JP6398785B2 - Active energy ray curable inkjet ink - Google Patents

Description

  The present invention relates to an active energy ray-curable inkjet ink.

The inkjet printing method is a printing method in which fine droplets of ink are ejected and landed from an inkjet head on a substrate to be printed to form images and characters on the substrate, and a plate is required. It is characterized by not. An electrophotographic method is widely recognized as a printing method that does not require a plate. However, the inkjet printing method is superior to the electrophotographic method in terms of the initial cost of the device, the running cost during printing, the device size, high-speed printing characteristics, and the like.

Conventional inks used in ink jet printing methods are diverse, such as solvent type, water type, and active energy ray curable type. However, in recent years, the demand for active energy ray-curable inkjet ink has increased. This is because the active energy ray-curable inkjet ink has many advantages as follows. For example, the active energy ray curable type is
Compared to solvent-type and water-type, which requires an ink drying process, the printing speed is excellent, and at the same time, the amount of solvent volatilization is reduced and the environment is friendly. In addition, it can be applied not only to non-absorbable substrates such as plastic and glass but also to various substrates such as paper substrates.

On the other hand, an on-demand printing method that does not require a plate is required for reprint printing that prints variable data such as small lot books, barcode and direct mail address printing, and mainly uses electronic photography. This is done by printing with the method.
For address printing of these bar codes and direct mails, a printed matter with a particularly high black density is required. The electrophotographic system can contain a lot of pigments in the toner, and is therefore suitable for obtaining a high-density printed matter. However, as described above, an ink jet printing method is required from the viewpoint of the initial cost of the apparatus, the running cost, the apparatus size, and the like.

The ink jet printing method has a great limitation on the ink viscosity due to its characteristics, cannot contain a large amount of colorant, and is inferior to the electrophotographic method in terms of coloring power. Inkjet printing has not yet been achieved in the reprint market, especially in markets where high density in black is required.

In order to achieve high density printing in an active energy ray curable inkjet ink,
Although it is conceivable to increase the amount of the colorant in the ink, the active energy rays such as ultraviolet rays are absorbed by the colorant and the penetration of the active energy rays to the inside of the film is obstructed, resulting in poor curing inside the ink coating film. Occurs, and hardening wrinkles occur. If the film thickness is reduced in order to prevent poor curing, the curability deteriorates due to the influence of oxygen inhibition at the forefront of the cured film.
It is also conceivable to obtain a high concentration by increasing the ink adhesion amount, but it is necessary to considerably increase the light irradiation amount during curing.

For example, in Patent Document 1, curability is improved by using titanium black with less ultraviolet absorption as a black colorant, but high concentration in a thin film cannot be achieved.
In Patent Document 2, although a color colorant that absorbs less active energy rays than a black pigment is used in combination to improve curability, an oxygen depletion unit is required to achieve sufficient curability, High density printing in the atmosphere has not been achieved.
In Patent Document 3, in order to obtain the required optical density (OD value) of a cured film, a long-wavelength light source with high transmittance and a polymerization initiator corresponding thereto are used. However, in order to achieve the required density, a film thickness of 10 μm or more is required. Therefore, curing failure occurs at a thin film thickness of 10 μm or less, and high density printing with a thin film cannot be achieved.

JP 2003-342503 A JP 2005-320541 A JP 2014-237752 A

An object of the present invention is to provide an active energy ray-curable inkjet ink having a high concentration and high curability while having a low film thickness.

That is, the present invention
An active energy ray-curable inkjet ink containing a pigment, a photopolymerization initiator, and a polymerizable monomer,
The pigment is contained in an amount of 4.0% by mass or more based on the total weight of the inkjet ink,
Containing 60% by weight or more of carbon black with respect to the total weight of the pigment,
The photopolymerization initiator includes an acylphosphine oxide photopolymerization initiator, a thioxanthone photopolymerization initiator, and an α-aminoalkylketone photopolymerization initiator,
The content of the photopolymerization initiator is 3 to 7 parts by weight with respect to 1 part by weight of the pigment,
The polymerizable monomer comprises 2- (2-vinyloxyethoxy) ethyl acrylate and dipropylene glycol diacrylate;
The present invention relates to an active energy ray-curable ink-jet ink having an OD value of 1.9 or more when an average film thickness upon curing is 6 μm.

The present invention is, A sill phosphine oxide-based photopolymerization initiator, about the active energy ray curable inkjet ink which comprises 2.1 to 4.5 parts by weight relative to the pigment 1 part by weight.

The present invention, Chi Okisanton based photopolymerization initiator, the pigment 1 part by weight, related to the active energy ray-curable inkjet ink, characterized in that it comprises from 0.65 to 1.5 parts by weight.

The present invention also relates to the above active energy ray-curable inkjet ink , wherein the α -aminoalkylketone photopolymerization initiator contains 0.45 to 1.0 part by weight with respect to 1 part by weight of the pigment.

The present invention, the active energy total amount of A acrylic acid 2- (2-vinyloxy ethoxy) ethyl and dipropylene glycol diacrylate, characterized in that it is a polymerizable monomer 100 parts by weight in 60 parts by weight or more The present invention relates to a linear curable inkjet ink.

The present invention further relates to the above active energy ray-curable inkjet ink, further comprising 1.0% by weight or more of a silicon-based surface tension adjusting agent in the inkjet ink.

According to the present invention, an active energy ray-curable inkjet ink having a high concentration and high curability can be provided.

  Hereinafter, the ultraviolet curable inkjet ink in the present invention will be described in detail.

The present invention is characterized in that it is an inkjet ink having an average film thickness upon curing of 6 μm and an OD value of 1.9 or more.
If it is the inkjet ink which is the said range, the film thickness of the cured film obtained will not be limited. The thickness of the cured film obtained is preferably 1 μm or more, and more preferably 1.5 μm or more. When the film thickness is 1 μm or more, the film is hardly affected by oxygen inhibition and good curability is obtained.

