Method for producing pigment dispersion, method for producing inkjet ink, and image recording method

Abstract

Provided are: a method for producing a pigment dispersion, which is capable of producing a pigment dispersion having excellent dispersion stability of a pigment; and an application thereof. Provided are a method for producing a pigment dispersion and an application thereof, the method comprising the steps of neutralizing a portion of an acid group in a polymeric dispersant containing an acid group and a (meth) acrylate unit containing an alkyl group having 10 or more carbon atoms, and dispersing a pigment by the neutralized polymeric dispersant to obtain an uncrosslinked dispersion, the acid value AV1 after neutralization, the acid value AV2 after crosslinking, the degree of neutralization ND1 after neutralization, and the degree of neutralization ND2 after addition of the acid in the polymeric dispersant satisfy inequality (1) and (2). Inequation (1) 0.60 < = AV1 (ND1-ND2) / (AV1-AV2) < = 2.00, and ineequation (2) 0.30 < = (1-ND1) / (ND1-ND2) < = 5.00.

Description

Technical Field

[0001] The present invention relates to a method for producing a pigment dispersion, a method for producing an inkjet ink, and an image recording method. Background Art

[0002] Conventionally, various studies have been conducted on methods for producing pigment dispersions used in the production of inkjet inks.

[0003] For example, Patent Document 1 listed below discloses a method for producing an aqueous pigment dispersion (ie, pigment dispersion) and a method for producing an aqueous ink having the following steps 1 to 3.

[0004] Step 1: A step of polymerizing a monomer (a) having an ionic group and a hydrophobic monomer (b) using a polymerization initiator (x) having an ionic group and a polymerization chain transfer agent (y) having an ionic group to obtain a polymer A having an ionic group.

[0005] Step 2: A step of mixing and dispersing the polymer A obtained in step 1 and the pigment in an aqueous medium to obtain a pigment aqueous dispersion.

[0006] Step 3: A step of cross-linking the polymer A in the aqueous pigment dispersion obtained in step 2 with a polyfunctional compound to obtain an aqueous pigment dispersion.

[0007] Patent Document 1 describes that these production methods can ensure excellent redispersibility and high fluidity, which can suppress clogging of the ink ejection nozzles due to solidification of the pigment or polymer in the ink ejection nozzles.

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-14879

[0009] However, from the viewpoint of further improving the ejection stability of inkjet ink over time (ie, ejection stability from an inkjet head), there is sometimes a demand for further improving the dispersion stability of the pigment in the pigment dispersion used to produce the inkjet ink. Summary of the Invention

[0010] An object of one embodiment of the present invention is to provide a method for producing a pigment dispersion having excellent pigment dispersion stability, an inkjet ink having excellent discharge stability after aging, and an image recording method capable of recording an image with suppressed bleeding.

[0011] The present invention includes the following aspects.

[0012] <1> A method for producing a pigment dispersion, comprising:

[0013] A preparation step of preparing a polymer dispersant N, wherein the polymer dispersant N comprises a structural unit L and a structural unit A, wherein the proportion of the structural unit L is 20% by mass or greater, the structural unit L being derived from at least one selected from the group consisting of an alkyl (meth)acrylate containing an alkyl group having 10 or more carbon atoms and an α-olefin containing an alkyl group having 10 or more carbon atoms, and the structural unit A containing an acid group; and a neutralization step of neutralizing a portion of the acid groups contained in the polymer dispersant N to obtain a polymer dispersant A having a neutralization degree of less than 100%.

[0014] A dispersion step in which the pigment is dispersed in an aqueous medium using a polymer dispersant A to obtain an uncrosslinked dispersion;

[0015] An acid addition step, in which an acid is added to the uncrosslinked dispersion to reduce the degree of neutralization of the polymer dispersant A in the uncrosslinked dispersion to obtain a polymer dispersant B; and a crosslinking step, in which the polymer dispersant B in the uncrosslinked dispersion after the acid addition step is crosslinked to obtain a polymer dispersant C, wherein the acid value of the polymer dispersant A in mgKOH / g, i.e., AV1, the acid value of the polymer dispersant C in mgKOH / g, i.e., AV2, the degree of neutralization of the polymer dispersant A in %, i.e., ND1, and the degree of neutralization of the polymer dispersant B in %, i.e., ND2, satisfy the following inequality (1) and the following inequality (2).

[0016] 0.60≤0.01×AV1×(ND1-ND2) / (AV1-AV2)≤2.00…Inequality (1)

[0017] 0.30≤(100-ND1) / (ND1-ND2)≤5.00…Inequality (2)

[0018] <2> The method for producing a pigment dispersion according to <1>, wherein

[0019] AV1 and AV2 satisfy the following inequality (3).

[0020] 120≤(1.2×AV2)≤AV1≤330…Inequality (3)

[0021] <3> The method for producing a pigment dispersion according to <1> or <2>, wherein:

[0022] In the polymer dispersant N prepared in the preparation step, the mass ratio of the structural unit A to the structural unit L, that is, the A / L ratio, is 0.5 to 2.0.

[0023] <4> The method for producing a pigment dispersion according to any one of <1> to <3>, wherein

[0024] The structural unit A is a structural unit derived from (meth)acrylic acid.

[0025] <5> A method for producing an inkjet ink, comprising: producing a pigment dispersion by the method for producing a pigment dispersion according to any one of <1> to <4>; and

[0026] The process of making inkjet inks using pigment dispersions.

[0027] <6> An image recording method, comprising:

[0028] A step of producing an inkjet ink by the method for producing an inkjet ink according to claim 5; and

[0029] In the ink application step, inkjet ink is applied to the substrate by an inkjet method.

[0030] <7> The image recording method according to <6>, wherein:

[0031] The substrate is a non-permeable substrate.

[0032] Before the ink application step, a pre-treatment liquid containing water and a coagulant is applied to the non-permeable substrate.

[0033] In the ink applying step, inkjet ink is applied to the area on the non-permeable substrate to which the pre-treatment liquid has been applied.

[0034] Effects of the Invention

[0035] According to one embodiment of the present invention, there are provided a method for producing a pigment dispersion having excellent pigment dispersion stability, an inkjet ink having excellent discharge stability after aging, and an image recording method capable of recording an image with suppressed bleeding. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 FIG. 1 is a diagram schematically showing an example of an image recording apparatus used in the image recording method of the present invention.

[0037] Figure 2 This is a diagram showing character images used in the examples. DETAILED DESCRIPTION

[0038] In this specification, the numerical range expressed using "to" indicates a range including the numerical values ​​described before and after "to" as the minimum value and the maximum value, respectively.

[0039] In the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may be replaced by the upper limit or lower limit of the numerical range described in another stage. Furthermore, in the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may be replaced by the value shown in the Examples.

[0040] In this specification, when a plurality of substances corresponding to each component are present in a composition, the amount of each component in the composition represents the total amount of the plurality of substances present in the composition unless otherwise specified.

[0041] In this specification, a combination of two or more preferred aspects is a more preferred aspect.

[0042] In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process can be achieved.

[0043] In this specification, "(meth)acrylate" is a concept encompassing both acrylate and methacrylate. Furthermore, "(meth)acrylic acid" is a concept encompassing both acrylic acid and methacrylic acid.

[0044] [Method for producing pigment dispersion]

[0045] The method for producing the pigment dispersion of the present invention comprises:

[0046] a preparation step of preparing a polymer dispersant N comprising a structural unit L and a structural unit A, wherein the proportion of the structural unit L is 20% by mass or greater, the structural unit L being derived from at least one selected from the group consisting of an alkyl (meth)acrylate containing an alkyl group having 10 or more carbon atoms and an α-olefin containing an alkyl group having 10 or more carbon atoms, and the structural unit A containing an acid group;

[0047] A neutralization step of neutralizing a portion of the acid groups contained in the polymer dispersant N to obtain a polymer dispersant A having a neutralization degree of less than 100%;

[0048] A dispersion step in which the pigment is dispersed in an aqueous medium using a polymer dispersant A to obtain an uncrosslinked dispersion;

[0049] an acid adding step of adding an acid to the uncrosslinked dispersion to reduce the degree of neutralization of the polymer dispersant A in the uncrosslinked dispersion to obtain the polymer dispersant B; and

[0050] The polymer dispersant C is obtained by cross-linking the polymer dispersant B in the uncross-linked dispersion after the cross-linking acid addition step.

[0051] The acid value of polymer dispersant A expressed in mgKOH / g, i.e., AV1, the acid value of polymer dispersant C expressed in mgKOH / g, i.e., AV2, the neutralization degree of polymer dispersant A expressed in %, i.e., ND1, and the neutralization degree of polymer dispersant B expressed in %, i.e., ND2, satisfy the following inequality (1) and the following inequality (2).

[0052] 0.60≤0.01×AV1×(ND1-ND2) / (AV1-AV2)≤2.00…Inequality (1)

[0053] 0.30≤(100-ND1) / (ND1-ND2)≤5.00…Inequality (2)

[0054] According to the method for producing a pigment dispersion of the present invention, a pigment dispersion having excellent pigment dispersion stability can be produced.

[0055] In the present invention, the dispersion stability of the pigment in the pigment dispersion is evaluated using the ejection stability of the inkjet ink produced using the pigment dispersion over time as an indicator.

[0056] The above-mentioned effects obtained by the method for producing a pigment dispersion of the present invention are considered to be achieved as follows.

[0057] In the method for producing a pigment dispersion of the present invention, a polymeric dispersant N is first prepared in which the proportion of structural units L is 20% by mass or greater. Structural units L are structural units containing a long-chain alkyl group having 10 or more carbon atoms. This long-chain alkyl group has excellent adsorption properties for pigments. Therefore, polymeric dispersant N has excellent adsorption properties for pigments, which is a prerequisite for achieving effective pigment dispersion stability.

[0058] The polymer dispersant N subsequently changes to polymer dispersant A, polymer dispersant B, and polymer dispersant C through the processes of neutralization, acid addition, and crosslinking. However, the structural unit L also remains in the polymer dispersant (i.e., in polymer dispersant A, polymer dispersant B, and polymer dispersant C) during this process.

[0059] Furthermore, the polymer dispersant N includes an acid group-containing structural unit A. The acid group in the structural unit A contributes to affinity for an aqueous medium (ie, water or a mixed solvent of water and a water-soluble organic solvent), which is a prerequisite for the dispersion stability of the pigment.

[0060] The concept of acid groups in the present invention includes unneutralized acid groups (e.g., -COOH groups (carboxyl groups)) and neutralized acid groups (e.g., -COOH groups (carboxyl groups)). - Both of them.

[0061] The method for producing a pigment dispersion of the present invention includes a neutralization step of neutralizing a portion of the acid groups contained in a polymer dispersant N to obtain a polymer dispersant A having a neutralization degree (ND1) of less than 100%.

[0062] Here, the degree of neutralization indicates the percentage of neutralized acid groups relative to the total number of unneutralized acid groups and neutralized acid groups.

[0063] Neutralized acid groups have a superior affinity for aqueous media compared to unneutralized acid groups.

[0064] Therefore, the affinity of the polymer dispersant for the aqueous medium is increased by the neutralization step.

[0065] The affinity of polymer dispersants for aqueous media to a certain extent helps to improve the dispersion stability of pigments.

[0066] However, if the polymer dispersant has too high an affinity for the aqueous medium, it cannot maintain adsorption to the pigment, and thus the dispersion stability of the pigment decreases. Taking this into account, neutralization is performed in the neutralization step to a degree of neutralization (ND1) of less than 100%.

[0067] The method for producing a pigment dispersion of the present invention includes a dispersing step of dispersing a pigment in an aqueous medium using a polymer dispersant A to obtain an uncrosslinked dispersion.

