# Patent

## Title
Fluorescent security enabled ink for digital offset printing applications

## Abstract

An ink composition useful for digital offset printing applications comprises a fluorescent colorant and a plurality of curable compounds. The compounds have Hansen solubility parameters as described herein, and the resulting ink composition is both compatible with certain dampening fluids and has certain rheological properties, including a low viscosity. The fluorescent ink composition is useful for printing security features at high speed in short runs with customized data to produce anti-counterfeit packaging.

## Background
BACKGROUND
The present disclosure relates to certain fluorescent ink compositions which are compatible with dampening fluids and are useful for providing security information in variable data lithographic printing applications. This disclosure also relates to methods of using such ink compositions, such as in variable lithographic printing applications.
Offset lithography is a common method of printing today. (For the purposes hereof, the terms “printing” and “marking” are interchangeable.) In a typical lithographic process a printing plate, which may be a flat plate, the surface of a cylinder, or belt, etc., is formed to have “image regions” formed of a hydrophobic/oleophilic material, and “non-image regions” formed of a hydrophilic/oleophobic material. The image regions correspond to the areas on the final print (i.e., the target substrate) that are occupied by a printing or marking material such as ink, whereas the non-image regions correspond to the areas on the final print that are not occupied by said marking material. The hydrophilic regions accept and are readily wetted by a water-based fluid, commonly referred to as a dampening fluid or fountain fluid (typically consisting of water and a small amount of alcohol as well as other additives and/or surfactants to reduce surface tension). The hydrophobic regions repel dampening fluid and accept ink, whereas the dampening fluid formed over the hydrophilic regions forms a fluid “release layer” for rejecting ink. The hydrophilic regions of the printing plate thus correspond to unprinted areas, or “non-image areas”, of the final print.
The ink may be transferred directly to a target substrate, such as paper, or may be applied to an intermediate surface, such as an offset (or blanket) cylinder in an offset printing system. The offset cylinder is covered with a conformable coating or sleeve with a surface that can conform to the texture of the target substrate, which may have surface peak-to-valley depth somewhat greater than the surface peak-to-valley depth of the imaging plate. Also, the surface roughness of the offset blanket cylinder helps to deliver a more uniform layer of printing material to the target substrate free of defects such as mottle. Sufficient pressure is used to transfer the image from the offset cylinder to the target substrate. Pinching the target substrate between the offset cylinder and an impression cylinder provides this pressure.
Typical lithographic and offset printing techniques utilize plates which are permanently patterned, and are therefore useful only when printing a large number of copies of the same image (i.e. long identical print runs), such as magazines, newspapers, and the like. However, they do not permit creating and printing a new pattern from one page to the next without removing and replacing the print cylinder and/or the imaging plate (i.e., the technique cannot accommodate true high speed variable data printing wherein the image changes from impression to impression, for example, as in the case of digital printing systems). Furthermore, the cost of the permanently patterned imaging plates or cylinders is amortized over the number of copies. The cost per printed copy is therefore higher for shorter print runs of the same image than for longer print runs of the same image, as opposed to prints from digital printing systems.
Accordingly, a lithographic technique, referred to as variable data lithography, has been developed which uses a non-patterned reimageable surface that is initially uniformly coated with a dampening fluid layer. Regions of the dampening fluid are removed by exposure to a focused radiation source (e.g., a laser light source) to form pockets. A temporary pattern in the dampening fluid is thereby formed over the non-patterned reimageable surface. Ink applied thereover is retained in the pockets formed by the removal of the dampening fluid. The inked surface is then brought into contact with a substrate, and the ink transfers from the pockets in the dampening fluid layer to the substrate. The dampening fluid may then be removed, a new uniform layer of dampening fluid applied to the reimageable surface, and the process repeated.
In the packaging industry, there is a growing need for security features to authenticate a given document and/or make the given document difficult to counterfeit.
BRIEF DESCRIPTION
The present disclosure relates to various ink compositions containing a fluorescent colorant and a plurality of curable compounds. Each curable compound has Hansen solubility parameters as described herein. The fluorescent colorant serves as a security feature for documents printed using the ink compositions of the present disclosure.
Disclosed in embodiments is an ink composition comprising a fluorescent colorant and a plurality of curable compounds, wherein the ink composition has a volume average Hansen fractional dispersion force parameter (fd) of from about 0.4 to about 0.62, a volume average Hansen fractional polar parameter (fp) of from about 0.1 to about 0.3, and a volume average Hansen fractional hydrogen bonding parameter (fh) of from about 0.2 to about 0.4.
The fluorescent colorant may be a pigment having a particle size of from about 0.1 microns to about 5 microns or can be a dye which is dissolved in the ink composition. In some embodiments, the fluorescent colorant is colored under ambient light. In other embodiments, the fluorescent colorant is colorless under ambient light. The fluorescent colorant may be present in an amount of from about 0.005 wt % to about 5 wt % of the ink composition.
The plurality of curable compounds may include a tetrafunctional acrylated ester, a polyethylene glycol diacrylate, or a tripropylene glycol diacrylate.
In some embodiments, the plurality of curable compounds includes from about 40 to about 55 wt % of a tetrafunctional acrylated polyester; from about 9 to about 11 wt % of a polyethylene glycol diacrylate; and from 0 to about 11 wt % of a tripropylene glycol diacrylate, based on the total weight of the ink composition.
The ink composition may further comprise from greater than 0 to about 20 wt % of an aliphatic acrylate ester. The ink composition may further comprise at least one additive. The additives may be selected from dispersants, thickening agents, photoinitiators, and stabilizers. In particular embodiments, the ink composition comprises from about 2 to about 10 wt % of a dispersant; from about 0.2 to about 5 wt % of a thickening agent; from 0 to about 10 wt % of a photoinitiator; and from about 0.1 to about 1 wt % of a thermal stabilizer, based on the total weight of the ink composition.
Optionally, the ink composition contains from about 10 to about 40 wt % of a non-fluorescent colorant, based on the total weight of the ink composition.
The ink composition may have a viscosity of from about 5,000 to about 1,000,000 centipoise at 25° C. and a shear rate of 5 sec−1. Alternatively, the ink composition may have a shear thinning index (50/5) at 25° C. of from about 0.10 to about 0.60. The ink composition could also have a surface tension of from about 25 dynes/cm to about 40 dynes/cm at 25° C.
The plurality of curable compounds may comprise more than 50 wt % of the ink composition.
Also disclosed in embodiments is a process for marking a substrate with a security feature. The process includes printing an image on the substrate with an ink composition that comprises a fluorescent colorant and a plurality of curable compounds, the ink composition having a volume average Hansen fractional dispersion force parameter (fd) of from about 0.4 to about 0.62, a volume average Hansen fractional polar parameter (fp) of from about 0.1 to about 0.3, and a volume average Hansen fractional hydrogen bonding parameter (fh) of from about 0.2 to about 0.4. In some specific embodiments, each curable compound has a Hansen fractional dispersion force parameter (fd) of from about 0.4 to about 0.62, a Hansen fractional polar parameter (fp) of from about 0.1 to about 0.3, and a Hansen fractional hydrogen bonding parameter (fh) of from about 0.2 to about 0.4.
In some embodiments, the fluorescent colorant is a pigment having a particle size of from about 0.1 microns to about 5 microns.
Also disclosed in embodiments is an ink composition including a fluorescent colorant and a plurality of curable compounds, wherein each curable compound has a Hansen fractional dispersion force parameter (fd) of from about 0.4 to about 0.62, a Hansen fractional polar parameter (fp) of from about 0.1 to about 0.3, and a Hansen fractional hydrogen bonding parameter (fh) of from about 0.2 to about 0.4.
These and other non-limiting aspects and/or objects of the disclosure are more particularly described below.



BRIEF DESCRIPTION OF THE DRAWINGS
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
The following is a brief description of the drawings, which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.
FIG. 1 illustrates a variable lithographic printing apparatus in which the ink compositions of the present disclosure may be used.
FIG. 2 is a Teas plot showing the Hansen solubility parameters for various curable compounds that can be used in the ink compositions.
FIG. 3 is a graph showing surface tension data for ink compositions with different pigment loadings.
FIG. 4 is a photograph showing three overlapping fluorescent UV inks of the present disclosure under UV light.
FIG. 5 is a photograph showing three fluorescent UV inks of the present disclosure under UV light.
FIG. 6 is a photograph showing a plate after each of three passes using a control ink.
FIG. 7 is a photograph showing the transfer of the control ink in the presence of NOVEC fountain solution.
FIG. 8 is a photograph showing the transfer of the control ink in the presence of D4 fountain solution.
FIG. 9 is a photograph showing the plate after each of three passes using a blue fluorescent ink of the present disclosure.
FIG. 10 is a photograph showing the transfer of the blue fluorescent ink in the presence of D4 fountain solution.
FIG. 11 is a photograph showing the plate after each of three passes using a green fluorescent ink of the present disclosure.
FIG. 12 is a photograph showing the transfer of the blue fluorescent ink in the presence of NOVEC 7600 fountain solution.



