JP2018138654A - Ink composition for uv-curable inkjet and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink composition for UV-curable inkjet which contains a yellow color material and a black color material, and has excellent adhesiveness when using ultraviolet rays of wavelengths of 380-405 nm, and an inkjet recording method using the ink composition.SOLUTION: An ink composition for UV-curable inkjet is used in an inkjet recording method including a hardening step of irradiating the ink composition for UV-curable inkjet adhered to a to-be-recorded medium with UV rays having a peak wavelength of 380-405 nm from a semiconductor light source so as to obtain a hardened film. The product of the light transmissivity (%) of the hardened film at the wavelength of 395 nm by the irradiated energy (mJ/cm) of the UV rays in the hardening step is 2.0 or greater. The hardened film contains at least one of the yellow color material and the black color material and a thioxanthone-based photopolymerization initiator, and the OD value of the hardened film of the ink composition is 1.8 or greater.SELECTED DRAWING: None

Description

  The present invention relates to an ultraviolet curable inkjet ink composition and an inkjet recording method.

  An inkjet recording method capable of recording a high-definition image with a relatively simple apparatus has been rapidly developed in various fields. For example, Patent Document 1 discloses a monofunctional (meta) ink for the purpose of providing an ultraviolet curable inkjet ink composition having excellent curability of the ink composition and excellent abrasion resistance and stretchability of the cured film. An ultraviolet curable inkjet ink composition comprising an acrylate monomer and a photopolymerization initiator, the molecular structure and content of the monofunctional (meth) acrylate monomer, and the cured product of the monofunctional (meth) acrylate An ultraviolet curable ink jet ink composition having a specified mole number average Tg is disclosed.

  Patent Document 2 aims to provide an ultraviolet curable inkjet ink composition that is excellent in curability of the ink composition and that can prevent coloring of the cured film in the initial stage after inkjet recording. An ultraviolet curable inkjet ink composition comprising a predetermined monomer, and a photopolymerization initiator containing an acylphosphine oxide photopolymerization initiator and a thioxanthone photopolymerization initiator, wherein the acylphosphine oxide light An ultraviolet curable inkjet ink composition is disclosed in which the total content of the polymerization initiator and the thioxanthone photopolymerization initiator is 8 to 16% by mass with respect to the total mass of the ink composition.

JP 2012-188612 A JP 2012-140583 A

  As described above, conventionally, it is considered effective to use a thioxanthone-based photopolymerization initiator that is not easily affected by oxygen inhibition in order to ensure the curability of the ink composition attached to the recording medium. . However, when the present inventors examined, when a thioxanthone photopolymerization initiator was used, the curability near the surface of the ink composition was good, but the curability inside the ink composition was not necessarily good. I understood.

  That is, since the thioxanthone photopolymerization initiator has a high light absorption rate at a wavelength of about 395 nm, particularly in photocuring using a semiconductor light source such as an LED, the light of the ink composition adhering to the recording medium is absorbed. It was found that the penetration was inhibited and the curability inside the ink composition was poor. As a result, it has been clarified that it causes poor adhesion to the recording medium. In addition to this thioxanthone photopolymerization initiator, an ink composition containing a yellow color material and / or a black color material having a low light transmittance at a wavelength of around 395 nm so that the cured film has a predetermined OD value (optical density) The object is further inferior in adhesion because the light transmission to the inside is further inhibited. Therefore, an ultraviolet curable ink composition for inkjet which has a yellow color material and / or a black color material and has excellent adhesion even when ultraviolet light having a peak wavelength of 380 to 405 nm is used will be a low-cost semiconductor light source such as an LED. It is believed that UV ink jet printers that cure using a resin are increasingly useful.

  The present invention has been made in order to solve at least a part of the above-described problems, and includes adhesion when yellow light containing a yellow color material and / or a black color material and having a peak wavelength at 380 to 405 nm is used. It is an object of the present invention to provide an ultraviolet curable ink composition for inkjet which is excellent in the performance and an inkjet recording method using the same.

  The present inventors diligently studied to solve the above problems. As a result, when ultraviolet rays having a peak wavelength of 380 to 405 nm were used, it was found that the above problems could be solved if the ink composition had a predetermined composition, and the present invention was completed.

That is, the present invention is as follows.
[1]
An ultraviolet curable type used in an inkjet recording method having a curing step of irradiating ultraviolet light having a peak wavelength of 380 to 405 nm from a semiconductor light source to obtain a cured film on an ultraviolet curable inkjet ink composition attached to a recording medium An inkjet ink composition comprising:
The product of the light transmittance (%) at a wavelength of 395 nm of the cured film and the irradiation energy (mJ / cm ² ) of ultraviolet rays in the curing step is 2.0 or more,
Including at least one of a yellow color material or a black color material, and a thioxanthone photopolymerization initiator,
The OD value of the cured film of the ink composition is 1.8 or more,
UV-curable ink composition for inkjet.
[2]
The ink jet recording method is a method for ultraviolet curable ink jet according to [1] above, wherein recording is performed by one-pass printing using a line printer having a line head having a width equal to or larger than the recording width of the recording medium. Ink composition.
[3]
The ultraviolet curable inkjet ink composition according to [1] or [2], wherein the ultraviolet ray is irradiated with an irradiation energy of 350 to 1000 mJ / cm ² .
[4]
The ultraviolet curable inkjet ink composition according to any one of [1] to [3], wherein the recording medium is a non-ink-absorbing recording medium.
[5]
The ultraviolet curable inkjet ink composition according to any one of [1] to [4], wherein the thioxanthone photopolymerization initiator is contained in an amount of 2.0 to 5.0% by mass.
[6]
The ultraviolet curable inkjet ink composition according to any one of [1] to [5] above, further containing 0.30% by mass or more of a silicone surfactant.
[7]
The ultraviolet curable inkjet ink composition according to any one of [1] to [6] above, further containing 5.0 to 15% by mass of an acylphosphine oxide photopolymerization initiator.
[8]
6. The ultraviolet curable ink composition for inkjet according to any one of [1] to [7] above, wherein the inkjet recording method records at a recording resolution of 600 dpi or more and 600 dpi or more.
[9]
The ultraviolet ray according to any one of [1] to [8] above, comprising any of the yellow colorant 2.5 to 2.9% by mass or the black colorant 1.5 to 1.9% by mass. A curable inkjet ink composition.
[10]
The ink jet recording method according to any one of [1] to [9], wherein the ultraviolet ray irradiation is performed a plurality of times.
[11]
The ultraviolet curable inkjet ink composition according to any one of [1] to [10], wherein the cured film has a thickness of 13 μm or less.
[12]
The cured film has an optical transmittance at a wavelength of 395 nm in the case of having a thickness of 10 μm is 0.0030% or more, and the ultraviolet curable inkjet according to any one of [1] to [11] above Ink composition.
[13]
A discharge step of discharging and adhering the ultraviolet curable inkjet ink composition according to any one of [1] to [12] to a recording medium;
Curing to obtain a cured film having an OD value of 1.8 or more by irradiating the ultraviolet ray curable inkjet ink composition attached to the recording medium with ultraviolet rays from a semiconductor light source having a peak wavelength of 380 to 405 nm. A process,
The product of the light transmittance (%) at a wavelength of 395 nm of the cured film of the ultraviolet curable inkjet ink composition and the irradiation energy (mJ / cm ² ) of the ultraviolet ray is 2 or more.
Inkjet recording method.