[0068] In the dispersion step, the pigment is dispersed in an aqueous medium using a polymer dispersant A whose neutralization degree is adjusted to a level that is neither too low nor too high.

[0069] It is considered that in the uncrosslinked dispersion obtained in the dispersing step, the pigment is dispersed in the aqueous medium in a state where the polymer dispersant A is adsorbed on the surface of the pigment.

[0070] As described above, the polymer dispersant A has excellent adsorption properties for pigments and also has excellent affinity for aqueous media to a certain extent.

[0071] Therefore, it is considered that a certain degree of pigment dispersibility is achieved in the uncrosslinked dispersion, which is a prerequisite for the effect of pigment dispersion stability.

[0072] The method for producing a pigment dispersion of the present invention includes an acid adding step of adding an acid to an uncrosslinked dispersion to reduce the degree of neutralization of a polymer dispersant A in the uncrosslinked dispersion to obtain a polymer dispersant B.

[0073] During the acid addition step, the degree of neutralization (ND1) of polymer dispersant A, which is less than 100%, is reduced to obtain polymer dispersant B having a degree of neutralization of ND2. The acid addition step reduces the number of neutralized acid groups in the polymer dispersant, while increasing the number of unneutralized acid groups. Thus, during the acid addition step, the affinity of polymer dispersant A adsorbed on the pigment surface for the aqueous medium is reduced, transforming it into polymer dispersant B, thereby suppressing the detachment of polymer dispersant B from the pigment surface.

[0074] The method for producing a pigment dispersion of the present invention comprises a cross-linking step and a cross-linking acid adding step to obtain a polymer dispersant C by removing the polymer dispersant B from the uncross-linked dispersion.

[0075] In the crosslinking step, the polymer dispersant B adsorbed on the pigment surface in the uncrosslinked dispersion after the acid addition step is crosslinked to obtain the polymer dispersant C. This further suppresses the detachment of the polymer dispersant C from the pigment surface.

[0076] In the cross-linking step, at least one of the unneutralized acid groups and the neutralized acid groups is consumed to form cross-links, thereby reducing the acid value of the polymer dispersant.

[0077] Here, the acid value (mgKOH / g) of the polymer dispersant corresponds to the number of acid groups in the polymer dispersant (that is, the total number of unneutralized acid groups and neutralized acid groups).

[0078] In the method for producing a pigment dispersion of the present invention, the acid value did not change in polymer dispersant N, polymer dispersant A, and polymer dispersant B, but decreased in the process of changing from polymer dispersant B to polymer dispersant C.

[0079] In the present invention, the acid value of the polymer dispersant A is defined as AV1 (mgKOH / g), and the acid value of the polymer dispersant C is defined as AV2 (mgKOH / g).

[0080] As described above, the acid groups are consumed by cross-linking, so the value of AV2 is lower than AV1.

[0081] In the method for producing a pigment dispersion of the present invention, the acid value of the polymer dispersant A expressed in mgKOH / g, i.e., AV1, the acid value of the polymer dispersant C expressed in mgKOH / g, i.e., AV2, the neutralization degree of the polymer dispersant A expressed in %, i.e., ND1, and the neutralization degree of the polymer dispersant B expressed in %, i.e., ND2, satisfy the following inequality (1) and the following inequality (2).

[0082] 0.60≤0.01×AV1×(ND1-ND2) / (AV1-AV2)≤2.00…Inequality (1)

[0083] 0.30≤(100-ND1) / (ND1-ND2)≤5.00…Inequality (2)

[0084] In the inequality (1), hereinafter, "0.01×AV1×(ND1-ND2) / (AV1-AV2)" is set as the value (1).

[0085] Inequality (1) can be rewritten as 0.60≤value(1)≤2.00.

[0086] The numerator "0.01×AV1×(ND1−ND2)" in the value (1) corresponds to the number of neutralized acid groups reduced by the acid addition step (ie, the degree of reduction of neutralized acid groups caused by the acid addition step).

[0087] The denominator "(AV1-AV2)" in the value (1) corresponds to the number of acid groups reduced by the cross-linking process (ie, the degree of reduction of acid groups caused by the cross-linking process).

[0088] In the inequality (1), "0.60 ≤ value (1)" indicates that, from a molecular point of view, the degree of reduction of the neutralized acid groups caused by the acid addition step is large to some extent.

[0089] This "0.60 ≤ value (1)" can prevent the affinity of the polymer dispersant B for the aqueous solvent from becoming too high, and as a result, can prevent the polymer dispersant B from being released from the pigment surface. This improves the dispersion stability of the pigment.

[0090] Furthermore, in the inequality (1), "0.60 ≤ value (1)" indicates that the degree of reduction of the acid groups due to the cross-linking step is not excessive from the viewpoint of the denominator.

[0091] This "0.60 ≤ value (1)" can prevent the affinity of the polymer dispersant C for the aqueous solvent from being excessively reduced, and as a result, can prevent precipitation of the pigment adsorbed with the polymer dispersant C. This improves the dispersion stability of the pigment.

[0092] In inequality (1), "value (1) ≤ 2.00" means that the degree of reduction of neutralized acid groups caused by the acid addition step is not too large from a molecular point of view.

[0093] By satisfying "value (1) ≤ 2.00", it is possible to suppress the affinity of the polymer dispersant B for the aqueous solvent from being excessively reduced, and as a result, it is possible to suppress precipitation of the pigment adsorbed with the polymer dispersant B. This improves the dispersion stability of the pigment.

[0094] In the inequality (1), "value (1) ≤ 2.00" means that the degree of reduction of the acid groups due to the cross-linking step is not too small from the viewpoint of the denominator.

[0095] By satisfying "value (1) ≤ 2.00", the affinity of the polymer dispersant C for the aqueous solvent can be prevented from becoming excessively high, and as a result, the polymer dispersant C can be prevented from being released from the pigment surface. This improves the dispersion stability of the pigment.

[0096] In the inequality (2), hereinafter, "(100-ND1) / (ND1-ND2)" is set to the value (2).

[0097] Inequality (2) can be rewritten as 0.30≤value(2)≤5.00.

[0098] The numerator "(100-ND1)" in the value (2) corresponds to the number of unneutralized acid groups remaining after the neutralization step (ie, the residual degree of unneutralized acid groups remaining after the neutralization step).

[0099] The denominator "(ND1-ND2)" in the value (2) corresponds to the number of neutralized acid groups reduced by the acid addition process (ie, the degree of reduction of neutralized acid groups caused by the acid addition process).

[0100] In the inequality (2), "0.30 ≤ value (2)" indicates that, from a molecular point of view, the number of unneutralized acid groups remaining after the neutralization step is large to some extent.

[0101] By satisfying "0.30 ≤ value (2)", the affinity of the polymer dispersant A for the aqueous solvent can be suppressed from being too high, and as a result, the polymer dispersant A is easily adsorbed on the surface of the pigment during the dispersion step. This improves the dispersion stability of the pigment.

[0102] In inequality (2), “0.30≦value (2)” means that, from the viewpoint of the denominator, the degree of reduction in the neutralized acid groups due to the acid addition step is not excessive.

[0103] This "0.30 ≤ value (2)" can prevent the affinity of the polymer dispersant B for the aqueous solvent from being excessively reduced, and as a result, can prevent precipitation of the pigment adsorbed with the polymer dispersant B. This improves the dispersion stability of the pigment.

[0104] In inequality (2), "value (2) ≤ 5.00" means that the number of unneutralized acid groups remaining after the neutralization step is not excessive from a molecular point of view.

[0105] When "value (2) ≤ 5.00", the affinity of the polymer dispersant A for the aqueous solvent can be suppressed from being excessively reduced. As a result, the pigment adsorbed with the polymer dispersant A is easily dispersed in the aqueous medium during the dispersion step. This improves the dispersion stability of the pigment.

[0106] In inequality (2), "value (2) ≤ 5.00" indicates that the degree of reduction in the neutralized acid groups caused by the acid addition step is not too small from the viewpoint of the denominator.

[0107] By setting "value (2) ≤ 5.00", the affinity of the polymer dispersant B for the aqueous solvent can be suppressed from being too high, and as a result, the polymer dispersant B can be suppressed from being peeled off from the pigment adsorbed with the polymer dispersant B. This improves the dispersion stability of the pigment.

[0108] As described above, it is considered that the method for producing a pigment dispersion of the present invention exhibits an effect of excellent dispersion stability of the pigment.

[0109] Hereinafter, the method for producing the pigment dispersion of the present invention will be described in more detail.

[0110] <Preparation process>

[0111] The method for producing a pigment dispersion of the present invention includes: a preparation step of preparing a polymer dispersant N, wherein the polymer dispersant N comprises a structural unit L and a structural unit A, wherein the proportion of the structural unit L is 20% by mass or more, the structural unit L is derived from an alkyl (meth)acrylate containing an alkyl group having 10 or more carbon atoms, and the structural unit A contains an acid group.

[0112] The preparation step may be a step of synthesizing the polymer dispersant N, or may be a step of simply preparing the synthesized polymer dispersant N for carrying out the method for producing a pigment dispersion of the present invention.

[0113] (Polymer dispersant N)

[0114] The polymer dispersant N comprises a structural unit L and a structural unit A, wherein the proportion of the structural unit L (i.e., the proportion of the structural unit L in the entire polymer dispersant) is 20% by mass or more, the structural unit L being derived from at least one selected from the group consisting of an alkyl (meth)acrylate containing an alkyl group having 10 or more carbon atoms and an α-olefin containing an alkyl group having 10 or more carbon atoms, and the structural unit A containing an acid group.

[0115] -Structural unit L-

[0116] The structural unit L is a structural unit derived from at least one selected from the group consisting of an alkyl (meth)acrylate containing an alkyl group having 10 or more carbon atoms and an α-olefin containing an alkyl group having 10 or more carbon atoms.

[0117] The polymer dispersant N may contain only one type of structural unit L, or may contain two or more types of structural units L.

[0118] The polymer dispersant N may contain at least one structural unit derived from an alkyl (meth)acrylate containing an alkyl group having 10 or more carbon atoms and at least one structural unit derived from an α-olefin containing an alkyl group having 10 or more carbon atoms.

[0119] In the structural unit L, an alkyl group having 10 or more carbon atoms (for example, R in the formula (L1) described later) 2 ) contributes to the adsorption of the pigment surface. Thus, the dispersion stability effect of the present invention is exerted.

[0120] From the viewpoint of achieving a more excellent dispersion stability effect, the alkyl group preferably has 14 or more carbon atoms, and more preferably 16 or more carbon atoms.

[0121] The upper limit of the number of carbon atoms in the alkyl group is not particularly limited, but the number of carbon atoms in the alkyl group is preferably 30 or less, more preferably 26 or less, and even more preferably 22 or less.

[0122] In the structural unit L, the structural unit derived from an alkyl (meth)acrylate containing an alkyl group having 10 or more carbon atoms is a structural unit represented by the following formula (L1).

[0123] [Chemical Formula 1]

[0124]

[0125] In formula (L1), R 1 represents a hydrogen atom or a methyl group, R 2 It represents an alkyl group having 10 or more carbon atoms.

[0126] By R 2 The preferred range of the number of carbon atoms in the alkyl group represented by is as described above.

[0127] The proportion of the structural unit L in the entire polymer dispersant is 20% by mass or more.

[0128] This exhibits the dispersion stabilization effect of the present invention.

[0129] From the viewpoint of achieving a more excellent dispersion stability effect, the proportion of the structural unit L in the entire polymer dispersant is preferably 25% by mass or more, more preferably 30% by mass or more.

