JP2024080207A - Aqueous ink set, method for manufacturing aqueous ink set, inkjet recording method and inkjet recording system - Google Patents

Abstract

To provide an aqueous ink set which makes a dot diameter formed of colored ink uniform regardless of presence/absence of treatment ink, and reduces unevenness in solid printing.SOLUTION: An aqueous ink set is an aqueous ink set which has treatment ink and colored ink and performs printing on a non/low absorptive base material, wherein the treatment ink contains a coagulant, the colored ink contains a coloring material and a surface adjusting agent, when a contact angle of the colored ink to the non/low absorptive base material having critical surface tension at 25°C of 44 mN/m is represented by A1[°], and a contact angle of the colored ink to the non/low absorptive base material obtained by coating and drying the treatment ink is represented by B1[°], the contact angles satisfy the following expression (1). Expression (1): |A1-B1|≤10°.SELECTED DRAWING: Figure 1

Description

The present invention relates to an aqueous ink set, a method for producing the aqueous ink set, an inkjet recording method, and an inkjet recording system. More specifically, the present invention relates to an aqueous ink set in which the dot diameters formed by the colored inks are uniform regardless of the presence or absence of a treatment ink, and in which unevenness during solid printing is reduced.

Inkjet recording (hereinafter also referred to as "inkjet printing") is capable of producing images simply and inexpensively, and is therefore applied to a variety of printing fields including photography, various types of printing, marking, and special printing such as color filters.
In particular, inkjet printing allows digital printing without using a plate, and is therefore particularly suitable for applications such as forming a variety of images in small quantities.

In inkjet printing, particularly when using water-based inks, when a pattern of letters or images is printed on the surface of a substrate (recording medium), the liquid components penetrate into the substrate and then dry, fixing the ink. When the substrate is made of a material with high ink absorption, such as plain paper, special paper, high-quality paper, or recycled paper, the ink is easily fixed and a high-quality image can be produced. On the other hand, when the substrate is made of a material with low or no ink absorption, such as coated paper, art paper, lightly coated paper, or film, the ink droplets do not penetrate into the substrate easily. As a result, drying by penetration does not occur, and the droplets bleed into each other, compromising image quality.

As a method for improving the image quality of recorded material, a method is known in which a treatment liquid for modifying the surface of a substrate with low or no ink absorption is applied. There are two types of treatment liquid (also called "reaction liquid" or "treatment ink"): one that forms a layer (ink receiving layer) that absorbs the liquid components of the ink and improves the drying property, and one that forms a layer (ink aggregation layer) that prevents bleeding between ink droplets and color unevenness by intentionally inducing thickening of the ink by agglomerating solid components.
A known method for forming an ink aggregation layer involves applying a treatment liquid and ink containing an aggregating agent to the surface of a substrate, quickly aggregating the coloring material in the ink and fixing the ink.

However, when using inkjet printing in a two-liquid system that uses both treatment liquid and ink, it is difficult to make all dots formed from a mixture of treatment liquid and ink. In addition to dots formed from a mixture of treatment liquid and ink, dots formed from treatment liquid alone and dots formed from ink alone will always be produced. In other words, three types of dots with different constituent components are produced, and so the dot diameters tend to vary. This variation in dot diameter causes the problem of unevenness easily occurring in solid printing.

To address this issue, methods are being considered that involve adding a surface modifier to the ink to control the surface tension of the ink.

Patent Document 1 discloses a technology for an ink that contains a specific colorant and a specific amount of wax particles as a surface conditioner. However, this technology is intended for coloring fabrics that have high ink absorbency, and is not intended for coloring substrates that have low or no ink absorbency.

Patent Document 2 discloses a two-liquid system technology that uses both a treatment liquid and an ink. More specifically, it combines a treatment liquid containing a calcium salt as an aggregating agent, a solvent, a surfactant, and water with an ink containing a colorant, a surfactant, a polyurethane binder, a solvent, and water. The ink may further contain wax. However, this technology combines a treatment liquid and ink that are suitable for wet-on-wet printing. Therefore, the problem of unevenness in solid printing due to variations in dot diameter remains unresolved.

JP 2020-002220 A US Patent Application Publication No. 2019/0375223

The present invention has been made in consideration of the above problems and circumstances, and the problem to be solved is to provide an aqueous ink set, a manufacturing method for the aqueous ink set, an inkjet recording method, and an inkjet recording system in which the dot diameter formed by the colored ink is uniform regardless of the presence or absence of treatment ink, and in which unevenness during solid printing is reduced.

The present inventors have investigated the causes of the above problems in order to solve the above problems, and as a result, have found that in an aqueous ink set which has a treated ink and a colored ink and is to be printed on a non-low absorbency substrate, the treated ink contains an aggregating agent, the colored ink contains a colorant and a surface conditioner, and when the contact angle of the colored ink with a non-low absorbency substrate having a critical surface tension of 44 mN/m at 25°C is A1 [°], and the contact angle of the colored ink with a non-low absorbency substrate on which the treated ink has been applied and dried is B1 [°], the unevenness during solid printing can be reduced by satisfying the following formula (1), which led to the present invention.
That is, the above-mentioned problems of the present invention are solved by the following means.

1. A water-based ink set for printing on a non-low absorbency substrate, comprising a treated ink and a colored ink,
the treated ink contains a flocculant;
the color ink contains a color material and a surface modifier;
When the contact angle of the colored ink with respect to the non-low absorbency substrate having a critical surface tension of 44 mN/m at 25° C. is A1 [°], and the contact angle of the colored ink with respect to the non-low absorbency substrate onto which the treated ink has been applied and dried is B1 [°], the following formula (1) is satisfied: |A1-B1|≦10°
A water-based ink set comprising:

2. The surface conditioner contains a wax,
When the content of the wax with respect to the total mass of the colored ink is X [mass %], the contact angle of the composition of the colored ink excluding only the wax with respect to the non-low absorbency substrate having a critical surface tension of 44 mN/m at 25°C is A2 [°], and the contact angle of the composition of the colored ink excluding only the wax with respect to the non-low absorbency substrate onto which the treated ink has been applied and dried is B2 [°], the following formula (2) is satisfied: Formula (2): 10 [°/mass %]≦|A2−B2|/X≦40 [°/mass %]
2. The water-based ink set according to claim 1.

3. The water-based ink set described in item 1, wherein the surface conditioner contains a polyolefin wax.

4. The water-based ink set according to item 3, wherein the polyolefin wax is nonionic.

5. The water-based ink set described in Item 2, wherein the content X [mass %] of the wax is within a range of 0.01 to 5 mass % with respect to the total mass of the color inks.

6. The color ink contains a dispersant,
2. The water-based ink set described in item 1, wherein the acid value of the dispersant is within a range of 50 to 120 mg KOH/g.

7. The water-based ink set described in item 1, wherein the water-based ink set comprises two or more of the color inks.

8. The water-based ink set described in item 1, wherein the coagulant is a metal salt.

9. The water-based ink set described in item 8, wherein the content of the metal salt is within a range of 1 to 10% by mass with respect to the total mass of the treatment ink.

10. A method for producing the water-based ink set according to any one of items 1 to 9, comprising the steps of:
adding the coagulant to the treatment ink; and adding the coloring material and the surface conditioner to the color ink,
When the contact angle of the colored ink with respect to the non-low absorbency substrate having a critical surface tension of 44 mN/m at 25° C. is A1 [°], and the contact angle of the colored ink with respect to the non-low absorbency substrate to which the treated ink has been applied and dried is B1 [°], the amount of the surface conditioner added is adjusted so as to satisfy the following formula (3): |A1-B1|≦10°
A method for producing a water-based ink set.

11. An ink-jet recording method, comprising using the water-based ink set according to any one of items 1 to 9.

12. The flocculant is a metal salt;
the content of the metal salt is within a range of 1 to 10% by mass based on the total mass of the treatment ink;
When the applied amount of the treatment ink is C _P [g/m ² ] and the applied amount of the color ink is C _I [g/m ² ], the following formula (4) is satisfied: 0.05≦C _P /C _I <1.00.
12. The ink-jet recording method according to item 11,

13. The ink-jet recording method described in item 11, wherein the non-low absorbency substrate has a critical surface tension at 25° C. in the range of 35 to 48 mN/m.

14. An inkjet recording system using a water-based ink set, comprising:
The water-based ink set is the water-based ink set according to any one of items 1 to 9,
an inkjet head for ejecting the treatment ink and the color ink;
The inkjet recording system, wherein the inkjet head has a piezoelectric element.

The above-mentioned means of the present invention make it possible to provide an aqueous ink set, an aqueous ink set manufacturing method, an inkjet recording method, and an inkjet recording system in which the dot diameters formed by the colored inks are uniform regardless of the presence or absence of a treatment ink, and in which unevenness during solid printing is reduced.

Although the mechanism by which the effects of the present invention are expressed or acted upon has not been clarified, it is speculated as follows.

As mentioned above, in a two-liquid system that uses a combination of a treatment liquid (hereinafter also referred to as "treatment ink") and an ink (hereinafter also referred to as "colored ink"), it is difficult to make all dots formed as a mixture of the treatment ink and the colored ink. There will inevitably be dots formed from the treatment ink alone and dots formed from the colored ink alone. In other words, at least three types of dots with different constituent components will be produced, and so the dot diameters are likely to vary. This variation in dot diameters creates the problem of unevenness easily occurring in solid printing.

Figure 1 shows a schematic diagram of the variation in dot diameter formed by the treatment ink and colored ink. In a two-liquid system that uses both treatment ink and colored ink, a total of four types of dots are formed: dots 101 formed by colored ink alone, dots 102 formed by treatment ink alone, dots (completely merged) 103 formed by a mixture of treatment ink and colored ink, and dots (partially merged) 104 formed by a mixture of treatment ink and colored ink (hereinafter, these will be simply referred to as "dots 101," "dots 102," "dots 103," and "dots 104," respectively).

On the left side of Figure 1 (large variation), there is a large difference in dot diameter between dot 101 and dots 102 and 103. In this case, in addition to the difference in dot diameter, dot (partially merged) 104 formed from a mixture of treatment ink and colored ink is likely to be distorted in shape. Therefore, unevenness is likely to occur when printing solid images.

On the other hand, on the right side of Figure 1 (small variation), the difference between the dot diameter of dot 101 and the dot diameters of dot 102 and dot 103 is small. In this case, the dot (partially merged) 104 formed from a mixture of the treatment ink and colored ink is also less likely to be distorted in shape. Therefore, unevenness is less likely to occur when printing solid images.

In other words, it is believed that by reducing the difference between the dot diameter of dot 101 and the dot diameters of dots 102 and 103, it is possible to reduce unevenness during solid printing.

Now, let us consider the case where the treatment ink is applied without gaps (not forming dots, but applying it uniformly) on the surface to which the colored ink is applied, and dots are formed with the colored ink. In this case, the dots formed with the colored ink all merge with the treatment ink, so the dot diameter is uniform. However, while increasing the amount of treatment ink applied makes it easier for the ink to aggregate, the aggregated ink also becomes more likely to fluctuate in the treatment ink. Fluctuations in the aggregated ink can lead to unevenness when printing solid images, so the amount of treatment ink needs to be optimized.

Therefore, in reality, the treatment ink is applied by forming dots on the substrate, so there are areas in the area where the colored ink is applied where the treatment ink is not applied. The larger (wider) the area where the treatment ink is not applied, the easier it is to form dots 101, 102, and 104 in addition to dot 103. And, if the area where the treatment ink is not applied is made even larger (wider), the dot configuration will have more dots 101 and 103 compared to dots 102 and 104.

In other words, by reducing the difference between the dot diameter of dot 101 and the dot diameter of dot 103, it is believed that unevenness during solid printing can be reduced when the amount of treatment ink applied (amount applied) is reduced.

However, by reducing the difference in dot diameter between dot 101 and dot 103, the difference in dot diameter between dot 102 and dot 104 will inevitably be reduced, and the shape of dot 104 will be less likely to become distorted. Therefore, by reducing the difference in dot diameter between dot 101 and dot 103, it is believed that unevenness during solid printing can be reduced, regardless of the amount of treatment ink applied.

In order to reduce the difference in dot diameter between the dot 101 and the dot 103, the wettability of the color ink and the wettability of the mixture of the treatment ink and the color ink may be approximately the same.
In the present invention, it is believed that the inclusion of a surface conditioner in the color ink makes it possible to make the wetting properties of the color ink and the wetting properties of the mixture of the treatment ink and the color ink comparable.
Specifically, it is believed that by adjusting the ratio so as to satisfy the following formula (1), the wettability of the color ink and the wettability of the mixture of the treatment ink and the color ink can be made to be approximately the same.
Even if a surface conditioner is selected and added for the purpose of increasing the contact angle of the color ink, the contact angle of the mixture of the treated ink and the color ink does not necessarily increase similarly, and may even decrease. In other words, since the wettability varies greatly depending on the constituents and contents of each ink and the surface conditioner, it is difficult to estimate the suitable content of the surface conditioner. Therefore, it is necessary to make the aqueous ink set satisfy the following formula (1).

