Note: Descriptions are shown in the official language in which they were submitted.
104~j330
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 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 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 electrophotograph-
ic 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 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. Lik~wise, the electrostatic charge
pattern can be transferred to a second element and developed
there.
Various photoconductive insulating materials have
-- 2 --
1046330
been employed in the manufacture of electrophotographic ele-
ments. For example, vapors of selenium and vapors of sel-
enium alloys deposited on a suitable support and particles
of photoconductive zinc oxide held in a resinous, film-form-
ing 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 photoconductive properties. As a result, a very large
number of organic compounds have been known to possess some
degree of photoconductivity. Many organic compounds have
revealed a useful level of photoconduction and have been in-
corporated into photoconductive compositions. Among these
organic photoconductors are the triphenylamines as described
in U.S. 3,180,730 issued April 27, 1965, and other aromatic
ring compounds such as those described 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.
Optically clear organic photoconductor-containing
elements having desirable electrophotographic properties can
be especially useful in electrophotography. Such electrophoto-
graphic elements can be exposed through a transparent base if
desired, thereby providing flexibility in equipment design.
Such compositions, when coated as a film or layer on a suit- .-
able 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 compositions 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
-- 3 --
1046330
which permits effective prediction, and therefore selection
of the particular compounds exhibiting the desired electro-
photographic properties.
A high speed "heterogeneous" or "aggregate" multi-
phase 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. The addenda disclosed therein are
responsible for the exhibition of desirable electrophoto-
graphic properties in photoconductive elements prepared there-
with. In particular, they have been found to enhance the
speed of many organic photoconductors when used therewith.
The degree of such enhancement is, however, variable, depend- ~ `
ing on the particular organic photoconductor so used.
Summary of the ~vention
In accord with the present invention there is provided
a novel photoconductive composition comprising as a photo-
conductor a compound having a central carbocyclic or sulfur
heterocyclic divalent aromatic ring joined to two amino-
substituted styryl radicals through the vinylene groups of the
styryl radicals.
In accord with one embodiment of the invention, we
have found that the distyryl-containing aromatic compounds
may be used as the photoconductive material of a homogeneous
organic photoconductive conductive composition.
In accord with another embodiment of the present
invention, it has been discovered that one or more of these
distyryl-containing aromatic compounds may be employed as the
~0 only organic photoconductor in the continuous polymer phase
of a multiphase aggregate photoconductive composition of
-
1046330
the type referred to hereinabove to extend the white light
speed and blue sensitivity of the aggregate photoconductive
composition.
In accord with still another embodiment of the in-
vention, we have found that the distyryl-containing aromatic
compounds may be incorporated as a photoconductive material
in a photoconductive composition which also contains one or
more inorganic photoconductors. For example, photoconductive
compositions comprising a mixture of the above-described
distyryl-containing aromatic compounds and lead oxide provide
elements exhibiting useful xeroradiographic properties.
Various closely related compounds having a cyano-
substituted vinylene moiety in place of the unsubstituted viny-
lene moieties contained in the photoconductive compounds used
in the present invention have been described in the prior
art. Representative of such prior art materials are compounds
having the following formula:
CN CN
Am ~ CH=C - Ar C=CH ~ Am
wherein Am represents an amino group and Ar represents a
divalent aromatic group. See Merrill, U.S. 3,653,887 issued
April 4, 1972.
According to the present invention, it has been
found that the photoconductors described herein have substan-
tially improved electrical speed over those related photo-
conductors described in U.S. 3,653,887.
In addition, it has been found that the photoconduc-
tors of the present invention enhance the blue sensitivity of
aggregate photoconductive compositions in comparison to the
use of other known prior art compounds employed in similar
agqregate photoconductive compositions, for example the
-- 5 --
10~330
triarylamines shown in U.S. Patent No. 3,180,730 and certain
of the active hydrogen-containing photoconductive materials
shown in Brantley et. al., U.S. Patent No. 3,567,450.
Description of the Preferred Embodiments
The preferred photoconductors of the invention may
be characterized by the following formula:
R ~ R3
N-Arl-CH=CH-Ar2-CH=CH-Ar3-N~
R2 R4
wherein
Rl, R2, R3, and R4, which can be the same or
different, represent alkyl or aryl radicals including substi-
tuted 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 con-
sisting of an alkyl, aryl, alkoxy, aryloxy and halogen sub-
stituent; 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 Ar
and Ar3.
