JP6748449B2 - Inkjet ink - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inkjet ink having photocurability and capable of printing a picture, a character or the like having excellent stretchability after photocuring.

A photocurable inkjet ink containing a radically polymerizable component and a photoradical polymerization initiator is used to print a pattern, characters, etc. by an inkjet printing method, and then the radically polymerizable component is irradiated with light such as ultraviolet rays to irradiate the radically polymerizable component. A technique for improving the resistance of the above-mentioned patterns, characters, etc. by curing reaction (polymerization and cross-linking) is widely used.
Further, in recent years, using the above-mentioned photocurable inkjet ink, for example, a pattern or characters are printed on the surface of a film that can be thermoformed by a vacuum forming method or the like to be photocured, and then the film is formed into a predetermined three-dimensional shape. By heat-forming (decorative forming) or printing on the surface of a flexible base material that is easy to bend and stretch and photo-curing it, it is possible to follow the bending and stretching of the base material such as patterns and letters. The technology to change to is being put to practical use.

Inkjet inks used for the above-mentioned applications are required to have excellent stretchability of patterns and characters after photocuring, and to sufficiently follow the thermoforming of films and the bending and stretching of base materials without causing cracks or the like. To be
Therefore, various compositions of photocurable inkjet inks have been studied in order to improve the stretchability of patterns and characters after photocuring.

For example, in Patent Document 1, it has been studied to improve the stretchability of patterns and letters after photocuring by setting the proportion of the monofunctional monomer in the radically polymerizable component to 80 to 99.9% by weight.
For the same purpose, for example, in Patent Document 2, phenoxyethyl acrylate as a radically polymerizable component and a specific monofunctional monomer are used in combination, and in Patent Document 3, a specific monofunctional monomer and a bifunctional monomer are prescribed. It is proposed to use them together in proportion.

However, all of the above-described conventional inkjet inks that take stretchability into consideration, particularly when printing a gradation such as a so-called low drop volume in which the volume of ink droplets ejected from the tip of the nozzle of an inkjet printer is reduced, There is a problem that ink dust, that is, ink droplets are not ejected straight from the tip of the nozzle in the density portion or the like, and are scattered vertically and horizontally to cause a defect that stains a pattern or a character.

Although the photocurable inkjet ink turns yellow once it is photocured, it usually becomes gradually lighter in yellow and returns to the original color tone. Therefore, there is also a problem that a defect in which the original correct color tone cannot be displayed is likely to occur, for example, white exhibits yellow and blue exhibits green.

JP, 2007-131755, A WO2007/097049A1 JP2012-188613A

The object of the present invention is not only excellent in photocurability and stretchability of patterns and characters after photocuring, but also good straightness of ink droplets, especially when printing with a low drop volume, causing defective dust. Another object of the present invention is to provide an inkjet ink that is difficult to be printed and that is easily yellowed after photocuring and that can display an original correct color tone.

The present invention comprises a radically polymerizable component and a photoradical polymerization initiator, wherein the radically polymerizable component contains a monofunctional monomer in a proportion of 70% by mass or more of the total amount of the radically polymerizable component, and Monofunctional monomers are
Formula (1):

And ethoxydiethylene glycol acrylate represented by the formula (2):

The ratio of 4-acryloylmorpholine represented by the formula (1)/(2) is 1.0 or more and 2.3 or less, and the total of both is 75 mass of the total amount of the monofunctional monomer. seen containing% or more of the total, yet the radical polymerizable component further equation (3):

[In the formula, R represents a hydrogen atom or a methyl group. ]
The mass ratio of the photoradical polymerization initiator (total amount of radically polymerizable components)/(photoradical polymerization initiator) containing 2-(2-vinyloxyethoxy)ethyl (meth)acrylate represented by The inkjet ink is 17 or more.

According to the present invention, not only is it excellent in photocurability and the stretchability of patterns and characters after photocuring, but also the straightness of ink droplets is good, especially when printing with a low drop volume, and defects of dust occur. It is difficult to provide an inkjet ink that is easy to remove yellowing after photocuring and can display an original correct color tone.

The inkjet ink of the present invention contains a radical polymerizable component and a photoradical polymerization initiator as described above, and the radical polymerizable component is a monofunctional monomer at a ratio of 70% by mass or more based on the total amount of the radical polymerizable component. And the monofunctional monomer contains ethoxydiethylene glycol acrylate represented by the formula (1) (hereinafter sometimes abbreviated as “ EC-A ”) and 4 represented by the formula (2). -Acryloylmorpholine (hereinafter sometimes abbreviated as "ACMO") in a mass ratio (1)/(2) of 1.0 or more and 2.3 or less, and both of them in total. seen containing a proportion of more than 75 wt% of the total amount of monofunctional monomers, yet the radical polymerizable component is further represented by formula (3) 2- (2-vinyloxy ethoxy) include ethyl (meth) acrylate The mass ratio of the photo-radical polymerization initiator (total amount of radical-polymerizable components)/(photo-radical polymerization initiator) is 17 or more .

According to the study by the inventor, the conventional stretchable inkjet ink is apt to cause dust defects especially when the LED (light emitting diode) having a narrow wavelength range is used as a light source for photocuring. The main cause is that a large amount of a photopolymerization initiator is contained in order to impart excellent photocurability.
That is, when the amount of the photopolymerization initiator is large, such a large amount of the photopolymerization initiator, although it appears to be dissolved in the monomer, reduces the cohesive force of the inkjet ink, and thus forms an ink droplet when ejected from the nozzle. The inkjet ink is likely to scatter, and the straightness of the ink droplet is likely to deteriorate.

Further, it is mainly due to the amine-based monomer used for ensuring good photocurability that yellowing is difficult to be eliminated in the conventional inkjet ink.
On the other hand, according to the present invention, as described above, 70% by mass or more of the total amount of the radical-polymerizable component is a monofunctional monomer, whereby the stretchability of a pattern, a character or the like after photocuring can be secured.
Further, as the monofunctional monomer, EC-A (1), which originally has a low affinity for the inner surface of the nozzle or the like, can be selected and used to ensure straightness of the ink droplets, and is good among monofunctional monomers. High photocurability is achieved by using ACMO of (2), which has excellent photocurability and good curability even for light with a narrow wavelength range from, for example, LEDs, and thereby photopolymerization. By reducing the amount of the initiator, the straightness of the ink droplet can be further improved.

