JP2005154537A - Ink and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active energy ray-curable ink which has good curability even with fine droplets, excels in ink adhesion and flexibility even when printed on a flexible base material, and reduces the monomer smell of recorded images, and an injet recording method using the ink. <P>SOLUTION: In the ink used in an inkjet printing method comprising injecting an ink onto a base material to a droplet size of ≤10 pl, and then polymerizing, curing, and fixing the ink on the base material by irradiation with active energy rays, the ink comprises a polymerizable compound and 10-30 mass% photopolymerization initiator. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink that is polymerized, cured, and fixed on a substrate by irradiating active energy rays such as visible light and ultraviolet light, and a high-definition ink jet recording method using the ink.

  In recent years, the inkjet recording method can create images easily and inexpensively, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters. In particular, the recording device that emits and controls fine dots, the ink that has improved color reproduction range, durability, emission suitability, etc., and the ink absorbability, the coloring of the coloring material, the surface gloss, etc. have been dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper. The image quality improvement of today's ink jet recording system is achieved only when all of the recording apparatus, ink, and special paper are available.

  However, in an inkjet system that requires dedicated paper, the recording medium is limited, and the cost of the recording medium increases. Therefore, many attempts have been made to record on a transfer medium different from dedicated paper by an ink jet method. Specifically, a phase change ink jet method using a wax ink solid at room temperature, a solvent ink jet method using an ink mainly composed of a fast-drying organic solvent, a UV ink jet method in which crosslinking is performed by ultraviolet rays (UV light) after recording, etc. It is.

  Among these, the UV inkjet method has been attracting attention in recent years in that it has a relatively low odor compared to the solvent-based inkjet method, and can be recorded on a recording medium having no quick-drying property and no ink absorption. 4 discloses an ultraviolet curable inkjet ink.

  However, the UV inkjet recording method is characterized by being capable of recording on various substrates, but with a single ink composition, it has an appropriate dot diameter and sufficient adhesion to all types of substrates. It is very difficult to give. In particular, it is difficult to obtain sufficient adhesion to an olefin-based substrate.

  Conventionally, in order to achieve high image quality by the ink jet recording method, a method of selecting a base material in order to stabilize the dot diameter of the landing ink, using a light color in combination with the ink, and reducing the ink droplet size has been taken. .

  In the UV inkjet recording method, since recording can be performed on various substrates, it is effective to use dark and light inks or small droplet sizes without improving the image quality by selecting the substrate. In recent years, with the development of inkjet nozzles, it has become possible to use small droplet sizes of less than 2 pl. In the UV curable ink jet, an attempt has been made to form an image with a droplet size of several pl.

  As the UV curable ink, there are known a type in which a polymerizable compound having a double bond group such as an acrylate monomer or maleimide is radically polymerized, and a type in which a cyclic ether such as epoxy or oxetane is cationically polymerized with an acid.

  The cationic polymerization type has been attracting attention because it is not affected by polymerization inhibition of oxygen, and ion polymerizable monomers such as oxetane and epoxy have small odor and low curing shrinkage. Various UV-curable ink jet inks have been proposed (see, for example, Patent Documents 5 to 9), but these UV ink jet inks have a problem that adhesion to various substrates is not sufficient, There is a need for further improvements. In particular, there is no disclosure regarding a preferred ink composition or a preferred recording method as means for improving the adhesion to the substrate.

  At present, the radical polymerization type ink is actively developed and put on the market from the viewpoint of the kind of material and cost. However, radical-curing type UV curable ink, when attempting to cure a small droplet size ink for high image quality, polymerization is inhibited by oxygen and the sensitivity is greatly lowered. As a result, blurring between uncured ink occurs and image quality deteriorates. Further, even when cured, unreacted monomer remains, the monomer odor of the recorded image remains, and physical properties such as oil resistance and scratch resistance are deteriorated. In other words, the radical polymerization type ink requires a technique for suppressing oxygen inhibition when attempting to improve the image quality using a nozzle capable of emitting small droplets.

  As a method for suppressing oxygen inhibition, there is a nitrogen purge, but the load on the apparatus is large. Although a method of increasing the illuminance of the light source is also conceivable, there is still a problem that the apparatus is increased in size and the light source generates heat, resulting in an increase in the cost of the apparatus and the inability to use a heat-sensitive substrate.

When applied to applications requiring high image quality using small droplets, it is preferable that recording can be performed on a flexible base material such as a soft packaging material, a label, or a package. Since UV curable ink does not shrink in volume due to solvent evaporation, printing on a flexible substrate tends to cause problems such as poor adhesion and cracking when bent. However, conventional inks have good curability even with small droplets, and there has been no curable ink and recording method excellent in ink adhesion and flexibility even when recorded on a flexible substrate.
Japanese Patent Publication No. 5-54667 JP-A-6-200204 Special Table 2000-504778 International Patent Publication No. 99-29787 Pamphlet JP 2001-220526 A JP 2002-188025 A JP 2002-317139 A JP 2003-55449 A JP 2003-73481 A

  The present invention has been made in view of the above circumstances, and the object of the present invention is excellent in curability even in small droplets, excellent in ink adhesion and flexibility even when recorded on a flexible substrate, It is an object to provide an active energy ray-curable ink with less monomer odor of a recorded image and an ink jet recording method using the same.

The above object of the present invention is achieved by the following configurations.
(Claim 1)
In an ink used for an ink jet recording method in which an ink is ejected onto a substrate from an ink jet nozzle with a droplet size of 10 pl or less, and then irradiated with active energy rays, the ink is polymerized, cured, and fixed to the substrate. An ink comprising a polymerizable compound and 10 to 30% by mass of a photopolymerization initiator.
(Claim 2)
The ink according to claim 1, wherein the polymerization reaction is radical polymerization.
(Claim 3)
The ink according to claim 1 or 2, comprising 25 to 60% by mass of a monofunctional acrylate as a polymerizable compound.
(Claim 4)
4. The ink according to claim 3, wherein the monofunctional acrylate has a phenyl group, an isobornyl group or a tetrahydrofurfuryl group.
(Claim 5)
The ink according to any one of claims 1 to 4, wherein the photopolymerization initiator contains bisacylphosphine oxide or α-aminoketone.
(Claim 6)
The ink according to claim 1, wherein the photopolymerization initiator has a hydroxyethoxy group.
(Claim 7)
An ink containing a polymerizable compound and 10-30% by mass of a photopolymerization initiator is ejected onto a substrate from an inkjet nozzle with a droplet size of 10 pl or less, and then the ink is polymerized by irradiating with active energy rays. An ink jet recording method comprising: curing, fixing, and fixing to the substrate.
(Claim 8)
The ink jet recording method according to claim 7, wherein the ink is the ink according to any one of claims 2 to 6.
(Claim 9)
9. The ink jet recording method according to claim 7, wherein after the ink has landed on the substrate, the active energy ray is irradiated at a timing when the dot diameter of the landed ink is 80 μm or less.
(Claim 10)
The ink jet recording according to any one of claims 7 to 9, wherein after the ink has landed on the substrate, active energy rays are irradiated before the landed ink penetrates 30% by mass or more into the substrate. Method.

  According to the present invention, an active energy ray-curable ink having good curability even in a small droplet, excellent in ink adhesion and flexibility even when recorded on a flexible substrate, and having a monomer odor of a recorded image, and the same The used inkjet recording method can be provided.

  As a result of earnest research, the inventor ejects ink onto a substrate from an inkjet nozzle with a droplet size of 10 pl or less, and then irradiates active energy rays to polymerize, cure, and fix the ink to the substrate. By including a polymerizable compound and 10 to 30% by mass of a photopolymerization initiator in the ink used in the ink jet recording method, the ink has good curability and is flexible even when recorded on a flexible substrate. The present invention has found that an active energy ray-curable ink having excellent properties and a low monomer odor of a recorded image and an ink jet recording method using the same are obtained.

  The present invention will be described in detail below.

  According to a first aspect of the present invention, there is provided an ink jet recording method in which an ink is ejected onto a substrate from an ink jet nozzle with a droplet size of 10 pl or less, and then the ink is polymerized, cured, and fixed on the substrate by irradiating an active energy ray. In the ink to be used, the ink contains a polymerizable compound and 10 to 30% by mass of a photopolymerization initiator.

  Small droplets of 10 pl or less have a large surface area per unit volume when the ink lands on the substrate, and are easily affected by outside air. There are two types of polymerization reaction, radical polymerization and cationic polymerization. The former is hindered by oxygen in the outside air and the latter is hindered by humidity in the outside air. By setting the content of the photopolymerization initiator to 10% by mass or more, such a small droplet ink can be cured without bleeding. Conventional droplets having a normal size exceeding 10 pl have been used with a photopolymerization initiator content of about 1 to 6% by mass. On the other hand, if the content of the photopolymerization initiator exceeds 30% by mass, the ink cost is increased and the properties of the ejected ink are deteriorated.

  The substrate (recording medium), active energy ray, polymerizable compound, and photopolymerization initiator will be described later.

  The ink according to claim 2 is characterized in that the polymerization reaction is radical polymerization. For small droplets of 10 pl or less, radically polymerizable ink is significantly affected by polymerization inhibition due to outside air as compared with cationically polymerizable ink. Therefore, the method of setting the photopolymerization initiator concentration of the present invention to 10 to 30% by mass is as follows. This is particularly effective for radically polymerizable inks. The concentration of the photopolymerization initiator amount is more preferably 15 to 30% by mass.

  A third aspect of the present invention is an ink characterized in that it contains 25 to 60% by mass of a monofunctional acrylate as a polymerizable compound. By setting the monofunctional acrylate to 25 to 60% by mass as the polymerizable compound, the ink cured film can be made flexible even on a flexible substrate, and problems such as cracking can be improved. If it is less than 25% by mass, the effect is small and cracking is unlikely to occur, and if it exceeds 60% by mass, the curing sensitivity is insufficient.

  A fourth aspect of the present invention is an ink characterized in that the monofunctional acrylate of the polymerizable compound has a phenyl group, an isobornyl group or a tetrahydrofurfuryl group. Among monofunctional acrylates, monofunctional acrylates having a phenyl group, an isobornyl group, and a tetrahydrofurfuryl group are preferable because of excellent adhesion, flexibility, and curability.

  The ink according to claim 5 is characterized in that the photopolymerization initiator contains bisacylphosphine oxide or α-aminoketone. As the photopolymerization initiator, a photopolymerization initiator containing bisacylphosphine oxide having photobleaching property and α-aminoketone which is not easily affected by oxygen inhibition is particularly preferable because of its high sensitivity enhancement effect in small droplets.

  A sixth aspect of the present invention is an ink characterized in that the photopolymerization initiator has a hydroxyethoxy group. In the present invention, since the photopolymerization initiator is added in a larger amount than usual, the decomposition product odor of the photopolymerization initiator tends to be a problem. An initiator containing a hydroxyethoxy group is preferable because it has a small degradation product odor.

  A ninth aspect of the present invention is the ink jet recording method, wherein after the ink has landed on the base material, the active energy ray is irradiated at a timing when the dot diameter of the landed ink is 80 μm or less. After landing, the ink continues to be leveled on the substrate until irradiation with the active energy ray, and the surface area per unit volume is increased, and the influence of polymerization inhibition is further increased. Irradiation with active energy rays at a timing when the dot diameter is 80 μm or less is preferable because bleeding and residual monomers can be reduced. The timing of the active energy ray irradiation is such that the dot diameter of a 10 pl droplet is 80 μm or less, more preferably 70 μm or less. A 5 pl droplet has a dot diameter of 70 μm or less, more preferably 60 μm or less.

  A tenth aspect of the present invention is the ink jet recording method, wherein after the ink has landed on the base material, the active energy ray is irradiated before the landed ink penetrates 30% by mass or more into the base material. When an ink-absorbing base material is used, the ink continues to permeate the base material after the landing until the irradiation of the energy ray, and the ink that permeates the base material becomes difficult to reach the active energy ray, resulting in poor curing. By irradiating the active energy ray before the ink penetrates 30% by mass or more into the base material, bleeding and residual monomers can be reduced. More preferably, the active energy ray is irradiated at less than 20% by mass.

(Color material)
In the ink of the present invention, various colorants that can be dissolved or dispersed in the main component of the polymerizable compound can be used as the colorant. The colorant is not particularly limited, for example, a pigment, a dye or a pigment, but among these, it is preferable to use a pigment from the viewpoint of weather resistance.

  Although the example of the dye used for this invention is given to the following, this invention is not limited to these.

<Direct dye>
C. I. Direct yellow 1, 4, 8, 11, 12, 24, 26, 27, 28, 33, 39, 44, 50, 58, 85, 86, 100, 110, 120, 132, 142, 144,
C. I. Direct Red 1, 2, 4, 9, 11, 13, 17, 20, 23, 24, 28, 31, 33, 37, 39, 44, 47, 48, 51, 62, 63, 75, 79, 80, 81, 83, 89, 90, 94, 95, 99, 220, 224, 227, 243,
C. I. Direct Blue 1, 2, 6, 8, 15, 22, 25, 71, 76, 78, 80, 86, 87, 90, 98, 106, 108, 120, 123, 163, 165, 192, 193, 194, 195, 196, 199, 200, 201, 202, 203, 207, 236, 237,
C. I. Direct Black 2, 3, 7, 17, 19, 22, 32, 38, 51, 56, 62, 71, 74, 75, 77, 105, 108, 112, 117, 154,
<Acid dye>
C. I. Acid Yellow 2, 3, 7, 17, 19, 23, 25, 29, 38, 42, 49, 59, 61, 72, 99,
C. I. Acid Orange 56, 64,
C. I. Acid Red 1, 8, 14, 18, 26, 32, 37, 42, 52, 57, 72, 74, 80, 87, 115, 119, 131, 133, 134, 143, 154, 186, 249, 254, 256,
C. I. Acid Violet 11, 34, 75,
C. I. Acid Blue 1, 7, 9, 29, 87, 126, 138, 171, 175, 183, 234, 236, 249,
C. I. Acid Green 9, 12, 19, 27, 41,
C. I. Acid Black 1, 2, 7, 24, 26, 48, 52, 58, 60, 94, 107, 109, 110, 119, 131, 155,
<Reactive dyestuff>
C. I. Reactive Yellow 1, 2, 3, 13, 14, 15, 17, 37, 42, 76, 95, 168, 175,
C. I. Reactive Red 2, 6, 11, 21, 22, 23, 24, 33, 45, 111, 112, 114, 180, 218, 226, 228, 235,
C. I. Reactive Blue 7, 14, 15, 18, 19, 21, 25, 38, 49, 72, 77, 176, 203, 220, 230, 235,
C. I. Reactive Orange 5, 12, 13, 35, 95,
C. I. Reactive Brown 7, 11, 33, 37, 46,
C. I. Reactive Green 8, 19,
C. I. Reactive violet 2, 4, 6, 8, 21, 22, 25,
C. I. Reactive Black 5, 8, 31, 39
<Basic dye>
C. I. Basic yellow 11, 14, 21, 32
C. I. Basic Red 1, 2, 9, 12, 13
C. I. Basic violet 3, 7, 14
C. I. Basic blue 3, 9, 24, 25
As the pigment used in the present invention, conventionally known colored organic or colored inorganic pigments can be used. For example, azo pigments such as azo lake, insoluble azo pigment, condensed azo pigment, chelate azo pigment, phthalocyanine pigment, perylene and perylene pigment, anthraquinone pigment, quinacridone pigment, dioxazine pigment, thioindigo pigment, isoindolinone pigment, quinophthalone pigment, etc. Examples include polycyclic pigments, dye lakes such as basic dye type lakes and acid dye type lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black and daylight fluorescent pigments, and inorganic pigments such as carbon black. However, the present invention is not limited to these.

  Examples of magenta or red pigments include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. Pigment red 222, C.I. I. Pigment violet 19 and the like.

  Examples of orange or yellow pigments include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 83, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 108, C.I. I. Pigment yellow 109, C.I. I. Pigment yellow 120, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 139, C.I. I. Pigment yellow 151, C.I. I. And CI Pigment Yellow 180.

  Examples of green or cyan pigments include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  In order to improve the dispersibility of the pigment, it is preferable to introduce a polar group on the pigment surface. Pigment particles having a polar group on the surface are pigments directly modified with a polar group on the surface of the pigment particle, or organic substances having an organic pigment mother nucleus and having a polar group bonded directly or via a joint , Referred to as pigment derivative).

  Examples of the polar group include a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a boric acid group, and a hydroxyl group, preferably a sulfonic acid group and a carboxylic acid group, and more preferably a sulfonic acid group.

  Examples of a method for obtaining pigment particles having a polar group on the surface include WO97 / 48769, JP-A-10-110129, JP-A-11-246807, JP-A-11-57458, JP-A-11-189739, JP-A-11-189739. A polar group such as a sulfonic acid group or a salt thereof is introduced into at least a part of the pigment surface by causing the pigment particle surface described in each publication such as JP-A-11-323232 and JP-A-2000-265094 to have an appropriate oxidizing agent. The method of doing is mentioned. Specifically, it is prepared by oxidizing carbon black with concentrated nitric acid, or in the case of color pigments by oxidizing with sulfamic acid, sulfonated pyridine salt, amide sulfuric acid, etc. in sulfolane or N-methyl-2-pyrrolidone. can do. In these reactions, the pigment dispersion can be obtained by removing and purifying the substance that has been excessively oxidized and becomes water-soluble. Moreover, when a sulfonic acid group is introduced onto the surface by oxidation, the acidic group may be neutralized with a basic compound as necessary.

  Other methods include a method of adsorbing the pigment derivatives described in JP-A-11-49974, JP-A-2000-273383, JP-A-2000-303014, etc. on the surface of the pigment particles by a treatment such as milling. Examples include a method of dissolving the pigment described in each publication such as 2002-179777, 2002-20141, and the like together with a pigment derivative, followed by crystallization in a poor solvent. Pigment particles having a polar group on the surface can be obtained.

  In the present invention, the polar group may be free or in a salt state, or may have a counter salt. Examples of the counter salt include inorganic salts (lithium, sodium, potassium, magnesium, calcium, aluminum, nickel, ammonium) and organic salts (triethylammonium, diethylammonium, pyridinium, triethanolammonium, etc.), preferably 1 A counter salt having a valence.

  For the dispersion of the pigment, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like can be used. Further, a dispersing agent can be added when dispersing the pigment.

  Other dispersants include hydroxyl group-containing carboxylic acid esters, long chain polyaminoamides and high molecular weight acid ester salts, high molecular weight polycarboxylic acid salts, long chain polyaminoamide and polar acid ester salts, high molecular weight unsaturated acid esters. , Polymer copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxy Examples thereof include ethylene nonyl phenyl ether, stearylamine acetate, and pigment derivatives.

  Specific examples of the dispersant include “Anti-Terra-U (polyaminoamide phosphate)”, “Anti-Terra-203 / 204 (high molecular weight polycarboxylate)”, “Disperbyk-101” (polyamino) manufactured by BYK Chemie. Amide phosphate and acid ester), 107 (hydroxyl group-containing carboxylic acid ester), 110 (copolymer containing acid group), 130 (polyamide), 161, 162, 163, 164, 165, 166, 170 (copolymer) Polymers) ”,“ 400 ”,“ Bykumen ”(high molecular weight unsaturated acid ester),“ BYK-P104, P105 (high molecular weight unsaturated acid polycarboxylic acid) ”,“ P104S, 240S (high molecular weight unsaturated acid poly) Carboxylic acid and silicon system "," Lactimon (long chain amine and unsaturated acid polycarboxylic acid) And silicon) ", and the like.

  Also, “Efka CHEMICALS” “Efka 44, 46, 47, 48, 49, 54, 63, 64, 65, 66, 71, 701, 764, 766”, “Efka Polymer 100 (modified polyacrylate), 150 (aliphatic) System modified polymer), 400, 401, 402, 403, 450, 451, 452, 453 (modified polyacrylate), 745 (copper phthalocyanine system) "," Kyoeisha Chemical Co., Ltd. "" Floren TG-710 (urethane oligomer) "," “Flonon SH-290, SP-1000”, “Polyflow No. 50E, No. 300 (acrylic copolymer)”, “Disparon KS-860, 873SN, 874 (polymer dispersing agent), # 2150, manufactured by Enomoto Kasei Co., Ltd. (Aliphatic polyvalent carboxylic acid), # 7004 (polyether ester type) ” It is done.

  Furthermore, “Demol RN, N (Naphthalenesulfonic acid formalin condensate sodium salt), MS, C, SN-B (aromatic sulfonic acid formalin condensate sodium salt), EP”, “Homogenol L-18 (Polyethylene)” manufactured by Kao Corporation Carboxylic acid type polymer) "," Emulgen 920, 930, 931, 935, 950, 985 (polyoxyethylene nonyl phenyl ether) "," Acetamine 24 (coconut amine acetate), 86 (stearyl amine acetate) ", General Corporation "Solspers 5000 (phthalocyanine ammonium salt type), 13240, 13940 (polyesteramine type), 17000 (fatty acid amine type), 24000, 32000", Nikko Chemical's "Nikkor T106 (polyoxyethylene sorbitan monooleate), Ltd. "AJISPER PB821, PB822 (basic comb polymer)", MYS-IEX (polyoxyethylene monostearate), Hexagline 4-0 (hexaglyceryl ruthenate Huwei rate) ", and the like.

  Among these, a polymer type dispersant is preferable because it has a high ability to reduce the shear dependency of viscosity. The dispersant is preferably contained in the ink in the range of 0.1 to 10% by mass.

  Moreover, it is also possible to use a synergist according to various pigments as a dispersion aid. These dispersants and dispersion aids are preferably added in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the pigment. The dispersion medium is a solvent or a polymerizable compound. The ultraviolet curable ink used in the present invention is preferably solvent-free because it reacts and cures immediately after ink landing. If the solvent remains in the cured image, the solvent resistance deteriorates and the VOC of the remaining solvent arises. Therefore, it is preferable in view of dispersibility that the dispersion medium is not a solvent but a polymerizable compound, and among them, a monomer having the lowest viscosity is selected.

  The pigment is preferably dispersed so that the average particle diameter of the pigment particles is 0.08 to 0.5 μm, and the maximum particle diameter is 0.3 to 10 μm, preferably 0.3 to 3 μm. The selection of the dispersion medium, the dispersion conditions, and the filtration conditions are appropriately set. By controlling the particle size, clogging of the head nozzle can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained.

  In the ink of the present invention, the color material concentration is preferably 1 to 10% by mass of the whole ink.

(Polymerizable compound)
Among the polymerizable compounds that can be used in the present invention, examples of the radical polymerizable compound include, for example, JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, and JP-A-10-863. The compounds described in each publication can be listed, and various known cationic polymerizable monomers can be used as the cationic polymerizable compound. For example, in JP-A-6-9714, JP-A-2001-31892, 2001-40068, 2001-55507, 2001-310938, 2001-310937, 2001-220526, etc. Examples include epoxy compounds, vinyl ether compounds, oxetane compounds and the like.

  The radical polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization, and may be any compound as long as it has at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. , Oligomers, polymers and the like having chemical forms. Only one kind of radically polymerizable compound may be used, or two or more kinds thereof may be used in combination at an arbitrary ratio in order to improve desired properties.

  Examples of compounds having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and their salts, esters, urethanes, amides. And radically polymerizable compounds such as various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides and unsaturated urethanes. Specifically, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, bis (4-acryloxypolyethoxyphenyl) propane, neopentyl glycol Diacrylate, 1,6-hexanediol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol Tetraacrylate, dipentaery Acrylic acid derivatives such as lithol tetraacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, oligoester acrylate, N-methylol acrylamide, diacetone acrylamide, epoxy acrylate, methyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate , Lauryl methacrylate, allyl methacrylate, glycidyl methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, trimethylol Methacryl derivatives such as tan trimethacrylate, trimethylolpropane trimethacrylate, 2,2-bis (4-methacryloxypolyethoxyphenyl) propane, and other derivatives of allyl compounds such as allyl glycidyl ether, diallyl phthalate, triallyl trimellitate More specifically, Shinzo Yamashita, “Cross-linking agent handbook”, (1981 Taiseisha); Kato Kiyomi, “UV / EB curing handbook (raw material)” (1985, Polymer publication) ); Rad-Tech Study Group, “Application and Market of UV / EB Curing Technology”, p. 79, (1989, CMC); Eiichiro Takiyama, “Polyester Resin Handbook”, (1988, Nikkan Kogyo Shimbun) Commercially available products described in the above, or radically polymerizable or crosslinkable monomers known in the industry, Oligomers and polymers can be used.

  Among these radically polymerizable compounds, the monofunctional acrylate is preferable even for a flexible substrate because the ink cured film can be made flexible and problems such as cracking can be improved. Furthermore, among monofunctional acrylates, monofunctional acrylates having a phenyl group, an isobornyl group, and a tetrahydrofurfuryl group are preferable because of excellent adhesion, flexibility, and curability.

  The addition amount of the radical polymerizable compound is preferably 1 to 97% by mass and more preferably 30 to 95% by mass with respect to the ink composition.

  In the case of a cationically polymerizable ink, it is preferable to contain at least one oxetane compound and at least one compound selected from an epoxy compound and a vinyl ether compound.

  As the epoxy compound, an alicyclic epoxide is particularly preferable. As the alicyclic epoxide, a compound having at least one cycloalkane ring such as cyclohexene or cyclopentene ring is converted to an appropriate oxidation such as hydrogen peroxide or peracid. A cyclohexene oxide or cyclopentene oxide-containing compound obtained by epoxidation with an agent is preferred.

  Preferred aliphatic epoxides include di- or polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof, and typical examples thereof include diglycidyl ether of ethylene glycol, diglycidyl ether of propylene glycol or Diglycidyl ether of alkylene glycol such as diglycidyl ether of 1,6-hexanediol, polyglycidyl ether of polyhydric alcohol such as di- or triglycidyl ether of glycerin or its alkylene oxide adduct, polyethylene glycol or its alkylene oxide adduct Of polyalkylene glycols such as diglycidyl ether, polypropylene glycol or diglycidyl ether of its alkylene oxide adduct Glycidyl ether, and the like. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

  Among these epoxides, in view of fast curability, aromatic epoxides and alicyclic epoxides are preferable, and alicyclic epoxides are particularly preferable. In the present invention, one of the epoxides may be used alone, or two or more may be used in appropriate combination.

  Examples of the vinyl ether compound include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, Di- or trivinyl ether compounds such as methylolpropane trivinyl ether, ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexane dimethanol monovinyl ether, n- B pills vinyl ether, isopropyl vinyl ether, isopropenyl ether -o- propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether.

  Among these vinyl ether compounds, in consideration of curability, adhesion, and surface hardness, di- or trivinyl ether compounds are preferable, and divinyl ether compounds are particularly preferable. In the present invention, one of the above vinyl ether compounds may be used alone, or two or more thereof may be used in appropriate combination.

  The oxetane compound is a compound having an oxetane ring, and any known oxetane compound as introduced in JP-A Nos. 2001-220526 and 2001-310937 can be used. In the oxetane compound, when a compound having 5 or more oxetane rings is used, the viscosity of the ink composition becomes high, which makes it difficult to handle and the glass transition temperature of the ink composition becomes high. The stickiness of will not be enough. The oxetane compound is preferably a compound having 1 to 4 oxetane rings.

  Although the specific example of an oxetane compound is demonstrated, it is not limited to these. An example of the compound having one oxetane ring is a compound represented by the following general formula (1).

In the general formula (1), R ¹ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group, or a butyl group, a fluoroalkyl group having 1 to 6 carbon atoms, an allyl group, or an aryl group. , Furyl group or thienyl group. R ² is an alkyl group having 1 to 6 carbon atoms such as methyl group, ethyl group, propyl group, butyl group, 1-propenyl group, 2-propenyl group, 2-methyl-1-propenyl group, 2-methyl- C2-C6 alkenyl group such as 2-propenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, phenyl group, benzyl group, fluorobenzyl group, methoxybenzyl group, phenoxyethyl group, etc. A group having an aromatic ring, an alkylcarbonyl group having 2 to 6 carbon atoms such as an ethylcarbonyl group, a propylcarbonyl group, and a butylcarbonyl group, an alkylcarbonyl group having 2 to 6 carbon atoms such as an ethoxycarbonyl group, a propoxycarbonyl group, and a butoxycarbonyl group; Alkoxycarbonyl group, ethylcarbamoyl group, propylcarbamoyl group, butylcarbamoyl group, pentylcarbamoyl Is N- alkylcarbamoyl group having a carbon number of 2-6 and the like. As the oxetane compound used in the present invention, it is particularly preferable to use a compound having one oxetane ring because the resulting composition has excellent tackiness, low viscosity and excellent workability.

  An example of a compound having two oxetane rings includes a compound represented by the following general formula (2).

In the general formula (2), R ¹ is the same group as that in the general formula (1). R ³ is, for example, a linear or branched alkylene group such as an ethylene group, a propylene group or a butylene group, a linear or branched poly (alkyleneoxy) such as a poly (ethyleneoxy) group or a poly (propyleneoxy) group. ) Group, propenylene group, methylpropenylene group, butenylene group or other linear or branched unsaturated hydrocarbon group, alkylene group containing carbonyl group or carbonyl group, alkylene group containing carboxyl group, alkylene containing carbamoyl group Group.

Moreover, as R < ³ >, the polyvalent group selected from the group shown by the following general formula (3), (4) and (5) can also be mentioned.

In the general formula (3), R ⁴ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, or a butyl group, a methoxy group, an ethoxy group, a propoxy group, or a butoxy group. An alkoxy group having 1 to 4 carbon atoms, a halogen atom such as a chlorine atom or a bromine atom, a nitro group, a cyano group, a mercapto group, a lower alkyl carboxyl group, a carboxyl group, or a carbamoyl group.

In the general formula (4), R ⁵ represents an oxygen atom, a sulfur atom, a methylene group, NH, SO, SO ₂ , C (CF ₃ ) ₂ , or C (CH ₃ ) ₂ .

In General formula (5), R < ⁶ > is a C1-C4 alkyl group, such as a methyl group, an ethyl group, a propyl group, a butyl group, or an aryl group. n is an integer of 0-2000. R ⁷ is a methyl group, an ethyl group, a propyl group, a butyl group having 1 to 4 carbon atoms, or an aryl group. R ⁷ may further include a group selected from the group represented by the following general formula (6).

In General formula (6), R < ⁸ > is a C1-C4 alkyl group, such as a methyl group, an ethyl group, a propyl group, a butyl group, or an aryl group. m is an integer of 0-100.

  Specific examples of the compound having two oxetane rings include the following exemplified compounds 1 and 2.

Illustrative compound 1 is a compound in which R ¹ is an ethyl group and R ³ is a carbonyl group in general formula (2). Exemplary compound 2 is a compound in which, in the general formula (2), R ¹ is an ethyl group, R ³ is the general formula (5), R ⁶ and R ⁷ are methyl groups, and n is 1.

Among the compounds having two oxetane rings, preferred examples other than the above compounds include compounds represented by the following general formula (7). In general formula (7), R ¹ has the same meaning as R ¹ in the general formula (1).

  An example of a compound having 3 to 4 oxetane rings is a compound represented by the following general formula (8).

In the general formula (8), R ¹ is the same meaning as R ¹ in the general formula (1). As R ⁹ , for example, a branched alkylene group having 1 to 12 carbon atoms such as groups represented by the following A to C, a branched poly (alkyleneoxy) group such as a group represented by the following D, or the following E And branched polysiloxy groups such as those shown. j is 3 or 4.

In the above A, R ¹⁰ is a lower alkyl group such as a methyl group, an ethyl group or a propyl group. Moreover, in said D, p is an integer of 1-10.

  Illustrative compound 3 is an example of a compound having four oxetane rings.

  Furthermore, examples of the compound having 1 to 4 oxetane rings other than those described above include compounds represented by the following general formula (9).

In the general formula (9), R ⁸ has the same meaning as R ⁸ in the general formula (6). R ¹¹ is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group or a trialkylsilyl group, and r is 1 to 4. R ¹ has the same meaning as R ¹ in the general formula (6).

  Preferred specific examples of the oxetane compound used in the present invention include the exemplified compounds 4, 5, and 6 shown below.

  The production method of each compound having an oxetane ring described above is not particularly limited, and may be a conventionally known method, for example, Pattisson (DB Pattison, J. Am. Chem. Soc., 3455, 79). (1957)) discloses a method for synthesizing an oxetane ring from a diol. In addition to these, compounds having 1 to 4 oxetane rings having a high molecular weight of about 1000 to 5000 are also included. Examples of these specific compounds include the following compounds.

(Photopolymerization initiator)
In the present invention, in order to perform the curing reaction more efficiently, a photopolymerization initiator is added and cured. The photopolymerization initiator is a radical generator when a radically polymerizable compound is used as the polymerizable compound, and a photoacid generator when a cationically polymerizable compound is used as the polymerizable compound. Radical generators can be broadly classified into two types: intramolecular bond cleavage type and intramolecular hydrogen abstraction type.

  Examples of the intramolecular bond cleavage type radical generator include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1- (4-isopropylphenyl) -2- Hydroxy-2-methylpropan-1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4- Acetophenone series such as thiomethylphenyl) propan-1-one; α-aminoketone series such as 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone; benzoin, benzoin methyl ether, benzoin isopropyl ether Benzoins such as bis (2,4,6 Such as trimethyl benzoyl) phenyl phosphine oxide bisacylphosphine oxide-based; benzyl - and methyl phenylglyoxylate esters.

  On the other hand, examples of the intramolecular hydrogen abstraction type radical generator include, for example, benzophenone, methyl 4-phenylbenzophenone, o-benzoylbenzoate, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl- Benzophenone series such as diphenyl sulfide, acrylated benzophenone, 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone, 3,3'-dimethyl-4-methoxybenzophenone; 2-isopropylthioxanthone, 2, Thioxanthone series such as 4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone; Amibenzotone, aminobenzophenone series such as 4,4'-diethylaminobenzophenone; 10-butyl 2-chloro-acridone, 2-ethyl anthraquinone, 9,10-phenanthrenequinone, camphorquinone, and the like. The blending amount in the case of using a radical generator is preferably 0.01 to 10.00% by mass of the ultraviolet curable ink.

  Of these photopolymerization initiators, bisacylphosphine oxide having photobleaching property and α-aminoketone which is not easily affected by oxygen inhibition are particularly preferable because of high sensitivity-up effect in small droplets. As the bisacylphosphine oxide and α-aminoketone, for example, Irgacure series of Ciba Specialty Chemicals can be used.

  In the present invention, since a photopolymerization initiator is added in a larger amount than usual, the degradation odor of the photopolymerization initiator tends to be a problem, and a photopolymerization initiator containing a hydroxyethoxy group is preferable because the degradation odor is small. For example, Irgacure 2959 from Ciba Specialty Chemicals has a low degradation product odor.

  As the photoacid generator, for example, a chemically amplified photoresist or a compound used for photocationic polymerization is used (edited by Organic Electronics Materials Research Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), 187. To page 192). Examples of compounds suitable for the present invention are listed below.

First, B (C ₆ F ₅ ) ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ SO ₃ ⁻ salt of aromatic onium compounds such as diazonium, ammonium, iodonium, sulfonium, phosphonium, etc. be able to.

  Specific examples of onium compounds that can be used in the present invention are shown below.

  Secondly, sulfonated substances that generate sulfonic acid can be mentioned, and specific compounds thereof are exemplified below.

  Thirdly, halides that generate hydrogen halide can also be used, and specific compounds thereof are exemplified below.

  Fourthly, an iron allene complex can be mentioned.

  In addition, the ink of the present invention is cured by irradiation with active energy rays such as ultraviolet rays, but a photosensitizer can also be used in combination in order to perform the curing reaction more efficiently. Examples of such a photosensitizer include triethanolamine, methyldiethanolamine, triisopropanolamine, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, benzoic acid ( 2-dimethylamino) ethyl, 4-dimethylaminobenzoic acid (n-butoxy) ethyl, amines such as 4-dimethylaminobenzoic acid 2-ethylhexyl, cyanine, phthalocyanine, merocyanine, porphyrin, spiro compound, ferrocene, fluorene, fulgide Imidazole, perylene, phenazine, phenothiazine, polyene, azo compound, diphenylmethane, triphenylmethane, polymethine acridine, coumarin, ketocoumarin, quinacridone, indigo, styryl, pyriri Compounds, pyromethene compounds, pyrazolotriazole compounds, benzothiazole compounds, barbituric acid derivatives, thiobarbituric acid derivatives and the like, and further, European Patent No. 568,993, US Patent No. 4,508,811 No. 5,227,227, JP-A-2001-125255, JP-A-11-271969, and the like can also be used. The amount of the photosensitizer used is preferably in the range of 0.01 to 10.00% by mass in the ink composition.

  In the present invention, it is preferable to use white ink in order to improve the color concealability on a transparent substrate such as a plastic film. In particular, in soft packaging printing and label printing, it is preferable to use white ink. However, since the amount of injection increases, from the viewpoint of the above-mentioned injection stability and the occurrence of curling and wrinkling of the recording material, There is a limit.

(Base material (recording medium))
As a recording medium that can be used in the present invention, a non-absorbent support can be used in addition to normal non-coated paper, coated paper, and the like. It is preferable.

  As the non-absorbent support, various non-absorbable plastics and films thereof can be used. Examples of the various plastic films include PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC. A film can be mentioned. As other plastics, polycarbonate, acrylic resin, ABS, polyacetal, PVA, rubbers and the like can be used. Moreover, it is applicable also to metals and glass. Among these recording media, the configuration of the present invention is effective particularly when an image is formed on a PET film, OPS film, OPP film, ONy film, or PVC film that can be shrunk by heat. In these recording media, not only the film curls and deforms easily due to the curing shrinkage of the ink and the heat generated during the curing reaction, but also the ink film hardly follows the shrinkage of the substrate.

  The surface energies of these various plastic films differ greatly, and it has been a problem in the past that the dot diameter after ink landing varies depending on the recording medium. The constitution of the present invention includes an OPP film having a low surface energy, an OPS film, and a PET having a relatively large surface energy, but the wetting index is preferably 40 to 60 mN / m as a recording medium.

(Inkjet recording method)
Next, the ink jet recording method of the present invention will be described.

  In the ink jet recording method of the present invention, the ink described above is ejected and drawn on a substrate by an ink jet recording method with a droplet size of 10 pl or less, and then within 1.0 seconds, 0.05 to 5.0 seconds. It is preferable that the ink is cured by irradiating active energy rays such as ultraviolet rays.

  In the present invention, after the ink has landed on the substrate, it is preferable to irradiate the active energy ray at a timing when the dot diameter of the landed ink is 80 μm or less. As described above, since the ink continues to level on the substrate after landing and until the irradiation with active energy rays, the surface area per unit volume is increased, and the influence of polymerization inhibition is further increased. By irradiating active energy rays at a timing of 80 μm or less, bleeding and residual monomers can be reduced. The timing of active energy ray irradiation is such that the dot diameter is 80 μm or less for a 10 pl droplet, more preferably 70 μm or less, and the dot diameter is 70 μm or less for a 5 pl droplet, more preferably 60 μm or less. The dot diameter is measured by a three-dimensional microscope (WYCO) after 10 dots of ink are ejected and the ink is cured by irradiation with active energy rays, and the average value is obtained.

  In the present invention, after the ink has landed on the substrate, it is preferable to irradiate the active energy ray before the landed ink penetrates 30% by mass or more into the substrate. As described above, when an ink-absorbing base material is used, the ink continues to permeate the base material until the irradiation with energy rays after landing, and the ink that permeates the base material becomes difficult to reach the active energy rays. Causes poor curing. By irradiating the active energy ray before the ink penetrates 30% by mass or more into the base material, bleeding and residual monomers can be reduced. More preferably, the active energy ray is irradiated when the permeation amount of the landed ink is less than 20% by mass. The amount of ink penetrating into the base material is measured by measuring the volume of dots on the base material (volume of non-penetrable ink) with a three-dimensional microscope (WYCO) after the ink is injected and irradiated with active energy rays to cure the ink. The amount of penetration into the substrate can be calculated from the difference between the ejected ink and this amount. The average value of 10 dots is also obtained for the penetration amount.

  In the present invention, the ink film thickness after the ink has landed on the substrate and cured by irradiation with active energy rays is preferably 2 to 80 μm, and more preferably 2 to 40 μm. In the field of flexible packaging printing, where the base material is often a thin plastic material, not only the problem of curl and wrinkles of the base material, but also the problem that the overall print material's strain and texture will change. Ink ejection is not preferred.

  In addition, "ink film thickness" means the maximum value of the film thickness of the ink drawn on the base material, and it is a single color or other two color overlap (secondary color), three color overlap, four color overlap Even when recording is performed by the (white ink base) inkjet recording method, the meaning of the ink film thickness is the same.

  As the ink ejection conditions, it is preferable from the viewpoint of ejection stability that the ink jet recording head and the ink are heated to 35 to 100 ° C. and ejected. UV curable ink has a large viscosity fluctuation range due to temperature fluctuation, and the viscosity fluctuation directly affects the droplet size and droplet ejection speed, causing image quality degradation, so keep the temperature constant while raising the ink temperature. It is necessary. The control range of the ink temperature is set temperature ± 5 ° C., preferably set temperature ± 2 ° C., more preferably set temperature ± 1 ° C.

  Further, in the present invention, in order to obtain adhesion with various substrates, it is preferable to eject and cure the droplet with a small size of 10 pl. More preferably, it is 4-10 pl.

  The smaller the droplet, the more difficult it is to completely cure the ink. This is because the influence of oxygen occurs in the case of radical polymerization type ink, and the influence of moisture in the air and the substrate occurs in the case of cationic polymerization type ink. In the present invention, as means for improving these, the photopolymerization initiator concentration is increased. In radical polymerization, a method of decreasing the oxygen concentration, such as nitrogen purge, and in cationic polymerization, a method of dehumidification and / or dehydration or heating of the substrate. It is preferable to use together.

  As a method for irradiating active energy rays, a basic method is disclosed in Japanese Patent Application Laid-Open No. 60-132767. According to this, the light source is provided on both sides of the head unit, and the head and the light source are scanned by the shuttle method. Irradiation is performed after a certain period of time after ink landing. Further, the curing is completed by another light source that is not driven. In US Pat. No. 6,145,979, as an irradiation method, a method using an optical fiber or a method of applying a collimated light source to a mirror surface provided on the side of the head unit and irradiating the recording unit with UV light is disclosed. Yes. Any of these irradiation methods can be used in the image forming method according to the present invention.

  Next, an ink jet recording apparatus (hereinafter also simply referred to as a recording apparatus) that can be used in the present invention will be described.

  Hereinafter, a recording apparatus according to the present invention will be described with reference to the drawings as appropriate. Note that the recording apparatus shown in the drawings is merely an embodiment of the recording apparatus that can be preferably used in the present invention, and the present invention is not limited to the drawing of the recording apparatus exemplified here.

  FIG. 1 is a front view showing an example of a configuration of a main part used in a serial printing method in an ink jet recording apparatus that can be used in the present invention. The recording apparatus 1 includes a head carriage 2, a recording head 3, an irradiation unit 4, a platen unit 5, and the like. In the recording apparatus 1, the platen unit 5 is installed under the base material P. The platen unit 5 has a function of absorbing ultraviolet rays, and absorbs excess ultraviolet rays that have passed through the substrate P. As a result, a high-definition image can be stably reproduced.

  The base material P is guided by the guide member 6 and moves from the near side to the far side in FIG. 1 by the operation of the conveying means (not shown). A head scanning unit (not shown) scans the recording head 3 held by the head carriage 2 by reciprocating the head carriage 2 in the Y direction in FIG.

  The head carriage 2 is installed on the upper side of the substrate P, and accommodates a plurality of recording heads 3 to be described later according to the number of colors used for image printing on the substrate P, with an ejection port positioned on the lower side. The head carriage 2 is installed with respect to the main body of the recording apparatus 1 in such a manner that it can reciprocate in the Y direction in FIG. 1, and reciprocates in the Y direction in FIG. 1 by driving the head scanning means.

  In FIG. 1, the head carriage 2 is illustrated as accommodating the recording heads 3 of yellow (Y), magenta (M), cyan (C), and black (K). The number of colors of the recording head 3 housed in the head carriage 2 can be determined as appropriate.

  The recording head 3 is operated by an ejection unit (not shown) provided with a plurality of active energy ray-curable inks (for example, UV curable ink) supplied by an ink supply unit (not shown). Injecting from the injection port toward the substrate P. The UV ink ejected by the recording head 3 is composed of a coloring material, a polymerizable monomer, an initiator, and the like. The monomer crosslinks when the initiator acts as a catalyst when irradiated with ultraviolet rays. It has the property of being cured by a polymerization reaction.

  The recording head 3 has a certain region (landing possible region) on the substrate P during scanning of moving from one end of the substrate P to the other end of the substrate P in the Y direction in FIG. ), UV ink is ejected as ink droplets, and ink droplets are landed on the landable area.

  The above-described scanning is performed as many times as necessary, and after UV ink is ejected toward one landable area, the substrate P is appropriately moved from the front to the back in FIG. 1, the recording head 3 ejects UV ink to the next landable area adjacent to the rearward direction in FIG.

  By repeating the above-described operation and ejecting the UV ink from the recording head 3 in conjunction with the head scanning unit and the conveying unit, an image composed of an aggregate of UV ink droplets is formed on the substrate P.

  The irradiation unit 4 includes an ultraviolet lamp that emits ultraviolet light in a specific wavelength region with stable exposure energy and a filter that transmits ultraviolet light of a specific wavelength. Here, as the ultraviolet lamp, a mercury lamp, a metal halide lamp, an excimer laser, an ultraviolet laser, a hot cathode tube, a cold cathode tube, a black light, an LED (light emitting diode), etc. can be applied. Cathode tubes, mercury lamps or black lights are preferred.

  The irradiating means 4 has substantially the same shape as the maximum one that can be set by the recording apparatus (UV inkjet printer) 1 among the landable areas in which the recording head 3 ejects UV ink by one scan driven by the head scanning means. , Having a shape larger than the landable area.

  The irradiating means 4 is fixed on both sides of the head carriage 2 so as to be substantially parallel to the substrate P.

  As described above, as a means for adjusting the illuminance of the ink ejecting portion, not only the entire recording head 3 is shielded, but in addition, the distance h1 between the irradiation means 4 and the substrate P, and the ink ejection of the recording head 3 It is effective to reduce both the distance h2 between the portion 31 and the substrate P (2 mm or less, preferably 1.5 mm or less), or to increase the distance d between the recording head 3 and the irradiation means 4 (d is increased). It is. Further, it is more preferable that a bellows structure 7 is provided between the recording head 3 and the irradiation means 4.

  Here, the wavelength of the ultraviolet rays irradiated by the irradiation unit 4 can be changed as appropriate by exchanging the ultraviolet lamp or the filter provided in the irradiation unit 4.

  When a cationically polymerizable ink is used in the recording method of the present invention, it is preferable to heat-treat the ink jet ink that has landed on the substrate during light irradiation or after light irradiation.

  As the heating means, a method using a heat plate that guides the conveyance of the substrate and generates heat is preferable. Heat is transmitted to the substrate from the heat plate that conveys and guides the substrate, and the ink jet ink landed by this heat is heated. Is done.

  It is also preferable that the heating means is a hot air blowing means for blowing hot air onto the ink jet ink landed on the substrate.

  The heating temperature of the ink jet ink landed on the substrate is preferably 30 to 60 ° C. If the heating temperature is less than 30 ° C., the landed ink is not cured depending on the environmental humidity, and the image quality is impaired. If the temperature exceeds 60 ° C., the film base material shrinks and wrinkles, which is not preferable.

  Hereinafter, the present invention will be more specifically illustrated by examples, but the present invention is not limited thereto.

Example 1
Inks 1 to 3 having the compositions shown in Table 1 below were prepared by a conventional method.

The compounds used are shown below.
POA: manufactured by Kyoeisha Chemical Co., Ltd., light acrylate PO-A, phenoxyethyl acrylate HDODA: manufactured by Daicel UCB, 1,6-hexanediol diacrylate I819: manufactured by Ciba Specialty Chemicals, Irgacure 819, bis (2,4,6-trimethylbenzoyl) -Phenylphosphine oxide PB15: 4: Pigment Blue 15: 4
PB822: Ajinomoto Fine Techno, Ajisper PB822
The obtained inks 1 to 3 were tested for curing speed and curability.

  The serial ink jet recording apparatus having the four color recording heads shown in FIG. 1 was used, and the prepared inks 1 to 3 were sequentially loaded thereon to evaluate the curability immediately after ink ejection.

  The recording head has a nozzle pitch of 360 dpi (dpi represents the number of dots per 2.54 cm), and has a piezo-type inkjet nozzle capable of ejecting different droplet sizes in the range of 4, 8, 12 pl. The ink flow path and the nozzle were controlled to a temperature suitable for emission (ink viscosity = 10 mPa · s) by a heater.

  A PET film was used as the substrate. Since PET has no ink permeability and high ink wettability, the dot diameter increases over time after ink landing. As the carriage moves in the sub-scanning direction by printing, the ink ejected from the recording head onto the substrate is sequentially irradiated with ultraviolet rays. A test was conducted to determine the curing speed of each ink by changing the UV irradiation time.

In addition, as an ultraviolet irradiation means, Vzero and H bulb made by Integration were used, and the setting was 140 W / cm. The integrated light quantity on the film at a carriage speed of 800 mm / s was 17 mJ / cm ² .

  For inks 1 to 3, droplets of 1 dot are set to 4, 8 and 12 pl, and the carriage speed is changed in the range of 100 to 800 mm / s (that is, the recording speed is changed), and curing occurs sufficiently (rubbing). The fastest carriage speed was measured and determined as the curing speed, and the curability of the film at this curing speed (the presence or absence of film peeling when rubbed) was evaluated. The dot diameter is measured with a three-dimensional microscope (WYCO) after being cured by irradiating with ultraviolet rays, and is represented by an average value of 10 dots. Table 2 shows the results. In addition, as for the penetration amount to the base material of the landed inks 1 to 3, all were less than 30% by mass as measured by the above method.

  From Table 2, the ink of the comparative example has no problem in curing speed and curability at the droplet size of 12 pl, but the curing speed and curability are inferior at the droplet size of 4, 8 pl or less, which is 10 pl or less, which is the contrast of the present invention. It is shown that. It can be seen that the ink of the present invention has higher curing speed and curability than the ink of the comparative example.

Example 2
Inks 4 to 6 having the compositions described in Table 3 below were prepared by a conventional method.

The compounds used are shown below.
TMP-3EO-A: manufactured by Kyoeisha Chemical Co., Ltd., light acrylate TMP-3EO-A, EO-modified trimethylolpropane triacrylate Ink 4 to 6 were used and emitted in the same manner as in Example 1 with a droplet size of 8 pl. In the same manner as in Example 1, the curing rate and the flexibility of the film were evaluated by the following method, and the results are shown in Table 4. The flexibility of the film was evaluated by applying 8 pl of ink per pixel of 720 × 720 dpi and forming a solid image, and then whether or not a crack would occur when the image was folded together with the substrate.

(Flexibility)
○: No crack at all △: Slight cracks

  Table 4 shows that the ink of the present invention has a high curing speed and high flexibility.

Example 3
Inks 7 to 9 having the compositions described in Table 5 below were prepared by a conventional method.

The compounds used are shown below.
IB-XA: manufactured by Kyoeisha Chemical Co., Ltd., light acrylate IB-XA, isobornyl acrylate THF-A: manufactured by Kyoeisha Chemical Co., Ltd., light acrylate THF-A, tetrahydrofurfuryl acrylate ink 7 to 9 and ink 3 prepared in Example 1 were used. With a droplet size of 8 pl, emission and ultraviolet exposure were performed in the same manner as in Example 2. Flexibility and adhesion were evaluated in the same manner as in Example 2 and the results are shown in Table 6. For the evaluation of adhesion, a tape peeling test was performed on the solid image portion. The recording surface side of each sample was cut by about 3 cm vertically and horizontally with a cutter, applied with cello tape (R), rubbed with 10 reciprocating claws, peeled in the 180 ° direction, and evaluated according to the following criteria.

○: Image does not peel Δ: Slightly peels off when the peeling speed is increased ×: All images peel

  From Table 6, it can be seen that the ink of the present invention has a high curing speed and high flexibility and adhesion.

Example 4
Inks 10 and 11 having the compositions shown in Table 7 below were prepared by a conventional method.

The compounds used are shown below.
I369: Irgacure 369, 2-benzyl-2-dimethylamino-1- (morpholinophenyl) -butanone-1 manufactured by Ciba Specialty Chemicals
I2959: Irgacure 2959, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one manufactured by Ciba Specialty Chemicals Ink 10, 11 and Example 1 The ink 3 was used and emitted with a droplet size of 8 pl and exposed to ultraviolet light in the same manner as in Example 2. In the same manner as in Example 2, in addition to flexibility and adhesion, the odor of the formed image was evaluated according to the following criteria, and the results are shown in Table 8.

(Odor)
○: Almost no odor △: Slightly decomposed product odor of photopolymerization initiator

  From Table 8, it can be seen that the ink of the present invention has high flexibility and adhesion, and less odor.

It is a front view which shows the structure of the principal part of the recording device used for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording device 2 Head carriage 3 Recording head 4 Irradiation means 5 Platen part 6 Guide member 7 Bellows structure P Recording medium

Claims (10)

In an ink used for an ink jet recording method in which an ink is ejected onto a substrate from an ink jet nozzle with a droplet size of 10 pl or less and then irradiated with active energy rays, the ink is polymerized, cured, and fixed to the substrate. An ink comprising a polymerizable compound and 10 to 30% by mass of a photopolymerization initiator. The ink according to claim 1, wherein the polymerization reaction is radical polymerization. The ink according to claim 1 or 2, comprising 25 to 60% by mass of a monofunctional acrylate as a polymerizable compound. 4. The ink according to claim 3, wherein the monofunctional acrylate has a phenyl group, an isobornyl group or a tetrahydrofurfuryl group. The ink according to any one of claims 1 to 4, wherein the photopolymerization initiator contains bisacylphosphine oxide or α-aminoketone. The ink according to claim 1, wherein the photopolymerization initiator has a hydroxyethoxy group. An ink containing a polymerizable compound and 10-30% by mass of a photopolymerization initiator is ejected onto a substrate from an inkjet nozzle with a droplet size of 10 pl or less, and then the ink is polymerized by irradiating with active energy rays. An ink jet recording method comprising: curing, fixing, and fixing to the substrate. The ink jet recording method according to claim 7, wherein the ink is the ink according to any one of claims 2 to 6. 9. The ink jet recording method according to claim 7, wherein after the ink has landed on the substrate, the active energy ray is irradiated at a timing when the dot diameter of the landed ink is 80 μm or less. The ink jet recording according to any one of claims 7 to 9, wherein after the ink has landed on the substrate, active energy rays are irradiated before the landed ink penetrates 30% by mass or more into the substrate. Method.

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