JP2009073881A - Cationic polymerization-curable inkjet ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cationic polymerization-curable ink that can suppress thickening or gelation of an ink caused by a long-term preservation and realize stable jetting without deteriorating curing sensitivity by adding an ordinary temperature-meltable salt. <P>SOLUTION: The cationic polymerization-curable inkjet ink includes a cationically polymerizable compound, a photopolymerization initiator, a coloring material and an ordinary temperature-meltable salt. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cationic polymerization curable ink that can suppress thickening of an ink due to a dark reaction during long-term storage without lowering the curing sensitivity.

  In recent years, the inkjet recording method can be easily and inexpensively produced images, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters. In particular, a recording device that emits and controls fine dots, ink that has improved color reproduction gamut, durability, and emission suitability, and ink absorbability, coloring material color development, 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, or cross-linking with active light such as ultraviolet (UV) light after recording. An actinic ray curable ink jet method.

  Among these, the actinic ray curable ink jet method has been attracting attention in recent years because it has a relatively low odor compared to the solvent-based ink jet method, and can be recorded on a recording medium having no quick drying and no ink absorption. A curable ink-jet ink is disclosed (for example, see Patent Documents 1 and 2).

  In addition, actinic ray curable ink jet ink is generally classified into radical polymerization type and cationic polymerization type, but the cationic polymerization type is not subject to oxygen inhibition, and the cationic monomer used has a relatively low odor and cure shrinkage. It has been attracting attention because of its advantages such as low

  In addition, a method in which a cationic polymerizable compound such as an oxetane compound or an epoxy compound is used for actinic ray curable ink by cationic polymerization has been proposed (see, for example, Patent Documents 3 and 4). However, if the cationic polymerization initiator is added and stored for a long period of time, cations may be spontaneously generated from the cationic polymerization initiator even when the ultraviolet rays are blocked. There was a problem that the polymerization started and thickening and gelation occurred.

In order to solve the above problems, a method for improving storage stability by adding a basic compound to an actinic ray curable inkjet ink has been proposed (see, for example, Patent Documents 5 and 6).
JP-A-6-200204 Special Table 2000-504778 JP 2002-348478 A JP 2003-221965 A JP 2000-186079 A JP 2003-292606 A

  However, when an alkali metal hydroxide or amine as disclosed in the above patent document is added to the ink, the long-term storage stability can be improved, but at the same time, the problem is that the curing sensitivity of the ink is reduced. Has arisen.

  Therefore, the object of the present invention is to add a room temperature molten salt, and without losing the curing sensitivity, it suppresses the thickening and gelation of the ink due to long-term storage, and can realize stable emission properties. The object is to provide a curable ink.

  The above object of the present invention can be achieved by the following configuration.

  1. A cationic polymerization curable ink-jet ink comprising a cationic polymerizable compound, a photopolymerization initiator, a coloring material, and a room temperature molten salt.

  2. 2. The cationic polymerization curing according to 1 above, wherein the room temperature molten salt is at least one selected from alkylamine salts, quaternary ammonium salts, alkylpyridinium salts, alkylimidazolium salts, and alkylpiperidinium salts. Type inkjet ink.

3. _3. The cationic polymerization curable inkjet according to 1 or 2 above, wherein the anion portion of the room temperature molten salt is at least one selected from BF ₄ ⁻ , PF ₆ ⁻ and (CF ₃ SO ₂ ) ₂ N ^−. ink.

4). The cation contains at least one selected from alkylamine ion, quaternary ammonium ion, alkylpyridinium ion, alkylimidazolium ion and alkylpiperidinium ion, and BF ₄ ⁻ , PF ₆ ⁻ and ( 4. The cationic polymerization curable inkjet ink according to any one of 1 to 3 above, which contains at least one selected from CF ₃ SO ₂ ) ₂ N ⁻ .

  5). 5. The cationic polymerization curable inkjet ink according to any one of 1 to 4, wherein the room temperature molten salt is contained in an amount of 0.01 to 15% by mass based on the total amount of the cationic polymerization curable inkjet ink.

