JP6638299B2 - Photocurable inkjet ink and image forming method - Google Patents

Description

  The present invention relates to a photocurable inkjet ink and an image forming method.

  The ink jet recording method is used in various printing fields because an image can be easily and inexpensively formed. As one of the ink jet recording methods, there is an actinic ray curable ink jet method in which droplets of actinic ray-curable ink are landed on a recording medium and then irradiated with actinic rays to be cured to form an image. The actinic ray-curable inkjet method has recently been receiving attention because it can form an image having high abrasion resistance and adhesion even on a recording medium having no ink absorption.

  Addition of a gelling agent has been studied as a method for improving the pinning properties of an actinic ray-curable inkjet ink used in the actinic ray-curable inkjet method. That is, it has been studied to suppress the coalescence of dots by discharging ink droplets in a liquid state at a high temperature and landing them on a recording medium, and simultaneously cooling and gelling the ink droplets.

  In addition, in the inkjet recording method, usually, a suitable combination of inks is selected from yellow ink, magenta ink, cyan ink and black ink according to a color to be formed, and the selected inks are overprinted to form a full-color ink. Form an image. At this time, green ink may be further combined to further expand the color gamut of an image to be formed.

  For the green ink, a pigment having a halogenated copper phthalocyanine structure is used. For example, as an actinic ray-curable inkjet ink compatible with Green in the Panton (registered trademark) color gamut, a light-fast gel ink containing a curable monomer, an organic gelling agent, a photoinitiator, and a colorant has been proposed. (For example, Patent Document 1).

  Further, as an actinic ray-curable inkjet ink with improved pinning properties, an ink containing a pigment, a photopolymerizable compound, a photopolymerization initiator, a gelling agent, and a pigment derivative having a hydrophilic group has been proposed. (For example, Patent Document 2).

JP 2014-118567 A JP 2015-83647 A

  However, since the ink of Patent Document 1 contains a large amount of a gelling agent, there is a problem that the viscosity is high and the ejection stability is low. In addition, depending on the type of the gelling agent, there is also a problem that liquid shift occurs between droplets during image formation. "Liquid" is caused by the fact that after the ink droplet lands on the recording medium, the solidification of the ink droplet due to the crystallization of the gelling agent contained in the ink droplet is inhibited and the gel crystal does not grow. It is a phenomenon. The cause of the liquid shift is not clear, but is considered to be because the pigment having a hydrophobic surface and the gelling agent having a hydrophobic group interact with each other to inhibit the crystal growth of the gelling agent. When the liquid shift occurs, a streak failure (also referred to as an image defect) easily occurs in the obtained image, and it is difficult to form a good quality image.

  In the ink of Patent Document 2, the pigment derivative having a hydrophilic group can reduce the interaction between the pigment and the gelling agent having a hydrophobic group by coating the pigment surface, but this interaction is further reduced. In addition, it is desired that liquid drift can be further suppressed.

  The present invention has been made in view of the above circumstances, and it is possible to suppress liquid drift without impairing ejection stability and to form a photocurable inkjet ink capable of forming a good quality image and image formation using the same. The aim is to provide a method.

[1] A photocurable inkjet ink containing a pigment, a dispersant, a photopolymerizable compound, a photopolymerization initiator, and a gelling agent, wherein the pigment has a halogenated copper phthalocyanine structure having an organic acid residue. Including a pigment, the organic acid residue has a hydrocarbon group having 16 to 20 carbon atoms, and is an organic acid residue having an affinity with the photopolymerizable compound, the photopolymerizable compound is A photocurable inkjet ink comprising a highly polar photopolymerizable compound having a total of 6 or more ethylene oxide groups or propylene oxide groups in an amount of 30% by mass or more based on the total mass of the photopolymerizable compound.
[2] The photocurable inkjet ink according to [1], wherein the organic acid is an abietic acid residue.
[3] The dispersant is a polymer dispersant having a basic group, and the ink further includes a pigment derivative having a copper phthalocyanine structure having a sulfonic acid group or a carboxyl group, [1] or [2]. ] The photocurable inkjet ink according to [1].
[4] The photocurable inkjet ink according to [3], wherein the content of the pigment derivative is 2% by mass or more and 10% by mass or less based on the total mass of the pigment.
[5] The photocurable inkjet ink according to any one of [1] to [4], wherein the content of the gelling agent is 1% by mass or more and 5% by mass or less based on the total mass of the ink.
[6] The light according to any of [1] to [5], wherein the photopolymerizable compound further includes a low-polarity photopolymerizable compound having a total of 3 to 5 ethylene oxide groups or propylene oxide groups. Curable inkjet ink.
[7] The gelling agent is one or more selected from the group consisting of aliphatic ketones, aliphatic esters, higher fatty acids and higher alcohols having a hydrocarbon group having 9 to 25 carbon atoms. The photocurable inkjet ink according to any one of [6].
[8] A step of ejecting the photocurable inkjet ink according to any one of [1] to [7] from a nozzle of an inkjet head to land on a recording medium, and irradiating the landed ink with actinic rays. Curing the ink.

  According to the present invention, it is possible to provide a photocurable inkjet ink capable of forming a good quality image by suppressing liquid drift without impairing the ejection stability, and an image forming method using the same.

  As described above, the cause of the liquid shift is due to the interaction between the “pigment having a hydrophobic surface” and the “gelling agent having a hydrophobic group”, thereby inhibiting the crystal growth of the gelling agent. it is conceivable that. Specifically, when a “pigment having a hydrophobic surface” and a “gelling agent having a hydrophobic group” interact, the pigment is more likely to be linked to the gelling agent (than a photopolymerizable compound), Concentration of the gelling agent in the active compound is reduced. As a result, it is considered that crystallization hardly occurs sufficiently in the photopolymerizable compound, and the liquid shifts when landing. Further, when the crystal growth in the photopolymerizable compound is insufficient, the gloss of the obtained image is excessively increased, and the difference in gloss from the image obtained with the other color ink may be conspicuous.

  On the other hand, the present inventors have found that “liquid-side” can be suppressed by combining “a pigment surface-treated with a specific organic acid” and “a highly polar photopolymerizable compound”. That is, the surface of the “pigment that has been surface-treated with a specific organic acid” is hydrophilic (weakened hydrophobicity), so that the gelling agent having a hydrophobic group is less likely to approach the pigment surface. The organic acid residue of the “pigment surface-treated with a specific organic acid” has a high affinity for the ethylene oxide group (EO group) or the propylene oxide group (PO group) of the highly polar photopolymerizable compound. Have. These make it easier for the pigment to be linked to the photopolymerizable compound (as compared to the gelling agent), so that the concentration of the gelling agent in the photopolymerizable compound can be increased. As a result, crystallization easily occurs in the photopolymerizable compound, so that the liquid can be prevented from drifting at the time of landing, and streak failure can be reduced. Further, since the droplet diameter penetrates into the recording medium without excessively widening, the color gamut can be suppressed from being lowered. Furthermore, since the crystallization of the gelling agent is promoted, it is considered that the difference in gloss from an image obtained with an ink containing another pigment can be reduced.

  Further, by adding a pigment derivative having a sulfonic acid group or a carboxyl group and having a copper phthalocyanine structure, the acidic group of the pigment derivative interacts with the basic group of the dispersant (acid-base bond). In addition, the copper phthalocyanine structure of the pigment derivative and the halogenated copper phthalocyanine structure of the pigment can interact (π-π bond). Thereby, the dispersant can be adsorbed on the surface of the pigment via the pigment derivative. Thereby, aggregation of the pigments can be highly suppressed, and the dispersibility of the pigments can be further enhanced. In addition, the interaction between the pigment and the gelling agent can be reduced, so that the liquid drift can be further suppressed.

