ELECTRICAL CIRCUITS AND COMPONENTS

Abstract: It is discovered that a liquid dispersion of polymer powder particles, predominantly of polyvinylidene fluoride, simultaneously: (a) can suspend electrical property additives, such as crystalline, hard, dense particles of generally spherical shape, uniformly in desired concentrations; (b) while containing a useful concentration of any of a wide range of such particles, can be deposited by high shear transfer to a substrate in accurately controllable thickness and contour; (c) when so deposited can be fused into a continuous uniform film which has low absorptivity, e.g., of moisture, and acts as a barrier film; (d) where desired, can, as one layer, be fused with other such layers, containing other electrical property additives, to form a monolithic electrical component; and, (e) in general, can meet all requirements for the making of any useful electrical circuit components, including electroluminescent lamps, by printing and coating techniques with a high degree of accuracy and controllability.

Description: ELECTRICAL CIRCUITS AND COMPONENTS BACKGROUND OF THE INVENTION This invention relates. to making electrical components by the deposit and drying of fluids that contain particles that have desired electrical and mechanical properties. In another aspect, the invention relates to electroluminescent lamps, which typically are formed of a phosphor-particle-containing layer disposed between corresponding electrodes adapted to apply an excitation potential to the phosphor particles, at least one of the electrode layers being semi-transparent to light emitted by the phosphors. The phosphor-containing layer is provided with a barrier against moisture penetration to prevent premature deterioration of the phosphors, and permanent adherence between adjacent layers is sought to avoid delamination, e.g. under constant flexing or changes in temperature, particularly where the layers are of materials having different physical properties as this can also lead to premature failure in prior art electroluminescent lamps. In the past, it has been recognized that deposit of fluids, as by printing with polymeric inks having electrical properties, would have a number of advantages to the manufacture of electrical components, including speed and accuracy of manufacture, low cost, small product dimensions, etc. Limitations of known inks and coating fluids as well as limitations in their manner of use, however, have limited the applicability of the techniques and the realizable electrical performance characteristics. In particular, high shear stress mass transfer techniques, such as screen printing and doctor blade coating, have not found wide use for products other than simple conductors. There have been numerous and apparently conflicting requirements for such techniques that have stood in the way. Because nonuniformity of particle distribution can result in non-uniform electrical performance, there is a need for any such fluid composition to hold the electrically active particles in uniform suspension and inhibit their settling prior to use and during the deposition and drying process. The very high density of some electrically active additives as compared to typical pigments, and their general spherical shape, increases this demand. It is important for any practical fluid composition to have a high percentage of polymeric binder, generally of the order of 50% percent, by weight, in order to achieve a substantial dried coating thickness in each application. Thickness is usually needed to achieve the desired electrical properties as well as mechanical strength and abrasion resistance. There is further a need for such composition to be highly thixotropic, i.e. have high-"false body", so that while it is able to suspend the high density additive particles, it yet can have temporary lower viscosity under shear (i.e., be capable of "shear thinning") to enable clean, accurate transfer of the fluid composition to the sjubstrate. Such accuracy of formation is important because uniformity of thickness determines uniformity of electrical properties. There are further requirements that such composition permit use of volatiles that have relatively low evaporation rates at ambient temperatures in order to achieve constant viscosity during an extended coating or printing run during which the ink is exposed to the atmosphere. Changes in viscosity and concentration can alter the characteristics of the deposit. There are still further requirements that any composition and its method of application be compatible with substrates to which it is applied and to material that may be subsequently applied to it so that no damage is done to the various components of.the circuit during manufacture or use. In the case of circuit components with additives susceptible to deterioration in the presence of moisture, such as phosphor particles for an electroluminescent lamp, there are further stringent requirements related to the protection of those particles. These and other requirements would present themselves as obstacles to anyone who would seek to broaden the use of fluid transfer techniques for the formation of electrical components and circuits and to lamps. Summary of the Invention According to the invention it has been discovered that a liquid dispersion of powder particles comprised of polyvinylidene fluoride (PVDF) simultaneously: a) can suspend uniformly in desired