U.S. patent number 3,660,086 [Application Number 05/000,394] was granted by the patent office on 1972-05-02 for electrophotographic plate and process employing inorganic photoconductive material with a photochromic sensitizing agent.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Satoru Honjo, Hisatake Ono, Chiaki Osada, Yasuo Tamai.
United States Patent |
3,660,086 |
Tamai , et al. |
May 2, 1972 |
ELECTROPHOTOGRAPHIC PLATE AND PROCESS EMPLOYING INORGANIC
PHOTOCONDUCTIVE MATERIAL WITH A PHOTOCHROMIC SENSITIZING AGENT
Abstract
An electrophotographic plate which comprises a photoconductive
layer comprising a photoconductive material, a binder material, and
a photochromic sensitizing agent selected from the group consisting
of: wherein: R.sub.1 = H, a halogen, R or OR where R is an alkyl
group having one to seven carbon atoms, R.sub.2 and R.sub.3 = an
alkyl group having one to seven carbon atoms, and R.sub.4 =
(CH.sub.2).sub.n SO.sub.3 H or (CH.sub.2).sub.n COOH, where n = 1
to 7; wherein: R.sub.1 = R, a halogen, R or OR where R is an alkyl
group having one to seven carbon atoms, R.sub.2 and R.sub.3 = an
alkyl group having one to seven carbon atoms, R.sub.4 =
(CH.sub.2).sub.n SO.sub.3 H or (CH.sub.2).sub.n COOH where n = 1 to
7, and R.sub.5 and R.sub.6 = H, NO.sub.2, a halogen, CN, OR, or
COOR where R is an alkyl group having one to seven carbon atoms,
providing R.sub.5 and R.sub.6 do not represent H atoms
simultaneously; And mixtures thereof, is disclosed.
Electrophotographic processes employing these plates are also
disclosed.
Inventors: |
Tamai; Yasuo (Asaka-shi,
JA), Osada; Chiaki (Asaka-shi, JA), Ono;
Hisatake (Asaka-shi, JA), Honjo; Satoru
(Asaka-shi, JA) |
Assignee: |
Xerox Corporation (Rochester,
NY)
|
Family
ID: |
11552512 |
Appl.
No.: |
05/000,394 |
Filed: |
January 2, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Jan 17, 1969 [JA] |
|
|
44/3261 |
|
Current U.S.
Class: |
430/91; 252/586;
548/409; 430/95 |
Current CPC
Class: |
G03G
5/09 (20130101) |
Current International
Class: |
G03G
5/04 (20060101); G03G 5/09 (20060101); G03g
005/00 (); G03g 007/00 () |
Field of
Search: |
;96/1.8,1.7,1.6,1.5,9PC
;252/300 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lesmes; George F.
Assistant Examiner: Miller; John R.
Claims
What is claimed is:
1. An electrophotographic member comprising a support substrate
having superimposed thereon a photoconductive layer comprising an
inorganic photoconductive material, a binder material, and a
photochromic sensitizing agent selected from at least one member of
the group consisting of: ##SPC7##
wherein: R.sub.1 = H, a halogen, R or OR where R is an alkyl group
having one to seven carbon atoms, R.sub.2 and R.sub.3 = an alkyl
group having one to seven carbon atoms, and R.sub.4 = (CH.sub.2)n
SO.sub.3 H or (CH.sub.2)n COOH, where n = 1 to 7; and ##SPC8##
wherein: R.sub.1 = H, a halogen, R or OR where R is an alkyl group
having one to seven carbon atoms, R.sub.2 and R.sub.3 = an alkyl
group having one to seven carbon atoms, R.sub.4 = (CH.sub.2)n
SO.sub.3 H or (CH.sub.2) n COOH where n =1 to 7, and R.sub.5 and
R.sub.6 = H, NO.sub.2, a halogen, CN, OR, or COOR where R is an
alkyl group having one to seven carbon atoms, providing R.sub.5 and
R.sub.6 do not represent H atoms simultaneously.
