U.S. patent number 3,658,520 [Application Number 04/706,780] was granted by the patent office on 1972-04-25 for photoconductive elements containing as photoconductors triarylamines substituted by active hydrogen-containing groups.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to Thomas B. Brantly, Lawrence E. Contois, Charles J. Fox.
United States Patent |
3,658,520 |
Brantly , et al. |
April 25, 1972 |
PHOTOCONDUCTIVE ELEMENTS CONTAINING AS PHOTOCONDUCTORS
TRIARYLAMINES SUBSTITUTED BY ACTIVE HYDROGEN-CONTAINING GROUPS
Abstract
Triarylamines having at least one of the aryl radicals
substituted by an active hydrogen-containing group are good organic
photoconductors in electrophotographic systems.
Inventors: |
Brantly; Thomas B. (Rochester,
NY), Contois; Lawrence E. (Rochester, NY), Fox; Charles
J. (Rochester, NY) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
|
Family
ID: |
24839017 |
Appl.
No.: |
04/706,780 |
Filed: |
February 20, 1968 |
Current U.S.
Class: |
430/73;
430/83 |
Current CPC
Class: |
G03G
5/0618 (20130101) |
Current International
Class: |
G03G
5/06 (20060101); G03g 005/00 (); G03g 007/00 () |
Field of
Search: |
;96/1.5 ;252/501 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lesmes; George F.
Assistant Examiner: Miller; John R.
Claims
We claim:
1. An electrophotographic element comprising an electrically
conductive support having coated thereon a photoconductive
composition comprising an electrically insulating polymeric binder,
a photoconductor and a sensitizing amount of a pyrylium salt, said
photoconductor having the structure:
wherein:
a. Ar.sub.1 and Ar.sub.2 are phenyl radicals;
b. Ar.sub.3 is an arylene radical selected from the group
consisting of:
1. a phenylene radical and
2. a naphthylene radical; and
c. X is an active hydrogen-containing group selected from the group
consisting of:
1. a carboxy radical,
2. an ester radical,
3. a hydroxy radical,
4. an alkylene hydroxy radical,
5. an acid anhydride radical,
6. an alkylene carboxy radical, and
7. an acyl halide radical.
2. A photoconductive element as described in claim 1 wherein said
pyrylium salt is present in an amount from about 0.005 to 5.0
percent by weight based on said photoconductive composition and
said active hydrogen-containing group is a carboxy radical.
3. A photoconductive element as described in claim 1 wherein said
pyrylium salt is present in an amount from about 0.005 to 5.0
percent by weight based on said photoconductive composition and
said active hydrogen-containing group is an alkylene carboxy
radical.
4. A photoconductive element as described in claim 1 wherein said
pyrylium salt is present in an amount from about 0.005 to 5.0
percent by weight based on said photoconductive composition and
said active hydrogen-containing group is an acyl halide
radical.
5. A photoconductive element as described in claim 1 wherein said
pyrylium salt is present in an amount from about 0.005 to 5.0
percent by weight based on said photoconductive composition and
said active hydrogen-containing group is an ester radical.
6. An electrophotographic element comprising a conducting support
having coated thereon a photoconductive composition comprising a
sensitizer which is a pyrylium salt, a polymeric binder and a
photoconductor selected from the group consisting of:
methyl p-diphenylaminobenzoate,
N,n-diphenylanthranilic acid,
ethyl 2,6-diphenyl-4-(p-diphenylaminophenyl)benzoate,
1-(p-diphenylaminophenyl)-1-hydroxy-3-butyne,
4-hydroxymethyltriphenylamine,
1-(p-diphenylaminophenyl)ethanol,
3-p-diphenylaminophenylpropionic acid,
3-p-diphenylaminophenyl-1-propanol,
4-hydroxytriphenylamine,
2-hydroxytriphenylamine,
1-(p-diphenylaminophenyl)hexanol,
1-(p-diphenylaminophenyl)dodeconal,
p-diphenylaminobenzoic acid anhydride,
p-diphenylaminobenzoic acid N,N-diphenylamide, and
p-diphenylaminobenzoic acid.
