Note: Descriptions are shown in the official language in which they were submitted.
~L3~2~75
~1
This invention relates generally to tensioned
foil color cathode ray tubesr and more particularly to a
tensioned foil shadow mask formed from an improved alloy
as well as to a process for the manufacture of such tubes,
including the heat treating of nickel-iron alloys to
provide a desired combination of mechanical and magnetic
properties necessary for effective operation of tensioned
foil shadow masks. Also disclosed is a front assembly
containing such a mask.
j lO Cathode ray tubes having flat faceplates and
correspondingly flat tensioned foil shadow masks are known
to provide many advantages over conventional cathode ray
tubes having a curved faceplate and a curved shadow mask.
A chief advantage of a flat Eaceplate cathode ray tube
with tensioned mask is a greater electron beam
power-handling capability, a capability which can provide
greater picture brightness. The power-handling capability
of tubes having the conventional curved mask is limited
due to the thickness of the mask (5 to 7 mils), and the
fact that it is not mounted under tension. As a result,
the mask tends to expand or ~dome" in picture areas of
high brightness where the intensity of electron beam
bombardment, and consequently the heat, is greatest.
Color impurities result when the mask expands toward the
25 faceplate and the beam-passing apertures in the mask move
out of registration with their associated phosphor dots or
lines on the faceplate.
A tensioned foil mask when heated acts in a
manner quite different from a curved, untensioned mask.
For example, if the entire mask is heated uniformly, the
mask expands and relaxes the tension. The mask remains
planar and there is no doming and no distortion until the
mask has expanded to the point that tension is completely
lost. Just before all tension is lost, wrinkling may
occur in the corners. When small areas of a tensioned
;
2~7~
foil mask are differentially heated, the heated areas
expand and the unheated areas correspondingly contract,
resulting in only small displacements within the plane of
the mask. However, the mask remains planar and properly
spaced from the faceplate and, consequently, any color
impurities are unnoticeable.
The mask must be supported in tension in order to
maintain the mask in a planar state during operation of
the cathode ray tube. The amount of tension required will
depend upon how much the mask material expands upon
heating during operation of the cathode ray tube.
Materials with very low thermal coefficients of expansion
need only a low tension. Generally, however, the tension
should be as high as possible because the higher the
tension, the greater the heat incurred, and the greater
the electron beam current that can be handled. There is a
limit to mask tension, however, as too great a tension can
cause the mask to tear.
The foil mask may be tensioned in accordance with
known practices. A convenient method is to thermally
expand the mask by means of heated platens applied to both
sides of the foil mask. The expanded mask is then clamped
in a fixture and, upon cooling, remains under tension.
The mask may also be expanded by exposure to infrared
radiation, by electrical resistance heating, or by
stretching through the application of mechanical forces to
its edges.
In addition to having the composition as
described herein, after heat treatment and slow cooling
according to the invention, a foil formed from the alloys
will have a unique combination of mechanical, thermal and
magnetic properties that makes it uniquely suited for use
as a tensioned foil shadow mask. The alloy, in as-cast or
in treated form, must have adequate ductility to permit it
to be hot or cold rolled to a foil having a thickness of
~?~5
-- 3
less than 2 mils, preferably to a thickness of l mil, or
even as thin as 0.5 mil. A 1 mil thick foil when rolled
will typically have a reduction in area of at least 0.8
percent and preferably at least 1.0 percent elongation.
To withstand the forces incident to the tensing operation,
the mask material should have a yield strength above about
80 ksi and preferably above about 100 ksi (0.2 percent
offset). The mask material should also be able to
withstand a tension load of at least about 25
Newton/centimeter, preferably at least about 65
Newton/centimeter. The mask material should also have a
thermal coefficient of expansion that is not substantially
less than that of the glass of the faceplate.
In addition to the mechanical properties
described, the mask material must have a particular
combination of magnetic properties. In this connection,
it is important that the mask material have as high a
permeability as is possible while maintaining the
~0 necessary mechanical properties. The permeability should
be at least about 6,000, preferably at least about 10,000,
and most desirably in excess of 60,000. A maximum
coercivity is desirably below about l.0 oersted and
preferably is below about 0.5 oersted.
