic metals. In other words, non-fluorine-based liquid-repellent films do not contain fluorine and contain at least one of silicone, hydrocarbons, metal oxides, and hydrophobic metals.

[0031] Fluorine-based liquid-repellent coatings exhibited excellent performance. This is because fluorine has high electronegativity, making it difficult for other elements to approach it. For this reason, fluorine-based liquid-repellent coatings, including DuPont's Teflon (registered trademark), are widely used.

[0032] Figure 1 is a schematic diagram showing an example of the state transitions when two ink droplets D1 and D2 are continuously ejected from a nozzle 304 located on the nozzle surface 302 of an inkjet head 300. Figure 1 shows that the state changes in the order of F1A, F1B, F1C, F1D, and F1E as time progresses.

[0033] Figure 1 shows the inkjet head 300 in a cross-section at the position of the nozzle 304. The inkjet head 300 has an abnormal area 306 near the nozzle 304 on the nozzle surface 302. The abnormal area 306 is, for example, a region where the liquid-repellent properties of the liquid-repellent film have deteriorated.

[0034] The state shown in F1A is when the ink I ejected from the nozzle 304 has flown as the first ink droplet D1. The state shown in F1B is when the ink I has overflowed from the nozzle 304 due to the vibration of the meniscus, compared to the state shown in F1A. In the state shown in F1B, the ink droplet D1 has separated into three ink droplets.

[0035] The state shown in F1C is the state in which the ink I has returned to the inside of the nozzle 304 from the state shown in F1B, and the meniscus of the ink I is stable (static state). However, in this case, the ink I that has adhered to the abnormal part 306 has not completely returned to the inside of the nozzle 304.

[0036] The state shown in F1D is the state in which ink I is ejected from nozzle 304 from the state shown in F1C. The state shown in F1E is the state in which the ejected ink I has flown away as a second ink droplet D2. Due to the fact that ink I could not completely return to the inside of nozzle 304 in F1C, ink droplet D2 is ejected shifted towards the abnormal part 306 side compared to ink droplet D1, resulting in what is known as ejection curvature.

[0037] If the liquid-repellent properties around the nozzle 304 are relatively low, even if there are no abnormalities, the ink I that spills around the nozzle 304 will have difficulty returning to the inside of the nozzle 304, resulting in the problem of ejection curvature occurring in the second and subsequent ink droplets, as shown in Figure 1.

[0038] Therefore, when using a non-fluorine-based liquid-repellent film, which has relatively inferior liquid-repellent properties, as the liquid-repellent film for an inkjet head instead of a fluorine-based liquid-repellent film, it is necessary to devise a method for handling the inkjet head in order to ensure ejection performance.

[0039] <First Embodiment> [Ink Pressure at the Nozzle of the Inkjet Head] As a solution to the above problem, for the same type of inkjet head, an inkjet head with a liquid-repellent film having poor liquid repellency applied to the nozzle surface will have a lower nozzle pressure compared to an inkjet head with a liquid-repellent film having superior liquid repellency applied to the nozzle surface, in order to reduce overflow around the nozzle. The pressure at the nozzle may be the pressure of the ink at the meniscus interface when the ink meniscus of the nozzle is in a static state. A liquid-repellent film with superior liquid repellency may be a fluorine-based liquid-repellent film, and a liquid-repellent film with poor liquid repellency may be a non-fluorine-based liquid-repellent film. The liquid-repellent film only needs to be applied to the nozzle surface and at least around the nozzle.

[0040] In other words, the inkjet printing apparatus of this disclosure includes an inkjet head. The inkjet head has either a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film on its nozzle surface. The processor or user of the inkjet printing apparatus changes the ink pressure of the nozzles of the inkjet head depending on whether the nozzle surface of the inkjet head has a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film. The processor or user of the inkjet printing apparatus may determine whether the nozzle surface of the inkjet head has a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film. The processor or user of the inkjet printing apparatus may determine whether the nozzle surface of the inkjet head has a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film based on information stored in memory. The processor of the inkjet printing apparatus may determine whether the nozzle surface of the inkjet head has a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film based on information input by the user. The processor or user sets the ink pressure of the nozzles of the inkjet head to a first pressure if the nozzle surface has a fluorine-based liquid-repellent film, and to a second pressure smaller than the first pressure if the nozzle surface has a non-fluorine-based liquid-repellent film. An inkjet printer only needs to have this kind of ink pressure relationship at least when printing an image. "When printing an image" includes the timing when the inkjet head and the substrate on which the image is printed are moving relative to each other.

[0041] In an inkjet printing device, the ink pressure of the nozzles of the inkjet head is set such that P1 > P2, where P1 is the first pressure and P2 is the second pressure. For example, if the inkjet printing device is set to P1 = -500 [Pa], it may be set to P2 = -1000 [Pa].

[0042] The difference between the first pressure and the second pressure is preferably greater than 500 [Pa]. That is, if P1 > P2 + 500 [Pa], it is desirable because the strength of ink drawing into the nozzle can be clearly demonstrated. Furthermore, it is practical for the difference between the first pressure and the second pressure to be 2500 [Pa] or less.

[0043] Whether P1 > P2 + 500 [Pa] is satisfied can be confirmed from the height difference between the nozzle surface of the inkjet head and the ink surface of the ink tank when controlling the pressure using the water head difference described later. Whether P1 > P2 + 500 [Pa] is satisfied may be confirmed from the measurement result of the pressure sensor in the inkjet head, or may be confirmed from the measurement result of the pressure sensor in the ink flow path and the height difference between the pressure sensor and the nozzle surface of the inkjet head.

[0044] If the second pressure is too low, air will be entrained from the nozzle. For this reason, it is preferable that the second pressure is 1000 [Pa] or more higher than the pressure at which air is entrained. That is, assuming that the pressure at which air is entrained into the nozzle is P3, it is desirable that P2 ≧ P3 + 1000 [Pa]. P3 may be considered as the pressure when the ejection abnormality rapidly increases when a negative pressure is applied to the nozzle 108. P3 is, for example, in the range of -3000 [Pa] to -8000 [Pa].

[0045] [Performance of the liquid-repellent film] There are several methods for comparative evaluation of the performance of the liquid-repellent film. For example, there are static contact angle measurement, dynamic contact angle measurement, sliding angle measurement, etc. In the following, the ink used is a predetermined ink used in an inkjet printing apparatus. The measurement temperature condition is a laboratory environment around 25 [°C]. The static contact angle, dynamic contact angle, and sliding angle measurement angles in the following can be measured using a fully automatic contact angle meter DMo-701 manufactured by Kyowa Interface Science Co., Ltd. respectively.

[0046] <Static contact angle measurement> FIG. 2 is a diagram for explaining the static contact angle measurement. The static contact angle θS is represented by the angle formed by the tangent line at the liquid surface end of the ink droplet stationary on the surface of the liquid-repellent film and the surface of the liquid-repellent film. The relatively larger the static contact angle θS, the relatively better the liquid-repellent property. The static contact angle measurement is, for example, a measurement compliant with ISO 19403-5.

