WO2023037471A1

WO2023037471A1 - Ink set

Info

Publication number: WO2023037471A1
Application number: PCT/JP2021/033153
Authority: WO
Inventors: 亮青山; 正幸牛久; 正則弓田; 真也渡辺; 孝彰黒木
Original assignee: コニカミノルタ株式会社
Priority date: 2021-09-09
Filing date: 2021-09-09
Publication date: 2023-03-16
Also published as: JPWO2023037471A1; CN117916331A

Abstract

The ink set according to the present invention is used for inkjet recording and comprises a first ink containing a first colorant and a second ink containing a second colorant, the ink set being characterized by satisfying the following requirements (1) to (3). (1) The first colorant content (mass%) of the first ink is less than the second colorant content (mass%) of the second ink. (2) The first ink contains a polymer having a viscosity within the range of 1.8-20 mPa∙s as measured at 25°C as an aqueous solution having a concentration of 20 mass%. (3) The value of the ratio of the total solids content in the second ink to the total solids content in the first ink is within the range of 0.4-2.5 in terms of mass.

Description

ink set

The present invention relates to an ink set for inkjet recording. More specifically, the present invention is an ink for ink jet recording that can be applied to ink jet heads that require higher viscosity and that can maintain the gradation or color balance of printed images even after the passage of time after printing. Regarding the set.

In the current inkjet recording method, a printed image ( hereinafter also simply referred to as an "image") is adopted. When ink for inkjet recording (hereinafter also simply referred to as "ink") adheres to a recording medium, it forms dots that permeate the recording medium and spread over the surface of the recording medium, with adjacent dots partially overlapping each other. spread out. Also, when the colorant penetrates deep into the recording medium, the optical density of the image often decreases.

In this way, the ink dots formed on the recording medium change in color with the passage of time due to changes in the dot diameter of each color or changes in the distribution of the colorant in the depth direction. If the way the colorant spreads over a long period of time differs between the dark and light inks, the gradation of the high-density portions of the image formed with the dark-colored inks and the low-density portions formed with the light-colored inks will change with the passage of time after printing. The gradation of the density part is not connected.

In other words, if the density change balance between the low-density portion and the high-density portion is lost, the gradation of the image deteriorates over time, and a problem arises that smooth gradation cannot be obtained. Furthermore, when the densities of the respective colors change at the same speed, the color fluctuations in the image are not conspicuous. If the amount of colorant between inks differs greatly, even if the surface tension is uniformed with a surfactant or the like, the permeability between the inks will not be uniform, resulting in the problem that the gradation and color balance of the image cannot be maintained for a long period of time. .

As a method for solving the above problem, Patent Document 1 proposes a technique for adjusting the surface tension between inks and controlling the amount of ions in the dye ink in an ink set having a plurality of inks of the same hue and different densities. there is

On the other hand, in recent years, in order to further improve the printing speed, an industrial head with an ejection frequency of 35 kHz or more, for example, an inkjet head (hereinafter also simply referred to as "head") with a higher ink ejection speed has been commercially available. It is becoming to be done. Industrial heads with increased ejection speed generally require higher viscosity, for example, 6 mPa·s or more, as physical properties of the ink to ensure ejection stability. In addition, since the head generally has an upper limit of applicable viscosity, when using the same head between ink sets, it is required that the viscosity range of each ink be uniform within a certain range.

In an ink set, if the amount of colorant between inks differs greatly, the amount of colorant also affects the viscosity of the ink. Considerable measures must be taken to match the desired viscosity. For example, it is conceivable to adjust the viscosity by adjusting the amount of a relatively high-viscosity organic solvent such as glycerin. It becomes difficult to uniform the permeability of the colorant between the color inks over time.

Further, Patent Document 2 describes a method of matching the viscosity of inks in an ink set by using a thickener, but does not describe a method of maintaining the gradation and color balance of a printed image over time. No description. As described above, there is no existing technology to provide an ink set that can be applied to a head that requires high viscosity and that can maintain the gradation and color balance of printed images even after the passage of time after printing. rice field.

Japanese Patent No. 4182649 Japanese Unexamined Patent Application Publication No. 2011-202029

The present invention has been made in view of the above problems and circumstances, and the problem to be solved is that it can be applied to a head that requires a higher viscosity, and the gradation or gradation of the printed image even after the passage of time after printing. To provide an ink set for ink jet recording capable of maintaining color balance.

In order to solve the above problems, the inventors of the present invention, in the process of studying the causes of the above problems, found that in an ink set comprising two types of inks with different colorant contents, the ink with a lower colorant content By containing a polymer and setting the total solid content of the two types of ink to a specific relationship, it can be applied to heads that require higher viscosity, and the gradation of printed images is maintained even after the passage of time after printing. Alternatively, the inventors have found that an ink set for ink jet recording can be obtained that can maintain color balance, and have completed the present invention. That is, the above problems related to the present invention are solved by the following means.

1. An ink set for inkjet recording comprising a first ink containing a first colorant and a second ink containing a second colorant, and satisfying the following requirements (1) to (3) An ink set characterized by:
(1) The content (% by mass) of the first coloring agent in the first ink is less than the content (% by mass) of the second coloring agent in the second ink.
(2) The first ink contains a polymer having a viscosity in the range of 1.8 to 20 mPa·s as measured at 25° C. as a 20 mass % aqueous solution.
(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. Item 2. The ink set according to item 1, wherein the first colorant and the second colorant have similar colors.

