Cyanine and diane dye mixture provides near I. R. sensitive, charge transport layer, electrophotographic photoconductive element

Dual layer organic photoconductive elements which are stable, have good negative charge acceptance and are sensitive over a broad range of the spectrum, including near the infrared band, and the process for preparing same. The charge-generating layer comprises a mixture of a charge-generating diane dye, such as Chlorodiane Blue, and a cyanine dye as a near-infrared sensitizer.

BACKGROUND OF THE INVENTION 
The present invention relates to the field of electrophotographic 
reproduction and, more particularly, to dual layer organic photoconductive 
elements such as belts, drums, webs, or the like, which are used in 
machines such as copying machines. Reference is made to U.S. Pat. Nos. 
3,615,415, 3,824,099 and 4,150,987 for their discussion of the general 
field of the present invention and for their disclosures of some of the 
specific materials and procedures over which the present invention 
represents an improvement. 
Aforementioned U.S. Pat. Nos. 3,824,099 and 4,150,987 relate to dual layer 
organic photoconductive elements comprising a conductive substrate such as 
a conductive paper, metallized plastic film or metal plate, supporting two 
basic layers, namely a charge-generating layer and a charge-transport 
layer. Either layer may be adjacent the conductive substrate, and an 
adhesive bonding layer may be interposed to bond the charge-generating 
layer. 
During use, the photoconductive element is charged, exposed to light passed 
from the light reflective areas of an imaged original sheet to conduct 
away the charge in the exposed areas, and the charge-retaining or 
unexposed areas are either "inked" with electroscopic toner which is 
transferred to a copy sheet or are first transferred to a copy sheet and 
then "inked" with toner thereon. The toner is fused on the copy sheet to 
form fixed images corresponding to the images present on the original 
sheet. 
Dual layer organic photoconductive elements were developed in order to 
provide extremely fast response to light exposure within the visible range 
of the spectrum. Preferred materials in this respect are diane blue dyes 
as the charge-generating organic chemicals of the charge-generating layer 
and p-type hydrazones or triaryl pyrazolines as the organic chemicals in 
the charge-transport layer. 
Diane dyes have the general moiety structure as follows: 
##STR1## 
. . . wherein Z is a substitutent group on the phenyl ring. Preferably, Z 
is selected from a group consisting essentially of hydrogen, alkyl, alkoxy 
and chlorine groups, more preferably hydrogen, methyl, methoxy and 
chlorine groups; and most preferably a chlorine group. Z is preferably 
attached to the ring in the 2 or 6 position. The most preferred diane 
blue, Chlorodiane Blue, has chlorine as the Z group in the 2 position. 
Chlorodiane Blue is a preferred charge-generating material because it has 
good stability and provides photoconductive elements having a relatively 
good shelf life or duration of storage prior to break-down and 
deterioration or loss of its charge-generating properties. Chlorodiane 
Blue also has superior light sensitivity and charge-generating properties 
over a broad portion of the visible light range, i.e., between about 400 
m.mu. and 700 m.mu.. However, Chlorodiane Blue lacks adequate light 
sensitivity in the near-infrared range, i.e., between about 780 m.mu. and 
1150 m.mu.. 
Cyanine dyes are also known for use as charge-generating organic chemicals 
in dual layer organic photoconductive elements. Reference is made to the 
following Japanese Public Disclosure documents of the Japan KoKai Tokkyo 
Koho Company--Nos. 143,231/78; 21,343/79; 21,344/79; 21,345/79; 121,741/79 
and 121,742/79. However, attempts to produce organic photoconductive 
elements according to these Public Disclosures, following the procedure 
outlined in Example 1 of U.S. Pat. No. 4,150,987 with the substitution of 
cyanine dye for Chlorodiane Blue, result in elements which do not have 
adequate negative charge acceptance with which therefore are substantially 
useless as photoconductive elements for duplication purposes. However, we 
discovered that by combining a certain amount of the cyanine dye with a 
diane dye, such as Chlorodiane Blue, charger-generating layers can be 
produced which have the desired negative charge acceptance and which are 
also sensitive over a broad range of the spectrum including near-infrared 
radiation. 
