MXPA97004927A - Method to produce a luminesce screen - Google Patents

Abstract

The present invention is directed to produce a luminescent screen, used in a cathode ray tube (CRT), suitable for monochromatic or chromatic images, such as, those used in televisions, computers or data inspection equipment, which require these CRT . The method of the present invention produces a removable layer of the luminescent screen, which has a smooth surface with reduced surface distortions, such as bands or corrugations, which are typically produced by conventional coating processes. When an aluminum reflective film is deposited on a smooth removable layer, this aluminum reflective film is also provided with a smooth surface, since it typically conforms to the underlying smooth surface of the removable layer. As a result, CRT images that have reduced distortions are produced. The method of the present invention also provides an increase in the brightness of the CRT images, which results from using polymers with low ash production in the removable layer, and the binder from a luminophore layer of the luminescent screen. The method of the present invention further provides the combination of the volatilization step of the removable layer and the binder, in the luminophore layer with the step of cementing the face plate of the CRT with the cone of this CRT, without rsely affecting the quality of the airtight seal between the face plate and the co

Description

METHOD TO PRODUCE A LUMINESCENT SCREEN The present invention relates, generally, to the production of a metallized luminescent screen of a cathode ray tube (CRT) and, more particularly, to a metallized luminescent layer which produces an image with increased brightness and reduced distortion. The luminescent screen of a color cathode ray tube (CRT) includes a luminophore layer placed on a face plate of a CRT. The luminophore layer means a layer that produces electroluminescent light when subjected to cathode rays. Such a layer typically includes an array or ordered pattern of a number of phosphoric substance deposits. In the most conventional case, which characterizes three colors, the phosphoric substances are deposited in the form of points or strips arranged to define triads through the internal surface of a plate of each of the CRT; each triad includes a phosphoric substance that emits red light, in the form of a point or a strip, a phosphoric substance that emits blue light, in the form of a point or a strip, and a phosphoric substance that emits green light, in the shape of a point or a strip. The process of producing the luminophore layer is known in the art, such as, for example, the process taught in the U.S. Patent No. 3,269,838. To produce an orderly arrangement, a coating of an aqueous paste containing phosphoric particles of a desired color and a binder, such as an aqueous dispersion of an acrylic polymer, is applied to the inner surface of the glass face plate of the CRT. . Such a layer is then conventionally coated with a photosensitizer, which is well known in the art, and then exposed through a photo-mask to the actinic light. The unprotected photo-protective coating is then removed by a conventional developer solution and the underlying uncoated phosphor layer is etched by immersion in a conventional etchant solution. The process is repeated to deposit particles of the phosphoric substances of each color, in the form of a point or strip, to produce the ordered arrangement, which is then typically dried by subjecting it to radiant heat. A thin reflective film of metallic aluminum is then deposited on the exposed surface of the luminophore layer. This film, typically of the order of 1000 to 5000 Angstroms, is sufficiently thin to allow a modulated pattern of an electron beam (cathode ray), produced by an electron gun placed at the other end of the CRT, to pass through the film without dispersing or losing beam intensity. The pattern of the electron beam, after passing through the aluminum film, makes an impact with the luminophore layer to produce electroluminescent light, which appears to the observer as an image. The reflective aluminum film acts as a mirror that prevents the light emitted backwards, produced from the luminophore layer, being lost inside the CRT and reflecting the light out to the observer, after passing through the face plate CRT glass. As a result, the image quality and brightness are significantly improved. The exposed surface of the luminophore layer tends to be irregular for a variety of reasons, including variations in the particle size of the phosphoric material used to produce the luminophore layer. Thus, if the metallic aluminum reflective film is to be deposited by the well-known technique of vaporizing an aluminum pellet, the resulting aluminum film will have a highly irregular surface, since it will tend to conform to the surface contour of the layer luminophores The irregularities in the aluminum film destroy the desired property of specular reflection of the pattern of the electron beam passing through it. These irregularities are highly inconvenient. Likewise, there is a distinct possibility that the aluminum film, while being deposited, will penetrate into the interstices of the luminophore layer and will deposit inconveniently in and around the phosphoric particles. In order to avoid these difficulties, the technique generally