JP2013121992A - Active ray-curable type inkjet ink and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active ray-curable inkjet ink containing wax, however, in which blooming is suppressed, and an inkjet recording method using the same.SOLUTION: The active ray-curable inkjet ink contains an active ray-curable compound, 0.01 mass% or more and less than 15 mass% of the wax, and inorganic fine particles having an average particle size from 5 nm or more and less than 60 nm. Preferably, the content of inorganic fine particles in the active ray-curable inkjet ink is 0.1 mass% or more and less than 2 mass%. Moreover, the content of wax in the active ray-curable inkjet ink is preferably 1 mass% or more.

Description

  The present invention relates to an actinic ray curable inkjet ink and an inkjet recording method.

  The ink jet recording system is used in various printing fields because it can form an image easily and inexpensively. As one of the ink jet recording methods, there is an ultraviolet curable ink jet method in which droplets of ultraviolet curable ink jet ink are landed on a recording medium and then cured by irradiation with ultraviolet rays to form an image. The ultraviolet curable ink jet method has been attracting attention in recent years because it can form an image having high scratch resistance and adhesion even on a recording medium having no ink absorbability.

  It is known to mix a wax with an ultraviolet curable ink-jet ink (see, for example, Patent Document 1), and thereby improving the slipperiness of the surface of an image obtained thereby to improve the scratch resistance. Are known.

  On the other hand, it is known to mix inorganic fine particles such as silica fine particles and alumina fine particles with ultraviolet curable ink-jet ink (see, for example, Patent Document 2), thereby improving the heat resistance of the ink. It has been.

JP-T-2005-504860 JP 2008-37898 A

  As described above, it is known that adding a wax to an ultraviolet curable ink jet ink increases the slipperiness of the image surface; on the other hand, the wax may precipitate on the image surface and cause a phenomenon called blooming. It was. Therefore, the present invention provides an ink capable of suppressing blooming while being an ultraviolet curable inkjet ink containing a wax.

The first of the present invention relates to the actinic ray curable inkjet ink shown below.
[1] An actinic ray curable inkjet ink comprising an actinic ray curable compound, a wax of 0.01% by mass or more and less than 15% by mass, and inorganic fine particles having an average particle size of 5 nm or more and less than 60 nm, An actinic ray curable inkjet ink in which a light transmittance at a wavelength of 400 nm of a 0.01% by mass tripropylene glycol diacrylate solution of the inorganic fine particles is 70% or more.
[2] The actinic ray curable inkjet ink according to [1], wherein the content of the inorganic fine particles in the actinic ray curable inkjet ink is 0.1% by mass or more and less than 2% by mass.
[3] The actinic ray curable inkjet ink according to [1] or [2], wherein the inorganic fine particles have an average particle size of 10 nm or more and less than 50 nm.
[4] The actinic ray curable inkjet ink according to any one of [1] to [3], wherein the inorganic fine particles are fine particles of silica, alumina, zinc oxide, and zirconium oxide.
[5] The actinic ray curable inkjet ink according to any one of [1] to [4], wherein the inorganic fine particles are alumina fine particles and are surface-treated with a silicone-based surface treatment agent.

[6] The actinic ray curable inkjet ink according to any one of [1] to [5], wherein the actinic ray curable compound is a radical polymerizable compound.
[7] The actinic ray curable inkjet ink according to any one of [1] to [6], wherein the actinic ray curable compound includes an ethylene oxide-modified (meth) acrylate compound.
[8] The actinic ray curable inkjet ink according to any one of [1] to [7], wherein the wax includes any one of an aliphatic diketone and a fatty acid ester.
[9] The actinic ray curable inkjet ink according to any one of [1] to [8], wherein the wax content in the actinic ray curable inkjet ink is 1% by mass or more and less than 7% by mass.
[10] The actinic ray curable inkjet ink according to any one of [1] to [9], which undergoes a sol-gel phase transition reversibly depending on temperature.

The second aspect of the present invention relates to the following inkjet recording method.
[11] A step of ejecting the actinic radiation curable inkjet ink according to any one of [1] to [10] onto a recording medium, and irradiating the ink ejected onto the recording medium with actinic rays to thereby form the ink. An inkjet recording method comprising a step of curing
The inkjet recording method, wherein the temperature of the actinic radiation curable inkjet ink when ejected to the recording medium is a temperature at which the content of the wax contained in the actinic radiation curable inkjet ink is equal to or less than a saturated dissolution amount.

  The actinic ray curable ink-jet ink of the present invention suppresses the phenomenon of “blooming” caused by the precipitation of wax on the image surface, even though the wax is blended. Therefore, according to the actinic ray curable inkjet ink of the present invention, it is possible to form a high quality image including scratch resistance and blooming suppression. In particular, the present invention is suitably used as a “sol-gel phase transition type” actinic ray curable inkjet ink to which a relatively large amount of wax is added.

It is a figure which shows an example of a structure of the principal part of the inkjet recording apparatus of a line recording system. It is a figure which shows an example of a structure of the principal part of the inkjet recording device of a serial recording system.

  The actinic ray curable inkjet ink of the present invention includes an actinic ray curable compound, a wax, and inorganic fine particles.

[Actinic ray curable compound]
The actinic ray curable compound is a photopolymerizable compound that is crosslinked or polymerized by actinic rays. The actinic rays are, for example, electron beams, ultraviolet rays, α rays, γ rays, and X-rays, and preferably ultraviolet rays and electron beams. The actinic ray curable compound is a radical polymerizable compound or a cationic polymerizable compound, and is preferably a radical polymerizable compound.

  The radically polymerizable compound is a compound (monomer, oligomer, polymer or mixture thereof) having a radically polymerizable ethylenically unsaturated bond. A radically polymerizable compound may be used independently and may be used in combination of 2 or more type.

  Examples of the compound having an ethylenically unsaturated bond capable of radical polymerization include an unsaturated carboxylic acid and a salt thereof, an unsaturated carboxylic acid ester compound, an unsaturated carboxylic acid urethane compound, an unsaturated carboxylic acid amide compound and an anhydride thereof, Examples include acrylonitrile, styrene, unsaturated polyester, unsaturated polyether, unsaturated polyamide, and unsaturated urethane. Examples of the unsaturated carboxylic acid include (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and the like.

  Especially, it is preferable that a radically polymerizable compound is an unsaturated carboxylic acid ester compound, and it is more preferable that it is a (meth) acrylate compound. The (meth) acrylate compound may be not only a monomer described later, but also an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group, and the like.

Examples of (meth) acrylate compounds include 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, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate , Methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (meth) ) Acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (Meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid, t-butylcyclohexyl (meth) acrylate, etc. Monofunctional monomer;
Triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butanediol di (Meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, bisphenol A bifunctional monomer such as PO adduct di (meth) acrylate of A, neopentyl glycol di (meth) acrylate hydroxypivalate, poly (tetramethylene glycol di (meth) acrylate);
Trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate And trifunctional or higher polyfunctional monomers such as pentaerythritol ethoxytetra (meth) acrylate.

  From the viewpoint of photosensitivity, (meth) acrylate compounds are stearyl (meth) acrylate, lauryl (meth) acrylate, isostearyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, isobornyl (meth) acrylate, tetraethylene glycol di (Meth) acrylate, glycerin propoxytri (meth) acrylate and the like are preferable.

  The (meth) acrylate compound may be a modified product. Examples of modified products include ethylene oxide-modified (meth) acrylate compounds such as ethylene oxide-modified trimethylolpropane tri (meth) acrylate and ethylene oxide-modified pentaerythritol tetraacrylate; caprolactone such as caprolactone-modified trimethylolpropane tri (meth) acrylate Modified (meth) acrylate compounds; and caprolactam-modified (meth) acrylate compounds such as caprolactam-modified dipentaerythritol hexa (meth) acrylate.

