WO2013154551A1

WO2013154551A1 - Solvent-based flexible packaging inks

Info

Publication number: WO2013154551A1
Application number: PCT/US2012/033070
Authority: WO
Inventors: Rurou MAI; Grant T. Shouldice; Philip D. ERNEST
Original assignee: Flint Group Inc
Current assignee: Flint Group Packaging Inks North America Holdings LLC
Priority date: 2012-04-11
Filing date: 2012-04-11
Publication date: 2013-10-17
Anticipated expiration: 2014-10-11

Description

SOLVENT-BASED FLEXIBLE PACKAGING INKS

FIELD OF THE INVENTION

[0001] The present invention relates to solvent-based flexographic inks and methods for flexographic printing on flexible packaging materials such as plastic films, laminates, or foils.

INTRODUCTION TO THE DISCLOSURE

[0002] This section provides information helpful in understanding the invention but that is not necessarily prior art.

[0003] Flexible packaging includes a wide variety of materials such as various plastic films, laminates, and foils that extend the shelf life and protect many products, such as food products, chocolate and other candy, pet food, industrial products, and the like. Messages and designs are printed on these packaging materials to inform and appeal to consumers. To better influence buying decisions, there is a desire for increasingly higher definition printing and improved print fidelity that enables impressive, eye-catching graphics that in turn facilitate brand positioning and brand identification by consumers.

[0004] A typical flexographic printing system uses either an enclosed doctor blade or a rubber roll that picks up the ink and transfers it to an anilox having engraved cells. The ink fills the engraved cells. The ink is then transferred in a uniform layer from the anilox roller to a rubber or photopolymer plate that has an image raised in relief as well as recessed non-image areas. A final transfer of the image then occurs from the plate to the substrate.

[0005] Current solvent-based flexographic inks tend to have problems on flexible packaging materials with high dot gain, unevenness or missing dots in halftone areas, ink drying on the plate, and cobwebbing as press speeds are increased, plate graphics resolution increases, and printing run lengthens. Dot gain or missing dots lead to loss of print fidelity. Ink drying on the plate or cobwebbing also results in dirty prints and plate edge build-up, which requires plate clean-up thus reducing press efficiency when the press must be stopped for plate cleaning.

[0006] Proposals for solving these problems have included improving the solvent resistance of the flexographic plate surface, changing the solvent system of the ink to adjust the evaporation rate to prevent ink drying on the printing plate or minimize the adverse effect of a given solvent on the plate, providing laser engraved ceramic aniloxes to control the amount of ink transferred to the plate surface to thereby prevent ink build-up, and identifying rheological parameter values for inks that would lead to clean printing especially at increased press speeds. Fickes et al, U.S. Pat. No. 4,451 ,553 teaches a process using high molecular weight butadiene/acrylonitrtile copolymer to develop an improved, solvent-resistant flexographic plate surface. Swatton, U.S Pat No. 5,135,837 teaches that a particular photosensitive elastomeric composition can be used to prepare an improved, solvent-resistant flexographic printing plate. Huang, U.S Pat. No. 6,881 ,533 discloses methods for making a relief printing plate, such as flexographic printing plates, from imageable lithographic printing plate precursors, which is said to provide better dimensional stability that improves reproducibility of the relief image and a corresponding improvement in printing quality. Yamazawa et al, U.S Pat. Application Publication No. US 2009/0155721 discloses a flexographic printing plate obtained by using a photosensitive resin can be used in flexographic printing to obtain print that has little printing density unevenness in halftone dots and the like in flexographic printing. Kim et al, U.S Pat. Application Publication No. US 201 1 /0244196 A1 discloses an ink composition for roll printing having a specific evaporation rate to provide good pattern transferability. Cockerham, U.S Pat. No. 3,450,663 teaches using a particular solvent composition for formulating and thinning flexographic inks based on polyamide resins. Saied et al., WO 2010/ 0126981 disclose ink or coating compositions with specific rheological parameters that are said to exhibit low misting and allow higher press speed. Lee, U.S Pat. Application Publication No. US 2010/0015354 A1 describes a method of casting a ceramic layer onto a roller surface to provide better resistance to erosion than a steel surface for a longer lifetime and a high-precision pattern on the roller. [0007] Baseeth et al., US Patent Application Publication No. 201 1 /0219983, teaches a combination of lecithin and a plasticizer (such as di-(2- ethylhexyl) adipate, propylene glycol monoesters, higher alcohols like 2- ethylhexanol itself, or epoxidized soybean oil) that is useful for dispersing pigments for inks, particularly in water-based inks. The combination with the plasticizer is said to decrease viscosity from that of lecithin used alone. The Baseeth patent does not discuss solvent-based flexographic inks or address the problems of high speed printing and long press runs.

