JP2017101245A - Ultraviolet-curable ink composition for ink jet recording, ink storage body, and inkjet recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultraviolet-curable ink composition for ink jet recording, an ink storage body that stores the ultraviolet-curable ink composition for ink jet recording, and an inkjet recording device including the ultraviolet-curable ink composition for ink jet recording.SOLUTION: An ultraviolet-curable ink composition for ink jet recording includes a thioxanthone photopolymerization initiator and a hindered amine compound and has a dissolved oxygen content of 20 ppm or less.SELECTED DRAWING: None

Description

  The present invention relates to an ultraviolet curable ink composition for ink jet recording, an ink container containing the ink composition, and an ink jet recording apparatus.

  Conventionally, various methods have been used as a recording method for forming an image on a recording medium such as paper based on an image data signal. Among these, the ink jet system is an inexpensive apparatus, and ink is ejected only to a required image portion to form an image directly on a recording medium. Therefore, the ink can be used efficiently, and the running cost is low. Furthermore, the inkjet method is excellent as a recording method because of its low noise.

  In recent years, an ultraviolet curable ink composition for ink jet recording that cures when irradiated with ultraviolet rays in an ink jet recording method in order to form an image having high water resistance, solvent resistance, scratch resistance, etc. on the surface of a recording medium. Things are being used.

  For example, Patent Document 1 discloses an inkjet ink containing a coloring material, water, and an active energy ray crosslinkable polymer compound, wherein the active energy ray crosslinkable compound has a plurality of side chains in the hydrophilic main chain, Disclosed is an inkjet ink that is a polymer compound that can be cross-linked between side chains by irradiating active energy rays, and the dissolved oxygen concentration in the ink at 25 ° C. is 0.05 ppm or more and 1.8 ppm or less, It is also disclosed that the ink has excellent light-emitting properties, excellent image-rendering gloss, bleed resistance, and scratch resistance (paragraph 0023 of Document 1).

  For example, Patent Document 2 is an ultraviolet curable inkjet ink containing at least a coloring material, an ultraviolet polymerizable compound, and a photopolymerization initiator in an aqueous medium, and the dissolved oxygen concentration in the ink at 25 ° C. An ink-jet ink of 0.1 to 2 ppm is disclosed, and it is also disclosed that stable ejection performance can be obtained even when recording is performed for a long period of time (paragraphs 0017 and 0019 of Document 2).

JP 2007-138070 A JP 2004-196936 A

  However, both the inks disclosed in Patent Documents 1 and 2 have a problem that they are inferior to at least one of curability, storage stability, and ejection stability.

  Accordingly, an object of the present invention is to provide an ultraviolet curable ink composition for ink jet recording excellent in curability, storage stability, and ejection stability.

  Another object of the present invention is to provide an ink container containing the ultraviolet curable ink jet recording ink composition and an ink jet recording apparatus using the ultraviolet curable ink jet recording ink composition.

  The present inventors have intensively studied to solve the above problems. First, the use of a thioxanthone photopolymerization initiator advantageous in terms of solubility, safety, and cost was examined. However, it has been found that when a thioxanthone photopolymerization initiator is used, the ejection stability from the head tends to be significantly inferior when the dissolved oxygen concentration of the ink composition is high. Accordingly, it is conceivable to improve the ejection stability by suppressing the generation of bubbles by setting the dissolved oxygen amount of the ink composition to a predetermined amount or less. However, if the amount of dissolved oxygen in the ink composition is low, the UV ink cannot obtain the effect of suppressing the polymerization (dark reaction) of the ink by oxygen and the storage stability is lowered. Therefore, it has been found that the storage stability can be ensured by further containing a hindered amine polymerization inhibitor in the ink composition. From the above, if the ink composition contains a thioxanthone photopolymerization initiator and a hindered amine compound and has a dissolved oxygen amount (dissolved air amount) reduced to a predetermined value or less by performing a degassing treatment or the like, the above-mentioned problem The present invention has been completed.

That is, the present invention is as follows.
[1]
Containing a thioxanthone photopolymerization initiator and a hindered amine compound,
The amount of dissolved oxygen is 20 ppm or less,
UV-curable ink composition for inkjet recording.
[2]
The ultraviolet curable ink composition for ink jet recording according to [1], wherein the content of the thioxanthone photopolymerization initiator is 0.5 to 4% by mass.
[3]
The ultraviolet curable ink jet recording ink composition according to [1] or [2], wherein the hindered amine compound is a compound having a 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton.
[4]
The ultraviolet ray according to any one of [1] to [3], wherein the thioxanthone photopolymerization initiator includes one or more selected from the group consisting of thioxanthone, diethylthioxanthone, isopropylthioxanthone, and chlorothioxanthone. A curable ink composition for inkjet recording.
[5]
5. The ultraviolet curable ink composition for ink jet recording according to any one of [1] to [4], wherein the thioxanthone photopolymerization initiator includes diethyl thioxanthone.
[6]
The ultraviolet curable ink composition for inkjet recording according to any one of [1] to [5], further comprising an acylphosphine oxide photopolymerization initiator.
[7]
6. The ultraviolet curable ink composition for ink jet recording according to any one of [1] to [6], wherein the dissolved oxygen amount is 5 ppm or more and 20 ppm or less.
[8]
An ink container containing the ultraviolet curable ink composition for ink jet recording according to any one of [1] to [7].
[9]
The oxygen permeability of the constituent material in contact with the ultraviolet ray curable ink jet recording ink composition is 5.0 cc · 20 μm / (m ² · day · atm) or less at 23 ° C. and a relative humidity of 65%. 8].
[10]
The ink composition for ultraviolet curable ink jet recording according to any one of [1] to [7] above is provided with a discharge means for discharging from the head in a state where the dissolved oxygen amount is 20 ppm or less.
Inkjet recording device.

It is a perspective view showing an ink pack which is an example of the ink container of the present invention. It is a figure which shows an example around the head of the inkjet recording device of this invention.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not restrict | limited to the following embodiment, A various deformation | transformation can be implemented within the range of the summary.

  In this specification, “curability” refers to a property of curing in response to light. “Storage stability” refers to the property that the viscosity of an ink composition is difficult to change before and after storage. “Ejection stability” refers to the property of ejecting droplets of a stable ink composition from a nozzle without clogging the nozzle.

  In the present specification, “(meth) acrylate” means at least one of acrylate and its corresponding methacrylate, “(meth) acryl” means at least one of acrylic and its corresponding methacryl, “(Meth) acryloyl” means at least one of acryloyl and methacryloyl corresponding thereto.

[UV-curable ink composition for inkjet recording]
The ultraviolet curable ink composition for ink jet recording of the present embodiment (hereinafter also simply referred to as “ink composition”) contains a thioxanthone photopolymerization initiator and a hindered amine compound, and the dissolved oxygen content is 20 ppm or less. .
Hereinafter, additives (components) that are or can be included in the ink composition of the present embodiment will be described.

[Thioxanthone photopolymerization initiator]
The ink composition of this embodiment includes a thioxanthone photopolymerization initiator that is excellent in solubility, safety, and cost. The thioxanthone photopolymerization initiator 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, and contains a thioxanthone photopolymerization initiator. The curability of the ink composition can be improved. By using ultraviolet rays (UV) among the radiation, the safety is excellent and the cost of the light source lamp can be suppressed.

