Abstract:
A latent image developing system, methods for imaging and developing images, and systems and methods for blocking or erasing latent images. The latent image developing system includes a substrate containing a colorless image deposited thereon. A developer instrument is used to provide a visible image. The developer instrument includes a developer composition reactive with the colorless image. An image blocking instrument is provided for concealing at least a portion of the visible image. The image blocking instrument is provided by a blocking composition applicator and an aqueous mixture of blocking composition and water.

Description:
FIELD  
       [0001]     The disclosure relates to multicolor novelty printed products, image developer systems for the products and to methods for developing and blocking or concealing images to provide clandestine messages and other unique effects.  
       BACKGROUND AND SUMMARY  
       [0002]     Substrates containing latent images have been used in the business forms market for producing security documents. The components used to develop images for the business forms are often self-contained in the forms typically by using microcapsules which are rupturable upon impact or contact with a suitable solvent. One such self-contained coating is described in U.S. Pat. No. 5,250,492 to Dotson et al. which relates to carbonless coating compositions for use with business forms or mailers. The business forms described by Dotson et al. are made using an admixture of a color former, a color developer, and a plurality of pressure-rupturable microcapsules containing solvent. A latent image printed with the admixture becomes visible upon application of pressure or solvent to the coated area to rupture or dissolve the microcapsules so that the solvent in the microcapsules interacts with the color developers and color formers in the coating.  
         [0003]     While the methods and compositions of Dotson et al. are particularly suitable for business forms, they are not particularly suitable for preparing games and novelty products which contain hidden or latent multicolor images. Inadvertent rupture of the microcapsules containing solvent may result in image development particularly in unintended areas of the form while handling or shipping the form. Furthermore, it is difficult and expensive to prepare multi-color latent images using microcapsule technology to provide a color density required to maximize the color intensity for use in novelty products. For example, it is generally cost prohibitive to use microcapsule technology to produce low cost children&#39;s books, games, puzzles, activity sets, and the like in high volume with a color intensity that would be suitable for such children&#39;s items. Such products made by conventional techniques typically require heavy ink coverage to obtain suitable color intensities. Accordingly, improvements in hidden image technology are required to achieve the desired level of reliability and image sharpness and intensity and to reduce the expense and production difficulty of multi-color latent image products for the novelty and game markets.  
         [0004]     With regard to the foregoing and other objects and advantages thereof, exemplary embodiments of the disclosure provide a latent image developing system, methods for imaging and developing images, and systems and methods for blocking or concealing latent images. The latent image developing system includes a substrate containing a colorless image deposited thereon. A developer instrument is used to provide a visible image. The developer instrument includes a developer composition reactive with the colorless image. An image blocking instrument is provided for concealing at least a portion of the visible image. The image blocking instrument is provided by a blocking composition applicator and an aqueous mixture of blocking composition and water.  
         [0005]     Another embodiment of the disclosure provides a latent image blocking system. The latent image blocking system includes a substrate containing a developer composition deposited thereon. At least one marking instrument having a substantially colorless compound reactive with the developer composition is provided to produce a visible image on the substrate. An image blocking instrument for preventing development of at least a portion of the visible image is also included. The image blocking instrument includes a blocking composition applicator and an aqueous mixture of a blocking composition and water.  
         [0006]     Other embodiments of the disclosure provide a method for selectively concealing a latent image developed on a substrate. The method includes providing a substrate containing a substantially colorless image deposited thereon. At least a portion of the colorless image is developed into a visible image by applying a developer composition with a developer instrument to the colorless image on the substrate to provide the visible image. An image concealing composition is applied to at least a portion of the visible image to conceal a portion of the visible image.  
         [0007]     Still another embodiment of the disclosure provides a system for printing and developing a colorless image on a substrate. The system includes a substantially colorless flexographic ink base comprising a binder resin and from about 5 to about 20 percent by weight of a substantially colorless compound dissolved in a solvent portion of the ink base for printing the colorless image on the substrate. A developer instrument containing a developer compound dissolved in from about 65 to about 85 percent isopropyl alcohol is also provided.  
         [0008]     An advantage of the systems, compositions, and methods described herein is that the images may be rapidly developed with high color intensity without having to apply relatively heavy ink coverage to a substrate to obtain the high color intensity images. The compositions and methods described herein are substantially more compatible with high speed printing techniques, such as four color processing, than conventional microcapsule latent image technology, and thus may provide optimum ink coverage with enhanced color intensity over conventional latent image printing technology. Accordingly, high volume, low cost activity sets, books, games, novelty items, and the like may be provided using the systems, methods and compositions described herein.  