[0047] <Dynamic Contact Angle Measurement> Figure 3 is a diagram illustrating dynamic contact angle measurement. F3A shows dynamic advancing contact angle measurement using the extension method. The dynamic advancing contact angle θA is expressed as the angle between the tangent to the liquid surface edge of an ink droplet and the surface of the liquid-repellent film when ink is supplied from a syringe needle inserted into an ink droplet on the surface of the liquid-repellent film, gradually increasing the amount of ink. A relatively larger value of the dynamic advancing contact angle θA indicates relatively superior liquid repellency. Dynamic advancing contact angle measurement is a measurement method that conforms to ISO 19403-6, for example.

[0048] F3B shows the dynamic receding contact angle measurement using the shrinkage method. The dynamic receding contact angle θR is expressed as the angle between the tangent to the edge of the liquid surface of an ink droplet and the surface of the liquid-repellent film when ink is gradually reduced by drawing ink from a syringe needle inserted into the surface of the liquid-repellent film. A relatively larger value of the dynamic receding contact angle θR indicates relatively better liquid repellency. The dynamic receding contact angle measurement is performed in accordance with, for example, ISO 19403-6.

[0049] <Slip Angle> Figure 4 is a diagram illustrating the measurement of the slip angle. The slip angle θT is the angle of inclination of the surface of the liquid-repellent film relative to the horizontal when the surface of the liquid-repellent film on which the ink droplet is placed is gradually tilted from a horizontal position, and the ink droplet begins to slide off. A relatively smaller value of the slip angle θT indicates relatively better liquid repellency. The slip angle measurement is performed in accordance with, for example, ISO 19403-7.

[0050] [Physical Properties of Ink] The static surface tension of the ink is preferably 21.0 m [mN / m] to 38.0 [mN / m], more preferably 23.0 [mN / m] to 33.0 [mN / m], and even more preferably 24.0 [mN / m] to 30.0 [mN / m]. The static surface tension of the ink is measured using an automatic surface tension meter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

[0051] The static surface tension of the ink is preferably 30.0 [mN / m] or less, more preferably 26.0 [mN / m] or less, and even more preferably 22.0 [mN / m] or less. The static surface tension of the ink as defined in this disclosure is a value measured using the pendant drop method.

[0052] The effects of this disclosure are more pronounced when the static surface tension of the ink is relatively low. This is because when the surface tension of the ink is relatively low, the ink that spills around the nozzle during ejection is less likely to be drawn into the nozzle, and is more susceptible to the effects of poor performance of the liquid-repellent film around the nozzle.

[0053] The effects of this disclosure are more pronounced when the ink is an active energy ray curable ink that hardens upon irradiation with active energy rays. This is because active energy ray curable inks have a relatively lower static surface tension compared to water-based inks, making them less likely to be drawn into the nozzle and more susceptible to the effects of poor performance of the liquid-repellent film around the nozzle.

[0054] [Ejection Frequency] The ink ejection frequency of the inkjet head is preferably 50 kHz or higher, more preferably 75 kHz or higher, and preferably 100 kHz or higher. In practice, the ink ejection frequency of the inkjet head is 150 kHz or lower. The ink ejection frequency is the number of ink droplets ejected from one nozzle per unit time. The ink ejection frequency may also be the frequency of the drive signal applied to the energy generating element for ink ejection (for example, the piezoelectric element 126 shown in Figure 13). The higher the ink ejection frequency, the more the effects of this disclosure are exhibited. This is because by continuously ejecting ink at a high frequency, the ink is more likely to overflow outside the nozzle and is more susceptible to the effects of poor performance of the liquid-repellent film around the nozzle.

[0055] [Mixed Print Bars] An inkjet printer may print an image in a single-pass manner by moving the print bar and the substrate relative to each other in the relative movement direction. An inkjet printer may have multiple print bars. Each of the multiple print bars may eject ink of a different color. An inkjet head having a fluorine-based liquid-repellent coating and an inkjet head having a non-fluorine-based liquid-repellent coating may be mixed in one print bar that ejects one color of ink. In this case as well, it is desirable to set the ink pressure of the nozzle of the inkjet head having a fluorine-based liquid-repellent coating as the first pressure, and the ink pressure of the nozzle of the inkjet head having a non-fluorine-based liquid-repellent coating as a second pressure that is smaller than the first pressure.

[0056] [Information on Liquid-Repellent Films] An inkjet head may retain information on whether the liquid-repellent film applied to the nozzle surface is a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film. An inkjet printing device may acquire information on the liquid-repellent film for each inkjet head and control the ink pressure of the nozzles of the inkjet head according to the information on the liquid-repellent film. Alternatively, the user may determine whether the liquid-repellent film applied to the nozzle surface is a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film, and set the ink pressure of the nozzles of the inkjet head according to whether the liquid-repellent film is a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film.

[0057] [Example of Pressure Control 1] Figure 5 shows an example of controlling the pressure of the ink in the nozzles (not shown in Figure 5) of an inkjet head 400, and illustrates an example of control using a head difference. As shown in Figure 5, the inkjet head 400 is connected to an ink tank 404 that stores the ink ejected by the inkjet head 400 via a supply channel 408. The pressure of the ink in the nozzles of the inkjet head 400 is controlled by adjusting the height distance h between the nozzle surface 402 of the inkjet head 400 and the liquid surface 406 of the ink in the ink tank 404.

[0058] In other words, an inkjet printing apparatus is equipped with an ink tank that stores ink supplied to the inkjet head, and the difference in water head between the nozzle surface of the inkjet head and the ink surface of the ink tank when printing an image is defined as a first water head difference if the nozzle surface has a fluorine-based liquid-repellent film, and a second water head difference that is larger than the first water head difference if the nozzle surface has a non-fluorine-based liquid-repellent film. A large water head difference means that the value of h is large in the positive range shown in Figure 5. As a result, the ink pressure at the nozzle of an inkjet head with a fluorine-based liquid-repellent film becomes the first pressure, and the ink pressure at the nozzle of an inkjet head with a non-fluorine-based liquid-repellent film becomes the second pressure, which is smaller than the first pressure.

[0059] [Example of Pressure Control 2] Figure 6 shows an example of controlling the ink pressure of the nozzles (not shown in Figure 6) of an inkjet head 400, and illustrates an example of control using the capillary force of a porous member. As shown in Figure 6, the inkjet head 400 is equipped with an ink cartridge 410. The ink cartridge 410 includes a porous member 412. The porous member 412 is filled with ink ejected by the inkjet head 400, and the capillary force of the porous member 412 maintains a negative pressure for the ink supplied to the inkjet head 400. The pressure of the ink in the nozzles of the inkjet head 400 is controlled by adjusting the coarseness (size of the holes) of the porous member 412.

