JP7453033B2 - Energy ray curable inkjet ink composition - Google Patents

Description

The present invention relates to an ink composition, and more particularly to an energy ray-curable inkjet ink composition that is cured by irradiation with energy rays.

The inkjet recording method is a method in which liquid ink is ejected from an ink head nozzle to record on a recording medium. Energy ray curable inkjet ink is one of the inks used in the inkjet recording method. In this method, after the ink is ejected, the polymerizable compound in the ink is crosslinked by irradiation with energy rays (for example, ultraviolet rays, etc.), so that the energy ray-curable inkjet ink is cured to form an ink layer. Energy beam curable inkjet inks can be roughly divided into solvent-based inks that contain organic solvents and water, and solvent-free inks that are substantially free of organic solvents, water, and the like.

Energy beam curable inkjet ink usually needs to be adjusted to have a viscosity that can be ejected from an ink head nozzle. Furthermore, in order to obtain high-definition printed matter, it is necessary to reduce the size of ejected ink droplets and to lower the viscosity so that the ink can be ejected stably.

As an example for obtaining an energy beam-curable inkjet ink having a low viscosity, Patent Document 1 states that the polymerizable compound has an acrylic equivalent of 300 or less and has one ethylenic double bond in one molecule. and a polyfunctional monomer having an acrylic equivalent of 150 or less and having two or more ethylenic double bonds in one molecule, and the photopolymerization initiator is α-aminoalkylphenone. An energy beam-curable ink composition containing a thioxanthone-based compound and a thioxanthone-based compound is described.

Further, Patent Document 2 describes that, as a polymerizable compound, a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of more than 150 and having two or more ethylenic double bonds in one molecule, and an acrylic An energy ray curable ink composition is described which has an equivalent weight of 150 or less and a second polyfunctional monomer having two or more ethylenic double bonds in one molecule.

Japanese Patent Application Publication No. 2009-275175 JP2018-065911A

In solvent-free energy beam curable ink compositions, especially those containing white pigments, if the amount of ink ejected during printing increases and the film thickness becomes thick, or if the amount of irradiation light during curing decreases. Since curability is insufficient and tackiness occurs in the coating film, further improvement of curability is required.

It is thought that an energy ray curable inkjet ink composition containing a white pigment has low reactivity to energy ray irradiation and a decrease in curability because light reflection occurs on the ink surface.

The present invention has been made in view of the above-mentioned problems, and provides a white inkjet ink composition with low viscosity that has good curability, and furthermore, when the ejection amount during printing is increased or the amount of irradiation light is small. To provide an inkjet ink composition capable of obtaining printed matter with excellent curability.

The present inventors conducted extensive studies and found that as a polymerizable compound, a first polyfunctional monomer having an acrylic equivalent of more than 150 and having two or more ethylenic double bonds in one molecule; is 150 or less, and contains a specific amount of a second polyfunctional monomer having two or more ethylenic double bonds in one molecule, and further contains a (meth)acrylated amine compound, thereby achieving the above-mentioned purpose. We obtained the knowledge that it is possible to achieve the following. That is, the present invention provides the following preferred embodiments.

[1] A white inkjet ink composition containing a polymerizable compound, a white pigment, and a photopolymerization initiator, wherein the polymerizable compound contains a monofunctional monomer, an acrylic equivalent of more than 150, and a first polyfunctional monomer having two or more ethylenic double bonds; a second polyfunctional monomer having an acrylic equivalent of 150 or less and two or more ethylenic double bonds in one molecule; ) an acrylated amine compound, the content of the first polyfunctional monomer is 1 to 20% by mass based on the entire inkjet ink composition, and the content of the second polyfunctional monomer is An inkjet ink composition in an amount of 15 to 30% by mass based on the entire inkjet ink composition.

[2] The inkjet ink composition according to [1], wherein the content of the (meth)acrylated amine compound is 0.1 to 15% by mass based on the entire inkjet ink composition.

[3] The (meth)acrylated amine compound is a (meth)acrylated amine compound having two ethylenic double bonds in one molecule and two amino groups in one molecule, [ 1] to [2].

[4] The inkjet ink composition according to [1] to [3], wherein the content of the monofunctional monomer is 50% by mass or less based on the entire inkjet ink composition.

[5] The monofunctional monomer has a glass transition temperature of -90°C or more and 30°C or less, the first polyfunctional monomer has a glass transition temperature of -25°C or more and 190°C or less, and the second The inkjet ink composition according to [1] to [4], wherein the polyfunctional monomer has a glass transition temperature of 40° C. or higher and 100° C. or lower.

[6] The inkjet ink composition according to [1] to [5], wherein the (meth)acrylated amine compound has an acrylic equivalent of more than 150.

[7] The ratio of the content of the (meth)acrylated amine compound to the total amount of the first polyfunctional monomer and the second polyfunctional monomer is 1.0:1.1 to 1.0: 15.0, the inkjet ink composition according to [1] to [6].

[8] The inkjet ink composition according to [1] to [7], wherein the inkjet ink composition has a viscosity at 25° C. of 15 mPa·s or less.

According to the present invention, an energy beam-curable white inkjet ink composition with a low viscosity has good curability, and even when the ejection amount during printing is increased or the amount of irradiation light is small, the curability remains high. An excellent energy ray curable inkjet ink composition can be provided.

