JP5884455B2 - Image forming method using photocurable ink-jet ink - Google Patents

Description

  The present invention relates to an image forming method using a photocurable 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 ink jet recording methods, there is an ultraviolet curable ink jet method in which droplets of ultraviolet curable ink are landed on a recording medium and then cured by irradiation with ultraviolet rays to form an image. The ultraviolet curable ink jet method has been attracting attention in recent years because it can form an image having high scratch resistance and adhesion even on a recording medium having no ink absorbability.

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

  Furthermore, when the light source used for the ultraviolet curable ink jet ink is a light source with high radiant heat such as a metal halide lamp, the ink droplets melt, leading to poor curing of the cured film surface of the ink droplets. Therefore, it has been studied to use an LED light source as a light source for curing ink droplets (for example, Patent Document 3). However, the LED light source has a small amount of light, and there may be a problem that the curability inside the cured film of ink droplets is not sufficient.

  In order to improve the curability inside the cured film of ink droplets, it has been studied to improve the curability inside the cured film by blending an ultraviolet curable inkjet ink with an oligomer as a photopolymerizable compound. As an example of the oligomer, a polyester acrylate oligomer or the like is disclosed (for example, Patent Document 4).

US Published 2007/0058020 Specification International Publication No. 2007/025893 JP 2011-25684 A JP 2009-132919 A

  However, in an ultraviolet curable ink containing an oligomer, the oligomer may be affected by oxygen inhibition, resulting in poor curing of ink droplets. This is because oligomers are inherently low in polymerization activity and are susceptible to oxygen inhibition. In order to reduce the influence of oxygen inhibition, it is conceivable to add a gelling agent to the ink. By adding the gelling agent, the ink droplets that have landed on the recording medium rapidly gel, and the amount of oxygen dissolved in the ink can be reduced. This makes the oligomer less susceptible to oxygen inhibition.

  However, depending on the type of oligomer added to the ink, gelation may become unstable or the ink droplets may not be sufficiently cured.

  The present invention has been made in view of the above circumstances, and forms an image using a photocurable inkjet ink that achieves both the dissolution stability of a gelling agent, the stability of gelation, and the curability of ink droplets. It aims to provide a method.

  In order to achieve both the dissolution stability of the gelling agent, the stability of gelation, and the curability of the ink droplets, the present inventors have designated a photopolymerizable compound as a photopolymerizable compound. By blending the “(meth) acrylate compound” and the “polyester acrylate oligomer”, the gel can be stably and reproducibly gelled, and the ink droplets that have landed on the recording medium are efficiently cured (that is, the LED's). It was found that even a light source with such a small amount of light can be cured.

  The reason for the stabilization of gelation is not limited, but it is because the balance between dissolution of the gelling agent and crystallization can be achieved by blending the two components. In other words, the “specific (meth) acrylate compound” appropriately dissolves the gelling agent in the ink under heating conditions; the “polyester acrylate oligomer” appropriately converts the gelling agent in the ink landed on the recording medium. Crystallize. The present invention has been made based on such findings.

That is, the first of the present invention relates to an image forming method using the following photocurable inkjet ink.
[1] On a recording medium, ink droplets of a photocurable inkjet ink that contains a colorant, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator and undergoes a sol-gel phase transition depending on temperature are ejected from an inkjet recording head. And a step of irradiating the droplets landed on the recording medium with light from an LED light source to cure the ink droplets,
The content of the gelling agent is in the range of 1.0 to 7.0% by mass with respect to the total mass of the ink,
The photopolymerizable compound includes a (meth) acrylate compound having a molecular weight in the range of 280 to 1500 and a ClogP value in the range of 4.0 to 7.0, and a polyester acrylate oligomer.
The content of the (meth) acrylate compound is in the range of 10 to 40% by mass with respect to the mass of the entire ink,
The content of the polyester acrylate oligomer is in the range of 5.0 to 20.0% by mass with respect to the mass of the entire ink,
The image forming method, wherein the light has a peak illuminance of 0.5 to 10.0 W / cm ² at 370 to 410 nm, and the light quantity of the light is less than 350 mJ / cm ² .

[2] The (meth) acrylate compound having the ClogP value in the range of 4.0 to 7.0 is at least one (meth) acrylate compound of the following (1) and (2). The image forming method according to [1].
(1) Trifunctional or higher (meth) acrylate compound (2) having a structure represented by (—C (CH ₃ ) H—CH ₂ —O—) _m (m is an integer of ₃ to 14) in the molecule Bifunctional or higher functional (meth) acrylate compound having a cyclic structure in the molecule [3] The gelling agent is at least one compound selected from the following general formulas (G1) and (G2). The image forming method according to [1] or [2], which is characterized.
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 may be branched.)
[4] The image forming method according to any one of [1] to [3],
The image formation is characterized in that the temperature of the recording medium when the photocurable ink-jet ink lands on the recording medium falls within the range of -20 to -10 ° C of the sol-gel phase transition temperature of the photocurable ink-jet ink. Method.
[5] The image forming method according to any one of [1] to [4],
An image forming method, wherein the LED light source has a peak illuminance of 1 to 5 W / cm ² .

