JP2005206715A - Ultraviolet-curable ink and inkjet recording method by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultraviolet-curable ink having excellent jetting stability, high impact accuracy and high sensitivity, and capable of outputting a highly minute image; and to provide an inkjet recording method by using the ink. <P>SOLUTION: The ultraviolet-curable ink is used by being jetted from an inkjet head at a drive frequency of ≥3 kHz and at a droplet speed of ≥5 m/s. The ink contains at least a pigment, a dispersing agent having an acid value larger than an amine value, a polymerizable compound and a photopolymerization initiator. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink that is cured by ultraviolet rays and an ink jet recording method using the same, and more particularly, to an ink jet recording method that uses an ultraviolet curable ink that has excellent emission stability, high landing accuracy, and can output a high-definition image.

  In recent years, a recording method in which an ink curable by ultraviolet rays is formed by an ink jet method and irradiated with ultraviolet rays has been developed, and its practical application is progressing. As the ink to be used, WO99 / 29787 pamphlet, 99/29788 pamphlet, 97/31071 pamphlet, JP-A-5-214280, JP-A-2002-188025 and the like are known.

  In the pamphlet of International Publication No. 99/29787, an ink viscosity at 30 ° C. ≦ 35 mPa · s is preferable. This shows a preferable condition for injection in ink jet recording. In the above-mentioned other documents relating to inks, formulation examples almost corresponding to this condition are shown.

  The ultraviolet curable ink jet recording system has the advantage of being able to record on a substrate that does not absorb ink, but on the other hand, reactive diluents (polymerizable compounds, oligomers, etc.) do not evaporate, Since it remains as it is, it has a drawback that the image becomes embossed and the texture is impaired.

  The present inventor has studied to obtain a high image quality by ejecting ink droplets of a finer size and appropriately leveling the droplets in an ultraviolet curable ink jet recording system. Many nozzles and driving methods for reducing the size of ink droplets are known. However, since UV curable inks usually have higher viscosities than water-based inks, it has been found that it is very difficult to perform high-speed, stable and accurate injection. In particular, in order to eject small droplets of less than 10 pl with a gray scale type head having a variable droplet size, the conventional inks can be used for stable ejection or landing. It was difficult to improve accuracy.

Further, when ink is continuously ejected, there is a problem that minute mist is generated and the inside of the apparatus and the recording material are contaminated. Furthermore, in the case of recording with an increased drive frequency, such as increasing the droplet velocity to increase the landing accuracy, or performing recording with small droplets or multi-gradation recording to give granularity and gradation. It was difficult to reduce mist and obtain sufficient stable injection properties. In order to obtain stable ejection properties, a technology relating to an ultraviolet curable ink jet recording composition containing a pigment derivative-treated pigment obtained by mixing a pigment and a pigment derivative having a hydrophilic group in water, followed by drying treatment (see, for example, Patent Document 1). Is known, but it is hard to say that it has been improved sufficiently. Such a phenomenon is different depending on the type of pigment, and is particularly problematic for yellow and magenta. Japanese Patent Laid-Open No. 2000-203020 proposes a driving method corresponding to a weak thixotropic behavior in water-based ink as a driving device and method for an inkjet printer head. A viscous liquid was insufficient.
JP 2003-253155 A

  An object of the present invention is to provide an ultraviolet curable ink capable of outputting a high-definition image with excellent emission stability, high landing accuracy, high sensitivity, and an ink jet recording method using the same.

(Claim 1)
An ultraviolet curable ink that is ejected from an inkjet head at a driving cycle of 3 kHz or more and at a droplet speed of 5 m / s or more, and then irradiated with ultraviolet rays, at least a pigment, a dispersant having a higher acid value than an amine value, polymerization An ultraviolet curable ink comprising a functional compound and a photopolymerization initiator.

(Claim 2)
The ultraviolet curable ink according to claim 1, wherein the pigment has a maximum particle size of 400 nm or less and an average particle size of 80 nm or more.

(Claim 3)
3. The ultraviolet curable ink according to claim 1, wherein the viscosity fluctuation range at 55 ° C. Shear Rate = 10, 1000 (1 / s) is 5 mPa · s or less.

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

(Claim 5)
Using the ultraviolet curable ink according to any one of claims 1 to 4, discharging from an inkjet head at a driving cycle of 3 kHz or more and a droplet speed of 5 m / s or more, and then irradiating with ultraviolet rays. An ink jet recording method.

(Claim 6)
Multi-tone recording is possible by changing the droplet size of the ultraviolet curable ink when ejected from the inkjet head at a driving cycle of 3 kHz or more and at a droplet velocity of 5 m / s or more and then irradiated with ultraviolet rays. 6. The ink jet recording method according to claim 5, wherein recording is performed by a multi-tone recording method.