This embodiment will be described below.

The energy ray-curable inkjet ink (hereinafter also referred to as ink) composition of the present embodiment includes at least a monofunctional monomer and a polyfunctional monomer that are polymerizable compounds, and a photopolymerization initiator. In addition, it includes colorants, additives, etc.

A polymerizable compound is a compound that undergoes a polymerization reaction and is cured by irradiation with energy rays (ultraviolet rays, electron beams, etc.). Among polymerizable compounds, monofunctional monomers have one ethylenic double bond in one molecule, and polyfunctional monomers have two or more ethylenic double bonds in one molecule. The polymerizable compound of this embodiment is preferably a radically polymerizable compound that is cured by a radical polymerization reaction.

Furthermore, the energy ray curable ink composition of this embodiment is solvent-free and substantially contains no solvent. Here, "containing substantially no solvent" means that it is not necessary to contain a diluting solvent, but for example, there are cases where a diluting solvent is unavoidably mixed into the ink when using an industrial product, and it is not necessary to contain a diluting solvent in the total mass of the ink. This means that the content of the solvent is 3% by mass or less. The term "solvent" refers to various known solvents such as alcohol, ether, ketone, aromatic, xylene, and the like. Since the energy beam curable ink composition is solvent-free, no volatile solvent remains in the ink layer, which is preferable from the viewpoint of suppressing the discharge of volatile organic compounds.

The energy beam-curable ink composition of the present embodiment does not substantially contain water because water is not intentionally added unless it is unavoidably mixed when preparing the ink composition. Water means, for example, deionized water, distilled water, ultrapure water, tap water, and the like.

<1. Polymerizable compound>
<1-1. Monofunctional monomer>
Specifically, monofunctional monomers include amyl (meth)acrylate, isoamyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, and lauryl (meth)acrylate. ) acrylate, isomyristyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tridecyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, Neo Pentyl glycol (meth)acrylic acid benzoate, butoxyethyl (meth)acrylate, ethoxy-diethylene glycol (meth)acrylate, methoxy-triethylene glycol (meth)acrylate, methoxy-polyethylene glycol (meth)acrylate, methoxydipropylene glycol ( meth)acrylate, phenoxyethyl (meth)acrylate, phenoxy-polyethylene glycol (meth)acrylate, 3,5,5-trimethylcyclohexyl acrylate 2-(2-ethoxyethoxyethyl acrylate) nonylphenol ethylene oxide adduct (meth)acrylate, tetrahydro Furfuryl (meth)acrylate, isobonyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate ) Acrylate, 2-(meth)acryloyloxyethyl-succinic acid, 2-(meth)acryloyloxyethyl-phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid, 1,4 - Cyclohexane dimethanol monoacrylate, ethoxylated nonylphenyl acrylate, etc. These may be used alone or in combination. Further, the above monomer may be substituted with a functional group such as phosphorus or fluorine.

Among these, tetrahydrofurfuryl (meth)acrylate, 3,5,5-trimethylcyclohexyl acrylate, 2-(2-ethoxyethoxyethyl acrylate), and 2-ethylhexyl (meth)acrylate are more preferable because of their low viscosity. . Furthermore, it is particularly preferable to use 2-hydroxy-3-phenoxypropyl (meth)acrylate in combination. By using 2-hydroxy-3-phenoxypropyl (meth)acrylate containing a functional group such as a hydroxyl group in combination, adhesion to the non-recording medium (substrate) can be imparted while maintaining low viscosity.

As mentioned above, two or more types of monofunctional monomers can be used in combination; one type uses a monofunctional monomer with a viscosity of 10 mPa·s or less at 25°C, and the other type uses a monofunctional monomer with a viscosity of 80 mPa·s at 25°C. - Monofunctional monomers with s or more can be used. Thereby, the viscosity of the energy beam curable ink can be made low, and the adhesion to the non-recording medium can be improved.

Specifically, monofunctional monomers having a viscosity of 10 mPa·s or less at 25°C include tetrahydrofurfuryl (meth)acrylate, 3,5,5-trimethylcyclohexyl acrylate, 2-(2-ethoxyethoxyethyl acrylate), 2 - Ethylhexyl (meth)acrylate. Specific examples of monofunctional monomers with a viscosity of 80 mPa・s or more at 25°C include 2-hydroxy-3-phenoxypropyl (meth)acrylate, 1,4-cyclohexanedimethanol monoacrylate, and ethoxylated nonylphenyl acrylate. It will be done. Even when using a monofunctional monomer with a viscosity of 80 mPa・s or more at 25°C, by using a monofunctional monomer with a viscosity of 10 mPa・s or less at 25°C, the viscosity of the ink can be kept low and the non-recording medium of the ink can be used. It is possible to improve the adhesion to.

Further, the monofunctional monomer preferably has a functional group, and specific examples include a hydroxyl group, a carboxyl group, and a phosphoric acid group. By having these functional groups, adhesion to non-recording media can be improved. Among these, hydroxyl groups are particularly preferred and can further improve adhesion.

Further, the glass transition temperature Tg of the monofunctional monomer is preferably -90°C or more and 30°C or less. This makes it possible to impart appropriate hardness (coating film strength) and stretchability to the coating film.

