JP2013226745A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming an image by using an active light curing type inkjet ink excellent in ejection stability from an inkjet recording device and in curability.SOLUTION: An image forming method includes: a step of ejecting ink droplets of an active light curing type inkjet ink which contains a gelling agent, a photopolymerizable compound and a photopolymerization initiator and performs a sol-gel phase transition reversibly in accordance with a temperature, from an inkjet recording head to attach the ink liquid droplets onto a recording medium; and a step of irradiating droplets landed onto the recording medium with active light beams to cure the ink droplets. The photopolymerizable compound includes: a (meth)acrylate compound A which has a molecular weight in a range of 280 to 1,500 and is solid at a normal temperature; and a (meth)acrylate compound B which has a molecular weight in a range of 280 to 1,500 and has a Clog P value in a range of 4.0 to 7.0.

Description

  The present invention relates to an image forming method using an actinic ray curable inkjet ink.

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

  In order to improve the pinning properties of ultraviolet curable ink-jet inks, it has been studied to add a gelling agent to the ink and cause the ink to undergo a sol-gel phase transition. In other words, it is considered that ink droplets in a liquid (sol) state are ejected at high temperature and landed on a recording medium, and at the same time, the ink droplets are cooled and gelled to suppress dot coalescence. Yes. As an example of the gelling agent added to the ink, stearone is cited (for example, Patent Document 1).

  However, when such a sol-gel phase transition ink is dropped onto a recording medium having high absorbency such as paper, a liquid component oozes out to the recording medium at room temperature contained in the ink, and the recording medium around the ink droplet May change color. Therefore, it has been proposed to add a photopolymerizable compound that is solid at room temperature to the ink to prevent the ink component from seeping out (penetrating) (for example, Patent Documents 2 and 3).

  Further, if the light source for curing the ultraviolet curable ink jet ink is a light source having high radiant heat (for example, a metal halide lamp), the ink droplets are melted by the radiant heat, and the ink droplets are liable to be hardened. Therefore, it has been studied to use an LED light source as a light source for ink curing (for example, Patent Document 4).

US Patent Application Publication No. 2007/0058020 JP 2011-127111 A JP 2011-127112 A JP 2011-25684 A

  However, like the sol-gel phase transition inks described in Patent Documents 2 and 3, when a photopolymerizable compound that is solid at room temperature is contained, the dissolution balance of the components contained in the ink changes when the ink is heated or lowered. It's easy to do. In particular, in the vicinity of the melting point of a photopolymerizable compound that is solid at room temperature, the solubility of the compound and the gelling agent is reduced, and they are likely to precipitate or phase-separate. Therefore, there are problems such as ink ejection becoming unstable and image quality being lowered.

  Further, the inks of Patent Documents 2 and 3 contain a large amount of gelling agent. That is, the photopolymerizable component contained in the ink is small and the cured film is brittle. In particular, when the ink is cured with an LED light source having a small amount of light, there is a problem that the strength of the cured film is further reduced.

  The present invention has been made in view of the above circumstances. The present invention provides a method of forming an image with an actinic ray curable inkjet ink excellent in ejection stability and curability from an inkjet recording apparatus.

  When a (meth) acrylate compound having a ClogP value within a specific range and a (meth) acrylate compound that is solid at room temperature are contained in a sol-gel phase transition type inkjet ink, the ink ejection stability increases, and gelation occurs. The present inventors have found that even if the amount of the agent is small, the ink sufficiently undergoes a sol-gel phase transition, and further the ink curability is enhanced.

The present invention relates to an image forming method described below.
[1] An actinic ray which contains a gelling agent containing a linear alkyl chain having 12 or more carbon atoms or a branched alkyl chain, a photopolymerizable compound, and a photopolymerization initiator and reversibly changes in sol-gel phase depending on temperature. A step of ejecting ink droplets of a curable ink jet ink from an ink jet recording head and adhering the ink droplets onto a recording medium; and a step of irradiating the droplets landed on the recording medium with actinic rays to cure the ink droplets The photopolymerizable compound has a molecular weight in the range of 280 to 1500, and is a solid (meth) acrylate compound A at room temperature, a molecular weight in the range of 280 to 1500, and ClogP (Meth) acrylate compound B having a value in the range of 4.0 to 7.0, and the gelling agent with respect to the total mass of the actinic radiation curable inkjet ink. The content is 0.5 to 7.0% by mass, the content of the (meth) acrylate compound A is 3.0 to 40.0% by mass, and the content of the (meth) acrylate compound B is 10%. An image forming method of 0.0 to 40.0% by mass.

[2] The image forming method according to [1], wherein the (meth) acrylate compound B is at least one (meth) acrylate compound of the following (1) and (2).
(1) Trifunctional or higher (meth) acrylate compound having 3 to 14 structures represented by (—C (CH ₃ ) H—CH ₂ —O—) in the molecule (2) cyclic in the molecule Bifunctional or higher functional (meth) acrylate compounds having a structure

[3] The image forming method according to [1] or [2], wherein the gelling agent is at least one compound selected from compounds represented by the following 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 group containing a straight chain portion having 12 or more carbon atoms.)
[4] The temperature of the recording medium when the actinic ray curable inkjet ink lands on the recording medium is set to a range of -20 to -10 ° C of the sol-gel phase transition temperature of the actinic ray curable inkjet ink. The image forming method according to any one of [1] to [3].
[5] Light is emitted from an LED light source in the step of curing the ink droplets, the light has a peak illuminance of 1.0 to 10 W / cm ² at a wavelength of 370 to 410 nm, and the conveyance speed of the recording medium is 50 m. The image forming method according to any one of [1] to [4], which is at least / min.

  According to the image forming method of the present invention, actinic ray curable inkjet ink can be stably ejected. Further, coalescence of ink droplets that have landed on the recording medium can be suppressed, and a high-quality image can be formed. Furthermore, since the curability of the ink is good, it can cope with high-speed printing.

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

  The image forming method of the present invention is a method for forming an image by applying a specific actinic ray curable inkjet ink.

[Actinic ray curable inkjet ink]
The actinic radiation curable inkjet ink applied by the image forming method of the present invention includes a gelling agent, a photopolymerizable compound, and a photopolymerization initiator. The actinic ray curable inkjet ink may contain a coloring material, other additives, and the like as necessary.

-About a gelatinizer The gelling agent contained in actinic-light curable inkjet ink has the function to carry out a sol-gel phase transition reversibly with temperature. Such a gelling agent needs to be at least 1) soluble in the liquid ink component at a temperature higher than the gelling temperature, and 2) crystallized in the ink at a temperature below the gelling temperature. It is.

