U.S. patent number 3,761,951 [Application Number 05/208,785] was granted by the patent office on 1973-09-25 for electrostatic image forming apparatus.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Eiichi Inoue, Takashi Saito, Hiroshi Tanaka, Keizo Yamaji.
United States Patent |
3,761,951 |
Inoue , et al. |
September 25, 1973 |
ELECTROSTATIC IMAGE FORMING APPARATUS
Abstract
Image-forming apparatus includes an electron beam generator
responsive to image-defining excitation signals to apply a pattern
of electron beams to a plate. The plate thereupon emits radiation
in pattern according with the electron beam pattern.
Inventors: |
Inoue; Eiichi (Tokyo,
JA), Yamaji; Keizo (Tokyo, JA), Tanaka;
Hiroshi (Tokyo, JA), Saito; Takashi (Tokyo,
JA) |
Assignee: |
Canon Kabushiki Kaisha (Toyko,
JA)
|
Family
ID: |
27455693 |
Appl.
No.: |
05/208,785 |
Filed: |
December 16, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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800962 |
Feb 20, 1969 |
3653064 |
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Foreign Application Priority Data
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Feb 25, 1968 [JA] |
|
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43/11875 |
Feb 27, 1968 [JA] |
|
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43/12739 |
Feb 27, 1968 [JA] |
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43/12740 |
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Current U.S.
Class: |
347/122; 355/20;
399/288 |
Current CPC
Class: |
G03G
5/04 (20130101); H01J 29/10 (20130101); G03G
15/328 (20130101) |
Current International
Class: |
H01J
29/10 (20060101); G03G 15/32 (20060101); G03G
5/04 (20060101); G03G 15/00 (20060101); G03g
005/02 (); G03g 013/00 (); G03g 015/00 () |
Field of
Search: |
;346/74ES,74EB,74P
;355/16 ;96/1PC |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Fears; Terrell W.
Assistant Examiner: Hecker; Stuart
Parent Case Text
This is a division of application Ser. No. 800,962, filed on Feb.
20, 1969, now U.S. Pat. No. 3,653,064.
Claims
What is claimed is:
1. Image-forming apparatus comprising means operably responsive to
information signals for emitting electron beams defining said image
along an axis and plate means including in succession along said
axis a radiation image-generating layer comprising a material
emitting radiation upon electron beam bombardment thereof and an
electrode transmissive to said radiation and coextensive with said
radiation image-generating layer.
2. The apparatus claimed in claim 1 wherein said electrode is
metallic film.
3. The apparatus claimed in claim 1 wherein said plate means
further includes a layer of optical fibers interposed between said
radiation image-generating layer and said electrode.
4. The apparatus claimed in claim 1 further including means for
applying blanket radiation to said plate means.
5. The apparatus claimed in claim 1 wherein said plate means
further includes a photoconductive layer sensitive to said
radiation and disposed successively along said axis from said
electrode.
6. The apparatus claimed in claim 5 wherein said plate means
further includes an insulative layer disposed successively along
said axis from said photoconductive layer.
7. The apparatus claimed in claim 1 wherein said plate means
further includes an insulative layer transmissive to said radiation
and disposed successively along said axis from said electrode.
8. The apparatus claimed in claim 7 wherein said plate means
further includes a photoconductive layer sensitive to said
radiation and disposed successively along said axis from said
insulative layer.
9. The apparatus claimed in claim 8 wherein said plate means
further includes a second insulative layer disposed successively
along said axis from said photoconductive layer.
Description
The present invention relates to electrostatic recording methods,
and to recording tubes with multilayer face plates responsive to
information signals for use in electrostatic image-forming
processes.
One known method for electrostatically recording information
signals is disclosed in U.S. Pat. No. 2,879,422, issued to H. C.
Borden et al. This method employs a cathode ray tube having a face
plate comprising an insulative layer in which conductive pins
electrically isolated from one another are embedded in a matrix.
Information signals are converted into electron beams by the
cathode ray tube and the electron beams are passed through these
pin-shaped conductors so as to cause atmospheric discharge in a
recording material, thereby recording electrostatic patterns in
accordance with the information signals. In this method, the
resolution of said patterns is significantly influenced by the
density of the conductive pins in the matrix. However, from the
standpoint of function and structure, it is extremely difficult to
arrange and dispose conductor pins in a high density matrix in the
face plate. Furthermore according to this method, the electrostatic
pattern formation is affected by atmospheric discharge, so that as
such discharge tends to become unstable under environmental
conditions, the images are distorted. Thus, it is difficult to form
high contrast electrostatic patterns.
Another method is disclosed in U.S. Pat. No. 3,132,206 issued to P.
F. King. According to this method, the information signals are
converted into images by the cathode ray tube and are displayed on
the phosphor screen thereof. Such displayed images are used as
light images for the electrophotographic image-forming in
accordance with the Carlson process, i.e., by projecting the light
images upon a xerographic plate, thereby forming electrostatic
patterns on the photoconductive layer of the plate. In this
process, in order to retain charge on the photoconductive layer,
the photoconductor material must have a relatively high resistance
and use of the relatively low resistance, highly sensitive
photoconductor material is impractical. Therefore, in this process,
formation of high contrast and highly sensitive electrostatic
patterns is not expected. Furthermore, in this process the signals
are first converted into an image displayed on the screen which in
turn is projected upon a photosensitized plate so as to
electrostatically record the signals. Therefore, the efficiency and
the speed of this process are rather inferior in practice.
The present invention contemplates recording processes by which
such defects encountered in conventional methods or processes are
completely eliminated.
In brief, according to the present invention, in formation signals
are first converted into electron beam signals, thereby
representing the signals as radiation images, more specifically
images displayed by a luminous body. These images are converted
further into electrostatic images upon a photosensitive member
composed fundamentally of an electric charge-retaining insulative
layer, a photoconductive layer and a substrate; and these
electrostatic images are transferred directly to a photosensitive
material or to other recording materials. The fundamental process
for forming electrostatic images herein is based upon the
inventions disclosed in U.S. applications Ser. Nos. 563,899/1966,
now abandoned and 571,538/1966 now abandoned. The fundamental
process herein includes the use of a photoconductor member in which
a photoconductive layer and charge-retaining insulative layer are
overlaid in order upon a conductive or insulating substrate or
lamination thereof and the process herein is characterized by the
first step of applying to said insulative layer a first voltage (DC
voltage) so as to mainain said insulative layer at a predetermined
potential level, thereby generating a strongly bound charge layer
at the interface between the photoconductive and insulative layers,
or the portion adjacent thereto, by utilizing the electrical field
provided by said potential, by the second step of applying a second
voltage having a polarity opposite to that of said first voltage,
or AC voltage, to said insulative layer and simultaneously
projecting light images so as to vary the state of the charge due
to the first voltage application by said second voltage, and by the
third step of applying uniform radiation to which said
photoconductive layer is sensitive, thereby forming an
electrostatic image upon said insulative layer. While the present
invention is based upon such fundamental process, the invention
includes other improved processes providing the same results,
advantages and features as said fundamental process.
