Method For Making An Image Screen Structure For An Apertured-mask Cathode-ray Tube Using A Mask Having Temporary Apertures

Abstract

Each of the final-sized apertures of an apertured-mask for a cathode-ray tube is closed with a film of an organic material. The central portion of the film closing each final-sized aperture is then opened so as to provide a temporary aperture smaller than the final-sized aperture. An image-screen structure is then photodeposited using the mask with the smaller temporary apertures as a photographic master. After the screen structure is deposited, the organic material is removed to restore the permanent mask with the larger final-sized apertures therein for use in the cathode-ray tube.

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of patent application Ser. No. 872,978, now abandoned, filed Oct. 31, 1969 by H. B. Law and assigned to the same assignee as this application.

Description

BACKGROUND OF THE INVENTION

This invention relates to a novel method for preparing an image screen structure for an apertured-mask cathode-ray tube, and particularly to a method wherein the mask apertures are temporarily reduced in size and then used to photodeposit elements of the image screen.

In one prior method of temporarily reducing the size of mask apertures, disclosed in U. S. Pat. No. 3,231,380 to H. B. Law, a nonferrous metal is deposited on the aperture walls by electroplating. In another prior method disclosed in U. S. Pat. No. 3,070,441 to J. W. Schwartz, an inorganic material is deposited on the aperture walls by cataphoretic coating. Both methods are undesirable because of problems encountered during the subsequent removal of the deposited material. In addition, these methods are not practical for salvage and reuse of the apertured-mask.

SUMMARY OF THE INVENTION

The novel method for making an image screen structure for an apertured-mask cathode-ray tube includes completely closing each aperture of the mask with a film of organic material. The central portions of the films are removed while a desired thickness of the films is retained adjacent the aperture walls so as to provide smaller temporary apertures. The image-screen structure is then produced by photodeposition using the mask with the smaller temporary apertures as a photographic master. After the screen elements are deposited, the organic material is removed to restore the mask with the larger final-sized apertures for use in the cathode-ray tube.

The film that closes each aperture may be produced by filling the apertures with the organic material as by spin-coating, dip-coating, or other suitable coating technique; or by applying a preformed or cast film to one surface of the mask. The central region of the film may be opened for example, by softening and breaking, melting and breaking, burning, selectively rendering soluble by exposure and dissolving, solvent dissolving, liquid honing or powder blasting to provide smaller temporary apertures. The organic material applied to the apertured-mask is easily removed by baking at about 400.degree.C during subsequent tube processing or by dissolving.

The novel method permits temporarily closing the apertures of a formed aperture mask in an economical manner. The material closing the apertures is easily removed by present manufacturing processes. In addition, a permanent aperture mask is used to make the temporary mask. Therefore, if a temporary mask is damaged, or if a screen structure is improperly made the mask can be salvaged and reused.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, partly in axial section, of an apertured-mask color kinescope including an image screen prepared with the use of a temporary mask made by the present invention, which temporary mask is produced from the permanent mask of the kinescope.

FIG. 2 is a fragmentary transverse sectional view of an apertured-mask after closing the final-sized apertures of the mask by simultaneously coating both major surfaces of the mask with an organic material.

FIG. 3 is a fragmentary transverse sectional view of FIG. 2 after the step of opening the central portions of the aperture closures.

FIG. 4 is a fragmentary plan view of the mask shown in FIG. 3.

FIG. 5 is a fragmentary perspective view of the mask shown in FIGS. 3 and 4 in position for use as a photographic master in preparing an image screen for a color kinescope.

FIGS. 6 and 8 are fragmentary transverse sectional views of an apertured-mask after closing the mask apertures by sequentially coating the major surfaces of the mask and then after opening the central portions of the aperture closures.

FIGS. 7 and 9 are fragmentary transverse sectional views of an apertured-mask after closing the mask apertures by applying a cast film to only one major surface of the mask and then after opening the central portions of the aperture closures.

FIGS. 10 and 11 are fragmentary transverse sectional views of an apertured-mask after closing the mask apertures by coating one major surface of the mask to include the aperture walls and then after opening the central portions of the aperture closures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a color kinescope 10 produced by the novel method which kinescope includes a glass envelope 12 comprising a funnel portion 14 and a cap 16, which cap 16 includes a transparent faceplate 18. A plurality of elemental phosphor areas 20, which collectively comprise two or more groups of different phosphors and which are individually capable of emitting luminescence of a particular color (e.g., red, blue, or green) when struck by an electron beam 21, are deposited on the internal surface 22 of the transparent faceplate 18. The faceplate 18 (or other transparent substrate), the elemental phosphor areas 20 and, optionally, a light absorbing matrix 23 (discussed below) are collectively referred to herein as an image screen structure 24. Generally, the image screen structure 24 also includes a light-reflective conductive layer (not shown) of aluminum as is well known, which covers the image screen and serves as an electrode.

The elemental phosphor areas 20, are, for illustration purposes, exaggerated in size and proportion (as are other parts of FIG. 1 and the other FIGURES) and shown as having a dot configuration, which dots may be arranged in the well-known hexagonal dot pattern (not shown). Alternatively, each phosphor areas may have a stripe configuration (not shown), these stripes being arranged in an alternating array of different color phosphors to provide a line screen. An apertured shadow mask used with the line screen differs only in that the apertures are slot shaped instead of round. The kinescope 10 further includes a number of electron guns and either electrostatic or magnetic deflection and convergence means, none of which are shown for simplicity.

