JP2006159417A - Inkjet recording method and uv-curing ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording method and ink for fixing a high definition image free from unevenness in color in a short time by using a flash light source. <P>SOLUTION: In the inkjet recording method where UV-curing ink ejected onto a substrate is irradiated with UV-rays and cured to form an image, the UV-rays are irradiated from a flash light source having emission energy in the range of 1.0-10 J/cm<SP>2</SP>(per flashing) and a half peak width of emission intensity (emission time) in the range of 0.5-5 msec. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultraviolet curable ink, and more particularly, to an ink jet recording method capable of fixing an image in a short time using a flash light source as an ultraviolet light source, and to an ultraviolet curable ink used in the ink jet recording method.

  In recent years, a recording method in which ink that can be cured by ultraviolet rays is formed by an ink jet method, and recording is fixed by irradiating ultraviolet rays has been developed, and its practical application is progressing. As inks to be used, WO99 / 29787, WO99 / 29788, WO97 / 31071, JP-A-5-214280, JP-A-2002-1888025, and the like are known.

  In WO99 / 29787, the ink viscosity at 30 ° C. is preferably ≦ 35 mPa · s. This shows a preferable condition for injection in ink jet recording.

  UV curable ink causes a curing reaction by photopolymerization on the substrate by irradiation with actinic rays such as UV rays, so it can be fixed and has good adhesion to substrates that do not absorb ink, such as plastic surfaces An image can be formed.

  However, a relatively large ultraviolet ray source is necessary in the vicinity of the printing portion in order to irradiate with sufficient ultraviolet rays for the curing reaction after the ink has landed on the substrate, and a high-pressure mercury lamp or the like is usually used. However, these ultraviolet ray sources not only emit ultraviolet rays but also simultaneously emit visible light, infrared rays, and the like, and therefore a portion near the light source is subjected to considerable heating. Therefore, the peripheral substrate such as the recording head is overheated, making it difficult to perform high-speed, stable and accurate injection, and measures against overheating are required.

  On the other hand, some attempts have been made to use flash light in an ink jet recording system. For example, Patent Document 1 describes that flash light is used to speed up ink drying in an inkjet recording system.

  Patent Document 2 describes a flash-curable inkjet ink having a high affinity for a plastic resin such as a water-based soft polyvinyl chloride resin, and the ink is cured by flash exposure. .

  However, in Patent Document 1, there is no particular description about the ink, and it is intended to accelerate the drying and evaporation of the solvent using a flash light source for the ink mainly composed of a solvent such as a normal water-based ink or a solvent ink. However, a considerable amount of heat is required for drying and evaporation of ink (evaporation of water or solvent), and the flash light source requires a large number of irradiations.

  Patent Document 2 proposes to form an image with good adhesion on a soft plastic film such as vinyl chloride by using an ultraviolet curable ink containing water and irradiating a flash lamp a plurality of times. By using flash exposure, an ink having a good fixing property is obtained by mixing a monomer having a hydrophilicity and a capability of softening vinyl chloride, as well as suppressing the amount of heat generated on the substrate, rather than using a normal high-pressure mercury lamp. It is described that since it is an ultraviolet curable ink, the ink can be fixed on a substrate such as a vinyl chloride resin without requiring the amount of heat required for evaporation of water as a solvent. In addition, since it is a short-time exposure using a flash light source, energy can be applied to the extreme surface of the base material while suppressing thermal diffusion to the base material. There is a description. However, in the ultraviolet curable ink containing water described above, since a very large amount of heat is required to remove the remaining water, it is difficult to obtain sufficient image durability by remaining only with flash exposure. In addition, a solvent such as moisture remains in the cured film due to instantaneous curing, thereby deteriorating film physical properties. A great amount of heat is required to remove the solvent from the film once polymerized.

  However, it has been found that when flash light is applied to cure UV curable ink, the flash lamp emits a large amount of light, and the light emission extends to the visible region, which may require further consideration. I came.

That is, since the flash lamp emits light from the visible portion to the infrared portion, the ink droplets are overheated by applying large light energy in a short time by the flash light. These thermal energies are preferably expended in accelerating photopolymerization, but if the energy of flash light is very large, the balance between the heating rate of the ink and the heat transfer (thermal convection) to the inside of the ink is balanced. This is not preferable because it collapses and only the ink surface is locally overheated, causing boiling or excessive heat convection to cause wrinkles of the cured film and color unevenness.
JP 2000-272101A JP-T-2001-512777

  Accordingly, an object of the present invention is to provide a recording method and ink that can fix a high-quality image without color unevenness in a short time using a flash light source.

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

(Claim 1)
An ink jet recording method in which an ultraviolet curable ink is landed on a substrate, and then the ink on the substrate is cured by irradiation with ultraviolet rays to form an image, wherein the ultraviolet rays are irradiated by a flash light source. And the emission energy of the flash light source is in the range of 1.0 to 10 J / cm ² (per flash), and the half-value width (emission time) of the emission intensity is 0.5 to 5 msec. Inkjet recording method.

(Claim 2)
The inkjet recording method according to claim 1, wherein the irradiation with the flash light source is intermittently performed a plurality of times.

(Claim 3)
The ink jet recording method according to claim 1 or 2, wherein the total content of water and water-soluble solvent in the ultraviolet curable ink is 5 mass% or less.

(Claim 4)
The inkjet recording method according to claim 1, wherein the ultraviolet curable ink is cationically polymerizable.

