JP2006213883A - Inkjet ink curable by active ray, method of forming image and device for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet ink curable by an active ray, which can be used to record extremely stable and highly precise images with an excellent letter quality without causing mixing up of colors under various printing conditions, and also to provide a method of image forming and a device for inkjet recording using the same. <P>SOLUTION: The inkjet ink curable by an active ray contains at least an oxetane compound or a cycloaliphatic epoxy compound as a photopolymerizable compound and also a (meta)acrylate compound, wherein 1-10 mass% of a photo acid generator as a photopolymerization initiator and 0-1 mass% of a photo-radical generator are incorporated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an actinic ray curable inkjet ink, an image forming method using the same, and an inkjet recording apparatus.

  In recent years, the inkjet recording method can easily and inexpensively create an image, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as a color filter. A recording device that emits and controls fine dots, and ink that has improved color reproduction range, durability, and emission suitability, ink absorption, color development, surface gloss, etc. Using paper, it is also possible to obtain image quality comparable to silver halide photography. The image quality improvement of today's inkjet recording system is achieved only when all of the recording apparatus, ink, and special paper are available.

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

  Among them, the UV inkjet method has been attracting attention in recent years because it has a relatively low odor compared to the solvent-based inkjet method, and can be recorded on a recording medium having no quick drying and no ink absorption. (For example, refer to Patent Documents 1 and 2).

  However, even if these inks are used, the dot diameter after landing greatly changes depending on the type of recording material and the working environment, and it is impossible to form high-definition images on various recording materials. It is.

In particular, in an ultraviolet curable ink jet ink, for example, an ink using a cationic polymerizable compound (see, for example, Patent Documents 3 to 6) does not receive an oxygen inhibition action, but has a moisture (humidity) at a molecular level. There is a problem of being easily affected. In addition, generation of wrinkles due to curing shrinkage becomes a problem depending on the curing environment.
JP-A-6-200204 Special Table 2000-504778 JP 2001-220526 A JP 2002-188025 A JP 2002-317139 A JP 2003-55449 A

  The present invention has been made in view of the above problems, and its purpose is to record highly stable images with excellent character quality and no color mixing even under various printing environments. The present invention provides an actinic ray curable inkjet ink, an image forming method using the same, and an inkjet recording apparatus.

  The above object of the present invention has been achieved by the following constitution.

(Claim 1)
In the actinic ray curable inkjet ink containing at least an oxetane compound or an alicyclic epoxy compound as a photopolymerizable compound and containing a (meth) acrylate compound, 1 to 10% by mass of a photoacid generator as a photopolymerization initiator An actinic ray curable inkjet ink comprising 0 to 1% by mass of a photoradical generator.

(Claim 2)
The actinic ray curable inkjet ink according to claim 1, wherein the oxetane compound is a monofunctional oxetane compound, and the (meth) acrylate compound is a trifunctional or higher functional (meth) acrylate compound.

(Claim 3)
The actinic ray curing according to claim 2, wherein the content of the monofunctional oxetane compound is 10 to 40% by mass, and the content of the tri- or higher functional (meth) acrylate compound is 5 to 40% by mass. Type inkjet ink.

(Claim 4)
The actinic ray curable type according to claim 1, wherein the alicyclic epoxy compound is a monofunctional alicyclic epoxy compound, and the (meth) acrylate compound is a tri- or higher functional (meth) acrylate compound. Inkjet ink.

(Claim 5)
The content of the monofunctional alicyclic epoxy compound is 10 to 40% by mass, and the content of the tri- or higher functional (meth) acrylate compound is 5 to 40% by mass. Actinic ray curable inkjet ink.

(Claim 6)
The actinic ray curable inkjet ink according to claim 4 or 5, wherein the monofunctional alicyclic epoxy compound is represented by any one of the following general formulas (1) to (4).

(In the general formulas (1) to (4), Ra, Rb, Rd, Re, Rg, Rh, Rj, and Rk each represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a substituted alkyl group. Rb, Rd and Re, Rg and Rh, Ri and Rk do not each represent a hydrogen atom, and R _{1 to} R ₃₂ each represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or a substituted alkyl group. , Rf, Ri and Rl each represents an alkyl group having 2 to 10 carbon atoms or a substituted alkyl group.)
(Claim 7)
The actinic ray curable inkjet ink according to claim 6, wherein the molecular weight of the monofunctional alicyclic epoxy compound represented by any one of the general formulas (1) to (4) is 190 to 300.

