Ultraviolet-curable water-based inkjet-printing ink, ultraviolet-curable water-based inkjet-printing composition, and printed matter

Abstract

To provide an inkjet printing ink which is excellent in environment and safety, highly satisfies characteristics required as a printing ink for a commercial inkjet printer such as high image quality performance, high coating film performance, high-speed printability and substrate versatility in a well-balanced manner, and is also excellent in pigment dispersion stability.SOLUTION: Provided is an ultraviolet-curable aqueous ink for inkjet printing contains at least an ultraviolet-curable oligomer and a colorant. The ultraviolet curable oligomer is an ultraviolet curable oligomer having a structural unit derived from the polyisocyanate compound (A), a structural unit derived from a compound (B') shown below, and a structural unit derived from a compound (C') shown below. Compound (B'): a compound that contains two or more polymerizable unsaturated bonds and can be bonded to the polyisocyanate compound (A). Compound (C'): a water-soluble compound capable of being bonded to the polyisocyanate compound (A).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an ultraviolet curable aqueous ink for inkjet printing. The present invention also relates to a printed matter using the ultraviolet curable aqueous ink for inkjet printing. The present invention also relates to a dispersion suitable for the ultraviolet curable aqueous ink for inkjet printing.

Background Art

[0002] Inkjet printers have features such as being easy to achieve full color, having little noise, being able to obtain high-resolution images at low cost, being able to perform high-speed printing, being able to print not only on flat surfaces but also on curved surfaces, and being able to easily print on large areas. Therefore, inkjet printers are not limited to personal use, and in recent years, they are rapidly spreading as commercial inkjet printers for applications such as signage, window films, posters, car wrapping, wallpapers, etc.

[0003] In commercial inkjet printers, there are cases where printing large-area printed matter or printed matter for outdoor use, and long-term durability and productivity of the printed film are emphasized. Therefore, the following characteristics are required for the printing ink used in commercial inkjet printers. (1) High image quality performance: There is no bleeding of the image (including printing. The same applies hereinafter), the thickness of the formed printed film (hereinafter referred to as "ink thickness") is thin, and the surface smoothness of the printed film is excellent. (2) High coating film performance: The coating film strength of the formed printed film is high, and it is excellent in solvent resistance such as water resistance and alcohol resistance, light resistance, and weather resistance. (3) High-speed printability: The ink has excellent ejection properties and quick-drying properties (tackiness). (4) Substrate versatility: It should be printable on various recording media (substrates) such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), polypropylene (PP), paper, TEXTILE (cloth and fabric). (5) Environment and safety: Low odor and low content of VOC (organic solvents, unreacted monomers).

[0004] Conventionally, the following inks have been provided as printing inks for commercial inkjet printers. In the following, "UV ink" means ultraviolet curable ink. Water-based ink in which pigments are dispersed in an aqueous medium Solvent UV ink in which pigments and ultraviolet curable monomers are dispersed or dissolved in an organic solvent Solvent-free UV ink in which pigments are dispersed in a solvent-free ultraviolet curable monomer Water-based latex ink in which pigments and resins are dispersed in an aqueous medium Ultraviolet curable water-based ink in which pigments and UV curable oligomers are dispersed in an aqueous medium (for example, Patent Documents 1 to 3)

[0005] Since water-based ink is water-based, it is excellent in environment and safety, has a thin ink thickness, and also has good surface smoothness of the printed film. However, water-based ink is inferior in coating film performance, high-speed printability, and substrate versatility, and there is also a problem of bleeding of image quality.

[0006] Solvent UV ink has good coating film performance, substrate versatility, ink thickness, and surface smoothness of the printed film. However, solvent UV ink has a problem of bleeding of image quality, is not sufficient in high-speed printability, and is inferior in environment and safety because it is a solvent-based system.

[0007] Solvent-free UV ink has no bleeding of image quality and is excellent in coating film performance, high-speed printability, and substrate versatility. However, solvent-free UV ink has poor environment and safety, has high viscosity, so the ink thickness becomes thick, and the surface smoothness of the printed film is also inferior.

[0008] Since water-based latex ink is water-based, it is excellent in environment and safety and also in substrate versatility, and other characteristics are also relatively good. However, water-based latex ink is not sufficient to satisfy coating film performance and high-speed printability, and there are variations in bleeding of image quality.

[0009] Among these, the ultraviolet curable aqueous ink has relatively well-balanced all characteristics, but further improvement is desired.

[0010] For the ink for printing of a commercial inkjet printer, in addition to the characteristics of the above (1) to (5) in terms of performance, a high degree of pigment dispersion stability is also required, in which the pigment does not aggregate or the viscosity does not increase during storage. Regarding this storage stability, for the following reasons, it is required to be excellent not only at room temperature but also at high temperature. The ink for printing of an inkjet printer may be held under high temperature conditions for a long time during storage or transportation. Therefore, even when stored in a high temperature atmosphere of 40 to 60 ° C for about 2 to 14 days, storage stability at high temperature is required, in which no property changes such as an increase in viscosity or precipitation of pigment occur.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0012] The invention according to the first aspect of the present invention (hereinafter referred to as "the first invention") is an ultraviolet curable aqueous ink for inkjet printing, which has characteristics superior to those of conventional ultraviolet curable aqueous inks and is also excellent in pigment dispersion stability, and an ultraviolet curable aqueous composition for inkjet printing therefor, and a printed matter using this ultraviolet curable aqueous ink for inkjet printing. However, the first invention does not necessarily have to have all the performances of the above (1) to (5).

[0013] By using an ultraviolet curable oligomer having a specific structure, the inventor has found that it is possible to highly and well balance the required characteristics as an ink for inkjet printers, such as excellent environmental and safety properties, high image quality performance, high coating film performance, high-speed printability, and substrate versatility, and also to realize an ink having excellent pigment dispersion stability. The first invention has the following gist of [1] to

[18] .

[0014] [1] An ultraviolet curable aqueous ink for inkjet printing containing at least an ultraviolet curable oligomer and a colorant, wherein the ultraviolet curable oligomer is an ultraviolet curable oligomer having a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') shown below, and a structural unit derived from a compound (C') shown below. Ultraviolet curable aqueous ink for inkjet printing. Compound (B'): A compound containing two or more polymerizable unsaturated bonds and capable of bonding to the polyisocyanate compound (A) Compound (C'): A water-soluble compound capable of bonding to the polyisocyanate compound (A)

[0015] [2] The ultraviolet curable aqueous ink for inkjet printing according to [1], wherein the compound (C') is a compound containing one hydroxyl group at the terminal.

[0016] [3] The ultraviolet curable aqueous ink for inkjet printing according to [1] or [2], wherein the compound (B') is a hydroxyl group-containing polyfunctional (meth)acrylate (B), and the compound (C') is a polyalkylene glycol (C).

[0017] [4] In the ultraviolet curable oligomer, the structural unit derived from the polyisocyanate compound (A) is bonded to the structural unit derived from the hydroxyl group-containing polyfunctional (meth)acrylate (B) and the structural unit derived from the polyalkylene glycol (C) via urethane bonds, respectively. Ultraviolet curable aqueous ink for inkjet printing according to [3].

[0018] [5] The ultraviolet curable aqueous ink for inkjet printing according to any one of [1] to [4], wherein the polyisocyanate compound (A) has three or more isocyanate groups.

[0019] [6] The ultraviolet curable aqueous ink for inkjet printing according to any one of [3] to [5], wherein the polyalkylene glycol (C) is a polyethylene glycol mono-substituted ether.

[0020] [7] The ultraviolet curable aqueous ink for inkjet printing according to any one of [1] to [6], wherein the ultraviolet curable oligomer is dispersed as particles in an aqueous medium.

[0021] [8] The ultraviolet curable aqueous ink for inkjet printing according to any one of [1] to [7], wherein the average particle diameter of the ultraviolet curable oligomer is 10 nm or more and 200 nm or less.

[0022] [9] The ultraviolet curable aqueous ink for inkjet printing according to any one of [1] to [8], wherein the viscosity at 25 °C is 1 mPa·sec or more and 25 mPa·sec or less.

[0023]

[10] The ultraviolet curable aqueous ink for inkjet printing according to any one of [1] to [9], wherein the content of the colorant is 0.1 mass% or more and 8 mass% or less, and the content of the ultraviolet curable oligomer is 3 mass% or more and 20 mass% or less.

[0024]

[11] The ultraviolet curable aqueous ink for inkjet printing according to any one of [1] to

[10] , further comprising one or more of a polymerization initiator, a sensitizer, and a surfactant.

[0025]

[12] The ultraviolet curable aqueous ink for inkjet printing according to

[11] , comprising a polymerization initiator and / or a sensitizer, and at least a part of the polymerization initiator and / or the sensitizer is encapsulated in the ultraviolet curable oligomer.

[0026]

[13] A printed matter having a cured product formed from the ultraviolet-curable aqueous ink for inkjet printing according to any one of [1] to

[12] on a recording medium.

[0027]

[14] An ultraviolet-curable aqueous composition for inkjet printing containing an ultraviolet-curable oligomer and at least one of a polymerization initiator, a sensitizer, and a surfactant, wherein the ultraviolet-curable oligomer is an ultraviolet-curable oligomer having a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B’) shown below, and a structural unit derived from a compound (C’) shown below. An ultraviolet-curable aqueous composition for inkjet printing. Compound (B’): A compound containing two or more polymerizable unsaturated bonds and capable of bonding to the polyisocyanate compound (A) Compound (C’): A water-soluble compound capable of bonding to the polyisocyanate compound (A)

[0028]

[15] The ultraviolet-curable aqueous composition for inkjet printing according to

[14] , wherein the compound (C’) is a compound containing one hydroxyl group at the terminal.

[0029]

[16] The ultraviolet-curable aqueous composition for inkjet printing according to

[14] or

[15] , wherein the compound (B’) is a hydroxyl group-containing polyfunctional (meth)acrylate (B), and the compound (C’) is a polyalkylene glycol (C).

[0030]

[17] The ultraviolet-curable aqueous composition for inkjet printing according to any one of

[14] to

[16] , containing at least one polymerization initiator and a sensitizer and / or a surfactant.

[0031]

[18] The ultraviolet-curable aqueous composition for inkjet printing according to any one of

[14] to

[17] , containing a polymerization initiator and / or a sensitizer, and at least a part of the polymerization initiator and / or the sensitizer is encapsulated in the ultraviolet-curable oligomer.

[0032] The invention according to the second aspect of the present invention (hereinafter referred to as "the second invention") is an ultraviolet curable aqueous ink for inkjet printing, which has properties superior to those of conventional ultraviolet curable aqueous inks and is also excellent in storage stability at high temperatures, as well as a dispersion liquid and an ultraviolet curable aqueous composition for inkjet printing therefor, and a printed matter using this ultraviolet curable aqueous ink for inkjet printing. However, it is not essential for the second invention to have all the performances of the above (1) to (5).

[0033] The present inventor has found that by using an ultraviolet curable oligomer and blending a compound having a specific structure as an additive, it is possible to suppress deterioration such as an increase in viscosity and precipitation of pigments during storage at high temperatures, and to realize an ultraviolet curable aqueous ink for inkjet printing having excellent storage stability at high temperatures. The second invention has the following gist in

[19] to

[44] .

[0034]

[19] An ultraviolet curable aqueous ink for inkjet printing containing at least an ultraviolet curable oligomer, a colorant, and a compound represented by the following general formula (I).

[0035] [Chemical formula]

[0036] (In formula (I), R 1 and R 2 each independently represent an alkyl group having 1 to 10 carbon atoms.)

[0037]

[20] The ultraviolet curable aqueous ink for inkjet printing according to

[19] , wherein the ultraviolet curable oligomer is nonionic.

[0038]

[21] The ultraviolet curable aqueous ink for inkjet printing according to

[19] or

[20] , wherein the compound represented by the general formula (I) is N,N-diethylhydroxylamine.

[0039]

[22] The ultraviolet curable oligomer is an ultraviolet curable oligomer having a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B’) shown below, and a structural unit derived from a compound (C’) shown below, which is an ultraviolet curable aqueous ink for inkjet printing according to any one of

[19] to

[21] . Compound (B’): A compound containing two or more polymerizable unsaturated bonds and capable of bonding with the polyisocyanate compound (A) Compound (C’): A water-soluble compound capable of bonding with the polyisocyanate compound (A)

[0040]

[23] The ultraviolet curable aqueous ink for inkjet printing according to

[22] , wherein the compound (C’) is a compound containing one hydroxyl group at the terminal.

[0041]

[24] The ultraviolet curable aqueous ink for inkjet printing according to

[22] or

[23] , wherein the compound (B’) is a hydroxyl group-containing polyfunctional (meth)acrylate (B), and the compound (C’) is a polyalkylene glycol (C).

[0042]

[25] The ultraviolet curable aqueous ink for inkjet printing according to

[24] , wherein the ultraviolet curable oligomer has a structural unit derived from the polyisocyanate compound (A) bonded to a structural unit derived from the hydroxyl group-containing polyfunctional (meth)acrylate (B) and a structural unit derived from the polyalkylene glycol (C) via urethane bonds, respectively.

[0043]

[26] The ultraviolet curable aqueous ink for inkjet printing according to any one of

[22] to

[25] , wherein the polyisocyanate compound (A) has three or more isocyanate groups.

