JP2017155246A - Inkjet ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet ink which exhibits excellent print image quality even with a hardly absorbing substrate such as coated paper, art paper and lightweight coated paper, can provide printed matter excellent in fastness, and is excellent in the discharge stability from an inkjet nozzle and the drying property in printing.SOLUTION: The inkjet ink contains at least water, a pigment, an organic solvent, and a binder resin. The organic solvent includes an organic solvent with surface tension of at least 20-30 mN/m. The binder resin is a water-soluble resin not being a pigment-dispersing resin. The molecular weight distribution width, which is represented by the ratio (Mw/Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), of the binder resin is from 1.0 to 2.5.SELECTED DRAWING: None

Description

  The present invention can provide a printed matter having excellent print image quality and excellent durability even when using a hardly absorbent substrate such as coated paper, art paper, or fine coated paper, and from an inkjet nozzle. The present invention relates to an inkjet ink that is excellent in ejection stability and drying properties during printing.

  Unlike conventional plate-type printing such as offset printing, digital printing does not require a plate, so that cost reduction and space saving can be realized. In particular, the ink jet recording method is a method for obtaining characters and images by directly ejecting and adhering ink droplets from a very fine nozzle to a recording member, and has only the advantages that the noise of the apparatus is small and the operability is good. In addition, it has the advantages of being easily colored and being able to use a paper substrate as a recording member, and is therefore widely used as an output device in offices and homes.

  In addition, due to improvements in inkjet technology, it is expected to be used as an output device for digital printing in industrial applications. In fact, devices for printing solvent inks and UV inks on plastic substrates such as PVC and PET are commercially available. Yes. On the other hand, in recent years, restrictions on the use of solvents and monomers have been promoted from the viewpoint of environmental and human hazards, and demand for water-based inks has increased instead.

  As water-based inks for inkjet, as described in Patent Documents 1 to 3, special paper such as plain paper and photographic glossy paper has been developed for a long time. On the other hand, in recent years, the application of the ink jet recording method is expected to be expanded, and the need for direct printing on hardly absorbable substrates such as art paper, coated paper, and fine coated paper is increasing. Since conventional ink performs drawing by absorbing liquid droplets on paper, if the ink is printed on a substrate having low water absorption, the image is blurred and cannot be used.

  Various studies have been made so far for the purpose of improving the image quality of hardly absorbable substrates. For example, in Patent Document 4, by using an ink using an alkylene polyol having a boiling point in a specific range and polymer particles, density unevenness on a hardly absorbable substrate is reduced, and a printed matter excellent in image quality can be obtained. It is disclosed. However, when polymer particles are used as the binder resin, there is a problem that the ink tends to solidify in the vicinity of the inkjet nozzle when the ink is kept in the inkjet head for a long period of time, and it is difficult to maintain excellent ejection stability. Met. Also, when the above ink is printed on a hard-to-absorb substrate, polymer particles are deposited before the ink that has landed on the substrate dries before the ink is sufficiently wetted and spread, resulting in There was also a problem that omissions occurred.

  In addition, Patent Document 5 improves printing image quality and coating film resistance on a hardly absorbent substrate by using an ink containing a water-soluble resin having a weight average molecular weight (Mw) in a specific range and a surfactant. Examples have been disclosed. However, among the above water-soluble resins, those having a large Mw (high molecular weight) cause a significant increase in viscosity when the liquid component in the ink is volatilized. There has been a problem that it may lead to delays or non-ejection.

  Further, Patent Document 6 discloses that it is possible to achieve both print image quality and ejection stability on a hardly absorbent substrate by using an ink in combination with a pigment dispersant having a specific structure, silicone oil, and an organic solvent. However, since the organic solvent used has a high boiling point, it is difficult to sufficiently dry in a short time on a hardly absorbent substrate, and it is difficult to obtain desired film resistance. It was.

JP 2001-354888 A JP 2004-210996 A JP 2008-247951 A JP 2012-251049 A Japanese Patent No. 5720679 JP2013-203910A

  The present invention has been made to solve the above-mentioned problems, and its purpose is to have excellent print image quality even when using a hardly absorbent substrate such as coated paper, art paper or fine coated paper, In addition, an object of the present invention is to provide an ink-jet ink that can obtain a printed matter having excellent durability and that is excellent in ejection stability from an ink-jet nozzle and in drying properties during printing.

  The inventors of the present invention have made extensive studies to solve the above problems, and found that an organic solvent having a surface tension of 20 to 30 mN / m and a water-soluble binder resin having a molecular weight distribution in a specific range are used. The present invention has been completed.

That is, the present invention is an inkjet ink containing at least water, a pigment, an organic solvent, and a binder resin,
The organic solvent includes at least an organic solvent having a surface tension of 20 to 30 mN / m,
The binder resin is a water-soluble resin, and the molecular weight distribution represented by the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the binder resin is 1.0-2. The present invention relates to an inkjet ink characterized by being 5.

  The present invention also relates to the inkjet ink as described above, wherein the organic solvent contains 0 to 15 wt% of an organic solvent having a boiling point of 230 to 400 ° C. with respect to the total amount of the inkjet ink.

  The present invention also relates to the inkjet ink as described above, wherein the organic solvent contains 0 to 5% by weight of an organic solvent having a boiling point of 270 to 400 ° C. based on the total amount of the inkjet ink.

  The present invention also relates to the ink-jet ink as described above, wherein the binder resin contains at least a styrene (meth) acrylic copolymer.

  The present invention also relates to the ink-jet ink as described above, wherein the binder resin has a glass transition temperature (Tg) of 30 to 110 ° C.

  The present invention also relates to the ink-jet ink as described above, wherein the binder resin has a weight average molecular weight (Mw) of 5,000 to 20,000.

  The present invention also relates to the ink-jet ink as described above, wherein the binder resin has an acid value of 5 to 60.

  The present invention also relates to the ink-jet ink as described above, wherein the binder resin has at least an alkyl chain having 8 to 30 carbon atoms.

  The present invention also relates to the inkjet ink as described above, wherein the content of the organic solvent having a surface tension of 20 to 30 mN / m is 0.5 to 10% by weight based on the total amount of the inkjet ink.

  According to the present invention, it is possible to obtain a printed matter having excellent print image quality and excellent durability even when using a hardly absorbent base material such as coated paper, art paper or fine coated paper, and from an inkjet nozzle. It has become possible to provide ink-jet inks that are excellent in ejection stability and drying properties during printing.

  In the following, preferred embodiments will be described to describe the ink-jet ink of the present invention (hereinafter also simply referred to as “ink”).

  The present invention uses an organic solvent having a surface tension of 20 to 30 mN / m and a water-soluble binder resin having a molecular weight distribution in a specific range, so that excellent printability can be obtained even on a hardly absorbent substrate. It is possible to secure the ejection stability from the inkjet nozzle, and to make the inkjet ink excellent in the drying property and durability of the coated film after printing.

  In general, difficult-to-absorbable substrates such as coated paper, art paper, and finely coated paper have a small surface energy of the substrate itself, and it is not easy to sufficiently wet the ink. If the wetting and spreading are insufficient, the ink filling in the printing portion is also insufficient, and image defects such as white spots occur. In addition, since the above-mentioned base material hardly absorbs ink, the drying property of the solvent in the ink is poor compared to when printing on fine paper, etc., and the solvent remains on the base material for a long time, so that the ink is fluid. , The dots are connected to each other, and mottling occurs (uneven density in the printed portion), and a clear image cannot be obtained. As described above, when printing on a hardly absorbent substrate, it is necessary to sufficiently ensure the wettability and drying property of the ink.

  In particular, water, which is the main component of the water-based ink, has a very high surface tension compared to other solvents and adversely affects wettability. In order to make up for the above problems, a water-soluble organic solvent is generally used in combination with a water-based ink. Since the water-soluble organic solvent has a lower surface tension than water, it is indispensable for improving the wettability on the hardly absorbent substrate. Further, by using a water-soluble organic solvent having a high hydrophobicity and a small surface tension, it is possible to promote the penetration into the hardly absorbable substrate, and it is possible to improve the drying property and improve the mottling. As a result, it is possible to suppress white spots and mottling even on a difficult-to-absorb base material and to obtain a printed matter with excellent print image quality.

  On the other hand, in water-based inks, it is common to use a binder resin in combination in order to impart sufficient coating film resistance to the printed matter, and it is known that a higher molecular weight binder resin has better resistance after printing. . Binder resins used in water-based inks are roughly classified into water-soluble resins and water-dispersible resin fine particles. In general, the water-dispersible resin fine particles having a molecular weight larger than that of the water-soluble resin can be used, and since they are present in the ink in a dispersed state, the blending amount can be increased as compared with the case of the water-soluble resin. There are features. However, when used together with a water-soluble organic solvent having a high hydrophobicity and a low surface tension, there arises a problem that resin fine particles are dissolved in the organic solvent. In particular, at the gas-liquid interface such as the end face of the ink jet nozzle, water is volatilized and the hydrophobic solvent is concentrated, so that the dissolution of the resin fine particles is promoted. Further, the hydrophobic solvent volatilizes with drying, so that the resin component is deposited and formed into a film and the ink is solidified. In the case of resin fine particles, once the film is formed, it is not redissolved in the ink, so that the ejectability is impaired by the fixed resin component, and it cannot be restored unless powerful head cleaning or the like is performed. Further, in the process of drying the ink on the hard-to-absorb substrate, the film is lost before the ink is sufficiently wetted and spread on the substrate, so that the fluidity is lost, and white spots or the like are likely to occur in the printed portion.

  In order to solve the above problems, it is necessary to improve the moisture retention of the ink by using a combination of water-dispersible resin fine particles and a high boiling point organic solvent. However, the organic solvent having a high boiling point tends to remain on the hardly absorbent base material, and mottling occurs as in the case where only water is used. Moreover, the drying property of the coating film after printing is reduced, leading to peeling of the coating film when touched or deterioration of resistance.

  On the other hand, when a water-soluble resin is used as the binder resin, unlike the water-dispersible resin fine particles, the resin itself is soluble, so when used with a water-soluble organic solvent having a high hydrophobicity and a low surface tension, Even after water is volatilized at the gas-liquid interface, the resin component does not immediately deposit or form a film. However, thickening of the ink occurs, and if such thickening occurs on the end face of the inkjet nozzle, it also leads to problems such as ejection delay. In particular, as the molecular weight of the resin increases, in the process where the solvent in the ink dries on the hard-to-absorb substrate, the ink loses its fluidity by thickening before it spreads out sufficiently and the image quality deteriorates such as white spots. May be incurred. Further, as described above, there are problems that the molecular weight of the resin that can be used and the blending amount in the ink are small as compared with the water-dispersible resin fine particles, and the effect of improving the coating film resistance is poor.

  The present inventors can obtain a printed matter having excellent print image quality and excellent durability even when using a hardly absorbent substrate such as coated paper, art paper, or fine coated paper, and an inkjet nozzle. As a result of intensive investigations to make an inkjet ink excellent in the discharge stability from printing and the drying property at the time of printing, it contains at least an organic solvent having a surface tension of 20 to 30 mN / m, and serves as a binder resin with respect to the number average molecular weight (Mn). By using a water-soluble binder resin having a molecular weight distribution range represented by a weight average molecular weight (Mw) ratio (Mw / Mn) of 1.0 to 2.5, an inkjet ink satisfying the above quality can be obtained. As a result, the present invention was reached.

  As described above, since the surface energy of the base material itself is low, the base material itself has a low surface tension, so that the wettability on the base material that is hard to absorb is reduced by using an organic solvent having a small surface tension of 20 to 30 mN / m. It is possible to ensure and obtain an image quality with less white spots. In addition, the area of the dots after landing on the base material is increased by spreading sufficiently, which can lead to improved drying by penetration and volatilization, resulting in less dot mottling and less mottling. It is thought that image quality can be obtained.