         [0009]     Another advantage of the compositions and methods described herein is that each of the components is substantially colorless until applied to a previously printed or coated substrate. Accordingly, the marking instruments and compositions may not stain or mark clothing, skin, furniture, walls or other objects.  
         [0010]     Still another advantage of the embodiments described herein is the ability to provide clandestine messages by selective blocking development of latent images on a substrate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above and other features of the disclosed embodiments may be further described in the following detailed specification in conjunction with the accompanying drawings in which:  
         [0012]      FIG. 1  is an elevational view, not to scale, of a latent image printed substrate, image developer device, and image blocker device according to a first embodiment of the disclosure;  
         [0013]      FIG. 2  is a plan view of a latent image printed on a substrate according to the first embodiment of the disclosure;  
         [0014]      FIG. 3  is a plan view of the latent image of  FIG. 3  after a blocker composition has been applied to the latent image in a particular area;  
         [0015]      FIG. 4  is a plan view of the developed image of  FIG. 3 ;  
         [0016]      FIG. 5  is an elevational view, not to scale, of a latent image printed substrate, image developer device, and image blocker device according to a second embodiment of the disclosure;  
         [0017]      FIG. 6  is a plan view of a latent image printed on a substrate according to the second embodiment of the disclosure;  
         [0018]      FIG. 7  is a plan view of the latent image of  FIG. 6  after a developer composition has been applied to the latent image;  
         [0019]      FIG. 8  is a plan view of the developed image of  FIG. 7  after an eraser composition has been applied to the developed image of  FIG. 7 ;  
         [0020]      FIG. 9  is an elevational view, not to scale, of a developer printed substrate, coloring device, and image blocking device according to a second embodiment of the disclosure;  
         [0021]      FIG. 10  is a plan view of a substrate having a developer compound printed thereon according to the second embodiment of the disclosure;  
         [0022]      FIG. 11  is a plan view of the substrate of  FIG. 10  after a blocking device has been used for preventing development of an image on a portion of the substrate containing developer compound in  FIG. 10 ; and  
         [0023]      FIG. 12  is a plan view of the substrate of  FIG. 11  after coloring devices have applied one or more chromogenic compounds to the substrate containing the developer. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0024]     In the methods and systems described herein, components of the methods and systems may be deposited or printed on a substrate, preferably as a latent or substantially invisible image or as a substantially invisible developer component. By “substantially invisible” means that the deposited area may have a slight discoloration or may vary in tint from the adjacent substrate, however, to the casual observer, the variation in tint or coloration is so slight as to be essentially imperceptible prior to developing the image by the techniques described herein.  
         [0025]     In a first embodiment of the disclosure illustrated in  FIGS. 1-4 , a substrate is provided with a latent image  12  printed thereon. The substrate  10  may be made from a wide variety of materials including, but not limited to, paper, wood, polyester, polystyrene, polypropylene, ceramic, metal, natural and synthetic cloth or fabric, and the like. A suitable plastic substrate  10  is polyester. Likewise, suitable paper substrates  10  include offset, matte or coated papers. A particularly useful paper substrate is offset paper available from Boise Cascade and MeadWestvaco paper companies and has a weight of about 50 to about 70 pounds per ream.  
         [0026]     The latent image  12  may be printed on the substrate  10  by a wide variety of printing techniques including, but not limited to, flexographic, lithographic, sheet fed, web offset, rotogravure, gravure, screen printing, ink jet printing, and variable image printing techniques. Printing techniques which may be used to print the latent image  12  on the substrate  12  include spot printing and process printing. A particularly preferred printing technique is 3 or 4 color process printing. Process printing may be used with a web-offset or flexographic printer to deposit the latent image  12  on the substrate  10 . When developed, 3 or 4 color process printed images may be more visually pleasing than spot printing the images because a wider variety of colors may be printed using process printed images. Also, process printed images enable use of lower weights of ink to be printed while providing higher intensity of printed images.  
         [0027]     In the case of printing the latent image  12  with a variety of substantially colorless chromogenic ink formulations, a flexographic printing technique is particularly suitable and provides the latent image  12  having a image thickness ranging from about 0.25 micron to about 3 microns. Thicker or thinner layers of the image  12  may be used to provide variation in color intensity upon development of the image.  