[0008] Despite prior efforts, there remains a need to improve print quality for solvent-based flexographic inks printed at higher press speeds, higher plate resolutions, and in longer press runs.

SUMMARY OF THE DISCLOSURE

[0009] This section provides a general summary rather than a comprehensive disclosure of the full scope of the invention and of all its features.

[0010] We disclose solvent-based flexographic inks comprising an additive that is at least one of: lecithin or phosphatidylcholine (a component of lecithin); fatty acid esters of phosphorylated amino alcohols such as diethanolamine or triethanolamine; saturated and unsaturated fatty acids having from 8 to 22 carbon atoms and soaps of these fatty acids with monovalent, divalent, and trivalent ions such as NH4+, Na+, K+, Mg+2, Ca+2, Zn+2, and AI+3. While not wishing to be bound by theory, it is believed that these additives modify elasticity of the ink and cohesive nature of the ink binder to facilitate ink-splitting and ink transfer while reducing misting. The lecithin or phosphatidylcholine, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol in the ink provides improved print fidelity at elevated press speed and reduces ink cobwebbing, misting, and plate build-up. The ink shows substantially reduced need for plate clean-up, resulting in increased press efficiency without a need to change the printing delivering system or equipment. "Solvent-based" indicates the flexographic inks are in an organic solvent medium (rather than an aqueous medium). "Lecithin" has commonly been used to refer to both phosphatidylcholine itself or a mixture containing phosphatidylcholine, particularly a mixture obtained from natural sources. "Lecithin" will be used in this way in this disclosure.

[0011] A method of making printed, flexible packaging material has a step of flexographic printing of a flexible packaging material with the disclosed solvent-based flexographic inks.

[0012] Further disclosed is a solvent-based pigment dispersion (also known as a "base") comprising an additive that is at least one of: lecithin; fatty acid esters of phosphorylated amino alcohols such as diethanolamine or triethanolamine; saturated and unsaturated fatty acids having from 8 to 22 carbon atoms and soaps of these fatty acids with monovalent, divalent, and trivalent ions such as NH4+, Na+, K+, Mg+2, Ca+2, Zn+2, and AI+3. The pigment dispersions can be of a wide range of colors and may include one or more pigments. The disclosed bases can be used to make solvent-based flexographic inks containing various binders, and further disclosed is a method of making a solvent-based, flexible packaging, flexographic printing ink by combining at least one of the solvent- based pigment dispersions with a resinous binder appropriate for a flexible packaging, flexographic printing ink. An ink prepared from the solvent-based pigment dispersion comprising at least one of the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol has an unexpectedly improved color density and provides improved print definition at higher press speeds. The disclosed ink compositions reduce ink cobwebbing and plate build-up and enable improved press efficiency without modifications to the printing press, ink delivery system, flexographic plates, or changing evaporation rates of the inks.

[0013] In another aspect, a solvent-based flexible packaging printing ink is prepared by combining, in any order, a solvent-based pigment dispersion, a resinous binder, and an additive that is at least one of: lecithin; fatty acid esters of phosphorylated amino alcohols such as diethanolamine or triethanolamine; saturated and unsaturated fatty acids having from 8 to 22 carbon atoms and soaps of these fatty acids with monovalent, divalent, and trivalent ions such as NH4+, Na+, K+, Mg+2, Ca+2, Zn+2, and AI+3. The lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol may first be combined with the solvent-based pigment dispersion, the resinous binder, or another ink component, or the lecithin may be added separately or as a solution in organic solvent.

[0014] In other aspects, we disclose flexographic printing methods for printing packaging substrates with the solvent-based flexible packaging inks and the printed products of these methods.

[0015] "A," "an," "the," "at least one," and "one or more" are used interchangeably to indicate that at least one of the item is present; a plurality of such items may be present unless the context clearly indicates otherwise. All numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term "about" whether or not "about" actually appears before the numerical value. "About" indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by "about" is not otherwise understood in the art with this ordinary meaning, then "about" as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range.

[0016] The terms "comprises," "comprising," "including," and "having," are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used in this specification, the term "or" includes any and all combinations of one or more of the associated listed items.

[0017] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DETAILED DESCRIPTION

[0018] A detailed description of exemplary, nonlimiting embodiments follows. [0019] The disclosed solvent-based pigment dispersions and solvent- based flexographic inks contain an additive that is at least one of: lecithin; fatty acid esters of phosphorylated amino alcohols such as diethanolamine or triethanolamine; saturated and unsaturated fatty acids having from 8 to 22 carbon atoms and soaps of these fatty acids with monovalent, divalent, and trivalent ions such as NH4+, Na+, K+, Mg+2, Ca+2, Zn+2, and AI+3. In one preferred embodiment a solvent-based pigment dispersion or solvent-based flexographic ink includes lecithin, which is readily available, inexpensive, environmental friendly, biodegradable, and compatible with typical printing ink components.