  ADVANTAGE OF THE INVENTION According to this invention, the image formation method using the photocurable inkjet ink which makes the stability of gelatinization and the sclerosis | hardenability of an ink droplet compatible can be provided, image quality is high, image hardness and image An image having excellent bending resistance can be provided.

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

1. About the photocurable inkjet ink The photocurable inkjet ink contains at least a coloring material, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator.

About Photopolymerizable Compound A photopolymerizable compound is a compound that crosslinks or polymerizes upon irradiation with light. The present invention is characterized in that the ink droplets are cured by irradiating the ink droplets with ultraviolet rays from an LED light source. The photopolymerizable compound is a radical polymerizable compound or a cationic polymerizable compound, and preferably a radical polymerizable compound.

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

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

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

  The inkjet ink of the present invention is a (meth) acrylate compound (hereinafter referred to as “polymerization”) having a molecular weight of 280 to 1500 and a ClogP value of 4.0 to 7.0 as a photopolymerizable compound. Compound A ″) and a polyester acrylate oligomer.

About the polymeric compound A Although the polymeric compound A is a compound which has a (meth) acrylate group, it is more preferable to have two or more (meth) acrylate groups.

  The molecular weight of the polymerizable compound A is preferably in the range of 280 to 1500, and more preferably in the range of 300 to 800. In order to stably eject ink droplets from the ink jet recording head, it is necessary that the ink viscosity at the ejection temperature be between 7 and 14 mPa · s. An ink composition containing a polymerizable compound having a molecular weight of less than 280 and a gelling agent has an excessively large change in the viscosity of the ink before and after the discharge temperature, so that the ink composition can be stably discharged from the ink jet recording head. It is difficult to maintain the temperature. Further, by selecting a polymerizable compound having a molecular weight of 280 or more, the problem of the odor of the ink itself or the odor of the printed matter, which has been a problem with the ink containing the conventional radical polymerizable compound, can be solved.

  Moreover, since the sol viscosity of the ink composition having a polymerizable compound having a molecular weight exceeding 1500 and a gelling agent is too high, it is not suitable as a composition for an inkjet ink.

  The ClogP value of the polymerizable compound A is preferably in the range of 4.0 to 7.0, and more preferably in the range of 4.5 to 6.0. If the ClogP value of the polymerizable compound A is less than 4.0, the inkjet ink becomes hydrophilic, the gelling agent is difficult to dissolve, and the gelling agent may not be completely dissolved even when heated. Therefore, gelation is not stable. On the other hand, when the ClogP value of the polymerizable compound A exceeds 7.0, the solubility of the photopolymerization initiator / initiator aid in the ink is lowered, the curability is lowered, or the ejection property from the ink jet recording head is decreased. Or drop.

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

The “CLogP value” is a LogP value calculated by calculation. The CLogP value can be calculated by a fragment method, an atomic approach method, or the like. More specifically, ClogP values can be calculated in the literature (C. Hansch and A. Leo, “Substituent Constants for Correlation Analysis in Chemistry and Biology” (John Wiley & Sons, New York, 69). Or the following commercially available software package 1 or 2 may be used.
Software Package 1: MedChem Software (Release 3.54, Aug. 1991, Medicinal Chemistry Project, Pomona College, Clarmont, CA)
Software package 2: Chem Draw Ultra ver. 8.0. (April 2003, CambridgeSoft Corporation, USA)

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

  The content of the polymerizable compound A in the inkjet ink is preferably in the range of 10 to 40% by mass. If it is less than 10% by mass, the ink becomes hydrophilic, the solubility of the gelling agent is lowered, and the stability of gelation is lowered. If it exceeds 40% by mass, shrinkage increases when the ink droplets are cured, the printed matter curls, and the image film may break when the image is folded.

More preferred examples of the polymerizable compound A have (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 are included. These polymerizable compounds have high photocurability, are suppressed from shrinkage when cured, and further improve reproducibility of the sol-gel phase transition.

(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; For example, a hydroxyl group of a compound having three 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, ClogP4.90, manufactured by Cognis), 3PO-modified trimethylolpropane triacrylate Miramer M360 (molecular weight 471, ClogP4.90, 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 P 4.69), tricyclodecane dimethanol dimethacrylate NK ester DCP (molecular weight 332, Clog P 5.12), and the like. included.

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

About Polyester Oligomer The inkjet ink of the present invention contains a polyester acrylate oligomer as a polymerizable compound. The polyester acrylate oligomer preferably has an average functional group number of 2 or more (having an average of 2 or more (meth) acryl groups per molecule) from the viewpoint of improving photocurability. The polyester acrylate oligomer is a compound obtained by esterifying a polyester oligomer having a hydroxyl group with (meth) acrylic acid.

  The viscosity of the polyester acrylate oligomer of the present invention at 25 ° C. is preferably 40 to 1000 mPa · s, and more preferably 50 to 700 mPa · s from the viewpoint of ejection stability.

