Black matrix and a phosphor screen for a color cathode-ray-tube and production thereof

The present invention provides with a black matrix, a phosphor screen, and a method of manufacturing thereof. For a method of manufacturing the black matrix formed on the inner surface of a panel of a color CRT, a photoresist is not used, but a wet electrophotographic method was employed, using graphite for a main component of the black matrix materials, and forming a phosphor screen by a dry electrophotographic method to improve the quality of a color cathode-ray-tube.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a black matrix, a phosphor screen, and a 
method of manufacturing thereof, and more particularly to developing the 
black matrix formed on the inner surface of a panel of a color 
cathod-ray-tube (CRT) by a wet electrophotographic method, using graphite 
for a main component of the black matrix materials, and forming a phosphor 
screen by a dry electrophotographic method to improve the quality of a 
color cathode-ray-tube (CRT). 
2. Description of the Related Art 
In a conventional shadow-mask-type CRT, graphic images are reproduced by 
red, green, and blue electron beams emitted from means for producing them 
which pass through a hole of a shadow mask, converge into a point, and 
collide with red, green, and blue phosphors formed on a phosphor screen of 
an inner surface of a panel. 
The phosphor screen comprises red, green, and blue phosphors which have a 
pattern and black matrix which is formed on the same surface and between 
the phosphors. Generally, the black matrix is a photo-absorptive layer 
produced by using photoresisting effect of a photoresist. 
The black matrix for a color CRT is produced by packing illuminescent 
absorptive materials between phosphors. The black matrix prevents the 
contrast of the CRT from decreasing, which is caused by luminescence of 
aluminium layer occurring when the electrons scattered around the inner 
panel of the CRT and the hole of a shadow mask collide with the phosphor 
screen. The black matrix also prevents the chromaticity from decreasing, 
which is caused by luminescence of dots and stripes of the phosphors when 
the neighboring dots and stripes are radiated by the electron beams. 
In general, a process of using a photoresist for forming a black matrix 
takes the following steps. 
A photoresist is coated on the inner surface of a panel, dried by heat or 
other means, and exposed by irradiation of ultraviolet rays through mask 
slots. The exposed panel is washed and developed to remove the unexposed 
photoresist and then dried. Black matrix materials are coated on the panel 
on which the photoresist-coated portion and photoresist-uncoated portion 
are regularly arranged. Then, the black matrix is produced by etching the 
panel. This process, however, has problems of complexity and much 
expenditures. 
To solve the above problems, U.S. Pat. No. 4,921,767 discloses a method of 
manufacturing a black matrix and a phosphor screen by adjusting an 
electrophotographic method to reduce the number of steps in the process. A 
conventional process for manufacturing a black matrix and a phosphor 
screen for a color CRT by a dry electrophotographic method is described in 
FIG. 1 as follows. 
A conductive layer and a photoconductive layer are coated on a washed 
panel, and then an electrical charge is established on the panel. The 
charged panel is exposed and developed by a dry electrophotographic 
method. A black matrix is fixed by irradiating infrared rays from an IR 
lamp on the panel. Electrostatically charged red, green, and blue 
phosphors are fixed on the panel on which the black matrix is not formed 
by a dry electrophotographic method. 
According to the disclosure, the black matrix is mainly composed of carbon 
black and contains proper pigments, such as Fe--Mn oxide, etc., a polymer, 
and a charge control agent as subsidiary components. The mixture is 
dissolved by heat and mixed. The size of the mixture is about 5 .mu.m. 
However, the size of the carbon black used in the disclosure is so large 
that the boundary of the pattern of the black matrix is not properly 
formed. The large size of the carbon black also causes a problem of 
micro-particle scattering around the pattern. Moreover, it is difficult to 
form a thin and dense layer on the inner surface of the panel because the 
carbon black used in the disclosure has a disordered hexagonal layer 
structure. 