applies on the luminophore layer, a layer, which can be removed or removed, from an organic polymer material, which then presents a smooth exposed surface on which the aluminum metal film it can be received. The removable or removable material is an organic material that can be easily volatilized when subjected to heating, such as by baking at about 380 to 450 ° C. Such a removable layer allows the metallic aluminum film deposited there to be smooth. As a result, the distortion in the image resulting therefrom is reduced and the penetration of the aluminum deposit within the interstices of the phosphoric deposits is substantially impeded. Also, the removable layer can be easily removed by subjecting it to heat, once the metallic aluminum film is deposited on it. Typically, such a removable layer includes one or more layers of an acrylic polymer that forms films, in the form of an aqueous colloidal dispersion or a powder. Such a removable layer can be applied on the luminophore layer by spraying the acrylic polymer in the form of a powder, an aqueous dispersion or preferably by coating the luminophore layer with an aqueous dispersion of the acrylic polymer that forms the film. Such coating methods are known in the art, some of which are described in the patents of U. U.A., Nos. 3,067,055, 3,583,390, 4,954,366 and 4,990,366. Once the removable layer is removed by the volatilization process, the edge of the face plate is coated with a sealer, such as glass frit. A cone of the CRT is then placed over the sealant and the assembly is subjected to a baking step to cement the cone to the face plate of the CRT to achieve an airtight seal between the face plate and the cone. One of the problems associated with the quality of the image produced by the CRT is the presence of distortion in such images. It is known in the art that the presence of irregularities, such as fissures and blisters, in the aluminum reflective film tends to create distortions in the images, which result from using such a luminescent layer. One approach described in U.S. Patent No. 3,579,367 provides a double layer of heat-removable acrylic resins in which a softer inner layer vaporizes at a lower temperature than the outer harder layer when subjected to a step. of baking. Thus, by controlling the vaporization of the organic material under the deposited aluminum film, such vaporized organic materials pass through the aluminum film without breaking or destroying the aluminum film. As a result, a substantially continuous aluminum film is obtained on the phosphor layer. Thus, using a double layer of organic material, which can be removed by heat, on the phosphoric material layer of the luminescent screen, an attempt is made to produce an aluminum reflective film with reduced fissures or blisters. However, there is a need to produce a reflective film of aluminum that is substantially free of distortions, such as waves and surface slats. The method of the present invention solves this problem by providing a removable layer that is substantially free of surface distortions, such as ribbons and surface corrugations, so that when an aluminum reflective film, which conforms to the removable layer, is deposited on such a removable layer, the film is provided with a surface which is substantially free of distortions. The present invention is directed to a method for reducing surface distortions in an aluminum reflective film of a luminescent layer of a CRT, which comprises: coating a luminophore layer, deposited on a face plate of the CRT, with a removable layer of an aqueous dispersion of acrylic polymer particles, having a particle size in the range of 180 to 450 nanometers, to reduce the surface distortions in the removable layer; and depositing the reflective aluminum film on the removable layer, in which the reflective film conforms to the removable layer. Another problem associated with the quality of the image produced by the CRT, is the degree of brilliance of the image achieved. One approach is described in U.S. Patent No. 3,582,390, in which smaller amounts of hydrogen peroxide and a water-soluble polymer in a water-based emulsion with higher amounts of acrylate resins are used to increase the output of light produced by the CRT. However, there is no recognition in the cited technique of the effect on the brightness of the image resulting from the presence of ashes in the polymers used in the binder of the luminophore layer or the removable layer. The inventors have discovered, unexpectedly, that by reducing the ash content in the removable layer and, if desired, in the luminophore layer, the brightness of the image produced by the CRT is increased. Therefore, the present invention is further directed to the volatilization of the removable layer, in which the acrylic polymer particles comprise combustible components to reduce the ash content in the luminescent layer and, if desired, further using a combustible acrylic binder. in the luminophore layer, to produce the luminescent layer that has a reduced ash content. Another aspect of the method of the present invention includes baking a luminescent layer of a CRT, applied along the inner surface of a face plate of this CRT, comprising: applying a sealant along the edge of the face plate of the CRT and then place a cone of the CRT on it; volatilizing the binder in a luminophore layer of the luminescent layer and the