[0020] Lecithins are obtained from various animal or vegetable sources, such as vegetable oil like soybean oil or egg yolk, and comprise a mixture of phosphatides and triglycerides, as well as lesser amounts of compounds such as glycolipids, carbohydrates, fatty acids, and/or sterols. Lecithin phosphatides include phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, phosphatidic acid, and others. Soy lecithin has been reported to contain about 20% phosphatidylcholine.

[0021] Commercial lecithins are most commonly produced from processing of crude soybean oil, although other sources include cottonseed oil, corn oil, and egg yolk. In a typical process, soybeans are dehulled, flaked, pressed, and extracted with solvent such hexane to recover crude soybean oil. The crude soybean oil contains glyceride oil as a major component in addition to phospholipids, sugars, sterols, sterol glucosides, fatty acids, and other components in minor amounts. Phospholipids are separated from the majority of the glyceride oil by "degumming," which is generally done by hydrating the phospholipids and removing the sludge containing the hydrated phospholipids by centrifuging. The sludge is dried to give a crude lecithin material, typically containing about 60 to 65% phospholipids as acetone insolubles, with the remainder primarily glycerides with minor amounts of other components. Jirjis et al., U.S. Pat. No. 6,207,209 describes an alternative method for membrane degumming of soybean oil. In membrane degumming, a vegetable oil miscella in a hydrocarbon solvent is fed to a membrane, producing a permeate stream which is depleted in phospholipids and a retentate stream which is enriched in phospholipids, relative to the phospholipid content of the miscella. The retentate is essentially a lecithin solution in the processing solvent, which is typically hexane. The phospholipid content of such a retentate can be up to about 85%, and it generally contains fewer impurities than lecithins obtained via water degumming.

[0022] Soy lecithin is one commercially available lecithin that may be used. Soy lecithin may be obtained, for example, from Archer Daniels Midland Company, Decatur, III., or Superior Materials, Inc., Garden City, NY.

[0023] In other embodiments, a solvent-based pigment dispersion or solvent-based flexographic ink comprises at least one of fatty acid esters of phosphorylated amino alcohols such as diethanolamine or triethanolamine; saturated and unsaturated fatty acids having from 8 to 22 carbon atoms and soaps of these fatty acids with monovalent, divalent, and trivalent ions such as NH4+, Na+, K+, Mg+2, Ca+2, Zn+2, and AI+3.

[0024] Nonlimiting examples of saturated and unsaturated fatty acids having from 8 to 22 carbon atoms that may be used include saturated fatty acids such as lauric, palmitic, and stearic fatty acids and unsaturated fatty acids such as oleic, linoleic, linolenic, and arachidonic fatty acids. Nonlimiting examples of fatty acid soaps include ammonium, alkali, alkaline salts, particularly sodium and potassium salts, of fatty acids having ten to twelve carbon atoms. Nonlimiting examples of fatty acid esters of phosphorylated amino alcohols are esters of phosphorylated diethanolamine or triethanolamine and any of the fatty acids just mentioned.

[0025] The lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol may be incorporated into a pigment dispersion further comprising a color pigment, a dispersing or grinding resin such as nitrocellulose, an acrylic polymer, a polyamide, or a polyurethane, and an organic solvent. The pigment dispersions contain from about 0.5 to about 10 percent by weight of the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol. In certain embodiment, the pigment dispersions contain from about 0.5 to about 5 percent by weight of the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol. The pigment dispersions may include from about 4 to about 18 percent by weight of the dispersing or grinding resin. Nonlimiting examples of suitable nitrocellulose dispersing resins are those having nitration levels of 10.7 to 12.25% (determined by the published method ASTM D1343-69) and a viscosity of from 3 to 1 10 cP (determined by the published method ASTM D4795). Nonlimiting examples of suitable acrylic dispersing resins are acrylic polymers having weight average molecular weights of five to twenty thousand Daltons, as may be determined by GPC using polystyrene standards, such as those that are polymerized from n-butyl methacrylate, ethyl methacrylate, styrene, methyl methacrylate, and other such monomers as homopolymers or copolymers. The acrylic dispersing resins may have glass transition temperatures, for example, of 20-1 10 °C. Glass transitions temperatures may be determined by known thermal methods, such as differential scanning calorimetry (DSC). Suitable acrylic dispersing resins are commercially available from many sources, including Evonik Industries of the Netherlands, DSM NeoResins Inc. of Wilmington, MA, Lucite International of Memphis, TN, Dianal America, Pasadena TX, and BASF Corporation of Wyandotte, Ml. Nonlimiting examples of suitable polyurethane dispersing resins have weight average molecular weights of five to ninety thousand Daltons, as may be determined by GPC using polystyrene standards, hydroxyl values of 1 to 5 mg KOH/g, and amine numbers of 1 to 9 meq/g. Suitable polyurethane dispersing resins are commercially available from many sources, including Kane International Corporation of Rye, NY; BASF Corporation of Wyandotte, Ml; DSM NeoResins Inc. of Wilmington, MA; and Flint Group Italia Spa. of Coronno, Pertusella, Italy. Nonlimiting examples of suitable polyamide dispersing resins are alcohol- and cosolvent-soluble polyamides having acid values of 1 to 12 mg KOH/g, amine values of 1 to 10 meq/g, and softening points of 100-145 °C. Such resins may be obtained commercially from, for examples, Arizona Chemical of Jacksonville, FL and BASF Corporation of Wyandotte, Ml.

