JP6569729B2 - Actinic ray curable ink jet ink containing crystal growth inhibitor and ink jet recording method - Google Patents

Description

  The present invention relates to an actinic ray curable inkjet ink containing a crystal growth inhibitor and an inkjet recording method.

  The image forming method based on the ink jet recording method is a method for forming an image by ejecting ink supplied from an ink tank through a flow path from a recording head for ejection. The ink jet recording method is used for forming various images because an image can be formed easily and inexpensively. One of the inks used in the ink jet recording system is actinic ray curable ink jet ink. Since the actinic ray curable inkjet ink contains a photopolymerizable compound in addition to the color material, the ink component can be cured by irradiating an actinic ray such as ultraviolet rays to polymerize the photopolymerizable compound. When an image is formed using an actinic ray curable inkjet ink, compared to a solvent-based ink composition, it is easier to fix the ejected ink and images with less bleeding can be formed on various recording media.

  In order to improve the pinning property of the ultraviolet curable inkjet ink, for example, an ultraviolet curable inkjet ink containing a gelling agent such as wax has been developed. In such a recording method using ink, a technique for forming a higher-quality image by preventing ink from being mixed with dots and causing dot coalescence is investigated by landing ink on a recording medium and gelling ink droplets. Has been.

  For example, a hot-melt ink composition containing a crystalline substance and a crystallization retarder in addition to a gelling agent is known (Patent Document 1). In the present invention, although the crystalline substance increases the strength of the ink cured on the recording medium, it may affect the image quality. Therefore, the addition of a crystallization retarder reduces the crystallization speed and improves the image quality. Yes. The crystallization retarder used in the hot melt ink composition is not a substance for suppressing crystallization of the gelling agent.

  Also known is an actinic ray curable inkjet ink in which blooming is suppressed by adding a non-polymerizable liquid component (Patent Document 2). Since this liquid component is a non-polymerizable component, it has low compatibility with the cured product of the actinic ray curable compound and exists at a high concentration in the vicinity of the surface of the ink cured product. When the wax in the cured product is dissolved in this liquid component, the wax becomes difficult to grow and blooming is suppressed.

International Publication No. 2014/016129 JP 2013-2221048 A

  In recent years, attention has been paid to a technique for printing at a low substrate temperature for the purpose of reducing energy consumption or expanding the type of substrate. However, when printing at low temperature using a conventional actinic radiation curable inkjet ink containing a wax as a gelling agent, the growth rate of the crystallized wax in the ink after landing is too high, so that the formation of ink dots There was a problem that the unevenness to be increased. In order to reduce the growth rate of this wax crystal, it is necessary to use a wax having a high solubility. However, a wax having a high solubility precipitates on the surface of the printed material after the ink is cured, and thus the powder is formed on the printing surface. A phenomenon called blooming occurs. Therefore, it has been difficult to obtain a high-quality image when printing is performed at a low temperature using a conventional actinic ray curable inkjet ink.

  The present invention has been made in view of the above circumstances, and is an actinic ray curable inkjet ink capable of obtaining a printed matter with high character quality and suppressed blooming even when printed at a low substrate temperature. The purpose is to provide. A further object of the present invention is to provide an actinic ray curable inkjet ink that can obtain a printed matter with good image quality in addition to good character quality and suppression of blooming.

In view of the above problems, a first aspect of the present invention relates to an actinic ray curable inkjet ink containing a crystal growth inhibitor.
[1] An actinic ray curable inkjet ink comprising an actinic ray curable compound, a photopolymerization initiator, a wax, and a crystal growth inhibitor,
The wax has at least one alkyl chain including a straight chain portion, and in all of the alkyl chains of the wax, the straight chain portion has 15 or more carbon atoms,
The crystal growth inhibitor is a substance having a sugar structure and an alkyl chain containing a straight chain portion having 15 or more carbon atoms bonded to the sugar structure,
The activity is characterized in that the content of the wax is 1% by mass or more and 10% by mass or less with respect to the total mass of the ink, and the content of the crystal growth inhibitor is 2.0% by mass or less. Light curable inkjet ink.
[2] The difference between the number of carbon atoms in the straight chain part in at least one of the alkyl chains of the wax and the number of carbon atoms in the straight chain part of the alkyl chain of the crystal growth inhibitor is 2 or less. The actinic ray curable inkjet ink according to [1], which is characterized in that it is characterized.
[3] Either of [1] or [2], wherein the sugar structure contained in the crystal growth inhibitor is a monosaccharide, disaccharide, trisaccharide or a sugar derivative obtained by a dehydration reaction thereof. The actinic ray curable inkjet ink described in 1.
[4] The actinic ray curable inkjet ink according to [3], wherein the sugar structure is sorbitan.
[5] The actinic ray curing according to any one of [1] to [4], wherein the content of the crystal growth inhibitor is 0.5% by mass or more and 2.0% by mass or less. Type inkjet ink.

A second aspect of the present invention relates to the inkjet recording method described below.
[6] a step of injecting the actinic radiation curable inkjet ink according to any one of [1] to [5] onto a recording medium;
Irradiating the ink ejected onto the recording medium with an actinic ray to cure the ink, and the temperature of the recording medium is in the range of 25 ° C. to 40 ° C. Inkjet recording method.

