JP7056351B2 - Active ray curable inkjet ink and image formation method - Google Patents

Description

The present invention relates to an active ray curable inkjet ink and an image forming method.

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

It is known that a gelling agent (wax) is added to an active light-curing inkjet ink. For example, Patent Document 1 discloses an active photocurable inkjet ink containing a photopolymerizable compound, a gelling agent (wax), and inorganic fine particles. In Patent Document 1, by blending a gelling agent with an active ray-curable inkjet ink, the slipperiness of the surface of an image is improved and the scratch resistance is enhanced.

Japanese Unexamined Patent Publication No. 2013-121992

As described above, when a gelling agent is added to an active ray-curable inkjet ink (hereinafter, “active ray-curable inkjet ink” is often abbreviated as “ink”), the slipperiness of the image surface is improved. However, since the gelling agent in the ink exists in a slightly dispersed state in the photopolymerizable compound which is the main component of the ink, it inhibits the intramolecular force of the photopolymerizable compound and increases the surface tension of the ink. May reduce. When the surface tension of the ink decreases, the ink droplets ejected from the nozzle of the inkjet head are easily torn off, so that satellites are likely to be generated. The satellite is a droplet (also referred to as “satellite droplet”) different from the main droplet constituting the printing portion, which is generated by dividing the ejected ink droplet in the air, and is the liquid. When the droplets land on a place away from the printed portion, the visible image may be displaced. If the surface tension of the ink is increased by adding a surfactant or the like in order to suppress the generation of such satellites, the adhesion to a recording medium such as paper is lowered. When the adhesion between the ink and the recording medium is lowered, the image fixing property is lowered, and the resistance to rubbing and folding is lowered, so that image defects are likely to occur.

In view of the above problems, it is an object of the present invention to provide an active ray-curable gel ink in which the generation of satellites is suppressed and the adhesion to a recording medium is good. Ideally, there are no satellites at all, but it is difficult to completely eliminate them because there is a problem of probability that the ejected ink droplets will split in the air. Therefore, in the present invention, it is assumed that the generation of satellites is suppressed by the decrease of satellites observed on the formed image.

In the present invention, as a first means for solving the above problems, a temperature-responsive polymer containing at least one monomer A selected from the group consisting of the following formulas (1) to (4), a gelling agent, and light. Provided is an active photocurable inkjet ink containing a polymerizable compound.

（式（１）中、Ｒはそれぞれ独立にメチル基またはエチル基であり、
式（４）中、Ｒはイソプロピル基またはノルマルプロピル基である。）

(In formula (1), R is an independently methyl group or ethyl group, respectively.
In formula (4), R is an isopropyl group or a normal propyl group. )

Further, in the present invention, as a second means for solving the above-mentioned problems, a step of injecting the active light-curable inkjet ink of the present invention from a nozzle of an inkjet head and landing it on a recording medium, and the ink landing on the recording medium. Provided is an image forming method by an inkjet method, which comprises a step of irradiating the ink with an active light beam to cure the ink.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an active ray-curable gel ink in which the generation of satellites is suppressed and the adhesion to a recording medium is good.

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

In a general active photocurable gel ink, the coloring material and the gelling agent are present in a slightly dispersed state in the photopolymerizable compound, so that the intermolecular force of the photopolymerizable compound is inhibited and the surface of the ink is surfaced. May reduce tension.

On the other hand, the ink of the present invention contains a temperature-responsive polymer containing at least one monomer A selected from the group consisting of the above formulas (1) to (4). The temperature-responsive polymer in the ink exists in a state where the polymer chains of the temperature-responsive polymer are aggregated at a high temperature (40 ° C. or higher) at the time of injection, and becomes hydrophobic. At this time, other hydrophobic compounds in the ink, such as coloring materials and gelling agents, can be incorporated inside the aggregated temperature-responsive polymer chains. As a result, it is considered that the inhibition of the intramolecular force of the photopolymerizable compound by the coloring material and the gelling agent is reduced, and the surface tension of the ink is improved. By improving the surface tension of the ink, the generation of satellites at the time of ink ejection is suppressed.

Next, the ink ejected from the nozzle of the inkjet head and landed on the recording medium is cooled on the recording medium (lower than 40 ° C.). At this time, the polymer chains of the temperature-responsive polymer that had been aggregated in the ink spread and become hydrophilic. As a result, the hydrophilicity of the ink is improved and the affinity with the recording medium is also improved, so that the adhesion between the ink and the recording medium is also improved.

Further, the gelling agent incorporated by the aggregate of the temperature-responsive polymer under high temperature is released when the polymer chain of the temperature-responsive polymer spreads on the recording medium. Therefore, on the recording medium, the improvement of the pinning property of the ink by the gelling agent is achieved.

Hereinafter, embodiments of the present invention will be described.

1. 1. Active light curable inkjet ink Inks contain temperature-responsive polymers, gelling agents, and photopolymerizable compounds.

[Temperature-responsive polymer]
The temperature-responsive polymer contained in the ink is a polymer in which the polymer chains aggregate and become hydrophobic at a high temperature of 40 ° C. or higher, and become hydrophilic in a expanded state at a low temperature of less than 40 ° C. It contains at least one monomer A selected from the group consisting of the following formulas (1) to (4).

（式（１）中、Ｒはそれぞれ独立にメチル基またはエチル基であり、
式（４）中、Ｒはイソプロピル基またはノルマルプロピル基である。）

(In formula (1), R is an independently methyl group or ethyl group, respectively.
In formula (4), R is an isopropyl group or a normal propyl group. )

The type of the monomer A contained in the temperature-responsive polymer is not particularly limited, and may contain only one type selected from the group consisting of the above formulas (1) to (4), or may contain two or more types. ..

The content of the monomer A is not particularly limited as long as the temperature-responsive polymer exhibits the above-mentioned behavior corresponding to the temperature, but is preferably 80 mol% or more and 100 mol% or less, and 90 mol% or more and 100 mol% or less. Is more preferable. When the content of the monomer A is within the above range, the responsiveness to the temperature of the polymer becomes good, the ink containing the polymer suppresses the generation of satellites, and the adhesion between the recording medium and the ink is enhanced. There is a tendency.

As the monomer unit other than the monomer A that can be contained in the temperature-responsive polymer, a (meth) acrylate compound is preferable. Examples of (meth) acrylate compounds include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, isoamyl (meth) acrylate, and stearyl. (Meta) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomilstyl (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxy Butyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxy Propylene 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 , Monofunctional monomers such as t-butylcyclohexyl (meth) acrylate,
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 (Meta) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecandi (meth) acrylate, bisphenol Bifunctional monomers such as PO adduct di (meth) acrylate of A, neopentyl glycol di (meth) acrylate of hydroxypivalate, polytetramethylene glycol di (meth) acrylate,
Trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, trimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate , Pentaerythritol ethoxytetra (meth) acrylate and other trifunctional or higher polyfunctional monomers and the like can be mentioned.

From the viewpoint of photosensitivity, the (meth) acrylate compound may be methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, or stearyl (meth). ) Acrylate, lauryl (meth) acrylate, isostearyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, isobornyl (meth) acrylate, tetraethylene glycol di (meth) acrylate, glycerin propoxytri (meth) acrylate and the like are more preferable.

The weight average molecular weight of the temperature-responsive polymer is not particularly limited, but is preferably 10,000 or more and 100,000 or less, and more preferably 20,000 or more and 80,000 or less. When the weight average molecular weight of the temperature-responsive polymer is 10,000 or more, the polymer can easily incorporate the gelling agent and the coloring material into the aggregate at high temperature. Further, when the weight average molecular weight is 100,000 or less, there is little possibility that the viscosity of the ink becomes too high and the ejection property deteriorates.

