Luminescent writing or display device
FIELD OF INVENTION 
     This invention is directed to an improved writing and display device for producing semi-permanent images or writings thereon that will appear as glowing or luminescent images. 
     PROBLEM AND PRIOR ART 
     Writing and display devices of the type disclosed in my prior U.S. Pat. No. 3,761,343 granted Sept. 25, 1973, are now well known and have been extensively applied to many toy type items and other writing or display products. U.S. Pat. No. 4,011,665 has also been granted for a similar type of writing and display device. The subject of both of the foregoing identified patents requires a transluscent or transparent plastic sheet that contains a luminescent dye and a complementary opaque sheet disposed contiguous thereto,so that when a pressure was applied thereto, the two sheets would tend to adhere to one another along the points of applied pressures to produce a glowing or luminescent type image. However, in the prior art devices embodying this principle, it has been observed that there is a tendency of luminescent dye to migrate out of the translucent or transparent sheet and &#34;bleed&#34; onto the adjacent opaque sheet. If permitted, the &#34;bleeding&#34; of the dye from the transparent or transluscent sheet and onto the interfacing surface of the opaque sheet would render the device inoperative or substantially negate the glowing or luminescent effect so as to minimize the operability of the device. To obviate this &#34;bleeding&#34; effect, it was heretofore necessary to place or insert a protective sheet of material or insert between the dye contained transparent or transluscent sheet and the opaque sheet, and which protective sheet or insert had to be removed whenever the device was to be used, and re-inserted between the two sheets when the device was not in use. Thus, the protective sheet or insert resulted in an added cost to the manufacturer and ultimately to the consumer or purchaser. Also, it frequently happened that the user would neglect to reinsert the protective sheet or insert between the transparent sheet and the opaque sheet when the device was not in use or stored. As a result, the dye of the transparent sheet would &#34;bleed&#34; out and in time would render the device inoperative and/or reduce the effectiveness thereof. 
     OBJECTS 
     An object of this invention resides in providing a writing or display device for producing a luminescent or glowing image with a transparent or luminescent sheet in which the migration of the luminescent dye or pigment therein is retarded or prohibited. 
     Another object is to provide a luminescent writing device or slate with a vinyl transparent sheet formulated with a plasticizer in which a luminescent dye or pigment is dispensed that retards the migration of the dye or pigment out of the sheet. 
     SUMMARY OF THE INVENTION 
     The foregoing objects and other features and advantages are attained by a luminescent writing device or display which includes a pair of contiguous or superposed sheets of material, one of which comprises a transluscent or transparent plastic sheet, e.g. a vinyl sheet, formulated with a primary plasticizer that resists migration; exudation or volatilization out of the surface of the vinyl sheet under normal or storage conditions and having disbursed therethrough a suitable fluorescent or luminescent dye or pigment. Disposed contiguous to such formulated transluscent or transparent sheet is an opaque sheet. The respective sheets are provided with a smooth surface at the interface thereof so that when a pressure is applied thereto, there is a tendency of the sheets to adhere to one another along the lines of applied pressure causing a glowing or luminescent image to appear along the lines of pressure. The images so formed are readily erased by separating the sheets to break the adhesive or cohesive forces between the sheets. Upon so erasing the glowing image, the writing device is again readied for use. 
     FEATURES 
     A feature of this invention resides in the provision of a luminescent writing or display device having a transparent or transluscent sheet impregnated with a fluorescent or luminescent pigment or dye formulated with a low volatile plasticizer that prohibits migration and/or &#34;bleeding&#34; of the luminescent materials out of the sheet. 
     Another feature of this invention resides in the provision of a luminescent writing or display device in which a separator or insert sheet is not required to be disposed between the transparent sheet and its continuous opaque sheet when the device is not being used and/or in storage so as to prohibit the &#34;bleeding&#34; effect. 
     Other features and advantages will become more readily apparent when considered in view of the following detailed description. 
    
    
     IN THE DRAWINGS 
     FIG. 1 illustrates a preferred embodiment of the invention. 
     FIG. 2 is a cross-sectional view taken along line 2--2 on FIG. 1. 
     FIG. 3 is a view similar to FIG. 1 illustrating how the formed image may be readily erased. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, there is shown a writing and display device 10 embodying the invention. While the writing and display device may take various forms, the simplest and preferred form may be made to resemble a writing tablet, pad or slate comprising a relatively rigid backing member 11, which can be made of any suitable rigid material, e.g. cardboard, non-pliable plastic and the like. Supported on or secured to the backing member 11 and rendered substantially co-extensive thereto is a relatively smooth pliable sheet of a plastic material 12 which is opaque and preferably having a white or &#34;milk color&#34; opacity. The plastic sheet 12 may be formed of a pliable vinyl type plastic having a smooth, wetable type surface appearance. 
     Disposed continuous to or immediately above the opaque sheet 12 in interfacing relationship thereto is a transparent or transluscent pliable sheet of material 13 which, according to this invention, has dispersed therethrough a luminescent or fluorescent or transluscent tinting material, e.g. a dye or pigment to result in a transparent/tinted sheet. For the purposes of description, it will be understood that luminescent, fluorescent, irridescent, phosphorescent and glowing are considered to be synonomous in describing the nature of the dye or pigment and the effect or appearance of the image or display produced thereby. Essentially, the nature of the dye or pigment dispersed throughout the transparent sheet is such so as to produce a glowing or luminescent image when a pressure is applied thereto, as will be described. The formulation or dispersement of the luminescent dye or pigment through the transparent sheet 13 is such that any tendency of the luminescent dye or pigment to &#34;bleed&#34; or migrate therefrom is prohibited. 