[0130] There is no particular upper limit on the proportion of structural unit L in the entire polymer dispersant. The proportion of structural unit L is preferably 80% by mass or less, more preferably 70% by mass or less, further preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0131] -Structural unit A-

[0132] The polymer dispersant N includes a structural unit A containing an acid group.

[0133] As described above, the acid groups may be neutralized or unneutralized.

[0134] The polymer dispersant N may contain only one type of structural unit A, or may contain two or more types of structural units A.

[0135] As the unneutralized acid group, a carboxyl group (—COOH group) is preferable.

[0136] The neutralized acid group is preferably a -COOM group (wherein M represents an alkali metal ion, an ammonium ion, or an organic cation).

[0137] The alkali metal is preferably a potassium ion or a sodium ion, more preferably a sodium ion.

[0138] Examples of the organic cation include alkylammonium cations having 1 to 10 carbon atoms, hydroxyl-substituted alkylammonium cations having 1 to 10 carbon atoms, carboxyl-substituted alkylammonium cations having 2 to 10 carbon atoms, and organic cations having 2 to 10 alkyleneimine units having 2 to 4 carbon atoms.

[0139] The structural unit A is preferably a structural unit derived from (meth)acrylic acid.

[0140] The proportion of the structural unit A in the entire polymer dispersant N is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more.

[0141] There is no particular upper limit on the proportion of structural unit A in the entire polymer dispersant N. The proportion of structural unit A is preferably 80 mass % or less, more preferably 70 mass % or less, further preferably 60 mass % or less, and even more preferably 50 mass % or less.

[0142] In the polymer dispersant N, the mass ratio of the structural unit A to the structural unit L, that is, the A / L ratio, is preferably 0.3 to 3.0, more preferably 0.5 to 2.0, and even more preferably 0.5 to 1.5.

[0143] -Other structural units-

[0144] The polymer dispersant N may contain at least one structural unit other than the above-mentioned ones.

[0145] As other structural units, for example, there can be mentioned a structural unit represented by the following formula (2) (hereinafter also referred to as a unit of formula (2)).

[0146] [Chemical Formula 2]

[0147]

[0148] In formula (2), R 21 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R 22 represents an alkylene group having 2 to 5 carbon atoms, R 23 represents an aromatic group, X 21 and X 22 Each independently represents -O- or -NH-, and m represents an integer of 2 or greater.

[0149] In formula (2), R 21 It represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0150] As R 21 , preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, more preferably a hydrogen atom, a methyl group or an ethyl group, further preferably a hydrogen atom or a methyl group.

[0151] In formula (2), R 22 It represents an alkylene group having 2 to 5 carbon atoms.

[0152] As R 22 , preferably an alkylene group having 2 to 4 carbon atoms, more preferably an alkylene group having 2 or 3 carbon atoms, and further preferably an alkylene group having 2 carbon atoms.

[0153] In formula (2), R 23 Represents an aromatic group.

[0154] By R 23 The aromatic group represented by contains at least one aromatic ring.

[0155] By R 23 The aromatic ring in the aromatic group represented by may be a monocyclic ring or a polycyclic ring (condensed ring).

[0156] By R 23 The aromatic group represented by may include a group in which monocyclic rings are linked (for example, biphenyl).

[0157] By R 23 The aromatic groups represented by may contain heteroatoms (eg, oxygen atoms).

[0158] By R23 The aromatic ring in the aromatic group represented by may have a substituent.

[0159] Examples of substituents on the aromatic ring include linear or branched hydrocarbon groups having 1 to 30 (more preferably 1 to 20) carbon atoms (e.g., linear or branched alkyl groups, linear or branched alkenyl groups, linear or branched alkynyl groups, etc.), and halogen atoms.

[0160] By R 23 The number of carbon atoms in the aromatic group represented by is preferably 4 to 30, more preferably 6 to 30, further preferably 6 to 25, and even more preferably 6 to 20.

[0161] As R 23 The aromatic group represented by is preferably a phenyl group, a naphthyl group, a furyl group, a biphenyl group, or an alkylphenyl group having 7 to 30 carbon atoms (preferably 7 to 25 carbon atoms, more preferably 7 to 20 carbon atoms).

[0162] In formula (2), X 21 and X 22 Each independently represents -O- or -NH-.

[0163] X 21 and X 22 Preferred is -O-.

[0164] In formula (2), m represents an integer of 2 or greater.

[0165] m is preferably an integer of 2-30, more preferably an integer of 2-20, and even more preferably an integer of 2-10.

[0166] When the polymer dispersant N contains the unit of formula (2), the proportion of the unit of formula (2) in the entire polymer dispersant N is preferably 50% by mass or less, more preferably 2% by mass to 50% by mass, more preferably 3% by mass to 40% by mass, and even more preferably 10% by mass to 40% by mass.

[0167] As another structural unit, a structural unit derived from methyl (meth)acrylate can also be mentioned, for example.

[0168] When the polymer dispersant N contains a structural unit derived from methyl (meth)acrylate, the proportion of the structural unit derived from methyl (meth)acrylate in the entire polymer dispersant N is preferably 10% by mass or less, more preferably 1% to 10% by mass, and even more preferably 1% to 5% by mass.

[0169] -Weight average molecular weight (Mw) of polymer dispersant N-

[0170] The weight average molecular weight (Mw) of the polymer dispersant N is not particularly limited, but is preferably 3,000 to 100,000, more preferably 5,000 to 80,000, further preferably 10,000 to 60,000, and even more preferably 15,000 to 50,000 from the viewpoint of pigment dispersibility.

[0171] In the present invention, weight average molecular weight (Mw) is measured by gel permeation chromatography (GPC). HLC-8220GPC (manufactured by Tosoh Corporation) is used in GPC, and as a column, TSKgeL SuperHZM-H, TSKgeLSuperHZ4000, TSKgel SuperHZ2000 (all product names manufactured by Tosoh Corporation) are connected in series. 3 roots, THF (tetrahydrofuran) is used as an eluent. In addition, as a condition, the sample concentration is set to 0.45% by mass, the flow rate is set to 0.35ml / min, the sample injection amount is set to 10μl, the measurement temperature is set to 40°C, and a differential refractive index detector is used. In addition, a calibration curve is prepared based on 8 samples of "standard sample TSK standard, polystyrene (polystyrene)" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

[0172] Neutralization process

[0173] The method for producing a pigment dispersion of the present invention includes a neutralization step of neutralizing a portion of the acid groups contained in a polymer dispersant N to obtain a polymer dispersant A having a neutralization degree (ie, ND1) of less than 100%.

[0174] The degree of neutralization ND1 is preferably 40% to 95%, more preferably 50% to 90%.

[0175] Neutralization can be performed by reacting a base (hereinafter also referred to as a “neutralizing base”) with the polymer dispersant N containing an unneutralized acid group.

[0176] Examples of the neutralizing base include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia; and organic amines such as dimethylethanolamine and diisopropylethylamine.

[0177] <Dispersion process>

[0178] The method for producing a pigment dispersion of the present invention includes a dispersing step of dispersing a pigment in an aqueous medium using a polymer dispersant A to obtain an uncrosslinked dispersion.

[0179] In the present invention, the aqueous medium refers to water or a mixed solvent of water and a water-soluble organic solvent.

[0180] In the present invention, "water-soluble" means a property of dissolving 1 g or more in 100 g of water at 25°C.

[0181] Specific examples of the water-soluble organic solvent are the same as the water-soluble organic solvent that can be contained in the inkjet ink described later.

[0182] The pigment is not particularly limited and may be either an organic pigment or an inorganic pigment.

[0183] Examples of pigments include "Encyclopedia of Pigments" edited by Seishiro Ito (published in 2000), "Industrial Organic Pigments" by W. Herbst, K. Hunger, and pigments described in known literature such as Japanese Patent Application Publication No. 2002-12607, Japanese Patent Application Publication No. 2002-188025, Japanese Patent Application Publication No. 2003-26978, Japanese Patent Application Publication No. 2003-342503, and Japanese Patent Application Publication No. 2015-193729.

[0184] Examples of the pigment include polycyclic pigments such as azo lake pigments, azo pigments, phthalocyanine pigments, perylene pigments, peroxycyclic pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; organic pigments such as nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments; and inorganic pigments such as titanium oxide, iron oxide, and carbon black.

[0185] The pigment is preferably an azo pigment, a phthalocyanine pigment, an anthraquinone pigment, a quinacridone pigment, or a carbon black pigment.

[0186] Regarding the pigment, the descriptions in known documents such as Japanese Patent No. 5404669 can also be appropriately referred to.

[0187] From the viewpoint of hue, examples of the pigment include cyan pigments, magenta pigments, yellow pigments, black pigments, and white pigments.

[0188] The content of the pigment is preferably 1 to 40% by mass, more preferably 3 to 30% by mass, further preferably 5 to 25% by mass, and even more preferably 10 to 20% by mass, relative to the total amount of the pigment dispersion.

[0189] The dispersion step can be carried out by a known method using a dispersion device such as a bead mill.

[0190] The total amount of the aqueous medium, pigment, and polymer dispersant N in the total amount of the uncrosslinked dispersion is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0191] Regarding the neutralization step and the dispersion step, the neutralization step and the dispersion step may be performed sequentially or simultaneously.

[0192] When the simultaneous dispersion is carried out, the pigment, polymer dispersant N, aqueous medium, and neutralizing base are added and dispersed. In this way, the pigment is dispersed while the polymer dispersant A is formed.

[0193] <Acid Addition Process>

[0194] The method for producing a pigment dispersion of the present invention includes an acid adding step of adding an acid to an uncrosslinked dispersion to reduce the degree of neutralization of a polymer dispersant A in the uncrosslinked dispersion to obtain a polymer dispersant B.

[0195] The acid addition step is an operation of reducing the acid groups neutralized in the neutralization step to unneutralized acid groups.

[0196] The acid addition step is one of the steps for adjusting the amount of neutralized acid groups having excellent affinity with the aqueous medium to an appropriate amount that is neither too much nor too little.

[0197] It is considered that in the acid addition step, the neutralization degree of the polymer dispersant A adsorbed on the pigment surface in the uncrosslinked dispersion decreases, thereby obtaining the polymer dispersant B having a neutralization degree ND2.

[0198] Examples of the acid used in the acid adding step include hydrochloric acid, acetic acid, citric acid, malonic acid, boric acid, and maleic acid.

[0199] As a specific operation of the acid addition step, a general operation of adding the acid to the uncrosslinked dispersion while stirring the uncrosslinked dispersion and further stirring the dispersion can be mentioned.

[0200] <Cross-linking process>

[0201] The method for producing a pigment dispersion of the present invention comprises a cross-linking step and a cross-linking acid adding step to obtain a polymer dispersant C by removing the polymer dispersant B from the uncross-linked dispersion.

[0202] Through the cross-linking step, a cross-linked dispersion (ie, a pigment dispersion) can be obtained in which the pigment is dispersed by the polymer dispersant C, which is a cross-linked polymer.

[0203] The crosslinking step of the present invention crosslinks the polymer dispersant B adsorbed on the pigment surface to prevent it from detaching and adjusts the amount of acid groups in the polymer dispersant B to an appropriate amount, neither too much nor too little, by crosslinking.

[0204] - Cross-linking agent -

[0205] Cross-linking can be performed using a cross-linking agent.

[0206] In this case, the polymer dispersant C is preferably a reaction product of the polymer dispersant B containing an acid group and a crosslinking agent. The crosslinked structure in this case is a structure formed by a reaction (e.g., an acid-epoxy reaction) between an acid group and a crosslinking agent (e.g., an epoxy group in an epoxy compound).

