U.S. patent number 3,649,269 [Application Number 04/880,497] was granted by the patent office on 1972-03-14 for method of forming fluorescent screens.
This patent grant is currently assigned to Tokyo Shibaura Electric Co., Ltd.. Invention is credited to Tsutomu Kubota.
United States Patent |
3,649,269 |
Kubota |
March 14, 1972 |
METHOD OF FORMING FLUORESCENT SCREENS
Abstract
A method of forming a fluorescent screen on the surface of a
substrate, comprising the steps of: applying a layer of a
fluorescent substance and a resin binder onto one side of a film
sheet which is soluble in a first solvent but insoluble in a second
solvent in which said binder is soluble so as to form a fluorescent
film assembly, coating a resin binder onto the substrate surface
and contacting said one side of said fluorescent film assembly
thereto to cause it to adhere to the substrate and bonding said one
side of said film sheet to said substrate surface by means of said
resin binder which is soluble also in said second solvent so that
said layer of fluorescent substance on said fluorescent film
assembly adheres to said substrate surface, and, then, removing
said film sheet by dissolving it in said first solvent.
Inventors: |
Kubota; Tsutomu (Tokyo,
JA) |
Assignee: |
Tokyo Shibaura Electric Co.,
Ltd. (Kawasaki-shi, JA)
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Family
ID: |
12132792 |
Appl.
No.: |
04/880,497 |
Filed: |
December 11, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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451479 |
Apr 28, 1965 |
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Foreign Application Priority Data
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Apr 30, 1964 [JA] |
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39/24243 |
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Current U.S.
Class: |
430/28; 430/23;
430/253; 430/327; 430/4; 430/139; 430/258; 430/935 |
Current CPC
Class: |
C09K
11/02 (20130101); H01J 9/221 (20130101); Y10S
430/136 (20130101) |
Current International
Class: |
H01J
9/22 (20060101); C09K 11/02 (20060101); H01j
009/22 (); H01j 029/22 (); G03c 011/12 () |
Field of
Search: |
;96/36.1,36,28,93
;117/33.5C,33.5CM,33.5CS,33.5CP,3.1,3.5,3.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
freedman et al., RCA Review, Vol. 12, Sept. 1951, p. 568 and pp.
577-578 relied on. .
Leoy et al., The Prep. of Phosphor Screens for Color Television
Tubes, Apr. 12-16, 1953, pp. 1-3 relied on. .
Sodowski et al., Photodeposition of Luminescent Screens, JOES, Vol.
105, No. 2, Feb. 1958, pp. 105-107 relied on..
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Primary Examiner: Bowers, Jr.; Charles L.
Parent Case Text
This application is a continuation of application Ser. No. 451,479,
now abandoned, filed Apr. 28, 1965.
Claims
I claim:
1. A method of forming a fluorescent screen on the surface of a
substrate, which method comprises:
a. forming a fluorescent film assembly by applying a layer of a
fluorescent material in a binder of polyvinyl alcohol to a support
consisting of a polystyrene paper:
b. converting the polyvinyl alcohol binder to a water insoluble
substance by treating the layer with formaldehyde;
c. bonding the fluorescent film assembly onto the surface of the
substrate by means of a water-soluble, organic solvent insoluble
binder, the fluorescent layer being bonded to the surface of said
substrate;
d. dissolving said polystyrene paper from the resulting article by
applying an organic solvent to said article; and
e. drying said organic solvent containing said polystyrene
dissolved therein, whereby a thin coating of polystyrene is formed
on the layer containing the fluorescent substance.
2. A method of forming a fluorescent screen according to claim 1,
wherein said method includes the steps of preparing a fluorescent
ink by mixing a fluorescent substance with polyvinyl alcohol,
applying said ink onto said one side of the polystyrene paper, and
irradiating said applied ink so as to render said ink
water-insoluble.
3. A method of forming a fluorescent screen according to claim 1,
wherein said method includes the steps of forming a light-sensitive
layer containing at least one fluorescent substance on said
polystyrene paper, exposing said light-sensitive layer to light
rays through a negative mask having a desired figure or pattern,
and developing said light-sensitive layer by removing the unexposed
areas thereof by water so as to leave the developed layer having
the desired figure or pattern of fluorescent material, said
remaining fluorescent material being subsequently transferred by
bonding to the surface of the said substrate in said desired figure
or pattern.
