WO2016125908A1

WO2016125908A1 - Ink set, and image formation method

Info

Publication number: WO2016125908A1
Application number: PCT/JP2016/053595
Authority: WO
Inventors: 克典五井; 征史池田
Original assignee: コニカミノルタ株式会社
Priority date: 2015-02-05
Filing date: 2016-02-05
Publication date: 2016-08-11
Also published as: JP6627782B2; JPWO2016125908A1

Abstract

　An objective of the present invention is to provide an ink set which comprises magenta ink and orange ink, which enables the formation of images having color regions that present difficulties for formation when only CMYK 4-color ink is used, and which enables the expansion of the color gamut in the red-orange region in the L*a*b* color space. The objective is achieved by an ink set comprising a plurality of inks that contain pigment, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator, and that can be cured by irradiation with actinic rays, wherein: the plurality of inks includes magenta ink and orange ink; the pigment contained in the magenta ink includes a magenta pigment having a solid solution of C.I. Pigment Violet 19 and C.I. Pigment Red 202 that has been surface treated with alumina and sulfonic acid; the content of the alumina in the magenta pigment is 1500-7500 mass ppm; and the content of the gelling agent in each of the inks is 1-5 mass%.

Description

Ink set and image forming method

The present invention relates to an ink set and an image forming method.

The ink jet recording method is used in various printing fields because it can form an image easily and inexpensively. As one of the ink-jet inks, an ink containing a photopolymerizable compound that cures when irradiated with actinic rays (hereinafter, also simply referred to as “actinic ray curable ink”) is known. In recent years, actinic ray curable ink has been attracting attention because it can form an image having high adhesion even on a recording medium having low water absorption.

The actinic ray curable ink can contain a pigment as a coloring material. At this time, the color gamut of the formed image can be expanded by ejecting ink so that a plurality of pigments exhibiting different colors land on the recording medium. For example, Patent Document 1 describes Pantone Red 032 (“Panthone” is a registered trademark of the company) published in various color sample books provided by Pantone Corporation using ink containing a red pigment and an orange pigment. It is described that it can exhibit a close color. On the other hand, C.I. I. Pigment Violet (hereinafter also simply referred to as “Pigment Violet”) 19 and C.I. I. Pigment Red (hereinafter, also simply referred to as “Pigment Red”) 202 was formed more than conventional red ink by ink containing a magenta pigment containing a solid solution with 202 (hereinafter also simply referred to as “magenta ink”). It is known that the color gamut of an image can be expanded. Pigment Violet 19 and Pigment Red 202 are both pigments having a quinacridone skeleton.

In the ink jet recording method, a suitable combination of inks is selected from yellow ink, magenta ink, cyan ink, and black ink according to the color to be formed, and the selected ink is overprinted. An image can be formed. At this time, in order to further widen the color gamut of the formed image, an image may be formed by further combining orange ink.

Patent Document 2 discloses an orange ink containing a gelling agent that can be used in combination with other colors to widen the color gamut of an image to be formed in the orange range. In Patent Document 2, when an ink having a color tone close to that of an orange printed in a Pantone color sample book is formed by preparing an ink so that an image having a desired reflectance (gloss) is obtained. Are listed. Patent Document 2 discloses C.I. as an orange pigment. I. An orange ink containing Pigment Orange (hereinafter, also simply referred to as “Pigment Orange”) 36 is described.

When the actinic ray curable ink contains a pigment, the storage stability of the ink can be increased by increasing the affinity between the photopolymerizable compound and the pigment. From this point of view, a technique for increasing the affinity between the photopolymerizable compound and the pigment by surface-treating the pigment with alumina is known. Alumina can be applied to the surface of the pigment particles by, for example, the methods described in Patent Document 3 and Patent Document 4.

In addition, it is known that when the actinic ray curable ink contains a pigment, the ink further contains a dispersant, thereby increasing the dispersibility of the pigment and increasing the storage stability of the ink. For example, Patent Document 5 describes that actinic ray curable ink has a high dispersion stability because it contains a larger amount of dispersant and dispersion synergist than the pigment in weight ratio. At this time, by applying a surface treatment to the pigment particles to impart an acidic adsorption functional group such as sulfonic acid, the affinity between the dispersant and the pigment can be increased, and the storage stability of the ink can be increased.

When the actinic radiation curable ink contains a gelling agent, when the ink lands on the recording medium and cools, the ink gels due to the crystallization of the gelling agent. Cohesion is unlikely to occur. In addition, since the viscosity of the ink containing the gelling agent is high even at a low temperature, it is possible to improve the scratching property of the formed image at room temperature. For example, in Patent Document 6, by adding an oil gelling agent to an inkjet ink containing a pigment and a photopolymerizable compound, solidification of ink droplets that have landed on a recording medium is completed in a short time, thereby preventing dot identity. It is out. In Patent Document 7, an image having good fastness is formed by adding a gelling agent that gels at a low temperature to a radiation curable ink containing a pigment or a dye.

U.S. Pat. No. 8,686,062 JP 2014-118570 A Japanese Patent Publication No.59-34737 JP 2002-121411 A US Pat. No. 8,197,584 Japanese Patent No. 4556414 JP 2006-193745 A

When an image is formed using an inkjet ink containing a plurality of different pigments as described in Patent Document 1, the pigment is separated during storage due to the difference in specific gravity between the pigments, and a clear image is obtained. It may not be obtained. In order to prevent blurring of the image due to the separation of the pigment, it is preferable that a plurality of actinic ray curable inks having different colors are landed at the same position on the recording medium and are cured with actinic rays in a short time after landing. The plurality of actinic ray curable inks can be used as an ink set. At this time, the color gamut of the formed image is further expanded by including the actinic ray curable ink containing the solid solution in the ink set.

Here, the actinic ray curable ink containing the gelling agent and the pigment may change the degree of crystallization of the gelling agent depending on the surface treatment state of the pigment. For example, in an actinic radiation curable ink containing a gelling agent and a pigment surface-treated only with sulfonic acid, the crystallization of the gelling agent is inhibited by the interaction between the pigment surface and the gelling agent, and the ink Pinning property tends to deteriorate. If the pinning property of the ink is lowered, the ink tends to wet and spread, so that the glossiness of the image surface is increased more than originally intended, and there is a possibility that a difference in glossiness from the ink having other pigments occurs. In addition, the gelling agent that has not been crystallized may be deposited on the surface of the ink over time after being cured to cause blooming. According to the knowledge of the present inventors, particularly when a magenta pigment containing a solid solution surface-treated with sulfonic acid is used, these problems of gloss difference are likely to occur.

In contrast, by reducing the amount of the gelling agent, it is possible to prevent the association between the alumina and the gelling agent, but on the other hand, since the gelling agent is small, the pinning property does not increase and the droplet diameter upon landing increases. Doing so will cause dot coalescence.

Also, an image formed with Orange Orange containing Pigment Orange 36 or other orange pigments may not have a color tone close to orange as described in Pantone's color sample book, or with other color inks. The glossiness may be different from the formed image. For this reason, there is still a need for an ink that can form an image having a color tone close to orange described in the Pantone color sample book and having a gloss closer to that of an image formed by an ink of another color.

In view of the above-described problems, the present invention is capable of producing an image having a color region that is difficult to form with only four colors of YMCK, such as Pantone Red 032 and Pantone Orange 021 described in the Pantone color sample book. It is an object of the present invention to provide an ink set including magenta ink and orange ink that can form and expand the color gamut of the red to orange region in the L * a * b * color space. Another object of the present invention is to provide an ink set including a magenta ink and an orange ink so that the magenta ink and the orange ink can form an image having a gloss close to that of an image formed by the other color ink. Another object of the present invention is to provide an ink set including magenta ink and orange ink having sufficient pinning property and storage stability and to provide an image forming method using such an ink set.

The present invention relates to the following ink set.
[1] An ink set comprising a plurality of types of inks containing a pigment, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator and cured by irradiation with actinic rays, wherein the plurality of types of inks are magenta ink and The pigment contained in the magenta ink containing orange ink was surface treated with alumina and sulfonic acid, C.I. I. Pigment Violet 19 and C.I. I. A magenta pigment containing a solid solution with Pigment Red 202, the amount of the alumina in the magenta pigment is 1500 mass ppm to 7500 mass ppm, and the content of the gelling agent in each ink is 1 mass%. The ink set is characterized by being 5% by mass or less.
[2] The C.I. in the magenta pigment. I. Pigment Violet 19 and the C.I. I. The ink set according to [1], wherein the mass ratio to Pigment Red 202 is 60/40 or more and 70/30 or less.
[3] The ink set according to [1] or [2], wherein the amount of the alumina with respect to the magenta pigment is 5000 mass ppm or more and 7500 mass ppm or less.
[4] An ink set containing a plurality of types of inks containing a pigment, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator and cured by irradiation with actinic rays, wherein the plurality of types of inks are magenta ink and An orange ink, the orange ink further containing a sulfonated derivative of an insoluble azo pigment in an amount of 2.0% by mass or more and 15.0% by mass or less based on a mass of the pigment contained in the ink; The pigment to be contained includes an orange pigment having a cyclic structure and a basic site in the cyclic structure, and the photopolymerizable compound contained in the orange ink has a total mass of the photopolymerizable compound. Each of the inks contains 30% by mass or more of a photopolymerizable compound having 6 or more ethylene oxide groups or propylene oxide groups. Kicking the content of the gelling agent is equal to or less than 1.5 mass% to 3.0 mass%, the ink set.
[5] The photopolymerizable compound having 6 or more ethylene oxide groups or propylene oxide groups in total has 2 or more segments having 3 or more ethylene oxide groups or propylene oxide groups in the molecule. The ink set according to [4].
[6] The ink set according to any one of [1] to [5], further including yellow ink, cyan ink, and black ink.
[7] An ink set comprising a plurality of types of inks containing a pigment, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator and cured by irradiation with actinic rays, wherein the plurality of types of inks are magenta ink and The pigment contained in the magenta ink containing orange ink was surface treated with alumina and sulfonic acid, C.I. I. Pigment Violet 19 and C.I. I. A magenta pigment containing a solid solution with Pigment Red 202, wherein the amount of the alumina in the magenta pigment is 1500 mass ppm or more and 7500 mass ppm or less, and the orange ink is 2 with respect to the mass of the pigment contained in the ink. The pigment further contains a sulfonated derivative of an insoluble azo pigment in an amount of from 0.0% by mass to 15.0% by mass, and the pigment contained in the orange ink has a cyclic structure and has a basic site in the cyclic structure. The photopolymerizable compound contained in the orange ink contains 6 or more ethylene oxide groups or propylene oxide groups in an amount of 30% by mass or more based on the total mass of the photopolymerizable compound. The content of the gelling agent in each ink is 1.0% by mass or more. And characterized in that 5.0 wt% or less, the ink set.
[8] The orange ink is C.I. I. Pigment Orange 36, C.I. I. Pigment Orange 64 and C.I. I. The ink set according to any one of [1] to [7], which contains at least one pigment selected from the group consisting of Pigment Orange 71.

The present invention also relates to the following image forming method.
[9] A step of ejecting the magenta ink and orange ink contained in the ink set according to any one of [1] to [8] from a nozzle of an inkjet head to land on a recording medium, and the landed magenta ink and And a step of irradiating the orange ink with an actinic ray to cure the magenta ink and the orange ink.

