Note: Descriptions are shown in the official language in which they were submitted.
2016257
LAMINATE TYPE PHOTOSENSITIVE MATERIAL
FOR ELECTROPHOTOGRAPHY
Background of the Invention
(1) Field of the Invention
The present invention relates to a laminate
type photosensitive material for the electrophotography,
which comprises a charge-generating layer and a charge-
transporting layer, which are formed on an
electroconductive substrate.
(2) Description of the Related Art
A laminate type photosensitive material having
the above-mentioned structure has been publicly known as
the so-called function-separated photosensitive
material.
In this laminate type photosensitive material,
by the imagewise exposure conducted after, for example,
negative charges have been uniformly given to the
surface, carriers (positive or negative charges) are
generated in the charge-generating layer and injection
and transportation of holes (positive holes) are
effected in the charge-transporting layer based on these
carriers, whereby the negative charges on the surface of
the photosensitive material are neutralized and an
electrostatic latent image is formed.
Accordingly, in the conventional laminate type
photosensitive material, in order to facilitate the
injection of holes, a substance having a higher
ionization potential than that of the charge-
transporting substance is used as the charge-generating
substance.
However, if the charge-generating material and
the charge-transporting material are used in the above-
mentioned combination, when the photosensitive material
is used repeatedly, the stability of the surface
2 2~16257
potential is bad.
Recently, incorporation of an antioxidant into
the charge-transporting layer has been proposed as the
means for preventing light deterioration or thermal
deterioration of the photosensitive material and
improving the stability at the repeated use. However,
some of various antioxidants heretofore used for
photosensitive materials for the electrophotography fail
to show a significant effect but have bad influences on
the photosensitive characteristics.
Summary of the Invention
It is therefore a primary object of the
present invention to provide a laminate type
photosensitive material for the electrophotography, in
which reduction of the surface potential of the
photosensitive material is effectively prevented even at
the repeated use without disturbing the injection of
holes into the charge-transporting layer and a good
charging capacity is manifested while maintaining a good
residual potential.
Another object of the present invention is to
provide a laminate type photosensitive material for the
electrophotography, in which the stability at the
repeated use is improved by preventing the deterioration
by light or heat.
In accordance with the present invention,
there is provided a laminate type photosensitive
material for the electrophotography, which comprises a
charge-generating layer and a charge-transporting layer,
which are formed on an electroconductive substrate,
wherein the charge-transporting layer comprises a first
charge-transporting material having an ionization
potential smaller than that of a charge-generating
material used for the charge-generating layer and a
second charge-transporting material having an ionization
20162S7
_ - 3 -
potential larger than that of the charge-generating
material.
The present invention is prominently
characterized in that a charge-transporting material
having an ionization potential smaller than that of an
charge-generating material used for the charge-
generating layer and a charge-transport-material having
an ionization potential larger than that of the charge-
generating material are used in combination as the
charge-transporting material constituting the charge-
transporting layer.
If only a charge-transporting material having
an ionization potential smaller than that of the charge-
generating material is used as in the conventional
technique, although the injection of holes into the
charge-transporting layer can be performed effectively,
the disadvantage of reduction of the surface potential
of the photosensitive material by the repeated use
cannot be avoided.
In contrast, if two kinds of the above-
mentioned charge-transporting materials are used in
combination according to the present invention, as is
apparent from the examples, reduction of the surface
potential of the photosensitive material at the repeated
use can be effectively prevented.
More specifically, as the result of
investigations made by us, it was found that if
substances having an ionization potential larger and an
ionization potential smaller than that of the charge-
generating material used for the charge-generating
layer, respectively, are combined and used as the
charge-transporting material so that each of the
differences of the absolute values of the ionization
potentials of the two charge-transporting materials from
that of the charge-generating material is within 0.2 eV,
2016257
_ - 4 -
a good residual potential can be maintained without
disturbing the injection of holes in the charge-
transporting layer, and a good charging capacity is
attained.
