Aqueous ink compositions

Abstract

To provide an ink having excellent resolubility while limiting the risks associated with the dried ink causing blockage in a printhead or ink supply system, and at the same time being able to produce prints with good water resistance.SOLUTION: The invention provides an aqueous printing ink composition comprising a polyurethane dispersion, where the polyurethane of the polyurethane dispersion comprises (a) properties of ketone or aldehyde groups present at one or more polymer chain ends; (b) properties of a number average molecular weight less than or equal to 50,000, preferably less than or equal to 25,000; and (c) properties of the content of ketone and / or aldehyde groups in the range from 0.02 to 4.0 mmol g-1, based on the dry polymer mass.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous printing ink composition containing a polyurethane dispersion ( "PUD") which is particularly suitable as an inkjet printing ink.

[0002] Advantageously, the aqueous printing ink composition according to the present invention is water-based and contains 35% (w / w) or less of an organic co-solvent, so it is more environmentally friendly than a comparative solvent-based ink composition containing PUD.

Background Art

[0003] Polyurethane dispersions (PUDs) are widely used in the preparation of printing inks. A problem with conventional PUDs, particularly when used in aqueous inks for inkjet printing, is that while they can impart beneficial printing properties such as wet rub resistance, they do not have particularly good redissolvability. Redissolvability of an ink means that it can redissolve in itself or a suitable flushing liquid after it has partially or completely dried. This is a beneficial attribute as it reduces the risk that the nozzles of the print head will become clogged, causing printing defects or, in the worst case, catastrophic loss of the print head itself.

[0004] The present invention provides an aqueous ink, particularly an aqueous inkjet printing ink, containing a novel self-curing PUD technology that has redissolvability and can produce a water-resistant (wet rub) printing. The self-curing PUD according to the present invention is not disclosed in the art.

[0005] Self-crosslinking PUDs and self-crosslinking styrene-acrylic dispersions (such as Daotan 7064, Joncryl FLX 5000, and Joncryl FLX 5060) have been described in the art but have attendant problems such as poor redissolvability and the potential risk of irreversibly drying and clogging the print head. The self-curing PUD technology encompassed by the present invention (referred to herein as "SC-PUD") is exclusively chain extension without crosslinking when combined with a bifunctional co-reagent such as adipic dihydrazide. Thus, as will be understood by those skilled in the art and further explained below, the SC-PUD disclosed herein is different from the self-crosslinking PUDs described in the art.

[0006] Inks made from conventional PUDs such as Neorez R605 and Neorez R650 also have poor redissolvability / redispersibility.

[0007] Hydroxy-functional PUDs (low molecular weight: typically with a number average molecular weight of less than 15,000) in inkjet printing inks have also been described in the art, but without using a crosslinking agent such as polycarbodiimide, they do not produce resistant prints. The inventors have found that when preparing inks using a combination of hydroxy-PUD and a polycarbodiimide crosslinking agent, the redissolvability of the ink is significantly deteriorated and the prints do not exhibit the same level of water (wet rub) resistance as those obtained by the present invention.

[0008] Crosslinkable PUDs are described in the art, for example, in U.S. Patent No. 7476705. These are polymers that contain crosslinkable groups such as ketones throughout the polymer chain (i.e., the polymer backbone). The problems with such PUDs are, similar to conventional PUDs, poor redissolvability and, since the crosslinkable PUD molecules can contain more than two ketone groups, the risk of producing crosslinked dry polymers in the print head when crosslinking with a polyfunctional crosslinking agent such as adipic dihydrazide ("ADH").

[0009] Self-crosslinking PUD The preparation of self-crosslinking PUDs containing keto-amine (or more broadly, keto-hydrazide) self-crosslinking chemical structures is described in U.S. Patent No. 8,568,889 and U.S. Patent No. 7,476,705. However, these PUDs are prepared using, for example, diol reagents having one or more ketone groups formed by the reaction of diepoxides and levulinic acid. Therefore, any PUD having at least two ketone groups in the polymer backbone and containing two or more of these diols as part of its structure in the polymer chain will contain four or more ketone groups in the molecular structure, and when the ink dries, there is a risk of generating a crosslinked polymer matrix within the inkjet print head.

[0010] An aqueous inkjet ink composition containing a self-crosslinkable styrene-acrylic dispersion The use of self-crosslinking styrene-acrylic dispersions containing keto-amine crosslinking chemical structures in inkjet applications has been described in the art.

[0011] International Publication No. 2001 / 036547 (Coates Brothers) describes, for example, compositions containing self-crosslinkable polymer (oligomer) emulsions containing carbonyl groups as part of the polymer structure that can be crosslinked with adipic dihydrazide. The polymer dispersions have polymer molecules containing more than two carbonyl groups as part of their molecular structure, which results in crosslinking that is considered undesirable in inkjet printing. The compositions further contain what is referred to as a "re-dissolving polymer," such as a water-soluble acrylic polymer. The inventors have found that the compositions provide excellent print resistance but very poor re-dissolvability. Indeed, the inherent re-dissolvability achieved by the self-curing PUDs of the present invention is a highly beneficial aspect of the present invention.

[0012] JP-A-2006-045334 (Asahi Kasei Chemicals Corporation), JP-A-2004-149600 (Sharp Kabushiki Kaisha), JP-A-2009-140774 (Sakata Inks Corporation), and JP-A-2012-241135 (General Corporation) also describe aqueous inkjet ink compositions containing self-crosslinking styrene-acrylic dispersions, but these are clearly significantly inferior in redissolution / redispersibility compared to the inks of the present invention. Chinese Patent Application Publication No. 110982344 (Zhuhai Dongchang Pigment) describes a white aqueous inkjet ink composition containing a self-crosslinking acrylic emulsion, as well as a PUD and a further crosslinking agent, such as a blocked isocyanate.

[0013] The use of self-crosslinking styrene-acrylic dispersions in conventional analog printing processes is well known. N. Kessel et al. (J. Coat. Technol. Res. (2008), (5), 285) have appropriately outlined the keto-amine chemical structure of this type of polymer dispersion. The polymer contains a ketone group or an aldehyde group as part of its molecular structure, which, upon drying, can react with a polyfunctional primary (or secondary) amine and affect the crosslinking reaction. A typical polyfunctional amine used for the self-crosslinking of styrene-acrylic emulsions is adipic acid dihydrazide, but other polyfunctional amines that can react with a carbonyl group or an aldehyde group can also be used.

[0014] PUD and crosslinking agent Polyurethane dispersions (PUDs) are regarded as the main resin chemical structures used in the preparation of colored aqueous inkjet printing inks. In particular, in the printing of textile products, there are several examples of the use of amino resins such as maleimide-formaldehyde to crosslink aqueous inkjet printing inks containing PUDs. International Publication No. WO 2009 / 137753 (DuPont) describes how PUDs can be crosslinked with Cymel 303, a melamine-formaldehyde crosslinking agent, at a temperature of 160 °C. Several other patents, including U.S. Patent No. 10,513,622, U.S. Patent No. 10,457,824, and U.S. Patent No. 9,249,324, mention the combined use of optional crosslinking agents and PUDs to enable improved resistance, and these refer to polyurethane pigment dispersants and suggest their usefulness for crosslinking polyurethanes having any of carboxylic acid, hydroxyl, or amine pendant functional groups. Crosslinking agents include carbodiimide, epoxy, isocyanate, amino resins (such as melamine-formaldehyde), and aziridine.

[0015] However, the advantages associated with the novel SC-PUD according to the present invention, particularly in inkjet printing, have not been disclosed or suggested. In fact, while many records discuss methods of crosslinking PUDs, the low molecular weight ketone (or aldehyde) end-functional self-curing PUD of the present invention has not been disclosed.

[0016] Crosslinked PUD U.S. Patent No. 8,186,822, U.S. Patent No. 9,255,207, and U.S. Patent Application Publication No. 2007 / 0060670 (all to DuPont) refer to aqueous inkjet ink compositions containing crosslinked PUDs. These crosslinked PUDs are produced by inducing crosslinking during the preparation of the PUD with a crosslinking reagent such as triethylenetetramine. The crosslinked PUDs help improve the water and washfastness of printed matter on various substrates including paper and fibrous product substrates. The optional use of crosslinking agents of the types already described such as amino resins is a further feature of these patents. Although useful for improving non-stickiness, when the crosslinked PUDs are used in ink compositions where the concentration of a co-solvent such as propylene glycol is less than 30% (w / w) of the ink composition, the ink's redissolvability / redispersibility is likely to be poor.

[0017] Redissolvable Crosslinked PUD Technology Recently, the use of acrylated polyurethane dispersions ("Ac-PUD") in the preparation of UV and EB curable aqueous inkjet printing compositions has been described, for example, in U.S. Patent No. 10,076,909 (to Fujifilm), European Patent No. 3,390,545 (to Fujifilm), International Publication No. 2017 / 174981 (to Fujifilm), and International Publication No. 2018 / 138525 (to Fujifilm). The crosslinking of these Ac-PUDs is induced by using a suitable photoinitiator in the case of UV curing. The Ac-PUDs can produce inks with good redissolvability / redispersibility, but the use of photoinitiators can pose a risk of unwanted migration of low molecular weight compounds from the cured ink, which is undesirable in many applications, especially in the printing of food packaging. Also, Ac-PUDs are prone to potential pH instability issues due to the hydrolysis of acrylate groups and the liberation of acrylic acid, which is also undesirable for inkjet printing.

[0018] Hydroxy-Functional Polyurethane Dispersion (OH-OUD) and Inkjet Inks containing hydroxy-functional PUDs are described, for example, in US Patent Application Publication No. 2018 / 0105710 (Sensient Imaging Technologies), which produce inks with enhanced redissolvability, but the printed matter has insufficient water resistance (wet rub resistance). This has been overcome by using crosslinking agents such as polycarbodiimides that react with carboxylic acid pendant groups on the PUD polymer. However, when inks based on such compositions dry, they can form crosslinked insoluble matrices that can pose a risk of clogging the printhead nozzles.

