Method of image formation which includes scanning exposure process

A photoconductive composition which exhibits excellent dark reduction retention, excellent sensitivity to radiation from the near infrared region to the infrared region as well as excellent long-term stability, is comprised of an inorganic photoconductor, a cyclic acid anhydride and a spectral sensitizing dye dispersed in a binding resin. A laser beam scanning exposure can be performed on said composition to produce electrophotographic images.

FIELD OF THE INVENTION 
This invention relates to a method of image formation which includes a 
scanning exposure process. More particularly, it relates to a method of 
image formation which includes a scanning exposure process in which use is 
made of a photoconductive composition, said composition comprising an 
inorganic photoconductor which has good dark charge-retaining properties 
and which has been spectrally sensitized to radiation from the near 
infrared region to the infrared region by a spectral sensitizing dye, and 
a cyclic acid anhydride dispersed in a binding resin. The invention also 
relates to electrophotographic recording systems. 
BACKGROUND OF THE INVENTION 
Recording systems in which a laser beam is used, which is to say laser beam 
recording systems, exist for electrophotographic recording purposes. In 
these systems a recording is made by focusing the laser light emerging 
from a laser with an f.theta. lens, forming a scanning image on a 
photosensitive body by means of a polygonal mirror and developing and 
transcribing this image as required. 
The development of photosensitive materials which are sensitive to the 
wavelength region about 700 nm has become desirable in recent years as a 
result of the development of low output semiconductor lasers (in practice, 
lasers which have an output of some 5 to 25 mW). The electrophotographic 
photosensitive materials used with semiconductor lasers of this type 
require various properties different from those of the conventional 
electrophotographic photosensitive materials. Thus, an adequate 
sensitivity to radiation from the near infrared region into the infrared 
region and good dark charge-retaining properties are especially important. 
The use of various spectral sensitizing dyes in electrophotographic 
photosensitive layers comprising photoconductor-resin dispersion based 
photoconductive composition is known. For example, dyes for spectral 
sensitization to red light and infrared radiation have been disclosed in 
U.S. Pat. Nos. 3,619,154 and 3,682,630, but these dyes are easily degraded 
particularly during the storage of the dye or during the manufacture and 
storage of the electrophotographic photosensitive layer and so their 
performance is poor and this is greatly disadvantageous in practice. 
Harazaki et al. have stated that the sensitizing dyes for red light and 
infrared radiation are more unstable that the sensitizing dyes for light 
of shorter wavelengths (visible light) (Industrial Chemistry Journal 
(Japanese), Vol. 66, No. 2, page 26 (1963)). 
Furthermore, cyanine dyes for spectral sensitization when zinc oxide is 
used as a photoconductor have been disclosed in Japanese Patent 
Application (OPI) Nos. 58554/83, 42055/83 and 59453/83 (the term "OPI" as 
used herein refers to a "published unexamined Japanese patent 
application"). However, these cyanine dyes do not extend into the near 
infrared and infrared wavelength regions nor are they sufficiently stable 
in the photosensitive body. Thus, in either case it is impossible to 
achieve a satisfactory level of sensitivity. 
Electrophotographic photosensitive materials comprising photoconductive 
compositions which contain heptamethine cyanine dyes which have a 
3,3-dialkylindole ring or a 3,3-dialkylbenzo[e]indole ring at both ends 
are disclosed in U.S. Pat. No. 4,362,800. The sensitized range of these 
photosensitive materials extends to 750 nm and above and they also have 
good stability. 
However, there is a disadvantage in that these prior art 
electrophotographic photosensitive materials have inadequate dark 
charge-retaining properties. As mentioned above, the situation when a 
semiconductor laser is used as a light source differs from that in 
conventional full-surface exposure systems in which visible light is used, 
in that a scanning exposure system is used and the period beginning from 
the time at which the photosensitive material is charged until the 
exposure is completed is longer. The unexposed parts must retain their 
charge satisfactorily during this time. Thus, dark charge-retaining 
properties are a very important feature for electrophotographic 
photosensitive materials for use with scanning exposures. 
Furthermore, the light sources have a low output and so a sufficiently high 
sensitivity in the near infrared to infrared region is required. The prior 
art electrophotographic photosensitive materials mentioned above are also 
inadequate in this respect. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a method of image formation which 
includes a process of scanning exposure with a laser beam using a 
photoconductive composition which has an adequate sensitivity to radiation 
in the near infrared to infrared region and which has superior dark 
charge-retaining properties. 
The above mentioned object is achieved by means of a method of image 
formation comprising exposing a photoconductive body comprising a 
photoconductive composition to a scanning laser beam and developing the 
exposed photosensitive body, wherein the photoconductive composition 
comprises at least an inorganic photoconductor, a spectral sensitizing 
dye, a cyclic acid anhydride dispersed in a binding resin, wherein the 
spectral sensitizing dye is a compound containing at least one carboxyl 
group, sulfo group and/or phospho group represented by the general formula 
(I): 
##STR1## 
In formula (I), R.sub.1, R.sub.2, R.sub.3 and R.sub.4 may be the same or 
different and each represents an alkyl group. 