It is well known in the manufacture of standard
color cathode ray tubes of the curved-mask, curved-screen
type to heat-treat the shadow masks prior to their being
formed into a domed shape. Conventional ~non-tensioned~
shadow masks are typically delivered to cathode ray tube
manufacturers in a work-hardened state due to the multiple
rolling operations which are performed on the steel to
reduce it to the specified thickness, typically about 6
; mils. In order that the masks may be stamped into a domed
shape, they must be softened by use of an annealing heat
treatment--typically to temperatures on the order of
~3~%~
700-800 degrees C. Annealing also enhances the magnetic
coercivity of the masks, a desirable property from the
standpoint of magnetic shielding of the electron beams.
After stamping, and the conse~uent moderate work hardening
of the mask which may result from the stamping operation,
it is known in the prior art to again anneal the masks
while in their domed shape to further enhance their
magnetic shielding properties.
Foils intended for use as tensioned masks are
also delivered in a hardened state--in fact, much harder
than standard masks in order to provide the very high
tensile strength needed to sustain the necessary high
tension levels; for example, 30,000 psi, or greater. The
prior art annealing process, with its relatively high
annealing temperatures, would be absolutely unacceptable
if applied to Elat tension masks, as any extensive
softening or reduction of tensile strength of the mask
resulting from the process would make the material
unsuited for use as a tension mask.
U.S. Patent No. 4,210,843 to Avedani, sets forth
an improved method of making a conventional color cathode
ray tube shadow mask; that is, a curved shadow mask having
a thickness of about 6 mils, and designed for use with a
correlatively curved faceplate. The method comprises
f 25 providing a plurality of shadow mask blanks composed of an
interstitial-free steel, each with a pattern of apertures
photo-etched therein, which blanks have been cut from a
foil of steel, precision cold-rolled to a full hard
condition, and with a thickness of from 6 to 8 mlls. A
30 stack of blanks is subjected to a limited annealing
operation carried out at a relatively low maximum
temperature, and for a relatively brief period sufficient
only to achieve recrystallization of the material without
causing significant grain growth. Each blank is clamped
35 and drawn to form a dished shadow mask without the
~ . ,.,,, ._.. , . . ..... .. . ,.. , .. ,.. . . , . , , ...... ...... ...... , .. _ .. . .. ,, , . , . , ..... ....
. " .... ... .. ...... . ... .. ... . . .
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- 5 -
imposition of vibration or roller leveling operations, and
thus avoids undesired creasing, roller marking, denting,
tearing or work-hardening of the blank normally associated
with these operations. The end-product shadow mask, due
to the use of the interstitial free steel material, has an
aperture pattern of improved definition as a result of
more uniform stretching of the mask blank. The annealing
operation has little effect on the magnetic properties of
this type of steel, and the coercivity of the material,
after forming, is above 2.0 oersteds.
Prior to the present invention, there was no foil
mask material available having the desired combination of
mechanical and magnetic properties described herein. One
material used in tensioned foil shadow mask applications
in flat faceplate cathode ray tubes has been
aluminum-killed, AISI 1005 cold-rolled capped steel,
generally referred to as "AK-steel.~ AK steel, has a
composition of 0.04 percent silicon, 0.16 percent
manganese, 0.028 percent carbon, 0.020 percent phosphorus,
0.018 percent sulfur, and 0.04 percent aluminum, with the
balance iron and incidental impurities.
(Throughout the specification and claims, all
percentages are considered weight-percentages, unless
otherwise indicated.)
2S Invar, which has a nominal composition of 36
percent nickel, balance iron, has also been suggested as a
possible material for tensioned foil shado~ masks. Invar
however has a thermal coefficient of expansion far lower
than that of the glass commonly used cathode ray tube
faceplates and so is considered generally unacceptable.
AK steel r while it can be formed into a fairly
acceptable foil shadow mask, is deficient in certain
important properties. For example, the yield strength of
AK steel foil one mil thick is typically in the range of
75-80 ksi. This makes it only marginally acceptable from
-- 6
a strength standpoint. More importantly, AK steel has a
permeability that is much lower than desired, for example,
5,000 in a 1 mil foil. Since the ability of a material to
car`ry magnetic flux decreases with decreasing
cross-section, cathode ray tubes having masks made of AK
steel thinner than about 1 mil may require both internal
and external magnetic shielding. ~ith internal shielding
only, the beam landing misregistration due to the earth's
magnetic field, i.e. the change in beam landing position
; 10 upon reversal of th~e axial field component, is typically
1.7 mils, which is much greater than the maximum of about
1 mil that is generally considered tolerable.
