Image formation method

Abstract

To provide an ink set and an image forming method which improve drawing property.SOLUTION: There is provided an ink set having a pretreatment ink containing a coagulant, a first ink containing a first color material and a second ink containing a second color material, the pretreatment ink and the first ink are mixed in a liquid state on a recording medium and the dynamic surface tension at 25[°C] in the surface lifetime 30 [ms] of the pretreatment ink, the first ink and the second ink satisfies the relation represented by the following expressions (1) and (2). γ0<γ2<γ1 (1) and 0<|γ1-γ2|≤12 (2) (γ0: the dynamic surface tension in the surface lifetime 30 [ms] of the pretreatment ink, γ1: the dynamic surface tension in the surface lifetime 30 [ms] of the first ink, γ2: the dynamic surface tension in the surface lifetime 30 [ms] of the second ink)SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ink set and an image forming method, and more particularly to an ink set and an image forming method that provide good printability. [Background technology]

[0002] BACKGROUND ART Inkjet recording methods can produce images simply and inexpensively, and therefore have been applied to a variety of printing fields, including photography, various types of printing, marking, and special printing such as color filters. In particular, the inkjet recording method is suitable for applications such as forming a variety of images in small quantities, since it allows digital printing without using a plate.

[0003] In the technology disclosed in Patent Document 1, in an ink set containing a water-based colored ink and a treatment liquid (also called a "pretreatment liquid" or "primer") containing a flocculant, the dynamic surface tension of the pretreatment liquid is set to be smaller than the dynamic surface tension of the water-based colored ink, and the surface tensions of both are controlled within a certain range, thereby preventing spreading or shrinkage of the printed layer and enabling stable printing of high-resolution images.

[0004] It is known that in an ink set containing colored inks and a pretreatment liquid, when multiple colored inks are used, bleeding between the inks can be prevented and clogging is less likely to occur (see Patent Document 2). However, there is no specification for the relationship between the dynamic surface tension of the pretreatment liquid and the dynamic surface tension of the multiple colored inks when multiple colored inks are used in the ink set disclosed in Patent Document 1, and problems remain with the drawing performance on the colored inks, for example, the wettability of the second ink on the first ink coating and the liquid concentration between the first ink and the second ink.

[0005] The technology disclosed in Patent Document 3 uses white ink and colored ink to control surface tension during the image recording process and image drying process, making it possible to prevent deterioration in color development due to mixing of the colored ink with the base layer, bleeding at the boundaries between colored inks, and deterioration in image quality due to insufficient color spread caused by the colored ink being repelled.

[0006] However, no pretreatment liquid is used, and similarly to the above, there is no specification for the relationship between the dynamic surface tension of the pretreatment liquid and the dynamic surface tension of the multiple colored inks, and the problem remains of achieving both the wettability of the white ink and the wettability of the second ink on the first ink coating film.

[0007] Furthermore, the technology disclosed in Patent Document 4 controls the difference between the surface tension of the background ink and the surface tension of the color ink within a certain range, thereby defining the similarity between the surface tensions of the two inks, and making it possible to suppress bleeding at the boundary between the background ink and the color inks, as well as aggregation of the background ink.

[0008] However, as in the above, there is no specification for the relationship between the dynamic surface tension of the pretreatment liquid and the dynamic surface tension of the plurality of colored inks, and the problem remains of achieving both the wettability of the white ink and the wettability of the second ink on the first ink coating film.

[0009] The technology disclosed in Patent Document 5 makes it possible to prevent cracks from occurring in the laminated film of colored ink and white ink by using a pretreatment liquid containing colored ink, white ink, and an alkanolamine compound as a flocculant.

[0010] However, there is no specification regarding the relationship between the dynamic surface tension of the pretreatment liquid and the dynamic surface tension of the plurality of colored inks, and there remains room for improvement in the problem of achieving both the wettability of the white ink and the wettability of the second ink on the first ink coating film by specifying the above-mentioned relationship between the dynamic surface tensions, without using a pretreatment liquid containing an alkanolamine compound. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2020-12080 [Patent Document 2] Japanese Patent Application Publication No. 2018-178131 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-199044 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-177527 [Patent Document 5] Patent Publication No. 2021-031603 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made in view of the above problems and circumstances, and an object of the present invention is to provide an ink set and an image forming method that provide good printability. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, the inventors investigated the causes of the above-mentioned problems and found that the above-mentioned problems could be solved by using an ink set that includes a pretreatment ink containing an aggregating agent and first and second inks each containing a colorant, in which the pretreatment ink and the first ink are mixed in liquid form and in which the dynamic surface tensions of the inks satisfy a specific relationship, thereby arriving at the present invention. That is, the above-mentioned problems of the present invention are solved by the following means.

[0014] 1. An ink comprising a pretreatment ink containing a flocculant, a first ink containing a first coloring material, and a second ink containing a second coloring material, wherein the pretreatment ink and the first ink are mixed in a liquid state on a recording medium; the pretreatment ink and the first ink contain one or more surfactants, and the HLB value of the at least one surfactant contained in the first ink is greater than the HLB value of the at least one surfactant contained in the pretreatment ink;an ink set in which the dynamic surface tensions of the pretreatment ink, the first ink, and the second ink at 25°C during a surface life of 30 ms satisfy the relationship expressed by the following formulas (1) and (2), the image forming method comprising the steps of: applying the pretreatment ink onto a recording medium; applying the first ink so that the pretreatment ink and the first ink are mixed in liquid form on the recording medium; drying the pretreatment ink and the first ink applied to the recording medium to form a first ink coating film that is a composite coating film; and applying the second ink onto the first ink coating film.

[0015] γ0<γ2<γ1(1) 0<|γ1-γ2|≦12 (2)

[0016] (γ0: dynamic surface tension of the pretreatment ink after a surface life of 30 ms, γ1: dynamic surface tension of the first ink after a surface life of 30 ms, γ2: dynamic surface tension of the second ink after a surface life of 30 ms)

[0017] 2. The method according to claim 1, characterized in that the dynamic surface tension at 25°C with a surface life of 30 ms is in the range of 24 to 34 mN / m for the pretreatment ink, in the range of 31 to 41 mN / m for the first ink, and in the range of 25 to 40 mN / m for the second ink. Image forming method .

[0019] 3 The first ink contains two or more types of surfactants, and the absolute value of the difference in HLB value between any two types of surfactants selected from the two or more types of surfactants is within the range of 1 to 9. 1 Item 1. The image forming method according to item 1.

[0020] 4 The first ink contains two or more types of surfactants, and the absolute value of the difference in HLB value between any two types of surfactants selected from the two or more types of surfactants is within the range of 6 to 16. 1Item 1. The image forming method according to item 1.

[0021] 5 The swelling ratio of the first ink coating film formed by the first ink satisfies the relationship expressed by the following formula (3). 4 Item 1. The image forming method according to any one of items 1 to 5.

[0022] -0.15≦Swelling ratio [mg / cm 2 ]≦0.15 (3) (Swelling ratio [mg / cm 2 ] = Water swelling mass [mg] / coating surface area [cm 2 ], where the minus sign indicates dissolution of ink.

[0023] 6 The glass transition temperature of the first ink coating film is within the range of 35 to 100°C. 5 Item 1. The image forming method according to item 1.

[0024] 7 The second ink film is characterized in that the water contact angle at 25°C after 60 ms has elapsed since the water was dropped onto the surface of the first ink film is within the range of 30 to 80°. 5 Section or Article 6 Item 1. The image forming method according to item 1.

[0026] 8 The method according to any one of claims 1 to 5, characterized in that it comprises a step of applying the pretreatment ink onto the first ink coating film, and a step of applying the second ink so that the pretreatment ink and the second ink are mixed in a liquid state on the first ink coating film. 7 Item 1. The image forming method according to any one of items 1 to 5.

[0027] 9The acid value of the dispersant for the first coloring material and the acid value of the dispersant for the second coloring material are within the range of 50 to 200 [mgKOH / g], and the sum of the amount of reactive groups per unit area in the aggregation reaction [mol] contained in the pretreatment ink and the amount of the first coloring material and the second coloring material [g] satisfies the relationship of the following formula (4). 8 Item 1. The image forming method according to any one of items 1 to 5.

[0028] 500<(sum of the amount [g] of the first colorant and the second colorant / sum of the amount [mol] of reactive groups contained in the first colorant and the second colorant per unit area of ​​the recording medium in the aggregation reaction contained in the pretreatment ink)<20,000 (4) [Effects of the Invention]

[0029] The above-described means of the present invention can provide an ink set and an image forming method that provide good printability. The mechanism by which the effects of the present invention are manifested or the mechanism of action is not clear, but is speculated as follows.

[0030] The ink set of the present invention comprises a pretreatment ink containing an aggregating agent, a first ink containing a first coloring material, and a second ink containing a second coloring material, and the pretreatment ink and the first ink are mixed in liquid form on a recording medium. Furthermore, when the dynamic surface tensions of the pretreatment ink, the first ink, and the second ink satisfy a specific relationship, good printability is achieved.

[0031] In the prior art, there is still room for improvement in terms of controlling the relationship between the dynamic surface tensions of the pretreated ink containing an aggregating agent and the multiple inks containing colorants within a specific range and appropriately improving the wetting properties of the inks.

[0032] When the pretreatment ink and the ink containing colorant (referred to as the "first ink" and the "second ink" in the present invention; hereinafter, when there is no need to particularly distinguish between the first ink and the second ink, both will also be referred to as the "colorant-containing ink") are mixed in liquid form, the colorant-containing ink aggregates uniformly and thickens, thereby preventing the colorant-containing ink from flowing off the recording medium, and the colorant-containing ink is fixed on the recording medium.

[0033] In the case of an inkjet process, for example, if a pretreatment ink containing a coagulant and an ink containing a colorant are mixed in advance rather than on the recording medium, a thickening reaction occurs before the mixed droplets land on the recording medium, which can change the trajectory of the droplets, causing them to land misaligned or deteriorating the adhesion of the mixed ink to the recording medium.

[0034] In the present invention, by mixing the pretreatment ink and the first ink on a recording medium, the timing at which the thickening reaction occurs can be controlled, allowing the pretreatment ink and the first ink to react uniformly and preventing uneven aggregation. Furthermore, it is possible to prevent misalignment of ink droplets and improve adhesion to the recording medium.

[0035] Furthermore, when the dynamic surface tensions of the pretreatment ink, the first ink, and the second ink at 25°C with a surface life of 30 ms satisfy the relationship expressed by the formulas (1) and (2), the wettability of the inks can be appropriately controlled, which is presumably why the printability is good. [Brief explanation of the drawings]

[0036] [Figure 1] Schematic diagram showing an example of an image forming apparatus preferred for the present invention. [Figure 2] Schematic diagram showing the inkjet head used in the examples DETAILED DESCRIPTION OF THE INVENTION

[0037] The ink set of the present invention is an ink set having a pretreatment ink containing an aggregating agent, a first ink containing a first colorant, and a second ink containing a second colorant, wherein the pretreatment ink and the first ink are mixed in liquid form on a recording medium, and the dynamic surface tensions of the pretreatment ink, the first ink, and the second ink at 25°C over a surface life of 30 ms satisfy the relationship expressed by the following equations (1) and (2): This feature is a technical feature common to or corresponding to each of the following embodiments (modes).

[0038] In one embodiment of the present invention, it is preferable from the viewpoint of appropriately controlling the wettability between the inks that the dynamic surface tension at 25°C with a surface life of 30 ms is in the range of 24 to 34 mN / m for the pretreatment ink, in the range of 31 to 41 mN / m for the first ink, and in the range of 25 to 40 mN / m for the second ink.

[0039] It is preferable that the pretreatment ink and the first ink contain one or more surfactants, and that the HLB value of at least one of the surfactants contained in the first ink is greater than the HLB value of at least one of the surfactants contained in the pretreatment ink, from the viewpoint of the wettability of the first ink and the second ink properly wetting and spreading on the first ink coating.

[0040] It is preferable from the viewpoint of the wettability and pinning property of the first ink that the first ink contains two or more types of surfactants, and that the absolute value of the difference in HLB value between any two types of surfactants selected from the two or more types of surfactants is within a range of 1 to 9.

[0041] It is preferable that the first ink contains two or more types of surfactants, and that the absolute value of the difference in HLB value between any two types of surfactants selected from the two or more types of surfactants is within a range of 6 to 16, from the viewpoint of the wettability of the first ink and the appropriate wetting and spreading of the second ink on the first ink coating film.

[0042] It is preferable that the swelling ratio of the first ink coating film formed by the first ink satisfies the relationship expressed by formula (3) from the viewpoint of predicting that the second ink will properly wet and spread on the first ink coating film, which is a composite coating film formed by the pretreatment ink and the first ink.

[0043] It is preferable that the glass transition temperature of the first ink coating film formed by the first ink is within the range of 35 to 100° C., from the viewpoint of predicting crack prevention properties after application of the second ink.

[0044] It is preferable from the viewpoint of predicting that the second ink will properly wet and spread on the first ink coating film, which is a composite coating film formed by the pretreatment ink and the first ink, that the water contact angle at 25°C 60 ms after water is dropped on the surface of the first ink coating film formed by the first ink be within the range of 30 to 80°.

[0045] The image forming method of the present invention is an image forming method using the ink set of the present invention, The method includes a step of applying the pretreatment ink onto a recording medium, a step of applying the first ink so that the pretreatment ink and the first ink are mixed in liquid form on the recording medium, a step of drying the pretreatment ink and the first ink applied onto the recording medium to form a first ink coating film which is a composite coating film, and a step of applying the second ink onto the first ink coating film.

[0046] As a method having a step different from the above-described image forming method, a method having a step of applying the pretreatment ink onto the first ink coating film, and a step of applying the second ink so that the pretreatment ink and the second ink are mixed in liquid form on the first ink coating film is preferred from the viewpoint of suppressing aggregation unevenness and from the viewpoint of pinning properties of the second ink.

[0047] In the image forming method, it is preferable from the viewpoint of appropriate aggregation properties of the first colorant and the second colorant that the acid value of the dispersant for the first colorant and the acid value of the dispersant for the second colorant are within a range of 50 to 200 [mgKOH / g], and that the sum of the amount of reactive groups per unit area in the aggregation reaction [mol] contained in the pretreatment ink and the amount of the first colorant and the second colorant [g] satisfies the relationship of formula (4).