(Claim 5)
The inkjet recording method according to claim 1, wherein the ultraviolet curable ink contains an infrared absorbing material having absorption at 800 to 1000 nm.

(Claim 6)
An ultraviolet curable ink used in an ink jet recording method for curing by irradiation with flash light, wherein the total content of water and a water-soluble solvent is 5% by mass or less.

(Claim 7)
The ultraviolet curable ink according to claim 6, which is cationically polymerizable.

(Claim 8)
8. The ultraviolet curable ink according to claim 6, further comprising an infrared absorbing material having absorption at 800 to 1000 nm.

  The inkjet recording method and the ultraviolet curable ink of the present invention can fix a high-quality inkjet image without color unevenness on a substrate.

  Next, the best mode for carrying out the present invention will be described, but the present invention is not limited thereto.

  In the present invention, an ultraviolet curable ink is used, and after the ultraviolet curable ink is landed on a substrate, it is cured by irradiation with ultraviolet rays to form an image. For this purpose, a flash light source is used as the ultraviolet light source, and the ultraviolet curable ink is cured in a short time and fixed on the substrate.

As a result of the study, the present inventor has found that the above-mentioned ink droplets or ink jet images that have landed on the substrate do not cause overheating. / Cm ² (per flash) or less, and the half-value width (light emission time) of the emission intensity is within a comparatively short range of 0.5 to 5 msec. The image is fixed without causing boiling or evaporation of the solvent due to overheating of the ink or the ink surface, or color unevenness due to excessive convection with the inside of the ink.

  The relationship between the light emission time and the light emission intensity is shown in FIG. 1. The light emission time is defined by a half-value width (a value between 50% and 50% of the light emission waveform) at 50% of the maximum light emission intensity (FIG. 1). .

  A typical example of the flash light source is a xenon flash. As described above, these flash light sources generally emit light for a short time of ≦ 1 msec, and the flash light has a very large energy amount per unit time per unit area per flash, that is, illuminance. In addition to the ultraviolet component used in the polymerization reaction (curing reaction) of the ultraviolet curable ink, it also includes visible light to infrared light, which are absorbed by the ink or the substrate, The ink causes overheating, such as boiling (flicking) and evaporation of the monomer.

  If excessive energy is given to ink droplets in a short time, for example, infrared absorption is absorbed at the surface even with a thickness of about 6 μm, and diffusion of heat into the interior is a relatively slow process. Ink thickness (in the range of several μm to several tens of μm) does not sufficiently diffuse, and the ink surface is excessively heated, causing problems such as boiling in the ink surface layer and monomer evaporation. . In addition, excessive convection between the ink surface and the inside also causes unevenness of ink density, curing wrinkles, and the like.

However, heating of the ink itself also has the effect of accelerating the polymerization reaction to some extent (particularly in the case of cationically polymerizable ink), so that the emission energy of the flash light source is 1.0 to 10 J / cm ² (1 If flash light having a (relatively long) emission time of 0.5 to 5 ms is used in an energy in the range of (per flash), excessive energy is not applied to the ink surface without giving excessive energy in a short time. Since heating can be suppressed and the whole can be heated uniformly, there is no disturbance due to volatilization of the ink droplets, boiling of the surface, etc., and a uniform curing reaction proceeds, which is preferable.

Therefore, in the present invention, the emission energy of the flash light source is in the range of 1.0 to 10 J / cm ² (per flash), and the emission time of the flash light is 0.5 to 5 ms. If the illuminance is high, such as when the light emission time is short or the light emission energy is large, only the extreme surface of the ink is heated, causing non-uniform ink, wrinkles, devitrification, etc. with uncured ink, resulting in non-uniform images become. On the other hand, when the illuminance decreases, the base material is heated by thermal diffusion, and the thermal efficiency is deteriorated, resulting in a decrease in reactivity and poor adhesion. Further, when the light emission time is long, good curability can be obtained with a color with little heat absorption, but problems such as ink bumping occur with ink such as black. Since the light emission time of the light source is longer than the pause time, problems such as heat storage and shortening of the lamp life occur.

  Since the present invention is a condition in which flash light is irradiated in a condition where the heat diffusion proceeds uniformly and sufficiently by balancing the light intensity and the light emission time, it can be applied to various colors with different heat absorption. There is no boiling (solvent) or bumping of the ink due to overheating of the ink surface, and there is no disturbance or unevenness on the uncured or curing ink surface, so that a uniform and uneven image can be obtained.

  Further, the increase in the temperature of the ink due to thermal energy can be effectively used for promoting the curing polymerization reaction, and is preferable because fixing is promoted.

  The acceleration of the curing reaction due to the increase in the ink temperature is preferable in the radical polymerizable ink and also in the cationic polymerizable ink. However, the acceleration effect by heating is more effective in the cationic polymerizable ink than in the radical polymerizable ink. Is very effective when using cationic ink.

  In order to effectively convert these visible light to infrared light components into heat, the ink according to the present invention preferably contains a component having absorption at 800 to 1000 nm. Thereby, the infrared rays of flash light can be efficiently absorbed, and the polymerization curing reaction can be further promoted. These heat conversion materials will be described later.