         [0028]     A suitable flexographic ink composition for providing the latent image  12  may include a solvent-based ink base suitable for use in a flexographic printing process. Ink compositions, as described herein, are substantially colorless and adaptable to four color processing operations. The substrate  10  containing the latent image  12 , before development is shown in  FIG. 2  wherein the broken line concentric circles  14 ,  16 ,  18 ,  20 , and  22 , represent different latent image colors.  
         [0029]     With respect to the embodiment illustrated in  FIGS. 1-8 , the ink composition used for applying the latent image  12  to the substrate  10  may include a solvent based ink base containing one or more substantially colorless chromogenic compounds selected from colorless dyes and colorless pigments. For the purpose of simplicity, the chromogenic compound may be referred to as a colorless dye, however, the term colorless dye, when used also includes other colorless chromogenic compounds such as colorless pigments and the like.  
         [0030]     Accordingly, the ink base may include a colorless dye, a polyamide resin, and one or more of ethanol, heptane, n-propyl acetate, isopropyl alcohol, n-propanol, and nitrocellulose. Such ink compositions may contain from about 1 to about 10 percent by weight colorless dye, from about 10 to about 45 percent by weight polyamide resin, from about 10 to about 45 percent by weight ethanol, from about 5 to about 15 percent by weight heptane, and from about 0.5 to about 10 percent by weight of one or more of the other components.  
         [0031]     The colorless dye may be dissolved in a solvent portion of the ink base using conventional high shear mixing with heating. After the colorless dye is dissolved in the solvent portion of the ink base, the dissolved dye and a varnish portion of the ink base are then mixed at relatively low speeds with other components of the ink base. Suitable colorless dyes may be available from Intense Printing, Inc., of Dallas, Tex. under the trade names IPI 2537 YL (yellow), IPI 21115 BK (black), IPI 32212 BL (blue), IPI 32219 BLS (higher solubility blue), and IPI 854 RD (red). Exemplary ink formulations containing one or more of the foregoing dyes are contained in the following tables.  
                           TABLE 1                                   Colorless Ink Component   Weight Percent Range                           N-propanol   0.5-1.5           Isopropyl Alcohol   1.0-4.0           N-propyl Acetate   1.0-4.0           Heptane   7.5-9.5           Ethanol   35.0-45.0           Polyamide Resin Flexographic Ink Base   35.0-45.0           Colorless Dye(s)   4.5-6.5                      
 
         [0032]     The foregoing ink formulation is generally considered a solvent-base ink formulation. However, the colorless dyes may also be used with a substantially aqueous-base ink formulation. As with the solvent-base formulation given in table 1, the colorless dye for the aqueous-base formulation may be dissolved in a solvent portion of the ink base containing a minor amount of the copolymer using conventional high shear mixing with heating. After the colorless dye is dissolved in the solvent portion of the ink base, the dissolved dye and the remaining copolymer portion of the ink base are then mixed at relatively low speeds. A suitable aqueous-base ink formulation is contained in the following table 2.  
                   TABLE 2                       Colorless Ink Component   Weight Percent Range                   Styrene/acrylic copolymer suspended in water   30.0-80.0       Isopropyl Alcohol    2.0-10.0       Dipropylene glycol monomethyl ether   1.0-3.0       2,4,7.9-tetramethyl-5-decyne-4,7-diol   1.0-3.0       Colorless Dye(s)   4.5-6.5                  
 
         [0033]     While the foregoing compositions are particularly suitable for the first embodiment of the disclosure, other colorless ink formulations may be used with suitable developers and blocker compounds to provide the benefits and advantages described herein. Additional, two or more of the dyes may be combined to provide higher intensity color development. For example, a relatively low solubility blue dye IPI 32212 BL) mixed with a relatively high solubility blue dye (IPI 32219 BLS) may provide a greater color intensity than either one of the dyes alone at a same dye concentration as the concentration of the mixed dyes.  
         [0034]     Additional components may be present in the ink formulations including, but not limited to, film formers, fillers, binders, waxes, non-volatile diluents, uv absorbers, antioxidants and starch particles (stilt). Film formers, which may be used include polyvinyl pyrrolidone, polyvinyl alcohol, starch, grafted starch and the like. In addition, the film former provides excellent rheological properties to the ink formulation that may permit the image to be spot coated or printed using conventional flexographic printing equipment. The film former may also aid in maintaining the chromogenic compound at the surface of the substrate  10  so that solvent interaction with a developer composition produces a sharp image on the surface of the substrate  10 .  