  6). 6. The cationic polymerization curable inkjet ink according to any one of 1 to 5, wherein the cationic polymerizable compound is at least one selected from an epoxy compound, an oxetane compound having an oxetane ring, and a vinyl ether compound. .

  7. 7. The cationic polymerization curable inkjet ink according to any one of 1 to 6, wherein the cationic polymerizable compound is an epoxy compound and an oxetane compound having an oxetane ring.

  8). The cationic polymerization curable inkjet according to any one of 1 to 7, wherein the photopolymerization initiator is a photoacid generator, and the photoacid generator contains a triarylsulfonium salt. ink.

  By adding the room temperature molten salt of the present invention to the cationic polymerization curable ink, without lowering the curing sensitivity, the dark reaction of the cationic ink during long-term storage is suppressed, and the ink is not thickened or gelled. Stable ejection performance was secured. Further, the room temperature molten salt acts as a solvent having good solubility with respect to the initiator which is also a salt, and as a result, it has an effect of suppressing precipitation of the initiator and the like even during long-term storage of the ink.

  The present invention will be described in more detail.

  In the present invention, by adding a room temperature molten salt to the cationic polymerization curable ink, the dark reaction of the cationic ink during long-term storage is suppressed and the viscosity of the ink is stabilized without decreasing the curing sensitivity. Ensure dischargeability. Also, the room temperature molten salt acts as a solvent having good solubility with respect to the initiator, which is also a salt, and as a result, has an effect of suppressing the precipitation of the initiator even during long-term storage of the ink.

  Although the detailed mechanism is unknown, it is presumed that the ionic liquid has an effect of suppressing the promotion of the dark reaction by trapping protons generated during long-term storage.

[Room temperature molten salt]
The salt is generally solid at room temperature, but when heated, it melts at a certain temperature to become a liquid (molten salt). This liquid salt, so-called molten salt, has a long history, and research has been developed focusing on inorganic salts. It is a very interesting material but hundreds ^O C of the height of the melting point becomes a barrier, application to a wide range, but failed to spread. However, at the end of the 20th century, salts that became liquid at room temperature using organic cations and anions were discovered. These are called room temperature molten salts or ionic liquids, and are distinguished from the previous system. Generally, a salt that takes a liquid state within 25 ° C. is called a room temperature molten salt, and is defined as such in the present invention.

The composition of the ions forming the ionic liquid varies, but the physical properties depend on the structure of the ions, so their combination is very important. For example, 1-ethyl-3-methylimidazolium cation and Br ^- salts consisting of is solid at room temperature. On the other hand, a system in which BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ (TFSI ⁻ ), or the like is combined becomes a liquid at room temperature. Furthermore, it is known that when a TFSI anion is used, it is a salt but insoluble in water. Since the ionic liquid is mainly composed of an organic material, it is not an exaggeration to say that the number of combinations thereof is infinite, and further excellent performance can be obtained. However, the preparation of ionic liquids is complicated to synthesize and purify, and although there is more information about the clear correlation between structure and physical properties (melting point, viscosity, ionic conductivity, etc.), it has not yet been elucidated. Absent.

  The room temperature molten salt according to the present invention is preferably contained in an amount of 0.01 to 15% by mass, more preferably 1.0 to 5% by mass, based on the total amount of the cationic polymerization curable inkjet ink.

[Cationically polymerizable compound and photopolymerization initiator]
The cationic polymerization curable inkjet ink of the present invention is characterized by containing at least a cationic polymerizable compound and a photopolymerization initiator. Moreover, it is preferable to contain 10-30 mass% of at least 1 type of monofunctional monomer as a cationically polymerizable compound. If the monofunctional monomer is 10% by mass or more, the effect can be sufficiently exerted, and if it is 30% by mass or less, excellent curability can be achieved and image quality problems such as color bleeding can be prevented. be able to.

