U.S. patent number 3,729,257 [Application Number 05/014,851] was granted by the patent office on 1973-04-24 for means and methods for exposing photoelectrostatic materials.
This patent grant is currently assigned to Addressograph-Multigraph Corporation. Invention is credited to Robert L. Gunto, Merton R. Staley.
United States Patent |
3,729,257 |
Gunto , et al. |
April 24, 1973 |
MEANS AND METHODS FOR EXPOSING PHOTOELECTROSTATIC MATERIALS
Abstract
Exposure of the conventional dye sensitized zinc oxide resin
binder copy material is accomplished with a radiation source that
emits a high level of energy at 535 nanometers. The
photoelectrostatic copying method involves illuminating the
original to be reproduced with a mercury-vapor type lamp which has
been modified to include thallium vapors through the introduction
of thallium halide into the lamp envelope. A high intensity green
light is emitted which performs as a monochromatic energy source
and finds particular application when reproducing originals having
more than one color indicia thereon so that all colors are
reproduced in accordance with their relative brightness on the
original.
Inventors: |
Gunto; Robert L. (Palatine,
IL), Staley; Merton R. (Palatine, IL) |
Assignee: |
Addressograph-Multigraph
Corporation (Mount Prospect, IL)
|
Family
ID: |
26686609 |
Appl.
No.: |
05/014,851 |
Filed: |
February 16, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
653090 |
Jul 13, 1967 |
|
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|
Current U.S.
Class: |
355/67; 313/639;
362/98; 399/220 |
Current CPC
Class: |
G03G
5/09 (20130101); H01J 61/125 (20130101); G03G
15/011 (20130101); G03G 15/04036 (20130101) |
Current International
Class: |
H01J
61/12 (20060101); G03G 15/01 (20060101); G03G
5/04 (20060101); G03G 5/09 (20060101); G03G
15/04 (20060101); G03b 027/54 () |
Field of
Search: |
;355/67 ;240/11.4R
;313/229 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Matthews; Samuel S.
Assistant Examiner: Hayes; Monroe H.
Parent Case Text
This application is a division of co-pending application Ser. No.
653,090, filed July 13, 1967 now abandoned.
BACKGROUND OF THE INVENTION
This invention relates to photoelectrostatic copying and more
particularly to the method and means of making a reproduction of a
multi-colored original which involves the use of a specially
adapted illuminating source capable of spectrally recognizing all
the colors comprising the original so that true reproduction of the
image may be cast or projected onto a photoelectrostatic
member.
The photoelectrostatic copying process involves the steps of
electrostatically charging in the dark a photoelectrostatic member,
such as a base support on which is coated a photoconductive
insulating layer, exposing said charged surface to a pattern of
light and shadow produced by irradiating a graphic original with a
suitable illuminating source. The areas on the photoconductive
layer which have been struck by the radiant energy are rendered
conductive and the charges in those areas are dissipated within the
photoelectrostatic member leaving a latent electrostatic image on
the surface which corresponds to the pattern of light and
shadow.
The latent image is developed by applying electroscopic particles,
usually highly colored thermoplastic resin particles, which adhere
to the portions of the latent image-bearing surface that correspond
to the image portions of the original. The powder image may then be
fixed to the base support by any of the well-known fixing
techniques.
The photoelectrostatic members in general use in this art comprise
a photoconductive insulating material, such as finely divided
particles of zinc oxide dispersed in an electrically insulating
film-forming resin binder and applied to a flexible base support
such as paper or other material having the proper degree of
conductivity. The response of the zinc oxide resin binder system as
a receptor of radiant energy in this process is most important. The
spectral response of the photoconductive, white zinc oxide binder
recording member peaks sharply in the near ultra-violet region of
the spectrum with sensitivity extending into the blue end of the
visible region of the spectrum.