L.sub.1 to L.sub.7 may be the same or different and each represents a 
substituted or unsubstituted methine group. The substituent group may be a 
halogen atom, a hydroxyl group, a carboxyl group, an alkyl group, an 
aralkyl group, an aryl group, an --OR'.sub.1 group, an --OCOR'.sub.2 group 
or a --COOR'.sub.3 group (wherein R'.sub.1, R'.sub.2 and R'.sub.3 each 
represents an alkyl group, an alkenyl group, an aralkyl group or an aryl 
group). 
X.sub.1 to X.sub.8 may be the same or different and each represents a 
hydrogen atom, a carboxyl group, a sulfo group, a halogen atom, a nitro 
group, a cyano group, a substituted or unsubstituted alkyl group, a 
substituted or unsubstituted aralkyl group, a substituted or unsubstituted 
aryl group, an --O--Z.sub.1 group (wherein Z.sub.1 represents a 
substituted or unsubstituted aliphatic group, a substituted or 
unsubstituted aromatic group or a substituted or unsubstituted 
heterocyclic group), an --OCOZ.sub.2 group (wherein Z.sub.2 has the same 
meaning as Z.sub.1), a --COOZ.sub.3 group (wherein Z.sub.3 has the same 
meaning as Z.sub.1), a 
##STR2## 
(wherein Z.sub.4 and Z.sub.5 may be the same or different and each 
represents a hydrogen atom, a substituted or unsubstituted aliphatic 
group, a substituted or unsubstituted aromatic group or together represent 
an organic group, which together with the adjacent atom, N, form a 
heterocyclic group), or an 
##STR3## 
(wherein Z.sub.6 and Z.sub.7 have the same meaning as Z.sub.4 and 
Z.sub.5). 
Furthermore, X.sub.5 and X.sub.6 may be connected to each other to form a 
benzene ring. 
Moreover, at least one of X.sub.1 to X.sub.8 represents a group other than 
a hydrogen atom. 
Y.sub.1 and Y.sub.2 may be the same or different and each represents a 
substituted or unsubstituted alkyl group. 
A.sup..crclbar. represents an anion. 
.gamma. represents 1 or 2, with the proviso that, when Y.sub.1 and/or 
Y.sub.2 contains a sulfo group or a phospho group, .gamma. is 1. 
DETAILED DESCRIPTION OF THE INVENTION 
Laser beam recording is normally carried out by focusing the laser light 
which emerges from a gas laser such as an He-Cd or He-Ne laser or a 
semiconductor laser such as a GaAlAs laser, etc., using an f.theta. lens, 
forming a scanning image on a photosensitive body by means of a polygonal 
mirror and developing and transcribing the image as required. When a gas 
laser is used, it is necessary to use a light modulator. Since a 
semiconductor laser is both smaller and lighter than a gas laser and has 
the advantage of not requiring the use of a modulator, semiconductor 
lasers are coming into greater use. However, the light from a practical 
GaAlAs semiconductor laser has an emitted wavelength of about 780 nm and 
so the photoconductive compositions which are used must be sensitive to 
laser light of this wavelength. 
In laser beam scanning recording, the laser light is deflected by a 
rotating mirror. In the case of planar scanning, the scanning rate is a 
function of the deflection angle and strain appears in the copy so an 
f.theta. lens, etc., is used in the optical system to improve linearity. 
The reflecting surfaces of the polygonal mirror can be made with a 
curvature to make up for the scanning strain instead of using an f.theta. 
lens. Other systems can be adopted for the scanning system; for example, 
systems in which a mirror is moved in a parallel manner and systems in 
which a plurality of mirrors is used can be adopted. 
Zinc oxide, titanium oxide, zinc sulfide, cadmium sulfide, zinc selenide, 
cadmium selenide, lead sulfide, etc., can be used as the inorganic 
photoconductor which is used in the method of image formation of this 
invention. Furthermore, these photoconductors may also be treated 
photoconductors as disclosed, for example, by H. Miyamoto and H. Takei in 
Imaqing, 1973 (No. 8). 
The specific compounds represented by the general formula (I) useful in the 
present invention are such that R.sub.1, R.sub.2, R.sub.3 and R.sub.4 can 
be the same or different and each preferably represents an alkyl group 
which has from 1 to 4 carbon atoms (for example, a methyl group, an ethyl 
group, a propyl group or a butyl group). 