[0019] Hydroxy-functional PUDs, which are relatively low molecular weight (i.e., typically having a number average molecular weight of less than 15,000), are typically produced by using a suitable end-capping reagent such as ethanolamine or diethanolamine to attach the necessary hydroxyl groups to the polymer chain ends by forming urea bonds between the amine of the end-capping reagent and the terminal isocyanate groups on the PUD prepolymer. As already mentioned, such OH-PUDs can produce inks with excellent redissolvability, but as a result of their hydroxyl functionality and low molecular weight, they produce printed matter with inferior water resistance (wet rub resistance) without using additional crosslinking agents such as polycarbodiimides or polyisocyanates. As already described, such techniques are described (e.g., in US Patent Application Publication No. 2018 / 0105710), but they pose a risk of forming crosslinked inks on the press, which can be significantly disadvantageous for inkjet printing.

[0020] US Patent No. 8,931,889 (DuPont Electronics) describes the synthesis of OH-PUDs containing polyether diols as part of their chemical structure and their use in aqueous inkjet ink compositions. The OH-PUDs are described as improving stability and lengthening nozzle life.

[0021] Chinese Patent Application Publication No. 111138626 (Trendvision Technology) describes the synthesis of PUD for the aqueous inkjet printing of textile products. End-capping reagents such as N-methylethanolamine can be used in the PUD synthesis for preparing hydroxy-terminated PUD. It is well-known to use such end-capping agents in the preparation of OH-PUD and is widely practiced in the art. For example, U.S. Patent No. 7875355 (Sherwin-Williams) describes how to prepare OH-PUD for the automotive industry by using diaminopropanol as an end-capping reagent.

[0022] U.S. Patent Application Publication No. 2018 / 0105710 describes how to crosslink an aqueous inkjet ink containing OH-PUD by using crosslinking agents such as carbodiimide, oxazoline, amino resin (such as melamine formaldehyde), blocked isocyanate, and zirconium complex. U.S. Patent Application Publication No. 2018 / 0105710 describes OH-PUD that can reduce clogging of the print head because the use of OH-PUD clearly improves the redissolubility of the ink. Although it is clear that the use of a crosslinking agent, in the example of U.S. Patent Application Publication No. 2018 / 0105710, the use of carbodiimide, improves the non-stickiness that would otherwise be inferior as a result of the use of OH-PUD, the accompanying problems already described remain.

Prior Art Documents

Patent Documents

[0023]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

[0024]

Non - Patent Document 1

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0025] The present invention overcomes some of the problems associated with commercially available materials and in particular some of the problems described in the art for inkjet printing. That is, the present invention provides an ink that can produce a printed matter having excellent redissolvability while limiting the risk associated with dry ink that causes clogging of the print head or ink supply system, and at the same time has good water resistance. Further, the present invention typically achieves an advantageous combination of these properties without relying on the use of co - solvents such as high - concentration (i.e., more than 35% (w / w)) glycerol or propylene glycol.

[0026] In particular, in the case of printing inks for inkjet printing, no records have been recognized regarding the use of the self - curing PUD of the invention prepared as described. The advantages brought about by the present invention are briefly described above and will be described in more detail below. The exceptional redissolvability of the ink containing this new type of PUD makes it possible to prepare redissolving ink by reducing the concentration of solvents such as propylene glycol. The inventor has shown that redissolving ink can be produced while preferably setting the content of the high - boiling solvent to 25% (w / w) or less, 20% (w / w) or less, 15% (w / w) or less, 10% (w / w) or less. This is an important aspect because inkjet ink compositions generally contain higher concentrations of solvents, such as propylene glycol, glycerol, and other high - boiling water - soluble solvents, to impart both the required viscosity and redissolvability to the ink.

MEANS FOR SOLVING THE PROBLEMS

[0027] The citation or introduction of documents in this application does not admit that they are prior art to the present invention.

[0028] The present invention provides an aqueous printing ink composition containing a polyurethane dispersion, wherein the polyurethane of the polyurethane dispersion has the following characteristics: (a) one or more ketone groups or aldehyde groups are present at the ends of one or more polymer chains; (b) the number average molecular weight is 50,000 or less, more preferably 25,000 or less; and (c) the content of ketone groups and aldehyde groups is in the range of 0.02 to 4.0 mmol / g based on the dry polymer mass. -1 The present invention provides an aqueous printing ink composition having such characteristics.

[0029] Unless otherwise specified, the content of ketone groups and aldehyde groups refers to the content of chain-end ketone groups and aldehyde groups.

[0030] In a particularly preferred embodiment of the present invention, the group present at the ends of one or more polymer chains is a ketone group. Thus, the present invention provides an aqueous printing ink composition containing a polyurethane dispersion, wherein the polyurethane of the polyurethane dispersion has the following characteristics: (a) one or more ketone groups are present at the ends of one or more polymer chains; (b) the number average molecular weight is 50,000 or less, more preferably 25,000 or less; and (c) the content of ketone groups is in the range of 0.02 to 4.0 mmol / g based on the dry polymer mass. -1 The present invention provides an aqueous printing ink composition having such characteristics.

[0031] As is understood, the group present at the polymer chain end is an "end-group", "chain-end group" or "terminal group", which is different from the group present on the polymer chain or as part of the polymer molecular structure, i.e., on the polymer backbone.

[0032] Preferably, the polyurethane has a mostly linear structure. That is, 5% or less of the polyurethane polymer chains (based on the dry polymer mass) contain a branched structure. More preferably, the polyurethane has a linear structure.

[0033] As is understood, since one or more ketone groups or aldehyde groups are present at one or more polyurethane chain ends, the polyurethane is end-capped with the ketone group or aldehyde group. The polyurethane used in the present invention preferably contains a ketone group or an aldehyde group at one or more polymer chain ends and does not contain it at other positions on the polymer chain. Preferably, the polyurethane is linear and contains no more than two ketone groups or aldehyde groups per average polymer chain present at the polymer chain ends.

[0034] The end-capping method for preparing the self-curing PUD and the use of the SC-PUD in the ink composition described herein are important features of the present invention. Thereby, not only a low molecular weight PUD (i.e., a PUD having a number average molecular weight of 50,000 or less) beneficial for ink redissolubility is produced, but also a PUD containing selectively two or less ketone (or aldehyde) groups per average polymer molecule is produced. As a result, when combined with a bifunctional co-reagent such as adipic acid dihydrazide, by curing in the ink, only chain extension occurs, and a higher molecular weight linear polymer can be produced without forming a difficult-to-handle insoluble cross-linked matrix. What distinguishes the SC-PUD of the present invention from the self-crosslinking PUD described in the art is this chain extension without the formation of a cross-linked matrix. In particular, self-crosslinking PUDs typically contain more than two ketone groups on the polymer chain and thus form crosslinks when combined with a bifunctional co-reagent such as adipic acid dihydrazide.

[0035] The inventors have shown that an ink containing a novel SC-PUD according to the present invention enables the preparation of a re-dissolvable ink in which the total concentration of a co-solvent such as propylene glycol is 35% (w / w) or less, preferably 30% (w / w) or less of the total ink composition. In particular, the inventors have shown that an ink containing a novel SC-PUD according to the present invention enables the preparation of a re-dissolvable ink in which the total concentration of a co-solvent such as propylene glycol is less than 30% (w / w) of the total ink composition. In a more preferred embodiment of the present invention, a solvent having a boiling point exceeding 200°C, for example, glycerol, is limited to less than 5% (w / w) of the ink composition. As will be understood by those skilled in the art, in order to ensure the required re-dissolvability, it is a common practice to use the co-solvent at a concentration exceeding 30% in the aqueous inkjet composition. However, the high concentration of the co-solvent particularly adversely affects the drying rate on an impermeable substrate.

Embodiments for Carrying Out the Invention

[0036] The present invention addresses the problems of the prior art by producing an ink having good water resistance (wet rub) and excellent redissolvability. This highly desirable balance of properties is achieved by using a novel self-curing PUD ("SC-PUD") having a number average molecular weight of 50,000 or less, preferably 25,000 or less, more preferably 15,000 or less, and most preferably 10,000 or less, and the polymer thereof being end-capped with a ketone group or an aldehyde group, preferably a ketone group. By end-capping with a ketone (or aldehyde) group, the SC-PUD becomes non-bifunctional (preferably linear) with respect to the reactive ketone functional group, and when this reacts with a bifunctional curing co-reagent such as adipic dihydrazide (ADH), it can produce exclusively linear polymers. In other words, the SC-PUD according to the present invention does not form a cross-linked matrix in the presence of a bifunctional curing co-reagent such as adipic dihydrazide (ADH). Since the reaction between the SC-PUD of the present invention and a bifunctional curing co-reagent such as adipic dihydrazide (ADH) stalls under alkaline conditions, the probability of forming a high molecular weight product in the print head is reduced by the neutralizing agent preferably used for the preparation of the SC-PUD and the ink.

[0037]

Chemical formula

[0038] The reaction of SC-PUD having two terminal ketone groups or aldehyde groups with a bifunctional amine or dihydrazide is shown in FIG. 1. The reaction does not produce any cross-linking but results in a chain extension reaction of the two bifunctional reagents. Basically, this can be regarded as an A2B2 type sequential polymerization reaction. In this figure, it is shown that as the reaction proceeds, an imine reaction product is obtained.

[0039] The preparation method of SC-PUD is not particularly limited and may be anionically stabilized, non-ionically stabilized (or either), but preferably it is an anionically stabilized SC-PUD. The present invention includes aromatic and aliphatic SC-PUDs and further includes polyether diols, polyester diols, polyacrylic diols, polycarbonate diols, and any aliphatic or aromatic diols, or any blend or mixture thereof.

[0040] When preparing SC-PUD, a capping reagent containing a ketone group or an aldehyde group is used to bond a reactive curable functional group to the chain ends of the polymer. The capping reagent selectively contains a primary or secondary amine that reacts with the isocyanate groups on the polyurethane precursor to form a urea bond, thereby forming the desired PC-PUD. The polyurethane precursor can be prepared from any blend of diisocyanate and diol. Examples of diols include, but are not limited to, polyester diols, polycarbonate diols, polyacrylic diols, and polyether diols. Preferably, the diols used to prepare the polyurethane precursor do not have any ketone groups or aldehyde groups in their molecular structures. The diisocyanates used in the preparation of SC-PUD can be aliphatic or aromatic types including, but not limited to, isophorone diisocyanate, hexamethylene-1,6-diisocyanate, methylene diphenyl diisocyanate, hydrogenated methylene diphenyl diisocyanate, and toluene diisocyanate. In the preparation of the polyurethane precursor, by using an excess of diisocyanate compared to the diol, the isocyanate-functional prepolymer is made ready for end-capping with the previously described carbonyl-functional reagent (i.e., a capping reagent containing an aldehyde group or a ketone group). Examples of such capping reagents include

[0041]

Chemical formula

[0042] is included.