  In addition, cationically polymerizable inks have conventionally had the drawback that when the temperature of the substrate is low, the reactivity rate is likely to be greatly reduced, and in particular, substrates with high thermal conductivity such as metal and glass cannot be cured at high speed. The flash exposure is a short-time exposure at high illuminance with a cationic polymerizable ink and a flash light source, and if the light emission time is within a range not giving excessive energy, the exposure is sufficiently short. The heat absorbed by the ink is preferable because the exposure is continued in a state where the heat conduction does not sufficiently proceed to the substrate, and only the ink layer can be locally heated.

  In addition, it is preferable to perform flash exposure sequentially after landing of the ink by a plurality of flash lights, so that sufficient ultraviolet light can be given even in multicolor solid exposure with a large amount of ink.

  As a flash lamp used in the present invention, a xenon flash lamp is generally used (a xenon rectangular pulse light source or the like is 0.5 msec to 1 msec), and various strobe light sources are available. For example, a xenon flash lamp is a discharge lamp in which Xe gas or the like is sealed in a glass tube, a main electrode is provided at both ends of the glass tube, and a trigger electrode is provided on the tube wall. When the trigger voltage is applied to the trigger electrode while the voltage is applied, the insulation in the tube is broken and the main discharge between the main electrodes is started at once, and a flash is emitted in the ultraviolet to infrared region for a predetermined period. For example, as shown in FIG. 1, light emission with high illuminance can be obtained in a short time.

  Therefore, if light emission with high illuminance (high energy) is irradiated for a short time, the above phenomenon occurs because energy concentrates on the ink surface before sufficient thermal diffusion is performed.

  In general, the emission intensity of flash light increases as the lamp input power per flash increases, and the emission time increases and decreases as the lamp input power decreases. However, a certain degree of emission intensity is required so that sufficient ink heating occurs. In addition, in order to obtain a relatively long light emission time, it is necessary to select an optimal flash light source. Further, as described in Japanese Patent Application Laid-Open No. 2001-142347, the flash light source and the drive circuit thereof can be set to have a relatively long flash light emission time while ensuring input power, for example, a flash lamp, a charge A method of controlling the light emission time by devising the circuit such as the capacitance of the capacitor and the charging voltage may be used.

  A typical example of these flash lamps is a xenon flash. For example, a xenon lamp manufactured by Hamamatsu Photonics Co., Ltd., a xenon lamp SXC-150L, Nisshin Denshi Kogyo Co., Ltd. Hard glass xenon flash lamps, Patlite XZ series can be used.

  The total content of water and water-soluble solvent in the ultraviolet curable ink according to the present invention is preferably 5.0% by mass or less. If there is too much moisture or solvent in the ink, the flash exposure with reduced intensity will be repeated over and over again to avoid sudden bumps and sudden evaporation. This is not preferable. Further, if it is 5.0% by mass or less, the water-soluble solvent does not remain even after the ink is cured, and mixing of water is suppressed, thereby forming a highly durable image on the substrate. can do.

  Therefore, it is very effective to heat the ink and perform the solvent removal treatment before the flash light exposure.

  In the present invention, the water-soluble solvent is a solvent such as alcohol, acetone, ethylene glycol, or the like that is freely mixed with water or has a solubility of 10% or more in water at 25 ° C.

  For example, when water is contained in an acrylic ink, water remains in the coating after curing, and the durability of the coating itself is not good. Separate dehydration is required.

  The ink-jet ink according to the present invention is an ink using a polymerizable compound having a polarity smaller than that of water or a water-soluble solvent used in an aqueous ink-jet ink.

  The ultraviolet curable ink according to the present invention is prepared by blending and dispersing a dispersant, a colorant, and other additives as appropriate in a photopolymerizable composition such as a photopolymerizable compound and a photopolymerization initiator.

  Among the polymerizable compounds, examples of the radical polymerizable compound include compounds described in JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, and JP-A-10-863. As the cationically polymerizable compound, various known cationically polymerizable monomers can be used. For example, Japanese Patent Laid-Open Nos. 6-9714, 2001-31892, 2001-40068, 2001-55507, 2001-310938, 2001-310937, 2001-220526. Examples thereof include epoxy compounds, vinyl ether compounds, oxetane compounds and the like exemplified in the publication.

  In the present invention, a colorant that can be dissolved or dispersed in the photopolymerizable compound can be used as the colorant, but a pigment is preferred from the viewpoint of weather resistance.

  Pigments that can be preferably used in the present invention are listed in JP-A No. 2004-131588, paragraph (0086).

  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. As the dispersant, a polymer dispersant is preferably used, and specific examples thereof include the dispersants and dispersion aids described in JP-A No. 2004-131588 and paragraphs (0088) to (0093). Is mentioned.

  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 of the pigment is carried out using a solvent or a polymerizable compound. However, in the actinic ray curable ink used in the present invention, since it reacts and cures in a short time immediately after ink landing, water or a water-soluble solvent is used as a dispersion medium. The content is preferably 5% by mass or less, and further preferably solvent-free. 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 according to the present invention, the amount of the color material is preferably 1% by mass to 10% by mass of the whole ink.

  Specific examples of the radical polymerizable compound among the polymerizable compounds that can be used in the present invention include the compounds described in JP-A-2004-131588, paragraphs (0026) to (0029). It is done.

  The amount of radically polymerizable compound added to the ink-jet ink is preferably 1 to 97% by mass, more preferably 30 to 95% by mass, based on the ink composition.

  Among the polymerizable compounds that can be used in the present invention, representative examples of the cationic polymerizable compound include compounds selected from oxetane compounds, epoxy compounds, and vinyl ether compounds.

