Method of making plastic EL lamp

In this invention a basic EL lamp structure is prepared by spray coating an EL phosphor compound onto one side of film substrate, and when the EL layer has dried, spray coating a translucent, electrically-conductive film of an indium oxide formulation onto the EL layer and the opposite side of the substrate. Although this structure will glow when an AC voltage is impressed thereacross, it is preferred to attach two foil leads to the basic lamp, and to laminate this assembly between a pair of tough, polyester films, which prevent the basic lamp from ripping or tearing. Moreover, for even greater protection, this assembly is laminated between two layers of a moisture resistant, fluorocarbon film, thus producing a panel suitable for illuminated room dividers, etc. If desired a thin metal film can be photo etched on one of the polyester films to project an image when the lamp is energized.

This invention relates to electroluminescent or EL lamps, and more 
particularly to an improved, plastic EL lamp capable of emitting light 
from each side thereof when energized. 
Most EL lamps of known construction are capable of emitting light from only 
one surface side of the lamp. Such lamps usually include an opaque 
substrate (for example, a solid sheet of aluminium), generally rigid, upon 
which are mounted the necessary electrodes, and the electro-luminescent 
phosphor, which produces the illumination when an alternating or 
intermittent voltage source is applied across the electrodes. 
Other disadvantages of prior EL lamps include the fact that they have been 
rather difficult to manufacture, and have been rather fragile, thus 
requiring extreme care in handling, storing, etc. Moreover, most such 
prior lamps have enjoyed rather limited utility, and as presently known, 
have seldom if ever been employed economically for decorative or design 
purposes. 
It is an object of this invention therefore, to provide an improved method 
of producing EL lamps which can be readily adapted both for utilitarian 
and design purposes. 
A further object of this invention is to provide an improved method which 
simplifies the manufacture of EL lamps, and which is relatively simple and 
inexpensive to perform as compared to prior such methods. 
Still another object of this invention is to provide an improved, plastic 
EL lamp which is capable of emitting light from opposite surfaces thereof. 
It is an object also of this invention to provide an EL lamp in which 
artistic designs can be readily incorporated to render the lamp 
particularly suitable for use as decorative room dividers or grilles, 
suspended ceiling light panels, decorative wall sections, etc. 
A further object of this invention is to provide an improved EL lamp which 
can be made in very thin, flexible, planar sections, which in turn can be 
readily formed into various configurations such as for example 
cylindrical, conical, etc. 
These and other objects of the invention will be apparent hereinafter from 
the specification and from the recital of the appended claims, 
particularly when read in conjunction with the accompanying drawings.

Referring now to the drawings by numeral of reference, and first to FIG. 1, 
10 denotes generally a basic EL lamp structure made according to a first 
embodiment of this invention. It comprises a transparent, dielectric film 
substrate 11, which is made from a flexible, plastic material such as 
polypropylene, polyvinylidene fluoride, or the like, and which is coated 
on one side with a layer 12 of electroluminescent phosphor. Translucent, 
electrically-conductive layers 13 and 14 of an indium oxide formulation 
cover, respectively, the EL layer 12, and the opposite side of substrate 
11. 
This basic lamp structure 10 may be prepared by spray coating the layer 12 
of electroluminescent phosphor onto the upper surface of substrate 11. 
After this EL layer has dried, the layers 13 and 14 of the indium oxide 
formulation may also be spray coated over the layer 12 completely to cover 
it, and over the underside of the substrate 11. After this the assembled 
layers 11 to 14 are baked in a drying oven until the coating layers are 
set. This takes from about twenty minutes to one half hour at a 
temperature of approximately 280.degree. F., and completes the production 
of the basic lamp structure of this invention. 
As shown in FIG. 1, if an alternating current power source or varying 
voltage source is connected, for example by lines L1 and L2 across the 
outer, electrically-conductive layers 13 and 14, respectively, the lamp 10 
will become energized, and light will be emitted from the excited EL layer 
12 through both of the outer, transluscent layers 13 and 14. This basic 
lamp structure 10 at this stage comprises a flexible sheet approximately 4 
to 5 mils thick, consequently can be easily inventoried in stock sizes for 
use when needed. Moreover, although the basic structure 10 is capable of 
being excited to emit light, it generally is not used until it has been 
enclosed, as noted hereinafter, within additional layers of plastic which 
protect it from environmental hazards. 
Referring now to FIG. 2, after the basic lamp structure 10 has been cut to 
a desired size and configuration (rectangular in the embodiment described 
hereinafter), two metal foil input leads 15 and 16 are "tacked" 
intermediate their ends by two, small pieces 17 of pressure-sensitive, 
thermosetting, dielectric tape to the outer, electrically-conductive 
layers 13 and 14 of the section 10 so as to project outwardly beyond the 
edges of the associated layers 13 and 14, and in spaced, offset relation 
to each other as shown for example in FIG. 4. The tape pieces 17 are 
located intermediate the ends of their respective leads 15 and 16, so that 
the leads project at their inner ends beyond the tape to overlie and to be 
pressed into contact with the respective conducting layers 13 and 14 when 
the assembly is laminated as noted hereinafter. Moreover, each strip of 
tape 17 projects slightly beyond the adjacent edge of the associated layer 
13 and 14 to function as an edge pad for the associated input lead 15 or 
16, where these leads project outwardly beyond the lamp section 10. 