In addition, AK steel is metallurgically dirty,
having inclusions, defects and dislocations which
interfere with both the foil rolling process and the photo
resist etching of the apertures in the foil resulting in
higher scrap rates and consequently lower yields.
Another significant disadvantage of an AK steel
tensioned foil shadow mask is the fact that as the tension
applied is increased, the permeability decreases and
coercivity increases. Translated into picture
performance, this means that as the tension of the
AK-steel foil shadow mask is increased in order to permit
increased beam current and, therefore, greater picture
25 brightness, its ability to shield the electron beams from
the earth's magnetic field deteriorates, resulting in
increased beam misregistration.
Finally, AK steel rusts and thus requires greater
care in storage and possibly the application of rust
inhibitors. If rust does appear, it must be removed in a
separate production operation, and without altering the
size or shape of the apertures, or the thickness of the
mask material.
In general, the invention aims to provide an
improved shadow mask material Eor use in color cathode ray
~3~
--7--
tubes having a tensioned foil shadow masX.
The present invention therefore provides a foil
shadow mask for use with a faceplate of a tensioned foil
color cathode ray tube, said foil mask being for~ed from
an alloy comprising between about 30 and about 85
weight-percent nickel, between about 3 and about 5
weight-percent molybdenum between O and about 2
weight-percent of an alloying agent selected from the
group consisting of vanadium, titanium, hafnium, niobium
and mixtures thereof, balance iron and incidental
impurities, said alloy having a coefficient of expansion
that is not less than about that of the faceplate of the
cathode ray tube.
Another general aspect of the invention is to
provide an improved process for manufacturing cathode ray
tubes containing tensioned foil masks having improved
mechanical and magnetic properties.
The present invention therefore provides a
process for the manufacture of a foil shadow mask for a
tension mask color cathode ray tube which includes a
faceplate having a phosphor screen on its inner surface
and a support structure for supporting a tensioned foil
shadow mask adjacent thereto comprising providing a
hardened nickel-iron alloy foil containing between about
75 and about 85 weight percent nickel and at least one of
the following in the indicated weight percent; molybdenum
. O and about 5%; vanadium O and about 2%; titanium O and
about 2%; hafnium O and about 2% and niobium O and about
2~, balance iron and incidental impurities; heat treating
said.hardened foil under condition which achieve favorable
magnetic shielding properties while maintaining strength
properties of the hardened material sufficient to
withstand normal operating mask tension levels, including
heat treating said foil at a temperature above 400C and
below that temperature at which the alloy forms a solid
solution for a period of at least about 30 minutes and
controlling the cooling rate of said foil from said
-7a-
temperatures as the temperature at which said alloy is
substantially recrystallized to provide a foil having a
yield strength in excess of 80 ksi, a permeability in
e~cess of 6000 and coercivity of 2.5 oersteds or below;
applying tension to said foil; and securing said foil to
said support structure while under tension.
Further features and advantages of the present
invention may best be understood by reference to the
following description of preferred embodiments o the
invention taken in conjunction with the accompanying
drawings ~not to scale~ in the several figures of which
like reference numerals identify like elements, and in
which:
Figure 1 is a side view in perspective of a color
cathode ray tube having a flat faceplate and a tensioned
foil shadow mask, with cut-away sections that indicate the
location and relation of the faceplate and tensioned Eoil
;;
-- 8 --
shadow mask to other major tube components;
Figure 2 is a plan view of an in-process foil
shadow mask;
Figure 3 is a plan view of an in-process flat
glass faceplate showing a phosphor screening area and a
foil shadow mask support structure secured thereto;
Figure 4 is a perspective view of a funnel
referencing and fritting fixture, with a funnel and the
faceplate to which it is to be attached shown as being
mounted on the fixture; and
Figure 5 is partial detail view in section and in
elevation depicting the attachment of a funnel to a
faceplate.
To facilitate understanding of the process and
material according to the invention and their relation to
the manufacture oE a color cathode ray tube having a
tensioned foil shadow mask, a brief description of a tube
of this type and its major components is offered in the
following paragraphs.
A color cathode ray tube 20 having a tensioned
foil shadow mask is depicted in Figure 1. The faceplate
assembly 22 essentially comprises a flat faceplate and a
tensioned flat foil shadow mask mounted adjacent thereto.