3. The ratio of the content (% by mass) of the second coloring agent in the second ink to the content (% by mass) of the first coloring agent in the first ink is 3. 3. The ink set according to item 1 or 2, characterized by being 0 or more.

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

5. Item 1, wherein 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. 4. The ink set according to any one of items 1 through 4.

6. Items 1 to 5, wherein the ratio of the viscosity of the second ink at 25° C. to the viscosity of the first ink at 25° C. is in the range of 0.7 to 1.3. The ink set according to any one of the preceding items.

7. Both the first ink and the second ink contain an organic solvent, and the content (% by mass) of the organic solvent in the first ink and the content of the organic solvent in the second ink ( %) is 10% by mass or less, the ink set according to any one of items 1 to 6.

8. Both the first ink and the second ink contain an organic solvent, and the content (% by mass) of the organic solvent in the first ink and the content of the organic solvent in the second ink ( %) is 30% by mass or less, the ink set according to any one of items 1 to 7.

9. Item 1 to Item 8, wherein the ratio of the polymer to the total solid content of the first ink excluding the first colorant is 50% by mass or more. The ink set according to any one of paragraphs.

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

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

12. 12. The ink set according to any one of items 1 to 11, wherein the polymer comprises a salt of polycarboxylic acid or a salt of naphthalenesulfonic acid formalin condensate.

13. The viscosity of the first ink at 25 ° C. and the viscosity of the second ink at 25 ° C. are both 6 mPa s or more, according to any one of items 1 to 12. Ink set as described.

Provided is an ink set for inkjet recording that can be applied to a head that requires a higher viscosity by the means of the present invention and that can maintain the gradation or color balance of a printed image even after the passage of time after printing. can do. The expression mechanism or action mechanism of the effect of the present invention is presumed as follows.

The ink set according to the present invention is an ink set comprising a first ink and a second ink having a coloring agent content (% by mass) greater than that of the first ink (requirements of (1)), wherein the first ink is It has a configuration in which the ink contains a specific polymer (requirement (2)) and the value of the ratio of the total solid content of the first ink and the second ink is set to a specific range (requirement (3)). .

Specifically, in the requirement (2), the specific polymer is a polymer having a viscosity in the range of 1.8 to 20 mPa s measured at 25°C as an aqueous solution with a concentration of 20% by mass. . In the requirement (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. Hereinafter, a polymer having a viscosity in the range of 1.8 to 20 mPa·s as measured at 25° C. as an aqueous solution having a concentration of 20% by mass is also referred to as “polymer A”.

As described above, in order to maintain the gradation or color balance of the printed image even after the passage of time after printing, the change in dot diameter over time and the permeability of the first ink and the second ink should be uniform. is required. In the present invention, in order to achieve this, in the requirement (2), the first ink contains a polymer having the viscosity characteristics described above, and in the requirement (3), the first ink and the second ink The value of the ratio of the total solid content in the ink is set within the above range.

Here, in order to make the change in dot diameter over time and the permeability uniform between the first ink and the second ink, not only the surface tension of each ink, but also the physical properties and amount of the solid content, and the viscosity at the time of water evaporation. Aligning the changes is important. Especially in high-viscosity ink, the increase in viscosity due to water evaporation is large, and the effect of solid content and viscosity change is particularly large. Therefore, it is necessary to match the change in dot diameter over time and the permeability of the first ink and the second ink. be done.

The ink set of the present invention satisfies the requirements (1) to (3), so that not only the surface tension of the first ink and the second ink, but also the physical properties and amount of the solid content, the viscosity at the time of water evaporation It is a set of changes in As a result, the change in dot diameter over time and the permeability 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 after the passage of time after printing. made it possible to

The ink set of the present invention is an ink set for inkjet recording comprising a first ink containing a first colorant and a second ink containing a second colorant, wherein the following requirement (1) is satisfied: (3) is satisfied.
(1) The content (% by mass) of the first coloring agent in the first ink is less than the content (% by mass) of the second coloring agent in the second ink.
(2) The first ink contains a polymer having a viscosity in the range of 1.8 to 20 mPa·s as measured at 25° C. as a 20 mass % aqueous solution.
(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.
This feature is a technical feature common to or corresponding to each of the following embodiments.

As an embodiment of the present invention, when the first coloring agent and the second coloring agent are similar in color, the ink set of the present invention exhibits the effect of maintaining the gradation of the printed image over time. can be expressed more.

As an embodiment of the present invention, from the viewpoint that the effect of the present invention can be further expressed, It is preferable that the ratio of the content (% by mass) of the two coloring agents is 3.0 or more. Moreover, it is preferable that the first coloring agent and the second coloring agent are dyes.

As an embodiment of the present invention, from the viewpoint that the effects of the present invention can be further expressed, the value of the ratio of the total solid content in the second ink to the total solid content in the first ink is 0 on a mass basis. It is preferably in the range of 0.6 to 1.5.

As an embodiment of the present invention, from the viewpoint of being able to further express the effects of the present invention, the ratio of the viscosity of the second ink at 25° C. to the viscosity of the first ink at 25° C. is 0.7 to It is preferably in the range of 1.3.

