Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention is described, but not claimed in
commonly assigned co-pending Canadian Application 223,992.
The present invention relates generally to electrophoto-
graphy and more particularly to improvements in developing an
image on an electrophotographic element.
In electrophotography, it is common to apply a uniform
electrostatic charge to the surface of a photoconductive layer.
The charge is then selectively dissipated in a pattern by expo-
sing the surface to a light image. The resulting pattern of
charges produces an electrostatic latent image on the photo-
30 conductive layer, which is rendered visible by applying to it
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5~34
electrostatically charged toner particles which adhere to the sur-
face o~ the photoconductive layer by electro~tatic attraction. A
permanent visible image can be obtained by using toner particles
which can be heat ~used to the photoconductive layer and subject-
S ing them to a heat application step.
In the conventional developing method using liquid
developer, which is a liquid carrier for finely divided electro-
static particle~ such as carbon particles, the image exposed film
is dipped in the liquid developer to produce a visible image
corresponding to the latent image thereon. While this method o
developing is satis~actory for some types of system~ and film, it
is not satisfactory for the type of system in which imaging and
developing takes place automatieally within a single apparatus.
In that mlcrophotographie eopying maehine, data from sueeessive
aocuments i~ sequentially recorded on individual frames of a multi-
~rame miGrofiehe. Because it i8 desirable to image and develop
eaeh frame quickly beforo ropeating the proeess for the next frame,
the proeess for developing the images must be one which ean be
carried out quiekly and eonveniently to a mierofiehe fixed within
a holder within tho reproduction apparatus. Additionally, the
developing system must bo eapable of quickly applying the eorreet
amount of developer, or toner partieles ~whieh are preferably
~u~pended in a liquid carrier) to the imaged area of the film and
removing the toner particles from the film without permitting
~5 leakage of the toner partieles into the interior of the reprodue-
tion apparatus. The system must also be eapa~le of quickly evap-
orating any of ~he toner carrier liquid remaining on the film to
immo~ilize the toner partieles remaining on the film and prevent
~mearing of the toned imaged.
~herefore, it is an object of the invention to provide
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a method and appar us for quickly applying a mea~ured ~uantity of
liquid toner to an imaged area of a film without permitting leak-
age of the liquid toner beyond the imaged area of the film. A
further object of the invention i~ to quickly evaporate residual
S toner carrier liquid remaining on the film after toning. And a
further object of the invention is to provide a method and
apparatus for accomplishing the above ob~ects while the film is held
in a carrier within a microphotographic reproduction apparatus.
According to one aspect o~ the invention there is pro-
vided an apparatus for developing an electrostatic latent imageon an electrophotographic film comprising: a developing chamber
forming a passageway through which electrostatically charged toner
particles are conducted to contact the film, the chamber having
an opening bordered by a mask agains~ which the film is placed to
lS form a seal, an inlet through which toner partiales and air enter
the chamber, and an outlet through which toner particles and air
leave the chamber; supply means for providing toner particles to be
passed through the chamber; toner flow control means for permitting
a predetermined quantity of toner particles to flow through the
developing chamber at predetermined times; air supply means for
- supplying drying air to the inlet of the chamber; and vacuum means
connected to the outlet of the chamber for drawing the toner par-
ticles and the air through the chamber, the vacuum means creating
sub-atmospheric pressure within the chamber to prevent leakage of
toner particles from the chamber around the film.
According to another aspect of the invention there is
provided a method of developing an electrostatic latent image on
an electrophotographic film comprising the steps of: positioning
the film against an opening in a developing chamber; drawing toner
particles through the chamber with a vacuum source which creates a
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sub-atmospheric pressure within the chamber to prevent leakage of
the toner particles from the chamber around the film.
In its preferred form, the invention includes control
means operably connected to the vacuum means for providing a high
vacuum level and a low vacuum level, the low vacuum level being
used to draw the toner particles through the developing chamber,
and the high vacuum level being used to draw the drying air through
the chamber. The preferred form of the apparatus further includes
a development electrode forming one wall of the passageway for con-
ducting the toner particles through the developing cham~er in a
position close to the opening through which the toner particles
contacts the film.
The invention will now be described by way of example with
reference to the accompanying drawings in which:
Fig. 1 i8 a diagrammatic view of the developing apparatus of
the invention.
Fig 2 is an enlarged cross-sectional view of the developing
chamber illustrated in Fig. 1, taken along lines 2-2.