Faceplate 24, indicated as being rectangular, is shown as
having on its inner surface 26 a centrally located
phosphor screen 28 depicted diagrammatically as having a
pattern of phosphors thereon. A film of aluminum 30 is
indicated as covering the pattern of phosphors. A funnel
34 is represented as being attached to faceplate assembly
3Q 22 at their interfaces 35, the funnel sealing surface 36
of faceplate 24 is indicated as being peripheral to screen
28. ~ frame-like shadow mask support structure 48 is
indicated as being located on opposed sides of the screen
between funnel sealing surface 36 and screen 28, and
mounted adjacent to faceplate 24. Support structure 48
~3i~2~
g
provides a sur~ace for receiving and mounting in tension a
metal foil shadow mask 50 a Q-distance away from the
screen 28. The pattern of phosphors corresponds to the
pattern of apertures in mask 50. The apertures depicted
are greatly exaggerated for purposes of illustration, in a
high-resolution color tube for example, the mask has as as
many as such 750,000 apertures, with aperture diameter
being on the average about 5 mils. As is well-known in
the art, the foil shadow mask acts as a color-selection
electrode, or "parallax barrier" which ensures that each
of the beamlets formed by the three beams lands only on
its assigned phosphor deposits on the screen.
The anterior-posterior axis of tube 20 is
indicated by reference number 56. A magnetic shield 58 is
lS shown as being enclosed within funnel 34. High voltage
for tube operation is indicated as being applied to a
conductive coating 60 on the inner surface of funnel 34 by
way of an anode button 62 connected in turn to a
high-voltage conductor 64.
The neck 66 of tube 20 is represented as
enclosing an in-line electron gun 68 depicted as providing
three discrete in-line electron beams 70, 72, and 74 for
exciting respective red-light-emitting,
green-light-emitting, and blue-light-emitting phosphor
elements deposited on screen 28. Yoke 76 receives
scanning signals and provides for the scanning of beams
70, 72 and 74 across screen 28. An electrical conductor
78 is located in an opening in shield 58 and is in contact
with conductive coating 60 to provide a high-voltage
connection between the coating 60, the screen 28, and
shadow mask 50.
Two of the major components, designated as being
"in-process," are depicted and described as follows. One
is a shadow mask indicated diagrammatically in Figure 2.
In process shadow mask 86 includes a central area 104 of
~L3~æ~
-- 10 --
apertures corresponding to the pattern of phosphors that
is photo-deposited on the screen of the faceplate by using
the mask as an optical stencil. Center field 104 is
indicated as being surrounded by an unperforated section
106, the periphery of which is engagecl by a tensing frame
during the mask tensing and clamping process, and which is
removed in a later procedure.
An in-process faceplate 108 is depicted
diagrammatically in Figure 3 as having on its inner
surface 110 a centrally located screening area 112 for
receiving a predetermined phosphor pattern in an ensuing
operation. A funnel sealing surface 113 is indicated as
being peripheral to screen 112. A frame-like shadow mask
support structure 114 is depicted as being secured on
opposed sides of screen 112, the structure provides a
surface 115 for receiving and mounting a foil shadow mask
under tension a Q-distance from the screen.
A process according to one aspect of the
invention essentially comprises providing an apertured
foil shadow mask 86 characterized by being composed of a
nickel-iron alloy, and securing the mask 86 to the
mask-support structure 114 of the faceplate 108 while
under tension, and in registration with the phosphor
screen. The process is further characterized by
subjecting the mask 86 to a thermal cycle to partially
anneal the mask to a state in which the mask has favorable
magnetic and mechanical properties.
According to the present invention, a class of
nickel-iron alloys, desirably containing minor additions
of certain alloying agents, when heat-treated and cooled
under controlled conditions, yield a material which, when
fabricated into a thin foil, have mechanical and magnetic
properties not found in known alloys that make them
uniquely suited for use as tensioned foil shadow masks.
The desired properties achieved by the inventive
~3~
-- 11 --
process are as follows: The alloy foil should have a
yield strength (0.2 percent offset) of at least about 80
ksi, preferably at least about 100 ksi and most desirably
at least about 150 ksi in order to be able to withstand
the tension loading applied to the foi:L when used as a
tensioned foil shadow mask. This yield strength should be
combined with the magnetic properties of high permeability
and low coercivity. The permeability should be in excess
of about 6,000 preferably in excess of about 10,000 and
most desirably in excess of 100,000. The coercivity
should not exceed about 2.5 oerstedsl and is preferably
below about 0.5 oersted.
A specific example of an alloy responsive to the
heat treatment according to the invention, and fabrication
into a tensioned foil shadow mask, is the known
nickel-iron-molybdenum alloy sold under the tradenames
HyMu80,YeP-C, and Moly-Permalloy. This alloy contains
about 80 percent nickel, 4 percent molybdenum, with
balance iron and incidental impurities. In the as-rolled
fully hardened condition, and 80Ni-4Mo-Fe foil has a high
yield strength, typically 155-160 ksi, but poor magnetic
properties, e~g., a permeability of less than 3,000. To
impart good magnetic properties, as for use in tape
recorder heads, the material is conventionally annealed at
1120 degrees C. for two to four hours followed by furnace
cooling to 600 degrees C. The fully annealed alloy foil
has excellent magnetic properties but poor mechanical
properties. The permeability may be as high as 300,000.
However, the yield strength is in the range of 20-40 ksi,
making this alloy, when fully annealed, clearly unsuited
for use as a tensioned foil shadow mask.
However, when the 80Ni-4Mo-Fe alloy foil is
partially annealed according to the inventive process, it
unexpectedly displays properties which make it superior
as a material for the fabrication of tensioned foil shadow
- 12 -
masks. As a result of this cycle of heating and cooling
according to the invention, the mechan:ical properties of
the alloy are substantially retained while its magnetic
properties are improved to a degree necessary for use as a
foil shadow mask.
Surprisingly, it has been found that the magnetic
properties of the 80Ni-4Mo-Fe foil, when treated in
accordance with this invention, actually improve, and
improve very significantly, when the foil is placed under
tension. For example, after heat treating and
conditioning according to the invention, an untensioned
80Ni-4Mo-Fe foil having a thickness of l mil has a
permeability of 60,000. When that same foil is placed
under a tension of about 60 Newton/centimeter, its
permeability is increased to 100,000. It is to be noted
that the same material exhibits no significant
permeability change under tension when in its conventional
full hard state. As a result of the increased
permeability, the amount o~ beam misregistration due to
the earth's magnetic field of an 80Ni-4Mo-Fe foil l mil
thick, when processed according to the invention, is far
less than that of an AK-steel foil of 1 mil thickness.
With regard to the alloy composition, a
nickel-iron alloy is provided comprising between about 30
and about 85 weight-percent of nickel, between about 0 and
5 weight-percent of molybdenum, between 0 and 2
weight-percent of one or more of vanadium, titanium,
hafnium, and niobium, with the balance iron and incidental
impurities; e.g., carbon, chromium, silicon, sulfur,
copper and manganese. Typically, the incidental
impurities combined do not exceed 1.0 percent.
Preferably, the alloy may comprise between about 75 and 85
weight-percent of nickel, between about 3 and 5
weight-percent of molybdenum, with the balance iron and
incidental impurities. In one specific example, the alloy
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- 13 -
may comprise about 80 weight-percent nickel, about 4
weight-percent molybdenum, with the balance iron and
incidental impurities.
A partial anneal of the preferred material may be
accomplished according to a further aspect of the
invention as a discrete step prior to installing the mask
on the mask support structure secured to the faceplate.
rro achieve the desired combination of mechanical and
magnetic properties, the foil must be subjected to a
specified procedure of heat treating and slow cooling
according to the invention to provide a foil having the
desired combination of magnetic and mechanical properties.
In a typical process according to the invention,
a group of 12 full-hard, apertured masks of the
configuration shown by Figure 2 are stacked for insertion
into an oven. rrhe process according to the invention is
characterized by subjecting each of the stacked masks to a
thermal cycle to partially anneal the mask to produce
favorable magnetic and mechanical properties, comprising
heating the mask to a temperature above about 400 degrees
C. and below that temperature at which the mask alloy
substantially forms a solid solution for a period of at
least about 30 minutes, preferably about at least 45
minutes, and slowly cooling the mask from that temperature
to the temperature at which the alloy from which the mask
is formed is substantially recrystallized at a cooling
rate of less than about 5 degrees C. per minute, and
preferably less than about 3 degrees C. per minute; and
then securing the mask to a mask support structure affixed
to or integral with the faceplate while the mask is under
tension and in registration with the phosphor screen. For
example, the mask may be heated to a temperature of
between about 400 degrees C. and 700 degrees C. for a
period between about 30 minutes and about 60 minutes. The
mask is then slowly cooled from that temperature to the
~3~2~i
- 14 -
temperature at which the material of the masks is
substantially recrystallized at cooliny rate of less than
about 5 degrees C. per minute, preferably less than 3
degrees C. per minute, and most desirably at a rate of
between about 2 degrees C. and about 3 degrees C. per
minute. Longer heat treatments are permissible but do not
appear to result in an improvement in properties. Heat
treating at the indicated temperatures followed by air
cooling or cooling at rates above 5 degrees C. per minute
resulted in foils having undesirably poor mechanical
properties. While not wishing to be bound by any
particular theory, it is believed that the disclosed heat
treatment, which is at temperatures well below annealing
temperatures, followed by slow cooling, results ln the
long range ordering of Ni3Fe as intergranular and
intergranular precip:itates.
