CA2261109A1 - Process for preparing high resolution emissive arrays and corresponding articles - Google Patents

Abstract

A process is described for forming an emissive or phosphor screen. The process comprises the steps of: a) providing a thermal mass donor element comprising a substrate with a front side and a back side, with a coating of emissive material or phosphor adhered to said front side of said substrate; b) placing said coating of emissive material or phosphor adjacent to a support layer; c) addressing said mass donor element with coherent radiation to heat at least a portion of said coating of emissive material or phosphor to locally transfer at least some of said emissive material or phosphor to said support layer; d) repeating step c) a sufficient number of times to provide a coating of transferred emissive material or phosphor on said support layer in an area of at least 1 square centimeter.

Description

CA 02261109 1999-01-1~

WO 98/03346 PCT/US97tl2368 PROCESS FOR PREPARING HIG~ RESOLUTION EMISSIVE ARRAYS
AND CORRESPONDING ARTICLES

Backvround of the Invention 5 Field of the Invention The present invention relates to therrnal transfer elem~nt~ and im~ging radiation addressed (e.g., laser addressed) thermal mass transfer processes for use in the m~nl-f~cture of high resolution emissive arrays. More particularly the invention relates to the use of radiation addressable therrnal transfer elements10 having emissive materials such as phosphors in the transfer layer.

Background of the Art Historically, phosphor arrays have been used in a variety of products inclu-1ing televisions, personal computer (PC) monitors, medical devices, oscilloscopes, radar tubes, optoelectronic image converters, personal safety products, bar coding, medical im~in~ screens (intensifying or storage phosphor screens), etc. Emissive arrays and phosphor display technology is expanding withthe introduction of emissive flat panel display devices such as field emission displays (FEDs), electroluminescent displays (ELs), plasma displays (PDPs), 20 vacuum fluorescent displays (VFD's), etc. A review of emissive display technology is provided in the Society for Inror,-,alion Display's publication Fundamentals of Emissive Technology by C. Curtin and C. Infante. As emissive display technology spreads into related product areas, the market continues to demand higher quality and higher resolution products. For example, mini~tllrized25 display devices for use in televisions, PC's, and camcorder viewfinders require a resolution of more than 50 lines/mm. (Oki, K. and L. Ozawa, ~'A Phosphor Screen for High-Resolution CRTs," Journal of the SID, 3, 51, 1995). For high-definitionprojection televisions having large picture formats, the require~ nl~ for the diameter of the electron spot is about a tenth of the di~meter of the spot in present 30 direct-view cathode ray tube screens and the maximum energy excitation density (approximately 2 W/cm2) is about a hundred times higher. (Raue, R., A. T. Vink and T. Welker, Philips ~ech. Rev., 44, 335, 1989) These pelro,..~ance standards are very difficult to achieve with the current phosphor screen methods of m~n~lf~ctllre, even though the phosphors available have the theoretic capability of 35 providing these characteristics.

CA 02261109 l999-01-l~

Phosphors are a critical component of cathode-ray tubes (CRTs), field electroluminescçnce devices (commonly rerel.ed to as EL devices), plasma displaypanels (PDP), light emitting diodes (LEDs), and field-emitting displays (FEDs).
In CRTs the quality of the screen image is dependent upon the 5 cathodoluminescent efficiency and resolution of the phosphor screen. Many methods exist for the production of phosphor screens. A review of the various methods and their applications is described in Hase, T., T. Kano, E. Nakazawa, and H. Yamamoto, "Phosphor Materials for Cathode-Ray Tubes," Advances in Elecfronic and Electron Physics, Academic Press, Inc., New York, 79, 271 10 ( I 990).
Traditionally, the sedimentation process has been and still is the predominant process for depositing phosphors onto screens for monochrome CRTs. In this process, a suspension of the phosphor in alcohol or water, with the addition of an aqueous silicate solution, is placed in the glass envelope or bulb of the CRT and is allowed to deposit onto the inner surface of the faceplate through se~limçnt~ion. The phosphor forms a layer whose adhesion, both to itself and to the glass, is effected by the slowly precipitating silicic acid. The coagulation time of the aqueous silicate is adapted to the sediment~tion rate of the phosphor by addition of electrolytes. The resultant screen has a relatively rough surface having 20 phosphor particles that are loosely packed due to the coagulation process. Even though the loosely packed phosphor screen may have a somewhat higher cathodoluminescent efficiency than screens having more closely packed phosphors, the resolution of the loosely packed screens is lower. Another disadvantage of this method is that it requires relatively thick (appro~-l..ately 6 25 mg/cm2) screens to insure a pinhole free coating, which thickness also decreases the resolution capability of the screen.
A slurry method is typically used in the production of shadow mask and aperture grill color CRTs where the screen consists of an array of multicolored dots or stripes. In this process, a slurry of a single color phosphor in a 30 photosensitive resin is initially spin-coated onto the glass panel as a continuous layer. The coating is exposed to ultraviolet (W) radiation from a point source through the apertures of a shadow mask, thus rendering the exposed areas insoluble in water. The non-exposed areas are removed by washing with water to form a phosphor image on the glass panel. This im~ging process is then repeated 35 at least two more times using phosphors of dilIe~ L colors to generate green, blue and red phosphor patterns. A dusting method is also sometimeS employed to m~nllf~cture multicolored shadow mask CRTs. In the dusting method, the same CA 02261109 l999-01-l~