Further more than 75 wt% of the total amount of monofunctional monomers, EC-A, and yellowing tends to leak after photocuring of some are in an amine to yellowing tends to leak (1) after photocuring not amine (2) As the ACMO, the yellowing can be easily removed after photocuring.
Moreover, 2-(2-vinyloxyethoxy)ethyl(meth)acrylate represented by the formula (3), which is used in combination with (1) EC-A and (2) ACMO, selectively (2) Since it has excellent compatibility with ACMO and does not aggregate, it has an ethylene oxide moiety in its molecule, has a low affinity for the inner surface of the nozzle, etc., and has good photocurability, and is used in combination with ACMO. This makes it possible to secure a higher photocurability and further reduce the amount of the photopolymerization initiator, and further improve the straightness of the ink droplet.
Therefore, according to the present invention, not only is it excellent in photocurability and the stretchability of patterns and characters after photocuring, but also the straightness of ink droplets is good even when printing with a low drop volume, and it is possible to prevent dust defects. It is possible to provide an ink-jet ink that is less likely to occur and that is easy to lose its yellowing after photocuring and can display an original correct color tone.

In the present invention, the mass ratio (1)/(2) of EC-A (1) and ACMO (2) is limited to 1.0 or more and 2.3 or less for the following reason.
That is, when the ratio of EC-A of (1) is less than this range, the effect of improving the straightness of the ink droplet cannot be obtained by selecting and using the EC-A .
On the other hand, when the ratio of the ACMO of (2) is less than the above range, the ACMO is selected and used to impart good photocurability to the inkjet ink, thereby reducing the amount of the photopolymerization initiator. As a result, the effect of improving the straightness of the ink droplet cannot be sufficiently obtained.

Therefore, in any case, a defect of dust is likely to occur.
On the other hand, by setting the mass ratio (1)/(2) of EC-A of (1) to ACMO of (2) within the above range, good photocurability of the inkjet ink is secured as described above. However, it is possible to improve the straightness of the ink droplets and prevent the occurrence of dust defects, especially when printing with a low drop volume.

In consideration of further improving such effects, the mass ratio (1)/(2) is 2 . It is preferably 0 or less.
Further, in the present invention, the total blending ratio of the EC-A of (1) and the ACMO of (2) is limited to 75% by mass or more of the total amount of the monofunctional monomer, because the total blending ratio is within this range. This is because if the amount is less than the above, the effect obtained by using the above-mentioned two kinds of monomers together cannot be sufficiently obtained.

In addition, when the total mixing ratio of the two types of monomers (1) and (2) is less than the above range and an amine-based monomer other than ACMO is selected as another monofunctional monomer to be used in combination, after photocuring This is also because there is a risk that the yellowing of the powder will be difficult to come off.
On the other hand, by setting the total mixing ratio of the two types of monomers of (1) and (2) above, it is possible to secure good photocurability of the inkjet ink as described above and It is possible to improve the straightness of the ink droplets while making it easy to get rid of the yellowing, and it is possible to prevent the occurrence of dust defects particularly when printing with a low drop volume.

The upper limit of the total mixing ratio of the two types of monomers (1) and (2) is not particularly limited, and may be 100% by mass, that is, the total amount of monofunctional monomers may be two types of monomers.

However, in consideration of adjusting the viscosity of the inkjet ink, further improving the stretchability of the pattern or letters after photocuring, and imparting good water resistance to the pattern or letters after photocuring, etc. Other monofunctional monomers capable of imparting these characteristics to the above-mentioned patterns and characters may be used in combination.
Further, in the present invention, the mixing ratio of the monofunctional monomer is limited to 70% by mass or more of the total amount of the radical-polymerizable components, as described above, to ensure the stretchability of the pattern, characters, etc. after photocuring. I collect.

That is, when the mixing ratio of the monofunctional monomer is less than the above range, the pattern and characters after photocuring become brittle and hard, and the stretchability decreases, so that the film sufficiently follows the thermoforming of the film and the bending and stretching of the base material. If it is not possible, cracks will occur easily.
On the other hand, by setting the mixing ratio of the monofunctional monomer within the above range, it is possible to secure the stretchability of the pattern, characters, etc. after photocuring.

In consideration of further improving such effects, the blending ratio of the monofunctional monomer is preferably 75% by mass or more of the total amount of the radical-polymerizable components.
Although the upper limit of the mixing ratio of the monofunctional monomer is not particularly limited, it improves the fixability of the picture and characters after photocuring, and better follows the thermoforming of the film and the bending and stretching of the base material so that cracks etc. In order to prevent the occurrence of the above, it is preferable to use a polyfunctional monomer having two or more functional groups in combination as the radically polymerizable component.

The blending ratio of the monofunctional monomer in the combined use system with the polyfunctional monomer is preferably 92% by mass or less, and particularly 87% by mass or less of the total amount of the radical-polymerizable components.
Note that Patent Document 1 exemplifies EC-A and ACMO described above as specific examples of monofunctional monomers. However, Patent Document 1 does not describe blending only these two types as monofunctional monomers in a predetermined ratio at a ratio of 75% by mass or more of the total amount of monofunctional monomers.

<Radical polymerizable component>
<Monofunctional monomer>
( EC-A : ethoxydiethylene glycol acrylate )
Among the monofunctional monomers, EC-A has the formula (1):

It is represented by .
E C-A, because it has high fluidity low viscosity, can be further improved straightness of ink droplets.
(ACMO: 4-acryloylmorpholine)
Among the monofunctional monomers, ACMO has the formula (2):

It is represented by.
By using the ACMO of (2) in combination with the EC-A of (1), as described above, good photocurability of the inkjet ink is ensured, and photopolymerization is performed while easily passing through yellowing after photocuring. By reducing the amount of the initiator, the straightness of the ink droplets can be improved, and it is possible to prevent the occurrence of dust defects particularly when printing with a low drop volume.

(Other monofunctional monomers)
As described above, it adjusts the viscosity of the inkjet ink, further improves the stretchability of the pattern or letters after photocuring, and imparts good water resistance to the pattern or letters after photocuring. As other monofunctional monomers that may be used together for this purpose, various monofunctional monomers that can be photocured together with the monofunctional monomers (1) and (2) can be used.

Examples of such other monofunctional monomers include those represented by the formula (4) :

A tetrahydrofurfuryl acrylate represented by (hereinafter sometimes abbreviated as “FA-THFA”), and a formula (5) :

At least one kind of isobornyl acrylate represented by (hereinafter sometimes abbreviated as “IBXA”) and the like can be given.
The blending ratio of the other monofunctional monomer can be arbitrarily set basically in the range of 25% by mass or less of the remaining amount of the two types of monomers (1) and (2), that is, the total amount of the monofunctional monomers.
In particular, stretching of patterns and characters after photocuring, which change depending on the light transmittance, reflectivity, shielding property, and the like of colorants such as pigments that are mixed according to the tint of inkjet ink, or the type of colorant. It is preferable to appropriately set the type and blending ratio of the other monofunctional monomer depending on the properties, water resistance and other factors.

