Note: Descriptions are shown in the official language in which they were submitted.
1~45879
Field of the Invention
This invention relates to electrophotography and in
particular to photoconductive compositions and elements.
Description of the Prior Art
The process of xerography, as disclosed by Carlson in
U.S. Patent No. 2,297,691, employs an electrophotographic element
comprising a support material bearing a coating of an insulating
material whose electrical resistance varies with the amount of
incident electromagnetic radiation it receives during an image- -
wise 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 adaptàtion. It is then
exposed to a pattern of actinic radiation which has the effect
of differentially reducing the potential of this 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
` e~ement is then made visible by contacting the surface with a
i suitable electroscopic marking material. Such marking material
`, 20 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 discharge pattern as desired. ; -
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 similarly be fixed. Likewise,
the electrostatic charge pattern 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
-2- ~
- :~,
' ~
1~45879
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 processes.
Since the introduction of electrophotography, a great
many organic compounds have also been screened for their photo-
conductive properties. As a result, a very large number of or-
ganic compounds have been known to possess some degree of photo-
conductivity. Many organic compounds have revealed a useful level
of photoconduction and have been incorporated into photocon-
ductive compositions. Among these organic photoconductors arethe triphenylamines as described in U.S. 3,18D,730 issued ~pril
27, 1965, and other aromatic ring compounds such as those des-
cribed in British Patent 944,326 dated December 11, 1963; U.S.
3,549,358 issued December 22, 1970 and U.S. 3,653,887 issued
April 4, 1972.
Opticallv clear organic photoconductor-containing
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 flexibility in equipment design. Such composi-
tions, 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 various compounds for incorporation into photoconductive com-
positions to form electrophotographic layers has proceeded on a
compound-by-compound basis. Nothing as yet has been discovered
from the large number of different photoconductive substances
tested which permits effective prediction, and therefore selec-
tion of the particular compounds exhibiting the desired electro-
photographic proper~ies.
. ~'. ~' ' .
~'~
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. . - . .
1q~45879
A high speed "heterogeneous" or "aggregate" multiphase
photoconductive system was developed by William A. Light which
overcomes many of the problems of the prior art. This aggregate
photoconductive composition (as it is referred to hereinafter) is
the subject matter of U.S. Patent No. 3,615,414 issued October
26, 1971 and is also described in Gramza et. al. U.S. 3,732,180
issued May 8, 1973. The addenda disclosed therein are responsible
for the exhibition of desirable electrophotographic properties
in photoconductive elements prepared therewith. In particular,
they have been found to enhance the speed of many organic photo-
conductors when used therewith. The degree of such enhancement
is, however, variable, depending on the particular organic
photoconductor so used.
Summary of the Invention
In accord with the present invention there is provided
; an "aggregate" photoconductive composition containing at least
two different organic photosensitive components in solid sol-
ution with the continuous phase of the multiphase aggregate
composition, one of said components being a non-blue light
absorbing organic photoconductor and one of said components being
an amount within the range of from about 0.1 to less than about
15 weight percent based on the dry weight of said composition ;~
of a compound having a central carbocyclic or sulfur hetero-
cyclic divalent aromatic ring joined to two amino-substituted
styryl radicals through the vinylene groups of the styryl radicals.
The improved aggregate photoconductive compositions
of the present invention offer a number of advantages. Among
others, it has been noted that these compositions provide
especially useful reusable photoconductive compositions because
of their ability to resist electrical fatigue upon being sub-
jected to a large number of repetitive electrophotographic
imaging cycles.
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1~4S879
In addition, the improved aggregate photoconductive
compositions of the invention offer an unexpected enhancement
in blue light sensitivity.
Moreover, it has also been found that aggregate
photoconductive compositions containing the distyryl-containing
aromatic compounds used in the present invention exhibit improved
temperature stability. Accordingly, the improved aggregate
photoconductive compositions of the invention containing these
compounds are useful over a wider range of operating temperatures.
In addition, it has been found that the above
- advantages provided by the improved aggregate photoconductive
compositions of the present invention are generally obtained
without any substantial deleterious effect on the totality of
electrophotographic properties which cooperate to produce a
useful photoconductive composition.
Description of the Preferred Embodiments -
` The term "non-blue light absorbing organic photocon- -
ductor" as used herein is defined as a photoconductor which ex-
hibits little or no light absorption in the spectral range ex- ~
tending from about 400 to 500 nm. Such photoconductors are ~-
typically transparent to visible light and therefore colorless;
or if colored, these materials are a color other than yellow, a
` yellow coloration of course, indicating that blue light is being
absorbed. Visible light is defined herein as radiation within -
the 400-700 nm. region of the spectrum.
The precise mechanism`(s) occurring in the improved
aggregate photoconductive compositions of the invention has not
been conclusively established and therefore the present invention
should not be limited by any specific theory. However, a number
of observations have been made relating to the photoconductive
compositions of the invention and are presente~ herein to provide
a better understanding of the invention.
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In the first place, the photoconductive mechanism(s)
which is believed to occur in the improved aggregate photo-
conductive compositions of the invention is considered to be
different than that which normally occurs in conventional
"homogeneous" organic photoconductive compositions. Such
homogeneous compositions consist of an organic photoconductor
such as a triphenylamine compound in solid solution with a
polymeric binder. Typically, a sensitizer is also present in
the composition. Photoconduction is believed to occur in a
uniformly electrostatically charged homogeneous photoconductive - ;
composition as a result of exposure to radiation of the type to
which the organic photoconductor is intrinsically sensitive (or
to which the organic photoconductor is made sensitive by the
addition of a sensitizer), thereby causing the generation of
charge carriers within the organic photoconductor. These charge ~
carriers are then transported through the photoconductive ~;
~` composition to a conductive layer where they are dissipated.
In the improved aggregate photoconductive compositions -
of the present invention charge carriers are believed to be
generated in the photoconductive composition from within the
particles of "aggregate" material contained therein. These
particles of aggregate material are generally composed of a co-
`~1 crystalline complex of an organic sensitizing dye, such as a
pyrylium type dye, and a polymeric material, such as a
polycarbonate, and are visible within the photoconductive
composition with the aid of a microscope. These aggregate
particles are thus dispersed as a discontinuous phase in the
photoconductive composition and are not in a solid solution with
the remainder of the composition. (Further detail relating to
the preparation and composition of these "aggregate" particlesis set forth hereinafter.)
. ' .
~.
: ~, ~ : , . . . . :
1~45879
In accord with the invention one or more non-blue
light absorbing organic photoconductor(s) is incorporated in
solid solution with the continuous phase of the aggregate
photoconductive composition of the invention. These materials
may aid the above-described aggregate particles in the formation
of charge carriers, and it is also believed that the organic
photoconductor(s) plays a primary role in the transport of the
charge carriers through the aggregate photoconductive composition.