4. The method of forming a fluorescent screen according to claim 1,
wherein said substrate is a face plate of a cathode ray tube.
Description
This invention relates to a method of forming a fluorescent film on
a substrate surface such as the surface of the face plate of a
cathode ray tube, for example, and more particularly to a method of
forming not only a conventional homogeneous fluorescent screen but
also fluorescent films of desired configuration or pattern on a
substrate surface.
Many methods have been used to form fluorescent films on the
surface of a certain kind of substrate. Typical examples of these
prior methods include a method wherein a fluorescent substance is
dispersed in a vehicle, and the vehicle is applied onto a substrate
surface by brushing or spraying to form a fluorescent film; a
method wherein a suspension of a fluorescent substance is caused to
flow down along the inner surface of a tube similar to the method
of preparing the fluorescent surface of a fluorescent lamp; a
method wherein a sulfur vapor is passed through a cathode ray tube
to cause sulfur to deposit on the wall thereof and then a powder of
fluorescent substance is introduced in the tube to be deposited on
the surface of the tube as in manufacturing of the fluorescent
screen of a cathode ray tube; a method wherein an alcoholic
suspension of a fluorescent substance is sprayed onto the surface
of a substrate to form a fluorescent film; a method wherein a
fluorescent substance suspended in water glass is caused to flow
along a substrate surface so as to precipitate the fluorescent
substance thereon; a method wherein a fluorescent screen is
provided by printing a fluorescent substance on a substrate surface
by the silk screen technique, for example; and a method comprising
the steps of flowing a slurry of light-sensitive fluorescent
substance on a substrate surface, rotating the substrate to spread
the slurry over the entire surface so as to dry the slurry, then
irradiating the slurry with ultraviolet ray to harden a binder, and
developing the film to remove undesired portions which were not
subjected to ultraviolet irradiation so as to form a desired
fluorescent film. Of these prior art methods, with regard to the
particular method of using a brush, it is difficult to provide a
fluorescent film of uniform thickness by this method. This is
especially true in a curved surface. While spraying can provide
coated films of relatively uniform thickness, loss of paint is
excessive. Where a slurry containing a fluorescent substance is
made to flow on the substrate surface it is necessary to maintain a
uniform thickness of the slurry such as by imparting a suitable
movement to the substrate until the slurry dries. This method is
not applicable to a substrate surface of irregular configuration. A
method wherein a fluorescent film is formed by applying a
fluorescent substance suspended in water glass onto a substrate is
limited to a substrate provided for a vessel that can contain water
and hence can not be applied to substrates having irregular
surfaces. Moreover by the prior art methods, in order to form a
fluorescent screen of the desired characteristics, for example a
screen that can emit light rays of different colors from different
stripes on dots it is necessary to have independent coating,
exposure and development operations for different stripes, dots and
colors, thus complicating the manufacturing procedures extremely.
Especially, when the light-sensitive substance is utilized as a
binder, the brightness of the fluorescent screen produced is
decreased.
An object of this invention is to provide a novel method capable of
forming a fluorescent film of uniform thickness, of the desired
configuration and pattern on a flat plate as well as a curved
surface of a substrate.
Another object of this invention is to provide a method of applying
a fluorescent substance onto a substrate surface without
appreciable loss of the material.
Still another object of the invention is to provide a method of
forming a fluorescent film without decreasing its brightness.
Yet another object of this invention is to provide a method of
forming a fluorescent film of any desired pattern.
Briefly stated, this invention contemplates the steps of forming a
layer of a fluorescent substance of a first color on a film which
is soluble in a first solvent for example an organic solvent, but
insoluble in a second solvent, for example water. The fluorescent
substance on the otherhand is insoluble in the first solvent but
soluble in the second solvent. The film is made to adhere onto a
substrate surface by means of a binder which is soluble in said
second solvent. Thereafter said film is removed by dissolving it by
means of said first solvent so to form a fluorescent film on the
substrate.