According to the present invention, a pigment containing a solid solution of Pigment Violet 19 / Pigment Red 202, which has been surface-treated with alumina and sulfonic acid, and a magenta ink containing a gelling agent, having good storage stability and pinning properties And an image forming method using such an ink set are provided.

1. Ink set The ink set according to the present invention is an ink set containing a plurality of types of inks containing a pigment, a photopolymerizable compound, a gelling agent, and a photopolymerization initiator, and cured by irradiation with actinic rays. The seed ink is an ink set including magenta ink and orange ink.

The ink set means a combination of two or more inks that are configured to be installed in an ink jet recording apparatus to form an image. Examples of ink sets include an ink cartridge in which a plurality of inks are individually stored in a plurality of ink cartridges, or an ink cartridge in which a plurality of ink storage portions are integrally formed and different inks are stored in the respective ink storage portions. Is included.

1-1. Magenta ink Magenta ink contains a pigment, a photopolymerizable compound, a gelling agent, and a photopolymerization initiator, and is an ink that is cured by irradiation with actinic rays. Only one type of magenta ink may be included in the ink set, or two or more types of magenta inks having different compositions may be included in the ink set.

1-1-1. Pigment The pigment contained in the magenta ink may be any pigment that allows the ink that has landed and cured on the recording medium to exhibit a magenta color. From the viewpoint of enhancing the storage stability of the ink by increasing the affinity between the photopolymerizable compound or dispersant and the pigment, the pigment is a magenta pigment containing a solid solution of Pigment Violet 19 and Pigment Red 202. It is preferable to include those obtained by surface treatment with an acid (hereinafter, the magenta pigment is referred to as “magenta pigment-A”, the magenta ink containing magenta pigment-A is also referred to as “magenta ink-A”, and others) This magenta ink is also referred to as “magenta ink-B.” “Magenta ink” simply means magenta ink that includes both. The amount of the alumina in the magenta pigment-A is preferably 1500 ppm to 7500 ppm by mass. The magenta pigment contained in the magenta ink is preferably magenta pigment-A. However, when the color gamut is expanded by another ink such as an orange ink as described below, it is contained in the magenta ink. The pigment need not be magenta pigment-A. Further, the pigment contained in the magenta ink may contain only one kind, or two or more kinds.

The magenta pigment-A can broaden the color gamut of an image formed by landing and curing the magenta ink contained in the ink set of the present invention on a recording medium as compared with a normal magenta pigment. Therefore, for example, by forming an image using only the magenta pigment, it becomes possible to produce a color closer to the magenta color described in Japan color 2011, which is a color sample, and ink containing magenta ink-A and orange ink. By forming an image as a set, it becomes possible to produce a color closer to Pantone Red 032.

The content of the pigment may be in a range that can sufficiently develop the magenta color in the obtained image and that the viscosity of the ink can be ejected from the inkjet head. The content is preferably from 20% by mass to 20% by mass, and more preferably from 0.4% by mass to 10% by mass from the above viewpoint.

Commercially available examples of magenta pigments containing the solid solution include CINQUASIA Magenta L4540, CINQUASIA Magenta D4500J and CINQUASIA Red K4330, manufactured by BASF (“CINQUASIA” is a registered trademark of the company), 228-2120m, Sic E7B, manufactured by Clariant, is included.

From the viewpoint of further expanding the color gamut of the image to be formed, and in particular, forming an image with a color gamut closer to Pantone Red 032 in combination with orange ink, the mass ratio of Pigment Violet 19 and Pigment Red 202 in the pigment Is preferably (Pigment Violet 19 mass) / (Pigment Red 202 mass) of 60/40 or more and 70/30 or less.

Examples of the magenta pigment containing the solid solution satisfying the mass ratio include CINQUASIA Magenta D4500J, manufactured by BASF (Pigment Violet 19 / Pigment Red 202 ratio: 60/40) and 228-2120, manufactured by Sun Chemical Co. (Pigment 19 / Pigment Red 202 ratio: 70/30).

The surface treatment of the magenta pigment can be performed by a known method. The surface treatment with alumina can be performed, for example, by the method described in Patent Document 2 or Patent Document 3, or the method of adjusting the pH of the suspension by suspending alumina in a dispersion in which a pigment is dispersed. The amount of alumina applied can be adjusted to a desired amount by changing the amount of alumina added in each method. The surface treatment with sulfonic acid can be performed, for example, by a method in which a sulfonating agent is added to a slurry-like pigment dispersion and both are reacted at a high temperature. The application amount of the sulfonic acid can be adjusted to a desired amount by adjusting the amount of the sulfonating agent to be added.

The amount of alumina in the magenta pigment-A is 1500 ppm or more and 7500 ppm or less with respect to 1 g of the pigment. By setting the applied amount of alumina to 1500 ppm or more, the affinity of the pigment to the photopolymerizable compound and the dispersant increases, and the pigment can be stably stored. Further, by setting the applied amount of alumina to 7500 ppm or less, it is possible to prevent insufficient crystallization of the gelling agent due to the association between the alumina and the gelling agent, and to suppress the occurrence of gloss due to excessive leveling. From the viewpoint of further increasing the affinity between the photopolymerizable compound and the pigment and further enhancing the storage stability of the magenta ink, the amount of alumina applied is preferably 5000 ppm or more and 7500 ppm or less with respect to 1 g of the pigment.

The amount of the sulfonic acid in the magenta pigment-A may be in a range where the storage stability of the ink is sufficient, and can be, for example, 1000 ppm or more and 1500 ppm or less with respect to 1 g of the pigment.

The amount of alumina and sulfonic acid in the pigment can be calculated from the amount of Al element and the amount of S element in the pigment obtained by measuring with an inductively coupled plasma emission spectrometer (ICP-AES), for example. When the pigment is dispersed in the ink, the value calculated from the amount of Al element and the amount of S element in the ink may be used as the amount of alumina and sulfonic acid in the pigment.

1-1-2. Gelling agent A gelling agent can temporarily fix (pinning) ink droplets landed on a recording medium in a gel state. When the ink is pinned in a gel state, wetting and spreading of the ink is suppressed and adjacent dots are less likely to be the same, so that a higher definition image can be formed. In addition, when the ink is in a gel state, the entry of oxygen in the environment into the ink droplets is suppressed and it becomes difficult for the ink to inhibit curing, so that a high-definition image can be formed at a higher speed. Only one kind of gelling agent may be contained in the ink constituting the ink set of the present invention, or two or more kinds may be contained.

The content of the gelling agent is 1% by mass to 5% by mass with respect to the total mass of the ink. By setting the content of the gelling agent to 1% by mass or more, the pinning property of the ink containing the magenta pigment surface-treated with alumina can be sufficiently enhanced, and a higher definition image can be formed. Further, by setting the content of the gelling agent to 1.5% by mass or more, it becomes difficult for the pigment to settle due to liquefaction of the ink during ink storage, and the storage stability of the ink can be further improved. By setting the content of the gelling agent to 5% by mass or less, it becomes difficult for the gelling agent to deposit on the surface of the formed image, and the gloss of the image can be made closer to the gloss of the image by other ink, and Ink ejection from the inkjet head can be further enhanced. From the above viewpoint, the content of the gelling agent in the magenta ink is more preferably 1.5% by mass or more and 3% by mass or less.

From the following viewpoint, the gelling agent is preferably crystallized in the ink at a temperature equal to or lower than the gelation temperature of the ink. The gelation temperature refers to a temperature at which the viscosity of the ink changes suddenly when the ink sol- lated or liquefied by heating is cooled and the gelling agent undergoes phase transition from sol to gel. Specifically, the sol or liquefied ink is cooled while measuring the viscosity with a viscoelasticity measuring device (for example, MCR300, manufactured by Physica), and the temperature at which the viscosity rapidly increases is measured. The gelation temperature can be set.

When the gelling agent is crystallized in the ink, a structure in which the photopolymerizable compound is included in the three-dimensional space formed by the gelling agent that has been crystallized in a plate shape may be formed (such a structure). , Hereinafter referred to as "card house structure"). When the card house structure is formed, since the liquid photopolymerizable compound is held in the space, the ink droplets are less likely to spread and the pinning property of the ink is further increased. When the pinning property of the ink is increased, the ink droplets that have landed on the recording medium are less likely to coalesce, and a higher definition image can be formed.

In order to form the card house structure, it is preferable that the photopolymerizable compound dissolved in the ink and the gelling agent are compatible. On the other hand, when the photopolymerizable compound dissolved in the ink and the gelling agent are phase-separated, it may be difficult to form a card house structure.

Examples of gelling agents suitable for forming a card house structure by crystallization include
Ketone waxes including dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone and palmityl stearyl ketone;
Behenyl behenate, icosyl icosanoate, stearyl stearate, palmityl stearate, cetyl palmitate, myristyl myristate, cetyl myristate, myristyl myristate, stearyl stearate, oleyl palmitate, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol Ester waxes including fatty acid esters, ethylene glycol fatty acid esters and polyoxyethylene fatty acid esters;
Petroleum-based waxes including paraffin wax, microcrystalline wax and petrolactam;
Plant waxes including candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax and jojoba ester;
Animal waxes including beeswax, lanolin and whale wax;
Mineral waxes including montan wax and hydrogenated wax;
Hydrogenated castor oil;
Modified waxes including hardened castor oil derivatives, montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, 12-hydroxystearic acid derivatives and polyethylene wax derivatives;
Higher alcohols including stearyl alcohol and behenyl alcohol;
Hydroxystearic acid including 12-hydroxystearic acid;
Fatty acid amides including lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide and 12-hydroxystearic acid amide;
N-substituted fatty acid amides including N-stearyl stearamide and N-oleyl palmitate amide;
Special fatty acid amides including N, N′-ethylenebisstearylamide, N, N′-ethylenebis-12-hydroxystearylamide and N, N′-xylylenebisstearylamide;
Higher amines including dodecylamine, tetradecylamine and octadecylamine;
Esters of sucrose fatty acids including sucrose stearic acid and sucrose palmitic acid;
Synthetic waxes including polyethylene waxes and α-olefin maleic anhydride copolymer waxes;
Dimer acid, as well as dimer diol are included.

Examples of commercially available fatty acid amides include the Nikka Amide series, manufactured by Nippon Kasei Co., Ltd. (“Nikka Amide” is a registered trademark of the company), ITOWAX series, manufactured by Ito Oil Co., Ltd., and FATTYAMID series, manufactured by Kao Corporation.

Examples of commercially available fatty acid ester compounds include the EMALLEX series, the Japan Emulsion Riquemar series and the Poem series, and Riken Vitamin Co., Ltd. ("Riquemar" and "Poem" are registered trademarks of the same company).

Examples of commercially available esters of sucrose fatty acid include the Ryoto Sugar Ester series, manufactured by Mitsubishi Chemical Foods (“Ryoto” is a registered trademark of the company).

Examples of commercially available synthetic waxes include the UNILIN series, Baker-Petrolite (“UNILIN” is a registered trademark of the company).

Examples of commercially available dimer diols include the PRIPOR series, manufactured by CRODA (“PRIPOR” is a registered trademark of the company).

Of these gelling agents, ketone waxes, ester waxes, higher fatty acids, higher alcohols and fatty acid amides are preferable from the viewpoint of further improving pinning properties. From the above viewpoint, ketones represented by the following general formula (G1) A wax and an ester wax represented by the following general formula (G2) are more preferable. The ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may contain only one kind or two or more kinds in magenta ink. Also good. In addition, the ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may contain only one or both of them in the magenta ink. It may be.

