U.S. patent number 3,574,909 [Application Number 04/748,110] was granted by the patent office on 1971-04-13 for method of reducing internal matrix arcing in electrostatic printing tubes.
Invention is credited to Kurt H. Brenner, Jr..
United States Patent |
3,574,909 |
Brenner, Jr. |
April 13, 1971 |
METHOD OF REDUCING INTERNAL MATRIX ARCING IN ELECTROSTATIC PRINTING
TUBES
Abstract
Internal matrix arcing is reduced by providing the tube with an
internal electrically conductive coating which is anhydrous or by
applying hydrated material and baking it in air to dehydrate the
material before the matrix is applied to the tube.
Inventors: |
Brenner, Jr.; Kurt H. (Seneca
Falls, NY) |
Family
ID: |
27047680 |
Appl.
No.: |
04/748,110 |
Filed: |
June 18, 1968 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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690688 |
Dec 14, 1967 |
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483510 |
Apr 30, 1965 |
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Current U.S.
Class: |
445/58; 427/58;
427/108; 445/53 |
Current CPC
Class: |
H01J
31/065 (20130101) |
Current International
Class: |
H01J
31/00 (20060101); H01J 31/06 (20060101); H01j
009/18 () |
Field of
Search: |
;29/25.1,25.11,25.13,25.17 ;117/201 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Campbell; John F.
Assistant Examiner: Lazarus; R. B.
Parent Case Text
CROSS REFERENCES TO RELATED APPLICATIONS
This application is a division of Ser. No. 690,688, filed Dec. 14,
1967, which in turn is a streamlined continuation of Ser. No.
483,510, filed Apr. 30, 1965.
Claims
I claim:
1. A method of reducing internal matrix arcing in electrostatic
writing tubes having a faceplate matrix portion, an envelope, and
an electron gun, which includes the steps of: coating said tubes
with an anhydrous material to form an electrically conductive
coating on the interior of said envelope to eliminate the
possibility of a hydrated vapor contacting the interior surface of
said matrix whereby the prevention of a deleterious reaction
between said vapor and said matrix is achieved.
2. A method of reducing internal matrix arcing in electrostatic
writing tubes having an envelope and an electron gun which includes
the steps of: coating said tubes with a hydrated material to form
an electrically conductive coating on the interior of said
envelope, baking said hydrated material in air to dehydrate said
hydrated material and to eliminate the possibility of a hydrated
vapor contacting the interior surface of said matrix whereby the
prevention of a deleterious reaction between said vapor and said
matrix is achieved, and subsequently sealing a matrix to said
envelop.
Description
BACKGROUND OF THE INVENTION
This invention relates to electrostatic writing tubes and more
particularly to improvements therein and in the method of
manufacturing the same.
Electrostatic writing tubes comprise an hermetically sealed,
electrically insulating, substantially funnel-shaped envelope
containing an electron gun for emitting a beam of electrons and a
matrix spaced therefrom on which the electron beam impinges. The
matrix is comprised of a plurality of laterally arrayed,
insulatingly spaced apart conductive members which extend from the
internal surface of the matrix to the external surface thereof. An
internal anode in the form of an electrically conductive coating of
some suitable material, such as Aquadag, is provided within the
tube and extends from the electron gun to a position spaced from
the matrix.
In the apparatus with which the tube is utilized is a conductive
plane and the matrix of the tube is aligned with and spaced from
this plane. Since this conductive plane is maintained at anode
potential it is often referred to as an external anode. Also
included in this apparatus are means for causing the electron beam
to scan the matrix in a given manner and means for passing a
dielectric material, such as paper, between the tube and the
conductive plane, or external anode.
In operation the electron beam emanating from the electron gun is
turned on or off in accordance with electrical signals fed to the
cathode of the gun from associated equipment and the beam is caused
to scan the matrix in a given manner in accordance with other
signals. As the electron beam strikes one of the conductive members
on its internally disposed surface the member will begin to charge
toward cathode potential. When the member has substantially reached
cathode potential it will discharge to the external anode. If a
dielectric material, such as paper, is present between the matrix
and external anode the discharge will pass to the paper leaving an
electrostatic charge substantially of the same diameter as the
conductive member thereon.
By causing the paper to move transversely past the tube in the
space between the tube and the external anode and by selectively
applying the electron beam to the interior surface of the
conductive members, a selected code array of electrostatic charges,
which may be in the form of letters or numbers, will be deposited
on the paper. The charges, which have a given polarity, may be
subsequently developed by dusting the paper with a dielectric
powder whose grains carry signs of the opposite polarity. The
powder will cling to the charged areas as distinguished from the
uncharged areas and may then be permanently fixed to the paper by
heat, pressure, or other suitable means.