It is a block diagram which shows an example of a structure of the inkjet recording device which can be used for this embodiment. 2 is a schematic cross-sectional view showing an example of the periphery of a head unit, a transport unit, and an irradiation unit in a line printer that is an example of an ink jet recording apparatus that can be used in the present embodiment.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary. However, the present invention is not limited to this, Various modifications are possible without departing from the scope of the invention. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, positional relationships such as up, down, left and right are based on the positional relationships shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[UV-curable inkjet ink composition]
The ultraviolet curable inkjet ink composition according to this embodiment (hereinafter also simply referred to as “ink composition”) has a wavelength of 380 to 405 nm with respect to the ultraviolet curable inkjet ink composition attached to the recording medium. An ultraviolet curable inkjet ink composition used in an inkjet recording method having a curing step of irradiating ultraviolet light having a peak wavelength from a semiconductor light source to obtain a cured film, wherein the cured film has a light transmittance (%) at a wavelength of 395 nm. And the ultraviolet irradiation energy (mJ / cm ² ) in the curing step is 2.0 or more, and includes at least one of a yellow color material or a black color material, and a thioxanthone photopolymerization initiator, and an ink The OD value of the cured film of the composition is 1.8 or more.

  In general, by including a thioxanthone photopolymerization initiator, surface tackiness can be reduced, and in particular, in the case of a thin film that is susceptible to oxygen inhibition, the ink surface can be cured to prevent color mixing and bleeding between dots. On the other hand, thioxanthone-based photopolymerization initiators tend to hinder the internal curability of the ink composition (decrease the light transmittance of the film), and deteriorate the adhesion (particularly the adhesion at the time of thick film). It was. In particular, when an ultraviolet ray having a peak wavelength of 380 to 405 nm is irradiated from an LED and a cured film having an OD value of 1.8 or more is cured, the decrease in adhesion becomes significant.

  Therefore, when an ink composition containing a thioxanthone photopolymerization initiator having excellent adhesion was studied, a predetermined semiconductor light source was used, and the ink composition was used in an ink jet recording method in which the product of irradiation energy and cured film transmittance was 2 or more. In some cases, it was found that the ultraviolet rays penetrated into the ink composition to ensure adhesion.

  In addition, since light having a lower wavelength is transmitted to the inside of the ink composition, when using a metal halide light source or a mercury lamp having a light emission wavelength to a lower wavelength region, the ink composition tends to have good internal curability and excellent adhesion. is there. However, these ultraviolet light sources are not preferable from the viewpoints of high heat generation, low life, high power consumption, and large light sources. Therefore, the ink composition according to this embodiment is used in an ink jet recording method using a semiconductor light source that is excellent from the above viewpoint.

[Thioxanthone photopolymerization initiator]
The ink composition of this embodiment contains a thioxanthone photopolymerization initiator. By including a thioxanthone-based photopolymerization initiator, surface tackiness can be reduced, and in particular, the ink surface can be cured at the time of a thin film susceptible to oxygen inhibition to prevent color mixing and bleeding between dots.

  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 2.0 to 5.0% by mass, more preferably 2.5 to 4.5% by mass with respect to the total mass (100% by mass) of the ink composition. 3-4 mass% is more preferable. When the content is 2.0% by mass or more, the surface tackiness can be further reduced, and the ink surface can be cured and the color mixing and bleeding between dots can be further prevented when the thin film is susceptible to oxygen inhibition. is there. Further, when the content is 5.0% by mass or less, the ink is less colored by the initiator itself, the hue is less yellowed, and the cured film tends to be more excellent in adhesion.

(Other photopolymerization initiators)
The ink composition may further contain other photopolymerization initiator. 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. Among these, 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. Acylphosphine oxide photopolymerization initiators are susceptible to oxygen inhibition, but are suitable for curing with long wavelength LEDs. Therefore, the combination of the acylphosphine oxide photopolymerization initiator and the thioxanthone photopolymerization initiator tends to be excellent in the curing process by UV-LED, and the curability and adhesion of the ink composition tend to be further improved.

  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).

  The content of the acylphosphine oxide photopolymerization initiator is preferably 5.0 to 15% by mass, more preferably 6.0 to 10.0% by mass with respect to the total mass (100% by mass) of the ink composition. 7.0-8.0 mass% is still more preferable. When the content is 5.0% by mass or more, the curability tends to be more excellent. When the content is 15% by mass or less, when the content is 15% by mass or less, dissolution and storage stability of the solid content are favorably maintained, and the reliability tends to be superior.

  Other radical photopolymerization initiators are not particularly limited. For example, acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone , Triphenylamine, carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyldimethyl ketal, 1- ( 4-Isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one , And 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino --1-one.

  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 photocationic polymerization initiator, Specifically, a sulfonium salt and an iodonium salt are mentioned.

  Although it does not specifically limit as a commercial item of a photocationic polymerization initiator, Specifically, Irgacure250 and Irgacure270 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 the range, the ultraviolet curing rate can be sufficiently exerted, and the undissolved portion of the photopolymerization initiator and the color derived from the photopolymerization initiator tend to be avoided.

[Color material]
The ink composition includes at least one of a yellow color material and a black color material, and may include other color materials as necessary. As the color material, at least one of a pigment and a dye can be used. A cured film containing a yellow color material or a black color material has a low transmittance and tends to make it difficult for ultraviolet light to reach the inside of the ink composition. In addition, it is possible to increase the transmittance of the cured film by reducing the content of the yellow color material or the black color material, but the OD value of the obtained cured film is lowered, and only a light colored cured product can be obtained. There is a problem. In this regard, if the ink composition according to this embodiment is used in an inkjet recording method in which ultraviolet light is irradiated so that the product of the light transmittance at a wavelength of 395 nm of the cured film and the irradiation energy of ultraviolet light is 2 or more, Even when a yellow color material or a black color material is included, the adhesiveness is excellent.

(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.

  The carbon black used as the black color material is not particularly limited. 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).

  Although it does not specifically limit as a pigment used as a yellow color material, For example, 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, 155, 167, 172, 180.

  Although it does not specifically limit as a pigment used as a white color material, For example, C.I. I. Pigment white 6, 18, and 21.

  Although it does not specifically limit as a pigment used as a magenta color material, For example, 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.

  Although it does not specifically limit as a pigment used as a cyan color material, For example, 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.

  The pigments other than magenta, cyan, and yellow color materials are not particularly limited. 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.

  Although it does not specifically limit as dye used as a yellow color material, For example, C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142,

  Although it does not specifically limit as dye used as a black color material, For example, 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. Directed Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. I. Reactive Black 3, 4, 35

  Although it does not specifically limit as dye used as another coloring material, For example, C.I. I. Acid Red 52, 80, 82, 249, 254, 289, C.I. I. Acid Blue 9, 45, 249, 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. Reactive red 14, 32, 55, 79, 249.

