JP6950257B2 - Active light curable inkjet ink - Google Patents

Description

The present invention relates to an active photocurable inkjet ink.

The inkjet recording method is used in various printing fields because it can form an image easily and inexpensively. As a kind of inkjet ink, an ink that is cured by being irradiated with active light rays is known. When an image is formed using an active light-curable ink, droplets of the ink are landed on the surface of a recording medium, and the landed droplets are irradiated with active light. As a result, the active photopolymerizable compound in the droplet is polymerized, and a cured product (image) is formed on the surface of the recording medium. According to the image forming method using the active ray-curable ink, there is an advantage that an image having high adhesion can be formed regardless of the water absorption of the recording medium.

In recent years, printing of various packages and the like using the above image forming method has also been studied. Images for packaging may be required to have gloss control such as gloss and matte, as well as resistance to post-processing such as folding and bending. However, it is difficult to obtain a matte-like cured product (image) with the conventional active light-curing ink, and when obtaining a matte-like image, a matte-like cured product (image) is placed on the cured product (image) of the active light-curing ink. It was common to apply more over-varnish.

On the other hand, an active photocurable ink containing a fluorescent whitening agent together with an amine-modified (meth) acrylate oligomer has been proposed for the purpose of improving the curability of the ink and suppressing yellowing of the obtained image. (For example, Patent Document 1). Further, an active photocurable ink containing a fluorescent whitening agent (sensitizing dye) together with a low molecular weight urethane (meth) acrylate oligomer has also been proposed (for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2011-213965 Japanese Unexamined Patent Publication No. 2006-249155

However, optical brighteners often have low compatibility with other components (various monomers, oligomers, etc.) in the active photocurable inkjet ink. When a fluorescent whitening agent is included in the active light-curable inkjet ink as in Patent Document 1 and Patent Document 2, the fluorescent whitening agent is likely to precipitate during storage of the ink, and component separation occurs in the ink. In addition, the crystals of the crystal whitening agent may cause clogging of the inkjet nozzle. That is, there is a problem that the conventional active photocurable inkjet ink containing a fluorescent whitening agent does not have sufficient long-term storage stability and ejection stability.

Further, as described above, in order to obtain an image having a matte surface in a package application or the like, it has been necessary to apply an overvarnish. However, from the viewpoint of simplification of the process and cost reduction, it has been required to control the gloss of the cured product itself of the active ray-curable inkjet ink.

The present invention has been made in view of the above problems. Specifically, we provide an active light-curable inkjet ink that can obtain a matte image and is excellent in long-term storage stability and ejection stability.

（上記一般式（１）中、Ｒ _１ 〜Ｒ _８ はそれぞれ独立に、水素原子、アルキル基、アミノ基から選ばれる置換基を表し（ただし、Ｒ _１ 〜Ｒ _８ から選ばれる２以上の基が結合して環を形成してもよい）、Ａは、下記式（２）〜（４）で表されるいずれかの連結基を表す）

The present invention relates to the following active light curable inkjet inks.
[1] A urethane (meth) acrylate oligomer having two or more unsaturated carbon-carbon double bonds and having a weight average molecular weight of 5000 to 15000, and / or a polyester (meth) acrylate oligomer having no amine structure. It contains an active photopolymerizable compound, a benzoxazole-based fluorescent whitening agent, and a radical-based polymerization initiator, and the content of the urethane (meth) acrylate oligomer is the total amount of the active photopolymerizable compound. The content of the polyester (meth) acrylate oligomer is 5% by mass or more and 20% by mass or less based on the total amount of the active photopolymerizable compound. when including both of the urethane (meth) acrylate oligomers and polyester (meth) acrylate oligomer, the total amount thereof is Ri 5-25% by mass based on the total amount of active ray polymerizable compound, a polymerization initiator of the radical system An active photocurable inkjet ink in which the agent is an intramolecular bond cleavage type polymerization initiator, and the fluorescent whitening agent has a structure represented by the following general formula (1).

(In the above general formula (1), R _{1 to} R ₈ independently represent a substituent selected from a hydrogen atom, an alkyl group, and an amino group (however, two or more groups selected from _{R 1 to} R _{8 are present.} (May be bonded to form a ring), A represents any of the linking groups represented by the following formulas (2) to (4))

（上記一般式（１）中、Ｒ_１〜Ｒ_８はそれぞれ独立に、水素原子、アルキル基、アミノ基から選ばれる置換基を表し（ただし、Ｒ_１〜Ｒ_８から選ばれる２以上の基が結合して環を形成してもよい）、Ａは、下記式（２）〜（４）で表されるいずれかの連結基を表す）

[2] The active photocurable inkjet ink according to [1], wherein the fluorescent whitening agent has a structure represented by the following general formula (1).

(In the above general formula (1), R _{1 to} R ₈ independently represent a substituent selected from a hydrogen atom, an alkyl group, and an amino group (however, two or more groups selected from _{R 1 to} R _{8 are present.} (May be bonded to form a ring), A represents any of the linking groups represented by the following formulas (2) to (4))

[3] The active photocurable inkjet ink according to [1] or [2], wherein the active photopolymerizable compound further contains a monomer having an alicyclic structure or a heterocyclic structure.
[4] The active light-curable inkjet ink according to any one of [1] to [3], which further contains wax.

According to the active photocurable inkjet ink of the present invention, it is possible to obtain a matte image. Further, the active ray-curable inkjet ink is excellent in long-term storage stability and also in ejection stability. Therefore, it is possible to stably produce various printed matter.

The active photocurable inkjet ink of the present invention (hereinafter, also simply referred to as “ink”) contains a urethane (meth) acrylate oligomer having a predetermined weight average molecular weight and / or a polyester (meth) acrylate oligomer having no amine structure. Includes an active photopolymerizable compound and a benzoxazole-based optical brightener. If necessary, the ink of the present invention may further contain an active photopolymerizable compound other than the above oligomer, a polymerization initiator, a wax, a pigment, various additives and the like. Here, the description of (meth) acrylate in the present specification includes one or both of acrylate and methacrylate. Similarly, the "(meth) acryloyl group" includes one or both of an acryloyl group and a methacryloyl group.

Conventionally, there has been a demand for an active light-curable inkjet ink capable of obtaining a matte image. On the other hand, for the purpose of improving curability and suppressing yellowing of images, it has been considered to include a fluorescent whitening agent in the active photocurable inkjet ink, but the fluorescent whitening agent is used as another component in the ink. The solubility of the ink was low, and it was easy to precipitate from the ink. Therefore, the ink containing the fluorescent whitening agent has a problem that its long-term storage stability is poor and the ejection stability of the ink tends to be lowered.

Here, as a result of diligent studies by the present inventor, an active photopolymerizable compound containing a urethane (meth) acrylate oligomer having a specific weight average molecular weight or a polyester (meth) acrylate oligomer having no amine structure, and a benzoxazole-based compound. It has been found that the stability of the fluorescent whitening agent in the ink is improved, the long-term storage stability of the ink is improved, and the ejection stability is improved by combining with the fluorescent whitening agent of. Furthermore, it was also found that a matte image can be obtained by combining these.

