Inkjet ink and primer fluid set

Abstract

To provide an improved inkjet ink set and primer fluid combination that can produce higher quality print images on non-porous plastic film surfaces, especially with better film clarity for clear non-porous plastic films.SOLUTION: There is provided an inkjet ink and primer fluid set comprising: (a) an aqueous primer composition comprising a multivalent cation salt and a polymeric binder; and (b) aqueous inkjet inks.SELECTED DRAWING: None

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 62 / 949,795, filed December 18, 2019.

[0002] The present disclosure relates to an inkjet ink and primer fluid set comprising an aqueous primer composition and an aqueous inkjet ink. The aqueous primer composition forms a coating on a print substrate. The inkjet ink includes a polymeric binder that interacts with the primer. The fluid set is particularly suitable for printing on non-porous plastic substrates. [Background technology]

[0003] Inkjet printing is a non-impact digital printing process in which droplets of ink are deposited on a substrate, such as paper, to form a desired image. For full-color printing, inkjet printers are equipped with an ink set that typically includes cyan, magenta, and yellow inks (CMY). Typically, the ink set also includes a black ink (CMYK), with black being the most common ink.

[0004] Inkjet printing is becoming increasingly important in markets outside of traditional desktop printing for small / home offices. Digital printing methods are gaining popularity in textile, commercial, and packaging printing, offering several potential advantages over traditional printing methods such as screen printing, offset printing, flexography, and gravure printing. Inkjet digital printing eliminates the setup costs associated with preparing screens and plates, potentially enabling cost-effective short-run production runs. Furthermore, inkjet printing enables visual effects such as color gradients and infinite pattern repeat sizes that are practically impossible to achieve with screen and other analog printing processes.

[0005] Water-based inkjet inks have seen rapid growth in packaging applications in recent years due to their environmentally friendly digital technology compared to UV and solvent digital inks. Non-porous plastics, including both flexible and rigid plastic films, are common media / substrates in packaging applications. The surfaces of these plastics are inherently non-liquid-absorbent and hydrophobic, posing numerous performance challenges to water-based pigmented inks. Key among these challenges is poor image quality due to slow ink droplet curing, resulting from the non-ink-absorbent nature of the printing surface and the low drying temperatures required to avoid distortion of the plastic substrate. Slow ink droplet settling and drying can result in blurred images and inter-color bleeding, which is particularly exacerbated when printing at high speeds.

[0006] To improve print quality on hydrophobic substrates, a common approach is to coat the hydrophobic surface with a primer or pretreatment fluid. U.S. Patent Application Publication No. 2008 / 0092309 discloses a pretreatment solution for treating textiles. The pretreatment solution includes a nonionic latex polymer and a multivalent cationic salt solution. U.S. Patent Application Publication No. 2014 / 356555 discloses an inkjet print medium including a base substrate and a coating layer. The coating layer includes a source of multivalent ions and a latex binder that forms a coherent film in the presence of the multivalent ions. The base substrate can include paper, cloth, nonwoven fabric, felt, and synthetic (non-cellulose) paper. However, these disclosures do not address printing on non-porous plastic substrates, which differ from other common substrates in that non-porous plastics are completely impermeable to liquids, are difficult to adhere to due to the weak interaction between the plastic polymer and the ink, and often require low drying and curing temperatures due to their poor resistance to heat. Furthermore, transparent non-porous plastic films, which are widely used in packaging applications, require special primers that can enhance the transparency of the film. In addition, unlike printing on paper, printing on transparent or sheer films typically requires printing a white ink above or below the color image to enhance contrast and make the color image more visually distinct.

[0007] There is a need for an improved inkjet ink set and primer fluid combination that can improve film clarity and produce higher quality printed images on non-porous plastic film surfaces, particularly on transparent non-porous plastic films. The present disclosure meets this need by providing an inkjet ink and primer fluid set that includes a primer and an inkjet ink. The primer forms a coating with limited haze increase and interacts with the polymer binder in at least one of the inkjet inks to achieve higher quality printed images on non-porous plastic films. Summary of the Invention [Means for solving the problem]

[0008] One embodiment of the present disclosure comprises: a) an aqueous primer composition comprising a polyvalent cation salt and a polymeric binder, the composition, when applied to a non-porous plastic substrate, forming a coating having a dry thickness of 0.4 to 5.0 microns, the coating resulting in an increase in haze on the substrate of less than 10; the polyvalent cation salt being present in an amount of less than 20 wt. %, based on the total weight of the primer composition; the polymeric binder being insoluble in water and stable in the presence of the polyvalent cation, and selected from the group consisting of urethane polymers, acrylic polymers, and vinyl polymers; (b) an inkjet ink and primer fluid set comprising: aqueous inkjet inks, at least one of the inks comprising a pigment dispersion, a first polymer binder, and a second polymer binder, wherein the first polymer binder forms aggregates with the aqueous primer composition and the second polymer binder does not form aggregates with the aqueous primer composition.

[0009] Another embodiment provides an aqueous inkjet ink comprising a white ink and a non-white ink.

[0010] Another embodiment provides an aqueous primer composition further comprising silica particles.

[0011] Another embodiment provides that the coating results in an increase in haze of less than 5 in the aforementioned substrate.

[0012] Another embodiment provides that the pigment dispersion is dispersed by an anionic polymeric dispersant.

[0013] Another embodiment provides that the anionic polymeric dispersant is a polyurethane.

[0014] Another embodiment provides that the anionic polymeric dispersant is an acrylic polymer.

[0015] Another embodiment provides that the anionic polymeric dispersant is different from the first polymeric binder and the second polymeric binder.

[0016] Another embodiment is (a) providing an inkjet printer responsive to digital data signals; (b) providing a non-porous plastic substrate; (c) applying an aqueous primer composition comprising a polyvalent cation salt and a polymeric binder to a non-porous plastic substrate to form a coating having a dry thickness of 0.4 to 5.0 microns, said coating resulting in an increase in haze of less than 10 on said substrate, said polyvalent cation salt being present in an amount of less than 20 weight percent based on the total weight of the primer composition, and said polymeric binder being insoluble in water and stable in the presence of said polyvalent cations and selected from the group consisting of urethane polymers, acrylic polymers, and vinyl polymers; (d) loading aqueous inkjet inks into the printer, at least one of the inks comprising a pigment dispersion, a first polymeric binder, and a second polymeric binder, said first polymeric binder forming aggregates with said aqueous primer composition and said second polymeric binder not forming aggregates with said aqueous primer composition; (e) printing the primer-coated substrate of step (c) using an aqueous inkjet ink in response to a digital signal.

[0017] Another embodiment provides that the white ink is printed by digital signals before the non-white inks in step (e) above.

[0018] Yet another embodiment provides that in step (e) above, the white ink is printed after the non-white ink by a digital signal. DETAILED DESCRIPTION OF THE INVENTION

[0019] Unless otherwise stated or defined, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0020] Unless otherwise specified, all percentages, parts, ratios, etc. are by weight.

[0021] When an amount, concentration, or other value or parameter is given as a range, preferred range, or list of upper and lower preferred values, this should be understood to specifically disclose all ranges formed from any pairing of any upper range limit or preferred value with any lower range limit or preferred value, whether or not the ranges are separately disclosed. When a range of numerical values ​​is recited herein, unless otherwise specified, the range is intended to include the endpoints thereof, and all integers and fractions within the range.

[0022] When the term "about" is used to describe a value or end-point of a range, the disclosure should be understood to include the specific value or end-point referred to.

[0023] As used herein, the term "dispersion" means a two-phase system in which one phase consists of fine particles (often in the colloidal size range) distributed throughout a bulk material, the particles being the dispersed or inner phase, and the bulk material being the continuous or outer phase.

