Inkjet clear ink composition and recording method

Abstract

The invention relates to an inkjet clear ink composition and a recording method. The purpose of the present invention is to provide an inkjet clear ink composition which has high environmental suitability, excellent curability and excellent low-temperature storage properties while suppressing yellowing of a coating film, and the like. The inkjet clear ink composition includes a photoinitiator including phenyl (2, 4, 6-trimethylbenzoyl) phosphonic acid ethyl ester, a fluorescent whitening agent, and polymerizable monomers including an aromatic ring-containing monomer and a hydroxyl group-containing monomer, with respect to the total amount of the inkjet clear ink composition, the amount of the fluorescent whitening agent being less than the amount of the aromatic ring-containing monomer, and the amount of the polymerizable monomers being less than the amount of the aromatic ring-containing monomer. The content of the fluorescent whitening agent is more than 0.2% by mass.

Description

Technical Field

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

[0002] The inkjet recording method can record high-definition images with a relatively simple device, and has been rapidly developed in various aspects. Among them, various studies have been proposed on curability, etc. For example, Patent Document 1 discloses an ultraviolet curable transparent ink composition, which includes a polymerizable compound and a photopolymerization initiator, and as a polymerizable compound, includes a (meth) acrylate containing a vinyl ether group and a polyurethane oligomer in an amount of 5 to 25% by mass relative to the total mass of the ink composition.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2013-203873

[0004] However, in recent years, due to the revision of environmental regulations, it is necessary to use safer ingredients to replace the conventional ingredients in radiation-curable inks that use various organic compounds as polymerizable compounds and photopolymerization initiators. In many cases, there is a technical problem that the same performance as before cannot be obtained by simply replacing the ingredients. Therefore, the following point of view is required in the research and development of inks: based on the premise of using alternative ingredients, how to adjust the composition of other ingredients to ensure the same level of performance as before. Summary of the invention

[0005] In the present invention, the inkjet transparent ink composition comprises a photoinitiator, a fluorescent brightener and a polymerizable monomer, wherein the photoinitiator comprises ethyl phenyl (2,4,6-trimethylbenzoyl) phosphonate, the polymerizable monomer comprises an aromatic ring-containing monomer and a hydroxyl-containing monomer, and the content of the fluorescent brightener is greater than 0.2% by mass relative to the total amount of the inkjet transparent ink composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a schematic diagram of a recording device used in this embodiment.

[0007] Figure 2 : is a table showing the results of the examples.

[0008] Figure 3 : is a table showing the results of the examples.

[0009] Figure 4 : is a table showing the results of the examples.

[0010] Description of Reference Numerals

[0011] 70: serial printer; 720: conveying unit; 730: recording unit; 731: inkjet head; 734: carriage; 735: carriage moving mechanism; F: recording medium; S1, S2: main scanning direction; T2: sub-scanning direction. DETAILED DESCRIPTION

[0012] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “this embodiment”) will be described in detail, but the present invention is not limited thereto and various modifications are possible without departing from the gist of the present invention.

[0013] 1. Inkjet transparent ink composition

[0014] The inkjet transparent ink composition involved in this embodiment (hereinafter, also referred to as "transparent ink composition") contains a photoinitiator, a fluorescent brightener, and a polymerizable monomer. The above-mentioned photoinitiator contains ethyl phenyl (2,4,6-trimethylbenzoyl) phosphonate, and the above-mentioned polymerizable monomer contains an aromatic ring-containing monomer and a hydroxyl-containing monomer. Relative to the total amount of the above-mentioned inkjet transparent ink composition, the content of the above-mentioned fluorescent brightener is 0.2% by mass or more.

[0015] In the past, diphenyl-2,4,6-trimethylbenzoylphosphine oxide (hereinafter, also referred to as "TPO") was typically used as a photoinitiator. However, TPO becomes a target in environmental regulations. Therefore, in the present embodiment, ethyl phenyl (2,4,6-trimethylbenzoyl) phosphonate (hereinafter, also referred to as "TPO-L") having high environmental adaptability is used instead of TPO as a photoinitiator.

[0016] On the other hand, the curability of ink compositions using TPO-L still needs to be improved compared to ink compositions using TPO. Therefore, if the content of TPO-L is increased to improve the curability, the coating film will turn yellow, which will cause a technical problem that the yellowing is noticeable, especially in a transparent ink composition that does not contain a colorant.

[0017] Therefore, in this embodiment, in order to improve the curability while suppressing the yellowing of the coating film, the transparent ink composition contains a fluorescent whitening agent. By containing the fluorescent whitening agent, even if the content of the photoinitiator, that is, TPO-L, which is the cause of the yellowing of the coating film, is reduced, good curability can be maintained. In addition, since it is believed that the fluorescent whitening agent will obtain a sensitizing effect by combining with the photoinitiator, which helps the curability of the transparent ink composition, it is believed that by making the transparent ink composition contain the fluorescent whitening agent, the curability is further improved while suppressing the yellowing of the coating film. However, the main factor for improving the curability while suppressing the yellowing of the coating film is not limited to this.

[0018] By including a fluorescent whitening agent in the ink composition, the curability can be improved while suppressing yellowing of the coating film. However, there is a technical problem that the fluorescent whitening agent precipitates in a low-temperature environment.

