JP5857866B2 - Actinic ray curable inkjet ink and inkjet recording method - Google Patents

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 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.

  As a method for improving the pinning property of the ultraviolet curable ink-jet ink, for example, it has been studied to add a gelling agent to the ink and cause a sol-gel phase transition by temperature. In other words, it has been studied to suppress dot coalescence by discharging ink droplets in a liquid state at a high temperature and landing them on a recording medium, and at the same time cooling the ink droplets to gel. As gelling agents added to the ink, stearons and the like are disclosed (see Patent Documents 1 and 2).

  On the other hand, in order to improve the curability of an image, an actinic ray curable inkjet ink containing a photopolymerizable gelling agent has been proposed (Patent Document 3).

US Patent Application Publication No. 2007/0058020 International Publication No. 2007/025893 JP 2006-193745 A

  However, when an actinic ray curable inkjet ink contains a gelling agent, the pinning property is improved, but the phenomenon that the gelling agent precipitates and crystallizes on the image surface (blooming) may occur.

  In Patent Document 3, a large amount of a photopolymerizable gelling agent is added to improve the curability of the image. When the actinic ray curable inkjet ink contains a large amount of the photopolymerizable gelling agent, the photopolymerizable gelling agent may not be sufficiently polymerized during photocuring due to the influence of oxygen inhibition. Therefore, a photopolymerizable gelling agent that has not been polymerized tends to appear on the image surface and tends to cause blooming. Moreover, since there are many photopolymerization gelling agents which are not superposed | polymerized, it is easy to become low in abrasion property.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an actinic ray curable inkjet ink and an inkjet recording method which form an image having abrasion resistance and less blooming.

  The present inventors can suppress blooming of the gelling agent by including the photopolymerizable gelling agent in the actinic ray curable inkjet ink; the photopolymerizable gelling agent and the photopolymerizable gelling agent in the ink The photopolymerizable gelling agent contained in the actinic radiation curable ink-jet ink can be reduced in content by combining the photopolymerizable compound that dissolves well, maintains uniform, and exists stably. I found it. As a result, oxygen inhibition to the photopolymerizable gelling agent is reduced, and there is a scratch resistance and an image with less blooming can be formed.

The first of the present invention relates to the actinic ray curable inkjet ink shown below.
[1] An actinic ray curable inkjet ink containing a photopolymerizable compound, a photopolymerization initiator, and a gelling agent and reversibly undergoing sol-gel phase transition depending on temperature,
The photopolymerizable compound includes at least one photopolymerizable compound A having a weight average molecular weight of 280 to 1500 and having a PO modification, or a (meth) acrylate compound having a cyclic structure in the molecule ,
The gelling agent contains at least one photopolymerizable gelling agent containing an alkyl chain having 12 or more carbon atoms,
An actinic radiation-curable inkjet ink comprising 10 to 40% by mass of the photopolymerizable compound A and 0.5 to 10.0% by mass of the gelling agent with respect to the mass of the whole ink.
[2] The actinic ray curable inkjet ink according to [1], wherein the photopolymerizable compound A has a ClogP value of 4.0 to 7.0.
[3] The photopolymerizable gelling agent according to [1] or [2] , wherein the photopolymerizable gelling agent is a polyfunctional photopolymerizable gelling agent having two or more photopolymerizable groups in one molecule. Actinic ray curable inkjet ink.
[4] The actinic ray-curable inkjet ink according to any one of [1] to [3], which does not contain a gelling agent that does not have photopolymerization properties.
[5] The photopolymerizable compound has a weight average molecular weight of 300 to 1500 and a photopolymerizable compound B having a structure represented by (—CH ₂ —CH ₂ —O—) in the molecule of 3 to 14. The actinic ray curable inkjet ink according to any one of [1] to [ 4 ], further comprising:

The second aspect of the present invention relates to the following inkjet recording method.
[6] An inkjet recording method using the actinic ray curable inkjet ink according to any one of [1] to [ 5 ],
A step of causing ink droplets of the actinic radiation curable inkjet ink to be ejected from an inkjet recording head and adhered onto a recording medium;
Irradiating the droplets landed on the recording medium with light from the LED to cure the ink droplets,
The inkjet recording method according to claim 1, wherein the light has a peak illuminance of 0.5 to 10.0 W / cm ² at 360 to 410 nm.

  The actinic ray curable ink-jet ink and ink-jet recording method of the present invention have scratch resistance and can form an image with little blooming.

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.

1. About actinic ray curable inkjet ink The actinic ray curable inkjet ink contains a photopolymerizable compound, a photopolymerization initiator, and a gelling agent, and may contain other additives as necessary.

<About photopolymerizable compounds>
The actinic ray curable inkjet ink contains a photopolymerizable compound. A photopolymerizable compound is a compound that crosslinks or polymerizes upon irradiation with actinic rays. The actinic rays are, for example, electron beams, ultraviolet rays, α rays, γ rays, and X-rays, and are preferably ultraviolet rays. The photopolymerizable compound is a radical polymerizable compound or a cationic polymerizable compound, and 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 compounds having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids and salts thereof, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds and anhydrides 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 but also an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group (photopolymerizable group), or the like. Here, “(meth) acrylate” refers to both and / or “acrylate” and “methacrylate”, and “(meth) acryl” refers to both and / or “acryl” and “methacryl”.

(Photopolymerizable compound A)
The actinic ray curable inkjet ink of the present invention has a (meth) acrylate compound having a molecular weight in the range of 280 to 1500 and a ClogP value in the range of 4.0 to 7.0 as the photopolymerizable compound. (Hereinafter also referred to as “photopolymerizable compound A”) is included. The photopolymerizable compound A preferably has two or more photopolymerizable groups. The photopolymerizable group may be a (meth) acryl group.

  The molecular weight of the photopolymerizable compound A is preferably in the range of 280 to 1500, and more preferably in the range of 300 to 800. In order to stably eject ink droplets from the ink jet recording head, it is necessary that the ink viscosity at the ejection temperature be between 7 and 14 mPa · s. An ink composition containing a photopolymerizable compound having a molecular weight of less than 280 and a gelling agent has a large change in ink viscosity before and after the ejection temperature. Therefore, it is difficult to adjust the ink viscosity within the above range. Moreover, since the photopolymerizable compound A having a molecular weight of 280 or more has little odor, it can reduce the odor of the actinic ray curable inkjet ink and its cured product. On the other hand, when the photopolymerizable compound A having a molecular weight exceeding 1500 is contained, the sol viscosity of the ink becomes excessively high.

