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Phosphor-Screening Method for Small CRT

IP.com Disclosure Number: IPCOM000099878D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 134K

Publishing Venue

IBM

Related People

Takamori, T: AUTHOR

Abstract

A method is described for fabricating a dense and uniform layer of phosphor powder on a flat face plate of small CRTs such as those for projection systems or avionic high-light ambient applications where high-light emission is required. In these applications, the phosphor layer is exposed to electron beams of much higher power density than those in many, more conventional CRTs, and, therefore, the good thermal dissipation properties of the phosphor screen is extremely important for its resistance to electron beam degradation. It has been known that the life time of phosphor screens prepared by conventional screening processes, such as sedimentation, dusting, etc., is very limited in such applications.

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Phosphor-Screening Method for Small CRT

       A method is described for fabricating a dense and uniform
layer of phosphor powder on a flat face plate of small CRTs such as
those for projection systems or avionic high-light ambient
applications where high-light emission is required. In these
applications, the phosphor layer is exposed to electron beams of much
higher power density than those in many, more conventional CRTs, and,
therefore, the good thermal dissipation properties of the phosphor
screen is extremely important for its resistance to electron beam
degradation.  It has been known that the life time of phosphor
screens prepared by conventional screening processes, such as
sedimentation, dusting, etc., is very limited in such applications.
This is believed to be caused by the poor contact of phosphor
particles with each other and also with the face plate, resulting in
the poor thermal dissipation from the electron-bombarded phosphor
layer.  In an attempt to solve this problem, a single crystal layer
has been tested as a phosphor screen instead of the conventional,
deposited powder screen.  Although resistance to electron beam damage
is increased by several orders of magnitude in this case, serious
light trapping in the face plate and some other accompanying demerit
seem to have discouraged one from further pursuit for any useful
applications.  Consequently, a dense and uniform powder phosphor
screen has been desired for such small CRT applications as mentioned
above, because densification of the powder will improve thermal
dissipation properties of the phosphor screen, while the powder form
of the phosphor itself will avoid the light-trapping problem.  The
present method significantly improves the thermal dissipation
properties of phosphor powder screens by preparing them much denser
than conventionally deposited screens.

      In many applications, on the other hand, the phosphor screen of
a small CRT is required to have better resolution than those of
larger CRTs to accommodate enough information in its smaller
effective area.  This is accomplished by the use of phosphor powders
with finer particle size, such as a micron or two, as compared with
five to fifteen microns in many commercial CRT phosphors.  However,
the finer the particle size is, the more difficult it is to obtain
dense powder layers by conventional screening processes, such as
sedimentation, which depend on gravitational compaction.  In other
words, according to conventional screening processes, the phosphor
screen with finer particles will tend to have even poorer thermal
dissipation properties.  The present method also significantly
improves the thermal dissipation properties of phosphor powder
screens with finer particles by preparing them much denser than
screens prepared by conventional processes.

      By using the present method in this disclosure, one can obtain
a uniform and much denser phosphor screen than those prepared by the
conv...