The weight average molecular weight of the temperature-responsive polymer is a polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography (GPC) performed under the following conditions.
Solvent: Tetrahydrofuran Column: Tosoh Corporation TSKgel G4000 + 2500 + 2000HXL
Column temperature: 40 ° C
Injection volume: 100 μl
Detector: RI Model 504 (manufactured by GL Science)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Weight average molecular weight = A calibration curve with 13 samples from 1,000,000 to 500 is used. The 13 samples are used at approximately equal intervals.

The content of the temperature-responsive polymer with respect to the total mass of the ink is preferably 5% by mass or more and 20% by mass or less, and more preferably 10% by mass or more and 15% by mass or less. When the content of the temperature-responsive polymer is 5% by mass or more, the effect of blending the temperature-responsive polymer described above can be easily obtained. Further, when it is 20% by mass or less, the curability of the ink does not decrease and the fixing property of the image is good.

[Gelling agent]
In the present invention, the gelling agent is generally defined as an organic substance that becomes a solid at room temperature and becomes a liquid when heated. The gelling agent contained in the active light-curing inkjet ink of the present invention is preferably 0.01% by mass or more and less than 15% by mass. If the content of the gelling agent is less than 0.01% by mass, the slipperiness of the image surface cannot be obtained, and the scratch resistance of the image becomes insufficient. On the other hand, when the content of the gelling agent is 15% by mass or more, the ink ejection property from the inkjet head deteriorates.

Further, the active light curable inkjet ink of the present invention may be a sol-gel phase transition type ink. The gelling agent content in the sol-gel phase transition type ink is preferably 1% by mass or more and less than 15% by mass, and more preferably less than 7% by mass. On the other hand, the gelling agent content in the non-sol-gel phase transition type ink is preferably 0.01% by mass or more and less than 1% by mass.

The gelling agent in the solgel phase transition type ink is at least 1) dissolved in a photopolymerizable compound at a temperature higher than the gelling temperature, and 2) crystallized in the ink at a temperature below the gelling temperature. ,is required.

When the gelling agent crystallizes in the ink (after being released from the temperature-responsive polymer aggregates in the ink droplets on the recording medium), the plate-like crystals that are the crystals of the gelling agent It is preferable to form a space that surrounds the space three-dimensionally and to enclose the photopolymerizable compound in the space. Such a structure in which a photopolymerizable compound is contained in a space three-dimensionally surrounded by plate-like crystals is sometimes called a “card house structure”. Once the cardhouse structure is formed, the liquid photopolymerizable compound can be retained and the ink droplets can be pinned. Thereby, the coalescence of the droplets can be suppressed. In order to form the card house structure, it is preferable that the photopolymerizable compound dissolved in the ink and the gelling agent are compatible with each other. On the other hand, if the photopolymerizable compound dissolved in the ink and the gelling agent are phase-separated, it may be difficult to form a cardhouse structure.

The type of gelling agent is not particularly limited, and examples thereof include higher fatty acids, higher alcohols, fatty acid esters, triglycerides, fatty acid amines, aliphatic ketones, and fatty acid amides, and fatty acid esters or aliphatic diketones are preferable.

Examples of the aliphatic diketone that can be suitably used as a gelling agent include a compound represented by the following formula (A).
R1- (C = O) -R2 (A)

In the formula (A), R1 and R2 are independently aliphatic hydrocarbon groups containing a linear moiety having 9 or more and 25 or less carbon atoms. The aliphatic hydrocarbon group may be a saturated or unsaturated aliphatic hydrocarbon group, but is preferably a saturated aliphatic hydrocarbon group (alkylene group) from the viewpoint of increasing the gelation temperature of the ink. If the number of carbon atoms of the aliphatic hydrocarbon groups of R1 and R2 of the formula (A) are about the same, the melting point of the compound in which R1 and R2 of the formula (A) are saturated aliphatic hydrocarbon groups is the formula. This is because R1 and R2 of (A) are often higher than the melting point of the compound which is an unsaturated aliphatic hydrocarbon group, and the gelation temperature of the ink tends to be high. The saturated aliphatic hydrocarbon group can be a branched or linear aliphatic hydrocarbon group, but in order to obtain high crystallinity, a linear saturated aliphatic hydrocarbon group (linear alkylene) is preferable. Based on).

If the number of carbon atoms in the linear moiety contained in the aliphatic hydrocarbon group is less than 9, the gelling agent does not function as a gelling agent because it does not have sufficient crystallinity, and the above-mentioned cardhouse structure is not only obtained. In, a sufficient space for containing the photopolymerizable compound cannot be formed. On the other hand, if the number of carbon atoms in the linear portion contained in the aliphatic hydrocarbon group exceeds 25, the melting point becomes too high, so that the gelling agent will not dissolve in the ink unless the ink ejection temperature is raised. .. When the number of carbon atoms in the linear moiety contained in the aliphatic hydrocarbon group is 9 or more and 25 or less, the above-mentioned cardhouse structure can be formed while having the crystallinity required as a gelling agent, and the melting point can be obtained. Will not be too high. The number of carbon atoms in the linear moiety contained in the aliphatic hydrocarbon groups of R1 and R2 is preferably 11 or more and less than 23. Therefore, it is particularly preferable that R1 and R2 are linear saturated aliphatic hydrocarbon groups (linear alkylene groups) having 11 or more carbon atoms and less than 23 carbon atoms.

Examples of aliphatic hydrocarbon groups containing a linear moiety having 9 or more carbon atoms and 25 or less carbon atoms include a docosanyl group (C22), an icosanyl group (C20), an octadecanyl group (C18), a heptadecanyl group (C17), and a hexadecanyl group ( C16), pentadecanyl group (C15), tetradecanyl group (C14), tridecanyl group (C13), dodecanyl group (C12), undecanyl group (C11), decanyl group (C10) and the like are included.

Examples of the fatty acid ester that can be suitably used as the gelling agent include compounds represented by the following formula (B).
R3- (C = O) -O-R4 (B)

In the formula (B), R3 and R4 are independently aliphatic hydrocarbon groups containing a linear moiety having 9 or more and 26 or less carbon atoms. The aliphatic hydrocarbon group can be a saturated or unsaturated aliphatic hydrocarbon group, but is preferably a saturated aliphatic hydrocarbon group (alkylene group). Further, the saturated aliphatic hydrocarbon group may be a branched or linear saturated aliphatic hydrocarbon group, but in order to obtain a certain level of crystallinity, a linear saturated aliphatic hydrocarbon is preferable. Group (straight-chain alkylene group).

When the number of carbon atoms in the linear moiety contained in the aliphatic hydrocarbon groups of R3 and R4 is 9 or more and 26 or less, the crystallinity required as a gelling agent is obtained as in the compound represented by the formula (A). While having, the above-mentioned card house structure can be formed, and the melting point does not become too high. In order to make the crystallinity of the compound represented by the formula (B) above a certain level, the number of carbon atoms in the linear moiety contained in the aliphatic hydrocarbon group of R3 is 11 or more and less than 23, and the fat of R4 The number of carbon atoms in the linear moiety contained in the group hydrocarbon group is preferably 12 or more and less than 24. Therefore, it is particularly preferable that R3 is a linear alkylene group having 11 or more and less than 23 carbon atoms, and R4 is a linear alkylene group having 12 or more and less than 24 carbon atoms.

The example of the aliphatic hydrocarbon group containing a linear moiety having 9 or more and 26 or less carbon atoms is the same as the aliphatic hydrocarbon group containing a linear moiety having 9 or more and 25 or less carbon atoms in the above formula (A). Includes.