Typically, Rl, 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 havin~ one to 18
carbon atoms such as
. ' ' ' '' ' '~ . , ' ' . '
. ' :' "'. '' .' ,, ' ~' :
1046330
a. alkoxyalkyl e.g., ethoxypropyl, methoxybutyl,
propoxymethyl, etc.,
b. aryloxyalkyl e.g., phenoxyethyl, naphthoxymethyl,
phenoxypentyl, etc.
c. aminoalkyl, e.g., aminobutyl, aminoethyl,
aminopropyl, etc.,
d. hydroxyalkyl e.g., hydroxypropyl, hydroxyoctyl,
etc.,
e. aralkyl e.g., benzyl, phenethyl, etc.
f. alkylaminoalkyl e.g., methylaminopropyl, methyl
aminoethyl, etc., and also including dialkyl-
aminoethyl, e.g. diethyaminoethyl, dimethyl-
aminopropyl, propylaminooctyl, etc.,
g. arylaminoalkyl, e.g., phenylaminoalkyl,
diphenylaminoalkyl, 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-
ethyl, etc., and
j. haloalkyl, e.g., chloromethyl, bromopentyl,
chlorooctyl, etc.,
k. alkyl substituted with an acyl group having the
formula
O
..
-C-R
wherein R is hydroxy, hydrogen, aryl, e.g., phenyl, naphthyl,
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 car- -
bon atoms, e.g., butoxy, methoxy, etc., aryloxy, e.g., phenoxy,
. :
.
1046330
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.
b. aryloxyaryl, e.g., phenoxyphenyl, naphthoxy-
phenyl, 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,
methylaminonaphthyl, etc. and also including
dialkylaminoaryl, e.g., diethylaminophenyl,
dipropylaminophenyl, etc.
g. arylaminoaryl, e.g., phenylaminophenyl, diphenyl-
aminophenyl, N-phenyl-N-ethylaminophenyl, naphthyl-
aminophenyl, etc.
h. nitroaryl e.g., nitrophenyl, nitronaphtyly,
nitroanthryl, etc.,
i. cyanoaryl, e.g., cyanophenyl, cyanonaphthyl,
cyanoanthryl, etc.,
j. haloaryl, e.g., chlorophenyl, bromophenyl,
chloronaphthyl, etc.,
k. alkaryl, e.g., totyl, ethylphenyl, propylnaphthyl,
etc., and
1. aryl substituted with an acyl group having the
formula
O '~
-C-R
wherein R is hydroxy, hydrogen, aryl, e.g., phenyl, naphthyl,
- 8 -
: :
10~6330
etc., amino including substituted amino, e.g., diloweralkyl-
amino, lower alkoxy having one to eight carbon atoms, e.g.,
butoxy, methoxy, etc., aryloxy, e.g., phenoxy, naphthoxy, etc.,
lower alkyl h~ing one to eight carbon atoms, e.g., methyl,
ethyl, propyl, butyl, etc.
Typically, when either Arl or Ar3 represent a sub-
stituted phenyl radical the substituents on the phenyl
radical are al~yl 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
of photoconductive compounds described herein include the
following materials listed in Table 1 below:
_ g _
~, 10~6330
o
o o o o o
P~ ,, o ~ CO
~ ~ ~ o
~ O~
~ o ,, ~ o
,, ~ ~ ~ ,,
_,
o
q~
~o .
O ~ ~1
,1 al ~1
.C 1~ N ~ _ 0
O ~r
~ u a
_, ~ ,1 m ~1
~I~ "., ~I _ ~ Z ~
_l ~ P: ~ Z I I
_I ~D ~ I h
~ ~
~n 11 ~ P:
~1 ~ ~ ~C,~ ~ ~1
~ ~ ~ ~ ~ m I ~ ~
o C~ ~I ~ C~ I C~
11 o I ~ ~ ~ / o
~ CJ ~ ~ 3 ~ ~ ~, ~ ` ~ ~ $~
,1 o ~ $ ,
~ ~ ~ ~ ~ C~
11 s
~ ~ Z Z
' ~ ' ~ '~ r~
~, o . o ~ ~ ~ o . . ,
l .~s ~ ~ ~ ~ ~ ~
~ ~ ~ $
,~ I O ~ 0-,1 ~r o ~I c~ c~
Z I ~ I u~ D I - 5
s~U. I m~ I- ~, m I ~ ~
C~ , C~ ~rl --\
ac~ a ~ a ~ a ~ ~ ~ . .
H H H
-- H H H
H
-
- 10 -
.
.' ' ' :' . ~.
- :
- :. - . , . : . - . ' . , :
10~6330
o~
'o o o o
P~ U~ O ~D
~ a~ o
b~ N N N
~ l l
CO e~
~ ~ O
_I N N N
X ..
: .
,~ O N ~1
lQ ~ ~ ~U \ /
s '~, m~D ~ \mN >~
o m
m~
~ .- ~ ~ Z s
~1 I s ~ ~ s
~r ~ m ,~
m n
~-) ~ N I 1~
~ _ _I m ~ ~ ~
_I I I ~ C~ o
m~ PC~ ~ ~ P ~
m~ m~ ô ~ ~ m
m c~
~-1 c~ o
Q ~ ~ m 1l ~
N '~ U p, ~ 3
a
m ~ z z
_I O ~ C) -- N N Z ~ \ ~7
o ~ ~ m m
I ~ / ~
~ m ~ m m~ m~ m
~ ~ \m a~
~r
~ ~ .
p ~ H H
H
~ 2
104t;330
Compounds which belong to the general class of
photoconductive compounds described herein and which are
preferred for use in accord with the present invention in-
clude those compounds having the structural formula shown
Rl, R2, R3, and R4 are aryl groups as defined
above and wherein Ar2 is an unsubstituted phenyl radical or a
substituted phenyl radical having alkyl substituents contain-
ing 1 to about 4 carbon atoms. These compounds are preferred
because of the generally higher electrical speeds which are
obtained from photoconductive compositions containing the
same.