  The content of the polyester acrylate oligomer in the inkjet ink of the present invention is preferably 5.0 to 20.0% by mass, and more preferably 7.0 to 15.0% by mass. When the content of the polyester acrylate oligomer in the ink-jet ink is less than 5% by mass, the gelation (crystallization) may not be stably performed; Not only is it high, but the solubility of the gelling agent at the time of sol formation (at high temperature) is deteriorated, so that it is not suitable as the ink-jet ink composition of the present invention. The mechanism of action of the polyester acrylate oligomer is not limited, but in a system in which the polyester acrylate oligomer having a large number of ester groups having weak polarity and the above-described polymerizable compound A having relatively high hydrophobicity are uniformly mixed. During gelation (at high temperatures), a gelling agent having a hydrophobic part and a hydrophilic part (polar group) can be stably present (= compatible) while maintaining high homogeneity. It is presumed that (crystallization) occurs quickly and ink coalescence can be effectively prevented. Content which can express such an effect is 5.0-20.0 mass%. In addition, urethane acrylate oligomers are well known as acrylate oligomers used in inks, inks, paints, etc., but due to the strong polarity of urethane groups, compatibility at the time of sol formation (at high temperatures) is impaired. It was found that the ink composition using a gelling agent cannot be used because gelation (crystallization) during cooling is inhibited.

Specific examples of the polyester acrylate oligomer include, but are not limited to, the following.
BASF's Laromer PE9074: average functional group number 2, 25 ° C. viscosity 7000-13000 mPa · s.
CN2270 manufactured by Sartomer: average functional group number 2, 25 ° C viscosity 55 mPa · s, CN2273: average functional group number 2, 25 ° C viscosity 100 mPa · s, CN2303: average functional group number 6, 25 ° C viscosity 350 mPa · s, CN2302: average functional group number 16, 25 degreeC viscosity 300mPa * s, ETERCURE6361-100 by ETERNAL CHEMICAL company: Average functional group number 8, 25 degreeC viscosity 200mPa * s, ETERCURE6362-100: Average functional group number 12-15, 25 degreeC viscosity 600mPa * s.
M-6200 manufactured by Toagosei Co., Ltd .: average functional group number 2, 25 ° C. viscosity 700-3700 mPa · s, M-6250: average functional group number 2, 25 ° C. viscosity 300-700 mPa · s.

Other Polymerizable Compound The inkjet ink of the present invention may further contain another polymerizable compound as the polymerizable compound. The other polymerizable compound may be a (meth) acrylate monomer and / or an oligomer.

  The other polymerizable 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 polymerizable compounds include, but are not limited to, the following.
4EO-modified hexanediol diacrylate CD561 from Sartomer, 3EO-modified trimethylolpropane triacrylate SR454, 6EO-modified trimethylolpropane triacrylate SR499, 4EO-modified pentaerythritol tetraacrylate SR494, polyethylene glycol diacrylate NK ester from Shin-Nakamura Chemical Co., Ltd. A-400, NK ester A-600, polyethylene glycol dimethacrylate NK ester 9G, NK ester 14G, tetraethylene glycol diacrylate V # 335HP manufactured by Osaka Organic Chemical Co., Ltd.

  In conventional photocurable inkjet inks that undergo sol-gel phase transition, the compatibility between the gelling agent and the polymerizable compound has not been studied in detail, and even if dot coalescence can be suppressed at the initial stage of printing, It sometimes became unstable. In addition, since the cured product of the photopolymerizable compound is greatly shrunk, the printed material is curled, and the image film is broken when the image is bent.

  The inventors of the present invention blended a specific amount of the polymerizable compound A and the polyester acrylate oligomer in an inkjet ink so that the sol-gel phase transition photocurable inkjet ink has good curability and high image quality (dot blending). It has been found that characteristics such as suppression, character crushing, and reproducibility (gelator dissolution stability = discharge stability) can be satisfied.

  The reason why the inkjet ink of the present invention gives a high-quality image is not limited, but can be considered as follows, for example. That is, the inclusion of the polymerizable compound A in the ink-jet ink increases the solubility of the gelling agent and increases the ejection stability of the ink droplets. Furthermore, since the gelling agent is stably and rapidly precipitated or crystallized by including the polyester acrylate oligomer in the inkjet ink, it is considered that coalescence of ink droplets is effectively suppressed.

  Furthermore, in the inkjet ink of the present invention, a polyester acrylate oligomer having a large number of weak polar groups and a (meth) acrylate having relatively high hydrophobicity are mixed relatively uniformly. Therefore, the gelling agent which has a hydrophobic part and a hydrophilic part can exist uniformly in these polymeric compounds.

  In this way, a high quality image can be obtained with the inkjet ink of the present invention.

About gelling agent The gelling agent contained in the ink-jet ink has a function of reversibly changing the sol-gel phase of the ink depending on the temperature. Such a gelling agent is at least 1) soluble in a solvent in the ink (in the present invention, photopolymerizable compound A and other polymerizable compounds and polyester acrylate oligomers) at a temperature higher than the gelation temperature. 2) It is necessary to crystallize in the ink at a temperature below the gelation temperature.

  In 1), the “sol-gel phase transition temperature” refers to the temperature at the change (transition) point at which the sol state changes to the gel state (transition). Gel transition temperature, gel dissolution temperature, gel softening temperature, sol-gel transition point gel It is synonymous with a term called a conversion point.