Those features of the invention which are believed to be novel are
specifically set forth in the claims attached hereto. The invention
will, however, be better understood and further advantages thereof
appreciated from a consideration of the following description and
drawings, in which:
FIG. 1 is a block diagram showing successive steps of forming a
fluorescent film in accordance with one example of this invention;
and
FIGS. 2a and 2b are sectional views showing different steps of said
example .
Referring now to the accompanying drawing, a suspension (in the
form of a paste or a slurry) is prepared by incorporating a
fluorescent substance into a water soluble binder. The suspension
is then applied to a desired thickness onto a sheet or film 11 of
plastic, for instance, which is soluble in organic solvents but
insoluble in water, by means of a film-coating machine provided
with a doctor knife or an air knife and then dried to form a
fluorescent film or layer 10. The layer may be applied on the
entire surface of the film 11 or a portion thereof, the latter mode
of coating being utilized to form a figure or pattern. Such a
partial coating may be provided by printing a portion of the
plastic film or by coating the entire surface thereof and then
removing undesired portions by mechanical working or by applying a
mixture of a fluorescent substance and a light sensitive substance
and then removing undesired portions by a photochemical
technique.
Then the coated film 11 is placed on one surface of a substrate 13
such as a face plate of a cathode ray tube by means of a
water-soluble binder 12 with the fluorescent film 10 facing the
substrate surface. After setting the binder, the film 11 is
dissolved off by a solvent capable of dissolving it to transfer the
film 10 onto the substrate surface so as to form the desired
fluorescent film 11a, as shown in FIG. 2b.
The configuration of the substrate utilized in this invention may
be any suitable shape. For example, where the surface of the
substrate is not flat the base film may be molded beforehand by
using a thermoplastic material to have a surface corresponding to
the surface of the substrate and then cemented to it.
The following specific examples are given by way of illustration
and are not to be construed as limiting in any way the scope and
spirit of the invention.
EXAMPLE 1
A slurry comprising 10g. of polyvinyl alcohol, 50g. of fluorescent
substance consisting of zinc sulfide and 100 cc. of water was
applied on a polystyrene paper of 0.50 mm. thick to a thickness of
about 0.02 mm. by a conventional method and then dried to form a
fluorescent film assembly. A convex substrate made of polyester was
used having the same surface as the internal surface of a cathode
ray tube, including a face plate whose diagonal dimension was 14
inches. The base film was molded at a temperature of about
105.degree. C. to the screen on the side of the base film which did
not engage said convex substrate. Thereafter the base film was cut
to have a configuration and dimensions corresponding to those of
said cathode ray tube internal surface. A solution of polyvinyl
alcohol was then applied by spraying on the face plate of the
cathode ray tube and said fluorescent film assembly was caused to
adhere with its fluorescent screen in contact with the inner
surface of the cathode ray tube. The assembly was dried at a
temperature of below 60.degree. C. After the entire surface of the
fluorescent film was in close adherence to the internal surface of
the cathode ray tube the interior of the tube is treated with 100
cc. of benzene to completely dissolve the polystyrene paper of the
fluorescent film assembly. After removing the solution, 100 cc. of
benzene was again introduced in the cathode ray tube to wash the
internal surface. When dried, polystyrene contained in the benzene
remained in the tube to form a thin film on the internal surface of
the cathode ray tube. This film served as the base film for a
vapor-deposited aluminum coating.
EXAMPLE 2
A suspension was prepared consisting of 8 g. of polyvinyl alcohol,
6 g. of zinc sulfide and 100 cc. of water. An enclosure of 10
cm..times.10 cm. was formed on a flat polystyrene paper mounted on
a glass sheet and the suspension was poured into the enclosure to
fill it. The suspension was then dried while the polystyrene paper
was maintained in the horizontal position to form a fluorescent
film assembly, including a film of zinc sulfide and polyvinyl
alcohol adhering to the polystyrene paper. A thin film of water
glass was coated on a separate glass sheet and the fluorescent film
assembly was caused to adhere to said water glass film by
contacting the film consisting of zinc sulfide and polyvinyl
alcohol therewith. After drying, the polystyrene paper was
dissolved by means of trichlene. Thereafter, the glass sheet was
fired at a temperature of 350.degree. C. to oxidize and evaporate
polyvinyl alcohol to obtain a glass sheet having a fluorescent film
of 10 cm..times.10 cm.
