MXPA96005437A - Method for making a shadow mask for cinescopes of co - Google Patents

Abstract

The present invention relates to a method for making a shadow mask for a color kinescope, characterized in that it comprises the steps of: forming a pattern, corresponding to the openings of the shadow mask, on a screen mesh fixed to a frame, provide a flat AK steel shadow mask under the screen mesh, print a layer of material with low thermal expansion on one side of the AK steel shadow mask by compressing a low thermal expansion material paste onto the sieve mesh with a constant pressure along one direction, and compress the flat shadow mask to form a shirt portion and a protruding portion of the mask

Description

METHOD OF MAKING A SHADOW MASK FOR COLOR CINESCOPES DESCRIPTION The present invention relates generally to a method for forming a material against the bulging of a shadow mask. A color kinescope of a type of shadow mask has beams of electrons emitted from an electron gun, which pass through openings in the shadow mask to reach the pixels R, G and B, respectively in a layer of match. However, part of the electron beams pass through the opening of the shadow mask and rest against the inner surface of the shadow mask to warm it. As a result, the shadow mask is thermally expanded and bulges, so that the position of the openings is changed against the electron beam. In this way, a demand is proposed to compensate the change. Referring to Figure 5, a conventional shadow mask 1 is illustrated which is secured to a frame 3, which is mounted on a panel by means of a spring 5. On the inner surface of the panel 7, a layer of a layer is deposited. phosphorus containing phosphorus pixels that emit light of red R, green G and blue B respectively.

The shadow mask 1 is separated at a predetermined distance from the phosphor layer. In addition, the shadow mask 1 is generally made of pure steel, for example aluminum suppressor steel (AK). Steel AK has a coefficient of thermal expansion of approximately 11.7 x 10"^ / K. When the kinescope operates, the electron beams emitted from an electron gun pass through the corresponding openings in the shadow mask 1 and correctly arrive To the phosphorus pixels proposed to display an image, however, approximately 80% of the electron beams hit the inner surface of the shadow mask thus increasing the temperature of the shadow mask to approximately 80-90 ° C. , the shadow mask 1 is thermally expanded and bulges out as shown in the interrupted line of Figure 5, so that the trajectories of the electron beams, which pass through the shadow mask, are displaced from the pixels of phosphorus to deteriorate the uniformity of the white color, that is, the trajectory of the electron beam is moved from a position Bl to a position B2 and from this The corresponding phosphor pixel is also shifted from a Pl position to a P2 position.

To solve the problem described above, shadow masks made of invar alloy having an extremely low coefficient of thermal expansion are described, are described in Japanese Patent Laid-Open No. S59-15861 and US Patent Nos. 647,924 and 4,528,246. However, invar alloy is difficult to form and the cost of it is high, which increases manufacturing costs. Therefore, Korean Patent No. 85-1589 describes a method for forming an electron radiation layer on the shadow mask to solve the bulging problem. European Patent No. 139,379 describes a method for forming a lower expansion layer on the shadow mask. However, since the methods described above are technically complicated, it is difficult to apply the methods to current production. It is an object of the present invention to provide a method for making a shade mask for a color kinescope with a much simpler manufacturing process, while providing low thermal expansion, and high electron reflection and a thermal radiation effect .

The above objects and other objects will be made in accordance with the present invention, which provides a method for making a shadow mask for a color kinescope, comprising the steps of: forming a pattern, corresponding to the openings of the mask shadow, on a screen mesh fixed to a frame; arrange a flat AK steel shadow mask under the screen mesh; printing a layer of low thermal expansion material on one side of the AK steel shadow mask by compressing pastes of a low thermal expansion material onto the screen mesh and with a constant pressure along the direction; and compressing the flat shadow mask to form a shirt portion and a projection portion of the shadow mask. Preferably, the pastes comprise one or more metals or an oxide selected from the group consisting of tungsten, carbonated tungsten and bismuth. According to an important aspect of the present invention, the step of printing the layer is performed two or more times to increase the thickness of the layer. If required, in order to further print the layer on the other side of the flat AK steel shadow mask, the procedure from the pattern forming step to the layer printing step is applied additionally to the other side of the shadow mask steel AK flat. According to another important aspect, the method further comprises the step of heating the shadow mask, which is obtained after pressing the flat AK steel shadow mask, in a reduction heating furnace to induce diffusion of both substances. of the layer of material such as the shadow mask of AK flat steel in order to obtain an alloy steel between the layer and the shadow mask of AK flat steel. According to the preferred embodiment, the temperature of the reduction heating oven is set at about 850-1, 200 ° C. BRIEF DESCRIPTION OF THE DRAWINGS The above objects and other objects of the present invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: Figure 1 is a partial sectional view to show a mask of shadow made by a method according to a first embodiment of the present invention. Figures 2A to 2E are views to show a method for manufacturing a shadow mask according to a first embodiment of the present invention; Figure 3 is a partial sectional view for showing a shadow mask made by a method according to a second embodiment of the present invention; Figure 4 is a partial sectional view for showing a shadow mask made by a method according to a third embodiment of the present invention; Y Figure 5 is a sectional view showing a conventional color kinescope. Since the invention will be described and illustrated together with certain preferred embodiments and examples, it should be understood that it is not intended to limit the invention to those particular embodiments and examples. On the contrary, it is intended to cover all alternatives, modifications and equivalents that fall within the spirit and scope of the present invention as defined by the appended claims. Reference will now be made in detail to the present invention, and examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or similar parts. Referring first to Figure 1, a shadow mask 21 made by a method according to a first embodiment of the present invention is partially illustrated.

The shadow mask 21 comprises a shadow mask 25 of steel AK having a coefficient of thermal expansion of approximately 11.7 x 10"^ / K and is provided with a plurality of openings through which electron beams pass. of steel shadow AK 21 is placed on a face facing an electron gun (not shown) with a layer of low thermal expansion material 27. The layer 27 comprises one more materials selected from the group consisting of tungsten (W) , carbonated tungsten (WC) and bismuth (Bi) Layer 27 is formed to have a thickness of less than 50 μm, so that when the electron beams pass through the openings, the passing characteristic of the electron beams it will not be deteriorated, now referring to the method for making such a shadow mask 21 according to a first embodiment of the present invention together with figures 2A to 2E, as the first step, a screen mesh 31 of a material selected from the group consisting of stainless steel, polyester and nylon, is mounted on a frame 35. And then, a photoresist material 33 is placed on the entire surface of the screen mesh 31 in a constant thickness and then dry (see Figure 2A).

Then, as a second step, the photoresist material 33 placed on the screen mesh 31 is exposed to light, from a light source 20, through the steel shadow mask AK 25 (see Figure 2B) and the The unexposed portion of the resistive photo material 33 is etched, in this way, as shown in Figure 2E, forming a photoresist pattern 33 'corresponding to the openings 23 of the steel shadow mask AK 25 as shown in Figure 2C. . As the third step, the screen mesh 31, which runs through the steps described above, is mounted on a screen printer, which is well known in the art. And then, a metal paste 27 'is applied on the upper surface of the screen mesh 31 to a constant thickness (see Figure 2C). The paste comprises one or more materials selected from W, WC and Bi. Next, as the fourth step, the shadow mask 25 is disposed under the screen mesh 31 having the resistive photo pattern 33 'and the metal paste 27', then compressed by a compressor 39 to be moved in a direction with in order to print the metal layer 27 on the steel shadow mask AK 25 (see Figure 2D), thereby obtaining the shadow mask 21 as shown in Figure 2E. This step can be repeatedly performed two or more times, if required, to increase the thickness of the layer 27 or to print another metal material. It is also possible to regulate the thickness of layer 27 according to the types of screen mesh and paste, and printing pressure and speed. And, as the fifth step, the shadow mask 25 is compressed to thereby form a shirt portion and a projection thereof, thereby obtaining a finished shadow mask. The layer 27 made by the steps described above results in a layer of low thermal expansion as well as an electron reflection layer and a thermal radiation layer to suppress the bulge of the shadow mask 25. In more detail, the material used for layer 27 it has a thermal expansion efficiency of less than 4.5 x 10"6 /? This shows that the thermal expansion of the shade can be considerably reduced when considering that AK steel has a thermal expansion of approximately 11.7 x 10" 6 / K. Also, since each of the materials W, WC and Bi have a relatively high electron reflection efficiency of about 0.45-0.50, the amount of extinction of the electron beams incident to the shadow mask is reduced to thereby suppress the bulging of the shadow mask.

In addition, each of the materials W, WC and Bi has a relatively high thermal radiation coefficient of about 0.8-0.9, this also helps to suppress the bulging of the shadow mask. Figure 3 shows a shadow mask 210 made by a method according to a second embodiment of the present invention. The steel shadow mask AK 25 is placed on its opposite sides with the layer 27. To achieve this, before the fifth step of the first mode, the first to fourth steps are performed to print the layer on the other side. Referring to Figure 4, which shows a shadow mask 211 made through a method according to a fourth embodiment of the present invention, an alloy layer 29 is formed between the AK 25 steel shadow mask and the layer 27. The alloy layer is formed by diffusing substance from both the layer 27 and the steel shadow mask AK 25. To form the alloy layer 29 between the shadow mask 25 of steel AK and layer 27, in this fourth embodiment, a cementing process is additionally carried out by heating the shade mask 21 or 210, which is obtained through the first or second mode, in a neutral heating or reduction oven. The temperature of the heating furnace is set at approximately 850-1,200 ° C, in consideration of the fact that the temperature of the transformation point of the AK steel is approximately 800 ° C. However, the temperature of the heating furnace can be set at a relatively higher temperature according to the type of material. By means of this cementing process, between the layer 27 and the AK 25 steel shadow mask, a diffusion of substance occurs which results in a change of the inherent characteristic of the same to form the alloy layer 29. In more detail , the alloy layer 29 comprises alloy steel selected from the group consisting of Fe-W, Fe-WC and Fe-Bi. The alloy layer 29 has a coefficient of thermal expansion of about 4.5-11.7 x 10 ~ 6 / K.

This shows that the shadow mask obtained by this fourth embodiment has a lower amount of thermal expansion than that obtained by the first or second mode. In addition, each of the Fe-W, Fe-WC and Fe-Bi alloy steels has a relatively high thermal radiation efficiency.

Claims (6)

1. CLAIMS 1. A method for making a shadow mask for a color kinescope, characterized in that it comprises the steps of: forming a pattern, corresponding to the apertures of the shadow mask, on a screen mesh fixed to a frame; arrange a flat AK steel shadow mask under the screen mesh; printing a layer of material with low thermal expansion on one face of the AK steel shadow mask by compressing pastes of a low thermal expansion material onto the screen mesh at a constant pressure along one direction; and compressing the flat shadow mask to form a shirt portion and a projection portion of the shadow mask. The method according to claim 1, characterized in that the dough comprises one or more materials selected from the group consisting of tungsten, carbonated tungsten and bismuth. 3. The method according to claim 1, characterized in that the step of printing the layer is performed two or more times to increase the thickness of the layer. 4. The method according to claim 1, further characterized in that the layer is formed on the other face of the shadow mask of flat steel AK, the step procedure of forming the pattern to the step of printing one layer is applied further to the other face of the AK steel shadow mask flat. The method according to claim 1, further characterized in that it comprises the step of cementing the shadow mask, which is obtained after compressing the flat AK steel shadow mask, in a neutral heating or reduction furnace for induce the diffusion of substance from both the layer and the shadow mask of AK flat steel in order to obtain an alloy steel between the layer and the shadow mask of AK flat steel. 6. The method of compliance with the claim 5, characterized in that the temperature of the reduction heating furnace is set at approximately 850-1,200 ° C.