  Specific examples of these oxetane compounds, epoxy compounds and vinyl ether compounds include compounds described in JP-A No. 2004-131588, paragraphs (0031) to (0036).

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

  Specific examples of these oxetane compounds include the compounds described in JP-A No. 2004-131588 and paragraphs (0037) to (0071).

  The addition amount of these cationically polymerizable compounds is also in the range of 1 to 97% by mass, more preferably 30 to 95% by mass with respect to the ink composition.

  In the present invention, in order to perform the curing reaction more efficiently, a photopolymerization initiator is added and cured. As the photopolymerization initiator, a radical polymerizable compound is a radical generator, and a cationic polymerizable compound is a photo acid generator. Radical generators can be broadly classified into two types: intramolecular bond cleavage type and intramolecular hydrogen abstraction type.

  Examples of these radical generators include compounds described in JP-A No. 2004-131588, paragraphs (0073) to (0074).

  The amount of the radical generator used is preferably in the range of 0.01 to 10.00% by mass of the ultraviolet curable ink.

  For cationically polymerizable compounds, for example, chemically amplified photoresists and compounds used for photocationic polymerization are used as photoacid generators (Organic Materials Research Group, “Organic Materials for Imaging”, (See Shin Publishing (1993), pages 187-192). Examples of compounds suitable for the present invention include the compounds described in JP-A No. 2004-131588, paragraphs (0076) to (0084).

  Moreover, although the inkjet ink of this invention hardens | cures by irradiation of an ultraviolet-ray, in order to perform hardening reaction more efficiently, a photosensitizer can also be used together. Examples of such a photosensitizer include compounds described in JP-A No. 2004-131588 and paragraph (0085). The amount of the photosensitizer used is preferably in the range of 0.01 to 10.00% by mass in the ink composition.

  In order to efficiently absorb the ultraviolet light of the flash lamp, it is preferable to use an initiator having a relatively long wavelength. In the case of a cationic polymerization system, an iodonium salt or a sulfonium salt is used, but thioxanthone, anthracene, or the like is preferably added for long-wave sensitization.

  As described above, the ultraviolet curable inkjet ink according to the present invention contains a pigment, a dispersant, a polymerizable compound, and a photopolymerization initiator. In addition to these components, the visible light in the flash light source is used. It is preferable to contain a light-absorbing material that can absorb a light component from the infrared region to the infrared region and convert it into heat. In particular, a component (infrared absorber) having absorption in a wavelength region of 800 to 1000 nm is preferable, and examples of the infrared absorber include the following.

  The infrared absorber is a dye or pigment that effectively absorbs near infrared rays, preferably a dye or pigment that effectively absorbs infrared rays having a wavelength of 760 to 1500 nm, and more preferably effectively absorbs infrared rays of 760 to 1200 nm. It is a dye or a pigment. These infrared absorbers preferably have an absorption maximum in the near infrared region, more preferably have an absorption maximum at a wavelength of 760 to 1500 nm, and particularly preferably have an absorption maximum at a wavelength of 760 to 1200 nm.

  Infrared absorbers do not substantially affect the required transparency and color reproducibility of visible light in applications that require transparency in the visible light region and applications where color reproducibility is required. It is preferable to add within the range. Therefore, a thing with little absorption in a visible part is preferable.

  In carrying out the present invention, the addition amount of the infrared absorber may be determined after examining various performance evaluations necessary for exhibiting the performance desired by the user. In particular, in applications that require color reproducibility, such as inkjet ink, it is preferable to add within a range that does not substantially affect the color reproduction. Specifically, it is preferable that it is 0.0001-10 mass% with respect to the total mass of a polymeric compound, Preferably it is 0.0001-5 mass%, More preferably, it is 0.001-1 mass%.

  If the infrared absorbent contained in the inkjet ink is an infrared absorbent having an absorbance between 410 and 690 nm of 0.15 or less when the absorbance at the maximum absorption wavelength of the infrared absorbent is 1, the inkjet absorbent is used for the inkjet ink. Absorption in the visible light region of the infrared absorber does not substantially affect the color reproducibility after ink curing, and sufficiently improves the curability of the ink composition, achieving both excellent curability and excellent image quality. This is preferable because an image can be obtained.

  The absorbance is measured using a spectrophotometer that can measure from a general ultraviolet to infrared range. As a solvent for measuring absorbance, a general organic solvent may be used, or it may be measured by dissolving in the polymerizable compound in the present invention.

  Among dyes that effectively absorb near-infrared rays, commercially available dyes and known ones described in documents such as “Dye Handbook (edited by the Society for Synthetic Organic Chemistry, published in 1970)” are the largest in the near-infrared region. Those having absorption can be used. Specifically, azo dyes, metal complex azo dyes, pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinoneimine dyes, methine dyes, cyanine dyes (including merocyanine dyes), squarylium dyes, immonium dyes Among dyes such as pyrylium salts and metal thiolate complexes, those having maximum absorption in the near infrared region can be mentioned.