It has been shown, for example, that the photoconductivity, i.e.
electrophotographic speed, of the compositions of the invention
when exposed to a white light source is significantly increased
by the addition of the organic photoconductor~s~. Without the
incorporation of one or more organic photoconductors, the white
light speed of the composition is so low that the compositions
of the present invention are unacceptable for use in conventional
office copier applications.
The distyryl-containing aromatic compound contained in
the aggregate photoconductive composition of the invention is
used as a "fatigue reducer" and as a "temperature stabilizer". ~
For example, the improved aggregate compositions of the invention ~ -
exhibit substantial improvement in resistance to electrical
fatigue even when sub~ected to a large number of repetitive
imaging cycles at relatively high ambient temperature
conditions. In addition, although these distyryl-containing
aromatic compounds are known to possess photoconductive
properties (as described in the cross-referenced Contois and ~ ;
Rossi Canadian patent application Serial No. 197,318, entitled
"Photoconductive Composition and Elements Containing Same" filed
April 10, 1974), these compounds are believed to act as a
blue light sensitizer in the compositions of the present invention.
That is, these compounds appear to absorb blue light and then,
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1q~45879
through some type of chemical, electronic or combined chemical-
electronic mechanism, intimately interact with the aggregate
particles to generate charge carriers.
The precise reason(s) that the distyryl-containing
; aromatic compounds act as a blue sensitizer in the photocon-
ductive composition of the invention are not completely under-
stood. Although these distyryl-containing compounds do possess
photoconductive properties and exhibit blue light absorption,
these factors alone do not account for the enhanced blue sensi-
tivity of the aggregate photoconductive compositions of the
invention. This is readily demonstrated by the fact that certain -
known nitro-substituted triphenylamine photoconductors which
also exhibit blue light absorption, such as compounds similar to
the nitro-substituted triarylamines shown in U.S. Patent 3,180,730
do not provide the above-described blue sensitization effect
when substituted for the distyryl-containing compounds incorpo-
rated in the photoconductive compositions of the invention.
Similarly, the precise reason(s) that the distyryl-
containing aromatic compounds improve the temperature stability
" 20 and act as a fatigue reducer in the aggregate photoconductive
composition of the invention is also not fully understood.
However, here again it is known that molecularly much simpler
nitro-substituted triphenylamine photoconductive compounds sim-
ilar to those shown in U.S. 3,180,730 do not provide these
advantages when substituted for the distyryl-containing aromatic
compounds used in the aggregate-containing photoconductive
compositions of the type described above.
The preferred distyryl-containing aromatic compounds
used in the invention may be characterized by the following ;
formul~a:
1~ N-Arl-CH=CH-Ar2-CH=CH-Ar3-N < 3
2 4
-8-
.
. . ~ . . . .
- .
1¢~45879
The preferred distyryl-containing aromatic compounds
used in the invention may be characterized by the following
formula:
l~N-Arl-CH=CH-Ar2-CH=CH-Ar3-N < 3
2 4
wherein
Rl, R2, R3, and R4, which can be the same or different,
represent alkyl or aryl radicals including substituted alkyl and
aryl radicals;
Arl and Ar3, which can be the same or different,
represent an unsubstituted or a substituted phenyl radical having
one or more substituents selected from the group consisting of
an alkyl, aryl, alkoxy, aryloxy, and halogen substituent; and
Ar2 represents a carbocylic or sulfur heterocyclic,
mononuclear or polynuclear, aromatic ring typically containing
~; 4 to 14 carbon atoms in the ring such as phenyl, naphthyl and
anthryl aromatic groups as well as substituted aromatic groups
having one or more substituents selected from the group of
substituents defined above as substituents for Arl and Ar3.
Y' 1~ R2, R3, and R4 represent one of the
following alkyl or aryl groups:
1. an alkyl group having one to 18 carbon atoms
e.g., methyl, ethyl, propyl, butyl, isobutyl, octyl, dodecyl, etc.
including a substituted alkyl group having one to 18 carbons
atoms such as
a. alkoxyalkyl e.g., ethoxypropyl, methoxybutyl,
propoxymethyl, etc.,
- b. aryloxyalkyl e.g., phenoxyethyl, naphthoxymethyl,
phenoxypentyl, etc., ~
c. aminoalkyl, e.g., aminobutyl, aminoethyl, ~-
aminopropyl, etc., ~
. 1 . '
_g_ ':
.~ .~
1~45879
d. hydroxyalkyl e.g., hydroxypropyl, hydroxyoctyl,
etc.,
e. aralkyl e.g., benzyl, phenethyl, etc.,
f. alkylaminoalkyl e.g., methylaminopropyl, methylamino-
ethyl, etc., and also including dialkylaminoalkyl
e.g., diethylaminoethyl, dimethylaminopropyl,
propyl-aminooctyl, etc.,
g. arylaminoalkyl, e.g., phenylaminoalkyl, diphenyl-
aminoalkyl, N-phenyl-N-ethylaminopentyl, N-phenyl-N
-ethylaminohexyl, naphthylaminomethyl, etc.,
h. nitroalkyl, e.g., nitrobutyl, nitroethyl, nitro-
pentyl, etc.,
i. cyanoalkyl, e.-g., cyanopropyl, cyanobutyl, cyano-
j ethyl, etc., and
j. haloalkyl, e.g., chloromethyl, bromopentyl, chloro-
`~ octyl, etc.,
k. alkyl substituted with an acyl group having the
formula
:. ~ O
-C-R
wherein R is hydroxy, hydrogen, aryl, e.g., phenyl, napthyl,
etc., lower alkyl having one to eight carbon atoms e.g., methyl,
ethyl, propyl, etc., amino including substituted amino, e.g.,
diloweralkylamino, lower alkoxy having one to eight carbon
` atoms, e.g., butoxy, methoxy, etc., aryloxy, e.g., phenoxy,
-I naphthoxy, etc; or
2. an aryl group, e.g., phenyl, naphthyl, anthryl,
fluorenyl, etc., including a substituted aryl group such as ~ ~ -
a. alkoxyaryl, e.g., ethoxyphenyl, methoxyphenyl,
propoxynaphthyl, etc.,
':
' , .'' :
'~, ,, ., :
'` ' . : . '' , ~ " ~ ' . ' '
1~45879
b. aryloxyaryl, e.g., phenoxyphenyl, naphthoxyphenyl,
phenoxynaphthyl, etc.,
c. aminoaryl, e.g. aminophenyl, aminonaphthyl,
aminoanthryl, etc.,
d. hydroxyaryl, e.g., hydroxyphenyl, hydroxynaphthyl,
hydroxyanthryl, etc.,
e. biphenylyl,
f. alkylaminoaryl, e.g., methylaminophenyl, methylamino-
naphthyl, etc. and also including dialkylaminoaryl,
; 10 e.g. diethylaminophenyl, dipropylaminophenyl, etc.