7. A photoconductive element for use in electrophotography
comprising a conducting support having coated thereon a
photoconductive composition comprising:
a. about 10 to 60 percent, by weight, based on said photoconductive
composition of methyl p-diphenylaminobenzoate,
b. about 0.005 to 5.0 percent, by weight, based on said
photoconductive composition of a pyrylium salt as a sensitizer,
and
c. a film-forming polymeric binder for said photoconductor.
8. A photoconductive element for use in electrophotography
comprising a conducting support having coated thereon a
photoconductive composition comprising:
a. about 10 to 60 percent by weight based on said photoconductive
composition of ethyl
2,6-diphenyl-4-(p-diphenylaminophenyl)benzoate,
b. about 0.005 to 5.0 percent by weight based on said
photoconductive composition of a pyrylium salt as a sensitizer
and
c. a film-forming polymeric binder for said photoconductor.
9. A photoconductive element for use in electrophotography
comprising a conducting support having coated thereon a
photoconductive composition comprising:
a. about 10 to 60 percent by weight based on said photoconductive
composition of 1-(p-diphenylamino-phenyl)-1-hydroxy-3-butyne,
b. about 0.005 to 5.0 percent by weight based on said
photoconductive composition of a pyrylium salt at a sensitizer
and
c. a film-forming polymeric binder for said photoconductor.
10. A photoconductive element for use in electrophotography
comprising a conducting support having coated thereon a
photoconductive composition comprising:
a. about 10 to 60 percent by weight based on said photoconductive
composition of 4-hydroxymethyltriphenylamine,
b. about 0.005 to 5.0 percent by weight based on said
photoconductive composition of a pyrylium salt as a sensitizer
and
c. a film-forming polymeric binder for said photoconductor.
11. A photoconductive element for use in electrophotography
comprising a conducting support having coated thereon a
photoconductive composition comprising:
a. about 10 to 60 percent by weight based on said photoconductive
composition of 1-(p-diphenylaminophenyl) ethanol,
b. about 0.005 to 5.0 percent by weight based on said
photoconductive composition of a pyrylium salt as a sensitizer
and
a film-forming polymeric binder for said photoconductor.
12. A photoconductive element for use in electrophotography
comprising a conducting support having coated thereon a
photoconductive composition comprising:
a. about 10 to 60 percent by weight based on said photoconductive
composition of p-diphenylaminobenzoic acid,
b. about 0.005 to 5.0 percent by weight based on said
photoconductive composition of a pyrylium salt as a sensitizer
and
c. a film-forming polymeric binder for said photoconductor.
13. The photoconductive element of claim 7 wherein the film-forming
polymeric binder is poly(vinyl meta-bromobenzoate-co-vinyl
acetate).
14. The photoconductive element of claim 8 wherein the film-forming
polymeric binder is poly(vinyl meta-bromobenzoate-co-vinyl
acetate).
15. The photoconductive element of claim 9 wherein the film-forming
polymeric binder is poly(vinyl meta-bromobenzoate-co-vinyl
acetate).
16. The photoconductive element of claim 10 wherein the
film-forming polymeric binder is poly(vinyl
meta-boromobenzoate-co-vinyl acetate).
17. The photoconductive element of claim 11 wherein the
film-forming polymeric binder is poly(vinyl
meta-bromobenzoate-co-vinyl acetate).
18. The photoconductive element of claim 12 wherein the
film-forming polymeric binder is poly(vinyl
meta-bromobenzoate-co-vinyl acetate).
Description
This invention relates to electrophotography, and in particular to
photoconductive compositions and elements.
The process of xerography, as disclosed by Carlson in U.S. Pat. No.
2,297,691, employs an electrophotographic element comprising a
support material bearing a coating of a normally insulating
material whose electrical resistance varies with the amount of
incident actinic radiation it receives during an imagewise
exposure. The element, commonly termed a photoconductive element,
is first given a uniform surface charge, generally in the dark
after a suitable period of dark adaptation. It is then exposed to a
pattern of actinic radiation which has the effect of differentially
reducing the potential of the surface charge in accordance with the
relative energy contained in various parts of the radiation
pattern. The differential surface charge or electrostatic latent
image remaining on the electrophotographic element is then made
visible by contacting the surface with a suitable electroscopic
marking material. Such marking material or toner, whether contained
in an insulating liquid or on a dry carrier, can be deposited on
the exposed surface in accordance with either the charge pattern or
the discharge pattern as desired. The deposited marking material
can then be either permanently fixed to the surface of the
sensitive element by known means such as heat, pressure, solvent
vapor, or the like, or transferred to a second element to which it
can be similarly be fixed. Likewise, the electrostatic latent image
can be transferred to a second element and developed there.