The reason is not clear, but it is inferred as follows. The urethane (meth) acrylate oligomer and the polyester (meth) acrylate oligomer have a urethane bond or an ester bond as a polar group in the molecule. It is considered that these groups interact with the benzoxazole structure contained in the fluorescent whitening agent to improve the solubility of the fluorescent whitening agent, which is generally poorly soluble, in an active photocurable compound or the like. Further, the effect of improving the solubility of such an oligomer is lost when the oligomer (active photopolymerizable compound) undergoes a polymerization reaction and solidifies. That is, in the ink of the present invention, the fluorescent whitening agent is precipitated only when the ink droplets are irradiated with active light rays, and fine crystals are formed on the surface of the cured product (image). Then, it is considered that the fine crystals produced by the fluorescent whitening agent diffusely reflect the light incident on the cured product of the ink, so that the image becomes matte.
Hereinafter, the components contained in the ink of the present invention will be described.

1. 1. Active Photopolymerizable Compound An active photopolymerizable compound is a compound that is crosslinked or polymerized by irradiation with active light. Here, the active light rays are electron beams, ultraviolet rays, α rays, γ rays, X-rays and the like, and are preferably ultraviolet rays and electron beams. In the present invention, the active photopolymerizable compound comprises one or both of a urethane (meth) acrylate oligomer having a predetermined weight average molecular weight and a polyester (meth) acrylate oligomer having no amine structure. When the active photopolymerizable compound contains these, the solubility of the fluorescent whitening agent in the ink tends to be good. Further, the obtained cured product (image) tends to be flexible, and it becomes easy to follow the folding and bending of the recording medium. Here, the active photopolymerizable compound is usually an active photopolymerizable compound other than urethane (meth) acrylate oligomer and / or polyester (meth) acrylate oligomer (hereinafter, also referred to as “other active photopolymerizable compound”). Is included.

The urethane (meth) acrylate oligomer contained in the active photopolymerizable compound contains a urethane bond and a (meth) acryloyl group in the molecule, has two or more unsaturated carbon-carbon double bonds, and has a weight average molecular weight of 5. The oligomer is not particularly limited as long as it is an oligomer of 000 to 15,000. The active photopolymerizable compound may contain only one type of urethane (meth) acrylate oligomer, or may contain two or more types. Here, when the weight average molecular weight of the urethane (meth) acrylate oligomer is 5000 or more, the affinity between the urethane (meth) acrylate oligomer and the fluorescent whitening agent becomes good, and the fluorescent whitening agent precipitates when the ink is stored. It becomes difficult to do. On the other hand, when the weight average molecular weight of the urethane (meth) acrylate oligomer is 15,000 or less, the viscosity of the ink falls within a desired range, and the ejection stability of the ink from the inkjet nozzle tends to increase. The weight average molecular weight of the urethane (meth) acrylate oligomer is preferably 5000 to 14000, and more preferably 5000 to 10000.

The weight average molecular weight is a value (polystyrene equivalent value) measured by gel permeation chromatography. The weight average molecular weight can be obtained, for example, by performing high performance liquid chromatography (“Waters 2695 (main body)” and “Waters 2414 (detector)” manufactured by Japan Waters Corp.) on a column (Shodex® GPC KF-806L (exclusion limit). molecular weight: 2 × 10 ^7, separation range: 100-2 × 10 ^7, theoretical plate number: 10000 steps / present, filler material: styrene - divinylbenzene copolymer, filler particle size: 10 [mu] m)) in three series It can be identified by arranging and measuring.

The viscosity of the urethane (meth) acrylate oligomer at 25 ° C. is preferably 1000 to 50000 mPa · s, and more preferably 1000 to 30000 mPa · s from the viewpoint of discharge stability.

The structure of the urethane (meth) acrylate oligomer is not particularly limited, but for example, polyester-based urethane (meth) acrylate, polyether-based urethane (meth) acrylate, or polycarbonate-based urethane (meth) acrylate is preferable. When the urethane (meth) acrylate oligomer has an ester bond, an ether bond, or a carbonate bond, the adhesiveness between the cured product of the ink and the recording medium tends to be enhanced. In addition, the toughness and flexibility of the cured product of the ink are likely to increase.

The urethane (meth) acrylate oligomer may contain two or more unsaturated carbon-carbon double bonds, but more preferably 2 to 5 unsaturated carbon-carbon double bonds. The number of unsaturated carbon-carbon double bonds contained in the urethane (meth) acrylate oligomer is an average value. Further, the unsaturated carbon-carbon double bond contained in the urethane (meth) acrylate oligomer is preferably an unsaturated carbon-carbon double bond in the (meth) acryloyl group.

The urethane (meth) acrylate oligomer may be prepared by polymerizing various monomers or the like, or may be a commercially available product. Examples of commercially available polyester urethane (meth) acrylates include UV-3010B manufactured by Nippon Synthetic Chemical Co., Ltd. (weight average molecular weight (Mw): 9,690, number of unsaturated carbon-carbon double bonds: 2). UV-3200B (weight average molecular weight (Mw): 10,000, number of unsaturated carbon-carbon double bonds: 2), UV-3520TL (weight average molecular weight (Mw): 14000, unsaturated carbon-carbon double bond) Number: 2), UT-5454 (weight average molecular weight (Mw): 10,000, number of unsaturated carbon-carbon double bonds: 2), UT-5449 (weight average molecular weight (Mw): 10,000, Number of unsaturated carbon-carbon double bonds: 2) and the like are included.

Specific examples of commercially available polyether urethane (meth) acrylates include UV-3300B (weight average molecular weight (Mw): 13,000, number of unsaturated carbon-carbon double bonds) manufactured by Nippon Synthetic Chemical Industry Co., Ltd. : 2), UV-6640B (weight average molecular weight (Mw): 5,000, number of unsaturated carbon-carbon double bonds: 2) and the like.

Specific examples of commercially available polycarbonate-based urethane (meth) acrylates include UV-3310B manufactured by Nippon Synthetic Chemical Industry Co., Ltd. (weight average molecular weight Mw: 5,000, number of unsaturated carbon-carbon double bonds: 2). , UV-3210EA (weight average molecular weight (Mw): 9,000, unsaturated carbon-carbon double bond number: 2), UN-9000PEP manufactured by Negami Kogyo Co., Ltd. (weight average molecular weight Mw: 5,000, unsaturated) The number of carbon-carbon double bonds: 2), UN-9200A (weight average molecular weight Mw: 13,000, number of unsaturated carbon-carbon double bonds: 2) and the like are included.

