EP1550143A1

EP1550143A1 - Cathode ray tube with reduced depth

Info

Publication number: EP1550143A1
Application number: EP03748091A
Authority: EP
Inventors: Paul Sterken; Mohammed Khalil
Original assignee: LG Philips Displays Netherlands BV
Current assignee: LG Philips Displays Netherlands BV
Priority date: 2002-10-02
Filing date: 2003-09-20
Publication date: 2005-07-06
Also published as: WO2004032173A1; CN100343940C; CN1708825A; AU2003267412A1

Abstract

A cathode ray tube (1) comprises a panel portion (2), a funnel portion (3) and a neck portion (4) with an electron gun (5). The screen of the cathode ray tube has a diagonal D of more than 28 inches. The panel portion (2) has a seal edge (21a) with a thickness (Tshort) at the end of the short axis of 0.019D to 0.0275D, where D is the length of the diagonal of the screen, and a front part (22) having a thickness (Tfront ) at least 10% smaller than the thickness (Tshort ) of the edge of the panel portion. The depth of the cathode ray tube at a point halfway between the centre of the screen and the end of the diagonal is less than 0.3D (HD/4<0.3D).

Description

TITLE

Cathode ray tube with reduced depth.

FIELD OF THE INVENTION

The invention relates to a cathode ray tube comprising an panel portion with a long axis, a short axis and a diagonal, a funnel portion and a neck portion comprising an electron gun for generating one or more electron beam(s), and a deflection system mounted on said funnel portion for generating electromagnetic fields for deflecting said electron beam(s).

The invention also relates to a panel portion for a cathode ray tube.

The invention also relates to a display apparatus comprising a CRT.

BACKGROUND OF THE INVENTION

Such cathode ray tubes (CRT's) are known. There exist various types of cathode ray tubes, the best known of which are cathode ray tubes with a shadow mask. Other types of cathode ray tubes are e.g. index tubes and tubes in which a stretched mask is used.

Cathode ray tubes as a type of display device have to compete with various other types of display devices, such as LCD's PDP' etc. These various types all have their advantages and disadvantages. One of the disadvantages of the CRT compared to other types of display devices is the depth of the CRT. To overcome this disadvantage various approaches in reducing the depth of the CRT have been proposed. However, up until now the depth of a CRT has (expressed as a function of the diagonal D of the CRT) been greater than approximately 0.6 times D, i.e. approximately 1.5 cm depth per inch diagonal. The depth reduction of the cathode ray tube is in particular of importance for CRT with a large diagonal D, above 27 inches.

Attempts to reduce the depth have been up to some level successful, however, only relatively small incremental gains have been obtained. SUMMARY OF THE INVENTION

It is an object of the invention to provide a cathode ray tube with a reduced depth. To this end the cathode ray tube is characterized in that the cathode ray tube has a diagonal of preferably more than 28 inches, that the panel portion has upstanding wall having a seal edge having a thickness at the end of the short axis of 0.019D to 0.0275D, preferably between 0.021D to 0.025D, where D is the length of the diagonal of the screen, and a front part having a thickness at least 10% smaller than the thickness of the seal edge of the panel portion and that the depth of the cathode ray tube at a point halfway between the centre of the screen and the end of the diagonal is smaller than 0.3D.