Preferred specific examples of the gelling agent include aliphatic ketone compounds such as 18-pentatoria contanone and 16-hentoria contanone (for example, Kao gelling agent T1 manufactured by Kao Co., Ltd.); cetyl palmitate, stearyl stearate, and the like. An aliphatic monoester compound such as behenyl behenate (for example, Unista-M-2222SL manufactured by Nichiyu Co., Ltd.), Exepearl SS (manufactured by Kao Co., Ltd.), EMALEX CC-18 (manufactured by Nippon Emulsion Co., Ltd.), Amrepus PC (for example) (Manufactured by Higher Alcohol Industry Co., Ltd.), Exepearl MY-M (manufactured by Kao Co., Ltd.), Spam Aceti (manufactured by Nichiyu Co., Ltd.), EMALEX CC-10 (manufactured by Nippon Emulsion Co., Ltd.), etc.); N-lauroyl-L-dibutyl glutamate) Amide compounds such as amides, N- (2-ethylhexanoyl) -L-glutamate dibutylamide (available from Ajinomoto Fine Techno); 1,3: 2,4-bis-O-benziliden-D-glucitol (New Japan) Divendilidene sorbitols such as gelol D) available from Rika; petroleum-based gelling agents such as paraffin gelling agent, microcrystallin gelling agent, petrolactam; candelilla gelling agent, carnauba gelling agent, rice gelling agent, Plant-based gelling agents such as wood wax, jojoba oil, jojoba solid wax, and jojoba ester; animal-based gelling agents such as honey wax, lanolin, and whale wax; mineral gels such as montan gelling agents and hydride gelling agents. Agent; Hardened castor oil or hardened castor oil derivative; Modified gelling agent such as Montan gelling agent derivative, Paraffin gelling agent derivative, Microcrystallin gelling agent derivative or Polyethylene gelling agent derivative; Bechenic acid, arachidic acid, stearic acid , Palmitic acid, myristic acid, lauric acid, oleic acid, and higher fatty acids such as erucic acid; higher alcohols such as stearyl alcohol, behenyl alcohol; hydroxystearic acid such as 12-hydroxystearic acid; 12-hydroxystearic acid derivative; lauric acid. Fatty acid amides such as amides, stearic acid amides, behenic acid amides, oleic acid amides, erucic acid amides, ricinoleic acid amides, and 12-hydroxystearic acid amides (for example, Nikka Amide series manufactured by Nippon Kasei Co., Ltd., ITOWAX manufactured by Ito Oil Co., Ltd.). Series, FATTYAMID series manufactured by Kao Co., Ltd.); N-substitution of N-stearyl stearyl amide, N-oleyl palmitate amide, etc. Fatty acid amides; special fatty acid amides such as N, N'-ethylene bisstearyl amides, N, N'-ethylene bis-12-hydroxystearyl amides, and N, N'-xylylene bisstearyl amides; dodecylamine, tetradecylamine. Or higher amines such as octadecylamine; fatty acid ester compounds such as stearyl stealic acid, oleyl palmitic acid, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, polyoxyethylene fatty acid ester (for example, Nippon Emulsion Co., Ltd.) EAMLEX series manufactured by RIKEN Vitamin, Rikemar series manufactured by RIKEN Vitamin, Poem series manufactured by RIKEN Vitamin, etc.); Sugar ester series); Synthetic gelling agents such as polyethylene gelling agents and α-olefin anhydride maleic acid copolymer gelling agents; Polymerizable gelling agents (UNILIN series manufactured by Baker-Petrolite); Dimeric acid; Dimer Esters (PRIPOR series manufactured by CRODA, etc.) are included. These gelling agents may be used alone or in combination of two or more.

[Photopolymerizable compound]
The photopolymerizable compound is a compound that is crosslinked or polymerized by active light. The active rays are, for example, electron beams, ultraviolet rays, α rays, γ rays, X-rays and the like, preferably ultraviolet rays and electron beams. The photopolymerizable compound is a radically polymerizable compound or a cationically polymerizable compound, and is preferably a radically polymerizable compound.

The radically polymerizable compound is a compound having a radically polymerizable ethylenically unsaturated bond (monomer, oligomer, polymer or a mixture thereof). The radically polymerizable compound may be used alone or in combination of two or more.

Examples of compounds 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 their anhydrides. Examples thereof 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.

Among them, the radically polymerizable compound is preferably an unsaturated carboxylic acid ester compound, more preferably a (meth) acrylate compound. The (meth) acrylate compound may be an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group, or the like, as well as the monomer described later.

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, methoxyethylene 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, Monofunctional monomers such as 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid, t-butylcyclohexyl (meth) acrylate;
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 (Meta) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecandi (meth) acrylate, bisphenol Bifunctional monomer such as PO adduct di (meth) acrylate of A, neopentyl glycol di (meth) acrylate of hydroxypivalate, polytetramethylene glycol di (meth) acrylate;
Trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, trimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate , Pentaerythritol ethoxytetra (meth) acrylate and other trifunctional or higher polyfunctional monomers and the like are included.

The (meth) acrylate compound may be stearyl (meth) acrylate, lauryl (meth) acrylate, isostearyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, isobornyl (meth) acrylate, or tetraethylene glycol di. (Meta) acrylate, glycerin propoxytri (meth) acrylate and the like are preferable.

The (meth) acrylate compound may be a modified product. Examples of modified products include ethylene oxide-modified (meth) acrylate compounds such as ethylene oxide-modified trimethylolpropane tri (meth) acrylate and ethylene oxide-modified pentaerythritol tetraacrylate; and caprolactone such as caprolactone-modified trimethylolpropane tri (meth) acrylate. Includes modified (meth) acrylate compounds; and caprolactam-modified (meth) acrylate compounds such as caprolactam-modified dipentaerythritol hexa (meth) acrylate.

When the active photocurable inkjet ink of the present invention is a solgel phase transition type, it is preferable that at least a part of the photopolymerizable compound is an ethylene oxide-modified (meth) acrylate compound. This is because the ethylene oxide-modified (meth) acrylate compound is highly photosensitive and easily forms a cardhouse structure (described later) when the ink gels at a low temperature. Further, since the ethylene oxide-modified (meth) acrylate compound is easily dissolved in other ink components at a high temperature and has little curing shrinkage, curling of printed matter is unlikely to occur.

Examples of ethylene oxide-modified (meth) acrylate compounds include 4EO-modified hexanediol diacrylate CD561 (molecular weight 358), 3EO-modified trimethylol propanetriacrylate SR454 (molecular weight 429), and 6EO-modified trimethylol propanetriacrylate SR499 manufactured by Sartomer. (Molecular weight 560), 4EO-modified pentaerythritol tetraacrylate SR494 (molecular weight 528); polyethylene glycol diacrylate NK ester A-400 (molecular weight 508), polyethylene glycol diacrylate NK ester A-600 (molecular weight 742) manufactured by Shin-Nakamura Chemical Co., Ltd. , Polyethylene glycol dimethacrylate NK ester 9G (molecular weight 536), Polyethylene glycol dimethacrylate NK ester 14G (molecular weight 770); Tetraethylene glycol diacrylate V # 335HP (molecular weight 302) manufactured by Osaka Organic Chemical Co., Ltd .; 3PO modification manufactured by Cognis Co., Ltd. Trimethylol propan triacrylate Photomer 4072 (molecular weight 471); 1,10-decanediol dimethacrylate NK ester DOD-N (molecular weight 310), tricyclodecanedimethanol diacrylate NK ester A-DCP (molecular weight) manufactured by Shin-Nakamura Chemical Co., Ltd. 304) and tricyclodecanedimethanol dimethacrylate NK ester DCP (molecular weight 332) and the like are included.