  The ClogP value of the photopolymerizable compound A is preferably in the range of 4.0 to 7.0, and more preferably in the range of 4.5 to 6.0. When the ClogP value of the photopolymerizable compound A is less than 4.0, the actinic ray curable inkjet ink becomes hydrophilic and the gelling agent is hardly dissolved. Therefore, even when heated, the gelling agent is not completely dissolved, and the ink does not sufficiently undergo sol-gel phase transition. Further, defective ejection from the ink jet recording apparatus is likely to occur. On the other hand, when the ClogP value of the photopolymerizable compound A exceeds 7.0, the solubility of the photopolymerization initiator in the ink is lowered, the curability of the ink is lowered, or the ejection property from the ink jet recording head is decreased. Or drop.

  Here, the “Log P value” is a coefficient indicating the affinity of an organic compound for water and 1-octanol. 1-octanol / water partition coefficient P is a distribution equilibrium when a trace amount of compound is dissolved as a solute in a two-liquid solvent of 1-octanol and water, and is a ratio of the equilibrium concentration of the compound in each solvent. Their logarithm LogP for the base 10 is shown. That is, the “log P value” is a logarithmic value of the 1-octanol / water partition coefficient, and is known as an important parameter representing the hydrophilicity / hydrophobicity of a molecule.

  The “CLogP value” is a LogP value calculated by calculation. The CLogP value can be calculated by a fragment method, an atomic approach method, or the like. More specifically, ClogP values can be calculated in the literature (C. Hansch and A. Leo, “Substituent Constants for Correlation Analysis in Chemistry and Biology” (John Wiley & Sons, New York, 69). Or the following commercially available software package 1 or 2 may be used.

Software Package 1: MedChem Software (Release 3.54, Aug. 1991, Medicinal Chemistry Project, Pomona College, Clarmont, CA)
Software package 2: Chem Draw Ultra ver. 8.0. (April 2003, CambridgeSoft Corporation, USA)

  The numerical value of the ClogP value described in this specification and the like is a “ClogP value” calculated using the software package 2.

  The content of the photopolymerizable compound A contained in the actinic radiation curable inkjet ink of the present invention is preferably in the range of 10 to 40% by mass with respect to the total mass of the ink. When the content of the photopolymerizable compound A is less than 10% by mass, the ink becomes hydrophilic, the solubility of the gelling agent is lowered, and the sol-gel phase transition is not sufficiently performed. On the other hand, when the content of the photopolymerizable compound A exceeds 40% by mass, the solubility of the photopolymerization initiator in the ink becomes insufficient. For this reason, the ejection of ink from the ink jet recording apparatus becomes unstable, and the shrinkage when the ink droplets are cured increases. Further, the printed material is curled, and the adhesion of the image film to the recording medium is significantly deteriorated. Further, the gelling agent is difficult to deposit and the pinning property of the ink is deteriorated.

More preferable examples of the photopolymerizable compound A include (1) a trifunctional or higher functional methacrylate having 3 to 14 structures represented by (—C (CH ₃ ) H—CH ₂ —O—) in the molecule. Or an acrylate compound, (2) a bifunctional or higher functional methacrylate or acrylate compound having a cyclic structure in the molecule. These (meth) acrylate compounds have high photocurability and little shrinkage when cured. Furthermore, the reproducibility of the sol-gel phase transition is high.

(1) A trifunctional or higher functional methacrylate or acrylate compound having 3 to 14 structures represented by (—C (CH ₃ ) H—CH ₂ —O—) in the molecule is, for example, 3 or more A hydroxyl group of a compound having a hydroxyl group is modified with propylene oxide, and the resulting modified product is esterified with (meth) acrylic acid. Specific examples of this compound include
3PO-modified trimethylolpropane triacrylate Photor 4072 (molecular weight 471, Clog P4.90, manufactured by Cognis),
3PO-modified trimethylolpropane triacrylate Miramer M360 (molecular weight 471, Clog P4.90, manufactured by Miwon) and the like are included.

(2) The bifunctional or higher functional methacrylate or acrylate compound having a cyclic structure in the molecule is obtained by esterifying the hydroxyl group of a compound having two or more hydroxyl groups and tricycloalkane with (meth) acrylic acid. is there. Specific examples of this compound include
Tricyclodecane dimethanol diacrylate NK ester A-DCP (molecular weight 304, Clog P4.69),
Tricyclodecane dimethanol dimethacrylate NK ester DCP (molecular weight 332, Clog P 5.12) and the like are included.

  Another specific example of the photopolymerizable compound A includes 1,10-decandiol dimethacrylate NK ester DOD-N (molecular weight 310, Clog P5.75, manufactured by Shin-Nakamura Chemical Co., Ltd.).

  The photopolymerizable compound preferably further contains a photopolymerizable compound other than the photopolymerizable compound A. Other than the photopolymerizable compound A, for example, a (meth) acrylate monomer or oligomer having a ClogP value of less than 4.0; a (meth) acrylate monomer or oligomer having a ClogP value of more than 7.0, or other polymerizability There are oligomers and the like.

(Photopolymerizable compound B)
The actinic ray curable inkjet ink of the present invention has a structure having a molecular weight in the range of 300 to 1500 and represented by (—CH ₂ —CH ₂ —O—) as a photopolymerizable compound. 3 to 14 (meth) acrylate compound (hereinafter also referred to as “photopolymerizable compound B”) is preferably included.

  The molecular weight of the photopolymerizable compound B is preferably in the range of 300 to 1500, and more preferably in the range of 300 to 800. By selecting the photopolymerizable compound B having a molecular weight of 300 or more, there is little volatilization at the nozzles of the inkjet ink, and the ejection stability is not impaired. On the other hand, when the photopolymerizable compound B having a molecular weight exceeding 1500 is contained, the sol viscosity of the ink becomes excessively high.

  The photopolymerizable compound B is a (meth) acrylic acid ester and has an ethylene glycol unit. In addition, the photopolymerizable compound B preferably has two or more (meth) acryl groups; specifically, it preferably has 2, 3 or 4 (meth) acryl groups.

