Daylight fluorescent pigments absorb radiation in both the ultraviolet and visible ranges of the spectrum and emit visible light by fluorescence. The emitted light adds to the normal reflected color to give brilliant colors which appear to glow in normal daylight. The effect can be very striking. A fluorescent color can be up to three times brighter than a conventional color in daylight. This fluorescent coloration is desirable in a variety of products including plastics and inks. However, if the pigment is to be used in a water based pigment system, particularly for graphic arts applications such as textile printing inks, gravure or flexographic printing inks, marker inks, and for fluorescent paints, particularly in a thin film, several properties are required of the pigment. The pigment must be of small particle size, preferably under 10 microns to provide a strong brightly colored ink. Conventional water soluble fluorescent inks or "toners" typically have high pH which is needed to maintain toner additives, thus the pigment must be stable at the high pH. Water soluble toners have several drawbacks: poor light fastness, and they require a cosolvent, such as, for example, alcohol to keep the pigment in solution. Toners are difficult to clean; high pH cleaners are required or organic solvent based cleaners are required. In aqueous toners, water soluble dyes are required; however many of the the water soluble fluorescent dyes color shift, that is turn brownish, within in weeks and sometimes even days of preparation of the toner. Toners frequently have a high viscosity which is not suitable for use as an ink for certain applications; the toner must be diluted for printing. However the dilution also dilutes color strength leading to a paler toner. The toners when diluting with water typically have a high "cut in time" that is, they typically require at least 30 minutes, often several hours, to dissolve in the water or cosolvent before use. Finely divided colored resins or colored pigments heretofore have been prepared as described in U.S. Patent Number 5,215,674. The pigments produced therein represent a significant improvement in the art, particularly over toners. However, the quest continues for

fluorescent pigments and dispersions made therefrom, that have still brighter, purer/ cleaner color.

It would be desirable to have fluorescent pigments for use in water based pigment systems for graphic arts applications such as textile printing inks, gravure or flexographic printing inks, marker inks, and for fluorescent paints, which do not require a cosolvent, that have improved water resistance, are easy to clean; have better lightfastness than toners, that can use both watesr soluble and insoluble dyes; that do not display the rapid color shifting of toners, that are stable over a wide pH range, that have long term color stability and display strong clean color, particularly with orange pigments.

Summary of the Invention The present invention provides a fluorescent pigment and aqueous dispersion of fluorescent pigment having improved cclor purity and fluoresence useful for graphic arts applications such as textile printing inks, gravure or flexographic printing inks, marker inks, and paints . The fluorescent pigment comprises a polymer and a fluorescent dye. The polymer is preferably water insoluble and comprises: from about 40% to about 85%, preferably about 52% to about 65% total weight, of a water insoluble vinyl monomer free of polar groups; from about 15% to about 35%, preferably about 25% to about 35% total polymer weight, of a vinyl nitrile monomer; from about 1.5% to about 4.5% total weight of a vinyl surface active monomer; from about 0% to about 40%, preferably about 5% to about 12% total weight of a polar vinyl monomer; and from about 0.25% to about 20%, preferably about 1% to 5% of a vinyl monomer containing carboxylic acid groups. The polar vinyl monomer is selected from the group consisting of : polar acrylate esters or methacrylate esters; vinyl acetate; and, a substituted acrylamide containing hydroxyl groups or carboxylic ester groups.

The invention also relates to a method of making the aqueous dispersion of the pigments.

Detailed Description of the Invention

The present invention provides an improved fluorescent pigment and aqueous dispersion of fluorescent pigment having strong, clean color that are suitable for graphic arts applications such as textile printing inks, gravure or flexographic printing inks, marker inks, and for fluorescent paints.

The pigment and dispersion of the present invention: is stable at pH of 8.5; are cleanable with tap water, have low viscosity and water resistance; have superior fade resistance as compared to water soluble toners; do not require a cosolvent, are water resistant, are lightfast, can use both water soluble and oil soluble dyes; and do not display the rapid color shifting of toners.

The fluorescent pigment has the following composition: from about 90% to about 99.99%, preferably 96 to 99%, by weight, of a water insoluble polymer, and a fluorescent dye in an amount sufficient to impart fluorescent color to the fluorescent pigment, preferably from about 0.01% to about 10%, more preferably about 1% to about 4%, by weight, of the fluorescent pigment.

The aqueous dispersion of the fluorescent pigment comprises from about 0.5% to about 99% fluorescent pigment, and water,and optionally, although preferably from about 0.01% to about 10%, preferably about 0.3% to about 6% by weight of emulsifier. Water is present in the dispersion in an amount to provide a total solids content of about 0.5% up to about 100%, preferably about 50% to about 60%.

