JP6194821B2 - 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 actinic ray curable ink jet method in which an actinic ray curable ink jet ink droplet is landed on a recording medium and then irradiated with an actinic ray to be cured to form an image. The actinic ray 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.

  However, in the recording method using the conventional actinic ray curable inkjet system, it is not possible to suppress the coalescence of adjacent dots when performing high-speed recording such as a single-pass recording method using a line recording head or a high-speed serial method, There was a problem that the image quality was inferior.

  One of the methods for preventing the joining of adjacent dots is a technique of adding a gelling agent to the actinic ray curable inkjet ink. As an inkjet ink to which a gelling agent is added, Patent Document 1 discloses a phase change ink having a photopolymerizable compound, a photoinitiator, a color pigment containing carbon black, and a gelling agent.

JP 2012-246478 A

  Ink jet inks containing a gelling agent are required to sufficiently function a so-called pinning effect in which the ink undergoes phase transition and is fixed by the action of the gelling agent. However, the present inventors have found that the pinning effect is suppressed when carbon black is used as a black pigment in an inkjet ink containing a gelling agent. If pinning is insufficient, the ink spreads and there is a risk of deterioration in image quality and character quality due to the unification of adjacent dots, and the leveling properties differ from other colors, resulting in glossiness with other colors. May cause a difference.

  Accordingly, an object of the present invention is to provide an actinic ray curable inkjet ink and an inkjet recording method capable of forming a high-definition image in which dot coalescence is suppressed while having sufficient curability. . Another object of the present invention is to provide an actinic ray curable inkjet ink and an inkjet recording method capable of providing an image having glossiness that does not give a sense of incongruity when used in combination with other colors.

The present invention first relates to the following actinic ray curable inkjet ink.
[1] An actinic ray curable inkjet ink containing carbon black, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator,
The pH of the carbon black is 2.0 to 5.0,
The molecular weight of the gelling agent is 200 or more and less than 800, ClogP of the gelling agent is 6.0 or more, and the ratio of the gelling agent in the total mass of the ink is 1.0 to 7.0% by mass. Is in range,
The actinic ray curable inkjet ink, wherein the photopolymerizable compound includes a (meth) acrylate compound having a molecular weight of 280 to 1500 and a ClogP value of 4.0 to 7.0.
[2] The actinic ray curable inkjet ink according to [1], wherein the volatile content of the carbon black is less than 10.0%.
[3] The ratio of the carbon black to the specific surface area of the volatile matter represented by volatile matter (%) / specific surface area (m ² / g) × 100 is 1.0 or more and 5.0 or less. [1 ] Or actinic ray curable inkjet ink according to [2].
[4] The actinic ray curable inkjet ink according to any one of [1] to [3], wherein the gelling agent is at least one of the compounds represented by the general formulas (G1) and (G2).
General formula (G1): R1-CO-R2
General formula (G2): R3-COO-R4
(In the formula, R1 to R4 each independently represents an alkyl chain having a straight chain portion having 12 or more carbon atoms and optionally having a branched portion.)

Secondly, the present invention relates to the following inkjet recording method.
[5] A step of causing the actinic ray curable ink-jet ink according to any one of [1] to [4] to be ejected from an ink-jet recording head and adhering to the recording medium, and the ink adhering to the recording medium to be active Irradiating light to cure the ink.
[6] In the curing step, actinic rays having a peak illuminance of 0.5 to 10.0 W / cm ² in a wavelength range of 370 to 410 nm and a light amount of less than 350 mJ / cm ² are irradiated. ] The inkjet recording method as described in.

  According to the present invention, there is provided an actinic ray curable inkjet ink and an inkjet recording method capable of forming an image having sufficient curability, high definition, and glossiness that does not give a sense of incongruity when used in combination with other colors. Provided.

1 is a side view illustrating an example of a configuration of a main part of a line recording type inkjet recording apparatus. FIG. 1B is a top view of FIG. 1A. FIG. 3 is a top view illustrating an example of a configuration of a main part of a serial recording type inkjet recording apparatus.

  Hereinafter, the present invention will be described with reference to embodiments, but the present invention is not limited to the following embodiments.

  The ink according to the present invention is an actinic radiation curable inkjet ink containing carbon black, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator, and the pH of the carbon black is 2.0 to 5.0. The molecular weight of the gelling agent is 200 or more and less than 800, the ClogP of the gelling agent is 6.0 or more, and the ratio of the gelling agent in the total amount of the ink is within the range of 1.0 to 7.0% by mass. The photopolymerizable compound is an actinic ray curable inkjet ink containing a (meth) acrylate compound having a molecular weight of 280 to 1500 and a ClogP value in the range of 4.0 to 7.0.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have used a gelling agent having a molecular weight of 200 or more and less than 800 and ClogP of 6.0 or more, and further lowering the pH of carbon black. Thus, it has been found that the gelling action by the gelling agent is promoted and a sufficient pinning effect can be obtained. As a result, a high-definition image with reduced white streaks and white spots and improved character quality can be obtained, and an image having gloss that does not give a sense of incongruity when used in combination with other colors through sufficient leveling. Can be obtained.