Various photoconductive insulating materials have been employed in
the manufacture of electrophotographic elements. For example,
vapors of selenium and vapors of selenium alloys deposited on a
suitable support and particles of photoconductive zinc oxide held
in a resinous, film-forming binder have found wide application in
present-day document copying applications.
Since the introduction of electrophotography, a great many organic
compounds have also been screened for their photoconductive
properties. As a result, a very large number of organic compounds
are known to possess some degree of photoconductivity. Many organic
compounds have revealed a useful level of photoconduction and have
been incorporated into photoconductive compositions. Optically
clear organic photoconductorcontaining elements having desirable
electrophotographic properties can be especially useful in
electrophotography. Such electrophotographic elements can be
exposed through a transparent base if desired, thereby providing
unusual flexibility in equipment design. Such compositions, when
coated as a film or layer on a suitable support also yield an
element which is reusable; that is, it can be used to form
subsequent images after residual toner from prior images has been
removed by transfer and/or cleaning. Thus far, the selection of
organic compounds for incorporation into photoconductive
compositions to form electrophotographic layers has proceeded on a
compound-by-compound basis. Nothing has yet been discovered from
the large number of different photoconductive substances tested
which permits effective prediction and therefore selection of
particular compounds exhibiting the desired electrophotographic
properties.
It is, therefore, an object of this invention to provide
photoconductive elements for use in electrophotography containing a
novel class of organic photoconductors having enhanced
photosensitivity when electrically charged.
It is also an object to provide electrophotographic elements having
a layer of a novel photoconductive composition which can be
positively or negatively charged.
It is another object to provide novel transparent
electrophotographic elements having high speed characteristics.
It is a further object of this invention to provide novel
electrophotographic elements useful for producing images
electrophotographically by reflex or bireflex processes.
These and other objects of this invention are accomplished with
electrophotographic elements having coated thereon organic
photoconductive compositions containing a triarylamine
photoconductor wherein at least one of the aryl radicals is
substituted by an active hydrogen-containing group and a sensitizer
for the photoconductor. Groups which contain active hydrogen are
well known in the art, the definition of this term being set forth
in several textbooks such as "Advanced Organic Chemistry," R. C.
Fuson, pp. 154-157, John Wiley & Sons, 1950. The term "active
hydrogen-containing group" as used herein includes those compounds
encompassed by the discussion in the textbook cited above and in
addition include those compounds which contain groups which are
hydrolyzable to active hydrogen-containing groups. Typical active
hydrogen-containing groups which are substituted on an aryl radical
of the triarylamine according to this invention include:
a. carboxy radicals;
b. hydroxy radicals;
c. ethynyl radicals including substituted ethynyl radicals such as
hydroxy ethynyl radicals, aryl ethynyl radicals and alkyl ethynyl
radicals;
e. lower alkylene hydroxy radicals (e.g., having one to eight
carbon atoms);
f. carboxylic acid anhydride radicals;
g. lower alkylene carboxy radicals (e.g., having two to eight
carbon atoms); ##SPC1##
k. semicarbazono radicals; and ##SPC2##
The preferred photoconductors of this invention are represented by
the following structure:
wherein:
a. Ar.sub.1 and Ar.sub.2 are each a phenyl radical including a
substituted phenyl radical such as a halophenyl radical, an alkyl
phenyl radical or an amino phenyl radical;
b. Ar.sub.3 is an arylene radical including a substituted arylene
radical such as a phenylene radical or a naphthylene radical;
and
c. X is an active hydrogen-containing group such as a carboxy
radical, and acyl halide radical, an amido radical, a carboxylic
acid anhydride radical, an ester radical, a cyano radical, a
semicarbazono radical, a hydroxy radical, an ethynyl radical, a
methylidyne oximido radical or a phenylene carboxy radical.