[0043] This specific end-capping reagent introduces both ketone and aldehyde groups to the ends of the SC-PUD polymer.

[0044] The present invention is preferably directed to the preparation of linear SC-PUD. However, when the SC-PUD is branched, the possibility of branched PC-PUD is also included on the premise that there are at most two ketone or aldehyde groups at the ends of the polymer chains. Thus, as is understood, PC-PUD is at most bifunctional with respect to reactive ketone or aldehyde functional groups and contains no aldehyde or ketone groups on the branches. The techniques for preparing such branched polyurethanes are well known and can be achieved, for example, by using trifunctional (e.g., biuret HMDI trimer) isocyanates, trifunctional or higher polyfunctional polyols, or trifunctional or higher polyfunctional primary and secondary amines. It should also be understood that SC-PUD can use bifunctional amines in their synthesis to introduce urea linkages into the polyurethane backbone, thereby further promoting non-stickiness.

[0045] When the SC-PUD is anionically stabilized, it contains acid groups as part of its polymer structure (i.e., on the polymer backbone), and these confer an anionic stabilization mechanism that enables its dispersion upon neutralization with a suitable inorganic or organic base. A typical reagent used to introduce carboxylic acid groups into the SC-PUD structure during its synthesis is dimethylpropionic acid (DMPA). It should be understood that other diol reagents containing one or more carboxylic acid groups can be used in the preparation of SC-PUD. It is also possible to use other acid-containing reagents in the preparation of SC-PUD. When DMPA, or other acid-containing species, are incorporated into the SC-PUD backbone, it can be neutralized with any organic or inorganic base to enable the anionic stabilization mechanism. In the case of non-ionically stabilized SC-PUD, the hydrophilic moiety is included as part of the polyurethane dispersion (such as poly(ethylene oxide), etc.) to enable its dispersion.

[0046] When the SC-PUD is anionically stabilized, the acid value of the SC-PUD is not limited, but it is preferably between 0 mg KOH / g and 100 mg KOH / g based on the dry polymer mass. More preferably, the acid value based on the dry polymer mass is at least 10 mg KOH / g, more preferably at least 20 mg KOH / g. Thus, the acid value based on the dry polymer mass is preferably between 10 mg KOH / g and 100 mg KOH / g, and more preferably between 20 mg KOH / g and 100 mg KOH / g. To disperse the anionic SC-PUD, any suitable base, including organic and inorganic types, can be used to neutralize the acid groups of the SC-PUD, thereby enabling its dispersion in water. Non-limiting examples of bases used to neutralize the carboxylic acid (or other acid) of the SC-PUD include triethylamine, N,N-dimethylethanolamine, any other tertiary amine, potassium hydroxide, and sodium hydroxide, but are not limited thereto. When the neutralizing agent is a tertiary amine, its boiling point is preferably higher than 125°C. Preferably, the neutralizing agent is N,N-dimethylethanolamine.

[0047] The dispersion of SC-PUD can also be promoted by using anionic and nonionic surfactants.

[0048] The particle size of the SC-PUD used in the preparation of the ink of the present invention is not limited. However, the average particle size is preferably 250 nm, more preferably less than 100 nm.

[0049] The total solids of SC-PUD in the final aqueous (inkjet) printing ink composition are not particularly limited. However, the total solids in the final ink formulation are preferably 2.5% (w / w) to 40% (w / w), more preferably 5.0% (w / w) to 20.0% (w / w) of the ink composition for the final inkjet composition, based on the dry polymer mass.

[0050] Another aspect of the present invention that helps to further promote the redissolution of inks containing novel SC-PUDs is that they can also be end-capped with hydroxy groups, i.e., the polyurethane can be end-capped with an end-capping reagent containing both hydroxy-functional and ketone or aldehyde functional groups, for example, the exemplary end-capping reagents shown above. Thus, the SC-PUD of the present invention may optionally contain chain-end (terminal) hydroxy groups. In this case, the hydroxyl value of the SC-PUD is preferably less than 100 mg KOH / g, more preferably less than 50 mg KOH / g -1 based on the dry polymer mass. -1 and most preferably less than that.

[0051] To control the molecular weight of the SC-PUD, an end-capping reagent containing a ketone (or aldehyde) group and optionally additional hydroxy groups is typically used. The SC-PUD of the invention has a number average molecular weight of 50,000 or less, preferably 25,000 or less, more preferably 15,000 or less, and most preferably 10,000 or less. The relatively small molecular weight of this novel PUD also contributes to the redissolution observed in printing inks.

[0052] The SC-PUD of the present invention uses a bifunctional amine or dihydrazide that affects curing by reaction with a terminal carbonyl group (i.e., a ketone group or an aldehyde group) on the polyurethane, such as adipic acid dihydrazide. However, the present invention also includes polyfunctional amines, i.e., polyfunctional amines having three or more primary amine groups.

[0053] The carbonyl terminal groups (i.e., ketone or aldehyde terminal groups) of the SC-PUD used in the ink of the present invention can also be cured by reaction with other co-reagents such as polyvalent metal complexes, as disclosed in U.S. Patent No. 7,947,760 (BASF). In fact, it is also possible to cure the ink containing SC-PUD by including a compound such as ammonium zirconium carbonate as a curing reagent in the ink instead of a preferred diamine or dihydrazide. The ink composition according to the present invention may optionally further contain one or more acids selected from the group consisting of tartaric acid, gluconic acid, citric acid, maleic acid, succinic acid, and their salts. In some embodiments, the ink composition may contain ammonium zirconium carbonate as a curing reagent, and one or more acids selected from the group consisting of tartaric acid, gluconic acid, citric acid, maleic acid, succinic acid, and their salts.

[0054] Preferably, the SC-PUD is combined with a bifunctional amine co-reagent such as adipic acid dihydrazide to enable self-curing of the ink of the present invention.

[0055] Preferably, the molar ratio of the SC-PUD to the co-reagent that enables self-curing is between 0.1:10 and 10:0.1, preferably between 0.2:5 and 5:0.2, more preferably between 0.5:2 and 2:0.5, with respect to the appropriate molar concentrations of the SC-PUD and the co-reagent. In a more preferred embodiment, the curing co-reagent is adipic acid dihydrazide (ADH), and the molar ratio of the SC-PUD to the ADH is between 0.1:10 and 10:0.1, preferably between 0.2:5 and 5:0.2, more preferably between 0.5:2 and 2:0.5, with respect to the appropriate molar concentrations of the SC-PUD and the co-reagent.

[0056] The aqueous ink of the present invention is mostly water-based. More specifically, the ink of the present invention contains water in the range of 5% to 90% by mass, for example, in the range of 5% to 80% by mass or 10% to 80% by mass. Preferably, the ink of the present invention contains water in the range of 10% to 80% by mass, more preferably in the range of 15% to 80% by mass.

[0057] The printing ink of the present invention may optionally contain any water-soluble organic co-solvent. Volatile solvents such as ethanol, propanol, and isopropanol may be used, but when the ink is intended for inkjet printing, those with low flammability or volatility are preferred. Typically, polyols, alkylene glycols, alkylene glycol ethers, or ether acetates are used. Non-limiting examples thereof include 3-methoxy-3-methyl-1-butanol, 4-hydroxy-4-methyl-2-pentanone, diethylene glycol, diethylene glycol butyl ether, diethylene glycol ethyl ether, diethylene glycol methyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monopropyl ether, dipropylene glycol, dipropylene glycol ethyl ether, dipropylene glycol methyl ether, ethylene glycol butyl ether, ethylene glycol ethyl ether, ethylene glycol isopropyl ether, ethylene glycol methyl ether, ethylene glycol propyl ether, glycerin carbonate, N-methyl-2-pyrrolidone, glycerol, propylene glycol, propylene glycol ethyl ether, propylene glycol ethyl ether acetate, propylene glycol methyl ether, propylene glycol n-propyl ether, triethylene glycol, triethylene glycol butyl ether, triethylene glycol methyl ether, tripropylene glycol, tripropylene glycol methyl ether, N-methylpyrrolidone, and urea.

[0058] Preferably, the ink of the present invention contains propylene glycol and / or 3-methoxy-3-methyl-1-butanol (MMB). When the ink of the present invention contains propylene glycol and / or 3-methoxy-3-methyl-1-butanol, the ratio thereof (the ratio of propylene glycol to 3-methyl-1-butanol) is preferably 3:1 to 1:3.

[0059] When using organic co-solvents, they preferably constitute 35% (w / w) or less of the ink composition, more preferably 30.0 (w / w)% or less. For example, when using organic co-solvents, they preferably constitute less than 35% (w / w) of the ink composition, more preferably less than 30.0 (w / w)%. In fact, the total concentration of the water-soluble organic solvent is preferably 35% (w / w) or less, more preferably 30.0% (w / w) or less, and still more preferably 25.0% (w / w) or less of the ink composition.

[0060] The present inventors have shown that by using the SC-PUD according to the present invention, it is possible to prepare a re-dissolving ink with the concentration of the water-soluble organic co-solvent being about 10% (w / w) of the ink composition. Therefore, in a further preferred embodiment, the ink according to the present invention contains 10% (w / w) or less of the water-soluble co-solvent.

[0061] As a further optional feature of the present invention, when any water-soluble organic co-solvent is used, it preferably has a boiling point of less than 250°C, more preferably less than 200°C. In fact, by using the SC-PUD according to the present invention, it is possible to prepare an ink with high redissolubility without depending on the use of a co-solvent having a boiling point exceeding 200°C, particularly exceeding 250°C, for example, glycerol and diethylene glycol, especially in amounts exceeding 35.0% (w / w). The use of such non-volatile solvents in ink formulations at concentrations often exceeding 35% (w / w) not only increases the viscosity of the ink but is also a conventional technique for imparting acceptable redissolubility to the ink. However, the use of such high-boiling solvents has the attendant disadvantage of causing an unacceptable stall in the drying time of the ink for high-throughput printing. Preferably, the ink according to the present invention does not contain a solvent having a boiling point higher than 250°C, and more preferably, the ink according to the present invention does not contain a solvent having a boiling point higher than 200°C. Further, when used, the concentration of the solvent having a boiling point higher than 250°C is preferably less than 10.0% (w / w) of the ink composition, and more preferably less than 5.0% (w / w).