[0048] The present invention, its components, and embodiments for carrying out the present invention will be described in detail below. In this application, the symbol "to" is used to mean that the numerical values ​​before and after it are included as lower and upper limits.

[0049] I. [Outline of the ink set of the present invention] The ink set of the present invention is an ink set having a pretreatment ink containing an aggregating agent, a first ink containing a first colorant, and a second ink containing a second colorant, wherein the pretreatment ink and the first ink are mixed in liquid form on a recording medium, and the dynamic surface tensions of the pretreatment ink, the first ink, and the second ink at 25°C over a surface life of 30 ms satisfy the relationship expressed by the following equations (1) and (2):

[0050] γ0<γ2<γ1(1) 0<|γ1-γ2|≦12 (2)

[0051] (γ0: dynamic surface tension of the pretreatment ink after a surface life of 30 ms, γ1: dynamic surface tension of the first ink after a surface life of 30 ms, γ2: dynamic surface tension of the second ink after a surface life of 30 ms)

[0052] By mixing the pretreatment ink and the first ink in liquid form on a recording medium, the first ink uniformly aggregates and thickens, becoming fixed on the recording medium, and a first ink coating film of the first ink is formed.

[0053] Here, "mixing in a liquid state" means, for example, mixing the pretreatment ink and the first ink while they are still in a liquid state to form a single liquid body.

[0054] In this specification, the term "composite coating film" refers to a composite coating film of the pretreatment ink and the first ink formed by mixing the pretreatment ink and the first ink in liquid form on a recording medium.

[0055] Furthermore, the term "first ink coating film formed by the first ink" refers to a first ink coating film formed directly on a recording medium using only the first ink without using a pretreatment ink in order to evaluate or predict the physical properties desired for the first ink constituting the ink set of the present invention, and is different from a "first ink coating film which is a composite coating film" formed by mixing the pretreatment ink and the first ink in liquid form.

[0056] Furthermore, the concept of the above-mentioned "first ink coating film" includes not only the "first ink coating film" being solid, but also the "semi-solid" state, and the "semi-solid" state includes the liquid state. In the present invention, the term "liquid" refers to a state in which the drying rate of the pretreatment ink, the first ink, and the second ink is 30% or less. The drying rate will be described later in the description of the image forming method of the present invention.

[0057] The wettability of a liquid to a solid surface (including a semi-solid state) is generally quantitatively expressed by the water contact angle of the liquid, and it is thought that the coatability (wettability) to the composite coating film increases as the surface tension of the second ink becomes lower than the surface tension of the composite coating film. Therefore, in order for the second ink according to the present invention to wet the composite coating film, the surface tension of the composite coating film must be greater than the surface tension of the second ink.

[0058] Since the composite coating film is formed by mixing the pretreatment ink and the first ink in liquid form on the recording medium, the dynamic surface tensions of the pretreatment ink, the first ink, and the second ink at 25°C during a surface life of 30 ms satisfy the relationship expressed by the above formulas (1) and (2), allowing the first ink and the second ink to wet and spread appropriately on the pretreatment ink.

[0059] In other words, in the present invention, by using a pretreatment ink containing an aggregating agent and first and second inks containing coloring materials to keep the dynamic surface tension within a specific range, the wetting and spreading of the first and second inks is promoted before the dots are fixed by the aggregating reaction, thereby improving drawing properties.

[0060] The "dynamic surface tension at 25°C for a surface life of 30 ms" according to the present invention refers to the surface tension (unit: mN / m) 30 ms after the liquid surface (gas-liquid interface) is formed, measured by the maximum bubble pressure method in an environment of 25°C.

[0061] Furthermore, "surface lifetime" refers to the time elapsed since the formation of a liquid surface (gas-liquid interface), i.e., the lifetime of a bubble generated in the maximum bubble pressure method. It is also called bubble lifetime and refers to the time from the generation of a new interface within the probe tip of a dynamic surface tensiometer until the maximum bubble pressure is reached.

[0062] The dynamic surface tension (γ0) of the pre-treatment ink at a surface life of 30 [ms] is smaller than the dynamic surface tension (γ2) of the second ink at a surface life of 30 [ms], and the dynamic surface tension (γ1) of the first ink at a surface life of 30 [ms] is larger than the dynamic surface tension (γ2) of the second ink at a surface life of 30 [ms], so that the first ink and the second ink properly wet and spread on the pre-treatment ink.

[0063] When the absolute value of the difference between the dynamic surface tension (γ1) of the first ink at a surface life of 30 [ms] and the dynamic surface tension (γ2) of the second ink at a surface life of 30 [ms] is greater than 0 and less than or equal to 12, the second ink will wet and spread appropriately on the composite coating film.

[0064] In the ink set of the present invention, it is preferable that the dynamic surface tension at 25°C with a surface life of 30 ms is in the range of 24 to 34 mN / m for the pretreatment ink, in the range of 31 to 41 mN / m for the first ink, and in the range of 25 to 40 mN / m for the second ink, from the viewpoint of appropriately controlling the wettability between the inks.

[0065] (Method for measuring dynamic surface tension) The "dynamic surface tension at 25°C with a surface life of 30 ms" of the pretreatment ink, the first ink, and the second ink according to the present invention can be measured using a dynamic surface tensiometer (for example, a bubble pressure dynamic surface tensiometer (manufactured by KRUSS, model "BP100")).

[0066] 1. Pre-treatment ink The pretreatment ink according to the present invention contains a flocculant, and the pretreatment ink is an ink that is mixed in a liquid state with the first ink described below on a recording medium.

[0067] (1.1) Physical properties of pretreatment ink (Dynamic surface tension of pre-treated ink) When the dynamic surface tensions of the pretreatment ink, the first ink, and the second ink according to the present invention at 25°C with a surface life of 30 ms satisfy the relationship expressed by the formulas (1) and (2), the wettability of the inks can be appropriately controlled, thereby improving the printability.

[0068] The pretreatment ink according to the present invention preferably has a dynamic surface tension at 25° C. within the range of 24 to 34 mN / m at a surface life of 30 ms. By setting the content within the above range, when the first ink is mixed in liquid form with the second ink, it is possible to promote wetting and spreading of the first ink. The dynamic surface tension of the pretreatment ink can be controlled by the type and content of the coagulant, solvent, surfactant, water, and other components described below.

[0069] When the pretreatment ink and the colorant-containing ink are mixed in liquid form, they aggregate and thicken uniformly, so that the colorant-containing ink is fixed on the recording medium without flowing off.

[0070] For example, by mixing the pretreatment ink and the first ink in liquid form on a recording medium, the first ink aggregates and thickens, becoming fixed on the recording medium, forming a first ink coating film, which is a composite coating film. From the viewpoint of suppressing aggregation unevenness, it is preferable that the second ink is a liquid ink that is applied onto the first ink coating film, which is a composite coating film. When the second ink is in a liquid state, the pretreatment ink and the second ink in the first ink coating film, which is a composite coating film, react uniformly, and aggregation unevenness can be suppressed.

[0071] In the case of an inkjet process, for example, if a pretreatment ink containing a coagulant and an ink containing a colorant are mixed in advance rather than on the recording medium, a thickening reaction occurs before the mixed droplets land on the recording medium, which can change the trajectory of the droplets, causing them to land misaligned or deteriorating the adhesion of the mixed ink to the recording medium.

[0072] In the present invention, by mixing the pretreatment ink and the first ink on a recording medium, the timing at which the thickening reaction occurs can be controlled, allowing the pretreatment ink and the first ink to react uniformly and preventing uneven aggregation. Furthermore, it is possible to prevent misalignment of ink droplets and improve adhesion to the recording medium. Furthermore, the wetting and spreading of the color ink can be promoted.

[0073] (1.2) Components of pretreatment ink The pretreatment ink contains an aggregating agent and is mixed in a liquid state with the first ink on the recording medium, and may contain a solvent, a surfactant, water, and other components.

[0074] (1.2.1) Flocculants The aggregating agent contained in the pretreatment ink is not particularly limited as long as it is a material that generates aggregates when it comes into contact with the ink, and examples thereof include polyvalent metal salts, organic acids, and inorganic acids. By including these, it is possible to enhance the interaction with the colorant-containing ink.

[0075] (polyvalent metal salts) When the pretreatment ink contains the polyvalent metal salt as an aggregating agent, the anionic components in the colorant-containing ink mixed with the pretreatment ink on the recording medium are agglomerated by salting out.

[0076] 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. For example, Ca 2+ , Cu 2+ , Ni 2+ , Mg 2+ , Zn 2+ , Ba 2+ Divalent metal ions such as Al 3+ , Fe 3+ , Cr 3+ , Y 3+ Trivalent metal ions such as Zr 4+ and the like.

[0077] The type of salt constituting the polyvalent metal salt is not particularly limited, but known salts such as carbonates, sulfates, nitrates, hydrochlorides, organic acid salts, borates, and phosphates can be used. Particularly preferred examples of polyvalent metal salts include calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, magnesium acetate, calcium acetate, magnesium lactate, calcium pantothenate, and other calcium or magnesium salts of carboxylic acids.

[0078] The content of the polyvalent metal salt is preferably in the range of 0.5 to 20% by mass, and more preferably in the range of 1 to 10% by mass, relative to 100% by mass of the total mass of the pretreatment ink. This makes it possible to effectively aggregate the anionic components in the colorant-containing ink, and adjust the balance between image quality and hot water resistance.

[0079] The content of the polyvalent metal salt in the aqueous solution can be measured by a known method, for example, ICP emission spectrometry.

[0080] (organic acid) The organic acid is capable of aggregating the pigment that may be contained in the coloring material-containing ink. When the pretreatment ink contains the organic acid as an aggregating agent, the anionic components in the colorant-containing ink can be aggregated by pH fluctuation.

[0081] The organic acid is preferably a monocarboxylic acid, since it does not weaken the cohesive force of the polyvalent metal salt.

[0082] Examples of the organic acid include formic acid, acetic acid, propionic acid, isobutyric acid, and benzoic acid.

[0083] It is preferable that the organic acid used is one that is not completely neutralized with a base.

[0084] "Neutralization by a base" means that the acidic groups of these acids are ionic bonded to other positively charged elements or compounds (eg inorganic compounds such as metals).

[0085] Furthermore, the phrase "not completely neutralized" means that among the acidic groups possessed by the organic acid, there are acidic groups that do not form the above-mentioned ionic bond.

[0086] Furthermore, by using the organic acid, the storage stability of the pretreatment ink can be easily maintained, and blocking is less likely to occur after the pretreatment ink is applied and dried.

[0087] From the above viewpoint, preferred organic acids include formic acid, acetic acid, propionic acid, and benzoic acid.

[0088] When an organic acid is contained, the content of the organic acid is preferably in the range of 0.1 to 10% by mass, and more preferably in the range of 1 to 3% by mass, relative to 100% by mass of the total mass of the pretreatment ink.

[0089] When an organic acid is used, the amount of the organic acid applied is preferably an amount that adjusts the pH of the pretreatment ink to a neutralization equivalent or less of the anionic components contained in the ink. Furthermore, when the anion component is a compound having a carboxy group, the first dissociation constant of the organic acid is preferably 3.5 or less, from the viewpoint of making the image less susceptible to bleeding.

[0090] The content of the organic acid in the aqueous solution can be measured by a known method, such as high performance liquid chromatography (HPLC).

[0091] (Inorganic acid) The inorganic acid is capable of aggregating the pigment that may be contained in the colorant-containing ink. The inorganic acid can cause the anionic components in the colorant-containing ink to aggregate by changing the pH.

[0092] Examples of the inorganic acid include hydrochloric acid, nitric acid, sulfuric acid, and sulfamic acid.

[0093] When an inorganic acid is contained, the content of the inorganic acid is preferably in the range of 0.1 to 10% by mass, and more preferably in the range of 1 to 3% by mass, relative to 100% by mass of the total mass of the pretreatment ink.

[0094] (1.2.2) Solvent (Water-soluble solvent) The pretreatment ink according to the present invention can use a water-soluble solvent with a boiling point in the range of 150 to 250°C as the solvent.

[0095] Examples of such water-soluble solvents include alcohols, polyhydric alcohols, amines, amides, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms.

[0096] 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.

[0097] Examples of polyalkylene glycols include diethylene glycol and dipropylene glycol.

[0098] The pretreatment ink may contain one or a combination of two or more selected from these water-soluble solvents.

[0099] It is preferable that the ink contains at least one water-soluble solvent having a boiling point in the range of 150 to 250°C, and may contain alcohols other than those mentioned above, polyhydric alcohols, amines, amides, glycol ethers, and 1,2-alkanediols having 4 or more carbon atoms.

[0100] The total content of the water-soluble solvent is preferably in the range of 5 to 40% by mass, and more preferably in the range of 10 to 40% by mass, relative to 100% by mass of the total mass of the pretreatment ink.

[0101] (non-water-soluble solvents) In the pretreatment ink according to the present invention, a solvent other than a water-soluble solvent having a boiling point in the range of 150 to 250°C can also be used as the solvent. Examples include glycerin, trimethylolpropane, triethylene glycol, and tetraethylene glycol.

[0102] (1.2.3) Surfactants It is preferable that the pretreatment ink and the first ink contain one or more surfactants, and that the HLB value of at least one of the surfactants contained in the first ink is greater than the HLB value of at least one of the surfactants contained in the pretreatment ink, from the viewpoint of the wettability of the first ink and the second ink properly wetting and spreading on the first ink coating.

[0103] Furthermore, it is sufficient that there is one set of surfactants that satisfy the following relationship, and surfactants that do not satisfy this relationship may also exist. (HLB value of surfactant contained in pretreatment ink < HLB value of surfactant contained in first ink)

[0104] In this specification, the HLB values ​​of the products used in the examples are those indicated by the manufacturer, and those not indicated by the manufacturer are calculated by the Griffin method.

[0105] (HLB value) "HLB value (hydrophilic lipophilic balance)" refers to a value that indicates the degree of affinity of a surfactant for water and oil (organic compounds insoluble in water), and is a value calculated using the Griffin method. Specifically, the HLB value of a surfactant can be calculated according to the following formula (H). HLB value = 20 × (formula weight sum of hydrophilic groups in molecular weight %) (H)

[0106] The HLB value is determined from the balance between the hydrophilic and lipophilic groups of a surfactant molecule; a high HLB value qualitatively indicates that the surfactant is highly hydrophilic, while a low HLB value qualitatively indicates that the surfactant is highly lipophilic.