  Although it does not specifically limit as a thioxanthone type photoinitiator, Specifically, it is preferable that 1 or more types chosen from the group which consists of thioxanthone, diethyl thioxanthone, isopropyl thioxanthone, and chloro thioxanthone is included. Although not particularly limited, 2,4-diethylthioxanthone is preferable as diethylthioxanthone, 2-isopropylthioxanthone is preferable as isopropylthioxanthone, and 2-chlorothioxanthone is preferable as chlorothioxanthone. An ink composition containing such a thioxanthone photopolymerization initiator tends to be more excellent in curability, storage stability, and ejection stability. Among these, a thioxanthone photopolymerization initiator containing diethyl thioxanthone is preferable. By including diethylthioxanthone, there is a tendency that a wide range of ultraviolet light (UV light) can be converted into active species more efficiently.

  Although it does not specifically limit as a commercial item of a thioxanthone type photoinitiator, Specifically, Speedcure DETX (2, 4- diethyl thioxanthone), Speedcure ITX (2-isopropyl thioxanthone) (above, Lambson company make), KAYACURE, DETX-S (2,4-diethylthioxanthone) (manufactured by Nippon Kayaku Co., Ltd.).

  The content of the thioxanthone photopolymerization initiator is preferably 0.5 to 4% by mass and more preferably 1 to 4% by mass with respect to the total mass (100% by mass) of the ink composition. When the content is 0.5% by mass or more, the curability of the ink tends to be further improved. Moreover, it exists in the tendency for the outstanding discharge stability to be more effectively maintained as content is 4 mass% or less. When using a thioxanthone photopolymerization initiator, when the dissolved oxygen concentration of the ink composition is high, the reason why the ejection stability from the head is remarkably inferior is that the thioxanthone photopolymerization initiator exists as fine particles in the ink composition. It is assumed that this particle becomes a bubble nucleus and oxygen dissolved in the ink composition is promoted to appear as bubbles during storage of the ink composition. The cause is not limited to this.

(Other photopolymerization initiators)
The ink composition may further contain other photopolymerization initiator. By using ultraviolet rays (UV) among the radiation, the safety is excellent and the cost of the light source lamp can be suppressed. Other photopolymerization initiators are not limited as long as they generate active species such as radicals and cations by light (ultraviolet) energy and initiate polymerization of the polymerizable compound. Or a cationic photopolymerization initiator, and it is preferable to use a radical photopolymerization initiator.

  The above radical photopolymerization initiator is not particularly limited. For example, aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (such as thiophenyl group-containing compounds), α- Examples include aminoalkylphenone compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon halogen bond, and alkylamine compounds.

  Among these, it is preferable that an acylphosphine oxide photopolymerization initiator (acylphosphine oxide compound) is further included. By the combination of the acylphosphine oxide photopolymerization initiator and the thioxanthone photopolymerization initiator, the curing process by UV-LED is excellent, and the curability of the ink composition tends to be further excellent.

  Although it does not specifically limit as an acylphosphine oxide type photoinitiator, Specifically, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide And bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide.

  Although it does not specifically limit as a commercial item of an acyl phosphine oxide type photoinitiator, For example, IRGACURE 819 (bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide), DAROCUR TPO (2,4,6-) Trimethylbenzoyl-diphenyl-phosphine oxide) and the like.

  Although it does not specifically limit as radical photopolymerization initiator, For example, acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, tria Phenylamine, carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, Michler's ketone, benzoinpropyl ether, benzoin ethyl ether, benzyldimethyl ketal, 1- (4- Isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, and - like-1-one - methyl-1- [4- (methylthio) phenyl] -2-morpholino.

  Although it does not specifically limit as a commercial item of radical photopolymerization initiator, For example, IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethane-1-one), IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-) Ketone), DAROCUR 1173 (2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959 (1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl -1-propan-1-one), IRGACURE 127 (2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl} -2-methyl-propane-1- ON}, IRGACURE 907 (2-methyl-1- (4-methylthiol Nyl) -2-morpholinopropan-1-one), IRGACURE 369 (2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1), IRGACURE 379 (2- (dimethylamino) -2-[(4-methylphenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone), IRGACURE 784 (bis (η5-2,4-cyclopentadien-1-yl)- Bis (2,6-difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium), IRGACURE OXE 01 (1.2-octanedione, 1- [4- (phenylthio)-, 2- (O -Benzoyloxime)]), IRGACURE OXE 02 (ethanone, 1- [9-ethyl-6- (2-methylbenzoy) ) -9H-carbazol-3-yl]-, 1- (O-acetyloxime)), IRGACURE 754 (oxyphenylacetic acid, 2- [2-oxo-2-phenylacetoxyethoxy] ethyl ester and oxyphenylacetic acid, 2 -(2-hydroxyethoxy) ethyl ester mixture (above, BASF), Speedcure TPO (above, Lambson), Lucirin TPO, LR8883, LR8970 (above, BASF), and Ubekrill P36 (UCB) Manufactured).

  Although it does not specifically limit as a cationic polymerization initiator, Specifically, a sulfonium salt, an iodonium salt, etc. are mentioned.

  Although it does not specifically limit as a commercial item of a cationic polymerization initiator, Specifically, Irgacure250, Irgacure270, etc. are mentioned.

  The said photoinitiator may be used individually by 1 type, and may be used in combination of 2 or more type.

  The content of the photopolymerization initiator is preferably 5 to 20% by mass with respect to the total mass (100% by mass) of the ink composition. When the content is within this range, the ultraviolet curing rate can be sufficiently exerted, and the undissolved portion of the photopolymerization initiator and coloring derived from the photopolymerization initiator can be avoided.

[Hindered amine compounds]
The ink composition of this embodiment contains a hindered amine compound. In general, the lower the amount of dissolved oxygen in the ultraviolet curable ink composition, the lower the storage stability because the effect of suppressing the polymerization (dark reaction) of the ink by oxygen is less likely to be obtained. However, the storage stability of the ink composition can be ensured by including a hindered amine polymerization inhibitor in the ink composition even when the amount of dissolved oxygen is low.

  Examples of the hindered amine compound include, but are not limited to, for example, a compound having a 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton, and a compound having a 2,2,6,6-tetramethylpiperidine skeleton. , A compound having a 2,2,6,6-tetramethylpiperidine-N-alkyl skeleton, a compound having a 2,2,6,6-tetramethylpiperidine-N-acyl skeleton, and the like.

  As a commercial product of a hindered amine compound, ADK STAB LA-7RD (2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl) (trade name, manufactured by ADEKA), IRGASTAB UV 10 (4,4 ′-[ 1,10-dioxo-1,10-decandiyl) bis (oxy)] bis [2,2,6,6-tetramethyl] -1-piperidinyloxy) (CAS. 2516-92-9), TINUVIN 123 (4-hydroxy-2,2,6,6, -tetramethylpiperidine-N-oxyl) (above, trade name manufactured by BASF), FA-711HM, FA-712HM (2,2,6,6-tetramethyl) Piperidinyl methacrylate, trade name manufactured by Hitachi Chemical Company, Ltd.), TI UVIN 111FDL, TINUVIN 144, TINUVIN 152, TINUVIN 292, TINUVIN 765, TINUVIN 770DF, TINUVIN 5100, SANOL LS-2626, CHIMASSORB 119FL, CHIMASSOLV 2020 FDL, CHIMASSODL6 44 LA-52, LA-57, LA-62, LA-63P, LA-68LD, LA-77Y, LA-77G, LA-81, LA-82 (1,2,2,6,6-pentamethyl-4- Piperidyl methacrylate), LA-87 (above, trade name of ADEKA).