The (meth) acrylate compound may be a polymerizable oligomer, and examples of such polymerizable oligomers include epoxy (meth) acrylate oligomers, aliphatic urethane (meth) acrylate oligomers, and aromatic urethane (meth) acrylates. Includes oligomers, polyester (meth) acrylate oligomers, linear (meth) acrylic oligomers and the like.

The cationically polymerizable compound can be an epoxy compound, a vinyl ether compound, an oxetane compound, or the like. The cationically polymerizable compound may be used alone or in combination of two or more.

The epoxy compound is an aromatic epoxide, an alicyclic epoxide, an aliphatic epoxide, or the like, and in order to enhance the curability, the aromatic epoxide and the alicyclic epoxide are preferable.

The aromatic epoxide can be a di or polyglycidyl ether obtained by reacting a polyhydric phenol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of the polyvalent phenol to be reacted or an alkylene oxide adduct thereof include bisphenol A or an alkylene oxide adduct thereof. The alkylene oxide in the alkylene oxide adduct can be ethylene oxide, propylene oxide and the like.

The alicyclic epoxide can be a cycloalkane oxide-containing compound obtained by epoxidizing a cycloalkane-containing compound with an oxidizing agent such as hydrogen peroxide or peracid. The cycloalkane in the cycloalkane oxide-containing compound can be cyclohexene or cyclopentene.

The aliphatic epoxide can be a di or polyglycidyl ether obtained by reacting an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of aliphatic polyhydric alcohols include ethylene glycol, propylene glycol, alkylene glycols such as 1,6-hexanediol and the like. The alkylene oxide in the alkylene oxide adduct can be ethylene oxide, propylene oxide and the like.

Examples of vinyl ether compounds include ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and isopropenyl ether. -O-Polyvinyl ether compounds such as propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether and octadecyl vinyl ether;
Divinyl ethers such as ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, and trimethylolpropane trivinyl ether. Alternatively, a trivinyl ether compound or the like is included. Among these vinyl ether compounds, di or trivinyl ether compounds are preferable in consideration of curability and adhesion.

The oxetane compound is a compound having an oxetane ring, and examples thereof include the oxetane compounds described in JP-A-2001-220526, JP-A-2001-310937, and JP-A-2005-255821. Among them, the compound represented by the following formula (C) described in paragraph No. 0088 of JP-A-2005-255821, the compound represented by the following formula (D) described in paragraph No. 0092 of JP-A-2005, paragraph. Examples thereof include the compound represented by the following formula (E) of No. 0107, the compound represented by the following formula (F) of paragraph No. 0109, the compound represented by the following formula (G) of paragraph No. 0116, and the like.

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

[Photopolymerization initiator]
The ink may further contain a photopolymerization initiator. Specifically, when the active light ray is an electron beam, the photopolymerization initiator may not usually be contained, but when the active light ray is ultraviolet rays, it is preferable that the photopolymerization initiator is contained.

The photopolymerization initiator includes an intramolecular bond cleavage type and an intramolecular hydrogen extraction type. Examples of intramolecular bond cleavage type photopolymerization initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 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) Propane-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -acetophenone such as butanone; benzoins such as benzoin, benzoin methyl ether, benzoin isopropyl ether; 2 , 4,6-trimethylbenzoindiphenylphosphine oxide and other acylphosphine oxides; benzyl and methylphenylglycoesters and the like are included.

Examples of intramolecular hydrogen abstraction-type photopolymerization initiators include benzophenone, o-benzoylmethyl-4-phenylbenzophenone benzoate, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl. Benzophenones such as sulfide, acrylicized benzophenone, 3,3', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone, 3,3'-dimethyl-4-methoxybenzophenone; 2-isopropylthioxanthone, 2,4 -Thioxanthone series such as dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone; aminobenzophenone series such as Michlerketone, 4,4'-diethylaminobenzophenone; 10-butyl-2-chloroacridone, 2-ethyl Includes anthraquinone, 9,10-phenanthrene quinone, benzophenone and the like.

The content of the photopolymerization initiator in the ink is preferably 0.01% by mass to 10% by mass, although it depends on the type of active light and the photopolymerizable compound.

The ink may contain a photoacid generator as the photopolymerization initiator. Examples of photoacid generators include chemically amplified photoresists and compounds used in photocationic polymerization (Organic Electronics Materials Study Group, "Organic Materials for Imaging", Bunshin Publishing (1993), 187. See page 192).

The active ray-curable inkjet ink may further contain a photopolymerization initiator auxiliary agent, a polymerization inhibitor, and the like, if necessary. The photopolymerization initiator auxiliary agent may be a tertiary amine compound, and an aromatic tertiary amine compound is 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, N, N-dimethylhexylamine and the like. Of these, N, N-dimethylamino-p-benzoic acid ethyl ester and N, N-dimethylamino-p-benzoic acid isoamyl ethyl ester are preferable. These compounds may be used alone or in combination of two or more.

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

[Color material]
The ink may further contain a coloring material, if necessary. The coloring material may be a dye or a pigment, but a pigment is preferable because it has good dispersibility with respect to the constituents of the ink and is excellent in weather resistance. The pigment is not particularly limited, but may be, for example, an organic pigment or an inorganic pigment having the following numbers listed in the Color Index.

Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, 53. 1, 57: 1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108, 112, 122, 123, 144 , 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange 13, 16, 20, 36 and the like are included. Examples of blue or cyan pigments include Pigment Blue 1, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36. , 60 and the like are included. Examples of green pigments include Pigment Green 7, 26, 36, 50. Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137. 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193 and the like are included. Examples of black pigments include Pigment Black 7, 28, 26 and the like.

Examples of commercially available pigments include Chromofine Yellow 2080, 5900, 5930, AF-1300, 2700L, Chromofine Orange 3700L, 6730, Chromofine Scarlet 6750, Chromofine Magenta 6880, 6886, 6891N, 6790, 6878, Chromo. Fine Violet RE, Chromo Fine Red 6820, 6830, Chromo Fine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4973, 5205, 5208, 5214, 5221, 5000P, Chromo Fine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, Chromo Fine Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200, 2270 , 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seika Fast Red 8040, C405 (F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262, 1537B , GY, 4R-4016, 3820, 3891, ZA-215, Seika Fast Carmine 6B1476T-7, 1843LT, 3840, 3870, Seika Fast Bordeaux 10B-430, Seika Light Rose R40, Seika Light Violet B800, 7805, Seika Fast Maroon. 460N, Seika Fast Orange 900, 2900, Seika Light Blue C718, A612, Cyanin Blue 4933M, 4933GN-EP, 4940, 4973 (manufactured by Dainichi Seika Kogyo);
KET Yellow 401, 402, 403, 404, 405, 406, 416, 424, KET Orange 501, KET Red 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106, 111, 118, 124, KET Green 201 (manufactured by Dainippon Ink and Chemicals);
Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow T-13, T-05, Pigment Yellow 1705, Colortex Orange 202, Color 103 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, USN, Colortex Maroon601, Colortex BrownB610N, Col. Red 122, Colortex Blue516, 517,518,519, A818, P-908,510, Colortex Green402, 403, Colortex Black 702, U905 (manufactured by Sanyo Pigment);
Lionol Yellow1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (manufactured by Toyo Ink),
Toner Magenta E02, Permanent RubinF6B, Toner Yellow HG, Permanent Yellow GG-02, Hostapeam BlueB2G (manufactured by Hoechst Industry);
Novoperm P-HG, Hostaparm Pink E, Hostaparm Blue B2G (manufactured by Clariant);
Carbon Black # 2600, # 2400, # 2350, # 2200, # 1000, # 990, # 980, # 970, # 960, # 950, # 850, MCF88, # 750, # 650, MA600, MA7, MA8, MA11 , MA100, MA100R, MA77, # 52, # 50, # 47, # 45, # 45L, # 40, # 33, # 32, # 30, # 25, # 20, # 10, # 5, # 44, CF9 (Made by Mitsubishi Chemical) and so on.