[0107] When the HLB value is 8 or more, the compound is easily dissolved in water, and when the HLB value is 12 or less, the surface tension of the aqueous solution is low, making it easier to apply to a recording medium.

[0108] By incorporating the surfactant according to the present invention into the pretreatment ink, it is possible to improve the ejection stability of the pretreatment ink from the nozzle and to control the spreading of droplets that land on the recording medium (enlargement of the dot diameter).

[0109] There are no particular restrictions on the surfactant that can be contained in the pretreatment ink of the present invention, but when an anionic compound is contained as another component of the colorant-containing ink, the ionicity of the surfactant contained in the pretreatment ink is preferably anionic, nonionic, or betaine type.

[0110] In the present invention, fluorine-based or silicone-based surfactants, which have a high ability to reduce static surface tension, anionic surfactants such as dioctyl sulfosuccinate, which have a high ability to reduce dynamic surface tension, and nonionic surfactants, such as relatively low-molecular-weight polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, acetylene glycols, Pluronic surfactants (Pluronic is a registered trademark), and sorbitan derivatives, are preferably used. It is also preferable to use a fluorine-based or silicone-based surfactant in combination with a surfactant having a high ability to reduce dynamic surface tension.

[0111] (Silicone surfactant) Adding a silicone-based or fluorine-based surfactant as the surfactant is preferred in that it can further suppress ink mixing (beading) on ​​recording media made of various hydrophobic resins, including vinyl chloride sheets, and on recording media with low ink absorption capacity, such as printing paper, thereby enabling high-quality printed images to be obtained.

[0112] The silicone surfactant is preferably a polyether-modified silicone, such as a siloxane having alkylene oxide groups on the side chain and / or both ends of a polydimethylsiloxane chain.

[0113] Specifically, BYK-Chemie's BYK-331, BYK-333, BYK-345, BYK-3450, BYK-3451, BYK-3455, BYK-346, BYK-347, BYK-348, and BYK-349, and Evonik's TEGOWetKL245, TEGOWet250, TEGOWet260, TEGOWet270, and TEGOWet 280, and Shin-Etsu Chemical Co., Ltd.'s 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.

[0114] As the polyether-modified silicone, a trisiloxane having alkylene oxide groups on the side chains and / or at both ends of the polydimethylsiloxane chain is particularly preferred. The use of trisiloxane effectively reduces the dynamic surface tension of the pretreatment ink, resulting in an image with good adhesion to the substrate. The trisiloxane preferably has a structure represented by the following general formula (1).

[0115] [ka]

[0116] In the general formula (1), "EO" represents a repeating unit structure of polyethylene oxide, that is, a structure in which ethylene oxide, which is a three-membered cyclic ether, is ring-opened. Furthermore, "PO" represents the repeating unit structure of polypropylene oxide, that is, a structure in which propylene oxide, which is a three-membered cyclic ether, is ring-opened. The order of [EO]m and [PO]n is irrelevant

[0117] Here, the phrase "the order of [EO]m and [PO]n does not matter" 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.

[0118] In the general formula (1), X is preferably an alkylene group having 3 carbon atoms (that is, a propylene group). In the general formula (1), it is preferable that m is an integer of 5 to 20 and n is an integer of 0 to 6.

[0119] Specific examples of silicone surfactants having a structure represented by the general formula (1) are shown below as (S-1) to (S-8), but are not limited to these.

[0120] (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, 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, n=0

[0121] Examples of the trisiloxane include BYK-3450 and BYK-3451 manufactured by BYK Japan, and TEGOWet KL245, TEGOWet 250, and TEGOWet 260 manufactured by Evonik.

[0122] The content of the polyether-modified silicone is preferably in the range of 0.5 to 2% by mass, and more preferably in the range of 0.5 to 1.5% by mass, relative to 100% by mass of the total mass of the pretreatment ink.

[0123] (Fluorosurfactant) The fluorine-based surfactant means a surfactant in which part or all of the hydrogen atoms bonded to the carbon atoms of the hydrophobic group of a normal surfactant are substituted with fluorine. Among these, those having a perfluoroalkyl group in the molecule are preferred.

[0124] Some of the above fluorine-based surfactants are commercially available from Dainippon Ink and Chemicals, Inc. under the trade name Megafac F, from Asahi Glass Co., Ltd. under the trade name Surflon, from Minnesota Mining and Manufacturing Company, Inc. under the trade name Fluorad FC, from Imperial Chemical Industries, Inc. under the trade name Monflor, from E.I. duPont Nemelas and Company, Inc. under the trade name Zonyls, and from Falbewerke-Hoechst under the trade name Licowet VPF.

[0125] [Surfactants suitable for pretreatment ink] In particular, when forming a first ink coating film, which is a composite coating film of the pretreatment ink and the first ink, it is preferable that the HLB value of the surfactant contained in the pretreatment ink according to the present invention is lower than the HLB value of the surfactant contained in the first ink. Furthermore, from the viewpoint of wetting and spreading the pretreatment ink and wetting and spreading the first ink and the second ink, it is more preferable that the pretreatment ink contains a surfactant with a low HLB value within a range that dissolves in the pretreatment ink. Furthermore, from the viewpoint of forming circular dots, it is more preferable that the surfactant contained in the pretreatment ink has an HLB value smaller than that of the activators of the first and second inks.

[0126] The content of the surfactant in the pretreatment ink is not particularly limited, but is preferably within the range of 0.1 to 5.0% by mass of the total mass of the pretreatment ink.

[0127] (1.2.4) Water The water that can be used in the pretreatment ink according to the present invention is not particularly limited, and may be ion-exchanged water, distilled water, or pure water.

[0128] (1.1.5) Other ingredients The pretreatment ink according to the present invention may contain other components such as a crosslinking agent, an antifungal agent, a bactericide, etc., as appropriate, provided that the effects of the present invention are not impaired.

[0129] Furthermore, for example, ultraviolet absorbers described in JP-A Nos. 57-74193, 57-87988 and 62-261476, anti-fading agents described in JP-A Nos. 57-74192, 57-87989, 60-72785, 61-146591, JP-A Nos. 1-95091 and 3-13376, anions, It is also possible to contain various known additives such as various cationic or nonionic surfactants, fluorescent brightening agents described in JP-A Nos. 59-42993, 59-52689, 62-280069, 61-242871, and 4-219266, antifoaming agents, lubricants such as diethylene glycol, preservatives, thickeners, antistatic agents, etc.

[0130] 2. First Ink (2.1) Physical properties of the first ink (2.1.1) Dynamic surface tension of the first ink The first ink in the ink set of the present invention contains a first colorant and is an ink that is mixed in a liquid state with the pretreatment ink on a recording medium, and is characterized in that the dynamic surface tension relationship with the other inks (the pretreatment ink and the second ink) satisfies the above formulas (1) and (2).

[0131] When the first ink and the pretreatment ink are mixed in liquid form, the coloring material contained in the first ink uniformly aggregates and thickens, and the first ink is fixed on the recording medium, forming a first ink coating film that is a composite coating film of the pretreatment ink and the first ink.

[0132] By mixing the pretreatment ink containing the aggregating agent and the first ink in liquid form, the pretreatment ink and the first ink react uniformly, making it possible to prevent uneven aggregation.

[0133] The dynamic surface tension of the first ink at 25°C with a surface life of 30 ms is preferably within the range of 31 to 41 mN / m from the viewpoint of proper wetting and spreading of the second ink on the first ink coating. The dynamic surface tension of the first ink can be controlled by the types and contents of the pigment, resin particles, solvent, surfactant, water, and other components.

[0134] The ink set of the present invention is an ink set having at least a pretreatment ink containing a flocculant, a first ink containing a first coloring material, and a second ink containing a second coloring material. It is preferable to optimize each element taking into consideration at least the interactions between the pretreatment ink, the first ink, and the second ink. For example, one possible method is to determine the preferred characteristics of the first ink and then adjust the performance of the pretreatment ink and the second ink to match those characteristics. From this perspective, the desired properties of the first ink will be described below.

[0135] (2.1.2) Swelling ratio of the first ink coating It is preferable from the viewpoint of predicting that the second ink will properly wet and spread on the first ink coating film, which is a composite coating film formed by the pretreatment ink and the first ink, that the swelling ratio of the first ink coating film formed only by the first ink, without using a pretreatment ink, satisfies the relationship expressed by the following formula (3).

[0136] As mentioned above, the concept of the above "first ink coating film" includes not only the "first ink coating film" being solid, but also the "semi-solid" state, and the "semi-solid" state includes the liquid state. In the present invention, the term "liquid" refers to a state in which the drying rate of the pretreatment ink, first ink, and second ink is 30% or less. The drying rate will be described later in the description of the image forming method of the present invention.

[0137] -0.15≦Swelling ratio [mg / cm 2 ]≦0.15 (3) (Swelling ratio [mg / cm 2 ] = Water swelling mass [mg] / coating surface area [cm 2 ], where the minus sign indicates dissolution of ink.

[0138] Here, "water swelling mass [mg]" refers to the amount of change in mass of the first ink coating film before and after immersion in water for 5 minutes, after which the printed matter having the first ink coating film is dried, and excess water is wiped off, in the method for measuring the swelling ratio described below.

[0139] For ease of measurement, the swelling ratio of the composite coating film was calculated using a first ink coating film formed using only the first ink without using any pretreatment ink (hereinafter also referred to as the "first ink coating film," which is treated separately from the "composite coating film" of the pretreatment ink and the first ink formed by mixing the pretreatment ink and the first ink in liquid form on a recording medium).

[0140] It is predicted that the drawability of an image formed with the second ink (hereinafter also referred to as the drawability of the second ink) will change depending on the degree to which the second ink penetrates into the first ink coating formed using only the first ink without using a pretreatment ink.

[0141] It can be inferred that the drawing properties of the second ink can be improved by measuring the degree of penetration in terms of the swelling ratio with water and controlling it so as to satisfy the relationship expressed by the above formula (3).

[0142] In other words, the swelling ratio is an index showing the physical properties of the first ink coating film for wetting and spreading the second ink, and serves as a guideline for preventing the first ink coating film from absorbing too much of the second ink.

[0143] (2.1.3) Glass transition temperature of the first ink coating It is preferable from the viewpoint of predicting crack prevention properties after application of the second ink that the glass transition temperature of the first ink coating film formed using only the first ink without using a pretreatment ink is within the range of 35 to 100°C.

[0144] If the glass transition temperature of the first ink coating film formed using only the first ink without using a pretreatment ink is within the above range when it dries after the second ink is applied, the flow of the first ink coating film is suppressed, and it is possible to predict the resistance to cracking when the second ink is applied to the composite coating film.

[0145] In this specification, the glass transition temperature (Tg [°C]) of the first ink coating film can be determined by reading the glass transition temperature (Tg [°C]) from the 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).

[0146] (2.1.4) Water contact angle The wettability of a liquid to a solid surface (including a semi-solid state) is generally quantitatively expressed by the water contact angle of the liquid, and it is thought that the applicability (wettability) to the first ink coating film increases as the surface tension of the second ink is lower than the surface tension of the first ink coating film. Therefore, in order for the second ink according to the present invention to wet the first ink coating film, the surface tension of the first ink coating film must be greater than the surface tension of the second ink.

[0147] It is preferable from the viewpoint of predicting that the second ink will properly wet and spread on the first ink coating film, which is a composite coating film formed by the pretreatment ink and the first ink, that the water contact angle at 25°C 60 ms after water is dropped on the surface of the first ink coating film formed only by the first ink without using any pretreatment ink is within the range of 30 to 80°.

[0148] In the present invention, the term "water contact angle" quantifies the degree of wetting and is defined as the angle between the liquid surface and the solid surface (the angle inside the liquid) where the free surface of a stationary liquid comes into contact with a solid wall.

[0149] (2.2) Components of the first ink The first ink according to the present invention is an ink that is mixed in a liquid state with the pretreatment ink on the recording medium, and contains a first coloring material. The ink may also contain resin particles, a solvent, a surfactant, water, and other components.

[0150] (2.2.1) First colorant As the first coloring material according to the present invention, either a pigment or a dye may be used, but it is preferable to use a pigment.

[0151] (pigment) As the pigment used in the first colorant according to the present invention, it is preferable to use an anionic dispersed pigment, for example, a self-dispersed pigment having anionic groups on the surface, a pigment dispersed with an anionic polymer dispersant, or a pigment dispersed with its surface coated with an anionic resin. In particular, it is preferable to use a pigment dispersed with an anionic polymer dispersant, as this has excellent dispersibility and allows the pretreatment ink and the pigment to react appropriately to form pinning.

[0152] As the pigment, any conventionally known pigment can be used without any particular limitation, and for example, organic pigments such as insoluble pigments and lake pigments, and inorganic pigments such as titanium oxide can be preferably used.

[0153] [Insoluble pigment] The insoluble pigment is not particularly limited, but preferred examples include azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindolinone, isoindoline, azine, oxazine, thiazine, dioxazine, thiazole, phthalocyanine, and diketopyrrolopyrrole.

[0154] [Organic pigments] Specific examples of organic pigments that can be preferably used include the following pigments.

[0155] Examples of pigments for magenta or red include CI Pigment Red 2, CI Pigment Red 3, CI Pigment Red 5, CI Pigment Red 6, CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48:1, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, CI Pigment Red 202, CI Pigment Red 222, and CI Pigment Violet 19.

[0156] Examples of orange or yellow pigments include CI Pigment Orange 31, CI Pigment Orange 43, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 15, CI Pigment Yellow 15:3, CI Pigment Yellow 17, CI Pigment Yellow 74, CI Pigment Yellow 93, CI Pigment Yellow 128, CI Pigment Yellow 94, CI Pigment Yellow 138, and CI Pigment Yellow 155. In particular, CI Pigment Yellow 155 is preferred in terms of the balance between color tone and lightfastness.

[0157] Examples of pigments for green or cyan include CI Pigment Blue 15, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 16, CI Pigment Blue 60, and CI Pigment Green 7.

[0158] Examples of black pigments include CI Pigment Black 1, CI Pigment Black 6, and CI Pigment Black 7.

[0159] [Inorganic pigments] In the case of titanium oxide, for which it is generally difficult to ensure ink ejection stability and adhesiveness, the present invention is particularly advantageous in that bleeding is prevented from occurring and adhesiveness can be improved.