(Claim 7)
The minimum ink droplet size is less than 10 pl when ejected from an inkjet head at a driving cycle of 3 kHz or more and at a droplet speed of 5 m / s or more, and then irradiated with ultraviolet rays. The ink jet recording method described in 1.

  According to the present invention, it is possible to provide an ultraviolet curable ink that is excellent in emission stability, has high landing accuracy, is highly sensitive, and can output a high-definition image, and an ink jet recording method using the same.

  Hereinafter, the present invention will be described in detail.

  It has been found that when UV curable ink is ejected at a droplet speed of 5 m / s or more at a high speed drive of 3 KHz or more, particularly UV curable ink containing a dispersant having an acid value larger than the amine value can be ejected stably. It was. Here, high-speed driving means that the driving cycle is 3 KHz or more and 100 KHz or less, and the droplet velocity is 5 m / s or more and 20 m / s or less. I do not know the reason why a dispersant having a larger acid value than the amine value is good as a dispersant for the ultraviolet curable ink, but similarly preparing a UV curable ink using a dispersant having an amine value greater than or equal to the acid value, Even when the particle size distribution and ink viscoelasticity are the same, the output stability (nozzle missing frequency, landing accuracy, mist generation rate) in high-speed driving is superior to the dispersant having a higher acid value than the amine value of the present invention. Become.

  To change the droplet size per pixel, the droplet size discharged from the nozzle is changed according to the driving conditions. A plurality of droplets of approximately the same size are ejected in succession, and the droplets are ejected before landing on the substrate. Includes both super drop methods to merge. In multi-gradation recording in which the droplet size can be changed by high-speed driving at 3 KHz or higher, the emission property tends to be unstable. A dispersant having an acid value larger than the amine value is excellent in emission stability in such multi-tone recording.

  In the case of ejecting droplets of less than 10 pl in multi-gradation recording or high-definition recording, the exitability tends to become more unstable. A dispersant having an acid value larger than the amine value is excellent in emission stability in such multi-tone recording.

  A dispersant having an acid value greater than the amine value is superior in emission stability to a dispersant having an amine value greater than or equal to the acid value, but the maximum particle size of the pigment is 400 nm or less and the average particle size is 80 nm or more. As a result, the emission stability is further improved. When the maximum particle size is 400 nm or more, variations in ink ejection speed, angle error, and mist deteriorate. Presumably, the presence of coarse particles in the ink makes the ink non-uniform, and the ink symmetry on the nozzle meniscus surface is impaired, and the liquid column after ejection is likely to break. In addition, when the average particle diameter is less than 80 nm, the driving voltage is likely to increase or the initial drop of the droplet speed during intermittent driving is likely to occur. If it is less than 80 nm, the number of pigment particles in the ink increases, and it is assumed that thixotropic properties are generated by flocculation between pigments.

  The smaller the dependency of the viscosity on the shear rate, the more stable the droplet speed during intermittent driving. When the viscosity fluctuation range is 5 mPa · s or more, the decap phenomenon occurs, such as the ejection pause, the initial speed after resumption is slowed, or the number of nozzles that do not eject increases.

  In particular, in the case of a cation polymerizable ultraviolet curable ink, a dispersant having an acid value larger than the amine value is particularly preferable because it not only improves the emission stability but also can achieve both sensitivity and storage stability.

(Pigment)
The amine value of the pigment is larger than the acid value, and the difference is preferably 1 mg / g KOH or more and less than 10 mg / g. If it is less than 1 mg / g KOH, the effect is not obtained, and if it is 10 mg / g or more, it is necessary to perform a basic treatment excessively, resulting in an increase in cost. As the pigment species, various pigments can be used as long as the amine value is larger than the acid value. The acid value and amine value can be determined by potentiometric titration. For example, it can be measured by the method described in Color Material Association Journal 61, [12] 692-698 (1988).

  As specific examples of the pigment, for example, the following pigments having an amine value larger than the acid value can be used, but the present invention is not limited thereto.

C. I. Pigment Yellow-1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 81, 83, 87, 93, 95, 97, 98, 109, 114, 120, 128, 129, 138 , 139, 151, 154, 180
C. I. Pigment Red-5, 7, 12, 22, 38, 48: 1, 48: 2, 48: 4, 49: 1, 53: 1, 57: 1, 63: 1, 101, 112, 122, 123, 144 , 146, 168, 180, 184, 185, 202
C. I. Pigment Violet-19, 23
C. I. Pigment Blue-1, 2, 3, 15: 1, 15: 2, 15: 3, 15: 4, 18, 22, 27, 29, 60
C. I. Pigment Green-7, 36
C. I. Pigment White-6, 18, 21
C. I. Pigment Black-7
For example, a process color ink set having preferable pigment types is prepared by appropriately combining four types of the following pigments.
Y: C.I. I. Pigment Yellow; 120, 128, 74, 83, 138, 151, 180
M: C.I. I. Pigment Violet; 19,122
C :. I. Pigment Blue; 15; 4
K: C.I. I. Pigment Black; 7
W: C.I. I. Pigment White; 6
The pigment is preferably subjected to any surface treatment of basic, acidic, or polar treatment. As the surface treatment method, it is preferable to use a synergist having a structure similar to that of the pigment and having any of basic, acidic and polar treatments. Synergists have the same structure as pigments, and are modified with polar groups such as acidic groups and basic groups, or organic substances having organic pigment mother nuclei, with polar groups bonded directly or through joints. Say what you are. The dispersibility of the pigment is improved by adsorbing it on the pigment surface and bonding it to the dispersant. Most of these synergists are inferior in light resistance, and excessive treatment cannot exhibit the light resistance of the original pigment. Examples of the polar group include a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a boric acid group, and a hydroxyl group, preferably a sulfonic acid group and a carboxylic acid group, and more preferably a sulfonic acid group.

