CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to the following co-pending and commonly assigned patent applications, the disclosures of all of which are incorporated herein by reference:

U.S. Pat. No. 10,858,529, by Irving and Dannhauser;

U.S. Pat. No. 10,730,331, by Dannhauser and Irving;

U.S. Publication No. 2020/0062017, filed Aug. 21, 2018, by Irving and Dannhauser, and recently allowed;

U.S. Ser. No. 16/551,868, filed Aug. 27, 2019, by Sowinski, Lussier, Griffin, Putnam, and Bugner, and entitled “Ink Set for Inkjet Printing”;

U.S. Ser. No. 16/551,890, filed Aug. 27, 2019, by Lussier, Sowinski, Irving, Putnam, Griffin, and Bugner, and entitled “Method for Inkjet Printing”;

U.S. Ser. No. 16/551,908, filed Aug. 27, 2019, by Irving, Putnam, Sowinski, Lussier, Griffin, and Bugner, and entitled “Article Prepared by Inkjet Printing” recently allowed, and;

U.S. Ser. No. 16/551,924, filed Aug. 27, 2019, by Putnam, Irving, Bugner, Sowinski, Griffin, and Lussier, and entitled “Laminated Article”, recently allowed.

FIELD OF THE INVENTION

This invention relates to the field of inkjet printing using aqueous pigment-based inks applied to ink-receptive media. More particularly, it relates to a method of making a laminated article that by forming an inkjet-printed image on an ink-receptive medium, followed by formation of a functional layer on the inkjet-printed image. A flexible polymeric film or paper is then laminated to the functional layer to provide a flexible inkjet-printed article.

BACKGROUND OF THE INVENTION

High speed digital inkjet printing systems have recently found considerable success in competing with traditional analog printing presses in applications such as commercial printing and publishing. In particular, inkjet printing systems that employ aqueous pigment-based inks can rival the print quality and productivity of printing systems that are based on analog impact printing, such as lithography, gravure, and flexographic printing systems. The ability of digital inkjet printing systems to print either short-run lengths or continuously variable information in a cost-effective manner offers distinct advantages over such traditional impact printing systems that require the presses to be idled between print jobs.

More recently, high productivity digital inkjet printing systems have been targeted toward décor and packaging printing, with the same advantages. However, such printing, unlike commercial printing and publishing, typically employ water-impermeable substrates such as polymeric films, metal foils, and glass, in addition to paper-based substrates on which images are printed. Plastic substrates are particularly challenging for the use of aqueous pigment-based inks due to the difficulty in getting such inks to wet and adhere to such substrates that are typically designed and chosen to repel or otherwise present a barrier to water. Although solvent-based and radiation-curable (for example UV-curable) inkjet inks have been used with some success on plastic substrates, their use is limited to certain types of inkjet printing systems, such as piezoelectric drop-on-demand (DOD) systems and they present some health, safety, and environmental concerns compared to the use of aqueous-based inks.

When aqueous-based inks are used in high-speed digital inkjet printing, especially inks that contain more than 80 weight % of water and less than 15 weight % of organic co-solvents (also known as “humectants”) and deposited on commonly available plastic substrates used for décor and packaging application, the ink drops tend to either bead up or flow across the substrate surface, resulting in significant defects known as mottle, coalescence, and intercolor bleeding. In addition, such inks are difficult to dry quickly due to the presence of the co-solvents, resulting in a very sticky or tacky printed layer or image.

The literature has proposed a number of ways to overcome the noted problems, for example, the incorporation of additives into the inks that change their viscosity when heated on the plastic substrate; the addition of polymer particles to fuse during heating after printing; the heating of the ink containing mixtures of co-solvents during printing; the use of a “fixing” fluid and ink with specific co-reactive polymers; the use of an adhesive layer on the water-impermeable substrate surface; the surface treatment of the water-impermeable substrate prior to inkjet printing, including the use of protective overcoats; and the use of high-boiling co-solvents in “fixing” fluids to modify the substrate surface.

It is also well known to deposit aqueous pigment-based inks onto a substrate having cations of a multivalent metal salt on the surface thereof. The presence of such multivalent metal cations can be used to prevent deposited ink drops from penetrating too far below the surface of a water-absorptive substrate, thereby preventing a lowering of optical density. The multivalent metal cations can also be used to prevent bleeding or coalescing of adjacent deposited ink drops of the same or different colors on a less absorbent substrate such as a water-impermeable substrate, thereby preventing the formation of blurry or grainy appearing images. Surface treatments comprising aqueous salts of multivalent metal ions are particularly advantageous for high speed printing with page-wide inkjet arrays whereby adjacent drops of ink are deposited within just a few microseconds of each other onto the substrate.

U.S. Pat. No. 9,434,201 (Dannhauser et al.) describes inkjet receiving media suitable for high speed inkjet printing, which media include a substrate having a topmost layer coated thereon comprising an aqueous soluble salt of a multivalent metal cation and a cross-linked hydrophilic polymer binder.

In U.S. Patent Application Publication 2011/0279554 (Dannhauser et al.), it is proposed to modify water-impermeable substrates by applying a pre-coating composition comprising water-soluble salts of multi-valent metal cations in combination with hydrophilic binders. While application of such pre-coats can improve the adhesion of aqueous pigment-based inks during high-speed inkjet printing, the adhesion and wetting may need improvement. Moreover, high-boiling co-solvents or humectants present in such aqueous pigment-based inks cannot readily penetrate into the substrate, leading to prolonged tackiness in the resulting printed image.