Formula (1): |A1-B1|≦10°
A1 and B1 are as follows.
A1 [°]: Contact angle of a colored ink to a non-low-absorbency substrate having a critical surface tension of 44 mN/m.
B1 [°]: The contact angle of the colored ink with respect to a non-low absorbency substrate on which the treated ink has been applied and dried.

Schematic diagram of the variation in dot diameter formed by treatment ink and color ink FIG. 1 is a schematic diagram showing an example of an inkjet recording apparatus preferred for the present invention.

The water-based ink set of the present invention has a treated ink and a colored ink, and is used for printing on a non-low absorbency substrate, wherein the treated ink contains an aggregating agent, the colored ink contains a colorant and a surface conditioner, and is characterized in that when the contact angle of the colored ink with respect to the non-low absorbency substrate having a critical surface tension of 44 mN/m at 25°C is A1 [°], and the contact angle of the colored ink with respect to the non-low absorbency substrate on which the treated ink has been applied and dried is B1 [°], the following formula (1) is satisfied:
Formula (1): |A1-B1|≦10°
This feature is a common or corresponding technical feature of the following embodiments.

In an embodiment of the present invention, from the viewpoint of controlling the wetting and spreading of the colored ink, it is preferable that the surface conditioner contains a wax, the content of the wax relative to the total mass of the colored ink is X [mass %], the contact angle of a composition of the colored ink excluding only the wax with respect to the non-low absorbency substrate having a critical surface tension of 44 mN/m at 25°C is A2 [°], and the contact angle of the composition of the colored ink excluding only the wax with respect to the non-low absorbency substrate onto which the treatment ink has been applied and dried is B2 [°], thereby satisfying the following formula (2).
Formula (2): 10[°/mass%]≦|A2−B2|/X≦40[°/mass%]

In an embodiment of the present invention, from the viewpoint of surface alignment ability in colored inks, it is preferable that the surface conditioner contains a polyolefin wax.

In an embodiment of the present invention, from the viewpoint of controlling the aggregation of the colored ink, it is preferable that the polyolefin wax is nonionic.

In an embodiment of the present invention, from the viewpoint of ejection stability of the colored ink, it is preferable that the wax content X [mass %] is within the range of 0.01 to 5 mass % with respect to the total mass of the colored ink.

In an embodiment of the present invention, from the viewpoint of controlling the aggregation of the colored ink, it is preferable that the colored ink contains a dispersant, and that the acid value of the dispersant is within the range of 50 to 120 mg KOH/g.

In an embodiment of the present invention, from the viewpoint of controlling color dots during multi-color printing, it is preferable that the water-based ink set contains two or more of the colored inks.

In an embodiment of the present invention, from the viewpoint of controlling the aggregation of the treated ink, it is preferable that the aggregating agent is a metal salt, and the content of the metal salt is preferably within the range of 1 to 10 mass % relative to the total mass of the treated ink.

The manufacturing method of the water-based ink set of the present invention is a manufacturing method of the water-based ink set of the present invention, which comprises the steps of adding the coagulant to the treatment ink, and adding the colorant and the surface conditioner to the colored ink, and is characterized in that the amount of the surface conditioner added is adjusted so as to satisfy the following formula (3), where A1 [°] is the contact angle of the colored ink with the non-low absorbency substrate having a critical surface tension of 44 mN/m at 25° C., and B1 [°] is the contact angle of the colored ink with the non-low absorbency substrate on which the treatment ink has been applied and dried.
Formula (3): |A1-B1|≦10°

The inkjet recording method of the present invention is characterized by using the water-based ink set of the present invention.

In an embodiment of the present invention, from the viewpoint of controlling aggregation of the treatment ink and the color ink, it is preferable that the aggregating agent is a metal salt, the content of the metal salt is within the range of 1 to 10 mass % relative to the total mass of the treatment ink, and when the application amount of the treatment ink is C _P [g/m ² ] and the application amount of the color ink is C _I [g/m ² ], the following formula (4) is satisfied:
Formula (4): 0.05≦C _P /C _I <1.00

An embodiment of the present invention is an ink set based on a two-liquid aggregation mechanism on a non-low absorbency substrate, and from the viewpoint of controlling the wetting and spreading of the treatment ink and color ink, it is preferable that the critical surface tension of the non-low absorbency substrate at 25°C is within the range of 35 to 48 mN/m.

The inkjet recording system of the present invention is an inkjet recording system that uses an aqueous ink set, the aqueous ink set being the aqueous ink set of the present invention, and having an inkjet head that ejects the treatment ink and the colored ink, the inkjet head having a piezoelectric element.

The present invention, its components, and the forms and modes for implementing the present invention are described in detail below. Note that in this application, "~" is used to mean that the numerical values before and after it are included as the lower and upper limits.

1. Overview of Water-Based Ink Set The water-based ink set of the present invention has a treated ink and a colored ink, and is used for printing on a non-low-absorbency substrate, the treated ink containing an aggregating agent, the colored ink containing a coloring material and a surface conditioner, and is characterized in that the following formula (1) is satisfied when the contact angle of the colored ink with respect to the non-low-absorbency substrate having a critical surface tension of 44 mN/m at 25° C. is A1 [°], and the contact angle of the colored ink with respect to the non-low-absorbency substrate on which the treated ink has been applied and dried is B1 [°].
Formula (1): |A1-B1|≦10°

The treatment ink and color ink according to the present invention are aqueous inks, and use at least water or a water-soluble solvent as a solvent. The aqueous ink set according to the present invention is an aqueous ink set for printing on a non- or low-absorbency substrate.
In the present invention, the term "non-low-absorbency substrate" refers to a substrate that has no or low absorbency for color inks. Details will be described later.

Furthermore, the treatment ink according to the present invention may be either a pre-treatment ink or a post-treatment ink.
Here, "pre-treatment ink" refers to a treatment ink that is applied to a non-low absorbency substrate before or simultaneously with the application of a colored ink to the non-low absorbency substrate, and "post-treatment ink" refers to a treatment ink that is applied to a non-low absorbency substrate after the application of a colored ink to the non-low absorbency substrate.

The water-based ink set of the present invention preferably contains two or more colored inks. By using the above-mentioned production method, even if a plurality of colored inks are used in combination, the dot diameter of the dots formed can be adjusted and unevenness during solid printing can be sufficiently suppressed.
By satisfying the above formula (1) in all the color inks used, the solid uniformity is improved in multicolor printing on non- or low-absorbency substrates, and it is possible to form high-quality images without unevenness. In addition, by satisfying the above formula (2) in all the color inks used, the effect is even more remarkable.

In the present invention, it is believed that by adjusting the above formula (1) to be satisfied, the wettability of the color ink and the wettability of the mixture of the treatment ink and the color ink can be made to be approximately the same.
Specifically, it is believed that by adjusting the content of the surface conditioner so as to satisfy the above formula (1), the wettability of the color ink and the wettability of the mixture of the treatment ink and the color ink can be made to be approximately the same.

Furthermore, when the surface conditioner contains a wax, the content of the wax relative to the total mass of the colored ink is X [mass %], the contact angle of the composition of the colored ink excluding only the wax with respect to a non-low absorbency substrate having a critical surface tension of 44 mN/m at 25°C is A2 [°], and the contact angle of the composition of the colored ink excluding only the wax with respect to a non-low absorbency substrate to which the treated ink has been applied and dried is B2 [°], it is preferable that the surface conditioner satisfies the following formula (2).
Formula (2): 10[°/mass%]≦|A2−B2|/X≦40[°/mass%]

When the surface conditioner is a wax, the wetting and spreading of the colored ink on non- or low-absorbency substrates can be controlled by adjusting the wax content to satisfy the above formula (2).

(1) Method for Measuring Contact Angle The contact angle according to the present invention is a static contact angle measured by a sessile drop method.
Specifically, the amount of the color ink droplet is 3 μL, and the contact angle is measured 65 ms (milliseconds) after the droplet lands on the substrate at room temperature of 25° C. For example, a contact angle meter “DM500” (manufactured by Kyowa Interface Science Co., Ltd.) can be used as the contact angle measuring device.
The contact angles A2 [°] and B2 [°] are measured when the surface conditioner is a wax. It is preferable that the relationship between the contact angle and the wax content satisfies the above formula (2).

The contact angle A1 [°] is the contact angle of the colored ink with respect to a non-low-absorbency substrate. In the measurement for evaluating whether the requirements of the present invention are met, specifically, the contact angle of the colored ink with respect to a non-low-absorbency substrate (hereinafter also referred to as "untreated substrate for measurement") having a critical surface tension of 44 mN/m at 25°C is measured.

The contact angle B1 [°] is the contact angle of the colored ink with respect to a non-low absorbency substrate on which the treated ink has been applied and dried.
Specifically, the treated ink is applied to the untreated substrate for measurement using a bar coater. As the bar coater, for example, a "Bar Coater #4" (manufactured by Daiichi Rika Co., Ltd.) can be used. The treated ink is applied so that the amount of ink applied is within the range of 9 to 10 g/ ^m2 . The treated ink is then dried on a hot plate at 80°C for 10 minutes to obtain a "treated substrate for measurement." The contact angle of the colored ink with respect to the treated substrate for measurement is then measured.

The contact angle A2 [°] is the contact angle of a composition (hereinafter referred to as "wax-removing ink") from the colored ink in which only the wax has been removed, with respect to a non-low-absorbency substrate. Specifically, a wax-removing ink is prepared in which only the wax in the colored ink is replaced with a solvent (e.g., water) and the content of the other components is kept constant. Then, the contact angle of the wax-removing ink with respect to an untreated substrate for measurement is measured.

The contact angle B2 [°] is the contact angle of the composition of the colored ink, excluding the wax, with a non-low-absorbency substrate on which the treated ink has been applied and dried. Specifically, the contact angle of the wax-removed ink with the treated substrate for measurement is measured.

The contact angles are summarized as follows:
[A1] Substrate: no treatment, colored ink: with surface conditioner.
[B1] Substrate: treated, colored ink: with surface conditioner.
[A2] Substrate: no treatment, colored ink: no wax.
[B2] Substrate: treated, colored ink: no wax.

The contact angle A1 [°] is preferably within the range of 45 to 60°, and more preferably within the range of 47 to 57°.
The contact angle B1 [°] is preferably within the range of 55 to 70°, and more preferably within the range of 55 to 65°.
The contact angle A2 [°] is preferably within a range of 35 to 50°, and more preferably within a range of 40 to 50°.
The contact angle B2 [°] is preferably within the range of 55 to 70°, and more preferably within the range of 55 to 65°.

(2) Content of Surface Conditioner It is preferable to adjust the content of the surface conditioner so that the contact angle of the color ink is approximately the same regardless of whether the substrate is treated or not, i.e., so that the above formula (1) is satisfied.

In addition, the content of the surface conditioner preferably satisfies the following formula (2).
Formula (2): 10[°/mass%]≦|A2−B2|/X≦40[°/mass%]
Here, X is the content [mass %] of the surface conditioner relative to the total mass of the color ink.

From the viewpoint of preventing unevenness during solid printing, it is preferable to satisfy the above formula (1) by adjusting the content of the surface conditioner. However, from the viewpoint of controlling the wetting and spreading of the colored ink, it is also preferable to satisfy the above formula (2).

The color ink according to the present invention contains a coloring material and a surface conditioner. It is preferable that the ink contains at least water or a water-soluble solvent as a solvent, and may further contain other components such as resin particles and a surfactant.

(1) Coloring Material The coloring material may be either a pigment or a dye, but from the viewpoint of recording on a non- or low-absorbency substrate, a pigment is preferred.

(1.1) Pigment The pigment is preferably an anionic pigment dispersion. Examples of the anionic pigment dispersion include a self-dispersing pigment dispersion having an anionic group on the surface, and a pigment dispersion dispersed with an anionic polymer dispersant.
Among these, from the viewpoint of excellent pigment dispersibility and appropriate reaction between the treated ink and the pigment for pinning, a pigment dispersion dispersed with an anionic polymer dispersant is preferred, and more specifically, a form in which the pigment particles are dispersed by coating their surfaces with an anionic polymer dispersant is preferred.

There are no particular limitations on the pigment, and any conventionally known pigment can be used. Pigments are broadly divided into organic pigments and inorganic pigments. Examples of organic pigments include insoluble pigments that are inherently insoluble in water, and lake pigments, which are dyes that have been made into metal lakes to be insoluble in water. Examples of inorganic pigments include titanium oxide.

There are no particular limitations on the pigment content. However, it is preferable that the organic pigment content be within the range of 0.5 to 7% by mass relative to the total mass of the colored ink, and that the titanium oxide content be within the range of 7 to 18% by mass relative to the total mass of the colored ink.

Among the organic pigments, the insoluble pigments are not particularly limited. Examples of insoluble pigments include azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindolinone, isoindoline, azine, oxazine, thiazine, dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole, etc.

