DE2333865A1 - METHOD OF MANUFACTURING A TEMPORARY PUNCHING MASK FOR PRINTING LUMINOUS ELEMENTS ON THE SCREEN OF A COLOR TUBE - Google Patents

Description

7 516-73 / Kö / s

RCA Docket No .: 65,112

Convention Date: OOOOOCC

July 3, 1972 ZOO O ODO

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

Process for the production of a provisional shadow mask for printing the phosphor elements

on the screen of a color picture tube

The invention relates to a method for producing a provisional shadow mask for printing the phosphor elements on the screen of a color picture tube, the provisional perforated mask made of a thin piece of sheet metal with a perforated mask part, unperforated edge parts and a reinforcing frame comprising the edge parts made of thicker metal, the sheet metal piece on at least one side with a covering made of a mixture containing a thermally reversible organic material is coated to form a thin film closing the holes of the mask part, the coated shadow mask on a Temperature at which the thin film rises above the individual holes with the formation of bulges that partially close the holes tears, is heated and the covering is hardened by cooling the piece of sheet metal.

The invention also relates to a cathode ray tube with a shadow mask electrode, the perforated mask part of an im essential unperforated edge part is bordered, which in turn is bordered by an edge stiffener.

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Normally, the edge parts of the shadow mask have a uniform thickness which is substantially equal to the thickness of the mask part is, wherein the edge parts are made of the same material as the mask part. The mask holes are then temporarily reduced in size or constricted, and the resulting makeshift shadow mask is used as a photographic stencil for printing the bilji screen arrangement used. The shadow mask is then returned to its original state so that it can be used after installation the color picture tube can fulfill its actual purpose.

In a known method (French patent specification 7O3852O, corresponding to German patent application P 20 53 469.4) the individual mask holes are closed with a film or a skin made of organic material. The shadow mask with the die Mask hole sealing skins are then heated so that the skins tear open in their central part, while on the hole walls the coating material remains in a desired thickness, so that temporary mask holes are formed which are smaller than the actual mask holes.

In this known method, applied to a known shadow mask electrode, it can happen that the outer rows of holes remain closed at or in the vicinity of the edge part or only be partially opened. It is believed that this is because the edge stiffener heats up from the edges of the mask part leads away, so that the outer rows of the closed mask holes have too low a temperature than that the temporary holes can open properly. Also by heating the edge reinforcement before and / or during the process step opening the mask holes did not fully resolve this difficulty.

The invention is based on the object of specifying a method which solves the problem mentioned.

A method of the type mentioned at the beginning is according to the invention characterized in that measures are taken to the Heat flow from the sheet metal piece to the stiffening frame during the

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to prevent heating of the shadow mask. When the coverings harden or Bulges on the hole walls then form provisional mask holes that are smaller than the actual or final mask holes. Then, using the coated shadow mask electrode with the smaller provisional mask holes than photographic Template ■ the screen arrangement is photographically printed. Then the coating material is removed from the shadow mask electrode, so that its original state with the larger final mask holes for use in the color picture tube is restored.

By using a shadow mask electrode, in which the flow of heat from the mask part to the edge stiffening element is impeded is, a more uniform temperature distribution over the coated mask part is achieved during the heating. The middle parts the films or skins closing the individual mask holes can all open or tear, especially in the outer rows of holes on the edge part. In addition, there is a more even opening of the middle parts of the skins, so that temporary Mask holes of the desired sizes are created. In this way, a color picture tube with greater uniformity can be obtained and brightness, so that the image fidelity is correspondingly better.

A cathode ray tube of the type mentioned at the outset is according to the invention characterized in that the edge part is so designed. is that it forms the heat flow between the mask part and the Edge stiffening opposes a resistance. The edge reinforcement surrounding the edge part serves as a heat sink for the heat, which is generated during operation of the color picture tube by the electron bombardment of the mask part. The resistance that the edge part to the Opposite the heat flow between the mask part and the edge stiffening is greater than with a shadow mask electrode Edge part is solid and with a uniform thickness, which is substantially equal to the thickness of the mask part, and from which the same material as the mask part. The shadow mask electrode of the cathode ray tube according to the invention is special

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suitable for production by the process according to the invention.

The invention is explained in detail below with reference to the drawing. Show it:

FIG. 1 shows a color television picture tube partially shown in axial section, whose screen is printed using the provisional shadow mask made in accordance with the present invention;

FIG. 2 shows a plan view of the perforated mask of the tube according to FIG

Figure 3 is an enlarged fragmentary view of a Part of the shadow mask according to FIGS. 1 and 2 with an illustration of the mask hole pattern or mosaic

Figure 4 is an enlarged fragmentary sectional view the shadow mask according to FIGS. 1 and 2 with an illustration of the hole cross-section j

FIG. 5 shows a partial perspective sectional illustration of part of a shadow mask according to the prior art;

FIG. 6 is a diagram showing the theoretical mass distribution of the known shadow mask according to FIG Theoretical temperature rise caused by heating of the shadow mask reproduces?

FIG. 7 is a partially perspective sectional illustration of a part of the shadow mask according to FIG. 2 with recesses on the outer surface of the edge part

Figure 8 is an enlarged fragmentary sectional view the perforated mask according to FIG. 7 with an illustration of the recesses;

FIG. 9 is a partially perspective sectional illustration another embodiment of the shadow mask according to Figure 2 with a thinned edge portion;

FIG. 10 is a diagram showing the theoretical mass distribution of the shadow mask in the embodiment according to the invention according to FIGS 9 and shows the theoretical temperature rise resulting from uniform heating of the shadow mask; and

Figure 11 is a diagram with comparison curves showing the calculated

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neten and extrapolated surface temperatures of the shadow mask for the method according to the invention and for methods according to the prior art the technology.

The color television picture tube 20 shown in Figure 1 has one
evacuated glass flask 21 with front plate part 22, funnel or
Cone part 23 and neck part 24. On the inside of the front plate part 22 is a screen 2 5 with phosphors for three colors
appropriate. Inside the glass bulb 21 at a close distance from
Screen 25, a perforated mask or mask electrode 26 is arranged. An electron beam system 27 accommodated in the neck part 24 acts on the screen 25 through the holes in the shadow mask 26 with three electron beams.

The shadow mask 26 shown in Figures 1 and 2 is generally right

and
angular shape / consists of a perforated, ie of a multitude

mask part 28 penetrated by holes, a mask part surrounding it
or bordering edge part 32 and an edge part 32 surrounding or bordering edge stiffening part 29, which acts as a heat sink for
by the electron bombardment of the mask part 28 during operation of the
Color picture tube 20 generated heat is used. In the embodiments
According to FIGS. 7 and 9, the surrounding edge part 32 engages over the separate edge stiffening part 29. The mask part 28 has a convexly curved outer surface 33 and a concavely curved inner surface 34 and a mosaic-like arrangement of mask holes 36 of finished size. The mask holes 36 of the mask part 28 form a generally hexagonal pattern with a mutual hole spacing a and an angle of 60 ° included between the rows of holes, as in FIG
Figure 3 shown.

In the embodiments according to FIGS. 7 and 9, the mask part 28 of the perforated mask consists of a conductor material such as steel with a
About 0.15 to 0.18 mm (0.006 to 0.007 inches) thick and is attached to the edge stiffener 29 by welds 37. The separate edge stiffener 29 shown in Figures 7 and 9 is made of approximately 23.6 mm (0.93 inch) thick steel with substantially
L-shaped profile with one vertical leg approximately 25.4 mm (1 inch) high to attach to edge portion 32 and one approximately 19.1 mm (0.75 inch)

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wide horizontal legs. The welds 37 are within of the area of overlap between the edge portion 32 and the edge stiffening portion 29 and are preferably approximately 3.18 mm (0.125 Inches) from the edge of the edge portion 32. A suitable method for attachment is described in U.S. Patent 3,368,098.

The final mask holes 36 can, as shown in FIG. 4, have the shape of truncated double spherical caps, consisting of a spherical cap 38 of large diameter in the convex outer surface 33 and a spherical cap 39 of small diameter in the concave inner surface 34. The two spherical caps 38 and 39 intersect to form a knife edge 40 which determines the size of the final mask hole 36. In FIG. 4, the thickness of the shadow mask electrode 28 is indicated by the dimension T and the depth of the large spherical cap 38 is indicated by the dimension t. In the above-described 2SV flat color picture tube shadow mask electrode, the large spherical caps 38 are approximately 0.53 mm (0.021 inches) in diameter at the convex outer surface 33 as shown in Figure 4, while the small spherical caps 39 are 0.3175 in diameter to 0.287 mm (0.0125 to 0.0113 inches) on the concave inner surface 34. The size of the large spherical caps 38 is essentially uniform over the surface of the mask part 28, and the size of the small spherical caps 39 is graduated from the center to the edge of the mask part 28, as is known. The center-to-center distance a (shown in Figure 3) of the mask holes is approximately 0.62 mm (0.0244 inches) and the intersection of the two spherical caps at knife edge 40 is approximately 0.127 mm (0.005 inches) from that convex outer surface 33 removed (dimension t in Figure 4).