g. arylaminoaryl, e.g., phenylaminophenyl, diphenyl-
aminophenyl, N-phenyl-N-ethylaminophenyl, naphthyl-
aminophenyl, etc.,
; h. nitroaryl e.g., nitrophenyl, nitronaphthyl,
nitroanthryl, etc.,
i. cyanoaryl, e.g., cyanophenyl, cyanonaphthyl,
.
cyanoanthryl, etc.,
- j. haloaryl, e.g., chlorophenyl, bromophenyl,
chloronaphthyl, etc.,
k. alkaryl, e.g., tolyl, ethylphenyl, propylnaphthyl,
etc., and
` 1. aryl substituted with an acyl group having the ~ -
formula
;~
-C-R
wherein R is hydroxy, hydrogen, aryl, e.g., phenyl, naphthyl,
.; .
etc., amino including substituted amino, e.g., diloweralkylamino,
lower alkoxy having one to eight carbon atoms, e.g., butoxy,
methoxy, etc., aryloxy, e.g., phenoxy,;naphthoxy,etc., lower
alkyl having one to eight carbon atoms, e.g., methyl, ethyl,
propyl, butyl, etc. ~-;
"',,"
i -11- - -
. ~ . . .
1~45879
Typically, when either Arl or Ar3 represent a
substituted phenyl radical the substituents on the phenyl
radical are alkyl or aryl groups as defined above for Rl, R2,
R3, R4 or also any of the following:
1. an alkoxy group having one to 18 carbon atoms, e.g.,
methoxy, ethoxy, propoxy, butoxy, etc.,
2. an aryloxy group e.g., phenoxy, naphthoxy, etc.; `
and
3. halogen such as chlorine, bromine, fluorine or
iodine.
Typical compounds which belong to the general class
or distyryl-containing aromatic compounds described herein
include the following materials listed in Table I below:
;' .~:.
'
, ................. .
1¢~45879 ~ ~
~, : :
o
o o o o
.,1 ~ o ~ a)
o ~ ~ ~ o
P~ ~ N C~ ~1
~D ~ ~
~ O ~ ~ O
rl ~ ~ ~ ~
. .
I
~ O
O tJ~ rl ~1
J,~ ~ N ~1
~ a) :.
R : ~
m ~
R
~ ~ Z - Z
P
`11 ' ~ ` s c~ c
:.~ ~ y ~r 11 ~ ~ :: ~
T ~ ~ ~ ~ ~ ~ Iz z
~ R ~ ~1 ~ 0 :
:
-I I _l rl I 'I ~ m m
~1 o ~r o ~ ~r o ~1 ~ C~ ~
m ~ U~ m
m m
c~ Q, S, c~ c~
m I ~ m I ~ ... ~ - .
; ~rl mrl ~ c~ c~ ~1
' a 'D ~ O Q, ~ ~ ~, a s ~ .
H H H
-- H ~-I H
-- H _ ..
:
--13--
.~ - . .. . -.
:.
1q~45879
C~
~ o o o
O U~ O ~D
~1 a~ o
~ l l
~ ~ ) ~r
.,, ~ CO o
. ~ Q
_I
:.
tn
~1 _I
~ ~ o
~ ,~,
_ O
. ~ ~ er ~C
.,, ~ ~9
~ ~ m ,~ ~
o ~
C~ o ~ s ~.
~ ~: Z
m
s m~ m
m~
m
~ C~
z z _1 1I m I I I
oc ~ 3 ,Z 1~
:~ m ,~
' _l o c~ ~ ~ z z
'' o a~ ' _
m m~ m~ m ~ Z
~ o ~) ~ I m/
a ~ ~ _l I I ~ ~ c~
I ~ m
-
:> H H. H
-- ~ HH
~,
--14--
;
:;
1~4S879
Compounds which belong to the general class of
distyryl-containing aromatic compounds described herein and which
are preferred for use in accord with the present invention include
those compounds having the structural formula shown above wherein
Arl, Ar2 and Ar3 are unsubstituted phenyl radicals or alkyl
substituted phenyl radicals having no more than two alkyl
substituents, said alkyl substituents containing 1 or 2 carbon
atoms. These compounds are preferred because aggregate
compositions containing the same exhibit increased blue
sensitivity and may also exhibit improved resistance to electrical
fatigue and improved temperature stability.
The aggregate compositions used in this invention
comprise an organic sensitizing dye and an electrically insulat-
ing, film-forming polymeric material. They may be prepared by
several techni~ues such as, for example, the so-called "dye
first" technique described in Gramza et. al., U.S. Patent No.
3,615,396 issued October 26, 1971. Alternatively, they may be
prepared by the so-called "shearing" method described in
Gramza, U.S. 3,615,415 issued October 26, 1971. This latter
method involves the high speed shearing of the photoconductive
composition prior to coating and thus eliminates subsequent
solvent treatment, as was disclosed in Light, U.S. 3,615,414 ~ -
referred to above. By whatever method prepared, the aggregate
composition is combined with the above-described disty~yl-
containing compounds and one or more organic photoconductors ;
in a suitable solvent to form an organic photoconductor-con-
taining composition which is coated on a suitable support to
form a separately identifiable multiphase composition, the
heterogeneous nature of which is generally apparent when viewed
under magnification although such compositions may appear to
be substantially optically clear to the naked eye in the absence
of magnification. There can, of course, be macroscopic
~; 5 : "
"
: - : . . : : .: , :
- . . : . :, :, ., ., ,.. .. . ~ . .
1~4S879
heterogeneity. Suitably, the dye-containing aggregate in the
discontinuous phase is predominantly in the size range of from
about 0.01 to about 25 microns.
In general, the aggregate compositions formed as
described herein are multiphase organic solids containing dye
and polymer. The polymer forms an amorphous matrix or
continuous phase which contains a discrete discontinuous phase -
as distinguished from a solution. The discontinuous phase is
the aggregate species which is a co-crystalline complex com-
prised of dye and polymer.
The term co-crystalline complex as used herein has
reference to a crystalline compound which contains dye and
polymer molecules co-crystallized in a single crystalline
structure to form a regular array of the molecules in a three-
dimensional pattern.
Another feature characteristic of the aggregate `
compositions formed as described herein is that the wavelength
of the radiation absorption maximum characteristic of such
compositions is substantially shifted from the wavelength of
the radiation absorption maximum of a substantially homogeneous
dye-polymer solid solution formed of similar constituents.
The new absorption maximum characteristic of the aggregates
formed by this method is not necessarily an overall maximum
for this system as this will depend upon the relative amount
of dye in the aggregate. Such an absorption maximum shift
in the formation of aggregate systems for the present in-
vention is generally of the magnitude of at least about 10 nm.