  In 2), when the gelling agent is crystallized in the ink, a plate crystal which is a crystallized product of the gelling agent forms a space three-dimensionally enclosed, and the photopolymerizable compound is included in the space. Is preferred. 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”. Once the card house structure is formed, the liquid photocurable compound can be retained and the ink droplets can be pinned. Thereby, coalescence of droplets can be suppressed. The card house structure means a state in which a liquid photopolymerizable compound is held in the space.

  In order to stably discharge ink droplets, the solvent (in the case of the present invention, photopolymerizable compound A and other polymerizable compounds and polyester acrylate oligomer) and a gelling agent in the ink at the time of sol formation (at high temperature) It is necessary to ensure compatibility. Furthermore, in order to stably suppress the coalescence of the droplets even during high-speed printing, it is required that the ink droplets are quickly cooled after landing on the recording medium, and the gelling agent is rapidly crystallized, which is preferable. Is required to form a strong card house structure. The reason why the present invention enables the compatibility of the gelling agent and quick crystallization is as described in the description of the polyester acrylate oligomer.

  The sol-gel transition temperature of the ink-jet ink is arbitrarily set, but is preferably in the range of 30 to 100 ° C. from the viewpoints of stable emission of ink droplets, adverse effects associated with high-temperature heating, and the like. The sol-gel transition temperature is preferably between the ink temperature in the ink jet recording head and the temperature of the recording medium.

  The sol-gel transition temperature is measured by, for example, placing a gel-like test piece on a heat plate, heating the heat plate, measuring the temperature at which the shape of the test piece collapses, and obtaining this as the sol-gel phase transition temperature. be able to. It can also be measured using a commercially available viscoelasticity measuring device (for example, viscoelasticity measuring device MCR300 manufactured by Physica).

  The sol-gel transition temperature can be adjusted by the type and amount of gelling agent and photopolymerizable compound described later.

  Examples of gelling agents include dialkyl ketones, fatty acid esters, fatty acid alcohols, fatty acid amides, oil gelling agents and the like.

  Specific examples of gelling agents include stearone (18-pentatriacontanone), 16-hentriacontanone, 12-tricosanone, UNILIN425 and other fatty alcohols, fatty acid esters, stearic acid inulin / fatty acid dextrin (Chiba as Leopearl series) Available from milling), L-glutamic acid derivatives (available from Ajinomoto Fine Techno Co., Ltd.), fatty acid amides (FATTY AMID series, available from Kao Corporation), eicosandioic acid glyceryl behenate (Nomcoat HK-G, Nisshin Oilio) Preferred examples include low molecular weight compounds having a molecular weight of less than 1000, such as jojoba ester (available from Floraester 70, Ikeda Bussan Co., Ltd.), and oil gelling agents described in JP-A-2005-126507 and JP-A-2005-255821. , This does not apply.

  Specific examples of gelling agents that are fatty acid amides include FATTY AMID E: erucic acid amide, FATTY AMID T: oleic acid amide, FATTY AMID ON: hardened beef fatty acid amide (available from Kao) , Nikkaamide AP1: stearic acid amide (available from Nippon Kasei Co., Ltd.), GP-1: N-lauroyl-L-glutamic acid dibutylamide (available from Ajinomoto Fitechno Co., Ltd.), and the like.

  However, a gelling agent having a polar group such as —OH or —COOH at the end of a fatty acid amide or urethane compound or an alkyl chain having 12 or more carbon atoms may have poor stability in heated ink and may precipitate. Or layer separation. Further, the gelling agent gradually elutes from the image film after UV curing with the passage of time, which causes a problem depending on the storage conditions of the image.

Thus, particularly preferred gelling materials include 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 chain having a straight chain portion having 12 or more carbon atoms and may have a branch.

  General formula (G1) is called a ketone wax, and general formula (G2) is called a fatty acid ester. These gelling agents are preferable because the ink droplets can be gelled more stably (with good reproducibility), and coalescence of ink droplets (dots) landed on the recording medium can be suppressed.

  Specific examples of the gelling agent which is a ketone wax and a fatty acid ester include those described in Table 1 below, but are not limited thereto.

  Since the ink-jet ink of the present invention contains a predetermined amount of the gelling agent, it is ejected from the ink-jet recording head, landed on the recording medium as ink droplets, and promptly when lowered to a temperature lower than the sol-gel phase transition temperature. It becomes a gel state. For this reason, mixing of dots and dot coalescence are suppressed, and high image quality can be formed during high-speed printing. Thereafter, the gelled ink droplets are irradiated with light and cured, whereby the ink droplets are fixed on the recording medium to form a strong image film.

  In the ink-jet ink of the present invention, the ink droplets that have landed on the recording medium rapidly gel, and the ink droplets do not diffuse on the recording medium, so that oxygen in the environment does not easily enter the ink droplets. As a result, curing is less susceptible to oxygen inhibition.

  The content of the gelling agent in the inkjet ink is preferably 0.5 to 10% by mass, more preferably 1 to 7% by mass. If it is less than 0.5% by mass, the ink droplet cannot be gelled (sol-gel phase transition due to temperature), and if it exceeds 10% by mass, it cannot be sufficiently dissolved in the ink, and the ink droplet is ejected. This is because the sex is lowered.

About Photopolymerization Initiator The photocurable inkjet ink may further contain a photopolymerization initiator as necessary.