It has been found desirable to extend the spectral response of the
photoelectrostatic members, of the zinc oxide resin binder, by the
addition of certain organic dyes. A detailed description of
dye-sensitization of such photoelectrostatic members may be found
in U.S. Pat. No. 3,052,540, issued Sept. 4, 1962 to H.G. Grieg.
Dye sensitization of the zinc oxide resin binder is desirable in
order to extend the spectral response of the photoelectrostatic
member to include the visible range of the spectrum.
Photoelectrostatic members sensitized in the visible range of the
spectrum has permitted the use of incandescent filament-type energy
sources instead of being limited to ultra violet sources. The
technique of extending the spectral sensitivity of the
photoelectrostatic member and illuminating it with an incandescent
filament lamp having a matching spectral energy distribution has
been successful in the photocopying art because of the simplicity
and convenience of using such incandescent lamps. However, they
have not been without certain deficiencies. The incandescent
illuminating sources are inefficient since they emit a great deal
of energy in the infra-red range of the spectrum and emit only a
relatively small proportion of electromagnetic radiation which can
be utilized by the photoelectrostatic member for the purpose of
producing latent images thereon.
SUMMARY OF THE INVENTION
It was found that a radiant energy source which approximates the
operation of a monochromatic energy source in the visible range of
the spectrum will photocopy a wide variety of colors appearing on
the original and the copy will have shades of gray to black images
in direct relation to the reflectivity of the colors at the wave
length of the dominant emission. The dominant emission should be in
the central portion of the luminosity function curve of the eye,
i.e., 520 - 590 nanometers, so that the sensitized copy sheet is
illuminated with energy that is optimum for the human eye. In this
manner the apparent brightness of the original is consistent with
its actual brightness in the usual white light. Reference to
multicolored originals includes typewritten copy bearing a pen-ink
signature, red markings on a letter, or the use of colors in an
ordinary letter head.
It is the general object of this invention to provide improved
reproduction methods and means in which a multi-colored graphic
original will have all the intelligence thereon recognized and
reproduced by the system.
It is another object of this invention to provide improved
reproduction methods and means in which a mercury vapor-type
radiant energy source is employed which emits a high concentration
of energy at a wavelength in the visible portion of the
spectrum.
It is another object of this invention to provide improved
reproduction methods and means using a radiant energy source which
is specially adapted to irradiate a multi-colored graphic original
from which is reflected a pattern of light and shadow and which
radiant energy source is capable of recognizing all the
intelligence on said original evidenced by the reproduction of the
graphic subject matter onto the photoelectrostatic member.
It is a specific object of this invention to provide an improved
reproduction method using a radiant energy source adapted to emit a
high energy level at a wave length in the visible range in
conjunction with a photoelectrostatic member, which energy source
provides the advantages of a monochromatic system.
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. In an apparatus for making reproductions of a graphic original
comprising means for feeding photoelectrostatic copy material, a
charging station for imparting a uniform electrostatic charge to
said copy material, an illuminating station for casting radiant
energy onto the graphic original to produce a pattern of light and
shadow upon the charged copy material corresponding to the graphic
subject matter on the graphic original, the improvement wherein
said illuminating station is equipped with an elongated
tubular-shaped radiation source of the mercury vapor-type having a
thallium iodide additive and power supply means for supplying
energy in the range of 40 watts - 200 watts per lineal inch to be
consumed by said tubular member, said radiation source having a
dominant emission at 535 nanometers and a secondary mercury
emission at 546 nanometers, and a ratio of the dominant energy
emission to the secondary emission is 1.75:1 to 10:1.
2. The apparatus as claimed in claim 1 wherein the ratio of the
dominant energy emission to the secondary energy emission is in the
range of from 4.5 : 1 to 7 : 1.
3. In apparatus for making copies of originals on copy material,
comprising:
a copy handling assembly including copy material charging, exposing
and developing stations spaced along a path and copy material
feeding means for feeding the copy material along the path,
an illuminating station at which an original is illuminated to
provide a light image that is applied to the copy material at the
exposing station,
a supporting means for receiving an original and mounted for
movement from a normal position in which an original is supplied to
a displaced position to move the original through the illuminating
station as the supporting means moves from the normal position to
the displaced position, the improvement wherein said illuminating
station is equipped with an elongated tubular-shaped radiation
source of the mercury vapor type having a thallium iodide additive,
said radiation source having a dominant emission at 535 nanometers
and a secondary emission at 546 nanometers, the ratio of the
dominant energy emission to the secondary emission being in the
range of 1.75:1 to 10:1, and a power supply connected to said
radiation source for supplying energy thereto in the range of from
40 to 200 watts per lineal inch to be consumed by said tubular
radiation source.
4. Apparatus as claimed in claim 3 wherein said radiation source is
a mercury-thallium vapor lamp in which the dominant emission at 535
nanometers corresponds to the thallium energy line and the
secondary emission at 546 nanometers corresponds to the mercury
energy line.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
A complete understanding of the invention and of these and other
features and advantages thereof may be gained from consideration of
the following detailed description taken in conjunction with the
accompanying drawings wherein one embodiment of the apparatus of
the invention is illustrated. It is to be expressly understood,
however, that the drawings are for the purpose of illustration and
description and are not intended to limit the invention.
In the drawings:
FIG. 1 is a curve of the spectral sensitivity of a conventional
dye-sensitized member;
FIG. 2 is a spectral curve showing the emission characteristics of
the prior art filament-type illuminating source;
FIGS. 3A and 3B are spectral emission curves for the illumination
source of this invention operated at different voltage levels;
FIG. 4 is a series of curves representing the spectral reflectance
of various colors which commonly appear on originals;
FIG. 5 is a schematic drawing of a copy apparatus employing the
radiation source of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The problem of reproducing all the intelligence on a graphic
original, particularly one that is multi-colored, has been
approached through one of three possible theoretical methods.
1. Use of a light-sensitive material which is equally responsive to
all wave lengths, with a radiation source having a spectral energy
distribution that is identical to the luminosity function curve of
the human eye.
2. Use of a radiation source which emits equal energy at all wave
lengths with a light-sensitive material having a spectral
sensitivity curve that is identical to the luminosity function
curve of the human eye.
3. A combination of light-sensitive material and radiation source
wherein the product of radiant energy emitted by the source and the
sensitivity value of the material at each wave length produces a
curve that corresponds to the luminosity function curve of the
human eye.
The first and second methods are purely theoretical while
heretofore known copying systems attempt to follow the third
method. The method and apparatus of the instant invention provide a
solution to the problem of reproducing an original containing
different colored inks through a fourth method exposure.
Referring to FIGS. 1 and 2, there is shown respectively the curve
for the spectral sensitivity of a conventional electrophotographic
paper and the spectral emission curve of a conventional
filament-type lamp, respectively. An example of typical
illuminating source used in this art heretofore is a lamp sold by
Sylvania, identified as their 10 lamp, No. 1500, tubular lamp 2 1/2
having a 12-inch lighted length rated at 1500 watts, 230 volts.
The spectral energy distribution of this lamp plotted in terms of
wave length versus relative energy produces a continuous curve, as
shown in FIG. 2. It will be observed that the curve is continuous
from 250 nanometers to 750 nanometers. A large part of the energy
is in the near infra-red portion of the spectrum which is in the
range of from 670 - 750 nanometers. There is only a small portion
of the available radiant energy in the visible portion of the
spectrum which is effective to produce a latent electrostatic
image.
The deficiencies of using an incandescent source of the type
described is best illustrated by relating it to the spectral
sensitivity curve of a typical photoelectrostatic member, as shown
in FIG. 1. This curve is typical of a member which has been
prepared in accordance with the aforementioned U.S. Pat. No.