L.sub.1 to L.sub.7 each represents a substituted or unsubstituted methine 
group. Suitable examples of substituent groups include, for example, a 
halogen atom (for example, a fluorine atom, a chlorine atom, a bromine 
atom, an iodine atom), a hydroxyl group, a carboxyl group, an alkyl group 
which has from 1 to 8 carbon atoms and which may be substituted (for 
example, a methyl group, an ethyl group, a propyl group, a butyl group, a 
hexyl group, an octyl group, a chloromethyl group, a hydroxymethyl group, 
a trifluoromethyl group, a methoxymethyl group, an ethoxymethyl group, a 
butoxymethyl group, etc.), an aralkyl group which has from 7 to 10 carbon 
atoms and which may be substituted (for example, a benzyl group, a 
phenethyl group, a chlorobenzyl group, a methoxybenzyl group, a 
methylbenzyl group, an ethoxybenzyl group, a phenoxybenzyl group, etc.), a 
phenyl group which may be substituted (for example, a phenyl group, a 
chlorophenyl group, a bromophenyl group, a dichlorophenyl group, a 
carboxyphenyl group, a methoxyphenyl group, a tolyl group, a xylyl group, 
an acetamidophenyl group, etc.), an OR'.sub.1 group, an -OCOR'.sub.2 group 
or a -COOR'.sub.3 group wherein R'.sub.1, R'.sub.2 and R'.sub.3 each 
preferably represents an alkyl group which has from 1 to 8 carbon atoms 
and which may be substituted (for example, a methyl group, an ethyl group, 
a propyl group, a butyl group, a hexyl group, a 2-chloroethyl group, a 
2-bromoethyl group, a 2-methoxyethyl group, a 2-cyanoethyl group, a 
3-methoxypropyl group, a 3-sulfopropyl group, a 4-sulfobutyl group, a 
carboxymethyl group, a 2-carboxyethyl group, a 3-carboxypropyl group, a 
4-carboxybutyl group, a 2-ethoxycarbonylethyl group, a 3-hydroxypropyl 
group, etc.), an alkenyl group which has from 2 to 8 carbon atoms and 
which may be substituted (for example, a vinyl group, an allyl group, a 
3-butenyl group, a 6-hexenyl group, a 2-pentenyl group, a 2-hexenyl group, 
an isoprene group, etc.), an aralkyl group which has from 7 to 12 carbon 
atoms and which may be substituted (for example, a benzyl group, a 
phenethyl group, a chlorobenzyl group, a dichlorobenzyl group, a 
methoxybenzyl group, a methylbenzyl group, a carboxybenzyl group, a 
sulfobenzyl group, etc.) or a phenyl group which may be substituted (for 
example, a phenyl group, a tolyl group, a xylyl group, a cumenyl group, a 
chlorophenyl group, a bromophenyl group, an indenyl group, a methoxyphenyl 
group, a dichlorophenyl group, a cyanophenyl group, a chloromethoxyphenyl 
group, an acetamidophenyl group, a chloromethylphenyl group, etc.). 
X.sub.1 to X.sub.8 may be the same or different and each represents a 
hydrogen atom; a carboxyl group; a sulfo group; a halogen atom (for 
example, a fluorine atom, a chlorine atom, a bromine atom, etc.); a nitro 
group; a cyano group; an alkyl group which preferably has from 1 to 6 
carbon atoms and which may be substituted (for example, a methyl group, an 
ethyl group, a propyl group, a butyl group, a hexyl group, a chloromethyl 
group, a trifluoromethyl group, a 2-methoxyethyl group, a 2-chloroethyl 
group, etc.); an aralkyl group which preferably has from 7 to 12 carbon 
atoms and which may be substituted (for example, a benzyl group, a 
phenethyl group, a chlorobenzyl group, a dichlorobenzyl group, a 
methoxybenzyl group, a methylbenzyl group, a dimethylbenzyl group, etc.); 
an aryl group which may be substituted (for example, a phenyl group, a 
naphthyl group, an indenyl group, a tolyl group, a xylyl group, a mesityl 
group, a chlorophenyl group, a dichlorophenyl group, an ethoxyphenyl 
group, a cyanophenyl group, an acetylphenyl group, a methanesulfonylphenyl 
group, etc.); an --O--Z.sub.1 group, an --OCOZ.sub.2 group or a 
--COOZ.sub.3 group [wherein Z.sub.1, Z.sub.2 and Z.sub.3 preferably have 
the same meaning as R'.sub.1, R'.sub.2 and R'.sub.3, respectively, 
described above or each represents a heterocyclic group (for example, a 
thienyl group, a pyridyl group, an imidazolyl group, a chlorothienyl 
group, a pyrrole group, etc.)]; a 
##STR4## 
or an 
##STR5## 
wherein Z.sub.4, Z.sub.5, Z.sub.6 and Z.sub.7 may be the same or different 
and each represents a hydrogen atom, an alkyl group which preferably has 
from 1 to 8 carbon atoms and which may be substituted (for example, a 
methyl group, an ethyl group, a propyl group, a butyl group, a hexyl 
group, an octyl group, a 2-chloroethyl group, a 3-chloropropyl group, a 
3-hydroxypropyl group, a 2-bromoethyl group, a 2-hydroxyethyl group, a 
2-sulfoethyl group, a 2-cyanoethyl group, a 2-methoxyethyl group, a 
2-ethoxyethyl group, a 2-carboxyethyl group, a 3-hydroxypropyl group, a 
4-hydroxypropyl group, a 2-(4-sulfobutyl)ethyl group, a 
2-methanesulfonylethyl group, a 3-ethoxypropyl group, a 
2,2,2-trifluoroethyl group, etc.), an alkenyl group which preferably has 
from 2 to 8 carbon atoms and which may be substituted (for example, a 
vinyl group, an allyl group, a 3-butenyl group, a 2-hexenyl group, a 
6-hexenyl group, etc.), an aralkyl group which preferably has from 7 to 12 
carbon atoms and which may be substituted (for example, a benzyl group, a 
phenethyl group, a chlorobenzyl group, a methylbenzyl group, a sulfobenzyl 
group, a carboxybenzyl group, a methoxycarbonylbenzyl group, an 
acetamidobenzyl group, a methoxybenzyl group, a dichlorobenzyl group, a 
cyanobenzyl group, a trimethylbenzyl group, etc.) or a phenyl group which 
may be substituted (for example, a phenyl group, a tolyl group, a xylyl 
group, a butylphenyl group, a chloromethylphenyl group, a methoxyphenyl 
group, an ethoxyphenyl group, a butoxyphenyl group, an acetamidophenyl 
group, a carboxyphenyl group, a sulfophenyl group, a 
trifluoromeothylphenyl group, a chloromethylphenyl group, etc.), or 
Z.sub.4 and Z.sub.5, or Z.sub.6 and Z.sub.7 together may be an organic 
group which together with the adjacent atom, N, form a heterocyclic group 
(for example, a piperazyl group, a piperidyl group, an indolinyl group, a 
morpholinyl group, an isoindolinyl group, etc.). 
