Inkjet clear ink composition, and recording method

Abstract

To provide an inkjet clear ink composition, and the like high in environmental adaptability, excellent in curability while suppressing yellow discoloration of a coated film, and excellent in cold storage property.SOLUTION: An inkjet clear ink composition includes: a photoinitiator; a fluorescent whitening agent; and a polymerizable monomer, where the photoinitiator includes ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, the polymerizable monomer includes an aromatic ring-containing monomer and a hydroxyl group-containing monomer, and the content of the fluorescent whitening agent is 0.2 mass% or more with respect to a total amount of the inkjet clear ink composition.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an inkjet clear ink composition and a recording method. [Background technology]

[0002] Inkjet recording methods are capable of recording high-definition images with a relatively simple device, and have made rapid progress in various fields. In the process, various studies have been conducted on curability, etc. For example, Patent Document 1 discloses an ultraviolet-curable clear ink composition that contains a polymerizable compound and a photopolymerization initiator, and that contains, as the polymerizable compound, vinyl ether group-containing (meth)acrylic acid esters and 5 to 25% by mass of a urethane oligomer relative to the total mass of the ink composition. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-203873 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, due to revisions to environmental regulations, radiation-curable inks that use various organic compounds as polymerizable compounds and photopolymerization initiators are now required to use safer ingredients instead of the ingredients that were previously used. In many cases, simply replacing an ingredient will not provide the same level of performance as before, so ink research and development must consider how to adjust the composition of other ingredients to ensure the same level of performance as before, under the prerequisite that an alternative ingredient is used. [Means for solving the problem]

[0005] The present invention provides an inkjet clear ink composition comprising a photoinitiator, a fluorescent brightening agent, and a polymerizable monomer, wherein the photoinitiator comprises ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, and the polymerizable monomer comprises an aromatic ring-containing monomer and a hydroxyl group-containing monomer, and the content of the fluorescent brightening agent is 0.2 mass % or more relative to the total amount of the inkjet clear ink composition. [Brief description of the drawings]

[0006] [Figure 1] FIG. 2 is a schematic diagram of a recording apparatus used in the present embodiment. [Diagram 2] 1 is a table showing the results of the examples. [Diagram 3] 1 is a table showing the results of the examples. [Figure 4] 1 is a table showing the results of the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Below, we will explain in detail the embodiment of the present invention (hereinafter referred to as the "present embodiment"). However, the present invention is not limited to this embodiment, and various modifications are possible without departing from the gist of the present invention.

[0008] 1. Inkjet clear ink composition The inkjet clear ink composition according to this embodiment (hereinafter also simply referred to as the "clear ink composition") comprises a photoinitiator, a fluorescent brightening agent, and a polymerizable monomer, wherein the photoinitiator comprises ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, the polymerizable monomer comprises an aromatic ring-containing monomer and a hydroxyl group-containing monomer, and the content of the fluorescent brightening agent is 0.2 mass % or more relative to the total amount of the inkjet clear ink composition.

[0009] Conventionally, diphenyl-2,4,6-trimethylbenzoylphosphine oxide (hereinafter also referred to as "TPO") has typically been used as a photoinitiator. However, TPO may be subject to environmental regulations. Therefore, in this embodiment, ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate (hereinafter also referred to as "TPO-L"), which has high environmental adaptability, is used as a photoinitiator instead of TPO.

[0010] On the other hand, ink compositions using TPO-L have room for improvement in curability compared to ink compositions using TPO. Therefore, when the content of TPO-L is increased in order to improve the curability, the coating film turns yellow, and the yellowing becomes particularly noticeable in transparent ink compositions that do not contain coloring materials.

[0011] Therefore, in this embodiment, the clear ink composition contains a fluorescent brightener in order to improve the curability while suppressing yellowing of the coating film. By containing a fluorescent brightener, good curability can be maintained even if the content of TPO-L, a photoinitiator that causes yellowing of the coating film, is reduced. Furthermore, it is considered that the fluorescent brightener obtains a sensitizing effect by being combined with the photoinitiator and contributes to the curability of the clear ink composition, so that by containing a fluorescent brightener, the curability is further improved while suppressing yellowing of the coating film. However, the factors that improve the curability while suppressing yellowing of the coating film are not limited to this.

[0012] By including a fluorescent brightening agent in the ink composition, yellowing of the coating film can be suppressed while improving the curing properties. However, a problem occurs in that the fluorescent brightening agent precipitates in a low temperature environment.

[0013] Therefore, in this embodiment, the clear ink composition contains an aromatic ring-containing monomer in order to improve the solubility of the fluorescent brightening agent. Since the aromatic ring-containing monomer has high compatibility with the fluorescent brightening agent, it is believed that by including the aromatic ring-containing monomer in the clear ink composition, the fluorescent brightening agent does not precipitate even in a low-temperature environment, and low-temperature storage stability is improved. However, the factors that improve low-temperature storage stability are not limited to this.

[0014] Furthermore, in this embodiment, the clear ink composition contains a hydroxyl group-containing monomer in order to improve the curability. The hydroxyl group-containing monomer has excellent curability because the hydroxyl groups contained in the hydroxyl group-containing monomer are strongly bonded to each other by hydrogen bonding, and it is considered that the curability is further improved by the clear ink composition containing a hydroxyl group-containing monomer. However, the factor of the improved curability is not limited to this.

