Title of Invention	AN IMPROVED PROCESS FOR THE PREPARATION OF PHOTORELEPTORS USEFUL FOR XERORADIOGRAPH AND PHTORELETORS MADE THEREBY
Abstract	An improved process for the preparation of photoreceptors useful for xeroradiography which comprises cleaning thoroughly an aluminium substrate by conventional methods, heating the said substrate in vaccum ≥ 10-5 Torr , prior to deposition, to a temperature in the range of 100°C to 130°C, cooling the .substrate in. vacuum to a temperature in the range of 50°C to 65°C, vaccum depositing pure/suitably doped selenium! onto the said substrate maintained at a temperature in the range of 57°C to 72°C to obtain photoreceptors.

Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF PHOTORELEPTORS USEFUL FOR XERORADIOGRAPH AND PHTORELETORS MADE THEREBY

Abstract

An improved process for the preparation of photoreceptors useful for xeroradiography which comprises cleaning thoroughly an aluminium substrate by conventional methods, heating the said substrate in vaccum ≥ 10-5 Torr , prior to deposition, to a temperature in the range of 100°C to 130°C, cooling the .substrate in. vacuum to a temperature in the range of 50°C to 65°C, vaccum depositing pure/suitably doped selenium! onto the said substrate maintained at a temperature in the range of 57°C to 72°C to obtain photoreceptors.