The pigment 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, a paint shaker, or the like. The dispersion of the pigment is carried out so that the average particle size of the pigment particles is preferably 0.08 to 0.5 μm, the maximum particle size is preferably 0.3 to 10 μm, and more preferably 0.3 to 3 μm. Is preferable. The dispersion of the pigment is adjusted by the selection of the pigment, the dispersant, and the dispersion medium, the dispersion conditions, the filtration conditions, and the like.

The ink may further contain a dispersant to enhance the dispersibility of the pigment. Examples of dispersants include hydroxyl group-containing carboxylic acid esters, long-chain polyaminoamide and high molecular weight acid ester salts, high molecular weight polycarboxylic acid salts, long chain polyaminoamide and polar acid ester salts, and high molecular weight unsaturated acid esters. , Polymer copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene Nonylphenyl ether, stearylamine acetate and the like are included. Examples of commercially available dispersants include Avecia's Solsperse series, Ajinomoto Fine-Techno's PB series, and the like.

The ink may further contain a dispersion aid, if desired. The dispersion aid may be selected according to the pigment.

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

The ink may further contain a dispersion medium for dispersing the pigment, if necessary. A solvent may be contained in the ink as a dispersion medium, but in order to suppress the residue of the solvent in the formed image, the above-mentioned photopolymerizable compound (particularly a monomer having a low viscosity) is used as the dispersion medium. Is preferable.

The dye can be an oil-soluble dye or the like. Examples of the oil-soluble dye include the following various dyes. Examples of magenta dyes include MS Magenta VP, MS Magenta HM-450, MS Magenta HSo-147 (all manufactured by Mitsui Toatsu Co., Ltd.), AIZENSOT Red-1, AIZEN SOT Red-2, AIZEN SOTRed-3, AIZEN SOT. Pink-1, SPIRON Red GEH SPECIAL (above, manufactured by Hodoya Chemical Co., Ltd.), RESOLIN Red FB 200%, MACROLEX Red Violet R, MACROLEX ROT5B (above, manufactured by Bayer Japan), KAYASET Red B, KAYASET 802 (above, manufactured by Nippon Kayaku Co., Ltd.), PHLOXIN, ROSE BENGAL, ACID Red (above, manufactured by Daiwa Kasei Co., Ltd.), HSR-31, DIARESIN Red K (above, manufactured by Mitsubishi Kasei Co., Ltd.), Oil Red (manufactured by BASF Japan). ) Is included.

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

Examples of yellow dyes include MS Yellow HSm-41, Yellow KX-7, Yellow EX-27 (Mitsui Toatsu), AIZEN SOT Yellow-1, AIZEN SOT YellowW-3, AIZEN SOT Yellow-6 (above, Hodogaya). Chemical Co., Ltd.), MACROLLEX Yellow 6G, MACROLLEX FLUOR. Yellow 10GN (above, manufactured by Bayer Japan), KAYASET Yellow SF-G, KAYASET Yellow2G, KAYASET Yellow AG, KAYASET Yellow EG (above, manufactured by Nippon Kayaku Co., Ltd.), DAIWA Yellow 330H , HSY-68 (manufactured by Mitsubishi Kasei Corp.), SUDAN Yellow 146, NEOPEN Yellow 075 (manufactured by BASF Japan, Inc.) and the like are included.

Examples of black dyes include MS Black VPC (manufactured by Mitsui Toatsu Co., Ltd.), AIZEN SOT Black-1, AIZEN SOT Black-5 (above, manufactured by Hodoya Chemical Co., Ltd.), RESORIN Black GSN 200%, RESOLIN BlackBS (above, RESOLIN BlackBS). Bayer Japan), KAYASET Black AN (Nippon Kayaku), DAIWA Black MSC (Daiwa Kasei), HSB-202 (Mitsubishi Kasei), NEPTUNE Black X60, NEOPEN Black X58 (above, BASF) Made by Japan) etc. are included.

The content of the pigment or dye is preferably 0.1 to 20% by mass, more preferably 0.4 to 10% by mass with respect to the ink. This is because if the content of the pigment or dye is too small, the color of the obtained image is not sufficient, and if it is too large, the viscosity of the ink becomes high and the ejection property deteriorates.

[Other ingredients]
The ink may further contain other components as needed. The other component may be various additives, other resins, or the like. Examples of additives include surfactants, leveling additives, matting agents, UV absorbers, infrared absorbers, antibacterial agents, basic compounds for enhancing the storage stability of inks, and the like. Examples of basic compounds include basic alkali metal compounds, basic alkaline earth metal compounds, basic organic compounds such as amines, and the like. Examples of other resins include resins for adjusting the physical properties of the cured film, and include, for example, polyester resins, polyurethane resins, vinyl resins, acrylic resins, rubber resins and the like.

The ink can be obtained by mixing the above-mentioned temperature-responsive polymer, a photopolymerizable compound, a gelling agent, and any components under heating. It is preferable to filter the obtained mixed solution with a predetermined filter.

[Sol-gel phase transition type active ray curable inkjet ink]
As described above, the ink of the present invention may be a solgel phase transition type ink that reversibly undergoes a solgel phase transition depending on the temperature. Since the sol-gel phase transition type ink is a liquid at a high temperature (for example, about 80 ° C.), it can be ejected from the inkjet recording head. When the active ray-curable inkjet ink is ejected at a high temperature, ink droplets (dots) land on the recording medium and then are naturally cooled to gel. As a result, it is possible to suppress the union of adjacent dots and improve the image quality.

In order to improve the ejection property of the sol-gel phase transition type ink, it is preferable that the viscosity of the ink at high temperature is constant or less. Specifically, the viscosity of the active ray-curable inkjet ink at 80 ° C. is preferably 3 to 20 mPa · s. On the other hand, in order to suppress the coalescence of adjacent dots, it is preferable that the viscosity of the ink at room temperature after landing is constant or higher. Specifically, the viscosity of the active ray-curable inkjet ink at 25 ° C. is preferably 1000 mPa · s or more.

The gelation temperature of the sol-gel phase transition type ink is preferably 40 ° C. or higher and 70 ° C. or lower, and more preferably 50 ° C. or higher and 65 ° C. or lower. When the injection temperature is around 80 ° C, if the gelation temperature of the ink exceeds 70 ° C, gelation tends to occur at the time of injection, resulting in low ejection property. If the gelation temperature is less than 40 ° C, the recording medium This is because it does not gel immediately after landing on the surface. The gelling temperature is a temperature at which the ink gelled and its fluidity decreases in the process of cooling the ink in the sol state.

The viscosity of the solgel phase transition type ink at 80 ° C., the viscosity at 25 ° C. and the gelation temperature can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer. Specifically, a temperature change curve of viscosity is obtained when the ink is heated to 100 ° C. and cooled to 20 ° C. under the conditions of a shear rate of 11.7 (/ s) and a temperature lowering rate of 0.1 ° C./s. The viscosity at 80 ° C. and the viscosity at 25 ° C. can be obtained by reading the viscosities at 80 ° C. and 25 ° C. on the temperature change curve of the viscosity, respectively. The gelation temperature can be obtained as a temperature at which the viscosity becomes 200 mPa · s in the temperature change curve of the viscosity.

As the rheometer, a stress-controlled rheometer Physica MCR series manufactured by Antonio Par can be used. The diameter of the cone plate can be 75 mm and the cone angle can be 1.0 °.