DETAILED DESCRIPTION
A more complete understanding of the processes and apparatuses disclosed herein can be obtained by reference to the accompanying drawings. These figures are merely schematic representations based on convenience and the ease of demonstrating the existing art and/or the present development, and are, therefore, not intended to indicate relative size and dimensions of the assemblies or components thereof.
Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function.
The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (for example, it includes at least the degree of error associated with the measurement of the particular quantity). When used with a specific value, it should also be considered as disclosing that value. For example, the term “about 2” also discloses the value “2” and the range “from about 2 to about 4” also discloses the range “from 2 to 4.”
The present disclosure relates to ink compositions that are suitable for use in digital offset printing processes. FIG. 1 illustrates a system for variable lithography in which the ink compositions of the present disclosure may be used. The system 10 comprises an imaging member 12. The imaging member comprises a substrate 22 and a reimageable surface layer 20. The surface layer is the outermost layer of the imaging member, i.e. the layer of the imaging member furthest from the substrate. As shown here, the substrate 22 is in the shape of a cylinder; however, the substrate may also be in a belt form, etc. The surface layer 20 is typically a silicone (e.g. a methylsilicone or fluorosilicone), which may have carbon black added to increase energy absorption of the surface layer.
In the depicted embodiment the imaging member 12 rotates counterclockwise and starts with a clean surface. Disposed at a first location is a dampening fluid subsystem 30, which uniformly wets the surface with dampening fluid 32 to form a layer having a uniform and controlled thickness. Ideally the dampening fluid layer is between about 0.05 micrometers and about 1.0 micrometers in thickness, is uniform, and is without pinholes. As explained further below, the composition of the dampening fluid aids in leveling and layer thickness uniformity. A sensor 34, such as an in-situ non-contact laser gloss sensor or laser contrast sensor, is used to confirm the uniformity of the layer. Such a sensor can be used to automate the dampening fluid subsystem 30.
At optical patterning subsystem 36, the dampening fluid layer is exposed to an energy source (e.g. a laser) that selectively applies energy to portions of the layer to image-wise evaporate the dampening fluid and create a latent “negative” of the ink image that is desired to be printed on the receiving substrate. Image areas are created where ink is desired, and non-image areas are created where the dampening fluid remains. An optional air knife 44 is also shown here to control airflow over the surface layer 20 for the purpose of maintaining clean dry air supply, a controlled air temperature, and reducing dust contamination prior to inking. Next, the ink composition is applied to the imaging member using inker subsystem 46. Inker subsystem 46 may consist of a “keyless” system using an anilox roller to meter an offset ink composition onto one or more forming rollers 46A, 46B. The ink composition is applied to the image areas to form an ink image.
A rheology control subsystem 50 may be present to partially cure or tack the ink image. This curing source may be, for example, an ultraviolet light emitting diode (UV-LED) 52, which can be focused as desired using optics 54. Another way of increasing the cohesion and viscosity employs cooling of the ink composition. This could be done, for example, by blowing cool air over the reimageable surface from jet 58 after the ink composition has been applied but before the ink composition is transferred to the target substrate. Alternatively, a heating element 59 could be used near the inker subsystem 46 to maintain a first temperature and a cooling element 57 could be used to maintain a cooler second temperature near the nip 16.
The ink image is then transferred to the target or receiving substrate 14 at transfer subsystem 70. This is accomplished by passing a recording medium or receiving substrate 14, such as paper, through the nip 16 between the impression roller 18 and the imaging member 12. The final receiving substrate 14 can be, for example, paper, plastic, or metal.
Finally, the imaging member should be cleaned of any residual ink or dampening fluid. Most of this residue can be easily removed quickly using an air knife 77 with sufficient air flow. Removal of any remaining ink can be accomplished at cleaning subsystem 72.
It should be noted that the apparatus depicted in FIG. 1 transfers the ink directly from the imaging member to the paper, so that the ink must fully release from the imaging member and should enable high quality printing at high speeds. Traditional offset inks are designed to work best with an intermediate transfer member between the imaging member and the final target substrate (i.e. paper). Traditional inks suffer from one or more shortfalls including: solubility in the dampening fluid, swelling of the silicone layer on the imaging member, poor release properties from the imaging member, and limited curing performance. The ink compositions of the present disclosure have certain wetting and release properties that are useful with the imaging member, and the ink compositions are also compatible with non-aqueous dampening fluids.
The ink compositions of the present disclosure comprise a fluorescent colorant and a plurality of selected curable compounds. The curable compounds can be cured under ultraviolet (UV) light to fix the ink in place on the final receiving substrate. The fluorescent colorant serves as a security feature.
Initially, the ink composition comprises a fluorescent colorant. As used herein, the term “colorant” includes pigments, dyes, quantum dots, mixtures thereof, and the like. Fluorescence is the emission of light by the colorant after absorbing light or other electromagnetic radiation, and is a form of luminescence. Usually, the light emitted by the fluorescent colorant has a longer wavelength (i.e. lower energy) than the absorbed radiation.
The fluorescent colorant should be able to withstand curing conditions without degradation, and meet various miscibility, emitted color, viscosity, and wetting requirements as well. Any fluorescent dye or pigment or quantum dot may be chosen, provided that it is capable of being dispersed or dissolved in the ink composition and is compatible with the other ink ingredients. Dyes and pigments have specific advantages. Dyes have good solubility and dispersibility within the ink vehicle. Pigments have excellent thermal and light-fast performance.
The fluorescent colorant may be included in one or more colored radiation curable inks of the ink composition. The fluorescent colorant may also be included in a radiation curable ink that does not include any non-fluorescent colorant so as to be a substantially colorless ink. The fluorescent colorant may also be included in a radiation curable ink such that the fluorescent colorant is colored when viewed in ambient light, and fluoresces a different color or the same color when exposed to activating radiation.
When the fluorescent colorant is included in one or more of the colored radiation curable inks of an ink set, the fluorescent colorant noticeably alters the appearance of the printed ink upon exposure to radiation. In ambient light, the printed ink will exhibit the intended color of the non-fluorescent colorant in the colored ink. However, upon exposure to radiation, fluorescence of the fluorescent colorant in the ink visibly changes the color exhibited by the ink. For example, a yellow fluorescent ink exhibits the intended yellow color in ambient light, but upon exposure to activating radiation, the fluorescence of the fluorescent colorant changes the color exhibited to a different color, for example to a red color.
When the fluorescent colorant is included in a radiation curable ink that does not include a colorant therein, the printed ink is not visible or apparent to a viewer in ambient light. Upon exposure to radiation, the fluorescence of the fluorescent colorant causes the ink to become visible.
Advantages of including a fluorescent colorant in an ink of an ink set include making images, texts, etc., that appear normal in ambient light, but which are noticeably altered in appearance upon exposure to radiation. When the images, texts, etc., printed with an ink having the fluorescent colorant are photocopied, the image, text, etc., will not visible in the photocopy. This is because the fluorescent colorant does not fluoresce under existing copying conditions, and thus will not appear in the copy. Moreover, the copy will not contain any ink with fluorescent colorant, so that the copy will not fluoresce at all. Such a feature is advantageous in that authentication is possible because falsified copies cannot be made to include the fluorescent property.
Also, this feature can permit one to intentionally embed hidden information in documents, which information is only revealed to one knowing to expose the document to radiation such as UV light.
One or more ink compositions of the present disclosure may be included in an ink set. When more than one ink compositions is included in an ink set, the ink compositions in the set may have different colors, e.g. yellow, cyan, magenta, and black.
Various fluorescent pigments and dyes are known in the art, and are commercially available from suppliers such as Risk Reactor Corp. or from Dayglo Corp., to name just a few. Examples of fluorescent dyes suitable for use herein include those belonging to the dye families known as rhodamines, fluoresciens, coumarins, napthalimides, benzoxanthenes, acridines, azos, mixtures thereof and the like. Other suitable fluorescent dyes include oil and solvent based dyes. Quantum dots are fluorescent inorganic semiconductor nanoparticle materials. An advantage of quantum dots is that they can be tuned so that they emit any desired wavelength (color) as a function of their size, by using one material only and the same synthetic process. In addition, quantum dots possess improved fatigue resistance when compared with organic dyes. Another advantage of quantum dots is their narrow emission bands, which increases the number of possible wavelength choices for designing customized colors. Quantum dots are available from a variety of companies, such as from Evident Technologies.
The fluorescent colorant is present in the ink composition in any desired amount, and is typically present in an amount of from about 0.005 to about 5 weight percent (wt %), based on the total weight of the ink composition. In more specific embodiments, the pigment is present in an amount of from about 0.01 to about 1 wt %.
In particular, many color emitting fluorescent pigments are commercially available. Such fluorescent pigments can have a particle size of from about 0.1 microns to about 5 microns, preferably to less than about 1 micron, or from about 2 microns to about 5 microns. This is a distinct advantage when compared with inkjet inks, which usually require pigments to have a particle size of about 300 nm or lower in order to prevent plugging of the nozzles.
In some embodiments, the fluorescent colorant is colorless under ambient light. In other words, the fluorescent colorant is clear. This provides an ink composition that, when printed, appears colorless under normal reading light but will emit a selected color when fluoresced under ultraviolet (UV) light.
In other embodiments, the fluorescent colorant is colored under ambient light. Put another way, the fluorescent colorant is colored. This provides an ink composition that, when printed, appears a given color under normal reading light, and emits a selected color when fluoresced under ultraviolet (UV) light. The selected color (emitted under UV light) may be the same or different from the given color (emitted under ambient light).
Fluorescent, or fluorescent ink, refers to, for example, the capability of a colorant or the ink to fluoresce upon exposure to an activating radiation, for example a radiation source having a wavelength from about 100 nm to about 1100 nm, such as from about 150 nm to about 900 nm or from about 200 nm to about 800 nm. The activating radiation may thus be in the ultraviolet (UV), visible or infrared regions, although the use of activating radiation in the UV region (from about 100 nm to about 400 nm) is most common. The fluorescing may occur instantaneously on exposure to the activating radiation, or may occur after overcoming any activation phase. The fluorescence is exhibited by the fluorescent ink only while subjected to the activating UV light. In other words, the fluorescent ink does not fluoresce once the UV light is removed.
In embodiments, the ink set herein comprises at least one radiation curable ink having therein a fluorescent colorant such that upon exposure to activating radiation, the at least one radiation curable ink having the fluorescent colorant fluoresces.
In further embodiments, the ink set disclosed herein includes at least one clear or non-colorant-containing ink having a fluorescent colorant that is substantially clear to the naked eye, but that fluoresces upon exposure to an activating radiation source. Such an ink set may further include at least one additional non-fluorescent radiation curable ink, which does not include any fluorescent colorant but desirably includes at least one colorant, and/or may also include additional colored fluorescent radiation curable inks.
The fluorescent ink(s) may be applied to a substrate after images using non-fluorescent ink have been formed, prior to images from the non-fluorescent inks being formed, and/or applied at the same time as any non-fluorescent inks. The non-fluorescent ink images may be overprinted with a substantially clear fluorescent radiation curable ink. The substantially clear fluorescent radiation curable ink disclosed herein may be applied over images printed using non-fluorescent ink and has an advantage in that the color of the base print is unimportant because in ambient light the base print may be easily viewed through the clear fluorescent ink. The substantially clear fluorescent radiation curable ink does not adversely affect the appearance of the visible image formed by the non-fluorescent inks of the ink set because the gloss of the images formed from the non-fluorescent ink and the gloss of the images formed from the fluorescent ink are similar. Of course, the substantially clear fluorescent ink, or colored fluorescent ink, may be applied alone in an ink set comprised of a single ink.
Each of the radiation curable inks of the ink set, including any fluorescent radiation curable ink, may be made to exhibit substantially the same gloss upon printing. As such, an advantage herein is that the differential gloss realized when overcoating a formed image with a conventional clear overcoat or ink may be avoided. Gloss is a measure of an image's shininess, which should be measured after the image has been formed on a print sheet. Gloss may be measured using a Gardiner Gloss metering unit. In embodiments herein, each of the inks used in the ink set, including the fluorescent radiation curable ink(s) of the ink set, are made to have substantially matched gloss. In this regard, each of the inks should have a gloss within about 5 Gardiner gloss units (ggu) of each other, for example a gloss value within from 0 to about 5 ggus or from about 0.5 to about 3 ggus or from about 0.5 to about 2 ggus, of each other. In doing so, the formed image having fluorescent capabilities exhibits substantially no differential gloss, and thus the appearance of the image is uniform.
In embodiments, only one of the inks of the ink set includes a fluorescent colorant. For example, the fluorescent colorant in an ink set of cyan, magenta, yellow, optionally with black, is included in one of the colored inks. The fluorescent colorant of the ink set may be in an ink having a color that does not mask fluorescing upon exposure to activating radiation. For example, fluorescence, manifested as a color change or appearance change of the color image may be more readily apparent when the fluorescent colorant is included in a lighter shade colored ink such as yellow or magenta. Fluorescence might not be noticeable in a very dark ink such as black. Of course, more than one ink of the ink set may include a fluorescent colorant, and in fact all may include fluorescent colorant such that each ink would fluoresce in a different color. Such an embodiment has an advantage in that differential gloss is further decreased because no colorless ink is over the printed image. The ink set may also include one or more colored fluorescent inks, as well as a fluorescent non-colored ink.
In yet further embodiments, the fluorescent colorant may exhibit a color even when viewed in ambient light. When exposed to the activation energy, that is, radiative energy, the fluorescent colorant fluoresces a color which may be the same or different from the color displayed in ambient light. A change in the appearance of the ink is visible due to fluorescence of the fluorescent colorant upon exposure to activating energy.
The colored fluorescent colorant may be included in a colored radiation curable ink. In such embodiments, the resulting color in ambient light is a combination of the colors of the fluorescent colorant and the colored non fluorescent colorant. When exposed to activating energy, the color is substantially changed due to the fluorescence emission of the fluorescent colorant.
Color refers to, for example, the overall absorption characteristic within the same range of wavelengths of the electromagnetic spectrum. Thus, differently colored inks exhibit a color, that is, an absorption characteristic, different from each other. For example, if a first ink exhibits a yellow color, then a second differently colored ink will exhibit a different shade of yellow or a different color altogether, for example such as cyan or magenta. In an embodiment of a three color ink herein, the three inks of the ink set may comprise the three subtractive primary colors yellow, cyan and magenta, or may comprise red, blue and green. An example four color ink set may comprise yellow, cyan, magenta and black. Additional differently colored inks, for example for highlight coloring inks, may be included in these ink sets.
Suitable fluorescent colorants include fluorescent dyes, fluorescent pigments and inorganic surface functionalized quantum dot colorants. Examples of fluorescent dyes suitable for use herein include those belonging to the dye families known as rhodamines, fluoresciens, coumarins, napthalimides, benzoxanthenes, acridines, azos, mixtures thereof and the like. Suitable fluorescent dyes include, for example, Basic Yellow 40, Basic Red 1, Basic Violet 11, Basic Violet 10, Basic Violet 16, Acid Yellow 73, Acid Yellow 184, Acid Red 50, Acid Red 52, Solvent Yellow 44, Solvent Yellow 131, Solvent Yellow 85, Solvent Yellow 135, solvent Yellow 43, Solvent Yellow 160, Fluorescent Brightner 61, mixtures thereof and the like. Other suitable fluorescent dyes include oil and solvent based dyes like DFSB class, DFPD class, DFSB-K class available from Risk reactor of Huntington Beach, Calif. Suitable fluorescent pigments include, but are not limited to, those available from Day-Glo Color Corp. of Cleveland, Ohio, such as aurora pink T-11 and GT-11, neon red T-12, rocket red T-13 or GT-13, fire orange T-14 or GT-14N, blaze orange T-15 or GT-15N, arc yellow T-16, satum yellow T-17N, corona magenta GT-21 and GT-17N, mixtures thereof and the like. Other suitable fluorescent pigments available from Risk Reactor are for example PFC class, like for example PFC-03 which switches from invisible to red when exposed to UV light, PF class like for example PF-09 which switches from invisible to violet when exposed to UV light. Other suppliers of fluorescent colorants include Beaver Luminescers from Newton, Mass. and Cleveland Pigment & Color Co. form Akron, Ohio.
Quantum dot materials are fluorescent inorganic semiconductor nanoparticle materials. The light emission of quantum dots is due to quantum confinement of electrons and holes. An advantage of quantum dots is that they can be tuned so that they emit any desired wavelength (color) as a function of their size, by using one material only and the same synthetic process. For example in a range comprised from about 2 to about 10 nm, one can obtain a full range of colors from the visible range of the spectrum. In addition, quantum dots possess improved fatigue resistance when compared with organic dyes. Another advantage of quantum dots is their narrow emission bands, which increases the number of possible wavelength choices for designing customized colors. Due to their small size, typically less than about 30 nm, such as less than about 20 nm, they can be easily ink jetted. Quantum dots are available from a variety of companies, such as from Evident Technologies (Troy, N.Y.).
In embodiments, the quantum dot materials used herein are functionalized quantum dots. Surface functionalized quantum dots may have better compatibility with radiation curable ink materials. Suitable functional groups present on the surface of the nanoparticle quantum dots for compatibility with radiation curable ink include long linear or branched alkyl groups, for example from about 1 carbon atom to about 150 carbon atoms in length, such as from about 2 carbon atoms to about 125 carbon atoms or from about 3 carbon atoms to about 100 carbon atoms. Other suitable compatable groups include polyesters, polyethers, polyamides, polycarbonates and the like.
Suitable colored fluorescent colorants, which are colored in ambient light and which fluoresce when exposed to the activating energy, include for example dyes such as DFWB-K41-80 that is red in ambient light and that fluoresces red-purple under UV light and DFSB-K401 that is red-purple in ambient light and that fluoresces red-purple under UV light, each of which is available from Risk Reactor. Other examples include DFSB-K400 that has a brown appearance in ambient light and that fluoresces orange under excitation with UV light, DFSB-K427 that is orange under ambient light and under exposure to UV light, and DFSB-K43 that is yellow in ambient light and under exposure to activating UV light.
If desired, the ink composition may include a second, non-fluorescent colorant. It is contemplated that in such embodiments, the fluorescent colorant is colorless, so as to avoid clashing with the second colorant. Any non-fluorescent dye or pigment may be chosen, provided that it is capable of being dispersed or dissolved in the ink composition and is compatible with the other ink ingredients. The non-fluorescent colorant is present in the ink composition in any desired amount, and is typically present in an amount of from about 10 to about 40 weight percent (wt %), based on the total weight of the ink composition. In more specific embodiments, the non-fluorescent colorant is present in an amount of from about 15 to about 30 wt %, or from about 19 wt % to about 25 wt %, based on the total weight of the composition. Various pigments and dyes are known in the art, and are commercially available from suppliers such as Clariant, BASF, and Ciba, to name just a few.
The ink composition also includes a plurality of curable compounds that have certain Hansen solubility parameters. Hansen solubility parameters were developed to help predict whether one material will dissolve in another and form a homogeneous solution. The parameters can also be used to identify materials that are not compatible and/or have limited solubility in one another.
The Hildebrand total solubility parameter can be divided into three Hansen parameters: a dispersion force parameter; a polar parameter; and a hydrogen bonding parameter. The relationship between the Hildebrand total solubility parameter and the three Hansen solubility parameters is governed by the following equation:

∂t2=∂d2+∂p2+∂h2 

wherein ∂t is the total solubility parameter; ∂d is the Hansen dispersion force parameter; ∂p is the Hansen polar parameter; and ∂h is the Hansen hydrogen bonding Hansen parameter.

In a triangular Teas graph, the three Hansen solubility parameters are presented in a single chart. To do so, the Hansen solubility parameters must be converted into normalized, i.e. fractional, values according to the following equations in order to be plotted in a single, useful chart:



  
    
      f
      d
    
    =
    
      
        ∂
        d
      
      
        
          ∂
          d
        
        ⁢
        
          +
          
            
              ∂
              p
            
            ⁢
            
              +
              
                ∂
                h
              
            
          
        
      
    
  




  
    
      f
      p
    
    =
    
      
        ∂
        p
      
      
        
          ∂
          d
        
        ⁢
        
          +
          
            
              ∂
              p
            
            ⁢
            
              +
              
                ∂
                h
              
            
          
        
      
    
  




  
    
      f
      h
    
    =
    
      
        ∂
        h
      
      
        
          ∂
          d
        
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          +
          
            
              ∂
              p
            
            ⁢
            
              +
              
                ∂
                h
              
            
          
        
      
    
  



wherein fd is the Hansen fractional dispersion force parameter; fp is the fractional polar parameter; and fh is the fractional hydrogen bonding parameter. The sum of the three normalized parameters will always be 1.