<OD value>
A cured film is formed on the non-permeable base material so as to have a film thickness of 6 μm. X-Rite, Inc. Using X-Rite 500 series manufactured by the manufacturer, it can be obtained by measuring any five of 100% solid print portions under the condition of status G and calculating the average value.
The OD value is preferably 1.9 or more, and more preferably 2.0 or more. If the density is 1.9 or more, it is possible to provide a printed matter having a density level that is visually inferior to that of an electrophotographic system regardless of whether it is a permeable base material or a non-penetrating base material.

<Pigment>
In the present invention, the pigment is preferably contained in the ink in an amount of 4% by weight or more, more preferably 4 to 15% by weight, still more preferably 4 to 8% by weight, in order to obtain a sufficient printing density (OD value) and light resistance. Range. Within the above range, the printing density and curability can be maintained even under low film thickness conditions that are susceptible to oxygen inhibition.

As the pigment, a pigment that is generally used in an ink composition for printing or paint can be used, and can be selected according to the required use such as color developability and light resistance.
As the pigment component, black pigments such as carbon black, achromatic pigments such as titanium oxide and calcium carbonate, and chromatic organic pigments can be used.

The black ink of the present invention preferably contains 60% by weight or more of carbon black with respect to the total weight of the pigment, more preferably 80% by weight or more, and further preferably 90% by weight or more.

As the carbon black used in the present invention, known carbon blacks such as channel black, furnace black, thermal black, and lamp black can be used.

Specific examples of carbon black include “Special Black 350” manufactured by Degussa.
, 250, 100, 550, 5, 4, 4A, 6 "" PrintexU, V, 140U, 1
40V, 95, 90, 85, 80, 75, 55, 45, 40, P, 60, L6, L, 30
"0, 30, 3, 35, 25, A, G", "REGAL400R, 660R" manufactured by Cabot Corporation
, 330R, 250R ”“ MOGUL E, L ”,“ MA7, 8, 11, 7 ”manufactured by Mitsubishi Chemical Corporation
7, 100, 100R, 100S, 220, 230 ""# 2700, # 2650, # 26
00, # 200, # 2350, # 2300, # 2200, # 1000, # 990, # 98
0, # 970, # 960, # 950, # 900, # 850, # 750, # 650, # 52
, # 50, # 47, # 45, # 45L, # 44, # 40, # 33, # 332, # 30, #
25, # 20, # 10, # 5, CF9, # 95, # 260 ”and the like.

The average particle diameter (D50) of carbon black is 10 to 20 as measured by laser scattering.
0 nm is preferable, and 50 to 150 nm is more preferable. When the average particle size is 10 nm or more, the curability is improved, and when it is 200 nm or less, the coloring power is improved.

The D50 is a value measured by diluting the ink 200 to 1000 times with ethyl acetate and using Microtrac UPA150 (Nikkiso Co., Ltd.).

Examples of the organic pigment used in the ink of the present invention include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow and pyrazolone red, soluble azo such as ritole red, heliobordeaux, pigment scarlet, and permanent red 2B. Pigments, derivatives from vat dyes such as alizarin, indanthrone, thioindigo maroon, phthalocyanine organic pigments such as phthalocyanine blue and phthalocyanine green, quinacridone organic pigments such as quinacridone red and quinacridone magenta, perylene red, and perylene scarlet Perylene organic pigments, isoindolinone yellow, isoindolinone organic pigments such as isoindolinone orange, pyranthrone red,
Pilanthrone organic pigments such as pyranthrone orange, thioindigo organic pigments, condensed azo organic pigments, benzimidazolone organic pigments, quinophthalone organic pigments such as quinophthalone yellow, isoindoline organic pigments such as isoindoline yellow, naphthol Examples of organic pigments and other pigments include Flavanthrone Yellow, Acylamide Yellow, Nickel Azo Yellow, Copper Azomethine Yellow, Perinone Orange, Anthrone Orange, Dianthraquinonyl Red, Dioxazine Violet and the like.

When organic pigments are exemplified by color index (CI) numbers, C.I. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 11
0, 117, 120, 125, 128, 129, 137, 138, 139, 147, 14
8, 150, 151, 153, 154, 155, 166, 168, 180, 185, C.I.
I. Pigment orange 16, 36, 43, 51, 55, 59, 61, 64 C.I. I. Pigment Red 9, 31, 48, 49, 52, 53, 57, 97, 122, 123, 146
147, 149, 168, 177, 180, 185, 192, 202, 206, 215
216, 217, 220, 223, 224, 226, 227, 228, 238, 240
269, C.I. I. Pigment Violet 19, 23, 29, 30, 37, 40, 50
, C.I. I. Pigment Blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 6
0, 64, C.I. I. Pigment green 7, 36, C.I. I. Pigment Brown 23, 2
5, 26 and the like.

Among the above organic pigments, quinacridone organic pigments, phthalocyanine organic pigments, benzimidazolone organic pigments, isoindolinone organic pigments, condensed azo organic pigments, quinophthalone organic pigments, isoindoline from the viewpoint of light resistance. Organic pigments are preferred.

The organic pigment is preferably a fine pigment having an average particle diameter (D50) of 10 to 500 nm as measured by laser scattering, and more preferably 50 to 400 nm. The average particle size of the pigment is 10n
When it is m or more, the light resistance is improved, and when it is 500 nm or less, the dispersion stability is improved.

The D50 is a value measured by diluting the ink 200 to 1000 times with ethyl acetate and using Microtrac UPA150 (Nikkiso Co., Ltd.).

In the present invention, the organic pigment is preferably less than 40% by weight based on the total weight of the pigment contained in the ink in order to obtain the required hue, color density and light resistance.