2. 2. Image forming method The image forming method of the present invention comprises 1) a step of injecting the above-mentioned active light-curable inkjet ink of the present invention from a nozzle of an inkjet head and landing it on a recording medium, and 2) the above-mentioned landing on the recording medium. The step of irradiating the ink with an active light beam to cure the ink is included.

1) In the ejection step, the inkjet ink stored in the ejection recording head may be ejected as droplets toward the recording medium through the nozzle. At this time, the temperature of the inkjet ink stored in the ejection recording head is such that the temperature-responsive polymer contained in the ink forms aggregates and becomes hydrophobic, and the content of the gelling agent is the gel in the ink. The temperature is preferably set to be equal to or lower than the saturated dissolution amount of the agent. That is, in the inkjet ink stored in the ejection recording head, it is preferable that the temperature-responsive polymer has a hydrophobic form and the gelling agent is dissolved as much as possible.

2) In the curing step, the ink that has landed on the recording medium is irradiated with light. The light to be irradiated may be appropriately selected depending on the type of the photopolymerizable compound, and may be ultraviolet rays, electron beams, or the like.

The active ray curable inkjet recording apparatus of the present invention will be described. The active ray curing type inkjet recording apparatus includes a line recording system (single pass recording system) and a serial recording system. It may be selected according to the required image resolution and recording speed, but from the viewpoint of high-speed recording, the line recording method (single-pass recording method) is preferable.

FIG. 1 is a diagram showing an example of the configuration of a main part of a line recording type inkjet recording device. Of these, FIG. 1A is a side view and FIG. 1B is a top view. As shown in FIG. 1, the inkjet recording device 10 covers the entire width of the head carriage 16 accommodating a plurality of ejection recording heads 14 and the recording medium 12, and is downstream of the head carriage 16 (in the transport direction of the recording medium). It has an active light irradiation unit 18 arranged on the side and a temperature control unit 19 arranged on the lower surface of the recording medium 12.

The head carriage 16 is fixedly arranged so as to cover the entire width of the recording medium 12, and accommodates a plurality of ejection recording heads 14 provided for each color. Ink is supplied to the ejection recording head 14. For example, ink may be supplied directly or by an ink supply means (not shown) from an ink cartridge (not shown) that is detachably attached to the inkjet recording device 10.

A plurality of ejection recording heads 14 are arranged in the transport direction of the recording medium 12 for each color. The number of ejection recording heads 14 arranged in the transport direction of the recording medium 12 is set by the nozzle density of the ejection recording head 14 and the resolution of the printed image. For example, when an image having a resolution of 1440 dpi is formed by using a discharge recording head 14 having a droplet amount of 2 pl and a nozzle density of 360 dpi, the four ejection recording heads 14 are shifted with respect to the transport direction of the recording medium 12. Just place it. Further, when an image having a resolution of 720 × 720 dpi is formed by using the ejection recording head 14 having a droplet amount of 6 pl and a nozzle density of 360 dpi, the two ejection recording heads 14 may be arranged in a staggered manner. dpi represents the number of ink droplets (dots) per 2.54 cm.

The active light irradiation unit 18 covers the entire width of the recording medium 12 and is arranged on the downstream side of the head carriage 16 in the transport direction of the recording medium. The active light irradiation unit 18 irradiates the droplets ejected by the ejection recording head 14 and landed on the recording medium with the active rays to cure the droplets.

When the active light is ultraviolet rays, examples of the active light irradiation unit 18 (ultraviolet irradiation means) include a fluorescent tube (low pressure mercury lamp, germicidal lamp), a cold cathode tube, an ultraviolet laser, and an operating pressure of several hundred Pa to 1 MPa. It includes low-pressure, medium-pressure, high-pressure mercury lamps, metal halide lamps, LEDs, and the like. From the viewpoint of curability, ultraviolet irradiation means for irradiating ultraviolet rays having an illuminance of 100 mW / cm ² or more; specifically, high-pressure mercury lamps, metal halide lamps, LEDs and the like are preferable. In addition, LEDs are more preferable because they consume less power. Specifically, a 395 nm, water-cooled LED manufactured by Phoseon Technology can be used.

When the active light beam is an electron beam, the example of the active light beam irradiating unit 18 (electron beam irradiating means) includes an electron beam irradiating means such as a scanning method, a curtain beam method, and a broad beam method. Therefore, a curtain beam type electron beam irradiation means is preferable. Examples of the electron beam irradiation means include "Curetron EBC-20-20-30" manufactured by Nissin High Voltage Co., Ltd., "Min-EB" manufactured by AIT Co., Ltd., and the like.

The temperature control unit 19 is arranged on the lower surface of the recording medium 12 and maintains the recording medium 12 at a predetermined temperature. The temperature control unit 19 may be, for example, various heaters, various coolers, or the like. When the recording medium 12 is heated by using the temperature control unit 19, the temperature of the ink droplets is reduced to less than 40 ° C. so that the temperature-responsive polymer in the ink takes a hydrophilic form.

Hereinafter, an image recording method using the line recording type inkjet recording apparatus 10 will be described. The recording medium 12 is conveyed between the head carriage 16 of the inkjet recording device 10 and the temperature control unit 19. On the other hand, the recording medium 12 is adjusted to a predetermined temperature by the temperature control unit 19. Next, high-temperature ink is ejected from the ink ejection recording head 14 of the head carriage 16 and adhered (landed) on the recording medium 12. Then, the active light irradiation unit 18 irradiates the ink droplets adhering on the recording medium 12 with the active light rays to cure the ink droplets.

When the temperature of the ink in the ejection recording head 14 when the ink is ejected from the ink ejection recording head 14 is filled in the ejection recording head in order to improve the ejection property of the ink from the ejection recording head. The temperature of the ink is preferably set to (gelling temperature +10) ° C. to (gelling temperature +30) ° C. of the ink. When the temperature of the ink in the ejection recording head is less than (gelling temperature +10) ° C., the ink gels in the ejection recording head or on the nozzle surface, and the ink ejection property tends to deteriorate. Further, when the temperature of the ink is low, the temperature-responsive polymer contained in the ink forms aggregates and takes in a gelling agent or the like, making it difficult to exert the effect of increasing the surface tension of the ink. On the other hand, if the temperature of the ink in the ejection recording head exceeds (gelling temperature +30) ° C., the ink becomes too hot, and the ink components may deteriorate. Furthermore, if the temperature of the ink becomes too high and the temperature of the ink droplets landing on the recording medium does not fall below 40 ° C., the polymer chain of the temperature-responsive polymer expands and the gelling agent or the like is not released, resulting in gelation. It becomes difficult for the agent to exert effects such as pinning.

The amount of droplets per drop ejected from each nozzle of the ink ejection recording head 14 depends on the resolution of the image, but is preferably 1 pl to 10 pl in order to form a high resolution image. It is more preferably 0.5 to 4.0 pl.

Irradiation with active light is performed within 10 seconds, preferably within 0.001 to 5 seconds, more preferably within 10 seconds after the ink droplets adhere to the recording medium in order to suppress the coalescence of adjacent ink droplets. It is preferably performed within 0.01 seconds to 2 seconds. It is preferable that the irradiation of the active light beam is performed after the ink is ejected from all the ink ejection recording heads 14 accommodated in the head carriage 16.

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.

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.

FIG. 2 is a diagram showing an example of the configuration of a main part of a serial recording type inkjet recording apparatus 20. As shown in FIG. 2, the inkjet recording apparatus 20 has a width narrower than the entire width of the recording medium and is used for ejecting a plurality of inks, instead of the head carriage 16 fixedly arranged so as to cover the entire width of the recording medium. FIG. 1 except that the head carriage 26 accommodating the recording head 24, the guide portion 27 for moving the head carriage 26 in the width direction of the recording medium 12, and the active light irradiation unit 28 instead of the active light irradiation unit 18. Can be configured in the same way as.