The aim of the invention is to provide a new type of cathode ray tube having a depth substantially smaller than conventional. A cathode ray tube in general at least comprises a panel portion and funnel portion, which are joined at a seal edge. However, when the depth of a CRT is reduced, the vacuum stress at the seal-edge is increased much above the allowed maximum limit (approximately 10 MPa). Normally, for large CRT's, the seal-edge thickness is in the range of 11-14 mm (i.e. between 0.013 and 0.017D, D expressed in cm). The stress is also increasing above allowed limit [ 10 Mpa] at the funnel body. Due to the fact that the cathode ray tube with reduced depth is subjected to increase vacuum stresses, an increase of glass thickness is required for static safety reason, resulting in a very heavy CRT and in very slow thermal processing speeds compared to standard Real Flat CRTs. Increase thickness [in weight] of the CRT and deceleration of processing thereof are disadvantageous for costs. The invention is based on the insight that by increasing substantially the thickness of the seal edge in particular at the end of the short axis relatively to the center face thickness, the weight of the tube as a whole may be kept within reasonable limits. This seems prima facie illogical, the thickness of the edge is increased substantially in comparison to standard design, by some 25-50%, which would seem to mean an substantial increase in weight, contrary to the object of the invention. However, for larger tube sizes the bulk of the weight is formed by the front part of the panel portion. By increasing the thickness of the seal edge considerably, the thickness of the front part may be kept the same or even reduced, which safes weight. Furthermore, because of the substantial increase in strength of the seal edge portion the funnel portion can be made much shorter than standard funnels, without substantial increase in thickness of the funnel which also reduces the weight of the tube further. In all, the weight of the tube is kept on pair or even reduced in comparison to standard designs, while the depth is strongly reduced without compromising the strength of tube. The depth at the quarter diagonal of the resulting tube is less than 0.3D. This enables a total depth of the tube to be approximately 0.4D, comparing this to the conventional depth of 0.6D, it follows that for a tube with a diagonal of D inches the reduction in depth is typical 0.2D, which, for a 32inch tube, means a reduction in depth of 16 cm, from typically 48 cm to approximately 32 cm. This is, in terms of gains made in reducing the depth of the tube so far, which typically measured cm or parts of cm, an astounding decrease in depth. To put this in perspective: most cupboards have standard depths of approximately 40, 50 or 60 cm. The total depth of a television set is some 5-10 cm more than the depth of the CRT. In order to be put safely into the cupboard at both front and back side of the television a few cm of free space should be available. Thus a standard 32 inch TV needs some 48+10+6=64 cm space. It will not or barely fit into a cupboard with standard depth, even the largest, without at least slightly protruding. A TV using the CRT of the invention needs 16 cm less space, i.e.32+10+6=48 cm, easily fitting into the 50 and 60 cm standard depth wall cabinets cupboard. A 60 cm standard depth cupboard can accommodate, using the invention, a TV of up to approximately 42 inches (105 cm), whereas at present only TV sets up to approximately 28 to 30, maximum 32 inches may be accommodated.

In preferred embodiment the panel height [H_panei see figure 2] is between 92 and 100 mm, preferably between 94 and 97 mm. This is substantially less than the conventional height that lies around 110-120 mm. The appreciable increase in thickness of the seal edge enables the reductions of the height of the panel without compromising the strength of the tube. This leads to a further reduction in weight and tube depth , and also increases the thermal processing speed of CRT's.

In embodiments the thickness of the seal edge is substantially uniform around the circumference of the tube.

However, in preferred embodiments the thickness of the seal edge is non uniform: highest at the ends of the short axis, smallest at the corners, and increasing from the corners, the thickness at the end of the long axis being smaller than at the end of the short axis. See figure 6.

This enables a further reduction in weight, an increase in thermal processing speed of CRT production and to the picture on pair with standard CRT. Preferably the height H_D/4 is equal or less than 0.25D (H_D/4≤0.25D)

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings: Fig. 1 illustrates a cathode ray tube and a picture display device in accordance with the invention.

Fig.2 shows a front panel of a cathode ray tube. Fig. 3 shows a cross-sectional view of a panel portion and a funnel portion.

Fig. 4 shows a panel portion.

Fig. 5 shows thermal speed as a function of a ratio of panel portion parameters.

Fig. 6 shows uniform and not uniform seal edge thickness distribution.

The figures are not drawn to scale. Generally, identical components are denoted by the same reference numerals in the figures.

A cathode ray tube and a picture display device according to a preferred embodiment of the invention is shown in FIG.1. It comprises a cathode ray tube 1, which includes a panel portion, sometimes also called a display window 2, a funnel portion 3, and a neck portion 4 (or neck as it is called hereinbelow). In the neck 4, there is as a means 5 for generating electron beam(s) in this example three in-line electron beams 6, the in-line plane being parallel to the long axis of the display screen, such means are herewithin in short described by the word "electron gun" . A means for generating an electron beam is usually an in-line electron gun. Such designs are standard designs. The inner surface of the panel portion 2 comprises a large number of phosphor elements which form a display screen 8. When one or more of the electron beams 6 hit phosphor elements, the latter become phosphorescent, thereby creating a visible spot on the display screen 8. In the undeflected state, the middle one of the electron beams 6 substantially coincides with the tube axis 7. The direction of the tube axis is hereinbelow denoted by the z-direction. The direction along the long axis of the display screen is denoted by the x-direction, the direction along the short axis of the display screen by the y-direction. The line scanning direction (i.e. the direction in which scanning with the highest frequency takes place is usually parallel to the long axis (the x-direction) of the display screen. On its way to the display screen 8, the electron beams 6 are deflected by means of a deflection system 9 covering a part 3a of the funnel portion 3. It is in particular this part 3a of the outer contour that the invention relates to. Said deflection system 9 comprises a line deflection subsystem 12 and a frame deflection subsystem 13, in order to create a two-dimensional picture on the display screen 8. In this exemplary embodiment, the deflection system 9 is made up of sets of coils, one set for the line deflection subsystem 12 and another set for the frame deflection subsystem 13. The outer circumference of the funnel portion comprises a first section I near the neck and a second portion II further away from the neck, more towards the screen. The figure shows a standard in-line CRT, it is remarked that, although the invention is very useful for such designs, other types of CRT, e.g. index tubes or CRT with stretched masks, or CRT in which the line scanning direction is along the short axis (so- called transverse scanning CRT's) exist and the present invention in equally applicable to such types of CRT's.