Furthermore, as the result of research made by
us, it was found that in a photosensitive material where
two kinds of the above-mentioned charge-transporting
materials are used in combination, if a phosphorus type
or amine type antioxidant as used for the conventional
photosensitive materials is used, the aimed stability at
the repeated use is not obtained but the surface
potential is drastically reduced by the repeated use,
and that if a phenol type antioxidant is used, the
stability at the repeated use is preferably improved.
Brief Description of the Drawings
Fig. 1 is a graph illustrating the relations
of the ratio of the combined charge-transporting
materials to the quantity of reduction of the surface
potential and the residual potential.
Fig. 2 is a diagram illustrating an apparatus
for use in the electrophotographic characteristics of a
photosensitive material.
Detailed Description of the Preferred Embodiments
The laminate type photosensitive material of
the present invention comprises an electroconductive
substrate, a charge-generating layer formed on the
substrate and a charge-transporting layer formed on the
charge-generating layer.
Electroconductive Substrate
A sheet or drum formed of a foil or sheet of a
metal such as aluminum, copper or tin or a tin plate is
used as the electroconductive substrate.
Furthermore, a substrate formed by depositing
a metal as mentioned above on a film substrate such as a
biaxially drawn polyester film or a glass substrate by
20162~7
_ - 5 -
vacuum deposition, sputtering or electroless plating can
be used. Moreover, an electroconductively treated paper
sheet can be used.
Charge-Generating Layer
S The charge-generating layer formed on the
above-mentioned electroconductive substrate is formed
of a dispersion of a charge-generating material in an
electrically insulating binder resin.
Known electrically insulating materials can be
used. For example, a polyester resin, an acrylic resin,
a styrene resin, an epoxy resin, a silicone resin, an
alkyd resin and a vinyl chloride/vinyl acetate copolymer
resin can be used.
Any of materials capable of generating
carriers on receipt of light, known in the field of the
electrophotography, can be used as the charge-generating
material.
For example, there can be mentioned a
phthalocyanine pigment, a perylene pigment, a
quinacridone pigment, a pyranthrone pigment, a disazo
pigment and a trisazo pigment.
In general, the charge-generating material is
finely dispersed in the form of particles having a
particle size smaller than 5 microns in the binder
resin, and the charge-generating material is used in an
amount of 5 to 100 parts by weight, especially 10 to 50
parts by weight, per 100 parts by weight of the binder
resn.
In general, the charge-generating layer is
formed in a thickness of 0.05 to 3,um, especially 0.3 to
1 ~m.
The structures and ionization potentials of
main charge-generating materials are shown in Table 1.
20162S7
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20162~7
_ - 8 -
Charge-Transporting Layer
The charge-transporting layer formed on the
charge-generating layer is formed of a dispersion of a
charge-transporting material in a binder resin as
described above with respect to the charge-generating
layer. In the present invention, a first charge-
transporting material having an ionization potential
smaller than that of the used charge-generating material
and a second charge-generating material having an
ionization potential larger than that of the used
charge-generating material are used in combination as
the charge-transporting material.
Known charge-transporting materials can be
used in the present invention, and two kinds of charge-
generating materials satisfying the above requirementare used in combination.
Main charge-transporting materials and
ionization potentials thereof are shown in Table Z.
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- 10 - 67616-177
It is preferred that the difference of each of
the ionization potentials of the first and second
charge-transporting materia1s from that of the charge-
generating material be within + 0.2 eV.
S More specifically, if the ionization potential
of the first charge-transporting material is too small,
the reduction of the surface potential is too large, and
if the ionization potential (abbreviated to "Ip"
hereinafter) of the second charge-transporting material
is too large, the injection of holes becomes difficult
and the accumulation of residual charges tends to
increase.
It is preferred that the first charge-
transporting material and second charge-transportion
lS material be used in such amounts that the weight ratio
of the first charge-transporting material to the second
charge-transporting material to the second charge-
transporting material be from 10/90 to 90/10,
especially from 30/70 to 70/30.
For example, in case of a laminate
photosensitive material comprising metal-free
phthalocyanine (Ip: 5.38 eV) as the charge-generating
material, N,N'-bis(o,p-dimethyl~henyl)-N,N'-
(diphenyl)benzidine (hereinafter referred to as "4Me-
TPD") having an Ip value of 5.43 eV as the second
charge-transporting material and l,l-bis(p-
diethylaminophenyl)-4,4-diphenyl-l,3-
butadiene (hereinafter referred to as "T-405") having an
Ip value of 5.32 eV as the first charge-transporting
material, the relation among the quantity of reduction
of the surface potential from the initial value, the
residual potential and the combination ratio between the
charge-transporting materials, observed at the 200-cycle
copying test, is as shown in Fig. l.
From the results shown in Fig. l, it will be
2016257
11
understood that if the amount incorporated of 4Me-TPD as
the second charge-transporting material is small,
reduction of the surface potential is conspicuous and if
the amount incorporated of 4Me-TPD is large, the
S residual potential is adversely influenced, and that
when the first and second charge-transporting materials
are used at the combination ratio specified in the
present invention, very good results can be obtained.
The charge-transporting materials are used in
a total amount of 50 to 300 parts by weight, especially
70 to 100 parts by weight, per 100 parts by weight of
the binder resin.
Phenol Type Antioxidant
As the phenol type antioxidant that can be
used in the present invention, there can be mentioned
2,6-t-butyl-p-cresol, triethylene glycol-bis~3-(3-t-butyl-
5-methyl-4-hydroxyphenyl)~ propionate, octadecyl-3-(3,5-
di-t-butyl-4-hydroxyphenyl) propionate, bis(1,2,2,6-
pentamethyl-4-piperidyl) 2-(3,5-di-t-butyl-4-
hydroxybenzyl)-2-n-butylmalonate and 4,4'-thiobis(3-
methyl-6-t-butylphenol). These phenol type
antioxidants can be used singly or in the form of
mixtures of two or more of them. Among these
antioxidants, octadecyl-3-(3,5-di-t-butyl-4-
hydroxydiphenyl) propionate and bis(1,2,2,6-pentamethyl-
4-piperidyl) 2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-
butyl-malonate are preferably used.
The phenol type antioxidant is used in an
amount of 5 to 50 parts by weight per 100 parts by
weight of the binder resin. If the amount used of the
phenol type antioxidant exceeds 50 parts by weight, the
sensitivity is reduced and the residual potential rises
at the repeated use. If the amount of the phenol type
antioxidant is smaller than 5 parts by weight, a
sufficient stability of the surface potential cannot be
2016257
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obtained at the repeated use.
In general, the charge-transporting layer is
formed in a thickness of 10 to 30,um, especially 15 to
20 ,um.
The present invention will now be described in
detail with reference to the following examples that by
no means limit the scope of the invention.
(Preparation of Photosensitive Material for Electro-
photography)
Example 1
A ball mill was charged with 100 parts by
weight polyvinyl butyral (S-Lec BLl~supplied by Sekisui
.
Kagaku) as the binder, 200 parts by weight of metal-free
phthalocyanine as the charge-generating material and a
predetermined amount of tetrahydrofuran, and the mixture
was stirred for 24 hours to form a charge-generating
layer-forming coating liquid. The obtained coating
liquid was coated on an aluminum drum by the dipping
method and dried with hot air at 110C for 30 minutes to
effect curing and form a charge-generating layer having
a thickness of 0.5 ,um.
By using a homomixer, 100 parts by weight of a
polycarbonate resin (Upiron~supplied by Mitsubishi Gas
Kagaku) as the binder, 70 parts by weight of N,N'-
bis(o,p-dimethylphenyl)-N,N'-(diphenyl)benzidine
(hereinafter referred to as "4Me-TPD") and 30 parts by
weight of 1,1-bis(p-diethylaminophenyl)-4,4-diphenyl-
1,3-butadiene (hereinafter referred to as "T-405") as
the charge-transporting material, and a predetermined
amount of toluene were mixed and stirred to form a
charge-transporting layer-forming coating liquid. The
coating liquid was coated on the surface of the charge-
generating layer by the dipping method and dried with
hot air at 110C for 30 minutes to form a charge-
transporting layer having a thickness of about 20 ~m.