Briefly, according to the present invention, the process includes
the first step of applying a first voltage to a photoconductive
member composed fundamentally of a substrate, a photoconductive
layer and a charge-retaining insulative layer, the second step of
applying a second voltage thereto and simultaneously projecting
thereupon a radiation image corresponding to the electron beam
signals of a cathode ray tube or projecting said radiation image
onto a photosensitive body disposed in contact with said
photoconductive member, and the third step of applying uniform
radiation thereto.
Alternatively, another process of the present invention includes
the first step of applying a first voltage to the face plate of a
cathode ray tube incorporating the above-described photoconductive
member, the second step of applying a second voltage to this face
plate and simultaneously projecting thereupon a radiation image
corresponding to the electron beam signals, and the third step of
uniformly illuminating the face plate with radiation interiorly or
exteriorly of the cathode ray tube, thereby forming an
electrostatic image directly upon the face plate, or transferring
said electrostatic image to copying material. A further alternative
process of the present invention includes the first step of
applying a first voltage to the face plate of a cathode ray tube
incorporating said photoconductive member in contact with the
charge-retaining member or applying said first voltage either to
said face plate or member before they are placed in close contact,
the second step of applying a second voltage to said face plate in
contact with said member and simultaneously projecting a radiation
image corresponding to the electron beams thereon, and the third
step of applying uniform radiation to the face plate from the
interior or exterior of the cathode ray tube, thereby forming an
electrostatic image upon said charge-retaining member.
These processes of the present invention are characterized by the
fact that the first voltage is applied directly or indirectly to
the charge-retaining recording member so as to maintain said
recording member at a predetermined potential and when the second
voltage is applied to the recording member with simultaneous
application of the radiation image corresponding to the electron
beams thereto, the substrate, the photoconductive layer and the
charge-retaining insulative layer, with or without the
charge-retaining recording member, are maintained in the form of a
lamination.
According to the process of the present invention, high contrast
electrostatic patterns can be obtained. For example, in the case of
the Carlson process disclosed in U.S. Pat. No. 3,041,167 when the
insulative layer has a thickness substantially equal to or slightly
greater than the photoconductive layer, electrostatic contrast as
high as 1,000 to 1,500 V can be attained. According to the
processes of the present invention, electrostatic charges are
maintained in the charge-retaining insulative layer of the
photoconductive member and it is not necessary to maintain these
charges in the photoconductive layer so that a highly sensitive
photoconductive material having a relatively low resistance may be
used, thereby providing a highly sensitive photoconductive
member.
According to the present invention, images displayed on the
phosphor screen by the electron beams of a cathode ray tube are
projected on a photoconductive member of the type described above
either in contact with or remote from the cathode ray tube or on a
photoconductive member or a recording member placed over a
multilayer face plate of a cathode ray tube, thereby forming an
electrostatic image in the charge-retaining member. Therefore,
light image loss is less, and generation of electron beams and
radiation and the formation of electrostatic images can be effected
with high efficiency.
As described above, in the processes of the present invention, the
electrostatic images are formed in the charge-retaining insulative
layer of the photoconductive member so that application of the
first voltage and processing following formation of the
electrostatic image can be effected even in ambient light.
Furthermore, when said insulative layer is made of a material which
is non-transmissive to radiation applied with the second voltage
and to which the photoconductive layer is sensitive, the entire
process can be carried out in ambient light.
The electrostatic charge images formed by the processes of the
present invention can be rendered permanently visible by applying
toner to color the image, by the frost method or by any suitable
method for recording. Alternatively, the electrostatic image can be
transferred to a copying or recording material.
One of the objects of the present invention is to provide a novel
electrostatic recording process.
Another object of the present invention is to provide a cathode ray
tube incorporating a multilayer face plate adapted to convert
electron beam signals into radiation images or patterns.
A further object of the present invention is to provide an improved
recording tube adapted to provide electrostatic patterns upon the
face plate thereof.
Another object of the present invention is to provide an improved
recording tube having means for uniformly illuminating the face
plate thereof with radiation.
A still further object of the present invention is to provide
recording processes for recording electrostatic patterns by
conversion of electron beam signals controlled by information
signals.
A further object of the present invention is to provide a recording
process comprising the step of applying voltage to a face plate
incorporating a photoconductive layer and simultaneously applying
electron beams thereto, thereby efficiency recording the electron
beam signals as electrostatic patterns upon a charge-retaining
member.
A still further object of the present invention is to provide a
recording process for forming high contrast electrostatic images
upon a photoconductive member having a charge-retaining insulative
layer.
A still further object of the present invention is to provide an
electrostatic recording process which permits the use of highly
sensitive photoconductive materials.
Another object of the present invention is to provide a recording
process for forming high contrast electrostatic images even in
ambient light.
Another object of the present invention is to provide an improved
process for permanently recording electrostatic images
corresponding to electron beam signals.
The above and other objects, advantages and features of the present
invention will become more apparent from the following description
taken in conjunction with the accompanying drawings.
FIG. 1 illustrates the structure of a photoconductive member used
in the present invention.
FIGS. 1a - 1c illustrate a process for forming electrostatic images
using the photoconductive member shown in FIG. 1.
FIG. 2 is a diagram of surface potential attained in the process of
FIGS. 1a - 1c.
FIG. 3a illustrates another photosensitive member structure
according to the present invention and FIGS. 3a - 3c illustrate a
process for forming an electrostatic image using the
photoconductive member shown in FIG. 3a.
FIG. 4 is a diagram of surface potential attained in the process of
FIGS. 3a - 3c.
FIGS. 5a - 5f illustrate structures of photoconductive members for
use in processes of the present invention.
FIGS. 6a - 6g illustrate structures of face plates for cathode ray
tubes according to the present invention.
FIGS. 7 - 16, 18, 19 and 21 illustrate further processes of the
present invention.
FIGS. 17 and 20 illustrate other embodiments of face plates for
cathode ray tubes according to the present invention.