[0024] As used herein, the term "dispersant" refers to a surfactant added to a suspension medium to promote uniform and maximum separation of very fine solid particles, often of colloidal size. In the case of pigments, the dispersant is most often a polymeric dispersant, and the dispersant and pigment are usually combined using dispersing equipment.

[0025] As used herein, the term "aqueous vehicle" refers to water or a mixture of water and at least one water-soluble or partially water-soluble (i.e., methyl ethyl ketone) organic solvent (co-solvent).

[0026] As used herein, the term "substantially" means to a great extent, almost entirely.

[0027] As used herein, the term "dynes / cm" refers to dynes per centimeter, a surface tension unit.

[0028] As used herein, the term "cP" refers to the viscosity unit centipoise.

[0029] Except only as expressly stated, the materials, methods, and examples herein are illustrative only and not intended to be limiting.

[0030] Additionally, unless the context clearly indicates otherwise, references in the singular may include the plural (e.g., "a" and "an" may refer to one or more than one).

[0031] Non-porous plastic substrate Non-porous plastic substrates or films are one of the primary substrates used in flexible packaging. Flexible packaging is a container made of a material that can quickly change shape when filled or closed. These containers can use any combination of paper, non-porous plastic film, or foil materials. Non-porous plastic films typically include, but are not limited to: High density polyethylene (HDPE), Low-density polyethylene (LDPE) includes linear low-density polyethylene (LLDPE), Polyethylene terephthalate (PET), metallized PET (Met-PET), glass-coated PET, acrylic-coated PET, Polypropylene (PP) includes cast PP (CPP), oriented PP (OPP), biaxially oriented PP (BOPP), and metallized OPP (MOPP). polystyrene, nylon, Polyvinyl chloride (PVC, vinyl), Ethylene vinyl acetate polymer (EVA), and Ethylene vinyl alcohol copolymer (EVOH).

[0032] Each film offers various functions and properties suited to specific applications. Alternatively, films can be combined to create multilayer films with remarkable barrier properties for better protection or longer shelf life. Custom design elements also extend to visual characteristics such as transparency, gloss, and high-quality printed graphics in a variety of colors and designs, stylishly encasing the product and including important information right on the packaging. These substrate films can be non-oriented or oriented. The thickness of the substrate film is not critical, but typically ranges from 1 to 500 μm. The printing surface of the substrate film is preferably treated with corona discharge. For example, silica or alumina can be deposited on the surface of the film.

[0033] Primer composition The aqueous primer fluid should contain enough ink coagulant to provide adequate fixation of the inkjet ink. Typically, the primer contains at least about 0.5 wt. % ink coagulant, with amounts up to the solubility limit of the particular ink coagulant used being acceptable. Preferably, the primer contains about 1 wt. % to about 30 wt. % ink coagulant, based on the total weight of the primer fluid.

[0034] The polymeric binder is combined with the ink coagulant to form the primer fluid. The polymeric binder is advantageously used at a level of at least about 5%, typically at least about 10%, based on the total weight of the ink. The upper limit is determined by the viscosity of the primer or other physical limitations. In more typical embodiments, no more than about 50% polymeric binder is present in the primer composition, based on the total weight of the primer fluid, and most typically no more than about 40%. The combined total weight of the polymeric binder and ink coagulant can be up to about 45% by weight, based on the total weight of the primer fluid.

[0035] The primer composition further comprises a surfactant to provide wetting to the film substrate. Suitable surfactants include those that are miscible with the ink flocculant and polymer, i.e., those that do not form precipitates or aggregates upon mixing. Useful surfactants include cationic, nonionic, and amphoteric surfactants. Suitable cationic surfactants include, for example, quaternized ammonium or pyridinium surfactants, such as dodecyltrimethylammonium chloride, cetyltrimethylammonium bromide, and cetyltrimethylpyridinium chloride. Some suitable nonionic surfactants include ethoxylated acetylenic diols (e.g., Evonik's Surfynol® series), ethoxylated primary alcohols (e.g., Shell's Neodol® series) and secondary alcohols (e.g., Dow Chemical's Tergitol® series), Pluronic® block copolymer surfactants, sulfosuccinates (e.g., Cytec's Aerosol® series), organosilicones (e.g., Evonik's Dynol® series), and fluorosurfactants (e.g., Chemours' Zonyl® series). Amphoteric surfactants that are cationic within a specific pH range can also be used. In this case, the pH of the liquid composition must be adjusted below the isoelectric point of the surfactant. Some examples of useful zwitterionic surfactants include N,N-dimethyl-N-tetradecylamine oxide (NTAO), N,N-dimethyl-N-hexadecylamine oxide (NHAO), and related amine oxide compounds. Another example is N-dodecyl-N,N-dimethylglycine. Further examples include phosphates, phosphites, phosphonates, lecithin, and phosphonate esters such as phosphomyelin. Surfactants may be used in amounts typically from about 0.1 to about 10%, more typically from about 0.5 to about 5%, based on the total weight of the primer fluid.

[0036] The primer may further contain additional additives to modify viscosity, prevent film curl, or improve block resistance, including, but not limited to, colloidal silica dispersions and wax emulsions. Preferred colloidal silica dispersions are nano-sized silica particles stabilized by cationic charge or without charge, as long as the silica dispersion remains stable when mixed with the ink flocculant. Examples include the surface-treated silica SNOWTEX® ST-AK, ST-AK-ML, ST-AK-L, ST-AK-A, and ST-AK-XK (Nissan Chemical America, Houston, TX), and the elongated silica SNOWTEX® ST-OUP and string-of-pearls SNOWTEX® ST-PS-SO and ST-PS-MO. Colloidal silica can typically be used in amounts of 1% to 50% based on the total weight of the primer fluid. Examples of wax emulsions include, but are not limited to, olefin waxes such as LDPE, HDPE, and PP, paraffin wax, carnauba wax, and nonionic emulsified, colloidally stabilized amide waxes that are stable when mixed with ink flocculants. Preferred examples of waxes are AQUACER 539, AQUACER 513, AQUACER 519, and AQUACER 497 (BYK-Chemie Wesel, Germany). Waxes can be used in amounts of typically 0.05% to 5% based on the total weight of the primer fluid, as long as the primer coating remains clear.

[0037] Other components in the primer solution may further include, but are not limited to, humectants and biocides. Biocides prevent microbial decomposition—their selection and use are well known in the art. Suitable humectants are the same as those suitable for use in the color inkjet inks described in more detail below.

[0038] Ink flocculant The primer solution contains an ink agglomerating agent that "precipitates" or "crashes" with the colorant or other components in the ink. Preferred ink agglomerating agents include polyvalent metal salts and / or organic acids.

[0039] "Multivalent" refers to two or more oxidation states, typically Z for element "Z". 2+ , Z 3+ , Z 4+ For simplicity, multivalent cations are referred to herein as Z x The multivalent cations are substantially dissolved in the aqueous primer solution and preferably present in a substantially ionized state (in solution) so that they are free and in a form capable of interacting with the inkjet ink.

[0040] Z x The polyvalent cations include, but are not limited to, polyvalent cations of the following elements: Mg, Ca, Sr, Ba, Sc, Y, La, Ti, Zr, V, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, Cu, Au, Zn, Al, Ga, In, Sb, Bi, Ge, Sn, Pb. In another embodiment, the polyvalent cations include at least one of Mg, Ca, Ba, Ru, Co, Zn, and Ga. In yet another embodiment, the polyvalent cations include at least one of Ca, Ba, Ru, Co, Zn, and Ga. Preferably, the polyvalent cations are Mg and Ca.

[0041] Z x can be incorporated into the primer solution by adding it in the form of a salt or in the form of an alkali, and can be used as a base in adjusting the pH of the primer solution.

[0042] The relevant anionic material can be selected from any common anionic material, particularly halides, nitrates, and sulfates. The form of the anion is selected so that the polyvalent cation is soluble in the aqueous primer solution. The polyvalent cationic salts can be used in their hydrated form. One or more polyvalent cationic salts can be used in the primer solution.