basic process is used as described above except that dry phosphor is dusted ontothe wet photosensitive coating prior to im~eine Exposure of the screen by W
radiation through shadow mask apertures immobilizes the phosphor coating in the irradiated areas. This process is then repeated until all three colored phosphor5 patterns are formed on the glass panel. The primary concerns with these methods is the trade-offbel~eell pinhole formation and co~ n.il~tion by other color phosphors in the wash-off step. If a strong rinse is used, pinholes may form and if a weak rinse is used, the color phosphors may not be co,-~p'etely washed away inthe non-exposed areas. An alternative dusting method uses a photot~ ifi~ble n resist. In this method, the photosensitive layer is exposed with W radiation prior to depositing the phosphor. The phosphor adheres to only the tackified image areas. Again, the primary concern with this method is cont~ ;on by other color phosphors.
For applications requiring highly dense monochro,natic phosphor screens 1S with small particles, a deposition method is typically used. In this process, the phosphor powders are suspended in a polar organic solvent and cationic additivesare adsorbed onto the surface of the phosphor. A negative potential is applied to a conductive substrate immersed in the solution with respect to a negative electrode held parallel to the substrate. The resulting applied electric field causes 20 the positively charged phosphor particles to migrate to the substrate, thus coating the surface.
One such application requiring a high density phosphor screen is medical X-ray im~ging These screens usually col"p,ise phosphors in a binder on a carrierlayer. The phosphors absorb X-ray radiation at a higher efficiency than does silver 2s halide which is normally used in the hard-copy output of radiographic images. The phosphors not only absorb X-rays at an efficient rate, but can also phosphoresce, e~ e radiation at a wavelength other than the wavelength of X-rays which the phosphor absorbed. Depending upon the chemical nature and properties of the phosphor, the emitted radiation may be at essPnti~lly any 30 wavelength between and inclu(line the infrared and ultraviolet wavt~lenethc of the electromagnetic spectrum. Silver halide naturally absorbs radiation in the ultraviolet and near blue waveleneths, and can be spectrally senciti7ed to efficiently absorb radiation in other portions of the ultraviolet, visible and the infrared regions of the electromagnetic spectrum. By exposing the phosphor 3s screen to X-rays, having the phosphor screen emit in the W, visible or infrared, and having a silver halide emulsion spectrally senciti7ed to the wavelength of emission of the phosphor screen and optically associated with the phosphor CA 02261109 1999-01-1~

WO 98/03346 rCT/US97/12368 screen, the entire efficiency of the X-ray im~ing system can be great}y enh~nced .
This allows for the use of lower doses of X-rays during exposure of the object.
The use of such phosphors is well known in the art as exemplified by such patents as U.S. Patent Nos. 3,883,747 and 4,204,125 where there is direct 5 emission of phosphorescent radiation upon X-ray stim~ tion~ and U.S. Patent Nos. 3,859,527 and 5,164,224 where there is exposure to X-rays, storage ofthe absorbed energy by the phosphor, and subsequent stimul~tion by stim-.l~ting radiation to cause the phosphor to emit the stored energy as W to infrared radiation. These phosphor systems are commercially succes.~fi-l and provide a 0 significant benefit to the radiographic art. In these types of systems, however, there is a trade-offbetween speed and sl.a.~ness. To absorb more X-rays and emit more light, the screen itself can be made thicker. But in this case, light generated within the thickness of the screen is scattered by the phosphor grains to a greater extent, thereby reduçing the resulting image sharpness recorded on the5 film. Conversely, to improve sharpness a thinner screen is desirable, but thisreduces the X-ray absorbing power, and ultim~tely requires a higher dosage to the patient or object being X-rayed.
Many methods of improving the image quality, particularly the sharpness of images generated from phosphor screens, without adversely affecting the 20 sensitivity or speed of the system, have been proposed. Reflective particulates, dyes, pigmÇnt~ and other light affecting materials have been proposed as additives to phosphor layers to improve sharpness as shown in EPO 102 790 (powdered glass), Japanese Application 146,447/1980 (white pigments), Japanese Patent Application 16-3,50011980 (colorants), and EPO 175 578 (sputtering or vacuum 25 evaporation of phosphors).
The objective of these methods primarily is to provide a high concentration of phosphor in the active layer of the screen and provide a screen of uniform properties. U.S. Patent No. ~,306,367 produces a storage phosphor screen by dispersing phosphor particles in a thermoplastic binder diluted with a solvent, then 30 coats the mixture, dries to remove the solvent, and con.plesses the coating at a temperature above the melting point of the binder. U. S. Patent No. 5,296,117 deposits phosphor particles in a binder by electrophoretic deposition of a dispersion of the phosphor particles in a solution of polymeric binder. The solution is coated onto a substrate, dried and the phosphor screen thus produced.
35 Each of these types of systems has shown some benefits, but there is still significant room for improvement in the sha- ~ness of radiographic phosphor screens. In particular, it is desired to elimin~te complicated deposition processes CA 02261109 l999-01-l~

W O 98/03346 PC~r~US97/12368 which can be costly, to çlimin~te the use of solvents which are harmful to the environment, and to çlimin~te or reduce high processing temperatures.
Some attempts have been made to provide a method of transferring a phosphor image directly onto a glass panel using a thermal ~ re, tape, ribbon or5 sheet and a thermal head printer. Examples of this type of application are disclosed in J~p~nese Application Nos. 63-02270A; 62-67416A; and 84-020466B.
The advantage of this type of method is the selective pl~cçn~ent of the phosphoron the substrate. However, the use of thermal printer heads limits the composition, shape and configuration of substrate used, produces low resolution o images limited by the size of the printhea~, makes the regisl,~lion of adjacent phosphors difficult to control, and reduces the through-put of m~m~f~ctllred materials because of the slow speed of printhea~lc For example, the substrate must be flat to achieve a uniform transfer of the image. In addition, thermal print heads are currently limited in size and face a practical limit in reducing the size of 15 the printing head.
Japanese Patent Application No. 62-95670A describes a thermal transfer construction which uses a conductive film layer within the construction. The transfer element is imaged by means of electrodes installed over the element. This construction suffers the same limitation as the conventional thermal transfer 20 elements in that the substrate must be flat to achieve uniform transfer of the image.
There is a need for an efficient dry process for forming an emissive material or phosphor image on a variety of substrate sizes and configuration. Inaddition, there is a need for materials that are capable of producing high resolution and large excitation density to meet the increasing dem~n~e in the m~nllf~ctllre of 25 high-definition televisions, field emission displays, and other hybrid display techniques.
- The increasing availability and use of higher output compact lasers, semi-conductor light sources, laser diodes and other radiation sources which emit in the ultraviolet, visible and particularly in the near-infrared and infrared regions of the 30 electrom~netic spectrum, have allowed the use of these sources as viable alternatives for the thermal printhead as an energy source. The use of a radiation source such as a laser or laser diode as the im~eing source is one of the primary and pre~l ed means for transferring electronic information onto an image recording media. The use of radiation to expose the media provides higher 35 resolution and more flexibility in format size of the final image than the traditional thermal printhead im~ing systems. In addition, radiation sources such as lasers and laser diodes provide the advantage of el;.-.;~ , the detrimental effects from CA 02261109 1999-01-1~ ' , ~ .