If mixtures of dyes are used, one dye may cause an absorption
maximum shift to a long wavelength and another dye cause an
absorption maximum shift to a shorter wavelength. In such
cases, a formation of the aggregate compositions can more easily
be identified by viewing under magnification.
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Sensitizing dyes and electrically insulating polymeric
materials are used in forming these aggregate compositions.
Typically, pyrylium dyes, including pyrylium, bispyrylium,
- thiapyrylium and selenapyrylium dye salts and also salts of
pyrylium compounds containing condensed ring systems such as
salts of benzopyrylium and naphthopyrylium dyes are useful in
forming such compositions. Dyes from these classes which may
be useful are disclosed in Light U.S. Patent No. 3,615,414.
Particularly useful dyes in forming the feature
aggregates are pyrylium dye salts having the formula~
R
R5 R6
wherein:
R5 and R6 can each be phenyl radicals, including
substituted phenyl radicals having at least one substituent
chosen from alkyl radicals of from 1 to about 6 carbon atoms
and alkoxy radicals having from l to about 6 carbon atoms;
R7 can be alkylamino-substituted phenyl radical having
from l to 6 carbon atoms in the alkyl moiety, and including
dialkylamino-substituted and haloalkylamino-substituted phenyl
radicals;
X can be an oxygen or a suIfur atom; and
Z~ is an anion.
The pol!ymers useful in forming the aggregate comp-
positions include a variety of materials. Particularly useful
are electrically insulating, fllm-forming polymers having an
alkylidene diarylene moiety in a recurring unit such as those
linear polymers, including copolymers, containing the following
moiety in a recurring unit:
' :'.
. - .
-
; ~ ; . , .: .:, . . ~.. . ..
~45~379
R8 Rg 11
C--`/~ R
wherein:
Rg and Rlo, when taken separately, can each be a
hydrogen atom, an alkyl radical having from one to about 10 car-
bon atoms such as methyl, ethyl, isobutyl, hexyl, heptyl, octyl,
nonyl, decyl, and the like including substituted alkyl radicals
such as trifluoromethyl, etc., and an aryl radical such as phenyl
and naphthyl, including substituted aryl radicals having such sub-
stituents as a halogen atom, an alkyl radical of from 1 to about
5 carbon atoms, etc.; and Rg and Rlo, when taken together, can
represent the carbon atoms necessary to complete a saturated
; cyclic hydrocarbon radical including cycloalkanes such as cyclo-
hexyl and polycycloalkanes such as norbornyl, the total number
of carbon atoms in Rg and Rlo being up to about 19;
R8 and Rll can each be hydrogen, an alkyl radical of
from 1 to about 5 carbon atoms, e.g~, or a halogen such as
chloro, bromo, iodo, etc.; and
R12 is a divalent radical selected from the following:
O S O O O CH
" " " " " ,3
-O-C-, -O-C-O-, -C-O-, -C-O-CH2-, -C-O-CH-,
O O
-CH2-O-C-O-, ~nd -O-P-O-
,: .
Preferred polymers useful for forming aggregate
crystals are hydrophobic carbonate polymers containing the
-18-
1~45879
following moiety in a recurring unit:
.
Rg O
..
-R-C-R-O-C-O-
' ~10
wherein:
each R is a phenylene radical including halo sub-
stituted phenylene radicals and alkyl substituted phenylene
radicals; and Rg and Rlo areas described above. Such compo-
sitions are disclosed, for example in U.S.Patent Nos.
3,028,365 and 3,317,466. Preferably polycarbonates containing
an alkylidene diarylene moiety in the recurring unit such as
those prepared with Bisphenol A and including polymeric
products of ester exchange between diphenylcarbonate and
~ 2,2-bis-(4-hydroxyphenyl) propane are useful in the practice
`~ of this invention. Such compositions are disclosed in the
following U.S. Patents: U.S. 2,999,750 by Miller et al, issued
September 12, 1961; 3,038,874 by Laakso et al, issued June 12,
1962; 3,038,879 by Laakso et al, issued June 12, 1962;
3,038,880 by Laakso et al, issued June 12, 1962; 3,106,544
by Laakso et al, issued October 8, 1963; 3,106,545 by Laakso
et al, issued October 8, 1963; and 3,106,546 by Laakso et al,
issued October 8, 1963. A wide range of film-forming poly-
carbonate resins are useful, with completely satisfactory
results being obtained when using commercial polymeric materials
.. . .
- which are characterized by an inherent viscosity of about 0.5
to about 1.8.
The following polymers are included among the -
materials useful in the practice of this invention:
~' .
~ ~ ,
-19-
' .', :
1'&45879
Table 2
No.Polymeric Material
1 poly(4,4'-isopropylidenediphenylene-co-
1,4-cyclohexanylenedimethylene carbonate)
2 poly(ethylenedioxy-3,3'-phenylene
thiocarbonate)
3 poly(4,4'-isopropylidenediphenylene
carbonate-co-terephthalate)
4 poly(4,4'-isopropylidenediphenylene
carbonate)
poly(4,4'-isopropylidenediphenylene
thiocarbonate)
6 poly(4,4'-sec-butylidenediphenylene
carbonate)
-- 7poly(4,4'-isopropylidenediphenylene '5
carbonate-block-oxyethylene)
8poly(4,4'-isopropylidenediphenylene
carbonate-block-oxytetramethylene)
9poly[4,4'-isopropylidenebis(2-methyl-
phenylene)-carbonate]
10 poly(4,4'-isopropylidenediphenylene-co-
1,4-phenylene carbonate)
11 poly(4,4'-isopropylidenediphenylene-co-
1,3-phenylene carbonate)
12 poly(4,4'-isopropylidenediphenylene-co-
4,4'-diphenylene carbonate)
13 poly(4,4'-isopropylidenediphenylene-co-
4,4'-oxydiphenylene carbonate)
:: 14 poly(4,4'-isopropylidenediphenylene-co-
4,4'-carbonyldiphenylene carbonate)
15 poly(4,4'-isopropylidenediphenylene-co- :
4,4'-ethylenediphenylene carbonate
16 poly[4,4'-methylenebis(2-methyl-
phenylene)carbonate] ~:
17 poly[l,l ~(p-bromophenylethylidene)bis(1,4-
phenylene)carbonate]
18 polyl4,4'-isopropylidenediphenylene-co-
4,4'-sulfonyldiphenylene) carbonat~r
19poly[4,4'-cyclohexanylidene(4-diphenylene)
carbonate]
.~ :
~' .