In generally parallel, spaced relation with the image screen structure 24 is a color-selection mask 30 (or mask electrode) which may be, for example, of the focusing or non-focusing variety, both of which are known in the art. The mask 30 (focusing or non-focusing variety) is produced by methods known in the art and is usually curved and contains final-sized apertures 34. A suitable frame 32 or other means can be used by support the shadow mask 30. Unless stated otherwise, for purposes of illustration, the mask 30 is understood to be of the non-focusing mask variety, which is operated at substantially the same potential as the image screen structure 24 to form a field-free region therebetween. The mask 30 is made from a sheet or band of conducting material (e.g., cold-rolled steel) and has a plurality of apertures 34 of desired final size therein. The apertures preferably have a double frustoconical shape, both cones 57a and 57b having their narrowest dimension located between the major surfaces 60 and 62 of the mask so as to form a knife edge 56a as shown in FIG. 2. While the apertures 34 are, for simplicity, shown in FIG. 1 to be substantially circular in shape, apertures having other shapes may be used. For example, the mask may be of the "grill" type (not shown), having slot-shaped apertures.

Color television picture tubes or color kinescopes may be described by the relative size of the elemental phosphor area excited by the electron beam. A tube where the electron-beam spot size, as defined by its associated aperture, is smaller than the phosphor dot it excites is described as a tube having a positive tolerance. In a positive-tolerance tube, the phosphor dots are sufficiently larger than each electron-beam spot to ensure that the entire beam strikes each dot, even with a limited amount of misregister. A positive-tolerance tube may be of the matrix or nonmatrix type. Where the tube is of the positive-tolerance-matrix type, the size of the elemental phosphor area excited by the electron beam is smaller than the size of the opening in the matrix.

A matrix-type structure in which the size of the electron spot as defined by its associate aperture is the same or larger than the associated opening in the matrix is described as a tube having a negative tolerance. In a negative-tolerance matrix tube the excited portions of the elemental phosphor areas (dots) are defined by the openings in the matrix, and the electron-beam spot is usually sufficiently larger than the matrix opening to ensure that the entire matrix opening is excited, even with a limited amount of misregister.

In FIG. 1, the final-sized apertures 34 are related in size and position to respective phosphor areas 20 of the image screen structure 24. The size relationship is such that, where the mask 30 is of the non-focusing variety, each final-size aperture 34 is of such dimension as to be capable of passing an electron beam 21 whose dimensions, as measured at the screen structure 24, (i.e., the spot size of the beam) are at least substantially equal to, or preferably larger than, the dimensions of the individual phosphor areas 20 upon which the electron beam impinges. The electron beam spot size is preferably sufficiently large to provide a negative tolerance but not so great that the electron beam impinges any phosphor areas other than the intended phosphor areas. In general, with a prior art mask having bifunctional apertures of a given size the size of the light spots produced during screen printing substantially exceeds that of the electron beam spots produced in the operation of the kinescope. This results in the size of the individual phosphor areas being considerably greater than the spot size of their associated electron beam so that the beam impinges only a portion of each phosphor area. Such differences in size between the printing light spots and the electron beam dots are familiar to the art, the difference therebetween being attributable to the more extensive penumbra-umbra effect taking place in the screen printing process. In the present invention, therefore, the final-size apertures 34 of the mask 30 (considered to be a non-focusing mask) should be of such size that the electron beam spot is at least equal in size to and preferably larger than, the respective phosphor areas. Generally, it is preferred that the final-size apertures 34 exceed in size their associated phosphor areas 20.

In the non-focusing variety color kinescope, the image screen structure and mask are maintained at the same potential; therefore the beam striking the image screen structure is substantially the same size as the size of the aperture. In a focusing-type apertured-mask tube, the image screen structure and the mask are maintained at different potentials, so that the beam is focused by the electric field between the image screen structure and the mask, and the beam striking the image screen structure is smaller than the size of the aperture. The non-focusing type and the focusing type tube may be of the positive- or negative-tolerance type. In the focusing-type matrix and nonmatrix-type tubes, if the apertures are of a size which permits the focused beam to excite a portion of the elemental phosphor area smaller than the size of the opening in the matrix, the tube has a positive tolerance. If the aperture of a matrix-type tube is of a size such that the focused beam is equal or larger than the size of the opening in the matrix, the tube has a negative tolerance.

The final-size apertures of a focusing-type mask are significantly greater in size than their respective individual phosphor areas whether the color tube is of the positive tolerance type (i.e., the beam spot is smaller than a corresponding phosphor area) or the negative tolerance type. In most color kinescopes in the prior art, there is a single aperture in the apertured-mask for each trio of phosphor dots (i.e., one dot each of red, green and blue phosphors). However, for purposes of simplicity, each aperture 34 is shown to correspond in position with only one phosphor area 20.

In the operation of the kinescope 10, electrons are emitted by the electron guns (not shown) and thereafter directed, by means known in the art, as an electron beam 21 through the apertures 34 to impinge upon the phosphor areas 20. Because a larger electron beam spot is produced and impinges upon an entire individual phosphor area, the kinescope 10 exhibits improved characteristics, such as increased image brightness and contrast, over prior art kinescopes.