concentrations any of a wiςle variety of electrical property additives, including crystalline, hard, dense particles that are generally spherical in shape, b) while containing a useful concentration of such particles, can be deposited by high shear transfer to a substrate " in accurately controllable thickness and contour, c) when so deposited can be fused into a continuous, uniform barrier film, the film itself having low absorptivity, e.g., of moisture. d) where desired, can, as one layer, be -fused with other such layers, containing other electrical property additives, to form a monolithic electrical component, and (e) in general, can meet all requirements for the making of many useful electrical circuit components, including electroluminescent lamps, especially those with additives harmed, e.g., by the presence of moisture, by printing and coating with a high degree of accuracy and controllability. The discovery can be employed to form products that are highly resistant to ambient heat and moisture and other conditions of use. Despite markedly different electrical properties between layers, the PVDF binding polymer is found to be capable of a controllable degree of interlayer penetration during fusing, which on the one hand is sufficient to provide monolithic properties, enabling, e.g. repeated bending without delamination, while on the other hand is sufficiently limited to avoid adverse mixing effects between different electrical additives in adjacent layers. PVDF can be employed as the binder with additive particles having widely different physical properties in adjacent layers, while the overall multilayer deposit exhibits the same coefficient of expansion, the same reaction to moisture, and a common processing temperature throughout. Thus each layer can be made under optimum conditions without harm to other layers and the entire system will respond uniformily to conditions of use. Remarkable results have been obtained by the simple techniques of silk screen printing and doctor blade coating of successive layers. Of special importance, it has been discovered that circuit components that contain light-emitting phosphors and covering layers can be made which have unusual moisture resistance, light emissivity and durability. The moisture sensitivity of phosphors makes this a particularly important discovery. The invention accordingly features a method of forming an electrica_l circuit component, and the resulting product, especially electroluminescent lamps, by depositing on a substrate, and drying, one or a succession of superposed thin layers of a suspension of polymer solid dispersed in a liquid phase, the ~ predominant constituent of the polymer being polyvinylidene fluoride (PVDF) , the liquid suspension for at least one of the layers containing a uniform dispersion of particles selected from the group consisting of dielectric, resistive and conductive substances of characteristic electrical values substantially different from the respective values of PVDF, the method including heating to fuse the polymer continuously throughout the extent of the layer and between layers, to form a monolithic unit. While in certain cases homologs with substantially similar properties may be employed, it is found that a polymer powder consisting essentially of the homopolymer of PVDF produces electrical components and layers of outstanding properties and, being also commercially available, this polymer is presently preferred. In the preferred embodiment, each layer, preceding the application of the next, is heated sufficiently to fuse the polymer particles to form a continuous film-like layer; the predominant constituent of the liquid phase has substantially no solubility for the polymer under the conditions of its deposit; the liquid phase is predominantly formed from one or more members selected from the group consisting of methyl isobutyl ketone (MIBK) , butyl acetate, cyclohexanone, diacetone alcohol, diisobutyl ketone, butyrolactone, tetraethyl urea, isophorone, triethyl phosphate, carbitol acetate, propylene carbonate, and dimethyl phthalate; the liquid phase includes a minor amount of active solvent selected to promote the stability of suspension of the polymer particles in the liquid phase without substantially dissolving the polymer; the liquid phase includes a minor amount of one or more members selected from the group consisting of acetone, tetrahydrofuran (THF) , methyl ethyl ketone (MEK) , dimethyl formamide (DMF) , dimethyl aceta ide (DMAC) , tetramethyl urea and trimethyl phosphate, in quantity to promote the stability of the suspension of the polymer particles in the liquid without substantially dissolving the polymer; the liquid dispersion for a layer exhibits a substantial reduction in viscosity under high shear stress and the layer is deposited by high shear transfer; the layer is deposited by silk screen printing; the layer is deposited by blade coating; the deposits are of predetermined, printed form; the substrate and the deposit thereon comprise a flexible unit; and the thickness of each of the layers is in the range of between about .003 inch to -.0001 inch. Preferred--Embodiment We first briefly describe the drawings: Fig. 1 is a perspective view in section of an electroluminescent lamp formed according to the invention; Fig. 2 is a side section view of the lamp taken at the line 2-2 of Fig. 1; Fig. 3 is side section view of a portion of side the lamp