JP6934554B1 - Black inkjet ink and ink set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a black inkjet ink having a high print density regardless of the type of a recording medium and a drying method, excellent in scratch resistance of a printed matter, and excellent in inkjet ejection stability, and further for improving the image quality of the printed matter. To provide an ink set containing the black inkjet ink, which is also excellent. A black inkjet ink containing water, a pigment, an organic solvent, and a wax, wherein the pigment contains a self-dispersing pigment and a resin-dispersed pigment, and the content of the organic solvent is the total amount of the ink. The amount of black inkjet ink, which is 29% by mass or less, and the amount of the black inkjet ink and an organic solvent having a boiling point of 250 to 300 ° C. at 1 atm is 5% by mass or less, cyan inkjet ink, magenta inkjet. An ink set containing ink and yellow inkjet ink. [Selection diagram] None

Description

The present invention relates to a black inkjet ink and an ink set containing the black inkjet ink.

The inkjet printing method is a method in which minute droplets of ink are ejected onto a recording medium from a very fine nozzle in an inkjet head and landed to form an image or a character (hereinafter, an image and / or a character). Recording media on which characters are recorded are collectively referred to as "printed matter"). The inkjet printing method is superior to other printing methods in terms of the size and cost of the printing apparatus, the running cost at the time of printing, the ease of full-color printing, and the like, and is widely used. Further, with the remarkable improvement in the performance of the inkjet head in recent years, it is expected that the inkjet printing method will be developed in the industrial printing market where the offset printing method has been conventionally used.

In the industrial printing market, in addition to high-absorbency recording media such as high-quality paper, plain paper, and copy paper, it is required to be able to print on low-absorbency recording media such as coated paper and art paper.

Simply printing on the above-mentioned recording medium causes, for example, the inkjet ink to permeate inside the high-absorbency recording medium and reduce the print density, or the inkjet ink droplets on the low-absorbency recording medium are combined with each other. Problems such as deterioration of image quality occur. Therefore, in general, after printing the inkjet ink, the action of drying the inkjet ink on the recording medium is taken. At that time, from the viewpoint of downsizing of the printing apparatus and speeding up of printing, an infrared drying method and a hot air drying method are often used as the drying method. Therefore, in order to promote the spread and development of the inkjet printing method, it is required to provide an inkjet ink suitable for any of these drying methods.

As described above, in general, when printing is performed on a high-absorbency recording medium by an inkjet printing method, there arises a problem that the inkjet ink permeates the inside of the high-absorbency recording medium and the print density is lowered. In order to solve this problem, for example, Patent Document 1 proposes an inkjet ink using a self-dispersing pigment. Further, for example, Patent Documents 2 to 3 disclose an inkjet ink in which a self-dispersing pigment and a pigment dispersed using a pigment-dispersed resin (resin-dispersed pigment) are used in combination.

However, as a result of verification by the present inventor, it has been found that these inkjet inks can reduce the density of the obtained printed matter depending on the recording medium used and the drying method after printing. For example, the inkjet ink described in Patent Document 1 is inferior in print density when printed on a low absorption recording medium, and the inkjet ink described in Patent Documents 2 to 3 is printed on a low absorption recording medium and dried by infrared rays. When the method was used, there was a problem that sufficient print density was not obtained.

The inkjet ink described in Patent Document 2 has a problem that the printed matter printed on a low-absorption recording medium is inferior in scratchability, and the inkjet ink described in Patent Document 3 has poor ejection stability from an inkjet head. , There is a further problem.

Japanese Unexamined Patent Publication No. 2001-89688 Japanese Unexamined Patent Publication No. 2015-183027 JP-A-2018-172502

The present invention has been made to solve the above-mentioned problems, and an object thereof is to obtain high print density regardless of the type of recording medium and a drying method, scratch resistance of printed matter, and ink jet ejection stability. Is also to provide excellent black inkjet inks. Another object of the present invention is to provide an ink set containing the black inkjet ink, which is excellent in image quality of printed matter in addition to the above.

As a result of diligent studies by the present inventors in order to solve the above-mentioned problems, the following black inkjet inks have been found.

That is, the present invention is a black inkjet ink containing water, a pigment, an organic solvent, and a wax.
The pigment contains a self-dispersing pigment and a resin-dispersed pigment.
The present invention relates to a black inkjet ink in which the content of the organic solvent is 29% by mass or less based on the total amount of the black inkjet ink.

The present invention also relates to the black inkjet ink having a P value defined by the following general formula (1) of 1.6 or less.

In (Formula (1), i, the black represents the type of the organic solvent contained in the inkjet ink. Further, b _i represents the boiling point (℃) at 1 atmosphere of an organic solvent i, c _i Represents the content (mass%) of the organic solvent i with respect to the total amount of the black inkjet ink, s _i represents the static surface tension (mN / m) of the organic solvent i at 25 ° C., and n represents the content. Indicates the number of types of organic solvents to be used.)

The present invention also relates to the black inkjet ink, wherein the wax contains a polyolefin wax.

Further, the present invention further contains resin particles as a binder resin.
The black inkjet containing one or more resin particles selected from the group consisting of acrylic resin particles, styrene acrylic resin particles, urethane resin particles, styrene butadiene resin particles, and vinyl chloride resin particles. Regarding ink.

The present invention further relates to the above-mentioned black inkjet ink, which further contains a water-soluble resin as a binder resin.

The present invention also comprises a surfactant.
The present invention relates to the above-mentioned black inkjet ink, wherein the surfactant contains a surfactant having an HLB value of 10 or less.

The present invention also relates to the black inkjet ink in which the content of the organic solvent having a boiling point of 250 to 300 ° C. under 1 atm is 9% by mass or less in the total amount of the black inkjet ink.

The present invention is an ink set containing black inkjet ink, cyan inkjet ink, magenta inkjet ink, and yellow inkjet ink.
The black inkjet ink is the black inkjet ink.
The cyan inkjet ink, magenta inkjet ink, and yellow inkjet ink each contain water, a pigment, and an organic solvent, and the amount of the organic solvent having a boiling point of 250 to 300 ° C. under 1 atm is 5% by mass. % Or less, related to ink sets.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a black inkjet ink having a high print density regardless of the type of recording medium and a drying method, and having excellent scratch resistance and inkjet ejection stability of printed matter. Further, in addition to the above, it has become possible to provide an ink set containing the above-mentioned black inkjet ink, which is excellent in image quality of printed matter.

Hereinafter, the black inkjet ink of the present invention (hereinafter, also simply referred to as “ink”) will be described with reference to preferred embodiments. In addition, in this specification, a "aqueous medium" means a medium composed of a liquid containing at least water.

First, the black inkjet ink of the present invention will be described. The black inkjet ink of the present invention contains water, a self-dispersing pigment, a resin-dispersed pigment, an organic solvent, and a wax.

As described above, in general, in order to increase the print density on a highly absorbent recording medium such as high-quality paper or plain paper, a method such as increasing the pigment density in the ink or using a self-dispersing pigment is adopted. However, when the pigment concentration is increased, there may be a problem that the ejection stability from the inkjet head is deteriorated. Further, when a self-dispersing pigment is used, a desired print density cannot be obtained because the wettability spreads poorly on a low-absorbency recording medium such as coated paper. For example, when the self-dispersing pigment is used in combination with an organic solvent and / or a surfactant in order to improve the wettability of the low-absorption recording medium, the dispersion of the self-dispersing pigment may be broken and the ejection stability may be deteriorated. There is sex.

On the other hand, a pigment (resin-dispersed pigment) dispersed in an ink using a pigment-dispersed resin has excellent stability against the above-mentioned organic solvent and surfactant, and is suitable for improving the print density on a low-absorption recording medium. It can be said that it is a material. However, by using the pigment-dispersed resin, the viscosity of the microscopic ink becomes large, which may adversely affect the ejection stability. Further, although the detailed reason is unknown, the ink containing only the resin dispersion pigment has a problem that the print density is inferior to that of the high-absorbency recording medium.

On the other hand, it is considered that by using the self-dispersion pigment and the resin dispersion pigment in combination, both the print density for the high absorption recording medium and the print density for the low absorption recording medium can be achieved at the same time. However, since the use of the above-mentioned organic solvent and / or surfactant is indispensable for improving the print density on the low-absorption recording medium, the adverse effect on the dispersion of the self-dispersing pigment contained in the ink remains. It will remain. In addition, there is a concern that the pigment-dispersed resin may have an adverse effect on discharge stability as described above. Further, as a result of the study by the present inventors, it was found that the printing density of the ink containing the self-dispersing pigment and the resin-dispersed pigment greatly changes depending on the drying method after printing. For example, in the cases of Patent Documents 2 and 3, as described above, such a change was remarkable when a self-dispersing carbon black pigment was used as the self-dispersing pigment and printed on a low-absorption recording medium.

As described above, as the drying method of the inkjet printing method, a method of directly or indirectly contacting the ink with a heat source (heat drying method, hot air drying method, drum drying method, etc.) and a method of irradiating electromagnetic waves (infrared rays). It is known as a drying method, a microwave drying method, an ultraviolet drying method, etc.). In the case of the former drying method, the print density tends to increase in proportion to the pigment density blended in the ink. On the other hand, in the latter drying method, components such as pigments contained in the ink absorb electromagnetic waves and generate heat, so that the aqueous medium (water and organic solvent) volatilizes from the inside of the ink. At that time, it is considered that the surface of the ink layer after drying is roughened due to a rapid temperature change locally, and a desired print density cannot be obtained. Although the details are not clear, carbon black absorbs electromagnetic waves of various wavelengths, and especially in the case of self-dispersing pigments, there is no resin around the pigments, and absorption of the electromagnetic waves and heat generation due to the absorption are likely to occur. Therefore, it is presumed that the print density is likely to decrease.

It is considered that the roughness of the surface of the ink layer described above also affects the deterioration of the scratch resistance of the printed matter.

As a result of diligent studies to solve the above problems, that is, the decrease in print density due to the recording medium type and the drying method, the ejection stability from the inkjet head, and the scratch resistance of the printed matter, the self-dispersing pigment and the resin dispersion We have found an ink in which a pigment, an organic solvent, and a wax are used in combination, and the content of the organic solvent is 29% by mass or less in the total amount of the ink. Although it is speculative, the mechanism will be explained below.

As described above, in order to improve the print density on both the high absorption recording medium and the low absorption recording medium, the combined use of the self-dispersion pigment and the resin dispersion pigment is indispensable. Further, in order to secure the print density for the low absorption recording medium, the ink needs to contain an organic solvent. However, if the ink contains an excessive amount of organic solvent, the dispersion of the self-dispersing pigment may be broken. In general, the specific heat of the organic solvent used in the ink is smaller than the specific heat of water. Therefore, if the amount of the organic solvent in the ink is too large, the heat source is used in a method of directly or indirectly contacting the ink with the heat source. When the temperature of the ink is high, or when the method of irradiating the ink with electromagnetic waves is adopted, a sudden temperature change is likely to occur, which may cause a decrease in print density and deterioration of scratch resistance of the printed matter. There is. From the above, in the present invention, by setting the amount of the organic solvent to 29% by mass or less in the total amount of the ink, a high printing density is maintained regardless of the drying method, the dispersion stability of the self-dispersing pigment is enhanced, and the inkjet ejection stability is improved. Furthermore, the scratch resistance of the printed matter is improved.

The ink of the present invention also contains wax. It is generally known that adding wax to an inkjet ink improves the scratch resistance of printed matter. However, the present inventors have found that not only the scratch resistance of the printed matter but also the print density and the inkjet ejection stability are improved.

As described above, when the self-dispersed pigment and the resin-dispersed pigment coexist, the print density may decrease depending on the drying method selected. On the other hand, it is considered that by further adding wax, the wax melts without being decomposed or volatilized during drying and remains so as to cover the surface of the print layer, so that a printed matter having a high print density can be obtained. Be done. Although the detailed mechanism is unknown, the presence of wax around the self-dispersing pigment prevents the organic solvent from interfering with the self-dispersing pigment, and the wax existing around the resin-dispersed pigment makes the pigment. It is considered that the inkjet ejection stability is improved by inhibiting the network that can be formed between the dispersed resin molecules and suppressing the microscopic increase in the viscosity of the ink.

As described above, in order to solve all the problems of the present invention at the same time, it can be said that the composition of the ink of the present application is indispensable.

Subsequently, each component constituting the ink of the present invention will be described in detail below.

<Autocovariant pigment>
In the present specification, the self-dispersing pigment is a pigment that can be dispersed in an aqueous medium without using a dispersant such as a pigment-dispersing resin or a surfactant for pigment dispersion, and is self-dispersing. It is the pigment that has been surface-treated to impart properties. As the self-dispersing pigment, a single type or a plurality of types may be used in combination.

Conventionally known achromatic pigments and / or chromatic pigments can be used as the pigments constituting the self-dispersing pigments, and it is preferable to use an achromatic pigment, and it is particularly preferable to use a black pigment. In the present specification, "achromatic color" refers to a color having no hue and saturation and is represented only by lightness, and "chromatic color" refers to a color other than achromatic color. Further, in the present invention, as the black pigment, for example, black organic pigments such as aniline black, perylene black and azo black, and black inorganic pigments such as carbon black, triiron tetroxide and copper chromium black can be used. .. In the present invention, it is preferable to use carbon black from the viewpoints of high blackness and colorability, obtaining a printed matter having a high printing density even with a small amount of addition, and easy availability.

The carbon black used in the self-dispersing pigment is not particularly limited, and examples are described below, but the carbon black is not limited thereto. For example, there are furnace black, lamp black, acetylene black, channel black and the like as classifications according to the manufacturing method, and any of them can be used. Further, as a classification based on the molecular structure, there are amorphous carbon, graphite, carbon nanotubes and the like, and any of them can be used.

As an example of self-dispersing carbon black, on the surface of carbon black, at least one functional group selected from carboxyl group, carbonyl group, hydroxyl group, sulfone group, phosphoric acid group, phenyl group, quaternary ammonium and salts thereof. However, those introduced by chemical bonding directly or via other functional groups can be mentioned. The type and amount of the functional group are appropriately determined in consideration of the dispersion stability, print density, ejection stability, drying property, etc. of the self-dispersed carbon black in the ink.

Above all, it is preferable to have an anionic functional group as the functional group in that a printed matter having a particularly high print density can be obtained. Examples of the anionic functional group include a carboxyl group, a carbonyl group, a hydroxyl group, a sulfone group, a phosphoric acid group, and a functional group selected from salts thereof. Above all, it is preferable that the functional group contains a carboxyl group, a carbonyl group, and a hydroxyl group.

Examples of the method for surface-treating the pigment include a physical treatment method using a vacuum plasma or the like, a chemical treatment method using a diazoalkyl compound (N = N-RX), and a radical reaction using a phenol compound. Examples thereof include a chemical treatment method according to the above method, a functional group, and a chemical treatment method by a graft reaction using a functional group or a molecule containing a functional group. Specifically, Japanese Patent Application Laid-Open No. 8-3498, Japanese Patent Application Laid-Open No. 2003-96372, Japanese Patent Application Laid-Open No. 2000-513396, Japanese Patent Application Laid-Open No. 2008-524400, Japanese Patent Application Laid-Open No. 2009-515007, Japanese Patent Application Laid-Open No. 2011-515535 It can be obtained by the method described in Japanese Patent Application Laid-Open No. 2018-70815 and the like.