2. The member as disclosed in claim 1 wherein said photochromic
sensitizing agent is the open form of the respective sensitizing
material.
3. The member as disclosed in claim 1 wherein said photochromic
sensitizing agent is the closed form of the respective sensitizing
material.
4. The member as disclosed in claim 1 wherein said inorganic
photoconducting material is selected from at least one member of
the group consisting of zinc oxide and titanium oxide.
5. The plate as disclosed in claim 4 wherein said inorganic
photoconductive material comprises zinc oxide.
6. The member as disclosed in claim 1 wherein said photoconductive
layer has a thickness of from about 5 to about 200 microns.
7. The photoconductive member as disclosed in claim 1 wherein said
sensitizing agent and said photoconductive material are present in
amounts ranging from about 1-1,000 parts by weight of said
sensitizing agent to about 100,000 parts by weight of said
photoconductive material.
8. The member as disclosed in claim 7 wherein said range comprises
1-20 parts by weight of said sensitizing agent to about 10,000
parts by weight of said photoconductive material.
9. An electrophotographic imaging process which comprises:
a. providing an electrophotographic member of the nature described
in claim 1,
b. forming an electrostatic latent image on the surface of said
plate, and
c. developing said latent image with electroscopic developing
materials.
10. The process as disclosed in claim 9 further including the step
of the uniformly exposing said developed member to visible
light.
11. The process as disclosed in claim 9 wherein said photochromic
sensitizing agent is the open form of said agent.
12. The process as disclosed in claim 9 wherein said photochromic
sensitizing agent is the closed form of said agent.
13. The process as disclosed in claim 9 wherein said inorganic
photoconductive material is selected from at least one member of
the group consisting of zinc oxide and titanium oxide.
14. The process as disclosed in claim 13 wherein said inorganic
photoconductive material comprises zinc oxide.
Description
BACKGROUND OF THE INVENTION
This invention relates, in general, to electrophotography, and,
more specifically, to binder plates containing a photochromic
sensitizing material as well as to electrophotographic processes
using said plates.
It is known that images may be formed and developed on the surface
of certain photoconductive insulating materials by electrostatic
means. The basic electrophotographic process, as taught by Carlson
in U.S. Pat. No. 2,297,691, involves uniformly charging a
photoconductive insulating layer and exposing said layer to a
light-and-shadow image which dissipates the charge on the portions
of the layer which are exposed to light. The electrostatic latent
image formed on the layer corresponds to the configuration of the
light-and-shadow image. Alternatively, a latent electrostatic image
may be formed on the plate by charging said plate in image
configuration. This image is rendered visible by depositing on the
imaged layer a developing material, comprising a colorant, called a
toner. The developing material is attracted to those portions of
the layer which retain a charge, thereby forming a toner image
corresponding to the latent electrostatic image. Where the base
sheet is relatively inexpensive, such as paper, the toner image may
be fixed directly to the plate as by heat or solvent fusing.
Alternatively, the toner image may be transferred to a sheet of
receiving material, such as paper, and fixed thereon. The above
general process is also described in U.S. Pat. Nos. 2,357,809;
2,891,011; and 3,079,342.
The photoconductive insulating layer to be effective must be
capable of holding an electrostatic charge in the dark and
dissipating the charge to a conductive substrate when exposed to
light.
The fact that various two-component materials may be used in
non-reusable photoconductive layers used in electrophotography is
known. These consist of a photoconductive insulating material in
particulate form dispersed in an insulating binder material. Where
the particles consist of a photoconductive material comprising
inorganic crystalline compounds containing a metalic ion,
electrophotographic plates are obtained which have unsatisfactory
photographic speeds and spectral responses for many
electrophotographic applications. Moreover, these plates are not
panchromatic, i.e., they are not sensitive to wavelength in the
near-ultraviolet range.