[0207] The cross-linking agent is preferably a compound having two or more reactive sites (preferably epoxy groups) with the polymer dispersant B containing an acid group.

[0208] Specific examples of bifunctional or higher-functional epoxy compounds as preferred embodiments of the crosslinking agent include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether.

[0209] Among them, polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, or trimethylolpropane triglycidyl ether is preferred.

[0210] As the cross-linking agent, a commercially available product can also be used.

[0211] As commercially available products, for example, Denacol EX-321, EX-821, EX-830, EX-850, and EX-851 (manufactured by Nagase ChemteX Corporation) can be used.

[0212] <Other Process>

[0213] The method for producing the pigment dispersion of the present invention may include other steps in addition to the above-mentioned steps.

[0214] Examples of other steps include a step of removing coarse particles from the cross-linked dispersion obtained in the cross-linking step by centrifugation, filtration, or the like.

[0215] <Inequality (1)>

[0216] 0.60≤0.01×AV1×(ND1-ND2) / (AV1-AV2)〔=value(1)〕≤2.00…Inequality(1)

[0217] The meaning of inequality (1) is as described above.

[0218] The value (1) is 0.60 or more, preferably 0.62 or more, and more preferably 0.65 or more.

[0219] The value (1) is 2.00 or less, preferably 1.50 or less, and more preferably 1.20 or less.

[0220] The acid value AV1 (unit: mgKOH / g) of the polymer dispersant A is preferably 100 to 350, more preferably 150 to 330, and even more preferably 150 to 300.

[0221] The acid value AV2 (unit: mgKOH / g) of the polymer dispersant C is preferably 100 to 300, more preferably 100 to 250. In principle, AV2 is a value smaller than AV1.

[0222] AV1 and AV2 preferably satisfy the following inequality (3).

[0223] 120≤(1.2×AV2)≤AV1≤330…Inequality (3)

[0224] “120≤(1.2×AV2)” in inequality (3) means that a value obtained by multiplying AV2 by 1.2 is 120 or greater.

[0225] "(1.2×AV2)≤AV1" in the inequality (3) indicates that AV1 is equal to or greater than 1.2 times the value of AV2.

[0226] “AV1≤330” in inequality (3) means that AV1 is 330 or less.

[0227] In the present invention, the acid values ​​(AV1 and AV2) of the polymer dispersant are calculated by the following method.

[0228] AV1 was calculated by preparing a 100-fold volume dilution of a solution of the polymer dispersant A with a tetrahydrofuran aqueous solution (THF / pure water = 4:1 aqueous solution), completely neutralizing the obtained dilution with KOH, and then titrating with HCl.

[0229] AV2 is calculated by preparing a pigment dispersion in which the pigment is dispersed using the polymer dispersant C (i.e., the cross-linked pigment dispersion) and diluting it 20 times by volume with an aqueous tetrahydrofuran solution (an aqueous solution of THF / pure water = 4:1). The resulting dilution is completely neutralized with KOH and then titrated with HCl.

[0230] In each of the measurements of AV1 and AV2, when the dispersant is not dissolved in THF, a solvent other than THF can be used. Examples of solvents other than THF include, but are not limited to, dimethyl sulfoxide, 2-methylpyrrolidone, or aqueous solutions thereof.

[0231] The neutralization degree ND1 (%) of the polymer dispersant A is preferably 40-95, more preferably 50-90.

[0232] ND2 (%), which is the degree of neutralization of the polymer dispersant B, is preferably 20 to 80, more preferably 30 to 70. In principle, ND2 is a value smaller than ND1.

[0233] In the present invention, the neutralization degree (ND1 and ND2) of the polymer dispersant is calculated by the following method.

[0234] ND1 is calculated as follows.

[0235] The uncrosslinked dispersion obtained in the dispersion step (i.e., the uncrosslinked dispersion in which the pigment is dispersed using polymer dispersant A) is diluted 20 times by volume with a tetrahydrofuran aqueous solution (THF / pure water = 4:1 aqueous solution). The resulting dilution is titrated with HCl to calculate the acid value of the neutralized acid groups. The obtained acid value is divided by the aforementioned AV1, and the obtained value is expressed as a percentage (%) to obtain ND1.

[0236] ND2 is calculated as follows.

[0237] The acid value of the neutralized acid groups was calculated by preparing a pigment dispersion (i.e., a cross-linked pigment dispersion) in which the pigment was dispersed using polymer dispersant C (THF / pure water = 4:1 aqueous solution) diluted 20 times by volume with a tetrahydrofuran aqueous solution. The resulting dilution was titrated with HCl. The obtained acid value was divided by the aforementioned AV2, and the obtained value was expressed as a percentage (%) to obtain ND2.

[0238] <Inequality (2)>

[0239] 0.30≤(100-ND1) / (ND1-ND2)〔=value(2)〕≤5.00…Inequality(2)

[0240] The meaning of inequality (2) is as described above.

[0241] The value (2) is 0.30 or more, preferably 0.40 or more, and more preferably 0.50 or more.

[0242] The value (2) is 5.00 or less, preferably 3.50 or less, and more preferably 2.50 or less.

[0243] [Method for producing inkjet ink]

[0244] The method for producing the inkjet ink (hereinafter also referred to as "ink") of the present invention comprises:

[0245] A step of producing a pigment dispersion by the above-mentioned method for producing a pigment dispersion of the present invention; and

[0246] A process for producing ink using the above-mentioned pigment dispersion.

[0247] The method for producing the ink of the present invention may include other steps as needed.

[0248] In the method for producing an ink of the present invention, the ink is produced using a pigment dispersion having excellent pigment dispersion stability. Therefore, an ink having excellent discharge stability over time can be produced.

[0249] <Process for producing pigment dispersion>

[0250] Regarding the process of producing the pigment dispersion, reference can be made to the aforementioned method for producing the pigment dispersion of the present invention.

[0251] <Ink Manufacturing Process>

[0252] The step of producing ink is a step of producing ink using the above-mentioned pigment dispersion.

[0253] In the step of producing the ink, it is preferred to produce the inkjet ink by mixing at least the pigment dispersion, water, and a water-soluble organic solvent (and, if necessary, other components).

[0254] The method for mixing the components is not particularly limited, and a common method such as a method of mixing the components while stirring can be applied. After mixing, filtration can be performed as needed.

[0255] (pigment)

[0256] In the produced ink, the content of the pigment is preferably 1 to 25% by mass, more preferably 2 to 25% by mass, and even more preferably 3 to 20% by mass relative to the total amount of the ink, from the viewpoint of image density and ejection properties.

[0257] (Polymer dispersant C)

[0258] In the produced ink, the ratio of the pigment content to the polymer dispersant C (i.e., polymer dispersant having a cross-linked structure) content is preferably 1:0.04 to 1:3, more preferably 1:0.05 to 1:1, and even more preferably 1:0.05 to 1:0.5 on a mass basis.

[0259] In the produced ink, the content of the polymer dispersant C is preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass, and even more preferably 0.5 to 2.5% by mass, relative to the total amount of the ink.

[0260] (water)

[0261] The water content in the produced ink is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, and particularly preferably 50% by mass or more, relative to the total amount of the ink.

[0262] The upper limit of the water content relative to the total amount of ink is appropriately determined depending on the contents of other components, but is, for example, 99% by mass, preferably 95% by mass, and more preferably 90% by mass.

[0263] The water content mentioned here is the total amount of the water contained in the pigment dispersion and the water added during the ink production stage.

[0264] (Water-soluble organic solvent)

[0265] In the present invention, the "water-soluble" in the "water-soluble organic solvent" means that 1 g or more of the solvent dissolves in 100 g of water at 25°C.

[0266] The types of water-soluble organic solvents that can be used to prepare inks are not limited. For example, the following can be mentioned: monoalcohols having 1 to 4 carbon atoms; diols such as 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, and 4-methyl-1,2-pentanediol; glycerol, 1,2,6-hexanediol, 1,3-butanediol, 1,4-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, and 4-methyl-1,2-pentanediol; triols such as alcohol and trimethylolpropane; alkylene glycols such as ethylene glycol and propylene glycol; alkylene glycol monoalkyl ethers such as ethylene glycol monoalkyl ether and propylene glycol monoalkyl ether; polyalkylene glycols such as diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, dipropylene glycol and polyoxyethylene polyoxypropylene glycol; polyalkylene glycol ethers such as diethylene glycol monoalkyl ether, triethylene glycol monoalkyl ether, tripropylene glycol monoalkyl ether and polyoxypropylene glycerol ether; 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0267] From the viewpoint of discharge stability, the water-soluble organic solvent that can be used for the production of the ink preferably contains at least one selected from the group consisting of alkylene glycols and alkylene glycol monoalkyl ethers.

[0268] In the produced ink, the content of the water-soluble organic solvent is preferably 10% by mass to 40% by mass, and more preferably 15% by mass to 30% by mass, relative to the total amount of the ink.

[0269] The content of the water-soluble organic solvent mentioned here is the total amount of the amount contained in the pigment dispersion and the amount added during the ink production stage.

[0270] -Resin-

[0271] In the process of producing the ink, at least one resin may be added in addition to the above-mentioned components.

[0272] The resin can contribute to the film-forming property of the ink (ie, the formability of the ink film).

[0273] The weight average molecular weight (Mw) of the resin is preferably 1,000 to 300,000, more preferably 2,000 to 200,000, and even more preferably 5,000 to 100,000.

[0274] In the present invention, unless otherwise specified, the weight average molecular weight (Mw) refers to a value measured by gel permeation chromatography (GPC).

[0275] For the measurement by gel permeation chromatography (GPC), an HLC (registered trademark)-8020GPC (TOSOH CORPORATION) was used as the measuring apparatus, three TSKgel (registered trademark) Super Multipore HZ-H (4.6 mm ID × 15 cm, TOSOH CORPORATION) columns were used, and THF (tetrahydrofuran) was used as the eluent. The measurement conditions were a sample concentration of 0.45% by mass, a flow rate of 0.35 ml / min, a sample injection volume of 10 μl, and a measurement temperature of 40°C, with an RI detector used.

[0276] The calibration curve was prepared using eight samples of TOSOH Corporation's "TSK standard, polystyrene": "F-40," "F-20," "F-4," "F-1," "A-5000," "A-2500," "A-1000," and "n-propylbenzene."

[0277] As the resin, resin particles are preferred.

[0278] The resin constituting the resin particles is preferably a water-insoluble resin. The term "water-insoluble" in a water-insoluble resin refers to a property in which the resin dissolves less than 2 g in 100 g of distilled water at 25°C.

[0279] The volume average particle size of the resin particles is preferably 1 nm to 300 nm, more preferably 3 nm to 200 nm, and even more preferably 5 nm to 150 nm.

[0280] In the present invention, the volume average particle size refers to a value measured by a laser diffraction / scattering particle size distribution analyzer.

[0281] As a measuring apparatus, the particle size distribution measuring apparatus "Microtrac MT-3300II" (made by Nikkiso Co., Ltd.) is mentioned, for example.

[0282] The resin particles are preferably at least one selected from the group consisting of acrylic resin particles, ester resin particles, a mixture of acrylic resin particles and ester resin particles, composite particles containing acrylic resin and ester resin, styrene acrylic resin particles, and polyurethane resin particles.

[0283] In the present invention, acrylic resin refers to a polymer (homopolymer or copolymer) containing at least one raw material monomer selected from the group consisting of acrylic acid, acrylic acid derivatives (eg, acrylic esters), methacrylic acid, and methacrylic acid derivatives (eg, methacrylic esters).