removable layer thereof, at a baking temperature below the softening point of the sealant; and raising the baking temperature above the softening point of the sealant, to cement the cone to the face plate, to produce the CRT. As used herein: "Weight average molecular weight by GPC" means the weight average molecular weight, determined by gel permeation chromatography (GPC), which is described on page 4, Chapter I of The Characterization of Polymers, published by Rohm and Haas Company, Philadelphia, Pennsylvania in 1976, which uses polymethyl methacrylate as the standard. The weight average molecular weight per GPC can be estimated by calculating the number average molecular weight of the theory. In systems containing chain transfer agents, the weight average molecular weight of the theory is simply the total weight of the copolymerizable monomer, in grams, divided by the total molar amount of the chain transfer agent used during the polymerization. The estimation of the molecular weight of an emulsion polymer system, which does not contain a chain transfer agent, is more complex. A rough estimate can be obtained by taking the total weight of the polymerizable monomer, in grams, and dividing the amount by the product of the molar amount of an initiator, multiplied by an efficiency factor (in our systems initiated by persulfate, we have used a factor of approximately 0.5). Additional information in the theoretical molecular weight calculations can be found in Principies of Polymer izat io, 2nd edition, by George Odian, published by John ile and Sons, NY, NY, in 1981 and in Emulsion Polymer izat ion, edited by Irja Pirma, published by Academic Press, NY, NY, in 1982. The "glass transition temperature (Tg)" is a narrow range of temperatures, as measured by conventional differential scanning calorimetry (DSC), during which amorphous polymers change from brittle, relatively hard glasses, to viscous, relatively soft rubber. To measure the Tg by this method, the copolymer samples are dried, preheated to 120SC, they are quickly cooled to -1002c and then heated to 1502C, at a speed of 202C / minute, while collecting the data. The Tg was measured at the midpoint of the inflection using the medium height method. Alternatively, the reciprocal of the glass transition temperature of a particular composition of copolymers can typically be estimated, with a high degree of accuracy, by calculating the sum of the respective ratios, obtained by dividing each of the weight fractions of the respective monomers , M ^, M2 ... Mn, from which the copolymer is derived, by the value of Tg for the homopolymer derived from the respective monomer, according to an equation of the form: n 1 / Tg. { copolymer) = T w (r ') / Tg (Mi) (I) done: tg (copolymer) is the estimated glass transition temperature of the copolymer, expressed in degrees Kelvin (SK); w (Mi) is the fraction of the weight of the units repeated in the copolymer derived from a monomer Mi of order i; and Tg (Mi) is the temperature of transition to glass, expressed in degrees Kelvin (2K) of the odor of a monomer Mi of order i. The glass transition temperature of various homopolymers can be found, for example, in Polymer Handbook, edited by J. Brandrup and E. H. Immergut, Interscience Publishers. The "polymer particle size" means the diameter of the polymer particles, measured using a Brookhaven Model Bl-90 Particle Sizer, supplied by Brookhaven Instruments Corporation, Holtsville, New York, employing a quasi light scattering technique. - Elastic, to measure the size of the polymer particles. The intensity of the scattering is a function of particle size. The diameter based on the average of the measured intensity was used. This technique is described in Chapter 3, pages 48-61, entitled Uses and Abuses of Photon Correlation Spectroscopy in Particle Sizing, by einer et al., In the 1987 edition of the American Chemical Society Symposium series. The "ash content" means the amount of ash, expressed as a percentage by weight, based on the total weight of the polymer solids, which remains when the polymer is subjected to volatilization.

The "softening point" means the temperature at which the glass sealant deforms due to the pressure exerted by its own weight. In one aspect of the method of the present invention, the inventors have discovered, unexpectedly, that by controlling the particle size of the polymer dispersed in an aqueous dispersion used in producing the removable layer, a substantially significant improvement in the smoothness of the surface is achieve When a coating of an aqueous dispersion of the polymer particles, having a size in the range of 180 to 450 nanometers, preferably in the range of 180 to 350 nanometers and more preferably in the range of 200 to 320 nanometers, applied to the luminophore layer, surface distortions, such as bands, surface waves, cracks and blisters, on the surface of the resulting removable layer, are substantially reduced. When the aluminum reflective film is deposited by well-known means, such as vacuum metallization or chemical vapor deposition on such a smooth removable layer, the resulting surface of the reflective film, which conforms to the surface of the underlying removable layer , it is also significantly improved. Such a smooth reflective film of aluminum, which has reduced surface distortions in it, produces images that have reduced distortions.