1. Photocurable Inkjet Ink The photocurable inkjet ink of the present invention contains a pigment, a dispersant, a photopolymerizable compound, a photopolymerization initiator, and a gelling agent.

1-1. Pigment The pigment includes a pigment having a halogenated copper phthalocyanine structure having a specific organic acid residue. This pigment is obtained by subjecting a pigment having a halogenated copper phthalocyanine structure as a raw material to a surface treatment with a specific organic acid, and is hereinafter also referred to as a “surface-treated pigment”.

  Examples of the pigment having a halogenated copper phthalocyanine structure as a raw material include Pigment Green 7 (PG7) and Pigment Green 36 (PG36). Examples of commercial products of PG7 include PV Fast Green GNX (manufactured by Clariant). Examples of commercially available PG36 include FASTOGEN Green 2YK (manufactured by DIC).

  The specific organic acid is an acid containing 16 to 20 hydrocarbon groups and having an affinity for the photopolymerizable compound. The hydrocarbon group of a specific organic acid is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group or an aromatic hydrocarbon group, and a specific organic acid residue and an EO group of a highly polar photopolymerizable compound. An alicyclic hydrocarbon group or an aromatic hydrocarbon group is preferred from the viewpoint of increasing the high affinity with the PO group. Examples of such specific organic acids include the organic acids contained in rosin and other carboxylic acids, preferably the organic acids contained in rosin.

  Rosin is a residue obtained by removing volatile components such as terpene from natural raw pine resin, and contains at least one selected from the group consisting of abietic acid, neoabietic acid, parastolic acid, bimalic acid, and dehydroabietic acid. Among the organic acids contained in rosin, preferred are abietic acid, neobitienic acid, and parastolic acid having a conjugated double bond, more preferably abietic acid, and even more preferably those containing 80% by mass or more of abietic acid. Commercial products of rosin include Harima Chemical Co., Ltd. Harimac, Arakawa Chemical Industry Co., Ltd. AA-L, and the like.

  The content of the specific organic acid residue in the surface-treated pigment may be 0.05 mol or more and 0.2 mol or less based on 1 mol of the surface-treated pigment. When the content of the specific organic acid residue is 0.05 mol or more per 1 mol of the surface-treated pigment, the hydrophilicity of the pigment is increased, so that the interaction with the gelling agent having a hydrophobic group is suppressed. It can be reduced and the affinity with the highly polar photopolymerizable compound can be increased. Thereby, the function of the gelling agent is hardly hindered. On the other hand, when the content of the specific organic acid residue is 0.2 mol or less per 1 mol of the surface-treated pigment, the proportion of the halogenated copper phthalocyanine structure in the pigment molecule is not too small, and Is not easily damaged.

The content of the specific organic acid residue in the surface-treated pigment is determined by measuring the content of the specific organic acid contained in the ink; calculating the number of moles of the specific organic acid with respect to the number of moles of the pigment. be able to. The content of the specific organic acid contained in the ink can be measured by high performance liquid chromatography (HPLC). HPLC measurement conditions may be as follows.
(Measurement condition)
Measurement device: HPLC (L2130, L2490 manufactured by Hitachi High-Technologies Corporation)
Column: ODS column (5 mm id x 25 cm length, stationary phase: silica gel)
Eluent: acetonitrile / water mixture (80/20 mass ratio)
Sample concentration: 500 ppm
Flow rate: 50 μL / s
Temperature: 40 ° C
Detector: UV
Detection wavelength: 210 nm
Quantification of a specific organic acid can be performed by comparing a previously prepared calibration curve with measured values.

  The content of the specific organic acid residue can be adjusted by, for example, the amount of the alkali salt solution of the specific organic acid added to the aqueous slurry containing the pigment when performing the surface treatment described below.

  The average particle diameter of the pigment particles is preferably from 0.08 μm to 0.5 μm from the viewpoint of further improving the dischargeability from the inkjet head, and the maximum particle diameter of the pigment particles is from 0.3 μm to 10 μm. Preferably, there is. The average particle diameter of the pigment particles means a value determined by a dynamic light scattering method using Datasizer Nano ZSP, manufactured by Malvern. Since the concentration of the ink containing the pigment is high and light is not transmitted by this measuring device, the measurement is performed after diluting the ink by 200 times. The measurement temperature is normal temperature (25 ° C.).

  The surface treatment method using a specific organic acid is not particularly limited.For example, after adding an alkali salt solution of a specific organic acid to an aqueous slurry in which a pigment having a copper phthalocyanine structure as a raw material is dispersed in water, an alkaline earth is added. It may be a method in which a specific organic acid is insolubilized with a salt, an acid, or the like, and precipitated on the pigment surface.

  The content of the surface-treated pigment in the ink is preferably from 1.0% by mass to 10.0% by mass, and more preferably from 2.0% by mass to 5.5% by mass based on the total mass of the ink. Is more preferable.

1-2. Dispersant The dispersant may have a function of increasing the dispersibility of the pigment by directly adsorbing on the pigment surface or indirectly adsorbing via a pigment derivative described below. Examples of dispersants include hydroxyl-containing carboxylic esters, salts of long-chain polyaminoamides and high-molecular-weight acid esters, salts of high-molecular-weight polycarboxylic acids, salts of long-chain polyaminoamides and polar-acid esters, and high-molecular-weight unsaturated acid esters. , High molecular weight copolymer, modified polyurethane, modified polyacrylate, polyetherester type anionic surfactant, naphthalene sulfonic acid formalin condensate, aromatic sulfonic acid formalin condensate, polyoxyethylene alkyl phosphate, polyoxyethylene Nonyl phenyl ether, and stearylamine acetate are included.

  Among them, a polymer dispersant having a basic group is preferable because it has a good affinity with a pigment derivative having a sulfonic acid group or a carboxyl group described below, and is easily indirectly adsorbed on the pigment surface via the pigment derivative. Comb block copolymers having basic groups are more preferred.

  The comb-type block copolymer in the comb-type block copolymer having a basic group refers to a linear polymer that forms a main chain and a graft polymerization of each structural unit derived from a monomer that forms a linear main chain. And other types of polymers. Examples of the comb-type block copolymer include those in which the main chain is a polymer of an acrylate ester and the side chain is a long-chain polyoxyalkyl group (EO-PO copolymer group).

  The basic group in the comb type block copolymer having a basic group is preferably a secondary or primary amine group.

  The basic group of the comb-type block copolymer having a basic group can favorably have affinity with a sulfonic acid group or a carboxyl group of the pigment derivative. Therefore, even at around 85 ° C. where the ink is ejected, the comb-type block copolymer having a basic group is not easily dissociated from the pigment derivative. Further, in the comb-type block copolymer having a basic group, side chains graft-polymerized cause steric hindrance, so that aggregation between pigment derivatives or between pigments can be suppressed. Since the pigment derivative and the pigment have a small primary particle diameter of 50 nm or less, the interaction between the particles is strong, and the pigment has a property of easily aggregating. Therefore, the improvement in the dispersibility by the comb block copolymer is particularly remarkable in a pigment derivative having such a small particle size or an ink containing a pigment. By increasing the dispersibility of the pigment by the above-described action, ejection failure due to agglomerated pigment particles and clogging of the ink ejection recording head hardly occur.