FIG. 5 shows part of a shadow mask electrode 41 according to the prior art. The shadow mask electrode 41 has an edge part 42 which is fastened to an edge reinforcement part 43 by welds 44. The perforated mask portion 45 has a convex outer surface 46 and a concave inner surface 47. It is provided with an arrangement of final mask holes 49. The edge portion 42 also has a face strip portion 50 with substantially the

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the same curvature as the mask part 45 and a side strip part 51 3 which is arranged essentially at right angles to a plane (not shown) of the mask part 45. The edge part is solid and has essentially the same thickness as the mask part 45 »and it consists of the same material as the mask part 45 · With the exception of the edge part, the known shadow mask electrode according to FIG. 5 is designed the same as the shadow mask electrodes according to the invention according to FIGS. 7 and 9 The edge part 42 in FIG. 5 is solid and of essentially the same thickness as the mask part 45, while the edge part 32 in FIG. 7 has depressions etched out and the edge part 60 in FIG. 9 is designed with a smaller thickness, as will be described below.

In FIG. 6, the hatched area gives the theoretical mass distribution for an ideal cross section of the known shadow mask electrode according to Figure 5 again. The hatched area 53 represents the mask part 45> the hatched area 54 the unperforated edge part 42 and the hatched area 55 the edge reinforcement part 43 represents. If the shadow mask electrode is heated uniformly (shown by the arrows 52), it points to a for a certain period of time (typically about 30 seconds) a temperature distribution corresponding to curve 56. Since the edge stiffening part 43 has a relatively large mass, the The temperature of the shadow mask electrode is not uniform, and it is particularly uneven in the area adjoining the edge part 42 of the mask part 45. In known methods of manufacturing screen assemblies for a color television picture tube, this inconsistency or unevenness in temperature result in the provisional mask holes, especially in the Mask holes 49 in the vicinity of the edge part 42, are not correct to open.

As indicated by curve 56 in Figure 6, the The temperature of the shadow mask electrode is approximately 200 ° C. in the center and approximately 150 ° C. at the edge of the mask part 45. The temperature then decreases further to about 100 C. at the edge part and to about 20 C. at the edge stiffening part. These temperatures are only given as an example in order to

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known shadow mask electrodes for the method according to the invention to illustrate problem occurring} but they are not in to be understood in a restrictive sense of the procedure.

In the method according to the invention, the edge part 32 is designed in such a way that it offers a greater resistance to the flow of heat than in the known shadow mask electrode when the shadow mask electrode 26 is heated essentially uniformly. Namely, the mass is reduced per unit area of the peripheral part 32 for this purpose. The preferred ideal mass per unit area of the edge portion 32 is substantially equal to the mass per unit area of the mask portion 28. In practice, the mass per unit area of the edge portion 32 is in the range of about 100 to 150 percent of the mass per unit area of the mask portion 28 In the present shadow mask electrode 26, the edge portion 32 has a reduced mass per unit area, or it is designed in such a way that it offers an increased resistance to the flow of heat or hinders the flow of heat, as explained in the following examples.

Example 1: FIG. 7 shows a shadow mask electrode in which spherical cap-shaped recesses 57 of large diameter in the same geometric pattern as the mask holes 36 (FIG. 3) are provided in the edge part 32. The pattern or arrangement of the recesses 57 extends over substantially the entire surface of the edge part 32. The recesses 57 (shown in Figure 8) in the edge part 32 are approximately the same size as the large spherical caps 38 in the mask part 28. With a diameter of large spherical cap 38 of 0.5716 mm (0.0229 inches), the small spherical cap 39 of 0.3 531 mm (0.0139 inches), a depth t of 0.127 mm (0.005 inches) and a thickness T of the mask portion 28 of 0.178 mm (0.007 inches) remains through the final mask holes 36 about 57 percent of the metal volume of the mask portion 28, while the large spherical caps 38 or depressions of the arrangement expanded into the rim portion 32 leave approximately 62 percent of the metal volume of the rim portion 32. With a reduced amount of material in the same volume and for the same area, this results in approximately the desired almost equal mass per

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Area unit for the mask part 28 and the edge part 32. Because of the stretching of the flat mask parts during the molding process there is a certain enlargement of the hole dimensions given above compared to the dimensions given above for flat mask parts.

For uniform areas of the mask part 28, the edge part 32 and the edge stiffening part 29 of a flat 2SV shadow mask electrode the following mass ratios were determined by weighing:

Mask part 0.565: 1

Edge portion 0.625: 1

Edge stiffener 11,700: 1

The actual mass per unit area can be determined using the following equation:

Mass per unit area = (ratio) (density of material) (unit area) (

The large spherical caps 38 or depressions in the edge part 32 can be carried out simultaneously with the conventional manufacturing processes final mask holes 36 are etched. Since the large spherical caps 38 do not fully penetrate the edge part 32, as in FIG As shown in FIG. 8, the deflection clearance is not affected, and since the thickness of the edge portion 32 is not reduced as a whole, the mechanical stability and rigidity remain essentially obtain.

Example 2: FIG. 9 shows a shadow mask electrode in which the thickness of the edge part 60 is approximately half the thickness of the mask part 62, approximately 0.076 to 0.089 mm (0.003 to 0.0035 inches). This increases the mass of the edge part 60 also significantly reduced to approximately the value of the mass of the mask part 62. Although the thinned edge portion 60 per se is useful for the present method, its use is less convenient for a cathode ray tube than that of the peripheral portion 32 with the large spherical caps 38 or recesses, since the rigidity of the edge part 60 is considerably lower and it is more difficult, the thin edge part 60 with the edge stiffening part 59 to be welded.

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Example 3: The edge portion 32 of Example 1 is elongated approximately 3.175 now (0.125 inches) and the mask portion 28 is dated Edge stiffener 29 further away approximately 3.175 mm (0.125 inches). Since the preferred position of the welds 37 in relation to is retained on the edge part 32, the distance (dimension χ in FIG. 7) increases at the edge part 32 between the mask part 28 and welds 37 also by approximately 3.175 mm (0.125 Inches), so that the edge portion 32 provides additional resistance to the flow of heat. For a 2SV color television picture tube shadow mask electrode according to the prior art, the dimension X, measured in the main axis of the tube, is approximately 19.05 mm (0.750 inches) while the rim portion 32 of the present shadow mask electrode has the new dimension χ approximately 25.23 mm (0.875 inches). As a result, the contact of the mask part 28 with the top side of the edge stiffening part 29 can also be caused in some places uneven or inadequate joining of the overlapping areas of the mask part 28 and the edge reinforcement part 29 should be avoided.

In FIG. 10, the hatched areas give a theoretical one Mass distribution for the preferred cross section of a shadow mask electrode 26 according to Examples 1 and 2 again. The hatched area 65 the mask part 28 or 62 that hatched Area 66 represents the edge part 32 (FIG. 7) or 60 (FIG. 9) and the hatched area 67 represents the frame stiffening part 29 or 59. If the mask electrode 26 is heated uniformly (indicated by the arrows 64), the temperature distribution corresponds to the shadow mask electrode after a certain period of time of curve 68. The non-uniformity or non-uniformity of the temperature at the edge of mask portion 45 (represented by curve 56 in Figure 6) substantially eliminated as shown by curve 68 in FIG.

The temperature of the mask part 28 remains at approximately 200 ° C. (see curve 68) and does not drop rapidly in the rows of holes on the edge part 32, as is the case with the known shadow mask electrode. Since the temperature of the mask part 28 can remain substantially uniform, the temperature change occurs more uniformly

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Change the heat supplied, as is necessary for opening the provisional Mask holes required evenly. This results in a more reliable opening of the temporary mask holes at least at the mask holes 36 at the edge part 32, as described below.

A shadow mask electrode is used for the method according to the invention with a perforated mask part, an edge stiffening part, which acts as a heat sink for the electron bombardment of the Mask part generated heat is used, and a mask part comprising, arranged between this and the edge stiffening part Edge part made. At least the mask part is coated with an organic material so that a thin film or a Skin of the coating material closes the individual final mask holes 36.