Various colored sensitizing pigments have been used to increase the
photosensitivity and panchromatic response of these single-use
photosensitive layers, i.e., layers where there is no image
transfer to white transfer paper, but rather, where the
photosensitive layer converts itself into the final print. While
these colored sensitizing agents enhance the photosensitivity and
panchromaticity of the photoconductive layer, they also impart
their color to the non-imaged area of the layer. Since, in
non-reusable electrophotography, said layer becomes the final
print, the background area of said print becomes colored or
darkened causing poor contrast between the final image and
background.
Known processes for removal of colored sensitizing pigment
contained in the photoconductive layer after development have
certain disadvantages. For example, processes for chemically
converting the sensitizing pigment into a colorless substance
results in destruction of toner particles deposited on the image.
Further, while it is possible to have the non-image area coated
with a white substance, the process of accomplishing this would be
expensive, very time consuming and commercially impractical.
It is, therefore, an object of this invention to provide a novel
electrophotographic plate devoid of the above-noted
disadvantages.
Another object of this invention is to provide a novel
electrophotographic process devoid of the above-noted
disadvantages.
Still another object of this invention is to provide a non-reusable
electrophotographic process capable of producing prints of high
contrast and quality.
A further object of this invention is to provide a novel
electrophotographic plate having improved photosensitivity and
panchromaticity.
SUMMARY OF THE INVENTION
The foregoing objects and others are accomplished in accordance
with this invention, generally speaking, by providing an
electrophotographic plate which comprises a photoconductive
material, a binder material, and a photochromic sensitizing agent
selected from the group consisting of: ##SPC1##
wherein: R.sub.1 = H, a halogen, R or OR where R is an alkyl group
having one to seven carbon atoms, R.sub.2 and R.sub.3 = an alkyl
group having one to seven carbon atoms, and R.sub.4 =
(CH.sub.2).sub.n SO.sub.3 H or (CH.sub.2).sub.n COOH, wherein n = 1
to 7; ##SPC2##
wherein: R.sub.1 = H, a halogen, R or OR where R is an alkyl group
having one to seven carbon atoms, R.sub.2 and R.sub.3 = an alkyl
group having one to seven carbon atoms, R.sub.4 = (CH.sub.2).sub.n
SO.sub.3 H or (CH.sub.2).sub.n COOH where n = 1 to 7, and R.sub.5
and R.sub.6 = H, NO.sub.2, a halogen, CN OR, or COOR where R is an
alkyl group having one to seven carbon atoms, providing R.sub.5 and
R.sub.6 do not represent H atoms simultaneously;
and mixtures thereof. These agents increase the photosensitivity
and panchromaticity of a photoconductive layer.
After a latent electrostatic image is formed on the surface of the
above-mentioned photoconductive layer which contains a photochromic
sensitizing agent of the general formulas described above, said
image is first developed and then the surface of said layer is
exposed uniformly to visible light in order to remove the color
imparted by said sensitizing agent to the background areas of said
layer.