Each compound in the plurality of curable compounds in the ink compositions of the present disclosure has a Hansen fractional dispersion force parameter (fd) of from about 0.4 to about 0.62, a Hansen fractional polar parameter (fp) of from about 0.1 to about 0.3, and a Hansen fractional hydrogen bonding parameter (fh) of from about 0.2 to about 0.4. When a curable compound having the fractional solubility parameters within these ranges is included in the ink composition of the disclosure, the ink composition has the required wetting and release properties. As explained further herein, it was surprisingly discovered that compounds within this design space were best suited for use with the non-aqueous dampening fluids that are useful for digital offset lithography. While one or two of the ink components may have properties outside these preferred ranges, it is best that the volume average solubility parameter for the ink base (no colorant) be within these ranges.
Suitable curable compounds having the required Hansen fractional parameters include several available from Sartomer.
For example, Sartomer CN294E is a tetrafunctional acrylated polyester oligomer. CN294E is a clear liquid having a specific gravity of 0.93 and a viscosity of 4,000 cps at 60° C.
Another example is Sartomer SR-259, which is a polyethylene glycol diacrylate. SR-259 is a clear liquid having a specific gravity of 1.122 at 25° C., a viscosity of 25 cps at 25° C., a surface tension of 41.3 dynes/cm, and a molecular weight of 302 g/mol.
Another example is Sartomer SR306F, which is a tripropylene glycol diacrylate. SR306F is a clear liquid having a specific gravity of 1.038 at 25° C., a viscosity of 15 cps at 25° C., a surface tension of 33.3 dynes/cm, and a molecular weight of 300 g/mol.
Another example is Sartomer SR-492 which is a propoxylated trimethylolpropane triacrylate. SR-492 is a clear liquid having a specific gravity of 1.050 at 25° C., a viscosity of 90 cps at 25° C., a surface tension of 34.0 dynes/cm, and a molecular weight of 470 g/mol.
Another example is Sartomer SR454, which is an ethoxylated trimethylolpropane triacrylate. SR454 is a clear liquid having a specific gravity of 1.103 at 25° C., a viscosity of 60 cps at 25° C., a surface tension of 39.6 dynes/cm, and a molecular weight of 428 g/mol.
Another example is Sartomer SR-368D, which is a tris(2-hydroxyethyl)isocyanurate triacrylate. SR-368D is a clear liquid having a specific gravity of 1.158 at 25° C. and a viscosity of 330 cps at 25° C.
Another example is Sartomer SR444, which is a pentaerythritol triacrylate. SR444 is a clear liquid having a specific gravity of 1.162 at 25° C., a viscosity of 520 cps at 25° C., a surface tension of 39.0 dynes/cm, and a molecular weight of 298 g/mol.
Another example is 1,6-hexanediylbis[oxy(2-hydroxy-3,1-propanediyl)]bisacrylate. This compound has a molecular weight of 374.43 g/mol and a density of 0.94 g/mL at 25° C.
Another example is glycerol 1,3-diglycerolate diacrylate. This compound has a molecular weight of 484.54 g/mol and a density of 1.18 g/mL at 25° C.
Three additional curable compounds which may be considered for use in the present disclosure are Sartomer SR-348, SR-349, and CN309. Sartomer SR-348 is an ethoxylated bisphenol A dimethacrylate. SR-348 is a clear liquid having a specific gravity of 1.119 at 25° C., a viscosity of 1082 cps at 25° C., a surface tension of 41.0 dynes/cm, and a molecular weight of 452 g/mol. Sartomer SR-349 is an ethoxylated bisphenol A diacrylate. SR-349 is a clear liquid having a specific gravity of 1.145 at 25° C., a viscosity of 1600 cps at 25° C., a surface tension of 43.6 dynes/cm, and a molecular weight of 468 g/mol. Sartomer CN309 contains an acrylate ester that derives from an aliphatic hydrophobic backbone, or in other words is an aliphatic acrylate ester. CN309 is a clear liquid having a specific gravity of 0.92, a density of 7.68 pounds/gallon, a surface tension of 26.3 dynes/cm, a viscosity of 150 centipoise (cps) at 25° C., and a viscosity of 40 cps at 60° C. When present, this aliphatic acrylate ester may be present in an amount of from greater than 0 to about 20 wt % of the ink composition, including from about 9 to about 12 wt %.
In particular embodiments, each compound in the plurality of curable compounds is an acrylate, or in other words contains at least one acrylate group (—O—CO—C(CH3)═CH2). The carbon-carbon double bond in the acrylate group is available for crosslinking during the curing of the ink composition.
The curable compounds can comprise any suitable curable monomer, oligomer, or prepolymer. Examples of suitable materials include radically curable monomer compounds, such as acrylate and methacrylate monomer compounds, which are suitable for use as phase change ink carriers. In embodiments, the at least one monomer, oligomer, or prepolymer is an acrylate monomer, a methacrylate monomer, a multifunctional acrylate monomer, a multifunctional methacrylate monomer, or a mixture or combination thereof.
Specific examples of relatively nonpolar solid acrylate and methacrylate monomers include, for example, lauryl acrylate, lauryl methacrylate, isodecylacrylate, isodecylmethacrylate, octadecylacrylate, behenyl acrylate, cyclohexane dimethanol diacrylate, and the like, as well as mixtures and combinations thereof.
Specific examples of nonpolar liquid acrylate and methacrylate monomers include, for example, isobornyl acrylate, isobornyl methacrylate, caprolactone acrylate, 2-phenoxyethyl acrylate, isooctylacrylate, isooctylmethacrylate, butyl acrylate, and the like, as well as mixtures and combinations thereof. In embodiments, the radiation curable solid ink composition herein further comprises at least one monomer, oligomer, or prepolymer that is a nonpolar liquid acrylate or methacrylate monomer selected from the group consisting of isobornyl acrylate, isobornyl methacrylate, caprolactone acrylate, 2-phenoxyethyl acrylate, isooctylacrylate, isooctylmethacrylate, butyl acrylate, or a mixture or combination thereof.
In addition, multifunctional acrylate and methacrylate monomers and oligomers can be included in the phase change ink carrier as reactive diluents and as materials that can increase the crosslink density of the cured image, thereby enhancing the toughness of the cured images. Examples of suitable multifunctional acrylate and methacrylate monomers and oligomers include (but are not limited to) pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, 1,2-ethylene glycol diacrylate, 1,2-ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,12-dodecanol diacrylate, 1,12-dodecanol dimethacrylate, tris(2-hydroxy ethyl)isocyanurate triacrylate, propoxylated neopentyl glycol diacrylate (available from Sartomer Co. Inc. as SR 9003®), hexanediol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, amine modified polyether acrylates (available as PO 83 F®, LR 8869®, and/or LR 8889® (all available from BASF Corporation), trimethylolpropane triacrylate, glycerol propoxylate triacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, ethoxylated pentaerythritol tetraacrylate (available from Sartomer Co. Inc. as SR 494®), and the like, as well as mixtures and combinations thereof.
The particular monomer, oligomer, prepolymer, etc. is not critical to the embodiments, and may include, for example, one or more of the following: allyl methacrylate; tetrahydrofurfuryl methacrylate; ethylene glycol demethacrylate; 1,3 butylene glycol diacrylate; 1,4 butane diol dimethacrylate; Urethane acrylate blended with tripropylene glycol diacetate; 2-(2-ethoxyethoxy)ethylacrylate; polyethylene glycol (200) diacrylate; pentaerythritol tetraacrylate; tripropylene glycol diacetate; lauryl methacrylate; lauryl acrylate; 2-phenoxyethyl acrylate; polyethylene glycol (400) diacrylate; di-trimethylopropane tetraacrylate; tris-(2hydroxy ethyl) isocyanurate triacrylate; isodecyl acrylate; dipentaerythritol pentaacrylate; ethoxylated (20) trimethylopropane triacrylate; pentaerythritol triacrylate; propoxylated (3) trimethylopropane triacrylate; tridecyl methacrylate; ethoxylated (4) pentaerythritol tetraacrylate; isobornyl acrylate; dipropylene glycol diacrylate; propoxylated neopentyl glycol dicrylate; alkoxylated trifunctional acrylate ester; trifunctional methacrylate ester; trifunctional acrylate ester; pentaacrylate ester; methoxy polyethylene glycol (350) monomethacrylate; alkoxylated cyclohexane dimethanol diacrylate; alkoxylated tetrahydrofurfuryl acrylate; trifunctional acid ester, trifunctional acid ester; tetrafunctional acrylated polyester oligomer; hydrophobic acrylate ester; Urethane acrylate blended with tripropylene glycol diacetate; Urethane acrylate blended with Urethane acrylate blended with tripropylene glycol diacetate; triacrylate urethane acrylate blended with ethoxylated (3) trimethylopropane; triacrylate; urethane acrylate blended with ethoxylated (4) nonyl phenol acrylate; urethane acrylate blended with 1,6-hexanediol diacrylate; urethane acrylate blended with isobornyl acrylate; hexafunctional urethane acrylate; or urethane acrylate.
Other suitable monomers, such as mono-, di-, tri-, or higher-functional monomers, some of which may the same or similar to those described above, may include one or more of the following:
Mono-Functional