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;
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, 4,4′-diethylaminobenzophenone;
Examples include 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, camphorquinone and the like.

  Of these, acylphosphine oxide and acylphosphonate can be preferably used from the viewpoint of sensitivity.

  Specifically, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide, and the like are preferable.

  A preferable addition amount of the photopolymerization initiator is 0.1 to 10% by mass, particularly preferably 2 to 8% by mass, based on the entire ink composition.

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

  Examples of polymerization inhibitors include (alkyl) phenol, hydroquinone, catechol, resorcin, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone , Nitrosobenzene, 2,5-di-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.

Regarding Color Material The ink-jet ink preferably contains at least one of various known dyes and pigments, and particularly preferably contains a pigment.

The pigments that can be included in the inkjet ink are listed below.
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 diameter of the pigment is preferably 0.08 to 0.5 μm, and the maximum particle diameter of the pigment is 0.3 to 10 μm, 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 that can be included in the inkjet ink can be an oil-soluble dye or the like. Examples of oil-soluble dyes include the following various dyes. Examples of magenta dyes include MS Magenta VP, MS Magenta HM-1450, MS Magenta HSo-147 (manufactured by Mitsui Toatsu), AIZENSOT Red-1, AIZEN SOT Red-2, AIZEN SOTRed-3, and AIZEN SOT. Pink-1, SPIRON Red GEH SPECIAL (above, manufactured by Hodogaya Chemical Co., Ltd.), RESOLIN Red FB 200%, MACROLEX Red Violet R, MACROLEX ROT5B (above, manufactured by Bayer Japan), KAYASET Red B, KAYASE RED130, 802 (above, Nippon Kayaku Co., Ltd.), PHLOXIN, ROSE Bengal, ACID Red (above, Daiwa Kasei Co., Ltd.), H R-31, DIARESIN Red K (manufactured by Mitsubishi Kasei Corp.), include Oil Red (manufactured by BASF Japan Ltd.).

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

  Examples of yellow dyes include MS Yellow HSm-41, Yellow KX-7, Yellow EX-27 (Mitsui Toatsu), AIZEN SOT Yellow-1, AIZEN SOT Yellow W-3, AIZEN SOT Yellow-6 (above, Hodogaya) 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 photocurable inkjet ink. This is because if the content of the pigment or dye is too small, the color of the resulting image is not sufficient, and if it is too large, the viscosity of the ink increases and the jetting property decreases.

  Moreover, the 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.

  The pigment must be dispersed in the inkjet ink. Therefore, it is preferable to obtain an inkjet ink by preparing a pigment dispersion and further mixing the pigment dispersion and other ink components.

  The pigment dispersion is prepared by dispersing the pigment in a dispersion medium. The pigment may be dispersed using, 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. Further, a dispersing agent can be added when dispersing the pigment. As the dispersant, a polymer dispersant is preferably used, and examples of the polymer dispersant include Avecia's Solsperse series and Ajinomoto Fine-Techno's PB series.

  The dispersion medium of the pigment dispersion can be a solvent or a polymerizable compound; however, the ink-jet ink in the present invention is preferably gel-free immediately after landing on the recording medium, and is preferably solvent-free. Further, if the solvent remains in the cured image, solvent resistance is deteriorated and VOC of the remaining solvent is caused. Therefore, the solvent-free ink is preferable. Therefore, the dispersion medium of the pigment dispersion is preferably not a solvent but a polymerizable compound, particularly a monomer having the lowest viscosity, in view of dispersion suitability.

Other components The photocurable inkjet ink may further contain other components as necessary. Other components may be various additives, other resins, and the like. Examples of the additive include a surfactant, a leveling additive, a matting agent, an ultraviolet absorber, an infrared absorber, an antibacterial agent, and a basic compound for enhancing the storage stability of the ink. Examples of 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.

About Sol-Gel Phase Transition Inkjet Ink Since the photocurable inkjet ink contains a gelling agent as described above, it undergoes a sol-gel phase transition reversibly depending on the temperature. Since the photocurable ink that undergoes a sol-gel phase transition is a liquid (sol) at a high temperature (for example, about 80 ° C.), it can be ejected in a sol state from an inkjet recording head. When the photocurable inkjet ink is discharged at a high temperature, ink droplets (dots) land on the recording medium, and then naturally cool to gel. Thereby, coalescence of adjacent dots can be suppressed and image quality can be improved.

  In order to improve the ejection properties of the ink droplets, it is preferable that the viscosity of the ink at a high temperature is not more than a certain level. Specifically, the viscosity of the photocurable inkjet ink at 80 ° C. is preferably 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 of the photocurable inkjet ink at 25 ° C. 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 °.

About the manufacturing method of an inkjet ink A photocurable inkjet ink can be obtained by mixing each component containing the above-mentioned photocurable compound and a gelatinizer under a heating. Preferably, a pigment dispersant in which a color material (particularly a pigment) is dispersed in a part of the polymerizable compound is prepared and mixed with the pigment dispersant and another ink component containing another polymerizable compound.