contact of the media with the heat source. The size, shape, energy and duration of the spot dwell time may be readily controlled acco~ding to the needs of the particular process and materials used. Various therrnal im~ging materials and processes are shown in U.S. Patent Nos. 5,171,650, 5,156,938, GB Patent Application 2 083 726 A and Jap~n~se Kokai Patent Publication Sho 63[1988]-60793.
U.S. Patent Nos. 5,171,650 and 5,156,938 disclose an info.l,la~ion transferring system and process in which materials are propulsively tlahsrc~l~d from a donor layer to a receptor layer. Amongst the many materials listed which o could be transferred in this information transferring system are ll~;n~sce~.l materials (IJ.S. PatentNo. 5,171,650, column 13, lines 8-23) and phosphors (e.g., U.S. Patent No. 5,278,023). The phosphors are included within the broad class ofmaterials which provide information density when tl ~r,sr~ ;d, and altho~
described as the types of phosphors used for television or medical im.~ging purposes, are not ~rahsre" ed to coat an entire surface, but are to be distributed in an inro".,alion bearing pattern.
U.S. Pat. No. 5,171,650 discloses methods and materials for thermal im~ging using an "ablation-transfer" technique. The donor ele~nerlt used in the imaging process comprises a support, an intermediate dynamic release layer, and 20 an ablative carrier topcoat con~ ing a colorant. Both the dynamic release layer and the color carrier layer may contain an infrared-absorbing (light-to-heat conversion) dye or pigrnent. A colored image is produced by placing the donor element in intim~te contact with a receptor and then irra~ ting the donor with acoherent light source in an imagewise pattern. The colored carrier layer is 25 simlllt~neously released and propelled away from the dynamic release layer in the light struck areas cfe~ ,g a colored image on the receptor. EP ,4-0 562 ~52 ICo ~cn~ U.S. a~plic~l;on Sc~;al No. 07/855,7n filed M~h 23, 1~2 1QS~S ablative imag~ng elo."e~-~s comprising a substrate coated on a portion thereof with an energy sensitive layer comprising a glycidyl azide polymer in 30 combination with a radiation absorber. Demonstrated imaging sources included infrared, visible, and ultraviolet lasers. Solid state lasers were disclosed as exposure sources, although laser diodes were not specifically mentioned. This application is primarily concerned with the formafion of relief printing plates and lithographic plates by ablation of the energy sensitive layer. No specific mention 3s of utility for thermal mass transfer was made.
U.S. Pat. No. 5,308,737 discloses the use of black metal layers on polymeric substrates with gas-producing polymer layers which generate relatively AMENDED SHEET
lP~Q,!F~

CA 02261109 l999-01-l=7 high volumes of gas when irradiated. The black metal (e.g., black ~lllminllm) absorbs the radiation efficiently and converts it to heat for the gas-generatingmaterials. It is observed in the examples that in some cases the black metal waselimin~ted from the substrate, leaving a positive image on the substrate.
s U.S. Pat. No. 5,278,023 discloses laser-addressable thermal l~al,s~r materials for producing color proofs, printing plates, films, printed circuit boards, and other media. The materials contain a substrate coated thereon with a propellant layer wherein the propellant layer contains a material capable of producing nitrogen (N2) gas at a temperature of preferably less than about 300~C;
o a radiation absorber; and a thermal mass transfer material. The thermal mass ~l ~r.srt;r material may be incorporated into the propellant layer or in an additional layer coated onto the propellant layer. The radiation absorber may be employed in one of the above-disclosed layers or in a separate layer in order to achieve localized heating with an electrom~gnetic energy source, such as a laser. Upon laser induced he~sin~ the transfer material is propelled to the receptor by the rapid expansion of gas. The thermal mass transfer material may contain, for example, pigments, toner particles, resins, metal particles, monomers, polymers, dyes, orcombinations thereof. Also disclosed is a process for forming an image as well as an imaged article made thereby.
Laser-inrluced mass ~1 ~n;,rer processes have the advantage of very short heating times (nanoseconds to microseconds); whereas, the conventional thermal mass transfer methods are relatively slow due to the longer dwell times (milliceconds) required to heat the printhead and transfer the heat to the donor.
The transferred images generated under laser-induced ablation im~ging conditionsare often fr~gmPnted (being propelled from the surface as particulates or fr~m~nt~) Summarv of the Invention The present invention provides a process for prepa. h~g and selectively transferring emissive material in uniformity (i.e., even distribution or continuous distributions of particul~tes) to substrates using laser addressed thermal im~ginf~
techniques to produce a high resolution emissive screen and panel. Such screens and panels include cathode-ray tubes (CRTs), field emission displays (FEDs), electrolumin~sc~nt displays (ELs), plasma displays (PDPs), vacuum fluolescenl displays (VFDs), X-ray intensifying screens, and the like. The present inventionrelates to an emissive thermal ll ansrer element comprising a substrate having deposited thereon (a) an optional light-to-heat conversion layer, (b) an optional CA 02261109 1999-01-1~