3,052,540. It will be observed that the curve shows sensitivity to
radiation at various wave lengths including some sensitivity in the
visible red range of from 600 - 630 nanometers. The illumination
source (FIG. 2) shows a steadily increasing emission from violet to
red. The sensitivity of the system, that is, one which uses a
material having the sensitivity curve shown in FIG. 1 and a radiant
energy source having a distribution curve shown in FIG. 2, may be
represented by taking the product of the two curves. Such a
sensitivity curve would show the system to have its greatest
sensitivity at about 620 nanometers represented by the product of
the lamp emission and copy paper sensitivity at this wave length.
The peak sensitivity is in the red portion of the spectrum.
In summary, it can be said that the prior methods of exposing the
electrophotographic papers have suffered because of their
continuous spectral sensitivity curves and radiant energy sources
that do not closely complement the sensitivity curve of the paper.
As a result, an original subject having a variety of colored
entries, such as cyan, green, red, violet, yellow and magenta, will
not be reproduced in its entirety. Using a system such as first
described, the red, yellow and magenta hues will not be recognized
by the illuminating source, i.e., the radiant energy is reflected
by the yellow, magenta and red colors and thereby dissipates the
electrostatic charge on the photoelectrostatic member.
The use of a source such as a mercury-vapor lamp will cause the
cyan color to go unrecognized, while the colors such as yellow, red
and green will reproduce as black images.
The effect of illuminating a colored original with the lamp of this
invention is analogous to the effect observed in viewing various
colors under monochromatic light in a darkened room. In the
circumstance that the light is from a sodium vapor source, the eye
would observe the color yellow as "white", white would appear
"white", and the colors red, green and black would range from
"gray" to "black". It is therefore desirable to emulate this system
wherein all the colors will be reproduced and their appearance on
the reproduction will be in the approximate order of brightness
appearing on the original.
The use of a radiant energy source that has an intense emission at
a wave length that is within the central portion of the luminosity
function curve of the eye (520 - 590 nanometers), and preferably
falls at approximately the peak position of the luminosity curve
(555 nanometers), would result in the optimum photocopying process
using an electrophotographic member that is responsive to radiation
at the specific wave length of the intense emission line of the
source. The radiation source is effective as a monochromatic
radiation source.
It was found that a radiation source having a high intensity
emission at a wave length corresponding as closely as possible to
the luminosity function curve of the human eye, gave an increased
range of color response, i.e., the ability to reproduce red,
magenta and yellow colors, as well as cyan green and violet. Such
an illuminating source is basically a mercury-vapor type lamp to
which has been added another metal, such as thallium in the form of
thallium iodide, to give the desired spectral emission. The
mercury-thallium discharge results in a primary or dominant
emission peak at 535 nanometers and a secondary emission of 546
nanometers. A lamp useful in the practice of this invention is
available from the Sylvania Electroproducts Corporation, Inc.,
Manchester, N.H.
The spectral energy distribution is represented in FIGS. 3A and 3B
showing a dominant emission of very high intensity at 535
nanometers. The introduction of thallium iodide into the mercury
type lamp produces other emissions at 351.9 nanometers and at 322.9
nanometers. The spectral emission lines produced by the mercury
discharge appear at 405, 436, 546 and 578 nanometers. The mercury
emission is greatly depressed in relation to the thallium emission
and in particular the thallium line appearing at 535 nanometers.
The appearance of the various mercury and thallium peaks other than
the dominant peak at 535 in the spectral energy distribution shown
in FIG. 3 are less significant in the photoelectrostatic copying
method of this invention.
The illuminating source is prepared by introducing metal halides
along with mercury as the active metals, comprising the discharge
medium of the lamp. The mercury-vapor-arc envelope is made of fused
silica having a diameter of about 6 - 12 mm, and the envelope may
be as large as 25 mm. Molybdenum foil-Tungsten electrode assemblies
are pressed and sealed into the ends of the tube envelope. The
electrode is a Tungsten coil wrapped on a Tungsten rod with the rod
extending beyond the coil. The envelope with the electrode
assemblies in position is then evacuated and the metal iodide,
namely thallium iodide in the instant case, is introduced into the
tube in addition to mercury in an atmosphere of argon gas under
moderate pressure. A lamp, having a diameter of 6.8 mm, when
connected in a circuit powered by a suitable power supply, consumes
120 watts of power per lineal inch and will generate an envelope
wall temperature in the range of from 500.degree. - 700.degree.C
yielding the high intensity emission spectral line at 535
nanometers. Operating under this condition of excitation, a
spectral energy distribution trace was made (as shown in FIG. 3)
using a spectroradiometer in which the band pass was 10 nanometers.
The recorder employed to produce the trace was manufactured by the
Hewlett-Packard Company, Mosely Model No. 135 using 8 1/2 .times.
11 paper.
The trace of the spectral energy distribution, covering the range
of from 250 - 750 nanometers, is presented in terms of the relative
intensity of the energy at each wavelength. The height of each peak
represents the relative energy value at that spectral line.
Intensity of the radiation at a particular spectral line is
measured in terms of the height of the peak and then comparing it
to the peak at an adjacent spectral line. Using the band pass width
of 10 nanometers and the particular recorder, the relative energy
values may be relied upon to yield quantitative ratio values at the
critical wave length. In the instant study the thallium line at 535
nanometers was compared to the adjacent mercury line at 546
nanometers in terms of the ratio of the heights of the two lines as
they appear on a curve obtained from the spectroradiometer study
using the 10-nanometer band pass. It will be appreciated that the
operation of the light source anywhere in the range of from 40 -
200 watts per lineal inch (diameter 6.8 mm), will produce a wall
temperature in the range of from 500.degree. - 700.degree.C and
hence will result in a spectral energy distribution curve such as
shown in FIGS. 3A and 3B. The envelope wall temperature must be in
this range in order to have the thallium emit the required amount
of energy.
Referring to FIGS. 3A and 3B, there is shown, respectively, the
distribution curves for the radiation source of this invention
operated at 125 watts per inch and at a lower level of 40 watts per
inch. The curves are shown in a reduced scale from the actual
curves taken from the recorder so that they may be more
conveniently shown in the drawings. The height of the emission at
535 nanometers is measured as well as the height of the mercury
line at 546. The ratio of the relative intensity values expressed
in terms of the height of the 535 nanometer line to the mercury
represents the monochromatic character of the radiation source. The
greater the ratio the greater will be the monochromatic effect of
the energy at 535 nanometers. The lower ratio values indicate that
the radiation at other wavelengths such as at 400 and 436 are being
emitted in sufficient quantity to dilute the effect of the thallium
radiation.
The traces in FIGS. 3A and 3B were produced on a spectroradiometer
using a 10-nanometer band pass. The spectroradiometer is adjusted
to produce a trace in which the peak at 535 nanometers is at a
predetermined height of six inches on the 8 1/2 .times. 11
coordinate paper. With the spectroradiometer adjusted in this
manner the peak heights at the various wave lengths are
proportional to one another.
FIG. 3A represents the distribution curve of the radiation source
of this invention operated at 125 watts per inch, 6.8 mm diameter
envelope. The ratio of the heights of the peaks recorded at 535
nanometers and at 546 nanometers, based on actual measurement, is 6
: 1. It has been found that unique results in the
photoelectrostatic copying process of this invention are observed
only when the intensity of the emission at 535 nanometers is
substantially greater than the intensity of the spectral line at
546 nanometers. At the higher intensity levels of the 535-nanometer
line the secondary mercury lines at 546 nanometers and 436
nanometers tend to be suppressed. The range of operability
expressed as the ratio of the height of the emission at 535
nanometers to the emission at 546 nanometers is from 1.75 : 1 to 10
: 1 with the preferred range being from 4.5 : 1 to 7 : 1. The ratio
measured in FIG. 3A is 6 : 1 for the 125 watt/lineal inch level of
operation is within the preferred range.
