Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
1999-03-03
2001-08-28
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S056000, C430S070000, C430S083000, C552S293000, C552S304000
Reexamination Certificate
active
06280893
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electrophotographic photoreceptors for use in, for example, photocopiers or laser printers, and particularly to electrophotographic photoreceptors using organic thin films and electron transfer agents used therefor.
PRIOR ART
Inorganic thin films made of inorganic materials such as selenium, selenium-tellurium, selenium-arsenic, amorphous silicon were originally used as photosensitive layers in electrophotographic photoreceptors of electrophotographic apparatus such as photocopiers or laser printers.
However, electrophotographic photoreceptors having photosensitive layers using organic thin films in place of conventional inorganic thin films have been prevailing to meet recent demands for inexpensive and less pollutive electrophotographic photoreceptors. Such photosensitive layers consisting of organic thin films are mainly classified by structure into monolayer-dispersed type and function-separated type.
Monolayer-dispersed type of photosensitive layers consist of a monolayer film comprising a carrier generation material in a medium for a carrier transport material, whereby the monolayer film has both functions of generating and transporting charge carriers. On the other hand, function-dispersed type of photosensitive layers consist of a multilayer film in which are layered a carrier generation layer (CGL) having a function of generating charge carriers and a carrier transport layer (CTL) having a function of transporting generated charge carriers.
At present, both types of photosensitive layers are commercialized, but there is a demand for developing a carrier transport material with high mobility to improve sensitivity for both types.
Organic photosensitive layers are also classified by charge type into positively charged photosensitive layers and negatively charged photosensitive layers. Most of presently known and commercialized carrier transport materials with high mobility are hole transfer type, so that commercially available electrophotographic apparatus use photoreceptors having negatively charged photosensitive layers.
However, corona discharge phenomenon used for negatively charging photosensitive layers produces a large amount of ozone as discharge occurs to pollute interior environments, accelerate deterioration of electrophotographic photoreceptors or otherwise cause various disadvantages.
Some attempts were made to eliminate disadvantages encountered during negatively charging photosensitive layers of electrophotographic apparatus of the prior art by, for example, adding an ozone-trapping filter or adopting a special ozone-free charging system, but additional problems occur such as increased bulk of apparatus or complication of electrophotographic processes and no solution has been attained.
In order to ameliorate such circumstances, recent markets require positively charged photoreceptors less likely to generate ozone, thus needing a development of an electron transfer agent with high mobility suitable for positively charged photosensitive layers.
Such electron transfer agents so far found to be suitable for positively charged photoreceptors by previous eager studies include trinitrofluorenone (TNF), tetracyanoethylene, tetracyanoquinodimethane (TCNQ), quinone, diphenoquinone, naphthoquinone, anthraquinone and derivatives thereof, etc. However, most of these electron transfer agents are less compatible with binder resins so that they can not be homogeneously dispersed in photosensitive layers at a high concentration. Thus, the content is not sufficient to satisfy electric characteristics. Asymmetric diphenoquinone compounds exceptionally show good compatibility with resins and high electron mobility, but they are so strongly colored that such compounds in photosensitive layers absorb rays which should reach carrier generation materials to lower the sensitivity.
Our examination of compounds described in JPA No. 34141/97 as electron transfer agents which solved the above problems revealed that, among compounds of the following general formula (1):
a compound wherein R
2
and R
3
represent a tBu group as represented by the following formula (5):
is more likely to increase sensitivity while a compound wherein R
2
and R
3
represent an Me group as represented by the following formula (6):
is difficult to increase sensitivity.
Assuming that the above difference in photosensitive characteristics between structures of compounds results from the difference in the stereostructure of molecules of compounds, we determined the stereostructure of molecules by the molecular orbital method.
The results are shown in
FIGS. 1 and 2
.
FIGS. 1
a
,
1
b
,
1
c
show the stereostructure of the molecule of the compound represented by the above chemical formula (5), while
FIGS. 2
a
,
2
b
,
2
c
show the stereostructure of the molecule of the compound represented by the above chemical formula (6).
In
FIGS. 1
a
,
1
b
,
1
c
and
FIGS. 2
a
,
2
b
,
2
c
,
FIGS. 1
a
and
2
a
show the neutral state,
FIGS. 1
b
and
2
b
show the state wherein one electron has been given, and
FIGS. 1
c
and
2
c
show the state wherein two electrons have been given. Each of
FIGS. 1
a
,
1
b
,
1
c
and
FIGS. 2
a
,
2
b
,
2
c
shows a plan view on the upper side and a side view on the lower side. In these figures, hydrogen atoms are omitted, and carbon atoms and nitrogen atoms are represented by open circles while oxygen atoms are represented by solid circles (similarly to
FIGS. 3
a
,
3
b
,
3
c
,
FIGS. 4
a
,
4
b
,
4
c
and
FIGS. 5
a
,
5
b
,
5
c
described later).
As shown in
FIG. 1
a
, the ring of the compound of the above chemical formula (5) is strained in the neutral state because of the presence of a bulky substituent such as tBu group.
When electrons are given in this state, it was found that the strain decreases and a slight torsion occurs in the dicyanomethylene group as electrons increase, as shown in
FIGS. 1
b
,
1
c.
However, the ring of the compound of chemical formula (6) is not strained in the neutral state as shown in
FIG. 2
a
, and no change occurred in the ring with no torsion in the dicyanomethylene group even if one or two electrons were given, as shown in
FIGS. 2
b
,
2
c.
Thus, a molecular structure deformed by giving electrons seems to cause molecular vibration.
The results of the foregoing examination suggest that electron transfer agents suitable for photoreceptors should require strong molecular vibration to obtain electron transfer by proximity effect.
However, electrophotographic photoreceptors using said compound can not actually reach the sensitivity and residual potential of negatively charged electrophotographic photoreceptors on the market, and further studies are needed to enhance molecular vibration in electron transfer agents.
DISCLOSURE OF THE INVENTION
In order to solve such problems of the prior art, an object of the present invention is to provide an electrophotographic photoreceptor which is excellent in sensitivity and residual potential and to provide a novel and useful electron transfer agent which can be dispersed in a photosensitive layer at a high concentration and which can be molecularly designed to have a desired magnitude of molecular vibration.
In order to attain the above object, the invention of claim
1
provides an electrophotographic photoreceptor comprising an organic thin film formed on a conductive substrate, characterized in that said organic thin film contains a compound of the following general formula (1):
wherein R
1
represents either a non-cyclic saturated hydrocarbon or a cyclic saturated hydrocarbon, R
2
and R
3
represent any one of a cyano group, a nitro group, a halogen, a heterocycle, a non-cyclic hydrocarbon, a cyclic saturated hydrocarbon, an alkoxy group of a non-cyclic hydrocarbon or an alkoxy group of a cyclic saturated hydrocarbon, R
4
represents any one of a hydrogen, a non-cyclic saturated hydrocarbon or a cyclic saturated hydrocarbon, provided that any two of R
1
, R
2
, R
3
and R
4
may be the same or all of them may be different, an
Suzuki Hiroki
Takano Mitsuyo
Dote Janis L.
Finnegan Henderson Farabow Garrett & Dunner LLP
Shindengen Electric Manufacturing Co. Ltd.
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