Tubes of the type described are extremely useful in many
applications such as printing labels or the like. When fed the
proper information words or names and addresses may be printed at
tremendous speed and of size smaller than the average elite or pica
typewriter type. One particular application of a tube of this type
is in printing labels containing thereon the names and addresses of
magazine subscribers. Since these labels will be subsequently
attached to the magazine and used as the mailing label, it will be
seen that to avoid errors in delivery the label must be clearly
printed. For example, if the letter "P" were improperly printed it
might appear as the letter "F" and could conceivably cause delivery
of a magazine or other article to the wrong address. A more
detailed account of the operation of a printing system of this type
may be found in U.S. Pat. No. 2,894,799.
One of the first methods employed in assembling these tubes
comprised coating the internal surfaces of the envelope with
Aquadag, care being used to see that no Aquadag was applied to the
matrix area. The envelope was then baked in air to drive off
occluded water vapor and other gases. The insertion of the gun and
its attached stem was accomplished next and then the stem was
sealed to the neck of the tube and the tube was exhausted and
tipped off.
Tubes built in accordance with this method frequently produced
improper printing because of a condition known as "butterflies."
Butterflies are caused by arcing on the internal surface of the
matrix. These arcs may discharge from conductive member to
conductive member, from member to glass or from glass to glass and,
since they are deposited on the dielectric material as unwanted
electrostatic charges, they appear on the printed matter (after
developing) as a combination of open spaces and/or extra dark areas
or simply as a spot where no spot should be.
While it is virtually certain that the "butterflies" are caused by
internal matrix arcing, the exact cause of the arcing has never
been determined beyond all doubt.
One current theory, which subsequent discussion will shown appears
to be reasonable, holds that some form of physical or chemical
change occurs on the internal surface of the matrix either during
processing or operation of the tube and that these changes are
responsible for the arcing.
A prior method of combating arcing involved sandblasting the
internal surface of the matrix during processing with a fine grain
sand. This roughened the internal surface of the matrix and
virtually eliminated internal matrix arcing and associated
butterflies; however, it introduced another problem in the form of
insufficient back-bar efficiency and uneven current distribution
across the matrix. Back-bar efficiency is the ratio of available
output current (at the external surface of the matrix) to total
anode input current, expressed as a percentage of total anode
current. The term is derived from the method of determining the
efficiency which consists of holding to the external surface of the
matrix, during operation, a "back-bar," a bar of insulating
material having a conductive surface and which is connected,
through a meter, to anode potential.
To be acceptable a tube should possess a back-bar efficiency of at
least 60 percent of total anode current and higher ratings would
definitely be desirable. Tubes having a sandblasted matrix can be
processed to provide this required minimum efficiency and a
substantially uniform current distribution by "burning in" the
matrix after completion of the tube. That is, operating the tube
with a full scan for a definite period of time. This approach,
while workable, is a time consuming and costly operation.
Another approach utilized to return the back-bar efficiency rating
to acceptable levels is to acid etch the matrix after sandblasting
with a mixture of hydrofluoric acid and sulphuric acid in the ratio
of 1 to 1. The acid etch smoothed out somewhat the roughened
surface of the matrix and improved the back-bar efficiency,
apparently by reducing the amount of secondary emission from the
internal matrix surface. Tubes produced by this method had reduced
internal matrix arcing and acceptable back-bar efficiency but,
again, another problem was introduced; i.e., the tubes did not have
an acceptable life expectancy. The reason for this may be made
clear by an understanding of the matrix construction.
A current type of writing tube now in use has a matrix area
approximately 3 inches long by 3/8 inches wide. It is composed of a
plurality of electrically conductive members, such as wires, having
a diameter of 0.0005 inches spaced apart on a center-to-center
distance of 0.003 inches. Since these members are all insulated one
from another by glass, a matrix of the size noted above would
contain over 40.000 individual glass to metal seals. It is felt
that the sandblasting and acid etching procedures used heretofore
had a deleterious effect on these seals since an undesirable number
of tubes produced by this method would develop air leaks in the
matrix area shortly after they were put into use.
OBJECTS AND SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to enhance the
manufacturing techniques utilized in the construction of
electrostatic writing tubes.
It is another object of the invention to produce an improved tube
of this type.
Still another object of the invention is the reduction of time
utilized in the manufacture of these tubes.
Other objects are the provision of an electrostatic writing tube
characterized by substantial freedom from internal matrix arcing,
improved resolution, improved back-bar efficiency, uniform current
distribution across the matrix, and long life.
These objects are achieved in one aspect of the invention by
providing a method of manufacturing electrostatic writing tubes
which comprises providing selected interior surfaces of the tube
with a substantially anhydrous, electrically conductive material.
This aspect of this method eliminates five of the steps previously
utilized in construction with consequent cost savings and results
in a tube having the desirable characteristics of substantial
freedom from internal matrix arcing, improved resolution, improved
back-bar efficiency, uniform current distribution, and long life
expectancy.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flow diagram of a prior art method utilized in the
manufacture of electrostatic writing tubes;
FIG. 2 is a flow diagram of an embodiment of the method of this
invention; and
FIG. 3 is a longitudinal sectional view of an electrostatic writing
tube constructed in accordance with this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
For a better understanding of the present invention, together with
other and further objects, advantages, and capabilities thereof,
reference is made to the disclosure and appended claims in
connection with the above-described drawings.