[0015] The viscosity of the clear ink composition at 25° C. is preferably 3 to 30 mPa·s, 5 to 29 mPa·s, 10 to 28 mPa·s, 15 to 25 mPa·s, 18 to 22 mPa·s, or 19 to 21 mPa·s. If the viscosity of the clear ink composition at 25° C. is within the above range, the clear ink composition tends to be suitable for inkjet recording methods.

[0016] The viscosity of the clear ink composition at 25° C. can be measured by a method conforming to JIS Z 8803. The viscosity of the clear ink composition is not particularly limited, but can be adjusted, for example, by changing the content of the photoinitiator, by changing the type and / or content of the polymerizable monomer, or by adding a viscosity modifier as an additional component described below.

[0017] Each component of the clear ink composition of this embodiment will be described in detail below.

[0018] 1.1.Colorants In this embodiment, the clear ink composition means that it does not contain a colorant or does not substantially contain a colorant. In this embodiment, the term "substantially does not contain a colorant" is not particularly limited, but for example, the content of the colorant relative to the total amount of the clear ink composition 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, or 0.01% by mass or less. In addition, it is not particularly limited, but 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, or 0.001 to 0.010% by mass.

[0019] Colorants include dyes and pigments.

[0020] The dye is not particularly limited, but examples thereof include acid dyes, direct dyes, reactive dyes, and basic dyes. Specific examples of the dye include 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, 55, 58, 86, 132, 142, 1 44, 173, CI Direct Red 1, 4, 9, 80, 81, 225, 227, CI Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, CI Direct Black 19, 38, 51, 71, 154, 168, 171, 195, CI Reactive Red 14, 32, 55, 79, 249, CI Reactive Black 3, 4, 35. These dyes may be used alone or in combination of two or more.

[0021] Examples of pigments include, but are not limited to, inorganic pigments and organic pigments. Examples of inorganic pigments include, but are not limited to, carbon blacks such as furnace black, lamp black, acetylene black, and channel black, iron oxide, and titanium oxide. Examples of organic pigments 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, and polycyclic pigments such as quinophthalone pigments, dye chelates, dye lakes, nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments. These pigments may be used alone or in combination of two or more.

[0022] The carbon black is not particularly limited, and examples thereof include No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc. (all manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. (all 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 Corporation). Examples of such inks include Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A, and Special Black 4 (all manufactured by Degussa).

[0023] The white pigment is not particularly limited, but examples thereof include CI Pigment White 6, 18, and 21.

[0024] The yellow pigment is not particularly limited, but examples thereof include CI 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, and 180.

[0025] The magenta pigment is not particularly limited, but examples thereof include CI 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, and 245, and CI Pigment Violet. 19, 23, 32, 33, 36, 38, 43, and 50.

[0026] Examples of cyan pigments include, but are not limited to, CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, and 66, and CI Vat Blue 4 and 60.

[0027] In addition, pigments other than magenta, cyan, and yellow are not particularly limited, but examples thereof include CI Pigment Green 7, 10, CI Pigment Brown 3, 5, 25, and 26, and CI Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, and 63.

[0028] The pigment may be dispersed by a dispersant. The dispersant for dispersing the pigment is not particularly limited, and examples thereof include polyoxyalkylene polyalkylene polyamines, 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 as the main component. Commercially available dispersants include the Ajisper series manufactured by Ajinomoto Fine-Techno Co., Ltd., the Solsperse series available from Avecia Co. (Solsperse 36000 (acid value 45), Solsperse 32000 (amine value 35), etc.), the Disperbyk series manufactured by BYK Chemie (DISPERBYK 168, 180, etc.), and the Disparlon series manufactured by Kusumoto Chemicals Co., Ltd. These dispersants may be used alone or in combination of two or more.

[0029] 1.2. Photoinitiators The clear ink composition of this embodiment contains a photoinitiator. When the clear ink composition contains a photoinitiator, when irradiated with radiation, active species (initiating species) such as radicals, acids, and bases are generated, and the polymerization reaction of the polymerizable monomer described below is promoted by the function of the initiating species.

[0030] The photoinitiator is not particularly limited, but examples thereof include aromatic ketones, hydroxyketones, acylphosphine compounds, aromatic onium salt compounds, organic peroxides, thio compounds such as thioxanthones, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds. These photoinitiators may be used alone or in combination of two or more.

[0031] The clear ink composition of this embodiment also contains ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate (hereinafter also referred to as "TPO-L"), an acylphosphine compound, as a photoinitiator. By containing TPO-L, the clear ink composition can be made highly environmentally adaptable.

[0032] The content of the photoinitiator is preferably 15.0% by mass or less, 12.0% by mass or less, 1.0 to 15.0% by mass, 2.0 to 12.0% by mass, 3.0 to 11.0% by mass, 4.0 to 10.5% by mass, or 5.0 to 10.0% by mass relative to the total amount of the clear ink composition. By having the content of the photoinitiator within the above range, there is a tendency for the yellowing of the coating film to be more effectively suppressed.

[0033] The content of TPO-L is preferably 1.0 to 15.0 mass%, 1.5 to 12.5 mass%, 2.0 to 10.0 mass%, 2.0 to 8.0 mass%, or 2.5 to 7.5 mass% relative to the total amount of the clear ink composition. By having the TPO-L content within the above range, it is possible to obtain a clear ink composition that is highly environmentally adaptable, and to further improve curability while further suppressing yellowing of the coating film.

[0034] The content of TPO-L is preferably 20.0 to 80.0 mass%, 30.0 to 70.0 mass%, 35.0 to 65.0 mass%, 37.5 to 62.5 mass%, or 40.0 to 60.0 mass% relative to the total amount of photoinitiators. By having the content of TPO-L within the above range, it is possible to obtain a clear ink composition that is highly environmentally adaptable, and to further improve curability while further suppressing yellowing of the coating film.