In the serial recording type inkjet recording apparatus 20, ink is ejected from the ejection recording head 24 housed in the head carriage 26 while the head carriage 26 moves in the width direction of the recording medium 12 along the guide portion 27. After the head carriage 26 has completely moved in the width direction of the recording medium 12 (for each pass), the recording medium 12 is sent in the transport direction. Except for these operations, an image is recorded in substantially the same manner as the above-mentioned line recording type inkjet recording apparatus 10. After that, the active light irradiation unit 28 irradiates the ink droplets adhering on the recording medium 12 with the active light rays to cure the ink droplets.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

1. 1. Synthesis of temperature-responsive polymer 1-1. Synthesis of Temperature Responsive Polymer 1 120 g of the monomer A represented by the formula (1), 12 g of the monomer B which is butyl methacrylate, and 0.35 g of azobisisobutyronitrile (AIBN) which is a polymerization opener are about 500 ml. Mixed with the monomer of. Next, after mixing nitrogen gas for about 1 hour, the temperature of the mixture was raised to 50 ° C. and stirred. After stirring for about 2 hours, about 0.3 g of hydroquinone was added to terminate the polymerization, and the mixture was allowed to flow into warm water (31 ° C. or higher). The obtained precipitate was recovered and dried to obtain a powdery temperature-responsive polymer 1.
The weight average molecular weight of the temperature-responsive polymer 1 was 58,000, and the content of the monomer A was 90 mol%.

1-2. Synthesis of Temperature-Responsive Polymers 2 to 4 The types and amounts of Monomer A and the amount of Monomer B are synthesized in the same manner as the Temperature-Responsive Polymer 1 except for changes as shown in Table 1 below, and are shown in Table 1. Temperature-responsive polymers 2 to 7 having a weight average molecular weight and a monomer A content were synthesized, respectively.

1-3. Synthesis of temperature-responsive polymer 5 The type and amount of monomer A and the amount of monomer B are changed as shown in Table 1 below, and about 500 ml of azobisisobutyronitrile (AIBN) as a polymerization developer is added. Mixed with the monomer of. Next, after mixing nitrogen gas for about 1 hour, the temperature of the mixture was raised to 50 ° C. and stirred. After stirring for about 1.5 hours, about 0.3 g of hydroquinone was added to terminate the polymerization, and the mixture was allowed to flow into warm water (31 ° C. or higher). The obtained precipitate was recovered and dried to obtain a powdery temperature-responsive polymer 5.

1-4. Synthesis of temperature-responsive polymer 6 The type and amount of monomer A and the amount of monomer B are changed as shown in Table 1 below, and about 500 ml of azobisisobutyronitrile (AIBN) as a polymerization developer is added. Mixed with the monomer of. Next, after mixing nitrogen gas for about 1 hour, the temperature of the mixture was raised to 50 ° C. and stirred. After stirring for about 1 hour, about 0.3 g of hydroquinone was added to terminate the polymerization, and the mixture was allowed to flow into warm water (31 ° C. or higher). The obtained precipitate was recovered and dried to obtain a powdery temperature-responsive polymer 6.

1-5. Synthesis of temperature-responsive polymer 7 The type and amount of monomer A and the amount of monomer B are changed as shown in Table 1 below, and about 500 ml of azobisisobutyronitrile (AIBN) as a polymerization developer is added. Mixed with the monomer of. Next, after mixing nitrogen gas for about 1 hour, the temperature of the mixture was raised to 50 ° C. and stirred. After stirring for about 4 hours, about 0.3 g of hydroquinone was added to terminate the polymerization, and the mixture was allowed to flow into warm water (31 ° C. or higher). The obtained precipitate was recovered and dried to obtain a powdery temperature-responsive polymer 7.

The polystyrene-equivalent weight average molecular weight of the temperature-responsive polymer measured by gel permeation chromatography (GPC) under the following conditions was defined as the weight average molecular weight.
Solvent: Tetrahydrofuran Column: Tosoh Corporation TSKgel G4000 + 2500 + 2000HXL
Column temperature: 40 ° C
Injection volume: 100 μl
Detector: RI Model 504 (manufactured by GL Science)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Weight average molecular weight = A calibration curve with 13 samples from 1,000,000 to 500 is used. Thirteen samples were used at approximately equal intervals.

Further, in the comparative example, the following polymers I and II were used instead of the temperature-responsive polymer.
Polymer I: Styrene (weight average molecular weight: 50,000)
Polymer II: Vinyl alcohol (weight average molecular weight: 60,000)

2. 2. Preparation of Pigment Dispersion Solution The pigment dispersant, photopolymerizable compound, and polymerization inhibitor shown below were placed in a stainless steel beaker and heated and stirred for 1 hour while heating on a hot plate at 65 ° C.
Pigment dispersant: Azisper PB824 (manufactured by Ajinomoto Fine-Techno) 9 parts by mass Photopolymerizable compound: APG-200 (tripropylene glycol diacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.) 70 parts by mass Polymerization inhibitor: Irgastab UV10 (Ciba Japan) (Manufactured by) 0.02 parts by mass

After cooling the above mixed solution to room temperature, 21 parts by mass of Pigment Red 122 (manufactured by Dainichiseika, Chromofine Red 6112JC), which is a magenta pigment, was added thereto. The obtained mixed solution was placed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, sealed, and dispersed in a paint shaker for 8 hours. Then, the zirconia beads were removed to obtain a pigment dispersion.

Examples 1-9 and Comparative Examples 10-12
(Preparation of active light curable inks 1 to 12)
Each compound was mixed at the composition ratio shown in Table 2 below (mass% with respect to the total mass of the ink), heated to 80 ° C., and stirred. Then, the obtained liquid was filtered with a # 3000 metal mesh filter under heating. This was cooled to obtain inks 1 to 12, respectively.

The compounds used are as follows.
Aliphatic diketone: Kao wax T1, polyethylene glycol # 400 diacrylate manufactured by Kao Corporation: A-400, 4EO modified pentaerythritol tetraacrylate manufactured by Shin-Nakamura Chemical Co., Ltd .: SR494, 6EO modified trimethylolpropane triacrylate manufactured by SARTOMER: SR499, SARTOMER Irgastab UV10: Ciba Specialty Chemical DAROCURE TPO: Ciba Specialty Chemical

(Image formation)
Inks 1 to 12 were used, respectively, and a monochromatic image was formed using a line-type inkjet recording device. The temperature of the inkjet head of the inkjet recording device was set to 80 ° C. On the recording medium, blank characters, a solid image of 5 cm × 5 cm, or a density gradation patch was printed. After forming the image, the ink was cured by irradiating the image with ultraviolet rays by an LED lamp (395 nm, water-cooled LED manufactured by Phoseon Technology) arranged in the downstream part of the recording device.

As the ejection recording head, a piezo head having a nozzle diameter of 20 μm and 512 nozzles (256 nozzles × 2 rows, staggered arrangement, 1 row nozzle pitch 360 dpi) was used. The ejection conditions were such that the droplet volume of one drop was 2.5 pl, and the droplet was ejected at a droplet speed of about 6 m / s and recorded at a resolution of 1440 dpi × 1440 dpi. The recording speed was 500 mm / s. Image formation was performed in an environment of 23 ° C. and 55% RH. dpi represents the number of dots per 2.54 cm.