interlayer, (c) a thermal transfer layer co~ ris;llg a coating of emissive material (e.g., phosphor, semiconductor electroln..~ escel-t materials, fluorescers, emissive organic polymers, etc.) and (d) optionally an adhesive co~tine and to the methodof transferring said emissive material to a substrate in a uniform distribution of 5 said emissive material so that a panel having uniform emissions may be formed by the transfer process. By 'uniform' it is meant that each type of emissive material I-~nsr~lled (where one or more emissive materials are llansrel~ed for example inthe m~nllf~ctllre of a color cathode ray tube) is sufficiently evenly distributed over the surface of the receptor surface in forming the emissive panel so that upon o flood stimulation of the entire surface of the emissive panel, there is no visible pattern of information in the emissions produced. This is a statistically even or uniform distribution of material. For example, when a color CRT screen is deposited, there are three continuous areas of phosphors and a black matrix between each of the continuous areas of phosphors. Looking under a microscope, 15 discrete particles or regions of uniformly distributed individual phosphors could be discerned as the phosphors will vary to some degree in alignment, even though statistically over even small dimensions (e.g., less than O. l mm, especially less than 0.05 mm) there will be an even distribution of individual types of particles.
It is highly unexpected that phosphors can be thermally transferred by high 20 energy im~ging radiation and retain its high quality phosphorescent emission ability. This is particularly true with the ablative ll ~n~r~l systems of the prior art as represented above with U.S. Patent No. 5,308,737 and others. Those systems propulsively or explosively transfer materials which would be expected to damagecrystals or break up particles during the ll~n~rer. ~t is well known that breaking 2s up or highly stressing phosphors can reduce their efficiency or alter their emission spectra. This would of course be undesirable in the formation of an emissive array.
The present invention also provides a method for using a contin~lous emissive array on a receptor using the above described thermal transfer element 3n by stim~ ting only selected areas on the uniformly coated panel. A uniform coating means that the coating is sufficiently evenly distributed over the surface of the receptor surface in forming the ernissive panel so that upon flood stim~lation of the entire surface of the emissive panel, there is no visible pattern of h~olmalion in the emissions produced. By visible it is meant upon e,~ tion by 35 the naked eye from a dist~nce of no less than 0.~ meters. These coali.~gs contain no information in themselves, but are merely the digitally acces~ible deposition of the emissive materials. A uniform coating is transferred onto a receptor by (a) ~' CA 02261109 1999-01-15 . ~ ., . . , ~ '. .
. ' 7 ; ~ '' 1 ''~ ' '~

placing in intim~te contact a receptor and the therrnal transfer layer of said thermal l~anSr~r elP~ t described above, (b) eAyos;ng the emissive material thermal transfer elPment in a uniform pattern of distribution with a radiation source, and (c) transferring the emissive thermal transfer layer corresponding to the uniform S pattern to the receptor, to provide a uniformly distributed pattem coating of t~nsre.l~,d emissive agent on said support layer Said uniform patterns ue preferably at least 1 square ce~ ..eter in area, more preferably at least 2 cm2., still more preferably at least S cm2. in area when formed in continuous lines. Square areas of these side dimencions ue also desired, e.g., I square cm, 4 square lo C4~ tPrs, 25 square ccnn~ ers of contin~Qus areas of phosphor particle distribution. Optionally step (c) may be rep~ated a sufficient number of times with -~ di~.'~ emissive thermal transfer donors to provide uniform coa~ C of multiple emissive agents on said support layer of at least 1 square cen~; ..etP~. In a color television cathode ray tube, for example, the three or more phosphors may be each 15 evenly distributed over the surface of the screen. Each phosphor is in a uniforrn (non-information-bearing) coating over the screen surface and the three phosphors togethcr form a uniform, multicolor emitting pattern of phosphor coating. Whcn the thermal transfer layer contains crosslinkihle materials, an additional curing step may be p~.ru,...ed where the t,ans~ d pattem is subsequently crosslin~ed 20 by exposure to heat or radiation, or lr~",c r ~ with chemical curatives. When the thermal 1- ~ns~- Iayer'contains thermally decG,-.posable materials, a bake-out step may be ~e.Çol l-.ed to remove organic residue.
Emissive materials are well known in the art. These are materials which ernit radiation when non-thermally stimulated (non-thermal stim~ tion e~ g 2~ the fact that all materials, when sufficiently heated, will emit radiation). In the practice of the present invention emissive materials jnrludes materials which are photQlominesc~nt and/or cathodolurninescPrlt and/or electrolu...inesc.,.l~. These emissive materials may also absorb (temporarily or for longer time periods, suchas days) radiation and, spontaneously or upon passage of time or upon 30 stimul~tion~ emit radiation which measurably differs in wavelength or wavelen~,~h band from the absorbed radiation. For example, X-ray intensifying phosphors absorb X-radiation and emit UV, infrared or visible radiation spontaneously (intensif,ving phosphors) or when subsequently stimulated by a third radiation (storage phosphors). Cathode ray tubes (CRT's) absorb electrons and emit visible35 radiation. In ELs light is generated by i3mF~aO~ctt e~xc~t~t~n of light emitting centers in phosphor materials by high energy (approxn-.aIe~y7 00 ev~e1ecl~ons. In color plasma panels a gas discharge emits ultraviolet light which excites a phosphor to AMENDED SHEET
IPE~/EP

CA 02261109 l999-01-l~

produce visible light. FEDs utilize a matrix addressed cold-cathode array in which cathodoluminescent phosphors are irradiated with electrons and emit visible light.
Each of these phosphors is an emissive material according to the practice of thepresent invention.
s The phrase "in intim~te contact" refers to sufficient contact between two surfaces such that the transfer of materials may be accomplished during the transfer process to provide a sufficient ~ nsrel of material within the im~ging radiation addressed, thermally stim--l~ted areas. In other words, no voids are present in the transferred areas which would render the ll ~nsre- - ed image non-functional in its interlded application. In the case of cathode ray screens, the black matrix must surround the phosphors, but this is considered functional and continuous within the CRT art. The individual phosphors may not form a sufficiently continuous coating for the purposes of a con~-,.ercially suitable CRT
system, but the three or more phosphors add together to form a functionally 1S continuous coating in the practice of the present invention.
~Tm~ing energy" refers to absorbed radiation such as that from a fl~chl~mp or laser (or other coherent radiation whether from a laser or solid state emitter such as a laser diode or other source) energy that can cause a unit transfer of an emissive material-cont~inin~ or phosphor-containing mass transfer layer from an emissive material-cont~ining or phosphor-con~ g mass transfer donor element to a receptor element.

