CN117916331A

CN117916331A - Ink set

Info

Publication number: CN117916331A
Application number: CN202180102097.5A
Authority: CN
Inventors: 青山亮; 牛久正幸; 弓田正则; 渡边真也; 黑木孝彰
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2021-09-09
Filing date: 2021-09-09
Publication date: 2024-04-19
Also published as: WO2023037471A1; JPWO2023037471A1

Abstract

The ink set of the present invention is an ink set for ink jet recording comprising a first ink containing a first colorant and a second ink containing a second colorant, and is characterized in that the following conditions (1) to (3) are satisfied. (1) The content (mass%) of the first colorant in the first ink is smaller than the content (mass%) of the second colorant in the second ink. (2) The first ink contains a polymer having a viscosity in the range of 1.8 to 20 mPas measured as a 20 mass% aqueous solution at 25 ℃. (3) The ratio of the total solid content in the second ink to the total solid content in the first ink is in the range of 0.4 to 2.5 on a mass basis.

Description

Ink set

Technical Field

The present invention relates to an ink set for inkjet recording. More specifically, the present invention relates to an ink set for ink jet recording which can be applied to an ink jet head requiring a higher viscosity and which can maintain gradation or color balance of a printed image even after printing.

Background

In the conventional inkjet recording method, a method is adopted in which a low-density portion is printed with a light-color ink having a small content of a colorant, and a high-density portion is printed with a heavy-color ink having a large content of a colorant, so that gradation in a resulting printed image (hereinafter also simply referred to as "image") is smoothly reproduced. When ink for ink jet recording (hereinafter also simply referred to as "ink") adheres to a recording medium, ink dots are formed, penetrate the recording medium, spread on the recording medium surface, and a part of adjacent ink dots overlap and spread. In addition, if the colorant permeates to a deep portion of the recording medium, the optical density of the image is reduced more.

As described above, with the passage of time, the ink dots of the ink formed on the recording medium change in diameter of the ink dots of each color or the distribution of the colorant in the depth direction, and color variation occurs. Further, if the manner of spreading the coloring agent for a long time is different between the dark ink and the light ink, the gradation of the high-density portion formed with the dark ink and the gradation of the low-density portion formed with the light ink in the image become disconnected as the time after printing elapses.

That is, if the balance of the density change of the low density portion and the high density portion is broken, the gradation of the image is broken with the passage of time, and there is a problem that the smooth gradation is not obtained any more. Further, when the density of each color changes at the same speed to the same extent, the color change in the image is not noticeable, but if the balance of the density of each color is broken, the color change becomes more noticeable. When the amounts of coloring agents vary greatly between inks, even if the surface tension is made uniform by using a surfactant or the like, the penetrability between inks is not uniform, and there is a problem that the gradation and color balance of an image cannot be maintained for a long period of time.

As a method for solving the above-described problems, patent document 1 proposes a technique for controlling the ion amount in dye ink by making the surface tension between inks uniform in an ink set having a plurality of inks having different concentrations in the same hue.

On the other hand, in recent years, in order to further increase the printing speed, an industrial ink head having a discharge frequency of 35khz or more, for example, which further increases the discharge speed of ink from an ink jet head (hereinafter also simply referred to as "ink head") has been commercially available. In an industrial ink head having an improved discharge speed, generally, higher viscosity, for example, physical properties of 6mpa·s or more, is required as ink physical properties for securing discharge stability. In general, since there is an upper limit of the applicable viscosity for ink heads, when the same ink head is used among ink sets, it is necessary to make the viscosity ranges of the respective inks uniform within a certain range.

In the case where the amounts of colorants vary greatly among ink sets, the amounts of colorants also affect the viscosity of the ink, and therefore, in order to match the time-dependent expansion of the colorants among the inks and to match the viscosity required for the ink head, a careful countermeasure must be taken. For example, it is also considered to adjust the amount of the organic solvent having a relatively high viscosity such as glycerin to match the viscosity, but if the composition and amount of the organic solvent vary greatly among the inks in the ink set, it becomes difficult to match the permeation properties with time of the colorant among the inks of different colors in the ink set.

Patent document 2 describes a method of matching the viscosity between the inks of the ink set by using a thickener, but does not describe a method of maintaining the gradation and color balance with time in a printed image. As described above, there is no method of providing an ink set which can be applied to an ink head requiring a high viscosity in the prior art and which can maintain the gradation and color balance of a printed image even after the lapse of time after printing.

Prior art literature

Patent literature

Patent document 1: japanese patent No. 4182649

Patent document 2: japanese patent laid-open publication No. 2011-202029

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above-described problems and situations, and an object of the present invention is to provide an ink set for inkjet recording which can be applied to an ink head requiring a higher viscosity and which can maintain gradation or color balance of a printed image even after printing.

Means for solving the problems

In order to solve the above problems, the present inventors have found that, in the course of studies on the cause of the above problems, they: the present invention has been completed by providing an ink set including 2 types of inks having different colorant contents, wherein the ink set includes a specific polymer in an ink having a small colorant content and the total solid content of the 2 types of inks is in a specific relationship, and thereby can be applied to an ink head requiring a higher viscosity and can be used for ink jet recording in which the gradation or color balance of a printed image can be maintained even after the lapse of time after printing. That is, the above-described problems of the present invention are solved by the following means.

1. An ink set for ink jet recording comprising a first ink containing a first colorant and a second ink containing a second colorant, wherein the following requirements (1) to (3) are satisfied,

(1) The content (mass%) of the first colorant in the first ink is smaller than the content (mass%) of the second colorant in the second ink;

(2) The first ink contains a polymer having a viscosity in the range of 1.8 to 20 mPas measured as a 20 mass% aqueous solution at 25 ℃;

(3) The ratio of the total solid content in the second ink to the total solid content in the first ink is in the range of 0.4 to 2.5 on a mass basis.

2. The ink set according to claim 1, wherein the first colorant and the second colorant are homologous colors.

3. The ink set according to claim 1 or 2, wherein a ratio of a content (mass%) of the second colorant in the second ink to a content (mass%) of the first colorant in the first ink is 3.0 or more.

4. The ink set according to any one of claims 1 to 3, wherein the first colorant and the second colorant are dyes.

5. The ink set according to any one of claims 1 to 4, wherein a value of a ratio of total solid component amounts in the second ink to total solid component amounts in the first ink is in a range of 0.6 to 1.5 on a mass basis.