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 causing a photocurable inkjet ink to be ejected from an inkjet recording head and adhering it onto a recording medium. (2) A droplet landed on the recording medium is irradiated with light from an LED light source to form the ink droplet. Process of curing

(1) Process The photocurable inkjet ink may be the inkjet ink described 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. Since the ink configuration of the present invention can ensure the dissolution stability of the gelling agent, a high-definition image can be stably formed even with the amount of droplets.

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

  In the inkjet ink according to the present invention, the gelling agent is stably dissolved in the ink solvent (polymerizable compound A, other polymerizable compound and polyester acrylate oligomer). The gloss can be adjusted. If it cannot be stably present in the ink solvent, part of the gelling agent is deposited during ejection, causing nozzle clogging and image quality degradation. Further, if the crystallization of the gelling agent is delayed after the ink has landed on the recording medium, the dots are mixed even if the temperature of the recording medium is adjusted, and the image is lowered.

  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 By irradiating the ink droplets landed on the recording medium with light, the photopolymerizable compound contained in the ink droplets is cross-linked or polymerized and the ink droplets are cured to form an image.

  The light applied to the ink droplets attached to the recording medium is preferably ultraviolet light from an LED light source. Specifically, a 395 nm, water-cooled LED manufactured by Phoseon Technology can be used. A metal halide lamp or the like may be used as an ultraviolet light source. However, by using an LED as a light source, it is possible to prevent defective curing of the ink droplet cured film surface due to melting of the ink droplet by the radiant heat of the light source. It is done.

The LED as the light source is preferably installed with ultraviolet rays of 370 to 410 nm so that the peak illuminance on the image surface is 0.5 to 10 W / cm ² in order to cure the ink droplets, and 1 to 5 W / cm. It is more preferable to install so as to be ² . The amount of light applied to the image is preferably less than 350 mJ / cm ² . This is to prevent the radiant heat from being applied to the ink droplets.

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

Inkjet recording apparatus The image recording method of the present invention can be carried out using a photocurable inkjet recording apparatus. There are two types of photo-curing type ink jet recording apparatuses: 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 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 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 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 diagram illustrating an example of a configuration of a main part of the serial recording type inkjet recording apparatus 20. As shown in FIG. 2, the inkjet recording apparatus 20 has a width narrower than the entire width of the recording medium, instead of the head carriage 16 fixedly arranged so as to cover the entire width of the recording medium, and a plurality of inkjet recording heads. 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. 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.

<< Preparation of pigment dispersion >>
The pigment dispersion was prepared according to the following procedure. The following two compounds were placed in a stainless beaker and dissolved by stirring and heating for 1 hour while heating on a hot plate at 65 ° C.
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 weight of Pigment Black 7 (Mitsubishi Chemical Co., Ltd., # 52) as a pigment is added thereto, and it is put in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm and sealed with a paint shaker for 5 hours. After the dispersion treatment, zirconia beads were removed.

Inks of the examples and comparative examples were prepared using the following components.
(Photopolymerizable compound A)
Miramer M360 (Miwon) Molecular weight 471, Clog P value 4.90
NK ester A-DCP (manufactured by Shin-Nakamura Chemical Co., Ltd.) Molecular weight 304, ClogP value 4.69
NK ester DOD-N (manufactured by Shin-Nakamura Chemical Co., Ltd.) Molecular weight 310, Clog P value 5.75
Photomer 4072 (manufactured by Cognis) Molecular weight 471, Clog P value 4.90

(Polyester acrylate oligomer)
Laromer PE9074 (BASF)
ETERCURE6361-100 (manufactured by ETERNAL CHEMICAL)
CN2270 (manufactured by Sartomer)
CN2273 (Sartomer)
CN2303 (Sartomer)

(Gelling agent)
Distearyl ketone (Kao wax T1, manufactured by Kao Corporation), (18-Pentatria cationone, reagent (Arfa Aeser))
Dipalmityl ketone (Hentriacontan-16-on, reagent (Arfa Aeser))
Dilauryl ketone (12-tricosanone, reagent (Arfa Aeser))
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, high alcohol industry)
Behenyl behenate (Unistar M-2222SL, NOF Corporation)

(Surfactant)
KF-352 (manufactured by Shin-Etsu Chemical)
(Photopolymerization initiator)
DAROCURE TPO (BASF)
ITX (made by DKSH Japan)
(Sensitization aid)
KayacureEPA (Nippon Kayaku)

<Preparation of ink>
Each component and the pigment dispersion were mixed according to the composition of the ink described in Tables 2 to 5, heated to 80 ° C. and stirred. The obtained solution was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC under heating. In addition, the unit of the component of each table | surface is a mass part.

<< Inks of Comparative Examples 3, 4, 5, 6 and Examples 1, 2, 3, 4 >>
The ink composition was prepared as shown in Table 2. Comparative Examples 3 to 6 are examples prepared by making the amount of the polymerizable compound A excessive or small, and Examples 1 to 4 are examples prepared by changing the kind and amount of the polymerizable compound A.

<< Inks of Comparative Examples 7 and 8 and Examples 5, 6, 7, and 8 >>
An ink was prepared in the same procedure as in Example 1 except that the composition of the ink was changed as shown in Table 3. Comparative Examples 7 and 8 are examples prepared by making the amount of the polyester acrylate oligomer excessive or small, and Examples 5 to 8 are examples prepared by changing the kind and amount of the polyester acrylate oligomer.