  When the actinic ray curable inkjet ink of the present invention is a sol-gel phase transition type, at least a part of the actinic ray curable compound is preferably an ethylene oxide-modified (meth) acrylate compound. This is because the ethylene oxide-modified (meth) acrylate compound has high photosensitivity and easily forms a card house structure (described later) when the ink gels at a low temperature. In addition, the ethylene oxide-modified (meth) acrylate compound is easily dissolved in other ink components at high temperatures and has little curing shrinkage, so that curling of the printed matter hardly occurs.

  Examples of ethylene oxide-modified (meth) acrylate compounds include 4EO-modified hexanediol diacrylate CD561 (molecular weight 358), 3EO-modified trimethylolpropane triacrylate SR454 (molecular weight 429), 6EO-modified trimethylolpropane triacrylate SR499 manufactured by Sartomer. (Molecular weight 560), 4EO-modified pentaerythritol tetraacrylate SR494 (molecular weight 528); polyethylene glycol diacrylate NK ester A-400 (molecular weight 508), polyethylene glycol diacrylate NK ester A-600 (molecular weight 742) manufactured by Shin-Nakamura Chemical Co., Ltd. , Polyethylene glycol dimethacrylate NK ester 9G (molecular weight 536), polyethylene glycol dimethacrylate NK ester 4G (molecular weight 770); Tetraethylene glycol diacrylate V # 335HP (molecular weight 302) manufactured by Osaka Organic Chemical Co .; 3PO-modified trimethylolpropane triacrylate Photomer 4072 (molecular weight 471, ClogP 4.90) manufactured by Cognis; Shin-Nakamura Chemical 1,10-decanediol dimethacrylate NK ester DOD-N (molecular weight 310, Clog P 5.75), tricyclodecane dimethanol diacrylate NK ester A-DCP (molecular weight 304, Clog P 4.69) and tricyclodecandi Methanol dimethacrylate NK ester DCP (molecular weight 332, Clog P 5.12) and the like are included.

  The (meth) acrylate compound may be a polymerizable oligomer, and examples of such a polymerizable oligomer include an epoxy (meth) acrylate oligomer, an aliphatic urethane (meth) acrylate oligomer, and an aromatic urethane (meth) acrylate. Examples include oligomers, polyester (meth) acrylate oligomers, and linear (meth) acrylic oligomers.

  The cationically polymerizable compound can be an epoxy compound, a vinyl ether compound, an oxetane compound, or the like. A cationically polymerizable compound may be used independently and may be used in combination of 2 or more type.

  The epoxy compound is an aromatic epoxide, an alicyclic epoxide, an aliphatic epoxide, or the like, and an aromatic epoxide or an alicyclic epoxide is preferable in order to increase curability.

  The aromatic epoxide may be a di- or polyglycidyl ether obtained by reacting a polyhydric phenol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of the polyhydric phenol to be reacted or its alkylene oxide adduct include bisphenol A or its alkylene oxide adduct. The alkylene oxide in the alkylene oxide adduct can be ethylene oxide, propylene oxide, and the like.

  The alicyclic epoxide can be a cycloalkane oxide-containing compound obtained by epoxidizing a cycloalkane-containing compound with an oxidizing agent such as hydrogen peroxide or peracid. The cycloalkane in the cycloalkane oxide-containing compound can be cyclohexene or cyclopentene.

  The aliphatic epoxide can be a di- or polyglycidyl ether obtained by reacting an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of the aliphatic polyhydric alcohol include alkylene glycols such as ethylene glycol, propylene glycol, and 1,6-hexanediol. The alkylene oxide in the alkylene oxide adduct can be ethylene oxide, propylene oxide, and the like.

Examples of vinyl ether compounds include ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether. monovinyl ether compounds such as -o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, octadecyl vinyl ether;
Diethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexane dimethanol divinyl ether, trimethylolpropane trivinyl ether, etc. Or a trivinyl ether compound etc. are contained. Of these vinyl ether compounds, di- or trivinyl ether compounds are preferred in view of curability and adhesion.

The oxetane compound is a compound having an oxetane ring, and examples thereof include oxetane compounds described in JP-A Nos. 2001-220526, 2001-310937, and JP-A-2005-255821. Among them, the compound represented by the general formula (1) described in paragraph No. 0089 of JP-A-2005-255821, the compound represented by the general formula (2) described in paragraph No. 0092 of the same publication, the paragraph Examples include a compound represented by general formula (7) of number 0107, a compound represented by general formula (8) of paragraph number 0109, a compound represented by general formula (9) of paragraph number 0116, and the like. General formulas (1), (2), and (7) to (9) described in JP-A-2005-255821 are shown below.

  The content of the actinic ray curable compound in the actinic ray curable inkjet ink is preferably 1 to 97% by mass, and more preferably 30 to 95% by mass.

[wax]
In the present invention, the wax is generally defined as an organic substance that is solid at room temperature and becomes liquid when heated. The wax contained in the actinic ray curable inkjet ink of the present invention is preferably 0.01% by mass or more and less than 15% by mass. If the wax content is less than 0.01% by mass, the image surface slipperiness cannot be obtained, and the scratch resistance of the image becomes insufficient; Ink ejection properties deteriorate.

  The actinic ray curable inkjet ink of the present invention may be a sol-gel phase transition ink. The wax content in the sol-gel phase transition type ink is preferably 1% by mass or more; it is preferably less than 15% by mass, preferably less than 7% by mass. On the other hand, the wax content in the ink that is not a sol-gel phase transition type is preferably 0.01% by mass or more and less than 1% by mass.

  The type of wax is not particularly limited, but examples include higher fatty acids, higher alcohols, fatty acid esters, triglycerides, fatty acid amines, aliphatic ketones, fatty acid amides; preferably fatty acid esters or aliphatic diketones. .

  The wax in the sol-gel phase transition type ink is at least 1) dissolved in an actinic ray curable compound at a temperature higher than the gelation temperature, and 2) crystallized in the ink at a temperature equal to or lower than the gelation temperature. is necessary.

  When the wax is crystallized in the ink, it is preferable to form a space three-dimensionally surrounded by plate crystals that are crystallized wax, and enclose the actinic ray curable compound in the space. Thus, the structure in which the actinic ray curable compound is encapsulated in the space three-dimensionally surrounded by the plate crystal is sometimes referred to as “card house structure”. Once the card house structure is formed, the liquid actinic radiation curable compound can be retained and the ink droplets can be pinned. Thereby, coalescence of droplets can be suppressed. In order to form the card house structure, it is preferable that the actinic ray curable compound dissolved in the ink and the wax are compatible. On the other hand, if the actinic ray curable compound dissolved in the ink and the wax are phase-separated, it may be difficult to form a card house structure.

The aliphatic diketone as the wax is represented by the following formula, for example.

  In Formula (1), R1 and R2 are each independently an aliphatic hydrocarbon group containing a straight chain portion having 9 to 25 carbon atoms. The aliphatic hydrocarbon group may be a saturated or unsaturated aliphatic hydrocarbon group, but is preferably a saturated aliphatic hydrocarbon group (alkylene group) from the viewpoint of increasing the gelation temperature of the ink. If the R1 and R2 aliphatic hydrocarbon groups in the formula (1) have the same number of carbon atoms, the melting point of the compound in which R1 and R2 in the formula (1) are saturated aliphatic hydrocarbon groups is This is because R1 and R2 in (1) are often higher than the melting point of the compound which is an unsaturated aliphatic hydrocarbon group, and the gelation temperature of the ink tends to be high. The saturated aliphatic hydrocarbon group may be a branched or straight chain aliphatic hydrocarbon group, but in order to obtain high crystallinity, a straight chain saturated aliphatic hydrocarbon group (straight chain alkylene) is preferable. Group).