[0035] The photoinitiator of the present embodiment may contain a photoinitiator other than TPO-L. The photoinitiator other than TPO-L is not particularly limited, but may be, for example, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, which is an acylphosphine compound.

[0036] The content of the photoinitiator other than TPO-L relative to the total amount of the clear ink composition is not particularly limited, but is, for example, 1.0 to 15.0 mass%, 2.0 to 12.5 mass%, 3.0 to 10.0 mass%, or 3.5 to 8.5 mass%.

[0037] The content of the photoinitiator other than TPO-L relative to the total amount of the photoinitiators is not particularly limited, but is, for example, 10.0 to 70.0 mass %, 15.0 to 60.0 mass %, or 20.0 to 55.0 mass %.

[0038] The photoinitiator of this embodiment preferably does not contain or substantially does not contain diphenyl-2,4,6-trimethylbenzoylphosphine oxide (TPO). Although not particularly limited, "substantially does not contain TPO" means that the content of TPO is, for example, 0.50 mass% or less, 0.25 mass% or less, 0.10 mass% or less, 0.05 mass% or less, or 0.01 mass% or less, relative to the total amount of the clear ink composition. Furthermore, although not particularly limited, for example, it is 0.001 to 0.500 mass%, 0.001 to 0.250 mass%, 0.001 to 0.100 mass%, 0.001 to 0.050 mass%, or 0.001 to 0.010 mass%.

[0039] 1.3.Fluorescent whitening agents The clear ink composition of the present embodiment contains a fluorescent brightening agent. The fluorescent brightening agent absorbs ultraviolet light and emits pale fluorescence. In addition, when combined with a photoinitiator, it exhibits a sensitizing effect. Therefore, by including a fluorescent brightening agent in the clear ink composition of the present embodiment, yellowing of the coating film is further suppressed, while curability is further improved.

[0040] Further, examples of the photoinitiator of the present invention that is classified as a fluorescent whitening agent include naphthalene benzoxazoyl derivatives, thiophene benzoxazoyl derivatives, stilbene benzoxazoyl derivatives, coumarin derivatives, styrene biphenyl derivatives, pyrazolone derivatives, stilbene derivatives, styryl derivatives of benzene and biphenyl, bis(benzazol-2-yl) derivatives, carbostyril, naphthalimide, dibenzothiophene-5,5'-dioxide derivatives, pyrene derivatives, and pyridotriazole.

[0041] More specifically, the fluorescent whitening agent is not particularly limited, but examples thereof include 1,4-bis(2-benzoxazolyl)naphthalene and 2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene.

[0042] The content of the fluorescent brightening agent is preferably 0.20% by mass or more, 0.20 to 5.00% by mass, 0.25 to 4.00% by mass, 0.30 to 3.00% by mass, 0.35 to 2.00% by mass, or 0.35 to 1.00% by mass, relative to the total amount of the clear ink composition. By having the content of the fluorescent brightening agent within the above range, yellowing of the coating film tends to be further suppressed while curability is further improved.

[0043] 1.4.Sensitizers The clear ink composition of this embodiment may contain a sensitizer. When irradiated with radiation, the sensitizer absorbs radiation and enters an excited state, and upon contact with the photoinitiator, promotes the decomposition of the photoinitiator, thereby further improving the curability of the clear ink composition.

[0044] Examples of the sensitizer include, but are not limited to, amine compounds (aliphatic amines, amines containing an aromatic ring, piperidine, reaction products of epoxy resins and amines, triethanolamine triacrylate, etc.), urea compounds (allylthiourea, o-tolylthiourea, etc.), sulfur compounds (2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propane, sodium diethyldithiophosphate, soluble salts of aromatic sulfinic acids, etc.), nitrile compounds (N,N-diethyl-p-aminobenzonitrile, etc.), phosphorus compounds (tri-n-butylphosphine, sodium diethyldithiophosphide, etc.), nitrogen compounds (Michler's ketone, N-nitrisohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds, condensates of formaldehyde or acetaldehyde with diamines, etc.), and chlorine compounds (carbon tetrachloride, hexachloroethane, etc.). These fluorescent whitening agents may be used alone or in combination of two or more.

[0045] The content of the sensitizer relative to the total amount of the clear ink composition is not particularly limited, but is, for example, 0.1 to 5.0% by mass, or 0.5 to 2.5% by mass, or the clear ink composition may not contain a sensitizer.

[0046] 1.3. Polymerizable monomers The clear ink composition of the present embodiment includes a polymerizable monomer. The polymerizable monomer is, but is not limited to, a photopolymerizable compound that polymerizes and solidifies when irradiated with light such as ultraviolet light. From the viewpoint of the number of polymerizable double bonds, examples of the polymerizable monomer include monofunctional monomers, bifunctional monomers, and polyfunctional monomers having three or more functional groups, and from the viewpoint of functional groups other than the polymerizable double bonds, examples of the polymerizable monomer include hydroxyl group-containing monomers and aromatic ring-containing monomers. Note that the terms "monofunctional", "bifunctional", and "trifunctional" refer to the number of functional groups of the polymerizable double bonds. The polymerizable monomer may be used alone or in combination of two or more types.