Specific examples of organic pigments that can be preferably used include the following pigments:

Examples of pigments for magenta or red include C.I. Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red 7, C.I. Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 48:1, C.I. Pigment Red 53:1, C.I. Pigment Red 57:1, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 139, C.I. Pigment Red 144, C.I. Pigment Red 149, C.I. Pigment Red 166, C.I. Pigment Red 177, C.I. Examples include C.I. Pigment Red 178, C.I. Pigment Red 202, C.I. Pigment Red 222, and C.I. Pigment Violet 19.

Examples of pigments for orange or yellow include C.I. Pigment Orange 31, C.I. Pigment Orange 43, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 15, C.I. Pigment Yellow 15:3, C.I. Pigment Yellow 17, C.I. Pigment Yellow 74, C.I. Pigment Yellow 93, C.I. Pigment Yellow 128, C.I. Pigment Yellow 94, C.I. Pigment Yellow 138, and C.I. Pigment Yellow 155.
Among these, C. I. Pigment Yellow 155 is preferred from the viewpoint of achieving both color tone and light resistance.

Examples of pigments for green or cyan include C.I. Pigment Blue 15, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 16, C.I. Pigment Blue 60, and C.I. Pigment Green 7.

Examples of black pigments include C.I. Pigment Black 1, C.I. Pigment Black 6, and C.I. Pigment Black 7.

(1.1.1) Pigment Dispersant The color ink according to the present invention preferably contains a pigment dispersant in order to disperse the pigment.
The pigment dispersant is not particularly limited, but is preferably a polymer dispersant having an anionic group. The molecular weight of the polymer dispersant is preferably within the range of 5,000 to 200,000.

Examples of the polymer dispersant include block copolymers and random copolymers having a structure derived from two or more monomers selected from styrene, styrene derivatives, vinylnaphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, and fumaric acid derivatives, and salts thereof. In addition, polyoxyalkylene and polyoxyalkylene alkyl ethers are also included.
Of these, the polymer dispersant preferably has an acryloyl group.

The polymer dispersant is preferably neutralized with a neutralizing base before addition.
The neutralizing base is not particularly limited, and examples thereof include organic bases such as ammonia, monoethanolamine, diethanolamine, triethanolamine, and morpholine.

In particular, when the pigment is titanium oxide, it is preferable that the titanium oxide is dispersed with a polymer dispersant having an acryloyl group.

In colored inks, the content of the polymer dispersant is preferably within the range of 10 to 100% by mass, and more preferably within the range of 10 to 40% by mass, relative to the total mass of the pigment.

It is preferable that the surface of the pigment particles be coated with an anionic polymer dispersant to form a dispersed form.

Methods for coating the surfaces of pigment particles with a polymeric dispersant can be any conventional method. Examples include phase inversion emulsification and acid precipitation. Another method is to disperse the pigment with a polymerizable surfactant, supply a monomer to the dispersion, and coat the surface while polymerizing it.

Among them, the following method is preferable.
A water-insoluble resin is dissolved in an organic solvent such as methyl ethyl ketone, and the acidic groups in the water-insoluble resin are partially or completely neutralized with a base. Then, a pigment and ion-exchanged water are added to disperse the pigment, and the organic solvent is removed and water is added as necessary to prepare a pigment dispersion.

The average dispersed particle diameter of the pigment in the colored ink is preferably 50 nm or more and less than 200 nm. By being within the above range, the dispersion stability of the pigment can be improved, and the storage stability of the colored ink can be improved.

The dispersed particle size of pigments can be measured using commercially available particle size measuring devices that use dynamic light scattering, electrophoresis, etc. Among these, measurement using dynamic light scattering is simple and can measure the dispersed particle size range with high accuracy.

The pigment is dispersed in a dispersing machine together with a dispersant and other additives.
Examples of the dispersing machine include conventionally known ball mills, sand mills, line mills, high-pressure homogenizers, etc. Among them, dispersing the pigment with a sand mill is preferred because it results in a sharp particle size distribution of the pigment particles.
The material of the beads used for dispersion in the sand mill is not particularly limited. However, from the viewpoint of preventing the generation of bead fragments and the contamination of ion components, it is preferable that the material is zirconia or zircon. The diameter of the beads is preferably within the range of 0.3 to 3 mm.

(Acid value)
The acid value of the pigment dispersant is preferably within the range of 50 to 120 mgKOH/g. By having the acid value within the above range, the reactivity with the flocculating agent is improved.

The "acid value" refers to the number of milligrams of potassium hydroxide [mgKOH/g] required to neutralize the carboxyl groups present in 1 g of sample. Specifically, it can be measured by the following method in accordance with JIS K0070-1992.

(Method of measuring acid value)
(1) Preparation of Reagents (a) Phenolphthalein Solution 1.0 g of phenolphthalein is dissolved in 90 mL of ethyl alcohol (95 vol %). Ion-exchanged water is added to make 100 mL to obtain a phenolphthalein solution.

(b) Potassium hydroxide solution 7 g of special grade potassium hydroxide is dissolved in 5 mL of ion-exchanged water, and ethyl alcohol (95 [vol%]) is added to make 1 L. The solution is then placed in an alkali-resistant container to avoid contact with carbon dioxide gas, and left for 3 days, after which it is filtered to obtain a potassium hydroxide solution. The obtained potassium hydroxide solution is stored in an alkali-resistant container.

(c) Factor of potassium hydroxide solution The factor of potassium hydroxide solution is calculated by placing 25 mL of 0.1 mol/L hydrochloric acid in an Erlenmeyer flask, adding a few drops of phenolphthalein solution, and titrating with potassium hydroxide solution.The factor is calculated from the amount of potassium hydroxide solution required for neutralization.

(d) Hydrochloric Acid Solution 0.1 mol/L hydrochloric acid prepared in accordance with JIS K8001-1998 is used.

(2) Procedure (a) Main Test 2.0 g of a dispersant sample was weighed out accurately into a 200 mL Erlenmeyer flask, and 100 mL of a mixture of toluene and ethanol (2:1) was added and dissolved over 5 hours. Then, several drops of phenolphthalein solution were added as an indicator, and the solution was titrated with potassium hydroxide solution.
The titration end point is when the indicator remains a pale red color for approximately 30 seconds.

(b) Blank test: A similar titration is carried out, except that no sample is used (i.e., only a mixture of toluene:ethanol (2:1) is used).

(3) The obtained result is substituted into the following formula to calculate the acid value.
Formula: A = ([C-D] x f x 5.611) / S
here,
A: Acid value [mg KOH / g]
C: Amount of potassium hydroxide solution added in this test [mL]
D: Amount of potassium hydroxide solution added for blank test [mL]
f: Factor of 0.1 [mol / L] potassium hydroxide ethanol solution 5.611: Molar mass of potassium hydroxide 56.11 [g / mol] × (1 / 10)
S: mass of sample [g]

Commercially available pigment dispersants may be used. Examples of commercially available products include "Joncryl (registered trademark) 819" (manufactured by BASF), "Joncryl (registered trademark) HPD-671" (manufactured by BASF), and "AW300P" (manufactured by Otsuka Chemical Co., Ltd.).

(2) Surface Conditioner By including a surface conditioner in the color ink, the wettability of the color ink can be controlled. More specifically, in the manufacturing method of the color ink, by adjusting the content of the surface conditioner so that the contact angle of the color ink with the non- or low-absorbency substrate satisfies the above formula (1), unevenness during solid printing can be reduced.

In the present invention, the "surface conditioner" refers to a compound that has the function of changing the surface tension of droplets when added.
The content of the surface conditioner is not particularly limited, but is preferably within the range of 0.01 to 5% by mass relative to the total mass of the color ink.

Surface conditioners are not particularly limited, and examples include wax-based, silicone-based, acrylic-based, vinyl-based, fluorine-based, and acetylene glycol-based surface conditioners.

(2.1) Wax The surface conditioner is not particularly limited, but is preferably a wax from the viewpoint of obtaining the desired wettability and the storage stability of the colored ink.
In the present invention, "wax" refers to an organic compound that is solid at room temperature (25°C) and becomes liquid when heated. It also refers to a compound that melts without decomposing in a temperature environment above its melting point. The melting point of the wax is preferably within the range of 50 to 170°C.

The wax is not particularly limited, but is preferably a polyolefin wax from the viewpoint of surface orientation in the colored ink.
In the present invention, the term "olefin" refers to a chain hydrocarbon compound having one or more carbon-carbon double bonds in the molecule, and the term "polyolefin" refers to a polymer obtained by using the above-mentioned olefin as a monomer.

The polyolefin wax is not particularly limited, and examples thereof include waxes produced from olefins such as ethylene, propylene, butylene, or derivatives thereof, and copolymers thereof. Specific examples include polyethylene-based waxes, polypropylene-based waxes, polybutylene-based waxes, etc. Among these, polyethylene-based waxes are preferred from the viewpoint of suppressing cracking of recorded matter.
These may be used alone or in combination of two or more.

It is preferable to use the polyolefin wax in the form of a polyolefin wax emulsion in which solid wax particles are dispersed in water using a surfactant, as described below.

From the viewpoint of storage stability of the colored ink, the dispersion form of the wax particles is preferably anionic or nonionic, and from the viewpoint of controlling aggregation of the colored ink, it is more preferable that the dispersion form be nonionic.

From the viewpoint of achieving both the storage stability of the colored ink and the abrasion resistance of the recorded matter, the melting point of the wax is preferably within the range of 60 to 150°C, and more preferably within the range of 80 to 150°C. By making the melting point 60°C or higher, the storage stability of the colored ink can be improved. Furthermore, by making the melting point 120°C or lower, the abrasion resistance can be improved.

From the viewpoint of ejection stability, the average particle size of the wax particles is preferably 0.3 μm or less, and more preferably 0.2 μm or less.

The polyethylene wax emulsion can be prepared by the following method.
Polyethylene wax is obtained by polymerizing ethylene, synthesizing it from a hydrocarbon compound, or by pyrolyzing polyethylene for general molding to reduce its molecular weight, etc. This polyethylene wax is then oxidized to add carboxyl and hydroxyl groups, and emulsified using a surfactant to obtain a polyethylene wax emulsion in the form of an aqueous wax emulsion with excellent stability.

Commercially available polyolefin waxes include the Chemipearl (registered trademark) series, such as "Chemipearl (registered trademark) WF4002" (manufactured by Mitsui Chemicals, Inc., polyethylene wax, particle size 200 nm, ring and ball softening point 110°C), "Chemipearl (registered trademark) S120," "Chemipearl (registered trademark) S650," and "Chemipearl (registered trademark) S75N."

Other products include "AQUACER (registered trademark) 513 (polyethylene wax, particle size 100-200 nm, melting point 130°C, solid content 30%)", "AQUACER (registered trademark) 501", "AQUACER (registered trademark) 506", "AQUACER (registered trademark) 515", "AQUACER (registered trademark) 517", "AQUACER (registered trademark) 526", "AQUACER (registered trademark) 531", "AQUACER (registered trademark) 582", and "AQUACER (registered trademark) 593" (all BYK Additives & Examples include the AQUACER (registered trademark) series (manufactured by Axel Instruments Co., Ltd.), the Hi-Tech series ("Hi-Tech E-7025P", "Hi-Tech E-2213", "Hi-Tech E-9460", "Hi-Tech E-9015", "Hi-Tech E-4A", "Hi-Tech E-5403P", "Hi-Tech E-6314", "Hi-Tech E-1000", and "Hi-Tech E-8237" (all manufactured by Toho Chemical Industry Co., Ltd.), and "Nopcoat PEM-17" (manufactured by San Nopco Ltd., polyethylene emulsion, particle size 40 nm).

Other examples include "Polylon L-787" (manufactured by Chukyo Yushi Co., Ltd., polyethylene, nonionic, melting point 102°C, particle size 0.1 μm), "Hydrin L-703" (manufactured by Chukyo Yushi Co., Ltd., paraffin, anionic, melting point 75°C, particle size 0.4 μm), "R108" (manufactured by Chukyo Yushi Co., Ltd., paraffin, nonionic, melting point 66°C, particle size 0.2 μm), "Cellosol (registered trademark) 524" (manufactured by Chukyo Yushi Co., Ltd., carnauba, nonionic, melting point 83°C, particle size 0.07 μm), and "Trasol PF60" (manufactured by Chukyo Yushi Co., Ltd., paraffin wax, nonionic, melting point 66°C, particle size 0.3 μm).

These are commercially available in the form of aqueous emulsions in which polyolefin waxes are dispersed in water by conventional methods. Therefore, they can be added directly to colored inks in the form of aqueous emulsions.

From the viewpoint of ejection stability from the nozzle, the wax content is preferably within the range of 0.01 to 5% by mass relative to the total mass of the colored ink.

(2.2) Surfactants Surface conditioners other than wax include surfactants.
By including a surfactant in the color ink, the wettability of the color ink can be controlled, and the ejection stability from the nozzles can be improved.

The surfactant is not particularly limited. However, when an anionic component is contained as a component other than the coloring material contained in the color ink, the ionicity of the surfactant may be anionic, nonionic (also called "nonionic"), or amphoteric (having both cationic and anionic functional groups). Furthermore, it is preferable that the amphoteric surfactant is of the betaine type.