  In addition to the above, a water-soluble binder resin having a molecular weight distribution range of 1.0 to 2.5 represented by a ratio (Mw / Mn) of a weight average molecular weight (Mw) to a number average molecular weight (Mn) as a binder resin. It has been found that a printed material having superior discharge stability, printed image quality and coating film resistance can be obtained by using. By using a water-soluble resin with a small molecular weight distribution width and a small amount of polymer, it is possible to suppress thickening of the ink at the gas-liquid interface even when used in combination with a water-soluble organic solvent having high hydrophobicity and low surface tension. Conceivable. This not only improves discharge delay and improves discharge stability, but also makes it possible for the ink to maintain fluidity and improve wettability even when the solvent is volatilized and to make uniform dots during printing. It is considered that it is possible to obtain a printed matter having excellent print image quality without white spots. Furthermore, it is considered that a printed matter having a sufficient film resistance can be obtained by using a water-soluble binder resin having a molecular weight distribution width in a suitable range, that is, having a low molecular weight.

  As described above, in order to obtain an ink having both ejection stability, printed image quality and coating film resistance, a combination of a water-soluble organic solvent having a small surface tension and a water-soluble binder resin having a suitable molecular weight distribution range Is essential. In addition, said mechanism is inference and does not limit this invention at all.

  The main components of this embodiment will be described below.

<Organic solvent>
As described above, the organic solvent used in the present embodiment is not only improved in wettability with respect to a substrate such as a poorly permeable substrate, but also in improving the drying property of the ink, as well as ensuring dischargeability from an inkjet nozzle, etc. Selected from the perspective.

  From the viewpoint of having excellent wettability even on a poorly permeable substrate and suppressing the bleeding between dots to obtain a print quality with less mottling, at least one of the organic solvents used in the present invention is The organic solvent must have a surface tension of 20 to 30 mN / m.

  The surface tension in the present embodiment refers to the surface tension measured by the Wilhelmy method (plate method, vertical plate method) in an environment of 25 ° C. The surface tension of the organic solvent used in the present embodiment is more preferably 22 mN / m to 30 mN / m, and still more preferably 24 mN / m to 30 mN / m.

  Further, in the present invention, an organic solvent having a surface tension of 20 to 30 mN / m is obtained in that an ink-jet ink having excellent printability on a hardly-absorbable substrate and further having drying property and ejection stability can be obtained. Among these, it is more preferable to use a water-soluble organic solvent having a boiling point lower than 230 ° C, and it is particularly preferable to use a water-soluble organic solvent having a temperature of 150 to 225 ° C. In addition, the said surface tension can be measured by a platinum plate method in 25 degreeC environment, for example using a surface tension meter (CBVP-Z by Kyowa Interface Science Co., Ltd.). In the present invention, the “boiling point” represents a boiling point under 1 atm, and can be measured using, for example, a thermal analyzer.

  Any organic solvent having a surface tension of 20 mN / m or more and 30 mN / m or less can be used alone or in combination. For example, 1,2-pentanediol, 1,2-hexanediol, ethylene glycol-2-ethylhexyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol mono Butyl ether, tripropylene glycol monomethyl ether, diethylene glycol methyl butyl ether, triethylene glycol methyl butyl ether, tripropylene glycol dimethyl ether, triethylene glycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monopropyl ether, diethylene glycol Rumonopentyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, 3-methoxy-1-butanol, 3-methoxy-3-methylbutanol, diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, Examples include, but are not limited to, diethylene glycol methyl ethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol methyl ethyl ether, tetraethylene glycol butyl methyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, and propylene glycol dimethyl ether. Of the organic solvents exemplified above, a glycol ether solvent having a boiling point of 230 ° C. or lower and an alkanediol type or having 3 or more carbon atoms in the terminal carbon chain is preferably used. Among them, an alkanediol solvent having a boiling point of 150 to 225 ° C. is more preferable, and 1,2-hexanediol is more preferable.

  The content of the organic solvent having a surface tension of 20 mN / m or more and 30 mN / m or less used in the present invention is the total weight of the ink-jet ink from the viewpoint of achieving both the printing image quality on the hardly absorbent substrate and the discharge stability. It is preferable to set it to 0.1 weight% or more and 20 weight% or less. More preferably, they are 0.5 weight% or more and 15 weight% or less, More preferably, they are 5 weight% or more and 10 weight% or less.

  In the inkjet ink of the present invention, an organic solvent having a high boiling point can be used as long as the content is in a range that does not impair the drying property and print image quality. As a high boiling point organic solvent used in the present invention, it has sufficient drying property even on a hardly absorbent substrate, and from the viewpoint of obtaining a clear print image quality with less mottling by suppressing dot bleeding. The organic solvent having a boiling point of 230 to 400 ° C. is preferably contained in an amount of 0 to 15% by weight, more preferably 0 to 10% by weight, based on the total amount of the inkjet ink. In the present invention, “0 wt%” means that the target organic solvent is not included.

  Furthermore, it is preferable to contain 0 to 5% by weight of an organic solvent having a boiling point of 270 to 400 ° C. with respect to the total amount of the ink-jet ink from the viewpoint of obtaining a suitable coating film resistance in addition to drying properties and printing image quality. More preferably, it is 0 to 2.5% by weight, and particularly preferably 0 to 1% by weight.

  Specific examples of the organic solvent having a boiling point of 230 to 400 ° C. that can be used in the present invention include glycerin, diethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 3 -Methyl-1,5-pentanediol, 1,6-hexanediol, triethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, 2-pyrrolidone, N-methyloxazolidinone, ε-caprolactone, and the like. It is not something. Of the organic solvents exemplified above, specific examples of organic solvents having a boiling point of 270 to 400 ° C. include glycerin and tetraethylene glycol dimethyl ether.

  In addition, if it is in the range which does not impair the effect of this invention, organic solvents other than the above can be used individually or in combination. Specifically, it is preferable to include an organic solvent having a boiling point of less than 230 ° C, and it is particularly preferable to include an organic solvent having a boiling point of less than 200 ° C. Examples of the preferable organic solvent include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, and diethylene glycol. Examples include, but are not limited to, monomethyl ether, diethylene glycol monoethyl ether, and γ-butyrolactone. Among these, it is preferable to use 1,2-alkanediols such as 1,2-propanediol and 1,2-butanediol from the viewpoint of ensuring excellent drying properties even on a hardly absorbent substrate. .

  The total amount of the organic solvent used in the present embodiment is preferably 5 to 40% by weight based on the total amount of the inkjet ink. Among these, from the viewpoint of ensuring sufficient wettability and drying properties even on a poorly permeable substrate and obtaining excellent image quality, it is more preferably 10 to 35% by weight or less as the total amount of blending. .

<Binder resin>
The binder resin used in the present invention has excellent wettability even on a difficult-to-absorbent substrate, and from the viewpoint that stable ejection properties can be secured from an inkjet nozzle even when a highly hydrophobic organic solvent is used. The water-soluble resin must have a molecular weight distribution range of 1.0 to 2.5 expressed by the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the resin. The Mw / Mn of the resin is particularly preferably 1.0 to 2.0 from the viewpoint that the wettability on the hardly absorbent substrate and the discharge stability in the inkjet head can be further improved. By setting Mw / Mn of the resin to 2.5 or less, when ink is allowed to stand by for a long time in the inkjet head, ink thickening at the nozzle end face is suppressed, and problems such as ejection delay and non-ejection are prevented. Can do. Further, the ink can be sufficiently wetted and spread in the process of volatilization of the ink on the hardly absorbent substrate, and a printed matter with excellent print image quality can be obtained. Moreover, the tolerance of printed matter becomes favorable by setting it as 1.0 or more.

  In the present invention, the “water-soluble resin” means that the resin has a solubility of 10% or more in water at room temperature (25 ° C.), that is, the resin and water form a uniform system.

  The weight average molecular weight (Mw) of the binder resin used in the present invention ensures stable discharge from an inkjet nozzle, has excellent wettability even on a hardly absorbent substrate, and on a hardly absorbent substrate. Even if it exists, it is preferable that it is 3000-30000 from a viewpoint of obtaining the outstanding coating-film resistance, and it is more preferable that it is 5000-25000. Particularly preferably, it is 10,000 to 20,000. By setting the weight average molecular weight (Mw) to 30000 or less, it is possible to suppress ink thickening when water in the ink volatilizes at the end face of the ink jet nozzle, and by setting the weight average molecular weight to 3000 or more, the printed matter has good resistance. Become.

  The weight average molecular weight of the binder resin in the present embodiment can be measured by a conventional method. For example, using TSKgel column (manufactured by Tosoh Corporation), GPC equipped with RI detector (manufactured by Tosoh Corporation, HLC-8120GPC), a value measured as a weight average molecular weight in terms of polystyrene measured using THF as a developing solvent. It is.

  Examples of the water-soluble binder resin used in the present invention include acrylic, styrene (meth) acrylic, urethane, styrene butadiene, vinyl chloride, and polyolefin. It is particularly preferable to use a binder resin of a styrene (meth) acrylic copolymer from the viewpoint of ensuring stable ejection from an inkjet nozzle.

  When a styrene (meth) acrylic copolymer is used as the binder resin, the binder resin is used from the viewpoint of suppressing the thickening of the ink when the water content of the ink volatilizes at the end face of the ink jet nozzle and ensuring stable ejection properties. It is preferable to have an alkyl chain having 8 to 30 carbon atoms in the structure. In addition, from the viewpoint of further improving discharge stability, the alkyl chain preferably has 10 to 28 carbon atoms, and more preferably 15 to 25 carbon atoms.

  The alkyl chain having 8 to 30 carbon atoms may be linear or branched, but is preferably linear. Specifically, 2-ethylhexyl group (C8), octyl group (C8), decyl group (C10), lauryl group (C12), myristyl group (C14), cetyl group (C16), stearyl group (C18), aralkyl Examples thereof include a group (C20), a behenyl group (C22), a lignoceryl group (C24), a serotoyl group (C26), a montanyl group (C28), and a merisyl group (C30).

  In general, copolymers are classified into random copolymers, alternating copolymers, block copolymers, graft copolymers, and the like depending on the arrangement of the constituent monomers. The binder resin of the present invention may be in any of the above forms, but is preferably a block copolymer or a graft copolymer from the viewpoint of sufficiently exhibiting the characteristics of the constituent monomers. In addition, each unit which forms a block copolymer and a graft copolymer may be formed from a single monomer, or may be a random copolymer of a plurality of monomers. Moreover, said binder resin can also synthesize | combine by a well-known method, and can also use a commercial item.

  In the present embodiment, by increasing the glass transition temperature (Tg) of the binder resin, it is possible to further improve resistance such as abrasion resistance and chemical resistance, and the temperature is set in the range of 30 to 110 ° C. Preferably, it is the range of 50-100 degreeC more preferably. When the glass transition temperature is 50 ° C. or higher, it is easy to obtain better resistance, and it is possible to suppress the peeling of printing from the printed matter even in practical use. Moreover, generation | occurrence | production of the crack of a printed surface at the time of bending printed matter as glass transition point temperature is 100 degrees C or less can be suppressed.

  In addition, the glass transition temperature of this embodiment is the value calculated | required using DSC (differential scanning calorimeter). Specifically, after weighing about 2 mg of a sample obtained by drying the binder resin on an aluminum pan, the test vessel is set on a DSC measurement holder, and the endothermic peak of the chart obtained under a temperature rising condition of 5 ° C./min. Let temperature be the glass transition temperature in this specification.

  The acid value of the binder resin used in the present embodiment is preferably 1 to 100 mgKOH / g and more preferably 5 to 60 mgKOH / g from the viewpoint of improving resistance such as water resistance and chemical resistance. .

  The content of the binder resin of the present embodiment in the ink composition is preferably in the range of 0.5% to 15% by weight of the total weight of the ink in terms of non-volatile content, preferably 3% to 10% by weight. More preferably.

<Pigment>
As the pigment used in the present invention, either an inorganic pigment or an organic pigment can be used. These pigments may be used alone or in combination of two or more. The pigment content is 0.1% to 20% by weight, preferably 1% to 10% by weight, more preferably 2% to 7% by weight, based on the total weight of the ink.

  When using inorganic pigments as pigments, titanium oxide, zinc white, zinc sulfide, white lead, calcium carbonate, precipitated barium sulfate, white carbon, alumina white, kaolin clay, talc, bentonite, black iron oxide, cadmium red, red rose , Molybdenum red, molybdate orange, chrome vermilion, yellow lead, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, viridian, titanium cobalt green, cobalt green, cobalt chrome green, Victoria green, ultramarine blue, bitumen, cobalt blue , Cerulean blue, cobalt silica blue, cobalt zinc silica blue, manganese violet, cobalt violet and the like.

  Examples of organic pigments include azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, isoindolinone pigments, quinophthalone pigments, dye lake pigments, and fluorescent pigments.

  Specific examples of the color index include C. I. Pigment Blue 1, 2, 3, 15: 1, 15: 3, 15: 4, 15: 6, 16, 21, 22, 60, 64 as cyan pigments. Etc.

  As the magenta pigment, CI Pigment Red 5, 7, 9, 12, 31, 48, 49, 52, 53, 57, 97, 112, 120, 122, 146, 147, 149, 150, 168, 170 , 177, 178, 179, 184, 188, 202, 206, 207, 209, 238, 242, 254, 255, 264, 269, 282, C. I. Pigment Violet 19, 23, 29, 30, 32, 36 , 37, 38, 40, 50 and the like.

  As the yellow pigment, CI Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120 , 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, 213 and the like.

Examples of the black pigment include carbon black produced by a furnace method or a channel method. Among these, these carbon blacks have a primary particle size of 11 to 40 nm, a specific surface area of 50 to 400 m ² / g according to the BET method, a volatile content of 0.5 to 10%, a pH value of 2 to 10 and the like. Those having the following are preferred. Examples of commercially available products having such characteristics include No. 33, 40, 45, 52, 900, 2200B, 2300, MA7, mA8, MCF88 (manufactured by Mitsubishi Chemical), RAVEN 1255 (manufactured by Columbian Carbon), REGA330R, 400R, 660R, MOGUL L, ELFTEX 415 (above, manufactured by Cabot), Nipex90, Nipex150T, Nipex160IQ, Nipex170IQ, Nipex75, Printex35, Printex85, Printex95, Printex90, etc. be able to.

  In addition to carbon black, examples of the black pigment that can be used in the present invention include aniline black, lumogen black, and azomethine azo black. Further, a plurality of chromatic pigments such as the above-mentioned cyan pigments, magenta pigments, yellow pigments, and the following brown pigments and orange pigments may be used to form black pigments.

  Pigments other than the above include CI Pigment Green 7, 10, 36, CI Pigment Brown 3, 5, 25, 26, CI Pigment Orange 2, 5, 7, 13, 14, 15 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71 and the like.

<Pigment dispersion resin>
In order to maintain the stability of the ink for a long period of time, the above pigment is used by being dispersed in the ink. As a method for dispersing the pigment, there are a method in which the pigment is surface-modified by oxidation treatment, resin coating, or the like, and the pigment is dispersed without a dispersant, or a method in which a surfactant or a resin is used as the dispersant. In order to obtain a more stable ink, it is preferable to use a dispersant to disperse the pigment, and it is particularly preferable to use a resin (hereinafter referred to as a pigment dispersion resin) as the dispersant.

  Examples of the pigment dispersion resin include acrylic, styrene (meth) acrylic, maleic acid, styrene maleic acid, α-olefin maleic acid, urethane, and ester. Among these, it is preferable to use an acrylic resin and / or a styrene (meth) acrylic resin from the viewpoint of strengthening the pigment adsorption and stabilizing the pigment dispersion.

  The weight average molecular weight of the pigment-dispersed resin is preferably 5,000 to 100,000. When the weight average molecular weight is 5000 or more, the dispersion stability can be improved, and when the weight average molecular weight is 100000 or less, the discharge stability can be improved. More preferably, the weight average molecular weight is 10,000 to 50,000, and even more preferably 15,000 to 30,000. In addition, the weight average molecular weight of pigment dispersion resin can be measured similarly to the case of said binder resin.

  The ratio of the pigment to the pigment dispersion resin is preferably 1/1 to 100/1. By setting the ratio of the pigment dispersion resin to 1/1 or more, the viscosity of the ink can be suppressed to be suitable as an inkjet ink, and by setting it to 100/1 or less, dispersibility and stability after dispersion can be improved. It can be good. The ratio of the pigment and the pigment dispersion resin is more preferably 2/1 to 50/1, and further preferably 3/1 to 20/1.

<Surfactant>
The water-based inkjet ink of the present embodiment is sometimes described as a surfactant (hereinafter simply referred to as “active agent”) for the purpose of adjusting surface tension and ensuring wettability on a substrate, particularly a hardly absorbent substrate. ) Can be used. A variety of surfactants are known for acetylene-based, silicon-based, acrylic-based, fluorine-based and other applications, but from the viewpoint of ensuring excellent wettability by sufficiently reducing the surface tension of the ink. It is preferable to use at least an acetylene surfactant and / or a silicon surfactant. As an example of the addition amount of the surfactant, 0.1 to 5% by weight is preferable and 0.2 to 4% by weight is more preferable with respect to the total weight of the ink.

<Water>
As water contained in the ink-jet magenta ink of the present invention, it is preferable to use ion-exchanged water (deionized water) instead of general water containing various ions.

  The content of water that can be used in the present invention is preferably in the range of 20 to 90% by weight of the total weight of the ink.

<Other ingredients>
In addition to the above components, the ink of the present embodiment can be appropriately added with additives such as an antifoaming agent and an antiseptic agent in order to obtain an ink having a desired physical property value as necessary. . The addition amount of these additives is preferably 0.01% by weight or more and 10% by weight or less based on the total weight of the ink.

<Ink set>
The ink of the present invention may be used in a single color, but can also be used as an ink set in which a plurality of colors are combined according to the application. The combination is not particularly limited, but a full color image can be obtained by using three colors of cyan, yellow, and magenta. Moreover, black feeling can be improved by adding black ink, and the visibility of a character etc. can be raised. Furthermore, color reproducibility can be improved by adding colors such as orange and green. When printing on a print medium other than white, a clear image can be obtained by using white ink together.

<Ink preparation method>
Examples of the method for preparing the ink of the present embodiment composed of the components described above include the following methods, but the method for preparing the ink of the present embodiment is not limited thereto.

  First, a pigment is added to an aqueous medium (hereinafter sometimes referred to as “aqueous solution”) in which at least a pigment dispersant (for example, a pigment dispersion resin) and water are mixed, and mixed and stirred (premixed). Thereafter, a dispersion process is performed using a dispersion means described later, and a centrifugal dispersion process is performed as necessary to obtain a pigment dispersion. Next, a binder resin, an organic solvent (preferably a water-soluble organic solvent) and additive components as mentioned above are appropriately added to the pigment dispersion as necessary, followed by stirring, and if necessary, filtration. And it can be set as the ink of this embodiment.

  In the above ink preparation method, it is effective to perform premixing before the dispersion treatment. The premixing operation is preferable because it improves wettability of the pigment surface and promotes adsorption of the dispersant to the pigment surface.

  Further, the disperser used for the pigment dispersion treatment may be any commonly used disperser, and examples thereof include a ball mill, a roll mill, a sand mill, a bead mill, and a nanomizer. Among them, a bead mill is preferably used. . Examples of the bead mill include a super mill, a sand grinder, an agitator mill, a glen mill, a dyno mill, a pearl mill, and a cobol mill (all are trade names).

  Since the ink of the present embodiment is for inkjet recording, it is preferable to use an ink having an optimum particle size distribution as a pigment from the request of nozzle clogging resistance and the like. As a method for obtaining a pigment having a desired particle size distribution, a method of reducing the size of the grinding media of the disperser as mentioned above, a method of increasing the filling rate of the grinding media, a method of increasing the processing time, and after grinding Examples include a method of classifying with a filter, a centrifuge, etc., and a combination of these methods. The particle size distribution of the ink can be measured using, for example, Microtrack UPA150 manufactured by Nikkiso Co., Ltd.

<Recording medium>
The ink of this embodiment can be particularly suitably used for a hardly absorbent substrate. The hardly absorbent substrate is a recording medium that hardly absorbs water or has a slow absorption rate, and specifically, measured by the Bristow method (J.TAPPI paper pulp test method No. 51-87). The water absorption coefficient is 0 to 0.6 ml / m ² msec ^1/2 . The above absorption coefficient can be measured, for example, by using an automatic scanning liquid absorption meter manufactured by Kumagai Riki Kogyo Co., Ltd. Specifically, the relationship between the water absorption amount (ml / m ² ) and the square root of contact time (msec ^1/2 ) obtained using the above device and water for a contact time of 100 to 1000 milliseconds. Therefore, the slope of the straight line obtained by the least square method is taken as the absorption coefficient.

  Specific examples of difficult-to-absorbent substrates include paper substrates such as coated paper, art paper, cast paper, finely coated paper, and synthetic paper; polycarbonate, hard vinyl chloride, soft vinyl chloride, polystyrene, foamed polystyrene, PMMA, polypropylene Examples include, but are not limited to, plastic substrates such as polyethylene and PET; metal substrates such as aluminum and stainless steel; and glass. In addition, the inkjet ink of this embodiment can be used suitably also for things other than a hardly absorptive base materials, such as plain paper, a fabric, and wood.

<Printing method>
The ink-jet ink of this embodiment is used in a printing method in which ink is ejected from the nozzles of an ink-jet head and ink droplets are deposited on a printing substrate.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In the following description, “parts” and “%” represent “parts by weight” and “% by weight”, respectively, unless otherwise specified.

<Example of production of binder resin 1>
A reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer was charged with 93.4 parts of butanol and replaced with nitrogen gas. The inside of the reaction vessel was heated to 110 ° C., 5 parts of acrylic acid as a polymerizable monomer, 80 parts of methyl methacrylate, 15 parts of 2-ethylhexyl acrylate, and V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator. ) 6 parts of the mixture was added dropwise over 2 hours to carry out the polymerization reaction. After the completion of the dropwise addition, the mixture was further reacted at 110 ° C. for 3 hours, and then 0.6 part of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the reaction was further continued at 110 ° C. for 1 hour, whereby Got. After cooling the binder resin 1 solution to room temperature, 7.1 parts of dimethylaminoethanol was added and neutralized, and then 100 parts of water was added to make it aqueous. Thereafter, the mixture is heated to 100 ° C. or higher, butanol is azeotroped with water to distill off butanol, and the solid content is adjusted to 40%, so that the water-soluble binder resin 1 is a random polymer. An aqueous solution with a solid content of 40% was obtained.

<Examples of production of binder resins 2-17>
40% solid content of water-soluble binder resins 2-17, which are random polymers, by the same operation as binder resin 1 except that the monomers listed in Table 1 are used as the polymerizable monomers. A solution was obtained.

<Example of production of binder resin 18>
Using the method described in International Publication No. 2008/139980, Example 21, a binder resin 18 as an AB block polymer was produced. Specifically, in the polymerization of the first block, methacrylic acid was used as a polymerizable monomer, reacted at 80 ° C. for 2 hours, and reprecipitated to obtain a first block copolymer to which iodine was added. The weight average molecular weight (Mw) of the first block copolymer was 6000.
Next, styrene, methyl methacrylate and lauryl methacrylate are used as a polymerizable monomer in a weight ratio of 15:65:15, and reacted at 80 ° C. for 2.5 hours for reprecipitation. Thereby, the binder resin 18 which is AB block copolymer by which the iodine addition site | part of the said 1st block was substituted by the 2nd block which consists of styrene, methyl methacrylate, and lauryl methacrylate was obtained. The binder resin 18 had a weight average molecular weight (Mw) of 18000.
The binder resin 18 obtained above is mixed and stirred with 1.5 times the weight of water and completely dissolved, whereby an aqueous solution of the binder resin 18 (solid content 40) which is an AB block polymer. %).

<Example of production of binder resin 19>
A reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, and a refluxing vessel was charged with 40 parts of ion exchange water and 0.2 part of Aqualon KH-10 (Daiichi Kogyo Seiyaku) as an emulsifier. Meanwhile, 15 parts of 2-ethylhexyl acrylate, 69 parts of methyl methacrylate, 1 part of acrylic acid, 15 parts of styrene, 53 parts of ion-exchanged water and 1.8 parts of Aqualon KH-10 (Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier, Separately stirred and mixed with a homomixer to obtain an emulsion.

  Five portions of the emulsion were taken and added to the reaction vessel. After the addition, the internal temperature was raised to 60 ° C. and the atmosphere was sufficiently substituted with nitrogen. Then, 3 parts of a 5% aqueous solution of potassium persulfate and 4 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added to initiate polymerization. After the start of the reaction, while maintaining the internal temperature at 60 ° C., the rest of the emulsion, 2 parts of a 5% aqueous solution of potassium persulfate, and 6 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added dropwise over 1.5 hours. Stirring was continued for another 2 hours. After completion of the reaction, the temperature was cooled to 30 ° C., and diethylaminoethanol was added to adjust the pH to 8.5. Furthermore, by adjusting the solid content to 40% with ion-exchanged water, an aqueous solution (40% solid content) of binder resin 19 which is water-dispersible resin fine particles was obtained.

In addition, the abbreviation described in Table 1 is as follows.
St: styrene AA: acrylic acid MAA: methacrylic acid MMA: methyl methacrylate BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate LMA: lauryl methacrylate SSMA: stearyl methacrylate VA: behenyl acrylate

<Production example of pigment dispersion>
As a pigment, C.I. I. 20 parts of Pigment Blue 15: 3, 10 parts of a 50% solids aqueous solution of styrene acrylic resin (molecular weight: 25000, acid value: 200) as a pigment dispersion resin, and 70 parts of water were mixed and predispersed with a disper. Thereafter, this dispersion was performed using a 0.6 L dyno mill filled with 1800 g of zirconia beads having a diameter of 0.5 mm to obtain a pigment dispersion.

<Example of production of ink of Example 1>
20 parts of the pigment dispersion, 15 parts of the aqueous solution of binder resin 1, 10 parts of diethylene glycol monobutyl ether, and 0.5 parts of Surfynol 440 (Acetylenediol surfactant made by Air Products) are sequentially added to the mixing container. After that, water was added to adjust the ink to 100 parts, and the mixture was stirred with a disper until it was sufficiently uniform. Thereafter, the ink was filtered with a membrane filter having a pore diameter of 1 μm to remove coarse particles that cause clogging of the head, and ink of Example 1 was prepared.

<Examples for producing inks of Examples 2-38 and Comparative Examples 1-4>
Using the raw materials shown in Table 2, inks of Examples 2-38 and Comparative Examples 1-4 were prepared in the same manner as in the ink production example of Example 1.

Abbreviations described in Table 2 are as follows.
MB: 3-methoxybutanol (boiling point: 157 ° C., surface tension: 29.3 mN / m)
1,2-PenD: 1,2-pentanediol (boiling point: 206 ° C., surface tension: 27.7 mN / m)
1,2-HexD: 1,2-hexanediol (boiling point: 224 ° C., surface tension: 26.4 mN / m)
BDG: Diethylene glycol monobutyl ether (boiling point: 231 ° C., surface tension: 27.9 ° C.)
1,2-PD: 1,2-propanediol (boiling point: 188 ° C., surface tension: 35.1 mN / m)
EG: ethylene glycol (boiling point: 198 ° C., surface tension: 47.1 mN / m)
1,2-BD: 1,2-butanediol (boiling point: 191 ° C., surface tension: 31.6 mN / m)
1,5-PenD: 1,5-pentanediol (boiling point: 242 ° C., surface tension: 42.2 mN / m)
DMTeG: Tetraethylene glycol dimethyl ether (boiling point: 275 ° C., surface tension: 33.3 mN / m)
Glycerin (boiling point: 290 ° C, surface tension: 62.0 mN / m)
Activator: Surfynol 440 (produced by Air Products, acetylenic diol surfactant)

<Examples 1-38, Comparative Examples 1-4: Evaluation of Ink>
The following evaluation was performed about the created ink. The obtained evaluation results are shown in Table 2.

<Evaluation 1: Initial ejection property>
Each ink was filled in an ink jet discharge apparatus equipped with a head (QA06NTB) manufactured by Kyocera Corporation. After printing a nozzle check pattern and confirming that ink is ejected normally from all nozzles, the ink is left for 1 minute, and then solid printing is performed with a printing rate of 100% under a printing condition of a frequency of 30 kHz and 600 × 600 dpi. It was. At that time, the initial discharge property was evaluated by confirming visually and with a loupe whether or not a 100% solid start portion was printed. The evaluation criteria are as follows, and AA, A, and B evaluations are practical areas. In addition, OK top coat + (coated paper) manufactured by Oji Paper Co., Ltd. was used as a printing substrate.
AA: Even when confirmed visually and with a magnifying glass, there was no chipping at the beginning of the shot, and the first shot appeared. A: No chipping was observed with visual observation, but a slight chipping was observed when confirmed with a loupe. B: Slight chipping was observed visually. C: Chipping was clearly observed at the beginning of hitting, and the first shot was not generated.

<Evaluation 2: Intermittent discharge>
Solid printing with a printing rate of 100% was performed using the same printing conditions and printing substrate as in Evaluation 1. After printing, the inkjet discharge device was kept on standby for a certain period of time in an environment of 25 ° C., and then a nozzle check pattern was printed, and the intermittent discharge property was evaluated by visually confirming whether nozzle missing occurred. The evaluation criteria are as follows, and AA, A, and B evaluations are practical areas.
AA: No nozzle missing even after printing after waiting for 3 hours A: No nozzle missing even after printing after waiting for 2 hours, but nozzle missing occurs after printing after waiting for 3 hours B: No nozzle missing even after printing after waiting for 1 hour, but nozzle missing occurred when printing after waiting for 2 hours C: Nozzle missing 1-9 when printing after waiting for 1 hour D was generated D: No more than 10 nozzles were missing when printing after waiting for 1 hour

<Evaluation 3: Solid filling>
Solid printing with a printing rate of 100% was performed using the same printing conditions and printing substrate as in Evaluation 1. After printing, the printed material was dried for 1 minute using a 70 ° C. air oven, and then the solid filling was evaluated by confirming the degree of whiteout of the printed material with eyes and a loupe. The evaluation criteria are as follows, and AA, A, and B evaluations are practical areas.
AA: No white spots were observed with the naked eye and with the loupe A: White spots were slightly seen with the loupe, but no white spots were visually observed B: Slight white spots were visually observed C : Clear white spots were observed visually

<Evaluation 4: Evaluation of Mottling>
Solid printing with a printing rate of 100% was performed using the same printing conditions and printing substrate as in Evaluation 1. After printing, the printed matter was dried for 1 minute using a 70 ° C. air oven, and the degree of mottling of the printed matter was confirmed visually and with a magnifier to evaluate the mottling. The evaluation criteria are as follows, and AA, A, and B evaluations are practical areas.
AA: Mottling did not occur, and density unevenness of the printed matter was not observed visually and with a magnifying glass. A: Density unevenness was slightly observed with the loupe, but density irregularity was not visually observed. B: Mottling was observed. Slightly generated and slight density unevenness was observed visually. C: Mottling was clearly generated, and density unevenness was also visually observed.

<Evaluation 5: Evaluation of paper dryness>
Solid printing with a printing rate of 100% was performed using the same printing conditions and printing substrate as in Evaluation 1. After printing, the sheet was left in an air oven at 70 ° C., taken out at regular intervals, and the printed material was touched to evaluate the paper surface drying property. The evaluation criteria are as follows, and AA, A, and B evaluations are practical areas.
AA: Even when touched with a drying time of 30 seconds, there was no tackiness and the coating was dry. A: Touching with a drying time of 1 minute had no tackiness and the coating was dry. It was not dry at 30 seconds B: There was no tackiness even when touched with a dry time of 1 minute 30 seconds, and the coating film was dry, but it was not dry at 1 minute C: There was a feeling of tack even when touched with a dry time of 1 minute 30 seconds, and the coating film was not dry

<Evaluation 6: Evaluation of coating film resistance>
Solid printing with a printing rate of 100% was performed using the same printing conditions and printing substrate as in Evaluation 1. After printing, use a 70 ° C air oven to dry the printed material for 1 minute, then rub the printed material with a cotton swab soaked with 50% aqueous ethanol and check the number of rubbing until the ink comes off and the substrate is visible. Then, the coating film resistance was evaluated. The evaluation criteria are as follows, and AA, A, and B evaluations are practical areas.
AA: The number of rubbing until the base was visible was 20 or more A: The number of rubbing until the base was visible was 15 to 19 B: The number of rubbing until the base was visible was 11 to 14 C: The number of rubbing until the base was visible was 10 or less

  The ink-jet ink of the present invention has excellent print image quality even when using a hardly absorbent substrate such as coated paper, art paper or fine coated paper, and is capable of obtaining a printed matter having excellent durability. In particular, it can be suitably used in high-speed, high-resolution inkjet printing for commercial printing using the substrate.

Claims (9)

An ink-jet ink containing at least water, a pigment, an organic solvent, and a binder resin,
The organic solvent includes at least an organic solvent having a surface tension of 20 to 30 mN / m,
The binder resin is a water-soluble resin, and the molecular weight distribution represented by the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the binder resin is 1.0-2. An inkjet ink characterized by being 5.   The inkjet ink according to claim 1, wherein the organic solvent contains 0 to 15 wt% of an organic solvent having a boiling point of 230 to 400C with respect to the total amount of the inkjet ink.   3. The inkjet ink according to claim 1, wherein the organic solvent contains 0 to 5 wt% of an organic solvent having a boiling point of 270 to 400 ° C. with respect to the total amount of the inkjet ink.   The inkjet ink according to claim 1, wherein the binder resin contains at least a styrene (meth) acrylic copolymer.   The inkjet ink according to any one of claims 1 to 4, wherein a glass transition temperature (Tg) of the binder resin is 30 to 110 ° C.   The ink-jet ink according to any one of claims 1 to 5, wherein the binder resin has a weight average molecular weight (Mw) of 5000 to 20000.   The inkjet ink according to any one of claims 1 to 6, wherein an acid value of the binder resin is 5 to 60 mgKOH / g.   The inkjet ink according to any one of claims 1 to 7, wherein the binder resin has at least an alkyl chain having 8 to 30 carbon atoms.   The inkjet ink according to any one of claims 1 to 8, wherein the content of the organic solvent having a surface tension of 20 to 30 mN / m is 0.5 to 10 wt% with respect to the total amount of the inkjet ink. .