In another aspect of the method of the present invention, the inventors have unexpectedly discovered that using combustible polymer particles in the removable layer or using a combustible acrylic binder in the luminophore layer, the ash content of the resulting, removable and luminophore layers , respectively, are substantially reduced, when these layers are subjected to the volatilization step. As a result, by reducing the ash content of the removable and luminophore layers, the brightness of the image produced by the luminophore layer is increased. It is believed, without verification, that by reducing the ash content in the luminophore layer, the amount of scattering or absorption of the electron beam pattern and the electroluminescent light, by the ashes present in the luminophore and removable layers, is also small proportions. nally. As a result, the brightness of the image produced by the CRT is increased. The inventors have discovered that the combustible particles of the polymer in the removable layer or the combustible acrylic binder in the luminophore layer, can be produced by substantially removing the ash from the polymer components, such as surfactants, regulators, initiators, biocides and monomers used to produce the aqueous dispersion of the polymer particles used in the removable layer or the acrylic binder of the luminophore layer . The combustible particles of the polymer in the removable layer or the acrylic binder in the luminophore layer result from the removal of the metal ions from the polymer components, which contain surfactants or monomers that tend to crosslink. The combustible particles of the polymer in the aqueous dispersions used in producing the removable layer or the combustible acrylic binder used in producing the luminophore layer are preferably homopolymers or copolymers which tend to burn cleanly with a substantially low ash content, when they undergo the volatilization stage. Polymers suitable for use in the present invention generally have a weight average molecular weight in the range of 100,000 to 10,000,000 and are prepared from monomers of the following formula: C - 0 R1 where R is a vinyl group and R1 is a group of linear or branched functionality, having C to C2n / preferably C3 to 201 of chain length. Some such preferred polymers include homopolymers or copolymers of at least one ethylenically unsaturated monomer, such as, for example, methacrylic ester monomers, including ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, methacrylate of 2-ethylhexyl, decyl methacrylate, lauryl methacrylate, isobornyl methacrylate, isodecyl methacrylate, oleyl methacrylate, palmityl methacrylate, stearyl methacrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate; methacrylamide or substituted methacrylamides; styrene or styrene substituted; vinyl acetate; vinyl ester of the "Versatic" acid (a tertiary monocarboxylic acid having a chain length of C9, CIO and Cll, the vinyl ester is also known as "vinyl versatate)"; amino monomers, such as, for example, N, N'-dimethylamino methacrylate; methacrylonitrile. Additionally, monomers of ethylenically unsaturated, copolymerizable acids, in the range of, for example, 0.1 to 10%, by weight, based on the weight of the polymer polymerized in emulsion, acrylic acid, methacrylic acid, crotonic acid, Itaconic acid, fumaric acid, maleic acid, monomethyl itaconate, monomethyl fumarate, monobutyl fumarate, maleic anhydride, 2-acrylamido-2-methyl-l-propanesulfonic acid, sodium vinyl sulfonate and phosphoethyl methacrylate, may be used. Some of the most preferred homopolymers and copolymers include at least one ethylenically unsaturated monomer, such as, for example, methacrylic ester monomers, including ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, methacrylate. of 2-ethylhexyl, decyl methacrylate, lauryl methacrylate, isodecyl methacrylate, oleyl methacrylate, palmityl methacrylate, stearyl methacrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate,; methacrylamide or substituted methacrylamides; show us replaced. Additionally, monomers of ethylenically acidic, copolymerizable acids, in the range of, for example, 0.1 to 5% by weight, based on the weight of the emulsion polymerized polymer, acrylic acid, methacrylic acid, can be used. Some of the most preferred homopolymers or copolymers include at least one ethylenically unsaturated monomer, such as, for example, alpha-methyl styrene and methacrylic ester monomers including ethyl methacrylate, butyl methacrylate, isobutyl methacrylate and propyl methacrylate. Monomers of ethylenically unsaturated acids, further copolymerizable, in the range of, for example, 0.1 to 5% by weight, based on the weight of the emulsion polymerized polymer, methacrylic acid. The