         [0035]     The binders with may be used to prepare the ink formulations for printing on the substrate  10  may be selected from partially or fully hydrolyzed polyvinyl alcohols, natural or modified starches, acrylics and the like. A preferred binder is a modified starch available under the trade name PENSIZE 730 binder available from Penford Products of Cedar Rapids, Iowa.  
         [0036]     Fillers which may be included in the ink formulations may be selected from any number of compounds such as calcium carbonate, wheat starch, rice starch, nitrous cellulose, and/or polyamide resin.  
         [0037]     Diluents may also be used to reduce the viscosity of the ink formulation for printing and to reduce curling of the coated substrate. Suitable diluents include, but are not limited to, ethyl alcohol, isopropyl alcohol, and methyl glucocide.  
         [0038]     The amount of ink formulation deposited or printed on the substrate  10  may vary with the characteristics of the substrate  10  and the use thereof. Higher coating weights may be used for more porous substrates  10 , whereas lower coating weights may be acceptable for substantially non-porous substrates  10 . For many substrates, it is desirable to apply a sub-layer between the substrate  10  and the latent image  12  in order to reduce the absorbence of ink into the substrate  10  or reduce the contrast between the latent image  12  and the non-printed portions of the substrate  10  adjacent the printed areas. Such sublayer may comprise a pigmented coating of ink such as an amine solubilized acrylic, overprint varnish or other material which substantially reduces the contrast between the substrate  10  and the latent image printed  12  printed on the substrate  10 . A preferred sublayer is a starch-based coating containing TiO 2  or CaCO 3  plus an optical brightener. It is particularly desirable to use a sublayer which provides a difference in reflectance between the substrate  10  and the latent image  12  of less than about five percent.  
         [0039]     The preferred coating weights of the latent image  12  printed on the substrate  10  may range from about 0.25 to about 2 pounds per 1300 square feet. Accordingly, the thickness of the latent image  12  after drying may range from about 0.25 micron to about 3 micron. The preferred thickness of the latent image  12  is about 0.65 micron.  
         [0040]     Before the substrate  10  is printed with the latent image  12 , it may be desirable to coat an opposing surface of the substrate  10  with a varnish or stiffening material to reduce substrate  10  curling particularly when the substrate  10  is a thin web such as paper or a plastic film. A particularly suitable varnish is a flexo applied sizing varnish.  
         [0041]     The ink formulations provided above in Table 1, may be spot printed on a substrate  10  using a COMPCO COMAMANDER printer with 10-11 billionths of a cubic meter (BCM), 200 line anilox rolls with a doctor blade or a NILPETER printer with 8-9 BCM, 300 anilox rolls. Other printing techniques may also be used to provide the latent image  12  on the substrate  10  according to the disclosed embodiments and the amount of base ink to dye may be adjusted for lower or higher BCM anilox rolls.  
         [0042]     In order to develop the latent image  12 , a device or instrument  24  containing a developer composition may be used to apply the developer composition to selected portions of the latent image  12 . The instrument  24  for applying the developer composition to the latent image  12  may include solvent pen having a felt solvent dispensing tip  26 . The production of suitable felt tipped pens for dispensing solvents is well known in the art. Other developer compositions may be applied by use of other devices such as fingers dipped into a finger paint type developer composition, crayon-like developers, developer towelettes, and other developer carrier vessels.  
         [0043]     Prior to developing the latent image  12 , a secret message may be written on the latent image as indicated by the broken-line rectangle  28  in  FIG. 3 . The secret message may be written by applying a blocking composition from a blocking marker  30  having a felt dispensing tip  32  to selected portions of the latent image  12 . The blocking marker  30  may be used to prevent development of selected portions of the latent image  12 .  
         [0044]     A suitable blocking composition for blocking development of the latent image  12  in the rectangle  28  may an amine compound dissolved in water. A particularly suitable amine compound is triethanolamine. Accordingly, the blocking formulation may include from about 15 to about 35 weight percent triethanolamine and from about 65 to about 85 weight percent water. Above this range, the blocking composition may be less effective. While not desiring to be bound by theory, it is believed that the blocking composition may absorb less into the substrate above about 35 wt. %. Accordingly, an optimal blocking formulation may include from about 20 to about 25 wt. % triethanolamine and from about 75 to about 80 wt. % water.  
