Printing fluorescent aqueous colored ink and inkjet printing method

Abstract

A fluorescent aqueous colored pigment base ink having a pigment colorant in an amount of 1-7 wt%; a non-polymeric fluorophore, the non-polymeric fluorophore exhibiting an emission peak of at least 400 nm and up to and including 750 nm when excited by a fluorescence excitation radiation having a peak of at least 200 nm and up to and including 400 nm, and the non-polymeric fluorophore being present in an amount of 0.1-2 wt%; and an aqueous medium. The aqueous coloured pigment base ink may be included in an ink set comprising one or more non-fluorescent aqueous coloured pigment base inks. All these inks can be applied image-wise onto a non-UV fluorescent substrate, for example, using inkjet printing, such as high-speed continuous inkjet printing, to provide an image detectable when excited as described above, which can be provided on articles such as security documents, currencies, and lottery tickets.

Description

Technical Field

[0001] The present invention relates to the field of inkjet printing. More particularly, it relates to fluorescent water-based colored pigment-based inks (especially fluorescent water-based black pigment-based inks). It also relates to a method of applying ink to a non-UV fluorescent substrate, for example by inkjet printing, to form a colored image that can exhibit fluorescence under appropriate excitation. In addition, the present invention relates to an article obtained by the method of the present invention. Background Art

[0002] The use of inkjet printing methods and apparatus to deposit aqueous inks, including aqueous color pigment-based inks, on a variety of substrates is well known. Inkjet printing is a standard method for printing such images, in which a stream of ink droplets is directed from a printing device to the surface of a suitable receiver element or substrate. Various means can be used to control the stream of droplets to print the desired image or information without requiring contact between the printing device and the surface to which the ink is applied.

[0003] There is a need for printing variable data such as security codes, symbols or other alphanumeric marks onto valuable documents such as lottery tickets, currency, stock certificates, bank checks, passports and other security or legal documents that typically contain special security paper substrates. Such printed data is typically easily visible to the naked eye. Variable data printing can be performed economically and safely using inkjet printing systems that utilize water-based (aqueous) inks. For example, it is desirable to print such variable data using aqueous black inks that exhibit high optical density and are resistant to smearing or removal in wet or dry states. In order to achieve high optical density and smear resistance, aqueous pigment-based inks are desirable relative to aqueous dye inks.

[0004] Various aqueous colored pigment-based inks have been developed for both drop-in-demand (DOD) and continuous inkjet (CIJ) printing systems. DOD printing systems are widely used in home or consumer inkjet printers as well as slower consumer printers. As the name implies, DOD inkjet printing uses a print head that ejects drops of ink only when signaled by a digital controller.

[0005] CIJ printing systems typically include two main components, a fluid system (which includes one or more ink reservoirs) and one or more print heads. Ink can be pumped from the ink reservoir to a manifold via a supply line, which distributes the ink to a plurality of orifices, typically arranged in a linear array, under sufficient pressure to cause a stream of ink to be continuously ejected from the orifices of the print head. Stimuli can be applied to the print head to cause these ink streams to form a stream of droplets of uniform size and spacing, which are deflected into printing and non-printing paths in an appropriate manner. Non-printing droplets are typically returned to the ink reservoir using a drop catcher and a return line.

[0006] Inks of all colors may be specifically designed for use in one or both of the DOD and CIJ systems. Creative efforts may be required to find the desired components and ink properties for one or both of DOD and CIJ inkjet printing. This is true for inks of various types of colored pigments that may be required for security printing as described above.

[0007] Fluorescent inks containing water-soluble dyes have been developed for printing security markings, images or other information on security documents. For example, US Pat. No. 8,349,211 (Cai) describes fluorescent inkjet ink compositions containing fluorescent dispersions.

[0008] Various schemes for incorporating security features into water-based pigment inks have been proposed in the field of inkjet printing. For example, U.S. Pat. No. 9,016,850 (Pawlik et al.) describes water-based inkjet inks incorporating a first black pigment colorant and a second sublimable or diffusible colorant. After the ink is inkjet printed onto the surface of a substrate, the sublimable or diffusible colorant can migrate through the substrate to the opposite surface under the influence of heat to produce a visible reverse image on the opposite surface of the document. Although a suitable black image with high optical density and wet friction resistance can be obtained, which can then be identified by exposing the printed document to heat with near-infrared radiation, once exposed to heat, the document is permanently changed.

[0009] U.S. Patent Application Publication 2004 / 0233465 (Coyle et al.) discloses solvent-based inkjet inks containing UV-fluorescent colorants, which, although invisible to the eye when viewed under visible light, emit various visible colors when exposed to UV light. A method for reproducing dark colors (e.g., black) is disclosed for use with paper types containing fluorescent whitening agents. In order to produce "black" on a substrate containing a fluorescent whitening agent, a colorless ink containing one or more fluorescent quenchers in the ink can be used to quench the fluorescent whitening effect of the bluish white fluorescence produced by the fluorescent whitening agent. In such embodiments, the "black" is invisible to the eye, but instead appears as "black" only when viewed under UV irradiation, due to the fact that it blocks the bluish white fluorescence of the fluorescent whitening agent present in the substrate. Similarly, an invisible fluorescent ink can be printed onto a substrate without a fluorescent whitening agent, resulting in a black background when viewed under UV irradiation. In either case, the black color is invisible to the eye when exposed to visible light, but when viewed under UV illumination, appears only black relative to the visible light emitted by the UV fluorescent ink.

[0010] U.S. Patent Application Publication 2014 / 0231674 (Cook) describes water-based inkjet inks containing colorless UV fluorescent pigment particles that exhibit good water resistance and light resistance. These inkjet inks may additionally contain one or more non-fluorescent colored pigments other than carbon black. Therefore, although these inkjet inks can produce visible marks on documents, the visible marks may also exhibit significant visible fluorescence when exposed to UV light, but they cannot be used to print black marks with high optical density. This is because black pigments, especially carbon black, strongly absorb throughout the UV region of the spectrum and thus prevent sufficient UV radiation from being absorbed by the fluorescent pigment to produce visible fluorescence. Using lower concentrations of black pigments can alleviate this limitation, but the printed marks are no longer high in optical density and appear gray rather than black. Using black dyes that are not too strongly absorbed in the UV region of the spectrum can produce darker black images that still exhibit UV fluorescence, but images printed with such dye black inks are generally poor in wet rubbing resistance. Due to the high cost of fluorescent pigments, increasing the concentration of these pigments is not practical, and there are problems with being able to reliably jet inkjet inks containing the total high pigment content required to achieve both high black density and acceptable levels of fluorescence.

[0011] U.S. Pat. No. 6,793,723 (Auslander et al.) and U.S. Pat. No. 6,827,769 (Auslander et al.) each disclose aqueous inkjet inks capable of producing dark machine-readable markings that exhibit fluorescence when exposed to UV radiation, the inks comprising: (a) a first colorant comprising a fluorescent dye, such as a non-polymeric fluorescent dye that may be embedded in a polymer matrix; (b) a second colorant comprising a mixture of visible dyes and / or pigments (e.g., blue with a black dye or pigment, or a blue dye or pigment with orange and red pigments to provide a relatively dense image); and (c) an aqueous liquid carrier comprising water. The use of black pigments as a single colorant or as a mixture of other colorants as non-fluorescent colorants is not described or suggested in these patents. Smear resistance or removal resistance in wet or dry operation is not described for these aqueous inkjet inks. In addition, the use of mixtures of polymeric and / or non-polymeric fluorescent colorants with polymeric and / or non-polymeric non-fluorescent colorants adds undesirable cost and complexity to the inkjet inks.

[0012] Despite the various efforts described in the art to provide non-smearing and high density images for security documents, there remains a need for water-based (aqueous) colored pigment-based inks that exhibit high optical density and resistance to smearing or removal from non-fluorescent substrates. In addition, it is desirable to provide high density images, especially high density black images, that produce strong visible emission when illuminated with UV light. There is a further need for such aqueous colored pigment-based inks to be compatible with both DOD and CIJ inkjet printing systems.

[0013] Brief description of the invention

[0014] In order to solve the above problems, the present invention provides an aqueous colored pigment-based ink capable of fluorescence, which comprises:

[0015] Pigment colorant in an amount of at least 1 wt % and up to and including 7 wt %;

[0016] a non-polymeric fluorophore that exhibits an emission peak of at least 400 nm and up to and including 750 nm when excited by fluorescent excitation radiation having a peak of at least 200 nm and up to and including 400 nm, and that is present in an amount of at least 0.1 wt. % and up to and including 2 wt. %; and

[0017] an aqueous medium comprising water,

[0018] All amounts are based on the total weight of the aqueous colored pigment-based ink capable of fluorescing.

[0019] Another embodiment of the present invention is an ink set comprising two or more aqueous pigment-based inks, the ink set comprising:

[0020] (I) at least one aqueous, inventive, coloured pigment-based ink according to the invention, which is capable of fluorescing; and

[0021] (II) at least one aqueous colored pigment-based ink which is non-fluorescent and comprises a pigment colorant in an amount of at least 1 wt. %; and an aqueous medium comprising water, wherein the amount of the colored pigment is based on the total weight of the non-fluorescent aqueous colored pigment-based ink.

[0022] The present invention also provides a method of providing a colored image, wherein the colored image exhibits fluorescence when exposed to fluorescence excitation radiation, the method comprising:

[0023] Any embodiment of the aqueous colored pigment-based ink capable of fluorescence of the present invention is applied imagewise on the outer surface of a non-UV fluorescent substrate to provide a colored latent fluorescent image on the outer surface of the non-UV fluorescent substrate. In some preferred embodiments, the aqueous colored pigment-based ink is applied imagewise using continuous inkjet printing.

[0024] According to the present invention, it is also possible

[0025] Continuously inkjet printing a non-fluorescent aqueous non-black colored pigment-based ink on the outer surface of the non-UV fluorescent substrate to provide a non-black colored image on the outer surface of the non-UV fluorescent substrate; and then

[0026] Continuously inkjet print the aqueous black pigment-based ink of the present invention capable of fluorescing onto at least a portion of the non-black colored image to provide a black latent fluorescent image capable of fluorescing on at least a portion of the non-black colored image, for example, to provide a non-black multi-color image.

[0027] The method according to the invention can be used to mark articles with a coloured latent fluorescent image as a security mark for identification, information or decoration, for example by providing the coloured latent fluorescent image on security documents, currency or lottery tickets.

[0028] A preferred inkjet printing method of the present invention uses a continuous inkjet printer, and the method comprises:

[0029] providing a primary fluid supply of one embodiment of an aqueous colored pigment-based ink capable of fluorescing according to the present invention;

[0030] supplying an aqueous colored pigment-based ink capable of fluorescing from a main fluid supply to a droplet generator mechanism;

[0031] ejecting from a droplet generator mechanism a continuous stream of an aqueous color pigment-based ink capable of fluorescing, the continuous stream being divided into spaced droplets of the aqueous color pigment-based ink capable of fluorescing;

[0032] controlling the spaced droplets of the aqueous color pigment based ink capable of fluorescence to distinguish between printed droplets of the aqueous color pigment based ink capable of fluorescence and non-printed droplets of the aqueous color pigment based ink capable of fluorescence, and the non-printed droplets of the aqueous color pigment based ink capable of fluorescence are collected and returned to the main fluid supply, and

[0033] A colored latent fluorescent image is thereby formed on the outer surface of the non-UV fluorescent substrate using printed drops of an aqueous colored pigment-based ink capable of fluorescing.

[0034] The present invention also provides an article obtained by any of the inventive methods described herein, the article comprising a non-UV fluorescent substrate having disposed on an outer surface thereof a colored latent fluorescent image derived from an embodiment of the aqueous colored pigment-based ink capable of fluorescing of the present invention, the colored latent fluorescent image comprising:

[0035] Pigments and colorants; and

[0036] A non-polymeric fluorophore that exhibits an emission peak of at least 400 nm and up to and including 750 nm when excited by fluorescent excitation radiation having a peak of at least 200 nm and up to and including 400 nm, wherein the weight ratio of the pigment colorant to the non-polymeric fluorophore in the fluorescent image is 70:1 to 0.5:1.