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

  The content of the yellow color material is preferably 2.5 to 2.9% by mass, more preferably 2.6 to 2.8% by mass, with respect to the total mass (100% by mass) of the ink composition. 6-2.7 mass% is still more preferable. When the content is within the above range, there is a tendency that better color development can be secured without increasing the ink viscosity more than necessary.

  The content of the black color material is preferably 1.5 to 1.9% by mass, more preferably 1.6 to 1.9% by mass with respect to the total mass (100% by mass) of the ink composition. 8 to 1.9% by mass is more preferable. When the content is within the above range, there is a tendency that better color development can be secured without increasing the ink viscosity more than necessary.

[Surfactant]
The ink composition according to this embodiment may further contain a surfactant. Although it does not specifically limit as surfactant, For example, silicone type surfactant (As a commercial item, BYK UV3500, UV3570 (BIC Chemie Japan brand name), for example), acrylic surfactant (BYK350 (BIC Chemie)・ Japan trade name)). Among these, by including a silicone surfactant, the surface tension lowering ability is excellent, the wettability to the recording medium is improved, the solid filling is excellent, and the surface tension tends to be easily adjusted.

  The content of the surfactant is preferably 0.20% by mass or more, more preferably 0.30% by mass or more, and further preferably 0.40% by mass or more with respect to the total mass (100% by mass) of the ink composition. 0.50% by mass or more is particularly preferable. Further, the content is preferably 1.0% by mass or less, more preferably 0.8% by mass or less, and further preferably 0.7% by mass or less. When the content of the surfactant is 0.20% by mass or more, the wettability to the recording medium tends to be more excellent. Further, when the content of the surfactant is 1.0% by mass or less, the liquid repellency of the head nozzle plate tends to be kept good and the ejection stability tends to be excellent.

  The surface tension of the ink composition is preferably 23 mN / m or less, and more preferably 22 mN / m or less. Further, the lower limit of the surface tension is not particularly limited, and the lower the better. When the surface tension is within the above range, the wettability to the recording medium tends to be more excellent. As a method for measuring the surface tension, a commonly used surface tension meter (for example, surface tension meter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.) is used and measured at a liquid temperature of 25 ° C. by the Wilhelmy method. A method can be exemplified.

  As the silicone surfactant, a polysiloxane compound is preferably used, and examples thereof include polyether-modified organosiloxane. Moreover, a commercial item can be used, for example, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-348 (above, trade name, manufactured by Big Chemie Japan Co., Ltd.) KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515 , KF-6011, KF-6012, KF-6015, KF-6017 (trade names, manufactured by Shin-Etsu Chemical Co., Ltd.).

(Polymerizable compound)
The ink composition may contain a polymerizable compound. The polymerizable compound can be polymerized alone or by the action of a photopolymerization initiator during light irradiation to cure the ink composition on the recording medium. 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.

  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; Saturated carboxylic acid salts; unsaturated carboxylic acid esters, urethanes, amides and anhydrides; acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. In addition, monofunctional, bifunctional, and trifunctional or higher polyfunctional oligomers are not particularly limited. For example, oligomers formed from the above monomers such as linear acrylic oligomers, epoxy (meth) acrylates, oxetanes ( Mention may be made of (meth) acrylates, aliphatic urethane (meth) acrylates, aromatic urethane (meth) acrylates and polyester (meth) acrylates.

  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. It is done.

  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 composition can be further reduced, the flash point is high, and the curability of the ink composition is excellent, 2- (vinyloxyethoxy) ethyl (meth) acrylate, that is, acrylic acid 2 At least one of-(vinyloxyethoxy) 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 composition 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 composition can be reduced, and the curability of the ink composition tends to be more excellent. On the other hand, when the content is 70% by mass or less, the storability of the ink composition is more excellent and the surface gloss of the printed matter tends to be more excellent.

  Among the (meth) acrylates, the bifunctional (meth) acrylate is not particularly limited. For example, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 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-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, EO (ethylene oxide) addition of bisphenol A Di (meth) acrylate, PO (propylene oxide) adduct of bisphenol A di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate , Triethylene glycol 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.

  5-60 mass% is preferable with respect to the total mass (100 mass%) of an ink composition, and, as for content of polyfunctional (meth) acrylate more than bifunctional, 15-60 mass% is more preferable, and 20-50. More preferred is mass%. By setting it as the said preferable range, it exists in the tendency which is excellent by sclerosis | hardenability, storage stability, discharge stability, and the surface gloss of printed matter.

  Among the above (meth) acrylates, trifunctional or higher polyfunctional (meth) acrylates are not particularly limited, and examples thereof include 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 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 cured film are increased, it is more preferable to use a monofunctional (meth) acrylate and a bifunctional (meth) acrylate together. Among them, phenoxyethyl (meth) acrylate and dipropylene glycol are more preferable. 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 and the surface gloss of the printed material should be further improved. Can do.

[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 in 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. The other additive is not particularly limited, and examples thereof include conventionally known fixing agents, antifungal agents, preservatives, antioxidants, ultraviolet absorbers, chelating agents, pH adjusting agents, and thickeners. Can be mentioned.

[Other Embodiments of Ink Composition]
The ink composition according to this embodiment has a light transmittance at a wavelength of 395 nm of a cured film having a thickness of 10 μm other than the ink composition containing at least one of the yellow color material and the black color material described above. The OD value of the cured film having a thickness of 0.002 to 0.015% and a film thickness of 10 μm is 1.8 or more, and the thioxanthone photopolymerization initiator and the color material (yellow color material) And an ink composition including, but not limited to, a black color material. The ink composition may include a color material other than a yellow color material and a black color material as a color material. Regarding the composition and characteristics of the ink composition other than this, the yellow color material or the black color material described above is used. It can be the same as the ink composition containing at least one of the following.

[Recording medium]
The recording medium is not particularly limited, and examples thereof include a non-ink-absorbing or ink-absorbing recording medium. Among these, a non-ink-absorbing recording medium is preferable. When a non-ink-absorbing recording medium is used, the film thickness of the coating film directly correlates with the color development. Easy to peel off at the interface. Therefore, the present invention is more effective when using a non-ink-absorbing recording medium. On the other hand, in an ink-absorbing recording medium, ink permeates into the recording medium, so that interfacial peeling tends not to occur although the internal curability is poor.

  Among the recording media, the non-ink-absorbing recording media are not particularly limited. For example, a plastic film or paper that is not surface-treated for inkjet recording (that is, has no ink absorbing layer formed) Examples thereof include those in which a plastic is coated on a base material such as those in which a plastic film is adhered. Examples of the plastic herein include polyvinyl chloride (vinyl chloride), polyethylene terephthalate (PET), polycarbonate (PC), polystyrene (PS), polyurethane (PU), polyethylene (PE), and polypropylene (PP). Examples of the recording medium with low ink absorption include printing paper such as art paper, coated paper, and matte paper.

  Here, as a non-ink-absorbing and low-absorbing recording medium, a recording surface is a recording medium having a water absorption amount of 10 mL / m 2 or less from the start of contact to 30 msec in the Bristow method. This Bristow method is the most popular method for measuring the amount of liquid absorbed in a short time, and is also adopted by the Japan Paper Pulp Technology Association (JAPAN TAPPI). For details of the test method, refer to Standard No. of “JAPAN TAPPI Paper Pulp Test Method 2000”. 51 "Paper and paperboard-Liquid absorbency test method-Bristow method".