As an embodiment of the present invention, from the viewpoint that the effects of the present invention can be further expressed, both the first ink and the second ink contain an organic solvent, and the first ink contains the organic solvent. The difference between the amount (% by mass) and the content (% by mass) of the organic solvent in the second ink is preferably 10% by mass or less. In addition, both the first ink and the second ink contain an organic solvent, and the content (% by mass) of the organic solvent in the first ink and the content of the organic solvent in the second ink are The amount (% by mass) is preferably 30% by mass or less.

As an embodiment of the present invention, from the viewpoint that the effects of the present invention can be further expressed, the ratio of the polymer to the solid content excluding the first colorant from the total solid content in the first ink is 50. % or more is preferable.

As an embodiment of the present invention, the polymer preferably has an anionic group from the viewpoint of being able to further express the effects of the present invention. Further, the polymer may have a degree of polymerization within the range of 2-10. Moreover, it is preferable that the polymer contains a salt of polycarboxylic acid or a salt of naphthalenesulfonic acid-formalin condensate.

As an embodiment of the present invention, the viscosity of the first ink at 25° C. and the viscosity of the second ink at 25° C. are both 6 mPa·s or more, from the viewpoint of being able to further express the effects of the present invention. is preferred.

The following is a detailed description of the present invention, its components, and the forms and modes for carrying out the present invention. In the present application, "-" is used to mean that the numerical values before and after it are included as the lower limit and the upper limit.

[Ink set]
The ink set of the present invention is an ink set for inkjet recording comprising a first ink containing a first colorant and a second ink containing a second colorant, wherein the following requirement (1) is satisfied: (3) is satisfied.
(1) The content (% by mass) of the first coloring agent in the first ink is less than the content (% by mass) of the second coloring agent in the second ink.
(2) The first ink contains a polymer (polymer A) having a viscosity in the range of 1.8 to 20 mPa·s as measured at 25° C. as a 20 mass % aqueous solution.
(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.

Each of the requirements (1) to (3) will be described below.
Requirement (1) The ink set of the present invention comprises a first ink containing a first colorant and a second ink containing a second colorant, and in the requirement (1), the first ink is The content (% by weight) of the first colorant in the ink is defined to be less than the content (% by weight) of the second colorant in the second ink.

Hereinafter, the units for the content of the first coloring agent in the first ink and the content of the second coloring agent in the second ink are % by mass unless otherwise specified.

In the ink set of the present invention, the relationship between the first colorant and the second colorant contained in each of the first ink and the second ink is not particularly limited, except that the content is different. do not have.

The first coloring agent and the second coloring agent may or may not have similar colors. In this specification, that two colorants have similar colors means that the values of hue angles that can be expressed by the respective colorants are not greatly different. The allowable range for the difference between the hue angles of the two differs depending on the hue. Hue angles have a specific range defined for each hue. If the hue angles of two colorants are within the range of the hue angle of the same hue, both are considered to have similar colors.

Specifically, when two colorants are similar in color to cyan, the hue angles of the two colorants in the L ^* a ^* b ^* color system are both in the range of 215° to 255°. preferably within. When the two colorants have the same magenta color, the hue angles in the L ^* a ^* b ^* color system of the two colorants are both in the range of 320° to 360° or in the range of 0° to It is preferably in the range of 20°. When the two colorants are similar in color to yellow, the hue angle of the two colorants in the L ^* a ^* b ^* color system is preferably in the range of 70° to 140°.

When the two colorants are similar in color to blue, the hue angles in the L ^* a ^* b ^* color system of the two colorants are both in the range of 270° to 285°. preferable. When two colorants are similar in color to red, the hue angles in the L ^* a ^* b ^* color system of the two colorants are both in the range of 20° to 35°. preferable.

When the first colorant and the second colorant have similar colors, the ink set of the present invention can more effectively retain the gradation of the printed image over time after printing. When the first coloring agent and the second coloring agent are not similar colors, that is, when the hues of the first coloring agent and the second coloring agent are different, the color of the printed image over time after printing in the ink set of the present invention The effect of maintaining balance can be exhibited more effectively.

Inkjet recording may use a combination of inks of a plurality of hues, for example, cyan, magenta, and yellow inks. In that case, it is preferable to use an ink set comprising the first ink and the second ink of the present invention for each hue. That is, in the first ink and the second ink that satisfy the requirements (1) to (3), the first colorant and the second colorant are both cyan, the cyan ink set, the requirement (1) In the first ink and the second ink that satisfy ~(3), both the first colorant and the second colorant are magenta color ink set, satisfying the requirements (1)~(3) In the first ink and the second ink, it is preferable to use a combination of a yellow ink set in which both the first coloring agent and the second coloring agent are yellow.

When the cyan ink set, magenta ink set, and yellow ink set are used together, the resulting printed image can retain both gradation and color balance even after the passage of time after printing. It becomes possible.

Regarding the requirement (1), the ratio of the content of the second coloring agent in the second ink to the content of the first coloring agent in the first ink is 3.0 or more. (hereinafter also referred to as “requirement (12)”), and more preferably 3.5 or more. As a result, graininess can be reduced and smooth gradation reproduction can be performed. The upper limit of the ratio of the content of the second coloring agent in the second ink to the content of the first coloring agent in the first ink is about 10 from the viewpoint of tone reproduction. It is preferably about 5, more preferably about 5.

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

In addition, the content of the second coloring agent in the second ink satisfies the requirement (1) in relation to the content of the first coloring agent in the first ink, and preferably the requirement (12 ) is satisfied, for example, the range is preferably 1.5 to 30% by mass, more preferably 3 to 21% by mass, with respect to the total amount of the second ink. 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 solid content of the second ink.