After the leads 15 and 16 have been "tacked" to the lamp section 10, this 
assembly is laminated between two layers 18 and 19 of tough, transparent, 
polyester-polyethylene laminating film to secure the inner ends of leads 
15 and 16 in electrical contact with layers 13 and 14, respectively, and 
to produce a monolythic lamp stack, which is denoted at 20 in FIGS. 2 and 
3. 
To produce the lamp stack 20 a laminating "pouch," which is denoted by 
broken lines at P in FIGS. 2 and 3, is placed upon the plane upper surface 
of an assembly table, or the like (not illustrated). The layer 19, which 
comprises a layer 21 of nylon having laminated to its upper surface a thin 
layer 22 of polyethylene, is then placed nylon-side-down on the lower 
surface S (FIG. 2) of the laminating pouch P, so that film 22 faces 
upwardly. The basic lamp section 10, with the leads 15 and 16 attached by 
the tape 17, is then placed on the surface 22 of the laminating layer 19, 
so that layer 19 overlaps the inner end of bottom lead 16 and the edges of 
section 10. Thereafter the upper laminating layer 18, which comprises a 
prelaminated assembly consisting of a layer 23 of clear, transparent nylon 
laminated between two outer, transparent layers 24 and 25 of polyethylene, 
is positioned over the top of the partially assembled lamp stack 20 as 
shown in FIG. 2, so that layer 18 overlaps the inner end of the upper lead 
15 and the edges of section 10. 
After the upper layer 18 has been placed over the assembly, the upper layer 
or surface of the laminating pouch P is placed over the assembled stack; 
and the pouch P is placed in a platen laminating press and held under heat 
and pressure until the layers 18 and 19 fuse with the intervening lamp 
section 10 into a monolythic, composite plastic sheet. This laminating 
step takes place at nominally 325.degree. F. for approximately ten 
minutes. After this laminating cycle, the lamp stack is cooled down to 
room temperature while still under pressure. (The laminating pressure is 
determined by trial for different lamp stack heights and areas.) After 
cooling, the laminated assembly is removed from the press and pouch P, and 
is trimmed around its edges to produce the completed stack assembly 20 as 
shown for example in FIGS. 3 and 4. 
After being trimmed into its final configuration, the lamp stack 20 is 
finally laminated between two layers 31 and 32 (FIG. 3) of moisture 
resistant plastic film, such as for example a fluorocarbon film with a 
polyethylene bonding surface. This is done, for example, by placing one of 
the layers 32 on the surface S of the pouch P, and then placing the 
finished lamp stack 20 on the layer 32 so that the latter overlaps the 
marginal edges of stack 20. The other moisture-resistant layer 31 is 
placed over the stack 20 to register with the layer 32; and the pouch P is 
closed over the top of the assembly and is again placed in the laminating 
press to laminate layers 31 and 32 over opposite sides of stack 20, and 
around the marginal edges thereof. If the finished lamp is to be employed 
out of doors, high temperature edge sealing of the fluorocarbon films 31 
and 32 may be employed. After the second and final lamination, the 
completed lamp is trimmed to size to produce the finished lamp as denoted 
at 30 in FIG. 4. 
The presence of the nylon films 21 and 23 (FIG. 2), which may be 
approximately 5 mils thick, stabilize the lamp stack assembly 20 
mechanically against tearing and stretching. The advantage of employing 
the polyethylene layers 22 and 25 (FIG. 3) on the nylon film enables these 
nylon layers to be fused at lower temperatures and with greater ease to 
opposite surfaces of the basic lamp stack 10. Similarly, the surfaces of 
the moisture-resistant layers 31 and 32 which are employed to enclose 
stack 20, can also be provided on the surfaces thereof which confront the 
stack 20 with polyethylene layers which would likewise ease the lamination 
of the layers 31 and 32 to the stack 20. 
As shown in FIG. 2, it is imperative that the inner ends of the foil leads 
15 and 16 overlie the layers 13 and 14, so that they will be secured in 
electrical contact therewith as a result of the laminating operation which 
produces the stack 20. The areas of the input leads 15 and 16 in contact 
with their respective conductive layers 13 and 14, should be proportional 
to the total area of the resultant lamp. For example, when the lamp 
increases in surface area, the amount of surface area of the leads 15 and 
16 in contact therewith must also increase. In very large lamps, for 
example, the inner ends of each lead 15 and 16 can be extended, as shown 
for example by broken lines at 15' in FIG. 4, to form narrow, perimetral 
contact surfaces around the edges of the lamp, thereby to distribute the 
electric current more evenly across the entire EL phosphor layer of the 
lamp. 