SUMMARY OF THE INVENTION 
The novel dual-layer organic photoconductive elements of the present 
invention were developed in order to provide improved sensitivity 
photoconductive elements having an extremely fast response to light 
exposure within a wide range of the spectrum including not only the 
visible spectrum but also extending into and including the near-infrared 
range, i.e., within a broad range of from about 400 m.mu. up to about 1150 
m.mu.. 
The present invention is based upon the discovery that while 
charge-generating layers containing Chlorodiane Blue are only highly 
sensitive to light exposure within the visible range, i.e., between 400 
m.mu. and 700 m.mu. and thus are unsuitable for use with certain lasers as 
a light exposure source, and charge-generating layers based upon cyanine 
dye(s) lack the required negative charge acceptance of charge-generating 
layers based upon a diane dye such as Chlorodiane Blue, unexpectedly the 
combination of certain amounts of these charge-generating organic 
chemicals within the same charge-generating layer results in a layer which 
has the stability, negative charge acceptance and excellent sensitivity to 
light possessed by a diane dye, such as Chlorodiane Blue, but extending 
into and including a range of the near-infrared, i.e., within a range of 
between about 400 m.mu. and about 1150 m.mu., and thus is suitable for use 
with visible light sources as well as certain near-infrared light sources, 
such as certain lasers especially within a spectrum range of about 800 to 
about 850 m.mu., as the light exposure source. 
The novel combination of charge-generating organic chemicals comprises at 
least one diane dye and at least one cyanine dye. The basic moiety of the 
present cyanine dyes has a general structure as follows: 
EQU (A--(CH.dbd.CH).sub.n CH.dbd.B) Z.sup.- 
. . wherein n is an integer selected from a range of 2 to 4 inclusive, 
preferably 3, Z is an anion, such as I.sup.- or ClO.sub.4.sup.- ; and A 
and B are non-fused or fused hetero-cyclic rings. Preferably A is selected 
from a group consisting essentially of: 
##STR2## 
. . . and B.dbd. is selected from a group consisting essentially of: 
##STR3## 
. . . wherein R is an alkyl, substituted alkyl or aryl groups, preferably 
a methyl or ethyl group and X is selected from the group consisting of S, 
Se, O, NMe, NEt, CMe.sub.2 and CEt.sub.2 
Most preferably the cyanine dye is selected from the group consisting 
essentially of: 
##STR4## 
Generally, the effective weight percent of the cyanine dye sensitizer 
relative to the total weight of the charge-generating materials of the 
mixture can range between about 0.05% and 50.0%. Preferably, the diane dye 
is the major ingredient of the mixture and the cyanine dye comprises from 
about 1% to about 10% by weight of the mixture to produce the desired 
stability and high degree of sensitivity within a broad range of the 
spectrum including near infrared radiation. 
The charge-generating layers of the present invention may be formulated and 
coated in any manner conventional in the art of dual layer organic 
photoconductive elements, such as taught for instances by U.S. Pat. Nos. 
4,150,987 and 3,824,099. For example, the dye mixture may be dispersed and 
ground in a suitable volatile vehicle such as tetrahydrofuran, preferably 
at a concentration of between about 1% and 3%. The cyanine dye may be 
dissolved or dispersed in the vehicle. 
A preferred embodiment involves the application of the charge-generating 
layer over an adhesive bonding layer present on a conductive support, 
which support may be a conventional aluminized polyethylene terephthalate 
film available from duPont under the registered trademark Mylar. A 
preferred adhesive bonding layer comprises a continuous coating of one or 
more adhesive resins known in the art, such as available from Goodyear 
under the registered trademark Vitel PE200 and PE307. Suitable conductive 
supports and bonding layers are disclosed in aforementioned U.S. Pat. No. 
