Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K4/00—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249986—Void-containing component contains also a solid fiber or solid particle
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249987—With nonvoid component of specified composition
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249987—With nonvoid component of specified composition
  • Y10T428/249991—Synthetic resin or natural rubbers
  • Y10T428/249992—Linear or thermoplastic
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/25—Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles
  • Y10T428/256—Heavy metal or aluminum or compound thereof
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/25—Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles
  • Y10T428/258—Alkali metal or alkaline earth metal or compound thereof
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31511—Of epoxy ether
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31551—Of polyamidoester [polyurethane, polyisocyanate, polycarbamate, etc.]
  • Y10T428/31565—Next to polyester [polyethylene terephthalate, etc.]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31551—Of polyamidoester [polyurethane, polyisocyanate, polycarbamate, etc.]
  • Y10T428/31591—Next to cellulosic

Definitions

• This invention relates to luminescent screens and in particular to luminescent screens which are useful as intensifying screens for radiographs. More specifically, this invention relates to luminescent screens which comprise a layer of finely-divided phosphor particles dispersed in a coating composition which is capable of being heat cured to form a cross-linked polymeric matrix.
• OKFI &? ⁇ 'AT10 it may lack the necessary cohesive strength. Due to the brittle character of some binders, the screen may not possess adequate flexibility and resistance to cracking and crazing. The radiographic speed of the screen may be unduly low due to the adverse effects of the binder, or the binder may not be able to accept sufficiently high loadings of phosphor particles. Because of inadequate durability of the phosphor layer or insufficient resistance to soiling, it may be essential to have a protective overcoat layer and because of the poor flatness characteristics of the screen, it may be essential to have an anti-curl layer. Such additional layers add substantially to the cost of the product and greatly complicate the manufacturing process.
• Improved luminescent screens having a highly desirable combination of properties are disclosed in Lu et al, United States patent 4,188,449. These screens are manufactured by a process comprising the steps of (1) coating a support with a radiation-curable composition comprising a suspension of finely-divided phosphor particles in a liquid coating composition containing a first component that is capable of being radiation-cured to form a cross-linked polymeric matrix surrounding the
• OMPI phosphor particles and a second component that is capable of being evaporated to generate voids within the matrix (2) irradiating the coating to cure the first component and form thereby a cross-linked polymeric matrix surrounding the phosphor particles, and (3) evaporating the second component simultaneously with or subsequently to the irradiating step to thereby generate voids within the matrix.
• screens prepared by this process represent an advance in the art, they suffer from certain significant disadvantages which have limited their usefulness.
• the radiation-cured phosphor layer is not soluble in common solvents, which makes it very difficult to recover phosphor from coating scrap and thereby adds significantly to manufacturing costs.
• luminescent screens are comprised of a support and a layer of finely-divided particles of a phosphor dispersed in a cross-linked void-containing polymeric matrix.
• the phosphor layer is formed by coating the support with a liquid coating composition comprising a suspension of finely-divided phosphor particles in a liquid coating composition that contains a first component treated to form a cross-linked polymeric matrix surrounding the phosphor particles and a second component evaporated to generate voids within the matrix.
• the first component comprises an unsaturated crosslinkable polymer, a polymerizable acrylic monomer, a thermoplastic polyurethane elastomer, and a heat-activatable polymerization initiator.
• the coating is heated for a time and at a temperature sufficient to cure the first component and thereby form the polymeric matrix and evaporate the second component to thereby generate the voids within the matrix.
• Luminescent screens produced by the method described herein are highly resistant to delamination, cracking or crazing in view of the excellent adhesive and cohesive strength of the phosphor layer. They have excellent dimensional stability, are resistant to the effects of temperature and humidity change and resistant to discoloration on aging. They are durable and abrasion resistant to such an extent that a protective overcoat layer is not needed, and they have excellent flatness characteristics which render unnecessary the inclusion of a curl control layer. At the same time, they possess high radiographic speed (the particular speed attained being, of course, dependent in part on the particular phosphor utilized) and are capable of providing excellent contrast and image sharpness.