  In the cationic polymerization curable ink-jet ink of the present invention, the cationically polymerizable compound is at least one selected from an epoxy compound, an oxetane compound having an oxetane ring, and a vinyl ether compound, so that the objective effect of the present invention can be further exhibited. It is preferable from the viewpoint, and further contains at least one monofunctional or bifunctional epoxy compound, at least one monofunctional or bifunctional oxetane compound, or at least one monofunctional or bifunctional vinyl ether compound. Is preferred.

  Examples of these cationically polymerizable compounds include, for example, Kaihei 6-9714, JP 2001-31892, JP 2001-40068, JP 2001-55507, JP 2001-310938, JP 2001-310937. And epoxy compounds, vinyl ether compounds, oxetane compounds and the like exemplified in JP-A-2001-220526.

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

  Preferred as the aromatic epoxide is a di- or polyglycidyl ether produced by the reaction of a polyhydric phenol having at least one aromatic nucleus or an alkylene oxide adduct thereof and epichlorohydrin, such as bisphenol A or its Examples thereof include di- or polyglycidyl ethers of alkylene oxide adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or alkylene oxide adducts thereof, and novolak-type epoxy resins. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

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

  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 Diglycidyl ethers of polyalkylene glycols such as diglycidyl ethers, polypropylene glycols or diglycidyl ethers of adducts thereof Tel and the like. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

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

  In the present invention, from the viewpoint of further improving curability and ejection stability, as a photopolymerizable compound, a compound having an oxetane ring is 30 to 95% by mass of a total photopolymerizable compound, and a compound having an oxirane group is 5 to 5. It is preferable to contain 70 mass% and 0-40 mass% of vinyl ether compounds.

  As the oxetane compound that can be used in the present invention, for example, any known oxetane compound described in JP-A Nos. 2001-220526 and 2001-310937 can be used.

  Examples of vinyl ether compounds that can be used in the present invention 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, Di- or trivinyl ether compounds such as cyclohexanedimethanol divinyl ether and trimethylolpropane 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 Bruno vinyl, n- propyl 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.

(Photopolymerization initiator)
In the ink of the present invention, as the photopolymerization initiator, all known photopolymerizations described in “Application and Market of UV / EB Curing Technology” (CMC Publishing Co., Ltd., edited by Yoneho Tabata / Edited by Radtech Research Association), etc. Although an initiator can be used, it is preferable to use a photoacid generator.

  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 ⁻ 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 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 particular, in the ink of the present invention, the photoacid generator is preferably a compound containing a triarylsulfonium salt.

  The photoacid generator is preferably contained at a ratio of 0.2 to 20 parts by mass with respect to 100 parts by mass of the cationic polymerizable compound. If the content of the photoacid generator is less than 0.2 parts by mass, it is difficult to obtain a cured product, and even if the content exceeds 20 parts by mass, there is no further effect of improving curability. These photoacid generators can be used alone or in combination of two or more.

[Color material]
The cationic polymerization curable inkjet ink of the present invention contains various known dyes or pigments together with the above-described cationic polymerizable compound and photopolymerization initiator. From the viewpoint of excellent weather resistance, it is preferable to apply a pigment as a coloring material.

  Examples of the pigment used in the present invention include carbon pigments such as carbon black, carbon refined, and carbon nanotubes, and metal oxide pigments such as iron black, cobalt blue, zinc oxide, titanium oxide, chromium oxide, and iron oxide. Sulfide pigments such as zinc sulfide, phthalocyanine pigments, pigments composed of salts such as metal sulfates, carbonates, silicates and phosphates, and aluminum powders, bronze powders, and zinc powders Inorganic pigments such as metallic powders, nitro pigments, aniline black, nitroso pigments such as naphthol green B, azo pigments such as Bordeaux 10B, Lake Red 4R, and chromoftal red (azo lakes, insoluble azo pigments, condensed azo pigments, Including chelate azo pigments), Peacock Blue Lake and Rhodamine Ray Lake pigments, phthalocyanine pigments such as phthalocyanine blue, polycyclic pigments (perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinofuranone pigments), thioindigo red Organic pigments such as selenium pigments such as Indatron Blue, quinacridone pigments, quinacridine pigments, and isoindolinone pigments can also be used.

Specific examples of pigments include
C. I Pigmen Yellow-1, 2, 3, 12, 13, 14, 16, 17, 42, 73, 74, 75, 81, 83, 87, 93, 95, 97, 98, 109, 114, 120, 128, 129, 138, 150, 151, 154, 180, 185,
C. I Pigmen Orange-16, 36, 38,
C. I Pigmen Red-5, 7, 22, 38, 48: 1, 48: 2, 48: 4, 49: 1, 53: 1, 57: 1, 63: 1, 101, 112, 122, 123, 144, 146, 168, 184, 185, 202,
C. I Pigmen Violet-19, 23,
C. I Pigmen Blue-1, 2, 3, 15: 1, 15: 2, 15: 3, 15: 4, 18, 22, 27, 29, 60,
C. I Pigmen Green-7, 36,
C. I Pigmen White-6, 18, 21,
C. I Pigmen Black-7, and the like.

  The amine value of the pigment is preferably larger than the acid value, and the difference is more preferably 1 mg / g KOH or more and less than 10 mg / g. If it is less than 1 mg / g KOH, the effect is not obtained, and if it is 10 mg / g or more, it is necessary to carry out the basic treatment excessively, which not only increases the cost but also causes polymerization inhibition.

  For the dispersion of the pigment, for example, a dispersion device such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, or a paint shaker can be used. Moreover, a dispersing agent can also be added when dispersing a pigment. As the dispersant, a polymer dispersant is preferably used. Examples of the polymer dispersant include Avecia's Solsperse series and Ajinomoto Fine-Techno's PB series. 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 used using a solvent or a polymerizable compound, but the ink of the present invention is preferably solvent-free because it is reacted and cured after printing. 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% by mass to 10% by mass of the whole ink.

<Inkjet recording method>
Next, an ink jet recording apparatus (hereinafter simply referred to as a recording apparatus) of the present invention will be described.

  The recording apparatus of the present invention will be described below with reference to the drawings as appropriate. Note that the recording apparatus of the drawings is merely one aspect of the recording apparatus of the present invention, and the recording apparatus of the present invention is not limited to this drawing.

  FIG. 1 is a front view showing the configuration of the main part of the recording apparatus of 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 recording material P. The platen unit 5 has a function of absorbing ultraviolet rays, and absorbs excess ultraviolet rays that have passed through the recording material P. As a result, a high-definition image can be reproduced very stably.

  The recording 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 recording material P, and stores a plurality of recording heads 3 to be described later according to the number of colors used for image printing on the recording material P, with the discharge ports arranged 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 yellow (Y), magenta (M), cyan (C), black (K), light yellow (Ly), light magenta (Lm), light cyan (Lc), and light black (Lk). The recording head 3 is drawn so as to accommodate the recording head 3, but the number of colors of the recording head 3 accommodated in the head carriage 2 can be determined as appropriate in the implementation.

  The recording head 3 has a discharge port by operating a discharge means (not shown) provided with a plurality of actinic ray curable inks (for example, UV curable ink) supplied by an ink supply means (not shown). To the recording material P. The UV ink ejected by the recording head 3 is composed of a coloring material, a polymerizable monomer, an initiator, and the like, and 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.

  During the scanning in which the recording head 3 moves from one end of the recording material P to the other end of the recording material P in the Y direction in FIG. 1 by driving the head scanning means, a certain area (landing possible area) in the recording material P On the other hand, UV ink is ejected as ink droplets, and ink droplets are landed on the landable area.

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

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

  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 irradiation means 4 is fixed on both sides of the head carriage 2 so as to be substantially parallel to the recording material P.

  As described above, as a means for adjusting the illuminance of the ink discharge portion, not only the entire recording head 3 is shielded, but in addition, the ink discharge of the recording head 3 is determined from the distance h1 between the irradiation means 4 and the recording material P. It is effective to increase the distance h2 between the portion 31 and the recording material P (h1 <h2), or to increase the distance d between the recording head 3 and the irradiation means 4 (d is increased). Further, it is more preferable to provide a bellows structure 7 between the recording head 3 and the irradiation means 4.