4,150,987. Alternatively, if desired, the present mixture of 
change-generating dyes can be mixed with a desired adhesive resin in a 
proper ratio, followed by coating onto the conductive surface of the 
substrate. Optionally, the substrate can also have an adhesive layer 
precoated on its conductive surface before the dye layer coating, as 
discussed above. 
As disclosed supra, the charge-transport layers suitable for use with the 
novel charge-generating layers of the present invention, and the method 
for preparing and applying the same in association with the present 
charge-generating layers, are conventional in the art and the pertinent 
disclosures of U.S. Pat. Nos. 3,615,415, 3,824,099 and 4,150,987 are 
incorporated herein by reference. The preferred charge-transport organic 
chemicals are the triaryl pyrazoline compounds of U.S. Pat. No. 3,824,099, 
such as 1-phenyl-3-[p-diethylaminostryl]-5-[p-diethylamino 
phenyl]-pyrazoline, and the hydrazone compounds of U.S. Pat. No. 
4,150,987, such as p-diethylaminobenzaldehyde-(diphenyl hydrazone). The 
charge-transfer chemical is dispersed or dissolved in a solution of one or 
more resinous binder materials and the charge-transport layer is applied 
and dried by evaporation of the volatile solvent, in known manner.

The following example is given to illustrate the present invention but is 
not to be considered as a limitation of the scope of the invention. 
EXAMPLE 1 
The general procedure disclosed in Example 1 of U.S. Pat. No. 4,150,987 was 
followed to prepare an organic photoconductive element according to the 
present invention except that the charge-generating layer was formulated 
and coated in the following manner. 
The charge-generating coating composition was produced by mixing together 
5.0 mg. of a cyanine dye, commercially-available from Eastman Organic 
Chemicals under the designation IR-140, and 0.267 g. of Chlorodiane Blue 
and adding to the mixture 15 ml. of tetrhydrofuran as a volatile vehicle 
to form a dispersion. The dispersion was ball milled for eight hours in a 
2-ounce jar using 1/8" chrome-plated balls until the maximum particle size 
of the dye particles is 0.25 mil or less, as measured with a fineness of 
Grind Measurer of the Precision Gauge and Tool Co. 
The conductive substrate of aluminized Mylar is first coated with an 
adhesive bonding layer comprising a mixture of equal parts by weight of 
Vitel PE-200 and Vitel PE-307, the bonding layer having a weight of about 
13 mg/ft.sup.2 over the aluminized surface of the Mylar substrate. 
The ground dye mixture dispersion is applied over the adhesive bonding 
layer using a Gardner-Ultra Applicator draw down blade with the blade set 
at a gap of 10, i.e., 1 mil. the dye coating was dried by evaporation of 
the vehicle to form the charge-generating layer. 
Thereafter, a hydrazone charge-transfer layer was formulated and applied 
over the dye layer in the manner disclosed in Example 1 of U.S. Pat. No. 
4,150,987 in a coat weight of about 1.8 g/ft.sup.2. 
The organic photoconductive element of Example 1 supra was compared with 
the photoconductive element product in exact accordance with Example 1 of 
U.S. Pat. No. 4,150,987 with respect to photosensitivity to light in the 
near-infrared region of the spectrum using a Victoreen Electrostatic Paper 
Analyzer with a Kodak #87 filter positioned between the tungsten lamp and 
the sample. 
The amount of energy required to discharge the charge acceptance from -400 
volts to -200 volts, i.e., E 1/2, was measured in identical fashion for 
each of the samples. The amount of energy required by the sample produced 
according to Example 1 herein was determined to be about 950 
.mu.J/cm.sup.2, whereas the amount of energy required by the sample 
produced according to Example 1 of U.S. Pat. No. 4,150,987 was determined 
to be about 7100 .mu.J/cm.sup.2, i.e., nearly 7.5 times less sensitivity 
to the near-infrared radiation transmitted by the Kodak #87 filter. 
Variations and modifications of the present invention will be apparent to 
those skilled in the art within the scope of the present claims.