[0044]

[27] The ultraviolet curable aqueous ink for inkjet printing according to any one of

[24] to

[26] , wherein the polyalkylene glycol (C) is a polyethylene glycol mono-substituted ether.

[0045]

[28] The ultraviolet curable aqueous ink for inkjet printing according to any one of

[19] to

[27] , wherein the average particle size of the ultraviolet curable oligomer is 10 nm or more and 200 nm or less.

[0046]

[29] The ultraviolet curable aqueous ink for inkjet printing according to any one of

[19] to

[28] , wherein the viscosity at 25 °C is 1 mPa·sec or more and 25 mPa·sec or less.

[0047]

[30] The ultraviolet curable aqueous ink for inkjet printing according to any one of

[19] to

[29] , wherein the content of the colorant is 0.1% by mass or more and 8% by mass or less, the content of the ultraviolet curable oligomer is 3% by mass or more and 20% by mass or less, and the content of the compound represented by the general formula (I) is 0.01% by mass or more and 5% by mass or less.

[0048]

[31] The ultraviolet curable aqueous ink for inkjet printing according to any one of

[19] to

[30] , further comprising one or more of a polymerization initiator, a sensitizer, and a surfactant.

[0049]

[32] The ultraviolet curable aqueous ink for inkjet printing according to

[31] , comprising a polymerization initiator and / or a sensitizer, and at least a part of the polymerization initiator and / or the sensitizer is encapsulated in the ultraviolet curable oligomer.

[0050]

[33] A dispersion of an ultraviolet curable oligomer, wherein the ultraviolet curable oligomer is nonionic and contains 0.01% by mass or more and 5% by mass or less of a compound represented by the following general formula (I).

[0051]

Chemical formula

[0052] (In formula (I), R 1 and R 2 each independently represents an alkyl group having 1 to 10 carbon atoms.)

[0053]

[34] The dispersion according to

[33] , wherein the ultraviolet curable oligomer is an ultraviolet curable oligomer having a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') shown below, and a structural unit derived from a compound (C') shown below. Compound (B'): A compound containing two or more polymerizable unsaturated bonds and capable of bonding to the polyisocyanate compound (A) Compound (C'): A water-soluble compound capable of bonding to the polyisocyanate compound (A)

[0054]

[35] The dispersion according to

[34] , wherein the compound (C') is a compound containing one hydroxyl group at the terminal.

[0055]

[36] A printed matter having a cured product formed from the ultraviolet curable aqueous ink for inkjet printing according to any one of

[19] to

[32] on a recording medium.

[0056]

[37] An ultraviolet curable aqueous composition for inkjet printing containing an ultraviolet curable oligomer, any one or more of a polymerization initiator, a sensitizer, and a surfactant, and a compound represented by the following general formula (I).

[0057] [Chemical formula]

[0058] (In formula (I), R 1 and R 2 each independently represent an alkyl group having 1 to 10 carbon atoms.)

[0059]

[38] The ultraviolet curable aqueous composition for inkjet printing according to

[37] , wherein the ultraviolet curable oligomer is nonionic.

[0060]

[39] The ultraviolet curable aqueous composition for inkjet printing according to

[37] or

[38] , wherein the compound represented by the general formula (I) is N,N - diethylhydroxylamine.

[0061]

[40] The ultraviolet curable oligomer is an ultraviolet curable oligomer having a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') shown below, and a structural unit derived from a compound (C') shown below, which is an ultraviolet curable aqueous composition for inkjet printing according to any one of

[37] to

[39] . Compound (B'): A compound containing two or more polymerizable unsaturated bonds and capable of bonding to the polyisocyanate compound (A) Compound (C'): A water-soluble compound capable of bonding to the polyisocyanate compound (A)

[0062]

[41] The ultraviolet curable aqueous composition for inkjet printing according to

[40] , wherein the compound (C') is a compound containing one hydroxyl group at the terminal.

[0063]

[42] The ultraviolet curable aqueous composition for inkjet printing according to

[40] or

[41] , wherein the compound (B') is a hydroxyl group-containing polyfunctional (meth)acrylate (B), and the compound (C') is a polyalkylene glycol (C).

[0064]

[43] The ultraviolet curable aqueous composition for inkjet printing according to any one of

[37] to

[42] , containing at least one or more polymerization initiators and a sensitizer and / or a surfactant.

[0065]

[44] The ultraviolet curable aqueous composition for inkjet printing according to any one of

[37] to

[43] , containing a polymerization initiator and / or a sensitizer, and at least a part of the polymerization initiator and / or the sensitizer is encapsulated in the ultraviolet curable oligomer.

Advantages of the Invention

[0066] The ultraviolet curable aqueous ink for inkjet printing of the first invention is excellent in environmental safety and highly satisfies the required characteristics of an ink for inkjet printers, such as high image quality performance, high coating film performance, high-speed printability, and substrate versatility, while also being excellent in pigment dispersion stability. According to the aqueous composition of the first invention, it is possible to provide an ultraviolet curable aqueous ink for inkjet printing that is excellent in the required characteristics and pigment dispersion stability.

[0067] The ultraviolet curable aqueous ink for inkjet printing of the second invention is excellent in environmental safety and highly satisfies the required characteristics of an ink for inkjet printers, such as high image quality performance, high coating film performance, high-speed printability, and substrate versatility, while also being excellent in storage stability at high temperatures. According to the dispersion liquid and aqueous composition of the second invention, it is possible to provide an ultraviolet curable aqueous ink for inkjet printing that is excellent in coating film strength and storage stability at high temperatures.

[0068] According to the ultraviolet curable aqueous ink for inkjet printing and the aqueous composition of the first invention, and the ultraviolet curable aqueous ink for inkjet printing, the dispersion liquid, and the aqueous composition of the second invention, it is possible to efficiently form a high-quality printed image with excellent coating film performance on a wide variety of recording media with high productivity by high-speed printing while maintaining environmental safety.

Embodiments for Carrying Out the Invention

[0069] The embodiments of the present invention will be described in detail below.

[0070] The description of the constituent elements described below is an example (representative example) of the embodiments of the present invention, and the present invention is not limited to these contents as long as it does not exceed the gist thereof.

[0071] In the present invention, when expressed as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less" as well as the meaning of "preferably larger than X" and "preferably smaller than Y".

[0072] Hereinafter, the "First Invention" and the "Second Invention" are collectively referred to as the "Present Invention".

[0073] In the present invention, "(meth)acrylate" means acrylate or methacrylate. The ultraviolet-curable aqueous ink for inkjet printing of the present invention (hereinafter, may be referred to as the "ink of the present invention") is synonymous with the "ink for ultraviolet-curable aqueous inkjet printing".

[0074] The ink of the present invention is ultraviolet-curable, but the active energy rays used for curing are not limited to ultraviolet rays at all. When curing the ink of the present invention, it is not limited to curing by active energy rays, and may be cured by heat, for example.

[0075] In the present invention, the "structural unit derived from X" means a structural unit that is incorporated into the molecular structure of the ultraviolet-curable oligomer by using compound X as a raw material and reacting compound X with other compounds. The "structural unit derived from X" is not necessarily limited to using compound X as a raw material. Even if it is formed from raw materials other than X, it corresponds to the "structural unit derived from X" if the chemical structure is the same.

[0076] 1: Ultraviolet-curable aqueous ink for inkjet printing The ink of the First Invention is an ultraviolet-curable aqueous ink for inkjet printing containing at least an ultraviolet-curable oligomer and a colorant, wherein the ultraviolet-curable oligomer has a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') shown below, and a structural unit derived from a compound (C') shown below (hereinafter, may be referred to as the "ultraviolet-curable oligomer of the First Invention"). Compound (B'): A compound containing two or more polymerizable unsaturated bonds and capable of bonding to the polyisocyanate compound (A) Compound (C'): A water-soluble compound capable of bonding to the polyisocyanate compound (A)

[0077] The ink of the second invention is an ultraviolet curable aqueous ink for inkjet printing containing at least an ultraviolet curable oligomer and a colorant, wherein the ultraviolet curable oligomer is preferably nonionic and further contains a compound represented by the following general formula (I) (hereinafter sometimes referred to as "compound (I)").

[0078]

Chemical formula

[0079] (In formula (I), R 1 and R 2 each independently represent an alkyl group having 1 to 10 carbon atoms.)

[0080] 1-1: Ultraviolet curable oligomer The ultraviolet curable oligomer of the first invention has a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') shown below, and a structural unit derived from a compound (C') shown below, and is usually produced by reacting a polyisocyanate compound (A), a compound (B'), and a compound (C'). Compound (B'): A compound containing two or more polymerizable unsaturated bonds and capable of bonding to the polyisocyanate compound (A) Compound (C'): A water-soluble compound capable of bonding to the polyisocyanate compound (A)

[0081] In the ultraviolet curable oligomer of the first invention, the structural unit portion derived from the polyisocyanate compound (A) contributes to the adhesion of the printed film to the recording medium. The structural unit portion derived from the compound (B') contributes to ultraviolet curability. Further, when the compound (B') is a hydroxyl group-containing polyfunctional (meth)acrylate (B), the (meth)acryloyl group contained in the structural unit derived from the hydroxyl group-containing polyfunctional (meth)acrylate (B) contributes to ultraviolet curability. The structural unit portion derived from the compound (C') contributes to the water dispersibility of the oligomer in the ink. Further, when the compound (C') is a polyalkylene glycol (C), the polyalkylene glycol chain of the structural unit derived from the polyalkylene glycol (C) contributes to the water dispersibility of the oligomer in the ink. It is a feature of the first invention to use an oligomer having all of these structural units in the same molecule. From the viewpoint of reactivity, the compound (B') is preferably a hydroxyl group-containing polyfunctional (meth)acrylate (B). Further, from the viewpoint of water dispersibility, the compound (C') is preferably a polyalkylene glycol (C). Hereinafter, the ultraviolet curable oligomer of the first invention in this case may be referred to as an "ultraviolet curable (meth)acrylate oligomer".

[0082] Furthermore, since it can be made excellent in solvent resistance such as alcohol resistance, the structural unit derived from the polyisocyanate compound (A) is preferably bonded to the structural unit derived from the hydroxyl group-containing polyfunctional (meth)acrylate (B) and the structural unit derived from the polyalkylene glycol (C) via urethane bonds, respectively.

[0083] From the above, the ultraviolet curable oligomer of the first invention is excellent in ultraviolet curability, coating film performance, substrate fixing property, and water dispersion stability.

[0084] By selecting specific ones as the polyisocyanate compound (A), the hydroxyl group-containing polyfunctional (meth)acrylate (B), and the polyalkylene glycol (C) constituting the ultraviolet curable oligomer of the first invention to form a nonionic oligomer, aggregation of the pigment can be suppressed and the pigment dispersion stability can be made more excellent.

[0085] The presence or absence of ionic properties of the ultraviolet curable oligomer used in the second invention is not particularly limited, and it may be nonionic or ionic (anionic, cationic or amphoteric). However, by being nonionic, aggregation of pigments can be suppressed and the storage stability of the ink can be enhanced. Here, nonionic means that the hydrophilic group of the ultraviolet curable oligomer has a structure in which it does not ionize in water. Specifically, ether bonds and hydroxyl groups are exemplified.

[0086] There are no particular restrictions on the ultraviolet curable oligomer used in the second invention, but those having a structural unit derived from (meth)acrylate, particularly those having a structural unit derived from a polyfunctional (meth)acrylate are preferred. Furthermore, those having a structural unit derived from a polyfunctional (meth)acrylate and a structural unit derived from a polyalkylene glycol are preferred. Since it is excellent in ultraviolet curability, fixing property, water dispersion stability, pigment aggregation suppressing effect, alcohol resistance, etc., the ultraviolet curable oligomer used in the second invention is preferably an ultraviolet curable oligomer having a structural unit derived from the polyisocyanate compound (A), the structural unit derived from the compound (B’) and the structural unit derived from the compound (C’), and more preferably an ultraviolet curable (meth)acrylate oligomer having a structural unit derived from the polyisocyanate compound (A), a structural unit derived from a hydroxyl group-containing polyfunctional (meth)acrylate (B) and a structural unit derived from a polyalkylene glycol (C). That is, it is preferably the ultraviolet curable oligomer of the first invention, and more preferably the aforementioned ultraviolet curable (meth)acrylate oligomer.

[0087] As described above, a hydroxyl group-containing polyfunctional (meth)acrylate (B) is exemplified as a preferred embodiment of the compound (B’), but a “compound (B’’) containing a hydroxyl group and containing two or more polymerizable unsaturated bonds” may also be a preferred embodiment of the compound (B’). As the "compound capable of binding to the polyisocyanate compound (A)" in the compound (B'), the hydroxyl group can be substituted with a carboxyl group, an amino group, or the like. Examples of the polymerizable unsaturated bond include a carbon-carbon double bond and a carbon-carbon triple bond, and among them, a carbon-carbon double bond is preferable. More specifically, examples include carbon-carbon double bonds derived from a vinyl group, a (meth)acryloyl group, or the like.