  Examples of a method for obtaining pigment particles having a polar group on the surface include, for example, International Publication No. 97/48769 pamphlet, JP-A Nos. 10-110129, 11-246807, 11-57458, and 11-189739. By treating the pigment particle surface described in JP-A-11-323232, JP-A-2000-265094, etc. with an appropriate oxidizing agent, at least a part of the pigment surface has a polar group such as a sulfonic acid group or a salt thereof. The method of introduce | transducing is mentioned. Specifically, it is prepared by oxidizing carbon black with concentrated nitric acid, or in the case of color pigments by oxidizing with sulfamic acid, sulfonated pyridine salt, amide sulfuric acid, etc. in sulfolane or N-methyl-2-pyrrolidone. can do. A pigment dispersion can be obtained by removing and purifying a substance that has been excessively oxidized and becomes water-soluble by these reactions. Moreover, when a sulfonic acid group is introduced onto the surface by oxidation, the acidic group may be neutralized with a basic compound as necessary.

  Other methods include a method of adsorbing the pigment derivatives described in JP-A-11-49974, JP-A-2000-273383, JP-A-2000-303014, etc. on the surface of the pigment particles by a treatment such as milling. Examples include a method of dissolving the pigment described in each publication such as 2002-179777, 2002-20141, and the like together with a pigment derivative, followed by crystallization in a poor solvent. Pigment particles having a polar group on the surface can be obtained.

  In the present invention, the polar group may be free or in a salt state, or may have a counter salt. Examples of the counter salt include inorganic salts (lithium, sodium, potassium, magnesium, calcium, aluminum, nickel, ammonium) and organic salts (triethylammonium, diethylammonium, pyridinium, triethanolammonium, etc.), preferably 1 A counter salt having a valence.

  As the synergist, those modified with acid such as sulfonic acid modification and carboxyl group modification and those having an amine value larger than the acid value are preferable.

  These synergists are preferably added in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the pigment.

  For pigment dispersion, the selection of the pigment, dispersant, and dispersion medium, dispersion conditions, and filtration conditions are appropriately set so that the average particle diameter of the pigment particles is 80 to 150 nm. The average particle diameter can be measured by observing the pigment dispersion with a transmission electron microscope or using an optical method such as a laser scattering method. By controlling the particle size, clogging of the head nozzle can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained.

  In the ink of the present invention, the pigment concentration is preferably 1 to 10% by mass of the whole ink.

(Dispersant)
In the present invention, the dispersion stability is improved by using a dispersant having an acid value larger than the amine value. The acid value and amine value of the dispersant can be measured by the potentiometric titration.

  As the dispersant, any of low molecular weight and high molecular weight can be used, but a polymer type dispersant is preferable. The polymer type dispersant preferably has a base or an acid as an adsorption site with the pigment, and good results can be obtained with either a base or an acid. Even with a basic polymer dispersant, the amine value is not necessarily higher than the acid value when the amine value and acid value are measured. The present invention pays attention to this point, and it has been found that, as a whole, the dispersant has a higher acid value than the amine value for the discharge stability rather than the type of anchor. The weighted average value can be used for the amine value and acid value when a plurality of dispersants are used.

  The acid value of the dispersant is larger than the amine value, and the difference is preferably 1 mg / g KOH or more and less than 30 mg / g KOH. If it is less than 1 mg / g KOH, the effect is not obtained, and if it is 30 mg / g KOH or more, there is a concern that it is cured by a thermal reaction.

  Preferable specific examples of the dispersant include Ajimoto PB822 and Ajisper PB821 manufactured by Ajinomoto Fine Techno Co., but the present invention is not limited thereto. PB822 and PB821 are known to be used in ultraviolet curable inks in Japanese Patent Application Laid-Open Nos. 2003-253155, 2003-147233, and 2001-288387, but constitute the structure of the present invention. It is not a thing.

  The amount of the dispersant used is 10 to 100% by mass, preferably 15 to 50% by mass, based on the pigment.