In this example, when the polystyrene paper with a thin fluorescent
film of zinc sulfide and polyvinyl is so worked as to obtain a
desired figure or pattern, a fluorescent film of the desired figure
or pattern can be provided on the glass sheet.
Instead of mechanically working the polystyrene paper as above
described for the purpose of providing a fluorescent film of the
desired figure or pattern, a light-sensitive aqueous solution
comprising 3 g. of ammonium bichromate and 100 cc. of water may
applied by brush on a zinc sulfide fluorescent substance-polyvinyl
alcohol film formed on the polyethylene paper and then dried. After
putting the film with the desired figure onto the dried film, the
composite film was then irradiating by a 100 v., 30 A. carbon arc
lamp situated at a distance of 50 cm. Thereafter, the film was
developed with water to set portions, of the polyvinyl alcohol
irradiated by light rays while dissolving in water the remaining
portions so as to form a fluorescent film of the desired figure or
pattern on the polystyrene paper. This fluorescent film was then
treated in the same manner as described hereinabove to provide on
the glass sheet a fluorescent film of the desired figure or
pattern.
EXAMPLE 3
A polystyrene paper of 0.25 mm..times.35 cm..times.30 cm. was
placed on a flat aluminum sheet of 30 cm..times. 25 cm. and the
peripheral edges of the polystyrene paper were folded back on the
aluminum sheet and fastened thereto by an adhesive tape. In this
case care was taken to closely contact the polystyrene paper with
the flat aluminum sheet. The aluminum sheet was placed on the
bottom of a glass vessel of the dimension 35.times. 30.times. 20
cm. and having a water drain port at the bottom. After closing the
water drain port 50 cc. of 5 percent aqueous solution of barium
nitride was added to the vessel and thereafter 15 L. of deionized
water was added. A suspension consisting of 5.5 g. of blue
fluorescent substance of zinc sulfide, 30 cc. of 15 percent aqueous
solution of water glass and 300 cc. of deionized water was poured
into the cushion liquid prepared as above described by means of a
sprinkling funnel. The mixture was left standing still for 20
minutes to precipitate the zinc sulfide fluorescent substance and
then the bottom drain port was opened to drain the remaining
liquid. Thereafter the aluminum sheet bonded with the polystyrene
paper was removed from the vessel and dried in a stream of drying
air. Subsequent to drying the aluminum sheet was mounted in a
whirler with the surface of the fluorescent substance directed
upward and a light sensitive liquid consisting of 5 g. of polyvinyl
alcohol, 100 cc. of deionized water and 0.5 g. of ammonium
bichromate was poured onto the aluminum sheet to uniformly cover
the fluorescent screen and the aluminum sheet was then dried at a
temperature of less than 50.degree. C. A separately prepared
negative film including stripes of black lines of 0.75 mm. width
each and white lines of 0.3 mm. width each was placed on the
fluorescent screen and the assembly was put in a printing frame to
be irradiated for 3 minutes by a 100 v. 30-A. carbon arc lamp
positioned at a distance of 50 cm. The aluminum sheet was removed
from the printing frame, immersed in water for 1 minute and then
developed by subjecting it to water spray to produce strips of the
fluorescent substance of 0.3 mm. wide and spacings 0.75 mm. Similar
procedures were made for green and red fluorescent substances. As
this time portions of the stripes of blue fluorescent substance
were covered by a cellulose tape to prevent adherance of the
subsequently applied fluorescent substances. When exposing to light
rays the white lines of the negative films were positioned close to
and in parallel with the stripes by utilizing the stripes as the
reference. Thus it is possible to prepare a polystyrene paper
having parallel stripes of blue, green and red fluorescent
substances. This polystyrene paper having stripes of the
fluorescent substances was then bonded to the internal surface of
the face plate of a cathode ray tube including a flat substrate
surface by means of a thin film of a 1 percent aqueous solution of
polyvinyl alcohol applied to said inner surface with the
fluorescent film in contact with the inner surface of the face
plate. At this time, care should be taken not to include air
bubbles. After standing still for 2 hours benzene was poured onto
the face plate to dissolve off said polystyrene paper and then
benzene was removed. After washing the surface of the fluorescent
substance with fresh benzene the assembly was dried to form a thin
film from a small amount of polystyrene contained in the benzene
remaining on the fluorescent substances so as to provide a face
plate for a cathode ray tube having a striped screen of three
colored fluorescent substances of uniform film thickness.