[0037] In addition, the present invention can be used to detect a fluorescent image in an inkjet-printed article obtained according to any method of the present invention, the fluorescent image detection method comprising:

[0038] A colored latent fluorescent image disposed on a non-UV fluorescent substrate having an emission peak of at least 400 nm and up to and including 750 nm is illuminated on an outer surface of the non-UV fluorescent substrate with fluorescent excitation radiation having a peak of at least 200 nm and up to and including 400 nm.

[0039] The present invention provides aqueous colored pigment-based inks, and particularly aqueous black pigment-based inks, which can be used in methods using DOD or CIJ printing systems to provide colored latent fluorescent images (particularly black latent fluorescent images). In addition, these colored latent fluorescent images are highly resistant to smearing or removal from printed substrates under both wet and dry conditions. That is to say, the colored latent fluorescent images prepared using the present invention have high rubbing resistance under both wet and dry states. These aqueous colored pigment-based inks are designed to be fluorescent in dry form because they contain suitable non-polymer fluorophores that enable viewers to see fluorescent security images or data under appropriate excitation by specific radiation with a peak of at least 200nm and up to and including 400nm. These advantages are particularly evident when aqueous colored pigment-based inks are applied to non-UV fluorescent substrates, for example, using inkjet printing (e.g., high-speed continuous inkjet printing) and dried thereon (as described below) to provide latent fluorescent images. These and various other advantages are described in the details disclosed below, and the details of the present disclosure include working examples of certain embodiments implemented to prove the practice used in the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a graphical representation of spectral emission data obtained from black latent fluorescent images obtained in the working examples by printing specific inventive and comparative aqueous black pigment-based inks and irradiating with UV light.

[0042] Figure 2 Also illustrated are the spectral emissions obtained from black latent fluorescent images obtained in the working examples by printing specific inventive and comparative aqueous black pigment-based inks and irradiating with UV light.

[0043] Figure 3Also illustrated is a graphical representation of spectral emission data obtained from black latent fluorescent images obtained in the working examples by printing certain inventive and comparative aqueous black pigment-based inks and irradiating with UV light.

[0044] Figure 4 Also illustrated is a graphical representation of spectral emission data obtained from black latent fluorescent images obtained in the working examples by printing certain inventive and comparative aqueous black pigment-based inks and irradiating with UV light. DETAILED DESCRIPTION OF THE INVENTION

[0046] The following discussion relates to various embodiments of the invention, and while some embodiments may be desirable for particular uses, the disclosed embodiments should not be interpreted or otherwise considered to limit the scope of the invention as described below. In addition, those skilled in the art will appreciate that the following disclosure has broader application than explicitly described in the discussion of any specific embodiment.

[0047] definition

[0048] Unless otherwise indicated, as used herein to define the various components of the aqueous composition of an aqueous colored (including black colored) pigment-based ink (whether an ink of the present invention or an ink not of the present invention), as well as other materials used in the practice of the present invention, the singular forms "a", "an", "an" and "the" are intended to include one or more components (i.e., include plural referents).

[0049] Each term not expressly defined in this application should be understood to have a meaning generally accepted by those skilled in the art. If the construction of a term would make it meaningless or essentially meaningless in its context, the term should be interpreted as having a standard dictionary meaning.

[0050] Unless otherwise expressly stated, the use of numerical values ​​in the various ranges specified herein should be considered approximate, as if both the minimum and maximum values ​​in the stated ranges were preceded by the word "about". In this manner, slight variations above and below the stated ranges may be useful to achieve substantially the same results as the values ​​within the ranges. In addition, unless otherwise stated, the disclosure of these ranges is intended as a continuous range including every value between the minimum and maximum values ​​and the endpoints of the ranges.

[0051] As used herein, the parameter "acid number" (also referred to as acid value) is defined as the number of milligrams (mg) of potassium hydroxide required to neutralize 1 g of the described acidic polymer.

[0052] The term "aqueous" in the aqueous colored pigment dispersion and aqueous colored pigment-based ink capable of fluorescence according to the present invention means that the water content is greater than 70% by weight, or at least 80% by weight, based on the total weight of all solvents. In each of such compositions, water is the main solvent.

[0053] The term "non-polymeric fluorophore" refers to a non-polymeric compound that can absorb electromagnetic radiation ("light") of a specific wavelength and re-emit electromagnetic radiation ("light") at a longer wavelength. The non-polymeric fluorophores used in the present invention absorb UV radiation of wavelengths typically between 200 nm and 400 nm, and emit ("fluoresce") substantially visible radiation of wavelengths typically between 400 nm and 750 nm. The fluorescence of the aqueous pigment-based ink according to the present invention or the printed colored latent fluorescent image obtained therefrom can be measured and characterized using, for example, a Perkin-Elmer LS-50B fluorescence spectrophotometer.

[0054] The term "colored latent fluorescent image" refers to an applied image of an aqueous colored pigment-based ink capable of fluorescence according to the present invention, which is capable of exhibiting fluorescence at an emission peak of at least 400 nm and up to and including 750 nm when exposed to excitation radiation having a peak of at least 200 nm and up to and including 400 nm. As provided by the present invention, a colored latent fluorescent image is also defined as "colored" due to the presence of colored pigments in the applied aqueous colored pigment-based inks, each of which is capable of fluorescence under the mentioned conditions.

[0055] In contrast, the non-fluorescent aqueous pigment-based inks described herein and present in the ink sets of the present invention, when exposed to excitation radiation, do not fluoresce to any perceptible or discernible extent under the conditions mentioned.

[0056] The term "optical density" is a measure of the darkness of a printed color image as measured by a densitometer; the decimal (base 10) logarithm of the reciprocal of transmittance is known as absorbance or optical density. For example, the optical density of a colored latent fluorescent image provided in accordance with the present invention can be measured using a suitable commercial spectrophotometer, such as the Gretag Macbeth Spectrophotometer and appropriate program to measure.

[0057] The CIELAB L*, a*, and b* values ​​described herein have known definitions according to the CIE 1976 color space, or a standard version of a color space known thereafter, and are calculated using the power distribution function of a standard D65 illuminant and a 10° standard observer function. These calculated values ​​can be used to represent a color as three numeric color values: L* represents the lightness (or brightness) of the color, a* represents the green-red component of the color, and b* represents the blue-yellow component of the color.

[0058] Median particle size (d 50 or D 50 ), in nanometers) can be determined using suitable particle measurement equipment and techniques, such as using NPA 150 dynamic light scattering particle size analyzer (Microtrac, Inc.), this commercial analyzer provides both intensity-weighted and volume-weighted particle size distributions. The standard procedure for using such an analyzer is described in National Institute of Standards and Technology (NIST) Special Publication 1200-6, Measuring the Size of Nanoparticles in Aqueous Media Using Batch-Mode Dynamic Light-Scattering NIST-NCL Joint Assay Protocol, PCC-1 Version 1.2, May 2015 and ISO 22412:2017 Particle Size Analysis-Dynamic Light-Scattering (DLS). Therefore, D 50 The 50th percentile particle size (or median particle size) refers to the fractional particle size distribution such that 50% of the particles have a diameter less than the indicated diameter. 95 (or d 95 ) or 95th percentile particle size refers to a fractional particle size distribution such that 95% of the particles have a diameter less than the indicated diameter.

[0059] Other particle size measurement techniques and equipment are also known in the art. For example, laser diffraction techniques will also provide a volume-weighted particle size distribution. Dynamic light scattering techniques will provide an intensity-weighted particle size distribution.

[0060] The term "water-soluble" when used in reference to an aqueous solution of a solute refers to a solubility in water of at least 0.1 g of solute (0.1 wt %) in 100 ml of water at 25°C.

[0061] The term "external surface" in relation to non-UV fluorescent substrates refers to any planar surface onto which an image is intended to be inkjet printed. It does not refer to an edge, such as the edge of paper, film or paperboard.

[0062] Dynamic viscosity can be measured by any known technique. Preferred methods include measuring the time of mass flow through a capillary such as in a capillary viscometer, or using, for example, a rolling ball viscometer to measure the falling ball velocity through the fluid. Both the capillary flow viscometer and the commercially available Anton Paar Automated MicroViscometer (AMVn) using rolling ball technology can be used to measure the dynamic viscosity reported herein. All dynamic viscosity values ​​disclosed herein are measured at about 24°C to 26°C under gravity-induced shear. It will be understood that the values ​​reported are reported in centipoise (cP) or millipascal seconds (mPa-sec), and 1cP=10 -3 Pascal-second (Pa-sec) is equal to 10 -2 Dyne-sec / cm 2 Although viscosity can be measured with high precision, viscosity values ​​are reported herein only to one or two decimal places, and they are generally rounded rather than truncated. All claims reciting dynamic viscosity are intended to be interpreted in terms of values ​​in mPa-sec, which are generally rounded to one decimal point.

[0063] For clarification of the definition of any term related to polymers, reference should be made to the "Glossary of Basic Terms in Polymer Science", as published by the International Union of Pure and Applied Chemistry ("IUPAC"), Pure Appl. Chem. 68, 2287-2311 (1996). However, any definition explicitly set forth herein should be considered controlling.

[0064] As used herein, the term "polymer" is used to describe a compound with a relatively high molecular weight formed by linking together many small reactive monomers. As the polymer chain grows, it folds onto itself in a random manner to form a coiled structure. With the choice of solvent, as the chain length grows, the polymer can become insoluble and become polymer particles dispersed in the solvent medium.

[0065] The term "copolymer" refers to a polymer comprising two or more different repeating or recurring units arranged along or pendant to the polymer backbone.

[0066] The recurring units in some of the polymers described herein are generally derived from the corresponding ethylenically unsaturated polymerizable monomers used in the polymerization process, which are available from various commercial sources or prepared using known chemical synthesis methods.

[0067] Unless otherwise stated, the term "wt%" refers to the amount of a component or material based on the total weight of an aqueous composition, aqueous formulation (e.g. aqueous color pigment-based ink) or dry layer (wherein it is substantially the same as the % solids in the dry layer).

[0068] Percent solids (%) refers to the percentage by weight of non-volatile materials in a composition or solution (eg, an aqueous color pigment-based ink), which can be determined using known gravimetric procedures.

[0069] As used herein, the term "layer" or "coating" may consist of one disposed or applied layer or a combination of several sequentially disposed or applied layers, such as a combination of sub-layers.

[0070] use

[0071] The aqueous colored pigment-based inks that may be capable of fluorescence prepared according to the present invention may be particularly useful for providing colored latent fluorescent images with high optical density on various substrates, and particularly on non-UV fluorescent substrates, which are resistant to smearing or removal in both wet and dry states, and may contain variable data that can be easily made to fluoresce under appropriate excitation, for example, for identification. Such colored latent fluorescent images are particularly useful when present on security documents (e.g., IDs, driver's licenses, and passports), stock certificates, currency, lottery tickets, bank checks, product security labels or tags, and other articles where data or images are required to provide identification.

[0072] Water-based pigment ink

[0073] The aqueous colored pigment-based ink capable of fluorescence according to the present invention can be prepared from a suitable aqueous dispersion of one or more particulate pigment colorants providing the desired color as a first essential component using known dispersants and dispersing means. According to the present invention, the aqueous colored pigment-based ink capable of fluorescence under the above-mentioned conditions may also be referred to herein as "aqueous fluorescent pigment-based ink" to distinguish it from aqueous non-fluorescent pigment-based ink, which may also be used in combination with one or more aqueous fluorescent pigment-based inks in various methods of the present invention.

[0074] The pigment colorant as part of the aqueous colored pigment-based dispersion can be mixed with one or more wetting agents (or co-solvents) and other optional components (as described below) that can be formulated in an aqueous medium (primarily water) to provide an aqueous colored pigment-based ink having a viscosity of at least 1 centipoise (1 mPa-sec) or at least 2 centipoise (2 mPa-sec) and up to and including 10 centipoise (10 mPa-sec) or up to and including 50 centipoise (50 mPa-sec) at 25°C, all measured using a rolling ball viscometer at 25°C, or as described above.

[0075] Each aqueous colored pigment-based ink capable of fluorescence according to the present invention can typically have a solids content of at least 1% solids and up to and including 10% solids or up to and including 20% ​​solids, and the remaining weight of the aqueous colored pigment-based ink is an aqueous medium, which may contain at least 80% by weight, at least 85% by weight or at least 90% by weight of water, including a liquid wetting agent or co-solvent, based on the total aqueous medium.

[0076] Thus, each aqueous colored pigment-based ink according to the present invention typically contains one or more particulate organic or inorganic pigment colorants that will provide the desired color or hue. For example, black pigments are particularly useful and may be present alone or in combination to provide a very intense black color in the resulting black latent fluorescent image. In addition, one or more black pigments, such as one or more carbon black pigments, may be combined with one or more pigments of different colors, such as cyan copper phthalocyanine or magenta quinacridone pigments, as long as the desired black appearance and optical density is obtained in the resulting black latent fluorescent image.

[0077] Typically, the pigment colorants used in the practice of the present invention are non-UV fluorescent, meaning that they do not fluoresce to any appreciable extent when illuminated at a wavelength of at least 200 nm and up to and including 400 nm.

[0078] Non-fluorescent black pigments are particularly useful in many embodiments of aqueous colored pigment-based inks in the practice of the present invention. Although any black pigment can be used to produce the aqueous black pigment-based ink of the present invention, which provides a colored latent fluorescent image that exhibits high optical density and resistance to smearing or removal from a non-fluorescent substrate, various commercially available carbon blacks are particularly useful. Representative suitable carbon black pigments include, but are not limited to 160IQ, 170IQ, 180IQ, Color Black FW 2, Color Black FW 200, ColourBlack FW 285, Color Black FW 1, Color Black FW 18, Color Black FW and ColourBlack FW 18, and 95 pigments, all of which are produced by Orion Engineered Carbons; Black produced by CabotCorp 1100, Black 900, Black 880, Black 600, 1100 and 900 pigment; and any Raven black pigment produced by Birla Specialty Carbons. Other black pigments are also acceptable and may contain inorganic particles such as magnetite, ferrite, titanium black or combinations thereof.

[0079] Colored, non-black pigment colorants can be combined in suitable proportions to provide images of different concentrations that appear visually black. Those skilled in the art will know how to select the desired colored, non-black pigment colorants in the desired proportions, combined with the necessary non-polymeric fluorophores described below, to achieve this purpose.

[0080] Other available organic or inorganic pigment colorants can be used to provide any desired non-black color or hue in the resulting non-black (but colored) latent fluorescent image, such as fluorescent green, red, yellow, blue, purple, magenta, cyan, white, brown, pink and gray images, as well as any other non-black hues known in the art. Pigment colorants can be present in each aqueous colored non-black pigment-based ink alone or in a mixture. For example, the aqueous colored non-black pigment-based ink that can be used in the present invention can contain one or more pigment colorants, including but not limited to cyan pigments, magenta pigments, yellow pigments, green pigments, orange pigments, white pigments, red pigments, blue pigments, purple pigments, or any combination of these pigment colorants,

[0081] It is particularly desirable that any or all of the pigment colorants used in the practice of this invention be anionically stabilized, as described below for black pigments.

[0082] Representative examples of usable colored pigments are described in, for example, U.S. Pat. Nos. 5,026,427 (Mitchell et al.), 5,141,556 (Matrick), 5,160,370 (Suga et al.), and 5,169,436 (Matrick). In general, usable pigment colorants include, but are not limited to, azo pigments, monoazo pigments, disazo pigments, azo pigment lakes, β-naphthol pigments, naphthol AS pigments, benzimidazolone pigments, disazo condensation pigments, metal complex pigments, isoindolinone and isoindolinone pigments, quinacridone pigments, polycyclic pigments, phthalocyanine pigments, perylene and perindole pigments, thioindigo pigments, anthraquinone pyrimidone pigments, flavanthronone pigments, dibenzopyrene dione pigments, dioxazine pigments, triarylcarbonium pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, and titanium dioxide. Useful pigment colorants are also described in US Pat. No. 8,455,570 (Lindstrom et al.) at column 10 (line 66) to column 11 (line 40). Mixtures of pigments can be used to provide the desired hue or color as described, for example, in US Pat. No. 9,605,169 (Lussier et al.).

[0083] The aqueous colored pigment-based ink according to the present invention, and in particular the aqueous black pigment-based ink, when applied (e.g. by inkjet printing) to a suitable non-UV fluorescent substrate (as described below), can provide a colored latent fluorescent image with a high optical density. This is particularly true when a black latent fluorescent image is desired, for example using an aqueous black pigment-based ink containing carbon black.

[0084] The visible density or darkness of an inkjet-printed colored latent fluorescent image can be at least partially defined by the following parameters: when an aqueous colored pigment-based ink that is an aqueous black pigment-based ink is present in dry form as a colored latent fluorescent image on a non-UV fluorescent substrate (defined below), the unprinted area exhibits an L* value of 50 or more, as measured under irradiation with UV light that does not include a wavelength less than 400nm (or excludes the fluorescence excitation wavelength), and an a* value of -20 to and including +20 and a CIE b* value of at least -15 to and including +20.

[0085] Available pigment coloring agent of all types can be accompanied by suitable polymer or non-polymeric dispersant (for example, dispersant with anionic group as described below) as known in the art, or pigment coloring agent can be self-dispersed, for example, due to having the group with anionic charge connected to the pigment particle surface, and therefore in pigment coloring agent dispersion and gained water-based colored pigment-based ink, be dispersible and stable.The example of available self-dispersed black pigment coloring agent is described in the 11th hurdle (49-53 row) of United States Patent (USP) 8,455,570 (mentioned above).

[0057] to

[0067] of U.S. Patent Application Publication 2014 / 0231674 (mentioned above) provides the discussion of the purposes of self-dispersion and dispersant for pigment particles.This principle can also be used for black pigment and other pigment coloring agents.

[0086] Thus, particularly useful are pigment colorants that are stabilized with anionic groups for use in the present invention to provide colored latent fluorescent images of any desired hue, and particularly pigment colorants for use in providing black latent fluorescent images (i.e., they are "anionically stabilized pigment colorants"). Such anionically stabilized pigment colorants, including anionically stabilized black pigments, are available from a variety of commercial sources, and the skilled artisan will know which pigment colorants can be used with the specific aqueous colored pigment-based inks and inkjet printing methods of the present invention.

[0087] Useful pigment colorants may have a median particle size of at least 10 nm, and typically less than 200 nm, and preferably less than 100 nm or even less than 50 nm. As mentioned above, the term "median particle size" refers to the fractional particle size distribution such that 50% of the volume of the pigment colorant particles is provided by pigment particles having a diameter less than the indicated diameter. 50 .

[0088] An organic or inorganic pigment colorant (or combination of pigment colorants), particularly those that are anionically stabilized black pigments, can be formulated as an essential component together with the other components described in the aqueous pigment-based ink in an amount of at least 1 wt %, or at least 3 wt %, or at least 4 wt %, and up to and including 6 wt %, or up to and including 7 wt %, based on the total weight of the aqueous pigment-based ink.

[0089] The second essential component of the aqueous colored pigment-based ink according to the present invention is a non-polymeric fluorophore, or a mixture of such compounds. "Non-polymeric" means that each of these fluorophore compounds has a molecular weight of less than about 1000 daltons and does not contain conventional repeating units as are usually contained in polymeric materials. In addition, these non-polymeric fluorophores are usually "water-soluble", as defined above. Therefore, when present in the aqueous colored pigment-based ink according to the present invention, such compounds are usually non-granular.

[0090] Each of the non-polymeric fluorophores is selected so that it can be excited by fluorescence excitation radiation in the UV region of the electromagnetic spectrum, i.e., having a peak (λ) of at least 200 nm and up to and including 400 nm. max ). In addition, each of these non-polymeric fluorophores may exhibit a visible radiation emission peak under such excitation of at least 400 nm and up to and including 750 nm, more preferably between 400 nm and 500 nm (or generally emission in the "blue" region of the electromagnetic spectrum).

[0091] Furthermore, each non-polymeric fluorophore used in the practice of the present invention is generally "colorless," meaning that it is not visible to the ordinary unaided human eye under ordinary viewing conditions, or exhibits no apparent color or hue to the ordinary unaided human eye.

[0092] The types of non-polymeric fluorophores that can be used are described, for example, in the "Colour Index TM, maintained by the Society of Dyers and Colourists & American Association of Textile Chemists and Colourists", and which is now published only on the World Wide Web and referenced in the regularly updated Wikipedia article "Welcome to Colour Index". Useful non-polymeric fluorophores may be labeled "optical brighteners", "fluorescent brightening agents", or "whiteners", and the skilled artisan will be able to determine whether a particular compound can be used in the present invention using the teachings provided herein and routine experimentation. The above-mentioned water solubility feature is quite important, and if a particular compound can be made to fluoresce at the desired visible wavelength after appropriate excitation, but it has unacceptable water solubility, it generally cannot be used in the practice of the present invention.

[0093] Some particularly useful non-polymeric fluorophores are compounds with multiple sulfonate groups or other groups that provide water solubility to the compound (e.g., carboxylates and polyethylene oxide groups). Representative compounds of this type include diaminostilbene with multiple sulfonate groups.

[0094] For example, using the teachings provided herein, a skilled artisan will be able to identify available non-polymeric fluorophores (or mixtures thereof) from commercially available compounds and from the literature describing fluorescent materials, and use routine experimentation to see whether the resulting inkjet-printed colored latent fluorescent image has the requisite readily detectable fluorescent emission after the desired UV (200-400 nm) excitation.

[0095] The total amount of one or more non-polymer fluorophores present in the aqueous pigment-based ink (and in particular the aqueous black pigment-based ink) according to the present invention can be at least 0.1 wt % or at least 0.2 wt %, and up to and including 1 wt % or up to and including 2 wt %, all based on the total weight of the aqueous pigment-based ink.

[0096] Each aqueous colored pigment-based ink according to the present invention generally comprises one or more wetting agents (or sometimes referred to as cosolvents) as optional but desirable components. The term "wetting agent" is generally a water-miscible cosolvent that slows down the evaporation rate of the aqueous pigment-based ink, thereby delaying the precipitation of the solid components of the ink. Therefore, the wetting agent has a higher boiling point and a lower vapor pressure than water at a given temperature, making it more difficult to evaporate than water. Therefore, the wetting agent is a water-miscible polar organic compound (usually a low-volatility solvent with a boiling point close to or greater than about 200° C. at sea level) or a combination of such compounds, which delays water from evaporating from aqueous-based ink to reduce nozzle blockage or jet bending caused by the formation of dried ink deposits. Any water-soluble or water-miscible wetting agent known in the field of inkjet inks compatible with other requirements used in the present invention can be used in the practice of the present invention. Although a single wetting agent can be used, a mixture of two or more wetting agents can be used, each of which imparts useful properties. Representative wetting agents are described, for example, in

[0074] to

[0080] of U.S. Patent Application Publication No. 2014 / 0231674 (referenced above) and in U.S. Patent No. 9,828,513 (Lussier et al.).

[0097] Particularly useful wetting agents include glycerol or compounds, each of which independently has a ratio of carbon atoms to oxygen atoms of at least 1.0:1.0 or at least 1.3:1.0 and up to and including 2.7:1.0. These wetting agents do not contain heteroatoms, such as nitrogen or sulfur, but only contain carbon, hydrogen and oxygen atoms. More specifically, each of such water-soluble or water-miscible wetting agents has only two hydroxyl oxygens (e.g., in two hydroxyls). Some of these available water-miscible wetting agents may have one or more oxy or ether bond oxygens. For example, useful wetting agents include, but are not limited to, 2-(2-hydroxyethoxy)ethanol and 2-[2-(2-hydroxyethoxy)ethoxy]ethanol ("TEG"); dihydroxyethane (or 1,2-ethylene glycol); dihydroxypropanes, such as 1,2-dihydroxypropane (or 1,2-propylene glycol) and 1,3-dihydroxypropane (or 1,3-propylene glycol); dihydroxybutanes, such as 1,2-dihydroxybutane (or 1,2-butylene glycol); , 1,3-dihydroxybutane (or 1,3-butanediol), 2,3-dihydroxybutane (or 2,3-butanediol), 1,4-dihydroxybutane (or 1,4-butanediol), 1,3-dihydroxy-2-methylpropane and 1-hydroxy-2-hydroxy-2-methylpropane; and dihydroxypentanes, such as 1,2-dihydroxy-n-pentane (or 1,2-n-pentanediol), 1,5-dihydroxy-n-pentane (or 1,5-n-pentanediol).

[0098] In addition, the wetting agent can be 1,2-ethanediol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 2,3-butylene glycol, 1,3-butylene glycol, 1,2-pentanediol, 2,3-pentanediol, 1,3-pentanediol, 2-(2-hydroxyethoxy)ethanol, 2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or a combination of two or more of these compounds.

[0099] One or more wetting agents may be present in the aqueous color pigment-based ink (and especially aqueous black pigment-based ink) according to the present invention in an amount of at least 0.5 wt%, or at least 1 wt%, or at least 3 wt%, and up to and including 7 wt%, or up to and including 10 wt%, or up to and including 15 wt%, all based on the total weight of the aqueous color pigment-based ink, especially if CIJ printing (described below) is intended. However, for aqueous color pigment-based inks designed for pressure DOD printing, one or more wetting agents may be present in an amount of at least 10 wt% up to and including 50 wt%.

[0100] Each aqueous colored pigment-based ink useful according to the present invention may also contain one or more anionically charged polymers as another optional component. Each of these anionically charged polymer components typically has an acid value of at least 50 or at least 60, and up to and including 90 or up to and including 150. Such anionically charged polymer materials are described in more detail below.

[0101] For example, useful anionically charged polymer components of this type include, but are not limited to, anionic polyurethanes, which are described in many of the patent publications discussed below.

[0102] As an alternative or in addition to anionic polyurethanes, the aqueous color pigment-based ink may include one or more anionically charged copolymers, such as styrene-(meth)acrylic acid copolymers, each of which has an acid number of at least 50 or at least 120 and up to and including 220 or up to and including 240, and the anionically charged polymer component is described in more detail below and in the cited patent literature. The term "(meth)acrylic acid" refers to a material derived at least in part from one or both of acrylic acid and methacrylic acid.

[0103] Representative examples of the two types of anionically charged polymers are described, for example, in U.S. Patent Application Publication No. 2014 / 0231674 (referenced above) and U.S. Patent Nos. 8,430,492 (Falkner et al.) and 9,783,553 (referenced above). Particularly useful anionically charged polyurethanes contain polyether diol units and can be identified as polyether polyurethanes and typically have a molecular weight (M) of at least 10,000 Daltons and up to and including 30,000 Daltons. w ). Some particularly useful polyether polyurethanes are each represented by structure (I) in U.S. Pat. No. 9,783,553 (referenced above). Useful water-soluble or water-dispersible anionically charged polyether polyurethanes can be prepared as described, for example, in

[0045] -

[0049] of U.S. Pat. No. 8,430,492 (referenced above). The acidic groups in the anionically charged polyether polyurethane can be at least partially and up to 100% neutralized (converted to a salt) using a monovalent inorganic base such as an alkali metal hydroxide or an organic amine such as dimethylethanolamine.

[0104] Representative anionic (meth) acrylic polymers and anionic styrene-(meth) acrylic polymers useful in the present invention are described, for example, in U.S. Patent Application Publication No. 2008 / 207811 (referenced above at

[0061] ). Examples of useful anionic styrene-acrylic polymers include those sold under the trademark (SCJohnson Co.), (Mead Westvaco Co.) and (Air Products and Chemicals, Co.) those commercially available.

[0105] In addition, modified polysiloxanes may be present in the aqueous color pigment-based ink as a further optional component. Examples of such materials are "surfactants" based on ethoxylated or propoxylated silicones, which are available under the trademarks (CL Witco) and (Byk Chemie) For example 348 and 381, and Dow Corning DC67, DC57, DC28, DC500W and DC51 are commercially available. Non-silicone surfactants may also be used, including but not limited to anionic, cationic, nonionic or amphoteric surfactants, such as Surfactants (Evonik), including Those available commercially are HYDROGENOL 440 and HYDROGENOL 465 acetylenic diol surfactants.

[0106] Some embodiments of aqueous black pigment-based ink of the present invention further comprise one or more water-soluble black dyes, for the purpose of enhancing the black concentration of the formed black latent fluorescent image, as long as they do not adversely affect the wet friction resistance of the black latent fluorescent image. Available water-soluble black dyes are known in the art, and can be derived from various commercial sources. For example, available water-soluble black dyes include but are not limited to food black (Food Black) 1, food black 2, food black 40, Carta black, various direct black (Direct Black) dyes (for example, 4,14,17,22,27,38,51,112,117,154 and 168), carboxylated food black 286 and acid black dyes (for example, 1,7,9,24,26,48,52,58,60,61,63,92,107,109,118,119,131,140,155,156,172 and 194). One or more of such water-soluble black dyes may be present in the aqueous black pigment-based ink according to the present invention in a total amount of at least 0.1 wt % and up to and including 2 wt % (of all black dyes present), based on the total weight of the aqueous black pigment-based ink.

[0107] Other optional additives that may be present in the aqueous color pigment-based ink in amounts that will be apparent to one skilled in the art include, but are not limited to, thickeners, surfactants, dispersants, desiccants, water repellents, viscosity modifiers, pH buffers, preservatives, antifoaming agents, wetting agents, corrosion inhibitors, biocides, fungicides, defoaming agents (e.g. DF110L, PC, MD-20 and DF-70, Evonik Industries), antioxidants and light stabilizers, which are sold under the trademark (Ciba) and Other additives that may be used in aqueous pigment-based inks are described in column 17 (lines 11-36) of US Pat. No. 8,455,570 (referenced above).

[0108] In particular, in addition to those compounds described above, other optional additives that may be present in the aqueous colored pigment-based ink (e.g., aqueous black pigment-based ink) of the present invention include one or more of a biocide, a defoamer, a dispersant, and an anionically charged polymer component (as described above) having an acid value of at least 50.

[0109] If necessary, the pH of each aqueous colored pigment-based ink according to the present invention can be adjusted to at least 8 and up to and including 12, or more likely to at least 8 and up to and including 10, or in some embodiments to at least 8 and up to and including 9.5. Any suitable base such as hydroxide or organic amine can be used to achieve this pH in a suitable amount. According to columns 17-19 of U.S. Patent 8,455,570 (mentioned above), a buffer can be included to maintain the desired pH, as will be apparent to those skilled in the art.

[0110] Method and apparatus for forming fluorescent colored images

[0111] According to the present invention, suitable substrates, and in particular those having suitable properties for use in, for example, security documents, currency and lottery tickets, can be provided with a colored latent fluorescent image, which can be black in color or have a color other than black, by suitably applying one or more aqueous colored pigment-based inks capable of fluorescence according to the present invention, for example using inkjet printing. The aqueous colored pigment-based ink can be applied (e.g., inkjet printing) to form a colored latent fluorescent image on the outer surface of a treated or untreated non-UV fluorescent substrate prepared from any of a variety of materials, as described in more detail below. According to the present invention, the colored latent fluorescent image can be provided directly on the outer surface of the substrate, or it can be applied in a suitable manner on a non-UV fluorescent image of a different color, which has been previously applied to the outer surface of the substrate, as described in more detail below. For example, a black latent fluorescent image can be formed on a non-fluorescent image of any color, such as a non-black monochrome or multicolor image.

[0112] The application of the aqueous colored pigment-based ink capable of fluorescence according to the present invention can be achieved by many means, including but not limited to inkjet printing, which includes continuous inkjet printing, thermal drop-on-demand inkjet printing and piezoelectric drop-on-demand inkjet printing, or any other type of printing that can utilize aqueous pigment inks, such as offset printing, gravure printing, letterpress printing, screen printing and other techniques known in the art.

[0113] In most embodiments of the present invention, a colored latent fluorescent image (eg, a black latent fluorescent image) may be provided on a suitable non-UV fluorescent substrate by inkjet printing of one or more aqueous colored pigment-based inks according to the present invention.

[0114] In the following discussion, consistent with the teachings provided above, the present disclosure relates to the primary means of forming a colored latent fluorescent image of any desired color or colors by inkjet printing one or more aqueous colored pigment-based inks according to the present invention. However, it should be understood that the discussion also relates to the use of the more desirable inkjet printing to form a black latent fluorescent image using an aqueous black pigment-based ink according to the present invention.

[0115] For example, the aqueous color pigment-based ink according to the present invention can be used in any configuration or mechanical system of drop-on-demand (hereinafter referred to as "DOD") printing systems, which are generally sold in the consumer market for home or office use, or for industrial use such as printing (imprinting) onto various articles. However, the advantages of the present invention are particularly evident when the method according to the present invention is implemented at high printing speeds on non-UV fluorescent substrates such as non-UV fluorescent paper, non-UV fluorescent polymer films, and non-UV fluorescent paperboard using continuous inkjet (CIJ) printing methods and equipment. Such CIJ printing methods and equipment can include the use of high-speed inkjet printers, such as those commercially available from Eastman Kodak Company under the brand names KODAK PROSPER S-Series and KODAK PROSPER Plus printing systems.

[0116] There are several CIJ printing methods and apparatuses known in the art, and the present invention is not limited to specific CIJ methods and apparatuses, but there may be certain CIJ methods and apparatuses that are more useful than other methods and apparatuses, such as the Eastman Kodak Company system and method mentioned above. Typically, such CIJ methods can use the aqueous color pigment-based ink capable of fluorescence according to the present invention alone to provide a colored latent fluorescent image, or it can use a combination of aqueous color pigment-based inks to provide a combination of images, some of which are colored latent fluorescent images and others are colored and non-fluorescent images, each of which is ejected from one or more ink reservoirs through one or more print heads (including nozzles), and unprinted ink (capable of fluorescence) and non-fluorescent aqueous color pigment-based inks are collected and recycled through the printing system multiple times until each ink is used up. In addition, available CIJ printing systems can have a replenisher system of one or more aqueous color pigment-based inks that can or cannot fluoresce incorporated. For example, details of available CIJ methods and apparatus are provided in, for example, U.S. Patent No. 8,173,215 (Sowinski et al.).

[0117] For example, an aqueous colored pigment-based ink capable of fluorescing can be applied to (inkjet printed onto) an outer surface of a non-UV fluorescent substrate using continuous inkjet printing, wherein the aqueous colored pigment-based ink is provided from a main fluid supply which can supply the aqueous colored pigment-based ink capable of fluorescing and can receive return unprinted aqueous colored pigment-based ink capable of fluorescing.

[0118] In a kind of available CIJ inkjet printing method, each aqueous color pigment-based ink capable of fluorescence of the present invention, such as aqueous black pigment-based ink capable of fluorescence, can be ejected or printed from the main fluid supply dedicated only to it, as a continuous stream of each aqueous color pigment-based ink capable of fluorescence, which can be divided into both printing droplets and non-printing droplets. The non-printing droplets of each aqueous color pigment-based ink capable of fluorescence can be collected and returned to its respective main fluid supply using a suitable collection device, such as a "catcher". This entire inkjet printing scheme can be implemented by inkjet printing an aqueous black pigment-based ink capable of fluorescence alone, or inkjet printing a variety of aqueous color pigment-based inks, all of which can provide colored latent fluorescent images. In other cases, one or more colored latent fluorescent images can be provided together with one or more non-fluorescent colored or colorless images using one or more non-fluorescent aqueous colored or colorless pigment-based inks, respectively. One or more aqueous colored pigment-based inks of all types (fluorescent or non-fluorescent) are inkjet printed in a selected sequence that can be controlled by software and digital input to provide a latent fluorescent monochrome or latent fluorescent multicolor image on the outer surface of a non-UV fluorescent substrate in a controlled manner.

