JP2023060416A - Aqueous inkjet ink and printed matter - Google Patents

Abstract

To provide aqueous inkjet ink which gives a printed matter excellent in image quality and color development property regardless of the type of a paper base material to be printed, and is also excellent in discharge stability.SOLUTION: Aqueous inkjet ink contains a pigment (A), a water-soluble acrylic urethane resin (B), a water-soluble organic solvent (C), a surface active agent (D) having an HLB value of 0-7, and water, wherein the water-soluble acrylic urethane rein (B) includes a constitutional unit derived from acrylic diol (b1) including a constitutional unit derived from a chain transfer agent (t) having one mercapto group and two hydroxyl groups, and a vinyl monomer having an acid group, a constitutional unit derived from polyisocyanate (b2), and a constitutional unit derived from low molecular diol (b3) having one acid group and two hydroxyl groups. The water-soluble acrylic urethane resin (B) has a weight average molecular weight of 9,000-32,000, and a content in the total amount of the aqueous inkjet ink is 2-10 mass%.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a water-based inkjet ink and printed matter produced using the water-based inkjet ink.

The inkjet printing method is a method in which fine droplets of ink are ejected onto a substrate from very fine nozzles in an inkjet head and made to land on a substrate to form an image or character (hereinafter referred to as an image and / or character The substrate on which is recorded is collectively referred to as the “printed matter”). Compared to other printing methods, the inkjet printing method is superior in terms of design flexibility and cost of the printing apparatus, running cost during printing, ease of full-color printing, and the like, and has been widely used. In addition, along with the remarkable improvement in inkjet head performance in recent years, it is expected that the inkjet printing method will be developed in the industrial printing market where the offset printing method was conventionally used.

In general, paper substrates are broadly classified into uncoated paper such as fine paper and medium-grade paper, and coated paper such as coated paper and art paper. It is required to be able to produce printed matter with excellent quality. However, the ink used in the inkjet printing method (inkjet ink), in particular, the water-based inkjet ink containing water as the main component (hereinafter also simply referred to as "ink") is compared to the ink used in the offset printing method. Due to the low viscosity, for example, when an image is printed on a coated paper having a surface coat layer, "mixed color bleeding" in which colors are mixed between inks of different colors, and in areas of the same color, the color A phenomenon such as "color unevenness" occurs in which the color becomes uneven, and the image quality deteriorates. Also, when printing on uncoated paper that does not have a surface coat layer, a phenomenon called "feathering" occurs, in which the ink bleeds irregularly along the fibers of the base material, resulting in a drop in image quality. In addition, a phenomenon called "bleed-through" occurs in which the ink penetrates to the back side of the paper, resulting in a decrease in the image density (color development) of the printed matter.

In order to solve the above problems, various studies have been made so far. For example, in Patent Document 1, an aqueous inkjet ink containing a 1,2-alkanediol having a low surface tension and an alkanediol at both ends having a normal boiling point of 250° C. or less and having 3 or more carbon atoms is used as an inkjet ink having a circulation mechanism. A method of printing with a head is disclosed. However, in Patent Document 1, the assurance and improvement of ejection stability are realized by designing a printing apparatus including an inkjet head equipped with the circulation mechanism. From the point of view of Further, the present inventors have studied and found that the formulation specifically disclosed in the examples of Patent Document 1 does not lead to complete suppression of feathering on uncoated paper.

Patent Document 2 discloses a water-based inkjet ink containing 2-ethyl-1,3-hexanediol or 1,2-hexanediol and an acrylic resin having structural units derived from stearyl methacrylate or α-methylstyrene. there is However, since the above water-soluble organic solvent has a high boiling point, when the ink described in Patent Document 2 is simply printed on, for example, coated paper, there is a strong possibility that the above-described mixed color bleeding and color unevenness will occur.
Furthermore, in Patent Document 3, a modified polyalkoxylate having a star structure is further added to the water-based inkjet ink disclosed in Patent Document 2 above. However, since the modified polyalkoxylate having the star structure is considered to be highly hydrophilic, it is expected that the image quality when printed on coated paper will be inferior, as in the case of Patent Document 2.

As described above, no water-based inkjet ink has existed until now, which gives printed matter with excellent image quality and color development regardless of the type of paper substrate on which it is printed, and also has excellent ejection stability. .

JP 2021-133555 A Japanese Unexamined Patent Application Publication No. 2014-91760 JP 2015-151482 A

The present invention has been made to solve the above-mentioned problems, and its object is to obtain a printed matter excellent in image quality and color development regardless of the type of paper substrate to be printed, and also to improve ejection stability. To provide an excellent water-based inkjet ink.

As a result of intensive studies by the present inventors in order to solve the above problems, a surfactant (D) containing a certain amount of a water-soluble acrylic urethane resin having a specific structure and having an HLB value of 0 to 7 The present invention has been completed by discovering a water-based inkjet ink that uses a combination of

That is, the present invention provides a water-based inkjet ink containing a pigment (A), a water-soluble acrylic urethane resin (B), a water-soluble organic solvent (C), a surfactant (D), and water, wherein the following (1) It relates to a water-based inkjet ink that satisfies all the conditions of (5).
(1) The water-soluble acrylic urethane resin (B) is
structural units derived from acrylic diol (b1),
A structural unit derived from a polyisocyanate (b2), and
A structural unit derived from a low-molecular-weight diol (b3) having a molecular weight of 100 to 500 and having one acid group and two hydroxyl groups.
(2) the acrylic diol (b1) is
a structural unit derived from a chain transfer agent (t) having one mercapto group and two hydroxyl groups;
A structural unit derived from a vinyl monomer (f1) having an acid group, and
A structural unit derived from (meth)acrylate (f2) having no acid group is included.
(3) The water-soluble acrylic urethane resin (B) has a weight average molecular weight of 9,000 to 32,000.
(4) The content of the water-soluble acrylic urethane resin (B) is 2 to 10 mass % of the total amount of the water-based inkjet ink.
(5) The HLB value of the surfactant (D) is 0-7.

The present invention also relates to the water-based inkjet ink, wherein the acrylic diol (b1) has an acid value of 25 to 310 mgKOH/g.

Further, in the present invention, the content of structural units derived from the chain transfer agent (t) contained in the acrylic diol (b1) is 1 to 8 with respect to the total amount of structural units derived from the acrylic diol (b1). .7% by weight of the water-based inkjet ink.

Further, the present invention provides the amount of acid groups derived from the vinyl monomer having an acid group (f1) and the amount of acid groups derived from the low-molecular-weight diol (b3), which are present per unit mass of the water-soluble acrylic urethane resin (B). and the amount of acid groups is 1:4 to 4:1.

The present invention also relates to a printed matter obtained by printing the water-based inkjet ink on a paper substrate.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a water-based inkjet ink that gives printed matter with excellent image quality and excellent color development regardless of the type of paper substrate on which it is printed, and that has excellent ejection stability. Specifically, the water-based inkjet ink of the present invention can provide printed matter with excellent color development without feathering and strike-through on uncoated paper, and on coated paper, color mixture can be obtained. A printed matter free from bleeding and color unevenness and excellent in color developability can be obtained, and furthermore, the ejection stability from the inkjet head is excellent regardless of the printing conditions.

Examples of preferred embodiments of the present invention are described below. The present invention is not limited to the following embodiments, and includes various modifications implemented within the scope of the invention.

As described above, since uncoated paper does not have a surface coat layer, printed ink easily permeates inside. As a result, the ink does not easily remain on the surface of the uncoated paper, and although the paper seems to dry quickly, problems such as feathering and loss of image density (color development) due to strike-through may occur. be. On the other hand, since the printed ink does not easily permeate the inside of the coated paper, problems such as mixed color bleeding and color unevenness occur in the printed matter when inks of different colors or a large amount of ink are printed.

The water-based inkjet ink of the present invention is intended to solve the above-described problems and to obtain printed matter excellent in image quality and color development regardless of the type of paper base material, and has the constitution described below. have.

First, the water-based inkjet ink of the present invention contains a surfactant (D) having an HLB value of 0-7. In general, the smaller the HLB value, the higher the hydrophobicity of the surfactant (D), and the easier it is to be oriented at the air-liquid interface of the water-based inkjet ink. As a result, when water-based inkjet ink is printed on coated paper, the droplets of the ink that landed on the coated paper spread quickly, and by suppressing the coalescence of the droplets, mixed color bleeding and color unevenness can be suppressed. On the other hand, water-based inkjet inks containing a surfactant (D) with a small HLB value have a significantly reduced surface tension, so the above-described problems when printing on uncoated paper tend to occur. Furthermore, the decrease in surface tension may cause deterioration in ejection stability from the inkjet head.

Therefore, the water-based inkjet ink of the present invention further contains a certain amount of a water-soluble acrylic urethane resin (B) to solve this problem.

The water-soluble acrylic urethane resin (B) is a urethane resin containing the acrylic diol (b1) as a structural unit, and the structural unit derived from the acrylic diol (b1) is grafted onto the urethane resin chain. there is Both the acrylic diol (b1) and the urethane resin chain have acid groups. The water-soluble acrylic urethane resin (B), which is "a water-soluble polymer having an acid group in both the main chain and the graft chain", is entangled with the pulp constituting the uncoated paper, and / or the uncoated paper It is thought that the permeation of the water-based inkjet ink containing the water-soluble acrylic urethane resin (B) is suppressed by interacting with the contained ionic component such as the sizing agent. As a result, when printed on uncoated paper, feathering is suppressed, and printed matter with excellent color development without strike-through is considered to be obtained. In addition, the hydrogen bond network formed by the acid groups present in the water-soluble acrylic urethane resin (B) makes it difficult for the droplets of the water-based inkjet ink to coalesce, and color bleeding and color mixing when printing on coated paper. It is also possible to further reduce unevenness.

As described above, the water-soluble acrylic urethane resin (B) contains a plurality of acid groups and is water-soluble, so it is highly hydrophilic. Therefore, it is difficult to mix with the surfactant (D) having high hydrophobicity, and the respective effects described above are not inhibited.

Furthermore, in addition to the above-mentioned hydrogen bond network, the water-soluble acrylic urethane resin ( The viscoelasticity of the water-based inkjet ink containing a certain amount of B) is optimized. In general, water-based inkjet inks containing a water-soluble resin are difficult to ensure ejection stability due to the structural viscosity and drying thickening due to the water-soluble resin. Due to the above effects obtained by employing the above, a significant improvement in ejection stability can be realized.

As described above, it is possible to obtain printed matter with excellent ejection stability from the inkjet head and excellent image quality and color development regardless of the type of paper substrate used for printing. Specifically, uncoated paper On the other hand, in order to obtain a water-based inkjet ink that gives printed matter with excellent color development without feathering, and gives printed matter with excellent color development without color mixture bleeding and color unevenness on coated paper, the above The adoption of composition is essential.

Constituent materials and the like of the water-based inkjet ink of the present invention are described in detail below.

<Water-soluble acrylic urethane resin (B)>
In general, the term "acrylic urethane resin" refers to resins containing acrylic resin chains and urethane resin chains. The water-soluble acrylic urethane resin (B) contained in the water-based inkjet ink of the present invention comprises a structural unit derived from the acrylic diol (b1), a structural unit derived from the polyisocyanate (b2), one acid group and two hydroxyl groups. and a structural unit derived from a low-molecular-weight diol (b3) having a molecular weight of 100 to 500.

In addition, the "water-soluble resin" in this specification means that a mixture of 1 g of the target resin and 99 g of water is transparent to the naked eye, or the particle size can be measured using the mixture as a sample. shall mean the state of being unable to However, the particle size is a value measured by a dynamic light scattering method, for example, using Microtrack Bell Co., Ltd. "Nanotrack UPA-EX150", measured under conditions of 25 ° C., volume-based median It is a system.

The water-soluble acrylic urethane resin (B) is preferably used at least as a binder resin. In addition, from the viewpoint of improving ejection stability, suppressing feathering and ensuring color development in printed matter on uncoated paper, and maintaining color development in coated paper, the preferred content is the total amount of water-based inkjet ink. 2 to 10% by mass, more preferably 2.5 to 9% by mass, particularly preferably 3 to 8% by mass.

In addition, the "binder resin" in the present application is a resin used to bind the pigment on the base material and to impart scratch resistance, water resistance, adhesion to the base material, etc. to the printed matter after drying. be. As will be described later, the water-based inkjet ink used in the present invention may contain a pigment dispersing resin. Its intended use is different from that of the binder resin.

Therefore, from the viewpoint of sufficiently expressing the function of the water-soluble acrylic urethane resin (B) and effectively obtaining the effects of the present invention, when the water-based inkjet ink of the present invention contains a pigment dispersion resin, the pigment part acid resin preferably contains a resin other than the water-soluble acrylic urethane resin (B). Also, the pigment (A) may be dispersed by a material or method (details will be described later) that is not a pigment dispersing resin.

The pigment dispersing resin and the binder resin are distinguished by their adsorption rate to the pigment. That is, a pigment dispersion containing a pigment (A), a resin to be judged, and an aqueous medium (liquid medium containing 50% by mass or more of water), wherein the concentration of the pigment (A) is 5% by mass, In the pigment dispersion containing 98% by mass or more of the total amount of water in the aqueous medium, a resin having a resin adsorption rate of 35% by mass or more with respect to the pigment (A) is referred to as a pigment dispersion resin, and a resin having an adsorption rate of less than 35% by mass is referred to as a pigment dispersion resin. Binder resin.

Further, the pigment dispersion liquid used for the measurement of the adsorption rate is prepared, for example, by the method described in the production example of the cyan pigment dispersion liquid described later, after producing a high-concentration pigment dispersion liquid having a pigment concentration of 20% by mass, It can be produced by diluting with water until the pigment concentration reaches 5% by mass. The adsorption rate is obtained by, for example, subjecting a pigment dispersion with a pigment concentration of 5% by mass to ultracentrifugation (for example, at 30,000 rpm for 4 hours) and measuring the amount of resin contained in the supernatant. After that, it can be calculated using the following formula 1.

(Formula 1) Adsorption rate (%) = (WR1-WR2) x 100/WR1

In Formula 1 above, WR1 represents the amount of resin contained in the pigment dispersion before ultracentrifugation, and WR2 represents the amount of resin contained in the supernatant.

The water-soluble acrylic urethane resin (B) has a weight average molecular weight of 9,000 to 32,000. When the weight-average molecular weight is 9,000 or more, it is possible to suppress the penetration of the water-based inkjet ink into the uncoated paper, and on the uncoated paper, there is no feathering and excellent color development is obtained. can be made. In addition, by strengthening the hydrogen bond network, it is also effective in suppressing color bleeding and color unevenness when printing on uncoated paper. Furthermore, it is also suitable from the viewpoint of the abrasion resistance of the printed matter. Further, when the weight average molecular weight is 32,000 or less, the structural viscosity of the water-soluble acrylic urethane resin (B) becomes small, and the viscoelasticity of the water-based inkjet ink is optimized, thereby improving the ejection stability. From the viewpoint of more preferably expressing the above effect, the weight average molecular weight is more preferably 10,000 to 30,000, more preferably 11,000 to 28,000, and 12,000 to 12,000. 26,000 is particularly preferred. Moreover, the weight average molecular weight of the water-soluble acrylic urethane resin (B) is a polystyrene conversion value measured by a method described later.

Further, the acid value of the water-soluble acrylic urethane resin (B) is preferably 25-90 mgKOH/g. When the acid value of the water-soluble acrylic urethane resin (B) is 25 mgKOH/g or more, the solubility in an aqueous medium is improved, so that it is easy to redissolve the resin (B) partially dried on an inkjet head, for example. , leading to an improvement in ejection stability. In addition, since the hydrogen bond network described above is preferably formed, feathering is suppressed and color development is improved when printing on uncoated paper, and color bleeding and color unevenness when printing on coated paper are suppressed. Suppression becomes easier. On the other hand, if it is 90 mgKOH/g or less, the drying thickening of the water-based inkjet ink can be suppressed, so the ejection stability can be improved. The acid value of the water-soluble acrylic urethane resin is preferably 30 to 80 mgKOH/g, more preferably 35 to 70 mgKOH/g, from the viewpoint of suitably expressing the above effects and from the viewpoint of synthetic handling. more preferred. In addition, the acid value of the water-soluble acrylic urethane resin (B) is an actual value measured by a method described later.

In addition, the amount of acid groups derived from the vinyl monomer having an acid group (f1) and the amount of acid groups derived from the low-molecular-weight diol (b3), which are present per unit mass of the water-soluble acrylic urethane resin (B), is preferably from 1:4 to 4:1. When the ratio of the acid group derived from each raw material is within the above range, the solubility in water based on the hydration of the acid group derived from the vinyl monomer (f1) having the acid group is increased, and the ejection stability is improved. At the same time, although the details are unknown, the hydrogen bond network described above is preferably formed, so feathering is suppressed and color development is improved when printing on uncoated paper, and when printing on coated paper This makes it easy to suppress mixed color bleeding and color unevenness. The above ratio is more preferably 1:3 to 3:1, particularly preferably 2:3 to 3:2.

The water-soluble acrylic urethane resin (B) is, for example, an acrylic diol (b1) produced by the method described later, and a polyol containing a low molecular weight diol (b3) having a molecular weight of 100 to 500 (compound having two or more hydroxyl groups ) and a polyisocyanate (b2) through polyaddition (urethane polymerization). Further, after the above polyaddition, it may be further reacted with a chain extender (urea reaction) to be described later. In this case, the water-soluble acrylic urethane resin (B) has urea bonds in addition to urethane bonds.

Next, each material used in the production example of the water-soluble acrylic urethane resin (B) will be described in detail below.

<Acrylic Diol (b1)>
The acrylic diol (b1) constituting the water-soluble acrylic urethane resin (B) comprises a structural unit derived from a chain transfer agent (t) containing one mercapto group and two hydroxyl groups, and a vinyl monomer having an acid group (f1 ) and a structural unit derived from (meth)acrylate (f2) having no acid group.

The acid value of the acrylic diol (b1) is preferably 25-310 mgKOH/g. When the acid value of the acrylic diol (b1) is 25 mgKOH/g or more, the water-based acrylic urethane resin (B) is easily dissolved in water, and the hydrogen bond network described above is preferably formed. When printed on a coated paper, a printed matter with no feathering and excellent color development is obtained, and when printed on coated paper, a printed matter without color bleeding and color unevenness is obtained. Further, when the acid value is 310 mgKOH/g or less, the ejection stability of the water-based inkjet ink using the water-soluble acrylic urethane resin (B) is improved. The acid value of the acrylic diol (b1) is more preferably 50 to 300 mgKOH/g, and even more preferably 65 to 280 mgKOH/g, from the point of view of the above effect and from the viewpoint of synthesis. . The acid value of acrylic diol (b1) is an actual value measured by a method described later.

The acrylic diol (b1) is prepared, for example, in the presence of a chain transfer agent (t) containing one mercapto group and two hydroxyl groups, a vinyl monomer (f1) having an acid group, and a vinyl monomer (f1) having no acid group ( It can be obtained by polymerizing meth)acrylate (f2).

(Vinyl monomer having an acid group (f1))
The vinyl monomer (f1) having an acid group is not particularly limited as long as it is a vinyl polymer having an acid group. For example, acrylic acid, methacrylic acid, vinylacetic acid, crotonic acid, cinnamic acid, mesaconic acid, citraconic acid, glutaconic acid, 3-allyloxypropionic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid Acid, fumaric acid monoester, vinyl phthalate, vinyl pyromellitic acid, 5-hexenoic acid, 5-heptenoic acid, 6-heptenoic acid, 7-octenoic acid, 8-nonenoic acid, 9-decenoic acid, 10-undecylenic acid , 11-dresylenic acid, 17-octadecylenic acid, oleic acid, 3-(2-allyloxyethoxycarbonyl)propionic acid, 3-(2-allyloxybutoxycarbonyl)propionic acid, 3-(2-vinyloxybutoxycarbonyl) Carboxy group-containing vinyl monomers such as propionic acid and 3-(2-vinyloxybutoxycarbonyl)propionic acid;
sulfonic acid group-containing vinyl monomers such as styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, and methacrylsulfonic acid;
(Meth)acryloyloxyalkyl (C1-C24) phosphoric acid monoesters such as 2-hydroxyethyl (meth)acryloyl phosphate, (meth)acryloyloxyalkyl (C1-24) phosphonic acid, acid phosphooxyethyl (meth) ) phosphate group-containing vinyl monomers such as acrylates, mono(2-hydroxyethyl (meth)acrylate) phosphates;
etc. Among those listed above, it is preferable to use a carboxy group-containing vinyl monomer because of the wide range of material selection and the ease of synthesis with (meth)acrylate (f2) or the like that does not have an acid group. . In particular, acrylic acid and/or methacrylic acid are more preferably used from the viewpoints of availability, handleability in synthesis, and the like.

((Meth)acrylate (f2) having no acid group)
Compounds that can be used as the (meth)acrylate having no acid group (f2) are not particularly limited, but examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl Alkyl (meth)acrylates such as (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cetyl (meth)acrylate, cyclohexyl (meth)acrylate;
aromatic ring-containing (meth)acrylates such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, (meth)acrylic acid-allylphenyl;
Perfluoromethylmethyl (meth)acrylate, perfluoroethylmethyl (meth)acrylate, 2-perfluorobutylethyl (meth)acrylate, 2-perfluorohexylethyl (meth)acrylate, 2-perfluorooctylethyl (meth)acrylate , 2-perfluoroisononylethyl (meth)acrylate, 2-perfluorononylethyl (meth)acrylate, perfluoroalkyl group-containing (meth)acrylates such as 2-perfluorodecylethyl (meth)acrylate;
Hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 4-hydroxyvinylbenzene, allyl alcohol, and glycerin mono(meth)acrylate ;
Polyethylene glycol (meth)acrylate, methoxypolyethyleneglycol (meth)acrylate, ethoxypolyethyleneglycol (meth)acrylate, propoxypolyethyleneglycol (meth)acrylate, n-butoxypolyethyleneglycol (meth)acrylate, n-pentoxypolyethyleneglycol (meth)acrylate Acrylate, phenoxy polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate, ethoxy polypropylene glycol (meth) acrylate, propoxy polypropylene glycol (meth) acrylate, n-butoxy polypropylene glycol (meth) acrylate , n-pentoxypolypropylene glycol (meth)acrylate, phenoxypolypropylene glycol (meth)acrylate, polytetramethylene glycol (meth)acrylate, methoxypolytetramethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, hexaethylene Polyether chain-containing (meth)acrylates such as glycol (meth)acrylate and methoxyhexaethylene glycol (meth)acrylate;
isobornyl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, propoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, ethoxypropyl (meth) acrylate, allyl (meth) acrylate, (meth) ) 1-methylallyl acrylate, 2-methylallyl (meth) acrylate, 1-butenyl (meth) acrylate, 2-butenyl (meth) acrylate, 3-butenyl (meth) acrylate, 2- (meth) acrylate Other (meth)acrylates such as chlorallyl, 3-chloroallyl (meth)acrylate, and vinyl (meth)acrylate;
ethylenically unsaturated group-containing esters such as diallyl maleate, diallyl itaconate, vinyl crotonate, and vinyl oleate;
etc. Among them, the alkyl (meth)acrylate has a long molecular chain, and the water-soluble acrylic urethane resin (B) is easily entangled with pulp, so when printing on uncoated paper, feathering is suppressed, image quality and color development are improved. It is preferably selected from the viewpoint that a printed matter having excellent properties can be obtained. In particular, alkyl (meth)acrylates in which the alkyl group has 4 to 18 carbon atoms can be preferably used.

(Other vinyl monomers (f3))
In the polymerization of the acrylic diol (b1), vinyl monomers other than the vinyl monomer (f1) having an acid group and the (meth)acrylate (f2) having no acid group (hereinafter referred to as " Other vinyl monomers (f3)”) may also be used. In this case, the acrylic diol (b1) also contains structural units derived from the other vinyl monomer (f3).

Examples of other vinyl monomers (f3) include α-olefin vinyl monomers such as 1-butene, 1-pentene, 1-hexene, 1-octene, 1-nonene, and 1-decene; styrene, α - aromatic vinyl monomers such as methylstyrene, 2-methylstyrene and allylbenzene; amide group-containing monomers such as acrylamide, methacrylamide, propylacrylamide, dimethylacrylamide, N-vinylpyrrolidone and N-vinylcaprolactam; acrylonitrile , nitrile group-containing monomers such as methacrylonitrile; fatty acid vinyl monomers such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl hexanoate, vinyl laurate and vinyl stearate;

(Chain transfer agent (t))
Acrylic diol (b1) contains structural units derived from a chain transfer agent (t) having one mercapto group and two hydroxyl groups. In order to include the structural unit derived from the chain transfer agent (t) having one mercapto group and two hydroxyl groups in the acrylic diol (b1), for example, in the presence of the chain transfer agent (t), A plurality of vinyl monomers may be polymerized. By doing so, the chain transfer agent (t) reacts with the vinyl monomer to obtain an acrylic diol (b1) having two hydroxyl groups at the molecular chain ends.

Chain transfer agents (t) that can be suitably used in the present invention include, for example, 3-mercapto-1,2-propanediol, 2-mercapto-1,3-propanediol, 2-mercapto-2-methyl-1,3 -propanediol, 2-mercapto-2-ethyl-1,3-propanediol, 2-mercaptoethyl-2-methyl-1,3-propanediol, 2-mercaptoethyl-2-ethyl-1,3-propanediol, etc. is mentioned.

The content of the structural units derived from the chain transfer agent (t) contained in the acrylic diol (b1) is 1 to 8.7% by mass with respect to the total amount of structural units derived from the acrylic diol (b1). is preferred. When the amount of structural units derived from the chain transfer agent (t) is 1% by mass or more with respect to the total amount of structural units derived from the acrylic diol (b1), the molecular weight of the acrylic diol (b1) and the acrylic It becomes easier to control the weight average molecular weight of the water-soluble acrylic urethane resin (B) produced using the diol (b1). As a result, it becomes easy to obtain a water-based inkjet ink excellent in image quality and ejection stability regardless of the type of paper substrate. Further, when the amount of structural units derived from the chain transfer agent (t) is 8.7% by mass or less, the amount of structural units derived from the vinyl polymer constituting the acrylic diol (b1) is relatively increased. , the effect of the acid group contained in the acrylic diol (b1) can be fully exhibited. From the viewpoint of more preferably expressing the above effects and improving the handling property during synthesis, the amount of structural units derived from the chain transfer agent (t) should be less than that of the structural units derived from the acrylic diol (b1). It is more preferably 1.1 to 7.8% by mass, particularly preferably 1.2 to 7.4% by mass, relative to the total amount.

(Polymerization initiator)
In the polymerization of the acrylic diol (b1), it is preferable to use a radical polymerization initiator (hereinafter also simply referred to as "polymerization initiator").The polymerization initiator should be capable of initiating radical polymerization. Conventionally known oil-soluble polymerization initiators and water-soluble polymerization initiators can be used.

Examples of oil-soluble polymerization initiators include benzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl hydroperoxide, tert-butyl peroxy (2-ethylhexanoate), tert-butyl peroxy-3, 5,5-trimethylhexanoate, organic peroxides such as di-tert-butyl peroxide; 2,2′-azobisisobutyronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, Azobis compounds such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis-cyclohexane-1-carbonitrile; and the like can be used.

Examples of water-soluble polymerization initiators that can be used include ammonium persulfate, potassium persulfate, hydrogen peroxide, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride.

One of the polymerization initiators listed above may be used alone, or a mixture of two or more may be used.

<Polyisocyanate (b2)>
Conventionally known polyisocyanates (b2) can be arbitrarily used, and examples thereof include aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and triisocyanates. Specifically, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6 -tolylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 3,3′-dimethyl-4,4′-biphenylene diisocyanate, 3,3′-dimethoxy-4,4′-biphenylene diisocyanate, naphthylene-1,5- aromatic diisocyanates such as diisocyanate, tetrahydronaphthylene-1,5-diisocyanate, 4,4'-bibenzyldiyl diisocyanate, xylylene diisocyanate;
Aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysine diisocyanate;
Alicyclic diisocyanates such as dicyclohexylmethane diisocyanate, isophorone diisocyanate, 1,4-cyclohexane diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tolylene diisocyanate;
triisocyanates such as triphenylmethane triisocyanate and lysine triisocyanate;
etc.

Adducts and isocyanurates obtained from isocyanate compounds may also be used as triisocyanates. The "adduct" is an adduct of an isocyanate compound and trimethylolpropane, and the "isocyanurate" is a trimer of the isocyanate compound.

One of the polyisocyanates (b2) listed above may be used alone, or two or more thereof may be used in combination.

<Low-molecular-weight diol (b3)>
The water-soluble acrylic urethane resin (B) contains structural units derived from a low-molecular-weight diol (b3) having a molecular weight of 100 to 500 and having one acid group and two hydroxyl groups. For example, during the polyaddition in the synthesis of the water-soluble acrylic urethane resin (B), by using a low-molecular-weight diol (b3) having one acid group and two hydroxyl groups and having a molecular weight of 100 to 500, the above structural unit It is possible to obtain a resin containing Examples of the acid group include a carboxy group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. Among them, the carboxy group is selected because it is excellent in forming hydrogen bonds and can improve the ejection stability of water-based inkjet ink. preferably. In addition, the molecular weight of the low-molecular-weight diol (b3) is 100 to 100 because the amount of acid groups derived from the low-molecular-weight diol (b3) can be easily adjusted and the ejection stability of the water-based inkjet ink can be improved. 200 is preferred, and 120-160 is particularly preferred.

Specific examples of the low-molecular-weight diol (b3) include dimethylolcarboxylic acid represented by the following general formula 2; aromatic dihydroxycarboxylic acids such as dihydroxybenzoic acid and dihydroxyphenylpropionic acid; and the like.

(General formula 2) R—C(CH ₂ OH) ₂ —COOH

In Formula 2 above, R is a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

Among those listed above, as the low-molecular-weight diol (b3), dimethylolpropionic acid and dimethylolbutyric acid (among the dimethylolcarboxylic acids represented by the general formula 2, those in which R is a methyl group or an ethyl group), and One or more selected from the group consisting of dihydroxybenzoic acid can be preferably used.

<Polyol not having acid group>
In the polyaddition (urethane polymerization) in the production example of the water-soluble acrylic urethane resin (B) described above, in addition to the acrylic diol (b1) and the low-molecular-weight diol (b3), a polyol having no acid group is used as the polyol. good too. Examples of polyols having no acid group include polymeric polyols such as polycarbonate polyols, polyester polyols, polyether polyols, polyurethane polyols, polyethylene glycol, polypropylene glycol, and polyesteramide polyols; ethylene glycol, 1,2-propanediol, 1 , 3-propanediol, diethylene glycol, butylene glycol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol and other acid group-free low-molecular-weight diols; triols such as trimethylolpropane and glycerin ; etc. can be used. Among them, various functions can be imparted to the water-soluble acrylic urethane resin (B), and the above-mentioned hydrogen bond network is strengthened, so it is also possible to suppress color mixture bleeding and color unevenness when printing on uncoated paper. From the viewpoint of effectiveness, it is preferable to use a polymer polyol as the polyol having no acid group. Moreover, it is preferable to use a polycarbonate polyol among high molecular polyols. By using a polycarbonate polyol, it is possible to improve the water resistance, scratch resistance, and solvent resistance of printed matter due to the high cohesion of the carbonate group.

In addition, when using the polyol which does not have an acid group, you may use 1 type individually or may use 2 or more types together. Moreover, the above-mentioned "high molecular weight polyol" represents a polyol having a molecular weight of more than 500.

Examples of polycarbonate polyols include carbonate components such as alkylene carbonate, diallyl carbonate and dialkyl carbonate, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol and 1,2-pentanediol. , 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 2 -methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butynediol, 2,2,4-trimethyl-1,3-pentanediol, 1,4 - Condensates with acid group-free low-molecular-weight polyols such as cyclohexanedimethanol, diethylene glycol, polypropylene glycol and dipropylene glycol can be used.

Further, as the polyester polyol, for example, polyvalent carboxylic acids such as terephthalic acid, isophthalic acid, adipic acid, azelaic acid, and sebacic acid, or dialkyl esters of the polyvalent carboxylic acids, and the acid group-free low molecular weight compounds listed above ester reaction products with polyols; or ring-opening polymerization reaction products of lactones such as polycaprolactone, polyvalerolactone and poly(β-methyl-γ-valerolactone); hydroxyl group-containing vegetable oils such as castor oil; can.

Further, as a polyether polyol, for example, an oxirane compound such as ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran is subjected to ring-opening polymerization using water, ethylene glycol, 1,2-propanediol, trimethylolpropane, glycerin, or the like as an initiator. can be used.

<Chain extender>
As shown in the production example of the water-soluble acrylic urethane resin (B) described above, after the polyaddition (urethane polymerization) of the polyol and the polyisocyanate (b2), the unreacted may be reacted (urea reaction) with the isocyanate group of the chain extender. This urea reaction forms a urea bond in the water-soluble acrylic urethane resin (B), which not only improves the water resistance and scratch resistance of the printed matter, but also improves the image quality and ejection stability of the printed matter, although the details are unknown. gets even better.

Examples of chain extenders include ethylenediamine, propylenediamine, hexamethylenediamine, isophoronediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, dicyclohexylmethane-4,4'-diamine. , N-ethyl-N-(2-hydroxyethyl)-p-phenylenediamine, 2-hydroxyethylethylenediamine, 2-hydroxyethylpropylenediamine, 1,3-diamino-2-propanol, N-(2-hydroxyethyl) Ethylenediamine, N-(2-hydroxyethyl)-1,3-propanediamine, N-(2-hydroxypropyl)ethylenediamine, N,N-bis(2-hydroxyethyl)ethylenediamine, di-2-hydroxyethylethylenediamine, di -2-Hydroxyethylpropylenediamine, 2-hydroxypropylethylenediamine, di-2-hydroxypropylethylenediamine, dimerdiamine (a compound obtained by converting the carboxyl group of dimer acid to an amino group) and the like can be used. The chain extenders listed above may be used singly or in combination of two or more.

<Method for measuring number average molecular weight (Mn) and weight average molecular weight (Mw)>
In the present application, the number average molecular weight (Mn) of the acrylic diol (b1), and the weight average molecular weight (Mw) of the water-soluble acrylic urethane resin (B) and the pigment dispersion resin described later are measured by gel permeation chromatography (GPC). Measured polystyrene conversion values are used. Detailed measurement equipment and measurement conditions are as described in the following conditions. However, depending on the type of resin to be measured, etc., the carrier and column are appropriately changed, and for resins that are difficult to dissolve in the carrier, the measurement is performed under conditions of soluble sample concentration. Other matters shall comply with JIS K 7252-1 to 4.
Carrier (eluent): Tetrahydrofuran Column: A combination of TOSOH TSKgel SuperHZM-H, TOSOH TSKgel SuperHZ4000, and TOSOH TSKgel SuperHZ2000 Measurement temperature: 40°C
Carrier flow rate: 1.0 mL/min
Sample concentration: 0.1% by mass
Detector: RI (refractive index) detector Injection volume: 0.1 mL

<Method for measuring acid value>
The acid value in the present application is an actual value measured by the following method according to JIS K 0070. Specifically, after accurately weighing 0.5 to 2 g of a sample, 10 mL of neutral ethanol is added and dissolved. Thereafter, using an automatic potentiometric titrator "AT-610" manufactured by Kyoto Electronics Industry Co., Ltd., the solution after dissolution is titrated with a 0.1 mol/L ethanolic potassium hydroxide solution. Then, the point at which the potential difference curve becomes maximum is defined as the end point, and the titration amount up to the end point is used to calculate the acid value using Equation 3 below.

(Formula 3) Acid value (mmol/g) = (A x F x 0.1)/S

In the above formula 3, A is the amount (mL) of the potassium hydroxide solution titrated to the end point, F is the titer of the potassium hydroxide solution, and S is the amount of the substance to be measured contained in the sample (solid content conversion value). (g).

<Surfactant>
The water-based inkjet ink of the present invention contains a surfactant (D) having an HLB value of 0-7. As described above, the water-based inkjet ink containing the surfactant (D) makes it possible to obtain a printed matter with excellent image quality without color mixture bleeding or color unevenness, especially when printed on coated paper. The surfactant (D) is also an essential material from the viewpoint of adjusting the static and dynamic surface tension and improving the ejection stability.

The HLB (Hydrophile-Lipophile Balance) value is one of the parameters representing the hydrophilicity/hydrophobicity of a material. Various methods for calculating the HLB value from the chemical structure are known, and various methods for actual measurement are also known. If the structure of the compound is clearly known, the Griffin method is used to calculate the HLB value. The Griffin method is a method of calculating the HLB value using the following formula 4 using the molecular structure and molecular weight of the target material.

(Formula 4) HLB value = 20 x (sum of molecular weights of hydrophilic portions) ÷ (molecular weight of material)

On the other hand, when a compound with an unknown structure is included, such as a siloxane-based surfactant, for example, "Surfactant Handbook" (edited by Nishiichiro et al., Sangyo Tosho Co., Ltd., 1960), p. 324, the HLB value of surfactants can be experimentally determined by the following method. Specifically, after dissolving 0.5 g of a surfactant in 5 mL of ethanol, the solution is titrated with a 2% by mass phenol aqueous solution while stirring at 25 ° C. The end point is when the solution becomes turbid. . When the amount of the phenol aqueous solution required to reach the end point is A (mL), the HLB value can be calculated by the following formula 5.

(Formula 5) HLB value = 0.89 × A + 1.11

Further, from the viewpoint of further improving the image quality when printed on coated paper, from the viewpoint of ensuring the dispersion stability of the pigment (A) contained in the water-based inkjet ink, and from the viewpoint of improving the ejection stability of the water-based inkjet ink. , And, from the viewpoint of lowering the affinity with the water-soluble acrylic urethane resin (B) and not inhibiting its function, the HLB value of the surfactant (D) is more preferably 1 to 6, and 2 to 4. It is particularly preferred to have

Various types of compounds such as acetylene diol-based, acetylene alcohol-based, siloxane-based, acrylic, fluorine-based, and polyoxyalkylene ether-based surfactants are generally known as surfactants. In the present invention, one or more of the surfactants listed above can be optionally used as the surfactant (D) as long as the HLB conditions are satisfied. Among them, in the case of the present invention, from the viewpoint of preventing miscibility with the water-soluble acrylic urethane resin (B) and not inhibiting each effect, a surfactant having a hydrophobic group having a certain size is used. It can be used preferably. Among the above-listed surfactants, it preferably contains one or more nonionic surfactants selected from the group consisting of acetylene diol-based surfactants, acetylene alcohol-based surfactants, and siloxane-based surfactants. It is particularly preferred to include a surfactant.

On the other hand, if the surfactant (D) is too hydrophobic, it may separate from the water-based inkjet ink. Therefore, the surfactant (D) is preferably a compound having 1 to 4 hydroxyl groups in the molecule, and is a compound having 1 to 2 hydroxyl groups in the molecule. is particularly preferred.

Acetylene diol-based surfactants that can be preferably used include, for example, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne- 5,8-diol, hexadec-8-yn-7,10-diol, 6,9-dimethyl-tetradeca-7-yn-6,9-diol, 7,10-dimethylhexadec-8-yn-7, 10-diols, and their ethylene oxide and/or propylene oxide adducts.

Acetylene alcohol surfactants that can be suitably used include, for example, 3,5-dimethyl-1-hexyn-3-ol, 3,6-dimethyl-1-heptyn-3-ol, and ethylene oxide and and/or propylene oxide adducts.

Examples of siloxane-based surfactants that can be suitably used include DOWSIL (registered trademark) FZ-2110, FZ-2164, FZ-2191, FZ-5609, and L-7001 manufactured by DuPont Toray Specialty Materials Co., Ltd. L-7002, SH8400, SH8700, Y-7006, FZ-2203; Evonik TEGO Wet 240, TEGO Wet 250, TEGO Wet 260, TEGO Wet 270, TEGO Wet 280, TEGO Twin 4000, Shin-Etsu Chemical Co., Ltd. KF-352A, KF-945, KF-6020, X-22-4515, KF-6012, KF-6015, KF-6017; In particular, siloxane-based surfactants in which one or more ethylene oxide groups and/or one or more propylene oxide groups are introduced into side chains and/or both ends of a polydimethylsiloxane chain can be preferably used.

From the viewpoint of suitably expressing the above effects, the content of the surfactant (D) is preferably 0.2 to 4% by mass, more preferably 0.3 to 3% by mass, relative to the total amount of the water-based inkjet ink. %, particularly preferably 0.5 to 2% by mass.

<Pigment (A)>
The water-based inkjet ink of the present invention contains a pigment (A). Conventionally known organic pigments and/or inorganic pigments can be arbitrarily used as the pigment (A). Also, as the pigment (A), only one pigment may be used, or two or more pigments may be used in combination for adjusting the hue and color development, for example. Further, the pigment (A) may be used in combination with conventionally known dyes for the purpose of improving coloring power.

From the viewpoint of obtaining a printed material with high color development and sharpness and excellent image quality and also improving the water resistance, light resistance, weather resistance, etc. of the printed material, the amount of the pigment (A) in the water-based inkjet ink is , is preferably set to a certain amount or more. In that case, it is preferable to determine the amount to be blended in consideration of the specific gravity of the pigment (A) to be used. Specifically, the value represented by "the amount of pigment (A) relative to the total amount of water-based inkjet ink / the specific gravity of the pigment (A)" (when the pigment (A) contains two or more pigments, each pigment The sum of the calculated values of "amount of pigment with respect to the total amount of water-based inkjet ink/specific gravity of the pigment") is preferably 0.2 to 6, more preferably 0.5 to 5. It is particularly preferable to be 0.8 to 4.5. By setting it within the above range, it is possible not only to obtain a printed matter excellent in the above-mentioned clarity, water resistance, light resistance, weather resistance, etc., but also to keep the viscosity of the water-based inkjet ink within a range suitable for inkjet printing. In addition, since the dispersion stability of the pigment (A) in the water-based inkjet ink is improved, ejection stability can be ensured over a long period of time.

Examples of cyan organic pigments that can be used in the water-based inkjet ink of the present invention include C.I. I. Pigment Blue 1, 2, 3, 15:3, 15:4, 15:6, 16, 22, 60, 64, 66 and the like. Among them, C.I. I. One or more selected from the group consisting of Pigment Blue 15:3 and 15:4 can be preferably used.

Further, as a magenta organic pigment, for example, C.I. I. Pigment Red 5, 7, 12, 22, 23, 31, 48, 49, 52, 53, 57 (Ca), 57:1, 112, 122, 146, 147, 150, 185, 202, 209, 238, 242 , 254, 255, 266, 269, 282, C.I. I. Pigment Violet 19, 23, 29, 30, 37, 40, 43, 50, etc. can be used. Among them, C.I. I. Pigment Red 122, 150, 166, 185, 202, 209, 266, 269, 282, and C.I. I. One or more selected from the group consisting of Pigment Violet 19 can be preferably used. From the viewpoint of further enhancing the color developability and obtaining printed matter with excellent image quality, it is also preferable to use a solid solution pigment containing a quinacridone pigment and/or a naphthol pigment as the magenta organic pigment.

Further, as a yellow organic pigment, for example, C.I. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120, 125, 128, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, 213, etc. can be used. Among them, C.I. I. Pigment Yellow 12, 13, 14, 74, 120, 180, 185, and 213 are preferably used.

As black organic pigments, for example, aniline black, lumogen black, azomethine azo black, etc. can be used. A black pigment can also be obtained by mixing a plurality of chromatic pigments such as the cyan pigment, magenta pigment and yellow pigment described above and the orange pigment, green pigment and brown pigment described below.

Special color pigments such as orange pigments, green pigments, and brown pigments can also be used. Specifically, C.I. I. Pigment Orange 16, 36, 43, 51, 55, 59, 61, 64, 71, C.I. I. Pigment Green 7, 36, 43, 58, Pigment Brown 23, 25, 26, etc. can be preferably used.

On the other hand, the inorganic pigments that can be used in the water-based inkjet ink of the present invention are also not particularly limited. For example, carbon black and/or iron oxide can be used as black pigments, and titanium oxide and/or zinc oxide can be used as white pigments.

The content of the pigment (A) is preferably 1 to 12% by mass, more preferably 2 to 10% by mass, even more preferably 2.5 to 8% by mass, based on the total amount of the water-based inkjet ink.

<Pigment dispersion resin>
Methods for stably dispersing and holding the above-described pigment (A) in the water-based inkjet ink include (1) a method of coating at least a portion of the surface of the pigment (A) with a pigment dispersing resin; A method of adsorbing a water-dispersible surfactant to the surface of the pigment (A), (3) chemically and physically introducing a hydrophilic functional group to the surface of the pigment (A), without a pigment dispersing resin or a surfactant. A method of dispersing in water-based inkjet ink (self-dispersing pigment) can be mentioned.

For the water-based inkjet ink of the present invention, the method (1) above, that is, the method using a pigment dispersion resin is preferably selected. This is because the ability of the pigment dispersion resin to cover the pigment (A) and the charge of the pigment dispersion resin can be easily adjusted by selecting and studying the composition and molecular weight of the polymerizable monomers that make up the resin. This is because dispersion stability can be imparted irrespective of the particle size of A), and a printed material excellent in ejection stability, color developability, and color reproducibility can be obtained.

The type of pigment dispersion resin is not particularly limited, and examples include acrylic resins, (anhydride) maleic acid resins, styrene (anhydrous) maleic acid resins, olefin (anhydrous) maleic acid resins, urethane resins, acrylic urethane resins, polyolefin resins, and polyesters. A resin (a polycondensate of a polyhydric carboxylic acid and a polyhydric alcohol) or the like can be used, but is not limited to these. Among them, it is selected from the group consisting of acrylic resins, urethane resins, and acrylic urethane resins in terms of improved ejection stability due to improved affinity with the water-soluble acrylic urethane resin (B) and high material selectivity. It is preferred to use one or more of The above "(anhydrous) maleic acid" represents maleic anhydride or maleic acid.

In another embodiment, although the details are unknown, from the viewpoint of obtaining printed matter free from feathering and strike-through when printing on uncoated paper, styrene (anhydride) maleic acid resin, olefin ( It is preferable to use one or more selected from the group consisting of maleic anhydride resins.

The pigment dispersion resin can be synthesized by a conventionally known method, or a commercially available product can be used. The structure is also not particularly limited, and for example, resins having a random structure, block structure, comb structure, star structure, or the like can be used. Furthermore, a water-soluble resin or a non-water-soluble resin may be selected as the pigment dispersion resin.

In the present invention, when a water-soluble resin is used as the pigment dispersion resin, its acid value is preferably 100 to 450 mgKOH/g, more preferably 120 to 400 mgKOH/g. Especially preferred 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 (A) and to stably eject it from the inkjet head. It is also preferable from the viewpoint that the solubility of the pigment dispersion resin in water can be ensured, and the interaction between the pigment dispersion resins becomes suitable, so that the viscosity of the pigment dispersion can be suppressed.
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 more preferably 10 to 80 mgKOH/g. More preferred. If the acid value is within the above range, a printed matter having excellent drying properties and scratch resistance can be obtained.

The acid value of the pigment dispersion resin is a value measured by the same method as the acid value of the water-soluble acrylic urethane resin (B) described above.

From the viewpoint of improving the adsorption ability to the pigment (A) and ensuring dispersion stability, the pigment dispersion resin preferably has an aromatic group. Aromatic groups include, but are not limited to, phenyl groups, naphthyl groups, anthryl groups, tolyl groups, xylyl groups, mesityl groups, anisyl groups, and the like. Among them, a phenyl group, a naphthyl group and a tolyl group are preferable from the viewpoint of sufficiently ensuring dispersion stability.

From the viewpoint of compatibility between the dispersion stability and ejection stability of the pigment (A), the image quality of the printed matter, and the drying property, the amount of the monomer containing the aromatic ring to be introduced should be equal to the total amount of the monomers constituting the pigment dispersion resin. It is preferably 5 to 75% by mass, more preferably 5 to 65% by mass, even more preferably 10 to 50% by mass.

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 500,000, more preferably in the range of 5,000 to 40,000. 000 to 35,000, and particularly preferably 15,000 to 30,000. When the weight-average molecular weight is within the above range, the pigment (A) is stably dispersed in water and ejection stability is improved. Further, when the weight average molecular weight is 1,000 or more, the pigment dispersion resin becomes difficult to dissolve in the water-soluble organic solvent (C) added to the water-based inkjet ink. Adsorption of the pigment dispersion resin is strengthened, and dispersion stability and ejection stability are improved. When the weight-average molecular weight is 50,000 or less, the viscosity at the time of dispersion can be kept low, and the dispersion stability of the water-based inkjet ink and the ejection stability from the inkjet head are improved, enabling stable printing over a long period of time. .

From the viewpoint of improving the affinity with the water-soluble acrylic urethane resin (B), improving the ejection stability, and obtaining printed matter with excellent color development, the weight of the water-soluble acrylic urethane resin (B) The difference between the average molecular weight and the weight average molecular weight of the pigment dispersion resin is preferably 12,000 or less, more preferably 10,000 or less, and particularly preferably 8,000 or less.

Also, the weight average molecular weight of the pigment dispersion resin is a value measured by the same method as for the water-soluble acrylic urethane resin (B) described above.

<Water-soluble organic solvent (C)>
The water-based inkjet ink of the present invention contains a water-soluble organic solvent (C). In addition, the "water-soluble organic solvent" in the present application is used to dissolve and / or disperse a substance, is liquid at 25 ° C. and 1 atmosphere, and has a solubility in water of 25 ° C. at 1 atmosphere. Represents an organic compound with a concentration of 1 g/100 g H ₂ O or more. Examples of the water-soluble organic solvent include monohydric alcohol solvents, dihydric alcohol solvents (diol solvents), trihydric alcohol solvents (triol solvents), alkylene glycol monoalkyl ether solvents, and alkylene glycol dialkyl ether solvents. A solvent such as an alkylene glycol dialkyl ether acetate solvent can be preferably used.

In the water-based inkjet ink of the present invention, the water-soluble organic solvent (C) has a boiling point of 80 to 195 at 1 atm from the viewpoint of improving the drying property and obtaining printed matter with excellent image quality regardless of the type of paper substrate. ° C. (hereinafter also referred to as “water-soluble organic solvent (c1)” in the present application) is preferably included. The boiling point under 1 atm can be measured using a thermal analysis device such as DSC (differential scanning calorimetry).

Examples of the water-soluble organic solvent (c1) include 1-propanol (boiling point 97° C.), isopropanol (boiling point 82° C.), 1-butanol (boiling point 117° C.), 2-butanol (boiling point 100° C.), isobutanol (boiling point 108° C.), ° C.), 1-pentanol (boiling point 137.8 ° C.), 3-methyl-1-butanol (boiling point 132 ° C.), 3-methyl-2-butanol (boiling point 112 ° C.), 2-methyl-2-butanol (boiling point 102°C), 3-pentanol (boiling point 115.6°C), cyclohexanol (boiling point 161°C), glycidol (boiling point 167°C), furfuryl alcohol (boiling point 170°C), tetrahydrofurfuryl alcohol (boiling point 178°C), Monohydric alcohol solvents such as 3-methoxy-1-butanol (boiling point 158° C.) and 3-methoxy-3-methyl-1-butanol (boiling point 174° C.);
Dihydric alcohol solvents (diol solvents) such as 1,2-propanediol (boiling point 188°C), 2,3-butanediol (boiling point 182°C), 1,2-butanediol (boiling point 193°C);
Ethylene glycol monomethyl ether (boiling point 124°C), ethylene glycol monoethyl ether (boiling point 135°C), ethylene glycol monobutyl ether (boiling point 171°C), ethylene glycol monoisobutyl ether (boiling point 161°C), ethylene glycol monoisopropyl ether (boiling point 142°C) ° C.), ethylene glycol monoallyl ether (boiling point 159° C.), diethylene glycol monomethyl ether (boiling point 194° C.), propylene glycol monomethyl ether (boiling point 121° C.), propylene glycol monoethyl ether (boiling point 160° C.), propylene glycol monopropyl ether ( alkylene glycol monoalkyl ether solvents such as propylene glycol monobutyl ether (boiling point 170°C), dipropylene glycol monomethyl ether (boiling point 187°C);
Ethylene glycol dimethyl ether (boiling point 85°C), ethylene glycol diethyl ether (boiling point 121°C), diethylene glycol dimethyl ether (boiling point 162°C), diethylene glycol methyl ethyl ether (boiling point 176°C), diethylene glycol diethyl ether (boiling point 189°C), dipropylene glycol dimethyl ether Alkylene glycol dialkyl ether solvents such as (boiling point 171° C.);
Alkylene glycol dialkyl such as ethylene glycol monoethyl ether acetate (boiling point 156°C), ethylene glycol monobutyl ether acetate (boiling point 192°C), propylene glycol monomethyl ether acetate (boiling point 146°C), propylene glycol monoethyl ether acetate (boiling point 160°C) an ether acetate-based solvent; and
N,N-dimethylformamide (boiling point 153°C), N,N-dimethylpropionamide (boiling point 176°C), piperazine (boiling point 110°C), morpholine (boiling point 129°C), N-methylmorpholine (boiling point 115°C), N - Ethylmorpholine (boiling point 138°C), ethyl lactate (boiling point 155°C), cyclohexanone (boiling point 156°C), etc.;
include, but are not limited to. Moreover, these water-soluble organic solvents may be used alone, or a plurality of them may be mixed and used.

Among those listed above, it is more preferable to contain one or more selected from the group consisting of monohydric alcohol-based solvents, dihydric alcohol-based solvents, and glycol monoalkyl ether-based solvents, particularly dihydric alcohol-based solvents and/or It preferably contains an alkylene glycol monoalkyl ether solvent. By containing these water-soluble organic solvents (c1), a printed matter with excellent image quality can be obtained regardless of the type of paper substrate. Furthermore, the improved solubility of the water-soluble acrylic urethane resin (B) improves the ejection stability of the water-based inkjet ink.

Moreover, from the viewpoint of exhibiting the above effects more preferably, the water-based inkjet ink of the present invention preferably contains two or more kinds of water-soluble organic solvents (c1). In that case, it is preferable to include two or more water-soluble organic solvents selected from the group consisting of monohydric alcohol solvents, dihydric alcohol solvents, and glycol monoalkyl ether solvents. Further, when two or more water-soluble organic solvents (c1) are used, the boiling point of the water-soluble organic solvent with the highest boiling point and the boiling point of the water-soluble organic solvent with the lowest boiling point among the water-soluble organic solvents (c1) is preferably 10 to 100°C, more preferably 25 to 90°C, and particularly preferably 30 to 70°C. By setting the boiling point difference within the above range, in printed matter on uncoated paper, problems such as feathering and loss of color development due to strike-through are suppressed, while in printed matter on coated paper, color mixture is suppressed. Bleeding and color unevenness can be reduced.

On the other hand, in the aqueous inkjet ink of the present invention, the water-soluble organic solvent (C) has a boiling point of 200 to 250° C. under 1 atm and a surface tension of 20 to 30 mN/m at 25° C. Solvents (hereinafter also referred to as “water-soluble organic solvents (c2)” in the present application) can also be suitably used. Since the water-based inkjet ink containing the water-soluble organic solvent (c2) spreads quickly on coated paper and has excellent drying properties, it is possible to obtain a printed material with excellent image quality free from color bleeding and color unevenness. In addition, although the details are unknown, it has a high affinity with the water-soluble acrylic urethane resin (B), so even when printing on uncoated paper, feathering does not deteriorate, and the ejection of water-based inkjet ink is stable. It is also possible to maintain a favorable performance.

Examples of the water-soluble organic solvent (c2) include 1,2-pentanediol (boiling point 206°C, surface tension 28mN/m) and 1,2-hexanediol (boiling point 224°C, surface tension 26mN/m). alcohol-based solvent (diol-based solvent);
Diethylene glycol monobutyl ether (boiling point 231°C, surface tension 28 mN/m), diethylene glycol isobutyl ether (boiling point 217°C, surface tension 25 mN/m), dipropylene glycol monopropyl ether (boiling point 212°C, surface tension 28 mN/m), dipropylene Alkylene glycol monoalkyl ether solvents such as glycol monobutyl ether (boiling point 229° C., surface tension 28 mN/m) and tripropylene glycol monomethyl ether (boiling point 242° C., surface tension 28 mN/m);
Alkylene glycol dialkyl ether solvents such as diethylene glycol methyl butyl ether (boiling point 212° C., surface tension 24 mN/m);
Alkylene glycol dialkyl ether acetate solvents such as dipropylene glycol monomethyl ether acetate (boiling point 213° C., surface tension 29 mN/m);
etc.

Among those listed above, the water-soluble organic solvent (c2) is selected as the water-soluble organic solvent (c2), although the details are unknown, because printed matter with excellent image quality can be obtained regardless of the type of paper substrate, and the ejection stability of the water-based inkjet ink is also improved. , a dihydric alcohol-based solvent, and/or an alkylene glycol monoalkyl ether-based solvent is preferably used. In addition, from the viewpoint of improving the drying property on coated paper and obtaining a printed material excellent in image quality and color development, a compound having a boiling point of 200 to 230° C. under 1 atm is selected as the water-soluble organic solvent (c2). is preferred.

The water-soluble organic solvent (C) contained in the water-based inkjet ink of the present invention preferably has a weighted average static surface tension of 22 to 40 mN/m at 25°C, more preferably 25 to 37 mN/m. More preferably, it is particularly preferably 28 to 34 mN/m. When the weighted average value of the static surface tension at 25°C is 22 mN/m or more, the wet spreadability and drying property on the coated paper are improved, and a printed matter with suppressed color bleeding and color unevenness can be obtained. The ejection stability of water-based inkjet ink is also improved. On the other hand, when the weighted average value of the static surface tension at 25° C. is 40 mN/m or less, the permeability of the water-based inkjet ink to the uncoated paper is controlled, feathering and strike-through are suppressed, and color development is improved. Excellent prints are obtained.

When two or more types of water-soluble organic solvents (C) are contained in the water-based inkjet ink, the "weighted average value of the static surface tension at 25°C" means the It is a value obtained by adding the multiplication value of the static surface tension and the mass ratio with respect to the total amount of the water-soluble organic solvent. Further, when the water-soluble organic solvent (C) contained in the water-based inkjet ink is one type, the above "weighted average value of static surface tension at 25°C" is read as "static surface tension at 25°C". shall be

The static surface tension of a water-soluble organic solvent at 25°C is a value measured by the Wilhelmy method. is the value to be

In the water-based inkjet ink of the present invention, the water-soluble organic solvent (c1) and the water-soluble organic solvent (c2) are used in combination from the viewpoint of obtaining prints with particularly excellent image quality regardless of the type of paper substrate. is preferred. At that time, from the viewpoint of obtaining a printed material excellent in image quality and color development regardless of the type of paper substrate, and from the viewpoint of obtaining a water-based inkjet ink excellent in ejection stability, the water-soluble organic solvent (c1) The ratio of the compounded amount to the compounded amount of the water-soluble organic solvent (c2) is (amount of water-soluble organic solvent (c1) compounded/amount of water-soluble organic solvent (c2) compounded) = 0.6 to 6. is preferred, 1 to 5 is more preferred, and 1.5 to 4.5 is particularly preferred.

The total amount of the water-soluble organic solvent (C) contained in the water-based inkjet ink is preferably 1 to 40% by mass with respect to the total amount of the water-based inkjet ink. In addition, from the viewpoint of ensuring ejection stability and obtaining prints having adhesion on coated paper, drying property, and image quality (suppression of bleeding and beading, etc.), 3 to 35 masses out of the total amount of water-based inkjet ink %, and particularly preferably 5 to 30% by mass.

<Water>
The water contained in the water-based inkjet ink of the present invention is preferably ion-exchanged water (deionized water) rather than general water containing various ions. The content thereof is preferably in the range of 40 to 90% by mass, particularly preferably 50 to 85% by mass, based on the total mass of the water-based inkjet ink.

<Hydrocarbon wax>
In addition to the components described above, the water-based inkjet ink of the present invention preferably contains a hydrocarbon wax. When printed on uncoated paper, the hydrocarbon wax entangles with the pulp that makes up the uncoated paper and/or closes the voids on the surface of the uncoated paper, resulting in excellent color development without feathering. A print is obtained. In addition, when printing on coated paper, the hydrocarbon wax is oriented on the surface of droplets of the water-based inkjet ink, so that a printed matter with excellent image quality can be obtained in which color bleeding and color unevenness are suppressed.

Specific examples of hydrocarbon waxes that can be used in the present invention include, for example, petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum; synthetic waxes such as polyolefin waxes (e.g., polyethylene waxes, and polypropylene waxes), Fischer-Tropsch waxes, paraffin wax derivatives; These hydrocarbon waxes may be used alone or in combination of two or more.

The hydrocarbon wax may be a water-soluble material or a water-insoluble material, but is preferably a water-insoluble material (eg, resin particles). Although the details are unknown, the water-soluble acrylic urethane resin (B) and the resin particles of the hydrocarbon wax each form microscopic clusters, suppressing the bias of the water-based inkjet ink components in the droplets during drying. and the image quality is improved. Furthermore, the clusters function to prevent local drying and viscosity increase in the inkjet head, thereby improving ejection stability.

When the hydrocarbon wax is resin particles, the particle size is preferably 10 to 300 nm, more preferably 30 to 250 nm, and particularly preferably 40 to 200 nm. When the particle diameter of the hydrocarbon wax resin particles is 10 nm or more, the abrasion resistance and image quality of printed matter are improved. Prints with excellent image quality can be obtained. The method for measuring the particle size of the hydrocarbon wax resin particles is the same as the method used in the determination of the water-soluble resin described above. Nanotrac UPA-EX150”) under the conditions of 25°C. Moreover, the above-mentioned "particle diameter" is a volume-based median system measured by a dynamic light scattering method.

The hydrocarbon wax in the form of resin particles can be produced, for example, by mixing a hydrocarbon wax that is solid at room temperature and melted by heating, hot water, and an emulsifier. In addition, a commercially available hydrocarbon wax can also be used. Nopcort PEM-17 manufactured by San Nopco Co., Ltd.; JONCRYL WAX4, WAX26, WAX28, WAX120 manufactured by BASF;

The content of the hydrocarbon wax is preferably 0.2 to 8% by mass based on the total amount of the water-based inkjet ink from the viewpoint of improving the ejection stability and the image quality, color development, and abrasion resistance of the printed matter. 0.3 to 5 mass % is more preferred, and 0.5 to 4 mass % is particularly preferred.

In addition, when printed on uncoated paper, printed matter with no feathering and excellent color development can be obtained, and when printed on coated paper, mixed color bleeding and color unevenness are suppressed. From the viewpoint of obtaining excellent printed matter, when the content of hydrocarbon wax in the total weight of water-based inkjet ink is W (mass%) and the amount of water-soluble acrylic urethane resin (B) is B (mass%) , the ratio of the two contents (B/W) is preferably 0.5 to 20, more preferably 1 to 15, and particularly preferably 5 to 15.

<Other ingredients>
In addition to the components described above, the water-based inkjet ink of the present invention may optionally contain additives such as pH adjusters, antifoaming agents, preservatives, infrared absorbers, and ultraviolet absorbers. The amount of these additives to be added is preferably 0.01 to 10% by mass with respect to the total mass of the water-based inkjet ink.

On the other hand, the water-based inkjet ink of the present invention preferably contains substantially no polymerizable monomer. In the present application, "substantially free" means that the intentional addition of the material is not permitted to the extent that it interferes with the manifestation of the effects of the present invention. It does not exclude unintentional contamination of Specifically, the target material should not be contained in an amount of 2.0% by mass or more, preferably 1.0% by mass or more, more preferably 0.5% by mass, based on the total amount of the water-based inkjet ink. % or more, and particularly preferably 0.1 mass % or more.

(pH adjuster)
For example, when using a pH adjuster as another material, alkanolamine such as triethanolamine, diethanolamine, diisopropanolamine, N-methyldiethanolamine, 2-amino-2-methyl-1-propanol;
Ammonia water, monoethylamine, diethylamine, triethylamine, cyclohexylamine, benzylamine, urea, other nitrogen-containing compounds such as piperidine;
alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide;
alkali metal carbonates such as lithium carbonate, sodium carbonate, sodium bicarbonate, potassium carbonate;
Acidic compounds such as hydrochloric acid, sulfuric acid, acetic acid, citric acid, (anhydrous) maleic acid, succinic acid, tartaric acid, malic acid, phosphoric acid, boric acid, fumaric acid, malonic acid, ascorbic acid, glutamic acid;
etc. can be used. These pH adjusters may be used alone or in combination of two or more.

When a pH adjuster is used, the amount thereof is preferably 0.01 to 5% by mass, more preferably 0.1 to 3% by mass, more preferably 0.2 to 5% by mass, based on the total amount of the aqueous inkjet ink. 1.5% by weight is particularly preferred.

<Method for producing water-based inkjet ink>
The water-based inkjet ink of the present invention containing the components described above is produced, for example, through the following processes. However, the method for producing the water-based inkjet ink is not limited to the following.

(1. Production of pigment dispersion)
When a water-soluble resin is used as the pigment-dispersing resin, the water-soluble resin, water, and, if necessary, the water-soluble organic solvent (C) are mixed and stirred to prepare a pigment-dispersing resin mixture. The pigment (A) is added to this pigment-dispersed resin mixture, mixed and stirred (premixed), and then dispersed using a disperser. Thereafter, centrifugal separation, filtration, adjustment of solid content concentration, etc. are performed as necessary to obtain a pigment dispersion.

Further, when producing a dispersion of the pigment (A) coated with a water-insoluble resin, the water-insoluble resin was dissolved in an organic solvent such as 2-butanone in advance, and the water-insoluble resin was neutralized as necessary. , to prepare a water-insoluble resin solution. The pigment (A) and water are added to this water-insoluble resin solution, mixed and stirred (premixed), and then dispersed using a disperser. Thereafter, the organic solvent is removed by distillation under reduced pressure, and if necessary, centrifugation, filtration, and adjustment of the solid content concentration are performed to obtain a pigment dispersion.

Any commonly used dispersing machine can be used as the dispersing machine for dispersing the pigment (A), and examples thereof include ball mills, roll mills, sand mills, bead mills and nanomizers. Among the above, a bead mill is preferably used, and specifically, it is commercially available under trade names such as super mill, sand grinder, agitator mill, grain mill, dyno mill, pearl mill and cobol mill. Glass, zircon, zirconia, titania, etc. can be used as the material of the grinding media.

(2. Preparation of aqueous inkjet ink)
Next, a water-soluble acrylic urethane resin (B), a water-soluble organic solvent (C), a surfactant (D), water, and optionally a hydrocarbon wax, a pH adjuster, and other materials are added to the pigment dispersion. Add, stir and mix. If necessary, the mixture may be stirred and mixed while being heated in the range of 40 to 100°C.

(3. Removal of coarse particles)
Coarse particles contained in the mixture are removed by filtration, centrifugation, or the like to obtain an aqueous inkjet ink. As a method for filtration separation, a known method can be appropriately used. The pore size of the filter is not particularly limited as long as it can remove coarse particles and dust, but it is preferably 0.3 to 5 μm, more preferably 0.5 to 3 μm. When performing filtration, a single kind of filter may be used, or multiple kinds of filters may be used in combination.

<Water-based inkjet ink set>
The water-based inkjet ink of the present invention may be used in a single color, but may also be used in the form of a water-based inkjet ink set by combining a plurality of types of water-based inkjet inks with different colors according to the application. Although the combination is not particularly limited, for example, by using three colors of cyan, yellow, and magenta, a full-color printed matter can be obtained. Further, by adding black ink, the feeling of blackness can be improved, and the visibility of characters and the like can be improved. In addition, color reproducibility can be improved by adding colors such as orange, green, and violet. The water-based inkjet ink set may also contain an ink (clear ink) that does not substantially contain a colorant component, excluding the pigment (A) from the water-based inkjet ink of the present invention.

<Ink - pretreatment liquid set>
The water-based inkjet ink of the present invention and the water-based inkjet ink set described above can also be used in combination with a pretreatment liquid containing a flocculant (ink (set) - pretreatment liquid set). A pretreatment liquid containing a flocculant is a layer (ink flocculation layer) can be formed. By landing the water-based inkjet ink on this ink aggregation layer, for example, when printing on coated paper, it is possible to prevent color mixture bleeding and color unevenness due to coalescence of the water-based inkjet ink droplets, and improve image quality. can be significantly improved. Furthermore, by blending a resin component in the pretreatment liquid, when printing on uncoated paper, the resin component entangles with the pulp constituting the uncoated paper and/or voids on the surface of the uncoated paper. By closing the opening, it is possible to obtain a printed material excellent in image quality and color development without problems such as feathering and strike-through.

The above-mentioned "aggregating agent" is contained in the water-based inkjet ink and destroys the dispersed state of the pigment (A) to cause it to aggregate, and/or makes the water-soluble acrylic urethane resin (B) insoluble and increases the viscosity of the water-based inkjet ink. means an ingredient that can From the viewpoint of improving image quality, the flocculant used in the pretreatment liquid combined with the water-based inkjet ink of the present invention preferably contains one or more selected from metal salts and cationic polymer compounds. Among them, it is preferable to use a metal salt, particularly containing a salt of one or more polyvalent metal ions selected from the group consisting of Ca ²⁺ , Mg ²⁺ , Zn ²⁺ and Al ³⁺ . preferable. When a metal salt is used as a flocculant, the content thereof is preferably 2 to 25% by mass, particularly preferably 3 to 20% by mass, based on the total amount of the pretreatment liquid.

In addition, when adding a resin component to the pretreatment liquid, the content is 1.5 to 20% by mass based on the total amount of the pretreatment liquid from the viewpoint of improving the image quality of printed matter on uncoated paper. is preferred, and 2.5 to 15% by mass is particularly preferred.

<Paper substrate>
As described above, the water-based inkjet ink of the present invention is suitable for use on paper substrates. Examples of the paper substrate include non-coated paper such as fine paper, medium-quality paper, raw paper, kraft paper, non-coated liner paper (non-coated corrugated cardboard); and coated paper, matte coated paper, art paper, cast Coated paper such as coated paper, aluminum-deposited paper, and coated liner paper (coated corrugated cardboard) can be used.

The paper substrates listed above may have smooth or uneven surfaces. Also, two or more of these may be adhered to each other. Furthermore, a release adhesive layer or the like may be provided on the opposite side of the printed surface, or an adhesive layer or the like may be provided on the printed surface after printing. The shape of the paper base material used for printing with the water-based inkjet ink of the present invention may be roll-like or sheet-like.

<Inkjet printing method>
The water-based inkjet ink of the present invention is used in a method (inkjet printing method) in which it is ejected from an inkjet head and printed on a paper substrate.

In addition, in order to improve the ejection stability of the water-based inkjet ink, uniformize the distribution of the components in the water-based inkjet ink, and improve the image quality and color development of the printed matter regardless of the type of paper substrate, the water-based inkjet ink The ink may be used in a printing device having an ink circulation mechanism configured to communicate with the inkjet head.

As a pass method in the inkjet printing method, there is a single-pass method in which the inkjet ink is ejected only once to the paper base material to record, and a short shuttle head is reciprocated in the direction perpendicular to the conveying direction of the paper base material. Either a serial method in which recording is performed by ejecting ink while the liquid is being discharged 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 deviation of the landing position is likely to occur. Therefore, when printing the water-based inkjet ink of the present invention, a single-pass method, particularly a method in which the paper substrate is passed under a fixed inkjet head, is preferably used.

There are no particular restrictions on the method of ejecting the water-based inkjet ink, and known methods include, for example, a drop-on-demand method (pressure pulse method) that utilizes the vibration pressure of a piezo element, a water-based inkjet ink that is heated to form air bubbles, A thermal ink jet (bubble jet (registered trademark)) method using the generated pressure can be used.

Further, the amount of droplets of the water-based inkjet ink ejected from the inkjet head is preferably 0.2 to 30 picoliters from the viewpoint of greatly reducing the drying load and improving the color developability and image quality. , 1 to 20 picoliters.

A printing apparatus in which the water-based inkjet ink of the present invention is mounted preferably has a mechanism for drying the ink on the paper substrate after printing with the water-based inkjet ink. As a drying method used in the drying mechanism, either one of a method of directly or indirectly contacting the ink with a heat source and a method of irradiating electromagnetic waves may be used, or a combination of a plurality of methods may be used. may For example, by using the infrared drying method and the hot air drying method together, the ink can be dried more quickly than when either method is used alone.

In particular, from the viewpoint of preventing bumping of the liquid component in the water-based inkjet ink and obtaining prints with excellent color development and image quality regardless of the type of paper substrate, the drying temperature is set to 35 when the heat drying method is used. It is preferable to set the temperature to 100° C. or to 50 to 250° C. when the hot air drying method is employed.
On the other hand, when a drying method using infrared rays as electromagnetic waves (infrared drying method) is adopted, from the viewpoint of obtaining printed matter with excellent color development and image quality regardless of the type of paper base material, the infrared rays used for infrared irradiation It is preferable that 50% or more of the integrated value of the total output of is present in the wavelength region of 700 to 1500 nm.

Further, examples of light sources for irradiating infrared rays used in the infrared drying method include infrared lamps (halogen lamps, sheath 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 infrared output conditions described above. An optical filter and/or a reflecting mirror may be used in combination with the light source for irradiating the infrared rays.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the examples below do not limit the scope of the present invention. In addition, "parts" in the examples and comparative examples represent "mass parts" and "mass%".

<Synthesis Example 1: Synthesis example of acrylic diol (b1-1)>
360 parts by mass of methyl methacrylate, 140 parts by mass of methacrylic acid, and 28 parts of 1-thioglycerol (used as a chain transfer agent (t)) were added to a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube. Parts by mass and 300 parts by mass of 2-butanone as an organic solvent were charged. After purging the inside of the reaction vessel with nitrogen gas, the inside temperature was heated to 65° C. while stirring. Furthermore, after reaching 65 ° C. and maintaining it for 15 minutes, 50 parts by mass of 2-butanone and 0.15 parts by mass of azobisisobutyronitrile (polymerization initiator) are added while stirring the contents, After the polymerization reaction for 12 hours, the resulting product was isolated to obtain acrylic diol (b1-1). The acrylic diol (b1-1) had a number average molecular weight of 1,770 and an acid value of 171 mgKOH/g, which were measured by the method described above.

<Synthesis Examples 2 to 8: Synthesis examples of acrylic diols (b1-2) to (b1-8)>
Acrylic diols (b1-2) to (b1) were prepared in the same manner and under the same conditions as for acrylic diol (b1-1), except that the types and amounts of raw materials charged in the reaction vessel were changed to those shown in Table 1. -8) was synthesized. A blank in Table 1 indicates that the raw material was not blended (the same applies to Tables 2 to 4 shown later).

The abbreviations in Table 1 have the following meanings.
・MAA: methacrylic acid ・MMA: methyl methacrylate ・BMA: butyl methacrylate ・LMA: lauryl methacrylate ・1-TG: 1-thioglycerol (molecular weight 108)
・AIBN: 2,2′-azobis(2-methylpropionitrile)
・MEK: 2-butanone

<Synthesis Example 9: Synthesis of water-soluble acrylic urethane resin (B-1)>
Polycarbonate polyol C-2090 (1,6-hexanediol and 3-methyl -Condensate with 1,5-pentanediol) is 150 parts by mass, 2,2-bis(hydroxymethyl)butyric acid is 15 parts by mass, acrylic diol (b1-1) is 43 parts by mass, and isophorone diisocyanate is 57 parts by mass. , and 220 parts by mass of 2-butanone were charged, respectively, and then the inside of the reaction vessel was heated to 75°C. After the temperature was raised, 0.02 part by mass of tin 2-ethylhexanoate was added while stirring the contents in the reaction vessel, and the inner temperature was further raised to 80°C. After that, polyaddition (urethane polymerization) was carried out for 3 hours while keeping the inside of the reaction vessel at 80° C., and then the inside temperature was cooled to 40° C. or lower.
Next, a mixture of 5 parts by mass of isophoronediamine and 50 parts by mass of 2-butanone was added dropwise into the reactor over 1 hour, and the mixture was allowed to react with urea for 3 hours. Then, 8 parts by mass of 28% ammonia water and 500 parts by mass of ion-exchanged water are dropped into the reaction vessel over 1 hour to neutralize and solubilize the obtained product, and then, under reduced pressure, , The total amount of 2-butanone was distilled off by keeping the internal temperature at 50 ° C., and water was added to adjust the solid content concentration to 25%, thereby obtaining an aqueous solution of the water-soluble acrylic urethane resin (B-1). got The water-soluble acrylic urethane resin (B-1) had a weight-average molecular weight of 17,000 and an acid value of 50 mgKOH/g, which were measured by the method described above.

<Synthesis Examples 10 to 21, Comparative Synthesis Examples 1 to 4: Synthesis of water-soluble acrylic urethane resins (B-2) to (B-13) and (B'-14) to (B'-17)>
The water-soluble acrylic urethane resin (B -2) to (B-13) and (B'-14) to (B'-17) were synthesized.

The abbreviations in Table 2 have the following meanings.
・PC: Polycarbonate polyol C-2090 manufactured by Kuraray Co., Ltd. (condensate of 1,6-hexanediol and 3-methyl-1,5-pentanediol)
・ PE: polyester polyol P-2010 manufactured by Kuraray Co., Ltd. (condensate of adipic acid and 3-methyl-1,5-pentanediol)
・DMBA: Dimethylolbutyric acid (molecular weight 148)
・BD: 1,4-butanediol ・IPDI: isophorone diisocyanate ・IPDA: isophorone diamine

<Production of pigment dispersion>
(Production of cyan pigment dispersion)
C. I. Pigment Blue 15:3 ("LIONOL BLUE 7358G" manufactured by Toyocolor Co., Ltd.) and 15 parts of styrene-acrylic resin (all acid groups are neutralized with dimethylaminoethanol, styrene/acrylic acid/behenyl acrylate = 45/ 30/25 (mass ratio) random polymer, acid value 230 mgKOH/g, weight average molecular weight 20,000) and 82 parts of water are charged into a mixing vessel equipped with a stirrer. Time premixing was performed. Thereafter, C.I. I. Cyan pigment dispersion was produced by circulating and dispersing until the particle size of Pigment Blue 15:3 reached about 150 nm. The above particle size is a value measured by the same apparatus and method as for the particle size of the hydrocarbon wax resin particles described above.

(Manufacture of magenta pigment dispersion, yellow pigment dispersion and black pigment dispersion)
A magenta pigment dispersion and a yellow pigment dispersion were prepared using the same raw materials and method as for the cyan pigment dispersion, except that the pigments shown below were used as the pigments and circulated and dispersed until the particle diameters shown below were obtained. , to prepare a black pigment dispersion.
- Magenta pigment dispersion: Toshiki Red 150TR (C.I. Pigment Red 150) manufactured by Tokyo Shikizai Kogyo Co., Ltd., particle size = 200 nm
・Yellow pigment dispersion: LIONOL YELLOW TT1405G (C.I. Pigment Yellow 14) manufactured by Toyocolor Co., particle size = 150 nm
・Black pigment dispersion: Print X85 (carbon black) manufactured by Orion Engineered Carbons, particle size = 100 nm

<Production example of water-based inkjet ink 1>
The following materials were sequentially put into a mixing vessel equipped with a stirrer and stirred until sufficiently uniform. After that, filtration was performed with a membrane filter having a pore size of 1 μm to remove coarse particles that cause clogging of the inkjet head, thereby obtaining water-based inkjet cyan ink 1 . Further, water-based inkjet magenta ink 1, water-based inkjet yellow ink 1, and water-based inkjet black ink 1 were manufactured by using magenta pigment dispersion, yellow pigment dispersion, and black pigment dispersion instead of cyan pigment dispersion. Aqueous inkjet ink set 1 is a combination of these four water-based inkjet inks.
・Cyan pigment dispersion liquid 33.3 parts ・Water-soluble acrylic urethane resin (B-1) (solid content concentration 25%) 20 parts ・1,2-propanediol 15 parts ・1,2-hexanediol 5 parts ・Surfinol 104 1 part ・TEGO Wet 280 1 part ・AQUACER 515 3 parts ・Triethanolamine 1 part ・Ion-exchanged water 20.7 parts The details of the above trade names will be described later.

<Manufacturing Examples of Inkjet Ink Sets 2 to 51>
Inkjet ink sets 2 to 51, each consisting of four colors of cyan, magenta, yellow, and black, were produced in the same manner as for inkjet ink set 1, except that the materials listed in Table 3 were used.

The abbreviations in Table 3 have the following meanings.
(Water-soluble organic solvent (C))
・ PG: 1,2-propanediol (boiling point 188 ° C., static surface tension 35 mN / m at 25 ° C.)
・ BD: 1,2-butanediol (boiling point 193 ° C., static surface tension 32 mN / m at 25 ° C.)
・ PeD: 1,2-pentanediol (boiling point 206 ° C., surface tension 28 mN / m at 25 ° C.)
・HD: 1,2-hexanediol (boiling point 224° C., surface tension 26 mN/m at 25° C.)
・ MB: 3-methoxy-1-butanol (boiling point 158 ° C., static surface tension 26 mN / m at 25 ° C.)
・MMB: 3-methoxy-3-methyl-1-butanol (boiling point 174° C., static surface tension at 25° C. 26 mN/m)
・PGM: propylene glycol monomethyl ether (boiling point 121°C, static surface tension 26 mN/m at 25°C)
・PGB: propylene glycol monobutyl ether (boiling point 170°C, static surface tension 26 mN/m at 25°C)
・BDG: diethylene glycol monobutyl ether (boiling point 231°C, static surface tension 28 mN/m at 25°C)
・dPGP: dipropylene glycol monopropyl ether (boiling point 212°C, static surface tension 28 mN/m at 25°C)
・dEGMB: diethylene glycol methyl butyl ether (boiling point 212° C., static surface tension 24 mN/m at 25° C.)
(Surfactant (D))
· SF104: Acetylene diol-based surfactant manufactured by Nissin Chemical Industry Co., Ltd., HLB value 3.0
· SF420: Acetylene diol-based surfactant manufactured by Nissin Chemical Industry Co., Ltd., HLB value 4.0
· SF440: Acetylene diol-based surfactant manufactured by Nissin Chemical Industry Co., Ltd., HLB value 8.1
・ DF110D: Dipropylene glycol solution of acetylene diol-based surfactant manufactured by Nissin Chemical Industry Co., Ltd. (32% active ingredient), HLB value 2.7
・ TW270: TEGO Wet 270 (siloxane-based surfactant manufactured by Evonik, HLB value 2.2)
・ TW280: TEGO Wet 280 (siloxane-based surfactant manufactured by Evonik, HLB value 3.5)
・ TT4000: TEGO Twin 4000 (siloxane-based surfactant manufactured by Evonik, HLB value 2.0)
· BYK3455: siloxane-based surfactant manufactured by BYK-Chemie, HLB value 7.4
・EMALEX602: Polyoxyalkylene ether-based surfactant manufactured by Nippon Emulsion Co., Ltd., HLB value 4.9
(hydrocarbon wax)
・ AQ515: AQUACER 515 (polyethylene wax resin particles manufactured by BYK-Chemie, solid content 35%)
(pH adjuster)
・TEA: Triethanolamine

[Examples 1 to 41, Comparative Examples 1 to 10]
Using the water-based inkjet inks 1-51 produced above, the following evaluations 1-6 were performed. The evaluation results were as shown in Table 4 below.

<Evaluation 1: Evaluation of initial ejection stability>
Prepare an inkjet printing device in which four Kyocera inkjet heads KJ4B-1200 (design resolution 1200 dpi) are arranged side by side in the conveying direction of the substrate, and one inkjet head installed on the most downstream side in the conveying direction It was filled with the black ink from the inkjet ink set.
Next, a nozzle check pattern was printed to confirm that black ink was being ejected normally from all nozzles (ejection ports). Solid printing was performed at a printing rate of 100% under printing conditions of 1200 dpi. Initial ejection stability was evaluated by checking visually and with a magnifying glass whether or not the printing start portion of the solid printing was completed without chipping. The evaluation criteria are as follows, and the ⊚ and ◯ evaluations are the practically usable areas.
◎: Checked visually and with a loupe, no chipping was observed at the start of printing ○: Chipping of less than 1 mm was confirmed at the start of printing △: Chipping of 1 mm or more and less than 5 mm was confirmed at the start of printing ×: Chipping of 5 mm or more was confirmed at the start of printing

<Evaluation 2: Intermittent Ejection Stability Evaluation>
Using the same printing apparatus as in Evaluation 1, one inkjet head installed on the most downstream side in the direction of conveyance of the substrate was filled with black ink from the water-based inkjet ink set.
Next, after printing a nozzle check pattern and confirming that black ink is being ejected normally from all nozzles (ejection ports), the inkjet printer is allowed to stand by for a predetermined time in an environment of 25°C. , the nozzle check pattern was printed again. Intermittent ejection stability was evaluated by visually confirming the presence or absence of missing nozzles. The evaluation criteria are as follows, and the ⊚, ◯, and △ evaluations are regarded as the practical usable range.
◎: No nozzle missing even after printing after waiting for 2 hours. ○: No nozzle missing even after printing after waiting for 1 hour. △: 1 to 9 nozzles were missing when printing after waiting for 1 hour ×: 10 or more nozzles were missing when printing after waiting for 1 hour

<Evaluation 3: Evaluation of color development on uncoated paper>
Using the same printing apparatus as in Evaluation 1, one inkjet head installed on the most downstream side in the direction of conveyance of the substrate was filled with black ink from the water-based inkjet ink set. Further, high-quality paper ("OK Prince high-quality" manufactured by Oji Paper Co., Ltd.) was fixed on the conveyor.
Next, the conveyor is driven at a speed of 50 m / min, and when the fine paper passes below the installation part of the inkjet head, the water-based inkjet ink is discharged at a drop volume of 2 pL, and a solid image with a printing rate of 100% (width 5 cm×10 cm in length), the printed material was immediately placed in an air oven at 70°C. After drying for 1 minute, the printed matter was taken out from the air oven, and the optical density (OD value) was measured using a spectrodensitometer (eXact manufactured by X-RITE) to evaluate the color development properties on uncoated paper. rice field. 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 ⊚, ◯, and △ evaluations are regarded as the practical usable range.
◎: OD value is 1.30 or more ○: OD value is 1.20 or more and less than 1.30 △: OD value is 1.10 or more and less than 1.20 ×: OD value is less than 1.10

<Evaluation 4: Evaluation of image quality (feathering) on uncoated paper>
Four types of water-based inkjet inks constituting a water-based inkjet ink set were applied to the inkjet printing apparatus used in Evaluation 1 in the order of black, cyan, magenta, and yellow from the inkjet head on the upstream side in the conveying direction of the substrate. was filled. Further, high-quality paper ("OK Prince high-quality" manufactured by Oji Paper Co., Ltd.) was fixed on the conveyor.
Next, the conveyor is driven at a speed of 50 m/min, and each water-based inkjet ink is ejected at a drop volume of 2 pL when the fine paper passes below the installation part of the inkjet head, and a monochromatic thin line of 5 cm in length is After printing images (thin-line images) in which cyan, magenta, yellow, and black were arranged at intervals in this order, the printed matter was immediately placed in an air oven at 70°C. In advance, the fine line image was printed on coated paper "OK Topcoat+" (basis weight: 104.7 g/m ² ) manufactured by Oji Paper Co., Ltd., and the image was printed so that the width of the monochromatic fine line was 100 μm. Data and head driving conditions were adjusted.
After drying for 1 minute, the printed material was taken out from the air oven, and the presence or absence of blurring of fine lines was visually observed to evaluate the image quality (feathering) on non-coated paper. The evaluation criteria are as follows, and the ⊚, ◯, and △ evaluations are defined as the practical usable range.
◎: In all colors, fine lines did not thicken due to bleeding, and ink bleeding along paper fibers was not observed. Ink bleeding was observed in less than 10 locations on average for 4 colors. Less than X: Severe thickening of thin lines due to bleeding, and ink bleeding along the paper fibers of woodfree paper was observed at 20 or more locations on average for four colors.

<Evaluation 5: Evaluation of color development on coated paper>
Using the same printing apparatus as in Evaluation 1, one inkjet head installed on the most downstream side in the direction of conveyance of the substrate was filled with black ink from the water-based inkjet ink set. Coated paper (“OK Topcoat+” manufactured by Oji Paper Co., Ltd., basis weight 104.7 g/m ² ) was fixed on the conveyor.
Next, the conveyor is driven at a speed of 50 m / min, and when the coated paper passes below the installation part of the inkjet head, the water-based inkjet ink is ejected at a drop volume of 2 pL, and a solid image with a printing rate of 100% (width 5 cm×10 cm in length), the printed material was immediately placed in an air oven at 70°C. After drying for 3 minutes, the printed matter was taken out from the air oven, and the optical density (OD value) was measured using a spectrodensitometer (eXact manufactured by X-RITE) to evaluate the color development properties on coated paper. . The colorimetry conditions were the same as those for Evaluation 3 above. The evaluation criteria are as follows, and the ⊚, ◯, and △ evaluations are defined as the practical usable range.
◎: OD value is 2.00 or more ○: OD value is 1.90 or more and less than 2.00 △: OD value is 1.80 or more and less than 1.90 ×: OD value is less than 1.80

<Evaluation 6: Image quality evaluation for coated paper>
Four types of water-based inkjet inks constituting a water-based inkjet ink set were applied to the inkjet printing apparatus used in Evaluation 1 in the order of black, cyan, magenta, and yellow from the inkjet head on the upstream side in the conveying direction of the substrate. was filled. Coated paper (“OK Topcoat+” manufactured by Oji Paper Co., Ltd., basis weight 104.7 g/m ² ) was fixed on the conveyor.
Next, the conveyor is driven at a speed of 50 m/min, and each water-based inkjet ink is ejected at a drop volume of 2 pL when the coated paper passes below the installation part of the inkjet head, and a monochromatic paper with a size of 5 cm × 5 cm is discharged. After printing an image (solid patch image) in which solid patches (printing rate 100%) are adjacent in the order of cyan, magenta, yellow, and black, the printed matter was quickly placed in an air oven at 70°C. After drying for 3 minutes, the printed material was removed from the air oven, and the degree of bleeding at the solid patch boundary and the degree of color unevenness in each solid patch were visually checked with a loupe to evaluate the image quality of the coated paper. did The evaluation criteria are as follows, and the ⊚, ◯, and Δ evaluations are defined as the practical usable range.
◎: When viewed with a magnifying glass and visually, no color mixture bleeding or color unevenness was observed at the boundary. The presence or absence of bleeding and color unevenness could not be determined. △: Some colors were visually observed with mixed color bleeding or color unevenness at the boundary, but the degree was small. ×: Clearly visible, at the boundary. mixed color bleeding or color unevenness was observed

From Examples 1 to 41 in Table 4, a water-based inkjet ink containing a certain amount of a water-soluble acrylic urethane resin (B) having a specific configuration and a surfactant (D) having an HLB value of 0 to 7 is used in combination. However, ejection stability (initial ejection stability and complete ejection stability), color development and image quality of printed matter on uncoated paper (feathering), and color development and image quality of printed matter on coated paper (mixed color bleeding) and color unevenness), it was confirmed that they had practically usable quality.

Claims (5)

A water-based inkjet ink containing a pigment (A), a water-soluble acrylic urethane resin (B), a water-soluble organic solvent (C), a surfactant (D), and water, and comprising the following (1) to (5) A water-based inkjet ink that meets all requirements.
(1) The water-soluble acrylic urethane resin (B) is
structural units derived from acrylic diol (b1),
A structural unit derived from a polyisocyanate (b2), and
A structural unit derived from a low-molecular-weight diol (b3) having a molecular weight of 100 to 500 and having one acid group and two hydroxyl groups.
(2) the acrylic diol (b1) is
a structural unit derived from a chain transfer agent (t) having one mercapto group and two hydroxyl groups;
A structural unit derived from a vinyl monomer (f1) having an acid group, and
A structural unit derived from (meth)acrylate (f2) having no acid group is included.
(3) The water-soluble acrylic urethane resin (B) has a weight average molecular weight of 9,000 to 32,000.
(4) The content of the water-soluble acrylic urethane resin (B) is 2 to 10 mass % of the total amount of the water-based inkjet ink.
(5) The HLB value of the surfactant (D) is 0-7. The water-based inkjet ink according to claim 1, wherein the acrylic diol (b1) has an acid value of 25 to 310 mgKOH/g. The content of the structural units derived from the chain transfer agent (t) contained in the acrylic diol (b1) is 1 to 8.7% by mass with respect to the total amount of the structural units derived from the acrylic diol (b1). 3. The aqueous inkjet ink of claim 1 or 2. The amount of acid groups derived from the vinyl monomer having an acid group (f1) and the amount of acid groups derived from the low-molecular-weight diol (b3), which are present per unit mass of the water-soluble acrylic urethane resin (B). is 1:4 to 4:1. A printed matter obtained by printing the water-based inkjet ink according to any one of claims 1 to 4 on a paper substrate.