Energy curable ink compositions and methods thereof

Abstract

An energy curable ink composition comprising: from 2 wt.% to 20 wt.%, based on the total weight of (a), (b), (c), and (d), of a pigment; from 5 wt.% to 30 wt.%, based on the total weight of (a), (b), (c), and (d), of a cellulose ester resin; from 40 wt.% to 91 wt.%, based on the total weight of (a), (b), (c), and (d), of one or more polyfunctional acrylates; and from 2 wt.% to 10 wt.%, based on the total weight of (a), (b), (c), and (d), of a free radical photoinitiator; wherein the composition has a viscosity of 2,000 to 6,000 mPa-s, as measured according to ASTM D4287 using a cone and plate viscometer (BYK CAP 2000+) with a spindle size 2 at a speed of 100 rpm.

Description

ENERGY CURABLE INK COMPOSITIONS AND METHODS THEREOFTECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to energy curable ink compositions, and more particularly, relate to energy curable ink compositions for use in offset or lithographic printing applications.BACKGROUND

[0002] Lithography is a common method of printing or marking images on an image receiving medium. In a typical lithographic process, the surface of a print image carrier, which may be a flat plate, cylinder or belt, is formed to have image regions and non-image regions. The image regions correspond to the areas on the final print on the image receiving medium that are occupied by a printing or marking material such as ink, whereas the non-image regions, e.g. background regions, are the regions corresponding to the areas on the final print on the image receiving medium that are not occupied by the printing or marking material. Conventional lithographic and offset lithographic printing techniques use plates that are permanently patterned, and are, therefore, generally considered to be useful only when printing a large number of copies of the same image in long print runs, such as for magazines, newspapers, and the like.

[0003] Offset / Litho ink comes in a wide variety of formulations addressing different aspects of the applications and related performances. One critical property of offset ink formulation is the ink tack to enable clean transfer of the ink on the transfer and the printing rollers on a proofer / printing machine. The ink must also be free of unwanted misting. Other factors are the fluidic carrier vehicle that contains selected UV cure monomers and oligomers, in addition to the colorant pigments or dyes. Another important aspect of the ink is the resin or the polymeric binder in addition to other additives for wetting and surface modification purposes.

[0004] The resin or polymeric binder is mainly responsible for the tack property and this can be more pronounced in case of the UV curing vehicles or diluents like low viscosity monomers, oligomers, and other highly branched curable reactive UV monomers. However, one problem with offset / lithographic inks is that the resins (e.g.,acrylates, polyurethanes, or other polymeric resins) have single or limited compatibility with media substrates. That is, they cannot adhere to multiple substrates (e.g., metal substrates, paper, Tyvek, vinyl, PVC, polyolefins, etc.), and issues may include adhesion, wetting and long-term performance issues, such as, image quality and durability. One solution is to use two or more resins / binders to address these performance issues. Also, polymeric resins can sometimes interfere with UV / e-beam curing as the resin absorb the UV energy light. To overcome this issue, photoinitiators may be added to the formulation to improve the cure efficiency.

[0005] Accordingly, there remains a need for an offset / litho ink composition that achieves a good balance of properties, including adhesion, wetting, image quality and durability, as well as being compatible with multiple substrates, and offering better UV cure with minimal-to-no photoinitiators needed (in the case of e-beam curing).SUMMARY

[0006] Disclosed in embodiments herein are energy curable ink compositions. The energy curable ink compositions comprise comprising: from 2 wt.% to 20 wt.%, based on the total weight of (a), (b), (c), and (d), of a pigment; from 5 wt.% to 30 wt.%, based on the total weight of (a), (b), (c), and (d), of a cellulose ester resin; from 40 wt.% to 91 wt.%, based on the total weight of (a), (b), (c), and (d), of one or more polyfunctional acrylates; and from 2 wt.% to 10 wt.%, based on the total weight of (a), (b), (c), and (d), of a free radical photoinitiator; wherein the composition has a viscosity of 2,000 to 6,000 mPa-s, as measured according to ASTM D4287 using a cone and plate viscometer (BYK CAP 2000+) using spindle size 2 at a speed of 100 rpm.

[0007] Further disclosed in embodiments herein are printing methods. The methods comprise providing the ink composition disclosed herein; depositing the ink composition onto a substrate: and curing the ink composition by irradiation with ultraviolet light to form a cured ink.