<Photopolymerization initiator>
The photopolymerization initiator contained in the black ink of the present invention is
3 parts by weight or more is preferably contained with respect to 1 part by weight of the pigment, more preferably 3 to 7 parts by weight, and still more preferably 4 to 7 parts by weight.
By including 3 parts by weight or more of the photopolymerization initiator with respect to 1 part by weight of the pigment, the curability becomes sufficient, and when it is 7 parts by weight or less, curing wrinkles due to uneven curing can be reduced.
In particular, at the time of thin film printing, it can be cured sufficiently without being inhibited by oxygen, and sufficient curability can be obtained with a high color density.

The photopolymerization initiator contained in the ink composition of the present invention is used to form a print by curing the ink present on the surface of the recording medium by photopolymerization by irradiation with ultraviolet rays. By using ultraviolet rays (UV) among the radiation, the safety is excellent and the cost of the light source lamp can be suppressed.

The photopolymerization initiator preferably contains any of an acylphosphine oxide photopolymerization initiator, a thioxanthone photopolymerization initiator, and an α-aminoalkylketone photopolymerization initiator.

Examples of the acylphosphine oxide photopolymerization initiator include 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2,4,6-triethylbenzoyl-
Monoacylphosphine oxides such as diphenylphosphine oxide, 2,4,6-triphenylbenzoyl-diphenylphosphine oxide,
Bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, bis (2
, 6-Dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide and the like.

Examples of commercially available acylphosphine oxide photopolymerization initiators include DAROCU.
R TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide),
IRGACURE 819 (bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide), and CGI 403 (bis (2,6-dimethoxybenzoyl) -2
, 4,4-trimethylpentylphosphine oxide).

Moreover, it is preferable that said acyl phosphine oxide type photoinitiator contains a monoacyl phosphine oxide. Thereby, since a photoinitiator melt | dissolves sufficiently in ink and hardening fully advances, there is no hardening wrinkle and it is excellent in sclerosis | hardenability of ink.

The acylphosphine oxide photopolymerization initiator is 1.8 to 5.7 with respect to 1 part by weight of the pigment.
It is preferable to contain a weight part, 2.1 to 4.5 weight part is more preferable, 2.5 to 4.0 weight part is still more preferable.
By including 1.8 parts by weight or more with respect to 1 part by weight of the pigment, curability is sufficient, and by containing 5.7 parts by weight or less with respect to 1 part by weight of the pigment, generation of curing wrinkles due to uneven curing is also suppressed. I can do it.

Examples of the thioxanthone photopolymerization initiator include 2,4-diethylthioxanthone,
Examples thereof include 2-isopropylthioxanthone and 4-isopropylthioxanthone.

Among the thioxanthone photopolymerization initiators, 2-isopropylthioxanthone is preferable from the viewpoint of the sensitizing effect on the acylphosphine oxide photopolymerization initiator.

The thioxanthone photopolymerization initiator is preferably contained in an amount of 0.5 to 2.0 parts by weight, more preferably 0.65 to 1.5 parts by weight, and 0.7 to 1.5 parts by weight with respect to 1 part by weight of the pigment. Part is more preferred.
By including 0.5 part by weight or more with respect to 1 part by weight of pigment, curability at the time of thin film is improved, and by containing 1.5 part by weight or less with respect to 1 part by weight of pigment, ink stability is not deteriorated.

As the α-aminoalkylketone photopolymerization initiator, for example,
2-Methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butane-1
-One, 2- (dimethylamino) -2-[(4-methylphenyl) methyl] -1- [4-
(4-morpholinyl) phenyl] -1-butanone and the like.
Among these, 2- (dimethylamino) -2-[(4-methylphenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone is preferable from the viewpoint of ink handling properties.

The α-aminoalkyl ketone compound is preferably contained in an amount of 0.2 to 2.0 parts by weight, more preferably 0.45 to 1.0 parts by weight, and 0.5 to 0.9 parts per 1 part by weight of the pigment. Part by weight is more preferred.
With the content, curability can be obtained without impairing the stability of the ink.

The photopolymerization initiator preferably contains an acylphosphine oxide photopolymerization initiator, a thioxanthone photopolymerization initiator, and an α-aminoalkylketone photopolymerization initiator.
By using these three types in combination, the curability is good even when the thin film is affected by oxygen inhibition, and the curability is good even when the pigment concentration is high.

Photopolymerization initiators other than those described above can be freely selected depending on the curing speed, cured coating film properties, and the like.
For example, benzoin isobutyl ether, oligo (2-hydroxy-2-methyl-1-
(4- (1-methylvinyl) phenyl) propanone),
4-benzoyl-4′-methyl-diphenyl sulfide, 1,2-octanedione, 1-
(4- (phenylthio) -2,2- (O-benzoyloxime)),
1-hydroxycyclohexyl phenyl ketone, benzoin ethyl ether, benzyldimethyl ketal, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-
(4-Isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, benzophenone, 4-phenylbenzophenone, isophthalphenone and the like can be mentioned.
These photopolymerization initiators are preferable in that the radical generation reaction due to light absorption of the coloring material and the polymerizable compound is not inhibited, and the radical generation efficiency is high and the curability of the ink composition can be increased.

For the above photopolymerization initiator, trimethylamine, methyldimethanolamine, triethanolamine, p-diethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, N, N-dimethylbenzyl as sensitizers. Amine, 4,4′-diethylaminobenzophenone, and 4,4′-bis (diethylamino) benzophenone can also be used in combination with amines that do not cause an addition reaction with the polymerizable compound. Of course, it is preferable to select and use the photopolymerization initiator and the sensitizer that are excellent in solubility in the ink composition and do not impair the ultraviolet transmittance.

In the present invention, a stabilizer can be used to increase the viscosity stability of the ink over time and the on-press viscosity stability in the recording apparatus. Seiko Chemical Co., Ltd. “BHT Swanox” as a hindered phenol compound in terms of solubility in polymerizable compounds and the color of the stabilizer itself
“Nonflex Alba”, “H-BHT” manufactured by Honshu Chemical Co., Ltd. “Phenothiazine” manufactured by Seiko Chemical Co., Ltd. as a phenothiazine compound, “Phenothiazine” manufactured by Sakai Chemical Industry Co., Ltd. As the phosphorus compound, “triphenylphosphine” manufactured by BASF is suitably selected.