General formula (G1): R1-CO-R2
In General Formula (G1), R1 and R2 are each a linear or branched hydrocarbon group having 1 to 24 carbon atoms. However, one of R1 and R2 includes a linear alkyl structure having 12 or more carbon atoms, and preferably both include a linear alkyl structure having 12 or more carbon atoms. From the viewpoint of easily taking a crystal structure and improving the pinning property of the ink, both R1 and R2 are linear hydrocarbon groups having 1 to 24 carbon atoms, and more preferably both have a carbon number. It is a linear hydrocarbon group having 8 or more and 22 or less.

General formula (G2): R3-COO-R4
In General Formula (G2), R3 and R4 are each a linear or branched hydrocarbon group having 1 to 24 carbon atoms. However, any one of R3 and R4 includes a linear alkyl structure having 12 or more carbon atoms, and preferably both include a linear alkyl structure having 12 or more carbon atoms. From the viewpoint of easily taking a crystal structure and improving the pinning property of the ink, both R3 and R4 are linear hydrocarbon groups having 1 to 24 carbon atoms, and more preferably both have a carbon number. It is a linear hydrocarbon group having 8 or more and 22 or less.

The ketone wax represented by the above general formula (G1) containing a linear alkyl structure having 12 or more carbon atoms or the ester wax represented by the above general formula (G2) increases the crystallinity of the gelling agent, and Sufficient space is generated in the card house structure. For this reason, the photopolymerizable compound can be easily contained in the space, and the pinning property of the ink becomes higher. Further, when the carbon number of the linear or branched hydrocarbon group is 24 or less, since the melting point of the gelling agent does not increase excessively, it is not necessary to excessively heat the ink when ejecting the ink. .

Examples of the ketone wax represented by the general formula (G1) include dilignoseryl ketone (carbon number: 23-24), dibehenyl ketone (carbon number: 21-22), distearyl ketone (carbon number: 17 -18), dieicosyl ketone (carbon number: 19-20), dipalmityl ketone (carbon number: 15-16), dimyristyl ketone (carbon number: 13-14), dilauryl ketone (carbon number: 11) -12), lauryl myristyl ketone (carbon number: 11-14), lauryl palmityl ketone (11-16), myristyl palmityl ketone (13-16), myristyl stearyl ketone (13-18), myristyl behenyl ketone (13 -22), palmityl stearyl ketone (15-18), valmityl behenyl ketone (15-22) and stearyl behenyl keto (17-22) are included. In addition, the carbon number in the said parenthesis represents the carbon number of each of the two hydrocarbon groups divided by a carbonyl group.

Examples of commercially available ketone waxes represented by the general formula (G1) include 18-Pentatria cationon, Alfa Aeser, Hentriacontan-16-on, Alfa Aeser, Kao wax T1, and Kao.

Examples of the fatty acid or ester wax represented by the general formula (G2) include behenyl behenate (carbon number: 21-22), icosyl icosanoate (carbon number: 19-20), stearyl stearate (carbon number: 17 -18), palmitic acid stearate (carbon number: 17-16), lauryl stearate (carbon number: 17-12), cetyl palmitate (carbon number: 15-16), stearyl palmitate (carbon number: 15-18) ), Myristyl myristate (carbon number: 13-14), cetyl myristate (carbon number: 13-16), octyldodecyl myristate (carbon number: 13-20), stearyl oleate (carbon number: 17-18) Stearyl erucate (carbon number: 21-18), stearyl linoleate (carbon number: 17-18), behenyl oleate (carbon) : 18-22) and linoleic acid arachidyl (carbon number: 17-20) are included. The number of carbons in the parenthesis represents the number of carbons of each of the two hydrocarbon groups that are divided by the ester group.

Examples of commercially available ester waxes represented by the general formula (G2) include UNISTAR M-2222SL and SPALM ACETI, manufactured by NOF Corporation (“Unistar” is a registered trademark of the company), EXCEPARL SS and EXCEPARL MY-M, Kao Corporation ("EXPEARL" is a registered trademark of the company), EMALEX CC-18 and EMALEX CC-10, manufactured by Nippon Emulsion Co., Ltd. ("EMALEX" is a registered trademark of the company), Amreps PC, and High Alcohol Industry Co., Ltd. The company's registered trademark). Since these commercially available products are often a mixture of two or more types, they may be separated and purified as necessary and contained in the ink.

1-1-3. Photopolymerizable Compound The photopolymerizable compound is crosslinked or polymerized by irradiation with actinic rays to cure the ink. Examples of actinic rays include ultraviolet rays, electron beams, α rays, γ rays and X rays. From the viewpoint of safety, and from the viewpoint that the polymerization and crosslinking can be generated even with a lower energy amount, the actinic rays are preferably ultraviolet rays or electron beams. Only one kind of photopolymerizable compound may be contained in the magenta ink, or two or more kinds thereof may be contained.

The content of the photopolymerizable compound may be in a range where the effects of the present invention can be obtained, and can be, for example, 1% by mass to 97% by mass with respect to the total mass of the magenta ink. From the above viewpoint, the content of the photopolymerizable compound is preferably 30% by mass to 95% by mass with respect to the total mass of the magenta ink.

The photopolymerizable compound includes a radical polymerizable compound and a cationic polymerizable compound. The photopolymerizable compound is preferably a radically polymerizable compound from the viewpoint that it is easy to cause polymerization and crosslinking and can be selected from various compounds according to the image to be formed.

The radical polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization. The radical polymerizable compound may be any of a monomer, a polymerizable oligomer, a prepolymer, or a mixture thereof. Only one kind of radically polymerizable compound may be contained in the magenta ink, or two or more kinds thereof may be contained.

Examples of the compound having an ethylenically unsaturated bond capable of radical polymerization include an unsaturated carboxylic acid and a salt thereof, an unsaturated carboxylic acid ester compound, an unsaturated carboxylic acid urethane compound, an unsaturated carboxylic acid amide compound and an anhydride thereof, Examples include acrylonitrile, styrene, unsaturated polyester, unsaturated polyether, unsaturated polyamide, and unsaturated urethane. Examples of the unsaturated carboxylic acid include (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and the like.

Among these, the radically polymerizable compound is preferably an unsaturated carboxylic acid ester compound, and more preferably (meth) acrylate. In the present invention, “(meth) acrylate” means acrylate or methacrylate, “(meth) acryloyl group” means acryloyl group or methacryloyl group, and “(meth) acryl” means acrylic. Or methacryl.

Examples of the monomer (meth) acrylate include monofunctional (meth) acrylate, bifunctional (meth) acrylate, and trifunctional or higher (meth) acrylate.

Examples of monofunctional (meth) acrylates include isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomustyl (meth) acrylate, isostearyl (Meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meta ) Acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxye (Meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid and t-butylcyclohexyl (meth) Acrylate is included.

Examples of bifunctional (meth) acrylates include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (Meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, Dimethylol-tricyclodecane di (meth) acrylate, PO adduct di (meth) acrylate of bisphenol A, neopentyl glycol di (meth) acrylate hydroxypivalate, polytetramethylene glycol di ( Data) acrylate, polyethylene glycol diacrylate and tripropylene glycol diacrylate.

Examples of tri- or higher functional (meth) acrylates include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane Tetra (meth) acrylate, glycerin propoxytri (meth) acrylate and pentaerythritol ethoxytetra (meth) acrylate are included.

Examples of (meth) acrylates that are polymerizable oligomers or prepolymers include epoxy (meth) acrylate oligomers, aliphatic urethane (meth) acrylate oligomers, aromatic urethane (meth) acrylate oligomers, polyester (meth) acrylate oligomers and straighteners. Chain (meth) acryl oligomers and the like are included.

The photopolymerizable compound preferably contains ethylene oxide-modified (meth) acrylate. Ethylene oxide modified (meth) acrylate has higher photosensitivity. Further, the ethylene oxide-modified (meth) acrylate is easily included in the card house structure when the ink is gelled at a low temperature, and more easily compatible with other ink components even at a high temperature. Furthermore, since ethylene oxide-modified (meth) acrylate has little curing shrinkage, curling of printed matter during image formation is less likely to occur.

Commercially available examples of ethylene oxide modified (meth) acrylates include CD561, SR454, SR499 and SR494, manufactured by Sartomer, and NK Ester A-400, NK Ester A-600, NK Ester 9G, NK Ester 14G, NK Ester DOD -N, NK ester A-DCP and NK ester DCP, manufactured by Shin-Nakamura Chemical Co., Ltd. are included.

Examples of the cationic polymerizable compound include an epoxy compound, a vinyl ether compound, and an oxetane compound. Only one kind of the cationic polymerizable compound may be contained in the magenta ink, or two or more kinds thereof may be contained.

Examples of epoxy compounds include aromatic epoxides, alicyclic epoxides and aliphatic epoxides. Aromatic epoxides and alicyclic epoxides are preferred from the viewpoint of further improving curability.

Examples of aromatic epoxides include di- or polyglycidyl ethers obtained by reacting polyphenols or their alkylene oxide adducts with epichlorohydrin. Examples of the polyhydric phenol or its alkylene oxide adduct include bisphenol A or its alkylene oxide adduct. Examples of the alkylene oxide in the alkylene oxide adduct include ethylene oxide and propylene oxide.

Examples of the alicyclic epoxide include a cycloalkane oxide-containing compound obtained by epoxidizing a cycloalkane-containing compound with an oxidizing agent such as hydrogen peroxide or peracid. Examples of the cycloalkane include cyclohexene and cyclopentene.

Examples of the aliphatic epoxide include di- or polyglycidyl ether obtained by reacting an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of the aliphatic polyhydric alcohols or alkylene oxide adducts thereof include alkylene glycols including ethylene glycol, propylene glycol and 1,6-hexanediol, and alkylene oxide adducts thereof. Examples of the alkylene oxide in the alkylene oxide adduct include ethylene oxide and propylene oxide.

Examples of vinyl ether compounds include monofunctional vinyl ether compounds and bifunctional or higher functional vinyl ether compounds. Among these, from the viewpoint of further improving the curability of the ink or further improving the adhesion between the recording medium and the image, a bifunctional or higher vinyl ether compound is preferable.

Examples of monofunctional vinyl ether compounds include ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, Isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether and octadecyl vinyl ether are included.

Examples of bifunctional or higher vinyl ether compounds include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol Divinyl ether and trimethylolpropane trivinyl ether are included. Of these vinyl ether compounds, di- or trivinyl ether compounds are preferred in view of curability and adhesion.

Examples of oxetane compounds include oxetane compounds described in JP-A Nos. 2001-220526, 2001-310937, and JP-A-2005-255821.

1-1-4. Photopolymerization initiator The photopolymerization initiator is a photoradical initiator when the photopolymerizable compound is a compound having a radical polymerizable functional group, and the photopolymerizable compound has a cationic polymerizable functional group. When it is a compound having a photoacid generator. Only one kind of the photopolymerization initiator may be contained in the magenta ink, or two or more kinds thereof may be contained. The photopolymerization initiator may be a combination of both a photo radical initiator and a photo acid generator.

The photo radical initiator includes a cleavage type radical initiator and a hydrogen abstraction type radical initiator.

Examples of the cleavage type radical initiator include acetophenone-based initiators, benzoin-based initiators, acylphosphine oxide-based initiators, benzyl and methylphenylglyoxyesters.