Im making an image screen structure 24 for an apertured-mask color kinescope shown in FIG. 1, a coating of an organic material is provided on a mask 30 having final-sized apertures. The coating is comprised of a portion forming a film which completely closes each final-sized aperture. The film closing each final-sized aperture may be produced by the methods of Examples 1 through 6 described below. The film may be produced by controllably applying material to both major surfaces of the mask as shown in FIGS. 2 and 6, or to only one major surface of the mask as shown in FIGS. 7 and 10. FIG. 2 illustrates simultaneous coating of both major surfaces of an apertured mask 30, while FIG. 6 illustrates sequential coating of both major surfaces of an apertured mask 30. FIG. 7 illustrates the film extending over and completely closing the mask apertures at one major surface, while FIG. 10 illustrates the coating disposed on the aperture walls and the film completely closing the mask apertures at the narrowest dimension.

In one embodiment shown in FIGS. 2 and 3 of the present invention, a color kinescope 10 as shown in FIG. 1 is manufactured by steps including the production of a temporary mask 70 (partially shown in FIG. 3) for screen printing. The first step in making the temporary mask 70 (partially shown in FIG. 3) is the provision of a coating 50 of an organic film-forming material on a completed mask 52 (similar to 30 of FIG. 1) to make a coated mask 40.

The coating 50 (shown in FIG. 2) is comprised of films 54 which extend across and substantially close the final-sized apertures 53 (similar to 34 of FIG. 1), and, preferably, are disposed at the aperture walls 56. The coating 50 of the organic film-forming material is further comprised of areas 58 which are integral with the films 54 and are disposed at the major surfaces 60 and 62 of the mask 52.

The films 54 are of a substantially concavo-concave shape and have relatively thin central regions 64 and relatively thick peripheral regions 66. Such a concavo-concave shape is attributable to surface tension forces acting on the fluid organic material during coating of the mask 52. The coating is then dried and the central regions 64 of the films 54 (shown in FIG. 2) are opened to provide smaller temporary apertures 74 as shown in FIG. 3.

In another embodiment shown in FIGS. 6 and 8, a color kinescope 10 shown in FIG. 1 wherein the electron beam spot size is at least as great as, and, preferably, greater than, the individual phosphor areas comprising the image screen, is manufactured with the use of a temporary mask 120 shown in FIG. 8. The temporary mask 120 is prepared by providing a first coating 104 and a second coating 112 to a mask 52 having final-size apertures 53 to obtain the coated mask 102 shown in FIG. 6. Those numerals in FIGS. 6 and 8 which are identical to those of FIGS. 2 and 3 indicate corresponding elements. The first coating 104 is comprised of first films 106 which are disposed at and completely close the final-size apertures 53 of the mask 52 shown in FIG. 6. These first films 106 are partially disposed on the walls 56 of the apertures 53. The first films 106 have relatively thin central regions 117 and relatively thick peripheral regions 122. The target mask 52 is also provided with a second coating 112 comprised of second films 114 which overlie and are substantially coextensive with the first films 106 these second films 114 are also being partially disposed on the aperture walls 56. The second films 114 also have relatively thin central regions 124 and relatively thick peripheral regions 126. The coatings 104 and 112 are of different materials, the second coating 112 consisting of a positive-type photosensitive resist, such as Shipley resist marketed by Shipley Co., Newton, Mass., and the first coating 104 consisting of an ultraviolet light-absorbing composition, such as polyvinyl alcohol with a carbon pigment. Both coatings 104 and 112 may optionally have respective areas 116 and 118 thereof disposed at respective major surfaces 60 and 62 of the mask 52. The double coating on the mask 52 can be made by sequentially applying each coating 104 and 112 from a different side thereof. The thin central regions 124 of the second films 114 of the second coating 112 are opened and the entire first coating 104 is removed to provide smaller temporary apertures 115 as shown in FIG. 8.

Where it is desired, a temporary mask may be produced from a mash 52 having a coating applied to only a single surface such as second coating 112 shown in FIG. 6 (as contrasted to a coating 50 shown in FIG. 2, applied to both surfaces) of a mask, the coating being disposed on parts of the aperture walls. the apertures and to open the central regions 134 of these films 132 such

In a further embodiment shown in FIGS. 7 and 9 a color kinescope 10 shown in FIG. 1 can be produced with a temporary mask 128 shown in FIG. 9. A temporary mask is produced by applying at one major surface 62 of a mask 52 a cast film 130 of a suitable organic material to form a coated mask 127 as shown in FIG. 7. The cast film 130 is comprised of opaque films 132 disposed at and extending above the final-sized apertures 53, these films 132 preferably having a concavo-concave shape. The cast film 130 is heated to cause the film to melt and conform to a portion of the walls of the such that opaque bands 133 as shown in FIG. 9 are formed at the periphery of the final-sized apertures 53 which partially close the apertures and define smaller temporary apertures 135. The organic film-forming material is subsequently removed to restore the mask to its original condition, after which, the mask is incorporated into a kinescope.