[0008] Additional features and advantages of the embodiments will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodimentsdescribed herein. It is to be understood that both the foregoing and the following description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter.DETAILED DESCRIPTION

[0009] Reference will now be made in detail to embodiments of energy curable ink compositions and methods of use thereof, as well as printing methods thereof. The energy curable ink compositions may be used in lithographic or offset printing. It is noted, however, that this is merely an illustrative implementation of the embodiments disclosed herein. The embodiments are applicable to other technologies that are susceptible to similar problems as those discussed above.

[0010] In embodiments herein, the energy curable ink composition comprises (a) a pigment, (b) a cellulose ester resin, (c) one or more polyfunctional acrylates, and (d) a free radical photoinitiator. In one or more embodiments herein, the energy curable ink composition comprises 2 wt.% to 20 wt.% of the pigment, based on the total weight of (a), (b), (c), and (d). All individual values and subranges are included and disclosed herein. For example, in some embodiments, the energy curable ink composition comprises 2 wt.% to 18 wt.%, 3 wt.% to 15 wt.%, 5 wt.% to 15 wt.%, or 5 wt.% to 13 wt.% of the pigment, based on the total weight of (a), (b), (c), and (d).

[0011] The pigment is a component for providing color to the energy curable ink composition and is mainly a color pigment. Examples of the pigment may include organic and / or inorganic pigments that have been used in traditional printing ink compositions. In some embodiments, the pigment is selected from an inorganic pigment, an organic pigment, or combinations thereof. In other embodiments, the pigment is an organic pigment.

[0012] Examples of the organic pigment may include, for example, perylene.perinon-based compound pigments, quinacridone -based compound pigments, phthalocyanine-based compound pigments, anthraquinone -based compound pigments, phthalon-based compound pigments, dioxazine-based compound pigments, isoindolinone-based compound pigments, methine.azomethine-based compoundpigments, diketopyrrolopyrrole-based compound pigments, insoluble azo-based compound pigments, and condensed azo-based compound pigments.

[0013] Examples of the inorganic pigments include, for example, titanium oxide, zinc sulfide, white lead, zinc oxide, lithopone, antimony trioxide, basic lead sulfate, basic lead silicate, barium sulfate, calcium carbonate, gypsum, silica, carbon black, black iron oxide, cobalt violet, vermilion, molybdenum orange, minium, bengala, chrome yellow, cadmium yellow, zinc chromate, yellow ocher, chromium oxide, ultramarine blue, Prussian blue, and cobalt blue. Specific examples of pigments (organic or inorganic) may include yellow pigments such as Disazo yellows (Pigment Yellows 12, 13, 14, 17, and 1) and Hansa yellow; magenta pigments such as Brilliant Carmine 6B, Lake Red C, and Watching Red; cyan pigments such as Phthalocyanine Blue, Phthalocyanine Green, and Alkali Blue; and black pigments such as carbon black.

[0014] In embodiments herein, the energy curable ink composition comprises a cellulose ester resin. In some embodiments herein, the energy curable ink composition comprises 5 wt.% to 30 wt.% of cellulose ester resin, based on the total weight of (a), (b), (c), and (d). All individual values and subranges are included and disclosed herein. For example, in some embodiments, the energy curable ink composition comprises 5 wt.% to 27.5 wt.%. 5 wt.% to 25 wt.%, or 6 wt.% to 20 wt.% of cellulose ester resin, based on the total weight of (a), (b), (c), and (d).

[0015] The cellulose ester resin may be a cellulose acetate propionate resin, a cellulose acetate butyrate resin, or combinations thereof. In some embodiments, the cellulose ester resin has an average degree of substitution for the unsubstituted hydroxyl group (DS OH) that is from 0 to 1.2 and an average degree of substitution for the acetyl substituent (DSAC) that is from 0.05 to 0.5. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the cellulose ester resin has an average degree of substitution for the unsubstituted hydroxyl group (DSOH) that is from 0.1 to 1.0, 0.1 to 0.75, 0.1 to 0.6, or 0.2 to 0.5 and an average degree of substitution for the acetyl substituent (DSAC) that is from 0.05 to 0.4, 0.05 to 0.3, 0.05 to 0.25, or 0.05 to 0.2.

