JP5640400B2 - Printing method - Google Patents

Description

The present invention relates to a printing method, and particularly to a printing method for suppressing bleeding in printing using a plurality of inks.

In recent years, ultraviolet curable inks have been used to form prints having high water resistance, solvent resistance, scratch resistance, and the like on the surface of print media. This ultraviolet curable ink has a polymerizable compound and a photopolymerization initiator, and printing is performed by discharging the ink onto a print medium, polymerizing the ink composition by ultraviolet irradiation, and solidifying. When multicolor printing is performed using a plurality of such ultraviolet curable inks, bleeding (bleeding or color mixing at the ink boundary line) may occur due to the difference in ink curability.

For example, Patent Document 1 below discloses a serial type ink jet having a recording head 10 capable of ejecting a plurality of active energy ray curable inks and an active energy ray irradiating means 20 on at least one side of the recording head in the main scanning direction. Using the recording apparatus, the plurality of active energy ray-curable inks are applied to the recording medium P in the order of low curability with respect to the active energy rays 21, and irradiation of active energy rays is performed for each ink application, An active energy ray-curable inkjet recording method is disclosed in which bleeding is suppressed and the degree of curing of the entire image is generally high.

Further, in Patent Document 2 below, a plurality of recording heads arranged along the conveying direction of the recording medium by the conveying device, and arranged downstream of the conveying direction in each recording head so as to correspond to each recording head. In the image recording apparatus having each light irradiation device, the relationship of the light energy of each light irradiation device is that the light energy of the most downstream light irradiation device is the largest, sequentially upstream,
There is disclosed a technique for suppressing variation in dot diameter and color mixing of ink droplets by setting the light energy of each light irradiation device to be small.

JP 2007-276248 A JP 2004-268549 A

The present inventor has been conducting research and development on improving the printing characteristics of ultraviolet curable ink, and is considering improving printing characteristics by taking measures against bleeding.

For example, in the techniques described in Patent Documents 1 and 2, by controlling the irradiation intensity of the light energy ray, the bleed is suppressed, and the control of the light irradiation unit becomes complicated.
Due to the necessity of increasing the light intensity, the cost of the apparatus is increased.

Accordingly, in a specific aspect according to the present invention, attention is paid to the curability on the ink side, and an object is to take measures against bleeding by a simpler method.

Specifically, an object is to improve printing characteristics by devising a sequence of ejection and curing for a plurality of ink compositions.

The printing method according to the present invention includes a first ink composition having a first color material, a first polymerizable compound, and a first photopolymerization initiator, a second color material, a second polymerizable compound, and a second photopolymerization start. And a second ink composition having an agent on a recording medium and printing by curing by light irradiation, wherein the photocurability of the first ink composition is the second ink. The first ink composition is higher than the photocurability of the composition, and the first ink composition is cured by irradiating light, and then the second ink composition is ejected to emit light. It has the process of hardening the said 2nd ink composition by irradiating. Note that the first and second polymerizable compounds may be the same material or different materials. Moreover, the mixture of 2 or more types of materials may be sufficient respectively. Similarly, the first and second photopolymerization initiators may be the same material or different materials. Moreover, the mixture of 2 or more types of materials may be sufficient respectively.

For example, the photo-curing property is a tack-free time during which the surface of the ink composition is cured so as not to be scratched, and the tack-free time of the first ink composition is the tack time of the second ink composition. Shorter than free time.
For example, at least one of the first photopolymerization initiator in the first ink composition and the second photopolymerization initiator in the second ink composition have the same material, and the first ink composition First in
The amount of the photopolymerization initiator is larger than the amount of the second photopolymerization initiator in the second ink composition.
For example, the first photopolymerization initiator in the first ink composition and the second photopolymerization initiator in the second ink composition have an absorption spectrum in a wavelength range of light irradiated in the light irradiation. The amount of the first photopolymerization initiator in the first ink composition and the amount of the second photopolymerization initiator in the second ink composition are 4% by mass to 15% by mass, respectively. .
For example, the first polymerizable compound in the first ink composition and the second polymerizable compound in the second ink composition each have an acrylate ester, and the acrylic acid in the first polymerizable compound The acrylic equivalent of the ester is smaller than the acrylic equivalent of the acrylic ester in the second polymerizable compound.
For example, the first polymerizable compound in the first ink composition and the second polymerizable compound in the second ink composition each have an acrylate ester, and the acrylic acid in the first polymerizable compound The acrylic equivalent of the acrylic ester in the ester and the second polymerizable compound is 100 or more and 300 or less, respectively.
For example, the viscosity at 25 ° C. in the first ink composition and the second ink composition is 40 mPa · s or less, respectively.
For example, the amount of light irradiated in the light irradiation is 3 mJ / cm ² or more and 40 mJ /
cm ² or less.