6. The ink set according to any one of claims 1 to 5, wherein a value of a ratio of a viscosity of the second ink at 25 ℃ to a viscosity of the first ink at 25 ℃ is in a range of 0.7 to 1.3.

7. The ink set according to any one of claims 1 to 6, wherein the first ink and the second ink each contain an organic solvent, and a difference between a content (mass%) of the organic solvent in the first ink and a content (mass%) of the organic solvent in the second ink is 10 mass% or less.

8. The ink set according to any one of claims 1 to 7, wherein the first ink and the second ink each contain an organic solvent, and wherein the content (mass%) of the organic solvent in the first ink and the content (mass%) of the organic solvent in the second ink are each 30 mass% or less.

9. The ink set according to any one of claim 1 to 8, wherein a proportion of the polymer to the total solid content amount of the first ink from which the solid content amount of the first colorant is removed is 50% by mass or more.

10. The ink set according to any one of claims 1 to 9, wherein the polymer has an anionic group.

11. The ink set according to any one of items 1 to 10, wherein the polymerization degree of the polymer is in the range of 2 to 10.

12. The ink set according to any one of claims 1 to 11, wherein the polymer contains a salt of a polycarboxylic acid or a salt of a naphthalene sulfonic acid formaldehyde condensate.

13. The ink set according to any one of claim 1 to claim 12, wherein the viscosity of the first ink at 25 ℃ and the viscosity of the second ink at 25 ℃ are each 6mpa·s or more.

ADVANTAGEOUS EFFECTS OF INVENTION

By the means of the present invention described above, it is possible to provide: the ink set can be applied to ink-jet recording ink sets which require a higher viscosity ink head and which can maintain the gradation or color balance of a printed image even after printing. The mechanism of appearance or action of the effect of the present invention is presumed as follows.

The ink set according to the present invention includes a first ink and a second ink having a larger content (mass%) of a colorant than the first ink (a necessary condition of (1): the first ink contains a specific polymer ((2) requirement), and the ratio of the total solid content of the first ink to the total solid content of the second ink is set to a value within a specific range ((3) requirement).

Specifically, the specific polymer as the essential condition of (2) is a polymer having a viscosity in the range of 1.8 to 20mpa·s measured as a 20 mass% aqueous solution at 25 ℃. In the requirement of (3), the value of the ratio of the total solid content in the second ink to the total solid content in the first ink is in the range of 0.4 to 2.5 on a mass basis. Hereinafter, a polymer having a viscosity in the range of 1.8 to 20mpa·s measured as a 20 mass% aqueous solution at 25 ℃ is also referred to as "polymer a".

As described above, in order to maintain the gradation or color balance of a printed image even when time passes after printing, it is required to match the change with time of the dot diameters of the first ink and the second ink with the saturation. In the present invention, in order to achieve this, the following constitution is formed: in the requirement of (2), the first ink is made to contain the polymer having the viscosity characteristic, and the ratio of the total solid component amount in the first ink to the total solid component amount in the second ink in the requirement of (3) is set to a value within the above range.

In order to make the change with time of the dot diameters and the permeability uniform in the first ink and the second ink, it is important to make the change in not only the surface tension of each ink but also the physical properties, the amount of the solid component and the viscosity at the time of evaporation of the water uniform. In particular, since the increase in viscosity due to the evaporation of water in the high-viscosity ink is large, and the influence of the solid content and the viscosity change is large, it is necessary that the first ink and the second ink have the same change in dot diameter with time and the same permeability.

In the ink set of the present invention, by satisfying the requirements (1) to (3), not only the surface tension in the first ink and the second ink but also the physical properties, the amount of the solid component, and the viscosity at the time of evaporation of the water are made uniform. As a result, the change with time and the permeability of the dot diameters of the first ink and the second ink can be made uniform, and as a result, the gradation or color balance of the printed image can be maintained even when the time passes after printing.

Detailed Description

The ink set of the present invention is an ink set for ink jet recording comprising a first ink containing a first colorant and a second ink containing a second colorant, and is characterized in that the following requirements (1) to (3) are satisfied.

(1) The content (mass%) of the first colorant in the first ink is smaller than the content (mass%) of the second colorant in the second ink.

(2) The first ink contains a polymer having a viscosity in the range of 1.8 to 20 mPas measured as a 20 mass% aqueous solution at 25 ℃.

This feature is common to or corresponding to the following embodiments.

As an embodiment of the present invention, in the case where the first colorant and the second colorant are homologous colors, the ink set of the present invention can further exhibit an effect related to the maintenance of the gradation property of a printed image with time.

As an embodiment of the present invention, from the viewpoint of further exhibiting the effects of the present invention, it is preferable that the ratio of the content (mass%) of the second colorant in the second ink to the content (mass%) of the first colorant in the first ink is 3.0 or more. In addition, the first colorant and the second colorant are preferably dyes.

As an embodiment of the present invention, from the viewpoint of further exhibiting the effects of the present invention, it is preferable that the value of the ratio of the total solid content in the second ink to the total solid content in the first ink is in the range of 0.6 to 1.5 on a mass basis.

As an embodiment of the present invention, from the viewpoint of further exhibiting the effects of the present invention, it is preferable that the ratio of the viscosity of the second ink at 25 ℃ to the viscosity of the first ink at 25 ℃ has a value in the range of 0.7 to 1.3.

As an embodiment of the present invention, from the viewpoint of further exhibiting the effects of the present invention, it is preferable that the first ink and the second ink each contain an organic solvent, and that a difference between the content (mass%) of the organic solvent in the first ink and the content (mass%) of the organic solvent in the second ink is 10 mass% or less. Preferably, the first ink and the second ink each contain an organic solvent, and the content (mass%) of the organic solvent in the first ink and the content (mass%) of the organic solvent in the second ink are each 30 mass% or less.

In the embodiment of the present invention, from the viewpoint of further exhibiting the effect of the present invention, the proportion of the polymer to the total solid content amount of the first ink from which the solid content amount of the first colorant is removed is preferably 50% by mass or more.

In the embodiment of the present invention, the polymer preferably has an anionic group from the viewpoint of further exhibiting the effect of the present invention. The polymerization degree of the polymer may be in the range of 2 to 10. In addition, the polymer preferably contains a salt of a polycarboxylic acid or a salt of a naphthalene sulfonic acid formaldehyde condensate.