Further, since the other monofunctional monomers have different functions depending on their types, it is preferable to use two or more different monofunctional monomers of different types together. When two or more other monofunctional monomers are used in combination, the total blending ratio may be set within the above range.
However, as described above, the total amount of monofunctional monomers may be two types of monomers (1) and (2), and other monofunctional monomers may be omitted.

<Multifunctional monomer>
Upper Symbol capable photocurable with monofunctional monomers, the bifunctional or higher polyfunctional monomer, formula (3):

[In the formula, R represents a hydrogen atom or a methyl group. ]
2-(2-vinyloxyethoxy)ethyl (meth)acrylate represented by is selected and used .
As 2-(2-vinyloxyethoxy)ethyl(meth)acrylate, for example, R in the formula (3) is a hydrogen atom, and the formula (6) :

(. Which may be hereinafter abbreviated as "VEEA") THAT represented by 2- (2-vinyloxy ethoxy) ethyl acrylate, and R is a methyl group in the formula (3), equation (7):

At least one kind of 2-(2-vinyloxyethoxy)ethyl methacrylate represented by (hereinafter sometimes abbreviated as “VEEM”) is included.
The above-mentioned VEEA and VEEM (hereinafter sometimes collectively referred to as “VEEA etc.” ) are selected as monofunctional monomers to be combined and, for example, when used in combination with N-vinylcaprolactam or the like, they aggregate to reduce ink droplet ejection properties and straightness. There is a risk.

However, VEEA and the like selectively have excellent compatibility with (2) ACMO and do not aggregate, so that VEEA itself has an ethylene oxide moiety in the molecule and has a low affinity for the inner surface of the nozzle and the like. In addition to having photocurability and being able to secure higher photocurability and further reduce the amount of photopolymerization initiator when used in combination with ACMO, the straightness of ink droplets can be further improved.

As the polyfunctional monomer, it is necessary to use VEEA or the like in view of the above effects, but it is also possible to use other polyfunctional monomers in combination . Examples of such other polyfunctional monomers include those represented by the formula (8) :

1,10-decanediol diacrylate represented by (hereinafter sometimes abbreviated as "DDA") and the like.
The mixing ratio of the polyfunctional monomer can be arbitrarily set basically in the range of 30% by mass or less, particularly 25% by mass or less of the remaining amount of the monofunctional monomer, that is, the total amount of the radical-polymerizable components.
However, by using a polyfunctional monomer together, the fixability of patterns and characters after photo-curing is improved, and it better follows thermoforming of the film, bending and stretching of the base material, etc. to prevent cracks etc. Considering that the effect is further improved, the compounding ratio of the polyfunctional monomer is preferably 8% by mass or more, and more preferably 12% by mass or more of the total amount of the radically polymerizable components even in the above range.

<Photo-radical polymerization initiator>
As the photo-radical polymerization initiator, various compounds capable of generating radicals upon irradiation with light having an arbitrary wavelength such as ultraviolet rays to photo-curing the radical-polymerizable component can be used.
Examples of such a radical photopolymerization initiator include one or more of the following compounds and the like.

Benzophenone, hydroxybenzophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bisdiethylaminobenzophenone, 4,4'-bisdimethylaminobenzophenone (Michler's ketone), 4-methoxy-4'-dimethylaminobenzophenone Benzophenones such as benzophenone compounds represented by the general formula (1) in JP-A-2008-280427, or salts thereof.

Thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2-isopropylthioxanthone, 2,4-diethylthioxanthone, 4-isopropylthioxanthone, isopropoxychlorothioxanthone, represented by the general formula (2) of JP2008-280427A. Thioxanthone compounds such as thioxanthone compounds or salts thereof.
Anthraquinones such as ethylanthraquinone, benzanthraquinone, aminoanthraquinone and chloroanthraquinone.

Acetophenones such as acetophenone, 2,2-diethoxyacetophenone and 4'-dimethylaminoacetophenone.
2-(o-chlorophenyl)-4,5-diphenylimidazole dimer, 2-(o-chlorophenyl)-4,5-di(m-methoxyphenyl)imidazole dimer, 2-(o-fluorophenyl) -4,5-Diphenylimidazole dimer, 2-(o-methoxyphenyl)-4,5-diphenylimidazole dimer, 2-(p-methoxyphenyl)-4,5-diphenylimidazole dimer, 2 -Di(p-methoxyphenyl)-5-phenylimidazole dimer, 2-(2,4-dimethoxyphenyl)-4,5-diphenylimidazole dimer, 2,4,5-triarylimidazole dimer Imidazoles such as.

Benzyl dimethyl ketal, 2-benzyl-2-dimethylamino-1-(4-morpholinophenylbutan)-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1- On, 2-hydroxy-2-methyl-1-phenyl-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl] 2-Hydroxy-2-methyl-1-propan-1-one, 9,10-phenanthrenequinone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-propyl ether, benzoin isobutyl ether , Benzoin such as benzoin-n-butyl ether.

Acridine derivatives such as 9-phenylacridine and 1,7-bis(9,9'-acridinyl)heptane.
Bisacylphosphine oxide, bisphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl) )-2,4,4-Trimethylpentylphosphine oxide and other phosphine oxides.

2,2-dimethoxy-1,2-diphenylethan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}2-methylpropan-1- On, 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2 -Methylpropan-1-one, methylbenzoyl formate, azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trihalomethyltriazine, benzyl and the like.

In particular, especially equation (9) :

Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide represented by is preferable.
The mixing ratio of the photo radical polymerization initiator is limited to 17 or more , and is 50 or less , in terms of mass ratio (total amount of radical polymerizable component)/(photo radical polymerization initiator) to the total amount of radical polymerizable component. Is preferred.

If the mixing ratio of the photo-radical polymerization initiator is less than this range, good curability cannot be secured especially for light with a narrow wavelength range from LEDs and the like, and the inkjet ink may not be sufficiently photo-cured by light irradiation. ..
On the other hand, when the mixing ratio of the photo-radical polymerization initiator exceeds the above range, excessive photo-radical polymerization initiator inhibits the straightness of the ink droplet as described above, and therefore, particularly when printing with a low drop volume. It is easy to cause dust defects.

Incidentally, the mass ratio in the conventional inkjet inks of Patent Documents 1 to 3 is about 6.4 to 9.6, which is less than the above range, and the blending ratio of the photoradical polymerization initiator is excessive. It is easy to cause dust defects.
On the other hand, by setting the mixing ratio of the photo-radical polymerization initiator in the above range, while maintaining good photocurability by light irradiation, the straightness of the ink droplets is improved, and particularly with a low drop volume. It is possible to prevent the occurrence of dust defects during printing of.