[0016] In some embodiments, the cellulose ester resin comprises at least 50 wt.% of a cellulose acetate propionate (CAP) resin. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the cellulose ester resin comprises at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 97.5, or 99 wt.%, based on the total amount of cellulose ester resin, of a cellulose acetate propionate (CAP) resin. In other embodiments, the cellulose ester resin comprises from 55 to 99, 60 to 99, 65 to 99, 70 to 99, 75 to 99, 80 to 99, 85 to 99, 90 to 99, or 95 to 99 wt.%, based on the total amount of cellulose ester resin, of a cellulose acetate propionate (CAP) resin and from 1 to 45, 1 to 40, 1 to 35, 1 to 30, 1 to 25, 1 to 20, 1 to 15, 1 to 10, or 1 to 5 wt.%, based on the total amount of cellulose ester resin, of a cellulose acetate butyrate (CAB) resin. In further embodiments, the cellulose ester resin is a cellulose acetate propionate (CAP) resin (i.e., 100 wt.% based on the total amount of cellulose ester resin).

[0017] In one or more embodiments herein, the CAP resin has an average degree of substitution for the unsubstituted hydroxyl group (DSOH) that is from 0 to 1.2, an average degree of substitution for the acetyl substituent (DSAC) that is from 0.05 to 0.5, and an average degree of substitution for the propionyl substituents (DSPr) from 1.3 to 2.8. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the CAP resin has an average degree of substitution for the unsubstituted hydroxyl group (DSOH) that is from 0.1 to 1.0, 0.1 to 0.75, 0.1 to 0.6, or 0.2 to 0.5, an average degree of substitution for the acetyl substituent (DSAC) that is from 0.05 to 0.4, 0.05 to 0.3, 0.05 to 0.25, or 0.05 to 0.2, and an average degree of substitution for the propionyl substituents (DSPr) from 1.5 to 2.8, 1.75 to 2.8, 2.0 to 2.8, or 2.2 to 2.8.

[0018] For cellulose esters, the substitution level is usually express in terms of degree of substitution (DS), which is the average number of non-OH substituents per anhydroglucose unit (AGU). Generally, conventional cellulose contains three hydroxyl groups in each AGU unit that can be substituted. As used herein, the term “degree of substitution” or “DS” refers to the average number of substituents per anhydroglucose ring of the cellulose polymer, wherein the maximum degree of substitution is 3.0. Because DS is a statistical mean value, a value of 1 does not assure that every AGU has a single substituent. In some cases, there can be unsubstituted anhydroglucose units,some with two and some with three substituents, and typically the value will be a noninteger. Total DS is defined as the average number of all of substituents per anhydroglucose unit. The degree of substitution per AGU can also refer to a particular substituent, such as, for example, hydroxyl (DSOH) or acetyl (DSAC).

[0019] In some embodiments herein, the cellulose ester resin has a ball drop viscosity of 0.1 to 5 seconds as measured according to ASTM D1343. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the cellulose ester resin may have ball drop viscosity of 0.1 to 5, 0.1 to 2.5, 0.1 to 1, or 0.1 to 0.5 seconds as measured according to ASTM DI 343. In further embodiments herein, the cellulose ester resin is a CAP having a ball drop viscosity of 0.1 to 5 seconds as measured according to ASTM D1343. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the cellulose ester resin is a CAP having a ball drop viscosity of 0.1 to 5, 0.1 to 2.5, 0.1 to 1, or 0.1 to 0.5 seconds as measured according to ASTM DI 343.