Examples of the photopolymerizable compound B include, but are not limited to, the following.
4EO-modified hexanediol diacrylate (CD561, molecular weight 358) manufactured by Sartomer, 3EO-modified trimethylolpropane triacrylate (SR454, molecular weight 429), 4EO-modified pentaerythritol tetraacrylate (SR494, molecular weight 528), 6EO-modified trimethylolpropane triacrylate Acrylate (SR499, molecular weight 560);
Shin-Nakamura Chemical Co., Ltd. polyethylene glycol diacrylate (NK ester A-400, molecular weight 508), (NK ester A-600, molecular weight 708), polyethylene glycol dimethacrylate (NK ester 9G, molecular weight 536; NK ester 14G, molecular weight 736) );
Examples include tetraethylene glycol diacrylate (V # 335HP, molecular weight 302) manufactured by Osaka Organic Chemical Co., Ltd.

  The content of the photopolymerizable compound B contained in the actinic ray curable inkjet ink of the present invention is preferably 30 to 70% by mass with respect to the total mass of the ink. When the content of the photopolymerizable compound B is less than 30% by mass, the content of the photopolymerizable compound A is relatively increased. For this reason, the gelling agent is not sufficiently precipitated (crystallized) in the ink after landing. On the other hand, when the content of the photopolymerizable compound B exceeds 70% by mass, not only the viscosity of the sol-like ink is increased but also the solubility of the gelling agent tends to be lowered in the sol-like ink.

(Other photopolymerizable compounds)
The actinic ray curable inkjet ink of the present invention may further contain other photopolymerizable compounds. Other photopolymerizable compounds preferably have an average functional group number of 2 or more (having an average of 2 or more (meth) acryl groups per molecule) from the viewpoint of improving photocurability.

Examples of other photopolymerizable compounds include, but are not limited to:
BASF Lamarer PE9074 (average functional group number: 2);
Sartomer CN2270 (average functional group number: 2), CN2273 (average functional group number: 2), CN2303 (average functional group number: 6), CN2302 (average functional group number: 16);
ETERCURE 6361-100 (average functional group number: 8), ETERCURE 6362-100 (average functional group number: 12 to 15) manufactured by ETERNAL CHEMICAL;
M-6200 (average functional group number: 2), M-6250 (average functional group number: 2) manufactured by Toagosei Co., Ltd.

  The content of the other photopolymerizable compound contained in the actinic ray curable inkjet ink of the present invention is preferably 5.0 to 20.0% by mass with respect to the total mass of the ink, and 7.0 to 15. More preferably, it is 0% by mass. When the content of the other photopolymerizable compound is less than 5% by mass, it is difficult to stably gel (crystallize). On the other hand, when the content of the other photopolymerizable compound exceeds 20% by mass, not only the viscosity of the sol ink becomes high, but also the solubility of the gelling agent at the time of sol formation (at high temperature) tends to be lowered.

  It is preferable to mix the photopolymerizable compound A having a relatively high hydrophobicity and the photopolymerizable compound B having a relatively high hydrophilicity into the actinic ray curable inkjet ink in a highly uniform state. Other photopolymerizable compounds may be hydrophilic or hydrophobic. It is presumed that a gelling agent having a hydrophobic part and a hydrophilic part can be stably present in these photopolymerizable compounds while maintaining high uniformity. Therefore, the sol-gel phase transition of the ink can be performed more stably and rapidly even with a small amount of the photopolymerizable gelling agent contained in the actinic ray curable inkjet ink.

<About gelling agent>
The gelling agent contained in the actinic ray curable inkjet ink has a function of reversibly sol-gel phase transition of the ink depending on the temperature. Such a gelling agent must be at least 1) soluble in the photopolymerizable compound at a temperature higher than the gelation temperature, and 2) crystallized in the ink at a temperature below the gelation temperature. is there.

  When the gelling agent crystallizes in the ink, it is preferable to form a space three-dimensionally surrounded by plate crystals which are crystallized products of the gelling agent, and to enclose the photopolymerizable compound in the space. Thus, the structure in which the photopolymerizable compound is encapsulated in the space three-dimensionally surrounded by the plate crystal is sometimes referred to as “card house structure”. When the card house structure is formed, the liquid photopolymerizable compound can be held and 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 photopolymerizable compound dissolved in the ink and the gelling agent are compatible. On the other hand, when the photopolymerizable compound dissolved in the ink and the gelling agent are phase-separated, it may be difficult to form a card house structure.

  In order to stably discharge ink droplets from the ink jet recording apparatus, it is necessary that the compatibility of the photopolymerizable compound and the gelling agent is good in the sol-like ink (at a high temperature). Furthermore, in order to stably suppress coalescence of droplets even during high-speed printing, after the ink droplets have landed on the recording medium, the gelling agent quickly crystallizes to form a strong card house structure. is necessary.

(Photopolymerizable gelling agent)
The actinic ray curable inkjet ink of the present invention contains at least one photopolymerizable gelling agent. The photopolymerizable gelling agent is a compound having an alkyl chain having 12 or more carbon atoms in the structure and having at least one photopolymerizable group. The photopolymerizable group may be a (meth) acryl group. From the viewpoint of curability, the photopolymerizable gelling agent is preferably a polyfunctional photopolymerizable gelling agent having two or more photopolymerizable groups per molecule. The alkyl chain may be any one of a linear alkyl chain, a branched alkyl chain, and a cyclic alkyl chain, and is preferably a linear alkyl chain or a branched alkyl chain.

  Examples of monofunctional photopolymerizable gelling agents include stearyl (meth) acrylate, isostearyl (meth) acrylate, lauryl (meth) acrylate, myristyl (meth) acrylate, cetyl (meth) acrylate, or oleyl (meth) Acrylate and the like are included. Examples of commercially available monofunctional photopolymerizable gelling agents include STA (stearyl acrylate, Osaka Organic Chemical Industry), S-1800A (isostearyl acrylate, Shin-Nakamura Chemical Co., Ltd.), or light acrylate L. -A (lauryl acrylate, Kyoeisha Chemical Company) and the like are included.

  The polyfunctional photopolymerizable gelling agent may be obtained by adding a photopolymerizable group to a diol having 12 or more carbon atoms, which will be described later.

  The content of the photopolymerizable gelling agent in the actinic ray curable inkjet ink of the present invention is preferably 0.5 to 10.0% by mass, and 1.0 to 7.0% by mass with respect to the total mass of the ink. % Is more preferable. When the content of the photopolymerizable gelling agent is less than 0.5% by mass, the ink droplets are hardly gelled (sol-gel phase transition depending on temperature), and thus the pinning property tends to be lowered. On the other hand, when the content of the photopolymerizable gelling agent exceeds 10.0% by mass, the photopolymerizable group of the photopolymerizable gelling agent is affected by oxygen and cannot be sufficiently polymerized. The unpolymerized photopolymerizable gelling agent tends to appear on the image surface and tends to cause blooming. Moreover, since there are many components which are not superposed | polymerized, the abrasion property of an image tends to become low.