[0047] The content of the polymerizable monomer relative to the total amount of the clear ink composition is preferably 60.0 to 95.0 mass%, 62.5 to 92.5 mass%, 65.0 to 90.0 mass%, or 67.5 to 87.5 mass%. If the content of the polymerizable monomer is within the above range, the curability tends to be further improved.

[0048] 1.3.1. Monofunctional monomers The monofunctional monomer is not particularly limited, but examples thereof include (meth)acryloylmorpholine, 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, and methoxypolyethylene glycol (meth)acrylate. 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, dicyclopentenyloxyethyl (meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, and vinylmethyloxazolidinone. Among these, 2-hydroxy-3-phenoxypropyl (meth)acrylate is preferred. These monofunctional monomers may be used alone or in combination of two or more.

[0049] The content of the monofunctional monomer relative to the total amount of the clear ink composition is preferably 25.0 to 70.0 mass%, 27.5 to 65.0 mass%, or 30.0 to 60.0 mass%. When the content of the monofunctional monomer is within the above range, the curability tends to be more excellent.

[0050] The content of the monofunctional monomer is preferably 25.0 to 70.0 mass%, 27.5 to 67.5 mass%, or 30.0 to 65.0 mass%, based on the total amount of the polymerizable monomers. When the content of the monofunctional monomer is within the above range, the curability tends to be more excellent.

[0051] 1.3.2. Bifunctional monomers The bifunctional monomer is not particularly limited, but examples thereof include diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, 2-(2-vinyloxyethoxy)ethyl 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 ... Examples of the difunctional monomer include, for example, 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 di(meth)acrylate of bisphenol A, PO (propylene oxide) adduct di(meth)acrylate of bisphenol A, hydroxypivalic acid neopentyl glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate. These bifunctional monomers may be used alone or in combination of two or more.

[0052] The content of the bifunctional monomer relative to the total amount of the clear ink composition is preferably 20.0 to 65.0 mass%, 25.0 to 60.0 mass%, or 30.0 to 55.0 mass%. If the content of the bifunctional monomer is within the above range, the viscosity characteristics and curability tend to be more excellent.

[0053] The content of the bifunctional monomer is preferably 25.0 to 70.0 mass%, 30.0 to 65.0 mass%, or 35.0 to 60.0 mass% based on the total amount of the polymerizable monomers. When the content of the bifunctional monomer is within the above range, the viscosity characteristics and curability tend to be more excellent.

[0054] 1.3.3. Polyfunctional Monomers The trifunctional or higher polyfunctional monomer is not particularly limited, but examples thereof include 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 propoxy tri(meth)acrylate, cowprolactone-modified trimethylolpropane tri(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, and caprolactam-modified dipentaerythritol hexa(meth)acrylate. These polyfunctional monomers can be used alone or in combination of two or more.

[0055] The content of the polyfunctional monomer relative to the total amount of the clear ink composition is not particularly limited, but is, for example, 1.0 to 15.0 mass%, 2.0 to 12.5 mass%, or 3.0 to 10.0 mass%. The clear ink composition does not necessarily have to contain a polyfunctional monomer.

[0056] The content of the polyfunctional monomer relative to the total amount of the polymerizable monomers is not particularly limited, but is, for example, 2.0 to 15.0 mass%, 3.0 to 12.5 mass%, or 4.0 to 10.0 mass%. The clear ink composition does not necessarily need to contain a polyfunctional monomer.

[0057] 1.3.4. Hydroxyl-containing monomers The clear ink composition of this embodiment contains a hydroxyl group-containing monomer. The hydroxyl group-containing monomer may be any of the monofunctional monomers, bifunctional monomers, and polyfunctional monomers described above. When the clear ink composition contains a hydroxyl group-containing monomer, the curability tends to be improved.

[0058] The hydroxyl group-containing monomer is not particularly limited as long as it is a monomer containing a hydroxyl group, but examples thereof include those monomers listed as monofunctional monomers, bifunctional monomers, and polyfunctional monomers that contain a hydroxyl group. Among these, from the viewpoint of further improving the curing property, at least one selected from the group consisting of 2-hydroxy-3-phenoxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 1,4-cyclohexanedimethanol mono(meth)acrylate is preferred.

[0059] The content of the hydroxyl group-containing monomer relative to the total amount of the clear ink composition is preferably 2.0 to 20.0 mass%, 3.0 to 17.5 mass%, 4.0 to 15.0 mass%, or 5.0 to 14.5 mass%. If the content of the hydroxyl group-containing monomer is within the above range, the curability tends to be further improved.

[0060] The content of the hydroxyl group-containing monomer is preferably 4.0 to 30.0 mass%, 5.0 to 20.0 mass%, or 6.0 to 15.0 mass%, based on the total amount of polymerizable monomers. When the content of the hydroxyl group-containing monomer is within the above range, the curability tends to be further improved.

[0061] 1.3.5. Aromatic ring-containing monomers The clear ink composition of the present embodiment contains an aromatic ring-containing monomer. The aromatic ring-containing monomer may be any of the monofunctional monomer, bifunctional monomer, and polyfunctional monomer described above. By containing an aromatic ring-containing monomer in the clear ink composition, the fluorescent brightener does not precipitate even in a low-temperature environment, and low-temperature storage stability tends to be improved.

[0062] The aromatic ring-containing monomer is not particularly limited as long as it is a monomer containing an aromatic ring, and examples thereof include those monomers listed as monofunctional monomers, bifunctional monomers, and polyfunctional monomers that contain an aromatic ring. Among these, from the viewpoint of further improving low-temperature storage stability, at least one selected from the group consisting of phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate is preferred.