[0160] Titanium oxide has three crystalline forms: anatase, rutile, and brookite, but the most commonly used types can be broadly classified into anatase and rutile. Although not particularly limited, rutile type is preferred because it has a high refractive index and high hiding power. Specific examples include the TR series from Fuji Titanium Industry Co., Ltd., the JR series from Teika Corporation, and Typec from Ishihara Sangyo Kaisha, Ltd.

[0161] (pigment dispersant) The first ink according to the present invention preferably contains a pigment dispersant for dispersing the pigment. The pigment dispersant is not particularly limited, but is preferably a polymer dispersant having an anionic group, and one having a molecular weight in the range of 5,000 to 200,000 can be suitably used.

[0162] Examples of polymer dispersants 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, as well as salts thereof, polyoxyalkylenes, and polyoxyalkylene alkyl ethers.

[0163] The polymer dispersant preferably has an acryloyl group and is preferably neutralized with a neutralizing base before addition. The neutralizing base is not particularly limited, but is preferably an organic base such as ammonia, monoethanolamine, diethanolamine, triethanolamine, or morpholine.

[0164] In particular, when the pigment is titanium oxide, the titanium oxide is preferably dispersed in a polymer dispersant having an acryloyl group.

[0165] The amount of polymer dispersant added is preferably within a range of 10 to 100% by mass, more preferably within a range of 10 to 40% by mass, relative to the pigment.

[0166] The pigment is particularly preferably in the form of a so-called capsule pigment, in which the pigment is coated with the polymer dispersant.

[0167] As a method for coating a pigment with a polymer dispersant, various known methods can be used. Preferred examples include a phase inversion emulsification method, an acid precipitation method, and a method in which a pigment is dispersed in a polymerizable surfactant, a monomer is supplied thereto, and the pigment is coated while being polymerized.

[0168] A particularly preferred method is to dissolve a water-insoluble resin in an organic solvent such as methyl ethyl ketone, partially or completely neutralize the acidic groups in the resin with a base, add a pigment and ion-exchanged water, disperse the pigment, remove the organic solvent, and add water as needed to prepare the dispersion.

[0169] The average particle size of the pigment in the dispersed state in the first ink is preferably 50 nm or more and less than 200 nm. This improves the dispersion stability of the pigment and the storage stability of the first ink.

[0170] The particle size of the pigment can be measured using a commercially available particle size measuring device that uses a dynamic light scattering method, electrophoresis method, or the like, but measurement using dynamic light scattering is simple and enables measurement of the particle size range with high accuracy.

[0171] The pigment can be dispersed in a dispersing machine together with a dispersant and other additives required for various desired purposes.

[0172] As the dispersing machine, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, etc. can be used. Among these, dispersing the pigment using a sand mill is preferred because it results in a sharp particle size distribution. The material of the beads used in the sand mill dispersion is not particularly limited, but from the viewpoint of preventing the generation of bead fragments and contamination with ionic components, zirconia or zircon is preferred. Furthermore, the bead diameter is preferably within the range of 0.3 to 3 mm.

[0173] The content of the pigment in the first ink is not particularly limited, but for titanium oxide, it is preferably in the range of 7 to 18 mass %, and for organic pigments, it is preferably in the range of 0.5 to 7 mass %.

[0174] [Acid value of dispersant for colorant] In the image forming method of the present invention, it is preferable, from the viewpoint of appropriate aggregation properties of the first colorant and the second colorant, that the acid value of the dispersant for the first colorant and the acid value of the dispersant for the second colorant are within a range of 50 to 200 [mgKOH / g], and that the sum of the amount of reactive groups per unit area in the aggregation reaction [mol] contained in the pretreatment ink and the amount of the first colorant and the second colorant [g] satisfy the relationship of the following formula (4):

[0175] 500<(sum of the amount [g] of the first colorant and the second colorant / sum of the amount [mol] of reactive groups contained in the first colorant and the second colorant per unit area of ​​the recording medium in the aggregation reaction contained in the pretreatment ink)<20,000 (4)

[0176] The acid value of a dispersant for a colorant is the number of mg of potassium hydroxide [mgKOH / g] required to neutralize the carboxyl groups present in 1 g of the dispersant for the colorant. Specifically, it is determined by the following method in accordance with JIS K0070-1992.

[0177] (1) Preparation of reagents (a) Phenolphthalein solution 1.0 g of phenolphthalein was dissolved in 90 mL of ethyl alcohol (95 vol%), and ion-exchanged water was added to make the total volume 100 mL to obtain a phenolphthalein solution.

[0178] (b) Potassium hydroxide solution Dissolve 7 g of special-grade potassium hydroxide in 5 mL of ion-exchanged water, and add ethyl alcohol (95 vol%) to bring the total volume to 1 L. Place in an alkali-resistant container to avoid contact with carbon dioxide, etc., leave for 3 days, then filter to obtain potassium hydroxide solution. The resulting potassium hydroxide solution is stored in an alkali-resistant container.

[0179] (c) Factor of potassium hydroxide solution The factor of the potassium hydroxide solution is determined by placing 25 mL of 0.1 mol / L hydrochloric acid in an Erlenmeyer flask, adding a few drops of the phenolphthalein solution, and titrating with the potassium hydroxide solution to determine the amount of potassium hydroxide solution required for neutralization.

[0180] (d) Hydrochloric acid solution The 0.1 [mol / L] hydrochloric acid used is prepared in accordance with JIS K8001-1998.

[0181] (2) Operation (a) Main test 2.0 g of toner is accurately weighed into a 200 mL Erlenmeyer flask, and 100 mL of a mixed solution of toluene:ethanol (2:1) is added and dissolved over 5 hours. Next, several drops of the phenolphthalein solution were added as an indicator, and the potassium hydroxide was The solution was titrated with HCl. The end point of the titration is when the indicator remains a pale red color for approximately 30 seconds.

[0182] (b) Blank test A similar titration is carried out, except that no sample is used (i.e., only the toluene:ethanol (2:1) mixture is used).

[0183] (3) Substitute the obtained results into the following formula to calculate the acid value. A = ([CD] × f × 5.611) / S where: A: Acid value [mgKOH / 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]

[0184] (2.2.2) Resin fine particles The resin particles (hereinafter simply referred to as "resin") contained in the first ink according to the present invention are preferably water-insoluble resin particles.

[0185] The glass transition temperature (Tg [°C]) of the resin particles is preferably within the range of 40 to 90°C.

[0186] In the present invention, in addition to the glass transition temperature of the resin microparticles, it is preferable that the glass transition temperature of the first ink coating film formed using only the first ink without using a pretreatment liquid is within the range of 35 to 100°C, from the viewpoint of preventing cracking after application of the second ink.

[0187] The glass transition temperature can be determined by reading the glass transition temperature (Tg [°C]) from the 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).

[0188] The water-insoluble resin preferably used in the present invention is a water-insoluble resin that can accept ink and exhibits solubility or affinity for the ink.

[0189] The "water-insoluble resin microparticles" used in the present invention are those which are inherently water-insoluble but have a form in which the resin disperses in an aqueous medium as microparticles, and are water-insoluble resins which are dispersed in water by forced emulsification using an emulsifier or the like, or water-insoluble resins which have hydrophilic functional groups introduced into their molecules and which can self-emulsify to form a stable aqueous dispersion without the use of an emulsifier or dispersion stabilizer.

[0190] These resins are usually used in the form of an emulsion dispersion in water or a water / alcohol mixed solvent.

[0191] 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 of dissolution is the amount of dissolution when the salt-forming group of the resin is 100% neutralized with acetic acid or sodium hydroxide depending on the type of resin.

[0192] The resin having a glass transition temperature in the range of 40 to 90°C is preferably any one of acrylic resin, urethane resin, polyester resin, or a composite resin of urethane resin and acrylic resin, and particularly preferably acrylic resin, urethane resin, polyester resin, or a composite resin of urethane resin and acrylic resin, and the resin particles of these resins preferably have an average particle size of 200 nm or less. In particular, the average particle size is preferably within the range of 100 to 150 nm.

[0193] The polyester resin, urethane resin, acrylic resin or composite resin particles of urethane resin and acrylic resin are preferably anionic or nonionic.

[0194] In particular, it is preferable that the resin microparticles contained in the first ink contain an acid structure, which allows them to be dispersed in water even with a small amount of surfactant added, thereby improving the water resistance of the first ink coating film. This is called a self-emulsifying type, and means that the resin can be dispersed and stabilized in water only by molecular ionicity without using a surfactant.

[0195] Examples of the acid structure include acid groups such as a carboxy group (-COOH) and a sulfonic acid group (-SO3H). The acid structure may be present on a side chain or at the end of the resin. The first ink according to the present invention preferably contains a water-dispersible polyester resin having a sulfonic acid group. This provides high adhesion to the substrate.

[0196] It is preferred that the acid structures are partly or entirely neutralized. Neutralizing the acid structure can improve the water dispersibility of the resin.

[0197] Examples of the neutralizing agent for neutralizing the acid structure include organic amines, and it is preferable to use organic amines such as trimethylamine, triethylamine, tripropylamine, tributylamine, N-methyldiethanolamine, and triethanolamine.

[0198] The first ink according to the present invention preferably contains 3 to 15% by mass of fine resin particles that have a coagulation property of 0.2 or less with a 0.15% by mass aqueous solution of calcium acetate.

[0199] By using such resin particles with low aggregating properties, high wettability to the substrate is ensured while high ejection stability is obtained, resulting in higher image quality and excellent adhesion to the substrate.

[0200] In the present invention, the value of "cohesion" is a value calculated by the following formula after measuring the remaining amount according to the following procedure.

[0201] (i) 5 g of a resin fine particle aqueous solution (solid content 10% by mass) containing resin fine particles is mixed with 5 g of a 0.3% by mass aqueous solution of calcium acetate monohydrate. (ii) The mixed solution is centrifuged. (iii) Collect 2 g of the supernatant separated by centrifugation. (iV) Measure the mass of the solids (remaining amount [g]) after drying 2 g of the collected supernatant at 150°C for 30 minutes. (V) Calculate the cohesiveness value using the following formula.

[0202] Formula: Coagulation = 1 - (mass of solids [g] / (mass of collected supernatant [g] × 5 [%])

[0203] Examples of resin particles having an agglomeration index of 0.2 or less include Vylonal MD2000 manufactured by Toyobo Co., Ltd., Movinyl 6969D manufactured by Japan Coating Resins Co., Ltd., and Evaphanol HA-560 manufactured by Nicca Chemical Co., Ltd.

[0204] Each resin will be described below. (polyester resin) The polyester resin having a polyester skeleton used as the water-insoluble resin particles can be obtained using a polyhydric alcohol component and a polycarboxylic acid component such as a polycarboxylic acid, a polycarboxylic acid anhydride, or a polycarboxylic acid ester.

[0205] The polyhydric alcohol component includes 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 (diols), and alkylene ether glycols having 6 to 36 carbon atoms (diols). Examples of suitable alkylene oxides include alicyclic diols (1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.), adducts of the above-mentioned alicyclic diols with alkylene oxides (ethylene oxide (hereinafter abbreviated as EO), propylene oxide (hereinafter abbreviated as PO), butylene oxide (hereinafter abbreviated as BO)) having 2 to 4 carbon atoms (number of moles added: 1 to 30), and adducts of bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.) with alkylene oxides (EO, PO, BO, etc.) having 2 to 4 carbon atoms (number of moles added: 2 to 30). These may be used alone or in combination of two or more.

[0206] Examples of the polyvalent carboxylic acid component include dicarboxylic acids (dicarboxylic acids), specifically alkanedicarboxylic acids having 4 to 36 carbon atoms (succinic acid, apidic acid, sebacic acid, etc.), alkenylsuccinic acids (dodecenylsuccinic acid, etc.), alicyclic dicarboxylic acids having 4 to 36 carbon atoms (dimer acids (dimerized linoleic acid), etc.), alkenedicarboxylic 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.

[0207] The polyester resin is preferably a polyester resin having an anionic group in the molecule, and more preferably a polyester resin containing a sulfonic acid group.

[0208] As a known synthesis method for obtaining a polyester containing a sulfonic acid group, for example, it can be obtained by a method such as a polycondensation reaction between a dicarboxylic acid having a sulfonic acid group and a diol, or a method such as a polycondensation reaction between a dicarboxylic acid and a diol having a sulfonate salt.

[0209] Examples of dicarboxylic acid components having a sulfonic acid group include 2-sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfonaphthaleneisophthalic-2,7-dicarboxylic acid, 5-(4-sulfophenoxy)isophthalic acid, and alkali metal salts thereof.

[0210] 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.

[0211] The number average molecular weight of the polyester resin is preferably within a range of 1,000 to 50,000, and more preferably within a range of 2,000 to 20,000.

[0212] As the polyester resin, commercially available products may be used. Examples of commercially available water-dispersible polyester resins having sulfonic acid groups include Vylonal MD-1100, MD-1200, MD-1245, MD-1480, MD-1500, and MD-2000 manufactured by Toyobo Co., Ltd.; Plascoat Z-221, Z-446, Z-561, Z-880, and Z-3310 manufactured by Goo Chemical Co., Ltd.; and PESRESIN A-520, A-613D, A-615GE, A-640, A-645GH, A-647GEX, A-110F, and A-160P manufactured by Takamatsu Oil & Fat Co., Ltd.

[0213] Among the above, resins having a glass transition temperature of 40 to 90°C are particularly preferred, and examples thereof include Vylonal MD-1100, MD-1200, MD-1245, MD-1500, and MD-2000 manufactured by Toyobo Co., Ltd., Plascoat Z-221, Z-446, and Z-561 manufactured by Goo Chemical Co., Ltd., and PES Resin A-520, A-613D, A-615GE, A-640, A-645GH, and A-647GEX manufactured by Takamatsu Oil & Fat Co., Ltd. These may be used alone or in combination of two or more.

[0214] (urethane resin) The urethane resin used as the water-insoluble resin particles according to the present invention may be one having a hydrophilic group.

[0215] The urethane resin is preferably an aqueous dispersion of a self-emulsifying urethane having water-soluble functional groups, i.e., hydrophilic groups, dispersed in its molecules, or an aqueous dispersion of a forced-emulsifying urethane emulsified under strong mechanical shearing force in combination with a surfactant. The urethane resin in the aqueous dispersion can be obtained by reacting a polyol with an organic polyisocyanate and a hydrophilic group-containing compound.