[0088] The water-soluble compound in the compound (C') includes a water-soluble polymer. Specifically, examples include polyglycerin, polyhydroxy(meth)acrylate, polyamine, quaternary aminoated polystyrene, sulfonated polystyrene, polyether, polyalkylene glycol, and the like. Among them, polyglycerin, polyhydroxy(meth)acrylate, and polyalkylene glycol, which are nonionic water-soluble compounds, are preferable, and polyalkylene glycol is particularly preferable. These water-soluble compounds may each be a copolymer. The compound (C') has the structure of such a water-soluble compound and the structure of the "compound capable of binding to the polyisocyanate compound (A)". Here, as the "compound capable of binding to the polyisocyanate compound (A)", it can be selected from the same structures as those exemplified for the compound (B') above.

[0089] The structural unit derived from the polyisocyanate compound (A) forms a urethane bond by bonding with the structural unit derived from the hydroxyl group-containing polyfunctional (meth)acrylate (B) and the structural unit derived from the polyalkylene glycol (C), and this urethane bond may be substituted with a urea bond or an amide bond, respectively. When forming a urea bond, the hydroxyl group in the hydroxyl group-containing polyfunctional (meth)acrylate (B) may be substituted with an amino group as the compound (B'), or the hydroxyl group-terminated end of the polyalkylene glycol (C) may be substituted with an amino group as the compound (C'). When forming an amide bond, the hydroxyl group in the hydroxyl group-containing polyfunctional (meth)acrylate (B) may be substituted with a carboxyl group as the compound (B'), or the hydroxyl group-terminated end of the polyalkylene glycol (C) may be substituted with a carboxyl group as the compound (C'). Instead of converting the hydroxyl group in this way, a compound capable of forming a urea bond or an amide bond in advance may be used as it is to obtain a substantially similar chemical structure. As described above, the structural unit derived from the polyisocyanate compound (A) contributes to the adhesion of the printed film to the recording medium, and as described above, it is considered that the isocyanate group in the polyisocyanate compound (A) forms a polar site such as a urethane bond, a urea bond or an amide bond in the ultraviolet curable oligomer.

[0090] In the present invention, when the hydroxyl group-containing polyfunctional (meth)acrylate (B) is extended to the compound (B') or the compound (B'') as described above, or when the polyalkylene glycol (C) is extended to the compound (C') as described above, in the preferred or specific embodiments at that time, the preferred or specific embodiments when using the hydroxyl group-containing polyfunctional (meth)acrylate (B) or the polyalkylene glycol (C) described later can be similarly applied.

[0091] Hereinafter, each compound constituting the ultraviolet curable oligomer of the first invention or the ultraviolet curable oligomer used in the second invention will be described. In the present invention, the term "oligomer" is not limited to a specific molecular weight or range of average molecular weight, etc., and any substance having the structure shown below is sufficient.

[0092] The ink of the first invention may contain only one kind of the ultraviolet curable oligomer of the first invention, or may contain two or more kinds. The ink of the second invention may contain only one kind of the ultraviolet curable oligomer, or may contain two or more kinds. The ultraviolet curable oligomer of the first invention is included in the ultraviolet curable oligomer used in the second invention.

[0093] 1-1-1: Polyisocyanate compound (A) The polyisocyanate compound (A) is a compound having a total of two or more isocyanate groups in one molecule.

[0094] The type of the polyisocyanate compound (A) is not particularly limited, and examples include chain aliphatic polyisocyanates, aromatic polyisocyanates, alicyclic polyisocyanates, etc. Among them, it is preferable for the polyisocyanate compound (A) to contain a trimer compound of polyisocyanate from the viewpoints of weather resistance and hardness.

[0095] The chain aliphatic polyisocyanate is a compound having a chain aliphatic structure and two or more isocyanate groups. The chain aliphatic polyisocyanate is preferable from the viewpoints of weather resistance and stretchability. The chain aliphatic structure in the chain aliphatic polyisocyanate is not particularly limited, but a linear or branched alkylene group having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms is preferable. Examples of the chain aliphatic polyisocyanate include aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, or trimer compounds of these polyisocyanates.

[0096] An aromatic polyisocyanate is a compound having an aromatic structure and two or more isocyanate groups. The aromatic polyisocyanate is preferable from the viewpoint of coating film strength. The aromatic structure in the aromatic polyisocyanate is not particularly limited, but an aromatic structure having 6 to 13 carbon atoms is preferable. Examples of the aromatic polyisocyanate include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, naphthalene diisocyanate, or trimer compounds of these polyisocyanates.

[0097] An alicyclic polyisocyanate is a compound having an alicyclic structure and two or more isocyanate groups. The alicyclic structure in the alicyclic polyisocyanate is not particularly limited, but its carbon number is usually 5 or more, preferably 6 or more, usually 15 or less, preferably 14 or less, and more preferably 13 or less. The alicyclic structure is particularly preferably a cycloalkylene group. Examples of the alicyclic polyisocyanate include diisocyanates having an alicyclic structure such as bis(isocyanatomethyl)cyclohexane, cyclohexane diisocyanate, bis(isocyanatocyclohexyl)methane, isophorone diisocyanate, or trimer compounds of these polyisocyanates.

[0098] For the ultraviolet curable oligomer of the first invention or the ultraviolet curable oligomer used in the second invention, only one kind of these polyisocyanate compounds (A) may be used, or two or more kinds may be used in combination. Further, as the polyisocyanate compound (A), a polyisocyanate having two or more structures among a chain aliphatic structure, an aromatic structure, and an alicyclic structure can also be used.

[0099] As the polyisocyanate compound (A), those having 3 to 6 isocyanate groups are preferred particularly from the viewpoint of adhesion to the substrate. Further, as the polyisocyanate compound (A), trimers obtained by a trimerization reaction from hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, phenylene diisocyanate, etc. are preferred, and particularly a trimer of hexamethylene diisocyanate is preferred.

[0100] 1-1-2: Compound (B’) The compound (B’) contains two or more polymerizable unsaturated bonds and is a compound capable of bonding to the polyisocyanate compound (A). Examples of the compound (B’) include compounds having any one of a hydroxyl group, an amino group, and a carboxyl group. Further, examples of the compound (B’) include polyfunctional vinyl monomers, polyfunctional allyl monomers, and polyfunctional (meth)acrylates. Among them, as the compound (B’), a hydroxyl group-containing polyfunctional (meth)acrylate (B) is preferred.

[0101] The hydroxyl group-containing polyfunctional (meth)acrylate (B) has one or more hydroxyl groups and two or more (meth)acryloyl groups. Specifically, (meth)acrylic acid partial esters of polyhydric alcohols are included. In the curing reaction, a plurality of (meth)acryloyl groups participate in the hydroxyl group-containing polyfunctional (meth)acrylate, thereby forming a good crosslinked structure and enabling good physical properties such as stain resistance and abrasion resistance.

[0102] The number of hydroxyl groups in the hydroxyl group-containing polyfunctional (meth)acrylate (B) is preferably 3 or less, more preferably 2 or less, and still more preferably 1. The number of (meth)acryloyl groups in the hydroxyl group-containing polyfunctional (meth)acrylate (B) is preferably 8 or less, more preferably 6 or less.

[0103] Examples of the hydroxyl group-containing polyfunctional (meth)acrylate (B) include pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, caprolactone-modified dipentaerythritol penta(meth)acrylate, caprolactone-modified pentaerythritol tri(meth)acrylate, ethylene oxide-modified dipentaerythritol penta(meth)acrylate, ethylene oxide-modified pentaerythritol tri(meth)acrylate, 2-hydroxy-1,3-dimethacryloxypropane, 2-hydroxy-3-acryloyloxypropyl methacrylate, and the like.

[0104] For the production of the ultraviolet curable oligomer of the first invention or the ultraviolet curable oligomer used in the second invention, only one of these hydroxyl group-containing polyfunctional (meth)acrylates (B) may be used, or two or more thereof may be used in combination.

[0105] As the hydroxyl group-containing polyfunctional (meth)acrylate (B), from the viewpoint of the coating film strength of the resulting cured film in particular, those having one hydroxyl group and three or more and five or less (meth)acryloyl groups, such as dipentaerythritol penta(meth)acrylate and pentaerythritol tri(meth)acrylate, are preferable. Dipentaerythritol penta(meth)acrylate is particularly preferable because it forms a particularly good crosslinked structure and enhances the mechanical strength of the cured film.

[0106] 1-1-3: Compound (C’) Compound (C’) is a water-soluble compound that can bind to the polyisocyanate compound (A). Since compound (C’) has good water dispersibility, it is preferably a compound containing one hydroxyl group at the terminal.

[0107] As compound (C’), as described above, water-soluble polymers are exemplified, and among them, polyalkylene glycol (C) is particularly preferable.

[0108] As the polyalkylene glycol (C), although not limited, a monosubstituted structure is preferred. That is, it is preferable that one of the hydroxyl groups of the glycol is substituted. The substitution structure is preferably a structure that does not bind to isocyanate. The polyalkylene glycol (C) may be a mixture of a compound having a monosubstituted structure and a compound not having a monosubstituted structure.

[0109] The monosubstituted structure is not limited, but from the viewpoint of making the ultraviolet curable oligomer of the first invention or the ultraviolet curable oligomer used in the second invention nonionic, polyalkylene glycol monosubstituted ether is preferred, and polyethylene glycol monosubstituted ether, polytrimethylene glycol monosubstituted ether or polypropylene glycol monosubstituted ether is more preferred, and polyethylene glycol monosubstituted ether is even more preferred.

[0110] The molecular weight of the polyalkylene glycol (C) (when not single, it means the number average molecular weight) is not limited, but is usually 100 or more, preferably 200 or more, and usually 5000 or less, preferably 2000 or less.

[0111] Among polyalkylene glycol monosubstituted ethers, polyalkylene glycol monosubstituted ethers that do not contain an ionic substituent in the ether moiety are more preferred, and for example, those represented by the following general formula (1) are even more preferred.

[0112]

Chemical formula

[0113] (In formula (1), X is an alkylene group, Y is an alkyl group, a (meth)acryloyl group, an allyl group, or an acyl group. n is an integer of 2 or more.)

[0114] Specific examples of the polyalkylene glycol monosubstituted ether represented by the above general formula (1) include, for example, the following. Y is an alkyl group: polyethylene glycol monomethyl ether, polyethylene glycol lauryl ether, polyethylene glycol cetyl ether, polyethylene glycol stearyl ether, polyethylene glycol tridecyl ether, polyethylene glycol oleyl ether, polyethylene glycol octyl phenyl ether, polyoxyethylene oleyl cetyl ether, polypropylene glycol monomethyl ether, etc. Y is a (meth)acryloyl group: polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, poly(ethylene glycol - propylene glycol) mono(meth)acrylate, poly(ethylene glycol - tetramethylene glycol) mono(meth)acrylate, poly(propylene glycol - tetramethylene glycol) mono(meth)acrylate, etc. Y is an allyl group: polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, poly(ethylene glycol - propylene glycol) monoallyl ether, etc. Y is an acyl group: polyethylene glycol monolaurate, polypropylene glycol monolaurate, poly(ethylene glycol - propylene glycol) monolaurate, polyethylene glycol monostearate, polyethylene glycol monooleate, etc.

[0115] Among these, in general formula (1), X is preferably an alkylene group having 1 to 3 carbon atoms, more preferably an ethylene group, a trimethylene group, or a propylene group, and even more preferably an ethylene group from the viewpoints of pigment dispersion stability or storage stability at high temperatures. Also, from the viewpoint of coating film strength, Y is preferably a (meth)acryloyl group, an allyl group, or an acyl group, and more preferably an allyl group.

[0116] From the viewpoint of the coating film strength of the resulting cured film, n in general formula (1) is usually 2 or more, preferably 5 or more, more preferably 6 or more, and is usually 500 or less, preferably 100 or less, more preferably 50 or less.

[0117] For the production of the ultraviolet-curable oligomer of the first invention or the ultraviolet-curable oligomer used in the second invention, only one of these polyalkylene glycols (C) may be used, or two or more thereof may be used in combination. The polyalkylene glycol (C) may be a mixture of compounds having different molecular weights (compounds in which n in the general formula (1) is different).

[0118] 1-1-4: Method for producing ultraviolet-curable oligomer The method for producing the ultraviolet-curable oligomer of the first invention or the ultraviolet-curable oligomer used in the second invention is not particularly limited, but it is preferably produced by reacting the above polyisocyanate compound (A), compound (B') and compound (C') to form chemical bonds respectively.

[0119] When the compound (B') is a hydroxyl group-containing polyfunctional (meth)acrylate (B) and the compound (C') is a polyalkylene glycol (C), the above polyisocyanate compound (A), hydroxyl group-containing polyfunctional (meth)acrylate (B) and polyalkylene glycol (C) are reacted to form urethane bonds with the isocyanate group of the polyisocyanate compound (A), the hydroxyl group of the hydroxyl group-containing polyfunctional (meth)acrylate (B) and the hydroxyl group of the polyalkylene glycol (C), respectively. It is preferably produced by doing so.

[0120] In the present invention, from the viewpoints of pigment dispersion stability and the coating film strength of the obtained cured film, it is preferable to use an oligomer in which two hydroxyl group-containing polyfunctional (meth)acrylates (B) and one polyalkylene glycol (C) form urethane bonds with respect to the polyisocyanate compound (A). The ultraviolet-curable oligomer may additionally have other structures as long as it has structural units derived from the polyisocyanate compound (A), structural units derived from the compound (B') and structural units derived from the compound (C').