[0063] The clear ink composition of this embodiment preferably contains 40% by mass or less of phenoxyethyl (meth)acrylate. The phenoxyethyl (meth)acrylate is preferably contained in an amount of 30% by mass or less, more preferably 20% by mass or less, more preferably 10% by mass or less, and more preferably 5% by mass or less. In addition, the clear ink composition may not contain phenoxyethyl (meth)acrylate. When the clear ink composition of this embodiment contains 40% by mass or less of phenoxyethyl (meth)acrylate, or when the clear ink composition of this embodiment does not contain phenoxyethyl (meth)acrylate, the coating film of the inkjet ink composition is prevented from yellowing, the viscosity of the inkjet ink composition is reduced, and the ejection stability tends to be excellent.

[0064] The content of the aromatic ring-containing monomer relative to the total amount of the clear ink composition is preferably 20.0 mass% or more, 30.0 mass% or more, 31.5 mass% or more, 20.0 to 60.0 mass%, 25.0 to 55.0 mass%, 30.0 to 50.0 mass%, or 35.0 to 47.5 mass%. By having the content of the aromatic ring-containing monomer within the above range, low-temperature storage stability tends to be further improved.

[0065] The content of the aromatic ring-containing monomer is preferably 35.0 to 70.0 mass%, 37.5 to 60.0 mass%, or 40.0 to 57.5 mass% based on the total amount of the polymerizable monomers. When the content of the aromatic ring-containing monomer is within the above range, low-temperature storage stability tends to be further improved.

[0066] 1.3.6. Aromatic ring and hydroxyl group-containing monomers The clear ink composition of the present embodiment preferably contains an aromatic ring- and hydroxyl group-containing monomer that contains both an aromatic ring and a hydroxyl group. The aromatic ring- and hydroxyl group-containing monomer may be any of the monofunctional monomer, bifunctional monomer, and polyfunctional monomer described above. By containing an aromatic ring- and hydroxyl group-containing monomer in the clear ink composition, the design freedom of the clear ink composition is improved, and the physical properties (e.g., viscosity characteristics, etc.) of the clear ink composition tend to be improved.

[0067] The aromatic ring and hydroxyl group-containing monomer is the above-mentioned hydroxyl group-containing monomer, and is also the above-mentioned aromatic ring-containing monomer. The aromatic ring and hydroxyl group-containing monomer is not particularly limited as long as it is a monomer containing an aromatic ring and a hydroxyl group, and examples thereof include 2-hydroxy-3-phenoxypropyl (meth)acrylate.

[0068] The content of the aromatic ring and hydroxyl group-containing monomer relative to the total amount of the clear ink composition is not particularly limited, and is, for example, 1.0 to 20.0 mass%, 1.5 to 17.5 mass%, 2.0 to 15.0 mass%, 2.5 to 12.5 mass%, or 3.0 to 10.0 mass%.

[0069] The content of the aromatic ring- and hydroxyl group-containing monomer relative to the total amount of polymerizable monomers is not particularly limited, and is, for example, 1.0 to 20.0 mass%, 1.5 to 17.5 mass%, 2.0 to 15.0 mass%, 2.5 to 12.5 mass%, or 3.0 to 10.0 mass%.

[0070] 1.4.Oligomers The clear ink composition of this embodiment may contain an oligomer. The oligomer of this embodiment refers to a compound that is a multimer such as a dimer or trimer, which contains a polymerizable compound as a constituent, and has one or more polymerizable functional groups. Note that the polymerizable compound referred to here is not limited to the monofunctional monomer, bifunctional monomer, and polyfunctional monomer described above.

[0071] Such oligomers are not particularly limited, but examples thereof include urethane acrylate oligomers in which the repeating unit is a urethane, polyester acrylate oligomers in which the repeating unit is an ester, and epoxy acrylate oligomers in which the repeating unit is an epoxy.

[0072] 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. The urethane acrylate oligomer is preferably a urethane acrylate oligomer having four or fewer functional groups, and more preferably a urethane acrylate oligomer having two functional groups. The functionality refers to the number of (meth)acryloyl groups. By including the urethane acrylate oligomer, the clear ink composition tends to have excellent viscosity characteristics.

[0073] The urethane acrylate oligomer is not particularly limited, but examples thereof include polyether-based urethane acrylate oligomers having a urethane bond and an ether bond, polyester-based urethane acrylate oligomers having a urethane bond and an ester bond, and polycarbonate-based urethane acrylate oligomers having a urethane bond and a carbonate bond.