The mixing ratio of the photo-radical polymerization initiator is, for example, in order to make the photo-curability as uniform as possible for each tint of the inkjet ink, depending on the light transmittance, reflectance, shielding property, etc. of the colorant such as a pigment. It is preferable to set it arbitrarily within the range.
For example, although not limited to this, in a system using a pigment as a colorant, the mass ratios are as follows: white: 27 to 45, cyan: 20 to 30, magenta: 27 to 45, yellow: 27 to 45, It is preferable to set the blending ratio of the photoradical polymerization initiator so that black: 17 to 25 is obtained.

《Other ingredients》
The inkjet ink of the present invention may further contain a sensitizer, a radical polymerization inhibitor, a colorant, a surfactant and the like.
<Sensitizer>
Among the above, the sensitizer is activated by irradiation with light, interacts with the photoradical polymerization initiator, and functions to assist the generation of radicals in the photoradical polymerization initiator.

Particularly when an LED is used as a light source for light irradiation, light such as ultraviolet rays from the LED has a narrow wavelength range as described above, so that the sensitivity is improved by expanding the wavelength range in which the inkjet ink has sensitivity, that is, It is preferable to add a sensitizer for sensitization.
Among the photoradical polymerization initiators described above, thioxanthones or salts thereof, particularly 2,4-diethylthioxanthone, are preferably used as the sensitizer.

Other sensitizers include, for example, naphthalene benzoxazolyl derivatives, thiophene benzoxazolyl derivatives, stilbene benzoxazolyl derivatives, coumarin derivatives, styrene biphenyl derivatives, pyrazolone derivatives, stilbene derivatives, benzene and biphenyl styryl derivatives. , Bis(benzazol-2-yl) derivative, carbostyril, naphthalimide, dibenzothiophene-5,5'-dioxide derivative, pyrene derivative, pyridotriazole, ethyl p-dimethylaminobenzoate, p-dimethylaminobenzoic acid Examples include isoamyl, ethanolamine, diethanolamine, triethanolamine and the like.

As the sensitizer, from among the various sensitizers described above, an absorption wavelength range suitable for sensitization is selected according to the wavelength range of the light from the light source and the absorption wavelength range of the photoradical polymerization initiator. Each of these compounds may be used alone or in combination of two or more.
The proportion of the sensitizer is preferably 0.01% by mass or more, particularly preferably 0.3% by mass or more, and particularly 6% by mass or less, particularly preferably 6% by mass, in view of obtaining a good sensitizing effect. It is preferably 4% by mass or less.

<Radical polymerization inhibitor>
The radical polymerization inhibitor causes a radical polymerization reaction of a radical polymerizable component when an inkjet ink is used for a thermal type inkjet printer and is heated to eject an ink droplet, resulting in ejection failure due to paddling. Function to prevent the
Paddling means that when an ink droplet is ejected through a nozzle, the ink jet ink that has separated from the ink droplet and remains on the nozzle side spreads around the nozzle outlet of the nozzle plate on which the nozzle is formed. It is a phenomenon that forms a puddle.

When the radical polymerizable component in the padded inkjet ink radically polymerizes, the ejection of ink droplets is hindered, the trajectory of the ejected ink droplets is changed, or the ink droplets of a predetermined volume are not ejected, or the ink droplets are not ejected. May not be ejected at all, and as a result, a good image may not be formed.
The radical polymerization inhibitor also functions to prevent the radical polymerizable component from undergoing a radical polymerization reaction and gelling during storage of the inkjet ink or storage in the package.

As the radical polymerization inhibitor, any of various compounds having the above functions can be used.
Examples of the radical polymerization inhibitor include one or more of hydroquinones, catechols, hindered amines, phenols, phenothiazines, and condensed aromatic ring quinones.

Among these, examples of hydroquinones include one or more of hydroquinone, hydroquinone monomethyl ether, 1-o-2,3,5-trimethylolhydroquinone, and 2-tert-butylhydroquinone.
Examples of catechols include one or more of catechol, 4-methylcatechol, and 4-tert-butylcatechol.

As the hindered amines, one kind or two or more kinds of arbitrary hindered amines having a polymerization inhibiting effect are preferable.
Examples of the phenols include one or more of phenol, butylhydroxytoluene, butylhydroxyanisole, pyrogallol, alkyl gallate, hindered phenols and the like.

Examples of phenothiazines include phenothiazine and the like.
Furthermore, examples of the condensed aromatic ring quinones include naphthoquinone.
Among them, the radical polymerization inhibitor is preferably at least one selected from the group consisting of hindered amines and hindered phenols, which has a high polymerization inhibiting effect and can efficiently inhibit the radical polymerization reaction of the radical polymerizable component.

Among these, hindered amines include, for example, 4,4'-[(1,10-dioxo-1,10-decanediyl)bis(oxy)]bis[2,2,6,6-tetramethyl]-1-piperid. Didinyloxy [alias: bis(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl) sebacate, Ilgastab (registered trademark) UV10 manufactured by BASF or its equivalent) and the like. To be

Examples of the hindered phenols include α,α′,α″-1,2,3-propanetriyltris[ω-[(1-oxo-2-propen-1-yl)oxy]-poly[oxy. (Methyl-1,2-ethanediyl)] and 2,6-bis(1,1-dimethylethyl)-4-(phenylmethylene)-2,5-cyclohexazin-1-one as an active ingredient. [Ilgastab UV22 manufactured by BASF, a mixture of the former in the proportion of 76 to 90% by mass and the latter in the proportion of active ingredient in the range of 24 to 10% by mass] and the like.

The proportion of the radical polymerization inhibitor is preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, and more preferably 3% by mass or less, especially 1% by mass or less, based on the total amount of the inkjet ink.
<Colorant>
Examples of the colorant include various pigments and dyes. As the colorant, any colorant of each color depending on the tint of the inkjet ink can be used. In particular, various inorganic pigments and/or organic pigments are preferable in view of improving the light resistance and weather resistance of the image.

Among these, examples of the inorganic pigment include metal compounds such as titanium oxide and iron oxide, and various carbon blacks such as neutral, acidic and basic produced by known methods such as a contact method, a furnace method and a thermal method. And the like.
Examples of organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (eg phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazines). Pigment, thioindigo pigment, isoindolinone pigment, quinophthalone pigment, etc.), dye chelate (for example, basic dye type chelate, acid dye type chelate, etc.), nitro pigment, nitroso pigment, aniline black, etc. Can be mentioned.

