Electroluminescent decals

April 25, 1961

2,981,858

J. A. O’CONNELL

ELECTROLUMINESCENT DECALS

Filed July 21, 1959

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FIG.3

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ATTORNEY

United States Patent Office

2,981,858

Patented Apr. 25, 1961

2,981,858

ELECTROLUMINESCENT DECALS

Janies A. O’Connell, Poughkeepsie, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York

Filed July 21, 1959, Ser. No. 828,599

Claims. (Cl. 313—108)

This invention relates to electroluminescent panels, and particularly to a pressure sensitive electroluminescent decal for forming illuminated displays.

The electroluminescent lamp, made up of a sandwich of electroluminescent phosphor between two conductive plate electrodes, at least one of which is transparent, is well known in the art. Electroluminescent “wallpaper,” and other electroluminescent devices in which both the electrodes and the phosphor-loaded dielectric are flexible have been proposed.

A known construction method for an electroluminescent panel is to, coat the conductive side of a transparent conductive plate electrode with a dispersion of electroluminescent phosphor in a dielectric plastic such as an alkyd resin with cellulose nitrate, and to evaporate a metallic electrode over the phosphor layer to complete the sandwich. This construction produces a quality product, but an expensive product. Though such a panel is rugged and hardy, it is subject to damage through breakage and age failure; repair of such damage is virtually impossible.

The need exists for an electroluminescent display lamp which is inexpensive to produce, rugged, hardy and readily repairable. For large signboard-type displays, such as marquees, the need exists for a changeable display which may be setup and altered by unskilled personnel. The need also exists for a means to repair electroluminescent panels.

It is therefore an object of this invention to provide a pressure-sensitive electroluminescent decal which may be formed into various display configurations and affixed to a plate electrode panel to form an illuminated display.

A further object of the invention is to provide a novel method of assembling an electroluminescent panel, by forming the mirror image of the desired pattern out of pressure-sensitive electroluminescent decal stock, affixing the pattern decal to a transparent conductive plate electrode and attaching connections to the electroluminescent decal and transparent electrode.

Another object of the invention is to provide an inexpensive display which may be altered or repaired by unskilled personnel.

Still another object is to provide an inexpensive repair medium for damaged electroluminescent panels.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments 60 of the invention, as illustrated in the accompanying drawings.

In the drawings:

Fig. 1 illustrates in cross-section a preferred embodiment of the invention, in which one electrode is integral with the decal backing.

Fig. 2 illustrates in cross-section a second embodiment of the invention, in which one electrode is metallized on a plastic decal backing.

Fig. 3 illustrates in cross-section a third embodiment of the invention, in which both electrodes are separate from the decal.

Fig. 4 illustrates the obverse side of a “Stop” sign made according to the invention.

Fig. 5 illustrates in cross-section a preferred novel con·, struction of the electroluminescent decal.

The electroluminescent decal stock is prepared in batches and stored in the form of sheets, rolls of tape, or preformed patterns such as numerals. Phosphor particles are suspended throughout the pressure-sensitive dielectric adhesive, and a suitable conductive electrode material may be incorporated into the backing. Patterns may be cut out of the decal with scissors, the decal pattern then being affixed in place on a transparent conductive electrode. Suitable electrical connections are made to complete the illuminated display.

Fig. 1—Flexible electrode

The electroluminescent decal illustrated comprises a backing of creaseless aluminum foil 1 spread with a layer of pressure-sensitive adhesive dielectric 2 throughout which phosphor particles 3 are dispersed. The decal is affixed to a transparent plate electrode 4 which may be made up of conductive layer 5 of tin oxide or the like on a glass plate 6. Silver paste connections 7 are then made to wires 8 and 9 which connect the electroluminescent lamp across potential source 10, which is suitable for operation with the phosphor chosen. Unless a mottled or crinkled design is desired, it is important that the backing of aluminum foil 1 be completely creaseless so that the pressure-sensitive adhesive phosphor layer is uniform in thickness.

Fig. 2—Metallized electrode

The electroluminescent decal illustrated comprises phosphor particles 3 suspended throughout a layer of pressure-sensitive dielectric 2, adhering to metallized layer 12 which is supported by a plastic backing 13. The tape is affixed by pressure to plate electrode 14, which may be identical to plate electrode 4 in Fig. 1. Connections 7: are made to wires 8 and 9 and potential source 10, which completes the illuminated display. Metallized layer 12 may be so thin as to be transparent, in which case the display may be viewed from either side, or plate electrode 14 may be of opaque material.