<Polymerizable monomer>
In this specification, for example, the expression “(meth) acrylate” means “acrylate and / or methacrylate” unless otherwise specified.

The present invention preferably contains vinyl ether group-containing (meth) acrylic acid esters. Vinyl ether group-containing (meth) acrylic acid esters are, for example, acrylic acid 2-
Examples include (2-vinyloxyethoxy) ethyl, 2- (2-vinyloxyethoxy) ethyl methacrylate, and the like, and preferably includes 2- (2-vinyloxyethoxy) ethyl acrylate. By including 2- (2-vinyloxyethoxy) ethyl acrylate, it is possible to suppress an increase in ink viscosity even when the pigment content in the ink is high. Furthermore, even when the pigment content is high, sufficient curability can be obtained.

In the present invention, it is preferable to use 2- (vinyloxyethoxy) ethyl acrylate and dipropylene glycol diacrylate in combination. Although these polymerizable compounds are polyfunctional, the viscosity is as small as 10 mPa · s or less, and there is a feature that there is little odor. Further, 2- (vinyloxyethoxy) ethyl acrylate is an excellent curable and low-viscosity polymerizable compound among polyfunctional groups, although the reason is not clear. However, the surface tension is slightly higher and acrylic acid 2-
With (vinyloxyethoxy) ethyl alone, wetting and spreading after ink landing is poor, and image quality after printing tends to be poor. Dipropylene glycol diacrylate is characterized by low viscosity and low surface tension. Therefore, wetting and spreading on the surface of the substrate after printing is improved, which contributes to higher image quality. However, it is inferior in curability as compared with 2- (hydroxyethoxy) ethyl acrylate. That is, by using these two kinds of polymerizable monomers, low viscosity, high image quality, low odor, and high curability can be achieved. Further, by using these two kinds of polymerizable compounds, the solubility of the photopolymerization initiator becomes good, and the curing reaction easily proceeds.

The optimum ratio for exhibiting these effects is 10% to 60% by weight, more preferably 20% to 50% by weight of 2- (vinyloxyethoxy) ethyl acrylate in the ink composition. On the other hand, dipropylene glycol diacrylate is preferably 10 wt% to 80 wt%, more preferably 30 wt% to 70 wt%.

As the polymerizable compound used in the present invention, conventionally known materials can be used as necessary in addition to the above-mentioned two types.

Specifically, as a monofunctional polymerizable compound, for example, benzyl (meth) acrylate,
2-phenoxyethyl (meth) acrylate, (ethoxy (or propoxy)) 2-phenoxyethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth)
Monofunctional (meth) acrylate having an aromatic ring such as acrylate, phenoxydiethylene glycol (meth) acrylate,
Dicyclopentanyl (meth) acrylate, dicyclopentenyl (oxyethyl) (meth) acrylate, cyclohexyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 1,4-cyclohexanedimethanol (meth) Acrylate, trimethylolpropane formal (meth) acrylate,
Acryloylmorpholine, N-acryloyloxyethylhexahydrophthalimide, N
-Monofunctional (meth) having a cyclic structure such as vinylcaprolactam and N-vinylpyrrolidone
Acrylate 2- (2-ethoxyethoxy) ethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, methoxytriethylene glycol (meth) acrylate, 2-ethoxyethyl (meth) acrylate, ethoxyethoxyethyl (meth) acrylate, Methoxydipropylene glycol (meth) acrylate, methoxy polypropylene glycol (
(Meth) acrylate, dipropylene glycol (meth) acrylate, polypropylene glycol mono (meth) acrylate, isoamyl (meth) acrylate, isooctyl (
(Meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate, β-carboxylethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (Meth) acrylate, 4-hydroxybutyl (meth) acrylate, N
-Monofunctional (meth) acrylates having no cyclic structure such as vinylformamide can be mentioned.
A monofunctional polymerizable compound can be used to lower the viscosity of the ink. As a monomer having relatively good curability, 2-phenoxyethyl (meth) acrylate is known, but 2-phenoxyethyl (meth) acrylate has an odor and a high surface tension (39
mN / m), the spread of the dot diameter is poor and the image is adversely affected.
Among them, a monofunctional (meth) acrylate having no aromatic ring is preferable in terms of curability and odor, and a monofunctional polymerizable compound having a surface tension of 38 mN / m or less is preferable in terms of printing image quality. . For example, in terms of odor and viscosity, lauryl acrylate, tetrahydrofurfuryl acrylate, isodecyl acrylate, isooctyl acrylate, tridecyl acrylate, isobornyl acrylate, and the like are preferable.
From the viewpoint of ink odor, curability, image quality, and initiator solubility, it is preferably 20% by weight or less, more preferably 10% by weight or less.

Examples of the polyfunctional polymerizable compound include bifunctional (meth) acrylate and polyfunctional (meth) acrylate.
Examples of the bifunctional (meth) acrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, 1,6-hexanediol di (Meth) acrylate, (ethoxy (or propoxy)) 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,1
0-decanediol di (meth) acrylate ethoxylated 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) Acrylate, tetraethylene glycol di (meth) acrylate, 2-n-butyl-2-ethyl-1,3
-Propanediol di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, ethoxylated tripropylene glycol di (meta ) Acrylate, neopentyl glycol modified trimethylolpropane di (meth) acrylate, stearic acid modified pentaerythritol di (meth) acrylate, neopentyl glycol oligo (meth) acrylate, dicyclopentanyl di (meth) acrylate, 1,4- Butanediol oligo (meth) acrylate, 1,6-hexanediol oligo (meth) acrylate, ethoxylated neopentyl glycol di (meth) acrylate, propoxylated neopen Diglycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, bisphenol A di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, propoxylated bisphenol A di (meth) acrylate, ethoxylated bisphenol A di (meth) acrylate, bisphenol F di (meth) acrylate, ethoxylated bisphenol F di (meth) acrylate, propoxylated bisphenol F di (meth) acrylate, cyclohexanedimethanol di (
Examples include meth) acrylate, dimethylol dicyclopentane di (meth) acrylate, isocyanuric acid di (meth) acrylate, and propoxylated isocyanuric acid di (meth) acrylate.