  Since the actinic radiation curable inkjet ink of the present invention contains a photopolymerizable gelling agent, the photopolymerizable gelling agent can be polymerized together with the photopolymerizable compound in the ink droplets. Therefore, the gelling agent hardly appears on the image surface, and blooming can be suppressed.

  The photopolymerizable gelling agent can be produced, for example, by a synthesis method described in JP-A-10-218946. Specifically, it can be produced by adding a photopolymerizable group to an alcohol having a linear or branched alkyl chain having 12 to 50 carbon atoms or a carboxylic acid having a linear or branched alkyl chain having 12 to 50 carbon atoms.

  For example, it is obtained by reacting an alcohol having a linear or branched alkyl chain having 12 to 50 carbon atoms with a carboxylate of (meth) acrylic acid. Hydroxyl-terminated polyethylene wax can be used for this alcohol. The hydroxyl-terminated polyethylene wax may have only one hydroxyl group or two or more. From the viewpoint of introducing a plurality of photopolymerizable groups, it is preferable to have two or more hydroxyl groups.

  Examples of hydroxyl-terminated polyethylene waxes having one or more hydroxyl groups include “Dimer Acids”, “Kird-Othmer Encyclopedia of Chemical Technology, Vol. 8,4th E.M. (1992), p223-237; examples of commercially available products include Pripol 2030, Pripol 2033 (above, Croda), UNILIN 350 alcohol, UNILIN 425 alcohol, UNILIN 550 alcohol, UNILIN 700 alcohol, etc. included.

  The photopolymerizable gel can also be obtained by reacting a carboxylic acid having a linear or branched alkyl chain having 12 to 50 carbon atoms with an alcohol having a (meth) acryl group. As this carboxylic acid, a carboxylic acid-terminated polyethylene wax can be used. The carboxylic acid-terminated polyethylene wax may have only one carboxyl group or may have two or more. From the viewpoint of introducing a plurality of photopolymerizable groups, it is preferable to have two or more carboxyl groups.

  Examples of carboxylic acid-terminated polyethylene waxes having a linear or branched alkyl chain with 12 to 50 carbon atoms include: n = 14 hexadecanoic acid or palmitic acid; n = 15 heptadecanoic acid, margaric acid or dullic acid; n = 16 Octadecanoic acid or stearic acid; n = 18 eicosanoic acid or arachidic acid; n = 20 docosanoic acid or behenic acid; n = 22 tetracosanoic acid or lignoceric acid; n = 24 hexacosanoic acid or serotic acid; n = 25 N = 26 octacosanoic acid or montanic acid; n = 28 triacontanic acid or melicic acid; n = 30 dotriacontanoic acid or raceroic acid; n = 31 tritriacontanoic acid, cellomelicin Acid or psylic acid; Underlying motive acid or Gejin acid; pentatriacontanoic proximal acid or Seropurasuchin acids such n = 33 is included.

  Examples of commercially available carboxylic acid-terminated polyethylene waxes having one or more carboxyl groups include Pripol 1009, Pripol 1012, Pripol 1013, Pripol 1017, Pripol 1022, or Pripol 1040 manufactured by Croda; about UNICID 350Mn manufactured by BAKER HUGHES: 390 g / mol), UNICID 425 (Mn: about 475 g / mol), UNICID 550 (Mn: about 565 g / mol), or UNICID 700 (Mn: about 720 g / mol).

  Examples of the alcohol having a photopolymerizable group to be reacted with the carboxylic acid include 2-allyloxyethanol; SR495B manufactured by Sartomer; TONE M-100, TONE M-101, and TONE M-201 manufactured by The Dow Chemical. A CD572 manufactured by Sartomer, SR604, and the like.

(Other gelling agents)
The actinic ray curable ink-jet ink of the present invention may further contain a gelling agent having no photopolymerizability (hereinafter also referred to as “other gelling agent”).

Other gelling agents are not particularly limited. Preferred examples of other gelling agents include
Dibehenyl ketone, distearyl ketone, dipalmityl ketone, dimyristyl ketone, dilauryl ketone, palmityl stearyl ketone, stearyl behenyl ketone, 18-Pentriacontanon (for example, reagent manufactured by Alfa Aeser), ketone wax (for example, manufactured by Kao Corporation) Aliphatic ketone compounds such as Kao wax T1);
Behenyl behenate (for example, Unistar M-2222SL manufactured by NOF Corporation), stearyl stearate (for example EXCEPARL SS manufactured by Kao Corporation), cetyl palmitate (for example, Amreps PC manufactured by Higher Alcohol Industry Co., Ltd.), palmitic acid stearate, myristic acid Aliphatic monoester compounds such as myristyl, lauryl laurate, myricyl cellotate, and behenyl montanate;
Petroleum waxes such as paraffin wax, microcrystalline wax, petrolactam;
Plant waxes such as candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and jojoba ester;
Animal waxes such as beeswax, lanolin and whale wax;
Mineral waxes such as montan wax and hydrogenated wax;
Hydrogenated castor oil or hydrogenated castor oil derivative;
Modified waxes such as montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives or polyethylene wax derivatives;
Higher fatty acids such as behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid;
Higher alcohols such as stearyl alcohol and behenyl alcohol;
Hydroxystearic acid such as 12-hydroxystearic acid;
12-hydroxystearic acid derivatives; fatty acid amides 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 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 stearamide and N-oleyl palmitate amide;
Special fatty acid amides such as N, N′-ethylenebisstearylamide, N, N′-ethylenebis-12-hydroxystearylamide, and N, N′-xylylenebisstearylamide;
Higher amines such as dodecylamine, tetradecylamine or octadecylamine;
Fatty acid ester compounds such as 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. Series, etc.);
Esters of sucrose fatty acids such as sucrose stearic acid and sucrose palmitic acid (eg Ryoto Sugar Ester series manufactured by Mitsubishi Chemical Foods);
Synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax (such as UNILIN series manufactured by Baker-Petrolite);
Dimer acid;
Dimer diol (such as PRIDA series manufactured by CRODA) is included.

  Only one kind of other gelling agent may be contained in the actinic ray curable ink-jet ink, or two or more kinds thereof may be contained. Moreover, when using a commercial item, since it is a mixture of 2 or more types in many cases, you may isolate | separate and refine | purify as needed.

