Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIFICATION
Background of -the Invention
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This invention relates in genera]. to the fabrication
of phosphor screens for ca-thode ray tubes, and more particula.rl.y
to imp.roved methods and structures for appl.ying a metal layer
on the phosphor screen of a television cathode ray tube of a
type havi.ng an envelope which includes a separate faceplate
section. The metal layer, typically aluminum, has the. following
primary functions~ First, it serves as the high voltage
accelerating a.node for the ca.thode ray tube and acts as an
electrically conductive layer for preventing the build up of
charge on the screen. ~econd, it reflects to the viewer light
emitted rearwardly by the phosphor screen. Third, it.. acts as
a phys.ical ba.rrier preventing negative ions from striking the
phosphor screen.
It is standard pra.ctice in the fabrication of cathode
ray tube screens to deposit a phosphor layer containing the
phosphor material and a binder on the inner surface of the
faceplate. Subsequently, a thin layer of aluminum is evaporated
on the phosphor layer. Before the metal layer is deposited on
the phosphor layer, an intermediate smoothing film is applied
; in order to improve the surface characteristics of the deposited
aluminum la.yer.
The deposition of the-thin metal layer, due to the
nature of the vacuum deposition process, involves mounting the
faceplate on a va.cuum chamber, pumping the chamber down to a
vacuum, heating a boa.t of aluminum and timing the evaporation
to insure deposition of a metal layer having the appropriate
thi~ness ~typically 1500 A). The metal layer is desirably
thick enough to reflect light emitted by the phosphor screen
and yet thi.n enough to be transpa.rent to the electron beam.
The described evaporation process, particularly w~en set up
on a. ~i.gh volume assembly line, is undesirably expensive.
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This inventioll is dir~cted to an improve~d catho~
xay tube screen meta]izatioll process i~volving the transfer of
a metal layer to the screen. It has been suggested in U. S.
patents No. 2,734,013; 3,389,030; and 3,649,269 that a phosphor
layer may be Eormed on the faceplate of a cathode ray tube by
a transfer process. These patents discuss transfer processes
in which a self-supporting we~ or decal containiny a phosphor
material and a binder is formed on a base and then subsequently
transferred to a flat plate or cathode ray tube faceplate.
Metalization of the transferred screen is achieved by conventional
evaporation techniques after formation of the screen. U.~. Patent
No~ 2,734,013 suggests as an alternative, without elaboration,
that the "...light-re~lecting layèr may be applied...during~
lS ~-abrication of the decalcomania..."
None of these teachings are useful in solving the
problem to which the present invention is addressed or at
least the following reasons. The present invention involves
the metalization of color phosphor screens, the phosphor
patterns on which are, in the most common application, formed
by photochemical processes which employ each tube's shadow
mask as the mask for the phosphor pattern. A phosphor screen
with a pre-formed phosphor pattern is thus not useful. Further,
none of these patents deal with the metalization of pre-ormed
phosphor screens.
. The brief suggestion in the '013 patent that the
light-reflective layer may be trans~erred along with the phosphor
layer is neither substantiated nor useful in the context of the
present invention. UOS.P. 2,73~,013 su~gests the feasibility of
tran~erring a metal layer to a cathode ray tube faceplalte,
which la~er is supported on a laminate comprisin~ a layer o~
p~vsphor in a binder and a second ~ilm layer serving as ~ s~ooth
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base for the metal layer. The present invention is addressed to
the much more difficult and dissimilar problem of transferring
a very thin and frayile, unsupported layer of metal, typically
only 1500 A thick, to a preformed patterned phosphor screen
without tea.ring of the layer and with satisfactory uniformity
and yield.
Metalization by direct tra.nsfer techniques has been
known to be successfully tried only on small articles, as dis-
closed, e.g., in the article "Application of the Transfex Tape
Technique in Electron Tubes", ADVANCES IN ELECTRO~ TUB~ TEC~IQUES ,
Proceedings of the 6th National Conference, ~eptember, 1962
Other Prior Art
U. S. Patent No. 2,858,233
objects of the Invention
~ It is a general object of this invention to provide
improved methods and structures for metalizing the phosphor
screen of a cathode ray tube.