(Claim 8)
The actinic ray curable inkjet ink according to any one of claims 1 to 7, further comprising at least one basic compound.

(Claim 9)
The actinic ray curable inkjet ink according to claim 1, wherein the viscosity at 25 ° C. is 7 to 50 mPa · s.

(Claim 10)
An image forming method in which the actinic ray curable inkjet ink according to any one of claims 1 to 9 is ejected from a inkjet recording head onto a recording material, and printing is performed on the recording material, the active ray An image forming method comprising irradiating an actinic ray for 0.001 to 1.0 seconds after landing of a curable inkjet ink.

(Claim 11)
An image forming method in which the actinic ray curable inkjet ink according to any one of claims 1 to 9 is ejected from a inkjet recording head onto a recording material, and printing is performed on the recording material, the active ray An image forming method, wherein the total ink film thickness after landing of a curable inkjet ink and curing by irradiation with actinic rays is 2 to 20 μm.

(Claim 12)
An image forming method in which the actinic radiation curable inkjet ink according to any one of claims 1 to 9 is ejected from a inkjet recording head onto a recording material, and printing is performed on the recording material. An image forming method, wherein the amount of ink droplets ejected from each nozzle of the head is 2 to 15 pl.

(Claim 13)
An image forming method in which the actinic ray curable inkjet ink according to any one of claims 1 to 9 is discharged from an inkjet recording head onto a recording material, and printing is performed on the recording material. An image forming method comprising forming an image by ejecting the actinic ray curable ink jet ink from the ink jet recording head.

(Claim 14)
14. The inkjet recording apparatus used in the image forming method according to claim 10, wherein the actinic ray curable inkjet ink and the inkjet recording head are heated to 35 to 100 ° C., and then the actinic ray curing is performed. An inkjet recording apparatus that discharges a type inkjet ink.

  According to the present invention, an actinic ray curable inkjet ink that is capable of recording a high-definition image with excellent character quality, no color mixing, and extremely stable recording under various printing environments, and an image using the same A forming method and an ink jet recording apparatus could be provided.

  Hereinafter, the present invention will be described in detail.

  As described in JP-A Nos. 2001-220526, 2002-188025, 2002-317139, and 2003-55449, a photopolymerizable compound having an oxetane ring and / or an alicyclic epoxy Actinic ray curable inkjet inks containing a compound are well known, but have problems such as generation of wrinkles due to curing shrinkage and poor curability depending on the curing environment (temperature, humidity).

  The present inventor uses an oxetane compound or an alicyclic epoxy compound and a (meth) acrylate compound as a photopolymerizable compound, or uses an oxetane compound, an alicyclic epoxy compound and a (meth) acrylate compound, and further initiates photopolymerization. It has been found that the above problem can be solved by using a photoacid generator as the agent and not containing a substantial photoradical generator (1% by mass or less). When the addition amount of the photo radical generator exceeds 1%, the curability of the oxetane compound and / or the alicyclic epoxy compound is remarkably deteriorated, the generation of wrinkles becomes remarkable, and a high-definition image can be stably formed. Can not.

  Furthermore, the present inventor not only solves the above problem by using a tri- or higher-functional (meth) acrylate compound and a monofunctional oxetane compound, or a tri- or higher-functional (meth) acrylate compound and a monofunctional alicyclic epoxy. , Ink viscosity variation due to differences in ink storage environment (temperature / humidity) can be reduced, ejection stability, which is the biggest problem in ink-jet recording, and curing environment ( It has been found that the Dot diameter can be easily controlled after the ink has landed on the recording material regardless of temperature and humidity, and a high-quality image can be formed with good reproducibility.

  Further, by using a basic compound, the ejection stability becomes better, and in particular when the photopolymerizable compound has the configuration of the present invention, it is very effective and can form a high-quality image with good reproducibility. it can.

