CA1111698A - Crt screen structure produced by photographic method - Google Patents
Crt screen structure produced by photographic methodInfo
- Publication number
- CA1111698A CA1111698A CA303,497A CA303497A CA1111698A CA 1111698 A CA1111698 A CA 1111698A CA 303497 A CA303497 A CA 303497A CA 1111698 A CA1111698 A CA 1111698A
- Authority
- CA
- Canada
- Prior art keywords
- film
- stencil
- aqueous solution
- overcoating
- method defined
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/20—Manufacture of screens on or from which an image or pattern is formed, picked up, converted or stored; Applying coatings to the vessel
- H01J9/22—Applying luminescent coatings
- H01J9/227—Applying luminescent coatings with luminescent material discontinuously arranged, e.g. in dots or lines
- H01J9/2278—Application of light absorbing material, e.g. between the luminescent areas
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)
- Photosensitive Polymer And Photoresist Processing (AREA)
Abstract
CRT SCREEN STRUCTURE PRODUCED BY PHOTOGRAPHIC METHOD
ABSTRACT OF THE DISCLOSURE
A method for preparing a luminescent-screen struc-ture for a cathode-ray tube comprising (a) exposing a water-soluble photopolymeric film to a light image to insolublize selected portions of the film, (b) developing the exposed film by flushing the exposed film with an aqueous medium to remove the still-soluble portions of the film, (c) rinsing the retained film regions with an aqueous solution containing borate ions, (d) overcoating the retained film regions with a layer containing particles of screen-structure material, (d) and then developing the overcoating by removing the retained film regions and the overcoating thereon.
ABSTRACT OF THE DISCLOSURE
A method for preparing a luminescent-screen struc-ture for a cathode-ray tube comprising (a) exposing a water-soluble photopolymeric film to a light image to insolublize selected portions of the film, (b) developing the exposed film by flushing the exposed film with an aqueous medium to remove the still-soluble portions of the film, (c) rinsing the retained film regions with an aqueous solution containing borate ions, (d) overcoating the retained film regions with a layer containing particles of screen-structure material, (d) and then developing the overcoating by removing the retained film regions and the overcoating thereon.
Description
"3~
RCA 6g,534 .
This invention relates to a novel photographic method for preparing a screen structure for a cathode-ray tube (CRT) and particularly, but not exclusively, to a novel method for preparing a light-absorbing matrix for a color television picture tube.
Color television picture tubes which include a light-absorbing matrix as a s-tructural part of the lumines-cent screen have been described previously; for example, in U. S. patents No. 2,842,697 to F. J. Bingley, and No.
3,146,368 to J. ~. Fiore et al. These patents describe color television picture tubes of the aperture-mask type (also called shadow-mask type) in which a light-absorbing matrix is located on the inner surface of the faceplate of the tube.
lS In this structure, the matrix has openings therein which are fiLled with phosphor material.
A reverse-printing method for preparing a light-absorbing matrix for a CRT is described in U. S. patent No.
3,558,310 to E. E. Mayaud. In a preferred embodiment of that method, the inner surface of the faceplate of a CRT is coated wi~h a film of water-based photopolymeric material, typically a dichromate-sensitized polyvinyl alcohol. A light image 1.5 pro~ected on the film to insolubilize selected regiorls of the film. The film is developed by flushing the film with`water to remove the still-soluble regions of the fi~lm while retaining the insolubilized regions in place.
~:hen, the developed film or stencil and the bare areas of the surface are overcoated with a layer containing particles of light-absorbing material, such as graphite. Finall~, the overcoating is developed by removi~g the stencil together ` ' '~
' "'-~ ~.1.6~
RCA 68,534 1 with the overlying overcoating, while retaining the over~
coating on the bare areas of the surface not covered by the stencil.
Such a process produces satisfac-tory light-absorb-ing matrices in automated and semiautomated factory produc-tion. However, frequently, the overall appearances of matrixes are marred by s~reaks and swirlsO Such streaks and swirls are believed to result from the leaching of soluble and/or pcrtially-soluble material from the stencil, which leached material is then redistributed in a random manner by gravitational and centrifugal forces during and after devel-opment of the film. Careful examination has shown that these streaks and swirls are merely cosmetic, resulting from very slight nonuniformities in the sizes of the openings in the matrix. Although they may have a trivial effect on the performance of the tube, nevertheless streaks and swirls adversely affect the salability of picture tubes which have them.
Polyvinyl alcohol as used by the CRT maker is a product of polyvinyl-acetate manufacturing whose main uses are in the paint and adhesive industry. Attempts have been made to supply a special electronic-grade of polyvinyl ~alcohol, but the cost is prohibitive because the total amount used is small. Therefore, the CRT maker uses materi-als made for the textile, paper and binder industries. The chemical character of those polyvinyl alcohols is dictated by the uses in the aforementioned industries.
The principal factors governing t~e properties of polyviny1 alcohol are the degree of polymerization and the 3 percent hydrolysis. While proper blending of batch-produced .
6~3~
RCA 68,534 1 polyvinyl alcohol can provide products within a given saponi-fication range, such materials will contain much larger amounts of high and low molecular weight fractions and of portions varying widely in degrees of hydrolysis. This type of manufacturing variation produces products with varying de~rees of cold-water solubility. The CRT maker, to make matrix stencils, dissolves away that part of the polyvinyl alcohol not insolubilized by the actinic radiation, while retaining the insolubilized part as a stencil. ~11 regions of the stencil have some partially-soluble material therein.
This partial solubility of the polyvinyl alcohol varies with the lots supplied by the manufacturer.
Prior to coating the photopolymeric film on the faceplate surface, the dry, powdered polyvlnyl alcohol is 15 dissolved in water. This step also may introduce variations in the cold-water solubility of the stencil-making material.
The method according to the invention is similar to the previous method disclosed in the above-cited Mayaud patent ~0 except that, after the exposed film is flushed with water or other àqueous medium to remove the more-soluble reqions of the film, the retained and sti]l wet fllm reqions are rin~s~ wifh an aqueous solution containinq borate ions. Solution~ of boric acid or borax are preferred, althou~h solutions of a ?5 soluble borate, perborate, or other boron com~ound sinql~ or :in combination may be used.
Rinsing the developed film or stencil with an aqueous solutlon containing borate ions essentially elimi-nates the cosmetic defects described above. It is believed that this rlnsing step has the effect of preventing soluble ; _ 4 _ -- .
~3B
RCA 6~,534 i and partially-soluble material in the film from being leache~
out by the aqueous me~lum and t11en being distributed in a random manner. Also, the variable cold-water solubility of the material of the stencil is suppressed by the method, according to the invention resulting in a more uni-form pro~uct.
A preferred embodiment for preparing a llght-absorbing matrix on the inner surface of the faceplate of an aperture-mask-type color television picture tube will now be described. First, the inner surface of the faceplate is cleaned in the usual way, as with water, ammonium bifluoride, hy~rofluoric acid, detergent, caustic, etc., to remove any foreign matter. Then the surface is coa-ted with a film of dichromate-sen~itized polyvinyl alcohol. The film may be produced by depositing on the surface of the faceplate a quantity of an aqueous solution containing about:
Weight Percent Polyvinyl alcohol 3.42 Ammonium dichromate O.34 Water Balance to lO0 The faceplate is rotated and tilted so that the quan-tity of solution spreads evenly over the surface. During the latter steps of rotation, infrared heat is applied so that the ` water in the solution evaporates and a dry photopolymeric 2S film is formed on the surface.
An aperture mask for the faceplate is positioned above and spaced from the film and the assembly is placed in a lighthouse, which is a known apparatus for ex~osing the film on the faceplate by projection of light through the apertures in the mask. In this example, the mask has .
RCA 6g,534 1 circular apertures with a diameter of about 0.33 mm. and a center-to-center spacing between apertures of about 0.71 mm.
near the center of the mask. The film is exposed for about 8 minutes to light from a l,000-watt quartz lamp positioned about 36 cm. from the aperture rask. During the exposure, light from the lamp is passed through a light pipe or colli-mator and projec-ted through the mask causing beamlets of light to pass through the apertures of the mask incident upon the film. The irradiated regions of the film harden;
that is, become insoluble in water. There is a slight en-largement of the exposed areas above the size of its associ-ated aperture (to about 0. 41 n~. ) and a araded hardening at the margins of the exposed areas. The exposure through the mask is repea-ted three times, each time with the light incident at a slightly different angle so that the beamlets harden the film in groups of three, as in the usual aperture-mask screen manufacture.
- Following exposure, the assembly is removed from the lighthouse and the mask is separated from the faceplate.
The exposed coating is subjected -to flushing with a forced spray of water, which may con-tain a detergent, for about 30 seconds, after which the faceplate is rinsed with water.
Then, the still-wet faceplate and retained fiim regions are rinsed for about 30 seconds with a solution containing borate ions. Such borate solutions are described in more detail below. In this example, the faceplate is rinsed with a 0.5 welght-percent solution of boric acid. Then the retained film regions and faceplate are dried with or without the assistance of applied heat. ~t this point in the process, the lacepla=e surface carries an adhcrcnt stenoil comprised . ' ' ' .
.
B
RCA 68,534 of open surface areas and of dots of hardened polymeric film coated on the surface.
The stencil is now overcoated with a composition comprised of light-absorbing particles. In this example, the overcoating is produced by applying to the said stencil a slurry containing about 5.0 weight percent of colloidal graphite in water and then drying the overcoating. It is de-sirable to include a trace of wettincj agent in the graphite slurry in order to facilitate the spreading of the slurry over the stencil. The overcoating is dried tho,oughly for about l.5 minutes with the aid of infrared heat. After coolin~, the overcoating is well adhered both to the stencil and to the bare faceplate surface not covered by the stencil.
Next, a chemically digestive agent for the poly-meric dots is applied to develop the overcoating. In this example, the digestive agent is an a~ueous solution contain-ing about 4.0 weight-percent hydrogen peroxide. This 501u-tion may be applied to the overcoating as a wash or as a spray under pressure. The hydrogen peroxide solu-tion pene-trates the overcoating and the stencil, causing the light~
hardened polyvinyl alcohol of the stencil to swell and soften.
Subse~uent flushing with water removes the softened stencil togethex with the ovexlying port1ons of the overcoating, but leaves behind that portion, or portions, of the overcoat-25 ing which is adhexed directly to the surface of the faceplate `not covered'by the stencil. At this point, the faceplate carries a black light-absorbing matrix having a multiplicity of circular holes therethrough about 0.41 mm in diameter.
The edges of the pattern are relatively smooth.
The black, l1ght-absorbing matrix is now rinsed .
RCA 68,534 1 with water and dried for about 4 minutes with the aid of infrared heat. ~hen, the faceplate is processed in the usual way to deposit red-emitting phosphor dots, green-emit-ting phosphor dots and blue-emitting phosphor dots about 0.a3 mm in diameter in the holes of the matrix. The slight enlarye-ment of the phosphor dots over the holes in the matrix is achieved by the spreading of light during projection, which may be enhanced by increasing the exposure time of the har-dened areas. The luminescent screen may now be processed in the usual way to apply a reflective metal layer on top of the phosphor dots and -the black matri~. The screen is baked and assembled with the aperture mask into a CRT in the usual way.
.
lS The particular steps described in the e~ample above may be varied within limits and still fall within the scope of the method according to the invention. Obviously, the - method maY be used to Produce screen structures of different ~aterials on other support surfaces, and for prepaxing other screen structures than that described above. By "scxeen structure" is meant a structure, luminescent or nonlumi-nescentj which is a part of the screen or -tarqet of a CRT.
Some variations in the -~ethod are described below.
The photopolymeric film may be produced by coating a support surfacle,las by dipping, spraying, flow coating or -spin coating, with a solution of a photopolymeric material.
The preferred photopolymeric material is a polyvinyl alcohol which is sensiti~ed with a small amount of ammonium dichromate, sodium dichromate, potassium dichromate, or a soluble salt of à metal such as iron or mercury; or with an organic RCA 68,534 1 photosensitizer for a water-based photosensitive material, such as a diazo compound.
sesides polyvinyl alcohol, other water-ba~ed photosensitizable polymeric materials may be used. Some suitable water~~ased materials which can be made photosensi-tive are proteins such as gelatin, albumen and fish glue;
carbohydrates such as ~um arabic and starch; and synthetic materials such as polyvinyl pyrollidone. The photopolymeric film may also contain a small amount of a less water-soluble polymer for the purpose of increasing the resistance of the stencil to the erosive action of the chemically-digestive agent. The photopolyme-ric material is of the type which is insolubilized when i~t is exposed to a light image. Such photopolymeric films are referred to as negative acting.
Any pattern form may be used as-a photographic master for exposing the photosensitive film. Thus~ conven-tional silver halide images may be used either by projection or ~ontact printing. In preparing screen structures for color television picture tubes of the aperture-mask type, it is prèferred to use the apert~re mask of the tube as a photographic master for exposin~ the photopolymeric film. In that case, the mask is closely spaced from the film and the li~ht source is placed at three separate locations in order to produce three separate exposures on the film, each at a different location on the film. The aperture mask may have apertures that are round or slit shaped or any other shape or size since the shape and size of the apertures are not critical. Also, the exposure may be used to produce dot or slit or line openings in the matrix.
The photosensitive material is exposed to a pattern ~ 9 _ .
R(A 6~,53 1 of ener~y rays in the range and of the type to which the photosensitive material is sensitive. Where dichromated - polyvinyl alcohol is the photosensitive material, radiant energy in the form of electron beams or as light in the blue and ultraviolet range of the spectrum may be used. Where a contact master is used, one may use a flood exposure. Where the exposure is by projection of an image, a small diameter source is preferred. A small circular light source is preferred for mak1ng dot screens, and a line light source is preferred for making slit and line screens.
Where a photoresist technique has been used for producing the stencil, the exposed photosensitive film is developed in the manner of the use for that material. In the, case of dichromated polyvinyl alcohol, the development is carried out by flushing the surface of the film with water or with other suitable solvent for the unexposed, still-soluble photosensitive material. With other films, the same or other solvents may be used. The development should leave the minimum residue on the bare support surface so as not to interfere w1th the subsequent overcoating step.
The solution of borate ions may be applied to the stencil in any convenient way as by spraying or with a limp stream while the panel is rotating. The solution is aqueous and may contain one,or more boron compounds. Some suitable water-soluble boron compounds are boric acid, borax, sodium perborate, potassium perborate, isobutyl boric acid, trimethyl borate and boric anhydr1de. The solutions may contain 0.2 to 5 weight percent of dissolved boron compound.
Washiilg or rinsing the wet stencil with a solution of a boron compound as described above has the e~fect o~
.
.
-- RCA 68,534 1 reducing or eliminating the physica~ appearance of streaks and swirls in the finished matrix when viewed in reflected ambient light. It is believed that the wash or rinse re-duces the amount of leaching of polymer from the stencil.
This reduces the deposition of the leached polymer. The variability in the solubility of the stencil is suppressed.
The overcoating may be of any material which is adherent to the support surface. The overcoating may incl~de a pigment or phosphor. Where it is desired to produce a light-absorbing matrix for a cathode-ray tube, it is pre-ferred to include in the overcoating a relatively high loading of a dark pigment. The pigment is preferably ele-mental carbon in the form of carbon black, acetylene black, or graphite. Other dark pigments that may be used are silver sulfide, iron oxide, lead sulfide, ferrites, and manganese dioxide. The pigment may be black, white or colored. Where it is desired to produce a lumine~cent structure, it is preferred to include a relative high loading of phosphor particles in thc overcoating. A process of this type for preparing patterns of phosphor particles is dis-closed in U. S. patent No. 2,840,470 to A. K. Levine.
The overcoating must make a bond to the supportsurface that will endure the subse~uent processing, such as removing the'image stencil and depositing the phosphor dots.
With some materials, such as some commercially-available dispersions of graphite in water, the graphite upon drying makes a bond to a glass faceplate which is ade~uate. With other materials, it may be necessary to include a small amount of a binder in the overcoating such that the dry overcoating develops a bond to the support surface through .
a~
RCA 68,53~
1 the use of the binder. Colloidal silica is a satisfactory binder for lamp black and acetylene black. For example, about 10% of a colloidal silica with respec-t to the percent pigment present produces a strong bond to the glass face-plate, especially where a small amount of ammonium dichromateis also present. sesides colloidal silica, alkali silicates may also be used as the binder.
Where a pigment is used for the purpose of making a light-absorbing matrix for a picture tube of the shadow-mask type, the pigment must be deposited in sufficient density to develop the necessary opacity for this purpose.In the case of acetylene black and lamp black, the pigment should be deposited in a weight of about 0.2 to 2.0 mg/cm2 of surface area and, preferably, about 1.0 mg/cm2 or more IS in order that sufficient thickness remains after tube pro-cessing. Where graphite or other pi.gments are used, slightlylower weights are required for achieving the same opacity in the ~inal graphic image.
The overcoating should also be permeable to and substantially unaffected by the graphic image developer, which must sweli or erode or dissolve at least a part of the image stencil. Where the overcoating is entirely particles, it is necessarily permeable. Where the overcoating contains a binder, the overcoating may be permeable by nature or may be made permeable by cra%ing the overcoating. The bond between the .supp,orting surface and the overcoating is prefer-ably not substantially attacked by the graphlc i.mage devel-oper. When the overcoc,ting-support sur~ace bond i5 both inert to the attack of the graphic image developer, and is adherent to the surface, it is possible to develop the graphlc - 12 ~
.
-\
9~3 RCA 68,534 Canada LAIMS
1. In a method for producing a screen structure for a cathode-ray tube including (a) exposing a film of wa-ter-soluble photopolymeric material on a support surface to a light image until the solubilities of the irradiated regions of said film are selectively xeduced, ~ b) flushing said exposed film with an aqueous medium to remove only the regions of greater solubilities, thereby producing a stencil on said surface, (c) overcoating said stencil and the surface not covered by said stencil with screen-structure material, (d) and then removing only said stencil and the over-coating thereon, the improvement comprising, subsequent to step (b) and prior to step (c), rinsing said stencil and support surface with an aqueous solution containing less than 5 weight percent of dissolved boron compound.
RCA 6g,534 .
This invention relates to a novel photographic method for preparing a screen structure for a cathode-ray tube (CRT) and particularly, but not exclusively, to a novel method for preparing a light-absorbing matrix for a color television picture tube.
Color television picture tubes which include a light-absorbing matrix as a s-tructural part of the lumines-cent screen have been described previously; for example, in U. S. patents No. 2,842,697 to F. J. Bingley, and No.
3,146,368 to J. ~. Fiore et al. These patents describe color television picture tubes of the aperture-mask type (also called shadow-mask type) in which a light-absorbing matrix is located on the inner surface of the faceplate of the tube.
lS In this structure, the matrix has openings therein which are fiLled with phosphor material.
A reverse-printing method for preparing a light-absorbing matrix for a CRT is described in U. S. patent No.
3,558,310 to E. E. Mayaud. In a preferred embodiment of that method, the inner surface of the faceplate of a CRT is coated wi~h a film of water-based photopolymeric material, typically a dichromate-sensitized polyvinyl alcohol. A light image 1.5 pro~ected on the film to insolubilize selected regiorls of the film. The film is developed by flushing the film with`water to remove the still-soluble regions of the fi~lm while retaining the insolubilized regions in place.
~:hen, the developed film or stencil and the bare areas of the surface are overcoated with a layer containing particles of light-absorbing material, such as graphite. Finall~, the overcoating is developed by removi~g the stencil together ` ' '~
' "'-~ ~.1.6~
RCA 68,534 1 with the overlying overcoating, while retaining the over~
coating on the bare areas of the surface not covered by the stencil.
Such a process produces satisfac-tory light-absorb-ing matrices in automated and semiautomated factory produc-tion. However, frequently, the overall appearances of matrixes are marred by s~reaks and swirlsO Such streaks and swirls are believed to result from the leaching of soluble and/or pcrtially-soluble material from the stencil, which leached material is then redistributed in a random manner by gravitational and centrifugal forces during and after devel-opment of the film. Careful examination has shown that these streaks and swirls are merely cosmetic, resulting from very slight nonuniformities in the sizes of the openings in the matrix. Although they may have a trivial effect on the performance of the tube, nevertheless streaks and swirls adversely affect the salability of picture tubes which have them.
Polyvinyl alcohol as used by the CRT maker is a product of polyvinyl-acetate manufacturing whose main uses are in the paint and adhesive industry. Attempts have been made to supply a special electronic-grade of polyvinyl ~alcohol, but the cost is prohibitive because the total amount used is small. Therefore, the CRT maker uses materi-als made for the textile, paper and binder industries. The chemical character of those polyvinyl alcohols is dictated by the uses in the aforementioned industries.
The principal factors governing t~e properties of polyviny1 alcohol are the degree of polymerization and the 3 percent hydrolysis. While proper blending of batch-produced .
6~3~
RCA 68,534 1 polyvinyl alcohol can provide products within a given saponi-fication range, such materials will contain much larger amounts of high and low molecular weight fractions and of portions varying widely in degrees of hydrolysis. This type of manufacturing variation produces products with varying de~rees of cold-water solubility. The CRT maker, to make matrix stencils, dissolves away that part of the polyvinyl alcohol not insolubilized by the actinic radiation, while retaining the insolubilized part as a stencil. ~11 regions of the stencil have some partially-soluble material therein.
This partial solubility of the polyvinyl alcohol varies with the lots supplied by the manufacturer.
Prior to coating the photopolymeric film on the faceplate surface, the dry, powdered polyvlnyl alcohol is 15 dissolved in water. This step also may introduce variations in the cold-water solubility of the stencil-making material.
The method according to the invention is similar to the previous method disclosed in the above-cited Mayaud patent ~0 except that, after the exposed film is flushed with water or other àqueous medium to remove the more-soluble reqions of the film, the retained and sti]l wet fllm reqions are rin~s~ wifh an aqueous solution containinq borate ions. Solution~ of boric acid or borax are preferred, althou~h solutions of a ?5 soluble borate, perborate, or other boron com~ound sinql~ or :in combination may be used.
Rinsing the developed film or stencil with an aqueous solutlon containing borate ions essentially elimi-nates the cosmetic defects described above. It is believed that this rlnsing step has the effect of preventing soluble ; _ 4 _ -- .
~3B
RCA 6~,534 i and partially-soluble material in the film from being leache~
out by the aqueous me~lum and t11en being distributed in a random manner. Also, the variable cold-water solubility of the material of the stencil is suppressed by the method, according to the invention resulting in a more uni-form pro~uct.
A preferred embodiment for preparing a llght-absorbing matrix on the inner surface of the faceplate of an aperture-mask-type color television picture tube will now be described. First, the inner surface of the faceplate is cleaned in the usual way, as with water, ammonium bifluoride, hy~rofluoric acid, detergent, caustic, etc., to remove any foreign matter. Then the surface is coa-ted with a film of dichromate-sen~itized polyvinyl alcohol. The film may be produced by depositing on the surface of the faceplate a quantity of an aqueous solution containing about:
Weight Percent Polyvinyl alcohol 3.42 Ammonium dichromate O.34 Water Balance to lO0 The faceplate is rotated and tilted so that the quan-tity of solution spreads evenly over the surface. During the latter steps of rotation, infrared heat is applied so that the ` water in the solution evaporates and a dry photopolymeric 2S film is formed on the surface.
An aperture mask for the faceplate is positioned above and spaced from the film and the assembly is placed in a lighthouse, which is a known apparatus for ex~osing the film on the faceplate by projection of light through the apertures in the mask. In this example, the mask has .
RCA 6g,534 1 circular apertures with a diameter of about 0.33 mm. and a center-to-center spacing between apertures of about 0.71 mm.
near the center of the mask. The film is exposed for about 8 minutes to light from a l,000-watt quartz lamp positioned about 36 cm. from the aperture rask. During the exposure, light from the lamp is passed through a light pipe or colli-mator and projec-ted through the mask causing beamlets of light to pass through the apertures of the mask incident upon the film. The irradiated regions of the film harden;
that is, become insoluble in water. There is a slight en-largement of the exposed areas above the size of its associ-ated aperture (to about 0. 41 n~. ) and a araded hardening at the margins of the exposed areas. The exposure through the mask is repea-ted three times, each time with the light incident at a slightly different angle so that the beamlets harden the film in groups of three, as in the usual aperture-mask screen manufacture.
- Following exposure, the assembly is removed from the lighthouse and the mask is separated from the faceplate.
The exposed coating is subjected -to flushing with a forced spray of water, which may con-tain a detergent, for about 30 seconds, after which the faceplate is rinsed with water.
Then, the still-wet faceplate and retained fiim regions are rinsed for about 30 seconds with a solution containing borate ions. Such borate solutions are described in more detail below. In this example, the faceplate is rinsed with a 0.5 welght-percent solution of boric acid. Then the retained film regions and faceplate are dried with or without the assistance of applied heat. ~t this point in the process, the lacepla=e surface carries an adhcrcnt stenoil comprised . ' ' ' .
.
B
RCA 68,534 of open surface areas and of dots of hardened polymeric film coated on the surface.
The stencil is now overcoated with a composition comprised of light-absorbing particles. In this example, the overcoating is produced by applying to the said stencil a slurry containing about 5.0 weight percent of colloidal graphite in water and then drying the overcoating. It is de-sirable to include a trace of wettincj agent in the graphite slurry in order to facilitate the spreading of the slurry over the stencil. The overcoating is dried tho,oughly for about l.5 minutes with the aid of infrared heat. After coolin~, the overcoating is well adhered both to the stencil and to the bare faceplate surface not covered by the stencil.
Next, a chemically digestive agent for the poly-meric dots is applied to develop the overcoating. In this example, the digestive agent is an a~ueous solution contain-ing about 4.0 weight-percent hydrogen peroxide. This 501u-tion may be applied to the overcoating as a wash or as a spray under pressure. The hydrogen peroxide solu-tion pene-trates the overcoating and the stencil, causing the light~
hardened polyvinyl alcohol of the stencil to swell and soften.
Subse~uent flushing with water removes the softened stencil togethex with the ovexlying port1ons of the overcoating, but leaves behind that portion, or portions, of the overcoat-25 ing which is adhexed directly to the surface of the faceplate `not covered'by the stencil. At this point, the faceplate carries a black light-absorbing matrix having a multiplicity of circular holes therethrough about 0.41 mm in diameter.
The edges of the pattern are relatively smooth.
The black, l1ght-absorbing matrix is now rinsed .
RCA 68,534 1 with water and dried for about 4 minutes with the aid of infrared heat. ~hen, the faceplate is processed in the usual way to deposit red-emitting phosphor dots, green-emit-ting phosphor dots and blue-emitting phosphor dots about 0.a3 mm in diameter in the holes of the matrix. The slight enlarye-ment of the phosphor dots over the holes in the matrix is achieved by the spreading of light during projection, which may be enhanced by increasing the exposure time of the har-dened areas. The luminescent screen may now be processed in the usual way to apply a reflective metal layer on top of the phosphor dots and -the black matri~. The screen is baked and assembled with the aperture mask into a CRT in the usual way.
.
lS The particular steps described in the e~ample above may be varied within limits and still fall within the scope of the method according to the invention. Obviously, the - method maY be used to Produce screen structures of different ~aterials on other support surfaces, and for prepaxing other screen structures than that described above. By "scxeen structure" is meant a structure, luminescent or nonlumi-nescentj which is a part of the screen or -tarqet of a CRT.
Some variations in the -~ethod are described below.
The photopolymeric film may be produced by coating a support surfacle,las by dipping, spraying, flow coating or -spin coating, with a solution of a photopolymeric material.
The preferred photopolymeric material is a polyvinyl alcohol which is sensiti~ed with a small amount of ammonium dichromate, sodium dichromate, potassium dichromate, or a soluble salt of à metal such as iron or mercury; or with an organic RCA 68,534 1 photosensitizer for a water-based photosensitive material, such as a diazo compound.
sesides polyvinyl alcohol, other water-ba~ed photosensitizable polymeric materials may be used. Some suitable water~~ased materials which can be made photosensi-tive are proteins such as gelatin, albumen and fish glue;
carbohydrates such as ~um arabic and starch; and synthetic materials such as polyvinyl pyrollidone. The photopolymeric film may also contain a small amount of a less water-soluble polymer for the purpose of increasing the resistance of the stencil to the erosive action of the chemically-digestive agent. The photopolyme-ric material is of the type which is insolubilized when i~t is exposed to a light image. Such photopolymeric films are referred to as negative acting.
Any pattern form may be used as-a photographic master for exposing the photosensitive film. Thus~ conven-tional silver halide images may be used either by projection or ~ontact printing. In preparing screen structures for color television picture tubes of the aperture-mask type, it is prèferred to use the apert~re mask of the tube as a photographic master for exposin~ the photopolymeric film. In that case, the mask is closely spaced from the film and the li~ht source is placed at three separate locations in order to produce three separate exposures on the film, each at a different location on the film. The aperture mask may have apertures that are round or slit shaped or any other shape or size since the shape and size of the apertures are not critical. Also, the exposure may be used to produce dot or slit or line openings in the matrix.
The photosensitive material is exposed to a pattern ~ 9 _ .
R(A 6~,53 1 of ener~y rays in the range and of the type to which the photosensitive material is sensitive. Where dichromated - polyvinyl alcohol is the photosensitive material, radiant energy in the form of electron beams or as light in the blue and ultraviolet range of the spectrum may be used. Where a contact master is used, one may use a flood exposure. Where the exposure is by projection of an image, a small diameter source is preferred. A small circular light source is preferred for mak1ng dot screens, and a line light source is preferred for making slit and line screens.
Where a photoresist technique has been used for producing the stencil, the exposed photosensitive film is developed in the manner of the use for that material. In the, case of dichromated polyvinyl alcohol, the development is carried out by flushing the surface of the film with water or with other suitable solvent for the unexposed, still-soluble photosensitive material. With other films, the same or other solvents may be used. The development should leave the minimum residue on the bare support surface so as not to interfere w1th the subsequent overcoating step.
The solution of borate ions may be applied to the stencil in any convenient way as by spraying or with a limp stream while the panel is rotating. The solution is aqueous and may contain one,or more boron compounds. Some suitable water-soluble boron compounds are boric acid, borax, sodium perborate, potassium perborate, isobutyl boric acid, trimethyl borate and boric anhydr1de. The solutions may contain 0.2 to 5 weight percent of dissolved boron compound.
Washiilg or rinsing the wet stencil with a solution of a boron compound as described above has the e~fect o~
.
.
-- RCA 68,534 1 reducing or eliminating the physica~ appearance of streaks and swirls in the finished matrix when viewed in reflected ambient light. It is believed that the wash or rinse re-duces the amount of leaching of polymer from the stencil.
This reduces the deposition of the leached polymer. The variability in the solubility of the stencil is suppressed.
The overcoating may be of any material which is adherent to the support surface. The overcoating may incl~de a pigment or phosphor. Where it is desired to produce a light-absorbing matrix for a cathode-ray tube, it is pre-ferred to include in the overcoating a relatively high loading of a dark pigment. The pigment is preferably ele-mental carbon in the form of carbon black, acetylene black, or graphite. Other dark pigments that may be used are silver sulfide, iron oxide, lead sulfide, ferrites, and manganese dioxide. The pigment may be black, white or colored. Where it is desired to produce a lumine~cent structure, it is preferred to include a relative high loading of phosphor particles in thc overcoating. A process of this type for preparing patterns of phosphor particles is dis-closed in U. S. patent No. 2,840,470 to A. K. Levine.
The overcoating must make a bond to the supportsurface that will endure the subse~uent processing, such as removing the'image stencil and depositing the phosphor dots.
With some materials, such as some commercially-available dispersions of graphite in water, the graphite upon drying makes a bond to a glass faceplate which is ade~uate. With other materials, it may be necessary to include a small amount of a binder in the overcoating such that the dry overcoating develops a bond to the support surface through .
a~
RCA 68,53~
1 the use of the binder. Colloidal silica is a satisfactory binder for lamp black and acetylene black. For example, about 10% of a colloidal silica with respec-t to the percent pigment present produces a strong bond to the glass face-plate, especially where a small amount of ammonium dichromateis also present. sesides colloidal silica, alkali silicates may also be used as the binder.
Where a pigment is used for the purpose of making a light-absorbing matrix for a picture tube of the shadow-mask type, the pigment must be deposited in sufficient density to develop the necessary opacity for this purpose.In the case of acetylene black and lamp black, the pigment should be deposited in a weight of about 0.2 to 2.0 mg/cm2 of surface area and, preferably, about 1.0 mg/cm2 or more IS in order that sufficient thickness remains after tube pro-cessing. Where graphite or other pi.gments are used, slightlylower weights are required for achieving the same opacity in the ~inal graphic image.
The overcoating should also be permeable to and substantially unaffected by the graphic image developer, which must sweli or erode or dissolve at least a part of the image stencil. Where the overcoating is entirely particles, it is necessarily permeable. Where the overcoating contains a binder, the overcoating may be permeable by nature or may be made permeable by cra%ing the overcoating. The bond between the .supp,orting surface and the overcoating is prefer-ably not substantially attacked by the graphlc i.mage devel-oper. When the overcoc,ting-support sur~ace bond i5 both inert to the attack of the graphic image developer, and is adherent to the surface, it is possible to develop the graphlc - 12 ~
.
-\
9~3 RCA 68,534 Canada LAIMS
1. In a method for producing a screen structure for a cathode-ray tube including (a) exposing a film of wa-ter-soluble photopolymeric material on a support surface to a light image until the solubilities of the irradiated regions of said film are selectively xeduced, ~ b) flushing said exposed film with an aqueous medium to remove only the regions of greater solubilities, thereby producing a stencil on said surface, (c) overcoating said stencil and the surface not covered by said stencil with screen-structure material, (d) and then removing only said stencil and the over-coating thereon, the improvement comprising, subsequent to step (b) and prior to step (c), rinsing said stencil and support surface with an aqueous solution containing less than 5 weight percent of dissolved boron compound.
2. The method defined in claim 1 wherein said aqueous solution contains dissolved boric acid.
3. The method defined in claim 1 wherein said aqueous solution contains dissolved borax.
j,~;
j,~;
Claims (10)
1. In a method for producing a screen structure for a cathode-ray tube including (a) exposing a film of water-soluble photopolymeric material on a support surface to a light image until the solubilities of the irradiated regions of said film are selectively reduced, b) flushing said exposed film with an aqueous medium to remove only the regions of greater solubilities, thereby producing a stencil on said surface, (c) overcoating said stencil and the surface not covered by said stencil with screen-structure material, (d) and then removing only said stencil and the over-coating thereon, the improvement comprising, subsequent to step (b) and prior to step (c), rinsing said stencil and support surface with an aqueous solution containing less than 5 weight percent of dissolved boron compound.
2. The method defined in claim 1 wherein said aqueous solution contains dissolved boric acid.
3. The method defined in claim 1 wherein said aqueous solution contains dissolved borax.
4. The method defined in claim 1 wherein said aqueous solution contains dissolved alkali perborate.
5. The method defined in claim 1 wherein said aqueous solution contains dissolved boric anhydride.
6. In a method for producing a luminescent-screen structure of a cathode-ray tube including (a) coating a supporting surface with a film of organic photopolymeric material whose solubility in aqueous media is reduced when it is exposed to light, (b) exposing said film to a light image until the soul-bilities of the irradiated regions of said film are selec-tively reduced, (c) removing the more soluble regions of said film with an aqueous medium while retaining the less soluble regions of said film in place, said retained film regions constituting a stencil on said surface, (d) overcoating said stencil and the exposed supporting surface with a layer of pigment particles, (e) removing the stencil and the overlying portions of the layer while retaining those portions of the layer in direct contact with said supporting surface, (f) and then depositing phosphor material on areas of said supporting surface previously occupied by said stencil, the improvement comprising, while said stencil is still wet subsequent to step (c), rinsing said stencil and said supporting surface with an aqueous solution containing less than 5 weight percent of dissolved boron compound.
7. The method defined in claim 6 wherein said organic polymeric material consists essentially of dichromate-sensitized polyvinyl alcohol.
8. The method defined in claim 7 wherein said pigment particles are carbon particles, which particles are applied from an aqueous slurry.
9. The method defined in claim 8 wherein said aqueous solution consists essentially of boric acid dissolved in water.
10. The method defined in claim 8 wherein said aqueous solution consists essentially of borax dissolved in water.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US80028577A | 1977-05-25 | 1977-05-25 | |
| US800,285 | 1977-05-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1111698A true CA1111698A (en) | 1981-11-03 |
Family
ID=25177985
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA303,497A Expired CA1111698A (en) | 1977-05-25 | 1978-05-16 | Crt screen structure produced by photographic method |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS53145554A (en) |
| CA (1) | CA1111698A (en) |
| DE (1) | DE2822836A1 (en) |
| FR (1) | FR2392490A1 (en) |
| IT (1) | IT1096226B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5868834A (en) * | 1981-10-20 | 1983-04-23 | Toshiba Corp | Formation of fluorescent screen |
| DE3142261A1 (en) * | 1981-10-24 | 1983-05-05 | Standard Elektrik Lorenz Ag, 7000 Stuttgart | METHOD FOR PRODUCING A BLACK MATRIX LAYER BETWEEN THE LUMINOUS SURFACES ON THE INSIDE OF THE TUBS OF COLORED PIPES |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3472672A (en) * | 1966-08-26 | 1969-10-14 | Nat Video Corp | Process for producing color television tubes |
| US3558310A (en) * | 1967-03-29 | 1971-01-26 | Rca Corp | Method for producing a graphic image |
| BE757125A (en) * | 1969-10-06 | 1971-03-16 | Rca Corp | PHOTOGRAPHIC PROCESS FOR FORMING THE LUMINESCENT SCREEN OF A CATHODIC RAY TUBE |
| US3813782A (en) * | 1972-05-17 | 1974-06-04 | American Hospital Supply Corp | Collet adjusting mechanism for dental handpieces |
| US3793035A (en) * | 1973-05-16 | 1974-02-19 | Westinghouse Electric Corp | Method of developing opaquely coated sensitized matrix with periodate containing solution |
-
1978
- 1978-05-16 CA CA303,497A patent/CA1111698A/en not_active Expired
- 1978-05-17 IT IT23525/78A patent/IT1096226B/en active
- 1978-05-24 JP JP6214578A patent/JPS53145554A/en active Granted
- 1978-05-24 DE DE19782822836 patent/DE2822836A1/en not_active Withdrawn
- 1978-05-25 FR FR7815518A patent/FR2392490A1/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| FR2392490A1 (en) | 1978-12-22 |
| JPS53145554A (en) | 1978-12-18 |
| DE2822836A1 (en) | 1978-11-30 |
| JPS5721224B2 (en) | 1982-05-06 |
| IT1096226B (en) | 1985-08-26 |
| IT7823525A0 (en) | 1978-05-17 |
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