Maintenance method and recording device

Abstract

Providing maintenance methods with superior cleaning performance. [Solution] A maintenance method for an inkjet head having a nozzle for discharging liquid, a channel for supplying the liquid to the nozzle, and a piezoelectric element provided in the channel, comprising: a bubble generation step of vibrating the piezoelectric element to generate bubbles in the cleaning liquid in the channel; and a cleaning liquid discharge step of discharging the cleaning liquid from the nozzle together with the bubbles, wherein the dissolved oxygen concentration DO0 of the cleaning liquid at the time it is supplied to the channel exceeds 4 mg / L, and the vibration frequency of the piezoelectric element in the bubble generation step is 5 kHz or higher.

Description

Technical Field

[0001] The present invention relates to a maintenance method and a recording device.

Background Art

[0002] The inkjet recording method uses a relatively simple device and can record high-definition images, and has been rapidly developed in various fields. Among them, various studies have been made on improving image quality and preventing clogging. For example, Patent Document 1 describes a maintenance liquid for an inkjet printer that contains a solvent having a predetermined structure for the purpose of efficiently cleaning printer members without corrosion and stably injecting ink after cleaning, and further having a dissolved oxygen amount of 45 mg / L to 10 mg / L.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional cleaning method of wiping the nozzles with a cleaning liquid or immersing the members in the cleaning liquid, the cleaning is insufficient, and clogging and removal of foreign matters may not be sufficiently performed.

Means for Solving the Problems

[0005] The present invention relates to a maintenance method for a recording device equipped with an inkjet head having a nozzle for discharging a liquid, a channel for supplying the liquid to the nozzle, and a piezoelectric element provided in the channel, comprising: a bubble generation step of vibrating the piezoelectric element to generate bubbles in the cleaning liquid in the channel; and a cleaning liquid discharge step of discharging the cleaning liquid from the nozzle together with the bubbles, wherein the dissolved oxygen concentration of the cleaning liquid at the time it is supplied to the channel exceeds 4 mg / L, and the vibration frequency of the piezoelectric element in the bubble generation step is 5 kHz or higher.

[0006] The recording method of the present invention comprises a maintenance step of performing the above maintenance method and an ink ejection step of ejecting ink from the inkjet head after maintenance and adhering it to a recording medium.

[0007] The present invention relates to a recording device for performing the above maintenance method, comprising an inkjet head having a nozzle for ejecting liquid, a channel for supplying the liquid to the nozzle, and a piezoelectric element provided in the channel, and a control unit for controlling the ejection of the liquid, wherein the control unit performs a bubble generation step in which the piezoelectric element is vibrated at 5 kHz or higher to generate bubbles in a cleaning solution in which the dissolved oxygen concentration inside the channel exceeds 4 mg / L, and a cleaning solution ejection step in which the cleaning solution is ejected from the nozzle together with the bubbles. [Brief explanation of the drawing]

[0008] [Figure 1] An example of a recording device used in this embodiment is shown. [Figure 2] An example of the configuration of the inkjet head used in this embodiment is shown. [Figure 3] Table 1 shows the composition of each composition used in the examples. [Figure 4] Table 2 shows the experimental conditions and evaluation results in the examples. [Modes for carrying out the invention]

[0009] The embodiments of the present invention (hereinafter referred to as "these embodiments") will be described in detail below, with reference to the drawings as necessary. However, the present invention is not limited thereto, and various modifications are possible without departing from its essence. In the drawings, the same elements will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Moreover, the dimensional ratios in the drawings are not limited to those shown.

[0010] 1. Maintenance Method The maintenance method of this embodiment is a maintenance method for a recording device equipped with an inkjet head having a nozzle for discharging liquid, a channel for supplying liquid to the nozzle, and a piezoelectric element provided in the channel, and includes a bubble generation step of vibrating the piezoelectric element to generate bubbles in the cleaning liquid in the channel, and a cleaning liquid discharge step of discharging the cleaning liquid from the nozzle together with the bubbles, wherein the dissolved oxygen concentration of the cleaning liquid at the time it is supplied to the channel exceeds 4 mg / L, and the vibration frequency of the piezoelectric element in the bubble generation step is 5 kHz or higher.

[0011] When ultraviolet light leaking from the irradiator hits the vicinity of the recording device's nozzle, the ink near the nozzle hardens or thickens, making it easy for solidified or thickened substances derived from the ink to adhere to the area near the nozzle in the ink flow path. This adhesion of thickened substances can obstruct ink ejection, resulting in dot loss or misalignment of the target area.

[0012] In contrast, in this embodiment, by using a cleaning solution with a high dissolved oxygen content and vibrating a piezoelectric element at a high frequency of 5 kHz or higher, a large number of bubbles with high cleaning power can be generated in the cleaning solution within the flow path. Then, by discharging the cleaning solution containing these bubbles from the nozzle, solid matter and viscous substances adhering to the surface of the nozzle and components near the nozzle can be efficiently removed. However, the mechanism in this embodiment is not limited to this.

[0013] The following describes each step of the maintenance method in this embodiment.

[0014] 1.1. Bubble generation process In this embodiment, the bubble generation process involves vibrating a piezoelectric element provided on the inkjet head to generate bubbles in the cleaning liquid within the flow path of the inkjet head. To explain the bubble generation process, Figure 1 shows a schematic partial cross-sectional view of the inkjet head 2, which is cut to include the nozzle N.

[0015] As shown in Figure 1, the inkjet head 2 comprises a nozzle N for ejecting liquid, a flow path 26 for supplying liquid to the nozzle N, and a piezoelectric element 25 provided in the flow path 26. The nozzle N is a through-hole provided in the nozzle plate 22 through which liquid such as an ink composition is ejected. The nozzle plate 22 is a plate-shaped member that constitutes the lower surface of the inkjet head 2. If solid matter or thickening agents derived from ink adhere to the nozzle, ejection may be hindered, but these solid matter and thickening agents can be efficiently removed by the maintenance method of this embodiment.

[0016] The flow path 26 is a space for supplying liquid to the nozzle N. The flow path 26 may be partitioned by the nozzle plate 22, the flow path substrate 23, and the diaphragm 24. The flow path 26 is in communication with the liquid supply pipe 20 via the inlet 27.

[0017] The diaphragm 24 may be positioned at the upper opening of the space formed by the nozzle plate 22 and the flow channel substrate 23. A piezoelectric element 25 is bonded to the upper surface of the diaphragm 24. When the piezoelectric element 25 is driven by a drive signal, the diaphragm 24 also deforms. For example, by driving the piezoelectric element 25, the diaphragm 24 is deformed, and the pressure in the flow channel 26 is changed, causing the liquid filled in the flow channel 26 to be discharged from the nozzle N. Alternatively, by driving the piezoelectric element 25, the diaphragm 24 can be vibrated, generating bubbles in the liquid in the flow channel 26.

[0018] Bubbles generated by the high-frequency vibration of the piezoelectric element are likely to adsorb foreign substances because their surfaces are charged, and they have a high cleaning power. By generating such bubbles, the cleaning performance of the cleaning liquid can be improved.

[0019] The generation of bubbles is performed as follows, for example. First, a drive signal is transmitted from the control unit to the piezoelectric element. The piezoelectric element that receives the drive signal vibrates together with the diaphragm. Due to this vibration, bubbles are generated in the cleaning liquid in the flow path.

[0020] The bubbles generated in the flow path undergo volume vibration due to the vibration of the piezoelectric element. When adjacent bubbles are in the same phase, an attractive force acts between the bubbles. Therefore, while the diaphragm is vibrating, the bubbles attract each other, so the bubbles stay near the diaphragm.

[0021] The vibration frequency of the piezoelectric element in the bubble generation process is 5 kHz or more, preferably 5 kHz or more and 100 kHz or less. When the vibration frequency is within the above range, the bubbles generated by the vibration have charged surfaces, are likely to adsorb foreign substances, and have a high cleaning power. The vibration frequency of the piezoelectric element is preferably 8 kHz or more and 90 kHz or less, 20 kHz or more and 80 kHz or less, 30 kHz or more and 70 kHz or less, 40 kHz or more and 60 kHz or less. When the vibration frequency of the piezoelectric element in the bubble generation process is within the above range, bubbles are more likely to be generated, and the cleaning performance tends to be further improved.

[0022] The vibration time of the piezoelectric element in the bubble generation process is preferably 3 seconds or more, 5 seconds or more, 8 seconds or more, 10 seconds or more. When the vibration time of the piezoelectric element in the bubble generation process is within the above range, bubbles are more likely to be generated, and the cleaning performance tends to be further improved. The vibration of the piezoelectric element may be continuous or intermittent. Also, the vibration time of the piezoelectric element is preferably 60 seconds or less, 50 seconds or less, 40 seconds or less, 30 seconds or less, 20 seconds or less.

[0023] The dissolved oxygen concentration (DO0) of the cleaning solution at the point of supply to the flow path is greater than 4 mg / L. When the dissolved oxygen concentration of the cleaning solution is sufficiently high, the number of bubbles generated in the bubble generation process increases, resulting in superior cleaning performance.

[0024] The dissolved oxygen concentration (DO0) is preferably 5 mg / L or higher, 9 mg / L or higher, and 14 mg / L or higher. Furthermore, the dissolved oxygen concentration (DO0) is preferably 100 mg / L or lower, 50 mg / L or lower, 30 mg / L or lower, and 20 mg / L or lower. When the dissolved oxygen concentration (DO0) is within the above range, it tends to generate bubbles more easily, further improving cleaning performance.

[0025] The dissolved oxygen concentration DO1 of the cleaning solution when it is contained in the liquid container may be lower or higher than the dissolved oxygen concentration DO0. If the dissolved oxygen concentration DO1 is lower than the dissolved oxygen concentration DO0, for example, the dissolved oxygen concentration of the cleaning solution may be increased by using an intake module provided in the liquid supply pipe, so that the dissolved oxygen concentration DO0 exceeds 4 mg / L by the time it is supplied to the flow path in the inkjet head. Also, even if the dissolved oxygen concentration DO1 is higher than the dissolved oxygen concentration DO0, the dissolved oxygen concentration may be further increased using an intake module or the like, or the dissolved oxygen concentration may be decreased using a degassing module provided in the liquid supply pipe, to adjust the dissolved oxygen concentration DO0 of the cleaning solution supplied to the inkjet head to a desired value.

[0026] The dissolved oxygen concentration DO1 is preferably 5 mg / L or higher, 9 mg / L or higher, and 14 mg / L or higher. The dissolved oxygen concentration DO1 is preferably 100 mg / L or lower, 50 mg / L or lower, 30 mg / L or lower, and 20 mg / L or lower. When the dissolved oxygen concentration DO1 is within the above range, the cleaning performance tends to improve further.

[0027] In this specification, the dissolved oxygen concentration can be measured by conventionally known methods, but the value obtained by the measurement method used in the experiments conducted in the examples described later shall be adopted. Examples of intake treatments to set the dissolved oxygen concentration to a predetermined value include air intake by an intake module and oxygen bubbling. Examples of degassing treatments include methods using degassing equipment such as vacuum degassing and inert gas bubbling.

[0028] 1.2. Washing solution dispensing process The cleaning solution discharge process involves discharging the cleaning solution from the flow path through a nozzle. By discharging a cleaning solution containing highly effective bubbles generated in the bubble generation process through the nozzle, solid ink particles and thickened substances adhering to the nozzle can be efficiently removed.

[0029] The method of discharging the liquid is not particularly limited. For example, the liquid may be discharged from the nozzle by changing the volume inside the flow path by driving a piezoelectric element. Alternatively, the cleaning liquid inside the flow path may be pressurized towards the nozzle by other means, or the outside of the nozzle may be depressurized to discharge the cleaning liquid from the nozzle. For example, the cleaning liquid may be discharged from the nozzle by pressurizing the cleaning liquid inside the flow path using a pressure change mechanism provided in the inkjet head or liquid supply pipe, or a suction mechanism may be used to cap the nozzle plate side of the inkjet head and depressurize and suck out the liquid inside the nozzle from the outside of the nozzle plate.

[0030] The cleaning solution is preferably discharged to a discharge port. Discharging the cleaning solution to a discharge port tends to make the disposal of the cleaning solution easier. The discharge port is not particularly limited, but examples include the discharge port of the recording device, a waste liquid tray, and a waste liquid pad.

[0031] 2. Recording device Next, the recording device in this embodiment will be described. The recording device in this embodiment is a recording device that performs the maintenance method described above, and comprises an inkjet head having a nozzle for ejecting liquid, a flow path for supplying the liquid to the nozzle, and a piezoelectric element provided in the flow path, and a control unit for controlling the ejection of the liquid. In the maintenance method described above, the control unit performs a bubble generation step in which the piezoelectric element is vibrated at 5 kHz or higher to generate bubbles in the cleaning liquid in which the dissolved oxygen concentration inside the flow path exceeds 4 mg / L, and a cleaning liquid ejection step in which the cleaning liquid is ejected from the nozzle together with the bubbles.

[0032] Figure 2 is a perspective view showing the configuration of the recording device in this embodiment. The recording device 1 shown in Figure 2 is a serial printer, but the recording device in this embodiment may be a line printer. A serial printer is a device in which a head unit is mounted on a carriage that moves in the main scanning direction (horizontal direction, width direction of the recording medium), and droplets are ejected from nozzles onto the recording medium as the carriage moves. A line printer is a device in which the head is fixed and the recording medium is moved along the sub-scanning direction (vertical direction, transport direction of the recording medium), and droplets are ejected from the nozzles of the head in conjunction with this movement.

[0033] As shown in Figure 2, the recording device 1 includes a carriage 3 on which an inkjet head 2 is mounted, a carriage movement mechanism 4 that moves the carriage 3 in the recording medium width direction of the recording medium P, and a media feeding mechanism 5 that transports the recording medium P in the recording medium feeding direction. The recording device 1 also includes a control unit 6 that controls the operation of the entire recording device 1. The recording medium width direction refers to the main scanning direction (head scanning direction). The media feeding direction refers to the sub-scanning direction (direction perpendicular to the main scanning direction).

[0034] As shown in Figure 2, the inkjet head 2 is connected to the liquid storage unit 10 via a liquid supply pipe 20. The inkjet head 2 is connected to the liquid storage unit 10, which individually stores the ink composition and cleaning solution, via the liquid supply pipe 20. The ink composition and cleaning solution may be supplied to the inkjet head 2 by a switching means, or the ink composition and cleaning solution may be supplied to the inkjet head 2 by swapping the liquid storage unit 10 that stores the ink composition with the liquid storage unit 10 that stores the cleaning solution.

[0035] The liquid storage section 10 contains the ink composition and cleaning solution ejected from the inkjet head 2. Examples of the liquid storage section 10 include a removable cartridge, a bag-shaped pack made of a flexible film, and a tank to which the ink and cleaning solution can be refilled.

[0036] The liquid supply pipe 20 may be fitted with an intake module that allows air to be drawn into the liquid. By drawing air into the cleaning solution using the intake module, the dissolved oxygen concentration of the cleaning solution can be increased. The intake module is not particularly limited, but a commercially available example is the EF-G3 (product name, manufactured by DIC Corporation).

[0037] In this embodiment, the recording device 1 is exemplified as a so-called off-carriage type printer, in which the ink storage unit 10 is mounted on the housing of the recording device 1 and ink is supplied to the inkjet head 2 via the ink supply pipe 20. However, it is not limited to this. For example, a so-called on-carriage type printer, in which the ink cartridges are mounted on a carriage, may be used. It may also be used in a linehead type printer that does not have a carriage.

[0038] The control unit 6 controls liquid ejection, liquid delivery, and maintenance operations. For example, it outputs a drive signal to the inkjet head 2 to control ink ejection to the recording medium. The control unit 6 may be composed of, for example, a processing circuit such as a CPU (Central Processing Unit) or FPGA (Field Programmable Gate Array) and a storage circuit such as a semiconductor memory. In particular, in this embodiment, the control unit 6 performs a bubble generation step in which a piezoelectric element is vibrated at 5 kHz or higher to generate bubbles in a cleaning solution in which the dissolved oxygen concentration inside the flow path exceeds 4 mg / L, and a cleaning solution ejection step in which the cleaning solution is ejected from the nozzle along with the bubbles.

[0039] The inkjet head 2, under the control of the control unit 6, ejects liquid, for example, by adhering an ink composition to a recording medium or ejecting a cleaning solution. The inkjet head 2 comprises one or more inkjet heads 2. The ink composition to be ejected is not particularly limited, and for example, a total of four ink compositions of black, cyan, magenta, and yellow may be ejected. Multiple inkjet heads may be provided for each color.

[0040] The recording device 1 may include an discharge unit for discharging ink or liquid from the nozzle N to a recording medium. The discharge unit may include, for example, an outlet, a waste liquid tray, and a waste liquid pad.

[0041] The recording device 1 may also include a pressure change mechanism. The pressure change mechanism is configured to pressurize or depressurize the flow path 26. The pressure change mechanism is connected to the flow path 26. The pressure change mechanism is, for example, a pump. The pressure change mechanism may pressurize or depressurize the liquid inside the flow path, thereby causing the liquid in the flow path 26 to be discharged from the nozzle N.

[0042] 3. Cleaning solution The cleaning solution according to this embodiment is supplied to the flow path inside the inkjet head, generates bubbles, and is then discharged from the nozzle to perform maintenance on the inkjet head.

[0043] The cleaning solution is not particularly limited, but examples include a radioactive curing ink composition and a radioactive curing ink from which the colorant and polymerization initiator have been removed. In this embodiment, a radioactive curing ink composition refers to one that hardens when irradiated with radiation. Examples of radiation include ultraviolet rays, electron beams, infrared rays, visible light, and X-rays. Among these, ultraviolet rays are preferred because radiation sources are readily available and widely used, and materials suitable for curing by ultraviolet radiation are readily available and widely used. The cleaning solution includes, for example, a colorant, a polymerizable compound, a polymerization initiator, a polymerization inhibitor, and a surfactant.

[0044] 3.1. Colorants The cleaning solution of this embodiment may contain a colorant. When an ink composition containing a colorant is used as the cleaning solution, there is no need to prepare a new cleaning solution, making maintenance easier. The colorant may be either a pigment or a dye. The pigment may be an organic pigment or an inorganic pigment. One type of colorant may be used alone, or two or more types may be used in combination.

[0045] Examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, condensed azo pigments, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, quinacridone pigments, perylene pigments, perinone pigments, anthraquinone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye chelates such as basic dye type chelates and acid dye type chelates; and nitro pigments and nitroso pigments.

[0046] In addition, examples of inorganic pigments include titanium dioxide, iron oxide yellow, iron oxide brown, chromium oxide, Prussian blue, ultramarine, molybdenum red, iron oxide black, lead yellow, composite oxide pigments, and carbon black such as Pigment Black 7.

[0047] The dyes used are not particularly limited and include acid dyes, direct dyes, reactive dyes, basic dyes, etc.

[0048] Specific examples of dyes are not limited to those mentioned above, but include, for example, CI Acid Yellow 17, 23, 42, 44, 79, 142; CI Acid Red 52, 80, 82, 249, 254, 289; CI Acid Blue 9, 45, 249; CI Acid Black 1, 2, 24, 94; CI Food Black 1, 2; CI Direct Yellow 1, 12, 24, 33, 50; CI Direct Red 1, 4, 9, 80, 81, 225, 227; CI Direct Blue 1, 2, 15, 71, 86, 87, 98; CI Direct Black 19, 38, 51, 71, 154; CI Reactive Red 14, 32, 55, 79, 249; and CI Reactive Black 3, 4, 35.

[0049] In the cleaning solution of this embodiment, the colorant content is preferably 0% to 20% by mass, 0.7% to 15% by mass, 1% to 10% by mass, or 1.5% to 5% by mass, relative to the total amount of the cleaning solution.

[0050] 3.2. Polymerizable compounds Polymerizable compounds are not particularly limited, but examples include monofunctional monomers and polyfunctional monomers. Polymerizable compounds can be used individually or in combination of two or more.

[0051] The monofunctional monomers are not particularly limited, but examples include dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, tert-butylcyclohexanol (meth)acrylate, 2-(meth)acrylate-1,4-dioxaspiro[4,5]decy-2-ylmethyl, phenoxyethyl (meth)acrylate, benzyl Examples include methyl(meth)acrylate, alkoxylated 2-phenoxyethyl(meth)acrylate, ethoxylated nonylphenyl(meth)acrylate, alkoxylated nonylphenyl(meth)acrylate, p-cumylphenol EO modified(meth)acrylate, and 2-hydroxy-3-phenoxypropyl(meth)acrylate, benzyl acrylate, cyclic trimethylolpropaneformal acrylate, 4-tetra-butylcyclohexyl acrylate, and 4-hydroxybutyl acrylate.

[0052] The polyfunctional monomers are not particularly limited, but examples include 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and 3-methyl-1,5-pentanediol diacrylate.

[0053] In the cleaning solution of this embodiment, the content of monofunctional monomers is preferably 0.5% to 90% by mass, 10% to 55% by mass, 20% to 50% by mass, and 30% to 45% by mass, relative to the total amount of the cleaning solution. When the content of monofunctional monomers is within the above range, the cleaning performance tends to be further improved.

[0054] In the cleaning solution of this embodiment, the content of the polyfunctional monomer is preferably 0.5% to 80% by mass, 20% to 75% by mass, 40% to 70% by mass, and 55% to 65% by mass, relative to the total amount of the cleaning solution. When the content of the polyfunctional monomer is within the above range, the cleaning performance tends to be further improved.

[0055] In the cleaning solution of this embodiment, the total content of polymerizable compounds is preferably 1% to 100% by mass, 80% to 99.9% by mass, 90% to 99.7% by mass, and 95% to 99.5% by mass, relative to the total amount of the cleaning solution. When the content of polymerizable compounds is within the above range, the cleaning performance tends to be further improved.

[0056] 3.3. Polymerization Initiators The cleaning solution according to this embodiment may contain a polymerization initiator. When an ink composition containing a polymerization initiator is used as a cleaning solution, there is no need to prepare a new cleaning solution, making maintenance easier. The polymerization initiator is not particularly limited, but examples include alkylphenone-based polymerization initiators, acylphosphine oxide-based polymerization initiators, titanocene-based polymerization initiators, and thioxanthone polymerization initiators.

[0057] Acylphosphine oxide polymerization initiators are not particularly limited, but examples include bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. These acylphosphine oxide polymerization initiators may be used individually or in combination of two or more.

[0058] Examples of commercially available acylphosphine oxide polymerization initiators include "IRGACURE819" (product name, manufactured by BASF, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), "IRGACURE TPO" (product name, manufactured by BASF, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide), "DAROCUR TPO" (product name, manufactured by BASF, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide), and "IRGACURE TPO-L" (product name, manufactured by BASF, ethyl(2,4,6-trimethylbenzoyl)-phenylphosphenate).

[0059] The thioxanthone polymerization initiator is not particularly limited, but examples include thioxanthone, 2-methylthioxanthone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, and 2,4-diethylthioxanthone, 2,4-diethylthioxanthe-9-one, diester of carboxymethoxythioxanthone and polytetramethylene glycol, and 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthone Examples include α-(1-chloro-9-oxo-9H-thioxanthene-4-yl)oxyacetylpoly[oxy(1-methylethylene)])oxy)-2,2-bis((1-chloro-9-oxo-9H-thioxanthene-4-yl)oxyacetylpoly[oxy(1-methylethylene)])oxymethylpropane) and alpha-(2-(9-oxo-9H-thioxantheneyl)oxy)acetyl)-omega-(2-(9-oxo-9H-thioxantheneyl)oxy)acetyl)oxy)poly(oxy-1,4-butanediyl).

[0060] A commercially available thioxanthone polymerization initiator is, for example, Speedcure DETX (manufactured by Lambson, 2,4-diethylthioxanthene-9-one).

[0061] In the cleaning solution of this embodiment, the content of the polymerization initiator is preferably 1% by mass or more and 30% by mass or less, 5% by mass or more and 25% by mass or less, or 10% by mass or more and 20% by mass or less, relative to the total amount of the cleaning solution.

[0062] In another embodiment, the cleaning solution may be substantially free of polymerization initiators. By substantially free of polymerization initiators, it is possible to prevent the cleaning solution from solidifying in the flow path. Substantially free of polymerization initiators means that the content of polymerization initiators is less than 1% by mass, 0 to 0.5% by mass, 0 to 0.3% by mass, or 0 to 0.1% by mass, relative to the total amount of the cleaning solution.

[0063] 3.4 Polymerization Inhibitors The cleaning solution of this embodiment may contain a polymerization inhibitor. The polymerization inhibitor is not particularly limited, but examples include phenol compounds, quinone compounds, amine compounds, nitro compounds, oxime compounds, and sulfur compounds. These polymerization inhibitors may be used individually or in combination of two or more.

[0064] The phenolic compounds are not particularly limited, but examples include p-methoxyphenol, cresol, tert-butylcatechol, di-tert-butylpara-cresol, hydroquinone monomethyl ether, α-naphthol, 3,5-di-tert-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-butylphenol), and 4,4'-thiobis(3-methyl-6-tert-butylphenol).

[0065] The quinone compounds are not particularly limited, but examples include p-benzoquinone, anthraquinone, naphthoquinone, phenanthraquinone, p-xyloquinone, p-toluquinone, 2,6-dichloroquinone, 2,5-diphenyl-p-benzoquinone, 2,5-diacetoxy-p-benzoquinone, 2,5-dicapoxy-p-benzoquinone, 2,5-diasiloxy-p-benzoquinone, hydroquinone, 2,5-dibutylhydroquinone, mono-t-butylhydroquinone, monomethylhydroquinone, and 2,5-di-t-amylhydroquinone.

[0066] The amine compounds are not particularly limited, but examples include phenyl-β-naphthylamine, p-benzylaminophenol, di-β-naphthylparaphenylenediamine, dibenzylhydroxylamine, phenylhydroxylamine, diethylhydroxylamine, compounds having a 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton, compounds having a 2,2,6,6-tetramethylpiperidine skeleton, compounds having a 2,2,6,6-tetramethylpiperidine-N-alkyl skeleton, and compounds having a 2,2,6,6-tetramethylpiperidine-N-acyl skeleton.

[0067] The nitro compounds are not particularly limited, but examples include dinitrobenzene, trinitrotoluene, picric acid, p-methoxyphenol, hydroquinone monomethyl ether, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl, and derivatives thereof.

[0068] Examples of oxime compounds include quinone dioxime and cyclohexanone oxime, although these are not particularly limited. Examples of sulfur compounds include phenothiazine, although these are not particularly limited.

[0069] In the cleaning solution of this embodiment, the content of the polymerization inhibitor is preferably 0.01% by mass or more and 5.0% by mass or less, 0.05% by mass or more and 3.0% by mass or less, or 0.1% by mass or more and 1.0% by mass or less, relative to the total amount of the cleaning solution. When the content of the polymerization inhibitor is within the above range, the cleaning performance tends to be further improved.

[0070] 3.5. Surfactants The cleaning solution of this embodiment may contain a surfactant. The surfactant is not particularly limited, but examples include silicone-based surfactants. The silicone-based surfactant is not particularly limited, but examples include polyester-modified silicones such as polyether-modified polydimethylsiloxane, and polyether-modified silicones such as polyester-modified polydimethylsiloxane.

[0071] Examples of commercially available silicone-based surfactants include "BYK-347," "BYK-348," "BYK-UV3500," "BYK-UV3510," "BYK-UV3530," and "BYK-UV3570" (all manufactured by BYK Corporation).

[0072] In the cleaning solution of this embodiment, the surfactant content is preferably 0.01% by mass or more and 5.0% by mass or less, 0.05% by mass or more and 3.0% by mass or less, or 0.1% by mass or more and 1.0% by mass or less, relative to the total amount of the cleaning solution. When the surfactant content is within the above range, the cleaning performance tends to be further improved.

[0073] 4. Ink composition The ink composition used in the recording device according to this embodiment is not particularly limited, but a radiation-curable ink composition is preferred.

[0074] The ink composition in this embodiment includes, for example, a colorant, a polymerizable compound, a polymerization initiator, a polymerization inhibitor, and a surfactant. Examples of each component are given below.

[0075] 4.1. Colorants The ink composition of this embodiment may contain a colorant. Examples of colorants in the ink composition include those exemplified as colorants in cleaning solutions.

[0076] In the ink composition of this embodiment, the colorant content is preferably 0.5% to 20% by mass, 0.7% to 15% by mass, 1% to 10% by mass, or 1.5% to 5% by mass, relative to the total amount of the ink composition. When the colorant content is within the above range, the cleaning effect during maintenance tends to be more easily obtained.

[0077] 4.2. Polymerizable compounds The ink composition of this embodiment may contain polymerizable compounds. Examples of polymerizable compounds in the ink composition include those exemplified as polymerizable compounds in the cleaning solution.

[0078] In the ink composition of this embodiment, the content of monofunctional monomers is preferably 0.5% to 90% by mass, 10% to 45% by mass, 15% to 40% by mass, and 20% to 35% by mass, based on the total amount of the ink composition. When the content of monofunctional monomers is within the above range, a better cleaning effect is more easily obtained when maintenance is performed.

[0079] In the ink composition of this embodiment, the content of the polyfunctional monomer is preferably 0.5% to 80% by mass, 20% to 70% by mass, 30% to 60% by mass, and 40% to 55% by mass, based on the total amount of the ink composition. When the content of the polyfunctional monomer is within the above range, a better cleaning effect is more easily obtained when maintenance is performed.

[0080] In the ink composition of this embodiment, the total content of polymerizable compounds is preferably 1% to 99% by mass, 50% to 95% by mass, 60% to 90% by mass, and 75% to 85% by mass, relative to the total amount of the ink composition. When the content of polymerizable compounds is within the above range, a better cleaning effect tends to be obtained when maintenance is performed.

[0081] 4.3. Polymerization Initiators The ink composition according to this embodiment may contain a polymerization initiator. Examples of polymerization initiators for the ink composition include those used as polymerization initiators for cleaning solutions.

[0082] In the ink composition of this embodiment, the content of the polymerization initiator is preferably 1% to 40% by mass, 5% to 35% by mass, 8% to 30% by mass, 10% to 25% by mass, or 12% to 20% by mass, relative to the total amount of the ink composition. When the content of the polymerization initiator is within the above range, the cleaning effect during maintenance tends to be more easily obtained.

[0083] 4.4 Polymerization Inhibitors The ink composition of this embodiment may contain a polymerization inhibitor. Examples of polymerization inhibitors in the ink composition include those used as polymerization inhibitors in cleaning solutions.

[0084] In the ink composition of this embodiment, the content of the polymerization inhibitor is preferably 0.01% by mass or more and 5.0% by mass or less, 0.05% by mass or more and 3.0% by mass or less, or 0.1% by mass or more and 1.0% by mass or less, relative to the total amount of the ink composition. When the content of the polymerization inhibitor is within the above range, the cleaning effect during maintenance tends to be more easily obtained.

[0085] 4.5. Surfactants The ink composition of this embodiment may contain a surfactant. Examples of surfactants include those exemplified as surfactants in cleaning solutions.

[0086] In the ink composition of this embodiment, the surfactant content is preferably 0.1% to 5.0% by mass, 0.2% to 3.0% by mass, or 0.3% to 1.0% by mass, relative to the total amount of the ink composition. Having the surfactant content within the above range tends to result in a more effective cleaning during maintenance.

[0087] 5. Recording Method The recording method according to this embodiment includes a maintenance step of performing the above-described maintenance method and an ink ejection step of ejecting ink from the inkjet head after maintenance and adhering it to the recording medium.

[0088] 6. Recording media The recording medium used in this embodiment is not particularly limited, and examples include absorbent recording media, low-absorbent recording media, or non-absorbent recording media.

[0089] Examples of absorbent recording media include plain paper such as electrophotographic paper with high ink permeability, and inkjet paper (inkjet-specific paper equipped with an ink-absorbing layer composed of silica particles or alumina particles, or an ink-absorbing layer composed of hydrophilic polymers such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP)).

[0090] Examples of low-absorption recording media include art paper, coated paper, and cast paper, which are commonly used in offset printing and have relatively low ink permeability.

[0091] Examples of non-absorbent recording media include films and plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane; plates of metals such as iron, silver, copper, and aluminum; metal plates or plastic films made by vapor deposition of these metals; plates of alloys such as stainless steel and brass; and recording media in which films of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane are bonded (coated) to a paper substrate.

[0092] Here, the "absorbent recording medium" is defined as having a water absorption rate of 10 mL / m³ from the start of contact to 30 msec in the Bristow method. 2 This refers to a medium that is less than 10 mL / m³. "Low absorption recording media and non-absorbent recording media" have a water absorption capacity of 10 mL / m³. 2 The following refers to the recording medium. The Bristow method is the most widely used method for measuring liquid absorption in a short time and is also adopted by the Japan Paper & Pulp Technology Association (JAPAN TAPPI). Details of the test method are described in standard No. 51 "Paper and cardboard - Liquid absorbency test method - Bristow method" of the "JAPAN TAPPI Paper & Pulp Test Methods 2000 Edition". [Examples]

[0093] The present invention will be described more specifically below using examples and comparative examples. The present invention is not limited in any way by the following examples.

[0094] 1. Ink composition and cleaning solution Each material was mixed according to the composition shown in Table 1 below, and thoroughly stirred to obtain the ink composition and cleaning solution. Specifically, the ink composition and cleaning solution were prepared by uniformly mixing each material and removing insoluble matter with a filter. For the cleaning solution, degassing was performed using a degassing module to obtain cleaning solutions No. 1 to No. 5 to achieve the dissolved oxygen concentration shown in Table 1. In Table 1, unless otherwise specified, the unit of the numerical values ​​is mass%, and the total is 100 mass%. Unless otherwise specified, the values ​​indicate the solid content. [Colorants] Pigment Black 7 [Polymerizable compound] • PEA (phenoxyethyl (meth)acrylate, monofunctional monomer) VEEA (2-(2-vinyloxyethoxy)ethyl acrylate, polyfunctional monomer) • DPGDA (Dipropylene glycol diacrylate, polyfunctional monomer) [Polymerization initiator] • IRGACURE 819 (Product name: Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, manufactured by BASF) • IRGACURE TPO (product name, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, manufactured by BASF) • DETX (2,4-diethylthioxanthene-9-one, manufactured by Lambson) [Polymerization inhibitor] • MEHQ (p-methoxyphenol, manufactured by Tokyo Chemical Industry Co., Ltd.) [Surfactants] • BYK-UV3500 (product name, manufactured by BYK Corporation)

[0095] The dissolved oxygen concentration of the cleaning solution was measured using the following method. [Measurement of dissolved oxygen concentration] The dissolved oxygen concentration (DO0), which is the value at the time the ink is supplied to the flow path inside the inkjet head, was measured using a gas chromatograph Agilent 7890B (manufactured by Agilent Technologies) to determine the amount of dissolved oxygen (gas) in a predetermined volume of washing solution. Helium (He) gas was used as the carrier gas.

[0096] 2. Evaluation Using the obtained cleaning solutions No. 1 to No. 5, the cleaning performance of each example was evaluated according to the following procedure, with the conditions shown in Table 2 as the maintenance conditions for each example.

[0097] [Evaluation of the cleaning effectiveness of each maintenance method] A printer was prepared that allows for the supply of cleaning solution with an arbitrary amount of dissolved oxygen to the inkjet head by attaching an air intake module (DIC Corporation, model EF-G3 (setting +0.03MPa)) to the liquid supply pipe between the liquid storage section and the inkjet head.

[0098] For this printer, the adjusted ink composition was filled into the ink tank, and the adjusted cleaning solution was filled into a separate cleaning solution tank. Printing was performed continuously for 40 minutes using the filled ink composition. This 40-minute continuous printing operation was repeated eight times without performing any maintenance on the inkjet head.

[0099] Next, the printer was operated to switch the connection to the inkjet head from the ink tank to the cleaning solution tank, and the flow path of the inkjet head that had printed was replaced with the cleaning solution. Then, with the inkjet head filled with the cleaning solution, the piezoelectric element was driven and vibrated at the vibration frequency and vibration time shown in Table 2. Next, the cleaning solution in the flow path of the inkjet head was discharged by pressurizing it using a pump installed in the liquid supply pipe of the printer.

[0100] In Example 10, an air intake module was used in the liquid supply pipe to introduce air into the cleaning solution before it was supplied to the inkjet head.

[0101] Subsequently, the ink composition tank was switched back on, and the flow path inside the inkjet head was replaced with the ink composition again before printing a nozzle check pattern to evaluate the cleanability of maintenance in each case. Dot placement deviation refers to a deviation of more than the diameter of one dot from the reference position. (Evaluation Criteria) A. Fewer than 10 out of 8800 nozzles had dot defects or dots with misaligned impact points. B. There were between 10 and 30 instances of dot missing or dot misalignment out of 8800 nozzles. C. More than 30 out of 8800 nozzles had missing dots or dots with misaligned impact points.

[0102] 3. Evaluation Results Examples 1-9, in which the dissolved oxygen concentration (DO0) of the cleaning solution at the point of supply to the flow path exceeded 4 mg / L and the vibration frequency of the piezoelectric element during the bubble generation process was 5 kHz or higher, showed good maintenance cleaning performance. On the other hand, all of the comparative examples showed poor maintenance cleaning performance.

[0103] Furthermore, Example 6, which used cleaning solution No. 3 with a dissolved oxygen content of 15 mg / L, showed superior cleaning performance. In addition, Example 1, in which the cleaning solution was vibrated at a vibration frequency of 50 kHz, also showed superior cleaning performance. Moreover, Example 10, in which cleaning solution No. 1 was used and air was taken in by an intake module, also showed superior cleaning performance. [Explanation of symbols]

[0104] 1...Printer, 2...Inkjet head, 3...Carriage, P...Recording medium, 4...Carriage movement mechanism, 5...Media feeding mechanism, 6...Control unit, 10...Liquid container, 20...Liquid supply pipe, 22...Nozzle plate, N...Nozzle, 23...Flow channel substrate, 24...Diaphragm, 25...Piezoelectric element, 26...Flow channel, 27...Inlet

Claims

1. A method for maintaining an inkjet head having an inkjet head having a nozzle for discharging liquid, a flow path for supplying the liquid to the nozzle, and a piezoelectric element provided in the flow path, A bubble generation step in which the piezoelectric element is vibrated to generate bubbles in the cleaning liquid in the flow path, The process includes a cleaning liquid discharge step in which the cleaning liquid is discharged from the nozzle along with the bubbles, The dissolved oxygen concentration DO0 of the cleaning solution at the time it is supplied to the flow path exceeds 4 mg / L. The vibration frequency of the piezoelectric element in the bubble generation process is 5 kHz or higher. Maintenance instructions.

2. In the cleaning liquid discharge step, the cleaning liquid inside the flow path is pressurized toward the nozzle, or the outside of the nozzle is depressurized, thereby discharging the cleaning liquid from the nozzle. The maintenance method according to claim 1.

3. The dissolved oxygen concentration DO0 of the cleaning solution at the time it is supplied to the flow path is 5 mg / L or more. The maintenance method according to claim 1.

4. The dissolved oxygen concentration DO1 of the cleaning liquid at the time it is contained in the liquid container is higher than the dissolved oxygen concentration DO0 of the cleaning liquid at the time it is supplied to the flow path. The maintenance method according to claim 1.

5. The vibration frequency of the piezoelectric element in the bubble generation process is 5 kHz or more and 100 kHz. The maintenance method according to claim 1.

6. The vibration time of the piezoelectric element in the bubble generation process is 10 seconds or more. The maintenance method according to claim 1.

7. The content of polymerizable compounds in the cleaning solution is 70% by mass or more of the total amount of the cleaning solution. The maintenance method according to claim 1.

8. In the cleaning liquid discharge step, the cleaning liquid is discharged from the nozzle to the drainage section. The maintenance method according to claim 1.

9. The cleaning solution substantially contains no polymerization initiator. The maintenance method according to claim 1.

10. The cleaning solution contains a polymerization initiator. The maintenance method according to claim 1.

11. A maintenance step of performing the maintenance method described in any one of claims 1 to 10, The system includes an ink ejection process for ejecting ink from the inkjet head after maintenance. Recording method.

12. A recording device for performing the maintenance method described in any one of claims 1 to 10, An inkjet head having a nozzle for dispensing liquid, a flow path for supplying the liquid to the nozzle, and a piezoelectric element provided in the flow path, The system comprises a control unit for controlling the discharge of the liquid, The control unit, in the maintenance method, performs a bubble generation step of vibrating the piezoelectric element at 5 kHz or higher to generate bubbles in the cleaning liquid in which the dissolved oxygen concentration inside the flow path exceeds 4 mg / L, and a cleaning liquid discharge step of discharging the cleaning liquid together with the bubbles from the nozzle. Recording device.

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