The organic photoconductors of this invention exhibit substantial
improvements in speed over comparable photoconductors which do not
have an active hydrogen-containing group (including groups
hydrolyzable to active hydrogen-containing groups). Also, those
compounds in which Ar.sub.1 and Ar.sub.2 in the above formula are
phenyl radicals generally have improved photoconducting properties
over those which are substituted by one or two alkyl radicals.
Thus, p-diphenylaminobenzoic acid generally displays higher
electrical speeds than p-diethylaminobenzoic acid of
p-N-methyl-N-phenylaminobenzoic acid.
Some typical photoconductors of this invention are:
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TABLE I
I methyl p-diphenylaminobenzoate, II N,N-diphenylanthranilic acid,
III 3-p-diphenylaminophenyl-1-propanol IV 4-acetyltriphenylamine
semicarbazone, V
ethyl-2,6-diphenyl-4-(p-diphenylaminophenyl)benzoate, VI
1-(p-diphenylaminophenyl)-1-hydroxy-3-butyne, VII
4-hydroxymethyltriphenylamine, VIII
1-(p-diphenylaminophenyl)ethanol, IX 4-hydroxytriphenylamine, X
2-hydroxytriphenylamine, XI 4-formyltriphenylamine oxime, XII
4-acetyltriphenylamine oxime, XIII
1-(p-diphenylaminophenyl)hexanol, XIV
1-(p-diphenylaminophenyl)dodeconal, XV p-diphenylaminobenzoic acid
anhydride, XVI 4-cyanotriphenylamine, XVII p-diphenylaminobenzoic
acid N,N-diphenylamide, XVIII p-diphenylaminobenzoic acid, XIX
p-diphenylaminobenzoyl chloride, 3-p-diphenylaminophenylpropionic
acid, and XXI 4-formyltriphenylamine semicarbazone.
__________________________________________________________________________
These compounds can be prepared by the methods set forth in a
copending application, Ser. No. 706,799 filed concurrently herewith
entitled "Novel Substituted Triarylamines."
Electrophotographic elements of the invention can be prepared with
these photoconducting compounds in the usual manner, i.e., by
blending a dispersion or solution of a photoconductive compound
together with a binder, when necessary or desirable, and coating or
forming a self-supporting layer with the photoconductor-containing
material. Mixtures of the photoconductors described herein can be
employed. Likewise, other photoconductors known in the art can be
combined with the present photoconductors. In addition,
supplemental materials useful for changing the spectral sensitivity
or electrophotosensitivity of the element can be added to the
composition of the element when it is desirable to produce the
characteristic effect of such materials.
Generally, the photoconducting compounds of this invention are not
sensitive to light unless a sensitizing compound is present. While
a wide variety of such substances impart spectral sensitivity to
the photoconductors of this invention, it has been found that
pyrylium salts, that is the pyrylium, thiapyrylium and
selenapyrylium salts of U.S. Pat. No. 3,250,615, are particularly
useful for sensitizing these compounds to the extent that they
exhibit relatively high electrical speeds compared to those
compounds which do not have an active hydrogen-containing group.
Other sensitizing compounds useful with the photoconductors of the
invention include fluorenes, such as
7,12-dioxo-13-dibenzo(a,h)-fluorene,
5,10-dioxo-4a,11diazodenzo(b)fluorene,
3,13-dioxo-7-oxadibenzo(b,g)fluorene, trinitrofluorenone,
tetranitroflurenone and the like; aromatic nitro compounds of U.S.
Pat. No. 2,610,120; anthrones of U.S. Pat. No. 2,670,285; quinones
of U.S. Pat. No. 2,670,286; benzophenones of U.S. Pat. No.
2,670,287; thiazoles of U.S. Pat. No. 2,732,301; mineral acids;
carboxylic acids, such as maleic acid, dichloroacetic acid, and
salicylic acid; sulfonic and phosphoric acids; and various dyes
such as triphenylmethane, diarylmethane, thiazine, azine, oxazine,
xanthene, phthalein, acridine, azo, anthraquinone dyes.