[0026] Any known pigment or combination of pigments can be used in the pigment dispersion with the additive. Examples of suitable pigments include inorganic pigments such as metal oxide like titanium dioxide, iron oxides of various colors, and zinc oxide; filler pigments such as talc, silicates, china clay, carbonates, and barytes; carbon blacks; a wide variety of organic pigments such as quinacridones, diketopyrrolopyrrols, phthalocyanines, perylenes, azo pigments, and indanthrones dioxazines such as carbazole violet, isoindolinones, isoindolons, thioindigo reds, and benzimidazolones. Flake pigments such as aluminum flake, mica pigments, and the like may be dispersed in nitrocellulose or another vehicle using mixing means that avoids damaging (e.g., bending or breaking) the flakes. Flake pigments are typically dispersed separately from particulate pigments, which generally require more intensive mixing such as milling. The pigment dispersions may typically include from about 5 to about 50 percent by weight, or from about 15 to about 30 percent by weight pigment; the amount of pigment used is highly dependent on pigment properties such as specific gravity, surface area, and oil absorption, as is well-known in the art. For example, pigment dispersion of carbon black generally has a very low loading of the carbon black pigment, for example 5% by weight carbon black, while a pigment dispersion of titanium dioxide generally has a much higher loading of pigment, for example 50% by weight titanium dioxide.

[0027] The pigment dispersion further includes one or more organic solvents, preferably from about 50 to about 90 percent by weight of the solvent or solvents. Nonlimiting examples of suitable organic solvents include lower aliphatic alcohols, including ethanol, n-propanol, isopropanol, and butanol; lower aliphatic esters, such as ethyl acetate, n-propyl acetate, butyl acetate; and glycol ethers or glycols. Other specific example of suitable solvents are listed in Kirk-Othmer Encyclopedia of Chemical Technical 3d ed., vol. 13 John Wiley & Sons (1981 ), Table 3, p. 387.

[0028] The pigment dispersion may be prepared by milling the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol along with the pigment, dispersing or grinding resin, and organic solvent. Nonlimiting examples of suitable milling and dispersion equipment include horizontal shot mills, ball mills, bead mills, roller mills, sand mills, and high-speed dispersers. Many different types of materials may be used as milling media, such as glass, ceramic, zirconium, metal, or plastic. The grinding media can include particles, preferably substantially spherical in shape, e.g., zirconium beads. In the process of mixing, milling, and dispersion, each process is performed with cooling to prevent build up of heat. The milling time can vary widely and depends upon the pigment, mechanical means, and residence conditions selected, the initial and desired final pigment particle size etc. In various embodiments, the pigment dispersion may be milled to an average pigment particle size of less than about 5 microns.

[0029] After milling is completed, the milling media is separated from the milled pigment dispersion using conventional separation techniques, such as by filtration, sieving through a mesh screen, and the like.

[0030] A solvent-based flexographic ink is made using the pigment dispersion with the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol by combining the pigment dispersion with a flexographic ink vehicle containing a binder resin or polymer or a combination of binder resins or polymers, an organic solvent or organic solvents, and optionally an ink additive or additives. In various alternative embodiments, a solvent-based flexographic ink is made by combining a pigment dispersion and a flexographic ink vehicle, where the ink vehicle contains the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol instead of or in addition to the pigment dispersion, or wherein the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol, optionally in an organic solution, is added separately from the pigment dispersion and the binder in making the solvent-based flexographic ink. The solvent-based flexographic ink has unexpectedly improved ink printability, substantially reduced ink cobwebbing and plate build-up, and improved print fidelity and color density even with increased press speed.

