JPWO2006090541A1 - Inkjet recording apparatus, inkjet recording method, and ultraviolet curable ink - Google Patents

Abstract

The present invention solves the problem of image quality degradation that occurs when an image formed with an ultraviolet curable ink that does not use an aqueous solvent or the like is cured using flash light, has high glossiness, and is suitable for concentration and recording media. Ink jet recording apparatus and ink jet recording method capable of quickly obtaining a high quality image without deterioration of adhesion, and similarly obtaining a high quality image even in color images including inks having different infrared absorption such as black An ultraviolet curable ink is provided. This ink jet recording apparatus is an ink jet recording apparatus provided with a flash light source, and has means for reducing at least a part of the amount of light in the infrared wavelength region of the flash light emitted from the flash light source.

Description

  The present invention relates to a novel ink jet recording apparatus and ink jet recording method, and an ultraviolet curable ink used therefor.

  A recording method in which an ink image curable by ultraviolet rays is formed by an ink jet method and recording is fixed by irradiating ultraviolet rays has been developed in recent years. As ink techniques to be used, those described in WO99 / 29787, WO99 / 29788, WO97 / 31071, JP-A-5-214280, JP-A-2002-188025 and the like are known.

  Ultraviolet curable ink causes a curing reaction by photopolymerization on the recording medium by irradiation with actinic rays such as ultraviolet rays, so that it can be fixed and has good adhesion to a recording medium that does not absorb ink, such as a plastic surface. Can be formed.

  However, after landing the ink on the support (recording medium), a relatively large ultraviolet light source is required in the vicinity of the printing part to irradiate with sufficient ultraviolet light for the curing reaction, and usually a high-pressure mercury lamp or the like is used. Is done. Moreover, since these ultraviolet ray sources emit not only ultraviolet rays but also visible light, infrared rays and the like at the same time, a portion close to the light source is considerably heated. Accordingly, overheating of the recording head and the recording medium occurs, 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 description about ink composition and characteristics suitable for this method, and solvent drying is performed using a flash light source for ink mainly composed of solvent such as normal aqueous ink and solvent ink.・ It is intended to speed up evaporation. In this case, a considerable amount of heat is required to dry and evaporate the 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 support such as vinyl chloride by irradiating a flash lamp a plurality of times using an ultraviolet curable ink containing water. Yes. By using flash exposure, rather than using a normal high-pressure mercury lamp, the amount of heat generated on the support is suppressed, and a hydrophilic monomer capable of softening vinyl chloride is blended to obtain an ink with good fixability. Because it is an ultraviolet curable ink, the ink can be fixed on the support without requiring the amount of heat required for evaporation of the solvent water, and it is supported by the short-time exposure using a flash light source. Since energy can be applied to the extreme surface of the support while suppressing heat diffusion to the body, it is considered effective for evaporating the moisture in the ink even in plastic films that are easily thermally deformed.

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 cannot be vaporized in time because of instantaneous curing, and remains in the cured film to deteriorate film properties. A large amount of heat is required to remove the solvent from the film once polymerized.
JP 2000-272101A JP-T-2001-512777

  When an ultraviolet curable ink that does not use a water solvent or the like is cured using flash light, it is not necessary to evaporate the solvent. However, in practice, it has been found that the flash lamp has a large emission energy and its emission wavelength extends beyond the visible region, which causes another problem and requires a solution. It was.

  UV curable inks that do not contain moisture do not have moisture with a large heat capacity and latent heat of vaporization, so if the infrared component contained in the flash light source is absorbed, the ink droplets are deformed by heating or the ink components are evaporated and the image quality is improved. to degrade. In particular, black ink has high light absorption efficiency, which causes convection of the ink, boiling of the monomer, etc. due to overheating before and after the ink liquid is cured, thereby reducing glossiness, density, adhesion, etc. The degree of image quality degradation is high.

  That is, according to the inventor's study, the flash lamp emits light from the visible part to the infrared part, so that the ink droplet is overheated by applying a large amount of light energy in a short time by the flash light. These thermal energy is preferably expended to accelerate photopolymerization, but if the energy of flash light is extremely large, the balance between the heating rate of the ink and the heat transfer (thermal convection) to the inside of the ink is lost. However, only the ink surface is locally overheated, causing boiling or excessive heat convection to cause wrinkling of the cured film, uneven color, and the like, resulting in a problem of lowering the image quality. In particular, when black ink that strongly absorbs infrared light and color ink with low absorption are mixed, it has been found that it is very difficult to suppress deterioration in image quality due to infrared absorption while maintaining the same UV curing sensitivity for all colors. .

  The present invention has been made to solve the above-mentioned problems, and its purpose is to reduce image quality degradation that occurs when an image formed with an ultraviolet curable ink that does not use an aqueous solvent or the like is cured using flash light. Solves the problem, provides high-quality images with high glossiness, no deterioration in density and adhesion to the recording medium, and high-quality images with color images containing inks with different infrared absorption such as black. An ink jet recording method and an ink jet recording apparatus for obtaining an image, and an ultraviolet curable ink used for the method are provided.

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

  1. An ink jet recording apparatus comprising a flash light source, wherein the ink jet recording apparatus has means for reducing at least a part of light in an infrared wavelength region of flash light emitted from the flash light source.

  2. 2. The ink jet recording apparatus according to item 1, wherein the means for reducing the amount of light in the infrared wavelength range is means for reducing the amount of light in the wavelength range of 800 to 1100 nm to ½ or less.

  3. An ink jet recording method in which an ultraviolet curable ink is landed on a recording medium and then cured and fixed using flash light emitted from a flash light source, wherein the flash light is at least part of an infrared light wavelength region. An ink jet recording method, wherein the amount of light is reduced.

  4). 4. The ink jet recording method according to 3 above, wherein the flash light is one in which the amount of light in the wavelength range of 800 to 1100 nm is reduced to ½ or less.

  5). 3 or 4 above, wherein the ratio (B / A) of the amount of light (B) in the wavelength region 800 to 1100 nm and the amount of light (A) in the wavelength region 250 to 450 nm of the flash light is smaller than 1/2. The ink jet recording method described in 1.

  6). 6. The inkjet according to any one of 3 to 5, wherein the total content of water and water-soluble solvent in the ultraviolet curable ink is 5% by mass or less of the total mass of the ultraviolet curable ink. Recording method.

  7). 7. The ink jet recording method according to any one of 3 to 6, wherein an image is formed using two or more kinds of ultraviolet curable inks having different infrared absorption capabilities.

  8). 8. An ultraviolet curable ink for use in the ink jet recording method according to any one of 3 to 7.

  9. 9. The ultraviolet curable ink as described in 8 above, wherein the total content of water and water-soluble solvent is 5% by mass or less of the total mass of the ultraviolet curable ink.

  The present invention solves the problem of image quality degradation that occurs when UV curable ink is cured using flash light, and has high glossiness and high quality images quickly without degradation of density and adhesion to the recording medium. In addition, an ink jet recording apparatus and an ink jet recording method that can similarly obtain a high-quality image even in a color image including ink having different infrared absorption, such as black, and an ultraviolet curable ink used therefor can be provided.

The emission spectrum figure of a flash light source. 1 is a front view illustrating an example of a configuration of a main part of an ink jet recording apparatus according to the present invention. Schematic which shows another example of an inkjet recording device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording apparatus 2 Head carriage 3, 19 Recording head 4, 24 Flash light source 5 Platen part 6 Guide member 20 Recording medium 41 Infrared light cut filter

  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 the ultraviolet curable ink is landed on a recording medium and then 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 recording medium.

  As a result of intensive studies on the above problems, the present inventor hardens the ink droplets that have landed on the recording medium or the formed inkjet image by using a flash light source with reduced infrared rays so as not to cause overheating. This makes it possible to fix an image without causing color unevenness due to boiling, evaporation, or excessive convection with the inside of the ink due to overheating of the ink or the ink surface, which is a drawback of fixing with flash light. Is found.

  Details of the present invention will be described below.

[Flash light source]
The flash light source according to the present invention is not particularly limited, but for example, a xenon flash is representative. In order to efficiently use ultraviolet rays, it is preferable to use ultraviolet ray transmissive tubes and filters for the light source lamp. As described above, the flash light source generally emits light for a short time of 1 msec or less, and the flash light has a very large energy amount per unit area / unit time, that is, illuminance. In addition to the ultraviolet component that mainly contributes to the polymerization reaction (curing reaction) of the ultraviolet curable ink, these flash lights include light in the visible to infrared region. As a result, the ink is boiled (flipped) or the monomer components are evaporated and scattered due to overheating of the ink.

  If excessive energy is applied to the ink droplets in a short time with high-intensity infrared light, the infrared light is mainly absorbed by the surface area of the ink and converted into heat, and the heat energy is diffused inside. Is a process that is relatively slower than the irradiation time of the flash light, so that thermal diffusion in the direction of the ink thickness (in the range of several μm to several tens of μm) does not occur sufficiently, resulting in excessive ink surface. To cause problems such as boiling in the ink surface layer and monomer evaporation. In addition, excessive convection occurs due to the temperature difference between the ink surface and the inside, thereby causing unevenness in the ink density of the formed image, curing wrinkles, and the like.

  For example, as shown in FIG. 1, the spectral emission spectrum of the flash light source according to the present invention has a large amount of emitted light in the infrared region as well as the ultraviolet region. The flash light with reduced infrared rays according to the present invention refers to light obtained by reducing light in the wavelength range of 800 to 1100 nm to ½ or less out of light emitted from the flash light source. Furthermore, it is particularly preferable that the ratio (B / A) of the light amount (B) in the wavelength region 800 to 1100 nm and the light amount (A) in the wavelength region 250 to 450 nm is less than 1/2. .

  In the present invention, the spectral energy measurement of flash light as described above can be performed using, for example, an OL-745 ultraviolet-visible-near infrared radiance measuring instrument (manufactured by Asahitsu Trading Co., Ltd.). . Specifically, the spectrum measured by OL-745-PMT and OL-745-Si is synthesized.

  The ink jet recording apparatus of the present invention is characterized by having means for reducing the amount of light in at least a part of the infrared wavelength range, but there are no particular limitations on the specific means, but the visible light region or red region is not limited. It is preferable to apply a filter that cuts off light in the outside light region, and examples of filters that cut off light in the visible light region and infrared light region include various optical devices such as colored glass filters, dielectric film filters, and interference filters. A filter can be used as appropriate. In particular, a cold filter in which a heat ray absorbing glass is coated with a dielectric film filter is preferable. As these cold filters, for example, those commercially available from Sigma Koki Co., Ltd. can be used. Further, when controlling the total amount of light, an ND filter can be used.

In the present invention, the emission energy of flash light with reduced infrared rays is in the range of 0.1 to 10 J / cm ² (per flash), and the emission time of flash light is 0.5 to 5 ms. preferable.

  The flash lamp used in the present invention is generally a xenon flash lamp, and may be a xenon rectangular pulse light source or the like, preferably 0.5 msec to 1 msec. Various strobe light sources can also be used. 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 a trigger voltage is applied to the trigger electrode in a state where is applied, the insulation in the tube is broken and 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. Light emission with high illuminance can be obtained in a short time.

  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, but it has a certain emission intensity so that sufficient ink curing occurs. In order to make the light emission time relatively long, 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 manufactured by Nisshin Denshi Kogyo Co., Ltd., and a product manufactured by Miyata Elevum Co. Copiers, hard glass xenon flash lamps for printers, and Patlite XZ series can be used.

[UV curable ink]
In the ultraviolet curable ink according to the present invention, the total content of water and water-soluble solvent in the ink is preferably 5.0% by mass or less. If the ink contains a large amount of water or water-soluble solvent, these solvents remain even after the ink is cured, and the durability of the image deteriorates. In addition, since the monomer is polymerized after the ink is cured, the diffusibility of the solvent is reduced, and a great amount of heat is required for volatilization. Therefore, it is preferable that the content of water and water-soluble solvent in the ink is small.

  In addition, when adding water and a water-soluble solvent in an ink, it is preferable to make it 5.0 mass% or less, and to perform a solvent removal process by heating an ink beforehand, before exposing flash light.

  The water-soluble solvent referred to in the present invention is a non-polymerizable solvent that is freely mixed with water or has a solubility of 10% by mass or more in water at 25 ° C., for example, alcohols, acetones, ethylene And glycols.

  There are two types of ultraviolet curable inks, radically polymerizable and cationically polymerizable, depending on the reaction mechanism, and both types can be used in the present invention. However, an ultraviolet curable ink using a radical polymerizable compound having a high polymerization rate is preferable from the viewpoint of reactivity in short-time irradiation such as flash light.

Although radically polymerizable ink has an inhibition of curing due to oxygen, the sensitivity can be drastically improved by performing high-intensity exposure for a short time with flash light as in the present invention. Preferably, the illuminance has an average value of incident light energy per emission time (half width) of 250 W / cm ² or more, and more preferably 500 W / cm ² . By increasing the illuminance, oxygen inhibition is reduced and the curing rate can be increased. However, if the illuminance is simply increased, the intensity of infrared light increases, and particularly in the formation of a black image, an overheating phenomenon occurs and the image quality deteriorates.

  The ultraviolet curable ink according to the present invention is prepared by blending and dispersing a dispersant, a coloring material, 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. Can be mentioned.

  Specific examples of the compound having radical polymerizability include aliphatic (meth) acrylates, alicyclic (meth) acrylates, aromatic (meth) acrylates, ether (meth) acrylates, vinyl monomers, (Meth) acrylamides and the like can be mentioned. (Meth) acrylate means one containing at least one of acrylate and methacrylate.

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

  The addition amount of the radical polymerizable compound to the ultraviolet curable ink is preferably 1 to 97% by mass, more preferably 30 to 95% by mass with respect to the total mass of the ink.

  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 preferable from the viewpoint of weather resistance.

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

  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, it is preferable to use a polymer dispersant. Specific examples of these dispersants include the dispersants and dispersion aids described in paragraphs (0088) to (0093) of JP-A No. 2004-131588. Agents.

  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 performed using a solvent or a polymerizable compound. In consideration of deterioration of solvent resistance, adverse effects due to volatilization of the remaining solvent, etc., the ultraviolet curable ink according to the present invention has a short time immediately after ink landing. Therefore, the content of water or a water-soluble solvent as a dispersion medium is preferably 5% by mass or less, and more preferably no solvent. 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, nozzle clogging of the ink jet recording head can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained.

  In the ultraviolet curable 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.

  In the present invention, in order to perform the curing reaction more efficiently, a photopolymerization initiator is added and cured. Photopolymerization initiators are radical generators, and 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 paragraph numbers (0073) to (0074) of JP-A No. 2004-131588.

  The addition amount is usually preferably in the range of 0.01 to 10.00% by mass in the ink composition. However, in the present invention, in order to perform high-illuminance exposure with flash light, the reaction start point increases with the addition amount of a normal photopolymerization initiator, and as a result, the degree of polymerization is prevented from decreasing. The addition amount of the radical generator is more preferably in the range of 0.01 to 3.0% by mass in the ink composition.

  Moreover, although the ultraviolet curable ink which concerns on 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 paragraph No. (0085) of JP-A No. 2004-131588. The usage-amount of a photosensitizer is 0.01-10.0 mass% in an ink composition, More preferably, it is the range of 0.01-3.0 mass%.

  In addition to these components, the ultraviolet curable ink according to the present invention includes a surfactant, a leveling additive, a matting agent, a polyester-based resin, a polyurethane-based resin, and a vinyl-based resin for adjusting film properties as necessary. 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 light into the ink. As the polymerization inhibitor, it is preferable to add various antioxidants (AO agents), nitrosamine compounds, and hydroquinone compounds. Specifically, for example, MEHQ (p-methoxyphenol) can be used.

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

  Note that it is also effective to add a trace amount of an organic solvent in order to improve the adhesion to a recording medium (also referred to as a base material or a support) after ink curing with ultraviolet rays. In this case, it is possible to add in the range where the solvent resistance and VOC problems 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.

  In the ink jet recording method of the present invention, it is preferable to form an image by using two or more kinds of ultraviolet curable inks having different infrared absorptivity from the viewpoint that the objective effect of the present invention can be exhibited. In this way, when two or more types of ultraviolet curable inks having different infrared absorption capabilities are used, for example, when a secondary color or a black image is formed, the infrared absorption capability varies depending on the color of the ink. In order to obtain, it was difficult to obtain high-quality images due to uneven heat generation of the ink, but a flash light source having means for reducing at least part of the light amount in the infrared wavelength range defined in the present invention is applied. As a result, a high-quality image can be obtained.

  Examples of the two or more kinds of ultraviolet curable inks having different infrared absorption capabilities in the present invention include, for example, yellow dark ink, magenta dark ink, cyan dark ink, black ink, white ink, yellow light ink, magenta light ink, Examples include cyan light ink, orange ink, green ink, and transparent ink.

[Production method and characteristics of UV curable ink]
In the method for producing an ultraviolet curable ink according to the present invention, there is no particular limitation as a method for mixing a coloring material such as a dye or a pigment. For example, the pigment is mixed with a pigment as a coloring material and polymerization as a medium. Using an organic compound, a solvent, a polymer dispersing agent or the like, further mixing necessary additives, and mixing and dispersing them. Examples of the mixing and dispersing device include various mills such as the above-described ball mill and sand mill, and dispersers such as a homogenizer.

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

  The discharge condition of the ultraviolet curable ink according to the present invention from the ink jet recording head is that the recording head and the ink are heated to 35 to 100 ° C., and the ink heated to the temperature range is discharged from the viewpoint of discharge stability. preferable. 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 ink 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 ink droplet amount needs to be in this range.

〔recoding media〕
As a recording medium that can be used in the inkjet recording method of 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. It is preferable to use a body.

  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. In these recording media, not only curling and deformation of the film are likely to occur due to curing shrinkage of the ink, heat generation during the curing reaction, and the like, but the ink film is difficult to follow the shrinkage of the recording medium.

  In the inkjet recording method of the present invention, the flash light is irradiated for 0.001 to 2.0 seconds after ink landing as the irradiation condition of the flash light in which the amount of light in the infrared wavelength region according to the present invention is reduced. Preferably, it is 0.001 to 1.0 seconds. In order to prevent ink beading and bleeding on a recording medium 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, compared with a recording head unit provided with a light source such as a high-pressure mercury lamp, the recording medium or the platen or the like, such as a recording medium or a platen, can be shortened for a short time without unnecessary heating. Thus, efficient ink fixing can be performed. Further, the flash light source according to the present invention has the advantage of being inexpensive and low in mass as compared with a high-pressure mercury lamp.

[Inkjet recording device]
Next, an ink jet recording apparatus of the present invention (hereinafter simply referred to as a 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 a configuration of a main part used in a serial printing method in an ink jet recording apparatus that can be used in the present invention. The recording apparatus 1 includes a head carriage 2, a recording head 3, 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 recording medium 20. An infrared light cut filter 41 for reducing the amount of light in the infrared region, for example, a cold filter that reflects near infrared light and transmits light having a wavelength shorter than visible light is installed on the front surface of the light emitting unit of the flash light source 4. .

  The platen unit 5 has a function of absorbing ultraviolet rays and absorbs extra ultraviolet rays that have passed through the recording medium 20. As a result, a high-definition image can be reproduced very stably.

  The recording medium 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 recording medium 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 recording medium 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 recording medium is ejected from the ejection port by the operation of ejection means (not shown) provided with a plurality of ultraviolet curable inks according to the present invention supplied by the ink supply means (not shown). It discharges toward 20. The ultraviolet curable ink ejected by the recording head 3 includes a color material and a photopolymerizable composition, and has a property of being cured by a polymerization reaction when irradiated with ultraviolet rays.

  The recording head 3 moves from one end of the recording medium 20 to the other end of the recording medium 20 in the Y direction in FIG. 2 by driving the head scanning means. ), 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 recording medium 20 is appropriately moved from the front to the back in FIG. While performing scanning by the scanning means, the recording head 3 discharges actinic ray curable ink to the landable area, which is adjacent in the back direction 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 recording medium 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 fixedly installed on both sides of the head carriage 2 so as to be substantially parallel to the recording medium 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 onto the recording medium are 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 ejection unit can be adjusted by the distance between the flash light source 4 and the recording medium 20. Further, the timing of flash light irradiation can be adjusted by the interval 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 suppress the illuminance of the ink discharge section so that the ink is irradiated with flash light before landing on the recording medium and does not cure at that time, the entire recording head 3 is shielded from light, or additionally, flash The distance h2 between the ink ejection part 31 of the recording head 3 and the recording medium 20 is made larger than the distance h1 between the light source and the recording medium 20 (h1 <h2), or the distance d between the recording head 3 and the flash light source 4 is increased. It is effective to adjust by increasing (d). 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 ejected 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 flash light 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), when the carriage moves fast and sufficient irradiation energy cannot be obtained, The flash timing, cycle, and flash exposure width (irradiation range in the main scanning width direction) are adjusted so that multiple flashes are performed.

  As described above, the serial printing method has been described as an example in FIG. 2, but other ink jet recording apparatuses such as those shown in FIG. 3 can also be used.

  3, a) in FIG. 3 is a method (line head method) in which the recording head 19 is arranged in the width direction of the recording medium 20 and the flash light is emitted from the printing and flash light source 24 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 described recording head 19 is a method (serial printing method) in which printing is performed while scanning the width direction on the recording medium, and flash light is intermittently emitted from the flash light source 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. Unless otherwise specified in the text, “part” means “part by mass”.

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

<Preparation of inkjet ink>
<Preparation of ink 1 (cyan)>
C. I. pigment blue 15: 3 5 parts tetraethylene glycol diacrylate 43 parts ε caprolactam-modified dipentaerythritol hexaacrylate 20 parts phenoxyethyl methacrylate 30 parts Polymerization initiator (Irgacure 907: manufactured by Ciba Geigy) 2 parts <Ink 2 ( Preparation of magenta)>
C. I. pigment Red 57: 1 5 parts tetraethylene glycol diacrylate 43 parts ε caprolactam-modified dipentaerythritol hexaacrylate 20 parts phenoxyethyl methacrylate 30 parts Polymerization initiator (Irgacure 907: manufactured by Ciba Geigy) 2 parts <Ink 3 ( Preparation of yellow)>
C. I. Pigment Yellow-13 5 parts Tetraethylene glycol diacrylate 43 parts ε caprolactam-modified dipentaerythritol hexaacrylate 20 parts Phenoxyethyl methacrylate 30 parts Polymerization initiator (Irgacure 907: Ciba Geigy) 2 parts <Ink 4 (Black ) Preparation>
Carbon black 5 parts Tetraethylene glycol diacrylate 43 parts ε Caprolactam-modified dipentaerythritol hexaacrylate 20 parts Phenoxyethyl methacrylate 30 parts Polymerization initiator (Irgacure 907: Ciba Geigy) 2 parts Was mounted on the apparatus shown in FIG. 2 and a printing test was conducted as follows. The print test is performed by using the inkjet recording head shown in FIG. 2 to set 5 gradations by expressing 4 drops of droplets of 4 pl per cycle at a driving cycle of 4 kHz, and 720 dpi × Four-pass printing was performed at 720 dpi (dpi is the number of dots per 2.54 cm). The ink flow path, the ink chamber, and the nozzle were heated by a heater and the ink liquid temperature 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.

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 0.8 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)
At this time, a cold filter that cuts light of 700 nm or more is installed in front of the flash light source, and the ratio (A / B) of the light quantity (A) having a wavelength of 250 to 450 nm and the light quantity (B) having a wavelength of 800 to 1100 nm is It was set to 0.6 and compared with the image characteristics when no filter was installed.

  The following points were evaluated using the obtained print samples.

《Ink bumping》
Observe the solid image portion of the recording medium after printing with the naked eye, and mark that the monomer volatile component is attached around the solid image portion as x. Δ.

《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.
○: Image peeling was not observed Δ: Image peeling was slightly observed ×: Image peeling was observed Table 1 shows the evaluation results.

Example 2
Moreover, the transmittance | permeability of the cold filter which cuts the light of 700 nm or more is adjusted using the ink 1-4 used in Example 1, and an inkjet recording device, and the light quantity (A) with a wavelength of 250-450 nm and the wavelength are 800-. The ratio (A / B) of the amount of light (B) at 1100 nm was 0.4.

  The result of having performed evaluation similar to Example 1 is shown.

  As is clear from Table 1 and Table 2 above, it can be seen that those obtained by cutting light in the infrared region under the conditions defined in the present invention have good characteristics.

Claims (9)

  An ink jet recording apparatus comprising a flash light source, wherein the ink jet recording apparatus has means for reducing at least a part of light in an infrared wavelength region of flash light emitted from the flash light source.   2. The ink jet recording apparatus according to claim 1, wherein the means for reducing the amount of light in the infrared wavelength range is means for reducing the amount of light in the wavelength range of 800 to 1100 nm to ½ or less.   An ink jet recording method in which an ultraviolet curable ink is landed on a recording medium and then cured and fixed using flash light emitted from a flash light source, wherein the flash light is at least part of an infrared light wavelength region. An ink jet recording method, wherein the amount of light is reduced.   4. The ink jet recording method according to claim 3, wherein the flash light has a light amount in a wavelength range of 800 to 1100 nm reduced to ½ or less.   The ratio (B / A) of the amount of light (B) in the wavelength region of 800 to 1100 nm and the amount of light (A) in the wavelength region of 250 to 450 nm of the flash light is smaller than 1/2. Item 5. The ink jet recording method according to Item 3 or Item 4.   6. The total content of water and a water-soluble solvent in the ultraviolet curable ink is 5% by mass or less of the total mass of the ultraviolet curable ink. 2. The ink jet recording method according to item 1.   The inkjet recording method according to any one of claims 3 to 6, wherein an image is formed using two or more kinds of ultraviolet curable inks having different infrared absorption capabilities.   An ultraviolet curable ink used in the ink jet recording method according to any one of claims 3 to 7.   9. The ultraviolet curable ink according to claim 8, wherein the total content of water and water-soluble solvent is 5% by mass or less of the total mass of the ultraviolet curable ink.