Moreover, at least one of X.sub.1 to X.sub.8 represents a group other than 
a hydrogen atom. 
Y.sub.1 and Y.sub.2 may be the same or different and each preferably 
represents an alkyl group which has from 1 to 12 carbon, atoms and which 
may be substituted with groups other than a carboxyl group, a sulfo group 
or a phospho group (for example, a methyl group, an ethyl group, a propyl 
group, a butyl group, a pentyl group, a hexyl group, an octyl group, a 
decyl group, a dodecyl group, a benzyl group, a phenethyl group, an allyl 
group, a 2-hydroxyethyl group, a 3-hydroxypropyl group, a 6-hydroxyhexyl 
group, a 10-hydroxydecyl group, a 2-methoxyethyl group, a 2-ethoxyethyl 
group, a 3-cyanopropyl group, a methoxycarbonylmethyl group, a 
3-ethoxycarbonylpropyl group, a 4-methoxycarbonylbutyl group, an 
N,N-dimethylaminoethyl group, an N-methyl-N-benzylaminopropyl group, a 
2-acetoxyethyl group, a 2-propionyloxyethyl group, a 3-butyryloxypropyl 
group, etc.) or an alkyl group which has from 1 to 12 carbon atoms and 
which is substituted with at least one carboxyl group, sulfo group and/or 
phospho group and which may have other substituent groups (for example, a 
carboxymethyl group, a 2-carboxyethyl group, a 3-carboxypropyl group, a 
4-carboxybutyl group, a 2-carboxypropyl group, a 2-carboxybutyl group, a 
5-carboxyheptyl group, a 2-chloro-3-carboxypropyl group, a propyl group, a 
2-(3'-carboxypropylcarbonyloxy)ethyl group, a 6-carboxyhexyl group, a 
2'-carboxybenzyl group, a 4'-carboxybenzyl group, a 
3-(2'-carboxyethylcarbonyloxy)propyl group, a 
2-(2'-carboxyethylcarbamoyl)ethyl group, a 2-(2'-carboxyethyloxy)ethyl 
group, a 2-sulfoethyl group, a 3-sulfopropyl group, a 4-sulfobutyl group, 
a 2-(3'-sulfopropyloxy)ethyl group, a 2-(4'-sulfobutyloxy)ethyl group, a 
3-(4'-sulfobutyloxy)propyl group, a 4-(o'-sulfobenzoyloxy)butyl group, a 
5-sulfo-pentyl group, an 8-sulfooctyl group, a 10-sulfodecyl group, a 
4-(4'-sulfobutyloxy)butyl group, a 6-( 4'-sulfobutyloxy)hexyl group, a 
2-(4'-sulfobutylamino)ethyl group, a 2'-sulfobenzyl group, a 
4'-sulfobenzyl group, a 2-phosphoethyl group, a 2-phosphooxyethyl group, a 
3-phosphooxypropyl group, a 4-phosphooxybutyl group, a 3-phosphooxybutyl 
group, a 6-phosphooxyhexyl group, a 4'-phosphobenzyl group, a 
4'-phosphooxybenzyl group, etc.). Furthermore, these carboxyl groups, 
sulfo groups and phospho groups may take the form of a carbonate, 
sulfonate or phosphonate which is bonded to a cation. Alkali metal ions 
(for example, lithium ions, sodium ions, potassium ions, etc.) and 
alkaline earth metal ions (for example, magnesium ions, calcium ions, 
barium ions, etc.), etc., are preferred as the cation. 
Moreover, the above carboxyl groups and sulfo groups may take the form of 
salts with organic bases (for example, pyridine, morpholine, 
N,N-dimethylaniline, triethylamine, pyrrolidine, piperidine, etc.). 