indicated in of Fig. 1, enlarged as viewed through a microscope. We first describe, in Examples A through D, examples of selected electrical circuit components formed as thin layers and then describe, in Example E, a complete electrical circuit, in this case an electroluminescent lamp, formed of a superposed series of the layers as described in Examples A through D. Examples EXAMPLE A - Dielectric Insulating Layer To prepare the dielectric composition, 10 grams of a PVDF dispersion of 45 percent, by weight, polyvinylidene fluoride (PVDF) in a liquid phase believed to be primarily carbitol acetate (diethyl glycol monoethyl ether) were measured out. This dispersion was obtained commercially from Pennwalt Corporation under the tradename "Kynar Type 202". As the electrical property-imparting additive, 18.2 grams of barium titanate particles (BT206 supplied by Fuji Titanium, having a particle size of less than about 5 microns) were mixed into the PVDF dispersion. An additional amount of carbitol acetate (4.65 grams) was added to the composition to maintain the level of solids and the viscosity of the composition at a proper level to maintain uniform dispersion of the additive particles while preserving the desired transfer performance. It was observed after mixing that the composition was thick and creamy and that the additive particles remained generally uniformly suspended in the dispersion without significant settling during the time required to prepare the example. This is due, at least in part, to the number of solid PVDF particles (typically less than about 5 microns in diameter) present in the composition. A substrate was selected for its resistance to the carrier fluid employed and for its ability to withstand the extreme temperatures of treatment, e.g. up to 500°F, as described below, in this case, a flexible 5 PVDF film. The composition was poured onto a 320 mesh polyester screen positioned 0.145 inch above the substrate. Due to its high apparent viscosity, the composition remained on the screen without-leaking through until the squeegee was passed over. " the screen ° exerting , shear stress on the fluid composition causing it to shear-thin due to its thixotropic character and pass through the screen to be printed, forming a thin layer on the substrate below. The deposited layer was subjected to drying for 2-1/2 minutes at 175 F to 5 drive off a portion of the liquid phase, ahd was then subjected to heating to 500 F (above the initial melting point of the PVDF) and was maintained at that temperature for 45 seconds. This heating drove off remaining liquid phase and also fused the PVDF into a u continuous smooth film on the substrate. The resulting thickness of the dried polymeric layer was 0.35 mil (3.5 X lθ "4 inch). A second layer of the composition as described was screen-printed over the first layer on the 5 substrate. The substrate now coated with both layers was again subjected to heating as above. This second heating step caused the separately applied PVDF layers to fuse together. The final- product was a monolithic dielectric unit having a thickness of 0.7 mil with" no 0 apparent interface between the layers of polymer, nor with the substrate, as determined by examination of a cross-section under microscope. The particles of the additive were found to be uniformly distributed throughout the deposit. The monolithic unit was determined to have a dielectric constant of about 30. EXAMPLE B, - Light Emitting Phosphor Layer To prepare the composition, 18.2 grams of a phosphor additive, zinc sulfide crystals (type #723 from GTE Sylvania, smoothly rounded crystals having particle size of about 15 to 35 microns) were introduced to 10 grams of the PVDF dispersion used in Example A. It was again observed after mixing that despite the smooth shape and relatively high density of the phosphor crystals, the additive particles remained uniformly suspended- in the dispersion during the remainder of the process without significant settling. The composition was screen printed onto a substrate, in this case a rigid sheet of polyepoxide, standard printed circuit board material, through a 280 mesh polyester screen positioned 0.145 inch above the substrate to form a thin layer. The deposited layer was subjected to the two stage drying and fusing procedure described in Example A to fuse the PVDF into a continuous smooth film on the substrate with the phosphor crystals uniformly distributed throughout. The resulting thickness of the dried polymeric -3 layer was 1.2 mils (1.2 X 10 inch). The deposited film was tested UV and found to be uniformly photoluminescent, without significant light or dark spots. EXAMPLE C - Semi-Transparent Conductive Front Lamp Electrode To prepare this conductive composition, 13.64 grams of indium oxide particles (from Indium Corporation of America, of 325 mesh particle size) were added to 10 grams of the PVDF dispersion used in Example A. An additional amount of carbitol acetate (4.72 grams) was added to lower the viscosity slightly to enhance the transfer properties. It was again observed after mixing that the additive particles remained uniformly suspended in the dispersion during the remainder of the process without significant settling. The composition was screen printed onto a substrate, in this case a polyamide film, e.g., KAPTON supplied by E.I. duPont, through a 280 mesh polyester screen positioned 0.5 inch above the substrate to form a thin layer. The