  Examples of pigments that effectively absorb near-infrared rays include commercially available pigments and color index (CI) manuals, “Latest Pigment Handbook (edited by the Japan Pigment Technology Association, published in 1977)”, “Latest Pigment Application Technology (CMC Publishing, 1986) and “Printing Ink Technology (CMC Publishing, 1984)”, pigments having maximum absorption in the near infrared region can be used. Examples of the pigment include black pigments, yellow pigments, orange pigments, brown pigments, red pigments, purple pigments, blue pigments, green pigments, fluorescent pigments, metal powder pigments, and other polymer-bonded dyes. Specifically, insoluble azo pigments, azo lake pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, perylene and perinone pigments, thioindigo pigments, quinacridone pigments, dioxazine pigments, isoindolinone pigments Among these, quinophthalone pigments, dyed lake pigments, azine pigments, nitroso pigments, nitro pigments, natural pigments, fluorescent pigments, inorganic tin oxides, indium compounds, and inorganic pigments having a maximum absorption in the near infrared region can be used.

  The infrared absorber in the present invention is preferably a dye that effectively absorbs near infrared rays, and specifically includes phthalocyanine dyes, carbonium dyes, quinoneimine dyes, methine dyes, cyanine dyes (including merocyanine dyes), squarylium dyes, Pyryllium salts and metal thiolate complexes, more preferably phthalocyanine dyes, quinoneimine dyes, cyanine dyes (including merocyanine dyes), squarylium dyes, and immonium dyes having maximum absorption in the near infrared region. .

  Preferable examples of infrared absorbers are compounds represented by general formula 1 to general formula 8 or general formula 11 described in JP-A No. 2001-117201, specifically, examples described on pages 11 to 25 of the same publication. Compounds (1) -1 to (1) -24, (2) -1 to (2) -38, (3, 5) -1 to (3, 5) -6, (4, 6) -1 to ( 4, 6) -6, P-1 to P-26, 1-15, and are compounds represented by general formulas (1) to (3) described in JP-A No. 2000-160042, specifically Are exemplified compounds S1 to S42 described on pages 8 to 15 of the publication, and are compounds represented by the formulas described in claims 1 to 14 of patent number 2633086. To Compounds represented by Exemplified Compounds (IR1) to (IR8) described on page 18; JP-A-2004-117 The compounds represented by the general formula (a), general formulas (a-1) to (a-4), and general formulas (b) to (f) described in No. 05, specifically, the publications 29 to 41 Exemplified compounds described in the page include Exemplified compounds (IR-1) to (IR-29) described in JP-A-2004-66482, pages 26-29, JP-A-2004-98332, pages 33-34 Exemplified compounds (IR-1) to (IR-11) described, and compounds represented by general formula (a) to general formula (d) described in JP-A No. 2004-77763, specifically Exemplified compounds described on pages 23 to 30 of the gazette are exemplified, and are compounds represented by the general formula (I) described in JP-A-10-140022. Specifically, exemplary compounds described on pages 6 to 8 of the gazette ( 1) to (57), and general formula (1) described in JP-A No. 2002-187879. Specific examples include compounds (1) to (51) described on pages 7 to 23 of the same publication, and compounds described in claim 1 of JP-A-9-188589, The compound according to claim 1 or 2 of 2004-10822, which is represented by the general formulas (1), (2) and general formulas (4) to (8) described in JP-A-7-191492 It is a compound represented by the formula (1) described in JP-A-2003-55643, and specifically produced in Examples 1 to 4 and Examples 7 and 8 described on pages 5 to 6 of the same publication. A compound represented by the general formula described in claim 1 of JP-A-2000-35689, specifically, a compound used in Examples 1 to 3 described on pages 4 to 5 of the same publication In addition, the compound Dye 1451 and the chemical compound described in the ORGANICA catalog Product BDN (CAS. 38465-55-3), KAYASORB IRG-022, KAYASORB IRG-040, KAYASORB IRG-050, KAYASORB IR-820 (B), KAYASORB CY-10, compound ST1139 described in the catalog of SYNTON, manufactured by Nippon Kayaku Co., Ltd. ST946, ST1226, ST959, ST990, ST1844, ST186, ST84, ST1133, ST380, ST798, ST1291, ST1292, ST1458 and the like can be given.

  Of these, those that are transparent, have a small polarity, and are less likely to cause polymerization inhibition are preferable.

  In addition to these components, the ultraviolet curable inkjet ink according to the present invention includes a surfactant, a leveling additive, a matting agent, a polyester resin for adjusting film properties, a polyurethane resin, Vinyl resins, acrylic resins, rubber resins, and waxes can be contained.

  It is also preferable to add a polymerization inhibitor that suppresses polymerization by heat or actinic rays into the ink. As the polymerization inhibitor, it is preferable to add various antioxidants (AO agents), amines and the like.

  Since excessive addition of these polymerization inhibitors causes a decrease in sensitivity as an ink, an amount that can prevent polymerization at the time of pigment dispersion is appropriately set and blended while maintaining the storage stability as an ink. Is desirable. The amount of the polymerization inhibitor in the ink is preferably 200 to 20,000 ppm.

  It is also effective to add a trace amount of an organic solvent in order to improve adhesion to a substrate (also referred to as a recording medium) after being cured with ultraviolet rays. In this case, it is possible to add in the range where the solvent resistance and VOC problem do not occur, but it is preferable not to use as much as possible. If necessary, the addition amount is preferably 0.1 to 5%, more preferably 0.1 to 3%.

  In addition, as a means to prevent a decrease in sensitivity due to the light-shielding effect due to the colorant in the ink, it is possible to combine a cationic polymerizable compound with a long initiator lifetime and an initiator into a radical-cation hybrid curable ink. is there.