Examples of acetophenone initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1- (4-isopropylphenyl) -2-hydroxy-2- Methylpropan-1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4-thiomethylphenyl) Propan-1-one and 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone are included.

Examples of benzoin-based initiators include benzoin, benzoin methyl ether, and benzoin isopropyl ether.

Examples of the acylphosphine oxide-based initiator include 2,4,6-trimethylbenzoin diphenylphosphine oxide.

Examples of hydrogen abstraction type radical initiators include benzophenone initiators, thioxanthone initiators, aminobenzophenone initiators, 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10- Phenanthrene quinone and camphor quinone are included.

Examples of benzophenone-based initiators include benzophenone, methyl-4-phenylbenzophenone o-benzoylbenzoate, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated benzophenone 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone and 3,3′-dimethyl-4-methoxybenzophenone.

Examples of the thioxanthone-based initiator include 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone and 2,4-dichlorothioxanthone.

Examples of aminobenzophenone-based initiators include Michler's ketone and 4,4'-diethylaminobenzophenone.

Examples of photoacid generators include compounds described in Organic Electronics Materials Research Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), pages 187-192.

The content of the photopolymerization initiator may be in a range in which the ink can be sufficiently cured, and can be, for example, 0.01% by mass or more and 10% by mass or less with respect to the total mass of the magenta ink.

1-1-5. Other Components The magenta ink may further contain other components including a dispersant, a photopolymerization initiator auxiliary agent, and a polymerization inhibitor as long as the effects of the present invention are obtained. Only one kind of these components may be contained in magenta ink, or two or more kinds thereof may be contained.

The dispersant is a compound having an affinity for both the pigment and the photopolymerizable compound described below, and can disperse the pigment in the photopolymerizable compound while adsorbing to the pigment, thereby enhancing the dispersibility of the pigment.

The content and type of the dispersant may be in a range that can further improve the dispersibility of the pigment. Only one type of dispersant may be included in the magenta ink, or two or more types of dispersants may be included.

The content of the dispersing agent can be, for example, 20% by mass to 70% by mass with respect to the total mass of the pigment. By setting the content of the dispersing agent to 20% by mass or more based on the total mass of the pigment, the dispersing agent coats the surface of the pigment, so that aggregation of the pigments during ink storage can be made less likely to occur. . By making the content of the dispersant 70% by mass or less with respect to the total mass of the pigment, the association between the dispersant and the gelling agent is less likely to occur, and the ink that has landed on the recording medium is more sufficiently gelled. Can be pinned. From the above viewpoint, the content of the dispersant is preferably 30% by mass to 60% by mass and more preferably 35% by mass to 50% by mass with respect to the total mass of the pigment.

Examples of the dispersant include a hydroxyl group-containing carboxylic acid ester, a salt of a long chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylic acid, a salt of a long chain polyaminoamide and a polar acid ester, a high molecular weight unsaturated acid ester , Polymer copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene Nonylphenyl ether, and stearylamine acetate are included.

From the viewpoint of suppressing aggregation between pigments due to steric hindrance due to the extended side chain and improving the dispersibility of the pigment, the dispersant is preferably a block copolymer having a comb block structure. The block copolymer having a comb block structure refers to a copolymer obtained by graft polymerization of another type of polymer as a side chain with respect to each constituent unit derived from a monomer constituting a linear main chain.

Examples of commercially available block copolymers having a comb block structure include BYK-2164, BYK-168, BYK N-22024, BYK JET-9150 and BYK JET-9151, manufactured by BYK Chemie ("BYK" is registered by the company) Trademark), EFKA 7701, EFKA 4310, EFKA 4320 and EFKA 4401, manufactured by BASF, SOLPERSE 24000GR and SOLPERSE 39000, manufactured by Lyubrizol (“SOLSPERSE” is a registered trademark of the same company), and manufactured by Ajisper PB821 and Ajisper PB8 Fine ("Ajisper" is a registered trademark of Ajinomoto Co., Inc.).

Examples of photopolymerization initiator auxiliaries include tertiary amine compounds including aromatic tertiary amine compounds. Examples of aromatic tertiary amine compounds include N, N-dimethylaniline, N, N-diethylaniline, N, N-dimethyl-p-toluidine, N, N-dimethylamino-p-benzoic acid ethyl ester, N, N-dimethylamino-p-benzoic acid isoamyl ethyl ester, N, N-dihydroxyethylaniline, triethylamine and N, N-dimethylhexylamine are included.

Examples of polymerization inhibitors include (alkyl) phenol, hydroquinone, catechol, resorcin, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone , Nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cuperone, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N- (3-oxyanilino- 1,3-Dimethylbutylidene) aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraloxime, methyl ethyl ketoxime and cyclohexanone oxy Beam are included.

1-1-6. Physical Properties From the viewpoint of further improving the ejection properties from the inkjet head, the viscosity of the magenta ink at 80 ° C. is preferably 3 mPa · s or more and 20 mPa · s or less. Further, from the viewpoint of sufficient gelation of the ink when landed and cooled to room temperature, the viscosity of the magenta ink at 25 ° C. is preferably 1000 mPa · s or more.

The gelation temperature of the magenta ink is preferably 40 ° C. or higher and 70 ° C. or lower. When the gelation temperature of the ink is 40 ° C. or higher, the ink gels quickly after landing on the recording medium, and therefore the pinning property is further improved. When the gelation temperature of the ink is 70 ° C. or lower, the ink is less likely to be gelled when the magenta ink is ejected from the inkjet head whose ink temperature is usually about 80 ° C., so that the ink can be ejected more stably.

The viscosity at 80 ° C., the viscosity at 25 ° C., and the gelation temperature of magenta ink and orange ink described later can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer. In the present invention, these viscosity and gelation temperature are values obtained by the following method. The magenta ink was heated to 100 ° C., and the shear rate 11.7 (1/1) was measured while measuring the viscosity by a stress-controlled rheometer Physica MCR301 (cone plate diameter: 75 mm, cone angle: 1.0 °) manufactured by Anton Paar. s) The ink is cooled to 20 ° C. under a temperature drop rate of 0.1 ° C./s to obtain a temperature change curve of the viscosity. The viscosity at 80 ° C. and the viscosity at 25 ° C. are obtained by reading the viscosities at 80 ° C. and 25 ° C. in the temperature change curve of the viscosity, respectively. The gelation temperature is determined as the temperature at which the viscosity becomes 200 mPa · s in the temperature change curve of the viscosity.

From the viewpoint of further improving the ejection properties from the inkjet head, the average particle size of the pigment particles contained in the magenta ink is 0.08 μm or more and 0.5 μm or less, and the maximum particle size is 0.3 μm or more and 10 μm or less. preferable. The average particle diameter of the pigment particles in the present invention means a value obtained by a dynamic light scattering method using Data Sizer Nano ZSP, manufactured by Malvern. Note that the ink containing the color material has a high concentration and does not transmit light with this measuring instrument. Therefore, the ink is diluted 200 times before measurement. The measurement temperature is room temperature (25 ° C).

1-2. Orange ink Orange ink is an ink that contains a pigment, a photopolymerizable compound, a gelling agent, and a photopolymerization initiator, and is cured by irradiation with actinic rays. One kind of orange ink may be included in the ink set, or two or more kinds of orange inks having different compositions may be included in the ink set.

1-2-1. Pigment The pigment contained in the orange ink may be any pigment that allows the ink that has landed and cured on the recording medium to exhibit an orange color. Examples of such pigments include Pigment Orange 16, Pigment Orange 34, Pigment Orange 36, Pigment Orange 38, Pigment Orange 43, Pigment Orange 64, and Pigment Orange 71.

From the viewpoint of reducing the interaction between the orange pigment and the gelling agent in combination with other materials and making it difficult to accumulate the gelling agent on the pigment surface, the pigment contained in the orange ink is It is a pigment having a basic site in a non-aromatic cyclic structure (hereinafter also simply referred to as “basic orange pigment”), and a sulfonated derivative of an insoluble azo pigment (hereinafter simply referred to as “azo derivative”). It is preferred to use an orange pigment containing Hereinafter, the orange pigment is also referred to as “orange pigment-C”, the ink containing orange pigment-C is also referred to as “orange ink-C”, and the other orange ink is also referred to as “orange ink-D”. When simply referred to as “orange ink”, it means conceptually an orange ink including both. Generally, gelling agents, especially crystalline gelling agents, crystallize in the ink by electronic interaction between highly polar sites and low polarity sites in the gelling agent as the temperature changes. It is known to increase viscosity and pin the ink. However, the present inventors have found that the pinning performance of the ink may decrease or become unstable depending on the composition of the ink, which is caused by gelation with other components in the ink such as pigment. It is presumed that the amount of gelling agent used for pinning by crystallization of the gelling agent is reduced or destabilized by the electronic interaction of the agent. Therefore, by combining a pigment having a basic site with a polymerizable compound having a high polarity, such as Orange Pigment-C, the pigment and the polymerizable compound preferentially interact electronically, Presumed to be in a “free” state that does not interact with the compound. Thereby, the temperature of the sol-gel phase transition of the ink can be stabilized, and the content of the gelling agent can be minimized. By reducing the content of the gelling agent, the orange ink-C can suppress an excessive increase in gloss of the formed image. Furthermore, the combination of Orange Ink-C and a polymerizable compound having a high polarity improves the dispersion stability of the pigment, so that the storage stability of the pigment is good, and excessive accumulation of pigments is also possible during image formation. It can be suppressed and an image of a desired color gamut can be easily formed. For the above reasons, the orange ink of the ink set of the present invention is preferably an orange ink-C containing an orange pigment-C. However, the color gamut may be expanded by other inks such as magenta ink as described above. In the case illustrated, the pigment contained in the orange ink does not need to be the orange pigment-C. However, from the viewpoint of forming an image having a good color gamut, the ink set of the present invention has at least the magenta pigment-A. It is more preferable that the ink set includes a magenta ink-A containing an orange ink and an orange ink-C containing an orange pigment-C. Moreover, the pigment contained in orange ink may contain only 1 type, and may contain 2 or more types.

At least one of the cyclic structures of the basic orange pigment is a non-aromatic cyclic structure having a basic site. Examples of such a cyclic structure include an alicyclic structure in which the cyclic structure is composed only of carbon and hydrogen, a heterocyclic structure in which the cyclic structure includes carbon and other atoms, and a plurality of the cyclic structures having one atom. A structure in which a basic site is included in a part of a partial structure selected from spiro ring structures sharing the above, or a structure in which a part of the structure is substituted with a basic site is included. If the cyclic structure does not have aromaticity, it may contain a double bond.

The basic site means a site that can have a positive charge. Examples of the basic moiety include a secondary amino group, an amino group containing a tertiary amino group and a quaternary ammonium group, and a nitrogen-containing heterocyclic group having a pyrrolidine or piperidine skeleton. From the viewpoint of preventing deterioration of the ink due to the reaction with the components in the ink containing the photopolymerizable compound, the basic site is preferably a secondary amino group or a tertiary amino group.

From the viewpoint of sufficiently associating an azo derivative described later with a basic orange pigment and further suppressing the occurrence of excessive gloss, the basic orange pigment preferably has two or more basic sites in the molecule. It is more preferable to have the above.

The content of the basic orange pigment is not particularly limited as long as the orange color in the obtained image is sufficient and the viscosity of the ink can be discharged from the inkjet head. From the above viewpoint, for example, the content of the pigment is preferably 0.1% by mass or more and 20% by mass or less with respect to the orange ink-C, and is 0.4% by mass or more and 10% by mass or less. Is more preferable.

