JP6841783B2 - Inkjet recording method - Google Patents

Description

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

The inkjet recording method, which can record high-definition images with a relatively simple device, is rapidly developing in various fields. For example, Patent Document 1 provides a monofunctional (meth) ink composition for providing an ultraviolet curable ink composition having excellent curability of the ink composition and excellent abrasion resistance and extensibility of the cured film. An ultraviolet curable ink composition for an inkjet ink containing an acrylate monomer and a photopolymerization initiator, wherein the molecular structure and content of the monofunctional (meth) acrylate monomer and the cured product of the monofunctional (meth) acrylate An ultraviolet curable ink composition for inkjet, which defines an average number of moles of Tg, is disclosed.

Another object of Patent Document 2 is to provide an ultraviolet curable ink composition for inkjet, which has excellent curability of the ink composition and can prevent coloring of the cured film at the initial stage after inkjet recording. An ultraviolet curable ink composition for inkjet, which comprises a predetermined monomer and a photopolymerization initiator containing an acylphosphine oxide-based photopolymerization initiator and a thioxanthone-based photopolymerization initiator. An ultraviolet curable ink composition for inkjet is disclosed in which the total content of the polymerization initiator and the thioxanthone-based photopolymerization initiator is 8 to 16% by mass with respect to the total mass of the ink composition.

Japanese Unexamined Patent Publication No. 2012-188612 Japanese Unexamined Patent Publication No. 2012-140583

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

That is, since the thioxanthone-based photopolymerization initiator has a high light absorption rate at a wavelength near 395 nm, light into the inside of the ink composition adhering to the recording medium is emitted particularly in photocuring using a semiconductor light source such as an LED. It was found that it inhibits permeation and is inferior in curability inside the ink composition. As a result, it has been clarified that it causes inferior adhesion to the recording medium. In addition to this thioxanthone-based 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 inferior in adhesion due to further obstruction of light transmission to the inside. Therefore, an ultraviolet curable inkjet ink composition containing a yellow color material and / or a black color material and having an excellent adhesion even when ultraviolet rays having a peak wavelength of 380 to 405 nm is used in the future as a low-cost semiconductor light source such as an LED. It is considered that UV inkjet printers that are cured by using the above are more and more useful in the hope.

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

The present inventors have diligently studied to solve the above problems. As a result, they have found that the above problems can be solved if the ink composition has a predetermined composition when ultraviolet rays having a peak wavelength in the range of 380 to 405 nm are used, and the present invention has been 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 an ultraviolet curable ink composition for an ultraviolet curable ink adhering to a recording medium with ultraviolet rays having a peak wavelength of 380 to 405 nm from a semiconductor light source to obtain a cured film. An ink composition for an inkjet
The product of the light transmittance (%) of the cured film at a wavelength of 395 nm and the ultraviolet irradiation energy (mJ / cm ² ) of the curing step is 2.0 or more.
Containing at least one of a yellow or black colorant and a thioxanthone-based photopolymerization initiator.
The OD value of the cured film of the ink composition is 1.8 or more.
UV curable inkjet ink composition.
[2]
The ultraviolet curable inkjet recording method according to the preceding item [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 the recording width of the recording medium. Ink composition.
[3]
The ultraviolet curable inkjet ink composition according to the preceding item [1] or [2], which irradiates the ultraviolet rays with an irradiation energy of 350 to 1000 mJ / cm ^2.
[4]
The ultraviolet curable inkjet ink composition according to any one of the preceding items [1] to [3], wherein the recording medium is an ink non-absorbable recording medium.
[5]
The ultraviolet curable inkjet ink composition according to any one of the preceding items [1] to [4], which contains 2.0 to 5.0% by mass of the thioxanthone-based photopolymerization initiator.
[6]
The ultraviolet curable inkjet ink composition according to any one of the above items [1] to [5], further containing 0.30% by mass or more of a silicone-based surfactant.
[7]
The ultraviolet curable inkjet ink composition according to any one of the preceding items [1] to [6], further containing 5.0 to 15% by mass of an acylphosphine oxide-based photopolymerization initiator.
[8]
The ultraviolet curable inkjet ink composition according to any one of the preceding items [1] to [7], wherein the inkjet recording method records at a recording resolution of 600 dpi or more × 600 dpi or more.
[9]
The ultraviolet ray according to any one of the preceding items [1] to [8], which contains either 2.5 to 2.9% by mass of the yellow color material or 1.5 to 1.9% by mass of the black color material. Curable inkjet ink composition.
[10]
The ultraviolet-curable inkjet ink composition according to any one of the preceding items [1] to [9], wherein the inkjet recording method is to irradiate the ultraviolet rays a plurality of times.
[11]
The ultraviolet curable inkjet ink composition according to any one of the above items [1] to [10], wherein the cured film has a film thickness of 13 μm or less.
[12]
The ultraviolet curable inkjet according to any one of the above items [1] to [11], wherein the cured film has a light transmittance of 0.0030% or more at a wavelength of 395 nm when the film has a film thickness of 10 μm. Ink composition.
[13]
A ejection step of ejecting and adhering the ultraviolet curable inkjet ink composition according to any one of the above items [1] to [12] to a recording medium.
The ultraviolet curable ink composition for an inkjet that adheres to the recording medium is irradiated with ultraviolet rays 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. Has a process and
The product of the light transmittance (%) at a wavelength of 395 nm and the irradiation energy of the ultraviolet rays (mJ / cm ² ) of the cured film of the ultraviolet curable inkjet ink composition is 2 or more.
Inkjet recording method.

It is a block diagram which shows an example of the structure of the inkjet recording apparatus which can be used in this embodiment. It is schematic cross-sectional view which shows an example around the head unit, the transport unit, and the irradiation unit in the line printer which is an example of an inkjet recording apparatus that can be used in this 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, but the present invention is not limited thereto. Various modifications are possible within the range that does not deviate from the gist. In the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted. In addition, the positional relationship such as up, down, left, and right shall be based on the positional relationship shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the ratios shown.

[UV curable inkjet ink composition]
The ultraviolet curable inkjet ink composition according to the present 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 adhering to the recording medium. An ultraviolet curable inkjet ink composition used in an inkjet recording method having a curing step of irradiating an ultraviolet ray having a peak wavelength from a semiconductor light source to obtain a cured film, wherein the light transmittance (%) of the cured film at a wavelength of 395 nm. The product of the ultraviolet irradiation energy (mJ / cm ² ) of the curing step is 2.0 or more, and the ink contains at least one of a yellow color material or a black color material and a thioxanthone-based photopolymerization initiator. The OD value of the cured film of the composition is 1.8 or more.

In general, by containing a thioxanthone-based photopolymerization initiator, surface tackiness can be reduced, and in particular, when a thin film is susceptible to oxygen inhibition, the ink surface can be cured to prevent color mixing and bleeding between dots. On the other hand, it was found that the thioxanthone-based photopolymerization initiator tends to hinder the internal curability of the ink composition (decreases the light transmittance of the film) and deteriorates the adhesion (particularly the adhesion when the film is thick). It was. In particular, when the cured film having an OD value of 1.8 or more is cured by irradiating the LED with ultraviolet rays having a peak wavelength of 380 to 405 nm, the decrease in adhesion becomes remarkable.

Therefore, when an ink composition containing a thioxanthone-based photopolymerization initiator having excellent adhesion was examined, it was used in an inkjet recording method in which the product of the irradiation energy and the transmittance of the cured film was 2 or more using a predetermined semiconductor light source. In that case, it was found that the ultraviolet rays penetrated into the ink composition and the adhesion could be ensured.

Since light with a lower wavelength is transmitted to the inside of the ink composition, when a metal halide light source or a mercury lamp having an emission wavelength up to a low wavelength range is used, the internal curability of the ink composition tends to be good and the adhesion tends to be excellent. is there. However, these ultraviolet light sources are not preferable from the viewpoints of high heat generation, low life, high power consumption, and large size of the light source. Therefore, the ink composition according to the present embodiment is used for an inkjet recording method using a semiconductor light source which is excellent from the above viewpoint.

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

The thioxanthone-based photopolymerization initiator is not particularly limited, but specifically, it preferably contains one or more selected from the group consisting of thioxanthone, diethylthioxanthone, isopropylthioxanthone, and chlorothioxanthone. Although not particularly limited, 2,4-diethylthioxanthone is preferable as diethylthioxanthone, 2-isopropylthioxanthone as isopropylthioxanthone, and 2-chlorothioxanthone as chlorothioxanthone. An ink composition containing such a thioxanthone-based photopolymerization initiator tends to be more excellent in curability, storage stability, and ejection stability. Among these, a thioxanthone-based photopolymerization initiator containing diethyl thioxanthone is preferable. By including diethylthioxanthone, there is a tendency that ultraviolet light (UV light) in a wide range can be converted into an active species more efficiently.

The commercially available thioxanthone-based photopolymerization initiator is not particularly limited, but specifically, Speedcure DETX (2,4-diethyl thioxanthone), Speedcure ITX (2-isopropylthioxanthone) (all manufactured by Rambson), KAYACURE DETX-S (2,4-diethylthioxanthone) (manufactured by Nippon Kayaku Co., Ltd.) can be mentioned.

The content of the thioxanthone-based photopolymerization initiator is preferably 2.0 to 5.0% by mass, more preferably 2.5 to 4.5% by mass, based on the total mass (100% by mass) of the ink composition. 3-4% by mass is more preferable. When the content is 2.0% by mass or more, the surface tackiness can be further reduced, and when the thin film is susceptible to oxygen inhibition, the ink surface tends to be cured to further prevent color mixing and bleeding between dots. 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 adhesion of the cured film tends to be superior.

(Other photopolymerization initiators)
The ink composition may further contain other photopolymerization initiators. Other photopolymerization initiators are not limited as long as they generate active species such as radicals and cations by the energy of light (ultraviolet rays) and initiate the polymerization of the polymerizable compound. Or a photocationic polymerization initiator can be used. Of these, it is preferable to use a photoradical polymerization initiator.

The above-mentioned photoradical polymerization initiator is not particularly limited, and for example, aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thiophenyl group-containing compounds, etc.), α- Examples thereof include aminoalkylphenone compounds, hexaarylbiimidazole compounds, ketooxime 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 to further contain an acylphosphine oxide-based photopolymerization initiator (acylphosphine oxide compound). Acylphosphine oxide-based photopolymerization initiators are susceptible to oxygen inhibition, but are suitable for curing with long-wavelength LEDs. Therefore, the combination of the acylphosphine oxide-based photopolymerization initiator and the thioxanthone-based photopolymerization initiator tends to be superior in the curing process by UV-LED, and the curability and adhesion of the ink composition tend to be further excellent.

The acylphosphine oxide-based photopolymerization initiator is not particularly limited, but specifically, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide and 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide. , And bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide.

The commercially available acylphosphine oxide-based photopolymerization initiator is not particularly limited, but 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-based photopolymerization initiator is preferably 5.0 to 15% by mass, more preferably 6.0 to 10.0% by mass, based on the total mass (100% by mass) of the ink composition. 7.0 to 8.0% by mass is more preferable. When the content is 5.0% by mass or more, the curability tends to be superior. When the content is 15% by mass or less and 15% by mass or less, the dissolution and storage stability of the solid content are kept good, and the reliability tends to be superior.

Other photoradical polymerization initiators are not particularly limited, but are, for example, acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexylphenylketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone. , Triphenylamine, carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-diaminobenzophenone, Michler ketone, benzoinpropyl ether, benzoin ethyl ether, benzyl dimethyl ketal, 1-( 4-Isopropyl) -2-hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, and 2-methyl-1- [4- (methylthio) phenyl ] -2-Molholino-propane-1-one.

Commercially available products of the photoradical polymerization initiator are not particularly limited, but for example, IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethane-1-one) and 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-Propane-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-methylthiophenyl) -2-morpholinopropane-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-cyclopentadiene-1-yl) -bis (2,6-difluoro-3- (1H-pyrrole-1-yl) -phenyl) titanium), IRGACURE OXE 01 (1.2-octane) Dione, 1- [4- (Phenylthio)-, 2- (O-benzoyloxime)]), IRGACURE OXE 02 (Etanone, 1- [9-ethyl-6- (2-methylbenzoyl) -9H-carbazole-3) -Il]-, 1- (O-acetyloxime)), IRGACURE 754 (oxyphenylacetic acid, 2- [2-oxo-2-phenylacetoxyethoxy] ethyl ester and oxyphenylacetic acid, 2- (2-hydroxyethoxy) A mixture of ethyl esters) (above, manufactured by BASF), Speedcure TPO (above, manufactured by Lambson), Lucirin TPO, LR8883, LR8970 (above, manufactured by BASF), and Yubekryl P36 (manufactured by UCB).

The photocationic polymerization initiator is not particularly limited, and specific examples thereof include a sulfonium salt and an iodonium salt.

Commercially available products of the photocationic polymerization initiator are not particularly limited, and specific examples thereof include Irgacare 250 and Irgacare 270.

The above photopolymerization initiator may be used alone or in combination of two or more.

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 above range, the ultraviolet curing rate tends to be sufficiently exhibited, and the undissolved residue of the photopolymerization initiator and the coloring derived from the photopolymerization initiator tend to be avoided.

[Color material]
The ink composition contains at least one of a yellow color material and a black color material, and may contain other color materials as required. As the coloring 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 ultraviolet light tends to be difficult to reach the inside of the ink composition, so that the adhesion tends to be low. It is also possible to reduce the content of the yellow color material or the black color material to increase the transmittance of the cured film, but the OD value of the obtained cured film becomes low, and only a light-colored cured product can be obtained. There is a problem. In this regard, the ink composition according to the present embodiment used in the inkjet recording method of irradiating ultraviolet rays so that the product of the light transmittance at the wavelength of 395 nm of the cured film and the irradiation energy of ultraviolet rays is 2 or more. Even when a yellow color material or a black color material is contained, the adhesion is excellent.

(Pigment)
By using a pigment as a coloring material, the light resistance of the ink composition can be improved. As the pigment, either an inorganic pigment or an organic pigment 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.

Examples of organic pigments include azo pigments such as insoluble azo pigments, condensed azo pigments, azolakes and chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments and the like. Polycyclic pigments, dye chelate (for example, basic dye type chelate, acidic dye type chelate, etc.), dyeing rake (basic dye type rake, acidic dye type rake), nitro pigment, nitroso pigment, aniline black, daylight Fluorescent pigments can be mentioned.

The carbon black used as the black coloring material is not particularly limited, but for example, No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc. (above, manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. Rega1 330R, Rega1 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc. , Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color B1ack S150, Color Black S160, Color Black Examples thereof include Black 4A and Special Black 4 (all manufactured by Degussa).

The pigment used as the yellow color material is not particularly limited, but 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 can be mentioned.

The pigment used as the white coloring material is not particularly limited, but for example, C.I. I. Pigment Whites 6, 18 and 21.

The pigment used as the magenta coloring material is not particularly limited, but 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.

The pigment used as the cyan color material is not particularly limited, but 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 can be mentioned.

The pigments other than magenta, cyan, and yellow coloring materials are not particularly limited, but for example, 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 pigment may be used alone or in combination of two or more.

When the above pigments are used, the average particle size thereof is preferably 300 nm or less, more preferably 50 to 200 nm. When the average particle size is within the above range, the reliability of the ink composition such as ejection stability and dispersion stability is further improved, and an image with excellent image quality can be formed. Here, the average particle size 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.

The dye used as the yellow color material is not particularly limited, but for example, C.I. I. Acid Yellow 17,23,42,44,79,142,

The dye used as the black coloring material is not particularly limited, but for example, C.I. I. Acid Black 1,2,24,94, C.I. I. Hood Black 1, 2, C.I. I. Direct Yellow 1,12,24,33,50,55,58,86,132,142,144,173, C.I. I. Dilekdo Black 19,38,51,71,154,168,171,195, C.I. I. Reactive Black 3, 4, 35

The dye used as another coloring material is not particularly limited, but 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 above dyes may be used alone or in combination of two or more.

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, based on the total mass (100% by mass) of the ink composition. 6 to 2.7% by mass is more preferable. When the content is within the above range, it tends to be possible to secure better color development 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, based on 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, it tends to be possible to secure better color development without increasing the ink viscosity more than necessary.

[Surfactant]
The ink composition according to this embodiment may further contain a surfactant. The surfactant is not particularly limited, but for example, a silicone-based surfactant (commercially available products include BYK UV3500 and UV3570 (trade name manufactured by Big Chemie Japan)) and an acrylic surfactant (BYK350 (Big Chemie)).・ Japan's product name)). Among these, by containing a silicone-based surfactant, the surface tension is excellently reduced, 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, still more preferably 0.40% by mass or more, based on the total mass (100% by mass) of the ink composition. , 0.50% by mass or more is particularly preferable. The content is preferably 1.0% by mass or less, more preferably 0.8% by mass or less, and even more 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 is kept good, and the discharge stability tends to be superior.

The surface tension of the ink composition is preferably 23 mN / m or less, more preferably 22 mN / m or less. Further, the lower limit of the surface tension is not particularly limited, and the lower the lower limit, the more preferable. 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 surface tension, a commonly used surface tension meter (for example, Kyowa Surface Science Co., Ltd., surface tension meter CBVP-Z, etc.) is used to measure the surface tension at a liquid temperature of 25 ° C. by the Wilhelmy method. The method can be exemplified.

As the silicone-based surfactant, a polysiloxane-based compound is preferably used, and examples thereof include polyether-modified organosiloxane. Commercially available products can also be used, for example, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-348 (trade names, 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 name, manufactured by Shin-Etsu Chemical Co., Ltd.).

[Polymerizable compound]
The ink composition may contain a polymerizable compound. The polymerizable compound can be polymerized by itself 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, but specifically, conventionally known monofunctional, bifunctional, and trifunctional or higher polyfunctional monomers and oligomers can be used. The polymerizable compound may be used alone or in combination of two or more. Hereinafter, these polymerizable compounds will be exemplified.

The monofunctional, bifunctional, and trifunctional or higher functional monomers are not particularly limited, and include, for example, unsaturated carboxylic acids of (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid; Salts of saturated carboxylic acids; esters of unsaturated carboxylic acids, urethanes, amides and anhydrides; acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. The monofunctional, bifunctional, and trifunctional or higher functional oligomers are not particularly limited, but are, for example, oligomers formed from the above-mentioned monomers such as linear acrylic oligomers, epoxy (meth) acrylates, and oxetane (Oxetane). Examples thereof include meta) acrylate, aliphatic urethane (meth) acrylate, aromatic urethane (meth) acrylate and polyester (meth) acrylate.

Further, an N-vinyl compound may be contained 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. Be done.

The monofunctional (meth) acrylate is not particularly limited, and is, for example, isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, and isomyristyl (meth). ) 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, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxy Propyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, lactone-modified flexible (meth) acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate, and dicyclo Examples include pentenyloxyethyl (meth) acrylate. Among these, phenoxyethyl (meth) acrylate is preferable.

The content of the monofunctional (meth) acrylate is preferably 30 to 85% by mass, more preferably 40 to 75% by mass, based on the total mass (100% by mass) of the ink composition. By setting the above preferable range, the curability, initiator solubility, storage stability, and discharge stability tend to be more excellent.

Examples of the monofunctional (meth) acrylate include those containing a vinyl ether group. Such monofunctional (meth) acrylate is not particularly limited, and for example, 2-vinyloxyethyl (meth) acrylate, 3-vinyloxypropyl (meth) acrylate, 1-methyl-2-methyl-2-methyl (meth) acrylate. Vinyloxyethyl, 2-vinyloxypropyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, 1-methyl-3-vinyloxypropyl (meth) acrylate, 1-vinyloxymethylpropyl (meth) acrylate, ( 2-Methyl-3-binyloxypropyl (meth) acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth) acrylate, 3-vinyloxybutyl (meth) acrylate, 1-methyl-2-bini (meth) acrylate Loxypropyl, 2-vinyloxybutyl (meth) acrylate, 4-vinyloxycyclohexyl (meth) acrylate, 6-vinyloxyhexyl (meth) acrylate, 4-vinyloxymethylcyclohexylmethyl (meth) acrylate, (meth) 3-Vinyloxymethylcyclohexylmethyl acrylate, 2-vinyloxymethylcyclohexylmethyl (meth) acrylate, p-vinyloxymethylphenylmethyl (meth) acrylate, m-vinyloxymethylphenylmethyl (meth) acrylate, ( Meta) O-vinyloxymethylphenylmethyl acrylate, 2- (vinyloxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxy) ethyl (meth) acrylate, 2- (bini) acrylate Loxyethoxy) propyl, 2- (vinyloxyethoxy) isopropyl (meth) acrylate, 2- (vinyloxyisopropoxy) propyl (meth) acrylate, 2- (vinyloxyisopropoxy) isopropyl (meth) acrylate, ( 2- (Vinyloxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) ethyl (meth) acrylate, (meth) acrylic Acid 2- (vinyloxyisopropoxyisopropoxy) ethyl, (meth) acrylic acid 2- (vinyloxyethoxyethoxy) propyl, (meth) acrylic acid 2- (vinyloxyethoxyisopropoxy) propyl, (meth) acrylic acid 2 -(Vinyloxyisopropoxyethoxy) propyl, (meth) acrylate 2- (vinyloxyisopropoxyisopropoxy) propyl, (meth) acrylate 2- (vinyloxyethoxyethoki) S) Isopropyl, 2- (vinyloxyethoxyisopropoxy) isopropyl (meth) acrylic acid, 2- (vinyloxyisopropoxyethoxy) isopropyl (meth) acrylic acid, 2- (vinyloxyisopropoxyisopropoxy) (meth) acrylic acid ) Isopropyl, 2- (vinyloxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxy) ethyl (meth) acrylate , (Meta) Acrylic Acid 2- (Isopropenoxyethoxyethoxy) Ethyl, (Meta) Acrylic Acid 2- (Isopropenoxyethoxyethoxyethoxy) Ethyl, (Meta) Acrylic Acid 2- (Isopropenoxyethoxyethoxyethoxyethoxy) Ethyl, polyethylene glycol monovinyl ether (meth) acrylate, and polypropylene glycol monovinyl ether (meth) acrylate, phenoxyethyl (meth) acrylate, isobonyl (meth) acrylate, and benzyl (meth) acrylate can be mentioned. Among these, 2- (vinyloxyethoxy) ethyl (meth) acrylate, phenoxyethyl (meth) acrylate, isobonyl (meth) acrylate, and benzyl (meth) acrylate are preferable.

Among these, 2- (meth) acrylic acid 2- (vinyloxyethoxy) ethyl (meth) acrylic acid, that is, acrylic acid 2 is used because the ink composition can be made to have a lower viscosity, has a high ignition point, and has excellent curability of the ink composition. 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. In addition, 2- (vinyloxyethoxy) ethyl acrylate is superior to 2- (vinyloxyethoxy) ethyl methacrylate in terms of curability.

The content of the vinyl ether group-containing (meth) acrylic acid esters, particularly 2- (vinyloxyethoxy) ethyl (meth) acrylate, is 10 to 70% by mass with respect to the total mass (100% by 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 storage stability of the ink composition is more excellent, and the surface gloss of the printed matter tends to be more excellent.

Among the above (meth) acrylates, the bifunctional (meth) acrylate is not particularly limited, but for example, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and the like. 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-Nonandiol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecanedi (meth) acrylate, EO (ethylene oxide) adduct di (meth) acrylate of bisphenol A, bisphenol A PO (propylene oxide) adduct di (meth) acrylate, neopentyl glycol di (meth) acrylate of hydroxypivalate, polytetramethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) Examples thereof include acrylates and trifunctional or higher functional (meth) acrylates 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 trifunctional or higher functions. (Meta) acrylate is preferred. More preferably, the ink composition contains a polyfunctional (meth) acrylate in addition to the monofunctional (meth) acrylate.

The content of the bifunctional or higher polyfunctional (meth) acrylate is preferably 5 to 60% by mass, more preferably 15 to 60% by mass, and 20 to 50% by mass with respect to the total mass (100% by mass) of the ink composition. Mass% is more preferred. By setting the above preferable range, the curability, storage stability, ejection stability, and surface gloss of printed matter tend to be superior.

Among the above (meth) acrylates, the trifunctional or higher functional (meth) acrylate is not particularly limited, and is, 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 ) Acrylate, pentaerythritol ethoxytetra (meth) acrylate, and caprolactam-modified dipentaerythritol hexa (meth) acrylate.

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

The content of the polymerizable compound is preferably 5 to 95% by mass, more preferably 15 to 90% by mass, based on 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 matter are further improved. Can be done.

[Dispersant]
When the ink composition contains a pigment, a dispersant may be further contained in order to improve the dispersibility of the pigment. The dispersant is not particularly limited, and examples thereof include dispersants commonly used for preparing a pigment dispersion such as a polymer dispersant. Specific examples thereof 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. Examples thereof include resins containing at least one type of resin as a main component. Commercially available polymer dispersants include Ajinomoto Fine-Techno's Ajisper series, Avecia and Noveon's Solspers series (Solsperse 36000, etc.), and BYK Chemie's Disperbic series. , Kusumoto Kasei Co., Ltd.'s Disparon series can be mentioned.

[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 accelerators, and wetting agents (moisturizers), and other additives. The above-mentioned other additives are not particularly limited, and examples thereof include conventionally known fixing agents, fungicides, preservatives, antioxidants, ultraviolet absorbers, chelating agents, pH adjusters, and thickeners. Can be mentioned.

[Other Embodiments of Ink Composition]
The ink composition according to the present embodiment has a light transmittance of 0 at a wavelength of 395 nm of a cured film having a film thickness of 10 μm, in addition to the ink composition containing at least one of the above-mentioned yellow color material or black color material. The cured film having a film thickness of 10 μm and in the range of .002 to 0.015% has an OD value of 1.8 or more, and the above-mentioned thioxanthone-based photopolymerization initiator and the above-mentioned coloring material (yellow coloring material). It is also possible to use an ink composition containing (and not limited to black colorants). The ink composition may contain a color material other than the yellow color material and the black color material as the color material, but the composition and characteristics of the ink composition other than this may be described in the above-mentioned yellow color material or the black color material. It can be the same as the ink composition containing at least one of.

[Recording medium]
The above-mentioned recording medium is not particularly limited, and examples thereof include an ink non-absorbent or ink-low-absorbable recording medium. Of these, an ink-non-absorbable recording medium is preferable. When an ink-non-absorbable recording medium is used, the film thickness of the coating film directly correlates with the color development, so that the adhesion tends to be inferior when trying to secure the color development, and the ink does not permeate the recording medium. Easy to peel off at the interface with. Therefore, the present invention is more effective when an ink-non-absorbable recording medium is used. On the other hand, in the ink-absorbing recording medium, since the ink permeates the recording medium, the internal curability is inferior, but the interfacial peeling tends to be difficult to occur.

Among the recording media, the ink-non-absorbable recording medium is not particularly limited, but for example, a plastic film or paper that has not been surface-treated for inkjet recording (that is, does not form an ink absorbing layer). Examples thereof include those in which plastic is coated on a base material such as, and those in which a plastic film is adhered. Examples of the plastic referred to here include polyvinyl chloride (vinyl chloride), polyethylene terephthalate (PET), polycarbonate (PC), polystyrene (PS), polyurethane (PU), polyethylene (PE), and polypropylene (PP). Examples of the recording medium having low ink absorption include printing paper such as art paper, coated paper, and matte paper.

Here, as the ink non-absorbent and low-absorbency recording medium, a recording medium whose recording surface has a water absorption amount of 10 mL / m2 or less from the start of contact to 30 msec in the Bristow method is shown. 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 Pulp and Paper Technology Association (JAPAN TAPPI). For details of the test method, refer to the standard No. of "JAPAN TAPPI Pulp and Paper Test Method 2000 Edition". 51 "Paper and Paperboard-Liquid Absorption Test Method-Bristow Method".

[Inkjet recording method]
The inkjet recording method according to the present embodiment includes a ejection step of ejecting and adhering the ultraviolet curable inkjet ink composition to the recording medium, and the ultraviolet curable inkjet ink composition adhering to the recording medium. On the other hand, it has a curing step of irradiating ultraviolet rays 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, and curing the ultraviolet curable ink composition for inkjet. The product of the light transmittance (%) at the wavelength of 395 nm of the film and the irradiation energy of the ultraviolet rays (mJ / cm ² ) is 2 or more.

[Discharge process]
The inkjet recording method according to the present embodiment includes a ejection step of ejecting and adhering an ultraviolet curable inkjet ink composition to a recording medium. It is preferable to eject the ink composition so that the recording resolution of the obtained cured product is 600 dpi or more × 600 dpi or more, and it is more preferable to eject the ink composition so that the recording resolution is 720 dpi or more × 720 dpi or more. It is more preferable to eject the ink composition so that the recording resolution is 1200 dpi or more × 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 poor wettability, a phenomenon occurs in which dots are difficult to spread due to interference between adjacent dots that have landed, and one dot is used compared to the serial printing method to ensure solid filling. The amount of ink per hit is required. This phenomenon occurs more prominently when the resolution is low. In the ink composition according to the present mobile phone, by setting the recording resolution to 600 × 600 dpi or more, the coating amount required for solid filling can be 10 μm or less. If solid filling can be secured with a relatively small amount of ink per dot in this way, the feeling of thickening of the printed matter can be suppressed, and the ink cost of the user tends to be kept more appropriate.

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

In the curing step, the ink composition adhered 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 promoted by the function of the starting species. Will be done. Alternatively, in this step, the polymerization reaction of the polymerizable compound is started by irradiation with ultraviolet rays.

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

In the curing step, ultraviolet rays are irradiated so that the product of the light transmittance (%) at the wavelength of 395 nm of the cured film and the irradiation energy of ultraviolet rays (mJ / cm ^{2) is 2 or more.} The product of the light transmittance (%) at the wavelength of 395 nm of the cured film and the irradiation energy of ultraviolet rays (mJ / cm ² ) is preferably 4.0 or more, and more preferably 6.0 or more. The upper limit of the product of the light transmittance (%) at the wavelength of 395 nm of the cured film and the irradiation energy of ultraviolet rays (mJ / cm ² ) is not particularly limited, but is preferably 10.0 or less. When it is 10.0 or less, it is not necessary to sacrifice color development more than necessary or increase the number of irradiators to increase the cost of the printer, so that the configuration tends to be more balanced. Generally, by using a thioxanthone-based 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 the thioxanthone-based photopolymerization initiator is contained, the ultraviolet rays reach the inside of the ink composition, which is more excellent. A cured product having good adhesion can be obtained. As a result, it is possible to reduce the surface tackiness and improve the adhesion at the same time.

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 cost of the irradiator and the size of the irradiator tend to be kept more appropriate.

The light transmittance (transmittance) of the cured film obtained in the curing step, which comprises the ink composition according to the present embodiment, at a wavelength of 395 nm is preferably 0.001% or more, preferably 0.002% or more, and 0. 003% or more is more preferable, and 0.004% or more is further preferable. When the light transmittance is 0.001% or more, the internal curability can be ensured, so that the adhesion tends to be superior and 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 more preferably 0.005% or less. preferable. When the light transmittance is 0.018% or less, the density of the coloring material can be appropriately secured, and the color development of the printed matter tends to be superior. The light transmittance is improved by lowering the colorant concentration and the thioxanthone-based initiator concentration and the ink injection amount, and by increasing the color material concentration and the thioxanthone-based initiator concentration and the ink injection amount. descend. The light transmittance can be measured by the method described in Examples. Further, the cured film for measuring the light transmittance is a sufficiently cured cured film suitable for using a recorded material. The transmittance of the cured film at a wavelength of 395 nm is determined by the recording conditions such as the amount of ink applied to the recording medium (the thickness of the cured film) and the type of coloring material mainly contained in the ink composition as the ink composition. It tends to be determined by the content and the content of the thioxanthone-based photopolymerization initiator, and it can be adjusted by changing these. The color material tends to be determined by the contents of the yellow color material and the black color material. The above-mentioned coloring material and thioxanthone-based photopolymerization initiator tend not to change the light transmittance at a wavelength of 395 nm before and after curing of the ink composition.

Among the light transmittances of the cured film at the wavelength of 395 nm, the light transmittance of the cured film having a film thickness of 10 μm at the wavelength of 395 nm is preferably 0.0015% or more, preferably 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 ensured, so that the adhesion 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 more preferably 0.004% or less. preferable. When the light transmittance is 0.015% or less, the density of the coloring material in the coating film can be appropriately secured, and the color development of the printed matter tends to be superior. The light transmittance decreases when the content of the coloring material is high, and improves when the content of the coloring material is low. In the range of 395 nm, it is particularly remarkable in Bk (black) and Y (yellow), and it affects 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 the present 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 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 deep color. When the OD value is 1.8 or more, the ultraviolet transmittance of the cured film becomes lower, so that the adhesiveness generally tends to be inferior. However, according to the inkjet recording method according to the present embodiment, a cured product having excellent adhesion 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 that of a cured film having a film thickness of 10 μm, and can be specifically measured by the method described in Examples.

In the present embodiment, it is preferable to irradiate the ultraviolet rays a plurality of times. The multiple irradiations may include irradiation for temporary curing. Here, "temporary curing" means temporary fixing (pinning) of the ink composition, and more specifically, curing is performed before the main curing in order to prevent bleeding between dots and control the dot diameter. means. Generally, the degree of polymerization of the polymerizable compound in the temporary curing is lower than the degree of polymerization 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 required cured state of the cured film. Here, the term "curing" in the present specification means the above-mentioned main curing unless otherwise specified. It is preferable to irradiate the ultraviolet rays a plurality of times in one pass.

When irradiating ultraviolet rays a plurality of times, it is preferable that the first irradiation energy is lower than the second and subsequent irradiation energies. 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 is more excellent, and the 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. When irradiating ultraviolet rays multiple times, the above product shall be calculated using the sum of the irradiation energies of the multiple times of ultraviolet rays.

The inkjet recording method according to the present embodiment is preferably performed by using a line printer that records by one-pass printing with a line head having a width equal to or larger than the recording width of the recording medium. Line printers (1 pass printing) that attach all dots in one pass and irradiate them are more common than serial printers that attach dots of adjacent pixels in separate passes and irradiate ultraviolet rays for each pass. In general, it tends to be inferior in internal curability and poor in adhesion. Therefore, the present invention is particularly useful in an inkjet recording method using a line printer.

The thickness of the obtained cured film is not limited, and in the cured film having a thickness formed at the time of recording, the irradiation energy is such that the product of the transmittance at the wavelength of the cured film of 395 nm × the irradiation energy is 2 or more. Irradiation may be performed. Among them, the film 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 feeling of thickening of the printed matter can be reduced. The film thickness of the cured film is preferably 1 μm or more, more preferably 1.5 μm or more, and even more preferably 2.0 μm or more. When the film thickness is 1 μm or more, the surface tackiness tends to be excellent because it is less susceptible to oxygen inhibition. The film thickness of the cured film is determined by the amount of coating during solid printing, and by controlling the ink mass of 1 dot and the ink Duty (the 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 device (printer) for carrying out the above-mentioned inkjet recording method will be described with reference to the drawings. The inkjet recording device used in the present embodiment is not limited to the inkjet recording device described below.

FIG. 1 is a block diagram showing an example of the configuration of an inkjet recording device that can be used in the present embodiment. A printer driver is installed in the computer 130, and in order for the printer 1 to record an image, print data corresponding to the image is output to the printer 1. The printer 1 has 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 the 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 the print data input via the interface 121 in the memory 123. The controller 120 has 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 thickness among the cured films formed at the time of recording with 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 the transmittance at the wavelength of 395 nm of the cured film × the irradiation energy can be 2 or more for the cured film of any film thickness formed at the time of recording. Alternatively, when the film thickness of the cured film having the maximum film thickness differs depending on the recording mode such as the type of recording medium and the recording resolution, the controller 120 is the product of the transmittance at the wavelength of 395 nm × the irradiation energy for each recording mode. Each unit is controlled to irradiate with different irradiation energies so that the value is 2 or more.

Examples of the type of printer used in this embodiment include a line printer and a serial printer. Of these, line printers are preferable. Line printers (1 pass printing) that attach all dots in one pass and irradiate them are more common than serial printers that attach dots of adjacent pixels in separate passes and irradiate ultraviolet rays for each pass. In general, it tends to be inferior in internal curability and poor in adhesion. Therefore, the present invention is particularly useful in an inkjet recording method using a line printer.

A line printer, which is a line-type inkjet recording device, includes a line head as a head having a length equal to or longer than the width of the recording medium. The ink composition is ejected from the line head toward the recording medium while moving its position relative to the scanning direction in which the line head and the recording medium intersect the width direction. That is, the ink composition is ejected from the line head toward the recording medium that is scanned relative to the line head. Then, in the line printer, the head is fixed without (almost) moving, and recording is performed in one pass (single pass). Line printers have an advantage over serial printers in that they have a high recording speed.

Here, the above-mentioned "line heads having a length corresponding to the width of the recording medium" are not limited to the case where the width of the recording medium and the length (width) of the line head completely match each other. It may be different. When they may be different from each other, for example, the length (width) of the line head corresponds to the width (recording width) of the recording medium on which the ink composition should be ejected (the image should be recorded). In some cases, it is the length to be used.

On the other hand, a serial printer, which is a serial type inkjet recording device, performs a main scan (pass) in which an ink composition is ejected while the head moves in a main scan direction intersecting the sub scan direction of the recording medium, and is usually 2. Recording is performed with a pass or more (multi-pass).

[Inkjet head]
The head unit 30 included in the inkjet recording device (printer 1) includes a head (inkjet head) that ejects an ink composition toward a recording medium to perform recording. The head includes a cavity for ejecting the contained ink composition from a nozzle, an ejection drive unit provided for each cavity to apply an ejection driving force to the ink, and a cavity provided for each cavity. It has a nozzle for ejecting the ink composition to the outside of the head. A plurality of cavities, and a plurality of discharge drive units and nozzles provided for each cavity may be provided independently of each other in one head. The discharge drive unit is formed by using an electromechanical conversion element such as a piezoelectric element that changes the volume of the cavity by mechanical deformation, or an electronic heat conversion element that generates air bubbles in ink by generating heat and discharges the ink. be able to. The inkjet recording device may be provided with one head or a plurality of heads for each color of ink. When a plurality of heads are provided, the line heads are arranged by arranging the plurality of heads in the width direction of the recording medium. In this case, the recording width described above can be increased. When recording using a plurality of color ink compositions, the inkjet recording device includes a head for each ink. The head can be configured, for example, as shown in FIG. 3 of Japanese Patent Application Laid-Open No. 2009-279830.

Hereinafter, a line printer, which is an example of an inkjet recording apparatus that can be used in the present embodiment, will be described in detail with reference to FIG. In FIG. 2 used in 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-mentioned line printer, which is an example of a printer that can be used in the present embodiment.

A transfer motor (not shown) rotates a transfer roller including an upstream roller 25A and a downstream roller 25B, and the transfer drum 26 is driven. The recording medium S is conveyed along the peripheral surfaces of the transfer rollers 25A and 25B and the transfer drum 26, which is a support, as the transfer rollers rotate. Each line head composed of a head K, a head C, a head M, and a head Y is arranged around the transport drum 26 so as to face the transport 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 transport drum 26 moves relative to the head while supporting the recording medium S, the time (cycle) from an arbitrary position to returning 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 cycle is not particularly limited, but is preferably 15 seconds or less in order to realize high-speed printing.

The movement of the support in a predetermined cycle may be performed at least while the inkjet recording is performed, and may be performed continuously or intermittently while the inkjet 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, a roller-shaped or belt-shaped support and a recording medium S are supported. A plate-shaped support (platen, etc.) can also be mentioned. The movement of the support relative to the head may be a movement that moves (rotates) in one direction and returns to the same position, and is a combination of movement in one direction and movement in another direction. It may be a movement to return to the same position. In the latter case, the movement in a certain direction is regarded as the movement accompanying the recording on the single-cut type one recording medium, and the movement in the other direction is the movement accompanying the recording on the one recording medium. Examples thereof include a form of movement for recording on the next recording medium.
In the case of a serial printer, the above movement in a certain direction corresponds to a sub-scanning. Further, the movement of the support relative to the head may be any movement relative to the head, and includes movement such that the head moves relative to the support.

The material of the support is not particularly limited, and examples thereof include metal, resin, and rubber. Of these, metal is preferable. Since the material is a metal, unlike the case where it is a polymer material such as rubber, even if the support is used for a long period of time, cracks that are considered to be deteriorated by heat do not occur, and long-term use is possible. The metal is not particularly limited, and examples thereof include aluminum, stainless steel, copper, and iron, and alloys thereof. Further, the surface of the metal support, that is, the transport surface of the recording medium S may be coated with a coating agent or the like. As a result, the hardness of the surface of the support can be improved as compared with the unpainted support, and it can be made less slippery with the recording medium. The coating agent is not particularly limited, and examples thereof include an organic coating agent such as a resin, an inorganic coating agent such as an inorganic compound, and a composite coating agent thereof. The above items relating to the support can be applied not only to line printers but also to serial printers.

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

Since it is sufficient that the ink composition is main-cured by irradiating ultraviolet rays from the main-curing irradiation unit 44, ultraviolet rays are irradiated from a part or all of the temporary curing irradiation units 42a, 42b, 42c, and 42d. Instead, the curing operation may be completed by irradiating ultraviolet rays from the main curing irradiation unit 44. As described above, the curing operation may be performed only by the main curing without performing the temporary curing.

As described above, according to the present embodiment, all of the curability, ejection stability, and suppression of temperature rise in the recording apparatus after continuous printing are excellent, and further, the generation of cured wrinkles can be suppressed in the inkjet recording. Equipment can be provided. Furthermore, even when the recording device of the present embodiment uses a low-viscosity ink composition, the temperature rise in the recording device after continuous printing is maintained while ensuring excellent curability and ejection stability. It is excellent in suppression.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to 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 (2- (2-vinyloxyethoxy) ethyl acrylate, manufactured by Nippon Shokubai Co., Ltd.)
・ PEA (phenoxyethyl acrylate, manufactured by Osaka Organic Chemical Co., Ltd.)
・ DPGDA (dipropylene glycol diacrylate, manufactured by Sartmer)
・ A-DPH (dipentaerythritol hexaacrylate, manufactured by Shin Nakamura Chemical Industry Co., Ltd.)
[Thioxanthone-based photopolymerization initiator]
-Speedcure DETX (trade name manufactured by Rambson, solid content 100% by mass)
[Other photopolymerization initiators]
-IRGACURE 819 (BASF product name, solid content 100% by mass)
・ DAROCUR TPO (BASF product name, solid content 100% by mass)
[Surfactant]
・ BYK UV3500
[Dispersant]
-Solspace 36000 (Product name manufactured by LUBRIZOL, hereinafter abbreviated as Sol36000)
[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 (part by mass) shown in Table 1 below and stirred well 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]
I prepared a line printer. This line printer was used by modifying SurePress L-4033A (manufactured by Seiko Epson) as follows. As shown in FIG. 2, four line heads (heads having a length substantially corresponding to the width at which the image of the recording medium should be recorded (recording width)) are arranged in the transport direction of the recording medium. A light source was placed downstream in the transport direction of each head. In the recording by the line printer, among the head and the light source shown in FIG. 2, the head K, the irradiation unit for temporary curing 42a, and the irradiation unit 44 for main curing were used, and the others were not used. The transport drum 26 was made of aluminum, the diameter of the transport drum 26 was 500 mm, the printing speed was 285 mm / sec, and the drum rotation period was 5.5 seconds. As the head, a nozzle having a nozzle density of 600 dpi in the recording medium width direction of the nozzle row was used.

The ink compositions shown in Table 1 were 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 amount of ink droplets per pixel was adjusted so that the film thickness after curing was 10 μm. In this way, a solid pattern image was formed. In the "solid pattern image", dots are recorded for all the pixels of the pixel which is the minimum recording unit area defined by the recording resolution, and the ground of the recording medium in the pattern is entirely covered with ink. Means an image.

Subsequently, the ink adhering to the PET film was irradiated with ultraviolet rays from a light source to cure the ink composition. Specifically, first, as the light source 42a, an LED having a peak wavelength of 395 nm and an irradiation peak intensity of 500 mW / cm ^{2 was used.} The LED was irradiated with ultraviolet rays having an irradiation energy of 20 mJ / cm ^{2 to perform temporary curing.} Further, 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 film thickness of 10 μm obtained by curing the solid pattern image was obtained. In addition, it was confirmed by a touch test that the tack feeling 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 above internal transmittance measurement was measured using Spectorolino (manufactured by Gretag).

[Evaluation method: 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 method for measuring light transmittance was applied to a PET film (Lumilar 125E20 [trade name], manufactured by Toray Co., Ltd.) with a film thickness of 10 μm (cured film). 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 film thickness of 10 μm. Adhesion of the cured film is based on JIS K-5600-5-6 (ISO 2409) (General paint test method-5: Mechanical properties of coating film-6: Adhesiveness (cross-cut method)). Evaluated. 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) are shown in Table 1. The unit of irradiation energy in the table is mJ, which means ^{mJ / cm 2.}

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

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

For the evaluation of adhesion, first, a single-blade cutting tool (generally commercially available cutter) and a guide for cutting at equal intervals using a single-blade cutting tool were prepared as cutting tools. First, the blade of the cutting tool was applied so as to be perpendicular to the obtained cured film, and six cuts (distance between cuts: 1 mm; the same applies hereinafter) were made in the cured film. After making these 6 cuts, the direction was changed by 90 °, and 6 more 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 was attached to the grid-cut portion formed on the cured film, and the tape was sufficiently rubbed with a finger so that the cured film could be seen through. It was. Next, within 5 minutes after applying the tape, the tape was surely peeled off from the cured film at 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.
◯: Peeling of the cured film was observed in less than 5% of the lattice.
Δ: Peeling 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 for the fact that the ink composition adhered to the recording medium was irradiated with ultraviolet rays by ejecting with an amount of ink droplets having a thickness of 1 μm of the cured film, and a cured film having a solid pattern thickness of 1 μm was obtained. A cured film was prepared in the same manner as the adhesion. Using a Johnson cotton swab manufactured by Johnson & Johnson, the number of rubbing was set to 5 reciprocations, and the rubbing strength was 3 g, and the surface of the cured film was rubbed. The surface of the cured film after rubbing was visually observed. By evaluating with a thin film, the evaluation is based on the condition that the surface of the coating film is hardly cured due to oxygen inhibition. The evaluation criteria are as follows. The results are shown in Table 2.
◯: No streaks were visible on the cured film, and the ink composition did not adhere to the cotton swab.
Δ: No streaks were visible on the cured film, but adhesion of the ink composition was observed on the cotton swab.
X: Streaks were visible on the cured film.

[Bleeding test]
The edges of the cured film prepared by the adhesion evaluation were visually observed. The evaluation criteria are as follows. The results are shown in Table 2.
◯: The end was clear.
Δ: The edge was blurred.
X: Bleeding occurred at the end.

A comparison between Example 7 and other examples showed that the surface tackiness was improved when the content of the thioxanthone-based photopolymerization initiator was 2% by mass or more. Further, by comparing Example 8 with other Examples, it was shown that when the thioxanthone-based photopolymerization initiator is 5% by mass or less, the adhesion is excellent and the irradiation energy used may be small.

Comparing Examples 9 and 13 with other Examples, it was found that the other Examples containing 0.3% by mass or more of the silicone-based surfactant tended to have excellent gloss on the surface of the obtained cured film. It was presumed that the ink composition adhered to the recording medium spreads well and the surface of the cured film becomes smoother. Furthermore, these other examples tended to have better adhesion, and it was presumed that the better the spread of the ink composition adhered to the recording medium, the better the adhesion.

Comparing Example 10 with other Examples, it was found that the other Examples having a recording density of 600 dpi × 600 dpi or more tended to have better gloss on the obtained cured film surface, and the cured film surface had a better gloss. I guess it's smoother. It was presumed that these other examples tended to have better adhesion, and that when the recording density was high, the adhesion tended to be even better.

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

According to the comparison of Examples 12 and 7 and the comparison of Examples 2 and 11, if the main curing is performed at the position of the irradiation portion 42a for temporary curing and the temporary curing is not performed, the temporary curing is performed and then the main curing is performed. It was found that the bleeding was better than that in the case where the main curing was performed at the position of the irradiation unit 44. On the other hand, since irradiation was performed with a large irradiation energy at the position of the temporary curing irradiation unit 42a, the head was easily exposed to the leaked light of the light source and the nozzle plate was cured, so that the nozzle plate became dirty and the temperature of the nozzle plate. It has been found that the present invention is particularly useful because the discharge may become unstable due to the increase in the amount of water, and when the temporary curing is performed and then the main curing is performed, the present invention is excellent in these respects.

By comparing Reference Example 1 and Reference Example 5 with Examples, in the ink composition containing a cyan color material having high transmittance, the irradiation energy reaches the inside of the ink composition even if the thioxanthone-based photopolymerization initiator is contained. However, it was found that the adhesion was not inferior and the adhesion was not inferior even when the irradiation energy was relatively small. This tendency is the same in the example using the magenta coloring material.

Comparing Reference Example 2 and Example, the cured film having a low OD value has good adhesion and surface tackiness even with a small irradiation energy, but since the OD value is low, a light-colored recording (cured film). It turns out that only can be obtained.

By comparing each Example with Comparative Example 5, it was found that the ink composition was excellent in surface tackiness and bleeding resistance because it contained a thioxanthone-based photopolymerization initiator.

By comparing Reference Examples 3 and 4 with Comparative Examples 1 and 3, when a serial printer is used, the adhesion is good even if the irradiation energy × transmittance is relatively small, but the surface tackiness is still inferior. It was shown not. This is because by irradiating each pass, all the ink required for recording is not attached (only a small amount of ink is attached), so the inside of the ink is sufficiently cured. It is presumed that the adhesion was improved because it was possible. However, since recording is performed in 2 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 adheres and irradiates all the inks necessary for recording in one pass.

1 ... Printer, 20 ... Conveying unit, 25A ... Upstream roller, 25B ... Downstream roller, 26 ... Conveying drum, 30 ... Head unit, 40 ... Irradiation unit, 42a, 42b, 42c, 42d ... Temporary 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 (12)

A ejection step of ejecting and adhering an ultraviolet curable inkjet ink composition to a recording medium in one pass using a line head having a width equal to or larger than the recording width of the recording medium.
A curing step of irradiating the ultraviolet curable inkjet ink composition adhering to the recording medium with ultraviolet rays having a peak wavelength of 380 to 405 nm from a semiconductor light source to obtain a cured film having an OD value of 1.8 or more. Have,
The product of the light transmittance (%) of the cured film at a wavelength of 395 nm and the ultraviolet irradiation energy (mJ / cm ² ) of the curing step is 2.0 or more.
The ultraviolet curable inkjet ink composition either contains 2.9% by mass or less of a yellow color material or 1.9% by mass or less of a black color material, and contains a thioxanthone-based photopolymerization initiator. , Contains 0.50% by mass or more of silicone-based surfactant,
Inkjet recording method. The inkjet recording method according to claim 1, wherein the ultraviolet rays are irradiated with an irradiation energy of 350 to 1000 mJ / cm ^2. The inkjet recording method according to claim 1 or 2, wherein the recording medium is an ink-non-absorbable recording medium. The inkjet recording method according to any one of claims 1 to 3, wherein the ink composition for an inkjet contains 2.0 to 5.0% by mass of the thioxanthone-based photopolymerization initiator. The inkjet recording method according to any one of claims 1 to 4, wherein the ink composition for an inkjet further contains 5.0 to 15% by mass of an acylphosphine oxide-based photopolymerization initiator. The inkjet recording method according to any one of claims 1 to 5, wherein the recording is performed at a recording resolution of 600 dpi or more x 600 dpi or more. The inkjet recording method according to any one of claims 1 to 6, which comprises either 2.5 to 2.9% by mass of the yellow color material or 1.5 to 1.9% by mass of the black color material. The inkjet recording method according to any one of claims 1 to 7, wherein the ultraviolet irradiation is performed a plurality of times. The inkjet recording method according to any one of claims 1 to 8, wherein the film thickness of the cured film is 13 μm or less. The inkjet recording method according to any one of claims 1 to 9, wherein the cured film has a light transmittance of 0.0030% or more at a wavelength of 395 nm when the film has a film thickness of 10 μm. The inkjet recording method according to any one of claims 1 to 10, wherein the irradiation of ultraviolet rays includes irradiation for temporary curing and irradiation for main curing. Irradiation of the ultraviolet comprises a radiation one time irradiation energy is 5~50mJ / cm ^2, and irradiation of the second and subsequent irradiation energy is 350~1000mJ / cm ^2, more of claims 1 to 11 The inkjet recording method according to item 1.

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