GB2132409A

GB2132409A - Cathode ray tube with a protruded face plate

Info

Publication number: GB2132409A
Application number: GB08330612A
Authority: GB
Inventors: Toshio Taniguchi; Tsunehiko Sugawara
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 1982-12-01
Filing date: 1983-11-16
Publication date: 1984-07-04
Also published as: JPS59101747A; JPH0234411B2; DE3343359A1; GB8330612D0

Abstract

A cathode ray tube with a protruded face plate having a panel face consisting of an useful screen area 1 and a panel face circumferential part 2 extending around said useful screen area, in which the panel face useful screen area 1 projects from said panel face circumferential part 2. The panel face useful screen area 1 is to be polished. A reinforcing rim 5 is attached to the tube. <IMAGE>

Description

SPECIFICATION Cathode ray tube with a protruded face plate The present invention relates to a cathode ray tube with a protruded face plate having a useful screen area of a panel; face projecting from a level of the circumferential part of the panel face.

In a cathode ray tube whose front imageviewing part is constituted by a glass panel, such panel portion is formed by a pressing operation.

When heat-softened glass contacts with a mold in press forming operation, the glass is cooled and solidified whereby a stain or cioudiness is produced in the useful screen area of the panel face portion to lower the quality of the products from the optical standpoint.

There has so far been conducted a polishing operation to the useful screen area to maintain an optical property of the panel face portion.

The panel face portion comprises as shown in Figure 1 a panel face useful screen area 1 and a panel face circumferential part or a blend radius area 2 extending around the useful screen area.

The useful screen area is usually formed by a continuously curved surface consisting of spherical, cylindrical and flat surfaces and so on and continues the blend radius area 2 of the panel.

The polishing operation is carried out along the curved surface above-mentioned. In this case, the area to be polished can not be limited to the useful screen area and is unnecessarily spread to the panel face circumferential part 2 with the result that fine scratches caused by polishing are contained in this area. Particularly, since working efficiency to polish the useful screen area contiguous to the circumferential part tends to decrease, relatively large scratches caused by grinding operation before the polishing operation may not be sufficiently removed, even though polishing operation is carried out after grinding.

On the other hand, the cathdoe ray tube is subjected to a heat cycle such as baking, exhausting air and so on during assembling process of it. In this case, a large thermal stress is produced in the blend radius area and its vicinity which have a thickness of glass greater than the other portions and presence of the fine scratches caused by polishing invites concentration of stress to thereby take place breaking of the cathode ray tube.

In the assembling process after the exhausting air, the cathode ray tube is highly evacuated so that atmospheric pressure is applied to the cathode ray tube from the outside. This external force causes a large tensile stress to the portion between the side wall part 3 of the panel and the blend radius area 2 because of the structure of the cathode ray tube. For a 20-inch cathode ray tube, for example, a tensile stress as much as 40 kg/cm80 kg/cm2 takes place. On account of this, when the cathode ray tube suffers a mechanical impact, destruction occurs at the above-mentioned portion. The derived destruction causes severe implosion because vacuum is rapidly lost whereby glass fragments scatter dangerously.In order to prevent such destruction, it is important to eliminate fine scratches as a source of stress concentration in an area where a high tensile stress stakes place.

As a method for preventing the implosion of the cathode ray tube, it is usual to reinforce the side wall portion of a panel as shown, for example, in Japanese Examined Publication No. 4858/1977.

There have been proposed various methods.

However, it is confirmed through mechanical impact tests that a method specified below has an effect to prevent the scattering of glass fragments, the method being such that as shown in Figure 3, the entire circumference of the side wall 3 of the panel including a part of panel face is covered by an L-shaped rim 5 which is tightened by an annular tension band 6. Use of the L-shaped rim covering the circumferential part of the face plate, however, renders the cathode ray tube set to project from the panel face for the thickness of the rim and a gap (a) is produced between the enclosure 7 and the cathode ray tube to lose fitness property. Under usual condition of using, for instance, a 20-inch cathode ray tube, a voltage as high as 20 KV-28 KV is also applied the rim.

When the fitness is poor, a foreign matter such as a conductive material puts into the gap between the enclosure and the panel face to cause an accident of electric shock.

It is an object of the present invention to overcome the disadvantages of the conventional cathode ray tube and to provide a cathode ray tube with protruded face panel having a useful screen area as a limited surface to be polished, by projecting the useful screen area of the panel face of the cathode ray tube from a circumferential part extending around the area.

It is another object of the present invention to provide such a cathode ray tube providing an excellent fitness between an enclosure and the panel face by attaching an implosion-protected rim at a panel face circumferential part which is recessed from the useful screen area of the panel face.

An externally enclosing body for a cathode ray tube is obtainable by sealing the panel and a body formed of glass (a TV bulb) of a funnel.

Accordingly, the present invention is featurized by a panel (a TV bulb) in which the useful screen area projects from the circumferential part so that only the useful screen part is polished.

The present invention is substantially attained by fabricating such panel.

The foregoing and the other objects of the present invention have been attained by providing a cathode ray tube with a protruded face plate comprising a useful screen area and a panel face circumferential part extending around the useful screen area, characterized in that the panel face useful screen area projects from the panel face circumferential part and the panel face useful screen area is provided as a surface to be polished.

Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawing in which like reference numerals designate like or corresponding parts throughout several views and wherein: Figure 1 is a cross sectional view, partly omitted, of the panel of the conventional cathode ray tube; Figure 2 is a cross sectional view, partly omitted, of an embodiment of the cathode ray tube of the present invention; Figure 3 is a cross sectional view, partly omitted, of the conventional reinforcing type cathode ray tube; Figure 4 is a cross sectional view, partly omitted, of an embodiment of the present invention; and Figure 5 is a cross sectional view, partly omitted, of the other embodiment of the present invention.

