MXPA99000811A - Shading mask for cathode rays tube and method for its manufacture - Google Patents

Abstract

What is described is a shadow mask for a cathode ray tube (CRT) and a method for its manufacture. The shadow mask includes a solid solution hardening material and a precipitation hardening material. The method includes the steps of heat treating a metal plate having a series of openings formed in it using a carburizing gas, and forming by means of a press the metal plate into a mask shape of a shadow

Description

SHADOW MASK FOR CATHODE RAY TUBE AND METHOD FOR ITS MANUFACTURE DESCRIPTION OF THE INVENTION The present invention relates to a shadow mask for a cathode ray tube (CRT) and a method for its manufacture. More particularly, the present invention relates to a shadow mask for a CRT and a method for its manufacture in which a carburization process is used to produce the shadow mask, whereby improvements in the tensile strength are realized. and a degree of elongation. A conventional CRT shadow mask comprises a vacuum ampoule having therein a display screen comprising a range of phosphor elements of three different color emissions arranged in a cyclic order, means for producing three convergent directed electron beams to the screen, and a shade selection structure or shadow mask comprising a thin sheet of metal with several apertures precisely disposed between the screen and the beam production means. The shadow mask shades the screen, and the differences in the angles of convergence allow the portions transmitted from each beam selectively to excite the phosphor elements of the desired emission color.

The conventional CRT shadow mask is typically manufactured in the following manner. First, a photoresist is coated on a thin metal plate made of ferro-nickel or steel deoxidized with aluminum. The plate is then exposed to light, and revealed and etched to form a series of holes in it. Then, the plate formed with the holes is annealed using a heat treatment process in a high temperature hydrogen atmosphere, whereby the internal strength is removed and the plate is malleable. The plate is then formed into a predetermined mask shape with the help of a press after which the plate is cleaned to remove all surface contaminants including fingerprints, dust and other foreign substances. Finally, a process of encrusting takes place in the formed plate to prevent the pandeamiento of the same with which the manufacture of the mask of shadow is completed. The shadow mask acts as a bridge between the electron beams emitted from the three electron guns (means to produce three convergent electron beams) and phosphorus pixels R, G, B, formed on a panel, ensuring that the electron beams they land on the correct phosphor pixels. Therefore, any deviation of the shadow mask from its original position acts to maldirigir the electron beams to excite the incorrect phosphor pixels. The shadow mask can be repositioned on the CRT if it receives an external shock or vibration, or as a result of the impact of the mounted horns on the system to which the CRT is applied. That is, if the CRT receives a substantial degree of such forces, the shadow mask moves in the CRT in such a way that the electron beams that pass through it land on the incorrect phosphor pixel, thereby deteriorates the purity of color. This will be described in more detail hereinafter. FIGURE 1 shows a partial sectional view of a conventional CRT used to describe the change of a shadow mask caused by an external shock. As shown in the drawing, the CRT includes a panel 1, a phosphor screen 2 formed on an inner surface of the panel 1, and a shadow mask 6 fixedly suspended at a predetermined distance from the phosphor pixel screen 2 and having a series of openings (not shown) formed therein. The shadow mask 6 is mounted to a side wall of the panel 1. That is, a mask box 5 attached to the periphery of the shadow mask 6 is connected to a spring 4, and the spring 4 is connected to a latch pin. projection 3 protruding from the side wall of the panel 1. An electron gun 11 is mounted on a funnel (not shown) of the CRT and emits electron beams 10 in a direction towards the shadow mask 6. When the CRT receives a shock substantial external or vibrations, the shadow mask 6 is vibrated and moved from its initial position to a deviated position 7, as a result, electron beams 10 emitted from the electron gun 11 pass through an incorrect opening of the shadow mask 6. This is, a beam of electrons passing through a predetermined aperture 8 of the shadow mask 6, passes through an incorrect aperture 9 as a result of the shadow mask 6 moving to the deviated position 7. Therefore, a position Pl in the phosphor screen 2 in which the electron beam 10 settles, is altered to the deviated position P2, resulting in the excitation of the incorrect phosphor pixel, this causes the movement of the displayed image, a reduction in purity of color and other problems of image quality. Furthermore, in the case where the CRT receives an extreme shock, as for example if the system in which the CRT is installed is dropped, it is possible that the shadow mask 6 is deformed. An example of this is shown in Figure 2 in which a deformed area 12 is illustrated. When the electron beams 10 pass through the deformed area 12, the aforementioned problems of the movement of the displayed image and the reduction in the purity of the color occur, in addition to the generation of false colors. To remedy the problems described above, Japanese Patent Laid-Open No. Sho 62-223950 describes a technique for improving the tensile strength of the shadow mask by forming an electrolytic layer below. However, the size of the opening is diminished when this technique is used. Also, Japanese Patent Laid-Open Nos. Sho 56-121257 and Hei 1-276542 each describe a technique for improving the tensile strength of the shadow mask by treating it by equal heat in a gaseous atmosphere. However, in these conventional methods the shadow mask is thermally deformed as a result of heat treating the same for long periods during the manufacturing process. The present invention has been made in an effort to solve the aforementioned problems. It is an object of the present invention to provide a shadow mask for a cathode ray tube (CRT) in which improvements in the tensile strength and the degree of elongation of the shadow mask are realized in such a way that the deformation of same caused by the external shock is prevented.