Examples of the surfactant include fluorine-based or silicone-based surfactants that have a high static surface tension reducing ability, and anionic surfactants such as dioctyl sulfosuccinate that have a high dynamic surface tension reducing ability, as well as nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, acetylene glycols, Pluronic (registered trademark) type surfactants, and sorbitan derivatives that have relatively low molecular weights.
A fluorine-based or silicone-based surfactant having a high static surface tension reducing ability may be used in combination with a surfactant having a high dynamic surface tension reducing ability.

The surfactant content is preferably within the range of 0.1 to 5.0% by mass, and more preferably within the range of 0.1 to 2.0% by mass, relative to the total mass of the colored ink.

(2.2.1) Silicone-based surfactants By using a silicone-based surfactant, it is possible to further suppress ink mixing (beading) on substrates made of hydrophobic resins, such as polyvinyl chloride sheets, and substrates with low ink absorbency, such as printing paper, thereby achieving high image quality.

The silicone surfactant is preferably a polyether-modified silicone, such as a siloxane having an alkylene oxide group at the side chain and/or at both ends of the polydimethylsiloxane chain.

Specifically, "BYK-331", "BYK-333", "BYK-345", "BYK-3450", "BYK-3451", "BYK-3455", "BYK-346", "BYK-347", "BYK-348", and "BYK-349" (all manufactured by BYK-Chemie), "TEGOWetKL245", "TEGOWet250", "TEGOWet260", "TEGOWet270", and "TEGOWet280" (all manufactured by Evonik) ), "KF-351A", "KF-352A", "KF-353", "KF-354L", "KF-355A", "KF-615A", "KF-640", "KF-642", "KF-643", "KF-644", "KF-945", "KF-6011", "KF-6012", "KF-6015", "KF-6017", "KF-6020", "KF-6204", and "X-22-4515" (all manufactured by Shin-Etsu Chemical Co., Ltd.).

Among these, trisiloxane having alkylene oxide groups at the side chain and/or both ends of a polydimethylsiloxane chain is preferable, since the dynamic surface tension of the treated ink can be effectively reduced and the fixation to the substrate can be improved.
The trisiloxane preferably has a structure represented by the following general formula (1).

In general formula (1), "EO" represents the repeating unit structure of polyethylene oxide, i.e., a structure in which ethylene oxide, a three-membered cyclic ether, is ring-opened. Also, "PO" represents the repeating unit structure of polypropylene oxide, i.e., a structure in which propylene oxide, a three-membered cyclic ether, is ring-opened.

The order of [EO]m and [PO]n may be in either order.
Here, the phrase "the order of [EO]m and [PO]n may be either" means that in the compound molecule represented by general formula (1), the order of the bonding positions to the parent siloxane skeleton may be changed as appropriate.

In general formula (1), X is preferably an alkylene group having 3 carbon atoms (i.e., a propylene group). In addition, in general formula (1), m is preferably an integer from 5 to 20, and n is preferably an integer from 0 to 6.

Specific examples of silicone surfactants having the structure represented by the general formula (1) are shown below as (S-1) to (S-8), but are not limited to these.

(S-1): In the general formula (1), R=methyl group, X=alkylene group having 3 carbon atoms, m=9, and n=0.
(S-2): In the general formula (1), R=butyl group, X=alkylene group having 3 carbon atoms, m=25, and n=6.
(S-3): In the general formula (1), R=hydrogen atom, X=alkylene group having 3 carbon atoms, m=3, and n=0.
(S-4): In the general formula (1), R=hydrogen atom, X=alkylene group having 3 carbon atoms, m=33, and n=0.
(S-5): In the general formula (1), R=hydrogen atom, X=alkylene group having 3 carbon atoms, m=22, and n=16.
(S-6): In the general formula (1), R=hydrogen atom, X=alkylene group having 3 carbon atoms, m=9, and n=0.
(S-7): In the general formula (1), R=hydrogen atom, X=alkylene group having 3 carbon atoms, m=12, and n=3.
(S-8): In the general formula (1), R=hydrogen atom, X=alkylene group having 3 carbon atoms, m=1, and n=0.

Commercially available trisiloxanes may be used. Examples of commercially available products include "BYK-3450" and "BYK-3451" (both manufactured by BYK Japan), "TEGOWetKL245", "TEGOWet250", and "TEGOWet260" (all manufactured by Evonik).

The content of the silicone surfactant is preferably within the range of 0.5 to 2% by mass, and more preferably within the range of 0.5 to 1.5% by mass, based on the total mass of the colored ink.

(3) Solvent The color ink according to the present invention preferably contains at least water or a water-soluble solvent.
The content of water or the water-soluble solvent is preferably within a range of 5 to 60% by mass, and more preferably within a range of 10 to 50% by mass, based on the total mass of the color ink.

(3.1) Water The water is not particularly limited, and examples thereof include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, and ultrapure water.

(3.2) Water-soluble solvent The water-soluble solvent is not particularly limited, but preferably has a boiling point within the range of 150 to 250° C. Examples of the water-soluble solvent include alcohols, polyhydric alcohols, amines, amides, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms.

Examples of polyhydric alcohols having 2 to 8 carbon atoms include 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, and 2-methylpentane-2,4-diol.
Examples of the polyalkylene glycols include diethylene glycol and dipropylene glycol.
These may be used alone or in combination of two or more.

It is preferable to use at least one water-soluble solvent with a boiling point in the range of 150 to 250°C. In addition, alcohols other than those mentioned above, polyhydric alcohols, amines, amides, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms may also be used.

(3.3) Other Solvents Other solvents contained in the color ink according to the present invention include solvents other than water-soluble solvents having a boiling point in the range of 150 to 250° C. Examples of such solvents include glycerin, trimethylolpropane, triethylene glycol, tetraethylene glycol, etc. When a water-soluble solvent having a boiling point of 250° C. or higher (for example, glycerin) is used, its amount is preferably 5% by mass or less relative to the total mass of the color ink.

(4) Resin Fine Particles The color ink according to the present invention preferably contains resin fine particles (hereinafter, also simply referred to as "resin").
By including resin fine particles in the color ink, the fixation of the color ink to the substrate can be improved.
From the viewpoint of ejection stability of the color ink, it is preferable to adjust the amount of the resin fine particles added in addition to the surface conditioner so as to satisfy the above formula (1).

Among these, the resin fine particles are preferably water-insoluble resin fine particles.
The water-insoluble resin is capable of accepting the colored ink and exhibits solubility or affinity for the colored ink.

In the present invention, "water-insoluble resin microparticles" refers to resins that are inherently water-insoluble but have a form in which the resin disperses in an aqueous medium as microscopic microparticles. Specific examples include water-insoluble resins that are forcibly emulsified using an emulsifier or the like and dispersed in water. In addition, examples include water-insoluble resins that form a stable aqueous dispersion by themselves, without the use of an emulsifier or dispersion stabilizer, by introducing a hydrophilic functional group into the molecule, i.e., that can self-emulsify.

These resin microparticles are usually used in an emulsified and dispersed state in water or a water/alcohol mixed solvent.

In the present invention, "water-insoluble" refers to a resin that, when dried at 105°C for 2 hours and then dissolved in 100 g of water at 25°C, dissolves in an amount of 10 g or less, preferably 5 g or less, and more preferably 1 g or less.
However, when the resin has a salt-forming group, the amount is the amount dissolved when the salt-forming group of the resin is 100% neutralized with acetic acid or sodium hydroxide depending on the type of resin.

The glass transition temperature (Tg) of the resin is preferably within the range of -30 to 90°C.
The glass transition temperature (Tg) can be read from an endothermic peak when the temperature is increased at a rate of 10° C./min in a temperature range of −30 to 200° C. using a DSC (differential scanning calorimeter).

Examples of resins having a glass transition temperature in the range of −30 to 90° C. include polyester resins, acrylic resins, urethane resins, olefin resins, composite resins of urethane resins and acrylic resins, etc. These resin fine particles are preferably anionic or nonionic.
Among these, the resin particles are preferably water-dispersible polyester resins having a sulfonic acid group or a carboxylic acid group as an acid structure, which provides high fixability to the substrate.

The average particle size of the resin microparticles is preferably 200 nm or less, and more preferably within the range of 50 to 150 nm.

It is preferable that the self-emulsifying resin microparticles contain an acid structure. By containing an acid structure, the microparticles can be dispersed in water even with a small amount of surfactant added, improving the water resistance of the coating film of the colored ink formed on the substrate. With self-emulsifying resin microparticles, dispersion and stabilization in water can be achieved only by the ionicity of the molecules, without the use of a surfactant.

Examples of the acid structure include acid groups such as a carboxy group (-COOH) and a sulfonic acid group (-SO ₃ H). The acid structure may be present in a side chain or at a terminal of the resin. It is preferable that a part or all of the acid structure is neutralized. By neutralizing the acid structure, the water dispersibility of the resin can be improved.

As a neutralizing agent for neutralizing the acid structure, for example, organic amines are preferable, and examples of such organic amines include trimethylamine, triethylamine, tripropylamine, tributylamine, N-methyldiethanolamine, and triethanolamine.

Each resin will be described below.
(4.1) Polyester Resin The polyester resin is obtained by using a polyhydric alcohol component and a polycarboxylic acid component such as a polycarboxylic acid, a polycarboxylic acid anhydride, or a polycarboxylic acid ester.

Examples of the polyhydric alcohol component include dihydric alcohols (diols), specifically alkylene glycols having 2 to 36 carbon atoms (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexanediol, etc.), alkylene ether glycols having 4 to 36 carbon atoms (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, etc.), alicyclic diols having 6 to 36 carbon atoms, and the like. Examples of such an alkylene oxide include alicyclic diols (1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.), adducts of the above-mentioned alicyclic diols with alkylene oxides having 2 to 4 carbon atoms (ethylene oxide (hereinafter abbreviated as EO), propylene oxide (hereinafter abbreviated as PO), butylene oxide (hereinafter abbreviated as BO)) (number of moles added is in the range of 1 to 30), and adducts of bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.) with alkylene oxides having 2 to 4 carbon atoms (EO, PO, BO, etc.) (number of moles added is in the range of 2 to 30).
These may be used alone or in combination of two or more.

Examples of the polyvalent carboxylic acid component include divalent carboxylic acids (dicarboxylic acids), specifically alkane dicarboxylic acids having 4 to 36 carbon atoms (succinic acid, apidic acid, sebacic acid, etc.), alkenyl succinic acids (dodecenyl succinic acid, etc.), alicyclic dicarboxylic acids having 4 to 36 carbon atoms (dimer acids (dimerized linoleic acid), etc.), alkene dicarboxylic acids having 4 to 36 carbon atoms (maleic acid, fumaric acid, citraconic acid, mesaconic acid, etc.), and aromatic dicarboxylic acids having 8 to 36 carbon atoms (phthalic acid, isophthalic acid, terephthalic acid, or derivatives thereof, naphthalenedicarboxylic acid, etc.).
These may be used alone or in combination of two or more.

The polyester resin is preferably a polyester resin having an anionic group in the molecule, and more preferably a polyester resin having a sulfonic acid group or a carboxylic acid group.

Known methods for synthesizing polyester resins having sulfonic acid groups include, for example, polycondensation reactions between dicarboxylic acids having sulfonic acid groups and diols. Also included are polycondensation reactions between dicarboxylic acids and diols having sulfonate salts.

Examples of dicarboxylic acid components having a sulfonic acid group include 2-sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfonaphthaleneisophthalic acid-2,7-dicarboxylic acid, 5-(4-sulfophenoxy)isophthalic acid, and alkali metal salts thereof.

Examples of diols having a sulfonic acid group include 2-sulfo-1,4-butanediol, 2,5-dimethyl-3-sulfo-2,5-hexanediol, and alkali metal salts thereof.

The number average molecular weight of the polyester resin is preferably in the range of 1,000 to 50,000, and more preferably in the range of 2,000 to 20,000.

The polyester resin used may be a commercially available product.
Examples of commercially available water-dispersible polyester resins having sulfonic acid groups include "Vylonal (registered trademark) MD-1100, MD-1200, MD-1245, MD-1480, MD-1500, MD-2000" (manufactured by Toyobo Co., Ltd.), "Pluscoat (registered trademark) Z-221, Z-446, Z-561, Z-880, Z-3310" (manufactured by GOO Chemical Co., Ltd.), and "Pesresin A-520, A-613D, A-615GE, A-640, A-645GH, A-647GEX, A-110F, A-160P" (manufactured by Takamatsu Oil Co., Ltd.).
These may be used alone or in combination of two or more.

Among them, those with a glass transition temperature in the range of 40 to 90°C are preferred, and examples thereof include "Vylonal (registered trademark) MD-1100, MD-1200, MD-1245, MD-1500, MD-2000" (all manufactured by Toyobo Co., Ltd.), "Pluscoat Z-221, Z-446, Z-561" (all manufactured by GOO Chemical Co., Ltd.), and "Pesresin A-520, A-613D, A-615GE, A-640, A-645GH, A-647GEX" (all manufactured by Takamatsu Oil Co., Ltd.).