The figure also indicates the x-direction, i.e. the direction along the long axis of the display screen and the z-direction. The z-coordinate of the deflection plane is usually (and hereinbelow) taken to be zero, with positive values of z being closer to the display screen.

As can be seen from FIG. 2, the panel portion (8) has an elongated shape with two perpendicular axes of symmetry : a long axis whose length, measured from screen end to screen end, is Lscr and a short axis whose length is Sscr. In order to quantify the amount of elongation of the display screen (8), the aspect ratio of the display screen (8) is defined as Ascr = Lscr/Sscr. The diagonal, measured from screen comer to an opposite screen comer has a length D wherein approximately D2= L2scr + S2scr. The panel portion comprises an upstanding wall 21 and a front part 22. The upstanding wall has a seal edge 21a. The seal edge is the position where the separately manufactured panel portion and funnel portion (which may form an integral unit with the neck portion) are sealed together. The thickness of the edge is given as T, wherein the thickness at the end of the short axis is denoted Ts_ho_rt, the thickness at the end of the long axis as Tι_on and the thickness in the corners (end of diagonal) as Tcorner- The height of the edge is denoted by H_pan6ι, the thickness of the front part as Tβ-ont, wherein the thickness is taken at the centre of the screen.

Figure 2 also shows the maximum deflection angle Θ as being the angle between the tube axis (7) and the deflected electron beam (10) when the electron beam is deflected so as to hit a point on the display screen which is the furthest away from the intersection between the tube axis (7) and the display screen.

The following relation holds

Tan(Θ)=Ascr

Depending on the design Ascr is usually 4/3 (1.333) or 16/9 (1.78)

It is remarked that the curvature of the front part is grossly exaggerated in this figure.

Figure 3 shows a CRT in cross-sectional view. In this figure are shown the depth H_D/4 which is the depth taken at a point D/4, i.e. a point on the diagonal a distance D/4 from the centre, i.e. halfway in between the centre and the comer of the screen. Also shown is Htotai . the total depth of the cathode ray tube. The present invention provides for a cathode ray tube having a reduced depth comparison to standard CRT's. The cathode ray tube has an increased seal-edge thickness T at least at the end of the short axis. Instead of using the standard range for the seal-edge thickness (10-14 mm) , the thickness is increased to a level between 15-22 mm, preferably 17-20 mm, the seal edge thickness when expressed as a function of diagonal dimension D is between 0.019D to 0.0275D, preferably 0.021 D to 0.025D. The center face thickness is kept lower than the thickness of the seal edge at the end of the short axis, e.g. at the standard level of 12-16 mm. This results in a reduction of the seal-edge vacuum stress to allowed stress levels and in thermal speeds competitive with standard CRT products.

By applying a seal-edge thickness T in the range of 15-22mm, preferably 17mm≤T_Shor_t≤20mm,fhe weight of the glass envelope of the CRT in accordance with the invention can be reduced to the level of standard Real Flat designs. Moreover, this results in vacuum seal-edge stresses lower than the allowed limit of approximately 10, e.g. 8.3 MPa and in panels having a standard center face thickness [12- 16mm]. As a consequence, the tube weight is reduced by about 10% and the fritting and the exhausting speed are at least 80% of the standard real flat designs.

The depth of the cathode ray tube at a point halfway between the centre of the screen and the end of the diagonal, i.e. HD/4, is smaller than 0.3D. This enables a very small total depth H_totai of the CRT.

Preferably the height of the panel portion 2 H_paneι lies between 92 and 100 mm, preferably between 94 and 97 mm. A reduction in weight and depth is thereby achieved.

In embodiments of the invention the thickness at the seal edge may be uniform, i.e. everywhere the same around the cfrcumference. In preferred embodiments the thickness is largest at the end of the short axis, smallest at the corners, and has an intermediate value at the end of the long axis, i.e. T_{S 0}rt^>Tiong^>T_COrner- A decrease in weight and making the picture view on pare with standard CRT as well as an increase in CRT thermal processing speed are possible. Table 1 shows this effect for a 32 inch tube.