SUMMARY OF THE INVENTION 
The present invention is to solve the above problems in the conventional 
art. The present invention provides with a process for preparing a black 
matrix by introducing a wet electrophotographic method improving 
substantially the steps of the process. And the use of graphite as a main 
component of black matrix materials prevents the scattering and improves 
the fineness of the boundary of the pattern of the black matrix and 
improves the cohesiveness to the panel and hiding power, an ability which 
prevents a light emitted when the black matrix and the neighboring 
phosphors are luminescent by electron beams from passing through the 
pattern of the black matrix, because a thin and dense black matrix layer 
is formed on the panel. The present invention also provides a phosphor 
screen where the above black matrix is adjusted to a dry 
electrophotographic method. 
To solve the above problems, the present invention provides with a black 
matrix and a process for preparing thereof comprising the steps of coating 
a conductive layer on the inner surface of a panel for a color CRT, 
overcoating a photoconductive layer on said conductive layer, establishing 
an electrostatic charge on said photoconductive layer, exposing selected 
areas of said photoconductive layer, developing the exposed panel with a 
light-absorptive material including an isoparaffin solvent, graphite, a 
polymer, and a charge control agent, removing a residual solution on the 
developed panel, and fixing said light-absorptive material on the panel. 
The present invention also provides a phosphor screen and a process for 
preparing thereof wherein electrostatically charged red, green, and blue 
phosphors are formed on the photoconductive layer on which the black 
matrix is not formed. 
In the present invention, it is preferable that the electrostatic charge is 
a corona electrical charging, the thickness of the black matrix is about 1 
to 3 .mu.m, and the average particle diameter of the graphite is 0.5 to 
1.5 .mu.m. The residual solution is preferably dried by a vacuum 
absorption method and the fixing of the light-absorptive material is 
preferably performed by using an infrared lamp as a heat source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance of FIGS. 2 and 3, a representative example is described as 
follows. 
FIG. 2 is a flow chart of a process for manufacturing a color CRT in which 
a black matrix is produced by a wet electrophotographic method and then a 
phosphor screen is produced by a dry electrophotographic method according 
to the present invention, and FIG. 3 is a section of a black matrix which 
is being developed by a wet electrophotographic method according to the 
present invention. 
As shown in FIGS. 2 and 3, a panel 1 is washed and 1 to 2 .mu.m of 
conductive layer 2 and 2 to 6 .mu.m of photoconductive (3 of FIG. 3) layer 
is coated on it. An electric charge is established on the photoconductive 
layer and a selected area of the photoconductive layer is exposed. The 
exposed panel is developed with a light-absorptive material including an 
isoparaffin solvent (5 of FIG. 3) having a thickness of 500 .mu.m 
containing 0.5 to 1.5 .mu.m of graphite used as a main component, a 
polymer, and a charge control agent to produce 1 to 3 .mu.m of a black 
matrix. The residual solution of the developed panel is dried by a vacuum 
absorption method and the light-absorptive material is fixed by an 
infrared lamp as a heat source to produce a black matrix 4. To produce a 
phosphor screen for a color CRT, electrostatically charged red, green, and 
blue phosphors are fixed on the photoconductive layer on which the black 
matrix is not formed by a dry electrophotographic method. 
Preferable working examples and reference examples are described below. 
These examples are exemplary only, and the present invention is not 
restricted to the scope of the example. 
WORKING EXAMPLE 1 
A panel was washed and a conductive layer and a photoconductive layer were 
coated on it. A corona electrical charging was established on the 
photoconductive layer and a selected area of the photoconductive layer was 
exposed. The exposed panel was developed with a light-absorptive material 
including an isoparaffin solvent containing 0.5 to 1.5 .mu.m of graphite 
used as a main component, a polymer, and a charge control agent to produce 
a black matrix. The residual solution of the developed panel was dried by 
a vacuum absorption method and the light-absorptive material was fixed by 
an infrared lamp as a heat source to produce a black matrix. 
WORKING EXAMPLE 2 
A black matrix was produced by the same method of the working example 1, 
and electrostatically charged red, green, and blue phosphors were fixed on 
the panel on which the black matrix was not formed by a dry 
electrophotographic method to produce a phosphor screen. 
REFERENCE EXAMPLE 1 
A panel was washed and a conductive layer and a photoconductive layer were 
coated on it. A corona electrical charging was established on the 
photoconductive layer and a selected area of the photoconductive layer was 
exposed. The exposed panel was developed with a light-absorptive material 
including an isoparaffin solvent containing carbon black used as a main 
component, a polymer, and a charge control agent to produce a black 
matrix. The residual solution of the developed panel was dried by a vacuum 
absorption method and the light-absorptive material was fixed by an 
infrared lamp as a heat source to produce a black matrix. 
REFERENCE EXAMPLE 2 
A black matrix was produced by the same method of the reference example 1, 
and electrostatically charged red, green, and blue phosphors were fixed on 
the panel on which the black matrix was not formed by a dry 
electrophotographic method to produce a phosphor screen. 
REFERENCE EXAMPLE 3 
A panel was washed and a conductive layer and a photoconductive layer were 
coated on it. A corona electrical charging was established on the 
photoconductive layer and a selected area of the photoconductive layer was 
exposed. The exposed panel was developed with carbon black used as a main 
component, a polymer, and a charge control agent by a dry 
electrophotographic method to produce a black matrix. The light-absorptive 
material was fixed by an infrared lamp as a heat source to produce a black 
matrix. 
REFERENCE EXAMPLE 4 
A black matrix was produced by the same method of the reference example 3, 
and electrostatically charged red, green, and blue phosphors were fixed on 
the panel on which the black matrix was not formed by a dry 
electrophotographic method to produce a phosphor screen. 
REFERENCE EXAMPLE 5 
A panel was washed and a conductive layer and a photoconductive layer were 
coated on it. A corona electrical charging was established on the 
photoconductive layer and a selected area of the photoconductive layer was 
exposed. To develop the exposed panel to a black matrix, a 
light-absorptive material including graphite used as a main component, a 
polymer, and a charge control agent by a dry electrophotographic method 
were used. 
FIG. 4a is an electron microphotograph in which the black matrix mainly 
composed of graphite and produced by a wet electrophotographic method 
according to the present invention is shown. As shown in the electron 
microphotograph, the diameter of a dot is 0.11 mm, the boundary of dots is 
fine, and the density of the graphite is excellent. 
FIG. 4b is an electron microphotograph in which the black matrix mainly 
composed of carbon black and produced by a wet electrophotographic method 
according to the reference example 1 is shown. As shown in the electron 
microphotograph, the diameter of a dot is 0.11 mm and the boundary of dots 
is somewhat fine but the density of the carbon black is inferior to that 
of FIG. 4a. 
FIG. 4c is an electron microphotograph in which the black matrix mainly 
composed of carbon black and produced by a dry electrophotographic method 
according to the reference example 3 is shown. As shown in the electron 
microphotograph, the thickness of the character is 0.3 mm, the boundary of 
dots is not fine. Moreover, the scattering 6 which is a cause of black dot 
defect is found. 
The process using graphite as a main component and developing by a dry 
electrophotographic method according to the reference example 5 can not 
form a pattern of a black matrix. 
The results of examination for the phosphor screens of working example 2, 
reference examples 2 and 4 are listed in the following Table. 
TABLE 
______________________________________ 
Fineness of the Density 
Boundary of Dots 
Scattering of BM 
______________________________________ 
Working .+-.1 .mu.m 
Not found 
Black 
Exam. 2 
Reference .+-.1 .mu.m 
Not found 
Grey 
Exam. 2 black 
Reference .+-.5 .mu.m 
Many 
Grey 
Exam. 4 black 
______________________________________ 
It will be apparent to those skilled in the art that various modifications 
and variations can be made in the disclosed process and product without 
departing from the scope or spirit of the invention. Other embodiments of 
the invention will be apparent to those skilled in the art from 
consideration of the specification and practice of the invention disclosed 
herein. It is intended that the specification and examples be considered 
as exemplary only, with a true scope and spirit of the invention being 
indicated by the following claims.