deposited layer was subjected to the two stage drying and fusing procedure described in Example .A to fuse the PVDF into a continuous smooth film on the substrate with the particles of indium oxide uniformly distributed throughout. The resulting thickness of the dried polymeric _3 layer was 0.5 mil (0.5 X 10 inch) . The deposited film was tested and found to have conductivity of 10 ohm-cm, and to be light transmissive to a substantial degree due to the light transmissivity of the semi-conductor indium oxide particles and of the matrix material. EXAMPLE D - Conductive Buss . To prepare this conductive composition, 15.76 grams of silver flake (from Metz Metallurgical Corporation, of 325 mesh #7 particle size) were added to 10 grams of the PVDF dispersion used in the examples above. The particles remained uniformly suspended in the dispersion during the remainder of the process without significant settling. The composition was screen printed onto a suitable substrate through a 320 mesh polyester screen positioned 0.15 inch above the substrate to.form a thin layer. The deposited layer was subjected to the two stage drying and fusing procedure described in Example A to fuse the PVDF into a continuous smooth film on the substrate with the silver flake uniformly distributed throughout. The resulting thickness of the dried polymeric _3 layer was 1.0 mil (1.0 X 10 inch) . The deposited film was tested and found to have -. 3 conductivity of 10 ohm-cm. In the following example we manufactured a complete electroluminescent lamp 10, comprised of a deposit of superposed thin polymeric layers as described above having different characteristic electrical properties, as described with reference to the drawings. EXAMPLE E Referring to Fig. 1, the substrate 12 used in this lamp configuration was flexible aluminum foil (4.2 mils) cut in pieces of size suitable for handling, e.g. 2 inches by 3 inches. The foil was cleaned with xylene solvent. A coating composition for forming dielectric layer 14 upon the substrate 12, in this case to act as an insulator between the substrate/electrode 12 and the overlying light-emitting phosphor layer 16 (described below) , was prepared as described in Example A and coated in two layers upon the substrate. A coating composition for forming the light emitting phosphor layer 16 was prepared as described in Example B. The composition was superposed by screen printing over the underlying insulator layer 14 and the substrate with its coatings- 14 and 16 was subjected to the heating conditions described. Subjecting the layers to temperatures above the melting temperature of the PVDF material caused the PVDF to fuse throughout the newly applied layer and between the layers to form a monolithic unit upon the substrate, as shown enlarged as under a microscope in Fig. 3. However, the interpenetration of the material of the adjacent layers having different electrical properties was limited by the process conditions to less than about 5 percent of the thickness of the thicker of the 5 adjacent layers, i.e. to less than about 0.06 mil so that the different electrical property-imparting additive particles remained stratified within the monolithic unit as well as remaining uniformly distributed throughout their respective layers. 1 -The coating composition for forming the semi-transparent top electrode 18 was prepared as described in Example C. The composition was superposed by screen printing upon the light-emitting phosphor layer 16. The substrate with the multiple layers coated 15 thereupon was again heated to above the PVDF melting temperature to cause the semi-transparent upper electrode layer to fuse throughout and to fuse with the underlying light-emitting layer to form a monolithic unit. The indium oxide, though typically characterized - • - as a semiconductor, serves as a conductor here, and its transparency enhances the light transmissivity of the deposited layer. The coating composition for forming the conductive buss 20 was prepared as described in Example 25 D and was screen printed upon semi-transparent upper electrode 18 as a thin narrow bar extending along one edge of the electrode layer, for the purpose of distributing current via relatively short paths to the upper electrode. ^ This construction with connecting wires 34, 36 (Fig. 1) and a power source 38, forms a functional electroluminescent lamp 10. Electricity is applied to the lamp via the wires and is distributed by the buss layer 20 to the front electrode 18 to excite the phosphor crystals in the underlying layer 16, which causes them to emit light. Due, however, to the damaging effect of, e.g., moisture on phosphor layer 16, it is desirable to add a protective and insulative- layer 22 about the exposed surfaces of the layers of the lamp to seal to the peripheral surface of the substrate 12. This layer 22 is also formed according to the invention, as follows. ,.The PVDF dispersion employed in Example A, devoid of electrical-property additives, is screen printed over the exposed surfaces of the lamp 10 through a 180 mesh polyester screen. The lamp was dried for two minutes at 175°F and heated for 45 seconds at 500°F. The coating and heating procedure was performed twice to provide a total dried film thickness of protective-insulative layer 22 of 1.0 mils. (By using PVDF as the binder material in this and all the underlying layers, each layer has the same processing requirements and restrictions. Thus