  According to the present invention, by adding a crystal growth inhibitor to an actinic radiation curable ink-jet ink, blooming is suppressed even when printing is performed at a substrate temperature as low as 15 ° C. to 40 ° C. An actinic ray curable inkjet ink that achieves printing with high character quality is provided.

1. Actinic ray curable inkjet ink The actinic ray curable inkjet ink of the present invention contains an actinic ray curable compound, a photopolymerization initiator, a wax, and a crystal growth inhibitor.

[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 ester compound, and it is more preferable that it is (meth) acrylate. The (meth) acrylate 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) acrylates 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 (meta 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. Functional monomers;
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 is 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 may be a modified product. Examples of modified products include ethylene oxide-modified (meth) acrylates such as ethylene oxide-modified trimethylolpropane tri (meth) acrylate and ethylene oxide-modified pentaerythritol tetraacrylate; caprolactone modifications such as caprolactone-modified trimethylolpropane tri (meth) acrylate (Meth) acrylates; and caprolactam-modified (meth) acrylates such as caprolactam-modified dipentaerythritol hexa (meth) acrylate.

  In the present invention, at least a part of the actinic ray curable compound is preferably ethylene oxide-modified (meth) acrylate. This is because ethylene oxide-modified (meth) acrylate has high photosensitivity and easily forms a card house structure (described later) when the ink gels at a low temperature. In addition, ethylene oxide-modified (meth) acrylate is easily dissolved in other ink components at high temperatures and has little curing shrinkage.

  Examples of ethylene oxide modified (meth) acrylates include 4EO modified hexanediol diacrylate CD561, 3EO modified trimethylolpropane triacrylate SR454, 6EO modified trimethylolpropane triacrylate SR499, 4EO modified pentaerythritol tetraacrylate SR494 manufactured by Sartomer; Shin-Nakamura Chemical Polyethylene Glycol Diacrylate NK Ester A-400, Polyethylene Glycol Diacrylate NK Ester A-600, Polyethylene Glycol Dimethacrylate NK Ester 9G, Polyethylene Glycol Dimethacrylate NK Ester 14G; Tetraethylene from Osaka Organic Chemical Co., Ltd. Glycol diacrylate V # 335HP; 3PO modified trimethylo from Cognis 1propane-didiol dimethacrylate NK ester DOD-N, tricyclodecane dimethanol diacrylate NK ester A-DCP and tricyclodecane dimethanol dimethacrylate NK ester DCP manufactured by Shin-Nakamura Chemical Co., Ltd. Etc. are included.

  The (meth) acrylate 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 oligomer. , Polyester (meth) acrylate oligomers, linear (meth) acrylic oligomers, and the like.

  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.

[Photopolymerization initiator]
The photopolymerization initiator contained in the actinic radiation curable inkjet ink includes a radical photopolymerization initiator and a cationic photopolymerization initiator, and the radical photopolymerization initiator includes an intramolecular bond cleavage type and There is 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 and 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone; benzoins such as benzoin, benzoin methyl ether and benzoin isopropyl ether; 2 , 4,6-Trimethylbenzoindiphenylphosphine oxy Acylphosphine oxide, such as de; as benzyl and methyl phenylglyoxylate esters include.

  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 Ansula Non, 9,10-phenanthrenequinone, include camphorquinone, and the like.

  Examples of the cationic photopolymerization initiator include a photoacid generator. As the photoacid generator, a chemically amplified photoresist or a compound used for photocationic polymerization is used (edited by Organic Electronics Materials Research Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), 187-192. Page).

  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 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, cupron, 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, etc. It is.

[wax]
The wax contained in the actinic radiation curable inkjet ink of the present invention is 1.0% by mass or more and 10% by mass or less, and preferably 2.0% by mass or more and 4.0% by mass or less. When the wax content is less than 1.0% by mass, the character quality of the image is deteriorated. When the wax content is more than 10% by mass, the image quality is deteriorated such as unevenness of gloss or generation of a granular cured film, and blooming. Will occur.

  The wax contained in the actinic ray curable inkjet ink of the present invention is a wax having at least one alkyl chain. Generally, the wax has 1 to 4 alkyl chains. In the present invention, in all of the alkyl chains of the wax, the straight chain portion must have 15 or more carbon atoms. If this condition is not met, the solubility of the wax will be too high for use in the present invention. For this reason, the obtained ink causes blooming at the time of low-temperature printing, and the character quality also deteriorates. The number of carbon atoms in the straight chain portion of the alkyl chain is preferably 15-25, more preferably 16-22. When the number of carbon atoms in the linear portion exceeds 25, the solubility becomes too low (the gelation temperature becomes too high), and the streak when printed is increased.

  Examples of the wax used in the actinic ray curable inkjet ink of the present invention include higher fatty acids, higher alcohols, fatty acid esters, fatty acid amines, aliphatic ketones, fatty acid amides, etc., preferably fatty acid esters or aliphatic ketones. is there.

  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, for example, a compound represented by the following general formula (G1).
General formula (G1): R1-CO-R2

  In the formula (G1), R 1 and R 2 are each independently an aliphatic hydrocarbon group containing a straight chain portion having 15 to 25 carbon atoms. The aliphatic hydrocarbon group can be a saturated or unsaturated aliphatic hydrocarbon group. The saturated or unsaturated aliphatic hydrocarbon group may be a branched or linear aliphatic hydrocarbon group, but in order to obtain high crystallinity, a linear saturated aliphatic hydrocarbon group ( A straight-chain alkylene group).