The content of the urethane (meth) acrylate oligomer is preferably 5% by mass or more and 15% by mass or less, and more preferably 5% by mass or more and 10% by mass or less, based on the total amount of the active photopolymerizable compound. preferable. By setting the amount of urethane (meth) acrylate oligomer in the active photopolymerizable compound to 5% by mass or more and 15% by mass or less, the solubility of the fluorescent whitening agent is improved, and the ink is ejected from the inkjet nozzle. Good stability. In addition, the flexibility of the cured product of the ink is increased.

On the other hand, the polyester (meth) acrylate oligomer contained in the active photopolymerizable compound is not particularly limited as long as it is an oligomer containing an ester bond and a (meth) acryloyl group in the molecule and does not have an amine structure. When the polyester (meth) acrylate oligomer contains an amine structure, the affinity between the oligomer and the fluorescent whitening agent is lowered, and the solubility of the fluorescent whitening agent in the ink becomes unstable, so that the ejection stability is lowered. It also tends to reduce long-term storage stability. The active photopolymerizable compound may contain only one type of polyester (meth) acrylate oligomer, or may contain two or more types.

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

Here, the structure of the polyester (meth) acrylate oligomer is not particularly limited, and for example, a compound obtained by reacting a polyester oligomer having a hydroxyl group with a compound having a (meth) acryloyl group such as (meth) acrylic acid is used. Can be done. The number of unsaturated carbon-carbon double bonds contained in the polyester (meth) acrylate oligomer is preferably 2 or more, and more preferably 2 to 5 from the viewpoint of increasing the strength of the cured product. The number of unsaturated carbon-carbon double bonds is an average value. Further, the unsaturated carbon-carbon double bond contained in the polyester (meth) acrylate oligomer is preferably an unsaturated carbon-carbon double bond in the (meth) acryloyl group.

The polyester (meth) acrylate oligomer may be prepared by polymerizing various monomers or the like, or may be a commercially available product. Examples of polyester (meth) acrylate oligomers include BASF's Laromer® PE9074 (number of unsaturated carbon-carbon double bonds: 2,25 ° C., viscosity: 7,000 to 13,000 mPa · s), manufactured by Sartomer. CN2270 (number of unsaturated carbon-carbon double bonds: 2, 25 ° C. viscosity: 55 mPa · s), CN2273 (number of unsaturated carbon-carbon double bonds: 2, 25 ° C. viscosity: 100 mPa · s), CN2303 ( Number of unsaturated carbon-carbon double bonds: 6, 25 ° C. viscosity: 350 mPa · s), CN2302 (number of unsaturated carbon-carbon double bonds: 16, 25 ° C., viscosity: 300 mPa · s), CN2373 (unsaturated) Number of saturated carbon-carbon double bonds: 2, 25 ° C viscosity: 100 mPa · s), ETERCURE 6361-100 manufactured by ETERNAL CHEMICAL (number of unsaturated carbon-carbon double bonds: 8, 25 ° C viscosity: 200 mPa · s) ), ETERCURE 6362-100 (number of unsaturated carbon-carbon double bonds: 12-15, 25 ° C. viscosity: 600 mPa · s), M-6200 manufactured by Toa Synthetic Co., Ltd. (number of unsaturated carbon-carbon double bonds: 2.25 ° C. viscosity: 700 to 3700 mPa · s), M-6250 (number of unsaturated carbon-carbon double bonds: 2,25 ° C. viscosity: 300 to 700 mPa · s) and the like.

The content of the polyester (meth) acrylate oligomer is preferably 5% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less, based on the total amount of the active photopolymerizable compound. preferable. By setting the amount of the polyester (meth) acrylate oligomer in the active photopolymerizable compound to 5% by mass or more and 20% by mass or less, the solubility of the fluorescent whitening agent is improved, and the ink is ejected from the inkjet nozzle. Good stability. In addition, the flexibility of the cured product of the ink is increased. Since the polyester (meth) acrylate oligomer has a lower viscosity than the urethane (meth) acrylate oligomer, it is possible to increase the amount of the polyester (meth) acrylate oligomer with respect to the total mass of the ink as compared with the case of using the urethane (meth) acrylate oligomer.

When both the urethane (meth) acrylate oligomer and the polyester (meth) acrylate oligomer are contained, the total amount thereof is preferably 5 to 25% by mass, preferably 5 to 25% by mass, based on the total amount of the active photopolymerizable compound. More preferably, it is 20% by mass. When the total amount of these is in the above range, the solubility of the fluorescent whitening agent in the ink tends to be good. In addition, the flexibility of the cured product of the ink tends to increase. On the other hand, if these amounts are too large, the strength of the film may decrease, but if it is 20% by mass or less, a film having high strength can be easily obtained.

On the other hand, the other active photopolymerizable compound is not particularly limited as long as it is a compound that can be crosslinked or polymerized by irradiation with active light, and is a compound having two or more active photopolymerizable functional groups. It may be a compound having only one active photopolymerizable functional group. Here, the active photopolymerizable compound may contain only one type of other active photopolymerizable compound, or may contain two or more types.

Further, the other active photopolymerizable compound may be a radical-polymerizable compound or a cationically polymerizable compound, but is preferably a radical-polymerizable compound.

The radically polymerizable compound can be a compound having a radically polymerizable unsaturated carbon-carbon double bond (monomer, oligomer, polymer or a mixture thereof). Examples of radically polymerizable compounds include unsaturated carboxylic acids and salts thereof, unsaturated carboxylic acid ester compounds (excluding the above polyester (meth) acrylate oligomers), and unsaturated carboxylic acid urethane compounds (the above urethane (meth) acrylate oligomers). Excludes), unsaturated carboxylic acid amide compounds and their anhydrides, acrylonitrile, styrene, unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, unsaturated urethanes, N-vinyl compounds such as N-vinylcaprolactam, and the like. Examples of unsaturated carboxylic acids include (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and the like.

Among them, the radically polymerizable compound is preferably an unsaturated carboxylic acid ester compound or an N-vinyl compound. More specifically, the unsaturated carboxylic acid ester compound is more preferably a (meth) acrylate compound. The (meth) acrylate compound may be not only a monomer but also an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group, and the like.

Examples of (meth) acrylate compounds include isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomilstill (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) acrylate , Methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl ( Meta) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (Meta) acryloyloxyethyl-2-hydroxyethyl-phthalic acid and t-butylcyclohexyl (meth) acrylate, (meth) acryloylmorpholine, adamantyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyl Monofunctional (meth) acrylate containing oxyethyl (meth) acrylate, 3,3,5-trimethylcyclohexane (meth) acrylate, cyclohexyl acrylate, 1,4-cyclohexanedimethanol monoacrylate, etc .; triethylene glycol di (meth) Acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (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-tricyclodecanedi (meth) acrylate, di (meth) having a bisphenol A structure. ) Acrylate, hydroxypivalate Bifunctional (meth) acrylates including opentyl glycol di (meth) acrylates, polytetramethylene glycol di (meth) acrylates, and tripropylene glycol di (meth) acrylates; trimethyl propantri (meth) acrylates, pentaerythritol. Tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropoxytetra (meth) acrylate, glycerin propoxytri (meth) acrylate, pentaerythritol ethoxytetra (meth) acrylate, etc. Includes trifunctional or higher functional (meth) acrylates; oligomers with (meth) acryloyl groups containing polyester acrylate oligomers; and modified products thereof. Examples of the modified product of the (meth) acrylate include ethylene oxide-modified (EO-modified) acrylate in which an ethylene oxide group is inserted, propylene oxide-modified (PO-modified) acrylate in which a propylene oxide is inserted, and the like.

Further, the radically polymerizable compound may be an oligomer obtained by polymerizing the above-mentioned (meth) acrylate and a compound having another functional group (for example, an epoxy group).

Here, the radically polymerizable compound preferably contains a compound having an alicyclic structure or a heterocyclic structure, and more preferably contains a monomer having an alicyclic structure or a heterocyclic structure. Examples of monomers having an alicyclic structure or a heterocyclic structure include isobornyl (meth) acrylate, (meth) acryloylmorpholine, adamantyl (meth) acrylate, dicyclopentenyl (meth) acrylate, and dicyclopentenyloxyethyl (meth) acrylate. , 3,3,5-trimethylcyclohexane (meth) acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, 1,4-cyclohexanedimethanol monoacrylate, N-vinylcaprolactam and the like. The active photopolymerizable compound may contain only one kind of these compounds, or may contain two or more kinds of these compounds. When these compounds having an alicyclic structure or a heterocyclic structure (particularly monomers) are included as other active photopolymerizable compounds, it is possible to further enhance the long-term storage stability of the ink containing the fluorescent whitening agent.

The content of the compound having an alicyclic structure or a heterocyclic structure (particularly the monomer) is preferably 5 to 95% by mass and 10 to 95% by mass with respect to the total amount of the active photopolymerizable compound. Is more preferable. When the content of the compound having an alicyclic structure or a heterocyclic structure (particularly a monomer) is in the above range, the long-term storage stability of the ink tends to be good.

The radically polymerizable compound also preferably contains a bifunctional or higher (meth) acrylate compound (particularly a monomer). When the active photocurable compound contains a bifunctional or higher (meth) acrylate compound, the strength of the cured product tends to increase. The content of the bifunctional or higher (meth) acrylate (particularly the monomer) is preferably 1 to 95% by mass, more preferably 5 to 95% by mass, based on the total amount of the active photopolymerizable compound. When the content of the bifunctional or higher (meth) acrylate is in the above range, the curability of the ink tends to be good.

On the other hand, examples of cationically polymerizable compounds include epoxy compounds, vinyl ether compounds, oxetane compounds and the like.

Here, the total amount of the active photopolymerizable compound (the above-mentioned urethane (meth) acrylate monomer, polyester (meth) acrylate monomer, compound having an alicyclic structure or heterocyclic structure, bifunctional or higher (meth) acrylate, etc.) is It is preferably 50 to 95% by mass, more preferably 70 to 95% by mass, based on the total mass of the ink. As a result, the adhesion of the cured product of the ink to the recording medium and the strength of the cured product are sufficiently increased.

2. Fluorescent whitening agent The fluorescent whitening agent contained in the ink of the present invention may be any benzoxazole-based fluorescent whitening agent, and the ink may contain only one kind of the fluorescent whitening agent, and may contain two or more kinds. You may be. The fluorescent whitening agent is a compound that generally absorbs light having a wavelength of about 300 to 450 nm and emits fluorescence having a wavelength of about 400 to 500 nm. The physical principles and chemical properties of optical brighteners are described in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, Electrical Release, Wiley-VCH 1998 and the like.

The benzoxazole-based fluorescent whitening agent is not particularly limited as long as it is a compound having a benzoxazole skeleton and having the above-mentioned characteristics, but it is preferably a benzoxazole-based compound represented by the following general formula (1). .. These compounds are easily crystallized after the ink is cured, and tend to have a relatively large effect on the gloss reduction (matte tone) of the cured product. One of the reasons for obtaining this effect is that the molecular structure has symmetry.

上記一般式（１）において、Ｒ_１〜Ｒ_８はそれぞれ独立に、水素原子またはアルキル基を表す。ただし、Ｒ_１〜Ｒ_８から選ばれる２以上の基が結合して環を形成していてもよい。

In the above general formula (1), R _{1 to} R ₈ independently represent a hydrogen atom or an alkyl group. However, _{two or more groups selected from R 1 to} R ₈ may be bonded to form a ring.

The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms, and may have a linear, branched, or cyclic structure. Further, the alkyl group may be substituted. Examples of the substituent include a carboxyl group, an alkoxy group, a hydroxyl group, a halogen atom and the like.

式（２）〜（４）における＊は、一般式（１）におけるベンゾオキサゾール基との結合手を表す。 On the other hand, in the above general formula (1), A represents any of the linking groups represented by the following formulas (2) to (4).

* In the formulas (2) to (4) represents a bond with the benzoxazole group in the general formula (1).

The compound represented by the general formula (1) has high solubility in urethane (meth) acrylate oligomers and polyester (meth) acrylate oligomers contained in the above-mentioned active photopolymerizable compound. On the other hand, it has high crystallinity, and when the polymerization of the active photopolymerizable compound starts, it precipitates on the surface of the cured product of the ink and crystallizes. That is, unevenness due to crystals of the fluorescent whitening agent is effectively formed on the surface of the cured product.

Among the above, the compound in which A in the general formula (1) is a linking group represented by the formula (4) is preferable from the viewpoint of less coloring on the ink and the cured product.

Examples of commercially available benzoxazole-based fluorescent whitening agents represented by the general formula (1) include FLUORESCENT BRIGHTENENER KCB (manufactured by Xcolor Pigment), in which A in the formula has the structure of formula (2). A in the formula is the structure of the formula (3) FLUORESCENT BRIGHTENENER OB and FLUORESCENT BRIGHTENENER PB (both manufactured by Xcolor Pigment), and A in the formula is the structure of the formula (4) FLUORESCENT BRIGHTENENER OB-1 Both are manufactured by Xcolor Pigment) and the like.

The fluorescent whitening agent is preferably contained in an amount of 0.01% by mass or more and 1.0% by mass or less, more preferably 0.05 to 0.5% by mass, based on the total mass of the ink. When the content of the fluorescent whitening agent is 0.01% by mass or more, it is possible to effectively increase the unevenness of the crystals formed on the surface of the cured product, and the cured product (image) becomes matte. It becomes easy. On the other hand, when the fluorescent whitening agent is 1.0% by mass or less, the cured product is less likely to be colored by the fluorescent whitening agent, and when the ink contains a pigment or the like, the effect on the color tone is less likely to occur.

The ink of the present invention may partially contain a fluorescent whitening agent other than the above-mentioned benzoxazole-based ink as long as the effects of the present invention are not impaired. Specific examples of fluorescent whitening agents other than benzoxazole-based compounds include coumarin-based compounds, styrene biphenyl-based compounds, pyrazolone-based compounds, stylben-based compounds, styryl derivatives of benzene and biphenyl, and bis (benzazole-2-yl) derivatives. Carbostilyl, naphthalimide, derivatives of dibenzothiophene-5,5'-dioxide, pyrene derivatives, pyridotriazole and the like are included. However, these amounts are preferably 3% by mass or less, and more preferably 1% by mass or less, based on the total mass of the ink, from the viewpoint of long-term storage stability of the ink and ejection stability from the inkjet nozzle. preferable.

3. 3. Polymerization Initiator The ink of the present invention may contain a polymerization initiator. When the active photopolymerizable compound is cured by an electron beam or the like, it is not always necessary to include a polymerization initiator, but when the active photopolymerizable compound is cured by ultraviolet rays or the like, it is preferable to include a polymerization initiator. ..

The type of polymerization initiator is appropriately selected according to the type of the active photopolymerizable compound. When the active photopolymerizable compound contains a radical-polymerizable compound, a radical-based polymerization initiator is used, and when the active photopolymerizable compound contains a cationically polymerizable compound, a cationic-based polymerization initiator is used. Be done.

Radical-based polymerization initiators include an intramolecular bond cleavage type and an intramolecular hydrogen abstraction type. Examples of intramolecular bond cleavage type polymerization initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl 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-) Acetphenone-based polymerization initiator containing thiomethylphenyl) propan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone, etc .; benzoin, benzoin methyl ether, benzoin isopropyl ether, etc. Includes benzoin polymerization initiators; acylphosphine oxide-based polymerization initiators including 2,4,6-trimethylbenzoindiphenylphosphine oxide and the like; benzyl and methylphenylglioxyesters; and the like.

Examples of intramolecular hydrogen abstraction-type polymerization initiators include benzophenone, methyl-4-phenylbenzophenone o-benzoyl benzoate, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide. , Benzophenone-based polymerization initiators including acrylicized benzophenone, 3,3', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone, 3,3'-dimethyl-4-methoxybenzophenone, etc .; 2-isopropylthioxanthone , 2,4-Dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone and the like; 10-Butyl-2-chloroacrydone; 2-ethylanthraquinone; 9,10-phenanthrene quinone; benzophenone; etc.

Examples of the cationic polymerization initiator include a photoacid generator. As the photoacid generator, chemically amplified photoresists and compounds used for photocationic polymerization are used (Organic Electronics Materials Research Association, "Organic Materials for Imaging", Bunshin Publishing (1993), 187-192. See page).

The content of the polymerization initiator is preferably 0.01% by mass to 10% by mass with respect to the total mass of the ink, although it depends on the type of the active light beam to be irradiated and the active photopolymerizable compound.

The ink may contain a polymerization initiator in addition to the above-mentioned polymerization initiator. Examples of the polymerization initiation aid include a tertiary amine compound, and among these, an aromatic tertiary amine compound is particularly preferable. 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 and the like. Among these, N, N-dimethylamino-p-benzoic acid ethyl ester and N, N-dimethylamino-p-benzoic acid isoamyl ethyl ester are preferable. Only one kind of these polymerization initiators may be contained in the ink, or two or more kinds thereof may be contained in the ink.

4. Wax The ink of the present invention may contain wax. Examples of waxes include, but are not limited to, dialkyl ketones, fatty acid esters, fatty acid alcohols, fatty acid amides, oil gelling agents and the like having a molecular weight of less than 1000.

Here, the wax is preferably a compound that is solid at room temperature but liquid when heated. The wax is dissolved in other components in the ink when ejected from the inkjet nozzle. On the other hand, when the temperature of the ink landing on the recording medium drops to the surface temperature of the recording medium, wax begins to precipitate. Then, the wax forms irregularities on the surface of the cured product, so that the image becomes more matte. Further, when the ink contains such wax, the ink droplets that have landed on the recording medium are less likely to get wet and spread, so that a high-definition image is likely to be formed. The melting point of the wax is preferably 30 ° C. or higher and lower than 150 ° C.

Here, specific examples of the wax include fatty acid alcohols such as stearone (18-pentatria-contanone), 16-hentoria-contanone, 12-tricosanone, UNILIN (registered trademark) 425 (manufactured by Baker-Huges); fatty acid. Ester; Inulin stearate / fatty acid dextrin (available from Chiba Flour Milling Co., Ltd. as Leopard series); L-glutamic acid derivative (available from Ajinomoto Fine Techno Co., Ltd.); Fatty acid amide (FATTY AMID series, available from Kao Co., Ltd.); Bechenic acid Glyceryl eicosanate (available from Nisshin Oillio Co., Ltd. (trade name: Nomcoat HK-G)); Hojoba ester (available from Ikeda Bussan Co., Ltd. (trade name: Floraester70)); The oil gelling agent described in Japanese Patent Application Laid-Open No. 2005-255821, and the like are included.

Further specific examples of fatty acid amides include FATTY AMID E: erucic acid amide, FATTY AMID T: oleic acid amide, FATTY AMID ON: cured beef fatty acid amide (all available from Kao), and Nikka amide AP1. : Steeric acid amide (available from Nippon Kasei Co., Ltd.), GP-1: N-lauroyl-L-glutamate dibutylamide (available from Ajinomoto Fight Techno Co., Ltd.) and the like are included.

The wax is preferably contained in an amount of 0.1% by mass or more and 5% by mass or less, more preferably 0.1 to 3% by mass, based on the total mass of the ink. When the wax content is 0.1% by mass or more, unevenness is likely to be formed in the image, and the cured product is likely to have a matte appearance. Further, when the content of the wax is 5% by mass or less, the wax is unlikely to affect the compatibility between the fluorescent whitening agent and the active photopolymerizable compound.

5. Other Components In addition to the components described above, the ink of the present invention may further contain other components including a coloring material, a dispersant, a polymerization inhibitor, a surfactant and the like. Only one kind of these components may be contained in the ink, or two or more kinds of these components may be contained in the ink.

The coloring material may be either a dye or a pigment, but from the viewpoint of forming an image having good weather resistance, the coloring material is preferably a pigment. The pigment can be selected from, for example, a yellow pigment, a red or magenta pigment, a blue or cyan pigment, and a black pigment, depending on the color of the image to be formed and the like.

When the ink contains a coloring material, the content (total amount) is preferably 0.1% by mass or more and 20% by mass or less, and 0.4% by mass or more and 10% by mass or less with respect to the total mass of the ink. More preferably.

Examples of dispersants include hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides with high molecular weight acids, salts of high molecular weight polycarboxylic acids, salts of long-chain polyaminoamides with polar acid esters, and high molecular weight unsaturateds. Acid ester, polymer copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, poly Oxyethylene nonylphenyl ether, stearylamine acetate and the like are included.

The content of the dispersant can be, for example, 20% by mass or more and 70% by mass or less with respect to the total mass of the pigment.

Examples of polymerization inhibitors include (alkyl) phenol, hydroquinone, catechol, resorcin, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiline, p-benzoquinone. , Nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyldisulfide, picric acid, cuperon, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N- (3-oxyanilino-) 1,3-Dimethylbutylidene) Aniline oxide, dibutyl cresol, cycloquinone oxime cresol, guayacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxim, cyclohexanone oxime and the like are included.

Examples of surfactants include anionic surfactants including dialkyl sulfosuccinates, alkylnaphthalene sulfonates, fatty acid salts, etc .; polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, etc. And nonionic surfactants including polyoxyethylene / polyoxypropylene block copolymers and the like; cationic surfactants including alkylamine salts and quaternary ammonium salts and the like; and silicone-based and fluorine-based surfactants; Is included.

Examples of commercially available silicone-based surfactants include KF-351A, KF-352A, KF-642 and X-22-4272, Shin-Etsu Chemical, BYK307, BYK345, BYK347 and BYK348, and Big Chemie (“BYK”). Is a registered trademark of the company), and includes TSF4452 and Toshiba Silicone Co., Ltd.

The content of the surfactant is preferably 0.001% by mass or more and less than 1.0% by mass with respect to the total mass of the ink.

6. Physical Properties of Active Light Curable Inkjet Ink The ink of the present invention preferably has a viscosity at the temperature of the inkjet head at the time of coating of 3 mPa · s or more and 20 mPa · s or less from the viewpoint of further improving the ejection property from the inkjet head. .. For example, the temperature of the inkjet head can be about 50 ° C. when the ink does not contain wax, and about 80 ° C. when the ink contains wax.

From the viewpoint of further improving the ejection property from the inkjet head, the average particle size of the pigment particles when the ink contains a pigment is preferably 0.08 μm or more and 0.5 μm or less, and the maximum particle size is 0.3 μm or more. It is preferably 10 μm or less. The average particle size of the pigment particles in the present specification means a value obtained by a dynamic light scattering method using a data sizer nano ZSP manufactured by Malvern. Since the ink containing the coloring material has a high density and does not transmit light with this measuring device, the ink is diluted 200 times before measurement. The measurement temperature is normal temperature (25 ° C).

7. Method for Preparing Active Photocurable Inkjet Ink In the ink of the present invention, the above-mentioned active photopolymerizable compound and fluorescent whitening agent are heated, if necessary, a polymerization initiator, wax, and any other component. It can be prepared by mixing. At this time, it is preferable to filter the obtained mixed solution with a predetermined filter. When preparing an ink containing a pigment and a dispersant, a pigment dispersion liquid in which the pigment and the dispersant are dispersed in an active photopolymerizable compound or the like is prepared in advance, and the remaining components are added thereto. You may mix while heating.

Dispersion of pigments and dispersants can be carried out, for example, by ball mills, sand mills, attritors, roll mills, agitators, Henschel mixers, colloid mills, ultrasonic homogenizers, pearl mills, wet jet mills, and paint shakers.

8. Applications of Active Ray Curable Inkjet Ink The ink of the present invention can form a matte image as described above. Therefore, it can be applied to printing of various packages and various printing.

As a method of using the ink, a droplet of ink is ejected from a nozzle of an inkjet head, landed on a recording medium, and then irradiated with active light to cure the ink droplet.

The inkjet head may be either an on-demand system or a continuous system. Examples of on-demand inkjet heads include electro-mechanical conversion methods including single cavity type, double cavity type, bender type, piston type, shared mode type and shared wall type, and thermal inkjet type and bubble jet ( Includes electrical-heat conversion methods, including registered trademark) types. Further, the inkjet head may be either a scan type or a line type.

Here, the ejection stability of the ink can be enhanced by ejecting the heated ink from the inkjet head. The temperature of the ink ejected from the inkjet head is preferably 35 ° C. or higher and 100 ° C. or lower, and more preferably 35 ° C. or higher and 80 ° C. or lower in order to further improve the ejection stability.

The temperature of the recording medium on which the ink droplets land is not particularly limited, but the melting point of the wax is considered from the viewpoint of promoting the crystallization of the fluorescent whitening agent and, when the ink contains wax, solidifying the wax. The temperature is preferably 40 ° C. or lower, more preferably 35 ° C. or lower, and even more preferably 35 ° C. or lower.

The amount of droplets at the time of ejecting ink is preferably 2 pL or more and 50 pL or less from the viewpoint of recording speed and image quality.

Further, the recording medium on which the ink is landed is not particularly limited. Examples of recording media include art paper, coated paper, lightweight coated paper, lightly coated cast paper, and absorbent media including coated and non-coated paper including corrugated paper, polyester, polyvinyl chloride, polyethylene. Non-absorbent recording medium (plastic substrate) composed of plastics including polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate and polybutadiene terephthalate, and metals and glass. Non-absorbent inorganic recording media such as, etc. are included.

On the other hand, the active light beam to irradiate the ink droplet is appropriately selected depending on the type of the active light-polymerizable compound, and can be ultraviolet rays, electron beams, or the like.

When the active light is ultraviolet light, examples of light sources include fluorescent tubes (low-pressure mercury lamps, germicidal lamps), cold-cathode tubes, ultraviolet lasers, and low-pressure, medium-pressure, and high-pressure mercury lamps with operating pressures of several hundred Pa to 1 MPa. , Metal halide lamps, LEDs and the like. From the viewpoint of efficiently curing the ink, ^{a light source capable of irradiating ultraviolet rays with an illuminance of 100 mW / cm 2} or more; specifically, a high-pressure mercury lamp, a metal halide lamp, an LED, or the like is preferable, and a viewpoint of low power consumption. Therefore, LED is more preferable. Specifically, a 395 nm, water-cooled LED manufactured by Phoseon Technology can be used.

When the active light beam is ultraviolet rays, the amount of light at the time of irradiation is preferably ^{200 mJ / cm 2} or more and 1000 mJ / cm ^2. When the amount of light is 200 mJ / cm ² or more, the active photopolymerizable compound can be sufficiently polymerized to sufficiently increase the hardness of the cured product. On the other hand, if the amount of light is excessive, it may affect the recording medium, but if the amount of light is 1000 mJ / cm ² or less, such a problem is unlikely to occur. From this point of view, the amount of active light to be irradiated ^{is more preferably 300 mJ / cm 2} or more and 800 mJ / cm ² or less, and further preferably 350 mJ / cm ² or more and 500 mJ / cm ² or less.

On the other hand, when the active light beam is an electron beam, examples of the electron beam irradiating device include an electron beam irradiating device such as a scanning method, a curtain beam method, and a broad beam method. It is preferable that the electron beam irradiation device is of the type. Examples of the electron beam irradiation device include "Curetron EBC-20-20-30" manufactured by Nissin High Voltage Co., Ltd., "Min-EB" manufactured by AIT Co., Ltd., and the like.

When the active ray is an electron beam, the acceleration voltage of the electron beam irradiation is preferably 30 to 250 kV, more preferably 30 to 100 kV in order to perform sufficient curing. When the acceleration voltage is 100 to 250 kV, the electron beam irradiation amount is preferably 30 to 100 kGy, more preferably 30 to 60 kGy.

Here, the timing of irradiating the ink landed on the recording medium with the active light is not particularly limited, but usually, the ink is irradiated with the active light within 0.001 seconds or more and 2.0 seconds or less after the ink lands on the recording medium. From the viewpoint of forming a high-definition image, it is more preferable to irradiate within 0.001 seconds or more and 1.0 seconds or less.

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

Hereinafter, specific examples of the present invention will be described. It should be noted that these examples do not limit the scope of the present invention.

1. 1. Preparation of active light-curable inkjet ink 1-1. Materials The following materials were used to prepare the active photocurable inkjet ink.
[Active photopolymerizable compound]
(Urethane (meth) acrylate oligomer)
-Polyester-based urethane acrylate oligomer (UV-3520TL, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., weight average molecular weight: 14000, unsaturated carbon-carbon double bond number: 2)
-Polyether-based urethane acrylate oligomer (UV-6640B, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., weight average molecular weight: 5000, unsaturated carbon-carbon double bond number: 2)
-Polycarbonate-based urethane acrylate oligomer (UV-3210EA, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., weight average molecular weight: 9000, unsaturated carbon-carbon double bond number: 2)
-Polyester-based urethane acrylate oligomer (UV-3000B, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., weight average molecular weight: 18,000, unsaturated carbon-carbon double bond number: 2)
-Urethane acrylate oligomer (UV-2750B, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., weight average molecular weight: 3000, unsaturated carbon-carbon double bond number: 2 to 3)

(Polyester (meth) acrylate oligomer)
-Polyester acrylate oligomer (CN2373, manufactured by SARTMER, unsaturated carbon-carbon double bond number: 2)
-Polyester acrylate oligomer (Etercure 6361-100, manufactured by ETERNAL CHEMICAL, unsaturated carbon-carbon double bond number: 8)
Amine-modified polyester acrylate oligomer (CN550, manufactured by SARTMER, unsaturated carbon-carbon double bond number: 4)

(Other active photopolymerizable compounds)
・ Phenoxyethyl acrylate (Viscoat # 192, manufactured by Osaka Organic Chemical Industry Co., Ltd.)
・ Acryloyl morpholine (ACMO, manufactured by KJ Chemicals)
-Tripropylene glycol diacrylate (M220, manufactured by Toagosei Co., Ltd.)
-Trimethylolpropane triacrylate (A-TMPT, manufactured by Shin-Nakamura Chemical Co., Ltd.)

・下記式で表される２，５−ビス（５−ｔｅｒｔ−ブチル−２−ベンゾオキサゾリル）チオフェン（ＦＬＵＯＲＥＳＣＥＮＴ ＢＲＩＧＨＴＥＮＥＲ ＯＢ、Ｘｃｏｌｏｒ Ｐｉｇｍｅｎｔ社製）

・下記式で表される４，４’−ビス（２−ベンゾオキサゾリル）スチルベン（ＦＬＵＯＲＥＳＣＥＮＴ ＢＲＩＧＨＴＥＮＥＲ ＯＢ−１、Ｘｃｏｌｏｒ Ｐｉｇｍｅｎｔ社製）

・下記式で表される１，２−ビス（５−メチルベンゾオキサゾール−２−イル）エテン（ＦＬＵＯＲＥＳＣＥＮＴ ＢＲＩＧＨＴＥＮＥＲ ＰＦ、Ｘｃｏｌｏｒ Ｐｉｇｍｅｎｔ社製）

・下記式で表される７−ジエチルアミノ−４−メチルクマリン（Ｈａｋｋｏｌ Ｐ、昭和化学工業社製）

[Optical brightener]
-1,4-Bis (2-benzoxazolyl) naphthalene (FLUORESCENT BRIGHTENENER KCB, manufactured by Xcolor Pigment) represented by the following formula.

-2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene represented by the following formula (FLUORESCENT BRIGHTNER OB, manufactured by Xcolor Pigment)

・ 4,4'-bis (2-benzoxazolyl) stilbene represented by the following formula (FLUORESCENT BRIGHTENENER OB-1, manufactured by Xcolor Pigment)

1,2-Bis (5-methylbenzoxazole-2-yl) ethene (FLUORESCENT BRIGHTENENER PF, manufactured by Xcolor Pigment) represented by the following formula.

7-diethylamino-4-methylcoumarin represented by the following formula (Hakcol P, manufactured by Showa Kagaku Kogyo Co., Ltd.)

[Polymerization initiator]
-Bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide (IRGACURE 819, manufactured by BASF)
2-Benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 (IRGACURE 369, manufactured by BASF)

[wax]
・ Lauric acid amide (Diamid Y, manufactured by Nihon Kasei Co., Ltd.)

[others]
(Polymerization inhibitor)
4,4'-[(1,10-dioxo-1,10-decandyl) bis (oxy)] bis [2,2,6,6-tetramethyl] -1-piperidinyloxy (Irgastab UV-) 10. Made by BASF)
(Surfactant)
-Polyether-modified polydimethylsiloxane (BYK307, manufactured by Big Chemie Japan)
(Pigment dispersant)
・ EFKA4130 (manufactured by BASF)
(Pigment)
・ Pigment Blue 15: 4 (manufactured by Dainichiseika Co., Ltd.)

1-2. Preparation of Cyan Pigment Dispersion Liquid A cyan pigment dispersion liquid was prepared by the following procedure. 9 parts by mass of EFKA4130 (manufactured by BASF), which is a pigment dispersant, and 71 parts by mass of tripropylene glycol diacrylate (M220, manufactured by Toa Synthetic Co., Ltd.), which is an active photopolymerizable compound, are placed in a stainless beaker and placed at 65 ° C. The mixture was heated and stirred for 1 hour while heating on a hot plate. The mixed solution was cooled to room temperature, and 20 parts by mass of PigmentBlue 15: 4 (manufactured by Dainichiseika Co., Ltd.) as a pigment was further added. The solution was placed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, sealed, and dispersed with a paint shaker for 5 hours. Then, the zirconia beads were removed to obtain a cyan pigment dispersion.

1-3. Preparation of Active Light Curable Inkjet Ink According to the composition shown in Table 1 below, each component and the above pigment dispersion liquid are mixed and heated to 50 ° C. (however, Examples 10 and 11 are 80 ° C.). Stirred. Then, while heating the mixed solution, filtration was performed with a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVANTEC to obtain an ink sample. The amount of components in the table is% by mass.