Referring now particularly to FIG. 1, which illustrates the
fundamental structure of a photoconductive member used in the
process of the present invention for converting radiation into an
electrostatic image, photoconductive layer 2 is formed upon
substrate 1 by a coater, wheeler, etc. or by sputtering, vacuum
deposition, etc. and, if required, a small quantity of a binder
such as resin or the like may be added to the material forming
photoconductive layer 2. Insulative layer 3 is formed upon
photoconductive layer 2. The photoconductive member must have
essentially these three layers, i.e., substrate 1, photoconductive
layer 2 and insulative layer 3 for electrostatic image-forming.
Substrate 1 may be made of an insulative or electrically conductive
material or a lamination composed of photoconductive and insulative
layers. Such conductive materials include metal conductors such as
aluminum, copper and the like, humid paper, Nesa coating, glass and
so on. Suitable insulative materials are selected from the same
materials used for insulative layer 3 which will be described in
more detail hereinafter, but are limited thereto and may be
selected from a wide range of insulative materials known in the
art.
Materials for photoconductive layer 2 include cadmium sulfide,
cadmium selenide, crystal and amorphous selenium, zinc oxide, zinc
sulfide, titanium dioxide, selenium telluride, lead oxide, sulfur
and other chalcogenide compounds, inorganic photoconductors and
organic photoconductors such as anthracenes, carbazoles and so on.
The material may be coated upon the substrate, or a mixture of the
above materials with or without a binding agent may be used or they
may be formed into laminations consisting of more than two layers.
Among the above-described photoconductive materials, the materials
best suited for use in the present invention are CdS, CdSe, SeTe,
and so on, and with use thereof sensitivity can be elevated to
higher than ASA 100. The present invention can employ
photoconductive materials having relatively low resistance values,
which materials have not been used in conventional processes in
which electric charges must be maintained in the photoconductive
layer. Such materials can be used in the present invention since
charge maintaining capability is imparted to the photoconductive
layer by the insulative layer superposed thereupon.
The characteristics required for insulative materials are (a)
sufficiently high resistivity to retain electrostatic charge and
(b) resistance to abrasion, and any material satisfying these
conditions may be used as the insulative layer in the present
invention. When the radiation image is applied to photoconductive
layer 2 through the insulative layer, the insulative material must
be transparent to activating radiation. On the other hand, when the
substrate is made of a material, for example, Nesa glass or the
like which permits the transmission of the activating radiation
therethrough and when the radiation image is applied to the
photoconductive layer through this substrate, the insulative layer
need not be transparent. For example, a film or coating of fluorine
resin, polycarbonate resin, polyethylene resin, cellulose acetate
resin, polyester resin and so on may be used. Furthermore, glass
made of Al.sub.2 O.sub.3, SiO.sub.2, etc., ceramic, inorganic
compound thin layers and so on, which are or are not transparent,
may be used.
The processes for forming electrostatic images upon insulative
layer 3 of the photoconductive member will now be described. First
a process will be described wherein substrate 1 is made of
conductive material and wherein application of a second voltage by
AC corona discharge is performed simultaneously with emission of
radiation. As shown in FIG. 1a, the surface of insulative layer 3
of photoconductive plate A is electrically charged, for example in
positive polarity, by corona device 5 connected to high voltage DC
source 4. In this case, it is presumed that negative charges are
injected from the conductive substrate side and are bound at the
interface between photoconductive layer 2 and insulative layer 3 or
within photoconductive layer 2 adjacent to insulative layer 3. In
this process, the surface potential of insulative layer 3 increases
as charging time elapses as illustrated in FIG. 2 by curve V.sub.P.
It is of course possible to effect the above-described charging by
using an electrode instead of corona discharge. It should be noted
that this charging step can be performed in ambient light.
When photoconductive layer 2 has n-type semiconductivity the
insulative layer is preferably charged positively. When
photoconductive layer 2 has p-type semiconductivity, the insulative
layer is preferably charged negatively.
Then as shown in FIG. 1b, a radiation image (a light image will be
used herein for the sake of convenience of description) is
projected upon insulative layer 3 while simultaneously AC corona
discharge is applied thereto from charging device 8 connected to
high voltage AC source 9. When the light image is projected through
insulative layer 3 as shown in FIG. 1b, the upper end of charging
device 8 must be optically open. After projection of the light
image and charging by AC corona discharge, the positive charges
provided by the first charging are all or almost all discharged by
the AC corona discharge where these positive charges are located at
portions of the surface of insulative layer 3 which were
illuminated by the light image. Such discharge is dependent upon AC
corona discharge time and intensity. In this case, the resistance
of photoconductive layer 2 is reduced where illuminated by the
light image so that layer 2 becomes conductive. Consequently, the
negative charges bound at the interface between photoconductive
layer 2 and insulative layer 3 or within photoconductive layer 2
adjacent to insulative layer 3 become free and are discharged as
the surface charges upon insulative layer 3 are discharged. Almost
all of these negative charges are discharged into conductive
substrate 1. Therefore, the surface potential of the
image-illuminated portions of insulative layer 3 is reduced as AC
corona discharge time elapses as shown in FIG. 2 by curve
V.sub.L.
The positive charges at portions of insulative layer not
illuminated by the light image are also discharged by the AC corona
discharge, but such discharge is less than that described above for
charges at illuminated portions. The negative charges bound in
image-unilluminated portions of the photoconductive member are not
discharged by AC corona discharge because of the high resistance of
such image-unilluminated portions of photoconductive layer 2.
Therefore, the positive charges in the corresponding portions of
insulative layer 3 are maintained or remain almost unchanged. In
image-unilluminated portions of insulative layer 3 many more
positive charges are retained than in image-illuminated portions
thereof. However, a large number of negative charges still remain
bound in photoconductive layer 2, so that the electrical field due
to the surface potential of insulative layer 3 is influenced rather
strongly by the negative charges bound in photoconductive layer 2,
whereby the external field due to the surface potential is
extremely slight or negligible. The surface potential in the
image-unilluminated portions is less than the surface potential in
the image-illuminated portions as illustrated in FIG. 2 by a curve
V.sub.D.
Thus, surface potential differences (V.sub.L - V.sub.D) are
provided upon the surface of insulative layer 3 in accordance with
the light image pattern, thereby forming an electrostatic image of
the light image. These surface potential differences (V.sub.L -
V.sub.D) vary as shown in FIG. 2 when the light image is projected
while simultaneously applying AC corona discharge, so that the
image projection and AC corona discharge time must be selected
suitably depending upon the sensitivity of the photoconductive
plate, AC discharge conditions and so on in order to obtain large
surface potential differences.