  If the straight chain portion contained in the aliphatic hydrocarbon group has less than 15 carbon atoms, the wax has high solubility and does not have sufficient crystallinity, so the wax does not function as a gelling agent. 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 15 or more and 25 or less, the above-mentioned card house structure can be formed while having the crystallinity necessary as a gelling agent, 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 16 or more and less than 22. Therefore, R1 and R2 are particularly preferably a linear saturated aliphatic hydrocarbon group (straight chain alkylene group) having 16 to 22 carbon atoms.

  Examples of the aliphatic hydrocarbon group containing a straight chain portion having 15 to 25 carbon atoms include docosanyl group (C22), icosanyl group (C20), octadecanyl group (C18), heptadecanyl group (C17), hexadecanyl group ( C16), pentadecanyl group (C15) and the like.

The fatty acid ester as the wax is, for example, a compound represented by the following general formula (G2).
General formula (G2): R3-COO-R4

  In the formula (G2), R3 and R4 are each independently an aliphatic hydrocarbon group containing a straight chain portion having 15 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 15 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 make the crystallinity of the compound represented by the formula (G2) a certain level or more, the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group of R3 and R4 is preferably 16 or more and less than 22 .

  Examples of the aliphatic hydrocarbon group containing a straight chain portion having 15 to 26 carbon atoms are the same as the aliphatic hydrocarbon group containing a straight chain portion having 15 to 25 carbon atoms in the aforementioned formula (G1). Is included.

Preferred specific examples of the wax include aliphatic ketone compounds such as 18-pentatriacontanone (stearon) and 16-hentriacontanone (for example, Kao Wax T1 manufactured by Kao Corporation); cetyl palmitate, stearyl stearate, behen Aliphatic monoester compounds such as behenyl acid (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 (manufactured by Higher Alcohol Industry Co., Ltd.), EXCEPARL MY-M (manufactured by Kao Corporation), SPALM ACETI (manufactured by NOF Corporation), EMALEX CC-10 (manufactured by Nippon Emulsion Co., Ltd.), etc.); 4-Bis-O-benzylidene-D-glucitol (Gerol D And other petroleum-based waxes such as paraffin wax, microcrystalline wax, and petrolactam; candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and jojoba ester Plant wax such as beeswax, animal wax such as beeswax, lanolin and whale wax; mineral wax such as montan wax and hydrogenated wax; hardened castor oil or hardened castor oil derivative; montan wax derivative, paraffin wax derivative, microcrystalline Modified waxes such as wax derivatives or polyethylene wax derivatives; higher fatty acids such as behenic acid, arachidic acid, stearic acid, palmitic acid, oleic acid, and erucic acid; stearyl alcohol, beheny Higher alcohols such as alcohol; hydroxystearic acid such as 12-hydroxystearic acid; 12-hydroxystearic acid derivatives; stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, 12-hydroxystearic acid amide Fatty acid amides such as Nikka Amide series manufactured by Nippon Kasei Co., Ltd. ITOWAX series manufactured by Ito Oil Co., Ltd., FATTYAMID series manufactured by Kao Corporation, etc .; N-substituted fatty acid amides such as N-stearyl stearic acid amide and N-oleyl palmitic acid amide; Special fatty acid amides such as N, N'-ethylenebisstearylamide, N, N'-ethylenebis-12-hydroxystearylamide, and N, N'-xylylenebisstearylamide; higher amines such as octadecylamine Stearyl stearic acid, 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, etc. Marl series, RIKEN Vitamin Co., Ltd. Poem series, etc.); Sucrose fatty acid esters such as sucrose stearic acid and sucrose palmitic acid (for example, Ryoto Sugar Ester series manufactured by Mitsubishi Chemical Foods); polyethylene wax, α-olefin maleic anhydride Synthetic waxes such as copolymer waxes; polymerizable waxes (such as UNILIN series manufactured by Baker-Petrolite); and the like. Among these, 18-pentatriacontanone (stearone), behenyl behenate, and stearyl stearate are preferable.
These waxes may be used alone or in combination of two or more.

[Crystal growth inhibitor]
The crystal growth inhibitor in the present invention is a substance having a sugar structure and at least one alkyl chain containing a straight chain portion having 15 or more carbon atoms bonded to the sugar structure. The sugar structure of the crystal growth inhibitor repels the alkyl chain of the wax, thereby stopping the crystallization of the wax, so that the growth of the wax can be inhibited.

  The crystal growth inhibitor contained in the actinic radiation curable inkjet ink of the present invention is 2.0% by mass or less and 0.5% by mass or more and 2.0% by mass or less with respect to the total mass of the ink. It is more preferable that it is 0.5 mass% or more and 1.0 mass% or less. When the content of the crystal growth inhibitor is 2.0% by mass or less, the character quality is good, fine characters can be read, and the occurrence of blooming is easily suppressed. In addition, when the content of the crystal growth inhibitor is 0.5% by mass or more, the effect of the crystal growth inhibitor is likely to be exhibited, and there is a phenomenon that leads to deterioration of image quality such as gloss variation and generation of a granular cured film. It becomes easy to be suppressed.

  The sugar structure contained in the crystal growth inhibitor is a monosaccharide, disaccharide, trisaccharide, or a sugar derivative obtained by subjecting these to a dehydration reaction.