Compounds which belong to the general class of
photoconductive compounds described herein and which are
especially preferred for use in accord with the present inven-
tion include those compounds having the structural formula shown
above wherein Rl, R2, R3, and R4 are alkaryl groups as defined
above, particularly tolyl radicals, and 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.
As set forth hereinabove, in accord with one embodi-
ment of the invention, the photoconductive compounds of the
invention can be used in aggregate photoconductive composi-
tions of the present invention. Those distyryl-containing aro-
matic compounds noted above as especially preferred have been
found particularly useful in aggregate photoconductive composi-
tions hecause ~ thEI~ a~ ity t6 i~G~e~se ~h~ ~l`ue sensitivityof t-~*se aggr~ga~e ~pQsii~ d~ àuse of their une~pected
a~it~ ~o ina~ease~b~ peedi~ th~se aggregate composlticn3 in
~c~paæls~`~;.thæ-photccon~w tlve materia~s shown in U.S. Patent
3j~53~-887-which h~ve a very similar molecular structure.
- 12 -
. - ~ , . . ........................................ .
104t~.~30
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 techniques, such as, for example, the so-called "dye
first" technique described in Gramza et al, U.S. 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 speecl 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 distyryl-containing photocon-
ductor of the invention in a suitable solvent to form a
photoconductor-containing 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 com-
positions may appear to be substantially optically clear to the
naked eye in the absence of magnification. There can, of course,
be macroscopic 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
comprised of dye and polymer.
The term co-crystalline complex as used herein has
reference to a crystalline compound which contains dye and
- 13 -
.
.
, ~ :
~. . . .
.. : ..
1046330
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 wave-
length of the radiation absorption maximum characteristic of such
compositions is substantially shifted from the wavelength of
the radiation absorption maximum of a substantially homo-
geneous dye-polymer solid solution formed of similar con-
stituents. 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
invention is generally of the magnitude of atleast 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.
Sensitizing dyes and electrically insulating poly-
meric materials are used in forming these aggregate composi-
tions. Typically, pyrylium dyes, including pyrylium, bispyry-
lium, 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:
- 14 -
...... - . - . . .
. ~ ,: . , . - .
1046330
~ Z~
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 1 to about 6 carbon atoms;
R7 can be an alkylamino-substituted phenyl radical
having from 1 to 6 carbon atoms in the alkyl moiety, and
including dialkylamino-substituted and haloalkylamino-sub-
stituted phenyl radicals;
X can be an oxygen or a sulfur atom; and
Z~ is an anion.
The polymers useful in forming the aggregate com-
positions include a variety of materials. Particularly use-
ful are electrically insulating, film-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:
R8 IR9 IRl 1
~} C--~R12
1 0
wherein:
Rg and Rlo, when taken separately, can each be a
hydrogen atom, an alkyl radical having from one to about 10
carbon 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
- 15 -
`` 10~6330
such as phenyl and naphthyl, including substituted aryl radi-
cals having such substituents 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 cyclohexyl 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 fol-
lowing:
O S O O O CH
1- .. - ,. " , 3
-O-C-O-, -O-C-O-, -C-O-, -C-O-CH2-, -C-O-CH-,
O O
,. .. .
-CH2-O-C-O-, and -O-P-O-
o~3 , .
Preferred polymers useful for forming aggregate
crystals are hydrophobic carbonate polymers containing the
following moiety in a recurring unit:
R9 0
..
-R-C-R-O-C-O- - ~
Rlo ~ -
20wherein:
each R is a phenylene radical including halo sub-
stituted phenylene radicals and alkyl substituted phenylene
radicals; and Rg and Rlo are as 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
- 16 -
104~330
those prepared with sisphenol 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:
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)
7 poly(4,4'-isopropylidenediphenylene
carbonate-block-oxyethylene)
8 poly(4,4'-isopropylidenediphenylene
carbonate-block-oxytetramethylene)
- 17 -
`
10~33~
Table 2 (continued)
No. _ Polymeric Material
9 poly[4,4'-isopropylidenebis(2-methyl-
phenylene)-carbonate]
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 r
poly(4,4'-isopropylidenediphenylene-co-
4,4'-ethylenediphenylene carbonate r
16 poly[4,4'-methylenebis (2-methyl-
phenylene)carbonate]
17 polyll,l-(p-bromophenylethylidene)bis(1,4-
phenylene)carbonate]
18 poly[4,4'-isopropylidenediphenylene-co-
4,4'-sulfonyldiphenylene) carbonat-r
19 polyl4,4'-cyclohexanylidene(4-diphenylene) .