  When the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group is less than 9, the wax does not function as a gelling agent because it does not have sufficient crystallinity. A sufficient space for encapsulating the actinic ray curable compound cannot be formed. On the other hand, when the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group exceeds 25, the melting point becomes too high, and the wax does not dissolve in the ink unless the ink ejection temperature is increased. When the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group is 9 or more and 25 or less, the above-mentioned card house structure can be formed while having the crystallinity necessary as a gelling agent, and the melting point Is not too high. The number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group of R1 and R2 is preferably 11 or more and less than 23. Therefore, R1 and R2 are particularly preferably a linear saturated aliphatic hydrocarbon group (straight chain alkylene group) having 11 to 23 carbon atoms.

  Examples of the aliphatic hydrocarbon group containing a straight chain portion having 9 to 25 carbon atoms include docosanyl group (C22), icosanyl group (C20), octadecanyl group (C18), heptadecanyl group (C17), hexadecanyl group ( C16), pentadecanyl group (C15), tetradecanyl group (C14), tridecanyl group (C13), dodecanyl group (C12), undecanyl group (C11), decanyl group (C10) and the like.

The fatty acid ester as the wax is represented by the following formula, for example.

  In formula (2), R3 and R4 are each independently an aliphatic hydrocarbon group containing a straight chain portion having 9 to 26 carbon atoms. The aliphatic hydrocarbon group may be a saturated or unsaturated aliphatic hydrocarbon group, but is preferably a saturated aliphatic hydrocarbon group (alkylene group). Further, the saturated aliphatic hydrocarbon group may be a branched or straight-chain saturated aliphatic hydrocarbon group, but in order to obtain a certain level of crystallinity, preferably a straight-chain saturated aliphatic hydrocarbon group Group (straight chain alkylene group).

  When the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group of R3 and R4 is 9 or more and 26 or less, the crystallinity necessary as a gelling agent can be obtained as in the case of the compound represented by the formula (1). While having the card house structure, the melting point is not too high. In order to maintain the crystallinity of the compound represented by formula (2) above a certain level, the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group of R3 is 11 or more and less than 23, and the fatty acid of R4 It is preferable that the straight chain portion contained in the group hydrocarbon group has 12 or more and less than 24 carbon atoms. Therefore, it is particularly preferable that R3 is a linear alkylene group having 11 to 23 carbon atoms, and R4 is a linear alkylene group having 12 to 24 carbon atoms.

  Examples of the aliphatic hydrocarbon group containing a straight chain part having 9 to 26 carbon atoms are the same as the aliphatic hydrocarbon group containing a straight chain part having 9 to 25 carbon atoms in the above formula (1). Is included.

Preferred specific examples of the wax include aliphatic ketone compounds such as 18-pentatriacontanone and 16-hentriacontanone (for example, Kao Wax T1 manufactured by Kao Corporation); cetyl palmitate, stearyl stearate, behenyl behenate, etc. Aliphatic monoester compounds (for example, UNISTA-M-2222SL (manufactured by NOF Corporation), EXCEPARL SS (manufactured by Kao Corporation, melting point 60 ° C.), EMALEX CC-18 (manufactured by Nippon Emulsion Co., Ltd.), Amrepus PC (high grade) Alcohol Kogyo Co., Ltd.), Exepar MY-M (Kao Co., Ltd.), Spalm Aceti (Nippon Oil Co., Ltd.), EMALEX CC-10 (Nihon Emulsion Co., Ltd.), etc.); N-lauroyl-L-glutamic acid dibutylamide N- (2-Ethylhexanoyl) -L-glutamate dibutyl Amide compounds such as amides (available from Ajinomoto Fine Techno); dibenzylidene sorbitols such as 1,3: 2,4-bis-O-benzylidene-D-glucitol (available from Gelol D Shin Nippon Rika); paraffin wax Petroleum waxes such as microcrystalline wax and petrolactam; plant waxes such as candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and jojoba ester; beeswax, lanolin and whale wax Animal waxes; mineral waxes such as montan wax and hydrogenated wax; hardened castor oil or hardened castor oil derivatives; modified waxes such as montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives or polyethylene wax derivatives X; behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid and higher fatty acids such as erucic acid; higher alcohols such as stearyl alcohol and behenyl alcohol; hydroxystearic acid such as 12-hydroxystearic acid A fatty acid amide such as lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, 12-hydroxystearic acid amide (for example, Nikka Amide manufactured by Nippon Kasei Co., Ltd.); Series, ITOWAX series made by Ito Oil Co., Ltd., FATTYAMID series etc. made by Kao Corporation); N-substituted fatty acid amides such as N-stearyl stearamide, N-oleyl palmitate amide; N, N′-ethylenebisstearyl Special fatty acid amides such as amides, N, N′-ethylenebis-12-hydroxystearylamide, and N, N′-xylylenebisstearylamide; higher amines such as dodecylamine, tetradecylamine or octadecylamine; stearylstearic acid , Fatty acid ester compounds such as oleyl palmitic acid, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, polyoxyethylene fatty acid ester (for example, EMALLEX series manufactured by Nihon Emulsion Co., Ltd. Riken Vitamin Co., Ltd. Poem series, etc.); sucrose fatty acid esters such as sucrose stearic acid and sucrose palmitic acid (eg Ryoto Sugar Ester series Mitsubishi Chemical Synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax; polymerizable waxes (UNILIN series etc. manufactured by Baker-Petrolite); dimer acids; dimer diols (such as PRIDA series produced by CRODA) Etc. are included.
These waxes may be used alone or in combination of two or more.

[Inorganic fine particles]
The average particle diameter of the inorganic fine particles contained in the actinic ray curable inkjet ink of the present invention is preferably 5 nm or more, and more preferably 10 nm or more. Moreover, the average particle diameter of the inorganic fine particles is preferably less than 60 nm, and more preferably less than 50 nm. The average particle size of the inorganic fine particles can be determined by dynamic light scattering (DLS); for example, it can be measured using a particle size measuring instrument Zetasizer nano S90 manufactured by Malvern. The average particle diameter is a value of Z-average particle diameter.

  Inorganic fine particles having a particle size that is too small are difficult to disperse in the ink; inorganic fine particles that have a particle size that is too large can sufficiently suppress blooming (wax depositing on the image surface) in an image. Can not. Moreover, since the image of inorganic fine particles having a particle size that is too large is colored by the color of the inorganic fine particles, the appearance of the image may be impaired. For example, if the particle size of inorganic fine particles made of titanium dioxide is too large, the image is colored white. Therefore, the particle diameter of the inorganic fine particles is preferably 100 nm or less.

  Further, since the inorganic fine particles having an average particle diameter of 5 nm to 60 nm have a large specific surface area, blooming of an image is easily suppressed even if a small amount is added to the ink. Blooming is a phenomenon that occurs when wax deposits on the image surface. The wax deposited on the image surface forms coarse crystals, which can be visually confirmed, and is thus recognized as blooming. In contrast, when nano-sized inorganic fine particles are added to the ink, the inorganic fine particles exist on the image surface. When inorganic fine particles are present on the image surface, the precipitated wax forms fine and homogeneous crystals with the inorganic fine particles as nuclei. A minute and homogeneous crystal cannot be visually confirmed, so it is considered that it is not recognized as blooming.

  Inorganic particles are typically metal oxide particles; examples include silica, alumina, zinc oxide, titanium oxide, cerium oxide, zirconium oxide, etc .; silica, alumina, zinc oxide, zirconium oxide Preferred is silica or alumina.