Thereafter, the surface of insulative layer 3 upon which such
electrostatic image has been formed is exposed to radiation 10 as
shown in FIG. 1c. In this case, the image-illuminated portions of
photoconductive layer 2 remain substantially unchanged, so that the
positive charges upon the surface of insulative layer 3 also remain
substantially unchanged, thereby maintaining the surface potential
as shown in FIG. 2 by the curve V.sub.LL. On the other hand, the
image-unilluminated portions of photoconductor layer 2 which have
maintained high resistance since they have not been exposed are now
exposed to activating radiation in this step and the resistance
thereof is rapidly reduced and they become conductive.
Consequently, the negative charges bound therein are almost all
discharged into electrically conductive substrate 1 and only a very
small portion of the charges are bound by the field of the positive
charges upon the surface of insulative layer 3. Thus, positive
surface charges, that is, charges having the same polarity as the
first or initial charges provided upon the surface of insulative
layer 3, which charges provide a field acting strongly upon
negative charges bound in photoconductive layer 2 in the previous
step, now act to provide an external field. The surface potential
of insulative layer 3 is thereby rapidly increased upon exposure of
the whole surface of the insulative layer 3 to activating radiation
as illustrated in FIG. 2 by curve V.sub.DL. As described above,
when the whole surface of insulative layer 3 is exposed to
activating radiation, the surface potentials V.sub.L and V.sub.D
become V.sub.LL and V.sub.DL respectively, so that the surface
potential of the image-unilluminated portions becomes higher than
that of the image-illuminated portions. That is, the respective
surface potentials are reversed, and the difference therebetween
increases.
According to one process of the present invention, the surface of
the insulative layer is charged in maintaining equilibrium with
charges induced in the photoconductive layer underlying the
insulative layer, and a surface differential is provided upon the
surface of the insulative layer by interaction of the charges upon
the insulative layer and those in the photoconductive layer,
thereby forming an electrostatic image in accordance with the
light-dark pattern of the original image. Therefore, as compared
with conventional electrophotographic methods in which
electrostatic images are formed upon the surface of the
photoconductive layer, the electrostatic image formed by the
present invention has a stronger external field and a large surface
potential, thus increasing sensitivity.
In the present invention, a fluorescent image formed upon the face
plate of a cathode ray tube is used as the radiation image and use
of the process of the present invention is very advantageous in
forming electrostatic patterns from such low intensity fluorescent
images, in providing rapid development and in providing high
sensitivity.
In FIG. 3, another embodiment of the present invention is shown
wherein the voltage application which is performed simultaneously
with the projection of the light image is provided by DC corona
discharge having the same polarity with that of the first charging.
Substrate 1 of photoconductive plate B is made of a radiation
transmissive material such as Nesa glass or the like having a Nesa
coating 11 thereon and the light image is projected upon the
photoconductive layer thereof through the substrate. Such process
is substantially similar to the process described above with
reference to FIG. 1.
The first step is, as in the case of FIG. 1a, to positively charge
the surface of insulative layer 3 (FIG. 3a). In the second step, as
shown in FIG. 3b, light image 12 is projected through substrate 12
while discharging device 8' supplied with a high negative potential
is simultaneously moved across the surface of insulative layer 3.
When insulative layer 3 is made of a material which is transmissive
to the light image, the upper end of the shield plate of
discharging device 8 is optically closed so as to prevent
radiation, except that from the substrate side, from impinging upon
the surface of insulative layer 3. On the other hand, when the
insulative layer 3. On the other hand, when the insulative material
is non-transmissive to the light image, the provision is not
necessary and furthermore this process may be carried out in
ambient light.
Portion L of photoconductive layer 2 is illuminated by the light
image in the second step and reduces its resistance to the charges
bound therein in the first charging step. Furthermore, the positive
charges upon the corresponding image-illuminated portion of the
surface of insulative layer 3 are discharged by the negative corona
discharge applied thereto simultaneously with the projection of the
light image and such portion is then negatively charged.
Concurrently, positive charges are induced at the interface between
the insulative and photoconductive layers or within the
photoconductive layer adjacent thereto.
On the other hand, in image-unilluminated portion D, the positive
charges applied to the surface of insulative layer 3 by the first
charging step are partially or completely neutralized by the
negative charges applied thereto in the second step. In this case,
the degree to which such portion of the insulative layer surface is
negatively charged is less than in the case of portion L as
described above. This means that the external field due to the
persistently bound carriers has a strong influence.
Next, the whole surface of insulative layer 3 upon which an
electrostatic charge pattern was formed in the second step is
exposed to activating radiation 13. In this case, in portion L the
condition of photosensitive plate A remains substantially unchanged
so that the surface potential of insulative layer 3 remains
substantially unchanged. On the other hand, at portion D which has
a high resistance, the resistance is rapidly reduced as this
portion is exposed to activating radiation in this third step and
portion D becomes electrically conductive. Therefore, the charges
bound internally in the previous step are discharged into the
electrically conductive substrate. Concurrently, positive charges
are induced in photoconductive layer 2 by the negative charges upon
the surface of insulative layer 3. Consequently, the surface
potential of the surface of insulative layer 3 is rapidly reduced
so that the field due to the negative charges on insulative layer 3
acts strongly upon the positive charges induced in photoconductive
layer 2 while the external field due to the surface charges becomes
negligible.
On the other hand, when the external field due to the internally
bound charges is very strong, the charges imparted in the first
step may not be completely neutralized even after the second step.
In this case, the external fields are superposed and provide a net
field of zero, and since the bound charge field is released upon
illumination of activating radiation over the whole surface of the
insulative layer, the electrostatic contrast of positive and
negative charge combination is obtained with resultant high
contrast. The surface potentials of the electrostatic pattern
formed upon photoconductive plate B after the third step are shown
in FIG. 4, the reference characters of which have the same meaning
as in FIG. 2.
So far the process of the present invention has been described with
particular reference to FIGS. 1 through 3 with use of the
above-discussed fundamental photoconductive plates. The
photoconductive plates whose structures are shown in FIG. 5 may be
used in applications of processes of the present invention based
upon the same concepts discussed heretofore.
The photoconductive plate shown in FIG. 5a is similar to that shown
in FIG. 1 with the exception that between photoconductive layer 2
and electrically conductive substrate 1 is interposed insulative
layer 14. In other words, the substrate is composed of electrically
conductive layer 1 and insulative layer 14 laminated thereupon.
Insulative layer 14 serves as a blocking layer upon charging to
block injection of charges from the electrode. During the
electrostatic image-forming process, charges active in
photoconductive layer 2 of the photoconductive plate shown in FIG.
5a are free carriers existing in photoconductive layer 2 and
photocarriers induced upon illumination thereof by radiation.