[0031] The binder may be a polymer suitable for film-forming on flexible packaging materials. Binder polymers for flexographic ink vehicles are commonly selected from polyamides, acrylics, polyurethanes, polyesters, celluloses, and ketone polymers. The best choice of polymer for an ink composition depends upon the particular substrate used and the functional properties required by the package material. All of the polymers of the ink vehicle must be compatible and also be compatible with the pigment dispersion, capable of being mixed together without undergoing separation or reaction. Among suitable, commercially available resins are nitrocellulose, which is available from many sources. Suitable polyamides are available under the tradename VERSAMID® from BASF Corporation and under the tradename UNI-REZTM from Arizona Chemical; suitable acrylic polymers are available under the tradename ELVACITE® from Lucite International, under the tradename NEOCRYL® from DSM, and under the tradename JONCRYL® from BASF; suitable polyurethanes are available under the tradename NeoRez® from DSM, under the tradenames KPLAST and KFILM from Kane International, and under the tradename PRINTPURTM from Flint Group; suitable cellulose polymers are cellulose acetate propionates available from Eastman Chemical under the designation CAP; and suitable ketone resins are available from EVONIK under the tradename TEGO® VariPlus.

[0032] Nonlimiting examples of suitable solvents that may be included in making the solvent-based flexographic inks include lower aliphatic alcohols, such as ethanol, n-propanol, isopropanol, and butanol; lower aliphatic esters, in particular ethyl acetate, n-propyl acetate, butyl acetate; and glycol ethers or glycols. Suitable solvents are listed in Kirk-Othmer Encyclopedia of Chemical Technical 3d ed., vol. 13 John Wiley & Sons (1981 ), Table 3, p. 387. The ink composition may be diluted with an organic solvent prior to the printing operation until an appropriate viscosity is obtained. In general, the inks for flexographic printing may be adjusted to a viscosity in the range 18 -30 seconds with Zahn Cup #2 or to a viscosity in the range 8 -40 seconds with Zahn Cup #3.

[0033] The solvent-based flexographic inks may further include one or more conventional additives and modifying agents such as a wax like polyethylene wax, polyethylene oxide wax, polypropylene wax, and fatty amides; silicone; silica; or plasticizers.

[0034] An ink vehicle mixture may be prepared by dissolving a binder, as well as mixing various additives that are used according to necessity, in an organic solvent. This is usually accomplished by mixing the required components in a stainless steel vessel which is equipped with a high-speed electric agitator.

[0035] Ink compositions are generally prepared by combining the pigment dispersion or dispersions, the ink vehicle, the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol if added separately from the pigment dispersion and ink vehicle, and solvent as needed to provide a desired viscosity. This is typically accomplished by mixing with a high-speed mixer. [0036] In various embodiments, the ink may include from about 8 to about 50 weight percent of binder resin or polymer; from about 5 to about 30 weight percent of a pigment and optionally filler; from about 30 to 75 weight percent of organic solvent; from about 0.1 to about 6 weight percent of the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol; and optionally from about 0.5 to about 10 weight percent of ink modifiers or additives. In various embodiments, the ink may include from about 0.1 weight percent to about 3 weight percent of the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol.

[0037] The solvent-based flexographic ink is printed by a flexographic printing process onto flexible packaging material such as plastic films or foils, examples of which include polyamide films, polyester films such as PET films, polyolefin films such as polyethylene and polypropylene films, metal foils such as tin foils, copper foils, gold foils, and especially aluminum foils, or metallized polymer films

[0038] A representative flexographic printing system includes an enclosed doctor blade, a rubber roll, an anilox roll, and a rubber or photopolymer plate, where the image is raised in relief from the background, non-image area. During the printing process, ink is constantly pumped into the chamber to fill up the anilox cells and excessive ink is removed by the doctor blade; the ink is then transferred from the anilox to the plate and from the plate to the substrate. Early work from Harper showed that the split between anilox and plate, plate and substrate is about 50%, which means that only about 25% of ink is transferred onto the substrate to form the graphic. Therefore, after the first rotation, the ink is actually transferring on and off the plate from already deposited ink on the plate surface. Fresh ink rewets the ink left on the plate, and then the old ink/new ink layer is split again. The physical properties, such as elasticity and tack, of the ink left on the plate are continually changing due to solvent evaporation, and these changes play a major role in ink splitting and thus affect printability. Misting and plate build up are believed to be closely related to the fluid elasticity in extension. It is believed that the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol additives modify elasticity, improving behavior of the ink-ink splitting and ink transfer and reducing misting.