[0020] In one or more embodiments herein, the cellulose ester resin is a cellulose acetate propionate (CAP) having an average degree of substitution for the unsubstituted hydroxyl group (DSOH) that is from 0 to 1.2, an average degree of substitution for the acetyl substituent (DSAC) that is from 0.05 to 0.5, and an average degree of substitution for the propionyl substituents (DSPr) from 1.3 to 2.8, and have a ball drop viscosity of 0.1 to 5 seconds as measured according to ASTM D1343. In one or more embodiments herein, the cellulose ester resin comprises at least 50 wt.% of a cellulose acetate propionate (CAP) having an average degree of substitution for the unsubstituted hydroxyl group (DSOH) that is from 0 to 1.2, an average degree of substitution for the acetyl substituent (DSAC) that is from 0.05 to 0.5, and an average degree of substitution for the propionyl substituents (DSPr) from 1.3 to 2.8, and have a ball drop viscosity of 0.1 to 5 seconds as measured according to ASTM D1343. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the cellulose ester resin is a cellulose acetate propionate (CAP) having an average degree of substitution for the unsubstituted hydroxyl group (DSOH) that is from 0.1 to 1.0, 0. 1 to 0.75, 0.1 to 0.6, or 0.2 to 0.5, an average degree of substitution for the acetyl substituent (DSAC) that is from 0.05 to 0.4, 0.05 to 0.3, 0.05 to 0.25, or 0.05 to 0.2, andan average degree of substitution for the propionyl substituents (DSPr) from 1.5 to 2.8, 1.75 to 2.8, 2.0 to 2.8, or 2.2 to 2.8, and a ball drop viscosity of 0.1 to 5, 0.1 to 2.5, 0.1 to 1, or 0.1 to 0.5 seconds as measured according to ASTM D1343.

[0021] In addition to the above, in some embodiments herein, the cellulose ester resin may have a glass transition temperature (Tg) of from 120 °C to 170 °C. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the cellulose ester resin may have a Tg of from 120 °C to 165 °C or from 130 °C to 165 °C. In other embodiments, the cellulose ester resin is a cellulose acetate propionate (CAP) having a glass transition temperature (Tg) of from 120 °C to 170 °C. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the cellulose ester resin is a cellulose acetate propionate (CAP) having a Tg of from 120 °C to 165 °C or from 130 °C to 165 °C.

[0022] In embodiments herein, the energy curable ink composition also comprises one or more polyfunctional acrylates. In some embodiments herein, the energy curable ink composition comprises from 40 wt.% to 91 wt.% of one or more polyfunctional acrylates, based on the total weight of (a), (b), (c), and (d). All individual values and subranges are included and disclosed herein. For example, in some embodiments, the energy curable ink composition comprises from 45 wt.% to 90 wt.%, from 50 wt.% to 90 wt.%, or from 55 wt.% to 85 wt.% of one or more polyfunctional acrylates, based on the total weight of (a), (b), (c), and (d).

[0023] The one or more polyfunctional acrylate may be a difunctional acrylate, trifunctional acrylate, tetrafunctional acrylate, pentafunctional acrylate, hexafunctional acrylate, or combinations thereof. In some embodiments, the one or more polyfunctional acrylate has a molecular weight of from 90 to 1,000 g / mol. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the one or more polyfunctional acrylate has a molecular weight of from 150 to 750 g / mol, 200 to 700 g / mol, or 250 to 650 g / mol. The molecular weight may be calculated as noted below in the test methods.

[0024] Examples of polyfunctional acrylates may include, but are not limited to, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1 ,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, dimethyloltricyclodecane diacrylate, bisphenol A EO (ethylene oxide) adduct diacrylate, bisphenol A PO (propylene oxide) adduct diacrylate, hydroxypivalate neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, alkoxylated dimethyloltricyclodecane diacrylate and polytetramethylene glycol diacrylate, trimethylolpropane triacrylate, EO modified trimethylolpropane triacrylate, tri (propylene glycol) triacrylate, caprolactone modified trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritolethoxy tetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, glycerolpropoxy triacrylate, dipentaerythritol pentaacrylate, dipentaerythritol monohydroxypentaacrylate, alkyloyl-modified dipenta-erythritol pentaacrylate, and caprolactam modified dipentaerythritol hexaacrylate. In some embodiments, the one or more polyfunctional acrylate is a trifunctional acrylate, a pentafunctional acrylate, or combinations thereof. In other embodiments, the one or more polyfunctional acrylate is a trifunctional acrylate, a pentafunctional acrylate, or combinations thereof, wherein the one or more polyfunctional acrylate has a molecular weight of from 90 to 1,000 g / mol (alternatively, from 150 to 750 g / mol, 200 to 700 g / mol, or 250 to 650 g / mol). In a further embodiment, the one or more polyfunctional acrylate is at least two triacrylates selected from the group consisting of trimethylolpropane triacrylate, EO modified trimethylolpropane triacrylate, tri (propylene glycol) triacrylate, caprolactone modified trimethylolpropane triacrylate, and pentaerythritol triacrylate, and a pentaacrylate selected from the group consisting of dipentaerythritol pentaacrylate, dipentaerythritol monohydroxypentaacrylate, and alkyloyl-modified dipenta-erythritol pentaacrylate. The at least two tricrylates will be different from each other.