  The inorganic fine particles are preferably surface-treated with a silicone treating agent. Thereby, the affinity with the wax is increased. Further, it is preferable that the inorganic fine particles are easily oriented on the image surface by the surface treatment. The silicone-based treatment agent preferably has a silanol group or has an alkoxy group that generates a silanol group by hydrolysis. In order to surface-treat the inorganic fine particles, a silicone-based treatment agent may be sprayed on the stirred inorganic fine particles, or a silicone-based treatment agent may be blended in a dispersion in which the inorganic fine particles are dispersed.

  The content of the inorganic fine particles contained in the actinic ray curable inkjet ink of the present invention is 0.05% or more, and more preferably 0.1% or more. Further, it is preferably less than 5%, more preferably less than 2%. If the content of the inorganic fine particles is too small, the scratch resistance of the resulting image is lowered; if the content of the inorganic fine particles is too large, the curability of the ink is lowered, so that the scratch resistance of the image is rather deteriorated.

  Inorganic fine particles are distinguished from colored fine particles (pigments). If the coloring power is strong like colored fine particles, the original function of the ink is impaired, which is not preferable. That is, it is preferable that the transmittance at a wavelength of 400 nm, 500 nm, and 600 nm of a solution having an inorganic fine particle concentration of 0.01% by weight is 70% or more. The solvent of the solution may be tripropylene glycol diacrylate. If the transmittance at wavelengths of 400 nm, 500 nm, and 600 nm is 70% or less, the inorganic fine particles may be colored in the ink, which is not preferable. The transmittance means the proportion of light transmitted through the sample when measured with a spectrophotometer with an optical path length of 1 cm.

  Inorganic fine particles can also be obtained as commercial products. Examples of commercially available inorganic fine particles include “NanoBYK-3601 (BYK Chemie) tripropylene glycol diacrylate in which alumina fine particles are dispersed”, “NanoBYK-3602 (BYK Chemie) hexanediol diacrylate "Alumina fine particles dispersed in", "NanoBYK-3650 (BYK Chemie) methoxypropyl acetate dispersed in silica fine particles", "Nano-BYK3821 (BYK Chemie Co.) methoxypropyl acetate in zinc oxide fine particles ”,“ NANOCRYL C145, C146, C350, C140, C150 (manufactured by Hanse-Chemie) photopolymerizable monomer in which silica fine particles are dispersed ”,“ Nanon5 ZR-010 (manufactured by Solar Co., Ltd.) ) Zirconium oxide dispersion ”,“ ETERQURE601Q-35 (Changxing Chemical Co., Ltd.) Acrylic oligomer dispersed with inorganic fine particles ”,“ Laromer PO9026 (BASF Corp.) ethoxylation “Trimethylolpropane acrylate ester in which silica fine particles are dispersed” is included.

[Photopolymerization initiator]
The actinic ray curable inkjet ink may further contain a photopolymerization initiator. Specifically, when the actinic ray is an electron beam, a photopolymerization initiator may ordinarily not be included. However, when the actinic ray is an ultraviolet ray, a photopolymerization initiator is preferably contained.

  Photopolymerization initiators include an intramolecular bond cleavage type and an intramolecular hydrogen abstraction type. Examples of intramolecular bond cleavage type photopolymerization initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1- (4-isopropylphenyl) -2. -Hydroxy-2-methylpropan-1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4 Acetophenones such as -thiomethylphenyl) propan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone; benzoins such as benzoin, benzoin methyl ether, benzoin isopropyl ether; 2 Acylphosphine oxide systems such as 1,4,6-trimethylbenzoindiphenylphosphine oxide; benzyl and And methylphenylglyoxyester.

  Examples of intramolecular hydrogen abstraction type photopolymerization initiators include benzophenone, methyl 4-phenylbenzophenone o-benzoylbenzoate, 4,4′-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4′-methyl-diphenyl. Benzophenones such as sulfide, acrylated benzophenone, 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone, 3,3′-dimethyl-4-methoxybenzophenone; 2-isopropylthioxanthone, 2,4 -Thioxanthone series such as dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone; Aminobenzophenone series such as Michler ketone, 4,4'-diethylaminobenzophenone; 10-butyl-2-chloroacridone, 2-ethyl Anthraquinone, 9,10-phenanthrene Non, include camphor quinone and the like.

  The content of the photopolymerization initiator in the actinic ray curable inkjet ink is preferably 0.01% by mass to 10% by mass, although it depends on the type of actinic ray or actinic ray curable compound.

  The actinic ray curable inkjet ink may contain a photoacid generator as a photopolymerization initiator. Examples of photoacid generators include chemically amplified photoresists and compounds used for photocationic polymerization (Organic Electronics Materials Study Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), 187. To page 192).

  The actinic ray curable inkjet ink may further contain a photopolymerization initiator auxiliary agent, a polymerization inhibitor, and the like as necessary. The photopolymerization initiator assistant may be a tertiary amine compound, preferably an aromatic tertiary amine compound. Examples of aromatic tertiary amine compounds include N, N-dimethylaniline, N, N-diethylaniline, N, N-dimethyl-p-toluidine, N, N-dimethylamino-p-benzoic acid ethyl ester, N, N-dimethylamino-p-benzoic acid isoamyl ethyl ester, N, N-dihydroxyethylaniline, triethylamine, N, N-dimethylhexylamine and the like are included. Of these, N, N-dimethylamino-p-benzoic acid ethyl ester and N, N-dimethylamino-p-benzoic acid isoamyl ethyl ester are preferred. These compounds may be used alone or in combination of two or more.

  Examples of polymerization inhibitors include (alkyl) phenol, hydroquinone, catechol, resorcin, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone , Nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cuperone, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N- (3-oxyanilino- 1,3-dimethylbutylidene) aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraloxime, methyl ethyl ketoxime, cyclohexanone oxime and the like.

[Color material]
The actinic ray curable ink-jet ink may further contain a coloring material as necessary. The coloring material can be a dye or a pigment, but is preferably a pigment because it has good dispersibility with respect to the components of the ink and is excellent in weather resistance. The pigment is not particularly limited, and may be, for example, an organic pigment or an inorganic pigment having the following numbers described in the color index.

  Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, 53. : 1, 57: 1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108, 112, 122, 123, 144 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange 13, 16, 20, 36, etc. are included. Examples of blue or cyan pigments include Pigment Blue 1, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36. , 60 and the like. Examples of green pigments include Pigment Green 7, 26, 36, 50. Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137. 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193 and the like. Examples of the black pigment include Pigment Black 7, 28, 26, and the like.

Examples of commercially available pigments include chromofine yellow 2080, 5900, 5930, AF-1300, 2700L, chromofine orange 3700L, 6730, chromofine scarlet 6750, chromofine magenta 6880, 6886, 6891N, 6790, 6887, chromo Fine Violet RE, Chromo Fine Red 6820, 6830, Chromo Fine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4972, 5205, 5208, 5214, 5221, 5000P, Chromofine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, Chromofine Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200, 2270, 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seica Fast Red 8040, C405 (F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262, 1537B, GY, 4R-4016, 3820, 3891, ZA-215, Seika Fast Carmine 6B1476T-7, 1483LT, 3840, 3870, Seika Fast Bordeaux 10B-430, Seikalite Rose R40, Seikalite Violet B800, 7805, Seika Fast Maroon 460N, Seika Fast Orange 900, 2900, Seika Light Blue C718, A6 2, Cyanine Blue 4933M, 4933GN-EP, 4940,4973 (manufactured by Dainichiseika Color & Chemicals Mfg.);
KET Yellow 401, 402, 403, 404, 405, 406, 416, 424, KET Orange 501, KET Red 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106, 111, 118, 124, KET Green 201 (Dainippon Ink Chemical Co., Ltd.);
Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow T-13, T-05, Pigment Yellow 1705, Colortex Orange 202, Color103 Red, 101 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, USN, Colortex Maroon601, Colortex Brownex600 Red 122, Colortex Blue 516, 517, 518, 519, A8 8, P-908,510, Colortex Green402,403, Colortex Black 702, U905 (manufactured by Sanyo Color Works);
Lionol Yellow 1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (manufactured by Toyo Ink),
Toner Magenta E02, Permanent RubinF6B, Toner Yellow HG, Permanent Yellow GG-02, Hostapeam Blue B2G (manufactured by Hoechst Industry);
Novoperm P-HG, Hostaperm Pink E, Hostaperm Blue B2G (manufactured by Clariant);
Carbon black # 2600, # 2400, # 2350, # 2200, # 1000, # 990, # 980, # 970, # 960, # 950, # 850, MCF88, # 750, # 650, MA600, MA7, MA8, MA11 , MA100, MA100R, MA77, # 52, # 50, # 47, # 45, # 45L, # 40, # 33, # 32, # 30, # 25, # 20, # 10, # 5, # 44, CF9 (Mitsubishi Chemical).

  The pigment can be dispersed by, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker. The pigment is dispersed so that the average particle size of the pigment particles is preferably 0.08 to 0.5 μm, and the maximum particle size is preferably 0.3 to 10 μm, more preferably 0.3 to 3 μm. Is preferred. The dispersion of the pigment is adjusted by the selection of the pigment, the dispersant, and the dispersion medium, the dispersion conditions, the filtration conditions, and the like.

  The actinic ray curable inkjet ink may further contain a dispersant in order to enhance the dispersibility of the pigment. Examples of the dispersant include a hydroxyl group-containing carboxylic acid ester, a salt of a long chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylic acid, a salt of a long chain polyaminoamide and a polar acid ester, a high molecular weight unsaturated acid ester , Polymer copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene Nonylphenyl ether, stearylamine acetate and the like are included. Examples of commercially available dispersants include Avecia's Solsperse series and Ajinomoto Fine-Techno's PB series.

  The actinic ray curable inkjet ink may further contain a dispersion aid as necessary. The dispersion aid may be selected according to the pigment.

  The total amount of the dispersant and the dispersion aid is preferably 1 to 50% by mass with respect to the pigment.

  The actinic radiation curable inkjet ink may further include a dispersion medium for dispersing the pigment as necessary. A solvent may be included in the ink as a dispersion medium. However, in order to suppress the residual solvent in the formed image, the actinic ray curable compound (particularly a monomer having a low viscosity) is used as the dispersion medium. It is preferable.

  The dye can be an oil-soluble dye or the like. Examples of oil-soluble dyes include the following various dyes. Examples of magenta dyes include MS Magenta VP, MS Magenta HM-1450, MS Magenta HSo-147 (manufactured by Mitsui Toatsu), AIZENSOT Red-1, AIZEN SOT Red-2, AIZEN SOTRed-3, and AIZEN SOT. Pink-1, SPIRON Red GEH SPECIAL (above, manufactured by Hodogaya Chemical Co., Ltd.), RESOLIN Red FB 200%, MACROLEX Red Violet R, MACROLEX ROT5B (above, manufactured by Bayer Japan), KAYASET Red B, KAYASE RED 130, 802 (above, Nippon Kayaku Co., Ltd.), PHLOXIN, ROSE Bengal, ACID Red (above, Daiwa Kasei Co., Ltd.), H R-31, DIARESIN Red K (manufactured by Mitsubishi Kasei Corp.), include Oil Red (manufactured by BASF Japan Ltd.).

  Examples of cyan dyes include MS Cyan HM-1238, MS Cyan HSo-16, Cyan HSo-144, MS Cyan VPG (manufactured by Mitsui Toatsu), AIZEN SOT Blue-4 (manufactured by Hodogaya Chemical Co., Ltd.), RESOLIN BR. Blue BGLN 200%, MACROLEX Blue RR, CERES Blue GN, SIRIUS SUPRATURQ. Blue Z-BGL, SIRIUS SUTRA TURQ. Blue FB-LL 330% (above, Bayer Japan), KAYASET Blue FR, KAYASET Blue N, KAYASET Blue 814, Turq. Blue GL-5 200, Light Blue BGL-5 200 (above, Nippon Kayaku Co., Ltd.), DAIWA Blue 7000, Oleosol Fast Blue GL (above, Daiwa Kasei), DIARESIN Blue P (Mitsubishi Kasei), SUDAN Blue 670, NEOPEN Blue 808, ZAPON Blue 806 (above, manufactured by BASF Japan Ltd.) and the like are included.

  Examples of yellow dyes include MS Yellow HSm-41, Yellow KX-7, Yellow EX-27 (Mitsui Toatsu), AIZEN SOT Yellow-1, AIZEN SOT Yellow W-3, AIZEN SOT Yellow-6 (above, Hodogaya) (Manufactured by Chemical Co., Ltd.), MACROLEX Yellow 6G, MACROLEX FLUOR. Yellow 10GN (above, Bayer Japan), KAYASET Yellow SF-G, KAYASET Yellow 2G, KAYASET Yellow AG, KAYASET Yellow EG (above, Nippon Kayaku), DAIWA Yellow 330H HSY-68 (manufactured by Mitsubishi Kasei Co., Ltd.), SUDAN Yellow 146, NEOPEN Yellow 075 (above, manufactured by BASF Japan Ltd.) and the like.

  Examples of black dyes include MS Black VPC (Mitsui Toatsu Co., Ltd.), AIZEN SOT Black-1, AIZEN SOT Black-5 (above, manufactured by Hodogaya Chemical Co., Ltd.), RESORIN Black GSN 200%, RESOLIN BlackBS (above, Bayer Japan), KAYASET Black A-N (Nippon Kayaku), DAIWA Black MSC (Daiwa Kasei), HSB-202 (Mitsubishi Kasei), NEPTUNE Black X60, NEOPEN Black X58 (above, BASF Japan product).

  The content of the pigment or dye is preferably 0.1 to 20% by mass, and more preferably 0.4 to 10% by mass with respect to the actinic ray curable inkjet ink. This is because if the content of the pigment or dye is too small, the color of the resulting image is not sufficient, and if it is too large, the viscosity of the ink increases and the jetting property decreases.

[Other ingredients]
The actinic ray curable inkjet ink may further contain other components as necessary. Other components may be various additives, other resins, and the like. Examples of the additive include a surfactant, a leveling additive, a matting agent, an ultraviolet absorber, an infrared absorber, an antibacterial agent, and a basic compound for enhancing the storage stability of the ink. Examples of basic compounds include basic alkali metal compounds, basic alkaline earth metal compounds, basic organic compounds such as amines, and the like. Examples of other resins include resins for adjusting the physical properties of the cured film, such as polyester resins, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes. It is.

  The actinic radiation curable inkjet ink can be obtained by mixing the actinic radiation curable compound, the wax, the inorganic fine particles, and any of the components under heating. It is preferable to filter the obtained liquid mixture with a predetermined filter.

[Sol-gel phase transition type actinic ray curable inkjet ink]
As described above, the actinic ray curable ink-jet ink of the present invention may be a sol-gel phase transition type ink that reversibly undergoes sol-gel phase transition depending on temperature. Since the sol-gel phase transition type actinic ray curable ink is liquid at a high temperature (for example, about 80 ° C.), it can be ejected from an ink jet recording head. When actinic ray curable inkjet ink is ejected at a high temperature, ink droplets (dots) land on the recording medium, and then naturally cool to gel. Thereby, coalescence of adjacent dots can be suppressed and image quality can be improved.

  In order to improve the ejection property of the sol-gel phase transition type ink, it is preferable that the viscosity of the ink at a high temperature is not more than a certain level. Specifically, the actinic ray curable inkjet ink preferably has a viscosity at 80 ° C. of 3 to 20 mPa · s. On the other hand, in order to suppress coalescence of adjacent dots, it is preferable that the viscosity of the ink at normal temperature after landing is a certain level or more. Specifically, the viscosity at 25 ° C. of the actinic ray curable inkjet ink is preferably 1000 mPa · s or more.

  The gelation temperature of the sol-gel phase transition ink is preferably 40 ° C. or higher and 70 ° C. or lower, and more preferably 50 ° C. or higher and 65 ° C. or lower. When the gelation temperature of the ink exceeds 70 ° C. when the ejection temperature is around 80 ° C., gelation tends to occur at the time of ejection, resulting in low ejection properties. When the gelation temperature is less than 40 ° C., the recording medium This is because it does not gel immediately after landing. The gelation temperature is a temperature at which the fluidity decreases due to gelation in the process of cooling the ink in the sol state.

  The viscosity at 80 ° C., the viscosity at 25 ° C. and the gelation temperature of the sol-gel phase transition type ink can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer. Specifically, a temperature change curve of viscosity is obtained when the ink is heated to 100 ° C. and cooled to 20 ° C. under conditions of a shear rate of 11.7 (/ s) and a temperature decrease rate of 0.1 ° C./s. And the viscosity in 80 degreeC and the viscosity in 25 degreeC can be calculated | required by reading the viscosity in 80 degreeC and 25 degreeC in the temperature change curve of a viscosity, respectively. The gelation temperature can be determined as the temperature at which the viscosity becomes 200 mPa · s in the temperature change curve of the viscosity.

  As the rheometer, a stress control type rheometer Physica MCR series manufactured by Anton Paar can be used. The cone plate can have a diameter of 75 mm and a cone angle of 1.0 °.

  In order to improve the ejection property of the ink from the ejection recording head, the sol-gel phase transition type ink has an ink temperature of (gelation temperature + 10) ° C. to ( The gelling temperature is preferably set to +30) ° C. When the temperature of the ink in the ejection recording head is less than (gelation temperature + 10) ° C., the ink is gelled in the ejection recording head or on the nozzle surface, and the ink ejection property is likely to deteriorate. On the other hand, when the temperature of the ink in the ejection recording head exceeds (gelation temperature + 30) ° C., the ink becomes too high, and the ink component may deteriorate.

[Inkjet recording method]
The inkjet recording method of the present invention includes 1) a step of ejecting the actinic ray curable inkjet ink of the present invention onto a recording medium, and 2) a step of irradiating the ink landed on the recording medium with an actinic ray to cure the ink. And including.

  1) In the ejection step, the inkjet ink stored in the ejection recording head may be ejected as droplets toward the recording medium through the nozzles. At this time, the temperature of the inkjet ink stored in the ejection recording head is preferably set to a temperature at which the content of the wax contained in the ink is equal to or lower than the saturated dissolution amount of the wax in the ink. That is, it is preferable that the wax is dissolved as much as possible in the inkjet ink stored in the ejection recording head.

  2) In the curing step, the ink that has landed on the recording medium is irradiated with light. What is necessary is just to select suitably the light irradiated according to the kind of actinic-light curable compound, and may be an ultraviolet-ray, an electron beam, etc.

  The actinic ray curable ink jet recording apparatus of the present invention will be described. Actinic ray curable ink jet recording apparatuses include a line recording method (single pass recording method) and a serial recording method. The line recording method (single-pass recording method) is preferable from the viewpoint of high-speed recording, although it may be selected according to the required image resolution and recording speed.

  FIG. 1 is a diagram illustrating an example of a configuration of a main part of a line recording type ink jet recording apparatus. Among these, Fig.1 (a) is a side view, FIG.1 (b) is a top view. As shown in FIG. 1, the inkjet recording apparatus 10 covers a head carriage 16 that accommodates a plurality of ejection recording heads 14 and the entire width of the recording medium 12, and is downstream of the head carriage 16 (the conveyance direction of the recording medium). The actinic ray irradiation unit 18 disposed on the side and the temperature control unit 19 disposed on the lower surface of the recording medium 12 are provided.

  The head carriage 16 is fixedly arranged so as to cover the entire width of the recording medium 12 and accommodates a plurality of ejection recording heads 14 provided for each color. Ink is supplied to the ejection recording head 14. For example, the ink may be supplied directly or by an ink supply unit (not shown) from an ink cartridge (not shown) that is detachably attached to the inkjet recording apparatus 10.

  A plurality of ejection recording heads 14 are arranged in the transport direction of the recording medium 12 for each color. The number of ejection recording heads 14 arranged in the conveyance direction of the recording medium 12 is set according to the nozzle density of the ejection recording head 14 and the resolution of the print image. For example, when an image having a resolution of 1440 dpi is formed using the ejection recording head 14 having a droplet amount of 2 pl and a nozzle density of 360 dpi, the four ejection recording heads 14 are shifted with respect to the conveyance direction of the recording medium 12. What is necessary is just to arrange. Further, when an image having a resolution of 720 × 720 dpi is formed using the ejection recording head 14 having a droplet amount of 6 pl and a nozzle density of 360 dpi, the two ejection recording heads 14 may be arranged in a shifted manner. dpi represents the number of ink droplets (dots) per 2.54 cm.

  The actinic ray irradiation unit 18 covers the entire width of the recording medium 12 and is disposed on the downstream side of the head carriage 16 in the recording medium conveyance direction. The actinic ray irradiation unit 18 irradiates the droplets ejected by the ejection recording head 14 and landed on the recording medium with actinic rays to cure the droplets.

When the actinic ray is ultraviolet ray, examples of the actinic ray irradiating unit 18 (ultraviolet ray irradiating means) include a fluorescent tube (low pressure mercury lamp, germicidal lamp), a cold cathode tube, an ultraviolet laser, and an operating pressure of several hundred Pa to 1 MPa. These include low pressure, medium pressure, high pressure mercury lamps, metal halide lamps and LEDs. From the viewpoint of curability, ultraviolet irradiation means for irradiating ultraviolet rays having an illuminance of 100 mW / cm ² or more; specifically, high-pressure mercury lamps, metal halide lamps, and LEDs are preferable, and LEDs are more preferable from the viewpoint of low power consumption. Specifically, a 395 nm, water-cooled LED manufactured by Phoseon Technology can be used.

  When the actinic ray is an electron beam, examples of the actinic ray irradiating unit 18 (electron beam irradiating unit) include electron beam irradiating means such as a scanning method, a curtain beam method, and a broad beam method. Therefore, a curtain beam type electron beam irradiation means is preferable. Examples of the electron beam irradiation means include “Curetron EBC-200-20-30” manufactured by Nissin High Voltage Co., Ltd., “Min-EB” manufactured by AIT Co., Ltd., and the like.

  The temperature control unit 19 is disposed on the lower surface of the recording medium 12 and maintains the recording medium 12 at a predetermined temperature. The temperature control unit 19 can be, for example, various heaters.

  Hereinafter, an image recording method using the line recording type inkjet recording apparatus 10 will be described. The recording medium 12 is conveyed between the head carriage 16 and the temperature control unit 19 of the inkjet recording apparatus 10. On the other hand, the recording medium 12 is adjusted to a predetermined temperature by the temperature control unit 19. Next, high-temperature ink is ejected from the ink ejection recording head 14 of the head carriage 16 and adhered (landed) on the recording medium 12. Then, the actinic ray irradiating unit 18 irradiates the ink droplets attached on the recording medium 12 with an actinic ray to cure.