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

(coloring agent)
As the coloring agent, for example, a pigment, a dye, a dye, or the like is not particularly limited, but the effect of the present invention is greater because the dye has a higher diffusibility. Dyes include acid dyes, direct dyes, basic dyes, reactive dyes, and food dyes.

Representative dyes are listed below, but the present invention is not limited to these.
<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 orange 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. Reactive 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. Reactive Orange 5, 12, 13, 35, 95,
C. I. Reactive Brown 7, 11, 33, 37, 46,
C. I. Reactive Green 8, 19,
C. I. reactive violet 2, 4, 6, 8, 21, 22, 25,
C. I. Reactive Black 5, 8, 31, 39

<Basic dye>
C. I. basic yellow 11, 14, 21, 32
C. I. Basic red 1, 2, 9, 12, 13
C. I. Basic Violet 3, 7, 14
C. I. basic blue 3, 9, 24, 25

Dyes that can be used as the coloring agent according to the present invention also include chelate dyes and azo dyes used in so-called silver dye bleaching photosensitive materials (eg Ciba-Geigy Cibachrome).

Chelate dyes are described, for example, in British Patent No. 1,077,484.

Azo dyes for silver dye bleaching photographic materials are described, for example, in British Patent Nos. 1,039,458, 1,004,957 and 1,077,628, and U.S. Pat. No. 2,612,448. there is

Conventionally known organic and inorganic pigments can be used as pigments that can be used as the colorant according to the present invention. For example, azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments and chelate azo pigments; Examples include cyclic pigments, dye lakes such as basic dye lakes and acid dye lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black and daylight fluorescent pigments, and inorganic pigments such as carbon black.

Requirement (2) The requirement (2) defines that the first ink contains the polymer A. In the ink set of the present invention, the first ink among the first ink and the second ink satisfying the requirements of (1) contains the polymer A and satisfies the requirements of (3). Thus, the above effects of the present invention can be achieved.

[Polymer A]
Polymer A is a compound having a viscosity in the range of 1.8 to 20 mPa·s when measured at 25° C. as an aqueous solution having a concentration of 20% by mass. Hereinafter, the viscosity measured at 25° C. as an aqueous solution with a concentration of 20% by mass is sometimes referred to as "20% aqueous solution viscosity". Here, the polymer A is a compound that can measure the viscosity of a 20% aqueous solution, that is, dissolved in water at 25 ° C. at a concentration of 20% by mass or more (the content of polymer A relative to the total amount of the aqueous solution is 20% by mass or more). It is a water-soluble compound that can In this specification, the viscosity is the viscosity at 25°C unless otherwise specified. Viscosity can be measured using, for example, an E-type viscometer.

When a polymer outside the category of polymer A, for example, a polymer having a 20% aqueous solution viscosity of less than 1.8 mPa s, is used, the permeability of the first ink is lower than that of the second ink. gradation or color balance over time cannot be maintained in the printed image. Further, as a polymer that does not fall under the category of polymer A, for example, when a polymer having a 20% aqueous solution viscosity of more than 20 mPa s is used, the permeability of the first ink becomes the permeability of the second ink. gradation or color balance over time cannot be maintained in the printed image. A 20% aqueous solution viscosity of polymer A is preferably in the range of 2 to 10 mPa·s, more preferably in the range of 2 to 4 mPa·s.

Generally, a polymer is a compound obtained by polymerizing a plurality of monomers, and units derived from the monomers in the polymer are called polymerized units (hereinafter also referred to as structural units). In the present specification, a polymer means a compound having two or more constitutional units, in other words, a compound having a degree of polymerization of two or more. Thus, polymers include oligomers and polymers. As the polymer A, a polymer having a degree of polymerization within the range of 2 to 10, for example, may be used depending on its constituent units.

In addition, the polymer A preferably has an anionic group from the viewpoint of maintaining the gradation or color balance of the printed image over time. 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, it is preferably 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. or a carboxylic acid group, more preferably a sulfonic acid group or a carboxylic acid group. As for the salt, a part of the anionic group may be a salt, or the whole anionic group may be a salt.

The polymer A may be used alone or in combination of two or more. Also, it may be a mixture in which two or more kinds of polymers are combined so that the viscosity of the 20% aqueous solution is in the range of 1.8 to 20 mPa·s. In the present invention, as the polymer A, it is preferable to use a polymer capable of achieving the above 20% aqueous solution viscosity by itself.

Examples of the polymer A include polycarboxylic acids and salts thereof, condensates of sulfonated aryl compounds and formaldehyde (hereinafter referred to as “sulfonated aryl compound formalin condensates”) and salts thereof, and polyalkylenes, which satisfy the above (2). Examples thereof include glycol (preferably alkylene having 2 to 3 carbon atoms), polyethylene glycol, polypropylene glycol and the like.

The polymer A is preferably at least one selected from polycarboxylic acids and their salts, sulfonated aryl compound formalin condensates and their salts, which satisfy the above (2) from the viewpoint of having an anionic group. Examples of the salt include metal salts such as alkali metal salts and alkaline earth metal salts, quaternary ammonium salts and the like, with alkali metal salts, particularly sodium salts being preferred.

The aryl compound in the sulfonated aryl compound includes polycyclic aromatic compounds, specifically, two or more aromatic rings (including heterocyclic rings) sharing two or more carbon atoms to form a condensed ring. and derivatives thereof, and compounds and derivatives thereof in which two or more aromatic rings (including heterocycles) are bonded directly or via an alkylene group are preferred.

