JP2009235322A - Water-based inkjet ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based inkjet ink which gives a high-quality and durable image on a non-absorptive or low-absorptive recording medium, rapidly dries on the recording medium, and exhibits an excellent jetting stability. <P>SOLUTION: The water-based inkjet ink includes a pigment, a lactate compound, a surfactant and a water-soluble copolymer obtained by neutralizing and dissolving a copolymer composed of a polymerized unsaturated vinyl monomer having a carboxyl group as a component in an amount of not less than 1 mass% and not more than 10 mass% of the total amount of the ink. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a novel water-based aqueous ink-jet ink provided with printing suitability for printing on a non-absorbing or low-absorbing recording medium containing a resin component such as vinyl chloride.

  In recent years, inks that can be directly printed on non-absorbent recording media such as vinyl chloride sheets have been developed as inkjet inks for industrial use. For example, a solvent-based inkjet ink using an organic solvent as a vehicle and an ultraviolet curable inkjet ink mainly containing a polymerizable monomer can be used. Since the solvent-based inkjet ink is dried and evaporated in the atmosphere, the viewpoint of environmental load is not perfect. On the other hand, ultraviolet curable ink-jet inks are cured immediately after printing, so there are few evaporation components, but some monomers may have skin sensitization, and it is necessary to incorporate an expensive UV irradiation light source into the printer. There is also a limited field of application.

  In such a background, a non-absorbent recording medium directly using a water-based ink-jet recording ink that has a small environmental load and has been widely used in home-use ink-jet recording methods. Ink-jet inks that can be printed on are also being developed.

  For example, Patent Document 1 proposes an aqueous inkjet ink containing a solvent compatible with water selected from the group excluding glycol and glycol ether, and further, a hydrophobic main chain, a nonionic Ink jet inks have been proposed that contain graft copolymer binders that have soluble and hydrophilic side chains and are soluble in aqueous vehicles but insoluble in water. However, this does not disclose the use of a polymer compound having a structure having an acidic group such as a carboxyl group as a binder to be applied. Further, in the study by the present inventors, the technique disclosed in Patent Document 1 is insufficient as the image quality formed on the non-absorbent recording medium, and the durability of the obtained image is also insufficient. It is.

  On the other hand, Patent Document 2 discloses a liquid medium, a water-insoluble colorant, and a polymer for printing on an untreated vinyl resin sheet or a base coated with a vinyl resin with a piezo-type printing system having at least one heating device. A printing ink comprising a binder, a drying inhibitor and other additives, wherein the liquid medium is composed of water and a water-miscible drying inhibitor, and contains at least 80% by mass of water as the liquid medium. In addition, the content of the drying inhibitor is composed of butyl diglycol and 1-methoxypropanol-2, the ink has a pH value greater than 8.5, and the binder is dissolved in the liquid inkjet ink Inkjet inks existing in However, as a result of studies by the present inventors, it has been found that the technique disclosed in Patent Document 2 still has problems such as image quality and drying properties, as in the technique described in Patent Document 1.

Patent Documents 3 to 6 propose water-based inkjet inks in which resin fine particles that are not soluble in inkjet inks are added as binder resins, and the injection is relatively stable, but is formed on a non-absorbent recording medium. Image quality has been found to be inadequate.
JP 2000-44858 A JP 2005-113147 A JP 2004-114692 A JP 2005-220352 A JP 2006-22328 A JP 2006-282822 A

  The present invention has been made in view of the above problems, and its purpose is to be able to record on a non-absorbent or low-absorbent recording medium with high image quality, excellent durability of the obtained image, and on the recording medium. An object of the present invention is to provide a water-based inkjet ink that has fast drying properties and excellent ejection stability.

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

  1. 1% by mass or more of a water-soluble copolymer obtained by neutralizing and dissolving a copolymer obtained by polymerizing a pigment, water, a lactic acid ester compound, a surfactant, and an unsaturated vinyl monomer having a carboxyl group with an amine. A water-based inkjet ink comprising 10% by mass or less.

  2. 2. The aqueous inkjet ink as described in 1 above, further comprising a pyrrolidone compound.

  3. 3. The aqueous solution according to 1 or 2 above, wherein the water-soluble organic solvent contains glycol ethers or 1,2-alkanediols in an amount of 2.0% by mass to 20% by mass with respect to the total mass of the ink. Inkjet ink.

  4). 4. The water-based inkjet ink as described in any one of 1 to 3 above, which contains water-based dispersed polymer fine particles.

  Furthermore, as a preferred embodiment in the present invention, the following configurations can be exemplified.

  5). 2. The water-based inkjet ink according to 1 above, wherein the acid value of the water-soluble copolymer is 80 mgKOH / g or more and less than 300 mgKOH / g.

  6. The aqueous inkjet ink as described in 1 above, wherein the lactic acid ester compound is contained in an amount of 1.0% by mass to 10% by mass with respect to the total amount of the ink.

  7. 2. The water-based inkjet ink according to 1 above, wherein the surfactant is a silicon-based surfactant, an acetylene-based surfactant, or a fluorine-based surfactant.

  8). 3. The aqueous inkjet ink as described in 2 above, wherein the pyrrolidone compound is N-methyl-2-pyrrolidone or N-ethyl-2-pyrrolidone.