<1-2. Polyfunctional monomer＞
The polyfunctional monomer includes a first polyfunctional monomer having an acrylic equivalent of more than 150 and two or more ethylenic double bonds in one molecule, and a first polyfunctional monomer having an acrylic equivalent of 150 or less and an ethylenic double bond in one molecule. Contains a second polyfunctional monomer having two or more double bonds. The polyfunctional monomer of the polymerizable compound used in this embodiment is composed of two types: a first polyfunctional monomer and a second polyfunctional monomer.

By using the first polyfunctional monomer and the second polyfunctional monomer as the polyfunctional monomers, it is possible to achieve both stretchability and hardness of the coating film. Moreover, the use of the polyfunctional monomer improves the curability of the coating film.

Acrylic equivalent is calculated as follows.
(Acrylic equivalent) = (molecular weight of monomer/number of functional groups of monomer)
Depending on the acrylic equivalent, if the molecular weight is the same, monomers with a lower acrylic equivalent have more acrylic groups in one molecule. Further, even for monomers having the same number of acrylic groups, the lower the molecular weight, the higher the acrylic equivalent. Therefore, monomers with a lower acrylic equivalent have more crosslinking points in the molecule and are more reactive, and monomers with a higher acrylic equivalent have a lower reactivity and a higher molecular weight, so they tend to thicken more easily. be. From the above viewpoint, by including specific amounts of the first polyfunctional monomer and the second polyfunctional monomer as the polyfunctional monomers of the polymerizable compound, an ink composition having both low viscosity and high reactivity can be obtained. Improves coating strength.

<1-2-1. First polyfunctional monomer>
Specifically, the first polyfunctional monomer having two ethylenic double bonds in one molecule includes polyethylene glycol (200) diacrylate, tetraethylene glycol diacrylate, polyethylene glycol (400) diacrylate, ethoxy Examples include (3) bisphenol A diacrylate, tricyclodecane dimethanol diacrylate, and propoxylated (2) neopentyl glycol diacrylate. These may be used alone or in combination.

Specifically, the first polyfunctional monomer having three or more ethylenic double bonds in one molecule includes ethoxylated (20) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, etc. can be mentioned. These may be used alone or in combination.

Among the above polyfunctional monomers, tricyclodecane dimethanol diacrylate, polyethylene glycol (400) diacrylate, and propoxylated (2) neopentyl glycol diacrylate are preferred. By using these polyfunctional monomers, the viscosity of the ink can be kept low, and the hardness and curability of the coating film can be increased.

Further, the glass transition temperature Tg of the first polyfunctional monomer is preferably -25°C or more and 190°C or less, more preferably 0°C or more and 190°C or less. Thereby, the hardness and curability of the coating film can be increased.

<1-2-2. Second polyfunctional monomer>
Specifically, the second polyfunctional monomer having two ethylenic double bonds in one molecule includes 1,3-butylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, , 1,4-butanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, Examples include tripropylene glycol diacrylate, cyclohexane dimethanol di(meth)acrylate, and dipropylene glycol di(meth)acrylate. These may be used alone or in combination.

Specifically, the polyfunctional monomers having three or more ethylenic double bonds in one molecule include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tris(2-hydroxyethyl)isocyar Examples include nurate tri(meth)acrylate, glyceryl tri(meth)acrylate, and ethylene oxide-modified, propylene oxide-modified, and caprolactone-modified products thereof. These may be used alone or in combination.

Among the above polyfunctional monomers, 1,6-hexanediol di(meth)acrylate, 1,4-butanediol diacrylate, and trimethylolpropane tri(meth)acrylate are preferred. By using these polyfunctional monomers, the viscosity of the ink can be kept low and the curability of the coating film can be improved.

Further, the glass transition temperature Tg of the second polyfunctional monomer is preferably 40°C or more and 100°C or less, more preferably 40°C or more and 80°C or less. Thereby, the hardness and curability of the coating film can be increased.

Among the first polyfunctional monomer and the second polyfunctional monomer, a combination of tricyclodecane dimethanol diacrylate and 1,6-hexanediol di(meth)acrylate is preferred. Thereby, the viscosity of the ink can be lowered, and the hardness and curability of the coating film can be increased.

<1-2-3. (Meth)acrylated amine compound>
By containing the (meth)acrylated amine compound in the ink composition of the present invention, the curability of the ink composition is improved, and the tackiness of the coating film and the adhesion to the substrate are improved. Furthermore, sufficient curability can be imparted even when the amount of ink composition ejected during printing is increased or when the amount of irradiation light during curing is small.

The (meth)acrylated amine compound is a compound having one or more amino groups and one or more (meth)acryloyl groups. The (meth)acryloyl group is polymerized together with the monofunctional monomer or the polyfunctional monomer. As the (meth)acrylated amine compound, a (meth)acrylated amine compound obtained by reacting a polyfunctional (meth)acrylate and an amine compound is preferable. Moreover, it is more preferable to contain a (meth)acrylated amine compound having two ethylenic double bonds in one molecule and two amino groups in one molecule.