Examples of the basic orange pigment include Pigment Orange 36 having a structure represented by the following (Formula 1), Pigment Orange 64 having a structure represented by (Formula 2), and a structure represented by (Formula 3). Pigment Orange 71 is included. Pigment Orange 36 and Pigment Orange 71 have two basic sites in the molecule, and Pigment Orange 64 has four basic sites in the molecule.

1-2-2. Azo Derivatives Azo derivatives are sulfonated derivatives of insoluble azo pigments. Since the azo derivative has a highly polar portion derived from sulfonic acid, the azo derivative can associate well with a basic orange pigment having the same highly polar portion. Therefore, when the ink contains an azo derivative and a basic orange pigment, the gelling agent accumulates on the surface of the basic orange pigment, thereby suppressing the relative decrease of the gelling agent molecules in the ink. it can. Therefore, according to the ink containing the azo derivative and the basic orange pigment, the gloss is not excessively high and an image having a color tone close to orange described in the Pantone color sample book can be formed. it is conceivable that.

In addition, the melted azo lake derivative has a high affinity with the photopolymerizable compound because it has many water-soluble functional groups, and more aggregates with the photopolymerizable compound than with the pigment. Easy to form. In addition, the quinacridone pigment derivative is inactive because the pigment surface is covered with thick π-electrons, and does not easily form an association with the basic group of the basic orange pigment. In contrast, sulfonated derivatives of azo pigments often form aggregates with basic orange pigments, so it is considered that the accumulation of gelling agents on the surface of basic orange pigments can be more effectively prevented.

The content of the azo derivative is 2% by mass to 15% by mass with respect to the mass of the pigment contained in the ink. If the content of the azo derivative with respect to the mass of the pigment is 2% by mass or more, the basic orange pigment and the azo derivative can be associated with each other well, so that it is considered that the gloss does not become too high. When the content of the azo derivative with respect to the mass of the pigment is 15% by mass or less, a change in gloss due to precipitation of the azo derivative on the image surface can be suppressed. From the above viewpoint, the content of the azo derivative is preferably 5% by mass or more and 13% by mass or less with respect to the mass of the pigment contained in the ink, and 7% by mass or more with respect to the mass of the pigment contained in the ink. More preferably, it is 12 mass% or less.

Examples of azo derivatives include solsperse 22000, manufactured by Lubrizol (“solsperse” is a registered trademark of the company) and BYK synergist 2105, manufactured by BYK Chemie (“BYK” is a registered trademark of the company).

1-2-3. Photopolymerizable compound

The photopolymerizable compound contained in the orange ink can be the same compound as the magenta ink.

The orange ink-C preferably contains a highly polar photopolymerizable compound described later. The orange ink-C may further contain a photopolymerizable compound (hereinafter also simply referred to as “low-polar photopolymerizable compound”) having a lower polarity than the high-polarity photopolymerizable compound.

The content of the photopolymerizable compound obtained by adding the high polarity photopolymerizable compound and the low polarity photopolymerizable compound in the orange ink-C may be in a range where the ink irradiated with actinic rays is sufficiently cured, for example, , And can be 1% by mass to 97% by mass with respect to the total mass of the orange ink-C. From the above viewpoint, the content of the photopolymerizable compound is preferably 30% by mass or more and 95% by mass or less with respect to the total mass of the orange ink-C.

1-2-3-1. Photopolymerizable compound The highly polar photopolymerizable compound is a photopolymerization having 6 or more ethylene oxide groups (hereinafter also simply referred to as “EO groups”) or propylene oxide groups (hereinafter also simply referred to as “PO groups”). It is a sex compound. Only one kind of the highly polar photopolymerizable compound may be contained in the orange ink, or two or more kinds thereof may be contained.

6 or more EO groups and PO groups may exist as one connected segment, or may exist in two or more segments. However, from the viewpoint of further increasing the dispersibility of the azo derivative and further reducing the accumulation of the gelling agent on the pigment surface, when the EO group and the PO group are divided into two or more segments, three or more It is preferable that there are two or more segments having an EO group or a PO group in the molecule.

Highly polar photopolymerizable compounds have 6 or more polar EO groups or PO groups, and have a high affinity with basic orange pigments having the same polarity. Therefore, basic orange pigments such as Orange Pigment-C It is considered that the dispersibility of the pigment having the above can be improved. Similarly, since the highly polar photopolymerizable compound has a high affinity with an azo derivative containing a polar moiety, it is considered that the dispersibility of a pigment having an azo derivative can be improved. Therefore, it is considered that the highly polar photopolymerizable compound makes it easy for the azo derivative to be present in the vicinity of the surface of the basic orange pigment, and as a result, can reduce the electronic interaction between the pigment and the gelling agent in the ink. It is done. By reducing the interaction between the pigment and the gelling agent, the sol-gel phase transition, which is the original function of the gelling agent, can proceed without being affected by other compounds in the ink. Even with a small amount of gelling agent, it is considered that glossiness can be improved by the function of phase transition.

Further, according to the knowledge of the present inventors, the highly polar photopolymerizable compound has a high ability to disperse the pigment even at a temperature of 60 ° C. or higher, which is the temperature at which the orange ink is emitted from the inkjet head. It is considered that nozzle missing due to deposition can be made difficult to occur.

From the viewpoint of sufficiently achieving the above effects, the content of the highly polar photopolymerizable compound is 30% by mass or more based on the total mass of the photopolymerizable compound. From the viewpoint of making it difficult for the gelling agent having a nonpolar part to precipitate during image formation and to make the surface of the image more glossy, the content of the highly polar photopolymerizable compound is the total mass of the photopolymerizable compound. It is preferable to set it as 30 mass% or more and 80 mass% or less with respect to 50 mass% or more and 70 mass% or less.

Examples of commercially available highly polar photopolymerizable compounds include the products listed in Table 1. In Table 1, “Number of EO groups or PO groups” represents the number of EO groups or PO groups contained in one molecule of the product represented by the brand. In Table 1, “New Frontier” is a registered trademark of Daiichi Kogyo Seiyaku Co., Ltd., and “Fankrill” is a registered trademark of Hitachi Chemical Co., Ltd.

1-2-3-2. Photopolymerizable compound The low-polarity photopolymerizable compound is a photopolymerizable compound in which the total number of EO groups and PO groups is less than six.

Examples of low-polarity photopolymerizable compounds that are (meth) acrylates include monofunctional (meth) acrylates, bifunctional (meth) acrylates, and trifunctional or higher functional (meth) acrylates.

From the viewpoint of making the phase separation between the photopolymerizable compound and the gelling agent less difficult during image formation and making the surface of the image less glossy, the low-polarity photopolymerizable compound has an EO group, a PO group, and the like. It is preferable to have a polar structure.

Examples of low-polarity photopolymerizable compounds having a polar structure include the products listed in Table 2. In Table 2, “Number of EO groups or PO groups” represents the number of EO groups or PO groups contained in one molecule of the product represented by the brand. In Table 1, “Aronix” is a registered trademark of Toagosei Co., Ltd., and “Miramar” is a registered trademark of Bigen Specialty Chemical Co., Ltd.

1-2-4. Other Components The dispersant, gelling agent, and photopolymerization initiator contained in the orange ink can be the same compound as the magenta ink. Orange ink contains the same compound as magenta ink as a photopolymerizable compound, a dispersant, a gelling agent and a photopolymerization initiator from the viewpoint of increasing the affinity between inks and forming a higher definition image. It is preferable to do. The amount of the gelling agent contained in the orange ink can be 1.0% by mass or more and 10.0% by mass or less with respect to the total mass of the ink. By setting the content of the gelling agent to 1.0% by mass or more, the pinning property of the ink can be sufficiently increased, a higher definition image can be formed, and the wetting and spreading of the ink can be reduced. The gloss of the image can be made closer to the gloss of the image with other ink. In addition, by enhancing the pinning properties of the ink, it is possible to reduce the occurrence of color shortage due to the ink entering the inside of the base material, particularly when an image is formed on the water-absorbing base material. It becomes easy to form an image. By making the content of the gelling agent 10.0% by mass or less, it becomes difficult for the gelling agent to deposit on the surface of the formed image, and the gloss of the image can be made closer to the gloss of the image by other ink, In addition, the ink ejectability from the ink jet head can be further enhanced. From the above viewpoint, the content of the gelling agent in the orange ink is preferably 1.0% by mass or more and 5.0% by mass or less, and 2.5% by mass or more and 5.0% by mass or less. Is more preferable, and it is further more preferable that it is 2.5 mass% or more and 4.0 mass% or less.

From the viewpoint of further improving the ejection properties from the inkjet head and improving the miscibility with the magenta ink after landing, the viscosity of the orange ink at 80 ° C. is 8.0 mPa · s or more and 9.5 mPa · s or less. preferable. From the above viewpoint, the viscosity of the orange ink at 80 ° C. is more preferably 8.5 mPa · s or more and 9.0 mPa · s or less.

From the viewpoint of further improving the ejection properties from the inkjet head, the average particle size of the pigment particles contained in the orange ink is preferably 0.13 μm or more and 0.22 μm or less. From the above viewpoint, the average particle diameter of the pigment particles contained in the orange ink is preferably 0.14 μm or more and 0.16 μm or less.

The other physical properties of the orange ink are preferably in the same range as the magenta ink described above for the same reason as the magenta ink.

1-3. Combination of Magenta Ink and Orange Ink The ink set of the present invention contains at least magenta ink-A or orange ink-C. That is, it is sufficient that the color gamut expansion in a good color gamut, particularly in the red color region such as Pantone Red 032, is achieved by magenta ink-A or orange ink-C. When it is included, the orange ink may be either orange ink-C or orange ink-D. When the ink set of the present invention includes orange ink-C, the magenta ink may be either magenta ink-A or magenta ink-B. . Further, from the viewpoint of image formation with good pinning properties and good glossiness, the ink set of the present invention is more preferably an ink set containing magenta ink-A and orange ink-C.

1-4. Other inks An ink set contains a pigment, a photopolymerizable compound, a dispersant, a gelling agent, and a photopolymerization initiator other than the magenta ink or orange ink, and is cured by irradiation with actinic rays (hereinafter simply referred to as an ink set) (It is also referred to as “other ink”.). For example, when the ink set further includes yellow ink, cyan ink, and black ink, a full-color image can be formed.

The pigment contained in the yellow ink may be any pigment that can be yellowed on the ink that has landed and cured on the recording medium. Examples of such pigments include C.I. I. Pigment Yellow (hereinafter, also simply referred to as “Pigment Yellow”) 1, Pigment Yellow 3, Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 37, Pigment Yig 34 55, Pigment Yellow 74, Pigment Yellow 81, Pigment Yellow 83, Pigment Yellow 93, Pigment Yellow 94, Pigment Yellow 95, Pigment Yellow 97, P gment Yellow 108, Pigment Yellow 109, Pigment Yellow 110, Pigment Yellow 137, Pigment Yellow 138, Pigment Yellow 139, Pigment Yellow 153, Pigment Yellow 154, Pigment Yellow 155, Pigment Yellow 157, Pigment Yellow 166, Pigment Yellow 167, Pigment Yellow 168, Pigment Yellow 180, Pigment Yellow 185, and Pigment Yellow 193 are included. Only one kind of these pigments may be contained in the yellow ink, or two or more kinds thereof may be contained.