[0284] From the viewpoint of further improving the abrasion resistance of the image, the glass transition temperature (Tg) of the resin particles is preferably 50°C to 250°C, more preferably 50°C to 150°C.

[0285] Here, the glass transition temperature (Tg) of the resin particles is measured Tg obtained by actual measurement. For the measurement method of the measured Tg, reference can be made to paragraph 0111 of Japanese Patent Application Laid-Open No. 2015-25076.

[0286] Regarding the resin particles, for example, reference can be made to paragraphs 0038 to 0114 of International Publication No. 2021 / 192720 and paragraphs 0109 to 0120 of Japanese Patent Application Laid-Open No. 2015-25076.

[0287] When the ink contains resin particles, the content of the resin particles in the ink is preferably 1 to 20% by mass, more preferably 2 to 15% by mass, and even more preferably 2 to 10% by mass, relative to the total amount of the ink.

[0288] -additive-

[0289] In the process of producing the ink, at least one additive may be added in addition to the above-mentioned components.

[0290] Examples of the additives include surfactants, water-soluble resins, co-sensitizers, ultraviolet absorbers, antioxidants, anti-fading agents, conductive salts, and basic compounds.

[0291] -Physical properties-

[0292] From the viewpoint of improving discharge stability, the pH (25° C.) of the produced ink is preferably 7 to 10, and more preferably 7.5 to 9.5.

[0293] The pH of the ink is measured at 25° C. using a pH meter, for example, a pH meter manufactured by DKK-TOA CORPORATION (product name “WM-50EG”).

[0294] The viscosity (25° C.) of the produced ink is preferably 0.5 to 30 mPa·s, more preferably 2 to 20 mPa·s, further preferably 2 to 15 mPa·s, and further preferably 3 to 10 mPa·s.

[0295] The viscosity of the ink is measured at 25° C. using a viscometer, for example, a TV-22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0296] The surface tension of the produced ink is preferably 60 mN / m or less, more preferably 20 mN / m to 50 mN / m, and even more preferably 25 mN / m to 40 mN / m.

[0297] The surface tension of the ink is measured at 25° C. using a surface tensiometer, for example, an automatic surface tensiometer manufactured by Kyowa Interface Science Co., Ltd. (product name “CBVP-Z”) by a flat plate method.

[0298] [Image Recording Method]

[0299] The image recording method of the present invention comprises:

[0300] A process for producing an ink by the method for producing an ink of the present invention; and

[0301] Ink application step of applying the ink onto a substrate by an inkjet method.

[0302] The ink produced by the method for producing an ink of the present invention is excellent in discharge stability over time, and therefore, in the image recording method of the present invention, an image with suppressed bleeding can be recorded.

[0303] <Ink Manufacturing Process>

[0304] Regarding the process of producing the ink, reference can be made to the aforementioned method of producing the ink of the present invention.

[0305] <Ink application process>

[0306] The ink application step is a step of applying the ink onto the substrate by an inkjet method.

[0307] (Base material)

[0308] As the substrate, a permeable substrate such as paper, a non-permeable substrate such as a resin substrate (details will be described later), and the like can be used without particular limitation.

[0309] In the present invention, the impermeability of an impermeable substrate refers to a 24-hour water absorption rate of 2.5% or less, as measured according to ASTM D570-98 (2018). The unit "%" for water absorption is based on mass. The water absorption rate is preferably 1.0% or less, and more preferably 0.5% or less.

[0310] Examples of materials for the impermeable substrate include glass, metals (e.g., aluminum, zinc, copper, etc.), and resins (e.g., polyvinyl chloride, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, nylon, acrylic resin, etc.).

[0311] The material of the impermeable substrate is preferably a resin. In other words, the impermeable substrate is preferably a resin substrate.

[0312] Among them, from the viewpoint of versatility, the material of the impermeable substrate is preferably polypropylene, polyethylene, polyethylene terephthalate, nylon, acrylic resin, or polyvinyl chloride.

[0313] The shape of the impermeable substrate is preferably a sheet (film) or flat. Examples of such impermeable substrates include glass plates, metal plates, resin sheets (resin films), plastic-laminated paper, metal-laminated or vapor-deposited paper, and metal-laminated or vapor-deposited plastic sheets (plastic films).

[0314] Examples of the resin-made impermeable substrate include resin sheets (resin films), and specifically, flexible packaging materials for packaging food and the like, and panels for floor guides in retail stores.

[0315] Examples of the impermeable substrate include sheet-shaped (film-shaped) or flat impermeable substrates and also include textiles (woven fabrics) and nonwoven fabrics formed of impermeable fibers.

[0316] The non-permeable substrate may also be subjected to a hydrophilic treatment. Examples of the hydrophilic treatment include, but are not limited to, corona treatment, plasma treatment, flame treatment, heat treatment, abrasion treatment, and light irradiation treatment (e.g., UV treatment). The corona treatment can be performed using, for example, a corona master (product name "PS-10S," manufactured by Shinko Electric & Instrumentation Co., Ltd.). The conditions for the corona treatment may be appropriately selected according to the type of the non-permeable substrate.

[0317] The impermeable substrate may be a transparent impermeable substrate.

[0318] Here, transparency means that the transmittance of visible light with a wavelength of 400 nm to 700 nm is 80% or more (preferably 90% or more).

[0319] When the impermeable substrate is a transparent impermeable substrate, the image can be easily visually recognized through the impermeable substrate from the image non-recording surface side of the impermeable substrate.

[0320] For example, when the non-permeable substrate is a transparent non-permeable substrate, when an image is recorded by sequentially applying a pre-treatment liquid, a non-white ink, and a white ink to the non-permeable substrate, the non-white image (e.g., a pattern image such as text or graphics) with a white image (e.g., a solid image) as a background can be easily visually recognized through the non-permeable substrate from the image non-recording surface side of the non-permeable substrate.

[0321] (Inkjet method)

[0322] There is no particular restriction on the ink ejection method in the inkjet method, and it may be any of the known methods, for example, a charge control method that utilizes electrostatic induction force to eject ink, a drop-on-demand inkjet method (pressure pulse method) that utilizes the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electrical signal into a sound beam and irradiates the ink to eject the ink using radiation pressure, and a thermal inkjet (Bubble Jet (registered trademark)) method that heats the ink to form bubbles and utilizes the generated pressure.

[0323] As an inkjet method, the method described in Japanese Patent Application Laid-Open No. 54-59936 can be particularly effectively utilized. In this inkjet method, the ink undergoes a rapid volume change upon exposure to thermal energy, and the force generated by this change in state causes the ink to be ejected from a nozzle. Another inkjet method that can be applied is the method described in paragraphs 0093 to 0105 of Japanese Patent Application Laid-Open No. 2003-306623.

[0324] The ink is applied to the substrate by the inkjet method by ejecting the ink from the nozzles of the inkjet head.

[0325] Inkjet head types include a reciprocating type, in which a short serial head records while scanning across the width of the recording medium, and a line type, in which a line head is used with recording elements arranged across the entire area of ​​one side of the recording medium.

[0326] In the linear method, the image can be recorded across the entire surface of the recording medium by scanning the recording medium in a direction intersecting the arrangement of the recording elements. The linear method eliminates the need for a transport system, such as a carriage, that enables scanning with a short printhead in the reciprocating method. Furthermore, compared to the reciprocating method, the linear method eliminates the need for carriage movement and complex scanning control of the recording medium; only the recording medium needs to be moved. Therefore, the linear method can achieve faster image recording than the reciprocating method.

[0327] However, the inkjet head type in the image recording method of the present invention is not limited to the line type, and may be a shuttle type. Even when any type is employed, the effects obtained by the image recording method of the present invention described above are exhibited.

[0328] The ink is preferably applied using an inkjet head having a resolution of 300 dpi or higher (more preferably 600 dpi or higher, and even more preferably 800 dpi or higher). Here, dpi is an abbreviation for dots per inch, and 1 inch is 2.54 cm.

[0329] From the viewpoint of obtaining high-definition images, the amount of ink droplets ejected from the nozzles of the inkjet head is preferably 1 pL (picoliter) to 10 pL, and more preferably 1.5 pL to 6 pL.

[0330] The ink application step may include a step of heating and drying the ink applied to the substrate, or may not include a step of heating and drying the ink.

[0331] In the case of a process including heating and drying the ink, there is no particular limitation on the method of heating and drying, but examples thereof include infrared (IR) drying, warm air drying (e.g., a dryer, etc.), heating and drying using a heating device (e.g., a heater, a hot plate, a heating furnace, etc.), and the like.

[0332] As the heat drying method, a method of combining two or more of these may be used.

[0333] Heat drying can be performed by heating the ink from at least one of the image recording surface side and the non-image recording surface side of the substrate.

[0334] When the step of heat-drying the ink is included, the heating temperature during heat-drying the ink is preferably 35° C. or higher, more preferably 40° C. or higher, further preferably 50° C. or higher, and further preferably 60° C. or higher.

[0335] The upper limit of the heating temperature is not particularly limited, but is preferably 100°C, more preferably 90°C.

[0336] When the step of heating and drying the ink is included, the heating time for heating and drying the ink is not particularly limited, but is preferably 1 to 180 seconds, more preferably 1 to 120 seconds, and even more preferably 1 to 60 seconds.

[0337] In the ink applying step, two or more inks (for example, two or more colors of ink) may be applied to the substrate.

[0338] When two or more inks are applied to the substrate, at least one of the two or more inks may be an ink produced by the method for producing an ink of the present invention.

[0339] When two or more inks are applied to the substrate, the two or more inks may be applied in a superimposed manner.

[0340] By applying two or more inks in a superimposed manner on a substrate, a multi-color image is recorded.

[0341] The ink produced by the method for producing an ink of the present invention has excellent ejection stability over time, and therefore, bleeding (hereinafter also referred to as multi-color bleed) is suppressed in recorded multi-color images.

[0342] Hereinafter, when two or more inks are applied to a substrate, the first ink (i.e., the first order) applied to the substrate is sometimes referred to as the first ink, and the nth ink (i.e., the nth order) applied to the substrate is sometimes referred to as the nth ink (here, n is an integer greater than 2).

[0343] <Step of applying pretreatment liquid>

[0344] An embodiment of the image recording method of the present invention includes a step of applying a pretreatment liquid containing water and a coagulant to the impermeable substrate prior to the ink application step. In this case, in the ink application step, ink is applied to the area of ​​the impermeable substrate to which the pretreatment liquid has been applied.

[0345] (Pretreatment liquid)

[0346] -water-

[0347] The pretreatment liquid contains water.

[0348] The water content is preferably 50% by mass or more, more preferably 60% by mass or more, based on the total amount of the pretreatment liquid.

[0349] The upper limit of the water content also depends on the amounts of other components, but is preferably 90% by mass or less, more preferably 80% by mass or less, based on the total amount of the pretreatment liquid.

[0350] - Coagulant -

[0351] The pretreatment solution contains at least one coagulant.

[0352] The coagulant in the pre-treatment liquid aggregates the components of the ink on the non-permeable substrate, thereby improving the image quality.

[0353] The coagulant is preferably at least one selected from the group consisting of organic acids and polyvalent metal compounds.

[0354] Preferred examples of the coagulant include those described in paragraphs 0122 to 0130 of International Publication No. 2020 / 195360.

[0355] Hereinafter, preferred embodiments of each of the organic acid, the polyvalent metal compound, the metal complex, and the cationic polymer that can be used as the coagulant will be described.

[0356] --Organic acid--

[0357] Examples of the organic acid include organic compounds having an acidic group.

[0358] Examples of the acidic group include a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, and a carboxyl group.

