Panel of metal backed color cathode ray tube and manufacturing method thereof

A panel of a metal backed color cathode ray tube and a manufacturing method thereof are disclosed which are characterized in that the height of the graphite remaining on the skirt is higher than or same as the metal deposition height of the deposited metal layer, and that a shielding plate having a height higher than or same as the cutting height of the graphite is used on a deposition dolly for forming the deposited metal layer. According to the present invention, the deposited metal layer is neither floated nor detached due to the combustion of the organic materials used in forming the luminescent layer or the intermediate layers such as the filming layer, and therefore, the defect rate due to the blocking of the holes of the shadow mask is markedly reduced, thereby making it possible to save labor and materials in producing the product, and concomitantly upgrading the quality of the metal backed color cathode ray tube.

FIELD OF THE INVENTION 
The present invention relates to a panel of metal backed color cathode ray 
tube, and a manufacturing method thereof. 
BACKGROUND OF THE INVENTION 
The metal backed cathode ray tube is manufactured by depositing a metal 
layer such as an aluminum layer on the back of the luminescent layer in 
order to improve the luminance, to reinforce the potential, and to prevent 
the burning of the luminescent layer. An example of such a metal backed 
color cathode ray tube is disclosed in Japanese Patent Publication No. Sho 
56-25736, the constitution of which is illustrated in FIG. 1. According to 
this technique, graphite is spread in the form of stripes on the inner 
surface of the face plate F of the panel P, thereby forming a black matrix 
B. This metal backed color cathode ray tube comprises: the above mentioned 
black matrix B; a luminescent layer L formed by alternately depositing 
R,G,B luminescent materials containing an organic ingredient such as PVA 
as the base through the use of a photo etching method; a filming layer M 
composed of organic ingredients such as acryl emulsion for separating the 
luminescent layer L from a deposited metal layer A to be described later; 
and a deposited metal layer A made of aluminum layer and the like and 
deposited through the use of an electric deposition method so as for the 
layer A to serve as a metal back. 
In the finishing process, such a panel is sealingly joined with a funnel 
(not shown), thereby forming a bulb. However, if impurities adhered to the 
seal edge E during the joining, cracks will be produced, and therefore, 
there will be the risk that the cathode ray tube might implode. Therefore, 
the portions of the layers deposited on unnecessary areas during the above 
described spreading processes are removed by proper methods. That is, the 
graphite forming the black matrix B is cut away by means of a chemical 
such as ammonium acid fluoride (NH.sub.4 FHF), and the superfluous 
portions of the luminescent layer L and the filming layer M are washed off 
by means of a wiper of high pressure water, while the deposited metal 
layer A is deposited in such a manner that a proper shielding plate is 
installed on the deposition dolly so as for only the required areas to be 
deposited. 
However, a stud pin T for installing a shadow mask (not shown) protrudes 
from a skirt S of the panel P, and therefore, it is difficult to carry out 
a complete washing by means or wiper with high pressure water, with the 
result that serious problems are generated during the baking process due 
to the residue of organic materials of the luminescent layer and the 
filming layer. 
A baking is carried out to burn off (remove) the organic materials such as 
PVA and acryl emulsion by heating the panel to a high temperature, so that 
the electron beams emitted from the electron gun should not lose their 
energies due to the organic materials before they reach the luminescent 
layer. However, if a deposited metal layer A is formed upon the surface of 
the residue organic materials O adhered on the skirt S, then the deposited 
metal layer will swell up to float above the residue organic material 
during the baking process due to the combustion gas of the organic 
materials, and this floated-up metal layer A will be detached away after 
the manufacturing of the cathode ray tube to block up the holes of the 
shadow mask, this having been one of the main factors for the 
hole-blocking defects. Therefore, in order to remove the detached 
materials, a salvaging process had to be carried out, with the adverse 
result that much labor and materials had to be squandered. According to 
the investigations carried out by the present inventor, the defective 
product rate due to the detachment of the deposited metal layer A such as 
aluminum layer occupies 20.about.30% of the total hole-blocking defects. 
SUMMARY OF THE INVENTION 
The present invention is intended to overcome the above described 
disadvantages of the conventional techniques. 
Therefore it is the object of the present invention to provide a panel of a 
metal backed color cathode ray tube and a manufacturing method thereof, in 
which the deposited metal layer is neither floated up nor detached after 
the combustion of the organic materials. 
The idea of the present inventor for achieving the above object lies in the 
fact that a deposited metal layer such as an aluminum layer attached upon 
a graphite layer is neither floated nor detached during the combustion of 
the organic materials in spite of the discharge of the combustion gas, 
because graphite has superior adherence and neither combusts nor produces 
combustion gases during a baking process. 