The pigment contained in the cyan ink may be any pigment that can give a cyan color when the ink landed on the recording medium and cured. Examples of such pigments include C.I. I. Pigment Blue (hereinafter, also simply referred to as “Pigment Blue”) 1, Pigment Blue 15, Pigment Blue 15: 1, Pigment Blue 15: 2, Pigment Blue 15: 3, Pigment 15: 4, Blue 15: 4 Includes Pigment Blue 16, Pigment Blue 17-1, Pigment Blue 22, Pigment Blue 27, Pigment Blue 28, Pigment Blue 29, Pigment Blue 36, and Pigment Blue 60. Only one kind of these pigments may be contained in the cyan ink, or two or more kinds thereof may be contained.

The pigment contained in the black ink is not particularly limited as long as the ink that has landed on the recording medium and cured can exhibit a black color. Examples of such pigments include C.I. I. Pigment Black (hereinafter, also simply referred to as “Pigment Black”) 7 (carbon black), Pigment Black 28, and Pigment Black 26 are included. Only one kind of these pigments may be contained in the black ink, or two or more kinds thereof may be contained.

The photopolymerizable compound, the dispersant, the gelling agent, and the photopolymerization initiator contained in the other ink can be the same compound as the magenta ink. From the viewpoint of increasing the affinity between the inks and forming a higher-definition image, other inks use the same compound as magenta ink as a photopolymerizable compound, a dispersant, a gelling agent, and a photopolymerization initiator. It is preferable to contain. From the viewpoint of forming a higher-definition image, bringing the gloss of the image closer to the gloss of the image by other ink, and further improving the ink ejection properties from the inkjet head, the content of the gelling agent in the other ink is , And 1.5 mass% or more and 3.0 mass% or less with respect to the total mass of the ink. From the above viewpoint, the content of the gelling agent in the other ink is preferably 2.0% by mass or more and 2.5% by mass or less.

1-5. Preparation of ink The above magenta ink, orange ink and other inks are prepared by mixing the above-described pigment, dispersant, gelling agent, photopolymerizable compound and photopolymerization initiator with any of the components under heating. Can be obtained. It is preferable to filter the obtained liquid mixture with a predetermined filter. At this time, a pigment dispersion in which a pigment and a dispersant are dispersed in a solvent may be prepared in advance, and the remaining components may be added thereto and mixed while heating.

The pigment and the dispersant can be dispersed by, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker.

2. Image Forming Method The image forming method of the present invention is known in that the magenta ink and orange ink are ejected from an inkjet head and landed on a recording medium and cured, except that the magenta ink and orange ink included in the ink set described above are used. The image forming method can be performed in the same manner.

For example, the image forming method of the present invention includes a first step of ejecting magenta ink and orange ink included in the ink set from a nozzle of an inkjet head and landing on a recording medium, and the landed magenta ink and orange ink. And a second step of curing the magenta ink and the orange ink by irradiating with an actinic ray.

2-1. First Step In the first step, magenta ink and orange ink droplets are ejected from an inkjet head and landed on a position corresponding to an image to be formed on a recording medium. For example, both orange ink and magenta ink are landed at a position where an intermediate color of orange and magenta is formed. Either orange ink or magenta ink may be ejected first.

The ejection method from the inkjet head may be either an on-demand method or a continuous method. On-demand inkjet heads include electro-mechanical conversion methods such as single cavity type, double cavity type, bender type, piston type, shear mode type and shared wall type, as well as thermal inkjet type and bubble jet. Any of electric-thermal conversion methods such as Canon Inc. registered trademark) may be used.

Ink droplets can be ejected from an inkjet head in a heated state to improve ejection stability. The temperature of the ink when ejected is preferably 35 ° C. or more and 100 ° C. or less, and more preferably 35 ° C. or more and 80 ° C. or less in order to further improve the ejection stability. In particular, the emission is preferably performed at an ink temperature such that the viscosity of the ink is 7 mPa · s or more and 15 mPa · s or less, more preferably 8 mPa · s or more and 13 mPa · s or less.

The sol-gel phase transition type ink has an ink temperature of (gelation temperature + 10) ° C. to (increase temperature) of the ink when filled in the ejection recording head in order to improve the ejection property of the ink from the ejection recording head. The gelling temperature is preferably set to +30) ° C. When the temperature of the ink in the ejection recording head is less than (gelation temperature + 10) ° C., the ink is gelled in the ejection recording head or on the nozzle surface, and the ink ejection property is likely to deteriorate. On the other hand, when the temperature of the ink in the ejection recording head exceeds (gelation temperature + 30) ° C., the ink becomes too high, and the ink component may deteriorate.

The method for heating the ink to a predetermined temperature is not particularly limited. For example, at least one of an ink tank constituting the head carriage, an ink supply system such as a supply pipe and an anterior chamber ink tank just before the head, a pipe with a filter, a piezo head, etc., is used among a panel heater, a ribbon heater, and warm water Either can be heated to a predetermined temperature.

The amount of ink droplets when ejected is preferably 2 pL or more and 20 pL or less from the viewpoint of recording speed and image quality.

2-2. Second Step In the second step, the magenta ink and orange ink landed in the second step are irradiated with active energy rays to form an image formed by curing these inks. The active energy ray is preferably irradiated for 0.001 second or more and 1.0 second or less after ink landing. In order to form a high-definition image, 0.001 second or more and 0.5 second or less. It is more preferable to irradiate in between.

The active energy ray applied to the ink can be selected from, for example, an electron beam, an ultraviolet ray, an α ray, a γ ray, an X-ray, etc. Among them, it is preferable to irradiate the ultraviolet ray. Ultraviolet rays can be irradiated by, for example, 395 nm, a water-cooled LED, manufactured by Phoseon Technology. By using the LED as the light source, it is possible to suppress the occurrence of poor curing of the ink due to the melting of the ink by the radiant heat of the light source.

The LED light source is installed so that the peak illuminance on the image surface of ultraviolet rays having a wavelength of 370 nm to 410 nm is 0.5 W / cm ^{2 to} 10 W / cm ² and is 1 W / cm ^{2 to} 5 W / cm ^2. It is more preferable to install so that it becomes. From the viewpoint of suppressing the radiant heat from being applied to the ink, the amount of light applied to the image is preferably less than 350 mJ / cm ² .

In addition, the irradiation of active energy rays is divided into two stages. First, after the ink has landed, the active energy rays are irradiated by the above-described method between 0.001 second and 2.0 seconds to temporarily cure the ink. After the printing, the ink may be further cured by irradiating an active energy ray. By dividing the irradiation of the active energy ray into two stages, the shrinkage of the recording material that occurs during ink curing is less likely to occur.

In the image forming method of the present invention, when the total ink film thickness after irradiating the ink landed on the recording medium with an active energy ray and being cured is 2 μm or more and 20 μm or less, the curling and wrinkle of the recording medium Occurrence and change in texture of the recording medium can be prevented more efficiently. The “total ink film thickness” is the total value of the film thicknesses of all inks applied or printed on the recording medium, or the film thickness measured at a plurality of points where the ink landing amount is expected to be large. Mean value.

[recoding media]
The recording medium used in the image forming method of the present invention is only required to form an image with the ink set. For example, polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene Non-absorbent recording media (plastic base) composed of plastics such as copolymers, polyethylene terephthalate and polybutadiene terephthalate, non-absorbing inorganic recording media such as metals and glass, and absorbent papers (for example, , Coated paper for printing and coated paper for printing B).

Hereinafter, the present invention will be described in more detail with reference to examples, but the scope of the present invention is not construed as being limited by these descriptions.

[Example 1]
1-1. Magenta ink 1-1-1. Surface Treatment of Magenta Pigment The following untreated magenta pigment (hereinafter also referred to as “magenta pigment before treatment”), which is a solid solution of Pigment Violet 19 and Pigment Red 202, was surface treated with alumina and sulfonic acid.

[Magenta pigment before treatment]
CINQUASIA Magenta L4540, manufactured by BASF (Pigment Violet 19 / Pigment Red 202 ratio: 50/50)
CINQUASIA Magenta D4500J, manufactured by BASF (Pigment Violet 19 / Pigment Red 202 ratio: 60/40)
228-2120, manufactured by Sun Chemical (Pigment Violet 19 / Pigment Red 202 ratio: 70/30)
Cinquasia Red K4330, manufactured by BASF (Pigment Violet 19 / Pigment Red 202 ratio: 80/20)

To an aqueous solution in which 1.0 kg of magenta pigment (L4540, manufactured by BASF) before treatment was added to water and stirred and dispersed, an aqueous sodium hydroxide solution was added to adjust the pH to 10. To this aqueous solution, an aqueous solution of sodium aluminate (manufactured by Wako Pure Chemical Industries, Ltd.) in an amount of 0.5 parts in terms of aluminum hydroxide (Al (OH) ₃ ) was added to 100 parts of the pigment and mixed with stirring. Thereafter, the pH was adjusted to 6 by adding an aqueous acetic acid solution with further stirring. Immediately after the pH reached 6, the aqueous solution was filtered, and the resulting solid was washed with water and dried to obtain an alumina-treated magenta pigment powder. Based on the amount of Al element contained in the pigment powder measured by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometer (device name), manufactured by SII Nanotechnology), 5000 ppm of alumina was applied to the magenta pigment powder. It was calculated that

The alumina-treated magenta pigment prepared above was dispersed in 2-pyrrolidone as a solvent. The dispersion is transferred to a container capable of vacuum degassing, heated to 100-120 ° C. while reducing the pressure to 50 Torr (6.67 Pa) or less with an aspirator, and water contained in the system is removed as much as possible. Controlled to ° C. To this dispersion, sulfur trioxide (sulfuric anhydride, manufactured by Nippon Soda Co., Ltd.) as a sulfonating agent in an amount of 0.15 part with respect to 100 parts of magenta pigment was added and stirred for 2 to 3 hours. The surface-treated magenta pigment obtained by filtering this was washed several times with excess 2-pyrrolidone, poured into water, and then filtered to obtain magenta pigment 1 for ink. Based on the amount of S element contained in the magenta pigment 1 ink ink measured by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometer (device name, manufactured by SII Nano Technology)), 1500 ppm of sulfonic acid is magenta for ink. It was calculated that it was imparted to Pigment 1.

Except for changing the magenta pigment before the treatment according to Table 3, and changing the amount of sodium aluminate so that the amount of alumina applied to the magenta pigment powder is the amount shown in Table 3, the same procedure was followed. Thus, magenta pigments for inks 2 to 10 and 13 having different amounts of alumina and sulfonic acid were prepared. On the other hand, the magenta pigment 11 for ink was subjected to surface treatment with alumina, but was not subjected to surface treatment with sulfonic acid.

The magenta pigment 12 for ink was not subjected to surface treatment with alumina or sulfonic acid. When the powder of the magenta pigment 12 for ink was measured by ICP-AES, only the Al element (usually about 1 to 15 ppm) and the S element (usually about 20 to 30 ppm) originally contained in the pigment were quantified.

Table 3 shows the physical properties of the untreated magenta pigment and the ink magenta pigments 1 to 13 used for the ink magenta pigments 1 to 12.