A.sup..crclbar. represents an anion such as a chlorine ion, a bromine ion, 
an iodine ion, a thiocyanate ion, a methyl sulfate ion, an ethyl sulfate 
ion, a benzenesulfonate ion, a p-toluenesulfonate ion, a perchlorate ion, 
a boron tetrabromide ion, etc. 
Moreover, .gamma. represents 1 or 2. In cases where a sulfo group or a 
phospho group is included in said dye molecule, an intramolecular salt is 
formed and has a value of 1. 
Furthermore, the compounds which can be represented by general formula (I) 
contain at least one carboxyl group, sulfo group and/or phospho group. 
Preferred compounds of formula (I) are those containing at least two 
groups selected from the carboxyl, sulfo and phospho groups, and more 
preferred compounds are those containing at least two sulfo groups. 
Examples of compounds which are represented by general formula (I) useful 
in the invention are indicated below, but the range of such compounds is 
not limited to these examples. 
##STR6## 
The heptamethine dyes which are used in the invention can be prepared using 
the conventional methods of preparation. For example, they can be prepared 
using the method disclosed in Japanese Patent Application (OPI) No. 
46245/82. Various other methods are disclosed by F. M. Hamer in The 
Cyanine Dyes and Related Compounds, published by John Wiley and Sons, New 
York, 1964. 
Cyclic anhydrides of organic acids are typical of the cyclic acid 
anhydrides which are used in the invention. The cyclic anhydride of an 
organic acid may be a cyclic anhydride of an aliphatic dicarboxylic acid 
which may be substituted (for example, succinic anhydride, 
2-methylsuccinic anhydride, 2-ethylsuccinic anhydride, 2-butylsuccinic 
anhydride, 2-octylsuccinic anhydride, decylsuccinic anhydride, 
2-dodecylsuccinic anhydride, 2-octadecylsuccinic anhydride, maleic 
anhydride, methylmaleic anhydride, dimethylmaleic anhydride, phenylmaleic 
anhydride, chloromaleic anhydride, dichloromaleic anhydride, fluoromaleic 
anhydride, difluoromaleic anhydride, bromomaleic anhydride, itaconic 
anhydride, citraconic anhydride, glutamic anhydride, adipic anhydride, 
diglycol anhydride, pimelic anhydride, suberic anhydride, 
cis-5-norborneneendo-2,3-dicarboxylic acid, d-camphoric anhydride, 
3-oxybicyclo[3,2,2]nonane-2,4-dione, 1,3-dioxolan-2,4-dione, etc.); an 
.alpha.-amino acid-N-carboxylic acid anhydride (for example, taking the 
.alpha.-amino acid starting material, glycine, N-phenylglycine, alanine, 
.beta.-phenylalanine, valine, leucine, isoleucine, 
.alpha.-aminophenylacetic acid, .alpha.-aminocaprylic acid, 
.alpha.-aminolauric acid, .gamma.-benzylglutamic acid, sarcosine, etc.); a 
cyclic aromatic acid anhydride (for example, phthalic anhydride, 
nitrophthalic anhydride, dinitrophthalic anhydride, methoxyphthalic 
anhydride, methylphthalic anhydride, chlorophthalic anhydride, 
cyanophthalic anhydride, dichlorophthalic anhydride, tetrachlorophthalic 
anhydride, tetrabromophthalic anhydride, 
3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, phthalonic 
anhydride, pyromellitic anhydride, mellitic anhydride, pulvinic anhydride, 
diphenic anhydride, thiophene dicarboxylic acid anhydride, furan 
dicarboxylic acid anhydride, 1,8-naphthalene dicarboxylic acid anhydride, 
pyrrole dicarboxylic acid anhydride, etc.). 
Any conventional binding resin can be used in this invention. For example, 
such resins are disclosed by H. Miyamoto and H. Takei on pages 9 to 12 of 
Imaging, 1973 (No. 8); by D. D. Tatt, S. C. Heidecker in Tappi, 49 (10), 
439 (1966); by E. S. Baltazzi, R. G. Banchette and R. Minnis in 
Photographic Science and Engineering, 16 (5), 354 (1972) and by Guen Chan 
Kee, E. Inoue and I. Shimizu in Journal of the Electrophotographic Society 
(Japanese), 18 (2), 28 (1980). In practice, vinyl chloride-vinyl acetate 
copolymers, styrene-butadiene copolymers, styrene-methacrylate copolymers, 
polymethacrylates, polyacrylates, acrylic resins, poly(vinyl acetate), 
poly(alkane acid vinyl esters), poly(vinyl butyral), alkyd resins, 
modified alkyd resins, silicone resins, polyamide resins, epoxy resins, 
maleic acid resins, epoxyester resins, polyester resins, etc., can be used 
for this purpose either individually or conjointly. Furthermore, they can 
be combined with aqueous acrylic emulsions and acrylic ester emulsions. 