         [0045]     In  FIG. 4 , the developer composition has been applied to the entire latent image  12  to provide a visible image  34  with the exception of a portion  36  of the image to which the blocking composition was applied. In the alternative, selective portions of the image may be developed by applying the developer composition to only such portions of the image as is desired to be developed. As shown in  FIG. 4 , each of the concentric circles  14 - 22  contains a different color upon development. The compositions used to provide the different colors in the concentric circles  14 - 22  may be applied in a three or four color printing process to provide a wide variety of colors that may be developed as described herein.  
         [0046]     In accordance with the foregoing embodiment, a user may encode secret messages by blocking development of selected areas of the latent image  12  using the blocking marker  30 . The secret messages  36  may only be revealed by another user having a developer suitable for developing the latent image as shown in  FIG. 4  so that the secret message  36  is revealed.  
         [0047]     The developer composition for developing the latent image  12  may be selected from acidic clays and unsubstituted or ring-substituted phenols, phenolic resins, sulfone compounds, alkylhydroxybenzoic acid compounds and salicylic acid or salicylate and their metal salts or combinations of two or more of the foregoing. A suitable color developer composition for developing latent images  12  may be a benzoic acid compound dissolved in an alcohol carrier fluid. For example, the developer composition may include from about 5 to about 15 weight percent salicylic acid, from about 65 to about 85 percent by weight isopropyl alcohol and from about 10 to about 20 percent by weight bisphenolic compounds.  
         [0048]     Another developer composition that may be used includes from about 30 to about 65 percent by weight metal chloride, from about 10 to about 25 weight percent water, from about 10 to about 25 weight percent propylene glycol, and from about 10 to about 25 weight percent isopropyl alcohol. While zinc chloride is a particularly desirable metal chloride, other metal cations may also be used, such as cadmium (III), zirconium (II), cobalt (II), strontium (II), aluminum (III), copper (III), and tin (II).  
         [0049]     In another embodiment of the disclosure, an eraser instrument  38  ( FIG. 5 ) containing an eraser composition may be used with the printed image  12  to erase or conceal selected portions of the image  12 . The eraser instrument  38  may be used as, as illustrated in  FIG. 8 , to “erase” or otherwise reverse or conceal selected portions  40  of the developed image  34  so that the portions  40  of the image  34  again become substantially colorless in the selected portions  40  as shown in  FIG. 8 . Accordingly, the eraser instrument  38  may be used to further create unique designs or coloration of images on the substrate  10  or provide concealed messages. As with the blocker composition, the eraser composition may be applied to the latent image  12  or developed image  34  using the eraser instrument  38  having a felt solvent dispensing tip  40 . The latent image  12  may be applied to the substrate  10  as described above with reference to  FIGS. 1-4 .  
         [0050]     Like the blocker composition, the eraser composition includes an amine compound dissolved in water. A particularly suitable amine compound is triethanolamine. Accordingly, an eraser formulation may include from about 15 to about 35 weight percent triethanolamine and from about 65 to about 85 weight percent water. Above this range, the eraser composition may be less effective. An optimal eraser formulation may include from about 20 to about 25 wt. % triethanolamine and from about 75 to about 80 wt. % water.  
         [0051]     A third embodiment of the disclosure is illustrated in  FIGS. 9-12 . In this embodiment, a substrate  42  has a developer layer  44  containing a developer compound printed thereon. The substrate  42  containing the printed developer layer  44  is illustrated in plan view in  FIG. 10 , wherein the developer layer  44  is indicated by the broken line  46 .  
         [0052]     A printing technique for applying the developer layer  44  to the substrate  42  may include any of the well known printing and substrate coating techniques. Application of the developer composition may be over the entire substrate  42  or may be in selected areas of the substrate  42 . Ink jet printing, screen printing, rotogravure printing, flexographic printing, and the like may be used to apply the developer layer  44  to selected portions of the substrate  42 . Roll coating, blade coating, dipping, spray coating, and the like may be used to coat an entire portion of the substrate  42 . The amount of developer composition applied to the substrate  42  to provide the developer layer  44  may range from about 0.35 micron to about 4.5 microns or more. The developer composition may be applied evenly over the entire substrate  42  or different amounts of developer composition may be applied to different portions of the substrate to provide variations in the intensity of the images and the speed at which the images become visible to provide different image effects.  