Full Text	This invention relates to an improved process for the [preparation of photoreceptors useful for xeroradiography. Xeroradiography (XR) is used in medical applications'as an X-ray imaging technique in radiology especially in the diagnosis of mammography, i.e., detection of breast cancer at an early stage, and also in some special extremities cases where its unique imaging characteristics such as edge enhancement and wider recording latitude provides superior diagnostic advantages over the conventionally used film-screen radiology. XR technique is based on the well known Xerox process. In this technique a specially prepared plate known as the xeroradiography phbtoreceptor is used as an X-ray imaging media. This plate is charged positively using the well known corona discharge technique and kept in dark using a metallic shutter which prevents the dissipation of charge on the plate as it is sensitive to light radiations. This charged plate is now exposed to X-ray via the object to be imaged which results in the dissipation of charge on the plate in proportion to the X-ray intensity falling on different parts of the plate. This results in the formation of the image in the form of remaining charge pattern on the plate which is called the electrostatic latent image. The image is not visible at this stage. It is made visible by the development process, i.e., developing it by using a special type of ink called the Toner'. The image at this 'stage itself can be used for diagnosis. However, to keep a permanent record of the image it is transferred onto an ordinary paper by electrostatic means. The image is fixed on the paper by using chemical solvents, heating techniques. This complete Xeroradiography process takes about 1 to 2 minutes only. Therefore, in addition to the diagnostic superiorities of Xeroradiography mentioned earlier this technique is also commercially viable and quick as compared to the conventional filial-screen .radiology. The most vital constituent of XR process described above is the xeroradiography plate/photoreceptor (XRP) on which depends primarily the quality of XR images .i.e., its contrast, resolution,definition,etc,. The XRP constitutes of a vacuum deposited layer of a knowia X-ray conducting material such as pure/doped amorphous selenium on a conducting aluminium substrate. Reference may be made to the US Patent No.4,770,965 to Fender et al and the other patents referred there-in for the art of state existing for the preparartion of XRP using the conventional vacuum deposition technique. Hentlon has been made in these references about the material compositions used in manufacturing the XRP,i.e., selenium doped and alloyed with suitable materials such as chlorine, arsenic ,etc. Mention has also been made of the preparation process of XRP where substrate temperature (Ts ) during deposition has been maintained between 71°C to 80°C. ' It is important to mention there that the TS used in these investigations has a possible drawback and it is that the Ts used is on a higher side and there is always a possibility of netting undeaired crystalline contents in the deposited films because the ideal requirement of the deposited films for X-ray imaging is the complete amorphousity and 'no crstalline content but at the same time free from artifacts and defects which indeed in known to depend on Ts ;higher the T- lower is the number of these defects. The objective of the present invention is to provide an improved process for the preparation of photoreceptors for xeroradiography using the vacuum deposition technique which obviates the drawbacks of the hitherto known processes. Another object is to provide photoreceptors made by: the improved process of the present invention. In the process of present invention the need to reduce the substrate temperatures during deposition to get better amorphousity in the films -and also without introducing additional detects in the films is achieved. In the improved process of the present invention we have introduced a new step in the vacuum deposition process. The step introduced is heating the substrate in vacuum, prior to vacuum deposition, to a temperature in the range of 100°C to 130°C and then cooling it in vacuum to a temperature in the range of 50°C to 65°C and; then starting the process of deposition. This new invented step enables, prior to deposition! in complete degassing of the substrate and also making it free from any remaining! impurities, traces, etc. (the known sources of defects, etc.), due to the simultaneous application of .heat and vacuum. This in turn enables to deposit the films at reduced temperature i.e., in the range of 57°C to 72°C. Therefore, this invented process of deposition meets both the requirements of higher amorphousity and less defects/artifacts in the films. Accordingly, the present invention provides an improved process for the preparation of photoreceptors useful for xeroradiography which comprises cleaning thoroughly an aluminium substrate by conventional methods, heating the said substrate in vacuum ≥ 10-5 Torr, prior to deposition, to a temperature in the range of 100°C to 130°C, cooling the substrate in vacuum to a temperature in the range of 50°C to 65°C, vacuum depositing pure/suitably doped selenium onto the said substrate maintained at a temperature in the range of 57°C to 72°C to obtain photoreceptors. in the range 57° C to 72 C. The conventional methods used for cleaning the sustrate thoroughly may be washing with detergents,followed by final cleaning and decreasing using ultrasonic cleaner. Prior to deposition the cleaned substrate is heated in vacuum preferably to a temperature in the range of 110 C to 120 C and then cooled down in vacuum to a temperature in the range of 55°C to 60°C. the vacuum deposition of pure/doped sjelenium way be effected at a rate in the range 2.5 µm to 3.5 µm per minute. The improved process of the present Invention starts with the thorough cleaning of the aluminium substrate. In the process developed this cleaning was achieved in two steps namely the pre-cleaning and the final cleaning. The