Furthermore, the numerous.well known methacrylic ester based copolymers 
which contain carboxyl groups and hydroxyl groups of Japanese Patent 
Document Nos. 13946/66, 2242/75 and 31011/75 and Japanese Patent 
Application (OPI) Nos. 54027/78 and 20735/79, etc., can be used as the 
binding resins for the inorganic photoconductor layers of original plates 
for lithographic printing (offset masters) in an electrophotographic 
system. 
In general, it is possible to vary the amount of binding resin which is 
present in a photoconductive composition of this invention. Typically, the 
useful quantity of resin is within the range from about 10 wt % to about 
90 wt % with respect to the total weight of the mixture of photoconductive 
material and resin. The preferred amount of resin is within the range from 
about 15 wt % to about 60 wt % with respect to the total amount of 
photoconductive material and resin. 
The sensitizing dyes used in the photoconductive compositions used in the 
invention are preferred to the conventional red light and infrared 
radiation sensitizing dyes in that they have much better stability and 
improved adsorption properties on the above mentioned inorganic 
photoconductors since at least one carboxyl group, sulfo group or phospho 
group is contained within the molecule and so the spectral sensitization 
efficiency is improved. As a result, these dyes provide superior spectral 
sensitization. 
Moreover, the photoconductive compositions used in the invention also 
contain a cyclic acid anhydride which interacts with the surface of the 
inorganic photoconductors. As a result of this, it improves the charging 
characteristics, brings about a marked improvement of the charge-retaining 
properties of the photoconductors in the dark, and functions in such a way 
as to enhance sensitizing action of the sensitizing dyes of this 
invention. Hence, a sulfo group or a phospho group is preferred for the 
acidic group which is contained in the sensitizing dye to provide a more 
efficient interaction between the sensitizing dyes, cyclic acid anhydrides 
and the photoconductor. 
Furthermore, methacrylic ester-based resins which contain polar groups such 
as carboxyl groups or hydroxyl groups which interact strongly with the 
surfaces of zinc oxide grains are used as the normal binding agents in 
photosensitive bodies for offset masters in which zinc oxide is used as 
the inorganic photoconductor. Sensitizing dyes which contain a sulfo group 
or a phospho group are also preferred in this case. 
The sensitizing dyes may be used in any known methods for preparing a 
photoconductive composition including methods in which a dye solution is 
added after dispersing the photoconductor in the binding resin, and 
methods in which the photoconductor is introduced into a dye solution and 
dispersed in the binding resin after adsorbing dye. The amount of 
sensitizing dye used in the invention is proportional to the degree of 
sensitization required and extends over a wide range. Amounts ranging from 
0.0005 to 2.0 parts by weight per 100 parts by weight of photoconductor 
can be used but the amount used is preferably within the range from 0.001 
to 1.0 part by weight per 100 parts by weight of the photoconductor. 
The cyclic acid anhydride can be used in this invention together with the 
sensitizing dye in the form of a powder or as a solution. It may be added 
before the addition of the dye, or the anhydride can be premixed with the 
photoconductor and followed by the introduction of the binding agent and 
the dye and dispersion. The method in which the photoconductor and the 
cyclic acid anhydride are treated beforehand is preferred. 
The amount of cyclic acid anhydride used in the present invention can be 
from 0.0001 to 1.0 part by weight per 100 parts by weight of the 
photoconductor. If the amount used is below the above range, the effect on 
the charging characteristics, dark charge-retaining properties and 
sensitization cannot be obtained. The use of an amount higher than the 
above range improves the apparent sensitivity but results in a marked 
decrease in the dark charge-retaining properties. 
The sensitizing dyes and cyclic acid anhydrides used in the present 
invention can be included individually or in combinations of two or more 
in the photosensitive layer. Furthermore, although the sensitizing dyes of 
this invention provide spectral sensitization from near infrared to 
infrared radiation, they can be used conjointly with conventional spectral 
sensitizing dyes for use in visible light (for example, fluorescein, rose 
bengal, rhodamine B, monomethine, trimethine and pentamethine type cyanine 
dyes, merocyanine dyes, etc.) depending on the intended purpose. 
Furthermore, various additives conventionally used in electrophotographic 
photosensitive layers can also be added (for example, the known materials 
indicated on page 12 of Imaging, 1973, (No. 8) by H. Miyamoto and H. 
Takei). The amounts added are selected such that they do not interfere 
with the effect of the invention; generally they are added in amounts from 
0.0005 to 2.0 parts by weight per 100 parts by weight of photoconductor. 
In general, the sensitizing dyes are weakly oxidizing, thus the conjoint 
use of catalytic compounds which promote oxidation should be avoided. For 
example, care is required with the use of peroxides such as benzoyl 
peroxide from among the vinyl polymerization initiators and the organic 
salts of heavy metals which are used to bring about the curing of 
unsaturated fatty acids. In this respect similar care must be taken with 
the sensitizing dyes used in the invention as with conventional 
sensitizing dyes. There is a difficulty in that with the conventional red 
light to infrared radiation sensitizing dyes degradation occurs in a short 
period of time even in systems where oxidation accelerators are not being 
used conjointly. However, the stability is appreciably improved when a dye 
of general formula (I) of this invention is used. 
The electrophotographic photosensitive layers of this invention can be 
provided on a conventional support. Electrically conductive supports are 
generally preferred for electrophotographic photosensitive layers. Metal 
sheets, plastic films on which an electrically conductive layer has been 
provided (for example, those which have a thin layer of aluminum, 
palladium, indium oxide, tin oxide, cuprous iodide, etc.) and paper which 
has been treated to render it electrically conductive can be used. 
Polymers which contain quaternary ammonium salts (for example, 
poly(vinylbenzyltrimethylammonium chloride); the polymers which contain 
quaternary nitrogen in the main chain as disclosed in U.S. Pat. Nos. 
4,108,802, 4,118,231, 4,126,467 and 4,137,217 and the quaternary salt 
polymer latexes as disclosed in U.S. Pat. No. 4,147,550 and Research 
Disclosure, 16258, etc.); sulfonic acid salts of polystyrene, and 
colloidal alumina, etc., are well known as agents for treating paper so as 
to render it electrically conductive. In normal practice, these are often 
used conjointly with poly(vinyl alcohol), styrene-butadiene latex, 
gelatin, casein, etc. 
Volatile hydrocarbon solvents having boiling points less than 200.degree. 
C. can be used as organic solvents for dispersion purposes. Halogenated 
hydrocarbons which have from 1 to 3 carbon atoms, such as dichloromethane, 
chloroform, 1,2-dichloroethane, tetrachloroethane, dichloropropane or 
trichloroethane, etc., are preferred. Aromatic hydrocarbons such as 
chlorobenzene, toluene, xylene or benzene, etc.; ketones such as acetone 
or 2-butanone, etc.; ethers such as tetrahydrofuran, etc.; various other 
solvents which can be used for coating compositions such as methylene 
chloride, etc., and mixtures of these solvents can also be used. The 
solvent is added at the rate of 1 to 100 g, and preferably 5 to 20 g, per 
g in total of dye, photoconductive material and other additives. 
The coated thickness on an appropriate support of the photoconductive 
composition of this invention can be varied over a wide range. Normally, 
it can be coated to a thickness within the range from about 10 .mu.m to 
about 300 .mu.m (before drying). The preferred range for the coated 
thickness before drying is within the range from about 50 .mu.m to about 
150 .mu.m. However, beneficial effects can be obtained even outside this 
range. The thickness of the dried coated material may be within the range 
from about 1 .mu.m to about 50 .mu.m. 
The photoconductive compositions used in the invention can be used for the 
photosensitive layers (photoconductive layers) of an electrophotographic 
photosensitive material of the single layer type. They may be also used as 
charge carrier generating layers in electrophotographic photosensitive 
materials of the separated function type which have two layers, namely a 
charge carrier generating layer and a charge carrier transporting layer. 
They may also be used as photoconductive photosensitive particles in 
photoelectrophoresis electrophotographic methods or for the 
photoconductive compositions which are used for said methods.

The present invention is further illustrated in greater detail by the 
following examples, but the present invention is not limited by these 
examples. Unless indicated otherwise, all parts, percents, ratios and the 
like are by weight. 
EXAMPLE 1 
100 Parts of fine particles of zinc oxide (average particle size 0.5 to 1 
.mu.m, Sazex 2000 .RTM., made by Sakai Kagaku) was mixed with 0.2 part of 
phthalic anhydride and this mixture was mixed with 40 parts of a 40 wt % 
toluene solution of a methyl methacrylate/n-butyl methacrylate/acrylic 
acid (weight ratio 39.2/58.8/2.0) copolymer, 60 parts of toluene and 10 
parts of a methanolic solution of dye containing 1.0.times.10.sup.-3 
mol/liter of Compound (8) of this invention, and a dispersion was formed 
by milling these together for 2 hours in a ceramic ball mill. The 
dispersion was then coated onto an aluminum foil using a wire rod so as to 
provide a dry film thickness of about 8 .mu.m. An electrophotographic 
photosensitive body was obtained on drying for 2 hours at 50.degree. C. in 
a constant temperature vessel. 
The photosensitive body was given a coronal charge at 6 kV using a static 
system, stored in the dark for a period of 60 seconds and then exposed to 
light, and the charging characteristics were investigated using a paper 
analyzer (model SP-428, made by Kawaguchi Denki). Thus, the initial charge 
potential (V.sub.0), the extent to which the potential was retained with 
respect to the initial potential (V.sub.0) after reducing in the dark for 
60 seconds, which is to say the dark reduction retention (DRR (%)), and 
the exposure required to reduce the potential to one half after charging 
to -400 V with a coronal discharge, which is to say the half reduction 
exposure E.sub.1/2 (erg/cm.sup.2), were measured. A 
gallium-aluminum-arsenic semiconductor laser (oscillating wavelength 780 
nm) was used for the light source. The results were as shown in Table 1. 
The optical densities at the peak absorption wavelength in the range from 
700 nm to 850 nm of the spectral reflecting powers immediately after 
manufacture and after storing for 2 weeks under conditions of 50.degree. 
C., 80% RH were measured for this photosensitive body. The stability was 
assessed by obtaining the value of the optical density after the 
accelerated test divided by the optical density immediately after 
production (the material being more stable as this ratio approaches a 
value of 1). There was virtually no change to be seen, the value being 
greater than 0.99, and there was no change in the electrostatic 
characteristics (V.sub.0, DRR, E.sub.1/2). 
COMATIVE EXAMPLE 1 
A photosensitive body was prepared in exactly the same way as in Example 1 
except that the phthalic anhydride was not added in this case. The dark 
reduction retention and the half reduction exposure were measured in the 
same way as in Example 1 and the results obtained were as shown in Table 
1. 
TABLE 1 
______________________________________ 
V.sub.0 DRR E.sub.1/2 
Photosensitive Body 
(-V) (%) (erg/cm.sup.2) 
______________________________________ 
Example 1 550 91 23.1 
Comparative Example 1 
540 73 80.6 
______________________________________ 
It is clear from these results that the combination of a cyclic acid 
anhydride and a sensitizing dye of this invention provides a greatly 
improved dark reduction retention and greatly improved sensitivity 
(corresponding to E.sub.1/2, a smaller value being better). 
EXAMPLES 2 TO 8 
Photosensitive bodies were prepared in exactly the same way as in Example 1 
except that the dyes shown in Table 2 were used in place of the 
sensitizing dye (compound (8)) which was used in Example 1. The 
electrostatic characteristics were measured in the same way as in Example 
1 and the results shown in Table 2 were obtained. 
TABLE 2 
______________________________________ 
Example Sensitizing Dye 
V.sub.0 DRR E.sub.1/2 
No. of the Invention 
(-v) (%) (erg/cm.sup.2) 
______________________________________ 
2 Compound (1) 550 93 20.0 
3 Compound (2) 555 90 19.8 
4 Compound (4) 550 90.5 21.2 
5 Compound (5) 550 91.1 20.5 
6 Compound (6) 545 89 26.8 
7 Compound (7) 560 88 30.0 
8 Compound (9) 555 90 23.2 
9 Compound (10) 540 85 24.1 
10 Compound (11) 550 90 20.3 
11 Compound (12) 550 91.5 21.4 
12 Compound (13) 555 89 24.7 
13 Compound (14) 550 90 35.0 
14 Compound (15) 545 91 31.6 
15 Compound (16) 550 89 28.5 
16 Compound (17) 540 91 25.5 
17 Compound (20) 550 88 26.1 
18 Compound (21) 545 90 36.5 
______________________________________ 
Furthermore, the electrostatic characteristics of these photosensitive 
bodies were measured again after storage for 2 weeks under conditions of 
50.degree. C., 80% RH but there was no real difference from the results 
obtained prior to storage under these conditions. 
It is clear from these results that the photoconductive compositions of 
this invention are stable even under rigorous conditions, and that they 
have markedly superior dark charge-retaining properties and 
photosensitivity as compared to the prior art photoconductive 
compositions. 
EXAMPLES 19 TO 30 
Photosensitive bodies were prepared in exactly the same way as in Example 1 
except for the conditions indicated below and the electrosrostatic 
properties were measured. The results obtained were as shown in Table 3. 
In this case the amount of phthalic anhydride and the compounds shown in 
Table 3 added was 7.times.10.sup.-4 mol per 100 parts by weight of zinc 
oxide. 
Furthermore, the electrostatic characteristics of these photosensitive 
bodies were measured again after storage for 2 weeks under conditions of 
50.degree. C., 80% RH but there was virtually no change from the values 
observed prior to storage under these conditions. 
It is clear from these results that the photoconductive compositions of 
this invention are stable even under rigorous conditions and that they 
have markedly superior dark charge-retaining properties and 
photosensitivity as compared to the prior art photoconductive 
compositions. 
TABLE 3 
______________________________________ 
Example 
Cyclic Acid Anhydride 
V.sub.0 DRR E.sub.1/2 
No. of the Invention (-V) (%) (erg/cm.sup.2) 
______________________________________ 
19 Phthalic anhydride 
550 91 60 
20 o-Sulfobenzoic anhydride 
550 90 59 
21 4-Nitrophthalic anhydride 
555 92 60 
22 Pyromellitic anhydride 
550 95 40.5 
23 Mellitic anhydride 
555 92 53 
24 Citraconic anhydride 
550 85 64 
25 1,8-Naphthalenedi- 
555 90 68 
carboxylic 
acid anhydride 
26 3,3',4,4'-benzo- 550 89 65 
phenonetetra- 
carboxylic acid anhydride 
27 Maleic anhydride 550 85 66 
28 Cis-5-norbornene-endo-2,3- 
550 86 65 
dicarboxylic 
acid anhydride 
29 3,4-Thiophenedicarboxylic 
550 85 65 
acid anhydride 
30 Dichloromaleic anhydride 
550 86 64 
______________________________________ 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.