• the luminescent screens of this invention can be prepared from a wide variety of different materials, with the choice of materials used
• the support for the luminescent screens can be composed of any suitable material.
• the support can be paper, baryta-coated paper, polymer-coating paper such as polyethylene-coated paper, a metal foil such as aluminum foil, or a foil-paper laminate.
• the support can also be a polymeric film such as a film formed from cellulose acetate, cellulose propionate, cellulose acetate propionate, cellulose acetate butyrate, polyethylene, polystryene, poly(vinyl chloride), polymethyl methacrylate, vinyl chlorideacetate copolymer, polypropylene, poly(vinyl acetals) , polycarbonates, polysulfones, polyethersulfones, polyimides, polyamides, or polyesters. Films formed from polyethylene terephthalate are especially useful.
• the thickness of the support will typically be in the range from about 4 to about 15 mils and preferably in the range from about 5 to about 7 mils.
• the phosphors that are useful in forming the luminescent screens of this invention are well known materials. Typical examples of such phosphors include calcium tungstate, barium lead sulfate, zinc cadmium sulfide, lead-activated barium silicate, lead-activated strontium sulfate, gadolinium-activated yttrium oxide, europium-activated barium strontium sulfate, europium-activated barium lead sulfate, europium-activated yttrium vanadate, europium-activated yttrium oxide, europium-activated barium phosphate, terbium-activated gadolinium oxysulfide, terbium-activated lanthanum oxysulfide, magnesium gallate, and the like.
• the phosphor is utilized in finely-divided particulate form.
• a preferred average particle size for the phosphor is in the range from about 1 to 100 microns and most perferably in the range from about 6 to about 18 microns.
• the support is coated with a suspension of the finely-divided phosphor particles in a liquid coating composition, as hereinafter described.
• the coating composition should be of a viscosity suitable to maintain the phosphor particles in suspension and yet permit easy coating at high coating speeds of a layer of uniform thickness.
• Optimum viscosity will, of course, be dependent upon numerous factors such as the particular method of coating and the size and density of the phosphor particles, but will typically be in the range from about 500 to about 30,000 centipoises at room temperature and more usually in the range from about 5,000 to about 15,000 centipoises.
• the phosphor layer can vary in wet thickness from about 2 mils or less up to about 25 mils or more and will most usually be in the range from about 3 to about 12 mils.
• the dry thickness of the phosphor layer will not usually be significantly different than the wet thickness after coating, since the heat-curing step forms the entire binder into a polymeric matrix, and the only component removed from the coating is the void-generating component.
• Coating of the support with the suspension of finely-divided phosphor particles in a liquid coating composition can be carried out in any suitable manner.
• it can be carried out by air-knife coating, roll coating, gravure coating, extrusion coating, bead coating, curtain coating, use of wire wound coating rods, and so forth.
• a first indispensable ingredient of the heat-curable component of the coating composition of this invention is. an unsaturated crosslinkable polymer.
• unsaturated crosslinkable polymer A wide variety of such materials are known and the term "an unsaturated crosslinkable polymer," as used herein, is intended to encompass all such materials, including oligomers as well as high polymers.
• Illustrative classes of polymers which are useful include epoxy diacrylates, unsaturated polyesters, unsaturated acrylics, unsaturated polybutadienes, unsaturated acrylic modified polyurethanes, unsaturated acrylic modified polythioethers, acrylated glycols and polyols, unsaturated acrylic-terminated polybutadienes and polybutadiene/acrylonitriles, and the like.
• useful polymers are in epichlorohydrin/bisphenol-A epoxy that is reacted with acrylic acid or methacrylic acid to form acrylate or methacrylate ester end groups at both ends of the epoxy chain, as well as similar polymers prepared from novolac epoxides (fusible and soluble epoxy resins formed by condensation of a phenol with an aldehyde under acid conditions) .
• novolac epoxides fuusible and soluble epoxy resins formed by condensation of a phenol with an aldehyde under acid conditions
• CM ⁇ I of useful polymers are a bisphenol-A/fumaric acid polyester and a di(hydroxypropyl acrylate-anhydride) modified bi ⁇ phenol-A/epichlorohydrin epoxy.