aqueous dispersion of the polymer particles of the removable layer or the binder in the luminophore layer of the present invention are produced by the emulsion polymerization. Any process of initiation, thermal or redox can be used. The polymerization process is typically initiated by conventional free-radical fuel initiators, such as, for example, hydrogen peroxide, benzoyl peroxide, t-butyl hydroperoxide, t-butyl peroctoate, ammonium persulfates, typically at one level from 0.05 to 3.0 weight percent, all percentages by weight are based on the weight of the total monomer. Redox systems using the same initiators coupled with a suitable fuel reducer, such as, for example, ammonium bisulfite, sodium hydrosulfite and ascorbic acid, can be used at similar levels. The particle size of the polymer is controlled by the amount of surfactants added during the emulsion polymerization process. As noted before, the inventors discovered that using combustible surfactants, the ash content in the polymer particles or the binder of the resulting removable layer and the luminophore layer, respectively, is reduced. Typical anionic fuel emulsifiers include carboxylic polymers and copolymers of an appropriate hydrophilic-lipophilic balance, alkyl ammonium sulfates, alkyl sulphonic acids, fatty acids, oxyethylated alkylphenol sulfates and their ammonium salts. Ammonium salts are preferred. Lauryl ammonium sulfate is the most preferred, Typical nonionic fuel emulsifiers include alkyl phenol ethoxylates, polyoxyethylenated alkyl alcohols, polyglycol amine condensates, modified polyethoxy adducts, esters of long chain carboxylic acids, ether modified alkylaryl and alkyl polyether alcohols. Typical ranges for surfactants are between 0.1 and 6, preferably between 0.1 and 2, and more preferably 0.6 to 1.5 weight percent, based on the total weight of the monomer. In yet another aspect, the method of the present invention is directed to reducing the number of baking steps used in producing the CRT of a conventional two-stage baking process, to a novel one-stage baking process, in which the volatilization of the binder in the luminophore layer and the removable layer are combined with the step of sealing the face plate of the CRT to the cone of this CRT. A major impediment in combining these two stages is the detrimental effect of the volatilized gases produced during the volatilization of the binder in the luminophore layer and the removable layer in the glass sealant, such as a CRT (glass powder) sealing frit, used in the cementation of the plate facing the cone of the CRT. The glass frits that seal the CRT are well known in the art, such as those provided by Corning Glass Company, Corning, New York. It is believed, without verification, that the volatilization gases tend to chemically attack the sealant, thus adversely affecting the quality of the seal required for proper operation of a typical CRT, which is maintained under a high degree of vacuum. The inventors of the present invention have discovered, unexpectedly, that using combustible polymers in the binder of the luminophore layer or the removable layer, which volatilize substantially at 5 to 80 ° C below the softening point of the sealant, seals are produced of the desired quality by the sealant, when the bake temperature rises to the softening point of the sealant, which generally tends to be in the range of 380 to 6002C. The softening point of the sealant is adjusted according to the type of glass used to produce the face plate or cone of the CRT. The method of the present invention is also suitable for producing monochromatic luminescent screens, such as those used in computer screens or in black and white television sets. The following test procedures were used to evaluate the polymer composition used in the method of the present invention: Ash Content Measurement The ash content of the Examples, described below, was measured by the thermogravimetric analysis performed on TGA-500, Model No. 602-400, manufactured by LECO Corporation, 3000 Lakeview Ave., St. Joseph, MI 49085-2396. Procedure: 1 ± 0.5 g of the samples of the Examples, described below, were placed in crucibles and then heated gradually in a series of stages, from room temperature until the content of the crucible reached 825 C, with intermediate periods, during which the temperature remained stable, to allow that the contents of the crucible will be balanced. The temperature gradually rose from room temperature to 1002C, at a rate of 992C per minute, then to 1502C at a rate of 10 C per minute, then to 4252C at a rate of 102C per minute and finally to 8252C at a rate of 10C. C per minute. A low acceptable ash content means an ash content in the range of 0 to 0.6 percent, preferably 0 to 0.3 