  In the present invention, the reason why the pinning effect is enhanced by setting the molecular weight of the gelling agent to 200 or more and less than 800 and ClogP to 6.0 or more is that the molecular weight of the gelling agent is decreased and ClogP is increased to increase the rule. This is probably because the gelling agent itself is easily gelled by increasing the ratio of the carbon chain.

  In the present invention, the reason why the pinning effect is enhanced by lowering the pH of the carbon black is considered to be due to the low affinity between the carbon black and the gelling agent. That is, since the gelling agent is generally low in polarity, the gelling agent is adsorbed on the carbon black due to hydrophobic interaction with the carbon black having a low polarity. This adsorption makes it difficult for the gelling agents to come close to each other, so that the gelation of the ink by the gelling agent becomes insufficient and the pinning effect is lowered. In contrast, in the present invention, by increasing the polar groups on the surface of the carbon black particles, the carbon black has a higher affinity than the gelling agent by making the carbon black more polar than the gelling agent. doing. Therefore, it becomes difficult for the gelling agent to be adsorbed on the carbon black, and the gelling action by the gelling agent tends to occur. Here, when the number of polar groups present on the surface of the carbon black particles increases, the pH of the carbon black decreases, and carbon black having a low pH tends to have a large number of polar groups on the particle surface. That is, when carbon black having a low pH is selected, the polarity of the selected carbon black is increased, so that a sufficient pinning effect can be obtained.

  The present invention has been made based on the above findings. Hereinafter, the ink according to the present invention will be described through a detailed description of each component.

1. Actinic ray curable inkjet ink The actinic ray curable inkjet ink according to the present invention contains carbon black, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator. Additives and the like may be included.

[About gelling agent]
As the gelling agent according to the present invention, a gelling agent having a molecular weight of 200 or more and less than 800 and ClogP of 6.0 or more is used.

  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. It is preferable that the gelling agent can be dissolved in the photopolymerizable compound at a temperature higher than the gelation temperature, and it can be crystallized in the ink at a temperature lower than the gelation temperature.

  When the gelling agent is crystallized in the ink, it is preferable that a plate crystal which is a crystallized product of the gelling agent forms a space three-dimensionally surrounded, and the photopolymerizable compound is included 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, a liquid photopolymerizable compound can be retained. Thereby, ink droplets can be pinned better, and coalescence of the 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 preferable that the compatibility of the photopolymerizable compound and the gelling agent is good in the sol-like ink (at high temperature). Further, in order to stably suppress the coalescence of the droplets even during high-speed printing, it is preferable that the gelling agent quickly crystallizes after the ink droplets land on the recording medium to form a strong card house structure.

Examples of such gelling agents include
An aliphatic ketone compound;
Aliphatic ester compounds;
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;
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 POM 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);
Fatty acid inulins such as inulin stearate;
Fatty acid dextrins such as dextrin palmitate and dextrin myristate (such as Leopard series manufactured by Chiba Flour Mills);
Glyceryl behenate eicosane diacid;
Eicosane polyglyceryl behenate (Nomshin Eulio Co., Ltd. Nomucoat series, etc.);
Amide compounds such as N-lauroyl-L-glutamic acid dibutylamide and N- (2-ethylhexanoyl) -L-glutamic acid dibutylamide (available from Ajinomoto Fine-Techno);
Dibenzylidene sorbitols such as 1,3: 2,4-bis-O-benzylidene-D-glucitol (available from Gelol D Shin Nippon Chemical);
Low molecular oil gelling agents described in JP-A-2005-126507, JP-A-2005-255821, and JP-A-2010-1111790;
Etc. are included.

  Among these, examples of gelling agents having a molecular weight of 200 or more and less than 800 and ClogP of 6.0 or more include ethylene glycol distearate, propylene glycol distearate, behenamidopropyldimethylamine, stearoamidoethyl. Stearate, N-stearyl stearic acid amide, N-oleyl stearic acid amide, N-stearyl oleic acid amide, N-stearyl erucic acid amide, palmitic acid amide, distearyl ketone, behenyl alcohol, behenic acid, batyl stearate, stearic acid Stearyl, behenyl behenate, pentaerythritol distearate, cetyl palmitate and the like are included. The gelling agent preferably has a molecular weight of 300 or more and less than 600 and a ClogP of 6.0 or more.

  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 actinic ray curable inkjet ink of the present invention includes a compound containing an alkyl chain having a straight chain portion having 12 or more carbon atoms and optionally having a branch as a gelling agent. When the gelling agent contains a linear alkyl group having 12 or more carbon atoms, the aforementioned “card house structure” is easily formed.

  Specific examples of the gelling agent containing a linear alkyl group having 12 or more carbon atoms include aliphatic ketone compounds, aliphatic ester compounds, higher fatty acids, higher alcohols having a linear alkyl group having 12 or more carbon atoms, Fatty acid amides and the like are included.