• Oligomers can be used in the heat-curable composition in place of or in addition to the aforesaid polymers, for example, a polyoxyethylene diacrylate oligomer.
• Particularly preferred heat curable component of the coating composition for the purpose of forming the luminescent screens are compositions comprising an acrylated epoxy resin.
• the acrylated epoxy resins are well known materials, and resins of this type have been described in numberous patents, for example in Unites States patents 3,661,576; 3,673,140; 3,713,864; and 3,772,062 and in British patent 1,375,177.
• Typical resins of this type are those derived from bisphenols.
• the acrylated epoxy resin is a reaction product of epichlorohydrin, bisphenol-A and an acrylic monomer, such reaction product being represented by the formula:
• reaction products are relatively viscous liquids when n is low, e.g., 1 to 3, which become increasingly viscous as the value of n
• O.-V- l increases and are solids when n is high, e.g., 10 to 20.
• a further example of a preferred class of unsaturated crosslinkable polymers useful for the purpose of forming the polymeric matrix of this invention is the class of acrylated urethane resins.
• Materials of this type are described, for example, in United States patents 3,509,234; 3,600,539; 3,694,415; 3,719,638 and 3,775,377 and in British patent 1,321,372.
• the acrylated urethane resins can be used by themselves or in combination with a different class of resins such as the acrylated epoxy resins.
• a second essential ingredient of the heat-curable component of the coating composition of this invention is a polymerizable acrylic monomer.
• These monomers are liquids of relatively low viscosity. In the curing step they are converted, together with the unsaturated crosslinkable polymer, to a solid cross-linked-polymeric matrix. Because they tend to be more reactive than the unsaturated crosslinkable polymers, they function to increase the rate of polymerization and cross-linking.
• Useful acrylic monomers include mono-functional monomers and polyfunctional monomers.
• monofunctional acrylic monomers examples include acrylic and methacrylic esters such as ethyl acrylate, butyl aerylate, 2-hydroxypropyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, and the like.
• polyfunctional acrylic monomers examples include: neopentylglycol diacrylate, pentaerythritol triacrylate, 1,6-hexanedio diacrylate, trimethylolpropane triacrylate, tetraethylene glycol diacrylate, 1,3-butylene glycol diacrylate, trimethylolpropane trimethacrylate, 1,3-butylene glycol dimethacrylate, ethylene glycol dimethacrylate, pentaerythritol tetraacrylate, tetraethylene glycol dimethacrylate, 1,6-hexanedio dimethacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, glycerol diacrylate, glycerol triacrylate, 1,3-propanediol diacrylate, 1,3-propanediol dimethacrylate,
• Preferred polyfunctional acrylic monomers are those of the formula:
• each R is independently selected from the group consisting of a hydrogen atom and an alkyl group of 1 to 2 carbon atoms, each R is independently selected from the group consisting of an alkyl group of 1 to 6 carbon atoms and a radical of the formula:
• R is a hydrogen atom or an alkyl group of 1 to 2 carbon atoms.
• thermoplastic polyurethane elastomer A third essential ingredient of the heat-curable component of the coating composition of this invention is a thermoplastic polyurethane elastomer.
• the thermoplastic polyurethane elastomers are well known materials. They include polyester-based polyurethanes and polyether-based polyurethanes.
• the polyester-based polyurethanes are prepared from a diol, such as 1,4-butanediol or 1,6-hexanediol, a diacid, such as adipic acid, and a diisocyanate, such as toluenediisocyanate or 4,4'-diphenylmethane-diisocyanate.
• the polyether-based polyurethanes are prepared from the polyether, such as a polyether derived from ethylene or propylene oxide, and a diisocyanate. Either aliphatic or aromatic diisocyanates can be used in the preparation of thermoplastic polyurethane elastomers. Details concerning thermoplastic polyurethane elastomers useful as a heat-curable component of the coating compositions of this invention are provided in United States patent 3,743,833, the disclosure of which is incorporated herein by reference.