[0121] 1-1-5: Weight-average molecular weight The ultraviolet curable oligomer of the first invention or the ultraviolet curable oligomer used in the second invention preferably has a polystyrene-equivalent weight average molecular weight of usually 1,000 or more, preferably 2,000 or more, and usually 100,000 or less, preferably 50,000 or less, from the viewpoints of the performance of the formed coating film and handleability.

[0122] 1-1-6: Average particle size In the ink of the present invention, the ultraviolet curable oligomer of the first invention or the ultraviolet curable oligomer used in the second invention preferably exists as particles having an average particle size of 10 nm or more and 200 nm or less, more preferably 20 nm or more and 150 nm or less, in the aqueous medium. When the average particle size of the ultraviolet curable oligomer of the first invention or the ultraviolet curable oligomer used in the second invention is within the above range, the dispersion stability becomes good.

[0123] The average particle size of the ultraviolet curable oligomer is, for example, the volume average particle size (D 50 ) measured by a particle size measuring instrument using the dynamic light scattering method. In the examples described later, the average particle size of the ultraviolet curable oligomer particles in the ultraviolet curable oligomer aqueous dispersion is measured. The average particle size of the oligomer particles in this aqueous dispersion is almost the same as the average particle size of the oligomer particles in the ink. In the ink of the present invention, as long as the ultraviolet curable oligomer exists as particles, even if there is aggregation or the particles contain other substances, it is included in the state of "existing as particles" described above. The average particle size of the above ultraviolet curable oligomer means the particle size (primary particle size) of the ultraviolet curable oligomer particles.

[0124] Hereinafter, components other than the ultraviolet curable oligomer contained in the ink of the present invention will be described.

[0125] 1-2: Colorant The ink of the present invention contains a colorant. As the colorant used in the ink of the present invention, various dyes or pigments known as colorants used in inkjet inks can be used. However, from the viewpoints of irradiation with ultraviolet rays and long-term storage durability of printed images, it is preferable to use pigments.

[0126] 1-2-1: Dye There is no particular limitation on the dyes that can be used in the present invention, and examples include water-soluble dyes such as acid dyes, direct dyes, and reactive dyes, and disperse dyes. Among these, anionic dyes are preferable.

[0127] Examples of water-soluble dyes include azo dyes, methine dyes, azomethine dyes, xanthene dyes, quinone dyes, phthalocyanine dyes, triphenylmethane dyes, diphenylmethane dyes, and the like. Specific compounds thereof are as shown below, but are not limited to the exemplified compounds.

[0128] 〈C.I. Acid Yellow〉 1, 3, 11, 17, 18, 19, 23, 25, 36, 38, 40, 42, 44, 49, 59, 61, 65, 67, 72, 73, 79, 99, 104, 110, 114, 116, 118, 121, 127, 129, 135, 137, 141, 143, 151, 155, 158, 159, 169, 176, 184, 193, 200, 204, 207, 215, 219, 220, 230, 232, 235, 241, 242, 246 〈C.I. Acid Orange〉 3, 7, 8, 10, 19, 24, 51, 56, 67, 74, 80, 86, 87, 88, 89, 94, 95, 107, 108, 116, 122, 127, 140, 142, 144, 149, 152, 156, 162, 166, 168 〈C.I. Acid Red〉 88, 97, 106, 111, 114, 118, 119, 127, 131, 138, 143, 145, 151, 183, 195, 198, 211, 215, 217, 225, 226, 249, 251, 254, 256, 257, 260, 261, 265, 266, 274, 276, 277, 289, 296, 299, 315, 318, 336, 337, 357, 359, 361, 362, 364, 366, 399, 407, 415 〈C.I. Acid Violet〉 17, 19, 21, 42, 43, 47, 48, 49, 54, 66, 78, 90, 97, 102, 109, 126

[0129] 〈C.I. Acid Blue〉 1, 7, 9, 15, 23, 25, 40, 62, 72, 74, 80, 83, 90, 92, 103, 104, 112, 113, 114, 120, 127, 128, 129, 138, 140, 142, 156, 158, 171, 182, 185, 193, 199, 201, 203, 204, 205, 207, 209, 220, 221, 224, 225, 229, 230, 239, 249, 258, 260, 264, 278, 279, 280, 284, 290, 296, 298, 300, 317, 324, 333, 335, 338, 342, 350 〈C.I. Acid Green〉 9, 12, 16, 19, 20, 25, 27, 28, 40, 43, 56, 73, 81, 84, 104, 108, 109 〈C.I. Acid Brown〉 2, 4, 13, 14, 19, 28, 44, 123, 224, 226, 227, 248, 282, 283, 289, 294, 297, 298, 301, 355, 357, 413 〈C.I. Acid Black〉 1, 2, 3, 24, 26, 31, 50, 52, 58, 60, 63, 107, 109, 112, 119, 132, 140, 155, 172, 187, 188, 194, 207, 222

[0130] 〈C.I. Direct Yellow〉 8, 9, 10, 11, 12, 22, 27, 28, 39, 44, 50, 58, 79, 86, 87, 98, 105, 106, 130, 132, 137, 142, 147, 153 〈C.I. Direct Orange〉 6, 26, 27, 34, 39, 40, 46, 102, 105, 107, 118 〈C.I. Direct Red〉 2, 4, 9, 23, 24, 31, 54, 62, 69, 79, 80, 81, 83, 84, 89, 95, 212, 224, 225, 226, 227, 239, 242, 243, 254 〈C.I. Direct Violet〉 9, 35, 51, 66, 94, 95 〈C.I. Direct Blue〉 1, 15, 71, 76, 77, 78, 80, 86, 87, 90, 98, 106, 108, 160, 168, 189, 192, 193, 199, 200, 201, 202, 203, 218, 225, 229, 237, 244, 248, 251, 270, 273, 274, 290, 291 〈C.I. Direct Green〉 26, 28, 59, 80, 85 〈C.I. Direct Brown〉 44, 106, 115, 195, 209, 210, 222, 223 〈C.I. Direct Black〉 17, 19, 22, 32, 51, 62, 108, 112, 113, 117, 118, 132, 146, 154, 159, 169

[0131] 〈C.I. Basic Yellow〉 1, 2, 11, 13, 15, 19, 21, 28, 29, 32, 36, 40, 41, 45, 51, 63, 67, 70, 73, 91 〈C.I. Basic Orange〉 2, 21, 22 〈C.I. Basic Red〉 1, 2, 12, 13, 14, 15, 18, 23, 24, 27, 29, 35, 36, 39, 46, 51, 52, 69, 70, 73, 82, 109 〈C.I. Basic Violet〉 1, 3, 7, 10, 11, 15, 16, 21, 27, 39 〈C.I. Basic Blue〉 1, 3, 7, 9, 21, 22, 26, 41, 45, 47, 52, 54, 65, 69, 75, 77, 92, 100, 105, 117, 124, 129, 147, 151 〈C.I. Basic Green〉 1, 4 〈C.I. Basic Brown〉 1

[0132] 〈C.I. Reactive Yellow〉 2, 3, 7, 15, 17, 18, 22, 23, 24, 25, 27, 37, 39, 42, 57, 69, 76, 81, 84, 85, 86, 87, 92, 95, 102, 105, 111, 125, 135, 136, 137, 142, 143, 145, 151, 160, 161, 165, 167, 168, 175, 176 〈C.I. Reactive Orange〉 1, 4, 5, 7, 11, 12, 13, 15, 16, 20, 30, 35, 56, 64, 67, 69, 70, 72, 74, 82, 84, 86, 87, 91, 92, 93, 95, 107 〈C.I. Reactive Red〉 2, 3, 5, 8, 11, 21, 22, 23, 24, 28, 29, 31, 33, 35, 43, 45, 49, 55, 56, 58, 65, 66, 78, 83, 84, 106, 111, 112, 113, 114, 116, 120, 123, 124, 128, 130, 136, 141, 147, 158, 159, 171, 174, 180, 183, 184, 187, 190, 193, 194, 195, 198, 218, 220, 222, 223, 228, 235 〈C.I. Reactive Violet〉 1, 2, 4, 5, 6, 22, 23, 33, 36, 38 〈C.I. Reactive Blue〉 2, 3, 4, 5, 7, 13, 14, 15, 19, 21, 25, 27, 28, 29, 38, 39, 41, 49, 50, 52, 63, 69, 71, 72, 77, 79, 89, 104, 109, 112, 113, 114, 116, 119, 120, 122, 137, 140, 143, 147, 160, 161, 162, 163, 168, 171, 176, 182, 184, 191, 194, 195, 198, 203, 204, 207, 209, 211, 214, 220, 221, 222, 231, 235, 236 〈C.I. Reactive Green〉 8, 12, 15, 19, 21 〈C.I. Reactive Brown〉 2, 7, 9, 10, 11, 17, 18, 19, 21, 23, 31, 37, 43, 46 〈C.I. Reactive Black〉 5, 8, 13, 14, 31, 34, 39 〈C.I. Food Black〉 1, 2

[0133] 1-2-2: Pigment As the pigment, conventionally known organic and inorganic pigments can be used. For example, azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments and other polycyclic pigments, dye lakes such as basic dye type lakes and acid dye type lakes, nitro pigments, nitroso pigments, aniline black, daylight fluorescent pigments and other organic pigments, carbon black, titanium oxide, iron oxide-based pigments and other inorganic pigments can be mentioned, but anionic pigments are preferred.

[0134] Specific organic pigments are exemplified below.

[0135] <Pigment for Magenta or Red> C.I. Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red 7, C.I. Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 48:1, C.I. Pigment Red 53:1, C.I. Pigment Red 57:1, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 139, C.I. Pigment Red 144, C.I. Pigment Red 149, C.I. Pigment Red 150, C.I. Pigment Red 166, C.I. Pigment Red 177, C.I. Pigment Red 178, C.I. Pigment Red 222, etc.

[0136] <Pigment for Orange or Yellow> C.I. Pigment Orange 31, C.I. Pigment Orange 43, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 15, C.I. Pigment Yellow 17, C.I. Pigment Yellow 74, C.I. Pigment Yellow 93, C.I. Pigment Yellow 94, C.I. Pigment Yellow 128, C.I. Pigment Yellow 138, C.I. Pigment Yellow 155, etc.

[0137] <Pigment for Green or Cyan> C.I. Pigment Blue 15, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 16, C.I. Pigment Blue 60, C.I. Pigment Green 7, etc.

[0138] These dyes and pigments may be used alone or in combination of two or more.

[0139] 1 - 3: Compound (I) The ink of the second invention contains a compound (I) represented by the following general formula (I).

[0140]

Chemical formula

[0141] (In formula (I), R 1 and R 2 each independently represents an alkyl group having 1 to 10 carbon atoms.)

[0142] The inventors of the second invention have found that by containing compound (I), an increase in viscosity during high-temperature storage is suppressed and the storage stability of the ink at high temperatures is enhanced. According to the present inventors, when the ink is stored at high temperatures, a phenomenon that the viscosity of the ink increases has been confirmed. This is presumably because the particles of the ultraviolet curable oligomer aggregate with the particles of other ultraviolet curable oligomers and pigment particles. The second invention is based on the fact that, unexpectedly, it has been first found that such a phenomenon is suppressed when a compound corresponding to compound (I) is contained. Compound (I) also has the effect of improving the curability of the ink of the second invention and improving the coating film strength of the ink.

[0143] The compound (I) used in the second invention may be any compound having a hydroxyl group directly bonded to a nitrogen atom and two alkyl groups having 1 to 10 carbon atoms bonded to the nitrogen atom, and there is no particular limitation. Specific examples of compound (I) include N,N-diethylhydroxylamine, N,N-dimethylhydroxylamine, N,N-dipropylhydroxylamine, N,N-dibutylhydroxylamine, N,N-methylethylhydroxylamine, N,N-ethylpropylhydroxylamine, N,N-propylbutylhydroxylamine, N,N-didecylhydroxylamine, etc., and N,N-dialkylhydroxylamines having 1 to 10 carbon atoms in the alkyl group are mentioned.

[0144] Compound (I) may be used alone or in a mixture of two or more.

[0145] As the compound (I), N,N-dialkylhydroxylamine having 1 to 4 carbon atoms in the alkyl group is preferable because of its excellent effect of suppressing the increase in viscosity during high-temperature storage, and particularly N,N-diethylhydroxylamine is preferable.

[0146] 1-4: Aqueous medium The ink of the present invention is an aqueous ink, and the "aqueous ink" means an ink containing an aqueous medium. The aqueous medium is water and / or a water-soluble organic solvent. The aqueous medium used in the present invention is preferably water or a mixture of water and a water-soluble organic solvent.

[0147] The water-soluble organic solvent functions as a humectant solvent for enhancing the moisture retention and wettability of the ink, and is also used for adjusting the viscosity, handleability, and ejection property of the ink as an aqueous medium. However, the two are not clearly distinguished, and the water-soluble organic solvent used as a humectant solvent also functions as an aqueous medium.

