US3069579A

US3069579A - Electroluminescent device

Info

Publication number: US3069579A
Application number: US15857A
Authority: US
Inventors: Berg Daniel; John A Tanaka
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1960-03-18
Filing date: 1960-03-18
Publication date: 1962-12-18
Anticipated expiration: 1979-12-18

Description

DecQlS, 1962 D. BERG ETAL 3,069,579

ELECTROLUMINESCENT DEVICE Filed March 18, 1960 FIG. I.

k\\\\\\\\\\\ m m it mm mm aims. m. mmaym wa\ i A C 22 FEXIBLE CONDUCTOR FLEXIBLE TRANSPARENT'CONDUCTING SLEEVE F|G.2. I F|G.3.

I6 I I4 26 FIG.4. 2830 JI INVENTORi. PAW/EL 5526 m1 BY oy 4. m/mm.

vania Filed Mar. 18, 1960, Ser. No. 15,857 13 Claims. (Cl. 313108) This invention relates to electroluminescent devices and, more particularly, to flexible electroluminescent devices which can be readily conformed into any desired shape and electroluminescent devices which have a substantially uniform light output.

The phenomenon of electroluminescence was first comprehensively disclosed by G. Destriau, one of his earlier publications appearing in London, Edinburgh and Dublin Philosophical Magazine, Series 7, vol. 38, No. 285, pages 700737 (October 1947). Since this early publication, electroluminescent devices have been marketed commercially.

Most electroluminescent devices are rigid in nature andare not adapted to be conformed into different shapes. Also, thelight emitted by electroluminescent devices often varies in intensity because of variations in electrode spacing.

It is the general object of this invention to provide a flexible electroluminescent device which can be readily conformed to various shapes.

It is another objectto provide an electroluminescent device which emits a very uniform light intensity.

It is a further object to provide constructional details for such flexible or uniform-appearing electroluminescent devices.

It is an additional object to provide light-transmitting, flexible and conducting solid substance.

The aforesaid objects of the invention, and other objects which will become apparent as the description proceeds, are achieved by providing a flexible electroluminescent device wherein a flexible, conducting core such as a wire has carried thereon a flexible layer comprising electroluminescent phosphor. Over the phosphor layer is carried a flexible, light-transmitting, electricallyconducting and solid layer. This electroluminescent structure in essence has the appearance of a wire and it is readily conformed into various shapes. There is also provided an electroluminescent device which emits light of substantially-uniform intensity by virtue of at least one additional layer of flexible, light-transmitting, electricallyconducting and solid material included between a lighttransmitting electrode and the phosphor of the device. This additional layer compensates for variations in electrode spacing, as are frequently encountered with electroluminescent devices.

For a better understanding of the invention, reference should be had to the accompanying drawings wherein:

FIG. 1 is an elevational view, partly in section, of a flexible electroluminescent device constructed in accordance with this invention;

FIG. 2 is a cross-sectional view taken on the line IIII in FIG. 1, in the direction of the arrows;

FIG. 3 illustrates a practical application for the device as shown in FIG. 1;

FIG. 4 is an elevational view, partly in section, of an alternative construction for the device as shown in FIG.

3,069,579 Patented Dec. 18, 1962 1, wherein an additional bus bar is embedded in the flexible, light-transmitting and solid electrode layer;

FIG. 5 is a cross-sectional view taken on the line V-V in FIG. 4;

FIG. 6 is a fragmentary perspective view of an electroluminescent device adapted to emit light from opposite faces and wherein additional layers of flexible, lighttransmitting, electrically-conducting and solid material are also included between the device electrodes, so that the emitted light is of substantially uniform intensity.

FIG. 7 is a fragmentary perspective view of an alternative embodiment for the device as shown in FIG. 6.