percent, all in weight percentages based on the total weight of polymer solids. Surface Distortions of the Removable Layer The measurement of the degree of surface distortions, produced in the removable layer, was made by measuring the degree of gloss obtained in the coating produced by the particles of the polymer of the present invention, in comparison with a comparative polymer currently used. . The gloss of a coating is a measure of the smoothness of the coating surface. A coating with a higher brightness measurement has a smoother surface. Procedure: The particles of the aqueous dispersion polymer, obtained according to the procedure described below, were mixed with 10 weight percent, based on the total weight of polymer solids, of the Texanol® ester-alcohol, which is supplied by Eastman Chemicals Company, of Kingsport, Tennessee. Deionized water (DI) was added to adjust the total percentage of solids in the aqueous dispersion to 36.5 percent total solids. The dispersions were stirred for 20 minutes with a magnetic stirrer and then allowed to stand overnight. Each dispersion was then applied on a black line graph with a film thickness of 254 to 508 microns. The resulting films were dried in an oven at 60 ° C. for one hour. The coated graphs were stored under ambient conditions for 24 hours before measuring the gloss by means of the Gardner Glossgard meter, manufactured by Paul N. Gardner Company, of Pompano Beach, Florida. An acceptable degree of surface smoothness, expressed as brightness, means a brightness of more than 5, when measured at 202, and more than 50 when measured at 602, using the Gardner Glossgard II brightness meter.

Some of the embodiments of the invention will now be described in detail in the following Examples. EXAMPLE 1 A 5-liter, four-necked round bottom flask, equipped with a condenser, stirrer and thermometer, was charged with 950 grams of deionized water and 1.4 g of surfactant (lauryl-ammonium sulfate, @ 27.5% of total solids). The flask was heated to 852C under nitrogen. A monomer emulsion mixture was prepared, described in the following Table 1. Table 1 Twenty grams of the monomer emulsion mixture was added to the flask. The transfer vessel was rinsed with 25 g of deionized water, which was then added to the flask. A solution of 1.2 g of ammonium persulfate, dissolved in 15 g of deionized water, was added to the flask. After 15 minutes, the remaining mixture of the monomer emulsion and 1.2 g of ammonium persulfate dissolved in 50 g of deionized water was gradually added to the flask over 180 minutes. After the addition was complete, the emulsion of the monomer mixture and the catalyst vessels were rinsed with a total of 35 grams of deionized water, which was then added to the flask. After 30 minutes, the flask was allowed to cool. While the flask was cooled, 0.58 grams of a 0.15% iron sulfate heptahydrate (II) solution was added to the flask. A solution of 0.58 grams of sodium hydrosulfite in 15 grams of deionized water and a solution of 0.1 gram of t-butyl hydroperoxide (70% active) in 15 grams of water were added to the flask. The resulting polymer had a particle size of 262 nm and 38.5% total solids. Examples 2-8 The same procedure was used to that used to prepare Example 1 in the preparation of Examples 2-8, using the monomer emulsion mixtures described in the following Table 2: Table 2 The surfactant # 1 is sodium dodecyl-diphenyl-disulfonate (45% solids). The surfactant # 2 is ammonium lauryl sulfonate (27.5% solids). The effect of the particle size of the polymer in the brightness obtained was measured and tabulated in the following Table 3. Table 3 The surfactant # 1 is sodium dodecyl-diphenyl-disulfonate (45% solids). The surfactant # 2 is ammonium lauryl sulfonate (27.5% solids). The data in Table 3 show that as the polymer particle size increases, the brightness of a coating prepared therefrom also improves (higher readings represent higher brightness). This is true regardless of how the brightness is measured, ie at an angle of 60 or 202. When the particle size of the polymer was less than 180 nm (Examples 2 and 4), the brightness of the prepared polymer coating was unacceptably low (less than 5, when measured at 202 and less than 50 when measured at 602), indicating a rough or irregular surface. When the particle size of the polymer was greater than or equal to 180 nm (Examples 3, 6 and 8), the brightness of the coating prepared from such a polymer was found acceptable (more than 5, when measured at 202 and more than 50 when measured at 602). The effect of the surfactant on the ash content was measured by the thermogravimetric analysis described above. The results of the analysis are tabulated below in Table 4: Table 4 The surfactant # 1 is sodium