Specific examples of difunctional (meth)acrylates include 1,6-hexanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and 2,4-dimethyl -1,5-pentanediol di(meth)acrylate, butylethylpropanediol (meth)acrylate, ethoxylated cyclohexane methanol di(meth)acrylate, polyethylene glycol di(meth)acrylate, oligoethylene glycol di(meth)acrylate, Ethylene glycol di(meth)acrylate, 2-ethyl-2-butyl-butanediol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, EO-modified bisphenol A di(meth)acrylate, bisphenol F polyethoxy di( meth)acrylate, polypropylene glycol di(meth)acrylate, oligopropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 2-ethyl-2-butylpropanediol di(meth)acrylate, 1, Examples include 9-nonane di(meth)acrylate, propoxylated ethoxylated bisphenol A di(meth)acrylate, tricyclodecane di(meth)acrylate, and the like. Among them, 1,6-hexane di(meth)acrylate is preferred.

Specific examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, alkylene oxide-modified tri(meth)acrylate of trimethylolpropane, and pentaerythritol tri(meth)acrylate. , dipentaerythritol tri(meth)acrylate, trimethylolpropane tri((meth)acryloyloxypropyl) ether, isocyanuric acid alkylene oxide modified tri(meth)acrylate, dipentaerythritol propionate tri(meth)acrylate, tri((meth)acrylate ) acryloyloxyethyl) isocyanurate, hydroxypivalaldehyde-modified dimethylolpropane tri(meth)acrylate, sorbitol tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, ethoxylated glycerin triacrylate, etc. can.

Specific examples of tetrafunctional (meth)acrylates include pentaerythritol tetra(meth)acrylate, sorbitol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol propionate tetra(meth)acrylate, and ethoxylated penta(meth)acrylate. Examples include erythritol tetra(meth)acrylate.

Specific examples of pentafunctional (meth)acrylates include sorbitol penta(meth)acrylate and dipentaerythritol penta(meth)acrylate.

Specific examples of hexafunctional (meth)acrylates include dipentaerythritol hexa(meth)acrylate, sorbitol hexa(meth)acrylate, alkylene oxide-modified hexa(meth)acrylate of phosphazene, and captolactone-modified dipentaerythritol hexa(meth)acrylate. etc. can be mentioned.

Examples of amine compounds include, but are not limited to, benzylamine, phenethylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, n-pentylamine, isopentylamine, n-hexylamine. , cyclohexylamine, n-heptylamine, n-octylamine, 2-ethylhexylamine, n-nonylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, n-octadecylamine, 2 - Monofunctional amine compounds such as aminoethanol and 3-amino-1-propanol, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,6-hexamethylenediamine, 1,8-octamethylenediamine, 1,12-dodeca Methylenediamine, o-phenylenediamine, p-phenylenediamine, m-phenylenediamine, o-xylylenediamine, p-xylylenediamine, m-xylylenediamine, menthanediamine, bis(4-amino-3-methylcyclohexyldiamine) Examples include polyfunctional amine compounds such as methane, isophorone diamine, 1,3-diaminocyclohexane, ethanol diamine, and spiroacetal diamine.Also, high molecular weight types such as polyethyleneimine, polyvinylamine, and polyallylamine can be mentioned. Also included are polyfunctional amine compounds.

Commercially available (meth)acrylated amine compounds include, for example, "CN371" (trade name) manufactured by Sartomer, "EBECRYL 7100" and "EBECRYL81" (trade name) manufactured by Cytec, "GC1100Z" manufactured by Qualipoly Chemical Corporation, Examples include "GC1000W" (product name). The (meth)acrylated amine compounds may be used alone or in combination of two or more.

Among these, it has two ethylenic double bonds in one molecule and two amino groups in one molecule, which is obtained by reacting a bifunctional (meth)acrylate with an amine compound ( A meth)acrylated amine compound is preferred, and for example, a compound obtained by reacting 1,6-hexane di(meth)acrylate with an amine compound is preferably used.

Commercially available products include CN371 (manufactured by Sartomer), EBECRYL 7100 (manufactured by Daicel Allnex), and GC1100Z (manufactured by Qualipoly Chemical Corporation). The (meth)acrylated amine compounds may be used alone or in combination of two or more.

The glass transition temperature Tg of the (meth)acrylated amine compound is preferably -50°C or more and 0°C or less, more preferably -30°C or more and 0°C or less from the viewpoint of curability and adhesion.

The acrylic equivalent of the (meth)acrylated amine compound is preferably larger than 150 from the viewpoint of curability and adhesion, and more preferably 200 or more and 700 or less from the viewpoint of dischargeability.

<1-3. About the content of each polymerizable compound>
The content of the polymerizable compound in the ink composition is preferably 70% by mass or more and 90% by mass or less, more preferably 78% by mass or more and 88% by mass or less, based on the entire ink composition. If the content of the polymerizable compound is within the above range, an ink having high curability and adhesiveness can be obtained while maintaining low viscosity.

Further, the content of the monofunctional monomer is preferably 50% by mass or less and 30% by mass or more, and more preferably 49% by mass or less and 35% by mass or more, based on the entire ink composition. If the content of the monofunctional monomer is 50% by mass or less, a highly reactive polyfunctional monomer can be contained accordingly, and curability and adhesion can be improved while achieving low viscosity.