A solution of approximately 24 liters of demineralized water, 180 g of the wetting agent, is preferably used as the organic material Gafac LO-529 from General Aniline and Film Corporation, Johnson City, N.Y., USA, 18 1 10 ^ strength polyvinyl alcohol-water solution, for example the product Vinol 540 from Airco Chemical Division of Air Reduction Company, New York, N.Y., USA, and 4.9 L ethylene glycol. The covering is preferably in Applied in such a way that one faces the shadow mask electrode with a limp or weak beam of the material in an upward direction directed web applied, as described in patent application P 22 62 510.1.

The shadow mask electrode 26 with the skins closing the individual mask holes (not shown) is then heated so that the skin at each mask hole 36 tears open in the middle, while on the walls of the mask holes 36 a bead of the covering material of desired thickness remains, so that provisional mask holes result which are smaller than the final mask holes.

Preferably, the shadow mask electrode is heated at two different rates, initially approximately 30 C. per minute until a temperature of approximately 95 ° C.

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is enough, so that the skins closing the individual mask holes arise. After that, the shadow mask electrode quickly becomes with it
heated about 450 ° C. per minute to a temperature of about 195 ° C., so that the skins in their central part tear and become
the smaller provisional mask holes result. A preferred method of heating the coated shadow mask electrode
for the purpose of forming the smaller provisional mask holes is in
the above-mentioned patent application P 22 62 510.1.

Act while heating in a known method
the known edge part 42 and the known edge reinforcement part 43 as a heat sink, through which the heat is dissipated from the mask holes 49 on the edge part 42. This creates a critical temperature gradient across the mask part 45 ', in particular at
the mask holes at or near the edge portion 42, resulting in
The result is that some of the skins in the mask holes 36 on the mask part 45 do not or only partially open, so that poorly formed provisional mask holes result. These
Difficulty occurs with about 5 to 10 rows of holes on the edge part
42 on.

One way of having a substantially uniform temperature across the mask portion 45 at all process temperatures
To achieve this, it would be that regions of the mask part 41 > the edge part 42 and the edge stiffening part 43 are heated selectively. However, this approach has proven difficult because of the rectangular shape of the shadow mask electrode and the need to rotate the shadow mask electrode during the process. With selective heating, it is very difficult to maintain a uniform temperature for all process steps, and
especially with the mask holes at or near the edge part 42. Temperature gradients or differences can arise because the edge stiffening part 43 and the edge part 42 remain at a different temperature than the mask part 45, the temperature difference having such an effect that improperly opened provisional mask holes around the circumference of the mask portion 45 in the range of 6.35 to 9.52 mm (1/4 to 3/8 of an inch) within the edge of the
Mask part 48 or occur at the edge part 42. It is believed,

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that this temperature difference has the consequence that the mask holes at the temperature limit between the edge stiffening part 43 and the heat acting on the mask part 45 only partially to open.

According to the invention, with a shadow mask electrode 26 Example 1 to 3 worked, which has an increased resistance to heat flow, whereby the heat flow between the mask part 28 and the attachment point of the edge part 32 on the edge stiffener ^ part 20 is obstructed during heating.

According to one embodiment, the edge part 3.2 has etched recesses, as described in example 1. According to another embodiment, the edge portion 60 is of lesser thickness, as described in Example 2. When using the edge parts 32 or 60, as described, the heat conduction loss from the mask part 28 to the edge reinforcement part 29 is limited to approximately 70 to 90 % of that heat loss, measured at the boundary between the mask part and the edge part, which is the case with a known shadow mask electrode with a solid edge part uniform thickness, which is substantially equal to the thickness of the mask part borrowed, and is obtained from the same material as the mask part.

It is believed that heat loss substantially by thermal conduction from the peripheral portion 32 through the welds 37 (not shown) for heavier edge reinforcement part 29 or, in the case of an integrally gen shadow mask electrode (not shown) by direct heat conduction to the heavier edge reinforcement portion arises. An additional resistance to heat dissipation is therefore achieved by increasing the length of the edge part 32 or the conduction path between the mask part 28 and the edge reinforcement part 29. When using a shadow mask electrode 26 with the enlarged pattern of large spherical caps 38, the heat conduction path increases and consequently the speed of heat conduction to the welds 37 and to the edge stiffening part 29 is reduced.