~r~
2016257
- 13 -
Thus, a photosensitive material for the
electrophotography was prepared.
Example 2
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 1 except that the charge-
transporting material used for the formation of the
charge-transporting material was changed to 60 parts by
weight of 4Me-TPD and 40 parts by weight of T-405.
Example 3
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 1 except that the charge-
transporting material used for the formation of the
charge-transporting layer was changed to 50 parts by
weight of 4Me-TPD and 50 parts by weight of T-405.
Example 4
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 1 except that the charge-
transporting material used for the formation of the
charge-transporting layer was changed to 40 parts by
weight of 4Me-TPD and 60 parts by weight of T-405.
Example 5
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 1 except that the charge-
transporting material used for the formation of the
charge-transporting layer was changed to 30 parts by
weight of 4Me-TPD and 70 parts by weight of T-405.
Example 6
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 1 except that 70 parts by weight of
4Me-TPD and 30 parts by weight of 4-(N,N-
20162~7
- 14 -
diethylamino)benzaldehyde-N,N-diphenylhydrazone instead
of T-405 were used as the charge-transporting material
for the formation of the charge-transporting layer.
Comparative Example 1
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 1 except that the charge-
transporting material used for the formation of the
charge-transporting layer was changed to 100 parts by
weight of 4Me-TPD.
Comparative Example 2
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 1 except that the charge-
transporting material used for the formation of thecharge-transporting layer was changed to 100 parts by
weight of T-405.
Example 7
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 1 except that 5 parts by weight of
2,6-di-t-butyl-p-cresol (BHT supplied by Kawaguchi
Kagaku) was added as the phenol type antioxidant.
Example 8
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 25 parts by weight of
2,6-di-t-butyl-p-cresol (BHT supplied by Kawaguchi
Kagaku) was used as the phenol type antioxidant.
Example 9
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 50 parts by weight of
2,6-di-t-butyl-p-cresol (BHT supplied by Kawaguchi
Kagaku) was used as the phenol type antioxidant.
20162S7
- 15 -
Example 10
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 5 parts by weight of
triethylene glycol bis~3-(3-t-butyl-5-methyl-4-hydroxy-
phenyl)propionate~ (Irganox~245 supplied by Ciba-Geigy)
was used as the phenol type antioxidant.
Example 11
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 25 parts by weight of
triethylene glycol bis~3-(3-t-butyl-5-methyl-4-hydroxy-
phenyl)propionate~ (Irganox~245 supplied by Ciba-Geigy)
was used as the phenol type antioxidant.
Example 12
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 50 parts by weight of
triethylene glycol bis~3-(3-t-butyl-5-methyl-4-hydroxy-
phenyl)propionate~ (Irganox~245 supplied by Ciba-Geigy)
was used as the phenol type antioxidant.
Example 13
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 5 parts by weight of
octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate
(Irganox~1076 supplied by Ciba-Geigy) was used as the
phenol type antioxidant.
Example 14
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 25 parts by weight of
octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate
(Irganox 1076 supplied by Ciba-Geigy) was used as the
phenol type antioxidant.
20162S7
- 16 -
Example 15
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 50 parts by weight of
octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate
(Irganox~1076 supplied by Ciba-Geigy) was used as the
phenol type antioxidant.
Example 16
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 5 parts by weight of
bis(1,2,2,6,6-pentamethyl-4-piperidyl 2-(3,5-di-t-
butyl-4-hydroxybenzyl)-2-n-butylmalonate (Tinuvin~144
supplied by Ciba-Geigy) was used as the phenol type
antioxidant.
Example 17
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 25 parts by weight of
bis(l,2,2,6,6-pentamethyl-4-piperidyl 2-(3,5-di-t-butyl-
4-hydroxybenzyl)-2-n-butyl-malonate (Tinuvin~144 supplied
by Ciba-Geigy) was used as the phenol type antioxidant.