Sartomer Code
Chemical Name







CD278
acrylate ester


CD420
acrylic monomer


CD421
3,3,5 trimethylcyclohexyl methacrylate


CD535
dicyclopentadienyl methacrylate


CD545
diethylene glycol methyl ether methacrylate


CD551
methoxy polyethylene glycol (350) monoacrylate


CD552
methoxy polyethylene glycol (550) monomethacrylate


CD553
methoxy polyethylene glycol (550) monoacrylate


CD585
acrylate ester


CD587
acrylate ester


CD588
acrylate ester


CD611
alkoxylated tetrahydrofurfuryl acrylate


CD612
ethoxylated (4) nonyl phenol methacrylate


CD613
ethoxylated nonyl phenol acrylate


CD730
triethylene glycol ethyl ether methacrylate


CD9050
monofunctional acid ester


CD9075
alkoxylated lauryl acrylate


CD9087
alkoxylated phenol acrylate


CD9088
alkoxylated phenol acrylate


SR203
tetrahydrofurfuryl methacrylate


SR242
isodecyl methacrylate


SR256
2(2-ethoxyethoxy) ethyl acrylate


SR257
stearyl acrylate


SR285
tetrahydrofurfuryl acrylate


SR313
lauryl methacrylate


SR324
stearyl methacrylate


SR335
lauryl acrylate


SR339
2-phenoxylethyl acrylate


SR340
2-phenoxylethyl methacrylate


SR395
isodecyl acrylate


SR423
isobomyl methacrylate


SR440
isooctyl acrylate


SR484
octadecyl acrylate


SR489
tridecyl acrylate


SR493
tridecyl methacrylate


SR495
caprolactone acrylate


SR504
ethoxylated (4) nonyl phenol acrylate


SR506
isobomyl acrylate


SR531
cyclic trimethylolpropane formal acrylate


SR550
methoxy polyethylene glycol (350) monomethacrylate


SR709
metallic monomethacrylate









Di-Functional














Sartomer Code
Chemical Name









CD262
1,12 Dodecandediol Dimethacrylate



CD401
cyclohexane dimethanol dimethacrylate



CD406
cyclohexane dimethanol diacrylate



CD536
acrylate ester



CD542
ethoxylated (8) bisphenol A dimethacrylate



CD560
alkoxylated hexanediol diacrylate



CD561
alkoxylated hexanediol diacrylate



CD562
alkoxylated hexanediol diacrylate



CD563
alkoxylated hexanediol diacrylate



CD564
alkoxylated hexanediol diacrylate



CD580
alkoxylated cyclohexane dimethanol diacrylate



CD581
alkoxylated cyclohexane dimethanol diacrylate



CD582
alkoxylated cyclohexane dimethanol diacrylate



CD595
acrylate ester



CD9038
ethoxylated (30) bisphenol A diacrylate



CD9043
alkoxylated neopentyl glycol diacrylate



CD9044
alkoxylated neopentyl glycol diacrylate



SR101
ethoxylated bisphenol A dimethacrylate



SR150
ethoxylated bisphenol A dimethacrylate



SR205
triethylene glycol dimethacrylate



SR206
ethylene glycol dimethacrylate



SR209
tetraethylene glycol dimethacrylate



SR210
polyethylene glycol dimethacrylate



SR212B
1,3-Butylene Glycol Diacrylate



SR213
1,4-butanediol diacrylate



SR214
1,4-butanediol dimethylacrylate



SR230
diethylene glycol diacrylate



SR231
diethylene glycol dimethacrylate



SR238
1,6-hexanediol diacrylate



SR239
1,6-hexanediol dimethacrylate



SR247
neopentyl glycol diacrylate



SR248
neopentyl glycol dimethacrylate



SR252
polyethylene glycol (600) dimethacrylate



SR259
polyethylene glycol (200) diacrylate



SR268
tetraethylene glycol diacrylate



SR272
triethylene glycol diacrylate



SR297
1,3-butylene glycol dimethacrylate



SR306
tripropylene glycol diacrylate



SR341
diacrylate ester



SR344
polyethylene glycol (400) diacrylate



SR348
ethoxylated (2) bisphenol A dimethacrylate



SR349
ethoxylated (3) bisphenol A diacrylate



SR480
ethoxylated (10) bisphenol dimethacrylate



SR508
dipropylene glycol diacrylate



SR540
ethoxylated (4) bisphenol A dimethacrylate



SR541
ethoxylated (6) bisphenol A dimethacrylate



SR601
ethoxylated (4) bisphenol A diacrylate



SR602
ethoxylated (10) bisphenol A diacrylate



SR603
polyethylene glycol (400) dimethacrylate



SR610
polyethylene glycol (600) diacrylate



SR644
polypropylene glycol (400) dimethacrylate



SR731
monomer



SR732
monomer



SR740
polyethylene glycol (1000) dimethacrylate



SR833S
tricyclodecane dimethanol diacrylate



SR9003
propoxylated (2) neopentyl glycol diacrylate



SR9036
ethoxylated (30) bisphenol A dimethacrylate



SR9045
alkoxylated neopentyl glycol diacrylate



SR9209A
alkoxylated aliphatic diacrylate










Tri-Functional














Sartomer Code
Chemical Name









CD501
propoxylated (6) trimethylolpropane triacrylate



CD9021
highly propoxylated (5.5) glycol triacrylate



CD9051
trifunctional acid ester



SR350
trimethylolpropane trimethacrylate



SR351
trimethylolpropane triacrylate



SR368
tris (2-hydroxy ethyl) isocyanurate triacrylate



SR415
ethoxylated (20) trimethylolpropane triacrylate



SR444
pentaerythritol triacrylate



SR454
ethoxylated (3) trimethylolpropane triacrylate



SR492
propoxylated (3) trimethylolpropane triacrylate



SR499
ethoxylated (6) trimethylolpropane triacrylate



SR502
ethoxylated (9) trimethylolpropane triacrylate



SR9020
propoxylated (3) glycerol triacrylate



SR9035
ethoxylated (15) trimethylolpropane triacrylate



SR9012
trifunctional actrylate ester










Higher-Functional














Sartomer Code
Chemical Name









SR295
PENTAERYTHRITOL TETRAACRYLATE



SR355
ditrimethylolpropane tetraacrylate



SR399LV
low viscosity dipentaerythritol pentaacrylate










In particular embodiments, the plurality of curable compounds includes a tetrafunctional acrylated polyester (e.g. CN294E), a polyethylene glycol diacrylate (e.g. SR-259), or a tripropylene glycol diacrylate (e.g. SR306F). The tetrafunctional acrylated polyester may be present in an amount of from 40 to about 55 wt % of the ink composition, including from about 45 to about 50 wt %. The polyethylene glycol diacrylate may be present in an amount of from 9 to about 11 wt % of the ink composition. The tripropylene glycol diacrylate may be present in an amount of from 0 to about 11 wt % of the ink composition, including from about 9 to about 11 wt %. Generally, the plurality of curable compounds makes up from about 40 to about 95 wt % of the ink composition.
In particular embodiments, the plurality of curable compounds includes the tetrafunctional acrylated polyester and the polyethylene glycol diacrylate. Sometimes, the plurality of curable compounds consists of the tetrafunctional acrylated polyester and the polyethylene glycol diacrylate, and optionally the aliphatic acrylate ester and/or the tripropylene glycol diacrylate.
As mentioned above, the ink composition may have a volume average solubility parameter, without colorant, within the recited Hansen ranges as well. Put another way, the ink compositions of the present disclosure may have a volume average Hansen fractional dispersion force parameter (fd) of from about 0.4 to about 0.62, a volume average Hansen fractional polar parameter (fp) of from about 0.1 to about 0.3, and a volume average Hansen fractional hydrogen bonding parameter (fh) of from about 0.2 to about 0.4. These average fractional parameters can be determined by first calculating the volume fraction of each individual compound in the ink composition, which then enables the calculation of the volume average solubility parameter for each of the individual dispersive, polar and hydrogen bonding contributions to the total solubility parameter of the composition. The fractional components are then calculated from these averages as defined earlier.
Other compounds may also be present in the ink composition and participate in crosslinking, but not have the fractional solubility parameters discussed above, and as a result such compounds should not be considered as being within the plurality of curable compounds. An example of one such compound is a polyether modified acryl functional polydimethylsiloxane, commercially available as BYK UV-3500, which functions as a thickening agent.
Other additives may also be present in the ink composition, such as one or more dispersants, thickening agents, photoinitiators, and/or thermal stabilizers. An exemplary dispersant is SOLSPERSE 39000, available from Lubrizol. A thickening agent is used to adjust the viscosity of the ink composition. Exemplary thickening agents include BYK UV-3500, CLAYTONE HY, an organoclay available from Southern Clay Products, and silica-type materials such as AEROSIL 200 from Degussa. Exemplary photoinitiators include IRGACURE 184 and IRGACURE 819, both available from Ciba Specialty Chemicals. IRGACURE 184 is 1-hydroxy-cyclohexyl-phenyl-ketone, having a molecular weight of 204.3. IRGACURE 819 is bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, having a molecular weight of 418.5. An exemplary stabilizer is IRGASTAB UV 10, available from Ciba Specialty Chemicals, which acts as a radical scavenger to prevent the degradation of UV curable compositions. The dispersant(s) may be present in an amount of from about 2 to about 10 wt % of the ink composition, or from about 3 wt % to about 7 wt %, or from about 5 wt %. The thickening agent(s) may be present in an amount of from about 0.2 to about 5 wt % of the ink composition. The photoinitiator(s) may be present in an amount of from 0 to about 10 wt % of the ink composition, including from about 0.5 to about 10 wt %. The thermal stabilizer(s) may be present in an amount of from about 0.1 to about 1 wt % of the ink composition.
The resulting ink compositions of the present disclosure may have a viscosity of from about 5,000 to about 1,000,000 centipoise at 25° C. and a shear rate of 5 sec−1, including a viscosity of from about 5,000 to about 300,000 centipoise, or from about 15,000 to about 250,000 cps, or from about 5,000 cps to about 75,000 cps, or from about 30,000 cps to about 60,000 cps.
The resulting ink compositions of the present disclosure may have a viscosity of from about 2,000 to about 90,000 centipoise at 25° C. and a shear rate of 50 sec−1, including a viscosity of from about 5,000 to about 65,000 cps.
The shear thinning index, or SHI, is defined in the present disclosure as the ratio of the viscosity of the ink composition at two different shear rates, here 50 sec−1 and 5 sec−1. This may be abbreviated as SHI (50/5). The SHI (50/5) may be from about 0.10 to about 0.60 for the ink compositions of the present disclosure, or from about 0.35 to about 0.55.
The ink compositions of the present disclosure may also have a surface tension of at least about 25 dynes/cm at 25° C., including from about 25 dynes/cm to about 40 dynes/cm at 25° C.
The ink compositions of the present disclosure possess many desirable physical and chemical properties. They are compatible with the materials with which they will come into contact, such as the dampening fluid, the surface layer of the imaging member, and the final receiving substrate. They also have the required wetting and transfer properties. They can be UV-cured and fixed in place. They also meet the demanding rheological requirements of the variable lithographic printing apparatus for which the inks of the present disclosure are intended for use. In addition, one of the most difficult issues to overcome is the need for cleaning and waste handling between successive digital images to allow for digital imaging without ghosting of previous images. The inks of the present disclosure are designed to enable very high transfer efficiency, thus overcoming many of the problems associated with cleaning and waste handling. The ink compositions of the present disclosure do not gel, whereas regular offset inks made by simple blending do gel and cannot be used due to phase separation. The ink compositions can contain a high pigment load, and may have a high viscosity suitable for digital offset printing.
Finally, these ink compositions provide the ability to print security features at high speed in short runs with customized data to produce anti-counterfeit packaging. When exposed to the selected radiation, the fluorescent colorant becomes noticeable. Upon being removed from exposure to the activating radiation, the fluorescent colorant returns to a non-fluorescent state. This feature can be useful in authentication of documents, because a forged document or photocopy would not have the ability to fluoresce. One can also intentionally embed hidden information in a document, which is only revealed to one knowing to expose the document to activating radiation. The change between the fluorescent and non-fluorescent state can be repeated an indefinite number of times, for example from about 10 to about 100 million times or more.
The ink compositions of the present disclosure can be made according to the methods disclosed in U.S. patent application Ser. No. 13/474,185, filed concurrently and entitled “Methods For Manufacturing Curable Inks For Digital Offset Printing Applications And The Inks Made Therefrom”, and fully incorporated by reference herein. Generally, the methods include: a) adding to a mixing vessel at least one monomer or oligomer and at least one dispersant; b) heating the mixing vessel; c) adding at least an initiator or a curing agent and a thermal stabilizer while mixing; d) slowly adding at least one pigment while stirring to form a pigmented radiation curable ink composition; e) cooling the pigmented radiation curable ink composition to about room temperature; and f) milling the pigmented radiation curable ink composition to reduce the particle size of the composition to less than about 1 μm to prepare a pigmented, curable, ink composition.
The fluorescent ink compositions of the present disclosure may be applied to a substrate after images using non-fluorescent ink have been formed, prior to images from the non-fluorescent inks being formed, and/or applied at the same time as any non-fluorescent inks. The non-fluorescent ink images may be overprinted with a substantially clear fluorescent ink composition. The substantially clear fluorescent ink compositions disclosed herein may be applied over images printed using non-fluorescent ink and has an advantage in that the color of the base print is unimportant because in ambient light the base print may be easily viewed through the clear fluorescent ink. The fluorescent ink does not adversely affect the appearance of the visible image formed by the non-fluorescent ink where the gloss of the images formed from the non-fluorescent ink and the gloss of the images formed from the fluorescent ink are similar.
The present disclosure contemplates a printing system where the dampening fluid is hydrophobic and the ink composition is somewhat hydrophilic (having a small polar component). This system can be used with an imaging member surface which has low surface energy which is mainly dispersive in character. Thus it can work with an imaging member that is a silicone, fluorosilicone, or Viton® based elastomer, which offers high temperature wear robustness to the laser energy used in variable lithographic printing.
By choosing the proper chemistry, it is possible to devise a system where both the ink and the dampening fluid will wet the imaging member surface, but the ink and the dampening fluid will not mutually wet each other. The system can also be designed so that it is energetically favorable for dampening fluid in the presence of ink residue to actually lift the ink residue off of the imaging member surface by having a higher affinity for wetting the surface in the presence of the ink. In other words, the dampening fluid could remove microscopic background defects (e.g. <1 μm radius) from propagating in subsequent prints.
The dampening fluid should have a slight positive spreading coefficient so that the dampening fluid wets the imaging member surface. The dampening fluid should also maintain a spreading coefficient in the presence of ink, or in other words the dampening fluid has a closer surface energy value to the imaging member surface than the ink does. This causes the imaging member surface to value wetting by the dampening fluid compared to the ink, and permits the dampening fluid to lift off any ink residue and reject ink from adhering to the surface where the laser has not removed dampening fluid. Next, the ink should wet the imaging member surface in air with a roughness enhancement factor (i.e. when no dampening fluid is present on the surface). It should be noted that the surface may have a roughness of less than 1 μm when the ink is applied at a thickness of 1 to 2 μm. Desirably, the dampening fluid does not wet the ink in the presence of air. In other words, fracture at the exit inking nip should occur where the ink and the dampening fluid interface, not within the dampening fluid itself. This way, dampening fluid will not tend to remain on the imaging member surface after ink has been transferred to a receiving substrate. Finally, it is also desirable that the ink and dampening fluid are chemically immiscible such that only emulsified mixtures can exist. Though the ink and the dampening fluid may have alpha-beta coordinates close together, often choosing the chemistry components with different levels of hydrogen bonding can reduce miscibility by increasing the difference in the Hanson solubility parameters.
The role of the dampening fluid is to provide selectivity in the imaging and transfer of ink to the receiving substrate. When an ink donor roll in the ink source of FIG. 1 contacts the dampening fluid layer, ink is only applied to areas on the imaging member that are dry, i.e. not covered with dampening fluid.
In this regard, a material is typically soluble in a solvent if the solvent lies within the solubility sphere of the material. Whether a solvent lies within the solubility sphere of the material may be determined by calculating whether the distance of the solvent from the center of the material's solubility sphere is less than the radius of interaction for the material according to the following equation (1):