the upper layers, and the protective coating, may be fully treated without damage to underlying layers, as might be the case if other different binder systems were employed.) The final heating step results in an electroluminescent lamp 10 of cross-section as shown magnified in Fig, 3. The polymeric material that was superposed in layers upon flexible substrate 12 has fused within the"layers and~between the layers to form a monolithic unit about 3.4 mils thick that flexes with the substrate. As all the layers are formed of the same polymeric material, all the layers of the monolithic unit have common thermal expansion characteristics, hence temperature changes during testing did not cause delamination. Also, due to the continuous film-like nature of each layer due to the fusing of its constituent particles of PVDF and the interpenetration of the polymeric material in adjacent layers, including the protective layer 22 covering the top and exposed side surfaces, the lamp was highly resistant to moisture during high humidity testing, and the phosphor crystals did not appear to deteriorate prematurely, as would occur if moisture had penetrated to the crystals in the phosphor layer. In the following examples, the physical properties of compositions useful according to the invention, prior to the addition of additives, were evaluated. Viscosity To determine the approximate range of viscosity prior to addition of additives over which the compositions of the invention are useful, two compositions were prepared using .isophorone as the liquid phase and polyvinylidene fluoride (PVDF) powder (461 powder, supplied by Pennwalt) , which is substantially insoluble in isophorone, i.e., it is estimated that substantially less than about 5 percent solvation occurs. The physical properties of the new compositions were adjusted by addition of PVDF powder or isophorone until the first composition (Composition A) had thickness or body at close to the lower end of the range useful for screen printing, and the second composition (Composition B) had body at close to the high end of the useful range. The weight proportions of the compositions and the resultant viscosities are as shown in TABLE A. TABLE A Composition A Composition B PVDF 65 83 Isophorone 56 58 Wt% solids 53.4 58.9 Viscosity 17,700 cps 200,000+ cps The viscosity of the compositions was measured using a Brookfield Viscosity Meter, Model LVF, at the #6 (low shear) setting. Composition A was tested using a #3 spindle at a multiplication factor of 200X and gave an average reading of 88.5. Composition B was tested using a #4 spindle at a multiplication factor of 2000X and gave an average reading that appeared well in excess of the maximum reading of 100. The viscosity of the commercially available Kynar 202 PVDF dispersion (Composition X) was tested on the same equipment and registered a viscosity of approximately 40,000 cps. (It is noted that while the weight percentage of PVDF solids is lower in the commercial product than in either of the test compositions, a different solvent is employed in the commercial system, so strict interpolation is not possible.) To demonstrate the shear thinning characteristic of the composition, a standard coating composition, in this case a dielectric composition prepared as in Example A, was subjected to further testing. The viscosity of the coating composition was tested in a Brookfield Viscosity Meter, Model LVF, as described above, with a #4 spindle operated at four selected, different speed settings, the speed of the spindle of course being directly proportional to the shear between the spindle and the composition. As shown in TABLE B, the viscosity of the composition decreased dramatically with increased shear. TABLE B Brookfield Viscosity Meter, Model LVF Spindle #4 Spindle Multiplier Setting Factor Reading Viscosity 6 1000 50 50,000 cps 12 500 64 32,000 cps 30 200 74 14,800 cps 60 100 86 8,600 cps Solids Range The weight percent solids of PVDF will vary depending, . upon the nature of the carrier fluids employed, and upon the physical properties of the additive, e.g * . upon particle surface area (particle shape, spherical or otherwise, as well as particle size) and particle density. The range of PVDF solids present in the overall coating composition can range between about 50 percent, by weight, down to about 15 percent, by weight. The preferred range is between about 25 and 45 percent, by weight. Other Embodiments Numerous other embodiments are within the following claims, as will be obvious to one skilled in the art. The protective layer 22 of the electroluminescent lamp may be applied as preformed film of polyvinylidene fluoride under pressure of 125 pounds per square inch, and the lamp heated at 350 F for one minute and then cooled whilerstill under pressure. Each separate layer applied may have a dry thickness of as much as .010 inch, although thickness in the range between about .003 inch to .0001 inch is typically preferred. The_ protective layer may be applied as preformed film of one or more other materials compatible with the lamp structure, which alone or in combination provide adequate protection against penetration of substances detrimental to performance of the underlying lamp. As mentioned, the composition may be applied by screen printing, or by various of the doctor blade coating techniques, e.g. knife over roll or knife over table. The shear-imparting conditions of screen printing