Specific examples of the sugar structure possessed by the crystal growth inhibitor include glucose, galactose, mannose, fructose, fucose, ribose, arabinose, rhamnose, xylose, sorbose, erythritol, xylitol, sorbitol, mannitol, arabitol, galactitol, inositol, etc. Monosaccharides;
Disaccharides such as sucrose, lactose, maltose, trehalose, lactulose, cellobiose, isomaltose, palatinose, melibiose, xylobiose, gentiobiose, sucralose, lactitol, maltitol, isomaltol;
And trisaccharides such as raffinose, melezitose, maltotriose, isomaltotriose, panose, xylotriose, 4′-galactosyl lactose, maltotriitol; and those obtained by dehydration reaction of the above saccharides such as sorbitan.

  As the saccharide possessed by the crystal growth inhibitor, sorbitan, stearic acid, and sucrose are preferable, and sorbitan is more preferable.

  The alkyl group possessed by the crystal growth inhibitor includes a straight chain portion having 15 or more carbon atoms, and includes docosanyl group (C22), icosanyl group (C20), octadecanyl group (C18), heptadecanyl group (C17), hexadecanyl. Examples thereof include a group (C16) and a pentadecanyl group (C15).

  Specific examples of the crystal growth inhibitor used in the present invention include sorbitan monostearate, inulin stearate, sorbitan monobehenate, sucrose behenate and the like.

  In the actinic ray curable compound of the present invention, the difference between the number of carbon atoms in the linear part of at least one of the alkyl chains of the wax and the number of carbon atoms of the linear part of the alkyl chain in the crystal growth inhibitor is It is preferable that it is 2 or less, that is, the length of the straight chain portion of the alkyl chain is similar. If the difference in the number of carbon atoms in the alkyl chain between the wax and the crystal growth inhibitor is 2 or less, the inhibitory effect of the crystal growth inhibitor is effectively exhibited and the crystallization of the wax stops, so that particularly high-quality printing is possible. It becomes possible.

  In the present invention, when a high-solubility wax and a crystal growth inhibitor that prevents crystal growth by stopping crystallization of the wax are used in combination, even after landing, even under low printing temperature (base material temperature) conditions. The growth rate of the crystallized wax in the ink becomes slow, and the unevenness formed by the ink dots can be reduced. As a result, it is possible to obtain an actinic ray curable inkjet ink that has uniform gloss, low graininess, can clearly print fine characters, and can further suppress blooming in an image. The crystal growth inhibitor used in the present invention includes the number of carbon atoms in the linear portion of at least one of the alkyl chains of the wax and the carbon of the linear portion in at least one of the alkyl chains of the crystal growth inhibitor. The highest effect is obtained when both the requirement that the difference from the number of atoms is 2 or less and the requirement that the sugar structure of the crystal growth inhibitor is sorbitol satisfy the two requirements at the same time. However, even for a crystal growth inhibitor that does not satisfy one or both of these two requirements, the amount added to the total mass of the ink is increased within the range of 0.5 mass% to 2.0 mass%. Thus, an effect equivalent to that of a crystal growth inhibitor that satisfies the above two requirements can be obtained.

[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 (Dainichiseika Color & Chemicals Mfg. Co., Ltd.);
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, Ltd.);
Lionol Yellow 1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (manufactured by Toyo Ink Co., Ltd.), Toner Magenta E02, Permanent RubinF6B, Toner Yellow GHG, Perman Yellow GHG, Perman Yellow G Company-made);
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 Corporation).

  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 according to 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 RED130, 802 (above, Nippon Kayaku Co., Ltd.), PHLOXIN, ROSE BENGAL, ACID Red (above, Daiwa Kasei Co., Ltd.), HSR-31, DIAR SIN Red K (manufactured by Mitsubishi Kasei Co., Ltd.), is included Oil Red (manufactured by BASF Japan Co., 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 (manufactured by Mitsui Toatsu), AIZEN SOT Yellow-1, AIZEN SOT YellowW-3, AIZEN SOT Yellow-6 (above, Manufactured by Hodogaya 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, and rubber resins.

  The actinic ray curable inkjet ink can be obtained by mixing the actinic ray curable compound, the photopolymerization initiator, the wax, the crystal growth inhibitor, and any of the components under heating. . It is preferable to filter the obtained liquid mixture with a predetermined filter.

2. Inkjet recording method The inkjet recording method of the present invention includes at least the following two steps.
(1) a step of injecting the actinic ray curable inkjet ink of the present invention onto a recording medium;
(2) A step of irradiating the ink ejected onto the recording medium with an actinic ray to cure the ink.

<About step (1)>
In step (1), inkjet ink droplets are ejected from an inkjet head and landed on a recording medium. The ink used may be the above-described actinic ray curable inkjet ink.

  The ejection method from the ink jet head may be either an on-demand method or a continuous method. Examples of on-demand inkjet heads include single-cavity, double-cavity, bender, piston, shear-mode, and shared-wall electro-mechanical conversion, and thermal inkjet and bubble jet (bubble) The jet includes an electric-thermal conversion system including a Canon (registered trademark) type.