         [0053]     An advantage of the developer composition in combination with colorless chromogenic compositions is that lighter weight color developer laydown may be used to provide fine detail images and images having vibrant colors, whereas conventional compositions require heavy weight laydown amounts of developer to provide image intensities that only approach the image intensities of the disclosed embodiments. Accordingly, a flexographic process using a 200-400 line anilox roll may apply sufficient developer composition to provide high resolution images upon application of a colorless chromogenic composition to the developer layer  44 .  
         [0054]     Developer compounds that may be used in the developer composition include, but are not limited to, acidic clays and unsubstituted or ring-substituted phenols, phenolic resins, sulfone compounds, alkylhydroxybenzoic acid compounds and salicylic acid or salicylate and their metal salts or combinations of two or more of the foregoing. Accordingly, a preferred color developer compound may be a benzoic acid, 2-hydroxy-3,5-bis(1-phenylethyl)-, zinc salt and (9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide) copolymer with a-methylstyrene, styrene, and polyvinylalcohol. Of the foregoing, compounds, a zinc salicylate resin may be particularly suitable as a component of the developer composition. While zinc is the preferred cation, other metal cations may also be used, such as cadmium (III), zirconium (II), cobalt (II), strontium (II), aluminum (III), copper (III), and tin (II).  
         [0055]     A formulation that may be used to print or apply the developer composition onto the substrate  42  may include binders, pigments, surfactacts, water and the like. A particularly useful formulation is provided in the following table.  
                           TABLE 3                                   Developer Composition   Weight Percent Range                           PENSIZE Starch binder   10-20           SATINTONE 5 HB pigment   10-20           Zinc salicylate resin   45-65           Glycol   1.0-3.0           Defoamer   1.0-2.0           Water    5-15                      
 
         [0056]     Another color developer formulation that may be used is a substantially aqueous color developer composition. The substantially aqueous color developer composition includes from about 30 to about 65 wt. % zinc chloride, from about 10 to about 25 wt. % water, from about 10 to about 25 wt. % propylene glycol, and from about 10 to about 25 wt. % isopropyl alcohol.  
         [0057]     In order to provide an image on the substrate  42 , a marking instrument  48 , or plurality of marking instruments  48  containing different substantially colorless chromogenic compounds may be used to apply the chromogenic compounds to the developer layer  44  to produce a visible image  50  as shown in  FIG. 12 . The marking instrument  48  may contain a mixture of the chromogenic compound dissolved in an organic solvent for application to the developer layer  44  through a felt tip  52  portion of the instrument  48 .  
         [0058]     A formulation containing the colorless chromogenic compound for use in the marking instruments  48  may include from about 75 to about 95 percent by weight alcohol, from about 2 to about 15 percent by weight of the chromogenic compound, and from about 1 to about 10 percent by weight glycol ether. Alcohol solvents which may be used, include, but are not limited to, C 1 , to C 4  alkyl alcohols such as is ethanol, methanol or isopropanol, n-propyl alcohol and the like. Other solvent that may be used include, but are not limited to, C 1 , to C 4  alkyl ethers, C 1  to C 4  alkyl esters, ketones and acetates. Ketones may include methyl ethyl ketone and acetone. The embodiments described herein also contemplate colorless chromogenic compounds that may be applied with fingers instead of the marking instruments  48 .  
         [0059]     Prior to applying one or more chromogenic compounds to the developer layer  44 , a blocking composition may be applied to the developer layer  44  to prevent development of color upon application of the chromogenic compound to the developer layer  44 . Accordingly, the blocking instrument  30  containing the blocking composition described above may be used to provide blocked areas  54 , illustrated in outline in  FIG. 11  on the developer layer  44 . Upon application of the chromogenic compounds to the developer layer  44 , the blocked areas  54  remain uncolored as illustrated in  FIG. 12  while the remaining portions of the developer layer  44  provide colored images represented by concentric circles  56 - 64 .  
         [0060]     Having described various aspects and exemplary embodiments and several advantages thereof, it will be recognized by those of ordinary skills that the disclosed embodiments are susceptible to various modifications, substitutions and revisions within the spirit and scope of the appended claims.