Therefore, when the first charging step is conducted with
accompanying uniform illuminating radiation, sufficient binding of
charges is provided adjacent both of photoconductive layer 2 and
insulative layer 3.
The photoconductive plate shown in FIG. 5b is similar to that shown
in FIG. 5a with the exception that the electrically conductive
substrate 1 is removed therefrom so that insulative layer 14
constitutes the only substrate of this photoconductive plate. When
this photoconductive plate is used, chargings and illuminating
radiation are carried out in conjunction with an additional
electrode, which will be described in more detailed hereinafter.
The photoconductive plate shown in FIG. 5c is similar to that shown
in FIG. 1 with the exception that substrate 1 is removed therefrom.
This plate may be used in a similar process as in the case of the
plate shown in FIG. 5b. The photoconductive plate shown in FIG. 5d
is similar to that shown in FIG. 1 with the exception that
insulative layer 3 is removed therefrom. This plate may be used in
a process wherein, after the first charging of the photoconductive
plate, an insulative layer (not shown) is overlaid thereupon or an
insulative film (not shown), which has been previously charged, is
overlaid thereupon. The photoconductive plate shown in FIG. 5e is
also similar to that shown in FIG. 5a with the exception that
insulative layer 3 is removed therefrom. This plate may be used in
the same manner as in the case of the photoconductive plate shown
in FIG. 5d. The photoconductive plate shown in FIG. 5f is similar
to that shown in FIG. 5e with the exception that substrate 1 is
removed therefrom. This plate may be used in a process wherein the
first charging step is carried out as in the case of the
photoconductive plate shown in FIG. 5d and then the second step is
carried out as in the case of the photoconductive plate shown in
FIG. 5b.
A special face plate for a cathode ray tube will now be described
with reference to FIG. 6. The face plate, as shown in FIG. 6a,
comprises at least phosphor layer 15 adapted to illuminate upon
bombardment thereof by electron beams, vacuum envelope 16
transmissive to light and made of glass or the like, and
light-transmissive thin layer electrode 17. This face plate may be
suitably utilized in combination with one of the photoconductive
plates shown in FIG. 5 in one of the processes which will be
described in more detail hereinafter. In the face plate shown in
FIG. 6b fiber optics are applied to the face plate of the cathode
ray tube envelope instead of glass layer 16 of the face plate shown
in FIG. 6a. This arrangement prevents diffraction within the glass
of the image formed at phosphor screen or layer 15. As shown in
FIG. 6b, thin conductive layer 19 may be interposed between
phosphor screen or layer 15 and glass envelope 18 to constitute the
anode of the cathode ray tube. Alternatively, a metal backing (not
shown) formed from thin layer aluminum may be coated upon the inner
surface of phosphor screen 15 if needs demand.
The above-described fiber optics, anode and metal backing will not
be discussed specifically in the following description of the face
plates shown in FIGS. 6c through 6g, but it should be understood
that same may be incorporated in these face plates as needs
demand.
In the face plate shown in FIG. 6c thin insulative layer 20 similar
to layer 14 in FIG. 5a is disposed upon transparent electrode 17 of
the face plate of FIG. 6a. In this case, this thin insulating layer
must be transmissive to the radiation employed. This face plate
cooperates with one of the photoconductive plates shown in FIG. 5b,
FIG. 5c and FIG. 5f in the second step of the process.
In the face plate shown in FIG. 6d photoconductive layer 21 is
disposed upon insulative layer 20 of the face plate shown in FIG.
6c. This plate may be used in forming electrostatic patterns upon a
recording insulative film overlaid upon this face plate.
In the face plate shown in FIG. 6e insulative layer 22 is disposed
upon the face plate shown in FIG. 6d. Such additional insulative
layer 22 itself can serve as a medium for generating a phosphor or
luminescent image and for converting this image into an
electrostatic image as will be described in more detail
hereinafter.
Face plates shown in FIG. 6f and FIG. 6g are respectively similar
to those shown in FIG. 6d and FIG. 6e with the exception that
blocking insulative layers 20 are removed therefrom.
The photoconductive materials and phosphors used in the
above-described photoconductive plates and face plates will be
described in more detail in examples hereinafter, but preferable
combinations of these materials are set forth in Table I.
TABLE I
Phosphors Photoconductive materials BaSO.sub.4 :Pb ZnO (without
sensitizer) (+ binder) ZnO:Zn ZnO (chromatically sensitized) (+
binder) (Zn,Cd)S:Ag CdS (+ binder) (Zn:Cd=58:42) (Zn,Be).sub.2
SiO.sub.4 :Mn CdSe (+ binder) (Zn:Be=9:1) CaWo.sub.4 SeTe ZnS:Ag
(Te= 15%) (Zn,Cd)S:Cu As.sub.2 S.sub.3 :As.sub.2 Se.sub.3
All of the materials in Table I are sensitive to electron beams,
ultraviolet rays, X-rays and to illumination.
So far the structures of the photoconductive plates employable in
the present invention have been described with reference to FIGS.
1, 3a and 5a through 5f. The structures of face plates adapted to
be applied to the cathode ray tubes according to the present
invention have been described with reference to FIGS. 6a through
6g. The results, advantages and features of the invention are
accomplished by combination of such photoconductive plates and
cathode ray tubes having such face plates.
As described hereinabove, it is imperative in the present invention
that at least a substrate, a photoconductive layer and a
charge-retaining insulative layer are maintained in the form of a
lamination in the first charging step of charging and in the second
charging step performed simultaneously with image irradiation by
electron beams in the electrostatic image-forming process of the
electrostatic recording process of the present invention. This
imperative condition can be met by arrangements of the
photoconductive plates or face plates having the foregoing
structures or by combination of photoconductive plates having some
of the required layers and face plates having the other layers,
whereby arrangements or combinations are provided to which the
above-described steps of the process of the present invention are
applicable.
When the plates shown in FIGS. 1, 3a, 5a and 6b which have all of
the required fundamental layers are used in forming electrostatic
patterns, in the second step of the process of the present
invention, the radiation image is either projected upon the
photoconductive plate as shown in FIG. 7 or the photoconductive
plate is disposed in close contact with the face plate as shown in
FIGS. 9 and 10 so as to directly receive the radiation image
therefrom. In both cases, the second voltage is applied to the
plate insulative layer simultaneously with emission of the electron
beams and the electrostatic image is formed directly upon the
photoconductive plate or upon a charge-retaining recording member
interposed between the face plate and the photoconductive plate as
shown in FIG. 11.
When such recording member is used, the process includes the step
of charging the recording member and then overlaying same upon the
photoconductive plate or the step of charging the photoconductive
plate and then overlaying the recording member thereupon.