  The acceleration of the curing reaction due to the increase in the ink temperature is much greater in the cationic polymerizable ink than in the radical polymerizable ink. Therefore, in the present invention, the increase in the temperature of the ink due to thermal energy is effectively increased in the curing polymerization reaction. Cationic polymerizable inks that can be used for promotion are preferred and more effective.

(Method for producing ultraviolet curable ink)
In the method for producing an ultraviolet curable inkjet ink according to the present invention, the method for mixing a coloring material such as a dye or a pigment is not particularly limited. For example, the pigment mixing is performed by polymerizing a pigment as a coloring material as a medium. This is carried out by mixing necessary additives using an organic compound, a solvent or the above-mentioned polymer dispersant, and mixing and dispersing together with these. Examples of the mixing and dispersing apparatus include various mills such as the above-described ball mill and sand mill, and dispersing machines such as a homogenizer.

  The ink of the present invention has a viscosity at 25 ° C. of 15 to 500 mPa · s and a surface tension of 22 to 38 mN / s so that the dots are appropriately leveled on the substrate after landing and to obtain adhesion. The range is preferably m, more preferably 24 to 35 mN / m.

  Furthermore, it is preferable from the viewpoint of inkjet recording to control the temperature by heating so that the ink viscosity at the time of ink ejection is 6 to 20 mPa · s.

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

  In the present invention, the amount of liquid droplets ejected from each nozzle of the ink jet recording head is preferably 2 to 40 pl. In order to form a high-definition image, the amount of droplets needs to be in this range.

(Base material)
As the base material according to the present invention, for example, a non-absorbent support can be used in addition to printing paper such as high-quality paper and coated paper, but a non-absorbent support is preferably used as the base material.

  In the present invention, various non-absorbable plastics and films thereof can be used as the non-absorbable support. Examples of the various plastic films include polyethylene terephthalate (PET), expanded polystyrene (OPS), and stretched nylon (ONy). ), Expanded polypropylene (OPP), polyvinyl chloride (PVC), various polyolefin films, PE films, and TAC films. As other plastics, polycarbonate, acrylic resin, ABS, polyacetal, PVA, rubbers and the like can be used. Moreover, it is applicable also to metals and glass. Among these recording materials, the structure of the present invention is effective particularly when an image is formed on a PET film, an OPS film, an OPP film, an ONy film, or a PVC film that can be shrunk by heat. These substrates are not only susceptible to curling and deformation of the film due to ink curing shrinkage and heat generation during the curing reaction, but also the ink film is difficult to follow the substrate shrinkage.

  In the inkjet recording method of the present invention, the flash light is preferably irradiated for 0.001 to 2.0 seconds after ink landing, and more preferably 0.001 to 1. 0 seconds. In order to prevent ink beading and bleeding on the base material and form a high-definition image, it is particularly important that the irradiation timing is as early as possible. The flash light is preferably irradiated a plurality of times and sufficiently cured.

  According to this, in a short period of time compared with a light source such as a high-pressure mercury lamp in the vicinity of the recording head unit, the substrate, platen and other members around the head are not heated unnecessarily. Thus, efficient ink fixing can be performed. The light source is also less expensive than the high-pressure mercury lamp and has the advantage of low weight.

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

  Hereinafter, the recording apparatus will be described with reference to the drawings as appropriate. Note that the recording apparatus in the drawings is only one aspect of the recording apparatus that can be preferably used in the present invention, and the present invention is not limited to the drawing of the recording apparatus exemplified here.

  FIG. 2 is a front view showing an example of the configuration of the main part used in the serial printing method in the ink jet recording apparatus that can be used in the present invention. The recording apparatus 1 includes a head carriage 2, a recording head 3, a flash light source 4 as an irradiation unit, a platen unit 5, and the like. In the recording apparatus 1, the platen unit 5 is installed under the base material 20. The platen unit 5 has a function of absorbing ultraviolet rays, and absorbs excess ultraviolet rays that have passed through the substrate 20. As a result, a high-definition image can be reproduced very stably.

  The base material 20 is guided by the guide member 6 and moves from the near side to the far side in FIG. 2 by the operation of the conveying means (not shown). Head scanning means (not shown) scans the recording head 3 held by the head carriage 2 by reciprocating the head carriage 2 in the Y direction in FIG.

  The head carriage 2 is installed on the upper side of the substrate 20 and accommodates a plurality of recording heads 3 to be described later according to the number of colors used for image printing on the substrate 20 and an ejection port 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. 2, and reciprocates in the Y direction in FIG. 2 by driving the head scanning means.

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

  The recording head 3 is configured so that the actinic ray curable ink supplied by the ink supply means (not shown) is discharged from the discharge port to the base material 20 by the operation of the discharge means (not shown) provided therein. Dispense towards. The actinic ray curable ink ejected by the recording head 3 includes a color material and the photopolymerizable composition (for example, containing an alicyclic epoxy compound, a photoacid generator, an initiator, etc.). It has the property of being cured by a cationic polymerization reaction when irradiated with ultraviolet rays.

  The recording head 3 is a fixed area (landing possible area) in the base material 20 during the scan of moving from one end of the base material 20 to the other end of the base material 20 in the Y direction in FIG. ), Actinic ray curable ink is ejected as ink droplets, and the ink droplets are landed on the landable area.

  The above scanning is performed as many times as necessary, and actinic ray curable ink is ejected toward one landable area, and then the substrate 20 is appropriately moved from the front to the back in FIG. While performing scanning by the scanning means, the recording head 3 discharges the actinic ray curable ink to the landing possible area adjacent to the back in FIG.

