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US-12617958-B2 - Aqueous ink compositions

US12617958B2US 12617958 B2US12617958 B2US 12617958B2US-12617958-B2

Abstract

Curable aqueous printing ink compositions, especially inkjet, having excellent resolubility, comprising self-crosslinkable styrene-acrylic polymer dispersions and hydroxy-functional PUDs.

Inventors

  • Derek Illsley

Assignees

  • SUN CHEMICAL CORPORATION

Dates

Publication Date
20260505
Application Date
20211006

Claims (20)

  1. 1 . An aqueous printing ink composition comprising: an aqueous dispersion or solution of a self-crosslinking polymer, an aqueous dispersion of a hydroxyl-functional polyurethane, and at least one amine having a boiling point of above 130° C. and less than 250° C.; wherein the ratio of the self-crosslinking polymer, based on dry polymer weight, to OH-PUD, based on dry polymer weight, is in the range of 0.2:1.0 to 1.0:1.0; and wherein the self-crosslinking polymer is produced by a free radical polymerization of a blend of ethylenically unsaturated monomers.
  2. 2 . The composition according to claim 1 , wherein the self-crosslinking polymer comprises a self-crosslinking acrylic copolymer or a self-crosslinking styrene-acrylic copolymer.
  3. 3 . The composition according to claim 1 , wherein the self-crosslinking polymer comprises an aldehyde group, a ketone group, a carboxylic acid group, an organosilane group, or a combination thereof, attached to the polymer.
  4. 4 . The composition according to claim 3 , wherein the aqueous dispersion or solution of the self-crosslinking polymer and further comprises at least one crosslinker selected from a multifunctional amine and a metal complex.
  5. 5 . The composition according to claim 1 , wherein the aqueous dispersion of the hydroxyl-functional polyurethane has a hydroxyl value of 130 mgKOH/g or greater, based on the dry weight of the polymer.
  6. 6 . The composition according to claim 1 , which is suitable for printing via an inkjet printing process and has a viscosity of 10 mPa·s, or less, at 32° C., wherein the viscosity is measured with a viscometer equipped with a spindle no. 18 at 100 rpm.
  7. 7 . The composition according to claim 1 , which has an initial viscosity that increases ≤5% after 14 days at 50° C.
  8. 8 . The composition according to claim 1 , which contains 30% or less (w/w) of any blend of organic water-soluble co-solvents having boiling points of greater than 150° C.
  9. 9 . The composition according to claim 8 , which contains less than 10% (w/w) of a water-soluble organic co-solvent with a boiling point in excess of 200° C.
  10. 10 . The composition according to claim 1 , in which the at least one amine has a boiling point of above 130° C. and less than 200° C.
  11. 11 . The ink composition according to claim 1 , in which the at least one amine is selected from the group consisting of N,N-dimethylethanolamine, N-methylethanol amine, 2-amino-2-methyl-1-propanol, and ethanolamine.
  12. 12 . The ink composition according to claim 1 , in which the at least one amine is selected from the group consisting of N,N-dimethylethanolamine and 2-amino-2-methyl-1-propanol.
  13. 13 . The composition according to claim 1 , which further comprises at least one crosslinker selected from the group consisting of carbodiimide, oxazoline, aziridine, amino resin, and a blocked isocyanate type crosslinker.
  14. 14 . The composition according to claim 1 , further comprising a colorant; wherein the colorant comprises at least one organic and/or inorganic pigment, at least one dye, or a combination thereof.
  15. 15 . The composition according to claim 14 , wherein the at least one organic and/or inorganic pigment is selected from the group consisting of carbon black, zinc oxide, titanium dioxide, phthalocyanine, anthraquinones, perylenes, carbazoles, monoazo and disazobenzimidazoles, rhodamines, indigoids, quinacridones, diazopyranthrones, dinitroanilines, pyrazoles, diazopyranthrones, pyrazoles, dianisidines, pyranthrones, tetracholoroisoindolines, dioxazines, monoazoacrylides, and anthrapyrimidines.
  16. 16 . The composition according to claim 14 , wherein the at least one dye is selected from the group consisting of azo dyes, anthraquinone dyes, xanthene dyes, and azine dyes.
  17. 17 . The composition of claim 1 , which reaches failure mode with less than or equal to 20 double water rubs after 15 min. at room temperature, and which reaches failure mode with greater than or equal to 50 double water rubs after heating at 100° C. for 2 minutes or after storing at room temperature for 2 days.
  18. 18 . The composition according to claim 1 which may be used in the printing of packaging, the printing of food packaging, the printing of metal substrates, the printing of textiles, the printing of decor laminates and the printing of graphics.
  19. 19 . A printed article comprising the composition of claim 1 .
  20. 20 . A method of making a composition of claim 1 , comprising combining the aqueous dispersion or solution of the self-crosslinking polymer, the aqueous dispersion of the hydroxyl-functional polyurethane, and the at least one amine, wherein the ratio of the self-crosslinking polymer, based on dry polymer weight, to OH-PUD, based on dry polymer weight, is in the range of 0.2:1.0 to 1.0:1.0.