As polyfunctional (meth) acrylate, for example,
Trimethylolpropane tri (meth) acrylate, hydroxypivalic acid trimethylolpropane tri (meth) acrylate, ethoxylated phosphoric acid tri (meth) acrylate, pentaerythritol tri (meth) acrylate, tetramethylolpropane tri (meth)
Acrylate, tetramethylol methane tri (meth) acrylate, caprolactone modified trimethylol propane tri (meth) acrylate, propoxylate glyceryl tri (
(Meth) acrylate, trimethylolpropane oligo (meth) acrylate, ethoxylated trimethylolpropane tri (meth) acrylate, propoxylated trimethylolpropane tri (meth) acrylate, ethoxylated isocyanuric acid tri (meth) acrylate, caprolactone modified tris- ( 2-acryloxyethyl) isocyanurate, tri (2-hydroxyethyl isocyanurate) tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, tetramethylolpropane tetra (meth) acrylate, tetramethylolmethane tetra (meth) acrylate, Ethoxylated pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol hydroxype Data (meth) acrylate, dipentaerythritol hexa (meth) acrylate, caprolactone-modified dipentaerythritol hexa (meth) acrylate, ethoxylated dipentaerythritol hexa (meth) acrylate, tripentaerythritol (meth) acrylate.

Of the polyfunctional polymerizable compounds, bifunctional or higher polyfunctional (meth) acrylates having no aromatic ring are preferable. For example, dipentaerythritol hexaacrylate is preferable in terms of curability, and 1,9-nonanediol diacrylate, 1 from the viewpoint of ink viscosity and odor.
, 10-decanediol diacrylate is preferred. The content in these inks is preferably 20% by weight or less, more preferably 10% by weight or less in the ink from the viewpoint of ink odor, curability, image quality, and initiator solubility.

In order to impart resistance to printed matter, oligomers and prepolymers can also be used in the ink composition of the present invention.

<solvent>
The ink composition of the present invention may contain an organic solvent in order to reduce the viscosity and improve the wetting and spreading property to the printing substrate.

Organic solvents include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl Ether acetate, ethylene glycol monomethyl ether propionate, ethylene glycol monoethyl ether propionate, ethylene glycol monobutyl ether propionate, diethylene glycol monomethyl ether propionate, diethylene glycol monoethyl ether pro ONATE, diethylene glycol monobutyl ether propionate, propylene glycol monomethyl ether propionate, dipropylene glycol monomethyl ether propionate, ethylene glycol monomethyl ether butyrate, ethylene glycol monoethyl ether butyrate, ethylene glycol monobutyl ether butyrate, diethylene glycol monomethyl Glycol monoacetates such as ether butyrate, diethylene glycol monoethyl ether butyrate, diethylene glycol monobutyl ether butyrate, propylene glycol monomethyl ether butyrate, dipropylene glycol monomethyl ether butyrate,
Ethylene glycol diacetate, diethylene glycol diacetate, propylene glycol diacetate, dipropylene glycol diacetate, ethylene glycol acetate propionate, ethylene glycol acetate butyrate, ethylene glycol propionate butyrate, ethylene glycol dipropionate, ethylene glycol acetate Dibutyrate, diethylene glycol acetate propionate, diethylene glycol acetate butyrate, diethylene glycol propionate butyrate, diethylene glycol dipropionate, diethylene glycol acetate dibutyrate,
Propylene glycol acetate propionate, propylene glycol acetate butyrate, propylene glycol propionate butyrate, propylene glycol dipropionate, propylene glycol acetate dibutyrate, dipropylene glycol acetate propionate, dipropylene glycol acetate butyrate, dipropylene Glycol diacetates such as glycol propionate butyrate, dipropylene glycol dipropionate, dipropylene glycol acetate dibutyrate,
Glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol,
Ethylene glycol monobutyl ether, propylene glycol monomethyl ether,
Propylene glycol monobutyl ether, diethylene glycol monoethyl ether,
Diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, propylene glycol n-propyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol Propylene glycol monomethyl ether, tetraethylene glycol monobutyryl ether,
Diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol-di-n-propyl ether, diethylene glycol-di-iso-
Glycols such as propyl ether, diethylene glycol dibutyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol ethyl methyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol ethyl methyl ether Ethers,
Examples thereof include lactic acid esters such as methyl lactate, ethyl lactate, propyl lactate, and butyl lactate.

Among the organic solvents, glycol ethers are preferable, and tetraethylene glycol dimethyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol diethyl ether, and diethylene glycol methyl ethyl ether are particularly preferable.
The (poly) ethylene glycol and (poly) propylene glycol skeletons of glycol ethers improve the reactivity of 2- (2-vinyloxyethoxy) ethyl acrylate, which is a polymerizable monomer, and the coating film has excellent curability. Excellent in curing wrinkles. Further, the ink viscosity becomes low, the discharge stability is excellent, and a good image quality is obtained.

The organic solvent is preferably contained in the ink in an amount of 0.01 to 5% by weight, more preferably 0.1 to 3% by weight.