[0074] Commercially available urethane oligomers include, but are not limited to, CN929 (polyester-based aliphatic urethane acrylate, functional group number 3), CN962 (polyester-based aliphatic urethane acrylate, functional group number 2), CN963 (polyester-based aliphatic urethane acrylate, functional group number 2), CN964 (polyester-based aliphatic urethane acrylate, functional group number 2), CN965 (polyester-based aliphatic urethane acrylate, functional group number 2), CN968 (polyester-based aliphatic urethane acrylate, functional group number 6), CN980 (polyether-based aliphatic urethane acrylate, functional group number 2), CN981 (polyester (polyether-based aliphatic urethane acrylate, functional group 2), CN982 (polyester-based aliphatic urethane acrylate, functional group 2), CN983 (polyester-based aliphatic urethane acrylate, functional group 2), CN996 (polyether-based aliphatic urethane acrylate, functional group 2), CN9001 (polyester-based aliphatic urethane acrylate, functional group 2), CN9002 (polyester-based aliphatic urethane acrylate, functional group 2), CN9788 (polyester-based aliphatic urethane acrylate, functional group 2), CN9893 (polyether-based aliphatic urethane acrylate, functional group 2) (all from Sartomer Corporation) Company) product name), EBECRYL 230 (number of functional groups 2), 270 (number of functional groups 2), 5129 (number of functional groups 6), 8210 (number of functional groups 4), 8301 (number of functional groups 6), 8311 (number of functional groups 3), 8402 (number of functional groups 2), 8405 (4 functional groups), 8701 (3 functional groups), 8804 (2 functional groups), 8807 (2 functional groups), 9260 (3 functional groups), 9270 (2 functional groups), KRM 8200 (number of functional groups: 6), 8296 (number of functional groups: 3), 8452 (number of functional groups: 10) (DAICEL-CYTEC Company LTD.) and other aliphatic urethane acrylate oligomers, as well as aromatic urethane acrylate oligomers such as CN971 (polyester-based aromatic urethane acrylate, functional group number 3), CN972 (polyester-based aromatic urethane acrylate, functional group number 3), CN975 (polyester-based aromatic urethane acrylate, functional group number 6), CN978 (polyester-based aromatic urethane acrylate, functional group number 2), CN9782 (polyester-based aromatic urethane acrylate, functional group number 2), CN9783 (polyester-based aromatic urethane acrylate, functional group number 2) (all of which are product names manufactured by Sartomer Corporation), EBECRYL 210 (functional group number 2), 220 (functional group number 6) (all of which are product names manufactured by Daicel-Cytec Corporation).

[0075] The content of the oligomer relative to the total amount of the clear ink composition is not particularly limited, but is, for example, 1.0 to 12.0 mass %, 2.0 to 11.0 mass %, or 3.0 to 10.0 mass %.

[0076] 1.5.Surfactants The surfactant is not particularly limited, but examples thereof include acetylene glycol-based surfactants, fluorine-based surfactants, and silicone-based surfactants. From the viewpoint of more effectively and reliably achieving the effects of the present invention, silicone-based surfactants are preferred.

[0077] Examples of silicone surfactants include, but are not limited to, BYK-UV3500, UV3570, and BYK350 (trade names manufactured by BYK Japan KK).

[0078] The content of the surfactant relative to the total amount of the clear ink composition is not particularly limited, but may be, for example, 0.1 to 1.0% by mass.

[0079] 1.6. Polymerization inhibitors The polymerization inhibitor is not particularly limited, but examples thereof include hydroquinones such as hydroquinone, hydroquinone monomethyl ether (MEHQ), 1-o-2,3,5-trimethylhydroquinone, and 2-tert-butylhydroquinone; catechols such as catechol, 4-methylcatechol, and 4-tert-butylcatechol; phenol, butylhydroxytoluene, butylhydroxyanisole, p-methoxyphenol, cresol, pyrogallol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'- Phenols such as methylenebis(4-ethyl-6-butylphenol) and 4,4'-thiobis(3-methyl-6-t-butylphenol); compounds having a 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton such as 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl, compounds having a 2,2,6,6-tetramethylpiperidine skeleton, compounds having a 2,2,6,6-tetramethylpiperidine-N-alkyl skeleton, and hindered amines such as compounds having a 2,2,6,6-tetramethylpiperidine-N-acyl skeleton. These polymerization inhibitors are used alone or in combination of two or more.

[0080] The content of the polymerization inhibitor relative to the total amount of the clear ink composition is not particularly limited, but may be, for example, 0.1 to 1.0% by mass.

[0081] 1.7.Other Ingredients In addition to the above-mentioned components, the clear ink composition of the present embodiment may contain other known components that can be used in conventional clear ink compositions. The other components are not particularly limited, but may include, for example, slip agents, dissolution aids, viscosity adjusters, pH adjusters, antioxidants, preservatives, and corrosion inhibitors. These other components may be used alone or in combination of two or more.

[0082] 2. Method for producing inkjet clear ink composition The method for producing the inkjet clear ink composition of this embodiment is not particularly limited. For example, the above components may be simultaneously charged into a mixture tank and mixed, or the components may be sequentially charged into a mixture tank and mixed.

[0083] 3. Recording medium The recording medium used for recording with the clear ink composition of this embodiment is not particularly limited, but examples thereof include absorbent recording media, low absorbent recording media, and non-absorbent recording media.

[0084] Examples of absorbent recording media include, but are not limited to, plain paper such as electrophotographic paper that has high ink permeability, inkjet paper (paper specifically for inkjet printers that has an ink absorbing layer made of silica particles or alumina particles, or an ink absorbing layer made of a hydrophilic polymer such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP)), fabrics, and the like.

[0085] The low-absorbency recording medium is not particularly limited, but examples thereof include art paper, coated paper, cast paper, and the like, which are used in general offset printing and have relatively low ink permeability.

[0086] Non-absorbent recording media are not particularly limited, but examples include plastic films and plates such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, polyurethane, etc.; metal plates such as iron, silver, copper, aluminum, etc.; or metal plates and plastic films produced by vapor deposition of these various metals, alloy plates such as stainless steel and brass, and recording media in which a plastic film such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, polyurethane, etc. is adhered (coated) to a paper substrate.

[0087] 4. Inkjet recording method The inkjet recording method of this embodiment (hereinafter also simply referred to as the "recording method") includes an ink deposition step of ejecting the clear ink composition of this embodiment from an inkjet head and depositing it on a recording medium, and an irradiation step of irradiating the clear ink composition deposited on the recording medium with radiation, and may also include other steps, such as a transport step of transporting the recording medium, as necessary.