[0019] Therefore, in this embodiment, in order to improve the solubility of the fluorescent whitening agent, the transparent ink composition contains an aromatic ring-containing monomer. Since the aromatic ring-containing monomer has high compatibility with the fluorescent whitening agent, the fluorescent whitening agent will not precipitate even in a low temperature environment by making the transparent ink composition contain an aromatic ring-containing monomer, and it is considered that the low-temperature storage property is improved. However, the main factor for improving the low-temperature storage property is not limited to this.

[0020] Furthermore, in the present embodiment, in order to improve curability, the transparent ink composition contains a hydroxyl-containing monomer. As for the hydroxyl-containing monomer, since the hydroxyl groups contained in the hydroxyl-containing monomer are firmly bonded to each other through hydrogen bonds, the curability is excellent, so it is considered that by making the transparent ink composition contain a hydroxyl-containing monomer, the curability is further improved. However, the main factor for improving curability is not limited to this.

[0021] The viscosity of the transparent 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. When the viscosity of the transparent ink composition at 25° C. is within the above range, the transparent ink composition tends to be suitable for the inkjet recording method.

[0022] The viscosity of the transparent ink composition at 25° C. can be measured by a method in accordance with JIS Z 8803. The viscosity of the transparent ink composition is not particularly limited, and can be adjusted, for example, by changing the content of the photoinitiator, changing the type and / or content of the polymerizable monomer, adding a viscosity modifier as another component described later, and the like.

[0023] Hereinafter, each component of the clear ink composition according to the present embodiment will be described in detail.

[0024] 1.1. Pigment

[0025] In the present embodiment, the transparent ink composition means that it does not contain or substantially does not contain a colorant. In the present embodiment, "substantially does not contain a colorant" is not particularly limited, and for example, it means that the content of the colorant is 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 transparent ink composition. In addition, 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%.

[0026] Examples of the coloring material include dyes and pigments.

[0027] 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 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, 14 2, 144, 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.

[0028] The pigment is not particularly limited, and examples thereof 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 organic pigment includes azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and complex azo pigments, polycyclic pigments such as phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments, dye complexes, dye lakes, nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments. These dyes may be used alone or in combination of two or more.

[0029] 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), Rega 400R, Rega 1330R, Rega 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 Black S150, Color Black S160, Color Black S170, Printex35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (all manufactured by Degussa).

[0030] The white pigment is not particularly limited, and examples thereof include CI Pigment White 6, 18, and 21.

[0031] The yellow pigment is not particularly limited, and 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.

[0032] The magenta pigment is not particularly limited, and 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, 245, and CI Pigment Violet 19, 23, 32, 33, 36, 38, 43, and 50.

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

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

[0035] Pigments can also be dispersed by dispersants. As dispersants for dispersing pigments, there are no particular limitations, and examples thereof include: dispersants with one or more of polyoxyalkylenes, polyenes, 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 main components. As commercially available dispersants, there are: AJISPER series manufactured by Ajinomoto Fine Technology Co., Ltd., SOLSPERSE series (Solsperse 36000 (acid value 45), Solsperse 32000 (amine value 35) etc.) available from Avecia Co., DISPERBYK series (DISPERBYK 168, 180 etc.) manufactured by BYK Chemie, and Di Sibalon series manufactured by Kusumoto Chemical Co., Ltd. These dispersants can be used alone or in combination of two or more.

[0036] 1.2. Photoinitiator

[0037] The transparent ink composition of this embodiment contains a photoinitiator. When the transparent ink composition contains a photoinitiator, active substances (initiators) such as free radicals, acids and bases are generated when irradiated with radiation, and the polymerization reaction of the polymerizable monomer described later is promoted by the function of the initiator.

[0038] The photoinitiator is not particularly limited, and examples thereof include: aromatic ketones, hydroxyketones, acylphosphine compounds, aromatic onium salt compounds, organic peroxides, sulfur compounds such as thioxanthone, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, nitrogen onium 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.

[0039] In addition, the transparent ink composition of the present embodiment contains an acylphosphine compound, namely ethyl phenyl (2,4,6-trimethylbenzoyl) phosphonate (hereinafter also referred to as "TPO-L") as a photoinitiator. By making the transparent ink composition contain TPO-L, it is possible to make a transparent ink composition with high environmental adaptability.

[0040] 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. When the content of the photoinitiator is within the above range, there is a tendency to further improve the suppression of yellowing of the coating film.

[0041] 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 transparent ink composition. By setting the content of TPO-L within the above range, a transparent ink composition having high environmental adaptability can be prepared, and yellowing of the coating film can be further suppressed while the curing property tends to be further improved.

[0042] 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 the photoinitiator. By setting the content of TPO-L within the above range, a transparent ink composition having high environmental adaptability can be prepared, and yellowing of the coating film can be further suppressed while the curing property tends to be further improved.

[0043] The photoinitiator of the present embodiment may further include a photoinitiator other than TPO-L. The photoinitiator other than TPO-L is not particularly limited, and an example thereof includes phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide as an acylphosphine compound.

[0044] The content of the photoinitiator other than TPO-L is not particularly limited, and 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 % relative to the total amount of the clear ink composition.

[0045] The content of the photoinitiator other than TPO-L is not particularly limited, and is, for example, 10.0 to 70.0 mass %, 15.0 to 60.0 mass %, or 20.0 to 55.0 mass % relative to the total amount of the photoinitiator.