  In the actinic ray curable inkjet ink of the present invention, as the photopolymerizable compound, for example, (meth) acrylate compounds described in JP-A-7-159983, JP-A-8-224982, JP-A-10-863 and the like However, trifunctional or higher functional (meth) acrylate compounds are preferred.

  In the present invention, any known tri- or higher functional (meth) acrylate compound can be used. For example, trimethylolpropane triacrylate, EO-modified trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate , Tri- or more functional monomers such as dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, glycerin propoxytriacrylate, caprolactone-modified trimethylolpropane triacrylate, pentaerythritol ethoxytetraacrylate, caprolactam-modified dipentaerythritol hexaacrylate It is done.

  Further, the oxetane compound used in the present invention as a photopolymerizable compound is a compound having an oxetane ring and is described in JP-A Nos. 2001-220526 and 2001-310937. Compounds can be used. Any known oxetane compound can be used, and examples include OXT221, OXT121, RSOX, HQOX, BPOX and the like manufactured by Toagosei Co., Ltd. in addition to the following monofunctional oxetane compound.

  In the present invention, among the oxetane compounds, monofunctional oxetane compounds are preferable, and examples include OXT101, OXT211, OXT212, OXT213 manufactured by Toagosei Co., Ltd., and the like.

  As a preferable configuration of the present invention in terms of improving both the emission stability and curability, the trifunctional or higher (meth) acrylate compound is contained in an amount of 5 to 40% by mass, and the monofunctional oxetane compound is contained in an amount of 10 to 40% by mass. To do. More preferably, it contains an alicyclic epoxy compound in addition to a trifunctional or higher functional (meth) acrylate compound and a monofunctional oxetane compound. Any known alicyclic epoxy compound can be used in the present invention.

  The cycloaliphatic epoxy compound is a cyclohexene 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. Oxide or cyclopentene oxide-containing compounds are preferred. Furthermore, monofunctional compounds are preferred as the alicyclic epoxy compounds.

  Another preferred configuration of the present invention in terms of improving both emission stability and curability includes 5 to 40% by mass of a tri- or higher functional (meth) acrylate compound and 10 monofunctional alicyclic epoxy compounds. Contains ~ 40% by mass. More preferably, it contains an oxetane compound in addition to a tri- or higher functional (meth) acrylate compound and a monofunctional alicyclic epoxy compound.

  A particularly preferred configuration of the present invention contains 5 to 30% by mass of a tri- or higher functional (meth) acrylate, 10 to 40% by mass of a monofunctional oxetane compound, and 5 to 30% by mass of an alicyclic epoxy compound. It is the structure to contain.

  In the present invention, any known monofunctional alicyclic epoxy compound can be used, and examples thereof include Celoxide 2000 and PNO manufactured by Daicel Chemical Industries. As a preferable example of the monofunctional alicyclic epoxy compound, the monofunctional alicyclic epoxy compound represented by any one of the general formulas (1) to (4) is particularly preferable in terms of emission stability. preferable.

In the general formulas (1) to (4), Ra, Rb, Rd, Re, Rg, Rh, Rj, and Rk represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a substituted alkyl group. , Rd and Re, Rg and Rh, and Ri and Rk do not represent hydrogen atoms at the same time. R _{1 to} R ₃₂ represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a substituted alkyl group. Rc, Rf, Ri, Rl represents an alkyl group having 2 to 10 carbon atoms or a substituted alkyl group. Examples of the alkyl group having 1 to 5 carbon atoms include linear or branched alkyl groups, and specific examples include a methyl group, an ethyl group, a propyl group, an iso-propyl group, a butyl group, a tert-butyl group, and a pentyl group. And examples thereof include halogen, hydroxyl group, alkoxy group, alkoxycarbonyl group and phenyl group. Examples of the alkyl group having 2 to 10 carbon atoms include linear or branched alkyl groups, and specifically, an ethyl group, a propyl group, an iso-propyl group, a butyl group, a tert-butyl group, a pentyl group, and a hexyl group. , An octyl group, a tert-octyl group, and a decyl group. Examples of the substituent in the substituted alkyl group include the same as those described above.