[0088] 4.1.Ink application process In the ink deposition step, the clear ink composition of the present embodiment is ejected from an inkjet head and deposited on a recording medium. More specifically, a pressure generating means provided in the inkjet head is driven to eject the clear ink composition filled in the pressure generating chamber of the inkjet head from the nozzle.

[0089] Inkjet heads used in the ink application step include line heads that perform recording by a line method and serial heads that perform recording by a serial method.

[0090] 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 a recording device. Then, the recording medium and the inkjet head are moved relatively in the sub-scanning direction (the conveying direction of the recording medium, i.e., the direction perpendicular 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.

[0091] In the serial method using a serial head, for example, the inkjet head is mounted on a carriage that can move in the width direction of the recording medium. The carriage is then moved in the main scanning direction (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.

[0092] 4.2.Irradiation process In the irradiation step, the clear ink composition attached to the recording medium is irradiated with radiation. When irradiated with radiation, a polymerization reaction of the monomer is initiated, curing the composition and forming a coating film. If a photoinitiator is present at this time, it generates active species (initiation species) such as radicals, acids, and bases, and the polymerization reaction of the monomer is promoted by the function of the initiation species.

[0093] Here, examples of the radiation include ultraviolet rays, infrared rays, visible light, and X-rays. The radiation source is provided downstream of the inkjet head and irradiates the composition with the radiation. The radiation source is not particularly limited, but may be, for example, a UV-LED. By using such a radiation source, the device can be made smaller and the cost reduced. The UV-LED as the ultraviolet ray source is small, so it can be installed in the inkjet recording device.

[0094] 4.3.Transportation process The recording method of the present embodiment may include a transport step. In the transport step, the recording medium is transported in a predetermined direction in the recording device. More specifically, the recording medium is transported from the paper feed section to the paper discharge section of the recording device using a transport roller or a transport belt provided in the recording device. In the transport process, the clear ink composition discharged from the inkjet head adheres to the recording medium to form a recorded matter. The order and timing of the ink attachment step, the irradiation step, and the transport step are not particularly limited, and for example, the three steps may be performed simultaneously or alternately. In addition, two of the three steps may be performed simultaneously, and the remaining step may be performed separately.

[0095] 5. Recording Equipment As an example of an inkjet device, a perspective view of a serial printer is shown in Fig. 1. As shown in Fig. 1, the serial printer 70 includes a conveying unit 720 and a recording unit 730. The conveying unit 720 conveys the recording medium F fed to the serial printer to the recording unit 730, and ejects the recording medium after recording outside the serial printer. Specifically, the conveying unit 720 has feed rollers and conveys the fed recording medium F in the sub-scanning direction T2.

[0096] The recording unit 730 also includes a carriage 734 carrying an inkjet head 731 having nozzles that eject a clear ink composition onto the recording medium F sent from the transport unit 720, and a carriage movement mechanism 735 that moves the carriage 734 in the main scanning directions S1 and S2 of the recording medium F.

[0097] In the case of a serial printer, an inkjet head 731 having a length smaller than the width of the recording medium is provided, and the head moves to perform recording in multiple passes. In a serial printer, the head 731 is mounted on a carriage 734 that moves in a predetermined direction, and the head moves with the movement of the carriage to eject the clear ink composition onto the recording medium F. In this way, recording is performed in two or more passes. A pass is also called a main scan. A sub-scan is performed between passes to transport the recording medium. In other words, main scans and sub-scans are performed alternately.

[0098] The inkjet device of the present embodiment is not limited to the serial printer, but may be the line printer described above. The line printer has a line head, which is an inkjet head having a length equal to or greater than the recording width of the recording medium, and a moving mechanism that relatively moves the recording medium and the inkjet head in a direction perpendicular to the width direction of the recording medium, and performs recording on the recording medium in one scan. EXAMPLES

[0099] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples. In addition, unless otherwise specified, the experiments were carried out at room temperature (25°C) and 1 atm.

[0100] 1. Preparation of Inkjet Clear Ink Composition The inkjet clear ink compositions of Examples and Comparative Examples were obtained by mixing and stirring each component in a stainless steel container, a mixing tank, so as to obtain the composition shown in Figures 2 to 4, and then filtering through a 5 μm membrane filter. Note that the numerical values ​​of each component shown in each example in the figures represent mass % unless otherwise specified.

[0101] The abbreviations and product components used in Figures 2 to 4 are as follows: Note that blank spaces in Figures 2 to 4 indicate that the component was not used. PEA (product name "Viscoat #192", manufactured by Osaka Organic Chemical Industry Co., Ltd., phenoxyethyl acrylate) BZA (product name "Viscoat #160", manufactured by Osaka Organic Chemical Industry Ltd., benzyl acrylate) M-600A (product name "Epoxy Ester M-600A", manufactured by Kyoeisha Chemical Co., Ltd., 2-hydroxy-3-phenoxypropyl (meth)acrylate) 4-HBA (Osaka Organic Chemical Industry Co., Ltd., 4-hydroxybutyl acrylate) CHDMM (product name "CHDMMA", manufactured by Mitsubishi Chemical Corporation, 1,4-cyclohexanedimethanol monoacrylate) IBXA (Osaka Organic Chemical Industry, Ltd., isobornyl acrylate) ACMO (Acryloylmorpholine, manufactured by KJ Chemicals Co., Ltd.) DPGDA (product name "Viscoat #310HP", manufactured by Osaka Organic Chemical Industry Ltd., tripropylene glycol diacrylate) VEEA (2-(2-vinyloxyethoxy)ethyl acrylate, manufactured by Nippon Shokubai Co., Ltd.) A-DPH (Dipentaerythritol hexaacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.) CN9893 (Sartomer, bifunctional urethane acrylate oligomer) Omnirad 819 (IGM Resins BV, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide) Omnirad TPO-L (manufactured by IGM Resins BV, ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate) Speedcure DETX (Sartomer, 2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propane) TELALUX KCB (Clariant Japan, 1,4-bis(2-benzoxazolyl)naphthalene) BYK-UV3500 (BYK Additives & Instruments, polyether-modified polydimethylsiloxane with acryloyl groups) MEHQ (product name "p-methoxyphenol", manufactured by Kanto Chemical Co., Ltd., hydroquinone monomethyl ether)