[0046] The photoinitiator of the present embodiment preferably does not contain or substantially does not contain diphenyl-2,4,6-trimethylbenzoylphosphine oxide (TPO). "Substantially free of TPO" is not particularly limited, and for example, means that the content of TPO is 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 transparent ink composition. In addition, 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%.

[0047] 1.3. Fluorescent brightener

[0048] The transparent ink composition of this embodiment contains a fluorescent whitening agent. The fluorescent whitening agent absorbs ultraviolet rays and emits bluish-white fluorescence. In addition, the fluorescent whitening agent exhibits a sensitizing effect by combining with a photoinitiator. Therefore, by making the transparent ink composition of this embodiment contain a fluorescent whitening agent, there is a tendency to further suppress yellowing of the coating film and further improve curability.

[0049] In addition, examples of the photoinitiator of the present invention classified as a fluorescent whitening agent include naphthoxybenzoxazolyl derivatives, thiophenebenzoxazolyl derivatives, styrylbenzoxazolyl derivatives, coumarin derivatives, styrenebiphenyl derivatives, pyrazolone derivatives, styrene derivatives, styrene derivatives of benzene and biphenyl, bis(benzoxazole-2-yl) derivatives, carboxystyrene, naphthylimide, dibenzothiophene-5,5'-dioxy derivatives, pyrene derivatives and pyridinetriazole.

[0050] More specifically, the fluorescent whitening agent is not particularly limited, and examples thereof include 1,4-bis(2-benzoxazolyl)naphthalene and 2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene.

[0051] The content of the fluorescent brightener 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 transparent ink composition. By making the content of the fluorescent brightener within the above range, there is a tendency to further suppress yellowing of the coating film and further improve curability.

[0052] 1.4. Sensitizer

[0053] The transparent ink composition of the present embodiment may further include a sensitizer. When irradiated with radiation, the sensitizer absorbs radiation to become excited, and contacts with the photoinitiator to promote the decomposition of the photoinitiator, thereby further improving the curability of the transparent ink composition.

[0054] As the sensitizer, there is no particular limitation, and examples thereof include: amine compounds (aliphatic amines, amines containing aromatic rings, piperidine, reaction products of epoxy resins and amines, triethanolamine triacrylate, etc.), urea compounds (arylthioureas, o-tolylthioureas, etc.), sulfur compounds (2-methyl-[4-(methylthio)phenyl]-2-morpholine-1-propane, sodium dithiophosphate, soluble salts of aromatic sulfinic acids, etc.), nitrile compounds (N,N-diethyl-p-aminobenzonitrile, etc.), phosphorus compounds (tri-n-butylphosphine, sodium diethyl dithiophosphate, etc.), nitrogen compounds (Michelle's ketone, N-nitrosohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds, condensates of formaldehyde or acetaldehyde and diamines, etc.), chlorine compounds (carbon tetrachloride, hexachloroethane, etc.), etc. These fluorescent whitening agents can be used alone or in combination of two or more.

[0055] The content of the sensitizer is not particularly limited, and is, for example, 0.1 to 5.0% by mass, or 0.5 to 2.5% by mass relative to the total amount of the clear ink composition. Alternatively, the sensitizer may not be contained.

[0056] 1.3. Polymerizable monomers

[0057] The transparent ink composition of this embodiment contains a polymerizable monomer. The polymerizable monomer is, for example, a photopolymerizable compound that polymerizes and cures when irradiated with light such as ultraviolet rays, and is not particularly limited. As polymerizable monomers, from the viewpoint of the number of polymerizable double bonds, for example, monofunctional monomers, difunctional monomers, and polyfunctional monomers with three or more functional groups can be listed. In addition, from the viewpoint of functional groups other than polymerizable double bonds, hydroxyl-containing monomers and aromatic ring-containing monomers can be listed. It should be noted that the terms "monofunctional", "difunctional" and "trifunctional" mean the number of functional groups of polymerizable double bonds. The polymerizable monomers can be used alone or in combination of two or more.

[0058] The content of the polymerizable monomer 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 % relative to the total amount of the clear ink composition. When the content of the polymerizable monomer is within the above range, curability tends to be further improved.

[0059] 1.3.1. Monofunctional monomers

[0060] The monofunctional monomer is not particularly limited, and examples thereof include (meth)acryloylmorpholine, benzyl(meth)acrylate, isopentyl(meth)acrylate, stearyl(meth)acrylate, lauryl(meth)acrylate, octyl(meth)acrylate, decyl(meth)acrylate, isomyristyl(meth)acrylate, isostearyl(meth)acrylate, 2-ethylhexyl-diethylene glycol(meth)acrylate, 2-hydroxybutyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, butoxyethyl(meth)acrylate, ethoxydiethylene glycol(meth)acrylate, methoxydiethylene glycol(meth)acrylate, methoxypoly(meth)acrylate. Ethylene 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, tert-butylcyclohexyl (meth) acrylate, dicyclopentyl (meth) acrylate, cyclic trimethylolpropane formaldehyde (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, 1,4-cyclohexanedimethanol mono (meth) acrylate and vinyl methyl oxazolidinone. Among them, 2-hydroxy-3-phenoxypropyl (meth) acrylate is preferred. These monofunctional monomers can be used alone or in combination of two or more.

