JP2004243761A - Ink-jet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink-jet recording method wherein a high-definition image, which is excellent in bleeding resistance for a formed image, uniform density and smoothness, can be obtained. <P>SOLUTION: The ink-jet recording method comprises the steps in which the ink containing a cation-polymerization component, which can be cured with an active energy beam, is discharged from an ink-jet recording head on a recording medium, and, after having reached the medium, the ink is cured by irradiation with the active energy beam and then forms an image. The absolute value (¾ A-B ¾) of the difference between the surface tension value (AmN/ m) of the recording medium and the surface tension value (BmN/ m) of the ink cured by irradiation with the active energy beam, is 0 to 20mN/ m. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a novel inkjet recording method using an active energy ray-curable ink.

  Conventionally, water-soluble liquid inks (water-based inks) have been widely used as inks for inkjet recording. Also, using a hot-melt ink made of a wax or the like that is solid at room temperature, it is liquefied by heating or the like, is injected by applying some energy, and is cooled and solidified while adhering to the recording medium to form recording dots. A melt type ink jet recording system has been proposed.

  Since this ink is solid at room temperature, it is not stained during handling, and the amount of evaporation of the ink during melting can be minimized, so that nozzle clogging does not occur. Furthermore, since it solidifies immediately after adhering on the recording medium, there is an advantage that various types of recording media such as Japanese paper, drawing paper, postcards, and plastic sheets can be used without pretreatment or the like without "bleeding".

  On the other hand, U.S. Pat. Nos. 4,391,369 and 4,484,948 disclose inks that provide good print quality regardless of paper quality. JP-A-56-93776 discloses an ultraviolet curable resin type ink having good adhesion to a metal surface. Further, as an ink for inkjet recording which is cured by exposing to ultraviolet light, for example, U.S. Pat. No. 4,228,438 discloses an ink using an epoxy-modified acrylic resin and a urethane-modified acrylic resin as a binder, and using a pigment having a particle diameter of 5 microns or less as a coloring component. JP-A-58-32674 discloses an ink using a cationically polymerizable epoxy resin as a binder, and JP-A-5-186725 uses a water-soluble or water-insoluble dye. In addition, there is disclosed an ink that facilitates printing on plain paper and recycled paper.

  As described above, there is a demand for an ink jet recording method capable of performing high-definition printing of photographic quality on various recording media such as a plastic sheet without the need for a dedicated ink jet paper or the like.

  However, when the above-mentioned water-soluble liquid ink is used for printing, it becomes difficult to print on a recording medium having no ink absorption, and a large-sized ink drying apparatus is required even when dedicated paper is used. In addition, high-definition printing is difficult due to the problem of bleeding and the resolution is limited, so that its use is currently limited.

  Even with the hot-melt type ink using the wax, it is possible to print on a non-absorbing recording medium having no ink absorption, and high-speed printing is possible, but the abrasion resistance is very low, and the formed image There is a problem that it is difficult to obtain high reliability and the smoothness is poor.

  On the other hand, an ink jet recording method using an organic pigment as a coloring agent has many advantages as compared with an ink jet recording method using a dye particularly in terms of weather resistance. It is expected to be applied not only to office printers but also to indoor and outdoor posters, large signboards, cars, glass, elevators, decorations on walls and buildings, and prints on fabrics.

  In addition, an ink jet recording method using an active energy ray-curable ink that cures the ink with an active energy ray such as ultraviolet light can print on a recording medium having no ink absorption. However, in the ink jet recording method using a pigment, particularly containing substantially no water and an organic solvent, and curing the ink liquid with active energy rays such as ultraviolet rays, a high-definition printing with a controlled dot diameter is formed. There are few disclosures and proposals on how to do this. In high-definition printing, it is important that the diameter of the dots to be formed is controlled to be small and that the outline is clear without bleeding. In the case of using a recording medium having a high ink absorbency, such as ink jet paper, the dot diameter to be formed can be adjusted by the amount of ink droplets, but it is difficult to adjust bleeding by itself. In addition, when printing on a recording medium having no ink absorption using an inkjet recording method, it is difficult to control the dot diameter only by the amount of ink droplets. Is a more difficult task to control.

  Furthermore, when an image is formed using a plurality of inks as in color printing, it is essential that there is no difference in the shape of dots formed by each ink in order to perform high-definition printing.

In order to control the dot shape, it is effective to adjust the surface tension of the ink. For example, a method has been proposed in which the surface tension of the ink is specified to be 25 to 35 mN / m (for example, Patent Document 1). reference.). However, simply specifying the surface tension of the ink as described above is insufficient for performing high-definition printing, and further technical improvements are required.
WO 99/29788 Pamphlet (Claims)

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an inkjet recording method capable of obtaining a high-definition image excellent in bleeding resistance, density uniformity, and smoothness of a formed image.

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
An ink containing a cationically polymerizable component curable with an active energy ray is ejected from an ink jet recording head onto a recording medium, and after landing, the ink is irradiated with an active energy ray and cured to form an image. The absolute value (| AB |) of the difference between the surface tension value (AmN / m) of the recording medium and the surface tension value (BmN / m) of the ink cured by irradiation with the active energy ray is 0 to 20 mN / m. m, an inkjet recording method.

(Claim 2)
An ink set consisting of two or more inks containing a cationically polymerizable component curable with an active energy ray is ejected from an ink jet recording head onto a recording medium, landed, and then irradiated with an active energy ray to cure the image to form an image. In the inkjet recording method to be formed, the absolute value of the difference between the surface tension value (AmN / m) of the recording medium and the surface tension value (BmN / m) of at least one color of the ink cured by irradiation with the active energy ray. (| AB |) is from 0 to 20 mN / m.

(Claim 3)
The surface tension value (BmN / m) of the ink cured by the irradiation of the active energy ray does not substantially change after the irradiation of 50% of the irradiation energy required for curing the ink. Item 3. The inkjet recording method according to item 1 or 2.

(Claim 4)
The maximum value of the difference in the surface tension value (BmN / m) of the ink cured by irradiation of the active energy ray between the two or more colors of ink is 10 mN / m or less. 3. The ink jet recording method according to item 1.

  According to the present invention, it is possible to provide an ink jet recording method capable of obtaining a high-definition image excellent in bleeding resistance, density uniformity and smoothness of a formed image.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  The present inventor has conducted intensive studies in view of the above problems, and as a result, an ink containing a cationically polymerizable component curable with an active energy ray, or an ink set including two or more colors has been transferred from an inkjet recording head to a recording medium. In an ink jet recording method in which an image is formed by irradiating an active energy ray to cure the ink after ejection and landing, the surface tension value (AmN / m) of the recording medium to be printed and the ink cured by the irradiation of the active energy ray By forming an image under the condition that the absolute value (| A-B |) of the difference from the surface tension value (BmN / m) is 0 to 20 mN / m, it is excellent in bleeding resistance, density uniformity and smoothness. It has been found that a high-definition image can be obtained, and the present invention has been reached.

  Furthermore, the surface tension value B of the ink cured by the irradiation of the active energy ray is set to a condition that does not substantially change after the irradiation of 50% of the irradiation energy required for curing the ink, or the two colors. In the ink set composed of a plurality of inks described above, by setting the maximum value of the difference in the surface tension value B between the plurality of inks to 10 mN / m or less, the above-described effect of the present invention can be further exhibited. It was found.

  Hereinafter, details of the present invention will be described.

  First, the details of the active energy ray-curable ink according to the present invention (hereinafter, also simply referred to as the ink according to the present invention) will be described.

  One feature of the active energy ray-curable ink according to the present invention is that it contains a cationically polymerizable component curable with active energy rays.

  In the present invention, various known cationically curable monomers can be used as the cationically curable component (hereinafter, also referred to as cationically curable monomer). For example, JP-A-6-9714, JP-A-2001-31892, JP-A-2001-40068, JP-A-2001-55507, JP-A-2001-310938, JP-A-2001-310937, JP-A-2001-220526 And the like. Epoxy compounds, vinyl ether compounds, oxetane compounds, and the like are exemplified.

  Examples of the epoxy compound include the following aromatic epoxides, alicyclic epoxides, and aliphatic epoxides.

  Preferred as aromatic epoxides are polyhydric phenols having at least one aromatic nucleus or di- or polyglycidyl ethers prepared by reacting an alkylene oxide adduct thereof with epichlorohydrin, for example, bisphenol A or its alkylene. Examples include di- or polyglycidyl ether of an oxide adduct, hydrogenated bisphenol A or a di- or polyglycidyl ether of an alkylene oxide adduct thereof, and a novolak-type epoxy resin. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

  As the alicyclic epoxide, cyclohexene oxide obtained by epoxidizing a compound having a cycloalkane ring such as at least one cyclohexene or cyclopentene ring with a suitable oxidizing agent such as hydrogen peroxide or peracid is used. Alternatively, a compound containing cyclopentene oxide is preferable.

  Preferred examples of the aliphatic epoxide include di- or polyglycidyl ether of an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof, and representative examples thereof are 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 alkylene oxide adduct thereof, polyethylene glycol or alkylene oxide adduct thereof Diglycidyl ethers of polyalkylene glycols such as diglycidyl ethers of polypropylene, diglycidyl ether of polypropylene glycol or an alkylene oxide adduct thereof Tel and the like. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

  Among these epoxides, an aromatic epoxide and an alicyclic epoxide are preferable, and an alicyclic epoxide is particularly preferable, in consideration of the rapid curing property. In the present invention, one of the above 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, cyclohexane dimethanol divinyl ether, and 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-propyl 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, di- or trivinyl ether compounds are preferable, and divinyl ether compounds are particularly preferable in consideration of curability, adhesion, and surface hardness. In the present invention, one of the above vinyl ether compounds may be used alone, or two or more thereof may be used in an appropriate combination.

  The ink according to the present invention preferably contains at least one compound having an oxetane ring as the cationically curable monomer.

  The oxetane compound that can be used in the present invention is a compound having an oxetane ring, and any known oxetane compound as described in JP-A-2001-220526 and JP-A-2001-310937 can be used. .

  In addition, the combined use of a monofunctional oxetane compound having one oxetane ring and a polyfunctional oxetane compound having two or more oxetane rings can improve film strength after curing and adhesion to a recording medium. preferable. However, when a compound having five or more oxetane rings is used, the viscosity of the ink composition becomes high, which makes handling difficult, and the glass transition temperature of the ink composition becomes high, so that the adhesiveness of the obtained cured product becomes high. Sex is not enough. The compound having an oxetane ring used in the present invention is preferably a compound having 1 to 4 oxetane rings.

  Hereinafter, specific examples of the compound having an oxetane ring according to the present invention will be described, but the present invention is not limited thereto.

  As an example of the compound having one oxetane ring, a compound represented by the following general formula (1) can be given.

In the general formula (1), R ¹ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, a fluoroalkyl group having 1 to 6 carbon atoms, an allyl group, or an aryl group. , A furyl group or a thienyl group. R ² is an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, a 1-propenyl group, a 2-propenyl group, a 2-methyl-1-propenyl group, a 2-methyl- 2-propenyl group, 1-butenyl group, 2-butenyl group, alkenyl group having 2 to 6 carbon atoms such as 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 ethoxycarbonyl group, a propoxycarbonyl group and a 2 to 6 carbon atoms such as 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, since the resulting composition has excellent tackiness, low viscosity and excellent workability.

  Examples of the compound having two oxetane rings include a compound represented by the following general formula (2).

In the general formula (2), R ¹ is the same group as 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) group 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, or carbonyl group or alkylene group containing carbonyl group, alkylene group containing carboxyl group, alkylene containing carbamoyl group And the like.

Further, as R ³ , a polyvalent group selected from the groups represented by the following formulas (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, a butyl group, a methoxy group, an ethoxy group, a propoxy group, a butoxy group, and the like. It is 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 alkylcarboxyl 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 the general formula (5), R ⁶ is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, or an aryl group. n is an integer of 0 to 2000. R ⁷ 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 an aryl group. R ⁷ can further include a group selected from groups represented by the following general formula (6).

In the general formula (6), R ⁸ is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, or an aryl group. m is an integer of 0 to 100.

  Specific examples of the compound having two oxetane rings include the following compounds.

Exemplary compound 1 is a compound in which R ¹ is an ethyl group and R ³ is a carboxyl group in the general formula (2). In addition, Exemplified 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).

  In addition, as an example of the compound having 3 to 4 oxetane rings, a compound represented by the following general formula (8) can be given.

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 a group 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 the groups 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. In the above D, p is an integer of 1 to 10.

  As an example of the compound having 3 to 4 oxetane rings, Exemplified Compound 3 is given.

  Further, examples of the compound having 1 to 4 oxetane rings other than those described above include a compound 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.

  Preferred specific examples of the oxetane compound used in the present invention include the following compounds.

  The method for producing each compound having an oxetane ring described above is not particularly limited, and may be in accordance with a conventionally known method. For example, Pattisson (DB Pattison, J. Am. Chem. Soc., 3455, 79) (1957)) discloses an oxetane ring synthesis method from a diol. In addition to these, compounds having 1 to 4 oxetane rings having a high molecular weight of about 1,000 to 5,000 are also exemplified. Specific examples of these compounds include the following compounds.

  In the ink according to the present invention, a photoacid generator can be used.

  As the photoacid generator, for example, a compound used for chemically amplified photoresist or photocation polymerization is used (Organic Materials Research Association, edited by "Organic Materials for Imaging", Bunshin Publishing (1993), 187). 192 pages).

  Examples of the cationic photopolymerization initiator include an aromatic onium salt. As the aromatic onium salt, a salt of a Group Va element in the periodic table, for example, a phosphonium salt (for example, triphenylphenacylphosphonium hexafluorophosphate), a salt of a Group VIa element, for example, a sulfonium salt (for example, tetra Triphenylsulfonium fluoroborate, triphenylsulfonium hexafluorophosphate, tris (4-thiomethoxyphenyl) hexafluorophosphate, sulfonium and triphenylsulfonium hexisafluoroantimonate), and salts of Group VIIa elements, such as And iodonium salts (for example, diphenyliodonium chloride and the like). Use of such an aromatic onium salt as a cationic polymerization initiator in the polymerization of an epoxy compound is disclosed in U.S. Pat. Nos. 4,058,401, 4,069,055, 4,101,513 and 4,101,513. No. 4,161,478.

  Preferred cationic cationic polymerization initiators include sulfonium salts of Group VIa elements. Among them, triarylsulfonium hexafluoroantimonate is preferred from the viewpoint of ultraviolet curability and storage stability of the ultraviolet curable ink. Also, known photopolymerization initiators described in Photopolymer Handbook (published by the Industrial Research Committee of the Photopolymer Society, 1989), pages 39 to 56, described in JP-A-64-13142 and JP-A-2-4804. Can be used arbitrarily.

  Specific examples of the compound suitable for the present invention are shown below, but the present invention is not limited thereto.

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

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

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

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

  Fourth, an iron allene complex can be mentioned.

  The ink according to the present invention preferably contains at least one photoacid generator selected from aromatic onium compounds of diazonium, iodonium or sulfonium having an aryl borate compound as a counter ion, and iron arene complexes.

  The ink according to the present invention contains, for the first time, JP-A-8-248561 and JP-A-9-34106, and contains an acid proliferating agent that newly generates an acid by an acid generated by irradiation with an actinic ray, which is already known. Is preferred. The use of the acid breeding agent makes it possible to further improve ejection stability.

  Further, the ink according to the present invention can contain a thermal base generator for the purpose of improving the ejection stability. By containing a thermal base generator, in ink-jet recording in which the printed ink film thickness becomes thicker than in normal printing, curling and wrinkling of the recording medium due to ink shrinkage occurring during ink curing can be significantly reduced. .

  As the thermal base generator, for example, a salt of an organic acid and a base that decomposes and decomposes by heating, a compound that decomposes by a reaction such as an intramolecular nucleophilic substitution reaction, a Rossen rearrangement, a Beckmann rearrangement, and releases amines, Those which cause some reaction by heating to release a base are preferably used. Specifically, salts of trichloroacetic acid described in British Patent No. 998,949, salts of alpha-sulfonylacetic acid described in U.S. Pat. No. 4,060,420, and propylic acids described in JP-A-59-157637 are disclosed. Salts, 2-carboxycarboxamide derivatives, salts with a thermally decomposable acid using an alkali metal or an alkaline earth metal in addition to an organic base as a base component described in JP-A-59-168440; And the aldoxime carbamates described in JP-A-59-195237, which produce nitriles by heating, and the like. In addition, UK Patent No. 998,945, US Patent No. 3,220,846, UK Patent No. 279,480, JP-A-50-22625, JP-A-61-32844, JP-A-61-51139, and JP-A-61-61139 The thermal base generators described in JP-A-52638, JP-A-61-51140, JP-A-61-53634 to JP-A-61-53640, JP-A-61-55644, and JP-A-61-55645 are useful. More specific examples include guanidine trichloroacetate, methylguanidine trichloroacetate, potassium trichloroacetate, guanidine phenylsulfonylacetate, guanidine p-chlorophenylsulfonylacetate, guanidine p-methanesulfonylphenylsulfonylacetate, potassium phenylpropiolate, and phenylpropiol. There are guanidine acid, cesium phenylpropiolate, guanidine p-chlorophenylpropiolate, guanidine p-phenylene-bis-phenylpropiolate, tetramethylammonium phenylsulfonylacetate, and tetramethylammonium phenylpropiolate. The above-mentioned thermal base generator can be used in a wide range.

  When coloring the ink according to the present invention, a coloring material is added. As the coloring material, various coloring materials that can be dissolved or dispersed in the cationically polymerizable component can be used, and a pigment is preferable from the viewpoint of weather resistance.

  As the pigment contained in the ink according to the present invention, achromatic inorganic pigments such as carbon black, titanium oxide and calcium carbonate or chromatic organic pigments can be used. As organic pigments, insoluble azo pigments such as toluidine red, toluidine maroon, Hanza yellow, benzidine yellow, pyrazolone red, etc., soluble azo pigments such as lithol red, helio bordeaux, pigment scarlet, permanent red 2B, alizarin, indanthrone, thiol Derivatives from vat dyes such as indigo maroon, phthalocyanine-based organic pigments such as phthalocyanine blue and phthalocyanine green, quinacridone-based organic pigments such as quinacridone red and quinacridone magenta, perylene-based organic pigments such as perylene red and perylene scarlet, isoindolinone Yellow, isoindolinone organic pigments such as isoindolinone orange, pyranthrone red, pyranthrone organic pigments such as pyranthrone orange, Oindigo organic pigments, condensed azo organic pigments, benzimidazolone organic pigments, quinophthalone organic pigments such as quinophthalone yellow, isoindoline organic pigments such as isoindoline yellow, and other pigments such as flavanthrone yellow and acylamide yellow , Nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet and the like.

  When an organic pigment is exemplified by a color index (CI) number, C.I. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 180, 185, C.I. I. Pigment Orange 16, 36, 43, 51, 55, 59, 61, C.I. I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 177, 180, 192, 202, 206, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, C.I. I. Pigment Violet 19, 23, 29, 30, 37, 40, 50, C.I. I. Pigment Blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64, C.I. I. Pigment Green 7, 36, C.I. I. Pigment Brown 23, 25, 26 and the like.

  Among the above pigments, quinacridone-based organic pigments, phthalocyanine-based organic pigments, benzimidazolone-based organic pigments, isoindolinone-based organic pigments, condensed azo-based organic pigments, quinophthalone-based organic pigments, and isoindoline-based organic pigments are light-fast. Is preferred because it is excellent. The organic pigment is preferably a fine pigment having an average particle size of 10 to 150 nm as measured by laser scattering. When the average particle size of the pigment is less than 10 nm, the light resistance is reduced due to the decrease in the particle size. When the average particle size is more than 150 nm, it becomes difficult to stably maintain the dispersion, and the pigment tends to precipitate.

  The organic pigment can be refined by the following method. That is, a mixture consisting of an organic pigment, at least three components of a water-soluble inorganic salt and a water-soluble solvent that is at least 3 times the mass of the organic pigment, is made into a clay-like mixture, kneaded strongly with a kneader or the like, finely divided, and then immersed in water. And stirred with a high-speed mixer or the like to form a slurry. Next, filtration and washing of the slurry are repeated to remove the water-soluble inorganic salt and the water-soluble solvent. In the miniaturization step, a resin, a pigment dispersant and the like may be added. Examples of the water-soluble inorganic salt include sodium chloride, potassium chloride and the like. These inorganic salts are used in a range of 3 times by mass or more, preferably 20 times by mass or less of the organic pigment. When the amount of the inorganic salt is less than 3 times by mass, a treated pigment having a desired size cannot be obtained. On the other hand, when the amount is more than 20 times by mass, the washing process in the subsequent step is large, and the substantial treatment amount of the organic pigment is reduced.

  A water-soluble solvent is used for forming an appropriate clay state of an organic pigment and a water-soluble inorganic salt used as a crushing aid, and is used for efficient crushing. Although not limited, a solvent having a boiling point of 120 to 250 ° C. is preferably used from the viewpoint of safety since the temperature rises during kneading and the solvent is easily evaporated. Examples of the water-soluble solvent include 2- (methoxymethoxy) ethanol, 2-butoxyethanol, 2- (isopentyloxy) ethanol, 2- (hexyloxy) ethanol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monoethyl ether. Butyl ether, triethylene glycol, triethylene glycol monomethyl ether, liquid polyethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, low And molecular weight polypropylene glycol.

  In the present invention, the pigment is preferably contained in the ink in a range of 3 to 15% by mass in order to obtain a sufficient concentration and a sufficient light resistance.

  Examples of the pigment dispersant used for dispersing the pigment include a hydroxyl group-containing carboxylic acid ester, a salt of a long-chain polyaminoamide and a high-molecular-weight acid ester, a salt of a high-molecular-weight polycarboxylic acid, a salt of a long-chain polyaminoamide and a polar acid ester, Molecular weight unsaturated acid ester, high molecular weight copolymer, modified polyurethane, modified polyacrylate, polyetherester type anionic activator, naphthalene sulfonic acid formalin condensate, aromatic sulfonic acid formalin condensate, polyoxyethylene alkyl phosphorus Examples thereof include acid esters, polyoxyethylene nonylphenyl ether, stearylamine acetate, and pigment derivatives.

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

  In addition, “Efka 44, 46, 47, 48, 49, 54, 63, 64, 65, 66, 71, 701, 764, 766” manufactured by Efka Chemicals, “Efka polymer 100 (modified polyacrylate), 150 (aliphatic) , 400, 401, 402, 403, 450, 451, 452, 453 (modified polyacrylate), 745 (copper phthalocyanine), Kyoei Chemical Co., Ltd., "Floren TG-710 (urethane oligomer)", " "Flonon SH-290, SP-1000", "Polyflow No. 50E, No. 300 (acrylic copolymer)", "Dispalon KS-860, 873SN, 874 (polymer dispersant), manufactured by Kusumoto Chemicals, # 2150 (Aliphatic polycarboxylic acid), # 7004 (polyetherester type) " That.

  Furthermore, Kao Corporation “Demol RN, N (sodium salt of naphthalenesulfonic acid formalin condensate), MS, C, SN-B (sodium salt of aromatic sulfonic acid formalin condensate), EP”, “Homogenol L-18 (poly) (Carboxylic acid type polymer) "," Emulgen 920, 930, 931, 935, 950, 985 (polyoxyethylene nonyl phenyl ether) "," Acetamine 24 (coconut amine acetate), 86 (stearylamine acetate) ", Zeneca "SOLSPERS 5000 (phthalocyanine ammonium salt type), 13240, 13940 (polyesteramine type), 17000 (fatty acid amine type), 24000, 32,000", Nikko Chemical Co., Ltd. "Nikkor T106 (polyoxyethylene sorbitan monooleate), MYS" IEX (polyoxyethylene monostearate), Hexagline4-0 (hexaglyceryl ruthenate Huwei rate) ", and the like.

  The pigment dispersant is preferably contained in the ink in a range of 0.1 to 10% by mass.

  The ink according to the present invention is produced by well dispersing a pigment together with an active energy ray-curable compound (cationic polymerizable component) and a pigment dispersant using a usual disperser such as a sand mill. It is preferable to prepare a concentrated solution having a high pigment concentration in advance and dilute it with an active energy ray-curable compound. Sufficient dispersion is possible even with a normal dispersing machine, so that excessive dispersion energy is not applied, and a large dispersion time is not required. An ink having excellent properties is prepared. The ink is preferably filtered with a filter having a pore size of 3 μm or less, more preferably 1 μm or less.

  Various additives other than those described above can be used in the ink according to the present invention. For example, in order to enhance the storage stability of the ink composition, a polymerization inhibitor can be added in an amount of 200 to 20,000 ppm. It is preferable that the ultraviolet curable ink is ejected after heating and lowering the viscosity. Therefore, it is preferable to add a polymerization inhibitor to prevent head clogging due to thermal polymerization. In addition, if necessary, a leveling additive, a matting agent, a polyester-based resin, a polyurethane-based resin, a vinyl-based resin, an acrylic-based resin, a rubber-based resin, and waxes for adjusting film properties may be added. Can be done. It is also effective to add a trace amount of an organic solvent in order to improve the adhesion to the recording medium. In this case, the addition is effective within a range in which the problem of solvent resistance and VOC does not occur, and the amount used is in the range of 0.1 to 5%, preferably 0.1 to 3%. It is also possible to combine a radical polymerizable monomer and an initiator to obtain a radical-cation hybrid cured ink.

  In the ink according to the present invention having the above-described structure, the absolute value of the difference between the surface tension value (AmN / m) of the recording medium and the surface tension value (BmN / m) of the ink cured by irradiation with the active energy ray is obtained. It is characterized in that the value (| AB |) is 0 to 20 mN / m, preferably 0 to 10 mN / m. If the absolute value (| AB |) of the difference between the surface tension value A and the surface tension value B exceeds 20 mN / m, the smoothness of the formed image may be impaired or density unevenness may occur. As a result, a high-definition image cannot be obtained.

  Further, in the ink according to the present invention, it is preferable that the value B does not substantially change after the irradiation of 50% of the irradiation energy required for curing the ink. This is because, when an image is formed by ejecting further ink on the ink image which has been ejected and cured on the recording medium first, if the recording speed is to be increased, the ink is not completely cured. Ink may land. In such a case, if the surface tension value B is a characteristic that largely depends on the irradiation energy, the ink lands on the image surface having various surface tensions, and as a result, the dot shape varies, and the image unevenness occurs. And it is difficult to obtain a high-definition image.

  The fact that the surface tension value B does not substantially change in the present invention means that the difference from the surface tension of the completely cured ink is within 5 dyn / cm.

  In addition, in the ink according to the present invention, when an image is formed using an ink set including a plurality of inks, it is preferable that the maximum value of the difference between the surface tension values B between the respective inks is 10 mN / m or less. If the difference between the inks exceeds 10 mN / m, variations occur between the dot shapes formed by the respective inks, causing image unevenness, and it is difficult to obtain a high-definition image.

  In the present invention, the method of setting the surface tension of the ink cured by irradiation with the active energy ray defined above as the condition defined in the present invention is not particularly limited, and the type and amount of the surfactant, or It can be realized by appropriately adjusting the type and amount of the pigment dispersant described above, the type and amount of the polymerizable component, and the type and amount of the polymerization initiator.

  The surfactant, which is one of the means for adjusting the surface tension, will be described below.

  The surfactant that can be used in the present invention is not particularly limited, and examples thereof include anionic surfactants such as dialkyl sulfosuccinates, alkylnaphthalene sulfonates, and fatty acid salts, polyoxyethylene alkyl ethers, and polyoxyethylene. Nonionic surfactants such as ethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene block copolymers, phosphate esters, etc .; cationic surfactants such as alkylamine salts and quaternary ammonium salts; fluorine Surfactants. Among these, anionic surfactants and nonionic surfactants are particularly preferred.

  As described above, the present invention is characterized by using a recording medium having a surface tension value A such that the difference from the surface tension of the cured ink is 0 to 20 mN / m.

  In the present invention, the surface tension value (mN / m) of the recording medium and the cured ink is determined by measuring the respective contact angles of water, methylene iodide and nitromethane on the recording medium or the cured inkjet image surface. After that, the solid surface tension value (mN / m) of the ink-jet image can be obtained by calculation according to the calculation formula described in Journal of the Adhesion Society of Japan, Vol. 8, page 131 (1972).

  The recording medium that can be used in the present invention is not particularly limited as long as it satisfies the above-mentioned conditions defined in the present invention with the ink to be used. Various non-absorbable plastics used for packaging and their films can be used. Examples of various plastic films include PET (polyethylene terephthalate) film, OPS (stretched polystyrene) film, OPP (stretched polypropylene) film, and ONy (stretched). Nylon) film, PVC (polyvinyl chloride) film, PE (polyethylene) film, and TAC (triacetylcellulose) film. As other plastics, polycarbonate, acrylic resin, ABS, polyacetal, PVA, rubbers and the like can be used. Further, the present invention can be applied to metals and glasses. Among these recording media, the structure of the present invention is particularly effective when an image is formed on a PET film, an OPS film, an OPP film, an ONy film, or a PVC film which can be shrunk by heat. In these recording media, not only the film is easily curled or deformed due to the curing shrinkage of the ink and the heat generated during the curing reaction, but also the ink film does not easily follow the contraction of the recording medium.

  These plastic films have greatly different surface energies, and it has conventionally been a problem that the dot diameter after ink landing varies depending on the recording medium.However, select a recording medium that satisfies the conditions specified in the present invention. By doing so, an image excellent in bleeding resistance, image density unevenness resistance and smoothness can be obtained.

  According to the configuration of the present invention, good high-definition images can be formed on a wide range of recording media having a surface energy of 35 to 60 mN / m, including OPP films and OPS films having a low surface energy and PET having a relatively high surface energy. .

  In the present invention, it is more advantageous to use a long (web) recording medium in terms of the cost of the recording medium such as packaging cost and production cost, the print production efficiency, and the ability to cope with prints of various sizes. is there.

  In the ink jet recording method of the present invention, the ink is ejected onto a recording medium by an ink jet recording method, drawing is performed, and then the ink is cured by irradiation with actinic rays such as ultraviolet rays.

  It is preferable that the recording head and the ink are heated to 35 to 100 ° C. and ejected from the viewpoint of ejection stability. Actinic ray-curable inks have large fluctuations in viscosity due to temperature fluctuations.Viscosity fluctuations directly affect the droplet size and droplet ejection speed and degrade image quality. It is necessary to keep. The control range of the ink temperature is set temperature ± 5 ° C., preferably set temperature ± 2 ° C., and more preferably set temperature ± 1 ° C.

  In the present invention, it is preferable that the amount of liquid droplets ejected from each nozzle is 2 to 15 pl.

  In the ink jet recording method of the present invention, as the irradiation condition of the generated light beam, it is preferable that the active light beam is irradiated during 0.001 to 2.0 seconds after the ink has landed, more preferably 0.001 to 1.0. Seconds. In order to form a high-definition image, it is particularly important that the irradiation timing is as early as possible.

  A basic method of irradiating actinic rays is disclosed in JP-A-60-132767. According to this, light sources are provided on both sides of the head unit, and the head and the light source are scanned in a shuttle system. Irradiation is performed at a fixed time after the ink has landed. Further, the curing is completed by another light source without driving. U.S. Patent No. 6,145,979 discloses a method using an optical fiber or a method in which a collimated light source is applied to a mirror provided on a side surface of a head unit to irradiate a recording unit with UV light. I have. In the image forming method of the present invention, any of these irradiation methods can be used.

  The irradiation of the actinic ray is divided into two stages. First, the actinic ray is irradiated by the above-described method for 0.001 to 2.0 seconds after the ink has landed, and the actinic ray is further irradiated after the completion of all printing. The method is also one of the preferred embodiments. By dividing the irradiation of the actinic ray into two stages, it is possible to further suppress the contraction of the recording medium that occurs when the ink is cured.

In the present invention, it is preferable to use an actinic ray having a low illuminance of 0.1 to 50 mW / cm ^{2 in} the wavelength range effective for curing. Conventionally, in the UV inkjet system, a high illuminance light source having a maximum illuminance exceeding 50 mW / cm ² in a wavelength region effective for curing is usually used in order to suppress dot spread and bleeding after ink landing. . However, when these light sources are used, especially in a shrink label or the like, the contraction of the recording medium is so large that it cannot be practically used.

  Examples of light sources used for actinic ray irradiation include, but are not limited to, low-pressure mercury lamps, UV lasers, xenon flash lamps, insect traps, black lights, germicidal lamps, cold cathode tubes, and LEDs.

In the present invention, it is also effective to use an actinic ray having a maximum illuminance of 50 to 3000 mW / cm ² in a wavelength range effective for curing. Although it is a high illuminance light source used in conventional UV inkjet recording, there is a problem of shrinkage of the recording medium as described above, and practically UV inkjet recording has not been used in the field of flexible packaging printing and label printing. According to the configuration of the present invention, this problem is solved, and a high-definition image can be formed on various plastic films using a conventionally used high-illuminance light source. Examples of the light source include, but are not limited to, a high-pressure mercury lamp, a metal halide lamp, and an electrodeless UV lamp.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

<< Preparation of pigment dispersion >>
Each of the following compositions was dispersed in a sand mill for 1 hour, and then filtered to prepare each pigment dispersion.

(Preparation of black pigment dispersion)
Carbon black 10 parts by mass Cationic polymerizable compound (OXT221, oxetane compound manufactured by Toa Gosei Chemical Co., Ltd.) 88 parts by mass Pigment dispersant (azispar PB822, manufactured by Ajinomoto Finetech) 2 parts by mass (preparation of yellow pigment dispersion)
C. I. Pigment Yellow 180 10 parts by mass Cationic polymerizable compound (OXT221, supra) 88 parts by mass Pigment dispersant (Azispar PB822, supra) 2 parts by mass (preparation of magenta pigment dispersion)
C. I. Pigment Red 146 10 parts by mass Cationic polymerizable compound (OXT221, supra) 88 parts by mass Pigment dispersant (Azispar PB822, supra) 2 parts by mass (preparation of cyan pigment dispersion)
C. I. Pigment Blue 15: 3 10 parts by mass Cationic polymerizable compound (OXT221, supra) 88 parts by mass Pigment dispersant (Azispar PB822, supra) 2 parts by mass << Preparation of ink >>
Using the pigment dispersions prepared as described above, inks of respective colors were prepared according to the configurations shown in Tables 1 to 4.

  In addition, the preparation of each color ink, after blending all additives other than the pigment dispersion described in each table, after confirming that it was sufficiently dissolved, the liquid temperature was set to 50 ° C., and each of the above pigment dispersion was slightly The mixture was added one by one, stirred sufficiently using a dissolver, and filtered with a 0.8 μm filter. In addition, pre-filtration with a 10 μm filter was performed as a pretreatment. In the above-mentioned filtration step, the occurrence of pressure loss was small, and a sufficient filtration speed was obtained.

  Next, the ink was heated to 50 ° C. and depressurized while being stirred to remove dissolved air and moisture, thereby preparing each ink.

<< Measurement of ink characteristic value >>
[Measurement of surface tension value B of cured inkjet image]
The solid surface tension of the cured inkjet image specified in the present invention was determined by the following method.

  After measuring the respective contact angles of water, methylene iodide and nitromethane on the cured inkjet image surface formed according to the inkjet recording method described later, the calculation described in the Journal of the Adhesion Society of Japan, vol. 8, p. 131 (1972). The solid surface tension value (mN / m) of the ink-jet image was calculated according to the formula.

[Measurement of surface tension (* 1) of ink-jet image at the time of irradiating 50% of irradiation energy required for curing ink]
After forming an ink-jet image according to the method described below, the surface tension of the ink image was measured in the same manner as described above when 50% of the irradiation energy required to cure the ink until it was not removed by rubbing with a finger was measured. .

  The surface tension measurement values obtained as described above are also shown in Tables 1 to 4.

  The details of each additive and abbreviations described in Tables 1 to 4 are as follows.

OXT221: Cationic polymerizable compound (supra)
2021P: Cationic polymerizable compound (celloxide 2021P epoxy compound, manufactured by Daicel Chemical Industries, Ltd.)
3000: Cationic polymerizable compound (Celloxide 3000 epoxy compound, manufactured by Daicel Chemical Industries, Ltd.)
INI: Photocationic polymerization initiator (triphenylsulfonium hexafluorophosphate)
178K: Fluorinated surfactant (MegaFac F178K manufactured by Dainippon Ink and Chemicals, Inc.)
ED152: Phosphate ester surfactant (PLAAD ED152 manufactured by Kusumoto Kasei Co., Ltd.)
* 1: Surface tension (mN / m) of the inkjet image at the time of irradiation with 50% of the irradiation energy required to cure the ink
《Inkjet image output》
Next, an OPP (stretched polypropylene) film having a surface tension (surface energy) of 47 mN / m and an OPP (easily 52 mN / m) were used as a recording medium by an ink jet recording apparatus having a nozzle diameter of 23 μm and 128 piezo-type ink jet nozzles. Adhesive product) Image recording on a film was performed.

  The used ink supply system was composed of an ink tank, a supply pipe, a front chamber ink tank immediately before the head, a pipe with a filter, and a piezo head, and heat insulation and heating were performed from the front chamber tank to the head. The temperature sensors were provided near the nozzles of the front chamber tank and the piezo head, and the temperature was controlled so that the temperature of the nozzle portion was always 60 ± 2 ° C. The droplet size was set to about 7 pl, and ejection was performed at a resolution of 720 × 720 dpi (dpi is the number of dots per 2.54 cm), and driving was performed at a driving frequency of 10 kHz.

The image formation was performed by a four-color full-color printer in which four color heads of Y, M, C, and K were mounted on a piezo head carriage in combinations shown in Tables 5 and 6. At both ends of the carriage, cold cathode tubes having a wavelength of 308 nm (custom-made by Hivec) were mounted, the head was scanned, and ultraviolet rays were irradiated within 1000 ms after ink landing. The exposure surface illuminance was 15 mW / cm ² . Exposure energy was adjusted by changing the speed of the head carriage so that all inks were irradiated.

<< Evaluation of inkjet image >>
The following evaluation was performed on each full-color image output using the above-described inkjet recording apparatus.

(Evaluation of bleeding resistance)
Each adjacent color dot was enlarged with a loupe, the degree of bleeding was visually observed, and bleeding resistance was evaluated according to the following criteria.

◎: The adjacent dot shape keeps a perfect circle and there is no bleeding. ：: The adjacent dot shape keeps almost a perfect circle and there is almost no bleeding. Δ: The adjacent dot does bleed a little and the dot shape is slightly distorted. , Barely usable level ×: level where adjacent dots are blurred and mixed and cannot be used (evaluation of image density unevenness resistance)
After outputting a solid black image with the above-mentioned ink jet recording apparatus and irradiating with ultraviolet rays, density unevenness was visually observed and evaluated according to the following criteria.

：: good without density unevenness ○: slight density unevenness, but no problem in high-definition printing △: density unevenness, but manageable level ×: density unevenness is noticeable and unusable level (smoothness Evaluation)
After outputting a solid black image with the above-mentioned inkjet recording apparatus and irradiating with ultraviolet rays, the ink film thickness and unevenness were visually observed and evaluated according to the following criteria.

◎: The image thickness is thin and the image quality is good. ：: The image is thick, but there is no unevenness, and the image is a high-definition printed image. ：: The image is thick and some unevenness is recognized, but it is practical. X: within the upper acceptable range x: the image is thick, the image unevenness is conspicuous, and the quality is problematic in practical use. The evaluation results obtained as described above are shown in Tables 5 and 6.

  As apparent from Tables 5 and 6, the absolute value of the difference between the surface tension value (AmN / m) of the recording medium and the surface tension value (BmN / m) of the ink cured by irradiation with active energy rays (| It can be seen that the inkjet recording method of the present invention in which (A−B |) is 0 to 20 mN / m is superior to the comparative example in terms of bleeding resistance, image density unevenness resistance, and smoothness of the formed image.

  Further, the above-mentioned effect is obtained when the surface tension value B is a level using ink that does not substantially change after irradiation of 50% of the irradiation energy required for curing the ink, and the difference in the value B between the inks. It was confirmed that the use of the ink set having the maximum value of 10 mN / m or less further improved the bleeding resistance, the image density unevenness resistance, and the smoothness.

Claims (4)

An ink containing a cationically polymerizable component curable by an active energy ray is ejected from an ink jet recording head to a recording medium, and after landing, an active energy ray is applied to cure the ink to form an image. The absolute value (| AB |) of the difference between the surface tension value (AmN / m) of the recording medium and the surface tension value (BmN / m) of the ink cured by irradiation with the active energy ray is 0 to 20 mN / m. m, an inkjet recording method. An ink set consisting of two or more inks containing a cationically polymerizable component curable by an active energy ray is ejected from an ink jet recording head onto a recording medium, landed, and then irradiated with an active energy ray to be cured to form an image. In the inkjet recording method to be formed, the absolute value of the difference between the surface tension value (AmN / m) of the recording medium and the surface tension value (BmN / m) of at least one color of the ink cured by irradiation with the active energy ray. (| AB |) is from 0 to 20 mN / m. The surface tension value (BmN / m) of the ink cured by irradiation with the active energy ray does not substantially change after irradiation of 50% of the irradiation energy required for curing the ink. Item 3. The inkjet recording method according to item 1 or 2. The maximum value of the difference in the surface tension value (BmN / m) of the ink cured by irradiation of the active energy ray between the two or more colors of ink is 10 mN / m or less. 3. The ink jet recording method according to item 1.