• thermoplastic polyurethane elastomers are used in small amounts in the coating composition. They function to improve flexibility and toughness of the cured layer and provide sites for solvent extraction in the phosphor recovery process. It is believed that they exist in the cured layer in the form of a "micro random dispersion." Because of their presence, the cured layer is soluble in common inexpensive solvents such as methylene chloride or methyl ethyl ketone. In contrast, the radiation-cured phosphor layers of U.S. patent 4,188,449 are not soluble in such solvents, which makes it very difficult to recover the phosphor from manufacturing scrap by the use of inexpensive and practical recovery techniques.
• a fourth essential ingredient of the heat-curable component of the coating composition of this invention is a heat-activatable polymerization initiator.
• Useful heat-activatable polymerization initiators include azo compounds, peroxides, peracetates, and percarbonates. The azo initiators are preferred since they provide cured layers which are free from such undesirable characteristics as brittleness. Examples of useful azo initiators include:
• the liquid coating composition in which the phosphor particles are suspended contain a void-generating agent, for example a solvent which is readily evaporable.
• a void-generating agent for example a solvent which is readily evaporable.
• This agent must, of course, be a material which is not cured by the heat-curing step and which can be evaporated to generate voids within the polymeric matrix. It must also be a material which does not adversely affect the binder materials, such as by chemically reacting therewith, or which renders the composition incapable of being coated or incapable of adhering to the support. Since the void-generating agent must not enter into the curing reaction to thereby become part of the matrix, it should not be a polymerizable material, for example, it should be free of ethylenic unsaturation.
• the void-generating agent should be relatively volatile in order to facilitate the generation of voids.
• the void-generating agent can, in addition to forming the voids, also serve to solubilize one or more of the components which form the polymeric matrix.
• the void-generating agent can be selected from a wide variety of suitable materials.
• Typical examples of classes of materials which are useful as the void-generating agent in the process of this invention include ketones such as acetone or methyl ethyl ketone, hydrocarbons such as benzene or toluene, ethers such as tetrahydrofuran, alcohols such as methanol or isopropanol, halogenated alkanes such as ethylene dichloride or propylene dichloride, esters such as ethyl acetate or butyl acetate, and the like. Combinations of two or more of these organic solvents can, of course, be utilized as the void-generating if desired.
• ketones such as acetone or methyl ethyl ketone
• hydrocarbons such as benzene or toluene
• ethers such as tetrahydrofuran
• alcohols such as methanol or isopropanol
• halogenated alkanes such as ethylene dichloride or propylene dichlor
• the void generating agent is an organic liquid having a normal boiling point in the range from about 40°C to about 85°C.
• a liquid material as the void-generating agent, there can be used, if desired, a solid which sublimes or decomposes on heating. Such solid materials should be utilized in very finely-divided form. Examples of solid materials which will sublime and thereby bring about the desired generation of voids include camphor, solid carbon dioxide, pyrogallol, salicylic acid, resorcinal, phenol, and the like.
• solid materials which will undergo heat decomposition and thereby bring about the desired generation of the voids include p-hydroxybenzoic acid, trihydroxybenzoic acid, sodium bicarbonate, azobisisobutyronitrile, benzene sulfonyl hydrazide,
• voids is intended to refer to microscopic-sized gas bubbles or pores.
• a component capable of being evaporated to generate voids it is, as indicated above, intended to include within the term “evaporated” the processes of sublimation or decomposition of a solid void-generating agent.
• the essential components of the coating composition are, in addition to the phosphor, the component that is heat-curable to form the solid cross-linked polymeric matrix and a void-generating agent. Other ingredients can optionally be included.
• the coating composition can contain viscosity regulating agents such as silica and surfactants which facilitate the formation of the phosphor dispersion such as fluorocarbons, silicones, alkyl aryl polyether sulfates, phosphate esters, and the like.
• viscosity regulating agents such as silica and surfactants which facilitate the formation of the phosphor dispersion
• fluorocarbons such as silicones, alkyl aryl polyether sulfates, phosphate esters, and the like.
• a preferred coating composition for use in forming the luminescent screens of this invention is a dispersion of a phosphor in a liquid medium composed of an acrylic ester, an acrylated epoxy resin, a thermoplastic polyurethane elastomer, an azo initiator, and a ketone.
• a particularly preferred coating composition is a dispersion of a phosphor in a liquid medium composed of butyl acrylate, an acrylated epoxy resin of the formula given hereinabove in which n is in the range of 10 to 15, a thermoplastic polyurethane elastomer, 2,2'-azobis(isobutyronitrile) and methyl ethyl ketone.
• Curing of the coated layer is carried out by heating for a time and at a temperature sufficient to cure the heat-curable component, to thereby form a cross-linked polymeric matrix surrounding the phosphor particles, and to evaporate the evaporable component, to thereby generate voids within the matrix.
• the specific curing conditions utilized should take into account the particular coating composition employed and the web thickness of the coated layer. Typical curing conditions involve heating at a temperature in the range of from about 50°C to about 150°C for a time in the range of from about 5 to about 30 minutes, preferably at a temperature in the range of from about 70°C to about 120°C for a time in the range of from about 10 to about 15 minutes.
• heating of the web coated layer first initiates polymerization and/or cross-linking at the surface with the result that there is a tendency for a crust to form.
• the polymerization and/or cross-linking proceeds deeper into the coated layer until eventually all of the binder is formed into a polymeric matrix. While the generation of the matrix is taking place, the void-generating agent gradually evaporates to form bubbles.
• the crust and the high viscosity of the coating composition inhibit escape, collapse or coalescence of the bubbles, but the gas diffuses to the surface where it passes into the atmosphere. This eventually results in the generation of voids with essentially no residual void-generating agent remaining in the phosphor layer.
• the percentage of voids is easily controlled to a desired level by the use of smaller or greater amounts of the void-generating agent in the coating composition.
• the amount of void-generating agent employed can be varied widely. Typically, the percentage by weight of void-generating agent based on the total weight of the coating composition will be in the range from about 2 to about 35% and preferably in the range from about 5 to about 15%/
• the phosphor layer be of relatively slight thickness, as a thick layer tends to result in lower radiographic speed and poorer image sharpness. At the same time it is desirable to provide a large quantity of phosphor per unit area of support in order to provide high radiographic speed. To meet these requirements it is necessary to provide a high ratio of phosphor to polymeric binder. Ratios of phosphor to binder of at least about 5 to 1 and more preferably at least about 10 to 1 on a weight basis are desirable. Phosphor coverage in the screen can vary widely, as"desired, and is typically in the range from about 10 to about
• the proportion ' s in which the unsaturated cross-linkable polymer, the polymerizable acrylic monomer, the thermoplastic polyurethane elastomer and the heat-activatable polymerization initiator are used can be varied as desired. Good results are usually obtained with coating compositions in which the unsaturated cross-linkable polymer makes up about 7 to about 15 percent of the total weight of the coating composition.
• the polymerizable acrylic monomer is advantageously employed in an amount of from about 0.1 to about 1.5 parts per part by weight of the unsaturated cross-linkable polymer.
• the thermoplastic polyurethane elastomer is used in small amounts, typically an amount of from about 0.05 to about 0.2 parts per part by weight of the unsaturated cross-linkable polymer. Amounts of the heat-activatable polymerization initiator in the range of from about 0.02 to about 0.1 parts per part by weight of the unsaturated cross-linkable polymer ordinarily provide satisfactory results.
• the luminescent screens of this invention comprise a phosphor layer with a percentage of void volume of about 1 percent to about 20 percent, by volume, more preferably from about 5 to about 15 percent, and most preferably about 10 percent.
• the luminescent screens are especially useful as intensifying screens for radiographs.
• the phosphor layer of the screen is held in contact with an image-forming layer of a separate photographic element, or in integral combination in a composite photographic element and intensifying screen combination comprised of a support, the phosphor layer, and an image-forming layer.
• the image-forming layer will be a gelatino/silver halide emulsion layer.
• the radiographic speed of the luminescent screen is increased by using a reflective support rather than a transparent support.