1-1-2. Preparation of Magenta Pigment Dispersion Put magenta pigment 1 for ink, photopolymerizable compound, dispersant and polymerization inhibitor into 200 ml of polybin, and add 120 g of zirconia beads with a diameter of 0.5 mmφ into it, and close the lid. Then, the mixture was dispersed for 4 hours with a vibration mill (Red Devil 4500L, manufactured by Nishimura Seisakusho). After dispersion, the beads were separated and the dispersion was taken out to obtain a magenta pigment dispersion 1a.
Magenta pigment for ink 1: 9.0 g
Photopolymerizable compound: 32.7 g of tripropylene glycol diacrylate
Dispersant: BYK Jet-9151, manufactured by Big Chemie Co., 3.2 g
Polymerization inhibitor: Irgastab UV-10, manufactured by BASF ("Irgastab" is a registered trademark of the company) 0.1 g

Magenta pigment dispersions 2a to 13a were prepared by the same procedure except that the magenta pigment 1 for ink was changed to magenta pigments 2 to 13 for ink.

1-1-3. Preparation of Magenta Ink After adding the following photopolymerizable compound, surfactant, photopolymerization initiator and gelling agent to magenta pigment dispersion 1 heated to 60 ° C., WAC filter (accuracy of 0.3 μm), Paul Corporation Then, magenta ink 1a was prepared by filtration.
Magenta pigment dispersion 1a: 20.0 g
Photopolymerizable compound: polyethylene glycol 600 diacrylate 6.2 g
Photopolymerizable compound: 3PO-modified trimethylolpropane triacrylate 6.2g
Surfactant: TSF-4442, manufactured by Shin-Etsu Chemical Co., Ltd. 0.3g
Photopolymerization initiator: Irgacure 819, manufactured by BASF (“Irgacure” is a registered trademark of the company) 0.3 g
Photopolymerization initiator: DAROCUR TPO, manufactured by BASF ("DAROCUR" is a registered trademark of the company) 0.3g
Gelling agent: Kao wax T-1, made by Kao Corporation

Magenta inks 2a to 13a were prepared in the same manner as magenta ink 1 except that magenta pigment dispersion 1a was changed to magenta pigment dispersions 2a to 13a.

For magenta inks 1a to 13a, inks were prepared as needed so that the content of the gelling agent in the ink was 0.5% to 6.0% by mass of the total mass of the ink.

1-2. Orange inks Orange inks 1a to 6a were prepared in the same manner as magenta ink 1a, except that magenta pigment 1 for ink was changed to the following orange pigments 1 to 6.

[Orange pigment]
Orange Pigment 1: Pigment Orange 36
Orange Pigment 2: Pigment Orange 71
Orange Pigment 3: Pigment Orange 64
Orange Pigment 4: Pigment Orange 16
Orange Pigment 5: Pigment Orange 34
Orange Pigment 6: Pigment Orange 38

1-2-1. Preparation of orange pigment dispersion Orange pigment 1, a photopolymerizable compound, a dispersant and a polymerization inhibitor are placed in 200 ml of polybin, 120 g of zirconia beads having a diameter of 0.5 mmφ are further placed therein, and the lid is closed. It was dispersed for 5 hours with a vibration mill (Red Devil 4500L, manufactured by Nishimura Seisakusho). After dispersion, the beads were separated and the dispersion was taken out to obtain Orange Pigment Dispersion 1.
Orange pigment 1: 8.5g
Pigment derivative: Solsperse 22000 (sulfonated Pigment Yellow 12) 0.5 g
Photopolymerizable compound: 32.7 g of tripropylene glycol diacrylate
Dispersant: BYK Jet-9151, manufactured by Big Chemie Co., 3.2 g
Polymerization inhibitor: Irgastab UV-10, manufactured by BASF ("Irgastab" is a registered trademark of the company) 0.1 g

Orange pigment dispersions 2a to 6a were prepared by the same procedure except that orange pigment 1 was changed to orange pigments 2 to 6.

1-2-2. Preparation of orange ink After adding the following photopolymerizable compound, surfactant, photopolymerization initiator and gelling agent to orange pigment dispersion 1a heated to 60 ° C., WAC filter (accuracy of 0.3 μm), Paul Corporation The orange ink 1a was prepared by filtration.
Orange pigment dispersion 1a: 5.0 g
Photopolymerizable compound: polyethylene glycol 600 diacrylate 10.5 g
Photopolymerizable compound: 3PO-modified trimethylolpropane triacrylate 4.5 g
Surfactant: TSF-4442, manufactured by Shin-Etsu Chemical Co., Ltd. 0.3g
Photopolymerization initiator: Irgacure 819, manufactured by BASF (“Irgacure” is a registered trademark of the company) 0.3 g
Photopolymerization initiator: DAROCUR TPO, manufactured by BASF ("DAROCUR" is a registered trademark of the company) 0.3g
Gelling agent: Kao wax T-1, made by Kao Corporation

Orange inks 2a to 6a were prepared in the same manner as the orange ink 1a except that the orange pigment dispersion 1a was changed to orange pigment dispersions 2 to 6.

For the orange inks 1a to 6a, inks were prepared as needed so that the gelling agent content in the ink was 0.5% to 6.0% by mass of the total mass of the ink.

1-3. Preparation of yellow ink, cyan ink and black ink Yellow ink is the same as orange ink 1 except that orange pigment 1 is changed to PY185 (yellow pigment), Pigment Blue 15: 4 (cyan pigment) and Pigment Black 7 (black pigment). A cyan ink and a black ink were prepared.

For each of the yellow ink, the cyan ink, and the black ink, an ink was prepared such that the gelling agent content in the ink was 0.5% to 6.0% by mass of the total ink.

1-4. Ink set Magenta ink and orange ink are combined as shown in Tables 4-5, and all the inks contained in the ink set contain any amount of gelling agent shown in Tables 4-5. Magenta ink, orange ink, yellow ink, cyan ink and black ink were combined to form ink sets 1-1 to 1-36.

Tables 4 to 5 show the combinations of magenta ink and orange ink contained in each ink set, and the amount of gelling agent contained in the ink contained in the ink set.

1-5. Evaluation Method and Evaluation Results The storage stability and pinning property of each ink set, and the gloss difference and color gamut difference between the image of each ink set and other images were evaluated according to the following criteria.

1-5-1. Storage Stability For the pigment particles contained in the magenta ink and orange ink contained in the ink sets 1-1 to 1-36, the average particle diameter of each ink diluted 200 times with polyethylene glycol diacrylate (PEGDA) is determined by the data sizer. Measurements were made by dynamic light scattering using Nano ZSP, Malvern. Each actinic ray curable ink was collected in a heat-resistant tube and stored in a high-temperature bath at 50 ° C. for 6 weeks. The average particle size of the pigment particles were measured in the same manner in each of the ink after storage, the difference between the average particle size after storage for the average particle diameter before storage _{_{(P A) (P B)}} (P A -P B) Was calculated.
A The difference in average particle size of both magenta ink and orange ink is less than 7 nm B The difference in average particle size of either magenta ink or orange ink is 7 nm or more and less than 15 nm C Average particle of either magenta ink or orange ink Difference in diameter is 15 nm or more D Difference in average particle diameter of both magenta ink and orange ink is 15 nm or more

1-5-2. Pinning Ink sets 1-1 to 1-36 were introduced into the inkjet head HA512 type (manufactured by Konica Minolta). Natural images (issued by the Japan Standards Association) under the conditions of a printing width of 100 mm x 100 mm and a resolution of 720 x 720 dpi High-definition color digital standard image data “fruit basket”) was landed on a printing substrate at 50 ° C. and printed using YMCKO's five-color ink. An OK top coat (printing paper) was used as a printing substrate. An LED lamp was used as a UV irradiation light source, and the ink was cured by irradiating the ink printed with ultraviolet rays with an energy of 250 mJ.

The above-mentioned images of the respective actinic ray curable inks were observed with a microscope (× 200), and the average value of 100 droplet sizes selected at random was determined.
A Average value is less than 45 μm, variation in droplet diameter is 10 μm or less B Average value is less than 45 μm C Average value is from 45 μm to 50 μm D Average value is greater than 50 μm E Average value from 50 μm Large, variation in droplet diameter is 10 μm or less

1-5-3. Gloss difference For each ink set, magenta ink and orange ink were heated to 50 ° C on a printing substrate, and the 60 ° C reflection gloss value of a solid image formed at a printing rate of 100% was measured with a digital handy gloss meter (Gloss Checker IG- 331, manufactured by HORIBA, Ltd.). The difference between the reflection gloss value (40) determined as a preferable value from the viewpoint of enhancing the aesthetics of the image and the reflection gloss value of the magenta and orange solid images included in the respective actinic ray curable ink sets was examined.
A The absolute value of the difference between the reflection gloss value of both magenta and orange magenta inks and the reflection gloss value (40) is less than 3.0 B. The reflection gloss value of either magenta or orange magenta ink and the above reflection gloss The absolute value of the difference from the value (40) is 3.0 or more and less than 5.0 C The absolute value of the difference between the reflection gloss value of the magenta ink of either magenta or orange and the reflection gloss value (40) is 5 0 or more D The absolute value of the difference between the reflection gloss value of either magenta or orange magenta ink and the reflection gloss value (40) is 5.0 or more.

1-5-4. Color Gamut Difference Pantone Red 032 and Pantone Orange 021 were measured with an ink set described in 1-5-2 by a portable integrating sphere spectrophotometer Ci6x, manufactured by X-lite, and a *, b * Got the value. Calculate the square root of the sum of the square of the difference of each a * value and the square of the difference of each b * value, and the color gamut difference between the image by each ink set and the standard sample It was.
The color gamut difference of both A Pantone Red 032 and Pantone Orange 021 is less than 1.0. The color gamut difference of either B Pantone Red 032 and Pantone Orange 021 is 1.0 or more and 2.0 or less. C Pantone Red 032 and The color gamut difference of either Pantone Orange 021 is greater than 2.0. The color gamut difference of both D Pantone Red 032 and Pantone Orange 021 is greater than 2.0.

1-5-5. Results The results are shown in Tables 6-8.

An ink set containing magenta ink in which the amount of alumina in the magenta pigment for ink is 1500 ppm or more and 7500 ppm or less by mass ratio to the magenta pigment and surface-treated with sulfonic acid has high storage stability, gloss difference and color An image with a small area difference could be formed. Further, when the content of the gelling agent in each ink included in the ink set is 1% by mass or more and 5% by mass or less based on the mass of the ink, the ink pinning property can be improved.

When the ratio of Pigment Violet 19 and Pigment Red 202 contained in the magenta pigment is within the range of 60/40 to 70/30, the color gamut difference with Pantone® Red 032 is further reduced. Furthermore, when an ink set containing magenta ink-A and orange ink-C is used, an image close to Pantone Red 032 and Pantone Orange 021 can be formed, and red to orange in the L * a * b * color space. The color gamut that can be expressed as the ink set of the area was expanded.

[Example 2]
2-1. Preparation of Ink Using one of the orange pigments shown in Table 9, one of the pigment derivatives shown in Table 10, two of the photopolymerizable compounds shown below, a gelling agent, and other materials, the ink Was prepared.

2-1-1. Pigment

2-1-2. Pigment derivative

2-1-3. Photopolymerizable compound [Highly polar photopolymerizable compound]
PEG400DA: Polyethylene glycol 400 diacrylate (A-400, manufactured by Shin-Nakamura Chemical Co., Ltd., number of ethylene oxide groups: 9)
FA-137M: EO-modified trimethylolpropane trimethacrylate (FA-137M, manufactured by Hitachi Chemical Co., Ltd., number of ethylene oxide groups: 21)
[Low polarity photopolymerizable compound]
BPP-4: PO-modified bisphenol A diacrylate (New Frontier BPP-4, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., number of propylene oxide groups: about 4)
TPGDA: Tripropylene glycol diacrylate (Aronix M220, Toagosei Co., Ltd.)