     Heretofore, the transparent sheets containing luminescent dyes for making the writing and display devices of the type referred to in U.S. Pat. Nos. 3,761,343 and 4,011,665 were made with the transparent sheet formulated with a dioctyle phthalate plasticizer or other more volatile plasticizer such as dibutyl phthalate and/or having excessive amounts of secondary plasticizer such as aromatic hydrocarbons and chloroparaform, wherein the luminiscent dye was dissolved in the plasticizer. As such, vinyl sheets were readily available. They have been used. However, it has been observed from experience that luminescent writing slates or devices utilizing the available transparent vinyl sheets with a luminescent dye dispersed therethrough so formulated that there was a decided tendency for the luminescent dye to &#34;bleed&#34; out of the transparent sheet and onto the underlying opaque sheet. In a relatively short period of time, the underlying opaque sheet, which was preferably white, would absorb the dye &#34;bleeding&#34; out of the luminescent transparent sheet, causing the opaque white sheet to assume the color of the dye initially dispersed throughout the transparent sheet. When this occurred, the brilliance or &#34;glowing&#34; effect of the images would be greatly diminished to a point where the device was no longer interesting or amusing. To obviate this difficulty, an inert or protective sheet was disposed between the transparent sheet and the opaque sheet to prevent the bleeding and/or absorbtion of the dye onto the opaque sheet when the device was not in use. Such inert or protective sheet was made of any material that would not absorb the dye, e.g. plain paper or non-absorbant cardboard. 
     To obviate the bleeding effect of the dye from the transparent sheet, the transparent sheet should be formulated with a primary plasticizer that has less migration and/or volatilization than that of dioctyl phthalate, that is conventionally used. The preferred plasticizers for formulating a transparent vinyl sheet for application in accordance with this invention would be one that will substantially resist or retard migration to and exudation or volatilization out of the surface of the vinyl sheet under normal or storage conditions. Such preferred plasticizers for formulating the luminescent transparent sheet 13 may include disodecyl phthalate, trialkyl trimellitates, e.g., trioctyl trimellitate; epoxidized soya oil or other opoxidized fatty esters; polymeric plasticizers such as adipic acid or azelaic acid polyesters of molecular weight 850-6000 made from dicarboxylic acids such as adipic or azelaic acid, e.g. the Paraplex plasticizers made by C.P. Hall Co. of Chicago, Ill. 
     It has been discovered that the utilization of transparent sheets having a luminescent dye or pigment dispensed therethrough that has been formulated with a primary plasticizer which is less volatile than dioclyl phthalate, that the bleeding of the luminescent dye therefrom is prohibited or substantially retarded so as to substantially improve and enhance the use and application of the luminescent or fluorescent writing or display device herein described. Bleeding can be further minimized or retarded by dispersing fluorescent pigments rather than dyes throughout the transparent sheet 13. While pigments, in contrast to dyes, are solid particles, they are so finely divided that they can be readily dispersed to form transparent colored or tinted plastic film or sheet that is extremely suitable for application as a luminescent or fluorescent writing and display device as herein described. 
     Referring to FIGS. 1 and 3, it will be noted that the transparent sheet 13 may be suitably secured in overlying position relative to the opaque sheet 12 along one edges thereof, e.g., along edge 13A by suitable means to define a hinging connection between the sheets 12 and 13. This may be effected by adhesively securing the edge portion 13A of sheet 13 to the contiguous edge 12A of sheet 12 by an adhesive, or by a binding hinge strip of material, tacking or other suitable well known hinging construction. As shown in FIG. 3, the hinging effect renders the sheets 12 and 13 readily separable by lifting one from another to effect the erasure of any image formed thereon. 
     With the construction herein described, the need of positioning a protective sheet or insert between the opaque sheet 12 and the overlying luminescent sheet 13, having a luminescent dye or pigment dispensed therethrough is not required when in storage or not in use. 
     In operation, it will be understood that whenever a pressure is applied onto one of the sheets, e.g. by a stylus S, the applied pressure thereon will cause the two sheets 12 &amp; 13 to adhere or be urged into intimate contact together at the points of applied pressure (see FIG. 2) so that light reflecting thereat will create an image that appears to be &#34;glowing&#34; or luminescent in appearance. As the interfacing surfaces of sheets 12 and 13 have a smooth, wet-like appearance, they will tend to remain adhered or cohered to one another along the points of applied pressure, to sustain the &#34;glowing&#34; or luminescent image thereat until such time that the cohesive bonding or intimate contact of the two sheets 12 and 13 is broken. This can be readily attained by lifting one sheet away from the other to erase the image. It will be understood that the image may be erased by any suitable separating means disposed between the respective sheets 12 and 13 that will effectively separate the sheets 12 and 13 along the points of applied pressure. 
     While the invention has been described with respect to a particular embodiment thereof, it will be understood that variations and modifications may be made without departing from the spirit or scope of the invention.