  When the ink is ejected from the ink ejection recording head 14, the temperature of the ink in the ejection recording head 14 is 10 to 30 ° C. higher than the gelation temperature of the ink in order to improve the ink ejection property. It is preferable to set to. When the ink temperature in the ejection recording head 14 is less than (gelation temperature + 10) ° C., the ink gels in the ejection recording head 14 or on the nozzle surface, and the ink ejection property is likely to deteriorate. On the other hand, when the temperature of the ink in the ejection recording head 14 exceeds (gelation temperature + 30) ° C., the ink becomes too high, and the ink component may deteriorate.

  The amount of droplets ejected from each nozzle of the ink ejection recording head 14 is preferably 1 pl to 10 pl in order to form a high resolution image, although it depends on the resolution of the image. More preferably, it is 0.5-4.0pl.

  Irradiation with actinic rays is performed within 10 seconds, preferably within 0.001 seconds to 5 seconds, more preferably after ink droplets are deposited on the recording medium, in order to prevent the adjacent ink droplets from coalescing. It is preferable to carry out within 0.01 second to 2 seconds. Irradiation with actinic rays is preferably performed after ink is ejected from all the ink ejection recording heads 14 accommodated in the head carriage 16.

  When the actinic ray is an electron beam, the acceleration voltage for electron beam irradiation is preferably 30 to 250 kV and more preferably 30 to 100 kV in order to perform sufficient curing. When the acceleration voltage is 100 to 250 kV, the electron beam irradiation amount is preferably 30 to 100 kGy, and more preferably 30 to 60 kGy.

  The total ink film thickness after curing is preferably 2 to 25 μm. The “total ink film thickness” is the maximum value of the ink film thickness drawn on the recording medium.

  FIG. 2 is a diagram illustrating an example of a configuration of a main part of the serial recording type inkjet recording apparatus 20. As shown in FIG. 2, the inkjet recording apparatus 20 has a width narrower than the entire width of the recording medium, instead of the head carriage 16 fixedly arranged so as to cover the entire width of the recording medium, and a plurality of ink ejection devices. Except for having a head carriage 26 that accommodates the recording head 24 and a guide portion 27 for moving the head carriage 26 in the width direction of the recording medium 12, the configuration can be the same as in FIG.

  In the serial recording type inkjet recording apparatus 20, the head carriage 26 ejects ink from the ejection recording head 24 accommodated in the head carriage 26 while moving in the width direction of the recording medium 12 along the guide portion 27. After the head carriage 26 has completely moved in the width direction of the recording medium 12 (for each pass), the recording medium 12 is fed in the transport direction. Except for these operations, an image is recorded in substantially the same manner as the line recording type inkjet recording apparatus 10 described above.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not construed as being limited by these descriptions.

[Production of actinic ray curable inkjet ink]
An actinic ray curable inkjet ink was prepared using the following components (wax, polymerizable compound, polymerization inhibitor, polymerization initiator, fine particle dispersion, pigment dispersion).

[wax]
Aliphatic diketone (Kao wax T1, Kao)
Behenyl behenate (Unistar M-2222SL, NOF)
Behenic acid (Lunac BA, Kao)
Erucamide (Neutron S, Nippon Seika)
Behenyl alcohol (behenyl alcohol 80R, higher alcohol industry)

[Polymerizable compound]
Polyethylene glycol # 400 diacrylate (A-400, Shin-Nakamura Chemical)
4EO modified pentaerythritol tetraacrylate (SR494, SARTOMER)
6EO modified trimethylolpropane triacrylate (SR499, SARTOMER)

[Polymerization inhibitor] Irgastab UV10 (Ciba Specialty Chemical)
[Polymerization initiator] DAROCURE TPO (Ciba Specialty Chemical)

[Fine particle dispersions A to D]
Fine particle dispersion A: NanoBYK 3601 (Tripropylene glycol diacrylate dispersion of alumina nanoparticles, manufactured by Big Chemi Japan) Solid content concentration 30%
Fine particle dispersion B: NanoBYK 3650 (Methoxypropyl acetate dispersion of silica nanoparticles, manufactured by Big Chemi Japan) Solid content concentration 25%
Fine particle dispersion C: NanoBYK 3821 (Methoxypropyl acetate dispersion of zinc oxide nanoparticles, manufactured by Big Chemi Japan) Solid content concentration 40%
Fine particle dispersion D: Titanium oxide dispersion Solid concentration 50% (refer to the preparation procedure below)

(Preparation of fine particle dispersion D)
The following dispersant, actinic ray curable compound and polymerization inhibitor were placed in a stainless beaker and dissolved by heating and stirring for 1 hour while heating on a hot plate at 65 ° C. After cooling the obtained solution to room temperature, 40 parts by mass of the following titanium dioxide was added, put into a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, sealed, and dispersed for 8 hours with a paint shaker. Thereafter, the zirconia beads were removed to prepare a fine particle dispersion D having the following composition.
[Composition of fine particle dispersion D]
Dispersant: Azisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd.) 10 parts by mass Actinic ray curable compound: APG-200 (tripropylene glycol diacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.) 50 parts by mass Polymerization inhibitor: Irgastab UV10 (Ciba Japan) 0.02 parts by mass Titanium dioxide: CR-90 (manufactured by Ishihara Sangyo Co., Ltd.) 40 parts by mass

(Measurement of particle diameter in fine particle dispersions A to D)
The fine particle dispersions A to D were diluted 100 times with APG-200 (tripropylene glycol diacrylate). The average particle size of the inorganic fine particles in the diluted dispersion was measured using a particle size measuring device Zetasizer nano S90 manufactured by Malvern. The average particle size was a value of Z-average particle size. The results are shown in Table 2.

(Measurement of transmittance of fine particle dispersions A to D)
The fine particle dispersions A to D were diluted with APG-200 (tripropylene glycol diacrylate) to give a concentration of 0.01% by weight, respectively. The diluted dispersion was put into a cell having an optical path length of 1 cm. The transmittance of the dispersion in the cell was measured using a spectrophotometer V-650 manufactured by JASCO at measurement wavelengths of 400 nm, 500 nm, and 600 nm. The results are shown in Table 1.

[Pigment dispersion]
Preparation of Pigment Dispersion Liquid 1 (M: Magenta) The following dispersant, actinic ray curable compound and polymerization inhibitor were placed in a stainless beaker and dissolved by heating and stirring for 1 hour while heating on a 65 ° C hot plate. It was. After cooling the resulting solution to room temperature, 21 parts by mass of the following magenta pigment 1 was added, sealed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, and dispersed for 8 hours with a paint shaker. Thereafter, the zirconia beads were removed to prepare a pigment dispersion 1 having the following composition.
[Composition of Pigment Dispersion Liquid 1]
Dispersant: Azisper PB824 (Ajinomoto Fine Techno Co., Ltd.) 9 parts by mass Actinic ray curable compound: APG-200 (Tripropylene glycol diacrylate, Shin-Nakamura Chemical Co., Ltd.) 70 parts by mass Polymerization inhibitor: Irgastab UV10 (Ciba Japan) 0.02 part by mass Magenta pigment 1: Pigment Red 122 (manufactured by Dainichi Seika, Chromo Fine Red 6112JC)

[Preparation of ink]
According to the composition shown in Table 2, the mixture obtained by mixing each component was heated to 80 ° C. and stirred. The obtained solution was filtered through a # 3000 metal mesh filter under heating, and then cooled to prepare an ink. In Table 2, the unit of the amount of each component is part by mass.