dodecyl diphenyldisulfonate. The surfactant # 2 is the ammonium lauryl sulphonate. The data in Table 4 show that the ash content in the polymer is dependent on the combustion capacity of the additives present in the polymer. For example, by comparing the ash content of Examples 3 and 4, it is seen that this content depends on the type of cation in the surfactant. The polymer prepared with a surfactant having an ammonium cation (surfactant # 2) has a lower ash level than a polymer prepared with a sodium cation (surfactant # 1). Also, by comparing Examples 3 and 5, it is seen that the ash content increases as the level of the surfactant present in the polymer increases. Thus, a greater amount of the surfactant present in Example 5 results in an ash content with unacceptable levels (0.70%). In contrast, minor amounts of the surfactant present in Example 3 resulted in an ash content at acceptable levels (0.48%). The data in Table 5 show the effect of the types of monomers used in preparing the polymers in the removable layer and the binder of the luminophore layer in the amount by weight of the polymers that are thermally decomposed at a given temperature. For example, the amount, in percent by weight of the polymer, which normally decomposes at a given temperature, was significantly higher in Examples 3 and 8 (prepared from a mixture of BMA and MAA monomers) compared to Examples 6. and 7 (preparations of the monomer mixture of EA, MMA and MAA). Thus, for example, at 400 ° C, more than 15 weight percent, based on the total weight of the polymer solids of Examples 3 and 8, are thermally decomposed. For comparison, less than 5 weight percent, based on the total weight of the polymer solids of Examples 6 and 7, are thermally decomposed. The decomposition rate was not significantly increased by the particle size of the polymer, as seen by comparing Examples 3 and 6, which have a larger particle size, against Examples 7 and 8, which have a smaller particle size.

Thus, it is seen that by decreasing the decomposition temperature of the polymers used in the binder in the luminophore layer and the removable layer, these polymers can be volatilized at temperatures below the softening point of the sealant used in cementing the face plate of the CRT at cone of this CRT. As a result, as the bake temperature at which the volatilization step is carried out is decreased, the gases produced during decomposition can be purified before gradually rising to a temperature at which the cementation of the face plate with the cone takes place. Table 5 Table 5 (Continued)

Claims (12)

1. CLAIMS A method to reduce the surface distortion of a reflective aluminum film of a luminescent layer of a cathode ray tube (CRT), this method comprises: coating a luminophore layer, deposited on the face plate of the CRT, with a layer that it can be removed or removed, from an aqueous dispersion of acrylic polymer particles, having a size in the range of from 180 to 450 nanometers, to reduce the surface distortion on said removable layer; and depositing the reflective aluminum film on the removable layer, in which the reflective film conforms to the removable layer.
2. The method of claim 1, further comprising volatilizing the removable layer, wherein the acrylic polymer particles comprise combustible components, to reduce the ash content in the luminescent layer.
3. 3. A method to reduce the ash content of a luminescent layer of a CRT, this method comprises: depositing on the face plate of the CRT a luminophore layer, which includes a combustible acrylic binder; coating the luminophore layer with a removable layer of an aqueous dispersion of combustible acrylic polymer particles; deposit an aluminum reflective film on the removable layer, in which this reflective film conforms to the removable layer; and volatilizing the removable layer and the combustible acrylic binder in the luminophore layer, to produce the luminescent layer having a reduced ash content.
4. 4. A method to produce a luminescent layer of a CRT, which provides an image with reduced distortion, which comprises reducing surface distortions in an aluminum reflective film of a CRT luminescent layer, this step of reducing surface distortions in the aluminum reflective film it comprises: coating a luminophore layer, deposited on the face plate of the CRT, with a removable layer of an aqueous dispersion of acrylic polymer particles, having a particle size in the range of 180 to 450 nanometers , to reduce surface distortions on the removable layer; deposit the reflective aluminum film on the removable layer, in which the reflective film conforms to the removable layer; and volatilizing the removable layer, to produce the luminescent layer having a reflective aluminum film.