  The ejection stability of the inkjet ink droplets can be improved by ejecting the droplets from the inkjet head in a heated state. The temperature of the inkjet ink when ejected is preferably 35 ° C. or more and 100 ° C. or less, and more preferably 35 ° C. or more and 80 ° C. or less from the viewpoint of further improving the ejection stability. From the viewpoint of further improving the ejection stability, it is preferable to emit at an ink temperature such that the viscosity of the inkjet ink is 7 mPa · s to 15 mPa · s, more preferably 8 mPa · s to 13 mPa · s.

  Examples of the method of heating the inkjet ink to a predetermined temperature include at least one of an ink tank constituting a head carriage, an ink supply system such as a supply pipe and an anterior chamber ink tank immediately before the head, a pipe with a filter, and a piezo head Is heated to a predetermined temperature by any one of a panel heater, a ribbon heater, warm water and the like.

  From the viewpoint of increasing the recording speed and improving the image quality, it is preferable that the droplet amount of the ink-jet ink when ejected is 2 pL or more and 20 pL or less.

  The recording media used in the inkjet recording method of the present invention are all applicable to printing paper and a wide range of synthetic resins that have been used in various applications. Specifically, plain paper used for copying, high-quality paper used for offset printing, coated paper, coated paper, art paper, etc., coated paper with both sides coated with resin, etc. And various non-absorbable plastics and films thereof used for soft packaging, such as various types of laminated paper, synthetic paper and thin cardboard. Examples of various plastic films include PET film, OPS film, OPP film, ONY film, PVC film, PE film, TAC film and the like. In addition, metals, glass, and the like may be used as the recording medium.

  In the ink jet recording method of the present invention, the ink droplets that have landed on the recording medium are cured, and the temperature of the recording medium (base material temperature) at this time is in the range of 25 ° C to 40 ° C. The ink-jet ink used in the ink-jet recording method of the present invention includes a wax having an alkyl chain containing a straight chain portion having 15 or more carbon atoms as a gelling agent, at least one sugar structure, and carbon bonded to the sugar structure. The ink further comprises a crystal growth inhibitor having an alkyl chain containing a linear portion having 15 or more atoms. In the ink of the present invention, the temperature of the recording medium is increased to a high temperature exceeding, for example, 40 ° C. by using a wax having a low gelation temperature but a high solubility wax and a crystal growth inhibitor that delays crystallization of the wax. High-quality printing is possible without heating.

  In the present invention, the temperature of the recording medium is set in the range of 25 ° C to 40 ° C, preferably 25 ° C to 35 ° C. When the actinic ray curable ink-jet ink of the present invention is used, it is not necessary to heat the recording medium to a high temperature (for example, 70 ° C.) as in the past, so printing on thick paper such as thin corrugated cardboard that is thicker than general coated paper When doing, energy consumption for heating can be suppressed. Furthermore, since the time for raising the temperature of the substrate to a desired temperature is also shortened, productivity is improved. In addition, since printing can be performed on a recording medium having low heat resistance that is easily deformed at high temperatures, the types of applicable base materials that can be used as the recording medium are also expanded.

  The recording medium does not necessarily have to be heated as long as the temperature is in the range of 25 ° C to 40 ° C. In the case of heating the recording medium, various heaters and heating rollers for heating the recording medium in a contact type may be used, or a lamp or the like for heating the front or back surface of the recording medium in a non-contact type. The heating means for heating the recording medium in a contact type is usually disposed on the back surface of the recording medium.

<About step (2)>
In step (2), the ink ejected onto the recording medium is irradiated with actinic rays to cure the ink. By this step, the actinic ray curable compound contained in the inkjet ink is photocured.

  Examples of the actinic rays to be irradiated include ultraviolet rays, near ultraviolet rays, natural light (including filter cut products) and the like, and ultraviolet rays are preferable. Examples of the ultraviolet irradiation light source include a mercury lamp, a metal halide lamp, an excimer laser, an ultraviolet laser, a cold cathode tube, a hot cathode tube, a black light, an LED (light emitting diode), and the like; a strip-shaped metal halide lamp, Cold cathode tubes, hot cathode tubes, mercury lamps or black lights are preferred; LEDs are particularly preferred because of their long lifetime and low cost.

  However, in general, an LED is a single wavelength light source, and its illuminance tends to be lower than a light source having a plurality of emission line spectra such as a high-pressure mercury lamp. In the case of curing by radical polymerization, if the illuminance is low, the proportion of radicals bonded to oxygen and deactivated increases. Therefore, even if the irradiation time is extended and the integrated light quantity is the same, it becomes difficult to cure. Therefore, it is required that the ink jet ink can be cured with low illuminance and low integrated light quantity.

  LEDs can be turned on instantaneously, have a long life, little radiant heat, easy light quantity control, an extremely narrow emission wavelength width (half-value width), and low power consumption. The wavelength of the irradiation light source is preferably 280 to 420 nm, and more preferably 350 to 410 nm. The wavelength is a long wavelength in the optical ultraviolet region and is highly safe.

It is preferable that the integrated light amount irradiated to the ink-jet ink droplets landed on the recording medium is in the range of 10 to 500 mJ / cm ² . Within this range, it is advantageous from the viewpoint of energy saving, space saving and cost.