[Inkjet recording method]
The inkjet recording method according to the present embodiment includes an ejection step of ejecting and adhering the ultraviolet curable inkjet ink composition to a recording medium, and the ultraviolet curable inkjet ink composition adhered to the recording medium. And curing the ultraviolet curable inkjet ink composition by irradiating ultraviolet light from a semiconductor light source having a peak wavelength of 380 to 405 nm to obtain a cured film having an OD value of 1.8 or more. The product of the light transmittance (%) at a wavelength of 395 nm of the film and the irradiation energy (mJ / cm ² ) of the ultraviolet ray is 2 or more.

[Discharge process]
The ink jet recording method according to the present embodiment includes a discharge step of discharging and adhering an ultraviolet curable ink jet ink composition onto a recording medium. The ink composition is preferably ejected so that the recording resolution of the obtained cured product is 600 dpi or more and 600 dpi or more, and the ink composition is more preferably ejected so that the recording resolution is 720 dpi or more and 720 dpi or more, More preferably, the ink composition is ejected such that the recording resolution is 1200 dpi or more and 1200 dpi or more. The upper limit of the recording resolution is not particularly limited, but can be, for example, 5000 dpi or less × 5000 dpi or less. In single-pass printing, when printing on a recording medium with inferior wettability, the phenomenon that the dots do not easily spread due to interference between adjacent dots that have landed is 1 dot compared to the serial printing method to ensure solid filling. The amount of ink per hit is required. This phenomenon occurs more remarkably when the resolution is low. In the ink composition according to the present embodiment, by setting the recording resolution to 600 × 600 dpi or higher, the coating amount necessary for solid filling can be set to 10 μm or lower. If solid filling can be secured with a relatively small amount of ink per dot in this way, the thick feeling of the printed matter can be suppressed, and the user's ink cost tends to be kept more appropriate.

[Curing process]
In the curing step, an ultraviolet curable inkjet ink composition attached to the recording medium is irradiated with ultraviolet light having a peak wavelength of 380 to 405 nm from a semiconductor light source to form a cured film having an OD value of 1.8 or more. It is a process to obtain.

  In the curing step, the ink composition attached to the recording medium is irradiated with ultraviolet rays (light) from a light source to cure the ink composition. In this step, the photopolymerization initiator contained in the ink is decomposed by irradiation with ultraviolet rays to generate starting species such as radicals, acids, and bases, and the polymerization reaction of the polymerizable compound is accelerated by the function of the starting species. Is done. Or in this process, the polymerization reaction of a polymeric compound starts by irradiation of an ultraviolet-ray.

  A semiconductor light source is used as the light source (ultraviolet light source). Examples thereof include LEDs (light emitting diodes) such as ultraviolet light emitting diodes (UV-LED) and ultraviolet laser diodes (UV-LD). By using the semiconductor light source, it is possible to reduce the size and life of the ink jet recording apparatus and to increase the efficiency and cost of the ink jet recording method as compared with the case of using a metal halide light source or a mercury lamp.

In the curing step, the ultraviolet ray is irradiated so that the product of the light transmittance (%) at a wavelength of 395 nm of the cured film and the irradiation energy (mJ / cm ² ) of the ultraviolet ray is 2 or more. The product of the light transmittance (%) at a wavelength of 395 nm of the cured film and the irradiation energy (mJ / cm ² ) of ultraviolet rays is preferably 4.0 or more, and more preferably 6.0 or more. The upper limit of the product of the light transmittance (%) at a wavelength of 395 nm of the cured film and the irradiation energy (mJ / cm ² ) of ultraviolet rays is not particularly limited, but is preferably 10.0 or less. By being 10.0 or less, it is not necessary to sacrifice color more than necessary, and it is not necessary to increase the number of irradiators and increase the cost of the printer. In general, by using a thioxanthone photopolymerization initiator, the surface tackiness is improved, but the adhesion tends to be lowered. This tendency becomes remarkable when the OD value of the cured film is 1.8 or more. However, when the product is 2 or more, the OD value of the cured film is 1.8 or more, and even if a thioxanthone-based photopolymerization initiator is contained, the ultraviolet rays reach the inside of the ink composition, which is more excellent. A cured product having excellent adhesion can be obtained. Thereby, reduction of surface tackiness and improvement of adhesion can be achieved simultaneously.

UV irradiation energy is preferably from 350~1000mJ / cm ^2, more preferably 380~750mJ / cm ^2, more preferably 400~600mJ / cm ^2. When the irradiation energy is 350 mJ / cm ² or more, the curability tends to be superior. Further, when the irradiation energy is 1000 mJ / cm ² or less, the irradiator cost and the size of the irradiator tend to be kept more appropriate.

  The light transmittance (transmittance) at a wavelength of 395 nm of the cured film obtained in the curing step, which is made of the ink composition according to the present embodiment, is preferably 0.001% or more, preferably 0.002% or more, and 003% or more is more preferable, and 0.004% or more is more preferable. When the light transmittance is 0.001% or more, the internal curability can be ensured, and therefore the adhesiveness tends to be more excellent. The light transmittance is preferably 0.018% or less, more preferably 0.015% or less, further preferably 0.010% or less, particularly preferably 0.008% or less, and particularly preferably 0.005% or less. preferable. When the light transmittance is 0.018% or less, the color material concentration can be appropriately ensured, and the color of the printed matter tends to be excellent. The light transmittance is improved by lowering the color material concentration and the thioxanthone initiator concentration or by lowering the ink injection amount, and by increasing the color material concentration and the thioxanthone initiator concentration or by increasing the ink injection amount. descend. The light transmittance can be measured by the method described in the examples. The cured film for measuring the light transmittance is a sufficiently cured film suitable for using a recorded material. The transmittance of the cured film at a wavelength of 395 nm is the amount of ink applied to the recording medium (the film thickness of the cured film) as a recording condition, and the type of color material mainly contained in the ink composition as the ink composition. And the content and the content of the thioxanthone-based photopolymerization initiator, and can be adjusted by changing these. In particular, the color material tends to be determined by the contents of the yellow color material and the black color material. Note that the above-described coloring material and thioxanthone photopolymerization initiator tend not to change the light transmittance at a wavelength of 395 nm before and after curing of the ink composition.

  The cured film has a light transmittance at a wavelength of 395 nm in the case of a cured film having a film thickness of 10 μm among the light transmittance at a wavelength of 395 nm of the cured film, preferably 0.0015% or more, 0.002% The above is more preferable, 0.003% or more is further preferable, and 0.004% or more is particularly preferable. When the light transmittance is 0.0015% or more, the internal curability can be secured, and therefore the adhesiveness tends to be superior. The light transmittance is preferably 0.015% or less, more preferably 0.010% or less, further preferably 0.008% or less, particularly preferably 0.005% or less, and particularly preferably 0.004% or less. preferable. When the light transmittance is 0.015% or less, the color material concentration in the coating film can be appropriately secured, and the printed matter tends to be more excellent in color development. The light transmittance is lowered when the content of the colorant is large, and is improved when the content is small. In the range of 395 nm, Bk (black) and Y (yellow) are particularly prominent and affect exponentially. The light transmittance here is the light transmittance of a cured film having a film thickness of 10 μm obtained by curing an ink composition having the same composition as the cured film formed in this embodiment. The light transmittance of the cured film itself formed in the form is not limited to the light transmittance here. The light transmittance can be measured by the method described in the examples.