[0102] 2. Evaluation method 2.1.Viscosity properties Using a rotational viscometer (product name "Rheometer MCR-301", manufactured by Anton Paar), the viscosity of the clear ink compositions of the Examples and Comparative Examples immediately after preparation was measured at room temperature (25° C.) in accordance with JIS Z 8803. [Evaluation Criteria] A: Viscosity is 19 mPa s or more and 21 mPa s or less. B: The viscosity is greater than 18 mPa·s and less than 19 mPa·s, or greater than 21 mPa·s and less than 22 mPa·s. C: Viscosity is 18 mPa·s or less or 22 mPa·s or more.

[0103] 2.2.Low temperature storage The clear ink compositions of the Examples and Comparative Examples were filled into glass bottles and stored for 7 days at −20° C. The properties of the clear ink compositions before and after storage were visually observed and evaluated. [Evaluation Criteria] A: No foreign matter was found. B: No foreign matter was observed with the naked eye, but when filtered through a 10 μm filter, foreign matter was observed. C: Foreign matter was visually observed.

[0104] 2.3. Curability The cotton swab load tackiness evaluation was carried out. Specifically, the clear ink composition of the examples and comparative examples was applied to a polyvinyl chloride medium with a bar coater so that the coating thickness was 10 μm to form a coating film, and the coating film was irradiated with ultraviolet light at a speed of 0.04 sec / cm at each predetermined irradiation intensity. At that time, an LED having a peak wavelength of 395 nm was used as the light source. Then, the coating film surface was rubbed with a cotton swab, and the irradiation energy at which the cotton swab no longer became colored was measured, and the curing property was evaluated. [Evaluation Criteria] A: The irradiation energy at which the cotton swab becomes uncolored is 150 mJ / cm 2 is less than. B: The cotton swab becomes uncolored when the irradiation energy is 150 mJ / cm 2 More than 250mJ / cm 2 is less than. C: The irradiation energy at which the cotton swab becomes uncolored is 250 mJ / cm 2 That's all.

[0105] 2.4. Coating color evaluation In the evaluation of curability, the coating film of the clear ink composition after irradiation with ultraviolet light was measured using a colorimeter Spectrolino (manufactured by GretagMacbeth) to measure b*. [Evaluation Criteria] A: b*<1.0. B: 1.0≦b*<2.0. C: 2.0≦b*.

[0106] 3. Evaluation results 2 to 4, it was found that the clear ink compositions of the Examples were all superior in low-temperature storage stability, curing properties, and / or coating film color evaluation compared to the clear ink compositions of the Comparative Examples. [Explanation of symbols]

[0107] 70: serial printer, 720: conveying section, 730: recording section, 731: inkjet head, 734: carriage, 735: carriage moving mechanism, F: recording medium, S1, S2: main scanning direction, T2: sub-scanning direction

Claims

1. A photoinitiator, a fluorescent whitening agent, and a polymerizable monomer, the photoinitiator comprises ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate; The inkjet clear ink composition, wherein the polymerizable monomer includes an aromatic ring-containing monomer and a hydroxyl group-containing monomer, the content of the fluorescent whitening agent is 0.2% by mass or more relative to the total amount of the inkjet clear ink composition; Inkjet clear ink composition.

2. the content of the photoinitiator is 12.0% by mass or less relative to the total amount of the inkjet clear ink composition; The ink-jet clear ink composition according to claim 1.

3. the content of the ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate is 2.0 to 8.0% by mass relative to the total amount of the inkjet clear ink composition; The ink-jet clear ink composition according to claim 1.

4. The hydroxyl group-containing monomer includes at least one monomer selected from the group consisting of 2-hydroxy-3-phenoxypropyl acrylate, 4-hydroxybutyl acrylate, and 1,4-cyclohexanedimethanol monoacrylate. The ink-jet clear ink composition according to claim 1.

5. The polymerizable monomer includes a monomer having both an aromatic ring and a hydroxyl group. The ink-jet clear ink composition according to claim 1.

6. The monomer having both an aromatic ring and a hydroxyl group includes 2-hydroxy-3-phenoxypropyl acrylate. The ink-jet clear ink composition according to claim 5.

7. the content of the aromatic ring-containing monomer is 31.5% by mass or more relative to the total amount of the inkjet clear ink composition; The ink-jet clear ink composition according to claim 1.

8. Further comprising a urethane acrylate oligomer, The ink-jet clear ink composition according to claim 1.

9. A discharge step of discharging the inkjet clear ink composition according to any one of claims 1 to 8 onto a recording medium; and an irradiation step of irradiating the inkjet clear ink composition with radiation. Recording method.

Images