Fig. 3 is a diagrammatic view of the pre~erred embodiment of
the developing apparatus of the invention, and
Fig. 4 is an enlarged _ross-sectional view of the developing
chamber illustrated in Flg. 3.
Referring to Fig. 1, the toner supply network in accor-
dance with one embodiment of the present invention i8 in the form of
a closed systein and include~ a suitable toner reservoir 11 con-
taining a su~ply of liquid toner 30. Liquid toner 30 may be of
any suitak~e type well known in the art, but preferably consist-
ing of ~lack colored electro3copic particles colloidally suspended
in a iiquid vehicle. A four-part connector block communicates
in~eriorly of the reser~oir 11 and support~ a toner pickup tube
14 which is connectea to a toner pump 13.
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The pump 13 supplies toner via line 15 to a pressure relief
or bypass valve 23 having first and second outlet ports communi-
cating respectively with reservoir 11 via tube 24, and with the
processing assembly via tube 16. Tube 16 feeds first solenoid
valve 19 through a suitable filter element 25. Solenoid valve
19 is vented to the atmosphere through tube 21 and has its out-~
let port connected to the inlet of a second solenoid valve 20 by
a short length of tube 16. Tube 16 between the first and second
solenoid valves 19 and 20 has an internal volume corresponding
to the amount of toner necessary to effectuate the development
of a single frame on a microfiche.
Solenoid valve 20 communicates with the fluid reservoir 11
by conduit 22 and has its outlet port coupled by a fluid line 17
to the inlet port 31 (Fig. 2) of the developing chamber 10. Out-
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let port 32 of the toner module is connected via conduit 18 to a
toner vacuum separator 26 which separates unused toner and con-
ducts it back to the reservoir 11 by gravity. A vacuum line 28
is also connected to the toner vacuum separator 26 and applies a
negative pressure to the system through a two stage regulator 29.
; 20 Regulator 29 may be of any suitable construction known to those
skilled in the art and is electrically controlled to selectively
provide low and high vacuum levels to the toner vacuum separator
. ~
~ 26. A vacuum pump 12 operably communicates with the two-stage
. ~
-~ regulator to complete the system.
Fig. 2 illustrates a microfiche 37 in position against the
developing chamber 10 with the photoconductive surface of the
micxofiche facing the developing chamber 10. The developing
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chamber 10 includes an inlet 31, a passageway 33, and an outlet
32. Within the passageway 33 is an opening 34 formed by rect-
angularly shaped flange or mask means 35. The frame of the
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microfiche 37 to be toned (or developed) is placed against the
opening 34 which is the same size as the frame, whereby toner
particles flowing through the passageway 33 will contact that
frame of the microfiche 37. Forming one wall of the chamber
passageway 33 opposite the opening 34 is a development electrode
36, provided by a thin plate of electrically conductive material
such as copper. The development electrode 36 is beneficial in
toning the image on the frame in a manner well known in the art.
The development electrode 36 is preferably positioned close to
the opening 34 to create a strong electric field between the
electrode 36 and microfiche 37 and to force liquid toner flowing
through the passageway 33 against the microfiche 37.
~ The developing chamber 10 is placed against the surface of
; the microfiche 37, and solenoid valve 19 of the toner supply
circuit is opened, causing toner fluid to be pumped from
~ reservoir 11 through solenoid valve 19 and tube 16 to the closed
solenoid valve 20. Fluid thus circulates through tube 16 and
solenoid valves 19 and 20 and is returned through tube 22 to the
: reservoir 30. In this manner, the portion of tube 16 between
- 20 solenoid valves 19 and 20 is filled with toner fluid in the
precise amount necessary for effectuating the development of the
latent image on a single frame of the microfiche 37. Solenoid
valve 19 is thereafter closed, opening vent tube 21, and
~ solenoid valve 20 is simultaneously opened, closing off conduit
~ 25 22, whereby the metered amount of toner fluid contained within
~ tube 16 is conducted through tube 17 to the inlet port 31 of the
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developing chamber 10. Toner fluid is drawn through the develop-
ing chamber 10 by the vacuum at a low vacuu~evel setting by
proper actuation of the two-stage-regulator 29.
The two-stag~ regulator 29 is then switched to its high
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105'~634
vacuum mode, thereby precluding the leakage of toner fluid from
the developing chamber 10 around the microfiche 37 and pulling
drying air through vent tube 21 to effect a substantial drying
of the developed microimage.