Light from the active ray irradiation source, the recording medium is preferably to 8W / cm ² or less illuminance, and more preferably set to 2W / cm ² or less. Light with an illuminance higher than 8 W / cm ² generates a large amount of heat, so that a recording medium with low heat resistance is easily deformed. Further, there may be a problem that the amount of leakage light increases and the ink is cured on the head nozzle surface. Furthermore, light with high illuminance consumes high energy, has a large light source space, and increases costs.

  The irradiation method of actinic rays is not specifically limited, For example, it can carry out with the following method. A light source is provided on both sides of the head unit, the head and the light source are scanned by a shuttle method, and irradiation is performed after a certain time from ink landing. Further, the curing is completed by irradiating light from another light source that is not driven (see Japanese Patent Application Laid-Open No. 60-132767). Alternatively, light may be irradiated using an optical fiber, or ultraviolet light from a collimated light source may be reflected by a mirror surface provided on the side surface of the head unit and irradiated to the recording unit (US Pat. No. 6,145). , 979).

  Moreover, you may divide actinic-light irradiation into two steps. The first irradiation is preferably performed within 0.001 to 1.0 seconds after the ink droplet has landed on the recording medium P. The second irradiation may be performed after the first irradiation; that is, the second irradiation may be performed on the downstream side in the transport direction of the recording medium with respect to the first irradiation. The integrated light quantity (D1) per recording medium unit area by the first irradiation is preferably smaller than the integrated light quantity (D2) per recording medium unit area by the second irradiation. That is, it is preferable that D1 <D2. By dividing the irradiation with actinic rays into two stages, the hardness of the image is increased and an image with less bleeding can be formed.

  In the ink jet recording method of the present invention, the total ink film thickness after the ink has landed on the recording medium and cured by irradiation with actinic rays is preferably 0.1 to 5 μm. “Total ink film thickness” means the maximum value of the film thickness of ink drawn on a recording medium. Whether it is a single color or a two-color overlap (secondary color), a three-color overlap, or a four-color overlap (white ink base), the total ink film thickness is preferably 0.1 to 5 μm.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless there is particular notice, "mass part" or "mass%" is represented.

<Preparation of pigment dispersion 1>
The following additives were sequentially mixed and dispersed to prepare magenta pigment dispersion 1 containing 21% by mass of magenta pigment.

  Each of the following compounds was placed in a stainless beaker and dissolved by heating and stirring for 1 hour while heating on a hot plate at 65 ° C.

Pigment dispersant: Ajisper PB824 (Ajinomoto Fine Techno Co., Ltd.) 9 parts Actinic ray curable compound: Tripropylene glycol diacrylate 70 parts Polymerization inhibitor: Irgastab UV10 (Ciba Japan Co., Ltd.) 0.02 parts

  Subsequently, after cooling the said solution to room temperature, 21 parts of the following magenta pigment was added to this solution, and it was put into a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, and was dispersed in a paint shaker for 8 hours. Thereafter, the zirconia beads were removed to obtain a pigment dispersion 1.

  Magenta pigment: Pigment Red 122 (manufactured by Dainichi Seika, Chromo Fine Red 6112JC)

<Preparation of ink>
(Preparation of ink 1)
The following additives were sequentially mixed, heated to 80 ° C. and stirred for 30 minutes, and then the resulting solution was filtered with a # 3000 metal mesh filter under heating at 80 ° C., cooled, and ink 1 It was.

Actinic ray curable compound: A-400 (polyethylene glycol # 400 diacrylate, manufactured by Shin-Nakamura Kogyo Co., Ltd.) 31.5 parts Actinic ray curable compound: SR494 (4EO-modified pentaerythritol tetraacrylate, manufactured by SARTOMER) 17.0 parts Actinic ray curable compound: SR499 (6EO-modified trimethylolpropane triacrylate, manufactured by SARTOMER) 17.9 parts Wax: pentatriacontan-18-one 3.0 parts Crystal growth inhibitor: sorbitan monostearate 0.5 part Polymerization inhibitor: Irgastab UV10 (manufactured by Ciba Specialty Chemicals) 0.1 part Photopolymerization initiator: TPO (phosphine oxide, DAROCURE TPO, manufactured by Ciba Specialty Chemicals) 6.0 parts Photopolymerization initiator auxiliary agent: ITX ( Iso Propylthioxanthone, Speedcure ITX, manufactured by Lambson) 2.0 parts Photopolymerization initiator assistant: EDB (Amine assistant, Speedcure EDB, manufactured by Lambson) 3.0 parts Pigment dispersion 1 19.0 parts

(Preparation of inks 2 to 8)
Inks 2 to 8 were prepared in the same manner as in the preparation of ink 1 except that the type and amount of the crystal growth inhibitor were changed as shown in Table 2. When the total amount of wax and crystal growth inhibitor increased or decreased from 3.50 parts, the amount of A-400, which is an actinic radiation curable compound, was appropriately adjusted so that the total amount was 100 parts.

(Preparation of inks 9 to 14)
Inks 9 to 14 were prepared in the same manner as in Preparation of Ink 1 except that the crystal growth inhibitor was changed to sorbitan monostearate and the addition amounts of wax and crystal growth inhibitor were changed as shown in Table 3. Was prepared. When the total amount of wax and crystal growth inhibitor increased or decreased from 3.50 parts, the amount of A-400, which is an actinic radiation curable compound, was appropriately adjusted so that the total amount was 100 parts.