The polymer preferably comprises: from about 40% to about 85%, preferably about 52% to about 65% total weight, of a water insoluble vinyl monomer free of polar groups; from about 15% to about 35%, preferably about 25% to about 35% total polymer weight, of a vinyl nitrile monomer; from about 1.5% to about 4.5% total weight of a vinyl surface active monomer; from about 0% to about 30%, preferably about 5% to about 12% total weight of a polar vinyl monomer; and from about 0.25% to about 10%, preferably about 0.5% to 2.5% of a vinyl monomer containing carboxylic acid. The polar vinyl monomer is selected from the group consisting of: polar acrylate esters or methacrylate esters; vinyl acetate; and, a substituted acrylamide containing hydroxyl groups or carboxylic ester groups. The invention also relates to a method of making the aqueous dispersion of the pigments.

The improved color purity, and fluorescence is attributable to the carboxylic acid containing monomer in the polymer.

Interestingly, a phenomena known as "quenching" is observed in certain conventional fluorescent pigments. The fluorescence of fluorescent pigments will increase as the concentration of the dye is increased but only up to a certain dye concentration. Beyond such certain dye concentration, further increases in dye concentration will not increase the fluorescence of the pigment. Instead, as the dye concentration is increased, the fluorescence will begin to decrease and the color will become dirtier.

Surprisingly, the pigments of the present invention do not display the quenching typical of certain conventional fluorescent pigments, particularly fluorescent emulsion pigments; that is, they do not display quenching at the dye concentration as seen with such other fluorescent pigments. The pigments of the present invention can contain higher dye concentrations before they exhibit quenching. As a result of the increased amount of dye incorporated into the pigment, the pigment color is stronger and brighter.

The pigment comprises a polymer and a fluorescent dye. The dye is closely associated with certain regions of the polymer. The fluorescent pigment has the following composition: from about 90 to about 99.99%, preferably 96% to 99%, by weight, of a water insoluble polymer, and a fluorescent dye in an amount sufficient to impart fluorescent color to the fluorescent pigment, preferably from about 0.01% to about 10%, more preferably about 1% to about 4%, by weight, of the fluorescent pigment. The aqueous dispersion comprises from about 0.5% fluorescent pigment, and from about 0.2% to about 10%, preferably about 0.3% to about 6% by weight of emulsifier. Water is present in the dispersion in an amount to provide a total solids content of about 0.5% up to about 100%. The amount of water may be adjusted as desired.

The Polymer The water insoluble polymer of the present invention is formed from at least one monomer selected from each of the following groups of monomers : water insoluble nonpolar vinyl monomers; vinyl nitrile monomers; vinyl surface active monomers monomers; and carboxylic acid monomers, and optionally polar vinyl monomers. As used herein, vinyl means molecules having any carbon-carbon double bond and is not limited to molecules having a carbon-carbon double bond at the end of the molecule.

The polymer preferably comprises: from about 40% to about 85%, preferably about 52% to about 65% by total polymer weight of a water insoluble vinyl monomer free of polar groups; from about 15% to about 35%, preferably about 25% to about 35% total polymer weight of vinyl nitrile monomer; from about 1.5% to about 4.5% total pclymer weight of a vinyl surface active monomer; from about 0% to about 30%, preferably about 5% to about 12% by total polymer weight of a polar vinyl monomer; and from about 0.25% to about 20%, preferably about 0.5% to 2.5% of a vinyl monomer containing carboxylic acid. The polar vinyl monomer is selected from the group consisting of: polar acrylate esters or methacrylate esters; vinyl acetate; and, a substituted acrylamide containing hydroxyl groups or carboxylic ester groups . The polymer has a weight average molecular weight as determined by gel permeation chromatography of from about 100,000 to about 10 million, preferably about 500,000 to about 5 million.

Water Insoluble Non Polar Vinyl Monomers

While a large number of suitable monomers fall within this category, a preferred group are the styrene monomers such as, for example, methylstyrene, ethylstyrene, isopropylstyrene and butylstyrene. Styrene is more preferred. Styrene may be obtained from Aldrich Chemical Company In addition to these monoaromatic compounds, poly aromatic compounds such as vinyl naphthalene can be used. Nonpolar acrylates including for example methylmethacrylate, ethyl methacrylate, isobutyl methacrylate, sobornyl methacrylate, and isobornyl acrylate are also suitable. These water insoluble vinyl monomers provide the polymer with a high glass transition temperature, enhanced organic solvent resistance, and solidity at room temperature. Vinyl Nitrile Monomers