<< Inks of Comparative Examples 9, 10 and Examples 9, 10, 11, 12, 13 >>
An ink was prepared in the same procedure as in Example 1 except that the composition of the ink was changed as shown in Table 4. Comparative Examples 9 and 10 are examples prepared by making the amount of the gelling agent excessive or small, and Examples 9 to 13 are examples prepared by changing the kind and amount of the gelling agent.

<< Inks of Comparative Examples 11 and 12 and Examples 14 , 15 and 16 >>
An ink was prepared in the same procedure as in Example 1 except that the composition of the ink was changed as shown in Table 5. Note that Comparative Examples 11 and 12 and Examples 14 , 15 , and 16 have the same ink composition but different image forming methods.

  In Comparative Example 1, ink for Phaser 860 manufactured by Xerox was used. Comparative Example 2 is a UV curable ink containing no gelling agent (ink 9 of Example Formulation 1 of US Pat. No. 7,432,072 B2) and a UV curable ink containing a gelling agent (tetrahydrofurfuryl acrylate). Was added 5%, and 3% stearyl stearate and 2% distearyl ketone were added instead).

<Ink evaluation>
<Sol-gel phase transition temperature>
Table 6 shows the sol-gel phase transition temperature of each ink. The sol-gel phase transition temperature was measured with a viscoelasticity measuring device MCR300 manufactured by Physica, share rate 11 (1 / s).
<Gelating agent dissolution stability>
The dissolution state after standing at 100 ° C. for 4 hours was visually observed. The evaluation results are shown in Table 6.
○: No separation or precipitation ×: Oil balls are gathered on the surface (separated layers)
<Ink odor>
The odor during heating at 100 ° C. was evaluated. The evaluation results are shown in Table 6.
○: Small smell ×: Strong pungent odor

  As shown in Table 6, when the amount of the polymerizable compound A is small (Comparative Examples 3 and 4), when the polymerizable compound A is large and does not contain the polyester acrylate oligomer (Comparative Example 6), the polyester acrylate oligomer When the amount of gel was large (Comparative Example 8), when the amount of the gelling agent was large (Comparative Example 10), the gel dissolution stability decreased. Further, the reason why odor is generated in the inks of Comparative Example 1 and Comparative Example 2 is considered to include a polymerizable compound having a molecular weight of less than 280.

<< Inkjet image forming 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. Using this apparatus, 500 sheets of image recording were continuously performed on chrysanthemum half-sized coated paper (OK top coat, manufactured by Oji Paper Co., Ltd.) and high-quality paper (OK Prince fine quality, manufactured by Oji Paper Co., Ltd.).

  The ink supply system includes 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. The ink is heated to 100 ° C. from the ink tank to the head portion. 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 white character) was formed in the solid image.

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. The conveyance speed of the recording medium was 30 m / s or 60 m / s. The amount of light was 400 mJ / cm ² at a conveyance speed of 30 m / s and 200 mJ / cm ² at a conveyance speed of 60 m / s. The photometers used were UV integrated photometers C9536 and H9958 manufactured by Hamamatsu Photonics. For comparison, a cured sample was also produced using a metal halide lamp MAP200NL manufactured by GS Yuasa. The amount of light was 200 mJ / cm ^{2 as} measured by a 365 nm sensor of a UVPF-A1 light meter made by Iwasaki Electric Co., Ltd. at a conveyance speed of 30 m / s.

As shown in Table 6, the recording medium conveyance speed, the type of light source (LED or metal halide lamp), and the heating temperature of the recording medium were adjusted, and ink jet images were obtained using the ink jet inks of the examples and comparative examples. Table 6 shows the evaluation results of the inks of Comparative Examples 1 to 12 and Examples 1 to 16 and the image forming conditions at the time of evaluation.

<Image formation evaluation>
<Image quality (white blank)>
Regarding the image output products of the inks of the examples and comparative examples, it was visually confirmed whether there were any white spots (unprinted portions due to dot coalescence) in the solid image portions when the 10th and 500th sheets were printed.
○: 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)>
The image output products of the inks of Examples and Comparative Examples were visually evaluated for the quality of 3pt Mincho characters when printing the 10th and 500th sheets.
○: Reproduced △: Some characters are crushed ×: Characters are crushed

<Image quality (glossy)>
The 60-degree gloss value of the 100% printed portion of the 10th sheet was measured for the OK top coat paper image output material of the chrysanthemum size of the ink of the example and the comparative example. The gloss meter was measured using Gloss Mobile GM-1 manufactured by Suga Test Instruments Co., Ltd.
○: 15-60
Δ: 61-100 and 1-14
(For many coated papers and art papers such as OK top-coated paper, the range of 15 to 60 is preferable because there is no sense of incongruity with the white paper)

<Curability evaluation (pencil hardness)>
With regard to the output image of the OK top coat paper of chrysanthemum size of the ink of the example and the comparative example, after leaving the 10th solid image part in an environment of 25 ° C. and 60% RH for 24 hours, it was changed to JIS-K-5400. Similarly, the pencil hardness of the surface was measured and evaluated according to the following rank, and was taken as one of the indicators of curability.
○: Pencil hardness of 2H or more △: B, F, H
×: 2B or less