It is to be understood that, in the processes or examples which
will be described hereinafter, when the recording member is
overlaid upon the photoconductive plate or upon the face plate of a
cathode ray tube, either of said two steps is practiced.
The photoconductive plate shown in FIG. 5c is used in combination
with one of the face plates shown in FIGS. 6a, 6b and 6c with the
photoconductive layer being maintained in contact with the face
plate as shown in FIG. 18, thereby forming an electrostatic image
upon insulative layer 3.
The photoconductive plates shown in FIGS. 5d, 5e and 5f are used in
combination with a conventional cathode ray tube and are maintained
in contact therewith as shown in FIG. 12. Alternatively, these
photoconductive plates may be used in the manner as shown in FIG. 8
wherein the radiation image is projected thereupon. In both cases,
the insulative layer is maintained in close contact with the
photoconductive layer when the radiation image is projected
thereupon and a second voltage is simultaneously applied thereto.
These photoconductive plates may be also utilized in combination
with one of the face plates shown in FIGS. 6a, 6b and 6c. In this
case, a charge-retaining recording member is interposed between the
photoconductive layer of the photoconductive plate and the face
plate while the radiation image is projected and a second voltage
is simultaneously applied thereto, thereby forming an electrostatic
image upon the recording member.
The face plates shown in FIGS. 6a through 6g can be used with or
without the above-described photoconductive plates to form an
electrostatic image. Thus, the face plates shown in FIGS. 6a, 6b
and 6c may be used in combination with the photoconductive plates
shown in FIGS. 5c, 5d, 5e and 5f or in combination with the
photoconductive plates shown in FIGS. 1, 3a, 5a and 5b in such an
arrangement shown in FIG. 13 or 14. In this arrangement, a high
voltage is applied to the face plate as the second voltage while
simultaneously projecting the radiation image corresponding to the
electron beam signals, thereby forming an electrostatic image upon
the photoconductive plate, or a charge-retaining recording member
is interposed between the face plate and the photoconductive
plate.
The face plates shown in FIGS. 6e and 6g are adapted to form
electrostatic images upon the face plates themselves. As shown in
FIG. 19, electrostatic images can be formed directly or, as shown
in FIG. 12, electrostatic images can be formed upon
charge-retaining recording members overlaid upon the face
plates.
The face plates shown in FIGS. 6d and 6f are used in such a manner
that the charge-retaining insulative layer is overlaid upon each of
these face plates when the secondary voltage is applied thereto
while simultaneously projecting thereupon the radiation image
corresponding to the electron beam signals, thereby forming the
electrostatic image upon the insulative layer. In this case, the
first charging may be applied either to the photoconductive layer
of the face plate or to the charge-retaining insulative layer.
Alternatively, the first and second voltages may be applied after
the insulative layer has been overlaid on the face plate.
So far the processes for forming electrostatic images by use of the
combinations of the photoconductive plates and face plates
according to the present invention have been described. But it will
be understood that the present invention is not limited thereto and
that the present invention covers variations and modifications made
in the following examples and in the processes defined in the
appended claims without departing from the true spirit of the
present invention.
One embodiment of a process for forming an electrostatic image
corresponding to electron beam signals according to the present
invention will now be described with reference to FIG. 7 which
illustrates a process in which facsimile signals are converted into
radiation images which in turn are recorded as electrostatic
images. The image provided on a cathode ray tube is projected upon
photoconductive plate A through an optical system including
reflecting mirror 4a, lens 5a, etc.
The facsimile or input signals are detected by detector 13a and
separated into video signals and synchronizing signals. The former
are amplified by amplifier 14a and applied to control grid 15a of a
CRT for controlling the electron beams emitted by cathode 16a. The
electron beams are accelerated by acceleration grid 17a and focused
by focusing grid 18a so as to produce a small electron beam
cross-sectional area. Then, by deflection electrodes 19a, the beams
scan phosphor screen 20a. The synchronizing signals are separated
by synchronizing separation circuit 21a into vertical and
horizontal sync. signals which are in turn applied to deflection
circuits 22a and 23a respectively and finally to the deflection
coils. These synchronizing signals also control motor 24a, which
rotates a drum carrying thereupon photoconductive plate A, through
control circuit 25a so as to synchronize the rotation of the drum
with the original transmission speed at the transmitting
terminal.
First, photoconductive plate A is charged by charging device 6a and
is then displaced to phosphor image exposure station 7a where DC or
AC secondary charging, having opposite polarity relative to that of
the first charging is applied to photoconductive plate A, whereby
an electrostatic image is formed upon insulative layer 3.
Thereafter, photoconductive plate A is completely exposed by a lamp
9a, thereby increasing the contrast of the electrostatic image,
whereby an electrostatic image having a strong external field and
large surface potential difference is formed.
Such electrostatic image may be electrostatically transferred to
copying paper, or as shown in FIG. 7, the image may be developed by
toner in processor 10a and then transferred to copying paper 11a.
Thereafter, photoconductive plate A is cleaned by cleaner 12a for
repetitive use.
In this embodiment, P 11 (ZnS activated by Ag) was used as the
phosphor screen of the cathode ray tube. As the photoconductive
plate A, amorphous SeTe (Te: 15 mol %) was vacuum deposited upon
the drum to a thickness of about 40 .mu. and upon this SeTe layer
was applied a polyester film 25 .mu. in thickness by using an
adhesive of epoxy resin. The first charging was made by corona
discharging device 6a supplied with a negative voltage of -8KV so
to negatively charge the polyester film to about -2,000V. Next,
simultaneously with the projection of the image, the second
charging was made by discharging device 8a having an optically open
upper end and being supplied with +7KV. Thereafter, by illumination
lamp 9a, such as a tungsten lamp, the whole surface of
photoconductive plate A was uniformly illuminated, whereby an
electrostatic image having about +600V was obtained.
In the above embodiment, the photoconductive plate shown in FIG. 1
was used, but the photoconductive plate shown in FIG. 5a may also
be used in this process. It will be understood that such plate
interchangeability is also possible in the embodiments or examples
which will be described hereinafter.
FIG. 8 illustrates one variation of the embodiment described
hereinabove with reference to FIG. 7. In this variation,
transparent insulative layer 3 of the photoconductive plate is
separated therefrom and is subjected to previous first charging by
device 6a. Thereafter the insulative layer is advanced so as to be
placed in close contact with the photoconductive plate secured
opposite charging means 7b. The electrostatic image can be formed
in the manner described above and then insulative layer 3 is
removed from the photoconductive plate for processing or
transferring of the formed image.
