Abstract:
Fluorescent Ink formulations have been conceived that result in inks having improved tack and flow properties so that problems relating to ink plugging with contemporary ink pads are reduced. Another advantage to the inks is that they have improved paper dust resistance, shelf life and flow properties. These inks are made of a coloring material having an organic non fluorescent pigment dispersed in a rosin ester and a solid solution of a fluorescent dye in triazine paraformaldehyde aryl sulfonamide resin dispersed in an alkyd resin. The solvent system is preferably composed of non drying solvents such as emollients and higher molecular weight glycols.

Description:
BACKGROUND OF THE INVENTION 
     Many advances have been made recently in the field of printing. Great demands have been made upon printing systems and materials therefor in light of the need of faster printing, in conjunction with the computer age, and the seeking of lower toxicity to comply with governmental environmental regulations. In high speed printing, a problem has been encountered with paper dust which is generated during paper transport and the impact of a printing element on the paper. This is particularly true of printing on envelopes which are made of paper with loose fibers. 
     One of the components of the printing system that has required extensive modification is the ink. In most printing applications, a pad or roller made of a porous material is supplied with ink for the purpose of transferring the ink to a printhead. The printing pad may be one which is self contained or one that is periodically supplied with ink from a reservoir. 
     Problems in producing a satisfactory ink are compounded when one seeks to produce an ink that results in printing wherein the printed matter can be seen visually in ordinary light and can be seen having the same or a different color when exposed to ultraviolet light. These inks are known as fluorescent inks and are useful because of their ability to be detected by an optical device. Such inks have wide spread use in the mail handling field where devices, referred to as postage meters or franking machines, print an indicia upon mail pieces. The fluorescent ink yield the ability to determine the location of an indicia on a mail piece and discern the authenticity of postage. 
     The problems in producing a satisfactory fluorescent ink are compounded because a plurality of dyes and pigments are required for achieving good color, fill in, edge acuity and the other qualities required from an ink. One of the major problems associated with inks is aging which results in printing that has a change in color and intensity with the passing of the time the ink is stored. An ink that overcomes the aging problem and shows low environmental sensitivity at high humidity and low and high temperature, low tackiness and flow properties, material compatibility and paper dust resistance would be advantageous. Another consideration is that the ink pad must function in an open environment without drying for at least six months; therefore, the ink solvents should be non volatile. 
     SUMMARY OF THE INVENTION 
     Non aqueous, fluorescent dispersion ink formulations have been discovered that are nontoxic and have flow properties which substantially reduce the tendency of the ink to cause plugging in an inking pad. Ink pad life has a variability caused mainly by the inherent properties of the ink with which it is used. The inking pad may be assembled with two layers of foam, the first layer serving as an ink reservoir layer and the second layer serving as a metering layer which contacts the print head. Because of its high density and smaller pore size, the metering layer can act as a filter as a consequence of the ink concentrating at the interface of the two layers. As a result, plugging tends to occur. Of course, what is meant by plugging is the fact that particles of the ink are captured within the pores of the inking member which prevent the flow of ink. 
     It has been found that the plugging onset can be delayed with the ink formulations of the instant invention because of decreased dissolved resin concentration, thereby decreasing the viscosity, even though the size of the pigments can vary from 0.1μ to 5.0μ. Plugging onset also is delayed through stabilization of the pigment dispersion by the macromolecules present in the alkyds of the fluorescent pigments and in the rosin esters used in the predispersed, non fluorescent pigments. 
     The ink formulation of the instant invention is based on combinations of organic non fluorescent pigments dispersed in a rosin ester and a solid solution of fluorescent dyes in amino formaldehyde resin dispersed in an alkyd resin. The resulting visual color of these inks can be red, blue, green or black. It has been found that these ink formulations reduce the effects of paper dust accumulations because the solvents of the instant ink formulations are non drying on the printing elements and maintains printing elements in a wet state. Preferably the solvent has emollient properties. This wet state causes the flushing of elements resulting in paper dust being carried away. Lower concentrations of dissolved resin produces a lower tack ink which results in less paper dust attraction in the ink. 
     The ink formulations of the instant invention have low environmental sensitivity due to small variation of the viscosity in the operating temperature range of 5° to 45° C. and the low hygroscopicity of the solvents. 
     The preferred embodiment of the invention is the inclusion of an emollient solvent in the ink formulation. Use of this type of solvent has been found to be compatible with the pigments used to produce the ink, provides low toxicity, ease of fabrication of the ink, is inert to materials in the inking system and provides a non-drying ink. Another advantage to the inclusion of an emollient solvent is that it is non-volatile and consequently results in the inking pad not drying. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The formulations of the instant invention provide inks with improved print quality, are inert to materials used in a printer such as inker foams and rubber, have low tack, good shelf life stability, and good flow through porous foam materials. 
     It has been found that the inks of the instant invention have an acceptable shelf life. The aged samples show no settling after two weeks of accelerated testing. The aging of the inks by temperature shock shows no settling for the inks during two weeks of accelerated testing that simulated one year of aging by varying the temperature between 70° C. to -20° C., every four hours of the working day. 
     The dual inker foam described above that is used for making the print pad in high speed flat bed systems is made of a polychloroprene foam bottom layer. The top layer is made of polyethylene sintered foam. The rubber used in the print head is made of polybutadiene acrylonitrile rubber, which is plasticized with dibutyl phthalate. The solvents used in the instant ink formulations are inert to all these materials. The print head should be usable for ten million prints, or ten years, and the pad materials should be compatible with the inks for six months and non drying in an open environment. 
     The non aqueous pigment dispersion used in the ink formulation is stabilized by using easily dispersible non fluorescent organic pigments predispersed in a vehicle such as rosin ester carrier, linseed oil alkyds, or other type of alkyds. The rosin ester dispersants are preferable because of the wide range of compatibility with solvents and resins. The non-fluorescent pigments also can be predispersed in a non-ionic surfactant such as oleyl alcohol ethoxylate and the like. 
     In one embodiment, the non fluorescent pigments are mixed with red fluorescent pigments in order to obtain red fluorescent inks. The solvent system makes up 40% to 90% of the formulation and is preferably of the emollient solvent type. The solvent system can be composed of 95% to 99% polyoxypropylene stearyl ether (an emollient solvent) and 1% to 5% of other additives such as nonyl phenoxy polyoxyethylene ethanol. All percentages in this disclosure and the accompanying claims are in weight percent. Other solvents that can be used are castor oil, polypropylene (10) cetyl ether, soy bean oil, oleic acid and polypropylene glycol or mixtures of solvents such as 70% stearyl polyoxypropylene ether and 30% polypropylene glycol. The pigment dispersion can be further stabilized with 0.2% to 1% of a coupling agent such as neoalkoxy titanite and 1% to 5% emulsifiers such as nonyl phenoxy polyethoxylated alcohols, which emulsifiers have an HLB (hydrophylic lipophylic balance) value from 2 to 16. The inks of the formulation may have visual red and non red color of acceptable purity, such as blue, black and green and red fluorescence that yields a high signal. The solvent system is inert to the materials used in the printer, such as inker foams, print elements, pumps, tubing, print pads, and the like. 
     The formulation of the instant invention involves unique color combinations based on mixtures of pigments such as the phthalocyanines and red fluorescent organic pigments and results in strong non red colors with high purity and a red fluorescent portion with high fluorescent signal. 
     The selection of the phthalocyanines is based also on their dichroic properties. They reflect highly in the red region of the spectrum where the transmitted color is much greener. 
     Non fluorescent organic pigments such as phthalocyanines are used in different forms such as powder or chips or predispersed pigments in rosin esters, pigments flushed with added rosin ester and soy bean oil or pigments flushed with non-ionic surfactants such as oleyl alcohol ethoxylates, the non-ionic surfactants representing 6 to 10% of the formulation. 
     The organic fluorescent pigments are solid solutions of fluorescent dyes in friable organic resins of the aminoaldehyde type. For example, organic resins such as triazine para formaldehyde and aryl sulfanomide which are dispersed in drying type alkyd vehicles, such as linseed oil alkyd and alkyd varnish manufactured and available from Lawter Company. 
     The average particle size of the pigments, non fluorescent and fluorescent, is between 0.1 and 0.5μ for at least 98% of the non fluorescent and between 0.1 to 0.5μ for at least 98% of the fluorescent pigments. Because of the larger size of the pigments, the collision probability followed by quenching is less probable than in a molecular solution. This results in the ability to achieve blue visual color with red fluorescence. 
     Dispersed pigments can be diluted with a mixture of solvents composed of: polyoxypropylene stearyl ether 15-60%, low molecular weight polypropylene glycol, 5 to 30%, polyoxyethylene oleyl ether 5 to 20%, and optionally emulsifiers such as nonyl phenoxypolyoxy ethylene alcohol with a hydrophilic lipophilic balance (HLB) from 4 to 13, l to 5%, and optionally a coupling agent for the dispersion stabilization such as titanate polyalkoxy complex (neopentyl diallyl) oxy, tri (dioctyl) pyro-phosphatotitanite, 0.3 to 0.5%. 
     Another component that may be included as an additive to the ink formulations is fumed silica with grafted polysiloxane groups. This additive controls the thixotropy of the ink, reduces surface tension and flattens the variation of the viscosity at different temperatures. At the same time, it reduces the hygroscopicity of the ink. 
     The present invention provides a new class of inks that are compatible with the inert to the polymeric materials used in contemporary printers. Examples of such inks are as follows: 
     
         ______________________________________General CompositionIngredients             Weight Percent______________________________________1.  Non fluorescent organic pigments                       1-10%    (≈33%) predispersed in a rosin    ester vehicle (≈67%) and,    optionally pigments, flushed in    a non ionic surfactant such as    oleylpolyoxy ethylene ether and    fatty acid ester C12 to C14:Example of non fluorescent organic pigments are:    a) C.I. Pigment Blue 15.1 and Blue 15.3    b) RED LAKE C (Pigment Red 53:1)    c) Pigment Red C.I. #144    d) PERMANENT RED 2B    (Pigment Red 48 CI 144)    e) LITHOL RED (Pigment Red 49:1)    f) Pigment Red 52:1    g) Pigment Yellow C.I. #110    h) Pigment Brown C.I #23    i) Pigment Green C.I. #7    j) Pigment Black C.I. #72.  Fluorescent pigments made of                       5.0 to 30%    solid solutions of fluorescent dyes    (≈20%) in triazine aryl sulfonamide/    paraformaldehyde resin dispersed in    linseed oil alkyd or in other alkyd    varnish (≈80%)Examples of Fluorescent dyes are:    a) Solvent Red 49    b) C.I. Basic Red 1    c) C.I. Basic Violet 11.1    d) ALBERTA YELLOW    e) POTOMAC YELLOW3.  Non aqueous continuous phase                       40 to 90%    a) Polypropylene glycol    b) Emollient solvent:    polyoxypropylene stearyl ether or    polyoxypropylene (10) cetyl ether    c) Oleic acid    d) Castor oil    e) Soy bean oil    f) a mixture of 10 to 30%    polypropylene glycol and 70 to    90% stearyl polyoxypropylene    ether or 70 to 90% polyoxypropylene    (10) cetyl ether4.  Low polarity emulsifier (optional)                       traces to 5%    nonylphenoxypolyoxyethylene ethanol    HLB value 2-4.95.  Moderate polarity emulsifier (optional)    with HLB value 11-16    1.0 to 5.0%6.  Surface tension modifier (optional)                       0.1 to 4.0%    a) silicon glycol    b) fumed silica with grafted    polysiloxane groups7.  Coupling Agent (optional)                       0.2 to 1%    titanite neoalkoxy8.  Linseed oil alkyd       trace to 10%______________________________________ 
    
     It will be appreciated that the above are given by way of example only and one skilled in the art will recognize that other components having similar properties can be used in the practice of the invention. 
     
         ______________________________________Example I Blue ink - Red FluorescentIngredient          Manufacturer wt %______________________________________Emollient Solvent   ICI          33.6ARLAMOL E (polyoxypropylenestearyl ether)Polypropylene glycol               BASF         30.0PLURACOL P-410Non-ionic surfactant               Amerchol     7.6AMEROXIL (oleyalcoholeth-oxylate) OE-5)Nonyl phenoxy       GAF          5.0polyethylene ethanolIGEPAL CO 530 (nonyl-phenoxy polyoxyethyleneoxyethanol)IGEPAL CO 210       GAF          3.0(nonylphenoxypolyoxyeth-yleneoxyethanol)Titanite couplying agent               Kenrich      0.3LICA 38 (titanite neoalkoxy)Red Fluorescent Pigment               Lawter Intl. 17.0LAWTER RED FLUSH C.I. 2D-536 MICROLITH BLUE TG               Ciba Geigy   3.5(C.I. Pigment Blue 15.1)______________________________________ 
    
     Properties 
     Brookfield viscosity: 
     #2 spindle/12 RPM/spindle guard 575±50 cps after 3 minutes. 
     The ink was shaken for 5 minutes and allowed to set for one hour prior to viscosity measurement. 
     Haake rotational viscometer (RV--20) Sensor SV DIN 
     Viscosity at 0.5 sec--1 after 13 min ≈1200 cps 
     Viscosity at 500 sec--1 after 10 min 229 cps 
     Color Hunter lab L 55±5; a--5.3±1.0; b--21.4±1.0 
     Fluorescence fresh drawdown is 35 pMU 
     Maximum wave length fluorescent emission when excited at 254 nm is 591 nm 
     Percentage of volume swell of an ESN 30 rubber print die increase after 28 days at 70° C. is ≈2% 
     Number of continuous prints from neoprene/polyethylene inker pad is 500K with a drop in PMU of less than 20% (compared to the first print). 
     Settling test: ASTM D 1309. After 2 weeks rating was 8. 
     
         ______________________________________           Manufacturer wt %______________________________________Example IIPigment Blue in rosin             Ciba Geigy     4.0ester Microlith Blue 4 GTFluorescent pigment D-536             Lawter Int.    20Arlamol E         ICI            76PropertiesFluorescence of drawdown             35 PMUHunter color parameters             L, 49.2 a, 5.1 b. 25.2Viscosity at 500 sec.sup.-1 is 209 cp.______________________________________ 
    
     The ASTM D-1309 test for settling shows a rating of 8 (perfect dispersion with no settling). 
     
         ______________________________________Example III Red Ink - Red FluorescenceIngredient            Manufacturer                            wt %______________________________________Pigment Red 52.1 (20%)                 Penn Color 2.0AMEROXOL flushed inOE5 (oleylalcoholethoxylate) (80%)Red Fluorescent Pigment                 Lawter Intl.                            18.0D-536Solid solution of Basic Red 1 in triazineparaformaldehyde aryl sulfonamideMICROLITH RED BRT     Ciba Geigy 1.0(Pigment red C.I. 144predispersed in rosin ester)MICROLITH BROWN       Ciba Geigy 0.5(Pigment Brown C.I. 123)MICROLITH YELLOW      Ciba Geigy 0.5(Pigment Yellow C.I. 110)BLAZE ORANGE          DayGlo     4.0(pigment consisting of a amino-formaldehyde/sulphonamide resinand Basic violet 11:1, BasicRed 1, Alkyd resin and hydrocarbon oils)Igepal CO - 210       GAF        2.0Igepal CO 530         GAF        2.0LICA 38 (titanium IV neo-                 Kenrich    0.6alkanolato, tris (diisooctyl)pyrophosphate)TITANATE and LICA 09Emollient Solvent     ICI        44.4Arlamol EPolypropylene Glycol  BASF       24.53Pluracol P-410Fumed Silica(CABOSIL TS-720)      Cabot      047grafted siloxanes on  chemicalfumed silicaProperties for Example IIIFluoresoence of drawdown                  160 PMUColor, Hunter parameters                  L = 61.16                  a = 48.58                  b = 20.89Viscosity at 15° C. at 500 sec.sup.-1                  462 cpsViscosity at 25° C. at 500 sec.sup.-1                  258 cpsViscosity at 45° C. at 500 sec.sup.-1                  96 cpsAverage particle size diameter                  0.3μShelf life by ASTM procedure D-1309                  Rating 10Water absorption at 29° C.,                  1.07 wt %95% RH after 23 hrs gr%Yield stress           1-1.4 PaPlastic viscosity      .210 cpNumber of prints obtained by                  500Kcontinuous printing without de-crease in print intensity______________________________________Example IV Blue Ink - Red FluorescenceIngredient            Manufacturer                            wt %______________________________________Red Fluorescent Pigment                 Lawter     16D536PHTHALOCYANINE BLUE/  Penn Color 4OE2 (Pigment Blue 15.1 andPigment Blue 15.3)Microlith Blue 4GT    Cibe Geigy 2Polypropylene Glycol  BASF       25(Pluracol P410)Nonyl phenoxy         Ciba Geigy 4polyoxyethylene ethanolIgepal CO 210 &amp; CO 530           2LICA 38 TITANATE      Kenrich    0.3(titanium IV neoalkanolato,tris (diisooctyl) pyrophosphate)coupling agentEmollient Solvent     ICI        44Arlamol ELinseed Oil Alkyd     Lawter     4.7                 Total      100.0%______________________________________ 
    
     The above embodiments have been given by way of illustration only, and other embodiments of the instant invention will be apparent to those skilled in the art from consideration of the detailed description. Accordingly, limitations on the instant invention are to be found only in the claims.