  Examples of commercially available comb-type block copolymers having a basic group include DISPERBYK-161, 168, 2155, Jet9150 and Jet9151 manufactured by BYK; efkaPX4701 and FA4431 manufactured by BASF; PB- manufactured by Ajinomoto Fine-Techno. 821, 822, 824; Solsperse 24000GR, 32000, 35000, 39000, J-100, J-180, J-200, X-300, etc., manufactured by Lubrizol Corporation. “DISPERBYK” is a registered trademark of BYK, “efka” is a registered trademark of BASF, and “Solsperse” is a registered trademark of Lubrizol.

  The content of the dispersant can be 20% by mass or more and 70% by mass or less based on the total mass of the pigment. When the total content is 20% by mass or more with respect to the total mass of the pigment, the dispersant coats the pigment surface directly or indirectly via a pigment derivative, so that the pigment during ink storage can be used. Aggregation between the particles can be made more difficult. When the total content is 70% by mass or less based on the total mass of the pigment, the association between the dispersant and the gelling agent is less likely to occur, and the ink that has landed on the recording medium is more sufficiently gelled. And can be pinned. The total content is preferably from 30% by mass to 60% by mass, more preferably from 35% by mass to 50% by mass, based on the total mass of the pigment.

1-3. Photopolymerizable compound A photopolymerizable compound is a compound that crosslinks or polymerizes when irradiated with actinic rays. Examples of actinic rays include ultraviolet rays, electron beams, α-rays, γ-rays, and X-rays. Ultraviolet rays or electron beams are preferred from the viewpoint of safety and from the viewpoint that polymerization and crosslinking can be caused even with a lower energy amount.

  The photopolymerizable compound can be a radically polymerizable compound or a cationically polymerizable compound. From the viewpoint that polymerization and cross-linking are easily generated and various compounds can be selected according to an image to be formed, a radical polymerizable compound is preferable.

  The radically polymerizable compound is a compound having a radically polymerizable ethylenically unsaturated bond. The radical polymerizable compound may be any of a monomer, a polymerizable oligomer, a prepolymer, and a mixture thereof. Only one radical polymerizable compound may be contained in the ink, or two or more radical polymerizable compounds may be contained.

  Examples of the compound having a radically polymerizable ethylenically unsaturated bond 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, unsaturated urethane, and the like. Examples of unsaturated carboxylic acids include (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, and the like.

  Above all, the radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, and more preferably (meth) acrylate. In the present invention, “(meth) acrylate” means acrylate or methacrylate, “(meth) acryloyl group” means acryloyl group or methacryloyl group, and “(meth) acryl” means acrylic Or methacrylic.

1-3-1. Highly polar photopolymerizable compound The photopolymerizable compound includes a highly polar photopolymerizable compound. The highly polar photopolymerizable compound has a total of 6 or more ethylene oxide groups (hereinafter, also simply referred to as “EO groups”) or propylene oxide groups (hereinafter, also simply referred to as “PO groups”). It is. The ink may contain only one kind of the highly polar photopolymerizable compound or two or more kinds thereof.

  A total of 6 or more EO groups and PO groups may be present as one connected segment or may be divided into two or more segments. However, from the viewpoint of further improving the dispersion stability of the pigment during storage and at the time of emission, when the EO group and the PO group are present in two or more segments, a segment having three or more EO or PO groups Is preferably two or more in the molecule. In addition, from the viewpoint of improving the ejection property, the total number of EO groups and PO groups is preferably 30 or less.

  The highly polar photopolymerizable compound can enhance the dispersibility of the pigment in the photopolymerizable compound and can easily crystallize the gelling agent. This is considered for the following reason. That is, the EO group and the PO group of the highly polar photopolymerizable compound have a high affinity for the organic acid residue (preferably, abietic acid residue) of the pigment. The dispersibility of the pigment in the compound can be increased. Thereby, even at the temperature (60 ° C. or higher) at which the ink is ejected from the ink jet head, the pigment can be dispersed well, and nozzle missing due to precipitation of the pigment during ejection can be suppressed.

  Furthermore, since the pigment is more strongly attracted to the highly polar photopolymerizable compound than the gelling agent, it is considered that the gelling agent is hardly trapped by the pigment and the pinning property of the ink is improved. In particular, when an image is formed on a water-absorbing recording medium, insufficient color formation due to ink entering the recording medium is less likely to occur, and an image in a desired color gamut is easily formed.

Examples of commercially available products of the highly polar photopolymerizable compound include the products shown in Table 1. In Table 1, “the number of EO groups or PO groups” indicates the number of EO groups or PO groups contained in one molecule of the product represented by the brand. In Table 1, "New Frontier" is a registered trademark of Daiichi Kogyo Seiyaku Co., Ltd., and "Fancryl" is a registered trademark of Hitachi Chemical Co., Ltd.

  The content of the highly polar photopolymerizable compound is preferably 30% by mass or more based on the total mass of the photopolymerizable compound. When the content of the highly polar photopolymerizable compound is 30% by mass or more with respect to the total mass of the photopolymerizable compound, the dispersibility of the pigment in the photopolymerizable compound is easily increased, and the gelling agent is used more. Easy to crystallize. On the other hand, if the content of the highly polar photopolymerizable compound in the photopolymerizable compound is too large, the gelling agent having a hydrophobic group is phase-separated from the photopolymerizable compound (the gelling agent precipitates), and the photopolymerization is performed. Since it is difficult to form a crystal structure containing a hydrophilic compound, the gloss of the image surface may be excessively increased. Therefore, from the viewpoint of suppressing the phase separation between the photopolymerizable compound and the gelling agent during image formation and making it difficult for the gloss of the image surface to be excessively generated, the content of the highly polar photopolymerizable compound is determined by the photopolymerizable compound. It is preferably from 30% by mass to 80% by mass, more preferably from 30% by mass to 60% by mass, based on the total mass of the compound.

1-3-2. Low-polarity photopolymerizable compound The photopolymerizable compound may further include a photopolymerizable compound (low-polarity photopolymerizable compound) having a lower polarity than the high-polarity photopolymerizable compound. The low-polarity photopolymerizable compound has a total of less than six ethylene oxide groups (hereinafter, also simply referred to as “EO groups”) or propylene oxide groups (hereinafter, also simply referred to as “PO groups”). It is. The ink may contain only one kind of the low-polarity photopolymerizable compound or two or more kinds thereof.

  Examples of the low-polarity photopolymerizable compound that is (meth) acrylate include monofunctional (meth) acrylate, difunctional (meth) acrylate, and trifunctional or higher (meth) acrylate.

  Examples of the monofunctional (meth) acrylate include isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomyristyl (meth) acrylate, and isostearyl. (Meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) A) acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (Meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid and t-butylcyclohexyl (meth) acrylate Is included.

  Examples of bifunctional (meth) acrylates include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, and polypropylene glycol di (meth) acrylate. (Meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, Dimethylol-tricyclodecane di (meth) acrylate, PO adduct of bisphenol A di (meth) acrylate, neopentyl glycol di (meth) acrylate hydroxypivalate, polytetramethylene glycol di (meth) acrylate ) Acrylate, polyethylene glycol diacrylate and tripropylene glycol diacrylate.

  Examples of the trifunctional or higher functional (meth) acrylate include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and ditrimethylolpropane. Includes tetra (meth) acrylate, glycerin propoxy tri (meth) acrylate and pentaerythritol ethoxy tetra (meth) acrylate.