[0025] In embodiments herein, the energy curable ink composition also comprises a photoinitiator. In some embodiments herein, the energy curable ink composition comprises from 2 wt.% to 10 wt.% of a free radical photoinitiator. All individual valuesand subranges are included and disclosed herein. For example, in some embodiments, the energy curable ink composition comprises 2 wt.% to 8 wt.% or 3 wt.% to 6 wt.% of the free radical photoinitiator.

[0026] Examples of suitable free radical photoinitiators may include, but is not limited to, a-hydroxyketone photo-initiator (including a-hydroxyketone photoinitiators sold under the trade name IRGACURE™ 184, IRGACURE™ 500, DAROCUR™ 1173, and IRGACURE™ 2959, which are manufactured by BASF, or OMNIRAD™ 184, OMNIRAD™ 500, OMNIRAD™ 1173, and OMNIRAD™ 2959, which are manufactured by IGM Group B.V. Waalwijk, The Netherlands), a-aminoketone photoinitiators (including a-aminoketone photo-initiators IRGACURE™ 369, IRGACURE™ 379, IRGACURE™ 907, and IRGACURE™ 1300, which are manufactured by BASF) and bisacyl phosphine photo-initiators (including bisacyl phospine photo-initiators sold under the trade name IRGACURE™ 819, IRGACURE™ 819DW, and IRGACURE™ 2022, which are manufactured by BASF). Other suitable photo -initiators include monoacylphosphine oxide and bisacylphosphine oxide, such as 2,4,6-trimethylbenzoybiphenylphosphine oxide (manufactured by BASF under the trade name LUCIRIN™ TPO); ethyl-2,4,6-trimethylbenzoylphenyl phosphinate (manufactured by BASF under the trade name LUCIRIN™ TPO-L); mono- and bis-acylphosphine photoinitiators (such IRGACURE™ 1700, IRGACURE™ 1800, IRGACURE™ 1850, and DAROCUR™ 4265, manufactured by BASF), benzyldimethyl-ketal photo-initiators (such as IRGACURE™ 651, manufactured by BASF) and oligo[2-hydroxy-2-methyl-l-[4-(l- methylvinyl)phenyl]propanone] (available as ESACURE™ KIP 150 from Lamberti); Type II Norrish photoinitiators (such as benzophenone, 2-isopropylthioxanthone, 4- isopropylthioxanthone, 2,4-dimethylthioxanthone, and 2,4-diethylthioxanthone), as well as combinations thereof. In some embodiments, the free radical photoinitiator is an a-hydroxyketone photoinitiator.

[0027] In one or more embodiments herein, the energy curable ink composition may further comprise one or more fillers. Suitable fillers may include, but are not limited to, amorphous, diatomaceous, fumed quartz and crystalline silica, clays, waxes, aluminum silicates, magnesium aluminum silicates, talc, mica, delaminated clays,calcium carbonates and silicates, gypsum, barium sulfate, zinc, calcium zinc molybdates, zinc oxide, phosphosilicates and borosilicates of calcium, barium and strontium, barium metaborate monohydrate, and the like. In some embodiments, the filler may be clays, waxes, talcs, calcium carbonates, or combinations thereof. In some embodiments, the one or more fillers may be present in the energy curable ink composition of the present disclosure in an amount from about 0 wt.% to about 20 wt.%, such as about 2 wt.% to about 16 wt.%, about 3 wt.% to about 15 wt.%, about 3 wt.% to about 8 wt.% or about 8 wt.% to about 15 wt.%, based upon the total weight of the ink composition.