[0148] In the present invention, the water-soluble organic solvent means a compound having solubility in water, and the solubility in water is not limited, but a compound that can be dissolved in water in any ratio is preferable. Further, even a compound that is difficult to have solvent properties alone (for example, a solid or highly viscous compound at normal temperature) is included in the water-soluble organic solvent as long as it can be used as a solvent by being uniformly mixed with water.

[0149] Examples of the water-soluble organic solvent include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, and the like.

[0150] Specific examples of the water-soluble organic solvent include, for example, polyhydric alcohols such as ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, petriol, etc.; polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, etc.; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, etc.; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, γ-butyrolactone, etc.; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, etc.; amines such as monoethanolamine, diethanolamine, triethylamine, etc.; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, thiodiethanol, etc.; propylene carbonate, ethylene carbonate, and the like.

[0151] As the water-soluble organic solvent, it is preferable to use an organic solvent having a boiling point of 250°C or lower because it not only functions as a moisturizing solvent but also provides good drying properties.

[0152] As the water-soluble organic solvent, polyol compounds having 8 or more carbon atoms and glycol ether compounds are also preferably used. Specific examples of the polyol compound having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol. Specific examples of the glycol ether compound include polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; and polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0153] These water-soluble organic solvents may be used alone or in combination of two or more.

[0154] 1-5: Polymerization initiator The ink of the present invention preferably contains a polymerization initiator.

[0155] The polymerization initiator is a photo radical polymerization initiator that generates radicals, which are active species, by the energy of light (ultraviolet rays) received when irradiated with ultraviolet rays, and initiates the photopolymerization of the ultraviolet curable oligomer. Thereby, the ink present on the surface of the recording medium can be cured to form an image.

[0156] The polymerization initiator may be contained in the ink in a state not encapsulated in the ultraviolet curable oligomer, or may be contained in the ink in a state encapsulated in the particles of the ultraviolet curable oligomer. Furthermore, it may be encapsulated in both of these states.

[0157] As the polymerization initiator, it may be a fat-soluble polymerization initiator (hereinafter sometimes referred to as a "fat-soluble initiator"), or a water-soluble polymerization initiator (hereinafter sometimes referred to as a "water-soluble initiator"). The "fat-soluble initiator" refers to a polymerization initiator that is compatible with the ultraviolet curable oligomer or dissolves in an organic solvent. The "water-soluble initiator" refers to a substance that dissolves 1 mass% or more in water. The same applies to the "fat-soluble sensitizer" and "water-soluble sensitizer" described later.

[0158] The polymerization initiator used in the present invention is not limited to the following, and examples include aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-containing compounds), α-aminoalkylphenone compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds.

[0159] Among these, it is preferable that the polymerization initiator contains at least one of an acylphosphine oxide compound and a thioxanthone compound. By using such a polymerization initiator, the curability of the ink tends to be made more excellent.

[0160] Examples of the fat-soluble polymerization initiator include, but are not limited to, acetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophenone, benzophenone, 2-chlorobenzophenone, p,p'-dichlorobenzophenone, p,p'-bisdiethylaminobenzophenone, Michler's ketone, benzyl, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-propyl ether, benzoin isobutyl ether, benzoin-n-butyl ether, benzyl methyl ketal, 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}2-methylpropane-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1, 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]2-morpholinopropane-1-one, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-hydroxy-2-methyl-1-phenyl-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one, methyl benzoylformate, azobisisobutyronitrile, benzoyl peroxide, and di-tert-butyl peroxide, etc.

[0161] Examples of water-soluble polymerization initiators include, but are not limited to, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, sodium phenyl(2,4,6-trimethylbenzoyl)phosphinate, 2-(3-dimethylamino-2-hydroxypropoxy)-3,4-dimethyl-9H-thioxanthen-9-one methochloride, and the like.

[0162] Examples of commercially available polymerization initiators include GENOPOL TX-2 manufactured by RAHN, Irgacure369, Irgacure500, Irgacure2959 manufactured by Ciba Specialty Chemicals, and the like.

[0163] The polymerization initiator may be used alone or in combination of two or more. For example, a fat-soluble initiator and a water-soluble initiator may be used in combination, and the fat-soluble initiator may be encapsulated in the particles of the ultraviolet curable oligomer, and the water-soluble initiator may be dissolved in the aqueous medium. In addition to the photo radical polymerization initiator as described above, a thermal radical polymerization initiator may be used in combination as the polymerization initiator.

[0164] 1-6: Surfactant The ink of the present invention preferably contains a surfactant for the flatness of the formed coating film and the wettability with the substrate.

[0165] As the surfactant, any of a silicone-based surfactant, a fluorine-based surfactant, an amphoteric surfactant, a nonionic surfactant, and an anionic surfactant can be used.

[0166] The silicone-based surfactant is not particularly limited and can be appropriately selected according to the purpose. Among them, those that do not decompose even at high pH are preferred. For example, side-chain modified polydimethylsiloxane, both-terminal modified polydimethylsiloxane, one-terminal modified polydimethylsiloxane, side-chain and both-terminal modified polydimethylsiloxane, etc. can be mentioned. Those having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as the modifying group are particularly preferred because they exhibit good properties as an aqueous surfactant. As the silicone-based surfactant, a polyether-modified silicone-based surfactant can also be used. For example, compounds in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylsiloxane can be mentioned.

[0167] As the fluorine-based surfactant, compounds having 2 or more and 16 or less carbon atoms substituted with fluorine are preferred, and compounds having 4 or more and 16 or less carbon atoms substituted with fluorine are more preferred. Examples of the fluorosurfactant include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl alkylene oxide adducts, and polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain, which are preferred because of their low foaming properties. Examples of the perfluoroalkyl sulfonic acid compounds include perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, and the like. Examples of the perfluoroalkyl carboxylic acid compounds include perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate, and the like. Examples of the perfluoroalkyl phosphate ester compounds include perfluoroalkyl phosphate ester, perfluoroalkyl phosphate ester salt, and the like. Examples of the perfluoroalkyl alkylene oxide adducts include perfluoroalkyl ethylene oxide adducts and the like. Examples of the polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain include sulfate ester salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group in the side chain, salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group in the side chain, and the like. Examples of the counter ions of the salts in these fluorosurfactants include Li, Na, K, NH4, NH3CH2CH2OH, NH2(CH2CH2OH)2, NH(CH2CH2OH)3, and the like.

[0168] Among these, the polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain are more preferred because of their particularly low foaming properties, and particularly preferred are the fluorosurfactants represented by the following general formulas (3A) and (3B).

[0169] CF3CF2(CF2CF2) s -CH2CH2O(CH2CH2O) t H …( 3A) In the compound represented by the general formula (3A), s is preferably an integer of 0 or more and 10 or less, and t is preferably an integer of 0 or more and 40 or less in order to impart water solubility.

[0170] C r F 2r+1 -CH2CH(OH)CH2-O-(CH2CH2O) c -Z …(3B) In the compound represented by the general formula (3B), Z is H, or CnF 2d+1 where d is an integer of 1 or more and 6 or less, or CH2CH(OH)CH2-CnF 2e+1 where e is an integer of 4 or more and 6 or less, or CpH 2f+1 where f is an integer of 1 or more and 19 or less. c is an integer of 4 or more and 14 or less.

[0171] Commercially available products can be used as the fluorosurfactant. Examples of commercially available products include Surflon S-111, S-112, S-113, S-121, S-131, S-132, S-141, S-145 (all manufactured by Asahi Glass Co., Ltd.); Fluorad FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, FC-431 (all manufactured by Sumitomo 3M Limited); Megafac F-470, F-1405, F-474 (all manufactured by DIC Corporation); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, UR (all manufactured by DuPont); FT-110, FT-250, FT-251, FT-400S, FT-150, FT-400SW (all manufactured by Neos Co., Ltd.), Polyfox PF-136A, PF-156A, PF-151N, PF-154, PF-159 (manufactured by Omnova Solutions), Neugen FN-1287 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), Unidine DSN-403N (manufactured by Daikin Industries, Ltd.), LE-604, LE-605, LE-606, LE-607 (manufactured by Kyoeisha Chemical Co., Ltd.), and the like.

[0172] Examples of amphoteric surfactants include lauryl aminopropionate, lauryldimethyl betaine, stearyldimethyl betaine, lauryldihydroxyethyl betaine, and the like.

[0173] Examples of nonionic surfactants include polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkyl amine, polyoxyethylene alkyl amide, polyoxyethylene propylene block polymer, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, acetylene alcohol derivative, acetylene glycol derivative, and the like.

[0174] Examples of anionic surfactants include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, laurate, salts of polyoxyethylene alkyl ether sulfate, and the like.

[0175] These may be used alone or in combination of two or more.

[0176] As described above, there is no particular limitation on the silicone-based surfactant, and it can be appropriately selected according to the purpose. However, polyether-modified silicone-based surfactants having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as aqueous surfactants.

[0177] As such surfactants, those synthesized as appropriate may be used, or commercially available products may be used. Commercially available products can be obtained, for example, from BYK-Chemie GmbH, Shin-Etsu Chemical Co., Ltd., Toray Dow Corning Silicone Co., Ltd., Nippon Emulsion Co., Ltd., Kyoeisha Chemical Co., Ltd., and the like.

[0178] There are no particular restrictions on the polyether-modified silicone-based surfactant, and it can be appropriately selected according to the purpose. For example, those in which a polyalkylene oxide structure is introduced into the Si-side chain of dimethylpolysiloxane represented by the following general formula (2) can be mentioned.

[0179] [Chemical formula]

[0180] (In formula (2), p, q, a, and b represent integers. R and R' represent hydrocarbon groups.)

[0181] As the polyether-modified silicone-based surfactant, commercially available products can be used. Examples of commercially available products include KF-618, KF-642, KF-643 (Shin-Etsu Chemical Co., Ltd.), SAG001, SAG002, SAG003, SAG005, SAG503, SAG008 (Nisshin Chemical Industry Co., Ltd.), EMALEX-SS-5602, SS-1906EX (Nippon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (Toray Dow Corning Silicone Co., Ltd.), BYK-33, BYK-387 (BYK-Chemie GmbH), TSF4440, TSF4452, TSF4453 (Toshiba Silicone Co., Ltd.), and the like.

[0182] 1-7: Sensitizer The ink of the present invention may contain a sensitizer. When a sensitizer is present together with a polymerization initiator in the ink, the sensitizer in the system absorbs active energy rays and becomes an excited state, and by contacting the polymerization initiator, the decomposition of the polymerization initiator is promoted, and a more sensitive curing reaction can be carried out.

[0183] The sensitizer may be fat-soluble or water-soluble, similar to the polymerization initiator. If it is a fat-soluble sensitizer, it can be encapsulated in the particles of the ultraviolet curable oligomer.

[0184] Examples of the sensitizer include aliphatic amines, amines having an aromatic group, or cyclic amine compounds such as piperidine; thioxanthone compounds; alkoxy anthracene compounds; urea compounds such as o-tolylthiourea; sulfur compounds such as soluble salts of sodium diethylthiophosphate or aromatic sulfinic acids; nitrile compounds such as N,N'-disubstituted-p-aminobenzonitrile; phosphorus compounds such as tri-n-butylphosphine or sodium diethyldithiophosphate; nitrogen compounds such as Michler's ketone, N-nitrosohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds, and condensates of formaldehyde or acetaldehyde and diamines.

[0185] These sensitizers may be used alone or in combination of two or more.

[0186] 1-8: Other oligomers, resins, monomers In addition to the above components, the ink of the present invention may contain, if necessary, an oligomer component other than the ultraviolet curable (meth)acrylate oligomer of the first invention or the ultraviolet curable oligomer used in the second invention, an arbitrary resin component, and an arbitrary monomer component (collectively referred to as "other resin components"). The other resin components may be encapsulated in the particles of the ultraviolet curable oligomer, dissolved in the aqueous medium, or present in the ink in a state of being individually dispersed or complexed with other components.

[0187] 1-9: Other additives In addition to the above components, the ink of the present invention may contain other additives, if necessary. Examples of the other additives include known additives such as anti-fading agents, emulsion stabilizers, penetration promoters, ultraviolet absorbers, preservatives, fungicides, rust preventives, pH adjusters, viscosity adjusters, dispersants, dispersion stabilizers, defoamers, solid wetting agents, and chelating agents. These various additives may be added directly after preparing the ink or may be added during the preparation of the ink. Regarding other additives, reference can be appropriately made to the descriptions in paragraphs 0088 to 0096 of JP-A-2010-65205 and the descriptions in paragraphs 0083 to 0090 of JP-A-2010-70669.

[0188] 1-10: Content of each component The water content in the ink of the present invention is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoints of the drying property and ejection reliability of the ink, it is usually 10% by mass or more, preferably 20% by mass or more, and usually 90% by mass or less, preferably 80% by mass or less.

[0189] When the ink of the present invention contains a water-soluble organic solvent, its content (the total content of the water-soluble organic solvent also serving as a humectant solvent and the water-soluble organic solvent used as an aqueous medium) is not particularly limited and can be appropriately selected according to the type of the water-soluble organic solvent used and the purpose. However, from the viewpoints of drying property, ejection reliability, wettability with a substrate, etc., it is usually 10% by mass or more, usually 50% by mass or less, preferably 40% by mass or less.