[0039] The solvent-based flexographic ink containing the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol can be printed at a higher press speed, such as at printing speeds from 300 ft/min to 3000 ft./min, while minimizing cobwebbing and with excellent ink transfer. The ink exhibits excellent printability and print fidelity on substrates made of metal, paper, and polymeric materials, including polyester, polypropylene, polyethylene, and polyvinylchloride flexible packaging materials.

[0040] While not wishing to be bound by theory, the inventors believe that the better print definition results from a modification of the elasticity character for the ink composition from the presence of lecithin in the ink composition. Such a modification is believed to be due to an interaction between the lecithin, fatty acid, fatty acid soap, or fatty acid ester of a phosphorylated amino alcohol and the ink binder in the nonaqueous, organic solvent system, and this interaction modifies the elasticity and tack of the system and provides an optimum "cohesive" structure under the stress of the printing process, which makes the ink behave better as it splits in the printing process.

[0041] The invention is further described in the following examples. The example is merely illustrative and does not in any way limit the scope of the invention as described and claimed. All parts are parts by weight unless otherwise noted.

Examples

[0042] Example 1 .

[0043] A varnish was prepared by dissolving 40 wt.% nitrocellulose SS

18-25 BN (wetted with 30 wt% isopropanol) (available from Nitro Quimica, Brazil) in a mixture of 40 wt.% of n-propanol, and 20 wt.% of n-butyl acetate under high speed mixing.

[0044] Example 2.

[0045] A flexographic lamination varnish was made by combining 35.6 wt% of n-propanol, 22 wt% of n-propyl acetate, 28 wt% of polyurethane (NeoRez® U-395, available from DSM NeoResins Inc, Wilmington, MA), 4.4 wt% of acrylic resin (Joncryl® 581 , available from BASF Corporation, Wyandotte, Ml), 5 wt% plasticizer (Uniplex 214, available from Unitex Chemical Corporation, Greensboro, NC), and 5 wt% adhesion promoter (PrintcatTM 508, available from Flint Group Italia Spa, Caronno, Pertusella, Italy).

[0046] Example 3.

[0047] A flexographic shrink sleeve varnish was made by combining 32.5 wt% of n-propanol, 19 wt% of n-butyl acetate, 14.5 wt% of polyurethane (NeoRez® U-471 , available from DSM NeoResins Inc, Wilmington, MA), 9 wt% of polyurethane (KFILMTM 2070, Kane International Corporation, Rye, NY), 19 wt% of acrylic resin (Joncryl® 581 , available from BASF Corporation, Wyandotte, Ml), 3.5 wt% plasticizer (Uniplex 214, available from Unitex Chemical Corporation, Greensboro, NC), and 2.5 wt% of PTFE wax (SST-3, available from Shamrock Technologies, Inc., Newark, NJ).

[0048] Example 4.

[0049] A flexographic surface varnish was made by combining 36 wt% of ethanol, 7 wt% of n-propanol, 8 wt% of n-propyl acetate, 7 wt% of nitrocellulose SS DLX 5-10 (available from Nobel Enterprise, Irvine, Scotland), 36 wt% of polyamide (UNI-REZTM 2229, available from Arizona Chemical Company, Jacksonville, FL), and 6 wt% of a polyethylene and polytetrafluoroethylene wax blend (NeptuneTM 5331 , available from Shamrock Technologies, Inc., Newark, NJ).

[0050] Example 5.

[0051] A pigment dispersion of Pigment Red 52:1 (Bon Red 52DT848, available from Flint Group Pigments, Elizabethtown, KY) was prepared incorporating lecithin (Yelkin® TS Lecithin, available from Archer Daniels Midland Company, Decatur, III., USA) according to the formulation presented in Table 1 . A premix was obtained by adding the pigment to a mixture of the nitrocellulose varnish of Example 1 and 85% by weight of the solvent with high speed mixing for about 30 minutes, then pumping the premix into a shotmill where it was milled to obtain a fineness of grind of 0/0 on a Hegman Grind Gauge. Then, the lecithin and remaining solvent were added. [0052] Example 6. (Comparative Example)

[0053] A comparative pigment dispersion of Pigment Red 52:1 (Bon Red 52DT848, available from Flint Group Pigments, Elizabethtown, KY) was prepared without the lecithin according to the formulation presented in Table 1 using the same procedure as in Example 5 but omitting the lecithin.

TABLE 1

[0054] Example 7.

[0055] A solvent-based flexographic lamination ink was made by combining 60 wt% of the pigment dispersion of Example 5 including lecithin and 40 wt% of the flexographic lamination varnish of Example 2. [0056] Example 8. (Comparative Example)

[0057] A comparative solvent-based flexographic lamination ink was made by combining 60 wt% of the comparative pigment dispersion of Example 6 (without lecithin) and 40 wt% of the flexographic lamination varnish of Example 2. Example 8 was used in testing as a control.