[0216] Examples of polyols that can be used to prepare the aqueous dispersion of the urethane resin include polyester polyols, polyether polyols, polycarbonate polyols, and polyolefin polyols.

[0217] Examples of polyester polyols include low molecular weight polyols such as 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; and condensates thereof with polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrofuran acid, endomethinetetrahydrofuran acid, and hexahydrophthalic acid.

[0218] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene polytetramethylene glycol, polypropylene polytetramethylene glycol, and polytetramethylene glycol.

[0219] Examples of polycarbonate polyols include those obtainable by reacting a carbonic acid derivative such as diphenyl carbonate, dimethyl carbonate or phosgene with a diol.

[0220] Examples of the diol 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.

[0221] Examples of organic polyisocyanates that can be used to prepare the aqueous dispersion of the urethane resin 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.

[0222] Examples of hydrophilic group-containing compounds that can be used to prepare the aqueous dispersion of the urethane resin 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, and derivatives thereof such as sodium salts, potassium salts, and amine salts; and sulfonic acid-containing compounds such as taurine (i.e., aminoethylsulfonic acid) and ethoxypolyethylene glycol sulfonic acid, and derivatives thereof such as sodium salts, potassium salts, and amine salts.

[0223] The urethane resin can be obtained by a known method. For example, the urethane prepolymer can be obtained by mixing the above-mentioned polyol, organic polyisocyanate, and hydrophilic group-containing compound and reacting them at a temperature in the range of 30 to 130° C. for 30 minutes to 50 hours.

[0224] The urethane prepolymer is polymerized by being extended with a chain extender to become a urethane resin having a hydrophilic group.

[0225] The chain extender is preferably water and / or an amine compound. By using water or an amine compound as a chain extender, it is possible to react with free isocyanate in a short time and efficiently extend the isocyanate-terminated prepolymer.

[0226] Examples of the amine compound as a chain extender 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.

[0227] The amine compound may contain, together with the polyamine, a monovalent amine such as dibutylamine or methyl ethyl ketoxime as a reaction terminator to the extent that the polymerization is not significantly inhibited.

[0228] In the synthesis of the urethane prepolymer, a solvent that is inert to isocyanate and capable of dissolving the urethane prepolymer may be used.

[0229] Examples of these solvents include 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 step are preferably finally removed.

[0230] In addition, in the synthesis of the urethane prepolymer, a catalyst such as an amine catalyst (e.g., triethylamine, N-ethylmorpholine, triethyldiamine, etc.), a tin-based catalyst (e.g., dibutyltin dilaurate, dioctyltin dilaurate, tin octoate, etc.), or a titanium-based catalyst (e.g., tetrabutyl titanate, etc.) may be added to promote the reaction.

[0231] The number average molecular weight of the urethane resin is preferably increased as much as possible by introducing a branched structure or an internal crosslinked structure, and the number average molecular weight is preferably 50,000 to 10,000,000.

[0232] By keeping the molecular weight within the above range, the urethane resin becomes less soluble in solvents, and a coating film having excellent weather resistance and water resistance can be obtained.

[0233] The number average molecular weight (Mn) is a value measured by gel permeation chromatography (GPC), and can be determined from a calibration curve prepared using a polystyrene standard sample, for example, using a Shimadzu Corporation "RID-6A" (column: Tosoh Corporation "TSK-GEL", solvent: tetrahydrofuran (THF), column temperature: 40°C).

[0234] The urethane resin may be a commercially available product. Examples of commercially available urethane resins with glass transition temperatures in the range of 40 to 90°C include Neorez R-967, R-600, and R-9671 manufactured by Kusumoto Chemicals Co., Ltd., Evaphanol HA-560 manufactured by Nicca Chemical Co., Ltd., and SF870 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0235] (acrylic resin) The acrylic resin used as the water-insoluble resin particles can be obtained by using a copolymer with an acrylic acid ester component, a methacrylic acid ester component, or a styrene component.

[0236] Examples of the acrylic acid ester component and the methacrylic 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, and 2-hydroxyethyl (meth)acrylate. -hydroxybutyl, 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.

[0237] Examples of the styrene component include styrene, 4-methylstyrene, 4-hydroxystyrene, 4-acetoxystyrene, 4-acetylstyrene, and styrene sulfonic acid. These components may be used alone or in combination of two or more.

[0238] The number average molecular weight (Mn) of the acrylic resin is preferably within a range of 1,000 to 50,000, and more preferably within a range of 2,000 to 20,000.

[0239] When the number average molecular weight (Mn) of the acrylic resin is 1,000 or more, the cohesive force of the coating film is strong and the adhesion is improved, and when it is 50,000 or less, the solubility in organic solvents is good and the particle size of the emulsion dispersion is promoted to be miniaturized.

[0240] The number average molecular weight (Mn) is a value measured by gel permeation chromatography (GPC), and can be determined from a calibration curve prepared using a polystyrene standard sample, for example, using a Shimadzu Corporation "RID-6A" (column: Tosoh Corporation "TSK-GEL", solvent: tetrahydrofuran (THF), column temperature: 40°C).

[0241] Moreover, commercially available acrylic resins may be used. 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 6899D, 6969D, and 6800 manufactured by Japan Coating Resins Co., Ltd., and TOCRYL W-7146, W-7147, W-7148, W-7149, and W-7150 manufactured by Toyochem Co., Ltd.

[0242] (Composite resin fine particles) The composite resin particles that can be contained in the first ink are preferably composite resin particles in which an acrylic resin is emulsified in a urethane resin. That is, it is preferable that the composite resin particles have an inner layer made of an acrylic resin and a surface layer made of a urethane resin.

[0243] Here, the urethane resin is present 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.

[0244] By emulsifying the acrylic resin with the urethane resin in this way to form composite resin microparticles, the physical properties of the image (coating film) can be improved, and the storage stability of the composite resin microparticles can also be improved, compared to when the acrylic resin and the urethane resin are emulsified separately and mixed.

[0245] In the composite resin particles obtained by emulsifying the acrylic resin in the urethane resin, the mass ratio (U / A) of the urethane resin (U) to the acrylic resin (A) is preferably 40 / 60 to 95 / 5.

[0246] When the content of the urethane resin (U) is within the above range, compatibility with the dispersant is improved, and solvent resistance is also improved.

[0247] Furthermore, when the content of the acrylic resin (A) is within the above range, the adhesiveness to the acrylic film is excellent. In the above-mentioned proportions, the mass ratio (U / A) of the urethane resin (U) to the acrylic resin (A) is preferably within the range of 40 / 60 to 80 / 20.

[0248] The total resin concentration of the acrylic resin and urethane resin in the composite resin particles 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. When the resin concentration is within the above range, the fixation of the first ink onto the recording medium is good.

[0249] 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. Here, by adding an emulsifier, the storage stability of the composite resin particles can be improved.

[0250] As the emulsifier, anionic surfactants and nonionic surfactants can be used.

[0251] The average particle size of the composite resin particles 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.

[0252] The average particle size can be measured using a commercially available particle size measuring device that uses dynamic light scattering, electrophoresis, or the like, but measurement using dynamic light scattering is simple and allows the particle size range to be measured with high accuracy.

[0253] By using composite resin particles in which an acrylic resin is emulsified in a urethane resin, it is possible to improve the fixability of an image (coating film) to an absorbent or non-absorbent substrate.

[0254] (2.2.3) Solvent Examples of solvents that can be contained in the first ink according to the present invention include the same solvents as those in the pretreatment ink.

[0255] (2.2.4) Surfactants It is preferable that the pretreatment ink and the first ink contain one or more surfactants, and that the HLB value of at least one surfactant contained in the first ink is greater than the HLB value of at least one surfactant contained in the pretreatment ink, because the first ink has a relatively high hydrophilicity, i.e., a low lipophilicity, which allows the first ink to have a high wettability and the second ink to adequately wet and spread on the first ink coating.

[0256] Furthermore, it is sufficient that there is one set of surfactants that satisfy the following relationship, and surfactants that do not satisfy this relationship may also exist. (HLB value of surfactant contained in pretreatment ink < HLB value of surfactant contained in first ink)

[0257] From the viewpoint of the wetting property and pinning property of the first ink, it is preferable that the first ink contains two or more types of surfactants, and that the absolute value of the difference in HLB value between any two types of surfactants selected from the two or more types of surfactants is within a range of 1 to 9. This also allows the second ink to properly wet and spread on the first ink coating film.

[0258] When the absolute value of the difference in HLB values ​​of the surfactants contained in the first ink is within the range of 6 to 16 as described below, the compatibility between the surfactants is relatively better when the absolute value of the difference in HLB values ​​is smaller, such as when the absolute value of the difference in HLB values ​​is within the range of 1 to 9, and therefore the pinning property of the ink itself is improved.

[0259] On the other hand, as the difference in HLB values ​​between the surfactants contained in the first ink increases, the compatibility between the surfactants decreases when the absolute value of the difference in HLB values ​​is within a range of 6 to 16, compared to when the absolute value of the difference in HLB values ​​is within a range of 1 to 9. This is preferable from the viewpoint that a hydrophobic surfactant with a small HLB value improves the wettability of the first ink, and a hydrophilic surfactant with a high HLB value allows the second ink to properly wet and spread on the first ink coating. This also improves the uniformity of the image density of the second ink.

[0260] That is, as compared with the case where the absolute value of the difference in HLB values ​​is within the range of 1 to 9, when the absolute value of the difference in HLB values ​​is within the range of 6 to 16, the compatibility between surfactants relatively decreases as the absolute value of the difference in HLB values ​​increases, but hydrophilicity and hydrophobicity are efficiently expressed, thereby improving the wettability of the first ink itself and the wettability of the second ink on the first ink coating.

[0261] Although it differs depending on the compounds that constitute the various inks, the absolute value of the difference in HLB values ​​of the surfactants contained in the first ink is preferably within the range of 1 to 9 when emphasis is placed on ink stability, and is preferably within the range of 6 to 16 when emphasis is placed on the wettability of the first ink, etc. Of the two ranges above, the intermediate range of 6 to 9 is preferred from the viewpoint of both the pinning property and the wettability of the ink.

[0262] Furthermore, as long as the absolute value of the difference in HLB value between any two surfactants selected from the two or more surfactants is within the range of 1 to 9 or within the range of 6 to 16, surfactants that do not satisfy the above relationship may exist.

[0263] By using a surfactant with a low HLB value for wetting and spreading the first ink in combination with a surfactant with a high HLB value for wetting and spreading the second ink, the second ink can be properly wetted and spread on the first ink coating film, which is a composite coating film formed by the pretreatment ink and the first ink.

[0264] The surfactant that can be contained in the first ink according to the present invention may be the same as that used in the pretreatment ink described above. However, as described above, for example, the surfactant that can be contained in the first ink may be one that acts as an emulsifier together with the urethane resin when the acrylic resin is emulsified with the urethane resin. The addition of an emulsifier can improve the storage stability of the composite resin particles.

[0265] As the emulsifier, it is preferable to use either an anionic surfactant or a nonionic surfactant, and it is more preferable to use both.

[0266] Here, the total amount of the anionic surfactant and the nonionic surfactant blended is preferably 1.0 to 20.0 parts by mass per 100 parts by mass of the total resin. Furthermore, by setting the total amount of the anionic surfactant and the nonionic surfactant to 20.0 parts by mass or less, it is possible to improve water resistance and solvent resistance.

[0267] The blending mass ratio (X / Y) of the anionic surfactant (X) to the nonionic surfactant (Y) is preferably 100 / 0 to 50 / 50. By adjusting the blending amount of the anionic surfactant to fall within the above range, emulsifiability and storage stability can be further improved.

[0268] 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, and phosphate esters. Of these, sulfosuccinates and alpha-olefin sulfonates are preferred. Examples of the salts include, but are not limited to, metal salts such as sodium salts, potassium salts, and magnesium salts, and triethanolamine salts.

[0269] Examples of nonionic surfactants that can be used for emulsification include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylamine ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, and sucrose fatty acid esters.

[0270] Among these, polyoxyethylene alkyl ethers and polyoxyethylene alkyl phenyl ethers are preferred.

[0271] (2.2.5) Water The water that can be used in the first ink according to the present invention is not particularly limited, and may be ion-exchanged water, distilled water, or pure water.

[0272] (2.2.6) Other ingredients As with the pretreatment ink described above, the first ink according to the present invention may contain other components such as crosslinking agents, antifungal agents, and bactericides, as appropriate, provided that the effects of the present invention are not impaired.

[0273] 3. Second ink (3.1) Physical properties of the second ink (3.1.1) Dynamic surface tension of the second ink The second ink in the ink set of the present invention contains a second coloring material. The dynamic surface tension relationship with the other inks (pretreatment ink and first ink) is also characterized by satisfying the above formulas (1) and (2).

[0274] The second ink is applied onto the first ink coating film after the first ink and the pretreatment ink are mixed in liquid form and then dried to form a first ink coating film, which is a composite coating film of the pretreatment ink and the first ink.

[0275] From the viewpoint of suppressing aggregation unevenness, it is preferable that the second ink is a liquid ink that is applied onto the first ink coating film, which is a composite coating film.

[0276] By applying the second ink in a liquid state onto the first ink coating film, which is a composite coating film, the pretreatment ink and the second ink in the first ink coating film react uniformly, preventing uneven aggregation.

[0277] The dynamic surface tension of the second ink at 25° C. during a surface life of 30 ms is preferably within the range of 25 to 40 mN / m, from the viewpoint of proper wetting and spreading of the second ink on the first ink coating. The dynamic surface tension of the second ink can be controlled by the types and contents of the pigment, resin particles, solvent, surfactant, water, and other components, which will be described later.

[0278] (3.1.2) Other From the viewpoint of predicting that the second ink will properly wet and spread on the first ink coating film, which is a composite coating film, it is preferable that the swelling ratio of the first ink coating film formed using only the first ink without using a pretreatment liquid satisfies the relationship expressed by formula (3), and it is predicted that the drawability of the second ink applied to the first ink coating film, which is a composite coating film, will change depending on the degree to which the second ink penetrates into the first ink coating film formed using only the first ink without using a pretreatment liquid.

[0279] From the viewpoint of predicting crack prevention properties after application of the second ink, it is preferable that the glass transition temperature of the first ink coating film formed using only the first ink without using a pretreatment liquid is within the range of 35 to 100°C. If the glass transition temperature is within the above range when the second ink is dried after application, the flow of the first ink coating film formed using only the first ink without using a pretreatment liquid is suppressed, and it is predicted that cracking can be prevented when the second ink is applied onto the first ink coating film, which is a composite coating film.