U.S. Pat. No. 8,562,126 (Xiang et al.) describes pre-treatment of glossy, semi-glossy, and matte-coated paper substrates for inkjet printing using a coating composition containing an aqueous salt of a multi-valent metal cation, a polyelectrolyte comprising amidine moieties, and another polymer such as a polyamide-epichlorohydrin, a polyamine solution polymer, or a water-based polyurethane. Waxes can be added to such compositions as described in U.S. Patent Application Publication 2003/0203134 (Sheng).

U.S. Pat. No. 9,376,582 (Dannhauser et al.) and U.S. Pat. No. 9,573,349 (Dannhauser et al.) provide a solution to the noted problems with a multi-structural substrate having a water-impermeable support (such as a thin plastic film), a first layer that contains a water-based tie-layer composition, and a second layer (aqueous-based ink-receptive layer) containing an aqueous-soluble salt of a multivalent cation and a hydrophilic binder polymer. One or more aqueous pigment-based inks can be applied to this multi-structural substrate to form an inkjet printed image, particularly when the pigments are anionically-stabilized and water-dispersible pigments. Additional layers can be applied to the inkjet printed images if desired. In particular, it can be advantageous to add an adhesive layer to the inkjet printed image so that another water-impermeable film can be laminated thereto to produce laminated flexible packaging with an “embedded” inkjet printed image.

However, it has been found recently that when the aqueous pigment-based inks used in these methods and with such multi-structural substrates, which contain certain humectants well known in the art, the final laminated flexible packaging material exhibits poor lamination bond strength and delamination can occur. There is a need to solve this problem without sacrificing high-speed inkjet printing and essential operational properties such as stable and accurate jetting, high productivity, machine throughput, and printed image quality. There is also a need to improve the adhesion of the aqueous-based ink-receptive layer directly to a water-impermeable substrate, thereby eliminating the need for a separate water-based tie-layer composition as required in the multi-layer structures methods disclosed in U.S. Pat. Nos. 9,376,582 and 9,573,349 (both noted above).

SUMMARY OF THE INVENTION

The present invention provides a method for making a flexible inkjet-printed article, the method comprising, in order:

A′) providing an ink receptive medium comprising a substrate and an aqueous-based ink-receptive layer disposed thereon, which aqueous-based ink-receptive layer has an outer surface, and comprises:(a) one or more water-soluble salts of a multivalent metal cation in an amount of at least 0.6 weight % and up to and including 49 weight %;(b) one or both of a polyvinyl alcohol and a polyvinyl amine, or a copolymer derived from a vinyl alcohol and a vinyl amine, in a total amount of at least 0.5 weight % and up to and including 30 weight %;optionally, (c) a crosslinking agent in an amount of at least 0.01 weight % and up to and including 5 weight %; andoptionally, (d) silica particles in an amount of up to and including 30 weight %,all amounts being based on the total weight of the aqueous-based ink-receptive layer; and

B) depositing directly on the outer surface of the aqueous-based ink-receptive layer, one or more aqueous pigment-based inks,each aqueous pigment-based ink having at least 75 weight % and up to and including 95 weight % of water, and comprising:a) one or more anionically-stabilized pigment colorants;b) one or more water-miscible humectants in a total amount of at least 1 weight % and up to and including 20 weight %, and consisting essentially of compounds, each of which has a carbon atom to oxygen atom ratio of at least 1.0:1.0 and only two hydroxy groups;and optionally,c) an acidic polymer that is an anionic polyurethane, an acidic acrylic polymer, an acidic styrene-acrylic polymer, or any combination of these materials, each acidic polymer having an acid number of at least 50 and up to and including 240, and each acidic polymer being neutralized with sufficient base to render it dispersible or soluble in each aqueous pigment-based ink,

C) drying the one or more aqueous pigment-based inks to remove substantially all water to form an inkjet-printed image;

D) forming a functional layer comprising an adhesive composition on the inkjet-printed image; and

E) adhering a flexible polymeric film or paper to the functional layer, to form a flexible inkjet printed article.

The present invention provides a solution to the delamination problem described above. Modification of the aqueous-based ink-receptive layer improves its capability to absorb residual humectants of specific classes from the aqueous pigment-based inks after drying, thereby improving lamination bond strength. At the same time, the improved aqueous-based ink-receptive layer provides the option of omitting water-based “tie” layers from between a water-impermeable substrate and an inkjet printed image. Minimization or exclusion of certain common humectant compounds from, and inclusions of other specific humectant compounds within, the aqueous pigment-based inks also improves lamination bond strength. Specifically, the present invention utilizes only dihydroxy humectants in which the carbon atom to oxygen atom molar ratio is at least 1.0:1.0 and up to and including 2.7:1.0, and 1,2,3-trihydroxypropane (glycerol) is used as little as possible, or omitted entirely. The dihydroxy humectants with carbon atom to oxygen atom molar ratio of at least 1.0:1.0 simultaneously provide aqueous pigment-based inks that exhibit stable jet formation without suffering ink drying on the printhead nozzle plate, which problem produces blocked nozzles, crooked jets and ragged jet curtains, or poor printhead start-ups after extended shutdowns. Stable and robust drop formation is essential for accurate printing without interference from excessive printhead maintenance service cycles. These features are described in more detail below.