Since the photoconductive plate is made of material having a quick
response, the photoconductive plate 4'b may be used in stationary
position. In this case, the scanning of the face plate by the
information signals and the advance of the recording film 3 are
controlled by synchronizing device 15b and motor 16b. Reference
numerals 4b, 5b and 8b designate respectively a mirror, a lens and
a charging device shield.
In FIGS. 9 and 10, another embodiment of the present invention is
shown wherein a photoconductive plate of the type shown in FIG. 1
and 5a is placed in contact with a face plate of a cathode ray tube
thereby forming an electrostatic image. Like reference numerals are
used to designate like parts in FIGS. 9 and 10.
Cathode ray tube 1c has a face plate comprising phosphor screen 2c
and glass plate 3c. Photoconductive plate 4c is composed of a
lamination of insulative layer 4c1, made of a material having high
resistivity and resistance to abrasion such as fluoroplastics,
polycarbonate resin, polyethylene resin, polyester resin or the
like, photoconductive layer 4c2 and transparent, conductive thin
layer electrode 4c3 formed by vacuum deposition of a metal.
Photoconductive plate 4c is adapted to be placed in contact with
the face plate of the CRT. For this purpose, photoconductive plate
4c is an endless belt advanced by annular frame 5c encircling the
CRT as shown in FIG. 9 or by guide rollers 6c, 7c and 8c disposed
about the cathode ray tube as shown in FIG. 10.
Insulative layer 4c1 of photoconductive plate 4c is first charged
by charging device 9c and then the charged photoconductive plate is
advanced toward the face plate of the CRT where phosphor screen 2c
of CRT is illuminated in accordance with signal information
converted into electron beams whereby photoconductive plate 4c is
exposed. At the same time, the photoconductive plate is subjected
to DC or AC corona discharge from discharging device 10c supplied
with a voltage having a polarity opposite to that of the first
charge, whereby an electrostatic image in accordance with the CRT
presentation is recorded upon insulative layer 4c1. Thereafter,
photoconductive plate 4c is further advanced and is illuminated
completely by ambient light or by illumination lamp 11c, thereby
imparting high contrast to the electrostatic image.
Thereafter, the electrostatic image is transferred to copying paper
12c (See FIG. 10) and developed and fixed according to well-known
methods of electrophotography. Alternatively, as shown in FIG. 9,
the electrostatic image thus formed upon photoconductive plate 4c
can be developed by toner in processor 13c and then transferred to
copying paper 14c. Thereafter, photoconductive plate 4c is cleaned
by cleaner 15c for repetitive use.
In this embodiment, in order to synchronize the CRT presentation
with the second charging and also with the stopping of
photoconductive plate 4c during this second charging, both motor
19c which advances photoconductive plate 4c and discharging device
10c are controlled through sync. separation circuit 18c and the CRT
is actuated by input information applied through signal amplifier
16c to deflection synchronizing circuit 17c. High voltage source
20c and transfer bias voltage source 21c provided for the CRT. When
a photoconductive material having a quick response is used,
electrostatic images can be formed even if drum 6c or belt 4c are
moved continuously. This effect was attained by the use of CdS.
In FIG. 11, insulative film 22c is overlaid upon photoconductive
plate 4 when this plate is placed upon the face plate of CRT.
Insulative film 22c may be made of the same material as insulative
layer 4c1, such as Mylar (polyethylene terephthalate). Insulative
film 22c is charged prior to being overlaid upon photoconductive
plate 4c by charging device 9c. After formation of the
electrostatic image, the insulative film is removed from
photoconductive plate 4c. The use of insulative film 22c much
facilitates processing following image-forming, such as
development, fixing, etc.
In this case, discharge occurs between insulative layer 4c1 and
insulative film 22c when the film is removed from plate 4c and
means for preventing this discharge must be provided such as is
shown in FIG. 12. Therein, insulative layer 4c1 of photoconductive
plate 4c is removed therefrom and insulative film 22 is overlaid
directly upon photoconductive layer 4c2. The whole surface of the
insulative film is illuminated completely after being removed from
photosensitive plate 4c so that the electrostatic image may have a
strong external field and hence improved constrast. Therefore,
illumination lamp 11c for illuminating the whole surface of
photoconductive plate 4c is not necessary in this embodiment.
Face plates of the type shown in FIGS. 6a, 6b and 6c may be used in
the manner shown in FIG. 13. That is, exterior of the glass plate
of the face plate of the CRT is formed thin layer electrode 23c
upon which is overlaid photoconductive plate 4c composed of
insulative layer 4c1, photoconductive layer 4c2 and electrically
conductive substrate 4c3. A voltage E is applied to electrode 23c
for secondary charging simultaneously with the exposure.
Alternative usages of insulative film 22c are shown in FIGS. 14 and
15.
In FIG. 16, photoconductive plate 4c is reciprocated upon the face
plate of CRT while insulative film 22c which has been previously
charged is advanced in only one direction.
When a separating agent such as silicon oil, Teflon
(polytetrafluoroethylene) oil, or the like is applied between
insulative film 22c, electrode 23c and insulative layer 4c1, their
service lines can be lengthened. This application of a separating
agent provided a remarkably better effect when the electrostatic
image was transferred because the latent image was transferred
through the separating agent in liquid form.
As shown in FIG. 17, when fiber optics 24c, each fiber of which has
a diameter of from 10 to 25 .mu., is used as the glass plate of the
face plate of the CRT in order to reduce loss due to diffraction of
light passing therethrough, resolution can be improved to about 20
lines/mm. For maintaining a high degree of vacuum in the envelope
of the CRT, mica 25c or the like may be interposed between phosphor
screen 2c and the fiber optics.
FIG. 18 shows a still further variation of the present invention.
Fiber optics 24c, each fiber of which has a diameter of from 10 to
25 .mu., is secured to the face plate of the CRT. At the end of
optics 24c, thin layer electrode 26c is provided by vacuum
deposition of metal or the like, and the photoconductive plate
composed of a lamination of photoconductive layer 4c2 and
insulative layer 4c1 are moved across the surface of electrode 26.
Electrode 26c is grounded and insulative layer 4c1 is charged by
charging device 9c. Upon exposure of the photoconductive plate to
the phosphor image of the CRT, the photoconductive plate is charged
with a polarity opposite to that of the first charging by means of
second charging device 10c, thereby forming an electrostatic image
upon insulative layer 4c1.
In this case, it is necessary to slide the insulative layer in
close contact with electrode 26c so that it is preferable to use a
material having a low coefficient of friction, such as polyester
resin, fluoroplastics and so on, as the insulative layer.