<Pigment dispersant>
In the present invention, it is preferable to add a pigment dispersant in order to improve the dispersibility of the pigment and the storage stability of the ink composition. Examples of the pigment dispersant include a hydroxyl group-containing carboxylic acid ester, a salt of a long chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylic acid, a salt of a long chain polyaminoamide and a polar acid ester, a high molecular weight unsaturated acid ester, Polymer copolymer,
Modified polyurethane, modified polyacrylate, polyether ester type anionic activator,
Naphthalenesulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene nonylphenyl ether,
Stearylamine acetate or the like can be used.
Among these, from the viewpoint of dispersion stability of the pigment, 0.1% by weight to 10% by weight in the ink is preferable.

Specific examples of the dispersant include “Anti-Terra-U (polyaminoamide phosphate)”, “Anti-Terra-203 / 204 (high molecular weight polycarboxylate)”, “Disperbyk-101” (polyamino) manufactured by BYK Chemie. Amide phosphate and acid ester), 107 (hydroxyl group-containing carboxylic acid ester), 110, 111 (copolymer containing acid group), 130 (polyamide), 161, 162, 163, 164, 165, 166, 1
70 (polymer copolymer) "," 400 "," Bykumen "(high molecular weight unsaturated acid ester)," BYK-P104, P105 (high molecular weight unsaturated acid polycarboxylic acid) "," P10
4S, 240S (high molecular weight unsaturated acid polycarboxylic acid and silicon system) "," Lactimo
n (long chain amine, unsaturated acid polycarboxylic acid and silicon) ".

In addition, “Efka 44, 46, 47, 48, 49, 5” manufactured by Efka CHEMICALS
4, 63, 64, 65, 66, 71, 701, 764, 766, 7701 "," Efka polymer 100 (modified polyacrylate), 150 (aliphatic modified polymer) ", 400, 4
01, 402, 403, 450, 451, 452, 453 (modified polyacrylate), 7
45 (copper phthalocyanine series) ”,“ Floren TG-710 (urethane oligomer) ”,“ Flonon SH-290, SP-1000 ”,“ Polyflow No. 50 ”manufactured by Kyoeisha Chemical Co., Ltd.
E, No. 300 (acrylic copolymer) ”,“ Disparon KS-86, manufactured by Enomoto Kasei Co., Ltd.
0, 873SN, 874 (polymer dispersant), # 2150 (aliphatic polycarboxylic acid), # 7
004 (polyether ester type) ".

Furthermore, “Demol RN, N (Naphthalenesulfonic acid formalin condensate sodium salt), MS, C, SN-B (aromatic sulfonic acid formalin condensate sodium salt), E, manufactured by Kao Corporation.
P ”,“ Homogenol L-18 (polycarboxylic acid type polymer), “Emulgen 920, 93
0, 931, 935, 950, 985 (polyoxyethylene nonylphenyl ether),
"Acetamine 24 (coconut amine acetate), 86 (stearylamine acetate)", "Lubrizol""Solsperse 5000 (phthalocyanine ammonium salt system)
13,940 (polyesteramine type), 17000 (fatty acid amine type), 24000G
R, 32000, 33000, 35000, 39000, 41000, 53000, J1
80 (polyethyleneimine-based basic dispersant) ", Nikko Chemical's" Nikkor T10 "
6 (polyoxyethylene sorbitan monooleate), MYS-IEX (polyoxyethylene monostearate), Hexagline 4-0 (hexaglyceryl tetraoleate), “Ajisper PB821, 822, 824, 827, 7” manufactured by Ajinomoto Fine Techno Co., Ltd.
11 (basic functional group-containing copolymer) "," TEGODisper6 "manufactured by Tego Chemi Service Co., Ltd.
85 "and the like.

Among them, a pigment dispersant having a basic functional group is preferable, for example, Solsperse 24000.
GR, 32000, 33000, 35000, 39000, 41000, 53000, J
180, Addisper PB821, 822, 824, 827, 711.

  The dispersant is preferably contained in the ink composition in an amount of 0.01 to 10% by weight.

In order to further improve the dispersibility of the pigment and the storage stability of the ink composition, it is preferable to add an acidic derivative of an organic pigment to the ink composition of the present invention when the pigment is dispersed.
The pigment derivative is a compound obtained by introducing an organic pigment as a base skeleton and introducing a substituent such as a sulfonic acid, a sulfonamide group, an aminomethyl group, or a phthalimidomethyl group into a side chain, or a metal salt compound.

<Surface tension modifier>
The present invention can include a surface tension modifier.
Examples of the surface tension adjusting agent include a silicon-based surface tension adjusting agent, a fluorine-based surface tension adjusting agent, an acrylic surface tension adjusting agent, and an acetylene glycol-based surface tension adjusting agent.
From the viewpoint of the ability to lower the surface tension and compatibility with the polymerizable monomer, it is preferable to use a silicon-based surface preparation agent.

Specific examples of the silicon-based surface tension adjusting agent include a modified dimethylsiloxane skeleton, and among them, a polyether-modified siloxane-based surface tension adjusting agent is preferable. Polyether refers to, for example, polyethylene oxide and polypropylene oxide. As a general product, a representative product from BYK (registered trademark) -378, 348, 349, etc. from BYK Chemie, a polyether-modified polydimethylsiloxane, such as BYK-UV3500, UV3510, from Evonik Degussa, TEGO (registered trademark) GL
Polyether-modified silicone surfactants such as polyether-modified siloxane copolymers such as IDE 450, 440, 435, 432, 410, 406, 130, 110, and 100 can be preferably used. Among these, from the viewpoint of good image quality formation, BYK-378,
348, TEGO GLIDE 450, 440, 432, 410 and the like, polyether-modified silicon-based surface tension modifiers are preferred.

The content of the silicon-based surface tension modifier is 0.5% by weight or more with respect to the total weight of the ink,
The range of less than 5.0% by weight is preferable, and 1.0% by weight or more and less than 5% by weight is more preferable.
By setting the content to 0.5% by weight or more, the wettability of the ink to the base material can be improved. Therefore, even when the discharge amount is small, sufficient solid filling property can be secured, and as a result, the color density is improved. On the other hand, the storage stability of ink can be ensured by making the content less than 5.0% by weight.