Deta;led D~ ;,.tion of the Invention Emissive display devices such as phosphor screens and panels are provided 2s according to the practice of the present invention by the provision of a thermal mass transfer donor element comprising, in order: (a) a support, (b) an optionallight-to-heat conversion layer, (c) an optional non-transferable interlayer, (d) a transferable emissive material-cor.~ -ing layer and (e) an optional adhesive layer.
One or more of optional layers (b), (c) and (e) may be present on any thermal 1, a~srer element used in the practice of the present invention. The process may be generally described as involving the follov~ing steps: (i) placing in intim~te contact a substrate with the llan~rel~ble emissive material- (e.g., phosphor-) co..l~inil~g layer (or the transferable layer and overlying adhesive layer) of the thermal transfer element described above, (ii) irr~ ting one or more of the therrnal transfer 3s element or the receptor element (or one or more portions of either, e.g. substrate, transfer layer, light-to-heat conversion layer, an adhesive layer, etc.) with radiation of sufficient intensity to effect local transfer from the thermal mass l,~n~re, Il ' ' ' ' .

ele.llent, and (iii) there~y llahsr~lh~g the transferable ernissive-(e.g., phosphor-)Cont~inirlg layer (and the adhesive layer, if present) in the irradiated areas to the substrate.
The use of radiation and espec~ y coherent radi~tion to transfer the 5 phosphor or emissive material increases the resolution, re~sll alion, and speed of m~mlfac~-re ofthe screens as compared to thermal printhead processes, while eYp~ntling the scope of substrates which may be used as the receptor with respect to shape (e.g., curved or irregular surfaces), cG.-.pos;~ion and configuration of the receptor.
The transferable emissive material-cont~inil~ donor elc.ncnt ofthe present invention can be prcp~l,d by providing the layers of a ~lanarclable emissive material-con~ ing donor ele,"e"l (i.e., a l,~.ar~"dble phosphor-cont~ining layer, and optionally one or more of a light-to-heat conversion layer, an non~ ns~r~bleinterlayer, transferable adhesive layer, etc.) onto a substrate. The donor substrate can be constructed of any material known to be useful as a substrate for a mass trans~r donor element. The donor substrate is generally either a rigid sheet material such as glas~, ceramics, composites, or a flexible film (e.g.,-organic polymeric film such as polyester, polycarbonate, etc.). The substrate can be smooth or rough, transparent, opaque, tranclucent~ sheet-like or non-sheet-like.Examples of suitable film substrates include polyesters, ~spee;~l1y polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polysulfones, polystyrenes,polycarbonates, polyimides, polyamides, cellulose esters such as cellulose acetate and cellulose butyrate, polyvinyl chlorides and derivatives thereof, and copolymers comprising one or more of the above materials. The polymeric substrate generally2s has a thic~ness from I to 200~rons~1more preferably 2 to 50~crons),Rigid glass or ceramic substrates generaily have thic~n~ss of from 20 to lOOd~rons)or more.
The transferable emissive material-cont~ining layer may contain organic binders. The binder can be any of a number of known polymers such as thermoset, thermosett~ble, or thermoplastic polymers, including acrylates (inclu~ing methacrylates, blends, mixtures, copolymers, terpolymers, tetrapolymers, oligomers, macromers, etc.), epoxy resins (also including copolymers, blends, mixtures, terpolymers, tetrapolymers, oligomers, macio-l,e.a, etc.), silanes, siloxanes (with all types of variants thereof), and polymerizable compositions comprising mixtures of these polymerizable active groups (e.g., epoxy-siloxanes,epoxy-silanes, acryloyl-silanes, acryloyl-siloxanes, acryloyl-epoxies, etc.). In one embodiment, the transferable emissive material-containing layer transfer layer i2_~ Sh'EET

CA 02261109 1999-01-1~

contains a thermosettable binder. After the l.al-sr~ ble emissive material-cont~inin~ transfer layer is transferred to the receptor element, the thermosettable binder can be crosslinked, for instance by exposing the therrnosettable binder to heat, a suitable radiation source, moisture, or a chemical curative, as is appropriate 5 for the particular thermosettable binder. In some applications it may be desirable to remove the binder from the emissive material co..~ layer subsequent to transfer to the receptor. In these cases it is desirable to employ binder materials which may be readily removed uti~ in~ for e.~a,.")l~ heat, radiation and/or chemical etch~nt.c lo The transferable emissive- or phosphor-cont~ining donor element can contain ingredients known to be useful with mass transfer donor elements.
Dispersants, surf~ct~nts and other additives (antioxidants, light stabilizers, bri~hteners, white pigment~, reflective partic~ tec~ colorants, coating aids, anti~t~tic agents, etc.) may be in~.luded to aid in the dispersion ofthe emissive materials or impart other desirable properties to transferable emissive material-cont~ining layer as known to those skilled in the art. Especially desirable are the inclusion of fluorinated surfact~nts and lubricants which facilitate smooth and clean transfer of the emissive material and especially the phosphor layers from the donor to the receptor. The transferable emissive-co.l~ donor elelnent can optionally contain a light absorbing material that absorbs im~ing radiation and converts that energy into heat energy. The light abso,l)ing material can be any material that will absorb a portion of incident im~ing radiation, converting theradiation energy to heat energy, and thereby f~rilit~ting transfer of the l, ans~el ~ble emissive-cont~ining layer from the donor element to a receptor elemPnt 2s Examples of materials that can be useful as light absorbing materials include suitably absorbing dyes (i.e., those that absorb light in the ultraviolet, infrared, etc.
wavelen~th.c), binders or other polymeric materials, organic or inorganic pigments that can be a black-body or a non-black-body absorber, metals or metal films, orother suitable absorbing materials.
Examples of dyes that have been found to be useful light absollJing materials include dyes absorbing of light in the infrared region of the spectrum.
These are described, for example in M~t~llol ~, M., Infrared AbsorbingMaterials,Plenum Press, New York, 1990, in Matsuoka, M., Absorption Spectra of Dyesfor Diode Lasers, Bunshin Publishing Co., Tokyo, 1990, in U.S. Patent Nos.
4,772,583, 4,833,124, 4,912,083, 4,942,141, 4,948,776, 4,948,777, 4,948,778, 4,950,639, 4,940,640, 4,952,552, 5,023,229, 5,024,990, 5,286,604, 5,340,699, 5,401,607 and in European Patent Nos. 321,923 and 568,993. Additional dyes CA 02261109 1999-01-1~

W098103346 PCTrUS97/12368 are described in Bello, K. A. et al., J. Chem. Soc., Chem. Commun.~ 452 (1993) and U.S. Patent No. 5,360,694. IR absorbers marketed by American Cyanamid or Glendale Protective Technologies under the design~tion IR-99, IR-126 and IR-165 may also be used, as disclosed in U.S. Patent No. 5,156,938. In addition to conventional dyes, U.S. Patent No. 5,351,617 describes the use of IR-absorbing conductive polymers as light absorbing materials.
Other examples of prefe. . ed light absorbing materials include organic and inorganic absorbing materials such as carbon black, metals, metal oxides, or metal sulfides and other known pigment~ and absorbers. Representative metals include 0 those metallic elçment~ of Groups Ib, IIb, IIIa, IVa, IVb, Va, Vb, VIa, VIb and VIII of the Periodic Table, as well as alloys thereof, or alloys thereof with elements of Groups Ia, IIa, and IIIb, or mixtures thereof. Particularly pl ere- I ed metals include Al, Bi, Sn, In or Zn, and alloys thereof or alloys thereof with elements of Groups Ia, IIa and IIIb of the Periodic Table, or compounds or S mixtures thereof. Suitable compounds of these metals include metal oxides andsulfides of Al, Bi, Sn, In, Zn, Ti, Cr, Mo, W, Co, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zr and Te, and mixtures thereof.
The light absorbing material can be added to one or more of the components of the transferable emissive-cont~ining donor element (e.g, the 20 substrate, transferable emissive-cont~inin~ layer, etc.).
In one embodiment of the present invention, the light absorbing material can be present in the transferable emissive-cont~ining donor element as a separate layer, referred to herein as a "light-to-heat conversion layer" (LTHC). The light-to-heat conversion layer can preferably include one or more layers of organic or25 inorganic materials that absorb im~in~ radiation. Plefe-~bly, the light-to-heat conversion layer is comprised of materials which are thermally stable. Preferably, the light-to-heat conversion layer remains substantially intact during the im~Ein~
process. These light-to-heat conversion layers can be comprised of 100% light absorbing material; for example if the light-to-heat conversion layer is in the form 30 of a metallic film. Metallic-type light-to-heat conversion layers can preferably have a thickness in the range from about 0.001 to 10 micrometers, more preferably in the range from about 0.002 to 1.0 micrometers.
Alternatively, a light-to-heat conversion layer can comprise particles of light absorbing material (e.g, carbon black) dispersed in a binder. The binder can 3s be any of a number of known film-forming polymers such as thermoset, thermosettable, or thermoplastic polymers, incluclin~ phenolic resins (e.g, novolak and resole resins), polyvinyl~cet~tes, polyvinylidene chlorides, polyacrylates, .

ce11~10se ethers and esters, nitrocelluloses, polycarbonates, and mixtures thereof.
Preferably, this type of light-to-heat conversion layer is coated to a dried thicL nPss of from 0.05 to 5.0 micrometers, more preferably from 0.1 to 2.0 micrometers.
Adjacent to the optional LTHC layer is coated an optional non-S l. ar.sr, . able interlayer. Examples of suitable interlayers are described in co-pending U.S. Patent~p~lic~tio~n2~h~n9, el ~1. titlcd "Thcrmal Tr3nsfeF Donor rle.~ , ContniniR~ an Intcrl~yer" filed en ~pril 1S, l9ÇC (FNff ~049TJ~A1~
incorporated herein Sy reference. The incorporation of an interlayer interposed between the light-to-heat conversion layer and the emissive material-co..lA;~-;n~, ll~rlsr~.~ble layer reduces the level of co~t~ ;on ofthe resulting t.~n~Llc~
image from the light-to-heat conversion layer and decreases thc amount of - distortion res~ nt in the transferred image. The interlayer may be either an organic or inorganic material. To ".;l~ .;>~; damage and co.~ ..;n~l;on ofthe resultant transferred ernissive-containing isn~e, the interlayer preferably is acontinuous coating which has a high thermal resist~nce and remains s~lbst~nti~ily intact and in contact with the LTHC layer during the imaging process. Suitable organic materials include both thermoset (crosslinked) and thermoplastic materials. The interiayer may be either tr~nc~issive or reflective at the jm~ging radiation wavelength output.
Suitable thermoset resins useful in the interlayer include both therrnal- and radiation-crosslin~ed materials, such as crosslinked poly(meth)acrylates, polyesters, epoxies, polyurethanes, etc. For ease of application, the thermoset materials are usually coated onto the light-to-heat conversion layer as thermoplastic precursors and subsequently crosslinked to form the desired 2S crosslinked interlayer. Classes of suitable thermoplastic include polysulfones, polyesters, polyimides, etc. and may be applied to the light-to-heat conversion layer using conventional coating techniques (solvent coating, etc.). The optimumt~ic~ness of the interlayer is determined by the minimum thic~ness at which transfer of the light-to-heat conversion layer and distortion of the transferred layer are elimin~ted~ typically between 0.05 ~m and 10 llm.
Suitable inorganic materials for use as interlayer materials include metals, metal oxides, metal sulfides, inorganic carbon coatings, etc., which are highly transmissive at the imaging radiation wavelength and may be applied to the light-to-heat-conversion layer using conventional techniques (e.g., vacuum sputtering,3s vacuum evaporation, plasma jet, etc.). The optimum thickness is determined by the minimum thickness at which transfer of the light-to-heat conversion layer and . ~

CA 02261109 l999-01-l~

W O 98/03346 PCTAUS97tl2368 distortion of the transferred layer are elimin~ted, typically between 0.01 ~lm and 10 ~lm.
Optionally, other non-emissive material-containing transfer layers may be present on the donor to provide additional functionality in the im~ing radiation5 ll a,ls~" ed areas. Of particular interest would be to have adhesive material, and pigmlonts (e.g., red, green and/or blue pigments) in the phosphor matrix or in the surface which adheres to the receptor surface (e.g., curved glass).
Optionally, transferable emissive material-cont~ining donor element may be coated with an adhesive layer which f~cilitates transfer of the ll ansr~l ~ble emissive 0 material-cont~ining layer to the receptor.
During im~ging radiation exposure it may be desirable to ...;l.;...i7e formation of interference patterns due to multiple reflections from the imaged material. This can be accomplished by various methods. The most common method is to effectively roughen the surface of the thermally imageable element on s the scale ofthe incident imaging radiation as described in U.S. Pat. No. 5,089,372.
An alternate method is to employ the use of an anti-reflection coating on the second interface that the incident illumin~tion encounters. The use of anti-reflection coatings is well known in the art, and may consist of quarter-wave thicknPs.se~ of a coating such as magn~cillm fluoride, as described in U.S. Pat No.
5,171,650. Due to cost and manufacturing constraints, the surface roughening approach is pl efel . ed in many applications.
The receptor may be any continuous coating emissive display element benefiting from the application of emissive materials and especially phosphors.
The receptor can be smooth or rough, tl~nspa-t;nt, opaque, translucent, sheet-like 2s or non-sheet-like, flat or curved (e.g., as the interior concave surface of a CRT
tube). Optionally, the receptor may be coated with an adhesive layer which f~cilit~tes transfer of the emissive material conl~inil~g or phosphor-cont~ininglayer to the receptor in the areas exposed to im~ing energy. As an alternative to a light absorbing material in the transferable emissive material-cont~ining donor element, a light absorbing material may be present in a component of the receptor element, for example within the substrate of the receptor element, or within a separate layer of the receptor element (for example, within the black matrix on the substrate, within an adhesive layer of the receptor element, etc.). If the lightabsorbing material is present in the receptor element, or is a portion of the 3s transferable emissive material-cont~ining donor clclenl that transfers to thereceptor element during im~ging, it follows that the light absorbing material will be present in the imaged receptor element. In such as case, it is pl ~re~ . ed that the CA 02261109 1999-01-1~
I 7 . I
.~ .~ ~ , , , ) ', -.