  By repeating the above operation and ejecting the actinic ray curable ink from the recording head 3 in conjunction with the head scanning means and the conveying means, an image comprising an aggregate of actinic ray curable ink droplets on the substrate 20. Is formed.

  In the present invention, the flash light source 4 is preferably a flash lamp such as a xenon flash.

  The flash light source 4 is fixed on both sides of the head carriage 2 so as to be substantially parallel to the substrate P. When ink is ejected from the recording head as the head carriage 2 scans in the Y direction (main scanning), the ink droplets ejected on the base material are the flash light sources 4 on the side opposite to the carriage moving direction. Are cured by being intermittently irradiated with flash light. The flash light intensity of the ink discharge unit can be adjusted by the distance between the flash light source 4 and the substrate 20. Further, the timing of flash light irradiation can be adjusted by the distance between the recording head 3 and the flash light source 4.

  Since the flash light source irradiates intermittently, the flash exposure width × flash cycle is 1 or more (that is, at least the scanning distance (ink landing area) with respect to the distance that the recording head travels on the recording medium per unit time. It is set to be one flash (so that it can be covered with multiple flashes). Preferably 2 or more. This condition applies to any of the serial, line, and drum recording methods.

  In order to prevent the ink from irradiating and curing before landing on the substrate, the illuminance of the ink discharge section is such that the entire recording head 3 is shielded from light, or in addition, from the distance h1 between the flash light source and the substrate 20. The distance h2 between the ink discharge portion 31 of the recording head 3 and the substrate 20 is increased (h1 <h2), or the distance d between the recording head 3 and the flash light source 4 is increased (d is increased). It is effective. Further, a bellows structure 7 may be provided between the recording head 3 and the flash light source 4.

  As described above, in the serial printing method, the ink discharged from the recording head is more preferably 0.001 to 2.0 seconds after ink landing from the flash light source 4 attached to the carriage by scanning the carriage in the Y direction. Is irradiated with actinic rays within 0.001 to 1.0 seconds. In order to form a high-definition image, it is important that the irradiation timing is as early as possible. In the case of high-speed printing (printing), if the carriage moves fast and sufficient irradiation energy cannot be obtained, a plurality of irradiation timings are required. The flash timing, cycle, and flash exposure width (irradiation range in the main scanning width direction) are adjusted so that the number of flashes is one.

  As described above, in FIG. 2, the serial printing method has been described as an example, but in addition, an ink jet recording apparatus of each ink jet printing method as shown in FIG. 3 can be used.

  3, a) of FIG. 3 is a method (line head method) in which the recording head 19 is arranged in the width direction of the base material 20 and the recording and the flash light source 24 emit flash light while conveying the recording medium. 3b) is a method in which the recording head 19 performs printing while moving in the sub-scanning direction, and further irradiates flash light from the flash light source 24 (flat head method). FIG. The above-described recording head 19 is a method (serial printing method) in which printing is performed while scanning in the width direction on the base material, and flash light is intermittently emitted from the flash light sources 24 provided at both ends. Can be used.

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

Example 1
An inkjet ink was prepared according to the following.

<Preparation of inkjet ink>
<Preparation of ink 1>
(Pigment dispersion)
C. I. pigment Red 122 15 parts Ajisper PB822 (dispersing agent; manufactured by Ajinomoto Fine Techno Co., Ltd.) 5 parts Aron Oxetane OXT-221 (polymerizable compound; manufactured by Toagosei Co., Ltd.) 80 parts Distributed. This was made into a pigment dispersion through a 5 μm filter.

(ink)
The above pigment dispersion 30 parts Celoxide 2021P (polymerizable compound; manufactured by Daicel) 30 parts Aron oxetane OXT-221 (polymerizable compound; manufactured by Toagosei Co., Ltd.) 26 parts Aron oxetane OXT-101 (polymerizable compound; manufactured by Toagosei Co., Ltd.) ) 5 parts Aron Oxetane OXT-212 (polymerizable compound; manufactured by Toa Gosei Co., Ltd.) 5 parts UVI6992 (photoacid generator; manufactured by Dow Chemical) 0.5 parts diethylthioxanthone; DETX-S (sensitizer; manufactured by Nippon Kayaku Co., Ltd.) ) 0.5 part IRG-050 (immonium salt infrared dye; manufactured by Nippon Kayaku Co., Ltd.) 0.5 part triisopropanolamine 0.1 part water 1.0 part Ink 1 was produced by passing through a 1 μm filter. The average particle size was 110 nm.

<Preparation of ink 2>
In the ink 1, the pigment is C.I. I. Ink 2 (yellow ink) was produced in the same manner except that Pigment Yellow 180 was used (average particle size 120 nm).

<Preparation of ink 3>
In the ink 1, the pigment is C.I. I. Ink 3 (cyan ink) was produced in the same manner except that Pigment Blue 15: 4 was used (average particle size 100 nm).

<Preparation of ink 4>
In the ink 1, the pigment is C.I. I. Ink 4 (black ink) was prepared in the same manner except that it was replaced with Pigment Black 7 (black ink; average particle size 95 nm). However, in the case of black ink, IRG-050 was not used.

<Preparation of ink 5>
In the ink 1, the pigment is C.I. I. Ink 5 (white ink) was produced in the same manner except that Pigment White 6 was used (average particle size 210 nm). However, the following formulation was used for pigment dispersion.