Examples of polycyclic aromatic compounds include naphthalene, anthracene, phenanthrene, pyrene, acenaphthene, indene, fluoranthene, chrysene, benzofluoranthene, benzopyrene, perylene, benzoperylene, fluorene, diphenyl, and dibenzofuran. At least one selected from naphthalene, anthracene, phenanthrene, pyrene, acenaphthene and fluorene is preferred, and naphthalene is more preferred. These may have a substituent. That is, the sulfonated aryl compound is preferably sulfonated naphthalene (naphthalenesulfonic acid) which may have a substituent.

The optionally substituted naphthalenesulfonic acid formalin condensate and its salt include at least a structural unit represented by the following general formula (I) (hereinafter also referred to as structural unit (I)). Combined A can be mentioned.

In formula (I), R is a substituent, and X represents 0, 1 or 2 as the number of R. Each M is independently a hydrogen atom, an alkali metal or a quaternary ammonium group. Examples of R include a hydroxy group, an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, and the like. When two or more R are present, they may be the same or different.

The polymer A having the structural unit (I) may contain other structural units as long as the properties of the polymer A are not impaired. Other structural units include structural units formed from copolymerizable monomers such as alkyl maleic anhydride and polycarboxylic acid. In this case, the content of the other structural units is preferably 30% by mass or less relative to the total amount of the polymer A.

The degree of polymerization of the polymer A having the structural unit (I) is preferably within the range of 2-10. In this case, the degree of polymerization of 2 to 10 means that the number of sulfonated naphthalene residues which may have substituents is 2 to 10. The weight-average molecular weight of the naphthalenesulfonic acid-formalin condensate and its salt containing the polymer A having the structural unit (I) 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 a gel permeation chromatography method (GPC method) using a polystyrene standard substance.

Furthermore, as the polymer A having the structural unit (I), a salt of a naphthalenesulfonic acid-formalin condensate that may have a substituent represented by the following general formula (II) (hereinafter also referred to as "compound (II)" ) is preferred.

In formula (II), R has the same meaning as in formula (I), and each M is independently an alkali metal or a quaternary ammonium group. x is an integer of 0-3 and n1 is an integer of 1-9.

Among compounds (II), a sodium salt of naphthalenesulfonic acid formalin condensate in which M is sodium, x is 0, and n1 is 1 is particularly preferable.

The naphthalenesulfonic acid formalin condensate (salt) can be produced by a generally known method, for example, condensation polymerization using naphthalenesulfonic acid (salt) and an equivalent amount of formaldehyde and, if necessary, other components. Other components include, for example, sulfonic acids (salts) such as β-methylnaphthalene, α-methylnaphthalene, acenaphthene, dibenzofuran, fluorene, phenanthrene, anthracene, fluoranthene, and pyrene.

As the sodium salt of naphthalenesulfonic acid formalin condensate, commercially available products such as Demol NL, Demol SS-L, Demol N, Demol MS, and Demol C (all trade names) manufactured by Kao Corporation can be used.

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

In formula (III), R ¹ to R ³ are each independently a hydrogen atom or a substituent, and each M is independently a hydrogen atom, an alkali metal or a quaternary ammonium group. The substituents represented by R ¹ to R ³ 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 above), —OH etc.

The polymer A having the structural unit (III) may contain other structural units as long as the properties of the polymer A are not impaired. Other structural units include structural units formed from copolymerizable monomers such as olefins, cyclic olefins, and aromatic vinyl compounds. When 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 form of polymerization in that case may be either block copolymerization or random copolymerization.

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

Polycarboxylic acids 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, and isobutylene. - Maleic acid copolymers and the like, and salts thereof and the like. 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 in the range of 1000 to 10000, more preferably in the range of 1500 to 5000, in order to keep the viscosity of the 20% aqueous solution within the above range. The weight average molecular weight can be measured by a gel permeation chromatography method (GPC method) using a polystyrene standard substance as described above.

Polycarboxylic acid and its salt include, for example, polyacrylic acid or its salt, Aron T-50 (manufactured by Toagosei Co., Ltd.), Aron A-210 (manufactured by Toagosei Co., Ltd.), Aron A-6001 (manufactured by Toagosei Co., Ltd.) etc. can also be used.

The first ink contains the first colorant and polymer A as solids. In addition to these, the first ink may contain various solid components such as water-soluble polymers other than the polymer A, water-insoluble resin fine particles, and surfactants. The content of the polymer A in the first ink is preferably 50% by mass or more with respect to the total solid content excluding the first colorant. The upper limit of the polymer A content relative to the total solid content excluding the first colorant is 100% by mass, and the content is more preferably in the range of 80 to 100% by mass. If the content of the polymer A in the first ink is within the above range, the permeability of the colorant between the inks can be uniformed, and the gradation and color balance of the printed image can be sufficiently maintained over time.

Requirement (3) In the ink set of the present invention, in the requirement (3), the ratio of the total solid content in the second ink to the total solid content in the first ink is 0.4 on a mass basis. It is specified to be in the range of ~2.5. The value of the ratio of the total solid content in the second ink to the total solid content in the first ink is the total solid content (mass) in the second ink/the total solid content (mass) in the first ink. , and hereinafter simply referred to as "ratio value of total solid content". Note that the solid content refers to components other than the solvent contained in the ink. Unless otherwise specified, the solids content of the ink is given by weight or weight percent.