  Of the above-mentioned commercially available products, LA-82 is a compound having a 2,2,6,6-tetramethylpiperidine-N-methyl skeleton, and Adekastab LA-7RD and IRGASTAB UV 10 are 2,2,6, It is a compound having a 6-tetramethylpiperidine-N-oxyl skeleton.

  Among these, a compound having a 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton is preferable because the storage stability of the ink can be further improved while maintaining excellent curability. .

  Specific examples of the compound having the above 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton include, but are not limited to, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1- Oxyl, 4,4 ′-[1,10-dioxo-1,10-decandiyl) bis (oxy)] bis [2,2,6,6-tetramethyl] -1-piperidinyloxy, 4-hydroxy- 2,2,6,6, -tetramethylpiperidine-N-oxyl, bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, bis (2,2) decanedioate , 6,6-tetramethyl-1- (octyloxy) -4-piperidinyl) ester.

  A hindered amine compound may be used individually by 1 type, and may be used in combination of 2 or more type.

  The content of the hindered amine compound is preferably 0.05 to 0.5% by mass and more preferably 0.1 to 0.5% by mass with respect to the total mass (100% by mass) of the ink composition. When the content is 0.05% by mass or more, the storage stability of the ink can be further improved, and when the content is 0.1% by mass or more, the storage stability of the ink is further improved. It can be excellent. Moreover, it exists in the tendency which is more excellent in sclerosis | hardenability as content is 0.5 mass% or less.

(Other polymerization inhibitors)
The ink composition of this embodiment may further contain a polymerization inhibitor other than a hindered amine compound. Other polymerization inhibitors include, but are not limited to, for example, p-methoxyphenol, hydroquinone monomethyl ether (MEHQ), hydroquinone, cresol, t-butylcatechol, 3,5-di-t-butyl-4-hydroxytoluene 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 2,2′-methylenebis (4-ethyl-6-butylphenol), and 4,4′-thiobis (3-methyl-6-t) -Butylphenol).

  Another polymerization inhibitor may be used individually by 1 type, and may be used in combination of 2 or more type. The content of other polymerization inhibitors is not particularly limited because it depends on the relationship with the content of other components.

[Amount of dissolved oxygen]
The ink composition in the present embodiment has a dissolved oxygen content of 20 ppm or less. In an ink composition containing a thioxanthone photopolymerization initiator, the thioxanthone photopolymerization initiator is present as fine particles in the ink, so that the particles become bubble nuclei, and the oxygen dissolved in the ink is absorbed in the ink. Appears as bubbles during storage. However, when the dissolved oxygen concentration is 20 ppm or less, even if a thioxanthone-based photopolymerization initiator is included, the generation of bubbles is suppressed, and the discharge stability is improved. The amount of dissolved oxygen can be reduced to 20 ppm or less by treatment such as deaeration.

  The ink composition in the present embodiment is excellent in ejection stability and can be suitably used for an ink jet recording apparatus. Note that the amount of dissolved oxygen may increase because air dissolves in the ink as it passes through the ink flow path in the ink jet recording apparatus. However, in the present embodiment, since the dissolved oxygen content of the ink composition is 20 ppm or less, the dissolved oxygen content can be kept low even if the air dissolves into the ink when the ink passes through the ink flow path. As a result, it is possible to obtain an ink composition having excellent ejection stability and curability when recording is performed by filling the ink from the ink container into the ink jet recording apparatus.

  Moreover, 1-20 ppm is preferable, as for the said dissolved oxygen amount, 3-20 ppm is more preferable, and 5-20 ppm is further more preferable. In particular, when the amount of dissolved oxygen is 1 ppm or more, preferably 5 ppm or more, the polymerization of the polymerizable compound is further inhibited, so that the storage stability tends to be superior. The ink composition of the present embodiment includes the above-mentioned hindered amine compound as a polymerization inhibitor and has a dissolved oxygen amount within a predetermined range, so that the storage stability is extremely excellent.

Here, the “dissolved oxygen amount” in the present specification may be at least within the above predetermined range when the ink composition is filled in the ink jet recording apparatus. More specifically, during a period when the dissolved oxygen amount needs to be within the predetermined range, the ink container or the ink composition in the container is recorded after the ink container containing the ink composition is shipped. Until just before installation, filling or use of the device. Further, in the case of a recording apparatus provided with a deaeration mechanism, the amount of dissolved oxygen can be reduced in the recording apparatus. However, even in this case, there is a limit to the deaeration capability, so the amount of dissolved oxygen in the ink container is preferably within the above range. On the other hand, in the case of a recording apparatus in which the amount of dissolved oxygen does not change (almost) in the recording apparatus, even if the recording apparatus is not equipped with a deaeration mechanism, at least the amount of dissolved oxygen in the ink container is determined. It may be within the above range.
In addition, although the dissolved oxygen amount in this specification can be measured by a conventionally well-known method, the value obtained by the measuring method implemented in the below-mentioned Example shall be employ | adopted for convenience.

  Here, when treatment such as deaeration is not performed for the purpose of reducing the amount of dissolved oxygen, the amount of dissolved oxygen in the ink composition is usually about 50 to 60 ppm. Therefore, a treatment such as deaeration is required to make the dissolved oxygen amount 20 ppm or less. Examples of the treatment include, but are not limited to, a method using a deaeration mechanism and bubbling of an inert gas.

(Polymerizable compound)
The ink composition may contain a polymerizable compound. The polymerizable compound can be polymerized at the time of light irradiation alone or by the action of a photopolymerization initiator to cure the printed ink composition. The polymerizable compound is not particularly limited, and specifically, conventionally known monofunctional, bifunctional, and trifunctional or higher polyfunctional monomers and oligomers can be used. A polymeric compound may be used individually by 1 type, and may be used in combination of 2 or more type. Hereinafter, these polymerizable compounds will be exemplified.

  The monofunctional, bifunctional, and trifunctional or higher polyfunctional monomers are not particularly limited, and examples thereof include unsaturated carboxylic acids such as (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid; Unsaturated carboxylic acid salts; esters, urethanes, amides and anhydrides of the unsaturated carboxylic acids; acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Examples of monofunctional, bifunctional, and trifunctional or higher polyfunctional oligomers include, for example, oligomers formed from the above monomers such as linear acrylic oligomers, epoxy (meth) acrylates, oxetane (meth) acrylates, and fats. Group urethane (meth) acrylate, aromatic urethane (meth) acrylate and polyester (meth) acrylate.

  Moreover, an N-vinyl compound may be included as another monofunctional monomer or polyfunctional monomer. The N-vinyl compound is not particularly limited, and examples thereof include N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, and derivatives thereof. Can be mentioned.

  Of the polymerizable compounds, esters of (meth) acrylic acid, that is, (meth) acrylates are preferred.

  Although it does not specifically limit as monofunctional (meth) acrylate, For example, isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomyristyl (meta) ) Acrylate, isostearyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) acrylate , Methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate, tetra Drofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, lactone-modified flexibility (meta ) Acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate, and dicyclopentenyloxyethyl (meth) acrylate. Among these, phenoxyethyl (meth) acrylate is preferable.

  The content of the monofunctional (meth) acrylate is preferably 30 to 85% by mass and more preferably 40 to 75% by mass with respect to the total mass (100% by mass) of the ink composition. By setting it as the said preferable range, it exists in the tendency which is excellent with sclerosis | hardenability, initiator solubility, storage stability, and discharge stability.