  The molecular weight of the monofunctional alicyclic epoxy compound represented by the general formulas (1) to (4) is 190 to 300. A compound smaller than 190 is not preferable for safety and health because the degree of positiveness is high in a mutagenicity (AMES) test or the like, and a compound exceeding 300 is too viscous to be handled.

  Although the exemplary compound of General formula (1)-(4) is shown below, it is not this limitation.

  These monofunctional alicyclic epoxy compounds may be produced by any method, for example, see Maruzen KK Publishing, 4th Edition Experimental Chemistry Course 20 Organic Synthesis II, 213, 1992, Ed. By Alfred Hasfner, The Chemistry of Heterocyclic Compounds-Small Ring Heterocycles part3, Oxilanes, John & Wiley and Sons, An Interc. 42, 1986, Yoshimura, Adhesion, Vol. 30, No. 7, 42, 1986, JP-A Nos. 11-100308, 4-36263, and 4-69360.

  As the basic compound, any known compounds can be used. Typical examples include basic alkali metal compounds, basic alkaline earth metal compounds, and basic organic compounds such as amines.

  Basic alkali metal compounds include alkali metal hydroxides (lithium hydroxide, sodium hydroxide, potassium hydroxide, etc.), alkali metal carbonates (lithium carbonate, sodium carbonate, potassium carbonate, etc.), alkali metal alcoholates. (Sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, etc.).

  Similarly, basic alkaline earth metal compounds include alkaline earth metal hydroxides (magnesium hydroxide, calcium hydroxide, etc.), alkali metal carbonates (magnesium carbonate, calcium carbonate, etc.), alkali metal alcoholates ( Magnesium methoxide, etc.).

  Examples of the basic organic compound include amines and nitrogen-containing heterocyclic compounds such as quinoline and quinolidine. Among these, amines are preferable from the viewpoint of compatibility with the photopolymerization monomer, for example, octylamine, naphthylamine, Xylenediamine, dibenzylamine, diphenylamine, dibutylamine, dioctylamine, dimethylaniline, quinuclidine, tributylamine, trioctylamine, tetramethylethylenediamine, tetramethyl-1,6-hexamethylenediamine, hexamethylenetetramine, triethanolamine, etc. Is mentioned.

  The concentration when the basic compound is present is preferably in the range of 10 to 1000 ppm by mass, particularly 20 to 500 ppm by mass with respect to the total amount of the photopolymerizable compound. In addition, a basic compound may be used individually or may be used in combination of multiple.

  Any known photoacid generator can be used in the actinic ray curable inkjet ink of the present invention. As the photoacid generator used in the present invention, those capable of radical polymerization are preferable.

  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 compounds 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 the actinic ray curable ink-jet ink of the present invention, any known photo radical generator may be used as the photo radical generator used at 0 to 1% by mass.

  Specifically, triazine derivatives described in JP-B-59-1281, JP-B-61-9621, JP-A-60-60104, and the like, JP-A-59-1504, and JP-A-61-243807. The organic peroxides described in each publication, such as JP-B 43-23684, JP-B 44-6413, JP-B 44-6413, and JP-B 47-1604, and US Pat. No. 567,453, diazonium compounds, U.S. Pat. Nos. 2,848,328, 2,852,379 and 2,940,853; Ortho-quinonediazides described in JP-B No. 22062, JP-B No. 37-13109, JP-B No. 38-18015, JP-B No. 45-9610, etc., No. 55-39162 Various onium compounds described in JP-A-59-14023 and other publications and “Macromolecules, Vol. 10, page 1307 (1977)”, and JP-A-59-142205 Azo compounds, JP-A-1-54440, European Patent Nos. 109,851, 126,712, etc., “Journal of Imaging Science” (J. Imag. Sci.), No. No. 30, page 174 (1986), metal allene complexes described in JP-A-5-213861, JP-A-5-255347, and (oxo) sulfonium organoboron complexes described in JP-A-61-151197. The titanocenes described in the gazette, “Coordination Chemistry Review” 84, pp. 85-277 (1988) and a transition metal complex containing a transition metal such as ruthenium described in JP-A-2-182701, described in JP-A-3-209477 2,4,5-triarylimidazole dimer, carbon tetrabromide, and organic halogen compounds described in JP-A-59-107344.