Fig. 3—Separate electrodes

The electroluminescent decal illustrated is made up of phosphor particles 3 dispersed throughout pressure-sensitive adhesive dielectric 2, which is supported by backing 15. The decal is affixed by pressure to plate electrode 14, and sandwiched between plate electrodes 14 and 16, either or both of which may be transparent conductors. Connections 7, wires 8 and 9, and potential source 10 complete the illuminated display. Plastic backing 15 is preferably very thin, or composed of conductive material, since electroluminescent lamps operate more effectively , when electrodes are closely spaced and the dielectric separating them is “lossy.” Suitable clamps 17, or a phosphor-free adhesive (not shown) are used to bind the complete display panel into a unit.

Fig. 4—Construction

I

Construction of an illuminated display, such as the “Stop” sign shown in Fig. 4, requires the following steps:

(1) Patterns such as characters 18 are cut out of electroluminescent decal stock such as is shown in Fig. 1, to, form pattern decals in the mirror image of the desired patterns.

(2) The pattern decals 18 are affixed by pressure to the conductive face of a transparent conductive plate electrode 4 to form the nfrror image of the desired display, , such as the text “Stop.” (3) Each pattern decal is manipulated for uniform adhesion to the plate electrode 4, preferably by rolling.

2.981.858 ·’· 3

Any air pockets are thus eliminated, as are creases which may have formed in the flexible backing. Such creases or pockets otherwise would detract from the display by presenting a mottled or lined appearance. Manipulation must be with care to prevent excessive pressure in certain spots from causing complete flow of the pressure-sensitive adhesive dielectric from a spot, which would shortcircuit the panel.

(4) Wires 8 and 9 are connected to transparent plate electrode 4 and to the flexible backing electrode 1 (see Fig. 1) of the decal, by silver paste connections 7. When Connected to a suitable potential source 10, the display luminesces and is readable through the transparent plate electrode.

' Should, for any reasons, it be desired to change the wording of the display to Post, the characters, which peel away from the conductive plate electrode, are carefully removed. Any remain ng phosphor-loaded adhesive from the plate is removed with solvent, and the characters reapplied in the desired sequence. Should a large character be damaged, even if originally made by ordinary methods, the panel may be patched by cutting out the damaged portion, using it as a pattern to make a duplicate from decal stock, applying the decal, and making suitable electrode connections, either from the decal patch to the old electrode in the character being patched, or to a wire 9.

For displays which may be read from two sides, or displays subject to tampering or weathering, the embodiment of Fig. 3 may be used, in which the decal is transparent and two plate electrodes are used. For large displays, however, it becomes expensive to provide plate electrodes with proper parallel faces within the close spacing tolerances required for proper luminescence. It is then advantageous to use decal stock such as illustrated in Figs. 1 and 2, make the usual connections and back up the display with an ordinary plate of glass in place of plate electrode 16.

The term “display” is to be broadly understood, since the invention may find uses in photologic devices in the computing industry, in laboratory applications, and in many other light-producing applications other than sign type displays.

Fig. 5—Formulation

Electroluminescent decal stock may be prepared in the following preferred manner:

(1) A backing of aluminum foil 19 is rolled to remove creases, and thoroughly cleaned with carbon tetrachloride.

(2) A primer coat 20 of tetrabutyl titanate is sprayapplied and air dried.

. (3) A thin layer 21 of a dispersion of .5 gm. electroluminescent phosphor 3 and 10 gm. of an elastomeric silicone such as that marketed by Dow Corning under the label “Silastic S-2007,” thinned in a suitable solvent such as xylene-toluene, is spray-coated and air dried for 3 minutes, then baked at 150° C. for 5 minutes. The layer may vary in thickness between .1 and 1.0 mil but should be uniform for best results. It contains phosphor, since the silicone is an insulator otherwise and would thus interfere with luminescence at low voltages.

(4) The primed and coated backing is then spraycoated with a thicker layer 22 of a dispersion of 36 gm. of a pressure-sensitive silicone adhesive (such as that marketed by Dow Corning as “C-274 Silicone”) having 60% solids and 5 gm. of activated zinc sulfide electroluminescent phosphor (finely ground). The mixture is thinned for spraying with a xylene-toluene solvent.

(5) The coated decal stock is finally baked at 215° C. for 8 minutes.

Storage of the decal stock may be in roll form, or in sheets. It may be advantageous to cover the adhesive side with a slick paper for protection during storage, especially when storage is in sheet form or in preformed patterns.

Care must be taken, in cutt’ng the desired pattern from decal stock to prevent a downturn of the raw edge of the electrode which might short-circuit the device. If scissors are used, the cutting blade should be on the scrap 5 side, with the supporting blade holding the pattern. If a knife is used, cutting should be done from the adhesive side, or extreme care should be taken to prevent downturned raw edges.

While the invention has been particularly shown and 10 described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.