  Other gelling agents are particularly preferably aliphatic ketone compounds, aliphatic monoester compounds, higher fatty acids, higher alcohols, and fatty acid amides, and more preferably aliphatic ketone compounds or aliphatic monoester compounds.

  The total content of the gelling agent contained in the actinic ray curable inkjet ink is 0.5 to 10.0% by mass, preferably 1.0 to 7.0% by mass, based on the total mass of the ink. . When the content of the gelling agent is less than 0.5% by mass, the ink droplets are hardly gelled (sol-gel phase transition depending on temperature), and thus the pinning property tends to be lowered. On the other hand, when the content of the gelling agent exceeds 10% by mass, the gelling agent cannot be sufficiently dissolved in the ink, and the ejection properties of the ink droplets are likely to be lowered. From the viewpoint of suppressing blooming, etc., it is preferable that the actinic ray curable ink-jet ink does not contain a gelling agent (other gelling agent) that does not have photopolymerizability.

<About photopolymerization initiator>
The actinic ray curable inkjet ink further contains a photopolymerization initiator.
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.

  When the photopolymerization initiator is acyl phosphine oxide or acyl phosphonate, the sensitivity is good. Specifically, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide, and the like are preferable.

  The content of the photopolymerization initiator in the actinic ray curable inkjet ink is preferably 0.1% by mass to 10% by mass, although it depends on the light irradiated at the time of ink curing and the type of the photopolymerizable compound. More preferably, it is 2-8 mass%.

  The photopolymerization initiator in the actinic ray curable inkjet ink may contain a photoacid generator. Examples of photoacid generators include chemically amplified photoresists and compounds used for photocationic polymerization (Organic Materials Research 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, if 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. Only one kind of these compounds may be contained in the actinic ray curable inkjet ink, or two or more kinds thereof may be contained.

  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.

<About color materials>
The actinic ray curable inkjet ink may further contain a coloring material. The colorant can be a dye or a pigment. A pigment is more preferable because it has good dispersibility with respect to the components of the ink and is excellent in weather resistance.

  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.), 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, manufactured by Bayer Japan), KAYASET Yellow SF-G, KAYASET Yellow 2G, KAYASET Yellow AG, KAYASET Yellow EG (above, manufactured by 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 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 average particle size of the pigment is preferably 0.08 to 0.5 μm, and the maximum particle size of the pigment is preferably 0.3 to 10 μm, more preferably 0.3 to 3 μm. By adjusting the particle size of the pigment, clogging of the nozzles of the ink jet recording head can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained.

  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.

  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.

  In order to improve the dispersibility of the pigment, the actinic ray curable inkjet ink may further contain a dispersant. 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. Although a solvent may be included in the ink as a dispersion medium, in order to suppress the residual solvent in the formed image, the above-described photopolymerizable compound (particularly a monomer having a low viscosity) should be a dispersion medium. Is preferred.

<About 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.

<About Sol-Gel Phase Transition Inkjet Ink>
Since the actinic radiation curable inkjet ink contains a gelling agent as described above, it undergoes a sol-gel phase transition reversibly depending on the temperature. Actinic ray curable ink that undergoes a sol-gel phase transition is a liquid (sol) at a high temperature (for example, about 80 ° C.), and therefore can be ejected in a sol state from an inkjet 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 properties of the ink droplets, 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 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 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 a conventional actinic ray curable inkjet ink that undergoes a sol-gel phase transition, the gelling agent sometimes blooms on the image surface even if dot coalescence of the formed image can be suppressed. In contrast, when the gelling agent contained in the actinic ray curable inkjet ink is a photopolymerizable gelling agent, blooming of the image surface can be suppressed.

  However, if the content of the photopolymerizable gelling agent contained in the actinic radiation curable inkjet ink is large, the photopolymerizable gelling agent may not be sufficiently polymerized during photocuring due to the influence of oxygen inhibition. Therefore, a photopolymerizable gelling agent that has not been polymerized tends to appear on the image surface and tends to cause blooming. Moreover, since there are many components which are not superposed | polymerized, it is easy to become low in abrasion property.

  In contrast, the inventors of the present invention provide a photopolymerizable gelling agent and a photopolymerizable compound that dissolves the photopolymerizable gelling agent well in ink, maintains it uniformly, and stably exists. , Combined. It has been found that by combining these, the sol-gel phase transition of the ink can be performed more stably and rapidly even with a small amount of the photopolymerizable gelling agent contained in the actinic ray curable inkjet ink. As a result, an image having scratch resistance and less blooming was obtained.

<About the preparation method of inkjet ink>
The actinic ray curable ink-jet ink is obtained by mixing the above-mentioned photopolymerizable compound, gelling agent, photopolymerization initiator, and coloring material under heating. Preferably, a pigment dispersant in which a color material (particularly a pigment) is dispersed in a part of the photopolymerizable compound is prepared and mixed with the pigment dispersant and other ink components. The obtained ink is preferably filtered through 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 ejecting an actinic ray curable ink jet ink from an ink jet recording head and adhering it onto a recording medium (2) The ink droplets landed on the recording medium are irradiated with light from an LED light source and the ink Curing the droplet

<About (1) process>
The actinic ray curable inkjet ink may be any inkjet ink as described above.
Ink droplets are ejected from the ink jet recording head. In order to improve the ejection properties of the ink droplets, it is preferable to set the temperature of the inkjet ink in the inkjet recording head to a temperature that is 10 to 30 ° C. higher than the gelation temperature of the ink. When the ink temperature in the ink jet recording head is less than the gelation temperature + 10 ° C., the ink gels in the ink jet recording head or on the nozzle surface, and the ejection properties of the ink droplets are likely to deteriorate. On the other hand, when the temperature of the ink in the ink jet recording head exceeds the gelation temperature + 30 ° C., the ink becomes too high, and the ink component may deteriorate.

  The ink is heated by an ink jet recording head of the ink jet recording apparatus, an ink flow path connected to the ink jet recording head, an ink tank connected to the ink flow path, or the like.

  The amount of droplets ejected from each nozzle of the inkjet recording head is preferably 0.5 to 10 pl, although it depends on the resolution of the image. In order to form a high-definition image, 0 More preferably, it is 5-2.5 pl. In order to form a high-definition image with such a droplet amount, the ink after landing does not coalesce; that is, the ink needs to undergo a sol-gel phase transition sufficiently. In the above-mentioned actinic ray curable inkjet ink, the sol-gel transition is rapidly performed. Therefore, a high-definition image can be stably formed even with such a droplet amount.