<Pigment dispersion>
C. I. Pigment White 6 50 parts Azisper PB822 5 parts Aron Oxetane OXT-221 45 parts <Preparation of Ink 6>
(Pigment dispersion)
C. I. Pigment Black 7 15 parts Azisper PB822 5 parts Phenoxyethyl acrylate 80 parts The above composition was dispersed by bead dispersion. This was passed through a 5 μm filter to obtain a pigment dispersion (average particle size 95 nm).

(ink)
30 parts trimethylolpropane ethylene oxide-modified triacrylate 30 parts phenoxyethyl acrylate 30 parts Irgacure 819 (photopolymerization initiator; manufactured by Ciba Specialty Chemicals) 10 parts Ink 6 was prepared by passing through a 1 μm filter. The average particle size was 95 nm.

  About each produced ink 1-6, it mounted | wore with the apparatus shown by said FIG. 2, and the printing test was done as follows. In the print test, the recording head shown in FIG. 2 is used to set 4 gradations so that 5 gradations can be expressed by continuously ejecting 4 drops of droplets of 4 pl per cycle at a driving cycle of 4 kHz, and 720 dpi × 720 dpi. Then, four-pass recording was performed. The ink flow path, ink chamber, and nozzle were heated by a heater and the ink was controlled at 55 ° C.

  As a recording medium, Yupo SGG # 110 manufactured by Oji Oil Synthetic Paper Co., Ltd. and a thickness of 110 μm were used, and the temperature of the base material could be controlled by a heater provided on the platen.

In addition, after printing, the ink ejected from the recording head onto the recording medium was sequentially and intermittently irradiated by the flash light source 4 (xenon flash lamp) as the carriage moved in the main scanning direction by printing. The carriage speed is 500 mm / s (main scanning), the energy on the recording medium (per flash) is 3.0 J / cm ² , and the flash light source has a flash emission time (half width) of 3.0 msec. Drive with a frequency of 10 Hz and a flash exposure width (light source width) of 100 mm, and at the carriage main scanning speed, the flash exposure width × flash cycle is 2 with respect to the scanning distance per unit time of the recording head. It was set. (In short, main scanning for the flash exposure width is performed in two flash cycles)
Further, the energy was printed per xenon flash and the flash emission time was set to 12 J / m ² and 0.8 msec, respectively. The light emission intensity and the light emission time were changed by changing the capacitor capacity, charging voltage, etc. of the xenon flash drive circuit.

  The following points were evaluated using the obtained print samples.

《Ink bumping》
The solid image portion of the recording medium after printing was visually observed, and the case where the monomer volatile component was adhered around the solid image portion was evaluated as x, and the case where the monomer volatile component was not adhered was evaluated as ◯.

《Hardening wrinkle》
The solid image portion was visually observed, and the solid image portion where no gloss reduction due to curing wrinkles was indicated as ◯, the slightly observed portion as Δ, and the clearly observed portion as X.

《Adhesion》
A cellophane tape (registered trademark) having a width of 25 mm was pasted on the surface of the solid image portion and pressed strongly, and then peeled quickly at a peeling angle of 90 ° to observe whether there was any peeling.
○: There was no peeling of the image.
X: Image peeling was observed.

  The evaluation results are shown in Table 1.

Example 2
In addition, using inks 1 and 4 used in Example 1, the same evaluation as in Example 1 was performed in the same manner as in Example 1, except that the flash exposure conditions were changed as shown in Table 2 below. .

From Tables 1 and 2 above, the light emission time per flash is in the range of the claims of the present invention and the light emission intensity is in the range of the claims of the present invention, the above evaluation is good, and 1 flash The light emission time per unit is shorter than that of the claims of the present invention, and light exposure (high energy) exposure of 10 J / m ² or more and short flash exposure were inferior in any of the above evaluations.

It is a figure which shows the relationship between light emission time and light emission intensity. It is a front view which shows an example of a structure of the principal part used with the serial printing system of the inkjet recording device which can be used by this invention. It is the schematic which shows the other example of an inkjet recording device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording device 2 Head carriage 3, 19 Recording head 4, 24 Flash light source 5 Platen part 6 Guide member 20 Base material

Claims (8)

An ink jet recording method in which an ultraviolet curable ink is landed on a substrate, and then the ink on the substrate is cured by irradiation with ultraviolet rays to form an image, wherein the ultraviolet rays are irradiated by a flash light source. And the emission energy of the flash light source is in the range of 1.0 to 10 J / cm ² (per flash), and the half-value width (emission time) of the emission intensity is 0.5 to 5 msec. Inkjet recording method. The inkjet recording method according to claim 1, wherein the irradiation with the flash light source is intermittently performed a plurality of times. The ink jet recording method according to claim 1 or 2, wherein the total content of water and water-soluble solvent in the ultraviolet curable ink is 5 mass% or less. The inkjet recording method according to claim 1, wherein the ultraviolet curable ink is cationically polymerizable. The inkjet recording method according to claim 1, wherein the ultraviolet curable ink contains an infrared absorbing material having absorption at 800 to 1000 nm. An ultraviolet curable ink used in an ink jet recording method for curing by irradiation with flash light, wherein the total content of water and a water-soluble solvent is 5% by mass or less. The ultraviolet curable ink according to claim 6, which is cationically polymerizable. 8. The ultraviolet curable ink according to claim 6, further comprising an infrared absorbing material having absorption at 800 to 1000 nm.

Images