[Image Forming Method]
With the actinic ray curable inkjet ink obtained in each example and comparative example, a monochromatic image was formed using a line inkjet recording apparatus. The temperature of the inkjet head of the inkjet recording apparatus was set to 80 ° C. A blank character, a solid image of 5 cm × 5 cm, or a density gradation patch was printed on the recording medium. After the image was formed, the ink was cured by irradiating the image with ultraviolet light using an LED lamp (395 nm manufactured by Phoseon Technology, water-cooled LED) disposed in the downstream portion of the recording apparatus.

  As the ejection recording head, a piezo head having a nozzle diameter of 20 μm and 512 nozzles (256 nozzles × 2 rows, staggered arrangement, 1 row nozzle pitch 360 dpi) was used. The ejection conditions were such that the amount of one droplet was 2.5 pl, and ejection was performed at a droplet velocity of about 6 m / s, and recording was performed at a resolution of 1440 dpi × 1440 dpi. The recording speed was 500 mm / s. Image formation was performed in an environment of 23 ° C. and 55% RH. dpi represents the number of dots per 2.54 cm.

[Image Evaluation]
(Evaluation of blooming)
A solid image of 5 cm × 5 cm formed on the coated paper A for printing, which is a recording medium by the above method (OK top coat, US basis weight 128 g / m 2 manufactured by Oji Paper Co., Ltd.) was stored for 1 month in an environment of 40 ° C. . The image after storage was visually observed and blooming was evaluated according to the following criteria.
○: No precipitate is observed on the image surface.
Δ: A thin precipitate is present on the image surface and can be visually confirmed.
X: The image surface is covered with the substance on the powder, and can be clearly confirmed visually.

(Evaluation of scratch resistance)
By the above method, a solid image of 5 cm × 5 cm formed on the coated paper A for printing which is a recording medium (OK top coat, US basis weight 128 g / m 2 manufactured by Oji Paper Co., Ltd.) was “JIS standard K5701-1-6.2.3 resistance. In accordance with the method described in “Friction test”, the coated paper A for printing cut out to an appropriate size was placed on the image and rubbed together under a load. Thereafter, the degree of reduction in image density was visually observed, and scratch resistance was evaluated according to the following criteria.
○: No change in image was observed even after rubbing 50 times or more. Δ: Image density decreased after 50 times of rubbing, but in practically acceptable range. X: Clear with rubbing less than 50 times. The image density is noticeable, and the quality is unusable.

(Evaluation of density unevenness)
By the above method, a solid image of 5 cm × 5 cm printed on the coated paper A for printing which is a recording medium (OK top coat, US basis weight 128 g / m 2 manufactured by Oji Paper Co., Ltd.) was visually evaluated, and density unevenness was observed according to the following evaluation criteria. Evaluation was performed.
○: Observed from a position 15 cm away, no density unevenness is observed in the image Δ: Observed from a position 15 cm away, density unevenness is observed in a part of the image, but from the position 30 cm away, the density unevenness is observed X: Observed from a position 30 cm away, density unevenness is observed in the image

[Evaluation of output stability]
Ink jet recording apparatus equipped with each of the inks prepared above ejected ink from the ink jet head, visually observed for the absence of nozzles and ejection bends, and evaluated the ejection stability according to the following criteria.
○: No nozzle missing was observed Δ: Nozzle missing was observed in 1 to 4 nozzles in all nozzles 512 ×: Nozzle missing was observed in 5 or more nozzles in all nozzles 512 The

  It can be seen that in the inks of Examples 1 to 12 containing the wax and the fine particle dispersion, the scratch resistance of the image is increased and the blooming is suppressed.

  On the other hand, the ink of Comparative Example 1 containing no wax or fine particle dispersion or the ink of Comparative Example 3 containing no fine particle dispersion without containing wax had low image scratch resistance. In addition, blooming could not be suppressed in the ink of Comparative Example 2 containing wax but not containing the fine particle dispersion or the ink of Comparative Example 4 having a large inorganic fine particle size in the fine particle dispersion. Furthermore, the ink of Comparative Example 5 in which the content of the fine particle dispersion was excessive decreased in scratch resistance.

  Inks of Examples 1 to 5 and 12 were inks having a wax content of 2 or 3% by mass and undergoing a sol-gel phase transition. In contrast, the inks of Examples 6 to 10 had a wax content of 0.2% by mass or less and did not undergo sol-gel phase transition. The density unevenness of the images formed with the inks of Examples 1 to 5, which are inks that undergo sol-gel phase transition, was reduced more than the density unevenness of the images formed with the inks of Examples 6 to 10. Ink droplets that undergo a sol-gel phase transition land on the recording medium, and then are pinned onto the recording medium without excessive wetting and spreading, thereby suppressing image unevenness.

  In addition, the ink of Example 11 having a wax content of 8% by mass slightly decreased the ejection stability from the inkjet head.

  The actinic ray curable ink-jet ink of the present invention has high scratch resistance of images formed with it, and blooming is suppressed. Therefore, the present invention can be particularly suitably applied to a sol-gel phase transition type actinic ray curable inkjet ink containing a relatively large amount of wax.

DESCRIPTION OF SYMBOLS 10, 20 Inkjet recording apparatus 12 Recording medium 14, 24 Ejection recording head 16, 26 Head carriage 18, 28 Actinic ray irradiation part 19 Temperature control part 27 Guide part

Claims (11)

An actinic ray curable inkjet ink comprising an actinic ray curable compound, a wax of 0.01% by mass or more and less than 15% by mass, and inorganic fine particles having an average particle diameter of 5 nm or more and less than 60 nm,
An actinic ray curable inkjet ink in which a light transmittance at a wavelength of 400 nm of a 0.01% by mass tripropylene glycol diacrylate solution of the inorganic fine particles is 70% or more.   The actinic radiation curable inkjet ink according to claim 1, wherein the content of the inorganic fine particles in the actinic radiation curable inkjet ink is 0.1% by mass or more and less than 2% by mass.   The actinic ray curable inkjet ink according to claim 1 or 2, wherein the inorganic fine particles have an average particle diameter of 10 nm or more and less than 50 nm.   The actinic ray curable inkjet ink according to claim 1, wherein the inorganic fine particles are fine particles of silica, alumina, zinc oxide, or zirconium oxide.   The actinic ray curable inkjet ink according to any one of claims 1 to 4, wherein the inorganic fine particles are alumina fine particles and surface-treated with a silicone-based surface treatment agent.   The actinic ray curable inkjet ink according to any one of claims 1 to 5, wherein the actinic ray curable compound is a radical polymerizable compound.   The actinic ray curable inkjet ink according to any one of claims 1 to 6, wherein the actinic ray curable compound comprises an ethylene oxide-modified (meth) acrylate compound.   The actinic ray curable inkjet ink according to claim 1, wherein the wax contains any one of an aliphatic diketone and a fatty acid ester.   The actinic ray curable inkjet ink according to any one of claims 1 to 8, wherein a content of the wax in the actinic ray curable inkjet ink is 1% by mass or more and less than 7% by mass.   The actinic ray curable inkjet ink according to claim 1, which reversibly undergoes sol-gel phase transition depending on temperature. A step of ejecting the actinic ray curable inkjet ink according to any one of claims 1 to 10 onto a recording medium, and a step of irradiating the ink ejected onto the recording medium with an actinic ray to cure the ink. An inkjet recording method comprising:
The inkjet recording method, wherein the temperature of the actinic radiation curable inkjet ink when ejected to the recording medium is a temperature at which the content of the wax contained in the actinic radiation curable inkjet ink is equal to or less than a saturated dissolution amount.

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