  Since the low-polarity photopolymerizable compound has a good affinity for the gelling agent having a hydrophobic group, the phase separation between the gelling agent and the photopolymerizable compound is suppressed (precipitation of the gelling agent is suppressed), Excessive luster on the image surface may be less likely to occur. From the viewpoint of enhancing the compatibility between the low-polarity photopolymerizable compound and the high-polarity photopolymerizable compound, the low-polarity photopolymerizable compound preferably has an EO group or a PO group. It is more preferable to have at least five and no more than five.

Examples of the low-polarity photopolymerizable compound having a polar structure include the products shown in Table 2. In Table 2, “the number of EO groups or PO groups” indicates the number of EO groups or PO groups contained in one molecule of the product represented by the brand. In Table 2, "Aronix" is a registered trademark of Toagosei Co., Ltd., and "Miramar" is a registered trademark of Bigen Specialty Chemical Co., Ltd.

  The total content of the high-polarity photopolymerizable compound and the low-polarity photopolymerizable compound may be within a range in which the ink irradiated with the actinic ray is sufficiently cured. % By mass or less. The content of the photopolymerizable compound is preferably 30% by mass or more and 95% by mass or less based on the total mass of the ink.

  From the viewpoint of further increasing both the dispersibility of the pigment and the crystallinity of the gelling agent, the highly polar photopolymerizable compound contains “polyethylene glycol diacrylate having 6 or more ethylene oxide groups”, and has a low polarity photopolymerization. It is preferable that the amphoteric compound contains "trimethylolpropane triacrylate modified with oxyalkylene".

1-4. Photopolymerization initiator The photopolymerization initiator is a photoradical initiator when the photopolymerizable compound is a radical polymerizable compound, and is a photoacid generator when the photopolymerizable compound is a cationic polymerizable compound. The ink may contain only one kind or two or more kinds of photopolymerization initiators. The photopolymerization initiator may be a combination of both a photoradical initiator and a photoacid generator.

  The photo radical initiator can be a cleavage type radical initiator or a hydrogen abstraction type radical initiator.

  Examples of the cleavage type radical initiator include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, and 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-thiomethylphenyl) Acetophenone-based initiators including propan-1-one and 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone, benzoin-based initiators including benzoin, benzoin methyl ether and benzoin isopropyl ether, 2,4,6-trimethylbenzoin diphenyl Acylphosphine oxide initiator containing a phosphine oxide, benzyl and methyl phenylglyoxylate ester.

  Examples of hydrogen abstraction type radical initiators include benzophenone, methyl 4-phenylbenzophenone o-benzoylbenzoate, 4,4′-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4′-methyl-diphenylsulfide, acrylated Benzophenone-based initiators including benzophenone, 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone and 3,3'-dimethyl-4-methoxybenzophenone, 2-isopropylthioxanthone, 2,4- Thioxanthone-based initiators including dimethylthioxanthone, 2,4-diethylthioxanthone and 2,4-dichlorothioxanthone, aminobenzophenone-based initiators including Michler's ketone and 4,4′-diethylaminobenzophenone, 10 Butyl-2-chloro acridone, 2-ethyl anthraquinone, include 9,10-phenanthrenequinone and camphorquinone.

  Examples of the photoacid generator include compounds described in “Organic Materials for Imaging”, edited by Society of Organic Electronics Materials, published by Bunshin Publishing (1993), pp. 187-192.

  The content of the photopolymerization initiator may be within a range capable of sufficiently curing the photopolymerizable compound, and may be, for example, 0.01% by mass or more and 10% by mass or less based on the total mass of the ink.

1-5. Gelling Agent The gelling agent has a function of temporarily fixing (pinning) the ink droplets that have landed on the recording medium in a gel state. When the ink containing the gelling agent is pinned in a gel state, the spread of the ink is suppressed and the adjacent dots are hardly identical, so that a higher definition image can be formed.

  The gelling agent preferably crystallizes at a temperature equal to or lower than the gelation temperature of the ink. The gelation temperature refers to a temperature at which the gelling agent undergoes a phase transition from a sol to a gel when the sol or liquid ink is cooled by heating, and the viscosity of the ink rapidly changes. Specifically, the sol or liquid ink is cooled while measuring the viscosity with a viscoelasticity measuring device (for example, MCR300, manufactured by Physica), and the temperature at which the viscosity sharply rises is determined by the temperature of the ink. It can be a gelling temperature.

  When the gelling agent is crystallized in the ink, a structure in which the photopolymerizable compound is included in the three-dimensional space formed by the gelling agent crystallized in a plate shape may be formed. , Hereinafter referred to as “card house structure”). When the card house structure is formed, the liquid photopolymerizable compound is held in the space, so that the ink droplets are less likely to spread and spread, and the pinning property of the ink is further improved. When the ink pinning property is enhanced, the ink droplets that have landed on the recording medium are less likely to coalesce, and a higher definition image can be formed.

  In order to form a card house structure, the photopolymerizable compound dissolved in the ink and the gelling agent are preferably compatible.

  Examples of gelling agents suitable for forming a card house structure include aliphatic ketones, aliphatic esters, petroleum waxes, plant waxes, animal waxes, mineral waxes, hydrogenated castor oil, modified waxes, higher fatty acids, It includes higher alcohols, fatty acids amides including hydroxystearic acid, N-substituted fatty acid amides and special fatty acid amides, higher amines, esters of sucrose fatty acids, synthetic waxes, dibenzylidene sorbitol, dimer acid and dimer diol. Among them, aliphatic ketones, aliphatic esters, higher fatty acids, and higher alcohols having a hydrocarbon group having 9 to 25 carbon atoms are preferable from the viewpoint of further improving pinning properties. The gelling agent may contain only one kind or two or more kinds in the ink.

  Examples of aliphatic ketones include dilignoseryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone and palmityl stearyl ketone. It is.

  Examples of the aliphatic esters include fatty acid esters of monoalcohols such as behenyl behenate, icosyl icosanoate and oleyl palmitate; glycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters and polyoxyethylene fatty acid esters. And fatty acid esters of polyhydric alcohols. Examples of commercially available products of the above aliphatic esters include EMALEX series, manufactured by Nippon Emulsion Co., Ltd. (“EMALEX” is a registered trademark of the company), Riquemar series and Poem series, manufactured by Riken Vitamin Co., Ltd. (“Riquemar” and “Poem” are Both are registered trademarks of the company).

  Examples of higher fatty acids include behenic, arachidic, stearic, palmitic, myristic, lauric, oleic, and erucic acids.

  Examples of higher alcohols include stearyl alcohol and behenyl alcohol.

  Among them, an aliphatic ketone represented by the following general formula (G1) and an aliphatic ester represented by the following general formula (G2) are particularly preferable.

General formula (G1): R1-CO-R2
In General Formula (G1), R1 and R2 are each a linear or branched hydrocarbon group having 9 to 25 carbon atoms.

General formula (G2): R3-COO-R4
In General Formula (G2), R3 and R4 are each a linear or branched hydrocarbon group having 9 to 25 carbon atoms.

  In the general formulas (G1) and (G2), the linear or branched hydrocarbon group has 9 or more carbon atoms, so that the aliphatic ketone represented by the general formula (G1) or the general formula (G2) The crystallinity of the aliphatic ester represented by the formula (1) is further increased, and more sufficient space is generated in the card house structure. For this reason, the photopolymerizable compound is easily sufficiently included in the space, and the pinning property of the ink is further improved. Since the linear or branched hydrocarbon group has 25 or less carbon atoms, the aliphatic ketone represented by the general formula (G1) or the aliphatic ester represented by the general formula (G2) has a melting point of It does not build up excessively and does not require excessive heating of the ink when ejecting it.