[0359] Among them, from the viewpoint of the aggregation speed of the ink, the acidic group is preferably a phosphoric acid group or a carboxyl group, and more preferably a carboxyl group.

[0360] It is preferred that at least a part of the acidic groups be dissociated in the pretreatment liquid.

[0361] Examples of the organic compound having a carboxyl group include (meth)acrylic acid, poly(meth)acrylic acid, acetic acid, formic acid, benzoic acid, glycolic acid, malonic acid, malic acid (preferably, DL-malic acid), maleic acid, succinic acid, glutaric acid, pimelic acid, adipic acid, fumaric acid, citric acid, tartaric acid, phthalic acid, 4-methylphthalic acid, lactic acid, pyrrolidonecarboxylic acid, pyronecarboxylic acid, pyrrolecarboxylic acid, furancarboxylic acid, pyridinecarboxylic acid, coumaric acid, thiophenecarboxylic acid, and nicotinic acid.

[0362] Among them, from the viewpoint of the aggregation speed of the ink, the organic compound having a carboxyl group is preferably a divalent or higher-valent carboxylic acid (hereinafter also referred to as a polyvalent carboxylic acid), and more preferably a dicarboxylic acid.

[0363] Specifically, the polycarboxylic acid is preferably malonic acid, malic acid, maleic acid, succinic acid, glutaric acid, pimelic acid, adipic acid, fumaric acid, tartaric acid, 4-methylphthalic acid or citric acid, and more preferably malonic acid, malic acid, tartaric acid, succinic acid, glutaric acid, pimelic acid, adipic acid or citric acid.

[0364] The organic acid preferably has a low pKa (e.g., 1.0 to 5.0). This reduces the surface charge of particles such as pigments and resin particles in the ink stabilized by weakly acidic functional groups such as carboxyl groups by contact with the organic acid with a lower pKa, thereby reducing dispersion stability.

[0365] The organic acid preferably has a low pKa, high solubility in water, and a valence of 2 or more. Furthermore, the organic acid more preferably has a high buffering capacity in a pH range lower than the pKa of the functional group (e.g., carboxyl group) that stabilizes particle dispersion in the ink.

[0366] --Polyvalent Metal Compounds--

[0367] Examples of the polyvalent metal compound include polyvalent metal salts.

[0368] Examples of the polyvalent metal salt include organic acid polyvalent metal salts and inorganic acid polyvalent metal salts.

[0369] As the organic acid polyvalent metal salt, polyvalent metal salts of the above-mentioned organic acids (for example, formic acid, acetic acid, lactic acid, benzoic acid, etc.) are preferred.

[0370] As the inorganic acid polyvalent metal salt, a nitrate polyvalent metal salt, a hydrochloric acid polyvalent metal salt or a thiocyanate polyvalent metal salt is preferable.

[0371] Examples of polyvalent metal salts include salts of alkaline earth metals of Group 2 of the periodic table (e.g., magnesium and calcium), salts of transition metals of Group 3 of the periodic table (e.g., lanthanum), salts of metals of Group 13 of the periodic table (e.g., aluminum), and salts of lanthanides (e.g., neodymium).

[0372] The polyvalent metal salt is preferably a calcium salt, a magnesium salt or an aluminum salt, more preferably a calcium salt or a magnesium salt.

[0373] The polyvalent metal compound is preferably an organic acid polyvalent metal salt, more preferably an organic acid calcium salt or an organic acid magnesium salt.

[0374] It is preferred that at least a portion of the polyvalent metal compound is dissociated into polyvalent metal ions and counter ions in the pretreatment liquid.

[0375] The content of the coagulant in the pretreatment liquid is preferably 0.1 to 40% by mass, more preferably 0.1 to 30% by mass, further preferably 1 to 20% by mass, and even more preferably 1 to 10% by mass, relative to the total amount of the pretreatment liquid.

[0376] -Resin-

[0377] The pretreatment liquid contains at least one resin.

[0378] The resin in the pretreatment liquid contributes to the film-forming property of the pretreatment liquid (ie, the formability of the pretreatment liquid film).

[0379] As the resin in the pre-treatment liquid, the same resin as that in the ink (for example, resin particles) can be used.

[0380] There is no particular limitation on the content of the resin in the pretreatment liquid.

[0381] The content of the resin is preferably 0.5% by mass to 30% by mass, more preferably 1% by mass to 20% by mass, and particularly preferably 1% by mass to 15% by mass, relative to the total amount of the pretreatment liquid.

[0382] -Water-soluble organic solvents-

[0383] The pretreatment liquid may contain at least one water-soluble organic solvent.

[0384] As the water-soluble organic solvent in the pre-treatment liquid, the same water-soluble organic solvent as that which can be contained in the ink can be used.

[0385] -additive-

[0386] The pretreatment liquid may contain additives such as a surfactant, a water-soluble resin, a co-sensitizer, an ultraviolet absorber, an antioxidant, an anti-fading agent, a conductive salt, and an alkaline compound as needed.

[0387] -Physical properties-

[0388] The pH (25° C.) of the pretreatment liquid is preferably 2.0 to 7.0, more preferably 2.0 to 4.0. The pH of the pretreatment liquid is measured by the same method as the pH of the ink.

[0389] From the perspective of coating properties, the viscosity of the pretreatment liquid is preferably 0.5 to 10 mPa·s, more preferably 1 to 5 mPa·s. The viscosity is measured at 25°C using a viscometer. The viscosity of the pretreatment liquid is measured using the same method as the viscosity of the ink.

[0390] The surface tension of the pretreatment liquid is preferably 60 mN / m or less, more preferably 20 mN / m to 50 mN / m, and even more preferably 30 mN / m to 45 mN / m. The surface tension is measured at 25°C. The surface tension of the pretreatment liquid is measured using the same method as the surface tension of the ink.

[0391] (Method of applying pretreatment liquid)

[0392] The method for applying the pretreatment liquid is not particularly limited, and examples thereof include known methods such as a coating method, a dipping method, and an inkjet recording method.

[0393] Examples of the coating method include known methods using a bar coater, extrusion die coater, air knife coater, blade coater, rod coater, knife coater, extrusion coater, reverse roll coater, and the like.

[0394] The application of the pretreatment liquid is preferably performed by a coating method.

[0395] The image recording method of the present invention may include, after the pre-treatment liquid applying step, a step of drying the pre-treatment liquid applied to the substrate.

[0396] The step of applying the pre-treatment liquid may include a step of drying the pre-treatment liquid applied to the non-permeable substrate.

[0397] The method for drying the pretreatment liquid is not particularly limited, and for example, the same method as exemplified as the method for drying the ink described later can be applied.

[0398] The preferred ranges of drying conditions (for example, heating temperature and heating time) for the pre-treatment liquid are the same as the preferred ranges of drying conditions for the ink described later.

[0399] <Example of an Image Recording Device>

[0400] Figure 1 FIG. 1 is a diagram schematically showing an example of an image recording apparatus used in the image recording method of the present invention.

[0401] like Figure 1 As shown, one embodiment of the image recording device is an example of an inkjet recording device having a conveying mechanism for conveying a resin substrate in a roll-to-roll manner, and the inkjet recording device is a device as follows: a non-permeable substrate A1 in the shape of a long film wound into a roll is unwound by an unwinding device R1, and the unwound non-permeable substrate A1 is conveyed in the direction of the hollow arrow under the application of tension, so that it passes through the pre-treatment liquid imparting device P1, the pre-treatment liquid drying area DP1, the first inkjet head IJ1, the first drying area D1, the second inkjet head IJ2 and the second drying area D2 in sequence, and finally, it is wound by a winding device R2 including a winding core under the application of tension P.

[0402] The impermeable substrate A1 is conveyed while being tensioned and wound while being tensioned P. The tension during conveyance may be the same as or different from the tension P during winding. Furthermore, the tension may vary depending on the position in the conveyance direction or may be the same.

[0403] The image recording apparatus according to one embodiment may include a tension adjustment mechanism for adjusting the tension applied to the impermeable substrate.

[0404] As tension adjustment mechanisms, there can be cited a magnetic powder brake provided in the unwinding device R1 and / or the winding device R2, a tension roller provided midway along the conveying path, a control device (e.g., a tension controller) that controls various tensions by adjusting various conditions of the image recording device, etc.

[0405] Furthermore, the image recording apparatus according to one embodiment may include a tension measuring mechanism (for example, a tensiometer) for measuring the tension of the non-permeable substrate.

[0406] in addition, Figure 1 This is a conceptual diagram, and thus the conveyance path of the impermeable substrate A1 is simplified. The diagram shows the impermeable substrate A1 being conveyed in one direction. However, it goes without saying that in reality, the conveyance path of the impermeable substrate A1 may be tortuous.

[0407] As a conveying method of the impermeable substrate A1, various web conveying methods such as a drum and a roll can be appropriately selected.

[0408] Relative to the unwinding device R1 for unwinding the non-permeable substrate A1, on the downstream side of the conveying direction of the non-permeable substrate A1, the pretreatment liquid applying device P1, the pretreatment liquid drying area DP1, the first inkjet head IJ1, the first drying area D1, the second inkjet head IJ2 and the second drying area D2 are arranged in sequence from the upstream side of the conveying direction of the non-permeable substrate A1.

[0409] The pre-treatment liquid applying device P1 , the first inkjet head IJ1 , and the second inkjet head IJ2 respectively apply the pre-treatment liquid, apply the first ink, and apply the second ink.

[0410] At this time, at least one of heating and drying the pretreatment liquid in the pretreatment liquid drying zone DP1 , heating and drying the first ink in the first drying zone D1 , and heating and drying the second ink in the second drying zone D2 can be performed.

[0411] In the first drying zone D1 , in addition to heating and drying the first ink, the pre-treatment liquid can also be heated and dried substantially.

[0412] In the second drying zone D2 , in addition to heating and drying the second ink, heating and drying the pre-treatment liquid and / or heating and drying the first ink can also be performed.

[0413] Furthermore, if the resin substrate is passed through each drying zone while the temperature of each drying zone is set to room temperature, heating and drying can be omitted.

[0414] A surface treatment unit (not shown) for performing a surface treatment (preferably a corona treatment) on at least one of the front and back surfaces of the impermeable substrate A1 may be provided upstream of the pretreatment liquid applying device P1.

[0415] Furthermore, a cooling zone for cooling the recorded multi-color image may be provided downstream of the second drying zone D2.

[0416] The first inkjet head IJ1 and the second inkjet head IJ2 may be reciprocating heads, but from the perspective of increasing the speed of image recording, they are preferably line heads having a plurality of ejection ports (nozzles) arranged in the width direction of the long film-shaped non-permeable substrate A1.

[0417] The number of each of the first inkjet head IJ1 and the second inkjet head IJ2 may be only one or a plurality.

[0418] As an example of a combination of the first inkjet head IJ1 and the second inkjet head IJ2, for example, the following combination can be cited: the first inkjet head IJ1 is four inkjet heads corresponding to the four colors of cyan, magenta, yellow and black (Note: these four inkjet heads are arranged along the conveying direction of the resin substrate), and the second inkjet head IJ2 is one inkjet head corresponding to white.

[0419] Furthermore, as another example of the combination of the first inkjet head IJ1 and the second inkjet head IJ2, the first inkjet head IJ1 can be an inkjet head corresponding to white, and the second inkjet head IJ2 can be four inkjet heads corresponding to the four colors of cyan, magenta, yellow and black (note: these four inkjet heads are arranged along the conveying direction of the substrate).

[0420] In inkjet recording using the image recording apparatus according to one embodiment,

[0421] First, the impermeable substrate A1 in the form of a long film wound into a roll is unwound by the unwinding device R1.