The heating of the assembly and the foil, and the
slow rate of cooling of the assembly and the foil
according to the invention, is effective to partially
anneal the foil mask and produce a yield strength in
excess of 80 Icsi, a permeability above about 6,000, a
coercivity below about 2.5 oersteds, and a thermal
coefficient of expansion that is not less than about that
of the faceplate (glass). Following the process as
described, the mask may well have a yield strength above
about 150 ksi, a permeability above about 10,000, and a
coercivity below about 1Ø The foil is able to withstand
tension loads in excess of about 65 Newton/centimeters,
and possibly above 75 Newton/centimeter.
The heat treatment and slow cooling treatment of
the masks described in following paragraphs closely
approximates the processing steps in frit sealing cathode
ray tube, and the sealing of the funnel and faceplate in
the manufacturing process.
Subsequent to the initial implementation of the
4~
- 15 -
inventive process, it was determined that the heating and
cooling conditions to which the tensioned mask is
sub]ected during a frit cycle are such that a substantial
improvement in the properties of the described alloy is
obtained without requiring the separate heat treatment and
slow cooling process described in the foregoing. The
properties of the tensioned foil mask are not as good as
those obtained when the mask material is heated to the
more desirable temperature of 500-600 degrees C. ~owever,
where the brightness and resolution demanded of the
cathode ray tube are not as high, it has been determined
that the slow heating oE an in-place 80Ni-4Mo-Fe tensioned
mask to about 435 degrees C. in the Erit cycle, followed
by slow cooling at a rate of less than about 5 clegrees C.
per minute, preferably between about 2 degrees and about 3
degrees C. per minute, which is the cooling rate in the
frit cycle, provides a finished mask having the desired
mechanical and magnetic properties.
For example, when untreated tensioned foil masks
are placed under a tension of 30 Newton/centimeter, and
run through the frit cycle, a yield strength of between
about 150 ksi and about 160 ksi and a permeability of
between about 60,000 and about 100,000, and a coercivity
of below about 0.~ oersted, is obtained. The beam
misregistration is somewhat higher than that obtained when
the foil is separately heat treated, but still below the
desired limit.
So a partial anneal according to the invention
may also be accomplished during, and as a result of, a
thermal cycle in the process of sealing the tube. The
process is described in the following paragraphs.
As indicated in Figure 3, a shadow mask support
structure 114 is secured on the inner surface 110 of
faceplate 108 between the peripheral sealing area, noted
as being the funnel sealing surface 113, and the screening
~3~%~7S
- 16 -
area 112. The mask support structure 114 provides a
surface 115 for receiving and supporting foil shadow mask
in tension. The mask support structure 114 may comprise,
by way of example, a stainless steel metal alloy.
5 Attachment of the support structure is preferably by means
of a devitrifying frit.
A nickel iron alloy is provided comprising
between about 30 and about 35 weight-percent of nickel,
between about 0 and ~ weight-percent of molybdenum,
3 10 between 0 and 2 weight-percent of one or more of vanadium,
titanium, hafnium, and niobium, with the balance iron and
incidental impurities; e.g., carbon, chromium, silicon,
sulfur, copper and manganese. Typically, the incidental
impurities combined do not exceed 1.0 percent.
15 Alternately and according to the invention, the alloy may
comprise between about 75 and 85 weight-percent of nickel,
between about 3 and 5 weight-percent of molybdenum, with
the balance iron and incidental impurities. Preferably,
- the alloy may comprise about 80 weight-percent nickel,
20 about 4 weight-percent molybdenum, with the balance iron
and incidental impurities.
The alloy according to the invention is formed
into a foil having a thickness of about 0.001 inch or less.
A central area 112 of the foil is apertured to
25 form a foil mask 108 consonant in dimensions with the
screening area 112 for color selection. Aperturing of the
mask can be accomplished by a photo-etching process in
which a light-sensitive resist is applied to the foil.