Any suitable organic or inorganic photoconductive material may be
employed in the plate of this invention. Typical inorganic
photoconductive materials are sulfur, selenium (vitreous, amorphous
alpha monoclinic), zinc sulfide, zinc oxide, zinc cadmium sulfide,
zinc magnesium oxide, cadmium selenide, zinc silicate,
calcium-strontium sulfide, cadmium sulfide, mercuric iodide,
mercuric oxide, mercuric sulfide, indium trisulfide, gallium
triselenide, arsenic disulfide, arsenic trisulfide, arsenic
triselenide, antimony trisulfide, cadmium sulfo-selenide, doped
chalcogenides of zinc and cadmium, aluminum oxide, bismuth oxide,
molybdenum oxide, lead oxide, titanium oxide, molybdenum iodide,
molybdenum selenide, molybdenum sulfide, molybdenum telluride,
aluminum iodide, aluminum selenide, aluminum sulfide, aluminum
telluride, bismuth iodide, bismuth selenide, bismuth sulfide,
bismuth telluride, cadmium telluride, mercuric selenide, mercuric
telluride, lead oxide, lead selenide, lead sulfide, lead telluride,
cadmium arsenide, lead chromate, gallium sulfide, gallium
telluride, indium sulfide, indium selenide, indium telluride, red
lead and mixtures thereof. Typical organic photoconductive
materials include aromatic polyvinyl compounds such as polyvinyl
naphthalene, polyvinyl anthracene, polyvinyl biphenyl, and
polyvinyl fluorene; heterocyclic polyvinyl compounds such as
polyvinyl carbazole, polyvinyl quinoline, and polyvinyl furane;
high molecular weight aromatic compounds such as
polyacenaphthylene, polyacephenanthracene, oxadiazoles,
imidazolones, imidazolethiones, triazoles, oxazoles, thiazoles,
triazines, and hydrazones; low molecular weight aromatic
carbocyclic or aromatic heterocyclic compounds such as imidazoles
and triazoles; azomethines; amino compounds with multinuclear
heterocyclic and aromatic ring system, anthracene and its
derivatives, styryl compounds, thiophenes, acylhydrazones, metal
compounds of mercapta-benzthiazol, mercaptobenzoxazole, and
mercapto-benzimidazole, triphenylamines, furans, pyrroles,
pyrazolones, cyclo-azaoctatetraene derivatives, stilbene
derivatives, fluorene derivatives, thiophene derivatives, pyrrole
derivatives, phthalocyanines, quinones, azo compounds, and charge
transfer complexes.
While any suitable photoconductive material may be used in this
invention it is preferred to employ zinc oxide for best
results.
Any suitable photoconductive or non-photoconductive binder material
may be used in this invention. Typical photoconductive insulating
materials include films of amorphous selenium, sulfur,
sulfur-selenium mixtures, arsenic-selenium mixtures,
selenium-tellurium mixtures, lead oxide, cadmium sulfide, zinc
sulfide and organic photoconductors (especially when these are
complexed with small amounts of a suitable Lewis acids). Typical of
these organic photoconductors are polyvinylcarbazole;
polyvinyl-anthracene; 4,5 -diphenylimidazolidinone;
4,5-diphenylimidazolidinethione; 4,5-bis-(4'
aminophenyl)-imidazolidinone; 1,5-cyanonaphthalene;
1,4-dicyanonaphthalene; aminophthalodinitrile;
nitrophthalidinitrile; 1,2,5,6-tetraazacyclooctatetraene-(2,4,6,8);
3,4-di(4'-methoxy-phenyl)-7,8-diphenyl-1,2,5,6-tetraazacycloactatetraene-(
2,4,6,8);
3,4-di-(4'-phenoxy-phenyl-7,8-diphenyl-1,2,5,6-tetraaza-cycyloctatotraene-
(2,4,6,8);
3,4,7,8-tetramethoxy-1,2,5,6-tetraaza-cyclooactatetraene-(2,4,6,8);
2-mercaptobenzthiazole; 2-phenyl-4-di-phenylidene-oxazolone;
2-phenyl-4-p-methoxybenzylidene-oxazolone;
6-hydroxy-2-phenyl-3-(p-dimethylamino phenyl)-benzofuran;
6-hydroxy-2,3-di(p-methoxyphenyl)-benzofuran;
4-dimethylamino-benzylidene-benzhdrazide;
4-dimethylaminobenzylideneisonicotinic acid hydrazide;
furfurylidene-(2)-4'-dimethylaminobenzhydrazide;