The content of the first polyfunctional monomer is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and 11% by mass or more and 18% by mass or less, based on the entire ink composition. It is more preferably less than % by mass. By controlling the content of the first polyfunctional monomer as described above, excellent curability and coating film strength can be imparted.

The content of the second polyfunctional monomer is preferably 15% by mass or more and 30% by mass or less, more preferably 17% by mass or more and 28% by mass or less, based on the entire ink composition. By setting the content of the second polyfunctional monomer to the above-described content, the curing speed of the coating film can be improved, and excellent curability and coating strength can be imparted.

Further, the proportion of the polyfunctional monomer in the polymerizable compound is preferably 30% or more and 62% or less, more preferably 40% or more and 60% or less, based on the entire polymerizable compound.

The proportion of the first polyfunctional monomer in the polymerizable compound is preferably 1% or more and 25% or less based on the total polymerizable compound. Furthermore, the proportion of the second polyfunctional monomer in the polymerizable compound is preferably 20% or more and 40% or less.

The ratio of the monofunctional monomer to the polyfunctional monomer in the polymerizable compound is the mass ratio of the content of the monofunctional monomer to the content of the polyfunctional monomer (monofunctional monomer/polyfunctional monomer) of 0.70 to 3. 00 is preferred, and 0.80 to 2.50 is more preferred.

The ratio of the first polyfunctional monomer having an acrylic equivalent of more than 150 and the second polyfunctional monomer having an acrylic equivalent of 150 or less in the polyfunctional monomer is determined based on the content of the first polyfunctional monomer and the second polyfunctional monomer. The mass ratio to the monomer content (second polyfunctional monomer/first polyfunctional monomer) is preferably 0.10 to 20.00, more preferably 1.00 to 19.00.

The content of the (meth)acrylated amine compound is 0.1 to 15% by weight, preferably 2 to 12% by weight based on the entire ink composition. If the content of the (meth)acrylated amine compound is less than 0.1% by mass of the entire ink composition, the curability of the ink composition will be insufficient, and if it exceeds 15% by mass, the ink viscosity will be reduced. I can't do anything.

The ratio of the content of the (meth)acrylated amine compound to the total amount of the first polyfunctional monomer and the second polyfunctional monomer is 1.0:1.1 to 1.0:15.0. The ratio is preferably 1.0:1.5 to 1:13.0, more preferably 1.0:2.8 to 1.0:13.0. Within the above range, the curability of the ink composition improves.

As described above, the polymerizable compound includes a monofunctional monomer, a first polyfunctional monomer with an acrylic equivalent of more than 150, a second polyfunctional monomer with an acrylic equivalent of 150 or less, and a (meth)acrylated amine compound. Accordingly, it is possible to provide an energy ray curable inkjet ink that does not substantially contain a solvent and has low viscosity and excellent curability. Furthermore, superior adhesion and coating strength can be imparted to the coating film.

<2. Photopolymerization initiator>
It contains at least one of an alkylphenone compound and a thioxanthone compound as a photopolymerization initiator. Thereby, polymerization of the ink composition can be started by energy irradiation.

Examples of alkylphenone compounds include α-aminoalkylphenone compounds and benzylmethyl ketal compounds, and specifically, 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1, 2-methyl-1-[4-(methoxythio)-phenyl]-2-morpholinopropan-2-one, 2,2- Examples include dimethoxy-1,2-diphenylethan-1-one. These may be used alone or in combination. Examples of commercially available alkylphenone compounds include Irgacure 369, Irgacure 907, and Irgacure 651 manufactured by Ciba.

Examples of thioxanthone compounds include thioxanthone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, and 2,4-diethyl. Examples include thioxanthone, 2,4-dichlorothioxanthone, and 1-chloro-4-propoxythioxanthone. These may be used alone or in combination. Examples of commercially available thioxanthone compounds include KAYACURE DETX-S manufactured by Nippon Kayaku Co., Ltd. and Chivacure ITX manufactured by Double Bond Chemical Company.

The content of the photopolymerization initiator in the ink composition is preferably 8% by mass or more and 15% by mass or less, more preferably 10% by mass or more and 13% by mass or less, based on the entire composition.

In addition to the above, the ink composition also contains acylphosphine oxide compounds, arylalkyl ketones, oxime ketones, acylphosphine oxides, acyl phosphonates, S-phenyl thiobenzoate, titanocene, aromatic ketones, benzyl, quinone derivatives, and ketocoumarins. It may further contain a conventionally known photopolymerization initiator such as.

Specific examples of these photopolymerization initiators include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and 1-hydroxy -Cyclohexyl-phenyl-ketone 1,2-octanedione-[4-(phenylthio)-2-(o-benzoyloxime)], bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, 2,4,6-trimethylbenzoyl-phosphine oxide, and the like.

Examples of commercially available acylphosphine oxide compounds include IRGACURE TPO manufactured by BASF and Omnirad TPO manufactured by IGM Resins.

<3. Coloring agent>
As the coloring material, various conventionally known dyes may be used, but from the viewpoint of weather resistance, it is preferable to use either or both of inorganic pigments and organic pigments.