-20-
1~45879
Table 2 (contlnued) ;
No. Polymeric Material
-
poly~4,4'-isopropylidenebis(2-chlorophenylene)
carbonate]
21 poly(4,4'-hexafluoroisopropylidenediphenyl- :
ene carbonate)
22 poly(4,4'-isopropylidenediphenylene 4,4'-
isopropylidenedibenzoate)
23 polyt4,4'-isopropylidenedibenzyl 4,4'- :
isopropylidenedibenzoate)
24 poly[4,4'-(1,2-dimethylpropylidene)di-
phenylene carbonate]
poly [4,4'-(1,2,2-trimethylpropylidene)-
diphenylene carbonate]
26 poly{4,4'-[1-(~-naphthy~)ethylidene]-
diphenylene carbonate~
27 poly[4,4'-(1,3-dimethylbutylidene)-
. diphenylene carbonate]
; 28 poly[4,4'-2-norbornylidene)diphenylene
carbonate]
29 poly[4,4'-(hexahydro-4,7-methanoindan-5-
ylidene) diphenylene carbonate]
.~ . .
~ : ~
~' ' .
. ~.
,
.
: ~ .:
.
.
~: . . .
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1~45879
Electrophotographic elements of ~he invention con-
taining the above-described aggregate photoconductive
composition can be prepared by blending a dispersion or solution
of the photoconductive composition together with a binder, when
necessary or desirable~ and coating or forming a self-supporting
layer with the materials. 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. If desired, other polymers can be incorporated in
the vehicle, for example, to alter physical properties such as
adhesion of the photoconductive layer to the support and the
like. A list of various other polymers which may be used may
be found in the publication Research Disclosure, Vol. No. 109,
; May 1973, p. 63, in Paragraph IV B of the article entitled
"Electrophotographic elements, materials, and processes".
Techniques for the preparation of aggregate photoconductive
layers containing such additional vehicles are described ~-
in C. L. Stephens, U. S. 3,679,407, issued July 25, 1972,
20 and entitled METHOD OF FORMING HETEROGENEOUS PHOTOCONDUCTIVE - -
COMPOSITIONS AND ELEMENTS. The photoconductive layers of the -~
invention can also be further sensitized by the addition of
effective amounts of other known sensitizing compounds to
exhibit improved electrophotosensitivity.
In accord with the invention, the above-described
distyryl-containing aromatic compounds are combined with one or
more non-blue light-absorbing organic photoconductors to form the
improved aggregate photoconductive compositions of the invention.
The non-blue light absorbing organic photoconductive materials are
'.
-22-
- : . -:
~lt~45879 ~:
advantageously incorporated by dissolving these materials in the
organic solvent dope used in coating the improved aggregate photo-
conductive compositions of the invention. As a result these
organic photoconductive materia]s are in solid solution with
the continuous polymer phase of the multiphase structure of
the resultant aggregate photoconductive composition. Incor-
poration of these organic photoconductors in the aggregate
compositions of the invention advantageously results in
significantly increasing the white light electrical speed of the
aggregate composition.
Especially useful organic photoconductors which exhibit
little or no blue light absorption and which may be incorporated
in the improved aggregate compositions of the invention include
` non-blue light absorbing materials selected from the following
classes of photoconductors: Arylamine photoconductors including
substituted and unsubstituted arylamines, diarylamines, -
. . .
nonpolymeric triarylamines and polymeric triarylamines such as
those described in Fox, U.S. patent No. 3,240,597, issued
March 15, 1966 and Klupfel et. al. U.S. Patent No. 3,180,730
issued April 27, 1965; and polyarylalkane photoconductors of
the types described in Noe et. al. U.S. Patent No. 3,274,000,
` issued September 20, 1966, Wilson, U.S. Patent 3,542,547, issued
November 24, 1970; Seus et. al. U.S. Patent No. 3,542,544,
issued November 24, 1970; and in Rule U.S. Patent No. 3,615,402,
issued October 26, 1971. Of course, if desired, other non-blue
light absorbing organic photoconductors such as those selected
from the various classes of organic photoconductors disclosed in
Light, U.S. 3,615,414 may also be incorporated in the
aggregate compositions of the invention.
'
~A
~ . . ,. ; , ... ........ ... .
1~45879
The amount of the above-described distyryl-containing
compound incorporated into the aggregate photoconductive composi-
tions and elements of the invention should be less than about 15
weight percent based on the total dry weight of the resultant
aggregate photoconductive compositions.
Particularly useful results are obtained where the
aggregate compositions of the invention contains 15 to about 40
percent by weight of one or more non-blue light absorbing organic
' photoconductors and as an additive an amount of the distyryl-
i 10
containing aromatic compound within the range of from about 0.1
to about 10 weight percent based on the total dry weight of the
resultant composition. As the amount of the distyryl-containing
aromatic compound is increased beyond the 15 weight percent level
specified herein, the absorption and photoconductive properties
of the compo~nd begin to have a substantial effect on the
resultant photoconductive composition. In addition, the enhance-
ment in electrical fatigue resistance (sometimes referred to in
: !
, ` the art as charge regeneration) provided in the present invention
; by use of a relatively small amount of the distyryl-containing
~ compound is impaired as very large amounts of the distyryl-
- ~ containing aromatic compound are used (i.e. amounts on the order
of about 25 weight percent or more). It has been found that
certain especially useful embodiments of the present invention
which contain in solid solution with the continuous phase of the
aggregate photoconductive composition (a) 25 weight percent or
more of one or more non-blue light absorbing organic photo-
_ conductors and (b) less than 15 weight percent, preferably 5
to 10 weight percent, of the distyryl-containing aromatic -
compounds described herein provide optimum reusable characteristics.
That is, the small amount of the distyryl compound appears to
function primarily as a fatigue reducer, temperature stabilizer, -
and blue light sensitizer for the particulate co-crystalline
,i ' .
l'
, . ....
: , . . .. ~ . ~, . - :
. . - . .. .. . .
1~4S~79
complex incorporated in the aggregate photoconductive com-
position as described previously herein and appears to have
little or no deleterious effect on the photoresponse of the com-
position to visible light outside the blue region, i.e., light
having a wavelength of from 500 to 700 nm.
As noted above, the amounts of the non-blue light
absorbing organic photoconductors incorporated in the compositions
of the invention which produce optimum results in terms of
electrical fatigue, speed, and temperature stability are usually
within the range of from about 15 to about 40, preferably 25 to -
about 40, percent by weight based on the total dry weight of
the resultant aggregate photoconductive composition. However,
larger and somewhat smaller amounts of these photoconductors
may also be used.
Suitable supporting materials on which the aggregate
~ photoconductive layers of this invention can be coated 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, aluminum and the like coated on paper
or conventional photographic film bases such as cellulose
acetate, polystyrene, etc. Such conducting materials as
nickel can be vacuum deposited on transparent film supports in
sufficiently thin layers to allow electrophotographic elements
prepared therewith to be exposed from either side of such
elements. An especially useful conducting support can be
prepared by coating a support material such as poly(ethylene
; 30 terephthalate) with a conducting layer containing a semiconductor
dispersed in a resin or vacuum deposited on the support. Such
-25-
, : .`
, ~ : ... . . .