  The actinic ray curable inkjet ink of the present invention contains various known dyes and / or pigments together with the actinic ray curable composition described above, and preferably contains a pigment.

  The pigments that can be preferably used in the present invention are listed below.

C. I. Pigment Yellow-1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 81, 83, 87, 93, 95, 97, 98, 109, 114, 120, 128, 129, 138 , 150, 151, 154, 180, 185
C. I. Pigment Red-5, 7, 12, 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. Pigment Violet-19, 23
C. I. Pigment Blue-1, 2, 3, 15: 1, 15: 2, 15: 3, 15: 4, 18, 22, 27, 29, 60
C. I. Pigment Green-7, 36
C. I. Pigment White-6, 18, 21
C. I. Pigment Black-7
In the present invention, it is preferable to use white ink in order to improve the color concealability on a transparent substrate such as a plastic film. In particular, white ink is preferably used in soft packaging printing and label printing.

  For the dispersion of the pigment, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like can be used. It is also possible to add a dispersant when dispersing the pigment. A polymer dispersant is preferably used as the dispersant, and examples of the polymer dispersant include Avecia's Solsperse series and Ajinomoto Fine-Techno's PB series. 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. In the actinic ray curable ink jet ink of the present invention, it is preferable that the dispersion medium be solvent-free because it is reacted and cured immediately after ink landing. If the solvent remains in the cured image, the solvent resistance deteriorates and the VOC of the remaining solvent arises. Therefore, it is preferable in view of dispersibility that the dispersion medium is not a solvent but a photopolymerizable compound, and among them, a monomer having the lowest viscosity is selected.

  The pigment is preferably dispersed so that the average particle size of the pigment particles is 0.08 to 0.5 μm, and the maximum particle size is 0.3 to 10 μm, preferably 0.3 to 3 μm. Select the dispersion medium, dispersion conditions, and filtration conditions as appropriate. 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 actinic ray curable inkjet ink of the present invention, the colorant concentration is preferably 1% by mass to 10% by mass of the whole ink.

  Various additives other than those described above can be used in the actinic ray curable inkjet ink of the present invention. For example, surfactants, leveling additives, matting agents, polyester resins for adjusting film properties, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes can be added.

  In the actinic ray curable inkjet ink of the present invention, the viscosity at 25 ° C. is preferably 7 to 50 mPa · s in order to obtain good curability. The viscosity in the present invention is a value of a shear rate of 1000 (1 / s) measured with a viscoelasticity measuring apparatus MCR300 manufactured by Physica.

  As a recording material that can be used in the present invention, in addition to ordinary uncoated paper, coated paper, etc., various non-absorbable plastics and films used for so-called soft packaging can be used. Examples thereof include PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film. As other plastics, polycarbonate, acrylic resin, ABS, polyacetal, PVA, rubbers and the like can be used. Moreover, it is applicable also to metals and glass.

  The surface energies of these various plastic films differ greatly, and it has been a problem in the past that the dot diameter after ink landing varies depending on the recording material. With the configuration of the present invention, a good high-definition image can be formed on a wide range of recording materials having a surface energy of 35 to 60 mN / m, including OPP films having a low surface energy, OPS films, and PET having a relatively large surface energy. .

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

  Next, the image forming method of the present invention will be described.

  In the image forming method of the present invention, a method is preferred in which the ink is ejected and drawn on a recording material by an ink jet recording method, and then the ink is cured by irradiation with an actinic ray such as ultraviolet rays.

(Total ink film thickness after ink landing)
In the present invention, the total ink film thickness after the ink has landed on the recording material and cured by irradiation with actinic rays is preferably 2 to 20 μm. In the actinic ray curable inkjet recording in the screen printing field, the total ink film thickness currently exceeds 20 μm, but in the flexible packaging printing field where the recording material is often a thin plastic material, the recording material described above is used. In addition to the problem of curling and wrinkles, there is a problem that the entire printed matter is changed in its strain and texture.