  The ink droplets that have landed on the recording medium are cooled and rapidly gelled by the sol-gel phase transition. As a result, the ink droplets can be pinned without diffusing. Furthermore, since it is difficult for oxygen to enter the ink droplets, the curing of the photopolymerizable compound is not easily inhibited by oxygen.

  The recording medium may be paper or a resin film. Examples of paper include coated paper for printing, coated paper B for printing, and the like. Examples of the resin film include a polyethylene terephthalate film, a polypropylene film, and a vinyl chloride film.

  Here, by ejecting ink droplets from the ink jet recording head, the ink droplets adhere to the recording medium. The temperature of the recording medium when the ink droplet lands is preferably set to a temperature that is 10 to 20 ° C. lower than the gelation temperature of the ink. If the temperature of the recording medium is too low, the ink droplets gel excessively and pinning, so that the ink droplets are not sufficiently leveled and the image gloss may be lowered. On the other hand, if the temperature of the recording medium is too high, the ink droplets are difficult to gel, and adjacent dots of the ink droplets may be mixed together. By appropriately adjusting the temperature of the recording medium, it is possible to achieve appropriate leveling and appropriate pinning so that adjacent dots of ink droplets do not mix with each other.

  In the actinic ray curable inkjet ink of the present invention, the gelling agent is stably dissolved in the ink droplet (photopolymerizable compound A). Therefore, the temperature of the recording medium may be adjusted to adjust the gloss of the image.

  The conveyance speed of the recording medium is preferably 500 to 2000 mm / s. The higher the conveyance speed, the higher the image forming speed, which is preferable. However, when the conveyance speed is too high, the image quality is deteriorated or the photocuring (described later) of the ink becomes insufficient.

<(2) Process>
By irradiating light from the LED light source to the ink droplets that have landed on the recording medium, the photopolymerizable compound contained in the ink droplets is cross-linked or polymerized to cure the ink droplets.

  The light applied to the ink droplets attached to the recording medium is preferably ultraviolet light from an LED light source. Specific examples include a 395 nm, water-cooled LED, etc. manufactured by Phoseon Technology. A metal halide lamp is an example of a general ultraviolet light source. By using an LED as a light source, ink droplets are melted by the radiant heat of the light source; it can.

The LED light source is installed such that ultraviolet rays of 360 nm or more and less than 410 nm are provided so that the peak illuminance on the image surface is 0.5 to 10 W / cm ^2, and more preferably 1 to 5 W / cm ² . Further, it is preferable that the amount of light applied to the image is less than 350 mJ / cm ² . This is to prevent the radiant heat from being applied to the ink droplets.

  The light irradiation to the ink droplets is performed within 10 seconds after the ink droplets adhere on the recording medium, preferably 0.001 seconds to 5 seconds, in order to prevent the adjacent ink droplets from being united with each other. Within a range of 0.01 second to 2 seconds. The light irradiation is preferably performed after ejecting ink droplets from all the ink jet recording heads accommodated in the head carriage.

3. Inkjet recording apparatus The inkjet recording method can be performed by an actinic ray curable inkjet recording apparatus. 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 stores a head carriage 16 that houses a plurality of inkjet recording heads 14, an ink flow path 30 connected to the head carriage 16, and ink supplied through the ink flow path 30. An ink tank 31 that covers the entire width of the recording medium 12, a light irradiation unit 18 that is disposed downstream of the head carriage 16 (in the conveyance direction of the recording medium), and a temperature control unit that is disposed on the lower surface of the recording medium 12. 19 and.

  On the other hand, in the ink jet recording apparatus 10 of FIG. 1, the head carriage 16 and the light irradiation unit 18 are arranged in this order. In this apparatus, ink is ejected onto the recording medium 12, and ink droplets are collectively exposed by the light irradiation unit 18.

  The head carriage 16 of the ink jet recording apparatus 10 includes a head carriage for each color. The head carriage 16 is fixedly arranged so as to cover the entire width of the recording medium 12, as shown in FIG. 1B, for example, and accommodates a plurality of ink jet recording heads.

  Ink is supplied to the ink jet 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 inkjet recording heads 14 are arranged in the conveyance direction of the recording medium 12 for each color. The number of inkjet recording heads 14 arranged in the conveyance direction of the recording medium 12 is set according to the nozzle density of the inkjet 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 inkjet recording head 14 having a droplet amount of 2 pl and a nozzle density of 360 dpi, the four inkjet recording heads 14 may be arranged so as to be shifted with respect to the conveyance direction of the recording medium 12. That's fine. Further, when an image having a resolution of 720 × 720 dpi is formed using the ink jet recording head 14 having a droplet amount of 6 pl and a nozzle density of 360 dpi, the two ink jet recording heads 14 may be arranged in a shifted manner. dpi represents the number of ink droplets (dots) per 2.54 cm.

  The ink tank 31 is connected to the head carriage 16 via the ink flow path 30. The ink flow path 30 is a path for supplying the ink in the ink tank 31 to the head carriage 16. In order to stably eject ink droplets, the ink in the ink tank 31, the ink flow path 30, the head carriage 16, and the ink jet recording head 14 is heated to a predetermined temperature to maintain the gel state.

  The light 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 conveyance direction of the recording medium. The light irradiation unit 18 irradiates the ink droplets ejected by the inkjet recording head 14 and landed on the recording medium 12 with light, thereby curing the droplets.

  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 ink jet recording method using the line recording type ink jet recording apparatus 10 will be described. In the recording apparatus of FIG. 1, 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 droplets are ejected from the ink jet recording head 14 of the head carriage 16 and adhered (landed) on the recording medium 12.

  After that, the light irradiating unit 18 irradiates the ink droplets attached on the recording medium 12 with light to cure.

  The total ink droplet thickness after curing is preferably 2 to 25 μm. The “total ink droplet thickness” is the maximum value of the thickness of the ink cured film 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 includes a plurality of inkjet recording heads that are narrower than the entire width of the recording medium, instead of the head carriage 16 that is fixedly arranged so as to cover the entire width of the recording medium. 1 can be configured except that a head carriage 26 that accommodates 24 and a guide portion 27 for moving the head carriage 26 in the width direction of the recording medium 12 are provided.

  In the serial recording type inkjet recording apparatus 20, an ink droplet is ejected from the inkjet recording head 24 accommodated in the head carriage 26 while the head carriage 26 moves 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. Then, the light irradiating unit 28 irradiates the ink droplets adhered on the recording medium 12 with light. Except for these operations, an image is recorded in substantially the same manner as the line recording type inkjet recording apparatus 10 described above.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the embodiments of the present invention are not limited to these examples.