[0280] In order for the second ink to wet the first ink coating film, the surface tension of the first ink coating film must be greater than the surface tension of the second ink, and it is preferable from the viewpoint of proper wetting and spreading of the second ink on the first ink coating film that the water contact angle at 25°C 60 ms after water is dropped onto the surface of the first ink coating film is within the range of 30 to 80°.

[0281] (3.2) Components of the second ink The second ink according to the present invention is an ink that is applied onto the first ink coating film, which is a composite coating film of the pretreatment ink and the first ink, after the first ink coating film has been formed, and contains a second colorant. Furthermore, the ink may contain resin particles, a solvent, a surfactant, water, and other components.

[0282] The second coloring material, resin particles, solvent, surfactant, water, and other components can be the same as those in the first ink.

[0283] II [Image formation method] The image forming method of the present invention is an image forming method suitable for using the ink set of the present invention, and is characterized by comprising the steps of: applying the pretreatment ink onto a recording medium; applying the first ink so that the pretreatment ink and the first ink are mixed in liquid form on the recording medium; drying the pretreatment ink and the first ink applied onto the recording medium to form a first ink coating film that is a composite coating film; and applying the second ink onto the first ink coating film.

[0284] Alternatively, a method including the steps of applying the pretreatment ink onto the first ink coating film and applying the second ink onto the first ink coating film so that the pretreatment ink and the second ink are mixed in liquid form is also preferable from the viewpoint of suppressing aggregation unevenness and from the viewpoint of the pinning properties of the second ink.

[0285] Typically, the pretreatment ink is responsible for pinning not only the first ink but also the second ink, but by adopting a method that includes a step of applying the pretreatment ink onto the first ink coating, and a step of applying the second ink so that the pretreatment ink and the second ink are mixed in liquid form on the first ink coating, the amount of pretreatment ink used in the step of applying the pretreatment ink onto the recording medium can be reduced, improving the uniformity of the image density of the first ink and the pinning ability of the second ink.

[0286] In the image forming method, it is preferable, from the viewpoint of appropriate aggregation properties of the first colorant and the second colorant, that the acid value of the dispersant for the first colorant and the acid value of the dispersant for the second colorant are within a range of 50 to 200 [mgKOH / g], and that the sum of the amount of reactive groups per unit area in the aggregation reaction [mol] contained in the pretreatment ink and the amount of the first colorant and the second colorant [g] satisfy the relationship of the following formula (4):

[0287] 500<(sum of the amount [g] of the first colorant and the second colorant / sum of the amount [mol] of reactive groups contained in the first colorant and the second colorant per unit area of ​​the recording medium in the aggregation reaction contained in the pretreatment ink)<20,000 (4)

[0288] (Recording medium) The pretreatment ink is applied onto a recording medium by, for example, an inkjet method. In this case, the applicable recording medium is not particularly limited, and may be an absorbent substrate made of an absorbent material or a non-absorbent substrate made of a non-absorbent material, but from the viewpoint of realizing the effects of the present invention, a non-absorbent substrate is preferable.

[0289] In the present invention, "absorbent" refers to the ability to absorb water, and "non-absorbent" refers to the ability not to absorb water.

[0290] As the non-absorbent substrate, a known plastic film can be used.

[0291] Specific examples of the 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.

[0292] In order to impart gas barrier properties, moisture resistance, aroma retention, etc., films coated on one or both sides with polyvinylidene chloride or films vapor-deposited with metal oxides can also be preferably used. The non-absorbent film may be either an unstretched film or a stretched film.

[0293] In the case of a plastic film, the thickness of the substrate is preferably within a range of 10 to 120 μm, more preferably 12 to 60 μm.

[0294] In addition, 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 as non-absorbent substrates, and can be suitably used as packaging materials for canned foods, for example, with a thermosetting resin coating layer.

[0295] Packaging materials for canned foods typically use epoxy-phenolic paints or polyester laminating agents on the food side, and polyester or acrylic thermosetting paints on the outside, to block out air, moisture, and light and seal the food inside.

[0296] (1) A step of applying a pretreatment ink onto a recording medium The pretreatment ink according to the present invention contains an aggregating agent, and serves to fix the first ink containing the first coloring material on the recording medium. The method for applying the pretreatment ink onto the recording medium is not particularly limited, but preferred examples include roller coating, curtain coating, spray coating, and inkjet methods.

[0297] Among these, the roller coating method is preferred from the viewpoint that a roller coating machine or the like can be connected to an inkjet device and can efficiently apply the composition even when the viscosity is relatively high.

[0298] In addition, using an inkjet method as the process for applying the pretreatment ink onto the recording medium is preferable because it eliminates the need to apply a coagulant to areas where the pretreatment ink is not applied, and therefore the coagulant that does not react with the ink is not liberated and causes the ink to become cloudy.

[0299] In this case, as will be described later, when the substrate used is a metal substrate or the like, it is also preferable to place the metal substrate on a conveyor belt and apply the pretreatment ink layer while conveying the belt, or to use a flatbed type printer in which the substrate is fixed to form the pretreatment ink layer.

[0300] The ink-jet method is not particularly limited, and a printer equipped with an ink-jet head loaded with ink can be used. Specifically, the first ink is ejected as droplets from the nozzles of the inkjet head based on a digital signal, and these droplets land on a pre-treatment ink layer on a recording medium, thereby performing printing.

[0301] The ink-jet head may be either an on-demand type or a continuous type. Examples of on-demand inkjet heads include electro-mechanical conversion heads, including single-cavity, double-cavity, bender, piston, shear-mode, and shared-wall types, as well as electro-thermal conversion heads, including thermal inkjet and bubble jet ("Bubble Jet" is a registered trademark of Canon Inc.) types.

[0302] Among the above inkjet heads, inkjet heads using a piezoelectric element as the electromechanical conversion element used in the electromechanical conversion system (also called piezo-type inkjet heads) are preferred.

[0303] The inkjet printer may be of either a scan type or a single pass type, but in the case of a single pass type, it is preferable to use a line head type inkjet head.

[0304] A line head type inkjet head is an inkjet head whose length is equal to or greater than the width of the printing range. As the line head type inkjet head, a single head having a width equal to or greater than the width of the printing range may be used, or a plurality of heads may be combined to form a configuration having a width equal to or greater than the width of the printing range.

[0305] Furthermore, a plurality of heads may be arranged in parallel so that the nozzles are arranged in a staggered pattern, thereby increasing the overall resolution of the heads.

[0306] The transport speed of the recording medium, which is the substrate, can be set within the range of, for example, 1 to 120 m / min. The faster the transport speed, the faster the image formation speed.

[0307] (2) applying the first ink so that the pretreatment ink and the first ink are mixed in liquid form on the recording medium; When the pre-treated ink containing the aggregating agent and the first ink containing the first coloring material are mixed, a thickening reaction occurs. When the pretreatment ink and the first ink are mixed in a liquid state, the first ink diffuses, improving the wettability of the first ink.

[0308] If the pretreatment ink and the first ink are mixed first and then applied to the recording medium, rather than being applied directly to the recording medium, which is the base material, the droplets formed by mixing the two inks will thicken before landing on the recording medium, which will change the droplet trajectory and cause the droplets to land misaligned. Furthermore, if the viscosity of both inks increases before they land on the recording medium, the adhesion of both inks to the recording medium deteriorates.

[0309] After the step of applying the pretreatment ink onto the recording medium, the pretreatment ink applied onto the recording medium may be heated and dried. However, since the pretreatment ink and the first ink need to be mixed in liquid form, the first ink must be applied when the drying rate of the pretreatment ink is 30% or less during the heating and drying step. If the first ink is applied when the drying rate of the pretreatment ink is greater than 30%, the pretreatment ink and the first ink may be in a liquid state and may not mix.

[0310] Hereinafter, in the present invention, the term "liquid" refers to a state in which the drying rate of the pretreatment ink, the first ink, and the second ink is 30% or less.

[0311] It is preferable that the first ink is applied within 10 seconds after the pretreatment ink is applied. In particular, it is preferable that the drying rate of the pretreatment ink is in the range of 1 to 10%, and that the first ink is applied within 0.1 to 5 seconds after the application of the pretreatment ink.

[0312] The "drying rate of the pretreatment ink" is defined by the following formula.

[0313] (Drying rate of pretreatment ink) = 1 - (mass of pretreatment ink after drying [g]) / (mass of pretreatment ink before drying [g])

[0314] By applying the first ink when the drying rate of the pretreatment ink is 30% or less, the first ink spreads and the wettability improves.

[0315] Furthermore, by applying the first ink within 10 seconds after applying the pretreatment ink to the recording medium, it is possible to suppress the penetration of the pretreatment ink into an absorbent substrate and the repelling of the pretreatment ink on a non-absorbent substrate, thereby achieving higher image quality.

[0316] In order to keep the drying rate of the pretreatment ink at 30% or less, the time between the application of the pretreatment ink and the application of the first ink can be adjusted, or the temperature of the recording medium can be appropriately adjusted.

[0317] Furthermore, when applying the first ink, it is preferable to adjust the amount of the first ink droplets so that the amount of the first ink applied (also referred to as the "application amount") per unit area of ​​the recording medium is within a range of 2 to 25 times the amount of the pretreatment ink applied, in order to achieve higher image quality, and a more preferable range for the application amount is 3 to 10 times.

[0318] (3) A step of drying the pretreatment ink and the first ink applied to the recording medium to form a composite coating film of the first ink. In the step of drying the pretreatment ink and the first ink applied to the recording medium to form a first ink coating film, the pretreatment ink and the first ink, which are mixed in liquid form on the recording medium, may be heated and dried to form the first ink coating film.

[0319] The heating temperature is preferably within a range of 60 to 200° C., and the heating time is adjusted appropriately depending on the type of recording medium, the amount of pretreatment ink applied, and the amount of first ink applied.

[0320] By heating the area to which the pretreatment ink and the first ink have been applied, the solvent components of the pretreatment ink and the first ink are removed, and at the same time, in the case of a metal substrate in particular, the polyvalent metal salt is dried and thermally decomposed at a temperature equal to or higher than the thermal decomposition temperature. Furthermore, the image has good abrasion resistance and adhesion to the substrate.

[0321] The heat drying may be carried out using a non-contact heating type drying device such as a drying oven or a hot air blower, or may be carried out using a contact heating type drying device such as a hot plate or a heat roller.

[0322] The drying temperature can be obtained by measuring any one of the following throughout the entire drying period of the pretreatment ink and the first ink: (a) when a non-contact heating drying device such as a drying oven or a hot air blower is used, the ambient temperature such as the temperature inside the oven or the hot air temperature; (b) when a contact heating drying device such as a hot plate or a heated roller is used, the temperature of the contact heating part; or (c) the surface temperature of the surface to be dried. It is more preferable to measure the surface temperature of (c) the surface to be dried.

[0323] The thickness of the first ink coating film obtained as described above is preferably within a range of 0.3 to 3.0 μm, and more preferably within a range of 0.3 to 2.0 μm. When the thickness of the first ink coating film is 0.3 μm or more, the adhesion and abrasion resistance of the image can be easily improved. Furthermore, when the thickness of the first ink coating film is 3.0 μm or less, the deformation stress applied to the ink layer can be reduced, so that the adhesion of the image is less likely to be impaired.

[0324] (4) A step of applying the second ink onto the first ink coating film, which is a composite coating film. From the viewpoint of suppressing aggregation unevenness, it is preferable that the second ink is an ink that is applied in a liquid state onto the first ink coating film. As mentioned above, another method is also preferable from the viewpoint of suppressing aggregation unevenness and pinning properties of the second ink, which includes a step of applying the pretreatment ink onto the first ink coating film and a step of applying the second ink onto the first ink coating film so that the pretreatment ink and the second ink are mixed in liquid form.

[0325] Typically, the pretreatment ink is responsible for pinning not only the first ink but also the second ink, but by adopting a method that includes a step of applying the pretreatment ink onto the first ink coating, and a step of applying the second ink so that the pretreatment ink and the second ink are mixed in liquid form on the first ink coating, the amount of pretreatment ink used in the step of applying the pretreatment ink onto the recording medium can be reduced, thereby improving the uniformity of the image density of the first ink.

[0326] It is preferable that the second ink be applied in a liquid state onto the first ink coating film so that the pretreatment ink and the second ink undergo an appropriate thickening reaction and react uniformly.To achieve this, it is preferable that the second ink be in a liquid state and that the drying rate of the first ink coating film be 95% or less. In addition, from the viewpoint of preventing color mixing between the first ink coating film and the second ink, the first ink coating film preferably has a drying rate of 30% or more.

[0327] The "drying rate of the first ink coating film" is defined by the following formula.

[0328] (Drying rate of first ink coating film)=1-(mass [g] of first ink after forming first ink coating film) / (mass [g] of first ink before forming first ink coating film)

[0329] III [Image forming equipment] FIG. 1 is a schematic diagram of an image forming apparatus preferred for the present invention. However, the present invention is not limited to this.

[0330] The image forming apparatus 1 is mainly composed of a pretreatment ink applying section 10, a first ink applying section 20, and a second ink applying section 30. A pretreatment ink 12 is applied by a pretreatment ink application section 10 onto a substrate P fed out from a feed roller 40, and a first ink 22 is applied by a first ink application section 20, whereby the pretreatment ink 12 and the first ink 22 are mixed in liquid form to form a first ink coating film F, which is a composite coating film. Thereafter, the second ink is applied by the second ink application unit 30 onto the first ink coating film F, which is the composite coating film, and the area where the second ink has been applied is heated and dried by the second drying unit .

[0331] Thereafter, the base material P to which the second ink 25 has been applied is wound up by the winding roller 50, thereby obtaining an image-recorded product.

[0332] The first drying section 23 heats and dries the area where the pretreatment ink 12 and the first ink 22, which are mixed in liquid form, have been applied, but since it is preferable to mix them in liquid form when the second ink 25 is applied later, it is preferable that the aforementioned drying rate be within the range of 30 to 95%.

[0333] The pretreatment ink application unit 10, the first ink application unit 20, and the second ink application unit 30 are not particularly limited as long as they are configured to be able to apply each ink to a substrate, but in the present invention, they are preferably inkjet heads. Other than the inkjet head, for example, a roll coater or the like may also be used. The pretreatment ink applying section 20, the first ink applying section 20, and the second ink applying section 30 are provided with inkjet heads 11, 21, and 24, respectively, that are capable of ejecting ink.

[0334] Furthermore, it is also preferable to use a flatbed type printer as an apparatus other than the image forming apparatus shown in FIG. 1 for applying the pretreatment ink and the ink. In a flatbed printer, the substrate is fixed and the inkjet head can be moved in the main scanning direction and the sub-scanning direction that intersects the main scanning direction, making it possible to print without transporting the substrate. For metal substrates such as tinplate, roll-to-roll transport is not possible as with resin film substrates, so it is preferable to use a flatbed type printer, which does not require transporting the substrate. Examples of such flatbed type printers include the printers described in FIG. 1 of JP-A-2015-74161 and FIG. 1 of JP-A-2017-177578. [Example]

[0335] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. In the examples, the terms "parts" and "%" are used, but unless otherwise specified, they represent "parts by mass" or "% by mass."

[0336] A. Pretreatment Ink Preparation (A.1) Preparation of pretreatment ink [1] 3.00% by mass of calcium acetate monohydrate as a flocculant (polyvalent metal salt), 25.00% by mass of dipropylene glycol (DPG) and 20.00% by mass of 1,2-hexanediol (1,2-HDO) as solvents, 1.00% by mass of "TEGOWet 250" (polyether-modified silicone; manufactured by Evonik) as a surfactant, 0.10% by mass of "Proxel GXL(S)" (1,2-benzisothiazolin-3-one; manufactured by Daiwa Chemical Industry Co., Ltd.) as a fungicide, and ion-exchanged water (the balance; the total amount was 100% by mass) were added with stirring, and the resulting mixture was filtered through a 1 μm filter to obtain pretreated ink [1].

[0337] (A.2) Preparation of pretreatment inks [2] to [5] Pretreated inks [2] to [5] were prepared in the same manner as in the preparation of pretreated ink No. 1, except that the types and amounts of the flocculant (polyvalent metal salt), solvent, surfactant, and antifungal agent, and the amount of water added were changed as shown in Table I below.

[0338] [Table 1]

[0339] The abbreviations in Table I are as follows:

[0340] (solvent) "DPG": Dipropylene glycol "1,2-HDO": 1,2-hexanediol "PG": Propylene glycol "Gly": Glycerin "2Me-1,3-PDO": 2-methyl-1,3-propanediol

[0341] (surfactant) "TEGOWet250": Polyether-modified silicone (manufactured by Evonik) (The HLB value of "TEGOWet250" in Table I is not disclosed by the manufacturer, so the value listed is calculated using the Griffin method based on the molecular structure stated by the manufacturer.) "E1010" Acetylene glycol surfactant Olfine (manufactured by Nissin Chemical Industry Co., Ltd.)

[0342] (Anti-mold agent) "Proxel GXL(S)": 1,2-benzisothiazolin-3-one (manufactured by Daiwa Chemical Industry Co., Ltd.)

[0343] B. Preparation of pigment dispersion liquid used in colorant-containing inks (first ink and second ink) (B.1) Preparation of White Pigment Dispersion WA A mixture was prepared by premixing 30% by mass of white pigment (CR-50-2; manufactured by Ishihara Sangyo Kaisha, Ltd.) with 8% by mass of "Joncryl 819" (anionic polymer dispersant, acrylic dispersant having a carboxy group neutralized with dimethylaminoethanol, acid value 75 mg KOH / g, solids content 20% by mass; manufactured by BASF) as a pigment dispersant, 20% by mass of propylene glycol (PG) as a solvent, 0.1% by mass of 1,2-benzisothiazolin-3-one (Proxel GXL(S)) as an antifungal agent, and ion-exchanged water (the remainder; an amount that would make the total amount 100% by mass).

[0344] Thereafter, the mixture was dispersed using a bead mill filled with 0.3 mm zirconia beads at a volumetric rate of 50%, to prepare a white pigment dispersion WA with a pigment content of 20 mass %.

[0345] (B.2) Preparation of white pigment dispersions WB, WC, and WD White pigment dispersions WB, WC and WD were prepared in the same manner as in the preparation of white pigment dispersion WA, except that the pigment dispersant was changed as shown in Table II.

[0346] (B.3) Preparation of magenta pigment dispersion MA A mixture of 20% by mass of magenta pigment (a mixed crystal of Pigment Red 122 and Pigment Violet 19) was premixed with 8% by mass of "Joncryl 819" (anionic polymer dispersant, acrylic dispersant with carboxyl groups neutralized with dimethylaminoethanol, acid value 75 mg KOH / g, solids content 20% by mass, manufactured by BASF) as a pigment dispersant, 20% by mass of propylene glycol (PG) as a solvent, 0.1% by mass of 1,2-benzisothiazolin-3-one (Proxel GXL(S); manufactured by Daiwa Chemical Industry Co., Ltd.) as a fungicide, and ion-exchanged water (the remainder; an amount that would make the total amount 100% by mass).

[0347] Thereafter, the mixture was dispersed using a bead mill filled with 0.3 mm zirconia beads at a volumetric rate of 50%, to prepare a magenta pigment dispersion MA with a pigment content of 20 mass %.

[0348] (B.4) Preparation of magenta pigment dispersions MB, MC, and MD White pigment dispersions WB, WC and WD were prepared in the same manner as in the preparation of magenta pigment dispersion MA, except that the pigment dispersant was changed as shown in Table II.

[0349] [Table 2]

[0350] C. Preparation of the first ink (C.1) Preparation of first ink [1] The white pigment dispersion liquid WA was 15.00% by mass, and Vylonal MD2000 (polyester resin, glass transition temperature of resin only, Tg: 67°C, manufactured by Toyobo Co., Ltd.) was 10.00% by mass as a resin particle dispersion liquid, propylene glycol (PG) was 20.00% by mass, diethylene glycol monobutyl ether (DEGBE) was 1.60% by mass, and 1,2-hexanediol (1,2-HDO) was 10.00% by mass as a solvent, and acetylene glycol surfactant Olfin E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) was 0.60% by mass and silicone-modified surfactant KF-351A (manufactured by Shin-Etsu Silicones Co., Ltd.) was 0.05% by mass as a surfactant, and 1,2-benzisothiazolin-3-one (Proxel) was used as an antifungal agent. 0.10% by mass of GXL(S) and 42.65% by mass of ion-exchanged water (the remainder; an amount that would make the total amount 100% by mass) were added with stirring, and the resulting mixture was filtered through a 1 μm filter to prepare a first ink [1]. There was no substantial change in composition before and after filtration.

[0351] (C.2) Preparation of first inks [2] to

[18] First inks [2] to

[18] were prepared in the same manner as first ink [1], except that the pigment dispersion, resin particle dispersion, solvent, type of surfactant, type and amount of antifungal agent and water were changed as shown in Table III.

[0352] [Table 3]

[0353] The abbreviations in Table III are as follows:

[0354] (pigment dispersion) "WA": White pigment dispersion WA (described in Table II) "WB": White pigment dispersion WB (described in Table II) "WC": White pigment dispersion WC (described in Table II) "WD": White pigment dispersion WD (listed in Table II) "MA": Magenta pigment dispersion MA (described in Table II)

[0355] (Resin particle dispersion) *1: Movinyl 6969D (Japan Coating Resin Co., Ltd.), acrylic resin *2: Vylonal MD2000 (manufactured by Toyobo Co., Ltd.), polyester resin *3: Evaphanol HA-560 (manufactured by Nicca Chemical Co., Ltd.), urethane resin *4: Vylonal MD1480 (manufactured by Toyobo Co., Ltd.), polyester resin *5: WS4022 (Mitsui Chemicals), urethane resin

[0356] (solvent) "PG": Propylene glycol "DEGBE": Diethylene glycol monobutyl ether "1,2-HDO": 1,2-hexanediol "2Me-1,3-PDO": 2-methyl-1,3-propanediol "Gly": Glycerin

[0357] (surfactant) *6: "E1010": Acetylene glycol surfactant Olfine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) *7: "KF-351A": Silicone-modified surfactant KF-351A (manufactured by Shin-Etsu Silicone Co., Ltd.) *8: "E1004": Acetylene glycol surfactant Olfine E1004 (manufactured by Nissin Chemical Industry Co., Ltd.) *9: "KF354L": Polyether-modified silicone (manufactured by Shin-Etsu Chemical Co., Ltd.) *10 "Surfynol 420": Acetylene glycol surfactant (Nissin Chemical Industry Co., Ltd.)

[0358] (Anti-mold agent) "Proxel GXL(S)": 1,2-benzisothiazolin-3-one

[0359] D. Preparation of the second ink (D.1) Preparation of second ink [1] To 5.00% by mass of the magenta pigment dispersion MA, 8.50% by mass of Vylonal MD2000 (polyester resin, glass transition temperature Tg of the resin alone: ​​67°C, manufactured by Toyobo Co., Ltd.) as a resin particle dispersion, 25.00% by mass of propylene glycol (PG), 1.90% by mass of diethylene glycol monobutyl ether (DEGBE), and 10.00% by mass of 1,2-pentanediol as solvents, 1.00% by mass of "TEGOWet250" (polyether-modified silicone, manufactured by Evonik) as a surfactant, 0.10% by mass of 1,2-benzisothiazolin-3-one (Proxel GXL(S)) as an antifungal agent, and 48.50% by mass of ion-exchanged water (the balance; an amount that would make the total amount 100% by mass) were added with stirring, and the resulting mixture was filtered through a 1 μm filter to prepare a second ink [1]. There was no substantial change in composition before and after filtration.

[0360] (D.2) Preparation of second inks [2] to [9] First inks [2] to [9] were prepared in the same manner as second ink [1], except that the types and amounts of pigment dispersion, resin particle dispersion, solvent, surfactant, antifungal agent, and water were changed as shown in Table IV.

[0361] [Table 4]

[0362] The abbreviations in Table IV are as follows:

[0363] (pigment dispersion) "MA": Magenta pigment dispersion MA (described in Table II) "MB": Magenta pigment dispersion MB (described in Table II) "MC": Magenta pigment dispersion MC (described in Table II) "MD": Magenta pigment dispersion MD (listed in Table II) "WA": White pigment dispersion WA (described in Table II)

[0364] (Resin particle dispersion) *1: Movinyl 6969D (Japan Coating Resin Co., Ltd.), acrylic resin

[0365] (solvent) "PG": Propylene glycol "DEGBE": Diethylene glycol monobutyl ether

[0366] (surfactant) "TEGOWet250": Polyether-modified silicone (manufactured by Evonik) (The HLB value of "TEGOWet250" in Table IV is not disclosed by the manufacturer, so the value shown is calculated using the Griffin method based on the molecular structure stated by the manufacturer.) *6: "E1010": Acetylene glycol surfactant Olfine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) *7: "KF-351A": Silicone-modified surfactant KF-351A (manufactured by Shin-Etsu Silicone Co., Ltd.)

[0367] (Anti-mold agent) "Proxel GXL(S)": 1,2-benzisothiazolin-3-one

[0368] E. Physical properties of each ink (E.1) Dynamic surface tension of pretreatment ink, first ink, and second ink For the pre-treatment ink, first ink, and second ink, the dynamic surface tension [mN / m] at 25° C. after a surface life of 30 [ms] was measured by the following method, and the results shown in Table V were obtained.

[0369] (Measurement of dynamic surface tension) The dynamic surface tension [mN / m] of the pre-treated ink was measured at 25°C with a surface life of 30 [ms] using a dynamic surface tensiometer (BP-100: manufactured by KRUSS) using the maximum bubble pressure method.

[0370] (E.2) Physical properties of the first ink coating For the first ink coating film formed using only the first ink without using the pretreatment liquid, the swelling ratio [mg / cm 2The glass transition temperature Tg [°C] and water contact angle [°] were measured by the following methods, and the results shown in Table V were obtained. The physical property values ​​of the various first ink coating films shown in Tables VI to VIII below are the physical property values ​​of the first ink coating film formed using only the first ink shown in Table V below.

[0371] (Measurement of swelling ratio) The first ink was applied to the PET film at 10 g / m 2 ] The ink was applied using a bar coder and dried on a hot plate at 80°C for 5 minutes to obtain a print on which a first ink coating film was formed. After drying, the print was immersed in water for 5 minutes, and after wiping off excess water, the change in mass of the first ink coating film before and after immersion in water was measured. If the mass becomes negative after immersion in water, this indicates that the ink is eluting from the ink film, and the mass is decreasing as a result of the ink dissolving in the water. First ink coating film 1 [cm 2 ] is the swelling mass [mg] of water per unit volume [mg / cm 2 ] was defined as follows.

[0372] (Measurement of glass transition temperature (Tg [℃])) 10 mg of the first ink alone was placed in a glass transition temperature measurement container and heated on a hot plate at 80° C. for 3 hours to form a first ink coating film. After confirming that the first ink coating film had been formed, the above-mentioned differential scanning calorimetry was carried out to measure the glass transition temperature (Tg [°C]), which was taken as the glass transition temperature (Tg [°C]) of the first ink coating film. For the measurements, a DSC differential scanning calorimeter "DSC1" manufactured by Mettler-Toledo K.K. was used.

[0373] (Water contact angle measurement) The water contact angle was measured using the same printed matter as in (Measurement of Swelling Ratio), and this was taken as the water contact angle of the first ink coating film. For the measurement, a water contact angle meter DM500 manufactured by Kyowa Interface Science Co., Ltd. was used.

[0374] [Table 5]

[0375] F. Evaluation of Drawability [Examples and Comparative Examples] (F.1) Preparation of print using first ink A PP substrate (FOS-AQ, Futamura Chemical Co., Ltd.) was used as the recording medium M, and the pre-treated ink and the first ink were mixed in liquid form on the substrate in the combination shown in Table VI, whereby printing was performed on the PP substrate, and the mixture was then heated and dried in a dryer for 3 minutes to produce a print using the first ink with cut-out characters and solid prints. Details are as follows:

[0376] A scanning printer (see Figure 2) equipped with two independently driven inkjet heads manufactured by Konica Minolta (360 npi, ejection volume of 6 pL or 14 pL, 1024 nozzles) was prepared, and the head H1, which was to be printed first, was filled with each pretreatment ink, and the head H2, which was to be printed later, was filled with the first ink.

[0377] The image with a resolution of 720 x 720 dpi was then divided into two halves in the scanning direction X and the transport direction Y to create four images (180 x 180 dpi). Printing was then carried out in one direction, always with the pretreatment ink being recorded first, in a four-pass mode in which one printing area is printed four times.

[0378] The transport speed of the carriage C was set to 300 mm / sec, and a drying step was not performed between the time when the pretreatment ink and the first ink were mixed in liquid form.

[0379] Printing was carried out in an environment of 25°C and 50% RH. The pretreatment ink was recorded with a liquid volume of 6 pL and a maximum printing ratio of 37%, and was applied in an image pattern in accordance with the image area of ​​the first ink. The first ink was recorded with a liquid volume of 14 pL and a maximum printing rate of 100%.

[0380] In the above settings, the amount of pre-treatment ink applied to the solid area was 1.9 g / m2 , the first ink application amount in the solid area is 11.9 g / m 2 Therefore, the ratio of the amount of first ink applied to the amount of pretreatment ink applied to the solid portion (amount of first ink applied / amount of pretreatment ink applied) is 6.3.

[0381] In the above printing process, the time from when the pretreatment ink was applied to when the first ink was applied was measured and calculated to be 0.2 seconds. When the drying rate of the pretreatment ink was measured 0.2 seconds after application in the above environment of 25°C and 50% RH, it was found to be less than 1%. The drying rate of the pretreatment ink was calculated by measuring the amount of change in mass of the pretreatment ink.

[0382] (Preparation of a print using the first ink for Example 29) In Example 1, the amount of pretreatment ink [1] applied was 0.75 g / m 2 and the pretreatment ink [2] is applied to the first ink coating film in an amount of 1.3 g / m 2 A print was produced using the first ink in the same manner as in Example 1, except that the second ink was applied after the first ink was applied so as to be:

[0383] (F.2) Evaluation of prints made with the first ink The above printed matter was visually evaluated, and the uniformity of the image density and pinning property of the first ink were evaluated according to the following evaluation criteria, and the results shown in Table VI were obtained.

[0384] (Uniformity of image density) A 5 cm x 5 cm solid image was recorded by the method described above, and after it was completely dried, the image was observed from a distance of 15 cm and evaluated visually for uniformity of density according to the following criteria.

[0385] [Evaluation criteria] ◎ Neither uneven density nor cracks are observed in the image. ○: Density unevenness is observed in some parts of the image, but no cracks are observed. △: Density unevenness or cracks are observed in some parts of the image, but neither density unevenness nor cracks are observed from a distance of 30 cm. x: Uneven density or cracks are noticeable throughout the image.

[0386] (Pinning property) Using the method described above, a 5 cm x 5 cm cut-out character image (an image in which only the character portion is not printed and the surrounding area is solidly printed) was recorded, and the pinning property was evaluated visually from a distance of 15 cm according to the following criteria, and the image was also observed under a microscope at 100x magnification (KEYENCE Digital Microscope VHX-1000).

[0387] [Evaluation criteria] ◎ When observed under a microscope, the dots around the cut-out characters do not extend into the cut-out character area, and the cut-out character image is clearly visible even when observed visually. When observed under a microscope, the dots around the cut-out characters extend slightly into the cut-out character area, but the cut-out character area remains clearly visible, and the cut-out character image can be clearly seen even when observed visually. △ When observed under a microscope, the dots around the cut-out characters extend into the cut-out character portion, and although the cut-out character portion remains, when observed visually, the character portion of the cut-out character image becomes slightly thinner. × When observed under a microscope, the dots around the cut-out characters extend into the cut-out character area, and when observed visually, the character area of ​​the cut-out character image is buried and cannot be seen.

[0388] [Table 6]

[0389] The symbols in Table VI are as follows: *11:-0.15≦swelling ratio [mg / cm 2 ]≦0.15 Those that satisfy formula (3) are evaluated as "○", and those that do not are evaluated as "×". *12: Those whose Tg is within the range of 45 to 100°C are evaluated as "○", and those that do not are evaluated as "×". *13: Those with a water contact angle of 30 to 80° are rated as "○", and those that do not are rated as "×".

[0390] (F.3) Creating a print using the second ink The pre-treated ink and the first ink printed by the above method were then dried for 3 minutes in a dryer, and the second ink [1] was inkjet printed on top of the print made with the first ink, followed by heating and drying on a hot plate at 80°C for 5 minutes to produce a print with cut-out characters and solid prints. Details are as follows:

[0391] A scanning printer (see Figure 2) equipped with two independently driven inkjet heads manufactured by Konica Minolta (360 npi, ejection volume of 6 pL or 14 pL, 1024 nozzles) was prepared, and the head H1 to be printed first was filled with each pretreatment ink, the head H2 to be printed later was filled with the first ink, and the head H3 (not shown) to be printed later was filled with the second ink.

[0392] Under the same environment and process as printing the printed matter with the first ink, the carriage C transport speed was set to 300 mm / sec, and the first ink coating was formed with the first print, dried in a dryer for 3 minutes, and then the second ink was applied onto the first ink coating.

[0393] The second ink was recorded with a liquid volume of 14 pL and a maximum printing rate of 100%.

[0394] (Preparation of print using second ink for Example 29) In Example 1, the amount of pretreatment ink [1] applied was 0.75 g / m 2 A print was made using the first ink in the same manner as in Example 1, except that the amount of the pretreatment ink [2] applied was 1.3 g / m. The print was dried for 3 minutes with a dryer, and then the amount of the pretreatment ink [2] applied was 1.3 g / m. 2The pre-treatment ink [2] was applied so that the ink was mixed with the pre-treatment ink [2], and the second ink [1] was then inkjet printed. The ink was then dried by heating on a hot plate at 80°C for 5 minutes, and a printed product with cut-out characters and solid prints was produced.

[0395] (F.4) Evaluation of prints made with the second ink The above prints were visually evaluated, and the uniformity of image density and pinning property of the prints using the second ink were evaluated using the same evaluation criteria as for the prints using the first ink, and the results in Tables VII and VIII were obtained.

[0396] In Tables VII and VIII, the formula (4) [g / mol] represents the value of (the sum of the amounts [g] of the first coloring material and the second coloring material / the sum of the amounts [mol] of reactive groups contained in the first coloring material and the second coloring material per unit area of ​​the recording medium in the aggregation reaction contained in the pretreatment ink).

[0397] The meanings of the symbols and terms in Tables VII and VIII are as follows:

[0398] "γ0": Dynamic surface tension of the pre-treated ink at a surface life of 30 [ms]. "γ1": Dynamic surface tension of the first ink at a surface life of 30 [ms]. "γ2": Dynamic surface tension of the second ink at a surface life of 30 [ms].

[0399] "Evaluation of formula (1)": If the relationship γ0<γ2<γ1(1) is satisfied, the evaluation is "○", otherwise it is "×". "Evaluation of formula (2)": 0<|γ1-γ2|≦12 If the relationship (2) is satisfied, the evaluation is "○", otherwise it is "×".

[0400] *14: If the dynamic surface tension of the pre-treatment ink is within the range of 24 to 34 [mN / m], the first ink is within the range of 31 to 41 [mN / m], and the second ink is within the range of 25 to 40 [mN / m], the evaluation is "Good", and if not, the evaluation is "Poor".

[0401] "HLB value evaluation A": If the HLB value of at least one surfactant contained in the first ink is greater than the HLB value of at least one surfactant contained in the pretreatment ink, the evaluation is "○", otherwise it is "×". "HLB value evaluation B": When the absolute value of the difference in HLB value between any two surfactants selected from two or more surfactants is within the range of 1 to 9, the evaluation is "○", otherwise it is "×". "HLB value evaluation C": When the absolute value of the difference in HLB value between any two surfactants selected from two or more surfactants is within the range of 6 to 16, the evaluation is "○", otherwise it is "×".

[0402] Swelling ratio [mg / cm 2 ] Evaluation": The swelling ratio of the first ink coating film is -0.15 to 0.15 [mg / cm 2 If it is within the range of [ ], the evaluation is "○", otherwise it is "×". "Tg [°C] evaluation": When the glass transition temperature of the first ink coating film is within the range of 35 to 100 [°C], the evaluation is "Good", and when not, the evaluation is "Poor". "Evaluation of water contact at each [°C]": If the water contact angle at 25 [°C] 60 [ms] after water was dropped onto the surface of the first ink coating was within the range of 30 to 80 [°], the evaluation was "○", and if not, the evaluation was "×".

[0403] "Acid value [mgKOH / g] evaluation": If the acid value of the dispersant for the first colorant contained in the first ink and the acid value of the dispersant for the second colorant contained in the second ink are within the range of 50 to 200 [mgKOH / g], the evaluation is "Good", and if not, the evaluation is "Poor".

[0404] *15: The relationship between the amount of colorant and the amount of reactive group. "Value of formula (4)": (the sum of the amounts [g] of the first coloring material and the second coloring material / the sum of the amounts [mol] of reactive groups contained in the first coloring material and the second coloring material per unit area of ​​the recording medium in the aggregation reaction contained in the pretreatment ink). "Equation (4) [g / mol] evaluation": When the value of the above equation (4) is greater than 500 and less than 20,000, the evaluation is "○", otherwise it is "×".

[0405] *16: If a pretreatment ink is applied onto a composite coating film, and then a process is performed in which the pretreatment ink and the second ink are applied so that they merge in a liquid state on the composite coating film, the result is marked as "○", and if not, the result is marked as "×".

[0406] *17: The pretreatment ink used to form the first ink coating is Pretreatment Ink 1, but the pretreatment ink applied to the composite coating of Pretreatment Ink 1 and First Ink 1 is Pretreatment Ink 2. Evaluation results when a printing method was performed in which Pretreatment Ink 2 was applied to the composite coating of Pretreatment Ink 1 and First Ink 1, and then the second ink was applied. The amount of Pretreatment Ink 1 applied was 0.75 g / m 2 , the amount of pretreatment ink 2 applied was 1.3 g / m 2 Let's say.

[0407] [Table 7]

[0408] [Table 8]

[0409] G. Summary From the evaluation results in Tables VII and VIII, it can be seen that the uniformity of image density and pinning property of the first ink and the second ink of the Examples all met or exceeded the pass criteria, whereas the Comparative Examples met the fail criteria for one or more of the items. This demonstrates that the printability of the Examples of the present invention exceeds and is superior to that of the Comparative Examples. In Table VII, Example 17 should be read as Reference Example 17. [Explanation of symbols]

[0410] 1. Image forming device 10 Pre-treatment ink application section 11, 21, 24 Inkjet head 12 Pretreatment ink 20 First ink application unit 22 1st Ink 23 1st drying section 25 Second Ink 26 2nd drying section 30 Second ink application unit 40 Feed roller 50 Winding roller P substrate (recording medium) F. First ink coating, which is a composite coating C Carriage H1 Head H2 Head X scanning direction Y conveying direction

Claims

1. a pretreatment ink containing a flocculant, a first ink containing a first coloring material, and a second ink containing a second coloring material; the pretreatment ink and the first ink are inks that are mixed in a liquid state on a recording medium, the pretreatment ink and the first ink contain one or more surfactants; the HLB value of the at least one surfactant contained in the first ink is greater than the HLB value of the at least one surfactant contained in the pretreatment ink; an ink set in which the dynamic surface tensions of the pretreatment ink, the first ink, and the second ink at 25° C. after a surface life of 30 ms satisfy the relationships expressed by the following formulas (1) and (2), applying the pretreatment ink onto a recording medium; applying the first ink so that the pretreatment ink and the first ink are mixed in a liquid state on the recording medium; a step of drying the pretreatment ink and the first ink applied onto the recording medium to form a first ink coating film which is a composite coating film; and applying the second ink onto the first ink coating. c ０ <c ２ <c １ (1) 0<|c １ -c ２ |≦12 (2) (γ ０ γ: dynamic surface tension of pretreatment ink after surface life of 30 [ms] １ γ: dynamic surface tension of the first ink at a surface life of 30 [ms] ２ : dynamic surface tension of the second ink at a surface life of 30 [ms]

2. The dynamic surface tension at 25°C for a surface life of 30 ms is the pretreatment ink has a viscosity in the range of 24 to 34 mN / m; the first ink has a viscosity in the range of 31 to 41 mN / m; The second ink has a viscosity in the range of 25 to 40 mN / m.

2. The image forming method according to claim 1.

3. the first ink contains two or more types of surfactants, The absolute value of the difference in HLB value between any two surfactants selected from the two or more surfactants is within the range of 1 to 9.

2. The image forming method according to claim 1.

4. the first ink contains two or more types of surfactants, the absolute value of the difference in HLB value between any two surfactants selected from the two or more surfactants is within the range of 6 to 16; 2. The image forming method according to claim 1.

5. The swelling ratio of the first ink coating film formed by the first ink satisfies the relationship expressed by the following formula (3):

5. The image forming method according to claim 1, wherein the image forming method is a method for forming an image on a recording medium. -0.15≦swelling ratio [mg / cm ２ ]≦0.15 (3) (Swelling ratio [mg / cm ２ ] = swelling mass of water [mg] / surface area of ​​coating film [cm ２ ], where the minus sign indicates dissolution of ink.

6. The glass transition temperature of the first ink coating film is within the range of 35 to 100°C.

6. The image forming method according to claim 5.

7. The water contact angle at 25° C. 60 ms after water is dropped onto the surface of the first ink coating film is in the range of 30 to 80°.

7. The image forming method according to claim 5 or 6.

8. applying the pretreatment ink onto the first ink coating; applying the second ink so that the pretreatment ink and the second ink are mixed in a liquid state on the first ink coating film.

8. The image forming method according to claim 1, wherein the image forming method is a method for forming an image on a recording medium.

9. the acid value of the dispersant for the first coloring material and the acid value of the dispersant for the second coloring material are within a range of 50 to 200 mgKOH / g, and the sum of the amount of reactive groups per unit area in an aggregation reaction [mol] contained in the pretreatment ink and the amount [g] of the first coloring material and the second coloring material satisfies the relationship of the following formula (4):

9. The image forming method according to claim 1, wherein the image forming method is a method for forming an image on a recording medium. 500<(the sum of the amounts [g] of the first coloring material and the second coloring material / the sum of the amounts [mol] of the reactive groups contained in the first coloring material and the second coloring material in the pretreatment ink per unit area of ​​the recording medium in the aggregation reaction)<20,000 (4)

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