5-benzilideneamino-aceneaphthene; 3-benzylideneaminocarbazole;
(4-N,N-dimethylamino-benzylidene)-p-N,N-dimethylaminoniline;
(2-nitro-benzylidene)-p-bromo-aniline;
N,N-dimethyl-N'-(2-nitro-4-cyano-benzylidene)-p-phenylene-diamino;
2,4-diphenylquinazoline; 2-(4'-amino-phenyl)-4-phenyl)-quinazoline;
2-phenyl-4-(4'-di-methyl-amino-phenyl)-7-methoxy-quinazoline;
1,3-diphenyltetra-hydroimidazole;
k,3-di(4'-chlorophenyl)-tetrahydroimidazole
1,3-diphenyl-2-4'-dimethyl amino phenyl)-tetrahydroimidazole;
1,3-di-(p-tolyl)-2-
3-(4'-dimethylamino-phenyl)-5-(4"-methoxyphenyl-6-phenyl-
1,2,4-triazine; 3-pyridil-(4')-
5-(4"-diemthylaminophenyl)-6-phenyl-1,2,4-triazine; 3,
(4'-amino-phenyl)-5,6-di-phenyl-1,2,4-triazine; 2,5-bis
4'-amino-phenyl-(1') -1,3,4-triazole; 2,5-bis
4'-(N-ethyl-N-acetyl-amino)-amino)-phenyl-(1') -1,3,4,-triazole;
1,5-diphenyl-3-methyl-pyrazoline; 1,3,4,5-tetraphenyl-pyrazoline;
1-methyl-2-(3', 4'-dihydroxymethylene-phenyl)-benzimidazole;
2-(4'-dimethyl-amino phenyl)-benzoxazole;
2-(4'-methoxyphenyl)-benzthiazole; 2,5-bis - p-aminophenyl-(1)
-1,3,4-oxadiazole; 4,5-diphenyl-imidazolone; 3-aminocarbazole;
copolymers and mixtures thereof. Typical insulating film forming
binders include thermoplastic and thermoset polymers such as
polyvinylchloride, polyvinylacetates, polystyrene,
polystyrene-polybutadiene copolymers, polymethacrylates,
polyacrylics, polyacrylonitriles, silicone resins, chlorinated
rubber, epoxy resins including halogenated epoxy and phenoxy
resins, phenolics, epoxy-phenolic copolymers, epoxy urea
formaldehyde copolymers, epoxy melamine formaldehyde,
polycarbonates, polyurethanes, polyamides, saturated polyesters,
unsaturated polyesters cross-linked with vinyl monomers and epoxy
esters, vinyl epoxy resins, tall-oil modified epoxys, and
copolymers and mixtures thereof. Other insulating film-forming
binder materials includes organics such as sucrose and its
derivates, resin and modified resins, etc; inorganic materials such
as low melting point insulating glasses including those made from
glass-forming oxides, sulfides, selenides, borates, phosphates,
arsonates, other well known glass formers and mixtures thereof. In
addition to the above noted materials, any other suitable binder
may be used if desired. The binder for the photoconductive material
used in the present invention should be of such a nature that it
will not adversely affect the photochromic sensitizing agent nor
will it impede the removal of color at the time of exposure to
visible light.
While any suitable binder material may be used in the present
invention, it is preferred to use alkyd resins, sytrene-butadiene
copolymers, polymethacrylic ester resins, and epoxy resins, for
excellent results. Optimum results are obtained with styrenated
alkyd binder materials.
While any suitable sensitizing material represented by the
above-mentioned general formulas may be used in the
electrophotographic plates of the present invention, particularly
good results have been achieved with the following materials and
accordingly, these materials are most preferred. ##SPC3##
Any suitable substrate material may be used in accordance with the
present invention. Typical non-conductive bases include paper,
plastics, polyurethane, polyvinylchloride, polyethylene,
polyethylene terephthalate, among others. If it is desired to use a
conductive base in a single charging application, any suitable
conductive base may be utilized in accordance with the present
invention. Typical conductive bases include NESA glass, aluminized
Mylar, conductive polymers, chromium, aluminum, brass, stainless
steel, copper, zinc and alloys thereof. A substantially white paper
substrate is preferred in the present invention.