[0028] The energy curable ink compositions described herein have a viscosity of 2,000 to 6,000 mPa-s, as measured according to ASTM D4287, using a cone and plate viscometer (BYK CAP 2000+) using spindle size 2 at a speed of 100 rpm. In some embodiments, the energy curable ink compositions described herein have a viscosity of 2,000 to 5,500 mPa-s, 2,000 to 5,000 mPa-s, 2,500 to 6,000 mPa-s, or 3,000 to 6,000 mPa-s, as measured according to ASTM D4287, using a cone and plate viscometer (BYK CAP 2000+) using spindle size 2 at a speed of 100 rpm. The energy curable ink compositions described herein have a viscosity of 5,000 to 20,000 mPa-s, as measured according to ASTM D4287, using a cone and plate viscometer (BYK CAP 2000+) using spindle size 3 at a speed of 100 rpm. In some embodiments, the energy curable ink compositions described herein have a viscosity of 5,000 to 17,500 mPa-s, 5,000 to 15,000 mPa-s, or 5,000 to 12,500 mPa-s, as measured according to ASTM D4287, using a cone and plate viscometer (BYK CAP 2000+) using spindle size 2 at a speed of 100 rpm.

[0029] Also disclosed in embodiments described herein are printing methods using the energy curable ink compositions described herein. The method comprises providing the energy curable ink compositions described herein; depositing the energy curable ink composition onto a substrate; and curing the energy curable ink composition by irradiation with ultraviolet light to form a cured ink. Exemplary substrates may include any substrate that can receive the printed image whether smooth or non-smooth, such as, paper, plastic (e.g., polyethylene, polypropylene), mylar, vinyl, metallized paper, folded paperboard, Kraft paper, clear substrates, metallic substrates, textured cardboard,textured plastic, uncoated paper, or labels. In embodiments herein, the cured ink may exhibit an IPA double rub, 500 g hammer head value of above 100 cycles.TEST METHODSBall Drop Viscosity

[0030] Ball drop viscosity is measured according to ASTM DI 343. The results are reported in seconds.Molecular Weight

[0031] The molecular weight for the polyfunctional acrylates may be calculated by its molecular mass of each atom. The results are reported in g / mol.Glass Transition Temperature (Tg)

[0032] A resin sample is placed in a differential scanning calorimeter (TA Instruments DSC Q2000 V24.9 Build 121). On the first heating cycle, the sample is heated under nitrogen atmosphere from 30°C to 150°C at a rate of 10°C / min. The sample is then quench cooled to 30°C. For the second heating cycle, the sample is heated under the same conditions as those used in the first heating cycle. The midpoint of the second heating cycle is reported as the Tg of the sample. The results are reported in °C.Ink Viscosity

[0033] The viscosity of the ink composition is measured according to ASTM 4287 using a cone and plate viscometer (BYK-CAP 2000+) using either spindle size 2 or 3 at a speed of 100 RPM. The results are reported in millipascal-seconds (mPa-s).Resin Viscosity

[0034] The viscosity of the resin is measured according to ASTM D3835. The results are reported in centipoise (cps).Viscosity @ Specified Shear Rates

[0035] Viscosity is measured according to ASTM D2196, Method A. Viscosity is reported in mPa-s.Tack

[0036] An Inkometer instrument with two spinning rubber rollers at 400 rpm, and 5 g of ink is applied on the top roller, and the ink is rubbed against the second roller at the speed. The instrument is calibrated to sense the ink transfer and how easy the ink transfer from one roller to the other and it will give a number ranging from 1 to 10.IPA Double Rub

[0037] In general, IPA Double rub is composed of an arm with hammer head that oscillates in a forward and backward movement (a double rub cycle) over the surface of an ink. The test is stopped once the ink starts lifting and the number of cycles is recorded. The ink passes the rub test if it passes 100 cycles. The test continues to 200 cycles, which means no failures have occurred after 200 cycles. A cheese cloth soaked in 5 g of IPA and covers a hammer head weighing 500g and a stroke counter which is set to 0 to count the number of cycle for forward and backward movement or one double rubs cycle.Print Quality

[0038] The appearance of printed ink is evaluated based on the evenness of ink on the metal substrate, the density of the color, and any coating defects, like crazing, pinhole, orange peel, blotching spots, etc. The quality is rated as follows:Optical Density

[0039] A Datacolor 500 instrument is first calibrated with a white tile for full reflection and with a black tile for full absorption. The sample with ink is tested. The instrument provides the optical color density on a scale of from 0 to 3. The units are dimensionless.Adhesion

[0040] Adhesion is measured according to ASTM D3359, with the results reported as a 0-5 rating as outlined in the ASTM method.EXAMPLES

[0041] The following specific examples are given to illustrate the process and performance properties associated with energy curable ink compositions and its components. The inventive and comparative examples are provided below with the details of the formulations and results are provided in the Tables below.Table 1 - Raw MaterialsTable 2 - Resin Properties