  From the viewpoint of increasing the gelling temperature of the ink, gelling the ink more rapidly after landing, and increasing the compatibility with a specific low molecular weight compound, at least one of R1 and R2 or at least one of R3 and R4 Is preferably a saturated hydrocarbon group having 14 to less than 23 carbon atoms; more preferably, both R1 and R2 or both R3 and R4 are saturated hydrocarbon groups having 14 to less than 23 carbon atoms. preferable.

  Examples of the aliphatic ketone represented by the general formula (G1) include dilignoseryl ketone (carbon number: 23 to 24), dibehenyl ketone (carbon number: 21 to 22), distearyl ketone (carbon number: 17). -18), dieicosyl ketone (carbon number: 19-20), dipalmityl ketone (carbon number: 15-16), dimyristyl ketone (carbon number: 13-14), dilauryl ketone (carbon number: 11) -12), lauryl myristyl ketone (carbon number: 11-14), lauryl palmityl ketone (11-16), myristyl palmityl ketone (13-16), myristyl stearyl ketone (13-18), myristyl behenyl ketone (13 -22), palmityl stearyl ketone (15-18), palmityl behenyl ketone (15-22) and stearyl behenyl ketone (17- 2) are included. The number of carbons in parentheses indicates the number of carbons of each of the two hydrocarbon groups separated by the carbonyl group. Examples of commercially available products of the aliphatic ketone represented by the general formula (G1) include 18-Pentriacontanon, manufactured by Alfa Aeser, Hentriacontan-16-on, manufactured by Alfa Aeser, and Kaowax T1, manufactured by Kao Corporation. .

  Examples of the aliphatic ester represented by the general formula (G2) include behenyl behenate (carbon number: 21-22), icosyl icosanoate (carbon number: 19-20), and stearyl stearate (carbon number: 17-). 18), palmityl stearate (carbon number: 17-16), lauryl stearate (carbon number: 17-12), cetyl palmitate (carbon number: 15-16), stearyl palmitate (carbon number: 15-18) , Myristyl myristate (carbon number: 13-14), cetyl myristate (carbon number: 13-16), octyl dodecyl myristate (carbon number: 13-20), stearyl oleate (carbon number: 17-18), Stearyl erucate (carbon number: 21-18), stearyl linoleate (carbon number: 17-18), behenyl oleate (carbon number: 18-22) Fine linoleic acid arachidyl (carbon number: 17-20) are included. The number of carbons in parentheses indicates the number of carbons of each of the two hydrocarbon groups separated by the ester group. Examples of commercially available products of the aliphatic ester represented by the general formula (G2) include Unistar M-2222SL and Sperm Acet, manufactured by NOF Corporation (“UNISTAR” is a registered trademark of the company), Exepar SS and Exepal MY-M, Kao Corporation (“Exepearl” is a registered trademark of the company), EMALEX CC-18 and EMALEX CC-10, manufactured by Nippon Emulsion Co., Ltd. (“EMALEX” is a registered trademark of the company), and AMLEPS PC; "Includes its registered trademark).

  The content of the gelling agent is preferably from 1.0% by mass to 10.0% by mass with respect to the total mass of the ink. By setting the content of the gelling agent to 1.0% by mass or more, the pinning properties of the ink can be sufficiently increased, and a higher definition image can be formed. In addition, by improving the pinning properties of the ink, it is possible to suppress insufficient color formation due to the ink entering the inside of the recording medium, particularly when an image is formed on a water-absorbing recording medium. When the content of the gelling agent is 10.0% by mass or less, the precipitation of the gelling agent from the surface of the formed image can be suppressed, and the ejection property of the ink from the inkjet head is hardly impaired. The content of the gelling agent is more preferably from 1.0% by mass to 5.0% by mass, and more preferably from 2.5% by mass to 5.0% by mass, based on the total mass of the ink. More preferably, it is most preferably 2.5% by mass or more and 4.0% by mass or less.

1-6. Other Components The photocurable inkjet ink of the present invention may further include other components such as a pigment derivative, a photopolymerization initiator auxiliary agent, and a polymerization inhibitor, as long as the effects of the present invention are obtained. These components may be contained in the ink alone or in combination of two or more.

1-6-1. Pigment derivative A pigment derivative having a sulfonic acid group or a carboxyl group is obtained by introducing a sulfonic acid group or a carboxyl group into a pigment.

  Although the basic structure of the pigment derivative is not particularly limited, it is an azo structure (including an insolubilized azo structure), a quinacridone structure, or a copper phthalocyanine structure. It preferably has a phthalocyanine structure.

  The pigment derivative having a sulfonic acid group or a carboxyl group can be synthesized by a known method. The pigment may be surface-modified with a chemical such as concentrated sulfuric acid to introduce a sulfonic acid group or a carboxyl group, or may be synthesized using a raw material having a sulfonic acid group or a carboxyl group as a starting material.

  The content of the pigment derivative may be 2% by mass or more and 10% by mass or less based on the total mass of the pigment. When the content of the pigment derivative is 2% by mass or more, the pigment is sufficiently dispersed, so that the ejection stability is easily increased. When the content of the pigment derivative is 10% by mass or less, aggregation of the pigment derivative is suppressed, and the ejection stability is not easily impaired. Further, the crystallization of the gelling agent is hardly inhibited, and the pinning effect is easily obtained. The content of the pigment derivative is preferably 2% by mass or more and 4% by mass or less based on the total mass of the pigment.

  In the pigment derivative having a copper phthalocyanine structure, the copper phthalocyanine structure easily forms a π-π bond with the halogenated copper phthalocyanine structure of the pigment; the sulfonic acid group or the carboxyl group has the basicity and the acid base of the dispersant. Easy to form bonds. Therefore, by further adding the pigment derivative, the dispersant can be indirectly adsorbed on the surface of the pigment particle via the pigment derivative, so that the dispersibility of the pigment particle can be further enhanced.

1-6-2. Photo-polymerization initiator assistant Examples of the photo-polymerization initiator assistant include tertiary amine compounds including aromatic tertiary amine compounds. 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, Includes N, N-dimethylamino-p-benzoic acid isoamylethyl ester, N, N-dihydroxyethylaniline, triethylamine and N, N-dimethylhexylamine.

1-6-3. Polymerization inhibitors Examples of polymerization inhibitors include (alkyl) phenol, hydroquinone, catechol, resorcinol, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cuperon, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N- (3 -Oxyanilino-1,3-dimethylbutylidene) aniline oxide, dibutyl cresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methylethylketoxime and cyclohexa Includes non-oximes.

1-7. Physical Properties of Photocurable Inkjet Ink From the viewpoint of further improving the dischargeability from the inkjet head, the viscosity of the ink at 80 ° C. is preferably from 3 mPa · s to 20 mPa · s. In addition, from the viewpoint of sufficiently gelling the ink when the ink has landed and cooled to room temperature, the viscosity of the ink at 25 ° C. is preferably 1000 mPa · s or more.

  The gelation temperature of the ink is preferably from 40 ° C. to 70 ° C. When the gelling temperature of the ink is 40 ° C. or higher, the ink quickly gels after landing on the recording medium, so that the pinning property is further improved. When the gelling temperature of the ink is 70 ° C. or lower, the ink is less likely to gel when the ink is ejected from an ink jet head whose ink temperature is usually about 80 ° C., so that the ink can be ejected more stably.

  The viscosity at 80 ° C., the viscosity at 25 ° C., and the gelling temperature of the ink can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer. Specifically, the viscosity and the gelation temperature can be measured by the following methods. The ink was heated to 100 ° C., and a shear rate of 11.7 (1/1) was measured while measuring the viscosity with a stress control type rheometer Physica MCR301 (cone plate diameter: 75 mm, cone angle: 1.0 °) manufactured by Anton Paar. s) The ink is cooled to 20 ° C. under the condition of a temperature decreasing rate of 0.1 ° C./s to obtain a temperature change curve of viscosity. The viscosity at 80 ° C. and the viscosity at 25 ° C. are determined by reading the viscosity at 80 ° C. and 25 ° C. in a temperature change curve of the viscosity, respectively. The gelation temperature is determined as a temperature at which the viscosity becomes 200 mPa · s in a temperature change curve of the viscosity.

2. Preparation of Photocurable Inkjet Ink The photocurable inkjet ink of the present invention can be obtained, for example, by mixing the above-described components under heating. It is preferable that the obtained mixture is further filtered through a predetermined filter.

  The ink may be prepared by preparing a pigment dispersion in which a pigment is dispersed with a dispersant in advance, adding the remaining components thereto, and heating the dispersion. The pigment and the dispersant can be dispersed by, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, or a paint shaker.

3. Image Forming Method The image forming method of the present invention includes a first step of discharging the photocurable ink of the present invention from a nozzle of an ink jet head to land on a recording medium, and irradiating the ink landed on the recording medium with actinic rays. And curing the ink.

3-1. First Step In the first step, ink droplets are ejected from an inkjet head and land on a recording medium at a position corresponding to an image to be formed.

  The discharge method from the inkjet head may be either an on-demand method or a continuous method. On-demand type inkjet heads include electro-mechanical conversion types such as single-cavity type, double-cavity type, bender type, piston type, shared mode type and shared wall type, as well as thermal inkjet type and bubble jet (bubble jet type). Any type such as an electric-heat conversion method such as a registered trademark of Canon Inc.) may be used.

  By ejecting the ink droplets from the inkjet head in a heated state, the ejection stability can be improved. The temperature of the ink at the time of ejection is preferably 35 ° C. or more and 100 ° C. or less, and more preferably 35 ° C. or more and 80 ° C. or less in order to further enhance ejection stability. In particular, it is preferable to perform ejection at an ink temperature such that the viscosity of the ink is 7 mPa · s or more and 15 mPa · s or less, more preferably 8 mPa · s or more and 13 mPa · s or less.

  The sol-gel phase transition type ink has a temperature of (gelation temperature +10) ° C. to (gelation temperature +30) of the ink when the ink is filled in the inkjet head in order to enhance the ejection property of the ink from the inkjet head. ) It is preferably set to ° C. If the temperature of the ink in the inkjet head is lower than (gelling temperature + 10) ° C., the ink gels in the inkjet head or on the nozzle surface, and the ink ejection property is likely to be reduced. On the other hand, if the temperature of the ink in the inkjet head exceeds (gelling temperature + 30) ° C., the temperature of the ink becomes too high, and the ink components may deteriorate.

  The method of heating the ink is not particularly limited. For example, at least one of an ink tank constituting a head carriage, an ink supply system such as a supply pipe and a front chamber ink tank immediately before the head, a pipe with a filter, and a piezo head is heated by a panel heater, a ribbon heater, or warm water. be able to.

  The amount of ink droplets when ejected is preferably 2 pL or more and 20 pL or less from the viewpoint of recording speed and image quality.

  The recording medium is not particularly limited, and is made of, for example, a plastic such as polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, and polybutadiene terephthalate. It can be a non-absorbable recording medium (plastic substrate), a non-absorbable inorganic recording medium such as metals and glass, and an absorbent paper (for example, coated printing paper and coated printing paper B). .

3-2. Second Step In the second step, the ink that has landed on the recording medium in the first step is irradiated with an actinic ray to form an image formed by curing the ink.

  The actinic ray can be selected from, for example, electron beams, ultraviolet rays, α-rays, γ-rays, and X-rays, but is preferably ultraviolet rays. Irradiation with ultraviolet rays can be performed, for example, using a water-cooled LED manufactured by Phoseon Technology under the condition of a wavelength of 395 nm. By using an LED as a light source, it is possible to suppress poor curing of the ink due to melting of the ink by radiant heat of the light source.

Irradiation with ultraviolet light has a peak illuminance on the image surface of ultraviolet light having a wavelength of 370 nm or more and 410 nm or less, preferably 0.5 W / cm ² or more and 10 W / cm ² or less, more preferably 1 W / cm ² or more and 5 W / cm ² or less. And so on. From the viewpoint of suppressing the irradiation of the ink with the radiant heat, the amount of light applied to the image is preferably less than 350 mJ / cm ² .

  Irradiation with actinic rays is preferably performed between 0.001 second and 1.0 second after the ink has landed, and between 0.001 second and 0.5 second in order to form a high-definition image. More preferably,

  Irradiation with actinic light may be performed in two stages. First, after the ink has landed, the ink is temporarily cured by irradiating an actinic ray for 0.001 second or more and 2.0 seconds or less, and after all printing is completed, the ink is fully cured by irradiating an actinic ray. Is also good. By dividing the irradiation of the actinic ray into two stages, the contraction of the recording material that occurs during the curing of the ink is less likely to occur.

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

1. Ink material <Surface treated pigment>
(Production Example 1)
Pigment Green 36 (PG36, see the following structural formula) as a raw material was dispersed in sulfuric acid to prepare a slurry. An aqueous solution of rosin containing 80% by mass of abietic acid was added to the obtained slurry, and then the rosin was insolubilized with water taken out and precipitated on the pigment surface. Thereby, a pigment surface-treated with rosin was obtained.

In this removal method, the solubility of the organic pigment dispersed in sulfuric acid is sharply reduced by contact with the removal water, and the organic pigment is precipitated as insoluble particles. On the other hand, the resinate (rosin) is returned from the state of the resinate to the resinic acid by contact with sulfuric acid, and is selectively and preferentially deposited on the surface of the fine organic pigment precipitated as an insoluble substance. It is considered that the surface of the organic pigment fine particles is coated.

(Production Example 2)
Pigment surface-treated with rosin was obtained in the same manner as in Production Example 1 except that Pigment Green 7 (PG7, see the following structural formula) was used as a raw material.

(Measurement of the content of abietic acid residues)
(1) Preparation of calibration curve Several abietic acid reagents of known concentrations were prepared, and these reagents were weighed and used as standard samples. The content of abietic acid in the obtained standard sample was measured by HPLC under the following measurement conditions to prepare a calibration curve.
(Measurement condition)
Measurement device: HPLC (L2130, L2490 manufactured by Hitachi High-Technologies Corporation)
Column: ODS column (inner diameter: 5 mmid x length 25 cm, stationary phase: silica gel)
Eluent: acetonitrile / water mixture (80/20 mass ratio)
Sample concentration: 500 ppm
Flow rate: 50 μL / s
Temperature: 40 ° C
Detector: UV
Detection wavelength: 210 nm

(2) Measurement of content of abietic acid residue The pigments surface-treated with rosin obtained in Production Examples 1 and 2 were weighed and dissolved in sulfuric acid to obtain measurement samples. The content of abietic acid in the obtained measurement sample was measured by HPLC.
As a result, the content of abietic acid residue in the pigment obtained in Production Example 1 was 0.05 mol per 1 mol of the surface-treated pigment; the content of the abietic acid residue in the pigment obtained in Production Example 2 was 0.05 mol. The content of the group was 0.1 mol per 1 mol of the surface-treated pigment.

<Dispersant>
Jet-9151 manufactured by BYK (comb-shaped block copolymer, amine value: 17 mgKOH / g, acid value: 7 mgKOH / g)

<Photopolymerizable compound>
(1) Highly polar photopolymerizable compound PEG600DA: polyethylene glycol 600 diacrylate (A-600, manufactured by Shin-Nakamura Chemical Co., Ltd., number of ethylene oxide groups: 14)
PEG400DA: polyethylene glycol 400 diacrylate (A-400, manufactured by Shin-Nakamura Chemical Co., Ltd., number of ethylene oxide groups: 9)
(2) Low-polarity photopolymerizable compound 3PO-modified TMPTA: 3PO-modified trimethylolpropane triacrylate (Miramar M360, manufactured by Bigen Specialty Chemical Co., Ltd., number of propylene oxide groups: 3)
TPGDA: Tripropylene glycol diacrylate

<Photopolymerization initiator>
ITX: 2- and 4-isopropylthioxanthone (manufactured by BASF)
Irgacure 819: bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide (manufactured by BASF)

<Gelling agent>
Kaowax T-1: Distearyl ketone (manufactured by Kao Corporation)

３Ｓ−１：下記式で表される不溶性アゾ誘導体−スルホン酸基

<Pigment derivative>
1S-1: Copper phthalocyanine derivative-sulfonic acid group (Solsperse 5000 manufactured by Lubrizol)
1S-2: Copper phthalocyanine derivative-carboxylic acid group (Solsperse 12000 manufactured by Lubrizol)
2S-1: a quinacridone derivative represented by the following formula-sulfonic acid group

3S-1: Insoluble azo derivative represented by the following formula-sulfonic acid group

<Polymerization inhibitor>
UV-10: Hindered amine polymerization inhibitor (manufactured by BASF)

2. Preparation and evaluation of ink <Preparation of ink 1A-1>
(Preparation of Pigment Dispersion 1)
The following components and 120 g of zirconia beads having a diameter of 0.5 mmφ were put in a 200 ml polybin, the lid was closed, and the mixture was dispersed in a vibration mill (Red Devil 4500L, manufactured by Nishimura Seisakusho) for 4 hours. After the dispersion, the beads were separated and the dispersion was taken out to obtain Pigment Dispersion 1.
Pigment (pigment) surface-treated with rosin prepared in Production Example 2: 15.0% by mass
Polyethylene glycol 600 diacrylate (highly polar photopolymerizable compound): 61.0% by mass
3PO-modified trimethylolpropane triacrylate (low-polarity photopolymerizable compound): 16.0% by mass
BYK Jet-9151 (polymer dispersant): 7.0% by mass
Irgastab UV-10 (polymerization inhibitor) manufactured by BASF: 1.0% by mass

(Preparation of ink)
While heating the obtained Pigment Dispersion 1 to 60 ° C., the following components were added at the following ratio to prepare Ink 1A-1.
Pigment dispersion 1: 16.0% by mass
Additional polyethylene glycol 600 diacrylate (highly polar photopolymerizable compound): 18.1% by mass
Additional 3PO-modified trimethylolpropane triacrylate (low-polarity photopolymerizable compound): 62.5% by mass
Kao wax T-1 (gelling agent) manufactured by Kao Corporation: 1.0% by mass
ITX (photopolymerization initiator) manufactured by BASF: 1.4% by mass
Irgacure 819 (photopolymerization initiator) manufactured by BASF: 1.0% by mass

<Inks 1A-2 to 1A-9>
Inks 1A-2 to 1A-9 (Examples) were prepared in the same manner as Ink 1A-1, except that at least one of the composition of the photopolymerizable compound and the content of the gelling agent was changed as shown in Table 3. Prepared. The content of the highly polar photopolymerizable compound in the photopolymerizable compound and the content of the gelling agent were adjusted by adjusting the amount of the photopolymerizable compound to be added.

<Preparation of Ink 2A-1>
(Preparation of Pigment Dispersion 2)
Pigment Dispersion 2 was obtained in the same manner as Pigment Dispersion 1 except that the following components were used.
Pigment (pigment) surface-treated with rosin prepared in Production Example 1: 15.0% by mass
Polyethylene glycol 600 diacrylate (highly polar photopolymerizable compound): 60.0% by mass
3PO-modified trimethylolpropane triacrylate (low-polarity photopolymerizable compound): 15.0% by mass
BYK Jet-9151 (polymer dispersant): 7.0% by mass
1S-1 (Solsperse 5000) (pigment derivative): 2.0% by mass
Irgastab UV-10 (polymerization inhibitor) manufactured by BASF: 1.0% by mass

(Preparation of ink)
While heating the obtained Pigment Dispersion 2 to 60 ° C., the following components were added in the following ratio to prepare Ink 2A-1.
Pigment Dispersion 2: 16.0% by mass
Additional polyethylene glycol 600 diacrylate (highly polar photopolymerizable compound): 18.2% by mass
Additional 3PO-modified trimethylolpropane triacrylate (low-polarity photopolymerizable compound): 62.4% by mass
Kao wax T-1 (gelling agent) manufactured by Kao Corporation: 1.0% by mass
ITX (photopolymerization initiator) manufactured by BASF: 1.4% by mass
Irgacure 819 (photopolymerization initiator) manufactured by BASF: 1.0% by mass

<Preparation of Inks 2A-2 to 7A-12 and 1B-1 to 1B-12>
Same as ink 1A-1 except that at least one of the type of pigment, the composition of the photopolymerizable compound, the content of the gelling agent, and the type and content of the pigment derivative was changed as shown in Tables 3 to 5 To prepare inks 1A-2 to 5A-15 (Examples) and inks 1B-1 to 1B-9 (Comparative Examples). The content of the highly polar photopolymerizable compound in the photopolymerizable compound and the content of the gelling agent were adjusted by adjusting the amount of the photopolymerizable compound to be added. In the inks 1B-10 to 1B-12, the composition ratio of the low-polarity photopolymerizable compound (mass ratio of 3PO-modified TMPTA / TPGDA) was 30/70 (ink 1B-10) and 50/50 (ink 1B- 10). 11) and 70/30 (Ink 1B-12).

  When an image was formed using the obtained ink, the presence or absence of liquid shift, the dot diameter, the color gamut difference of the image, and the ejection stability were evaluated by the following methods.

(Whether or not there is liquid dripping)
The obtained ink was introduced into an ink jet head HA1024, manufactured by Konica Minolta. At a resolution of 360 × 360 dpi and a voltage of 16 V, the ink is ejected at a temperature of 25 ° C. and an ambient humidity of 55% to land on a recording medium, and the landed ink is applied with an LED lamp at 250 mJ / cm ² . The ink was cured by irradiation with ultraviolet rays of energy to form a solid image (30 mm × 100 mm) with a print width of 30 mm. As a recording medium, an OK top coat (print paper) was used.

  The number of missing pixels contained in the obtained solid image was magnified 30 times with a magnifying microscope, and observed and counted in the 30 mm width direction of the solid image. An image defect refers to a concavo-convex portion formed by folding of a liquid droplet in a portion close to a liquid. If the number of image defects was 5.0 or less, it was determined to be good.