  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 enclosed, and the liquid component in the ink is included in the space. . In this way, a structure in which the liquid component in the ink is included in the space three-dimensionally surrounded by the plate-like crystal is sometimes referred to as a “card house structure”. When the card house structure is formed, the liquid component in the ink can be retained, and the ink droplet can be pinned. Thereby, coalescence of droplets can be suppressed. In order to form a card house structure, it is preferable that the liquid component in the ink and the gelling agent are compatible with each other. On the other hand, if the liquid component in the ink and the gelling agent are phase-separated, it may be difficult to form a card house structure.

  In order to stably eject ink droplets from the ink jet recording apparatus, it is necessary that the liquid component in the ink and the gelling agent are compatible with each other 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.

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.) ITOHWAX 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 and other fatty acid ester compounds (for example, Emullex series manufactured by Nihon Emulsion Co., Ltd., Riken Vitamin Co., Ltd. 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.

  The gelling agent of the actinic radiation curable inkjet ink applied by the image forming method of the present invention includes a compound containing a linear alkyl chain having 12 or more carbon atoms or a branched alkyl chain. When the linear structure or branched alkyl chain having 12 or more carbon atoms is included in the molecular structure of the gelling agent, the aforementioned “card house structure” is easily formed. In particular, when a linear alkyl chain having 12 or more carbon atoms is included in the molecular structure of the gelling agent, a stronger “card house structure” is formed.

  Specific examples of the gelling agent in which a linear alkyl chain having 12 or more carbon atoms can be included in the structure include aliphatic ketone compounds, aliphatic ester compounds, higher fatty acids, higher alcohols, fatty acid amides and the like.

However, a gelling agent having a polar group such as —OH or —COOH at the end of the alkyl chain has low stability in a sol-like ink and may precipitate or phase-separate. In addition, the gelling agent may gradually bleed out with time from the cured film of the ink. Therefore, the gelling agent is preferably an aliphatic ketone compound or an aliphatic ester compound. That is, a compound represented by the following general formulas (G1) and (G2) is preferable.
General formula (G1): R1-CO-R2
General formula (G2): R3-COO-R4
In general formulas (G1) and (G2), R1 to R4 each independently represents an alkyl group having a straight chain portion having 12 or more carbon atoms. R1 to R4 may have a branched portion.

  In General Formula (G1), the alkyl groups represented by R1 and R2 are each independently preferably an alkyl group including a linear portion having 12 to 25 carbon atoms. When the number of carbon atoms in the linear portion contained in the alkyl group represented by R1 and R2 is less than 12, there may be a case where the crystallinity is not sufficient and the gelling agent may not function. Moreover, in the above-mentioned card house structure, there is a possibility that a sufficient space for encapsulating the photopolymerizable compound cannot be formed. On the other hand, when the number of carbon atoms in the straight chain portion contained in the alkyl group exceeds 25, the melting point becomes too high, so that the ink may not be dissolved in the ink unless the ink ejection temperature is increased.

  Examples of the aliphatic ketone compound represented by the general formula (G1) include dilignoceryl ketone (C24-C24), dibehenyl ketone (C22-C22, melting point 88 ° C.), distearyl ketone (C18-C18, 84 ° C.), dieicosyl ketone (C20-C20), dipalmityl ketone (C16-C16, melting point 80 ° C.), dimyristyl ketone (C14-C14), dilauryl ketone (C12-C12, melting point 68 ° C.) , Lauryl myristyl ketone (C12-C14), lauryl palmityl ketone (C12-C16), myristyl palmityl ketone (C14-C16), myristyl stearyl ketone (C14-C18), myristyl behenyl ketone (C14-C22), palmityl Stearyl ketone (C16-C18), Valmityl behenyl ketone (C 6-C22), include stearyl and behenyl ketone (C18-C22) and the like.

  Examples of commercially available compounds represented by the general formula (G1) include 18-Pentriacontanon (made by Alfa Aeser), Hentriacontan-16-on (made by Alfa Aeser), Kao wax T1 (made by Kao Corporation), and the like. Is 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 alkyl group represented by R3 and R4 is not particularly limited, but is preferably an alkyl group including a linear portion having 12 to 26 carbon atoms. When the number of carbon atoms in the linear portion contained in the alkyl group represented by R3 and R4 is 12 or more and 26 or less, the crystallinity necessary for the gelling agent is the same as in the compound represented by the general formula (G1). The above-mentioned card house structure can be formed while having a melting point, and the melting point is not too high.

  Examples of the aliphatic ester compound represented by the formula (2) include behenyl behenate (C21-C22, melting point 70 ° C.), icosyl icosanoate (C19-C20), stearyl stearate (C17-C18, melting point 60 ° C.). ), Palmitic acid stearate (C17-C16), lauryl stearate (C17-C12), cetyl palmitate (C15-C16, melting point 54 ° C.), stearyl palmitate (C15-C18), myristyl myristate (C13-C14), Melting point 43 ° C), cetyl myristate (C13-C16, melting point 50 ° C), octyldodecyl myristate (C13-C20), stearyl oleate (C17-C18), stearyl erucate (C21-C18), stearyl linoleate ( C17-C18), behenyl oleate (C18-C2) ), Myricyl cellotate (C25-C16), stearyl montanate (C27-C18), behenyl montanate (C27-C22), arachidyl linoleate (C17-C20), palmityl triacontanoate (C29-C16), etc. It is.

  Examples of commercially available products of the aliphatic ester compound represented by the formula (2) include Unistar M-2222SL (manufactured by NOF Corporation), EXCEPARL SS (manufactured by Kao Corporation, melting point 60 ° C.), EMALEX CC-18 ( Nippon Emulsion Co., Ltd.), Amreps PC (manufactured by Higher Alcohol Industry Co., Ltd.), Exepal MY-M (manufactured by Kao Co., Ltd.), Spam Acechi (manufactured by NOF Corporation), EMALEX CC-10 (manufactured by Nippon Emulsion Co., Ltd.), etc. Is included. 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 preferably 0.5 to 7.0% by mass, more preferably 1 to 5% by mass with respect to the total mass of the ink. If the content of the gelling agent is less than 0.5% by mass, the ink droplets may not be gelled (sol-gel phase transition due to temperature). On the other hand, when the content of the gelling agent exceeds 7.0% by mass, the amount of the photopolymerizable compound contained in the ink is relatively reduced. Therefore, the hardness of the cured film after photocuring tends to be insufficient, and the rub resistance of the cured film may be reduced.