[0422] The unwound impermeable substrate A1 is conveyed in the direction of the hollow arrow under tension.

[0423] The pretreatment liquid applying device P1 applies the pretreatment liquid to the conveyed non-permeable substrate A1.

[0424] Then, the pre-treatment liquid is dried in the pre-treatment liquid drying area DP1 as needed.

[0425] Next, the first ink (ie, either the non-white ink or the white ink) is applied by the first inkjet head IJ1.

[0426] Next, the first ink is dried in the first drying zone D1 as needed.

[0427] Next, the second ink (ie, the other of the non-white ink and the white ink) is applied by the second inkjet head IJ2.

[0428] Next, the second ink is dried in the second drying zone D2 as needed.

[0429] Thus, a multi-color image including a first image derived from the first ink (i.e., one of the non-white image and the white image) and a second image derived from the second ink (i.e., the other of the non-white image and the white image) can be obtained.

[0430] Next, the obtained multi-color image is cooled as needed, and finally, the non-permeable substrate A1 with the multi-color image is wound with tension P applied thereto by a winding device R2 including a winding core.

[0431] The image recording device involved in one embodiment may include other inkjet heads (for example, a third inkjet head for the third ink, a fourth inkjet head for the fourth ink, and an inkjet head for white ink, etc.) on the downstream side of the second inkjet head IJ2 and upstream side of the second drying area D2 as needed.

[0432] Example

[0433] Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples unless it departs from the gist of the present invention.

[0434] [Examples 1 to 7, Comparative Examples 1 to 5]

[0435] <Preparatory Step (Synthesis of Polymer Dispersant N)>

[0436] The polymer dispersants N of Examples 1 to 6 and Comparative Examples 1 to 3 were synthesized as follows.

[0437] Into a reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer, 153.5 parts by mass of tripropylene glycol monomethyl ether (product name "MFTG", manufactured by Nippon Nyukazai Co., Ltd.) as a reaction solvent was charged, and then the interior of the reaction vessel was substituted with nitrogen.

[0438] Next, the interior of the reaction vessel was heated to 85°C, and a mixture of MFTG (76.8 parts by mass) as a reaction solvent, raw material monomers of the types and mass ratios shown in Table 1 (a total of 100 parts by mass), and V-601 (manufactured by FUJIFILM Wako Pure Chemical Corporation) (3.0 parts by mass) as a polymerization initiator was added dropwise thereto over 3 hours to carry out a polymerization reaction. After completion of the dropwise addition, the reaction was further carried out at 85°C for 3 hours to complete the polymerization, thereby obtaining a solution containing polymeric dispersant N.

[0439] Table 1 shows the weight average molecular weight of the obtained polymer dispersant N.

[0440] The polymer dispersant N of Example 7 was synthesized as follows.

[0441] [First reaction]

[0442] A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, a dropping funnel, and a stirrer was charged with 61 parts by mass of maleic anhydride as a monomer mixture, 87 parts by mass of 1-hexadecene as an α-olefin, and 63 parts by mass of the following "UNILUBE PKA-5013" as an allylated polyether 1. Furthermore, 100 parts by mass of methyl ethyl ketone (MEK) and 0.5 parts by mass of octyl thioglycolate as a chain transfer agent were added. After nitrogen substitution, the reaction vessel was heated to 105° C. while stirring. A mixture of 2.0 parts by mass of dimethyl azobisisobutyrate (manufactured by FUJIFILM Wako Pure Chemical Corporation, product name: V-601) as a free radical polymerization initiator and 5 parts by mass of MEK was added dropwise over 1 hour. Thereafter, a mixture of V-601 (5 parts by mass) and MEK (12 parts by mass) was added dropwise over 6 hours while stirring at 85°C, and the mixture was reacted for 1 hour while maintaining the temperature at 85°C to obtain a polymer having maleic anhydride as anhydride groups.

[0443] [Second reaction]

[0444] Next, 37 parts by mass of isopropyl alcohol and 0.1 parts by mass of a diazabicyclo catalyst were added, and the mixture was stirred for 6 hours while maintaining the temperature at 85°C to allow the maleic anhydride to undergo ring-opening and half-esterification. The solvent of the resulting product was removed by reduced pressure distillation, and the dispersant solids concentration was adjusted to 35% by mass using MFTG, thereby obtaining a solution containing polymeric dispersant N.

[0445] Table 1 shows the weight average molecular weight of the obtained polymer dispersant N.

[0446] The details of the raw material monomers shown in Table 1 are as follows.

[0447] MAA…Methacrylic acid

[0448] ·C18MA……octadecyl methacrylate

[0449] IBOMA…Isobornyl methacrylate

[0450] ·PDEGA…phenoxydiethylene glycol acrylate

[0451] ·MMA…methyl methacrylate

[0452] Allylated polyether 1: "UNILUBE (registered trademark) KPA-5013" manufactured by NOF CORPORATION (polyethylene glycol-polypropylene glycol-allyl ether random polymer)

[0453] α-Olefin: 1-hexadecene (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0454] Neutralization process

[0455] After the solution containing the polymer dispersant N obtained above was cooled to room temperature, an aqueous NaOH solution was added thereto as an aqueous solution of a neutralizing base to neutralize 80 mol% of the carboxyl groups in the polymer dispersant N. Thus, a solution containing the polymer dispersant A (i.e., the polymer dispersant obtained by neutralizing the polymer dispersant N) having a neutralization degree ND1 of 80% was obtained.

[0456] The solid content concentration in the obtained solution was adjusted to 30% by mass, thereby obtaining an MFTG solution of the polymer dispersant A (30% by mass solid content concentration).

[0457] In addition, NaOH aqueous solution was added according to the neutralization degree ND1 of each example in Table 1.

[0458] Table 1 shows the acid value AV1 (mgKOH / g) of the polymer dispersant A.

[0459] In addition, the acid value is related to the unneutralized acid group (-COOH group) and the neutralized acid group (-CO - Since the acid value is related to the total amount of the polymer (in the presence of a base), the neutralization step does not change the acid value. Therefore, the acid value AV1 (mgKOH / g) of the polymer dispersant A is the same as the acid value (mgKOH / g) of the polymer dispersant N.

[0460] <Dispersion process>

[0461] The mixture of the following composition was uniformly pre-dispersed and then dispersed for 3 hours using a bead mill (Ashizawa Finetech Ltd. Star Mill, bead diameter: 0.3 mm, zirconia beads). This yielded an uncrosslinked dispersion A in which a magenta pigment was dispersed by a polymer dispersant A.

[0462] -composition-

[0463] Pigment Red 122 (hereinafter, also referred to as "PR-122") (magenta pigment as a quinacridone pigment)

[0464] ...120.0 parts by mass

[0465] MFTG solution of polymer dispersant A (30% solid content by mass)

[0466] ...120.0 parts by mass

[0467] ·MFTG

[0468] ...6.0 parts by mass

[0469] ·water

[0470] ...230.0 parts by mass

[0471] <Acid Addition Process>

[0472] The uncrosslinked dispersion A was diluted with ion-exchanged water so that the pigment concentration became 15% by mass, thereby obtaining an uncrosslinked dispersion A diluted liquid.

[0473] While stirring the obtained uncrosslinked dispersion A dilution (500 parts by mass), a mixture of a 1 mol / L aqueous hydrochloric acid solution (19.4 parts by mass) and ultrapure water (225.2 parts by mass) was added over 5 minutes to reduce the degree of neutralization of the polymer dispersant A in the uncrosslinked dispersion A dilution from 80% to 60%. The mixture was then stirred for 60 minutes using a magnetic stirrer. This yielded an uncrosslinked dispersion B in which a magenta pigment was dispersed using a polymer dispersant B having a neutralization degree ND2 of 60% (i.e., a polymer dispersant obtained by reducing the neutralization degree of the polymer dispersant A to 60%).

[0474] <Cross-linking process>

[0475] Next, the mixture of the following composition was reacted at 70° C. for 6 hours and cooled to 25° C., thereby crosslinking the polymer dispersant B in the uncrosslinked dispersion B with the crosslinking agent, thereby obtaining a crosslinked dispersion (i.e., pigment dispersion) containing the polymer dispersant C (i.e., the polymer dispersant obtained by crosslinking the polymer dispersant B) and the magenta pigment.

[0476] -composition-

[0477] Uncrosslinked dispersion B

[0478] ...744.6 parts by mass

[0479] "Denacol EX-321" (manufactured by Nagase ChemteX Corporation) (trimethylolpropane polyglycidyl ether; crosslinking agent)

[0480] ...5.4 parts by mass

[0481] The acid value AV2 (mgKOH / g) of the polymer dispersant C is shown in Table 1.

[0482] In the cross-linking process, the unneutralized acid groups (-COOH groups) and the neutralized acid groups (-CO - A crosslinked structure is formed in the polymer compound by reacting at least one of the epoxy groups (specifically, the epoxy group in the structure of the glycidyl group) with the epoxy group of the crosslinking agent.

[0483] In this manner, in the cross-linking step, at least one of the unneutralized acid groups and the neutralized acid groups is consumed to form cross-links, and thus the acid value of the polymer dispersant is reduced by the cross-linking step.

[0484] Therefore, in principle, the acid value AV2 (mgKOH / g) of the polymer dispersant C becomes a value lower than the acid value AV1 (mgKOH / g) of the polymer dispersant A.

[0485] Centrifugal treatment and filtration of pigment dispersions

[0486] The cross-linked dispersion obtained above (ie, pigment dispersion) was centrifuged at 7000 G for 20 minutes using a centrifuge to remove coarse particles.

[0487] Next, the cross-linked dispersion subjected to the centrifugal treatment was filtered using a LABO-PURE filter (0.5 μm) manufactured by ROKI Co., Ltd. to further remove coarse particles.

[0488] The filtered cross-linked dispersion was then passed through an ultrafiltration device (cross-flow ultrafilter (UF), manufactured by Sartorius) equipped with a polyethersulfone (PESU) membrane (pore size: 0.1 μm) at a flow rate of 600 mL per minute for ultrafiltration. The liquid temperature was adjusted to 25°C, and ultrafiltration was performed 10 times the volume of the added liquid.

[0489] Thereafter, ion-exchanged water was added so that the concentration of the magenta pigment became 15% by mass, thereby obtaining a pigment dispersion 1 (magenta pigment concentration 15% by mass) for preparing the following ink.

[0490] <Preparation of the first ink>

[0491] A mixture having the following composition was stirred for 60 minutes using a magnetic stirrer and filtered using a LABO-PURE filter (0.5 μm) manufactured by ROKI Co., Ltd. to obtain a magenta ink as a first ink.

[0492] - Composition of the first ink -

[0493] Pigment dispersion 1

[0494] ...the content of magenta pigment is 5.5% by mass

[0495] Propylene glycol monomethyl ether (PGmME) (water-soluble organic solvent)

[0496] ...3% by mass

[0497] Propylene glycol (PG) (other water-soluble organic solvents)

[0498] ...20% by mass

[0499] Neocryl A-1105 (acrylic resin particle dispersion) (manufactured by Koninklijke DSM NV)

[0500] ...the content of the resin particles is 3.4% by mass

[0501] OLFINE E1010 (acetylene glycol surfactant manufactured by Nissin Chemical Co., Ltd.)