(Preparation of inks 15 to 22)
Inks 15 to 22 were prepared in the same manner as in the preparation of ink 1 except that the wax was changed to behenyl behenate and the type and amount of the crystal growth inhibitor were changed as shown in Table 4. In addition, when the total amount of the wax and the crystal growth inhibitor increased or decreased from 3.50 parts, the addition amount of A-400 which is an actinic ray curable compound was appropriately adjusted so that the total amount became 100 parts.

(Preparation of inks 23 to 28)
In the preparation of the inks 23 to 28, the ink growth was similarly performed except that the crystal growth inhibitor was changed to sorbitan monobehenate and the addition amounts of the wax and the crystal growth inhibitor were changed as shown in Table 5. -28 were prepared. In addition, when the total amount of the wax and the crystal growth inhibitor increased or decreased from 3.50 parts, the addition amount of A-400 which is an actinic ray curable compound was appropriately adjusted so that the total amount became 100 parts.

(Preparation of inks 29 to 36)
Inks 29 to 36 were prepared in the same manner as in Preparation of Ink 1 except that the wax was changed to stearyl stearate and the type and amount of the crystal growth inhibitor were changed as shown in Table 6. In addition, when the total amount of the wax and the crystal growth inhibitor increased or decreased from 3.50 parts, the addition amount of A-400 which is an actinic ray curable compound was appropriately adjusted so that the total amount became 100 parts.

(Preparation of inks 37 to 42)
Ink 37 was prepared in the same manner as in the preparation of the inks 29 to 36 except that the crystal growth inhibitor was changed to sorbitan monostearate and the addition amounts of wax and crystal growth inhibitor were changed as shown in Table 7. -42 were prepared. In addition, when the total amount of the wax and the crystal growth inhibitor increased or decreased from 3.50 parts, the addition amount of A-400 which is an actinic ray curable compound was appropriately adjusted so that the total amount became 100 parts.

(Preparation of inks 43 to 51)
Inks 43 to 51 were prepared in the same manner as in the preparation of ink 1 except that the types of wax and crystal growth inhibitor were changed as shown in Table 8.

(Preparation of inks 52 to 58)
Inks 52 to 58 were prepared in the same manner as in the preparation of ink 1 except that the wax was changed to 12-tricosanone and the type of the crystal growth inhibitor was changed as shown in Table 9.

(Preparation of inks 59 to 66)
Inks 59 to 66 were prepared in the same manner as in the preparation of ink 1 except that the types of wax and crystal growth inhibitor were changed as shown in Table 10.

(Preparation of inks 67 to 74)
In the preparation of the ink 1, the types of the wax and the crystal growth inhibitor were changed as shown in Table 11, the addition amount of the crystal growth inhibitor was 0.10 parts, and A-400 which is an actinic ray curable compound. Inks 67 to 74 were prepared in the same manner except that the addition amount of was changed to 31.9 parts.

(Preparation of ink 75 to 82)
In the preparation of the ink 1, the types of the wax and the crystal growth inhibitor were changed as shown in Table 12, the addition amount of the wax was 12.00 parts, and the addition amount of the crystal growth inhibitor was 1.00 parts. Inks 75 to 82 were prepared in the same manner except that the amount of A-400 added as the actinic ray curable compound was changed to 22.0 parts.

(Preparation of inks 83 to 90)
In the preparation of the ink 1, the types of the wax and the crystal growth inhibitor were changed as shown in Table 13, the addition amount of the wax was 0.50 part, and the addition amount of the actinic radiation curable compound A-400. Ink 83 to 90 were prepared in the same manner except that was changed to 34.0 parts.

  Details of the wax and crystal growth inhibitor used in the preparation of inks 1 to 90 are as described in Table 1.

<Image forming method>
Using the produced inks 1 to 86, a monochromatic image was formed by a line type ink jet recording apparatus. The temperature of the inkjet head of the inkjet recording apparatus was set to 80 ° C. The temperature of the recording medium (OK top coat, US basis weight 128 g / m ² manufactured by Oji Paper Co., Ltd.) was adjusted to 35 ° C., and a blank image of 5 cm × 5 cm was printed on the recording medium. After the image was formed, the ink was cured by irradiating the image with ultraviolet light with an LED lamp (manufactured by Phoseon Technology, 395 nm, 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. The dpi is the number of dots per 2.54 cm.

<Evaluation>
(image quality)
About the 5 * 5 cm solid image printed on said conditions, the dispersion | variation in glossiness and generation | occurrence | production of a granular cured film were confirmed visually.
A: The gloss was uniform and the graininess was low.
○: The gloss was slightly non-uniform, but the graininess was low.
Δ: The gloss was non-uniform, but the graininess was low.
X: The gloss was uneven and the graininess was high.

(Blooming)
A 5 × 5 cm solid image printed under the above conditions was stored in an environment of 40 ° C. for 1 month. 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.

(Character quality)
By using the above-described image forming method, characters without the Chinese characters “mouth, fourth, day, times, cause, trouble, gut, country, eyes, figure, country” were printed on the recording medium. The extracted characters were MS Mincho with a resolution of 1400 dpi × 1440 dpi, 3 points, and 5 points. The printed character image was visually observed. The character quality was evaluated based on the following criteria.
○: All three-point characters are clearly recorded in detail.
Δ: Only a part of 3-point extracted characters can be read, but all 5-point extracted characters can be read.
X: Some of the 5 point missing characters cannot be read.