(4.2) Urethane Resin The urethane resin preferably has a hydrophilic group (a water-soluble functional group).
The urethane resin is obtained by using a polyol, an organic polyisocyanate, and a hydrophilic group-containing compound.

The urethane resin is preferably in the form of an aqueous dispersion of a self-emulsifying urethane resin having hydrophilic groups in the molecule. It is also preferably in the form of an aqueous dispersion of a forced-emulsifying urethane resin emulsified under strong mechanical shearing force in combination with a surfactant.

Examples of polyols include polyester polyols, polyether polyols, polycarbonate polyols, polyolefin polyols, etc.

Polyester polyols are obtained by reacting low molecular weight polyols with polycarboxylic acids. Examples of low molecular weight polyols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2- and 1,3-propylene glycol, neopentyl glycol, 1,3- and 1,4-butanediol, 3-methylpentanediol, hexamethylene glycol, 1,8-octanediol, 2-methyl-1,3-propanediol, bisphenol A, hydrogenated bisphenol A, trimethylolpropane, and cyclohexanedimethanol. Examples of polycarboxylic acids include succinic acid, glutaric acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrofuran acid, endomethinetetrahydrofuran acid, and hexahydrophthalic acid.

Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene polytetramethylene glycol, polypropylene polytetramethylene glycol, polytetramethylene glycol, etc.

Examples of polycarbonate polyols include diphenyl carbonate and dimethyl carbonate.
Polycarbonate polyols can be obtained by reacting a carbonic acid derivative such as phosgene with a diol.

Examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2- and 1,3-propylene glycol, neopentyl glycol, 1,3- and 1,4-butanediol, 3-methylpentanediol, hexamethylene glycol, 1,8-octanediol, 2-methyl-1,3-propanediol, bisphenol A, hydrogenated bisphenol A, trimethylolpropane, and cyclohexanedimethanol.

Examples of the organic polyisocyanate include aromatic isocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, xylylene diisocyanate (XDI), and tetramethylxylylene diisocyanate (TMXDI); aliphatic isocyanates such as hexamethylene diisocyanate (HMDI); and alicyclic isocyanates such as isophorone diisocyanate (IPDI) and 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI, H12MDI).
These may be used alone or in combination of two or more.

Further examples of hydrophilic group-containing compounds include carboxylic acid-containing compounds such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, and glycine, as well as derivatives thereof (sodium salts, potassium salts, amine salts, etc.); and sulfonic acid-containing compounds such as taurine (i.e., aminoethylsulfonic acid), and ethoxypolyethylene glycol sulfonic acid, as well as derivatives thereof (sodium salts, potassium salts, amine salts, etc.).

The urethane resin can be obtained by a known method.
For example, the polyol, the organic polyisocyanate, and the hydrophilic group-containing compound are mixed and reacted at a temperature in the range of 30 to 130° C. for 30 minutes to 50 hours to obtain a urethane prepolymer.
The urethane prepolymer is polymerized by extending the chain with a chain extender, thereby obtaining a urethane resin having a hydrophilic group.

The chain extender is preferably water or an amine compound.
Water or an amine compound reacts with free isocyanate in a short period of time, and can efficiently extend the isocyanate-terminated prepolymer.

Examples of amine compounds that can be used as chain extenders include aliphatic polyamines such as ethylenediamine and triethylenediamine; aromatic polyamines such as metaxylenediamine and toluylenediamine; and polyhydrazino compounds such as hydrazine and adipic acid dihydrazide.

The amine compound may contain, in addition to the polyamine, a monovalent amine such as dibutylamine, methyl ethyl ketoxime, etc. as a reaction terminator to the extent that the polymerization is not significantly inhibited.

In the synthesis of the urethane prepolymer, a hydrophilic organic solvent that is inert to the isocyanate and capable of dissolving the urethane prepolymer may be used, such as dioxane, methyl ethyl ketone, dimethylformamide, tetrahydrofuran, N-methyl-2-pyrrolidone, toluene, and propylene glycol monomethyl ether acetate.
These hydrophilic organic solvents used in the reaction steps are preferably finally removed.

In addition, in the synthesis of urethane prepolymers, catalysts such as amine catalysts (e.g., triethylamine, N-ethylmorpholine, triethyldiamine, etc.), tin-based catalysts (e.g., dibutyltin dilaurate, dioctyltin dilaurate, tin octoate, etc.), and titanium-based catalysts (e.g., tetrabutyl titanate, etc.) may be added to promote the reaction.

The number average molecular weight (Mn) of the urethane resin is preferably made as large as possible by introducing a branched structure or an internal crosslinked structure, and is preferably within the range of 50,000 to 10,000,000. By keeping it within the above range, the urethane resin is less likely to dissolve in a solvent, and the weather resistance and water resistance of the recorded matter are excellent.

The number average molecular weight (Mn) can be measured by gel permeation chromatography (GPC). For example, the number average molecular weight can be determined from a calibration curve prepared using a polystyrene standard sample using the following apparatus and conditions.
Differential refractometer: "RID-6A" (Shimadzu Corporation)
Column: "TSK-GEL" (manufactured by Tosoh Corporation)
Solvent: Tetrahydrofuran (THF)
Column temperature: 40 ° C.

The urethane resin may be a commercially available product.
Examples of commercially available urethane resins having a glass transition temperature in the range of 40 to 90° C. include “Neorez (registered trademark) R-967, R-600, R-9671” (all manufactured by Kusumoto Chemical Industries, Ltd.), “Evaphanol (registered trademark) HA-560” (manufactured by Nicca Chemical Industries, Ltd.), and “SF870” (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

(4.3) Acrylic Resin The acrylic resin is obtained using a (meth)acrylic acid ester component and a styrene component.

Examples of the (meth)acrylic acid ester component include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, benzyl (meth)acrylate, glycidyl (meth)acrylate, (meth)acrylic acid, (di)ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin di(meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and acrylamide.
In this specification, the term "(meth)acrylic acid ester" is a general term for "acrylic acid ester" and "methacrylic acid ester" and means one or both of them. For example, "methyl (meth)acrylate" means one or both of "methyl acrylate" and "methyl methacrylate".

Examples of the styrene component include styrene, 4-methylstyrene, 4-hydroxystyrene, 4-acetoxystyrene, 4-acetylstyrene, and styrenesulfonic acid.
These may be used alone or in combination of two or more.

The number average molecular weight (Mn) of the acrylic resin is preferably in the range of 1,000 to 50,000, and more preferably in the range of 2,000 to 20,000.

By making the number average molecular weight (Mn) of the acrylic resin 1000 or more, the cohesive force of the coating film is increased, and the fixation to the substrate is improved. Also, by making the number average molecular weight (Mn) 50000 or less, the solubility in organic solvents is good, and the dispersed particle size can be made smaller.
The number average molecular weight (Mn) can be measured by the method described above.

The acrylic resin may be a commercially available product.
Examples of commercially available acrylic resins having a glass transition temperature in the range of 40 to 90° C. include acrylic emulsions such as “Mowinyl (registered trademark) 6899D, 6969D, 6800” (manufactured by Japan Coating Resins Co., Ltd.) and “TOCRYL (registered trademark) W-7146, W-7147, W-7148, W-7149, W-7150” (manufactured by Toyochem Co., Ltd.).

(4.4) Composite Resin Particles The composite resin particles are preferably composite resin particles formed by emulsifying an acrylic resin in a urethane resin, that is, composite resin particles having an inner layer made of an acrylic resin and a surface layer made of a urethane resin.

Here, the urethane resin exists at the interface between the acrylic resin as water-insoluble resin particles and the water as the continuous phase, and functions as a water-insoluble resin particle layer that is different from the resin that protects the water-insoluble resin particles.

In this way, by using composite resin microparticles in which acrylic resin is emulsified in urethane resin, the physical properties of the printed matter can be improved compared to when the acrylic resin and the urethane resin are emulsified separately and mixed. In addition, the storage stability of the resin microparticles in the colored ink can also be improved.

In composite resin microparticles in which acrylic resin is emulsified in urethane resin, the mass ratio (U/A) of urethane resin (U) to acrylic resin (A) is preferably within the range of 40/60 to 95/5, and more preferably within the range of 40/60 to 80/20.

When the proportion of urethane resin (U) is within the above range, compatibility with the dispersant is improved, and solvent resistance is also improved. In addition, when the proportion of acrylic resin (A) is within the above range, the colored ink has excellent adhesion to the acrylic film used as the base material.

The resin content (total of acrylic resin and urethane resin) is not particularly limited, but is preferably 5.0% by mass or more, and more preferably within the range of 10.0 to 70.0% by mass, relative to the total mass of the composite resin microparticles. By being within the above range, the fixation of the colored ink to the substrate is excellent.

In addition, when emulsifying the acrylic resin with the urethane resin, a surfactant that acts as an emulsifier can be used together with the urethane resin. By including an emulsifier, the storage stability of the composite resin particles in the colored ink can be improved. As the emulsifier, an anionic surfactant or a nonionic surfactant can be used.

The average particle diameter of the composite resin microparticles is not particularly limited, but is preferably within the range of 10 to 500 nm, more preferably within the range of 10 to 300 nm, and even more preferably within the range of 10 to 200 nm. The average particle diameter can be measured by the method described above.

By using composite resin microparticles in which acrylic resin is emulsified in urethane resin, the fixation of colored inks to non- and low-absorbency substrates can be improved.

(Surfactant)
As described above, when the color ink contains the composite resin microparticles, the color ink contains a surfactant as an emulsifier, which can improve the storage stability. Also, the color ink contains a surfactant, which can control the wettability of the color ink and improve the ejection stability from the nozzles.
As the surfactant, an anionic surfactant or a nonionic surfactant can be used, and it is more preferable to use both.

The content of surfactants (total of anionic surfactants and nonionic surfactants) is preferably within the range of 1.0 to 20.0% by mass relative to the total mass of the composite resin microparticles. By keeping it 20.0% by mass or less, the water resistance and solvent resistance of the recorded matter can be improved.

Examples of anionic surfactants that can be used for emulsification include alkyl sulfates, polyoxyethylene alkyl ether sulfates, sulfosuccinates, alpha-olefin sulfonates, N-acylamino acid salts, carboxylates, phosphates, etc. Among these, sulfosuccinates or alpha-olefin sulfonates are preferred.
The type of salt is not particularly limited, but examples include metal salts such as sodium salts, potassium salts, and magnesium salts, and triethanolamine salts.

Examples of nonionic surfactants that can be used for emulsification include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkylamine ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, etc. Among these, polyoxyethylene alkyl ethers or polyoxyethylene alkyl phenyl ethers are preferred.

(5) Other Components The color ink according to the present invention may contain other components (various additives) such as a crosslinking agent, an antifungal agent, a bactericide, etc., as long as the effects of the present invention are not impaired.

Furthermore, for example, ultraviolet absorbents described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, discoloration inhibitors described in JP-A-57-74192, JP-A-57-87989, JP-A-60-72785, JP-A-61-146591, JP-A-1-95091, and JP-A-3-13376, and anionic It may also contain various known additives such as various cationic or nonionic surfactants, fluorescent brighteners described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-242871, and JP-A-4-219266, antifoaming agents, lubricants such as diethylene glycol, preservatives, thickeners, and antistatic agents.

3. Constituents of the treatment ink The treatment ink according to the present invention is not particularly limited, but preferably contains a flocculant. In addition, it is preferable that the treatment ink contains at least water or a water-soluble solvent as a solvent, and may further contain other components such as a surfactant.
The solvent may be the same as that contained in the color ink.

(1) Flocculant The treatment ink according to the present invention preferably contains a flocculant.
By including an aggregating agent in the treatment ink, an ink aggregating layer can be formed on the surface of the non- or low-absorbency substrate, and the coloring material in the color ink can be quickly aggregating, thereby fixing the mixture of the treatment liquid and the color ink.
The flocculant is not particularly limited as long as it is a material that generates flocs when it comes into contact with the color ink. Examples of the flocculant include polyvalent metal salts, organic acids, inorganic acids, and soluble cationic polymers.

(1.1) Polyvalent Metal Salt When the treatment ink contains a polyvalent metal salt as an aggregating agent, anionic components such as coloring materials in the color ink can be agglomerated on the substrate by salting out.

As the polyvalent metal salt, a salt of a metal having a valence of two or more can be used.
The type of metal (cation) constituting the polyvalent metal salt is not particularly limited, and examples include divalent metal ions such as Ca2 ⁺ , Cu2 ⁺ , Ni2 ⁺ , Mg2 ⁺ , Zn2 ⁺ , and Ba2 ⁺ , trivalent metal ions such as Al3 ⁺ , Fe3 ⁺ , Cr3 ⁺ , and Y3 ^+, and tetravalent metal ions such as Zr4 ⁺ , and the like.