In the embodiment of the present invention, from the viewpoint of further exhibiting the effects of the present invention, it is preferable that the viscosity of the first ink at 25 ℃ and the viscosity of the second ink at 25 ℃ are each 6mpa·s or more.

The present application and its constituent elements, and modes for carrying out the present application will be described in detail below. In the present application, "to" is used in the sense of including the numerical values described before and after the "to" as the lower limit value and the upper limit value.

[ Ink set ]

(2) The first ink contains a polymer (polymer A) and has a viscosity in the range of 1.8 to 20 mPas measured as a 20 mass% aqueous solution at 25 ℃.

The following describes the respective requirements of (1) to (3).

(1) Is the necessary condition of (2)

The ink set of the present invention includes a first ink containing a first colorant and a second ink containing a second colorant, and in the necessary conditions of (1), the content (mass%) of the first colorant in the first ink is specified to be smaller than the content (mass%) of the second colorant in the second ink.

Hereinafter, the unit of the content of the first colorant in the first ink and the unit of the content of the second colorant in the second ink are mass% unless otherwise specified.

The relationship between the first ink and the second ink in the ink set of the present invention is not particularly limited, except that the content of the first colorant and the second colorant are different.

The first colorant and the second colorant may or may not be homologous colors. In the present specification, the term "2 kinds of colorants are homologous colors" means that the values of hue angles that can be exhibited by the respective colorants are not greatly different. The allowable range of the difference in hue angle between the two varies depending on the hue. The hue angle has a specific range defined for each hue. The hue angle of 2 colorants is considered to be homologous colors if they are within the range of hue angles of the same hue.

Specifically, in the case where the 2 colorants are homologous colors of cyan, it is preferable that the hue angle in the L ^＊a^＊b^＊ color system of these 2 colorants be in the range of 215 ° to 255 °. When the 2 colorants are homologous colors of magenta, it is preferable that the hue angle in the L ^＊a^＊b^＊ color system of these 2 colorants be in the range of 320 ° to 360 ° or in the range of 0 ° to 20 °. In the case where the 2 colorants are homologous colors of yellow, it is preferable that the hue angle in the L ^＊a^＊b^＊ color system of these 2 colorants is in the range of 70 DEG to 140 deg.

When the 2 colorants are homologous colors of blue, it is preferable that the hue angle in the L ^＊a^＊b^＊ color system of these 2 colorants is in the range of 270 ° to 285 °. In the case where the 2 colorants are homologous colors of red, it is preferable that the hue angle in the L ^＊a^＊b^＊ color system of these 2 colorants is in the range of 20 DEG to 35 deg.

In the case where the first colorant and the second colorant are homologous colors, the ink set of the present invention can further exhibit an effect related to the maintenance of the gradation of the printed image with time after printing. In the case where the first colorant and the second colorant are different from each other in color, that is, in the case where the first colorant and the second colorant are different in hue, the ink set of the present invention can further exhibit the effect related to the maintenance of the color balance of the printed image with time after printing.

In inkjet recording, a plurality of hues of ink, for example, cyan, magenta, and yellow ink may be used in combination. In this case, it is preferable to use an ink set composed of the first ink and the second ink of the present invention for each hue. That is, it is preferable to use a cyan ink set in which the first colorant and the second colorant are both cyan among the first ink and the second ink satisfying the requirements (1) to (3), a magenta ink set in which the first colorant and the second colorant are both magenta among the first ink and the second ink satisfying the requirements (1) to (3), and a yellow ink set in which the first colorant and the second colorant are both yellow among the first ink and the second ink satisfying the requirements (1) to (3).

If the above-described cyan ink set, magenta ink set, and yellow ink set are used together, the resulting printed image can maintain both gray scale and color balance even after the lapse of time after printing.

According to the requirement of (1), the ratio of the content of the second colorant in the second ink to the content of the first colorant in the first ink is preferably 3.0 or more (hereinafter, this requirement is also referred to as "requirement (12)"), more preferably 3.5 or more. This reduces the graininess and enables smooth gradation reproduction. The upper limit of the value of the ratio of the content of the second colorant in the second ink to the content of the first colorant in the first ink is preferably about 10, more preferably about 5, from the viewpoint of gradation reproducibility.

The specific composition of the first ink and the second ink will be described later, but the requirement (1) is satisfied, preferably the requirement (12) is satisfied, and for example, the range of 0.5 to 10 mass% is preferable, and the range of 1 to 7 mass% is more preferable, with respect to the total amount of the first ink, in the relation to the content of the second colorant in the second ink as the content of the first colorant in the first ink. Further, the solid content of the first ink is preferably in the range of 2 to 50% by mass, more preferably in the range of 5 to 30% by mass.

In addition, as the content of the second colorant in the second ink, the requirement (1) is satisfied, preferably the requirement (12) is satisfied in relation to the content of the first colorant in the first ink, and for example, the range of 1.5 to 30 mass% is preferable, and the range of 3 to 21 mass% is more preferable, with respect to the total amount of the second ink. In addition, the range of 30 to 100 mass% is preferable, and the range of 50 to 90 mass% is more preferable, with respect to the total amount of the solid components of the second ink.

Specific examples of the first colorant and the second colorant are described below. In the following description, when it is not necessary to distinguish between the first colorant and the second colorant, that is, when they are common, they are collectively referred to as "colorant".

(Colorant)

The colorant is not particularly limited, and may be, for example, a pigment, a dye, or a pigment, and the dye has high diffusivity, so that the effect of the present invention is great. Examples of the dye include an acid dye, a direct dye, a basic dye, a reactive dye, and a food dye.

Representative dyes are listed below, but the present invention is not limited thereto.