Furthermore, as described above, where a separating agent such as
silicon oil, Teflon oil or the like is applied between electrode
26c and photoconductive layer 4c2, their service lines can be
lengthened. When the elctrostatic image is transferred, remarkably
better results are obtained because the electrostatic image is
transferred through such oil.
The use of a face plate of the type as shown in FIGS. 6e and 6g in
combination with a cathode ray tube will now be described.
Referring particularly to FIG. 19, the CRT includes phosphor screen
1d adapted to be illuminated by bombardment of electron beams.
Transparent electrode layer 4d1 is applied to the exterior of the
CRT face plate, for example, by vacuum deposition of a metal.
Photoconductive plate 4d composed of a lamination of
photoconductive layer 4d2 and high resistance transparent
insulative layer 4d3, made for example, of Mylar or the like, is
overlaid upon electrode layer 4d1.
Insulative layer 4d3 of photoconductive plate 4d is charged by
first discharging device 2d and, at the instant when
photoconductive plate 4d is exposed to illumination from phosphor
screen 1d in response to information signals, the photoconductive
plate is discharged by DC secondary charging, or AC corona
discharge, having a polarity opposite to that of the first charge
provided by second charging device 3d, whereby an electrostatic
image is formed upon insulative layer 4d3 of photoconductive plate
4d. Thereafter, the whole surface of the photoconductive plate is
illuminated whereby contrast of the electrostatic image is further
improved.
Then, the electrostatic image is toner-developed upon the surface
of photoconductive plate 4d and transferred to a copying paper. The
surface of the photoconductive plate is cleaned and the remaining
charges are removed therefrom for repetitive use. Repetitive
recordings of luminescent CRT images are thus effected.
In one method for illuminating the whole surface of the
photoconductive plate insulative layer 4d3 is made of a material
which is transparent to the radiation to which photoconductive
layer 4d3 of the photoconductive plate is sensitive and such
radiation is directly uniformly from outside of the face plate of
CRT. In an alternative method, such radiation is directed uniformly
upon the face plate from inside the cathode ray tube as shown in
FIG. 19 by electron gun 5d which is adapted to emit such radiation
or by ultraviolet ray generating means 6d and lens 7d.
Alternatively, an electron gun to whose grid is applied a constant
negative potential may be used for bombardment of the face plate
with electron beams.
One example of the structure of a face plate of the type described
in the above embodiment is shown in FIG. 20. Upon one side of
chromium iron frame le was fixedly attached by molten glass 9e,
glass layer 2e having a Nesa coating with Nesa film 3e being
directed outwardly. Next a mixture, in which CdS powder was
uniformly dispersed in epoxy resin with a weight ratio of 96 : 4,
was applied to a thickness of about 30 .mu. use of a squeegee upon
Nesa film 3e, thereby forming photoconductive layer 6e. Polyester
film 7e about 25 .mu. in thickness was secured to layer 6e by resin
adhesive. After the resin adhesive has been sufficiently cured, a
mixture consisting of ZnS activated by Ag, CdS (ratio = 58 : 42)
and a synthetic resin was applied to the surface of the Nesa glass
opposite the Nesa film, thereby forming phosphor screen 4e. A
coating 5e of aluminum of about 500 A thickness was applied to the
phosphor screen by vacuum deposition, thereby providing a metal
backing. Frame 1e of the thus-obtained face plate was secured to
metallic tube 8e, and then electron gun 5d and an ultraviolet ray
emission means, e.g. hydrogen discharge lamp 6d and lens 7d in FIG.
19, were incorporated in the tube. Thereafter, the lamp was
evacuated and sealed.
In FIG. 19, first charging device 2d having an optically open front
end (it is not necessarily open) and second charging device 3d
having a light shield plate are moved over the surface of
photoconductive plate 4 upon the face plate of the CRT. In practice
the process of FIG. 19 takes substantial time, thus causing a slow
speed operation. This defect is eliminated by the arrangement shown
in FIG. 21. Over the surface of photoconductive plate 4f is moved a
transparent or non-transparent insulative film 5f made of the same
material as insulative layer 4f3 of photoconductive plate 4f such
as fluoroplastics, polycarbonate resin, polyethylene resin,
polyester resin or the like having sufficiently high resistance to
retain electrostatic charge and high resistance to abrasion.
Insulative film 5f is charged before it is placed in contact with
photoconductive plate 4f. The other steps of forming electrostatic
images are similar to those described in the above embodiment. The
electrostatic image may be recorded by either developing and fixing
or by developing and transferring. Thus, this arrangement
facilitates high speed recording operations. In this case, the
second charging device may be replaced with electrode charging
means. Furthermore, insulative layer 4f3 may be eliminated.
When phosphor screen 1f of the CRT is illuminated for display of an
information image, the second charging of photoconductive plate 4f
must be performed. In order to synchronize these two opeations,
motor 10f for driving photoconductive plate 4f and second
discharging device 3f are controlled through sync. separation
circuit 9f, when the information inputs are applied to the CRT,
through signal amplifier 7f and deflection synchronization circuit
8f. Reference numeral 11f designates a high voltage source.
Furthermore, as described above, the use of fiber optics, each
fiber of which has a diameter of from 10 to 25 .mu., for
eliminating the loss due to light scattering, provides a resolution
of about 20 lines/mm. For maintaining a high degree of vacuum in
the CRT, mica or the like may be interposed between the phosphor
screen and the ends of fiber optics.
The face plate of the CRT of the present invention described
hereinabove includes at least a luminous body adapted to be
illuminated upon bombardment thereof by electron beams, a
transparent electrode layer, a photoconductive layer and an
insulative layer. For example, in the case of the face plate shown
in FIGS. 19 and 21, the face plate is one of a conventional CRT and
includes luminous body 1d or 1f illuminated upon bombardment
thereof by electron beams and a tubular glass surface g. A
photoconductive plate on surface g comprises transparent electrode
layer 4d1 or 4f1, photoconductive layer 4d2 or 4f2 and insulative
layer 4d3 or 4f3 made of Mylar or the like. In one variation a
transparent electrode layer, a luminous body layer, a
photoconductive layer and an insulative layer may be attached to
the front face plate of a cathode ray tube. In another variation an
insulative layer is interposed between the luminous body layer and
the photoconductive layer. In a further variation a luminous body
layer, fiber optics, a transparent electrode layer, an insulative
layer (this may be eliminated), a photoconductive layer, and an
insulative layer may be used. In a still further variation another
electrostatic image-forming insulative film is used instead of
insulative layer 4f.sub.3 as shown in FIG. 21.
* * * * *