(Dot diameter)
The solid image formed by the measurement of the liquid shift was observed under a condition of × 100 with a microscope, and the average dimensional value of 10 droplets was obtained. If the dot diameter was 60 μm or less, it was determined to be good.

(Color gamut difference)
The obtained ink was introduced into an ink jet head HA1024, manufactured by Konica Minolta. Under the conditions of a resolution of 720 × 720 dpi and a voltage of 16 V, ink is ejected at a temperature of 25 ° C. and an ambient humidity of 55% to land on a recording medium. The ink droplets were cured by irradiating ultraviolet rays having energy of cm ² to form a solid image (30 mm × 100 mm) having a print width of 30 mm. As a recording medium, an OK top coat (print paper) was used.

The values of a * 0 and b * 0 in the maximum area of Panton green in the Pantone color gamut (brightness 50) as a standard sample were measured with a portable integrating sphere spectrophotometer Ci6X (manufactured by X-Rite). Similarly, the values of a * 1 and b * 1 of the solid image formed above were measured. Then, these values were applied to the following equation to obtain a color gamut difference ΔE between the image using each ink and the standard sample.
Color gamut difference ΔE = [(a * 0) ² + (b * 0) ² ] ^1/2 -[(a * 1) ² + (b * 1) ² ] ^1/2
If the color gamut difference ΔE was 10 or less, it was determined to be good.

(Discharge stability)
The number of missing dots in a 30 mm wide solid image formed by measuring the color gamut difference was visually counted. The dot missing is a white streak (a portion where the color of the base material of the unprinted portion is directly observed) that is visually confirmed in the obtained solid image. If the number of missing dots was 10 or less, it was determined to be good.

The evaluation results of Inks 1A-1 to 4A-9 (Examples) are shown in Table 3, and the evaluation results of Inks 5A-1 to 7A-12 (Examples) are shown in Table 4, and Inks 1B-1 to 1B-12. Table 5 shows the evaluation results of Comparative Example.

  As shown in Tables 3 and 4, in the inks 1A-1 to 7A-12 of the examples in which the pigment surface-treated with rosin and the highly polar photopolymerizable compound were combined, liquid drift was suppressed, and ejection was stable. It shows that the properties are also good. In addition, the obtained image has a small color gamut difference from the standard sample, indicating that a good tint can be obtained.

  On the other hand, as shown in Table 5, the inks 1B-1 to 1B-6 of the comparative examples using the pigments that had not been subjected to the surface treatment show that the liquid shift was remarkably generated. It is considered that this is because the pigment which has not been surface-treated interacts with the gelling agent, and the function of the gelling agent is inhibited. Further, the inks 1B-7 to 1B-9 of Comparative Examples in which the content of the highly polar photopolymerizable compound is less than 30% by mass, and the inks 1B-10 to 1B- of Comparative Examples not containing the highly polar photopolymerizable compound. 12 also indicates that liquid shift occurs. Since the affinity between the surface-treated pigment and the photopolymerizable compound is low, the interaction between the surface-treated pigment and the gelling agent cannot be sufficiently suppressed, and the function of the gelling agent is sufficiently obtained. It is thought that it is not. In addition, it can be seen that when the content of the high-polarity compound is small or the high-polarity compound is not contained, the dispersion stability of the surface-treated pigment is low and the ejection stability is low.

  It is shown that by setting the content of the gelling agent to 5% by mass or less, the ejection stability is improved (the inks 7A-1 to 7A-3 of Examples and the inks 2A-1 to 2A-9 of Examples). Contrast). This is considered to be because the viscosity of the ink does not increase too much when the content of the gelling agent is equal to or less than a certain value. It is shown that when the content of the gelling agent is 1% by mass or more, the liquid shift is easily suppressed and the dot diameter is reduced. This is considered to be because when the content of the gelling agent is equal to or more than a certain value, the function of the gelling agent is easily obtained sufficiently.

  It is shown that the use of a pigment derivative having a copper phthalocyanine structure can enhance the ejection stability as compared with the use of a pigment derivative having a quinacridone structure or an azo structure (the inks of Examples 7A-4 to 7A-6 are used). (Comparison with Ink 3A-1 to 3A-9 and Comparison between Ink 7A-7 to 7A-9 of Example and Ink 2A-1 to 2A-9 of Example). This is presumably because the pigment derivative having a copper phthalocyanine skeleton is more likely to form π-π bonds with the pigment surface-treated with rosin than the other pigment derivatives, thereby increasing the dispersibility of the pigment.

  It is shown that when the content of the pigment derivative is 2% by mass or more and 10% by mass or less with respect to the pigment, the effect of suppressing liquid drift and the ejection stability are improved (the inks 7A-10 to 7A-12 of Examples). And inks 2A-1 to 2A-9 of Examples. This is thought to be because when the content of the pigment derivative is too small, the effect of suppressing the interaction between the pigment and the gelling agent is less than when the content of the pigment derivative is large, and the liquid shift tends to occur slightly. Can be On the other hand, if the content of the pigment derivative is too large, it is considered that the pigment derivatives are likely to aggregate with each other and the ejection stability is reduced.

  According to the present invention, it is possible to provide a photocurable inkjet ink capable of forming a good quality image by suppressing liquid drift without impairing the ejection stability, and an image forming method using the same.

Claims (7)

Pigment, dispersant, photopolymerizable compound, photopolymerization initiator, and a photocurable inkjet ink containing a gelling agent,
The pigment comprises a pigment having a halogenated copper phthalocyanine structure with abietic acid groups, and the content of the abietic acid is 0.05 to 2 moles with respect to the pigment 1 mol,
The photopolymerizable compound contains a highly polar photopolymerizable compound having a total of 6 or more ethylene oxide groups or propylene oxide groups in an amount of 30% by mass or more based on the total mass of the photopolymerizable compound,
The gelling agent has a hydrocarbon group having 9 to 25 carbon atoms, and is one or more selected from the group consisting of aliphatic ketones, aliphatic esters, higher fatty acids and higher alcohols.
Photocurable inkjet ink. The photocurable type according to claim 1 , wherein the dispersant is a polymer dispersant having a basic group, and the ink further includes a pigment derivative having a copper phthalocyanine structure having a sulfonic acid group or a carboxyl group. Inkjet ink. The photocurable inkjet ink according to claim 2 , wherein the content of the pigment derivative is 2% by mass or more and 10% by mass or less based on the total mass of the pigment. The photocurable inkjet ink according to any one of claims 1 to 3 , wherein the content of the gelling agent is 1% by mass or more and 5% by mass or less based on the total mass of the ink. The photocurable inkjet according to any one of claims 1 to 4 , wherein the photopolymerizable compound further includes a low-polarity photopolymerizable compound having a total of 3 to 5 ethylene oxide groups or propylene oxide groups. ink. The photocurable inkjet ink according to any one of claims 1 to 4 , wherein the gelling agent is a compound represented by the general formula (G1) or (G2) .

(In the general formula (G1), R1 and R2 are each a linear or branched hydrocarbon group having 9 to 25 carbon atoms.)

(In the general formula (G2), R3 and R4 are each a straight-chain or branched-chain hydrocarbon group having 9 to 25 carbon atoms.) A step of discharging the photocurable inkjet ink according to any one of claims 1 to 6 from a nozzle of an inkjet head to land on a recording medium,
Irradiating the landed ink with actinic light to cure the ink,
An image forming method, comprising: