Method for photodepositing smaller size image screen areas for cathode ray tube from larger size mask apertures

[57] ABSTRACT

A method for producing a color kinescope having an image screen and a color selection mask having final-size apertures that are temporarily reduced in size for use as a photographic master in producing the image screen. The method includes providing a substrate having apertures of final size; providing at one surface of the substrate a perforated layer of electroless deposition-initiating material, portions of the layer partially extending across the apertures; electrolessly depositing a suitable material at these portions of the layer to produce opaque light-barriers that define respective light-transmitting Corridors; providing the image screen by photographic exposure through the corridors; removal of the light-barriers to restore the apertures to their original condition and provide the final mask; and incorporation of the mask and image screen into a kinescope.

Claims, 8 Drawing Figures

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PATENTED may 91972

3,661,581

SHEET 1 OF 2

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INVENTOR _DV Nathan, Feldstein

BY &gt;/ ✓

ATTORNEY

PATENTEDMAY 91972

3,661,581

SHEET 2 OF 2

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<img file="US3661581A_D0004.tif" />

INVENTOR.

Nathan Feldstein

<img file="US3661581A_D0005.tif" />

ATTORNEY

3,661,581

METHOD FOR PHOTODEPOSITING SMALLER SIZE IMAGE SCREEN AREAS FOR CATHODE RAY TUBE FROM LARGER SIZE MASK APERTURES

BACKGROUND OF THE INVENTION

The present invention relates to color kinescopes and particularly to a novel method for making a masked-type color kinescope wherein the image screen is produced with the use of the color selection mask having its apertures temporarily reduced in size.

The prior art discloses color kinescopes having both an image screen, which includes a multiplicity of groups of closely spaced elemental phosphor deposits, the elemental deposits of each of such groups emitting light of a different color when struck by an electron beam, and a color selection mask disposed between the image screen and the electron source of the kinescope. Such masks (including focusing and non-focusing masks) and their mode of operation are well known. Such color selection masks may be of a planar or non-planar contour, the contour of a particular mask generally being similar to that of the image screen with which it is used. The apertures of the masks can be circular or of some other cross-sectional configuration (e.g., slot-shaped).

Generally, commercial screen printing procedures involve using a color selection mask having apertures of a desired final size as a master for photographically printing the phosphor areas thereof. This mask, with the size of its apertures unchanged, is then used as such in a color kinescope for color selection. Those same size apertures used for both the screen printing function and for the color selection function, are usually referred to as “bifunctional apertures”. However, the apertures of many masks used in prior art color kinescopes are of such size and/or the electrode operating voltages of such mask kinescopes are of such magnitudes that an electron beam usually impinges only a respective part of each one of its associated phosphor areas.

To increase the image brightness of a color kinescope, the prior art discloses color selection masks having apertures which are individually larger than the respective phosphor areas of the image screens associated therewith. Such larger (in comparison with the phosphor areas) apertures provide kinescopes exhibiting “negative leaving tolerance” (which is defined herein to be where the electron beam spots, as measured at the screen, are of greater size than respective individual phosphor areas of the screen) so that a larger proportion of each phosphor area is impinged than in previous kinescopes. However, because of optical considerations (i.e., penumbra-umbra effect) known in the art, the increase in electron beam spot size with the use of masks with larger apertures is normally accompanied by an even larger increase in the size of the phosphor areas printed with such masks; that is, the size of the light spot produced by the printing-light beams which pass through the mask apertures is greater than the size of the electron beam spot produced by the electron beams passing through these apertures. Therefore, color selection masks with such larger apertures are not satisfactory for screen printing because they generally lead to oversize (and, therefore, overlapping) phosphor areas and associated problems with color purity and white uniformity.

One method disclosed in the prior art for printing phosphor areas smaller than the bifunctional apertures of an associated non-focusing mask involves selecting the size of the light source used in screen printing so that, because of penumbra effects, a proper size phosphor area can be obtained by controlling the exposure time. This method is not commercially attractive because the obtainable difference in size between the apertures and the phosphor areas is limited so that comparatively large differences therebetween (and, therefore, relatively large negative tolerances) are difficult, if not impossible, to achieve. The phosphor dot size is a function of exposure time so that the process requires very carefully measured exposure times to obtain properly-sized phosphor dots. This method is very sensitive to non-uniformities in the amounts of light striking various parts of the screen being printed so that the light distribution must be very carefully regulated to minimize size variations among the printed phosphor dots.

In focusing-type kinescopes where the completed focusing mask is used for printing the phosphor dots, the electron beam spot size would be considerably smaller than that of the phosphor dots because of the focusing action on the beam and because of the aforementioned optical considerations. To obtain higher image brightness in such focusing-type kinescopes, the focusing masks usually have final-size apertures which are considerably larger than the individual phosphor areas associated therewith, so that larger electron beam spots can be obtained. However, such focusing masks are not satisfactory for printing the phosphor areas of the image screen, as previously explained, because the larger final-size apertures would provide corresponding larger (and overlapping) phosphor dots. In order to allow the use of such a focusing mask, first, as a photographic master for screen printing, and, then, as a focusing mask exhibiting increased electron transmissivity, the prior art has sought ways to provide, and use for screen printing, a preliminary mask having temporary apertures of a first size, and thereafter convert the preliminary mask to a focusing mask having significantly larger final-size apertures, this with the substantial maintenance of the desired kinescope operating tolerances.

In a first such method disclosed in the prior art, opaque materials are deposited on focusing masks having final-size apertures (which are sufficiently large to provide an increase in electron transmissivity) so as to temporarily reduce the size of these apertures for the screen printing operation. In this method, the opaque material is cataphoretically deposited on the mask, including the entire walls of the respective final-size apertures. The preliminary mask thus produced is then used in the screen printing operation and the opaque materials are then removed from the preliminary mask to restore the finalsize apertures to the focusing mask. The opaque material is removed prior to mounting the focusing mask in the kinescope envelope, as by subjecting the opaque material, in a fluid medium, to sustained compressional waves of a sonic or ultrasonic frequency. Such a method requires expensive equipment for the application and removal of the opaque material and adds steps (i.e., those for such removal of the opaque material) to the kinescope manufacturing operation. Furthermore, this removal process can produce small particles of the opaque material, which particles might remain in the finished kinescope and lead to voltage breakdown and/or electrical shorting of the kinescope electrodes. Because of these drawbacks, this method is not completely commercially satisfactoryIn a second method disclosed in the prior art, the final-size apertures of a focusing mask are temporarily reduced in size in the following way. The final-size apertures are produced in a metal sheet by etching the sheet through openings in a resist pattern located thereon, the etching being carried out such that parts of the resist pattern are undercut (i.e., the walls of the final-size apertures so produced are located beneath the resist pattern). The final-size apertures are then temporarily reduced to a size required for printing the phosphor screen, by electrically depositing (by electroplating or by electrophoresis) an opaque lining of a non-ferrous metal on the walls to the apertures. The lining is “grown” from the aperture wall toward the center of the aperture as the deposition process is continued, the lining thickness varying with processing time. The opaque lining is removed after the completion of the screen-printing operation using the temporarily-reduced apertures. This method is not completely satisfactory in that where relatively long (i.e., long in a radial direction) opaque linings are required, the provision thereof by electrical deposition, particularly by electroplating, may lead to non-uniformly shaped holes defined by such a lining, thereby causing phosphor areas printed therewith also to be of non-uniform shape. Furthermore, the provision of an opaque lining by this

3,661,581 process results in a thick (approximately equal to the mask thickness) deposit of material along the entire wall of each aperture, this resulting in a relatively large quantity of such material, which necessitates a longer time for removing such material from the mask. Also, the process requires relatively costly electrical equipment associated with such electrical deposition.

In a third method disclosed in the prior art, a matching pattern of a resist material, such as bichromated glue or shellac, is applied to each major surface of a sheet of conductive material. Each pattern includes perforations of a predetermined size providing access to the conductive sheet. This resist-covered sheet is then immersed in an etching solution to open, at accessible portions thereof, apertures of a final size desired for the focusing mask. The mask etching is carried out so that parts of the resist pattern are undercut, these final-size apertures thereby being larger than the individual perforations in the resist pattern. Then the resist-covered sheet containing the apertures is used as a master in the screen printing operation, the printing light rays passing through the being defined by the perforations in the resist patterns. The resist patterns are subsequently removed so that the apertured conductive sheet can be used as a final focusing mask. However, for several reasons, this method is not commercially satisfactory. While such a resist pattern with portions thereof overhanging the final-size apertures of a focusing mask (which pattern is required, in this third method, to be on the completed mask during the screen printing operation) can be provided on a focusing mask after the completion of such a mask, this cannot be done (by methods in the prior art) without considerable effort and expense. Therefore, the resist pattern is preferably provided on the abovementioned (unapertured) conductive sheet at the beginning of the mask-making operation and allowed to remain on the sheet throughout the entire mask-making operation. Generally, in continuous mask-making operations known in the art, a flat band of a suitable conductive material (e.g., cold rolled steel) that is in a relatively hard condition, is passed through the mask-making equipment where it is processed into sheets having suitable-size apertures. Then the apertured sheet, which is still in a comparatively hard condition, is annealed (e.g., at about 900° F for 10 minutes) to reduce its hardness and thereby facilitate the shaping thereof, such shaping being known in the art. After the apertured sheet is annealed and shaped, it is generally mounted on a frame and the thus-completed mask is used as a master for printing the phosphor areas of the image screen in a manner known in the art (see U.S. Pat. No. 3,406,068). However, the bichromated glue and shellac, as well as comparable materials, deteriorate upon exposure to the annealing temperatures generally employed in the art so that this method is not desirable at least because it is generally not applicable to the production of masks by the above-outlined operations involving annealing.

SUMMARY OF THE INVENTION

This invention relates to a novel method for producing a color kinescope of the type comprising an image screen including a mosaic, of phosphor and/or a light-absorbing matrix and a color selection mask having final-size apertures therein. The color selection mask is produced by steps comprising the perforation of an electrically conductive substrate. The apertures of the color selection mask are temporarily reduced in size to provide light-transmitting corridors and the temporary mask so-produced is used as a photographic master in screen printing. The size reduction of the apertures is achieved by steps including the provision of a perforated catalytic layer of an electroless deposition-initiating agent at one of two opposed major surfaces of an apertured electrically conductive substrate, the apertures of the substrate being of final size and portions of the catalytic layer extending partially across the apertures. A suitable material is then deposited (by either electroless deposition or by a combination of electroless and electrolytic deposition) at these portions of the catalytic layer to provide opaque light-barriers that define light-transmitting corridors that are smaller than the apertures of final size. Then the abovementioned image screen is produced by steps including photographic exposure through the corridors of the temporary mask. The light barriers and other materials, if any, are subsequently removed from the apertured substrate, the apertures thereof being restored to their original dimensions (i.e., the final-size), the resulting structure being the abovementioned color selection mask. The target mask and the previously produced image screen are then incorporated into a color kinescope,

Among the advantages of the present invention are the ability to control closely and with relative ease the size of the light-transmitting corridors; the deposition of no material, or, at most, a relatively small amount thereof, at the walls of the substrate during the deposition of the material comprising the opaque light-barriers; the knife-edge configuration of the opaque light-barriers that are producible, which configuration provides better definition of the light beams in the screen printing operation, such a knife edge generally being available independent of the aperture configuration (i.e., regardless of whether the apertures are ellipsoidal, or cylindrical, spherical, or frusto conical in configuration); and the light-barriers are eliminable from the substrate with comparative ease and economy.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIGS. 2 through S are fragmentary, transverse sectional views of a work piece schematically showing the various processing steps for the conversion thereof to a temporary mask according to the present invention.

FIG. 6 is a fragmentary transverse sectional view of a temporary mask made according to the steps shown in FIGS. 2 through 5.

FIG. 7 is a fragmentary sectional view of a temporary mask produced according to another embodiment of the present invention.

FIG. 8 is a fragmentary perspective view of the temporary mask shown in FIG. 6 in position for uses as a photographic master in preparing an image screen for a color kinescope.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a color kinescope 10 produced by the novel method and temporary mask structure disclosed herein, which kinescope 10 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 phosphor areas 20 and, optionally, a light absorbing matrix 23 (discussed below), are collectively referred to herein as an image screen 24. Generally, there is included on the image screen a light-reflective conductive layer (not shown) of aluminum, for example, which covers the phosphor areas and serves as an electrode. The 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 wellknown hexagonal dot pattern (not shown). Alternatively, each phosphor area may have a stripe configuration (not shown), these stripes being arranged in an alternating array of different color phosphors to provide a line screen. The kinescope 10 further includes an electron gun for producing a number of electron beams and either electrostatic or magnetic deflection

3,661,581 and convergence means, none of which are shown for simplicity. In generally parallel, spaced relation with the screen 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. A suitable frame 32 or other means can be used to support the 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 screen 24 to form a field-free region therebetween. The mask 30 is made from a thin sheet or band of conducting material (e.g., coldrolled steel) and has a plurality of apertures 34 of a desired final size therein. 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. The apertures 34 are related in size and position to respective phosphor areas 20 of the image screen 24. The size relationship is such that, where the mask 30 is of the nonfocusing 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 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 preferably is sufficiently large to provide a negative leaving tolerance but not so great that the electron beam impinges any ones 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 target 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. 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 leaving tolerance type (i.e., the beam spot is smaller than a corresponding phosphor area) or the negative leaving tolerance type. In mask type color kinescopes in the prior art, there is a single aperture in the color selection 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 electron beams 21 through the apertures 34 to impinge upon the phosphor areas 20. Because a larger electron beam spot is produced therein 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.

In the first step (FIG. 2) of the process (schematically illustrated in FIGS. 2 through 5), one surface (e.g., 40) of a substrate of an electrically conducting material (e.g., cold-rolled steel) having two substantially parallel surfaces 40 and 44, is provided with a thin catalytic layer 46 of a material which is capable of initiating the electroless deposition of a suitable material described hereinafter. The initiating material of the catalytic layer 46 can be palladium, copper, nickel, cobalt, or chromium, for example, the catalytic layer 46 being believed to be comprised of finely divided nuclei of the initiating material. A catalytic layer of palladium, for example, can be produced by first bringing one major surface 40 of the substrate 42 into contact with an acidic stannous solution and then immersing the same major surface 40 in an acidic palladium solution. The basic surface reactions believed to occur are: SnCl₂ (HC1) + S* - S* · SnCl₂ and

S* SnCl₂ + PdCl₂ (HC1) - S* · Pd + S⁺⁴where S* denotes the substrate surface (e.g., 40) to which the layer 46 is to be applied. Where the substrate 42 is made of iron, which is usually the case for color selection masks, a catalytic layer of palladium can be provided by a one-step operation of contacting one surface of the substrate with an acidic palladium chloride solution. Such a one-step operation is possible because of the relative positions of iron and palladium in the E.M.F. series. The reaction taking place is: Fe + Pd+z _ Fe⁺² + Pd. These treatments provide a catalytic layer 46 having a substantially uniform distribution over the major surface 40 of the substrate 42.

In the next step (FIG. 3) of the process, a first perforated pattern 48 of an etch-resistant material is formed on the catalytic layer 46. The perforations 50 of the pattern 48 preferably are of substantially the same size as the light-transmitting corridors 64 (FIG. 6) used in the screen-printing operation, for reasons given below. This is done, for example, by providing a layer (not shown) of a suitable photosensitive resist material, such as bichromated fish glue, Shipley resist marketed by Shipley Co., Newton, Mass. 02162, or bichromated polyvinyl alcohol, on the catalytic layer 46; exposing the photosensitive resist layer to light passed through a suitable mask (not shown); and removing, as by washing with a suitable solvent, those areas of the layer of resist material that are soluble, this general process being known in the art. The areas of the resist layer remaining on the substrate comprise the perforated pattern 48. In the steps (e.g., washing) for removing certain areas of the resist material to provide the perforations 50 in the resist layer, those portions of the catalytic layer 46 covered by the perforated pattern 48 remain at the major surface 40 and are not washed off or otherwise removed, while those portions of the catalytic layer 46 that are located beneath the areas of the resist layer which are removed may or may not be removed, it not being necessary in the preferred embodiment that these portions of the catalytic layer remain on the substrate 42. Portions of the substrate 42 are accessible through the perforations 50 of the first perforated pattern 48. A second perforated pattern 52 of a suitable etch-resistant material is provided on the second major surface 44 of the substrate 42. This second pattern 52 is optional and may be produced in the same way as the perforated pattern 48. The perforations 54 of the second pattern 52 are in substantial register with the perforations 50 of the first pattern 48, the perforations 54 of the second pattern 52 preferably being larger than those of the first pattern 48. It is not necessary, however, that the perforations 54 of the second pattern be larger than those of the first; the perforations of the respective patterns may be of the same size or perforations 50 of the first pattern 48 may be larger.

In the next step (FIG. 4) of the process, the portions of the substrate 42 which are generally located in the regions between the perforations SO and 54 of the respective patterns 48 and 52 are removed by etching, for example, with ferric chloride in a manner known in the art, through either or both of these perforations 50 and 54, to produce apertures 34 extending through the substrate 42 and in substantial register with the perforations 50 and 54. The apertures 34 are of a final size (e.g., 14 mils) desired for the color-selection mask. While the apertures 34 are shown as having a double frustoconical configuration, other configurations may be used. Also, the present invention can be practiced with kinescopes employing mask apertures that are of a non-circular cross-sectional shape; e.g., slot-shaped apertures. Etching is carried out such that there result both portions 58 of the catalytic layer 46

3,661,581 and areas 60 of the resist pattern 48 that partially extend across the various apertures 34, these portions 58 of the catalytic layer 46 being coextensive with the areas 60 and directly accessible through either or both of the perforations 50 and 54. Any parts of the catalytic layer 46 remaining on the substrate 42 at the perforations 50 are eliminated by the etching operation. The dimension of the apertures 34 preferably is significantly larger than the(fmal size) of the larger ones (i.e., 54) of the two types of perforations (50 and 54). It is believed that the portions 58 of the catalytic layer 46 remain on the areas 60 of the pattern 48 that partially extend across the apertures 34 because of an adsorption-type phenomenon.

In the next step, shown in FIG. 5, opaque deposits 62 of a suitable metallic material reproduced at these exposed portions 58 of the catalytic layer 46 partially extending across the aperture 34, this being done by, for example, electrolessly depositing (e.g., electrolessly plating) the metal at those overhanging regions of the pattern. Such electroless deposition is initiated by the portions 58 of the catalytic layer 46, the opaque deposits 62 partially extending across the apertures 34 and being substantially coextensive with the portions 58 of the catalytic layer 46 (and, therefore, areas 60 of the pattern 48). The opaque deposits 62 provide opaque light-barriers that define light transmitting corridors 64 (FIG. 6) of a dimension suitable for producing the phosphor areas of a screen (e.g., 24 of FIG. 1); for example, where a 14 mil diameter phosphor dot is desired, the corridor diameter should be about 12 mils. The corridors 64 are substantially concentric with the apertures 50. Because the size of the perforations 50 of the first pattern 48 can be accurately controlled so that the perforations 50 are substantially equal to the desired corridors and because the opaque deposits are substantially coextensive with the areas 60 of the pattern 48, the size of the light-transmitting corridors 64 can be controlled with relative accuracy and ease via the control of the perforation size. A variety of metals can be electrolessly deposited at the portions 58 of the layer 46, including nickel-phosphorous alloys; copper; cobalt; nickel; alloys of at least two of copper, cobalt, and nickel; and nickel-boron alloys, the last one being preferred primarily because of the lower activation energy required for the deposition thereof. Electroless plating compositions are generally known in the art. By way of example, an aqueous bath for electrolessly plating a nickel-boron alloy has the formulation:

NiSO, · 6H,O - 25 grams/liter

Na&lt;P₂O₇ · 10H₂O-50 grams/liter (CH₃)₂ NHBHj-1.5 grams/liter

ΝΗ,ΟΗ (58%) -20 c.c./liter

The opaque deposits (e.g., 62) may be produced with a nonmetallic material that lends itself to electroless deposition on the catalytic layer; also, the material that is electrolessly deposited may be non-opaque, this material subsequently being converted to an opaque condition.

Where it is necessary, the opaque deposits 62 may be increased in thickness to a sufficient dimension that allows the deposits to be self-supporting when the perforated pattern 48 is removed, such a self-supportable opaque deposit being shown as 62α in FIG. 6. The thickened opaque deposit 62a can be produced by continuing the process of electrolessly depositing material on the exposed portions 58 of the catalytic layer 46 until a desired deposit thickness (e.g., ½ mil) has been achieved.

At the conclusion of the process (FIG. 6), the resist patterns 48 and 52 have been removed by, for example, treatment with sodium hydroxide (in the case of fish glue resist) or with other suitable agents known in the art, to provide a temporary mask 70. The thickened metallic deposits 62α remain at the apertures 56 of the substrate 42 and provide a temporary reduction in the size thereof, the corridors 64 defined by those metal deposits 62α being substantially equal to the size desired for screen printing. The temporary mask 70 may then be shaped to the desired contour and annealed in a manner known in the art.

Where it is desired, (FIG. 7) the opaque deposits 62 of the temporary mask 70 can be increased in thickness by the electrodeposition (e.g., by electroplating) of a suitable material thereon. Such electroplating is satisfactory but generally not preferred because additional material is deposited at the walls of the apertures 34, as illustrated in FIG. 7, the depth of such material on the walls being less than the thickness of the thickened opaque deposit 62α comprising the light barrier.

While in this invention it is preferred that the perforated patterns 48 and 52 of resist material be removed before the screen printing operation, they may be allowed to remain on the temporary mask 70 during such screen printing in certain instances (e.g., where the temporary mask is not going to be annealed). Where it is allowed to remain on the temporary mask 70, the perforated pattern 48 carrying the portions 58 of the catalytic layer 46 provides support to the opaque deposit 62 so that there is less need for increasing the thickness of the deposit, the opaque deposit 62 acting as a light barrier.

The subsequent operation of screen printing (as shown in FIG. 8) utilizes the temporary mask 70 positioned in spaced relation with a suitable transparent substrate 80 (e.g., faceplate) 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. The printing process is known in the art (see, for example U.S. Pat. No. 3,406,068 to Η. 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 photosensitive material and then exposed to a suitable light which is passed through and defined by the corridors 64 of the temporary mask 70. The light-barriers of the temporary mask 70 have a knife-edge configuration, which particular configuration provides better definition of the light beams used in screen printing, there resulting therefrom more sharply defined phosphor areas. Because the light-barriers depend from the pattern areas extending over the apertures, opaque light-barriers having a knife-edge configuration are generally available regardless of the particular configuration (i.e., elliposoidal, cylindrical, spherical, or frusto-conical) of the final-size apertures. 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 (e.g., 82) of phosphor areas of a first color 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. Generally, a temporary mask corridor 64 about 12 mils diameter and a final mask aperture 56 having a diameter of about 16 mils will respectively provide a phosphor dot of about 14 mils diameter and an electron beam spot size of about 17.8 mils diameter. In first order printing, an electron beam source (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 (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 the temporary mask 70 disclosed herein, a light-absorbing matrix (e.g., 23 of FIG. 1) of an opaque, non-lightreflective material to the image screen (e.g., 24 of FIG. 1). For purposes of this invention, such a matrix provided to an image screen is considered to be included in the term “image screen.” This can be done, for example, by coating a surface of the bare transparent substrate (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,

3,661,581 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 corridors 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. 8) 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 openings. 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 both of these operations (i.e., matrix- and phosphor area- production). 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 opaque deposits 62α comprising the light barriers are eliminated from the temporary mask 70 by electro-chemical stripping or by chemical etching, for example, using reagents and steps known in the art. The elimination of the opaque deposits 62α restores the apertures 34 to their original size (i.e., their final size), the resulting apertured structure constituting the color selection kinescope mask (e.g., 30 in FIG. 1). The kinescope mask and the screen are subsequently incorporated into a color kinescope (FIG. 1).

Among the advantages of the present invention are the ability to control closely and with relative ease the size the light-transmitting corridors; the deposition of no material, or, at most, a relatively small amount thereof, at the walls of the substrate apertures during the deposition of the material comprising the opaque light-barriers; the producibility of light-barriers having a knife-edge configuration, which configuration provides better definition of the light beams in the screen printing operation, such a knife edge generally being available independent of the aperture configuration (i.e., regardless of whether the apertures are ellipsoidal; cylindrical; spherical; or frusto-conical in configuration); and the eliminability of the light-barriers from the substrate with comparative ease and economy.