[0061] The content of the monofunctional monomer is preferably 25.0 to 70.0 mass %, 27.5 to 65.0 mass %, or 30.0 to 60.0 mass % relative to the total amount of the clear ink composition. When the content of the monofunctional monomer is within the above range, the curing property tends to be more excellent.

[0062] 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 % relative to the total amount of the polymerizable monomers. When the content of the monofunctional monomer is within the above range, the curing property tends to be more excellent.

[0063] 1.3.2. Bifunctional monomers

[0064] The bifunctional monomer is not particularly limited, and 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 di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethyloltricyclodecane di(meth)acrylate, EO (ethylene oxide) adduct di(meth)acrylate of bisphenol A, PO (propylene oxide) adduct di(meth)acrylate of bisphenol A, hydroxypiperidinic 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.

[0065] The content of the bifunctional monomer is preferably 20.0 to 65.0 mass %, 25.0 to 60.0 mass %, or 30.0 to 55.0 mass % relative to the total amount of the clear ink composition. When the content of the bifunctional monomer is within the above range, the viscosity characteristics and curability tend to be more excellent.

[0066] 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 % relative to 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.

[0067] 1.3.3. Multifunctional monomers

[0068] The polyfunctional monomer having three or more functional groups is not particularly limited, and 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, glycerol propoxy tri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, and caprolactam-modified dipentaerythritol hexa(meth)acrylate. These polyfunctional monomers may be used alone or in combination of two or more.

[0069] The content of the multifunctional monomer is not particularly limited, and is, for example, 1.0 to 15.0 mass %, 2.0 to 12.5 mass %, or 3.0 to 10.0 mass % relative to the total amount of the clear ink composition.

[0070] The content of the multifunctional monomer is not particularly limited, and is, for example, 2.0 to 15.0 mass %, 3.0 to 12.5 mass %, or 4.0 to 10.0 mass % relative to the total amount of the polymerizable monomers. In addition, the clear ink composition may not contain the multifunctional monomer.

[0071] 1.3.4. Hydroxyl-containing monomers

[0072] The transparent ink composition of this embodiment includes a hydroxyl-containing monomer having a hydroxyl group. The hydroxyl-containing monomer may be any of the monofunctional monomers, bifunctional monomers, and polyfunctional monomers described above. When the transparent ink composition includes a hydroxyl-containing monomer, curability tends to be further improved.

[0073] The hydroxyl-containing monomer is not particularly limited to a monomer containing a hydroxyl group, and examples thereof include monomers containing a hydroxyl group among the monomers listed in the monofunctional monomers, the bifunctional monomers, and the polyfunctional monomers. Among them, from the viewpoint of further improving the curability, 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.

[0074] The content of the hydroxyl-containing monomer 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 % relative to the total amount of the clear ink composition. When the content of the hydroxyl-containing monomer is within the above range, curability tends to be further improved.

[0075] 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 % relative to the total amount of the polymerizable monomers. When the content of the hydroxyl group-containing monomer is within the above range, the curability tends to be further improved.

[0076] 1.3.5. Aromatic ring-containing monomers

[0077] The transparent ink composition of this embodiment contains an aromatic ring-containing monomer having an aromatic ring. The aromatic ring-containing monomer may be any of the monofunctional monomer, bifunctional monomer, and polyfunctional monomer described above. By making the transparent ink composition contain an aromatic ring-containing monomer, the fluorescent whitening agent will not precipitate in a low temperature environment, and the low temperature storage property tends to be further improved.

[0078] The aromatic ring-containing monomer is not particularly limited to any monomer containing an aromatic ring, and examples thereof include monomers containing an aromatic ring among the monomers listed in the monofunctional monomers, the bifunctional monomers, and the polyfunctional monomers. Among them, from the viewpoint of further improving the low-temperature storage property, at least one selected from the group consisting of phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate is preferred.

[0079] The transparent ink composition of the present 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, preferably 20% by mass or less, preferably 10% by mass or less, and preferably 5% by mass or less. In addition, phenoxyethyl (meth) acrylate may not be contained. When the transparent ink composition of the present embodiment contains 40% by mass or less of phenoxyethyl (meth) acrylate or when the transparent ink composition of the present embodiment does not contain phenoxyethyl (meth) acrylate, there is a tendency to prevent yellowing of the coating film of the inkjet ink composition, reduce the viscosity of the inkjet ink composition, and achieve excellent ejection stability.

[0080] The content of the aromatic ring-containing monomer is preferably 20.0% by mass or more, 30.0% by mass or more, 31.5% by mass or more, 20.0 to 60.0% by mass, 25.0 to 55.0% by mass, 30.0 to 50.0% by mass, or 35.0 to 47.5% by mass relative to the total amount of the transparent ink composition. When the content of the aromatic ring-containing monomer is within the above range, there is a tendency for low-temperature storage properties to be further improved.

[0081] 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 % relative to the total amount of the polymerizable monomers. When the content of the aromatic ring-containing monomer is within the above range, the low-temperature storage property tends to be further improved.

[0082] 1.3.6. Monomers containing aromatic rings and hydroxyl groups

[0083] The transparent ink composition of the present embodiment preferably contains an aromatic ring- and hydroxyl-containing monomer containing both an aromatic ring and a hydroxyl group. The aromatic ring- and hydroxyl-containing monomer may be any of the monofunctional monomers, bifunctional monomers, and polyfunctional monomers described above. By making the transparent ink composition contain an aromatic ring- and hydroxyl-containing monomer, there is a tendency that the design freedom of the transparent ink composition is improved and the physical properties (such as viscosity characteristics, etc.) of the transparent ink composition can be improved.