It is a less general object to provide methods for
meta.lizing ca.thode ray tu~e screens whlch are vastly more
simple and economical than the prior art vacuum metalization
methods.
It is yet another object to provide such metalization
methods and structures which yield a. meta.l layer having greater
reflect~v~ty than prior art methods and structures, and thus -
to provide metalization methods and structures which result in
a greater luminous output from the processed cathode ra.y tube~
Brief Descrip_ion of the Drawings
The features of the invention which are believed to be
novel are set forth with particularity in the appended claims.
3~ The invention, together with further obje-cts and advantages
thereof, ma.y best be understood by reference to the following
descripti.on taken in conjunction with the accompa.nying dr.awings
and in which:
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E`igures 1-8 show, in highly schematic fashion, a
method and structure for metali~ing a cathode ray tube screen
in accordance with this invention, and
Figures ~ depict an alternative method for imple-
menting the principles of this invention.
Description of the Preferred Embodiments
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This invention has general applicability to the metal-
ization of phosphor screens of cathode ray tubes of the types
having envelopes including a discrete faceplate or front panel~
~n accordance with -this invention, the phosphor screen o:E a
cathode ray tube is metalized by a transfer process which involves
:Eorming a layer of metal to be applied to the screen on a
substrate and subsequently transferring the metal la.yer to the
phosphor screen. In a preferred method of practicing the in
vention, shown diagrammatically in Figures 1-8, the-substrate
is adapted to be stripped from the tra.nsferred metal layer.
Before engaging a. discussion of the preferred screen
metaliæation process, there will first be described a preferred
method for forming a metalized web from which the metal layer is
transferred. Figure 1 illustrates a substra.te 10. For reasons
which will become clear as this description proceeds, the substrate
10 is preferably composed of a flexible and deformable ~aterial
which may, for reasons stated below, be a thermoplastic material,
such as a polyester, having a~thickness approximately .0005 inch,
however, it is contemplated that substrates composed of other
materiais such as polypropylene and shrinkable polyester may
be used.
A release agent 12 is preferably employed to release
from the substrate 10 layers subsequently deposited thereon.
The release agent must be compatible with the operatiorL and ~:~
manufacture of the involved cathode ray tube and must provide
a smooth ba~e for successively deposited layers; it may be
removable~ as by dissolution or volatilization.
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By wa~ of example, i.t has been found ~hat a 4 x 10 7
inch layer o~ evaporated sodium chlor:Lcle wor]cs very satisfactorily~
It is contcmpl.atcd that other materials such as potas~ium chloride,
or other salts may also be emplo~ed. Sodium chloride has ~een
used previously as a release agent i.n an experimental image
tube manufacturing process wherein a layer thereof was deposited
upon a.-Elat glass substrate, followed by evaporation of a layer
. of a].uminum. The substrate was immersed in a solvent which
dissolved the sodium chloride, permit-tin~ the aluminum layer
to float free in the solvent. The aluminum layer was lifted
from the solv_nt and deposited upon the faceplate of a pre-
screened image tube.
. Figure 2 SllOWS the Figure 1 substrate 10 a.nd release
agent 12, upon which is deposited a thin layer 14 of electrically
conductive, light reflective material such as alumi.num. In
success~ul reductions to practice of the present invention, a
layer of aluminum approximately 1500 A thick was evaporated on
~he substrate 10 and release agent 12 in a conventiona.l vacuum
deposition chamber.
~0 To cause the metal layer 14 to adhere to a phosphor
layer on the inner surface o a cathode ray tube faceplate (to
be aescribed in d~tail be.low), a thin layer of adhesive 16 is
deposited upo~ the metal layer 14 and cured. In accordance
with this e~bodiment of the invention, the adhesive is pre~exably
a. pressure-sensitive adhesive su~h as K-396N or 86-2003, manu-
~a~ture~ by National Starch & Chemical Corporation, which is
capable of being converted to gaseous form if heated to tempera-
tures above about 400~C. By way of example~ a 100-400 A layer
o~ such adhesive may be employed as the adhesive 16.
The adhesive 16 preerably ~as a high flash point in
the intere~t of saety; it a.lso must be compatible with cathode
ray tub~ m~nufacture and ope.rationO It is desirably used i~ the
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smallest amount as possible which will cause satisfactory
adhesion of the metal layer since lt will ul.timately have to
be baked out through the transferred metal layer. In the pre-
ferred method of application the adhesive .is sprayed upon the
metal layer 14 so as to form a discontinuous layer comprising
discrete adhesive drops spaced on the surface of the metal
layer 14. It is contemplated that other adhesives than those
described and other application methods may be employed to
carxy out the teachings of this invention.
Figure 4 depicts a cathode ray tube faceplate 18
having disposed on an inner surface 20 thereof a phosphor layer ~.'
22 comprising a phosphor material held in a pho-tosensitized
binder. The phosphor layer 22 may be deposited by conventional
slurry techniques and comprises, ,in a color cathode ray tube,
e.,g., successively-deposited layers of red-emissive, blue-
emissive and green-emissive phosphor materials carried typically
in a photosensitized binder of PVA (polyvinyl alcohol).
Figure 5 illustrates a step wherein the web 24, com-
. pri'sing subs~rate 10, release agent 12, metal layer 14 and
adhesive 16, is applied to the phosphor layer 22. In the
schematic Figure 5 illustration, the application is accomplished
by first draping the web 24 o,ver a mandril 26. In the Figure 5
illustration, the mandril 26 is shown as comprising a base 28
having an upper surface 30 having generally the contour of the
-~ inner surface 20 of the faceplate 18. Disposed on ~he base 28 , ~-
is a resilient cushion 32 which is somewhat thicker in the center ~ -
than on the edges in order that the mandril will have a yiel,dable
upper surface and in order that the mandril will cause the web 24
to engage the phosphor layer 22 initially in the center of the
: 30 faceplate and thereaftar to cause the web to be pressed against
.the phosphor layer 22 progressively outwardly from the :Eaceplate :
centerO By this technique, ~ormation o~ -
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bubblcs under the ~eb is precluded. ~ simi.lar presCli.ng technique
is disclosec~ in thc referent patent 3,389,030 in thc manufacture
of black and white cathode ray tubes. Other mandril structures
~nd applica~ion techniques may be employed. It may be desir~hle,
in order to effect a more rapid or more conforming applica~ion of
the web 24 to the phosphor layer 22, to apply heat and/or air
pressure to the web 2~ as it is applied to t.he mandril or to
the phosphor layer 22.
After the web 24 is adhered to the phosphor layer 22,
the mandril 26 is removed, leaving on the faceplate.a decal
having the shape of the cathode ray tube screenO The invention
is preferably employed for metalizing a phosphor screen of the
"black surround" type describe~ and claimed in U. S. Patent No.
3,146,368.- Fiore et al. A phosphor screen formed according
to this patent has black material separating phosphor elements
which emit different colored light. The black materia1 typically
extends beyond the electron-illuminated fieId and onto the sides
of the faceplate. The decal preferably overlaps the black
material in a screen of this t~pe, precluding any need to form the
decal to the exact shape of the electron-illuminated field. The
decal may be formed by pre-cutting an outline of the decal
configuration with perforations befoxe transferring the decal,
~r, alternatively, the decal may be trimmed in situ. The shape
of the metal layer deposited`on the substrate can be determined,
if desired, by evaporating the metal layer onto ~le substrate
through a mask having an opening corresponding in configuratlon
to ~he screen configuration. Alternatively, a pre-cut decal,
ra~her than a ~ontinuous web, hAving the configuration of the
screen may be employed~ .
In order to minimize breaking of the metal layer during
~he web draping operation, it ma~ be desirable to pxe~:Eorm or
partiall~ pre-form the substxatQ to the contour of the ma~dril
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or the f~ceplate be~ore ~eposition of th~ metal 3.ayer thereon.
So that the substrate may nevertheless be handled in roll form,
~ pre-contoured decals may be ~ormed at intervals on a substrate
. roll~ the decal~ corresponding generally in size and configura~
tion to the screen and having concentric circular or rectangular
flutes or corrugations defining a flat bellows whi.ch is expan~
sible out of the plane of the we~ without stretching thereof.
When the decals.are drawn over the mandri]., the bellows will
open and permit the decal to assume the shape of the mandril
without excessive stretching thereof.
As shown in Figure 6, the substrate 10 is then
stripped away, leaving on the inner surface of the faceplate 18
the phosphor layer 22, the adhesive 16, the metal layar 14 and
the release agent 12. . ,
- If the release agent is sodium chloride, or example,
or some other composition which is capable of being dissolved,
the release agent may be removed by a suitable solvent. See
Figure 7. If sodium chloride is used, the solvent ma.y be water.
The solvent, of course, will vary with the release agent used. ~:
Alternatively, i ~he release agent is sodium chloride, it may : .
be desirable for reasons o~ economy to eliminate the release
agent removal.operation altogether. Tests have shown that the
presence of sodium chloride in the tube does not result, upon
electron bombardment, in poisoning of the electron guns.
Figure 8 illustrates a baking operation for driving
off the photosensitized binder from .the phosphor layex, the
adhesive layer 16 and, where the release agent may ba of a . .
nature as to be readily volatilized, the release agent~ It i~
conventional in the manufaeture of cathode ray tubes to include
a "bake-out" operation during which the photosensitized binder
and the afore-described smoothing layer or "film" deposited
to ~orm a base for tha avapo~ated aluminum layer, are driven
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off. Thus, since a bake-out operation is required as a
. necessary step in the conventional manufacture of a cathode
ray tube, the removal of the adhesive 16 can be achieved without
the necessity of a.dding any speci.al tube processing operations.
Thus, by the use of the above-described metal transfer web,
: and by the above-described method, the phosphor screen of a.
. cathode ray tube may be rapidly and economi.cally me~alized.
It has been found in a number o~ screens built and
tested, that beca.use the metal layer 14 is deposited upon a
` 10 smooth surface, iOe., the prepared upper surface of the substrate
10, rather than on a relatively rough surface as in the case
I of conventiona.l metalization of phosphor screens, the resulting
¦ metal layer is smoother tha.n the metal layers deposited by
I conventional evaporation techniques. Tests ha.ve shown tha.t in
some ca.ses, gains in brightness of the end product cathode ray
tubes have been achleved.
Figures 9~15 portray in highly schematic form a second
embodiment of the invention wherein the substxate comprising the
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base for a transfer web or decal is not strippable, but rather
is adapted to be removed by dissolution or volatilization.
As above, before enga.ging a. discussion of the Figures
9-15 screen metaliza.tion process, there will first be described
a pr~ferred method for forming the metalized decal or web from
which the metal layer is transferred. Figure 9 illustrates a
substrate 40. For reasons which will become clear as this
description proceeds, the substrate 40 is preferably composed
of a. flexible plastic material which may, for reasons stated
below, be dissolved or voIatilized. A suitable substrate material
is an acrylic fi.lm having a thickness approximately .0005 to
.0010 i~ch, however, i.t i5 contemplated that a substrate
composed of other materials such as nitro-cellulose may be
used.
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Figure lO shows the Figure 9 substra.te 42, upon which
is deposited a thin layer 44 of electrically conductive, lic~ht-
reflective material such as aluminum. rrO cause the metal layer
44 to adhere to a phosphor layer on the lnner surface of a
cathode ray tube faceplate (to be described in detail below),
a layer 46 of adhesive is deposited upon the metal layer 44
(see Figure lP) or on the inner surface 48 of the faceplate 50O
In accordance with this embodiment of the invention, the adhesive
preferably takes the form of a thin film of ethyl silicate.
Figure ll depicts a cathode ray tube faceplate 50
having a novel flangeless configuration, on an inner surface
48 of which is disposed a phosphor layer 52 comprising a phosphor
material held in a binder. The phosphor layex 52 may be as layer
22 descri.bed above. L
Figure 12 illustrates a step wherein a decal 54, com- :
prising substrate 42, meta.l layer 44 and a.dhesive layer 46, is
applied to the phosphor layer 52. As discussed a.bove, the decal
54 is preferably formed to the shape and curvature of the inner
surface 48 o~ the faceplate 50 to minimize wrinkling of the decal
54 upon transfer thereto and to minimize stretching of the metal
layer ~4.
In the schematic Fiyure 12 illustration, the a.pplication
is accomplished by first draping the deca.l 54 over a mandril 56
and securing it thereto. A tension band 57 is shown to sche-
matically illustrate mea.ns for securing the deca.l 54. Themandril 56 and the decal application operation represented by
Figure 1~ ma.y be as described above with respect to Figure 5.
After ~he decal 54 is adhered to the phosphor layer
52, the mandril 56 is removed, leaving on the faceplate 50 a
decàl 54 having the shape of the cathode ray tube screen~
The substrate 42 is then removed, preferably in thi.s
method embodiment by dissoluti.on, as shown schema.tically in
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Figure 14, leaving on the inner surface 48 of the faceplate
50 the phosphor layer 52, the adhesive layer 46 and the metal
layer 44. If the substrate 42 comprises an acrylic, the
solvent is preferably toluene. If the substrate 42 comprises
nitro-cellulose, the solvent is preferably acetone and amyl
acetate.
If the substrate 42 is of a composition such as
acrylic which is readily volatilized rathex than dissolved,
the dissolution step shown in E~igure 14 would, of course, be
eliminated. Rather, the faceplate would be baked, as shown
~ schematically in Figure 15 to volatilize and drive off the
i substrate.
~ he bakiny operation, represented in Figure 15 by an
oven S8, may be the conventional "bake-out" operation during
which the phosphor binder and the afore-described smookhing
layer or "film" deposited to form a base for the evapora,ed
aluminum layer, are driven off. Thus, since a bake-out opera-
tion is required as a necessary step in the conventional manu-
facture of a cathode ray tube, the removal of the substrate 12
and the adhesive layer 16 can be achieved without the necessity
of adding any special tube processing operations.
The invention is not limited to the particular details
of construction of the embodiments depicted and other modifi-
cations and applications are -contemplated. Certain changes
25 may be made in the above-described methods and apparatus without
departing from the true spirit and scope of the invention herein
involved. For example, to minimize the possibility of blistering
of the metal layer during the baXe-out operation, the metal layer
deposited upon the substrate may be caused to have tiny per-
forations whi~h will serve ultimately as out-gassing openings
for the materials volatilized under the metal layer. In the
Fig~res 1-8 embodiment, rather than using a release agent, as
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described, satisfactory results may be obtainable by the use
of a non-stic]s substrate, the sur:Eace of whi.ch inherently has
low adherance to the metal layer. Alternatively, other forces
than adhesion, e.g., electrostatic, may be employed to hold
the metal layer upon the strippable suhstrate until. the transfer
of the metal layer is accomplished. Whereas in the above-
described methods the binder in the phosphor layer -to which the
metal layer is transferred is described a.s a photosensitized
binder, the invention is e~ually applicable to transferring a
metal layer onto phosphor layers ha.ving non-sensitized organic
binders or phosphor layers of other compositions. It is
intended, therefore, that the subject matter of the above
depiction shall be interpreted as illustrative and not in a
limiting sense.
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