The diagram according to Figure 11 gives the comparison temperature

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curves for the known shadow mask electrode and for the inventive Shadow mask electrode with measures to increase the resistance to heat flow again. The curve 60 gives the temperature of the coated shadow mask electrode during the opening of the provisional mask holes using the known edge part 42 again, while curve 70 shows the temperature of the coated shadow mask electrode during the opening of the provisional mask holes when using the edge part 32 or 00 with increased resistance against heat flow. It can be seen from curves 69 and 70 that the temperature of the mask part 45 of the known perforated mask electrode 41 at the edge of the mask part 45, in particular at the mask holes 36 at or near the edge portion 4 2 decreases, while the Temperature of the mask part 28 or 62 of the shadow mask electrode 26 with increased resistance to heat flow at the edge of the mask part 2S or 62 does not decrease but remains at a substantially uniform value.

According to the method, the temperature of the shadow mask electrode during the opening of the provisional mask holes is preferably in the range from 200 to 220 C, corresponding to the temperature range 71 in FIG. 11.

In the diagram according to FIG. II there are also curve parts 72 and 73 available. These curves apply to the heating of the edge stiffener 29 to a temperature of about ISO C. When heated of the edge stiffening part 29 to a higher temperature such as 150 C. A large part of the edge part 32 or 60 on the mask part 28 and 62 are kept at the same temperature as the mask part 28 and 62, so that there is a greater latitude in the process. The diagram according to FIG. 11 is an estimation approach (with calculations and extrapolations) for better illustration of the process and should not be interpreted in a restrictive sense «The actual tensperature values at Depending on the particular construction of the shadow mask electrode, the heating scheme and the base composition may be different *

The method can also be used with a

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Shadow mask electrode with an unperforated edge part, as described in Examples 1 and 2, or with a known shadow mask electrode with perforations or cutouts in the edge part, which provide increased resistance to heat dissipation from the mask part, as described, for example, in U.S. Patent 2,795,718.

Instead of in the manner described above by thinning the edge part or by removing parts of the edge part in one The pattern of large spherical cap-shaped recesses corresponding to the mask hole pattern can increase the resistance to heat loss can also be achieved by other means, for example by having a high for the mask part of the shadow mask electrode conductive metal such as copper and a low conductive metal such as steel are used for the edge part.

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Claims (8)

Claims Iy method for the production of a provisional shadow mask for printing the fluorescent elements on the screen of a color picture tube, wherein the provisional shadow mask consists of a thin piece of sheet metal with a perforated mask part, unperforated edge parts and a stiffening frame made of thicker metal comprising the edge parts, the sheet metal piece on at least one Side is coated with a coating of a mixture containing a thermally reversible organic material to form a thin film which closes the holes of the mask part, the coated shadow mask to a temperature at which the thin film over the individual holes tears open to form beads which partially close the holes, is heated and the covering is hardened by cooling the piece of sheet metal, characterized in that measures are taken to prevent the flow of heat from the piece of sheet metal (28, 62) to the stiffening frame (29, 59) during the heating of the shadow mask. 2. The method according to claim 1, characterized that the heat flow from the mask part (28, 62) of Shadow mask is hindered in that the mass per unit area of the unperforated edge parts (32, 6θ) is reduced. 3. The method according to claim 1, characterized in that the edge parts contain an edge part (32, 60), whose mass per unit area is essentially equal to the mass per unit area of the mask part (28, 62). 4. The method according to claim 3, characterized in that that the edge portion has a uniform thickness and the mass per unit area of the edge portion is substantially is equal to the mass per unit area of the mask part. 5. The method according to claim 3, characterized in that that areas of the edge part are provided with an arrangement of recesses (57), the areas of lesser thickness 309883/1177 2333365 and form mass per unit area. 6. Cathode ray tube with a shadow mask electrode, the perforated mask part of which has an essentially unperforated edge part is bordered, which in turn is bordered by an edge stiffener, characterized in that the edge portion (32, 60) is formed (57) so that it is exposed to the flow of heat opposed a resistance between the mask part (28, 62) and the edge reinforcement (29, 59). 7. Cathode ray tube according to claim 6, characterized in that the edge part has a smaller one Has thickness than the mask part. 8. Cathode ray tube according to claim 6, characterized in that at least in parts of the An arrangement of recesses (57) is provided on the edge part, which form parts with reduced mass per unit area. 309883/1177 ORIGINAL INSPECTED