In the course of experimentation into methods of improving
electrostatic writing tubes it has been discovered that by applying
an anhydrous, electrically conductive material to selected interior
surfaces of the tube, in place of the Aquadag and with the
consequent elimination of the preliminary air bake to drive off
occluded water vapor, a tube is produced that has virtually no
internal matrix arcing. Apparently, a reaction occurred between
gases and water vapor driven off in the air bake and the internal
surface of the matrix. As noted above with reference to the prior
art and as is shown in FIG. 1, the internal matrix arcing was
reduced by sandblasting even though the air bake was performed
subsequent thereto. Therefore, it may be assumed that roughening
the surface prevented or greatly retarded whatever this reaction
was. The exact nature of the deleterious phenomena that occurred
are unknown at this time.
Further advantages in this method occur because of the elimination
of the sandblasting or roughening of the internal matrix surface.
Since roughening of the surface is known to cause an increase in
secondary emission and, since as noted hereinbefore, this
apparently caused a decrease in back-bar efficiency, it became
possible to provide a polished internal matrix surface. By
providing a surface having a smoothness comparable to that
obtainable with a 400 grit polish, back-bar efficiencies ranging
from 65 percent to 75 percent of total anode current are achieved.
These are well into the acceptable range and, of course, eliminates
the need for any pre-use "burn-in."
Utilization of this method also provides for increased resolution.
The improved resolution occurs because the greater back-bar
efficiency of tubes produced by this method allows reducing the
total anode current while still maintaining a current output value
equivalent to that of tubes having lower efficiency. Since the beam
spot diameter is dependent upon beam current, i.e., total anode
current, (the higher the beam current, the larger the spot
diameter) a lower beam current provides a smaller beam spot
diameter with subsequent better resolution.
A still further improvement will be explained with reference to
FIG. 3 wherein is shown an electrostatic writing tube 10 comprised
of an envelop 12 having a faceplate 14 closing one end thereof. The
faceplate 14 contains therein a matrix 16. The envelope 12 and
faceplate 14 are preferably of some suitable electrically
insulating material, such as glass; however, the faceplate may be
metal provided that the matrix is insulated therefrom. Spaced from
the matrix and aligned therewith is an electron gun 18 for
providing a beam of electrons 20. An internal, electrically
conductive anode coating 22 is disposed about the inside surface of
the envelope and extends from a position spaced from the matrix to
the electron gun. The anode electrode of gun 18 is electrically
connected to anode coating 22 by suitable means, as snubbers 24. An
anode connector 26 contacts the coating 22 and projects from the
envelope so that a suitable source of potential may be connected
thereto. Adjacent the outside surface of the matrix 16 and spaced
therefrom is an external anode electrode 28 which is connected to
the same potential source as coating 22.
A dielectric material 30 such as paper is passed between external
anode 30 and matrix 16 for the reception of electrostatic
charges.
In tubes constructed by prior methods; i.e., with the Aquadag
coating, it was customary to leave at least one small uncoated area
inside the tube adjacent the matrix. This area is indicated in the
drawing as 32. Since the Aquadag is opaque, this area was necessary
to permit visual inspection of the beam alignment. Problems again
were present however, in that lack of a conductive coating in this
area caused capacitive charges to build up thereon and cause
misregistry of the beam when it was in that region.
This problem may be avoided with this invention by the use of a
transparent conductive coating such as stannous chloride, which is
anhydrous and does not need an air bake. Another applicable
approach is to coat only the viewing area 32 with a transparent
conductor and the rest of the tube with an opaque, anhydrous
conductor, such as aluminum. Obviously, suitable masking techniques
would be necessary.
When stannous chloride is used as the internal conductive coating
it is customary to apply a small amount of Aquadag around the
internal end of anode connector 26 and also around the neck area
contacted by the snubbers. This ensures good electrical contact at
these points because of the greater electrical conductivity of the
Aquadag relative to the stannous chloride. The small amount of
moisture added to the tube with the addition of the Aquadag is
adequately driven off during exhaust and no separate bake is
required.
It is to be noted that in addition to applying an anhydrous coating
to the tube it is possible to apply a hydrated or hygroscopic
coating to the tube before the matrix is attached thereto. In this
instance the coating and tube would be air baked before the
attachment of the matrix and then would be maintained in an
anhydrous atmosphere until such attachment could take place. Thus,
by this technique a hydrated coating would be applied to the
envelope, but an anhydrous coating would be provided for the
tube.
The invention described above has provided significant advances in
the art of manufacturing electrostatic writing tubes. The
elimination of five previously performed steps has resulted in
considerable cost savings. Additionally, the tube produced has
substantially no internal matrix arcing, improved resolution,
improved back-bar efficiency, uniform current distribution and
greater life expectancy than tubes produced by methods used
heretofore.
While there have been shown and described what are at present
considered the preferred embodiments of the invention, it will be
obvious to those skilled in the art that various changes and
modifications may be made therein without departing from the scope
of the invention as defined by the appended claims.
* * * * *