[0502] ...1.0% by mass

[0503] BYK3450 (silicone surfactant manufactured by BYK)

[0504] ...1.0% by mass

[0505] PVPK15 (polyvinyl pyrrolidone K15)

[0506] ...0.15% by mass

[0507] ST-XS (colloidal silica dispersion) (manufactured by Nissan Chemical Corporation)

[0508] ...the content of colloidal silica particles is 0.05% by mass

[0509] ·water

[0510] ...the remaining amount in the total ink to make 100% by mass

[0511] <Preparation of the Second Ink>

[0512] The second ink was prepared in the same manner as the first ink except that the type of pigment was changed to a cyan pigment (Pigment Blue 15:3).

[0513] <Preparation of pretreatment solution>

[0514] The following components were mixed to prepare a pretreatment liquid having the following composition.

[0515] -Composition of pretreatment solution-

[0516] Calcium acetate (coagulant)

[0517] ...0.2% by mass

[0518] Calcium formate (coagulant)

[0519] ...1.7% by mass

[0520] Calcium lactate (coagulant)

[0521] ...2.2% by mass

[0522] Propylene glycol (solvent)

[0523] ...2.0% by mass

[0524] OLFINE E1010 (manufactured by Nissin Chemical Co., Ltd.) [Surfactant]

[0525] ...0.5% by mass

[0526] SUPERFLEX 500M (DKS Co., Ltd.) [Aqueous dispersion of urethane resin particles]

[0527] ...9.3% by mass

[0528] Ultrapure water

[0529] ...the remaining amount of the pretreatment liquid as a whole becomes 100% by mass

[0530] <Preparation of image recording equipment>

[0531] As an image recording device for evaluation, a Figure 1 The image recording device shown.

[0532] As the pretreatment liquid applying apparatus P1, a gravure coater was used.

[0533] The drying method in the pretreatment liquid drying zone DP1 is set to warm air drying.

[0534] An inkjet head for ejecting the first ink is arranged as the first inkjet head IJ1 , and an inkjet head for ejecting the second ink is arranged as the second inkjet head IJ2 .

[0535] It is directly passed through the first drying zone D1.

[0536] The drying method in the second drying zone D2 is warm air drying.

[0537] An air cooling zone (not shown) is provided between the second drying zone D2 and the winding device R2.

[0538] As the first inkjet head IJ1 and the second inkjet head IJ2, both use 1200 dpi (dot per inch, 1 inch is 2.54 cm) / 20 inch width piezoelectric full array heads (total number of nozzles: 2048).

[0539] The driving frequency of the first inkjet head IJ1 and the second inkjet head IJ2 was set to 30 kHz.

[0540] <Image Record>

[0541] Image recording was performed using the above-mentioned image recording device.

[0542] The above-mentioned pre-treatment liquid, the first ink, and the second ink are loaded in the image recording device.

[0543] As the non-permeable substrate, an OPP film (product name "PYREN film-OT", manufactured by Toyobo Co., Ltd., thickness 25 μm) was used.

[0544] First, the impermeable substrate is unwound by the unwinding device R1 and conveyed under tension, and the pretreatment liquid is applied to the conveyed impermeable substrate by the gravure coater as the pretreatment liquid applying device P1.

[0545] Next, the pre-treatment liquid is dried in the pre-treatment liquid drying zone DP1.

[0546] Next, the first ink is applied in a solid image form by the first inkjet head IJ1 to the area of ​​the non-permeable substrate to which the pre-treatment liquid has been applied, and then directly passes through the first drying zone D1.

[0547] Next, the second inkjet head IJ2 applies the second ink in a solid image onto the area of ​​the non-permeable substrate to which the pre-treatment liquid and the first ink have been applied.

[0548] Next, the second ink is dried in the second drying zone D2.

[0549] By the above operation, a multi-color image (solid image) having a structure in which a solid image derived from the second ink was superimposed on a solid image derived from the first ink was recorded on an impermeable substrate having a length of 100 m, thereby obtaining an image record.

[0550] Next, the obtained image recorded material is air-cooled and then wound up by a winding device R2 including a winding core, thereby obtaining a roll of the image recorded material.

[0551] The amount of pretreatment liquid applied was set to 1.7 g / m 2 .

[0552] The drying conditions of the pretreatment liquid were set at 40° C. and 3 seconds.

[0553] The drying conditions for the second ink were set to 70° C. and 20 seconds.

[0554] <Evaluation>

[0555] The first ink and the second ink obtained above were evaluated as follows.

[0556] The results are shown in Table 1.

[0557] (Ink ejection stability after time)

[0558] As the first ink and the second ink, each of the inks heated at 80° C. for one day after ink preparation was used, and the image was recorded as described above to obtain a roll of image recorded material.

[0559] The roll of the obtained image recorded material was unwound, and an image corresponding to the width of the nozzle was visually observed at a distance of 100 m to check the number of streaks generated along the conveyance direction of the non-permeable substrate in the solid image of the image recorded material.

[0560] Based on the confirmed results, the ejection stability of the ink after a period of time was evaluated according to the following evaluation criteria.

[0561] In the following evaluation criteria, the most excellent ink ejection stability after the passage of time was rated as A.

[0562] --Evaluation criteria for ink ejection stability over time--

[0563] A: The number of streaks is 0 or more and less than 10.

[0564] B: There are 10 or more and less than 20 streaks.

[0565] C: The number of streaks is 20 or more and less than 30.

[0566] D: There are 30 or more stripes.

[0567] -Evaluation of multiple color penetration-

[0568] In addition to ejecting the second ink in the form of a text image, a multi-color image is recorded under the same conditions as the above image recording. The multi-color image has a structure in which a text image based on the second ink is recorded on a solid image based on the first ink. The text image based on the second ink is set to Figure 2 The text image was recorded in 6pt, 8pt, 10pt, and 12pt sizes.

[0569] The character images in the obtained multi-color images were visually observed, and image bleeding was evaluated based on the following evaluation criteria.

[0570] --Evaluation criteria for multiple color penetration--

[0571] A: The text image is not distorted in all sizes of 6pt, 8pt, 10pt and 12pt.

[0572] B: There is no text image distortion at the 8pt, 10pt, and 12pt sizes, but distortion is observed at the 6pt size.

[0573] C: There is no text image distortion at 10pt and 12pt sizes, but distortion is observed at 6pt and 8pt sizes.

[0574] D: There is no distortion of the text image at the 12pt size, but distortion is observed at the 6pt, 8pt, and 10pt sizes. Alternatively, distortion of the text image is observed at all sizes: 6pt, 8pt, 10pt, and 12pt.

[0575]

[0576] As shown in Table 1, compared with the comparative examples, in the embodiments corresponding to the method for manufacturing a pigment dispersion, the method for manufacturing an ink, and the image recording method of the present invention, the ink has excellent ejection stability over time, and color bleeding (i.e., multi-color penetration) in multi-color images is suppressed.

[0577] Here, each embodiment uses a polymer dispersant A having a neutralization degree ND1 of less than 100% and an acid value of AV1 to disperse the pigment, then reduces the neutralization degree of the polymer dispersant A in the uncrosslinked dispersion by adding an acid to obtain a polymer dispersant B having a neutralization degree ND2, then crosslinks the polymer dispersant B in the uncrosslinked dispersion to obtain a polymer dispersant C having an acid value of AV2, thereby producing an example of a pigment dispersion, and the following inequalities (1) and (2) are satisfied.

[0578] 0.60≤value(1)≤2.00…inequality(1)

[0579] 0.30≤value(2)≤5.00…Inequality(2)

[0580] The polymer dispersant A is a polymer dispersant obtained by neutralizing a part of the acid groups contained in the polymer dispersant N.

[0581] The polymer dispersant N comprises a structural unit L and a structural unit A, wherein the proportion of the structural unit L is 20% by mass or more, the structural unit L is derived from at least one selected from the group consisting of an alkyl (meth)acrylate containing an alkyl group having 10 or more carbon atoms and an α-olefin containing an alkyl group having 10 or more carbon atoms, and the structural unit A contains an acid group.

[0582] On the other hand, Comparative Example 1 is an example that does not satisfy "0.60 ≤ value (1)" in inequality (1).

[0583] Comparative Examples 2 and 3 are examples in which the value (2) is 0, that is, examples in which all the acid groups contained in the polymer dispersant N are neutralized and the degree of neutralization ND1 is 100%.

[0584] Comparative Example 3 is an example in which no acid was added for reducing the degree of neutralization (neutralization degree ND1 = neutralization degree ND2 = 100%).

[0585] In Comparative Example 2, “0.30 ≤ value (2)” in inequality (2) is not satisfied.

[0586] In Comparative Example 3, "0.60 ≤ value (1)" in inequality (1) is not satisfied. With respect to inequality (2), value (2) becomes "0 / 0", so it cannot be said that inequality (2) is not satisfied either.

[0587] Comparative Example 4 is an example that does not satisfy "value (1) ≤ 2.00" in inequality (1).

[0588] Comparative Example 5 is an example in which the proportion of the structural unit L in the polymer dispersant N is less than 20% by mass.

Claims

1. A method for producing a pigment dispersion, comprising: a preparation step of preparing a polymer dispersant N, the polymer dispersant N comprising a structural unit L and a structural unit A, wherein the proportion of the structural unit L is 20% by mass or greater, the structural unit L is derived from at least one selected from the group consisting of an alkyl (meth)acrylate containing an alkyl group having 10 or more carbon atoms and an α-olefin containing an alkyl group having 10 or more carbon atoms, and the structural unit A contains an acid group; a neutralization step of neutralizing a portion of the acid groups contained in the polymer dispersant N to obtain a polymer dispersant A having a neutralization degree of less than 100%; a dispersing step of dispersing the pigment in an aqueous medium using the polymer dispersant A to obtain an uncrosslinked dispersion; an acid adding step of adding an acid to the uncrosslinked dispersion to reduce the neutralization degree of the polymer dispersant A in the uncrosslinked dispersion to obtain a polymer dispersant B; and a cross-linking step of cross-linking the polymer dispersant B in the uncross-linked dispersion after the acid addition step to obtain a polymer dispersant C, The acid value of the polymer dispersant A in mgKOH / g, i.e., AV1, the acid value of the polymer dispersant C in mgKOH / g, i.e., AV2, the neutralization degree of the polymer dispersant A in %, i.e., ND1, and the neutralization degree of the polymer dispersant B in %, i.e., ND2, satisfy the following inequality (1) and the following inequality (2). 0.60≤0.01×AV1×(ND1-ND2) / (AV1-AV2)≤2.00 Inequality (1), 0.30≤(100-ND1) / (ND1-ND2)≤5.00Inequality (2).

2. The method for producing a pigment dispersion according to claim 1, wherein The AV1 and the AV2 satisfy the following inequality (3): 120≤(1.2×AV2)≤AV1≤330 Inequality (3).

3. The method for producing a pigment dispersion according to claim 1, wherein In the polymer dispersant N prepared in the preparation step, the mass ratio of the structural unit A to the structural unit L, that is, the A / L ratio, is 0.5 to 2.

0.

4. The method for producing a pigment dispersion according to claim 1, wherein The structural unit A is a structural unit derived from (meth)acrylic acid.

5. A method for producing an inkjet ink, comprising: A step of producing a pigment dispersion by the method for producing a pigment dispersion according to any one of claims 1 to 4; and A process for producing an inkjet ink using the pigment dispersion.

6. An image recording method, comprising: A step of manufacturing an inkjet ink by the method for manufacturing an inkjet ink according to claim 5; and The ink applying step is to apply the inkjet ink onto the substrate by an inkjet method.

7. The image recording method according to claim 6, wherein: The substrate is a non-permeable substrate, Before the ink application step, the method further includes applying a pre-treatment liquid containing water and a coagulant to the non-permeable substrate. In the ink applying step, the inkjet ink is applied to the area on the non-permeable substrate to which the pre-treatment liquid is applied.

Images