DE2053413A1 - Process for the production of a provisional shadow mask for a color picture tube - Google Patents

Description

7088-70 / Kö / s
RCA 62,374
Convention Date:
October 31, 1969

RCA Corporation, New York, N.Y., V.St.A.

Method for producing a provisional shadow mask for a

Color picture tube

The invention relates to a method for producing a provisional shadow mask for a color picture tube, the provisional shadow mask consisting of a thin piece of sheet metal with a pattern of permanent holes, on one surface of which a material layer with provisional holes is attached which correspond in position to the holes in the piece of sheet metal , however, are smaller than these, and which are used to print the phosphor elements on the screen of the color picture tube. Ä

Known color picture tubes both have a screen with a multiplicity of groups of closely spaced phosphor coverings or elements, each of which in each group emits a different color when an electron beam hits it than also a perforated or colored mask (perforated Electrode). Such color masks, both of the non-focusing and of the focusing type, and their mode of action are all ^ commonly known (U.S. Patents 2,961,313 and 1,961,314).

Common screen printing methods generally use a Color mask with holes of a desired finished size as a template

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for photographic printing of the phosphor elements on the Screen used. The color mask with unchanged hole size is then in the finished color picture tube together with the screen used for the purpose of color selection. Such mask holes uri changed size, which are useful for both screen printing and for the choice of color are used in the following as "double function holes" designated.

With color picture tubes, their color mask has such double function holes the width of the individual phosphor elements, be they lines (dashes) or dots, is usually greater than that of the Beam spot, as the beam passes through the focussing field between the color mask and screen may be squeezed or narrowed. Furthermore, the light spot forming the phosphor elements is open the screen larger than the mask holes through which the light passes. The phosphor elements can also turn out to be larger as a result of the fact that their size is directly dependent on the exposure time depends.

So that the color picture tube works with greater light output and better efficiency, the entire surface of each should Phosphor element can be detected by the incident electron beam. That is, the width of the beam spot should be as large as or greater than the width of each individual phosphor element be. For this purpose, the mask holes should be smaller when screen printing than when the tube is in operation.

The invention is based on the object of specifying a method for producing a provisional perforated or colored mask, whose holes in the photographic printing of the fluorescent screen are smaller than the permanent mask holes that are made during operation of the Tube can be used.

To solve this problem , the invention provides a method of the type mentioned at the outset, which is characterized in that at least one surface of a perforated electrode is coated with a liquid film made of a material which solidifies through drying and which shrinks spatially during drying

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each mask hole forms an opening through the film; and that the film is dried until a ring of hardened film material is formed in each mask hole, which ring partially fills the mask hole, in such a way that the provisional shadow mask with smaller holes is obtained.

In the drawings show:

FIG. 1 shows a partially sectioned side view of a color picture tube with a color mask produced according to the invention

Figures 2 to 5 and 7 are fragmentary cross-sectional views of the color mask with illustration of different execution | shaping the method according to the invention; and

Figure 6 is a fragmentary plan view of the mask design according to Figure 5

The invention is explained below with reference to a color picture tube type, in which the holes of the color mask and corresponding the phosphor elements are round in shape.

FIG. 1 shows a color picture tube 10 with a glass bulb 12 which has a funnel or cone part 14 and an end cap 16 with a transparent front plate 18. On the inner surface 22 of the front plate 18, a plurality of flat phosphor elements 20 are attached, which comprise a total of two or more groups of% different phosphors and each luminesce individually in a certain color (e.g. red, blue or green) when an electron beam 21 hits. The front plate 18 together with the fluorescent elements 20 and a light-absorbing matrix 23 optionally attached thereon are summarized below under the collective term "screen" (24). In general, an electron-permeable, light-reflecting conductive layer (not shown) made of, for example, aluminum, which covers the phosphor elements and serves as an electrode, is generally provided on the screen. The fluorescent elements 20 (like other parts in FIG. 1 and the other figures) are exaggerated in size and proportion and shown as point-shaped, the points being designed in a known hexagonal grouping (not shown)

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could be. Instead, the individual phosphor elements also be linear or strip-shaped (not shown), these strips alternating each from phosphors of other Color exist, so that there is a line grid screen.

The color picture tube 10 also has a number of electron beam systems as well as electrostatic or magnetic deflection and convergence devices (not shown). Normally a single hole is provided in the color mask for each triple of phosphor dots (ie one phosphor dot each for red, green and blue). In FIG. 1, however, only one fluorescent element 20 is assigned to each mask hole 34 for the sake of simplicity. When the color picture tube is in operation, the electrons emitted by the beam systems (not shown) are directed as electron beams 21 through the mask holes 34 onto the phosphor elements 20.

The color mask (perforated mask or perforated electrode) 30 is arranged at a generally parallel distance from the screen 24 and can only provide the choice of color or also additionally a beam focusing. The color mask 30 can be supported by a suitable frame 32 or other means. In the present case, it is assumed, for example, that the color mask 30, unless otherwise stated, is a non-focusing mask which has essentially the same potential as the screen 24, so that there is a field-free area between the two . The color mask 30 is made from a thin piece or tape of conductive material (eg, cold rolled steel) and has a plurality of holes 34 of a desired finished size. While the holes 34 in the figure are essentially circular in shape, other hole shapes can also be used. For example, the coloring mask can be designed like a grill with slot-shaped holes (not shown).

The holes 34 are sized to correspond to fluorescent elements 20 of the screen 24 related, the size relationship is such that with non-focusing color mask 30 the individual Finished-size holes 34 are of a width or diameter to allow an electron beam 21 to pass through.

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Let pass, whose width or diameter, measured on the screen 24, (ie whose beam size) at least Lm substantially the same or preferably greater than the ¹ diameter of the individual luminescent substances Lamento 20 Lit, on which the electron beam strikes. The beam spot diameter is preferably so much larger than the area of the individual fluorescent elements that there is a negative emission tolerance (i.e. the beam leak is greater than the area of the corresponding fluorescent element), but not so large that the electron beam also covers something other than the intended fluorescent element.

In general, in a mask with holes of a given size, the size of the light spot that is generated during screen printing by the light passing through the mask holes is considerably larger than that of the beam spots that are generated when the electron beam passes through the same mask holes, because the light spot is enlarged by the penumbra, which exits when the light passes through the mask holes. This has the consequence that the area of the individual phosphor elements is considerably larger than the associated beam spot, so that the beam only covers part of each phosphor element when it hits. In some operating modes of the tube, however, it is desirable for the electron beam spot to be at least as large as, preferably larger than, the area of the corresponding phosphor λ elements. This assumes that the mask holes 34 are larger than the associated phosphor elements 20.

According to one embodiment of the present method, a temporary mask 50 (FIG. 5) for printing the fluorescent screen is produced for the production of a color picture tube. A color mask 52 (FIG. 2) which is usually curved or arched and has mask holes 58 of essentially double truncated cone shape with a knife edge between the two cone parts 55 and 57 is used to produce the temporary mask. This shape is created when the sheet metal 52 is etched through from both sides.

To produce the temporary mask 50, the color mask 52 is covered with a covering or a layer 54 of film-forming

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2U53A13

Material that shrinks as it dries, coated (figure .) ). The covering 54 is opaque (non-permeable) and essentially completely covers both main surfaces 66 and 68 (eg at 64) and fills the holes 58 (eg at L 60). In another embodiment of the method (FIG. 7), a similar opaque coating 54 'is provided, which consists of film plates 60' which are arranged over the holes 58, although only on one main surface 66 of the mask 52 'hang over the holes 58 or reach into them. In Figure 7, like reference numerals denote like in figure) corresponding parts.

The coating 54 can be applied in that, for example, the mask 52 Ln is immersed in a bath of the forming material or the film material is sprayed onto the mask 52. The coating 54 'can be applied, for example, that which one surface 66 of the mask is wetted in a controlled manner in a bath of the shrinkable film-forming material. The material can be provided in the fluid state by placing it in a suitable vaporizable solvent (e.g. V / water, ToLuol or alcohol) or by heating it or by adding a Chooses material that is naturally in a fluid state. The immersion of the mask 52 can be accomplished using simple containers (not shown) happen that contain the shrinkable film-forming material in the fluid state, with one during coating the color mask 52 either intermittently or continuously can.

The film portions 60 and 60 'preferably substantially have double concave shape with relatively thin central areas and 70 'and relatively thick edge areas 72 and 72'. Such a double-concave shape results from surface tension forces that act on the fluid or liquid material during coating the mask act. For this reason, the fluid film-forming material should be able to wet the mask to be coated, since film-forming materials with such property have the desirable high surface tension.

A "film-forming" material is defined here as a material

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rial which, when applied to a mask in the fluxing state, can wet the mask so that filtciles are formed at the corresponding holes which essentially close the openings in the wet or moist state and preferably (but not necessary) a relatively thin central area and For the purposes of the present process, the film-forming material should experience a spatial shrinkage (or contraction) as it dries, which is controlled and to such an extent by appropriate selection and adjustment of the specific composition and / or concentration of the material used can be brought about Λ that translucent corridors or openings arise in the film parts. The film parts preferably have a double-concave or plano-concave shape, but can also have other (e.g. concave-convex) shapes. The film parts should be essentially opaque (opaque), ie the film-forming the materials should be largely intrinsically opaque or mixed with known opaque substances. Instead, you can also use film-forming materials that result in non-opaque film parts, the middle areas of which are then removed in the manner described, while the remaining areas of these film parts are then converted into an opaque state (e.g. by coating with a dye or an opaque substance such as carbon) . The term "opaque" in connection with the film parts or individual areas of the same is intended to denote both impermeability to radiant energy and the property of a scattering or scattering of radiant energy so that it is deflected away from its original beam path and thereby causing this during screen printing Radiant energy is essentially limited to the portion that passes through the corridors in the film parts »

The shrinkable film-forming material is preferably removed from the mask by burning in air and / or by evaporation (both preferably at or below the processing temperatures that are generally used in color picture tube manufacture, for example at or below 500 ° C.) and / or by dissolving away

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in solvents (preferably, but not necessary, water) which do not attack the mask and preferably substantially leave no residue, removed. Suitable combustion or evaporation temperatures are those temperatures (e.g. about 400 to 450 ° C), with which protective agent or reserve deposits (not shown) on the screen 24 (Figure 1), which are attached during the manufacture of the same, in the course of Manufacturing process are burned away in a known manner.

Compositions or mixtures useful as drying shrinkable film-forming materials include acryloid emulsions (e.g. Rhoplex B74 »that from Rohm and Haas and contains approximately 38 percent solids by weight), which are alkaline. Plasticizers (e.g. glycol ether) are preferably added to the acryloid emulsions in order to prevent the Avoid film parts when shrinking. A specific composition that can be used contains between 18 and 50 percent by volume Acryloid emulsion (with a solids content of approximately 38 percent by weight), 1 to 5 percent by volume ethylene glycol (as a plasticizer), the remainder water. Instead you can also for example use a composition that is 14 to 42 percent by volume Acryloid emulsion (with a solids content of approximately 38 percent by weight), 10 to 15 percent by volume dipropylene glycol methyl ether (as a plasticizer), the remainder water. The pH these compositions are adjusted (e.g. with sodium hydroxide) to be higher than 7 * 0, where for the compositions with acryloid emulsions, a pH between 9.0 and 10.0 is generally preferred. When the film-forming material Forms non-opaque film parts, one can either add opaque substances (e.g. dyes) to the film-forming material or apply such substances to the film parts on the mask.

After the coated mask 56 (Figure 3) is made, the central areas 70 of the shrinkable film portions 60 are through Drying of the covering 54 removed. This can take place, for example, in still air or in a moderately warm air flow, provided that that essentially the entire surface of the covering dem

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Drying medium is exposed, so that an essentially uniform drying takes place. Figures 4 and 7 show the coated mask during the drying process, as a general one Thinning of the Mifctelbereich 70 takes place and in the individual A meniscus-shaped skin 60a, 60 'is created for each mask hole. It it is believed that as the more volatile constituents of the film portions dry off, their increasing solids content increases causes the surface tension in these film parts and that this increased surface tension leads to shrinkage of the film parts, which lasts until the moisture content has dropped that far is that the film parts exhibit solid-like behavior. This point at which the shrinkage of the film parts or individual f Areas of which essentially ceases, is dependent on the composition and concentration of the shrinkable film-forming material different, materials with a higher proportion of volatiles generally showing greater shrinkage. The point at which the shrinkage essentially ceases is approximately at the point in time at which the meniscus-like skin 60a, 60 'tears and an opening or a Breakthrough 76 arises in each mask hole. This preferred situation (and consequently adjustment of the hole size) can be accomplished by changing the composition and / or concentration of the shrinkable film-forming material accordingly chooses. It may be desirable to equip the screen with a provisional | Soric mask to print in which the holes are more desired Size are already formed before the shrinkable film-forming Provisional mask material has dried to the point where the shrinkage substantially stops. In this case there is however, the possibility of shrinkage during screen printing and thereby enlarging holes 76, so that the resulting phosphor dots are larger than intended will.

The term "removal" in connection with the formation of the openings or corridors 76 designates here both the complete elimination of the central areas of the relevant film parts with the formation of free openings or holes at these locations and the reduction in the thickness of these central areas to the extent that these

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essentially become crystal clear. The term "corridor" includes both the free openings or holes and the thin, crystal-clear parts of the central areas.

By removing the thinner central areas 70 of the film pieces 60 a provisional mask 50 (FIG. 5) is created which is not opaque Rings 74 on the walls 62 of the individual holes 58. These Rings 74 consist at least in part of the edge areas / '- the opaque film parts 60 (Figure 3) and form or limit the translucent corridors 76, which are much smaller in diameter are than the mask holes 58. By checking accordingly the composition and / or the concentration of the shrumpj? The size or diameter of the film-forming material can be used the corridors 76 with comparatively high accuracy so adjust that fluorescent dots (e.g. 20 in Figure l) result in the desired dimensions. For example With the composition first mentioned above, one can achieve a corridor approximately 0.30 mm (12 mils) in diameter in one Mask hole approximately 0.39 mm (15> 4 mils) in diameter obtained (i.e., the hole diameter is plugged by approximately 0.09 mm (3.4 mils)) with the hole having an electron beam spot of approximately 0.45 mm (17 »8 mil) in diameter and the corridor has a fluorescent dot of approximately 0.36 mm (14 mils). The thickness distribution of the individual film parts 60 (Figure 3) is such that the corresponding Central areas 70 spaced substantially evenly can be so that corridors 76 (Figure 5) of substantially uniform size and shape. The rings 74 lie on the walls 62 of the holes 53 so that they are supported thereby and are reinforced and have a relatively high resistance to breakage and other damage.

The provisional mask 50 is then spaced (not shown) from a suitable transparent base (e.g. front panel) and used as a photographic template for the "Printing" the various phosphor elements used. That Printing processes are known and are described, for example, in US Pat. No. 3,406,068. One surface becomes one a transparent base (not shown) with a mixture

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from a first of the desired phosphors and a suitable one light-sensitive material coated and the fluorescent coating then with suitable light coming through the corridors (e.g. 76 in Figure 5) of the temporary mask (e.g. 50) is exposed. The opaque rings 74 of the temporary mask 50 form or shape the printing light rays by restricting the light passing through to essentially the corridors. Those Areas of the fluorescent coating on which the light rays impact, are.hardened, and the unhardened parts of the covering are washed away, for example, so that a pattern or grid of phosphor elements of a first color is mixed with the hardened protective agent, remains. This procedural f steps are repeated for the phosphors of the other colors. The hardened protective material is then from the fluorescent dots by firing or chemical dissolving in known Way removed.

When screen printing, a light absorbing stencil (e.g., 23rd in Figure l) made of opaque, non-light-reflecting material on the Screen (e.g. 24 in Figure 1). As already mentioned, the term "screen" here includes the phosphor elements and optionally such a light-absorbing matrix. To attach this, you can, for example, a surface (e.g. 22 in Figure 1) of the bare transparent base with a " relatively translucent (translucent) mixture (not shown) of a material that is relatively little Light is absorbed, but can be converted into a light-absorbing state (e.g. manganese oxalate or manganese carbonate, which through Heating in a known manner from a comparatively transparent state to an opaque, non-light-reflecting state can be transferred) and a photosensitive reserve of the "positive type" (i.e. the one where they have been exposed is soluble) and then expose this surface with suitable light through the corridors of the temporary mask. then the soluble parts of the covering are washed away and the relatively weak light-absorbing material is washed away

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Parts of the covering converted into the light-absorbing state. Then the fluorescent elements are printed in openings of the matrix, as described above. The phosphor elements can, if desired be slightly larger than the openings of the die, so that parts of the corresponding fluorescent surface elements on the Die itself. The effective size of these phosphor elements is therefore equal to the size of the corresponding die openings. With "size" of the fluorescent elements of a screen with Die is meant according to its effective size. If desired, the phosphor elements can also be used before transferring the Material can be printed in the light-absorbing state. Stati; of this, the phosphor elements can also be printed before the stencil is attached, the temporary mask being used for both the printing of the phosphor elements as well as the production of the Die is used. If desired, a light-absorbing Die with the help of a provisional mask can be formed on a transparent base, with the subsequent phosphor print in such a way that a mixture of fluorescent material and light-sensitive protective agent (reserve) is applied to the one Surface of the base on which the template is located is applied and then the mixture is exposed to a light source which is arranged on the opposite side of the base as the die. The light passes through the Die openings through and is defined by them.

After the screen has finished printing, the rings 74 of the temporary mask 50 (by burning or chemical Removal) removed, so that the color mask 52 is back to its original State receives (similar to the mask 30 in Figure l). The removal of the rings 74 can be performed in conjunction with the aforementioned Removal of the reserve material from the fluorescent screen can be done, for example, by removing the makeshift mask and the fluorescent screen burns out together or both treated at the same time with appropriate chemical solvents. That way you can Use the existing equipment to restore the mask to its original state without additional procedural steps. The color mask 52 is then inserted into a color picture tube in the FIG 1 installed in the manner shown.

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The present method of temporarily reducing the hole size of the shadow or color mask for the purpose of screen printing has the advantage, among other things, that it is simple and relatively inexpensive, in that no solvents or caustic agents are used to apply the translucent corridors. Furthermore, the formation of the translucent corridors of the temporary mask can take place simultaneously with the drying of the mask covering, so that no separate process steps are necessary for the drying of the covering and the subsequent attachment of the corridors. Since no solvents are used for the production of these corridors, those devices and apparatus (eg separate containers, pumps, etc.) which are usually required for the removal of the "solvents" are dispensed with, so that considerable expenditure is saved Manufacture color picture tubes in a more economical and simpler way.

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Claims (6)

Claims Method for producing a provisional shadow mask for ^ ine color picture tube, with the provisional shadow mask from consists of a thin smelling piece with a pattern of permanent holes, on one surface of which a layer of material with pro- visor holes that are in register with the holes match in the sheet metal piece, but are smaller than this, and those used to print the phosphor elements on the screen of the Serve color picture tube, characterized in that at least one surface (66) of a perforated Electrode coated with a liquid film (54, 54 ') made of a material which solidifies through drying and shrinks spatially during drying and an opening (76) through each mask hole the film forms and that the film is dried until in each mask hole a ring (74) of hardened film material is created, which partially fills the mask hole, so that the provisional Shadow mask with smaller holes is obtained. 2. The method according to claim 1, characterized in that that the film initially forms a meniscus-like skin (60a, 60 ') in each mask hole as it dries. 3. The method according to claim 1 or 2, characterized in that that the film material consists essentially of an alkaline acryloid emulsion. 4. Method according to one of Claims 1 to 3, characterized in that the film material essentially from an alkaline mixture of an acryloid emulsion and essentially a glycol ether or ethylene glycol as plasticizer consists. 5. The method according to any one of claims 1 to 4, characterized characterized in that the film material consists essentially of about 18 to 50 volume percent of an acryloid emulsion 10 9 8 19/1360 with a solids content of about 38 weight percent, about 1 to 5 percent by volume of ethylene glycol, remainder water / water and has a pH greater than 7.0. 6. The method according to any one of claims 1 to 4j because you rch gekennz eich net that the film material consists essentially of about 14 to 42 percent by volume of an acryloid emulsion with a solids content of 38 percent by weight, about 10 to 15 percent by volume of dipropylene glycol methyl ether, remainder V / water and has a pH greater than 7.0 . 109819 / 13G0