In order to improve the surface appearance of the lamp 30 when it is not 
lit, an extra polyethylene film can be laminated to the outer surfaces 
thereof by means of a roller laminator. The lamp, having these extra 
"impressable" coatings on opposite sides thereof, is then run between a 
set of heated texturing rolls. The texturing operation can also be 
accomplished in a heated press with textured laminating plates. Moreover, 
the flat lamps 30 can be formed readily into conical or cylindrical shapes 
by wrapping the laminates, during the assembly thereof, around forming 
mandrels, and heat sealing the overlapping edges. Obviously the EL lamp 
disclosed herein can also be formed into other geometrical shapes by 
similar procedures. 
The EL lamp may be esthetically enhanced by incorporating artistic designs 
within the lamp structure itself during processing. One manner of 
effecting this enhancement is illustrated by the modified basic lamp 
structure 10', which is illustrated in FIG. 5, wherein like numerals are 
employed to denote elements similar to those employed in the previously 
described embodiment. This modified structure comprises the usual 
dielectric substrate layer 11, the underside of which is coated by a layer 
14 of indium oxide, as in the first embodiment. Photo-etched onto the 
upper surface of layer 11 is an image-producing layer or metallic film 35. 
This film is coated by a layer 12 of EL phosphor, as in the first 
embodiment, and this layer is in turn covered by the outer, indium oxide 
layer 13. 
When an AC signal source is connected by lines L1 and L2 across opposite 
sides of this modified construction 10', the image produced by the layer 
35 is projected from opposite sides of the assembly. In use, of course, 
the modified lamp section 10' would be formed into a lamp stack 20 of the 
type previously described; and this stack in turn would be enclosed within 
the layer 31 and 32 to form the finished lamp. 
The steps involved in forming this modified lamp structure 10' comprises 
depositing a thin metallic layer on one side (the upper side as shown in 
FIG. 5) of the substrate 11. The metallic layer is then photosensitized in 
known manner with "resist," and is exposed to ultra-violet radiation 
through a photographic film having the desired image. When the resist is 
thereafter developed, the metallic film not covered by the resist will 
etch away to leave the desired metallic pattern or metallic image layer 35 
on the face of the substrate 11. Thereafter, the additional layers 12 to 
14 are applied, as of the case in the first embodiment. 
The picture or image produced by the modified lamp section 10' is generated 
in two ways; (a) the metal image blocks EL light in one direction through 
the transparent dielectric film substrate 11, and (b) the metal affects 
the electric field across the phosphor in the areas where the EL phosphor 
overlies the metal image. 
FIGS. 6 and 7 illustrate still another EL lamp 40 and a different method of 
generating therein an image of the type described. This method is similar 
to that disclosed in connection with FIG. 5, except that the desired 
image-producing metallic film 41 is photoetched onto the upper surface of 
the lower laminating layer 19 rather than onto the face of the film 
substrate 11. The image film 41 in this embodiment, moreover, includes a 
rectangular, metallic border 41' or diffusion ring, which completely 
surrounds the etched image portion of the film inwardly of the marginal 
edges of the supporting laminate 19. In this method an upper image sheet 
may also be employed comprising a layer 42 of nylon, which is coated with 
a film 43 of polyethylene on which, in turn, a metallic, image-producing 
film 44 is photo-etched on the polyethylene film 43 in a manner similar to 
that of the film 41. The metallic film 44 also includes around its 
marginal edge a diffusion ring 44' similar to that denoted at 41' on the 
lower image sheet. 
The manner of assembling and laminating the lamp 40 (FIG. 7) is otherwise 
similar to those embodiments previously described. A lamp 40 made in 
accordance with this method will produce, when energized, an illuminated 
image within the boundary defined by its registering diffusion rings 41' 
and 44', both of which serve to distribute electric current completely 
around the perimeters of the respective image layers 41 and 44. 
From the foregoing it will be apparent that the method disclosed herein 
provides a relatively simple and inexpensive means for producing extremely 
versatile EL lamps, which can be produced and stored in various shapes and 
configurations, and which can be utilized for various decorative, as well 
as functional purposes. The disclosed lamps emit light from both sides 
thereof when in alternating or varying voltages are applied to their 
inputs 15 and 16. The lamps disclosed herein are intended for operation on 
ordinary household current and at conventional 60 Hertz voltage 
frequencies. Since the lamps are voltage and frequency sensitive, any 
increase in either of these two parameters will, of course, increase the 
brightness of the respective lamps. The lamps are particularly suitable 
for decorative room dividers or grilles, suspended ceiling light panels, 
decorative sections for wall illumination purposes, pole lamps, etc. The 
lamps can be heat sealed and textured on one or both sides, by heated 
texturing plates or rolls and, if desired, metallic layers can be 
incorporated directly within the lamp during manufacture thereof. The 
above-described spray coating steps can be performed by any standard spray 
coating equipment; and the basic lamp structures 10, 10' , as well as the 
lamp stacks 20, are so thin that they can be punched, and or sheared by 
inexpensive steel-roll dies, and paper cutting equipment. 
While this invention has been described in detail with only certain 
embodiments thereof, it will be apparent that this application is intended 
to cover any such modifications thereof as may fall within the scope of 
one skilled in the art, or the appended claims.