Here, when a gelling agent such as an aliphatic ketone compound or an aliphatic ester compound that does not have a polar group such as —OH or —COOH at the end of the alkyl chain is used, the stability in the sol-like ink is improved. It becomes better, and it becomes difficult to precipitate or separate layers. Moreover, such a gelling agent is hard to elute from the cured film of the ink after hardening. Therefore, the gelling agent can be a compound represented by the following general formula (G1) or (G2).
General formula (G1): R1-CO-R2
General formula (G2): R3-COO-R4
In the general formulas (G1) and (G2), R1 to R4 each independently represent an alkyl chain having a straight chain portion having 12 or more carbon atoms and which may have a branch.

  In the general formula (G1), the hydrocarbon groups represented by R1 and R2 are preferably each independently an aliphatic hydrocarbon group including a straight chain portion having 12 or more carbon atoms, and 12 or more and 25 or less. It is more preferable that it is an aliphatic hydrocarbon group containing the linear part of. By setting the number of carbon atoms of the straight chain portion contained in the aliphatic hydrocarbon group represented by R1 and R2 to 12 or more, sufficient crystallinity to function as a gelling agent can be obtained. In the card house structure, a sufficient space for encapsulating the photopolymerizable compound can be formed. By setting the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group to 25 or less, the melting point becomes an appropriate range. Therefore, the gelling agent is sufficiently contained in the ink even at the injection temperature of a commonly used ink. Can be dissolved.

  Among the aliphatic ketone compounds represented by the general formula (G1), examples of those that can be used as the gelling agent of the present invention include distearyl ketone (C18-C18, melting point 84 ° C.), dipalmityl ketone. (C16-C16, melting point 80 ° C.), dilauryl ketone (C12-C12, melting point 68 ° C.) and the like.

  Examples of commercially available compounds represented by the general formula (G1) include 18-Pentriacontanon (manufactured by Alfa Aeser), Hentriacontan-16-on (manufactured by Alfa Aeser), Kao wax T1 (manufactured by Kao Corporation), and the like. included.

  The aliphatic ketone compound contained in the actinic ray curable inkjet ink may be only one kind, or may be a mixture of two or more kinds.

  In the general formula (G2), the hydrocarbon group represented by R3 and R4 is not particularly limited, but is preferably an aliphatic hydrocarbon group including a straight chain portion having 12 or more carbon atoms, and is 12 to 26. It is more preferable that it is an aliphatic hydrocarbon group containing the linear part of. By setting the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group represented by R3 and R4 to 12 or more, sufficient crystallinity to function as a gelling agent can be obtained. In the card house structure, a sufficient space for encapsulating the photopolymerizable compound can be formed. By setting the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group to 26 or less, the melting point becomes an appropriate range, so that the gelling agent is sufficiently contained in the ink even at the injection temperature of a commonly used ink. Can be dissolved.

  Examples of the aliphatic ester compound represented by the formula (G2) that can be used as the gelling agent of the present invention include stearyl stearate (C17-C18, melting point 60 ° C.), behenyl behenate (C21— C22, melting point 70 ° C.), cetyl palmitate (C15-C16, melting point 54 ° C.) and the like.

  Examples of commercially available products of the aliphatic ester compound represented by the formula (G2) include Unistar M-2222SL, Unistar M-9676 (manufactured by NOF Corporation), Exepal SS (manufactured by Kao Corporation, melting point 60 ° C.), EMALEXCC-18 (manufactured by Nippon Emulsion Co., Ltd.), Amrep SS, Amrep PC (manufactured by Higher Alcohol Industry Co., Ltd.), etc. Since these commercial products are often a mixture of two or more types, they may be separated and purified as necessary.

  The aliphatic ester compound contained in the actinic ray curable inkjet ink may be only one type or a mixture of two or more types.

  The amount of the gelling agent contained in the actinic ray curable inkjet ink is 1.0 to 7.0% by mass, preferably 1.0 to 3.0% by mass, based on the total amount of the ink. By setting the content to 1.0% by mass or more, the ink can be gelled well (sol-gel phase transition due to temperature), and by setting the content to 7.0% by mass or less, the gelling agent is sufficiently dissolved in the ink. By doing so, the ejection property of the ink can be improved.

[About photopolymerizable compounds]
The actinic ray curable inkjet ink contains a photopolymerizable compound, and the photopolymerizable compound has a molecular weight in the range of 280 to 1500 and a ClogP value in the range of 4.0 to 7.0. A certain (meth) acrylate compound (hereinafter also referred to as “(meth) acrylate compound A”) is included. 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. As the photopolymerizable compound that can be contained in addition to the (meth) acrylate compound A, a radical polymerizable compound can be preferably used, but a cationic polymerizable compound may be used in combination with the (meth) acrylate compound A. The (meth) acrylate compound A preferably has two or more (meth) acrylate groups. Here, “(meth) acrylate” refers to both and / or “acrylate” and “methacrylate”, and “(meth) acryl” refers to both and / or “acryl” and “methacryl”.