If the value of the total solid content ratio is less than 0.4, the permeability of the first ink is lower than that of the second ink, and the gradation or color balance of the printed image cannot be maintained over time. . If the value of the total solid content ratio exceeds 2.5, the permeability of the first ink becomes greater than the permeability of the second ink, and the gradation or color balance of the printed image cannot be maintained over time. . The solid content ratio is more desirably in the range of 0.6 to 1.5.

The first ink and the second ink consist of a solid content and a solvent, and the solvent typically consists of water or water and an organic solvent. Preferably, the organic solvent is hydrophilic.

The solid content in the first ink and the second ink can be in the range of 5 to 50% by mass, provided that the requirements (1) to (3) above are satisfied. A range of up to 25% by mass is preferred.

The requirements (1) to (3) for the ink set of the present invention have been 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) Both the first ink and the second ink contain an organic solvent, and the content (% by mass) of the organic solvent in the first ink and the content of the organic solvent in the second ink are The difference in content (% by mass) is 10% by mass or less.
(5) Both the first ink and the second ink contain an organic solvent, and the content (% by mass) of the organic solvent in the first ink and the content of the organic solvent in the second ink are The contents (% by mass) are all 30% by mass or less.
(6) The ratio of the viscosity of the second ink at 25° C. to the viscosity of the first ink at 25° C. is in the range of 0.7 to 1.3.
(7) Both the viscosity at 25° C. of the first ink and the viscosity at 25° C. of the second ink are 6 mPa·s or more.

Requirements for (4) and (5) As described above, the first ink and the second ink typically contain water or a solvent composed of water and an organic solvent. The content of the solvent in the first ink and the second ink is in the range of 100% by mass excluding the content of the solid content, specifically, in the range of 50 to 95% by mass. preferably within the range of 75 to 85% by mass.

From the viewpoint of jettability and image quality, it is preferable to use both water and an organic solvent as solvents in the first ink and the second ink. Requirements (4) and (5) are requirements that define the content of the organic solvent when the first ink and the second ink contain the organic solvent.

Requirement (5) is a requirement that the upper limit of the content of the organic solvent in the first ink and the second ink is 30% by 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% by mass. This is preferable from the viewpoint of suppressing fluctuations.

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

Requirement (4) is a requirement that the difference between the organic solvent content in the first ink and the organic solvent content in the second ink be within 10% by mass. Either the content of the organic solvent in the first ink or the content of the organic solvent in the second ink may be greater, but the difference is within 10% by mass, so that the gradation or It is possible to more sufficiently suppress changes in color balance over time. More preferably, the difference in organic solvent content between the first ink and the second ink is within 5% by mass.

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

Examples of monohydric alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, and benzyl alcohol.

Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, 1,2-butanediol, 1,4-butanediol, 1,2-pentanediol, thiodiglycol, glycerin, pentaerythritol, and the like. is mentioned.

Examples of polyhydric alcohol ethers 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, tripropylene glycol dimethyl ether and the like.

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

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

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

In addition to the above organic solvents, the first ink and the second ink may contain sulfoxide (eg, dimethyl sulfoxide, etc.), sulfone (eg, sulfolane, etc.), sulfonate (eg, sodium 1-butanesulfonate), salts, etc.), urea, acetonitrile, acetone, etc. can also be used.

Requirements of (6) and (7) The requirements of (6) and (7) are requirements that define the viscosities of the first ink and the second ink.

Requirement (6) defines the value of the ratio of the viscosity of the second ink to the viscosity of the first ink within the 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 the value obtained by the viscosity of the second ink/the viscosity of the first ink, and is hereinafter simply referred to as the "value of the viscosity ratio". say.

When the viscosity ratio is within the above range, the permeability of the first ink and the second ink can easily be matched, and the gradation or color balance of the printed image can be easily maintained over time. More preferably, the viscosity ratio value is in the range of 0.9 to 1.1.

　Requirement (7) defines the viscosity of both the first ink and the second ink to be 6 mPa·s or more. By setting the viscosities of the first ink and the second ink to 6 mPa·s or more, for example, it is possible to ensure ejection stability in an industrial head with an increased ejection speed. The viscosities of the first ink and the second ink are preferably about 6 to 13 mPa·s, more preferably about 6 to 10 mPa·s, from the viewpoint of ejection stability.

The essential requirements (1) to (3) and preferable requirements (4) to (7) in the ink set of the present invention have been described above. Specific compositions of the first ink and the second ink constituting the ink set of the present invention are described below. In the following description, the relationship between the contents of the components of both inks such as requirements (1), (3), and (4) is not mentioned, but requirements (1) and (3) are essential requirements. The composition is based on the assumption that it is preferable to satisfy the requirement of (4).

[First ink]
The first ink consists of solids and solvent. In the first ink, the solid content contains the first colorant and polymer A as essential components. The specific types and contents of the first colorant and polymer A in the solid content are as described above.

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

Surfactants preferably used in the first ink include anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, and higher fatty acid salts, polyoxyethylene alkyl ethers, and polyoxyethylene alkyl allyl ethers. acetylene glycols, nonionic surfactants such as polyoxyethylene/polyoxypropylene block copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts.

In the present invention, it is preferable to use nonionic surfactants such as acetylene glycols. A commercially available product may be used as the surfactant. Commercially available products such as acetylene glycols include, for example, Olfine E series such as Olfine E1010 (manufactured by Nissin Kagaku Kogyo Co., Ltd.).

