JPH028007B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a material for a shadow mask with excellent magnetic properties, and more specifically, the present invention relates to a method for producing a material for a shadow mask that is not affected by external magnetic fields and therefore does not cause color shift. Regarding manufacturing methods. Conventional materials for shadow masks are mainly made by first cold rolling continuously cast low carbon aluminum killed hot rolled steel strip, passing it through an electric cleaning line, decarburizing it by open coil annealing, and then second cold rolling. It was manufactured by making a cold-rolled coil of a predetermined thickness and making it into a slit coil of a predetermined width. The reason for choosing continuous casting low-carbon aluminum killed steel as a raw material steel is that it is more suitable for the mask material for the product shadow mask than the previous ingot material rimmed steel or capped steel (both of which may be referred to as rimmed steel hereinafter). It has excellent etching properties and mechanical properties in the manufacturing process. In other words, the previous ingot-based rimmed steel had a high-purity rim layer on the surface and was characterized by a beautiful surface, but because it was an ingot material, there was a difference in composition between the top and bottom parts of the ingot. In addition, many impurities such as nonmetallic inclusions were present, making it impossible to obtain a homogeneous product shadow mask material. For this reason, for example, there was a tendency for so-called gaza holes to occur during the etching process. Furthermore, since the N in rimmed steel is not fixed as AlN as in aluminum killed steel, there is a problem in mechanical properties that stretcher strain occurs during press forming in the subsequent process. Therefore, the previous problems were successfully solved by using continuous cast aluminum killed steel material, which is homogeneous and has high cleanliness. However, surprisingly, there were hidden problems with this latest material for shadow masks, which was thought to be perfect. This is a color shift phenomenon in completed color cathode ray tubes. That is, it is true that color cathode ray tubes are constantly exposed to the earth's magnetic field and other external disturbing magnetic fields, and that the electron beams in the cathode ray tubes are affected by this. As a countermeasure against this problem, color TV receivers usually incorporate a degaussing mechanism. However, from the viewpoints of cost reduction, compactness, and energy saving, this demagnetization mechanism is not perfect, and re-magnetization always occurs after demagnetization. Therefore, the magnetic properties of the shadow mask itself in the color cathode ray tube are related to the color shift phenomenon. As a result of the study, it is the coercive force that has the most influence on the demagnetizing characteristics among the magnetic properties.
It was confirmed that it was Hc. In other words, it has been found that the smaller the coercive force, the easier it is to demagnetize, and therefore the less likely color misregistration will occur. It was discovered that the coercive force of the shadow mask made from continuously cast aluminium-killed steel was slightly larger than that of conventional rimmed steel. Further investigation revealed that the reason why the coercive force of the shadow mask made from continuously cast aluminium-killed steel material is rather large is mainly due to the fineness of the crystal grains, and therefore the grain boundaries become an obstacle to domain wall movement. It was inferred. Therefore, the inventors of the present invention devised a manufacturing process for a material for a shadow mask using continuously cast aluminium-killed steel as a raw material, and by growing the crystal grains of the product shadow mask to a larger size, the magnetic properties of the product could be improved.
We have discovered that color shift can be reduced, and have arrived at the present invention. The method of the present invention was found to be effective not only for continuously cast aluminum killed steel materials but also for rimmed steel (capped steel) ingot materials. The purpose of the present invention is to provide a method for manufacturing a material for a shadow mask that not only has good etching properties and press formability, but also has excellent magnetic properties, especially low coercive force, and does not cause color shift in product color cathode ray tubes. be. Another object of the present invention is to provide a method for producing a shadow mask material with improved magnetic properties by simply adding the steps of high dew point annealing and tertiary cold rolling to the conventional manufacturing process for shadow mask materials. It is in. According to the present invention, a hot-rolled steel strip made of aluminum killed steel continuous casting material, which is a raw material, is subjected to first cold rolling, open coil decarburization annealing, second cold rolling, and dew point adjustment using a mixed gas of N ₂ and H ₂ in the atmosphere. A material for shadow masks with excellent magnetic properties, which is subjected to the following steps: high dew point annealing, which is box-type annealing at temperatures between 0°C and 25°C, and tertiary cold rolling at a rolling reduction of 10% to 50%. A manufacturing method is provided. The present invention will be explained in detail below. First, for comparison, a conventional method of manufacturing a shadow mask material and a method of manufacturing a shadow mask using the shadow mask material will be briefly described. Conventional materials for shadow masks are made by first cold-rolling a hot-rolled steel strip of low-carbon rimmed steel or aluminium-killed steel, passing it through an electric cleaning device, and decarburizing it by so-called open coil annealing.
It was usually manufactured by cold rolling the coil to a predetermined thickness to form a slit coil. The slit coil then goes through a photoetching process and a mask forming process. That is, the slit coil is coated with photoresist on both sides, dried, and then a reference pattern (slot or dot shape) is vacuum-adhered to both sides, exposed to light from both sides, and then developed. The photoresist in the unexposed area (the area to be perforated) is dissolved and removed by development, and then the remaining photoresist is hardened by heating (burning). The slit coil is then etched with holes of a predetermined size in the portions not protected by the photoresist using a ferric chloride solution. The remaining photoresist on the surface of the slit coil is then dissolved and removed by a hot alkaline solution. The slit coil that has undergone the etching process is then sheared and subjected to an inspection process to become a flat mask. The flat mask is then annealed in a gas atmosphere (flat mask annealing). This annealing includes so-called dry annealing in a dry atmosphere for the sole purpose of removing distortion, and so-called wet annealing in a wet atmosphere for the purpose of decarburization treatment to further improve workability. The flat mask after annealing is then passed through a leveler (leveling). This eliminates the elongation at yield point and prevents stretcher strain in the next press forming process.
This is also to correct plate distortion caused by annealing. Subsequently, the flat mask is press-molded to have a predetermined curved surface, and finally subjected to a blackening treatment using a vapor phase or liquid phase to become a shadow mask. The above is a conventional general shadow mask material and a method for manufacturing a shadow mask. Therefore, the feature of the present invention is that, as mentioned above, two steps of high dew point annealing and tertiary cold rolling are added to the conventional manufacturing process of a material for a shadow mask. However, since the purpose is to improve the performance of preventing color shift in color cathode ray tubes, it is not unrelated to the shadow mask manufacturing process mentioned above. The characteristic steps of the present invention will be described below. High dew point annealing High dew point annealing is a process applied to a hot rolled steel strip after it has undergone the following steps: primary cold rolling, electrical cleaning, open coil decarburization annealing, secondary cold rolling, and electrical cleaning. . The electric cleaning step after the secondary cold rolling is for removing rolling lubricating oil that adhered during the secondary cold rolling. In principle, high dew point annealing is performed by the box annealing method. The thickness of the steel strip after secondary cold rolling is approximately 0.1 to 0.6 mm, and if it is thicker than approximately 0.4 mm, open coil annealing using a loose coil is also possible.
Generally, box annealing is performed using tight coils. However, in the present invention, the soaking time is not particularly regulated, but only the dew point of the annealing atmosphere is regulated, so a continuous annealing method may be used. It goes without saying that a more homogeneous product can be obtained in a shorter time by open coil annealing or continuous annealing. The annealing temperature in this process is 560
The temperature is about 700℃. This is because recrystallization may not occur at temperatures below 560°C, and on the other hand, when the temperature exceeds 700°C, sticking occurs between the surfaces of the steel strips. The dew point of the annealing atmosphere is increased to create a decarburizing atmosphere. That is, the dew point of the atmosphere inside the annealing furnace is set to 0°C to +60°C, preferably 0°C to +25°C. Various metamorphic gases are mainly used as the carrier gas.
Metamorphic gases include exothermic gases such as NX gas, HNX gas, and BC gas. Also HX gas, AX gas, _N2
Non-carburizing (low CO/CO ₂ partial pressure ratio) endothermic metamorphosed gases such as gas and SAX gas are also used. In addition, the carrier gas may be one or a combination of two or more of H ₂ gas, N ₂ gas, and inert gases such as Ar and He. In short, the atmospheric gas in the high dew point annealing of the present invention only needs to be a decarburizing atmosphere, and includes not only a decarburizing non-oxidizing region but also an oxidizing region. Therefore, although it is called high dew point annealing, a low dew point (dry) gas with a dew point of 0° C. or lower may be used in some cases. For example, in the case of _H2 gas, it is not necessary to
Even if the partial pressure of H ₂ O (water vapor) is not high, it may function as a decarburizing gas if the partial pressure ratio of CO/CO ₂ is sufficiently small. In the present invention, annealing using such a low dew point gas is also included in the concept of high dew point annealing to distinguish it from other processing steps. In short, the C content of the steel strip is 0.004% due to the preceding open coil decarburization annealing.
(wt%) or less, so
This is to deal with the fact that it is extremely easy to carburize. Therefore, the atmospheric gas dew point range mentioned above is 0°C to +60°C.
℃ does not necessarily limit the invention. That is, high dew point annealing in the present invention means non-carburizing annealing.
In the case of box annealing, a well-known decarburization cycle is used: a low dew point (dry) atmosphere gas is supplied into the furnace at the initial stage of heating, and a high dew point (wet) atmosphere is supplied after the coil temperature reaches a certain temperature. supply gas,
Gradually lower the dew point and perform so-called dry soaking.
It is desirable to adopt a decarburization cycle in which the material is cooled in a low dew point (dry) atmospheric gas. This is to prevent oxidation of the steel strip surface. It is also possible to apply the same cycle with continuous annealing. Tertiary cold rolling Tertiary cold rolling is performed on the steel strip subjected to the above-mentioned high dew point annealing. Although a two-stand four-high cold rolling mill is used in the embodiments described below, the rolling mill type may be any other type other than the four-high rolling mill. That is, it may be a cluster mill such as a Sendzimir mill or a Y-type mill, a five- or six-stage HC mill or VC mill, or a multi-stand tandem mill of these mills. The rolling lubricating oil can also be palm oil, tallow-based rolling oil, other synthetic rolling oils, or emulsions. That is, there are no particular regulations regarding rolling oil. In the tertiary cold rolling process, for example, 10% to
This involves applying a reduction rate of approximately 50% to the steel strip. However, due to the nature of the product, sufficient roughness and shape control must be performed. FIG. 1 is a semi-logarithmic graph showing the relationship between the tertiary cold rolling ratio and coercive force after flat mask annealing at 700°C for 10 minutes. As shown in Figure 1, the tertiary cold rolling ratio of the present invention is 10% to 10%.
It can be seen that the coercive force is the smallest in the 50% region. The reason is that when the tertiary cold rolling rate is less than 10%,
This is because the recrystallization temperature during flat mask annealing becomes high due to the small rolling strain, and grain growth is insufficient, so a decrease in coercive force cannot be expected. This is because sufficient crystal grain growth cannot be achieved under normal flat mask annealing heating conditions due to excessive rolling strain. In addition, Fig. 1 shows comparative examples No. 3, No. 5, and No. 6, which will be described later.
The results in Table 1 are also listed to facilitate comparison. Steel strips that have been given a rolling reduction of 10 to 50% through tertiary cold rolling have been subjected to moderate processing strain, so their crystal grains grow during the flat mask annealing process of the shadow mask manufacturing process, resulting in fewer grain boundaries. . However, if the grains grow excessively, orange peel (rough skin) will occur during the pressing process, so the final grain size may be reduced.
Conditions for ASTM No. 5 to 9, preferably,
Conditions must be selected that result in ASTM No. 6-7. All of the above objectives are achieved by implementing the invention as detailed above. In other words, by simply adding two processes, high dew point annealing and tertiary cold rolling, to the manufacturing process of the material for shadow masks, it is possible to create a color with minimal color shift while satisfying all the conventionally required performances such as etching properties and press formability.
Materials for shadow masks for TV cathode ray tubes can be obtained. The present invention will be explained in more detail below using Examples. [Example] Table 1 shows examples of materials for shadow masks manufactured using continuous cast aluminum killed steel, rimmed steel ingot, and vacuum degassing material as raw material hot-rolled steel strips. Nos. 1 to 4 in Table 1 are continuous cast aluminum killed steel materials.
Open coil decarburization annealing (hereinafter abbreviated as OCA) after the next cold rolling, No. 5 and 6 are continuous cast aluminum killed steel materials without OCA (however, normal bright box annealing is performed), No. 7, 8 is ingot material rimmed steel,
Those subjected to OCA, Nos. 9 and 10 are comparative examples using a vacuum degassing material, and Nos. 2 and 4 are examples of the present invention. The manufacturing process for the No. 1 continuous cast aluminum killed steel material/decarburized OCA is the same as that for ordinary shadow mask materials, and because it does not undergo high dew point box annealing or tertiary cold rolling, it has poor magnetic properties and beam misalignment. It's also big.
However, since it uses continuously cast aluminium-killed steel, it has excellent etching and press formability.
No. 2 is the same as No. 1, but the magnetic properties are greatly improved by performing the high dew point box annealing (dew point +10°C) and tertiary cold rolling (reduction ratio 20%) of the present invention. Therefore, the beam shift was also improved. Furthermore, since it is a continuously cast aluminium-killed steel material, it has excellent etching properties and press formability.

【table】

[Table] The material of No. 3 is tertiary cold rolled (reduction rate
20%), but because the dew point during box annealing was low (dew point -40°C), the magnetic properties and beam deviation are at the limit. Although it has excellent etching properties, the aluminum killed continuous cast steel shadow mask material is very sensitive to the dew point during annealing, and in a dry atmosphere, the properties tend to vary locally (particularly the yield point after flat mask annealing tends to vary). The press formability was unstable and it was unsuitable as a shadow mask material. No. 4 is a shadow mask material within the scope of the present invention, which is the same as No. 2. However, the tertiary cold rolling rate was 10% higher than that of No. 2, and the magnetic properties and beam deviation were also worse than in Example 2. However, with this magnetic property and beam deviation, it can be used for color television cathode ray tubes. Nos. 5 and 6 use continuously cast aluminium-killed steel materials, but because they are non-OCA materials (normal bright box annealing), their magnetic properties are poor even after high dew point annealing and tertiary cold rolling. . Furthermore, since it was a non-OCA material, its mechanical properties were poor and press molding was impossible. No. 7 is an ingot rimmed steel that has been used as a material for shadow masks for a long time before continuous cast aluminum killed steel, but it has good magnetic properties even without tertiary cold rolling or high dew point box annealing. The beam shift is also small and good. However, the etching property and press formability are inferior to the continuous cast aluminum killed steel OCA samples (No. 1, 2, and 4). No. 8 is the same material as No. 7, and is subjected to high dew point box annealing and tertiary cold rolling, so its magnetic properties and beam deviation are even better than No. 7. . However, apart from etching properties, it is of course inferior to No. 7 in terms of press formability, not to mention the continuous casting of aluminum killed steel. As described above, this is due to the poor press formability due to the scheme of improved magnetic properties, coarsening of crystal grains, and deterioration of press formability. Vacuum degassing material OCA samples No. 9 and 10 are 3
The magnetic properties are good even without subsequent cold rolling or high dew point box annealing. However, it could not be used in cathode ray tubes for color televisions due to poor press moldability.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between tertiary cold rolling ratio and coercive force.

Claims (1)

[Claims] 1 A hot-rolled steel strip made of aluminum killed steel continuous casting material, which is a raw material, is subjected to primary cold rolling, open coil decarburization annealing, and secondary cold rolling in a mixed gas atmosphere of N ₂ and H ₂ and a dew point of 0°C. A method for producing a material for a shadow mask with excellent magnetic properties, which is characterized by performing the following steps: high dew point annealing, which is box-shaped annealing at a temperature of 10% to 50%.