< Direct dye >)

C.i. direct yellow 1, 4, 8, 11, 12, 24, 26, 27, 28, 33, 39, 44, 50, 58, 85, 86, 100, 110, 120, 132, 142, 144,

C.i. direct red 1、2、4、9、11、13、17、20、23、24、28、31、33、37、39、44、47、48、51、62、63、75、79、80、81、83、89、90、94、95、99、220、224、227、243、

C.i. direct blue 1、2、6、8、15、22、25、71、76、78、80、86、87、90、98、106、108、120、123、163、165、192、193、194、195、196、199、200、201、202、203、207、236、237、

C.i. direct black 2, 3, 7, 17, 19, 22, 32, 38, 51, 56, 62, 71, 74, 75, 77, 105, 108, 112, 117, 154,

< Acid dye >)

C.i. acid yellow 2,3, 7, 17, 19, 23, 25, 29, 38, 42, 49, 59, 61, 72, 99,

C.i. acid oranges 56, 64,

C.i. acid red 1, 8, 14, 18, 26, 32, 37, 42, 52, 57, 72, 74, 80, 87, 115, 119, 131, 133, 134, 143, 154, 186, 249, 254, 256,

C.I. acid violet 11, 34, 75,

C.i. acid blue 1, 7, 9, 29, 87, 126, 138, 171, 175, 183, 234, 236, 249,

C.I. acid green 9, 12, 19, 27, 41,

C.i. acid black 1,2, 7, 24, 26, 48, 52, 58, 60, 94, 107, 109, 110, 119, 131, 155,

< Reactive dye >)

C.I. active yellow 1,2, 3, 13, 14, 15, 17, 37, 42, 76, 95, 168, 175,

C.i. reactive red 2, 6, 11, 21, 22, 23, 24, 33, 45, 111, 112, 114, 180, 218, 226, 228, 235,

C.i. reactive blue 7, 14, 15, 18, 19, 21, 25, 38, 49, 72, 77, 176, 203, 220, 230, 235,

C.I. active oranges 5, 12, 13, 35, 95,

C.I. active brown 7, 11, 33, 37, 46,

C.I. active green 8, 19,

C.I. active violet 2, 4, 6, 8, 21, 22, 25,

C.i. active black 5, 8, 31, 39

< Basic dye >)

C.i. basic yellow 11, 14, 21, 32

C.i. basic reds 1,2, 9, 12, 13

C.i. basic violet 3, 7, 14

C.i. basic blue 3, 9, 24, 25

As the dye that can be used as the colorant according to the present invention, besides a dye that is a color lake and an azo dye that is used in a so-called silver-pigment-bleaching photosensitive material (for example, a device) can be mentioned.

The lake dye is described, for example, in British patent 1077484.

Azo dyes for silver pigment bleaching process photosensitive materials are described in, for example, british patent nos. 1039458, 1004957, 1077628 and us patent No. 2612448.

As the pigment that can be used as the colorant according to the present invention, conventionally known organic and inorganic pigments can be used. Examples thereof include azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments and chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, polycyclic pigments such as isoindolone pigments and quinophthalone pigments, dye lakes such as basic dye type lakes and acid dye type lakes, nitro pigments, nitroso pigments, aniline black, organic pigments such as fluorescent pigment for daylight and inorganic pigments such as carbon black.

(2) Is the necessary condition of (2)

(2) The requirement of (2) specifies that the first ink contains polymer a. In the ink set of the present invention, the above-described effects of the present invention can be achieved by containing the polymer a in the first ink among the first ink and the second ink that satisfy the requirement of (1), and satisfying the requirement of (3).

[ Polymer A ]

The polymer A is a compound having a viscosity in the range of 1.8 to 20 mPas measured as a 20 mass% aqueous solution at 25 ℃. Hereinafter, the viscosity measured as a 20 mass% aqueous solution at 25℃may be referred to as "20% aqueous solution viscosity". The polymer a is a compound capable of measuring the viscosity of a 20% aqueous solution, that is, a water-soluble compound capable of being dissolved in water at a concentration of 20 mass% or more (the content of the polymer a relative to the total amount of the aqueous solution is 20 mass% or more) at 25 ℃. In the present specification, the viscosity is 25℃unless otherwise specified. The measurement of viscosity can be performed by using, for example, an E-type viscometer.

When a polymer other than the polymer a, for example, a polymer having a 20% aqueous solution viscosity of less than 1.8mpa·s is used, the penetrability of the first ink becomes larger than the penetrability of the second ink, and the gradation or color balance cannot be maintained with time in the printed image. In addition, for example, when a polymer having a 20% aqueous solution viscosity of more than 20mpa·s is used as the polymer not falling within the range of the polymer a, the penetrability of the first ink becomes smaller than the penetrability of the second ink, and the gradation or color balance cannot be maintained with time in the printed image. The viscosity of the 20% aqueous solution of the polymer A is preferably in the range of 2 to 10 mPas, more preferably in the range of 2 to 4 mPas.

In general, a polymer is a compound obtained by polymerizing a plurality of monomers, and a unit derived from a monomer in the polymer is referred to as a polymerized unit (hereinafter also referred to as a structural unit). In the present specification, the polymer means a compound having a structural unit of 2 or more, in other words, a degree of polymerization of 2 or more. That is, the polymer includes oligomers and polymers. As the polymer a, for example, a polymer having a polymerization degree in the range of 2 to 10 can be used depending on the structural unit thereof.

In addition, the polymer a preferably has an anionic group from the viewpoint of maintaining the gradation property or color balance with time in a printed image. The anionic group is not particularly limited as long as it has a negative charge. In the present invention, from the viewpoint of dispersion stability, a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, or a carboxylic acid group is preferable, a phosphoric acid group, a sulfonic acid group, or a carboxylic acid group is more preferable, and a sulfonic acid group or a carboxylic acid group is still more preferable. As the salt, a part of the anionic group may be a salt or all of the anionic group may be a salt.

The polymer A may be used alone in an amount of 1 or in an amount of 2 or more. In addition, it is possible to use a mixture in which 2 or more polymers are combined so that the viscosity of a 20% aqueous solution is in the range of 1.8 to 20 mPas. In the present invention, as the polymer a, a polymer capable of achieving the above-mentioned 20% aqueous solution viscosity alone is preferably used.

Examples of the polymer a include polycarboxylic acids and salts thereof, condensates of sulfonated aryl compounds with formaldehyde (hereinafter referred to as "sulfonated aryl compound formaldehyde condensates") and salts thereof, polyalkylene glycols (alkylene groups are preferably alkylene groups having 2 to 3 carbon atoms), polyethylene glycol, polypropylene glycol, and the like, which satisfy the above (2).

The polymer a is preferably at least 1 selected from the group consisting of polycarboxylic acids and salts thereof, sulfonated aryl formaldehyde condensates and salts thereof satisfying the above (2) from the viewpoint of having an anionic group and the like. Examples of the salt include metal salts such as alkali metal salts and alkaline earth metal salts, and quaternary ammonium salts, and alkali metal salts, particularly sodium salts are preferable.