  The OD value of the cured film is 1.8 or more, preferably 2.0 or more, and more preferably 2.1 or more from the viewpoint of having a dark color. When the OD value is 1.8 or more, the ultraviolet transmittance of the cured film becomes lower, so that the adhesion generally tends to be inferior. However, if it is the inkjet recording method which concerns on this embodiment, the hardened | cured material excellent in adhesiveness can be obtained. The upper limit of the OD value is not particularly limited, but is, for example, 2.5 or less, 2.3 or less, 2.1 or less, and 2.0 or less. The OD value is a cured film having a thickness of 10 μm, and can be specifically measured by the method described in the examples.

  In the present embodiment, it is preferable to perform ultraviolet irradiation a plurality of times. Multiple times of irradiation may include irradiation for temporary curing. Here, “temporary curing” means temporary pinning of the ink composition, and more specifically, curing before the main curing in order to prevent bleeding between dots and control of the dot diameter. means. Generally, the polymerization degree of the polymerizable compound in the temporary curing is lower than the polymerization degree of the polymerizable compound by the main curing performed after the temporary curing. Further, “main curing” means that the dots formed on the recording medium are cured to a necessary cured state. Here, “curing” in the present specification means the above-mentioned main curing unless otherwise specified. A plurality of times of ultraviolet irradiation are preferably performed in one pass.

When irradiating ultraviolet rays a plurality of times, the first irradiation energy is preferably lower than the second and subsequent irradiation energy. Specifically, the irradiation energy of the first time is preferably 5~50mJ / cm ^2, more preferably 10~30mJ / cm ^2, more preferably 15~25mJ / cm ^2. When the first irradiation energy is within the above range, the surface curability tends to be excellent, and bleeding between dots tends to be further suppressed. The irradiation energy of the secondary and subsequent is preferably ^{350~1000mJ / cm 2, 400~600mJ / cm} 2 is more preferable. When the second irradiation energy is within the above range, the internal curability tends to be further improved. In addition, when the ultraviolet irradiation is performed a plurality of times, the product is calculated using the sum of the irradiation energy of the plurality of ultraviolet rays.

  The inkjet recording method according to the present embodiment is preferably performed using a line printer that performs recording by one-pass printing with a line head having a width equal to or larger than the recording width of the recording medium. A line printer (one-pass printing) that attaches and irradiates all dots in one pass is more common than a serial printer that attaches dots in adjacent pixels in separate passes and irradiates ultraviolet rays for each pass. In particular, it tends to be poor in internal curability and poor in adhesion. Therefore, the present invention is particularly useful in an ink jet recording method performed using a line printer.

  The thickness of the cured film to be obtained is not limited, and in the cured film having a film thickness formed at the time of recording, the irradiation energy is such that the product of transmittance x irradiation energy at a wavelength of 395 nm of the cured film is 2 or more. Irradiation may be performed. Of these, the thickness of the cured film is preferably 13 μm or less, more preferably 11 μm or less, and even more preferably 10 μm or less. When the film thickness is 13 μm or less, the adhesion is excellent, and the thickness of the printed material can be reduced. The thickness of the cured film is preferably 1 μm or more, more preferably 1.5 μm or more, and further preferably 2.0 μm or more. When the film thickness is 1 μm or more, it tends to be excellent in surface tackiness by being less susceptible to oxygen inhibition. The thickness of the cured film is determined by the amount of application at the time of solid printing, and by controlling the ink mass of one dot and the ink duty (ratio of the number of pixels forming dots out of a predetermined number of pixels in the pattern). The film thickness can be controlled.

[Inkjet recording device]
Hereinafter, an inkjet recording apparatus (printer) for carrying out the inkjet recording method will be described with reference to the drawings. The ink jet recording apparatus used in the present embodiment is not limited to the ink jet recording apparatus described below.

  FIG. 1 is a block diagram showing an example of the configuration of an ink jet recording apparatus that can be used in this embodiment. A printer driver is installed in the computer 130, and print data corresponding to the image is output to the printer 1 in order to cause the printer 1 to record an image. The printer 1 includes a transport unit 20, a head unit 30, an irradiation unit 40, a detector group 110, a memory 123, an interface 121, and a controller 120. The printer 1 that has received the print data from the computer 130, which is an external device, controls each unit by the controller 120, and records an image on a recording medium according to the print data. The situation in the printer 1 is monitored by the detector group 110, and the detector group 110 outputs the detection result to the controller 120. The controller 120 controls each unit based on the detection result output from the detector group 110 and stores print data input via the interface 121 in the memory 123. The controller 120 includes a CPU 122 and a unit control circuit 124. The memory 123 also stores control information for controlling each unit. The controller 120 controls each unit to perform irradiation with irradiation energy such that the product of transmittance × irradiation energy at a wavelength of 395 nm of the cured film is 2 or more. As an example, the controller 120 irradiates the cured film having the maximum film thickness among the formed cured films with an irradiation energy such that the product of transmittance × irradiation energy at a wavelength of 395 nm is 2 or more. Control each unit to do. By doing so, the product of transmittance × irradiation energy at a wavelength of 395 nm of the cured film can be made 2 or more for any cured film formed at the time of recording. Alternatively, the controller 120 may calculate the product of transmittance × irradiation energy at a wavelength of 395 nm for each recording mode when the thickness of the cured film having the maximum thickness differs depending on the recording mode such as the type of recording medium and the recording resolution. Each unit is controlled to perform irradiation with different irradiation energies so that the value becomes 2 or more.

  Examples of the type of printer used in this embodiment include a line printer and a serial printer. Among these, a line printer is preferable. A line printer (one-pass printing) that attaches and irradiates all dots in one pass is more common than a serial printer that attaches dots in adjacent pixels in separate passes and irradiates ultraviolet rays for each pass. In particular, it tends to be inferior in internal curability and poor in adhesion. Therefore, the present invention is particularly useful in an ink jet recording method performed using a line printer.

  A line printer, which is a line-type ink jet recording apparatus, includes a line head having a length equal to or longer than the length of a recording medium as a head. The ink composition is ejected from the line head toward the recording medium while the line head and the recording medium move relative to each other in the scanning direction intersecting the width direction. That is, the ink composition is ejected from the line head toward a recording medium that is scanned relative to the line head. In the line printer, the head is fixed without moving (almost), and recording is performed in one pass (single pass). A line printer is advantageous over a serial printer in that the recording speed is high.

  Here, the above-mentioned “line head having a length corresponding to the width of the recording medium” is not limited to the case where the width of the recording medium and the length (width) of the line head completely match each other. May be different. For example, the length (width) of the line head corresponds to the width (recorded width) of the recording medium on which the ink composition is to be ejected (image should be recorded). The case where it is the length to do is mentioned.

  On the other hand, a serial printer, which is a serial ink jet recording apparatus, performs main scanning (pass) in which the ink composition is discharged while the head moves in the main scanning direction intersecting the sub-scanning direction of the recording medium. Recording is performed with more than a pass (multipass).

[Inkjet head]
The head unit 30 included in the inkjet recording apparatus (printer 1) includes a head (inkjet head) that performs recording by discharging an ink composition toward a recording medium. The head is provided for each cavity, a cavity for discharging the accommodated ink composition from the nozzle, an ejection driving unit that is provided for each cavity, and applies ejection driving force to the ink. And a nozzle for discharging the ink composition to the outside of the head. A plurality of cavities, and ejection drive units and nozzles provided for each cavity may be provided in one head independently of each other. The ejection drive unit is formed using an electromechanical conversion element such as a piezoelectric element that changes the volume of the cavity by mechanical deformation, or an electrothermal conversion element that generates and discharges bubbles in ink by generating heat. be able to. The ink jet recording apparatus may be provided with one head or a plurality of heads for each color ink. When a plurality of heads are provided, a line head is formed by arranging a plurality of heads in the width direction of the recording medium. In this case, the above-mentioned recorded width can be increased. When recording is performed using a plurality of color ink compositions, the ink jet recording apparatus includes a head for each ink. The head can be configured, for example, as shown in FIG. 3 of JP-A-2009-279830.

  Hereinafter, a line printer as an example of an ink jet recording apparatus that can be used in the present embodiment will be described in detail with reference to FIG. In FIG. 2 used for the following description, the scale of each member is appropriately changed in order to make each member a recognizable size.

[Line printer]
FIG. 2 is a schematic cross-sectional view showing an example of the periphery of the head unit, the transport unit, and the irradiation unit in the above-described line printer that is an example of a printer that can be used in this embodiment.

  A transport motor (not shown) rotates a transport roller including the upstream roller 25A and the downstream roller 25B, and the transport drum 26 is driven. The recording medium S is transported along with the rotation of the transport rollers along the peripheral surfaces of the transport rollers 25A and 25B and the transport drum 26 as a support. Around the conveyance drum 26, each line head including the head K, the head C, the head M, and the head Y is arranged to face the conveyance drum 26.

  The transport drum 26 has a surface for transporting the recording medium S, supports the recording medium S on the surface, and moves relative to the head. When the conveyance drum 26 moves relative to the head while supporting the recording medium S, the time (cycle) until returning from the arbitrary position to the same position is preferably 5 seconds or more, more preferably 6 seconds or more. preferable. When the time is within the above range, the heat dissipation time of the support is secured, and the temperature rise tends to be suppressed. The upper limit of the period is not particularly limited, but is preferably within 15 seconds, for example, in order to realize high-speed printing.

  It should be noted that the movement in the predetermined cycle by the support may be performed at least while ink jet recording is performed, and may be performed continuously or intermittently while ink jet recording is performed.

The shape of the support is not limited to the drum-shaped support as shown in FIG. 2 and is not particularly limited. For example, the support in the form of a roller and a belt and the recording medium S are supported. A plate-like support (platen or the like) is also included. The movement of the support relative to the head may be movement (rotation) in one direction and return to the same position, or a combination of movement in one direction and movement in another direction. It is good also as a movement which returns to the same position. In the latter case, the movement in the certain direction is the movement accompanying the recording on the single recording medium, and the movement in the other direction is finished after the recording on the one recording medium. There is a form in which movement for recording on the next recording medium is performed.
In the case of a serial printer, the movement in a certain direction corresponds to sub-scanning. Further, the movement of the support relative to the head may be a relative movement of the support relative to the head, and includes movement such that the head moves relative to the support.

  Although it does not specifically limit as a material of a support body, For example, a metal, resin, and rubber | gum are mentioned. Of these, metals are preferred. When the material is a metal, unlike the case of a polymer material such as rubber, even if the support is used for a long period of time, it does not generate cracks that may be caused by heat, and can be used for a long period of time. The metal is not particularly limited, and examples thereof include aluminum, stainless steel, copper, iron, and alloys thereof. Further, the surface of the metal support, that is, the transport surface of the recording medium S may be painted with a coating agent or the like. As a result, the hardness of the support surface can be improved as compared to a support that is not coated, and it can be made less slippery with the recording medium. Examples of the coating agent include, but are not limited to, organic coating agents such as resins, inorganic coating agents such as inorganic compounds, and composite coating agents thereof. The above-mentioned matters relating to the support can be applied not only to a line printer but also to a serial printer.

  In this way, recording is performed by an ejection operation for ejecting and adhering the ink composition toward the recording medium S facing each line head. Preliminary curing irradiation units 42a, 42b, 42c, and 42d are arranged on the downstream side in the transport direction of each line head, and irradiate the recording medium S with ultraviolet rays. A main curing irradiation unit 44 is disposed further downstream in the transport direction. Such a recording apparatus can be configured, for example, as shown in FIG. 11 of JP 2010-269471 A.

  Since the ink composition only needs to be fully cured by being irradiated with ultraviolet rays from the main curing irradiation unit 44, the ultraviolet rays are irradiated from some or all of the temporary curing irradiation units 42a, 42b, 42c, and 42d. Alternatively, the curing operation may be terminated by irradiating with ultraviolet rays from the main curing irradiation unit 44. As described above, the curing operation may be performed only for the main curing without performing the temporary curing.

  Thus, according to the present embodiment, ink jet recording that is excellent in all of curability, ejection stability, and suppression of temperature rise in the recording apparatus after continuous printing, and can also suppress the occurrence of curing wrinkles. An apparatus can be provided. Furthermore, the recording apparatus of the present embodiment is capable of increasing the temperature in the recording apparatus after continuous printing while ensuring excellent curability and ejection stability even when using a low-viscosity ink composition. It is excellent in suppression.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The present invention is not limited in any way by the following examples.

[Material for ink composition]
The main materials for the ink compositions used in the following examples, comparative examples, and reference examples are as follows.
(Polymerizable compound)
VEEA (acrylic acid 2- (2-vinyloxyethoxy) ethyl, manufactured by Nippon Shokubai Co., Ltd.)
・ PEA (phenoxyethyl acrylate, manufactured by Osaka Organic Chemical Co., Ltd.)
・ DPGDA (dipropylene glycol diacrylate, manufactured by Sartomer)
A-DPH (dipentaerythritol hexaacrylate, manufactured by Shin-Nakamura Kogyo Co., Ltd.)
[Thioxanthone photopolymerization initiator]
-Speedcure DETX (trade name, manufactured by Lambson, solid content: 100% by mass)
[Other photopolymerization initiators]
IRGACURE 819 (trade name, manufactured by BASF, solid content: 100% by mass)
・ DAROCUR TPO (BASF brand name, solid content 100% by mass)
[Surfactant]
・ BYK UV3500
[Dispersant]
Solsperse 36000 (trade name manufactured by LUBRIZOL, abbreviated as Sol36000 below)
[Color material]
・ C. I. Pigment Blue 15: 3
・ C. I. Pigment Yellow 155
·Carbon black

[Preparation of ink composition]
Each material was mixed with the composition (parts by mass) shown in Table 1 below, and stirred sufficiently to prepare an ink composition in the air.

[Measurement method: ink compositions 1 to 11]
[Light transmittance at a wavelength of 395 nm when the film thickness is 10 μm]
A line printer was prepared. This line printer used SurePress L-4033A (Seiko Epson) modified as follows. As shown in FIG. 2, four line heads (heads having a length substantially corresponding to a width (recording width) on which an image of the recording medium is to be recorded) are arranged side by side in the conveyance direction of the recording medium, A light source was disposed downstream of each head in the transport direction. In the recording by the line printer, among the head and the light source shown in FIG. 2, the head K, the pre-curing irradiation unit 42a, and the main curing irradiation unit 44 were used, and the others were not used. The conveyance drum 26 was made of aluminum, the conveyance drum 26 had a diameter of 500 mm, a printing speed of 285 mm / second, and a drum rotation period of 5.5 seconds. A head having a nozzle density of 600 dpi in the recording medium width direction of the nozzle row was used.

  The ink composition shown in Table 1 was ejected from the head K toward a PET film (TORAY Lumirror S10 (thickness: 100 μm)) under the conditions of a recording resolution of 600 dpi × 600 dpi and one pass (single pass). At this time, the ink droplet amount per pixel was adjusted so that the film thickness after curing was 10 μm. In this way, a solid pattern image was formed. Note that the “solid pattern image” means that dots are recorded for all the pixels of the minimum recording unit area defined by the recording resolution, and the background of the recording medium in the pattern is covered with ink. Means an image.

Subsequently, the ink adhered to the PET film was irradiated with ultraviolet rays from a light source to cure the ink composition. Specifically, first, an LED having a peak wavelength of 395 nm and an irradiation peak intensity of 500 mW / cm ² was used as the light source 42a. The LED was irradiated with ultraviolet rays having an irradiation energy of 20 mJ / cm ² to perform temporary curing. As the light source 44, an LED having a peak wavelength of 395 nm and an irradiation peak intensity of 1,500 mW / cm ² was used. The solid pattern image was cured by irradiating the LED with ultraviolet rays having an irradiation energy of 400 mJ / cm ² for a predetermined time. In this way, a cured film having a thickness of 10 μm was obtained by curing the solid pattern image. In addition, it was confirmed by the finger touch test that the tackiness on the surface of the cured film disappeared. The light transmittance of this cured film at 395 nm was measured using a spectrophotometer U3300 (manufactured by Shimadzu Corporation).

[OD value of solid pattern]
The OD value of the cured film used for the internal transmittance measurement was measured using Spectrolino (manufactured by Gretag).

[Evaluation Methods: Examples 1 to 14, Comparative Examples 1 to 5, Reference Examples 1 to 5]
[Adhesion]
An ink composition prepared using the same line printer as that used in the above light transmittance measurement method is applied to a PET film (Lumillar 125E20 [trade name], manufactured by Toray Industries, Inc.) with a film thickness of 10 μm (cured film). The ink composition was ejected in the amount of ink droplets, and the ink composition adhered to the recording medium was irradiated with ultraviolet rays having a predetermined irradiation energy (irradiation Eng) to obtain a cured film having a solid pattern thickness of 10 μm. The adhesion of the cured film is in accordance with JIS K-5600-5-6 (ISO 2409) (Paint General Test Method-Part 5: Mechanical Properties of Coating Film-Section 6: Adhesion (Cross Cut Method)) And evaluated. Table 1 shows the irradiation energy of ultraviolet rays (irradiation energy from the main curing irradiation unit 44 and the temporary curing irradiation unit 42a, and the total thereof). The unit of irradiation energy in the table is mJ means mJ / cm ² .

  In Example 10, the head is replaced with a head having a nozzle density of 400 dpi in the width direction of the recording medium in the nozzle row, the recording density is set to 400 dpi × 400 dpi, and the ink amount per dot is increased compared to Example 1, The ink composition was ejected with an ink droplet amount of 10 μm (cured film), and ultraviolet rays were applied to the ink composition attached to the recording medium to obtain a cured film having a solid pattern thickness of 10 μm.

Further, in Reference Examples 3 to 4, a serial printer was used instead of the line printer. As a serial printer, a product name SC-S30650 manufactured by EPSON was modified and used. Specifically, a light source of the same type as that used for the line printer having the same length as that of the head in the sub-scanning direction is arranged next to both of the head on the carriage in the main scanning direction. Irradiation was possible with respect to the ink adhering to the recording medium. The nozzle density of the head was set to 300 dpi. Under recording conditions using a serial printer, the recording resolution per pass is set to 300 × 300 dpi, the sub-scanning is performed between the passes at a distance half the length of the head in the sub-scanning direction, and the recording is performed facing the head in two passes. The recording on the medium was completed, and the final recording resolution was 600 × 600 dpi. Further, during the main scanning of the head, only the downstream light source in the main scanning direction was irradiated, and the upstream light source stopped irradiation. Also, the irradiation energy per pass is 100 mJ / pass, and among the inks attached to the same area of the recording medium, the ink attached in the first pass is also irradiated in the second pass, so the total irradiation energy There was 200 mJ / cm ^2, ink deposited in the second pass is the total irradiation energy of a 100 mJ / cm ^2. Therefore, there are two types of irradiation energy × transmittance.

In order to evaluate adhesion, first, as a cutting tool, a single blade cutting tool (generally available cutter) and a guide for cutting at equal intervals using a single blade cutting tool were prepared. First, the blade of the cutting tool was applied so as to be perpendicular to the obtained cured film, and six cuts (distance between the cuts: 1 mm, the same applies hereinafter) were made in the cured film. After making these six cuts, the direction of 90 ° was changed, and another six cuts were made so as to be orthogonal to the cuts already made. Next, a transparent adhesive tape (width: 25 ± 1 mm) with a length of about 75 mm is applied to the part of the cured film cut in a lattice shape, and the tape is rubbed with fingers enough to see through the cured film. It was. Next, within 5 minutes after applying the tape, the tape was reliably peeled off from the cured film in an angle close to 60 ° in 0.5 to 1.0 seconds, and the state of the cured film was visually observed. . The evaluation criteria are as follows. The results are shown in Table 2.
○: Exfoliation of the cured film was observed in less than 5% of the lattice.
Δ: Separation of the cured film was observed in 5% or more and less than 35% of the lattice.
X: Peeling of the cured film was observed in 35% or more of the lattice.

(Surface tackiness)
Except that a cured film having a solid pattern thickness of 1 μm was obtained by discharging the ink composition with an ink drop amount of 1 μm and irradiating the ink composition attached to the recording medium with ultraviolet rays. A cured film was prepared in the same manner as the adhesion. The surface of the cured film was rubbed with a Johnson swab manufactured by Johnson & Johnson, with the number of rubs being 5 times reciprocating and the rub strength being 3 g load. The surface of the cured film after rubbing was visually observed. By evaluating with a thin film, the surface of the coating film is evaluated under conditions that are difficult to cure due to oxygen inhibition. The evaluation criteria are as follows. The results are shown in Table 2.
○: No streaks were observed on the cured film, and the ink composition did not adhere to the cotton swab.
Δ: No streaks were seen in the cured film, but the ink composition was observed to adhere to the cotton swabs.
X: Streaks were seen in the cured film.