One kind or two or more kinds of inorganic or organic pigments can be used depending on the color of the inkjet ink. For example, in the case of expressing black with carbon black, a cyan pigment may be added in order to make it look more bluish black.
The surface of the pigment may be treated in order to improve the dispersion stability in the inkjet ink.

Further, the pigment may be used in the production of an inkjet ink in the state of, for example, an arbitrary solvent capable of favorably dispersing the pigment or a pigment dispersion liquid dispersed in a low-viscosity radically polymerizable component.
Examples of the radically polymerizable component include monofunctional monomers such as EC-A. A dispersant or the like may be added to the pigment dispersion liquid in order to disperse the pigment well.

As the white pigment, titanium oxide excellent in hiding property is particularly preferable, and as the titanium oxide, various titanium oxides such as rutile type and anatase type can be used.
Titanium oxide has an average particle size of 0.15 μm or more, particularly 0.2 μm or more, in consideration of both improving dispersibility in an inkjet ink and imparting high concealing property to a picture or a character. The thickness is preferably 0.4 μm or less, and particularly preferably 0.3 μm or less.

Specific examples of pigments having a tint other than white include the following various pigments.
(Yellow pigment)
C. I. Pigment Yellow 1, 2, 3, 12, 13, 14, 14C, 16, 17, 20, 24, 73, 74, 75, 83, 86, 93, 94, 95, 97, 98, 109, 110, 114, 117, 120, 125, 128, 129, 130, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, 213, 214.
(Magenta pigment)
C. I. Pigment Red 5, 7, 9, 12, 48 (Ca), 48 (Mn), 49, 52, 53, 57 (Ca), 57:1, 97, 112, 122, 123, 149, 168, 177, 178. 179, 184, 202, 206, 207, 209, 242, 254, 255
(Cyan pigment)
C. I. Pigment Blue 1, 2, 3, 15, 15:1, 15:3, 15:4, 15:6, 15:34, 16, 22, 60
(Black pigment)
C. I. Pigment Black 7
(Orange pigment)
C. I. Pigment Orange 36, 43, 51, 55, 59, 61, 71, 74
(Green pigment)
C. I. Pigment Green 7,36
(Violet pigment)
C. I. Pigment Violet 19, 23, 29, 30, 37, 40, 50
The proportion of the colorant is preferably 0.1% by mass or more, more preferably 1% by mass or more, and preferably 12% by mass or less, particularly preferably 10% by mass or less, based on the total amount of the inkjet ink.

When a pigment dispersion liquid is used, the ratio of the pigment as the colorant is the ratio of the pigment itself as the active ingredient contained in the pigment dispersion liquid. When two or more pigments are used in combination, the total amount may be set within the above range.
<Surfactant>
The surfactant adjusts the surface tension of the inkjet ink, thereby adjusting the wettability of the inkjet ink with respect to the nozzles of the inkjet printer, and improving the dischargeability to improve the sharpness of a picture or letters, It functions to suppress the occurrence of paddling described above.

As the surfactant, a silicone-based surfactant is particularly preferable.
The proportion of the surfactant is preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, and more preferably 3% by mass or less, particularly preferably 1% by mass or less, based on the total amount of the inkjet ink.
By blending the components described above, according to the present invention, not only excellent in photocurability and stretchability of patterns and characters after photocuring, but also particularly when printing with a low drop volume, etc. Since the ink droplets have a good straight-traveling property and are less likely to cause dust defects, and yellowing easily occurs after photocuring, it is possible to provide an inkjet ink capable of displaying the above-mentioned patterns, characters and the like in the original correct color tone.

<Example 1>
(Preparation of pigment dispersion)
The following components were mixed, stirred, and then dispersed using a bead mill to prepare a pigment dispersion liquid.
Titanium oxide [JR 707, rutile type manufactured by Teika Co., Ltd.]: 8.7 parts by mass Dispersant [SOLSPERSE (registered trademark) 32000 manufactured by Nippon Lubrizol Co., Ltd.]: 1.0 part by mass EC-A [Kyoeisha Chemical Light Acrylate (registered trademark) EC-A]: 12.6 parts by mass (preparation of inkjet ink)
The following components were mixed in the proportions shown in Table 1 and stirred until they were sufficiently dissolved, and then the pigment dispersion prepared above was added in the proportions shown in Table 1 and further stirred, and then a 5 μm membrane plan filter was used. Was filtered to prepare a white inkjet ink.

(Monofunctional monomer)
EC-A: Kyoeisha Chemical Co., Ltd. Light Acrylate (registered trademark) EC-A
ACMO: KJ Chemicals Co., Ltd. (multifunctional monomer)
VEEA: Nippon Shokubai Co., Ltd. (photo radical polymerization initiator)
Irgacure (registered trademark) 819: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, manufactured by BASF (radical polymerization inhibitor)
Irgastab UV22, manufactured by BASF

The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 42.6 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were adjusted. The mass ratio (1)/(2) was 1.4, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.
The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.

< Comparative Example 1 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the same amount of MTG-A was blended in place of EC-A and EC-A in the pigment dispersion was replaced with the same amount of MTG-A. Prepared.
The amount of MTG-A as the monofunctional monomer of (1) to which MTG-A was added in the pigment dispersion was 42.6 parts by mass, and the MTG-A and the ACMO as the monofunctional monomer of (2) were used. The mass ratio (1)/(2) was 1.4, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.

The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.
<Example 2 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the same amount of VEEM was used instead of VEEA.

The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 42.6 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were adjusted. The mass ratio (1)/(2) was 1.4, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.
The proportion of the monofunctional monomer in the total amount of radically polymerizable components including VEEM was 82.9% by mass, and the mass ratio (total amount of radically polymerizable components)/(photoradical polymerization initiator) was 35.0.

< Comparative Example 2 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the same amount of DDA was added instead of VEEA.
The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 42.6 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were adjusted. The mass ratio (1)/(2) was 1.4, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.

The proportion of the monofunctional monomer in the total amount of radically polymerizable components including DDA was 82.9% by mass, and the mass ratio (total amount of radically polymerizable components)/(photoradical polymerization initiator) was 35.0.
<Example 3 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the amount of EC-A was 23.7 parts by mass and the amount of ACMO was 36.3 parts by mass.

The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 36.3 parts by mass, and the EC-A and the ACMO as the monofunctional monomer of (2) were used. The mass ratio (1)/(2) was 1.0, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.
The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.

<Example 4 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the amount of EC-A was 35.8 parts by mass and the amount of ACMO was 24.2 parts by mass.
The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 48.4 parts by mass, and the EC-A and the ACMO of (2) as the monofunctional monomer were The mass ratio (1)/(2) was 2.0, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.