Among the sulfonated aryl compounds, preferred are polycyclic aromatic compounds, specifically, compounds in which 2 or more aromatic rings (including heterocyclic rings) share 2 or more carbon atoms to form condensed rings and derivatives thereof, and compounds in which 2 or more aromatic rings (including heterocyclic rings) are bonded directly or via an alkylene group and derivatives thereof.

Examples of the polycyclic aromatic compound include naphthalene, anthracene, phenanthrene, pyrene, acenaphthylene, indene, fluoranthene,Benzofluoranthene, benzopyrene, perylene, benzopyrene, fluorene, biphenyl, dibenzofuran, etc. Preferably at least 1 selected from naphthalene, anthracene, phenanthrene, pyrene, acenaphthene, and fluorene, and more preferably naphthalene. These may have a substituent. That is, as the sulfonated aryl compound, sulfonated naphthalene (naphthalene sulfonic acid) which may have a substituent is preferable.

Examples of the naphthalene sulfonic acid formaldehyde condensate and salts thereof which may have a substituent include a polymer a having at least a structural unit represented by the following general formula (I) (hereinafter also referred to as a structural unit (I)).

[ Chemical 1]

(. About.

In the formula (I), R is a substituent, X is the number of R, and 0, 1 or 2 is represented. Each M is independently a hydrogen atom, an alkali metal or a quaternary ammonium group. Examples of R include a hydroxyl group, an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, and the like. Where there are plural R's, they may be the same or different.

The polymer a having the above-mentioned structural unit (I) may contain other structural units within a range that does not impair the characteristics as the polymer a. Examples of the other structural unit include a structural unit formed from a copolymerizable monomer such as an alkyl maleic anhydride or a polycarboxylic acid. In this case, the content of other structural units is preferably 30% by mass or less based on the total amount of the polymer a.

In the polymer a having the structural unit (I), the polymerization degree is preferably in the range of 2 to 10. In this case, the term "polymerization degree" is 2 to 10, and means that the number of sulfonated naphthalene residues which may have a substituent is 2 to 10. The weight average molecular weight of the naphthalene sulfonic acid formaldehyde condensate containing the polymer a having the structural unit (I) and its salt is preferably in the range of 400 to 3000, more preferably in the range of 450 to 950. The weight average molecular weight can be measured by gel permeation chromatography (GPC method) using a polystyrene standard.

Further, as the polymer a having the structural unit (I), a salt of a naphthalene sulfonic acid formaldehyde condensate which may have a substituent (hereinafter also referred to as "compound (II)") represented by the following general formula (II) is preferable.

[ Chemical 2]

Formula (II)

In formula (II), R is as defined for formula (I), and M is each independently an alkali metal or quaternary ammonium group. x is an integer of 0 to 3, and n1 is an integer of 1 to 9.

Of the compounds (II), sodium salts of naphthalene sulfonic acid formaldehyde condensate in which M is sodium, x is 0 and n1 is 1 are particularly preferred.

The naphthalene sulfonic acid formaldehyde condensate (salt) can be produced by polycondensation using a generally known method, for example, naphthalene sulfonic acid (salt) and formaldehyde in equivalent amount and other components as needed. Examples of the other component include sulfonic acids (salts) such as β -methylnaphthalene, α -methylnaphthalene, acenaphthene, dibenzofuran, fluorene, phenanthrene, anthracene, fluoranthene, and pyrene.

As the sodium salt of the naphthalene sulfonic acid formaldehyde condensate, commercially available products such as the duel NL, the duel SS-L, the duel N, the duel MS, the duel C (trade names) manufactured by the queen corporation may be used.

Examples of polycarboxylic acids and salts thereof include polymers a having at least a structural unit represented by the following general formula (III) (hereinafter also referred to as structural unit (III)).

[ Chemical 3]

11. The method of the invention

In formula (III), R ¹～R³ are each independently a hydrogen atom or a substituent, and M are each independently a hydrogen atom, an alkali metal or a quaternary ammonium group. Examples of the substituent represented by R ¹～R³ include an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, -COOM (M means the same atom or group as described above), and-OH.

The polymer a having the above-mentioned structural unit (III) may contain other structural units within a range that does not impair the characteristics of the polymer a. Examples of the other structural unit include structural units formed from copolymerizable monomers such as olefins, cyclic olefins, and aromatic vinyl compounds. In the case where the polymer A contains other structural units, the molar ratio of the structural unit (III) to the other structural units is preferably 10/0 to 1/10, more preferably 10/0 to 8/2. The polymerization mode in this case may be block copolymerization or random copolymerization.

The structural unit (III) is preferably 1 or more selected from (meth) acrylic acid (acrylic acid or methacrylic acid), maleic acid, derivatives thereof, and salts thereof. The both ends of the polymer A containing the structural unit (III) are not particularly limited, and examples thereof include a hydrogen atom, -OH, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, SO ₃ M (M is the same as M in the formula (III)), and the like, and may be the same or different.

Examples of the polycarboxylic acid and salts thereof in the present invention include (meth) acrylic acid homopolymers, (meth) acrylic acid-maleic acid copolymers, α -hydroxyacrylic acid homopolymers, C5 olefin-maleic acid copolymers, isobutylene-maleic acid copolymers, and the like, and salts thereof. Preferred are acrylic acid homopolymers, acrylic acid-maleic acid copolymers, isobutylene-maleic acid copolymers and salts thereof.

The weight average molecular weight of the polycarboxylic acid and its salt is preferably 1000 to 10000, more preferably 1500 to 5000, in order to make the viscosity of the 20% aqueous solution fall within the above range. The weight average molecular weight can be measured by gel permeation chromatography (GPC method) using a polystyrene standard.

As the polycarboxylic acid and its salt, for example, as the polyacrylic acid or its salt, commercial products such as a. Mu. Tan T-50 (manufactured by east Asia Synthesis Co., ltd.), a. Mu. Tan A-210 (manufactured by east Asia Synthesis Co., ltd.), a. Mu. Tan A-6001 (manufactured by east Asia Synthesis Co., ltd.) and the like can be used.

The first ink contains a first colorant and a polymer a as solid components. The first ink may contain various solid components such as a water-soluble polymer, water-insoluble resin fine particles, and a surfactant other than the polymer a, in addition to these. The content of the polymer a in the first ink is preferably 50% by mass or more relative to the amount of the solid component to be removed from the entire solid components. The upper limit of the content of the polymer a with respect to the amount of the solid component removed from the first colorant is 100% by mass, and the content is more preferably in the range of 80 to 100% by mass. When the content of the polymer a in the first ink is within the above range, the penetrability of the colorant between the inks can be made uniform, and the gradation and color balance of the printed image can be sufficiently maintained with time.