[0062] One advantage of the present invention is that excellent redissolvability is unexpectedly achieved when the concentration of a water-soluble cosolvent such as propylene glycol is 35% (w / w) or less, more specifically 30% (w / w) or less. In fact, the inventors have shown that redissolvable inks can be produced at cosolvent concentrations of 25% (w / w) or less and about 10% (w / w). Having an ink that can be easily redissolved without relying on the use of high-boiling solvents such as propylene glycol and glycerol (also known as humectants) at high concentrations is advantageous because it results in an inkjet printing ink with a faster drying response. This helps the inkjet ink of the present invention contribute to the more throughput-intensive industrial inkjet printing market, such as packaging corrugated label printing and textile products. Also, the faster drying response achievable with the inkjet ink of the present invention also allows for a reduction in the energy input required to dry them. This is beneficial not only for the aforementioned printing market but has also been demonstrated to be beneficial in the multi-pass inkjet graphics printing market. Currently, UV curable inkjet compositions and solvent-based inkjet compositions are making a large contribution to the multi-pass inkjet graphics market. Concerns regarding the health and safety of UV curable inkjet compositions are increasing due to the ongoing toxicological evaluation of the monomers and photoinitiators used in their preparation. Solvent-based inkjet printing ink compositions typically contain as part of their composition a blend of over 70% organic solvents. The ink of the present invention contains water as the majority of the solvent content (i.e., typically more than 70% of the solvent blend used in the present invention is water), and the inherently polymeric SC-PUD has a much lower health risk than the monomers and photoinitiators used in UV curable inkjet printing ink compositions. Also, in the composition of the invention, solvents derived from recyclable resources such as propylene glycol can be used, but it is preferably used at 30% (w / w) or less of the composition.

[0063] As a further optional feature of the present invention, the ink contains a solvent having a boiling point higher than 150°C at a concentration of 30% (w / w) or less, preferably 25% (w / w) or less. By minimizing the concentration of the solvent, and particularly the solvent having a heat of vaporization greater than 500 J / g, faster drying of the ink, which is very beneficial for high-speed inkjet printing, becomes possible. Further benefits of lowering the co-solvent concentration are the reduction in the amount of energy required to dry the ink. The inventor has shown that a stable ink can be prepared containing 3-methoxy-3-methyl-1-butanol ("MMB"), a water-soluble co-solvent having a boiling point of 174°C and a heat of vaporization of 385 J / g, as opposed to propylene glycol having a boiling point of 187°C and a heat of vaporization of 880 J / g. By using the solvent having a small heat of vaporization, an ink with a higher drying rate is produced. Therefore, the ink according to the present invention preferably contains a solvent having a heat of vaporization of 500 J / g or more at 30% (w / w) or less. For example, the ink according to the present invention preferably contains less than 30% (w / w) of a solvent having a heat of vaporization greater than 500 J / g. -1 By minimizing the concentration of the solvent, and particularly the solvent having a heat of vaporization greater than 500 J / g, faster drying of the ink, which is very beneficial for high-speed inkjet printing, becomes possible. Further benefits of lowering the co-solvent concentration are the reduction in the amount of energy required to dry the ink. The inventor has shown that a stable ink can be prepared containing 3-methoxy-3-methyl-1-butanol ("MMB"), a water-soluble co-solvent having a boiling point of 174°C and a heat of vaporization of 385 J / g, as opposed to propylene glycol having a boiling point of 187°C and a heat of vaporization of 880 J / g. By using the solvent having a small heat of vaporization, an ink with a higher drying rate is produced. Therefore, the ink according to the present invention preferably contains a solvent having a heat of vaporization of 500 J / g or more at 30% (w / w) or less. -1 whereas the boiling point is 174°C and the heat of vaporization is 385 J / g -1 and has shown that a stable ink can be prepared containing 3-methoxy-3-methyl-1-butanol ("MMB"), a water-soluble co-solvent. By using the solvent having a small heat of vaporization, an ink with a higher drying rate is produced. Therefore, the ink according to the present invention preferably contains a solvent having a heat of vaporization of 500 J / g or more at 30% (w / w) or less. -1 or more at 30% (w / w) or less. -1 For example, the ink according to the present invention preferably contains less than 30% (w / w) of a solvent having a heat of vaporization greater than 500 J / g.

[0064] Therefore, a further preferred embodiment of the present invention is that the concentration of the water-soluble organic co-solvent, particularly the water-soluble organic co-solvent having a heat of vaporization of 500 J / g or more and a boiling point exceeding 150°C, is preferably less than 30% (w / w), more preferably 25% (w / w) or less, of the entire ink composition. When using the co-solvent, any combination of solvents having a boiling point higher than 200°C is preferably less than 10% (w / w) of the ink composition. -1 or more and a boiling point exceeding 150°C, is preferably less than 30% (w / w), more preferably 25% (w / w) or less, of the entire ink composition. When using the co-solvent, any combination of solvents having a boiling point higher than 200°C is preferably less than 10% (w / w) of the ink composition.

[0065] Furthermore, a further benefit of using the novel self-curing PUD according to the present invention in printing ink compositions is that they can produce re-dissolving / redispersing inks comprising pigment dispersions containing an anionic dispersant (e.g., an anionic acrylic copolymer dispersant) and pigment dispersions containing a non-ionic dispersant. The latter result is particularly noteworthy because the non-ionic dispersant tends to be very sensitive to water, and the ability of this novel PUD to produce inks that enable prints with good water (wet rub) resistance enhances the usefulness of this new technology.

[0066] A further benefit of the present invention is that excellent water (wet rub) resistance of prints can be achieved without using an excessively high temperature. In fact, after initial drying, the prints develop their resistance over time and can achieve a high level of non-stickiness within 24 hours after printing.

[0067] After printing and drying of the inks of the present invention, they can cure at room temperature or at a high temperature, for example, 50 °C or higher. The inventor has found that under atmospheric conditions (i.e., 22 - 25 °C), ink curing can occur more than one day after printing. Curing of the ink can be accelerated by heating the print at a temperature of 50 °C or higher.

[0068] The benefit of inks having both good re-dissolvability and the ability to produce prints with excellent water resistance enables the use of the inks prepared according to the present invention in a range of applications. In particular, the inks of the present invention are suitable for a wide range of applications including printing of packaging, including flexible packaging (front and back printing) and flexible film packaging, rigid packaging (printing of coated metal substrates, i.e., including metal decoration), cardboard and paper packaging, corrugated packaging, printing of decorative laminates, printing of textile products, graphics printing, etc. When printing packaging materials using the inks of the present invention, this may include food packaging. In inkjet printing, the present invention is suitable for both single-pass and multi-pass printing, which are well recognized terms in the industry.

[0069] The excellent water resistance of the printed matter achievable by the technology of the present application is suitable for surface printing applications without the need for overprint varnish. Also, the redissolvable / redispersible ink can be manufactured using a cosolvent such as propylene glycol at a concentration of 25% (w / w) or less, enabling high-speed printing of these inks in both multi-pass inkjet printing and single-pass inkjet printing. The use of SC-PUD provides the excellent redissolvability of the ink of the present invention.

[0070] The present invention is mainly directed to inkjet printing inks, but also includes aqueous inks that can be printed by flexographic and gravure printing methods. In fact, considering the rapid decontamination between operations and the reduction of risks associated with filling anilox cylinders, the excellent redissolvability of the SC-PUD technology according to the present invention is highly beneficial in these printing markets. A potential problem with currently used self-crosslinking (acrylic) technology is that the ink can dry within the anilox cylinder, causing causal print quality issues.

[0071] In inkjet printing, in order to improve print quality, the ink of the present invention can be printed on any substrate that has been pre-coated with a suitable primer composition. The primer typically contains a polyvalent metal salt that helps reduce print quality issues such as droplet spread and color bleeding by "fixing" the ink. The primer does not form an essential part of the present invention, and any suitable primer that enhances the print quality achievable by the ink of the invention can be used. Alternatively, the ink of the present invention can be printed on any substrate that has not been pre-coated with a primer.

[0072] The present invention discloses the finding that an aqueous printing ink having excellent redissolvability / redispersibility and the ability to cure after printing to produce a water-resistant printed matter can be prepared by using a novel polyurethane dispersion (hereinafter referred to as "SC-PUD"). The ink of the present invention is particularly suitable for inkjet printing, and the excellent redissolvability imparted by this technology reduces the risk of the ink drying irreversibly within the nozzles of the print head. The PC-PUD used in the ink composition of the present invention contains a ketone group or an aldehyde group located at the end of the polymer chain. When these SC-PUDs are cured with a bifunctional co-reagent such as diamine or dihydrazide (e.g., adipic acid dihydrazide), they can be cured exclusively to produce a higher molecular weight linear polymer with chain extension. This unique feature differentiates the ink of the present invention from inks using a crosslinked chemical structure. Crosslinked chemical structures currently used in the art include self-crosslinking styrene-acrylic dispersions and self-crosslinking polyurethane dispersions. When these chemical structures are dried and fully cured, a crosslinked polymer matrix that may be insoluble is produced, which can cause problems for printing inks, and particularly for inkjet.

[0073] The use of SC-PUD according to the present invention imparts redissolvability / redispersibility of the ink, which is a particularly useful feature for aqueous inkjet printing inks. The redissolvability / redispersibility from the perspective of the present invention, and more broadly inkjet printing, can be described as the ink being able to redissolve or redisperse in itself or a suitable "flushing" liquid after drying at a temperature up to 40 °C, and further up to 50 °C for a time up to 1 hour (or more), for example, over 30 minutes. Conventional PUDs, conventional self-crosslinking PUDs, and inks containing styrene-acrylic typically have poor redissolvability.

[0074] By using hydroxy-functional PUD (“OH-PUD”), inks having excellent redissolvability can be prepared, but without adding a crosslinking agent, prints with poor water resistance (wet rub resistance) are produced from these inks. In fact, the inks containing the SC-PUD of the present invention have been shown to have redissolvability compared to what can be achieved with inks containing OH-PUD. Also, when a crosslinking agent is used to enhance the non-stickiness of the inks containing OH-PUD, the redissolvability of the inks is significantly impaired.