With specific reference to the form of the invention illustrated in the drawings, the device 10 as shown in FIGS. 1 and 2 generally comprises a flexible metallic body 12 carrying thereon a flexible layer 14 comprising electroluminescent phosphor. Over the phosphor layer 14 is carried a flexible, light-transmitting, electricallyconducting and solid layer 16. As a specific example, the core 12 is formed of copper wire having a diameter of 64 mils. The layer 14 comprises any electroluminescent phosphor, an example being the well-known Zinc sulfide activated by copper and coactivated by chlorine. Desirably, there is mixed with the phosphor a light-transmitting dielectric material such as an epoxy-modified polyester varnish or polyvinyl-chloride acetate. The relative parts by weight of phosphor and dielectric are not critical and equal parts by weight of phosphor and dielectric are satisfactory. The thickness of the layer .14 is not critical and as an example is 2 mils. The layer 46 can be formed of any material which is flexible, light transmitting, electrically conducting and solid. As a specific example, the layer 16 is formed of waxy solids such as succinonitrile (MP. 57 C.) or 2,2-dinitropropane (M.P. 53 C.) as base material. To render these indicated materials electrically conductive, there is dissolved in them a predetermined amount of an ionizable organic or inorganic salt. Examples of suitable dissolved salts are ammonium chloride, potassium bromide, ammonium acetate, (CH =NCl or triethyl acetomethyl ammonium bromide (the triethyl quaternary ammonium bromide of glycinonitrile). These indicated materials can be added in amount of from 0.03% to 2.5% by weight of the indicated base material and even this range can be extended. As a specific example, when 0.128 gram of triethyl acetomethyl ammonium bromide is dissolved in 5.29 grams of succinonitrile the composite material will have a resistance in the order of 2500 ohms as measured across a /8 inch spacing. The succinonitrile for example displays a very high resistance, but when the foregoing inorganic or organic ionizable salts are dissolved therein, the resulting composite material becomes electrically conducting in nature. It should be noted that the foregoing indicated amounts of ionizable dissolved material are not meant to be limiting and other salts can be substituted for those indicated. Apparently the reason for the conductivity of these modified waxy solid materials is that the dissolved electrolytes apparently form free ions which are mobile in the solid base material. The layer 16 preferably has a considerable thickness as compared to the phosphor layer 14, in order to facilitate application and to minimize any tendency for overly-thin coating portions which could form discrete high resistance points. As an example, the layer 16 has a thickness of 60 mils and this thickness is subject to considerable variation. As with other electroluminesrials can be substituted therefor.

cent devices, the spaced electrodes of the device are adapted to have an alternating potential applied therebetween. In the embodiment as shown in FIGS. 1 and 2, the copper core wire 12 extends beyond the coatings thereon and a contacting sleeve 20 fits over this extending portion to facilitate electrical connection. An additional contacting sleeve 22 fits about the electrode layer 16 in order to facilitate electrical connection to this electrode layer.

In FIG. 3 is shown a practical application for the electroluminescent wire as shown in FIGS. 1 and 2, wherein the device 24 has been conformed as a letter W for display purposes.

In FIGS. 4 and is shown an alternative embodiment 26 for the device as shown in FIGS. 1 and 2, wherein an additional elongated, flexible and electrically-conducting body 28 generally parallels the center core portion 12. This additional conducting body 28 preferably has a cross section which is considerably smaller than that of the center core section 12 so that it will not absorb or block off any appreciable amount of light generated by the phosphor layer 14. The member 28 can be positioned along the surface of the conducting layer 16 although preferably it is embedded therein, as is shown in FIGS. 4 and 5. As an example, the member 28 is fabricated of nickel-plated copper wire having a diameter of 2 mils. The purpose of this additional conducting member 28 is to serve as a bus bar for connection to the power supply so that any tendencies for voltage drops through the layer 16 are minimized. The device embodiment 26 is also modified from that embodiment shown in FIGS. 1 and 2 in that a layer of insulating and light-transmitting material 30, such as a two-mil layer of polyvinyl-chloride acetate, is carried over the conducting layer 16, in order to prevent shock hazard. Other than the indicated differences, the device embodiment 26 as shown in FIGS. 4 and 5 is similar to the device embodiment 19 shown in FIGS. 1 and 2.

The device embodiments as shown in FIGS. 1 through 5 are subject to considerable variation. For example, the central core wire 12 as shown in FIG. 1 can be replaced by any :flexible electrically-conducting body which is considerably elongated in comparison to its thickness and width. As an example, the wire 12 can be replaced by a copper tube.

In FIG. 6 is shown an electroluminescent device 32 which comprises two fiat, light-transmitting and vitreous foundation members 34, each of which has one surface closely spaced from a corresponding surface of the other member. These closely spaced surfaces each carry thereon a thin, light-transmitting and electrically-conducting layer 36 of tin oxide. Other known electrode mate- Between the electrode layers 36 is included a substantially-uniform-thick layer 38 comprising electroluminescent phosphor, which as an example is similar in thickness and composition to the layer 14 as shown in FIG. 1, except that this layer 38 is substantially planar. While the phosphor layer 38 can be provided with a substantially uniform thickness, the tin-oxide-coated glass is subject to some deviation from a planar configuration. If the phosphor or phosphor and dielectric are sandwiched directly between such tin-oxide-coated lglass foundations, there will normally be some variation in electrode spacing. In addition, it is difficult to maintain a constant average spacing between the electrode layers 36. Accordingly, when an alternating potential is applied between the electrodes of such a device, there Will normally be some variations in the applied electric field. Variations in the applied electric field will cause the electroluminescent layer to respond with varying brightness. In order to eliminate such variable electric fields so that the device can emit a substantially uniform light intensity from its opposite faces, at least one layer of conducting solid material is also included between the electrode layers. In fabricating such a device, either of the solid conducting materials as indicated hereinbefore is formed as a layer 40 onto a tin oxide electrode layer 36. A heated gauge block is then placed over this layer of solid conducting material in order to cause the surface portion thereof to melt to eliminate any surface irregularities. The phosphor-dielectric layer 38 is then sprayed over this firstapplied layer 443 and such phosphor-dielectric layers can he sprayed to a substantially uniform thickness of 2 mils for example. An additional layer 40 of solid conducting material is then formed over the applied phosphor-dielectric layer 38. The remaining vitreous foundation 34 is heated and the tin oxide coating thereon is pressed over the last-applied conducting layer 40. With this construction, when a potential is applied between the tin oxide electrode layers 36, the resulting electric field will actually be applied between the solid conducting layers 40 and will be substantially uniform across the phosphor layer 38, even though the spacing between the tin oxide electrode layers 36 varies.

In FIG. 7 is shown an alternative embodiment 42 for the device embodiment as shown in FIG. 6. The embodiment 42 essentially corresponds to the device as shown in FIG. 6 except that one of the con-ducting solid layers 40 has been eliminated and an additional separate layer 44 of light tr-ansmitting dielectric such as a plastic material has been placed between the phosphor-dielectric layer 38 and the remaining layer 40. Such plastic layers are well known and as an example, the layer 44 is formed of an acrylic resin having a thickness of 1 mil. The ad.- vantages to be realized from the device embodiment 42 are that the tin oxide electrodes 36 need not be maintained with a constant average spacing therebetween, since the conducting layer 40 in effect serves as an electrode and can vary with respect to its thickness without introducing electric field variations. In either of the embodiments as shown in FIGS. 6 and 7, each of the conducting layers 40 desirably has an average thickness at least about as great as the phosphor layer 38 in order to permit adequate tolerances in manufacturing with respect to positioning the vitreous foundations 34.

As a possible alternative construction for the embodiments as shown in FIGS. 6 and 7, the foundations can be formed of non-vitreous material such as light-transmitting resins, an example being polystyrene. In addition, the electrode layers can be formed of a metal mesh embedded in the surface of the polystyrene- With such a construction, the effect of discontinuities in spacing between the metal mesh electrode layers will be eliminated by the use of the light-transmitting, solid and conducting layers as specified hereinbefore. The use of such solid, conducting layers in conjunction with a metal mesh electrode layer also has utility in conjunction with an electro-luminescent device such as is illustrated in FIG. 2 of U. S. Patent No. 2,765,419, dated October 2, 1956, wherein a solid conducting layer as described hereinbefore can be placed between the metal mesh electrode layer and the electro-luminescent phosphor layer to form a planar electrode. In addition, the other electrode for such a device embodiment can be formed of opaque material, such as vacuum-metallized aluminum. Constructional details for such devices with respect to the phosphor-dielectric layers and additional layers of lighttransmitting, solid and conducting materials can be specified hereinbefore.

The electroluminescent devices described hereinbefore are intended for operation with alternating potential .excitation. Any of these devices can be operated with D.C potential excitation if the amount of dielectric material mixed with the phosphor is decreased a sufiicient amount so that the phosphor-dielectric layers will conduct D.C. As an example, any of the foregoing embodiments will be operable under D.C. excitation if the phosphor con-- stitutes at least by weight of the phosphor-dielectnic layers.

It will be recognized that the objects of the invention have been achieved by providing a flexible electroluminescent device which can be conformed to various shapes as well as an electroluminescent device which emits a very uniform light intensity. There have also been provided constructional details for such flexible and uniform appearing devices as Well as light-transmitting, flex-ible and conducting solid substance.

While best embodiments of the invention have been i1- lustrated and described hereinbefore, it is to be particu larly understood that the invention is not limited thereto or thereby.

We claim:

1. An electroluminescent device comprising, a first flexible electrically-conducting body considerably elongated in comparison to its thickness and width, a flexible layer comprising electroluminescent phosphor over said first flexible elongated body, a flexible light-transmitting electrically-conducting and solid layer of considerable thickness and at least principally comprising organic compound over said layer comprising electroluminescent phosphor, an additional elongated flexible and electricallyconducting body having a cross section considerably smaller than that of said first flexible body and electrically contacting throughout its length said light-transmitting conducting layer, and said first flexible elongated body and said additional conducting body adapted to have an alternating potential applied therebetween.

2. An electroluminescent device comprising, a first flexible electrically-conducting body considerably elongated in comparison to its thickness and width, a flexible layer comprising electroluminescent phosphor over said flexible elongated body, a flexible light-transmitting electricallyconducting and solid layer of considerable thickness and at least principally comprising organic compound over said layer comprising electroluminescent phosphor, an additional elongated flexible electrically-conducting body generally paralleling said first conducting body and having a cross-section considerably smaller than that of said first conducting body, said additional conducting body embedded throughout substantially all its length in said light-transmitting conducting layer, and said first flexible elongated body and said additional conducting body adapted to have an alternating potential applied therebetween.

3. An electroluminescent device comprising, a flexible electrically-conducting body considerably elongated in comparison to its thickness and width, a flexible layer comprising electroluminescent phosphor over said flexible elongated body, a flexible light-transmitting electricallyconduoting and solid layer over said layer comprising electroluminescent phosphor, said flexible solid layer selected from one of the group consisting of succinonitrile and 2,2-dinitropropane and having dissolved therein a predetermined amount of ionized salt to impart electrical conductivity thereto, and said flexible elongated body and said conducting solid layer adapted to have an alternating potential applied therebetween.

4. An electroluminescent device comprising, two lighttransmitting foundation members each having a surface closely spaced from a surface of the other member, a thin light transmitting and electrically-conducting electrode layer carried on each of the closely-spaced surfaces of said foundation member, a substantially-uniform-thick layer comprising electroluminescent phosphor included between said spaced electrode layers, and at least one light-transmitting said electrically-conducting solid layer at least principally comprising organic compound also included between said electrode layers and having an average thickness at least about as great as said layer comprising electroluminescent phosphor.

5. An electroluminescent device comprising, two lighttransmitting vitreous foundation members each having a surface closely spaced from a surface of the other member, a thin light-transmitting and electrically-conducting electrode layer carried on each of the closely-spaced surfaces of said foundation members, a substantially-uniform-thick layer comprising electroluminescent phosphor included between said spaced electrode layers, an additional flexible light-transmitting and electrically-conducting solid layer at least principally comprising organic compound also included between said electrode layers and having an average thickness at least about as great as said phosphor layer, and an additional light-transmitting dielectric layer included between said additional conducting layer and said phosphor layer, whereby any deviations from a uniform average spacing between said electrode layers are compensated for by said additional solid conducting layer.

6. An electroluminescent device comprising, two lighttransmitting vitreous foundation members each having a surface closely spaced from a corresponding surface of the other member, a thin light-transmitting and electrically-conducting electrode layer carried on each of the closely-spaced surfaces of said foundation members, a substantially-uniform-thick layer comprising electroluminescent phosphor included between said spaced electrode layers, at least one additional flexible light-transmitting and electrically-conducting solid layer also included between said electrode layers and having an average thickness at least about as great as said layer comprising electroluminescent phosphor, and said additional conducting layer selected from one of the group consisting of succinonitrile and 2,2-dinitropr0pane and having dissolved therein a predetermined amount of ionized salt to impart electrical conductivity thereto.

7. An electroluminescent device comprising, spaced electrodes, a substantially-uniform-thick layer comprising electroluminescent phosphor between said spaced electrodes, and at least one layer of flexible light-transmitting and electrically-conducting materials at least principally comprising organic compound also included between said spaced electrodes.

8. An electroluminescent device comprising, spaced electrode layers, a substantially-uniform-thick layer comprising electroluminescent phosphor between said spaced electrode layers, one of said electrode layers being light transmitting, a variable spacing between said one electrode layer and said phosphor layer, and a light-transmitting and electrically-conducting solid layer at least principally comprising organic compound between said phosphor layer and said one electrode layer.

9. An electroluminescent device comprising, spaced electrode layers, a substantially-uniform-thick layer comprising electroluminescent phosphor between said spaced electrode layers, one of said electrode layers being light transmitting, a variable spacing between said one electrode layer and said phosphor layer, a flexible lighttransmitting and electrically-conducting solid layer at least principally comprising organic compound between said phosphor layer and said one electrode layer, and said flexible solid layer having an average thickness at least about as great as the thickness of said phosphor layer.

10. A light-transmitting electrically-conducting solid substance principally comprising material selected from the group consisting of succinonitrile and 2,2-dinitropropane, and said material having dissolved therein a predetermined amount of selected ionizable salt.

11. A flexible light-transmitting electrically-conducting solid substance principally comprising material selected from the group consisting of succinonitrile and 2,2-dinitropropane, and said material having dissolved therein a predetermined amount of one of the group consisting of ammonium chloride, potassium bromide, ammonium acetate, trimethyl acetomethyl ammonium bromide and (CH NCl.

12. A flexible light-transmitting electrically-conducting solid substance principally comprising material selected from the group consisting of succinonitrile and References Cited in the file of this patent UNITED STATES PATENTS Gillson Jan. 31, 1956 Payne June 10, 1958 Kazan Sept. 9', 1958 Fridrich Aug. 25, 1959 Bartels Mar. 8, 1960 Swindells June 14, 1960

Claims

1. AN ELECTROLUMINESCENT DEVICE COMPRISING, A FIRST FLEXIBLE ELECTRICALLY-CONDUCTING BODY CONSIDERABLY ELONGATED IN COMPARISON TO ITS THICKNESS AND WIDTH, A FLEXIBLE LAYER COMPRISING ELECTROLUMINESCENT PHOSPHOR OVER SAID FIRST FLEXIBLE ELONGATED BODY, A FLEXIBLE LIGHT-TRANSMITTING ELECTRICALLY-CONDUCTING AND SOLID LAYER OF CONSIDERABLE THICKNESS AND AT LEAST PRINCIPALLY COMPRISING ORGANIC COMPOUND OVER SAID LAYER COMPRISING ELECTROLUMINESCENT PHOSPHOR, AN ADDITIONAL ELONGATED FLEXIBLE AND ELECTRICALLYCONDUCTING BODY HAVING A CROSS SECTION CONSIDERABLY SMALLER THAN THAT OF SAID FIRST FLEXIBLE BODY AND ELECTRICALLY CONTACTING THROUGHOUT ITS LENGTH SAID LIGHT-TRANSMITTING CONDUCTING LAYER, AND SAID FIRST FLEXIBLE ELONGATED BODY AND SAID ADDITIONAL CONDUCTING BODY ADAPTED TO HAVE AN