Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B33/00—Electroluminescent light sources
  • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B33/00—Electroluminescent light sources
  • H05B33/10—Apparatus or processes specially adapted to the manufacture of electroluminescent light sources
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B33/00—Electroluminescent light sources
  • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
  • H05B33/20—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of the material in which the electroluminescent material is embedded
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B33/00—Electroluminescent light sources
  • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
  • H05B33/26—Light sources with substantially two-dimensional radiating surfaces characterised by the composition or arrangement of the conductive material used as an electrode
  • H05B33/28—Light sources with substantially two-dimensional radiating surfaces characterised by the composition or arrangement of the conductive material used as an electrode of translucent electrodes

Definitions

• This invention relates. to making electrical components by the deposit and drying of fluids that contain particles that have desired electrical and mechanical properties.
• the invention in another aspect, 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.
• any practical fluid composition 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.
• compositions 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.
• 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.
• a liquid dispersion of powder particles comprised of polyvinylidene fluoride (PVDF) simultaneously: a) can suspend uniformly in desired concentrations any of a wi ⁇ le 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.
• PVDF polyvinylidene fluoride
• 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.
• 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.
• 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.
• PVDF polyvinylidene fluoride
• 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) ,
• 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.
• Example 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.
• PVDF polyvinylidene fluoride
• BT206 barium titanate particles supplied by Fuji Titanium, having a particle size of less than about 5 microns
• 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 l ⁇ "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 A 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.
• zinc sulfide crystals type #723 from GTE Sylvania, smoothly rounded crystals having particle size of about 15 to 35 microns
• 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 deposited film was tested UV and found to be uniformly photoluminescent, without significant light or dark spots.
• Example A 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.
• 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.
• 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.
• _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.
• 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.
• 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.
• 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
• - • - 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
• 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.
• 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.
• each layer has the same processing requirements and restrictions.
• 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.
• 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.
• 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.
• 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.
• PVDF polyvinylidene fluoride
• composition A had thickness or body at close to the lower end of the range useful for screen printing
• second composition had body at close to the high end of the useful range.
• composition A Composition B
• 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.
• composition X 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.)
• 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.
• TABLE B the viscosity of the composition decreased dramatically with increased shear.
• 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.
• 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.
• 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.
• PVDF 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.
• PMMA polymethyl methacrylate
• 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.
• PVDF Polyvinylidene Fluoride
• 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.
• PVDF substantially soluble
• 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.
• 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.
• active solvent e.g., acetone, tetrahydrofuran (THF) , methyl ethyl ketone (MEK) , dimethyl formamide (DMF) , dimethyl acetamide (DMAC) , tetramethyl urea and trimethyl phosphate
• THF tetrahydrofuran
• MEK methyl ethyl ketone
• DMF dimethyl formamide
• DMAC dimethyl acetamide
• tetramethyl urea and trimethyl phosphate tetramethyl
• 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.
• 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.
• 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.
• 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.
• dopants zinc sulfide crystals with deliberately induced impurities
• 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.

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• 1985
  • 1985-02-04 DE DE8585900937T patent/DE3580877D1/de not_active Expired - Fee Related
  • 1985-02-04 EP EP85900937A patent/EP0171420B1/fr not_active Expired
  • 1985-02-04 WO PCT/US1985/000183 patent/WO1985003596A1/fr not_active Ceased
  • 1985-02-04 JP JP60500738A patent/JPH0766855B2/ja not_active Expired - Lifetime
  • 1985-02-04 CA CA000473478A patent/CA1227522A/fr not_active Expired
  • 1985-02-05 IT IT67111/85A patent/IT1182413B/it active

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