In preparing the photoconducting layers disclosed herein, it is
conventional practice to mix a suitable amount of the sensitizing
compounds with the coating composition so that, after thorough
mixing, the sensitizing compound is uniformly distributed
throughout the desired layer of the coated element. The amount of
sensitizer that can be added to a photoconductor-incorporating
layer to give effective increases in speed can vary widely. The
optimum concentration in any given case will vary with the specific
photoconductor and sensitizing compound used. In general,
substantial speed gains can be obtained where an appropriate
sensitizer is added in a concentration range from about 0.0001 to
about 30 percent by weight based on the weight of the film-forming
coating composition. Generally, a sensitizer is added to the
coating composition in an amount by weight from about 0.005 to
about 5.0 percent by weight of the total coating composition.
Preferred binders for use in preparing the present photoconductive
layers are film-forming polymeric binders having fairly high
dielectric strength which are good electrically insulating
film-forming vehicles. Materials of this type comprise
styrene-butadiene copolymers; silicone resins; styrene-alkyd
resins; silicone-alkyd resins; soya-alkyd resins; poly (vinyl
chloride); poly(vinylidene chloride); vinylidene
chloride-acrylonitrile copolymers; poly(vinyl acetate); vinyl
acetate-vinyl chloride copolymers; poly(vinyl acetals), such as
poly (vinyl butyral); polyacrylic and methacrylic esters, such as
poly(methylmethacrylate), poly(n-butylmethacrylate), poly (isobutyl
methacrylate), etc.; polystyrene; nitrated polystyrene;
polymethylstyrene; isobutylene polymers; polyesters, such as
poly(ethylenealkaryloxyalkylene terephthalate); phenol-formaldehyde
resins; ketone resins; polyamides; polycarbonates;
polythiocarbonates; poly(ethyleneglycol-co-bishydroxyethoxy phenyl
propane terephthalate); nuclear substituted vinyl haloarylates such
as poly(vinyl meta-bromobenzoate-co-vinyl acetate; etc. Methods of
making resins of this type have been described in the prior art,
for example, styrene-alkyd resins can be prepared according to the
method described in U.S. Pat. Nos. 2,361,019 and 2,258,423.
Suitable resins of the type contemplated for use in the
photoconductive layers of the invention are sold under such trade
names as Vitel PE-101, Cymac, Piccopale 100, Saran F-220 and Lexan
105. Other types of binders which can be used in the
photoconductive layers of the invention include such materials as
paraffin, mineral waxes, etc.
Solvents of choice for preparing coating compositions of the
present invention can include a number of solvents such as benzene,
toluene, acetone, 2-butanone, chlorinated hydrocarbons, e.g.,
methylene chloride, ethylene chloride, etc., ethers, e.g.,
tetrahydrofuran, or mixtures of these solvents, etc.
In preparing the coating composition useful results are obtained
where the photoconductor substance is present in an amount equal to
at least about 1 weight percent of the coating composition. The
upper limit in the amount of photoconductor substance present can
be widely varied in accordance with usual practice. In those cases
where a binder is employed, it is normally required that the
photoconductor substance be present in an amount from about 1
weight percent of the coating composition to about 99 weight
percent of the coating composition. A preferred weight range for
the photoconductor substance in the coating composition is from
about 10 weight percent to about 60 weight percent.
Coating thicknesses of the photoconductive composition on a support
can vary widely. Normally, a coating in the range of about 0.001
inch to about 0.01 inch before drying is useful for the practice of
this invention. The preferred range of coating thicknesses was
found to be in the range from about 0.002 inch to about 0.006 inch
before drying although useful results can be obtained outside of
this range.
Suitable supporting materials for coating the photoconductive
layers of the present invention can include any of a wide variety
of electrically conducting supports, for example, paper (at a
relative humidity above 20 percent); aluminum-paper laminates;
metal foils such as aluminum foil, zinc foil, etc.; metal plates,
such as aluminum, copper, zinc, brass, and galvanized plates; vapor
deposited metal layers such as silver, nickel, or aluminum and the
like. Metal (e.g., nickel, etc.) conducting layers deposited by
high vacuum deposition techniques can be coated at low coverages so
as to be substantially transparent to facilitate image exposure
through the support. An especially useful conducting support can be
prepared by coating a support material such as polyethylene
terephthalate with a layer containing a semiconductor dispersed in
a resin. Suitable conducting layers both with and without
insulating barrier layers are described in U.S. Pat. No. 3,245,833.