Referring to FIG. 3B, there is shown the trace of the distribution
curve for a tubular lamp operated at 40 watts per lineal inch. At a
lower power level the wall temperature is about 500.degree.C which
is the lower temperature limit at which the thallium metal is
activated. It will be observed that the mercury lines at 546 and
436 show up with a greater relative energy level tending to become
more effective. The ratio of the height of the thallium emission to
the adjacent mercury line is 2 : 1 which is still in the range of
operability.
As the ratio decreases below the 1.75 : 1 level, the lamp behaves
as a mercury source so that emission at 436 is the dominant energy.
The result is that yellow and magenta colors will reproduce as dark
images and the green, blue and violet hues will reproduce as
"white".
Referring to FIG. 4, there is presented a series of spectral
reflectance curves for various colored inks and the like over the
spectral range from 400 - 660 nanometers. The curves are identified
as Y, G, C, V, M, and R corresponding to the colors yellow, green,
cyan, violet, magenta and red. At 535 nanometers there is drawn a
line L corresponding to the dominant emission of the lamp above
described.
Each of the curves intersect the dominant emission line somewhere
along its height. The point of intersection measured along the
ordinate represents the amount of reflectance from the surface when
irradiated with radiation at 535 nanometers. The points of
intersection are identified with the corresponding letter bearing a
"prime" designation. Proceeding along the line L from zero
reflectance, it will be observed that the first point is V'
followed in succession by R', M', G', C', and Y'. The points at
which the curves intersect the line L correlate to the degree of
reflectance of that particular color in the system. V and R have
the least reflectance and will reproduce as dark gray or black. C
and G have reflectance values of 25 and 30 percent, respectively. Y
has the greatest degree of reflectance, about 80% and, hence, will
appear light gray to white in the final reproduction.
Referring now more specifically to FIG. 5 of the drawings, therein
is illustrated a copy making apparatus 10 which embodies the
present invention. The apparatus includes a slidably mounted
assembly 16 for receiving a graphic original 18, such as a book,
from which a copy is to be made. The assembly 16 is reciprocated
into and out of a housing (not shown) to print the graphic original
18 to be scanned in order to develop a corresponding pattern of
light and shadow. The left side of the apparatus includes a copy
sheet feeding assembly 20 which feeds a photoelectrostatic copy
sheet 22 in synchronism with the moving original 18 through a
station 24 to receive a uniform electrostatic charge. This sheet is
then moved past an exposing area 26 in synchronism with the
movement of the original 18 so that the charged surface is
selectively discharged in accordance with the pattern of light and
shadow produced by scanning the original, thereby producing a
latent electrostatic image.
The copy sheet 22 is then fed through a developer station 28 in
which the latent image is developed into a powder image, and
subsequent movement of the copy sheet 22 carries it into a fixing
station 29 where the image is placed in permanent form.
The assembly 20 includes a pair of drive rollers 30 secured to a
shaft 32 which rest on the uppermost copy sheet 22 of a stock of
sheets to provide means for feeding a single copy sheet 22 from the
assembly to the processing stations. The rollers 30 are driven by a
series of belts 34, 36, passing around drive pulleys or sprockets
38, 40, which are driven by a main drive motor 42.
A pair of feed rollers 44, 46 advance the copy sheet into the
charging station 24. Roller 46 is secured to a shaft 48 which is
driven by the main drive motor 42 through the belt 50 and pulley
52. Rollers 54 and 56 receive the sheet as it leaves the exposing
area 26 and advance it into the developing station 28 and the
fusing station 29.
The exposing assembly includes a radiation source 60 which has been
made as described herein above to include thallium iodide. The
emission characteristics of the radiation source corresponds to the
curve shown in FIG. 3A of the drawings. The quartz envelope of the
radiation source 60 is mounted in a reflector 62 to focus the
radiation on an illuminating area 64 disposed in the path of
movement of the original 18.