  According to the present invention, a water-based inkjet ink which can be recorded on a non-absorbing or low-absorbing recording medium with high image quality, and the obtained image has excellent durability, quick drying on the recording medium, and excellent injection stability. Could be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

As a result of intensive studies in view of the above problems, the present inventor has found that at least 1) a pigment,
2) Lactic acid ester compound,
3) surfactant,
Containing
Furthermore,
4) A water-soluble copolymer obtained by neutralizing and dissolving a copolymer obtained by polymerizing an unsaturated vinyl having at least a carboxyl group as a monomer component with an amine is contained in an amount of 1.0% by mass to 10% by mass with respect to the total mass of the ink. To
The water-based ink-jet ink can record a high-quality image on a non-absorbing or low-absorbing recording medium, and the obtained image has high durability and can be dried on the recording medium. As a result, it has been found that a water-based ink-jet ink having high performance and excellent ejection stability can be obtained.

  Hereinafter, the present invention will be described in detail.

  The water-based inkjet ink of the present invention (hereinafter also referred to as the ink of the present invention) is characterized in that it contains both a water-soluble copolymer neutralized and dissolved with an amine and a lactic acid ester. Mainly due to the action of the water-soluble copolymer, the viscosity of the ink of the present invention is increased by drying after landing, and a high-quality image can be obtained without causing ink bleeding or color mixing. The color material can be firmly fixed. When the content of the water-soluble copolymer is 10% by mass or less, sufficient dissolution in the ink can be maintained, and storage stability can be satisfied.

  On the other hand, when a lactic acid ester compound is inkjet-recorded on a plastic substrate such as a vinyl chloride resin, the vinyl chloride resin is swollen or dissolved, and the pigment coexisting in the ink is embedded in the vinyl chloride resin surface to record the pigment. We believe that we will be responsible for firmly fixing the media. Furthermore, the ink containing a lactic acid ester compound increases in viscosity by drying after landing and can form a high-quality image without causing ink bleeding or color mixing. Therefore, by using the water-soluble copolymer and lactic acid ester together in the effect of thickening the ink during landing and drying, a high-quality image with reduced bleeding and color mixing can be formed, and the fixing property of the colorant It is considered that a recorded image having excellent durability can be obtained.

  Further, since the degree to which the recording medium such as vinyl chloride resin of the lactic acid ester swells and dissolves is not so strong, it is preferable to use a pyrrolidone compound together in order to more effectively swell and dissolve. Thereby, it is considered that the color material in the ink can be more firmly fixed to the recording medium.

  The ink of the present invention further contains glycol ethers or 1,2-alkanediols as water-soluble organic solvents in an amount of 2.0% by mass or more and 20% by mass or less based on the total mass of the ink. A thickened action in the drying process can be exerted to obtain a recorded image with high image quality and high durability. In addition, it has been found that the lactic acid ester used in the present invention has a function of swelling and dissolving a resin such as vinyl chloride, which is more remarkably expressed when used in combination with glycol ethers and 1,2-alkanediols. .

  Therefore, in addition to the embodiment using the water-soluble copolymer and lactate compound according to the present invention, the embodiment using the water-soluble copolymer, lactate compound and pyrrolidone compound in combination, the water-soluble copolymer and lactate compound And a combination of glycol ethers or 1,2-alkanediols, water-soluble copolymers, lactic acid ester compounds, pyrrolidone compounds, and glycol ethers or 1,2-alkanediols. Embodiments are also preferred.

  First, a water-soluble copolymer obtained by neutralizing and dissolving a copolymer obtained by polymerizing unsaturated vinyl having a carboxyl group as a monomer component according to the present invention with an amine will be described.

  The water-based inkjet ink of the present invention exhibits the effect of the present invention that an image having high image quality and excellent scratch resistance can be formed particularly when recording on a non-absorbing or low-absorbing recording medium. That is, the water-soluble copolymer according to the present invention rapidly increases in viscosity in the drying process after ink landing, forms a high-quality image with suppressed bleeding, and the pigment is a non-absorbent recording medium such as a vinyl chloride resin. It has a function of fixing on the surface of the like.

  The present inventors estimate this phenomenon as follows.

  That is, in the water-based inkjet ink of the present invention, the carboxyl group of the water-soluble copolymer is stably present by neutralization with an amine. The concentration of the water-soluble copolymer increases. At the same time, the amine used for neutralization at the time of drying also volatilizes, thereby further increasing the concentration of the water-soluble copolymer. As a result, it is possible to obtain a high-quality recorded image in which the viscosity of the ink is increased and the occurrence of color mixing is suppressed.

  Furthermore, since the amines which are neutralizing agents are volatilized after drying, even if moisture is given to the recorded image again, the water-soluble copolymer is solidified without being redissolved in water, and the pigment is The effect of being fixed and excellent in scratch resistance and water resistance is recognized.

  The water-soluble copolymer according to the present invention is designed and used having a hydrophilic component that is a carboxyl group and a hydrophobic component in an appropriate balance. Under the present circumstances, the water-soluble copolymer based on this invention which provided the water solubility by neutralizing with a base component which can volatilize a carboxyl group fully exhibits said function. Examples of such water-soluble copolymers include acrylic resins, styrene-acrylic resins, acrylonitrile-acrylic resins, vinyl acetate-acrylic resins, polyurethane resins, and polyester resins.

  Examples of the hydrophobic monomer constituting the water-soluble copolymer according to the present invention include acrylic acid esters (for example, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, etc.), methacrylic acid esters. (For example, ethyl methacrylate, butyl methacrylate, glycidyl methacrylate, etc.), styrene and the like.

  Examples of the hydrophilic monomer constituting the water-soluble copolymer according to the present invention include acrylic acid, methacrylic acid, and acrylamide.

  The carboxyl group possessed by the water-soluble copolymer must be partially or completely neutralized with amines. Examples of amines include ammonia, triethylamine, 2-dimethylaminoethanol, 2-di-n-butylaminoethanol, methyldiethanolamine, 2-amino-2-methyl-1-propanol, diethanolamine, triethanolamine, 2- Methylaminoethanol or the like can be preferably used.

  In particular, neutralization with amines having a boiling point of less than 200 ° C. is more preferable because amines are likely to volatilize during drying, and the hydrophobicity is increased rapidly to contribute to improvement in image durability.

  The content of the water-soluble copolymer according to the present invention is 1.0% by mass or more and 10% by mass or less, and the content of the water-soluble copolymer is 1.0% by mass or more with respect to the total mass of the ink. If present, the thickening effect at the time of drying is sufficient, and bleeding can be prevented and a high-quality image can be obtained. Further, if it is 10% by mass or less, the ink can be stably dissolved in the ink, the storage stability of the ink is high, the ink can be stably ejected, and the print can be obtained stably over a long period of time.

  Further, the water-soluble copolymer according to the present invention preferably has an acid value of 80 mgKOH / g or more and less than 300 mgKOH / g, but a water-soluble copolymer compound having an acid value in the range specified above is used. By applying this, the effect of the present invention is remarkably recognized in that the increase in viscosity during drying becomes remarkable and the pigment is firmly solidified after drying to improve the fixability of the pigment. A more preferred acid value is about 90 to 250 mg KOH / g. The polymerization method is preferably solution polymerization. The acid value defined in the present invention can be measured according to JIS K0070.

  As a molecular weight of the water-soluble copolymer according to the present invention, an average molecular weight of 3000 to 30000 can be preferably used, and more preferably 7000 to 20000.

  The Tg of the water-soluble copolymer according to the present invention is preferably about -30 ° C to 100 ° C, more preferably -10 ° C to 80 ° C.

  Next, the lactic acid ester compound contained in the ink of the present invention will be described. The lactic acid ester compound in the ink composition has a characteristic that evaporation is slower than water. When ink-jet recording is performed, when the water content of the printed ink composition evaporates, the concentration of the lactic acid ester compound component becomes high. The lactic acid ester compound has a property of dissolving plastic, and when the concentration of the lactic acid ester compound increases, the action of swelling and dissolving the plastic material constituting the recording medium is enhanced.

  Further, it is considered that the high concentration of the lactic acid ester compound after landing increases the viscosity of the ink together with the water-soluble copolymer, thereby contributing to the formation of a high-quality image without bleeding.

  Examples of the lactic acid ester compound used in the ink of the present invention include methyl lactate, ethyl lactate, butyl lactate, amyl lactate, hexyl lactate and the like, preferably ethyl lactate and butyl lactate. Two or more kinds of these lactic acid ester compounds may be mixed and used. The content of the lactic acid ester compound is not limited, but is preferably 1.0 to 20.0% by mass, and more preferably 2.0 to 15.0% by mass with respect to the total mass of the ink.

  In the ink of the present invention, an embodiment further containing a pyrrolidone compound is preferable.

  The pyrrolidone compound that can be preferably used in the present invention is considered to have a function of firmly fixing the pigment on the recording medium by swelling and dissolving a resin used for the recording medium such as vinyl chloride together with the lactic acid ester compound. Preferable specific examples of the pyrrolidone compound include 2-pyrrolidone, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone. In particular, N-methyl-2-pyrrolidone and N-ethyl- 2-pyrrolidone is preferred. You may use these in combination of 2 or more types. The content of the pyrrolidone compound is generally 0.1 to 12.0% by mass with respect to the total amount of the ink, and if it is 0.1% by mass or more, the resin solubility to the extent that the pigment can be fixed is exhibited. If it is 0% by mass or less, it is possible to prevent destruction of the ink contact parts of the printer. In the same viewpoint, it is preferably 1.0 to 10.0% by mass.

  In the present invention, an embodiment containing glycol ethers or 1,2-alkanediols as the water-soluble organic solvent is preferable. The glycol ethers and 1,2-alkanediols become stronger as the concentration of glycol ethers and the like increases in the drying process after ink landing due to hydrophobic interaction with the pigment dispersion and water-soluble copolymer. By acting together, the ink is thickened. Therefore, it is considered that the bleeding suppression effect is remarkably exhibited by using the water-soluble copolymer in combination with glycol ethers or 1,2-alkanediols.

  Examples of the glycol ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether. It is done. Examples of the 1,2-alkanediols include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and the like.

  The glycol ethers or 1,2-alkanediols according to the present invention are particularly preferably contained in an amount of 2 to 20% by mass with respect to the total mass of the ink from the standpoint that the effects of the present invention are remarkably exhibited.

  In the ink according to the present invention, a surfactant is used to ensure wettability to a recording medium containing vinyl chloride resin or the like.

  Preferable examples of the surfactant used in the present invention include silicon surfactants, acetylene surfactants, and fluorine surfactants.

  The silicon-based surfactant that can be used in the present invention is preferably a dimethylpolysiloxane whose side chain or terminal is polyether-modified (polyether-modified polysiloxane compound). For example, KF- manufactured by Shin-Etsu Chemical Co., Ltd. 351A, KF-642, BigKemi's BYK347, BYK348, etc. are mentioned.

  The acetylene surfactant that can be used in the present invention is particularly preferably an acetylene glycol surfactant, having a triple bond in the molecule, a hydroxyl group and an alkyl group on the adjacent carbon atom, and a triple bond. Are preferably symmetrical structures. The acetylene glycol compound and acetylene alcohol compound used in the present invention can be obtained as commercial products, and examples thereof include Surfinol and Olphine manufactured by Nissin Chemical Industry Co., Ltd. and acetylenol manufactured by Kawaken Fine Chemical Co., Ltd.

  The fluorine-based surfactant that can be used in the present invention means a compound in which a part or all of the surfactant is substituted with fluorine in place of hydrogen bonded to carbon of a hydrophobic group of a normal surfactant. Of these, those having a perfluoroalkyl group in the molecule are preferred.