2. Image formation [Image formation method]
Using each of the active light-curable inkjet inks shown in Table 1, ^{a solid image of 5 cm × 5 cm was formed on an OK top coat (rice basis weight 128 g / m 2} , manufactured by Oji Paper Co., Ltd.) by the following procedure. As the ejection recording head of the line-type inkjet recording apparatus, a piezo head of KM512LH (512 nozzles, nozzle pitch 360 npi) manufactured by Konica Minolta Co., Ltd. was used. The temperature of the inkjet head is set to 50 ° C. (however, only Examples 10 and 11 are 80 ° C.), and the ejection conditions are the condition that the amount of one drop is 42pl, the resolution of 360 dpi × 360 dpi, and the recording speed of 500 mm. Recording was performed in one pass under the condition of / s.

After forming the image, the ink was cured by irradiating the image with ultraviolet rays with an LED lamp (395 nm, water-cooled LED manufactured by Phoseon Technology Co., Ltd.) arranged in the downstream part of the recording device. At this time, ultraviolet rays of 500 mJ / cm ^{2 were irradiated as the integrated light amount.}

[Evaluation method]
The gloss of the obtained image was evaluated by the following method. In addition, the long-term stability and ejection stability of the active ray-curable inkjet ink were evaluated by the following methods.

(Glossiness of image)
A 60 ° gloss value of a solid image was measured using a gloss meter PG-II manufactured by Nippon Denshoku Kogyo Co., Ltd. The obtained gloss value was evaluated according to the following criteria.
⊚: Gloss value is less than 20 (matte) and no in-plane gloss unevenness is observed. ○: Gloss unevenness is partially visible in the surface, but the gloss value is less than 20. Δ: Gloss value is 20. More than 50 and less than 50 ×: Gloss value is 50 or more In addition, Δ or more was regarded as acceptable.

(Long-term stability of activated light-curable inkjet ink)
Each active light-curable inkjet ink was stored at 70 ° C. for 1 month. Then, the mixture was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVANTEC, and evaluated according to the following criteria.
◯: No increase in filtration pressure is observed even after filtering 500 mL of ink △: When 500 mL of ink is filtered, an increase in filtration pressure is observed in the second half compared to the first half ×: Filtering 500 mL of ink In addition, it was judged that the result was △ or higher.

(Discharge stability)
The ejection stability of each active light-curable inkjet ink from the inkjet nozzle was evaluated from the state of the solid portion of the obtained image. Specifically, it was visually evaluated according to the following criteria.
◯: No white spots due to ejection defects such as nozzle missing or bending △: White spots due to ejection defects such as nozzle missing or bending are observed in 1 to 4 places ×: White spots due to ejection defects such as nozzle missing or bending Is recognized in 5 or more places. In addition, △ or more was regarded as a pass.

As shown in Table 1, a urethane (meth) acrylate oligomer having a weight average molecular weight (Mw) of 5,000 to 15,000 having two or more unsaturated carbon-carbon double bonds and / or an unsaturated carbon having no amine structure. -According to an active photocurable inkjet ink containing an active photopolymerizable compound containing a polyester (meth) acrylate oligomer having one or more carbon double bonds and a benzoxazole-based fluorescent whitening agent, a matte image A printed matter having the above was obtained. Further, the active photocurable inkjet ink had good long-term storage stability and ejection stability (Examples 1 to 11). It is presumed that these active light-curable inkjet inks have a matte tone due to the precipitation of the fluorescent whitening agent when the ink is cured. Furthermore, in these active photocurable inkjet inks, the affinity between the urethane (meth) acrylate oligomer or polyester (meth) acrylate oligomer and the fluorescent whitening agent is good, and long-term storage stability and ejection stability are improved. It is presumed that it has improved. Further, particularly when a monomer having an alicyclic structure or a heterocyclic structure (ACMO) is contained, long-term storage stability tends to be good (Examples 3 to 7, 9 to 11 and the like). However, as the amount of the fluorescent whitening agent increased, the long-term storage stability and ejection stability tended to decrease slightly (Example 8).

On the other hand, when the fluorescent whitening agent was not included, the image could not be made matte (Comparative Example 1). Further, when both the urethane (meth) acrylate oligomer and the polyester (meth) acrylate oligomer were not contained, both the long-term storage stability and the discharge stability were lowered (Comparative Example 2). Further, in this case, nozzle clogging occurred and a desired image could not be obtained. On the other hand, when the weight average molecular weight of the urethane (meth) acrylate oligomer was too large, the discharge stability was lowered, and when the weight average molecular weight was too small, the long-term storage stability was lowered (Comparative Examples 3 and 4). Further, when the polyester (meth) acrylate oligomer had an amine structure, the discharge stability was lowered (Comparative Examples 5 and 6). Further, when a coumarin-based fluorescent whitening agent was contained, the desired texture could not be obtained in the image, and the long-term storage stability was further reduced (Comparative Example 6).

According to the active photocurable inkjet ink according to the present invention, a matte image can be produced. In addition, the active ray-curable inkjet ink has high long-term storage stability, and also has excellent ejection stability from the inkjet nozzle. Therefore, the active ray-curable inkjet ink according to the present invention can be applied to various image formations such as package printing.

Claims (4)

An active ray containing a urethane (meth) acrylate oligomer having two or more unsaturated carbon-carbon double bonds and a weight average molecular weight of 5000 to 15000, and / or a polyester (meth) acrylate oligomer having no amine structure. With polymerizable compounds
Benzoxazole-based optical brighteners and
Radical-based polymerization initiator and
Contains,
The content of the urethane (meth) acrylate oligomer is 5% by mass or more and 15% by mass or less with respect to the total amount of the active photopolymerizable compound, and the content of the polyester (meth) acrylate oligomer is the active ray. When it is 5% by mass or more and 20% by mass or less based on the total amount of the polymerizable compound and contains both the urethane (meth) acrylate oligomer and the polyester (meth) acrylate oligomer, the total amount thereof is the active photopolymerizable compound. 5-25% by mass relative to the total amount is,
The radical-based polymerization initiator is an intramolecular bond-cleaving type polymerization initiator.
The fluorescent whitening agent has a structure represented by the following general formula (1).
Active light curable inkjet ink.

(In the above general formula (1), R _{1 to} R ₈ independently represent a substituent selected from a hydrogen atom, an alkyl group, and an amino group (however, two or more groups selected from _{R 1 to} R _{8 are present.} (May be bonded to form a ring), A represents any of the linking groups represented by the following formulas (2) to (4))

The fluorescent whitening agent is contained in an amount of 0.01% by mass or more and 1.0% by mass or less with respect to the total mass of the ink.
The active light curable inkjet ink according to claim 1. The active photopolymerizable compound further comprises a monomer having an alicyclic structure or a heterocyclic structure.
The active photocurable inkjet ink according to claim 1 or 2. Including more wax,
The active photocurable inkjet ink according to any one of claims 1 to 3.