  Here, “total ink film thickness” means the maximum value of the film thickness of the ink drawn on the recording material, and it is a single color or other two-color overlap (secondary color), three-color overlap, and four-color overlap. Even when recording is performed by the (white ink base) ink jet recording method, the meaning of the total ink film thickness is the same.

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

  In the present invention, the amount of ink droplets ejected from each nozzle is preferably 2 to 15 pl. Originally, in order to form a high-definition image, it is necessary for the amount of droplets to be within this range, but when discharging with this amount of droplets, the above-described discharge stability becomes particularly severe. According to the present invention, even when the ink is ejected with a small droplet amount such as 2 to 15 pl, the ejection stability is improved and a high-definition image can be stably formed.

(Light irradiation conditions after ink landing)
In the image forming method of the present invention, the actinic ray is preferably irradiated for 0.001 to 1.0 seconds after the ink landing, more preferably 0.001 to 0.5. Seconds. 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, a 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 irradiating a recording unit with UV light by applying a collimated light source to a mirror surface provided on the side of the head unit is disclosed. ing. Any of these irradiation methods can be used in the image forming method of the present invention.

  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, a 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 white (W), yellow (Y), magenta (M), cyan (C), black (K), light yellow (Ly), light magenta (Lm), and light cyan (Lc). In the drawing, the recording head 3 for light black (Lk) and white (W) is drawn. However, in practice, the number of colors of the recording head 3 stored in the head carriage 2 is appropriately determined. Is.

  The recording head 3 is activated by an ejection unit (not shown) provided with a plurality of actinic ray curable inks (for example, UV curable ink) supplied from an ink supply unit (not shown) through an ejection port. The ink is discharged toward the recording material P. The UV ink ejected by the recording head 3 is composed of a coloring material, a photopolymerizable compound, an initiator, etc., and is a monomer that accompanies the action of the initiator as a catalyst when irradiated with ultraviolet rays. It has the property of being cured by crosslinking and polymerization reactions.

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

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

  The 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 that a bellows structure 7 is provided between the recording head 3 and the irradiation means 4.

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

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

  The ink jet recording apparatus shown in FIG. 2 is called a line head system, and a plurality of ink jet 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, on the downstream side of the head carriage 2, there is provided irradiation means 4 arranged so as to cover the entire width of the recording material P and cover the entire area of the ink printing surface. As the ultraviolet lamp used in the illuminating means 4, the same one as described in FIG. 1 can be used.

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

  Examples of the present invention will be specifically described below, but the embodiments of the present invention are not limited to these examples.

<< Preparation of Dispersion A >>
The pigment was dispersed with the following composition. The following two compounds are put into a stainless beaker and dissolved by heating and stirring for 1 hour while heating on a 65 ° C. hot plate.

PB822 (dispersant manufactured by Ajinomoto Fine Techno Co., Ltd.) 9 parts OXT-221 (manufactured by Toagosei Co., Ltd.) 71 parts After cooling to room temperature, 20 parts of the following pigment is added thereto, and 200 g of zirconia beads having a diameter of 0.5 mm are added to a glass bottle. The container was sealed and dispersed with a paint shaker for the following time, and then the zirconia beads were removed.

Pigment 1: Pigment Black-7 (Mitsubishi Chemical Corporation, # 52): 10 hours Pigment 2: Pigment Blue-15: 4 (Sanyo Dye, Cyanine Blue 4044): 6 hours Pigment 3: Pigment Yellow-150 ( LANXESS, E4GN-GT CH20003): 10 hours Pigment 4: Pigment Red-122 (manufactured by Dainichi Seika Co., Ltd., special order): 10 hours Pigment 5: Titanium oxide (anatase type: particle size 0.2 μm): 10 hours.

<< Preparation of Dispersion B >>
The pigment was dispersed with the following composition. The following two compounds are put into a stainless beaker and dissolved by heating and stirring for 1 hour while heating on a 65 ° C. hot plate.

PB822 (dispersant manufactured by Ajinomoto Fine Techno Co., Ltd.) 9 parts Tetraethylene glycol diacrylate (bifunctional) 71 parts After cooling to room temperature, 20 parts of the following pigment is added to this, and 200 g of zirconia beads having a diameter of 0.5 mm are added to a glass bottle. The container was sealed and dispersed with a paint shaker for the following time, and then the zirconia beads were removed.

Pigment 1: Pigment Black-7 (Mitsubishi Chemical Corporation, # 52): 10 hours Pigment 2: Pigment Blue-15: 4 (Daiichi Seika Co., Ltd., Blue No. 32): 6 hours Pigment 3: Pigment Yellow-180 (Manufactured by Dainichi Seika Co., Ltd., special order): 10 hours Pigment 4: Pigment Red-19 (manufactured by Dainichi Seika Co., Ltd., custom order): 10 hours Pigment 5: titanium oxide (anatase type: particle size 0.2 μm): 10 hours.

<Preparation of ink set>
Ink sets 1 to 10 were prepared with the ink compositions described in Tables 1 to 4, and filtered with a PP3 μm disk filter manufactured by Loki Techno. Each ink set viscosity is as shown in the table.

  The indications in the table are as follows.

K: Dark black ink C: Dark cyan ink M: Dark magenta ink Y: Dark yellow ink W: White ink Lk: Light black ink Lc: Light cyan ink Lm: Light magenta ink Ly: Light yellow ink

[Photoacid generator]
CI-5102: Nippon Soda Co., Ltd. γ-butyrolactone 50% solution UVI6992: Triphenylsulfonium salt (Syracure UVI6992 manufactured by Union Carbide) Propylene carbonate 50% solution SP152: Triphenylsulfonium salt (Adekaoptomer SP-152, manufactured by Asahi Denka Co., Ltd. ) 50% solution of propylene carbonate.

<< Inkjet image forming method >>
The ink sets 1 to 3, 7 and 8 prepared above are loaded into an ink jet recording apparatus having the structure shown in FIG. 1 having a piezo type ink jet nozzle, and a long length of 600 mm and a length of 500 m shown in Table 5 is used. The following image recording was continuously performed on each recording material. As the image data, “high-definition color digital standard image data“ N5 / bicycle ”(issued in December 1995 by the Japanese Standards Association) was used. The ink supply system was composed of an ink tank, a supply pipe, a front chamber ink tank just before the head, a pipe with a filter, and a piezo head. The ink was insulated from the front chamber tank to the head portion and heated at 50 ° C. The piezo head was driven so that multi-size dots of 2 to 15 pl could be ejected at a resolution of 720 × 720 dpi (dpi represents the number of dots per inch, that is, 2.54 cm), and each ink was ejected continuously. After landing, it is cured instantaneously (less than 1 second after landing) by the lamp units on both sides of the carriage. After recording, the total ink film thickness was measured and found to be in the range of 2.3 to 13 μm.

  Inkjet images were formed in an environment of 10 ° C. and 20% RH, an environment of 25 ° C. and 50% RH, and an environment of 27 ° C. and 80% RH, respectively.

  The details of the abbreviations of the recording materials shown in Table 5 are as follows.

PET: Polyethylene terephthalate
PVC: polyvinyl chloride
In addition, the line head recording type ink jet recording apparatus shown in FIG. 2 was used in the same manner, and images were formed using ink sets 4 to 6, 9, and 10.

<Evaluation of inkjet recording image>
Each image recorded by the above image forming method was subjected to the following evaluations when outputting 1 m and 100 m.

(Character quality)
Using each color ink of Y, M, C, and K, a 6-point MS Mincho character was printed at a target density, and the character roughness was enlarged and evaluated with a loupe, and character quality was evaluated according to the following criteria.

◎: No rusting ○: Slight rustling is visible △: Gashesiness is visible, but it can be recognized as text and can be used at the last minute ×: Level that is rustling and the text is faint and cannot be used.

(Mixed colors (bleeds, wrinkles))
At 720 dpi, printing was performed so that 1 dot of each color of Y, M, C, and K was adjacent to each other, each adjacent color dot was enlarged with a loupe, the degree of bleeding was visually observed, and color mixing was evaluated according to the following criteria.

◎: Adjacent dot shape maintains a perfect circle and no blurring ○: Adjacent dot shape maintains a perfect circle and almost no blur Δ: Adjacent dot is slightly blurred and the dot shape is slightly displaced , The level that can be used at last *: Table 6 shows the evaluation results obtained when the adjacent dots are smeared and mixed, and wrinkles are generated in the overlapping portion, and the level is not usable.

  From Table 6, the configuration of the present invention can form high-definition images very stably on various recording materials regardless of the printing environment.

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 Inkjet recording device 2 Head carriage 3 Inkjet recording head 31 Ink discharge port 4 Irradiation means 5 Platen part 6 Guide member 7 Bellows structure 8 Irradiation light source P Recording material

Claims (14)

In the actinic ray curable inkjet ink containing at least an oxetane compound or an alicyclic epoxy compound as a photopolymerizable compound and containing a (meth) acrylate compound, 1 to 10% by mass of a photoacid generator as a photopolymerization initiator An actinic ray curable inkjet ink comprising 0 to 1% by mass of a photoradical generator. The actinic ray curable inkjet ink according to claim 1, wherein the oxetane compound is a monofunctional oxetane compound, and the (meth) acrylate compound is a trifunctional or higher functional (meth) acrylate compound. The actinic ray curing according to claim 2, wherein the content of the monofunctional oxetane compound is 10 to 40% by mass, and the content of the tri- or higher functional (meth) acrylate compound is 5 to 40% by mass. Type inkjet ink. The actinic ray curable type according to claim 1, wherein the alicyclic epoxy compound is a monofunctional alicyclic epoxy compound, and the (meth) acrylate compound is a tri- or higher functional (meth) acrylate compound. Inkjet ink. The content of the monofunctional alicyclic epoxy compound is 10 to 40% by mass, and the content of the tri- or higher functional (meth) acrylate compound is 5 to 40% by mass. Actinic ray curable inkjet ink. The actinic ray curable inkjet ink according to claim 4 or 5, wherein the monofunctional alicyclic epoxy compound is represented by any one of the following general formulas (1) to (4).

(In the general formulas (1) to (4), Ra, Rb, Rd, Re, Rg, Rh, Rj, and Rk each represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a substituted alkyl group. Rb, Rd and Re, Rg and Rh, Ri and Rk do not each represent a hydrogen atom, and R _{1 to} R ₃₂ each represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or a substituted alkyl group. , Rf, Ri and Rl each represents an alkyl group having 2 to 10 carbon atoms or a substituted alkyl group.) The actinic ray curable inkjet ink according to claim 6, wherein the molecular weight of the monofunctional alicyclic epoxy compound represented by any one of the general formulas (1) to (4) is 190 to 300. The actinic ray curable inkjet ink according to any one of claims 1 to 7, further comprising at least one basic compound. The actinic ray curable inkjet ink according to claim 1, wherein the viscosity at 25 ° C. is 7 to 50 mPa · s. An image forming method in which the actinic ray curable inkjet ink according to any one of claims 1 to 9 is ejected from a inkjet recording head onto a recording material, and printing is performed on the recording material, the active ray An image forming method comprising irradiating an actinic ray for 0.001 to 1.0 seconds after landing of a curable inkjet ink. An image forming method in which the actinic ray curable inkjet ink according to any one of claims 1 to 9 is ejected from a inkjet recording head onto a recording material, and printing is performed on the recording material, the active ray An image forming method characterized in that a total ink film thickness after landing of a curable inkjet ink and curing by irradiation with actinic rays is 2 to 20 μm. An image forming method in which the actinic radiation curable inkjet ink according to any one of claims 1 to 9 is ejected from a inkjet recording head onto a recording material, and printing is performed on the recording material. An image forming method, wherein the amount of ink droplets ejected from each nozzle of the head is 2 to 15 pl. An image forming method in which the actinic ray curable inkjet ink according to any one of claims 1 to 9 is discharged from an inkjet recording head onto a recording material, and printing is performed on the recording material. An image forming method comprising forming an image by ejecting the actinic ray curable ink jet ink from the ink jet recording head. 14. The inkjet recording apparatus used in the image forming method according to claim 10, wherein the actinic ray curable inkjet ink and the inkjet recording head are heated to 35 to 100 ° C., and then the actinic ray curing is performed. An inkjet recording apparatus that discharges a type inkjet ink.

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