(3) Is the necessary condition of (2)

In the ink set of the present invention, in the requirement of (3), the value defining the ratio of the total solid content in the second ink to the total solid content in the first ink is in the range of 0.4 to 2.5 on a mass basis. The value of the ratio of the total solid content in the second ink to the total solid content in the first ink is a value obtained by using the total solid content (mass) in the second ink/the total solid content (mass) in the first ink, and is hereinafter also referred to simply as "the value of the ratio of the total solid content". The solid component refers to a component other than the solvent contained in the ink. Unless otherwise specified, the solid component amount of the ink is expressed as mass or mass%.

When the ratio of the total solid content is less than 0.4, the first ink becomes less permeable than the second ink, and the gradation or color balance cannot be maintained with time in the printed image. When the ratio of the total solid component amounts exceeds 2.5, the first ink becomes more permeable than the second ink, and the gradation or color balance cannot be maintained with time in the printed image. The solid content ratio is more preferably in the range of 0.6 to 1.5.

The first ink and the second ink are composed of solid components and a solvent, which is typically composed of water, or water and an organic solvent. The organic solvent is preferably hydrophilic.

The content of the solid components in the first ink and the second ink can be set in a range of 5 to 50% by mass, preferably 15 to 25% by mass, while satisfying the above-described requirements (1) to (3).

The requirements (1) to (3) in the ink set of the present invention are described above. The ink set of the present invention preferably satisfies at least one of the following requirements (4) to (7), and more preferably satisfies all of the requirements.

(4) The first ink and the second ink each contain an organic solvent, and the difference between the content (mass%) of the organic solvent in the first ink and the content (mass%) of the organic solvent in the second ink is 10 mass% or less.

(5) The first ink and the second ink each contain an organic solvent, and the content (mass%) of the organic solvent in the first ink and the content (mass%) of the organic solvent in the second ink are each 30 mass% or less.

(6) The ratio of the viscosity of the second ink at 25 ℃ to the viscosity of the first ink at 25 ℃ is in the range of 0.7 to 1.3.

(7) The viscosity of the first ink at 25 ℃ and the viscosity of the second ink at 25 ℃ are each 6 mPas or more.

(4) And (5) the requirements

As described above, the first ink and the second ink typically contain a solvent composed of water or water and an organic solvent. The content of the solvent in the first ink and the second ink is in a range of 100 mass% excluding the content of the solid component, and specifically, can be set to be in a range of 50 to 95 mass%, preferably 75 to 85 mass%, respectively.

The solvent in the first ink and the second ink is preferably water and an organic solvent in combination from the viewpoints of the ejection property and image quality. (4) And (5) the organic solvent content in the case where the first ink and the second ink contain an organic solvent.

(5) The requirement of (2) is a requirement that the upper limit of the content of the organic solvent in the first ink and the second ink be set to 30 mass%. The upper limit of the content of the organic solvent in the first ink and the second ink can be increased to about 80 mass%, and is preferably set to 30 mass% in order to suppress the temporal variation in gradation or color balance in the printed image.

The content of the organic solvent in the first ink and the second ink can be set in a range of 5 to 30 mass%, preferably in a range of 10 to 30 mass%.

(4) The requirement of (2) is a requirement that the difference between the content of the organic solvent in the first ink and the content of the organic solvent in the second ink is defined to be 10 mass% or less. The content of the organic solvent in the first ink and the content of the organic solvent in the second ink can be made to be larger than each other, and the difference is 10 mass% or less, whereby the gradation or the temporal change in color balance in the printed image can be more sufficiently suppressed. More preferably, the difference in the content of the organic solvent between the first ink and the second ink is within 5 mass%.

Examples of the organic solvent used in the first ink and the second ink include monohydric alcohols, polyhydric alcohol ethers, amines, amides, nitrogen-containing heterocyclic compounds, and the like.

Examples of the monohydric alcohol include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, tert-butanol, pentanol, hexanol, cyclohexanol, and benzyl alcohol.

Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, 1, 2-butanediol, 1, 4-butanediol, 1, 2-pentanediol, thiodiglycol, glycerol, pentaerythritol, and the like.

Examples of the polyhydric alcohol ether include ethylene glycol monoethyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, and tripropylene glycol dimethyl ether.

Examples of the amine include ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, and tetramethylpropylenediamine.

Examples of the amide include formamide, N-dimethylformamide, and N, N-dimethylacetamide.

Examples of the nitrogen-containing heterocyclic compound include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, 2-oxazolidone, and 1, 3-dimethyl-2-imidazolidinone.

In addition, in the first ink and the second ink, as an organic solvent, sulfoxide (for example, dimethyl sulfoxide or the like), sulfone (for example, sulfolane or the like), sulfonate (for example, sodium salt of 1-butanesulfonate or the like), urea, acetonitrile, acetone or the like can be used in addition to the above.

(6) And (7) the requirements

The requirements of (6) and (7) are requirements for defining the viscosities of the first ink and the second ink.

(6) The requirement of (2) is that the ratio of the viscosity of the second ink to the viscosity of the first ink is set to a value within a range of 0.7 to 1.3. The value of the ratio of the viscosity of the second ink to the viscosity of the first ink is a value obtained from the viscosity of the second ink/the viscosity of the first ink, and is hereinafter also simply referred to as "value of the ratio of the viscosities".

When the value of the ratio of the viscosities is within the above range, the penetrability of the first ink and the penetrability of the second ink are easily matched, and the gradation and the color balance are easily maintained with time in the printed image. The value of the ratio of the viscosities is more preferably in the range of 0.9 to 1.1.

(7) The requirement of (2) is that the viscosity of each of the first ink and the second ink is set to 6 mPas or more. By setting the viscosities of the first ink and the second ink to 6mpa·s or more, for example, discharge stability in an industrial ink head with an improved discharge speed can be ensured. The viscosity of the first ink and the second ink is preferably about 6 to 13mpa·s, more preferably about 6 to 10mpa·s, from the viewpoint of discharge stability.