precleaning involved 'washing the subbatrate with soap solution!detergents,etc., and rinsing it thoroughly with water. This removed the dust,contamin- tion,etc,visible on the substrate. The plate was then dried and put into an ultrasonic machine for final cleaning. This machine contained two tanks one the ultrasonic and the other vapour degreaser. The chemical used for cleaning in both the tanks was trichloroethylene. The plate was first put for about 5 minutes in the ultrasonic cleaner and then for about 5 minutes in the vapour degreaser. This process resulted in the desired cleaning and degreasing of the substrate. The cleaned substrate was then put in a specially designed frame and loaded in the vacuum chamber for vacuum deposition. The vacuum chamber contained a boat of quartz specially designed and used for keeping the material to be vacuum deposited such as in this case It ibeing either pure selenium or selenium doped suitably with' chlorine and arsenic. The pressure in the chamber being ≥ 10-5 Torr. Prior to deposition of the material the substrate was heated i'n vacuum to a temperature in the range 110 C to 120°C and then cooled down in vacuum to a temperature in the range 55°C to 60°C. The TS during deposition was maintained between 57°C to 72° C. The thickness of the film deposited was between 170 µm to 200 µm. Accordingly, the present invention provides a photoreceptor nade by the improved process of the present invention. The general scope and the nature I of the invention is illustrated by the following examples which should not be construed to limit the scope of the present invention. EXAMPLE 1 Xeroradiography photoreceptor was prepared by evaporating pure\doped selenium onto an alurainiura substrate of size 23.5 en x 36.5 cm. The substrate was heated in vacuiia ≥ 10-5 Torr,prior to deposition,to a temperature of 114 C and then cooled down in vacuum to a temperature of 57 C. The substrate temperature was naintained between 57 C and 70 C during the deposition process. The thickness of the deposited film was of a conventional xerora- diography layer, i.e., about 180µm , EXAHPLE 2 Xeroradiography photoreceptor was prepared by evaporating pure/doped selenium onto an aluminium substrate of size 23.5 ere x 36.5 cm. The substrate was heated in vacuum ≥10-5 Torr,prior to deposition, to a temperature of 117 C and! then cooled dowlimr vacuum to a temperature of 59°C. The substrate temperature was maintained between 59°G to 71° C during the! deposition process. The thickness of the deposited film was of a conventional Xeroradiography layer ,i.e., about 185 µm. EXAMPLE 3 Xeroradiography photoreceptor was prepared by evaporating pure/doped selenium onto an aluminium substrate of size 23.5 cm X 36.3 cm. The substrate was heated in vacuum ≥ 10-5 Torr, prior to deposition,to a temperature of 120 C and then cooled down in vacuum to a temperature of 60°C. The substrate temperature was maintained between 60 C to 72 C during the deposition process. The thickness of the deposited film was of a conventional Xeroradiography layer,i.e., about 190 µm. EXAMPLE 4 Xeroradiography photoreceptor was prepared by evaporating pure/doped selenium onto an aluminum substrate of size 23.5 cm x 1-5 36.5 cm. The substrate was heated in vacuum ≥ 10-5 Torr,prior to deposition, to a temperature of 120 C and then cooled down in vacuum to a temperature of 58°C. The substrate temperature was maintained between 58 C to 72 C during the (deposition process. The thickness of the deposited film was of a conventional Xeroradiography layer,i.e., about 195 µm. EXAMPLE 5 Xeroradiography photoreceptor was prepared by evaporating pure/doped selenium onto an aluminium substrate of size 23.5 cm x ' 1 -5 36.5 cm. The substrate was heated in vacuum ≥ 10-5 Torr,prior to deposition, to a temperature of 111 C and th«n cooled-down-in vacuum to a temperature of 55 C, The substrate temperature was maintained between 57*C to 71 C during the deposition process. The thickness of the deposited film was of a conventional xeroradiography layer,i.e., about 175 µm. The inference drawn from the above examples is that the heating of the substrate in vacuum,prior to deposition,to a temperature between in the range 100 C to 130 C and then cooling it in vacuum to a lower temperature of about 50 C to 65 C, is an inventive step in the preparation of xerorladiography photoreceptors using the vacuum deposition technique. The advantages of the improved process of the present invention are: 1. The photoreceptors made by the process have less possibility of getting high crystalline contents in the deposited films. 2. The photoreceptors made by the process are prone to less defects/artifacts in the deposited films generally introduced by the solvent traces,etc. We claim: 1. An improved process for the preparation of, photoreceptors useful for xeroradiography which comprises cleaning thoroughly an aluminium substrate by conventional methods, heating the said substrate in vacuum ≥ 10-5 Torr, prior to deposition, to a temperature in the range of 100°C to 130°C, cooling the substrate in vacuum to a temperature in the range of 50°C; to 65°C, vacuum depositing pure/suitably doped selenium onto the [said substrate maintained at a temperature in the range of 57DC to 72°C to obtain photoreceptors. 2. An improved process as claimed in claim 1 wherein the cleaning of the substrate by conventional methods is effected by pre-deaning such as washing with detergents, followed by final deaning and degreasing using ultrasonic cleaner. 3. An improved process as daimed in claims 1-2 wherein the substrate is heated in vacuum, prior to deposition, to a temperature preferably in the range of 110°C to 120°C and then cooled in vacuum to a temperature preferably in the range of 55°Cto60°C. 4. An improved process as daimed in daims 1-3 wherein the vacuum deposition of pure/doped selenium is effected at a rate of deposition in the range of 2.5 µm to 3.5 µm per minute. 5. An improved process for the preparation of photoreceptors useful for xeroradiography substantially as herein described with reference to the examples.

Full Text

This invention relates to an improved process for the [preparation of photoreceptors
useful for xeroradiography.
Xeroradiography (XR) is used in medical applications'as an X-ray imaging technique
in radiology especially in the diagnosis of mammography, i.e., detection of breast cancer at an
early stage, and also in some special extremities cases where its unique imaging
characteristics such as edge enhancement and wider recording latitude provides superior
diagnostic advantages over the conventionally used film-screen radiology. XR technique is
based on the well known Xerox process. In this technique a specially prepared plate known
as the xeroradiography phbtoreceptor is used as an X-ray imaging media. This plate is
charged positively using the well known corona discharge technique and kept in dark using a
metallic shutter which prevents the dissipation of charge on the plate as it is sensitive to light
radiations. This charged plate is now exposed to X-ray via the object to be imaged which
results in the dissipation of charge on the plate in proportion to the X-ray intensity falling on
different parts of the plate. This results in the formation of the image in the form of remaining
charge pattern on the plate which is called the electrostatic latent image. The image is not visible at this stage. It is made visible by the development process, i.e., developing it by using
a special type of ink called the Toner'. The image at this 'stage itself can be used for
diagnosis. However, to keep a permanent record of the image it is transferred onto an
ordinary paper by electrostatic means. The image is fixed on the paper by using chemical
solvents, heating techniques. This complete Xeroradiography process
takes about 1 to 2 minutes only. Therefore, in
addition to the diagnostic superiorities of Xeroradiography
mentioned earlier this technique is also commercially viable and
quick as compared to the conventional filial-screen .radiology.
The most vital constituent of XR process described above
is the xeroradiography plate/photoreceptor (XRP) on which
depends primarily the quality of XR images .i.e., its contrast,
resolution,definition,etc,. The XRP constitutes of a vacuum
deposited layer of a knowia X-ray conducting material such as pure/doped amorphous selenium on a conducting aluminium
substrate. Reference may be made to the US Patent No.4,770,965
to Fender et al and the other patents referred there-in for the
art of state existing for the preparartion of XRP using the
conventional vacuum deposition technique. Hentlon has been made
in these references about the material compositions used in
manufacturing the XRP,i.e., selenium doped and alloyed with
suitable materials such as chlorine, arsenic ,etc. Mention has
also been made of the preparation process of XRP where substrate
temperature (Ts ) during deposition has been maintained between
71°C to 80°C. ' It is important to mention there that the TS used in these investigations has a possible drawback and it is that the Ts used is on a higher side and there is always a possibility
of netting undeaired crystalline contents in the deposited films
because the ideal requirement of the deposited films for X-ray
imaging is the complete amorphousity and 'no crstalline content
but at the same time free from artifacts and defects which indeed
in known to depend on Ts ;higher the T- lower is the number of
these defects.
The objective of the present invention is to provide an
improved process for the preparation of photoreceptors for
xeroradiography using the vacuum deposition technique which
obviates the drawbacks of the hitherto known processes.
Another object is to provide photoreceptors made by: the improved process of the
present invention.
In the process of present invention the need to reduce the substrate temperatures
during deposition to get better amorphousity in the films -and also without introducing
additional detects in the films is achieved.
In the improved process of the present invention we have introduced a new step in the vacuum deposition process. The step introduced is heating the substrate in vacuum, prior
to vacuum deposition, to a temperature in the range of 100°C to 130°C and then cooling it in
vacuum to a temperature in the range of 50°C to 65°C and; then starting the process of
deposition. This new invented step enables, prior to deposition! in complete degassing of the
substrate and also making it free from any remaining! impurities, traces, etc. (the known
sources of defects, etc.), due to the simultaneous application of .heat and vacuum. This in turn
enables to deposit the films at reduced temperature i.e., in the range of 57°C to 72°C.
Therefore, this invented process of deposition meets both the requirements of higher amorphousity and less defects/artifacts in the films.
Accordingly, the present invention provides an improved process for the preparation
of photoreceptors useful for xeroradiography which comprises cleaning thoroughly an
aluminium substrate by conventional methods, heating the said substrate in vacuum ≥ 10-5 Torr, prior to deposition, to a temperature in the range of 100°C to 130°C, cooling the
substrate in vacuum to a temperature in the range of 50°C to 65°C, vacuum depositing
pure/suitably doped selenium onto the said substrate maintained at a temperature in the
range of 57°C to 72°C to obtain photoreceptors.