The photoconductive layer of the present invention may have any
suitable thickness. Thicknesses ranging from about 5 microns to
about 200 microns have been found convenient. For best operation it
is preferred that the layer have a thickness of about 10 microns to
about 100 microns.
Any suitable ratio of sensitizing agent represented by the
above-mentioned general formulas to photoconductive material may be
employed in this invention. A range of about 1 part to about 1,000
parts by weight of sensitizing agent to about 100,000 parts by
weight of photoconductive material has been found convenient. A
preferred ratio lies in the range of about 1 part to about 20 parts
by weight of sensitizing agent to about 10,000 parts by weight of
photoconductive material.
The photoconductive material may be incorporated in a dissolved or
melted binder by any suitable means, such as strong shear
agitation, preferably with simultaneous grinding. The methods
include ball milling, roller milling, sand milling, ultrasonic
agitation, high speed blending, and any desirable combination of
these methods. In addition to adding the photoconductive material
to the dissolved or melted binder material, it may also be added
and blended into a dry or slurried form of the powdered binder
material before it is heated or dissolved to make it film
forming.
Any suitable range of photoconductor-binder ratios may be used. On
a photoconductor-dried binder weight basis, the ratio between
binder and photoconductive material is from about 1 part binder and
10 parts photoconductor to about 2 parts binder and 1 part
photoconductor, by weight. Best results are achieved in the range
of about 1 part binder and 1 part photoconductor to about 1 part
binder and 9 parts photoconductor, by weight, and, accordingly,
this range is preferred.
The sensitizing agent of this invention may be added to the
photoconductive material in several ways. For example, said agent
may be dissolved in a suitable solvent and the photoconductive
material added to the resultant solution so as to permit the
sensitizing substance to be deposited on the photoconductive
material. Alternatively, the photoconductive material may be mixed
and kneaded with the binder and the solution of sensitizing
substance added to the resulting mixture.
In effecting absorption of the colored sensitizing agent on the
photoconductive material, the nature of the surface of the
photoconductive material should be known. For example, zinc oxide
which is comparatively basic on its surface satisfactorily absorbs
a photochromic sensitizing agent possessing an acid radical.
Titanium oxide, on the other hand, is acidic on its surface, as
compared to zinc oxide, and therefore tends to absorb a basic
colored sensitizing agent. By this absorption treatment, the
photoconductive material comes to possess photosensitivity to the
portion of wavelengths corresponding to the light absorption by the
sensitizing agent.
The sensitized photoconductor-binder-solvent slurry or the
photoconductor-binder melt may be applied to substrate materials by
any of the well known coating methods, including spray, flow
coating, hydrolic coating, knife-coating, electro-coating, mayer
bar drawdown coating, dip coating, reverse roll coating, etc.
Spraying in an electric field may be preferred for smoothest finish
and dip coating for convenience in the laboratory.
The toner image may be formed by an conventional
electrophotographic process. For example, in the art of xerography
as originally disclosed by Carlson in U.S. Pat. No. 2,297,691, an
electrostatic latent image is formed on a photoconductive
insulating layer and is developed thereon by finely divided
electroscopic developing materials. The developed image may then be
fixed in place or transferred to a copy sheet where it is
permanently fixed. Generally the photoconductive insulating layer
is first charged to sensitize it and is then exposed to a light
image or other pattern of activated electromagnetic radiation to
dissipate the charge in radiation struck areas. Thus the charge
pattern formed conforms to the electromagnetic radiation pattern
which impinges upon the plate. This charge pattern may then as
above discussed be developed or made visible by a charge wise
deposition on the plate of an electroscopic or electrostatically
attractable, finely divided colored material which is referred to
in the art as "toner."
Any of several known methods for applying the electroscopic
particles to the electrostatic latent image to be developed may be
used in this invention. One development method, as disclosed by E.