<Preparation of ink>
The actinic ray curable ink-jet ink of each example and comparative example was prepared with the following components.

(Pigment dispersion)
Preparation of Pigment Dispersion A pigment dispersion was prepared according to the following procedure. The following two compounds were placed in a stainless beaker and dissolved by stirring and heating for 1 hour while heating on a hot plate at 65 ° C.
Pigment dispersant: EFKA7701 (manufactured by BASF) 9 parts by mass Actinic radiation curable monomer: APG-200 (tripropylene glycol diacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.) 71 parts by mass Pigment Black as a pigment after cooling to room temperature 7 (Mitsubishi Chemical Co., Ltd., # 52) 20 parts by mass was added together with 200 g of zirconia beads having a diameter of 0.5 mm, sealed in a glass bottle, and dispersed with a paint shaker for 5 hours. Thereafter, the zirconia beads were removed to prepare a pigment dispersion.

(Photopolymerizable compound A)
Miramer M360 (manufactured by Miwon): trimethylolpropane PO-modified triacrylate, molecular weight 471, ClogP value 4.90
NK ester A-DCP (manufactured by Shin-Nakamura Chemical Co., Ltd.): tricyclodecane dimethanol diacrylate, molecular weight 304, ClogP value 4.69
NK ester DOD-N (manufactured by Shin-Nakamura Chemical Co., Ltd.): 1,10-decanediol dimethacrylate, molecular weight 310, ClogP value 5.75
Photomer 4072 (manufactured by Cognis): 3PO-modified trimethylolpropane triacrylate, molecular weight 471, Clog P value 4.90

(Photopolymerizable compound B)
NK ester A-400 (manufactured by Shin-Nakamura Chemical Co., Ltd.): polyethylene glycol diacrylate, molecular weight 508, EO unit amount 9, ClogP value 0.47
CD561 (manufactured by Sartomer): 4EO-modified hexanediol diacrylate, molecular weight 358, ClogP value 2.52
SR499 (manufactured by Sartomer): 6EO-modified trimethylolpropane triacrylate, molecular weight 560, ClogP value 3.57
SR494 (manufactured by Sartomer): 4EO-modified pentaerythritol tetraacrylate, molecular weight 528, Clog P value 2.28

(Other photopolymerizable compounds)
Laromer PE9074 (BASF)
CN2270 (Sartomer)

(Gelling agent)
Photopolymerizable gelling agent STA (manufactured by Osaka Organic Chemical Industry Co., Ltd.): Compound obtained by acrylated stearyl acrylate Pripol 2033 (Croda) Unilin350 (BAKER HUGHES) acrylated compound Other gelling agent Kao wax T1 ( Manufactured by Kao)
Behenic acid (Lunac BA, manufactured by Kao Corporation)
FATTY AMID T (manufactured by Kao Corporation)

(Surfactant)
KF-352 (manufactured by Shin-Etsu Chemical Co., Ltd.)

(Photopolymerization initiator)
DAROCURE TPO (made by BASF)
ITX (manufactured by DKSH Japan)

(Sensitization aid)
Kayacure EPA (manufactured by Nippon Kayaku Co., Ltd.)

  Each component was mixed according to the composition (parts by mass) shown in Tables 1 and 2 below, and the mixture was heated to 80 ° C. and stirred. While maintaining the temperature of the obtained solution, the solution was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC to prepare inks of Examples 1 to 11 and Comparative Examples 1 to 8. The following evaluation was performed on this ink.

<Ink state>
(Gel dissolution stability)
The actinic ray curable ink-jet ink was allowed to stand in a constant temperature bath at 105 ° C. for 2 hours. About the ink after stationary, the melt | dissolution state of the gelatinizer was confirmed visually and evaluated based on the following reference | standard. The results are shown in Tables 1 and 2.
○: No separation or precipitation ×: Oil balls are gathered on the surface (separated layers)

(Sol-gel phase transition temperature)
The sol-gel phase transition temperature was measured with a viscoelasticity measuring device MCR300 manufactured by Physica, share rate 11 (1 / s). In the temperature change curve of the viscosity, the temperature at which the viscosity becomes 200 mPa · s was defined as the sol-gel phase transition temperature. The results are shown in Tables 1 and 2.

<Inkjet recording method>
Each ink prepared in Examples and Comparative Examples was loaded into a Bk head of a single-pass ink jet recording apparatus (FIG. 1) having a piezo ink jet recording head. From this apparatus, recording was performed on a printing coat (OK Kanto +, rice basis weight 127.9 g / m ² , manufactured by Oji Paper Co., Ltd.).

  As the ink jet recording apparatus, an ink supply system having an ink tank, an ink flow path, a sub ink tank immediately before the ink jet recording head, a pipe with a filter, and a piezo head was used. During image formation, the ink from the ink tank to the head portion was heated to 90 ° C. A voltage was applied so that a 2 pl droplet was ejected from the ink jet recording apparatus. In addition, the ink jet recording head has two nozzle heads with a nozzle resolution of 600 dpi and has a nozzle resolution of 1200 dpi (where dpi represents the number of dots per 2.54 cm). Using this inkjet recording apparatus, a monochrome solid image of 1200 × 1200 dpi, 3pt Mincho black characters, 3pt Mincho white characters (outline characters in the solid image) were formed.

After printing, light (395 nm, 8 W / cm ² , water cooled unit) was irradiated from an LED lamp manufactured by Phoseon Technology to cure the ink. The amount of light was measured with a UV integrating light meter C9536, H9958 manufactured by Hamamatsu Photonics. The distance from the LED lamp to the recording medium surface was 20 mm.

  The conveyance speed of the recording medium was 800 mm / second. The temperature of the paper transport table was adjusted and the recording medium was heated to 45 ° C.

<Image evaluation>
(Image quality (outline))
The formed image was evaluated on the basis of the following criteria for the presence of white spots in the solid image portion (unprinted portions due to dot coalescence). The results are shown in Tables 1 and 2.
○: No white spots △: There are white spots in one or two places, but there is no practical problem ×: Many white spots are generated

(Image quality (character quality))
About the formed image, the quality of 3pt Mincho characters was evaluated based on the following criteria. The results are shown in Tables 1 and 2.
○: Both black and white characters are reproduced. △: Some characters are crushed on either black or white characters. ×: Both black and white characters are crushed.