[0190] From the viewpoints of drying property and ejection reliability, the total solid content concentration, which is a component other than the aqueous medium of water and / or a water-soluble organic solvent, in the ink of the present invention is usually 5% by mass or more, preferably 7% by mass or more, more preferably 9% by mass or more, usually 30% by mass or less, preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0191] When a mixed liquid of water and a water-soluble organic solvent is used as the aqueous medium, the ratio of water to the water-soluble organic solvent (the total of the water-soluble organic solvent also serving as a humectant solvent and the water-soluble organic solvent used as an aqueous medium) is preferably such that the ratio of water: water-soluble organic solvent is usually 1:0.05 to 1:1.5 (mass ratio), preferably 1:0.1 to 1:1.2 (mass ratio), and more preferably 1:0.15 to 1:1.1 (mass ratio) from the viewpoints of improving drying property and ejection property.

[0192] The content of the ultraviolet curable oligomer in the ink of the present invention (in the first invention, the ultraviolet curable (meth) acrylate oligomer of the first invention) is usually 3% by mass or more, preferably 5% by mass or more, more preferably 7% by mass or more from the viewpoints of the obtained printed coating film performance and ultraviolet curability. On the other hand, from the viewpoint of ejection stability, it is usually 20% by mass or less, preferably 15% by mass or less, more preferably 12% by mass or less. From the same viewpoints, the content of the ultraviolet curable oligomer in the total solid content of the ink of the present invention is usually 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and usually 90% by mass or less, preferably 85% by mass or less, more preferably 80% by mass or less.

[0193] Here, the total solid content in the ink of the present invention can be equivalently adopted for the numerical ranges described above by rephrasing it as the constituent components of the cured film (printed film) formed by the ink of the present invention. The content of each component in the total solid content is almost equal to the content of the component in the cured film (printed film) formed by the ink of the present invention. Therefore, the fact that the content of the ultraviolet curable oligomer in the total solid content of the ink of the present invention is usually 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and usually 90% by mass or less, preferably 85% by mass or less, more preferably 80% by mass or less means that the content of the component derived from the ultraviolet curable oligomer in the cured film (printed film) formed by the ink of the present invention is usually 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and usually 90% by mass or less, preferably 85% by mass or less, more preferably 80% by mass or less, and can be treated in the same way. The same applies to the contents of the following colorants and other components.

[0194] The content of the colorant in the ink of the present invention is usually 0.1% by mass or more, preferably 1% by mass or more, and usually 8% by mass or less, preferably 6% by mass or less, from the viewpoints of improving image density, good fixing property, and ejection stability. From the same perspective, the content of the colorant in the total solid content of the ink of the present invention is usually 1% by mass or more, preferably 5% by mass or more, usually 40% by mass or less, and preferably 30% by mass or less.

[0195] From the perspective of suppressing the increase in viscosity during high-temperature storage and enhancing the storage stability of the ink of the second invention at high temperatures, the content of the compound (I) in the ink of the second invention is usually 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.05% by mass or more, still more preferably 0.08% by mass or more, and particularly preferably 0.30% by mass or more. On the other hand, from the perspective of enhancing the curability, it is usually 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less, still more preferably 1% by mass or less. From the same perspective, the content of the compound (I) in the total solid content of the ink of the second invention is usually 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, and usually 10% by mass or less, preferably 7% by mass or less, more preferably 5% by mass or less.

[0196] When the ink of the present invention contains a polymerization initiator, its content is usually 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.4% by mass or more, and usually 8% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 2% by mass or less, and particularly preferably 1% by mass or less. When the content of the polymerization initiator is within this range, the curing rate can be sufficiently improved, and the undissolved residue of the polymerization initiator and the coloring derived from the polymerization initiator can be avoided. From the same perspective, the content of the polymerization initiator in the total solid content of the ink of the present invention is usually 0.5% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, and usually 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, and particularly preferably 8% by mass or less.

[0197] When the ink of the present invention contains a surfactant, its content is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoints of excellent wettability and ejection stability and improved image quality, the content of the surfactant in the ink is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and is usually 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less. From the same viewpoint, the content of the surfactant in the total solid content of the ink of the present invention is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less.

[0198] When the ink of the present invention contains a sensitizer, its content is usually 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.05% by mass or more, and is usually 4% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less, still more preferably 0.7% by mass or less. If the content of the sensitizer is within the above range, the effect of the sensitizer can be sufficiently obtained. Also, from the same viewpoint, the content of the sensitizer in the total solid content of the ink of the present invention is usually 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, and is usually 8% by mass or less, preferably 6% by mass or less, more preferably 5% by mass or less.

[0199] 2: UV-curable aqueous composition for inkjet printing The UV-curable aqueous composition for inkjet printing of the first invention (hereinafter, may be referred to as "the aqueous composition of the first invention") is an aqueous composition containing a UV-curable oligomer and at least one of a polymerization initiator, a sensitizer, and a surfactant, wherein the UV-curable oligomer is the UV-curable oligomer of the first invention described above.

[0200] The ultraviolet curable aqueous composition for inkjet printing of the first invention is an aqueous composition and contains an aqueous medium, similar to the ink of the first invention. That is, the aqueous composition of the first invention corresponds to the mode in which the ink of the first invention does not contain a colorant. Regarding the aqueous medium, polymerization initiator, photosensitizer, surfactant, and other additives contained in the aqueous composition, they are the same as those described in the section of the ink of the present invention above, and their contents are also the same as the contents of the components excluding the colorant in the ink of the present invention.

[0201] The ultraviolet curable aqueous composition for inkjet printing of the second invention (hereinafter, may be referred to as "the aqueous composition of the second invention") is an ultraviolet curable aqueous composition for inkjet printing containing an ultraviolet curable oligomer and at least one of a polymerization initiator, a photosensitizer, and a surfactant, and is characterized by further containing the aforementioned compound (I).

[0202] The ultraviolet curable aqueous composition for inkjet printing of the second invention is an aqueous composition and contains an aqueous medium, similar to the ink of the second invention. Also, in the aqueous composition of the second invention, the ultraviolet curable oligomer is preferably nonionic, and the aforementioned ultraviolet curable oligomer of the first invention is preferred, and an ultraviolet curable (meth)acrylate oligomer having a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a hydroxyl group-containing polyfunctional (meth)acrylate (B), and a structural unit derived from a polyalkylene glycol (C) is particularly preferred. That is, the aqueous composition of the second invention corresponds to the mode in which the ink of the second invention does not contain a colorant. Regarding the ultraviolet curable oligomer, compound (I), aqueous medium, polymerization initiator, photosensitizer, surfactant, and other additives contained in the aqueous composition of the second invention, they are the same as those described in the section of the ink of the present invention above, and their contents are also the same as the contents of the components excluding the colorant in the ink of the present invention above.

[0203] The usage form of the aqueous composition of the present invention is not particularly limited, but a usage form in which the above-described colorant is added to the aqueous composition of the present invention to prepare the ink of the present invention is preferable. The colorant to be added may be one color or two or more colors. By arbitrarily adding two or more colorants, the color tone of the ink can be adjusted to a desired color tone. In addition, the aqueous composition of the present invention can be used as a clear ink.

[0204] 3: Method for manufacturing ink The method for manufacturing the ink of the present invention is not particularly limited, but a dispersion liquid in which the ultraviolet curable oligomer of the first invention or particles of the ultraviolet curable oligomer used in the second invention (hereinafter sometimes referred to as "oligomer particles") are dispersed in an aqueous medium (hereinafter sometimes referred to as "oligomer dispersion liquid"), and a dispersion liquid in which a colorant such as a pigment is dispersed in an aqueous medium (hereinafter sometimes referred to as "pigment dispersion liquid") are respectively prepared, and a method of mixing the oligomer dispersion liquid and the pigment dispersion liquid with a polymerization initiator (water-soluble initiator), other additives and an organic solvent can be mentioned. In addition, a method of adding a colorant to the aqueous composition of the present invention can also be mentioned. No matter which method is used for manufacturing, inks with the same performance can be obtained.

[0205] By adding and mixing a fat-soluble initiator and a fat-soluble sensitizer during the preparation of the oligomer dispersion liquid, these can be encapsulated in the oligomer particles. In addition, the fat-soluble initiator and the fat-soluble sensitizer can also be mixed with other components as a solution dissolved in an organic solvent at a concentration of about 0.1% by mass or more and 10% by mass or less.

[0206] The dispersion liquid of the second invention can be prepared by adding the compound (I) to the dispersion liquid of the ultraviolet curable oligomer in such an ink manufacturing process. In this case, the addition amount of the compound (I) may be an amount such that the above-described preferred content is obtained in the ink of the second invention. For example, it is used in an amount of about 0.5% by mass or more and 10% by mass or less with respect to the ultraviolet curable oligomer.

[0207] 3-1: Preparation of oligomer dispersion liquid The oligomer dispersion can be prepared by mixing the ultraviolet curable oligomer of the first invention or the ultraviolet curable oligomer used in the second invention with an aqueous medium (preferably water). By adjusting the temperature and stirring speed at this time, the average particle size of the obtained oligomer particles can be adjusted. From the viewpoint of handleability, the oligomer particle concentration of the oligomer dispersion prepared in this way is preferably about 10% by mass or more and 30% by mass or less.

[0208] By further adding and mixing a fat-soluble initiator and a fat-soluble sensitizer during the preparation of the oligomer dispersion, a dispersion of oligomer particles encapsulating them can be obtained. In this case, in order to prevent the generation of particles of the initiator or sensitizer alone without containing the oligomer, it is preferable to add a fat-soluble initiator and / or a fat-soluble sensitizer to the ultraviolet curable oligomer and then mix it with an aqueous medium such as water. When the oligomer particles encapsulate the fat-soluble initiator and / or the fat-soluble sensitizer, the content of the fat-soluble initiator and / or the fat-soluble sensitizer in the oligomer particles is preferably about 0.1% by mass or more and 8% by mass or less with respect to the ultraviolet curable oligomer from the viewpoint of production stability.

[0209] 3-2: Preparation of Pigment Dispersion The pigment dispersion can be prepared by adding and mixing a colorant such as a pigment to an aqueous medium such as water. From the viewpoints of handleability and storage stability, the concentration of the colorant such as the pigment in the pigment dispersion is usually 5% by mass or more, preferably 10% by mass or more, and usually 40% by mass or less, preferably 35% by mass or less.

[0210] Commercially available products may be used as they are as the pigment dispersion.

[0211] 4: Manufacturing Method of Aqueous Composition The method for producing the aqueous composition of the first invention is not particularly limited, but an oligomer dispersion is prepared in the same manner as in the method for producing the ink of the present invention described above, and the prepared oligomer dispersion is mixed with one or more of a polymerization initiator (water-soluble initiator), a sensitizer, and a surfactant, and other additives and organic solvents that are used as necessary.

[0212] The method for producing the aqueous composition of the second invention is not particularly limited, but an oligomer dispersion is prepared in the same manner as in the method for producing the ink of the present invention described above, compound (I) is added to the prepared oligomer dispersion, and one or more of a polymerization initiator (water-soluble initiator), a sensitizer, and a surfactant, and other additives and organic solvents that are used as necessary are mixed.

[0213] As described above, by adding and mixing a fat-soluble initiator or a fat-soluble sensitizer during the preparation of the oligomer dispersion, these can be encapsulated in the oligomer particles. The fat-soluble initiator and the fat-soluble sensitizer can also be mixed with other components as a solution dissolved in an organic solvent at a concentration of about 0.1% by mass or more and 10% by mass or less.

[0214] The method for preparing the oligomer dispersion and the method for preparing the dispersion of the oligomer particles encapsulating the fat-soluble initiator and the fat-soluble sensitizer are the same as those in the method for producing the ink of the present invention described above.

[0215] 5: Viscosity of the ink Since the ink of the present invention is excellent in pigment dispersion stability, the viscosity of the ink can be kept low. As a result, the ink ejection property is good even during high-speed printing. The viscosity of the ink of the present invention at 25°C is preferably 25 mPa·sec or less, more preferably 20 mPa·sec or less, and even more preferably 10 mPa·sec or less. The lower limit value of the viscosity of the ink is not particularly limited, but is preferably 1 mPa·sec or more, and more preferably 2 mPa·sec or more.

[0216] 6: Viscosity of the aqueous composition The viscosity of the aqueous composition of the present invention at 25°C is preferably 50 mPa·sec or less, more preferably 30 mPa·sec or less, and even more preferably 20 mPa·sec or less. The lower limit of the viscosity of the aqueous composition is not particularly limited, but is preferably 0.5 mPa·sec or more, and more preferably 1 mPa·sec or more.

[0217] 7: Ink storage container The ink of the present invention can be stored in an ink cartridge or an ink bottle. Thereby, in operations such as ink conveyance and ink replacement, it is not necessary to directly touch the ink, and it is possible to prevent soiling of fingers and clothing. In addition, it is possible to prevent the entry of foreign substances such as dust into the ink.

[0218] The shape, size, material, etc. of the ink storage container itself may be suitable for the inkjet printer or the like to be applied, and are not particularly limited. The material of the ink storage container is preferably a light-shielding material that does not transmit light, or the container is covered with a light-shielding sheet or the like.