may also be varied, e.g. the squeegee may be advanced along the screen at rates between about 2 and 200 inches per minute, and the size of the screen orifices may range between about 1.4 and 7 mils on a side. Materials which consist essentially of homopolymers of PVDF are preferred. However, other materials may be blended with PVDF, e.g. for improving surface printability, for improving processability during manufacturing, or for improving surface bonding. An example of one material miscible in a blend with PVDF is polymethyl methacrylate (PMMA) , e.g. employed at 1 to 15 percent by weight of PVDF, preferably 5 to 10 percent by weight. Also, other materials may be employed in place of PVDF. The guiding criteria for selection are low moisture absorptivity, ability of particles to fuse at elevated temperature to form a continuous moisture barrier film, and, when applied to flexible substrate, flexibility and strength. The general physical and mechanical properties of PVDF (in homopolymer form) appear in Table C. TABLE C General Physical and Mechanical Properties of Polyvinylidene Fluoride (PVDF) Property ASTM Method Values Specific Gravity D 792 1.75-1.78 g/ml (109.3-111.3 lb/ft 3 ) Property ASTM Method Values Specif ic Volume D 792 0.56-0.57 ml/g (15.5-15.8 inVlb) Refractive Index D 542 1.42 n 0 25 Melting Point D 3418 156-168°C (312-334°F) Water Absorption D 570 0.04-0.06% Tensile Strength § D 638 25°C 36-51 MPa Yield 100 O C 19-23 MPa (77°F 5200-7400 psi 212°F 2700-3400 psi) Tensile Strength @ D 638 25°C 36-52 MPa Break 100 O C 19-23 MPa (77°F 5200-7500 psi 212°F 2700-3400 psi) Elongation @ Break D 638 25°C (77°F) 25-500% 100°C (212°F) 400-600% Tensile Module D 638 1340-1515 MPa (194-219 X 103 psi) Stiffness in Flex D 747 1100-1730 MPa (160-250 X 10 3 psi) Flexural Strength D 790 59-75 MPa (8.6-10.8 X 10 3 psi) Flexural Modulus D 790 1200-1800 MPa (175-260 X 10 3 psi) Compressive Strength p 695 25°C 55-69 MPa (77°F 8-10 X 10 3 • psi) izod Impact D 256 25°C 160-530 kJ/ro (notched) (77° 3.0-10.3 ft-lb/in.) Izod Impact D 256 25°C 1710-3100 kJ/ (unnotched) (77°F 32-58 ft-lb/in.) Hardness, Shore D 2240 70-80 Proper ty ASTM Method Values Hardness, Knoop Tukon 9.4-9.6 Coefficient of 0.14-0.17 Sliding Friction to Steel Sand Abrasion D 968 4.01/um (1021/0.0011 3 ) Tabor Abrasion Wheel 7.0-9.0 mg/1000 cycle C5-17 1000 g The liquid phase of the composition may be selected from the group of materials categorized in the literature as "latent solvents" for PVDF, i.e., those with enough affinity for PVDF to solvate the polymer at elevated temperature, but in which at room temperature PVDF is not substantially soluble, i.e., less than about 5 percent. These include: methyl isobutyl ketone (MIBK) , butyl acetate, cyclohexanone, diacetone alcohol, diisobutyl ketone, butyrolactone, tetraethyl urea, isophorone, triethyl phosphate, carbitol acetate, propylene carbonate, and dimethyl phthalate. Where additional solvation is desired, a limited amount of "active" solvent which can, in greater concentrations, dissolve PVDF at room temperature, e.g., acetone, tetrahydrofuran (THF) , methyl ethyl ketone (MEK) , dimethyl formamide (DMF) , dimethyl acetamide (DMAC) , tetramethyl urea and trimethyl phosphate, may be added to the carrier. Such limited amounts are believed to act principally in the manner of a surfactant, serving to link between the PVDF polymer particles and the predominant liquid phase, thus to stabilize the PVDF powder dispersion ^ As will also be obvious to a person skilled in the art, the viscosity and weight percent of PVDF solids in the coating composition may also be adjusted, e.g. to provide the desired viscosity, suspendability and transfer characteristic to allow the composition to be useful with additive particles of widely different physical and electrical characteristics. - The additives mentioned above are employed merely by way of example, and it will be obvious to a person skilled in the art that other additives alone or in combination, or other proportions of the additives mentioned may be employed according to the invention. For example, for forming resistors, semiconductors and conductors, suitable additives may be selected on the basis of bulk resistivity or bulk density, or on the basis of other criteria such as cost. The bulk resistivities and bulk densities of examples of materials useful as additives are shown in TABLE D. TABLE D Material Resistivity Density (ohm cm) (gm/cc) Gold < 10~ 6 19.3 S Siillvveerr < < 1 100"" 66 loiδ Copper < 10- 6 8.9 Brass < 10-6 8.5 Iron < 10-6 7.9 Tungsten < 10-5 19.4 N Niicckkeell < < 1 100-- 5 8.9 Cobalt < 10-5 8.6 Stainless Steel < 10-5 8.0 Tin < 10-5 6.5 I Innddiiuumm OOxxiiddee ~ ~ 0 0..11 7.2 Zinc Oxide ~ 1.0 5.6 Mica powder > 106 Aluminum oxide > 10 6 4.0 Of course many other suitable materials are available, e.g., alloys of the listed metals or others may in some cases be employed in forming a conductor; salts rendered stably semiconductive by the addition of donor or acceptor dopants may in some case be employed in forming a semiconductor; and glass (fiber, shot or beads) or clay may in some cases be employed for electrical resistance. Similarly, additives useful as insulators or as capacitors may be selected on the basis of dielectric constant of the material as used in the composition, or, again, on the basis of density or other factors. For example, materials resulting in a composition having a dielectric constant above 