[0060] In other words, the inkjet printing apparatus includes a porous member impregnated with ink supplied to the inkjet head. When printing an image, the pore diameter of the porous member is set to a first pore diameter if the nozzle surface has a fluorine-based liquid-repellent film, and to a second pore diameter smaller than the first pore diameter if the nozzle surface has a non-fluorine-based liquid-repellent film. The pore diameter of the porous member may be adjusted by replacing the porous member or by replacing the ink cartridge containing the porous member. As a result, the ink pressure at the nozzle of an inkjet head with a fluorine-based liquid-repellent film becomes the first pressure, and the ink pressure at the nozzle of an inkjet head with a non-fluorine-based liquid-repellent film becomes the second pressure smaller than the first pressure. The pore diameter may be an average value.

[0061] [Example 3 of pressure control] Figure 7 shows an example of controlling the ink pressure of the nozzles (not shown in Figure 7) of an ink-circulating inkjet head 420, illustrating an example of control using the pressure of the ink input and output.

[0062] As shown in Figure 7, the inkjet head 420 is connected to an ink tank 404, which stores the ink ejected by the inkjet head 420, via a supply channel 430. A supply pump 432 is located in the supply channel 430 to supply ink from the ink tank 404 to the inkjet head 420.

[0063] Furthermore, the inkjet head 420 is connected to an ink tank 404 via a recovery channel 434. The recovery channel 434 is equipped with a recovery pump 436 for recovering from the inkjet head 420 to the ink tank 404 any ink that is not ejected from the nozzles, which has been supplied from the ink tank 404 to the inkjet head 420 by a supply pump 432.

[0064] The pressure in the supply channel 430 and the recovery channel 434 is adjusted to control the ink pressure in the nozzles of the inkjet head 420. The pressure in the supply channel 430 and the recovery channel 434 is adjusted by the supply pump 432 and the recovery pump 436.

[0065] In other words, the inkjet printing apparatus includes a supply channel for supplying ink to an inkjet head, and a recovery channel for recovering ink from the inkjet head that is not ejected from the nozzles. The difference between the pressure in the supply channel and the pressure in the recovery channel when printing an image is defined as a first difference if the nozzle surface has a fluorine-based liquid-repellent film, and a second difference smaller than the first difference if the nozzle surface has a non-fluorine-based liquid-repellent film. As a result, the ink pressure at the nozzles of an inkjet head with a fluorine-based liquid-repellent film becomes the first pressure, and the ink pressure at the nozzles of an inkjet head with a non-fluorine-based liquid-repellent film becomes the second pressure smaller than the first pressure.

[0066] [Example 4 of pressure control] Figure 8 shows an example of controlling the ink pressure of the nozzle (not shown in Figure 8) of an ink-circulating inkjet head 420, and illustrates an example of control using the resistance of the ink flow path.

[0067] As shown in Figure 8, the supply channel 430 is provided with a flow resistance element 438 to increase the flow resistance of the supply channel 430. The flow resistance element 438 may be a restricting member that reduces the flow area of ​​the supply channel 430, or a filter member that obstructs the flow of ink. The flow resistance element 438 may also increase the flow resistance by reducing the overall flow area of ​​the supply channel 430. By adjusting the flow resistance of the supply channel 430 with the flow resistance element 438, the ink pressure of the nozzles of the inkjet head 420 is controlled.

[0068] In other words, an inkjet printing apparatus is equipped with a supply channel for supplying ink to an inkjet head, and the flow resistance of the supply channel when printing an image is set to a first flow resistance when supplying ink to an inkjet head whose nozzle surface has a fluorine-based liquid-repellent film, and to a second flow resistance greater than the first flow resistance when supplying ink to an inkjet head whose nozzle surface has a non-fluorine-based liquid-repellent film. Furthermore, if the inkjet printing apparatus is equipped with a plurality of inkjet heads and a plurality of supply channels for supplying ink to each of the plurality of inkjet heads, the flow resistance of the supply channel when printing an image may be set to a first flow resistance for the supply channel supplying ink to an inkjet head whose nozzle surface has a fluorine-based liquid-repellent film, and to a second flow resistance greater than the first flow resistance for the supply channel supplying ink to an inkjet head whose nozzle surface has a non-fluorine-based liquid-repellent film. As a result, the ink pressure at the nozzle of the inkjet head with a fluorine-based liquid-repellent film becomes a first pressure, and the ink pressure at the nozzle of the inkjet head with a non-fluorine-based liquid-repellent film becomes a second pressure less than the first pressure.

[0069] The inkjet printing apparatus may control the pressure by using a combination of adjusting the pressure in the supply channel 430 and the recovery channel 434 with the supply pump 432 and the recovery pump 436, and adjusting the flow resistance of the supply channel 430 with the flow resistance element 438.

[0070] By controlling the pressure in this way, regardless of which of the multiple types of water-repellent coatings is applied to the inkjet printing device, the ink pressure of the nozzles of the inkjet heads with inferior water-repellent coatings can be made relatively lower than the ink pressure of the nozzles of the inkjet heads with superior water-repellent coatings. This ensures that the ejection performance of the inkjet heads with inferior water-repellent coatings can be maintained.

[0071] <Second Embodiment> [Configuration of Inkjet Printing Apparatus] An inkjet printing apparatus is a device that prints an image by ejecting ink onto a substrate. The substrate may be a single sheet or a continuous long sheet. Here, an example in which a single sheet substrate, which is a general-purpose printing paper, is used will be described. General-purpose printing paper refers to cellulose-based paper such as coated paper used in general offset printing, etc., rather than so-called inkjet-specific paper. The ink may be an aqueous ink in which a colorant such as a dye or pigment is dissolved or dispersed in water or a water-soluble solvent, or it may be an active energy ray curing ink that hardens when irradiated with active energy rays. Here, an example in which an ultraviolet-curing ink that hardens when irradiated with ultraviolet light is used will be described.

[0072] Figure 9 shows the configuration of an inkjet printing apparatus 10. The inkjet printing apparatus 10 includes a transport device 12 for transporting the substrate 1. The transport device 12 includes a paper feed side transfer cylinder 20, a printing cylinder 30, and a paper discharge side transfer cylinder 40.

[0073] The paper feed side transfer cylinder 20 is provided with a gripping claw device 22 that holds the leading edge of the base material 1, which is transferred by a paper feeding device (not shown), in a gripping position.

[0074] The paper feed side transfer cylinder 20 is rotatably supported. The printing cylinder 30 is positioned opposite the paper feed side transfer cylinder 20 on the downstream side in the substrate transport direction. The printing cylinder 30 is equipped with three printing cylinder gripping claw devices 32 that receive and hold the leading edge of the substrate 1 from the gripping claw device 22 of the paper feed side transfer cylinder 20.