(Glossy)
About the formed image, the glossiness of the solid image part was evaluated based on the following criteria. The results are shown in Tables 1 and 2.
◎: Very homogeneous gloss ○: Uniform gloss △: Image with low gloss overall ×: No gloss

(Abrasion)
About the formed solid image, according to the method described in “JIS standard K5701-1-6.2.3 Friction resistance test”, an appropriately sized recording paper was placed on the image and rubbed together under a load. . Thereafter, the degree of density reduction of the image was visually observed and evaluated based on the following criteria. The results are shown in Tables 1 and 2.
○: No change in image was observed even after rubbing 100 times or more. Δ: Image density decreased at the stage of rubbing 100 times, but in practically acceptable range. X: Clear with rubbing less than 50 times. The image density is noticeable, and the quality is unusable.

(Bending resistance)
For the formed image, the solid image portion was left in an environment of 25 ° C. and 60% RH for 24 hours. Then, this was folded in half and evaluated based on the following criteria. The results are shown in Tables 1 and 2.
○: Image film does not break ×: Image film breaks at the folded part

(Appendability)
A line was drawn on the formed solid image with oily white magic (Pentel Paint Marker Medium White MMP20-W) and evaluated based on the following criteria. The results are shown in Tables 1 and 2.
○: Beautiful lines and characters could be drawn. △: Lines could be drawn, but the lines were slightly thin.

(Image preservation)
The printing surfaces of two printing coats on which solid images were formed were overlapped. The superimposition was subjected to a load of 1 g / cm ² and stored at 60 ° C. for 1 month. Thereafter, the image surface of the printing coat was observed and evaluated based on the following criteria. The results are shown in Tables 1 and 2.
○: The surface gloss is not different from the pre-storage image. Δ: Slight cloudiness was observed on the surface, but it was acceptable for practical use. ×: The surface was denatured such as whitening or powder blowing.

  As shown in Table 1, the inks of Examples 1 to 11 each containing a predetermined amount of the photopolymerizable compound A, the photopolymerization initiator, and the photopolymerizable gelling agent are excellent in gel dissolution stability. In addition, since a predetermined amount of the photopolymerizable gelling agent is contained, blooming of the gelling agent can be suppressed, and writeability, image storage stability, and the like are good. Furthermore, an image with high scratching properties can be formed. In particular, since the inks of Examples 5, 6, and 9 contain a polyfunctional photopolymerizable gelling agent and no other gelling agent, all the evaluation results are excellent.

  On the other hand, as shown in Table 2, the inks of Comparative Examples 1 to 8 that do not contain a predetermined amount of at least one of the photopolymerizable compound A, the photopolymerization initiator, and the photopolymerizable gelling agent are any evaluation items. Has fallen. In Comparative Examples 1 and 2 in which the photopolymerizable compound A is less than the predetermined amount, the photopolymerizable gelling agent cannot be dissolved, and the gel dissolution stability is lowered. In Comparative Example 3 in which the photopolymerizable compound A exceeds a predetermined amount, the curability of the image is lowered and the adhesiveness to the recording medium is lowered, so that the bending resistance is lowered. In Comparative Examples 4 and 5 that do not contain a photopolymerizable gelling agent, the other gelling agent blooms on the image surface, and the write-ontability and image preservability deteriorate. In Comparative Example 6 in which the gelling agent is less than the predetermined amount, the ink droplet cannot be gelled. For this reason, ink droplets cannot be pinned, and white spots and character quality deteriorate. Further, since the content of the photopolymerizable gelling agent is small, the scratching property is also lowered. In Comparative Examples 7 and 8 in which the gelling agent exceeds a predetermined amount, the gelling agent cannot be dissolved in the ink, and the gel dissolution stability is lowered. In Comparative Example 7, the amount of the other gelling agent is large among the gelling agents. Therefore, there are many components that are not polymerized, and the scratching property is also reduced. In addition, other gelling agents cause blooming, and the write-once performance and image resistance are also reduced. Since Comparative Example 8 contains a large amount of a photopolymerizable gelling agent, it is easily affected by oxygen inhibition. Therefore, there are many components that are not polymerized, and the scratching property is also lowered.

  According to the actinic ray curable inkjet ink and the inkjet recording method of the present invention, it is possible to form an image having abrasion resistance and less blooming.

DESCRIPTION OF SYMBOLS 10, 20 Inkjet recording device 12 Recording medium 14, 24 Inkjet recording head 16, 26 Head carriage 18, 28 Light irradiation part 19 Temperature control part 27 Guide part 30 Ink flow path 31 Ink tank

Claims (6)

An actinic ray curable inkjet ink containing a photopolymerizable compound, a photopolymerization initiator, and a gelling agent, and reversibly sol-gel phase transition depending on temperature,
The photopolymerizable compound includes at least one photopolymerizable compound A having a weight average molecular weight of 280 to 1500 and having a PO modification, or a (meth) acrylate compound having a cyclic structure in the molecule ,
The gelling agent contains at least one photopolymerizable gelling agent containing an alkyl chain having 12 or more carbon atoms,
An actinic radiation-curable inkjet ink comprising 10 to 40% by mass of the photopolymerizable compound A and 0.5 to 10.0% by mass of the gelling agent with respect to the mass of the whole ink. The actinic ray curable inkjet ink according to claim 1, wherein the photopolymerizable compound A has a ClogP value of 4.0 to 7.0. The actinic ray curable inkjet according to claim 1 or 2 , wherein the photopolymerizable gelling agent is a polyfunctional photopolymerizable gelling agent having two or more photopolymerizable groups in one molecule. ink. The actinic ray curable inkjet ink according to any one of claims 1 to 3, which does not contain a gelling agent having no photopolymerizability. The photopolymerizable compound further comprises a photopolymerizable compound B having a weight average molecular weight of 300 to 1500 and having a structure represented by (—CH ₂ —CH ₂ —O—) in the molecule of 3 to 14. The actinic ray curable inkjet ink according to any one of claims 1 to 4 , which is contained. An inkjet recording method using the actinic ray curable inkjet ink according to any one of claims 1 to 5 ,
A step of causing ink droplets of the actinic radiation curable inkjet ink to be ejected from an inkjet recording head and adhered onto a recording medium;
Irradiating the droplets landed on the recording medium with light from the LED to cure the ink droplets,
The inkjet recording method according to claim 1, wherein the light has a peak illuminance of 0.5 to 10.0 W / cm ² at 360 to 410 nm.

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