N. Wise in U.S. Pat. No. 2,618,552, is known as "cascade"
development. In this method, a developer material comprising
relatively large carrier particles having finely divided toner
particles electrostatically coated thereon is conveyed to and
rolled or cascaded across the electrostatic latent image bearing
surface. The composition of the carrier particles is so selected as
to triboelectrically charge the toner particles to the desired
polarity. As the mixture cascades or rolls across the image bearing
surface, the toner particles are electrostatically deposited and
secured to the charged portion of the latent image and are not
deposited on the uncharged or background portions of the image.
Most of the toner particles accidentally deposited in the
background are removed by the rolling carrier, due apparently, to
the greater electrostatic attraction between the toner and the
carrier than between the toner and the discharged background. The
carrier and excess toner are then recycled. This technique is
extremely good for the development of line copy images.
Another method of developing electrostatic images is the "magnetic
brush" process as disclosed, for example, in U.S. Pat. No.
2,874,063. In this method, a developer material containing toner
and magnetic carrier particles are carried by a magnet. The
magnetic field of the magnet causes alignment of the magnetic
carrier into a brush-like configuration. This "magnetic brush" is
engaged with the electrostatic image-bearing surface and the toner
particles are drawn from the brush to the latent image by
electrostatic attraction.
Still another technique for developing electrostatic latent images
is the "powder cloud" process as disclosed, for example, by C.F.
Carlson in U.S. Pat. No. 2,221,776. In this method, a developer
material comprising electrically charged toner particles in a
gaseous fluid is passed adjacent the surface bearing the
electrostatic latent image. The toner particles are drawn by
electrostatic attraction from the gas to the latent image. This
process is particularly useful in continuous tone development.
Other development methods such as "touchdown" development as
disclosed by R.W. Gundlach in U.S. Pat. No. 3,165,432 may be used
where suitable.
Although development may be accomplished by any of the
above-mentioned methods, the liquid and powder cloud processes
which are particularly suitable for reproduction of graded tone,
are preferable for development according to the present
invention.
After the development step the toner is fixed. The fixing of the
toner image may be accomplished by a heat-fixing process, a process
which causes the toner to be deposited fast and solidified, or a
process which provides uniform lacquering.
The removal of color from the background areas of the sensitized
photoconductive layer may be carried out before or after the fixing
step. The exposure of the colored sensitized photoconductive layer
may be accomplished by placing said layer open to sufficiently
intense light emanating from a suitable light source for a short
length of time. This is accomplished, for example, by exposure to
sunlight, exposure to light from a tungsten light source, or
exposure to light from other visible light sources. For the removal
of color, a light which absorbs the activated coloring matter
proves effective. Where the color need not be removed at once, the
fixed print may be left in a light room. On the other hand, where
immediate removal of color from background areas of the print is
required, said print may be exposed to a light having an
illumination exceeding 10,000 luxes from, for example, a tungsten
light source having a color temperature of about 2,800.degree. K.
The exposure time may, of course, be reduced where a brighter light
source is void. For example, when the print is exposed to sunlight,
about 1 to 5 minutes of exposure time is sufficient to remove color
from the background areas. After exposure to visible light, there
is obtained a final print which is excellent in image quality.
This, in part, is due to a white background and a consequent high
contrast.
In general, a substance which manifests photochromism is
characterized by the fact that reversible change of color takes
place quite rapidly. In the case of the photochromic sensitizing
agents of the present invention, i.e., those represented in the
general formulas mentioned above, once the color is removed, it is
not easily restored. In fact, such resumption of color cannot be
achieved unless the decolorized layer is heated and/or exposed to
ultraviolet rays. Thus, when the background color is removed, after
development of the image, through exposure to visible light, no
resumption of color takes place under ordinary storage conditions.
Even if the color is allowed to reappear under defective storage
conditions it can be removed again by exposing the layer to visible
light once more.