The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.
< Comparative Example 3 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the amount of EC-A was 17.3 parts by mass and the amount of ACMO was 42.7 parts by mass.

The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 29.9 parts by mass, and the EC-A and the ACMO as the monofunctional monomer of (2) were used. The mass ratio (1)/(2) was 0.7, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.
The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.

<Example 5 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the amount of EC-A was 38.0 parts by mass and the amount of ACMO was 22.0 parts by mass.
The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 50.6 parts by mass, and the amount of EC-A and ACMO as the monofunctional monomer of (2) were The mass ratio (1)/(2) was 2.3, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.

The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.
<Example 6>
The amount of EC-A was 19.2 parts by mass, the amount of ACMO was 22.8 parts by mass, and FA-THFA [FANCRYL (registered trademark) FA-THFA manufactured by Hitachi Chemical Co., Ltd.] 9.0 parts by mass, A white inkjet ink was prepared in the same manner as in Example 1, except that 9.0 parts by mass of IBXA [light acrylate IB-XA manufactured by Kyoeisha Chemical Co., Ltd.] was added.

The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 31.8 parts by mass, and the EC-A and the ACMO as the monofunctional monomer of (2) were used. The mass ratio (1)/(2) was 1.4, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 75% by mass.
In addition, the proportion of the monofunctional monomer in the total amount of radically polymerizable components including VEEA was 82.9% by mass, and the mass ratio (total amount of radically polymerizable components)/(photoradical polymerization initiator) was 35.0.

< Comparative Example 4 >
Examples except that the amount of EC-A was 17.0 parts by mass, the amount of ACMO was 21.2 parts by mass, the amount of FA-THFA was 10.9 parts by mass, and the amount of IBXA was 10.9 parts by mass. A white inkjet ink was prepared in the same manner as in 6 .
The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 29.6 parts by mass, and the EC-A and the ACMO as the monofunctional monomer of (2) were used. The mass ratio (1)/(2) was 1.4, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 70% by mass.

The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.
<Example 7 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the amount of VEEA was 15.5 parts by mass and the amount of the photoradical polymerization initiator was 2.0 parts by mass.

The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 42.6 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were adjusted. The mass ratio (1)/(2) was 1.4, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.
The proportion of monofunctional monomers in the total amount of radically polymerizable components including VEEA was 82.4% by mass, and the mass ratio (total amount of radically polymerizable components)/(photoradical polymerization initiator) was 44.1.

<Example 8 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the amount of VEEA was 16.0 parts by mass and the amount of the photoradical polymerization initiator was 1.5 parts by mass.
The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 42.6 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were adjusted. The mass ratio (1)/(2) was 1.4, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.

The proportion of monofunctional monomers in the total amount of radically polymerizable components including VEEA was 81.9% by mass, and the mass ratio (total amount of radically polymerizable components)/(photoradical polymerization initiator) was 59.1.
< Comparative Example 5 >
(Preparation of pigment dispersion)
The following components were mixed, stirred, and then dispersed using a bead mill to prepare a pigment dispersion liquid.

Carbon black LFF [MA8 manufactured by Mitsubishi Chemical Co., Ltd.]: 2.0 parts by mass Dispersant [SOLSPERSE (registered trademark) 32000 manufactured by Nippon Lubrizol Co., Ltd.]: 1.0 part by mass EC-A [Kyoeisha Chemical ( Light acrylate (registered trademark) EC-A]: 10.0 parts by mass (preparation of inkjet ink)
The following components were mixed in the proportions shown in Table 2 and stirred until they were sufficiently dissolved, and then the pigment dispersion prepared above was added in the proportions shown in Table 2 and further stirred, and then a 5 μm membrane filter was used. To prepare a black inkjet ink.

(Monofunctional monomer)
EC-A: Light acrylate EC-A manufactured by Kyoeisha Chemical Co., Ltd.
ACMO: KJ Chemicals Co., Ltd. (multifunctional monomer)
VEEA: Nippon Shokubai Co., Ltd. (photo radical polymerization initiator)
Irgacure 819: Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, manufactured by BASF Corporation (radical polymerization inhibitor)
Irgastab UV22, manufactured by BASF

The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 48.8 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were adjusted. The mass ratio (1)/(2) was 1.6, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.
The ratio of the monofunctional monomer to the total amount of the radically polymerizable component containing VEEA was 86.8% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 15.1.

<Example 9 >
A black inkjet ink was prepared in the same manner as in Example 7 except that the amount of EC-A was 40.3 parts by mass and the amount of the photoradical polymerization initiator was 4.5 parts by mass.
The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 50.3 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were The mass ratio (1)/(2) was 1.7, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.

The proportion of the monofunctional monomer in the total amount of radically polymerizable components including VEEA was 87.0% by mass, and the mass ratio (total amount of radically polymerizable components)/(photoradical polymerization initiator) was 20.5.
<Example 10 >
(Preparation of pigment dispersion)
The following components were mixed, stirred, and then dispersed using a bead mill to prepare a pigment dispersion liquid.

Phthalocyanine pigment [C. I. Pigment Blue 15:4, Heliogen (registered trademark) Blue D7110F manufactured by BASF: 2.0 parts by mass Dispersant [SOLSPERSE (registered trademark) 32000 manufactured by Nippon Lubrizol Co., Ltd.]: 1.0 part by mass EC- A [light acrylate (registered trademark) EC-A manufactured by Kyoeisha Chemical Co., Ltd.]: 10.0 parts by mass (preparation of inkjet ink)
The following components were mixed in the proportions shown in Table 3 and stirred until they were sufficiently dissolved, and then the pigment dispersion prepared above was added in the proportions shown in Table 3 and further stirred, and then a 5 μm membrane filter was used. To prepare a cyan inkjet ink.

(Monofunctional monomer)
EC-A: Light acrylate EC-A manufactured by Kyoeisha Chemical Co., Ltd.
ACMO: KJ Chemicals Co., Ltd. (multifunctional monomer)
VEEA: Nippon Shokubai Co., Ltd. (photo radical polymerization initiator)
Irgacure 819: Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, manufactured by BASF Corporation (radical polymerization inhibitor)
Irgastab UV22, manufactured by BASF

The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 47.8 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were adjusted. The mass ratio (1)/(2) was 1.6, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.
The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 83.8% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 23.2.

<Example 11 >
Pigment dispersion prepared by adjusting the amount of VEEA to 15.0 parts by mass and the amount of the photo-radical polymerization initiator to 3.0 parts by mass, mixing the following components, and stirring and dispersing them using a bead mill. A magenta inkjet ink was prepared in the same manner as in Comparative Example 5 except that 13 parts by mass was added.