[0075] The rotating shaft (not shown) of the printing cylinder 30 is connected to a drive motor (not shown). Furthermore, multiple suction holes (not shown) are formed on the outer surface of the printing cylinder 30. These multiple suction holes are connected to a negative pressure source (not shown).

[0076] The suction operation range of the substrate 1 by the suction holes of the printing cylinder 30 is from a suction start position P1 near the downstream side in the substrate transport direction from the contact portion of the printing cylinder 30 with the paper feed side transfer cylinder 20 to a suction end position P2 near the upstream side in the substrate transport direction from the contact portion with the paper discharge side transfer cylinder 40. Within the suction operation range, the entire surface of the substrate 1 is adsorbed to the outer surface of the printing cylinder 30.

[0077] Downstream in the substrate transport direction from the portion of the printing cylinder 30 that contacts the paper feed side transfer cylinder 20, an ink ejection section 34 is positioned facing the outer circumferential surface of the printing cylinder 30.

[0078] The ink ejection unit 34 comprises a plurality of print bars 36a, 36b, 36c, and 36d, each set with ink of a different color. Each of the plurality of print bars 36a, 36b, 36c, and 36d may be supplied with ink of a different color by a supply pump (not shown). Each of the plurality of print bars 36a, 36b, 36c, and 36d may be equipped with an ink circulation mechanism including a supply pump (not shown) and a recovery pump (not shown). The plurality of print bars 36a, 36b, 36c, and 36d are arranged side by side along the outer circumferential surface of the printing cylinder 30 in the substrate transport direction, and each is directed toward the outer circumferential surface of the printing cylinder 30. The print bars 36a, 36b, 36c, and 36d are arranged close to the printing cylinder 30 such that there is a small gap between them and the substrate 1 which is adsorbed to the entire outer circumferential surface of the printing cylinder 30 by a plurality of suction holes.

[0079] Downstream from the printing area of ​​the ink ejection section 34 of the printing cylinder 30 in the substrate transport direction, an ink drying lamp 38 is provided, positioned in contact with the printing cylinder 30, and serves as a drying device that irradiates the substrate 1 with ultraviolet light to dry the ink printed on the substrate 1. Drying includes evaporating the water in the ink by applying thermal energy and hardening the ink, and can be rephrased as solidification.

[0080] A paper discharge cylinder 40 is positioned opposite the printing cylinder 30, downstream of the ink drying lamp 38 in the substrate transport direction. The paper discharge cylinder 40 is rotatably supported. The paper discharge cylinder 40 is equipped with a gripping claw device 42 that receives and holds the leading edge of the substrate 1 transported by the printing cylinder 30 from the printing cylinder gripping claw device 32.

[0081] [Overall configuration of the inkjet head] The same configuration can be applied to print bars 36a, 36b, 36c, and 36d. In the following, print bars 36a, 36b, 36c, and 36d may be referred to simply as print bar 36 without distinction.

[0082] Figure 10 is a perspective view showing the configuration of the tip portion of the print bar 36. The tip portion of the print bar 36 includes the end of the print bar 36 that ejects ink. The print bar 36 is a line-type head having a nozzle row 106 (see Figure 11) that enables image recording at a specified recording resolution across the entire recording area of ​​the substrate 1 in a single scan, with respect to the width direction of the substrate 1. The width direction of the substrate 1 is perpendicular to the transport direction of the substrate 1 and parallel to the printing surface of the substrate 1.

[0083] The tip of the print bar 36 has a nozzle surface 100. The nozzle surface 100 has a liquid-repellent film 100A (see Figure 13). In addition, nozzles 108 (see Figure 12) for ejecting ink are arranged on the nozzle surface 100.

[0084] The print bar 36 has a structure in which n inkjet heads 102-i (an example of "multiple inkjet heads") are connected in a line along the longitudinal direction. Here, n is an integer and i is an integer from 1 to n. The inkjet heads 102-i are mounted and integrated with the support frame 110. Each inkjet head 102-i may be replaceable by the user. Each inkjet head 102-i is equipped with an electrical connection cable 114.

[0085] [Nozzle Arrangement] Figure 11 is a magnified view of a portion of the nozzle surface 100-i. The nozzle surface 100-i of the inkjet head 102-i is parallelogram-shaped. Dummy plates 112 are attached to both ends of the support frame 110. The nozzle surface 100 of the print bar 36, together with the surface 112A of the dummy plate 112, forms a rectangular shape overall.

[0086] A strip-shaped nozzle arrangement section 104-i is provided in the central part of the nozzle surface 100-i of the inkjet head 102-i. The nozzle arrangement section 104-i functions as the actual nozzle surface 100-i. The nozzle 108 is provided on the nozzle arrangement section 104-i.

[0087] A liquid-repellent film 100A is applied to at least the nozzle arrangement portion 104-i of the nozzle surface 100-i. The liquid-repellent film 100A includes a liquid-repellent film 100A with relatively superior liquid repellency and a liquid-repellent film 100A with relatively inferior liquid repellency, and each of the multiple inkjet heads 102-i is applied to one of the liquid-repellent films 100A. The liquid-repellent film 100A with superior liquid repellency is a fluorine-based liquid-repellent film, and the liquid-repellent film 100A with inferior liquid repellency may be a non-fluorine-based liquid-repellent film.

[0088] All inkjet heads 102-i of a single print bar 36 may be coated with a single type of liquid-repellent film 100A having the same performance. For example, all inkjet heads 102-i of print bar 36a may be coated with a liquid-repellent film 100A having relatively superior liquid-repellent properties, and all inkjet heads 102-i of print bar 36b may be coated with a liquid-repellent film 100A having relatively inferior liquid-repellent properties.

[0089] Furthermore, two types of inkjet heads 102-i with different liquid-repellent coating performances may be mixed on a single print bar 36. For example, the inkjet head 102-1 of the print bar 36a may be provided with a liquid-repellent coating 100A that has relatively superior liquid-repellent properties, while the inkjet head 102-2 of the print bar 36a may be provided with a liquid-repellent coating 100A that has relatively inferior liquid-repellent properties.

[0090] Figure 11 shows a nozzle row 106 composed of multiple nozzles 108, with each nozzle 108 not shown individually.

[0091] Figure 12 is a plan view of the nozzle arrangement section 104-i. The nozzle arrangement section 104-i has a parallelogram shape with a long side end face along the V direction which is inclined at an angle β with respect to the X direction which is the width direction of the substrate 1, and a short side end face along the W direction which is inclined at an angle α with respect to the Y direction which is the transport direction of the substrate 1.

[0092] Multiple nozzles 108 are arranged in two dimensions in the nozzle arrangement section 104-i, in the row direction along the V direction and in the column direction along the W direction.

[0093] The projected nozzle array, obtained by projecting each nozzle 108 along the Y direction, can be considered equivalent to a single row of nozzles where each nozzle 108 is arranged at approximately equal intervals at a nozzle density that achieves the maximum recording resolution in the Y direction.