R(S-P)=√{square root over (4(∂ds−∂dm)2+(∂ps−∂pm)2+(∂hs−∂hm)2)}  (1)

wherein R(S-P) is the distance between the solvent and the center of the material solubility sphere (i.e. the radius); ∂xs is the Hansen component for the solvent; and ∂xm is the Hansen component for the material. R is also referred to as the radius of interactions.

In the present disclosure, the dampening fluid corresponds to the solvent of equation (1), and the ink composition corresponds to the material of equation (1). Desirably, the ink composition is insoluble in the dampening fluid, so it is preferable that the radius of interactions be as large as possible.
In embodiments, the ink composition contains at least one curable compound which has a radius of interaction greater than 16 with the dampening fluid. In more specific embodiments, the radius of interaction is 18 or greater, or 20 or greater.
It is contemplated that the dampening fluid which is compatible with the ink compositions of the present disclosure is a volatile hydrofluoroether (HFE) liquid or a volatile silicone liquid. These classes of fluids provides advantages in the amount of energy needed to evaporate, desirable characteristics in the dispersive/polar surface tension design space, and the additional benefit of zero residue left behind once evaporated. The hydrofluoroether and silicone are liquids at room temperature, i.e. 25° C.
In specific embodiments, the volatile hydrofluoroether liquid has the structure of Formula (I):

CmHpF2m+1−p—O—CnHqF2n+1−q  Formula (I)

wherein m and n are independently integers from 1 to about 9; and p and q are independently integers from 0 to 19. As can be seen, generally the two groups bound to the oxygen atom are fluoroalkyl groups.

In particular embodiments, q is zero and p is non-zero. In these embodiments, the right-hand side of the compound of Formula (I) becomes a perfluoroalkyl group. In other embodiments, q is zero and p has a value of 2 m+1. In these embodiments, the right-hand side of the compound of Formula (I) is a perfluoroalkyl group and the left-hand side of the compound of Formula (I) is an alkyl group. In still other embodiments, both p and q are at least 1.
In this regard, the term “fluoroalkyl” as used herein refers to a radical which is composed entirely of carbon atoms and hydrogen atoms, in which one or more hydrogen atoms may be (i.e. are not necessarily) substituted with a fluorine atom, and which is fully saturated. The fluoroalkyl radical may be linear, branched, or cyclic.
The term “alkyl” as used herein refers to a radical which is composed entirely of carbon atoms and hydrogen atoms which is fully saturated and of the formula —CnH2n+1. The alkyl radical may be linear, branched, or cyclic. It should be noted that an alkyl group is a subset of fluoroalkyl groups.
The term “perfluoroalkyl” as used herein refers to a radical which is composed entirely of carbon atoms and fluorine atoms which is fully saturated and of the formula —CnF2n+1. The perfluoroalkyl radical may be linear, branched, or cyclic. It should be noted that a perfluoroalkyl group is a subset of fluoroalkyl groups, and cannot be considered an alkyl group.
In particular embodiments, the hydrofluoroether has the structure of any one of Formulas (I-a) through (I-h):




Of these formulas, Formulas (I-a), (I-b), (I-d), (I-e), (I-f), (I-g), and (I-h) have one alkyl group and one perfluoroalkyl group, either branched or linear. In some terminology, they are also called segregated hydrofluoroethers. Formula (I-c) contains two fluoroalkyl groups and is not considered a segregated hydrofluoroether.
Formula (I-a) is also known as 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)pentane and has CAS #132182-92-4. It is commercially available as NovecTM 7300.
Formula (I-b) is also known as 3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-(trifluoromethyl)hexane and has CAS #297730-93-9. It is commercially available as NovecTM 7500.
Formula (I-c) is also known as 1,1,1,2,3,3-Hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)pentane and has CAS #870778-34-0. It is commercially available as NovecTM 7600.
Formula (I-d) is also known as methyl nonafluoroisobutyl ether and has CAS #163702-08-7. Formula (I-e) is also known as methyl nonafluorobutyl ether and has CAS #163702-07-6. A mixture of Formulas (I-d) and (I-e) is commercially available as NovecTM 7100. These two isomers are inseparable and have essentially identical properties.
Formula (I-f) is also known as 1-methoxyheptafluoropropane or methyl perfluoropropyl ether, and has CAS #375-03-1. It is commercially available as NovecTM 7000.
Formula (I-g) is also known as ethyl nonafluoroisobutyl ether and has CAS #163702-05-4. Formula (I-h) is also known as ethyl nonafluorobutyl ether and has CAS #163702-06-5. A mixture of Formulas (I-g) and (I-h) is commercially available as NovecTM 7200 or NovecTM 8200. These two isomers are inseparable and have essentially identical properties.
It is also possible that similar compounds having a cyclic aromatic backbone with perfluoroalkyl sidechains can be used. In particular, compounds of Formula (A) are contemplated:

Ar—(CkF2k+1)t   Formula (A)

wherein Ar is an aryl or heteroaryl group; k is an integer from 1 to about 9; and t indicates the number of perfluoroalkyl sidechains, t being from 1 to about 8.

The term “aryl” refers to an aromatic radical composed entirely of carbon atoms and hydrogen atoms. When aryl is described in connection with a numerical range of carbon atoms, it should not be construed as including substituted aromatic radicals. For example, the phrase “aryl containing from 6 to 10 carbon atoms” should be construed as referring to a phenyl group (6 carbon atoms) or a naphthyl group (10 carbon atoms) only, and should not be construed as including a methylphenyl group (7 carbon atoms).
The term “heteroaryl” refers to a cyclic radical composed of carbon atoms, hydrogen atoms, and a heteroatom within a ring of the radical, the cyclic radical being aromatic. The heteroatom may be nitrogen, sulfur, or oxygen. Exemplary heteroaryl groups include thienyl, pyridinyl, and quinolinyl. When heteroaryl is described in connection with a numerical range of carbon atoms, it should not be construed as including substituted heteroaromatic radicals. Note that heteroaryl groups are not a subset of aryl groups.
Hexafluoro-m-xylene (HFMX) and hexafluoro-p-xylene (HFPX) are specifically contemplated as being useful compounds of Formula (A) that can be used as low-cost dampening fluids. HFMX and HFPX are illustrated below as Formulas (A-a) and (A-b):




It should be noted any co-solvent combination of fluorinated damping fluids can be used to help suppress non-desirable characteristics such as a low flammability temperature.
Alternatively, the dampening fluid solvent is a volatile silicone liquid. In some embodiments, the volatile silicone liquid is a linear siloxane having the structure of Formula (II):




wherein Ra, Rb, Rc, Rd, Re, and Rf are each independently hydrogen, alkyl, or perfluoroalkyl; and a is an integer from 1 to about 5. In some specific embodiments, Ra, Rb, Rc, Rd, Re, and Rf are all alkyl. In more specific embodiments, they are all alkyl of the same length (i.e. same number of carbon atoms).