((Meth) acrylate compound A)
The molecular weight of the (meth) acrylate compound A is in the range of 280 to 1500, and preferably in the range of 300 to 800. In order to stably eject ink from the ink jet recording head, the ink viscosity at the ejection temperature needs to be between 7 and 14 mPa · s. By including a (meth) acrylate compound having a molecular weight of 280 or more and a gelling agent in the ink composition, the change in the viscosity of the ink before and after the discharge temperature can be reduced, and the ink viscosity is adjusted within the above range. It becomes easy. Moreover, since the (meth) acrylate compound having a molecular weight of 280 or more has less odor, the odor of the actinic ray curable inkjet ink and its cured product can be reduced. On the other hand, an excessive increase in the sol viscosity of the ink can be suppressed by including a (meth) acrylate compound having a molecular weight of 1500 or less.

  The ClogP value of the (meth) acrylate compound A is in the range of 4.0 to 7.0, and preferably in the range of 4.5 to 6.0. When the ClogP value of the (meth) acrylate 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 (meth) acrylate compound A exceeds 7.0, the solubility of the photopolymerization initiator in the ink is lowered, and the curability of the ink is lowered or the ejection property from the ink jet recording head is decreased. Or drop.

  The amount of (meth) acrylate compound A contained in the actinic ray curable inkjet ink is preferably in the range of 10 to 40% by mass. By setting the amount of the (meth) acrylate compound A to 10% by mass or more, the ink does not become too hydrophilic and the gelling agent is sufficiently dissolved in the ink, so that the ink easily undergoes sol-gel phase transition. On the other hand, when the amount of the (meth) acrylate compound A is 40% by mass or less, the photopolymerization initiator can be sufficiently dissolved in the ink. Therefore, ink discharge from the ink jet recording apparatus becomes stable, and shrinkage when the ink is cured is reduced. In addition, curling of printed matter and deterioration of adhesion of the image film to the recording medium can be suppressed.

More preferable examples of the (meth) acrylate compound A include (1) a trifunctional or higher functional group having 3 to 14 structures represented by (—C (CH ₃ ) H—CH ₂ —O—) in the molecule. A methacrylate or acrylate compound and (2) a bifunctional or higher functional methacrylate or acrylate compound having a cyclic structure in the molecule are included. 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)
Etc. 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)
Etc. are included.

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

(Radical polymerizable compounds other than (meth) acrylate compound A)
The radical polymerizable compound other than the (meth) acrylate compound A that can be included in the actinic ray curable inkjet ink is a compound (monomer, oligomer, polymer, or mixture thereof) having a radical 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.

  The radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, and more preferably 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, or the like.

  Examples of (meth) acrylate compounds other than (meth) acrylate compound A include (meth) acrylate monomers or oligomers having a ClogP value of less than 4.0; (meth) acrylate monomers having a ClogP value of more than 7.0, Or there are oligomers and other polymerizable oligomers.

  Examples of these (meth) acrylate monomers or oligomers include 4EO modified hexanediol diacrylate (CD561, manufactured by Sartomer, molecular weight 358); 3EO modified trimethylolpropane triacrylate (SR454, manufactured by Sartomer, molecular weight 429); 4EO-modified pentaerythritol tetraacrylate (SR494, manufactured by Sartomer, molecular weight 528); 6EO-modified trimethylolpropane triacrylate (SR499, manufactured by Sartomer, molecular weight 560); caprolactone acrylate (SR495B, manufactured by Sartomer); polyethylene glycol diacrylate (NK ester A-400, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 508), (NK ester A-600, manufactured by Shin-Nakamura Chemical Co., Ltd., molecule 708); polyethylene glycol dimethacrylate (NK ester 9G, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 536), (NK ester 14G, manufactured by Shin-Nakamura Chemical Co., Ltd.); tetraethylene glycol diacrylate (V # 335HP, manufactured by Osaka Organic Chemical Co., Ltd.) Molecular weight 302); stearyl acrylate (STA, manufactured by Osaka Organic Chemical Co.); phenol EO-modified acrylate (M144, manufactured by Miwon); nonylphenol EO-modified acrylate (M166, manufactured by Miwon) and the like.

  Examples of other polymerizable oligomers include epoxy acrylate, aliphatic urethane acrylate, aromatic urethane acrylate, polyester acrylate, and linear acrylic oligomer.

(Cationically polymerizable compound)
The cationically polymerizable compound that can be contained in the actinic ray curable inkjet ink can be an epoxy compound, a vinyl ether compound, an oxetane compound, or the like. Only one kind of cationic polymerizable compound may be contained in the actinic ray curable inkjet ink, or two or more kinds thereof may be contained.

  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.

活性光線硬化型インクジェットインクにおける光重合性化合物の含有量は、１〜９７質量％であることが好ましく、３０〜９５質量％であることがより好ましい。 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), (7), (8), and (9) described in JP-A-2005-255821 are shown below.

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

[About photopolymerization initiator]
The actinic ray curable inkjet ink 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 carbon black]
The actinic ray curable inkjet ink contains carbon black.
The type of carbon black is not particularly limited as long as the pH is 2.0 to 5.0. Carbon black produced by a known method such as a channel black method, a furnace black method, or an acetylene black method can be used.

  Examples of the carbon black having a pH of 2.0 to 5.0 include, for example, a carbon black containing an acidic functional group such as a sulfonic acid group, a carboxyl group or a hydroxyl group, or a surface treatment of the carbon black to form a sulfonic acid group, a carboxyl group or Carbon black into which an acidic functional group such as a hydroxyl group is introduced is included.