[0094] "Approximately equal spacing" means that the droplet points that can be recorded in the inkjet printing device 10 are substantially equally spaced. For example, even if the spacing is slightly different to account for manufacturing errors and at least one of the movement of droplets on the medium due to impact interference, this is still included in the concept of equal spacing.

[0095] The arrangement of the nozzles 108 is not limited to the example shown in Figure 12. Examples of nozzle arrangements include a straight line arrangement, a V-shaped arrangement, and a W-shaped arrangement with the V-shaped arrangement repeated as a unit.

[0096] [Ejector Configuration] Figure 13 is a cross-sectional view showing an example of the structure of a print bar 36. The print bar 36 comprises an ejector 122, a supply-side common flow path 134, a diaphragm 136, a recovery-side common flow path 142, individual recovery paths 144, and a cover plate 146.

[0097] The ejector 122 comprises a nozzle 108, a pressure chamber 124, a piezoelectric element 126, a nozzle flow path 128, and an individual supply path 130. The nozzle 108 communicates with the pressure chamber 124 via the nozzle flow path 128. The nozzle section 132 is formed by the nozzle 108 and the nozzle flow path 128. The pressure chamber 124 communicates with the supply-side common flow path 134 via the individual supply path 130.

[0098] Additionally, individual recovery paths 144 are connected to the nozzle flow path 128. The nozzle flow path 128 communicates with the recovery-side common flow path 142 via the individual recovery paths 144.

[0099] When there is a pressure difference between the supply-side common flow path 134 and the recovery-side common flow path 142, and ink is not ejected from the nozzle 108, ink flows from the individual supply path 130 through the pressure chamber 124 and the individual recovery path 144 to the recovery-side common flow path 142.

[0100] The piezoelectric element 126 comprises individual electrodes 138 and a piezoelectric body 140. The diaphragm 136, which forms the top surface of the pressure chamber 124, is provided with a conductive layer (not shown) that functions as a common electrode corresponding to the lower electrode of the piezoelectric element 126. The pressure chamber 124, the walls of other flow path portions, and the diaphragm 136 are formed of silicone. The material of the diaphragm 136 is not limited to silicone; it can also be formed from a non-conductive material such as resin. The diaphragm 136 itself may be made of a metal material such as stainless steel and may also serve as a common electrode.

[0101] A piezoelectric unimorph actuator is constructed by stacking a piezoelectric element 126, which consists of a piezoelectric body 140 and individual electrodes 138, on a diaphragm 136. When a drive voltage of the drive waveform is applied to the individual electrodes 138, which are the upper electrodes of the piezoelectric element 126, the piezoelectric body 140 deforms. As the piezoelectric body 140 deforms, the diaphragm 136 flexes, and the volume of the pressure chamber 124 changes. Due to the change in the volume of the pressure chamber 124, the ink inside the pressure chamber 124 is pressurized, and the ink is ejected from the nozzle 108. Ink that is not used for ejection is recovered from the nozzle flow path 128 through the individual recovery path 144 to the recovery side common flow path 142.

[0102] When the piezoelectric element 140 returns to its original state after the ink has been ejected, new ink is supplied to the pressure chamber 124 from the common supply channel 134 through the individual supply channel 130. The process of filling the pressure chamber 124 with ink is called refilling. There are no particular limitations on the planar shape of the pressure chamber 124; it can take various forms such as a rectangle, other polygons, a circle, or an ellipse.

[0103] The cover plate 146 is a member that holds the movable space 148 of the piezoelectric element 126 and seals the area around the piezoelectric element 126. Above the cover plate 146, a supply-side ink chamber and a recovery-side ink chamber (not shown) are formed. The supply-side ink chamber is connected to the supply-side common flow path 134 via a connecting passage (not shown). The recovery-side ink chamber is connected to the recovery-side common flow path 142 via a connecting passage (not shown).

[0104] [Electrical Configuration of Inkjet Printing Apparatus] Figure 14 is a block diagram showing the electrical configuration of an inkjet printing apparatus. As shown in Figure 14, the inkjet printing apparatus 10 comprises a general control unit 500, a transport control unit 502, an ejection control unit 504, a drying control unit 506, an input device 510, and an output device 512.

[0105] The central control unit 500 centrally controls each part of the inkjet printing apparatus 10. In this embodiment, each process is executed on any computer. Alternatively, any computer may execute these processes using a processor as hardware, a program as software, or a combination thereof. In that case, the processor is configured to work in cooperation with the program to execute the various processes in this embodiment, and can function as each part (Unit) or each means (Means) in this embodiment. Furthermore, the execution order of the processes by the processor is not limited to the order described and may be changed as appropriate. Any computer may be a general-purpose computer, a computer for a specific application, a workstation, or any other system capable of executing each process.

[0106] A processor may consist of one or more hardware components, and the type of hardware is not limited. For example, a processor may consist of programmable logic devices such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), FPGA (Field Programmable Gate Array), dedicated circuits for performing specific processing such as an ASIC (Application Specific Integrated Circuit), a GPU (Graphics Processing Unit), or an NPU (Neural Processing Unit). Furthermore, the type of hardware may be a combination of different types of hardware. When multiple hardware components are configured to execute one or more processes of a processor, these components may reside in physically separate devices or in the same device. Furthermore, in any embodiment, the order of the processes performed by the processor is not limited to the order described above and may be changed as appropriate. The hardware components are composed of electrical circuits (circuits) and the like, which are combinations of circuit elements such as semiconductor elements.

[0107] Furthermore, the program may be firmware or software such as microcode. Alternatively, the program may be, for example, a group of program modules, each function of which may be implemented by a processor configured to perform its respective function. The program may be program code or multiple code segments stored on one or more non-temporary computer-readable media (e.g., storage media or other storage). The program may be divided and stored on multiple non-temporary computer-readable media located in physically separate devices. Program code or code segments may represent any combination of procedures, functions, subprograms, routines, subroutines, modules, software packages, classes, or instructions, data structures, or program statements. Program code or code segments may be connected to other code segments or hardware circuits by sending and receiving information, data, arguments, parameters, or memory contents.

[0108] The transport control unit 502 controls the transport device 12 to transport the substrate 1 along the transport path.

[0109] The ejection control unit 504 controls an ink circulation mechanism (not shown) to circulate different colored inks to the print bars 36a, 36b, 36c, and 36d, respectively. The ejection control unit 504 also controls the ink ejection unit 34 to eject different colored inks from the print bars 36a, 36b, 36c, and 36d at a predetermined ejection frequency, thereby printing a color image onto the substrate 1.

[0110] For example, the ejection control unit 504 circulates cyan ink, magenta ink, yellow ink, and black ink to the print bars 36a, 36b, 36c, and 36d, respectively. The ejection control unit 504 also ejects cyan ink, magenta ink, yellow ink, and black ink to the print bars 36a, 36b, 36c, and 36d, respectively, to print a color image onto the substrate 1.