[0119] In a particularly useful embodiment, the aqueous color pigment-based ink capable of fluorescence can be supplied as a continuous stream from a suitable main fluid supply, and the continuous stream can be divided into printing droplets and non-printing droplets, and the non-printing droplets are collected and returned to the main fluid supply from the continuous stream for future use. This main fluid supply of the aqueous color pigment-based ink capable of fluorescence can be supplemented with additional ink or with a supplementary fluid that is mainly water, so that the ink viscosity is maintained. For example, the method of the present invention can include continuously recycling unused aqueous color pigment-based ink capable of fluorescence to an inkjet printer.

[0120] After applying an aqueous colored pigment-based ink capable of fluorescence to the outer surface of a suitable non-UV fluorescent substrate to provide a colored latent fluorescent image, a colorless aqueous composition or fluid can be applied to the colored latent fluorescent image, for example, using continuous inkjet printing. For example, according to U.S. Patent Application Publication 2018 / 0051184 (Lussier et al.), a colorless paint or a colorless aqueous composition can be applied to a colored latent fluorescent image of any color, a black latent fluorescent image, or a multicolor latent fluorescent image. However, it is important that such a colorless aqueous composition or fluid does not absorb a significant amount of light at the excitation wavelength of the non-polymer fluorophore after it is applied to the colored latent fluorescent image, or when the colored latent fluorescent image is "excited" to display the fluorescent text or image to be observed. In addition, the applied colorless aqueous composition should not absorb a significant amount at the emission wavelength after the excitation of the colored latent fluorescent image. "Significant" means that such excitation absorption or emission absorption does not exceed 5% of the excitation absorption or emission absorption that would be performed if the colorless aqueous composition was not present.

[0121] A press replenishment system for maintaining the quality of aqueous colored pigment-based inks capable of fluorescence and counteracting the effects of evaporation of volatile components may also be used in the practice of the present invention, and the press replenishment system measures ink resistivity. Such systems are described in, for example, U.S. Patent 5,526,026 (Bowers) and EP 0597628B1 (Loyd et al.). Available CIJ printing methods and apparatus for sensing aqueous colored pigment-based ink concentrations using other means are disclosed in U.S. Patent 7,221,440 (McCann et al.), and are also disclosed in EP 0571,784B1 (McCann et al.) and EP 1,013,450B1 (Woolard et al.).

[0122] In some embodiments, the basic replenishment of the aqueous color pigment-based ink can be performed as a fluid system comprising an ink resistivity measurement unit, through which the aqueous color pigment-based ink capable of fluorescence is passed when it is recirculated through the ink processing portion (including the print head) of the system. The computing device determines the resistance of the ink resistivity unit. The logic and control unit controls the transfer of the aqueous color pigment-based ink from the supplementary "ink" supply and the transfer of the aqueous particle-free fluid ("carrier fluid") from the supplementary carrier fluid supply to the main fluid supply of the system in response to the computing device to maintain the desired resistivity in the aqueous colored inkjet ink composition. The volume of the aqueous color pigment-based ink capable of fluorescence can be monitored by the float valve position, and when the predetermined volume has been exhausted, the predetermined volume is replaced by the aqueous color pigment-based ink from the supplementary "ink" supply or the carrier fluid from the supplementary carrier fluid supply.

[0123] In other embodiments, the method according to the present invention may further include supplementing the main fluid supply of the aqueous colored pigment-based ink capable of fluorescence with an aqueous particle-free fluid, wherein the aqueous particle-free fluid has a dynamic viscosity less than or equal to 5 centipoise (5 mPa-sec) as measured using a rolling ball viscometer at 25°C.

[0124] Further details on available CIJ printing systems and equipment are provided in, for example, U.S. Patents 6,943,037 (Anagnostopoulos et al.), 6,588,888 (Jeanmaire et al.), 6,554,410 (Jeanmaire et al.), 6,682,182 (Jeanmaire et al.), 6,793,328 (Jeanmaire et al.), 6,866,370 (Jeanmaire et al.), 6,575,566 (Jeanmaire et al.), and 6,517,197 (Hawkins et al.) and U.S. Patent Application Publication 2002 / 0202054 (Jeanmaire et al.).

[0125] Thus, it is possible to continuously inkjet print an aqueous colored pigment-based ink onto the outer surface of a non-UV fluorescent substrate to form a colored latent fluorescent pattern (or image), and this can be achieved using a suitable continuous inkjet (CIJ) deposition system using non-fluorescent aqueous colored pigment-based inks (described below) to provide a colored latent fluorescent image that is registered with other printed (non-fluorescent) color patterns.

[0126] As described above, the aqueous colored pigment-based ink capable of fluorescence according to the present invention can be used in a continuous inkjet printing method in combination with the application or continuous inkjet printing of a non-fluorescent aqueous colored pigment-based or non-fluorescent colored dye-based ink. Various non-fluorescent aqueous colored pigment-based or dye-based inks are known in the art, and they can be suitable for a method in which one or more of them and the aqueous colored pigment-based ink capable of fluorescence of the present invention are used in combination in the same or different continuous inkjet printing devices.

[0127] In some embodiments, the aqueous colored pigment-based ink capable of fluorescing is an aqueous black pigment-based ink, and the colored latent fluorescent image is a black latent fluorescent image. As used herein, the term "colored latent fluorescent image" refers to an image that visually appears colored in the absence of fluorescent excitation radiation.

[0128] The non-fluorescent aqueous colored pigment-based ink can be prepared from a suitable aqueous dispersion of one or more colored particulate pigments using known dispersants and dispersing means (e.g., as described above). The resulting aqueous colored pigment-based dispersion can be mixed with one or more wetting agents (as described above), and the components can be formulated in an aqueous medium (primarily water) to provide a non-fluorescent aqueous colored pigment-based ink, each having a dynamic viscosity of less than or equal to 10 centipoise (10 mPa-sec), or less than or equal to 5 centipoise (3 mPa-sec), or even less than or equal to 3 centipoise (1.5 mPa-sec), all of which are measured at 25° C. using a rolling ball viscometer as described above.

[0129] Useful non-fluorescent aqueous colored pigment-based inks may also contain one or more polymeric or non-polymeric dispersants known in the art (as described above), or the pigment may be self-dispersible and therefore dispersible.

[0130] Such non-fluorescent aqueous colored pigment-based inks may contain the above-mentioned pigment colorants, as well as various humectants, anionically charged polymers and other addenda as described above. The amounts of the various components will be apparent to those skilled in the art from a number of published literature including those described above.

[0131] Water is typically present in each non-fluorescent aqueous colored pigment-based ink in an amount of at least 75 wt % or at least 80 wt %, and typically not more than 90 wt %, based on the total weight of the aqueous colored pigment-based ink.

[0132] Furthermore, if desired, the pH of each non-fluorescent aqueous colored pigment-based ink may be adjusted to at least 8 and up to and including 12, or more likely to at least 8 and up to and including 10, or in some embodiments to at least 8 and up to and including 9.5 using known chemicals and processes.

[0133] The technician can use routine experiments to determine the best time to inkjet print one or more non-fluorescent aqueous colored or colorless pigment-based inks relative to inkjet printing the aqueous colored pigment-based ink of the present invention. Therefore, the inkjet printing of the aqueous colored pigment-based ink of the present invention can be performed before, at the same time or after the inkjet printing of one or more non-fluorescent aqueous colored pigment-based inks outside the present invention, as long as the advantages of the present invention as described above are not significantly reduced.

[0134] Inkjet printed products

[0135] In order to obtain optimal colored latent fluorescent image density and reduced smearing, the substrates to which the aqueous colored pigment-based ink capable of fluorescence is applied, for example by inkjet printing, such as continuous inkjet printing, are those that are considered to be "non-UV fluorescent" substrates, which means that when excited by fluorescent excitation radiation having a peak of at least 200 nm and up to and including 400 nm, the substrate does not exhibit an emission peak of at least 400 nm and up to and including 750 nm to any detectable extent. This allows the colored latent fluorescent image printed using the present invention to stand out in contrast to the unprinted non-UV fluorescent substrate outer surface.

[0136] In addition, in order to obtain the final advantage of the present invention, it is particularly useful that this type of non-UV fluorescent substrate usually has limited porosity, so that before the aqueous colored pigment-based ink applied is dried, the aqueous colored pigment-based ink applied is not absorbed in a large amount into the inside of the non-UV fluorescent substrate. Except the porosity of substrate, the physical properties of ink, such as viscosity, surface tension and pigment particle size, can determine the degree that aqueous colored pigment-based ink penetrates into the inside of porous non-UV fluorescent substrate. On the contrary, those skilled in the art will be able to use the teaching provided herein and test various aqueous colored pigment-based inks to see which kind of will provide the desired colored latent fluorescent image relative to the outer surface of non-UV fluorescent substrate before drying. In some applications used in the present invention, lighter colored latent fluorescent images can be suitable, and in other applications used in the present invention, more visible (more concentrated) colored latent fluorescent images can be required, and non-UV fluorescent substrates will need to have very small surface porosity, such as from other waterproof coatings known in resin coating or paper industry.

[0137] Typically, available non-UV fluorescent substrate materials with these properties can be paper-like and contain cellulosic materials that are coated with resin- or clay-based treatment surfaces to reduce surface porosity. Supercalendering is another method that can be used to reduce the surface porosity of paper-based substrates. However, it is generally desirable that non-UV fluorescent substrates have matte surfaces and are generally not reflective or shiny substrates. Such available non-UV fluorescent substrates can be obtained from various commercial sources, including but not limited to International Paper, Sappi, NewPage, Appleton Coated, Abitib-Bowater, Mohawk Papers, Verso, Mitsubishi, Norpac and Domtar. Non-paper-based or so-called synthetic paper-based substrates can also be used, as long as they are non-UV fluorescent as defined above.

[0138] Additionally, the non-UV fluorescent substrates used in the practice of the present invention may have an opacity of at least 30% or at least 50% as measured using the standard TAPPI 425 Op-16 opacity test, and may have a colorimetry defined by an a* value of at least -5 and up to and including +5, and a b* value of independently at least -5 and up to and including +5, or more likely each of the a* and b* values ​​are independently at least -3 and up to and including +3.

[0139] On the other hand, in certain embodiments, transparent or translucent film-based substrates may also be used in combination with the aqueous colored pigment-based inks of the present invention, as long as the film is non-UV fluorescent as defined above.

[0140] Thus, articles prepared according to the present invention include a non-UV fluorescent substrate (as described above) onto which an aqueous colored pigment-based ink capable of fluorescence (e.g., an aqueous black pigment-based ink capable of fluorescence) has been disposed, for example, by DOD or continuous inkjet printing (as described above) to provide a colored latent fluorescent image, for example, a black latent fluorescent image. As described above, a non-fluorescent colored or non-fluorescent colorless image may also be present on the same non-UV fluorescent substrate.

[0141] In each colored latent fluorescent image provided on such an article, one or more pigment colorants (e.g., one or more black pigments) as described above may be present in an amount of at least 10 weight percent or at least 40 weight percent, and up to and including 60 weight percent or up to and including 80 weight percent, based on the total weight of the colored latent fluorescent image.

[0142] In addition, one or more non-polymeric fluorophores as described above may be present in each colored latent fluorescent image in an amount of at least 1 wt % or at least 5 wt %, and up to and including 10 wt % or up to and including 20 wt %, based on the total weight of the colored latent fluorescent image.

[0143] More particularly, the sum of the non-polymeric fluorophores and pigment colorants may be present in the colored latent fluorescent image in a weight ratio of sum of pigment colorants to sum of non-polymeric fluorophores of 70:1 to 0.5:1, or more likely in a weight ratio of 50:1 to 1:1.

[0144] The present invention provides at least the following embodiments and combinations thereof, but other combinations of features as would be understood by a skilled artisan from the teachings of this disclosure are considered to be within the present invention:

[0145] 1. A water-based colored pigment-based ink capable of fluorescence, comprising:

[0146] Pigment colorant in an amount of at least 1 wt % and up to and including 7 wt %;

[0147] a non-polymeric fluorophore that exhibits an emission peak of at least 400 nm and up to and including 750 nm when excited by fluorescent excitation radiation having a peak of at least 200 nm and up to and including 400 nm, and that is present in an amount of at least 0.1 wt. % and up to and including 2 wt. %; and

[0148] an aqueous medium comprising water,

[0149] All amounts are based on the total weight of the aqueous colored pigment-based ink capable of fluorescing.