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

A combination of water and an organic solvent is preferable as the solvent in the first ink. The specific type and content of the organic solvent are as described above. The water content is the remainder of the solvent minus the organic solvent content.

[Second ink]
The second ink consists of solids and solvent. In the second ink, the solid content contains the second colorant as an essential component. The specific type and content of the second colorant in the solid content are as described above.

The second ink may further contain other solid components such as a water-soluble polymer, water-insoluble resin fine particles, surfactants, etc., as a solid content 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 content, and preferably contains the polymer A as a water-soluble polymer. Specific aspects of the polymer A when the second ink contains the polymer A are the same as those of the polymer A in the first ink, including preferred aspects.

In addition, when the second ink contains the polymer A, the content of the polymer A is, as in the case of the first ink, with respect to the total solid content excluding the second coloring agent, 50 mass % or more is preferable. The upper limit of the polymer A content relative to the total solid content excluding 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 preferably does not contain water-soluble polymers other than the polymer A and water-insoluble resin fine particles, as in the first ink. In addition, it is preferable to contain a surfactant as another solid component in order to adjust the surface tension of the second ink. The surfactant can be the same as in the first ink, including the type and content.

A combination of water and an organic solvent is preferable as the solvent in the second ink. The specific type and content of the organic solvent are as described above. The water content is the remainder of the solvent minus the organic solvent content.

The first ink and the second ink can each be produced by mixing each component of the above composition.

The ink set of the present invention is an ink set for inkjet recording. When the ink set according to the present invention is ejected to print on a recording medium, the ink jet head used may be of the on-demand system or the continuous system. In addition, as a discharge method, an electro-mechanical conversion method (eg, single cavity type, double cavity type, bender type, piston type, share mode type, shared wall type, etc.), an electro-thermal conversion method (eg, thermal Any ejection method such as an inkjet type, a bubble jet (registered trademark) type, or the like may be used.

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

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

A fabric can also be mentioned as a recording medium to which the ink set of the present invention can be applied. The material of the fibers that constitute the fabric is not particularly limited. Examples include cellulose fibers (natural cotton), natural fibers (hydrophilic fibers) such as hemp, wool, or silk, and chemical fibers such as rayon, vinylon, nylon, acrylic, polyurethane, polyester, or acetate. The fabric may be made of these fibers in any form such as woven fabric, non-woven fabric, or knitted fabric. Also, the fabric may be a blended woven fabric or a blended nonwoven fabric of two or more types of fibers.

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

(manufacture of ink)
Inks 1-11 were prepared by mixing the ingredients shown in Table I. In addition, in the column of composition in Table I, a blank column means that the component is not contained. Inks 1, 2, 4 to 6, 8, 9, and 11 are magenta inks, and inks 3, 7, and 10 are cyan inks.
In addition, each component in Table I is as follows.

<Colorant>
- RR24; I. reactive red 24
- RB49; I. reactive blue 49

<Polymer A and other water-soluble polymers>
Demoll N: sodium salt of β-naphthalenesulfonic acid formalin condensate (CAS number: 9084-06-4), manufactured by Kao Corporation, 20% aqueous solution viscosity: 2 mPa s
· Polyacrylic acid sodium salt (MW 1200); sodium salt of polyacrylic acid, weight average molecular weight: 1200, manufactured by Sigma-Aldrich, 20% aqueous solution viscosity: 5 mPa s
· Polyacrylic acid sodium salt (MW8000); sodium salt of polyacrylic acid, weight average molecular weight: 8000, manufactured by Sigma-Aldrich, 20% aqueous solution viscosity: 11 mPa s
· Polyethylene glycol 2000; polyethylene glycol, weight average molecular weight: 2000, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., 20% aqueous solution viscosity: 2 mPa s
· Sodium polyacrylate (MW 25000); sodium salt of polyacrylic acid, weight average molecular weight: 25000, manufactured by Sigma-Aldrich, 20% aqueous solution viscosity: 25 mPa s
· ULV-1; sodium alginate, manufactured by Kimika, 20% aqueous solution viscosity; 1000 mPa s

<Surfactant>
· Olfine E1010; acetylene glycol-based nonionic surfactant (manufactured by Nissin Chemical Industry Co., Ltd.)

In the above, the 20% aqueous solution viscosities of polymer A and other water-soluble polymers are values measured at 25°C and 20 rpm with an E-type viscometer (TV-25, manufactured by Toki Sangyo Co., Ltd.). The viscosity of the obtained ink was measured in the same manner as above, and the surface tension was measured by the following method. Table I also shows the results.

The surface tension (mN/m) of the ink was measured using a Wilhelmy surface tensiometer in an environment with a relative humidity of 55% and 23°C.

In addition, Table I also shows the total solid content [mass%], the total organic solvent content [mass%], and the proportion [mass%] of the polymer A in the solid content excluding the colorant.

[Ink set 1-9]
Inks 1 to 11 obtained above were combined as shown in Table II to obtain ink sets 1 to 9 of Examples and Comparative Examples. In Table II, in the column of ink category, the ink corresponds to either the first ink or the second ink.

In addition, whether or not each ink set satisfies the requirements (1) to (7) is indicated in Table II, with "O" if satisfied and "X" if not satisfied. 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 examples of the present invention, and the other ink sets (ink sets of the comparative examples) set 2, 6, 7).