Quinacridone pigment [C. I. Pigment Violet 19, Hostaperm (registered trademark) Red E5B02 manufactured by CLARIANT: 2.0 parts by mass Dispersant [SOLSPERSE (registered trademark) 32000 manufactured by Nippon Lubrizol Co., Ltd.]: 1.0 part by mass EC-A [ Kyoeisha Chemical Co., Ltd. Light acrylate (registered trademark) EC-A]: 10.0 parts by mass EC-A in the pigment dispersion is added, and the amount of EC-A as the monofunctional monomer of (1) is 48.
8 parts by mass, the mass ratio (1)/(2) of the above EC-A and ACMO as the monofunctional monomer of (2) is 1.6, and the monomer of (1)(2) occupies the total amount of the monofunctional monomer. The proportion of the functional monomer was 100% by mass.

The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 84.0% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 31.3.
<Example 12 >
Pigment dispersion prepared by adjusting the amount of VEEA to 15.0 parts by mass and the amount of the photo-radical polymerization initiator to 3.0 parts by mass, mixing the following components, and stirring and dispersing them using a bead mill. A magenta inkjet ink was prepared in the same manner as in Comparative Example 5 except that 13 parts by mass was added.

Azo pigment [C. I. Pigment Yellow 150, Fanchon (registered trademark) Fast Yellow Y-5688 manufactured by Bayel Co., Ltd.: 2.0 parts by mass Dispersant [SOLSPERSE (registered trademark) 32000 manufactured by Nippon Lubrizol Co., Ltd.]: 1.0 part by mass EC -A [Light acrylate (registered trademark) EC-A manufactured by Kyoeisha Chemical Co., Ltd.]: 10.0 parts by mass EC-A as a monofunctional monomer of (1) to which EC-A in a pigment dispersion liquid was added. Is 48.8 parts by mass, the mass ratio (1)/(2) of EC-A and ACMO as the monofunctional monomer of (2) is 1.6, and the total amount of the monofunctional monomer is (1). The proportion of the monofunctional monomer (2) was 100% by mass.

The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 84.0% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 31.3.
<Comparative Example 6 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the amount of EC-A was 11.6 parts by mass and the amount of ACMO was 48.4 parts by mass.

The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 24.2 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were The mass ratio (1)/(2) was 0.5, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.
The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.

<Comparative Example 7 >
A white inkjet ink was prepared in the same manner as in Example 1 except that the amount of EC-A was 39.3 parts by mass and the amount of ACMO was 20.7 parts by mass.
The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 51.9 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were adjusted. The mass ratio (1)/(2) was 2.5, and the proportion of the monofunctional monomers (1) and (2) in the total amount of the monofunctional monomers was 100% by mass.

The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.
<Comparative Example 8 >
In the same manner as in Example 1 except that the amount of EC-A was 20.4 parts by mass, the amount of ACMO was 23.6 parts by mass, and FA-THFA 15.5 parts by mass and IBXA 15.5 parts by mass were added. To prepare a white inkjet ink.

The amount of EC-A as the monofunctional monomer of (1) to which EC-A was added in the pigment dispersion was 33.0 parts by mass, and the amount of EC-A and the ACMO as the monofunctional monomer of (2) were The mass ratio (1)/(2) was 1.4, and the ratio of the monofunctional monomers of (1) and (2) to the total amount of monofunctional monomers was 65% by mass.
The proportion of the monofunctional monomer in the total amount of the radically polymerizable components including VEEA was 85.4% by mass, and the mass ratio (total amount of the radically polymerizable components)/(photoradical polymerization initiator) was 41.0.

<Comparative Example 9 >
Instead of EC-A, the same amount of formula (10) :

Phenoxyethyl acrylate (light acrylate PO-A manufactured by Kyoeisha Chemical Co., Ltd., which may be abbreviated as “PO-A” hereinafter) represented by the following formula is added, and EC-A in the pigment dispersion is the same. A white inkjet ink was prepared as in Example 1 except that the amount of PO-A was replaced.
The amount of PO-A added with PO-A in the pigment dispersion is 42.6 parts by mass, the mass ratio of PO-A to ACMO as the monofunctional monomer (2) is 1.4, and the monofunctional monomer is 1.4. The proportion of both monofunctional monomers in the total amount of was 100% by mass.

The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.
<Comparative Example 10 >
Instead of ACMO, the same amount of equation (11) :

A white inkjet ink was prepared in the same manner as in Example 1 except that N-vinyl-ε-caprolactam (hereinafter, sometimes abbreviated as “V-CAP”) represented by
The amount of EC-A as the monofunctional monomer of (1) to which EC-A in the pigment dispersion is added is 42.6 parts by mass, and the mass ratio of the EC-A and V-CAP is 1.4. The proportion of both monofunctional monomers in the total amount of the functional monomers was 100% by mass.

The proportion of the monofunctional monomer in the total amount of the radically polymerizable component containing VEEA was 82.9% by mass, and the mass ratio (total amount of the radically polymerizable component)/(photoradical polymerization initiator) was 35.0.
<Evaluation of straightness of ink drop>
By using the inkjet ink prepared in each of the above Examples and Comparative Examples, a ruled line (nozzle check pattern) was formed on the surface of the soft pinyl chloride film by inkjet printing, and the formed ruled line was observed, and the ink droplet went straight according to the following criteria. The sex was evaluated.

◯: Ruled lines could be formed neatly in every corner. Good.
X : Although the ruled line was formed, there was some irregularity in the straight line portion of the ruled line . Alternatively, the ink droplets were scattered to cause a large disorder in the straight line portion of the ruled line, or the straight line was not formed at all. Bad.

<Evaluation of yellowing loss after photocuring>
After forming a solid image by inkjet printing on the surface of a white soft pinyl chloride film with the white inkjet ink prepared in each of the above Examples and Comparative Examples, an LED lamp [Phoseon Technology's Fire JetFJ200 was manufactured. ], the solid image was photocured by irradiating ultraviolet rays under the conditions of output: 8 W, measured peak illuminance: 7.2 W/cm ² , and integrated light amount: ² J/cm ² .

Then, the Lab value of the formed solid image was measured using a handheld gloss meter PG-1M manufactured by Nippon Denshoku Co., Ltd., and the Lab of the surface of the white soft pinyl chloride film previously measured as a reference was measured. The difference ΔE from the value was determined. Then, the yellowing defect after photocuring was evaluated based on the following criteria.
◯: ΔE was less than 3. Good omission of yellowing.