EXAMPLE 4
A polystyrene paper of 40 cm. diameter and 0.5 mm. thick was put on
a Bakelite lamination of the same diameter and 10 mm. thick, and a
Bakelite cylinder of 40 cm. outside diameter, 10 mm. wall thickness
and 50 mm. height was put thereon in concentric relation. The
bottom of the Bakelite cylinder was fastened to the Bakelite
lamination by means of four clips. A rubber packing was provided at
the lower surface of the Bakelite cylinder to form a shallow bucket
with a bottom of polystyrene paper. This bucket was mounted on a
slurry machine utilized in preparing shadow mask color cathode ray
tubes. After wetting the polystyrene paper with an aqueous solution
of a suitable surface active agent (Dryzell diluted with 200 parts
of water) a slurry of green fluorescent substance was applied by a
process commonly utilized for applying slurries. The composition of
this slurry comprised 30 g. of a green fluorescent substance, 100
cc. of a 10 percent aqueous solution of polyvinyl alcohol, 80 cc.
of ion exchange water and 5 cc. of a 20 percent aqueous solution of
ammonium bichromate. While rotating the bucket said slurry was
poured onto the polystyrene paper to spread it over the entire
surface of the paper and while heating and drying from above at a
temperature of less than 50.degree. C. the bucket was inclined to
remove surplus slurry from the bottom portion thereof so as to form
a fluorescent film of uniform thickness on the polystyrene paper.
Thereafter the polystyrene paper formed with the fluorescent film
was removed from the bucket and then irradiated and developed in
the same manner as described in connection with Example 3 by
utilizing a negative film having a stripe pattern consisting of
white lines of 0.2 mm. width each and black lines of 0.3 mm. width
each so as to provide stripes of blue fluorescent substance of 0.3
mm. width. Then portions of the stripes were covered by a cellulose
tape and a blue fluorescent substance was applied thereon by the
procedure described above. A negative film was used to effect
similar printing and development by utilizing as the reference,
stripes of the green fluorescent substance remaining outside of
what was coated by the blue fluorescent substance owing to the
presence of a cellulose tape so as to cause the blue fluorescent
substance to remain so as to fill alternate spaces between stripes
of green fluorescent substance. By the same process as above
described, red fluorescent substance was applied on the remaining
spaces between stripes of green fluorescent substance so as to
obtain a polystyrene paper with stripes of fluorescent substances
arranged in the order of green-blue-green-red-green-blue-green-red.
0.5 percent aqueous solution of polyvinyl alcohol was applied on
the inside of a cathode ray tube having a cylindrical screen
surface of type 10 to form a thin film and said polystyrene paper
which has been cut to the same size of the screen surface with due
consideration of the position of stripes of fluorescent substances
was bonded to the face plate with the fluorescent film in contact
with the inner surface of the face plate. After standing still for
one night toluene was poured on said face plate to dissolve the
polystyrene film and by removing most of the remaining polystyrene
by additional toluene a fluorescent film protected by a very thin
film of polystyrene was resulted.
EXAMPLE 5
Instead of utilizing a slurry having incorporated therein a
light-sensitive substance as in Example 4, a fluorescent film of
any desired figure may be produced by spraying polyvinyl alcohol or
other suitable binder on a polystyrene paper so as to apply a
fluorescent substance thereon, forming a film of a light-sensitive
resin on the fluorescent substance, producing a fluorescent film of
a desired pattern by utilizing negative film having said pattern,
and bonding the fluorescent film to the substrate surface by a
method analogous to that described above. Alternatively, similar
fluorescent film may be produced by applying a fluorescent
substance on a polystyrene paper by the aid of polyvinyl binder,
imparting light-sensitive characteristic to the fluorescent film by
means of a solution of ammonium bichromate and then treating the
film in the same manner as above described.