[0043] In the case of Ca, the preferred polyvalent cation salts are calcium chloride, calcium nitrate, calcium nitrate hydrate and mixtures thereof.

[0044] For Mg, the preferred polyvalent cation salts are magnesium chloride, magnesium nitrate, magnesium nitrate hydrate, and mixtures thereof.

[0045] Organic acids used as flocculants lower the pH of the ink, coagulating the pigment dispersion and other ink components, thereby causing ink droplets to precipitate. Specific examples of acids include polyacrylic acid, acetic acid, glycolic acid, malonic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid, sulfonic acid, orthophosphoric acid, pyrrolidonecarboxylic acid, pyronecarboxylic acid, pyrrolecarboxylic acid, furancarboxylic acid, pyridinecarboxylic acid, coumaric acid, thiophenecarboxylic acid, nicotinic acid, and derivatives of these compounds. Polyacrylic acid and acetic acid are particularly preferred.

[0046] Primer Polymer Binder The primer solution contains a compatible polymer binder that does not "precipitate" or "clash" with the coagulant. The primer polymer binder and ink coagulant solution thus formed must be stable as a solution or stable emulsion to allow coating of the film substrate. If the primer polymer binder gels or its emulsion precipitates in the presence of the ink coagulant, such as a polyvalent cationic salt solution, it cannot be used as a primer additive. A screening test to determine whether a primer polymer binder is stable in the presence of an ink coagulant involves mixing 10% by weight of the polymer (dry basis) with 15% by weight of calcium nitrate tetrahydrate and observing whether the solution / emulsion is stable. Stability is observed at 10-minute and 24-hour intervals at ambient temperature (approximately 25°C). The primer polymer binder must result in a stable polymer / polyvalent cationic solution / emulsion mixture.

[0047] Some suitable compatible polymeric binders include nonionic water-insoluble polymers in colloidal particle form, including, for example, acrylic latexes, polyurethane dispersions, vinyl acetate copolymer latexes, polyester and polyamide dispersions. These polymers can be made by any known process, including, but not limited to, free radical, group transfer, ionic, RAFT, condensation, and other types of polymerization.

[0048] The primer polymer binder can be formed by incorporating a nonionic stabilizer chemically bonded or physically absorbed into the polymer. Examples of nonionic reactive components include ethylene oxide derivatives, acrylamide, hydroxyethyl-substituted monomers, vinylpyrrolidone, ethyleneimine, and the like. Incorporation can occur during or after the polymerization process to prepare the latex polymer. In the case of the ethylene oxide nonionic component, the substitution is sufficient (-CH2-CHO-) to impart nonionic stability. n The nonionic latex polymer may take the form of incorporating a glycol having a unit. For example, a polyurethane may have an alkyl polyethylene glycol incorporated into the nonionic polyurethane. The nonionic component may be the major component in the nonionic latex polymer, as long as its properties meet the stability test described above.

[0049] The primer polymer binder may also have ionic components incorporated into the polymer. For example, for polyurethanes, an ionic component such as an acid can be used in the polyurethane reaction; a specific example of an acid is dimethylolpropionic acid. For acylamide and hydroxyethyl-substituted nonionic latex polymers, the ion source can be from (meth)acrylic acid. The content of ionic components in the polymer is limited because they may form complexes with the ink flocculant, leading to instability of the polymer / multivalent cation solution. A balance of nonionic and ionic components must result in a stable solution, as described above.

[0050] Primer application Prior to printing inkjet ink, the film substrate is coated with a primer fluid via a variety of available coating methods, including flexographic, gravure, rod, spray, roll, curtain, and knife coating methods. Preferred methods are flexographic, gravure, and rod coating. Primer application can be inline or offline with the inkjet ink printing process, depending on the printer design and machine integration. Regardless of the coating method, the primer must be thoroughly dried before printing inkjet ink. The drying process can be performed using hot air, infrared, or near-infrared, and is not limited to any particular method, as long as the temperature is not so high as to distort the integrity of the film. Typical drying temperatures range from 40°C to 120°C, preferably 50°C to 100°C. The thickness of the dried primer coating can vary from 0.3 to 10 μm, preferably 0.5 to 8 μm, and more preferably 0.6 to 5 μm. Adjusting the primer coating thickness allows for tuning and optimization of the coating's tackiness, drying speed, haze, adhesion, and ink image quality.

[0051] An important desirable feature of transparent film packaging is the film's clarity, typically measured by haze. Haze is the percentage of light transmitted through the film that is deflected more than 2.5° from the direction of the incident beam. The lower the haze value, the more transparent the film; thicker films and extra coatings typically lead to increased haze. Preferably, after the primer coating, the haze change from the base film substrate is less than 10, more preferably less than 5.

[0052] Ink set The term "ink set" refers to all the individual inks or other fluids that an inkjet printer is equipped to jet. A white ink used to print an image after printing colored inks or a white ink used to print before printing colored inks is considered part of the ink set. This ink set, together with a primer fluid, forms an inkjet ink and primer fluid set.

[0053] In one preferred embodiment, the ink set comprises at least two different colored inkjet inks, at least one of which is a white pigment-based inkjet ink as described above.

[0054] In another preferred embodiment, the ink set comprises at least four inkjet inks of different colours, at least one being a cyan inkjet ink, at least one being a magenta inkjet ink, at least one being a yellow inkjet ink and at least one being a white inkjet ink.

[0055] In addition to the color inkjet inks just described, it is also preferred to include a black inkjet ink in the ink set.

[0056] In addition to the CMYKW inks described above, the ink set may include additional inks of different colors, as well as different strength versions of the CMYKW and other inks.

[0057] For example, an ink set of the present invention may include a full strength version of one or more of the inks in the ink set and a "light" version thereof.

[0058] Additional colors of the inkjet ink set may include, for example, orange, violet, green, red, and / or blue.

[0059] The preferred inks of the ink set are pigment-based inks.

[0060] pigment The colorants used to print color images can be dyes or pigments. Dyes include disperse dyes, reactive dyes, acid dyes, etc. As used herein, the term "pigment" refers to an insoluble colorant that needs to be dispersed in a dispersant and processed under dispersing conditions in the presence of the dispersant. Pigment-based inks are preferred.

[0061] Suitable pigments for use are those generally well known in the art for aqueous inkjet inks. The selected pigment can be used in dry or wet form. For example, pigments are typically manufactured in aqueous media, with the resulting pigment being obtained as a water-moistened presscake. In presscake form, the pigment does not agglomerate to the same extent as it does in dry form. Therefore, pigments in the form of water-moistened presscake do not require as much mixing energy to deagglomerate in the premixing process as pigments in dry form. Representative commercially available dry pigments are listed in U.S. Pat. No. 5,085,698.

[0062] Some examples of pigments having colorant properties useful in inkjet inks include, but are not limited to, the following: cyan pigments Pigment Blue 15:3 and Pigment Blue 15:4, magenta pigments Pigment Red 122 and Pigment Red 202, yellow pigments Pigment Yellow 14, Pigment Yellow 74, Pigment Yellow 95, Pigment Yellow 110, Pigment Yellow 114, Pigment Yellow 128 and Pigment Yellow 155, Pigment Orange 5, Pigment Orange 34, Pigment Orange 43, Pigment Orange 62, Pigment Red 17, Pigment Red 49:2, Pigment Yellow 59:3, Pigment Yellow 69:4, Pigment Yellow 69:5, Pigment Yellow 69:6, Pigment Yellow 69:7, Pigment Yellow 69:8, Pigment Yellow 69:9, Pigment Yellow 69:1, Pigment Yellow 69:1, Pigment Yellow 69:2, Pigment Yellow 69:3, Pigment Yellow 69:4 ... red pigments, Pigment Red 112, Pigment Red 149, Pigment Red 177, Pigment Red 178, Pigment Red 188, Pigment Red 254, Pigment Red 184, Pigment Red 264, and Pigment Red PV19; green pigments, Pigment Green 1, Pigment Green 2, Pigment Green 7, and Pigment Green 36; blue pigments, Pigment Blue 60, Pigment Violet 3, Pigment Violet 19, Pigment Violet 23, Pigment Violet 32, Pigment Violet 36, and Pigment Violet 38; and the black pigment carbon black. Pigment names and abbreviations used herein are the "CI" designations for pigments established by the Society of Dyers and Colourists, Bradford, Yorkshire, UK, and published in The Color Index, Third Edition, 1971.