[0219] 8: Inkjet recording method The inkjet recording method using the ink of the present invention preferably includes a step of discharging the ink of the present invention from a discharge nozzle of an inkjet printer and attaching it to a recording medium, a heating step of heating the recording medium to which the ink has adhered, and an irradiation step of irradiating the ink adhered to the recording medium with active energy rays. The step of attaching the ink of the present invention to the recording medium is sufficient if the ink is attached to the recording medium in a misty (misty, spray-like) state, and is not necessarily limited to the method using an inkjet printer.

[0220] 8-1: Recording medium There are no particular restrictions on the recording medium to which the ink of the present invention is applied. Since the ink of the present invention is an ultraviolet curable aqueous ink with excellent substrate versatility, it can be used on various substrates such as plastics materials like polyester such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), etc., paper, TEXTILE (cloth or fabric), leather, glass, ceramic, wood, metal, or composites thereof, etc., and can form a high-quality printed image with good adhesion.

[0221] 8-2: Heating step In the heating step, it is preferable to heat the recording medium to which the ink of the present invention is attached to 40°C or higher. The heating temperature is more preferably 45°C or higher, and even more preferably 50°C or higher. By performing the above heating, volatile components such as water in the ink can be dried, and the curability tends to be further enhanced. The upper limit of the heating temperature is not particularly limited, but generally, since there is a tendency for ejection failure to occur due to the drying of the ink on the nozzle surface in the presence of heating means, it is preferably 120°C or lower, and more preferably 100°C or lower. Here, the heating temperature is the surface temperature of the recording surface of the recording medium.

[0222] The heating means is not particularly limited, and examples thereof include a ceramic heater, a halogen heater, a quartz tube heater, etc.

[0223] The timing of heating may be any of before, during, or after the ink of the present invention is attached to the recording medium, but it is more preferable to continuously perform heating in all processes before, during, and after attachment.

[0224] 8-3: Irradiation step In the irradiation step, the polymerization reaction of the ultraviolet curable oligomer of the first invention or the ultraviolet curable oligomer used in the second invention is initiated by irradiating active energy rays. Further, the polymerization initiator contained in the ink is decomposed by the irradiation of active energy rays to generate initiation species such as radicals, acids, and bases, and the polymerization reaction of the ultraviolet curable oligomer is promoted by the function of the initiation species. At this time, if a sensitizer is present in the ink together with the polymerization initiator, the sensitizer in the system absorbs the active energy rays and becomes an excited state, and by contacting the polymerization initiator, the decomposition of the polymerization initiator is promoted, and a higher-sensitivity curing reaction can be performed.

[0225] As the light source (active energy ray source), a mercury lamp, a metal halide lamp, a gas / solid laser, etc. are widely known. On the other hand, from the perspective of environmental protection, mercury-free conversion is strongly desired at present, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. Furthermore, ultraviolet light-emitting diodes (UV-LEDs) and ultraviolet laser diodes (UV-LDs) are small, have a long lifespan, high efficiency, and low cost, and are expected as light sources for ultraviolet curable inkjet. Among these, UV-LEDs are preferred.

[0226] The emission peak wavelength of the active energy ray source to be irradiated is preferably in the range of 350 to 450 nm. The irradiation energy is 20 J / cm 2 Hereinafter, for example, 0.5 to 10 J / cm 2 is preferred.

[0227] The emission peak wavelength may be one or more within the above wavelength range.

[0228] The irradiation step is not limited to only the intentional step as described above, and may be, for example, sunlight irradiation by outdoor exposure. When the reactivity (curability) of the ultraviolet curable oligomer of the first invention or the ultraviolet curable oligomer used in the second invention is high, it is not necessary to go through the irradiation step only by the heating step. That is, the ink of the present invention only needs to have ultraviolet curability and is not limited to being used in a printing method having an irradiation step.

[0229] 9: Use Since the ink of the present invention is aqueous, it is excellent in environmental and safety properties, and highly satisfies the required characteristics of an ink for inkjet printers, such as high image quality performance, high coating film performance, high-speed printability, and substrate versatility, in a well-balanced manner. Moreover, the ink of the first invention is also excellent in pigment dispersion stability, and the ink of the second invention is also excellent in storage stability at high temperatures. Therefore, due to the feature that the ink of the present invention can print a printed image excellent in high image quality performance and high coating film performance on various recording media with high productivity, it can be used for various applications such as posters, road signs, signboards, billboards, various display boards for outdoor and indoor use, building materials (surface materials for exterior, interior, walls, floors, ceilings, windows, etc.), exteriors of vehicles (automobiles, railways, airplanes, etc.), surface materials for furniture and OA equipment, and printed matter on paper.

Examples

[0230] The present invention will be described more specifically with reference to the following examples.

[0231] [Preparation of ultraviolet curable oligomer] 0.4 mol of a trimer of hexamethylene diisocyanate, 0.8 mol of dipentaerythritol pentaacrylate, and 0.4 mol of polyethylene glycol monoallyl ether (n = 30 to 40 in the general formula (1)) were reacted to produce a nonionic ultraviolet curable oligomer.

[0232] [Preparation of aqueous dispersion α of ultraviolet curable oligomer] The ultraviolet curable oligomer obtained above was kept at 60°C and dropped dropwise with stirring into ion-exchanged water preheated to 60°C to obtain an aqueous dispersion α of ultraviolet curable oligomer particles with an oligomer concentration of 20% by mass. The average particle diameter (D 50 ) of the ultraviolet curable oligomer particles in this aqueous dispersion was measured using a particle size distribution analyzer MICROTRAC UPA (MODEL: 9340-UPA, manufactured by Nikkiso Co., Ltd.) and was 36 nm.

[0233] [Preparation of Fat-Soluble Initiator Solution] To 100 parts by mass of diethylene glycol mono-isobutyl ether as a water-soluble organic solvent, 1 part by mass of GENOPOL TX-2 manufactured by RAHN was added as a fat-soluble initiator, and it was completely dissolved with stirring at 40 °C to obtain a fat-soluble initiator solution.

[0234] [Preparation of Fat-Soluble Initiator-Encapsulated UV-Curable Oligomer Aqueous Dispersion β] To 20 parts by mass of the UV-curable oligomer obtained above, 0.2 parts by mass of GENOPOL TX-2 manufactured by RAHN was added as a fat-soluble initiator, and while maintaining the temperature at 60 °C and stirring, ion-exchanged water pre-heated to 60 °C was added dropwise until the oligomer concentration reached 20% by mass to obtain a fat-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion β. The average particle diameter (D 50 ) of the UV-curable oligomer particles in this aqueous dispersion was measured using a particle size distribution analyzer MICROTRAC UPA (MODEL: 9340-UPA, manufactured by Nikkiso Co., Ltd.) and was 29 nm.

[0235] [Preparation of Fat-Soluble Initiator-Encapsulated UV-Curable Oligomer Aqueous Dispersion γ] To 20 parts by mass of the UV-curable oligomer obtained above, 0.2 parts by mass of GENOPOL TX-2 manufactured by RAHN and 0.2 parts by mass of Irgacure 369 manufactured by Ciba Specialty Chemicals were added as fat-soluble initiators, and while maintaining the temperature at 60 °C and stirring, ion-exchanged water pre-heated to 60 °C was added dropwise until the oligomer concentration reached 20% by mass to obtain a fat-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion γ. The average particle diameter (D 50 ) of the UV-curable oligomer particles in this aqueous dispersion was measured using a particle size distribution analyzer MICROTRAC UPA (MODEL: 9340-UPA, manufactured by Nikkiso Co., Ltd.) and was 33 nm.

[0236] [Examples and Comparative Examples of the First Invention] [Example I-1] Ion-exchanged water, an ultraviolet-curable oligomer aqueous dispersion α, 1,2-butanediol as a humectant solvent, diethylene glycol mono-isobutyl ether as a water-soluble organic solvent, a water-soluble initiator B, Neugen FN1287 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. as a surfactant, and EMACOL SF CYAN AE2034F manufactured by Sanyo Color Works Co., Ltd. as a pigment dispersion were added and mixed so as to have the composition shown in Table 1 to obtain an ink composition liquid 1. The viscosity of the ink composition liquid I-1 measured at 25 °C using a digital viscometer DV-I+ manufactured by BROOKFIELD was 14.0 mPa·sec. In Table 1, the ultraviolet-curable oligomer of the first invention is distinguished as the "product of the first invention", and other ultraviolet-curable oligomers are distinguished as "comparative products".

[0237] [Example I-2] Water-soluble initiator A was used in place of the water-soluble initiator B in Example I-1, and added and mixed so as to have the composition shown in Table 1 to obtain an ink composition liquid I-2.

[0238] [Example I-3] Ultraviolet-curable oligomer aqueous dispersion β was used in place of the ultraviolet-curable oligomer aqueous dispersion α, and a water-soluble sensitizer was added. Otherwise, it was carried out in the same manner as in Example I-2, and added and mixed so as to have the composition shown in Table 1 to obtain an ink composition liquid I-3. The viscosity of the ink composition liquid I-3 measured in the same manner as in Example I-1 was 8.6 mPa·sec.

[0239] [Example I-4] A fat-soluble initiator solution and a water-soluble sensitizer were used in place of the diethylene glycol mono-isobutyl ether in Example I-2, and added and mixed so as to have the composition shown in Table 1 to obtain an ink composition liquid I-4. The viscosity of the ink composition liquid I-4 measured in the same manner as in Example I-1 was 8.0 mPa·sec.

[0240] [Example I-5] Irgacure 500 manufactured by Ciba Specialty Chemicals was added as a fat-soluble initiator to the ink composition of Example I-1, and added and mixed so as to obtain the composition shown in Table 1 to obtain Ink Composition I-5. The viscosity of Ink Composition I-5 measured in the same manner as in Example I-1 was 14.5 mPa·sec.

[0241] [Comparative Example I-1] An anionic acrylic emulsion (Acrit 3MF-587 manufactured by Dainippon Fine Chemical Co., Ltd.) was used as the ultraviolet curable oligomer, and ethoxylated glycerin triacrylate (NK Ester A-GLY-20E manufactured by Shin-Nakamura Chemical Co., Ltd.) was used as the water-soluble monomer. Ink Composition I-6 was obtained in the same manner as in Example I-1 except that the composition shown in Table 1 was used.

[0242] [Comparative Example I-2] Ink Composition I-7 was obtained in the same manner as in Example I-1 except that an anionic core-shell type ultraviolet curable urethane resin dispersion (Acrit WBR-829DA manufactured by Dainippon Fine Chemical Co., Ltd.) was used as the ultraviolet curable oligomer.

[0243] [Comparative Example I-3] Ink Composition I-8 was obtained in the same manner as in Example I-2 except that an aqueous urethane resin dispersion (Takerac WR-620 manufactured by Mitsui Chemicals, Inc.) was used as the ultraviolet curable oligomer.

[0244] [Comparative Example I-4] Ink Composition I-9 was obtained in the same manner as in Example I-2 except that a polyurethane resin dispersion (ETERNACOLL UW-9102 manufactured by Ube Industries, Ltd.) was used as the ultraviolet curable oligomer.

[0245] [Comparative Example I-5] Ink Composition I-10 was obtained in the same manner as in Example I-2 except that ethoxylated dipentaerythritol hexaacrylate (NK Ester A-DPH-12E manufactured by Shin-Nakamura Chemical Co., Ltd.) was used as the water-soluble monomer instead of the ultraviolet curable oligomer.

[0246] [Comparative Example I-6] An ink composition liquid I-11 was obtained in the same manner as in Example I-4, except that an aqueous emulsion (UAW-1000WO20 manufactured by Kyoeisha Chemical Co., Ltd.) was used as the ultraviolet curable oligomer and the composition shown in Table 1 was used.

[0247] [Comparative Example I-7] An ink composition liquid I-12 was obtained in the same manner as in Example I-5, except that an anionic acrylic emulsion (Acrit 3MF-587 manufactured by Dainippon Fine Chemical Co., Ltd.) was used as the ultraviolet curable oligomer and ethoxylated glycerin triacrylate (NK Ester A-GLY-20E manufactured by Shin-Nakamura Chemical Co., Ltd.) was used as the water-soluble monomer, and the composition shown in Table 1 was used.

[0248] [Comparative Example I-8] An ink composition liquid I-13 was obtained in the same manner as in Example I-5, except that ethoxylated glycerin triacrylate (NK Ester A-GLY-20E manufactured by Shin-Nakamura Chemical Co., Ltd.) was used as the water-soluble monomer instead of the ultraviolet curable oligomer, and the composition shown in Table 1 was used.

[0249] [Example I-6] An ink composition liquid I-14 was obtained in the same manner as in Example I-3, except that EMACOL SF MAGENTA AE2033F manufactured by Sanyo Color Works was used instead of EMACOL SF CYAN AE2034F manufactured by Sanyo Color Works as the pigment dispersion liquid, and the composition shown in Table 1 was used.

[0250] [Example I-7] An ink composition liquid I-15 was obtained in the same manner as in Example I-3, except that EMACOL SF YELLOW AG2242F manufactured by Sanyo Color Works was used instead of EMACOL SF CYAN AE2034F manufactured by Sanyo Color Works as the pigment dispersion liquid, and the composition shown in Table 1 was used. The viscosity of the ink composition liquid I-15 measured in the same manner as in Example I-1 was 8.5 mPa·sec.