15 are useful for forming capacitive dielectrics. Use of additives according to the invention provides a composite layer with electrical characteristics significantly different in degree from that of PVDF above. Examples of materials with sufficiently high dielectric constant are shown in TABLE E for comparison with PVDF. TABLE E Dielectric Constant Material (approx.) Density Barium Titanate 10,000 6.0 Strontium Titanate 200 5.1 Titanium Dioxide 100 3.8 PVDF 10 1.8 Additive particles suitable for use in formation of an electroluminescent lamp include zinc sulfide crystals with deliberately induced impurities ("dopants"), e.g., of copper or magnesium. Representative materials are sold by GTE, Chemical and Metallurgical Division, Towanda, Pennsylvania, under the trade designations type 723 green, type 727 green, and type 813 blue-green. What is claimed is:

Claims: 1 1. An electrical circuit component comprised 2 of a deposit, on a substrate, of superposed thin layers 3 of polymer, 4 each layer being the product of the steps of 5 depositing a fluid dispersion of particles of said 6 polymer followed by drying and fusing, 7 the predominant constituent of said polymer 8 particles being polyvinylidene fluoride (PVDF) , 9 at least one of said layers containing a 10 uniform dispersion of additional particles selected from H the group consisting of dielectric, resistive, and 1 conductive substances of characteristic electrical 1 3 values substantially different from the respective 4 values of said polymer, 15 - said polymer being in a fused state 16 continuously throughout the extent of said layers and I "7 between said layers, forming a monolithic unit. 1 2. The electrical circuit component of claim 1 2 wherein said polymer consists essentially of the 3 homopolymer of polyvinylidene fluoride. 1 3. An electroluminescent lamp having the 2 ' construction as claimed in claim 1, wherein one of said 3 layers contains phosphor particles, and an upper 4 adjoining layer contains electrically conductive 5 particles and is light-conductive for light emitted by 6 said phosphor particles. 1 4. The lamp of claim 3 wherein said 2 electrically conductive particles are transparent, 3 semi-conductive particles. 1 5. The product of claim 3 including a further 2 light-transmitting outer layer devoid of any of the 3 additional particles mentioned in claim 1, said layer 4 lying over and being fused with the layer therebelow, - > forming part of said monolithic unit. 1 6. The product of claim 1 or 3 wherein said 2 layers are the result of deposit by high-shear transfer. 1 7. The product of claim 6 wherein said 2 deposits are of predetermined, printed form. 1 8. The product of claim 1 or 3 wherein said - substrate and said deposit thereon comprise a flexible 3 unit. 1 - 9. The product of claim 1 or 3 wherein the 2 thickness of each of said layers is in the range of 3 .003" to .0001". 10. A method of forming an electrical circuit 2 component by depositing on a substrate, and drying, a 3 succession of superposed thin layers of a suspension of polymer solid dispersed in a liquid phase, the 5 predominant constituent of said polymer being 6 polyvinylidene fluoride (PVDF) , "7 ' the liquid suspension for at least one of said p layers containing a uniform dispersion of particles • 9 selected from the group consisting of dielectric, 10 resistive and conductive substances of characteristic 11 electrical values substantially different from the 12 respective values of said polymer, 13 said method including heating to fuse said 14 polymer continuously throughout the extent of said layer 15 and between said layers, to form a monolithic unit. 11. The method of claim 10 in which each layer, preceding the application of the next, is heated sufficiently to fuse said polymer particles to form a continuous film-like layer. 12. The method of claim 10 in which the predominant constituent of said liquid phase has substantially no solubility for said polymer under the conditions of its deposit. 13. The method of claim 10 wherein said liquid phase is predominantly formed from one or more members selected from the group consisting of methyl isobutyl ketone (MIBK) , butyl acetate, cyclohexanone, diacetone alcohol, diisobutyl ketone, butyrolactone, tetraethyl urea, isophorone, triethyl phosphate, carbitol acetate, propylene carbonate, and dimethyl phthalate. 14. The method of claim 12 or 13 in which said liquid phase includes a minor amount of active solvent selected to promote the suspension of said polymer particles in said liquid phase without substantially dissolving said polymer. 15. The method of claim 12 or 13 in which said liquid phase includes a minor amount of one or more members selected from the g-roup consisting of acetone, tetrahydrofuran (THF) , methyl ethyl ketone (MEK) , dimethyl formamide (DMF) , dimethyl acetamide (DMAC) , tetramethyl urea and trimethyl phosphate, in quantity to promote the suspension of said polymer particles in said liquid without substantially dissolving said polymer. 16. The method of claim 10 wherein said liquid dispersion for one of said layers exhibits a substantial reduction in viscosity under high shear stress and said layer is deposited by high shear transfer. 17. The method of ' claim 16 wherein said layer is deposited by silk screen printing. 18. The method of claim 16 wherein said layer is deposited by blade coating. 