Phosphor slurry composition for color Braun tubes

The present invention discloses a phosphor slurry composition for color Braun tubes comprising deionized water, phosphor powder, polyvinyl alcohol, sodium dichromate, ethyl silicate and zinc sulfate. A color Braun tube manufactured using a phosphor slurry composition of the present invention shows an excellent mirror reflection effect and high luminescent brightness.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a phosphor slurry composition for color Braun 
tubes, more particularly, to a phosphor slurry composition comprising an 
aqueous ethyl silicate solution and an aqueous zinc sulfate solution in 
addition to the ingredients of the conventional phosphor slurry 
composition and usable to manufacture color Braun tubes exhibiting 
significantly increased luminescent brightness. 
2. Description of the Prior Art 
In general, the inner face of a color Braun tube is provided with a 
fluorescent screen which contains red phosphor, blue phosphor and green 
phosphor uniformly deposited thereon. As a method to form such a 
fluorescent screen, the slurry method is widely used. In this method, a 
procedure of coating a phosphor slurry composition containing a 
photoresist material on the inner face of a color Braun tube to form a 
photoresist film, and carrying out the developing process by exposure to 
light through a shadowmask is sequentially carried out as to green 
phosphor, blue phosphor and red phosphor, thereby a fluorescent screen is 
formed. 
As an example of the phosphor slurry composition used in the slurry method, 
a phosphor slurry consisting of phosphor powder, polyvinyl alcohol, sodium 
hexametaphosphate, sodium dichromate and deionized water is disclosed in 
Japanese Patent No. Sho 59-19156. 
The fluorescent screens produced by using the conventional phosphor slurry 
compositions have a low packing density of phosphor layer and poor 
evenness so that the mirror reflection effect of the aluminum vacuum 
evaporation film will be insufficient, leading to a decrease of 
luminescent brightness of the fluorescent screens. 
Besides the slurry method, the phosphor powder coating method is another 
method to produce a phosphor coating. This method is disclosed by way of 
example in Japanese Patent Publication No. Sho 57-20651. 
According to this method, when phosphors are coated over the surface of the 
panel in the shape of fine dots or stripes a in the case of color Braun 
tubes, parts of the phosphor dots or stripes with the second and/or third 
color peel off or fail to be deposited to a sufficient thickness, leading 
to a problem that the obtained fluorescent screen has low grade quality. 
To solve this problem, in Japanese patent laid-open No. Sho. 62-110230 is 
disclosed a method which further comprises a step to heat the 
photosensitive adhesive film prior to the step to deposit each phosphor 
powders. 
However, this method has a defect that a large quantity of heat energy is 
consumed and the processes get more complicated. 
SUMMARY OF THE INVENTION 
This invention has been developed to solve the problems of the prior art as 
described above. Therefore, the object of this invention is to provide a 
phosphor slurry composition which can be used to manufacture color Braun 
tubes exhibiting increased luminescent brightness due to the fact that a 
high packing density of phosphor layer and good evenness of fluorescent 
screen is obtained, thereby the mirror reflection effect of aluminum 
vacuum evaporation film is improved. 
To achieve the above object, the present invention provides a phosphor 
slurry composition for color Braun tubes, comprising: 
a) 100 parts by weight of phosphor powder, 
b) 120-130 parts by weight of polyvinyl alcohol, 
c) 5-6 parts by weight of sodium dichromate, 
d) 0.0009-0.5 parts by weight of ethyl silicate, 
e) 0.002-0.04 parts by weight of zinc sulfate and 
f) 120-130 parts by weight of deionized water. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to the present invention, the added amount of ethyl silicate is 
preferably in the range of from 0.0009 to 0.5 parts by weight based on 100 
parts by weight of phosphor. When it is added in the amount of less than 
0.0009 parts by weight, it can not be anticipated to obtain an increased 
packing density. On the contrary, when it is added in the amount of more 
than 0.5 parts by weight, the dispersity of the phosphor can be lowered. 
Ethyl silicate is generally added in the form of a solubilized aqueous 
solution into the phosphor slurry composition. 
In the composition of the present invention, dichromate is used as a 
photosensitive agent and polyvinyl alcohol is used as a photosetting 
binder. 
According to the present invention, the added amount of zinc sulfate is 
preferably in the range of from 0.002 to 0.04 parts by weight based on 100 
parts by weight of phosphor. When it is added in the amount of less than 
0.002 parts by weight, partial peeling off of the fluorescent screen can 
occur due to insufficient adhesion between the fluorescent screen and the 
inner face of the panel. On the contrary, when it is added in the amount 
of more than 0.04 parts by weight, the adhesive power is so high that the 
so-called residual color phenomenon owing to a poor resolution can occur 
in the resolution of the fluorescent screen. 
A typical method to manufacture a fluorescent screen using a phosphor 
slurry composition for color Braun tubes according t the present invention 
is as follows. 
(A) Preparation of a phosphor slurry composition for color Braun tubes 
A predetermined amount of green, blue or red phosphor are added with 
deionized water and polyvinyl alcohol, and is added with sodium 
dichromate, to this mixture are added an aqueous ethyl silicate solution 
and an aqueous zinc sulfate solution instead of an surface active agent 
used in the prior art. Then, the obtained mixture is charged into a ball 
mill and subjected to milling at 10-300 rpm for 3-15 hours to prepare a 
phosphor slurry composition for color Braun tubes. 
The ball mill container is desirably one with its interior made of PVC in 
order to inhibit the phosphor surfaces from being damaged. To achieve the 
optimum effect of ball milling, it is desirable to fill the phosphor 
slurry to 70-80 percent of the total volume of the ball mill container. At 
this time, it is desirable to add a suitable amount of alumina balls or 
glass balls to increase the dispersion effect. 