-About photopolymerizable compound A photopolymerizable compound is a compound which bridge | crosslinks or superposes | polymerizes by irradiation of light. In the image forming method of the present invention, the ink droplets are cured by irradiating the ink droplets with actinic rays. Therefore, the photopolymerizable compound is preferably a radical polymerizable compound or a cationic polymerizable compound, and more preferably a radical polymerizable compound.

  The radically polymerizable compound may be a compound (monomer, oligomer, polymer or mixture thereof) having an ethylenically unsaturated bond capable of radical polymerization. Only one kind of radically polymerizable compound may be contained in the actinic ray curable inkjet ink, or two or more kinds thereof may be contained.

  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, or the like.

  The photopolymerizable compound of the actinic ray curable inkjet ink applied by the image forming method of the present invention includes (1) a (meth) acrylate compound ((meta) having a molecular weight in the range of 280 to 1500 and solid at room temperature. ) Acrylate compound A), and (2) a (meth) acrylate compound ((meth) acrylate compound B) having a molecular weight in the range of 280 to 1500 and a ClogP value in the range of 4.0 to 7.0. ) Is included.

  In conventional sol-gel phase transition inks, the compatibility between the gelling agent and the photopolymerizable compound has not been studied in detail, and even if dot coalescence can be suppressed at the initial stage of printing, printing can be continued or the temperature can be increased.・ Sometimes it became unstable when the temperature was lowered repeatedly. In particular, if the sol-gel phase transition ink contains (meth) acrylate compound A; that is, a solid compound at room temperature, the dissolution balance of each component contained in the ink is lost near the melting point of (meth) acrylate compound A. It was easy to precipitate the gelling agent and (meth) acrylate compound A, or they were easy to phase separate. For this reason, there are problems such as a decrease in ejection stability from the ink jet recording apparatus (dissolution stability of the gelling agent) and a decrease in image quality.

  In addition, depending on the type of the photopolymerizable compound, there is a problem that the cured product is greatly contracted, the printed product is curled, and the image film is broken when the image is bent.

  In order to solve such a problem, the present inventors can use a specific amount of (meth) acrylate compound A and a specific amount of (meth) acrylate compound B together in the ink even in the vicinity of the melting point of (meth) acrylate compound A. It was found that the dissolution balance of each of the components was good. The reason is guessed as follows. Since (meth) acrylate compound A and (meth) acrylate compound B are both (meth) acrylate compounds, they are easily compatible with each other. Further, the (meth) acrylate compound B has high hydrophobicity and is easily compatible with a very hydrophobic gelling agent. Therefore, the (meth) acrylate compound A, the (meth) acrylate compound B, and the gelling agent are easily compatible with each other, and their dissolution balance is easily stabilized. That is, the gelling agent and (meth) acrylate compound A are not deposited or phase-separated even when the temperature of the ink is raised and lowered repeatedly.

  On the other hand, if the (meth) acrylate compound A is contained in the ink, after the ink is dropped, the (meth) acrylate compound A forms a “card house structure” together with the gelling agent. Therefore, coalescence of ink droplets can be suppressed without adding a large amount of gelling agent. That is, the amount of the photopolymerizable component contained in the ink can be increased, and the hardness of the image is increased. Further, a film having a sufficiently high hardness can be formed even with a small amount of light. Furthermore, when the (meth) acrylate compound A and the (meth) acrylate compound B are combined, the effects of reducing the shrinkage of the cured product and reducing cracks in the image film can be obtained.

About (Meth) acrylate Compound A (Meth) acrylate Compound A is a compound that is solid at room temperature, that is, a melting point higher than 25 ° C. The melting point of the (meth) acrylate compound A is preferably 30 to 70 ° C, more preferably 40 to 60 ° C. When the (meth) acrylate compound A, which is solid at normal temperature, is contained in the ink, after landing on the recording medium, it is crystallized together with the gelling agent and easily forms the aforementioned “card house structure”. Therefore, even if the amount of the gelling agent is less than that of the conventional sol-gel ink, the ink after landing on the recording medium is easily gelled.

  The molecular weight of the (meth) acrylate compound A is 280-1500, preferably 300-800. When the (meth) acrylate compound A having a molecular weight of less than 280 is included, the viscosity of the ink at the ink discharge temperature is likely to change. For this reason, the ink ejection stability tends to decrease. Moreover, the (meth) acrylate compound A whose molecular weight is 280 or more has few odors. Therefore, the odor of the ink itself and the odor of the printed matter can be suppressed. On the other hand, when the (meth) acrylate compound A having a molecular weight exceeding 1500 is contained in the ink, the viscosity of the ink in the sol state increases, and the ejection stability of the ink decreases.

  The number of (meth) acrylate groups that (meth) acrylate compound A has is not particularly limited, and may be one or may be two or more. However, if the content of the (meth) acrylate compound A having only one (meth) acrylate group is increased, the curability tends to be lowered.

  Examples of (meth) acrylate compound A include octadecyl methacrylate, octadecyl acrylate, behenyl acrylate, behenyl methacrylate, hydroxyoctadecyl acrylate, hydroxyoctadecyl methacrylate, phenyl lauryl acrylate, phenyl lauryl methacrylate, 3-nitrophenyl-18-octadecyl acrylate, isocyania Examples include, but are not limited to, nurate triacrylate and acrylic acid ester having 14 or more carbon atoms.

  The (meth) acrylate compound A is preferably a compound having a linear alkyl chain having 12 or more carbon atoms, preferably 14 to 34, particularly preferably octadecyl methacrylate, octadecyl acrylate, behenyl acrylate, or behenyl methacrylate. When the (meth) acrylate compound A has a linear alkyl chain, it becomes easy to form a “card house structure” together with the gelling agent, and the effect of suppressing the coalescence of ink droplets increases.

  Content of (meth) acrylate compound A is 3.0-40.0 mass% with respect to the total mass of actinic-light curable inkjet ink, Preferably it is 4-20 mass%. When the content of the (meth) acrylate compound A is less than 3.0% by mass, it is difficult to obtain an ink droplet coalescence suppressing effect. On the other hand, if the content of the (meth) acrylate compound A exceeds 40.0% by mass, the viscosity of the ink at room temperature becomes very high, and the ink handling property is lowered.