~45879
conducting layers both with and without insulating barrier layers
are described in U.S. Patent 3,245,833 by Trevoy, issued
April 12, 1966. 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. 3,007,901 by Minsk, issued November 7,
1961 and 3,262,807 by Sterman et al, issued July 26, 1966.
Coating thicknesses of the photoconductive compositions
on the support can vary widely. Normally, a coating in the
range of about 10 microns to about 300 microns before drying
is useful for the practice of this invention. The preferred
range of coating thickness is found to be in the range from
about 50 microns to about 150 microns before drying, although
useful results can be obtained outside of this range. The
resultant dry thickness of the coating is preferably between
about 2 microns and about 50 microns, although useful results
can be obtained with a dry coating thickness between about 1
and about 200 microns.
After the photoconductive elements prepared according
to the method of this invention have been dried, they can be
employed in any of the well-known electrophotographic processes
which require photoconductive layers. One such process is the
xerographic process. In a process of this type, an electrophoto-
graphic element is held in the dark and given a blanket electro-
static charge by placing it under a corona discharge. This
uniform charge is retained by the layer because of the sub-
stantial dark 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 photoconductive layer is then
.
' ~:
-26-
:.; - . . . - . , ~ ~ : - - .
: . ' .:, ' . ' :
:1~45879
selectively dissipated from the surface of the layer by image-
wise exposure to light by means of a conventional exposure
operation such as, for example, by a contact printing technique,
or by lens projection of an image, and the like, to thereby
form a latent electrostatic image in the photoconductive layer.
Exposing the surface in this manner forms a pattern of electro-
static charge by virtue of the fact that light energy striking
the photoconductor causes the electrostatic charge in the light
struck areas to be conducted away from the surface in pro- ~
portion to the intensity of the illumination in a particular ~ --
area.
The charge pattern produced by exposure is then
developed or transferred to another surface and developed
there, i.e., either the charge or uncharged areas rendered ;
visible, by treatment with a medium comprising electrostatically
responsive particles having optical density. The developing
electrostatically responsive particles can be in the form of
a dust, i.e., powder, or a pigment in a resinous carrier, i.e.,
toner. A preferred method of applying such toner to a latent
electrostatic image for solid area development is by the use
of a magnetic brush. Methods of forming and using a magnetic
brush toner applicator are described in the following U.S.
Patents: 2,786,439 by Young, issued March 26, 1957; 2,786,440
by Giaimo, issued March 26, 1957; 2,786,441 by Young, issued
March 26, 1957; 2,874,063 by Greig, issued February 17, 1959.
Liquid development of the latent electrostatic image may also
be used. In liquid development, the developing particles are
carried to the image-bearing surface in an electrically
insulating liquid carrier. Methods of development of this
type are widely known and have been described in the patent
literature, for example, U.S. Patent 2,907,674 by Metcalfe
.: '
-27- ~
~, ,
-,: , . . . . . :
.. ' .- . ' , : .
1C~45879
et al, issued October 6, 1959. In dry deYelopin~ processes,
the most widely -used method of obtaining a permanent record
is achieved by selecting a developing particle which has as
one of its components a low-melting resin. Heating the powder
image then causes the resin to melt or fuse into or on the
element. The powder is, therefore, caused to adhere per-
manently to the surface of the photoconductive layer. In other
cases, a transfer of the electrostatic charge image formed on
the photoconductive layer can be made to a second support such
as paper which would then become the final print after development
and fusing. Techniques of the type indicated are well known
in the art and have been described in the literature such as in
"RCA Review" Vol. 15 (1954) pages 469-484.
The following examples are included for a further
understanding of this invention.
Preparation of Distyryl-Containing Aromatic Compounds
The distyryl-containing aromatic compounds used in
the compositions of the invention may be prepared by known
methods of chemical synthesis. Specifically, the compounds
used herein are prepared by reacting any of various
; dialkylarylphosphonates with an appropriate aldehyde in the
presence of a strong base to give the desired olefin product.
By this procedure, the reaction of p-diphenylaminobenzaldehyde
or 4-di-(p-tolylamino)-benzaldehyde with an appropriate bis-
phosphonate and two equivalents of sodium methoxide in
dimethylformamide solution is used to prepare the distyryl
compounds I-VIII listed in Table 1 hereinbefore.
For purposes of illustration the specific reaction
procedure used to prepare compound V of Table 1 is as follows: I
To a solution of 6.1 g- of tetraethyl 4,6-dimethyl-m-
xylylenediphosphonate and 2.0 g. of sodium methoxide in 50 ml
of dimethylformamide is added dropwise at room temperature 9.0 g ~-
-28-
:,.
1~4S87g
of 4-di-p-tolylaminobenzaldehyde in 50 ml of dimethylformamide;
an exotherm to 40C occurs. A solid separates after several
minutes and the mixture is stirred overnight at room temperature.
The mixture is poured onto 100 g of ice, and the yellow solid
; is collected, washed with 50 ml of water and air-dried to give
10.5 g of crude product, m.p. 91-102C. Two recrystallizations
from dimethyl-formamide gives 4.1 g of compound V in the form
of yellow crystals, m.p. 211-215C.
The other compounds of Table 1 are prepared by a
similar procedure.
Example l
Using aggregate formulation methods as described
; earlier herein, a series of aggregate organic photoconductive
compositions are prepared containing two different organic
photoconductors. The basic dry formulation of each aggregate
photoconductive composition tested is as follows: Bisphenol
A polycarbonate (56% by weight) purchased from General Electric
Co.) + total amount of organic photoconductor (40-30% by weight)
+ total amount of 4-di-p-tolylamino-4'[4-di-p-tolylaminostyryl]-
stilbene (0-10% by weight) + 4-(4-dimethylaminophenyl-2,6-
diphenyl thiapyrylium fluoroborate (3.4% by wt.) + 4-(4-dimethyl-
aminophenyl)-2-(4-ethoxyphenyl)-6-phenyl thiapyrylium fluoroborate
..
; (.6% by wt.). Each aggregate composition is prepared as follows: ~-
; 4-(4-Dimethylaminophenyl)-2,6-diphenyl thiapyrylium
fluoroborate (0.17g) and 4-(4-dimethylaminophenyl)-2-(4-
ethoxyphenyl)-6-phenyl thiapyrylium fluoroborate (0.03 g) are
dissolved in 15 mls. of dichloromethane. Three grams of
bisphenol A polycarbonate are then dissolved in this solution
and to this dope is added 2.0 grams (total) of organic photo-
conductor and 4-di-p-tolylamino-4'-[4-di-p-tolylaminostyryl]-
stilbene. After allowing the dope to stand overnight 12.5 mls.
of dichloromethane is added and the resulting dope is hand
-29-
.. .: :, . , - . . ,
;: ::, ' '
' - ' :
1¢~45879
coated on a nickel coated conductive support to obtain a dry
coating thickness of 9~. Significant increases especially in
blue speeds are observed when 4-di-p-tolylamino-4'-[4-di-p-
tolylaminostyr~l]-stilbene is combined with conventional
organic photoconductors as shown in Table 3.
In this example of the present application Relative
E & D Electrical Speeds are reported. The relative H & D
electrical speeds measure the speed of a given photoconductive
material relative to other materials typically within the same
test group of materials. The relative speed values are not
absolute speed values. However, relative speed values are
related to absolute speed values. The relative electrical
speed (shoulder or toe speed) is obtained simply by arbi-
trarily assigning a value, Ro, to one particular absolute
shoulder or toe speed of one particular photoconductive material.
The relative shoulder or toe speed, Rn, of any other photocon-
ductive material; n, relative to this value, Ro, may then be -
calculated as follows: Rn = (An) (Ro/Ao) wherein An is the
absolute electrical speed of material n, Ro is the speed value
arbitrarily assigned to the first material, and Ao is the
absolute electrical speed of thefirst material. The absolute
H & D electrical speed, either the shoulder (SH) or toe speed,
of a material may be determined as follows: The material is ~ -
electrostatically charged under, for example, a corona source
un~il the surface potential, as measured by an electrometer
probe, reaches some suitable initial value VO~ typically about `~
600 volts. The charge element is then exposed to 3000K
tungsten light source through a stepped density gray scale.
The exposure causes reduction of the surface potential of the
element under each step of the gray scale from its initial
potential VO to some lower potential V the exact value of which
: .
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1~45879
depends upon the amount of exposure in meter-candle-seconds
received by the area. The results of these measurements are
then plotted on a graph of surface potential V vs. log exposure
for each step, thereby forming an electrical characteristic
curve. The electrical or electrophotographic speed of the
photoconductive composition can then be expressed in terms of
the reciprocal of the exposure required to reduce the surface
potential to any fixed selected value. The actual positive or
negative shoulder speed is the numerical expression of 104
divided by the exposure in meter-candle-seconds required to
reduce the initial surface potential VO to some value equal
to VO minus 100. This is referred to as the 100 volt shoulder
speed. Sometimes it is desirable to determine the 50 volt
shoulder speed and, in that instance, the exposure used is that
required to reduce the surface potential to VO minus 50.
Similarly, the actual positive or negative toe speed is the
numerical expression of 104 divided by the exposure in meter~
candle-seconds required to reduce the initial potential VO to
an absolute value of 100 volts. Again, if one wishes to deter-
mine the 50 volt toe speed, one merely uses the exposure
required to reduce VO to an absolute value of 50 volts. An
apparatus useful for determining the electrophotographic speeds
of photoconductive compositionsis described in Robinson et al.,
U.S. Patent No. 3,449,653 1ssued ~une 10, 1969.
, ,~ .~' .
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u~ a~
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u~ u~ o o o o ~ In
o o o o ~ U~
a~ ~ ,, ~ ~ ~1 ~1
o a
E~ ~ ~
~ .,,
~ a~ ~ ' 1
o
O a) _ :
~, o
+
o ~
~ ~ u~ o ~ o o In o
.,~ ~ o ~ ~ o ~ ~ .,,
U~ ~ ,, ~ ~ ~ ~ ~ "
U~
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~ E~ ~
U~ id ~, ,
o ~
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e
~o ~o ~ ~o e ~ a) -:
E~~ ~1 o ~ o ~ o ~n o
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q~O I ~ ~1 0 1 U~ .
e ~ o ~ ~ ~
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~~ I ~O U~ O O ~ I ~ O U~ O .~,
h~1 ~ :~ _I h --I ~ ~ ~1 h
O I h a) O I h t~
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I ~ ~ I ~ ~ ~ ~
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1~P45879
Example 2
Three transparent photoconductive films containing
aggregate photoconductive compositions are prepared similar to
certain of the films of Example 1. The electrophotographic
sensitivity of these films (evaluated as the inverse sensitivity
of the exposure requried to discharge the film from 500 v. to
100 v.) is determined as a function of wavelength for all
electrophotographic modes, positive and negative surface charging
and front and rear exposure. In addition, absorption spectra
for each of the three films is recorded and evaluated. ,~
; Each of the three films tested is identical except
for the particular aggregate photoconductive composition used
in each film. Each of the aggregate photoconductive compositions ~
of the three films contains a particulate co-crystalline comple~ ~ -
of a thiapyrylium dye and Lexan~3polycarbonate as a discontinuous
phase dispersed in a continuous polymer phase composed of Lexan~
polycarbonate. The particular thiapyrylium dye used in each of
the three films is 2~6-diphenyl-4-tp-dimethylaminophenyl)
:.
thiapyrylium fluoroborate and the total amount of dye contained
in each composition is 3% by weight based on the total dry
weight of the aggregate photoconductive composition used in
each film. The total amount of Lexan~ polycarbonate contained
in each of the photoconductive compositions used in the films
is 57% by weight.
A. The remaining 40% by weight of the aggregate
photoconductive composition of Film No. 1 (which
is a control outside the scope of the present
invention) is composed entirely of the organic
photoconductor 4,4'-bis-diethylaminotetraphenyl--
methane (TPM) which is in solid solution with
the Lexan~polycarbonate contained in the con-
tinuous phase of the photoconductive composition
- .
33
~ . ' 1 -
,
l~S879
of Film No. 1.
B. The remaining 40% of the aggregate photoconductive
composition of Film No. 2 (which is within the
scope of the present invention) is composed of
30% by weight of TPM and 10% by weight of com-
pound II of Table 1 of the present application as
an additive. The TPM and compound II used in
Film No. 2 is in solid solution with the Lexan~
polycarbonate contained in the continuous phase
of the photoconductive composition of Film No. 2.
C. The remaining 40% of the aggregate photoconductive
composition of Film No. 3 ~which is also a control
outside the present invention) is composed of 30%
by weight of TPM and 10% by weight of ditolyl-p-
`` nitrophenylamine (DTN). DTN is a yellow appearing
prior art compound known to have photoconductive ;
properties and also known to absorb blue light.
` The TPM and DTN used in Film No. 3 is in solid
solution with the Lexan~ polycarbonate contained
in the continuous phase of the photoconductive --
composition of Film No. 3.
The absorption spectra of Film Nos. 1-3 reveals that
Film No. 1 possesses a "window" to blue light, i.e., visible
light having a wavelength of from about 400-500 nm. That is,
Film No. 1 exhibits very little absorption of blue light. Film
No. 1, however, readily absorbs visible light having a wave-
length within the spectral range of from about 500-700nm. Film
Nos. 2 and 3 exhibit an absorption spectra similar to Film No. 1
with respect to visible light having a wavelength within the
spectral range of from about 500-700 nm. However, in contrast
to Film No. 1, Film Nos. 2 and 3 also absorb blue light so that
.
.,
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.. - ' : , ,: , .. ,. . , ,. ~ :~ -
S8~9
the blue "window" of Film No. 1 does not appear in either Film
No. 2 or 3.
The electrophotographic sensitivity of each of Film
Nos . 1-3 reveals that both controls, i.e., Film Nos. 1 and 3,
exhibit rather poor electrophotographic sensitivity when ex-
posed to blue light but exhibit good and substantially similar
electrophotographic sensitivity to visible light having a
wavelength extending from about 500-700 nm. Film No. 2 of the
present invention, however, exhibits good electrophotographic
sensitivity to blue light. Film No. 2 also exhibits good
electrophotographic sensitivity to light having a wavelength
extending from about 500-700 nm. Except for the increased
electrophotographic sensitivity to blue light exhibited by
Film No. 2 of the present invention, the electrophotographic
sensitivity of Film Nos. 1-3 to light having a wavelength
within the range of from 500-700 nm is quite similar.
The results of the tests shown in this example
indicate that the blue sensitization capability of aggregate
photoconductive compositions containing compound II of Table
1 (which is representative of the distyryl-containing aromatic
compounds of the present invention) is a unique effect and
cannot be obtained simply by substituting other known blue
absorbing organic photoconductors, such as DTN, for compound
II.
Of perhaps even greater significance are the additional
test findings that when temperature stability and electrical
fatigue tests are run on Film Nos. 1-3, the results show that
Film No. 2 (which contains as an additive one of the distyryl-
containing aromatic compounds used in the present invention)
exhibits substantially better resistance to electrical fatigue
and substantially better temperature than either Film No. 1 or
3. For example, Film No. 2 appears to provide good reusable
-35-
.
. - . ~ - ' - : . ' . ~ . . . :
- . , :. .
.. , . . , . , ~ ... . .. .. ::
. . . .. . . . . . . ..
1~4S~
electrophotographic imaging characteristics similar to room
temperature (ie. about 28C) imaging characteristics up to
temperatures approaching 65-70C. In contrast, the electro-
photographic imaging characteristics of Film Nos. 1 and 3
begins to fall off quite noticeably at a temperature of about
55C in comparison to the normal room temperature (about 28C)
imaging characteristics provided by these same films.
Example 3
; To further illustrate certain of the preferred
aggregate photoconductive compositions of the present invention,
a 500 cycle electrical regeneration test and an evaluation of
relative white light speed is performed on a series of three
aggregate photoconductive elements to determine optimum amounts
of the distyryl-containing aromatic compound to be incorporated
therein for use as an additive. These elements are prepared
having coated thereon an aggregate photoconductive composition
containing the following materials expressed in weight percent:
~, Bis-phenol A polycarbonate (56%) purchased from General
; Electric Co. under the trademark Lexan~ 145; 4-(4-dimethylamino-
phenyl)-2,6-diphenyl thiapyrylium hexafluorophosphate
sensitizing dye salt (4%); and the remaining 40% of each com-
` position is as shown in Table 4. Each of the three aggregate
photoconductive elements is prepared by coating the a~ove-
described aggregate composition on a conductive film support
to obtain a dry coating thickness of about 9 microns. The
aggregate photoconductive compositions coated on each of the
three elements tested has an identical composition as indicated
' above except as shown in Table 4 hereinafter.
~; The evaluation of white light speed used in this
` 30 example is carried out by subjecting each of the three aggregate
photoconductive compositions for equal times to an identical
source of white light radiation using a lens system which is
, ::
' ~'
.. . , . . . :
. . . . . . . . . . .
1~45879
e~uivalent to a photographic f-number of f/ll. Before the
f~ll light exposure, each of the three compositions is ~iven in
the dark a uniform negative charge level of -500 volts. Accord-
ingly, the composition which exhibits the highest white light
speed in this test is the composition which most completely
discharges to the zero charge level.
Each cycle of the 500 cycle electrical charge fatigue
; test carried out on these three aggregate elements comprises
the steps of (a) subjecting the element to an initial uniform
charge, Vo, in the dark of -500 volts, imagewise exposing the
uniformly negatively charged surface of the elementto white
light using a Xenon flashlamp to form an imagewise charge pattern
on the surface of the element corresponding to the original
light image pattern, and erasing the imagewise charge pattern
by a uniform light exposure of the charge-bearing surface of
the element. Since only the electricalPrOpertieS of each
element are being tested no development of the charge pattern
or transfer thereof is carried out. After completing 500
, repetitions of the foregoing cycle, the ability of the photo-
¦ 20~ conductive element to accept completély the initial charge,
~) Vo, of -500 volts is measured. If the element retains its
ability to accept completely the -500 volt charge, no electrical
~; fatigue is measurable; therefore the difference in initial charge
acceptance capability, ~Vo as set forth in Table 4, is zero. If
after completing the 500 repetitions of the fatigue test, the photo-
i conductive element is no longer capable of completely accepting the
¦ full initial charge of~500 volts, the amount of charge it does ac-
; cept is measured and the difference between this value and the in-
itial -500 volts, ie.aVo, is calculated and appears under the col-
umn ~Vo in Table 4. As indicated in Table 4 an element containing
j an aggregate photoconductive composition which has only a conven-
t tional photoconduc~or known to be useful in aggregate photo-
-37-
:.
: . . . - . ~
1~4S~379
conductive materials (i.e. bis(4-diethylamino)tetraphenyl
methane) exhibits a ~Vo of -25 volts indicating that it de-
finitely experiences significant electrical fatigue when sub-
jected to repeated re-charging and re-exposure. This fatigue
characteristic is, of course, disadvantageous for any such
photoconductive element contemplated for use as a reusable
photoconductive element. In contrast, as Table 4 clearly
shows, when an amount of compound II of Table 1 is added to
the aggregate photoconductive elements tested in this example,
the amount of electrical fatigue as meausred by the foregoing
500 cycle test is substantially reduced=-- ultimately no
measurable fatigue is obtained as the amount of compound II
of Table 1 added to the aggregate photoconductive compositions
tested in this example is increased. However, as is also shown
in Table 1, the element which exhibits little or no measureable -
. ~
` fatigue also shows a white light speed loss relative to the - -
elements containing lesser amounts of compound II. Thus in
accord with the invention, the amount of the distyryl-containing
compound wh~ch shouldbe added to obtain an optimum reusable
aggregate photoconductive composition should be less than about
15 weight percent.
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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. :
-40
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