The type of salt constituting the polyvalent metal salt is not particularly limited, and for example, known salts such as carbonates, sulfates, nitrates, hydrochlorides, organic carboxylates, organic sulfonates, borates, phosphates, hydrobromides, hydroiodides, and thiocyanates can be used.
Examples of the organic carboxylate include acetic acid, oxalic acid, lactic acid, fumaric acid, citric acid, salicylic acid, and benzoic acid.

Among these, calcium salts or magnesium salts are preferred. Specific examples include calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, calcium acetate, magnesium acetate, magnesium lactate, calcium pantothenate, etc.

The content of the polyvalent metal salt is preferably within the range of 0.5 to 20% by mass, and more preferably within the range of 1 to 10% by mass, based on the total mass of the treated ink. By being within the above range, anionic components such as coloring materials in the colored ink can be effectively aggregated, achieving both high image quality and hot water resistance.

The content of polyvalent metal salts can be measured by known methods, such as ICP emission analysis.

(1.2) Organic Acid When the treatment ink contains an organic acid as an aggregating agent, anionic components such as coloring materials in the color ink can be agglomerated on the substrate by pH fluctuation.
The treatment ink preferably further contains an organic acid as an aggregating agent in addition to the polyvalent metal salt.

The organic acid preferably has a first dissociation constant of 3.5 or less, and more preferably in the range of 1.5 to 3.5. By keeping the first dissociation constant within the above range, liquid shifting in low concentration areas is further prevented, and ink mixing (beading) in high concentration areas is improved.

The organic acid is preferably a monovalent carboxylic acid, since it does not weaken the cohesive force of the polyvalent metal salt. Examples of monovalent carboxylic acids include formic acid, acetic acid, propionic acid, isobutyric acid, and benzoic acid.

It is preferable to use an organic acid that is not completely neutralized with a base.
The term "neutralization with a base" refers to the formation of an ionic bond between the acidic group of the organic acid and another positively charged element or compound (for example, an inorganic compound such as a metal).
The term "not completely neutralized" means that among the acidic groups contained in the organic acid, there are acidic groups that do not form the above-mentioned ionic bond.

In addition, the treatment ink contains an organic acid, which makes it easier to maintain storage stability, and further makes it possible to prevent blocking from occurring after the treatment ink is applied and dried.
From this viewpoint, the organic acid is preferably formic acid, acetic acid, propionic acid or benzoic acid.

The organic acid content is preferably within the range of 0.1 to 10% by mass, and more preferably within the range of 1 to 3% by mass, relative to the total mass of the treated ink.

When using an organic acid, it is preferable to adjust the pH value of the treatment ink so that the amount of organic acid applied is equal to or less than the neutralization equivalent of the anionic components, such as the coloring material, in the colored ink.

The organic acid content can be measured by known methods, such as high performance liquid chromatography (HPLC).

(1.3) Inorganic Acid When the treatment ink contains an inorganic acid as an aggregating agent, anionic components such as coloring materials in the color ink can be agglomerated on the substrate by pH fluctuation.

Examples of inorganic acids include hydrochloric acid, nitric acid, sulfuric acid, and sulfamic acid.

The content of inorganic acid is preferably within the range of 0.1 to 10% by mass, and more preferably within the range of 1 to 3% by mass, relative to the total mass of the treatment ink.

(1.4) Dissolved Cationic Polymer By containing a dissolved cationic polymer as an aggregating agent in the treatment ink, anionic components such as coloring materials in the color ink can be agglomerated on the substrate by neutralizing the surface charge of the particles. Furthermore, large and strong aggregates can be formed by adsorption and cross-linking with countless active groups.

Examples of the soluble cationic polymer include polyallylamine, polyvinylamine, polyethyleneimine, and polydiallyldimethylammonium chloride.
Commercially available dissolving cationic polymers include, for example, "KHE100L" and "FPA100L" (both manufactured by Senka Chemical Co., Ltd.), "PAS-92A", "PAS-M-1A", "PAS-21CL", and "PAS-H-1L" (all manufactured by Nittobo Medical Co., Ltd.).

(2) Solvent The treatment ink according to the present invention preferably contains at least water or a water-soluble solvent.
The content of water or the water-soluble solvent is preferably within a range of 5 to 60% by mass, and more preferably within a range of 10 to 50% by mass, based on the total mass of the treatment ink.

(2.1) Water The water is not particularly limited, and examples thereof include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, and ultrapure water.

(2.2) Water-soluble solvent The water-soluble solvent is not particularly limited, but preferably has a boiling point within the range of 150 to 250° C. Examples of the water-soluble solvent include alcohols, polyhydric alcohols, amines, amides, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms.

Examples of polyhydric alcohols having 2 to 8 carbon atoms include 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, and 2-methylpentane-2,4-diol.
Examples of the polyalkylene glycols include diethylene glycol and dipropylene glycol.
These may be used alone or in combination of two or more.

It is preferable to use at least one water-soluble solvent with a boiling point in the range of 150 to 250°C. In addition, alcohols other than those mentioned above, polyhydric alcohols, amines, amides, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms may also be used.

(2.3) Other Solvents Examples of other solvents contained in the treatment ink according to the present invention include solvents other than the water-soluble solvent having a boiling point in the range of 150 to 250° C. Examples of such solvents include glycerin, trimethylolpropane, triethylene glycol, and tetraethylene glycol. When a water-soluble solvent having a boiling point of 250° C. or higher is used, the amount is preferably 5% by mass or less relative to the total mass of the treatment ink, from the viewpoint of the drying property of the treatment ink.

(3) Other Components The treatment ink according to the present invention may contain other components (various additives) such as surfactants, crosslinking agents, antifungal agents, bactericides, etc., as appropriate, in the same manner as the colored ink, within the scope of not impairing the effects of the present invention. As the surfactant, the surfactants used in the colored inks can be used.

4. Manufacturing Method of Water-Based Ink Set The manufacturing method of the water-based ink set of the present invention is a manufacturing method of the water-based ink set of the present invention, which comprises a step of adding the coagulant to the treatment ink, and a step of adding the coloring material and the surface conditioner to the colored ink, and is characterized in that the amount of the surface conditioner added is adjusted so as to satisfy the following formula (3), where A1 [°] is the contact angle of the colored ink with respect to the non-low absorbency substrate having a critical surface tension of 44 mN/m at 25° C., and B1 [°] is the contact angle of the colored ink with respect to the non-low absorbency substrate on which the treatment ink has been applied and dried.
Formula (3): |A1-B1|≦10°

In the present invention, it is believed that the addition of a specific amount of surface conditioner to the colored ink can make the wetting properties of the colored ink, and the wetting properties of the mixture of the treated ink and the colored ink, comparable.
Specifically, it is believed that by adjusting the amount of surface conditioner added so as to satisfy the above formula (3), the wettability of the color ink and the wettability of the mixture of the treatment ink and the color ink can be made to be approximately the same.

The method for producing the water-based ink set of the present invention includes a step of adding a coagulant to the treatment ink, and a step of adding a coloring material and a surface conditioner to the colored ink. In the step of adding the coloring material and the surface conditioner to the colored ink, the amount of the surface conditioner added is appropriately adjusted.

Furthermore, when the surface conditioner contains a wax, the amount of wax added relative to the total mass of the colored ink is X [mass %], the contact angle of the composition of the colored ink excluding only the wax with respect to a non-low absorbency substrate having a critical surface tension of 44 mN/m at 25°C is A2 [°], and the contact angle of the composition of the colored ink excluding only the wax with respect to a non-low absorbency substrate to which the treated ink has been applied and dried is B2 [°], it is preferable to adjust the amount of wax added so as to satisfy the following formula (5).
Formula (5): 10[°/mass%]≦|A2−B2|/X≦40[°/mass%]

When the surface conditioner is a wax, the amount of wax added can be adjusted to satisfy the above formula (5), thereby controlling the wetting and spreading of the colored ink on non- or low-absorbency substrates.

The water-based ink set of the present invention can be produced by mixing the components of the treatment ink and color ink described below. There are no particular limitations on the method for producing the treatment ink, and any known method can be used. There are also no particular limitations on the method for producing the color ink, except for adjusting the amount of surface conditioner added, and any known method can be used.

The water-based ink set of the present invention preferably contains two or more colored inks. By using the production method, even when a plurality of colored inks are used in combination, the dot diameter of the dots formed can be adjusted and unevenness during solid printing can be sufficiently suppressed.
By satisfying the above formula (1) in all the color inks used, the solid uniformity is improved in multicolor printing on non-low-absorbency substrates, and high-quality images can be formed without unevenness. In addition, by satisfying the above formula (2) in all the color inks used, the effect is even more remarkable. Therefore, it is preferable to adjust the amount of wax added so that the above formula (3) and the above formula (5) are satisfied in all the color inks used.

5. Inkjet Recording Method The inkjet recording method of the present invention is characterized by using the above-mentioned water-based ink set.

In addition, it is preferable that the coagulant is a metal salt, the content of the metal salt is within the range of 1 to 10 mass % relative to the total mass of the treatment ink, and when the application amount of the treatment ink is C _P [g/m ² ] and the application amount of the color ink is C _I [g/m ² ], the following formula (4) is satisfied:
Formula (4): 0.05≦C _P /C _I <1.00

As described above, in the water-based ink set of the present invention, the difference in dot diameter between the dot formed by the color ink alone and the dot formed by the mixture of the treatment ink and the color ink is relatively small, so unevenness during solid printing can be sufficiently suppressed even if the application amount _CP of the treatment ink is significantly reduced relative to the application amount _CI of the color ink.

The inkjet recording method of the present invention preferably includes a step of applying the above-mentioned treatment ink to a non-low absorbency substrate, and a step of applying the above-mentioned color ink. The treatment ink may be a pre-treatment ink or a post-treatment ink, and the order of each step is not limited. Furthermore, the method may include a step of drying the non-low absorbency substrate after applying both the treatment ink and the color ink to the non-low absorbency substrate.

(1) Non-Low Absorbency Substrate The water-based ink set of the present invention is applied onto a substrate by an ink-jet method. The substrate is not particularly limited as long as it is a non-low absorbency substrate.

In the present invention, the term "non-low absorbency substrate" refers to a substrate that has no or low absorbency for water-based colored ink. Specifically, the term refers to a substrate that has a water absorption amount of 10 mL/ ^m2 or less from the start of contact to 30 msec in the Bristow method. Details of the test method are described, for example, in Standard No. 51 "Paper and paperboard - Liquid absorbency test method - Bristow method" of "JAPAN TAPPI Paper and Pulp Test Method 2000 Edition".

Moreover, the non-low absorbency substrate preferably has a critical surface tension at 25° C. in the range of 35 to 48 mN/m.
The critical surface tension can be measured by Zisman plot (J. Phys. Chem., vol. 58, p. 236 (1954)). In detail, the contact angle θ of liquids with different surface tensions is measured with respect to the substrate, and the surface tension at which cosθ=0 is obtained by extrapolating the proportional relationship between cosθ and the surface tension of the liquid is defined as the critical surface tension of the substrate.

Examples of non-low absorbency substrates include known plastic films.
Examples of known plastic films include polyester films such as polyethylene terephthalate, polyethylene films, polypropylene films, polyamide films such as nylon, polystyrene films, polyvinyl chloride films, polycarbonate films, polyacrylonitrile films, and biodegradable films such as polylactic acid films.

For the purpose of imparting gas barrier properties, moisture resistance, aroma retention, etc., the plastic film may be coated with polyvinylidene chloride or vapor-deposited with a metal oxide on one or both sides of the film. The plastic film may be either an unstretched film or a stretched film.

It may also be a multi-layer substrate in which a layer such as a PVA (polyvinyl alcohol) coating is provided on the surface of a highly absorbent substrate such as paper, thereby reducing or eliminating the absorbency of the area where recording is to be performed.

As non- or low-absorbency substrates, metal substrates such as tinplate for three-piece cans and tin-free steel plates (TFS plates, thickness 0.1 to 0.6 μm) are also preferably used. For example, packaging materials for canned foods that have a thermosetting resin coating layer can be used.

Packaging materials for canned foods, for example, must block air, moisture, light, etc. and seal the food inside. For this reason, epoxy-phenolic paints or polyester laminating agents are generally used on the food side, and polyester or acrylic thermosetting paints are generally used on the outside.

There are no particular limitations on the thickness of the non-low absorbency substrate. If it is a plastic film, it is preferably within the range of 10 to 120 μm, and more preferably within the range of 12 to 60 μm.

(2) Step of applying treated ink to non-low absorbent substrate The treated ink according to the present invention contains a flocculant and fixes a colored ink containing a coloring material onto a non-low absorbent substrate (hereinafter also simply referred to as "substrate").

The treatment ink is applied onto the substrate by an ink jet process.
By using the inkjet method, it is not necessary to apply the treatment ink to the areas on the substrate where the color ink is not to be applied, and therefore it is possible to prevent the color ink from being released and becoming cloudy due to the unreacted coagulant.
Furthermore, from the viewpoint of reducing the amount of unreacted coagulant, even if the amount of treatment ink applied is significantly less than the amount of color ink applied, unevenness during solid printing can be sufficiently suppressed, as described above.