<Ink production method>
When a pigment is contained in the ink composition of the present invention, a polymerizable compound, a pigment dispersant, a pigment, and additives are dispersed in advance using a normal dispersing machine such as a sand mill, and a concentrated solution containing the pigment in a high concentration. Is preferably diluted with the remaining polymerizable compound. By this method, sufficient dispersion is possible even with dispersion by a normal disperser, and since excessive dispersion energy is not required and a large amount of dispersion time is not required, the raw material is not altered during dispersion and stable. An ink composition having excellent properties can be produced.

About the ink composition of this invention, in order to improve printability and printed matter tolerance, additives, such as a surface tension regulator, a leveling agent, a ultraviolet absorber, and antioxidant, can be used as needed.

When the ink composition of the present invention contains a polymerizable compound, a stabilizer, a photopolymerization initiator, an additive, and a colorant, the above pigment concentrate is added and mixed to dissolve the photopolymerization initiator. It is manufactured by. At this time, in order to prevent clogging at the head, after dissolution of the photopolymerization initiator,
It is preferable to filter with a filter having a pore size of 3 μm or less, preferably 1 μm or less.

In the ink composition of the present invention, the viscosity at 25 ° C. is preferably adjusted to 5 to 50 mPa · s, and more preferably 5 to 30 mPa · s. If it is this viscosity area | region, the stable discharge characteristic will be shown also in the high frequency head of 10-50 KHz especially from the head which has a frequency of normal 5-30 KHz. Here, when the viscosity is less than 5 mPa · s, a decrease in the followability of the discharge is recognized in the high-frequency head, and when it exceeds 50 mPa · s, the discharge is performed even if a mechanism for reducing the viscosity by heating is incorporated in the head. As a result, the stability of the discharge becomes poor and the discharge becomes impossible at all.

<Recording method>
In order to use the ink composition of the present invention, the ink composition is first supplied to a printer head of a printer for an ink jet recording system, discharged from the printer head onto a substrate, and then activated energy such as ultraviolet rays or electron beams. Irradiate the line. As a result, the ink composition on the printing medium is quickly cured.

In addition, when irradiating ultraviolet rays as a light source of active energy rays, for example, a high-pressure mercury lamp,
Metal halide lamps, low pressure mercury lamps, ultra high pressure mercury lamps, ultraviolet lasers, gallium lamps, LEDs, and sunlight can be used.

The ultraviolet light is preferably in the range of 350 nm to 450 nm.
The irradiation amount of ultraviolet rays, 10 mJ / cm ² or more, preferably at 10000 mJ / cm ² or less. In particular, the ink-jet ink of the present invention includes 3 to 7 parts by weight of a photopolymerization initiator with respect to 1 part by weight of the pigment, and the solubility of the photopolymerization initiator is good. It can be cured sufficiently.
Therefore, sufficient curability can be obtained by using either a metal halide lamp or an LED lamp which is generally widely used.

<recoding media>
Although there is no limitation in particular about the printing base material used by this invention, Plastic base materials, such as a polycarbonate, a hard vinyl chloride, a soft vinyl chloride, a polystyrene, a foamed polystyrene, PMMA, a polypropylene, polyethylene, PET, these mixed or modified goods, a fine paper And paper base materials such as art paper, coated paper and cast coated paper, and metal base materials such as glass and stainless steel.

The ink composition of the present invention can obtain sufficient color density (OD value) and curability even with a thin film. Therefore, it can be used not only for general non-penetrating base materials such as plastic but also for penetrating base materials such as paper and wood. In particular, a plastic substrate such as PET, fine paper, and coated paper are preferable.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the embodiments of the present invention are not limited to these examples. In the following, all parts represent parts by weight. The detailed conditions of the following Examples and Comparative Examples are shown in Table 1 below, and the results are shown in Table 2.

The components used in Examples and Comparative Examples are as follows.
・ Black pigment: Carbon black (“Special Bla manufactured by Evonik Degussa)
ck 350 ")
Cyan pigment: Pigment Blue 15: 3 (“Lio” manufactured by Toyo Color Co., Ltd.)
nol Blue 7351 ")
-Magenta pigment: Pigment Red 122 (manufactured by Clariant, "Host
aperm Pink E ")
Pigment dispersant: Lubrizol, basic pigment dispersion resin “Solsperse 32000”
VEEA: 2- (2-vinyloxyethoxy) ethyl acrylate (manufactured by Nippon Shokubai Co., Ltd., “V
EEA ")
・ DPGDA: Dipropylene glycol diacrylate (manufactured by BASF)
PEA: 2-phenoxyethyl acrylate DPHA: dipentaerythritol hexaacrylate (manufactured by Toagosei Co., Ltd.)
TPO: 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (B
ASF "Darocur TPO")
ITX: 2-Isopropylthioxanthone Irg379: 2- (Dimethylamino) -2-[(4-methylphenyl) methyl] -1
-[4- (4-morpholinyl) phenyl] -1-butanone ("IRGACUR" manufactured by BASF
E379 ")
・ DEDG: Diethylene glycol diethyl ether (“DEDG” manufactured by Nippon Emulsifier Co., Ltd.)
・ Phenothiazine: “Phenothiazine” manufactured by Seiko Chemical Co., Ltd.
-TEGO Glide 432: polyether modified polydimethylsiloxane "TEGO Glide 432" manufactured by Evonik
-TEGO Glide 450: Evonik's polyether-modified polydimethylsiloxane "TEGO Glide 450"

(Creation of pigment dispersion)
The material shown in Table 1 was stirred with a high-speed mixer or the like until uniform, and then the obtained mill base was dispersed with a horizontal sand mill for about 1 hour to prepare pigment dispersion 1.

  In the same manner, pigment dispersions 2 to 3 listed in Table 1 were obtained.