  Among the fluorosurfactants, certain types are traded under the trade name Megafac F from Dainippon Ink & Chemicals, Inc., and the trade name Surflon from Asahi Glass Co., Minnesota Mining and Under the trade name Fluorad FC from Manufacturing Company, under the trade name Monflor from Imperial Chemical Industry, and Zonyls from EI Dupont Nemeras & Company. It is commercially available under the trade name and also under the trade name Licobet VPF from Farbeberke Hoechst.

  Examples of nonionic fluorosurfactants include Megafax 144D manufactured by Dainippon Ink and Surflon S-141 and 145 manufactured by Asahi Glass Co., and amphoteric fluorosurfactants. Examples of the agent include Surflon S-131 and 132 manufactured by Asahi Glass Co., Ltd.

  Next, the pigment according to the present invention will be described.

  The pigment applicable to the present invention is not particularly limited as long as it can be stably dispersed in an aqueous system. A pigment dispersion dispersed with a polymer resin, a capsule pigment coated with a water-insoluble resin, a dispersion resin modified with a pigment surface is used. It is possible to select from self-dispersing pigments that can be dispersed without such. When emphasis is particularly placed on the storage stability of the ink, it is preferable to select a capsule pigment coated with a water-insoluble resin.

  When a pigment dispersion dispersed with a polymer resin is used, a water-soluble one can be used as the polymer resin. As the water-soluble resin, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-maleic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester copolymer are preferably used. Styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer It is a water-soluble resin such as.

  Various methods such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used as a pigment dispersion method.

  In order to prepare the pigment dispersion according to the present invention, it is preferable to use a centrifugal separator or a filter for the purpose of removing coarse particles of the pigment dispersion.

  In the case of using capsule pigments coated with a water-insoluble resin, the water-insoluble resin is a resin that is insoluble in weakly acidic or weakly basic water, and preferably has a solubility in an aqueous solution of pH 4 to 10. The resin is less than mass%.

  Such resins include acrylic, styrene-acrylic, acrylonitrile-acrylic, vinyl acetate, vinyl acetate-acrylic, vinyl acetate-vinyl chloride, polyurethane, silicon-acrylic, acrylic silicon, polyester Examples thereof include epoxy resins and epoxy resins.

  In the present invention, a resin prepared using a hydrophobic monomer and a hydrophilic monomer as constituent components can be used as the resin used to disperse the pigment.

  Examples of hydrophobic monomers include acrylic acid esters (such as n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate), methacrylic acid esters (such as ethyl methacrylate, butyl methacrylate, glycidyl methacrylate), and styrene. Etc.

  Examples of the hydrophilic monomer include acrylic acid, methacrylic acid, acrylamide and the like, and those having an acidic group such as acrylic acid can preferably be those neutralized with a base after polymerization.

  As molecular weight of resin, the thing of 3000-500000 can be used with the weight average molecular weight Mw. Preferably, the thing of 7000-200000 can be used.

  Resin having a Tg of about −30 to 100 ° C. can be used. Preferably about -10-80 degreeC can be used.

  As the polymerization method, solution polymerization or emulsion polymerization can be used. The polymerization may be performed separately from the pigment in advance, or may be performed by supplying a monomer into the system in which the pigment is dispersed.

  As a method of coating the pigment with the resin, various known methods can be used. Preferably, in addition to the phase inversion emulsification method and the acid precipitation method, the pigment is dispersed with a polymerizable surfactant, A method of supplying a monomer and coating while polymerizing can be selected.

  As a more preferable method, a water-insoluble resin is dissolved in an organic solvent such as methyl ethyl ketone, and after partially or completely neutralizing an acidic group in the resin with a base, a pigment and ion-exchanged water are added and dispersed. A production method in which an organic solvent is removed and water is added as necessary is preferable.

  The mass ratio of the pigment and the resin can be selected from 100/40 to 100/150 as a pigment / resin ratio. In particular, the range of 100/60 to 100/110 has good image durability, injection stability, and ink storage stability.

  The average particle size of the pigment particles coated with the water-insoluble resin is preferably about 80 to 150 nm from the viewpoint of ink storage stability and color development.

  The average particle diameter can be determined by a commercially available particle size measuring instrument using a light scattering method, an electrophoresis method, a laser Doppler method, or the like. It is also possible to obtain a particle image with a transmission electron microscope on at least 100 particles and perform statistical processing on the image using image analysis software such as Image-Pro (manufactured by Media Cybernetics). Is possible.

  In addition, as the self-dispersing pigment, commercially available products that have been surface-treated can be used, and examples thereof include CABO-JET200, CABO-JET300 (manufactured by Cabot), and Bonjet CW1 (manufactured by Orient Chemical Industries). .

  As the pigment that can be used in the present invention, conventionally known organic and inorganic pigments can be used. For example, azo lake, insoluble azo pigment, condensed azo pigment, chelate azo pigment azo pigment, phthalocyanine pigment, perylene and perylene pigment, anthraquinone pigment, quinacridone pigment, dioxazine pigment, thioindigo pigment, isoindolinone pigment, quinophthalone pigment, etc. Examples include polycyclic pigments, dye lakes such as basic dye-type lakes and acid dye-type lakes, organic solvents such as nitro pigments, nitroso pigments, aniline black and daylight fluorescent pigments, and inorganic pigments such as carbon black.

  Specific organic pigments are exemplified below.

  Examples of pigments for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the orange or yellow pigment include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. And CI Pigment Yellow 138.

  Examples of pigments for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  The aqueous inkjet ink of the present invention preferably further contains water-based dispersed polymer fine particles. In the present invention, by using a water-soluble copolymer, after ink landing, the ink thickens at the time of drying and promotes pigment fixation on the recording medium. By appropriately leveling the droplets, it is possible to keep the image clarity good by preventing irregularities on the image surface. At this time, if it is attempted to control the degree of increase in viscosity in the drying process only by reducing the water-soluble copolymer, it is not easy to balance leveling and bleeding, but the water-based dispersion type according to the present invention By using the polymer in combination with a water-soluble copolymer, it is possible to easily control to increase the viscosity increasing rate in the subsequent drying process by suppressing the viscosity increasing rate immediately after landing of the ink and leveling the ink. .

  Further, the Tg of the water-based dispersed polymer fine particles is preferably 35 ° C. or more from the viewpoint of exhibiting an image scratch resistance effect, and more preferably 49 ° C. or more. The upper limit of Tg is not particularly limited, but is preferably about 100 ° C. or less because a flexible ink film can be obtained and cracking of an image due to bending of a printed matter can be suppressed.

  The acid value of the aqueous dispersion type polymer fine particles is preferably 44 mgKOH / g or more, and more preferably 60 mgKOH / g or more. The upper limit of the acid value is not particularly limited, but is preferably less than 110 mgKOH / g from the viewpoint of easily obtaining a more stable dispersion.

  The average particle size of the water-dispersible polymer fine particles is preferably 300 nm or less, more preferably 130 nm or less, from the viewpoint that clogging of the nozzles of the ink jet recording head is not caused and good glossiness is obtained. The lower limit of the average particle diameter is preferably 30 nm from the viewpoint of production stability of fine particles. The average particle diameter of the water-dispersed polymer fine particles can be easily measured by using a commercially available measuring apparatus using a light scattering method or a laser Doppler method. Alternatively, the dispersion of the aqueous dispersion polymer fine particles can be freeze-dried, and the average particle diameter can be converted from the particles observed with a transmission microscope.

  The content of the water-based dispersed polymer fine particles is preferably 0.7 to 6% by mass with respect to the total mass of the ink, and it is easy to obtain good fixability (abrasion resistance, alcohol resistance) and long-term storage stability of the ink. Especially preferably, it is 1-3 mass%.

  As the aqueous dispersion type polymer fine particles, a dispersion polymerized in an aqueous system may be used as it is or may be treated, or a dispersion polymerized in a solvent system may be used in an aqueous system. Is selected from, for example, acrylic, urethane, styrene, vinyl acetate, vinylidene chloride, vinyl chloride, styrene-butadiene, styrene-acrylonitrile, polybutadiene, polyethylene, polyisobutylene, polyester, etc. can do.

  In addition, as a physical property of the ink, from the viewpoint of satisfying the ejection stability, it is preferable that there is no shear dependency on the viscosity, and from this viewpoint, as a dispersion form of the polymer fine particles, an emulsifier such as a surfactant is made as low as possible, Soap-free dispersed polymer particles that do not use an emulsifier are preferred. Particularly preferred aqueous dispersion polymer fine particles are self-dispersion dispersions of a copolymer obtained by polymerizing unsaturated vinyl having a carboxyl group as a monomer component. For example, acrylic monomers such as ethyl acrylate alone or acrylic Mechanically sheared after a dispersion obtained by emulsion polymerization or suspension polymerization of acrylic acid or maleic acid as a carboxylic acid monomer in a composition comprising an ethylenically unsaturated monomer that can be copolymerized with a monomer is swelled with alkali, and then mechanically sheared. Is an acrylic hydrosol obtained by dividing the particles. Among acrylic hydrosols, it is preferable to contain styrene in the monomer composition from the viewpoint of increasing the refractive index of the resin and obtaining high glossiness.

  Examples of the alkali used in the swelling operation of the dispersion include ammonia, triethylamine, 2-dimethylaminoethanol, 2-di-n-butylaminoethanol, methyldiethanolamine, 2-amino-2-methyl-1-propanol, diethanolamine, triethanolamine, An amine such as ethanolamine or 2-methylaminoethanol is preferable, and ammonia, 2-amino-2-methyl-1-propanol, and 2-methylaminoethanol are particularly preferable in terms of dispersion stability of the aqueous dispersion polymer fine particles. preferable.

  As the acrylic hydrosol, Jonkrill (trademark) manufactured by Johnson Polymer Co., Ltd. is commercially available.

  The ink of the present invention can contain various compounds other than those described above. For example, what is used as the solvent is preferably an aqueous liquid medium, and more preferably a mixed solvent such as water and a water-soluble organic solvent. For example, alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, etc.), polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol) , Dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, etc.), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyl) Diethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenedi Amine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (for example, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.) and the like. It is done.

  The ink of the present invention exhibits the effects of the present invention remarkably when recording on a non-absorbing recording medium such as a vinyl chloride sheet or a low-absorbing recording medium. In addition, it is suitable for printing on plain paper, coated paper, ink jet dedicated paper, and the like.

  Non-absorbent recording media include polymer sheets, boards (soft vinyl chloride, hard vinyl chloride, acrylic plates, polyolefins, etc.), glass, tile, rubber, synthetic paper, and the like.

  Examples of the low absorption or absorption recording medium include plain paper (copy paper, plain paper for printing), coated paper, art paper, inkjet paper, inkjet glossy paper, cardboard, and wood.

  In particular, it is a recording medium having at least polyvinyl chloride on the recording surface side that exhibits the effects of the present invention remarkably. For example, specific examples of the recording medium having polyvinyl chloride include SOL-371G, SOL-373Mm, SOL-4701 (big technos) and glossy vinyl chloride (manufactured by Stemgraph).

  The ink of the present invention is more preferably printed by heating a recording medium. By heating the recording medium, the drying and thickening speed of the ink is remarkably improved, and high image quality is obtained. Also, the durability of the image is improved. As the heating temperature, it is particularly preferable that the recording surface temperature of the recording medium is 40 to 80 ° C. If it is 40 ° C. or higher, the image quality is sufficient and sufficient image durability is obtained, and the drying time is relatively short. On the other hand, when the temperature is 80 ° C. or lower, it is possible to ensure stable ink ejection and stably print. More preferably, the recording surface temperature of the recording medium is 40 to 60 ° C.

  As a heating method, it is possible to select a method in which a heating heater is incorporated in the recording medium conveyance system or the platen member and heated from the lower side of the recording medium in a contact manner, or a method of heating in a non-contact manner from the lower side or the upper side by a lamp or the like.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<< Preparation of pigment dispersion >>
[Preparation of Pigment Dispersion-C]
As a pigment dispersant, 3 parts of a styrene-acrylic acid copolymer (John Cryl 678, molecular weight 8500, acid value 215), 1.3 parts of dimethylaminoethanol, and 80.7 parts of ion-exchanged water are stirred and mixed at 70 ° C to dissolve. did.

  Next, C.I. I. After adding 15 parts of Pigment Blue 15: 3 and premixing, the mixture was dispersed using a sand grinder filled with 50% by volume of 0.5 mm zirconia beads, and a pigment dispersion having a cyan pigment content of 15% -C was prepared.

[Preparation of Pigment Dispersion-Y, Pigment Dispersion-M, Pigment Dispersion-Bk]
In the preparation of Pigment Dispersion-C, cyan pigment C.I. I. Instead of CI Pigment Blue 15: 3, C.I. I. Pigment Yellow-74, C.I. I. Pigment Dispersion-Y, Pigment Dispersion-M, and Pigment Dispersion-Bk were prepared in the same manner except that Pigment Red 122 and carbon black were used as the black pigment.

<Synthesis of water-soluble copolymer>
[Synthesis of water-soluble copolymer 1]
50 g of methyl ethyl ketone was added to a flask equipped with a dropping funnel, a nitrogen introducer, a reflux condenser, a thermometer and a stirrer, and heated to 75 ° C. while bubbling nitrogen.

  Thereto, a mixture consisting of 80 g of n-butyl methacrylate, 20 g of acrylic acid, 50 g of methyl ethyl ketone, and 500 mg of a polymerization initiator (AIBN) was dropped over 3 hours from the dropping funnel. After the dropwise addition, the mixture was further heated to reflux for 6 hours. After allowing to cool, the mixture was heated under reduced pressure, and methyl ethyl ketone was distilled off to obtain a polymer residue.

  In 450 ml of ion-exchanged water, dimethylaminoethanol corresponding to 1.05 moles of acrylic acid added as a monomer was dissolved, and the polymer residue was added and dissolved therein. Next, the concentration was adjusted with ion-exchanged water to obtain an aqueous solution of water-soluble copolymer 1 (acid value 117 mgKOH / g) having a water-soluble copolymer content of 20%.

[Synthesis of water-soluble copolymers 2, 3]
In the synthesis of the water-soluble copolymer 1, a water-soluble copolymer 2 (acid value 155 mgKOH / g), a water-soluble copolymer 3 and a monomer other than those used in Table 1 were used in the same manner. (Acid value 194 mg KOH / g) was synthesized to obtain an aqueous solution of water-soluble copolymers 2 and 3 having a water-soluble copolymer content of 20%.

[Synthesis of water-soluble copolymer A for comparison]
50 g of methyl ethyl ketone was added to a flask equipped with a dropping funnel, a nitrogen introducer, a reflux condenser, a thermometer and a stirrer, and heated to 75 ° C. while bubbling nitrogen.

  Thereto, a mixture of 80 g of n-butyl methacrylate, 20 g of acrylic acid, 50 g of methyl ethyl ketone, and 500 mg of a polymerization initiator (AIBN) was dropped from a dropping funnel over 3 hours. It heated and refluxed for 6 hours after dripping. After allowing to cool, the mixture was heated under reduced pressure to distill off methyl ethyl ketone to obtain a polymer residue.

  Sodium hydroxide equivalent to 1.05 moles of acrylic acid added as a monomer was dissolved in 450 ml of ion-exchanged water, and the polymer residue was dissolved therein. The concentration was adjusted with ion-exchanged water to obtain an aqueous solution of water-soluble copolymer A having a water-soluble copolymer content of 20%.

<Preparation of ink set>
[Preparation of ink set 11: the present invention]
(Preparation of ink C11)
While stirring 26.7 parts of the pigment dispersion-C prepared above, 16.5 parts of an aqueous solution of the water-soluble copolymer 1 having a hydrophobic monomer as a polymerization component and a water-soluble copolymer content of 20% were added. Then, the following compounds were sequentially added to prepare an ink composition, which was filtered through a 0.8 μm filter to obtain an ink C11.

Pigment dispersion-C 26.7 parts Aqueous solution of water-soluble copolymer 1 (water-soluble copolymer content: 20%) 16.5 parts Triethylene glycol monobutyl ether 10.0 parts 1,2-hexanediol 5. 0 parts Butyl lactate 3.5 parts Diethylene glycol 11.2 parts Silicone surfactant: KF-351A (manufactured by Shin-Etsu Chemical Co., Ltd.) 0.6 parts Ion exchange water was added to prepare a total amount of 100 parts. The content of the water-soluble copolymer 1 in the ink C11 is 3.3% by mass.

(Preparation of ink Y11)
Ink Y11 was prepared in the same manner as in the preparation of Ink C11 except that Pigment Dispersion-Y was used instead of Pigment Dispersion-C, and the addition amount of butyl lactate was changed to 4.0 parts.

(Preparation of ink M11)
Ink M11 was prepared in the same manner as in the preparation of Ink Y11 except that Pigment Dispersion-M was used instead of Pigment Dispersion-Y.

(Preparation of ink Bk11)
Ink Bk11 was prepared in the same manner as in the preparation of Ink C11 except that Pigment Dispersion-Bk was used instead of Pigment Dispersion-C.

[Preparation of ink set 12: the present invention]
(Preparation of ink C12, ink Y12, and ink M12)
Ink C12, ink Y12, and ink M12 were prepared in the same manner as in the preparation of ink C11, ink Y11, and ink M11 except that 5.0 parts of N-methyl-2-pyrrolidone was added.

(Preparation of ink Bk12)
Ink Bk12 was prepared in the same manner as in the preparation of Ink Bk11 except that 7.0 parts of N-methyl-2-pyrrolidone was added.

[Preparation of ink set 13: the present invention]
In the preparation of the ink C12, the ink Y12, the ink M12, and the ink Bk12, an aqueous dispersion type polymer fine particle dispersion (PDX-7667, manufactured by Johnson Polymer Co., Ltd., acid value: 82 mgKOH / g, Tg: 75 ° C., solid content concentration) Ink C13, Ink Y13, Ink M13, and Ink Bk13 were prepared in the same manner except that 3.3 parts of each was added.

[Preparation of ink set 14: the present invention]
In the preparation of the inks C13, Y13, M13, and Bk13, inks C14, Y14, M14, and Bk14 were prepared in the same manner except that the water-soluble copolymer 2 was used instead of the water-soluble copolymer 1. This was designated as an ink set 14.

[Preparation of ink set 15: the present invention]
In the preparation of the inks C13, Y13, M13, and Bk13, inks C15, Y15, M15, and Bk15 were prepared in the same manner except that the water-soluble copolymer 3 was used instead of the water-soluble copolymer 1. This was designated as an ink set 15.

[Preparation of ink set 16: Comparative example]
Inks C16, Y16, M16, and Bk16 were prepared in the same manner as the inks C13, Y13, M13, and Bk13 except that the water-soluble copolymer A was used instead of the water-soluble copolymer 1. This was designated as Ink Set 16.

[Preparation of ink set 17: comparative example]
In the preparation of the inks C13, Y13, M13, and Bk13, the inks C17, Y17, and M17 were similarly prepared except that the addition amount of the water-soluble copolymer 1 was changed to 4.0 parts (0.8% by mass). , Bk17 was prepared and used as an ink set 17.

[Preparation of ink set 18: the present invention]
Inks C18, Y18, M18, Bk18 were prepared in the same manner as in the preparation of the inks C13, Y13, M13, Bk13, except that the amount of the water-soluble copolymer 1 was changed to 10 parts (2.0% by mass). This was designated as Ink Set 18.

[Preparation of ink set 19: the present invention]
In the preparation of the aqueous solution of the water-soluble copolymer 1 having a water-soluble copolymer content of 20%, the concentration of the ion-exchanged water is adjusted to change the content of the water-soluble copolymer 1 to 40%. An aqueous solution of the water-soluble copolymer 1A thus prepared was prepared.

  In the preparation of the inks C13, Y13, M13, and Bk13, instead of the aqueous solution of the water-soluble copolymer 1 having a water-soluble copolymer content of 20%, the content of the water-soluble copolymer 1 is 40%. Inks C19, Y19, M19, and Bk19 were prepared in the same manner except that 22.5 parts (9.0% by mass) of an aqueous solution of the water-soluble copolymer 1A was added.

[Preparation of ink set 20: the present invention]
In the preparation of the inks C19, Y19, M19, and Bk19, the inks C20, Y20, M20, and Bk19 were similarly prepared except that the amount of the aqueous solution of the water-soluble copolymer 1A was changed to 27.5 parts (11%). Bk20 was prepared and used as an ink set 20.

[Preparation of ink set 21: the present invention]
(Preparation of ink C21)
Ink C21 was prepared in the same manner as in the preparation of Ink C13 except that 4.0 parts of ethyl lactate was used instead of butyl lactate.

(Preparation of ink Y21)
Ink Y21 was similarly prepared except that 4.5 parts of ethyl lactate was used instead of butyl lactate in the preparation of ink Y13.

(Preparation of ink M21)
Ink M21 was prepared in the same manner as in the preparation of ink M13 except that 4.5 parts of ethyl lactate was used instead of butyl lactate.

(Preparation of ink Bk21)
Ink Bk21 was prepared in the same manner as in the preparation of Ink Bk13 except that 3.5 parts of ethyl lactate was used instead of butyl lactate.

[Preparation of ink set 22: the present invention]
Inks C22, Y22, M22 and Bk22 were prepared in the same manner as in the preparation of the inks C21, Y21, M21 and Bk21 except that the same amount of methyl lactate was used instead of ethyl lactate. It was.

[Preparation of ink set 23: the present invention]
(Preparation of inks C23, Y23, M23)
Ink C13, Y13, and M13 were prepared in the same manner except that 4.5 parts of N-ethyl-2-pyrrolidone was used instead of 5.0 parts of N-methyl-2-pyrrolidone. C23, Y23 and M23 were prepared.

(Preparation of ink Bk23)
Ink Bk23 was prepared in the same manner as in the preparation of Ink Bk13 except that 6.5 parts of N-ethyl-2-pyrrolidone was used instead of 7.0 parts of N-methyl-2-pyrrolidone.

[Preparation of ink set 24: the present invention]
(Preparation of inks C24, Y24, M24)
In the preparation of the inks C13, Y13, and M13, inks C24, Y24, and M24 were prepared in the same manner except that 8.0 parts of 2-pyrrolidone was used instead of 5.0 parts of N-methyl-2-pyrrolidone. M24 was prepared.

(Preparation of ink Bk24)
Ink Bk24 was prepared in the same manner as in the preparation of Ink Bk13 except that 10 parts of 2-pyrrolidone was used instead of 7.0 parts of N-methyl-2-pyrrolidone.

[Preparation of ink set 25: the present invention]
In the preparation of the inks C13, Y13, M13, and Bk13, the same amount of acetylene surfactant (Surfinol 465, manufactured by Nissin Chemical Industry Co., Ltd.) was used in place of the silicon surfactant (KF-351A). Ink C25, Y25, M25, and Bk25 were prepared in the same manner as described above, and this was designated as ink set 25.

[Preparation of ink set 26: the present invention]
In preparation of the inks C13, Y13, M13, and Bk13, the same amount of fluorosurfactant (Megafax 144D, manufactured by Dainippon Ink & Chemicals, Inc.) was used in place of the silicon surfactant (KF-351A). Ink C26, Y26, M26, and Bk26 were prepared in the same manner as described above, and this was designated as ink set 26.

[Preparation of ink set 27: comparative example]
Inks C27, Y27, M27, and Bk27 were prepared in the same manner as in the preparation of the inks C13, Y13, M13, and Bk13 except that butyl lactate, which is a lactic acid ester, was removed.

<Characteristic value measurement of water-soluble copolymer>
(Measurement of acid value)
The acid value of the water-soluble copolymer was measured according to JIS K0070.

[Measurement of weight average molecular weight Mw]
The weight average molecular weight Mw of the water-soluble copolymer was measured using high performance liquid chromatography.

  The results obtained as described above are shown in Table 1.

<< Image formation and evaluation >>
(Image formation)
Each color image was formed according to the following method using each prepared ink set.

  Each ink constituting each ink set was loaded into an ink jet printer equipped with a drop on demand piezo type ink jet head (720 dpi, droplet amount 16 pl). Subsequently, each color solid image of 35 × 35 mm was recorded on the recording medium by one scan.

  Incidentally, for 3 minutes after the start of image formation from the start of printing, the recording medium was heated from the back side with a heater to control the surface temperature of the recording medium at 45 ± 2 ° C. In the present invention, dpi represents the number of dots per 2.54 cm.

  The evaluation conditions are as follows.

-Print resolution: 720 dpi x 720 dpi
・ Head transport speed: 200 mm / sec, bi-directional printing ・ Recording medium: Vinyl chloride resin sheet (Metamark, digitalvinil)
・ Evaluation environment: 30 ° C, relative humidity 65%
[Image quality evaluation: bleeding resistance]
In each ink set, each solid image was recorded adjacent to each other using cyan ink and magenta ink, and the occurrence of bleeding in the adjacent portion of each solid image was visually observed, and bleeding resistance was evaluated according to the following criteria.

1: No bleeding at the adjacent part 2: Slight bleeding at the adjacent part 3: Bleeding at the adjacent part 4: Severe bleeding at the adjacent part [Durability evaluation]
A solid image was created for each color of each ink set, and durability was evaluated according to the following criteria. The cloth used was Bencott (Asahi Kasei Co., Ltd.).

1: A dry cloth, a cloth soaked in water, a mixture of water / alcohol = 1/1 cannot take an image. 2: An image cannot be taken with a dry cloth, a cloth soaked in water, but water / alcohol = 1. The image can be taken with the mixture of 1: 3. The image cannot be taken even if wiped with a dry cloth, but the image can be taken slightly with the cloth soaked with water. 4: The image cannot be taken even if wiped with a dry cloth. Images can be taken with a cloth soaked in water.
After continuously producing 10 solid images (A4 size), the images were created again at intervals of 60 minutes. The obtained image quality was visually observed, and the emissivity was evaluated according to the following criteria.

1: No image defect is seen including the image writing part 2: There is no image defect, but a slight blur is seen in the image writing part (several mm) 3: Although there is almost no image defect, Splashes are observed around the dots. 4: Image defects are observed.

[Evaluation of dryness]
After each color solid image was created in the same manner as in the above durability evaluation, heating was continued at 50 ° C. from the bottom of the recording medium, and the solid image portion formed with a cotton swab was rubbed every 30 seconds until the swab no longer colored. Time was measured and dryness was evaluated according to the following criteria.

1: Less than 3 minutes until the cotton swabs are not colored 2: Time until the cotton swabs are not colored 3 minutes or more and less than 4 minutes 3: Time until the cotton swabs are not colored 4 minutes or more, Table 2 shows the evaluation results of the bleeding resistance, durability, emission property and drying property obtained by less than 5 minutes or more.

  As is apparent from the results shown in Table 2, the ink set composed of the ink having the configuration defined in the present invention is superior in bleeding resistance, durability, emission property and drying property to the comparative example. I understand.

Claims (4)

1% by mass or more of a water-soluble copolymer obtained by neutralizing and dissolving a copolymer obtained by polymerizing a pigment, water, a lactic acid ester compound, a surfactant, and an unsaturated vinyl monomer having a carboxyl group with an amine. A water-based inkjet ink comprising 10% by mass or less. The aqueous inkjet ink according to claim 1, further comprising a pyrrolidone compound. 3. The water-soluble organic solvent according to claim 1, wherein glycol ethers or 1,2-alkanediols are contained in an amount of 2.0% by mass or more and 20% by mass or less based on the total mass of the ink. Water-based inkjet ink. The water-based inkjet ink according to any one of claims 1 to 3, comprising water-based dispersed polymer fine particles.