[0150] 2. An ink set comprising two or more aqueous pigment-based inks, the ink set comprising:

[0151] (I) at least one aqueous colored pigment-based ink capable of fluorescence according to Embodiment 1; and

[0152] (II) at least one aqueous colored pigment-based ink which is non-fluorescent and comprises a pigment colorant in an amount of at least 1 wt. %; and an aqueous medium comprising water, the amount of colored pigment being based on the total weight of the non-fluorescent aqueous colored pigment-based ink.

[0153] 3. The ink set according to embodiment 2, wherein the (II) at least one non-fluorescent aqueous colored pigment-based ink comprises at least one pigment colorant selected from the group consisting of a cyan pigment, a magenta pigment, a yellow pigment and a black pigment.

[0154] 4. An aqueous colored pigment-based ink according to embodiment 1 or an ink set according to embodiment 2 or 3, wherein the pigment colorant is a black pigment, and when in dry form on a non-UV fluorescent substrate, the aqueous colored pigment-based ink capable of fluorescence exhibits a CIE L* value of 50 or less, an a* value of -20 to and including +20 and a CIE b* value of at least -15 to and including +20 when observed under illumination excluding the fluorescence excitation wavelength, and the aqueous colored pigment-based ink is present in dry form on a non-UV fluorescent substrate.

[0155] 5. An aqueous colored pigment-based ink capable of fluorescence in an ink set according to embodiment 1 or 4 or according to any one of embodiments 2 to 4, wherein the pigment colorant is an anionically stabilized pigment.

[0156] 6. An aqueous colored pigment-based ink capable of fluorescence in an ink set according to any one of embodiments 1, 4 or 5 or according to any one of embodiments 2 to 6, having a viscosity of at least 1 centipoise (1 mPa-sec) and up to and including 50 centipoise (50 mPa-sec), as measured using a rolling ball viscometer at 25°C.

[0157] 7. An aqueous colored pigment-based ink capable of fluorescence in an ink set according to any one of embodiments 1 and 4 to 6 or according to any one of embodiments 2 to 6, wherein the non-polymeric fluorophore has a water solubility of at least 0.1 wt. % at 25°C.

[0158] 8. An aqueous colored pigment-based ink capable of fluorescence in an ink set according to any one of embodiments 1 and 4 to 7 or according to any one of embodiments 2 to 7, wherein the non-polymeric fluorophore is colorless.

[0159] 9. An aqueous colored pigment-based ink capable of fluorescence in an ink set according to any one of embodiments 1 and 4 to 8 or according to any one of embodiments 2 to 8, wherein the non-polymeric fluorophore is a diaminostilbene compound comprising a plurality of sulfonic acid groups.

[0160] 10. An aqueous colored pigment-based ink capable of fluorescence in an ink set according to any one of embodiments 1 and 4 to 9 or according to any one of embodiments 2 to 9, wherein the non-polymer fluorophore is present in an amount of at least 0.2 wt % and up to and including 1 wt % based on the total weight of the aqueous colored pigment-based ink capable of fluorescence.

[0161] 11. The aqueous colored pigment-based ink capable of fluorescence in the ink set according to any one of embodiments 1 and 4 to 10 or according to any one of embodiments 2 to 10, which is an aqueous black pigment-based ink capable of fluorescence, wherein the pigment colorant is an anionically stabilized black pigment, and the pigment colorant is present in an amount of at least 3 weight % and up to and including 7 weight % based on the total weight of the aqueous black pigment-based ink capable of fluorescence.

[0162] 12. The aqueous colored pigment-based ink capable of fluorescence in the ink set according to any one of embodiments 1 and 4 to 11 or according to any one of embodiments 2 to 11, which is an aqueous black pigment-based ink capable of fluorescence, and based on the total weight of the aqueous black pigment-based ink capable of fluorescence, the aqueous colored pigment-based ink further contains one or more water-soluble black dyes in a total amount of at least 0.1 weight % and up to and including 2 weight %.

[0163] 13. The aqueous colored pigment-based ink capable of fluorescence in the ink set according to any one of embodiments 1 and 4 to 12 or according to any one of embodiments 2 to 12, which is an aqueous black pigment-based ink capable of fluorescence, wherein the pigment colorant is carbon black.

[0164] 14. An aqueous colored pigment-based ink capable of fluorescing in an ink set according to any one of embodiments 1 and 4 to 13 or according to any one of embodiments 2 to 13, having a solids content of at least 1% solids and up to and including 20% ​​solids.

[0165] 15. An aqueous colored pigment-based ink capable of fluorescence in an ink set according to any one of embodiments 1 and 4 to 14 or according to any one of embodiments 2 to 14, which contains one or more of a biocide, a wetting agent, a defoamer, a dispersant and an anionically charged polymer component having an acid value of at least 50.

[0166] 16. The aqueous colored pigment-based ink capable of fluorescence in the ink set according to any one of embodiments 1 and 4 to 15 or according to any one of embodiments 2 to 15, which is an aqueous black pigment-based ink capable of fluorescence, and the aqueous colored pigment-based ink further contains an anionically charged styrene-acrylic acid copolymer having an acid value of at least 50, or an anionically charged polyurethane having an acid value of at least 50.

[0167] 17. A method of providing a colored image that exhibits fluorescence when exposed to fluorescence stimulating radiation, the method comprising:

[0168] The aqueous colored pigment-based ink capable of fluorescing according to any one of embodiments 1 to 16 is image-wise applied onto the outer surface of a non-UV fluorescent substrate to provide a colored latent fluorescent image on the outer surface of the non-UV fluorescent substrate.

[0169] 18. The method of embodiment 17, wherein the aqueous colored pigment-based ink is applied imagewise using inkjet printing.

[0170] 19. The method according to embodiment 17 or 18, wherein the aqueous colored pigment-based ink is applied imagewise using continuous inkjet printing.

[0171] 20. A method according to embodiment 19, wherein the fluorescent aqueous pigment-based ink is provided for continuous inkjet printing from a main fluid supply, and the main fluid supply can supply the fluorescent aqueous pigment-based ink and can receive returned fluorescent unprinted aqueous pigment-based ink.

[0172] 21. The method according to embodiment 19 or 20, comprising:

[0173] Continuously inkjet printing a non-fluorescent aqueous non-black colored pigment-based ink on the outer surface of the non-UV fluorescent substrate to provide a non-black colored image on the outer surface of the non-UV fluorescent substrate; and

[0174] continuously inkjet printing the aqueous black pigment-based ink capable of fluorescing onto at least a portion of the non-black colored image to provide a black latent fluorescent image capable of fluorescing onto at least a portion of the non-black colored image,

[0175] The non-fluorescent aqueous colored non-black pigment-based ink comprises a colored non-black pigment in an amount of at least 1 wt % and an aqueous medium comprising water, wherein the amount of the colored non-black pigment is based on the total weight of the aqueous colored non-black pigment-based ink.

[0176] 22. A method according to embodiment 21, wherein the non-black colored image is a multi-color image.

[0177] 23. The method according to any one of embodiments 19 to 22, further comprising:

[0178] A colorless composition is continuously inkjet printed onto a colored latent fluorescent image on the outer surface of a non-UV fluorescent substrate.

[0179] 24. The method according to any one of embodiments 17 to 23, wherein the non-UV fluorescent substrate is an article to be used as a security document, currency or lottery ticket.

[0180] 25. The method according to any one of embodiments 17 to 24, which is a method for marking an article with a colored latent fluorescent image as a security mark for identification, information or decoration.

[0181] 26. A method according to embodiment 25, wherein the article marked with the colored latent fluorescent image is a security document, currency or lottery ticket, and the method comprises continuous inkjet printing of an aqueous colored pigment-based ink capable of fluorescing, and the aqueous colored pigment-based ink is an aqueous black pigment-based ink capable of fluorescing, to provide a colored latent fluorescent image on the security document, currency or lottery ticket.

[0182] 27. The method according to any one of embodiments 17 to 26, using a continuous inkjet printer, comprising:

[0183] providing a main fluid supply of said aqueous colored pigment-based ink capable of fluorescing;

[0184] supplying an aqueous colored pigment-based ink capable of fluorescing from said primary fluid supply to a droplet generator mechanism;

[0185] ejecting from a droplet generator mechanism a continuous stream of an aqueous color pigment-based ink capable of fluorescing, the continuous stream being divided into spaced droplets of the aqueous color pigment-based ink capable of fluorescing;

[0186] controlling the spaced droplets of the aqueous color pigment based ink capable of fluorescence to distinguish between printed droplets of the aqueous color pigment based ink capable of fluorescence and non-printed droplets of the aqueous color pigment based ink capable of fluorescence, and the non-printed droplets of the aqueous color pigment based ink are collected and returned to the main fluid supply,

[0187] Thereby a colored latent fluorescent image is formed on the outer surface of the non-UV fluorescent substrate using the printed droplets of the aqueous colored pigment-based ink capable of fluorescing.

[0188] 28. The method according to embodiment 27, further comprising:

[0189] Unused fluorescent capable aqueous colored pigment based ink is continuously recycled to the inkjet printer.

[0190] 29. An article obtained by the method according to any one of embodiments 17 to 28, the article comprising a non-UV fluorescent substrate having a colored latent fluorescent image disposed on an outer surface thereof, the colored latent fluorescent image comprising:

[0191] Pigments and colorants; and

[0192] A non-polymeric fluorophore that exhibits an emission peak of at least 400 nm and up to and including 750 nm when excited by fluorescent excitation radiation having a peak of at least 200 nm and up to and including 400 nm, wherein the weight ratio of the pigment colorant to the non-polymeric fluorophore in the fluorescent image is 70:1 to 0.5:1.

[0193] 30. The inkjet-printed article of embodiment 29, wherein the pigment colorant is an anionically stabilized black pigment.

[0194] 31. An inkjet printed article according to embodiment 29 or 30 which is a security document, currency or lottery ticket.

[0195] 32. A method of detecting a fluorescent image in an inkjet-printed article according to any one of embodiments 29 to 31, the method comprising:

[0196] A colored latent fluorescent image disposed on a non-UV fluorescent substrate is illuminated on an outer surface of the non-UV fluorescent substrate with fluorescent excitation radiation having a peak of at least 200 nm and up to and including 400 nm, the colored latent fluorescent image having an emission peak of at least 400 nm and up to and including 750 nm.

[0197] The following examples are provided to illustrate the practice of the present invention and are not intended to be limiting in any way. Materials for which a specific commercial source is not described can be obtained from a variety of commercial sources, as will be apparent to those skilled in the art.

[0198] The following specific materials were used in the following examples. All other materials used in the following examples were obtained from various commercial sources.

[0199] The non-polymeric fluorophores FA-1, FA-2 and FA-3 used in the working examples are identified by the following structures:

[0200] FA-1

[0201] CAS No. 41098-56-0

[0202]

[0203] 1,4-Benzene disulfonic acid, 2,2'-[1,2-ethylenediylbis[(3-sulfo-4,1-phenylene)imino[6-(diethylamino)-1,3,5-triazine-4,2-diyl]imino]]di-, hexasodium salt (as SFP is commercially available).

[0204] FA-2

[0205] CAS No. 16470-24-9

[0206]

[0207] 5-[[4-[Bis(2-hydroxyethyl)amino]-6-(4-sulfonatoanilino-1,3,5-triazin-2-yl]amino]-2-[(E)-2-[4-[[4-[bis(2-hydroxyethyl)amino]-6-(4-sulfonatoanilino)-1,3,5-triazin-2-yl]amino]-2-sulfonatophenyl]vinyl]benzenesulfonate, tetrasodium salt (commercially available as Fluorescent Brightener 220 from various sources).

[0208] FA-3

[0209] CAS No. 16090-02-1

[0210]

[0211] 2,2'-Stilbene disulfonic acid, 4,4'-bis((4-anilino-6-morpholino-s-triazin-2-yl)amino)-, disodium salt (commercially available as Fluorescent Brightener 71 from various commercial sources).

[0212] "Direct black dye" is a water-soluble dye and is available, for example, from Colorant Solutions under the name DB-168.

[0213] "MDEA acetate" means methyldiethanolammonium acetate, and can be obtained by mixing appropriate molar amounts of methyldiethanolamine and acetic acid.

[0214] TT-50S is a corrosion inhibitor available from PMC Specialties Group.

[0215] GXL is a biocide available from various commercial sources.

[0216] 440 is a nonionic surfactant available from Evonik Industries.

[0217] DF110L is a defoamer available from Evonik Industries.

[0218] "TEG" stands for triethylene glycol, and is available from various commercial sources.

[0219] Glycerol can be obtained from various commercial sources.

[0220] Anionically charged "polyurethane" dispersion polymers can be prepared using the teachings of US Patent No. 8,430,492 (referenced above).

[0221] Solution polymer "SA" refers to an anionically charged styrene-acrylic acid copolymer available from BASF.

[0222] Solution Polymer "PVP" refers to poly(vinylpyrrolidone), which is available from various commercial sources.

[0223] Polymeric Dispersant PI is an acrylic polymeric dispersant prepared using the synthesis method described in Example 1 of US Patent Application Publication No. 2007 / 0043144 (House et al.).

[0224] The P-2 active component is the anionically charged polyurethane described above.

[0225] The P-3 active ingredient is the anionically charged styrene-acrylic acid copolymer described above.

[0226] All examples of aqueous color pigment-based inks described below, labeled with "Inv," are in accordance with the present invention, while examples labeled with "C" are comparative (outside the present invention).

[0227] Water-based pigment dispersions

[0228] Black Pigment Dispersion KD-1:

[0229] In a 10 liter mixing vessel, water (1,000 g) and a solution of polymer dispersant P-1 (1,000 g of a 19.9 wt% solution) were added. Agitation was initiated using a 10.2 cm, annular disperser impeller (Hockmeyer Equipment Corp. D-Blade) driven by a high shear mixer and centered 5 cm above the bottom of the mixing vessel. A Cabot Corp. BLACK 900 carbon black pigment (500 g) was slowly added to the stirred mixture. Grinding media (3000 g) containing polystyrene resin beads having an average particle size of 50 μm was slowly added while increasing the impeller speed. The resulting mixture containing black pigment was ground at an internal temperature of 25-35° C. at an impeller blade tip speed of about 19 m / sec for 20 hours.

[0230] The dispersion / media grind mixture was then diluted with a solution of water (1,667 g) to a final black pigment concentration of 12 wt%, a polymer dispersant concentration of 4.8 wt%, and a theoretical dispersion batch size of about 4,167 g. The impeller was removed and the grinding media was separated from the black pigment-containing dispersion by filtration. The dispersion was filtered through a 0.3-μm Pall Corp. PROFILE Additional filtration through a depth filter yielded about 4 kg of a dispersion containing black pigment.

[0231] Black pigment dispersion particle size was determined by Microtrac, Inc. The particle size distribution was determined by an NPA 150 dynamic light scattering particle size analyzer to have a volume weighted 50th percentile particle size distribution diameter of about 55 nm, and a 95th percentile particle size distribution diameter of about 99 nm.

[0232] Cyan Pigment Dispersion CD-1:

[0233] Pigment dispersion CD-1 is an aqueous dispersion containing 12 wt % PB15 / 4 cyan pigment (obtained from Sun Chemical) and 6-9 wt % of polymer dispersant P-1 having a weight average molecular weight of 9000, and the pigment dispersion CD-1 was prepared as described in Example 1 of U.S. Patent Application Publication 2007 / 0043144 (mentioned above).

[0234] Yellow pigment dispersion YD-1:

[0235] Pigment Dispersion YD-1 is an aqueous dispersion containing 12 wt % yellow pigment 74 (obtained from Sun Chemical) and 3-4 wt % of polymer dispersant P-1 having a weight average molecular weight of 9000, and the pigment dispersion YD-1 was prepared as described in Example 1 of U.S. Patent Application Publication 2007 / 0043144 (mentioned above).

[0236] Magenta Pigment Dispersion MD-1:

[0237] Pigment dispersion MD-1 is an aqueous dispersion containing 12 wt % Cinquasia magenta pigment (obtained from BASF) and 3-5 wt % of polymer dispersant P-1 having a weight average molecular weight of 9000, and the pigment dispersion MD-1 was prepared as described in Example 1 of U.S. Patent Application Publication No. 2007 / 0043144 (mentioned above).

[0238] Preparation of water-based pigment-based ink

[0239] Preparation of water-based black pigment-based ink:

[0240] All of the aqueous black pigment-based inks described below (both the inventive aqueous black pigment-based inks capable of fluorescence according to the present invention and comparative aqueous black pigment-based inks outside the present invention) were prepared using the above-described black pigment dispersion KD-1 in combination with the components in Table I shown below in the relative proportions listed. In a representative process, 2.0 kg of each aqueous black pigment-based ink was prepared as follows: the components of Table I were added to a 2-liter high-density polyethylene or stainless steel container, using a 2-inch (5.1 cm) top impeller or a 1-inch (2.54 cm) magnetic stirring bar rotating at about 500 rpm to provide good mixing. The components were added in the functional component order listed in Table I. Each resulting aqueous black pigment-based ink was mixed for about 2 minutes between component additions, and then the final mixture was stirred for 1 hour after all components were added. Each aqueous black pigment-based ink was passed through a 1-inch (2.54 cm) Pall Corp. 0.45 μm The N66 cartridge filter filters at a rate of 0.2-0.5 liters / min / inch of media (equivalent to 0.079-0.20 liters / min / cm of media).

[0241] Thus, Table I below shows the composition of both inventive ("Inv") and comparative ("C") aqueous black pigment-based inks.

[0242]

[0243]

[0244] Each of the inventive (Inv) and comparative (C) aqueous black pigment-based inks shown in Table I was evaluated by inkjet printing a step wedge on a sample of non-UV fluorescent security paper (typically used for lottery tickets) and by drawdown on digital book paper using a Gardco ACCU-LAB drawdown machine using a No. 3 wire-wound rod to form a black latent fluorescent image on the non-UV fluorescent security paper sample. Such black latent fluorescent images applied on the non-UV fluorescent security paper sample thus formed both the inventive articles according to the present invention and the comparative articles outside the scope of the present invention. When viewed under UV irradiation using a commercially available UV lamp, all of the black latent fluorescent images on the inventive articles appeared to glow bluish white (fluorescent) to varying degrees, but under UV irradiation, the black latent fluorescent images on the comparative article samples appeared black (no obvious latent fluorescent image). The fluorescence of a 100% laydown patch of each of the applied black latent fluorescent images was evaluated using a Perkin-Elmer LS-50B fluorescence spectrophotometer to provide 365 nm excitation radiation to characterize each black latent fluorescent image obtained from the corresponding aqueous black pigment-based ink from Table I. The following test conditions were used in this analysis:

[0245] Luminescent substance: Pulsed xenon

[0246] Slit width: emission: 2.5nm; excitation: 2.5nm

[0247] Scanning speed: 250nm / min

[0248] Excitation wavelength: 365nm

[0249] Figure 1 The emission spectra observed for the inventive examples Inv-1, Inv-4 and Inv-5, all of which contain the non-polymeric fluorophore FA-1, and the comparative example C-1, which is the same as the inventive examples Inv-1, Inv-4 and Inv-5 except that it does not contain the non-polymeric fluorophore FA-1, are shown. Figure 1 As can be seen, even inventive example Inv-5, which contains only 0.5 wt% of the non-polymeric fluorophore FA-1, exhibits strong emission between 400 and 500 nm compared to comparative example C-1, for which no emission was observed. Increasing the concentration of the non-polymeric fluorophore to 0.75 wt% (inventive example Inv-4) produces a stronger emission spectrum in the resulting black latent fluorescent image, but increasing the amount to 1.0 wt% (inventive example Inv-1) shows only a small additional increase in the intensity of the emission spectrum of the black latent fluorescent image obtained with the aqueous black pigment-based ink.

[0250] Figure 2The emission spectra obtained for the inventive example Inv-2 containing the non-polymeric fluorophore FA-2 and the comparative example C-1 are shown, which is the same as the inventive example Inv-2 except that it does not contain the non-polymeric fluorophore FA-2. This shows that the non-polymeric FA-2 is also effective in producing a strong fluorescence emission spectrum in a black latent fluorescent image.

[0251] Figure 3 The emission spectra obtained for the inventive example Inv-3 containing the non-polymeric fluorophore FA-3 and the comparative example C-1 are shown, which is the same as the inventive example Inv-3 except that it does not contain the non-polymeric fluorophore FA-3. The results show that the non-polymeric fluorophore FA-3 is also effective in producing a strong fluorescence emission spectrum in a black latent fluorescent image.

[0252] Figure 4 The emission spectra obtained from the inventive example Inv-6, which contains the non-polymeric fluorophore FA-1 in an aqueous black pigment-based ink without added black dye, and the comparative example C-2 are shown, which are the same as the inventive example Inv-6 except that it does not contain the non-polymeric fluorophore FA-1. These results show that the emission spectrum of the non-polymeric fluorophore FA-1 is about four times stronger in the absence of added black dye than in the inventive example Inv-4, which contains the same amount of non-polymeric fluorophore FA-1 but also contains 1.5 wt% black dye.

[0253] The printed inventive and comparative samples were also qualitatively evaluated for darkness and wet rub resistance and all were found to exhibit satisfactory performance.

[0254] Prepare aqueous cyan, yellow, and magenta pigment-based inks:

[0255] Aqueous colored pigment-based inks capable of fluorescence with non-black pigment colorants of the present invention were also prepared to demonstrate the desired objectives of the present invention. These aqueous colored pigment-based inks of the present invention (Inv-7, Inv-8 and Inv-9) were prepared using the components described in Table II below, which were combined using a method similar to that described above for aqueous black pigment-based inks.

[0256] Table II

[0257]

[0258]

[0259] The aqueous colored pigment-based inks of the present invention containing non-black pigment colorants shown in Table II also exhibit the fluorescent properties used in the present invention when the drawdown or printed samples (latent colored fluorescent images) on non-UV fluorescent substrates are viewed under a commercially available UV lamp. In each case, the fluorescence observed in the colored latent fluorescent image is a bluish white color and is not the color of the aqueous colored pigment-based ink that has been applied.

[0260] Samples prepared in the same manner with comparative cyan, magenta and yellow aqueous pigment inks without added non-polymeric fluorophores appeared dark and did not exhibit any fluorescence when viewed under the same commercially available UV lamp. These inks are commercially available from Eastman Kodak Company as KODAK PROSPER Press Pigment Cyan, Magenta and Yellow inks, respectively.

[0261] The following examples illustrate the practice of the present invention using a commercial DOD inkjet printer (described below) and are not intended to be limiting in any way. Materials used in these examples without specifying a particular commercial source may be obtained from a variety of commercial sources, which will be apparent to those skilled in the art.

[0262] Each of the inventive (Inv; able to fluoresce) and comparative (C; not able to fluoresce) aqueous black pigment-based inks shown in Table I above was evaluated by inkjet printing some random text and stepped light wedges on three different substrates. Each aqueous black pigment-based ink was loaded into a T0441 compatible aftermarket refillable ink cartridge sold by InkOwl.com and inkjet printed on samples of each of the three substrates using an Epson Stylus C86 printer. Substrate 1 was a conventional paper known in the industry as DataSpeed ​​Laser. Substrate 2 was a non-UV fluorescent security paper, of which the typical is used for lottery tickets. Substrate 3 comprised a clear poly(ethylene terephthalate) film known in the industry as LPX-2, which had been coated on the surface to be inkjet printed with a primer commercially available from Eastman Kodak Company as KODAK PROSPER PRESS2-Part Film Optimizer Agent.

[0263] Substrate 1 contains a conventional fluorescent brightener that fluoresces brightly under UV irradiation. This fluorescent emission effectively eliminates any fluorescence to be provided by the colored latent fluorescent images that may be provided by the aqueous black pigment-based ink of the present invention, making them appear under UV irradiation identical to the non-fluorescent colored images provided by the comparative aqueous pigment-based ink. Under conventional visible light with no perceptible UV component, all inkjet printed image samples (from both the aqueous black pigment-based ink of the present invention and the comparative) appear black. For these experiments, it should be understood that the fluorescent brightener in Substrate 1 emits at the same wavelength as the non-polymeric fluorophore present in the aqueous black pigment-based ink of the present invention, but if the wavelength of the colored latent fluorescent image emission is already different from the wavelength of the emission from Substrate 1, then the skilled person would reasonably expect to see the characteristic emission from the aqueous colored pigment-based ink of the present invention.

[0264] Substrate 2 does not contain any fluorescent brightener, and therefore under UV irradiation, all black latent fluorescent images obtained from the aqueous colored pigment-based ink of the present invention appear to emit bluish white light (fluorescence) to varying degrees, while the colored images obtained from the comparative aqueous black pigment-based ink appear only black. Under conventional visible light without any perceptible UV component, all colored images (whether colored latent fluorescent images or not) appear black.

[0265] Substrate 3 also does not contain any fluorescent whitening agent, and under UV irradiation, all black latent fluorescent images obtained by the aqueous black pigment-based ink of the present invention appear as bluish white light (fluorescence) from the front side, while the colored images obtained by the comparative aqueous black pigment-based ink appear simply black. When the rear side of substrate 3 is irradiated with UV radiation, the black latent fluorescent images obtained by the aqueous black pigment-based ink of the present invention appear completely bluish white, to the extent that no underlying black concentration can be detected. Under the same illumination on the rear side, all colored images obtained by the comparative aqueous black pigment-based ink appear black. Under conventional visible light without any perceptible UV component, all colored images (whether latent fluorescent images or not) appear black from both the front and rear sides of substrate 3.

Claims

1. A water-based colored pigment-based ink capable of fluorescence, comprising: Pigment colorant in an amount of at least 1 wt % and up to and including 7 wt %; a non-polymeric fluorophore that exhibits an emission peak of at least 400 nm and up to and including 750 nm when excited by fluorescent excitation radiation having a peak of at least 200 nm and up to and including 400 nm, and that is present in an amount of at least 0.1 wt. % and up to and including 2 wt. %; and an aqueous medium comprising water, All amounts are based on the total weight of the aqueous colored pigment-based ink capable of fluorescing.

2. An ink set comprising two or more aqueous pigment-based inks, the ink set comprising: (I) at least one aqueous colored pigment-based ink capable of fluorescing according to claim 1; and (II) at least one aqueous colored pigment-based ink which is non-fluorescent and comprises a pigment colorant in an amount of at least 1 wt. %; and an aqueous medium comprising water, wherein the amount of the colored pigment is based on the total weight of the non-fluorescent aqueous colored pigment-based ink.

3. The ink set according to claim 2, wherein the (II) at least one non-fluorescent aqueous colored pigment-based ink comprises at least one pigment colorant selected from the group consisting of a cyan pigment, a magenta pigment, a yellow pigment and a black pigment.

4. An aqueous colored pigment-based ink in an ink set according to claim 1 or according to claim 2 or 3, wherein the pigment colorant is a black pigment and when in dry form on a non-UV fluorescent substrate, the aqueous colored pigment-based ink capable of fluorescing exhibits a CIE L* value of 50 or less, an a* value of -20 to and including +20 and a CIE b* value of at least -15 to and including +20 when viewed under illumination excluding the fluorescence excitation wavelength, and the aqueous colored pigment-based ink is present in dry form on a non-UV fluorescent substrate.

5. An aqueous coloured pigment-based ink capable of fluorescing in an ink set according to claim 1 or 4 or according to any one of claims 2 to 4, wherein the pigment colorant is an anionically stabilized pigment.

6. An aqueous colored pigment-based ink capable of fluorescing in an ink set according to any one of claims 1, 4 or 5 or according to any one of claims 2 to 6, having a viscosity of at least 1 centipoise (1 mPa-sec) and up to and including 50 centipoise (50 mPa-sec), as measured using a rolling ball viscometer at 25°C.

7. An aqueous coloured pigment-based ink capable of fluorescing in an ink set according to any one of claims 1 and 4 to 6 or according to any one of claims 2 to 6, wherein the non-polymeric fluorophore has a water solubility of at least 0.1 wt% at 25°C.

8. An aqueous coloured pigment-based ink capable of fluorescing in an ink set according to any one of claims 1 and 4 to 7 or according to any one of claims 2 to 7, wherein the non-polymeric fluorophore is colourless.

9. An aqueous coloured pigment-based ink capable of fluorescence in an ink set according to any one of claims 1 and 4 to 8 or according to any one of claims 2 to 8, wherein the non-polymeric fluorophore is a diaminostilbene compound comprising a plurality of sulfonic acid groups.

10. An aqueous colored pigment-based ink capable of fluorescence in an ink set according to any one of claims 1 and 4 to 9 or according to any one of claims 2 to 9, wherein the non-polymeric fluorophore is present in an amount of at least 0.2 wt. % and up to and including 1 wt. %, based on the total weight of the aqueous colored pigment-based ink capable of fluorescence.

11. The aqueous colored pigment-based ink capable of fluorescence in the ink set according to any one of claims 1 and 4 to 10 or according to any one of claims 2 to 10, which is an aqueous black pigment-based ink capable of fluorescence, wherein the pigment colorant is an anionically stabilized black pigment, and the pigment colorant is present in an amount of at least 3 wt.% and up to and including 7 wt.%, based on the total weight of the aqueous black pigment-based ink capable of fluorescence.

12. The aqueous colored pigment-based ink capable of fluorescence in the ink set according to any one of claims 1 and 4 to 11 or according to any one of claims 2 to 11, which is an aqueous black pigment-based ink capable of fluorescence, and the aqueous colored pigment-based ink further contains one or more water-soluble black dyes in a total amount of at least 0.1 wt. % and up to and including 2 wt. %, based on the total weight of the aqueous black pigment-based ink capable of fluorescence.

13. The aqueous colored pigment-based ink capable of fluorescence in the ink set according to any one of claims 1 and 4 to 12 or according to any one of claims 2 to 12, which is an aqueous black pigment-based ink capable of fluorescence, wherein the pigment colorant is carbon black.

14. An aqueous coloured pigment-based ink capable of fluorescing in an ink set according to any one of claims 1 and 4 to 13 or according to any one of claims 2 to 13 having a solids content of at least 1% solids and up to and including 20% ​​solids.

15. An aqueous colored pigment-based ink capable of fluorescence in an ink set according to any one of claims 1 and 4 to 14 or according to any one of claims 2 to 14, containing one or more of a biocide, a wetting agent, a defoamer, a dispersant and an anionically charged polymer component having an acid value of at least 50.

16. The aqueous colored pigment-based ink capable of fluorescence in the ink set according to any one of claims 1 and 4 to 15 or any one of claims 2 to 15, which is an aqueous black pigment-based ink capable of fluorescence, further comprising an anionically charged styrene-acrylic acid copolymer having an acid value of at least 50, or an anionically charged polyurethane having an acid value of at least 50.

17. A method of providing a colored image that exhibits fluorescence when exposed to fluorescence stimulating radiation, the method comprising: An aqueous colored pigment-based ink capable of fluorescing according to any one of claims 1 to 16 is image-wise applied onto an outer surface of a non-UV fluorescent substrate to provide a colored latent fluorescent image on the outer surface of the non-UV fluorescent substrate.

18. The method of claim 17, wherein the aqueous colored pigment-based ink is applied imagewise using inkjet printing.

19. A method according to claim 17 or 18, wherein the aqueous coloured pigment-based ink is applied imagewise using continuous inkjet printing.

20. A method according to claim 19, wherein the fluorescent aqueous pigment-based ink is provided for continuous inkjet printing from a main fluid supply, and the main fluid supply can supply the fluorescent aqueous pigment-based ink and can receive return fluorescent unprinted aqueous pigment-based ink.

21. The method according to claim 19 or 20, comprising: continuously inkjet printing a non-fluorescent aqueous non-black colored pigment-based ink on the outer surface of a non-UV fluorescent substrate to provide a non-black colored image on the outer surface of the non-UV fluorescent substrate; as well as continuously inkjet printing the aqueous black pigment-based ink capable of fluorescing onto at least a portion of the non-black colored image to provide a black latent fluorescent image capable of fluorescing onto at least a portion of the non-black colored image, The non-fluorescent aqueous colored non-black pigment-based ink comprises a colored non-black pigment in an amount of at least 1 wt % and an aqueous medium comprising water, wherein the amount of the colored non-black pigment is based on the total weight of the aqueous colored non-black pigment-based ink.

22. The method of claim 21, wherein the non-black colored image is a multi-color image.

23. The method according to any one of claims 19 to 22, further comprising: A colorless composition is continuously inkjet printed onto the colored latent fluorescent image on the outer surface of the non-UV fluorescent substrate.

24. A method according to any one of claims 17 to 23, wherein the non-UV fluorescent substrate is an article to be used as a security document, currency or lottery ticket.

25. The method according to any one of claims 17 to 24, which is a method for marking an article with a coloured latent fluorescent image as a security mark for identification, information or decoration.

26. A method according to claim 25, wherein the article marked with the colored latent fluorescent image is a security document, currency or lottery ticket, and the method includes continuously inkjet printing the aqueous colored pigment-based ink capable of fluorescing, and the aqueous colored pigment-based ink is an aqueous black pigment-based ink capable of fluorescing, to provide a colored latent fluorescent image on the security document, currency or lottery ticket.

27. A method according to any one of claims 17 to 26 using a continuous inkjet printer, the method comprising: providing a main fluid supply of an aqueous colored pigment-based ink capable of fluorescing; supplying the aqueous colored pigment-based ink capable of fluorescing from the primary fluid supply to a droplet generator mechanism; ejecting a continuous stream of the aqueous color pigment-based ink capable of fluorescing from the droplet generator mechanism, the continuous stream being divided into spaced droplets of the aqueous color pigment-based ink capable of fluorescing; controlling the spaced droplets of the aqueous color pigment based ink capable of fluorescence to distinguish between printed droplets of the aqueous color pigment based ink capable of fluorescence and non-printed droplets of the aqueous color pigment based ink capable of fluorescence, the non-printed droplets being collected and returned to the main fluid supply, Thereby a colored latent fluorescent image is formed on the outer surface of the non-UV fluorescent substrate using the printed droplets of the aqueous colored pigment-based ink capable of fluorescing.

28. The method of claim 27, further comprising: Unused fluorescent capable aqueous colored pigment based ink is continuously recycled to the inkjet printer.

29. An article obtained by the method according to any one of claims 17 to 28, comprising a non-UV fluorescent substrate having a colored latent fluorescent image disposed on an outer surface thereof, the colored latent fluorescent image comprising: Pigments and colorants; and A non-polymeric fluorophore that exhibits an emission peak of at least 400 nm and up to and including 750 nm when excited by fluorescent excitation radiation having a peak of at least 200 nm and up to and including 400 nm, wherein the weight ratio of the pigment colorant to the non-polymeric fluorophore in the fluorescent image is 70:1 to 0.5:

1.

30. The inkjet printed article of claim 29, wherein the pigment colorant is an anionically stabilized black pigment.

31. An inkjet printed article according to claim 29 or 30 which is a security document, currency or lottery ticket.

32. A method for detecting a fluorescent image in an inkjet-printed article according to any one of claims 29 to 31, the fluorescent image detection method comprising: A colored latent fluorescent image disposed on a non-UV fluorescent substrate is illuminated on an outer surface of the non-UV fluorescent substrate with fluorescent excitation radiation having a peak of at least 200 nm and up to and including 400 nm, the colored latent fluorescent image having an emission peak of at least 400 nm and up to and including 750 nm.

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