in the range 57° C to 72 C.
The conventional methods used for cleaning the sustrate
thoroughly may be washing with detergents,followed by final
cleaning and decreasing using ultrasonic cleaner.
Prior to deposition the cleaned substrate is heated in
vacuum preferably to a temperature in the range of 110 C to 120 C
and then cooled down in vacuum to a temperature in the range of
55°C to 60°C.
the vacuum deposition of pure/doped sjelenium way be effected
at a rate in the range 2.5 µm to 3.5 µm per minute.
The improved process of the present Invention starts with
the thorough cleaning of the aluminium substrate. In the process
developed this cleaning was achieved in two steps namely the
pre-cleaning and the final cleaning. The precleaning involved
'washing the subbatrate with soap solution!detergents,etc., and
rinsing it thoroughly with water. This removed the dust,contamin-
tion,etc,visible on the substrate. The plate was then dried and
put into an ultrasonic machine for final cleaning. This machine
contained two tanks one the ultrasonic and the other vapour degreaser. The chemical used for cleaning in both the tanks was
trichloroethylene. The plate was first put for about 5 minutes
in the ultrasonic cleaner and then for about 5 minutes in the
vapour degreaser. This process resulted in the desired cleaning
and degreasing of the substrate. The cleaned substrate was then
put in a specially designed frame and loaded in the vacuum chamber
for vacuum deposition. The vacuum chamber contained a boat of
quartz specially designed and used for keeping the material to be
vacuum deposited such as in this case It ibeing either pure
selenium or selenium doped suitably with' chlorine and arsenic.
The pressure in the chamber being ≥ 10-5 Torr. Prior to deposition
of the material the substrate was heated i'n vacuum to a temperature
in the range 110 C to 120°C and then cooled down in vacuum to a
temperature in the range 55°C to 60°C. The TS during deposition
was maintained between 57°C to 72° C. The thickness of the film deposited was between 170 µm to 200 µm.
Accordingly, the present invention provides a photoreceptor
nade by the improved process of the present invention.
The general scope and the nature I of the invention is
illustrated by the following examples which should not be
construed to limit the scope of the present invention.
EXAMPLE 1
Xeroradiography photoreceptor was prepared by evaporating
pure\doped selenium onto an alurainiura substrate of size 23.5 en x
36.5 cm. The substrate was heated in vacuiia ≥ 10-5 Torr,prior
to deposition,to a temperature of 114 C and then cooled down in
vacuum to a temperature of 57 C. The substrate temperature was
naintained between 57 C and 70 C during the deposition process.
The thickness of the deposited film was of a conventional xerora-
diography layer, i.e., about 180µm ,
EXAHPLE 2
Xeroradiography photoreceptor was prepared by evaporating
pure/doped selenium onto an aluminium substrate of size 23.5 ere x
36.5 cm. The substrate was heated in vacuum ≥10-5 Torr,prior
to deposition, to a temperature of 117 C and! then cooled dowlimr
vacuum to a temperature of 59°C. The substrate temperature was
maintained between 59°G to 71° C during the! deposition process. The thickness of the deposited film was of a conventional
Xeroradiography layer ,i.e., about 185 µm.
EXAMPLE 3
Xeroradiography photoreceptor was prepared by evaporating
pure/doped selenium onto an aluminium substrate of size 23.5 cm X
36.3 cm. The substrate was heated in vacuum ≥ 10-5 Torr, prior to
deposition,to a temperature of 120 C and then cooled down in vacuum
to a temperature of 60°C. The substrate temperature was maintained
between 60 C to 72 C during the deposition process. The thickness
of the deposited film was of a conventional Xeroradiography
layer,i.e., about 190 µm.
EXAMPLE 4
Xeroradiography photoreceptor was prepared by evaporating
pure/doped selenium onto an aluminum substrate of size 23.5 cm x
1-5 36.5 cm. The substrate was heated in vacuum ≥ 10-5 Torr,prior to
deposition, to a temperature of 120 C and then cooled down in
vacuum to a temperature of 58°C. The substrate temperature was
maintained between 58 C to 72 C during the (deposition process.
The thickness of the deposited film was of a conventional Xeroradiography layer,i.e., about 195 µm.
EXAMPLE 5 Xeroradiography photoreceptor was prepared by evaporating
pure/doped selenium onto an aluminium substrate of size 23.5 cm x
' 1 -5 36.5 cm. The substrate was heated in vacuum ≥ 10-5 Torr,prior to
deposition, to a temperature of 111 C and th«n cooled-down-in vacuum

to a temperature of 55 C, The substrate temperature was maintained
between 57*C to 71 C during the deposition process. The thickness of the deposited film was of a conventional xeroradiography layer,i.e., about 175 µm.
The inference drawn from the above examples is that the
heating of the substrate in vacuum,prior to deposition,to a
temperature between in the range 100 C to 130 C and then cooling
it in vacuum to a lower temperature of about 50 C to 65 C, is an
inventive step in the preparation of xerorladiography photoreceptors using the vacuum deposition technique.
The advantages of the improved process of the present
invention are:
1. The photoreceptors made by the process have less possibility
of getting high crystalline contents in the deposited films.
2. The photoreceptors made by the process are prone to less
defects/artifacts in the deposited films generally introduced by
the solvent traces,etc.

We claim:
1. An improved process for the preparation of, photoreceptors useful for
xeroradiography which comprises cleaning thoroughly an aluminium substrate by
conventional methods, heating the said substrate in vacuum ≥ 10-5 Torr, prior to
deposition, to a temperature in the range of 100°C to 130°C, cooling the substrate
in vacuum to a temperature in the range of 50°C; to 65°C, vacuum depositing
pure/suitably doped selenium onto the [said substrate maintained at a
temperature in the range of 57DC to 72°C to obtain photoreceptors.
2. An improved process as claimed in claim 1 wherein the cleaning of the substrate
by conventional methods is effected by pre-deaning such as washing with
detergents, followed by final deaning and degreasing using ultrasonic cleaner.
3. An improved process as daimed in claims 1-2 wherein the substrate is heated in
vacuum, prior to deposition, to a temperature preferably in the range of 110°C to
120°C and then cooled in vacuum to a temperature preferably in the range of
55°Cto60°C.
4. An improved process as daimed in daims 1-3 wherein the vacuum deposition of
pure/doped selenium is effected at a rate of deposition in the range of 2.5 µm to
3.5 µm per minute.
5. An improved process for the preparation of photoreceptors useful for
xeroradiography substantially as herein described with reference to the examples.

Documents:

1093-del-1995-abstract.pdf

1093-del-1995-claims.pdf

1093-del-1995-complete specification (granted).pdf

1093-del-1995-correspondence-others.pdf

1093-del-1995-correspondence-po.pdf

1093-del-1995-description (complete).pdf

1093-del-1995-form-1.pdf

1093-del-1995-form-2.pdf

1093-del-1995-form-4.pdf

1093-del-1995-form-9.pdf

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Patent Number

191288

Indian Patent Application Number

1093/DEL/1995

PG Journal Number

44/2003

Publication Date

01-Nov-2003

Grant Date

24-May-2004

Date of Filing

14-Jun-1995

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	MR. SURESH CHAND	NATIONAL PHYSICAL LABORATORY, DR. K.S. KRISHNAN ROAD, NEW DELHI-110012, INDIA.
2	MR. RAM CHAND BHATHEJA	NATIONAL PHYSICAL LABORATORY, DR. K.S. KRISHNAN ROAD, NEW DELHI-110012, INDIA.
3	MR. GAURI DATT SHARMA	NATIONAL PHYSICAL LABORATORY, DR. K.S. KRISHNAN ROAD, NEW DELHI-110012, INDIA.
4	MR. JAI KARAN SINGH	NATIONAL PHYSICAL LABORATORY, DR. K.S. KRISHNAN ROAD, NEW DELHI-110012, INDIA.
5	MR. SUBHAS CHANDRA	NATIONAL PHYSICAL LABORATORY, DR. K.S. KRISHNAN ROAD, NEW DELHI-110012, INDIA.

PCT International Classification Number

G03C 1/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA