Method for producing ink and inkjet recording method

Abstract

To provide a method for producing an ink that exhibits excellent continuous printing stability and enables downsizing of an inkjet recording apparatus.SOLUTION: A method for producing an ink comprises: an ultrasonic irradiation step of irradiating a dispersion liquid containing a pigment, a dispersant and a polymerizable compound with ultrasound; and an initiator mixing step of mixing the dispersion liquid with an initiator. The output of the ultrasound is 100 W or more. When a batch-type ultrasonic irradiation device is used in the ultrasonic irradiation step, the ultrasound is irradiated for 2 minutes or more per 20 L of the dispersion liquid. When an inline-type ultrasonic irradiation device is used in the ultrasonic irradiation step, the residence time of the dispersion liquid in a reaction tube of an ultrasonic oscillator of the inline-type ultrasonic irradiation device is 3 seconds or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing ink and an inkjet recording method.

Background Art

[0002] Since the inkjet recording method can record high-definition images with a relatively simple device, it has been rapidly developed in various fields. Among them, various studies have been conducted on the dispersibility of coloring materials in ink. For example, Patent Document 1 discloses an image recording method using an inkjet ink composition containing a pigment. At the time of ink production, without including a pigment dispersion liquid, monomers, photoinitiators, etc. are put into a tank and mixed, and further irradiated with ultrasonic waves to dissolve the initiator, and then the pigment dispersion liquid is added. A method of mixing all raw materials of the ink and then performing vacuum degassing in the final step is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the method described in Patent Document 1, it has been found that in a line printer of a type where degassing is not sufficient and nozzle cleaning is not performed for a long time in particular, air bubbles are generated in the head, leading to printing defects such as nozzle clogging.

Means for Solving the Problems

[0005] The method for manufacturing an ink of the present invention includes an ultrasonic irradiation step of irradiating a dispersion liquid containing a pigment, a dispersant, and a polymerizable compound with ultrasonic waves, and an initiator mixing step of mixing the dispersion liquid and an initiator. The output of the ultrasonic waves is 100 W or more. When a batch-type ultrasonic irradiation device is used in the ultrasonic irradiation step, ultrasonic irradiation is performed for 2 minutes or more per 20 L of the dispersion liquid. When an in-line type ultrasonic irradiation device is used in the ultrasonic irradiation step, the time for which the dispersion liquid stays in the reaction tube of the ultrasonic oscillator of the in-line type ultrasonic irradiation device is 3 seconds or more.

[0006] The inkjet recording method of the present invention includes an adhesion step of discharging the ink obtained by the above manufacturing method from an inkjet head and attaching it to a recording medium, and a drying step of drying the ink attached to the recording medium, and performs long-time recording without performing a nozzle clogging countermeasure step.

Brief Description of Drawings

[0007] [Figure 1] It is a figure which shows an example of the batch type ultrasonic irradiation device used with the manufacturing method of this embodiment. [Diagram 2] It is a figure which shows an example of the in-line type ultrasonic irradiation device used with the manufacturing method of this embodiment. [Diagram 3] It is a schematic cross-sectional view of a line type printer used with the recording method of this embodiment. [Figure 4] It is a table showing the conditions and evaluation results of the examples. [Diagram 5] It is a table showing the conditions and evaluation results of the examples. [Figure 6] It is a table showing the conditions and evaluation results of the examples.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary. However, the present invention is not limited thereto, and various modifications are possible without departing from the gist thereof. In the drawings, the same elements will be denoted by the same reference numerals, and redundant descriptions will be omitted. Also, the positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[0009] 1. Method for manufacturing ink The method for manufacturing ink according to the present embodiment includes an ultrasonic irradiation step of irradiating an ultrasonic wave to a dispersion liquid containing a pigment, a dispersant, and a polymerizable compound, and an initiator mixing step of mixing the dispersion liquid and an initiator. The output of the ultrasonic wave is 100 W or more. When a batch-type ultrasonic irradiation device is used in the ultrasonic irradiation step, ultrasonic irradiation is performed for 2 minutes or more per 20 L of the dispersion liquid. When an in-line type ultrasonic irradiation device is used in the ultrasonic irradiation step, the residence time of the dispersion liquid in the reaction tube of the ultrasonic oscillator of the in-line type ultrasonic irradiation device is set to 3 seconds or more.

[0010] In the conventional method for manufacturing an inkjet ink (hereinafter also simply referred to as "ink"), a degassing step is performed on the ink in the final step from the viewpoint of ensuring that the resulting final product of the ink does not contain bubbles. However, it has been found that when the ink degassed in this way is used in a high-speed printer, nozzle clogging due to bubbles in the ink occurs. Note that nozzle clogging means that bubbles in the ink are present near the nozzle, resulting in nozzles where the ink is not properly ejected and not properly printed.

[0011] In a high-speed printer, the vibration frequency of a piezo element or the like, which is a discharge mechanism of an inkjet head, becomes high, and a phenomenon similar to cavitation occurs inside the head, making it easy for dissolved gas or microbubbles to be vaporized. As a result, dissolved gas and microbubbles, which are not a problem in a normal printer, become a factor of nozzle clogging when used in a high-speed printer.

[0012] Furthermore, it has been found that such nozzle clogging problems become issues in high-speed line printers that perform printing continuously for a long time (e.g., 15 minutes or more) without nozzle cleaning. Different from serial printers, line printers perform continuous printing without cleaning by suction, pressurization, or flushing, etc., so it is considered that bubbles that are not removed easily cause nozzle clogging.

[0013] On the other hand, in the method for manufacturing ink of the present embodiment, there is an ultrasonic irradiation step of irradiating a dispersion liquid containing a pigment, a dispersant, and a polymerizable compound with ultrasonic waves for degassing. Thereby, compared with the case where a degassing step is performed on the ink in the final step, the degassing of the dispersion liquid can reduce the volume of the liquid to be treated. Therefore, by increasing the degassing efficiency and shortening the degassing time, degassing can be performed more effectively. In addition, since bubbles that cause problems are often brought into the ink from the pigment or brought into the ink by the dispersion treatment, by performing ultrasonic degassing on the dispersion liquid, the dissolved gas or microbubbles in the ink obtained using the dispersion liquid can be significantly reduced. Furthermore, since the degassing of the dispersion liquid can reduce the volume of the liquid to be treated, the ultrasonic treatment device can be miniaturized, and it is also possible to save space in the manufacturing equipment. Hereinafter, each step constituting the method for manufacturing ink will be described in detail.

[0014] 1.1. Ultrasonic irradiation step The ultrasonic irradiation step of this embodiment is a step of irradiating a dispersion liquid containing a pigment, a dispersant, and a polymerizable compound with ultrasonic waves. At this time, the output of the ultrasonic waves is 100 W or more. When a batch-type ultrasonic irradiation device is used for ultrasonic irradiation, ultrasonic irradiation is performed for 2 minutes or more per 20 L of the dispersion liquid. When an in-line type ultrasonic irradiation device is used, the residence time of the dispersion liquid in the reaction tube of the ultrasonic oscillator of the in-line type ultrasonic irradiation device is set to 3 seconds or more. By having such an ultrasonic irradiation step, the dispersibility of the pigment in the dispersion liquid is improved, and nozzle clogging is reduced even in a printer that does not perform nozzle cleaning for a long time, that is, the continuous printing stability is improved.

[0015] FIG. 1 shows an example of a batch-type ultrasonic irradiation device used in this embodiment. The batch-type ultrasonic irradiation device shown in FIG. 1 is an ultrasonic irradiation device of a type in which an ultrasonic vibrator 101 that transmits ultrasonic waves is installed in a dispersion liquid 103, and ultrasonic waves are irradiated while the dispersion liquid 103 is stirred by a stirring motor 102.

[0016] When a batch-type ultrasonic irradiation device is used, the irradiation time of the ultrasonic waves is 2 minutes or more per 20 L of the dispersion liquid, preferably 3 minutes or more, 5 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more. By performing ultrasonic irradiation on the dispersion liquid for such a period of time, nozzle clogging is reduced and the continuous printing stability tends to improve. Also, the upper limit of the irradiation time of the ultrasonic waves is not particularly limited, but is 90 minutes or less, 80 minutes or less, 70 minutes or less, 60 minutes or less, 50 minutes or less, 40 minutes or less.

[0017] When a batch-type ultrasonic irradiation device is used, the output of the ultrasonic waves is preferably 200 W or more, 300 W or more, 400 W or more. By performing the treatment with such an output of the ultrasonic waves, nozzle clogging is reduced and the continuous printing stability tends to improve. Also, the upper limit of the output of the ultrasonic waves is not particularly limited, but is 1000 W or less, 800 W or less, 600 W or less.

[0018] Figure 2 shows an example of an in-line type ultrasonic irradiation device used in this embodiment. In the in-line type ultrasonic irradiation device shown in Figure 2, the dispersion liquid and the ultrasonic vibrator 201 are separated. The dispersion liquid 203 before treatment is moved into the container where the ultrasonic vibrator 201 is located using the pump 202, allowed to stay for 10 seconds or more for treatment, and then the dispersion liquid 204 after treatment is moved to another container for storage. When performing ultrasonic irradiation for two passes (PASS) or more, that is, when repeatedly performing in-line type ultrasonic irradiation, the dispersion liquid 204 after treatment may be transferred to the container that houses the dispersion liquid 203 before treatment, and the pump 202 may be rotated again. Alternatively, the dispersion liquid 204 after treatment and the dispersion liquid 203 before treatment may be housed in the same container, and the pump 202 may be continuously operated for a desired time.

[0019] When using an in-line type ultrasonic irradiation device, as the output of the ultrasonic wave, it is preferably 150 W or more, 200 W or more, and 400 W or more. By performing treatment with such an ultrasonic wave output, nozzle dripping is reduced and the continuous printing stability tends to improve. Also, the upper limit of the ultrasonic wave output is not particularly limited, but it is 1000 W or less, 800 W or less, and 600 W or less.

[0020] Also, when using an in-line type ultrasonic irradiation device, as the irradiation time of the ultrasonic wave, it is preferably 5 seconds or more, 10 seconds or more, and 50 seconds or more. By performing ultrasonic irradiation on the dispersion liquid for such a time, nozzle dripping is reduced and the continuous printing stability tends to improve. Also, the upper limit of the above ultrasonic irradiation time is not particularly limited, but for example, it is 30 minutes or less, 10 minutes or less, 5 minutes or less, and 3 minutes or less.

[0021] 1.2. Mixing step The mixing step of this embodiment is to mix the dispersion liquid that has undergone the ultrasonic irradiation step with an initiator. By mixing the initiator after the ultrasonic irradiation step of the dispersion liquid, nozzle clogging can be reduced and continuous printing stability can be improved even in a printer that does not perform nozzle cleaning for a long time. Furthermore, since degassing can be performed more efficiently than mixing the initiator before the ultrasonic irradiation step of the dispersion liquid, downsizing of the apparatus for the ultrasonic irradiation step becomes possible, and also shortening of the manufacturing time required for the entire ink production becomes possible. In addition to the initiator, various additives such as a polymerizable compound and a polymerization inhibitor may be mixed.

[0022] In the mixing step, in addition to the dispersion liquid that has undergone the ultrasonic irradiation step and the initiator, other components may be added and mixed. Such other components are not particularly limited as long as they can be contained in the ink, and examples include a polymerizable compound, a photoinitiator, a fluorescent brightening agent, a surfactant, and a polymerization inhibitor.

[0023] 1.3. Other steps The manufacturing method of this embodiment may include other steps as necessary in addition to the above-described steps. Such steps are not particularly limited, and for example, it may be a preliminary mixing step of preliminarily mixing components other than the dispersion liquid after ultrasonic irradiation, or a second mixing step of separately mixing components required for the ink in a separate container after the mixing step, or a filtering step of filtering the ink through a filter.

[0024] 2. Ink The inkjet ink composition according to this embodiment (hereinafter, also simply referred to as "ink") is a radiation-curable ink containing a pigment, a dispersant, a polymerizable compound, and an initiator.

[0025] 2.1. Dispersion liquid The dispersion liquid contains a pigment, a dispersant, and a polymerizable compound, and may contain other components as necessary. Note that the polymerizable compound contained in the dispersion liquid may be a part of the entire ink. In this case, by further adding a polymerizable compound to the dispersion liquid, the final ink is prepared.

[0026] In this embodiment, the content of the dispersion is preferably 5.0% by mass or more and 30% by mass or less, 8.0% by mass or more and 20% by mass or less, and 10% by mass or more and 18% by mass or less with respect to the total amount of the ink. By setting the content of the pigment within the above range, there is a tendency to more surely exhibit the effect of improving the continuous printing stability according to the present invention.

[0027] 2.1.1. Pigment Examples of the pigment include inorganic pigments and organic pigments. The inorganic pigment is not particularly limited, and examples thereof include carbon blacks such as furnace black, lamp black, acetylene black, and channel black, iron oxide, and titanium oxide. The pigment of this embodiment preferably contains carbon black. By containing carbon black, the problem of nozzle dripping becomes prominent, and there is a tendency to more surely exhibit the effect on the continuous printing stability according to the present invention.

[0028] Examples of the organic pigment include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments and other polycyclic pigments, dye chelates, dyed lakes, nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments. The pigment may be used alone or in combination of two or more.

[0029] The carbon black is not particularly limited. For example, No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc. (manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. (manufactured by Carbon Columbia), Rega1 400R, Rega1 330R, Rega1 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc. (manufactured by CABOT JAPAN K.K.), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color B1ack S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Degussa) may be mentioned.

[0030] The white pigment is not particularly limited. For example, C.I. Pigment White 6, 18, 21 may be mentioned.

[0031] The yellow pigment is not particularly limited, and examples thereof include C.I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 155, 167, 172, 180. From the viewpoint of more surely achieving the effect of improving the continuous printing stability according to the present invention, Pigment Yellow 155 is preferred.

[0032] The magenta pigment is not particularly limited, and examples thereof include C.I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C.I. Pigment Violet 19, 23, 32, 33, 36, 38, 43, 50.

[0033] The cyan pigment is not particularly limited, and examples thereof include C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, C.I. Vat Blue 4, 60.

[0034] In addition, the pigments other than magenta, cyan, and yellow are not particularly limited, and examples thereof include C.I. Pigment Green 7, 10, C.I. Pigment Brown 3, 5, 25, 26, C.I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63.

[0035] In this embodiment, the pigment content is preferably more than 10% by mass and 35% by mass or less, 11% by mass or more and 30% by mass or less, and 12% by mass or more and 25% by mass or less with respect to the total amount of the dispersion liquid. By setting the pigment content of the dispersion liquid within the above range, the degassing efficiency in the ultrasonic irradiation step tends to be further improved.

[0036] In this embodiment, the pigment content is preferably 1.0% by mass or more and 10% by mass or less, 1.5% by mass or more and 5.0% by mass or less, and 2.0% by mass or more and 4.0% by mass or less with respect to the total amount of the ink. By setting the pigment content within the above range, the effect of improving the continuous printing stability according to the present invention tends to be more surely achieved.

[0037] The ink of this embodiment may contain color materials other than the pigment, and for example, may contain a dye. The dye is not particularly limited, and examples thereof include acid dyes, direct dyes, reactive dyes, and basic dyes. Specific examples of the dye include, for example, C.I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. Acid Red 52, 80, 82, 249, 254, 289, C.I. Acid Blue 9, 45, 249, C.I. Acid Black 1, 2, 24, 94, C.I. Food Black 1, 2, C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C.I. Direct Red 1, 4, 9, 80, 81, 225, 227, C.I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. Direct Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. Reactive Red 14, 32, 55, 79, 249, C.I. Reactive Black 3, 4, 35.

[0038] 2.1.2. Dispersant The dispersant of this embodiment is a solvent for dispersing pigments. The dispersant is not particularly limited. For example, those mainly composed of one or more of polyoxyalkylene polyalkylene polyamine, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxy resins can be mentioned. Commercially available products of dispersants include the Ajisper series manufactured by Ajinomoto Fine-Techno Co., the Solsperse series available from Avecia Co. (such as Solsperse 36000 (acid value 45), Solsperse 32000 (amine value 35), etc.), the Disperbyk series manufactured by BYK Chemie (DISPERBYK 168, 180, etc.), and the Disparon series manufactured by Kusumoto Chemicals, Ltd. Among these, from the viewpoint of more surely achieving the effect of improving the continuous printing stability according to the present invention, Solsperse 32000 or Solsperse 36000 is preferable. Note that the dispersant may be used alone or in combination of two or more kinds.

[0039] In this embodiment, the content of the dispersant is preferably 0.05% by mass or more and 1.0% by mass or less, 0.08% by mass or more and 0.5% by mass or less, and 0.1% by mass or more and 0.3% by mass or less with respect to the total amount of the dispersion liquid. By setting the content of the dispersant within the above range, there is a tendency to more surely achieve the effect of improving the continuous printing stability according to the present invention.

[0040] In this embodiment, the content of the dispersant is preferably 0.5% by mass or more and 10% by mass or less, 1.0% by mass or more and 5.0% by mass or less, and 1.5% by mass or more and 3.0% by mass or less with respect to the total amount of the ink. By setting the content of the dispersant within the above range, there is a tendency to more surely achieve the effect of improving the continuous printing stability according to the present invention.

[0041] 2.1.3. Polymerizable Compound The polymerizable compound in this embodiment is a base monomer contained during the preparation of the dispersion liquid and the ink. The polymerizable compound may be, for example, a photopolymerizable compound that polymerizes and solidifies upon irradiation with light such as ultraviolet light. The polymerizable compound is not particularly limited, and examples thereof include monofunctional monomers, difunctional monomers, and polyfunctional monomers having three or more functional groups.

[0042] The content of the polymerizable compound is preferably 50% by mass or more and 80% by mass or less, 55% by mass or more and 75% by mass or less, and 60% by mass or more and 70% by mass or less with respect to the total amount of the dispersion liquid. By setting the content of the polymerizable compound in the dispersion liquid within the above range, the degassing efficiency in the ultrasonic irradiation step tends to be further improved.

[0043] The content of the polymerizable compound is preferably 70% by mass or more and 95% by mass or less, 75% by mass or more and 90% by mass or less, and 80% by mass or more and 85% by mass or less with respect to the total amount of the ink.

[0044] The content of the polymerizable compound contained in the dispersion liquid is preferably 1.0% by mass or more and 30% by mass or less, 5.0% by mass or more and 20% by mass or less, and 6.5% by mass or more and 15% by mass or less with respect to the total amount of the ink. By setting the content of the polymerizable compound contained in the dispersion liquid within the above range, the effect of improving the continuous printing stability according to the present invention tends to be more surely exhibited.

[0045] 2.1.3.1. Monofunctional monomer The monofunctional monomer is not particularly limited. For example, benzyl (meth)acrylate, isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomyristyl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, lactone-modified flexible (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, dicyclopentenyl oxyethyl (meth)acrylate, and vinyl methyl oxazolidinone can be mentioned. Among these, from the viewpoint of more surely achieving the effect of improving the continuous printing stability according to the present invention, phenoxyethyl (meth)acrylate is preferable. The monofunctional monomer may be used alone or in combination of two or more kinds.

[0046] The content of the monofunctional monomer is preferably 50% by mass or more and 80% by mass or less, 55% by mass or more and 75% by mass or less, and 60% by mass or more and 70% by mass or less with respect to the total amount of the dispersion liquid. By setting the content of the polymerizable compound in the dispersion liquid within the above range, the degassing efficiency in the ultrasonic irradiation step tends to be further improved. Further, by setting the content of the monofunctional monomer contained in the dispersion liquid within the above range, the effect of improving the continuous printing stability according to the present invention tends to be more surely achieved.

[0047] 2.1.3.2.2 Functional Monomer The difunctional monomers are not particularly limited. For example, diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, EO (ethylene oxide) adduct of bisphenol A di(meth)acrylate, PO (propylene oxide) adduct of bisphenol A di(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate, and vinyl ether group-containing (meth)acrylate represented by the following formula (1) may be mentioned. Among these, from the viewpoint of more surely achieving the effect of improving the continuous printing stability according to the present invention, vinyl ether group-containing (meth)acrylate represented by the following formula (1) or dipropylene glycol di(meth)acrylate is preferable. In addition, as the difunctional monomer, one kind may be used alone, or two or more kinds may be used in combination. H 2 C=CR 1 -CO-OR 2 -O-CH=CH-R 3 ···(1) (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.)

[0048] In the above formula (1), R 2Examples of the divalent organic residue having 2 to 20 carbon atoms represented by [the formula] include linear, branched or cyclic alkylene groups having 2 to 20 carbon atoms, which may be substituted; alkylene groups having 2 to 20 carbon atoms, which may be substituted and have an oxygen atom due to an ether bond and / or an ester bond in the structure; and divalent aromatic groups having 6 to 11 carbon atoms, which may be substituted. Among these, alkylene groups having 2 to 6 carbon atoms, such as an ethylene group, an n-propylene group, an isopropylene group, and a butylene group; and alkylene groups having 2 to 9 carbon atoms, such as an oxyethylene group, an oxy n-propylene group, an oxyisopropylene group, and an oxybutylene group, which have an oxygen atom due to an ether bond in the structure, are preferable. Further, from the viewpoint of making the composition have a lower viscosity and further improving the curability of the composition, R 2 is more preferably a compound having a glycol ether chain, in which R is an alkylene group having 2 to 9 carbon atoms, such as an oxyethylene group, an oxy n-propylene group, an oxyisopropylene group, and an oxybutylene group, which has an oxygen atom due to an ether bond in the structure.

[0049] In the above formula (1), examples of the monovalent organic residue having 1 to 11 carbon atoms represented by R 3 include linear, branched or cyclic alkyl groups having 1 to 10 carbon atoms, which may be substituted; and aromatic groups having 6 to 11 carbon atoms, which may be substituted. Among these, alkyl groups having 1 to 2 carbon atoms, such as a methyl group or an ethyl group; and aromatic groups having 6 to 8 carbon atoms, such as a phenyl group and a benzyl group, are preferably used.

[0050] When each of the above organic residues is a group that may be substituted, the substituents can be classified into groups containing a carbon atom and groups not containing a carbon atom. First, when the substituent is a group containing a carbon atom, the carbon atom is counted as part of the number of carbon atoms of the organic residue. Examples of the group containing a carbon atom include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing a carbon atom include, but are not limited to, a hydroxyl group and a halo group.

[0051] Specific examples of the compound of formula (1) are not particularly limited, and for example, 2-vinyloxyethyl (meth)acrylate, 3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl (meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate, 1-vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl (meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate, 3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl (meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl (meth)acrylate, 6-vinyloxyhexyl (meth)acrylate, 4-vinyloxymethylcyclohexylmethyl (meth)acrylate, 3-vinyloxymethylcyclohexylmethyl (meth)acrylate, 2-vinyloxymethylcyclohexylmethyl (meth)acrylate, p-vinyloxymethylphenylmethyl (meth)acrylate, m-vinyloxymethylphenylmethyl (meth)acrylate, o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxyethoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate,(Meth)acrylic acid 2-(vinyloxyethoxyethoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyethoxyisopropoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyisopropoxyethoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyisopropoxyisopropoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyethoxyethoxyethoxy)ethyl, (meth)acrylic acid 2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl, (meth)acrylic acid 2-(isopropenoxyethoxy)ethyl, (meth)acrylic acid 2-(isopropenoxyethoxyethoxy)ethyl, (meth)acrylic acid 2-(isopropenoxyethoxyethoxyethoxy)ethyl, (meth)acrylic acid 2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl, (meth)acrylic acid polyethylene glycol monovinyl ether, and (meth)acrylic acid polypropylene glycol monovinyl ether may be mentioned. In this embodiment, acrylic acid 2-(2-vinyloxyethoxy)ethyl may also be referred to as VEEA.,

[0052] The content of the bifunctional monomer is preferably 0% by mass or more and 10% by mass or less, and 0% by mass or more and 5% by mass or less with respect to the total amount of the dispersion liquid. By setting the content of the polymerizable compound in the dispersion liquid within the above range, the degassing efficiency in the ultrasonic irradiation step tends to be further improved.

[0053] 2.1.3.3. Polyfunctional monomer The polyfunctional monomers having three or more functional groups are not particularly limited. For example, trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxytri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, pentaerythritol ethoxytetra(meth)acrylate, and caprolactam-modified dipentaerythritol hexa(meth)acrylate can be mentioned. Note that as the polyfunctional monomer, one kind may be used alone, or two or more kinds may be used in combination.

[0054] The content of the polyfunctional monomer is preferably 0% by mass or more and 10% by mass or less, and 0% by mass or more and 5% by mass or less with respect to the total amount of the dispersion liquid. By setting the content of the polymerizable compound in the dispersion liquid within the above range, the degassing efficiency in the ultrasonic irradiation step tends to be further improved.

[0055] 2.2. Monomers In this specification, the term "monomers" refers to the polymerizable compound added to the dispersion liquid when the final ink is prepared by further adding a polymerizable compound to the dispersion liquid in addition to the polymerizable compound pre-contained in the dispersion liquid. The polymerizable compound includes monomers and oligomers, but here, it is referred to as "monomers" as a concept to distinguish from oligomers.

[0056] Such monomers may include the monofunctional monomers, bifunctional monomers, and polyfunctional monomers described in the above polymerizable compounds. Note that as the monomers, one kind may be used alone, or two or more kinds may be used in combination.

[0057] The monofunctional monomers contained in the ink other than the dispersion liquid are preferably PEA (phenoxyethyl acrylate), IBXA (isobornyl acrylate), CTFA (cyclic trimethylolpropane formal acrylate), VMOX (vinyl methyl oxazolidinone), 4-HBA (4-hydroxybutyl acrylate), ACMO (acryloylmorpholine), etc., from the viewpoints of reducing the viscosity of the ink, reducing the odor, or improving the adhesion of the coating film after printing.

[0058] Also, the bifunctional monomers contained in the ink other than the dispersion liquid are preferably VEEA (2-(2-vinyloxyethoxy)ethyl acrylate), DPGDA (dipropylene glycol di(meth)acrylate, manufactured by Sartomer Co., Ltd.), TPGDA (tripropylene glycol diacrylate), etc., from the viewpoints of reducing the viscosity of the ink, reducing the odor, and high curability.

[0059] Furthermore, the polyfunctional monomers contained in the ink other than the dispersion liquid are preferably A-DPH (dipentaerythritol hexaacrylate), TPGDA (tripropylene glycol diacrylate), etc., from the viewpoints of high curability of the ink and scratch resistance of the coating film.

[0060] The content of the monomers is preferably 55% by mass or more and 90% by mass or less, 60% by mass or more and 90% by mass or less, and 65% by mass or more and 85% by mass or less based on the total amount of the ink. By setting the content of the monomers within the above range, the color development, curability, and coating film properties of the ink become good.

[0061] The content of the monofunctional monomer is preferably 10% by mass or more and 50% by mass or less, 20% by mass or more and 45% by mass or less, and 25% by mass or more and 40% by mass or less based on the total amount of the ink. By setting the content of the monofunctional monomer within the above range, the balance between the flexibility and scratch resistance of the coating film after curing is achieved, and a good coating film is obtained.

[0062] The content of the bifunctional monomer is preferably 20% by mass or more and 60% by mass or less, 30% by mass or more and 55% by mass or less, and 40% by mass or more and 50% by mass or less with respect to the total amount of the ink. By setting the content of the bifunctional monomer within the above range, the abrasion resistance of the cured coating film is improved and the curability is also good.

[0063] The content of the polyfunctional monomer is preferably 0.1% by mass or more and 20% by mass or less, 0.5% by mass or more and 15% by mass or less, and 1.0% by mass or more and 10% by mass or less with respect to the total amount of the ink. By setting the content of the polyfunctional monomer within the above range, the curability is good and there is an advantage that the ink does not become too highly viscous.

[0064] 2.3. Oligomer The ink composition of the present embodiment may contain an oligomer. The oligomer of the present embodiment is a multimer such as a dimer or a trimer composed of a polymerizable monomer, and refers to a compound having one or more polymerizable functional groups. Here, the polymerizable monomer is not limited to the above-mentioned monofunctional monomer, bifunctional monomer, and polyfunctional monomer.

[0065] Such oligomers are not particularly limited, and examples thereof include urethane acrylate oligomers having a urethane repeating structure, polyester acrylate oligomers having an ester repeating structure, and epoxy acrylate oligomers having an epoxy repeating structure.

[0066] Among these, urethane acrylate oligomers are preferred, aliphatic urethane acrylate oligomers and aromatic urethane acrylate oligomers are more preferred, and aliphatic urethane acrylate oligomers are even more preferred. Further, the urethane acrylate oligomer is preferably a urethane acrylate oligomer having 4 or less functional groups, and more preferably a urethane acrylate oligomer having 2 functional groups. Here, the number of functional groups means the number of (meth)acryloyl groups.

[0067] Commercially available urethane oligomers include, but are not limited to, for example, CN929 (polyester-based aliphatic urethane acrylate, functionality 3), CN962 (polyester-based aliphatic urethane acrylate, functionality 2), CN963 (polyester-based aliphatic urethane acrylate, functionality 2), CN964 (polyester-based aliphatic urethane acrylate, functionality 2), CN965 (polyester-based aliphatic urethane acrylate, functionality 2), CN968 (polyester-based aliphatic urethane acrylate, functionality 6), CN980 (polyether-based aliphatic urethane acrylate, functionality 2), CN981 (polyester-based aliphatic urethane acrylate, functionality 2), CN982 (polyester-based aliphatic urethane acrylate, functionality 2), CN983 (polyester-based aliphatic urethane acrylate, functionality 2), CN996 (polyether-based aliphatic urethane acrylate, functionality 2), CN9001 (polyester-based aliphatic urethane acrylate, functionality 2), CN9002 (polyester-based aliphatic urethane acrylate, functionality 2), CN9788 (polyester-based aliphatic urethane acrylate, functionality 2), CN9893 (polyether-based aliphatic urethane acrylate, functionality 2) (trade names of products manufactured by Sartomer Company), EBECRYL 230 (functionality 2), 270 (functionality 2), 5129 (functionality 6), 8210 (functionality 4), 8301 (functionality 6), 8311 (functionality 3), 8402 (functionality 2), 8405 (functionality 4), 8701 (functionality 3), 8804 (functionality 2), 8807 (functionality 2), 9260 (functionality 3), 9270 (functionality 2), KRM 8200 (functionality 6), 8296 (functionality 3), 8452 (functionality 10) (above, products of DAICEL-CYTEC Company LTD.Aliphatic urethane acrylate oligomers such as [[product name]]), and aromatic urethane acrylate oligomers such as CN971 (polyester-based aromatic urethane acrylate, functionality 3), CN972 (polyester-based aromatic urethane acrylate, functionality 3), CN975 (polyester-based aromatic urethane acrylate, functionality 6), CN978 (polyester-based aromatic urethane acrylate, functionality 2), CN9782 (polyester-based aromatic urethane acrylate, functionality 2), CN9783 (polyester-based aromatic urethane acrylate, functionality 2) (above are product names of Sartomer), EBECRYL 210 (functionality 2), 220 (functionality 6) (above are product names of Daicel Cytec) etc. can be mentioned.

[0068] In this embodiment, the content of the oligomer is preferably 0.1% by mass or more and 10.0% by mass or less, 0.5% by mass or more and 7.5% by mass or less, 1.0% by mass or more and 7.0% by mass or less with respect to the total amount of the ink. By setting the content of the oligomer within the above range, there is a tendency to more surely exhibit the effect of improving the continuous printing stability according to the present invention.

[0069] 2.4. Photoinitiator The photoinitiator (also simply referred to as "initiator") of this embodiment generates active species (initiating species) such as radicals, acids, and bases when irradiated with radiation, and promotes the polymerization reaction of the monomer by the function of the initiating species. Note that the photoinitiator may be used alone or in combination of two or more.

[0070] The photoinitiator is not particularly limited, and examples include known photoinitiators such as acylphosphine oxide-based photoinitiators and thioxanthone-based photoinitiators. From the viewpoint of more surely exhibiting the effect of improving the continuous printing stability according to the present invention, it is preferable to contain an acylphosphine oxide-based photoinitiator or a thioxanthone-based photoinitiator.

[0071] The acylphosphine oxide-based photoinitiators are not particularly limited. For example, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, etc. can be mentioned.

[0072] Examples of commercially available products of such acylphosphine oxide-based photoinitiators include, by trade name, Omnirad 819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), Omnirad TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide), Omnirad TPO-L (ethyl 2,4,6-trimethylbenzoylphenylphosphinate), IRGACURE1800 (a mixture of bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and 1-hydroxy-cyclohexyl-phenyl ketone with a mass ratio of 25:75), IRGACURE TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide), etc. Among these, from the viewpoint of more surely achieving the effect of improving the continuous printing stability according to the present invention, it is preferable to contain Omnirad 819, Omnirad TPO, or Omnirad TPO-L.

[0073] The thioxanthone-based photoinitiators are not particularly limited. For example, thioxanthone, diethylthioxanthone, isopropylthioxanthone, and chlorothioxanthone can be mentioned.

[0074] Examples of commercially available products of such thioxanthone-based photoinitiators include, but are not particularly limited to, Speedcure DETX (2,4-diethylthioxanthone-9-one), Speedcure ITX (2-isopropylthioxanthone) (both manufactured by Lambson), and KAYACURE DETX-S (2,4-diethylthioxanthone) (manufactured by Nippon Kayaku Co., Ltd.). Among these, from the viewpoint of more surely achieving the effect of improving the continuous printing stability according to the present invention, it is preferable to contain Speedcure DETX.

[0075] In this embodiment, the content of the photoinitiator is preferably 2.0% by mass or more and 25% by mass or less, 5.0% by mass or more and 20% by mass or less, and 10% by mass or more and 15% by mass or less with respect to the total amount of the ink. By setting the content of the photoinitiator within the above range, there is a tendency to more surely achieve the effect of improving the continuous printing stability according to the present invention.

[0076] In this embodiment, the total content of the acylphosphine oxide-based photoinitiator is preferably 2.0% by mass or more and 25% by mass or less, 5.0% by mass or more and 20% by mass or less, and 10% by mass or more and 12% by mass or less with respect to the total amount of the ink. By setting the content of the acylphosphine oxide-based photoinitiator within the above range, there is a tendency to more surely achieve the effect of improving the continuous printing stability according to the present invention.

[0077] In this embodiment, the total content of the thioxanthone-based photoinitiator is preferably 0.5% by mass or more and 10% by mass or less, 1.0% by mass or more and 5.0% by mass or less, and 1.5% by mass or more and 3.0% by mass or less with respect to the total amount of the ink. By setting the content of the thioxanthone-based photoinitiator within the above range, there is a tendency to more surely achieve the effect of improving the continuous printing stability according to the present invention.

[0078] 2.5. Fluorescent brightening agent The fluorescent brightening agent is not particularly limited, and for example, it can absorb light with a wavelength in the vicinity of 300 nm to 450 nm and emit light with a wavelength in the vicinity of 400 nm to 500 nm. Such fluorescent brightening agents are not particularly limited, and examples include naphthalene benzoxazolyl derivatives, thiophene benzoxazolyl derivatives, stilbene benzoxazolyl derivatives, coumarin derivatives, styrene biphenyl derivatives, pyrazolone derivatives, stilbene derivatives, styryl derivatives of benzene and biphenyl, bis(benzazol-2-yl) derivatives, carbostyryl, naphthalimide, derivatives of dibenzothiophene-5,5'dioxide, pyrene derivatives, and pyridotriazole. Note that the fluorescent brightening agent may be used alone or in combination of two or more kinds.

[0079] Examples of commercially available products of the fluorescent brightening agent include TELALUX KCB, TELALUX OB, etc. Among these, from the viewpoint of more surely achieving the effect of improving the continuous printing stability according to the present invention, it is preferable to contain TELALUX KCB.

[0080] In this embodiment, the content of the fluorescent brightening agent 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, and 0.1% by mass or more and 1.0% by mass or less with respect to the total amount of the ink. By setting the content of the fluorescent brightening agent within the above range, there is a tendency to more surely achieve the effect of improving the continuous printing stability according to the present invention.

[0081] 2.6. Surfactant The ink may contain a surfactant. The surfactant is not particularly limited, and examples include acetylene glycol-based surfactants, fluorine-based surfactants, and silicone-based surfactants. Note that the surfactant may be used alone or in combination of two or more kinds.

[0082] The acetylene glycol-based surfactant is not particularly limited, and examples thereof include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, as well as 2,4-dimethyl-5-decyne-4-ol and alkylene oxide adducts of 2,4-dimethyl-5-decyne-4-ol.

[0083] The fluorine-based surfactant is not particularly limited, and examples thereof include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkyl amine oxide compounds.

[0084] Examples of the silicone-based surfactant include polysiloxane-based compounds, polyester-modified silicones, or polyether-modified organosiloxanes.

[0085] Examples of the polyester-modified silicone include BYK-347, 348, BYK-UV3500, 3510, 3530 (manufactured by BYK Additives&Instruments), and examples of the polyether-modified silicone include BYK-3570 (manufactured by BYK Additives&Instruments). Among these, from the viewpoint of more surely achieving the effect of improving the continuous printing stability according to the present invention, it is preferable to contain BYK-UV3500 as the surfactant.

[0086] In the present embodiment, the content of the surfactant is preferably 0.1% by mass or more and 5.0% by mass or less, 0.3% by mass or more and 3.0% by mass or less, and 0.5% by mass or more and 1.0% by mass or less with respect to the total amount of the ink. By setting the content of the surfactant within the above range, there is a tendency to more surely achieve the effect of improving the continuous printing stability according to the present invention.

[0087] 2.7. Polymerization inhibitor The polymerization inhibitor is not particularly limited. For example, hydroquinone, hydroquinone monomethyl ether (MEHQ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (LA-7RD), hindered amine compounds, 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) hydroquinone, cresol, t-butylcatechol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), or derivatives thereof can be mentioned. Among these, from the viewpoint of more surely achieving the effect of improving the continuous printing stability according to the present invention, it is preferable to contain hydroquinone monomethyl ether (MEHQ) or 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (LA-7RD). Note that as the polymerization inhibitor, one kind may be used alone, or two or more kinds may be used in combination.

[0088] In this embodiment, the content of the polymerization inhibitor is preferably 0.01% by mass or more and 5% by mass or less, 0.05% by mass or more and 3.0% by mass or less, and 0.1% by mass or more and 1.0% by mass or less with respect to the total amount of the ink. By setting the content of the polymerization inhibitor within the above range, there is a tendency to more surely achieve the effect of improving the continuous printing stability according to the present invention.

[0089] 2.8. Water The ink according to this embodiment does not contain water or substantially does not contain water. In this embodiment, "substantially does not contain water" is not particularly limited. For example, the water content is 0.50% by mass or less, 0.25% by mass or less, 0.10% by mass or less, 0.05% by mass or less, 0.01% by mass or less with respect to the total amount of the ink composition. Also, not particularly limited, for example, it is 0.001 to 0.500% by mass, 0.001 to 0.250% by mass, 0.001 to 0.100% by mass, 0.001 to 0.050% by mass, 0.001 to 0.010% by mass.

[0090] In addition, in this specification, when simply referring to water, although not particularly limited, examples include ion-exchanged water, ultrafiltration water, reverse osmosis water, distilled water, and the like.

[0091] 2.9. Other Components In addition to the above components, the ink of this embodiment may contain other components that can be used in conventional inks. Such components are not particularly limited, and examples include slip agents, dissolution aids, viscosity modifiers, pH adjusters, antioxidants, preservatives, and corrosion inhibitors. Note that other components may be included alone or in combination of two or more.

[0092] 3. Recording Medium The recording medium used for recording the ink composition of this embodiment is not particularly limited, and examples include absorbent recording media, low-absorbent recording media, and non-absorbent recording media.

[0093] Examples of absorbent recording media include, but are not limited to, plain paper such as electrophotographic paper with high ink permeability, inkjet paper (inkjet dedicated paper having an ink absorption layer composed of silica particles or alumina particles, or an ink absorption layer composed of a hydrophilic polymer such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP)), and fabrics.

[0094] Examples of low-absorbent recording media include, but are not limited to, art paper, coated paper, and cast paper used for general offset printing with relatively low ink permeability.

[0095] The non-absorbent recording medium is not particularly limited. For example, films or 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; or metal plates or plastic films manufactured by vapor deposition of these various metals, plates of alloys such as stainless steel and true casting; and recording media in which films of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane are adhered (coated) to a paper substrate can be mentioned.

[0096] 4. Inkjet recording method The inkjet recording method of the present embodiment includes an adhesion step of discharging the ink obtained by the above-described manufacturing method from an inkjet head and adhering it to a recording medium, and a drying step of drying the ink adhered to the recording medium, and performs long-time recording without performing a nozzle clogging countermeasure step. When performing long-time recording without performing a nozzle clogging countermeasure step, the decrease in continuous printing stability due to nozzle clogging becomes remarkable, and by using the ink obtained by the above-described manufacturing method, the effects of the present invention are more effectively exhibited. Note that "performing long-time recording without performing a nozzle clogging countermeasure step" is not particularly limited. For example, it includes performing long-time recording without performing a nozzle clogging countermeasure step such as pressure nozzle cleaning, suction nozzle cleaning, or flushing during printing.

[0097] Here, "long time" means, for example, excluding short-time printing such as printing for several minutes or several seconds, passing through a nozzle clogging countermeasure step, and then printing for several minutes or several seconds. As an example of the purpose of defining "long time", it includes cases where long-time printing is performed without performing a nozzle clogging countermeasure step while transporting a recording medium, such as in a line printer, or cases where long-time printing is performed without performing a nozzle clogging countermeasure step when the carriage equipped with the head moves to the end of the recording medium even in a serial printer. From this perspective, if we define "a long time" numerically in this embodiment, it refers to 10 minutes or more. Further, 20 minutes or more is preferable, 30 minutes or more is more preferable, 40 minutes or more is more preferable, and 50 minutes or more is even more preferable. The upper limit is not particularly limited, but it is 24 hours or less, 18 hours or less, 12 hours or less, 6 hours or less, and 3 hours or less.

[0098] 4.1. Adhesion Process In the adhesion process, the ink obtained by the above-described manufacturing method is ejected from the inkjet head and adhered to the recording medium. More specifically, the pressure generating means provided in the inkjet head is driven to eject the ink composition filled in the pressure generating chamber of the inkjet head from the nozzle.

[0099] Examples of the inkjet head used in the ink adhesion process include a line head that performs recording by a line method and a serial head that performs recording by a serial method.

[0100] In the line method using a line head, for example, an inkjet head having a width equal to or greater than the recording width of the recording medium is fixed to the recording apparatus. Then, the recording medium and the inkjet head are relatively moved in the sub-scanning direction (the conveyance direction of the recording medium, that is, the direction orthogonal to the width direction of the recording medium), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement to record an image on the recording medium.

[0101] In the serial method using a serial head, for example, an inkjet head is mounted on a carriage movable in the width direction of the recording medium. Then, the carriage is moved along the main scanning direction (the width direction of the recording medium), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement to record an image on the recording medium.

[0102] In the recording method of the present embodiment, the inkjet head is a line head, and in the above-mentioned adhesion step, it is preferable to eject the ink while relatively moving the line head and the recording medium in the main scanning direction perpendicular to the width direction of the recording medium. When using such a recording method, by using the ink obtained by the above-mentioned manufacturing method, the effect of improving the continuous printing stability of the present invention is more remarkably achieved.

[0103] The ink obtained by the manufacturing method of the present embodiment is an ink particularly suitable for a recording method in which, using a line head corresponding to the width of the recording medium, the ink is ejected while relatively moving the line head and the recording medium in the main scanning direction perpendicular to the width direction of the recording medium. That is, when using the ink obtained by the above-mentioned manufacturing method in the above-mentioned recording method, the effect of improving the continuous printing stability of the present invention is more remarkably achieved.

[0104] Furthermore, the ink obtained by the manufacturing method of the present embodiment is preferably used in a high-speed printer. In a high-speed printer, nozzle clogging is likely to occur as described above, and the present invention is particularly useful. From this point, 1PASS printing is preferable for the printer, and further, the printing speed is preferably 20 m / min or more.

[0105] 4.2. Drying step The drying step is a step of drying the ink composition adhered to the recording medium by heating or the like.

[0106] In drying by heating, known drying means may be used, and the drying temperature may be 80°C to 150°C, may be 100°C to 145°C, or may be 120°C to 140°C. The drying temperature means the average temperature in the region where recording is performed on the surface of the recording medium. Also, the drying time may be 5 minutes or more and 15 minutes or less, or may be 7 minutes or more and 12 minutes or less.

[0107] 4.3. Irradiation step The recording method of this embodiment may include an irradiation step. In the irradiation step, radiation is irradiated onto the ink adhered to the recording medium. When the radiation is irradiated, the polymerization reaction of the monomer starts, causing the ink to harden and form a coating film. At this time, if there is a photoinitiator, active species (initiating species) such as radicals, acids, and bases are generated, and the polymerization reaction of the monomer is promoted by the function of the initiating species.

[0108] Here, examples of the radiation include ultraviolet rays, infrared rays, visible light rays, X-rays, etc. The radiation source irradiates the composition by a radiation source provided downstream of the inkjet head. The radiation source is not particularly limited, and for example, a UV-LED can be mentioned. By using such a radiation source, miniaturization of the device and cost reduction can be achieved. Since the UV-LED as an ultraviolet source is small, it can be installed in the inkjet recording device.

[0109] 4.4. Nozzle Clogging Countermeasure Step The recording method of this embodiment does not include a nozzle clogging countermeasure step. By using the ink manufacturing method of this embodiment, even when there is no nozzle clogging countermeasure step, nozzle clogging of the head tends to be suppressed.

[0110] The nozzle clogging countermeasure step is not particularly limited, and examples include pressure nozzle cleaning, suction nozzle cleaning, and flushing. Bubbles present near the nozzle can be discharged or removed from near the nozzle to prevent nozzle clogging. Processes such as wiping the ink ejection surface of the nozzle, such as wiping, are not included in the nozzle clogging countermeasure step because it is difficult to obtain an effect on nozzle clogging countermeasures.

[0111] 4.5. Conveying Step The recording method of this embodiment may include a conveyance process. In the conveyance process, the recording medium is conveyed in a predetermined direction within the recording apparatus. More specifically, the recording medium is conveyed from the paper feeding unit to the paper discharging unit of the recording apparatus using conveyance rollers or a conveyance belt provided within the recording apparatus. In the course of this conveyance, the ink composition ejected from the inkjet head adheres to the recording medium, forming a recorded matter. The order and timing of performing the ink adhesion process, the irradiation process, the nozzle clogging countermeasure process, and the conveyance process are not particularly limited. For example, the four processes may be performed simultaneously or alternately. Also, some of the four processes may be performed simultaneously, and the remaining processes may be performed separately.

[0112] FIG. 3 shows a schematic diagram of a line-type printer used in the recording method of this embodiment. As shown in FIG. 3, the inkjet recording apparatus 100 includes an irradiation unit 10, an inkjet head 20, and a conveyance unit 30. In the inkjet recording apparatus 100 of the line type, the recording medium M is conveyed from the conveyance unit 30 in the conveyance direction F, and the ink obtained by the manufacturing method of this embodiment is ejected from the inkjet head 20 onto the recording surface of the recording medium M. Thereafter, the irradiation surface 12 of the ink that has landed on the recording medium M is further conveyed in the conveyance direction F, irradiated with light by the irradiation unit 10 to be cured, and wound up and stored by the conveyance unit 30 at the front in the conveyance direction F. The ink manufacturing method and the inkjet recording method of the present invention are particularly suitable for continuous recording in which the recording medium M is immediately recovered and stored after one ejection process, drying process, irradiation process, etc. as shown in FIG. 3, because it is difficult to perform nozzle cleaning.

[0113] The inkjet apparatus 100 may have an air outlet 11. By blowing an inert gas from the air outlet 11, the oxygen concentration in the atmosphere can be reduced, and the curability of the coating film can be made more excellent. As the inert gas, a known inert gas such as a noble gas or nitrogen gas can be blown, and nitrogen or argon is more preferable. The inkjet apparatus 100 may have an irradiation unit 12. Also, assuming the distance h1 between the air outlet 11 and the recording medium M in the direction from the air outlet 11 toward the recording medium M, and the distance h2 between the irradiation unit 12 and the recording medium M in the direction from the air outlet 11 toward the recording medium M, it is more preferable that h1 is greater than h2. When h1 is greater than h2, the inert gas blown from the air outlet 11 is more likely to stay around the air outlet 11, the oxygen concentration in the atmosphere can be lowered, and the curability of the coating film is excellent.

Example

[0114] Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The present invention is not limited by the following examples at all.

[0115] In FIGS. 1 to 3, Tables 1 to 3 showing the composition of the dispersion liquid, the processing conditions of the ultrasonic irradiation step, the composition of the ink, and the evaluation results of each example are described.

[0116] 1. Ink production 1.1. Ultrasonic irradiation step The pigment, dispersant, and polymerizable compound were weighed to have the compositions described in Tables 1 to 3 and placed in a tank for pigment dispersion. A ceramic bead mill with a diameter of 1 mm was placed in the tank and stirred to obtain a dispersion liquid. Further, ultrasonic irradiation was performed using a batch-type or circulation-type ultrasonic irradiation apparatus according to the processing conditions described in Tables 1 to 3.

[0117] 1.2. Mixing step Each component including the dispersion liquid obtained above was placed in another tank for mixture to have the compositions described in Tables 1 to 3, mixed and stirred, and further filtered through a membrane filter to obtain the inkjet ink compositions of each example. Note that the numerical values of each component shown in the table represent the mass % of the solid content in the ink composition unless otherwise specified.

[0118] [Ultrasonic irradiation apparatus] · Batch type (see FIG. 1) · Inline type (see FIG. 2) [Pigment] · Carbon black (Pigment Black 7) ·P.Y.155 (Pigment Yellow 155) [Dispersant] ·Solsperes32000 (Trade name, amine value 35, manufactured by Lubrizol) ·Solsperse36000 (Trade name, acid value 45, manufactured by Lubrizol) [Monomers] ·PEA (Phenoxyethyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.) ·IBXA (Isobornyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.) ·CTFA (Cyclic trimethylolpropane formal acrylate, trade name "Biscote #200", manufactured by Osaka Organic Chemical Industry Co., Ltd.) ·VMOX (Vinyl methyl oxazolidinone, manufactured by BASF) ·4-HBA (4-Hydroxybutyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.) ·VEEA (2-(2-Vinyloxyethoxy)ethyl acrylate, manufactured by Nippon Shokubai Co., Ltd.) ·DPGDA (Dipropylene glycol di(meth)acrylate, manufactured by Sartomer Co., Ltd.) ·A-DPH (Dipentaerythritol hexaacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.) [Oligomer] ·CN9893 (Trade name, polyether-based aliphatic urethane acrylate oligomer, manufactured by Sartomer, number of functional groups 2) [Photoinitiator] ·Omnirad TPO-L (Trade name, ethyl 2,4,6-trimethylbenzoyl phenylphosphinate, manufactured by Accela ChemBio Inc.) ·Omnirad 819 (Trade name, bis(2,4,6-trimethylbenzoyl), manufactured by IGM Resins B.V.) ·Omnirad TPO (Trade name, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, manufactured by IGM Resins B.V.) ·Speedcure DETX (Trade name, 2,4-diethylthioxanthone-9-one, manufactured by LAMBSON) [Fluorescent brightener] ·TELALUX KCB (1,4-bis(2-benzoxazolyl)naphthalene, manufactured by Clariant Japan Ltd.) [Surfactant] ·BYK-UV3500 (polyether-modified polydimethylsiloxane having acryloyl groups, manufactured by BYK Additives & Instruments) [Polymerization inhibitor] ·LA-7RD (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, manufactured by ADEKA Corporation) ·MEHQ (hydroquinone monomethyl ether, manufactured by Kanto Chemical Co., Inc.)

[0119] 3. Evaluation: Continuous printing stability Regarding the inkjet head, an inkjet printer of the line type with a discharge nozzle diameter of 20 μm, a driving frequency of discharge of 15 kHz, and an ink discharge amount per shot adjusted to 7 ng, and equipped with 360 nozzles per head was prepared. Continuous discharge was performed from this head (360 nozzles) at the above discharge frequency. Every 5 minutes, an inspection was carried out to check whether ink was discharged from all the nozzles, and continuous discharge was performed up to a maximum of 50 minutes in total. During that time, nozzle cleaning, flushing, etc. were not performed. (Evaluation criteria) A: Even after 50 minutes or more from the start of discharge, no non-discharge or discharge disturbance was observed. B: No non-discharge or discharge disturbance was observed between 20 minutes or more and less than 50 minutes from the start of discharge. C: No non-discharge or discharge disturbance was observed between 10 minutes or more and less than 20 minutes from the start of discharge. D: Non-discharge was observed when less than 10 minutes had passed from the start of discharge.

Explanation of symbols

[0120] 101…Ultrasonic vibrator, 102…Stirring motor, 103…Dispersion liquid, 201…Ultrasonic vibrator, 202…Pump, 203…Dispersion liquid before treatment, 204…Dispersion liquid after treatment, 10…Irradiation unit, 11…Nozzle surface, 12…Irradiation surface, 20…Inkjet head, 21…Nozzle plate surface, 30…Conveyor unit, 100…Inkjet recording apparatus, F…Conveyor direction, h1…Distance, h2…Distance, M…Recording medium.

Claims

1. An ultrasonic irradiation step of irradiating a dispersion liquid containing a pigment, a dispersant, and a polymerizable compound with ultrasonic waves; An initiator mixing step of mixing the dispersion liquid and an initiator, having: The output of the ultrasonic waves is 100 W or more; When using a batch-type ultrasonic irradiation device in the ultrasonic irradiation step, ultrasonic irradiation is performed for 2 minutes or more per 20 L of the dispersion liquid; When using an in-line type ultrasonic irradiation device in the ultrasonic irradiation step, the residence time of the dispersion liquid in the reaction tube of the ultrasonic oscillator of the in-line type ultrasonic irradiation device is set to 3 seconds or more; A method for manufacturing ink.

2. When using a batch-type ultrasonic irradiation device in the ultrasonic irradiation step, ultrasonic irradiation is performed for 20 minutes or more per 20 L of the dispersion liquid. The method for manufacturing ink according to Claim 1.

3. The pigment contains carbon black. The method for manufacturing ink according to Claim 1.

4. The content of the pigment is 1.0 mass% or more and 10 mass% or less with respect to the total amount of the ink. The method for manufacturing ink according to Claim 1.

5. A method for manufacturing ink used in a recording method in which ink is ejected while relatively moving a line head corresponding to the width of a recording medium and the line head and the recording medium in a main scanning direction perpendicular to the width direction of the recording medium. The method for manufacturing ink according to Claim 1.

6. An adhesion step of ejecting the ink obtained by the method according to any one of Claims 1 to 5 from an inkjet head and attaching it to a recording medium; A drying step of drying the ink attached to the recording medium, comprising: Performing long-time recording without performing a nozzle clogging countermeasure step. An inkjet recording method.

7. The inkjet head is a line head. In the adhesion step, the ink is ejected while relatively moving the line head and the recording medium in a main scanning direction perpendicular to the width direction of the recording medium. The inkjet recording method according to Claim 6.

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