About (Meth) acrylate Compound B (Meth) acrylate compound B is a compound having a (meth) acrylate group and having a ClogP value in the range of 4.0 to 7.0. The ClogP value of the (meth) acrylate compound B is preferably 4.5 to 6.0. When the ClogP value of the (meth) acrylate compound B is less than 4.0, the ink becomes hydrophilic and the gelling agent is hardly dissolved. Therefore, the gelling agent may not be completely dissolved even when heated. On the other hand, when the ClogP value of the (meth) acrylate compound B exceeds 7.0, the solubility of the photopolymerization initiator / initiator in the ink is lowered, the curability is lowered, Dischargeability tends to decrease. Furthermore, the compatibility with the (meth) acrylate compound A tends to decrease.

  Here, the “Log P value” is a coefficient indicating the affinity of an organic compound for water and 1-octanol. The 1-octanol / water partition coefficient P is the 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 the 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 a 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 molecular weight of the (meth) acrylate compound B is preferably 280 to 1500, and more preferably 300 to 800. When the (meth) acrylate compound B having a molecular weight of less than 280 is included, the viscosity of the ink at the ink discharge temperature is likely to change. Moreover, the (meth) acrylate compound B whose molecular weight is 280 or more has few odors. Therefore, the odor of the ink itself and the odor of the printed matter can be reduced. On the other hand, when the (meth) acrylate compound B having a molecular weight exceeding 1500 is contained, the viscosity of the sol-like ink is increased and the ejection stability is lowered.

  The number of (meth) acrylate groups contained in the (meth) acrylate compound B is not particularly limited, but is preferably 2 or more from the viewpoint of curability.

  The content of the (meth) acrylate compound B is preferably 10.0 to 40.0% by mass, more preferably 15 to 35% by mass with respect to the total mass of the actinic ray curable inkjet ink. When the content of the (meth) acrylate compound B is less than 10.0% by mass, the dissolution stability of the gelling agent and the (meth) acrylate compound A is lowered. When the content of the (meth) acrylate compound B exceeds 40.0% by mass, the dissolution stability of the photopolymerization initiator becomes unstable, and the ink curability tends to be insufficient.

The (meth) acrylate compound B preferably has (1) a structure represented by (—C (CH ₃ ) H—CH ₂ —O—) _m (m is an integer of ₃ to 14) in the molecule. A trifunctional or higher functional methacrylate or acrylate compound, and (2) a bifunctional or higher functional methacrylate or acrylate compound having a cyclic structure in the molecule. These (meth) acrylate compounds B have high photocurability and little shrinkage when cured. Moreover, the reproducibility of the sol-gel phase transition is good.

(1) A trifunctional or higher functional methacrylate or acrylate compound having a structure represented by (—C (CH ₃ ) H—CH ₂ —O—) _m (m is an integer of ₃ to 14) in the molecule is, for example, The hydroxyl group of a compound having 3 or more hydroxyl groups 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 Photomer 4072 (molecular weight 471, ClogP 4.90, manufactured by Cognis), 3PO-modified trimethylolpropane triacrylate Miramer M360 (molecular weight 471, ClogP4.90, manufactured by Miran) ) Etc. are included.

  (2) The bifunctional or higher functional methacrylate or acrylate compound having a cyclic structure in the molecule is obtained by esterifying a hydroxyl group of a compound having two or more hydroxyl groups and a tricycloalkane with (meth) acrylic acid. is there. Specific examples of this compound include tricyclodecane dimethanol diacrylate NK ester A-DCP (molecular weight 304, Clog P 4.69), tricyclodecane dimethanol dimethacrylate NK ester DCP (molecular weight 332, Clog P 5.12), and the like. included.

  Other specific examples of the (meth) acrylate compound B include 1,10-decanediol dimethacrylate NK ester DOD-N (molecular weight 310, ClogP 5.75, manufactured by Shin-Nakamura Chemical Co., Ltd.), nonylphenol 8EO modified acrylate Miramer M166 (ClogP6) .42, manufactured by Miwon).

Other Photopolymerizable Compounds The actinic ray curable inkjet ink may contain other photopolymerizable compounds. Other photopolymerizable compounds can be (meth) acrylate monomers and / or oligomers.

  The other photopolymerizable compound may be, for example, a (meth) acrylate monomer and / or oligomer having a ClogP value of less than 4.0, or a (meth) acrylate monomer and / or oligomer having a ClogP value of more than 7.0. .

  Specific examples of other photopolymerizable compounds include 4EO-modified hexanediol diacrylate (CD561), 3EO-modified trimethylolpropane triacrylate (SR454), 6EO-modified trimethylolpropane triacrylate (SR499), and 4EO-modified by Sartomer. Pentaerythritol tetraacrylate (SR494), ditrimethylolpropane tetraacrylate (SR355); polyethylene glycol diacrylate (NK ester A-400 and NK ester A-600) manufactured by Shin-Nakamura Chemical Co., Ltd., polyethylene glycol dimethacrylate (NK ester 9G and NK ester 14G); Tetraethylene glycol diacrylate (V # 335HP) manufactured by Osaka Organic Chemical Co., Ltd .; 9EO modified trimethylol group manufactured by Miwon Including but bread triacrylate (MiramerM3190) or the like, not limited thereto.

-About photoinitiator Actinic-light curable inkjet ink contains a photoinitiator.
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 Acetophenone systems such as -thiomethylphenyl) propan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone;
Benzoins such as benzoin, benzoin methyl ether, benzoin isopropyl ether;
Acylphosphine oxide systems such as 2,4,6-trimethylbenzoindiphenylphosphine oxide;
Acyl phosphonates;
Benzyl and methylphenylglyoxyesters are included.

Examples of intramolecular hydrogen abstraction type photopolymerization initiators include benzophenone, methyl 4-phenylbenzophenone o-benzoylbenzoate, 4,4′-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4′-methyl-diphenyl. Benzophenone series such as sulfide, acrylated benzophenone, 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone, 3,3′-dimethyl-4-methoxybenzophenone;
Thioxanthone systems such as 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone;
Aminobenzophenone series such as Mihira-ketone and 4,4′-diethylaminobenzophenone;
Examples include 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, camphorquinone, and the like.

  The photopolymerization initiator is preferably an acyl phosphine oxide or an acyl phosphonate from the viewpoint of sensitivity. In particular, 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 is preferably 0.1 to 10% by mass, particularly preferably 2 to 8% by mass, based on the total mass of the actinic ray curable inkjet ink.

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

  The actinic ray curable inkjet ink may further contain a photopolymerization initiator auxiliary agent, a polymerization inhibitor, and the like, 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. These compounds may be used alone or in combination of two or more.