When the substrate is a metal substrate or the like, it is preferable to place the metal substrate on a conveyor belt and apply the treatment ink while conveying the belt. A flatbed type printer to which the substrate is fixed may also be used to apply the treatment ink.

The inkjet method is not particularly limited, and a printer equipped with an inkjet head loaded with the treated ink can be used. Specifically, the treated ink is ejected as droplets from the nozzles of the inkjet head based on a digital signal, and the droplets are caused to land on the substrate.

The inkjet head is not particularly limited, and may be of an on-demand type or a continuous type.
Examples of on-demand inkjet heads include single-cavity, double-cavity, bender, piston, shear mode and shared wall electromechanical conversion heads, as well as thermal inkjet and bubble jet ("Bubble Jet" is a registered trademark of Canon Inc.) electrothermal conversion heads.

Among them, it is preferable to use an inkjet head that uses a piezoelectric element as the electromechanical conversion element used in the electromechanical conversion method (also called a "piezo type inkjet head").

The inkjet printer is not particularly limited and may be of a scanning type or a single-pass type. In the case of a single-pass type, it is preferable to use an inkjet head of a line head type.
It should be noted that the "line head type inkjet head" refers to an inkjet head whose length is equal to or greater than the width of the printing range.
A line head type inkjet head may be configured so that a single head covers a width equal to or greater than the printing range, or a plurality of heads may be combined to cover a width equal to or greater than the printing range.

In addition, multiple heads can be arranged side by side with their nozzles in a staggered arrangement to increase the overall resolution of the heads.

The transport speed of the substrate is not particularly limited, but is preferably within the range of 1 to 120 m/min. The faster the transport speed, the faster the recording speed.

When the treatment ink is used as a pretreatment ink, after the treatment ink is applied onto the substrate, the treatment ink may be heated to dry it.

(3) Step of applying color ink to non-low absorbent substrate The color ink is applied onto the substrate by the inkjet method, similarly to the treatment ink.
By using the inkjet method, recorded matter (images) can be produced easily and inexpensively. In addition, because digital printing is possible without using plates, a variety of recorded matters can be produced in small quantities.

The colored ink is preferably applied onto the substrate under the same conditions as the treatment ink.
In particular, the inkjet head used for applying the color inks preferably has a piezoelectric element as an electromechanical conversion element used in the electromechanical conversion method. By using a piezoelectric element, deterioration of the color ink due to heating can be suppressed.

When the treatment ink is used as a pretreatment ink, the colored ink may be applied after the treatment ink on the substrate has completely dried, or the colored ink may be applied while the treatment ink is still in liquid form.
On the other hand, when the treatment ink is used as a post-treatment ink, from the viewpoint of fixing the color ink on the substrate by the treatment ink, it is preferable to apply the treatment ink while the color ink on the substrate is still in a liquid state.

(4) Step of drying the non-low absorbent substrate After applying both the treatment ink and the color ink to the non-low absorbent substrate, a step of drying the non-low absorbent substrate may be included. The drying method is not particularly limited, but is preferably drying by heating.

The heating temperature is preferably within the range of 60 to 200°C. The heating time is preferably selected appropriately depending on the type of substrate, the amount of treatment ink and color ink applied, etc.

By heating the areas on the substrate to which the treatment ink and color ink are applied, the solvent components of the treatment ink and color ink can be removed. Furthermore, when the substrate is a metal substrate and the coagulant is a polyvalent metal salt, the polyvalent metal salt can be thermally decomposed. Furthermore, the fixation and abrasion resistance of the recorded matter are improved.

For the heating and drying, a non-contact heating type drying device such as a drying oven or a hot air blower may be used, or a contact heating type drying device such as a hot plate or a heated roller may be used.

The drying temperature is preferably selected appropriately depending on the type of drying device.
When a non-contact heating type drying device is used, it is preferable to adjust the atmospheric temperature such as the furnace temperature, the hot air temperature, etc. When a contact heating type drying device is used, it is preferable to adjust the temperature of the contact heating part or the surface temperature of the surface to be dried (substrate).

The thickness of the color ink coating is preferably within the range of 0.3 to 3.0 μm, and more preferably within the range of 0.3 to 2.0 μm. When the thickness of the color ink coating is 0.3 μm or more, the fixation and abrasion resistance of the recorded matter are improved. When the thickness of the color ink coating is 3.0 μm or less, the deformation stress applied to the color ink coating can be reduced, and the adhesion of the color ink coating to the substrate is less likely to be impaired.

6. Inkjet Recording System The inkjet recording system of the present invention is an inkjet recording system that uses an aqueous ink set, the aqueous ink set being the above-described aqueous ink set, and having an inkjet head that ejects the treatment ink and the color ink, the inkjet head having a piezoelectric element.

That is, the inkjet recording system of the present invention uses the above-mentioned water-based ink set and inkjet recording apparatus. The inkjet recording apparatus also has an inkjet head for ejecting the treatment ink and the color ink, and the inkjet head has a piezoelectric element.
As described above, by providing the inkjet head with a piezoelectric element, deterioration of the color ink due to heating can be suppressed.

FIG. 2 is a schematic diagram showing an example of a recording apparatus preferable for the present invention.
Although an example in which the treatment ink is used as a pretreatment ink is shown, the present invention is not limited to this example.
The inkjet recording apparatus 1 is mainly composed of a treatment ink application section 10 and a color ink application section 20. In the treatment ink application section 10, a treatment ink is applied onto a substrate F, and in the color ink application section 20, a color ink is applied.
The treatment ink application section 10 has an inkjet head 11 capable of ejecting the treatment ink onto the substrate. The color ink application section 20 has an inkjet head 21 capable of ejecting the color ink onto the substrate.

In the inkjet recording apparatus 1 as described above, droplets 12 of the treated ink are ejected from the inkjet head 11 onto the substrate F fed from the feed roller 30, thereby forming a treated ink layer C.
Next, droplets 22 of color ink are ejected from an inkjet head 21 onto the treated ink layer C, and the treated ink and the color ink are united.
Thereafter, the drying unit 23 heats and dries the area to which the color ink has been applied, forming an image layer G. Next, the base material F on which the image layer G has been formed is wound up by the winding roller 40, thereby obtaining a recorded matter.

2 shows a case where the substrate F is a film-like substrate. When the substrate F is a metal substrate or the like, the metal substrate is placed on a transport belt, and the treatment ink and the color ink are applied in one pass while the belt is transported, so that the image layer G can be formed.
2 shows an apparatus configured to apply the treatment ink onto the substrate and then the color ink, but the apparatus may also be configured to apply the treatment ink and the color ink simultaneously, or may be configured to apply the treatment ink after applying the color ink while the color ink is still in liquid form.

As an apparatus other than the inkjet recording apparatus shown in Fig. 2, a flatbed type printer may be used to apply the treatment ink and the color ink. In a flatbed type printer, the substrate is fixed, and the inkjet head can be moved in the main scanning direction and the sub-scanning direction intersecting the main scanning direction. Therefore, it is possible to perform inkjet recording without transporting the substrate.
Metal substrates such as tinplate cannot be transported from roll to roll like film substrates, so it is preferable to use a flatbed type printer that does not require transporting the substrate.
Examples of flatbed type printers include the printers described in FIG. 1 of JP-A-2015-74161 and FIG. 1 of JP-A-2017-177578.

The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. In the examples, the terms "parts" and "%" are used, but they represent "parts by mass" or "% by mass" unless otherwise specified.
In the following examples, operations were carried out at room temperature (25° C.) unless otherwise specified.

1. Preparation of Water-Based Ink Set (1) Preparation of Treated Ink (1.1) Preparation of Treated Ink 1 The following components were mixed, and the resulting mixture was filtered through a 1 μm filter to obtain treated ink 1.
Flocculant: calcium acetate monohydrate 3.00% by mass
Solvent: propylene glycol (PG) 15.00% by mass
Solvent: dipropylene glycol (DPG) 15.00% by mass
Solvent: 2-methyl-1,3-propanediol (2-Me-1,3-ProDO)
10.00% by mass
Surfactant: "BYK-3450" (polyether modified siloxane, manufactured by BYK-Chemie)
1.00% by mass
Antifungal agent: "Proxel (registered trademark) GXL (S)" (1,2-benzisothiazolin-3-one, manufactured by Daiwa Chemical Industry Co., Ltd.)
0.10% by mass
Ion exchange water remaining
(Remainder: total amount is 100% by mass)

(1.2) Preparation of Treated Inks 2 to 4 Treated inks 2 to 4 were prepared in the same manner as in the preparation of treated ink 1, except that the type and content of the flocculant were changed as shown in Table I below.

The composition of each treatment ink is shown in Table I below.
The diallyldimethylammonium chloride polymer (cationic polymer) used was "PAS-H-1L" (manufactured by Nittobo Medical Co., Ltd.).

(2) Preparation of Colored Inks (2.1) Preparation of Colored Ink 1 The following components were mixed. Then, the mixture was dispersed using a bead mill filled with 0.3 mm zirconia beads at a volume ratio of 50%, to prepare a pigment dispersion with a pigment content of 20 mass %.
Pigment: C.I. Pigment Yellow 155
20.00% by mass
Dispersant: "Joncryl (registered trademark) 819" (anionic polymer dispersant, acrylic dispersant having a carboxy group neutralized with dimethylaminoethanol, acid value 75 [mgKOH/g], solid content 20% by mass, manufactured by BASF)
8.00% by mass
Solvent: Propylene glycol 20.00% by mass
Antifungal agent: "Proxel (registered trademark) GXL (S)" (1,2-benzisothiazolin-3-one, manufactured by Daiwa Chemical Industry Co., Ltd.)
0.10% by mass
Ion exchange water remaining
(Remainder: total amount is 100% by mass)

Next, the following components were mixed, and the resulting mixture was filtered through a 1 μm filter to obtain colored ink 1.
The above pigment dispersion
(Amount that results in a pigment solid content of 5.00% by mass)
Resin particles: "Vylonal (registered trademark) MD2000" (polyester resin, manufactured by Toyobo Co., Ltd.)
(Amount that results in a solid content of resin fine particles of 8.00% by mass)
Surface conditioner (wax): "AQUACER (registered trademark) 515" (nonionic oxidized high-density polyethylene wax, manufactured by BYK Additives & Instruments)
(Amount that results in a solid content of wax particles of 0.50% by mass)
Solvent: propylene glycol (PG) 25.00% by mass
Solvent: 1,2-pentanediol (1,2-PenDO)
2.00% by mass
Solvent: Diethylene glycol monobutyl ether (DEGBE)
0.90% by mass
Surface conditioner (surfactant): "TEGO Wet 250" (polyether modified silicone, manufactured by Evonik)
0.50% by mass
Antifungal agent: "Proxel (registered trademark) GXL (S)" (1,2-benzisothiazolin-3-one, manufactured by Daiwa Chemical Industry Co., Ltd.)
0.10% by mass
Ion exchange water remaining
(Remainder: total amount is 100% by mass)

(2.2) Preparation of Colored Inks 2 to 14 Colored inks 2 to 14 were prepared in the same manner as in Preparation of Colored Ink 1, except that the types and contents of the pigment, dispersant, resin fine particles, surface conditioner (wax), and solvent were changed as shown in Table II below.

The composition of each colored ink is shown in Table II below.
The contents of the pigment, the resin particles and the surface conditioner are expressed as the solid content in units of [mass %], and the acid value of the dispersant is expressed in units of [mg KOH/g].
In addition, "-" indicates that it is not contained.

The terms in the table are as follows:
(Pigment)
PY155:C. I. Pigment Yellow 155
PR122:C. I. Pigment Red 122
PV19: C. I. Pigment Violet 19
PB15:3:C. I. Pigment Blue 15:3
PB7: C. I. Pigment Black 7
Note that PY155 alone was used as yellow (Y) ink, PB15:3 alone was used as cyan (C) ink, and PB7 alone was used as black (K) ink.
The magenta (M) ink was prepared by mixing PR122 and PV19 in a mass ratio of 1:1 (indicated as "PR122/PV19" in the table).
(Dispersant)
J819: "Joncryl (registered trademark) 819" (manufactured by BASF)
AW300P: "AW300P" (Otsuka Chemical Co., Ltd.)
HPD-671: "Joncryl (registered trademark) HPD-671" (manufactured by BASF)
(Resin fine particles)
MD2000: "Vylonal (registered trademark) MD2000" (polyester resin, manufactured by Toyobo Co., Ltd.)
(Surface conditioner)
*1: "AQUACER (registered trademark) 515" (nonionic oxidized high-density polyethylene wax, manufactured by BYK Additives & Instruments)
*2: "AQUACER (registered trademark) 539" (nonionic modified paraffin wax, manufactured by BYK Additives & Instruments)
*3: "Cellosol (registered trademark) 524" (nonionic polyester wax, carnauba wax, melting point 83°C, particle size 0.07 μm, manufactured by Chukyo Yushi Co., Ltd.)
*4: "Chemipearl (registered trademark) WF4002" (anionic low molecular weight polyolefin wax, manufactured by Mitsui Chemicals, Inc.)
In addition, *1, *2 and *4 correspond to polyolefin waxes.
(solvent)
PG: Propylene glycol 1,2-PenDO: 1,2-pentanediol DEGBE: Diethylene glycol monobutyl ether

2. Evaluation The following evaluations were carried out. With regard to the inkjet head, a thermal type inkjet head was used in Example 22, and a piezo type inkjet head was used in the other examples.