Although in the above-described examples, a light-sensitive
fluorescent film was formed on a polystyrene paper, then the film
was exposed to light and developed and the resultant film of a
desired pattern was bonded to the surface of a substrate, it should
be understood that this invention is not limited in any way to such
particular process steps. For example, after bonding a film of a
fluorescent substance to a substrate surface a fluorescent film of
the desired figure or pattern can be produced by utilizing a
negative mask.
Printing techniques can also be used, for example, fluorescent
substances for emitting desired primary colors are added to an
aqueous solution containing one or more water-soluble binders such
as polyvinyl alcohol, polyacrylamide, carboxylmethyl cellulose, et
cetra so as to prepare several types of printing ink. Thereafter
these inks are used to print successive stripes on a film such as a
polystyrene paper, cellulose acetate and the like which are soluble
in benzene, toluene, xylene or mixed organic solvent consisting of
one or more of these organic solvents and ketone or alcohol but not
insoluble in water. The printing technique used can be a silk
screen or intaglio-printing technique which can apply inks in a
relatively large thickness. After drying the fluorescent inks
printed on the film, thus providing a fluorescent screen, the film
is bonded to the desired substrate surface within a cathode ray
tube by using an aqueous solution of polyvinyl alcohol, polyacrylic
amide, carboxylmethyl cellulose or water glass with printed side
thereof contacted with the substrate surface. Thereafter, the
substrate film is dissolved by said organic solvent so as to form a
fluorescent screen.
The thickness of the substrate film soluble in organic solvents
utilized in this example is not limited to any particular value but
preferable thickness is in a range of from 0.1 to 0.2 mm. when
easiness of handling and dissolving and mechanical strength are
considered. Formed polystyrene sheet is suitable because of its
good solubility. Where the substrate film is made of thermoplastic
material such as polystyrene or cellulose acetate, it is possible
to readily form fluorescent films on curved surfaces because such a
substrate can be deformed under heat to align with the curved
surface after it has been printed with an ink containing
fluorescent substance.
While the concentration of an aqueous solution of the water soluble
binder utilized as the printing ink is not limited by the quantity
of incorporation of the fluorescent substance, where the ink is
prepared from 2 parts of the fluorescent substance and 1 part of
said aqueous solution concentration of 7 to 25 percent by weight,
results in inks of suitable viscosity and easy to use. Water glass
is not suitable because an ink utilizing it requires relatively
long drying time after printing. Also the concentration of the
binder utilized to bond said printed and shaped fluorescent layer
to the surface of a substrate is not limited to any particular
value but 10 percent, by weight, was found suitable.
In this embodiment the principle of transfer picture is utilized.
More particularly, fluorescent films of the desired shape and
pattern are sequentially printed on a sheet or film of substrate
which is readily soluble in organic solvents by utilizing inks
containing fluorescent substances of different primary colors, and
then the printed film of substrate (if required after being shaped)
is bonded to the desired substrate surface of the cathode ray tube.
Instead of tearing off the bonded substrate film, it is dissolved
off means of organic solvents so as to form the desired fluorescent
screen. Although in the prior method of preparing screen for use in
chromatron-type color-receiving tubes, fluorescent films of
different shape, stripes pattern and color were successively formed
on the surface of a substrate, this invention can not only
eliminate such a troublesome procedure but also can be practiced at
room temperature and without utilizing any light source. Even when
the surface of the substrate which constitutes the fluorescent
screen is curved as in conventional cathode ray tubes, it is
possible to closely bond the fluorescent film to such a curved
surface by printing the fluorescent film on a sheet of a
thermoplastic material and then premolding this thermoplastic sheet
under heat to the same contour as the substrates surface.
Moreover, as the binder utilized as the ink and for bonding the
fluorescent film to the substrate is soluble in water it would not
affect these films and substrate. As a result the printed and
molded layer of the fluorescent substance would not be deformed or
damaged because of the absence of elongation and extension of the
substrate film. Further the substrate film can be readily removed
by dissolving it in an organic solvent after the fluorescent film
has been bonded thereto. As a result of experiment I have found
that a polystyrene substrate having a thickness of 0.2 mm. and
adapted to form the fluorescent screen of a 16 inch cathode ray
tube could be dissolved in less than 1 minute by benzene and was so
perfectly removed that there was no impurity remaining on the
fluorescent screen prepared according to the method of this
invention.
As can be noted from the foregoing description according to the
method of this example fluorescent screens of any desired shapes
and patterns can be very simply and readily formed on substrates
having flat or curved surfaces, and as the fluorescent screens thus
formed are free from any light sensitive substance there is no fear
of decreasing their brightness.
EXAMPLE 6
It was found that when a water-soluble binder is used not only to
bond a plastic film provided with the desired fluorescent substance
to the substrate but also as an ink for printing the fluorescent
substance, this substance tends to blur. By this reason it is
necessary to convert the binder mixed with the fluorescent
substance to a state insoluble in water after the fluorescent
substance has been bonded to the substrate. This example shows use
of a binder which can be convertible to water-insoluble state when
irradiated by light rays or other radiations.
More particularly, as the fluorescent substance, zinc sulfide was
used; and as the binder convertible to water insoluble state upon
being irradiated by radiations, polyvinyl alcohol containing
ammonium bichromate was used. The composition of the fluorescent
ink was as follows
polyvinyl alcohol 20 g. ammonium bichromate 1 g. zinc sulfide
fluorescent substance 200 g. water 100 cc.
The fluorescent ink prepared by thoroughly mixing this composition
was applied by printing on a foamed polystyrene paper of 0.2 mm.
thick .times. 450 mm. .times. 500 mm. As the polystyrene paper is
insoluble in water and not swollen by water it would not undergo
any deformation when printed with this fluorescent ink. Then the
printed surface was irradiated for 10 minutes by ultraviolet rays
which emanated from a 15 A. carbon arc situated at a distance of
1.5 meter. When this radiation source is used, irradiation for 5 to
10 minutes from a distance of 1 to 1.5 meter is generally
satisfactory. As a result of this irradiation, polyvinyl alcohol
contained in the fluorescent ink will set to a water-insoluble
state. Then the polysytrene paper having a printing of fluorescent
film was molded in a mold having the same curved surface as the
inside substrate of the cathode ray tube. A 10 percent aqueous
solution of polyvinyl alcohol serving as a binder was applied on
the surface of a substrate contained in a cathode ray tube, and the
film printed with the fluorescent substance was urged against the
substrate by means of a resilient body such as a soft polyurethane
foam with the printed surface in contact with the applied
binder.
In this state as the fluorescent ink has been converted to
water-insoluble state there was no fear of disintegrating the
printed pattern when contacted with the water contained in the
binder. After drying the assembly at room temperature to solidify
the binder, benzene was poured onto the assembly to dissolve the
polystyrene paper. After removing the benzene solution the assembly
was dried to remove nearly all of polystyrene. Since polyvinyl
alcohol is not soluble in water the desired printed pattern of the
fluorescent substance remained on the substrate surface.
When a relatively small quantity of benzene is used a portion of
polystyrene will be left as a thin film covering the printed
fluorescent film after benzene has been evaporated, so that is is
possible to form a so-called metal back by depositing thereon
aluminum by vacuum deposition.
EXAMPLE 7
While in Example 6 polyvinyl alcohol containing ammonium bichromate
was used as a binder for the fluorescent substance that can be
hardened by irradiation, such a binder is disadvantageous in that
it decrease the brightness of the fluorescent substance.
This example is directed to obviate such difficulty. More
particularly, a fluorescent film was prepared on a water insoluble
film by printing or coating a fluorescent ink utilizing polyvinyl
alcohol as the binder and a portion of the polyvinyl alcohol was
converted to formal to render it water resistant. Thus the
formalized polyvinyl alcohol is effective to firmly secure the
fluorescent film when it is bonded by an aqueous binder so that the
fluorescent film will not blur when it is transferred onto the
surface of a substrate of a cathode ray tube by using an aqueous
binder, thus forming sharply defined fluorescent screen.
For example, a fluorescent slurry consisting of 60 g. of polyvinyl
alcohol, 500 cc. of water and 180 g. of zinc sulfide fluorescent
substance was applied on a polystyrene paper to a thickness of 0.25
mm. by means of a dip coating machine, and then dried. When this
polystyrene paper provided with a uniform coating of the
fluorescent slurry was dipped in water it was noted that a portion
of white powders of the fluorescent substance was released in water
within less than 30 seconds. On the other hand said polystyrene
paper was immersed for 20 minutes in a formalizing bath consisting
of 100 g. ammonium sulfate, 20 g. of 37 percent formaline, 80 g. of
nitric acid (d = 1.84) and 200 cc. of distilled water to formalize
a portion of the fluorescent film applied on said polyethylene
paper. The paper was washed with water followed by drying. Even
when the partially formalized fluorescent film was immersed in
water for more than 10 minutes it was found that powders of the
fluorescent substance were not released in water. A separately
prepared glass substrate was covered by pouring on it a 2 percent
aqueous solution of polyvinyl alcohol and after removing excess
aqueous solution by inclining the glass sheet said polystyrene
paper was bonded to it with said partially formalized fluorescent
film in contact with the binder. During this transfer printing no
spot was formed in the fluorescent film. The glass sheet bonded
with the paper was left at a standstill for one night and then
dipped in a bath filled with toluene to dissolve polystyrene paper.
The glass was taken out of the bath and then washed with fresh
toluene to remove most of the remaining polystyrene. After drying,
fluorescent film transferred on the glass sheet was obtained. When
the quantity of toluene is reduced to a proper value a small amount
of polyethylene will remain on the sheet so that a thin film of
polyethylene is for providing a metal back may be produced on the
fluorescent film after evaporation of toluene.
As a further example a fluorescent ink consisting of 20 cc. of 10
percent aqueous solution of polyvinyl alcohol and 200 g. of zinc
sulfide fluorescent substance was printed on a polystyrene paper of
0.25 mm. thick by using a silk screen printing technique and the
printed paper was dried for one night at room temperature.
Thereafter the paper was immersed for 10 minutes in a liquid
consisting of 100 g. of ammonium sulfate, 28 g. of 27 percent
formaline, 70 g. of sulfuric acid (d = 1.84) and 200 cc. of
distilled water, and then dried. When the polystyrene paper not
subjected to this treatment was immersed in water it was noted that
a portion of the fluorescent substance had dissolved in water in
less than approximately 20 seconds, but the polystyrene paper
treated as above described did not show any release of the
fluorescent substance even when it was immersed in water for more
than 10 minutes. A binder consisting of 5 cc. of 10 percent
solution of polyvinyl alcohol and 55 cc. of water was applied to
coat the entire surface of a face plate of a cathode ray tube said
fluorescent film which has been undergone said formalizing
treatment was bonded under pressure to the face plate. Since the
fluorescent film transfer printed in this manner has no tendency of
dissolving and disintegration by the water soluble binder it can
preserve its brightness during the life of the cathode ray
tube.
Thus in accordance with the method of this invention, layers of
fluorescent substances of the desired color and pattern are applied
on a film to a desired thickness then these layers are bonded to
the surface of a substrate to which the layers are finally to be
transferred, and then the layer is dissolved away to leave only the
fluorescent layers. Moreover as the film is flexible, and can be
shaped into a curved surface it is able to readily form layers of
fluorescent substance of the desired shape, pattern and uniform
thickness not only on flat plate but also on curved plate. Further
as the layers of fluorescent substance are placed on the film by
printing or other method it is not only possible to avoid undesired
loss of the fluorescent substance but also to readily form desired
patterns, so that the invention is particularly suitable for
providing fluorescent screens in color cathode ray tubes.
While the invention has been explained by describing particular
embodiments thereof, it will be apparent that improvements and
modifications may be made without departing from the scope of the
invention as defined in the appended claims.
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