2-1-4. Gelling agent T1: Kao wax T-1, manufactured by Kao Corporation

2-1-5. Other materials [Polymerization inhibitor]
UV10: Irgastab UV-10, manufactured by BASF ("Irgastab" is a registered trademark of the company)
ITX: ITX, manufactured by BASF 819: Irgacure 819, manufactured by BASF ("Irgacure" is a registered trademark of the company)
TPO: DAROCUR TPO, manufactured by BASF (DAROCUR is a registered trademark of BASF)
[Dispersant]
BYK Jet-9151, manufactured by Big Chemie

2-1-6. Preparation of orange ink The following ingredients were prepared to a total of 100 parts by mass, placed in a 250 ml pot together with 120 g of zirconia beads having a diameter of 0.5 mmφ, the lid was closed, and a vibration mill (Red Devil 4500L, manufactured by Nishimura Seisakusho) For 5 hours. After the dispersion, the beads were separated and the dispersion was taken out to obtain an orange pigment dispersion 1b.
Orange pigment: Pigment Orange 36 18.0 parts by weight Polymerization inhibitor: UV10 0.1 part by weight Dispersant: 9151 6.0 parts by weight Pigment derivative: 1S-1 0.18 part by weight Photopolymerizable compound: BPP-4 balance

Then, while heating the dispersion to 60 ° C., the following gelling agent and photopolymerization initiator were added so that the following ratio was obtained, and the weight ratio of the high polarity photopolymerizable compound and the low polarity photopolymerizable compound: An orange ink having a ratio of 30:70 was prepared. This orange ink was used as the orange ink of ink set 2-1.
Pigment dispersion: Orange pigment dispersion 12.0 parts by mass Photopolymerizable compound: FA-137M 24.3 parts by mass Photopolymerizable compound: BPP-4 56.7 parts by mass Surfactant: TSF-4442 0.3 parts by mass Parts Gelling agent: T-1 3.0 parts by weight Photopolymerization initiator: ITX 1.0 part by weight Photopolymerization initiator: 819 2.0 parts by weight Photopolymerization initiator: TPO 2.0 parts by weight Orange pigment, light In the same manner as in the orange ink 1b except that the type and ratio of the polymerizable compound and the type and amount of the gelling agent or pigment derivative were changed to the combinations or values shown in Tables 11 to 13, An ink was prepared. These orange inks were used as the inks of ink sets 2-2 to 2-42.

2-1-7. Preparation of magenta ink The following ingredients were prepared to a total of 100 g, put into a 250 ml pot together with 120 g of zirconia beads having a diameter of 0.5 mmφ, tightened with a lid, and 5 with a vibration mill (Red Devil 4500L, manufactured by Nishimura Seisakusho). Time dispersed. After dispersion, the beads were separated and the dispersion was taken out to obtain a magenta pigment dispersion.
Magenta pigment: Magenta pigment 13 18.0 parts by weight Polymerization inhibitor: UV10 0.1 part by weight Dispersant: 9151 6.0 parts by weight Pigment derivative: 1S-1 0.18 parts by weight Photopolymerizable compound: BPP-4 balance

Then, while heating the dispersion to 60 ° C., the following gelling agent and photopolymerization initiator were added so that the following ratio was obtained, and the weight ratio of the high polarity photopolymerizable compound and the low polarity photopolymerizable compound: A magenta ink 1b having a ratio of 30:70 was prepared. This magenta ink was used as the magenta ink of ink set 2-1.
Pigment dispersion: Magenta pigment dispersion 12.0 parts by weight Photopolymerizable compound: FA-137M 24.3 parts by weight Photopolymerizable compound: BPP-4 56.7 parts by weight Surfactant: TSF-4442 0.3 parts by weight Parts Gelling agent: T-1 3.0 parts by weight Photopolymerization initiator: ITX 1.0 part by weight Photopolymerization initiator: 819 2.0 parts by weight Photopolymerization initiator: TPO 2.0 parts by weight Except for the type of magenta pigment and the pigment derivative, a magenta ink was prepared in the same manner under the same conditions as the orange ink with the same number and ratio of the photopolymerizable compound and the gelling agent content. These magenta inks were used as magenta inks of ink sets 2-2 to 2-42.

2-1-8. Preparation of yellow ink, cyan ink and black ink Pigment in Orange Ink 1 is changed to Pigment YELLOW 185 (yellow pigment), Pigment Blue 15: 4 (cyan pigment) and Pigment Black 7 (black pigment) The yellow ink 1b, the cyan ink 1b and the black ink are the same as the orange ink except that the photopolymerizable compound type and ratio, and the gelling agent content are the same as the orange ink of the same number. Ink 1b was prepared respectively. Ink sets 2-1 to 2-42 were obtained by combining yellow ink 1b, cyan ink 1b, and black ink 1b with orange ink and magenta ink having pigments described in Tables 11 to 13.

Tables 11 to 13 show the types of orange pigments, types and contents of photopolymerizable compounds, ratios of highly polar photopolymerizable compounds, contents of gelling agents, and types and contents of pigment derivatives in each ink. Indicates the amount. In Tables 11 to 13, the numerical values described in the columns of “high polar photopolymerizable compound” and “low polar photopolymerizable compound” are the amounts of the respective photopolymerizable compounds relative to the total mass of the photopolymerizable compound ( The numerical value described in the column “ratio of highly polar photopolymerizable compound” is the amount (mass%) of the highly polar photopolymerizable compound relative to the total mass of the photopolymerizable compound. In Tables 11 to 13, the numerical value described in the column of “gelling agent content” is the amount (mass%) of the gelling agent with respect to the total mass of each ink. The numerical value described in the column “” is the amount (mass%) of the pigment derivative with respect to the mass of the pigment contained in each ink.

2-2. Evaluation Method and Evaluation Results The storage stability and pinning property of each ink set, and the gloss difference and color gamut difference between the image of each ink set and other images were evaluated according to the same criteria as in Example 1. .

2-3. Results The results are shown in Tables 14-16.

An image formed using an ink containing a basic orange pigment and an azo derivative and having a mass ratio of the high-polarity photopolymerizable compound to the monomer composition of 30% by mass or more has a color tone from the Pantone color gamut. The deviation and the deviation from the gloss values of the other color inks were small, and the dot diameter was also in the desired range.

On the other hand, an image formed using an ink containing an orange pigment that does not have a basic site in the ring structure has a large color shift from the Pantone color gamut and a shift from the gloss value of the other color ink. This is considered to be because the orange pigment and the azo derivative could not be sufficiently associated, and the accumulation of the gelling agent on the orange pigment could not be sufficiently prevented.

Also, an image formed using an ink having a high polar photopolymerizable compound content of less than 30% by mass had a large color shift from the Pantone color gamut. This is probably because the basic orange pigment and the azo derivative could not be sufficiently associated, and the accumulation of the gelling agent on the basic orange pigment could not be sufficiently prevented by the azo derivative.

An image formed using an ink having a gelling agent content of 1.0% by mass or more had a small deviation from the gloss value of other color inks, and the dot diameter was in a desired range. This is considered to be because the ink was sufficiently pinned by the gelling agent. Further, the ink set provided with both magenta ink-A and orange ink-C according to the present invention has good storage stability, excellent pinning property, small gloss difference, and in the L * a * b * color space. An ink set having good color reproducibility in the red to orange color gamut could be provided.

The ink set of the present invention can be used to form an image having a variety of color tones and a glossiness equivalent to that of a conventional image.

This application claims priority based on Japanese application No. 2015-021455 filed on February 5, 2015 and Japanese application No. 2015-049543 filed on March 12, 2015. The contents of the claims and the specification of the application are incorporated in the present application.

Claims

An ink set comprising a plurality of types of inks containing a pigment, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator and cured by irradiation with actinic rays,
The plurality of types of ink include magenta ink and orange ink,
The pigment contained in the magenta ink was surface treated with alumina and sulfonic acid, C.I. I. Pigment Violet 19 and C.I. I. A magenta pigment containing a solid solution with Pigment Red 202;
The amount of the alumina in the magenta pigment is 1500 mass ppm or more and 7500 mass ppm or less,
The ink set, wherein the content of the gelling agent in each ink is 1% by mass or more and 5% by mass or less.
C. in the magenta pigment. I. Pigment Violet 19 and the C.I. I. The ink set according to claim 1, wherein a mass ratio with respect to Pigment Red 202 is 60/40 or more and 70/30 or less.
The ink set according to claim 1 or 2, wherein the amount of the alumina with respect to the magenta pigment is 5000 mass ppm or more and 7500 mass ppm or less.
An ink set comprising a plurality of types of inks containing a pigment, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator and cured by irradiation with actinic rays,
The plurality of types of ink include magenta ink and orange ink,
The orange ink further contains a sulfonated derivative of an insoluble azo pigment in an amount of 2.0% by mass to 15.0% by mass with respect to the mass of the pigment contained in the ink,
The pigment contained in the orange ink includes an orange pigment having a cyclic structure and having a basic site in the cyclic structure,
The photopolymerizable compound contained in the orange ink includes a photopolymerizable compound having 6 or more ethylene oxide groups or propylene oxide groups in total of 30% by mass or more based on the total mass of the photopolymerizable compound. ,
The ink set, wherein the content of the gelling agent in each ink is 1.5% by mass or more and 3.0% by mass or less.
The photopolymerizable compound having 6 or more ethylene oxide groups or propylene oxide groups in total has 2 or more segments having 3 or more ethylene oxide groups or propylene oxide groups in the molecule, The ink set according to claim 4.
The ink set according to any one of claims 1 to 5, further comprising yellow ink, cyan ink, and black ink.
An ink set comprising a plurality of types of inks containing a pigment, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator and cured by irradiation with actinic rays,
The plurality of types of ink include magenta ink and orange ink,
The pigment contained in the magenta ink was surface treated with alumina and sulfonic acid, C.I. I. Pigment Violet 19 and C.I. I. A magenta pigment containing a solid solution with Pigment Red 202;
The amount of the alumina in the magenta pigment is 1500 mass ppm or more and 7500 mass ppm or less,
The orange ink further contains a sulfonated derivative of an insoluble azo pigment in an amount of 2.0% by mass to 15.0% by mass with respect to the mass of the pigment contained in the ink,
The pigment contained in the orange ink includes an orange pigment having a cyclic structure and having a basic site in the cyclic structure,
The photopolymerizable compound contained in the orange ink includes a photopolymerizable compound having 6 or more ethylene oxide groups or propylene oxide groups in total of 30% by mass or more based on the total mass of the photopolymerizable compound. ,
The ink set, wherein the content of the gelling agent in each ink is 1.0% by mass or more and 5.0% by mass or less.
The orange ink is C.I. I. Pigment Orange 36, C.I. I. Pigment Orange 64 and C.I. I. The ink set according to any one of claims 1 to 7, further comprising at least one pigment selected from the group consisting of Pigment Orange 71.
A step of ejecting magenta ink and orange ink contained in the ink set according to any one of claims 1 to 8 from a nozzle of an inkjet head to land on a recording medium, and the landed magenta ink and orange ink Irradiating actinic rays to cure the magenta ink and orange ink.