  A known method can be used for the surface treatment of carbon black. Examples of surface treatment methods include a wet surface treatment method in which carbon black is immersed in an acidic solution such as an acetic acid solution or a sulfonic acid solution, an air oxidation method, and a mixture of nitric acid or nitrogen oxide as an oxidizing agent and air. Examples include a dry surface treatment method in which carbon black is brought into contact with gas or ozone.

As a method for measuring the pH of carbon black, a method of measuring a mixed solution of carbon black and distilled water with a glass electrode pH meter, which can be performed by the following procedure, is known.
(1) Collect 5 g of a carbon black sample in a 100 ml container, and add 50 ml of distilled water thereto.
(2) After boiling this for 15 minutes, cool to room temperature.
(3) The electrode of a pH meter (HM-20P, manufactured by Toa DKK Corporation) is immersed in this solution, and the value is read.

  Moreover, carbon black of various pH can be obtained from each manufacturer. Examples of commercially available carbon black products having a pH of 2.0 to 5.0 or less include MA7 (pH 3.0 (manufactured by Mitsubishi Chemical Corporation)), MA100 (pH 3.5 (manufactured by Mitsubishi Chemical Corporation)), Black Pearls L (pH 2.5 (manufactured by Cabot)), MOGUL-L (pH 2.5 (manufactured by Cabot)), MONARCH1300 (pH 2.5 (manufactured by Cabot)) Printex V (pH 3.0 (manufactured by Degussa)) , Special Black 4 (pH 3.0 (manufactured by Degussa)), CX-GLF-50 (pH 4.0 (manufactured by Nippon Shokubai Co., Ltd.)), Raven7000 (pH 2.1 (manufactured by Colombian Chemicals)), etc. It is.

  Since these carbon blacks having a low pH have many polar groups on the surface, they repel each other with a gelling agent having a low polarity. Therefore, the use of these carbon blacks makes it difficult for the gelling agent to be adsorbed on the carbon black, and the gelling action by the gelling agent is sufficiently generated, so that the pinning effect can be enhanced.

In general, the total amount of polar groups on the surface of carbon black can be estimated from the volatile content of carbon black. Carbon black with a high volatile content tends to exhibit a low pH. The volatile matter can be expressed by the ratio (%) of the mass of the polar group to the mass of the carbon black. The mass of these polar groups is, for example, H ₂ O (corresponding to OH groups), CO ₂ (corresponding to COOH groups), and CO (corresponding to CO groups) generated when carbon black is heated at 950 ° C. for 7 minutes. It can measure by analyzing the mass of gas by GC / MS (gas chromatograph mass spectrometry). In addition, the elements on the surface of carbon black are measured using XPS (X-ray photoelectron spectroscopy), and the OH group, COOH group, CO group, sulfonic acid group, etc. are quantified from the component ratio of each detected element. Is possible. Information on each commercially available carbon black can be obtained from each manufacturer.

However, these functional groups may trap radicals generated by irradiation with actinic rays and suppress curing by the photopolymerization initiator. Therefore, by setting the volatile content of carbon black to less than 10.0%, it is possible to reduce the affinity between the gelling agent and carbon black while preventing a decrease in the curability of the ink. Furthermore, the ratio of the volatile matter contained in the carbon black to the specific surface area is more efficient when the volatile matter (%) / specific surface area (m ² / g) × 100 is 1.0 or more and 5.0 or less. In addition, the affinity between the gelling agent and carbon black can be lowered, and the curability of the ink can be prevented from being lowered. This is because if the ratio of the volatile component contained in the carbon black to the specific surface area is 1.0 or more, there is a sufficient polar group on the surface of the carbon black, so the affinity with the gelling agent can be lowered. On the other hand, if this value is 5.0 or less, it is considered that excessive capture of the radical by the polar group can be suppressed.

  The specific surface area of carbon black can be measured by a low temperature nitrogen adsorption method specified in JIS K6217-2.

  The volume average particle size of carbon black is preferably 0.08 to 0.5 μm, and the maximum particle size of carbon black is preferably 0.3 to 10 μm, more preferably 0.3 to 3 μm. By adjusting the particle size of the carbon black, 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 carbon black 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. When the carbon black content is 0.1% by mass or more, the color of the obtained image can be sufficiently developed, and when the carbon black content is 10% by mass or less, the viscosity of the ink is increased. Can be adjusted appropriately to ensure injection.

  The carbon black 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 dispersion of carbon black is such that the volume average particle size of carbon black particles is preferably 0.08 to 0.5 μm, the maximum particle size is preferably 0.3 to 10 μm, more preferably 0.3 to 3 μm. Preferably, it is done. The dispersion of carbon black is adjusted by selecting carbon black, a dispersant, and a dispersion medium, dispersion conditions, filtration conditions, and the like.

  The actinic ray curable inkjet ink may further contain a dispersant in order to enhance the dispersibility of the carbon black. 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, Ajinomoto Fine-Techno's PB series, BYK Japan Japan's BYK series, BASF's efka series, and the like.

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

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

  The actinic ray curable inkjet ink may further include a dispersion medium for dispersing carbon black 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.

[Other ingredients]
The actinic ray curable inkjet ink may further contain other components as necessary. Other components may be other colorants such as pigments other than the carbon black, 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.

[Physical properties of actinic radiation curable 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 inkjet ink that undergoes a sol-gel phase transition is a liquid (sol) at a high temperature (for example, about 80 ° C.), and thus 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) adhere (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 ink ejection properties, 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 °.

[Method for preparing actinic ray curable inkjet ink]
The actinic ray curable inkjet ink is obtained by mixing the above-described carbon black, a photopolymerizable compound, a photopolymerization initiator, and a gelling agent under heating. Preferably, a pigment dispersant in which carbon black is dispersed in a part of the photopolymerizable compound is prepared and mixed with the pigment dispersion material 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 to a recording medium (2) A step of irradiating the ink adhering to the recording medium with an actinic ray to cure the ink

[(1) Process]
The actinic ray curable ink-jet ink described above is ejected from the ink-jet recording head and adhered onto the recording medium.
In order to improve the ink ejection properties, it is preferable to set the temperature of the actinic ray curable inkjet ink in the inkjet recording head to a temperature 10 to 30 ° C. higher than the gelation temperature of the ink. If 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 ink ejection properties tend to decrease. 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 droplet volume per droplet of ink ejected from each nozzle of the inkjet recording head is preferably 0.5 to 10 pl depending on the resolution of the image. In order to form a high-definition image, 0.5 to 2.5 pl is more preferable. 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 actinic ray curable inkjet ink of the present invention, the sol-gel transition is rapidly performed. Therefore, a high-definition image can be stably formed even with such a droplet amount.

  The ink that has landed on the recording medium is cooled and quickly gelled by the sol-gel phase transition. As a result, the ink can be pinned without diffusing. Furthermore, since oxygen does not easily enter the ink, the curing of the photopolymerizable compound is difficult to be 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. Conventional ink cured products have low adhesion to a recording medium made of polyethylene terephthalate or polypropylene. On the other hand, the cured product of the actinic ray curable inkjet ink used in the inkjet recording method of the present invention has excellent adhesion to polyethylene terephthalate and polypropylene. Therefore, according to the inkjet recording method of the present invention, a high-quality image can be formed on a recording medium made of polyethylene terephthalate or polypropylene.

  Here, ink is deposited on the recording medium by ejecting ink from the ink jet recording head. The temperature of the recording medium when the ink 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 gels excessively and pinning, so that ink leveling does not occur sufficiently and the image gloss may decrease. On the other hand, if the temperature of the recording medium is too high, the ink is difficult to gel, and adjacent dots of the ink may be mixed together. By appropriately adjusting the temperature of the recording medium, it is possible to achieve appropriate pinning and appropriate leveling so that adjacent dots of ink 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 ((meth) acrylate 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 30 to 120 m / 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]
The ink deposited on the recording medium is irradiated with actinic rays to cure the ink. At this time, the ink is cured by irradiating the ink attached to the recording medium with actinic rays to crosslink or polymerize the photopolymerizable compound contained in the ink.

  The actinic ray applied to the ink 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. As a general ultraviolet light source, there is a metal halide lamp. By using an LED as a light source, the ink is melted by the radiant heat of the light source; that is, it is possible to suppress the occurrence of poor curing on the surface of the cured film of the ink.

The LED light source is installed such that the peak illuminance on the image surface is 0.5 to 10 W / cm ² with ultraviolet rays of 370 to 410 nm, and more preferably 1 to 5 W / cm ² . The amount of light applied to the image is preferably less than 350 mJ / cm ² . This is to prevent the ink from being irradiated with radiant heat.

  Irradiation of actinic rays to the ink is performed within 10 seconds after the ink droplets are deposited on the recording medium, preferably 0.001 seconds to 5 seconds, in order to prevent the adjacent ink droplets from coalescing. Within a range of 0.01 second to 2 seconds. The irradiation with actinic rays is preferably performed after ejecting ink droplets from all the ink jet recording heads accommodated in the head carriage.

[Inkjet recording device]
The ink jet recording method of the present invention can be performed using an actinic ray curable ink jet 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. 1A is a diagram illustrating an example of a configuration of a main part of a line recording type ink jet recording apparatus, and FIG. 1B is a top view thereof.

  As shown in FIGS. 1A and 1B, the inkjet recording apparatus 10 supplies 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 an ink flow path 30. An ink tank 31 that stores ink, a light irradiation unit 18 that covers the entire width of the recording medium 12 and is arranged downstream of the head carriage 16 (in the conveyance direction of the recording medium), and a lower surface of the recording medium 12 And a temperature control unit 19.

  The head carriage 16 is fixedly arranged so as to cover the entire width of the recording medium 12, and accommodates a plurality of inkjet recording heads 14 provided for each color. 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 transport 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 droplets ejected by the inkjet recording head 14 and landed on the recording medium with an actinic ray to cure 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. 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. Then, the light irradiating unit 18 irradiates the ink droplets attached on the recording medium 12 with light and cures them.

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

  FIG. 2 is a top view 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. 1A and 1B except that it includes 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.

  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 sent in the transport direction, and light is irradiated by the light irradiation unit 28. Except for these operations, an image is recorded in substantially the same manner as the line recording type inkjet recording apparatus 10 described above.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
[Preparation of pigment dispersion]
A pigment dispersion was prepared by 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.
EFKA7701 (manufactured by BASF) 9 parts by mass Tripropylene glycol diacrylate (APG-200, manufactured by Shin-Nakamura Chemical Co., Ltd.) 71 parts by mass

  After cooling to room temperature, 20 parts by mass of carbon black as a pigment according to the level shown in Table 1 was added thereto, sealed in a glass bottle with 200 g of zirconia beads having a diameter of 0.5 mm, and dispersed with a paint shaker for 8 hours. Carbon black dispersions 1-7 were prepared by removing the zirconia beads.

[Preparation of ink]
Each component shown below and the pigment dispersion were mixed according to the composition of the ink described in Table 2 and Table 3, heated to 80 ° C. and stirred. Under heating, the solution obtained with a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVANTEC was filtered to obtain carbon black inks 1-16. In addition, the unit of the component of each table | surface is the mass%.

A gelling agent distearyl ketone having a molecular weight of 200 or more and less than 800 and ClogP of 6.0 or more (Kao wax T1: Kao Corporation, molecular weight 520, ClogP 15 or more)
Behenyl behenate (Unistar M-2222SL: NOF Corporation, molecular weight 648, ClogP 15 or more)
Palmitic acid amide (Diamid KP: Nippon Kasei Co., Ltd., molecular weight 255, ClogP 6.3)
Other gelling agent N-lauroyl-L-glutamic acid dibutylamide (LGBA: Wako Pure Chemical Industries, Ltd., molecular weight 439, ClogP 5.4)
Sorbitan tristearate (SS-30V: Nikko Chemicals, molecular weight 962, ClogP 15 or more)

・ (Meth) acrylate compound A
3PO-modified trimethylolpropane triacrylate (Miramer M360: manufactured by Miwon, molecular weight 471, ClogP 4.9)
1,10-decanediol dimethacrylate (NK ester DOD-N: manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 310, ClogP 5.75)
Tricyclodecane dimethanol diacrylate (NK ester A-DCP: manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 304, ClogP 4.69)

-Other photopolymerizable compound Polyethylene glycol # 400 diacrylate (NK ester A-400: manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 508, ClogP 0.5)
6EO-modified trimethylolpropane triacrylate (SR499: manufactured by SARTOMER, molecular weight 560, ClogP 3.6)

-Polymerization inhibitor Irgastab UV10: manufactured by Ciba Specialty Chemicals-photopolymerization initiator TPO: manufactured by Ciba Specialty Chemicals ITX: manufactured by DKSH-surfactant KF-352: manufactured by Shin-Etsu Chemical

[Ink evaluation]
(Gelating agent dissolution stability)
The dissolution state after standing at 100 ° C. for 4 hours was visually observed. The evaluation results are shown in Tables 2 and 3.
○: No separation or precipitation ×: Oil balls are gathered on the surface (separated layers)

  As shown in Table 3, when the (meth) acrylate compound A was not contained (ink 15), and when the amount of the gelling agent was large (ink 16), the dissolution stability of the gelling agent was lowered.

[Inkjet recording method]
Each ink composition prepared in Examples and Comparative Examples was loaded into an ink jet recording apparatus having an ink jet recording head equipped with a piezo ink jet nozzle.

  The ink supply system consists of an ink tank, an ink flow path, a sub ink tank just before the ink jet recording head, a pipe with a filter, and a piezo head. Warm up.

The piezo head applied a voltage so as to form a 2 pl droplet, ejected using four 360 dpi resolution heads, a 1440 × 1440 dpi solid color solid image, 3 pt Mincho black characters, 3 pt Mincho white characters ( A solid image) was formed on A4 size coated paper (OK Kanto, US basis weight 104.7 g / m ² manufactured by Oji Paper Co., Ltd.).

After printing, light was irradiated from a LED lamp manufactured by Phoseon Technology (395 nm, 8 W / cm ² , water cooled unit) and cured. The distance from the lamp to the recording medium surface was 20 mm, and the conveyance speed of the recording medium was 40 m / s (light quantity, 300 mJ / cm ² ). The amount of light was measured using an ultraviolet integrated light meter (C9536, H9958, manufactured by Hamamatsu Photonics).

[Image evaluation]
(White stripe)
The image output of each ink was visually checked for white streaks and white spots (unification of dots due to insufficient pinning) in the solid image portion.
○: No white stripes △: There are white spots in one or two places, but there is no problem in practical use ×: Many white stripes occur

(Character quality)
The image output of each ink was visually evaluated for the quality of 3pt Mincho characters.
○: Reproduced △: Some characters are crushed, but there are no practical problems ×: Characters are crushed

(Curable)
About the image output product (single color solid image) of each ink, the image surface after rubbing 30 times with a coated paper with a weight of 500 g was visually evaluated.
○: No change in image Δ: Slight decrease in image density is observed, but there is no problem in practical use ×: Image density is significantly reduced.

  The evaluation results are shown in Table 4.

  In the inks of Comparative Examples 10 and 11 in which the pH of the pigment was outside the range of the present invention, the white streak and the character quality were significantly deteriorated. It is considered that the pinning effect due to the phase transition is not sufficiently functioning because the gelling action of the gelling agent is suppressed by the pigment.

  Even if the pH of the pigment is within the range of the present invention, the inks of Comparative Examples 12 and 13 in which the molecular weight of the gelling agent and the ClogP value are out of the range of the present invention have improved white stripes and deterioration of character quality. There wasn't. When a gelling agent having a large molecular weight or a gelling agent having a small ClogP value is used, it is considered that the gelling action of the gelling agent itself is delayed and pinning is insufficient.

  In the ink of Comparative Example 14 containing no gelling agent, the curability was remarkably deteriorated in addition to the white stripes and the deterioration of the character quality. It is considered that the pinning effect due to the phase transition is not obtained and the influence of oxygen inhibition is increased by not gelling.

  On the other hand, in the inks 1 to 9 according to the present invention, white stripes and character quality were improved. In particular, even when the pH of the pigment is within the range of the present invention, when a pigment having a volatile content or a volatile content / specific surface area within a specific range is used, white stripes and character quality are improved by improving pinning properties. It turns out that not only curability is excellent.

Example 2
[Preparation of pigment dispersion]
In Example 1, pigment dispersions C, M, and Y were obtained in the same manner except that the following pigment was used instead of carbon black.
Pigment Blue 15: 4 (manufactured by Dainichi Seika, Chromo Fine Blue 6332JC)
Pigment Red 122 (manufactured by Dainichi Seika, Chromo Fine Red 6112JC)
Pigment Yellow 180 (manufactured by Dainichi Seika, Chromo Fine Yellow 62)

[Preparation of ink]
Inks C, M, and Y were obtained in the same manner except that the pigment dispersion of ink 1 in Example 1 was changed to pigment dispersions C, M, and Y, respectively.

[Inkjet recording method]
Carbon black and four colors of inks C, M, and Y at the levels shown in Table 5 were loaded into the ink jet recording apparatus used in Example 1. The piezo head applies a voltage so that it becomes a 2 pl droplet, discharges it using four 360 dpi resolution heads per color, and produces a natural image at 1440 × 1440 dpi (high definition published by the Japan Standards Association). Color digital standard image data “fruit basket”) was printed on the same coated paper as in Example 1. After printing, curing by LED exposure was performed in the same manner as in Example 1.

[Image evaluation]
(Gloss uniformity)
The obtained image was visually observed and evaluated according to the following criteria.
◯: Gloss non-uniformity is not observed when observed from a position 15 cm away. Δ: Gloss difference is observed in a part of the image observed from a position 15 cm away. Observed from a different position, a noticeable difference in gloss is observed in the image area, making it unusable

The evaluation results are shown in Table 5.

  As shown in Table 5, in the ink sets 10 to 14 of the comparative examples, the difference in gloss between the images due to the pinning failure was noticeable, but in the ink sets 1 to 9 according to the present invention, the gloss between the images was uniform. A good image could be obtained.

  The actinic ray curable inkjet ink and inkjet recording method of the present invention can be suitably used for an inkjet recording method.

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

Claims (5)

An actinic ray curable inkjet ink containing carbon black, a gelling agent, a photopolymerizable compound and a photopolymerization initiator,
The pH of the carbon black is 2.0 to 5.0, the volatile content of the carbon black is less than 10.0%,
The molecular weight of the gelling agent is 200 or more and less than 800, the ClogP of the gelling agent is 6.0 or more, and the ratio of the gelling agent in the total mass of the ink is 1.0 to 7.0% by mass. Is in range,
Photopolymerizable compound has a molecular weight of 280 to 1500 ClogP values observed contains a is in the range of 4.0 to 7.0 (meth) acrylate compounds, the photopolymerizable compound has a molecular weight of 280-1500 An actinic ray curable inkjet ink that does not contain a (meth) acrylate compound that is solid at room temperature . Volatiles (%) / the specific surface area ^(m 2 / g) represented by × 100, ratio specific surface area of the volatile content of the carbon black is 1.0 to 5.0, according to claim 1 Actinic ray curable inkjet ink. The gelling agent has the general formula (G1) and (G2) is at least one of compounds represented by the actinic ray curable ink-jet ink according to claim 1 or 2.
General formula (G1): R1-CO-R2
General formula (G2): R3-COO-R4
(In the formula, R1 to R4 each independently represents an alkyl chain having a straight chain portion having 12 or more carbon atoms and optionally having a branched portion.) A step of ejecting the actinic radiation curable inkjet ink according to any one of claims 1 to 3 from an inkjet recording head and adhering the ink to the recording medium, and irradiating the ink adhering to the recording medium with an actinic ray And a step of curing the ink. In the curing step, it has a peak irradiance 0.5~10.0W / cm ² in a wavelength range of 370～410Nm, and the amount of light irradiating active light rays is less than 350 mJ / cm ^2, according to claim 4 Inkjet recording method.

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