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

  The ink of the present invention has excellent ejection stability and is particularly effective when an image is formed using a line head type recording apparatus.

  FIG. 2 is a top view illustrating another example of the configuration of the main part of the ink jet recording apparatus.

  The ink jet recording apparatus shown in FIG. 2 is called a line head system, and a plurality of recording heads 3 of each color are fixedly arranged on the head carriage 2 so as to cover the entire width of the recording material P. Yes.

  On the other hand, an irradiation unit 4 is provided on the downstream side of the head carriage 2 so as to cover the entire width of the recording material P.

  In this line head system, the head carriage 2 and the irradiating means 4 are fixed, and only the recording material P is conveyed, and ink ejection and curing are performed to form an image.

  In the ink jet printer according to the present invention, as described above, the ink jet printer represented by FIGS. 1 and 2 is used to discharge the cationic polymerization curable ink jet ink of the present invention from the ink jet head onto the recording material. An image is formed by irradiating and curing actinic rays. A curing method using an inkjet head, actinic radiation irradiating apparatus and actinic radiation is described below.

  Examples of actinic rays used for curing the cationic polymerization curable inkjet ink of the present invention include ultraviolet rays, X-rays, and electron beams. As the light source that can be used when the ink of the present invention is cured by ultraviolet rays, various light sources can be used, for example, mercury lamp, metal halide lamp, electrodeless lamp, excimer laser, ultraviolet laser, cold cathode tube, heat A cathode tube, black light, LED (light emitting diode), etc. are mentioned. In the case of curing with an electron beam, various irradiation devices can be used, for example, a cockroft-warthin type, a bandegraph type, or a resonance transformer type, and the electron beam has an energy of 50 to 1000 eV. Preferably, it is 100 to 300 eV. In this invention, since an inexpensive apparatus can be used, it is preferable to use an ultraviolet-ray for hardening of an active energy ray hardening composition.

  Next, an inkjet image forming method applicable to the present invention will be described.

  The inkjet image forming method according to the present invention is a method in which the cationic polymerization curable inkjet ink of the present invention is ejected and drawn on a recording material by an inkjet recording method and then irradiated with actinic rays such as ultraviolet rays to cure the ink. is there.

(Ink ejection conditions)
When forming an image using the ink of the present invention, the ink is preferably discharged from the inkjet head and the ink of the present invention at 35 to 100 ° C. for discharge stability. Cationic polymerization curable ink-jet 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. Therefore, the temperature is kept constant while raising the ink temperature. It is necessary to keep on. The control range of the ink temperature is set temperature ± 5 ° C., preferably set temperature ± 2 ° C., more preferably set temperature ± 1 ° C.

(Light irradiation conditions after ink landing)
In the inkjet image forming method according to the present invention, as the irradiation condition of the actinic ray, it is preferable that the actinic ray is irradiated for 0.001 seconds to 1.0 seconds after the ink has landed on the recording material. More preferably, it is 0.001 second to 0.5 second. In order to form a high-definition image, it is particularly important that the irradiation timing is as early as possible.

  As a method for irradiating actinic rays, the basic method is disclosed in JP-A-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 of the present invention.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<< Preparation of pigment dispersion >>
[Preparation of yellow pigment dispersion]
A yellow pigment dispersion was prepared according to the method described below.

  The following two compounds were placed in a stainless beaker and dissolved while heating and stirring on a hot plate at 65 ° C.

Azisper PB822 (dispersant manufactured by Ajinomoto Fine Techno Co., Ltd.) 8 parts by mass Aron Oxetane OXT-221 (Oxetane compound manufactured by Toagosei Co., Ltd.) 72 parts by mass Next, after cooling to room temperature, C.I. I. 20 parts by weight of Pigment Yellow 150 was added together with 200 parts of zirconia beads having a diameter of 0.3 mm and sealed in a glass bottle. After a dispersion process for 4 hours using a paint shaker, the zirconia beads were removed and a yellow pigment was added. A dispersion was prepared.

[Preparation of magenta pigment dispersion]
In the preparation of the yellow pigment dispersion, the pigment is C.I. I. In place of Pigment Yellow 150, C.I. I. A magenta pigment dispersion was prepared in the same manner except that it was changed to Pigment Red 122.

(Preparation of cyan pigment dispersion)
In the preparation of the yellow pigment dispersion, the pigment is C.I. I. In place of Pigment Yellow 150, C.I. I. A cyan pigment dispersion was prepared in the same manner except that it was changed to Pigment Blue 15: 4.

[Preparation of black pigment dispersion]
In the preparation of the yellow pigment dispersion, the pigment is C.I. I. In place of Pigment Yellow 150, C.I. I. A black pigment dispersion was prepared in the same manner except that it was changed to Pigment Black 7.

Example 1
<Preparation of ink>
(Preparation of yellow ink)
Using the yellow pigment dispersion prepared above (yellow pigment: 20% by mass, dispersant PB822: 8% by mass, photopolymerizable compound OX-221: 72% by mass) and each additive shown in Table 1, yellow An ink was prepared.

  Specifically, after mixing all the additives shown in Table 1 except for the yellow pigment dispersion and confirming that they were sufficiently dissolved, this mixed solution was added to the yellow pigment dispersion little by little while stirring. After stirring for 15 minutes, filtration was performed with a PP3 μm disk filter manufactured by Loki Techno.

  As shown in Table 1, 8 inks were added to each of the inks with the addition of 6 points between 0 to 20% of the normal temperature molten salt and 2 points of the amine compound added instead of the normal temperature molten salt. Y1 to Y8.

Example 2
(Preparation of magenta ink)
M ink was prepared using the M dispersion in the same procedure as that for preparing Y ink in Example 1.

  The ink shown in Table 2 was added in 6 points between 0 to 20% of room temperature molten salt and 2 points were added with an amine compound instead of room temperature molten salt. M1-M8.

Example 3
(Preparation of cyan ink)
C ink was produced using the C dispersion in the same procedure as that for producing Y ink in Example 1.

  As shown in Table 3, the ink was added 6 times between 0 to 20% of the ambient temperature molten salt and the addition of an amine compound instead of the ambient temperature molten salt was 2 points. C1-C8.

Example 4
(Preparation of black ink)
K ink was prepared using the K dispersion in the same procedure as that for preparing Y ink in Example 1.

  As shown in Table 4, the ink was added 6 times between 0 to 20% of the ambient temperature molten salt and the addition of an amine compound in place of the ambient temperature molten salt was 2 points. K1 to K8.

  The structures of the additives used in Tables 1 to 4 are shown below.

  The curing sensitivity and long-term storage stability of each of Y, M, C, and K inks were evaluated.

<< Inkjet image forming method >>
An ink set prepared with each of the above-prepared cured compositions is loaded into an ink jet recording apparatus having the structure shown in FIG. 1 having a piezo-type ink jet nozzle, and each recording material is 600 mm wide and 20 m long. The following image recording was performed continuously. The 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 was heated from the front chamber tank to the head portion and heated at 50 ° C. In addition, the head portion is heated in accordance with the viscosity of each curable composition ink, and driven so that multi-sized dots having a droplet amount of 2 to 15 pl can be ejected at a resolution of 720 × 720 dpi. The ink prepared in (1) was continuously discharged. The recording material was heated to 40 ° C. by a surface heater. After landing, 300 mJ / cm ² ultraviolet rays were irradiated by a metal halide lamp on both sides of the carriage, and cured instantaneously (less than 0.5 seconds after landing). The ink discharge amount was adjusted so that the ink amount irradiated with UV at one time was 11 to 13 μg / m ² for each color. The inkjet image was formed by printing in an environment of 30 ° C. and 80% RH according to the above method.

  In addition, the illumination intensity of each irradiation light source measured the integrated illumination intensity of 254 nm using UVPF-A1 by Iwasaki Electric Co., Ltd.

  Moreover, the following two types were used as recording materials, the curability of the coating film was evaluated, and the results are shown in Tables 5-8.

PVC: polyvinyl chloride
PET: polyethylen-terephthalate
[Evaluation of curability of coating film]
The curability of the coating film was evaluated according to the following criteria from the tactile sensation.

5: The coating film is solidified and is not sticky. 4: The coating film is solid, but is slightly sticky when touched. 3: The coating film is solid, but is slightly sticky when touched. 2: Coating film There is a place where does not partially cure. Or it becomes a wrinkle 1: The coating film is not cured at all, and 3 or more is a composition suitable for practical use with respect to curability.

[Evaluation of preservability]
Measurement of Viscosity The viscosity of each of the cationic polymerization curable inkjet inks prepared above was measured before and after forced degradation at 70 degrees four days using a rheometer MCR300 (manufactured by Physica) and increasing the viscosity. Storage stability is evaluated by the width value. The measurement conditions were a temperature of 55 ° C. and a shear rate of 1000 (1 / s).
The following criteria evaluated from the value of the thickening width.

5: Thickening width value Δ is less than 0.2 mPa · s 4: Thickening width value Δ is 0.2 m0 or more and less than 0.3 Pa · s 3: Thickening width value Δ is 0.3 m0 2 or more and less than 0.5 Pa · s 2: Thickening width value Δ is 0.5 m0 or more and less than 1.0 Pa · s 1: Thickening width value Δ is 1.0 mPa · s or more and 3 or more It is a composition suitable for practical use with respect to storage stability.

Precipitate evaluation Each ink is stored in a transparent plastic container and left to stand for one week in an inverted state, and it is confirmed whether or not the precipitate is attached to the bottom of the inverted plastic container.

  A composition having no precipitate is a composition suitable for practical use.

  From Tables 5 to 8, the ink of the present invention can ensure long-term storage stability without deteriorating curability.

It is a front view which shows an example of a structure of the principal part of the inkjet recording device of this invention. It is a top view which shows another example of a structure of the principal part of the inkjet recording device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording apparatus 2 Head carriage 3 Recording head 31 Ink ejection port 4 Irradiation means 5 Platen part 6 Guide member 7 Bellows structure 8 Irradiation light source P Recording material

Claims (8)

A cationic polymerization curable ink-jet ink comprising a cationic polymerizable compound, a photopolymerization initiator, a coloring material, and a room temperature molten salt. The cationic polymerization according to claim 1, wherein the room temperature molten salt is at least one selected from alkylamine salts, quaternary ammonium salts, alkylpyridinium salts, alkylimidazolium salts, and alkylpiperidinium salts. A curable inkjet ink. _3. The cationic polymerization curable type according to claim 1, wherein the anion portion of the room temperature molten salt is at least one selected from BF ₄ ⁻ , PF ₆ ⁻ and (CF ₃ SO ₂ ) ₂ N ^−. Inkjet ink. The cation contains at least one selected from alkylamine ion, quaternary ammonium ion, alkylpyridinium ion, alkylimidazolium ion and alkylpiperidinium ion, and BF ₄ ⁻ , PF ₆ ⁻ and ( CF ₃ SO _{2) 2} N ^- cationic polymerization curable inkjet ink according to any one of claims 1 to 3, characterized in that it contains at least one selected from the. 5. The cationic polymerization curable inkjet ink according to claim 1, wherein the normal temperature molten salt is contained in an amount of 0.01 to 15 mass% with respect to the total amount of the cationic polymerization curable inkjet ink. 6. The cationic polymerization curable ink jet according to claim 1, wherein the cationic polymerizable compound is at least one selected from an epoxy compound, an oxetane compound having an oxetane ring, and a vinyl ether compound. ink. The cationic polymerization curable inkjet ink according to any one of claims 1 to 6, wherein the cationic polymerizable compound is an epoxy compound and an oxetane compound having an oxetane ring. The cationic polymerization curable type according to any one of claims 1 to 7, wherein the photopolymerization initiator is a photoacid generator, and the photoacid generator contains a triarylsulfonium salt. Inkjet ink.

Images