carbonate]
poly~4,4'-isopropylidenebis(2-chlorophenylene)
carbonate]
21 poly(4,4'-hexafluoroisopropylidenediphenylene
carbonate)
22 poly(4,4'-isopropylidenediphenylene 4,4'-
isopropylidenedibenzoate)
23 poly(4,4'-isopropylidenedibenzyl 4,4'-
isopropylidenedibenzoate)
24 poly[4,4'-(1,2-dimethylpropylidene)diphenylene
carbonate]
poly[4,4'-(1,2,2-trimethylpropylidene)-
diphenylene carbonate]
26 poly ~4,4'-[1-(Q-naphthyl)ethylidene]-
diphenylene carbonate~
27 poly[4,4'-(1,3-dimethylbutylidene)-
diphenylene carbonate]
28 poly[4,4'-(2-norbornylidene)diphenylene
carbonate]
- 18 -
1046;330
Table 2 (continued)
No.Polymeric Material
29poly[4,4'-(hexahydro-4,7-methanoindan-5-
ylidene) diphenylene carbonate]
Electrophotographic elements of the invention con-
taining the above-described aggregate photoconductive com-
position 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 electrophoto-
sensitivity 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 in-
corporated in the vehicle, for example, to alter physical
properties such as adhesion of the photoconductive layer to
the support and the like. 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, and entitled METHOD OF FORMING HETEROGENEOUS
PHOTOCONDUCTIVE coMæosITIoNs AND ELEMENTS. The photoconductive
layers of the invention can also be sensitized by the addition
of effective amounts of sensitizing compounds to exhibit
improved electrophotosensitivity.
The amount of distyryl-containing photoconductor incor-
porated into the aggregate photoconductive compositions and
elements of the invention can be varied over a relatively
wide range. However, when used as a photoconductor in an ag-
gregate photoconductive composition the distyryl-containing com-
pounds described herein or a mixture thereof should be the only
organic photoconductor present in the continuous phase of the
aggregate composition and should be present in an amount in
~ - 19 -
1046330
excess of about 15% by weight (based on the dry weight of
the aggregate
- l9a -
0~6~3~)
photoconductive composition). Small amounts of the distyryl-
containing compound (i.e., amounts less than about 15 percent by
weight of the total dry weight of the aggregate photoconductive
composition) may be advantageously incorporated in an aggregate
photoconductlve composition (as described in the previously
cross-referenced Contois and Rossi, Canadian patent
application Serial No. 198,352), as an additive in combination
with a non-blue light absorbing organic photoconductor to provide
enhanced resistance to electrical fatigue, improved temperature
stability, and enhanced blue sensitivity. But, in accord with
the present invention, larger amounts of the distyryl-containing
compound (e.g. amounts in the range of 15 to 35 weight percent
or more~ are incorporated in the continuous polymer phase of
an aggregate photoconductive composition as the sole organic
photoconductor contained in said continuous phase, thereby
significantly increasing the overall white light electrophoto-
graphic speed of the resultant aggregate composition as well as
providing enhanced blue sensitivlty. At the same tlme, however,
aggregate photoconductlve compositions containlng very large
amounts of the distyryl-containing compound (i.e., amounts on the
order of about 25 welght percent or more) do not appear to exhibit
as good electrical fatigue resistance (sometimes referred to as
charge regeneration) as ls provlded when smaller amounts of the
dlstyryl-contalnlng compound ls lncorporated thereln as an addltlve
ln comblnatlon wlth a non-blue llght absorblng organlc photocon-
ductor. Accordingly, aggregate photoconductive composltions of the
present inventlon whlch contaln a large amount of the distyryl-
contalnlng aromatic compound as a photoconductor are particularly
useful, ~or example, in electrographic elements and processes re-
quiring relatively high speed non-reusable photoconductive com-
positions. In contrast, small amounts of the distyryl-containing
aromatic compound are particularly useful as an additive for a
reusable aggregate photoconductive composition, which even without
:
-2Q-
-. ' ' '', ~-'' . '
.
-
104~330
the distyryl-containing aromatic compound possesses a white
light speed at or near the desired level, to provide improved
resistance to electrical fatigue, improved temperature stability,
and enhanced blue light sensitivity.
In addition to electrographic elements containing the
above-described aggregate photoconductive compositions there
are other useful embodiments of the present invention. For
example, "non-aggregate-containing"electrographic elements
can be prepared with the photoconductive compounds of the in-
vention in the usual manner, i.e., by blending a dispersion orsolution of a photoconductive compound together with a binder,
when necessary or desirable, and coating or forming a self-
supporting layer with the photoconductor-containing materials.
Mixtures of the photoconductors described herein can be employed.
Likewise, other inorganic and organic 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.
The "non-aggregate" photoconductive layers of the in-
vention such as homogeneous organic photoconductive composi-
tions, photoconductive compositions comprising an organic com-
pound used in the present invention together with an inorganic
compound such as lead oxide, and the like can be sensitized by
the addition of effective amounts of sensitizing compounds to
exhibit improved electrophotosensitivity. Sensitizing compounds
useful with the photoconductive compounds of the present inven-
tion can be selected from a wide variety of materials, including
such materials as pyrylium dye salts including thiapyrylium dye
materials as pyrylium dye salts including thiapyrylium dye
salts and selenapyrylium dye salts disclosed in VanAllan et
- 21 -
104~330
al U.S. Patent No. 3,250,615; fluorenes, such as 7,12-dioxo-
13-dibenzo(a,h)fluorene, 5,10-dioxo-4a,11-diazobenzo(b)-
fluorene, 3,13-dioxo-7-oxadibenzo (b,g)fluorene, and the
like; aromatic nitro compounds of the kinds described in
U.S. Patent No. 2,610,120; anthrones like those disclosed
in U.S. Patent No. 2,670,284; quinones, U.S. Patent No.
2,670,286; benzophenones U.S. Patent No. 2,670,287;
thiazoles,U.S. Patent No. 2,732,301; mineral acids;
carboxylic acids, such as maleic acid, dichloroacetic
acid, trichloroacetic acid and salicyclic acid, sulfonic
and phosphoric acids, and various dyes, such as cyanine
(including carbocyanine), merocyanine, diarylmethane, thi-
azine, azine, oxazine,XQn~nO , phthalein, acridine, azo,
anthraquinone dyes and the like and mixtures thereof. The
sensitizers preferred for use with the compounds of this
invention are selected from pyrylium salts including selena-
pyrylium salts and thiapyrylium salts, and cyanine dyes
including carbocyanine dyes.
Where a sensitizing compound is employed with the
binder and organic photoconductor to form a sensitized electro-
photographic element, it is the normal practice to mix a
suitable amount of the sensitizing compound with the coating
composition so that, after thorough mixing, the sensitizing
compound is uniformly distributed in the coated layer.
Other methods of incorporating the sensitizer or
the effect of the sensi~izer may, however, be employed
consistent with the practice of this invention. In pre-
paring the non-aggregate photoconductive layers, no sen-
sitizing compound is required to give photoconductivity in the
layers which contain the photoconducting substances, there-
fore, no sensitizer is required in a particular photoconductive
layer. However, since relatively minor amounts of sensitizing
- 22 -
." . .
,
104ti330
material can provide relatively large increases in photocon-
ductivity, the use of the sensitizer is preferred. The amount
of sensitizer that can be added to a photoconductor-incorporating
layer to give effective increases ln 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
0.001 to about 30 percent by weight based on the weight
of the film-forming coating composition. Normally, a sensi-
tizer 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 presentnon-aggregate photoconductive layers are film-forming, hydro-
phobic polymeric binders having fairly high dielectric strength
and good electrical insulating properties.
Typical of these materlals are:
I. Natural resins including gelatin, cellulose
ester derivatlves such as alkyl esters of carboxylated
cellulose, hydroxy ethyl cellulose, carboxy methyl cellulose,
carboxy methyl hydroxy ethyl cellulose, etc.;
II. Vinyl resins including
a. polyvinyl esters such as a vinyl acetate
resin~ a copolymer of vinyl acetate and
crotonic acid, a copolymer of vinyl acetate
with an ester of vinyl alcohol and a higher
aliphatic carboxylic acid such as lauric ;~
acid or stearic acid, polyvinyl stearate, a
copolymer of vinyl acetate and maleic acid,
-23-
~A
104~330
a poly(vinylhaloarylate) such as poly(vinyl-
m-bromobenzoate-covinyl acetate), a ter-
polymer of vinyl butyral with vinyl alcohol
and vinyl acetate, etc.;
b. vinyl chloride and vinylidene chloride
polymers such as a poly(vinylchloride), a
copolymer of vinyl chloride and vinyl
isobutyl ether, a copolymer of vinylidene
chloride and acrylonitrile, a terpolymer
of vinyl chloride, vinyl acetate and vinyl - -
alcohol, poly(vinylidene chloride) a ter-
polymer of vinyl chloride, vinyl acetate and
maleic anhydride, a copolymer of vinyl
chloride and vinyl acetate, etc.;
c. styrene polymers such as polystyrene, a
nitrated polystyrene, a copolymer of
styrene and monoisobutyl maleate, a copoly-
mer of styrene with methacrylic acid, a co-
polymer of styrene and butadiene, a copolymer
of dimethylitaconate and styrene,
polymethylstyrene, etc.;
d. methacrylic acid ester polymers such as a
poly(alkylmethacrylate), etc.;
e. polyolefins such as chlorinated poly-
; ethylene, chlorinated polypropylene,
poly(isobutylene), etc.;
f. poly(vinyl acetals) such as poly(vinyl
butyral), etc.; and
g. poly(vinyl alcohol);
III. Polycondensates including
a. a polyester of 1,3-disulfobenzene and
2,2-bis(4-hydroxyphenyl)propane;
- 24 -
- : . ' :
10~330
b. a polyester of diphenyl-p,p'-disulphonic
acid and 2,2-bis(4-hydroxyphenyl) propane;
c. a polyester of 4,4'-dicarboxyphenyl ether
and 2,2-bis(4-hydroxyphenyl)propane;
d. a polyester of 2,2-bis(4-hydroxyphenyl)-
propane and fumaric acid;
e. polyester of pentaerythritol and phthalic
acid;
f. resinous terpene polybasic acid;
g. a polyester of phosphoric acid and
hydroquinone;
h. polyphosphites;
i. polyester of neopentylglycol and iso-
phthalic acid;
j. polycarbonates including polythiocarbonates
such as the polycarbonate of 2,2-bis(4-
hydroxyphenyl)propane;
k. polyester of isophthalic acid, 2,2-bis[4-
(~ -hydroxyethoxy)phenyl]propane and
ethylene glycol;
1. polyester of terephthalic acid, 2,2-bis[4-
( ~-hydroxyethoxy)phenyl]propane and
ethylene glycol;
m. polyester of ethylene glycol, neopentyl,
glycol, terephthalic acid and isophthalic
acid;
n. polyamides;
o. ketone resins; and
p. phenol-formaldehyde resins;
IV Silicone resins;
V Alkyd resins including styrene-alkyd resins,
silicone-alkyd resins, soya-alkyd resins, etc.;
- 25 -
.
104f~330
VI. Polyamides;
VII. Paraffin; and
VIII. Mineral waxes.
Solvents useful for preparing coating compositions
containing the photoconductors of the present invention can
include a wide variety of organic solvents for the components
of the coating composition.
Typical solvents include:
1) Aromatic hydrocarbons such as benzene, naph- -
thalene, etc., including substituted aromatic hydrocarbons such
as toluene, xylene, methylene, etc.;
2) Ketones such as acetone, 2-butanone, etc.;
3) Halogenated aliphatic hydrocarbons such as
methylene chloride, chloroform, ethylene chloride, etc.;
4) Ethers including cyclic ethers such as tetra-
hydrofuran,ethylether;
5) Mixtures of the above.
In preparing the non-aggregate-containing photo-
conductive coating compositions of the present invention useful
results are obtained where the photoconductor is present in an
amount equal to at least about 0.1 weight percent of the coating
composition. The upper limit in the amount of photoconductive
material present can be widely varied to at least 90~ by weight
in accordance with usual practice.
Suitable supporting materials on which the photocon-
ductive layers of this invention can be coated include any of a
wide variety of electrically conduct mg 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
- 26 -
:: .
~- 1046330
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 de-
posited on transparent film supports in sufficiently thin lay-
ers 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 terephthalate) with a conducting
layer containing a semiconductor dispersed in a resin or vacuum
deposited on the support. Such 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 compo-
sition 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 be-
tween abo~t 2 micron~ aRd abou~ 50 mi~ro~a, although usef~l
results can be obtained with a dry coating thickness between
about 1 and about 200 microns.
After the photoconductive elements prepared
- 27 -
~04~30
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 pro-
cess is the xerographic process. In a process of this type,
an electrophotographic element is held in the dark and given
a blanket electrostatic charge by placing it under a corona
discharge. This uniform charge is retained by the layer be-
cause of the substantial 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 photocon-
ductive layer is then selectively dissipated from the surface
of the layer by imagewise exposure to light by means of a con-
ventional 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 ;i`
photoconductive layer. Exposing the surface in this manner
forms a pa~ern of electrostatic charge by virtue of the fact
that light energy striking the photoconductor causes the electro-
static charge in the light struck areas to be conducted away
from the surface in proportion to the intensity of the illumi-
nation in a particular area.
The charge pattern produced by exposure is then de-
veloped or transferred to another surface and developed there,
i.e., either the charged or uncharged areas rendered visible,
by treatment with a medium comprising electrostatically respon-
sive particles having optical density. The developing electro-
statically 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
- 28 -
, . : . :.
~- '' ~ .
10~330
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 in-
sulating 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 et
al, issued October 6, 1959. In dry developing 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 permanently to the
surface of the photoconductive layer. In other cases, a trans-
fer of the electrostatic charge image formed on the photo-
conductive 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 Photoconductors
The photoconductive materials used in the composi-
tions of the invention may be prepared by known methods of che-
mical 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
- 29 -
10~i330
give the desired olefin product. By this procedure, the reac-
tion of p-diphenylaminobenzaldehyde or 4-di-(p-tolylamino)
benzaldehyde with an appropriate bis-phosphonate and two equi-
valents of sodium methoxide in dimethylformamide solution is
used to prepare the distyryl compounds I-VI listed in Table 1
hereinbefore.