[0111] Furthermore, the ejection control unit 504 controls the ink pressure of the nozzles 108 of the inkjet head 102-i when printing a color image, according to the liquid-repellent film on the inkjet head 102-i provided on each of the print bars 36a, 36b, 36c, and 36d.

[0112] The inkjet head 102-i is equipped with memory 102-iA. Memory 102-iA is a non-volatile memory element such as EEPROM (Electronically Erasable and Programmable Read Only Memory). The manufacturer of the inkjet head 102-i stores information about the liquid-repellent film of the inkjet head 102-i in memory 102-iA during the manufacturing of the inkjet head 102-i. The liquid-repellent film information is, for example, information on whether the applied liquid-repellent film 100A is a liquid-repellent film 100A with relatively superior liquid-repellent properties or a liquid-repellent film 100A with relatively inferior liquid-repellent properties. The ejection control unit 504 obtains the liquid-repellent film information from the memory 102-iA of the inkjet head 102-i.

[0113] The drying control unit 506 controls the ink drying lamp 38 to dry the ink adhering to the substrate 1.

[0114] The input device 510 includes, for example, a mouse (not shown) and a keyboard (not shown). The input device 510 receives input from the mouse and keyboard to the inkjet printer 10.

[0115] The output device 512 includes, for example, a display (not shown). The output device 512 presents information about the inkjet printer 10 to the user. The central control unit 500 may display information about the liquid-repellent film obtained from memory 102-iA on the display of the output device 512.

[0116] The input device 510 and the output device 512 may include a communication interface (not shown) for sending and receiving information between the inkjet printing device 10 and other devices.

[0117] [Printing Operation of Inkjet Printing Machine] When printing is instructed, the transport control unit 502 supplies the substrate 1 from a paper feed device (not shown) to the printing cylinder 30 via the paper feed side transfer cylinder 20. The transport control unit 502 uses one of the three printing cylinder gripping claw devices 32 on the printing cylinder 30 to grip the tip of the substrate 1 and rotates the printing cylinder 30 to transport the substrate 1. Since suction force acts on the suction holes of the printing cylinder 30 downstream from the suction start position P1 in the rotational direction, when the substrate 1 passes the suction start position P1, the entire surface of the substrate 1 is attracted to the outer surface of the printing cylinder 30 and adheres tightly.

[0118] The ejection control unit 504 ejects ink from the print bars 36a, 36b, 36c, and 36d of the ink ejection unit 34 at an ejection frequency of 50 kHz or higher onto the surface of the substrate 1 being transported by the printing cylinder 30, thereby forming a color image on the surface of the substrate 1. In this way, the inkjet printing apparatus 10 prints an image in a single-pass manner by moving the print bars 36a, 36b, 36c, and 36d relative to the substrate 1 in the relative movement direction.

[0119] Since the substrate 1 is in close contact with the outer surface of the printing cylinder 30, it is transported while maintaining a minute gap between it and the print bars 36a, 36b, 36c, and 36d. Maintaining this minute gap allows the ejected ink to land on the substrate 1 with high precision, enabling high-quality printing.

[0120] Furthermore, during printing, an inkjet head 102-i with a liquid-repellent film 100A having inferior liquid-repellent properties applied to the nozzle surface 100 has the ink pressure of the nozzles 108 adjusted or controlled to be lower compared to an inkjet head 102-i with a liquid-repellent film 100A having superior liquid-repellent properties applied to the nozzle surface 100.

[0121] The transport control unit 502 rotates the printing cylinder 30 to transport the substrate 1, which has been printed by the ink ejection unit 34, to a position facing the ink drying lamp 38.

[0122] The drying control unit 506 irradiates the substrate 1 with light from the ink drying lamp 38 to dry the ink on the surface of the substrate 1. Since the substrate 1 is in close contact with the outer surface of the printing cylinder 30 during the suction operation range from the suction start position P1 to the suction end position P2, the ink drying lamp 38 irradiates the entire surface of the substrate 1 uniformly, resulting in even ink drying.

[0123] Subsequently, the transport control unit 502 discharges the substrate 1 from the printing cylinder 30 via the paper discharge side transfer cylinder 40 to a paper discharge device (not shown). When the substrate 1 is transferred from the printing cylinder 30 to the paper discharge side transfer cylinder 40, the leading edge of the substrate 1 has passed the suction end position P2, so the suction force from the suction hole is gone, and the substrate 1 is easily peeled off from its outer surface.

[0124] <Third Embodiment> [Method for Adjusting an Inkjet Printing Apparatus] Figure 15 is a flowchart showing a method for adjusting an inkjet printing apparatus 10. The method for adjusting the inkjet printing apparatus 10 is achieved by the control unit 500 executing an adjustment program. The method for adjusting the inkjet printing apparatus 10 may also be achieved by a computer (not shown) connected to the inkjet printing apparatus 10 via a communication interface (not shown) executing an adjustment program. The control unit 500 or the computer may read and execute an adjustment program stored in a temporary, computer-readable storage medium. The method for adjusting the inkjet printing apparatus 10 may also be performed manually by the user.

[0125] The adjustment method for the inkjet printer 10 is performed when the inkjet printer 10 is powered on. The adjustment method for the inkjet printer 10 may also be performed when the inkjet printer 10 is shipped, when the inkjet printer 10 is installed at the factory, when the print bar 36 is replaced, or when the inkjet head 102-i is replaced.

[0126] In step S1, the central control unit 500 determines whether the liquid-repellent film 100A on the nozzle surface 100-i of the inkjet head 102-i is a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film. The central control unit 500 may also read the liquid-repellent film information from the memory 102-iA of the inkjet head 102-i and determine whether the liquid-repellent film 100A is a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film from the read liquid-repellent film information. The central control unit 500 may also determine whether the liquid-repellent film 100A is a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film from the liquid-repellent film information input by the user using the input device 510. The central control unit 500 makes this determination for all the nozzle surfaces 100-i of the inkjet heads 102-i on the print bars 36a, 36b, 36c, and 36d.

[0127] In step S1, the user may visually determine whether the liquid-repellent film 100A on the nozzle surface 100-i of the inkjet head 102-i is a fluorine-based liquid-repellent film or a non-fluorine-based liquid-repellent film.

[0128] In step S2, the control unit 500 sets the ink pressure of the nozzles 108 of the inkjet head 102-i when printing an image to a first pressure if the liquid-repellent film 100A is a fluorine-based liquid-repellent film, and to a second pressure that is smaller than the first pressure if the liquid-repellent film 100A is a non-fluorine-based liquid-repellent film.

[0129] The inkjet printer 10 changes the ink pressure of the nozzles 108 of the inkjet head 102-i to a set pressure when printing an image. For example, when controlling using head difference, the inkjet printer 10 changes the head difference using a head difference changing device (not shown) to achieve the set pressure. When controlling using the capillary force of a porous material, the inkjet printer 10 changes the porous material to one with a pore diameter that achieves the set pressure. When controlling using the pressure of ink input and output, the inkjet printer 10 changes at least one of the pressures in the supply channel and the recovery channel using the supply pump and the recovery pump to achieve the set pressure. When controlling using the flow resistance of the supply channel, the inkjet printer 10 changes the flow resistance of the supply channel to achieve the set pressure. These changes may be performed manually by the user.

[0130] As a result, the ink pressure at the nozzle 108 of the inkjet head 102-i having a fluorine-based liquid-repellent film becomes the first pressure, and the ink pressure at the nozzle 108 of the inkjet head 102-i having a non-fluorine-based liquid-repellent film becomes the second pressure, which is smaller than the first pressure. Therefore, the ejection performance of the inkjet head 102-i with a non-fluorine-based liquid-repellent film having inferior liquid-repellent properties can be made equivalent to the ejection performance of the inkjet head 102-i with a fluorine-based liquid-repellent film having superior liquid-repellent properties.

[0131] For example, suppose the liquid-repellent coating 100A of all inkjet heads 102-i of the print bar 36 is a fluorine-based liquid-repellent coating. In this case, when printing an image, the ink pressure of the nozzles 108 of the inkjet heads 102-i of the print bar 36 will be the first pressure for all inkjet heads 102-i.

[0132] Subsequently, due to a malfunction of the inkjet head 102-i, some of the inkjet heads 102-i are replaced, and the liquid-repellent film 100A of the replaced inkjet heads 102-i is a non-fluorine-based liquid-repellent film. In this case, when printing an image, the ink pressure of the nozzles 108 of the inkjet heads 102-i on the print bar 36 will be a first pressure for the inkjet heads 102-i that have not been replaced, and a second pressure lower than the first pressure for the replaced inkjet heads 102-i.

[0133] Furthermore, suppose all inkjet heads 102-i are replaced, and the liquid-repellent film 100A of the replaced inkjet heads 102-i is a non-fluorine-based liquid-repellent film. In this case, the ink pressure of the nozzles 108 of the inkjet heads 102-i on the print bar 36 when printing an image becomes the second pressure for all inkjet heads 102-i. An inkjet printing apparatus 10 equipped with a print bar 36 in this state is included in this disclosure.

[0134] <Fourth Embodiment> [Details of the Non-Fluorine Liquid-Repellent Film] The contact angle of the non-fluorine liquid-repellent film with respect to the ink is preferably 60 degrees or more, more preferably 70 degrees or more, and even more preferably 80 degrees or more. By forming the non-fluorine liquid-repellent film on the outermost surface of the nozzle surface 100 (see Figure 13), the wipe resistance of the nozzle surface 100 (see Figure 13) is excellent, and it becomes easy to recover ink that overflows from the nozzle 108 during ink discharge back into the nozzle 108. The contact angle referred to here corresponds to the static contact angle θS shown in Figure 2.

[0135] The non-fluorinated liquid-repellent film has a substructure represented by the following formula 1: (L-Y-) k Si-(O-*) 4-k ...Formula 1

[0136] In formula 1, L is a hydrocarbon group, Y is a single bond or a divalent linking group that does not contain a fluorine atom, k is an integer between 1 and 3, and * indicates the bond position with other structures.

[0137] The hydrocarbon group represented by L in Formula 1 may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The hydrocarbon group is preferably an aliphatic hydrocarbon group, and more preferably an alkyl group. The alkyl group may be a linear alkyl group, a branched alkyl group, or a cyclic alkyl group.

[0138] The hydrocarbon group preferably has 1 to 30 carbon atoms, and more preferably 1 to 20 carbon atoms. The hydrocarbon group may have substituents. Preferably, the substituents do not contain fluorine atoms.

[0139] In formula 1, a divalent linking group that does not contain a fluorine atom, represented by Y, can be, for example, a combination of at least one selected from the group consisting of -O-, -C(=O)-, and NR-, and a hydrocarbon group. R represents a hydrogen atom or a hydrocarbon group. However, the linking portion of Y with L is not a hydrocarbon group.

[0140] When Y is a divalent linking group, examples of Y include: *1-O-C(=O)-(hydrocarbon group)-C(=O)-O-(hydrocarbon group)-*2 *1-O-(hydrocarbon group)-O-(hydrocarbon group)-*2 *1-C(=O)-NH-(hydrocarbon group)-*2 *1-NH-C(=O)-NH-(hydrocarbon group)-*2 *1-O-C(=O)-NH-(hydrocarbon group)-*2

[0141] *1 indicates the bonding position with L, and *2 indicates the bonding position with Si.

[0142] The hydrocarbon group contained in the divalent linking group that does not contain a fluorine atom and is represented by Y in Formula 1 may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The above hydrocarbon group is preferably an aliphatic hydrocarbon group, and more preferably an alkylene group. The alkylene group may be a linear alkylene group, a branched alkylene group, or a cyclic alkylene group. The alkylene group is preferably a linear alkylene group.

[0143] From the viewpoint of improving the durability of the non-fluorinated liquid-repellent film by further agglomerating the hydrocarbon groups, it is preferable that Y is a single bond. Also, from the viewpoint of discharge reliability, it is preferable that k is 3 or greater.

[0144] The substructure represented by formula 1 above is preferably formed using a compound represented by the following formula 11 or formula 12: L-Y-SiX3 ...Formula 11 L-Y-SiNR 11 NSi-Y-L...Formula 12

[0145] In formula 11, L is a hydrocarbon group, Y is a single bond or a divalent linking group that does not contain a fluorine atom, and X is independently a hydrolyzable group. Compounds represented using formula 11 and compounds represented using formula 12 may be used in combination, and compounds other than those represented using formula 11 and formula 12 that do not contain a fluorine atom may be used in combination, to the extent that the effects resulting from the use of the above compounds are not impaired.

[0146] In formula 12, L is independently a hydrocarbon group, Y is independently a single bond or a divalent linking group that does not contain a fluorine atom, and R 11 This is either a hydrogen atom or a methyl group.

[0147] A preferred embodiment of the hydrocarbon group represented by L in formulas 11 and 12 is the same as that of the hydrocarbon group represented by L in formula 1. A preferred embodiment of the fluorine-free divalent linking group represented by Y in formulas 11 and 12 is the same as that of the fluorine-free divalent linking group represented by Y in formula 1. In formulas 11 and 12, Y is preferably a single crystal.

[0148] Examples of hydrolyzable groups represented by X in formula 11 include halogen atoms, alkoxy groups, and acyloxy groups. Hydrolyzable groups are preferably halogen atoms or alkoxy groups, and more preferably alkoxy groups.

[0149] Examples of halogen atoms include chlorine, bromine, and iodine atoms. Chlorine atoms are preferred as the halogen atom. The alkoxy group is preferably an alkoxy group having 1 to 6 carbon atoms, and more preferably an alkoxy group having 1 to 3 carbon atoms. When the hydrolyzable group is an alkoxy group, the density of the non-fluorine-based liquid-repellent film is relatively improved, and the alkali resistance is also relatively improved.

[0150] A non-fluorinated liquid-repellent film having a substructure represented by formula 1 can be obtained using a compound represented by formula 11 or formula 12. The non-fluorinated liquid-repellent film may contain hydrolysates of the compound represented by formula 11 or formula 12. The hydrolysates of the compound represented by formula 11 or formula 12 have Si-O-Si bonds, which can relatively improve the durability of the non-fluorinated liquid-repellent film.

[0151] The thickness of the non-fluorine-based liquid-repellent film is preferably 50 nanometers or less, and more preferably 0.5 nanometers or more and 40 nanometers or less. When the thickness of the non-fluorine-based liquid-repellent film is 50 nanometers or less, discharge curvature is suppressed and the straightness of discharge is improved.

[0152] <Other> The technical scope of the present invention is not limited to the scope described in the embodiments above. The configurations and other elements in each embodiment can be appropriately combined with those in each embodiment without departing from the spirit of the present invention.

[0153] 1...Substrate 10...Inkjet printing device 12...Transport device 20...Cylinder 22...Claw device 30...Printing cylinder 32...Printing cylinder claw device 34...Ink ejection section 36...Print bar 36a...Print bar 36b...Print bar 36c...Print bar 36d...Print bar 38...Ink drying lamp 40...Cylinder 42...Claw device 100...Nozzle surface 100A...Liquid-repellent film 100-i...Nozzle surface 102-i...Inkjet head 102-iA...Memory 104-i...Nozzle arrangement section 106...Nozzle row 108...Nozzle 110...Support frame 112...Dummy plate 112A...Surface 114...Cable 122...Ejector 124...Pressure chamber 126...Piezoelectric element 128...Nozzle flow path 130...Individual supply path 132...Nozzle section 134...Common supply channel 136...Diaphragm 138...Individual electrode 140...Piezoelectric element 142...Common recovery channel 144...Individual recovery channel 146...Cover plate 148...Movable space 300...Inkjet head 302...Nozzle surface 304...Nozzle 306...Abnormal part 400...Inkjet head 402...Nozzle surface 404...Ink tank 406...Liquid level 408...Supply channel 410...Ink cartridge 412...Porous material 420...Inkjet head 430...Supply channel 432...Supply pump 434...Recovery channel 436...Recovery pump 438...Flow resistance element 500...Integration control unit 502...Transportation control unit 504...Discharge control unit 506...Drying control unit 510...Input device 512...Output device D1...Ink droplet D2...Ink droplet F1A...State F1B...State F1C...State F1D...State F1E...State I...Ink P1...Suction start position P2...Suction end position S1, S2...Steps for adjusting the inkjet printer

Claims

1. An inkjet printing apparatus for printing an image by ejecting ink onto a substrate, comprising an inkjet head in which nozzles for ejecting ink are arranged on the nozzle surface, wherein the inkjet head has one of a fluorine-based liquid-repellent film and a non-fluorine-based liquid-repellent film on the nozzle surface, and the ink pressure of the nozzles of the inkjet head when printing the image is set to a first pressure when the nozzle surface has the fluorine-based liquid-repellent film, and to a second pressure smaller than the first pressure when the nozzle surface has the non-fluorine-based liquid-repellent film.

2. The inkjet printing apparatus according to claim 1, wherein the non-fluorine-based liquid-repellent film comprises at least one of silicone, hydrocarbon, metal oxide, and hydrophobic metal.

3. The difference between the first pressure and the second pressure is greater than 500 [Pa], the inkjet printing apparatus according to claim 1.

4. The inkjet printing apparatus according to claim 1, wherein the static contact angle of the fluorine-based liquid-repellent film with respect to the ink is greater than the static contact angle of the non-fluorine-based liquid-repellent film with respect to the ink.

5. The inkjet printing apparatus according to claim 1, wherein the dynamic contact angle of the fluorine-based liquid-repellent film with respect to the ink is greater than the dynamic contact angle of the non-fluorine-based liquid-repellent film with respect to the ink.

6. The inkjet printing apparatus according to claim 1, wherein the static surface tension of the ink is 38.0 [mN / m] or less.

7. The inkjet printing apparatus according to claim 1, wherein the ink is an active energy ray curable ink that hardens upon irradiation with active energy rays.

8. The inkjet printing apparatus according to claim 1, wherein the ink is an aqueous ink.

9. The ink ejection frequency of the inkjet head is 50 kHz or higher, as described in claim 1.

10. The inkjet printing apparatus according to claim 1, wherein the inkjet head is equipped with a memory for storing information on the liquid-repellent film.

11. An inkjet printing apparatus according to claim 1, comprising a processor, wherein the processor sets the pressure of the ink in the nozzles of the inkjet head when printing the image to the first pressure when the nozzle surface has the fluorine-based liquid-repellent film, and to the second pressure when the nozzle surface has the non-fluorine-based liquid-repellent film.

12. An inkjet printing apparatus according to any one of claims 1 to 11, comprising a plurality of inkjet heads, wherein the plurality of inkjet heads constitute a print bar that ejects one color of ink.

13. An inkjet printing apparatus according to claim 12, comprising a plurality of supply channels for supplying ink to each of the plurality of inkjet heads, wherein the flow resistance of the supply channels when printing the image is set such that the supply channel supplying ink to the inkjet head whose nozzle surface has the fluorine-based liquid-repellent film has a first flow resistance, and the supply channel supplying ink to the inkjet head whose nozzle surface has the non-fluorine-based liquid-repellent film has a second flow resistance greater than the first flow resistance.

14. An inkjet printing apparatus according to claim 12, comprising a plurality of print bars, each ejecting ink of a different color, and printing the image in a single-pass manner by moving the plurality of print bars and the substrate relative to each other in the relative movement direction.

15. A method for adjusting an inkjet printing apparatus that prints an image by ejecting ink onto a substrate, wherein the inkjet printing apparatus comprises an inkjet head on which nozzles for ejecting ink are arranged on the nozzle surface, the inkjet head has one of a fluorine-based liquid-repellent film and a non-fluorine-based liquid-repellent film on the nozzle surface, and the pressure of the ink in the nozzles of the inkjet head when printing the image is set to a first pressure when the nozzle surface has the fluorine-based liquid-repellent film, and to a second pressure smaller than the first pressure when the nozzle surface has the non-fluorine-based liquid-repellent film.

16. A program that causes a computer to execute the adjustment method for an inkjet printing apparatus according to claim 15.

17. A non-temporary and computer-readable recording medium on which the program described in claim 16 is recorded.

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