FIG. 10 illustrates an apertured-mask 52 with the organic material controllably applied on one major surface 62 to provide a coating on the walls 56 of the final-sized apertures 53 and a thin film 140 completely closing each of the final-sized apertures 53. The thin film 140 includes relatively thin central regions 142 and relatively thick peripheral regions 143. During coating, the material initially fills the apertures without passing through to coat the opposite major surface 60 of the mask 52. FIG. 11 illustrates the coated mask 138 of FIG. 10 with the central regions 142 of the thin film 140 opened to provide a smaller temporary aperture 144.

Methods for Closing the Apertures

Example 1: Position a mask 52 having a plurality of final-sized apertures 53 therein so as to permit rotation about an axis perpendicular to the mask 52. A liquid organic material coating 136 is then applied on the surface of the mask 52. The preferred method of applying the coating 136 is to contact one major surface 62 of the mask 52 against a tank of liquid while rotating and tilting the mask 52. Other alternative methods include spraying, flowing, or pouring the liquid over one major surface 62 of the mask 52. After the coating 136 is applied, the mask 52 may be rotated to spread the material and remove excess material from the final-sized apertures 53. The coating 136 is then dried to a nonviscous or semisolid condition, producing a film 140 completely closing each of the apertures as shown in FIG. 10. The coating 136 may be dried prior to or during the process of opening the films 140, which is described below.

The preferred formulation of liquid organic material is a polyvinyl alcohol solution containing about 3.3 percent solids. Alternative formulations which may also be used substitute either gelatin or fish glue for the polyvinyl alcohol in similar proportions. Cellulose acetate dissolved in acetone with 1 to 8 percent content, vinyl acetate dissolved in acetone with 1 to 8 percent solids content, and methyl methacrylate dissolved in toluene with 1 to 8 percent solids content may also be used.

Example 2: Apply a preformed thermoplastic solid film in sheet form over one surface of the mask 52 as shown in FIG. 7. The solid film is then heated to substantially conform the solid film to one major surface of the mask 52. During the heating, the central region of the film closing each of the apertures melts to form a thin film. The thin film may extend over the apertures 53 at one major surface 62 as shown by the coating 130 in FIG. 7 or conform to the large frustum shape of a double frusto-conical shaped aperture completely closing each aperture 53 at the knife edge formed by the intersection of the two cones as shown by the second coating 112 in FIG. 6.

The preferred material of the solid film is polyvinyl acetate. Other materials such as lacquer, wax, gelatin, fish glue, cellulose acetates, polyvinyl acetate and methyl methacrylate may also be used.

Example 3: Prepare an organic film by flotation casting and then apply the film to a mask 52 by contacting one major surface of the mask 52 against the film. The mask 52 and flotation film as then heated to dry the film and produce a thin film closing each of the apertures substantially as shown by first coating 104 or second coating 112 in FIG. 6. The film substantially conforms to one major surface of the mask 52 including a portion of the walls 56 of each final-sized aperture 53. The preferred materials of the liquid flotation film are methyl methacrylate or cellulose nitrate.

Example 4: Dip or immerse a mask 52 in an organic material to obtain a coating over all the surfaces of the mask 52, and closing, but not filling, each of the final-sized apertures 53.

Such immersion can be done with the use of simple tanks (not shown) containing the fluid organic material, batch-type or continuous processes being employable for coating the mask 52. Then the organic coating is dried, as by air drying, or controllably dried, as with a moisture chamber or oven to form films 54 completely closing the final-sized apertures 53 as shown in FIG. 2.

A temporary mask can also be produced by controlled immersion of the mask in an organic film-forming material or by other controlled application of the organic film-forming material to the mask. Such a mask having a coating on a single surface thereof would be comparable to the mask 52 of FIG. 6 with only second coating 112 thereon. The preferred materials are the same as described in Examples 1 and 3.

Example 5: Prepare a positive-type photosensitive, film-forming resist (i.e., one whose solubility is increased by exposure to suitable radiation), such as, for example, a Shipley resist, marketed by Shipley Co., Newton, Mass., to produce a coated mask 40 similar to that shown in FIG. 2 or a coated mask 138 similar to that shown in FIG. 10. Apply the resist coating by either of the methods described in Examples 1 or 4. The apertures of the mask 52 are completely closed by the coating 50. The coating 50 is dried to provide films 54 which completely close the final-sized apertures 53 and are opaque as shown in FIG. 2.

Example 6: Apply a coating to a mask 52 as in Example 1 to about line 6--6, which coincides with the narrowest dimension of the apertures 53 of the respective film-forming materials. Thus, in the application of the first coating 104 the film-forming material is substantially restricted by surface tension forces to the parts of the aperture walls located between the major surface 60 and line 6--6. Continuing the example, the first coating 104 is then dired to produce thin films 106. The second coating 112 is then applied as in Example 1, to the opposite major surface 62 of the target mask 52 and dried to produce thin films 114. Each of the films 114 and 106 preferably have at least one concave surface (e.g., the film configuration is substantially plane-concave), relatively thin central regions 117 and 124 respectively and relatively thick peripheral regions 122 and 126 respectfully. It is preferred that the second coating 112 is a photosensitive resist material such as Shipley resist, marketed by Shipley Co., Newton, Mass., and the first coating 104 is an ultraviolet light-absorbing material such as polyvinyl alcohol with a carbon pigment.

The films produced by the methods described in anyone of the Examples 1 through 6 are then opened as described in Examples A through H to provide smaller temporary apertures.

Methods for Opening the Film

Example A: Subject the coated mask produced by either of Examples 2 and 3 to a heat lamp or uniform temperature to soften the coating material. The heat is applied at a slow rate to decrease the surface tension of the material causing the films to break and the material to pull back towards the walls of the apertures forming smaller temporary apertures 115 and 135 as shown in FIGS. 8 and 9. It is believed that the amount of opening obtained is a function of film thickness, surface tension and viscosity of the material composition, and amount of heat applied.

Example B: Open the central regions of the films produced by either of Examples 2 and 3 by exposing the coated mask to a controlled flash of radiant energy emitted from a Xenon flash lamp 68 located at the vicinity of the center of curvature of the mask 52 or closer to the mask. As used herein with respect to the films, the terms "open" or "remove" means the total elimination of the central regions of the films so that no obstruction remains and smaller temporary apertures are produced. The level of energy of the flash is adjusted so as to melt and rupture the thinner central regions of the films, thereby producing a temporary mask 70 (FIG. 3) 120 (FIG. 8) or 128 (FIG. 9) having, at the walls of the various apertures 53, bands of organic film-forming material comprising at least part of the peripheral regions of the films. These bands define temporary apertures 115 (FIG. 8) and 135 (FIG. 9) which are substantially smaller in size than the mask apertures 53 so as to provide in screen printing, phosphor dots (e.g., 20 of FIG. 1) of desired dimension on the target screen.

The important feature is that high heat is applied by radiation for a very short time so that the shadowed part of the films are not heated. The melted central regions then rupture, forming a ring of material on the walls 56 of the final-sized apertures 53 producing smaller temporary apertures 115 and 135 as shown in FIGS. 8 and 9. It is preferred that this process by used with Examples 2 and 3 which have one coating on one major surface of the mask. Where the apertures are of double frusto-conical shape, it is preferred that the coating is on the screen side or major surface 62 of the mask 52.

For a mask with a final-size aperture 53 of about 16 mils diameter, a temporary aperture of about 12 mils diameter will respectively provide an electron beam spot size of about 17.8 mils diameter and a phosphor dot of about 14 mils diameter. The bands are supported by the walls 56 of the apertures 53, thereby being strengthened and having comparatively high resistance to breaking and other injury. Generally, the thickness of the film portions can be controlled by adjusting the viscosity of the compositions used to apply the film-forming materials, the more viscous compositions generally providing thicker film portions.

Example C. Follow the method described in Example B except that the lamp 68 is positioned about 6 to 7 inches from the coated mask and operated with high energy such as 1350 joules. The central region of each of the films produced by any of the methods described in Examples 1 through 4 is then opened by burning or vaporization producing smaller temporary apertures 74, 115, 135 and 144 respectfully as shown in FIGS. 3, 8, 9 and 11. Such removal is achieved by a more rapid heating of the organic film-forming material at the thinner central regions by the radiant energy than at the thicker peripheral regions, the former having a lower heat capacity. The radiant energy causes the central regions to be vaporized or burned off. The thickness distribution of the films are comparable so that their respective central regions can be eliminated substantially uniformly, thereby providing smaller temporary apertures of substantially uniform size and shape.

Example D: The coated mask 102 prepared by the method of Example 6 (shown in FIG. 6) is exposed to ultraviolet light for a sufficient time to permit removal of the central regions 124 of the films 114 to produce smaller temporary apertures 115 as shown in FIG. 8. The films 114 (consisting of positive-type photoresist) are exposed to ultraviolet radiation from a lamp 68 which is first passed through the ultraviolet light-absorbing films 106. The light-absorbing films 106 act as a light filter, more ultraviolet light being transmitted through the thinner central regions 117 thereof than through the thicker peripheral regions 122 As a result of this higher transmission, the central regions 124 of the films 114 are rendered completely soluble before much of the peripheral regions 126 thereof. The central regions 124 of the films 114 are then removed by "developing" in a manner known in the art (e.g., washing with developing compositions such as Shipley developer marketed by Shipley Co., Newton, Mass.) to produce opaque bands at the walls 56 of the final-size apertures 53, which bands define smaller temporary apertures 115 used in screen printing. The first coating 104 is completely removed after the exposure of the central regions 124. In the preferred method the first coating 104 is also removed by the Shipley developer. The remaining bands are eliminated after completion of the screen printing operation shown in FIG. 5 either by baking, or chemical dissolution (in suitable solvents known in the art) such elimination preferably being carried out in conjunction with the removal of resist material from the printed screen.

Example E: The closed apertures in the coated mask 40 produced by anyone of the methods of Examples 1, 3 and 4 are opened by liquid honing. In liquid honing a coated mask is immersed in a tank and a liquid containing silica particles of approximately 40 to 100 microns in size is flowed over the coated mask. The particles cut away parts of the coating. Since the central regions of the films are relatively thin, these parts are removed first to produce smaller temporary apertures 74, 115, and 144 as shown in FIGS. 3, 8, and 11 respectfully.

Example F: The closed apertures in the coated mask produced by anyone of the methods of Examples 1, 3, 4 and 5 may be opened by dissolving the central regions of the films. The central regions of the various dry film portions can be removed with a slow-acting solvent that uniformly dissolves material from the coating. Where the material is an acrylic or a polyvinyl alcohol, toluene and alcohol are respectively suitable as solvents. Non-Active diluents can be added to the solvents to adjust the dissolution rate of the coating. While dissolution takes place at most, if not all, of the exposed surfaces of the coating, considerable amounts of the peripheral regions remain after the central regions are removed because of the differences in thickness therebetween. There then result the bands such as 72 shown in FIG. 3 of the organic film-forming material located at the walls 56 of the final-size apertures 53.

For the polyvinyl alcohol of Example 1, a preferred solvent is a solution of 95 percent denatured alcohol and 5 percent 2-propanol. One method of dissolving is to immerse the coated mask 40 for about 10 seconds in the solvent, remove from the solvent and then remove excess solvent on the mask by an air blast. An ethylene glycol solution may also be used as a solvent. The undissolved peripheral region 66 describes a temporary aperture 74 smaller than the final-sized aperture 53 as shown in FIG. 3. The edge of the opening in the films 54 contains a small bead formed by surface tension forces after dissolution of the central region 64 on the softened but not dissolved peripheral region 66.

Example G: The closed apertures in the coated mask produced by any one of the methods of Examples 1, 3 and 4 may be opened by a dry-powder blast. The powder blast removes the central region of the films by attrition leaving a peripheral region describing a temporary aperture 74, 115 and 144 smaller than the final-sized apertures 53 as shown in FIGS. 3, 8, and 11 respectfully. In a preferred method small particles of silica approximately 40 to 100 microns in size are air blasted over the coated mask. Since the central regions are very thin they are removed producing smaller temporary apertures.

Example H: Expose the coated mask 40 produced by Example 5 to suitable radiation (e.g., ultraviolet light) from a lamp 68 located in the vicinity of the center of curvature of the mask, such that the films 54 (shown in FIG. 2) are rendered soluble in developing compositions known in the art and the central regions 64 develop out. Some of the peripheral regions 66 of the films 54 (shown in FIG. 2) may be incidentally exposed to the radiation and rendered soluble to a certain depth but because these peripheral regions are considerably thicker than the central regions 64, a portion of the peripheral regions 66 will remain on the mask 52 after the central regions 64 are removed. The soluble central regions 64 are then removed to produce smaller temporary apertures 74.

Method for Removing The Coating

The organic film forming material is eliminable from the mask preferably by air baking (combustion or decomposition and/or vaporization or volatilization) thereof (either or both of these preferably being achievable at or below the maximum processing temperatures generally employed in color kinescope manufacturing, for example, at or below 500.degree.C.) and/or dissolution in agents (preferably, but not necessarily limited to, water) which are not detrimental to the mask, and leave substantially no residue. A suitable temperature for such combustion (decomposition) or evaporation (volatilization) is about 400.degree. to 450.degree.C. This temperature is employed in known kinescope manufacturing processes, for removing resist deposits (not shown) which are employed in image screen production from the image screen 24 (FIG. 1).

If it is so desired, the film-forming material may be eliminated from the mask separately from those operations involving the removal of resist deposits from the image screen. Such elimination of the film-forming material can be done before or after the removal of the screen resist materials and can be done by the abovementioned methods such as, for example, by baking or dissolution.

General Considerations

It is preferred that the organic material be "film forming." A "film-forming" material is defined to be one which, when applied in a fluid condition, to a mask is capable of wetting the mask so as to provide films at individual ones of the apertures closing the apertures. The film may be in a wet, dry or plastic condition dependent on the organic material selected, the method of producing the film and the method of opening the film. The film portion is preferably of a concavo-concave shape, as shown in FIG. 2, or a plano-concave configuration, but it can be of other (e.g., concavo-convex configuration). In general materials which are film-forming and exhibit relatively high surface tension properties facilitate the production of such concavo-concave film portions.

Several organic compositions, as previously described, are suitable film-forming materials for practicing this invention, including those which are strong absorbers of printing-light (e.g., ultraviolet) and, particularly, those which are plastic- and thermoplastic-type materials. Specific examples of these organic compositions are: cellulose, vinyl copolymers, and acrylic copolymers; polyvinyl alcohols; gelatin; and fish glue. The organic compositions can be provided in the fluid state by dissolving in a suitable evaporable solvent (e.g., toluene or alcohol for acrylic materials), or by heating the organic compositions.

It is preferred that the coating at the walls of the apertures forming the smaller temporary apertures be substantially opaque during the depositing of the viewing screen. Film-forming materials may be used which are naturally substantially opaque or which may be provided with opaquing materials known in the art. Alternatively, the film-forming materials can be such as to provide non-opaque film portions, the central regions of which film portions are removed as discussed below, and the other regions of these film portions subsequently converted to an opaque conduction by coating these other regions with an opaque material, such as carbon.

A preferred method of opaquing is to spray the coated mask with about 1 percent carbon dispersed in acetone after the films are opened. A pigment of about 1 percent carbon dispersed in the polyvinyl alcohol water film-forming material composition may also be used. There also can be added to these compositions a water-soluble dye such as for example Uvinul, marketed by General Aniline and Film which is strongly ultraviolet light absorbing. As used with respect to the film-forming coatings herein, the term "opaque" is defined to include both coatings which are impervious to radiant energy and coatings which scatter or diffuse radiant energy so as to redirect the radiant energy from its original path, thereby substantially limiting the radiant energy performing the screen printing to that passing through the temporary apertures in the films.

The temporary mask 70, 120, 128 or l46 produced by any one of the Examples A through H is then positioned in spaced relation with a suitable transparent substrate 80 such as faceplate 18 (FIG. 1) and used as a photographic master to "print" the various elemental phosphor areas 82, 84, and 86 of the respective phosphor groups (red, blue, and green) on the substrate 80 as shown in FIG. 5. The printing process is known in the art (see, for example, U.S. Pat. No. 3,406,068 to H. B. Law). Briefly, one surface 88 of the transparent substrate 80 is coated with a mixture (not shown) comprising a first one of the desired phosphors and a suitable photo-sensitive material and then exposed to a suitable light which is passed through the smaller temporary apertures of the temporary mask. Those portions of the phosphor coating (not shown) struck by the light rays are hardened, the unhardened portions of the coating being removed, by washing, for example, to leave a pattern (not shown) of phosphors of a first color mixed with the hardened resist material. This sequence of steps is repeated for the other phosphors. The hardened resist material is subsequently removed from the phosphor dots by baking or by chemical dissolution methods known in the art. An electron gun (not shown) intended for a particular phosphor group is located at each point 90, 92, or 94 so as to be in substantially the same spatial relation with the image screen structure (e.g., 24 of FIG. 1) as the light source (not shown) used for printing that particular phosphor group. The paths followed by the light rays during printing and by the electrons during operation of the kinescope are indicated, for purposes of illustration, by the lines 96, 98, and 100.

The screen printing operation may include providing, with the use of any of the temporary masks disclosed herein, a light-absorbing matrix (e.g., 23 of FIG. 1) of an opaque, non-light-reflective material to the image screen structure (e.g., 24 of FIG. 1). For purposes of this invention, such a matrix provided to an image screen structure is considered to be included in the term "image screen structure." Color television picture tubes which may include a light-absorbing matrix on the inner surface of the faceplate forming a part of the screen structure are described in U.S. Pat. Nos. 2,842,697 to E. J. Bingley and U.S. Pat. No. 3,146,368 to J. P. Fiore et al. This can be done, for example, by coating a surface of the bare transparent substrate 80 (e.g., 18) with a relatively translucent mixture (not shown) comprised of a material which has a relatively low light absorption and is convertible to a condition which is more light-absorbing (e.g., manganese oxalate or manganese carbonate, which can be converted from a comparatively translucent condition to an opaque, non-light-reflective condition by heating in a manner known in the art) and a "positive-type" photosensitive resist (i.e., one which is soluble where exposed to light and remains insoluble elsewhere) and then exposing the coating to suitable light passed through the smaller temporary apertures of the temporary mask. Then, the unhardened portions of the coating are washed away and the relatively low light-absorbing material of the remaining portions of the coating is converted to its light-absorbing condition. The phosphor areas (e.g., 82, 84, and 86 of FIG. 5) are then printed at openings in the matrix, as described above. The phosphor areas may, if desired, be somewhat larger than the openings of the matrix so that portions of the respective phosphor areas are disposed on the matrix itself. The "effective size" of such phosphor areas is, therefore, equal to the size of their respective matrix opening. As used with respect to the phosphor areas of a matrix-bearing image screen, the term "size" is defined to be the effective size thereof. Where it is desired, the phosphor areas may be printed before the conversion of the material to its light-absorbing condition. Alternatively, the phosphor areas may be printed before the provision of the matrix, the preliminary mask being used for producing both of these. Where it is desired, a light-absorbing matrix can, with a temporary mask, be provided to a transparent substrate, with the subsequent phosphor printing being done by applying a phosphor-photoresist mixture to the substrate surface on which the matrix is located and, then, exposing the mixture to light from a source located on the side of the substrate opposite the surface thereof bearing the matrix. The light passes through and is defined by the matrix openings.

Upon completion of the printing of the image screen, the organic film-forming material is eliminated (by baking or chemical dissolution) to provide a target mask 52 (similar to 30 of FIG. 1). Such elimination of the bands can be done by processing the temporary mask in conjunction with the previously mentioned removal of the resist material from the phosphor screen. In this way, existing equipment can be used for restoring the target mask to its original condition with no increase in the number of processing steps being required to remove the bands. The target mask 52 is then incorporated into a kinescope in the manner shown in FIG. 1.

The production of color kinescopes according to the method disclosed herein results in a number of advantages. Among them is the producibility of kinescopes having relatively large negative tolerances, this with presently available commercial apparatus. Also, the present method does not require costly equipment for the application of the organic materials and does allow the combination of the operation for the removal of the film-forming material with that of the removal of resist deposits from the screen, thereby avoiding both additional processing steps and the need for costly film-removing equipment. Furthermore, the present method allows the manufacture of kinescopes having target masks of non-planar contour by means of known mask-making processes, without the subjection of the material for temporarily reducing the aperture size to the mask-annealing steps involved in such processes. Still further, the bands of film-forming material which serve to reduce the aperture size of the target masks can be physically supported by the walls of the apertures, thereby imparting strength to the bands and minimizing breakage of such bands.