<Bending resistance>
For the OK top coat paper image output material of the ink size of Example and Comparative Example, the 10th solid image portion was left in an environment of 25 ° C. and 60% RH for 24 hours and then folded in half.
○: Image film does not break ×: Image film breaks at the folded part

<Image preservation>
For the OK top coat paper image output products of chrysanthemum size inks of the examples and comparative examples, the 10th solid image part was left for 1 month in an environment of 40 ° C. and 80% RH, and then the image surface was visually confirmed.
○: No precipitate Δ: Slightly white precipitate is present ×: Gelling agent is deposited on the entire surface of the image and cannot be used as a printed matter The evaluation results are shown in Table 7.

  When the polymerizable compound A was not included (Comparative Example 3), white spots and character quality deteriorated on the 500th sheet. This is thought to be due to a decrease in the ejection stability of the ink droplets. When the amount of the polymerizable compound A was large (Comparative Example 5), when the amount of the polymerizable compound A was large and the polyester acrylate oligomer was not included (Comparative Example 6), the bending resistance was lowered. This is thought to be because the cured density of the cured product increased and the cured film became brittle.

  When there were few polyester acrylate oligomers (comparative example 7), the 500th white blank, character quality, and bending resistance fell. This is considered to be due to the fact that the gelling agent becomes difficult to crystallize, the pinning property is lowered, and the image characteristics such as character quality are lowered.

  When there were many polyester acrylate oligomers (comparative example 8), the pencil hardening degree fell. This is probably because a sufficient photocuring reaction did not proceed.

  When the amount of the gelling agent was small (Comparative Example 9), white spots and deterioration in character quality occurred on both the 10th and 500th sheets. This is considered to be because ink droplets cannot be pinned after landing on the recording medium. When there were many gelling agents (comparative example 10), the pencil hardening degree fell. This is considered to be because the gelling agent inhibited the photocuring of the polymerizable compound.

When the conveyance speed of the recording medium was slow ( Comparative Example 11 ), the solid portion image surface gloss and bending resistance were lowered. This is thought to be because the leveling was lowered and the cured density of the cured product was increased, and the cured film became brittle. When the light source for irradiating the ink droplets was a metal halide lamp (Comparative Example 12), white spots, character quality, and solid image surface gloss were reduced on the 10th and 500th sheets. This is presumably because the ink droplets melt due to the radiant heat of the metal halide lamp, resulting in poor curing of the cured film surface of the ink droplets.

  From the results shown in Table 7, it can be seen that in various evaluations, an image formed using the photocurable inkjet ink of the present invention is superior to an image formed using the comparative ink.

  That is, it can be seen that the means of the present invention can provide a photocurable ink-jet ink that can stably form a fine image even in high-speed recording and has good adaptability to various recording media. It can also be seen that an image forming method using the same can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the image formation method using the photocurable inkjet ink which makes the stability of gelatinization and the sclerosis | hardenability of an ink droplet compatible can be provided.

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

Claims (5)

Ink droplets of a photo-curable inkjet ink containing a coloring material, a gelling agent, a photopolymerizable compound and a photopolymerization initiator and undergoing a sol-gel phase transition with temperature are ejected from an inkjet recording head and adhered onto a recording medium. And a step of irradiating the droplets landed on the recording medium with light from an LED light source to cure the ink droplets,
The content of the gelling agent is in the range of 1.0 to 7.0% by mass with respect to the total mass of the ink,
The photopolymerizable compound includes a (meth) acrylate compound having a molecular weight in the range of 280 to 1500 and a ClogP value in the range of 4.0 to 7.0, and a polyester acrylate oligomer.
The content of the (meth) acrylate compound is in the range of 10 to 40% by mass with respect to the mass of the entire ink,
The content of the polyester acrylate oligomer is in the range of 5.0 to 20.0% by mass with respect to the mass of the entire ink,
The light have a peak irradiance 0.5~10.0W / cm ² to 370～410Nm, and light quantity of the light is less than 350 mJ / cm ^2, an image forming method. Wherein the ClogP value is in the range of 4.0 to 7.0 (meth) acrylate compound, which is characterized in that at least one (meth) acrylate compound of the following (1) and (2) Item 4. The image forming method according to Item 1 .
(1) Trifunctional or higher (meth) acrylate compound (2) having a structure represented by (—C (CH ₃ ) H—CH ₂ —O—) _m (m is an integer of ₃ to 14) in the molecule Bifunctional or higher (meth) acrylate compounds with a cyclic structure in the molecule The image forming method according to claim 1 , 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 chain having a straight chain portion having 12 or more carbon atoms and may have a branch.) An image forming method according to any one of claims 1 to 3 ,
The image formation is characterized in that the temperature of the recording medium when the photocurable ink-jet ink lands on the recording medium falls within the range of -20 to -10 ° C of the sol-gel phase transition temperature of the photocurable ink-jet ink. Method. The image forming method according to any one of claims 1 to 4 , wherein:
An image forming method, wherein a peak illuminance at 370 to 410 nm of light irradiated from the LED light source is 1 to 5 W / cm 2.

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