light absorbing material not interfere with thc perfol l,.ance properties (c.g., the desired optical properties) of the imaged receptor.
The emissive materials may be coated onto the donor substrate by any method which provides sufficient adherence to the substrate to enable it to be used S in a thermal im~ging process. The emissive material such as a phosphor may be deposited for example by vapor deposition, sol drying, therm. al dr,ving, binderless adherel-ce to a receptor coating on the substrate, coating and drying of a dispersion/solution of phosphor particles and binder, coating and drying of a dispersion/solution of organic luminescent material, and the like. A contin~lo~s10 coating requires that there are no physical holes of visually observable dimen~;onc in the coating which render the article non-functional. The t, ans~r of emissive-~ materials in this method provides highly uniform (thickness and orient~tion), evenly distributed, high resolution distributions of emissive materials in an emissive array. The resolution at least equals that of etched deposited emissivematerials and the edges of the phosphor units can be sharper than those providedby etching since undercutting and other etch anomalies are avoided.
In the present invention, emissive materials may be any materials which emit radiation when non-thermally stimulated (non-therrnal stim~ tion excluding the fact that all materials, when sufficiently heated, will emit radiation). In the practice of the present invention preferable emissive materials may be any materials which: 1) absorb electromagnetic radiation and subsequently.emit radiation between 200 nm and I lOO nm (photolllmirlesence) and/or; 2) emit radiation between 200 nm and 1 100 nm when impacted by electrons (cathodoluminescence) and/or; 3) emit radiation between 200 nm and 1100 nm when exposed to an electric field (electrol~ nesce~ce). Emissive materials according to the present invention includes both inorgan c emissive materials (for eY~ple, phosphors) and organic emissive materials (for example, emissive organic polymers) and combinations thereo~ Normally those phosphors are to be provided into the coating compositions used in the practice of the present invention as particulates, particularly with ~yerage particle sizes between 0.3 and SO~rons~lpreferably between 0.5 and 40~ rons~lmore preferably between 0.7 and 35~crons)and most preferably between I and 3(~rons). Amongst the many phosphors known in the art which may be considered in the practice of the present invention are alkali halides, doped alkali halides, rare earth oxy-halides, 3s and others such as are described in U.S. Patent No. 5,302,423 which is included herein by referen~e for its disclosure of phosphors. Other literature disclosingphosphors which are contemplated within the scope of the present invention AMENDED SHEET
IP~/EP

CA 02261109 1999-01-1~

W O 98/03346 PCTrUS97/12368 include U.S. Patent Nos. 4,258,264; 4,261,854; 5,124,564; 4,225,653; 4,387,141;

3,795,814,3,974,389; 4,405,691, and the like.
Another characteristic ofthe-present invention which cli~tingl.i.ches from previous transfer processes where emissive materials might have been 5 contemplated is in the ability of the present process to uniformly transfer emissive particles of larger size and ".~il"~i" consistent size distribution as within the . original size distribution of the particles within the donor element. This is accomplished by emph~i7ing the thermal melt stick form of transfer rather than the ablative transfer effected in U.S. Patents 5,171,650 and 5,156,938. The o ablative form of transfer would not be useful in producing emissive material and especially phosphor screens as the particles are literally broken or blasted into smaller sizes by the ablative process which would not be as controllable or as suitable for emissive panels or screens. It is pl ere~ I ed that the size distribution of particles be m~int~ined in this relatively larger size domain in the creation ofphosphor screens, wherein the phosphors are at least 50 number % greater than 4 micrometers (and more preferably greater than 5 micrometers), more preferably atleast 60 number percent are greater than 4 micrometers (and again more preferably greater than 5 micrometers), and most preferably at least 75 number percent of the phosphor particles are greater than 4 micrometers (and still more20 preferably greater than 5 micrometers). It is pl er~. . ed that the dimensions of the transferred phosphor are less than 150 micrometers in line width and between 0.5and 50 micrometers in height (thickness). It is more plt;r~l,ed that the line width is less than 100 micrometers and the thickness is between 1 and 10 micrometers.
It is most preferred if the line width is between 10 and 90 micrometers and the 2s thickness is between 2 and 5 micrometers.
It is practical in the present invention to produce 'structured' phosphor screens, that is screens with a built-in raster orientation of the phosphor so that stimul~tion of the screen, when used in a storage phosphor mode, can be effectedby an entire surface irradiation rather than by only a point-by-point irradiation by 30 stiml-l~ting radiation. This can be accomplished by transferring the desired pattern of phosphor distribution onto the surface of a carrier element, the pattern usually being columns and rows of closely spaced dots, and then hardening the composition of the invention within the pattern. These patterns are not information patterns, but merely accessihle arrays of phosphors which lend 35 themselves to stimul~tion by the stim-ll~tin~ mech~ni~m of choice, e.g., raster sc~nning along the columns and/or rows.

., CA 02261109 1999-01-15 i ~ . . ~ . . ~ . . .