In a preferred embo~diment, the drying step also includes
separating the microfiche 37 slightly from the mask means 35 to
draw additional drying air into the developing chamber 10 from
around the frame being developed for more effective drying. The
use of vacuum creates an effective seal between the chamber 10
and the microiche 37 for purposes of preventing toner fluid
from leaking out.
Referring to Figs. 3 and 4, the preferred embodiment of the
invention is disclosed (with the indicating numerals which are
identical to indicating numerals in Figs. 1 and 2 representing
; 15 system components which are identical to the system components
, .
in Figs. 1 and 2). The preferred system includes toner
reservoir 11 containing liquid toner '30, and from which toner
fluid is drawn through conduit 14, through solenoid valve 38 and
line 17 into the inlet 41 of developing chamber 40 by way of
orifice needle 42. The liquid toner 30 is drawn through chamber
passageway 33, through the developing chamber outlet 32, and
into the toner vacuum separator 26 by way of conduit 18. Tonex
vacuum separator 26 is a conventional liquid/gas separator and
is connected by way of conduit 28 to vacuum pump 12 through two-
:~ ,
stage regulator 29. Leading from the bottom of toner vacuum
1 separator 26 is toner return line 27, which conducts the toner
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'J, ~ fluid back into the toner reservoir 11.
Drying air is conducted through solenoid valve 44 and con-
duit 39 into developing chamber inlet 41. Developing chamber 40
includes an opening 34 communicating with the chamber passageway
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105;~34
33 and formed by rectangularly shaped mask means 35. The frame
of the microfiche 37 to be toned is placed against opening 34 to
form a seal with mask means 35. Of course, the photoconductive
layer of the microfiche 37 is faced lnward into the developing
chamber 40. One wall of the chamber passageway 33 is formed by
development electrode 36 positioned opposite the opening 34 and
very close to the opening to create a strong electric field be-
tween the electrode 36 and the microfiche 37 and to f~rce the
liquid toner flowing through the chamber passageway 33 against
the microfiche 37. The development electrode can be ~rovided by
a very thin electrically conductive plate, and functions in a
manner well known to those skilled in the art. Covering develop-
ment electrode 36 is a finely woven fabric 43, such as silk,
which is saturated by the toner fluid during the toning process.
The fabric 43 retains enough of the liquid carrier to remain
moist during the drying step which will be.described subsequent-
; ly. In this way, permanent deposition of toner particles upon
- the development electrode 36 is prevented. The fabric 43 also
can cover other portions of the passageway 33 walls to prevent
~- 20 permanent deposition of toner on them.
- The operation of the preferred form of the invention will
now be described. As soon as an imaged frame of a microfiche 37
is placed against opening 34 in the developing chamber 40, the
vacuum pump 12 applies a low-level vacuum, controlled by a two-
stage regulator 29, through conduit 28, toner vacuum separator
26, conduit 18, developing chamber 40, conduit 17, solenoid
valve 38, and conduit 14 to draw toner particles 30 through the
:
chamber passageway 33 of the developing chamber 40. During this
operation the solenoid valve 38 is opened, and the solenoid valve
43 is closed to prevent air from being pulled through the conduit
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39. The needle orifice 42 is sized to meter the liquid toner 30
through at a predetermined rate. A timer closes solenoid valve
38 when the desired quantity of toner fluid 30 has been pulled
through the developing chamber 40. ~Immediately upon closing of
solenoid valve 38, solenoid valve 43 opens, permitting drying
air to be drawn through conduit 39 into the chamber passageway
33. At the same time the two-stage regulator 29 is switched to
the high-vacuum level stage to draw air through at a fast rate.
The air being drawn through at a fast rate assures quick evapora-
; 10 tion of residual toner carrier liqui~ remaining on the microfiche
37, as well as drawing air in from any opening which might exist
- between the microfiche 37 and the mask means 35, thereby prevent-
- ing toner fluid from flowing along the microfiche beyond the
frame being toned or into the interior of the reproduction
apparatus. Pulling the toner liquid 30 through the solenoid by
,vacuum means also creates a pressure within the passageway
chamber 33 that is lower than the pressure of the outside air
and draws air through any opening inadvertently formed between
mask means 35 and the microfiche 37, thereby forming an air
seal to prevent the liquid toner from leaking from the
developing chamber 40.
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