(Evaluation of image)
(1) Confirmation and evaluation of satellites Using an OK top coat (manufactured by Oji Paper Co., Ltd., basis weight 104.7 g / m ² ) as a recording medium, an image of 5 cm × 5 cm with a printing rate of 50% was printed. The printed material was observed with an optical microscope to confirm the presence or absence of satellites. Specifically, 10 randomly selected spots were observed for one image, and the distance between the observed main droplet and the satellite droplet was measured. The average value of the distance between the main drop and the satellite drop measured at 10 points was obtained, and the presence or absence of satellite was evaluated by using the average value as the distance between the main drop and the satellite drop.
The following evaluation criteria are based on the finding that when the distance between the recording medium and the human eye is 30 cm, it becomes easy to detect a deviation of 60 μm or more.
⊚: The distance between the main droplets constituting the image and the satellite droplets is 0 μm, and there is no satellite. ○: Satellites were observed, but the distance between the main droplets constituting the image and the satellite droplets was less than 60 μm × : Satellites were observed, and the distance between the main droplets constituting the image and the satellite droplets was 60 μm or more.

(2) Rubbing resistance For solid images formed with each ink, the rubbing resistance was evaluated according to the method described in "JIS standard K5701-1 6.2.3 friction resistance test". Specifically, a recording medium cut to an appropriate size was placed on the image, and a load was applied to the images to rub them together. Then, the degree of decrease in image density was visually observed and evaluated based on the following criteria.
⊚: No change in the image is visible even after rubbing 100 times or more. ○: When rubbed 100 times or more, some marks are left on the surface, but the density does not decrease, which is within the practically acceptable range. A decrease in image density is observed, but it is within the practically acceptable range. ×: A clear decrease in image density is observed after rubbing less than 50 times, and the quality is unbearable for practical use.

(3) Folding resistance An OK top coat (manufactured by Oji Paper Co., Ltd., basis weight 104.7 g / m ² ) was used as a recording medium, and an image was output under the above printing conditions. For the image output of each sample, the 10th 100% printed portion was left in an environment of 25 ° C. and 60% RH for 24 hours. After that, the image was folded in half (mountain fold), a cellophane tape (registered trademark) manufactured by 3M Co., Ltd. was attached to the folded portion, the image was slowly peeled off, and the image after the peeling was visually observed.
◯: The image film does not peel off △: The image film peels off slightly at the fold part, but there is no problem in practical use ×: The image film peels off at the fold part

The results of the above evaluation are shown in Table 3 below.

As is clear from the results shown in Table 3 above, a temperature-responsive polymer containing at least one monomer A selected from the group consisting of the above formulas (1) to (4), a gelling agent, and photopolymerizability. Inks 1 to 9 containing the compound were able to suppress the generation of satellites and form an image having good rubbing resistance and folding resistance. Further, from the comparison of the inks 1 to 4, even if the monomer A contained in the temperature-responsive polymer is the monomer A represented by any of the above formulas (1) to (4), the same result can be obtained. Understand.

The ink 1 having a temperature-responsive polymer monomer A content of 80 mol% or more contained in the ink has the same composition except that the temperature-responsive polymer monomer A content is less than 80 mol%. In comparison, the generation of satellites was suppressed and the rubbing resistance was improved. From this result, the temperature-responsive polymer having a monomer A content of 80 mol% or more has better temperature responsiveness, suppresses the generation of satellites, and tends to improve the adhesion between the recording medium and the ink. It is thought to be in.

Ink 1 having a temperature-responsive polymer having a weight average molecular weight of 10,000 or more and 100,000 or less has the same composition except that the temperature-responsive polymer has a weight average molecular weight of less than 10,000. Compared with a certain ink 6, the generation of satellite was suppressed. From this result, if the weight average molecular weight of the temperature-responsive polymer is 10,000 or more, the polymer can easily incorporate the gelling agent and the coloring material into the aggregate at high temperature, and thus the surface tension. It is considered that the decrease in the temperature was suppressed. Further, as compared with the ink 7 having the same composition except that the weight average molecular weight of the temperature-responsive polymer exceeds 100,000, the generation of satellites was suppressed and the rubbing resistance was improved. From this result, it is considered that if the weight average molecular weight of the temperature-responsive polymer is 100,000 or less, there is little possibility that the viscosity of the ink becomes too high and the ejection property deteriorates.

Ink 1 having a temperature-responsive polymer content of 5% by mass or more and 20% by mass or less with respect to the total mass of the ink is that of ink 8 having a temperature-responsive polymer content of less than 5% by mass and temperature-responsive polymer. Compared with the ink 9 having a content of more than 20% by mass, the generation of satellites was suppressed and the rubbing resistance was improved. From this result, if the content of the temperature-responsive polymer is 5% by mass or more, the effect of blending the above-mentioned temperature-responsive polymer can be easily obtained, and if it is 20% by mass or less, the ink can be easily obtained. It is considered that the fixing property of the image is good without deteriorating the curability.

On the other hand, in an image formed by using ink 10, which has the same composition as ink 1 except that it does not contain a temperature-responsive polymer, satellites are generated, and although it is at a practical level, it has scratch resistance and folding resistance. It has declined. From this result, it can be seen that in the absence of the temperature-responsive polymer, the gelling agent in the ink lowers the surface tension of the ink and generates satellites.

Further, in the image formed by using the ink 11 having the same composition as the ink 1 except that the hydrophobic polymer styrene is contained instead of the temperature-responsive polymer, satellites were not generated, and the rubbing resistance and the rubbing resistance were obtained. The folding resistance was at a level that was not practical. This result indicates that the surface tension of the ink was increased and the generation of satellites was suppressed by blending the hydrophobic polymer, but the adhesion to the recording medium was lowered, and the rubbing resistance and the folding resistance were lowered. Further, in the image formed by using the ink 12 having the same composition as the ink 1 except that the hydrophilic polymer vinyl alcohol is contained instead of the temperature-responsive polymer, the rubbing resistance and the folding resistance were good. , Satellite occurred. This result shows that the blending of the hydrophilic polymer lowers the surface tension of the ink, improves the adhesion between the ink and the recording medium, and improves the rubbing resistance and folding resistance, but tends to generate satellites. ing.

According to the present invention, it is possible to provide an active photocurable gel ink and an image forming method in which the generation of satellites is suppressed and the adhesion to a recording medium is good. Therefore, the present invention can be particularly preferably applied to a sol-gel phase transition type active photocurable inkjet ink containing a relatively large amount of a gelling agent.

10, 20 Inkjet recording device 12 Recording medium 14, 24 Discharge recording head 16, 26 Head carriage 18, 28 Active light irradiation unit 19 Temperature control unit 27 Guide unit

Claims (5)

A copolymer of at least one monomer A selected from the group consisting of the following formulas (1) to (4) and butyl methacrylate, and the monomer A with respect to all moles of the monomers constituting the copolymer. An active photocurable inkjet ink containing a temperature-responsive polymer having a content of 70 mol% or more and 100 mol% or less, a gelling agent which is a fatty acid ester or an aliphatic diketone, and a photopolymerizable compound.

(In formula (1), R is an independently methyl group or ethyl group, respectively.
In formula (4), R is an isopropyl group or a normal propyl group. ) The active photocurable inkjet ink according to claim 1, wherein the content of the monomer A with respect to all the moles of the monomers constituting the temperature-responsive polymer is 80 mol% or more and 100 mol% or less. The active photocurable inkjet ink according to claim 1 or 2, wherein the content of the temperature-responsive polymer with respect to the total mass of the active photocurable inkjet ink is 5% by mass or more and 20% by mass or less. The active photocurable inkjet ink according to any one of claims 1 to 3, wherein the temperature-responsive polymer has a weight average molecular weight of 10,000 or more and 100,000 or less. A step of injecting the active ray-curable inkjet ink according to any one of claims 1 to 4 from a nozzle of an inkjet head and landing it on a recording medium.
A method for forming an image by an inkjet method, which comprises a step of irradiating the ink that has landed on the recording medium with active light rays to cure the ink.

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