The printing method according to the present invention includes a first ejection unit filled with a first ink composition having a first color material, a first polymerizable compound, and a first photopolymerization initiator, and adjacent to the first ejection unit. A first light irradiation unit disposed; a second discharge unit disposed next to the first light irradiation unit; a second colorant disposed next to the second discharge unit; and a second polymerizable compound. And a second light irradiation part filled with a second ink composition having a second photopolymerization initiator and having a lower photocurability than the first ink composition, and discharged from the first discharge part. The first ink composition is cured by irradiating the first ink composition with light from the first light irradiation unit, and then the second ink composition discharged from the second discharge unit is applied to the second ink composition. Printing method using an apparatus for curing the second ink composition by irradiating light from the first light irradiator It is.

Thus, by discharging and curing the ink composition in order from the one with higher curability, bleeding can be suppressed and printing characteristics can be improved.

It is the schematic of the recording region periphery in one mode of a line printer.

Hereinafter, embodiments for carrying out the present invention will be described in detail.
[Printing method]
One embodiment of the present invention relates to a printing method. First, the present embodiment will be described in detail while explaining a printing apparatus used in the printing method.

[Printer configuration]
FIG. 1 is a schematic view of the periphery of a recording area in one aspect of a line printer used in the present embodiment.
The printer used in this embodiment is an ultraviolet (UV) as an example of ink (liquid).
Is an apparatus that prints an image on a recording medium by discharging ultraviolet curable ink that is cured by irradiation of. The ultraviolet curable ink is an ink containing an ultraviolet curable resin such as a polymerizable compound and a photopolymerization initiator, and is cured by a polymerization reaction upon irradiation with ultraviolet rays.
The specific composition of the ultraviolet curable ink will be described later. For example, the printer 1 is CMYK
An image is printed using the four-color ultraviolet curable ink and a colorless and transparent ultraviolet curable ink (clear ink). CMYK means four colors of black (K), cyan (C), magenta (M), and yellow (Y).

A recording area for transporting a recording medium in a predetermined direction (hereinafter referred to as a transport direction) is shown in FIG.
As shown in FIG. 4, for example, the belt includes the upstream conveyance roller 23A and the downstream conveyance roller 23B, and the belt 24. When the transport motor (not shown) rotates, the upstream transport roller 23A and the downstream transport roller 23B rotate, and the belt 24 rotates. The recording medium fed by a paper feed roller (not shown) is conveyed by the belt 24 to a printable area (area facing the head). As the belt 24 transports the recording medium, the recording medium moves in the transport direction with respect to a printer headset (not shown). The recording medium that has passed through the printable area is discharged to the outside by the belt 24. The recording medium being conveyed is the belt 24.
It is electrostatically adsorbed or vacuum adsorbed. Here, for convenience, the term “paper feed” is used, but a print medium described later is used as a recording medium in the present embodiment.

Ultraviolet curable ink is ejected onto a recording medium from a printer headset as an ejection unit. In this embodiment, color ink for forming an image and colorless and transparent clear ink are ejected as ultraviolet curable ink. Each printer head constituting the printer headset (hereinafter also simply referred to as “head”) ejects ink of each color onto the recording medium being transported to form dots on the recording medium and record an image. Print on media.
The printer used in this embodiment is a line printer, and each head of the printer headset can form dots corresponding to the medium width at a time. That is, as shown in FIG. 1, in order from the upstream side in the transport direction, a black ink head K that discharges black ultraviolet curable ink, a cyan ink head C that discharges cyan ultraviolet curable ink, and a magenta ultraviolet curable ink are discharged. In the case where there are provided a magenta ink head M, a yellow ink head Y that discharges yellow ultraviolet curable ink, and a clear ink head CL that discharges clear ink, each head is directed from the back to the front of the paper (conveying direction). Are arranged in such a manner that dots corresponding to the medium width can be discharged. Therefore, by controlling each head from the upstream side and forming dots at necessary positions in one line corresponding to the medium width, an image can be printed by scanning the recording medium once in the transport direction.

Ultraviolet rays are irradiated from the light source as the light irradiation unit toward the ultraviolet curable ink landed on the recording medium. The dots formed on the recording medium are cured by being irradiated with ultraviolet rays from the light irradiation unit. As shown in FIG. 1, the light irradiation unit in the present embodiment includes provisional curing irradiation units 42 a to 42 d and a main curing irradiation unit 44.

The pre-curing irradiation units 42a to 42d irradiate ultraviolet rays for pre-curing the dots formed on the recording medium. Temporary curing (pinning) means temporary fixing of ink, and refers to curing performed to prevent bleeding between dots and to control the dot diameter. Therefore, it is sufficient that at least a part of the surface or the like of the dots (droplets) is cured.

The provisional curing irradiation units 42a to 42d are provided on the downstream side in the transport direction of the black ink head K, the cyan ink head C, the magenta ink head M, and the yellow ink head Y, respectively. That is, a provisional curing irradiation unit is provided for each ink color.

The temporary curing irradiation units 42a to 42d are light emitting diodes (LE) as light sources for ultraviolet irradiation.
D: Light Emitting Diode). The LED can easily change the irradiation energy by controlling the magnitude of the input current. There is no limitation on the amount of light for pre-curing, that is, the energy of ultraviolet irradiation, and it varies depending on the ink composition.
cm ² or less, preferably 3 to 40 mJ / cm ² .

The main curing irradiation unit 44 irradiates ultraviolet rays for substantially completely curing the dots formed on the recording medium. The main curing irradiation unit 44 is provided on the downstream side in the transport direction from the clear ink head CL. Further, the length of the main curing irradiation unit 44 in the medium width direction is equal to or greater than the medium width.
The main curing irradiation unit 44 then irradiates the dots formed by each head of the printer headset with ultraviolet rays.

The main curing irradiation unit 44 in the present embodiment is an LED or a lamp (metal halide lamp, xenon lamp, carbon arc lamp, chemical lamp,
Low pressure mercury lamp, high pressure mercury lamp, etc.). The irradiation light source is not particularly limited, but the irradiation light source is preferably light having a wavelength of 450 nm or less. The amount of light irradiation for main curing, that is, ultraviolet irradiation energy is not limited and varies depending on the ink composition, but is, for example, 100 mJ / cm ² or more, which is about 2 to 300 times that of pre-curing ultraviolet irradiation energy.

[Printing operation]
As shown in FIG. 1, first, black ink is ejected from the black ink head K when the recording medium passes under the black ink head K. Thereafter, the recording medium is a provisional curing irradiation unit 4.
Ultraviolet rays are irradiated when passing through 2a, and the dots formed by the black ink head K are temporarily cured. Similarly, dot formation and ultraviolet irradiation are performed for cyan ink, magenta ink, and yellow ink.

In this way, immediately after the color dots of the color ink are formed for each color, ultraviolet irradiation is performed from the corresponding provisional curing irradiation unit.

Then, clear ink is applied to the entire surface by the clear ink head CL, and the dots formed on the recording medium are irradiated with ultraviolet rays and finally cured by the main curing irradiation unit 44.

Here, the characteristic configuration (method) of the present embodiment is that printing is performed by ejecting / temporarily curing inks in descending order of photocurability. Photocurability means the ease of curing by light, and high photocurability means that it is easy to cure. For example, the photocurability can be determined by a tack-free time (tack-free value) described later.

Therefore, bleed can be suppressed by filling the head with ink from the upstream side of the printing apparatus in the order of photocuring. When the photocurability decreases in the order of K → C → M → Y, that is, when the tack-free time described later is K <C <M <Y, as described in detail with reference to FIG. A series of ejection and curing may be performed in the order of K → C → M → Y. When ink sets having different photocurability are used, it is only necessary to fill ink having high photocurability from the upstream side of the plurality of heads arranged in the transport direction. Further, the ink color is not limited to four colors. For example, when (n + 1) types of ink are used, the first head and the light irradiation unit,...
In an apparatus in which the nth head and the light irradiation unit, and the (n + 1) th head and the light irradiation unit are sequentially arranged from the upstream side, the nth head is more than the ink filled in the (n + 1) th head. What is necessary is just to fill ink with high photocurability.

In particular, in a line printer, as described above, an image is printed only by scanning the recording medium once in the transport direction. Therefore, compared to a serial printer or the like, there is a high possibility that dots of different colors are adjacent to each other. Therefore, bleeding (bleeding, color mixing) is likely to occur, and measures against bleeding are more important.

Even in such a line printer, as described above, the bleed can be reduced and the printing characteristics can be improved by discharging and temporarily curing the ink in the order of higher photocurability.

In the printing method, it is preferable to use an ink jet method. That is, when an image is formed on a recording medium using the above-described photocurable ink composition, an inkjet recording method is used. As this inkjet recording method, any conventionally known method can be used,
In particular, excellent image recording can be performed by using a method of ejecting droplets using the vibration of a piezoelectric element (a recording method using an ink jet head that forms ink droplets by mechanical deformation of an electrostrictive element). Is possible.

[Ink composition]
The ink composition used in the printing method according to the present embodiment includes 1) a polymerizable compound and 2
) It has at least a photopolymerization initiator.

1) Polymerizable compound The polymerizable compound used in the ink composition in the present embodiment is not particularly limited as long as it is a compound that polymerizes and solidifies upon irradiation with light such as ultraviolet rays by the action of a photopolymerization initiator described later. However, various monomers and oligomers having a monofunctional group, a bifunctional group, and a polyfunctional group having three or more functional groups can be used.

Examples of the monomer include unsaturated carboxylic acids such as (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid and maleic acid and salts or esters thereof, urethane, amide and anhydride thereof, acrylonitrile, styrene, various Unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Also,
Examples of the oligomer include oligomers formed from the above monomers such as linear acrylic oligomers, epoxy (meth) acrylates, aliphatic urethane (meth) acrylates, aromatic urethane (meth) acrylates, and polyester (meth) acrylates. Can be mentioned.

Moreover, an N-vinyl compound may be included as another monofunctional monomer or polyfunctional monomer. Examples of the N-vinyl compound include N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, and derivatives thereof.

Among those listed above, esters of (meth) acrylic acid, that is, (meth) acrylates are preferred.

Among the (meth) acrylates, monofunctional (meth) acrylates include, for example, isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, iso Myristyl (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-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, lactone-modifiable Examples include flexible (meth) acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, and isobornyl (meth) acrylate.

Among the (meth) acrylates, examples of the bifunctional (meth) acrylate include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and 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) adduct di (meth) acrylate of bisphenol A, PO (propylene oxide) adduct di (meth) acrylate of bisphenol A, hydroxypivalic acid Examples include neopentyl glycol di (meth) acrylate and polytetramethylene glycol di (meth) acrylate.

Among the (meth) acrylates, the trifunctional or higher polyfunctional (meth) acrylates include, for example, trimethylolpropane tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, and pentaerythritol tri (meth) acrylate. ,
Pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate, cowprolactone-modified trimethylolpropane tri (meth) acrylate, pentaerythritol ethoxy Tetra (meth) acrylate,
And caprolactam-modified dipentaerythritol hexa (meth) acrylate.

Among these, a monofunctional (meth) acrylate is included as a polymerizable compound from the viewpoint of easy injection stability at the time of ink jet recording because the coating film has a high elongation at curing and low viscosity. It is preferable. Further, from the viewpoint of increasing the hardness of the coating film, it is more preferable to use a monofunctional (meth) acrylate and a bifunctional (meth) acrylate in combination. Said polymeric compound may be used individually by 1 type, and may use 2 or more types together.

Further, the monofunctional (meth) acrylate preferably has one or more skeletons selected from the group consisting of an aromatic ring skeleton, a saturated alicyclic skeleton, and an unsaturated alicyclic skeleton. When the polymerizable compound is a monofunctional (meth) acrylate having the skeleton, the viscosity of the ink composition can be reduced, and the epoxy group-containing polymer can be effectively dissolved in the ink composition. it can.

As a monofunctional (meth) acrylate having an aromatic ring skeleton, for example, phenoxyethyl (
And (meth) acrylate and 2-hydroxy-3-phenoxypropyl (meth) acrylate. Examples of the monofunctional (meth) acrylate having a saturated alicyclic skeleton include isobornyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, and dicyclopentanyl (meth) acrylate. Examples of the monofunctional (meth) acrylate having an unsaturated alicyclic skeleton include dicyclopentenyloxyethyl (meth) acrylate. In the above, (meth) acrylate is exemplified, but simple acrylate is also useful.

2) Photopolymerization initiator The polymerization initiator contained in the ink composition in the present embodiment generates active species such as radicals and cations by the energy of light such as ultraviolet rays, and initiates polymerization of the polymerizable compound. As long as it is a thing, although there will be no restriction | limiting, a radical polymerization initiator and a cationic polymerization initiator can be used, It is preferable to use a radical polymerization initiator especially.

Examples of the radical polymerization initiator include aromatic ketones, acylphosphine compounds, aromatic onium salt compounds, organic peroxides, thio compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, and azinium compounds. , Metallocene compounds, active ester compounds, compounds having a carbon halogen bond, and alkylamine compounds.

Specific examples of the radical polymerization initiator include 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, thioxanthone, diethylthio Sandone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propan-1-one, bis (2,4,6-trimethylbenzoyl) -phenyl Examples include phosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethylthioxanthone and bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide. It is done.

Examples of commercially available radical polymerization initiators include 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 29
59 (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-propan-1-one}, IRGACURE 907 (2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one), IRGACURE 36
9 (2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1), IRGACURE 379 (2- (dimethylamino) -2-[(4-methylphenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone), DAR
OCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE 819 (bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide), IRGACURE 784 (bis (η5-2,4 -Cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H-pyrrole-1)
-Yl) -phenyl) titanium), IRGACURE OXE 01 (1.2-octanedione, 1- [4- (phenylthio)-, 2- (O-benzoyloxime)]), IR
GACURE OXE 02 (ethanone, 1- [9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl]-, 1- (O-acetyloxime)), IRGA
CURE 754 (a mixture of oxyphenylacetic acid, 2- [2-oxo-2-phenylacetoxyethoxy] ethyl ester and oxyphenylacetic acid, 2- (2-hydroxyethoxy) ethyl ester) (above, Ciba Japan KK)), DETX-S
(2,4-diethylthioxanthone) (manufactured by Nippon Kayaku Co., Ltd.),
Examples include Lucirin TPO, LR8883, LR8970 (above, manufactured by BASF), and Ubekrill P36 (manufactured by UCB).

The said photoinitiator may be used individually by 1 type, and may be used in combination of 2 or more type.
Although it is possible to omit the addition of a photopolymerization initiator by using a photopolymerizable compound as the polymerizable compound described above, it is easier to start polymerization by using a photopolymerization initiator. It can be adjusted and is preferred.

3) Coloring material The ink composition in the present embodiment may further include a coloring material. The coloring material is
At least one of a pigment and a dye.

(Pigment)
In the present embodiment, the light resistance of the ink composition can be improved by using a pigment as the coloring material. 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.

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, and quinophthalone pigments. Polycyclic pigments, dye chelates (for example, basic dye chelates, acid dye chelates, etc.), dye rakes (basic dye rakes, acid dye rakes), nitro pigments, nitroso pigments, aniline black, daytime A photofluorescent pigment is mentioned. The said pigment may be used individually by 1 type, and may use 2 or more types together.

Specific examples of the pigment include carbon black, No. manufactured by Mitsubishi Chemical Corporation. 2300, N
o. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7,
MA8, MA100, no. 2200B, etc., are Raven 5750, 5250, 5000, 3500, 1255, 700, etc. manufactured by Columbia, and Rebot, manufactured by Cabot.
gal400R, 330R, 660R, Mogu L, 700, Monarch
800, 880, 900, 1000, 1100, 1300, 1400, etc.
Color Black FW1, FW2, FW2V, FW18, FW200, ColorBlack S150, S160, S170, Printe made by Degussa
x35, U, V, 140U, Special Black 6, 5, 4A, 4 and the like.

Examples of pigments used in yellow ink include C.I. I. Pigment Yellow 1, 2, 3,
12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 1
09, 110, 114, 120, 128, 129, 138, 150, 151, 154, 1
55, 180, 185, 213 and the like.

Examples of pigments used for magenta ink include C.I. I. Pigment Red 5, 7,
12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123
168, 184, 202, 209, C.I. I. Pigment violet 19 and the like.

Further, examples of pigments used for cyan ink include C.I. I. Pigment Blue 1, 2,
3, 15: 3, 15: 4, 60, 16, and 22.

According to a preferred embodiment of the present invention, the pigment preferably has an average particle size in the range of 10 to 200 nm, more preferably about 50 to 150 nm.

The addition amount of the color material in the photocurable ink composition is preferably in the range of about 0.1 to 25% by mass, and more preferably in the range of about 0.5 to 15% by mass.

(dye)
In the present embodiment, a dye can be used as the color material. The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. Examples of the dye include C.I. I. Acid Yellow 17, 23, 42, 44, 79,
142, C.I. I. Acid Red 52, 80, 82, 249, 254, 289, C.I. I.
Acid Blue 9, 45, 249, C.I. I. Acid Black 1, 2, 24, 94, C.I.
I. Food Black 1, 2, C.I. I. Direct yellow 1, 12, 24, 33, 50,
55, 58, 86, 132, 142, 144, 173, C.I. I. Direct red 1, 4
, 9, 80, 81, 225, 227, C.I. I. Direct blue 1, 2, 15, 71, 8
6, 87, 98, 165, 199, 202, C.I. I. Directed Black 19, 38, 5
1, 71, 154, 168, 171, 195, C.I. I. Reactive Red 14, 32,
55, 79, 249, C.I. I. Reactive black 3, 4, and 35 are mentioned.

The photocurable ink composition of the present invention can also be applied to clear inks that do not contain a color material.

The pigment can be used by being dispersed in a medium with a dispersant or a surfactant. As a preferable dispersant, a dispersant commonly used for preparing a pigment dispersion, for example, a polymer dispersant can be used in addition to those described later.

4) Conditioner (other ingredients)
The ink composition in the present embodiment may contain components other than the components listed above.
For example, a surfactant may be included.

As the surfactant, for example, polyester-modified silicone or polyether-modified silicone can be used as a silicone-based surfactant, and it is particularly preferable to use polyether-modified polydimethylsiloxane or polyester-modified polydimethylsiloxane. Specific examples include BYK-347, BYK-348, BYK-UV3500, 3510.
, 3530, 3570 (Bicchemy Japan Co., Ltd.).

Further, a polymerization inhibitor may be added. By adding a polymerization inhibitor, the storage stability of the ink composition is improved. As the polymerization inhibitor, for example, hindered amine polymerization inhibitors IRGASTAB UV10, UV22 (Ciba Specialty Chemicals) and the like can be used.

Further, a dispersant, a polymerization accelerator, a slip agent, a penetration accelerator and a wetting agent (humectant), and other additives may be included. Examples of other additives include fixing agents, antifungal agents, preservatives, antioxidants, ultraviolet absorbers, chelating agents, pH adjusters, and thickeners.

[Print media]
The print medium (recording medium) is not particularly limited as long as it is a non-absorbing medium. For example, a resin material such as polyethylene terephthalate (PET), polypropylene, or polyethylene can be used. Moreover, you may have a process layer (coat layer) etc. on the surface of these base materials.

The viscosity of the ink is 40 mP at 25 ° C. from the viewpoint of ejection by inkjet.
It is preferable that it is below a * s. A more preferable range is 32 mPa · s or less.
In the case of exceeding 40 mPa · s, in the dots ejected from the inkjet head,
In some cases, the dot shape is inferior and the image quality is adversely affected, such as when the dots are elongated and have tails, or when the dots are scattered in multiple pieces.

Hereinafter, the present embodiment will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1
The ink composition was prepared as shown in Table 1 below. In Table 1 below, in the term of tack-free time, a 395 nm LED was irradiated with 70 mW / cm ² .

That is, 40% by mass of N-vinylcaprolactam as a polymerizable compound and 5% by mass of IRGACURE 819 and IRGACURE 369 as photopolymerization initiators, respectively.
As various adjusters, BYK UV3500 is 0.1% by mass, IRGASTAB UV1
0. 0.2% by weight, C.I. I. Pigment Red 122 was added at a ratio of 3% by mass, and tripropylene glycol diacrylate was further used as the polymerizable compound, and ink A-1 was adjusted so that the total amount became 100% by mass. At this time, tripropylene glycol diacrylate is 46.7% by mass.

Similarly, ink A-2 was prepared. The difference from ink A-1 is that, as a photopolymerization initiator, I
4% by mass of RGACURE 819 and IRGACURE 369 were added,
As a coloring material, C.I. I. Only the point that Pigment Yellow 180 was added at a ratio of 3% by mass, other additives were added at the same ratio, and tripropylene glycol diacrylate was used as the polymerizable compound, so that the total amount became 100% by mass. A-2 was adjusted. In this case, tripropylene glycol diacrylate is 48.7% by mass.

Similarly, ink A-3 was prepared. The difference from ink A-1 is that, as a photopolymerization initiator, I
Add 3.1% by weight of RGACURE 819 and 4% by weight of IRGACURE 369,
As a coloring material, C.I. I. Only the point that Pigment Blue 15: 3 was added at a rate of 3% by mass, other additives were added at the same rate, and tripropylene glycol diacrylate was used as the polymerizable compound, resulting in a total amount of 100% by mass. Ink A-3 was adjusted. At this time, tripropylene glycol diacrylate is 49.6% by mass.

Similarly, ink A-4 was prepared. The difference from ink A-1 is that, as a photopolymerization initiator, I
RGACURE 819 and IRGACURE 369 were added in an amount of 2.4% by mass, respectively, and C.I. I. The pigment black 7 was added only at a rate of 3% by mass, the other additives were added at the same rate, and tripropylene glycol diacrylate was used as the polymerizable compound so that the total amount became 100% by mass. A-4 was adjusted. In this case, tripropylene glycol diacrylate is 51.9% by mass.

Moreover, tack-free time [sec] was measured for the ink compositions A-1 to A-4. The tack-free time is a parameter indicating the photocuring property of the ink composition. Specifically, the tack-free time is cured to such an extent that even if the surface of the cured ink is rubbed with a cotton swab while applying a load of 100 g, there is no scratch mark. Refers to the irradiation time. Therefore, it can be said that the shorter the tack-free time, the higher the photocurability. About each of the ink compositions A-1 to A-4, each ink composition was applied onto a recording medium using a bar coater (hand coater Bar No. 2 manufactured by RK Print Coat Instruments Ltd.) and applied to the coating film. On the other hand, light irradiation was performed at an intensity of 70 mW / cm ² using an LED having a peak wavelength of 395 nm (manufactured by Phoseon) as a light source, and the degree of curing of the ink composition was examined every predetermined time. At this time, the ink film thickness was about 12 μm. As a result, the tack-free time of each ink composition was A-
1 was 13 s, A-2 was 28 s, A-3 was 59 s, and A-4 was 85 s. The viscosity [mPa · s] at 25 ° C. of each ink composition is 32 in A-1.
It was 28 for A-2, 31 for A-3, and 32 for A-4.

By selecting two colors from the ink compositions (A-1 to A-4) and irradiating the first ink ejected from the first head with light, the first ink is temporarily cured (10 mJ / cm ² ). And
Next, the second ink ejected from the second head was irradiated with light, whereby the second ink was temporarily cured (10 mJ / cm ² ), and then the main curing (300 mJ / cm ² ) was performed.
The first ink and the second ink are respectively solid-printed in a rectangular shape having long sides in the recording medium conveyance direction and arranged so that the short sides are adjacent to each other, and these boundaries are visually observed with a magnifying glass. The bleed state was evaluated based on the following levels A to C. The results are shown in Table 2 below.
A: As a result of observation with a loupe, the level where the two colors are not mixed and the boundary is clear.
B: As a result of observation with a loupe, it is confirmed that the two colors are mixed and the boundary looks slightly blurred, but the color mixture is not visually confirmed.
C: A level where the two colors are confirmed to be mixed and the boundary line is not clear.

As shown in Table 2 above, Example 1: A-1 → A-2, Example 2: A in which a series of ejection and curing (in this case, temporary curing) was performed in the order of tack-free time from small to large. -1 → A-3, Example 3: A-1 → A-4, Example 4: A-2 → A-4 and Example 5: A-3 → A-4, bleed evaluation: A or Good results for B were obtained. Comparative Example 1: A-2 → A-1, Comparative Example 2: A-3 → A series of discharge and curing in the order of tack-free time from large to small
For A-2, Comparative Example 3: A-4 → A-1, the bleed evaluation was C. In particular, in Examples 1 to 4, it was found that bleed evaluation was A, and bleed was improved by performing a series of discharge and curing in the order of tack-free time from small to large.

(Example 2)
The ink composition was prepared as shown in Table 3 below. In Table 3 below, in the term of tack-free time, a 395 nm LED was irradiated with 70 mW / cm ² .

That is, 30% by mass of 1,6-hexanediol diacrylate as a polymerizable compound,
As photopolymerization initiators, IRGACURE 819 and IRGACURE 369 were each 4% by mass, and as various regulators, BYK UV3500 was 0.1% by mass, IRGAS
0.2% by mass of TAB UV10, C.I. I. Pigment Red 122 was added at a rate of 3% by mass, N-vinylcaprolactam was further used as the polymerizable compound, and Ink B-1 was adjusted so that the total amount became 100% by mass. At this time, N-vinylcaprolactam is 58.7% by mass.

Similarly, ink B-2 was prepared. The difference from Ink B-1 is that 30% by mass of dipropylene glycol diacrylate is added as a polymerizable compound, and C.I. I. This is only the point where Pigment Yellow 180 was added at a ratio of 3% by mass.

Similarly, ink B-3 was prepared. The difference from ink B-1 is that 30% by mass of polypropylene glycol diacrylate (PO: 7) is added as a polymerizable compound, and C is used as a colorant.
. I. This is only the point where Pigment Blue 15: 3 was added at a ratio of 3% by mass.

Similarly, ink B-4 was prepared. The difference from Ink B-1 is that 30% by mass of instearyl acrylate is added as a polymerizable compound, and C.I. I. It is only the point which added the pigment black 7 in the ratio of 3 mass%.

Moreover, tack-free time [sec] was measured for the ink compositions B-1 to B-4. The measurement results for the ink compositions B-1 to B-4 are 1 for the ink composition B-1.
It was 24 s for 8 s and B-2, 65 s for B-3, and 102 s for B-4. The viscosity [mPa · s] at 25 ° C. of each ink composition was 29 for B-1, 31 for B-2, 34 for B-3, and 35 for B-4.

By selecting two colors from the ink compositions (B-1 to B-4) and irradiating the first ink ejected from the first head with light in the same manner as in Example 1, the temporary provision of the first ink is performed. Curing (10mJ
/ Cm ² ), and then, the second ink ejected from the second head is irradiated with light, whereby the second ink is temporarily cured (10 mJ / cm ² ), and then the main curing (300 mJ / cm ² ).
cm ² ). The first ink and the second ink are respectively solid-printed in a rectangular shape having long sides in the recording medium conveyance direction and arranged so that the short sides are adjacent to each other, and these boundaries are visually observed with a magnifying glass. The bleed state was evaluated based on the above levels A to C. The results are shown in Table 4 below.

As shown in Table 4 above, Example 6: B-1 → B-2, Example 7: B-1 → B-3, in which a series of ejection and curing was performed in the order of tack-free time from small to large. Example 8: B-2 → B-3
And for Example 9: B-3 → B-4, good results of bleed evaluation: A or B were obtained. Comparative Example 5 in which a series of ejection and curing was performed in the order of tack-free time from large to small:
For B-3 → B-1 and Comparative Example 6: B-4 → B-2, the bleed evaluation was C. In particular, in Examples 6 to 8, the bleed evaluation was A, and it was found that bleed was improved by performing a series of discharge and curing in the order of tack-free time from small to large.

(Tack-free time and ink composition)
In Examples 1 and 2 above, it has been found that bleeding is improved by performing a series of ejection and curing in the order of the tack-free time from small to large, but here, the tack-free time and the ink composition are examined. .

As shown in Table 1, for the ink compositions A-1 to A-4, a photopolymerization initiator (IRGA
It can be seen that the tack-free time increases as the total amount of CURE 819 and IRGACURE 369) decreases.

Moreover, as shown in Table 3, it can be seen that the ink compositions B-1 to B-4 change the tack-free time by using different components as the polymerizable compound. Ink composition B
For -1 to B-4, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate (PO: 7) and instearyl acrylate are the same amount (30% by mass) as the polymerizable compound. Used. For these, the acrylic equivalents were calculated as 113, 121, 268 and 3 in order.
24.

Acrylic equivalent is molecular weight / number of acrylic groups. As the acrylic equivalent is smaller, the number of functional groups per unit weight (reaction site, polymerization site, double bond portion) increases, and curing becomes easier. The acrylic equivalent of tripropylene glycol diacrylate shown in Example 1 is
150.
From the above, the following matters can be understood.

(1) As is clear from Example 1 (Table 1), a photopolymerization initiator (IRGACURE 81)
9 and IRGACURE 369), the tack free time decreases. That is, photocurability becomes high.
The photopolymerization initiator often has an absorption spectrum in the wavelength range of the irradiated light, and the total amount is 4.8% by mass or more, more preferably 5% by mass shown in ink A-4 in Table 1. % Or more is preferably used. Moreover, it is preferable to set it as 15 mass% or less from a soluble viewpoint.

(2) As is clear from Example 2 (Table 3), when an acrylic ester is used as the polymerizable compound, the tack-free time can be reduced by using a low acrylic equivalent.
In addition, although shown here as an acrylic equivalent, tack-free time can be adjusted also about polymeric compounds other than an acrylate ester by using molecular weight / functional group number as a parameter.

(3) Further, as the characteristics of the ink composition, when an acrylic ester is used as the polymerizable compound, the acrylic equivalent is desirably 100 or more and 300 or less. In addition, the viscosity of the ink composition is desirably 40 mPa · s or less at 25 ° C. The irradiation amount of light irradiated in the temporary curing, 3 mJ / cm ² or more 40 mJ / cm ²
The following is desirable.

Therefore, by adjusting the ink composition so as to satisfy the above conditions, the tack-free time can be controlled, and the photocurability of the ink composition can be adjusted.

23A Upstream conveying roller, 23B Downstream conveying roller, 24 belt, 42a provisional curing irradiation unit, 42b provisional curing irradiation unit, 42c provisional curing irradiation unit, 42d provisional curing irradiation unit, 44 main curing irradiation unit.

Claims (13)

A first ink composition having a first color material, a first polymerizable compound and a first photopolymerization initiator, and a second ink composition having a second color material, a second polymerizable compound and a second photopolymerization initiator Is a printing method in which printing is performed by discharging to a recording medium in one scan using a line printer and curing by light irradiation,
The photocurability of the first ink composition is higher than the photocurability of the second ink composition,
The first ink composition is ejected and irradiated with light to temporarily cure the first ink composition, and then the second ink composition is ejected and irradiated with light , whereby the first ink composition is irradiated. A printing method comprising a step of temporarily curing a two-ink composition and then subjecting the first ink composition and the second ink composition to main curing by irradiation with light . The photo-curing property is a tack-free time during which the ink composition surface is cured to such an extent that no scratch marks are left on the surface.
The printing method according to claim 1, wherein the tack-free time of the first ink composition is shorter than the tack-free time of the second ink composition. At least one of the first photopolymerization initiator in the first ink composition and the second photopolymerization initiator in the second ink composition has the same material,
The printing method according to claim 1 or 2, wherein an amount of the first photopolymerization initiator in the first ink composition is larger than an amount of the second photopolymerization initiator in the second ink composition. The first photopolymerization initiator in the first ink composition and the second photopolymerization initiator in the second ink composition have an absorption spectrum in the wavelength range of light irradiated in the light irradiation. And
The amount of the first photopolymerization initiator in the first ink composition and the amount of the second photopolymerization initiator in the second ink composition are 4% by mass or more and 15% by mass or less, respectively. Or the printing method of 2. The first polymerizable compound in the first ink composition and the second polymerizable compound in the second ink composition each have an acrylate ester,
The printing method according to claim 1 or 2, wherein an acrylic equivalent of the acrylic ester in the first polymerizable compound is smaller than an acrylic equivalent of the acrylic ester in the second polymerizable compound. The first polymerizable compound in the first ink composition and the second polymerizable compound in the second ink composition each have an acrylate ester,
The printing method according to claim 5, wherein the acrylic equivalents of the acrylic ester in the first polymerizable compound and the acrylic ester in the second polymerizable compound are 100 or more and 300 or less, respectively. The printing method according to claim 1, wherein the first ink composition and the second ink composition each have a viscosity at 25 ° C. of 40 mPa · s or less. The printing method according to any one of claims 1 to 7, wherein an irradiation amount of light irradiated in the light irradiation of the temporary curing is 3 mJ / cm ² or more and 40 mJ / cm ² or less. A line printer, in order from the upstream side in the conveyance direction of the recording medium, a first ejection unit filled with the first ink composition, a first light irradiation unit that performs temporary curing of the first ink composition, and the second ink The printing method according to claim 1, further comprising: a second ejection unit filled with the composition; and a second light irradiation unit that performs temporary curing of the second ink composition. The amount of light irradiated in the main curing light irradiation is 100 mJ / cm. ² The printing method according to any one of claims 1 to 9, which is as described above. The printing amount according to any one of claims 1 to 10, wherein an irradiation amount of light irradiated in the light irradiation of the main curing is 2 to 300 times a irradiation amount of light irradiated in the light irradiation of the temporary curing. Method. The printing method according to claim 1, further comprising a step of applying a clear ink between the temporary curing of the second ink composition and the main curing. The printing method according to claim 1, wherein the temporary curing light irradiation is performed by a light emitting diode.