It is another object of the present invention to provide a shadow mask for a cathode ray tube (CRT) in which an improvement in a modulus of elasticity for the shadow mask is obtained so that it is not negatively influenced by external vibrations. and vibrations caused by the operation of horns in a system for which the CRT is applied. It is still another object of the present invention to provide a method for manufacturing a shadow mask for a CRT in which no thermal deformation of the shadow masks occurs during the manufacture of the same. To achieve the aforementioned objectives, the present invention provides a shadow mask for a CRT and a method for manufacturing it, the shadow mask includes a solid solution hardening material and a precipitation hardening material. The method includes the steps of heat treating a metal plate having a series of openings formed in it using a carburizing gas, and a press forming the metal plate to the shape of a shadow mask. According to one feature of the present invention, the solid solution hardening material and the precipitation hardening material comprise carbon.

According to another feature of the present invention, the amount of carbon contained in the shadow mask is 0.01 to 2.0 parts by weight based on the weight of the shadow mask. According to yet another feature of the present invention, the shadow mask is made of a low thermal expansion material. According to yet another feature of the present invention, the shadow mask is made of deoxidized steel with aluminum or ferro-nickel. According to yet another feature of the present invention, the carburizing gas comprises an RX gas and a propane gas. According to yet another feature of the present invention, a temperature of the heat treatment step is 600 to 1000 ° C. According to yet another feature of the present invention, the heat treatment step is conducted for a period of 0.1 to 5 hours. * BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated and constitute a part of the specification, show an embodiment of the invention, and, together with the description, serve to explain the principles of the invention: FIGURE 1 is a partial cross-sectional view of a conventional CRT used to describe the change of a shadow mask caused by an external shock; FIGURE 2 is a partial cross-sectional view of a conventional CRT used to describe the damage to a shadow mask caused by extreme external shock; and FIGURE 3 is a graph showing a tensile strength and a degree of elongation of a shadow mask manufactured without having undergone a conventional annealing process; FIGURE 4 is a graph showing a tensile strength and a degree of elongation of a shadow mask manufactured after having undergone the conventional annealing process; and FIGURE 5 is a graph showing a tensile strength and a degree of elongation of a shadow mask manufactured using a carburization process according to a preferred embodiment of the present invention. A shadow mask for a CRT of the present invention is made of a low thermal expansion material such as a steel deoxidized with aluminum or ferro-nickel including a solid solution hardening material and a hardening precipitation material.

An inventive method for making a shadow mask for CRT will be described hereafter. A predetermined number of metal plates made of a low thermal expansion material such as deoxidized steel with aluminum or ferro-nickel, and having a series of openings formed in a predetermined area to form the opening portions, it is stacked and loaded on a tray. After setting a temperature of a preheating oven of between 500 to 700 ° C, the tray having the metal plates stacked next is placed in the preheating oven. After a temperature in a reaction furnace is increased to more than 150 ° C, a carburizing gas comprising an RX gas and a propane gas is fed to the reaction furnace. Here, the RX gas is composed of 40% H2, 40% N2 and 20% CO in terms of the speed at which the carburizing gas is injected into the reaction furnace, the RX gas is injected into it. speed of 5 to 25 liters per minute and propane gas is injected into it at a rate of 1 to 10 liters per minute. Subsequently, the temperature in the reaction furnace is increased from 600 to 1000 ° C, and the gaseous atmosphere therein is suitably maintained, after the metal plates in the preheating furnace are transferred to the reaction furnace.

In the above, if the temperature of the reaction furnace is maintained within the range described above, the RX gas and the propane gas are split so that they generate free carbon and a minimum amount of nitrogen. Free carbon and nitrogen effectively penetrate the shadow mask. At this time, since carbon is mainly generated, the resulting effects are almost entirely those resulting from the penetration of free carbon, different from that of nitrogen. The metal plates are treated with heat in the atmosphere of carburizing gas inside the reaction furnace for between 0.1 and 5 hours. A heat treatment time of less than 0.1 hours results in an insufficient reaction between the metal plates and the gases, while it is not necessary to exceed 5 hours since the effects of heat treating the metal plates is completely carried out before This weather. With respect to the preferred temperature range of the reaction furnace, if the temperature in it is not increased until it reaches the lower limit of 600 ° C, while the gas separation does not occur, the heat treatment process is not effective , whereas if the temperature exceeds 1000 ° C, deformation of the shadow mask can occur. On the other hand, it is possible to directly place the metal plates in the reaction furnace without first heating them in the preheating furnace. However, placing the metal plates first in the preheating oven allows a more gradual increase in the temperature of the metal plates, in addition to preventing an abrupt temperature decrease thereof after the heat treatment process. After the carburization process is completed, the temperature in the reaction furnace is reduced to 150 ° C while the atmosphere in it is maintained in the present state. When this temperature is reached, the injection of the gas into the reaction furnace is discontinued. Then, the metal plates are removed from the reaction furnace, and the metal plates are then formed into a press in the form of desired shade masks. Due to the limited thickness of the metal plates used to form the shadow masks, a rolling process must be carried out a number of times during its manufacture. Therefore, followed by the formation of the openings in the metal plates using a gravure process, an annealing process is required before forming the metal plates in the desired shape by means of a press. As shown in FIGURE 3, if the annealing process is not carried out, although a resistance to the tension of the shadow mask is high, a degree of elongation is. low, with which it becomes impossible to form by means of a press the metal plates in the form of shadow mask. Therefore, it is necessary to conduct the annealing process. However, as shown in FIGURE 4, annealing the metal plates significantly lowers the tensile strength while increasing the degree of elongation. Therefore, the present invention, instead of using the conventional annealing process, uses a carburization process, whereby both the degree of elongation and the tensile strength of the metal plates used to make the masks are increased. of Shadows. With respect to the carburization process, carbon monoxide (CO) is generated using RX gas and propane gas in a reaction furnace maintained at high temperatures. Carbon monoxide is penetrated or diffused in the shadow mask such that a Fe-Ni-C compound or a reaction material such as Fe3C is formed as a result of a reaction between carbon monoxide and the shadow mask. The carbon compound is used and precipitated in a matrix of the metal plates used to make the shadow masks, thereby hardening them. At this time, the amount of carbon contained in the shadow masks is 0.01 to 2.0 parts by weight based on the weight of the shadow masks.

As can be seen in the graphs, the tensile strength of the shadow masks manufactured using the method of the present invention approaches that of the previous shadow mask without having to undergo the annealing process and is significantly larger (approximately 100 Mpa) to the conventional annealed shadow mask. In addition, the degree of elongation of the inventive shadow mask is larger than the conventional non-annealed shadow mask, and slightly improved over the conventional annealed shadow mask. Consequently, defects of the shadow mask that occur during the various manufacturing processes are minimized, and the change in shadow mask deformation caused by external shocks is reduced. Furthermore, the rolling formation of the metal plates used for the manufacture of the shadow mask after they have been subjected to the heat treatment process is more easily done and a dye can be more uniformly formed in such a way that a sufficient degree of elongation can be obtained. Additionally, since a modulus of elasticity of the inventive shadow mask is increased, the vibration caused by external vibrations and the vibration generated by the horns is reduced. The present invention is explained in more detail with reference to the following example.

Example 1 A predetermined number of metal plates, having a series of openings formed over a predetermined area to form the opening portions, were stacked and loaded onto a tray. Then, a temperature of a preheat oven was set and maintained at 650 ° C, after which the tray having the metal plates stacked next was placed in the preheating oven. A temperature in a reaction furnace was increased to more than 150 ° C, and a carburizing gas comprising an RX gas and a propane gas was fed into the reaction furnace at a rate of 15 liters per minute for the RX gas and three liters per minute for propane gas. Subsequently, the temperature in the reaction furnace was increased to 850 ° C and the gaseous atmosphere therein was suitably maintained, after which the metal plates in the preheating furnace were transferred into the reaction furnace. Following the foregoing, the metal plates were treated with heat in the atmosphere of carburizing gas inside the reaction furnace for 1 hour, then the temperature in the reaction furnace was reduced to 150 ° C while the atmosphere in it was maintained in the present state. After this temperature was reached, the injection of gas into the reaction furnace was discontinued.

Then, the metal plates were removed from the reaction furnace, and then formed by means of a press to the desired shadow mask shape. The amount of carbon contained in the shadow mask was found to be 0.01 parts by weight based on a weight of the shadow mask. Although the present invention has been described in detail hereinbefore, it should be clearly understood that many variations and / or modifications of the inventive basic concepts taught herein, which may seem to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.

Claims (11)

1. CLAIMS 1. A shadow mask characterized in that it comprises: a solid solution hardening material and a precipitation hardening material. The shadow mask according to claim 1, characterized in that the solid solution hardening material and the precipitation hardening material comprise carbon. 3. The shadow mask according to claim 1, characterized in that the amount of carbon contained in the shadow mask is 0.01 to 2.0 parts by weight based on the weight of the shadow mask. 4. The shadow mask according to claim 1, characterized in that the shadow mask is made of a low thermal expansion material. 5. The shadow mask according to claim 1, characterized in that the shadow mask is made of steel deoxidized with aluminum or ferro-nickel. 6. A method for manufacturing a shade mask characterized in that it comprises the steps of: heat treating a metal plate having a series of openings formed therewith using a carburizing gas; and forming by means of a press the metal plate to a shadow mask shape. 7. The method according to claim 6, characterized in that the shadow mask is made of a low thermal expansion material. 8. The method according to claim 6, characterized in that the shadow mask is made of steel deoxidized with aluminum or ferro-nickel. 9. The method according to claim 6, characterized in that the carburizing gas comprises a gas RX and a propane gas. The method according to claim 6, characterized in that a temperature of a heat treatment step is 600 to 1000 ° C. 11. The method according to the claim 6, characterized in that the step of treating with heat is conducted for a period of 0.1 to 5 hours.