Note: Descriptions are shown in the official language in which they were submitted.
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This invention generally relates to making small openings or
slots in shadow masks ~or colored television tubes, more specifically,
this is an etching process for producing accurate holes or openings in a
continuous sheet or web of material in which the openings have a dimension
smaller than the thickness of the material by utilizing a protective
coating between the initial and final etching of the article.
In a colored television picture tube a shadow mask or aperture
mask is located between electron guns at the rear of the tube and the
phosphor faceplate on the face of the tube. Electron beams pass through
tiny openings or apertures in the shadow mask and impinge upon a suitable
color producing phosphor dot on the faceplate. Located in line with the
openings of the shadow mask are three phosphor dots, a triad, one dot for
each of the three primary colors. During the operation of the picture
tube, the shadow mask opening acts as a guide for the electron beams.
Thus, one of the uses of the present invention is a process for making a
shadow mask for a television tube which requires the formation of aper-
tures on an intermittently moving web.
The problem of making small holes or apertures in thicker
materials is that it is difficult if not impossible to accurately
etch an opening which has a minimum dimension less than the thickness of
the material unless some special procedures are used. That is, the con-
ventional etching techniquesr i.e., etching from both sides produces
over-etching as well as irregular etching. The over-etching is produced
by lateral etching of the material that inherently accompanies etching
perpendicular to the surface of the material. Consequently, the process
of accurately making holes having a minimum dimension of less than the
thickness of the material is a difficult and time consuming task. The
task is even more difficult when applied to a continuous production of -
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etched material in web form. An example of a prior art process for
etching a single opening in a thick material is shown in United States Mears
et al patent 2,~37,228 where a small opening is etched to a depth of .002~1
to .010 inches while the opposite side is protec~ed. Then a protective coat-
ing of asphaltum or other resis~ is filled in the opening and the opposite
side of the article is etched until the plugs of asphaltum show through.
Thus, the present invention comprises a process for continuously -
and accurately etching openings which have a minimum dimension less than the
thickness of the material being etched. Although the present invention is
specifically for the problem of etching openings having a dimension less than
the material, it is apparent that it can also be used for etching dimensions
greater than the thickness of the material. However, its greatest contri-
bution is that the process can enable one to accurately etch openings having
dimensions less than the thickness of the material on a continuous or
intermittently moving web of material.
According to the present invention, there is provided a process of
accurately etching an opening which has a minimum dimension that is less
than the thickness of the article comprising:
applying a first layer of etchant resist on one side of a web having
~, 20 a thickness T;
applying a second layer of etchant resist on the opposite side of
the web, with said first layer of etchant resist having a first unprotected
region of dimension Xl, said second layer of etchant resist having a second
mprotected region of dimension X2 with X2 being substantially larger than
X
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subjecting said web to etching from both sides until a dished out
region is produced on the first unprotected region of the web and on the second
~ unprotected region located on the opposite side of said web and until the
^~ unetched portion located between the dished out region located in the first
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-~ 30 unprotected region and the dished out region located in the second unprotected
region has a dimension H, said unetched portion dimension H ranging from
about 20% *o ~0% of the thickness of said web;
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then applying a resist coating on top of the resist layer and into
the dished out opening of dimension Xl; and
then etching on the side of the web having the dimension designated
by X2, said etching removing sufficient material to produce a thinning of the
web in the region of the web opposite the unprotected region of dimension
Xl until an opening having a minimum final dimension less than the thickness
T is etched through the web.
Thus, the present invention comprises a process where a web is
partially etched from both sides. A protecting coating is then applied on
one side of the web. Next, the unprotected side of the web is etched for a
predetermined time to provide an accurate opening in the central portion of
the web.
A particlar embodiment of-the present invention will now be
described by way of example only, with reference to the accompanying drawings,
in which:
Fig. 1 shows in schematic form an etching system of the present ln-
vention; and
Fig. 2 shows an enlarged sectional view of the appearance of the
web as it is ready to undergo the final stages of etching.
Referring ~o the drawing, reference numerals 11, 12, 13, 14, 15 and
16 all designate different types of chambers in the etching system. Reference
numeral 11 designates an etching chamber
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having upper spray nozzles 19 a~d lower spray nozzles 20. Re~erence
numeral 12 designates a station having spray nozzles 21 and 22
therein. Re~erence numeral 13 designates a heating or drying
station having heating elements 23 and 24 therein and re~erence
numeral 14 designates a spray coating station having spray nozzles
25 therein. Located immediately after coating station 14 is a
drying station 15 having heating elements 26 and 27 therein~ The
last station in the etching system is a spray etching station 16
having a set of spray nozzles 28 ~or spraying etchant on a travel-
ing web 9. Traveling web 9 passes through the chambers around aroller 30, between a pair o~ rollers 31 and onto a larger take-up
roller 32.
Referring to Figr 2, an enlarged cross sectional view
o~ web 9 is shown having thickness designated To Located on the
top side o~ web 9 is a resist layer 42 and located on the bottom
side is a resist layer 44. Located on top o~ resist layer 42 is
a shield or coating 43 which is applied at station 14. The dimen-
sions of the opening in resist layer 42 are designated Xl and the
dimens~on o~ the opening in resist layer 44 is designa-ted by X2.
The article has a central unetched portion o~ dimension H. By
controlling the time and temperature o-f the etching solution, the
portion o~ the article designated by thickness H can be le~t to
be etched i~ a later step.
In the process o~ $he present invention a web 9 having
an etchant resist pattern on both sides o~ the web is subjected
to spray etching ~rom above by no~zles 19 and ~rom below by nozzles
20 which are located in etching chamber 11. In order to etch to
the proper depth, the time and temperature o~ the etchan-t are
controlled. A~ter a predetermined time the etchant spray is re-
moved khus leaving the article having recesses on opposite sideso~ the web. Typically, with a material having a thickness T o~
.006" the unetched central dimension ~ is about .002". A~ter
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etching both sides of web 9 the web enters station 12 where the
web is rinsed to remove any etchant adhering to the web. Next,
the web is dried by heatexs 23 and 24 which are located in station
13. Next, a protective resist is applied or sprayed on the side
of the web having the smaller opening designated by Xl. The
spray coating is then dried in station 15 by heaters 26 and 27.
Typical coating materials are paraffin or the like,
however, polymer plastics that are resistant to the etchant are
also suitable.
Next, the wèb 9 having the larger opening denoted by
X2 is etched in etching chamber lS by a set of spray nozzles 28
that direct etchant vertically upward to impinge against the
recess region located beneath resist 44. The time and temperature
of the etchant axe controlled so the final dimension H is etched .
completely through. By etching from the side having the larger
opening, one produces an opening in the article which corresponds
to the opening Xl in resist layer 42.
Thus~ it is apparent the present process provides a
method for accurateIy e~ching openings which have a minimum
dimension which is as small as 4.0% of the:thickness of the material
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