Specifically, the inorganic pigments include titanium oxide, zinc white, zinc oxide, tripone, iron oxide, aluminum oxide, silicon dioxide, kaolinite, montmorillonite, talc, barium sulfate, calcium carbonate, silica, alumina, cadmium red, Red iron, molybdenum red, chrome vermilion, molybdate orange, chrome yellow, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, pyridian, cobalt green, titanium cobalt green, cobalt chrome green, ultramarine blue, ultramarine blue , dark blue, cobalt blue, cerulean blue, manganese violet, cobalt violet, mica, etc.

Examples of organic pigments include azo-based, azomethine-based, polyazo-based, phthalocyanine-based, quinacridone-based, anthraquinone-based, indigo-based, thioindigo-based, quinophthalone-based, benzimidazolone-based, and isoindoline-based organic pigments. Can be mentioned. Furthermore, hollow particles of crosslinked acrylic resin may also be used as the organic pigment.

Specific examples of pigments having a white color include Pigment White 6, 18, and 21, basic lead carbonate (2PbCO3Pb(OH)2, so-called silver white), zinc oxide (ZnO, so-called zinc white), ), titanium oxide (TiO2, so-called titanium white), strontium titanate (SrTiO3, so-called titanium strontium white), and the like. Among these, titanium oxide has a low specific gravity, a high refractive index, and is chemically and physically stable compared to other white pigments, so it has great hiding power and coloring power as a pigment, and it is also resistant to acids and It also has excellent durability against alkali and other environments. Therefore, it is more preferable to use titanium oxide as the white pigment.

The content of the colorant in the ink composition is preferably 1 to 15% by mass, more preferably 1 to 10% by mass, and even more preferably 1 to 9% by mass, based on the entire ink composition.

When a pigment is used as the coloring material, a pigment derivative or a pigment dispersant may be further used to improve the dispersibility of the pigment.

Specific examples of the pigment derivative include pigment derivatives having a dialkylaminoalkyl group and pigment derivatives having a dialkylaminoalkylsulfonic acid amide group.

Specific examples of the pigment dispersant include ionic or nonionic surfactants, anionic, cationic, or nonionic polymer compounds, and the like. Among these, polymer compounds containing a cationic group or anionic group are preferred from the viewpoint of dispersion stability. Pigment dispersants available on the market include SOLSPERSE manufactured by Lubrizol, DISPERBYK manufactured by Byk Chemie, and EFKA manufactured by Efka Additives.

The content of the pigment derivative and the pigment dispersant in the ink composition is preferably 0.05 to 5% by mass, respectively, based on the total ink composition.

<4. Additive>
<4-1. Surface conditioning agent>
A silicone compound having a polydimethylsiloxane structure can be contained as a surface conditioner. If the silicone compound is used as a surface conditioner together with the polymerizable compound, the physical properties of the ink, such as the surface tension, can be adjusted to a range suitable for inkjet recording.

Specific examples of the silicone compounds include BYK-UV3500, BYK-UV3510, BYK-UV3570 manufactured by BYK Chemie, Tego-Rad2100, Tego-Rad2200N, Tego-Rad2250, Tego-Rad2300, and Tego-Rad2200N manufactured by Degussa. Rad2500, Tego-Rad2600, Tego-Rad2700, and UCR-L72 and UCR-L93 manufactured by Kyoeisha Chemical Co., Ltd. are preferred. Since these contain a polydimethylsiloxane structure having an ethylenic double bond in the molecule, it is possible to further improve adhesion.

The content of the silicone compound in the ink composition is preferably 0.005% by mass or more and 1% by mass or less based on the entire ink composition.

<4-2. Anti-gelling agent>
It is preferable to further contain a hindered amine compound having a 2,2,6,6-tetramethylpiperidinyl group as an antigelation agent. If the above-mentioned hindered amine compound is used as a gelling inhibitor together with a highly reactive polymerizable compound and a photopolymerization initiator, an ink with excellent storage stability can be obtained without reducing the reactivity of the ink. . Specifically, the above-mentioned anti-gelling agent includes bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)sebacate, 2,2,6,6-tetramethylpiperidin-4-yl and decanedioic acid bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl) ester. These may be used alone or in combination. Examples of anti-gelling agents available on the market include IRGASTAB UV-10 and TINUVIN 123 manufactured by Ciba, and HYDROXY-TEMPO manufactured by Evonik Degussa Japan.

The content of the antigelation agent in the ink composition is preferably 0.1% by mass or more and 4% by mass or less based on the entire ink composition. When the content of the antigelation agent is less than 0.1% by mass, radicals generated during storage cannot be sufficiently captured, and storage stability tends to decrease. On the other hand, when the content of the antigelation agent is more than 4% by mass, the effect of trapping radicals is saturated and the polymerization reaction during energy ray irradiation tends to be inhibited.

Other hindered amine compounds, phenolic antioxidants, phosphorus antioxidants, hydroquinone monoalkyl ethers, and the like may be further included as gelling inhibitors. Specifically, such anti-gelling agents include hydroquinone monomethyl ether, hydroquinone, t-butylcatechol, pyrogallol, TINUVIN 111 FDL, TINUVIN 144, TINUVIN 292, TINUVIN XP40, TINUVIN XP60, TINUVIN 400 manufactured by Ciba Corporation. Examples include.

<4-3. Other additives>
The ink composition of this embodiment may further include a surfactant, a leveling agent, an antifoaming agent, an antioxidant, a pH adjuster, a charge imparting agent, a bactericide, a preservative, a deodorant, and a charge adjuster. , a humectant, an anti-scaly agent, a perfume, and other known general additives may be added as optional ingredients.