[0058] Example 9.

[0059] A solvent-base flexographic shrink sleeve ink was made by combining 60 wt% of the pigment dispersion of Example 5 comprising the lecithin and 40 wt% of the flexographic shrink sleeve varnish of Example 3.

[0060] Example 10. (Comparative Example)

[0061] A comparative solvent-based flexographic shrink sleeve ink was made by combining 60 wt% of the comparative pigment dispersion of Example 6 (without lecithin) and 40 wt% of the flexographic shrink sleeve varnish of Example 3. Example 10 was used in testing as a control.

[0062] Example 1 1 .

[0063] A solvent-base flexographic surface ink was made by combining 60 wt% of the pigment dispersion of Example 5 comprising the lecithin and 40 wt% of the flexographic surface varnish of Example 4.

[0064] Example 12.

[0065] A solvent-based flexographic surface ink was made by combining

60 wt% of the comparative pigment dispersion of Example 6 (without lecithin) and 40 wt% of the flexographic surface varnish of Example 4. Example 12 was used in testing as a control.

[0066] Example 13.

[0067] A solvent-base flexographic surface white ink was made by combining 26 wt% of n-propanol, 5 wt% of n-propyl acetate, 1 .5 wt% of nitrocellulose SS DLX 5-10 (available from Nobel Enterprise, Irvine, Scotland), 15 wt% of polyamide (UNI-REZTM 2229, available from Arizona Chemical Company, Jacksonville, FL), 50 wt% of titanium dioxide pigment (Tioxide® TR52, Huntsman Pigment Division, Billingham, England), 1 .0 wt% of lecithin (Yelkin® TS Lecithin, available from Archer Daniels Midland Company, Decatur, III., USA), and 1 .5 wt% of a polyethylene and polytetrafluoroethylene wax blend (NeptuneTM 5331 , available from Shamrock Technologies, Inc., Newark, NJ). To make a white pigment dispersion, the propanol, n-propyl acetate, nitrocellulose, and polyamide were combined with high-speed mixing to dissolve the resin in the solvent. The titanium dioxide pigment was added to the resin / solvent mixture and ground using a shotmill to a 0/0 on a Hegman Grind Gauge. After the grind was obtained, the lecithin and wax blend were added and dispersed so that there were no particles present on the Hegman Grind Gauge.

[0068] Example 14. (Comparative Example)

[0069] A solvent-base flexographic surface white ink was made using 27.5 wt% of n-propanol, 5 wt% of n-propyl acetate, 1 .5 wt% of nitrocellulose SS DLX 5-10 (available from Nobel Enterprise, Irvine, Scotland), 15 wt% of polyamide (UNI-REZTM 2229, available from Arizona Chemical Company, Jacksonville, FL), 50 wt% of titanium dioxide pigment (Tioxide® TR52, Huntsman Pigment Division, Billingham, England), and 1 .5 wt% of a polyethylene and polytetrafluoroethylene wax blend (NeptuneTM 5331 , available from Shamrock Technologies, Inc., Newark, NJ) using the procedure of Example 13, omitting the lecithin.

[0070] The inks were tested according to the following test methods.

[0071] Fineness of grind was measured on a NPIRI (25 micron) grind gauge.

[0072] Viscosity of pigment dispersions was measured on a Brookfield viscometer; viscosity of inks was measured using a Zahn Cup #2 or Zahn Cup # 3.

[0073] Colorimetric measurement of prints was measured using X-Rite 900 series spectrodensitometer.

[0074] Ink cobwebbing and anti-misting was determined by visual observation of the ink applied on a clean 3" wide hand-proofer and the hand- proofer was manually rolled back and forth until the ink reached a dried phase. Cobwebbing and anti-misting of an ink was then categorized poor to excellent on scale of 1 to 5, 1 being poor and 5 as excellent.

[0075] Printability evaluation of the inks was carried out by printers with different printing press set up, ink delivery system, and flexographic plates.