The radiation reflected from the original 18 is transmitted by the
optical system including reflective surfaces 66 and 68 on either
side of a lens 70 forming an optical path between the illuminating
area 64 and the exposing area 26.
The assembly 16 is moved by a drive assembly identified generally
as 72 to a position in which the original is disposed adjacent the
illuminating area 64 and the assembly is moved in synchronism with
the movement of the copy sheet 22 past the exposing area 26 for
selectively discharging the charged surface of the copy sheet
22.
The assembly 16 includes a transparent table 74 which is slidably
mounted on rail elements 76. The drive means 72 includes a flexible
element or connecting cable 78 secured at one end to the table.
The cable 78 passes around a pulley 80 and a pulley 82 secured to
the shaft 84 of a return drive motor 86. The table 74 in the
forward or copying direction is driven by motor 42 connected to the
cable 78 through the shaft 88 acting through a clutch mechanism 90
which couples shaft 88 with shaft 84.
It should be understood that the colors or hues under consideration
are not pure colors. However, the discussion will be applicable
generally. However, where highly impure colors are employed, the
actual reflectance data may vary from the data presented herein. It
should be stressed that this data will fit most cases.
These same colors, red, yellow and magenta when exposed to the
conventional radiation sources (FIG. 1) would escape recognition or
very likely appear as a light gray reproduction. This will become
apparent by referring to FIG. 4 and observing the high reflectance
for these colors in the portion of the spectrum above 600
nanometers.
Since the zinc-oxide photoconductive particles are sensitive to
radiation in the ultra-violet portion of the spectrum, that is 376
- 426, early attempts were made in this art to employ mercury-vapor
lamps to expose the electrophotographic members. It was found that
the colors yellow, green and red would reproduce as dark images and
the cyan appear as white. Further, the use of certain ultra-violet
absorptive materials employed in paper making cause the original
subject to have a low reflectance and, hence, produce a copy with a
darkened background. Referring again to FIG. 4, it will be seen
that at 426 nanometers the curves Y, R and G have reflectance
values less than 10 percent, and V less than 30 percent. The curve
C at 426 nanometers would tend to reproduce as a light color. The
mercury-vapor source would not distinguish the various colors Y, R
and G according to their relative brightness, but they would all
reproduce with the same degree of darkness of print. It should be
pointed out that operating the lamp of this invention at ratios
below 1.75 : 1 will have the effect of a mercury-vapor lamp.
A significant advantage in increased speed is realized in using the
radiation sources of the instant invention. The combination of
spectral emission in the ultra-violet range together with the high
intensity emission along the 535-nanometer spectral emission
results in decreasing the exposure time necessary to produce a
latent electrostatic image on the copy sheet.
Sensitivity studies using a photoelectrostatic member of the type
described in U.S. Pat. No. 3,052,540 were carried out comparing the
conventional incandescent source with the lamps used in this
invention. The test procedures called for charging the member up to
the same voltage level and first measuring the sensitivity
expressed in volts per second to a thallium source at a given
wattage input. The test was then repeated substituting the
incandescent type source and varying the wattage input until the
sensitivity measured in the first run was duplicated. The test
results revealed that an 80 watt thallium source, 1.5 inches
lighted length, gave a sensitivity of 610 volts per second at a
charging level of 580 volts. The incandescent source required 400
watts of energy input, 1.5 inches lighted length, to realize the
same sensitivity.
The speed increase is significant in that an electrophotographic
member irradiated with a conventional lamp rated at 1500 watts, as
herein above described, is processed at 15 feet per minute past an
exposure window, and with the lamp of this invention rated at 800
watts the processing speed is increased to 30 feet per minute.
Exposure was made on an electrostatic copier identified as a
Bruning brand Model 2000 copier.
In summation it can be said the electrophotographic copying process
of this invention permits the reproduction of a wider range of
colored subject matter, produces reproductions in which the image
brightness approximates the relative brightness of the original,
and finally results in decreasing the time necessary to expose the
electrophotographic material.
* * * * *