[0084] The aromatic ring and hydroxyl group-containing monomer is both the above-mentioned hydroxyl group-containing monomer and 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 an example thereof includes 2-hydroxy-3-phenoxypropyl (meth)acrylate.

[0085] The content of the aromatic ring- and hydroxyl-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 %.

[0086] The content of the aromatic ring- and hydroxyl group-containing monomer relative to the total amount of the polymerizable monomer 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 %.

[0087] 1.4. Oligomers

[0088] The transparent ink composition of this embodiment may further include an oligomer. The oligomer of this embodiment refers to a polymer such as a dimer, trimer, etc. having a polymerizable compound as a constituent component and having one or more polymerizable functional groups. It should be noted that the polymerizable compound mentioned here is not limited to the above-mentioned monofunctional monomer, difunctional monomer, and multifunctional monomer.

[0089] Such an oligomer is not particularly limited, and examples thereof include a urethane acrylate oligomer having a urethan repeating structure, a polyester acrylate oligomer having an ester repeating structure, and an epoxy acrylate oligomer having an epoxy repeating structure.

[0090] Among them, polyurethane acrylate oligomers are preferred, aliphatic polyurethane acrylate oligomers and aromatic polyurethane acrylate oligomers are more preferred, and aliphatic polyurethane acrylate oligomers are further preferred. In addition, polyurethane acrylate oligomers are preferably polyurethane acrylate oligomers having a functional group number of four or less, and more preferably polyurethane acrylate oligomers having a functional group number of two functional groups. It should be noted that the functional group number refers to the number of functional groups of (meth)acryloyl groups. By including polyurethane acrylate oligomers, the transparent ink composition tends to have excellent viscosity characteristics.

[0091] The urethane acrylate oligomer is not particularly limited, and examples thereof include polyether urethane acrylate oligomers having a urethane bond and an ether bond, polyester urethane acrylate oligomers having a urethane bond and an ester bond, and polycarbonate urethane acrylate oligomers having a urethane bond and a carbonate bond.

[0092] Commercially available products of polyurethane oligomers are not limited to the following, and examples thereof include CN929 (polyester-based aliphatic polyurethane acrylate, functional group number 3), CN962 (polyester-based aliphatic polyurethane acrylate, functional group number 2), CN963 (polyester-based aliphatic polyurethane acrylate, functional group number 2), CN964 (polyester-based aliphatic polyurethane acrylate, functional group number 2), CN965 (polyester-based aliphatic polyurethane acrylate, functional group number 2), CN968 (polyester-based aliphatic polyurethane acrylate, functional group number 6), CN980 (polyether-based aliphatic polyurethane acrylate, functional group number 2), CN981 (polyester-based aliphatic polyurethane acrylate, functional group number 2), and CN982 (polyester-based aliphatic polyurethane acrylate, functional group number 2). aliphatic polyurethane acrylate, functional group number 2), CN982 (polyester aliphatic polyurethane acrylate, functional group number 2), CN983 (polyester aliphatic polyurethane acrylate, functional group number 2), CN996 (polyether aliphatic polyurethane acrylate, functional group number 2), CN9001 (polyester aliphatic polyurethane acrylate, functional group number 2), CN9002 (polyester aliphatic polyurethane acrylate, functional group number 2), CN9788 (polyester aliphatic polyurethane acrylate, functional group number 2), CN9893 (polyether aliphatic polyurethane acrylate, functional group number 2) (the above are Sartomer ), EBECRYL 230 (functional group number 2), 270 (functional group number 2), 5129 (functional group number 6), 8210 (functional group number 4), 8301 (functional group number 6), 8311 (functional group number 3), 8402 (functional group number 2), 8405 (functional group number 4), 8701 (functional group number 3), 8804 (functional group number 2), 8807 (functional group number 2), 9260 (functional group number 3), 9270 (functional group number 2), KRM 8200 (functional group number 6), 8296 (functional group number 3), 8452 (functional group number 10) (the above are trade names of DAICEL-CYTEC Company LTD.) and aliphatic urethane acrylate oligomers such as CN971 (polyester aromatic urethane acrylate, functional group number 3), CN972 (polyester aromatic urethane acrylate, functional group number 3), CN975 (polyester aromatic urethane acrylate, functional group number 6), CN978 (polyester aromatic urethane acrylate, functional group number 2), CN9782 (polyester aromatic urethane acrylate, functional group number 2), CN9783 (polyester aromatic urethane acrylate, functional group number 2) (all trade names manufactured by Sartomer Co., Ltd.), EBECRYL210 (functional group number 2), 220 (functional group number 6) (all trade names manufactured by DAICEL-CYTEC Co., Ltd.) and aromatic urethane acrylate oligomers such as CN971 (polyester aromatic urethane acrylate, functional group number 3), CN972 (polyester aromatic urethane acrylate, functional group number 3), CN975 (polyester aromatic urethane acrylate, functional group number 6), CN978 (polyester aromatic urethane acrylate, functional group number 2), CN9782 (polyester aromatic urethane acrylate, functional group number 2), CN9783 (polyester aromatic urethane acrylate, functional group number 2) (all trade names manufactured by Sartomer Co., Ltd.), EBECRYL210 (functional group number 2), 220 (functional group number 6) (all trade names manufactured by DAICEL-CYTEC Co., Ltd.)

[0093] The content of the oligomer is not particularly limited, and is, for example, 1.0 to 12.0% by mass, 2.0 to 11.0% by mass, or 3.0 to 10.0% by mass relative to the total amount of the clear ink composition.

[0094] 1.5. Surfactants

[0095] The surfactant is not particularly limited, and examples thereof include acetylene glycol surfactants, fluorine-based surfactants, and silicone-based surfactants. From the viewpoint of more effectively and reliably exhibiting the effects of the present invention, silicone-based surfactants are preferred.

[0096] The silicon-based surfactant is not particularly limited, and examples thereof include BYK-UV3500, UV3570, and BYK350 (trade names manufactured by BigChem Japan Co., Ltd.).

[0097] The content of the surfactant is not particularly limited, and may be, for example, 0.1 to 1.0% by mass relative to the total amount of the clear ink composition.

[0098] 1.6. Inhibitors

[0099] The polymerization inhibitor is not particularly limited, and examples thereof include: hydroquinones represented by hydroquinone, hydroquinone monomethyl ether (MEHQ), 1-o-2,3,5-trimethylhydroquinone, and 2-tert-butylhydroquinone; catechols represented by catechol, 4-methylcatechol, and 4-tert-butylcatechol; phenol, butylhydroxytoluene, butylhydroxyanisole, p-methoxyphenol, cresol, pyrogallol, 3,5-di-tert-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-tert-butylphenol); ), 2,2'-methylenebis(4-ethyl-6-butylphenol) and 4,4'-thiobis(3-methyl-6-tert-butylphenol) as the representative phenols; hindered amines represented by compounds having a 2,2,6,6-tetramethylpiperidine-N-oxy skeleton represented by 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 compounds having a 2,2,6,6-tetramethylpiperidine-N-acyl skeleton. These inhibitors can be used alone or in combination of two or more.

[0100] The content of the polymerization inhibitor is not particularly limited, and may be, for example, 0.1 to 1.0% by mass relative to the total amount of the clear ink composition.

[0101] 1.7. Other ingredients

[0102] The transparent ink composition of the present embodiment may contain other known components that can be used in existing transparent ink compositions in addition to the above components. The other components are not particularly limited, and examples thereof include lubricants, cosolvents, viscosity modifiers, pH modifiers, antioxidants, preservatives, and corrosion inhibitors. These other components may be used alone or in combination of two or more.

[0103] 2. Method for producing inkjet clear ink composition

[0104] The method for producing the inkjet clear ink composition of the present embodiment is not particularly limited. For example, the above-mentioned components may be simultaneously added to a mixing kettle and mixed, or the components may be added to a mixing kettle in sequence and mixed.

[0105] 3. Recording medium

[0106] The recording medium used for recording with the clear ink composition of the present embodiment is not particularly limited, and examples thereof include absorptive recording media, low-absorptive recording media, and non-absorptive recording media.

[0107] The absorptive recording medium is not particularly limited, and examples thereof include: ordinary paper such as electronic photographic paper with high ink permeability, inkjet paper (inkjet paper having an ink absorbing layer composed of silicon particles and aluminum oxide particles or an ink absorbing layer composed of a hydrophilic polymer such as polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP), etc.), cloth, etc.

[0108] The low-absorption recording medium is not particularly limited, and examples thereof include coated paper, coated paper, glossy paper, and the like used in ordinary offset printing, which have low ink permeability.

[0109] The non-absorbent recording medium is not particularly limited, and examples thereof include: films and plates of plastics such as polyvinyl chloride, polyethylene, allyl chloride, ethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane; plates of metals such as iron, silver, copper, and aluminum, or metal plates made by vapor deposition of these various metals, plastic films, plates of alloys such as stainless steel and cast iron; recording media in which a film of plastics such as polyvinyl chloride, polyethylene, allyl chloride, ethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane is adhered (coated) to a paper substrate; and the like.

[0110] 4. Inkjet recording method

[0111] The inkjet recording method of the present embodiment (hereinafter referred to as the "recording method") includes: an ink adhesion process, in which the transparent ink composition of the present embodiment is ejected from the inkjet head and adheres to the recording medium; and an irradiation process, in which the transparent ink composition adhered to the recording medium is irradiated with radiation. In addition, as needed, other processes such as a conveying process for conveying the recording medium may also be included.

[0112] 4.1. Ink adhesion process

[0113] In the ink adhesion step, the transparent ink composition of the present embodiment is ejected from the inkjet head and adhered to the recording medium. More specifically, the pressure generating unit provided in the inkjet head is driven to eject the transparent ink composition filled in the pressure generating chamber of the inkjet head from the nozzle.

[0114] Examples of the inkjet head used in the ink adhesion step include a line head that performs recording in a line manner and a serial head that performs recording in a serial manner.

[0115] In a line type using a line head, for example, an inkjet head having a width greater than the recording width of a recording medium is fixed to a recording device. Then, the recording medium and the inkjet head are relatively moved in a sub-scanning direction (a conveying direction of the recording medium, i.e., a 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 the movement, thereby recording an image on the recording medium.

[0116] In a serial type using a serial head, for example, an inkjet head is mounted on a carriage that is movable in the width direction of a recording medium. Then, the carriage is moved in a main scanning direction (width direction of the recording medium), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with the movement, thereby recording an image on the recording medium.

[0117] 4.2. Irradiation process

[0118] In the irradiation step, the transparent ink composition attached to the recording medium is irradiated with radiation. When irradiated with radiation, the composition is cured by initiating the polymerization reaction of the monomers to form a coating film. At this time, if a photoinitiator is present, active substances (initiators) such as free radicals, acids and bases are generated, and the polymerization reaction of the monomers is promoted by the function of the initiator.

[0119] Here, as radiation, ultraviolet rays, infrared rays, visible rays, X-rays, etc. can be cited. As for the radiation source, the composition is irradiated by a radiation source provided downstream of the inkjet head. As the radiation source, there is no particular limitation, and for example, UV-LED can be cited. By using such a radiation source, it is possible to achieve miniaturization of the device and reduction of cost. UV-LED as an ultraviolet source is small, so it can be installed in the inkjet recording device.

[0120] 4.3. Transport process

[0121] The recording method of this embodiment may also include a conveying process. In the conveying process, the recording medium is conveyed in a predetermined direction in the recording device. More specifically, the recording medium is conveyed from the paper supply section of the recording device to the paper discharge section using a conveying roller and a conveying belt provided in the recording device. During the conveying process, the transparent ink composition ejected from the inkjet head adheres to the recording medium to form a recorded object. The order and timing of performing the ink adhesion process, the irradiation process, and the conveying process are not particularly limited. For example, the three processes may be performed simultaneously or alternately. In addition, two of the three processes may be performed simultaneously, and the remaining processes may be performed separately.

[0122] 5. Recording device

[0123] As an example of an inkjet device, Figure 1 Figure 2 shows a perspective view of a serial printer. Figure 1 As shown, 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 discharges the recorded recording medium to the outside of the serial printer. Specifically, the conveying unit 720 includes conveying rollers, and conveys the conveyed recording medium F in the secondary scanning direction T2.

[0124] The recording unit 730 also includes a carriage 734 on which an inkjet head 731 having nozzles for ejecting a transparent ink composition onto the recording medium F conveyed from the conveying unit 720 is mounted, and a carriage moving mechanism 735 for moving the carriage 734 in the main scanning directions S1 and S2 of the recording medium F.

[0125] In the case of a serial printer, a head having a length smaller than the width of the recording medium is used as the inkjet head 731, and the head moves and records in a multi-path (Pass) manner. In addition, in the serial printer, a carriage 734 that moves in a predetermined direction is equipped with the inkjet head 731, and the head moves along with the movement of the carriage, thereby ejecting a transparent ink composition onto the recording medium F. Thus, recording is performed in two or more paths. It should be noted that the path is also referred to as the main scan. A sub-scan for transporting the recording medium is performed between the paths. That is, the main scan and the sub-scan are performed alternately.

[0126] In addition, the inkjet device of this embodiment is not limited to the above-mentioned serial printer, and can also be the above-mentioned line printer. The line printer has: a line head, which is an inkjet head having a length greater than the recording width of the recording medium; and a moving mechanism, which relatively moves the recording medium and the inkjet head in a direction orthogonal to the width direction of the recording medium, and is a printer that records on the recording medium in a single scan.

[0127] Example

[0128] The present invention is described in more detail below using examples and comparative examples. The present invention is not limited to the following examples. Unless otherwise specified, the reaction was carried out at room temperature (25° C.) and 1 atmosphere.

[0129] 1. Preparation of inkjet clear ink composition

[0130] In a stainless steel container, the mixture is stirred in a kettle. Figures 2 to 4 The components were added in the described composition, mixed and stirred, and then filtered through a 5 μm membrane filter to obtain inkjet clear ink compositions of Examples and Comparative Examples. It should be noted that the values ​​of the components shown in the examples in the figures are expressed in mass % unless otherwise specified.

[0131] exist Figures 2 to 4 The abbreviations used in the product and the ingredients are as follows. Figures 2 to 4 A blank column indicates that the ingredient was not used.

[0132] PEA (trade name "Biscoat #192", manufactured by Osaka Organic Chemical Industry Co., Ltd., phenoxyethyl acrylate)

[0133] · BZA (trade name "Biscoat #160", manufactured by Osaka Organic Chemical Industry Co., Ltd., benzyl acrylate)

[0134] ·M-600A (trade name "Epoxy Ester M-600A", manufactured by Kyoeisha Chemical Co., Ltd., 2-hydroxy-3-phenoxypropyl (meth)acrylate)

[0135] ·4-HBA (manufactured by Osaka Organic Chemical Industry Co., Ltd., 4-hydroxybutyl acrylate)

[0136] ·CHDMM (trade name "CHDMMA", manufactured by Mitsubishi Chemical Corporation, 1,4-cyclohexanedimethanol monoacrylate)

[0137] ·IBXA (manufactured by Osaka Organic Chemical Industry Co., Ltd., isobornyl acrylate)

[0138] ・ACMO (manufactured by KJ Chemical Co., Ltd., acryloylmorpholine)