Table 1 : improvement using non uniform seal edge thickness

Comparing the data of the tubes in accordance with the invention to the prior art tube it is clear that the depth H_D/4 is strongly reduced (by up to more than 10 cm). The weight has somewhat increased by 2.5 kilograms to 4 kilograms, i.e. 6% to 10%, however, because the tube is smaller, the TV set casing may also be made smaller, reducing the weight of the casing, so that the total weight of the TV set is hardly increased, if at all. Comparing the uniform seal edge thickness designs to the preferred embodiment of the invention in which the seal edge thickness is non-uniform it is clear that the weight has been reduced by 1 kilo and the picture view increased by 5 mm. Figures 4 and 5 illustrate preferred embodiments of the invention relating to non-uniform seal edge thickness distribution. These embodiments are directed to the ratio between the thickness of the seal edge at the comer T_corner and the thickness of the front part at the end of the screen diagonal T_end-screen- Experiments, schematically shown in figure 5 has demonstrated that the thermal processing speed, i.e. the speed with which the panel portion can be fritted and exhausted is a function of the ratio T_end-screen /T_COmer- A ratio in between 1.5 and 1.75, preferably in between 1.5 and 1.65 increases the thermal processing speed.

Figure 6 illustrate at the left hand side in cross-section a panel for which it holds and on the right hand side a panel for which it holds T_Short^>Tiong^>T_Corne_r. The invention is applicable to any type of CRT. However, in preferred embodiments the funnel portion has, under the deflection unit, a substantially rectangular cross-section. Such so-called RAC (RectAngular Coil)-type tubes allow the deflection coils of the deflection unit to come closer to the electron beam, thereby reducing energy consumption and reducing heat production.

In short the invention may be described as follows:

A cathode ray tube (1) comprises an panel portion (2), a funnel portion (3) and a neck portion (4) with an electron gun (5). The screen of the cathode ray tube has a diagonal D of preferably more than 27 inches. The panel portion (2) has a seal edge (21a) with a thickness (Tshort ) at the end of the short axis of 0.019D to 0.0275D, where D is the length of the diagonal of the screen, and a front part (22) having a thickness (T&_0nt ) at least 10% smaller than the thickness (T_Sh_0rt) of the edge of the panel portion. The depth of the cathode ray tube at a point halfway between the centre of the screen and the end of the diagonal is less than 0.3D (H_D/4<0.3D).

It will be clear that within the concept of the invention many variations are possible. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Reference numerals in the claims do not limit their protective scope. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements other than those stated in the claims. Use of the article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

CLAIMS:

1 . A cathode ray tube (1) comprising an panel portion (2) with a long axis, a short axis and a diagonal, a funnel portion (3) and a neck portion (4) comprising an electron gun (5) for generating one or more electron beam(s) (6), and a deflection system (9) mounted on said funnel portion (3) for generating electromagnetic fields for deflecting said electron beam(s) (6), characterised in that that the cathode ray tube has a diagonal D, that the panel portion (2) has an upstanding wall (21) having a seal edge (21a) having a thickness (Tshort ) at the end of the short axis of 0.019D to 0.0275D, where D is the length of the diagonal of the screen, and a front part (22) having a thickness (Tfr₀m ) at least 10% smaller than the thickness (T_sh_ort ) of the edge of the panel portion and in that the depth of the cathode ray tube at a point halfway between the centre of the screen and the end of the diagonal is smaller than 0.3D (H_D/4<0.3D).

2 . A cathode ray tube as claimed in claim 1, characterised in that the diagonal D>27".

3 . A cathode ray tube as claimed in claim 1, characterised in that the seal edge (21) has a thickness at the end of the short axis (T_Sh_ort) between 0.021D to 0.025D.

4 . A cathode ray tube as claimed in claim 1, characterised in that the height of the panel (2) (H_panei) is between 92 and 100 mm.

5 . A cathode ray tube as claimed in claim 3, characterised in that said height is between 94 and 97 mm.

6. A cathode ray tube as claimed in claim 1 , characterised in that the height D is equal or less than 0.25D (H_D/4<0.25D)

7 . A cathode ray tube as claimed in claim 1, characterised in that the thickness of the seal edge (21) is highest at the ends of the short axis, smallest at the comers, and increasing from the comers, the thickness at the end of the long axis being smaller than at the end of the short axis (T_Short^>Tiong^> comer)-

8 . Cathode ray tube as claimed in claim 1, characterised in that the ratio between the thickness of the seal edge at the comer T_COrner and the thickness of the front part at the end of the screen diagonal T_end-screen lies in between 1.5 and 1.75 (l^^end-_screen/Tc_orne^l-75).

9. Cathode ray tube as claimed in claim 1, characterised in that the funnel portion has, under the deflection system (9) a substantially rectangular cross-section.

10. Panel portion for use in a cathode ray tube as claimed in any of the claims 1 to 8.

11. Display apparatus comprising a cathode ray tube as claimed in any of the claims 1 to 9.