A commercially available product may be used as the self-dispersing pigment. Examples of the commercially available products include CAB-O-JET series manufactured by Cabot Corporation, BONJET series manufactured by Orient Chemical Industries Co., Ltd., Aqua-Black series manufactured by Tokai Carbon Co., Ltd., and Fuji-JET Black series manufactured by Fuji Dye Co., Ltd. Can be mentioned.

The average secondary particle size of the self-dispersing pigment is, for example, preferably 30 nm to 200 nm, more preferably 50 nm to 170 nm, and particularly preferably 80 nm to 150 nm. The average secondary particle size (D50) is measured by a dynamic light scattering method using a particle size distribution measuring machine (in the present specification, Nanotrack UPAEX-150 manufactured by Microtrack Bell Co., Ltd. is used). Represents a volume-based median diameter.

The self-dispersing pigment is preferably contained in an amount of 0.5 to 10% by mass, more preferably 1 to 8% by mass, and particularly preferably 2 to 7% by mass in the total amount of the ink.

<Resin dispersion pigment>
The resin-dispersed pigment is a pigment in which at least a part of the surface is coated with a pigment-dispersed resin so that it can be dispersed in an aqueous medium. Unlike the self-dispersing pigment described above, the pigment constituting the resin-dispersed pigment requires a pigment-dispersed resin as a dispersant for dispersing the pigment.

The example of the pigment constituting the resin-dispersed pigment is the same as that of the self-dispersed pigment. Among them, carbon black is used because it has high blackness and colorability, and a printed matter having a high print density can be obtained on both a high absorption recording medium and a low absorption recording medium, and it is easy to obtain. Is preferable. Specifically, for example, the primary particle size of carbon black is preferably 11 to 40 nm, more preferably 11 to 30 nm. BET specific surface area 50 to 400 m ² / g are preferred, 90~360m ² / g is more preferable. The volatile content is preferably 0.5 to 10% by weight.

When carbon black is used as the pigment, it is preferable to use a slurry having a pH value of 2 to 10, and it is particularly preferable to use acidic carbon or neutral carbon.

Here, the acidic carbon is carbon black showing an acidic pH value (for example, a pH value of 2 or more and less than 6), and an acidic group such as a carboxyl group is present on the surface thereof. It is similar to the above-mentioned self-dispersed carbon black in that it has a functional group on the surface. Generally, although acidic carbon shows a certain degree of hydrophilicity, it can be dispersed alone in an aqueous medium without using a dispersant. Can not.

Further, the neutral carbon is carbon black showing a neutral pH value (for example, a pH value of 6 or more and 8 or less), and is generally not subjected to an oxidation treatment like acidic carbon.

The pigment constituting the resin dispersion pigment may be the same as or different from the pigment used as the self-dispersion pigment. Further, as in the case of the self-dispersion pigment, the pigment constituting the resin dispersion pigment may be a single substance or a mixture.

<Pigment dispersion resin>
The type of the pigment-dispersed resin used for the resin-dispersed pigment is not particularly limited, and for example, (meth) acrylic resin, styrene (meth) acrylic resin, (anhydrous) maleic acid-based resin, and styrene (anhydrous) maleic acid-based resin. , Olefin (anhydrous) maleic acid-based resin, urethane-based resin, polyester-based resin (for example, a polycondensate of polyvalent carboxylic acid and polyhydric alcohol) and the like can be used, but the present invention is not limited thereto. Among them, from the group consisting of (meth) acrylic resin, styrene (meth) acrylic resin, urethane resin, and polyester resin in terms of discharge stability, large material selectivity, ease of synthesis, etc. It is preferable to use one or more selected. Further, from the viewpoint of improving the dispersion stability and ejection stability of the ink, when a binder resin described later is used, it is preferable to use a resin of the same type as the binder resin as the pigment dispersion resin.

In the present specification, "(meth) acrylic resin" means an acrylic resin, a methacrylic resin, or an acrylic-methacrylic resin. Here, the "acrylic-methacrylic resin" means a resin using acrylic acid and / or acrylic acid ester and methacrylic acid and / or methacrylic acid ester as a polymerizable monomer. Further, "(maleic) maleic acid" means maleic anhydride or maleic acid.

The pigment-dispersed resin described above can be synthesized by a known method or a commercially available product can be used. Further, the structure is not particularly limited, and for example, a resin having a random structure, a block structure, a comb-shaped structure, a star-shaped structure, or the like can be used. Further, as the pigment dispersion resin, a water-soluble resin may be selected, or a water-insoluble resin may be selected. In the present specification, the "water-soluble resin" refers to a resin in which the 25 ° C., 1% by mass water mixture of the target resin is transparent to the naked eye, and the "water-insoluble resin" is the same. Other than that, that is, the target pigment-dispersed resin in which the 25 ° C., 1% by mass water mixture is not transparent to the naked eye.

In the present invention, when a water-soluble resin is used as the pigment dispersion resin, its acid value is preferably more than 100 mgKOH / g and 450 mgKOH / g or less, and more preferably 120 to 400 mgKOH / g. Particularly preferably, it is 150 to 350 mgKOH / g. By setting the acid value within the above range, it is possible to maintain the dispersion stability of the pigment, and it is possible to stably eject the pigment from the inkjet head. Further, it is preferable from the viewpoint that the solubility of the pigment-dispersed resin in water can be ensured and the viscosity of the pigment-dispersed liquid can be suppressed by making the interaction between the pigment-dispersed resins suitable.

On the other hand, when a water-insoluble resin is used as the pigment dispersion resin, its acid value is preferably 0 to 100 mgKOH / g, more preferably 5 to 90 mgKOH / g, and preferably 10 to 80 mgKOH / g. More preferred. When the acid value is within the above range, a printed matter having excellent drying property and scratch resistance can be obtained.

The acid value of the resin can be measured by a known device. The acid value of the resin in the present specification is a value measured by a potentiometric titration method according to JIS K 2501. As an example of a specific measurement method, AT-610 manufactured by Kyoto Denshi Kogyo Co., Ltd. is used, the resin is dissolved in a mixed solvent of toluene-ethanol, titrated with a potassium hydroxide solution, and the acid value is determined from the titration to the end point. There is a method of calculating.

In the pigment-dispersed resin used for the resin-dispersed pigment of the present invention, it is preferable to introduce an aromatic group into the pigment-dispersed resin from the viewpoint of improving the adsorption ability to the pigment and ensuring the dispersion stability. In particular, in the present invention, when carbon black is used as the pigment, the surface of the carbon black interacts with the aromatic ring structure contained in the pigment-dispersed resin, so that the ability of the pigment-dispersed resin to be adsorbed on the carbon black is increased. Significantly improved. As a result, it is possible to secure the dispersion stability and the ejection stability of the ink for a long period of time. Examples of the aromatic group include, but are not limited to, a phenyl group, a naphthyl group, an anthryl group, a tolyl group, a xsilyl group, a mesitylene group, an anisyl group and the like. Of these, a phenyl group, a naphthyl group and a tolyl group are preferable from the viewpoint of ensuring sufficient dispersion stability.

From the viewpoint of achieving both dispersion stability, ejection stability, print quality, and dryness of the resin-dispersed pigment, the amount of the monomer containing an aromatic ring introduced into the resin is 5 to 75 with respect to the total amount of the pigment-dispersed resin. It is preferably 5% by mass, more preferably 5 to 65% by mass, and even more preferably 10 to 50% by mass.

Further, in addition to the aromatic group, it is particularly preferable to introduce an alkyl group having 8 to 36 carbon atoms into the pigment dispersion resin. This is because the dispersion stability of the ink containing the resin-dispersed pigment, the scratch resistance of the printed matter, and the ejection stability can be improved by setting the number of carbon atoms of the alkyl group to 8 to 36. The number of carbon atoms of the alkyl group is more preferably 10 to 30, and even more preferably 12 to 24 carbon atoms. Further, the alkyl group can be either linear or branched as long as it has 8 to 36 carbon atoms, but a linear group is preferable. As linear alkyl groups, octyl group (C8), lauryl group (C12), myristyl group (C14), cetyl group (C16), stearyl group (C18), araquil group (C20), behenyl group (C22), Lignoceryl group (C24), cellotoyl group (C26), montanyl group (C28), melissyl group (C30), dotria-contanyl group (C32), tetratria-contanyl group (C34), hexatria-contanyl group (C36) And so on.

The amount of the monomer containing an alkyl chain having 8 to 36 carbon atoms introduced into the resin is 5 with respect to the total amount of the pigment dispersion resin from the viewpoint of achieving both low viscosity of the pigment dispersion and scratch resistance of the printed matter. It is preferably ~ 60% by mass, more preferably 10 to 55% by mass, and particularly preferably 15 to 50% by mass.

When a water-soluble resin is used as the pigment-dispersed resin, it is preferable that the acid groups in the resin are neutralized with a base in order to increase the solubility in the ink. Whether or not the amount of the base added is excessive can be confirmed, for example, by preparing a 10% by mass aqueous solution of the pigment-dispersed resin and measuring the pH of the aqueous solution. From the viewpoint of improving the dispersion stability and ejection stability of the ink containing the resin dispersion pigment, the pH of the aqueous solution is preferably 7 to 11, and more preferably 7.5 to 10.5.

Examples of the base for neutralizing the pigment-dispersed resin include organic amine-based solvents such as triethylamine, monoethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, dimethylaminoethanol, diethylaminoethanol, and aminomethylpropanol, and aqueous ammonia. Alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide, alkali metal carbonates such as lithium carbonate, sodium carbonate, sodium hydrogencarbonate and potassium carbonate can be mentioned, but are limited to these. Not done.

When a water-soluble resin is used as the pigment dispersion resin, its weight average molecular weight is preferably in the range of 1,000 to 50,000, more preferably in the range of 5,000 to 40,000, 10. It is more preferably in the range of 000 to 35,000, and particularly preferably in the range of 15,000 to 30,000. When the weight average molecular weight is in the above range, the pigment is stably dispersed in water, and it is easy to adjust the viscosity when used in ink. When the weight average molecular weight is 1,000 or more, the pigment-dispersed resin is difficult to dissolve in the organic solvent added to the ink, so that the adsorption of the pigment-dispersed resin to the pigment is strengthened, and the dispersion stability and dispersion stability are improved. Discharge stability is improved. When the weight average molecular weight is 50,000 or less, the viscosity at the time of dispersion is suppressed to a low level, the dispersion stability of the ink and the ejection stability from the inkjet head are improved, and stable printing over a long period of time becomes possible.

The weight average molecular weight of the resin in the present invention is a polystyrene-equivalent value that can be measured by, for example, a method according to JIS K 7252. As an example of a specific measurement method, there is a method of measuring using a TSKgel column manufactured by Tosoh Corporation and an HLC-8120GPC manufactured by Tosoh Corporation equipped with an RI detector, and using THF as a developing solvent.

The blending amount of the pigment-dispersed resin is preferably 1 to 100% by mass with respect to the blending amount of the pigment (also referred to as “resin dispersion pigment” in the present specification) constituting the resin-dispersed pigment. By setting the blending amount of the pigment dispersion resin within the above range, the viscosity of the pigment dispersion liquid is suppressed, and the dispersion stability and ejection stability of the ink are improved. The blending amount of the pigment-dispersed resin with respect to the resin-dispersing pigment is more preferably 2 to 50% by mass, and particularly preferably 4 to 45% by mass.

In general, since a part of the pigment-dispersed resin is released in the ink, a part of the pigment-dispersed resin may be adsorbed on the surface of the self-dispersed pigment. In the present invention, a small amount of the liberated pigment-dispersed resin may be adsorbed on a part of the surface of the self-dispersed pigment. However, if a large amount of the pigment-dispersed resin is adsorbed, its characteristics are the same as those of the resin-dispersed pigment. From the above, the adsorption rate of the pigment-dispersed resin with respect to the self-dispersed pigment is preferably 50% by mass or less (however, it may be 0% by mass). Further, when the ink is produced by a method of mixing the dispersion liquid of the resin dispersion pigment and the dispersion liquid of the self-dispersion pigment, the amount of the free pigment dispersion resin contained in the dispersion liquid of the resin dispersion pigment is the amount of the self-dispersion pigment. It is preferable that the amount is 50% by mass or less (however, it may be 0% by mass) with respect to the amount of the self-dispersing pigment contained in the dispersion liquid of.

As the pigment dispersion resin, a single type or a plurality of types may be used in combination.

<Dispersion aid>
From the viewpoint of significantly improving the dispersion stability and discharge stability of the resin dispersion pigment of the present invention, a dispersion aid may be used in combination. The dispersion aid is a material that contributes to improving the adsorption rate of the pigment-dispersed resin with respect to the pigment. In the present invention, conventionally known materials can be arbitrarily used as the dispersion aid, and in particular, a compound called a dye derivative can be preferably used. The dye derivative is a compound in which a substituent is introduced into the organic dye molecule, and the organic dye includes a monoazo dye, a disazo dye, a polyazo dye, an anthraquinone dye, an isoindolinone dye, and an isoindrin dye. , Kinaclidene pigments, quinophthalone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, slene pigments, thioindigo pigments, naphthalocyanine pigments, phthalocyanine pigments, perinone pigments, perylene pigments, benzimidazolone pigments , Metal complex dyes and the like. The above-mentioned "dye" is a general term for pigments and dyes.

When the dispersion aid is used in the present invention, the blending amount thereof is preferably 0.1 to 10% by mass, particularly preferably 0.5 to 5% by mass, based on the blending amount of the pigment. In the above range, the addition ratio of the dispersion aid to the pigment becomes sufficient, and the dispersion stability and the discharge stability are improved.

<Manufacturing of dispersion liquid of resin dispersion pigment>
The dispersion liquid of the resin dispersion pigment used in the ink of the present invention can be produced, for example, by the following method.

(1) Method for dispersion treatment using a pigment-dispersed resin which is a water-soluble resin When a water-soluble resin is used as a pigment-dispersed resin, the pigment-dispersed resin, water, and an organic solvent, if necessary, are mixed and stirred to form a pigment. Prepare a dispersed resin aqueous solution. A pigment for resin dispersion and, if necessary, a dispersion aid, additional water, and an additional organic solvent are added to the pigment-dispersed resin aqueous solution, mixed and stirred (premixed), and then dispersed using a disperser. Perform processing. Then, if necessary, centrifugation, filtration, and adjustment of the solid content are performed to obtain a dispersion liquid of the resin dispersion pigment.

(2) Method of Dispersing Using Pigment Dispersed Resin, which is a Water-Insoluble Resin In addition, when producing a dispersion liquid of a resin-dispersed pigment coated with a pigment-dispersed resin, which is a water-insoluble resin, methyl ethyl ketone or the like is used in advance. A pigment-dispersed resin solution is prepared by dissolving a pigment-dispersed resin in an organic solvent for dissolving the resin and neutralizing the pigment-dispersed resin, if necessary. A pigment for resin dispersion, water, a dispersion aid, an organic solvent, and an additional organic solvent are added to the pigment dispersion resin solution, and the mixture and stirring (premixing) are performed using a disperser. Perform distributed processing. Then, the organic solvent for dissolving the resin is distilled off by vacuum distillation, and if necessary, centrifugation, filtration, and adjustment of the solid content are performed to obtain a dispersion liquid of the resin dispersion pigment.