  Examples of polymerization inhibitors include (alkyl) phenol, hydroquinone, catechol, resorcin, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone , Nitrosobenzene, 2,5-di-tert-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 a color material A color material is contained in actinic-light curable inkjet ink as needed. 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 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.
C. I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 81, 83, 87, 93, 95, 97, 98, 109, 114, 120, 128, 129, 138, 150, 151, 154, 155, 180, 185, 213
C. I. Pigment Red 5, 7, 12, 22, 38, 48: 1, 48: 2, 48: 4, 49: 1, 53: 1, 57: 1, 63: 1, 101, 112, 122, 123, 144, 146, 168, 184, 185, 202
C. I. Pigment Violet 19, 23
C. I. Pigment Blue 1, 2, 3, 15: 1, 15: 2, 15: 3, 15: 4, 18, 22, 27, 29, 60
C. I. Pigment Green 7,36
C. I. Pigment White 6, 18, 21
C. I. Pigment Black 7

  The average particle size of the pigment is preferably 0.08 to 0.5 μm. 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.

  On the other hand, the dye may 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 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 total mass of the actinic ray curable inkjet ink. If the pigment or dye content is too low, the resulting image will not be sufficiently colored. On the other hand, when the content of the pigment or dye is too large, the viscosity of the ink is increased, and the ejectability from the ink jet recording head tends to be lowered.

  In addition, the actinic ray curable inkjet ink may contain a synergist corresponding to various pigments as a dispersion aid. The total amount of the dispersant and the dispersion aid is preferably 1 to 50% by mass with respect to the pigment content (mass).

  The pigment needs to be dispersed in the ink. When the pigment is dispersed in the dispersion medium, the pigment is easily dispersed in the ink. The pigment can be dispersed in the dispersion medium by, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like. The dispersion medium may include a dispersant. The dispersant is preferably a polymer dispersant. Examples of the polymer dispersant include Avecia's Solsperse series and Ajinomoto Fine Techno's PB series.

  The dispersion medium in which the pigment is dispersed can be a solvent or the aforementioned photopolymerizable compound. However, the actinic ray curable inkjet ink is preferably gelled immediately after landing on the recording medium. Therefore, it is preferable that there is no solvent. In addition, when a cured image contains a solvent, the image may deteriorate over time due to the solvent. Another problem is that volatile organic compounds (VOC) are released from the image film into the atmosphere. Therefore, the dispersion medium is preferably not a solvent but a photopolymerizable compound, particularly a monomer having a low viscosity.

Other components The actinic ray curable inkjet ink may 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 the basic compound 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.

Inkjet ink Since the actinic ray 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. In the present invention, the (meth) acrylate compound A is also crystallized together with the gelling agent, and a strong card house structure is formed. When a strong card house structure is formed, coalescence between adjacent dots is suppressed, and image quality is improved. Further, when the ink is gelled, it becomes difficult for oxygen to diffuse into the ink droplets, so that the photopolymerization of the photopolymerizable compound is hardly inhibited by oxygen and the curability of the ink is also increased.

  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. If the gelation temperature of the ink exceeds 70 ° C. when the ejection temperature is in the vicinity of 80 ° C., gelation tends to occur at the time of ejection, resulting in poor ejection properties. On the other hand, if the gelation temperature is less than 40 ° C., it is difficult to quickly gel after landing on the recording medium. 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 it can obtain | require 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 a temperature at which the viscosity greatly increases in the temperature change curve of the viscosity, for example, a temperature at which the viscosity becomes 200 mPa · s.

  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 °.

About the manufacturing method of an inkjet ink Actinic-light curable inkjet ink can be obtained by mixing each component containing the above-mentioned photocurable compound and a gelatinizer under a heating. Preferably, it is produced by preparing a pigment dispersion in which a color material (particularly a pigment) is dispersed in a part of the photopolymerizable compound, and mixing the pigment dispersion with other ink components.

2. Inkjet recording apparatus and image recording method using the same The image 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 the ink onto a recording medium (2) The ink liquid is obtained by irradiating the droplets landed on the recording medium with light from an LED light source. Curing the drops

(1) About process The actinic-light curable inkjet ink should just be the inkjet ink mentioned above.

  Ink droplets are ejected from the ink jet recording head. In order to improve the ejection property 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. When the ink temperature in the ink jet recording head is less than (gelation temperature + 10) ° C., the ink is gelled 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 (gelation temperature + 30) ° C., the ink becomes too hot and the ink component may deteriorate.

  Therefore, it is only necessary to heat the ink jet ink in the ink jet recording head, the ink flow path connected to the ink jet recording head, or the ink tank connected to the ink flow path, and discharge the ink jet ink droplets at the above temperature.

  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 the amount of droplets, it is necessary to dissolve the gelling agent in the ink. According to the component configuration of the actinic ray curable inkjet ink described above, the dissolution stability of the gelling agent can be ensured. 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, as described above, oxygen inhibition during polymerization of the photopolymerizable compound can also be reduced.

  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 and a vinyl chloride film.

  By ejecting ink droplets from the inkjet recording head, the ink droplets adhere to the recording medium. The temperature of the recording medium when the ink droplets land 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.

  The conveyance speed of the recording medium is preferably 50 to 120 m / min. 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.

  If the gelling agent or the (meth) acrylate compound A is poorly dissolved in the sol-like ink, a part of these precipitates during ink ejection and causes nozzle clogging, resulting in a reduction in image quality. If the gelation speed of the ink after landing on the recording medium is low, dots are mixed even if the temperature of the recording medium is adjusted, and the image is lowered. On the other hand, in the above-mentioned actinic ray curable inkjet ink, the gelling agent and the photopolymerizable compound ((meth) acrylate compound A and (meth) acrylate compound B) are mutually compatible. Moreover, after ink landing, the gelling agent and the (meth) acrylate compound A quickly crystallize. Accordingly, the ink ejection stability is very good, and the image quality of the printed image is also very good.

(2) Process By irradiating the ink droplet landed on the recording medium with an actinic ray, the photopolymerizable compound contained in the ink droplet is crosslinked or polymerized to cure the ink droplet.

  The actinic ray applied to the ink droplets attached to the recording medium is preferably ultraviolet rays from an LED light source. Specifically, a 395 nm, water-cooled LED manufactured by Phoseon Technology can be used. The ultraviolet light source may be a metal halide lamp or the like, but by using an LED as a light source, dissolution of ink droplets can be suppressed by the radiant heat of the light source.