[0251] [Example I-8] EMACOL SF BLACK AE2078F manufactured by Sanyo Color was used instead of EMACOL SF CYAN AE2034F as the pigment dispersion, and Ink Composition Liquid I-16 was obtained in the same manner as in Example I-3 except that the composition shown in Table 1 was used.

[0252] [Example I-9] Ink Composition Liquid I-17 was obtained in the same manner as in Example I-8 except that UV curable oligomer aqueous dispersion γ was used instead of UV curable oligomer aqueous dispersion α and the composition shown in Table 1 was used.

[0253]

Table 1

[0254] [Evaluation of Ink Composition Liquid] The following evaluations were performed on the ink composition liquids obtained in Examples I-1 to I-9 and Comparative Examples I-1 to 8, and the results are shown in Table 2. In addition, the following adhesion evaluations were performed on the ink composition liquids obtained in Example I-4 and Example I-7, and the results are shown in Table 3.

[0255] [Evaluation of Pigment Dispersion Stability in Ink Composition Liquid] After storing each ink composition in a sealed container at room temperature for 7 days, the appearance of the ink composition was visually observed and evaluated according to the following evaluation criteria. 〇: No change visually. ×: Pigment is precipitated. Or the ink has changed to a gel state, or has clearly thickened.

[0256] [Evaluation of Hardened Film Strength] A hardened film was formed by the following method (1) or (2), and its strength was evaluated by the method (3). (1) LED curing The ink composition liquid prepared above was applied to a PVC film with a bar coater to a film thickness of 15 μm, heated at 80 °C for 10 minutes, and then irradiated with ultraviolet light having an irradiation energy of 7 J / cm 2 with a peak wavelength of 385 nm from an LED to form a hardened film. (2) Metal halide curing The ink composition prepared above was applied at a film thickness of 15 μm on a PVC film using a bar coater, and irradiated with ultraviolet light having an irradiation energy of 7 J / cm 2 with 365 nm light from a metal halide lamp to form a cured film. (3) Evaluation of cured film strength The cured film obtained above was used to evaluate alcohol resistance and water resistance. The evaluation was performed by visually observing the presence or absence of color transfer to the absorbent cotton when the absorbent cotton was dipped in anhydrous ethanol and gently rubbed on the surface of the cured film, and the presence or absence of color transfer when the absorbent cotton was dipped in water and strongly rubbed on the surface of the cured film, and evaluated according to the following evaluation criteria. 〇: No color transfer occurs when rubbed with either ethanol or water. △: No color transfer occurs when rubbed with ethanol, but color transfer occurs when rubbed with water. ×: Color transfer occurs when rubbed with either ethanol or water.

[0257] <Evaluation of adhesion>[ In the ink compositions of Example I-4 and Example I-7, the adhesion was evaluated using the cured film obtained in the evaluation of cured film strength (1) and the cured film formed on a PET film by the same method. Eleven parallel cuts with a length of 20 mm and a spacing of 1 mm were made in the cured film with a cutter knife, and further eleven parallel cuts with a length of 20 mm and a spacing of 1 mm were made perpendicular to the cuts to form a 10 mm × 10 mm grid pattern. An adhesive tape with an adhesive strength of 3.93 N / 10 mm and a width of 18 mm was applied thereon, firmly adhered with fingertips, and then the tape was vigorously peeled off while holding down the base material on both sides of the tape so that it did not float, and the state of the cured film was visually observed. Evaluation was performed according to the following evaluation criteria. 〇: No peeling is observed at the grid intersections or along the cuts. ×: Peeling is observed at the grid intersections or along the cuts.

[0258]

Table 2

[0259] From Table 2, it can be seen that the ink of the first invention using the ultraviolet curable oligomer of the first invention is excellent in pigment dispersion stability, and by irradiating with ultraviolet rays to cure, a high-strength printed image excellent in water resistance and alcohol resistance can be formed. On the other hand, Comparative Examples I-5 and I-8 using water-soluble monomers and Comparative Examples I-1 and I-7 using water-soluble monomers and anionic acrylic emulsions are inferior in water resistance and alcohol resistance. Comparative Example I-6 using an aqueous emulsion is also inferior in water resistance. In Comparative Examples I-2 to 4 using polyurethane resins, the pigment dispersion stability is poor, and the evaluation of the cured film strength has not been carried out for these.

[0260]

Table 3

[0261] From Table 3, it can be seen that the ink of the first invention using the ultraviolet curable oligomer of the first invention is excellent in adhesion to both PVC film and PET film, and has high substrate versatility.

[0262] 〔Examples and Comparative Examples of the Second Invention〕 [Example II-1] Ion-exchanged water, an ultraviolet curable oligomer aqueous dispersion α, 1,2-butanediol as a humectant solvent, a fat-soluble initiator solution, a water-soluble initiator, a water-soluble sensitizer, Neugen FN1287 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. as a surfactant, N,N-diethylhydroxylamine (DEHA) as an additive, and EMACOL SF CYAN AE2034F manufactured by Sanyo Color Works as a pigment dispersion were added and mixed so as to have the composition ratio shown in Table 4 to obtain an ink composition liquid II-1.

[0263] [Example II-2] An ink composition liquid II-2 was obtained in the same manner as in Example II-1, except that the amount of the humectant solvent and the amount of the water-soluble organic solvent were changed.

[0264] [Example II-3 to 5] Inks II-3 to 5 were obtained in the same manner as in Example II-2, except that the amount of N,N-diethylhydroxylamine was changed.

[0265] [Example II-6] Ink II-10 was obtained in the same manner as in Example II-1, except that an aqueous emulsion (UAW-1000WO20 manufactured by Kyoeisha Chemical Co., Ltd.) was used as the ultraviolet curable oligomer instead of the ultraviolet curable oligomer aqueous dispersion α.

[0266] [Comparative Example II-1] Ink II-6 was obtained in the same manner as in Example II-2, except that no additive was added.

[0267] [Comparative Example II-2] Ink II-7 was obtained in the same manner as in Example II-1, except that no additive was added.

[0268] [Comparative Example II-3] Ink II-8 was obtained in the same manner as in Example II-2, except that 3-pentanol was used as the additive.

[0269] [Comparative Example II-4] Ink II-9 was obtained in the same manner as in Example II-2, except that 1-dimethylamino-2-propanol (DMAP) was used as the additive.

[0270] [Comparative Example II-5] Ink II-11 was obtained in the same manner as in Example II-6, except that no additive was added.

[0271]

Table 4

[0272] [Evaluation of Ink Compositions] The following evaluations were performed on the ink compositions obtained in Examples II-1 to 6 and Comparative Examples II-1 to 5, and the results are shown in Table 5.

[0273] <Evaluation of High - temperature Storage Stability of Ink Composition Liquid> The ink composition liquid was put into sample bottles respectively and stored at 60 °C for 14 days. The state of the ink composition liquid before and after storage was visually observed, and the viscosity was measured using a digital viscometer DV - I+ manufactured by BROOKFIELD, and evaluated according to the following criteria. A: There is no change in the viscosity of the ink. B: The viscosity of the ink has increased slightly. C: The viscosity of the ink has increased slightly, but it is at a level with no practical problems. D: The ink has changed into a gel state. E: The solid content of the ink has separated. Also, when Example II - 1 was put into a sample bottle and stored at 40 °C for 14 days, there was no change in the viscosity of the ink before and after storage.

[0274] <Evaluation of Alcohol Resistance of Cured Film> The cured film was formed by the method of (1) below, and the alcohol resistance was evaluated by the method of (2). (1) LED curing The ink composition liquid prepared above was applied with a bar coater on a PVC film with a film thickness of 15 μm, heated at 80 °C for 10 minutes, and then irradiated with ultraviolet light having an irradiation energy of 7 J / cm 2 at a peak wavelength of 385 nm to form a cured film. (2) Evaluation of Alcohol Resistance of Cured Film The alcohol resistance was evaluated using the cured film obtained above. The evaluation was carried out by visually observing the presence or absence of color transfer to the absorbent cotton when the absorbent cotton was dipped in anhydrous ethanol and strongly rubbed on the surface of the cured film, and evaluated according to the following evaluation criteria. ◎: No color transfer to the absorbent cotton. 〇: There is a slight color transfer to the absorbent cotton, but it is at a level with no practical problems. ×: There is color transfer to the absorbent cotton.

[0275]

Table 5

[0276] From Table 5, it can be seen that the ink of the second invention containing compound (I) has excellent storage stability at high temperatures, and by irradiating with ultraviolet light and curing, a printed image excellent in alcohol resistance can be formed. On the other hand, in Comparative Examples II-1 and II-2 that do not contain compound (I), there is a problem that they change to a gel state during high-temperature storage, and the alcohol resistance of the cured film is also poor. In Comparative Examples II-3 and II-4 to which additives different from compound (I) were added, the high-temperature storage stability is very poor, and the evaluation of the cured film has not been performed for these.

[0277] Although the present invention has been described in detail using specific embodiments, it is obvious to those skilled in the art that various changes can be made without departing from the intention and scope of the present invention. This application is based on Japanese Patent Application No. 2019-216741 filed on November 29, 2019, Japanese Patent Application No. 2019-216742 filed on November 29, 2019, Japanese Patent Application No. 2020-033702 filed on February 28, 2020, and Japanese Patent Application No. 2020-033703 filed on February 28, 2020, the entire contents of which are incorporated herein by reference.

Claims

1. An ultraviolet curable aqueous composition for inkjet printing containing at least an ultraviolet curable oligomer and a polymerization initiator, wherein the ultraviolet curable oligomer is an ultraviolet curable oligomer having a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') shown below, and a structural unit derived from a compound (C') shown below, and the polymerization initiator is a photo radical polymerization initiator, and the photo radical polymerizable initiator contains a water-soluble initiator, an ultraviolet curable aqueous composition for inkjet printing. Compound (B'): A compound containing two or more polymerizable unsaturated bonds and capable of bonding to the polyisocyanate compound (A) Compound (C'): A water-soluble compound capable of bonding to the polyisocyanate compound (A)

2. The ultraviolet curable aqueous composition for inkjet printing according to claim 1, further containing a fat-soluble initiator.

3. The ultraviolet curable aqueous composition for inkjet printing according to claim 1 or 2, further containing a sensitizer.

4. The ultraviolet curable aqueous composition for inkjet printing according to any one of claims 1 to 3, further containing a surfactant.

5. The ultraviolet curable aqueous composition for inkjet printing according to any one of claims 1 to 4, wherein the compound (C') is a compound containing one hydroxyl group at the terminal.

6. The ultraviolet curable aqueous composition for inkjet printing according to any one of claims 1 to 5, wherein the compound (C') is a polyalkylene glycol (C).

7. The ultraviolet curable aqueous composition for inkjet printing according to any one of claims 1 to 6, wherein the compound (B') is a hydroxyl group-containing polyfunctional (meth)acrylate (B).

8. The ultraviolet curable aqueous composition for inkjet printing according to any one of claims 1 to 7, wherein the polyisocyanate compound (A) has three or more isocyanate groups.

9. The ultraviolet curable aqueous composition for inkjet printing according to any one of claims 1 to 8, wherein the ultraviolet curable oligomer is nonionic.

10. The ultraviolet curable aqueous composition for inkjet printing according to any one of claims 1 to 9, wherein the ultraviolet curable oligomer is dispersed as particles in an aqueous medium.

11. The ultraviolet curable aqueous composition for inkjet printing according to any one of claims 1 to 10, wherein the average particle size of the ultraviolet curable oligomer is 10 nm or more and 200 nm or less.

12. An ultraviolet curable ink for inkjet printing containing the ultraviolet curable aqueous composition for inkjet printing according to any one of claims 1 to 11.

13. The ultraviolet curable ink for inkjet printing according to claim 12, further comprising a colorant.

14. The ultraviolet curable ink for inkjet printing according to claim 12 or 13, wherein the content of the polymerization initiator in the ink is 0.05% by mass or more and 8% by mass or less.

15. The ultraviolet curable aqueous ink for inkjet printing according to any one of claims 12 to 14, having a viscosity at 25 °C of 1 mPa·sec or more and 25 mPa·sec or less.

16. A method for producing an ultraviolet curable aqueous ink for inkjet printing, The method for producing an ultraviolet curable aqueous ink for inkjet printing, including the following steps 1 to 3. (Step 1) A step of preparing a dispersion (oligomer dispersion) in which particles of an ultraviolet curable oligomer having a structural unit derived from a polyisocyanate compound (A), a structural unit derived from the following compound (B'), and a structural unit derived from the following compound (C') are dispersed in an aqueous medium. Compound (B'): A compound containing two or more polymerizable unsaturated bonds and capable of bonding to the polyisocyanate compound (A) Compound (C'): A water-soluble compound capable of bonding to the polyisocyanate compound (A) (Step 2) A step of preparing a dispersion (pigment dispersion) in which a colorant is dispersed in an aqueous medium. (Step 3) A mixing step of mixing the oligomer dispersion obtained in Step 1, the pigment dispersion obtained in Step 2, and a water-soluble initiator.

17. The method for producing an ultraviolet curable aqueous ink for inkjet printing according to claim 16, including a step of adding and mixing a fat-soluble initiator and / or a fat-soluble sensitizer during the oligomer preparation in the (Step 1).

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