[Example 1]
The materials listed in Table 2 were added and mixed with sequential stirring, mixed gently until the photopolymerization initiator was dissolved, then filtered through a membrane filter with a pore size of 1 μm to remove coarse particles, and the inkjet ink Got.

[Examples 2 to 18 and Comparative Examples 1 to 3]
Inkjet inks were prepared as described in Table 2 as in Example 1.

The following evaluation was performed about the obtained ink. The results are shown in Table 2.

[Evaluation item]
(Curing property (Metahara)
Using the ink prepared above, after ejecting onto a substrate under a printing condition of 600 × 600 dpi by an inkjet ejection device equipped with a head (KJ4A) manufactured by Kyocera, one metal halide lamp manufactured by Harrison Toshiba Lighting, 140 W / cm, conveyor speed 25-5
UV curing was performed at 0 m / min and 1 Pass to obtain a cured film. At this time, the film thickness after curing is 6 μm.
The appropriate amount of ink liquid was adjusted to m. When printing was performed at different printing speeds, the degree of curability was judged from the printing speed at which a 100% solid print portion was cured at 1 Pass. Palpate the printed material,
Curing judgment was made when the ink was not attached to the hand. The evaluation criteria are as follows, and 3 or more is considered to have good curability. PET K2411 (manufactured by Lintec) was used as the printing substrate.
5: Curing at 50 m / min 4: Curing at 40 m / min or more and less than 50 m / min 3: Curing at 30 m / min or more and less than 40 m / min 2: Curing at 20 m / min or more and less than 30 m / min 1:10 m Does not cure at / min

(Curing property (LED))
In the above-described evaluation of sclerosis (meta-harassment), a metal halide lamp manufactured by Integration Technology Co., Ltd., LED lamp (385 nm, integrated light quantity at 10 m / sec, 566 mW / c)
Change in m ^2), it was evaluated in the same manner as the curable (Metahara) evaluation.

(Cured wrinkles)
Evaluation was performed under the conditions of 600 × 600 dpi, 100% solid printing, and a conveyor speed of 30 m / min using the same apparatus and base material as those for the above-described curable evaluation.

(Curing wrinkle evaluation)
The score was given visually from the following viewpoints. Three or more are acceptable.
5: There is no hardening wrinkle and it is glossy.
4: The area where hardening wrinkles are generated is 10% or less.
3: The area where hardened wrinkles are generated is 10% or more and less than 20%.
2: Curing wrinkles are generated in an area of 20% or more.

(Film thickness 6μm concentration)
The OD value of the cured film prepared during the above-described curability evaluation test was measured using X-Rite, Inc. X-R made by
Using ite 500 series, arbitrary 5 locations of 100% solid print portion were measured under the condition of status G, and the average value was obtained.

From Examples 1-7 and Comparative Examples 1-3, the pigment is 4.
It was found that an active energy ray-curable inkjet ink having a high concentration and high curability can be provided by containing 0% by mass or more and containing 60% by mass or more of carbon black in the total weight of the pigment.

From Examples 7-12, it turned out that the active energy ray curable inkjet ink which has a high concentration and high curability can be provided by containing 3-7 weight part of polymerization initiator with respect to 1 weight part of pigment.

From Examples 13 to 14, curable and cured even when a monofunctional or trifunctional or higher polyfunctional monomer is contained in addition to 2- (vinyloxyethoxy) ethyl acrylate and dipropylene glycol diacrylate as polymerizable monomers. It has been found that a high-concentration active energy ray-curable ink-jet ink can be provided without significantly damaging wrinkles. In particular, when a polyfunctional monomer is contained, curability and curing wrinkle are good.

From Examples 15 to 17, it was found that a high-concentration active energy ray-curable ink-jet ink can be provided without extremely impairing curability and curing wrinkles even when a solvent or resin is contained as an additive.

From Example 1 and Example 18, it was found that by including 1.0% by weight or more of the surface tension adjusting agent in the ink, the wet spreadability of the ink with respect to the base material was improved and a high OD value could be obtained.

As described above, the present invention can provide an active energy ray-curable inkjet ink having a high concentration and high curability.

Claims (6)

An active energy ray-curable inkjet ink containing a pigment, a photopolymerization initiator, and a polymerizable monomer,
The pigment is contained in an amount of 4.0% by mass or more based on the total weight of the inkjet ink,
Containing 60% by weight or more of carbon black with respect to the total weight of the pigment,
The photopolymerization initiator includes an acylphosphine oxide photopolymerization initiator, a thioxanthone photopolymerization initiator, and an α-aminoalkylketone photopolymerization initiator,
The content of the photopolymerization initiator is 3 to 7 parts by weight with respect to 1 part by weight of the pigment,
The polymerizable monomer comprises 2- (2-vinyloxyethoxy) ethyl acrylate and dipropylene glycol diacrylate;
An active energy ray-curable ink jet ink having an OD value of 1.9 or more when an average film thickness upon curing is 6 μm. A sill phosphine oxide-based photopolymerization initiator, an active energy ray curable ink-jet ink according to claim 1, characterized in that it comprises 2.1 to 4.5 parts by weight relative to the pigment 1 part by weight. Chi Okisanton based photopolymerization initiator, the pigment 1 part by weight, the active energy ray curable ink-jet ink according to claim 1 or 2, characterized in that it comprises from 0.65 to 1.5 parts by weight. The active energy ray-curable inkjet according to any one of claims 1 to 3, wherein the α -aminoalkylketone photopolymerization initiator contains 0.45 to 1.0 part by weight with respect to 1 part by weight of the pigment. ink. The total amount of A acrylic acid 2- (2-vinyloxy ethoxy) ethyl and dipropylene glycol diacrylate, any claims 1 to 4, characterized in that the polymerizable monomer 100 parts by weight in 60 parts by weight or more The active energy ray-curable inkjet ink described. The active energy ray-curable inkjet ink according to any one of claims 1 to 5, further comprising 1.0% by weight or more of a silicon-based surface tension adjusting agent in the inkjet ink.