For purposes of illustration the specific reac-
tion procedure used to prepare compound V of Table 1 is as
follows:
To a solution of 6.1 g of tetraethyl 4,6-
dimethyl-m-xylylenediphosphonate and 2.0 g of sodium methox-
ide in 50 ml of dimethylforamide is added dropwise at room tem-
perature 9.0 g 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 com-
pound V if the form of yellow crystals, m.p. 211-215C.
The other photoconductive compounds of Table 1 are
prepared by a similar procedure.
Example 1
In this example aggregate and homogeneous organic
photoconductive compositions of the present invention are com-
pared to the somewhat similar photoconductors described in
Merrill, U.S. Patent 3,653,887 to demonstrate the unexpected
improvement in 100 volt positive toe speed provided by the photo-
conductive compositions of the present invention. A set of
four different photoconductive compositions coated on a con-
ductive film support are tested for each photoconductor, three
- 30 -
.. . . , . , ,. . :. .
10~330
homogeneous photoconductive compositions, i.e., Nos. 1-3 below,
and one aggregate composition, i.e., No. 4 below, the type des-
cribed in Light, U.S. Patent 3,615,414. The formulation of
the compositions used in this example is as follows:
No. 1: 78.4 weight percent polyester binder, 20 weight
percent photoconductor, 1.6 weight percent of the
sensitizer 4-(n-butyl amino) -2-(4-methoxy phenyl)
benzo[b] pyrylium perchlorate
No. 2: 79.2 weight percent polyester binder, 20 weight
percent photoconductor, 0.8 weight percent of the
sensitizer Rhodamine B
No. 3: 80.0 weight percent polyester binder, 20.0 weight
percent photoconductor, no sensitizer
No. 4: 78.0 weight percent polycarbonate binder, 20.0 weight
percent photoconductor, and 2.0 weight percent of
the sensitizer 4-p-dimethylaminophenyl-2,6-diphenyl-
pyrylium perchlorate
The above four compositions are tested using two different
photoconductors, A and B. Photoconductor A is a compound of
the type described in U.S. 3,653,887 and has the formula
CH3 CH3
CH~ ~ CN=C ~ C-C~ ~ N ~
Photoconductor B is compound II of Table 1 of the present
invention. The following data is ob~ained:
- 31 -
.
104~i330
TABLE 3
RELATIVE ELECTRICAL H & D SPEED
(+ 100 VOLT TOE)
Photoconductor No. 1 No. 2 No. 3 No. 4
A 100* 170 0 500
B 160 250 50 1600
*arbitrarily assigned a relative speed value of 100 for this
example
The relative positive 100 volt toe speeds in Table 3 are
measured as described in Example 4 hereinafter. As shown in ;
Table 3, the relative 100 volt positive toe speeds of photo-
conductor B of the present invention are substantially higher
than prior art photoconductor A.
Example 2
This example illustrates the blue sensitivity of
aggregate photoconductive compositions of the present invention.
The following aggregate photoconductive composition consisting
` of:
j polycarbonate resin 1.0 parts by weight
photoconductor II of Table 1 0.25 parts by weight
2,6-Diphenyl-4-~-dimethylamino- 0.025 parts by weight
phenyl thiapyrylium perchlorate
is prepared as follows:
The formulation is made up by a seed-shear technique
which consists of the preparation of two stock solutions:
Solution I
3.92 g of polycarbonate resin
0.08 g of 4-p-dimethylaminophenyl-2,6-diphenylthia-
pyrylium perchlorate
26.8 ml dichloromethane
-32-
- - . : - . . :
10~30
The above dope is sheared in a Waring Blender
for 30 minutes at 70F.
Solution II
A dye solution is prepared consisting of 0.03 g
of 4-_-dimethylaminophenyl-2,6-diphenylthiapyrylium per-
chlorate and lO.2 ml of dichloromethane.
A dope containing these solutions is prepared
as follows:
7.7 g of Solution I
4.5 g of Solution II
0.25 g of photoconductor II of Table l
0.25 g of Lexa ~ 145
The above-described dope is then coated on a
conductive poly(ethylene terephthalate) support to provide
a resultant aggregate photoconductive element. Wedge
spectrograms of this aggregate photoconductive element
are obtained when the element is exposed to visible light
after being sub~ected to uniform positive charging. As a
result is it found that thls aggregate photoconductive
element of the invention exhibits a secondary peak of light
sensitivity at 460 nm.
In contrast, when a series of prior art photo-
conductors including triphenylamine, tri-p-tolylamine, 4,4'-
diethylamino-2,2'-di-methyl-triphenyl methane, and _-
diphenylaminocinnamic acid are substituted for the photo-
conductors used in the present invention in aggregate
photoconductive elements otherwise identical to that
described above; it is found that wedge spectrograms of such
aggregate photoconductive elements when sub~ected to light
exposure after uniform positive charging exhibit a sensitivity
: `
-33-
.