Exemplary compounds of Formula (II) include hexamethyldisiloxane and octamethyltrisiloxane, which are illustrated below as Formulas (II-a) and (II-b):




In other embodiments, the volatile silicone liquid is a cyclosiloxane having the structure of Formula (III):




wherein each Rg and Rh is independently hydrogen, alkyl, or perfluoroalkyl; and b is an integer from 3 to about 8. In some specific embodiments, all of the Rg and Rh groups are alkyl. In more specific embodiments, they are all alkyl of the same length (i.e. same number of carbon atoms).

Exemplary compounds of Formula (III) include octamethylcyclotetrasiloxane (aka D4) and decamethylcyclopentasiloxane (aka D5), which are illustrated below as Formulas (III-a) and (III-b):




In other embodiments, the volatile silicone liquid is a branched siloxane having the structure of Formula (IV):




wherein R1, R2, R3, and R4 are independently alkyl or —OSiR1R2R3.

An exemplary compound of Formula (IV) is methyl trimethicone, also known as methyltris(trimethylsiloxy)silane, which is commercially available as TMF-1.5 from Shin-Etsu, and shown below with the structure of Formula (IV-a):




Any of the above described hydrofluoroethers/perfluorinated compounds are miscible with each other. Any of the above described silicones are also miscible with each other. This allows for the tuning of the dampening fluid for optimal print performance or other characteristics, such as boiling point or flammability temperature. Combinations of these hydrofluoroether and silicone liquids are specifically contemplated as being within the scope of the present disclosure. It should also be noted that the silicones of Formulas (II), (III), and (IV) are not considered to be polymers, but rather discrete compounds whose exact formula can be known.
In particular embodiments, it is contemplated that the dampening fluid comprises a mixture of octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5). Most silicones are derived from D4 and D5, which are produced by the hydrolysis of the chlorosilanes produced in the Rochow process. The ratio of D4 to D5 that is distilled from the hydrolysate reaction is generally about 85% D4 to 15% D5 by weight, and this combination is an azeotrope.
In particular embodiments, it is contemplated that the dampening fluid comprises a mixture of octamethylcyclotetrasiloxane (D4) and hexamethylcyclotrisiloxane (D3), the D3 being present in an amount of up to 30% by total weight of the D3 and the D4. The effect of this mixture is to lower the effective boiling point for a thin layer of dampening fluid.
The volatile hydrofluoroether liquids and volatile silicone liquids of the present disclosure have a low heat of vaporization, low surface tension, and good kinematic viscosity.
Aspects of the present disclosure may be further understood by referring to the following examples. The examples are illustrative, and are not intended to be limiting embodiments thereof.
EXAMPLES
A description of the materials used in the examples is provided here in Table 1.









TABLE 1





Material
Description
Supplier







Irgalite
Pigment
Ciba


Blue GLO


CN309
Oligomeric acrylate ester derived from an
Sartomer



aliphatic hydrophobic backbone


CN293
Hexafunctional acrylated polyester oligomer
Sartomer


CN294E
Tetrafunctional acrylated polyester oligomer
Sartomer


SR259
Polyethylene glycol (200) diacrylate monomer
Sartomer


Solsperse
Polymeric dispersant
Lubrizol


39000


Claytone HY
Rheological additive
Southern




Clay


Irgacure 184
Photoinitiator
Ciba


Irgacure 819
Photoinitiator
Ciba


Irgastab
Stabilizer
Ciba


UV10


BYK 3500
Surface additive
BYK


SR306F
Tripropylene glycol diacrylate monomer
Sartomer









Example 1
Initially, the Hildebrand solubility parameter approach was used to identify curable monomers and oligomers that were most likely to be compatible with the digital offset printing systems contemplated herein. Screening of suitable ink ingredients was also conducted by measuring the degree of mixability between the ink ingredient and the dampening fluid. NOVEC 7600 was used in the dampening fluid. Other screening criteria included curability, surface tension, viscosity, and safety.
Ninety-nine different monomers and oligomers (i.e. possible ink ingredients) were tested and ranked according to the following experimental procedure. Roughly equal amounts (0.5 to 1 mL each) of the monomer/oligomer and NovecTM 7600 were pipetted into a 4 mL vial. The vial was shaken vigorously by hand. Mixability was then visually measured on a scale of 0 to 3. 0 indicated that the materials were not mixable and exhibited rapid phase separation. 1 indicated that the materials exhibited slow phase separation. 2 indicated that the materials formed a cloudy solution without phase separation. 2.5 indicated that the materials formed a clear solution but showed some signs of phase separation over time. 3 indicated that the materials formed a mixable, clear solution. Low mixability was more desirable, as this indicated that the possible ink ingredient might be suitable for inclusion in the ink composition.
Next, the radius of interaction was calculated for nine possible ink ingredients with NovecTM 7600. The mixability was plotted as a function of the radius of interaction for each ingredient. Mixability may be minimized by selecting curable ingredients (or mixtures) that have low mixability or a radius of interaction greater than 16. Ingredients meeting this criteria included Sartomer SR348 and SR349.
Next, a Teas plot of the various ink ingredients and dampening fluids was produced, as shown in FIG. 2 using the Hansen fractional parameters. Some silicones are also shown to indicate the space occupied by materials that are models for the imaging plate used in the imaging system. Unexpectedly, it was found that the ink ingredients that were immiscible with NOVEC 7600 fell within narrow ranges for each fractional solubility parameter. In particular, the optimal range for the fractional dispersion component (fd) was found to be from about 0.4 to about 0.62. The optimal range for the fractional polar component (fp) was found to be from about 0.1 to about 0.3. Lastly, the optimal range for the fractional hydrogen-bonding component (fh) was found to be from about 0.2 to about 0.4. Suitable ink ingredients meeting these parameters included Sartomer CN309, CN294E, SR-259, SR306F, SR-492, SR-368D, SR-348, and SR-349.
The Hansen fractional parameters for various materials are listed in Table 2:












TABLE 2







Material
fH
fP
fD





















Novec 7600
0.16079
0.18967
0.64954



D4
0.47027
0
0.52973



Silicone (500 units)
0.3134
0.00974
0.67686



Silicone (100 units)
0.31468
0.02174
0.66358



Silicone 2%
0.31654
0.02177
0.6617



propylamine, 100



units



SR454
0.2668
0.19376
0.53944



SR306F
0.2571
0.21932
0.52359



SR259
0.27272
0.21538
0.5119



mfcd_001289181
0.31684
0.18146
0.5017



mfcd_016326782
0.35177
0.2246
0.42363



SR349
0.18876
0.28947
0.52177



SR348
0.18845
0.27743
0.53412



CD564
0.14996
0.2844
0.56564



SR492
0.26515
0.18162
0.55323



SR368D
0.21991
0.27371
0.50638



CM309
0.12258
0.12211
0.75531



CN293
0.2264
0.22566
0.54794



CN294E
0.22258
0.15992
0.61751



Fluorosilicone
0.25008
0.02135
0.72857



SR833S
0.157
0.25008
0.59291



SR444
0.2856
0.28171
0.43269



CD406
0.1529
0.26956
0.57754







11,6-Hexanediylbis[oxy(2-hydroxy-3,1-propanediyl)] bisacrylate



2Glycerol 1,3-diglycerolate diacrylate






Next, a number of different UV curable ink compositions were formulated. The amounts for each ingredient and properties of the exemplary compositions are listed below in Tables 3A and 3B.











TABLE 3A






C6
C7
C8
C9B


Chemical
wt %
wt %
wt %
wt %



















Ciba Irgalite Blue GOL
24
21.62
24
17


Sartomer CN309
10.5
9.46
18.56
10.2


Sartomer CN293
0
0
0
0


Sartomer CN294e
51.3
46.22
42.24
49.8


Sartomer SR259
0
9.01
0
9.75


Solsperse 39000
6
5.41
6
4.25


Southern Clay HY
2
1.8
2
1.8


Irgacure 184
3.5
3.15
3.5
3.5


Irgacure 819
2.5
2.25
2.5
2.5


Ciba Irgastab UV10
.2
0.18
0.2
0.2


BYK 3500
0
0.9
1
1


SR306F
0
0
0
0


Viscosity (5 Hz)
141,900
64.525
96,200
32,505


Viscosity (50 Hz)
87,900
24.991
41,100
14,916


SHI (50/5)
0.62
0.39
0.43
0.46





















TABLE 3B






C10B
C11B
C9A
C10A
C11A


Chemical
wt %
wt %
wt %
wt %
wt %




















Ciba Irgalite Blue GOL
20
20
17
20
20


Sartomer CN309
9.65
0
11.08
10.53
0


Sartomer CN293
0
0
0
0
0


Sartomer CN294e
47.12
47.12
54.08
51.4
51.4


Sartomer SR259
9.23
9.23
10.59
10.07
10.07


Solsperse 39000
5
5
4.25
5
5


Southern Clay HY
1.8
1.8
1.8
1.8
1.8


Irgacure 184
3.5
3.5
0
0
0


Irgacure 819
2.5
2.5
0
0
0


Ciba Irgastab UV10
0.2
0.2
0.2
0.2
0.2


BYK 3500
1
1
1
1
1


SR306F
0
9.65
0
0
10.53


Viscosity (5 Hz)
47,674
34,450
32,505
42,827
26,773


Viscosity (50 Hz)
19,209
34,450
32,505
42,827
26,773


SHI (50/5)
0.4
0.39
0.51
0.44
0.4









Rheological data was obtained for the above-described ink compositions using a 25 mm parallel plate and an ARES G2 controlled strain rheometer with a Peltier temperature control system for rapid heating/cooling. An oscillation frequency sweep at 25° C. with a frequency of 0.1 to 400 rad/s and a strain of 10% initial with auto-strain activated was conducted. The shear flow rate at 25° C. was from 0.1 to 500 1/s.
Surface tension of offset inks is difficult to measure at room temperature due to extremely high viscosity. Surface tension was measured using the Wilhelmy plate method with a Kruss K-100 Tensiometer. FIG. 3 shows the results for dilute cyan offset ink with SR259 at 7.5% pigment loading and 10 wt % pigment loading. Surface tension was measured at various temperatures. Data was collected from 0.1 to 120 seconds using logarithmic decade data sampling. The average of the last points taken is shown in FIG. 3. Using these measurements, extrapolation of surface tension at 25° C. and 21.6 wt % pigment in offset ink resulted in a surface tension of from 30 dynes/cm to 38 dynes/cm.
The curable inks of the present disclosure were imaged on a test fixture. Improved imaging performance was observed, particularly for the inks of lower viscosity, typically less than about 30,000 cPs, and for the inks that were formulated from the concentrates above by adding additional low viscosity monomers. For example, Ink C11B was further diluted with additional SR306F (about 20% by weight) to yield prints that had improved color characteristics. The shear thinning index (SHI) may be adjusted to improve performance.
Example 2
A clear ink base was prepared by mixing the components shown in Table 4:










TABLE 4







Component
Amount (wt %)



















Sartomer CN309
9.90



Sartomer CN294E
74.83



Sartomer SR259
9.43



Ciba Irgacure 184
3.30



Ciba Irgacure 819
2.35



Ciba Irgastab UV10
0.19










Three colored fluorescent inks were then prepared using the clear ink base.
A blue fluorescent ink was prepared by adding 0.200 grams of DFSB-C0 (blue emitting fluorescent dye from Risk Reactor Corporation) to 10 grams of the clear ink base. The composition was heated at 70° C. and stirred at 300 rpm for 1 hour.
A green fluorescent ink was prepared by adding 0.200 grams of 2,2-hydroxyphenyl benzothiazole (green fluorescent dye available from Sigma-Aldrich) to 10 grams of the clear ink base. The composition was heated at 70° C. and stirred at 300 rpm for 1 hour.
A red fluorescent ink was prepared by adding 0.200 grams of DFKY-C7 (red fluorescent dye available from Risk Reactor). to 10 grams of the clear ink base. The composition was heated at 70° C. and stirred at 300 rpm for 1 hour.
Fluorescence Evaluation
The three inks were then evaluated to determine the overall compatibility and suitability of the fluorescent additives with the clear UV-curable ink base. In particular, the following aspects were investigated: (a) solubility/dispersibility in the ink base; (b) fluorescence emission capability in a range suitable for colored UV inks; and (c) compatibility with the printing/curing process (the dye needs to be both thermally and UV stable).
The three inks were deposed on a rubber stamp, then transferred to paper substrate. The stamped images were cured by using a UV Fusion LC-6B Benchtop Conveyor equipped with UV Fusion F300S Ultraviolet Lamp System. The cured images were tested for fluorescence when exposed to UV light (365 nm).
FIG. 4 and FIG. 5 show images of the fluorescent inks under UV light after curing. These figures confirm that the ink was cured, the fluorescent component was not degraded by the UV curing process, the images are colorless under normal viewing light, and the inks emit bright colors when exposed to UV light. The exposure to UV light was repeated many times without any visible sign of decay in the fluorescence performance.
Ink Transfer Evaluation
Next, the fluorescent security inks were evaluated to determine whether they displayed equivalent ink transfer performance to ink compositions that did not contain the fluorescent colorant. A “pass” for the transfer performance evaluation translates typically into a good performance of the tested ink in a “print fixture” based on Digital Offset Technology.
The evaluations were carried out via a hand experiment using a rubber inking roller, a cotton applicator to apply fountain solution, a conformable rubber pressure roller, and DCEG (digital colour elite gloss) paper. The plate material used was prepared from Toray silicone containing 10% carbon black, and textured with  ̃1 micron surface roughness using a mold (Allied plate). This plate was chosen because it showed good de-inking performance. The fountain solutions used for testing were NOVEC 7600 hydrofluoroether (from 3M) and octamethylcyclotetrasiloxane (D4) fountain solution.
The ink transfer procedure was as follows. Initially, the plate surface was wiped with isopropanol and dried. If fountain solution blocking was evaluated, the fountain solution was applied with a cotton applicator to the surface as a narrow, thin layer. Next, the ink was thinned over a plastic substrate, then applied to the plate. If the fountain solution was applied, the ink was applied over the fountain solution. Then, paper was placed over the inked plate surface, and three passes of moderate pressure were applied over the paper surface with the conformable rubber pressure roller. The paper was then peeled from the plate.
The ink transfer procedure was repeated three times in succession in order to evaluate the efficiency of ink transfer and residual ink left on the plate surface. Inking/blocking/de-inking results are all evaluated with respect to the Toray plate surface and mainline ink formulation. After three passes, little to no ink should remain on the plate surface, and the third transfer should display significantly less ink than the first. The fountain solution should block ink wetting of the surface and completely prevent ink showthrough in the area where fountain solution was applied. This performance is considered a “pass” for subsequent development.
Comparative Example: Mainline Ink with Cyan Pigment, No Fluorescent Colorant
The ink transfer test was first performed using a mainline ink with cyan pigment and no fluorescent colorant to serve as a control. FIG. 6 shows the ink transfers after each pass (no fountain solution). The ink transferred well, so that after the third pass, only a small amount of ink could be detected on the plate surface.
Ink transfer in the presence of fountain solution is shown in FIG. 7 (NOVEC) and FIG. 8 (D4). The fountain solutions performed very well: no ink was transferred onto the paper in the areas where the plate contained the fountain solutions.
First Example: Blue Fluorescent Ink
The ink transfer test was then performed using the blue fluorescent ink. FIG. 9 shows the ink transfers after each pass (no fountain solution). The performance was similar to or better than that of the Comparative Example. Little ink was transferred on the third pass. After three passes, little to no residual ink remained on the plate surface.
Ink transfer in the presence of fountain solution is shown in FIG. 10 (D4). Again, the D4 fountain solution performed well: no ink was transferred onto the paper in the areas where the plate contained the fountain solution.
Second Example: Green Fluorescent Ink
The ink transfer test was then performed using the green fluorescent ink. FIG. 11 shows the ink transfers after each pass (no fountain solution). The results were equivalent to the blue fluorescent ink. Little ink was transferred on the third pass. After three passes, little to no residual ink remained on the plate surface.
Ink transfer in the presence of fountain solution is shown in FIG. 12 (NOVEC). The NOVEC fountain solution performed well: no ink was transferred onto the paper in the areas where the plate contained the fountain solution.
To summarize, the ink transfer tests showed that the fluorescent inks had image transfer properties comparable to the Comparative Example. There was minimal image transfer after the third pass, and no ink transferred to the paper in the areas covered by fountain solution.
The present disclosure has been described with reference to exemplary embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the present disclosure be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

## Claims

1. An ink composition comprising a fluorescent colorant, a thickening agent comprising a polyether modified acrylfunctional polydimethylsiloxane, and a plurality of curable compounds, wherein the ink composition has a volume average Hansen fractional dispersion force parameter (fd) of from about 0.4 to about 0.62, a volume average Hansen fractional polar parameter (fp) of from about 0.1 to about 0.3, and a volume average Hansen fractional hydrogen bonding parameter (fh) of from about 0.2 to about 0.4,
wherein the fluorescent colorant comprises quantum dots, and
wherein the plurality of curable compounds consist of a tetrafunctional acrylated polyester, a polyethylene glycol diacrylate, an aliphatic acrylate ester, and a tripropylene glycol diacrylate.

2. The ink composition of claim 1, wherein the fluorescent colorant further comprises a pigment having a particle size of from about 0.1 microns to about 5 microns.

3. The ink composition of claim 1, wherein the fluorescent colorant further comprises a fluorescent dye.

4. The ink composition of claim 1, wherein the fluorescent colorant is colorless under ambient light.

5. The ink composition of claim 1, wherein the fluorescent colorant is present in an amount of from about 0.005 to about 5 wt % of the ink composition.

6. The ink composition of claim 1, wherein the plurality of curable compounds includes, based on the total weight of the ink composition:
from about 40 to about 55 wt % of the tetrafunctional acrylated polyester;
from about 9 to about 11 wt % of the polyethylene glycol diacrylate; and
greater than 0 to about 11 wt % of the tripropylene glycol diacrylate.

7. The ink composition of claim 1, wherein the plurality of curable compounds includes, based on the total weight of the ink composition: from greater than 0 to about 20 wt % of an aliphatic acrylate ester.

8. The ink composition of claim 1, further comprising at least one additive selected from the group consisting of dispersants, photoinitiators, and stabilizers.

9. The ink composition of claim 1, further comprising, based on the total weight of the ink composition:
from about 2 to about 10 wt % of a dispersant;
from about 0.2 to about 5 wt % of the thickening agent;
from 0 to about 10 wt % of a photoinitiator; and
from about 0.1 to about 1 wt % of a thermal stabilizer.

10. The ink composition of claim 1, wherein the ink composition has a viscosity of from about 5,000 to about 1,000,000 centipoise at 25° C. and a shear rate of 5 sec−1.

11. The ink composition of claim 1, wherein the ink composition has a viscosity of from about 2,000 to about 90,000 centipoise at 25° C. and a shear rate of 50 sec−1.

12. The ink composition of claim 1, wherein the ink composition has a shear thinning index (50/5) at 25° C. of from about 0.10 to about 0.60.

13. The ink composition of claim 1, wherein the ink composition has a surface tension of from about 25 dynes/cm to about 40 dynes/cm at 25° C.

14. The ink composition of claim 1, wherein the plurality of curable compounds comprises more than 50 wt % of the ink composition.

15. A process for marking a substrate with a security feature, comprising:
printing an image on the substrate with an ink composition that comprises a fluorescent colorant, a thickening agent comprising a polyether modified acrylfunctional polydimethylsiloxane, and a plurality of curable compounds, the ink composition having a volume average Hansen fractional dispersion force parameter (fd) of from about 0.4 to about 0.6, a volume average Hansen fractional polar parameter (fp) of from about 0.1 to about 0.3, and a volume average Hansen fractional hydrogen bonding parameter (fh) of from about 0.2 to about 0.4,
wherein the fluorescent colorant comprises quantum dots, and
wherein the plurality of curable compounds consist of a tetrafunctional acrylated polyester, a polyethylene glycol diacrylate, an aliphatic acrylate ester, and a tripropylene glycol diacrylate.