Other suitable conducting layers are described in U.S. Pat. No.
3,120,028. Likewise, a suitable conducting coating can be prepared
from the sodium salt of a carboxyester lactone of maleic anhydride
and a vinyl acetate polymer. Such kinds of conducting layers and
methods for their optimum preparation and use are disclosed in U.S.
Pat. Nos. 3,007,901 and 3,267,807.
The elements of the present invention can be employed in any of the
well-known electrophotographic processes which require
photoconductive layers. One such process is the aforementioned
xerographic process. As previously explained, in a process of this
type the electrophotographic element is given a blanket
electrostatic charge by placing the same under a corona discharge
which serves to give a uniform charge to the surface of the
photoconductive layer. This charge is retained by the layer owing
to the substantial insulating property of the layer, i.e., the low
conductivity of the layer in the dark. The electrostatic charge
formed on the surface of the photoconducting layer is then
selectively dissipated from the surface of the layer by exposure to
light through an image-bearing transparency by a conventional
exposure operation such as, for example, by contact-printing
technique, or by lens projection of an image, etc., to form a
latent image in the photoconducting layer. By exposure of the
surface in this manner, a charge pattern is created by virtue of
the fact that light causes the charge to be conducted away in
proportion to the intensity of the illumination in a particular
area. The charge pattern remaining after exposure is then
developed, i.e., rendered visible, by treatment with a medium
comprising electrostatically attractable particles having optical
density. The developing electrostatically attractable particles can
be in the form of a dust, e.g., powder, pigment in a resinous
carrier, i.e., toner, or a liquid developer may be used in which
the developing particles are carried in an electrically insulating
liquid carrier. Methods of development of this type are widely
known and have been described in the patent literature in such
patents, for example, as U.S. Pat. No. 2,297,691 and in Australian
Pat. No. 212,315. In processes of electrophotographic reproduction
such as in xerography, by selecting a developing particle which has
as one of its components, a low-melting resin, it is possible to
treat the developed photoconductive material with heat to cause the
powder to adhere permanently to the surface of the photoconductive
layer. In other cases, a transfer of the image formed on the
photoconductive layer can be made to a second support, which would
then become the final print. Techniques of the type indicated are
well known in the art and have been described in a number of U.S.
and foreign patents, such as U.S. Pat. Nos. 2,297,691 and
2,551,582, and in "RCA Review," vol. 15 (1954), page 469-484.
The present invention is not limited to any particular mode of use
of the new electrophotographic materials, and the exposure
technique, the charging method, the transfer (if any), the
developing method, and the fixing method as well as the materials
used in these methods can be selected and adapted to the
requirements of any particular technique.
Electrophotographic materials according to the present invention
can be applied to reproduction techniques wherein different kinds
of radiations, i.e., electromagnetic radiations as well as nuclear
radiations, can be used. For this reason, it is pointed out herein
that although materials according to the invention are mainly
intended for use in connection with methods comprising an exposure,
the term "electrophotography" wherever appearing in the description
and the claims, is to be interpreted broadly and understood to
comprise both xerography and xeroradiography.
The following examples are included for a further understanding of
the invention.
EXAMPLE 1
Organic photoconductors of the type described herein are separately
incorporated into a coating dope having the following
composition:
Organic photoconductor 0.5 g. Polymeric binder 1.5 g. Sensitizer
0.02 g. Methylene chloride 11.7 ml.
The resulting compositions are handcoated at a wet thickness of
0.004 inch on a conducting layer comprising the sodium salt of a
carboxyester lactone, such as described in U.S. Pat. No. 3,120,028
which in turn is coated on a cellulose acetate film base. The
coating blocks are maintained at a temperature of 90.degree. F.