Δ: ΔE was 3 or more and less than 6. Normal level with slight yellowing.
X: ΔE was 6 or more. Poor yellowing.
<Stretchability evaluation>
After forming a solid image by inkjet printing on the surface of a soft-formable pinyl chloride film that can be thermoformed with the inkjet inks prepared in each of the above Examples and Comparative Examples, using the same LED lamp, output: 8 W, measured peak illuminance : 7.2 W/cm ² , and the integrated light quantity: ² J/cm ² were irradiated with ultraviolet rays to photo-cure the solid image.

Then, the state of a solid image when the soft pinyl chloride film was stretched in one direction while heating at 150° C. was observed, and the stretchability was evaluated according to the following criteria.
◯: No cracks were found in the solid image even at a stretching ratio of 200%. Good.
B: Cracking occurred at a stretch ratio of 200%, but no cracking occurred at 150%. Normal level.

×: it produced cracking in extension Elongation 150%. Bad.
<Evaluation of photocurability>
After forming a solid image by inkjet printing on the surface of the same soft pinyl chloride film as in the stretchability evaluation using the inkjet ink prepared in each of the above Examples and Comparative Examples, using the same LED lamp, output: 8 W, measured peak illuminance : 7.2 W/cm ² and an integrated light amount: 1 J/cm ² were irradiated with ultraviolet rays to photo-cure the solid image.

Then, the state when the solid image was touched with a finger was observed, and the photocurability was evaluated according to the following criteria.
◯: There was no tackiness and no fingerprint was attached to the solid image. Good.
Δ: There was a feeling of tackiness, but no fingerprint was attached to the solid image. Normal level.
X: There was a tackiness, and fingerprints were attached to the solid image. Bad.

<Fixability evaluation>
After forming a solid image by inkjet printing on the surface of the same soft pinyl chloride film as in the stretchability evaluation using the inkjet ink prepared in each of the above Examples and Comparative Examples, using the same LED lamp, output: 8 W, measured peak illuminance : 7.2 W/cm ² and an integrated light amount: 1 J/cm ² were irradiated with ultraviolet rays to photo-cure the solid image.

Next, a paper waste was contacted with a load of 900 g on the solid image, and after 100 reciprocations, the state was observed, and the fixability was evaluated according to the following criteria.
◯: No rubbing was observed on the solid image, and no stain was observed on the paper waste. Good.
Δ: No rubbing was observed in the solid image, but slight stains were observed in the paper waste. Normal level.

X: Rubbing was seen in the solid image, and stains were also seen in the paper waste. Bad.
The above results are shown in Tables 4 to 7.

Tables 4 7 Examples 1 12, the results of Comparative Example 1, 9, 10, is excellent in stretchability of the picture and characters after photocuring, ink in particular to a printing or the like at a low drop volume In addition to the good straightness of the droplets and the less likely occurrence of dust defects, yellowing is likely to occur after photocuring and the correct color tone can be displayed, as a monofunctional monomer, the EC-A of (1) and ( It was found that it is necessary to use two types of ACMO of 2) together.

The Examples 1 12 From the results of Comparative Example 3, 6, 7, together with the advantages mentioned above, good light-curing to light from a narrow LED wavelength ranges in order to impart to the ink-jet ink, both It was found that the mass ratio (1)/(2) of the monofunctional monomer needs to be 1.0 or more and 2.3 or less.
From the results of Examples 1 and 3 to 5 , considering that such effects are further improved, the mass ratio (1)/(2) of both monofunctional monomers is 2 . It was found that it is preferably 0 or less.

Furthermore, from the results of Examples 1 to 12 and Comparative Examples 4 and 8 , in order to obtain the above effects, both monofunctional monomers (1) and (2) are added in a total amount of 75% by mass or more based on the total amount of the monofunctional monomers. It turns out that it needs to be included in proportion.

From the results of Examples 1 to 12 and Comparative Example 2 , it was found that VEEA and VEEM of (3) should be selected and used as the polyfunctional monomer in order to improve the straightness of the ink droplets . ..
From the results of Examples 1, 6 and Comparative Example 4 , in addition to the monofunctional monomers (1) and (2), FA-THFA or IBXA as another monofunctional monomer may be used in combination, in which case However, in order to improve the straightness of ink droplets and to make it easier to remove yellowing after photocuring to display the correct color tone, the monofunctional monomers of (1) and (2) are also used as a single unit. It has been found that it is necessary to contain the functional monomer in a proportion of 75% by mass or more of the total amount.

From the results of Examples 1 to 12 and Comparative Example 5, in order to improve the straightness of the ink droplets, the photoradical polymerization initiator was used in a mass ratio (of the radical polymerizable component) to the total amount of the radical polymerizable component. It was found that the total amount)/(photoradical polymerization initiator) needs to be added in a proportion of 17 or more.
From the results of Examples 1, 7 , and 8 , in the white inkjet ink, the photo radical polymerization initiator was used in a mass ratio (total amount of radical polymerizable component)/(photo radical polymerization) to the total amount of the radical polymerizable component. It has been found that it is preferable to blend the initiator in the range of 27 to 45.
Furthermore, from the results of Examples 9 to 12 , the above mass ratios are 17 to 25 for the black inkjet ink, 20 to 30 for the cyan inkjet ink, 27 to 45 for the magenta inkjet ink, and 27 to 45 for the yellow inkjet ink. It has been found that a range of 45 is preferable.

Claims (3)

A radically polymerizable component and a photoradical polymerization initiator are included, and the radically polymerizable component contains a monofunctional monomer in a proportion of 70% by mass or more of the total amount of the radically polymerizable component, and the monofunctional monomer is ,
Formula (1):

And ethoxydiethylene glycol acrylate represented by the formula (2):

The ratio of 4-acryloylmorpholine represented by the formula (1)/(2) is 1.0 or more and 2.3 or less, and the total of both is 75 mass of the total amount of the monofunctional monomer. seen containing% or more of the total, yet the radical polymerizable component further equation (3):

[In the formula, R represents a hydrogen atom or a methyl group. ]
The mass ratio of the photoradical polymerization initiator (total amount of radically polymerizable components)/(photoradical polymerization initiator) containing 2-(2-vinyloxyethoxy)ethyl (meth)acrylate represented by An inkjet ink that is 17 or more . The inkjet ink according to claim 1 , wherein the radically polymerizable component further contains at least one selected from the group consisting of tetrahydrofurfuryl acrylate and isobornyl acrylate. The photoradical polymerization initiator is contained in a ratio of 50 or less expressed by mass ratio (total amount of radical polymerizable component)/(photoradical polymerization initiator) with respect to the total amount of the radical polymerizable component. The inkjet ink according to 1 or 2 .