The resist is hardened by exposure to light except in
30 those areas where apertures are defined. The exposed
metal defining the apertures is then etched way.
The foil mask is then tensed in a tensing frame
to a tension of at least about 2~ Newton/centimeters. In
essence, the foil may be expanded by enclosing it between
- 35 two platens heated to 360 degrees C for one minute,
~3~
clamped in the tensing frame, and air cooled it to provide
a tensioned foil having a greater length and width than
the faceplate to which it will be secured. A pattern of
red-light-emitting, green-light-emitting, and
blue-light-emitting phosphor deposits are sequentially
photo-screened on screening area 112. The photoscreening
process includes repetitively registering the foil of the
phosphor screening area by registering the tensing frame
with the faceplate.
The foil comprising the mask 86 is secured to the
mask support structure 114, with the apertures of the mask
in registration with the pattern of phosphor deposits on
screening area 112. The means of securement of the mask
to the mask support structure may be by welding with a
laser beam, with the excess mask material removed ~y the
same beam. Inasmuch as the faceplate 108 and the
tensioned Eoil shadow mask 86 are rigidly interconnected
by their mutual attachment to the mask support structure,
the thermal coefficient of expansion of the alloy foil
must approximate that of the faceplate, which is typically
a glass having a coefficient of expansion of between about
12 x 10 6 and about 14 x 10 6 in/in/degrees C. This
is necessary due to the relatively high temperatures to
which the faceplate and mask are subjected during the
cathode ray tube manufacturing process. A coefficient of
expansion somewhat greater than that of the faceplate can
be tolerated, but a coefficient of expansion substantially
less than that of the faceplate is to be avoided as this
may lead to mask failure during the manufacturing process.
Figures 4 and 5 depict the use of a funnel
referencing and fritting fixture 186 for mating of a
faceplate 108 with a funnel 188 to form a faceplate-funnel
assembly. Faceplate 108 is indicated as being installed
face down on the surface 190 of fixture 186. Funnel 188
is depicted as being positioned thereon and in contact
~3~æ~
- 13 -
with funnel sealing surface 113, noted as being peripheral
to screening area 112 on which is deposited a pattern of
phosphors 187 as a result of the preceding screening
operation. With reference to Figure 4, three posts 192,
193 and 194 are indicated as providiny for alignment of
the funnel and faceplate. Figure 5 depicts details of the
interface between post 194, the faceplate 108, and funnel
188. Flat 117c on faceplate 108 is shown as being in
alignment with reference area "c" on funnel 188. Shadow
mask 86, noted as being in tension, is preferably depicted
as being mounted on shadow mask support structure 114.
Post 194 is shown as having two reEerence points
196 and 198 for locating the funnel 188 with reference to
the faceplate 108. The reference points preferably
comprise buttons of carbon as they must be immune to the
effects of the elevated oven temperature incurred during
the frit cycle.
A devitrifiable frit in paste form is applied to
the peripheral sealing area of the faceplate 108, noted as
being funnel sealing area 113, for receiving funnel 188.
The faceplate 108 is then mated with the funnel 188 to
form a faceplate-funnel assembly. The frit, which is
indicated by reference No. 200 in Figure 5, may for
example comprise frit No. CV-130, manufactured by
7 25 Owens-Illinoisr Inc. of Toledo, Ohio.
The faceplate-funnel assembly is then heated to a
temperature effective to devitrify the frit and
permanently attach the funnel to the faceplate, after
which the assembly is cooled. The process of fusing of
30 the funnel to the faceplate is generally carried out under
conditions referred to as the frit cycle. In a typical
frit cycle, the faceplate, to which the tensioned foil
mask is adhered, and funnel are slowly heated to 435
degrees C., then cooled to room temperature or slightly
35 thereabove over a period of three to three-and-one-half
-- 19 --
hours. The foil must be cooled to the temperature at
which the alloy is substantially recrystallized at a
cooling rate of less than about 5 degrees C. per minute,
preferably less than about 3 degrees C. per minute and
most desirably at a rate of between about 2 degrees C. and
about 3 degrees C. per minute.
The heating of the assembly and the foil, and the
slow rate of cooling of the assembly and the foil
according to the invention and during the frit cycle, is
effective to partially anneal the foil mask and produce
the desired mechanical and magnetic properties set forth
in the foregoing.
Test results in support of the concept according
to the invention are summarized by the following examples.
Example I
An 80Ni-~Mo-Fe cold-rolled foil is 1 mil thick.
In the as-received condition, the foil has a permeability
of 3,000, a coercivity of 2.2 oersteds and a yield
strength of 156 ksi.
The foil is heat treated in a dry hydrogen
atmosphere at 500 degrees C. for 60 minutes and is then
cooled to 200 degrees C. at a cooling rate of 3 degrees C.
per minute. The heat treatment results in a foil having a
yield strength of 192 ksi, a permeability of 60,000, a
coercivity of 0.31 oersteds, and a coefficient of
expansion of 13xlO 6 in/in/degrees C.
Example II
A 42Ni-Fe cold-rolled foil 1 mil thick may be
usedO In the as-received condition, the foil will have a
permeability of 3,000, coercivity of 4.0 oersteds and
yield of 110 ksi.
The foil may be heat treated at 600 degrees C. in
a dry hydrogen furnace for two hours and cooled to below
200 degrees C. at a cooling rate of 2 degrees C. per
minute. The heat~treated and slow-cooled foil will have a
~3~Z~L~5
- 20 -
permeability of 9,000, a coercivity of 1.1 oersteds and a
yield strength of 80 ksi.
Example III
A 49Ni-Fe foil 1 mil thick in the as-received
condition, will have a permeability of 3,200, a coercivity
of 4.2 oersteds and a yield strength of 115 ksi. After
heat treatment and slow cooling in accordance with Example
I, the foil will have a permeability of 10,000, a
coercivity of 0.4 oersteds and a yield strength of 85 ksi~
i 10 Example IV
A 49Ni-4Mo-Fe foil 1 mil thick in the as-received
condition will have physical and magnetic properties
similar to the foil of Example I. After heat treating and
slow cooling, in accordance with Example I, the foil will
have a permeability of 20,000, a coercivity of 0.3
oersteds and a yield strength oE 160 ksi.
Example V
A 79Ni-2Mo-IV-Fe foil 1 mil thick in the
as-received condition will be expected to have physical
and magnetic properties similar to the foil of Example I.
The foil may be heat-treated and slow cooled in accordance
with Example I. After heat treatment and slow cooling,
the foil will be expected to have permeability of 30,000,
a coercivity of 0.30 oersteds and yield strength of 160
i 25 ksi.
Example VI
A 79Ni-2V-lTi-Fe foil 1 mil thick in the
as-received condition will be expected to have physical
and magnetic properties similar to the foil of Example I.
The foil may be heat-treated and slow cooled in accordance
with Example I, after which the foil will be expected to
have a permeability above 30,000, a coercivity of 0.30
oersteds, and a yield strength of 170 ksi.
Example VII
A 79Ni-4Mo-Fe foil 1 mil thick in the as-received
~3~2~
- 21 -
condition will be expected to have physical and magnetic
properties similar to the foil of Example I, after
heat-treating and slow cooling through the conventional
frit cycle. The frit cycle comprises an open furnace with
a peak temperature of about 435 degrees C. The total time
duration for the sample to pass through from the entry of
the furnace to the outlet is about 3-1/2 hours. The foil
is expected to have a permeability of about 60,000,
coercivity of about 0.4 oersteds, and a yield strength of
about 155 ksi.
A foil shadow mask according to the invention for
use in a tensioned foil color cathode ray tube, or a
faceplate assembly for such a tube, is preferably formed
from an alloy comprising between about 30 and about 85
weight-percent nickel, between about 0 and 5
weight-percent molybdenum, between 0 and 2 weight-percent
of one or more of vanadium, titanium, hafnium, and
niobium, the alloy having a yield strength in excess of 80
ksi, a permeability above about 6,000, coercivity below
about 2.5 oersteds and a thermal coefficient of expansion
that is not less than about that of the faceplate~
Further, the mask may be under a tension of at least about
25 Newton/centimeters when the tube is at ambient
temperature. The alloy according to the invention may
have a yield strength above about 150 ksi, a permeability
above about 10,000, and a coercivity below about 1Ø
Further with regard to the content of the alloy of the
mask, the content may comprise between about 75
weight-percent and about 85 weight-percent of nickel,
between about 3 weight-percent and about 5 weight-percent
of molybdenum, with the balance iron and incidental
impurities; and preferably, the content may comprise
about 80 weight-percent of nickel, about 4 weight-percent
of molybdenum, with the balance iron and incidental
impurities.