[0063] Examples of white materials include, but are not limited to, white inorganic pigments such as titanium oxide, zinc oxide, zinc sulfide, antimony oxide, and zirconium oxide. In addition to these inorganic white pigments, white organic pigments such as white hollow resin particles and polymer particles can also be used. A preferred pigment for aqueous pigment-based white inks is titanium dioxide. Useful titanium dioxide (TiO2) pigments can be in rutile or anatase crystalline form. They are generally produced by either the chloride process or the sulfate process. In the chloride process, TiCl4 is oxidized to form TiO2 particles. In the sulfate process, sulfuric acid and titanium-containing ores are dissolved, and the resulting solution undergoes a series of steps to produce TiO2. Both the sulfate and chloride processes are described in more detail in "The Pigment Handbook," Vol. 1, 2nd Ed., John Wiley & Sons, NY (1988), the relevant disclosures of which are incorporated herein by reference for all purposes as if fully set forth.

[0064] The titanium dioxide particles can have a variety of average particle sizes up to about 1 micron, depending on the desired end use of the ink. For applications requiring high hiding or decorative printing applications, the titanium dioxide particles preferably have an average size of less than about 1 micron (1000 nanometers). Preferably, the particles have an average size of about 50 to about 950 nanometers, more preferably about 75 to about 750 nanometers, and even more preferably about 100 to about 500 nanometers. These titanium dioxide particles are commonly referred to as pigmentary TiO.

[0065] For applications requiring a white color with some degree of transparency, "nano" titanium dioxide is preferred as a pigment. "Nano" titanium dioxide particles typically have an average size ranging from about 10 to about 200 nanometers, preferably from about 20 to about 150 nanometers, and more preferably from about 35 to about 75 nanometers. Inks containing nano titanium dioxide can improve saturation and transparency while still maintaining good resistance to light fading and an appropriate hue angle. A commercially available example of uncoated nano-grade titanium dioxide is P-25, available from Degussa (Parsippany, NJ).

[0066] Titanium dioxide pigments can be substantially pure titanium dioxide or can contain other metal oxides, such as silica, alumina, and zirconia. Other metal oxides can be incorporated into the pigment particles, for example, by co-oxidizing or co-precipitating the titanium compound with other metal compounds. When co-oxidized or co-precipitated metals are present, they are preferably present in an amount of from about 0.1% to about 20% by weight, more preferably from about 0.5% to about 5% by weight, and even more preferably from about 0.5% to about 1.5% by weight, as metal oxide, based on the total weight of the titanium dioxide pigment.

[0067] Titanium dioxide pigments can also have one or more metal oxide surface coatings. These coatings can be applied using techniques known to those skilled in the art. Examples of metal oxide coatings include silica, alumina, alumina-silica, boria, and zirconia, among others. Such coatings can optionally be present in an amount of about 0.1% to about 10% by weight, preferably about 0.5% to about 3% by weight, based on the total weight of the titanium dioxide pigment. These coatings can provide improved properties, such as reducing the photoreactivity of titanium dioxide. Commercial examples of such coated titanium dioxides include R700 (alumina-coated, available from Chemours, Wilmington Del.), RDI-S (alumina-coated, available from Kemira Industrial Chemicals, Helsinki, Finland), R706 (available from Chemours, Wilmington Del.), and W-6042 (silica-alumina-treated nano-grade titanium dioxide from Tayco Corporation, Osaka, Japan).

[0068] Titanium dioxide pigments can also have one or more organic surface coatings, such as, for example, carboxylic acids, silanes, siloxanes, and hydrocarbon waxes, and their reaction products with the titanium dioxide surface. The amount of organic surface coating, if present, generally ranges from about 0.01% to about 6% by weight, preferably from about 0.1% to about 3% by weight, more preferably from about 0.5% to about 1.5% by weight, and even more preferably about 1% by weight, based on the total weight of the pigment.

[0069] polymer dispersants Traditionally, pigments are stabilized by dispersants, such as polymeric dispersants or surfactants, to produce a stable dispersion of the pigment in the vehicle. More recently, however, so-called "self-dispersing" or "self-dispersing" pigments (hereinafter "SDPs") have been developed. As the name suggests, SDPs are dispersible in water without a dispersant. Disperse dyes are also considered pigments because they are insoluble in the aqueous inks used herein.

[0070] Polymeric dispersants for non-self-dispersing pigments can be random or structured polymers. Typically, acrylic polymeric dispersants are copolymers of hydrophobic and hydrophilic monomers. Some examples of hydrophobic monomers that can be used are methyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate, 2-phenylethyl methacrylate, and the corresponding acrylates. Examples of hydrophilic monomers include methacrylic acid, acrylic acid, dimethylaminoethyl (meth)acrylate, and their salts. Quaternary salts of dimethylaminoethyl (meth)acrylate can also be used. "Random polymer" refers to a polymer in which the molecules of each monomer are randomly arranged in the polymer backbone. For a reference to suitable random polymeric dispersants, see U.S. Pat. No. 4,597,794. "Structured polymer" refers to a polymer with a block, branched, graft, or star structure. Examples of structured polymers include AB or BAB block copolymers such as those disclosed in U.S. Patent No. 5,085,698, ABC block copolymers such as those disclosed in EP 0 556 649, and graft polymers such as those disclosed in U.S. Patent No. 5,231,131. Other polymeric dispersants that can be used are described, for example, in U.S. Patent Nos. 6,117,921, 6,262,152, 6,306,994, and 6,433,117.

[0071] "Random polymer" also includes polyurethanes. Particularly useful are the polyurethane dispersants disclosed in U.S. Patent Application Publication No. 2012 / 0214939, in which the polyurethane dispersant is crosslinked after dispersing the pigment to form the pigment dispersion.

[0072] Colored pigment dispersions Colored pigment dispersions stabilized by added polymeric dispersants can be prepared by methods known in the art. It is generally desirable to have the stabilized pigment in a concentrated form. The stabilized pigment is prepared by first premixing the selected pigment and polymeric dispersant in an aqueous carrier medium (such as water and, optionally, a water-miscible solvent), and then dispersing or deflocculating the pigment. The premixing step is generally carried out in an agitated mixing vessel, and a high-speed disperser (HSD) is particularly suitable for the mixing step. Cowels-type blades attached to the HSD, operating at 500 rpm to 4000 rpm, more typically 2000 rpm to 3500 rpm, provide optimal shear to achieve the desired blend. Sufficient mixing is typically achieved after 15 to 120 minutes of mixing under the above conditions. The subsequent dispersion step can be accomplished in a two-roll mill, media mill, horizontal mini-mill, ball mill, attritor, or by passing the mixture through multiple nozzles in a liquid jet interaction chamber at a liquid pressure of at least 5,000 psi to produce a uniform dispersion of pigment particles in an aqueous carrier medium (microfluidizer). Alternatively, concentrates can be prepared by dry-milling the polymeric dispersant and pigment under pressure. Media for media mills are selected from commonly available media such as zirconia, YTZ, and nylon. These various dispersion processes are generally well known in the art, as exemplified by U.S. Pat. Nos. 5,022,592, 5,026,427, 5,310,778, 5,891,231, 5,976,232, and U.S. Patent Application Publication No. 20030089277. The disclosures of each of these publications are incorporated herein by reference for all purposes as if fully set forth. Preferably by two-roll mills, media mills, and by passing the mixture through multiple nozzles in a liquid jet interaction chamber at a liquid pressure of at least 5,000 psi.

[0073] After the milling process is complete, the color pigment concentrate can be "let down" into an aqueous system. "Let down" refers to the dilution of the concentrate by mixing or dispersion, the intensity of the mixing / dispersion usually determined by trial and error using conventional methodologies and often dependent on the combination of polymeric dispersant, solvent, and pigment.

[0074] The useful particle size range after dispersion is typically about 0.005 micrometers to about 15 micrometers. Typically, the pigment particle size should be in the range of about 0.005 micrometers to about 5 micrometers, especially about 0.005 micrometers to about 1 micrometer. The average particle size, as measured by dynamic light scattering, is less than about 500 nm, typically less than about 300 nm.

[0075] White pigment dispersion One or more dispersants described in the colored pigment formulation are also used to stabilize the titanium dioxide. It is generally desirable to prepare the stabilized TiO pigment in the form of a concentrated slurry. The TiO slurry is typically prepared in an agitated mixing vessel, with a high-speed disperser (HSD) being particularly suitable for the mixing process. A Cowels-type disperser, operating at 500 rpm to 4000 rpm, more typically 2000 rpm to 3500 rpm, attached to the HSD provides optimal shear to achieve the desired mixing. Sufficient mixing is typically achieved after 15 to 600 minutes of mixing under the above conditions. The amount of titanium dioxide present in the slurry composition is preferably about 35% to about 80% by weight, based on the total weight of the slurry, and more preferably about 50% to about 75% by weight, based on the total weight of the slurry. The titanium dioxide preferably has a 50% average particle size (hereinafter referred to as "D50") in the range of 50 to 500 nm, more preferably in the range of 150 to 350 nm. Titanium dioxide having a D50 within these ranges allows the printed film to exhibit sufficient opacity of the image, which allows for the formation of high quality images.

[0076] In the case of colored pigments, the inks may contain up to about 30% by weight of the pigment, preferably about 0.1 to about 25%, and more preferably about 0.25 to about 10% by weight, based on the total weight of the ink. When inorganic pigments such as TiO2 pigments are selected, the inks tend to contain a higher weight percent of the pigment than comparable inks using colored pigments, sometimes as much as about 75%, because inorganic pigments generally have a higher specific gravity than organic pigments.

[0077] Post-modification of polymeric dispersants after formation of pigment dispersions The polymeric dispersant used to disperse the pigment can be crosslinked after the pigment dispersion is prepared to form a crosslinked pigment dispersion before it is incorporated into the inkjet ink. The crosslinkable polymeric dispersant is a polymer substituted with a crosslinkable moiety selected from the group consisting of acetoacetoxy, acid, amine, epoxy, hydroxyl, blocked isocyanate, and mixtures thereof. The crosslinking agent is selected from the group consisting of acetoacetoxy, acid, amine, anhydride, epoxy, hydroxyl, isocyanate, blocked isocyanate, and mixtures thereof. The crosslinking step involves adding a crosslinking agent to the pigment dispersion after dispersing the pigment and heating the mixture at an elevated temperature for several hours. After the crosslinking step, excess polymer can be removed by a purification process such as ultrafiltration. Specific examples of crosslinking moiety / crosslinking agent pairs are hydroxyl / isocyanate and acid / epoxy.

[0078] Ink polymer binder An ink binder is a polymeric compound or mixture of polymeric compounds added to an ink formulation. Binders can be used alone or in combination with other binders. Binders can impart properties to printed materials, such as greater durability. Polymers used as binders in inkjet inks include aqueous polymer solutions and colloidal polymer particles in an aqueous phase, interchangeably referred to as latexes, emulsions, and aqueous dispersions. Polymer emulsion particles are typically stabilized by hydrophilic segments that are covalently bonded to the polymer or physically absorbed into the polymer as external dispersants or surfactants. The hydrophilic segments provide stabilization through two interaction mechanisms: electrostatic and steric. To provide effective electrostatic stabilization, hydrophilic segments are typically made of ionic substituents such as neutralized carboxyl-, sulfonic-, or phosphonic-acid-containing monomers. The ionic substituents provide stabilization via a charged double layer mechanism, whereby ionic repulsion prevents polymer aggregation and flocculation. However, the stability of polymer particles is affected by salt, pH, and polyelectrolytes. The addition of salt, acid, and polyelectrolytes causes the polymer particles to precipitate. To provide effective steric stabilization, the hydrophilic segments have nonionic substituents that extend into the aqueous medium and stabilize the polymer particles in the aqueous vehicle. Polyvinyl alcohol, cellulose derivatives, ethylene oxide derivatives, acrylamide, hydroxyethyl-substituted monomers, vinylpyrrolidone, ethyleneimine, etc. can all be used as nonionic substituents. When the nonionic component is ethylene oxide, the introduction of ethylene oxide can provide steric stabilization by incorporating sufficient glycol (-CH2-CHO-)n units. Sterically stabilized polymer particles are unaffected by changes in pH and ionic additives. Therefore, such polymer particles do not form aggregates upon the addition of salt, acid, and polyelectrolytes. Some polymer particles are designed with a dual stabilization mechanism that provides both steric and electrostatic stabilization.Depending on what the primary stabilizing function is, the polymer particles may exhibit different degrees of sensitivity to ionic strength due to the addition of multivalent salts, in one embodiment, the multivalent salts in the primer fluids of the present disclosure.

[0079] A method for evaluating the interaction of polymer ink binders with primer fluids has been developed. A typical primer fluid composition is made of a 5% aqueous solution of calcium nitrate on a solids basis. One drop of the polymer ink binder is added to 2.0 g of the typical primer solution described above in a 5 ml glass vial and gently mixed. For a polymer ink binder with a total solids content of approximately 30% by weight, one drop typically contains approximately 0.06 g of total dry polymer. Stability is observed after the mixture is allowed to stand at room temperature for 24 hours. If solid particles are observed in the mixture, the polymer ink binder is considered to be cohesive with the primer. Otherwise, the polymer ink binder is considered to be stable with the primer or non-cohesive with the primer.

[0080] Surprisingly, it has been found that inks comprising a blend of two polymer binders, a first polymer binder that aggregates with the primer fluid and a second polymer binder that does not aggregate with the primer fluid, can be printed with better image quality, particularly with improved wetting and film formation. Such inks provide better image quality while being fixable by a primer coating, preventing excessive spreading and coalescence of the ink droplets.

[0081] Generally, both primer-cohesive and primer-non-cohesive polymeric binders include polyurethanes, polyesters, polyolefins, acrylics, styrene-acrylics, styrene-butadiene, styrene-butadiene-acrylonitrile, neoprene, ethylene-acrylic acid, ethylene-vinyl acetate emulsions. Preferably, the polymeric binders are polyurethanes, polyesters, acrylics, and vinyl polymers.

[0082] Typical polyurethanes are prepared from isocyanate compounds, isocyanate-reactive compounds, and isocyanate or isocyanate-reactive compounds with either or both ionic and nonionic substituents. Ionic substituents, such as neutralized carboxyl, sulfonic acid, and phosphonic acid, provide electrostatic stability. Nonionic substituents, such as (-CH2-CH2O-), n Polyols with polyvinyl alcohol segments provide steric stabilization. These polyurethanes are often prepared as polyurethane prepolymers with excess isocyanate groups. Chain extension or crosslinking isocyanate-reactive groups are then added to provide the final polyurethane binder. If the polyurethane is stabilized primarily by electrostatic interactions via ionic substituents, it will coalesce with the primer fluid. If the polyurethane is stabilized primarily by steric interactions via nonionic interactions, it will not coalesce with the primer fluid.

[0083] Suitable primer cohesive polyurethane binders are described in U.S. Patent Application Publication No. 20050182154, the disclosure of which is incorporated herein by reference for all purposes as if fully set forth. Examples of commercially available primer cohesive binders include polyurethane polymers such as Takelac® WS5100, Takelac® WS4022, Takelac® W5030, XW-Um601, and XW-Um602A from Mitsui Chemicals (Tokyo, Japan), and acrylic polymers such as Johncryl® FLX5000-A, Johncryl® FLX5220, and Johncryl® FLX5026A from BASF (Ludwigshafen, Germany).

[0084] Suitable primer non-agglomerating polyurethane binders are described in U.S. Patent Application Publication No. 20080092309, the disclosure of which is incorporated herein by reference for all purposes as if fully set forth. Examples of commercially available primer non-agglomerating binders include polyurethane polymers such as Takelac® XW-Um1, XW-Um2, and XW-Um3 from Mitsui Chemicals (Tokyo, Japan), Baybond PU1810 / 1, a polyurethane polymer from Covestro, Mowinyl 6950, an acrylic polymer, and Mowinyl 3500, a vinyl acetate polymer, from Japan Coating Resin Corporation. The primer non-agglomerating binder can be the same as or different from the aforementioned primer binders.

[0085] Unlike the polymeric dispersants mentioned above, binders typically lack pigment affinity or are non-reactive with colorants. They are typically added to the ink during the final formulation stage, rather than during the preparation of the pigment dispersion. The binder is typically present in the ink in an amount of at least 0.2% by weight based on the total weight of the ink. The amount can range from 1 to 15 weight percent based on the total weight of the ink. The ratio of the primer-cohesive first polymeric binder to the primer-non-cohesive second polymeric binder is 15:1 to 1:10 by weight. More typically, the ratio of the primer-cohesive first polymeric binder to the primer-non-cohesive second polymeric binder is 10:1 to 1:5 by weight.

[0086] Ink Vehicle The pigment-based inks of the present disclosure include an ink vehicle, typically an aqueous ink vehicle, also known as an aqueous carrier medium, an aqueous dispersion, and optionally other ingredients.

[0087] An ink vehicle is a liquid carrier (or medium) for an aqueous dispersion and optional additives. The term "aqueous ink vehicle" refers to an ink vehicle consisting of water or a mixture of water and one or more organic, water-soluble vehicle components, commonly referred to as cosolvents or humectants. The selection of an appropriate mixture depends on the requirements of the specific application, such as the desired surface tension and viscosity, the pigment selected, the drying time of the pigment-based inkjet ink, and the type of medium onto which the ink will be printed.

[0088] Examples of water-soluble organic solvents and humectants include alcohols, ketones, keto-alcohols, ethers, and others, such as thiodiglycol, sulfolane, 2-pyrrolidine, 1,3-dimethyl-2-imidazolidinone, and caprolactam; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, trimethylene glycol, butylene glycol, and hexylene glycol; addition polymers of oxyethylene or oxypropylene such as polyethylene glycol and polypropylene glycol; triols such as glycerol and 1,2,6-hexanetriol; lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl, and diethylene glycol monoethyl ether; lower dialkyl ethers of polyhydric alcohols such as diethylene glycol dimethyl or diethyl ether; urea and substituted ureas.

[0089] A mixture of water and a polyhydric alcohol, such as diethylene glycol, is typical of aqueous ink vehicles. In the case of a mixture of water and diethylene glycol, the ink vehicle typically contains from 30% water and 70% diethylene glycol to 95% water and 5% diethylene glycol, more typically from 60% water and 40% diethylene glycol to 95% water and 5% diethylene glycol. Percentages are based on the total weight of the ink vehicle. A mixture of water and butyl carbitol is also an effective ink vehicle.

[0090] The amount of ink vehicle in the ink is typically in the range of about 70% to about 99.8%, more typically about 80% to about 99.8%, based on the total weight of the ink.

[0091] The ink vehicle can be made fast-drying by including solvents such as glycol ethers and 1,2-alkanediols. Glycol ethers include ethylene glycol monobutyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-isopropyl ether, diethylene glycol mono-isopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-isopropyl ether, propylene glycol mono-n-butyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-n-propyl ether, and dipropylene glycol mono-isopropyl ether. Typical 1,2-alkanediols are C4-C6 alkanediols, with 1,2-hexanediol being the most typical. The amount of glycol ether and 1,2-alkanediol added is typically in the range of about 1% to about 15% by weight, more typically about 2% to about 10% by weight, based on the total weight of the ink.

[0092] Surfactants are typically added to inks to adjust surface tension and wetting properties. Suitable surfactants include ethoxylated acetylenic diols (e.g., the Surfynol® series available from Evonik), ethoxylated alkyl primary alcohols (e.g., the Neodol® series available from Shell), and secondary alcohols (e.g., the Tergitol® series available from Dow Chemical), sulfosuccinates (e.g., the Aerosol® series available from Cytec), organosilicones (e.g., the DYNOL® series available from Evonik), and fluorosurfactants (e.g., the CAPSTONE® series available from Chemours). Typically, surfactants are used in amounts up to about 3% by weight, more typically up to 1% by weight, based on the total weight of the ink.

[0093] Other ingredients, additives, may be incorporated into the ink-jet ink to the extent that such other ingredients do not interfere with the stability and jettability of the ink-jet ink, which can be readily determined by one skilled in the art through routine experimentation.

[0094] The inclusion of a capping (or chelating) agent such as ethylenediaminetetraacetic acid, iminodiacetic acid, ethylenediamine-di(o-hydroxyphenylacetic acid), nitrilotriacetic acid, dihydroxyethylglycine, trans-1,2-cyclohexanediaminetetraacetic acid, diethylenetriamine-N,N,N',N'',N''-pentaacetic acid, and glycoletherdiamine-N,N,N',N'-tetraacetic acid, and salts thereof, can be beneficial, for example, to remove the deleterious effects of heavy metal impurities.

[0095] Biocides may be used to inhibit microbial growth.

[0096] Ink characteristics Jet velocity, droplet separation length, droplet size, and stream stability are greatly affected by the surface tension and viscosity of the ink. Typically, pigmented inkjet inks have a surface tension ranging from about 20 dynes / cm to about 45 dynes / cm at 25°C. Viscosity can be as high as 30 cP at 25°C, but is typically much lower, more typically less than 10 cP at 25°C. The ink has physical properties that are compatible with a wide range of ejection conditions, i.e., the drive frequency of the piezoelectric element or the ejection conditions of the thermal head in a drop-on-demand or continuous device, as well as the nozzle shape and size. The ink must have excellent storage stability over long periods of time so as not to significantly clog in the inkjet device. Furthermore, the ink must not corrode parts of the inkjet printing device it comes into contact with and must be essentially odorless and non-toxic. The preferred pH of the ink is in the range of about 6.5 to about 8.5.

[0097] printing The method of the present invention relates to digitally printing a non-porous plastic film substrate. Typically, this involves the following steps: (a) providing an inkjet printer responsive to digital data signals; (b) providing a non-porous plastic substrate; (c) applying an aqueous primer composition comprising a polyvalent cation salt and a polymeric binder to a non-porous plastic substrate to form a coating having a dry thickness of 0.4 to 5.0 microns, said coating resulting in an increase in haze on said substrate of less than 10, said polyvalent cation salt being present in an amount of less than 20 weight percent based on the total weight of the primer composition, and said polymeric binder being insoluble in water and stable in the presence of said polyvalent cations and selected from the group consisting of urethane polymers, acrylic polymers, and vinyl polymers; (d) loading aqueous inkjet inks into the printer, at least one of the inks comprising a pigment dispersion, a first polymeric binder, and a second polymeric binder, said first polymeric binder forming aggregates with said aqueous primer composition and said second polymeric binder not forming aggregates with said aqueous primer composition; and (e) printing the primer-coated substrate of step (c) using an aqueous inkjet ink in response to a digital signal.

[0098] In step (e), the aqueous inkjet ink may include a white ink and multiple non-white inks. In step (e), the white ink may be printed first as a background image, followed by the color inks. Alternatively, the non-white ink may be printed first and then covered with the white ink using the reverse printing setting. Drying between the non-white inks or between the white and non-white inks is optional.

[0099] Printing can be performed with any inkjet printer equipped to handle and print film substrates. Films printed with pigmented inks are dried at elevated temperatures after printing. The temperature range varies depending on the printer and dryer design and line speed, as long as it is not too high to damage the film. Generally, drying temperatures are up to 120°C, preferably below 100°C, and more preferably below 95°C. [Example]

[0100] The invention is further illustrated, but not limited, by the following examples in which parts and percentages are by weight unless otherwise noted.

[0101] Ingredients and Abbreviations DBTL = dibutyltin dilaurate DMPA = dimethylolpropionic acid EDA = ethylenediamine IPDI = Isophorone diisocyanate TEA = triethylamine TETA = triethylenetetramine DETA = diethylenetriamine MEK = methyl ethyl ketone TMP = Trimethylolpropane DMEA = dimethylethanolamine CHDM = 1,4-cyclohexanedimethanol

[0102] Unless otherwise stated, the above chemicals were obtained from Aldrich (Milwaukee, Wis.) or other similar research chemical suppliers.

[0103] Denacol® 321 - Trimethylolpropane polyglycidyl ether, a crosslinker from Nagase Chemicals Ltd., Osaka, Japan Terathane® T650—a polyether polyol from Invista (Wilmington, DE) Desmorphen® C1200 - polyester polyol from Covestro (Leverkusen, Germany) Tegomer® D3403 - Polyether polyol from Evonik, Essen, Germany Eternacoll® UC-100 and UH-50—polycarbonate polyols from UBE Industries, Tokyo, Japan P-2010 - Polyester polyol from Kuraray Co. (Tokyo, Japan) Surfynol® 440, 420, and 465—nonionic surfactants from Evonik (Essen, Germany) Byk® 348 - Silicone surfactant from BYK (Wesel, Germany) Disperbyk® 190 - Dispersing additive from BYK (Wesel, Germany) Dispex® Ultra PX4585 - acrylate block copolymer dispersant from BASF (Ludwigshafen, Germany) Dynol™ 980—a silicone surfactant from Evonik, Essen, Germany SNOWTEX® ST-AK-ML - Nanosilica Dispersion from Nissan Chemical America (Houston TX) Aquacer® 513-BYK (Wesel, Germany) wax emulsion Takelac™ W6355 - Waterborne polyurethane resin from Mitsui Chemicals (Tokyo, Japan) Baybond® PU1810 / 1, Implanil® DLU - a waterborne polyurethane resin from Covestro (Leverkusen, Germany) Mowinyl 6950 - Acrylic emulsion resin from Japan Coating Resin Corp. (Osaka, Japan) Mowinyl 3500 - Vinyl acetate copolymer resin from Japan Coating Resin Corp. (Osaka, Japan)

[0104] Preparation of primer binder Primer Binder P-1 A dry, alkali- and acid-free flask equipped with an addition funnel, condenser, stirrer, and nitrogen line was charged with 55 g of CHDM, 130 g of Terathane T650, 75 g of Tegomer D3403, 10 g of DMPA, 7.5 g of TEA, and 235 g of MEK. The contents were heated to 50°C and thoroughly mixed. 195 g of IPDI was then added to the flask via the addition funnel over 5 minutes at 40°C, and the remaining IPDI was rinsed into the flask from the addition funnel with 10 g of MEK.

[0105] The temperature of the flask was raised to 65°C and held until the NCO% was 2.0% or less. The flask was cooled to 55°C and 877g of deionized (DI) water was added over 10 minutes, followed by 73g of DETA (as a 10% solution in water) via addition funnel over 5 minutes. The mixture was held at 50°C for 1 hour and then cooled to room temperature.

[0106] The MEK (about 245 g) was removed under vacuum, leaving a final dispersion of polyurethane with a solids content of about 30.0 wt %.

[0107] Following a procedure similar to that for preparing primer binder P-1, primer binders P2 to P5 were prepared using the components listed in Table 1 below.

[0108] [Table 1]

[0109] Additional primer binders used included Takelac W6355, a polyurethane from Mitsui Chemical; Baybond PU1810 / 1, a polyurethane polymer from Covestro; Mowvinyl 6950, an acrylic polymer from Japan Coating Resin Corporation; and Movinyl 3500, a vinyl acetate polymer.

[0110] Primers A-N were prepared using the ingredients listed in Tables 2 and 3 below by combining the listed ingredients with stirring and mixing until a uniform mixture was obtained.

[0111] [Table 2]

[0112] [Table 3]

[0113] Comparative primers A and B were prepared using the components listed in Table 4 below.

[0114] [Table 4]

[0115] Another comparative primer, Comparative Primer C, PP-17, was supplied by Meisei Chemical Works, LTD. Koyto, Japan.

[0116] DuPont Teijing Film's Mylar MLBT, a transparent PET film, was coated with primer fluid using a 2.5 wire size Gardco film applicator rod (Paul N. Gardner Inc., Florida, USA) to produce coatings with dry thicknesses ranging from 0.5 to 2.0 microns, depending on solids content and viscosity. The coatings were dried in a convection oven at 65°C for 3 minutes. Two types of film were coated: one was a PET film, DuPont Teijing Film's Mylar MLBT. The film haze was measured before and after coating using a BYK HazeGuard™ according to ASTM D1003 method. Before the primer coating, the Mylar MLBT film had a haze measurement of 4.80.

[0117] The clarity of each treated film was assessed by visual inspection and given a rating of 1 to 3, with "1" indicating no change from the base film, "2" indicating slight cloudiness, and "3" indicating cloudiness or crack formation.

[0118] Blocking resistance was tested by folding the printed film face-to-face immediately after drying. 2A weight was placed on the film to maintain a pressure of 0.05 for 12 hours. The weight was then lifted and the folded film was pulled apart. Blocking resistance was evaluated according to the following protocol, and the results are shown in Table 5 below. Rating 1: No damage to the coating, no sound, film breaks Rating 2: No damage to the coating, film breaks with a cracking sound Rating 3: Slight damage to the coating or the coating appears cloudy Rating 4: The coating is severely damaged, such as easily peeling off from the base film.

[0119] [Table 5]

[0120] Preparation of First Cyan Pigment Dispersion Terathane® 650 (300 g), DMPA (180 g), sulfolane (876 g), and DBTL (0.12 g) were added to a dry, alkali- and acid-free flask equipped with an addition funnel, condenser, and stirrer under a nitrogen atmosphere. The resulting mixture was heated to 60°C and thoroughly mixed. IPDI (438 g) was added to the mixture via an addition funnel attached to the flask, followed by rinsing the remaining IPDI from the addition funnel into the flask with sulfolane (15 g). The temperature of the reaction mixture was increased to 85°C and maintained at 85°C until the isocyanate content was 0.8% or less. The temperature was then cooled to 60°C and maintained at 60°C, and morpholine (30 g) was added via the addition funnel over 5 minutes, followed by rinsing the remaining morpholine from the addition funnel into the flask with sulfolane (5 g). After the temperature was held at 60°C for 1 hour, an aqueous solution of KOH (1755 g, 3 wt%) was added via an addition funnel over 10 minutes, followed by deionized water (207 g). The mixture was held at 60°C for 1 hour and then cooled to room temperature to yield a polyurethane dispersion with a solids content of 25%.

[0121] The first pigment dispersion, Cyan Dispersion 1, designed to agglomerate with the primer fluid, was prepared by premixing the polyurethane dispersant described above with Dainichiseika TRB-2 (PB 15:3 Cyan) pigment in an Eiger Minimill. Premixes were typically prepared at 20-30% pigment loading, targeting a dispersant level measured in a P / D (pigment / dispersant) ratio of 3.0. A cosolvent, triethylene glycol monobutyl ether (TEB, supplied by Dow Chemical), was added at 10% of the total dispersion formulation to promote pigment wetting and dissolution in the resin during the premix stage and facilitate grinding during the milling stage. During the premix stage, the pigment level was typically maintained at 27% and then reduced to approximately 24% during the milling stage by adding deionized water for optimal media mill grinding conditions. After completion of the milling stage, which typically lasted 4 hours, the remaining letdown of deionized water was added and thoroughly mixed to dilute the pigment level to approximately 10% by weight. The crude pigment dispersion thus obtained was purified by an ultrafiltration process to remove TEB. In the next crosslinking step, a crosslinker, Denacol 321, in an amount equal to 1.0% of the pigment was added to the pigment dispersion and reacted at 80°C for 6 hours. After the crosslinking reaction was completed, the pigment dispersion was purified again by another ultrafiltration process to remove impurities and by-products from the crosslinking process, and the pH was adjusted to about 8.0.

[0122] Preparation of Second Cyan Pigment Dispersion Cyan Dispersion 2 was dispersed using Disperbyk® 190 as the dispersant polymer. Disperbyk® 190 was pre-neutralized with KOH or an amine to promote water solubility and dissolution. The dispersion was prepared by first pre-mixing the pre-neutralized Disperbyk® 190 with Dainichiseika TRB-2 (PB 15:3 Cyan) pigment in an Eiger Minimill. Pre-mixes were typically prepared at a pigment loading of 20-30%, targeting a dispersant level measured as a P / D (pigment / dispersant) ratio of 2.75. During the pre-mixing stage, the pigment level was typically maintained at 27% and then reduced to approximately 24% during the milling stage by adding deionized water for optimal media milling conditions. After completion of the milling stage, which typically lasted 4 hours, the remaining letdown of deionized water was added and thoroughly mixed. Upon completion, the cyan pigment level in the dispersion was reduced to approximately 15%.

[0123] First polymer binder for ink - primer cohesive binder PUD-A1 To a dry, alkali- and acid-free flask equipped with an addition funnel, condenser, stirrer, and nitrogen gas line was added 15.8 g of CHDM, 104.7 g of Terathane T650, 4.0 g of TMP, and 118 g of acetone. The contents were heated to 40°C and mixed thoroughly. 120 g of IPDI was then added to the flask via the addition funnel over 5 minutes at 40°C, and the remaining IPDI was rinsed into the flask from the addition funnel with 2 g of acetone.

[0124] The temperature of the flask was increased to 50° C. After holding at 50° C. for 240 minutes, an additional 15.8 g of DMPA, followed by 11 g of TEA, was added to the flask via the addition funnel, followed by a 2 g acetone rinse. The temperature of the flask was then increased again to 50° C. and held at 50° C. until the NCO% reached 2.0% or less.

[0125] At a temperature of 50° C., 570 g of deionized (DI) water was added over 10 minutes, followed by 38 g of EDA (as a 10% solution in water) added via addition funnel over 5 minutes. The mixture was held at 50° C. for 1 hour and then cooled to room temperature.

[0126] Acetone (about 122.0 g) was removed under vacuum, leaving a final dispersion of polyurethane at about 30.0 wt. % solids.

[0127] All PUD-type polymers in Table 6 below were made using a similar process: Polyurethane PUD EX2, described in US Patent No. 9,255,207, was used as the polyurethane polymer binder PUD-A7.

[0128] [Table 6]

[0129] Second polymer binder for inks - primer non-agglomerating binder PUD-B A dry, alkali- and acid-free flask equipped with an addition funnel, condenser, stirrer, and nitrogen line was charged with 65 g of CHDM, 150 g of P-2010, 70 g of Tegomer D3403, 10 g of DMPA, 7.5 g of TEA, and 235 g of MEK. The contents were heated to 50°C and thoroughly mixed. 180 g of IPDI was then added to the flask via the addition funnel over 5 minutes at 40°C, and the remaining IPDI was rinsed into the flask with 10 g of MEK from the addition funnel.

[0130] The temperature of the flask was raised to 65°C and held until the NCO% was 1.7% or less, then cooled to 55°C. To the mixture was added 935g of deionized (DI) water over 10 minutes, followed by 137g of DETA (as a 5% solution in water) via addition funnel over 5 minutes. The mixture was held at 50°C for 1 hour, then cooled to room temperature.

[0131] The MEK (about 245 g) was removed under vacuum, leaving a final dispersion of polyurethane with a solids content of about 30.0 wt %.

[0132] Ink binder stability test One drop of the ink binder solution containing approximately 0.06 g of polymer was added to 2.0 g of 5% aqueous calcium nitrate solution in a 5 ml glass vial, and the resulting mixture was gently mixed. The mixture was allowed to stand at room temperature for 24 hours before stability was observed. The test results are shown in Table 7 below.

[0133] [Table 7]

[0134] Ink preparation The inks used in the examples were made according to standard procedures in the inkjet art. Component amounts are in weight percent of the final ink. Polymer binders and colorants are listed on a solids basis. For ink preparation examples, an ink vehicle was prepared and added to an aqueous ink binder with stirring. After stirring until a uniform mixture was obtained, the solution was added to the pigment dispersion and again mixed until uniform. Inventive Inks A-B and Comparative Inks A-B were prepared using the components listed in Table 8 below.

[0135] [Table 8]

[0136] Print Testing and Evaluation The film used for printing was Mylar MLBT from DuPont Teijing Film. The film was first coated with Primer E and then printed with the example ink using a Ricoh IPSiO GX e5500 printer. Approximately 7-10 g / m 2A 3x9 inch solid block with an ink coverage of 1000µm was printed with the printer set to 8-pass color mode. The printed film was then dried at 65°C for 3 minutes. Image quality was assessed by visually judging color uniformity with the following rating: Rating 1, excellent color uniformity and coverage Rating 2, uniform color with some white lines due to incorrect ink direction or missing jetting Rating 3, heavy ink lines with dewetting at the edge of the block color. Color OD was measured using an X-Rite Greytag Macbeth spectrophotometer. Jetting reliability was checked by printing nozzle check patterns before and after printing eight pages of a 7x10 inch solid block with the printer set to 8-pass color mode.

[0137] As shown in Table 9 below, both Inventive Ink A and Inventive Ink B, which comprise a blend of a first polymeric binder that aggregates with the primer and a second polymeric binder that does not aggregate with the primer, demonstrated more uniform color and better image quality as reflected by higher OD and better image quality ratings when compared to Comparative Ink A and Comparative Ink B.

[0138] [Table 9]

Claims

[Claim 1] (a) an aqueous primer composition comprising a polyvalent cation salt and a polymeric binder, the composition, when applied to a non-porous plastic substrate, forming a coating having a dry thickness of 0.4 to 5.0 microns, the coating resulting in an increase in haze in the substrate of less than 10; the polyvalent cation salt being present in an amount of less than 20 weight percent, based on the total weight of the primer composition; and the polymeric binder being a nonionic, water-insoluble polymer in colloidal particle form that is stable in the presence of the polyvalent cations, and selected from the group consisting of acrylic latexes, polyurethane dispersions, vinyl acetate copolymer latexes, polyesters, and polyamide dispersions; (b) aqueous inkjet inks, at least one of the inks comprising a pigment dispersion, a first polymer binder, and a second polymer binder, the first polymer binder forming an aggregate with the aqueous primer composition, and the second polymer binder not forming an aggregate with the aqueous primer composition; and 1. An inkjet ink and primer fluid set comprising:

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