- EXAMPLE
The materials employed below werc obtained from Aldrich Chemical Co.
(Milwaukee, WI) unless otherwise specified.
Laser transfer was accomplished using a single mode, Nd:YAG laser in a 5 flat field sc~nnillg configuration. Sc~ning was pc. ro....ed with a linear galvanometer and was focused onto the image plane using an f-theta scan lens.
The power on the image plane was 8 watts, the laser spot size (me cured at the l/e2 intensity) was 140 x 150r~ronsJ,The linear laser spot velocity was 4.6 meters/second, measured at the image plane.
lo The glass receptor substrate was held in a rccessed vacuum frame, the donor sheet was placed in contact with the ~ce~llor and was held in place via ,-~ applic~tion of a vacuum. Following exposure, the donor is removet.
s- - .
Phosphor Donor Li~ht-to-~eat Con~ersion La~er A carbon black light-to-heat conv9e8rs6ion layer was prepared by coating the following "LTHC Coating Solution 1" onto ~g8 milJPET substrate with a Yasui Seiki La2b5C~oater, Model CAG- 1 S0 using a microgravure roll with 90 helical cells per lineal~rhJ.
L 7~C Coatin~ Solu~ion 1 ComDonent Pants bY Wei~ht Sunsperse Black LHD-9303 WB4850 (48.6 6. 87 weight % non-volatiles in water, available from Sun Chemicals, Arnelia, OH) NeoratTM NR440 (40% nonvolatiles in water, 58.38 available from Zeneca Resins, ~llmington, MA) DuracureTM 1173 (2-hydroxy-2 methyl-1-phenyl- 1.15 l-propanone photoinitiator, available from Ciba-Gei~, Hawthorne, NY) Water 33.60 ~O~I5J
The coating was in-line drif~3~t~)dO0~C and W-cured atl~20 feet/minute)using a Fusion Systems Model I600~U wattsrtnch~lJV curing system fitted with H-bulbs. The cured coating had an optical density of 1.2 at 1064 nm.

AM~NDFD SHEET
IPEA/E~

. _ . . ..

' , . ; . , , . - ' PhosDhor Donor Interla~vcr Onto the carbon black coating of thc light-to-heat conversion layer was rotogravure coated "Protective Tnterlayer Coating Solution 1" using the Yasui Seiki Lab Coater, Model CAG-150 with a microgravure roll with 150 helical s cells per lineak~nch~ This coating was in-line~d2~d~00~C) and uv-cured' a~
feet/minute)using a Fusion Systems Model I6001~ wattsfinch))uv-curing system fitted with H-bulbs. This LITI donor element was denoted as "I,ITI
Donor Element r~.
Protective Interlayer Cootin~ Solution ' ComDoncnt Parts b~ W~;sht - ~eorad~ 440 45.00 ~uracure~ 1173 0.90 Water 54.10 PhosDhor Donor Transfcr Layer The protective interlayer of LITI Donor Element I was overcoated with "Phosphor Transfer Laye80Coating Solution 1" using a #12 coating rod. The lS coating was then dried fo~rninute~)at 60~C.

PhosDhor Tran~fer kyer Coating Solution I
ComDonent ~arts bv W~isht NP-1056 Y2O3:Eu red phosphor (available from 23.53 Nichia Arnerica Co- I,or~tion, Lancaster, PA) ElvaciteT~ 2776 (acrylic resin, available from ICI 5.89 Acrylics, St. Louis, MO) N,N-dimethyletl-~nol~mine 3 53 Water 67.06 ~2,~ x ~2,~ c~, The phosphor donor was imaged onto afi(5 x 5 inch)l. 1 mm thick glass plate using 20 the laser im~ging conditions des.,- ibed above. Phosphor and binder were transferred success~lly as a film from the donor to the glass receptor to give lines of approximately 90 llm width and 3.3 llm in height, as measured by a profilometer. The phosphor packing appearcd to be uniform and dense. Greater than 95% of the area was covered by phosphor particles by visual inspection at 2s 1000X magnification in an optical microscope. The transferred spots were excited AME.~J~ ! ,S~ ~ t- ~

with a hand held UV source and were observed to phosphoresce under e ~-.,;n~l;on with the naked eye in a darkened room.

Claims (17)

1. A process for selectively patterning an emissive material on a receptor, the process comprising the steps of:
providing a donor element having a substrate, a light-to-heat conversion layer, a thermally transferable layer of emissive material and an interlayer disposed between the light-to-heat conversion layer and the thermally transferable layer of emissive material, the interlayer remaining substantially intact when the donor element is exposed to imaging radiation;
placing the thermally transferable layer of emissive material adjacent the receptor; and selectively irradiating portions of the light-to-heat conversion layer with an imaging radiation having an intensity sufficient to effect thermal transfer of a portion of the emissive material to selected locations of the receptor without substantial transfer of the interlayer.

2. The process of claim 1 wherein said imaging radiation is coherent radiation.

3. The process of claim 2 wherein said emissive material comprises a phosphor.

4. The process of claim 2 wherein said coating of transferred emissive material comprises a continuous coating of binder ant phosphor.

5. The process of claim 4 wherein said receptor comprises glass.

6. The process of claim 4 wherein said receptor layer comprises curved glass.

7. The process of claims 3 or 4 wherein said phosphor on said thermal donor element is in a layer comprising phosphor, antistatic agent and organic polymeric binder.

8. The process of claims 3 or 4 wherein said phosphor on said thermal donor element in a layer comprising phosphor ant organic polymeric binder.

9. The process of claim 2 wherein said coherent radiation has a wavelength between 720 nm and 1100 nm.

10. The process of claims 1 or 2 wherein the emissive material comprises a phosphor which is transferred and the dimensions of the transferred phosphor are less than 150 micrometers in line width and between 0.5 and 10 micrometers in height.

11. The process of claim 1 wherein said receptor is an emissive array selected from the group consisting of field emission devices, plasma display panels, light emitting diodes, electroluminescent elements, and vacuum fluorescent displays.

12. The process of claim 1 wherein an adhesive is present on top of said thermally transferable layer, and transfer of said emissive material also causes transfer of said adhesive material so that said adhesive material is between said emissive material and said receptor.

13. The process of claims 1, 2 or 11 wherein said emissive material is an inorganic material.

14. The process of claims 1, 2 or 11 wherein said emissive material is an organic material.

15. The process of claims 1, 2 or 11 wherein a layer of pigments is present on top of said thermally transferable layer, and transfer of said emissive material also causes transfer of said pigments so that said pigments are between said emissive material and said receptor.

16. A process as recited in claim 1, wherein the emissive material comprises a phosphor.

17. A process as recited in claim 1, wherein the emissive material comprises an electroluminescent material.