• a transparent support it transmits some luminescence, generated from the excited phosphor during the exposure to X-ray radiation, to the side opposite the photographic film where it produces no exposure of the photographic film and thereby lowers the radiographic speed.
• the luminescence is re-directed toward the photograhic film to increase its exposure.
• a reflective support for example, baryta-coated paper or bright silver coated polyester film, such as a film with a 300 mg/ft coating of electrolytically deposited silver
• the luminescence is re-directed toward the photograhic film to increase its exposure.
• reference to void content refers to measurement of the percentage voids by volume in the phosphor layer measured in the following manner:
• Void volume is determined by subtracting the volume of the support, phosphor and binder, as determined using the known density and weight fraction of each, from the total volume of the screen. Percentage voids is calculated from the value obtained for void volume.
• radiographic speed refers to speed measurement made in the following manner:
• a film-screen combination which serves as a standard of comparison is formed by sandwiching a section of high contrast blue-sensitive silver bromide silver iodide medical X-ray film (Kodak X-Omatic G Film 4510) between a pair of europium-activated barium strantium phosphor screens (Kodak X-Omatic screens).
• a second film-screen combination is prepared by sandwiching a section of the same film between a pair of screens, each of which has been prepared by the method of the present invention. Each combination is exposed to X-ray radiation at the same dose and dose rate and then the exposed film is processed at standard conditions and the neutral density is determined.
• the X-OMATIC screen is assigned a radiographic speed (SR) of 103.
• SR radiographic speed
• a coating composition was prepared from the following ingredients:
• the acrylated epoxy resin was a condensation product of epichlorohydrin and bisphenol-A (molar ratio of 1.6:1) reacted with a methacrylic acid to form ester end groups and is represented by the formula:
• n has a value of about 13.
• thermoplastic polyurethane elastomer was
• the coating composition was coated as a layer with a wet thickness of 12 mils on a poly(ethylene terephthalate) film having a thickness
• the phosphor layer was dried overnight at room temperature and then cured by heating at 80°C for 10 minutes.
• the void content of the phosphor layer was 19.5%, the phosphor coverage was 58 gm/ft , and the radiographic speed was 118.
• a second sample was prepared in which the coating composition was coated as a layer with a wet thickness of 10.4 mills, dried overnigh -at room temperature, and then cured by heating at 80°C for 10 minutes.
• the void content of the phosphor layer was
• the phosphor layer was found to dissolve readily in common solvents such as methylene chloride and methyl ethyl ketone, thereby making it an easy matter to recover the phosphor from coating scrap.
• a coating composition was prepared from the following ingredient :
• the coating composition was coated as a layer with a wet thickness of 4.7 mils on a poly(ethylene terephthalate) film having a thickness of 7 mils, and the phosphor layer was cured by heating at 88°C for 15 minutes.
• the void content of the phosphor layer was 2.3%
• the phosphor coverage was 25 gm/ft
• the radiographic speed was 98.
• Three additional samples were prepared in which the coating composition was coated at greater thicknesses and cured under the same conditions. Results obtained were as follows: Phosphor coverage Void Content Radiographic ( « /ft2j a. Speed
• the phosphor layer was found to dissolve readily in common solvents such as methylene chloride and methyl ethyl ketone.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Conversion Of X-Rays Into Visible Images (AREA)
• Luminescent Compositions (AREA)
• Paints Or Removers (AREA)

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• 1980
  • 1980-03-31 US US06/136,144 patent/US4298650A/en not_active Expired - Lifetime
• 1981
  • 1981-03-26 JP JP56501482A patent/JPH0143920B2/ja not_active Expired
  • 1981-03-26 DE DE813141806T patent/DE3141806A1/de not_active Withdrawn
  • 1981-03-26 WO PCT/US1981/000386 patent/WO1981002866A1/en not_active Ceased
  • 1981-03-30 FR FR8106266A patent/FR2479253A1/fr active Granted
  • 1981-03-31 BE BE0/204325A patent/BE888211A/fr not_active IP Right Cessation

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