Light from the LED light source preferably has a peak irradiance 1.0~10W / cm ² in the wavelength 370～410Nm, it is more preferable peak irradiance is 1~5W / cm ^2. The peak illuminance is the illuminance on the surface of the recording medium. The conveyance speed of the recording medium during light irradiation is preferably 50 to 120 m / min. The higher the conveyance speed, the less the influence of radiant heat, and the higher the image forming speed, which is preferable. However, if the conveying speed is too high, photocuring may be insufficient.

  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.

Inkjet recording apparatus The image recording method of the present invention can be carried out using 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.

  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 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 inkjet recording head 14 is heated to a predetermined temperature to maintain the sol 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 irradiating unit 18 irradiates the droplets ejected by the inkjet recording head 14 and landed on the recording medium 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 image recording method using the line recording type inkjet recording apparatus 10 will be described. The recording medium 12 is conveyed between the head carriage 16 and the temperature control unit 19 of the inkjet recording apparatus 10. On the other hand, the recording medium 12 is adjusted to a predetermined temperature by the temperature control unit 19. Next, high temperature ink 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 image film thickness after curing is preferably 2 to 25 μm. “Total image film thickness” is the maximum film thickness of an image formed on a 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 n attached 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.

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

The actinic ray curable ink-jet ink of each example and comparative example was prepared with the following components.
(Photopolymerizable compound)
[(Meth) acrylate compound A]
STA (manufactured by Osaka Organic Chemicals): Octadecyl acrylate (molecular weight 325, melting point 30 ° C.)
Blemmer VA (manufactured by NOF Corporation): behenyl acrylate (molecular weight 381, melting point 46 ° C.)
NK ester A-9300 (manufactured by Shin-Nakamura Chemical Co., Ltd.): isocyanurate triacrylate (molecular weight 423, melting point 53 ° C.)
CD587 (manufactured by Sartomer): a mixture of acrylate esters having a carbon number of 18, 20, and 22 (molecular weight 300-500, melting point 55 ° C.)
[(Meth) acrylate compound B]
Miramer M166 (manufactured by Miwon): nonylphenol 8EO modified acrylate (molecular weight 626, Clog P value 6.42)
Miramer M360 (manufactured by Miwon): trimethylolpropane 3PO-modified triacrylate (molecular weight 471, Clog P value 4.90)
NK ester DOD-N (manufactured by Shin-Nakamura Chemical Co., Ltd.): 1,10-decanediol dimethacrylate (molecular weight 310, Clog P value 5.75)
NK ester A-DCP (manufactured by Shin-Nakamura Chemical Co., Ltd.): tricyclodecane dimethanol diacrylate (molecular weight 304, Clog P value 4.69)

[Other photopolymerizable compounds]
CD-406 (manufactured by Sartomer): dimethanol diacrylate cyclohexane (melting point 78 ° C., molecular weight 252)
NK ester A-600 (manufactured by Shin-Nakamura Chemical Co., Ltd.): polyethylene glycol diacrylate Miramar M3190 (manufactured by Miwon): 9EO-modified trimethylolpropane triacrylate SR355 (manufactured by Sartomer): ditrimethylolpropane tetraacrylate CD561 (Sartomer) Manufactured by): alkoxylated hexanediol diacrylate

(Gelling agent)
Stearyl stearate (Exepal SS, manufactured by Kao Corporation), (Unistar M-9676, manufactured by NOF Corporation), (EMALEX CC-18, manufactured by Nippon Emulsion Co., Ltd.), (AmrepSS SS, manufactured by Higher Alcohol Industry Co., Ltd.)
-Cetyl palmitate (Amreps PC, manufactured by Higher Alcohol Industry)
-Distearyl ketone (Kao wax T1, manufactured by Kao Corporation) (18-Pentatria cationone, reagent (Arfa Aeser))
・ Behenyl behenate (Unistar M-2222SL, manufactured by NOF Corporation)
・ Behenic acid (Lunac BA, manufactured by Kao Corporation)

(Surfactant)
・ TSF4452 (Momentive Performance Materials Japan)
(Photopolymerization initiator)
・ IRGACURE 819 (manufactured by BASF)
・ DETX (manufactured by Lambson)
・ IRGACURE 907 (Ciba)
・ IRGACURE 184 (Ciba)
(Sensitization aid)
・ SpeedcureEDB (Lambson)
・ TX-1 (manufactured by RAHN)
(Polymerization inhibitor)
・ Irgastab UV-10 (Ciba)

(Preparation of pigment dispersion a)
Three compounds shown below were put in a stainless beaker. This was heated and stirred for 1 hour while heating on a hot plate at 65 ° C.
-PB824 (Ajinomoto Fine Techno Co., Ltd.) 9 parts by mass-Tripropylene glycol diacrylate (Aronix M220, manufactured by Toagosei Co., Ltd., molecular weight 300) 51 parts by mass-Octadecyl acrylate (STA, manufactured by Osaka Organic Chemicals) 20 parts by mass

  The mixed solution was cooled to room temperature, and 20 parts by mass of a pigment (Pigment Black 7 (manufactured by Mitsubishi Chemical Corporation, MA7)) was added. This solution was placed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, sealed, and dispersed in a paint shaker for 5 hours. Thereafter, the zirconia beads were removed to obtain a pigment dispersion a.

(Preparation of pigment dispersion b)
The following two compounds were put in a stainless beaker and dissolved by stirring and heating for 1 hour while heating on a hot plate at 65 ° C.
-PB824 (Ajinomoto Fine Techno Co., Ltd.) 9 parts by mass-Dipropylene glycol diacrylate (APG-100, Shin-Nakamura Chemical Co., Ltd. molecular weight 242) 71 parts by mass

  The mixed solution was cooled to room temperature, and 20 parts by mass of a pigment (Pigment Black 7 (manufactured by Mitsubishi Chemical Corporation, MA7)) was added. This solution was placed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, sealed, and dispersed in a paint shaker for 5 hours. Thereafter, the zirconia beads were removed to obtain a pigment dispersion b.

[Examples 1 to 4 and Comparative Examples 1 to 5]
(Preparation of ink)
Each compound was mixed at the composition ratio shown in Table 1 below, and the mixture was heated and stirred at 80 ° C. The obtained mixed solution was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC under heating. The unit of the component in Table 1 is a mass part.

  The actinic ray curable inkjet inks of Comparative Examples 1 and 2 are inks described in Examples of JP 2011-74385 A and JP 2011-127111 A, respectively. These inks contain (meth) acrylate compound A but do not contain (meth) acrylate compound B. The inks of Comparative Examples 3 and 4 also contain (meth) acrylate compound A, but do not contain (meth) acrylate compound B. On the other hand, the ink of Comparative Example 5 contains (meth) acrylate compound B but does not contain (meth) acrylate compound A.