[0075] Preferably, the ink composition according to the present invention contains no carbodiimide (e.g., polycarbodiimide), oxazoline (e.g., polyoxazoline), aziridine (e.g., polyaziridine), epoxy, amino resin (such as melamine-formaldehyde), isocyanate (e.g., blocked isocyanate) and / or silane at all. More preferably, the ink composition according to the present invention contains no polycarbodiimide at all.

[0076] In inkjet printing, the present invention is particularly advantageous because good redissolvability helps prevent irreversible drying of the ink in the print head. If such irreversible drying of the ink occurs in the print head, it can lead to nozzle clogging, a consequential decrease in print quality performance, and even damage to the print head itself. Therefore, it can be seen that the ideal solution for inkjet printing inks is a solution that has good redissolvability (utilizing open time) and at the same time can cure after printing and drying to produce a water-resistant print. The present invention achieves this without using high-boiling co-solvents such as excessive concentrations of glycerol and propylene glycol. In fact, the inks of the invention maintain good redissolvability / redispersibility while setting the propylene glycol concentration to about 5.0% (w / w) of the ink composition.

[0077] The problems associated with using conventional PUDs themselves in the preparation of aqueous inkjet ink compositions are that when they are dried at 40 °C for a period of time between 15 and 60 minutes, their solubility in the inks themselves and their solubility in the flushing liquid both decrease significantly. This problem is solved by the present invention. In contrast, OH-PUDs, especially those having a hydroxyl value greater than 50 mg KOH / g, can produce inks with excellent redissolution / redispersion properties, but generally produce dry prints with poor water resistance. This problem is also solved by the present invention. Even if the ink dries on the faceplate rather than in the body of the printhead and the ink supply system, it is limited. The printhead faceplate is often coated with what is called a non-wetting coating ("NWC"). The NWC is a delicate structure containing a thin layer of ceramic, and attempting to remove insoluble residues from the NWC can damage it and affect print quality.

[0078] When the composition of the present invention is intended for inkjet printing, it preferably has a viscosity of less than 10.0 mPa·s as measured at 32 °C using a Brookfield DV-II+Pro viscometer equipped with an 18th spindle at 100 rpm.

[0079] The pH of the ink is preferably in the range of 5.0 to 10.0, more preferably in the range of 6.0 to 9.5.

[0080] The SC-PUD according to the present invention contains pendant ketone groups or aldehyde groups bonded to at least one end (i.e., the terminal end) of the polyurethane. Also, the SC-PUD contains at least 0.02 to 4.0 mmol of chain-end ketone groups and aldehyde groups per gram of SC-PUD based on the dry polymer mass (mmol(C=O)g -1 ). The amount of chain-end ketone groups and aldehyde groups in the SC-PUD (based on the dry polymer mass) is preferably in the range of 0.05 to 2.0 mmol g -1 .

[0081] Self-crosslinking PUD (and styrene-acrylic) is known, the keto-hydrazide crosslinking chemical structure is well-known and is used in commercially available products. A ketone group or an aldehyde group in the polymer backbone involved in this crosslinking reaction can be introduced into the PUD backbone by using a diol containing a ketone group in the production of PUD. This can be achieved by reacting a ketone-functional acid such as levulinic acid with a diepoxide to produce the desired ketone diol. Another approach includes reacting diacetone acrylamide with an alkanolamine such as diethanolamine. These self-crosslinking PUDs differ from the self-curing PUD according to the present invention in that a part of the polymer molecules contains more than two ketone groups or aldehyde groups as part of their molecular structure. When an ink containing these self-crosslinking PUDs is dried in the presence of a crosslinking co-reagent such as adipic acid dihydrazide, they can react to form a crosslinked structure. The crosslinked polymer network in the ink during drying or in the dried ink has an adverse effect on the re-solubility / re-dispersibility of the ink and may irreversibly clog the nozzles in an inkjet print head.

[0082] Conventional (non-crosslinked) PUDs such as Neorez R605 are also inferior in redissolubility for inkjet printing ink applications. This is probably due to the fact that the molecular weights of these polymers (i.e., number average molecular weights exceeding 50,000) are greater than the molecular weights of the SC-PUDs used in the ink compositions of the present invention and the molecular weights of the hydroxy-functional PUDs ( "OH-PUDs") described in the art. The inventors have confirmed that inks containing OH-PUDs, such as those described in the art, actually have excellent redissolubility. However, probably due to both their hydroxyl content and low molecular weight (typically number average molecular weight less than 15,000), the water resistance of prints of inks containing such OH-PUDs is insufficient. Interestingly, the inventors have found that for the novel SC-PUDs according to the present invention, in addition to ketone or aldehyde groups, the presence of hydroxyl groups at the polymer chain ends can promote the redissolubility of the ink, although this is not essential for imparting redissolubility. Probably, the molecular weight of the PUD is more important. In some cases, the SC-PUD may have a number average molecular weight of less than 10,000, even less than 5,000. By knowing the ketone or aldehyde content or hydroxyl value of the PUD based on the composition of the SC-PUD, it is possible to calculate the number average molecular weight (basically end-chain analysis). The weight average molecular weight was also measured by gel permeation chromatography (GPC). Note that the measurement of the molecular weight of SC-PUD by GPC was carried out in the absence of a self-curing chemical structure, typically a co-reagent of ADH.

[0083] The SC-PUD used in the ink of the present invention is preferably combined with a diamine or dihydrazide co-solvent that affects the curing of the SC-PUD when the ink is printed and dried, preferably a primary amine and a hydrazide. When a preferred bifunctional SC-PUD, i.e., a linear polyurethane having ketone groups at both polymer chain ends, (optionally a monofunctional SC-PUD) is combined with a bifunctional amine or hydrazide co-reagent, the curing process proceeds without crosslinking to produce a chain-extended linear adduct of the SC-PUD and the bifunctional co-reagent. This differential feature of the SC-PUD makes it particularly suitable for aqueous inks applied by flexographic and gravure printing as well as inkjet printing applications. The curing process can proceed for 24 hours or more at room temperature or can be accelerated by heating the printed material to a high temperature, for example, a temperature of 50 °C or higher. Water-soluble polyfunctional reagents capable of curing the ketone (or aldehyde) groups of the SC-PUD include, but are not limited to, adipic acid dihydrazide ("ADH"), pimelic acid dihydrazide, and any other dihydrazide derived from bifunctional acids, aliphatic di-, tri- and higher polyfunctional amines. The latter may include polyethylene oxide containing polyfunctional amines commercially available from Huntsman under the trade name "Jeffamine". It is also possible to cure the ketone-containing PUD using a polymer dispersion containing a primary or secondary amine as part of its structure. The ketone groups of the SC-PUD can also be cured by using a metal complex such as zirconium ammonium carbonate. However, for the reasons already explained, bifunctional amine and hydrazide co-reagents are preferred.

[0084] Self-crosslinking PUD can be prepared using metal complexes such as ammonium zirconium carbonate ("AZC"). When the metal complex is present in the aqueous phase of the polymer dispersion, it can react with the carboxylic acid and carbonyl groups present in the PUD backbone after the ink is printed and dried. This has already been achieved for acrylic dispersions as described in U.S. Patent No. 7,947,760. The quality retention period of the composition, which can be a problem when using AZC, was extended by using ammonium tartrate. This technique has not yet been adopted in the PUD chemical structure. In the present invention, the inventors have found that when AZC is added to an ink containing SC-PUD (which contains no ADH at all), an ink having a certain degree of redissolubility and non-stickiness is produced, although not to the extent achieved when using an ink containing a similar SC-PUD using ADH as a curing co-reagent.

[0085] Although not an essential feature, the ink prepared according to the present invention may contain any further water-soluble, alkali-soluble or water-dispersible resin other than SC-PUD. As will be understood, alkali-soluble resins typically contain acidic functional groups as part of a monomer blend that can be neutralized with a suitable base so that the resin can be dissolved in water to form an aqueous solution. Further resins include, but are not limited to, polyurethane dispersions, self-crosslinking polyurethane dispersions, alkali-soluble acrylic resins, acrylic dispersions, self-crosslinking acrylic dispersions, polyester dispersions, copolymers of poly(vinyl acetate) and vinyl acetate dispersions, poly(vinyl alcohol), poly(vinyl pyrrolidone). Those skilled in the art will understand that the addition of further resins can modify the ink prepared according to the present invention, but such modifications are within the scope of the present invention.

[0086] In an alternative embodiment of the present invention, the ink does not contain any further water-soluble, alkali-soluble or water-dispersible resin other than SC-PUD. The ink of the present invention does not contain a further polyurethane dispersion (i.e., a polyurethane dispersion other than SC-PUD), a self-crosslinking polyurethane dispersion, an alkali-soluble acrylic resin, an acrylic dispersion, a self-crosslinking acrylic dispersion, a polyester dispersion, a copolymer of poly(vinyl acetate) or a vinyl acetate dispersion, poly(vinyl alcohol), poly(vinyl pyrrolidone), and may preferably not contain any self-crosslinking acrylic dispersion at all.

[0087] The total amount of resin that can be used in the ink prepared according to the present invention is not limited, but may be in the range of 2.5% (w / w) to 40.0% (w / w), more preferably 5.0% (w / w) to 30.0% (w / w), and most preferably 5.0% (w / w) to 20.0% (w / w) based on the total dry mass of SC-PUD and other resins in the total ink composition.

[0088] Since the product of the present invention is inherently mainly aqueous, it is also preferable to include a biocide or a fungicide. Suitable examples include, but are not limited to, the following biocide structural types, namely products based on benzisothiazolinone, bromo-nitro-propane-diol, isothiazolinone, ethylenedioxydimethanol or iodopropynyl butylcarbamate. Some commercially available grades include those sold under the trade names Intercide (Akcros Chemicals) or Nipasol N (Clariant). Other possible types of biocides include sodium dehydroacetate (Geogard 111S from Lonza), sodium benzoate (Vancide 51 from RT VANDERBILT), sodium pyridine thiol-1-oxide (Sodium Omadine from Arch Chemicals), the sodium salt of o-phenylphenol (Dowicide A from DOW Chemicals, and Nipastat Sodium from Aako). These are preferably used in an amount of 0.01 to 1.00% by mass in the ink composition.

[0089] Defoamers can also be optionally included in the formulation. These prevent the formation of bubbles during ink production and spraying. Defoamers are particularly important for recirculating printheads. Examples of suitable defoamers include, but are not limited to, TEGO FOAMEX N, FOAMEX 1488, 1495, 3062, 7447, 800, 8030, 805, 8050, 810, 815N, 822, 825, 830, 831, 835, 840, 842, 843, 845, 855, 860 and 883, TEGO FOAMEX K3, TEGO FOAMEX K7 / K8 and TEGO TWIN 4000, commercially available from Evonik. From BYK, BYK-066N, 088, 055, 057, 1790, 020, BYK-A530, 067A and BYK354 are commercially available. From Dow Corning, additives DC62, DC65, DC68, DC71 and DC74 are commercially available. From Munzing, Agitan 120, 150, 160, 271, 290, 298, 299, 350, 351, 731, 760, 761 and 777 are commercially available. From Air products, Surfynol 104PA, AD01, DF-110, DF-58, DF-62, DF-66, DF-695, DF-70 and MD-20 are commercially available.

[0090] Surface conditioning additives are often optionally used to adjust the wetting on the faceplate of the printhead and to impart a desired spread of droplets on the substrate, or, in the case of multi-pass inkjet printing, to adjust the surface tension of the ink necessary to wet the spread of the dried droplets. They can also be used to adjust the levels of slip resistance and abrasion resistance. Examples of suitable surface conditioning additives include, but are not limited to, TEGO FLOW 300, 370 and 425, TEGO GLIDE 100, 110, 130, 406, 410, 411, 415, 420, 432, 435, 440, 482, A115, and B1484, TEGO GLIDE ZG 400, TEGO RAD 2010, 2011, 2100, 2200N, 2250, 2300, 2500, 2600, 2650, and 2700, TEGO TWIN 4000 and 4100, TEGO WET 240, 250, 260, 265, 270, 280, 500, 505 and 510 and TEGO WET KL245, all commercially available from Evonik. From BYK, BYK333 and 337, BYK UV 3500, BYK 378, 347 and 361, BYK UV 3530 and 3570, CERAFLOUR 998 and 996, NANOBYK 3601, 3610 and 3650, and CERMATT 258 are commercially available. From Cytec, EBECRYL 350 and 1360, MODAFLOW 9200 and EBECRYL 341 are commercially available. The aliphatic silicone acrylate CN9800 from Sartomer can be used. From Air Products, Surfynol 104, 420, 440, 465, 485, 61, 82 and 2502 are commercially available. From Croda, Multiwet BD, EF, SU, SO and VE are commercially available. From Du Pont, Capstone FS-30, 31, 34, 35, 50, 51, 60, 61, 63, 64, 65 and 3100 are commercially available.

[0091] The ink formulation can optionally include a suitable degassing agent. These prevent the formation of air inclusions and pinholes in the cured ink film. They also reduce the regulatory diffusion that can cause reliability issues in the print head. Non-limiting examples include the following products commercially available from Evonik, namely TEGO AIREX 900, 910, 916, 920, 931, 936, 940, 944, 945, 950, 962, 980 and 986.

[0092] The ink composition of the present invention may optionally contain one or more colorants including pigments and / or dyes. Examples of suitable organic or inorganic pigments include carbon black, zinc oxide, titanium dioxide, phthalocyanine, anthraquinone, perylene, carbazole, monoazo and diazobenzimidazole, rhodamine, indigoid, quinacridone, diazopyrantrone, dinitroaniline, pyrazole, diazopyrantrone, pyrazole, dianisidine, pyrantrone, tetrachloroisoindoline, dioxazine, monoazoacrid and anthrapyrimidine. Dyes include, but are not limited to, azo dyes, anthraquinone dyes, xanthene dyes, azine dyes, and combinations thereof.

[0093] Commercially available organic pigments classified according to the Color Index International can be used, which include, without limitation, the following trade names, namely PB1, PB15, PB15:1, PB15:3, PB15:4, PB15:6, PB16, PB60 as blue pigments, PB5, PB23 and PB265 as brown pigments, PG1, PG7, PG10 and PG36 as green pigments, PY3, PY14, PY16, PY17, PY24, PY65, PY73, PY74, PY83, PY95, PY97, PY108, PY109, PY110, PY113, PY128, PY129, PY138, PY139, PY150, PY151, PY154, PY156, PY175, PY180 and PY213 as yellow pigments, PO5, PO15, PO16, PO31, PO34, PO36, PO43, PO48, PO51, PO60, PO61 and PO71 as orange pigments, PR4, PR5, PR7, PR9, PR22, PR23, PR48, PR48:2, PR49, PR112, PR122, PR123, PR149, PR166, PR168, PR170, PR177, PR179, PR190, PR202, PR206, PR207, PR224 and PR254 as red pigments, PV19, PV23, PV32, PV37 and PV42 as purple pigments, and PBk1, PBk6, PBk7, PBk8, PBk9, PBk10, PBk11, PBk12, PBk13, PBk14, PBk17, PBk18, PBk19, PBk22, PBk23, PBk24, PBk25, PBk26, PBk27, PBk28, PBk29, PBk30, PBk31, PBk32, PBk33, PBk34, PBk35, NBk1, NBk2, NBk3, NBk4, NBk6 commercially available ones, as well as combinations thereof, etc.

[0094] Those pigments are typically ground to less than 1 micron, and after grinding, the particle size distribution preferably becomes 10 - 500 nm, more preferably 10 - 350 nm, so as to have better transparency and a wide color gamut.

[0095] In order to include the above pigments in the composition of the invention, it is preferable to manufacture the pigments and store them stably as a concentrate in water. This is typically achieved by using a water-soluble and / or water-dispersible surfactant that introduces hydrophilic functional groups to the surface of the pigment particles, and dispersing the pigment in a water-soluble or water-dispersible resin. There are a great many examples of these dispersion resins, including polyvinyl alcohol, polyacrylic acid, acrylic acid-acrylonitrile copolymer, vinyl acetate-acrylate copolymer, acrylic acid-acrylate copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylate copolymer, styrene-alpha-methylstyrene-acrylic acid copolymer, styrene-alpha-methylstyrene-acrylic acid-acrylate copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl acetate-maleate copolymer, vinyl acetate-crotonic acid copolymer, and vinyl acetate-acrylic acid copolymer, as well as their salts. These copolymers can be used in the form of random copolymers, block copolymers, alternating copolymers, and graft copolymers. Examples of such resins include Joncryl 67, 678, 8500, 586, 611, 680, 682, 683, and 69, which are commercially available from BASF. These resins are generally neutralized with ammonia to enable the preparation of polymer solutions. It is also possible to neutralize the resin with any other organic amine or inorganic base.

[0096] The ink according to the present invention may optionally contain a pigment dispersion, for example, an aqueous dispersion containing a pigment and one or more of the water-soluble and / or water-dispersible resins listed above. The aqueous pigment dispersion may further optionally contain one or more water-soluble and / or water-dispersible surfactants.

[0097] Examples of surfactants used in pigment dispersions include anionic surfactants such as alkane sulfonates, alpha-olefin sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, acylmethyl taurinates, dialkyl sulfosuccinates, alkyl sulfates, sulfurized olefins, polyoxyethylene alkyl ether phosphates, polycarboxylic acids, and monoglycerol phosphates; amphoteric surfactants such as alkylpyridinium salts; and nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkyl amides, glycerol alkyl esters, and sorbitan alkyl esters, but are not limited thereto. Examples include products of the EFKA 1000, 4000, 5000, and 6000 series from BASF, products of the Tamol series from Dow, and Solsperse 27,000, 40,000, 44,000, 46,000, and 47,000 from Lubrizol.

[0098] The present inventors have produced an inkjet ink composition capable of producing printed matter having excellent redissolvability and excellent water (wet rub) resistance using a pigment dispersion containing an anionic and / or nonionic dispersant. Since inks produced with nonionic dispersants (surfactants) that are essentially susceptible to water can be inferior in water resistance, the finding that inks containing SC-PUD and pigment dispersions prepared using nonionic dispersants can produce water-resistant printed matter is a significant finding for inkjet applications. Therefore, an optional feature of the present invention relates to inks containing pigment dispersions prepared using anionic or nonionic dispersants, or a combination of both. When the ink contains a pigment dispersion prepared using an anionic dispersant, the anionic dispersant is preferably an anionic acrylic copolymer dispersant.

[0099] The inkjet composition prepared according to the present invention is suitable for printing by multi-pass or single-pass processing. Applications to which the present invention pertains include multi-pass printing of textile products containing cotton-rich fabrics, single-pass printing of textile products, multi-pass printing of packaging including cardboard, single-pass printing of packaging including labels, corrugated cardboard, and flexible packaging, single-pass and multi-pass printing of metal substrates including metal decoration and decorative printing of cans, although not limited thereto. The inkjet composition prepared according to the present invention is also ideal for the multi-pass graphics printing market. In the graphics market, the inkjet composition of the invention can be printed on any soft or hard substrate including, but not limited to, paper, vinyl, acrylic, polystyrene, polycarbonate, metal, etc. The inventor has shown that the inkjet ink of the present invention has excellent performance (i.e., excellent adhesion and water (wet rub) resistance) on vinyl, acrylic, and polycarbonate substrates used in the graphics inkjet printing market, particularly on vinyl, acrylic, and polycarbonate substrates used in the multi-pass inkjet graphics market. The present invention is directed to inkjet compositions, but is also useful for aqueous flexographic and gravure inks.

[0100] In any case, prior to printing the inkjet composition of the invention, a printing-receptive primer can be applied to the substrate to be printed. The substrate to be printed, in particular, packaging substrates including polyester films, polypropylene films, nylon films, cellulose acetate films, polyethylene films, aluminum foils, metal sheets and rolls, and any coatings thereof can be further treated by corona discharge or plasma treatment before printing to enhance adhesion and printing receptivity. Similarly, further treatments including, but not limited to, overcoating, lamination, etc. can be applied to the printed material to realize the final product. In the packaging market, the printing ink of the present invention is useful for the preparation of laminates that can be produced by an adhesive or a thermal lamination method. Those skilled in the art will recognize various methods and the details of such methods that enable the ink of the present invention to function properly in the above-mentioned market. Therefore, in a further optional embodiment of the present invention, the inkjet printing ink according to the present invention is printed on a substrate pre-coated with the primer.

[0101] Definitions Boiling point: Unless otherwise specified, any boiling point is measured under a standard atmospheric pressure of 101 kPa.

[0102] Heat of vaporization: It is defined as the amount of energy (enthalpy) that should be added to a certain amount of a liquid substance to convert it into a gas. For the purposes of the present disclosure, the heat of vaporization is that indicated at the standard boiling point of the substance in question, and the standard boiling point is the boiling point of the substance at one atmosphere.

[0103] As used herein, room temperature is 25°C.

[0104] Unless otherwise specified, solubility is measured at 25°C.

[0105] Hydroxyl value (OHV): This is defined as the number of milligrams of potassium hydroxide required to neutralize the acetic acid absorbed by the acetylation of 1 gram of a chemical substance containing free hydroxyl groups. The hydroxyl value is preferably measured in accordance with ISO 4629-1:2016(E).

[0106] Acid value (AV): The mass in milligrams of potassium hydroxide (KOH) required to neutralize 1 gram of a chemical substance. Unless otherwise specified, the acid value refers to the total acid value and is preferably measured in accordance with the ISO 2114:2000(E) (Method B) standard.

[0107] Molecular weight: Refers to both the number average molecular weight and the mass average molecular weight throughout. The number average molecular weight and the mass average molecular weight are determined by gel permeation chromatography (GPC). Preferably, the molecular weight is measured by comparison with polystyrene standards. For example, the measurement of the molecular weight can be carried out on a Hewlett Packard 1050 series HPLC system equipped with two GPC Ultrastyragel columns, 103 and 104 Å (5 μm mixed, 300 mm × 19 mm, Waters Millipore (Milford, Massachusetts, USA)) and THF as the mobile phase. Those skilled in the art will understand that this definition is typically applied to polymeric materials having a molecular weight distribution. In the experimental work carried out here, the theoretical number average molecular weight is calculated by end group analysis (also referred to as chain end analysis) based on the carbonyl (i.e., ketone and / or aldehyde) content and the mass of the polymer, assuming that the carbonyl groups are present at each of the two chain ends of the polymer.

[0108] Carbonyl content: The carbonyl content (i.e., ketone and / or aldehyde content) is preferably measured using quantitative 13 13C NMR spectroscopy. Preferably, the carbonyl content is measured by comparison with a suitable calibration reagent, for example, the end-capping reagent used to prepare SC-PUD. For example, several 13A 13C NMR experiment can be performed to create a calibration curve by integrating specific carbon peaks on the NMR spectrum, such as carbonyl peaks. Then, by comparing the carbon integration value of the polymer to be measured with the calibration curve, the carbonyl content of the polymer can be obtained. In the experimental work carried out here, the carbonyl content is calculated from the number of moles of raw materials used to produce SC-PUD.

[0109] Particle size / average particle size: From the perspective of the present invention, the term "particle size" or "average particle size" refers to the median particle size of the volume distribution (the equivalent spherical diameter corresponding to 50% of the volume of all particles read on the cumulative distribution curve associating volume% with particle diameter - often referred to as the "D(v,0.5)" value). The particle size is preferably measured by laser light diffraction.

[0110] Redissolution of the inkjet ink: Unless otherwise specified, the redissolution is measured as follows. An ink layer of about 60 μm was applied onto a slide glass using a No. 6 K bar (RK Print). Then, the ink film was dried at 40 °C for 30 minutes. Next, the dried ink was immersed in an aqueous mixture containing 25% (w / w) propylene glycol, 0.2% Tegowet KL245 (surfactant, e.g., Evonik) and 0.15% (w / w) triethanolamine, with the remainder being deionized water. This aqueous solution is a good simulation of the ink varnish. Inks with high redissolution typically redissolve / redisperse easily into the immersion liquid within 2 - 5 minutes, while insoluble inks do not redisperse into the immersion liquid within 60 minutes after immersion.

[0111] As those skilled in the art will understand, the terms redissolution and redispersibility are used interchangeably in the art to refer to the same ink property.

[0112] The present invention has been described in detail including its preferred embodiments. However, it is understood that those skilled in the art can make modifications and / or alterations to the present invention within the scope and spirit of the present disclosure by considering the present disclosure.

[0113] Numbered items of the present invention The present invention will be further described by the following numbered items. 1. An aqueous printing ink composition containing a polyurethane dispersion, wherein the polyurethane of the polyurethane dispersion has the following characteristics: (a) a carbonyl group is present at one or more polymer chain ends; (b) the number average molecular weight is 50,000 or less, more preferably 25,000 or less; and (c) the carbonyl group content is in the range of 0.02 to 4.0 mmol / g based on the dry polymer mass -1 An aqueous printing ink composition having the above characteristics. 2. The composition according to item number 1, which is selected from the group consisting of inkjet ink, flexographic ink, and gravure ink. 3. The composition according to item number 1 or 2, wherein the polyurethane has a mostly linear structure and the average number of carbonyl groups on the polymer is 2 or less. 4. The composition according to any one of item numbers 1 to 3, wherein the polyurethane dispersion has an acid value of 10 mgKOH / g or more based on the dry polymer mass -1 or more. 5. The composition according to any one of item numbers 1 to 4, wherein the polyurethane dispersion has an average particle size of 200 nm or less, more preferably 150 nm or less. 6. The composition according to any one of item numbers 1 to 5, wherein the polyurethane dispersion further contains a reagent capable of reacting with a carbonyl compound to cure the composition. 7. The composition according to item number 6, wherein the reagent is a bifunctional, trifunctional, or higher polyfunctional primary diamine, or dihydrazide, and the reagent is preferably a bifunctional reagent. 8. The composition according to item number 6, wherein the bifunctional reagent is adipic acid dihydrazide. 9. The composition according to item number 6, wherein the reagent is a polyvalent metal crosslinking agent, preferably a zirconium complex. 10. The composition according to any one of item numbers 1 to 9, which further contains one or more acids selected from the group consisting of tartaric acid, gluconic acid, citric acid, maleic acid, succinic acid, and their salts. 11. The polyurethane in the polyurethane dispersion further contains a hydroxyl group, and the hydroxyl value of the polyurethane is preferably 100 mg KOH / g -1 more preferably 50 mg KOH / g or less -1 The composition according to any one of item numbers 1 to 10, which is as follows. 12. The composition according to any one of item numbers 1 to 11, which contains 25% (w / w) or less of a blend of any solvent having a boiling point of 150°C or higher and an evaporation heat of 500 J / g or higher. -1 13. The composition according to any one of item numbers 1 to 12, which contains a pigment dispersion prepared using an anionic dispersant or a nonionic dispersant, or a blend thereof. 14. The composition according to any one of item numbers 1 to 13, which further contains any additional polyurethane dispersion that does not meet the criteria of claim 1. 15. The composition according to any one of item numbers 1 to 14, which further contains an additional styrene-acrylic dispersion. 16. A method for printing an article, which includes a step of printing the composition according to any one or more of item numbers 1 to 15 on a substrate and a step of curing. 17. The method according to item number 16, wherein the substrate is suitable for printing on packaging, food packaging, metal substrates, textile products, decorative laminates, and graphics. 18. A printed article containing the composition according to any one or more of item numbers 1 to 15.

Examples

[0114] The present invention will be further illustrated by the following non-limiting examples, which are not intended to limit the scope of the present invention and should not be construed as such.

[0115] Materials Daotan 6425: A conventional hydroxyl-functional polyurethane dispersion (manufactured by Allnex) with a solid content of approximately 40% and a hydroxyl value of approximately 55 mg KOH / g. Neorez R605: A conventional polyurethane dispersion (DSM Resins) with a solids content of approximately 33% and a hydroxyl value of less than about 5 mg KOH / g. Daotan TW7064: A conventional self-crosslinking ketone-containing polyurethane dispersion (Ornex) with a solids content of approximately 40% and polymer chain ends having no ketone groups. Joncryl FLX5000: A self-crosslinking acrylic dispersion (BASF) with a solids content of approximately 42%. Joncryl FLX5060: A self-crosslinking acrylic dispersion (BASF) with a solids content of approximately 43% and described as having good redissolvability for printing ink applications. Tego Wet KL245: A surfactant (Evonik).

[0116] Triethanolamine Propylene glycol: A water-soluble cosolvent having a boiling point of approximately 188 °C and an evaporation heat of approximately 880 J / g. MMB (3-methoxy-3-methyl-1-butanol): A water-soluble cosolvent having a boiling point of approximately 174 °C and an evaporation heat of approximately 384 J / g. Cyan pigment dispersion A: An aqueous dispersion of Cyan 15:3 pigment containing approximately 16% (w / w) pigment and an anionic dispersant. Cyan pigment dispersion B: An aqueous dispersion of Cyan 15:3 pigment containing a content of approximately 20% (w / w) and further containing a non-ionic dispersant. Carbodilite SV-02: A polycarbodiimide crosslinking agent (Nisshinbo Chemical Inc.).

[0117] SC-PUD used in the examples Table 1 shows the details of the SC-PUD used in the preparation of the aqueous ink composition suitable for the inkjet composition meeting the requirements of the present invention described above. Unless otherwise specified, all SC-PUDs contain the co-reagent adipic acid dihydrazide (molar ratio of ADH of SC-PUD is 1:1) to effectively cure the printed matter after drying. All SC-PUDs except SC-PUD C, which used triethylamine as the neutralizing base, used N,N-dimethylethanolamine as the neutralizing agent.

[0118]

Table 1

[0119] Test The viscosity was measured at 32 °C using a Brookfield DV-II+Pro viscometer equipped with a No. 18 spindle at 100 rpm.

[0120] Redissolution test: An ink film of about 60 μm was applied onto a slide glass using a No. 6 K-bar applicator (RK Print). Then, the ink was dried at 40 °C for 30 minutes and then immersed in an aqueous solution containing 25% propylene glycol, 0.2% Tegowet KL245, and 0.15% triethanolamine. The redissolution was evaluated according to the following criteria. "High redissolution" (the dried ink film was dispersed in the immersion liquid within 3 minutes and no trace of undissolved ink was observed). "Some redissolution" (the dried ink film was dispersed in the immersion liquid within 3 - 5 minutes and no trace of undissolved ink was observed). "Slow redissolution" (the dried ink film was dispersed in the immersion liquid within 30 minutes and no trace of undissolved ink was observed). "Partial redissolution" (the dried ink film was dispersed in the immersion liquid within 30 minutes and a trace of undissolved ink was observed). "Insoluble" (hardly any trace of the dried ink film being dispersed in the immersion liquid was observed within 30 minutes).

[0121] Preparation of printed matter: The ink was applied at 8 μm onto a white polyester-coated steel plate using a K-bar applicator (RK Print). Then, the printed matter was dried for 20 seconds using a hot air blower. After the printed matter was left standing at room temperature for an additional 15 minutes, it was subjected to a solvent resistance test. Then, the printed matter was heated at 50 °C and 75 °C for 2 minutes and subjected to a solvent resistance test. In a further test, the printed matter was heated at 50 °C for 2 minutes and then left standing under ambient conditions (22 - 25 °C) for 1 - 7 days to evaluate the solvent resistance through this post-printing curing process.

[0122] Water resistance: The water resistance was measured by rubbing the printed matter with a cotton swab dipped in water. The number of double rubs required to remove or damage the printed matter was recorded. This is a test well-known in the industry.

[0123] Table 2 shows the results for several comparative inks suitable for inkjet printing, including polyurethanes and acrylic dispersions that do not meet the requirements of the present invention. The results for inks containing hydroxy-functional PUD and polycarbodiimide crosslinking agents based on the teachings of US Patent Application Publication No. 2018 / 0105710 are also included in Table 2.

[0124] [Table 2]

[0125] The results in Table 2 reflect the problems solved by the present invention, namely, a method for producing an aqueous printing ink for inkjet printing that combines ink properties (i.e., redissolvability) and printed matter properties (i.e., the ability to produce a printed matter with good water resistance demonstrated by double rubs). Conventional polyurethanes and acrylic dispersions do produce resistant printed matters, but the inks containing them are extremely difficult to dissolve. In contrast, the ink produced by OH-PUD Dao Tan 6425 has high redissolvability but is inferior in non-stickiness. When a polycarbodiimide crosslinking agent is added to this ink, although the non-stickiness is improved, the redissolvability is greatly impaired. Also, Comparative Examples C5 and C6 do not exhibit sufficient water resistance even after a 24-hour post-curing period at room temperature after initial drying at 50°C.

[0126] Table 3 shows the results for inks prepared using the SC-PUDs described in Table 1, including SC-PUD A and H, which are SC-PUDs without ketone groups as part of their polymer structures, to calibrate Comparative Examples 7 and 8. Those inks were tested by the method described above. As a further test, the inks were stored at 50°C for 7 days and the stability of the inks was evaluated by re-measuring the viscosity. An increase in viscosity of 10% or more is considered unstable. Inks containing PUD usually show a slight decrease in viscosity.

[0127]

Table 3

[0128] The results in Table 3 indicate the benefits of the aqueous ink containing SC-PUD. Comparing I1 with C7 and I2 with C8, it can be seen that the removal of the ketone functional group from SC-PUD affects the water resistance of the printed matter. All examples of the present invention show that, in particular, the balance between ink redissolvability and non-stickiness of the ink containing SC-PUD with the curing reagent ADH is excellent. Example I3 containing ketone-functional SC-PUD but not containing the ADH curing agent, although not at the same level as I2 which is basically the same SC-PUD except for containing ADH, can produce printed matter with a certain degree of water resistance, which is interesting. Ink example I4 containing SC-PUD C which is basically the same as SC-PUD except that SC-PUD is neutralized with triethylamine instead of N,N-dimethylethanolamine is further noted. This more volatile neutralizing amine has a slight adverse effect on the redissolvability of the ink but enables the non-stickiness to appear more rapidly. It is reasonable to consider that this is due to the slowdown of the reaction between the ketone group of SC-PUD and ADH in the presence of the tertiary amine. As a result, inks containing SC-PUD neutralized with a less volatile amine such as N,N-dimethylethanolamine (the boiling point of triethylamine is 89 °C while having a boiling point of 134 °C) cure more slowly. To promote redissolvability, a further aspect of the present invention is that the tertiary amine for neutralization preferably has a boiling point exceeding 125 °C.

[0129] It is considered that inks can be prepared using blends of SC-PUD and other resins. Table 4 shows the results for some inks prepared along these lines, i.e., ink compositions following those described previously.

[0130]

Table 4

[0131] The results in Table 4 show that ink compositions can be prepared by combining SC-PUD with other aqueous resins. Regarding the water resistance of the final printed product, there is no clear benefit in doing so, and the excellent ink redissolvability may be impaired. However, those skilled in the art will understand that other resins can be used to enhance specific properties such as adhesion. The inventors have shown that Ink Examples I1 and I2 have excellent adhesion to a wide range of substrates including corona-discharge-treated PET and OPP films, acrylic-coated PET films, and graphic substrates containing acrylic, vinyl, and polycarbonate. All of the inks showed good adhesion to the coated steel plates used in the examples.

[0132] Table 5 shows aqueous compositions containing various concentrations of SC-PUD, as well as different solvent blends and concentrations. Again, inks were prepared according to the compositions already shown. Differences in SC-PUD or solvent concentration were compensated for by adding additional deionized water to the ink.

[0133]

Table 5

[0134] The results in Table 5 show that the inventive compositions can be prepared with lower concentrations of SC-PUD, as well as alternative solvent blends and lower total solvent concentrations. A notable feature is how the drying response after 2 minutes at 50 °C is enhanced in inks containing 15% (w / w) or less propylene glycol. All of the inks shown in Table 5 maintain a high level of redissolvability. Table 5 also shows that the addition of MMB results in a lower organic solvent concentration (%) of the inventive composition (being replaced by water). As the content of the organic solvent decreases and at the same time the content of water increases, an ink composition of the invention that is more environmentally friendly than the comparative ink compositions while showing the desired performance characteristics can be obtained.

[0135] In any of the above examples, a cyan pigment dispersion A, which is a dispersion using a nonionic dispersant in its preparation, was used. SC-PUD enables the production of inks with a good balance between ink redissolubility and imparting good non-stickiness using pigment dispersions that use nonionic dispersants in their production. To demonstrate this, further ink examples were prepared using cyan pigment dispersion B. The details of these inks and the related results are shown in Table 6.

[0136]

Table 6

[0137] From Table 6, it can be seen to what extent the pigment dispersion B affects the printing water resistance compared to the pigment dispersion A, that is, C9 compared to C4. Ink example I19 of the invention was able to produce a printed matter with high redissolubility and excellent water resistance compared to Comparative Example C10 based on the conventional self-crosslinking acrylic dispersion Joncryl FLX5060. Also, the ink of Comparative Example C10 has very poor redissolubility.

Claims

1. 1. An aqueous printing ink composition comprising a polyurethane dispersion, The polyurethane of the polyurethane dispersion is (a) the presence of a ketone or aldehyde group at one or more polymer chain ends but not elsewhere on the polymer chain; (b) a number average molecular weight of 50,000 or less; and (c) The content of ketone groups and aldehyde groups is 0.02 to 4.0 mmol g based on the dry polymer mass. -1 The property of being in the range Including, (i) the polyurethane of the polyurethane dispersion is linear and contains no more than two ketone or aldehyde groups per average polymer chain, present at the polymer chain ends but not elsewhere on the polymer chain; or (ii) the polyurethane of the polyurethane dispersion is branched, with up to two ketone or aldehyde groups present at the polymer chain ends and no other positions along the polymer chain; The aqueous printing ink composition is an inkjet ink.

2. The composition of claim 1, wherein the polyurethane of the polyurethane dispersion has the property of having a number average molecular weight of 25,000 or less.

3. 2. The composition of claim 1, wherein the group present at one or more polymer chain ends is a ketone group.

4. The polyurethane dispersion has a concentration of 10 mg KOH / g based on the dry polymer mass. -1 2. The composition of claim 1, having an acid number of at least 100 ppm.

5. 10. The composition of claim 1, wherein the polyurethane dispersion has an average particle size of 200 nm or less.

6. The composition of claim 5, wherein the polyurethane dispersion has an average particle size of 150 nm or less.

7. 10. The composition of claim 1, wherein the polyurethane dispersion further comprises an agent capable of reacting with a ketone or aldehyde group at one or more polymer chain ends to cure the composition.

8. 8. The composition of claim 7, wherein curing occurs via linear chain extension.

9. 8. The composition of claim 7, wherein the reagent is a di-, tri-, or higher functional primary diamine or dihydrazide.

10. The composition of claim 9, wherein the reagent is adipic acid dihydrazide, a difunctional primary diamine.

11. 8. The composition of claim 7, wherein the reagent is a polyvalent metal crosslinker.

12. The composition of claim 11, wherein the polyvalent metal crosslinking agent is a zirconium complex.

13. 10. The composition of claim 1, further comprising one or more acids selected from the group consisting of tartaric acid, gluconic acid, citric acid, maleic acid, succinic acid, and salts thereof.

14. The polyurethane of the polyurethane dispersion further comprises hydroxyl groups, and the hydroxyl value of the polyurethane is 100 mg KOHg -1 2. The composition of claim 1, wherein:

15. The composition of claim 14, wherein the polyurethane has a hydroxyl number of 50 mg KOHg −1 or less.

16. 15. The composition of claim 14, wherein the hydroxyl groups are present at one or more polymer chain ends.

17. Boiling point above 50℃ and 500Jg -1 10. The composition of claim 1, wherein any blend containing a solvent having a heat of vaporization equal to or greater than 25% (w / w) is included.

18. 10. The composition of claim 1, comprising a pigment dispersion prepared with an anionic dispersant or a nonionic dispersant, or a blend thereof.

19. 10. The composition of claim 1 further comprising any additional polyurethane dispersion not meeting the criteria of claim 1.

20. 10. The composition of claim 1 further comprising an additional styrene-acrylic dispersion.

21. 10. The composition of claim 1, wherein the polyurethane is anionically stabilized by including a carboxylic acid in the polyurethane chain.

22. 22. The composition of claim 21, wherein the anionically stabilized polyurethane is neutralized with a tertiary amine, potassium hydroxide, or sodium hydroxide.

23. The anionically stabilized polyurethane is a tertiary amine having a boiling point greater than 125°C.

23. The composition of claim 22, wherein the composition is neutralized with amine.

24. 23. The composition of claim 22, wherein the anionically stabilized polyurethane is neutralized with triethylamine or N,N-dimethylethanolamine.

25. 25. A method of printing an article, comprising printing the composition of any one of claims 1 to 24 onto a substrate and curing.

26. 26. The method of claim 25, wherein the substrate is suitable for packaging, food packaging, metal substrates, textiles, decorative laminates and printing of graphics.

27. 25. A printed article comprising the composition of any one of claims 1 to 24.