[0042] Energy curable ink compositions are formulated according to the following procedure: The resin is mixed with TA-1 , PA, and TA-2. A photoinitiator is used with a flow additive and added to the resin mixture. The weight percent of each component is shown below in Table 3. The inventive examples, IE1, IE4, and IE7, use CAP as the resin. CE2 and CE3 use A-81 as the resin. CE5 and CE8 use V-AP as the resin. CE6 uses E-546 as the resin. Table 3 - Energy Curable Ink Compositions

[0043] The viscosity of the ink compositions is measured and shown in Table 4. The ink compositions are applied with a 3-inch square frame precision tool, gaps 0.5 mil to 6 mil, to LDPE, Tin metal, or Aluminum metal with a range of 10 - 25 micron ink thickness. The coated substrates are cured under UV-A lamp using Fusion lab UV tower with 300 watts / cm power at 25 fpm conveyer speed. The ink cured instantly and the performance properties (tack, IPA double rub, print quality, optical density, and adhesion) are measured. The results are shown in Table 4.Table 4 - Results0044] As shown in the Table 4, it has been surprisingly found that the energy curable ink formulations of the present invention exhibit improved viscosity, and when cured, exhibit improved IPA double rub, print quality, and optical density when compared to the comparative examples.

[0045] The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”

[0046] Every document cited herein, if any, including any cross- referenced or related patent or application and any patent application or patent to which this application claims priority or benefit thereof, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

[0047] While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

What is claimed is:

1. An energy curable ink composition comprising: a. from 2 wt.% to 20 wt.%, based on the total weight of (a), (b), (c), and (d), of a pigment; b. from 5 wt.% to 30 wt.%, based on the total weight of (a), (b), (c), and (d), of a cellulose ester resin; c. from 40 wt.% to 91 wt.%, based on the total weight of (a), (b), (c), and (d), of one or more polyfunctional acrylates; and d. from 2 wt.% to 10 wt.%, based on the total weight of (a), (b), (c), and (d), of a free radical photoinitiator; wherein the composition has a viscosity of 2,000 to 6,000 mPa-s, as measured according to ASTM D4287 using a cone and plate viscometer (BYK CAP 2000+) with a spindle size 2 at a speed of 100 rpm.

2. The composition of claim 1, wherein the cellulose ester resin comprises at least 50 wt.% of cellulose acetate propionate (CAP) having an average degree of substitution for hydroxyl substituents from 0 to 1.2 (DSOH), an average degree of substitution for the acetyl substituents (DSAc) from 0.05 to 0.5, an average degree of substitution for the propionyl substituents (DSPr) from 1.3 to 2.8, and a ball drop viscosity of 0.1 to 5 seconds as measured according to ASTM DI 343.

3. The composition of claims 1 or 2, wherein the one or more polyfunctional acrylates is a trifunctional acrylate, pentafunctional acrylate, or combinations thereof.

4. The composition of claims 1-3, wherein the one or more polyfunctional acrylates has a molecular weight of from 90 to 1 ,000 g / mol.

5. The composition of claims 1-4, wherein the one or more polyfunctional acrylates is at least two triacrylates selected from the group consisting of trimethylolpropane triacrylate, EO modified trimethylolpropane triacrylate, tri (propylene glycol) triacrylate, caprolactone modified trimethylolpropane triacrylate, and pentaerythritol triacrylate, and a pentaacrylate selected from the group consistingof dipentaerythritol pentaacrylate, dipentaerythritol monohydroxypentaacrylate, and alkyloyl-modified dipenta-erythritol pentaacrylate.

6. The composition of claims 1-5, wherein the photoinitiator is an a- hydroxyketone photoinitiator.

7. The composition of claims 1-6, wherein the pigment is selected from an inorganic pigment, organic pigment, or combinations thereof.

8. The composition of claims 1-7, wherein the composition further comprises one or more fillers.

9. A printing method, the method comprising: providing the ink composition of claims 1-8; depositing the ink composition onto a substrate: and curing the ink composition by irradiation with ultraviolet light to form a cured ink.

10. The method of claim 9, wherein the cured ink exhibits an IPA double rub, 500g hammer head value of above 100 cycles.

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