[Bleeding test]
The edge part of the cured film produced by adhesive evaluation was observed visually. The evaluation criteria are as follows. The results are shown in Table 2.
○: The edge was clear.
Δ: The edge was blurred.
X: Bleeding occurred at the end.

  Comparison between Example 7 and other examples showed that the surface tackiness was improved when the content of the thioxanthone photopolymerization initiator was 2% by mass or more. Further, a comparison between Example 8 and other examples showed that if the thioxanthone photopolymerization initiator was 5% by mass or less, the adhesiveness was excellent and the irradiation energy to be used could be small.

  Comparison of Examples 9 and 13 with other examples shows that other examples containing 0.3% by mass or more of a silicone surfactant tend to have excellent gloss on the surface of the obtained cured film. This is presumed that the ink composition adhered on the recording medium spreads well and the surface of the cured film becomes smoother. Furthermore, it was speculated that these other examples tended to have better adhesion, and that the better the spread of the ink composition adhering to the recording medium, the better the adhesion.

  Comparison of Example 10 with other examples shows that the other examples having a recording density of 600 dpi × 600 dpi or more tend to have better gloss on the surface of the obtained cured film. I guessed it was smoother. These other examples showed a tendency to further improve the adhesion, and when the recording density was high, it was estimated that the adhesion tends to be further improved.

  From a comparison between Example 14 and other examples, it was found that when the ink composition contains an acylphosphine oxide photopolymerization initiator, the adhesion is further improved.

  In the comparison between Examples 12 and 7 and the comparison between Examples 2 and 11, when the temporary curing was not performed at the position of the pre-curing irradiation portion 42a and the temporary curing was not performed, the temporary curing was performed. It has been found that the bleeding is better than when the main curing is performed at the position of the irradiation unit 44. On the other hand, since the irradiation was performed with a large irradiation energy at the position of the pre-curing irradiation unit 42a, the light leaked from the light source easily hits the head, and the nozzle plate was cured by the nozzle plate. In some cases, the discharge becomes unstable due to an increase in the viscosity, and it has been found that the present invention is particularly useful when pre-curing and then performing main curing, because these are excellent in these respects.

  By comparison between Reference Example 1 and Reference Example 5 and the Examples, the ink composition containing a cyan material having a high transmittance reaches irradiation energy inside the ink composition even if it contains a thioxanthone photopolymerization initiator. It was also found that the adhesion is not inferior, and the adhesion is not inferior even when the irradiation energy is relatively small. This tendency is the same for the example using the magenta color material.

  A comparison between Reference Example 2 and Example shows that a cured film with a low OD value has good adhesion and surface tack even with a small amount of irradiation energy, but because of its low OD value, a light color recorded matter (cured film). It turns out that it can only be obtained.

  Comparison between each Example and Comparative Example 5 revealed that the ink composition contained a thioxanthone-based photopolymerization initiator and was excellent in surface tackiness and bleeding resistance.

  Comparison between Reference Examples 3 and 4 and Comparative Examples 1 and 3 shows that when a serial printer is used, the adhesion is good even if the irradiation energy × transmittance is relatively small, but the surface tackiness is inferior. Not shown. By irradiating each pass, it is irradiated in a state where all the ink necessary for recording is not attached (only a small amount of ink is attached), and thus the inside of the ink is sufficiently cured. It was estimated that the adhesion was improved. However, since recording is performed in two passes, the recording speed tends to be slow. From this, it was found that the present invention is particularly useful in the case of a line printer that attaches and irradiates all ink necessary for recording in one pass.

  DESCRIPTION OF SYMBOLS 1 ... Printer, 20 ... Conveyance unit, 25A ... Upstream roller, 25B ... Downstream roller, 26 ... Conveyance drum, 30 ... Head unit, 40 ... Irradiation unit, 42a, 42b, 42c, 42d ... Preliminary curing irradiation unit, 44 ... Irradiation unit for main curing, 110 ... Detector group, 120 ... Controller, 121 ... Interface, 122 ... CPU, 123 ... Memory, 124 ... Unit control circuit, 130 ... Computer, K, C, M, Y ... Head, S: Recording medium.

Claims (13)

An ultraviolet curable type used in an inkjet recording method having a curing step of irradiating ultraviolet light having a peak wavelength of 380 to 405 nm from a semiconductor light source to obtain a cured film on an ultraviolet curable inkjet ink composition attached to a recording medium An inkjet ink composition comprising:
The product of the light transmittance (%) at a wavelength of 395 nm of the cured film and the irradiation energy (mJ / cm ² ) of ultraviolet rays in the curing step is 2.0 or more,
Including at least one of a yellow color material or a black color material, and a thioxanthone photopolymerization initiator,
The OD value of the cured film of the ink composition is 1.8 or more,
UV-curable ink composition for inkjet.   The ultraviolet curable inkjet ink according to claim 1, wherein the inkjet recording method performs recording by one-pass printing using a line printer having a line head having a width equal to or larger than a recording width of the recording medium. Composition. The ultraviolet rays and the irradiation energy of 350~1000mJ / cm ^2, UV-curable inkjet ink composition according to claim 1 or 2.   The ultraviolet curable inkjet ink composition according to claim 1, wherein the recording medium is a non-ink-absorbing recording medium.   The ultraviolet curable inkjet ink composition according to any one of claims 1 to 4, comprising 2.0 to 5.0% by mass of the thioxanthone photopolymerization initiator.   Furthermore, the ultraviolet curable inkjet ink composition of any one of Claims 1-5 containing 0.30 mass% or more of silicone type surfactant.   Furthermore, the ultraviolet curable inkjet ink composition of any one of Claims 1-6 containing 5.0-15 mass% of acyl phosphine oxide type photoinitiators.   The ultraviolet curable inkjet ink composition according to any one of claims 1 to 7, wherein the inkjet recording method records at a recording resolution of 600 dpi or more and 600 dpi or more.   The ultraviolet curable ink jet according to any one of claims 1 to 8, comprising any one of the yellow color material 2.5 to 2.9% by mass and the black color material 1.5 to 1.9% by mass. Ink composition.   10. The ultraviolet curable inkjet ink composition according to claim 1, wherein the inkjet recording method is performed by irradiating the ultraviolet rays a plurality of times. 11.   The ultraviolet curable inkjet ink composition according to claim 1, wherein the cured film has a thickness of 13 μm or less.   The ultraviolet curable inkjet ink composition according to any one of claims 1 to 11, wherein the cured film has a light transmittance of 0.0030% or more at a wavelength of 395 nm when having a film thickness of 10 µm. . A discharge step of discharging and adhering the ultraviolet curable inkjet ink composition according to any one of claims 1 to 12 to a recording medium;
Curing to obtain a cured film having an OD value of 1.8 or more by irradiating the ultraviolet ray curable inkjet ink composition attached to the recording medium with ultraviolet rays from a semiconductor light source having a peak wavelength of 380 to 405 nm. A process,
The product of the light transmittance (%) at a wavelength of 395 nm of the cured film of the ultraviolet curable inkjet ink composition and the irradiation energy (mJ / cm ² ) of the ultraviolet ray is 2 or more.
Inkjet recording method.

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