[0139] DPGDA (trade name "Biscoat #310HP", manufactured by Osaka Organic Chemical Industry Co., Ltd., tripropylene glycol diacrylate)

[0140] VEEA (Nippon Shokubai Co., Ltd., 2-(2-diethenyloxyethoxy)ethyl acrylate)

[0141] ·A-DPH (manufactured by Shin-Nakamura Chemical Industry Co., Ltd., dipentaerythritol hexaacrylate)

[0142] CN9893 (manufactured by Sartomer, bifunctional polyurethane acrylate oligomer)

[0143] · Omnirad 819 (manufactured by IGM Resins BV, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide)

[0144] · Omnirad TPO-L (manufactured by IGM Resins BV, ethyl phenyl (2,4,6-trimethylbenzoyl) phosphonate)

[0145] Speedcure DETX (manufactured by Sartomer, 2-methyl-[4-(methylthio)phenyl]-2-morpholine-1-propane)

[0146] ·TELALUX KCB (manufactured by Clariant Japan, 1,4-bis(2-benzoxazolyl)naphthalene)

[0147] BYK-UV3500 (manufactured by BYK Additives & Instruments, polyether-modified polydimethylsiloxane with an acryl group)

[0148] ·MEHQ (trade name "p-methoxyphenol", manufactured by Kanto Chemical Co., Ltd., hydroquinone monomethyl ether)

[0149] 2. Evaluation Method

[0150] 2.1. Viscosity characteristics

[0151] The viscosity of the clear ink compositions of Examples and Comparative Examples immediately after preparation was measured at room temperature (25° C.) using a rotational viscometer (product name “Rheometer MCR-301”, manufactured by Anton Paar AG) in accordance with JIS Z8803.

[0152] Evaluation Criteria

[0153] A: The viscosity is 19 mPa·s or more and 21 mPa·s or less.

[0154] 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.

[0155] C: The viscosity is 18 mPa·s or less or 22 mPa·s or more.

[0156] 2.2. Low temperature storage

[0157] The clear ink compositions of Examples and Comparative Examples were filled in glass bottles and stored at -20°C for 7 days. The properties of the clear ink compositions before and after the storage were visually observed and evaluated.

[0158] Evaluation Criteria

[0159] A: No foreign matter was found.

[0160] B: No foreign matter was visually observed, but foreign matter was observed when filtering with a 10 μm filter.

[0161] C: The generation of foreign matter is visually detected.

[0162] 2.3. Curing

[0163] The cotton swab load viscosity evaluation was performed. Specifically, the transparent ink composition of the embodiment and the comparative example was applied to a polyvinyl chloride medium with a bar coater in a coating thickness of 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 this time, an LED with a peak wavelength of 395 nm was used as a light source. Then, the coating surface was wiped with a cotton swab, and the irradiation energy at which the cotton swab was no longer colored was measured to evaluate the curability.

[0164] Evaluation Criteria

[0165] A: The irradiation energy at which the cotton swab no longer discolors is less than 150mJ / cm 2 .

[0166] B: The irradiation energy at which the cotton swab no longer discolors is 150 mJ / cm 2 Above and less than 250mJ / cm 2 .

[0167] C: The irradiation energy at which the cotton swab no longer discolors is 250 mJ / cm 2 above.

[0168] 2.4. Evaluation of coating color tone

[0169] The color of the coating film of the clear ink composition after ultraviolet irradiation in the evaluation of curability was measured using a colorimeter Spectrolino (manufactured by GretagMacbeth), and b* was measured.

[0170] Evaluation Criteria

[0171] A: b*<1.0.

[0172] B: 1.0≤b*<2.0.

[0173] C: 2.0≤b*.

[0174] 3. Evaluation results

[0175] according to Figures 2 to 4 The evaluation results show that the clear ink compositions of Examples are superior to the clear ink compositions of Comparative Examples in terms of low-temperature storage stability, curability, and / or coating film color tone.

Claims

1. An inkjet transparent ink composition, characterized in that: The inkjet transparent ink composition comprises a photoinitiator, a fluorescent brightener and a polymerizable monomer. The photoinitiator comprises ethyl phenyl (2,4,6-trimethylbenzoyl) phosphonate, The polymerizable monomers include aromatic ring-containing monomers and hydroxyl-containing monomers. The content of the fluorescent brightener is 0.2 mass % or more relative to the total amount of the inkjet clear ink composition.

2. The inkjet clear ink composition according to claim 1, characterized in that: The content of the photoinitiator is 12.0 mass % or less relative to the total amount of the inkjet clear ink composition.

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

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

5. The inkjet clear ink composition according to claim 1, characterized in that: The polymerizable monomer includes a monomer having both an aromatic ring and a hydroxyl group.

6. The inkjet clear ink composition according to claim 5, characterized in that: The monomer having both an aromatic ring and a hydroxyl group includes 2-hydroxy-3-phenoxypropyl acrylate.

7. The inkjet clear ink composition according to claim 1, characterized in that: 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.

8. The inkjet clear ink composition according to claim 1, characterized in that: The inkjet clear ink composition further comprises a urethane acrylate oligomer.

9. A recording method, characterized in that: The recording method has: a discharge step of discharging the inkjet clear ink composition according to any one of claims 1 to 8 and causing the inkjet clear ink composition to adhere to a recording medium; and The irradiation step is to irradiate the inkjet clear ink composition with radiation.

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