5. 5. A method for producing a luminescent layer of a CRT, which provides an image with increased brightness, this method comprises reducing the ash content in the luminescent layer, the step of reducing this ash content in the luminescent layer of the CRT comprises: depositing on a CRT spider plate a luminophore layer, which includes a combustible acrylic binder; coating the luminophore layer with a removable layer of an aqueous dispersion of polymer fuel particles; deposit an aluminum reflective film on the removable layer and volatilize the removable layer and the combustible acrylic binder of the luminophore layer, to produce the luminescent layer having a reduced ash content.
6. 6. The method of claim 5, further comprising reducing the surface distortions in the aluminum reflective film of the luminescent layer, to reduce distortions in the image, this step of reducing the surface distortions in the aluminum reflective film comprises controlling the particle size of the acrylic polymer within the range of 180 to 450 nanometers.
7. 7. The method of claim 3, 4 or 5, further comprising: applying, prior to the volatilization step, a sealant along the edge of the face plate and then placing a cone of the CRT thereon; conducting the volatilization stage at a baking temperature below the softening point of the sealant; and raising the baking temperature above the softening point of the sealant, to cement the cone to the face plate.
8. 8. A method to produce a CRT that has an improved image quality, this method comprises: reducing the ash content in a luminescent layer of the CRT, to increase the brightness of an image produced by the CRT and reduce the surface distortions in a reflective aluminum film of the luminescent layer, to reduce distortions in the image produced by the CRT; the step of reducing the ash content in the luminescent layer of the CRT comprises: depositing on a face plate of the CRT a luminophore layer, comprising an arrangement of particles of a phosphoric substance and a combustible acrylic binder; coating the luminophore layer with a removable layer of an aqueous dispersion of polymer fuel particles, in which the binder of the luminophore layer and the particles of the removable layer are colloidally stabilized with lauryl ammonium sulfate; and the step of reducing the surfdistortions in the aluminum reflective film comprises controlling the particle size of the acrylic polymer, within the range of from 180 to 450 nanometers.
9. The method of claim 8, further comprising: drying the phosphoric substance layer, which has the removable layer coated thereon; depositing the reflective aluminum film on the exposed surfof the removable layer, in which the reflective aluminum film conforms to the exposed surfof the removable layer having reduced surfdistortions; apply a sealant along the edge of the fplate and then pla cone of the CRT on it; volatilizing the binder in the luminophore layer and the removable layer at a baking temperature below the softening point of the sealant, to produce a luminescent layer having a reduced ash content and having an aluminum reflective film with reduced surfdistortions; and raising the baking temperature above the softening point of the sealant, to cement the cone to the fplate and produce the CRT having an improved image quality.
10. 10. A cathode ray tube, produced according to the method of claims 1, 3, 4, 5 or 8.
11. 11. A method for baking a luminescent layer of a cathode ray tube, applied along the surfinternal of a fplate of the CRT, this method comprises: applying a sealant along the edge of the fplate of the CRT and then placing a cone of the CRT of said CRT thereon; volatilizing a binder in a luminophore layer of the luminescent layer and a removable layer of the luminescent layer, at a bake temperature below the softening point of the sealant; and raising the baking temperature above the softening point of the sealant, to cement the cone to the fplate and produce the CRT.
12. 12. A cathode ray tube, produced according to the method of claim 11. SUMMARY OF THE INVENTION The present invention is directed to producing a luminescent screen, used in a cathode ray tube (CRT), suitable for monochromatic or chromatic images, such as those used in televisions, computers or inspection equipment. data, which these CRTs require. The method of the present invention produces a removable layer of the luminescent screen, which has a smooth surfwith reduced surfdistortions, such as bands or corrugations, which are typically produced by conventional coating processes. When an aluminum reflective film is deposited on a smooth removable layer, this reflective aluminum film is also provided with a smooth surf since it typically conforms to the underlying smooth surfof the removable layer. As a result, CRT images that have reduced distortions are produced. The method of the present invention also provides an increase in the brightness of the CRT images, which results from using polymers with low ash production in the removable layer, and the binder from a luminophore layer of the luminescent screen. The method of the present invention further provides the combination of the volatilization step of the removable layer and the binder, in the luminophore layer with the step of cementing the fplate of the CRT with the cone of this CRT, without adversely affecting the quality of the hermetic seal between the fplate and the cone.