The second type of monomer to be included in the polymer is a vinyl nitrile monomer While acrylonitrile is preferred, other vinyl mtriles may be employed that are homologs or analogs of acrylonitrile, such as, for example, 3-pentenenιtrιle, and methacrylonitrile. A suitable acrylonitrile may be obtained from Aldrich Chemical Company The vinyl nitrile monomers serve as dye solvents. As a result, the presence of the vinyl nitrile monomer improves the solubility of the fluorescent dyes n the monomer phase and the resulting polymer In addition, the vinyl nitrile monomers provide a more favorable electronic environment for dye fluorescence. The greater the amount of vinyl mtriles present in the polymer, the better the color development of the fluorescent dye and the brighter the resulting pigment. Vinyl Surface Active Monomers

The vinyl surface active monomers include, for example, the vinyl sulfonates described in Hoke U S Patent 3,666,810, the disclosure of which is incorporated herein by reference, and nonionic and anionic polymerizable vinyl surfactants which have both polar and non-polar ends.

The preferred vinyl monomers containing sulfonate groups are sodium 2-acrylamιdo-2-methylpropane-sulfonate, referred to herein as "NaAMPS" or "Sodium AMPS" available under the trade name "Lubrizol 2405" from Lubrizol Corporation and methacryloyloxyethylsulfonic acid also known as 2-sulfoethylmethacrylate available under the trade name "SEM" from Hampshire Chemical.

Other vinyl monomers containing sulfonates that are suitable include, for example, ethylenically unsaturated sulfonic acids such as vmylsulfonic ac d, allylsulfonic acid, styrene-sulfonic acid, vinylbenzylsulfonic acid, acryloyloxyethylsulfonic acid, and a vinyl ester of an alkylsulfosucc ic acid, and salts thereof such as lithium, sodium, potassium and ammonium salts.

Nonionic polymerizable surfactants include, for example, polyethyleneglycol methacrylate, available as Sipomer HEM-5 from Rhone Poulenc, polyethylene glycol allyl ether, ethylenically substituted polypropylene glycols, ethylenically substituted polyethylene glycols, and Mazon SAM 185 from PPG Industries, whose chemical composition is proprietary.

The vinyl surface active monomer imparts a high degree of process stability to the emulsion by physically bonding to and stabilizing the forming polymer particles The Polar Vinyl Monomers

The polar vinyl monomers, which are optional, include, for example, the polar acrylate esters or methacrylate esters, vinyl acetate and substituted acrylamide containing hydroxyl groups or carboxylic ester groups. As used herein, "polar" means more polai than styrene and less polar than sodium AMPS

The polar methacrylate esters are the preferred group, of which hydroxypropyl methacrylate, ("HPMA") is the most preferred A suitable hydroxypropyl methacrylate may be obtained under the trade name "Rocryl 410" from Rohm and Haas. Illustrative of the other polar vinyl monomers are N- (2, 2, 2-trιchloro-l-hydroxyethyl) acrylamide, tetrahydrofurfuryl methacrylate, hydroxyethyl methacrylate, N/N- (dimethylamino ethyl) acrylamide, methyl acrylamidoglycolate methyl ether, and vinyl acetate. The polar vinyl monomers, like the vinyl nitrile monomers, act as dye solvents, thereby rrprovmg color, particularly with yellow, red and orange pigments. Vinyl Monomer Containing Carboxylic Acid Groups

The preferred monomers are , 3-unsaturated carboxylic acids which are capable of undergoing copolymerization and include methacrylic acid, acrylic acid or maleic acid, itaconic acid, monomethylmaleate, furanacrylic acid and fumaric ac d. The carboxylic ac d monomer improves the fluorescence response and color cleanliness, particularly in orange and red pigments and permits increased dye loading. Anhydrides monomers, including for example, maleic ahydride, acrylic anhydride, methacrylic anhydride can also be used during the formation of the polymer, however they are typically hydrolyzed to carboxylic acid by the water present in system for polymerizing the polymer. Emulsifiers

The emulsifier is optional, although prefferec Two general types of emulsifiers may be used in the present invention, surfactants and dispersants. Surfactants are comprised of anionic surfactants and nonionic surfactants; an anionic surfactant is preferred.

Surfactants which are necessary to make a dispersion polymer, generally yield polymer particle sizes of less than 1 micron.

Surfactants are used from an effective amount to emulsify the monomers during polymerization, up to 10% of the dispersion.

Anionic surfactants that may be used in the practice of the invention include for example surfactants broadly described as the water-soluble salts, particularly the alkali metal or ammonium salts, of organic sulfuric or phosphoric acid reaction products having in their molecular structure an alkyl or alkylaryl radical containing from about 3 to 50 carbon atoms and a radical selected from the group consisting of sulfonic, sulfuric, carboxylic or phosphoric acid ester radicals. (Included in the term alkyl is the alkyl portion of higher acyl radicals) .

Anionic surfactants also suitable in the practice of the present invention include for example, the sodium, potassium, or ammonium alkyl sulfates, especially those obtained by sulfating the higher alcohols, that is those alcohols having C ₆ -C ₅₀ carbon atoms) produced by reducing the glycerides of tallow or coconut oil such as for example, sodium lauryl sulfate, available under the trade name "Sipon UB" from Rhone- Poulenc or sodium lauryl phosphate. Other examples include sodium, potassium, or ammonium alkyl aromatic sulfonates, in which the alkyl group contains from about 9 to about 15 carbon atoms, the alkyl radical is a straight or branched aliphatic chain, the aromatic group is benzene or polycyclic group such as naphthalene; such examples include: sodium dodecyl benzene sulfonate, available under the trade name "Siponate DS-4" from Rhone-Poulenc, or sodium alkyl naphthalene sulfonate, available under the trade name "Nekal BA-77" from Rhone- Poulenc. Other examples include paraffin sulfonate surfactants having the general formula RS0 ₃ M, wherein R is a primary or secondary alkyl group containing from about 8 to 22 carbon atoms (preferably 10 to 19 carbon atoms) and M is an alkali metal, e.g., sodium or potassium, for example, sodium olefin sulfonate, available under the trade name "Siponate 301-10" from Rhone-Poulenc) . Further examples include: sodium alkyl glycerol ether sulfonates, especially those ethers of the higher alcohols derived from tallow and coconut oil; and sodium coconut oil fatty acid monoglyceride sulfates, sulfonates or phosphates. Additional examples include sodium, potassium, or ammonium salts of sulfuric acid esters of the reaction product of one mole of a linear or branched higher alcohol (e.g. , tallow or coconut oil alcohols) , and about 1 to about 40 moles of ethylene oxide, such as the surfactants available under the trade name "Sipex EST-30" from Rhone-Poulenc. Further examples include sodium, potassium, or ammonium salts of alkyl phenol ethylene oxide ether sulfates having about 1 to about 100 units of ethylene oxide per molecule and in which the alkyl radicals contain from about 8 to about 12 carbon atoms, such as, for example: the sodium salt of sulfated alkyl phenol ethoxylate (n=4) , available under the

trade name "Alipal Cθ-436"; the ammonium salt of sulfated nonylphenol ethoxylate (10EO) , available under the trade name "Alipal EP-llO"; the ammonium salt of sulfated nonylphenol ethoxylate (30EO) , available under the trade name "Alipal EP-120"; and other "Alipal" surfactants from Rhone-Poulenc and a sodium salt of an alkylaryl polyether sulfonate available under the trade name "Triton x-200" from Rohm & Haas . Additional examples include: the reaction products of fatty acids esterified with isethionic acid and neutralized with sodium hydroxide where, for example, the fatty acids are derived from coconut oil, available under the trade name "Igepon AC-78" surfactants from Rhone-Poulenc; and sodium or potassium salts of fatty acid amides of a methyl taurine in which the fatty acids, for example, are derived from coconut oil and sodium or potassium B-acetoxy- or B-acetamido-alkane- sulfonates where the alkane has from 8 to 22 carbon atoms. Still further examples include: sodium alkyl sulfosuccinates where the alkyl moiety is from 4 to 26 carbon atoms such as dihexyl ester sulfosuccinate, available under the trade name "Aerosol MA 80" from American Cyanamid, or OT surfactants from American Cyanamid or Alconate surfactants from Rhone-Poulenc; disodium ethoxylated alcohol or ethyoxylated alkyl phenol half esters of sulfosuccinic acid, such as the disodium salt of ethoxylated lauryl alcohol ester sulfosuccinate, available under the trade name "Aerosol A-102" or the disodium salt of ethoxylated nonyl phenol ester sulfosuccinate, available under the trade name "Aerosol A-103" from American Cyanamid; and alkylated disulfonated diphenyl oxides such as disodium mono and didodecyl diphenyl oxide disulfonate, available under the trade names "Aerosol DPOS-45" from American Cyanamid or "Dowfax" from Dow Chemical Company. Further suitable surfactants include fluorinated derivatives of above mentioned classes of surfactants such as the Zonyl surfactants from DuPont or the Fluorad surfactants from 3M. Also, mixtures of the above listed surfactants are also suitable.

Nonionic surfactants suitable in the practice of the present invention include, for example: the higher alcohols (C8 to C18 carbon atoms) such as 1-dodecanol, available from Aldrich Chemical; and the reaction products of one mole of a higher linear or branched fatty alcohol (e.g. tallow or coconut oil alcohols) with about 1 to about 100 moles of ethylene oxide, such as tridecyloxypoly(ethyleneoxy) ethanol, commercially available under the trade name "Emulphogene" from Rhone- Poulenc, or ethoxylated cetylalcohol, commercially available under the trade name "Siponic E" from Rhone-Poulenc, or ethoxylated (n=23) lauryl alcohol, commercially available under the trade name "Siponic L25" from Rhone-Poulenc. Further suitable nonionic surfactants include: ethoxylated alkyl phenols having from about 1 to about 100 units of ethylene oxide per molecule and in which the alkyl moiety contains from

about 8 to about 12 carbon atoms, such as, for example, ethoxylated (n=2) nonyl phenol, available under the trade name "Igepal CO-210," ethoxylated (n=4) nonyl phenol, available under the trade name "Igepal CO-430, " ethoxylated (n=9) nonyl phenol, available under the trade name "Igepal CO-660", ethoxylated (n=30) octyl phenol, available under the trade name "Igepal CA-887" which, like the preceding, are from Rhone- Poulenc, or "Siponic F-300" from Rhone-Poulenc, and dmonylphenol ethoxylate (n=49) , available under the trade name "Igepal DM-880" from Rhone-Poulenc and other ethoxylated alkyl phenol surfactants available under the trade names "Igepal" or "Siponic F" from Rhone-Poulenc. Further suitable surfactants include: alkyl polyether carboxylates with about 1 to about 100 units of ethylene oxide per molecule, available under the trade name "Akypo" from Rhone-Poulenc; block copolymers of ethylene oxide and propylene oxide such as, for example, those surfactants available under the trade names "Pluronic" or "Tetronic" from BASF; and acetylenic glycols reacted with from 1 to 100 moles of ethylene oxide such as diethoxylated (n=30) 2,4, 7, 9-tetra-methyl-decyn- 4,7-dιol available under the trade name "Surfynol 485" from Air Products. Further suitable nonionic surfactants include the fluonnated derivatives of above mentioned classes of surfactants which are available under the trade name "Zonyl" from DuPont, or the "Fluorad" surfactants from 3M.

Dispersants are also surface active agents, but they do not form micelles. When used, the dispersant is used from an effective amount up to about 10% by weight of the dispersion, promotes the dispersion of the monomers during polymerization and enhances the dispersion of the polymer particles n water.

Suitable dispersants include. water soluble polymers such as: gelatin, starch, methylcellulose, methylcellulose derivatives such as, for example hydroxypropyl methylcellulose, polyvmyl alcohol, available under the trade name "Airvol" from Air Products, polyacrylic acid salts, or sodium salts of naphthalene formaldehyde condensates. Other suitable dispersants include: barely water soluble salts such as, for example, barium sulfate, calcium sulfate, barium carbonate, calcium carbonate, and, calcium phosphate, and, inorganic macromolecules such as, for example, talc, bentomte, and clay. The most preferred dispersant for use with anionic and/or nonionic surfactants is polyvmyl alcohol.

The Fluorescent Dyes The fluorescent dyes employed m the composition include fluorescent organics which are brilliantly fluorescent when in solution or dissolved in a polymer. These daylight fluorescent-types are well known in the art, and belong to the dye families known as benzothioxanthene, xanthene, coumaπn, naphthalimide, benzoxanthene,

perylene, and acr dine. The dyes employed in the practice of the present invention may be either water soluble or water insoluble.

Typical dyes include Basic Red 1, a cationic Rhodamine F5G dye commercially available as "Basonyl Red 482," from BASF, Basic Violet 10, a cationic Rhodamine B dye commercially available as "Basonyl Red 540," from BASF; Basic Violet 11, Basic Violet 15 a cationic methine dye, Basic Violet 11:l a cationic Rhodamine F3B dye, commercially available as "Basonyl Red 560," from BASF; Basic Violet 16, a methine dye commercially available as "Basacryl Brilliant Red BG, " from BASF; Basic Violet 27 a cationic methine dye, Basic Yellow 40, a cationic Coumann dye commercially availabLe as "Maxilon Brilliant Flavme 10GFF, " from Ciba-Gigy; Solvent Yellow 43, a nonionic Naphthalimide dye commercially available as "Hudson Yellow"; Solvent Yellow 44, a nonionic Naphthalimide dye commercial]y available as "Yukon Yellow"; Solvent Yellow 131, a nonionic NaDhthali ide dye commercially available as "Mohawk Yellow"; Solvent Yellow 135, a nonionic Coumann dye commercially available as "Alberta Yellow" ; and, Solvent Yellow 160, a nonionic Coumann dye commercia] ly available as "Potomac Yellow, " all of which are available from Day-Glo Color Corporation.

The dye is added from an effective amount, that is, an amount that provides the desired fluorescent hue and brightness, preferably about 0.01% to about 10% by weight of the pigment weight more preferably about 1 to about 3% of pigment/dispersion weight. Particle Size of the Polymer

The pigments have small median particle size, from about 0 01 to about 10 microns which is obtained without grinding. Pigments having particles with median size of about 0 01 to about 0.25 micron size are particularly useful in pen inks. Such pigments may be prepared by using dispersion polymerization techniques. Employing an anionic surfactant, depending on the particular anionic sirfactant, will typically produce pigments having a median particle s ze of less than 0.25 microns.

For applications such as flexographic and gravure printing ink, textile printing ink and paper coating, pigment particles having a median size of 0.25 to 1.0 micron are desired. Pigm€'nt particles of such size may be obtained using dispersion polymerization or suspension polymerization techniques. To obtain such particle sizes nonionic surfactants may be used m addition to anionic surfactants during polymerization. Alternatively, the median particle size may be increased above 0.25 microns by decreasing the amount of anionic surfactants.

In order for anionic surfactant to have effect on the particle size, there must be free anionic surfactant. It has been found that

where a cationic dye is used, the number of moles of the cationic dye will bind a corresponding number of moles of anionic surfactant. Accordingly, it is the amount of free or unbound anionic surfactant that is available to emulsify the monomers and thereby determine the particle size of the polymer. To determine the amount of free anionic surfactant when using a given cationic dye, a series of dispersion polymerizations may be performed in which the surfactant amount is varied and the pigment particle size measured.

For certain coating applications paints and thicker film printing inks including screen printing inks a median particle size in the range from about 1.0 to 10 microns is preferred to maximize color brightness. These pigments are made using classic suspension polymerization techniques. In suspension polymerization, the median particle size is determined by the rate of mixing of the monomers and water; the faster the rate of mixing, the smaller the particle.

Preparation of the Polymer

While a variety of conventional initiators may be used to initiate the free radical polymerization of the monomers, good results have been obtained using an oxidizing agent such as ammonium persulfate, also referred to as "APS" from EM Science, and a reducing agent such as erythorbic acid, referred to as "EA" available from Pfizer. Sodium formaldehyde sulfoxylate, referred to as "SFS" from Aceto Corporation, is also suitable.

Optionally, although preferably, a catalyst is used such as for example, an iron EDTA complex, to catalyze the reaction. Iron sulfate heptahydrate from J.T. Baker and tetrasodium EDTA, available under the trade name "Versene 220" from Dow Chemical Co. is also a suitable catalyst. The amount and rate at which the initiators are added controls the rate of polymerization; good results have been obtained using from about 0.02% to about 0.3% by weight, preferably about 0.04% to about 0.2% by weight of ammonium persulfate; from about 0.02% to about 0.6% by weight, preferably about 0.04% to about 0.4% by weight of erythorbic acid and from about 0.01% to about 0.2% by weight, preferably about 0.02% to about 0.1% by weight of the total dispersion weight; of iron EDTA complex. Other suitable initiators, include for example, t-amyl-peroxy-neodecanoate, also referred to as "t-APND" from ATOCHEM, or 2, ' -azobis (2-amidino-propane) dihydrochloride, available under the trade name "V-50" from Wako Pure Chemical Industries. From about 0.02% to about 0.3% t-amyl-peroxy-neodecanoate or 2,2' -azobis (2- amidino-propane) dihydrochloride is suitable.

The dispersions in the following examples were prepared using typical dispersion polymerization techniques utilizing free radical catalysts such as the persulfates, peroxides and azo compounds.

EXAMPLE 1

The following ingredients were added to a 1500 ml baffled reaction flask equipped with a 2-inch pitched blade, heat tape, reflux condenser, and cooling water: 366g water, 2.4g tetrasodium EDTA, available as "Versene 220" from Dow Chemical, 4.25g 2-sulfoethylmethacrylate available for Hampshire Chemical as "SEM, " 5.1g maleic anhydride, 0.12g ferrous sulfate heptahydrate, 11.9g 30% tridecylethersulfate in water, available as "Rhodapex EST-30" from Rhone Poulenc, 27.54 g of 28% nonylphenolethersulfate surfactant in water available under the trade name "Triton X-200" from Rohm and Haas, 10.2g of 50% aqueous 2-acrylamido-2-methylpropane sulfonate sodium salt, available under the trade name "Lubrizol 2405" from Lubrizol, 4.51g of C.I. Solvent Yellow 160:1 available as "Potomac Yellow Dye" from Day-Glo Color Corp., 0.54g of C.I. Basic Violet 11 available as "Basonyl Red 560" from BASF, 2.4g of C.I. Basic Red 1 available as "Basonyl Red 482" from BASF, and 2.13g sodium hydroxide as a pH adjustment to a pH between 2 and 4. The mixture was agitated at about 800 rpm and heated under nitrogen to 60°C. The maleic anhydride was hydrolyzed to maleic acid. Then 34g hydroxypropylmethacrylate, 196.5g styrene, 86.7g acrylonitrile, and 6.8g methacrylic acid were added. After about 5 minutes, a solution of 1.13g ammonium persulfate in lOg water and a solution of 1.976g erythoribic acid in 9.52g water were simultaneously added at a rate of 8 cc/hour the initiator solution flow rates were adjusted after approximately 1 hour to maintain a constant temperature of 60°C. Once all the initiators were added, 4.25g styrene was added and stirred for 5 minutes. A solution of 5.lg 70% t-butylhydroperoxide in 21.25g water and a solution of 3.49g erythorbic acid in 25.5g water were simultaneously added over 2 hours. After all the initiator was added, a final pH adjustment to 7.5 with ammonium hydroxide was performed. The resultant dispersion was highly fluorescent and orange. EXAMPLE 2

A pigment was prepared as in Example 1 except that the Triton X-200 and 50% aqueous 2-acrylamido-2-methylpropane sulfonate sodium salt were omitted and the following ingredients were added in the amount indicated: 3.77g C.I. Basic Red 1, 1.42g C.I. Basic Violet 11, and 5.53g C.I. Basic Yellow 40, 4.76g maleic anhydride, 34g hydroxypropyl methacrylate, 204g styrene; 09.8g acrylonitrile; 8.16g of 2-sulfoethylmethacrylate; 2.98g Airvol 203 from Air Products and 40.46g of Rhodapex EST-30. The resultant pigment was highly fluorescent and red orange in color.

EXAMPLE 3

A pigment was prepared as in Example 1 except that the following ingredients were added in the amount indicated: 2.8g C.I. Basic Red 1,

2.55g C.I. Basic Violet 11, 1.96g C.I. Basic Yellow, 40, 14.7g 50% aqueous 2-acrylamιdo-2-methylpropane sulfonate sodium salt, 34g of hydroxypropyl methacrylate, 204g of styrene, 91.8g of acrylonitrile,

22.95g Rhodapex EST-30 and 19.55g Triton X-200. The resultant pigment was red and highly fluorescent.

EXAMPLE 4 A pigment was prepared as in Example l except that Triton X-200 was omitted, and the following ingredients were added in the amount indicated: 4.42g C.I. Basic Red 1, 102.g C.I. Basic Violet 11; 0.3g

Solvent Yellow 160:1; 8.5g C.I. Basic Yellow 40; 47.6g Rhodapex EST-30;

2.98g Airvol 203; 5.lg 50% aqueous 2-acrylamιdo-2-methylpropane sulfonate sodium salt, 6.38g 2-sulfoethylmethacrylate; and 1 7g maleic anhydride. The resultant pigment was highly fluorescent and orange.

EXAMPLE 5

A pigment was prepared as in Example 1 except that the following ingredients were added in the amount indicated- 2l.03g Triton X-200, 3.54g C.I. Basic Red 1; 2.88g C.I. Basic Violet 11;

10.2g Rhodapex EST-30; 33.06 Abex EP-120. The resultant pigment was pink.

EXAMPLE 6

A pigment was prepared as n Example 1 except that the following ingredients were added in the amount indicated: 8.5g Solvent

Yellow 160:1, 1.13g benzyltriethylammoniumchloπde, 21.25g Triton X-200, 10.3g Rhodapex EST-30; 31.79 Alipal EP-120 The resultant pigment was yellow. EXAMPLE 7 A pigment was prepared as m Example l except no polar vinyl monomer was added, that is, the HPMA was ommitted and the following ingredients were added with 2.88 g Basic Violet 11 and 3.54 g Basic Red 1, 221 g of styrene was used and 17 g of methacrylic acid was used. The pigment was highly fluorescent and pink. EXAMPLE 8

A fluorescent ink containing 75% of the pigment of Example 4, was prepared by mixing the pigment of Example 4 with an acrylic binder comprised of 12.5% G-Cryl 250 available from Henkel Corp. and 12.5% Lucidene 602 emulsion from Morton International. Comparative Examples

Comparative examples A through D, m which the polymer lacked the vinyl monomers that contain carboxylic acid groups, were prepared as follows.

COMPARATIVE EXAMPLE A

A pigment was prepared as in Example 1 except that maleic anhydride and 2-sulfoethylmethacrylate were omitted, and 204g of styrene, 91.8g of acrylonitrile, and 20.4g of Lubrizol 2405 were used. The resultant pigment was orange. COMPARATIVE EXAMPLE B

A pigment was prepared as in Example 2 except that maleic anhydride and C.I. Basic Yellow 40 were omitted and 3.88g C.I. Solvent Yellow 160 was added, 19.39g of Rhodapex EST-30 was used, 2-sulfoethylmethacrylate was omitted and 20.4g of Lubrizol 2405 was used. The resultant pigment was red orange. COMPARATIVE EXAMPLE C

A pigment was prepared as in Example 3 except that πaleic anhydride, 2-sulfoethylmethacrylate, and C.I. Basic Yellow 4C were omitted, and 1.34g C.I. Solvent Yellow 160, 20.4g Lubrizol 2405, and 21.lg of Rhodapex EST-30 were used. The resultant pigment was red. COMPARATIVE EXAMPLE D

A pigment was prepared as in Example 4 except that maleic anhydride was omitted. The resultant pigment was orange. COMPARATIVE EXAMPLE E

An orange fluorescent ink was prepared by mixing 30 g of LWO- 001, a water soluble resin for toners commercially available from Louis Wernke Ink, to 10 g of 28 g aqueous ammonium hydroxide, 16 g isopropyl alcohol and 44 g water.

EVALUATION OF THE PIGMENT

Several different pigment formulas of the above examples with and without maleic acid were evaluated for color brightness. The results are shown in Table I .

TABLE I

Example % dye color Fluor. color color response ¹ purity purity ²

(visual) (CEI)

A 2.19 orange 1,036 good 82.53%

B 2.67 red orange 980 good 75.14%

C 1.97 red 894 good 57.64%

D 4.85 orange 989 medium 84.5%

1 2.19 orange 1,135 excellent 83.25%

2 3.15 red orange 994 excellent 79.77%

3 2.142 red 1,018 excellent 65.91%

4 4.85 orange 1,110 good 86.00%

1 - Fluorescence response measured as the front surface response of a 12 meyer rod draw down of the neat dispersion through a 25 mm ² aperture at 354nm on a Hitachi F-4500 fluorescence spectrophotometer. Slit widths: emission = 1 nm, excitation = 2.5nm.

2- CIE color purity determined on a Spectraflash 500 from Datacolor International.

3- color cleanliness determined visually.

As shown in Table 1, the addition of the monomer containing carboxylic acid to examples 1-4, significantly improves the color of the pigment. The fluorescence response, of examples 1-3 exceed the values for the corresponding comparative examples. The color purity of examples 1-3, determined by the CIE color purity standard and visually, exceed the values for the corresponding comparative examples A-C. As seen in comparative example D when the dye concentration was increased by a factor of 1.2 the color purity and fluorescence decreased. Surprisingly, Example 4, which contains the same amount of dye as in comparative example D, and more than twice the dye as in Example 1, possesses greater fluorescence response and also increased color purity, with respect to comparative example D or example 1. Accordingly, the pigment of the present invention permits an increase in the amount of dye that may be loaded into the polymer without observing the negative deterioration of color seen with the certain conventional fluorescent pigments.

The viscosity of a representative sample of Example 4, having 45% solids was measured using a #2 Zahn cup and determined to be 15 sec. The viscosity of a representative sample of Example 1, having 45% solids was measured using a #2 Zahn cup and determined to be 18 sec. This lower viscosity permits the dispersion to be used directly for many ink and printing techniques without requiring further dilution. Thus the color and fluorescence will not be diluted upon use.

Evaluation of Fade

A sample of fluorescent ink of Example 8 was drawn down with a No. 3 Myer rod on coated stock and subjected to fading in a xenon arc fadometer for 16 hours. For comparision, a fluorescent soluble toner of comparative Example E was placed in the fadometer for comparision.

The ink of Example 8 retained greater than 50% of its original color while the toner of comparative Example E, faded to less than 5% of its original color, as determined visually.

Water/pH Resistance A sample of the ink of Example 8 and a sample of the fluorescent soluble toner of example E, were oven aged at 50°C at a pH of 8.4 for five days.

The ink of example 8, showed minimal, that is less than about a

5% color shift and no increase in viscosity or settling. In contrast, the soluble toner exhibited marked color shift to a red, and an unacceptable, dirty non-fluorescent color. The toner polymer also settled out from the toner solution.

The dispersion polymerization techniques used in the above examples, produce an aqueous disperson which is ready for use as a pigment in ink or coatings formulations. However, the dispersion may be concentrated, dried or diluted depending on the end use of the dispersion or the pigment. The dispersion may be dried by conventional techniques, such as freeze drying, vacuum oven drying or spray drying, to recover the pigment. The dispersion may be concentrated by distillation to remove water to yield a "presscake" form having a solid contents greater than normally produced by the dispersion polymerization techniques.

Also, a dry or concentrated pigment may be re-emuslsified in either an aqueous system when ready to use.