These electrophotographic elements are charged under a positive or
negative corona source until the surface potentials, as measured by
an electrometer probe, reach between about 500 and 600 volts. They
are then subjected to exposure from behind a stepped density gray
scale to a 3,000.degree. K. tungsten source. The exposure causes
reduction of the surface potentials of the elements under each step
of the gray scale from their initial potential V.sub.o, to some
lower potential V, whose exact value depends on the actual amount
of exposure in meter-candle-seconds received by the areas. The
results of the measurements are plotted on a graph of surface
potential V vs. log exposure for each step. The speed is the
numerical expression of 10.sup.4 multiplied by the reciprocal of
the exposure in meter-candle-seconds required to reduce the 500 to
600 volt charged surface potentials to 100 volts above 0 volts. The
reduction of the surface potential to 100 volts or below is
significant in that it represents a requirement for suitable broad
area development of a latent image. This speed at 100 volts is a
measure of the ability to produce and henceforth to develop or
otherwise utilize the latent image, higher speeds requiring less
illumination to produce a latent image. When the photoconductor is
absent from the coating, the surface potential does not drop to or
below 100 volts and no speed value can be assigned. This is also
the case when a compound is present in the composition but is
ineffective as a photoconductor. The sensitizers used are referred
to below as follows:
A -- no sensitizer added
C -- 2,4,7-trinitrofluorenone
D -- crystal violet
E -- rhodamine B
F ' 2,4-bis(4-ethyoxyphenyl)-6-(4-n-amyloxystyryl)-pyrylium
fluoborate
H -- 2,6-bis(4-ethyoxyphenyl)-4-(4-n-amyloxyphenyl)-thiapyrylium
perchlorate
The data in the following Table II represents the positive speeds
at 100 volts of various compositions prepared as described above
containing some of the organic photoconductors set forth in Table
I. Included for comparison purposes is triphenylamine which has no
active hydrogen-containing group. In each case it is noted that the
photoconductive compounds of this invention show substantial
improvements in speed compared to triphenylamine. The binder
employed is poly(vinyl meta-bromobenzoate-co-vinyl acetate).
TABLE II
Speed at 100 Volts for Sensitizer Photoconductor F H V 160 200 VII
200 130 IX 200 120 Triphenylamine 123 103
EXAMPLE 2
Example 1 is repeated except the photoconductive coating has the
following composition:
Organic photoconductor: p-diphenylaminobenzoic acid 1.0 g. Binder
poly(vinyl meta-bromobenzoate-co-vinyl-acetate) acetate) 1.0 g.
Sensitizer F 0.02 g. Methylene chloride 11.7 ml.
The 100 volt positive speed is 250. When the organic photoconductor
is replaced by triphenylamine, the 100 volt positive speed is
71.
EXAMPLE 3
In order to show the ineffectiveness of sensitizing compounds other
than the pyrylium, thiapyrylium and selena-pyrylium salts, Example
1 is repeated using the following composition:
Photoconductor: p-diphenylaminobenzoic acid 0.15 g. Binder: Vitel
101* 0.50 g. Sensitizer (see Table III) 0.002 g. Dichloromethane
5.0 ml. * A polyester of terephthalic acid and a mixture of
ethylene glycol (1 part by weight) and
2,2-bis[4-(.beta.-hydroxyethoxy)p henyl] propane (9 parts by
weight).
The 100 volt positive speeds are set forth in Table III. It is
apparent that while some of these sensitizers impart light
sensitivity to the organic photoconductor, the speed is so trivial
as to have no practical effect.
TABLE III
Sensitizer 100 Volt Positive Speed A 0 C 5 D 0 E 8
EXAMPLE 4
Coating dopes prepared in the manner set forth in Example 1
containing the compounds in Table I are coated in the manner
described in Example 1. In a darkened room, the surface of each of
the photoconductive layers so prepared is charged to a potential of
about +600 volts under a corona charger. The layer is then covered
with a transparent sheet bearing a pattern of opaque and light
transmitting areas and exposed to the radiation from an
incandescent lamp with an illumination intensity of about 75
meter-candles for 12 seconds. The resulting electrostatic latent
image is developed by conventional electrophotographic liquid
developers (e.g., U.S. Pat. No. 2,907,674) and also by cascading
over the surface of the layer a mixture of negatively charged black
thermoplastic toner particles and glass beads. A good reproduction
of the pattern results in each instance.
The invention has been described in detail with particular
reference to preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention as described hereinbefore and
as defined in the appended claims.
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