[0076] The results are listed in Table 2. Attorney Docket No. 5898-330PC

[0077] The ink formulations containing the lecithin provided superior and excellent results compared to the standard ink formulations without the lecithin. As may be seen from Table 2, the ink compositions of the present invention exemplified by Examples 7, 9, 1 1 , and 13 and the comparative inks of Examples 8, 10, 12, and 14 were trialed on different flexographic printing press using different types of flexographic plates and aniloxes. Trial results showed that red inks prepared with lecithin (Examples 7, 9, and 1 1 ) showed 10 % higher in color density than the comparative inks without lecithin (Examples 8, 10, and 12). Examples 7, 9, 1 1 , and 13 exhibited superior printability at press speeds ranging from 300 ft min to 1300 ft/min. At an elevated speed of 1300 ft/min, the ink compositions of the present invention, Examples 7, 9, 1 1 , and 13, performed without any issues such as dirty print, plate build-up, or misting for an extensive length, so that after 350,000 plate impressions no dirty printing is seen. The industry standard is 100,000 plate impressions before any printing defect is observed. The comparative inks without lecithin, Examples 8, 10, 12, and 14, could only achieve a maximum print speed of 1000 ft/min, and a flexographic plate clean-up was needed after only a short printing period. Tone reproduction and neutral determination at 1 % tone scale were compared for the red ink examples. The ink compositions of the present invention, Examples 7, 9, and 1 1 , exhibited better dot formation (print fidelity) and better ink transfer at 1 % tone scale as compared to the Comparative Examples 8, 10, and 12 without lecithin, which showed a lot of missing dots and donut shape dots, which indicates poor ink transfer. The ink compositions of the present invention, Examples 7, 9, and 1 1 , provided improved flexographic printing quality. In particular, Examples 7, 9, 1 1 , and 13 provided better tone reproduction dot formation, reduced plate clean up, allowed for higher printing speeds, and resulted in higher color density as compared to Comparative Examples 8, 10, 12, and 14.

[0078] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.

Claims

CLAIMS What is claimed is:

1 . A solvent-based, flexographic ink, comprising a binder resin or polymer, a pigment, and an additive selected from the group consisting of: lecithin, phosphatidylcholine, fatty acid esters of phosphorylated amino alcohols, fatty acids having from 8 to 22 carbon atoms, soaps of fatty acids having from 8 to 22 carbon atoms, and combinations thereof.

2. A solvent-based, flexographic ink according to claim 1 , wherein the additive comprises lecithin.

3. A solvent-based, flexographic ink according to claim 2, wherein the lecithin is soy lecithin.

4. A solvent-based, flexographic ink according to any one of claims 1 -3, wherein the ink comprises from about 0.1 to about 6 weight percent of the additive.

5. A solvent-based, flexographic ink according to any one of claims 1 -4, comprising from about 8 to about 50 weight percent of the binder resin or polymer; from about 5 to about 30 weight percent of the pigment and optionally a filler; from about 30 to about 75 weight percent of organic solvent; and from about 0.1 to about 6 weight percent of the additive.

6. A method of making a solvent-based, flexographic ink, comprising combining an ink vehicle comprising a binder resin or polymer, a pigment dispersion, an organic solvent, and an additive selected from the group consisting of: lecithin, phosphatidylcholine, fatty acid esters of phosphorylated amino alcohols, fatty acids having from 8 to 22 carbon atoms, soaps of fatty acids having from 8 to 22 carbon atoms, and combinations thereof.

7. A method according to claim 6, wherein the additive is incorporated into the ink vehicle and the ink vehicle comprising the additive is combined with the pigment dispersion and organic solvent.

8. A method according to claim 6, wherein the additive is incorporated into the pigment dispersion and the pigment dispersion comprising the additive is combined with the ink vehicle and organic solvent.

9. A method according to claim 6, wherein the additive is added separately from the ink vehicle and the pigment dispersion.

10. A method of flexographic printing, comprising printing flexible packaging material with a solvent-based, flexographic ink according to any one of claims 1 -5.

1 1 . A method of flexographic printing according to claim 10, wherein the printing is carried out at a press speed of 300 ft./min. to 3000 ft./min.

12. Printed flexible packaging prepared according to a method according to claim 10 or claim 1 1 .

13. A solvent-based pigment dispersion, comprising nitrocellulose; a pigment; an organic solvent; and an additive selected from the group consisting of: lecithin, phosphatidylcholine, fatty acid esters of phosphorylated amino alcohols, fatty acids having from 8 to 22 carbon atoms, soaps of fatty acids having from 8 to 22 carbon atoms, and combinations thereof.

14. A solvent-based pigment dispersion according to claim 13, wherein the additive comprises lecithin.

15. A solvent-based pigment dispersion according to claim 13 or claim 14, comprising from about 4 to about 16 percent by weight of the nitrocellulose; from about 5 to about 50 percent by weight pigment; from about 0.5 to about 10 percent by weight of the additive; and the organic solvent.

16. A method of making a solvent-based, flexographic ink, comprising combining a solvent-based pigment dispersion according to any one of claims 13- 15 with an ink vehicle comprising a binder resin or polymer and an organic solvent.

17. A solvent-based, flexographic ink prepared according to the method of claim 16.