19. A method of forming an electrical circuit component by depositing by shear transfer on a substrate, and drying, a thin layer of a suspension of polymer solid dispersed in a liquid phase, the predominant constituent of said polymer particles being polyvinylidene fluoride (PVDF) , the liquid suspension for said layer containing a uniform dispersion of particles selected from the group consisting of dielectric, resistive and conductive substances of characteristic electrical values substantially different from the respective values of said polymer, said method including heating to fuse said polymer particles continuously throughout to form a continuous layer. 20. A method of forming an electroluminescent lamp by depositing by shear transfer on a substrate, and drying, thin layers of a suspension of polymer solid dispersed in a liquid phase, the predominant constituent of said polymer particles being polyvinylidene fluoride (PVDF) , one of said layers containing a uniform dispersion of phosphor particles, and another of said layers containing an electrically conductive substance, so provided that said layer when dried is transmissive to light emitted by said phosphor particles, said method including heating to fuse said polymer particles continuously throughout the extent of said layers and between said layers, to form a monolithic unit. 21. The method of claim 19 or 20 wherein said layer is deposited by silk screen printing or doctor blade coating. 22. An electroluminescent lamp comprising a phosphor-particle-containing layer disposed between corresponding electrodes that are adapted to apply an excitation potential to said phosphor particles, the upper electrode being light transmissive to radiation from said particles, wherein said phosphor layer comprises a thin layer of polymer the predominant constituent of which is polyvinylidene fluoride (PVDF) , said layer containing a uniform dispersion of phosphor, said layer being the product of the steps of depositing a fluid dispersion of particles of said polymer and phosphor upon the substrate followed by drying, and said polymer being in a fused state continuously throughout the extent of said layer. 23. An electroluminescent lamp comprising a phosphor-partide-containing layer disposed between . corresponding electrodes that are adapted to apply an excitation potential to said phosphor particles, the upper electrode being light transmissive to radiation from said particles, wherein said upper electrode comprises a thin layer of polymer the predominant constituent of which is polyvinylidene fluoride (PVDF) , said layer containing a uniform dispersion of additional particles that are substantially more electrically conductive than said polymer, said layer being the product of the steps of depositing a fluid dispersion of particles of said polymer and said additional particles upon a phosphor-containing layer followed by drying, and said polymer being in a fused state continuously throughout the extent of said layer. 1 24. The lamp of claim 23 wherein said 2 electrically conductive particles are transparent, 3 semi-conductive particles. 1 25. The lamp of claim 23 wherein said 2 phosphor-containing layer comprises a thin layer of 3 polymer the predominant constituent of which is polyvinylidene fluoride (PVDF) , 5 . said layer containing a uniform dispersion 6 of phosphor, 7 said layer being the product of the steps of 8 depositing a fluid dispersion of particles of said 9 polymer and phosphor upon the substrate followed by 10 drying, and U said polymer being in a fused state 1 continuously throughout the extent of said layer, 13 said polymer of said layers being fused 1 4 together forming a monolithic unit. 1 26. The lamp of claim 23 or 25 including a 2 further light-transmitting outer layer the predominant 3 constituent of which is PVDF and devoid of any of said 4 additional particles , said layer lying over and being 5 fused with said upper electrode layer therebelow, 6 forming part of said monolithic unit. 1 27. The lamp of claim 22, 23 or 25 wherein a said PVDF layer is the result of deposit by high-shear 3 transfer. 1 28. The lamp of claim 27 wherein said layer is 2 of predetermined, printed form. 1 29. An electrical circuit component comprising 2 a thin layer of polymer consisting essentially of 3 polyvinylidene fluoride (PVDF) , 4 said layer containing a uniform dispersion 5 of additive particles, 6 said layer being the product of the steps of 7 depositing a fluid dispersion of particles of said 8 polymer and said additive upon a substrate followed by 9 drying, and 0 " said polymer being in a fused state 1 continuously throughout the extent of said layer. 1 30. The electrical circuit component of claim 2 29 in the form of an electrical conductor having volume -j -2 -5 Λ . resistivity in the range of about 10 to 10 4 ohm-cm. 1 31. The electrical circuit component of claim 2 29 in the form an electrical semiconductor having volume J ■ a resisti.vi.ty in the range of about 10-1 to 103 ohm-cm. 1 32. The electrical circuit component of claim 2 29 in the form of an electrical resistor having volume • -*> resi.sti.vi.ty i.n the range of about 1 to 106 ohm-cm. 1 33. The electrical circuit component of claim 29 in the form of a capacitive dielectric having a 3 dielectric constant above about 15.

Inventors: HARPER WILLIAM P, LUNT MICHAEL S, HARPER, WILLIAM, P., LUNT, MICHAEL, S.
Applicants: ROGERS CORP, ROGERS CORPORATION
Application year: 1985
Main classification: H01J1
IPC codes: H05B33