Example 18
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 50 parts by weight of
bis(l,2,2,6,6-pentamethyl-4-piperidyl 2-(3,5-di-t-butyl-
4-hydroxybenzyl)-2-n-butylmalonate (Tinuvin~144 supplied
by Ciba-Geigy) was used as the phenol type antioxidant.
Comparative Example 3
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 10 parts by weight of
4,4'-isopropylidene-diphenol alkyl (C12 to C15)
phosphite (Mark 1500 supplied by Adeca-Argus) was used
~ t~
20162~7
- 17 -
as the phosphorus type antioxidant.
Comparative Example 4
A photosensitive material for the
electrophotography was prepared in the same manner as
5~ described in Example 7 except that 10 parts by weight of
diisodecyl pentaerythritol diphosphite (Himo~supplied by
Sanko Kagaku) was used as the phosphorus type antioxidant.
Comparative Example 5
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 10 parts by weight of
1,3-bis(dimethylaminopropyl-2-thiourea (Nolax NS10
supplied by Ouchi Shinko Kagaku) was used as the amine
type antioxidant.
Comparative Example 6
A photosensitive material for the
electrophotography was prepared in the same manner as
described in Example 7 except that 10 parts by weight of
bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (Sanol~770
supplied by Sankyo Kagaku) was used as the amine type
antioxidant. (Evaluation of Photosensitive Materials
for Electrophotography).
Photographic characteristics such as the
charging capacity and residual potential were measured
by using an apparatus as shown in Fig. 2.
A photosensitive material 5 obtained in each
example was negatively charged by carrying out corona
discharge under -6 KV by using Corontron~ 1 while
rotating the photosensitive material 5, and the surface
potential Vsp (V) was measured by a surface
potentiometer arranged at a position 7.
Then, by using a semiconductor laser 2 (~ =
780 nm, exposure intensity = 0.7 mW/cm2, exposure time =
260 ~sec), the photosensitive material was light-
exposed, and the surface potential after the passage of
20162~7
- 18 -
400 msec from the light exposure was measured as the
residual potential VRp (V).
Then, corona discharge was carried out under
+4 KV by using Corontron 3, and the photosensitive
material was exposed to light by using LED (~ = 630 nm)
to effect an electricity-removing operation 4.
The surface potential V10Osp (V) was measured
after 100 cycles of the above-mentioned
electrophotographic process and the difference AVSp (V)
between this surface potential and the initial surface
potential Vsp (V) of the photosensitive material was
calculated.
The obtained results shown in Tables 3 and 4.
2016257
-- 19 --
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20162~7
_ - 20 -
Table 4
VRp (V) ~Vsp (V)
Example 7 11 - 50
Example 8 7 - 35
Example 9 15 - 30
Example 10 8 - 70
Example 11 8 - 40
Example 12 10 - 30
Example 13 12 - 60
Example 14 12 - 25
Example 15 10 - 35
Example 16 15 - 25
Example 17 21 - 30
Example 18 50 - 30
Comparative Example 3 210 - 50
Comparative Example 4 16 - 75
Comparative Example 5 110 - 50
Comparative Example 6 65 - 25
20162~7
- 21 -
From the results shown in Table 3, it is seen
that each of the photosensitive materials obtained in
Examples 1 through 6, the residual potential was low and
the stability of the surface potential at the repeated
use was good, and each of these photosensitive materials
had excellent photographic characteristics.
In contrast, the photosensitive material of
Comparative Example 1 had a high residual potential,
though the stability of the surface potential at the
repeated use was good. The photosensitive material of
Comparative Example 2 had no stability of the surface
potential at the repeated use, though the residual
potential was low.
From the results shown in Table 4, it is seen
that each of the photosensitive materials of Examples 7
through 18 comprising a phenol type antioxidant had a
low residual potential and a good stability of the
surface potential at the repeated use, and it was
confirmed that each of these photosensitive materials
had excellent electrophotographic characteristics.
In contrast, the photosensitive materials of
Comparative Examples 3, S and 6 had a high residual
potential, and the photosensitive material of
Comparative Example 4 was poor in the stability of the
surface potential at the repeated use.