Description

CROSS REFERENCE TO RELATED APPLICATIONS The present application is a § 371 National Phase application based on PCT/GB2021/052578 filed Oct. 6, 2021, which claims the benefit of U.S. Provisional Application No. 63/091,377 filed Oct. 14, 2020, the subject matter of each of which is incorporated by reference in their entirety. The present invention relates to aqueous ink compositions and methods of preparing them, as well as methods of printing such compositions and printed articles produced thereby. The present invention particularly relates to inkjet printing and inkjet printing ink. The present invention particularly relates to resoluble, yet crosslinkable aqueous ink compositions, especially inkjet but also other types of inks such as for example aqueous flexographic and gravure printing inks. The inks of the present invention represent a significant advance for ink technology, especially inkjet ink technology, and especially for inks where the amount of humectant co-solvent needs to be restricted to enable faster single pass printing. The inventors have shown that inks prepared according to the present invention show excellent stability, showing very little change in viscosity or pH when stored at 50° C., for 2 weeks. This is an especially advantageous feature for inkjet printing where any changes in viscosity can be detrimental to the printing (jetting) quality. A further benefit of this stable ink technology is that when the inks partially or fully dry at temperatures used in printing (typically up to 40° C.) the inks can be re-dissolved quite readily, reducing the risk of irreversibly blocking printheads. The use of self-crosslinking styrene-acrylic dispersions in conventional, analogue, printing processes is well known. A good overview of the keto-amine chemistry of this type of polymer dispersion is provided by N. Kessel et. al. (J. Coat. Technol. Res. (2008), (5), 285). The polymer contains ketone, or aldehyde, groups as part of its molecular structure which can then react, upon drying, with multifunctional primary (or secondary) amines to affect the crosslinking reaction. A typical multifunctional amine used in self-crosslinking styrene-acrylic emulsions is adipic dihydrazide, although any other multifunctional amine that can react with either carbonyl or aldehyde groups may also be used. Polyurethane dispersions (PUDs) are seemingly the predominant resin chemistry used in the preparation of pigmented aqueous inkjet printing inks. There are a number of instances in the prior art of the use of amino resins, such as melamine-formaldehydes, to crosslink aqueous inkjet printing inks containing PUDs, especially in the printing of textiles. WO2009/137753 describes how PUDs can be crosslinked with Cymel 303, a melamine-formaldehyde crosslinker, at a temperature of 160° C. A number of other patents describe the use of optional crosslinkers in combination with PUDs to enable improved resistance properties, including; WO2019074683, US20190106587, U.S. Pat. No. 10,513,622, JP2002294112. U.S. Pat. No. 9,249,324, which discloses polyurethane pigment dispersants, usefully lays out the crosslinking possibilities for polyurethanes having any of carboxylic acid, hydroxyl or amine pendant functional groups. Crosslinkers include carbodiimides, epoxies, isocyanates, amino resins (e.g. melamine-formaldehyde), aziridines. However, these references do not disclose the use of self-crosslinking styrene-acrylic dispersions (or solutions), nor their combination with hydroxyl-functional PUDs to deliver a resoluble, yet crosslinkable inkjet technology. US20170029639 and US20170218565 describe the preparation of encapsulated resin particles, where the capsules may comprise compositions which are thermally curable. Again, various conventional crosslinking chemistries are disclosed including; ketone-hydrazine, epoxy-amine, melamine-formaldehyde, with a preference for the use of blocked isocyanates. Again, no reference to the preferential use of hydroxyl-functional PUDs to promote the resolubility of the inks is disclosed. WO2017021278 describes composite resin particles comprising low molecular weight conventional crosslinkers, such as epoxies, oxetanes, aziridines, amino resins (such as melamine-formaldehydes) and blocked isocyanates, where the molecular weight of the crosslinker is preferably less than 2000 Daltons. WO2020102788 discloses aqueous inkjet printing inks comprising carboxylic acid functional acrylic resins which may be crosslinked with well-known, conventional, crosslinkers such as polycarbodiimides, polyoxazolines, aziridines, melamine-formaldehydes, ammonium zirconium carbonate. Again, no mention of the use of self-crosslinking styrene-acrylic dispersions was made. It should be understood that the present invention may optionally use crosslinking agents as disclosed in the prior art. Thus, the aqueous inkjet compositions of the present invention may comprise hydroxyl-functional PUDs and self-crosslinking styrene-