  Tables 2 to 13 show the composition and evaluation results of each ink.

  As is apparent from the evaluation results in Tables 2 to 7, when printing is performed using the inks 1 to 42 that are the inkjet inks of the present invention, the image quality and the character quality are high even when the temperature of the recording medium is as low as 35 ° C. Printing was possible and blooming could be suppressed. The excellent effect of the present invention is that the difference between the number of carbon atoms in the straight chain portion of at least one of the alkyl chains of the wax and the number of carbon atoms of the straight chain portion in at least one of the alkyl chains of the crystal growth inhibitor. In the case of a combination of a wax and an inhibitor that simultaneously satisfies the two requirements that is 2 or less (Requirement 1) and the sugar structure of the crystal growth inhibitor is sorbitol (Requirement 2), a small amount (0.50) of inhibition (Ink 1, 11, 25, 29, 39). On the other hand, in the case of a crystal growth inhibitor that does not satisfy one or both of the two requirements described above, the image quality of the printed matter is slightly reduced at the same use amount as the crystal growth inhibitor that satisfies both of the two requirements (ink 2, 4, 6, 7, 15, 17, 21, 30, 32, 34). Even with such a crystal growth inhibitor, when the amount used was increased to 1.00 or 1.50, it was possible to achieve the same high image quality as a crystal growth inhibitor that satisfied all two requirements. (Inks 3, 5, 8, 16, 19, 22, 31, 33, 36).

  On the other hand, as is apparent from the evaluation results in Table 8, stearyl alcohol (inks 43, 46, and 49) that has 15 or more linear carbon atoms in the alkyl chain but does not have a sugar structure has a sugar structure. Sorbitan monolaurate (inks 44, 47, 50) in which the alkyl chain has less than 15 linear carbon atoms, and the alkyl chain has less than 15 linear carbon atoms and a sugar structure Ink using no lauryl alcohol (inks 45, 48, 51) as a crystal growth inhibitor had a non-uniform gloss on a printed solid image and a low image quality.

  In addition, as is apparent from the evaluation results in Table 9, the ink using 12-tricosanone having a linear carbon atom number of less than 15 as the wax as the wax has character quality regardless of the type of the crystal growth inhibitor. Low and blooming occurred.

  When the amount of the crystal growth inhibitor added to the ink exceeded 2.0 parts, the quality of the solid image did not change much, but the character quality was low and blooming occurred (Table 10). On the other hand, when the amount of the crystal growth inhibitor added to the ink is less than 0.5, there is not much change in the character quality and the blooming suppression effect, and the solid image quality is reduced, but it is within the range that can withstand practical use. (Table 11).

  Further, when the amount of the wax added to the ink exceeds 10.0 parts, the gloss is not uniform and the graininess is increased, so that the image quality is lowered, the blooming suppressing effect is not exhibited, and the character quality is also lowered (Table). 12). On the other hand, when the amount of wax added to the ink is less than 1.0, the image quality and the blooming suppression effect are not significantly changed, but the character quality is reduced and fine characters cannot be distinguished (Table 13). .

  This application claims the priority based on Japanese Patent Application No. 2015-050965 of an application on March 13, 2015. All the contents described in the claims and specification of the application are incorporated herein by reference.

  The ink-jet ink of the present invention is effective in reducing energy consumption because it can suppress the occurrence of blooming in printed matter and achieve high image quality and character quality printing even when printed at a low substrate temperature. . Furthermore, since the ink of the present invention can be printed on a recording medium having low heat resistance, the use of the ink also leads to an increase in the types of base materials that can be used as the recording medium.

Claims (6)

An actinic ray curable inkjet ink comprising an actinic ray curable compound, a photopolymerization initiator, a wax, and a crystal growth inhibitor,
The wax has at least one alkyl chain including a straight chain portion, and in all of the alkyl chains of the wax, the straight chain portion has 15 or more carbon atoms,
The crystal growth inhibitor is a substance having a sugar structure and an alkyl chain containing a straight chain portion having 15 or more carbon atoms bonded to the sugar structure,
The activity is characterized in that the content of the wax is 1% by mass or more and 10% by mass or less with respect to the total mass of the ink, and the content of the crystal growth inhibitor is 2.0% by mass or less. Light curable inkjet ink.   The difference between the number of carbon atoms of the straight chain portion in at least one of the alkyl chains of the wax and the number of carbon atoms of the straight chain portion of the alkyl chain of the crystal growth inhibitor is 2 or less, The actinic ray curable inkjet ink according to claim 1.   The actinic ray curable ink jet according to claim 1 or 2, wherein the sugar structure contained in the crystal growth inhibitor is a monosaccharide, disaccharide, trisaccharide or a sugar derivative obtained by a dehydration reaction thereof. ink.   The actinic ray curable inkjet ink according to claim 3, wherein the sugar structure is sorbitan.   The actinic ray curable inkjet ink according to any one of claims 1 to 4, wherein the content of the crystal growth inhibitor is 0.5% by mass or more and 2.0% by mass or less. . A step of injecting the actinic ray curable inkjet ink according to any one of claims 1 to 5 onto a recording medium;
Irradiating the ink ejected onto the recording medium with an actinic ray to cure the ink, and the temperature of the recording medium is in the range of 25 ° C. to 40 ° C. Inkjet recording method.