Claims

I claim:

1. In the manufacture of a cathode-ray tube including an apertured-mask and an image-screen structure, said mask having therein a plurality of final-sized apertures, the method of making said image-screen structure for said tube comprising the steps of:

a. completely closing each of said final-sized apertures of said mask with a film of organic material,

b. opening the central portion of said film that closes each final-sized aperture so as to provide a temporary aperture that is smaller than said final-sized aperture,

c. producing an image screen structure for said tube using said smaller temporary apertures of said mask as a photographic master,

d. and then removing said organic material to restore the mask with the larger final-sized apertures for use in the cathode-ray tube.

2. The method defined in claim 1 wherein said closing step (a) comprises

i. coating at least one surface of said mask and substantially filling each of said final-sized apertures with a slurry comprised of said organic material and a vehicle therefor,

ii. rotating said mask about an axis perpendicular to the surface of the center of the mask to spread said slurry over said mask surface and to remove excess slurry from said surface and said permanent apertures,

iii. and then drying said coated mask to form a thin film completely closing each of said final-sized apertures.

3. The method defined in claim 1 wherein said closing step (a) comprises

i. preparing a preformed solid film of said material,

ii. applying said preformed solid film to at least the apertured portion of one surface of said mask,

iii. and heating said preformed solid film to adhere said preformed solid film to said mask surface thereby producing a film completely closing each of said apertures.

4. The method defined in claim 1 wherein said closing step (a) comprises

i. casting a film of said organic material by flotation on the surface of a liquid, the area of said cast film being adequate to cover at least the apertured portion of said mask,

ii. applying said cast film to at least the apertured portion of one surface of said mask,

iii. and heating said mask and film to adhere said film to said mask and a portion of said aperture wall, thereby producing a thin film closing each of said apertures.

5. The method defined in claim 1 wherein said closing step (a) comprises

i. immersing said mask in a slurry comprised of said organic material and a vehicle therefor to form a coating on a surface of said mask, said material of said coating substantially filling and completely closing each of said apertures,

ii. and drying said coating to form a film closing each of said apertures.

6. The method defined in claim 1 wherein said organic material is a positive-type photosensitive material, and said closing step (a) comprises coating said photosensitive material on a surface of said mask, so that a film of said photosensitive material substantially closes each of said apertures.

7. The method defined in claim 2 wherein said step (i) comprises

a. coating a first surface of said mask with a slurry comprised of a photosensitive material

b. coating a second surface of said mask with a slurry comprised of an ultraviolet light-absorbing material.

8. The method defined in claim 1 wherein said organic material is selected from the group consisting of acrylic polymers, polyvinyl alcohols, cellulose acetate polymers, vinyl polymers, colloids, waxes and lacquers.

9. The method defined in claim 1 wherein said opening step (b) comprises

i. slowly heating said maks and said films closing said apertures to soften said films and to cause each of said films to rupture,

ii. and continuing to heat said mask to permit said ruptured material to pull back toward the walls of said final-sized apertures thereby producing said smaller temporary apertures.

10. The method defined in claim 1 wherein said opening step (b) comprises

directing a flash of radiant energy to said films closing the final-sized apertures of said mask, said energy being sufficient

i. to melt and rupture a central region of each of said films, and

ii. to cause said melted and ruptured film to form a ring of material at the walls of each final-sized aperture thereby producing smaller temporary apertures.

11. The method defined in claim 6 wherein said opening step (b) comprises

i. exposing portions of said film closing each of said final-sized apertures to radiant energy to completely solublize only said central portions and incompletely solublize the peripheral portions

ii. and completely dissolving away said soluble central portions of said photosensitive material closing each final-sized aperture thereby forming said smaller temporary aperture.

12. The method defined in claim 7 wherein said opening step (b) comprises

i. exposing portions of said photosensitive material coating through portions of said ultraviolet light-absorbing material to radiant energy to completely solubilize only said central portions and incompletely solubilize the peripheral portions of said photosensitive material

ii. completely dissolving away said soluble central portions of said photosensitive material closing each final-sized aperture thereby forming said smaller temporary aperture

iii. and completely dissolving away said ultra-violet light-absorbing material.

13. The method defined in claim 1 wherein said opening step (b) comprises

completely dissolving the central portions of said film closing each permanent aperture thereby forming smaller temporary apertures.

14. The method defined in claim 1 wherein said opening step (b) comprises

liquid honing the film closing each final-sized aperture to completely remove the central portion therefrom to form a smaller temporary aperture.

15. The method defined in claim 1 wherein said opening step (b) comprises

removing only the central portion of said film closing each final-sized aperture by powder blasting said film, thereby forming said smaller temporary aperture.

16. The method defined in claim 1 wherein said opening step (b) comprises

directing a flash of radiant energy to said films closing the final-sized apertures of said mask, said energy being sufficient

i. to burn and vaporize a central region of each of said films

ii. to cause a peripheral region of each of said burned and vaporized films to form a ring of material at the walls of each final-sized aperture thereby producing smaller temporary apertures.

17. The method defined in claim 1 wherein said removing step (d) comprises heating said mask to an elevated temperature sufficient to volatilize and decompose said organic material but insufficient to cause damage to said mask.

18. The method defined in claim 1 wherein said removing step (d) comprises dissolving said organic material.