Ink sets 4 and 7 are ink sets in which the hues of the first coloring agent (cyan) and the second coloring agent (magenta) are different. The colorant and the second colorant are ink sets of the same color (magenta color). The ink set 9 is an ink set in which the first colorant and the second colorant are of the same color (cyan).

〔evaluation〕
For the above ink sets, the following printing tests were performed. For ink sets 1 to 3, 4, 6, 8, and 9, gradation continuity was evaluated, and for ink sets 4 and 7, color balance was evaluated. gone. The results are also shown in Table II.

<Print test>
Using the Konica Minolta inkjet head KM1024aSAE-Q, the ink of the above ink set is ejected under the following conditions, and an image is printed under the following conditions on a 100% cotton fabric (with cotton broadsil, manufactured by Shikisen Co., Ltd.). printed.

(Printing conditions)
Drive frequency: 35 kHz
Drop volume: 13pl
Recording density (resolution): 720 x 720 dpi
Printed image: An image having gradation was produced by changing the dot density per fixed area. Specifically, patch patterns were printed with the duty changed from 100% to 10% in 10% increments. The 100% ink coverage was 13 g/m ² . When the first ink and the second ink are similar in color, the dots are arranged so that the gradation is smoothly connected one minute after the image is recorded. When the first ink and the second ink are not similar in color, they are arranged so that the printing ratios of the first ink and the second ink are equal in each duty.

(Image storage conditions and evaluation criteria)
After observing the image one minute after the image recording, the image was allowed to stand in an atmosphere of 25° C. and a relative humidity of 60% for one week. Images were visually observed 3 hours, 24 hours and 1 week after image recording, and the gradation (connection of gradations) or color balance was evaluated according to the following criteria. In any evaluation, if it is evaluated as A or B, it can be used without problems in practical use.

(1) Evaluation criteria for gradation connection A: Gradation connection was smooth at all times B: Poor gradation connection was observed when observed after 1 week C: Observed after 24 hours Poor continuity of gradation was observed occasionally D: Poor continuity of gradation was observed when observed after 3 hours.

(2) Criteria for evaluation of color balance between low-density and high-density areas A: Color balance was maintained from low-density areas to high-density areas at all times. The color balance was different in the high-density area. C: The color balance was different in the low-density area and the high-density area when observed after 24 hours. D: The low-density area and the high-density area were observed after 3 hours. The color balance was different.

[Combination of ink sets]
Two types of ink sets, an ink set 1 in which the first ink and the second ink have the same color (magenta color) and an ink set 9 in which the first ink and the second ink have the same color (cyan color) are used. The above evaluation was performed using the gradation test, and both the connection of gradation and the color balance were evaluated. Results are shown in Table III. The printed image in this case uses the same image data (patch pattern) as the printed image used in the evaluation of the ink sets 1 to 9, and the image of the ink set 1 and the image of the ink set 2 are placed in the same place. It was formed by printing so as to overlap.

It is possible to provide an ink set for inkjet recording that can be applied to a head that requires higher viscosity and that can maintain the gradation or color balance of a printed image over time after printing.

Claims

An ink set for inkjet recording comprising a first ink containing a first colorant and a second ink containing a second colorant, and satisfying the following requirements (1) to (3) An ink set characterized by:
(1) The content (% by mass) of the first coloring agent in the first ink is less than the content (% by mass) of the second coloring agent in the second ink.
(2) The first ink contains a polymer having a viscosity in the range of 1.8 to 20 mPa·s as measured at 25° C. as a 20 mass % aqueous solution.
(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.
The ink set according to claim 1, wherein the first coloring agent and the second coloring agent have similar colors.
The ratio of the content (% by mass) of the second coloring agent in the second ink to the content (% by mass) of the first coloring agent in the first ink is 3. 3. The ink set according to claim 1, wherein the number is 0 or more.
The ink set according to any one of claims 1 to 3, wherein the first coloring agent and the second coloring agent are dyes.
2. 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. 5. The ink set according to any one of claims 1 to 4.
1 to 1, wherein a ratio of the viscosity of the second ink at 25° C. to the viscosity of the first ink at 25° C. is in the range of 0.7 to 1.3. 5. The ink set according to any one of items 1 to 5.
Both the first ink and the second ink contain an organic solvent, and the content (% by mass) of the organic solvent in the first ink and the content of the organic solvent in the second ink ( %) is 10% by mass or less, the ink set according to any one of claims 1 to 6.
Both the first ink and the second ink contain an organic solvent, and the content (% by mass) of the organic solvent in the first ink and the content of the organic solvent in the second ink ( %) is 30% by mass or less, the ink set according to any one of claims 1 to 7.
9. The method according to any one of claims 1 to 8, wherein the polymer accounts for 50% by mass or more of the total solid content of the first ink, excluding the first colorant. The ink set according to any one of paragraphs.
The ink set according to any one of claims 1 to 9, wherein the polymer has an anionic group.
The ink set according to any one of claims 1 to 10, wherein the degree of polymerization of the polymer is within the range of 2-10.
The ink set according to any one of claims 1 to 11, wherein the polymer contains a salt of polycarboxylic acid or a salt of naphthalenesulfonic acid formalin condensate.
The viscosity of the first ink at 25° C. and the viscosity of the second ink at 25° C. are both 6 mPa·s or more, according to any one of claims 1 to 12. Ink set as described.