Glass bulb for a cathode ray and a method of producing the same

Abstract

A glass panel 3 for a glass tube for a cathode ray tube has a flat panel face portion 7 and a reduced thickness while maintaining a sufficient strength without increasing a difference of brightness, and with less shrinking deformation due to the cooling and solidification of the glass panel. Compressive stress layers 20, 21 having a thickness of to / 10 or more are formed in outer and inner surfaces of the face portion 7 of the glass panel 3 respectively. The relation to the wall thickness td of the central portion of the face portion to the wall thickness to of a portion near an edge portion on a diagonal line is 1.0< / =td / to< / =1.2. Compressive stress layers 22, 23 are formed in outer and inner surfaces of a skirt portion 6 wherein the compressive stress value of the face portion 7 is larger than the compressive stress value of the skirt portion, and the compressive stress value of the outer surface 20 of the face portion is larger than that of the inner surface 21.

Description

BACKGROUND OF THE INVENTIONFIELD OF THE INVENTIONThe present invention relates to a glass bulb for a cathode ray tube (a Braun tube) used for TVs and a method of producing the same. More particularly, the present invention concerns the structure of a glass panel constituting the display surface of the glass bulb and method of producing the glass panel.DISCUSSION OF BACKGROUNDFIG. 3 shows the construction of a cathode ray tube used for a TV or the like. The cathode ray tube 1 comprises a glass bulb 2 which is basically constituted by a glass panel portion 3 constituting a picture displaying surface, a funnel portion 4 in a funnel-like form which is airtightly joined to the glass panel portion 3 and a neck portion 5 in which an electron gun 17 is installed. The glass panel 3 comprises a substantially rectangular face portion 7 for constituting a picture displaying surface and a skirt portion 6 extending from the circumferential portion of the face portion 7 in substantially perpendicu...

AI Technical Summary

Benefits of technology

It is an object of the present invention to provide a glass bulb of a cathode ray tube and a method of producing the same wherein the outer surface of the face portion is flat; the wall thickness of the entire portion of the glass panel is reduced and the strength to a mechanical shock is improved without causing a large difference of brightness between the central portion and a peripheral portion of the face portion.

In the present invention, the compressive stress layers are formed by cooling the face portion faster than the skirt portion of the glass panel portion. Accordingly, deformation in the face portion due to the shrinkage and solidification of the skirt portion can be minimized. Accordingly, improvement in accuracy of radius of the inner surface of the face portion is more than double in comparison with that of the conventional face portion. Further, the compressive stress layers are so formed that the stress value of the compressive layer in the outer surface of the face portion is equal to or larger than that of the inner surface. Accordingly, the effect of preventing the deformation of the face portion is further increased.

Problems solved by technology

Accordingly, if a mechanical shock is applied to the glass bulb and a crack or breakage is resulted in a local portion, the local crack or the local breakage is instantaneously developed to release a stored strain energy; thus, implosion is resulted.

However, the inside of the glass is in a state having a sufficient fluidity and expansion, and a temporal distortion is instantaneously released by the fluidity.

When the glass bulb is further cooled, the inside of the glass tends to shrink.

However, the movement of shrinkage is limited by the solidified surface layer.

In the conventional glass bulb for a cathode ray tube, when the radius of curvature of the glass panel is made small in order to increase the strength of the panel to a shock, visibility becomes poor and pictures are unclear.

However, there arises a problem that when the face portion is made flat, it becomes weak to a mechanical shock.

Further, when the reinforcing band is attached to the glass panel, an uneven fastening force is applied to the skirt portion which is joined to the peripheral edge of the face portion, and stable and highly reliable implosion-proof properties can not be obtained with the result that the purpose of reinforcing of the face portion can not be sufficiently achieved.

On the other hand, when the entirety of the face portion is made thick to obtain sufficient reinforcement, the weight of the face portion is increased, and handling properties becomes worse.

Although such structure reduces the weight of the glass panel, there arises a problem that the light transmittance at the central portion of the face portion differs from that at a peripheral portion of the face portion due to the difference of thickness, and difference in brightness in picture image becomes large to thereby decrease the quality of display.

However, when the wall thickness is made uniform while the face portion is formed to be flat, the implosion-proof properties are decreased, and the glass panel portion is apt to be broken by a slight impact.

In order to reduce the weight, when the radius of curvature of the front surface of the face portion is reduced so that the central portion of the face portion is formed to be thin while the end portions are formed to be thick, there arises problems that there is a large difference of brightness between the central portion and the end portions of the face portion and visibility decreases.

This reduces the accuracy of the radius of curvature in the inner wall of the face portion, and the face portion becomes unstable.

When a color TV with such glass panel is used, there may cause a fault in electron beam landing characteristics and a stable colored picture can not be obtained.

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