(Ink evaluation)
For each ink, the sol-gel phase transition temperature, ink ejection stability, and ink odor were evaluated as follows.
Sol-gel phase transition temperature The sol-gel phase transition temperature of each ink was measured with a viscoelasticity measuring device MCR300 manufactured by Physica. Specifically, the ink was 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. From the obtained 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 Table 1.

Ink ejection stability Each ink was allowed to stand at 25 ° C. for 2 hours, then heated to 100 ° C. and allowed to stand for 2 hours. Thereafter, the temperature was lowered to 25 ° C. The cycle of standing at 25 ° C. and standing at 100 ° C. was performed four times. Thereafter, the ink was loaded into an ink jet recording apparatus having an ink jet recording head provided with a piezo ink jet nozzle, and the ink was ejected from the ink jet nozzle. The discharge situation was observed with a high-speed video and evaluated as follows. The results are shown in Table 1.
○: No discharge failure ×: No discharge nozzle exceeds 5% of the total.

Ink odor The actinic ray curable inkjet ink was heated to 100 ° C., and the odor at that time was evaluated based on the following criteria. The results are shown in Table 1.
○: Odor is not felt ×: Strong irritating odor

(Image formation)
Each ink was loaded into an ink jet recording apparatus having an ink jet recording head equipped with a piezoelectric ink jet nozzle. From this apparatus, ink was ejected onto chrysanthemum size coated paper (OK top coat; manufactured by Oji Paper Co., Ltd.), and 500 images were continuously formed.

  The ink supply system was composed of 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. In the ink jet recording apparatus, four piezo heads with a resolution of 360 dpi were arranged to obtain a recording resolution of 1440 × 1440 dpi.

  The ink was heated to 100 ° C. from the ink tank to the head portion. Further, a voltage was applied to the piezo head so that the amount of each droplet was 2 pl, thereby forming a monochromatic solid image, 3 pt Mincho body black character, 3 pt Mincho body character (outline character in the solid image).

After the image formation, the ink was cured by irradiating light with a wavelength of 395 nm and 8 W / cm ² from a water-cooled LED lamp manufactured by Phoseon Technology. The distance from the LED lamp surface to the recording medium surface was 50 mm. At this time, the maximum illuminance on the surface of the recording medium was 4 W / cm ² and the conveyance speed of the recording medium was 60 m / min. The amount of light applied to the recording medium was 200 mJ / cm ² . The measurement of the amount of light was carried out with a UV integrated light meter C9536, H9958 manufactured by Hamamatsu Photonics.

The formed images were evaluated as follows.
・ Image quality (white blank)
Regarding the image formed on the coated paper, the image formed on the 10th sheet and the image formed on the 500th sheet were visually checked to see if there were any white spots (unprinted portions due to dot coalescence) in the solid image portion. . Evaluation was performed according to the following criteria.
○: 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)
Of the images formed on the coated paper, the quality of the 3pt Mincho characters was visually confirmed for the 10th image and the 500th image. Evaluation was performed according to the following criteria.
○: Characters are accurately reproduced △: Some characters are crushed ×: Characters are crushed

・ Curability evaluation (pencil hardness)
A solid image portion (100% printed portion) formed on the 10th sheet of OK top coat paper of chrysanthemum size was left in an environment of 25 ° C. and 60% RH for 24 hours. Thereafter, the pencil hardness of the surface was measured according to JIS-K-5400. Evaluation was performed according to the following criteria.
○: Pencil hardness 2H or more △: Pencil hardness B, F, H
X: Pencil hardness 2B or less

Bending resistance evaluation A solid image part (100% printed part) formed on the 10th sheet of OK top coat paper of chrysanthemum size was left in an environment of 25 ° C. and 60% RH for 24 hours. Then, it was folded in half and the bending resistance was confirmed visually. Evaluation was performed according to the following criteria.
○: Image film does not break ×: Image film breaks at the folded part

  As shown in Table 1, when (meth) acrylate compound A was included but (meth) acrylate compound B was not included (Comparative Examples 1 to 4), the ink ejection stability was poor. It is inferred that the dissolution balance between the (meth) acrylate compound A and the gelling agent was lost while repeating the temperature increase and temperature decrease, and the gelling agent and (meth) acrylate compound A were separated. Furthermore, in any case, the image quality of the 500th printed material was lower than the image quality of the 10th printed material. It is presumed that the gelling agent was separated in the ink tank or the like while printing was continued.

  On the other hand, when an appropriate amount of (meth) acrylate compound A and (meth) acrylate compound B is contained (Examples 1 to 4), the ink ejection stability is excellent, and an image of the tenth printed matter is further obtained. There was no difference between the quality and the image quality of the 500th printed material.

  Further, when (meth) acrylate compound B was included but (meth) acrylate compound A was not included (Comparative Example 5), the ink ejection stability was good, but the image quality was poor. Since the (meth) acrylate compound A that forms the card house structure together with the gelling agent is not included, it is presumed that the ink could not be sufficiently pinned.

  On the other hand, when (meth) acrylate compound A and (meth) acrylate compound B are contained in appropriate amounts (Examples 1 to 4), (meth) acrylate compound A forms a card house structure together with the gelling agent. In addition, the image quality (white spots and character quality) was good.

  When the content of the gelling agent exceeds 7% by mass (Comparative Examples 1 and 2), the strength of the cured film (pencil hardness) decreases and the gelling agent is contained in a large amount (about 22% by mass). In the case (Comparative Example 2), the bending resistance was also deteriorated.

  When the ink contains a photopolymerizable compound (CD-406 or dipropylene glycol diacrylate in pigment dispersion b) having a molecular weight of less than 280 (Comparative Examples 1, 2 and 5), strong irritation when heated to 100 ° C. There was an odor.

[Examples 5 to 8 and Comparative Examples 6 to 8]
An image was formed in the same manner as in Example 1 except that each compound was mixed at the composition ratio shown in Table 2 below. The unit of the component in Table 2 is a mass part.

  Comparative Examples 6 and 8 are examples in which the (meth) acrylate compound B is excessively contained, and Comparative Example 7 is an example in which the (meth) acrylate compound B is too small.