The essential requirements (1) to (3) and the preferable requirements (4) to (7) in the ink set of the present invention are described above. Hereinafter, specific compositions of the first ink and the second ink constituting the ink set of the present invention will be described. In the following description, the relation between the contents of the two ink components such as the requirements of (1), (3), and (4) is not mentioned, but the requirements of (1) and (3) are satisfied, and the requirements of (4) are satisfied.

[ First ink ]

The first ink is composed of a solid component and a solvent. In the first ink, the solid component contains a first colorant and a polymer a as essential components. The specific types and contents of the first colorant and the polymer a in the solid component are as described above.

As described above, the first ink may further contain, as a solid component, a water-soluble polymer other than the polymer a, water-insoluble resin fine particles, a surfactant, and other solid components within a range that does not impair the effects of the present invention. However, it is preferable that the water-soluble polymer other than the polymer A and the water-insoluble resin fine particles are not contained. In order to adjust the surface tension of the first ink, a surfactant is preferably contained as another solid component.

The surfactant preferably used in the first ink includes anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, and higher fatty acid salts, nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylenic glycols, polyoxyethylene-polyoxypropylene block copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts.

In the present invention, nonionic surfactants such as acetylenic diols are preferably used. The surfactant may be commercially available. Examples of commercial products such as acetylenic diols include the E-series (manufactured by the westerner chemical industry company) such as the E1010-series.

The content of the surfactant in the first ink is preferably in the range of about 0.01 to 1% by mass, more preferably 0.02 to 0.2% by mass, relative to the total amount of solid components.

As the solvent in the first ink, a combination of water and an organic solvent is preferable. The specific kind and content of the organic solvent are as described above. The water content is the balance of the organic solvent content subtracted from the solvent.

[ Second ink ]

The second ink is composed of a solid component and a solvent. In the second ink, the solid component contains a second colorant as an essential component. The specific kind and content of the second colorant in the solid component are as described above.

The second ink may further contain, as a solid component, other solid components such as a water-soluble polymer, water-insoluble resin fine particles, and a surfactant, within a range that does not impair the effects of the present invention. Among these, the second ink preferably contains a water-soluble polymer as a solid component, and preferably contains a polymer a as a water-soluble polymer. The specific embodiment of the polymer a in the case where the second ink contains the polymer a includes a preferable embodiment, and is the same as the polymer a in the first ink described above.

In addition, in the case where the second ink contains the polymer a, the content of the polymer a is preferably 50 mass% or more with respect to the amount of the solid component to be removed from the entire solid components, similarly to the case of the first ink. The upper limit of the content of the polymer a with respect to the amount of the solid component removed from the second colorant is 100% by mass, and the content is more preferably in the range of 80 to 100% by mass.

When the second ink contains the polymer a, it is preferable that the second ink does not contain a water-soluble polymer or water-insoluble resin fine particles other than the polymer a, as in the case of the first ink. In order to adjust the surface tension of the second ink, a surfactant is preferably contained as another solid component. The surfactant may be the same as the first ink, including the type and content.

As the solvent in the second ink, a combination of water and an organic solvent is preferable. The specific kind and content of the organic solvent are as described above. The water content is the balance of the organic solvent content subtracted from the solvent.

The first ink and the second ink can each be produced by mixing the components having the above-described composition.

The ink set of the present invention is an ink set for ink jet recording. The ink jet head used in discharging the ink set according to the present invention for printing on a recording medium may be either an on-demand type or a continuous type. As the discharge method, any discharge method such as an electro-mechanical conversion method (for example, a single-chamber type, a double-chamber type, a supplier type, a piston type, a shared mode type, a shared wall type, or the like), an electro-thermal conversion method (for example, a thermal inkjet type, a Bubble Jet (registered trademark) type, or the like) can be used.

In the ink set of the present invention, since the viscosity of the ink constituting the ink set can be made high as described above, discharge stability can be ensured even when used in an industrial ink head in which the discharge speed is increased.

The recording medium to which the ink set of the present invention is applicable is not particularly limited. As the recording medium, specifically, plain paper, coated paper, swelling type inkjet recording paper provided with an ink-receiving layer that swells by absorbing ink, void type inkjet recording paper having a porous ink-receiving layer, and recording medium using a resin support such as polyethylene terephthalate film instead of base paper can be used.

As a recording medium to which the ink set of the present invention can be applied, a fabric can be exemplified. The material of the fibers constituting the fabric is not particularly limited. Examples thereof include natural fibers (hydrophilic fibers) such as cellulose fibers (natural cotton), hemp, wool, and silk, and chemical fibers such as rayon, vinylon, nylon, acrylic, polyurethane, polyester, and acetate. The fabric may be any of fabrics, nonwoven fabrics, woven fabrics, and the like, which are produced from these fibers. The fabric may be a blended fabric or a blended nonwoven fabric of 2 or more fibers.

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(Production of ink)

The respective components shown in table I were mixed to produce inks 1 to 11. In table I, the blank column in the column of the composition means that the composition thereof is not contained. Inks 1,2, 4 to 6, 8, 9, 11 are magenta inks, and inks 3, 7, 10 are cyan inks.

The components in table I are as follows.

< Colorant >

RR24; c.i. reactive Red 24

RB49; c.i. active blue 49

< Polymer A and other Water-soluble Polymer >

One end N: sodium salt of formaldehyde beta-naphthalenesulfonate condensate (CAS number: 9084-06-4), manufactured by Huawang corporation, 20% aqueous solution viscosity: 2 mPas

Sodium polyacrylate (MW 1200): sodium salt of polyacrylic acid, weight average molecular weight: 1200. the package contains 20% aqueous solution viscosity: 5 mPas

Sodium polyacrylate (MW 8000): sodium salt of polyacrylic acid, weight average molecular weight: 8000. the package contains 20% aqueous solution viscosity: 11 mPas

Polyethylene glycol 2000: polyethylene glycol, weight average molecular weight: 2000. fuji film and photo-pure chemical Co., ltd., viscosity of 20% aqueous solution: 2 mPas

Sodium polyacrylate (MW 25000): sodium salt of polyacrylic acid, weight average molecular weight: 25000. the package contains 20% aqueous solution viscosity: 25 mPas

ULV-1: na alginate, manufactured by the mitro company, 20% aqueous solution viscosity: 1000 mPas

< Surfactant >)

On E1010: acetylenic diol nonionic surfactant (manufactured by Nissan chemical industry Co., ltd.)