The step of removing the color from the non-image areas of a print
after development can be applied to electrophotographic processes
other than described above. For example, it may be applied to a
non-charging electrophotographic process, an electrolytic
electrophotographic process, and the like.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following examples will further define various preferred
embodiments of the present invention. Parts and percentages are by
weight unless otherwise specified.
EXAMPLE I
About 6 mg. of a photochromic sensitizing material having the
formula: ##SPC4##
is dissolved in about 40 ml. of methanol. To the resultant solution
about 5 g. of photoconductive zinc oxide is added, and the mixture
is stirred. The resultant dispersion is then subjected to
centrifugal separation in order to obtain zinc oxide having the
aforementioned sensitizing material deposited thereon.
The zinc oxide having said sensitizing material deposited there is
then added to a solution containing a binder resin which comprises
about 0.6 g. (as involatile component) of Styresol 4400 (made by
Nippon Reichheld Co.) and about 4.0 g. (as involatile component) of
Desmodule L (made by Bayer Co. of West Germany). Styresol 4400 is a
styrenated alkyd resin and is marketed as a 5.0 percent toluene
solution. Desmodule L is the reaction product of 1 mol of
trimethylol propane and 3 mol of tolylenediisocyanate and is
marketed as a 75 percent ethyl acetate solution. These substances
are weighed out in the above-mentioned quantities in terms of
involatile component and dissolved in butyl acetate which is added
thereto.
The resultant resin solution and the treated zinc oxide are mixed
together by means of a ball mill. This dispersion which is obtained
is then spread to a dry thickness of about 6 microns on a
conductive paper. After spreading, the layer is dried and kept in
an air thermostat bath at about 40.degree. C for about 24 hours.
All the preceding treatments are carried out in a darkroom. The
photoconductive layer thus obtained assumes a light blue color by
virtue of the sensitizing material. The reflective optical density
is found to be 0.32.
This photosensitive layer is then uniformly charged by exposure to
a negative corona at - 7000 V. It acquires a surface electric
potential of - 320 V. In this state, the sensitive layer is held
directly in contact with a positive original and exposed, through
the original to light from a tungsten light source at 1,000 luxes
for 0.4 seconds. Immediately after the exposure, the sensitive
layer is developed with a liquid developer comprising commercial
blue offset ink and cyclohexane.
After development, the sheet containing the sensitive layer is
rinsed in a bath of clean isoparafin to wash off the remaining
toner particles. After the subsequent step of drying, the image is
fixed by spraying thereon commercial clear lacquer. The lacquer is
dried, and, subsequently, the sheet is exposed in its entire
surface to the sunlight for about 5 minutes.
As the sunlight decreases the color produced in the sensitive layer
through the sensitizing material, the reflective optical density
falls to 0.24 in the non-image area.
EXAMPLE II
Example I is repeated using the following sensitizing materiaL:
##SPC5##
at a ratio of 2 mg. per 5 g. of zinc oxide.
The reflective optical density of the electrophotographic layer
itself is 0.37. When the photosensitive layer is exposed to light
from a tungsten light source at 60,000 luxes for about 4 minutes
subsequent to developing and fixing the electrostatic latent image
on the sensitive layer, the reflective optical density falls to
0.28.
EXAMPLE III
Example I is repeated using a methanol solution of the following
sensitizing agent which is absorbed by zinc oxide: ##SPC6##
In the absorbed state, this is assumed a red color. Upon exposure
to visible light, the color is removed.
While specific components of the present system are defined in the
working examples above, any of the other typical materials
indicated above may be substituted in said working examples where
appropriate. In addition, many other variables may be introduced in
the present process such as other reaction components which may in
any way affect, enhance, or otherwise improve the present plate or
process.
While various specifics are cited in the present application, many
modifications and ramifications will occur to those skilled in the
art upon a reading of the present disclosure. These are intended to
be encompassed within the scope of this invention.
* * * * *