  For the dispersion of the pigment, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, or the like can be used.

(Polymerizable compound)
Among the polymerizable compounds that can be used in the present invention, examples of the radical polymerizable compound include, for example, JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, and JP-A-10-863. The compounds described in each publication can be listed, and various known cationic polymerizable monomers can be used as the cationic polymerizable compound. For example, in JP-A-6-9714, JP-A-2001-31892, 2001-40068, 2001-55507, 2001-310938, 2001-310937, 2001-220526, etc. Examples include epoxy compounds, vinyl ether compounds, oxetane compounds and the like.

  The radical polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization, and may be any compound as long as it has at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. , Oligomers, polymers and the like having chemical forms. Only one kind of radically polymerizable compound may be used, or two or more kinds thereof may be used in combination at an arbitrary ratio in order to improve desired properties. Examples of compounds 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, maleic acid and their salts, esters, urethanes, amides. And radically polymerizable compounds such as various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides and unsaturated urethanes.

  The addition amount of the radical polymerizable compound is preferably 1 to 97% by mass and more preferably 30 to 95% by mass with respect to the ink composition.

  In the case of a cationically polymerizable ink, it is preferable to contain at least one oxetane compound and at least one compound selected from an epoxy compound and a vinyl ether compound. Among these epoxy compounds, in view of fast curability, aromatic epoxy compounds and alicyclic epoxy compounds are preferable, and alicyclic epoxy compounds are particularly preferable. In the present invention, one of the epoxides may be used alone, or two or more may be used in appropriate combination. Of the vinyl ether compounds, in view of curability, adhesion, and surface hardness, di- or trivinyl ether compounds are preferable, and divinyl ether compounds are particularly preferable. In the present invention, one of the above vinyl ether compounds may be used alone, or two or more thereof may be used in appropriate combination.

  The oxetane compound is a compound having an oxetane ring, and any known oxetane compound as described 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.

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

  Examples of the intramolecular bond cleavage type radical generator include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1- (4-isopropylphenyl) -2- Hydroxy-2-methylpropan-1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4- Acetophenone series such as thiomethylphenyl) propan-1-one; α-aminoketone series such as 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone; benzoin, benzoin methyl ether, benzoin isopropyl ether Benzoins such as bis (2,4,6 Such as trimethyl benzoyl) phenyl phosphine oxide bisacylphosphine oxide-based; benzyl - and methyl phenylglyoxylate esters.

  On the other hand, examples of the intramolecular hydrogen abstraction type radical generator include, for example, benzophenone, methyl 4-phenylbenzophenone, o-benzoylbenzoate, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl- Benzophenone series such as diphenyl sulfide, acrylated benzophenone, 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone, 3,3'-dimethyl-4-methoxybenzophenone; 2-isopropylthioxanthone, 2, Thioxanthone series such as 4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone; Amibenzotone, aminobenzophenone series such as 4,4'-diethylaminobenzophenone; 10-butyl 2-chloro-acridone, 2-ethyl anthraquinone, 9,10-phenanthrenequinone, camphorquinone, and the like. The blending amount in the case of using a radical generator is preferably 0.01 to 10.00% by mass of the ultraviolet curable ink.

  Of these photopolymerization initiators, bisacylphosphine oxide having photobleaching property and α-aminoketone which is not easily affected by oxygen inhibition are particularly preferable because of high sensitivity-up effect in small droplets. As the bisacylphosphine oxide and α-aminoketone, for example, Irgacure series of Ciba Specialty Chemicals can be used.

  Also, in the case of curing a small droplet size of less than 20 pl in a radical polymerization system, a curing failure due to oxygen occurs, and as a result of adding more initiator than usual, the degradation odor of the photopolymerization initiator tends to be a problem. The photopolymerization initiator containing a hydroxyethoxy group is preferable because it has a small decomposition product odor. For example, Irgacure 2959 from Ciba Specialty Chemicals has a low degradation product odor.

  As the photoacid generator, for example, a chemically amplified photoresist or a compound used for photocationic polymerization is used (edited by Organic Electronics Materials Research Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), 187. To page 192). Examples of compounds suitable for the present invention are listed below.

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

  Examples of the photopolymerization initiator preferably used in the present invention include the compounds described in JP-A Nos. 2003-213184, 2003-306622, 2003-342499, 2003-252979, and 2003-253155. Is mentioned.

(Polymerization inhibitor)
In the present invention, a polymerization inhibitor that suppresses polymerization by heat or actinic rays can be added to the ink. As the polymerization inhibitor, various compounds are known, and those widely blended in general polymerizable compositions can be used as they are.

  As a polymerization inhibitor, it is possible to use phenolic antioxidants, amine compounds, phosphorus antioxidants, hydroquinone monomethyl ether widely used for (meth) acrylic monomers, hydroquinone, t-butylcatechol, pyrogallol, water, etc. Is possible. These are detailed in “Development Technology of Polymer Additives” (issued by CMC). Since phenolic compounds with double bonds derived from acrylic acid in the molecule can capture R · from their reaction mechanism, they can suppress polymerization even when heated in a system without sealed oxygen. Is preferable. Specifically, Sumitizer Chemical's Sumilizer GA-80, Sumilizer GM, Sumilizer GS, etc. can be mentioned.

  These polymerization inhibitors are preferably added at the time of preparing the pigment dispersion, but excessive addition of the polymerization inhibitor causes a decrease in sensitivity as an ink, while maintaining the storage stability as an ink, It is desirable that the amount capable of preventing polymerization at the time of pigment dispersion is appropriately set and blended. Or it is preferable to mix | blend excessively and to extract after dispersion | distribution and to reduce the quantity of a polymerization inhibitor.

  When the photopolymerization is cationic polymerizable, the polymerization inhibitor is preferably an amine compound. The amine compound can synergistically maintain a balance between storage stability and sensitivity in combination with a dispersant having an acid value higher than the amine value. Among amine compounds, a quaternary ammonium salt is particularly preferable for a cationic polymerizable ink because it can suppress a dark reaction during storage without suppressing a reaction during exposure. When the dispersibility is unstable, a tertiary amine having a small polarity is a particularly preferred polymerization inhibitor. The addition amount of the amine compound is preferably 0.01 to 1% by mass of the total ink. If it is less than 0.01% by mass, storage stability cannot be obtained. When it is larger than 1% by mass, the curing sensitivity is lowered.

(moisture)
The water content in the ink varies depending on the type and content ratio of the polymerizable compound, the type and content ratio of the photopolymerization initiator, the storage conditions, the curing conditions, etc., but the water content in the ink is 1 to 3 masses. Storage stability improves by setting it as%. In particular, the storage stability of the cationically polymerizable ink is greatly improved. The sensitivity to the storage period can be improved as compared with the case where only the amine compound is added. If it is 1% by mass or less, this effect is poor, and if it is 3% by mass or more, problems such as precipitation during low-temperature storage occur.

  The water content can be measured by the Karl Fischer method (automatic moisture measuring device, AQV-2000, manufactured by Hiranuma Sangyo Co., Ltd.).

  The surface tension of the ink is 22 to 38 mN / m, more preferably 24 to 35 mN / m.

(Other additives)
Moreover, although the ink of the present invention is cured by irradiation with ultraviolet rays, a photosensitizer can be used in combination in order to perform the curing reaction more efficiently. Examples of such a photosensitizer include triethanolamine, methyldiethanolamine, triisopropanolamine, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, benzoic acid ( 2-dimethylamino) ethyl, 4-dimethylaminobenzoic acid (n-butoxy) ethyl, amines such as 4-dimethylaminobenzoic acid 2-ethylhexyl, cyanine, phthalocyanine, merocyanine, porphyrin, spiro compound, ferrocene, fluorene, fulgide , Imidazole, perylene, phenazine, phenothiazine, polyene, azo compound, diphenylmethane, triphenylmethane, polymethine acridine, coumarin, ketocoumarin, quinacridone, indigo, styryl, pyriri Compounds, pyromethene compounds, pyrazolotriazole compounds, benzothiazole compounds, barbituric acid derivatives, thiobarbituric acid derivatives and the like, and further, European Patent No. 568,993, US Patent No. 4,508,811 The compounds described in the specification, No. 5,227,227, JP-A No. 2001-125255, JP-A No. 11-271969 and the like can also be used. As the cationic photosensitizer, known ones are used, and specific examples include anthracene, pyrene, perylene, acridine orange, thioxanthone, 2-chlorothioxanthone, benzoflavin, eosin, rose bengal, erythrosine, methylene blue, and the like. is there. The amount of the photosensitizer used is preferably in the range of 0.01 to 10.00% by mass in the ink composition.

  The ink of the present invention preferably contains a surfactant. As the surfactant, any of cationic, anionic, amphoteric and nonionic can be used, and a nonionic surfactant is particularly preferable.

  Nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether (eg, Emulgen 911), polyoxyethylene sterol ether, polyoxyethylene lanolin derivative, polyoxy Ethylene polyoxypropylene alkyl ether (for example, Newpol PE-62), polyoxyethylene glycerin fatty acid ester, polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid Esters, fatty acid monoglycerides, polyglycerol fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters , Sucrose fatty acid esters, fatty acid alkanolamides, polyoxyethylene fatty acid amides, polyoxyethylene alkyl amines, alkyl amine oxides, acetylene glycol, acetylene alcohol, and the like, especially those fluorosurfactants preferred.

  In the present invention, the nonionic surfactant is particularly preferably a fluorosurfactant having a perfluoroalkyl group in the molecule. Examples of the fluorosurfactant having a perfluoroalkyl group in the molecule include perfluoroalkylethylene oxide adducts, perfluoroalkylamine oxides, perfluoroalkyl-containing oligomers, specifically, for example, “SURFLON S- 141 "," Surflon S-145 "," Surflon S-381 "," Surflon S-383 "," Surflon S-393 "," Surflon SC-101 "," Surflon SC-105 "," Surflon KH-40 "Surflon SA-100" (product of Seimi Chemical Co., Ltd.), "Megafuck F-171", "Megafuck F-172", "Megafuck F-173", "Megafuck F-177" ”,“ Megafuck F-178A ”,“ Megafuck F-178K ” “Megafuck F-179”, “Megafuck F-183”, “Megafuck F-184”, “Megafuck F-815”, “Megafuck F-470”, “Megafuck F-471” (above, Dainippon Ink & Chemicals, Inc.).

  When these surfactants are used, they can be used singly or as a mixture of two or more, and by adding them in the range of 0.001 to 1.0% by mass with respect to the total amount of the ink, the surface of the ink The tension can be adjusted arbitrarily. When implementing this invention, it is not limited to these. In order to maintain the long-term storage stability of the ink, an antiseptic and an antifungal agent may be added to the ink.

(Inkjet recording method)
Next, the ink jet recording method of the present invention will be described.

  Next, an ink jet recording method using the ink of the present invention will be described.

  In the present invention, ink is ejected and drawn on a substrate with a small droplet size by an ink jet recording method, and then the ink is cured by irradiation with ultraviolet rays. By irradiating the landed ink with ultraviolet rays, the ink is cured and an image is completed.

  Since the ink continues to be leveled on the base material after landing and the surface area per unit volume increases, it is more strongly affected by polymerization inhibition. Therefore, the dot diameter is small, for example, 80 μm or less. By irradiating ultraviolet rays at the timing, bleeding and residual monomers can be reduced.

  Moreover, it is preferable to irradiate ultraviolet rays after the ink has landed on the substrate and before the landed ink penetrates into the substrate, for example, before it penetrates 30% by mass or more. When an ink-absorbing base material is used, the ink continues to permeate the base material after the landing until the ultraviolet irradiation, and the ink that permeates the inside of the base material makes it difficult for the ultraviolet light to reach, resulting in poor curing.

  In the present invention, the ink film thickness after the ink has landed on the substrate and cured by irradiation with ultraviolet rays is preferably 2 to 80 μm. In the field of flexible packaging printing, where the base material is often a thin plastic material, not only the problem of curl and wrinkles of the base material, but also the problem that the overall print material's strain and texture will change. Ink ejection is not preferred.

  In addition, "ink film thickness" means the maximum value of the film thickness of the ink drawn on the base material, and it is a single color or other two color overlap (secondary color), three color overlap, four color overlap Even when recording is performed by the (white ink base) inkjet recording method, the meaning of the ink film thickness is the same.

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

  A basic method for irradiating ultraviolet rays is disclosed in Japanese Patent Application Laid-Open No. 60-132767. According to this, the light source is provided on both sides of the head unit, and the head and the light source are scanned by the shuttle method. Irradiation is performed after a certain period of time after ink landing. Further, the curing is completed by another light source that is not driven. In US Pat. No. 6,145,979, as an irradiation method, a method using an optical fiber or a method of irradiating a recording unit with UV light by applying a collimated light source to a mirror surface provided on the side surface of the head unit is disclosed. Has been. Any of these irradiation methods can be used in the image forming method according to the present invention.

  As the ink jet head used in the present invention, a droplet speed piezo head having a driving cycle of 3 kHz or more and 5 m / s or more is preferable, and one having a heating function so that ink temperature can be controlled is more preferable.

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

  Hereinafter, a recording apparatus according to the present invention will be described with reference to the drawings as appropriate. Note that the recording apparatus shown in the drawings is merely an embodiment 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. 1 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, an irradiation unit 4, a platen unit 5, and the like. In the recording apparatus 1, the platen unit 5 is installed under the base material P. The platen unit 5 has a function of absorbing ultraviolet rays, and absorbs excess ultraviolet rays that have passed through the substrate P. As a result, a high-definition image can be stably reproduced.

  The base material P is guided by the guide member 6 and moves from the near side to the far side in FIG. 1 by the operation of the conveying means (not shown). A head scanning unit (not shown) scans the recording head 3 held by the head carriage 2 by reciprocating the head carriage 2 in the Y direction in FIG.

  The head carriage 2 is installed on the upper side of the substrate P, 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 P, with an ejection port positioned on the lower side. The head carriage 2 is installed with respect to the main body of the recording apparatus 1 in such a manner that it can reciprocate in the Y direction in FIG. 1, and reciprocates in the Y direction in FIG. 1 by driving the head scanning means.

  In FIG. 1, the head carriage 2 is 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 directed from the ejection opening toward the substrate P by the operation of the ejection means (not shown) provided in a plurality of ultraviolet curable inks supplied by the ink supply means (not shown). Eject. The ultraviolet curable ink ejected by the recording head 3 is composed of a coloring material, a polymerizable compound, a photopolymerization initiator, and the like, and the initiator acts as a catalyst when irradiated with ultraviolet rays. It has the property of being cured by crosslinking and polymerization reaction of monomers.

  The recording head 3 has a certain region (landing possible region) on the substrate P during scanning of moving from one end of the substrate P to the other end of the substrate P in the Y direction in FIG. ), Ultraviolet 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 after the ultraviolet curable ink is ejected toward one landing possible region, the substrate P is appropriately moved from the front to the back in FIG. While performing scanning according to the above, the recording head 3 ejects the ultraviolet curable ink to the next landable area adjacent to the rearward direction in FIG.

  By repeating the above operation and ejecting the ultraviolet curable ink from the recording head 3 in conjunction with the head scanning means and the conveying means, an image made up of an aggregate of ultraviolet curable ink droplets is formed on the substrate P. .

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

  The irradiating means 4 is the largest one that can be set by the recording apparatus (ultraviolet curable ink jet printer) 1 among the landable areas in which the recording head 3 ejects the ultraviolet curable ink by a single scan driven by the head scanning means. The shape is almost the same or larger than the landable area.

  The irradiating means 4 is fixed on both sides of the head carriage 2 so as to be substantially parallel to the substrate P.

  As described above, as a means for adjusting the illuminance of the ink ejecting portion, not only the entire recording head 3 is shielded, but in addition, the distance h1 between the irradiation means 4 and the substrate P, and the ink ejection of the recording head 3 It is effective to reduce both the distance h2 between the portion 31 and the substrate P (2 mm or less, preferably 1.5 mm or less), or to increase the distance d between the recording head 3 and the irradiation means 4 (d is increased). It is. Further, it is more preferable that a bellows structure 7 is provided between the recording head 3 and the irradiation means 4.

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

  When a cationically polymerizable ink is used in the recording method of the present invention, it is preferable to heat-treat the ink jet ink that has landed on the substrate during light irradiation or after light irradiation.

  As the heating means, a method using a heat plate that guides the conveyance of the substrate and generates heat is preferable. Heat is transmitted to the substrate from the heat plate that conveys and guides the substrate, and the ink jet ink landed by this heat is heated. Is done. It is also preferable that the heating means is a hot air blowing means for blowing hot air onto the ink jet ink landed on the substrate.

  The heating temperature of the ink jet ink landed on the substrate is preferably 30 to 60 ° C. If the heating temperature is less than 30 ° C., the landed ink is not cured depending on the environmental humidity, and the image quality is impaired. If the temperature exceeds 60 ° C., the film base material shrinks and wrinkles, which is not preferable.

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

[Preparation of ink]
Inks having the compositions shown in Table 1 below were prepared by a conventional method. The pigment, dispersant and polymerizable compound were dispersed in a bead mill for 2 hours, and then a photopolymerization initiator, a surfactant and an amine compound were added, mixed and filtered to obtain an ink. All of these inks are cationically polymerizable. The compounds used are shown below.

PY138: C.I. I. Pigment Yellow 138 surface acid-treated product PR122: C.I. I. Pigment Red122 surface acid-treated product PB15: 4: C. I. Pigment Blue 15: 4 surface acid-treated product PBk7: C.I. I. Pigment Black surface acid-treated product PB821: Ajinomoto Fine Techno Co., Ltd., Ajisper PB821 (dispersant, acid value 30.4, amine value 10.2)
PB822: Ajinomoto Fine Techno Co., Ajisper PB822 (dispersant, acid value 18.5, amine value 15.9)
ED-251: manufactured by Enomoto Kasei Co., Ltd., ED-251 (dispersant, acid value 19, amine value 13.4)
S32000: manufactured by Avecia, Solsperse 32000 (dispersant, acid value 24.8, amine value 27.1)
disperbyk161: manufactured by Byk Chemie, 161 (dispersant, acid value 4.4, amine value 10.9)
OXT221: Aron Oxetane OXT221 (polymerizable compound) manufactured by Toa Gosei Co., Ltd.
C2021P: Daicel Corporation, Celoxide 2021P (polymerizable compound)
UVI6992: manufactured by Dow Chemical Company, UVI6992 (photopolymerization initiator)
F1405: Daifuku Ink, MegaFuck F1405 (surfactant)
TIPA: Triisopropanolamine (amine compound)

  Table 2 shows the amine value and acid value of the pigment and dispersant.

[Measurement and evaluation of ink characteristic values]
<Average particle size>
After the ink was diluted 10,000 times with the monomer used for the ink, and subjected to ultrasonic treatment with an ultrasonic cleaner at 100 W and 28 kHz for 5 minutes, measurement was performed with a photon correlation method Zetasizer 1000HS manufactured by malvern. ZAve. Is the value of

<viscosity>
The viscosity was measured using a rheometer MCR300 (manufactured by Physica) under the conditions of 55 ° C. and Shear Rate = 1000 (1 / s), 10 (1 / s).

<Drive voltage>
Voltage at which the droplet velocity is 6 m / s.

<Satellite generation speed>
Using a piezo-type head that can express 6 gradations by continuously ejecting 5 drops of ink droplets 4 pl heated to 55 ° C. per cycle at a drive frequency of 4 kHz, while adjusting the drive voltage and changing the droplet speed The minimum droplet velocity (m / s) at which satellites began to occur following the main drop was measured.

<Intermittent discharge speed reduction rate>
Using a piezo-type head capable of expressing 6 gradations by continuously ejecting 5 drops of ink droplets 4 pl heated to 55 ° C per cycle at a driving frequency of 4 kHz, it is driven so that the droplet velocity is 6 m / s. The voltage was adjusted, and the first drop speed reduction rate (%) immediately after stopping for 5 seconds after continuous discharge was measured.

<Continuous discharge>
Using a piezo-type head capable of expressing 6 gradations by continuously ejecting 5 drops of ink droplets 4 pl heated to 55 ° C per cycle at a driving frequency of 4 kHz, it is driven so that the droplet velocity is 6 m / s. The voltage was adjusted and discharged continuously for 30 minutes, the discharge state from the nozzles of each recording head was visually observed, and the continuous discharge property was evaluated according to the following criteria.

○: No nozzle missing even after 30 minutes of continuous discharge △: No nozzle missing due to continuous 30 minute discharge, but slightly satellite generated ×: No nozzle missing at several nozzles over 30 minutes of continuous ejection Will occur.

<Speed variation>
Variation in the same nozzle.

<Curing speed>
Under an environment of 30 ° C. and 60% RH, the piezo head speed is changed in units of 50 mm / s from 50 to 800 mm / s, and each ink droplet 4 pl heated to 55 ° C. is 5 dots (drop). After discharging with the H bulb (1.5 kW light source) and curing with each finger, the surface of each dot is rubbed with a finger to determine the maximum piezo head speed at which the cured ink droplets will not peel off the substrate. (Mm / s).

  From Table 3, the ink properties of C1 and K1 (both of the present invention) are not changed compared to the corresponding C2 and K2 (both of them are compared), but there are fewer satellites, which are due to the amine value and acid value of the dispersant. is there. In comparisons Y2, M2, C2, and K2, the satellite generation start speed is low, and mist is likely to appear. In particular, Y2 and M2 are highly dependent on the shear rate, and therefore the intermittent emission speed is greatly reduced, and there are many defects in continuous emission. Y6 has a small average particle size and a high driving voltage. In addition, the ultraviolet curable ink of the present invention is highly sensitive from the values of curing speed and driving voltage, satellite generation speed, intermittent blowing speed reduction rate, continuous emission properties, and speed variation values, and landing accuracy is high, and stable emission. It turns out that it is excellent in property.

It is a front view which shows the structure of the principal part of the recording device used for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording device 2 Head carriage 3 Recording head 4 Irradiation means 5 Platen part 6 Guide member 7 Bellows structure P base material

Claims (7)

An ultraviolet curable ink that is ejected from an inkjet head at a driving cycle of 3 kHz or more and at a droplet speed of 5 m / s or more, and then irradiated with ultraviolet rays, at least a pigment, a dispersant having a higher acid value than an amine value, polymerization An ultraviolet curable ink comprising a functional compound and a photopolymerization initiator. The ultraviolet curable ink according to claim 1, wherein the pigment has a maximum particle size of 400 nm or less and an average particle size of 80 nm or more. 3. The ultraviolet curable ink according to claim 1, wherein the viscosity fluctuation range at 55 ° C. Shear Rate = 10, 1000 (1 / s) is 5 mPa · s or less. The ultraviolet curable ink according to claim 1, wherein the polymerizable compound is cationically polymerizable. Using the ultraviolet curable ink according to any one of claims 1 to 4, discharging from an inkjet head at a driving cycle of 3 kHz or more and a droplet speed of 5 m / s or more, and then irradiating with ultraviolet rays. An ink jet recording method. Multi-tone recording is possible by changing the droplet size of the ultraviolet curable ink when ejected from the inkjet head at a driving cycle of 3 kHz or more and at a droplet velocity of 5 m / s or more and then irradiated with ultraviolet rays. 6. The ink jet recording method according to claim 5, wherein recording is performed by a multi-tone recording method. The minimum ink droplet size is less than 10 pl when ejected from an inkjet head at a driving cycle of 3 kHz or more and at a droplet speed of 5 m / s or more, and then irradiated with ultraviolet rays. The ink jet recording method described in 1.

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