Thus the panel of a metal backed color cathode ray tube according to the 
present invention comprises a black matrix, a luminescent layer and a 
deposited metal layer, each of which is sequentially deposited on the 
inner surface of the panel consisting of a face plate and a skirt, 
characterized in that the height of graphite on the skirt after the 
formation of the black matrix is made to be higher than or same as the 
height of the deposited metal layer. 
The manufacturing method suitable for manufacturing the panel of the 
present invention is characterized in that a shielding plate having a 
height higher than or same as the cutting height of the graphite is 
applied on the deposition dolly for forming the above described deposited 
metal layer.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The panel P of the metal backed color cathode ray tube according to the 
present invention illustrated in FIG. 2 is manufactured by sequentially 
depositing: a black matrix B formed by spreading graphite in the form of 
stripes on the inner surface of a face plate F through the use of a photo 
etching method and the like; a luminescent layer L formed by alternately 
depositing three (R,G,B) luminescent materials between the black matrices 
B; a filming layer M for separating the luminescent layer L and a 
deposited metal layer A; and the deposited metal layer A, desirably an 
aluminum layer deposited on the filming layer M through the use of an 
electric deposition method and the like. This constitution so far is not 
much different from that of the conventional panel. 
The unique feature of the present invention lies in the portion of the 
skirt S of the panel P, and is constituted such that the height of the 
graphite (to be called hereinafter "graphite height Hc") from the inner 
surface of the face plate of the panel (or the luminescent layer) where 
the graphite is cut off in the graphite cutting process after adhering it 
on the inner surface of the skirt S during the spreading of the black 
matrix, B is made to be higher than or same as the height of the deposited 
metal layer A (to be called hereinafter "metal layer height Ha"). 
The method of forming the graphite height Hc higher than or same as the 
metal layer height Ha on the panel P is carried out as shown in FIG. 3 in 
such a manner that a shielding plate G is used during the deposition of 
the deposited metal layer A on the inner surface of the panel so as for 
the metal not to be deposited on the place where the graphite is cut off. 
It is desirable that the shielding plate G should be made of a material 
such as fluoric resin (trade name: Teflon) which is strong against the 
heat and not harmful to a glass panel, and the shielding plate G is 
provided with a contour substantially corresponding to the inner boundary 
of the skirt S of the panel P. The height Hg of this shielding plate G 
should be higher than or same as the cutting height Hk in the place where 
the graphite adhered on the skirt S of the panel P is cut off. In FIG. 3, 
Reference code D indicates a deposition dolly, I an ingot for the 
deposited metal, and H a heater. 
The process of forming the panel of the present invention through the use 
of the shielding plate G having a height Hg higher than or same as the 
cutting height Hk will be described more specifically below. The black 
matrix B is spread on the inner surface of the face plate F of the panel 
P, and the superfluous graphite adhered on the skirt S is cut off as much 
as the cutting height Hk by means of a proper chemical such as ammonium 
fluoride, so that the graphite should remain as high as the graphite 
height Hc. 
Then the R,G,B luminescent materials are alternately deposited using an 
organic medium such as PVA together with an adhesive or photoresist so as 
for the luminescent layer to be formed, and thereafter, a filming layer M 
is spread in order to prevent the lowering of the reflecting function of 
the deposited metal layer A, while the deposited metal layer A is 
deposited on the rear side of the filming layer M. 
The space between the panel P and the deposition dolly D is evacuated by 
means of a vacuum pump (not shown) to form a required vacuum space, and 
then, the deposition metal ingot I is heated by the heater H to produce 
deposition metal vapors which are to be made to adhere on the inner 
surfaces of the face plate F and the skirt S of the panel P. Here, the 
shielding plate G according to the present invention is installed on the 
inner circumference of the skirt S, and the height Hg of the shielding 
plate G is higher than or same as the cutting height Hk of the graphite, 
with the result that the deposited metal layer A is not formed on the 
surface of the organic material O where the graphite layer does not exist. 
The panel P which has undergone the process of forming the deposited metal 
layer A is subjected to a proper cleaning step, and then, is put into a 
baking furnace where a baking process is carried out, and where the 
organic ingredients contained in the luminescent layer L and the filming 
layer M are all burned and discharged in the form of gas. 
Even if the organic materials contained in the portions of the layers where 
the graphite layer exists on the skirt S are burned and discharged across 
the deposited metal layer A, the graphite layer located below maintains a 
strong adherent strength, and therefore, the deposited metal layer A is 
neither floated nor is detached, while the portions where no graphite 
layer exists are not provided with a deposited metal layer A so as for the 
organic materials to be burned and discharged freely, and so as for them 
not to give any adverse effect to other portions. 
According to the present invention as described above, the deposited metal 
layer is neither floated nor detached due to the combustion of the organic 
materials used in forming the luminescent layer or the intermediate layers 
such as the filming layer, and therefore, the defect rate due to the 
blocking of the hole of the shadow mask is markedly reduced, thereby 
making it possible to save the labor and materials, and making it possible 
to produce a high quality color cathode ray tube.