An embodiment of the cathode ray tube with a protruded face plate of the present invention will be described with reference to drawing.

Figure 2 shows a partially cross sectional view of the panel of a cathode ray tube according to the present invention. In the figure, the cathode ray tube is shown to have a face plate comprising a useful screen area 1, a circumferential part 2 and a panel skirt part 3 wherein the useful screen area 1 projects from the circumferential part 2. The useful screen area 1 is a part for forming an image reflecting surface of the cathode ray tube and has a continuously curved surface consisting of spherical, cylindrical and flat surfaces and so on.

On the other hand, the circumferential part 2 is a part extending around the useful screen part 1, which is covered by an enclosure or an escutcheon mask when it is used as a part of a television set.

In the present invention, the useful screen area 1 and the circumferential part 2 constituting the face plate part of the cathode ray tube are constructed in such a manner that the former is projected with respect to the latter with the consequence that the surface of the circumferential part 2 is recessed or retracted from the extension b of the useful screen area 1.

The shape of the circumferential part 2 can be obtained by making the face forming surface of a mold for forming a panel coincide with the shape of the panel after forming and following by a press-forming operation with use of the mold. In this case, in forming the recess of the circumferential part 2, it is important that the recess should have a depth to an extent that the circumferential part is not polished at the time of polishing the outer surface of the useful screen area of the panel face after it has been pressformed.

With the useful screen area 1 of the panel face part projected, the circumferential part 2 is not polished even though the outer surface of the face plate part and possesses a strong molded face in the original form so that there is no reduction in strength at the circumferential part where stress is apt to be concentrated.

With regard to projecting of the useful screen area 1 from the circumferential part 2, when the cathode ray tube is reinforced by an L-shaped rim 5, it is preferable that the useful screen area further projects in an amount of the thickness of the rim 5. Thus, the circumferential part 2 to be attached with the rim 5 is recessed from the useful screen area 1 for an amount of the thickness of the rim 5 and accordingly, it provides an excellent fitness of the panel face to an enclosure 7.

Figure 5 shows the other embodiment of the present invention in which the depth of the recess, namely the projection of the panel face useful screen area is substantially equal to the thickness obtained by summing the thickness of the rim 5 and the enclosure 7. As a result, when the enclosure is to be mounted onto the face plate, the front surace of the enclosure 7 is made to be flush with the front surface of the useful screen area 1 of the face plate as shown in the figure.

The structure as above-mentioned provides advantages not only that excellent appearance is given but also that easy viewing cathode ray tube can be obtained. It is particularly desirable when the cathode ray tube is used as one for display because-of easy viewing and handling.

In the present invention, the depth of the recess formed at the circumferential part 2 varies dependent on purposes of use. Normally, the thickness of the circumferential part is greater than that of the useful screen area and the recess is formed by reducing the thickness of the circumferential part.

The circumferential part 2 may be connected to the useful screen area 1 by a stepped portion or an analogous stepped portion. It is, however, preferable to form the boundary of the recess by a smooth continuous surface to reduce the concentration of stress as possible. Particularly, in case that the useful screen area 1 is projected with respect to the circumferential part 2 for only the purpose that polishing of the circumferential part 2 is eliminated, an extent of projecting the useful screen area or of recessing the circumferential part 2 should be minimum as far as the purpose is accomplished.

The ratio of the depth of the recess to the thickness of the circumferential part is in the range of 1:3-1:35 preferably 1:5--1:35, from the viewpoint of maintaining the strength of the cathode ray tube.

Thus, the panel face of a cathode ray tube according to the present invention is so constructed that a recess is formed at the circumferential part so as to raise the useful screen area constituting a main part of the panel face. As a result, the circumferential part is not polished at the time of polishing the useful screen area and maintains the molded surface which is free from fine scratches caused by polishing. The molded surface prevents the breaking of the cathode ray tube caused by reduction in strength due to the concentration of stress and the fine scratches.

Further, even when the cathode ray tube is reinforced by the L-shaped rim, excellent fitness of the panel face to an enclosure can be obtained since the rim is attached to a recessed portion of the circumferential part iower than the useful screen area.

Claims

1. A cathod ray tube with a protruded face plate having a panel face consisting of a useful screen area and a panel face circumferential part extending around said useful screen area, characterized in that said panel face useful screen area projects from said panel face circumferential part and said panel face useful screen area is provided as a surface to be polished.

2. A cathode ray tube with a protruded face plate according to Claim 1, wherein said panel face circumferential part is recessed from the extension of the surface of said panel face useful screen area so as to raise said panel face useful screen area with respect to said panel face circumferential part so that only said panel face useful screen area is a surface to be polished.

3. A cathode ray tube with a protruded face plate according to Claim 2, wherein a reinforcing rim is attached to said panel face circumferential part which is recessed from the extension of the surface of said panel face screen area.

4. A cathode ray tube with a protruded face plate according to Claim 3, wherein said panel face useful screen area projects from an amount of the thickness of said reinforcing rim.

5. A cathode ray tube with a protruded face plate according to Claim 1, wherein the projection of said panel face useful screen area is substantially equal to the thickness obtained by summing the thickness of said rim and said escutcheon mask.

6. A cathode ray tube with a protruded face plate according to claim 1, substantially as hereinbefore described with reference to any of Figures 2,4or 5.