In the above methods (1) and (2), the disperser used for the dispersion treatment of the resin dispersion pigment may be any generally used disperser, and for example, a ball mill, a roll mill, a sand mill, or a bead mill. And nanomizers and the like. Among the above, bead mills are preferably used, and specifically, they are commercially available under trade names such as super mills, sand grinders, agitator mills, grain mills, dyno mills, pearl mills and cobol mills.

In the above methods (1) and (2), as a method of controlling the particle size distribution of the resin dispersion pigment, adjusting the size of the pulverized media used in the above-mentioned disperser, changing the material of the pulverized media, and the above. Increasing the filling rate of the crushed media, changing the shape of the stirring member (agitator), lengthening the dispersion treatment time, classifying by filtration or centrifugation after dispersion treatment, and a combination of these methods Can be mentioned. In order to keep the resin dispersion pigment within a suitable particle size distribution range, the diameter of the pulverized media of the disperser is preferably 0.1 to 3 mm. Further, as the material of the pulverized media, glass, zircon, zirconia and titania are preferably used.

(3) Method of Grinding and Kneading Using Pigment Dispersed Resin Further, in the present invention, the following method of grinding and kneading can also be preferably used. A pigment for resin dispersion, a pigment dispersion resin, an organic solvent, an inorganic salt, and, if necessary, a dispersion aid are kneaded by a kneader, and then water is added to the obtained mixture, and the mixture is mixed and stirred. Then, the inorganic salt and, if necessary, the organic solvent are removed by centrifugation, filtration, and washing, and the solid content is further adjusted to obtain a dispersion liquid of the resin dispersion pigment.

The kneader used in the above method (3) may be any disperser that is generally used, but a high-viscosity mixture can be kneaded and a pigment dispersion liquid containing fine pigments can be used to obtain image quality. A kneader or trimix is preferably used from the viewpoint of obtaining a printed matter having excellent color development and color reproducibility. By adjusting the temperature at the time of kneading, the particle size distribution of the obtained pigment dispersion can be controlled.

Further, as the inorganic salt, sodium chloride, barium chloride, potassium chloride, sodium sulfate, potassium sulfate and the like can be preferably used.

The average secondary particle size (D50) of the resin dispersion pigment is preferably 40 to 500 nm, more preferably 50 to 400 nm, and particularly preferably 60 to 300 nm. In order to keep the average secondary particle size within the above-mentioned suitable range, the pigment dispersion treatment step may be controlled as described above. The average secondary particle size (D50) of the resin-dispersed pigment can be measured by the same method as in the case of the self-dispersed pigment.

The resin-dispersed pigment of the present invention is preferably contained in an amount of 0.5 to 10% by mass, more preferably 1 to 8% by mass, and particularly preferably 2 to 7% by mass, based on the total amount of the ink.

<Pigment concentration>
The total amount of the self-dispersing pigment and the resin-dispersed pigment is preferably 5 to 15% by mass, more preferably 6 to 10% by mass, based on the total amount of the ink, in order to improve the printing density on various recording media. It is particularly preferably 7 to 9% by mass. Within the above range, in addition to the print density, the ink storage stability and ejection stability are also excellent.

The blending ratio of the self-dispersed pigment and the resin-dispersed pigment is preferably in the range of self-dispersed pigment amount: resin-dispersed pigment amount = 60:40 to 10:90 (mass ratio), preferably 50:50. It is more preferably in the range of 10:90 (mass ratio), and particularly preferably in the range of 40:60 to 20:80 (mass ratio). Within the above range, a printed matter having a high print density can be obtained regardless of the drying method.

<Organic solvent>
The black inkjet ink of the present invention contains an organic solvent in an amount of 29% by mass or less based on the total amount of the ink. The term "organic solvent" as used herein refers to an organic compound used for dissolving and / or dispersing a substance, which is a liquid at 25 ° C. and 1 atm. The "water-soluble organic solvent" refers to an organic solvent having a solubility in water of 5 g / 100 gH _{2 O or more at 25 ° C. and 1 atm.}

Generally, the organic solvent is selected from the viewpoints of permeability to a recording medium, drying property and wettability of ink, and ensuring moisturizing property. For example, the amount of the organic solvent in the ink is preferably large in consideration of the permeability to the recording medium and the dryness and wettability of the ink. However, in the case of an ink containing an organic solvent in an amount of more than 29% by mass in the total amount of the ink, the dispersion of the self-dispersing pigment may be destroyed. Further, when the self-dispersed pigment and the resin-dispersed pigment coexist in the ink as in the present invention, when the amount of the organic solvent exceeds 29% by mass in the total amount of the ink, the resin-dispersed pigment interacts with the self-dispersed pigment. , The effect of the present invention may be weakened. As a result, the inkjet ejection stability deteriorates due to the above phenomenon.

Therefore, from the viewpoint of ensuring high print density and ejection stability, the amount of the organic solvent contained in the ink of the present invention is preferably 1 to 29% by mass, preferably 5 to 27% by mass, based on the total amount of the ink. Is more preferable, and 10 to 25% by mass is particularly preferable.

Further, for example, in terms of permeability to a recording medium, by selecting an organic solvent having a suitable permeability, the ink permeates into the inside of the highly absorbent recording medium, especially in a highly absorbent recording medium. Is gone. As a result, the amount of pigment remaining on the surface increases, and the print density increases. Furthermore, by selecting an organic solvent having suitable drying properties, it is possible to prevent rapid volatilization of the organic solvent in the ink, especially in a low-absorption recording medium. As a result, unevenness does not occur on the surface of the ink layer after drying, and a decrease in print density can be prevented. In addition, by adjusting the wettability of the organic solvent used, it is possible to prevent a decrease in print density due to the occurrence of white spots, especially in a low absorption recording medium. Further, by selecting an organic solvent having high moisturizing property, it is possible to suppress the occurrence of nozzle omission, ensure ejection stability from the inkjet nozzle and high print density.

As described above, in order to obtain a printed matter having a high print density regardless of the recording medium and the drying method and an ink having excellent ejection stability, the organic solvent to be used is appropriately selected and permeated into the recording medium. It is preferable to adjust the property, the drying property and the wet spreading property of the ink, and the moisturizing property. From this point of view, in the ink of the present invention, the P value defined by the following general formula (1) is preferably 1.6 or less. Among them, the P value is more preferably 0.2 to 1.6, and particularly preferably 0.5 to 1.5.

In the general formula (1), i represents the type of organic solvent contained in the ink. Further, b _i represents the boiling point (℃) at 1 atmosphere of an organic solvent i, c _i represents the amount contained in ink total amount of the organic solvent i (wt%), s _i, the organic solvent i It represents the static surface tension (mN / m) at 25 ° C. n represents the number of types of organic solvents contained.

The boiling point under 1 atm can be measured by using a thermal analyzer such as DSC (Differential Scanning Calorimetry). The static surface tension at 25 ° C. is a value measured by the Wilhelmy method, and specifically, a value that can be measured using a platinum plate using CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

Also, high print density and from the viewpoint of achieving both the ejection stability, in the general formula (1), b _i organic solvent ÷ s _i becomes 7 or more, organic solvent total amount in less than 75% by weight contained in the ink It is preferably (may be 0% by mass), more preferably less than 50% by mass (may be 0% by mass), and particularly preferably less than 40% by mass (0% by mass). May be%).

In the above general formula (1), b _i as examples of the organic solvent ÷ s _i becomes 7 or more, e.g., 1,2-pentanediol (boiling point 206 ° C., a surface tension 27.7mN / m), 1, 2-Hexanediol (boiling point 224 ° C., surface tension 25.9 mN / m), triethylene glycol monomethyl ether (boiling point 249 ° C., surface tension 31.9 mN / m), ethylene glycol monobutyl ether (boiling point 171 ° C., surface tension 24 mN / m) m), diethylene glycol monobutyl ether (boiling point 231 ° C., surface tension 26.2 mN / m), triethylene glycol monobutyl ether (boiling point 271 ° C., surface tension 27.7 mN / m), ethylene glycol monoisobutyl ether (boiling point 161 ° C., surface tension) Tension 22.5 mN / m), diethylene glycol monoisobutyl ether (boiling point 220 ° C., surface tension 24.6 mN / m), ethylene glycol monohexyl ether (boiling point 208 ° C., surface tension 24.5 mN / m), diethylene glycol monohexyl ether (both boiling point 208 ° C., surface tension 24.5 mN / m) Boiling point 259 ° C., surface tension 26mN / m), ethylene glycol mono2-ethylhexyl ether (boiling point 229 ° C., surface tension 24.4mN / m), diethylene glycol mono2-ethylhexyl ether (boiling point 272 ° C., surface tension 25.6mN / m) ), Ethylene glycol monobenzyl ether (boiling point 256 ° C., surface tension 35.5 mN / m), diethylene glycol monobenzyl ether (boiling point 302 ° C., surface tension 36.3 mN / m), dipropylene glycol monomethyl ether (boiling point 187 ° C., surface). Tension 25.1 mN / m), dipropylene glycol monoethyl ether (boiling point 198 ° C, surface tension 27 mN / m), tripropylene glycol monomethyl ether (boiling point 242 ° C, surface tension 25.7 mN / m), dipropylene glycol monopropyl Ether (boiling point: 212 ° C., surface tension: 27.9 mN / m), dipropylene glycol mono-n-butyl ether (boiling point: 231 ° C., surface tension: 23.7 mN / m), triethylene glycol dimethyl ether (boiling point: 216 ° C., surface tension: 27.5 mN) / M), Diethylene glycol methyl ethyl ether (boiling point 176 ° C., surface tension 24mN / m), diethylene glycol diethyl ether (boiling point 189 ° C., surface tension 23.3mN / m), diethylene glycol dibutyl ether (boiling point 255 ° C., surface tension 23.6mN) / M), Dipropylene glyco Ludimethyl ether (boiling point 171 ° C., surface tension 21.1 mN / m), diethylene glycol methyl butyl ether (boiling point 212 ° C., surface tension 26.7 mN / m), triethylene glycol methyl butyl ether (boiling point 261 ° C., surface tension 28.7 mN / m). m), tetraethylene glycol dimethyl ether (boiling point 275 ° C., surface tension 33 mN / m) and the like.

On the other hand, boiling point at one atmosphere (the general formula (b _i in 1)) The content of the organic solvent is 250 to 300 ° C. is (may be 0 mass%) 9% by mass or less with respect to the total amount of the ink composition Is preferable. In particular, the boiling point at 1 atm is 250 to 300 ° C. from the viewpoint of obtaining a printed matter having excellent print density and scratch resistance with respect to a low-absorbency recording medium such as coated paper regardless of the drying method. The content of the water-soluble organic solvent is more preferably 0.1 to 5% by mass, particularly preferably 0.1 to 3% by mass, based on the total amount of the ink.

Examples of organic solvents having a boiling point of 250 to 300 ° C. under 1 atm include glycerin (boiling point 290 ° C.), 1,6-hexanediol (boiling point 250 ° C.), triethylene glycol monobutyl ether (boiling point 271 ° C.), and the like. Triethylene glycol methylbutyl ether (boiling point 261 ° C), tetraethylene glycol dimethyl ether (boiling point 275 ° C), triethylene glycol (boiling point 287 ° C), tripropylene glycol (boiling point 271 ° C), tetrapropylene glycol (boiling point 250 ° C or higher), polyethylene Glycol 200 (boiling point 250 ° C. or higher), polyethylene glycol 400 (boiling point 250 ° C. or higher), polyethylene glycol 600 (boiling point 250 ° C. or higher), N-methyloxazolidinone (boiling point 257 ° C.) and the like can be mentioned.

To exemplify the organic solvent preferably used in the present invention,
As a monohydric alcohol solvent, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, 3-butanol, isobutanol, 3-methoxy-1-butanol, 3-methoxy-3-methyl-1-butanol, etc. but,
As divalent alcohol-based solvent (diol-based solvent), 1,2-propanediol (propylene glycol, boiling point 188 ° C.), 1,2-butanediol (boiling point 194 ° C.), 1,2-ethanediol (ethylene glycol, boiling point). 197 ° C), 2-methylpentane-2,4-diol (boiling point 197 ° C), 3-methyl-1,3-butanediol (boiling temperature 203 ° C), 1,3-butanediol (butylene glycol, boiling point 208 ° C) , 1,2-Pentanediol (boiling point of 210 ° C), 1,3-propanediol (boiling point of 210 ° C), 2,2-dimethyl-1,3-propanediol (boiling point of 210 ° C), 2-methyl-1,3 -Propanediol (boiling point of 214 ° C), 1-propen-1,3-diol (boiling point of 214 ° C), 1,2-hexanediol (boiling point of 223 ° C), 2-ethyl-2-methyl-1,3-propanediol (Boiling 226 ° C), 1,4-butanediol (boiling 230 ° C), 2-methyl-2-propyl-1,3-propanediol (boiling 230 ° C), dipropylene glycol (boiling 232 ° C), 2-butene -1,4-diol (boiling point of 235 ° C), 1,5-pentanediol (boiling point of 242 ° C), 2-ethyl-1,3-hexanediol (boiling point of 244 ° C), diethylene glycol (boiling point of 245 ° C), 3-methyl -1,5-pentanediol (boiling point 249 ° C), 1,6-hexanediol (boiling point 250 ° C), diethylene glycol, triethylene glycol (boiling point 287 ° C.), tetraethylene glycol, dipropylene glycol, tripropylene glycol (boiling point 271) ℃), tetrapropylene glycol (boiling point of 250 ℃ or more), polyethylene glycol 200 (boiling point of 250 ℃ or more), polyethylene glycol 400 (boiling point of 250 ℃ or more), polyethylene glycol 600 (boiling point of 250 ℃ or more), etc.
Glycerin, 1,2,4-butanetriol, diglycerin, etc. are used as trivalent or higher valent alcohol solvents (polyol solvents).
As glycol monoalkyl ether-based solvents, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, triethylene glycol Monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether (boiling point 271 ° C), tetraethylene glycol monomethyl ether, tetraethylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether , Dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol mono n-butyl ether, etc.
As glycol dialkyl ether-based solvents, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether (boiling point of 275 ° C), diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol methyl Ethyl ether, tetraethylene glycol methyl ethyl ether, diethylene glycol butyl methyl ether, triethylene glycol methyl butyl ether (boiling point 261 ° C.), tetraethylene glycol butyl methyl ether, etc.
As chain amide-based solvents, N, N-dimethylformamide, N, N-dimethyl-β-methoxypropionamide, N, N-dimethyl-β-ethoxypropionamide, N, N-dimethyl-β-butoxypropionamide, N, N-dimethyl-β-pentoxypropionamide, N, N-dimethyl-β-hexoxypropionamide, N, N-dimethyl-β-heptoxypropionamide, N, N-dimethyl-β-2-ethyl Hexoxypropionamide, N, N-dimethyl-β-octoxypropionamide, N, N-diethyl-β-butoxypropionamide, N, N-diethyl-β-pentoxypropionamide, N, N-diethyl-β -Hexoxypropionamide, N, N-diethyl-β-heptoxypropionamide, N, N-diethyl-β-octoxypropionamide, etc.
Heterocyclic compounds include 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-methyloxazolidinone, N-ethyloxazolidinone, piperazine, morpholine, N-methylmorpholine, N-ethylmorpholine, γ-butyrolactone, ε-caprolactone. Etc.,
As alkanolamine-based solvents, N, N-dimethylaminoethanol (boiling point: 134 ° C.), N, N-diethylaminoethanol (boiling point: 162 ° C.), N, N-dibutylaminoethanol (boiling point: 226 ° C.), N- (β-amino). Ethyl) Ethanolamine (boiling point 244 ° C), N-methylethanolamine (boiling point 156 ° C), N-methyldiethanolamine (boiling point 245 ° C), 2-ethylaminoethanol (boiling point 169 ° C), N-ethyldiethanolamine (boiling point 251 ° C) ), Mono-n-butylethanolamine (boiling point 199 ° C.), mono-n-butyldiethanolamine (boiling point 270 ° C.), N-tert-butylethanolamine (boiling point 177 ° C.), diethylisopropanolamine (boiling point 159 ° C.), tri Ethanolamine (boiling point 335 ° C), etc.
Each is listed, but not limited to these. Further, these organic solvents may be used alone, or a plurality of these organic solvents may be mixed and used.

The organic solvent used in the present invention preferably contains a water-soluble organic solvent, and in particular, among those listed above, a monohydric alcohol solvent, a dihydric alcohol solvent (diol solvent), and a trihydric or higher alcohol. It is preferable to use a based solvent (polycol-based solvent), a glycol monoalkyl ether-based solvent, or the like. Further, from the viewpoint of permeability to a recording medium, print density, and inkjet ejection stability, a compound having one or two hydroxyl groups is particularly preferably selected as the water-soluble organic solvent. As the organic solvent having one or two hydroxyl groups, it is preferable to include the above-mentioned glycol monoalkyl ether solvent or divalent alcohol solvent (diol solvent).
Among them, although the details are unknown, it is particularly preferable to contain a dihydric alcohol solvent (diol solvent) from the viewpoint that the dispersion stability of both the self-dispersion pigment and the resin dispersion pigment is unlikely to be adversely affected and the discharge stability is excellent. preferable. Further, among the diol-based solvents, it is preferable to use at least one kind of alkanediol having at least 2 to 5 carbon atoms, more preferably to use an alkanediol having 3 or 4 carbon atoms, and particularly preferably to use an alkanediol having 3 or 4 carbon atoms. 3 is the use of alkanediol.

The compound having one or two hydroxyl groups preferably contains 5% by mass or more, more preferably 10% by mass or more, and particularly preferably 15% or more, based on the total amount of the ink.

Further, the diol solvent is preferably contained in an amount of 5% by mass or more, more preferably 10% by mass or more, and particularly preferably 15% or more in the total amount of the ink.

As described above, it is considered that the temperature change of the ink in the drying step is affected by the specific heat of the organic solvent contained in the ink. Therefore, from the viewpoint of suppressing abrupt temperature changes in the ink drying step and improving the print density and the scratch resistance of the printed matter, the organic solvent has a specific heat of 0.40 to 0.70 cal / at 20 ° C. It is preferably g · ° C., more preferably 0.45 to 0.65 cal / g · ° C., and particularly preferably 0.50 to 0.60 cal / g · ° C. When the specific heat is 0.70 cal / g · ° C. or less, not only the drying property of the ink is improved, but also the compatibility of the resin component contained in the ink is improved, and the scratch resistance is improved. When the ink contains two or more kinds of organic solvents, it is preferable that all of the two or more kinds of organic solvents have a specific gravity satisfying the above conditions.

For the same reason as above, when the ink contains two or more kinds of organic solvents, the weighted average value of the specific heat is preferably 0.40 to 0.70 cal / g · ° C., and 0.45 to 0.65 cal. It is more preferably / g · ° C., and particularly preferably 0.52 to 0.60 cal / g · ° C.

The specific heat of the organic solvent can be measured by, for example, DSC (Differential Scanning Calorimetry). Specifically, using a high-sensitivity differential scanning calorimeter Thermo plus EV02 DSC8231 (manufactured by Rigaku), about 10 g of an organic solvent to be measured was added to an aluminum sample pan, and then the sample was sealed using a sample sealer. The specific heat of the organic solvent can be calculated from the obtained DSC chart by measuring the bread (empty container) and the three substances whose specific heats are known under the same conditions.

The organic solvent used in the ink of the present invention preferably has a weighted average boiling point of 100 to 235 ° C., more preferably 120 to 220 ° C., and more preferably 150 to 215 ° C. under 1 atm. Especially preferable. When the weighted average value of the boiling point is 100 ° C. or higher, the ejection stability from the inkjet head is improved, and the density of the printed matter when printed on a high-absorption recording medium is improved. Further, when the weighted average value of the boiling point is 235 ° C. or less, drying failure does not occur on the recording medium, and the remaining organic solvent does not cause a sudden temperature change of the ink coating film, so that the drying method can be used. Therefore, the density of printed matter is improved. Further, when the weighted average value of the boiling point is 235 ° C. or lower, the scratch resistance of the printed matter to a low-absorption recording medium such as coated paper is also improved. The weighted average value of the boiling point shall include the organic solvent having a boiling point of 250 ° C. or higher under 1 atm described above.

The weighted average value of the specific heat or the weighted average value of the boiling point at 1 atm is the product of the boiling point at the specific heat or 1 atm calculated for each organic solvent and the mass ratio to the total amount of the organic solvent. , It is a value obtained by adding.

<Water>
As the water contained in the water-based inkjet ink of the present invention, it is preferable to use ion-exchanged water (deionized water) instead of general water containing various ions. The content thereof is preferably in the range of 30 to 90% by mass, more preferably 40 to 80% by mass, based on the total mass of the ink.

<Wax>
The water-based inkjet ink of the present invention contains wax. As used herein, the term "wax" is an organic compound that is solid at room temperature (25 ° C.) and becomes liquid when heated. For example, it has a melting point of 40 to 200 ° C. and melts in a temperature environment higher than the melting point without decomposition.

The melting point of the wax is preferably 60 to 200 ° C, more preferably 100 to 180 ° C, and particularly preferably 120 to 160 ° C. Although the reason is not clear, it is possible to obtain a printed matter having a high print density within the above range, especially when it is dried by a method of irradiating electromagnetic waves such as an infrared drying method.

The wax may be a water-soluble material or a water-insoluble material, but is preferably a water-insoluble material, particularly resin particles (emulsion). Further, examples of chemical structures include hydrocarbon waxes, ester waxes (for example, fatty acid ester waxes), silicone waxes, and polyalkylene glycol waxes.
For example, an acrylic-silicone copolymer emulsion having a glass transition temperature of 50 ° C. or higher is generally likely not to satisfy the above melting point conditions, and therefore does not fall under the wax in the present invention.

More specific waxes that can be used in the present invention include, for example, natural waxes and synthetic waxes. Natural waxes include petroleum waxes such as paraffin wax, microcrystallin wax, petrolatum; plant waxes such as carnauba wax, candelilla wax and rice wax; animal waxes such as lanolin and beeswax; mineral waxes. Some Montan wax, Celesin, etc .; can be mentioned. Synthetic waxes include polyolefin wax, Fisher Trobsch wax, acrylic silicone copolymer, urethane silicone copolymer, polyethylene glycol (however, the average molecular weight is 1,000 or more), paraffin wax derivative, montan wax derivative, and micro. Examples thereof include crystallin wax derivatives. These waxes can be used alone or in combination of two or more in a water-based inkjet ink.

Among the above-exemplified examples, hydrocarbon wax or silicone wax is preferable in that high scratch resistance and high printing density can be obtained, and polyolefin wax, which is a hydrocarbon wax, is more preferably used in that it is also excellent in discharge stability. Be done.

Examples of the polyolefin wax include polyethylene wax and polypropylene wax. Of these, polypropylene wax is preferable from the viewpoint of obtaining a high printing density, and polyethylene wax is preferable from the viewpoint of ejection stability and scratch resistance. In each case, one type or two or more types can be used in combination.

The polyolefin wax is preferably a soft polyolefin having a molecular weight of less than 10,000.

When the wax is a resin particle, its average particle size is preferably 5 to 300 nm, more preferably 30 to 250 nm, and particularly preferably 40 to 200 nm. If the average particle size of the wax is 5 nm or more, the scratch resistance of the printed matter is improved, and if it is 300 nm or less, not only the inkjet ejection stability is improved, but also high printing is performed regardless of the drying method and the type of recording medium. A printed matter of density can be obtained.

The wax having the form of resin particles can be produced, for example, by mixing a room temperature solid wax melted by heating, hot water, and an emulsifier. Commercially available waxes can also be used, for example, AQUACER-507, AQUACER-513, AQUACER-515, AQUACER-526, AQUACER-531, AQUACER-533, AQUACER-535, AQUACER-535 manufactured by BASF. 537, AQUACER-539, AQUACER-552, AQUACER-840, AQUACER-1547, etc., San Nopco's Nopcoat PEM-17, BASF's JONCRYLWAX4, JONCRYLWAX26, JONCRYLWAX26, JONCRYLWAX28, JONCRYLWAX28 , High-tech P series, etc., Charine FE230N manufactured by Shin-Etsu Chemical Co., Ltd., Charine FE502, etc. can be mentioned.

The blending amount of the wax is preferably 0.2 to 8% by mass, preferably 0.2 to 8% by mass, based on the total amount of the ink, in that it has excellent ejection stability, excellent scratch resistance of the printed matter, and a high-concentration printed matter can be obtained. It is more preferably ~ 5% by mass, and particularly preferably 0.5-4% by mass.

<Binder resin>
In the water-based inkjet ink of the present invention, it is preferable to use a binder resin because of high print density, scratch resistance of printed matter, and ejection stability.

The "binder resin" in the present specification is a resin used for binding a layer of printed matter (printing layer, ink layer) to a recording medium. As described above, the ink of the present invention contains a pigment-dispersed resin, but when the resin contained in the ink is a water-soluble resin, whether or not the resin corresponds to a binder resin is adsorbed on the resin-dispersing pigment. Distinguished by rate. For example, when an attempt is made to produce a resin-dispersed pigment dispersion 1 using the materials and methods described in Examples, except that the same amount of the target resin is used instead of the aqueous solution of the pigment-dispersed resin 1. Even if the dispersion liquid of the resin dispersion pigment cannot be produced due to poor dispersion or the like, or even if the dispersion liquid of the resin dispersion pigment can be produced, the adsorption rate of the target resin with respect to the resin dispersion pigment is 50 mass by mass. If it is less than%, it is determined that the target resin is a binder resin.

As an example of the method for measuring the adsorption rate on the pigment, if necessary, the ink diluted with water is subjected to a centrifugation treatment (for example, at 30,000 rpm for 4 hours) to separate the pigment and the supernatant liquid. Then, when the solid content contained in the supernatant is measured, if the solid content is 50% by mass or more with respect to the total amount of the resin having the same composition contained in the ink, the resin is a binder resin. Judge.

As a form of a binder resin for a water-based inkjet ink, a water-soluble resin and a (water-dispersible) resin particle (a form of a water-insoluble resin) are generally known, and in the present invention, either one is selected and used. Alternatively, both may be used in combination.
For example, the resin particles have a higher molecular weight than the water-soluble resin, can improve the scratch resistance of the printed matter, and are also excellent in the image quality of the printed matter. Further, when printing on a high-absorbency recording medium, the voids in the high-absorbency recording medium can be effectively filled, so that a printed matter having a high print density can be obtained. On the other hand, the water-based inkjet ink using a water-soluble resin as the binder resin is excellent in ejection stability.

The water-based inkjet ink of the present invention preferably contains resin particles as a binder resin. As described above, the inclusion of the resin particles not only enhances the scratch resistance of the printed matter, but also makes it possible to obtain a printed matter having a high print density on various recording media. In particular, it is preferable because a printed matter having a high print density can be obtained when it is dried by a method of irradiating electromagnetic waves such as an infrared drying method.

Further, the water-based inkjet ink of the present invention preferably contains resin particles and a water-soluble resin as the binder resin. By containing the resin particles and the water-soluble resin, not only a printed matter having a higher print density can be obtained, but also the ejection stability is excellent.

<Resin particles>
As the resin particles, resin particles of acrylic type, styrene acrylic type, epoxy type, urethane type, styrene butadiene type, polyether type, polyamide type, polyester type, vinyl chloride type and the like, or copolymers thereof can be used. (However, those containing silicone chains are excluded). From the viewpoint of scratch resistance and ejection stability of printed matter, acrylic, styrene acrylic, urethane, styrene butadiene, and vinyl chloride resin particles are preferable, and acrylic, styrene acrylic, and urethane resin particles are further preferable. Acrylic-based and styrene-acrylic-based resin particles are particularly preferable from the viewpoint of the density and ejection stability of the printed matter.
The above resin particles can be synthesized by a known method or a commercially available product can be used. Further, the structure is not particularly limited, and for example, a resin having a random structure, a block structure, a comb-shaped structure, a star-shaped structure, or the like can be used.

The content of the resin particles with respect to the total amount of the ink is preferably 1 to 10% by mass, more preferably 2 to 8% by mass, and further preferably 3 to 7% by mass in terms of solid content. By setting the amount of the resin particles within the above range, it is possible to obtain an ink having excellent scratch resistance and print density of the printed matter without deteriorating the dispersion stability and the ejection stability.

In addition, it is said that an ink having excellent dispersion stability and ejection stability, good image quality for a non-absorbent recording medium, and excellent color development and color reproducibility when printed on a high-absorbency recording medium can be obtained. From the viewpoint, when the binder resin contains resin particles and a water-soluble resin, the content of the resin particles is 20 with respect to the total amount of the binder resin (the total amount of the resin particles and the water-soluble resin). It is preferably ~ 95% by mass, more preferably 35 to 90% by mass, and particularly preferably 50 to 80% by mass.

<Water-soluble resin>
On the other hand, examples of the type of the water-soluble resin include acrylic type, styrene acrylic type, urethane type, urethane / acrylic type, styrene butadiene type, vinyl chloride type, styrene maleic acid type, polyester type and the like (however, the silicone chain is used. Except for those included). Above all, from the viewpoint of obtaining an ink having excellent dispersion stability and ejection stability, use one or more kinds of resins selected from the group consisting of acrylic type, styrene acrylic type, urethane type, and urethane / acrylic type. Is preferable.
The above water-soluble resin can be synthesized by a known method or a commercially available product can be used. Further, the structure is not particularly limited, and for example, a resin having a random structure, a block structure, a comb-shaped structure, a star-shaped structure, or the like can be used.

The content of the water-soluble resin with respect to the total amount of the ink is preferably 0.1 to 10% by mass, more preferably 0.5 to 8% by mass, and 1 to 5% by mass in terms of solid content. Is more preferable. By setting the amount of the water-soluble resin within the above range, it is possible to obtain a printed matter having a high print density without deteriorating the dispersion stability and the ejection stability.

The acid value of the resin particles or the water-soluble resin used as the binder resin is preferably 1 to 80 mgKOH / g, preferably 3 to 60 mgKOH / g, and particularly preferably 5 to 40 mgKOH / g. .. Within the above range, the dispersion stability of both the self-dispersed pigment and the resin-dispersed pigment can be ensured, and the binder resin quickly moves to the gas-liquid interface to obtain a printed matter having excellent image quality. When a high-absorption recording medium is used, a printed matter having a high print density can be obtained by rapidly moving so as to fill the voids on the surface of the recording medium.
The acid value of the resin particles or the water-soluble resin can be measured in the same manner as the acid value of the pigment-dispersed resin described above.

The glass transition temperature of the resin particles or the water-soluble resin used as the binder resin is preferably 60 to 140 ° C., more preferably 70 to 135 ° C. from the viewpoint of scratch resistance and ejection stability of the printed matter. It is preferably 80 to 130 ° C., particularly preferably 80 to 130 ° C. In particular, when a method of irradiating electromagnetic waves such as an infrared drying method is adopted, the glass transition temperature is preferably 80 ° C. or higher. When the self-dispersing pigment suddenly generates heat due to irradiation with electromagnetic waves such as infrared rays, the resin particles form a film in the vicinity of the self-dispersing pigment, so that the surface of the self-dispersing pigment is uniformly covered and the surface of the recording medium is smooth. Therefore, a printed matter having a high print density can be obtained.

The glass transition temperature is a value measured using a DSC (Differential Scanning Calorimetry), and can be measured according to JIS K7121 as follows, for example. Approximately 2 mg of a sample obtained by drying the resin is weighed on an aluminum pan, and the aluminum pan is set as a test container in a holder in a DSC measuring device (for example, DSC-60Plus manufactured by Shimadzu Corporation). Then, the temperature at the intersection of the baseline on the low temperature side and the tangent line at the inflection point, which was measured under the temperature rising condition of 5 ° C./min and read from the obtained DSC chart, is referred to as the glass transition temperature in the present specification. do.

The weight average molecular weight of the water-soluble resin used as the binder resin is from the viewpoint of ensuring the ejection stability from the inkjet nozzle and obtaining a printed matter having excellent scratch resistance against various recording media. It is preferably 5,000 to 50,000, and more preferably 8,000 to 45,000 from the viewpoint of excellent color development and color reproducibility when printed on a high absorption recording medium. It is more preferably 10,000 to 40,000.
The weight average molecular weight of the water-soluble resin can be measured in the same manner as the acid value of the pigment-dispersed resin described above.

<Surfactant>
In the present invention, it is preferable to contain one or more surfactants from the viewpoints of ejection stability, scratch resistance of the printed matter, and obtaining a printed matter having a high print density.
Examples of the surfactant include acetylenediol-based, acetylene alcohol-based, siloxane-based, acrylic-based, fluorine-based, polyoxyalkylene ether-based, and various other surfactants depending on the intended use. Among them, it is preferable to contain one or more nonionic surfactants selected from the group consisting of acetylene diol-based surfactants, siloxane-based surfactants, and polyoxyalkylene ether-based surfactants, and acetylene diol-based surfactants. It is more preferable to contain one or more selected from the group consisting of a surfactant and a siloxane-based surfactant, and it is particularly preferable to contain a siloxane-based surfactant.

The surfactant that can be used in the present invention may be water-soluble or water-insoluble. The siloxane-based surfactant that is solid at room temperature and melts at, for example, 40 to 200 ° C. when heated may be a material that also serves as the above-mentioned silicone wax.

The acetylene diol-based surfactant and the siloxane-based surfactant can be rapidly applied to the ink droplets after landing on the recording medium without being affected by the self-dispersing pigment and the resin-dispersing pigment present in the droplets. , It is considered to be oriented toward the gas-liquid interface and the recording medium-droplet interface. As a result, the wettability of the ink can be improved and the ink droplets can be quickly smoothed even on a low-absorption recording medium. It is possible to obtain a printed matter having excellent image quality with a small amount of ink. In addition to the above, when a siloxane-based surfactant is used, the scratch resistance of the printed matter is also improved, and although the details are unknown, when printing is performed on a highly absorbent recording medium such as uncoated paper, Excessive penetration and diffusion of ink are suppressed, and a printed matter having a high print density can be obtained. In particular, in the present invention, although the details are unknown, an ink having excellent ejection stability in addition to the above-mentioned improvement in characteristics can be obtained. Therefore, an acetylene diol-based surfactant and a siloxane-based surfactant are used in combination. Is preferable.

Examples of the acetylene diol-based surfactant used in the present invention include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,5,8,11-tetramethyl-6-dodecyne. -5,8-diol, hexadeca-8-in-7,10-diol, 6,9-dimethyl-tetradeca-7-in-6,9-diol, 7,10-dimethylhexadeca-8-in-7 , 10-Glycol, and ethylene oxide and / or propylene oxide adducts thereof, but are not limited thereto.

Further, as a siloxane-based surfactant that can be suitably used in the present invention, for example, 8032ADDITIVE, FZ-2104, FZ-2120, FZ-2122, FZ-2162, FZ-2164, FZ-2166 manufactured by Toray Dow Corning Co., Ltd. FZ-2404, FZ-7001, FZ-7002, FZ-7006, L-7001, L-7002, SF8427, SF8428, SH3748, SH3479, SH3771M, SH3772M, SH3773M, SH3775M, SH8400, BYK-331 manufactured by BYK Chemie. , BYK-333, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, BYK-UV3500, BYK-UV3510, BYK-UV3530, BYK-UV3570, TEGO Wet 240, TEGO manufactured by Ebonic. Wet 250, TEGO Wet 260, TEGO Wet 270, TEGO Wet 280, TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, TEGO Glide 440, TEGO Glide 440, TEGO Glide 450, TEGO Shin-Etsu Chemical Co., Ltd. -351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-640, KF-642, KF-643, KF-644, KF-945, KF-6011, KF-6012 , KF-6015, KF-6017, KF-6020, KF-6204, X-22-4515, Silface SAG series of Nissin Chemical Industry Co., Ltd. and the like. In particular, a siloxane-based surfactant in which one or more ethylene oxide groups and / or one or more propylene oxide groups are introduced into the side chains and / or both ends of the polydimethylsiloxane chain can be preferably used.

Examples of the polyoxyalkylene ether-based surfactant that can be suitably used in the present invention include compounds represented by the following general formula (2).

General formula (2):

RO- (EO) m- (PO) n-H

In the above general formula (2), R has an alkyl group having 8 to 22 carbon atoms, an alkenyl group having 8 to 22 carbon atoms, an alkylcarbonyl group having 8 to 22 carbon atoms, or an alkyl carbonyl group having 8 to 22 carbon atoms. Represents an alkenylcarbonyl group. The R may have a branched structure. Further, EO represents an ethylene oxide group and PO represents a propylene oxide group. m indicates the average number of added moles of EO and is a number of 2 to 50, and n indicates the average number of added moles of PO and is a number of 0 to 50. When n is not 0, the addition order of (EO) m and (PO) n does not matter, and the addition may be block or random.

It is preferable that the surfactant used in the present invention is present in the molecule separately as a hydrophobic group and a hydrophilic group. Therefore, among the surfactants exemplified above, those having a hydrophilic ethylene oxide group are particularly preferably selected.

On the other hand, the HLB value is 10 from the viewpoint of enhancing the affinity with the self-dispersion pigment, the resin dispersion pigment and the wax, obtaining an ink having excellent dispersion stability and ejection stability, and obtaining a printed matter having a high print density. It preferably contains the following surfactants, more preferably 0 to 5, and particularly preferably 0 to 4.

Further, in one embodiment, in addition to dispersion stability and ejection stability, a printed matter having a high print density can be obtained regardless of the recording medium and the drying method, and the HLB value is 0 to 12 (preferably 0 to 8). It is preferable to use the polyoxyalkylene ether-based surfactant and the siloxane-based surfactant which are 0 to 6) in combination.

The HLB (Hydrophile-Lipophile Balance) value is one of the parameters indicating the hydrophilicity / hydrophobicity of the material, and the smaller the value, the higher the hydrophobicity, and the larger the value, the higher the hydrophilicity. Various methods for calculating the HLB value from the chemical structure are known, and various methods for actually measuring the HLB value are also known. However, in the present invention, as in the case of an acetylenediol-based surfactant and a polyoxyalkylene ether-based surfactant. If the structure of the compound is clearly known, the HLB value is calculated using the Griffin method. The Griffin method is a method of calculating an HLB value using the following formula (3) using the molecular structure and molecular weight of the target material.

Equation (3):

HLB value = 20 x (total molecular weight of hydrophilic part) ÷ (molecular weight of material)

On the other hand, when a compound having an unknown structure is contained, such as a siloxane-based surfactant, for example, p. The HLB value of the surfactant can be determined experimentally by the following method described in 324. Specifically, after dissolving 0.5 g of a surfactant in 5 mL of ethanol, the solution is titrated with a 2 mass% phenol aqueous solution while stirring at 25 ° C., and the end point is where the solution becomes turbid. .. When the amount of the aqueous phenol solution required up to the end point is A (mL), the HLB value can be calculated by the following formula (4).

Equation (4):

HLB value = 0.89 x A + 1.11

The content of the surfactant in the inkjet ink of the present invention is preferably 0.2 to 4% by mass with respect to the total amount of the ink. More preferably, it is 0.5 to 2% by mass.

<Other ingredients>
In the water-based inkjet ink of the present invention, in addition to the above-mentioned components, a pH adjuster can be added, if necessary, in order to obtain an ink having a desired physical property value. As the pH adjuster, the above-mentioned alkanolamine-based solvent can be used, and in addition,
Other nitrogen-containing compounds include aqueous ammonia, monoethylamine, diethylamine, triethylamine, cyclohexylamine, benzylamine, urea, piperidine, etc.
As alkali metal hydroxides, lithium hydroxide, sodium hydroxide, potassium hydroxide, etc.
As alkali metal carbonates, lithium carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, etc.
Acidic compounds include hydrochloric acid, sulfuric acid, acetic acid, citric acid, maleic acid, maleic anhydride, succinic acid, tartaric acid, malic acid, phosphoric acid, boric acid, fumaric acid, malonic acid, ascorbic acid, glutamate, etc.
Can also be used. Further, the above pH adjuster may be used alone or in combination of two or more.

The blending amount of the pH adjuster is preferably 0.01 to 5% by mass, more preferably 0.1 to 3% by mass, and 0.2 to 1.5% by mass with respect to the total amount of the ink. Is most preferable.

Further, in the ink of the present invention, in addition to the above-mentioned components, additives such as an antifoaming agent, a preservative, an infrared absorber, and an ultraviolet absorber are appropriately added as necessary in order to obtain an ink having desired physical property values. Can be added to. The amount of these additives added is preferably 0.01 to 10% by mass with respect to the total mass of the ink.

It is preferable that the ink of the present invention does not substantially contain a polymerizable monomer.

<PKa value of nitrogen-containing compound>
As described above, a nitrogen-containing compound can be used as an organic solvent and / or a pH adjuster in the ink of the present invention. On the other hand, depending on the nitrogen-containing compound used, the dispersion stability and discharge stability of the pigment may be adversely affected. Therefore, in the present invention, it is preferable to limit the amount of the nitrogen-containing compound, particularly the amount of the nitrogen-containing compound having a molecular weight of 500 or less, which easily affects the above-mentioned characteristics.

Generally, in a water-based ink, the dispersed state of the pigment is maintained by the charge repulsion generated between the pigment particles, and the dispersion stability is ensured. As a method of maintaining dispersion stability for a long period of time, there is a method of adjusting the pH of the ink to neutral to weakly basic. By maintaining the pH at neutral to weakly basic, the ion concentration in the electric double layer covering the pigment surface can be increased, the repulsive force of the electric double layer can be increased, and a large repulsive force can be generated between the pigment particles. However, some nitrogen-containing compounds are acidic or strongly basic, and by using these compounds in combination with a self-dispersing pigment and a resin-dispersed pigment, the self-dispersing pigment and the self-dispersing pigment can be used. The dispersion stability of the resin dispersion may be deteriorated, and the print density and ejection stability of the printed matter may be deteriorated accordingly. In addition, when wax is used in combination, the compatibility of the wax with ink may deteriorate, and the image quality and print density of the printed matter may deteriorate.

As a result of diligent studies by the present inventors, among the nitrogen-containing compounds, the pKa value at 25 ° C. is 2 or less (preferably, the pKa value is less than 4), or 10 or more (preferably, the pKa value is 5 or more). The total amount of the nitrogen-containing compound having a molecular weight of 500 or less, which is more than 9.5), is preferably 3% by mass or less, more preferably 1% by mass or less, based on the total amount of the aqueous inkjet ink. .. This is because these compounds are acidic or strongly basic, and if they are blended in a large amount, they may adversely affect the dispersion stability, ejection stability, print density of printed matter, and image quality as described above.

On the other hand, when a nitrogen-containing compound is used, it is preferable to use a basic organic compound having a pKa value of 4 to 9.5 at 25 ° C. Although the detailed factors are unknown, it is considered that the acid dissociation constant (pKa value) is moderately small and the organic compound suppresses damage to the self-dispersing pigment, the resin-dispersed pigment and the wax. Be done.

Specific examples of the nitrogen-containing compound having a pKa value of 4 to 9.5 at 25 ° C. are diethanolamine (pKa = 8.9), methyldiethanolamine (pKa = 8.5), and triethanolamine (pKa = 7.8). ), 1-Amino-2-propanol (pKa = 9.4), diisopropanolamine (pKa = 9.0), triisopropanolamine (pKa = 8.0), trishydroxymethylaminomethane (pKa = 8.1). ), Imidazole (pKa = 7.0), and aniline (pKa = 4.6). Among the above, it is preferable to use alkanolamine from the viewpoint of high solubility in an aqueous medium and safety to the human body, and it is particularly preferable to contain triethanolamine having a small pKa value. It should be noted that only one type of the above compound may be used, or two or more types may be used in combination.

When a nitrogen-containing compound having a pKa value of 4 to 9.5 is used, the content thereof is preferably 1.25% by mass or less based on the total amount of the ink. Further, it is more preferably 0.1 to 1.0% by mass. Within the above range, deterioration of print density and image quality of printed matter can be prevented without deteriorating dispersion stability and ejection stability.

From the viewpoint of comprehensively achieving both ink dispersion stability, ejection stability, print density, and image quality, the total amount of the nitrogen-containing compound compounded should be the total amount of the water-based inkjet ink regardless of the pKa value. It is preferably 3% by mass or less, and more preferably 1.25% by mass or less.

The pKa value of the present invention can be measured by a known method, for example, a potentiometric titration method. Further, as an example of a nitrogen-containing compound having a pKa value of 2 or less at 25 ° C., urea (pKa value = 0.2) can be mentioned. Further, as examples of nitrogen-containing compounds having a pKa value of 10 or more at 25 ° C., cyclohexylamine (pKa value = 10.6), monoethylamine (pKa value = 10.7), diethylamine (pKa value = 11.0). , Triethylamine (pKa value = 10.7), piperidine (pKa value = 11.2).

<Manufacturing method of water-based inkjet ink>
The water-based inkjet ink of the present invention containing the above-mentioned components can be produced by a known method. In particular, from the viewpoint of obtaining an ink having excellent dispersion stability and ejection stability, after producing a dispersion liquid of a self-dispersing pigment and a dispersion liquid of a resin dispersion pigment in advance, the dispersion liquid of the self-dispersion pigment and the resin dispersion pigment A production method of mixing a dispersion liquid, an organic solvent, a wax, and, if necessary, a binder resin, a surfactant, or the like is preferably selected. An example of the method for producing the water-based inkjet ink of the present invention will be described below, but as described above, the production method is not limited to the following.

An example of a method for producing a dispersion liquid of a resin dispersion pigment is as described above. The self-dispersed pigment is also mixed well with water and, if necessary, an organic solvent or other additives, and then filtered or centrifuged as necessary to remove coarse particles. Manufacture a dispersion of self-dispersing pigments.

The dispersion liquid of the self-dispersion pigment and the dispersion liquid of the resin dispersion pigment thus obtained are mixed, and further, an organic solvent, a wax, and, if necessary, a binder resin, a surfactant, water, and pH. Add the adjusting agent and other additives, and stir and mix. If necessary, the mixture may be stirred and mixed while heating in the range of 40 to 100 ° C.

Then, the coarse particles contained in the mixture are removed by a method such as filtration or centrifugation to obtain a water-based inkjet ink. As a method for filtration separation, a known method can be appropriately used, but when a filter is used, the opening diameter thereof is preferably 0.3 to 5 μm, more preferably 0.5 to 3 μm. Further, when performing filtration, the filter may be a single type or a plurality of types may be used in combination.

<Characteristics of water-based inkjet ink>
The aqueous inkjet ink of the present invention preferably has a viscosity at 25 ° C. adjusted to 3 to 20 mPa · s. Within this viscosity range, stable ejection characteristics are exhibited not only in a head having a frequency of 4 to 10 KHz but also in a head having a high frequency of 10 to 70 KHz. In particular, by setting the viscosity at 25 ° C. to 4 to 10 mPa · s, stable ejection can be achieved even when used for an inkjet head having a design resolution of 600 dpi or more. The viscosity can be measured by a conventional method. Specifically, it can be measured using an E-type viscometer (TVE25L-type viscometer manufactured by Toki Sangyo Co., Ltd.) and 1 mL of ink.

In addition, the water-based inkjet ink of the present invention has a static surface tension of 18 to 35 mN / m at 25 ° C. from the viewpoint of producing a water-based inkjet ink that can be ejected stably and obtaining a printed matter having excellent print density and image quality. It is preferably 20 to 32 mN / m, and particularly preferably 20 to 32 mN / m. The static surface tension refers to the surface tension measured by the Wilhelmy method in an environment of 25 ° C. Specifically, CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. can be used, and measurement can be performed using a platinum plate.

Further, from the viewpoint of obtaining excellent image quality by quickly orienting the surfactant after landing on the recording medium and obtaining suitable wettability on the recording medium, the inkjet ink of the present invention uses the maximum foam pressure method. The dynamic surface tension at 10 ms is preferably 26 to 36 mN / m, more preferably 28 to 36 mN / m, and particularly preferably 30 to 36 mN / m. The dynamic surface tension in the present specification is a value measured in an environment of 25 ° C. using a bubble pressure dynamic surface tension meter BP100 manufactured by Kruss.

<Aqueous inkjet ink set>
The black inkjet ink of the present invention may be used as a single color, or may be used as a set of water-based inkjet inks by combining a plurality of colors according to the intended use.
Above all, the black inkjet ink of the present invention is preferable because a color printed image having a jet-black feeling and excellent image quality can be obtained by using it in combination with an ink exhibiting process colors such as cyan, magenta, and yellow.
Further, when printing on a recording medium other than white, a clear image can be obtained by using white ink together.

Color inkjet inks that exhibit process colors such as cyan ink, magenta ink, and yellow ink, which are used in combination with the black inkjet ink of the present invention, include pigments and water. In addition to the pigment and water, these color inkjet inks may contain an organic solvent, a pigment dispersion resin, a dispersion aid, a binder resin, a surfactant, a pH adjuster, and other components. The details regarding these components are the same as in the case of the black inkjet ink described above.

On the other hand, from the viewpoint of obtaining printed matter having excellent image quality and scratch resistance, an organic solvent contained in each of cyan inkjet ink, magenta inkjet ink, and yellow inkjet ink and having a boiling point of 250 to 300 ° C. under 1 atm. The content of the ink is preferably 5% by mass or less (may be 0% by mass) with respect to the total amount of ink, and is 3% by mass or less (may be 0% by mass) with respect to the total amount of ink. Is more preferable, and 2% by mass or less (may be 0% by mass) is particularly preferable.

Further, from the viewpoint of obtaining a printed matter having excellent image quality, in each of the cyan inkjet ink, the magenta inkjet ink, and the yellow inkjet ink, the boiling point of the organic solvent contained in the ink at 1 atm (two or more kinds of the organic solvent). When it is contained, the weighted average value of the boiling point) is 1 ° C. or more smaller than the boiling point of the organic solvent contained in the black inkjet ink under 1 atm (when two or more kinds of the organic solvent are contained, the weighted average value of the boiling point). It is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, and particularly preferably 10 ° C. or higher. As a result, when the black inkjet ink, the cyan inkjet ink, the magenta inkjet ink, and the yellow inkjet ink are dried at the same time by using a drying method that irradiates an electromagnetic wave such as an infrared drying method, the print density of all colors is increased. Can be enhanced.

Further, from the viewpoint of obtaining a printed matter having excellent scratch resistance, it is preferable that the cyan inkjet ink, the magenta inkjet ink, and the yellow inkjet ink each contain wax. As the wax, those exemplified above can be used as the wax that can be used for the black inkjet ink. The blending amount of the wax is preferably 0.2 to 8% by mass, and 0.3 to 5% by mass, respectively, based on the total amount of the ink, from the viewpoint of obtaining an ink having excellent ejection stability and scratch resistance of the printed matter. Is more preferable, and 0.5 to 4% by mass is particularly preferable.

When the cyan inkjet ink, magenta inkjet ink, and yellow inkjet ink contain wax, the blending amount thereof is preferably 0.5% by mass or more less than the blending amount of wax in the black inkjet ink, and 1.0 mass. It is preferably less than%, and particularly preferably less than 1.5% by mass. As a result, when the black inkjet ink, the cyan inkjet ink, the magenta inkjet ink, and the yellow inkjet ink are dried at the same time by using a drying method that irradiates an electromagnetic wave such as an infrared drying method, the print density of all colors is increased. Can be enhanced.

<Cyan inkjet ink>
Examples of the cyan pigment contained in the cyan inkjet ink include C.I. I. Pigment Blue 1, 2, 3, 15: 3, 15: 4, 15: 6, 16, 22, 60, 64, 66 and the like. Above all, from the viewpoint of excellent color development and light resistance, C.I. I. One or more selected from the group consisting of Pigment Blue 15: 3 and 15: 4 is preferable. In addition, for the purpose of improving color reproducibility, C.I. I. Pigment Green 7, 36, 43, 58 and other green pigments may be mixed.

<Magenta Inkjet Ink>
Examples of the magenta pigment used in the magenta inkjet ink include C.I. I. Pigment Red 5, 7, 12, 22, 23, 31, 48 (Ca), 48 (Mn), 49, 52, 53, 57 (Ca), 57: 1, 112, 122, 146, 147, 150, 185 , 238, 242, 254, 255, 266, 269, and 282, and C.I. I. Pigment Violet 19, 23, 29, 30, 37, 40, 43, 50 and the like. Above all, from the viewpoint of excellent color development and light resistance, C.I. I. Pigment Red 122, 146, 150, 185, 202, 209, 254, 266, 269, and 282, and C.I. I. One or more pigments selected from the group consisting of Pigment Biored 19 are preferred.

<Yellow inkjet ink>
Examples of the yellow organic pigment used in the yellow inkjet ink include C.I. I. Pigment Yellow 10, 11, 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120, 125, 128, 137, 138, 139, 147, Examples thereof include 148, 150, 151, 154, 155, 166, 168, 180, 185, and 213. Above all, from the viewpoint of excellent color development, C.I. I. Pigment Yellow 12, 13, 14, 74, 83, 120, 150, 151, 154, 155, 180 and 185 are preferably one or more selected from the group.

The above-mentioned set of water-based inkjet inks includes black inkjet inks, and in addition to the above-mentioned cyan inkjet inks, magenta inkjet inks, and yellow inkjet inks, inkjet inks exhibiting spot colors such as violet, blue, red, orange, green, and brown. May include.

<Ink-pretreatment liquid set>
The black inkjet ink of the present invention or a set of an aqueous inkjet ink containing the black inkjet ink can also be used in the form of an ink (or ink set) -pretreatment liquid set in combination with a pretreatment liquid containing a coagulant. By applying the pretreatment liquid containing the coagulant onto the recording medium, it is possible to form a layer (ink coagulation layer) that intentionally coagulates the solid components contained in the ink. Then, by landing the ink on the ink agglomerate layer, bleeding and color unevenness can be prevented, and the image quality of the printed matter can be remarkably improved. Further, depending on the material used for the pretreatment liquid, the scratch resistance and blocking resistance of the printed matter can also be improved. Further, when a highly absorbent recording medium is used as the recording medium, it is possible to obtain a printed matter having excellent color development and color reproducibility as well as image quality.

The term "coagulant" as used herein refers to a component contained in an ink that can destroy and aggregate the dispersed state of pigments and resin particles, and / or insolubilize a water-soluble resin to thicken the ink. means. Such a flocculant preferably contains one or more selected from metal salts and cationic polymer compounds from the viewpoint of significantly improving image quality, color development and color reproducibility. Above all, from the viewpoint of obtaining excellent image quality, color development and color reproducibility, it is preferable to use a metal salt as the flocculant, and the group consisting of ^{Ca 2+} , Mg ²⁺ , Zn ²⁺ and Al ^3+. It is particularly preferred to include salts of polyvalent metal ions selected from. When a metal salt is used as the flocculant, the content thereof is preferably 2 to 30% by mass and particularly preferably 3 to 25% by mass with respect to the total amount of the pretreatment liquid.

In addition, an organic solvent, a surfactant, a pH adjuster, an antifoaming agent, an antiseptic, and the like can be appropriately added to the pretreatment liquid. The materials that can be specifically used are the same as in the case of black inkjet ink.

The static surface tension of the pretreatment liquid is preferably 20 to 45 mN / m from the viewpoint of obtaining a printed matter having excellent image quality when used in combination with the black inkjet ink of the present invention. It is more preferably 23 to 40 mN / m. Particularly preferably, it is 25 to 37 mN / m. The static surface tension of the pretreatment liquid can be measured by the same method as the static surface tension of the black inkjet ink.

<Inkjet recording method>
The black inkjet ink of the present invention or a set of water-based inkjet ink containing the black inkjet ink is used in a recording method (inkjet recording method) in which the ink is ejected from an inkjet head and applied onto a recording medium.

It should be noted that, before being applied onto the recording medium, the components in the black inkjet ink are uniformly dispersed from the viewpoint of preventing the organic solvent from drying and forming wax, which significantly enhances the inkjet ejection stability of the black inkjet ink. From the viewpoint of improving the print density and ejection stability of the printed matter, the black inkjet ink is preferably used in a printing apparatus having an ink circulation mechanism configured to communicate with the inkjet head.

The pass method in the inkjet recording method includes a single pass method in which inkjet ink is ejected to a recording medium only once for recording, and a short shuttle head is reciprocally scanned in a direction perpendicular to the transport direction of the recording medium. Either the serial method of discharging and recording may be adopted. However, in the case of the serial method, it is necessary to adjust the ejection timing in consideration of the movement of the inkjet head, and the landing position is likely to shift. Therefore, when printing the black inkjet ink of the present invention, a single-pass method, particularly a method in which a recording medium is passed under a fixed inkjet head is preferably used.

There is no particular limitation on the method of ejecting black inkjet ink, and it is generated by a known method, for example, a drop-on-demand method (pressure pulse method) that utilizes the vibration pressure of a piezo element, or a method that heats ink to form bubbles. A thermal inkjet (bubble jet (registered trademark)) method that uses pressure can be used.

Further, the amount of ink droplets ejected from the inkjet head is preferably 0.2 to 30 picolitres from the viewpoint of greatly reducing the drying load and improving color reproducibility and image quality. More preferably, it is 1 to 20 picolitres.

The printing apparatus equipped with the black inkjet ink of the present invention or a set of water-based inkjet ink containing the black inkjet ink records the black inkjet ink or the set of the water-based inkjet ink containing the black inkjet ink as a recording medium by an inkjet printing method. It is preferable to have a mechanism for drying the ink on the recording medium after applying the ink on the surface. As described above, as the drying method used in the drying mechanism, one of a method of directly or indirectly contacting the ink and the heat source and a method of irradiating electromagnetic waves may be used, or a plurality of types may be used. May be used in combination. For example, by using the infrared drying method and the hot air drying method in combination, the ink can be dried more quickly than when each of them is used alone.

In the present invention, from the viewpoint of preventing bumping of liquid components in ink and obtaining printed matter having excellent print density, color reproducibility, and image quality, when the heat drying method is adopted, the drying temperature is set to 35 to 100 ° C. In addition, when the hot air drying method is adopted, it is preferable that the hot air temperature is 50 to 250 ° C.

On the other hand, it is preferable to adopt an infrared drying method as a method for drying the black inkjet ink of the present invention. At that time, from the viewpoint of obtaining a printed matter having excellent print density, color reproducibility, and image quality, 50% or more of the integrated value of the total output of infrared rays used for infrared irradiation exists in the wavelength region of 700 to 1500 nm. Is preferable.

Examples of light sources that irradiate infrared rays used in the infrared drying method include infrared lamps (halogen lamps, sheathed lamps, carbon lamps, etc.), infrared LEDs, infrared LDs, and the like. Among these, halogen lamps and infrared LEDs are preferably selected from the viewpoint of easily achieving the above-mentioned infrared output conditions. An optical filter and / or a reflection mirror may be used in combination with the light source that irradiates the infrared rays.

<Recording medium>
The recording medium for printing the black inkjet ink of the present invention or a set of water-based inkjet ink containing the black inkjet ink is not particularly limited, and is a high-absorbency recording medium, a low-absorbency recording medium, and a non-absorbent recording medium. Etc., all known ones can be used arbitrarily. As described above, the ink of the present invention can obtain a printed matter having excellent scratch resistance and print density regardless of the permeability of the recording medium.

In the present specification, the permeability of the recording medium shall be judged by the amount of water absorption measured by the dynamic scanning liquid absorption meter. Specifically, a recording medium in which the amount of pure water absorbed at a contact time of 100 msec, which is measured by the following method ^{, is less than 1 g / m 2} , is referred to as a “non-absorbable recording medium”, and is 1 g / m ² or more and 10 g / m ^2. A recording medium having a value of less than or less than 10 g / m ² is referred to as a “low-absorption recording medium”, and a recording medium having a value of 10 g / m 2 or more is referred to as a “high-absorption recording medium”.

The amount of water absorbed by the recording medium can be measured under the following conditions. Using a KM500win manufactured by Kumagai Riki Kogyo Co., Ltd. as a dynamic scanning liquid absorption meter, and using a recording medium having a size of about 15 to 20 cm square under the conditions of 23 ° C. and 50% RH, pure water under the following conditions. The amount of metastasis of is measured.
-Measurement method: Spiral Method
・ Measurement start radius: 20 mm
・ Measurement end radius: 60 mm
・ Contact time: 10 to 1,000 msec
・ Number of sampling points: 19 (measured so that they are approximately equal to the square root of the contact time)
・ Scanning interval: 7 mm
・ Speed switching angle of rotary table: 86.3 degrees ・ Headbox condition: width 5 mm, slit width 1 mm

Examples of high-absorbency recording media include uncoated paper such as stencil paper, medium-quality paper, wood-free paper, and recycled paper, cloth such as cotton, synthetic fiber woven fabric, silk, linen, and non-woven fabric, and leather. Of these, uncoated paper such as stencil paper, medium-quality paper, high-quality paper, and recycled paper is preferable from the viewpoint of obtaining printed matter having excellent ink print density, color development, and image quality.

In addition, examples of non-absorbent recording media or low-absorbent recording media include plastic substrates such as polyvinyl chloride, polyethylene terephthalate (PET), polypropylene, polyethylene, nylon, polystyrene, and polyvinyl alcohol, coated paper, and art paper. Examples thereof include coated paper base materials such as cast paper, metal base materials such as aluminum, iron, stainless steel, and titanium, and glass base materials.

The recording medium listed above may have a smooth surface, an uneven surface, or may be transparent, translucent, or opaque. Further, two or more kinds of these recording media may be bonded to each other. Further, a peeling adhesive layer or the like may be provided on the opposite side of the printing surface, or an adhesive layer or the like may be provided on the printing surface after printing. Further, the shape of the recording medium used in the above-mentioned inkjet recording method may be a roll shape or a single-wafer shape.

It should be noted that the wettability of the black inkjet ink is improved, the image quality, the print density and the dryness are improved, and since the surface of the printed matter is made uniform, the scratch resistance can also be improved. It is also preferable to perform surface modification such as corona treatment and plasma treatment.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In the following description, "parts" and "%" represent "parts by mass" and "% by mass", respectively, unless otherwise specified.

<Self-dispersing pigment dispersion 1>
As a self-dispersing pigment, "BONJET BLACK CW-3" (manufactured by Orient Chemical Industries Co., Ltd., carbon black with carboxyl groups, hydroxyl groups, etc. introduced on the surface, average particle size 100 nm, pigment concentration 13%) is used, and the pigment concentration is used. Partially volatilized and removed from water so that the content was 15%, and the self-dispersing pigment dispersion liquid 1 was obtained.

<Self-dispersing pigment dispersion liquid 2>
As a self-dispersing pigment, "BONJET BLACK CW-1" (manufactured by Orient Chemical Industries Co., Ltd., carbon black with carboxyl groups, hydroxyl groups, etc. introduced on the surface, average particle size 65 nm, pigment concentration 20%) is used, and the pigment concentration is used. Water was added so that the content was 15%, and the self-dispersing pigment dispersion liquid 2 was prepared.

<Self-dispersing pigment dispersion liquid 3>
As the self-dispersing pigment dispersion liquid 3, "CAB-O-JET 200" (manufactured by Cabot Corporation, carbon black with sodium sulfonate salt added, average particle size 80 nm, pigment concentration 15%) was used as it was.

<Production example of pigment dispersion resin 1>
93.4 parts of butanol was charged in a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, and replaced with nitrogen gas. The inside of the reaction vessel is heated to 110 ° C., and a mixture of 30 parts of acrylic acid, 35 parts of styrene, 35 parts of lauryl methacrylate as a polymerizable monomer, and 6 parts of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator is added. The mixture was added dropwise over 2 hours to carry out a polymerization reaction. After completion of the dropping, the reaction was carried out at 110 ° C. for 3 hours, 0.6 part of V-601 was added, and the reaction was further continued at 110 ° C. for 1 hour. Then, the reaction system was cooled to room temperature, 39 parts of dimethylaminoethanol was added to neutralize the reaction system, and then 100 parts of water was added. Then, the mixed solution is heated to 100 ° C. or higher to distill off butanol, and then water is used to adjust the solid content to 30% to obtain an aqueous solution of the pigment dispersion resin 1 (solid content 30%). Obtained. The pigment-dispersed resin 1 was water-soluble. The weight average molecular weight of the pigment-dispersed resin 1 and the acid value of 230 were measured by the method described above.

<Production example of methyl ethyl ketone solution of pigment dispersion resin 2>
95 parts of methyl ethyl ketone was charged into a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, and replaced with nitrogen gas. The inside of the reaction vessel is heated to 80 ° C., and 70 parts of styrene, 5 parts of acrylic acid, 10 parts of methyl methacrylate, 15 parts of polypropylene glycol methacrylate (Blemmer PP-500 manufactured by Nichiyu Co., Ltd.), and a polymerization initiator are used as polymerizable monomers. A mixture of 3.5 parts of V-65 (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise over 3 hours to carry out a polymerization reaction. After completion of the dropping, the reaction was carried out at 80 ° C. for 1 hour, 0.7 part of V-65 (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the reaction was further continued at 80 ° C. for 4 hours to prepare a solution of the pigment dispersion resin 2. Obtained. Then, 25 parts of methyl ethyl ketone was added, the reaction system was cooled to room temperature, and then the mixed solution was taken out from the reaction vessel and adjusted with methyl ethyl ketone so that the solid content became 30%. Minutes 30%) was obtained. The pigment-dispersed resin 2 was water-insoluble. The weight average molecular weight of the pigment-dispersed resin and the acid value were 30 as measured by the method described above.

<Production example of resin dispersion pigment dispersion liquid 1>
In a mixing container equipped with a stirrer, 15 parts of carbon black (primary particle diameter 16 nm, BET specific surface area 200 nm), 15 parts of an aqueous solution of pigment dispersion resin 1 (solid content 30%), and 70 parts of water are placed. After putting them in order, premixing was performed. Then, the resin-dispersed pigment dispersion 1 (pigment concentration 15%, solid content 19.5%) was obtained by performing the main dispersion using a dynomill having a volume of 0.6 L filled with 1800 g of zirconia beads having a diameter of 0.5 mm. Obtained.
The "aqueous solution" means a solution containing an aqueous medium and components dispersed and / or dissolved in the aqueous medium.

<Production example of resin dispersion pigment dispersion liquid 2>
This dispersion was carried out in the same manner as in the resin-dispersed pigment dispersion 1 except that the methyl ethyl ketone solution of the pigment-dispersed resin 2 was used instead of the aqueous solution of the pigment-dispersed resin 1. Then, methyl ethyl ketone was distilled off by vacuum distillation, and water was added so that the pigment concentration became 15% (solid content 19.5%) to obtain a resin-dispersed pigment dispersion liquid 2.

<Production example of resin particles 1 to 3 (styrene methacrylic resin particles)>
40 parts of water and 0.2 parts of Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as a surfactant are charged in a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, and an aqueous surfactant solution is prepared. Created. In another mixing container, 25 parts of styrene as a polymerizable monomer, 3 parts of methacrylic acid, 62 parts of methyl methacrylate, 10 parts of butyl acrylate, 1.8 parts of Aqualon KH-10 as a surfactant, and 51 parts of water. . Two parts were added and mixed well to prepare an emulsion precursor.

1.5 parts of the prepared emulsion precursor was added to a reaction vessel containing an aqueous surfactant solution and mixed well. Next, the temperature inside the reaction vessel was raised to 60 ° C., replaced with nitrogen gas, and then 1 part of a 5% aqueous solution of potassium persulfate and 0.2 part of a 1% aqueous solution of anhydrous sodium bicarbonate were added to the inside of the reaction vessel. The polymerization reaction was started while keeping the temperature at 60 ° C. After reacting at 60 ° C. for 5 minutes, the residue of the emulsion precursor (151.5 parts), 9 parts of a 5% aqueous solution of potassium persulfate, and 1.8 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added. The mixture was added dropwise over 5 hours, and then the reaction was continued for another 2 hours. Then, after cooling the reaction system to 30 ° C., diethylaminoethanol was added to adjust the pH of the mixed solution to 8.5, and water was used to adjust the solid content to 30% to obtain styrene (meth). ) An aqueous dispersion (solid content 30%) of the resin particles 1 which is the acrylic resin fine particles was obtained.

Further, the aqueous dispersion (solid) of the resin particles 2 and 3, which are styrene (meth) acrylic resin particles, was carried out by the same operation as the resin particles 1 except that the polymerizable monomer was changed as shown in Table 1. Minutes 30%) was obtained.

Table 1 also shows the acid value of the resin particles 1 to 3, the glass transition temperature, and the weight average molecular weight. The abbreviations of the polymerizable monomers shown in Table 1 are as follows.
-St: Styrene-MAA: Methacrylic acid-MMA: Methyl methacrylate-BA: Butyl acrylate-PME-400: Methoxypolyethylene glycol methacrylate (NOF Brenmer PME-400)

<Production example of resin particles 4 (urethane resin particles)>
In a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, 150 parts of methyl ethyl ketone and 69 parts of polycarbonate diol (molecular weight 2,000) having 1,6-hexanediol as the main skeleton as a polymerizable monomer. , 11.8 parts of isophorone diisocyanate, 9 parts of hexamethylene diisocyanate, and 8.3 parts of dimethylol propionic acid were charged, replaced with nitrogen gas, and then the inside of the reaction vessel was heated to 80 ° C. to carry out a polymerization reaction for 6 hours. Then, 1.9 parts of trimethylolpropane was further added, and the reaction was continued at 80 ° C. Then, after cooling the reaction system to room temperature, water was added, and an aqueous potassium hydroxide solution was further added with stirring to neutralize. Then, the mixed solution is heated under reduced pressure to distill off the methyl ethyl ketone, and then water is used to adjust the solid content to 40%. Solid content 40%) was obtained. The weight average molecular weight of the resin particles 4 and the acid value of 37 were 20,000 and the acid value was 37, as measured by the method described above.

<Production examples of water-soluble resins 1 to 3>
Composition of the mixture added dropwise to butanol (type and amount of polymerizable monomer and amount of V-601), amount of V-601 added after reacting at 110 ° C. for 3 hours, and used for neutralization. (Meta) acrylic water-soluble resin or styrene (meth) acrylic water-soluble resin by the same operation as the above pigment-dispersed resin except that the amount of dimethylaminoethanol (DMAE) was changed as shown in Table 2. An aqueous solution of the water-soluble resins 1 to 3 (solid content 40%) was obtained. Table 2 also shows the acid values of the water-soluble resins 1 to 3 and the glass transition temperature.

<Manufacturing example of black inkjet inks 1-42>
The following materials were sequentially added to the mixing vessel while stirring with a disper, and stirred until sufficiently uniform. Then, filtration was performed with a membrane filter having a pore size of 1 μm to obtain Black Inkjet Ink 1.
・ Self-dispersed pigment dispersion 1 (pigment concentration 15%) 15 parts ・ Resin dispersion pigment dispersion 1 (pigment concentration 15%) 35 parts ・ Hi-Tech P5300 (solid content 30%) 10 parts ・ Resin particles 1 (solid content 40%) ) 8 parts, water-soluble resin 1 (solid content 40%) 4 parts, 1,2-propanediol 15 parts, 1,2-hexanediol 6 parts, glycerin 2 parts, surfinol 104 1 part, TEGO Wet 280 1 part・ Triethanolamine 0.5 part ・ Proxel GXL 0.05 part ・ Ion exchanged water 2.45 part

Further, black inkjet inks 2 to 42 were obtained by the same method as the water-based inkjet ink 1 except that the materials shown in Table 3 below were used.

The materials listed in Table 3 are as follows.
(wax)
-P5300: Hi-Tech P5300 (manufactured by Toho Chemical Industry Co., Ltd., polypropylene-based wax, aqueous dispersion with a solid content of 30%, melting point 146 ° C., average particle size 78 nm)
-AQ515: AQUACER 515 (manufactured by BYK Chemie, polyethylene wax, 35% solid content aqueous dispersion, melting point 135 ° C., average particle size 36 nm)
AQ541: AQUACER 541 (manufactured by BYK Chemie, polyethylene wax, aqueous dispersion with 30% solid content, melting point 80 ° C., average particle size 180 nm)
FE230N: Charine FE230N (manufactured by Nissin Chemical Industry Co., Ltd., silicone wax, aqueous dispersion with 30% solid content, average particle size 270 nm)
(Water-soluble organic solvent)
· PG: 1,2-propanediol (propylene glycol, surface tension 35 mN / m, the boiling point _{188 ℃, b i × (c} i ÷ 100) = 5.4)
· 1,2-BD: 1,2- butanediol (surface tension 32 mN / m, the boiling point _{192 ℃, b i × (c} i ÷ 100) = 6.1)
· 1,2-HeD: 1,2- hexanediol (surface tension 26 mN / m, boiling _{22 4 ℃, b i × (} c i ÷ 100) = 8.6)
· MFG: Propylene glycol monomethyl ether (surface tension 23 mN / m, boiling point _{121 ℃, b i × (c} i ÷ 100) = 5.2)
· BDG: Diethylene glycol monobutyl ether (surface tension 28 mN / m, the boiling point _{230 ℃, b i × (c} i ÷ 100) = 8.2)
· EG: Ethylene glycol (surface tension 47 mN / m, the boiling point _{196 ℃, b i × (c} i ÷ 100) = 4.2)
Glycerin: surface tension of 62 mN / m, the boiling point _{290 ℃, b i × (c} i ÷ 100) = 4.7
(Surfactant)
-S104: Surfinol 104 (acetylene diol-based surface activator manufactured by Nissin Chemical Industry Co., Ltd., HLB value: 3.0)
-S465: Surfinol 465 (acetylene diol-based interface activator manufactured by Nisshin Kagaku Kogyo Co., Ltd., HLB value: 13.2)
TW280: TEGO Wet 280 (siloxane-based surfactant manufactured by Evonik, HLB value: 3.5)
(PH regulator)
-TEA: Triethanolamine (pKa value: 7.8, boiling point: 335 ° C)
DMAE: Dimethylaminoethanol (pKa value: 9.9, boiling point: 133 ° C.)
-28% NH ₃ : 28% aqueous ammonia (pKa value of ammonia: 9.3)
(Preservative)
-Proxel GXL: 1,2-benzoisothiazole-3-one solution manufactured by Arch Chemicals Co., Ltd.

[Examples 1-38, Comparative Examples 1-4]
Evaluations 1 to 7 shown below were carried out for the black inkjet inks 1-42 produced above. The evaluation results are as shown in Table 4.

<Evaluation 1: Evaluation of printed matter density (high quality paper, hot air drying)>
An inkjet head KJ4B-QA (manufactured by Kyocera, design resolution 600 dpi) is installed on the top of a conveyor capable of transporting a recording medium, and after filling each of the black inkjet inks 1-42 manufactured above, Oji Paper Co., Ltd. has a drop volume of 12 pL. A solid image (printing rate 100%, equivalent to ink film thickness 6 μm) was printed on OK Prince high-quality (high-quality paper) manufactured by the company, and the printed matter was put into an air oven at 70 ° C. within 10 seconds. After drying for 1 minute, the printed matter was taken out from the oven, and the optical density (OD value) was measured using a spectrophotometer (eXact manufactured by X-RITE). The light source was D50, the viewing angle was 2 °, the density status was ISO Status T, and the density white standard was an absolute value. The evaluation criteria are as follows, and the evaluation reference values 2 to 4 are set as the practical range.
4: OD value 1.30 or more 3: OD value 1.20 or more and less than 1.30 2: OD value 1.10 or more and less than 1.20 1: OD value less than 1.10

<Evaluation 2: Evaluation of printed matter density (coated paper, hot air drying)>
The inkjet printing apparatus used in Evaluation 1 was filled with the black inkjet inks 1 to 42 produced above, respectively, and then with a drop volume of 12 pL, Oji Paper Co., Ltd. OK Top Coat + (coated paper, basis weight 104.7 g / m). ² ) A solid image (printing rate 100%, equivalent to ink film thickness 6 μm) was printed on the paper, and the printed matter was put into an air oven at 70 ° C. within 10 seconds. After drying for 1 minute, the printed matter was taken out from the oven, and the optical density (OD value) was measured using a spectrophotometer (eXact manufactured by X-RITE). The light source, viewing angle, density status, and density white standard were the same as the conditions in Evaluation 1 above. The evaluation criteria are as follows, and the evaluation reference values 2 to 4 are set as the practical range.
4: OD value 2.00 or more 3: OD value 1.90 or more and less than 2.00 2: OD value 1.80 or more and less than 1.90 1: OD value less than 1.80

<Evaluation 3: Evaluation of printed matter density (coated paper, infrared drying)>
The inkjet printing apparatus used in Evaluation 1 was filled with the black inkjet inks 1 to 42 produced above, respectively, and then with a drop volume of 12 pL, Oji Paper Co., Ltd. OK Top Coat + (coated paper, basis weight 104.7 g / m). ² ) A solid image (printing rate 100%, equivalent to ink film thickness 6 μm) was printed on the top. Next, the obtained solid image was passed through the infrared drying device at a speed of 50 m / min.
In the infrared drying device used, an infrared lamp having a peak wavelength of 1.5 μm was arranged so that infrared rays were irradiated over 12 cm in a direction parallel to the transport direction of the recording medium. Further, the output power was adjusted in advance so that the surface temperature of the solid image portion immediately after the completion of infrared irradiation was 90 ° C.
Then, the optical density (OD value) of the printed matter after passing through the infrared drying device was measured in the same manner as in Evaluation 2. The evaluation criteria are as follows, and the evaluation reference values 2 to 4 are set as the practical range.
4: OD value 2.00 or more 3: OD value 1.90 or more and less than 2.00 2: OD value 1.80 or more and less than 1.90 1: OD value less than 1.80

<Evaluation 4: Evaluation of scratch resistance>
The inkjet printing apparatus used in Evaluation 1 was filled with the black inkjet inks 1 to 42 produced above, respectively, and then with a drop volume of 12 pL, Oji Paper Co., Ltd. OK Top Coat + (coated paper, basis weight 104.7 g / m). ² ) A solid image (printing rate 100%, equivalent to ink film thickness 6 μm) was printed on the paper, and the printed matter was put into an air oven at 70 ° C. within 10 seconds. After drying for 1 minute, the printed matter is taken out of the oven, rubbed with a test white cotton cloth (Kanakin No. 3) a predetermined number of times while applying a load of 200 g, and the scratch resistance is evaluated by visually observing whether the ink can be removed. bottom. The evaluation criteria are as follows, and the evaluation reference values 2 to 4 are set as the practical range.
No scratches or ink peeling on the printed surface was observed after rubbing 4:20 times. No scratches or ink peeling was observed on the printed surface even after rubbing 3: 10 times, but printing was performed after rubbing 20 times. Surface scratches and ink peeling were observed 2: 5 times rubbing did not show scratches on the printed surface or ink peeling, but 10 times rubbing showed scratches on the printed surface and ink peeling. After rubbing 1: 5 times, scratches on the printed surface and peeling of ink were observed.

<Evaluation 5: Evaluation of discharge stability>
The inkjet printing apparatus used in Evaluation 1 was filled with the black inkjet inks 1 to 42 produced above, respectively. After printing the nozzle check pattern and confirming that there was no nozzle omission, the mixture was allowed to stand by for a predetermined time in an environment of 25 ° C. After that, the nozzle check pattern was printed again and the number of missing nozzles was counted to evaluate the ejection stability. The evaluation criteria are as follows, and the evaluation reference values 2 to 4 are set as the practical range.
There was no nozzle omission even after waiting for 4: 3 hours. Nozzle omission was not found even after waiting for 3: 2 hours, but nozzle omission was 1 after waiting for 3 hours. Nozzle omission occurred at all even after waiting for 2: 1 hour, but after waiting for 2 hours, one or more nozzles had occurred. Waiting for 1: 1 hour. Later, one or more nozzles were missing.

As a result of the evaluation, the water-based inkjet inks 1 to 38 containing the self-dispersing pigment, the resin-dispersing pigment, and the wax and having an organic solvent content of 29% by mass or less were printed when the recording medium and the drying method were changed. It was confirmed that the printed matter had practical quality in all of the density, the scratch resistance of the printed matter, and the ejection stability.

<Manufacturing and evaluation of ink sets>
<Production example of cyan pigment dispersion liquid 1>
As a pigment, C.I. I. 20 parts of Pigment Blue 15: 3, 10 parts of an aqueous solution of pigment dispersion resin 1 and 70 parts of water were mixed, pre-dispersed with a disper, and then filled with 1,800 g of zirconia beads having a diameter of 0.5 mm. This dispersion was carried out using a 0.6 L dynomill to obtain a cyan pigment dispersion solution 1.

<Manufacturing of cyan inkjet inks 1 to 5>
The following materials were sequentially added to the mixing vessel while stirring with a disper, and stirred until sufficiently uniform. Then, filtration was performed with a membrane filter having a pore size of 1 μm to obtain cyan inkjet ink 1 (C1):
・ Cyan pigment dispersion 1 (pigment concentration 20%) 20 parts ・ AQUACER 515 (solid content 35%) 4 parts ・ Resin particles 1 (solid content 40%) 8 parts ・ Water-soluble resin 1 (solid content 40%) 4 parts・ 15 parts of 1,2-propanediol ・ 6 parts of 1,2-hexanediol ・ Surfinol 104 1 part ・ TEGO Wet 280 1 part ・ Triethanolamine 0.5 part ・ Proxel GXL 0.05 part ・ Ion exchange water 40 .45 copies

Further, cyan inkjet inks 2 to 5 (C2 to C5) were produced in the same manner as in the production example of cyan inkjet ink 1 except that the raw materials shown in Table 5 were used.

<Production example of magenta pigment dispersion liquid 1>
As a pigment, C.I. I. 20 parts of Pigment Red 150, 10 parts of an aqueous solution of pigment dispersion resin 1 and 70 parts of water were mixed, pre-dispersed with a disper, and then filled with 1,800 g of zirconia beads having a diameter of 0.5 mm. This dispersion was carried out using a 6 L dynomill to obtain a cyan pigment dispersion solution 1.

<Manufacturing of magenta inkjet inks 1 to 5>
The following materials were sequentially added to the mixing vessel while stirring with a disper, and stirred until sufficiently uniform. Then, filtration was performed with a membrane filter having a pore size of 1 μm to obtain magenta inkjet ink 1 (M1):
・ Magenta pigment dispersion 1 (pigment concentration 20%) 20 parts ・ AQUACER 515 (solid content 35%) 4 parts ・ Resin particles 1 (solid content 40%) 8 parts ・ Water-soluble resin 1 (solid content 40%) 4 parts・ 15 parts of 1,2-propanediol ・ 6 parts of 1,2-hexanediol ・ Surfinol 104 1 part ・ TEGO Wet 280 1 part ・ Triethanolamine 0.5 part ・ Proxel GXL 0.05 part ・ Ion exchange water 40 .45 copies

Further, magenta inkjet inks 2 to 5 (M2 to M5) were produced in the same manner as in the production example of magenta inkjet ink 1 except that the raw materials shown in Table 5 were used.

<Production example of yellow pigment dispersion liquid 1>
As a pigment, C.I. I. 20 parts of Pigment Yellow 14, 10 parts of an aqueous solution of pigment dispersion resin 1 and 70 parts of water were mixed, pre-dispersed with a disper, and then filled with 1,800 g of zirconia beads having a diameter of 0.5 mm. This dispersion was carried out using a 6 L dyno mill to obtain a yellow pigment dispersion liquid 1.

<Manufacturing of yellow inkjet inks 1 to 5>
The following materials were sequentially added to the mixing vessel while stirring with a disper, and stirred until sufficiently uniform. Then, filtration was performed with a membrane filter having a pore size of 1 μm to obtain Yellow Inkjet Ink 1 (Y1):
・ Yellow pigment dispersion 1 (pigment concentration 20%) 20 parts ・ AQUACER 515 (solid content 35%) 4 parts ・ Resin particles 1 (solid content 40%) 8 parts ・ Water-soluble resin 1 (solid content 40%) 4 parts・ 15 parts of 1,2-propanediol ・ 6 parts of 1,2-hexanediol ・ Surfinol 104 1 part ・ TEGO Wet 280 1 part ・ Triethanolamine 0.5 part ・ Proxel GXL 0.05 part ・ Ion exchange water 40 .45 copies

Further, yellow inkjet inks 2 to 5 (Y2 to Y5) were produced in the same manner as in the production example of yellow inkjet ink 1 except that the raw materials shown in Table 5 were used.

<Examples 39 to 43>
The black inkjet ink, cyan inkjet ink, magenta inkjet ink, and yellow inkjet ink produced above were used in the combinations (ink sets) shown in Table 6 and evaluated as follows. The evaluation results obtained were as shown in Table 6.

<Evaluation 6: Evaluation of image quality (coated paper) of ink set>
The ink combinations shown in Table 6 were used as an ink set, and the ink jet heads (KJ4B-QA model, design resolution 600 dpi) manufactured by Kyocera Corporation were filled in an inkjet ejection device equipped with four ink jet heads (design resolution 600 dpi). Next, a color chart image (black, cyan, ^{104.7 g / m 2} ) on an OK top coat + (coated paper, basis weight 104.7 g / m 2) manufactured by Oji Paper Co., Ltd. under printing conditions of a frequency of 30 kHz, 600 × 600 dpi, and a drop volume of 12 pL. An image in which four color patches of magenta and yellow were printed at the same location at the same printing rate) was printed, and the printed matter was placed in a 70 ° C. air oven within 10 seconds and dried for 1 minute. .. The four colors were dried together by putting them in an air oven after printing all the inks without drying each color.
Then, in the obtained printed matter, the portion where the total print rate (total of the print rates of each color) is 280% (that is, the print rate of each color is 70%) is visually confirmed with a loupe. , Color mixing bleeding was evaluated. The evaluation criteria are as follows, and the evaluations of 2 and 3 are set as practical areas.
4: No color mixing bleeding was observed with the loupe and visually. 3: Slight color mixing bleeding was observed with the loupe, but no color mixing bleeding was observed visually. 2: Color mixing bleeding was also observed visually. Was slight 1: Color bleeding was clearly seen visually

<Evaluation 7: Evaluation of print density (sharpness)>
After filling each of the ink jet printing devices used in Evaluation 6 with the ink combinations shown in Table 6 as an ink set, the drop volume is 12 pL, and Oji Paper Co., Ltd. OK Top Coat + (coated paper, basis weight 104.7 g / A natural image N1 (portrait) of JIS X 9201 high-definition color digital standard image data (CMYK / SCID) was printed on m ^2). Then, the obtained image was passed through the infrared drying device at a speed of 50 m / min.
In the infrared drying device used, an infrared lamp having a peak wavelength of 1.5 μm was arranged so that infrared rays were irradiated over 12 cm in a direction parallel to the transport direction of the recording medium. Further, the output power was adjusted in advance so that the surface temperature of the image portion immediately after the completion of infrared irradiation was 90 ° C.
Then, the printed matter after passing through the infrared drying device was visually observed to evaluate the print density (sharpness). The evaluation criteria are as follows, and the evaluations of 2 and 3 are set as practical areas.
3: Sufficiently clear and sufficiently high print density 2: Slightly unclear but sufficiently high print density, or slightly low print density but sufficiently clear image 1 : The sharpness was clearly low, and the print density was also low.

<Evaluation 8: Evaluation of scratch resistance>
Of the color chart image printed matter produced in Evaluation 6, the same method and evaluation as in Evaluation 4 described above are used except that the portion having a total print rate of 320% (that is, the print rate of each color is 80%) is used. The scratch resistance was evaluated according to the evaluation criteria.

Claims (8)

A black inkjet ink containing water, pigments, organic solvents, and wax.
The pigment contains a self-dispersing pigment and a resin-dispersed pigment.
A black inkjet ink in which the content of the organic solvent is 29% by mass or less based on the total amount of the black inkjet ink. The black inkjet ink according to claim 1, wherein the P value defined by the following general formula (1) is 1.6 or less.

In (Formula (1), i, the black represents the type of the organic solvent contained in the inkjet ink. Further, b _i represents the boiling point (℃) at 1 atmosphere of an organic solvent i, c _i Represents the content (mass%) of the organic solvent i with respect to the total amount of the black inkjet ink, s _i represents the static surface tension (mN / m) of the organic solvent i at 25 ° C., and n represents the content. Indicates the number of types of organic solvents to be used.) The black inkjet ink according to claim 1 or 2, wherein the wax contains a polyolefin wax. Furthermore, it contains resin particles as a binder resin,
1. The resin particles include one or more resin particles selected from the group consisting of acrylic resin particles, styrene acrylic resin particles, urethane resin particles, styrene butadiene resin particles, and vinyl chloride resin particles. The black inkjet ink according to any one of 3 to 3. The black inkjet ink according to any one of claims 1 to 4, further comprising a water-soluble resin as a binder resin. In addition, it contains a surfactant and
The black inkjet ink according to any one of claims 1 to 5, wherein the surfactant contains a surfactant having an HLB value of 10 or less. The black inkjet ink according to any one of claims 1 to 6, wherein the content of the organic solvent having a boiling point of 250 to 300 ° C. under 1 atm is 9% by mass or less in the total amount of the black inkjet ink. An ink set containing black inkjet ink, cyan inkjet ink, magenta inkjet ink, and yellow inkjet ink.
The black inkjet ink is the black inkjet ink according to any one of claims 1 to 7.
The cyan inkjet ink, magenta inkjet ink, and yellow inkjet ink each contain water, a pigment, and an organic solvent, and the amount of the organic solvent having a boiling point of 250 to 300 ° C. under 1 atm is 5% by mass. % Or less, ink set.