  Examples of the monofunctional (meth) acrylate include those containing a vinyl ether group. Such monofunctional (meth) acrylates are not particularly limited, and examples thereof include, for example, 2-vinyloxyethyl (meth) acrylate, 3-vinyloxypropyl (meth) acrylate, and 1-methyl-2- (meth) acrylate. Vinyloxyethyl, 2-vinyloxypropyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, 1-methyl-3-vinyloxypropyl (meth) acrylate, 1-vinyloxymethylpropyl (meth) acrylate, ( 2-methyl-3-vinyloxypropyl (meth) acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth) acrylate, 3-vinyloxybutyl (meth) acrylate, 1-methyl-2-vinyl (meth) acrylate Loxypropyl, 2-vinyloxybutyl (meth) acrylate, 4-vinyloyl (meth) acrylate Cycyclohexyl, 6-vinyloxyhexyl (meth) acrylate, 4-vinyloxymethylcyclohexylmethyl (meth) acrylate, 3-vinyloxymethylcyclohexylmethyl (meth) acrylate, 2-vinyloxymethyl (meth) acrylate Cyclohexylmethyl, (meth) acrylic acid p-vinyloxymethylphenylmethyl, (meth) acrylic acid m-vinyloxymethylphenylmethyl, (meth) acrylic acid o-vinyloxymethylphenylmethyl, (meth) acrylic acid 2- ( Vinyloxyethoxy) ethyl, 2- (vinyloxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxy) propyl (meth) acrylate, 2- (vinyloxyethoxy) isopropyl (meth) acrylate, ( 2-methacrylic acid (meth) acrylic acid Poxy) propyl, 2- (vinyloxyisopropoxy) isopropyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) propyl (meth) acrylate, (meth ) 2- (vinyloxyethoxyisopropoxy) propyl acrylate, 2- (vinyloxyisopropoxyethoxy) propyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) propyl (meth) acrylate, (meth) Acrylic acid 2- (vinyloxyethoxyethoxy) Ii) Isopropyl, 2- (vinyloxyethoxyisopropoxy) isopropyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) isopropyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) (meth) acrylate ) Isopropyl, 2- (vinyloxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxy) ethyl (meth) acrylate , 2- (Isopropenoxyethoxyethoxy) ethyl (meth) acrylate, 2- (Isopropenoxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (Isopropenoxyethoxyethoxyethoxyethoxy) acrylate (meth) acrylate ethyl,( Data) Polyethylene glycol monovinyl ether acrylate, and (meth) acrylic acid polypropylene glycol monovinyl ether, phenoxyethyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate. Among these, 2- (vinyloxyethoxy) ethyl (meth) acrylate, phenoxyethyl (meth) acrylate, isobornyl (meth) acrylate, and benzyl (meth) acrylate are preferable.

  Among these, since the viscosity of the ink can be further lowered, the flash point is high, and the curability of the ink is excellent, 2- (vinyloxyethoxy) ethyl (meth) acrylate, that is, 2- (vinyloxy) acrylate At least one of ethoxy) ethyl and 2- (vinyloxyethoxy) ethyl methacrylate is preferable, and 2- (vinyloxyethoxy) ethyl acrylate is more preferable. Since both 2- (vinyloxyethoxy) ethyl acrylate and 2- (vinyloxyethoxy) ethyl methacrylate have a simple structure and a small molecular weight, the viscosity of the ink can be significantly reduced. Examples of 2- (vinyloxyethoxy) ethyl (meth) acrylate include 2- (2-vinyloxyethoxy) ethyl (meth) acrylate and 2- (1-vinyloxyethoxy) ethyl (meth) acrylate. Examples of 2- (vinyloxyethoxy) ethyl acrylate include 2- (2-vinyloxyethoxy) ethyl acrylate and 2- (1-vinyloxyethoxy) ethyl acrylate. Incidentally, 2- (vinyloxyethoxy) ethyl acrylate is superior in terms of curability compared to 2- (vinyloxyethoxy) ethyl methacrylate.

  The vinyl ether group-containing (meth) acrylic acid esters, particularly the content of 2- (vinyloxyethoxy) ethyl (meth) acrylate, is 10 to 70 mass with respect to the total mass (100 mass%) of the ink composition. % Is preferable, and 30 to 50% by mass is more preferable. When the content is 10% by mass or more, the viscosity of the ink can be reduced and the curability of the ink can be further improved. On the other hand, when the content is 70% by mass or less, the storage stability of the ink can be maintained in an excellent state.

  Among the (meth) acrylates, examples of the bifunctional (meth) acrylate include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and dipropylene glycol di ( (Meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonane Di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, EO (ethylene oxide) adduct di (meth) acrylate of bisphenol A Bisphenol A PO (propylene oxide) adduct di (meth) acrylate, hydroxypivalate neopentyl glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol Examples thereof include di (meth) acrylate and trifunctional or higher functional (meth) acrylate having a pentaerythritol skeleton or a dipentaerythritol skeleton. Among these, dipropylene glycol di (meth) acrylate is preferable. Among them, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, pentaerythritol skeleton or dipentaerythritol skeleton having 3 or more functional groups (Meth) acrylate is preferred. More preferably, the ink composition contains polyfunctional (meth) acrylate in addition to monofunctional (meth) acrylate.

  The content of the bifunctional or higher polyfunctional (meth) acrylate is preferably 5 to 60% by mass and preferably 15 to 60% by mass with respect to the total mass (100% by mass) of the ink composition. More preferably, it is 20-50 mass%. By setting it as the said preferable range, it exists in the tendency which is excellent with sclerosis | hardenability, storage stability, and discharge stability.

  Among the above (meth) acrylates, trifunctional or more polyfunctional (meth) acrylates include, for example, trimethylolpropane tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, and pentaerythritol tri (meth) acrylate. , Pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate, cowprolactone modified trimethylolpropane tri (meth) acrylate, pentaerythritol Examples include ethoxytetra (meth) acrylate and caprolactam-modified dipentaerythritol hexa (meth) acrylate.

  Among these, it is preferable that a polymeric compound contains monofunctional (meth) acrylate. In this case, the ink composition has a low viscosity, is excellent in solubility of the photopolymerization initiator and other additives, and is easy to obtain ejection stability during ink jet recording. Furthermore, since the toughness, heat resistance, and chemical resistance of the coating film are increased, it is more preferable to use a monofunctional (meth) acrylate and a bifunctional (meth) acrylate, and among them, phenoxyethyl (meth) acrylate and dipropylene glycol. It is more preferable to use di (meth) acrylate in combination.

  The content of the polymerizable compound is preferably 5 to 95% by mass and more preferably 15 to 90% by mass with respect to the total mass (100% by mass) of the ink composition. When the content of the polymerizable compound is within the above range, the viscosity and odor can be further reduced, and the solubility and reactivity of the photopolymerization initiator can be further improved.

[Color material]
The ink composition may further include a color material. As the color material, at least one of a pigment and a dye can be used.

(Pigment)
By using a pigment as the color material, the light resistance of the ink composition can be improved. As the pigment, both inorganic pigments and organic pigments can be used.

  As the inorganic pigment, carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black and channel black, iron oxide, and titanium oxide can be used.

  Organic pigments include insoluble azo pigments, condensed azo pigments, azo lakes and chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Polycyclic pigments, dye chelates (eg basic dye chelates, acid dye chelates, etc.), dye rakes (basic dye rakes, acid dye rakes), nitro pigments, nitroso pigments, aniline black, daylight A fluorescent pigment is mentioned.

  More specifically, as a carbon black used for black ink, No. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, no. 2200B, etc. (Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. (above, Columbia Carbon, Carbon 1 Rubbi 400, Carbon Co. Rega1 330R, Rega1 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc. (Cabot Corp. CA Kol. , Color B lack FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color B1ack S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A , Special Black 4 (manufactured by Degussa).

  Examples of pigments used in white ink include C.I. I. Pigment white 6, 18, and 21.

  Examples of pigments used in yellow ink include C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172, 180.

  Examples of pigments used in magenta ink include C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C.I. I. Pigment violet 19, 23, 32, 33, 36, 38, 43, 50.

  Examples of pigments used for cyan ink include C.I. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15:34, 15: 4, 16, 18, 22, 25, 60, 65, 66, C.I. I. Bat Blue 4, 60.

  Examples of pigments other than magenta, cyan, and yellow include C.I. I. Pigment green 7,10, C.I. I. Pigment brown 3, 5, 25, 26, C.I. I. Pigment orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63.

  The said pigment may be used individually by 1 type, and may use 2 or more types together.

  When using said pigment, the average particle diameter has preferable 300 nm or less, and 50-200 nm is more preferable. When the average particle diameter is in the above range, the ink composition is more excellent in reliability such as ejection stability and dispersion stability, and an image with excellent image quality can be formed. Here, the average particle diameter in the present specification is measured by a dynamic light scattering method.

(dye)
A dye can be used as the coloring material. The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. Examples of the dye include C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. I. Acid Red 52, 80, 82, 249, 254, 289, C.I. I. Acid Blue 9, 45, 249, C.I. I. Acid Black 1, 2, 24, 94, C.I. I. Food Black 1, 2, C.I. I. Direct Yellow 1,12,24,33,50,55,58,86,132,142,144,173, C.I. I. Direct Red 1,4,9,80,81,225,227, C.I. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. I. Directed Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. I. Reactive Red 14, 32, 55, 79, 249, C.I. I. Reactive black 3, 4, and 35 are mentioned.

  The said dye may be used individually by 1 type, and may use 2 or more types together.

  The content of the color material is preferably 1 to 20% by mass with respect to the total mass (100% by mass) of the ink composition because excellent concealability and color reproducibility are obtained.

[Dispersant]
When the ink composition contains a pigment, it may further contain a dispersant in order to improve pigment dispersibility. Although it does not specifically limit as a dispersing agent, For example, the dispersing agent currently used for preparing pigment dispersion liquids, such as a polymer dispersing agent, is mentioned. Specific examples include polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxies. The thing which has 1 or more types of resin as a main component is mentioned. Commercially available polymer dispersants include Ajinomoto Fine Techno's Ajisper series, Solspers series (Solsperse 36000, etc.) available from Avecia and Noveon, and BYK Chemie's Dispersic series. , Disparon series manufactured by Enomoto Kasei.

[Other additives]
The ink composition may contain additives (components) other than the additives listed above. Such components are not particularly limited, and may include, for example, conventionally known slip agents (surfactants), polymerization accelerators, penetration enhancers, wetting agents (humectants), and other additives. Examples of the other additives include conventionally known fixing agents, antifungal agents, preservatives, antioxidants, ultraviolet absorbers, chelating agents, pH adjusting agents, and thickeners.

[Ink container]
The ink container of the present embodiment contains an ink composition for ultraviolet curable ink jet recording. Examples of the ink container of the present embodiment are not limited to the following, and examples include an ink cartridge, a pack, a bottle, a tank, a bottle, and a can. Among these, ink cartridges, packs, bottles and tanks are preferred, packs are more preferred, and film packs are particularly preferred because they are widely used and the oxygen permeability described below can be easily controlled to a desired value.

  In addition, as a usage mode of the ink container of the present embodiment, (A) a separate body from the recording apparatus, a form such as an ink cartridge that is attached to the recording apparatus and sequentially supplies ink to the recording apparatus, and (B ) Separate from the recording apparatus, and when ink is used, only the ink is transferred from the ink container such as a bottle to the recording apparatus; and (C) a tank or the like that is provided in advance in the recording apparatus and stores the ink; At least.

The above (A) and (B) can be said to be ink containers from when the ink containers are shipped to just before the ink is supplied (transferred) to the recording apparatus. The above (C) can be said to be an ink container from when the recording apparatus is shipped to before the first use of ink in the recording apparatus is started.
Note that the above (A) and (C) can be referred to as an ink container that performs printing on the recording apparatus in a state where ink is supplied from the ink container to the recording apparatus via a connecting portion such as an ink tube. it can.

  The above (B) can be said to be an ink container that performs printing with the recording apparatus after ink is transferred from the ink container to the recording apparatus. In addition, as the target to which the ink is transferred in (B), a tank or the like provided in the recording apparatus can be cited.

  In addition, the constituent material of the ink container is not limited to the following. For example, plastics such as polyethylene terephthalate (PET) and polypropylene (PP), various metals (including alloys), polyethylene, and ethylene vinyl acetate are used. Examples include polymers and polyolefins such as polypropylene. Further, the present invention is not limited thereto, and a polymer obtained by blending or laminating each of the above polymers at an appropriate ratio, a film thereof, or the like may be used.

Among the constituent materials of the ink container, the oxygen permeability (hereinafter simply referred to as “oxygen permeability”) of the constituent material in contact with the ink composition is 5.0 cc · 20 μm / (m ² · day · atm) or less. Is preferably 2.0 cc · 20 μm / (m ² · day · atm) or less. If the oxygen permeability is within the above range, the dissolved oxygen amount of the ink composition being stored tends to be difficult to change. The constituent material or member is not particularly limited. In the case of an ink pack, the film can be heat-sealed (heat sealed) and processed into a bag shape. Examples of the film used for the ink pack include high-density, low-density, or linear low-density polyethylene, polypropylene, an ethylene-vinyl alcohol copolymer, and stretched plastic films such as polystyrene. It is good also as a laminated film which bonded together the film of two or more layers. When the oxygen permeability can be obtained with the above film, the film may be composed only of the film, or the oxygen permeability may be ensured by laminating a gas barrier layer on the film. As the gas barrier layer, a metal layer such as an aluminum layer, an inorganic oxide layer such as a silicon oxide or an aluminum oxide layer may be used, and among the above films, an ethylene-vinyl alcohol copolymer having a low oxygen permeability, polyvinyl Alcohol or the like may be laminated. The total film thickness of the film is preferably 50 μm or more, preferably 70 μm or more, and more preferably 70 to 200 μm. When the film thickness is above, the dissolved oxygen content of the ink composition being stored is unlikely to change, and the strength and flexibility of the pack can be obtained. Among these, a film made of an ethylene-vinyl alcohol copolymer is preferable in terms of low oxygen permeability and excellent strength. In addition, in the case of a container other than a pack, in addition to the above, other synthetic resins, glass, metal and the like can be mentioned.

In this specification, the oxygen permeability is expressed in units of cc · 20 μm / (m ² · day · atm), and the “atm” is a pressure (atm) at 23 ° C. and a relative humidity of 65%. . In addition, the oxygen permeability was determined according to the method defined in ISO 14663-2: 1999 (Annex C), that is, the oxygen permeation rate permeating the film using a coulometric sensor (relative humidity reached an equilibrium state). Sometimes it can be calculated by measuring.

  Although the capacity | capacitance of the ink composition which an ink container can accommodate is not restrict | limited below, 100-2,000 mL is preferable, 100-1,000 mL is more preferable, 200-800 mL is further more preferable. When the capacity is within the above range, all of the curability, storage stability, and ejection stability can be further improved.

  If the volume is within the above range, the ink composition can be used up or stored while the amount of dissolved oxygen in the ink container is almost unchanged after the start of use of the ink container. There are advantageous effects such as the amount of dissolved oxygen of the ink composition hardly changing. Further, it is particularly preferable that the ink container has the oxygen permeability of the member of the ink container and the capacity of the ink composition that can be stored is in the above range. Further, “capacity” in this specification means volume.

  Here, an ink pack which is an example of the ink container of the present embodiment will be described. FIG. 1 is a perspective view showing the ink pack 1. The ink pack 1 includes an ink outlet 2 and a film 10. The material of the film 10 can use the above-mentioned thing. The ink pack 1 may be stored in a box-shaped container (not shown) for protection during transportation. The ink pack 1 can be used as an ink cartridge as in the above-described usage mode (A), but the usage mode of the ink pack 1 is not limited thereto.

  As described above, according to the present embodiment, it is possible to provide an ink container containing an ultraviolet curable ink composition for ink jet recording excellent in all of storage stability, curability, and ejection stability.

[Inkjet recording device]
The ink jet recording apparatus according to the present embodiment includes discharge means for discharging the ultraviolet curable ink jet recording ink composition from the head in a state where the dissolved oxygen amount is 20 ppm or less. In addition to the ejection means, the ink jet recording apparatus can also include a curing means for curing the ink composition ejected on the recording medium by irradiation with ultraviolet rays.

(Discharge means)
The discharging means discharges the ultraviolet curable ink composition for inkjet recording from the head in a state where the dissolved oxygen amount is 20 ppm or less. Hereinafter, although it demonstrates concretely using drawing, a discharge means is not restricted to the following. FIG. 2 is a schematic view showing an example of the periphery of the head of the ink jet recording apparatus of the present embodiment. The sub tank 200 is supplied with ink from an ink cartridge (not shown), and passes through a deaeration module 204, which is an example of a deaeration mechanism, and a heater 220 in order by a pressure pump 202. 100.

  The head 100 ejects ink onto a recording medium (not shown). The pressure adjusting valve 108 is opened by a valve opening actuator 320 to adjust the pressure of ink when supplying ink from the sub tank 200 to the head 100.

  The ink that has passed through the deaeration module 204 flows into the branch joint 106 when the pressure adjustment valve 108 is opened. Inside the branch joint 106, the forward path 214 is branched into a plurality of passages and connected to the plurality of heads 100.

  The ink that has not been ejected from the head 100 is circulated to the sub tank 200 via the integrated joint 210 and the return path 216 in a state where the opening / closing valve 212 is open. By circulating the ink between the sub tank 200 and the head 100, when the ink stays for a long time and the ink components are separated and settled, it can be recovered or the temperature of the circulating ink can be made constant. . When the ink is heated by the heaters 218, 220, and 222, the viscosity decreases, the viscosity becomes suitable for ejection from the head 100, and the ink is ejected from the head 100.

  These devices are provided in the main scanning movement table 64, and main scanning is performed to eject ink from the head 100 to the recording medium while moving with respect to the recording medium together with the main scanning movement table 64.

  In the deaeration module 204, a deaeration chamber (not shown) into which ink flows and a decompression chamber (not shown) in contact with the deaeration chamber through a separation membrane that does not allow a liquid such as ink to pass through such as air. ) And are provided. When the decompression chamber is depressurized by a decompression pump (not shown), bubbles such as oxygen and oxygen dissolved in the ink in the deaeration chamber are released, so there is no contamination of the bubbles. Ink having a dissolved oxygen concentration lower than that of the ink sent to the module 204 can be supplied to the head 100 and discharged from the head 100. The deaeration module 204 of the recording apparatus can continuously deaerate ink while supplying ink from the sub tank 200 to the head 100.

  The above recording apparatus can be configured as shown in FIG. 4 (FIG. 2 of the present specification) of Japanese Patent Application Laid-Open No. 2011-240565, for example. Note that a configuration such as a line printer in which ink is ejected from the head toward the recording medium while the recording medium moves relative to the head without moving the above-described apparatus may be employed. Further, instead of the degassing module continuously degassing the ink as described above, the pressure adjusting valve is closed without providing the separation membrane, and the pressure reducing chamber is depressurized to reduce the ink. And when the deaeration is completed, the decompression chamber is returned to the normal pressure and the pressure adjusting valve 108 is opened to supply the ink to the head alternately. Also good. The former is preferable in that the ink can be continuously deaerated, and the latter is preferable in that the deaeration ability is high.

  Here, when the amount of dissolved oxygen in the ink stored in the ink cartridge is 20 ppm or less, it is preferable that the recording device does not increase the amount of dissolved oxygen in the process of supplying ink. As a result, it is possible to eject ink in a state where the ejection stability is good. On the other hand, even if the recording apparatus increases the amount of dissolved oxygen in the process of supplying ink, the amount of dissolved oxygen can be reduced by providing a degassing module. At this time, if the dissolved oxygen amount of the ink stored in the ink cartridge is 20 ppm or less, the dissolved oxygen amount of the ink is kept at 20 ppm or less even when the deaeration capability of the deaeration module is limited. Can be discharged. The increase in the amount of dissolved oxygen occurs due to the length and material of the supply pipe that supplies the ink in the recording apparatus to the head, the time during which the ink is in the process of supplying ink, the pressurization conditions required for supplying the ink, and the like. Therefore, the ink container of the present embodiment is preferable in terms of the degree of freedom in designing the recording apparatus.

[Recording medium]
A recorded matter is obtained by discharging the ink composition onto a recording medium using the following inkjet recording method. Examples of the recording medium include an absorptive or non-absorbable recording medium. The following inkjet recording methods are widely used for recording media having various absorption performances, from non-absorbing recording media that are difficult to penetrate water-soluble ink compositions to absorbent recording media that are easy to penetrate ink compositions. Applicable. However, when the ink composition is applied to a non-absorbable recording medium, it may be necessary to provide a drying step after being cured by irradiation with ultraviolet rays.

  The absorbent recording medium is not particularly limited. For example, plain paper such as electrophotographic paper having high ink permeability, ink jet paper (an ink absorbing layer composed of silica particles or alumina particles, or polyvinyl alcohol ( Art paper, coated paper, etc. used for general offset printing with relatively low ink permeability, such as PVA) and polyvinyl pyrrolidone (PVP). Examples include cast paper.

  The non-absorbable recording medium is not particularly limited. For example, films and plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, and polyethylene terephthalate (PET), and metals such as iron, silver, copper, and aluminum are used. Examples thereof include a plate, a metal plate produced by vapor deposition of these various metals, a plastic film, a plate made of an alloy such as stainless steel or brass.

[Inkjet recording method]
An ink jet recording method using the ultraviolet curable ink composition for ink jet recording contained in the ink container of the present embodiment includes a discharge step of discharging the ink composition onto a recording medium, and the discharge step. And a curing step of curing the ink composition by irradiating the ejected ink composition with ultraviolet rays. In this way, a coating film (cured film) is formed by the ink composition cured on the recording medium.

[Discharge process]
In the ejection step, an ink jet recording apparatus described later can be used. When discharging the ink composition, the viscosity of the ink composition is preferably 25 mPa · s or less, more preferably 5 to 20 mPa · s. If the viscosity of the ink composition is as described above with the temperature of the ink composition set to room temperature or without heating the ink composition, the temperature of the ink composition is set to room temperature or the ink composition is not heated. Can be discharged. On the other hand, the ink composition may be discharged to a preferable viscosity by heating to a predetermined temperature. In this way, good discharge stability is realized.

  Since the ultraviolet curable ink composition has a higher viscosity than the water-based ink composition used in a normal inkjet ink, the viscosity fluctuation due to temperature fluctuation at the time of ejection is large. Such fluctuations in the viscosity of the ink have a great influence on the change in the droplet size and the change in the droplet discharge speed, which can cause image quality deterioration. Therefore, it is preferable to keep the temperature of the ink during ejection as constant as possible.

[Curing process]
Next, in the curing step, the ink composition ejected on the recording medium is cured by irradiation with ultraviolet rays (light). In other words, the ink coating film formed on the recording medium becomes a cured film when irradiated with ultraviolet rays. This is because the photopolymerization initiator that can be contained in the ink composition is decomposed by irradiation with ultraviolet rays to generate radicals, acids, bases, and other starting species, and the polymerization reaction of the photopolymerizable compound is the starting species. This is because it is promoted by function. Or it is because the photopolymerization reaction of a polymeric compound starts by irradiation of an ultraviolet-ray. At this time, if a sensitizing dye is present together with the photopolymerization initiator in the ink composition, the sensitizing dye in the system absorbs actinic radiation to be in an excited state and comes into contact with the photopolymerization initiator. Degradation can be accelerated and a more sensitive curing reaction can be achieved.

  Mercury lamps and gas / solid lasers are mainly used as ultraviolet sources, and mercury lamps and metal halide lamps are widely known as light sources used for curing ink compositions for ultraviolet curable ink jet recording. Yes. On the other hand, there is a strong demand for mercury-free from the viewpoint of environmental protection, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. Furthermore, an ultraviolet light emitting diode (UV-LED) and an ultraviolet laser diode (UV-LD) are small, have a long lifetime, high efficiency, and low cost, and are expected as light sources for ultraviolet curable ink jets. Among these, UV-LED is preferable.

Here, it is preferable to use an ink composition that can be cured by irradiating ultraviolet rays having an emission peak wavelength of preferably 365 to 405 nm, more preferably 380 to 400 nm. The irradiation energy is preferably ^{50~500mJ / cm 2, 100~400mJ / cm} 2 is more preferable.

  In the above case, curing at low energy and high speed is possible due to the composition of the ink composition. The irradiation energy is calculated by multiplying the irradiation time by the irradiation intensity. The irradiation time can be shortened by the composition of the ink composition, and in this case, the printing speed is increased. On the other hand, the irradiation intensity can be reduced by the composition of the ink composition in the present embodiment, and in that case, the apparatus can be downsized and the cost can be reduced. In this case, UV-LED is preferably used for ultraviolet irradiation. Such an ink composition can be obtained by including a photopolymerization initiator that is decomposed by irradiation with ultraviolet rays in the above wavelength range and a polymerizable compound that initiates polymerization by irradiation with ultraviolet rays in the above wavelength range. The emission peak wavelength may be one or plural within the above wavelength range. Even in the case where there are a plurality, the total irradiation energy of the ultraviolet rays having the emission peak wavelength is set as the irradiation energy.

  Hereinafter, the embodiments of the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples.

[Raw materials]
The raw materials used in the following examples and comparative examples are as follows.
[Color material]
・ C. I. Pigment Black 7 (Microlith Black CK [trade name], manufactured by BASF, abbreviated as “black pigment” in the following table)
[Dispersant]
・ Solsperse 36000 (trade name, manufactured by Noveon)
[Vinyl ether group-containing (meth) acrylic acid esters]
VEEA (2- (2-vinyloxyethoxy) ethyl acrylate, trade name of Nippon Shokubai Co., Ltd., abbreviated as “VEEA” in the table below)
[Polymerizable compounds other than the above]
-Biscote # 192 (Phenoxyethyl acrylate, trade name of OSAKA ORGANIC CHEMICAL INDUSTRY LTD., Abbreviated as “PEA” in the table below)
SR508 (dipropylene glycol diacrylate, trade name of Sartomer, abbreviated as “DPGDA” in the table below)
[Hindered amine compound (polymerization inhibitor)]
Adeka Stub LA-82 (1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, trade name of ADEKA, abbreviated as “LA-82” in the table below)
Adekastab LA-7RD (2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, trade name of ADEKA, abbreviated as “LA-7RD” in the table below)
(Photopolymerization initiator)
・ DAROCURE TPO (BASF brand name, solid content 100%)
・ IRGACURE 369 (trade name, manufactured by BASF, solid content: 100%)
・ Speedcure DETX (trade name, solid content 100%, manufactured by Lambson)
-Speedcure ITX (trade name, manufactured by Lambson, solid content: 100%)

[Examples 1 to 21, Comparative Examples 1 to 6]
(Preparation of pigment dispersion)
Prior to preparation of the ink composition, a pigment dispersion was prepared. The black pigment was mixed at a ratio of 18% by mass and the dispersant was 9% by mass, respectively, and stirred with a stirrer for 1 hour. The mixed liquid after stirring was dispersed with a bead mill to obtain a pigment dispersion. The dispersion conditions were such that zirconia beads having a diameter of 0.65 mm were filled at a filling rate of 70%, the peripheral speed was 9 m / s, and the dispersion time was 2 to 4 hours.

[Preparation of ink composition for ultraviolet curable ink jet recording]
The components described in the following table were added so as to have the composition (unit: mass%) described in the following table, and this was stirred with a high-speed water-cooled stirrer, whereby a black UV-curable inkjet recording ink A composition was prepared. After preparation, the ink composition was degassed. At that time, taking advantage of the fact that the dissolved oxygen amount decreases as the degassing time increases, the degassing time is adjusted so that the oxygen amounts shown in Tables 1 and 2 are obtained for each example.

[Measurement of dissolved oxygen content]
The dissolved oxygen content of the ink composition was measured using Gas Chromatography Agilent 6890 (manufactured by Agilent Technologies). Helium (He) gas was used as the carrier gas.

  Here, the positioning of each example and each comparative example will be described. First, in Examples 1 to 5, the difference in each evaluation result when the ink compositions were the same and the dissolved oxygen amount was changed was examined. On the other hand, although Comparative Example 1 has the same ink composition as Examples 1-5, the amount of dissolved oxygen is very high (30 ppm), and is a comparative control with respect to Examples 1-5. Moreover, the comparative example 2 is a comparative control with respect to the said Examples 1-5 by the point that the amount of dissolved oxygen is very high (30 ppm) and a thioxanthone compound is not included.

  Moreover, Examples 6-11 mainly investigated the difference of each evaluation result when changing content of the thioxanthone compound as a photoinitiator. On the other hand, Comparative Examples 5 and 6 are almost the same as the ink composition of Example 6 except that they do not contain a thioxanthone compound, and are comparative controls for Examples 6 to 11.

  Moreover, Examples 12-16 mainly investigated the difference of each evaluation result when content of VEEA was changed.

  Moreover, Examples 17-21 mainly investigated the difference in each evaluation result when the kind and content of a hindered amine compound were changed. On the other hand, Comparative Examples 3 and 4 are comparative controls for Examples 17 to 21 in that none of the hindered amine compounds is included.

[Evaluation item]
For the ink composition for ultraviolet curable ink jet recording prepared in each example and each comparative example and adjusting the amount of dissolved oxygen by changing the deaeration time, the curability, storage stability, and ejection stability were as follows. Evaluated. For evaluation of curability and ejection stability, and measurement of dissolved oxygen amount in the table, the ink composition after storage under the conditions of storage stability evaluation was used.

[1. Storage stability)
As an ink container, an ink pack as shown in FIG. 1 was prepared. The ink compositions of Examples and Comparative Examples were sealed in the ink pack and stored in an oven at 60 ° C. for 20 days. And the thickening rate before and behind storage was calculated | required. The capacity of the ink pack is 700 mL, the film is an ethylene-vinyl alcohol copolymer film (the oxygen permeability of the film is 2.0 cc · 20 μm / (m ² · day · atm), and the film thickness is 100 μm. ).
The evaluation criteria are as follows. The evaluation results are shown in the above table.
A: 3% or less B: Over 3% to 6% or less C: Over 6% to 9% or less D: Over 9% to 12% or less E: Over 12%

[2. Curability)
Using a bar coater, the ink composition of each example and each comparative example was applied on a PET film (PET50A PL Thin [trade name], manufactured by Lintec Corporation) to prepare an ink coating having a thickness of 10 μm. Thereafter, the coating film was cured by irradiating with ultraviolet rays having an irradiation intensity of 1,100 mW / cm ² and a wavelength of 395 nm. The cured coating film (cured film) was rubbed 10 times with a cotton swab at a load of 100 g, and the curing energy (irradiation energy) at the time when the scratch was not found was determined.
The irradiation energy [mJ / cm ² ] was determined from the product of the irradiation intensity [mW / cm ² ] on the irradiated surface irradiated from the light source and the irradiation duration [s]. The irradiation intensity was measured using an ultraviolet intensity meter UM-10 and a light receiving unit UM-400 (both manufactured by Konica Minolta Sensing, Inc.).
The evaluation criteria are as follows. The evaluation results are shown in the above table.
A: 150mJ / cm ² or less B: 150mJ / cm ² Beyond 200 mJ / cm ² or less C: 200mJ / cm ² Beyond 250 mJ / cm ² or less D: 250mJ / cm ² to greater than 300 mJ / cm ² or less E : Over 300mJ / cm ²

[3. (Discharge stability)
An ink jet evaluation machine (prototype) having 180 nozzles having a discharge nozzle diameter of 20 μm, a drive frequency of 24 kHz, and an ink discharge amount per time adjusted to 5 ng was prepared. Then, using the evaluation machine, the number of nozzles in which nozzle omission occurred when ink was ejected continuously for 60 minutes was determined.
The evaluation criteria are as follows. The evaluation results are shown in the above table.
A: None (0)
B: 1 to 5 C: 6 to 10 D: 11 to 15 E: 16 or more

  From the above results, an ink composition (each example) containing at least a thioxanthone-based photopolymerization initiator and a hindered amine compound and having a dissolved oxygen content of 20 ppm or less is not an ink composition (each comparative example). ), The curability, the storage stability, and the discharge stability were all excellent.

  Furthermore, the same ink composition as the ink composition of Example 2 was used, and the above-mentioned condition was used after storing in an oven at 60 ° C. for 20 days under the same conditions as in Example 2 except that the ink pack had a capacity of 50 mL. Each evaluation was performed. As a result, it was found that the dissolved oxygen amount was 18 ppm, the storage stability A, the curability A, and the discharge stability B.

An ink pack using the same ink composition as the ink composition of Example 2 and having a polyacrylonitrile film (oxygen permeability 10.0 cc · 20 μm / (m ² · day · atm), film thickness 70 μm) Except for the points described above, each of the above evaluations was performed after storage in an oven at 60 ° C. for 20 days under the same conditions as in Example 2. As a result, it was found that the dissolved oxygen amount was 20 ppm, the storage stability A, the curability A, and the discharge stability C.

  It was found that if there is a large amount of dissolved oxygen without a thioxanthone photopolymerization initiator, the curability is poor, and if there is a large amount of dissolved oxygen with a thioxanthone photopolymerization initiator, the discharge stability is improved but the curability is poor. . In addition, comparing Comparative Examples 1 and 2, it can be seen that when the dissolved oxygen amount is the same value, it is inferior in discharge stability when the thioxanthone compound is included.

  Further, using the recording apparatus of FIG. 2 and mounting the ink pack containing ink therein as an ink cartridge, supplying the ink to the head 100, collecting the ink in the sub tank 200 and the ink in the head 100, The amount of dissolved oxygen was measured. As a result, when the ink pack of Example 1 was installed as an ink cartridge, the ink in the sub tank 200 was 27 ppm and the ink in the head 100 was 20 ppm, whereas the ink pack of Comparative Example 1 was used as the ink. In the cartridge mounted, the ink in the sub tank 200 was 36 ppm, and the ink in the head 100 was 31 ppm.

  DESCRIPTION OF SYMBOLS 1 ... Ink pack, 2 ... Ink take-out port, 10 ... Film, 64 ... Main scanning movement table, 100 ... Head, 106 ... Branch joint, 108 ... Pressure adjustment valve, 200 ... Sub tank, 202 ... Pressure pump, 204 ... Desorption 210, integrated joint, 212, open / close valve, 214, forward path, 216, return path, 218, 220, 222, heater, 320, valve opening actuator.

Claims (10)

Containing a thioxanthone photopolymerization initiator and a hindered amine compound,
The amount of dissolved oxygen is 20 ppm or less,
UV-curable ink composition for inkjet recording.   The ultraviolet curable ink composition for ink-jet recording according to claim 1, wherein the content of the thioxanthone photopolymerization initiator is 0.5 to 4% by mass.   The ink composition for ultraviolet curable ink jet recording according to claim 1 or 2, wherein the hindered amine compound is a compound having a 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton.   The ultraviolet curable inkjet according to any one of claims 1 to 3, wherein the thioxanthone photopolymerization initiator includes one or more selected from the group consisting of thioxanthone, diethylthioxanthone, isopropylthioxanthone, and chlorothioxanthone. A recording ink composition.   The ultraviolet curable ink composition for inkjet recording according to any one of claims 1 to 4, wherein the thioxanthone photopolymerization initiator includes diethyl thioxanthone.   The ink composition for ultraviolet curable ink jet recording according to any one of claims 1 to 5, further comprising an acylphosphine oxide photopolymerization initiator.   The ink composition for ultraviolet curable ink jet recording according to any one of claims 1 to 6, wherein the dissolved oxygen amount is 5 ppm or more and 20 ppm or less.   An ink container containing the ultraviolet curable ink composition for inkjet recording according to any one of claims 1 to 7. The oxygen permeability of a constituent material that comes into contact with the ultraviolet curable ink composition for inkjet recording is 5.0 cc · 20 μm / (m ² · day · atm) or less at 23 ° C. and a relative humidity of 65%. The ink container according to 8. The ink composition for ultraviolet curable ink jet recording according to any one of claims 1 to 7 is provided with a discharge means for discharging from the head in a state where the dissolved oxygen amount is 20 ppm or less.
Inkjet recording device.

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