(1) Measurement of Contact Angle The amount of the colored ink droplet was 3 μL, and the contact angle was measured 65 ms (milliseconds) after the droplet landed on the substrate at room temperature of 25° C. A contact angle meter “DM500” (manufactured by Kyowa Interface Science Co., Ltd.) was used to measure the contact angle.

(1.1) Measurement of Contact Angle A1 [°] The contact angle of each colored ink with respect to an untreated substrate for measurement was measured.
The untreated substrates used for measurement were as follows: The critical surface tension was measured by the method described above.
Examples 1 to 15 and 18 to 22: Polyester film "FE2001" (critical surface tension 44 mN/m, manufactured by Futamura Chemical Co., Ltd.)
Example 16: MSF-100 (critical surface tension 30 mN/m, manufactured by Chukoh Chemical Industries, Ltd.)
Example 17: N1202 (critical surface tension 50 mN/m, manufactured by Toyobo Co., Ltd.)
In Examples 16 and 17, the non-low absorbent substrate was changed and the contact angle was measured in the same manner. In the following, in B1, A2, and B2, the non-low absorbent substrate was changed and the contact angle was measured in the same manner.

(1.2) Measurement of Contact Angle B1 [°] Each of the above treated inks was applied to an untreated substrate for measurement using a bar coater "Bar Coater #4" (manufactured by Daiichi Rika Co., Ltd.). Each treated ink was applied so that the amount of ink applied was within the range of 9 to 10 g/ ^m2 . After that, the substrate was dried at 80°C for 10 minutes on a hot plate to obtain a treated substrate for measurement. Then, the contact angle of each colored ink with respect to the treated substrate for measurement was measured.

(1.3) Measurement of Contact Angle A2 [°] In each colored ink, the wax shown in Table II was replaced with water to prepare a wax-removed ink. Then, the contact angle of each wax-removed ink with respect to an untreated substrate for measurement was measured.

(1.4) Measurement of Contact Angle B2 [°] The contact angle of each wax removal ink with respect to the treated substrate for measurement was measured.
The treated substrate and wax-removing ink for measurement were obtained as described above.

The contact angles were measured for each water-based ink set, and the values represented by "|A1-B1|" and "|A2-B2|/X" were calculated. X [mass %] is the content of the surface conditioner as solids.

(2) Ink ejection stability Each color ink was filled into an independently driven inkjet head (360 npi, ejection volume 6 pL, 1024 nozzles) manufactured by Konica Minolta, and a continuous ejection test was carried out for 30 minutes using a strobe-synchronized droplet observation device. The ejection stability was evaluated according to the following criteria. A grade of A or higher (A to AAA) was considered to be acceptable.

AAA: Of the 256 nozzles evaluated, colored ink was ejected normally from all nozzles (256 nozzles), and no nozzle chipping (omissions) or nozzle bending was observed.
AA: Of the 256 nozzles evaluated, no nozzle chipping (missing) was observed in any of the 256 nozzles (256 nozzles), but one or two nozzles were bent.
A: Of the 256 nozzles evaluated, no nozzle chipping (missing) was observed in any of the 256 nozzles (256 nozzles), but nozzle bending was observed in 3 or more nozzles.
B: Nozzle chipping (missing) was observed in the 256 nozzles evaluated.

(3) Variation in dot diameter Dots were printed with each treated ink on the untreated substrate for measurement by adjusting the voltage so that the droplet volume was 9.0 pL, resulting in one size dot. Then, dots were printed on top of the treated ink with a colored ink. Among the dots obtained, dots formed by complete merging of the treated ink and the colored ink were extracted, and 10 dots were randomly extracted and the dot diameter was measured. The dot diameter was measured by observing the printed dots under an optical microscope at a magnification of 500 times.
The arithmetic mean value of the dot diameters of the 10 dots was then calculated. The difference (variation) between each of the 10 dot diameters and the average dot diameter was calculated, and the maximum value of the variation was evaluated according to the following criteria. A grade of A or higher (A to AAA) was considered to be acceptable.
AAA: The maximum value of variation is 3 μm or less.
AA: The maximum value of variation is more than 3 μm and 4 μm or less.
A: The maximum value of variation is more than 4 μm and 5 μm or less.
B: The maximum value of variation exceeds 5 μm.

(4) Solid Uniformity A solid image of 5 cm x 5 cm was prepared by the following method.
A scan-type printer was prepared, which was equipped with two independently driven inkjet heads (360 npi, ejection volume 6 pL, 1024 nozzles) manufactured by Konica Minolta, Inc. The head to be recorded first was filled with each treatment ink, and the head to be recorded later was filled with each color ink.
Thereafter, the image with a resolution of 720 x 720 dpi was divided into two in each of the scanning direction X and the transport direction Y to create four images (180 x 180 dpi). In a four-pass mode in which one print area is printed four times, printing was performed in one direction, always with the treatment ink being recorded first.
The carriage transport speed was set to 300 mm/sec, and no drying process was provided between recording of the treatment ink and the color ink. The printing test was performed in an environment of 25° C. and 50% RH.
The recording with the treatment ink was performed by setting the application amount C _P of each treatment ink to 4.5 g/m ² and the maximum printing rate to 25%, in accordance with the recording area of the color ink. The recording with the color ink was performed by setting the application amount C _I of each color ink to 18 g/m ² in a solid state. The ratio C _P /C _I of the application amount C _P [g/m ² ] of the treatment ink to the application amount C _I [g/m ² ] of the color ink was 0.25.
After the color ink was applied, the substrate was placed in a dryer set at 90° C. and dried by heating for 5 minutes to obtain a solid image.
In Examples 18 to 21, solid images were obtained in the same manner except that the C _P /C _I value was changed as shown in Table IV below.

The obtained solid image was observed visually from a distance of 15 cm or with an optical microscope and evaluated according to the following criteria, with A or higher (A to AAA) being considered as passing.
AAA: No unevenness is observed even when magnified 100 times with an optical microscope.
AA: No unevenness is observed with the naked eye.
A: Visually, unevenness is observed only in some areas.
B: Visually, unevenness is observed throughout the entire surface.

The evaluation results are shown in Tables III and IV below.
In the table, "*(1)" is a value expressed by |A1-B1| [°]. Furthermore, "*(2)" is a value expressed by |A2-B2|/X [°/mass %]. Furthermore, "critical surface tension" is the critical surface tension of the substrate. Similarly to the above-mentioned C _P /C _I , C _P /C _I is the ratio of the amount of treatment ink applied C _P [g/m ² ] to the amount of color ink applied C _I [g/m ² ].
In Examples 16 and 17, as described above, the non-low absorbency substrate was changed, and the contact angle was measured in the same manner.

From the examples and comparative examples, it can be seen that the water-based ink set produced by the method for producing a water-based ink set of the present invention has a uniform dot diameter formed by the colored ink, regardless of the presence or absence of treated ink, and reduces unevenness during solid printing (reducing variation in dot diameter and improving solid uniformity).

A comparison of Examples 4, 6 and 10 shows that satisfying formula (2) above improves the ejection stability of the colored ink.

A comparison of Examples 4 and 7 to 9 shows that using a polyolefin wax as a surface conditioner reduces the variation in dot diameter and improves the uniformity of the solid print.

Comparing Examples 4, 7 and 9, it can be seen that the nonionic nature of the polyolefin wax reduces the variation in dot diameter and improves the uniformity of the solid print.

A comparison of Examples 4 and 10 shows that the ejection stability of the colored ink is improved when the wax content X [mass %] is within the range of 0.01 to 5 mass % relative to the total mass of the colored ink.

Comparing Examples 4, 11, and 12, it can be seen that the colored ink contains a dispersant and the acid value of the dispersant is within the range of 50 to 120 mgKOH/g, which improves cohesion and reduces variation in dot diameter. It can also be seen that solid uniformity is improved.

Comparing Examples 4 and 13, it can be seen that using a metal salt as the aggregating agent improves aggregability and reduces variation in dot diameter. It can also be seen that solid uniformity is improved.

Comparing Examples 4, 14, and 15, it can be seen that by having the metal salt content be within the range of 1 to 10% by mass relative to the total mass of the treated ink, coagulation is improved and the variation in dot diameter is reduced. It can also be seen that solid uniformity is improved.

From a comparison between Examples 4 and 18 to 21, it is clear that by making the C _P /C _I ratio satisfy the above formula (4), the aggregation of the treatment ink and the color ink can be controlled, and the solid uniformity is improved.

A comparison of Examples 4, 16 and 17 shows that this ink set is suitable for non- and low-absorbency substrates with a critical surface tension at 25°C in the range of 35 to 48 mN/m (improving solid uniformity).

A comparison of Examples 4 and 22 shows that the inkjet head has a piezoelectric element (is a piezo type), which reduces the variation in dot diameter and improves the ejection stability and solid uniformity of the colored ink.

REFERENCE SIGNS LIST 1 Inkjet recording device 10 Treated ink application section 11 Inkjet head 12 Droplets of treated ink 20 Colored ink application section 21 Inkjet head 22 Droplets of colored ink 23 Drying section 30 Delivery roller 40 Take-up roller C Treated ink layer G Image layer F Substrate 101 Dots formed with colored ink alone 102 Dots formed with treated ink alone 103 Dots formed with a mixture of treated ink and colored ink (completely united)
104 Dots formed with a mixture of treated ink and colored ink (partially merged)

Claims (14)

A water-based ink set for printing on a non-low absorbency substrate, the water-based ink set having a treatment ink and a color ink, comprising:
the treated ink contains a flocculant;
the color ink contains a color material and a surface modifier;
When the contact angle of the colored ink with respect to the non-low absorbency substrate having a critical surface tension of 44 mN/m at 25° C. is A1 [°], and the contact angle of the colored ink with respect to the non-low absorbency substrate onto which the treated ink has been applied and dried is B1 [°], the following formula (1) is satisfied: |A1-B1|≦10°
A water-based ink set comprising: The surface conditioner contains a wax,
When the content of the wax with respect to the total mass of the colored ink is X [mass %], the contact angle of the composition of the colored ink excluding only the wax with respect to the non-low absorbency substrate having a critical surface tension of 44 mN/m at 25°C is A2 [°], and the contact angle of the composition of the colored ink excluding only the wax with respect to the non-low absorbency substrate onto which the treated ink has been applied and dried is B2 [°], the following formula (2) is satisfied: Formula (2): 10 [°/mass %]≦|A2−B2|/X≦40 [°/mass %]
The water-based ink set according to claim 1 . The water-based ink set according to claim 1 , wherein the surface conditioner contains a polyolefin wax. The water-based ink set according to claim 3 , wherein the polyolefin wax is nonionic. The water-based ink set according to claim 2, wherein the content X [mass %] of the wax is within a range of 0.01 to 5 mass % with respect to the total mass of the color inks. The color ink contains a dispersant,
2. The water-based ink set according to claim 1, wherein the acid value of the dispersant is within the range of 50 to 120 mgKOH/g. The water-based ink set according to claim 1 , wherein the water-based ink set comprises two or more types of the colored inks. The water-based ink set according to claim 1 , wherein the coagulant is a metal salt. 9. The water-based ink set according to claim 8, wherein the content of the metal salt is within a range of 1 to 10 mass % relative to the total mass of the treatment ink. A method for producing the water-based ink set according to any one of claims 1 to 9, comprising the steps of:
adding the coagulant to the treatment ink; and adding the coloring material and the surface conditioner to the color ink,
When the contact angle of the colored ink with respect to the non-low absorbency substrate having a critical surface tension of 44 mN/m at 25° C. is A1 [°], and the contact angle of the colored ink with respect to the non-low absorbency substrate to which the treated ink has been applied and dried is B1 [°], the amount of the surface conditioner added is adjusted so as to satisfy the following formula (3): |A1-B1|≦10°
A method for producing a water-based ink set. An inkjet recording method, comprising using the water-based ink set according to any one of claims 1 to 9. the flocculant is a metal salt;
the content of the metal salt is within a range of 1 to 10% by mass based on the total mass of the treatment ink;
When the applied amount of the treatment ink is C _P [g/m ² ] and the applied amount of the color ink is C _I [g/m ² ], the following formula (4) is satisfied: 0.05≦C _P /C _I <1.00.
The inkjet recording method according to claim 11 . The ink-jet recording method according to claim 11, wherein the non-low absorbency substrate has a critical surface tension at 25° C. in the range of 35 to 48 mN/m. 1. An inkjet recording system using a water-based ink set, comprising:
The water-based ink set according to any one of claims 1 to 9,
an inkjet head for ejecting the treatment ink and the color ink;
The inkjet recording system, wherein the inkjet head has a piezoelectric element.

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