<4-4. Ink viscosity>
According to this embodiment, a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of more than 150 and having two or more ethylenic double bonds in one molecule, and an acrylic equivalent of 150 or less and , contains a specific amount of a second polyfunctional monomer having two or more ethylenic double bonds in one molecule, and furthermore, the polymerizable compound is composed of a (meth)acrylated amine compound, so at 25°C, 15 mPa - An ink composition with a low viscosity of s or less can be prepared. From the viewpoint of ejection properties, the viscosity of the ink composition at 25° C. is preferably 15 mPa·s or less, more preferably 6 to 14 mPa·s, and even more preferably 8 to 13 mPa·s.

<5. About the adjustment method>
Conventionally known preparation methods can be used to prepare the ink, but when a pigment is used as a coloring material, the following preparation method is preferred.

First, a liquid mixture is prepared by premixing a coloring material, a part of a polymerizable compound, and, if necessary, a pigment dispersant, and this liquid mixture is dispersed using a dispersion machine to prepare a primary dispersion. Specific examples of the dispersing machine include a disper; a container-driven media mill such as a ball mill, a centrifugal mill, and a planetary ball mill; a high-speed rotation mill such as a sand mill; and a media stirring mill such as a stirring tank type mill.

Next, the remaining polymerizable compound, photopolymerization initiator, surface conditioner, and other additives such as anti-gelling agent, if necessary, are added to the primary dispersion, and the mixture is uniformly mixed using a stirrer. Mix. Specific examples of the stirrer include a three-one motor, a magnetic stirrer, a disperser, and a homogenizer. Alternatively, the ink composition may be mixed using a mixer such as a line mixer. Further, the ink composition may be mixed using a dispersing machine such as a bead mill or a high-pressure jet mill for the purpose of making particles in the ink composition finer.

When a pigment is used as a coloring material, the dispersed average particle diameter of pigment particles in the ink composition is preferably 20 to 250 nm, more preferably 50 to 230 nm.

In addition, the ink composition of this embodiment does not need to be diluted with a diluting solvent, has a low viscosity even without heating, and has good pigment dispersibility when the colorant is a pigment, and has good storage stability. It has good dispersion stability without causing problems such as viscosity increase or pigment sedimentation during use. Therefore, in the inkjet recording method, stable ejection can be obtained at room temperature without heating the ink.

<6. About others＞
Inkjet recording methods include, but are not limited to, a charge control method that uses electrostatic attraction to eject ink, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezo element, and an electric charge control method that uses electrostatic attraction to eject ink. Examples include acoustic inkjet recording, which uses radiation pressure to convert a signal into an acoustic beam and irradiates the ink, and thermal inkjet recording, which heats ink to form bubbles and uses the resulting pressure. The inkjet recording methods mentioned above include a method in which a large number of low-density inks called photo ink are ejected in a minute volume, a method in which image quality is improved by using multiple inks of substantially the same hue but different concentrations, and a method in which colorless and transparent inks are used to improve image quality. This includes methods that use ink.

In this embodiment, examples of the irradiation means include ultraviolet irradiation means such as a mercury lamp, a metal halide lamp, and an LED lamp. With the ink composition of this embodiment, a low energy of 200 mJ/cm 2 or less can be used as the cumulative amount of ultraviolet light.

It is preferable that the ink composition is irradiated with the energy rays 1 to 1,000 ms after the ink composition is ejected onto the recording medium. If the elapsed time is less than 1 ms, the distance between the head and the light source becomes short, and the head may be directly irradiated with energy rays, leading to an unexpected situation. On the other hand, if the elapsed time exceeds 1,000 ms, ink bleeding tends to occur and image quality deteriorates when other colors such as cyan, magenta, yellow, etc. are used in addition to the ink composition of the present invention. .

Hereinafter, the present embodiment will be described in more detail based on Examples, but the present embodiment is not limited to these Examples. In addition, "parts" below means "parts by mass."

The components of the ink compositions used in each Example and Comparative Example are shown in Table 1 below.

[Preparation of ink composition]
Examples 1 to 13 and Comparative Examples 1 to 8 were prepared according to the amounts of ink compositions shown in Tables 2 and 3. Note that the display in Tables 2 and 3 corresponds to the description in Table 1.

Into a 100 cc plastic bottle, weigh out the colorant, pigment dispersant, and monofunctional monomer in the amounts shown in Table 2, add 100 parts of zirconia beads, and apply paint conditioner (manufactured by Toyo Seiki Co., Ltd.) for 2 hours. A primary dispersion was obtained by dispersing. Next, the remaining components were added to the obtained primary dispersion in the amounts shown in Table 2, and the mixture was stirred for 30 minutes using a magnetic stirrer. After stirring, the mixture was suction-filtered using a glass filter (manufactured by Kiriyama Seisakusho) to prepare an ink composition.

[evaluation]
The viscosity of each of the ink compositions of Examples and Comparative Examples prepared as described above was measured. Furthermore, the adhesion, coating strength, and curability of coating films (printed films) recorded on recording media using each of the ink compositions of Examples and Comparative Examples were evaluated. The evaluation results for each example and comparative example shown in Table 2 are shown in Tables 4 and 5. In addition, each item was evaluated using the method shown below.