In the above, the 20% aqueous solution viscosity of the polymer A and other water-soluble polymers was measured by an E-type viscometer (TV-25, manufactured by Tokyo Co., ltd.) at 25℃and 20 rpm. The viscosity of the obtained ink was similar to that described above, and the results of the surface tension measurement by the following method are shown in table I.

The surface tension (mN/m) of the ink was measured by a hanging-sheet type surface tensiometer under an environment of a relative humidity of 55%23 ℃.

Further, table I shows the total amount of solid components [ mass% ], the total amount of organic solvents [ mass% ], and the proportion of polymer a in the solid components excluding the colorant [ mass% ] together.

[ Ink sets 1 to 9]

The inks 1 to 11 obtained above were combined as shown in Table II to prepare ink sets 1 to 9 of examples and comparative examples. In table II, in the column for classifying the inks, which ink corresponds to the first ink and the second ink is described.

In table II, whether or not each ink set satisfies the requirements (1) to (7) is indicated by "o" and the case where the ink set does not satisfy is indicated by "x". The ink sets satisfying all of the requirements (1) to (3) are the ink sets (ink sets 1, 3 to 5, 8, 9) of the embodiment of the present invention, except for the ink sets (ink sets 2, 6, 7) of the comparative example.

The ink sets 4 and 7 are ink sets having different hues of the first colorant (cyan) and the second colorant (magenta), and the ink sets 1 to 3, 4, 6, and 8 are ink sets having the same color (magenta) as the first colorant and the second colorant. Ink set 9 is an ink set in which the first colorant and the second colorant are homologous colors (cyan).

[ Evaluation ]

The following printing tests were performed for the ink sets 1 to 3,4, 6, 8, and 9, and gray scale continuous (i.e., one-by-one) was evaluated, and color balance was evaluated for the ink sets 4 and 7. The results are shown together in Table II.

< Printing test >)

The ink of the ink set was discharged by an ink jet head KM1024aSAE-Q manufactured by konikama meidao corporation under the following conditions, and an image was printed on a 100% cotton fabric (with a cotton width seam, manufactured by color dyeing corporation) under the following printing conditions.

(Printing conditions)

Drive frequency: 35kHz

Drop amount: 13pl

Recording density (resolution): 720×720dpi

Printing an image: the density of ink dots per certain area is changed to produce an image with gray scale. Specifically, the Duty is changed from 100% to 10% every 10%, and a block pattern is printed. The ink adhesion amount of 100% was 13g/m ². In the case where the first ink and the second ink are of the same color, the ink dots are arranged so that the connection with the gradation of 1 minute becomes smooth after the image recording. When the first ink and the second ink are not homologous colors, the first ink and the second ink are arranged so that the printing rates of the first ink and the second ink become equal at each Duty.

(Conditions for placing images and evaluation criteria)

After recording the images 1 minute after observing the images, the images were left for 1 week in an atmosphere having a relative humidity of 60% at 25 ℃. The images recorded after 3 hours, 24 hours and 1 week were visually observed, and the grayscales (gradation connection) or the color balance was evaluated using the following criteria. In all the evaluations, if the evaluation is a or B, the evaluation can be used without any problem in practical use.

(1) Evaluation criterion for gradation connection

A: at all times, gray scale connected smoothing

B: when observed after 1 week, the gray scale phase difference was found

C: when observed after 24 hours, the gray scale phase difference was found

D: when observed after 3 hours, a poor connection of grayscales was found.

(2) Evaluation criterion for color balance between low-density portion and high-density portion

A: at all times, a color balance is obtained from the low density portion to the high density portion

B: the color balance was different between the low concentration portion and the high concentration portion when observed after 1 week

C: the color balance was different between the low concentration portion and the high concentration portion when observed after 24 hours

D: when observed after 3 hours, the color balance was different between the low-concentration portion and the high-concentration portion.

[ Combination of ink sets ]

The above evaluation was performed using 2 ink sets, that is, ink set 1 in which the first ink and the second ink are in the same color (magenta) and ink set 9 in which the first ink and the second ink are in the same color (cyan), and both of the gradation connection and the color balance were evaluated. The results are shown in Table III. The print image at this time was formed by printing with the same image data (patch pattern) as the print image used in the evaluation of the ink sets 1 to 9 so that the image of the ink set 1 and the image of the ink set 2 overlapped at the same portion.

TABLE 3

Industrial applicability

Can provide: the ink set can be applied to an ink jet recording ink set which requires a higher viscosity and which can maintain the gradation or color balance of a printed image even when time passes after printing.

Claims

1. An ink set comprising: an ink set for ink jet recording comprising a first ink containing a first colorant and a second ink containing a second colorant, characterized in that the following conditions (1) to (3) are satisfied,

(2) The first ink contains a polymer having a viscosity in the range of 1.8 to 20 mPas measured as a 20 mass% concentration aqueous solution at 25 ℃;

(3) The value of the ratio of the total solid component amount in the second ink to the total solid component amount in the first ink is in the range of 0.4 to 2.5 on a mass basis.

2. The ink set as defined in claim 1 wherein the first colorant and the second colorant are homologous colors.

3. The ink set according to claim 1 or 2, wherein a ratio of a content (mass%) of the second colorant in the second ink to a content (mass%) of the first colorant in the first ink has a value of 3.0 or more.

4. The ink set as recited in any one of claims 1 to 3, wherein the first colorant and the second colorant are dyes.

6. The ink set according to any one of claims 1 to 5, wherein a value of a ratio of a viscosity at 25 ℃ of the second ink to a viscosity at 25 ℃ of the first ink is in a range of 0.7 to 1.3.

9. The ink set according to any one of claims 1 to 8, wherein a proportion of the polymer to the amount of solid components from which the first colorant is removed with respect to the total amount of solid components in the first ink is 50% by mass or more.

10. The ink set as defined in any one of claims 1 to 9 wherein the polymer has anionic groups.

11. The ink set according to any one of claims 1 to 10, wherein the degree of polymerization of the polymer is in the range of 2 to 10.

12. The ink set according to any one of claims 1 to 11, wherein the polymer comprises a salt of a polycarboxylic acid or a salt of a naphthalene sulfonic acid formaldehyde condensate.

13. The ink set according to any one of claims 1 to 12, wherein the viscosity at 25 ℃ of the first ink and the viscosity at 25 ℃ of the second ink are each 6 mPa-s or more.