(B) Manufacturing of a fluorescent screen 
A given amount of a photosetting resin which has the photoadhesive property 
when being exposed to ultraviolet light is coated on the inner face of 
panel of a Braun tube and dried, thereafter it is exposed to light to form 
a photoadhesive film. On this film, the green phosphor slurry obtained 
from the process of (A) above described is coated and dried, then exposed 
to light using a high-pressure mercury lamp. After the exposure is ended, 
washing with war water is carried out to obtain a green phosphor screen 
with a uniform stripe or dot pattern. Subsequently, the same procedure as 
above is repeated sequentially with blue phosphor and red phosphor to 
prepare a fluorescent screen.

EXAMPLES AND COMATIVE EXAMPLES 
Now, examples and comparative examples will be presented to illustrate this 
invention. However, it is understood that this invention is not limited to 
these examples. 
EXAMPLE 1 
After the following ingredients were mixed and milled in a ball mill at 150 
rpm for 10 hours to prepare a phosphor slurry composition, the commonly 
used process for manufacturing a fluorescent screen was carried out using 
the obtained phosphor slurry compositions to manufacture a fluorescent 
screen. 
______________________________________ 
Ingredients Amounts 
______________________________________ 
ZnS: Ag phosphor powder 
1.0 kg 
Polyvinyl alcohol 1.3 kg 
Sodium dichromate 0.06 kg 
3 wt % aqueous ethyl silicate solution 
20 ml 
2 wt % aqueous zinc sulfate solution 
5 ml 
Deionized water 1.3 kg 
Glass ball 1.0 kg 
______________________________________ 
EXAMPLE 2 
After the following ingredients were mixed and milled in a ball mill at 150 
rpm for 10 hours to prepare a phosphor slurry composition, the commonly 
used process for manufacturing a fluorescent screen was carried out using 
the obtained phosphor slurry compositions to manufacture a fluorescent 
screen. 
______________________________________ 
Ingredients Amounts 
______________________________________ 
Y.sub.2 O.sub.2 S: Eu phosphor powder 
1.0 kg 
Polyvinyl alcohol 1.2 kg 
Sodium dichromate 0.05 kg 
3 wt % aqueous ethyl silicate solution 
15 ml 
2 wt % aqueous zinc sulfate solution 
5 ml 
Deionized water 1.2 kg 
Glass ball 1.0 kg 
______________________________________ 
COMATIVE EXAMPLE 1 
After the following ingredients were mixed and milled in a ball mill at 150 
rpm for 10 hours to prepare a phosphor slurry composition, the commonly 
used process for manufacturing a fluorescent screen was carried out using 
the obtained phosphor slurry compositions to manufacture a fluorescent 
screen. 
______________________________________ 
Ingredients Amounts 
______________________________________ 
ZnS: Ag phosphor powder 1.0 kg 
Surface active agent 100 ml 
(Tritol-CF54, SIGMA Co. Ltd., U.S.A.) 
Polyvinyl alcohol 1.2 kg 
Ethylene glycol 60 ml 
Sodium dichromate 0.05 kg 
Deionized water 1.3 kg 
______________________________________ 
COMATIVE EXAMPLE 2 
Except that the amount of 3 wt % aqueous ethyl silicate solution was 
changed to 0.2 ml, a substantially similar procedure as Example 1 was 
repeated to manufacture a fluorescent screen. 
COMATIVE EXAMPLE 3 
Except that the amount of 3 wt % aqueous ethyl silicate solution was 
changed to 170 ml, a substantially similar procedure as Example 1 was 
repeated to manufacture a fluorescent screen. 
COMATIVE EXAMPLE 4 
Except that the amount of 2 wt % aqueous ethyl silicate solution was 
changed to 0.5 ml, a substantially similar procedure as Example 1 was 
repeated to manufacture a fluorescent screen. 
COMATIVE EXAMPLE 5 
Except that the amount of 2 wt % aqueous ethyl silicate solution was 
changed to 25 ml, a substantially similar procedure as Example 1 was 
repeated to manufacture a fluorescent screen. 
With the fluorescent screens manufactured in the above Example 1 to 2 and 
Comparative examples 1 to 5, reflection efficiency of aluminium vacuum 
evaporation film and luminescent brightness of color Braun tube were 
measured according to the following methods. 
The obtained results will be listed in table 1 below. 
TABLE 1 
______________________________________ 
Test results of fluorescent screens 
Reflection efficiency of 
aluminium vacuum 
Luminescent brightness 
Example No. 
evaporation film 1) 
of Braun tube 2) 
______________________________________ 
Example 1 
80% 111% 
Example 2 
78% 108% 
Comparative 
60% 100% 
example 1 
Comparative 
59% 99% 
example 2 
Comparative 
62% 101% 
example 3 
Comparative 
61% 101% 
example 4 
Comparative 
63% 103% 
example 5 
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Note: 
1) The value obtained from measurement of reflection efficiency for the 
aluminium vacuum evaporation film using a Spectrogard Color System, 
Pacific Scientific Co., Ltd. 
2) The relative value obtained from comparing the luminescent brightness 
measured at 23.5 kV, 500 .mu.A using a MECC system to that measured with 
the fluorescent screen of Comparative example 1. 
As is apparent from the results of table 1, the luminescent brightnesses of 
the fluorescent screens in Example 1 and 2 are higher by 10 percent than 
that of the fluorescent screen manufactured in Comparative example 1 using 
a conventional phosphor slurry composition. Also, it is apparent from the 
above test results of Comparative examples 2 t 5 that the added amounts of 
ethyl silicate and zinc sulfate are desirably each in the range of from 
0.0009 to 0.5 percent by weight and from 0.002 to 0.04 percent by weight 
based upon the phosphor in a phosphor slurry composition of the present 
invention.