〔viscosity〕
The viscosity was measured using an R100 type viscometer (manufactured by Toki Sangyo Co., Ltd.) under conditions of 25° C. and a cone rotation speed of 20 rpm.
〇: 15 mPa・s or less ×: 16 mPa・s or more

[Adhesion]
The ink composition was printed on each film recording medium made of polyvinyl chloride (PVC) to form a printed film with a thickness of 2 μm. This printed film was cured by irradiating ultraviolet rays using a metal halide lamp as an irradiation means so that the total amount of irradiation light was 200 mJ/cm 2 .

The thus cured printed film was subjected to a checkerboard test (1 mm square, 100 pieces) to check the peeling state with Cellotape (registered trademark) according to JIS-K-5400. The number of peeled pieces out of 100 pieces was examined and evaluated based on the following criteria.
〇: The number of peelings is 10 or less in the grid test ×: The number of peelings is 21 or more in the grid test

[Coating film strength]
The ink composition was printed on a recording medium of an acrylic plate to form a printed film with a thickness of 2 μm. This printed film was cured by irradiating ultraviolet light using a metal halide lamp as an irradiation means such that the total amount of irradiation light was 200 mJ/cm 2 .

The pencil hardness of the printed film thus cured was measured and evaluated according to the following criteria. The pencil hardness was measured using a surface property tester "HEIDON-14DR" manufactured by Shinto Kagaku Co., Ltd. based on the method for measuring pencil hardness stipulated in Japanese Industrial Standards (JIS) K5400.
〇: Pencil hardness 4H or higher
×: Pencil hardness less than 4H

[Curability]
The ink composition was printed on a film recording medium made of polyethylene terephthalate (PET) to form printed films with thicknesses of 2 μm and 20 μm, respectively. This printed film was cured by irradiating ultraviolet light using a metal halide lamp as an irradiation means at a total irradiation amount of 200 mJ/cm 2 and 100 mJ/cm 2 , respectively. The conditions for forming the printing film are shown below.
Curability 1: Thickness 2 μm, total irradiation light amount 200 mJ/cm2
Curability 2: Thickness 2 μm, total irradiation light amount 100 mJ/cm2
Curability 3: Thickness 20 μm, total irradiation light amount 200 mJ/cm2

The printed film thus cured was touched with fingers and nails, and the presence or absence of ink adhesion to the fingers and nails was visually examined and evaluated according to the following criteria.
〇: Ink does not stick to fingers and nails, and the printing film surface does not get damaged even if rubbed with nails. ×: Ink sticks to fingers.

As shown in Table 4 above, the polymerizable compounds include a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of more than 150, and having two or more ethylenic double bonds in one molecule. , which has an acrylic equivalent of 150 or less and contains a specific amount of a second polyfunctional monomer having two or more ethylenic double bonds in one molecule, and further contains a (meth)acrylated amine compound. The ink composition of the present invention has a viscosity of 15 mPa·s or less at 25°C.

As shown in Examples 1 to 13 in Tables 2 and 4, the present invention provides an energy source with low viscosity and excellent curing properties even when the integrated light amount is reduced or the discharge amount is increased. A line-curable white inkjet ink composition can be obtained. Further, since the ink composition of the present invention has a low viscosity, it has excellent ejection stability and can provide high-definition printed matter.

On the other hand, Comparative Examples 1 to 7 in Tables 3 and 5 had poor results in any of the viscosity, adhesion, coating strength, and curability. Comparative Example 8 containing more than 15% by mass of the (meth)acrylated amine compound could not achieve low viscosity.

Claims (5)

A white inkjet ink composition comprising a polymerizable compound, a white pigment, and a photopolymerization initiator,
The polymerizable compound is
a monofunctional monomer,
a first polyfunctional monomer having an acrylic equivalent of more than 150 and less than or equal to 254 , and having two or more ethylenic double bonds in one molecule;
a second polyfunctional monomer having an acrylic equivalent of 150 or less and having two or more ethylenic double bonds in one molecule;
Furthermore, it contains a (meth)acrylated amine compound,
The content of the first polyfunctional monomer is 1 to 20% by mass based on the entire inkjet ink composition,
The content of the second polyfunctional monomer is 15 to 30% by mass based on the entire inkjet ink composition,
The content of the (meth)acrylated amine compound is 0.1 to 15% by mass based on the entire inkjet ink composition,
The ratio of the content of the (meth)acrylated amine compound to the total amount of the first polyfunctional monomer and the second polyfunctional monomer is 1.0:1.1 to 1.0:15.0. An inkjet ink composition. The (meth)acrylated amine compound has two ethylenic double bonds in one molecule,
The inkjet ink composition according to claim 1 , which is a (meth)acrylated amine compound having two amino groups in one molecule. The inkjet ink composition according to claim 1, wherein the content of the monofunctional monomer is 50% by mass or less based on the entire inkjet ink composition. The inkjet ink composition according to claim 1, wherein the (meth)acrylated amine compound has an acrylic equivalent weight of greater than 150. The inkjet ink composition according to claim 1 , wherein the inkjet ink composition has a viscosity at 25° C. of 15 mPa·s or less.