-` ~04~ 30
minimum at 460 nm, thereby indicating the absence of blue
sensitivity possessed by these photoconductive elements.
Example 3
To illustrate the advantages of using the organic
photoconductors of the present invention in combination with
various inorganic photoconductors, three different photo- :
conductive compositions are made having the composition shown
below as follows:
Photoconductor II of Table 1 is combined with
tetragonal PbO in a polyester binder and coated on a
conductive support to yield the following data shown in
Table 4:
-34-
, . . . .
104~330
o
~o
~ ~ c o ~n er
U~I ~ ~ N 11
~_ O ~ ~J O
a ~
0
O
~ O
rl ~
s
o ~q
~, _
li3
a~ In _
O O
~1 ~ ~ u~
_ o ~ ~r
0 + ~ ~ O 11
~1-- O ~ O~ O
~I
a
U _I ~ ~
R ~ O- ~ ,1
0
oE~ a~ 3 3
U~ R X
HO R R
ai S H dP d~
~ ~ U~
O
~ .
' .
O
~1 .,1 .,1 ~1
o a~ a~ O
U ~ 3 ~ 3 o
R ~ R _I
U~ 0
O d~ ,~ dP
U ~D l'C ~
~0 ~ _1 ~1 0
H o
~ .q R
P. P~
0
::
0
~ .
a~ a~ ~1
3 3 3 R~
R R R
dP d~
~ In o~
co ~ r-
-35
-
Example 4 104~330
Each of photoconductors I-VI of Table 1 are used to
form both homogeneous and aggregate photoconductive compositions
of the invention. The homogeneous photoconductive compositions
prepared in this example are prepared containing about 80~ by
weight of a polyester binder, about 0.8% by weight of the
sensitizer 2,6-bis(p-ethylphenyl)-4-(p-n-amyloxyphenyl)-thia-
pyrylium perchlorate, and about 19% by weight of each of photo-
conductors I-VI. The aggregate photoconductive compositions
10 prepared in this example contain about 80% by weight of poly-
carbonate binder, about 2.0% by weight of the sensitizer
2,6-diphenyl-4-(p-dimethylaminophenyl)-thiapyrylium perchlorate,
and about 18~ by weight of each of photoconductors I-VI of
Table 1. Relative H and D positive and negative shoulder and
100 toe volt electrical speeds are measured for each of these
photoconductive compositions as shown in Table 5.
In Examples 1-4 of the present application Relative
H & D Electrical Speeds are reported. The relative H & D
electrical speeds measure the speed of a given photoconductive
20 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 arbitrarily
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 photoconductive
material, n, relative to this value, Ro, may then be calculated as
follows: Rn = (An)(R/Ao) wherein An is the absolute
30 electrical speed of material n, Ro is the speed value .-
arbitrarily assigned to the first material, and Ao is the
-36-
10~30
absolute electrical speed of the first 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
until the surface potential, as measured by an electrometer
probe, reaches some suitable initial value VO' typically about
600 volts. The charged element is then exposed to a 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
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 character-
istic 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
20 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
30 an absolute value of 100 volts. Again, if one wishes to deter-
mine the 50 volt toe speed, one merely uses the exposure
-37-
10'~i33~)
required to reduce VO to an absolute yalue of 50 volts. Anapparatus useful for determining the electrophotographic speeds
of photoconductive compositions is described in Robinson et al,
U.S. Patent No. 3,449,658, issued June 10, 1969.
-38-
, - - , '::
~;
1046330
a) I ~ o ~ I~
O ~r ~D. O .. 00 . O
a) E~ ~ ,1~ co ~~ 1~ ~ 00 0
~ ~ ~ :
Z a) ~ :
~ O O~D OOO OO O ~D
,, o o~ ~U~U~ o~ o
_, ~ ,` U~
o
o o
~ U~ ,~
Cq ~ ~
~1 ~1
.
~ . . .. .. . a~
o U~ ~ ~ ,, ~ ~ oo
a~ ~ _I
.,,
~o ~ .,,
O ~ ~ I
P~ ~ O 1`~1 1~ 0 ~ o a
~1 O a:~_I co o oo ~ ~ o ~ Q,
~ ~ I o n
o ~ ~ ~ ~
~ o o
U~V~ ~ ~
o o
o o
~ ,.
o o
o ~ ~ ~
P:: ~ ~ ~ .
__
m Q~
~ s~ o ~o ~ oo ~ o ~ o ~ ~
m ,1 ,
tO 10
~ ~ ul la
o
:~
_I ~I
......
~ s~
o ~ ~C
_
115 0 H HH H H~ ~ p ~ H
E~l O H H HH H p
O H
-39-
.. . ..
104~330
The invention has been described in detail with
particular reference to preferred embodiments thereof but it
will be lmderstood that variations and modifications can be
effected within the spirit and scope of the invention.
~40-
.
,
"