  As shown in Table 2, when the content of the (meth) acrylate compound B exceeds 40% by mass (Comparative Examples 6 and 8), the curability of the ink is lowered and the bending resistance is lowered. On the other hand, when the content of the (meth) acrylate compound B is less than 10% by mass (Comparative Example 7), the ink ejection stability was poor. It is presumed that the gelling agent and (meth) acrylate compound A were phase-separated while repeating the temperature increase and the temperature decrease. Furthermore, the image quality of the 500th printed material was lower than the image quality of the 10th printed material. It is presumed that the gelling agent was separated in the ink tank or the like while printing was continued.

  On the other hand, when appropriate amounts of (meth) acrylate compound A and (meth) acrylate compound B are included (Examples 5 to 8), the ink ejection stability is excellent, and further, the image of the tenth printed matter There was no difference between the quality and the image quality of the 500th printed material. In addition, when the monofunctional (meth) acrylate compound A (STA) was contained in an amount of about 10% by mass (Comparative Examples 6 and 7, and Examples 5 and 6), the hardness of the film slightly decreased.

[Examples 9 to 13 and Comparative Examples 9 and 10]
An image was formed in the same manner as in Example 1 except that each compound was mixed at the composition ratio shown in Table 3 below. The unit of the component in Table 3 is a mass part.

  Comparative Example 9 is an example in which the gelling agent is excessively contained, and Comparative Example 10 is an example in which the amount of the gelling agent is too small.

  As shown in Table 3, when the amount of the gelling agent exceeded 7.0% by mass (Comparative Example 9), the strength (pencil hardness) of the cured film was low. Further, the image quality of the 500th printed material was lower than the image quality of the 10th printed material. It is presumed that the gelling agent was separated in the ink tank or the like while printing was continued.

  On the other hand, when the amount of the gelling agent is less than 0.5% by mass (Comparative Example 10), the ink after landing on the recording medium does not sufficiently undergo the sol-gel phase transition, and the image quality (white spots or character quality) is poor. It became.

  In addition, when the gelling agent was a ketone or ester containing a straight chain portion having 12 or more carbon atoms (Examples 10 to 13), the image quality (white spots and character quality) was good. On the other hand, when the gelling agent was behenic acid (Comparative Example 9), the image quality was slightly lowered. It is presumed that the dissolution stability of the gelling agent in the ink is inferior to that of the ketone or ester.

[Examples 14 to 16 and Comparative Example 11]
An image was formed in the same manner as in Example 1 except that the respective compounds were mixed at the composition ratio shown in Table 4 below and an image was formed under the printing conditions shown in Table 4. The unit of the component in Table 4 is a mass part. In Example 15, the amount of light when the recording medium conveyance speed was 30 m / s was 200 mJ / cm ² . The measurement of the amount of light was carried out with a UV integrated light meter C9536, H9958 manufactured by Hamamatsu Photonics.

In Comparative Example 11, the ink was cured with a metal halide lamp MAP200NL manufactured by GS Yuasa. The conveyance speed of the recording medium at this time was 30 m / s. The amount of light was 200 mJ / cm ² . The amount of light was measured with a 365 nm sensor of a light meter UVPF-A1 manufactured by Iwasaki Electric Co., Ltd.

  As shown in Table 4, when an image was formed with a metal halide lamp, the surface of the ink droplet landed on the recording medium was melted by the radiant heat from the light source, and white spots and character quality were deteriorated. Further, when the number of printed sheets increases, it is presumed that the heat from the light source tends to be higher and the image quality of the 500th sheet is lowered.

  Even when the LED lamp was used as the light source, the image quality of the 500th sheet was deteriorated when the conveyance speed of the recording medium was low (Example 15). Even with an LED lamp, heat is accumulated in the LED lamp when exposed for a long time. If the paper conveyance speed is low, it is likely that the image quality is deteriorated because it is easily affected by the heat.

  Further, when the temperature of the recording medium upon landing of the ink was 25 ° C. lower than the sol-gel phase transition temperature of the ink, white spots were slightly generated. This is presumed that the ink that landed on the recording medium immediately gelled and therefore could not be sufficiently leveled.

  The inks of Comparative Example 11 and Examples 14 to 16 contain about 10% by mass of the monofunctional (meth) acrylate compound A (STA), but because the tetrafunctional (meth) acrylate compound (SR355) was used in combination, The film hardness (pencil hardness) was good.

  According to the image forming method of the present invention, actinic ray curable inkjet ink can be stably ejected. Further, coalescence of ink droplets that have landed on the recording medium can be suppressed, and a high-quality image can be formed. Furthermore, since the curability of the ink is good, it can cope with high-speed printing.

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 which contains a gelling agent containing a linear alkyl chain having 12 or more carbon atoms or a branched alkyl chain, a photopolymerizable compound, and a photopolymerization initiator, and reversibly changes to a sol-gel phase depending on temperature. A step of causing ink droplets of ink to be ejected from an ink jet recording head and deposited on a recording medium;
Irradiating the droplets landed on the recording medium with an actinic ray to cure the ink droplets,
The photopolymerizable compound has a molecular weight in the range of 280 to 1500 and a (meth) acrylate compound A that is solid at room temperature, a molecular weight in the range of 280 to 1500, and a ClogP value of 4.0. (Meth) acrylate compound B within the range of -7.0,
The content of the gelling agent is 0.5 to 7.0% by mass with respect to the total mass of the actinic radiation curable inkjet ink, and the content of the (meth) acrylate compound A is 3.0 to 40.%. The image forming method, wherein the content is 0% by mass and the content of the (meth) acrylate compound B is 10.0 to 40.0% by mass. The image forming method according to claim 1, wherein the (meth) acrylate compound B is at least one (meth) acrylate compound of the following (1) and (2).
(1) Trifunctional or higher (meth) acrylate compound having 3 to 14 structures represented by (—C (CH ₃ ) H—CH ₂ —O—) in the molecule (2) cyclic in the molecule Bifunctional or higher functional (meth) acrylate compounds having a structure The image forming method according to claim 1, wherein the gelling agent includes at least one compound selected from compounds represented by the following 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 group containing a straight chain portion having 12 or more carbon atoms.)   The temperature of the recording medium when the actinic radiation curable ink-jet ink lands on the recording medium is in the range of -20 to -10 ° C of the sol-gel phase transition temperature of the actinic radiation curable ink-jet ink. The image forming method according to claim 1. Light is emitted from an LED light source in the step of curing the ink droplets, the light has a peak illuminance of 1.0 to 10 W / cm ² at a wavelength of 370 to 410 nm, and the conveyance speed of the recording medium is 50 m / min or more. The image forming method according to claim 1, wherein:

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